|
A Practical Physiology
A Text-Book for Higher Schools
By
Albert F. Blaisdell, M.D.
Author of "Child's Book of Health," "How to Keep Well,"
"Our Bodies and How We Live," Etc., Etc.
Preface.
The author has aimed to prepare a text-book on human physiology for use in
higher schools. The design of the book is to furnish a practical manual of
the more important facts and principles of physiology and hygiene, which
will be adapted to the needs of students in high schools, normal schools,
and academies.
Teachers know, and students soon learn to recognize the fact, that it is
impossible to obtain a clear understanding of the functions of the various
parts of the body without first mastering a few elementary facts about
their structure. The course adopted, therefore, in this book, is to devote
a certain amount of space to the anatomy of the several organs before
describing their functions.
A mere knowledge of the facts which can be gained in secondary schools,
concerning the anatomy and physiology of the human body, is of little real
value or interest in itself. Such facts are important and of practical
worth to young students only so far as to enable them to understand the
relation of these facts to the great laws of health and to apply them to
daily living. Hence, it has been the earnest effort of the author in this
book, as in his other physiologies for schools, to lay special emphasis
upon such points as bear upon personal health.
Physiology cannot be learned as it should be by mere book study. The
result will be meagre in comparison with the capabilities of the subject.
The study of the text should always be supplemented by a series of
practical experiments. Actual observations and actual experiments are as
necessary to illuminate the text and to illustrate important principles in
physiology as they are in botany, chemistry, or physics. Hence, as
supplementary to the text proper, and throughout the several chapters, a
series of carefully arranged and practical experiments has been added. For
the most part, they are simple and can be performed with inexpensive and
easily obtained apparatus. They are so arranged that some may be omitted
and others added as circumstances may allow.
If it becomes necessary to shorten the course in physiology, the various
sections printed in smaller type may be omitted or used for home study.
The laws of most of the states now require in our public schools the study
of the effects of alcoholic drinks, tobacco, and other narcotics upon the
bodily life. This book will be found to comply fully with all such laws.
The author has aimed to embody in simple and concise language the latest
and most trustworthy information which can be obtained from the standard
authorities on modern physiology, in regard to the several topics.
In the preparation of this text-book the author has had the editorial help
of his esteemed friend, Dr. J. E. Sanborn, of Melrose, Mass., and is also
indebted to the courtesy of Thomas E. Major, of Boston, for assistance in
revising the proofs.
Albert F. Blaisdell.
Boston, August, 1897.
Contents.
Chapter I. Introduction
Chapter II. The Bones
Chapter III. The Muscles
Chapter IV. Physical Exercise
Chapter V. Food and Drink
Chapter VI. Digestion
Chapter VII. The Blood and Its Circulation
Chapter VIII. Respiration
Chapter IX. The Skin and the Kidneys
Chapter X. The Nervous System
Chapter XI. The Special Sense
Chapter XII. The Throat and the Voice
Chapter XIII. Accidents and Emergencies
Chapter XIV. In Sickness and in Health
Care of the Sick-Room; Poisons and their Antidotes; Bacteria;
Disinfectants; Management of Contagious Diseases.
Chapter XV. Experimental Work in Physiology
Practical Experiments; Use of the Microscope; Additional Experiments;
Surface Anatomy and Landmarks.
Glossary
Index
Chapter I.
Introduction.
1. The Study of Physiology. We are now to take up a new study, and in
a field quite different from any we have thus far entered. Of all our
other studies,--mathematics, physics, history, language,--not one comes
home to us with such peculiar interest as does physiology, because
this is the study of ourselves.
Every thoughtful young person must have asked himself a hundred questions
about the problems of human life: how it can be that the few articles of
our daily food--milk, bread, meats, and similar things--build up our
complex bodies, and by what strange magic they are transformed into hair,
skin, teeth, bones, muscles, and blood.
How is it that we can lift these curtains of our eyes and behold all the
wonders of the world around us, then drop the lids, and though at noonday,
are instantly in total darkness? How does the minute structure of the ear
report to us with equal accuracy the thunder of the tempest, and the hum
of the passing bee? Why is breathing so essential to our life, and why
cannot we stop breathing when we try? Where within us, and how, burns the
mysterious fire whose subtle heat warms us from the first breath of
infancy till the last hour of life?
These and scores of similar questions it is the province of this deeply
interesting study of physiology to answer.
2. What Physiology should Teach us. The study of physiology is not
only interesting, but it is also extremely useful. Every reasonable person
should not only wish to acquire the knowledge how best to protect and
preserve his body, but should feel a certain profound respect for an
organism so wonderful and so perfect as his physical frame. For our bodies
are indeed not ourselves, but the frames that contain us,--the ships in
which we, the real selves, are borne over the sea of life. He must be
indeed a poor navigator who is not zealous to adorn and strengthen his
ship, that it may escape the rocks of disease and premature decay, and
that the voyage of his life may be long, pleasant, and successful.
But above these thoughts there rises another,--that in studying physiology
we are tracing the myriad lines of marvelous ingenuity and forethought, as
they appear at every glimpse of the work of the Divine Builder. However
closely we study our bodily structure, we are, at our best, but imperfect
observers of the handiwork of Him who made us as we are.
3. Distinctive Characters of Living Bodies. Even a very meagre
knowledge of the structure and action of our bodies is enough to reveal
the following distinctive characters: our bodies are continually
breathing, that is, they take in oxygen from the surrounding air; they
take in certain substances known as food, similar to those composing the
body, which are capable through a process called oxidation, or through
other chemical changes, of setting free a certain amount of energy.
Again, our bodies are continually making heat and giving it out to
surrounding objects, the production and the loss of heat being so adjusted
that the whole body is warm, that is, of a temperature higher than that of
surrounding objects. Our bodies, also, move themselves, either one part
on another, or the whole body from place to place. The motive power is not
from the outside world, but the energy of their movements exists in the
bodies themselves, influenced by changes in their surroundings. Finally,
our bodies are continually getting rid of so-called waste matters, which
may be considered products of the oxidation of the material used as food,
or of the substances which make up the organism.
4. The Main Problems of Physiology briefly Stated. We shall learn in
a subsequent chapter that the living body is continually losing energy,
but by means of food is continually restoring its substance and
replenishing its stock of energy. A great deal of energy thus stored up is
utilized as mechanical work, the result of physical movements. We shall
learn later on that much of the energy which at last leaves the body as
heat, exists for a time within the organism in other forms than heat,
though eventually transformed into heat. Even a slight change in the
surroundings of the living body may rapidly, profoundly, and in special
ways affect not only the amount, but the kind of energy set free. Thus the
mere touch of a hair may lead to such a discharge of energy, that a body
previously at rest may be suddenly thrown into violent convulsions. This
is especially true in the case of tetanus, or lockjaw.
The main problem we have to solve in the succeeding pages is to ascertain
how it is that our bodies can renew their substance and replenish the
energy which they are continually losing, and can, according to the nature
of their surroundings, vary not only the amount, but the kind of energy
which they set free.
5. Technical Terms Defined. All living organisms are studied usually
from two points of view: first, as to their form and structure; second, as
to the processes which go on within them. The science which treats of all
living organisms is called biology. It has naturally two
divisions,--morphology, which treats of the form and structure of
living beings, and physiology, which investigates their functions, or
the special work done in their vital processes.
The word anatomy, however, is usually employed instead of morphology.
It is derived from two Greek words, and means the science of dissection.
Human anatomy then deals with the form and structure of the human
body, and describes how the different parts and organs are arranged, as
revealed by observation, by dissection, and by the microscope.
Histology is that part of anatomy which treats of the minute
structure of any part of the body, as shown by the microscope.
Human physiology describes the various processes that go on in the
human body in health. It treats of the work done by the various parts of
the body, and of the results of the harmonious action of the several
organs. Broadly speaking, physiology is the science which treats of
functions. By the word function is meant the special work which an
organ has to do. An organ is a part of the body which does a special
work. Thus the eye is the organ of sight, the stomach of digestion, and
the lungs of breathing.
It is plain that we cannot understand the physiology of our bodies without
a knowledge of their anatomy. An engineer could not understand the working
of his engine unless well acquainted with all its parts, and the manner in
which they were fitted together. So, if we are to understand the
principles of elementary physiology, we must master the main anatomical
facts concerning the organs of the body before considering their special
functions.
As a branch of study in our schools, physiology aims to make clear certain
laws which are necessary to health, so that by a proper knowledge of them,
and their practical application, we may hope to spend happier and more
useful, because healthier, lives. In brief, the study of hygiene, or
the science of health, in the school curriculum, is usually associated
with that of physiology.[1]
6. Chemical Elements in the Body. All of the various complex
substances found in nature can be reduced by chemical analysis to about 70
elements, which cannot be further divided. By various combinations of
these 70 elements all the substances known to exist in the world of nature
are built up. When the inanimate body, like any other substance, is
submitted to chemical analysis, it is found that the bone, muscle, teeth,
blood, etc., may be reduced to a few chemical elements.
In fact, the human body is built up with 13 of the 70 elements, namely:
oxygen, hydrogen, nitrogen, chlorine, fluorine, carbon, phosphorus,
sulphur, calcium, potassium, sodium, magnesium, and iron. Besides
these, a few of the other elements, as silicon, have been found; but they
exist in extremely minute quantities.
The following table gives the proportion in which these various elements
are present:
Oxygen 62.430 per cent
Carbon 21.150 " "
Hydrogen 9.865 " "
Nitrogen 3.100 " "
Calcium 1.900 " "
Phosphorus 0.946 " "
Potassium 0.230 " "
Sulphur 0.162 " "
Chlorine 0.081 " "
Sodium 0.081 " "
Magnesium 0.027 " "
Iron 0.014 " "
Fluorine 0.014 " "
-----
100.000
As will be seen from this table, oxygen, hydrogen, and nitrogen, which are
gases in their uncombined form, make up 3/4 of the weight of the whole
human body. Carbon, which exists in an impure state in charcoal, forms
more than 1/5 of the weight of the body. Thus carbon and the three gases
named, make up about 96 per cent of the total weight of the body.
7. Chemical Compounds in the Body. We must keep in mind that, with
slight exceptions, none of these 13 elements exist in their elementary
form in the animal economy. They are combined in various proportions, the
results differing widely from the elements of which they consist. Oxygen
and hydrogen unite to form water, and water forms more than 2/3 of the
weight of the whole body. In all the fluids of the body, water acts as a
solvent, and by this means alone the circulation of nutrient material is
possible. All the various processes of secretion and nutrition depend on
the presence of water for their activities.
8. Inorganic Salts. A large number of the elements of the body unite
one with another by chemical affinity and form inorganic salts. Thus
sodium and chlorine unite and form chloride of sodium, or common salt.
This is found in all the tissues and fluids, and is one of the most
important inorganic salts the body contains. It is absolutely necessary
for continued existence. By a combination of phosphorus with sodium,
potassium, calcium, and magnesium, the various phosphates are formed.
The phosphates of lime and soda are the most abundant of the salts of the
body. They form more than half the material of the bones, are found in the
teeth and in other solids and in the fluids of the body. The special place
of iron is in the coloring matter of the blood. Its various salts are
traced in the ash of bones, in muscles, and in many other tissues and
fluids. These compounds, forming salts or mineral matters that exist in
the body, are estimated to amount to about 6 per cent of the entire
weight.
9. Organic Compounds. Besides the inorganic materials, there exists
in the human body a series of compound substances formed of the union of
the elements just described, but which require the agency of living
structures. They are built up from the elements by plants, and are called
organic. Human beings and the lower animals take the organized
materials they require, and build them up in their own bodies into still
more highly organized forms.
The organic compounds found in the body are usually divided into three
great classes:
1. Proteids, or albuminous substances.
2. Carbohydrates (starches, sugars, and gums).
3. Fats.
The extent to which these three great classes of organic materials of the
body exist in the animal and vegetable kingdoms, and are utilized for the
food of man, will be discussed in the chapter on food (Chapter V.). The
Proteids, because they contain the element nitrogen and the others do
not, are frequently called nitrogenous, and the other two are known
as non-nitrogenous substances. The proteids, the type of which is egg
albumen, or the white of egg, are found in muscle and nerve, in glands, in
blood, and in nearly all the fluids of the body. A human body is estimated
to yield on an average about 18 per cent of albuminous substances. In the
succeeding chapters we shall have occasion to refer to various and allied
forms of proteids as they exist in muscle (myosin), coagulated blood
(fibrin), and bones (gelatin).
The Carbohydrates are formed of carbon, hydrogen, and oxygen, the
last two in the proportion to form water. Thus we have animal starch, or
glycogen, stored up in the liver. Sugar, as grape sugar, is also found in
the liver. The body of an average man contains about 10 per cent of
Fats. These are formed of carbon, hydrogen, and oxygen, in which the
latter two are not in the proportion to form water. The fat of the body
consists of a mixture which is liquid at the ordinary temperature.
Now it must not for one moment be supposed that the various chemical
elements, as the proteids, the salts, the fats, etc., exist in the body in
a condition to be easily separated one from another. Thus a piece of
muscle contains all the various organic compounds just mentioned, but they
are combined, and in different cases the amount will vary. Again, fat may
exist in the muscles even though it is not visible to the naked eye, and a
microscope is required to show the minute fat cells.
10. Protoplasm. The ultimate elements of which the body is composed
consist of "masses of living matter," microscopic in size, of a material
commonly called protoplasm.[2] In its simplest form protoplasm
appears to be a homogeneous, structureless material, somewhat resembling
the raw white of an egg. It is a mixture of several chemical substances
and differs in appearance and composition in different parts of the body.
Protoplasm has the power of appropriating nutrient material, of dividing
and subdividing, so as to form new masses like itself. When not built into
a tissue, it has the power of changing its shape and of moving from place
to place, by means of the delicate processes which it puts forth. Now,
while there are found in the lowest realm of animal life, organisms like
the amoeba of stagnant pools, consisting of nothing more than minute
masses of protoplasm, there are others like them which possess a small
central body called a nucleus. This is known as nucleated protoplasm.
[Illustration: Fig. 1.--Diagram of a Cell.
A, nucleus;
B, nucleolus;
C, protoplasm. (Highly magnified)
]
11. Cells. When we carry back the analysis of an organized body as
far as we can, we find every part of it made up of masses of nucleated
protoplasm of various sizes and shapes. In all essential features these
masses conform to the type of protoplasmic matter just described. Such
bodies are called cells. In many cells the nucleus is finely granular or
reticulated in appearance, and on the threads of the meshwork may be one
or more enlargements, called nucleoli. In some cases the protoplasm at the
circumference is so modified as to give the appearance of a limiting
membrane called the cell wall. In brief, then, a cell is a mass of
nucleated protoplasm; the nucleus may have a nucleolus, and the cell
may be limited by a cell wall. Every tissue of the human body is formed
through the agency of protoplasmic cells, although in most cases the
changes they undergo are so great that little evidence remains of their
existence.
There are some organisms lower down in the scale, whose whole activity is
confined within the narrow limits of a single cell. Thus, the amoeba
begins its life as a cell split off from its parent. This divides in its
turn, and each half is a complete amoeba. When we come a little higher
than the amoeba, we find organisms which consist of several cells, and a
specialization of function begins to appear. As we ascend in the animal
scale, specialization of structure and of function is found continually
advancing, and the various kinds of cells are grouped together into
colonies or organs.
12. Cells and the Human Organism. If the body be studied in its
development, it is found to originate from a single mass of nucleated
protoplasm, a single cell with a nucleus and nucleolus. From this
original cell, by growth and development, the body, with all its various
tissues, is built up. Many fully formed organs, like the liver, consist
chiefly of cells. Again, the cells are modified to form fibers, such as
tendon, muscle, and nerve. Later on, we shall see the white blood
corpuscles exhibit all the characters of the amoeba (Fig. 2). Even such
dense structures as bone, cartilage, and the teeth are formed from cells.
[Illustration: Fig. 2.--Amoeboid Movement of a Human White Blood
Corpuscle. (Showing various phases of movement.)]
In short, cells may be regarded as the histological units of animal
structures; by the combination, association, and modification of these
the body is built up. Of the real nature of the changes going on within
the living protoplasm, the process of building up lifeless material into
living structures, and the process of breaking down by which waste is
produced, we know absolutely nothing. Could we learn that, perhaps we
should know the secret of life.
13. Kinds of Cells. Cells vary greatly in size, some of the smallest
being only 1/3500 an inch or less in diameter. They also vary greatly in
form, as may be seen in Figs. 3 and 5. The typical cell is usually
_globular_ in form, other shapes being the result of pressure or of
similar modifying influences. The globular, as well as the large, flat
cells, are well shown in a drop of saliva. Then there are the _columnar_
cells, found in various parts of the intestines, in which they are closely
arranged side by side. These cells sometimes have on the free surface
delicate prolongations called cilia. Under the microscope they resemble a
wave, as when the wind blows over a field of grain (Fig. 5). There are
besides cells known as _spindle, stellate, squamous_ or pavement, and
various other names suggested by their shapes. Cells are also described as
to their contents. Thus _fat_ and _pigment_ cells are alluded to in
succeeding sections. Again, they may be described as to their functions or
location or the tissue in which they are found, as _epithelial_ cells,
_blood_ cells (corpuscles, Figs. 2 and 66), _nerve_ cells (Fig. 4), and
_connective-tissue_ cells.
14. Vital Properties of Cells. Each cell has a life of its own. It
manifests its vital properties in that it is born, grows, multiplies,
decays, and at last dies.[3] During its life it assimilates food, works,
rests, and is capable of spontaneous motion and frequently of locomotion.
The cell can secrete and excrete substance, and, in brief, presents nearly
all the phenomena of a human being.
Cells are produced only from cells by a process of self-division,
consisting of a cleavage of the whole cell into parts, each of which
becomes a separate and independent organism. Cells rapidly increase in
size up to a certain definite point which they maintain during adult life.
A most interesting quality of cell life is motion, a beautiful form of
which is found in ciliated epithelium. Cells may move actively and
passively. In the blood the cells are swept along by the current, but the
white corpuscles, seem able to make their way actively through the
tissues, as if guided by some sort of instinct.
[Illustration: Fig. 3.--Various Forms of Cells.
A, columnar cells found lining various parts of the intestines (called
_columnar epithelium_);
B, cells of a fusiform or spindle shape found in the loose tissue under
the skin and in other parts (called _connective-tissue cells_);
C, cell having many processes or projections--such are found in
connective tissue, D, primitive cells composed of protoplasm with
nucleus, and having no cell wall. All are represented about 400 times
their real size.
]
Some cells live a brief life of 12 to 24 hours, as is probably the case
with many of the cells lining the alimentary canal; others may live for
years, as do the cells of cartilage and bone. In fact each cell goes
through the same cycle of changes as the whole organism, though doubtless
in a much shorter time. The work of cells is of the most varied kind, and
embraces the formation of every tissue and product,--solid, liquid, or
gaseous. Thus we shall learn that the cells of the liver form bile, those
of the salivary glands and of the glands of the stomach and pancreas form
juices which aid in the digestion of food.
15. The Process of Life. All living structures are subject to
constant decay. Life is a condition of incessant changes, dependent upon
two opposite processes, repair and decay. Thus our bodies are not
composed of exactly the same particles from day to day, or even from one
moment to another, although to all appearance we remain the same
individuals. The change is so gradual, and the renewal of that which is
lost may be so exact, that no difference can be noticed except at long
intervals of time.[4] (See under "Bacteria," Chapter XIV.)
The entire series of chemical changes that take place in the living body,
beginning with assimilation and ending with excretion, is included in one
word, metabolism. The process of building up living material, or the
change by which complex substances (including the living matter itself)
are built up from simpler materials, is called anabolism. The
breaking down of material into simple products, or the changes in which
complex materials (including the living substance) are broken down into
comparatively simple products, is known as katabolism. This reduction
of complex substances to simple, results in the production of animal force
and energy. Thus a complex substance, like a piece of beef-steak, is built
up of a large number of molecules which required the expenditure of force
or energy to store up. Now when this material is reduced by the process of
digestion to simpler bodies with fewer molecules, such as carbon dioxid,
urea, and water, the force stored up in the meat as potential energy
becomes manifest and is used as active life-force known as _kinetic
energy_.
16. Epithelium. Cells are associated and combined in many ways to
form a simple tissue. Such a simple tissue is called an epithelium or
surface-limiting tissue, and the cells are known as epithelial
cells. These are united by a very small amount of a cement substance which
belongs to the proteid class of material. The epithelial cells, from their
shape, are known as squamous, columnar, glandular, or ciliated. Again, the
cells may be arranged in only a single layer, or they may be several
layers deep. In the former case the epithelium is said to be simple; in
the latter, stratified. No blood-vessels pass into these tissues; the
cells derive their nourishment by the imbibition of the plasma of the
blood exuded into the subjacent tissue.
[Illustration: Fig. 4.--Nerve Cells from the Gray Matter of the
Cerebellum. (Magnified 260 diameters.)]
17. Varieties of Epithelium. The squamous or pavement epithelium
consists of very thin, flattened scales, usually with a small nucleus in
the center. When the nucleus has disappeared, they become mere horny
plates, easily detached. Such cells will be described as forming the outer
layer of the skin, the lining of the mouth and the lower part of the
nostrils.
The columnar epithelium consists of pear-shaped or elongated cells,
frequently as a single layer of cells on the surface of a mucous membrane,
as on the lining of the stomach and intestines, and the free surface of
the windpipe and large air-tubes.
The glandular or spheroidal epithelium is composed of round cells or
such as become angular by mutual pressure. This kind forms the lining of
glands such as the liver, pancreas, and the glands of the skin.
The ciliated epithelium is marked by the presence of very fine
hair-like processes called cilia, which develop from the free end of the
cell and exhibit a rapid whip-like movement as long as the cell is alive.
This motion is always in the same direction, and serves to carry away
mucus and even foreign particles in contact with the membrane on which
the cells are placed. This epithelium is especially common in the air
passages, where it serves to keep a free passage for the entrance and exit
of air. In other canals a similar office is filled by this kind of
epithelium.
18. Functions of Epithelial Tissues. The epithelial structures may be
divided, as to their functions, into two main divisions. One is chiefly
protective in character. Thus the layers of epithelium which form the
superficial layer of the skin have little beyond such an office to
discharge. The same is to a certain extent true of the epithelial cells
covering the mucous membrane of the mouth, and those lining the air
passages and air cells of the lungs.
[Illustration: Fig. 5.--Various Kinds of Epithelial Cells
A, columnar cells of intestine;
B, polyhedral cells of the conjunctiva;
C, ciliated conical cells of the trachea;
D, ciliated cell of frog's mouth;
E, inverted conical cell of trachea;
F, squamous cell of the cavity of mouth, seen from its broad surface;
G, squamous cell, seen edgeways.
]
The second great division of the epithelial tissues consists of those
whose cells are formed of highly active protoplasm, and are busily engaged
in some sort of secretion. Such are the cells of glands,--the cells of the
salivary glands, which secrete the saliva, of the gastric glands, which
secrete the gastric juice, of the intestinal glands, and the cells of the
liver and sweat glands.
19. Connective Tissue. This is the material, made up of fibers and
cells, which serves to unite and bind together the different organs and
tissues. It forms a sort of flexible framework of the body, and so
pervades every portion that if all the other tissues were removed, we
should still have a complete representation of the bodily shape in every
part. In general, the connective tissues proper act as packing,
binding, and supporting structures. This name includes certain tissues
which to all outward appearance vary greatly, but which are properly
grouped together for the following reasons: first, they all act as
supporting structures; second, under certain conditions one may be
substituted for another; third, in some places they merge into each other.
All these tissues consist of a ground-substance, or matrix, cells, and
fibers. The ground-substance is in small amount in connective tissues
proper, and is obscured by a mass of fibers. It is best seen in hyaline
cartilage, where it has a glossy appearance. In bone it is infiltrated
with salts which give bone its hardness, and make it seem so unlike other
tissues. The cells are called connective-tissue corpuscles, cartilage
cells, and bone corpuscles, according to the tissues in which they occur.
The fibers are the white fibrous and the yellow elastic tissues.
The following varieties are usually described:
I. Connective Tissues Proper:
1. White Fibrous Tissue.
2. Yellow Elastic Tissue.
3. Areolar or Cellular Tissue.
4. Adipose or Fatty Tissue.
5. Adenoid or Retiform Tissue.
II. Cartilage (Gristle):
1. Hyaline.
2. White Fibro-cartilage.
3. Yellow Fibro-cartilage.
III. Bone and Dentine of Teeth.
20. White Fibrous Tissue. This tissue consists of bundles of very
delicate fibrils bound together by a small amount of cement substance.
Between the fibrils protoplasmic masses (connective-tissue corpuscles)
are found. These fibers may be found so interwoven as to form a sheet, as
in the periosteum of the bone, the fasciae around muscles, and the capsules
of organs; or they may be aggregated into bundles and form rope-like
bands, as in the ligaments of joints and the tendons of muscles. On
boiling, this tissue yields gelatine. In general, where white fibrous
tissue abounds, structures are held together, and there is flexibility,
but little or no distensibility.
[Illustration: Fig. 6.--White Fibrous Tissue. (Highly magnified.)]
21. Yellow Elastic Tissue. The fibers of yellow elastic tissue
are much stronger and coarser than those of the white. They are yellowish,
tend to curl up at the ends, and are highly elastic. It is these fibers
which give elasticity to the skin and to the coats of the arteries. The
typical form of this tissue occurs in the ligaments which bind the
vertebrae together (Fig. 26), in the true vocal cords, and in certain
ligaments of the larynx. In the skin and fasciae, the yellow elastic is
found mixed with white fibrous and areolar tissues. It does not yield
gelatine on boiling, and the cells are, if any, few.
[Illustration: Fig. 7.--Yellow Elastic Tissue. (Highly magnified.)]
22. Areolar or Cellular Tissue. This consists of bundles of delicate
fibers interlacing and crossing one another, forming irregular spaces or
meshes. These little spaces, in health, are filled with fluid that has
oozed out of the blood-vessels. The areolar tissue forms a protective
covering for the tissues of delicate and important organs.
23. Adipose or Fatty Tissue. In almost every part of the body the
ordinary areolar tissue contains a variable quantity of adipose or
fatty tissue. Examined by the microscope, the fat cells consist of a
number of minute sacs of exceedingly delicate, structureless membrane
filled with oil. This is liquid in life, but becomes solidified after
death. This tissue is plentiful beneath the skin, in the abdominal cavity,
on the surface of the heart, around the kidneys, in the marrow of bones,
and elsewhere. Fat serves as a soft packing material. Being a poor
conductor, it retains the heat, and furnishes a store rich in carbon and
hydrogen for use in the body.
24. Adenoid or Retiform Tissue. This is a variety of connective
tissue found in the tonsils, spleen, lymphatic glands, and allied
structures. It consists of a very fine network of cells of various sizes.
The tissue combining them is known as adenoid or gland-like tissue.
[Illustration: Fig. 8.--Fibro-Cartilage Fibers. (Showing network
surrounded cartilage cells.)]
25. Cartilage. Cartilage, or gristle, is a tough but highly elastic
substance. Under the microscope cartilage is seen to consist of a
matrix, or base, in which nucleated cells abound, either singly or in
groups. It has sometimes a fine ground-glass appearance, when the
cartilage is spoken of as hyaline. In other cases the matrix is
almost replaced by white fibrous tissue. This is called white
fibro-cartilage, and is found where great strength and a certain
amount of rigidity are required.
Again, there is between the cells a meshwork of yellow elastic fibers, and
this is called yellow fibro-cartilage (Fig. 8). The hyaline cartilage
forms the early state of most of the bones, and is also a permanent
coating for the articular ends of long bones. The white fibro-cartilage is
found in the disks between the bodies of the vertebrae, in the interior of
the knee joint, in the wrist and other joints, filling the cavities of the
bones, in socket joints, and in the grooves for tendons. The yellow
fibro-cartilage forms the expanded part of the ear, the epiglottis, and
other parts of the larynx.
26. General Plan of the Body. To get a clearer idea of the general
plan on which the body is constructed, let us imagine its division into
perfectly equal parts, one the right and the other the left, by a great
knife severing it through the median, or middle line in front, backward
through the spinal column, as a butcher divides an ox or a sheep into
halves for the market. In a section of the body thus planned the skull and
the spine together are shown to have formed a tube, containing the brain
and spinal cord. The other parts of the body form a second tube (ventral)
in front of the spinal or dorsal tube. The upper part of the second tube
begins with the mouth and is formed by the ribs and breastbone. Below the
chest in the abdomen, the walls of this tube would be made up of the soft
parts.
[Illustration: Fig. 9.--Diagrammatic Longitudinal Section of the Trunk and
Head. (Showing the dorsal and the ventral tubes.)
A, the cranial cavity;
B, the cavity of the nose;
C, the mouth;
D, the alimentary canal represented as a simple straight tube;
E, the sympathetic nervous system;
F, heart;
G, diaphragm;
H, stomach;
K, end of spinal portion of cerebro-spinal nervous system.
]
We may say, then, that the body consists of two tubes or cavities,
separated by a bony wall, the dorsal or nervous tube, so called
because it contains the central parts of the nervous system; and the
visceral or ventral tube, as it contains the viscera, or general
organs of the body, as the alimentary canal, the heart, the lungs, the
sympathetic nervous system, and other organs.
The more detailed study of the body may now be begun by a description of
the skeleton or framework which supports the soft parts.
Experiments.
For general directions and explanations and also detailed suggestions for
performing experiments, see Chapter XV.
Experiment 1. _To examine squamous epithelium._ With an ivory
paper-knife scrape the back of the tongue or the inside of the lips or
cheek; place the substance thus obtained upon a glass slide; cover it
with a thin cover-glass, and if necessary add a drop of water. Examine
with the microscope, and the irregularly formed epithelial cells will be
seen.
Experiment 2. _To examine ciliated epithelium._ Open a frog's
mouth, and with the back of a knife blade gently scrape a little of the
membrane from the roof of the mouth. Transfer to a glass slide, add a
drop of salt solution, and place over it a cover-glass with a hair
underneath to prevent pressure upon the cells. Examine with a microscope
under a high power. The cilia move very rapidly when quite fresh, and
are therefore not easily seen.
For additional experiments which pertain to the microscopic examination of
the elementary tissues and to other points in practical histology, see
Chapter XV.
[NOTE. Inasmuch as most of the experimental work of this chapter
depends upon the use of the microscope and also necessarily assumes a
knowledge of facts which are discussed later, it would be well to
postpone experiments in histology until they can be more
satisfactorily handled in connection with kindred topics as they are
met with in the succeeding chapters.]
Chapter II.
The Bones.
27. The Skeleton. Most animals have some kind of framework to support
and protect the soft and fleshy parts of their bodies. This framework
consists chiefly of a large number of bones, and is called the
skeleton. It is like the keel and ribs of a vessel or the frame of a
house, the foundation upon which the bodies are securely built.
There are in the adult human body 200 distinct bones, of many sizes and
shapes. This number does not, however, include several small bones found
in the tendons of muscles and in the ear. The teeth are not usually
reckoned as separate bones, being a part of the structure of the skin.
The number of distinct bones varies at different periods of life. It is
greater in childhood than in adults, for many bones which are then
separate, to allow growth, afterwards become gradually united. In early
adult life, for instance, the skull contains 22 naturally separate bones,
but in infancy the number is much greater, and in old age far less.
The bones of the body thus arranged give firmness, strength, and
protection to the soft tissues and vital organs, and also form levers for
the muscles to act upon.
28. Chemical Composition of Bone. The bones, thus forming the
framework of the body, are hard, tough, and elastic. They are twice as
strong as oak; one cubic inch of compact bone will support a weight of
5000 pounds. Bone is composed of earthy or mineral matter
(chiefly in the form of lime salts), and of animal matter
(principally gelatine), in the proportion of two-thirds of the former to
one-third of the latter.
[Illustration: Fig. 10.--The Skeleton.]
The proportion of earthy to animal matter varies with age. In infancy the
bones are composed almost wholly of animal matter. Hence, an infant's
bones are rarely broken, but its legs may soon become misshapen if walking
is allowed too early. In childhood, the bones still contain a larger
percentage of animal matter than in more advanced life, and are therefore
more liable to bend than to break; while in old age, they contain a
greater percentage of mineral matter, and are brittle and easily broken.
Experiment 3. _To show the mineral matter in bone_. Weigh a large
soup bone; put it on a hot, clear fire until it is at a red heat. At
first it becomes black from the carbon of its organic matter, but at
last it turns white. Let it cool and weigh again. The animal matter has
been burnt out, leaving the mineral or earthy part, a white, brittle
substance of exactly the same shape, but weighing only about two-thirds
as much as the bone originally weighed.
Experiment 4. _To show the animal matter in bone_. Add a
teaspoonful of muriatic acid to a pint of water, and place the mixture
in a shallow earthen dish. Scrape and clean a chicken's leg bone, part
of a sheep's rib, or any other small, thin bone. Soak the bone in the
acid mixture for a few days. The earthy or mineral matter is slowly
dissolved, and the bone, although retaining its original form, loses its
rigidity, and becomes pliable, and so soft as to be readily cut. If the
experiment be carefully performed, a long, thin bone may even be tied
into a knot.
[Illustration: Fig. 11.--The fibula tied into a knot, after the hard
mineral matter has been dissolved by acid.]
29. Physical Properties of Bone. If we take a leg bone of a sheep, or
a large end of beef shin bone, and saw it lengthwise in halves, we see two
distinct structures. There is a hard and compact tissue, like ivory,
forming the outside shell, and a spongy tissue inside having the
appearance of a beautiful lattice work. Hence this is called cancellous
tissue, and the gradual transition from one to the other is apparent.
It will also be seen that the shaft is a hollow cylinder, formed of
compact tissue, enclosing a cavity called the medullary canal, which is
filled with a pulpy, yellow fat called _marrow_. The marrow is richly
supplied with blood-vessels, which enter the cavity through small openings
in the compact tissue. In fact, all over the surface of bone are minute
canals leading into the substance. One of these, especially constant and
large in many bones, is called the _nutrient foramen_, and transmits an
artery to nourish the bone.
At the ends of a long bone, where it expands, there is no medullary canal,
and the bony tissue is spongy, with only a thin layer of dense bone around
it. In flat bones we find two layers or plates of compact tissue at the
surface, and a spongy tissue between. Short and irregular bones have no
medullary canal, only a thin shell of dense bone filled with cancellous
tissue.
[Illustration: Fig 12.--The Right femur sawed in two, lengthwise. (Showing
arrangement of compact and cancellous tissue.)]
Experiment 5. Obtain a part of a beef shin bone, or a portion of a
sheep's or calf's leg, including if convenient the knee joint. Have the
bone sawed in two, lengthwise, keeping the marrow in place. Boil,
scrape, and carefully clean one half. Note the compact and spongy parts,
shaft, etc.
Experiment 6. Trim off the flesh from the second half. Note the
pinkish white appearance of the bone, the marrow, and the tiny specks of
blood, etc. Knead a small piece of the marrow in the palm; note the oily
appearance. Convert some marrow into a liquid by heating. Contrast this
fresh bone with an old dry one, as found in the fields. Fresh bones
should be kept in a cool place, carefully wrapped in a damp cloth, while
waiting for class use.
A fresh or living bone is covered with a delicate, tough, fibrous
membrane, called the periosteum. It adheres very closely to the bone,
and covers every part except at the joints and where it is protected with
cartilage. The periosteum is richly supplied with blood-vessels, and plays
a chief part in the growth, formation, and repair of bone. If a portion of
the periosteum be detached by injury or disease, there is risk that a
layer of the subjacent bone will lose its vitality and be cast off.[5]
30. Microscopic Structure of Bone. If a very thin slice of bone be
cut from the compact tissue and examined under a microscope, numerous
minute openings are seen. Around these are arranged rings of bone, with
little black bodies in them, from which radiate fine, dark lines. These
openings are sections of canals called _Haversian canals_, after Havers,
an English physician, who first discovered them. The black bodies are
minute cavities called _lacunae_, while the fine lines are very minute
canals, _canaliculi_, which connect the lacunae and the Haversian canals.
These Haversian canals are supplied with tiny blood-vessels, while the
lacunae contain bone cells. Very fine branches from these cells pass into
the canaliculi. The Haversian canals run lengthwise of the bone; hence if
the bone be divided longitudinally these canals will be opened along their
length (Fig. 13).
Thus bones are not dry, lifeless substances, but are the very type of
activity and change. In life they are richly supplied with blood from the
nutrient artery and from the periosteum, by an endless network of
nourishing canals throughout their whole structure. Bone has, therefore,
like all other living structures, a _self-formative_ power, and draws from
the blood the materials for its own nutrition.
[Illustration: Fig. 13.
A, longitudinal section of bone, by which the Haversian canals are seen
branching and communicating with one another;
B, cross section of a very thin slice of bone, magnified about 300
diameters--little openings (Haversian canals) are seen, and around
them are ranged rings of bones with little black bodies (lacunae), from
which branch out fine dark lines (canaliculi);
C, a bone cell, highly magnified, lying in lacuna.
]
The Bones of the Head.
31. The Head, or Skull. The bones of the skeleton, the bony framework
of our bodies, may be divided into those of the head, the trunk,
and the limbs.
The bones of the head are described in two parts,--those of the
cranium, or brain-case, and those of the face. Taken together,
they form the skull. The head is usually said to contain 22 bones, of
which 8 belong to the cranium and 14 to the face. In early childhood, the
bones of the head are separate to allow the brain to expand; but as we
grow older they gradually unite, the better to protect the delicate brain
tissue.
32. The Cranium. The cranium is a dome-like structure, made up
in the adult of 8 distinct bones firmly locked together. These bones are:
One Frontal,
Two Parietal,
Two Temporal
One Occipital,
One Sphenoid,
One Ethmoid.
The frontal bone forms the forehead and front of the head. It is
united with the two parietal bones behind, and extends over the forehead
to make the roofs of the sockets of the eyes. It is this bone which, in
many races of man, gives a dignity of person and a beauty of form seen in
no other animal.
The parietal bones form the sides and roof of the skull. They are
bounded anteriorly by the frontal bone, posteriorly by the occipital, and
laterally by the temporal and sphenoid bones. The two bones make a
beautiful arch to aid in the protection of the brain.
The temporal bones, forming the temples on either side, are attached
to the sphenoid bone in front, the parietals above, and the occipital
behind. In each temporal bone is the cavity containing the organs of
hearing. These bones are so called because the hair usually first turns
gray over them.
The occipital bone forms the lower part of the base of the skull, as
well as the back of the head. It is a broad, curved bone, and rests on the
topmost vertebra (atlas) of the backbone; its lower part is pierced by a
large oval opening called the _foramen magnum_, through which the spinal
cord passes from the brain (Fig. 15).
The sphenoid bone is in front of the occipital, forming a part of the
base of the skull. It is wedged between the bones of the face and those of
the cranium, and locks together fourteen different bones. It bears a
remarkable resemblance to a bat with extended wings, and forms a series of
girders to the arches of the cranium.
The ethmoid bone is situated between the bones of the cranium and
those of the face, just at the root of the nose. It forms a part of the
floor of the cranium. It is a delicate, spongy bone, and is so called
because it is perforated with numerous holes like a sieve, through which
the nerves of smell pass from the brain to the nose.
[Illustration: Fig. 14.--The Skull]
33. The Face. The bones of the face serve, to a marked extent, in
giving form and expression to the human countenance. Upon these bones
depend, in a measure, the build of the forehead, the shape of the chin,
the size of the eyes, the prominence of the cheeks, the contour of the
nose, and other marks which are reflected in the beauty or ugliness of the
face.
The face is made up of fourteen bones which, with the exception of
the lower jaw, are, like those of the cranium, closely interlocked with
each other. By this union these bones help form a number of cavities which
contain most important and vital organs. The two deep, cup-like sockets,
called the orbits, contain the organs of sight. In the cavities of the
nose is located the sense of smell, while the buccal cavity, or mouth, is
the site of the sense of taste, and plays besides an important part in the
first act of digestion and in the function of speech.
The bones of the face are:
Two Superior Maxillary,
Two Malar,
Two Nasal,
Two Lachrymal,
Two Palate,
Two Turbinated,
One Vomer,
One Lower Maxillary.
34. Bones of the Face. The superior maxillary or upper jawbones
form a part of the roof of the mouth and the entire floor of the orbits.
In them is fixed the upper set of teeth.
The malar or cheek bones are joined to the upper jawbones, and help
form the sockets of the eyes. They send an arch backwards to join the
temporal bones. These bones are remarkably thick and strong, and are
specially adapted to resist the injury to which this part of the face is
exposed.
The nasal or nose bones are two very small bones between the eye
sockets, which form the bridge of the nose. Very near these bones are the
two small lachrymal bones. These are placed in the inner angles of
the orbit, and in them are grooves in which lie the ducts through which
the tears flow from the eyes to the nose.
The palate bones are behind those of the upper jaw and with them form
the bony part of the roof of the mouth. The inferior turbinated are
spongy, scroll-like bones, which curve about within the nasal cavities so
as to increase the surface of the air passages of the nose.
The vomer serves as a thin and delicate partition between the two cavities
of the nose. It is so named from its resemblance to a ploughshare.
[Illustration: Fig. 15.--The Base of the Skull.
A, palate process of upper jawbone;
B, zygoma, forming zygomatic arch;
C, condyle for forming articulation with atlas;
D, foramen magnum;
E, occipital bone.
]
The longest bone in the face is the inferior maxillary, or lower jaw.
It has a horseshoe shape, and supports the lower set of teeth. It is the
only movable bone of the head, having a vertical and lateral motion by
means of a hinge joint with a part of the temporal bone.
35. Sutures of the Skull. Before leaving the head we must notice the
peculiar and admirable manner in which the edges of the bones of the outer
shell of the skull are joined together. These edges of the bones resemble
the teeth of a saw. In adult life these tooth-like edges fit into each
other and grow together, suggesting the dovetailed joints used by the
cabinet-maker. When united these serrated edges look almost as if sewed
together; hence their name, sutures. This manner of union gives unity
and strength to the skull.
In infants, the corners of the parietal bones do not yet meet, and the
throbbing of the brain may be seen and felt under these "soft spots," or
_fontanelles_, as they are called. Hence a slight blow to a babe's head
may cause serious injury to the brain (Fig. 14).
The Bones of the Trunk.
36. The Trunk. The trunk is that central part of the body which
supports the head and the upper pair of limbs. It divides itself into an
upper cavity, the thorax, or chest; and a lower cavity, the
abdomen. These two cavities are separated by a movable, muscular
partition called the diaphragm, or midriff (Figs. 9 and 49).
The bones of the trunk are variously related to each other, and some of
them become united during adult life into bony masses which at earlier
periods are quite distinct. For example, the sacrum is in early life made
up of five distinct bones which later unite into one.
The upper cavity, or chest, is a bony enclosure formed by the
breastbone, the ribs, and the spine. It contains the heart and the lungs
(Fig. 86).
The lower cavity, or abdomen, holds the stomach, liver, intestines,
spleen, kidneys, and some other organs (Fig. 59).
The bones of the trunk may be subdivided into those of the spine, the
ribs, and the hips.
The trunk includes 54 bones usually thus arranged:
I. Spinal Column, 26 bones:
7 Cervical Vertebrae.
12 Dorsal Vertebrae.
5 Lumbar Vertebrae.
1 Sacrum.
1 Coccyx.
II. Ribs, 24 bones:
14 True Ribs.
6 False Ribs.
4 Floating Ribs.
III. Sternum.
IV. Two Hip Bones.
V. Hyoid Bone.
37. The Spinal Column. The spinal column, or backbone, is a
marvelous piece of mechanism, combining offices which nothing short of
perfection in adaptation and arrangement could enable it to perform. It is
the central structure to which all the other parts of the skeleton are
adapted. It consists of numerous separate bones, called vertebrae. The
seven upper ones belong to the neck, and are called cervical
vertebrae. The next twelve are the dorsal vertebrae; these belong to
the back and support the ribs. The remaining five belong to the loins, and
are called lumbar vertebrae. On looking at the diagram of the backbone
(Fig. 9) it will be seen that the vertebrae increase in size and strength
downward, because of the greater burden they have to bear, thus clearly
indicating that an erect position is the one natural to man.
[Illustration: Fig. 16.--The Spinal Column.]
This column supports the head, encloses and protects the spinal cord, and
forms the basis for the attachment of many muscles, especially those which
maintain the body in an erect position. Each vertebra has an opening
through its center, and the separate bones so rest, one upon another, that
these openings form a continuous canal from the head to the lower part of
the spine. The great nerve, known as the spinal cord, extends from
the cranium through the entire length of this canal. All along the spinal
column, and between each two adjoining bones, are openings on each side,
through which nerves pass out to be distributed to various parts of the
body.
Between the vertebrae are pads or cushions of cartilage. These act as
"buffers," and serve to give the spine strength and elasticity and to
prevent friction of one bone on another. Each vertebra consists of a body,
the solid central portion, and a number of projections called processes.
Those which spring from the posterior of each arch are the spinous
processes. In the dorsal region they are plainly seen and felt in thin
persons.
The bones of the spinal column are arranged in three slight and graceful
curves. These curves not only give beauty and strength to the bony
framework of the body, but also assist in the formation of cavities for
important internal organs. This arrangement of elastic pads between the
vertebrae supplies the spine with so many elastic springs, which serve to
break the effect of shock to the brain and the spinal cord from any sudden
jar or injury.
The spinal column rests on a strong three-sided bone called the
sacrum, or sacred-bone, which is wedged in between the hip bones and
forms the keystone of the pelvis. Joined to the lower end of the sacrum is
the coccyx, or cuckoo-bone, a tapering series of little bones.
Experiment 7. Run the tips of the fingers briskly down the
backbone, and the spines of the vertebrae will be tipped with red so that
they can be readily counted. Have the model lean forward with the arms
folded across the chest; this will make the spines of the vertebrae more
prominent.
Experiment 8. _To illustrate the movement of torsion in the spine, or
its rotation round its own axis_. Sit upright, with the back and
shoulders well applied against the back of a chair. Note that the head
and neck can be turned as far as 60 degrees or 70 degrees. Now bend
forwards, so as to let the dorsal and lumbar vertebrae come into play,
and the head can be turned 30 degrees more.
Experiment 9. _To show how the spinal vertebrae make a firm but
flexible column._ Take 24 hard rubber overcoat buttons, or the same
number of two-cent pieces, and pile them on top of each other. A thin
layer of soft putty may be put between the coins to represent the pads
of cartilage between the vertebrae. The most striking features of the
spinal column may be illustrated by this simple apparatus.
38. How the Head and Spine are Joined together. The head rests upon
the spinal column in a manner worthy of special notice. This consists in
the peculiar structure of the first two cervical vertebrae, known as the
axis and atlas. The atlas is named after the fabled giant who
supported the earth on his shoulders. This vertebra consists of a ring of
bone, having two cup-like sockets into which fit two bony projections
arising on either side of the great opening (_foramen magnum_) in the
occipital bone. The hinge joint thus formed allows the head to nod
forward, while ligaments prevent it from moving too far.
On the upper surface of the axis, the second vertebra, is a peg or
process, called the _odontoid process_ from its resemblance to a tooth.
This peg forms a pivot upon which the head with the atlas turns. It is
held in its place against the front inner surface of the atlas by a band
of strong ligaments, which also prevents it from pressing on the delicate
spinal cord. Thus, when we turn the head to the right or left, the skull
and the atlas move together, both rotating on the odontoid process of the
axis.
39. The Ribs and Sternum. The barrel-shaped framework of the chest is
in part composed of long, slender, curved bones called ribs. There
are twelve ribs on each side, which enclose and strengthen the chest; they
somewhat resemble the hoops of a barrel. They are connected in pairs with
the dorsal vertebrae behind.
The first seven pairs, counting from the neck, are called the _true_ ribs,
and are joined by their own special cartilages directly to the breastbone.
The five lower pairs, called the _false_ ribs, are not directly joined to
the breastbone, but are connected, with the exception of the last two,
with each other and with the last true ribs by cartilages. These elastic
cartilages enable the chest to bear great blows with impunity. A blow on
the sternum is distributed over fourteen elastic arches. The lowest two
pairs of false ribs, are not joined even by cartilages, but are quite free
in front, and for this reason are called _floating_ ribs.
The ribs are not horizontal, but slope downwards from the backbone, so
that when raised or depressed by the strong intercostal muscles, the size
of the chest is alternately increased or diminished. This movement of the
ribs is of the utmost importance in breathing (Fig. 91).
The sternum, or breastbone, is a long, flat, narrow bone forming the
middle front wall of the chest. It is connected with the ribs and with the
collar bones. In shape it somewhat resembles an ancient dagger.
40. The Hip Bones. Four immovable bones are joined together so as to
form at the lower extremity of the trunk a basin-like cavity called the
pelvis. These four bones are the sacrum and the coccyx,
which have been described, and the two hip bones.
[Illustration: Fig. 17.--Thorax. (Anterior view.)]
The hip bones are large, irregularly shaped bones, very firm and
strong, and are sometimes called the haunch bones or _ossa innominata_
(nameless bones). They are united to the sacrum behind and joined to each
other in front. On the outer side of each hip bone is a deep cup, or
socket, called the _acetabulum_, resembling an ancient vinegar cup, into
which fits the rounded head of the thigh bone. The bones of the pelvis are
supported like a bridge on the legs as pillars, and they in turn contain
the internal organs in the lower part of the trunk.
41. The Hyoid Bone. Under the lower jaw is a little horseshoe shaped bone
called the hyoid bone, because it is shaped like the Greek letter upsilon
([Greek: u]). The root of the tongue is fastened to its bend, and the
larynx is hung from it as from a hook. When the neck is in its natural
position this bone can be plainly felt on a level with the lower jaw and
about one inch and a half behind it. It serves to keep open the top of the
larynx and for the attachment of the muscles, which move the tongue. (See
Fig. 46.) The hyoid bone, like the knee-pan, is not connected with any
other bone.
The Bones of the Upper Limbs.
42. The Upper Limbs. Each of the upper limbs consist of the upper
arm, the forearm, and the hand. These bones are classified
as follows:
Upper Arm:
Scapula, or shoulder-blade,
Clavicle, or collar bone,
Humerus, or arm bone,
Forearm:
Ulna,
Radius,
Hand:
8 Carpal or wrist bones,
5 Metacarpal bones,
14 Phalanges, or finger bones,
making 32 bones in all.
43. The Upper Arm. The two bones of the shoulder, the scapula
and the clavicle, serve in man to attach the arm to the trunk. The
scapula, or shoulder-blade, is a flat, triangular bone, placed point
downwards, and lying on the upper and back part of the chest, over the
ribs. It consists of a broad, flat portion and a prominent ridge or
_spine_. At its outer angle it has a shallow cup known as the _glenoid
cavity_. Into this socket fits the rounded head of the humerus. The
shoulder-blade is attached to the trunk chiefly by muscles, and is capable
of extensive motion.
The clavicle, or collar bone, is a slender bone with a double curve
like an italic _f_, and extends from the outer angle of the shoulder-blade
to the top of the breastbone. It thus serves like the keystone of an arch
to hold the shoulder-blade firmly in its place, but its chief use is to
keep the shoulders wide apart, that the arm may enjoy a freer range of
motion. This bone is often broken by falls upon the shoulder or arm.
The humerus is the strongest bone of the upper extremity. As already
mentioned, its rounded head fits into the socket of the shoulder-blade,
forming a ball-and-socket joint, which permits great freedom of motion.
The shoulder joint resembles what mechanics call a universal joint, for
there is no part of the body which cannot be touched by the hand.
[Illustration: Fig. 18.--Left Scapula, or Shoulder-Blade.]
When the shoulder is dislocated the head of the humerus has been forced
out of its socket. The lower end of the bone is grooved to help form a
hinge joint at the elbow with the bones of the forearm (Fig. 27).
44. The Forearm. The forearm contains two long bones, the
ulna and the radius. The ulna, so called because it forms
the elbow, is the longer and larger bone of the forearm, and is on the
same side as the little finger. It is connected with the humerus by a
hinge joint at the elbow. It is prevented from moving too far back by a
hook-like projection called the _olecranon process_, which makes the sharp
point of the elbow.
The radius is the shorter of the two bones of the forearm, and is on
the same side as the thumb. Its slender, upper end articulates with the
ulna and humerus; its lower end is enlarged and gives attachment in part
to the bones of the wrist. This bone radiates or turns on the ulna,
carrying the hand with it.
Experiment 10. Rest the forearm on a table, with the palm up (an
attitude called supination). The radius is on the outer side and
parallel with the ulna If now, without moving the elbow, we turn the
hand (pronation), as if to pick up something from the table, the radius
may be seen and felt crossing over the ulna, while the latter has not
moved.
[Illustration: Fig. 19.--Left Clavicle, or Collar Bone. (Anterior
surface.)]
45. The Hand. The hand is the executive or essential part of the
upper limb. Without it the arm would be almost useless. It consists of 27
separate bones, and is divided into three parts, the wrist, the
palm, and the fingers.
[Illustration: Fig. 20.--Left Humerus.]
[Illustration: Fig. 21.--Left Radius and Ulna.]
The carpus, or wrist, includes 8 short bones, arranged in two rows of
four each, so as to form a broad support for the hand. These bones are
closely packed, and tightly bound with ligaments which admit of ample
flexibility. Thus the wrist is much less liable to be broken than if it
were to consist of a single bone, while the elasticity from having the
eight bones movable on each other, neutralizes, to a great extent, a
shock caused by falling on the hands. Although each of the wrist bones has
a very limited mobility in relation to its neighbors, their combination
gives the hand that freedom of action upon the wrist, which is manifest in
countless examples of the most accurate and delicate manipulation.
The metacarpal bones are the five long bones of the back of the hand.
They are attached to the wrist and to the finger bones, and may be easily
felt by pressing the fingers of one hand over the back of the other. The
metacarpal bones of the fingers have little freedom of movement, while the
thumb, unlike the others, is freely movable. We are thus enabled to bring
the thumb in opposition to each of the fingers, a matter of the highest
importance in manipulation. For this reason the loss of the thumb disables
the hand far more than the loss of either of the fingers. This very
significant opposition of the thumb to the fingers, furnishing the
complete grasp by the hand, is characteristic of the human race, and is
wanting in the hand of the ape, chimpanzee, and ourang-outang.
The phalanges, or finger bones, are the fourteen small bones arranged
in three rows to form the fingers. Each finger has three bones; each
thumb, two.
The large number of bones in the hand not only affords every variety of
movement, but offers great resistance to blows or shocks. These bones are
united by strong but flexible ligaments. The hand is thus given strength
and flexibility, and enabled to accomplish the countless movements so
necessary to our well-being.
In brief, the hand is a marvel of precise and adapted mechanism, capable
not only of performing every variety of work and of expressing many
emotions of the mind, but of executing its orders with inconceivable
rapidity.
The Bones of the Lower Limbs.
46. The Lower Limbs. The general structure and number of the bones of
the lower limbs bear a striking similarity to those of the upper limbs.
Thus the leg, like the arm, is arranged in three parts, the thigh,
the lower leg, and the foot. The thigh bone corresponds to the
humerus; the tibia and fibula to the ulna and radius; the ankle to the
wrist; and the metatarsus and the phalanges of the foot, to the metacarpus
and the phalanges of the hand.
The bones of the lower limbs may be thus arranged:
Thigh: Femur, or thigh bone,
Lower Leg:
Patella, or knee cap,
Tibia, or shin bone,
Fibula, or splint bone,
Foot:
7 Tarsal or ankle bones,
5 Metatarsal or instep bones,
14 Phalanges, or toes bones,
making 30 bones in all.
[Illustration: Fig. 22.--Right Femur, or Thigh Bone.]
47. The Thigh. The longest and strongest of all the bones is the
femur, or thigh bone. Its upper end has a rounded head which fits into the
_acetabulum_, or the deep cup-like cavity of the hip bone, forming a
perfect ball-and-socket joint. When covered with cartilage, the ball fits
so accurately into its socket that it may be retained by atmospheric
pressure alone (sec. 50).
The shaft of the femur is strong, and is ridged and roughened in places
for the attachment of the muscles. Its lower end is broad and irregularly
shaped, having two prominences called _condyles_, separated by a groove,
the whole fitted for forming a hinge joint with the bones of the lower leg
and the knee-cap.
48. The Lower Leg. The lower leg, like the forearm, consists of
two bones. The tibia, or shin bone, is the long three-sided bone
forming the front of the leg. The sharp edge of the bone is easily felt
just under the skin. It articulates with the lower end of the thigh bone,
forming with it a hinge joint.
The fibula, the companion bone of the tibia, is the long, slender
bone on the outer side of the leg. It is firmly fixed to the tibia at each
end, and is commonly spoken of as the small bone of the leg. Its lower end
forms the outer projection of the ankle. In front of the knee joint,
embedded in a thick, strong tendon, is an irregularly disk-shaped bone,
the patella, or knee-cap. It increases the leverage of important
muscles, and protects the front of the knee joint, which is, from its
position, much exposed to injury.
[Illustration: Fig. 23.--Patella, or Knee-Cap.]
49. The Foot. The bones of the foot, 26 in number, consist of
the tarsal bones, the metatarsal, and the phalanges. The
tarsal bones are the seven small, irregular bones which make up the
ankle. These bones, like those of the wrist, are compactly arranged, and
are held firmly in place by ligaments which allow a considerable amount of
motion.
One of the ankle bones, the _os calcis_, projects prominently backwards,
forming the heel. An extensive surface is thus afforded for the attachment
of the strong tendon of the calf of the leg, called the tendon of
Achilles. The large bone above the heel bone, the _astragalus_,
articulates with the tibia, forming a hinge joint, and receives the weight
of the body.
The metatarsal bones, corresponding to the metacarpals of the hand,
are five in number, and form the lower instep.
The phalanges are the fourteen bones of the toes,--three in each
except the great toe, which, like the thumb, has two. They resemble in
number and plan the corresponding bones in the hand. The bones of the foot
form a double arch,--an arch from before backwards, and an arch from side
to side. The former is supported behind by the os calcis, and in front by
the ends of the metatarsal bones. The weight of the body falls
perpendicularly on the astragalus, which is the key-bone or crown of the
arch. The bones of the foot are kept in place by powerful ligaments,
combining great strength with elasticity.
[Illustration: Fig. 24.--Right Tibia and Fibula (Anterior surface.)]
[Illustration: Fig. 25.--Bones of Right Foot. (Dorsal surface.)]
The Joints.
50. Formation of Joints. The various bones of the skeleton are
connected together at different parts of their surfaces by joints, or
articulations. Many different kinds of joints have been described, but the
same general plan obtains for nearly all. They vary according to the kind
and the amount of motion.
The principal structures which unite in the formation of a joint are:
bone, cartilage, synovial membrane, and ligaments. Bones make
the chief element of all the joints, and their adjoining surfaces are
shaped to meet the special demands of each joint (Fig. 27). The joint-end
of bones is coated with a thin layer of tough, elastic cartilage. This is
also used at the edge of joint-cavities, forming a ring to deepen them.
The rounded heads of bones which move in them are thus more securely held
in their sockets.
Besides these structures, the muscles also help to maintain the
joint-surfaces in proper relation. Another essential to the action of the
joints is the pressure of the outside air. This may be sufficient to keep
the articular surfaces in contact even after all the muscles are removed.
Thus the hip joint is so completely surrounded by ligaments as to be
air-tight; and the union is very strong. But if the ligaments be pierced
and air allowed to enter the joint, the union at once becomes much less
close, and the head of the thigh bone falls away as far as the ligaments
will allow it.
51. Synovial Membrane. A very delicate connective tissue, called the
synovial membrane, lines the capsules of the joints, and covers the
ligaments connected with them. It secretes the _synovia_, or joint oil, a
thick and glairy fluid, like the white of a raw egg, which thoroughly
lubricates the inner surfaces of the joints. Thus the friction and heat
developed by movement are reduced, and every part of a joint is enabled to
act smoothly.
52. Ligaments. The bones are fastened together, held in place, and
their movements controlled, to a certain extent, by bands of various
forms, called ligaments. These are composed mainly of bundles of
white fibrous tissue placed parallel to, or closely interlaced with, one
another, and present a shining, silvery aspect. They extend from one of
the articulating bones to another, strongly supporting the joint, which
they sometimes completely envelope with a kind of cap (Fig. 28). This
prevents the bones from being easily dislocated. It is difficult, for
instance, to separate the two bones in a shoulder or leg of mutton, they
are so firmly held together by tough ligaments.
While ligaments are pliable and flexible, permitting free movement, they
are also wonderfully strong and inextensible. A bone may be broken, or its
end torn off, before its ligaments can be ruptured. The wrist end of the
radius, for instance, is often torn off by force exerted on its ligaments
without their rupture.
The ligaments are so numerous and various and are in some parts so
interwoven with each other, that space does not allow even mention of
those that are important. At the knee joint, for instance, there are no
less than fifteen distinct ligaments.
53. Imperfect Joints. It is only perfect joints that are fully
equipped with the structures just mentioned. Some joints lack one or more,
and are therefore called imperfect joints. Such joints allow little or no
motion and have no smooth cartilages at their edges. Thus, the bones of
the skull are dovetailed by joints called sutures, which are immovable.
The union between the vertebrae affords a good example of imperfect joints
which are partially movable.
[Illustration: Fig. 26.--Elastic Tissue from the Ligaments about Joints.
(Highly magnified.)]
54. Perfect Joints. There are various forms of perfect joints,
according to the nature and amount of movement permitted. They an divided
into hinge joints, ball-and-socket joints and pivot joints.
The hinge joints allow forward and backward movements like a hinge.
These joints are the most numerous in the body, as the elbow, the ankle,
and the knee joints.
In the ball-and-socket joints--a beautiful contrivance--the rounded
head of one bone fits into a socket in the other, as the hip joint and
shoulder joint. These joints permit free motion in almost every direction.
In the pivot joint a kind of peg in one bone fits into a notch in
another. The best example of this is the joint between the first and
second vertebrae (see sec. 38). The radius moves around on the ulna by
means of a pivot joint. The radius, as well as the bones of the wrist and
hand, turns around, thus enabling us to turn the palm of the hand upwards
and downwards. In many joints the extent of motion amounts to only a
slight gliding between the ends of the bones.
55. Uses of the Bones. The bones serve many important and useful
purposes. The skeleton, a general framework, affords protection,
support, and leverage to the bodily tissues. Thus, the bones of
the skull and of the chest protect the brain, the lungs, and the heart;
the bones of the legs support the weight of the body; and the long bones
of the limbs are levers to which muscles are attached.
Owing to the various duties they have to perform, the bones are
constructed in many different shapes. Some are broad and flat;
others, long and cylindrical; and a large number very irregular
in form. Each bone is not only different from all the others, but is also
curiously adapted to its particular place and use.
[Illustration: Fig. 27.--Showing how the Ends of the Bones are shaped to
form the Elbow Joint. (The cut ends of a few ligaments are seen.)]
Nothing could be more admirable than the mechanism by which each one of
the bones is enabled to fulfill the manifold purposes for which it was
designed. We have seen how the bones of the cranium are united by sutures
in a manner the better to allow the delicate brain to grow, and to afford
it protection from violence. The arched arrangement of the bones of the
foot has several mechanical advantages, the most important being that it
gives firmness and elasticity to the foot, which thus serves as a support
for the weight of the body, and as the chief instrument of locomotion.
The complicated organ of hearing is protected by a winding series of
minute apartments, in the rock-like portion of the temporal bone. The
socket for the eye has a jutting ridge of bone all around it, to guard the
organ of vision against injury. Grooves and canals, formed in hard bone,
lodge and protect minute nerves and tiny blood-vessels. The surfaces of
bones are often provided with grooves, sharp edges, and rough projections,
for the origin and insertion of muscles.
[Illustration: Fig. 28.--External Ligaments of the Knee.]
56. The Bones in Infancy and Childhood. The bones of the infant,
consisting almost wholly of cartilage, are not stiff and hard as in after
life, but flexible and elastic. As the child grows, the bones become more
solid and firmer from a gradually increased deposit of lime salts. In time
they become capable of supporting the body and sustaining the action of
the muscles. The reason is that well-developed bones would be of no use to
a child that had not muscular strength to support its body. Again, the
numerous falls and tumbles that the child sustains before it is able to
walk, would result in broken bones almost every day of its life. As it is,
young children meet with a great variety of falls without serious injury.
But this condition of things has its dangers. The fact that a child's
bones bend easily, also renders them liable to permanent change of shape.
Thus, children often become bow-legged when allowed to walk too early.
Moderate exercise, however, even in infancy, promotes the health of the
bones as well as of the other tissues. Hence a child may be kept too long
in its cradle, or wheeled about too much in a carriage, when the full use
of its limbs would furnish proper exercise and enable it to walk earlier.
57. Positions at School. Great care must be exercised by teachers
that children do not form the habit of taking injurious positions at
school. The desks should not be too low, causing a forward stoop; or too
high, throwing one shoulder up and giving a twist to the spine. If the
seats are too low there will result an undue strain on the shoulder and
the backbone; if too high, the feet have no proper support, the thighs may
be bent by the weight of the feet and legs, and there is a prolonged
strain on the hips and back. Curvature of the spine and round shoulders
often result from long-continued positions at school in seats and at desks
which are not adapted to the physical build of the occupant.
[Illustration: Fig. 29.--Section of the Knee Joint. (Showing its internal
structure)
A, tendon of the semi-membranosus muscle cut across;
B, F, tendon of same muscle;
C, internal condyle of femur;
D, posterior crucial ligament;
E, internal interarticular fibro cartilage;
G, bursa under knee-cap;
H, ligament of knee-cap;
K, fatty mass under knee-cap;
L, anterior crucial ligament cut across;
P, patella, or knee-cap
]
A few simple rules should guide teachers and school officials in providing
proper furniture for pupils. Seats should be regulated according to the
size and age of the pupils, and frequent changes of seats should be made.
At least three sizes of desks should be used in every schoolroom, and more
in ungraded schools. The feet of each pupil should rest firmly on the
floor, and the edge of the desk should be about one inch higher than the
level of the elbows. A line dropped from the edge of the desk should
strike the front edge of the seat. Sliding down into the seat, bending too
much over the desk while writing and studying, sitting on one foot or
resting on the small of the back, are all ungraceful and unhealthful
positions, and are often taken by pupils old enough to know better. This
topic is well worth the vigilance of every thoughtful teacher, especially
of one in the lower grades.
58. The Bones in After Life. Popular impression attributes a less
share of life, or a lower grade of vitality, to the bones than to any
other part of the body. But really they have their own circulation and
nutrition, and even nervous relations. Thus, bones are the seat of active
vital processes, not only during childhood, but also in adult life,
and in fact throughout life, except perhaps in extreme old age. The final
knitting together of the ends of some of the bones with their shafts does
not occur until somewhat late in life. For example, the upper end of the
tibia and its shaft do not unite until the twenty-first year. The separate
bones of the sacrum do not fully knit into one solid bone until the
twenty-fifth year. Hence, the risk of subjecting the bones of young
persons to undue violence from injudicious physical exercise as in rowing,
baseball, football, and bicycle-riding.
The bones during life are constantly going through the process of
absorption and reconstruction. They are easily modified in their growth.
Thus the continued pressure of some morbid deposit, as a tumor or cancer,
or an enlargement of an artery, may cause the absorption or distortion of
bones as readily as of one of the softer tissues. The distortion resulting
from tight lacing is a familiar illustration of the facility with which
the bones may be modified by prolonged pressure.
Some savage races, not content with the natural shape of the head, take
special methods to mould it by continued artificial pressure, so that it
may conform in its distortion to the fashion of their tribe or race. This
custom is one of the most ancient and widespread with which we are
acquainted. In some cases the skull is flattened, as seen in certain
Indian tribes on our Pacific coast, while with other tribes on the same
coast it is compressed into a sort of conical appearance. In such cases
the brain is compelled, of course, to accommodate itself to the change in
the shape of the head; and this is done, it is said, without any serious
result.
59. Sprains and Dislocations. A twist or strain of the ligaments and
soft parts about a joint is known as a sprain, and may result from a
great variety of accidents. When a person falls, the foot is frequently
caught under him, and the twist comes upon the ligaments and tissues of
the ankle. The ligaments cannot stretch, and so have to endure the wrench
upon the joint. The result is a sprained ankle. Next to the ankle, a
sprain of the wrist is most common. A person tries, by throwing out his
hand, to save himself from a fall, and the weight of the body brings the
strain upon the firmly fixed wrist. As a result of a sprain, the ligaments
may be wrenched or torn, and even a piece of an adjacent bone may be torn
off; the soft parts about the injured joint are bruised, and the
neighboring muscles put to a severe stretch. A sprain may be a slight
affair, needing only a brief rest, or it may be severe and painful enough
to call for the most skillful treatment by a surgeon. Lack of proper care
in severe sprains often results in permanent lameness.
A fall or a blow may bring such a sudden wrench or twist upon the
ligaments as to force a bone out of place. This displacement is known as a
dislocation. A child may trip or fall during play and put his elbow
out of joint. A fall from horseback, a carriage, or a bicycle may result
in a dislocation of the shoulder joint. In playing baseball a swift ball
often knocks a finger out of joint. A dislocation must be reduced at once.
Any delay or carelessness may make a serious and painful affair of it, as
the torn and bruised parts rapidly swell and become extremely sensitive.
60. Broken Bones. The bones, especially those of the upper limbs, are
often fractured or broken. The _simple_ fracture is the most common
form, the bone being broken in a single place with no opening through the
skin. When properly adjusted, the bone heals rapidly. Sometimes bones are
crushed into a number of fragments; this is a _comminuted_ fracture.
When, besides the break, there is an opening through the soft parts and
surface of the body, we have a _compound_ fracture. This is a serious
injury, and calls for the best surgical treatment.
A bone may be bent, or only partly broken, or split. This is called "a
green-stick fracture," from its resemblance to a half-broken green stick.
This fracture is more common in the bones of children.
Fractures may be caused by direct violence, as when a bone is broken at a
certain point by some powerful force, as a blow from a baseball bat or a
fall from a horse. Again, a bone may be broken by indirect violence, as
when a person being about to fall, throws out his hand to save himself.
The force of the fall on the hand often breaks the wrist, by which is
meant the fracture of the lower end of the radius, often known as the
"silver-fork fracture." This accident is common in winter from a fall or
slip on the ice.
Sometimes bones are broken at a distance from the point of injury, as in a
fracture of the ribs by violent compression of the chest; or fracture may
occur from the vibration of a blow, as when a fall or blow upon the top of
the head produces fracture of the bones at the base of the brain.[6]
61. Treatment for Broken Bones. When a bone is broken a surgeon is
needed to set it, that is, to bring the broken parts into their natural
position, and retain them by proper appliances. Nature throws out between
and around the broken ends of bones a supply of repair material known as
plastic lymph, which is changed to fibrous tissue, then to cartilage, and
finally to bone. This material serves as a sort of cement to hold the
fractured parts together. The excess of this at the point of union can be
felt under the skin for some time after the bone is healed.
With old people a broken bone is often a serious matter, and may cripple
them for life or prove fatal. A trifling fall, for instance, may cause a
broken hip (popularly so called, though really a fracture of the neck of
the femur), from the shock of which, and the subsequent pain and
exhaustion, an aged person may die in a few weeks. In young people,
however, the parts of a broken bone will knit together in three or four
weeks after the fracture is reduced; while in adults, six or even more may
be required for firm union. After a broken bone is strong enough to be
used, it is fragile for some time; and great care must be taken,
especially with children, that the injured parts may not be broken again
before perfect union takes place.[7]
62. The Effect of Alcohol upon the Bones. While the growth of the
bones occurs, of course, mainly during the earlier years of life, yet they
do not attain their full maturity until about the twenty-fifth year; and
it is stated that in persons devoted to intellectual pursuits, the skull
grows even after that age. It is plainly necessary that during this period
of bone growth the nutrition of the body should be of the best, that the
bones may be built up from pure blood, and supplied with all the materials
for a large and durable framework. Else the body will be feeble and
stunted, and so through life fall short of its purpose.
If this bony foundation be then laid wrong, the defect can never be
remedied. This condition is seen in young persons who have been underfed
and overworked. But the use of alcoholic liquors produces a similar
effect, hindering bone cell-growth and preventing full development.[8]
The appetite is diminished, nutrition perverted and impaired, the stature
stunted, and both bodily and mental powers are enfeebled.
63. Effect of Tobacco upon the Bones. Another narcotic, the
destructive influence of which is wide and serious, is tobacco. Its
pernicious influence, like that of alcohol, is peculiarly hurtful to the
young, as the cell development during the years of growth is easily
disturbed by noxious agents. The bone growth is by cells, and a powerful
narcotic like tobacco retards cell-growth, and thus hinders the building
up of the bodily frame. The formation of healthy bone demands good,
nutritious blood, but if instead of this, the material furnished for the
production of blood is poor in quality or loaded with poisonous narcotics,
the body thus defrauded of its proper building material becomes undergrown
and enfeebled.
Two unfavorable facts accompany this serious drawback: one is, that owing
to the insidious nature of the smoky poison[9] (cigarettes are its worst
form) the cause may often be unsuspected, and so go on, unchecked; and the
other, that the progress of growth once interrupted, the gap can never be
fully made up. Nature does her best to repair damages and to restore
defects, but never goes backwards to remedy neglects.
Additional Experiments.
Experiment 11. Take a portion of the decalcified bone obtained from
Experiment 4, and wash it thoroughly in water: in this it is insoluble.
Place it in a solution of carbonate of soda and wash it again. Boil it
in water, and from it gelatine will be obtained.
Experiment 12. Dissolve in hydrochloric acid a small piece of the
powdered bone-ash obtained from Experiment 3. Bubbles of carbon dioxid
are given off, indicating the presence of a carbonate. Dilute the
solution; add an excess of ammonia, and we find a white precipitate of
the phosphate of lime and of magnesia.
Experiment 13. Filter the solution in the preceding experiment, and
to the filtrate add oxalate of ammonia. The result is a white
precipitate of the oxalate of lime, showing there is lime present, but
not as a phosphate.
Experiment 14. To the solution of mineral matters obtained from
Experiment 3, add acetate of soda until free acetic acid is present,
recognized by the smell (like dilute vinegar); then add oxalate of
ammonia. The result will be a copious white precipitate of lime salts.
Experiment 15. _To show how the cancellous structure of bone is
able to support a great deal of weight_. Have the market-man saw out a
cubic inch from the cancellous tissue of a fresh beef bone and place it
on a table with its principal layers upright. Balance a heavy book upon
it, and then gradually place upon it various articles and note how many
pounds it will support before giving way.
Experiment 16. Repeat the last experiment, using a cube of the
decalcified bone obtained from Experiment 4.
[NOTE. As the succeeding chapters are studied, additional experiments
on bones and their relation to other parts of the body, will readily
suggest themselves to the ingenious instructor or the thoughtful
student. Such experiments may be utilized for review or other
exercises.]
Review Analysis: The Skeleton (206 bones).
/ / 1 Frontal,
/ / 2 Parietal,
/ I. Cranium | 2 Temporal,
/ (8 bones) | 1 Occipital,
/ \ 1 Sphenoid,
| \ 1 Ethmoid.
|
| / 2 Superior Maxillary,
The Head | / 2 Malar,
(28 bones). | / 2 Nasal,
| II. Face | 2 Lachrymal Bones,
| (14 bones) | 2 Palate Bones,
| \ 2 Turbinated,
| \ 1 Vomer,
\ \ 1 Lower Maxillary.
\
\ / Hammer,
\ III. The Ear | Anvil,
\ (6 bones) \ Stirrup.
/ / 7 Cervical Vertebrae.
/ / 12 Dorsal Vertebrae,
/ I. Spinal Column | 5 Lumbar Vertebrae,
| (26 bones) \ Sacrum,
| \ Coccyx.
The Trunk |
(54 bones). | / 7 True Ribs,
| II. The Ribs | 3 False Ribs,
| (24 bones) \ 2 Floating Ribs.
|
\ III. Sternum.
\ IV. Two Hip Bones.
\ V. Hyoid Bone.
/ / Scapula,
/ I. Upper Arm | Clavicle,
| \ Humerus.
|
The Upper Limbs | II. Forearm / Ulna,
(64 bones). | \ Radius.
|
| / 8 Carpal Bones,
\ III. Hand | 5 Metacarpal Bones,
\ \ 14 Phalanges.
/ I. Thigh Femur.
/
| / Patella,
The Lower Limbs | II. Lower Leg | Tibia,
(60 bones). | \ Fibula.
|
| / 7 Tarsal Bones,
\ III. Foot | 5 Metatarsal Bones,
\ \ 14 Phalanges.
Chapter III.
The Muscles.
64. Motion in Animals. All motion of our bodies is produced by means
of muscles. Not only the limbs are moved by them, but even the movements
of the stomach and of the heart are controlled by muscles. Every part of
the body which is capable of motion has its own special set of muscles.
Even when the higher animals are at rest it is possible to observe some
kind of motion in them. Trees and stones never move unless acted upon by
external force, while the infant and the tiniest insect can execute a
great variety of movements. Even in the deepest sleep the beating of the
heart and the motion of the chest never cease. In fact, the power to
execute spontaneous movement is the most characteristic property of
living animals.
65. Kinds of Muscles. Most of the bodily movements, such as affect
the limbs and the body as a whole, are performed by muscles under our
control. These muscles make up the red flesh or lean parts, which,
together with the fat, clothe the bony framework, and give to it general
form and proportion. We call these muscular tissues voluntary
muscles, because they usually act under the control of the will.
The internal organs, as those of digestion, secretion, circulation, and
respiration, perform their functions by means of muscular activity of
another kind, that is, by that of muscles not under our control. This work
goes on quite independently of the will, and during sleep. We call the
instruments of this activity involuntary muscles. The voluntary
muscles, from peculiarities revealed by the microscope, are also known as
striped or striated muscles. The involuntary from their smooth, regular
appearance under the microscope are called the unstriped or non-striated
muscles.
The two kinds of muscles, then, are the red, voluntary, striated
muscles, and the smooth, involuntary, non-striated muscles.
66. Structure of Voluntary Muscles. The main substance which clothes
the bony framework of the body, and which forms about two-fifths of its
weight, is the voluntary muscular tissue. These muscles do not cover and
surround the bones in continuous sheets, but consist of separate bundles
of flesh, varying in size and length, many of which are capable of
independent movement.
Each muscle has its own set of blood-vessels, lymphatics, and nerves. It
is the blood that gives the red color to the flesh. Blood-vessels and
nerves on their way to other parts of the body, do not pass through the
muscles, but between them. Each muscle is enveloped in its own sheath of
connective tissue, known as the fascia. Muscles are not usually
connected directly with bones, but by means of white, glistening cords
called tendons.
[Illustration: Fig. 30.--Striated (voluntary) Muscular Fibers.
A, fiber serparating into disks;
B, fibrillae (highly magnified);
C, cross section of a disk
]
If a small piece of muscle be examined under a microscope it is found to
be made up of bundles of fibers. Each fiber is enclosed within a
delicate, transparent sheath, known as the sarcolemma. If one of
these fibers be further examined under a microscope, it will be seen to
consist of a great number of still more minute fibers called
fibrillae. These fibers are also seen marked cross-wise with dark
stripes, and can be separated at each stripe into disks. These cross
markings account for the name _striped_ or _striated_ muscle.
The fibrillae, then, are bound together in a bundle to form a fiber, which
is enveloped in its own sheath, the sarcolemma. These fibers, in turn, are
further bound together to form larger bundles called fasciculi, and
these, too, are enclosed in a sheath of connective tissue. The muscle
itself is made up of a number of these fasciculi bound together by a
denser layer of connective tissue.
Experiment 17. _To show the gross structure of muscle._ Take a
small portion of a large muscle, as a strip of lean corned beef. Have it
boiled until its fibers can be easily separated. Pick the bundles and
fasciculi apart until the fibers are so fine as to be almost invisible
to the naked eye. Continue the experiment with the help of a hand
magnifying glass or a microscope.
67. The Involuntary Muscles. These muscles consist of ribbon-shaped
bands which surround hollow fleshy tubes or cavities. We might compare
them to India rubber rings on rolls of paper. As they are never attached
to bony levers, they have no need of tendons.
[Illustration: Fig. 31.--A, Muscular Fiber, showing Stripes, and Nuclei, b
and c. (Highly magnified.)]
The microscope shows these muscles to consist not of fibers, but of long
spindle-shaped cells, united to form sheets or bands. They have no
sarcolemma, stripes, or cross markings like those of the voluntary
muscles. Hence their name of _non-striated_, or _unstriped_, and _smooth_
muscles.
The involuntary muscles respond to irritation much less rapidly than do
the voluntary. The wave of contraction passes over them more slowly and
more irregularly, one part contracting while another is relaxing. This may
readily be seen in the muscular action of the intestines, called
vermicular motion. It is the irregular and excessive contraction of the
muscular walls of the bowels that produces the cramp-like pains of colic.
The smooth muscles are found in the tissues of the heart, lungs,
blood-vessels, stomach, and intestines. In the stomach their contraction
produces the motion by which the food is churned about; in the arteries
and veins they help supply the force by which the blood is driven along,
and in the intestines that by which the partly digested food is mainly
kept in motion.
Thus all the great vital functions are carried on, regardless of the will
of the individual, or of any outward circumstances. If it required an
effort of the will to control the action of the internal organs we could
not think of anything else. It would take all our time to attend to
living. Hence the care of such delicate and important machinery has wisely
been put beyond our control.
Thus, too, these muscles act instinctively without training; but the
voluntary need long and careful education. A babe can use the muscles of
swallowing on the first day of its life as well as it ever can. But as it
grows up, long and patient education of its voluntary muscles is needed to
achieve walking, writing, use of musical instruments, and many other acts
of daily life.
[Illustration: Fig. 32.--A Spindle Cell of Involuntary Muscle. (Highly
magnified.)]
Experiment 18. _To show the general appearance of the muscles._
Obtain the lower part of a sheep's or calf's leg, with the most of the
lean meat and the hoof left on. One or more of the muscles with their
bundles of fibers, fascia, and tendons; are readily made out with a
little careful dissection. The dissection should be made a few days
before it is wanted and the parts allowed to harden somewhat in dilute
alcohol.
68. Properties of Muscular Tissue. The peculiar property of living
muscular tissue is irritability, or the capacity of responding to a
stimulus. When a muscle is irritated it responds by contracting. By this
act the muscle does not diminish its bulk to any extent; it simply changes
its form. The ends of the muscle are drawn nearer each other and the
middle is thicker.
Muscles do not shorten themselves all at once, but the contraction passes
quickly over them in the form of a wave. They are usually stimulated by
nervous action. The delicate nerve fibrils which end in the fibers
communicate with the brain, the center of the will power. Hence, when the
brain commands, a nervous impulse, sent along the nerve fibers, becomes
the exciting stimulus which acts upon the muscles and makes them shorter,
harder, and more rigid.[10]
Muscles, however, will respond to other than this usual stimulus. Thus an
electrical current may have a similar effect. Heat, also, may produce
muscular contraction. Mechanical means, such as a sharp blow or pinching,
may irritate a muscle and cause it to contract.
We must remember that this property of contraction is inherent and belongs
to the muscle itself. This power of contraction is often independent of
the brain. Thus, on pricking the heart of a fish an hour after removal
from its body, obvious contraction will occur. In this case it is not the
nerve force from the brain that supplies the energy for contraction. The
power of contraction is inherent in the muscle substance, and the stimulus
by irritating the nerve ganglia of the heart simply affords the
opportunity for its exercise.
Contraction is not, however, the natural state of a muscle. In time it is
tired, and begins to relax. Even the heart, the hardest-working muscle,
has short periods of rest between its beats. Muscles are highly elastic as
well as contractile. By this property muscle yields to a stretching force,
and returns to its original length if the stretching has not been
excessive.
[Illustration: Fig. 33.--Principal Muscles of the Body. (Anterior view.)]
69. The Object of Contraction. The object of contraction is obvious.
Like rubber bands, if one end of a muscle be fixed and the other attached
to some object which is free to move, the contraction of the muscle will
bring the movable body nearer to the fixed point. A weight fastened to the
free end of a muscle may be lifted when the muscle contracts. Thus by
their contraction muscles are able to do their work. They even
contract more vigorously when resistance is opposed to them than when it
is not. With increased weight there is an increased amount of work to be
done. The greater resistance calls forth a greater action of the muscle.
This is true up to a certain point, but when the limit has been passed,
the muscle quickly fails to respond.
Again, muscles work best with a certain degree of rapidity provided the
irritations do not follow each other too rapidly. If, however, the
contractions are too rapid, the muscles become exhausted and fatigue
results. When the feeling of fatigue passes away with rest, the muscle
recovers its power. While we are resting, the blood is pouring in fresh
supplies of building material.
Experiment 19. _To show how muscles relax and contract_. Lay your
left forearm on a table; grasp with the right hand the mass of flesh on
the front of the upper arm. Now gradually raise the forearm, keeping the
elbow on the table. Note that the muscle thickens as the hand rises.
This illustrates the contraction of the biceps, and is popularly called
"trying your muscle" Reverse the act. Keep the elbow in position, bring
the forearm slowly to the table, and the biceps appears to become softer
and smaller,--it relaxes.
Experiment 20. Repeat the same experiment with other muscles. With
the right hand grasp firmly the extended left forearm. Extend and flex
the fingers vigorously. Note the effect on the muscles and tendons of
the forearm. Grasp with the right hand the calf of the extended right
leg, and vigorously flex the leg, bringing it near to the body. Note the
contractions and relaxations of the muscles.
70. Arrangement of Muscles. Muscles are not connected directly with
bones. The mass of flesh tapers off towards the ends, where the fibers
pass into white, glistening cords known as tendons. The place at
which a muscle is attached to a bone, generally by means of a tendon, is
called its origin; the end connected with the movable bone is its
insertion.
There are about 400 muscles in the human body, all necessary for its
various movements. They vary greatly in shape and size, according to their
position and use. Some are from one to two feet long, others only a
fraction of an inch. Some are long and spindle-shaped, others thin and
broad, while still others form rings. Thus some of the muscles of the arm
and thigh are long and tapering, while the abdominal muscles are thin and
broad because they help form walls for cavities. Again, the muscular
fibers which surround and by their contraction close certain orifices, as
those of the eyelids and lips, often radiate like the spokes of a wheel.
Muscles are named according to their shape, position, division of origin
or insertion, and their function. Thus we have the _recti_ (straight), and
the _deltoid_ ([Greek: D], delta), the _brachial_ (arm), _pectoral_
(breast), and the _intercostals_ (between the ribs), so named from their
position. Again, we have the _biceps_ (two-headed), _triceps_
(three-headed), and many others with similar names, so called from the
points of origin and insertion. We find other groups named after their
special use. The muscles which bend the limbs are called _flexors_ while
those which straighten them are known as _extensors_.
After a bone has been moved by the contraction of a muscle, it is brought
back to its position by the contraction of another muscle on the opposite
side, the former muscle meanwhile being relaxed. Muscles thus acting in
opposition to each other are called antagonistic. Thus the biceps serves
as one of the antagonists to the triceps, and the various flexors and
extensors of the limbs are antagonistic to one another.
71. The Tendons. The muscles which move the bones by their
contraction taper for the most part, as before mentioned, into
tendons. These are commonly very strong cords, like belts or straps,
made up of white, fibrous tissue.
Tendons are most numerous about the larger joints, where they permit free
action and yet occupy but little space. Large and prominent muscles in
these places would be clumsy and inconvenient. If we bend the arm or leg
forcibly, and grasp the inside of the elbow or knee joint, we can feel the
tendons beneath the skin. The numerous tendons in the palm or on the back
of the hand contribute to its marvelous dexterity and flexibility. The
thickest and strongest tendon in the body is the tendon of Achilles,
which connects the great muscles in the calf of the leg with the heel bone
(sec. 49).
When muscles contract forcibly, they pull upon the tendons which transmit
the movement to the bones to which they are attached. Tendons may be
compared to ropes or cords which, when pulled, are made to act upon
distant objects to which one end is fastened. Sometimes the tendon runs
down the middle of a muscle, and the fibers run obliquely into it, the
tendon resembling the quill in a feather. Again, tendons are spread out in
a flat layer on the surface of muscles, in which case they are called
aponeuroses. Sometimes a tendon is found in the middle of a muscle as well
as at each end of it.
[Illustration: Fig. 34.--The Biceps Muscle dissected to show its Tendons.]
72. Synovial Sheaths and Sacs. The rapid movement of the tendons
over bony surfaces and prominences would soon produce an undue amount of
heat and friction unless some means existed to make the motion as easy as
possible. This is supplied by sheaths which form a double lining around
the tendons. The opposed surfaces are lined with synovial
membrane,[11] the secretion from which oils the sheaths in which the
tendons move.
Little closed sacs, called synovial sacs or bursae, similarly lined
and containing fluid, are also found in special places between two
surfaces where much motion is required. There are two of these bursae near
the patella, one superficial, just under the skin; the other deep beneath
the bone (Fig. 29). Without these, the constant motion of the knee-pan and
its tendons in walking would produce undue friction and heat and
consequent inflammation. Similar, though smaller, sacs are found over the
point of the elbow, over the knuckles, the ankle bones, and various other
prominent points. These sacs answer a very important purpose, and are
liable to various forms of inflammation.
Experiment 21. Examine carefully the tendons in the parts dissected
in Experiment 18. Pull on the muscles and the tendons, and note how they
act to move the parts. This may be also admirably shown on the leg of a
fowl or turkey from a kitchen or obtained at the market.
Obtain the hoof of a calf or sheep with one end of the tendon of
Achilles still attached. Dissect it and test its strength.
73. Mechanism of Movement. The active agents of bodily movements, as
we have seen, are the muscles, which by their contraction cause the bones
to move one on the other. All these movements, both of motion and of
locomotion, occur according to certain fixed laws of mechanics. The bones,
to which a great proportion of the muscles in the body are attached, act
as distinct levers. The muscles supply the power for moving the
bones, and the joints act as fulcrums or points of support. The weight of
the limb, the weight to be lifted, or the force to overcome, is the
resistance.
74. Levers in the Body. In mechanics three classes of levers are
described, according to the relative position of the power, the fulcrum,
and the resistance. All the movements of the bones can be referred to one
or another of these three classes.
Levers of the first class are those in which the fulcrum is between
the power and the weight. The crowbar, when used to lift a weight at one
end by the application of power at the other, with a block as a fulcrum,
is a familiar example of this class. There are several examples of this in
the human body. The head supported on the atlas is one. The joint between
the atlas and the skull is the fulcrum, the weight of the head is the
resistance. The power is behind, where the muscles from the neck are
attached to the back of the skull. The object of this arrangement is to
keep the head steady and balanced on the spinal column, and to move it
backward and forward.
[Illustration: Fig. 35.--Showing how the Bones of the Arm serve as Levers.
P, power;
W, weight;
F, fulcrum.
]
Levers of the second class are those in which the weight is between
the fulcrum and the power. A familiar example is the crowbar when used for
lifting a weight while one end rests on the ground. This class of levers
is not common in the body. Standing on tiptoe is, however, an example.
Here the toes in contact with the ground are the fulcrum, the power is the
action of the muscles of the calf, and between these is the weight of the
body transmitted down the bones of the leg to the foot.
Levers of the third class are those in which the power is applied at
a point between the fulcrum and weight. A familiar example is where a
workman raises a ladder against a wall. This class of levers is common in
the body. In bending the forearm on the arm, familiarly known as "trying
your muscle," the power is supplied by the biceps muscle attached to the
radius, the fulcrum is the elbow joint at one end of the lever, and the
resistance is the weight of the forearm at the other end.
Experiment 22. _To illustrate how the muscles use the bones as
levers._ First, practice with a ruler, blackboard pointer, or any other
convenient object, illustrating the different kinds of levers until the
principles are familiar. Next, illustrate these principles on the
person, by making use of convenient muscles. Thus, lift a book on the
toes, by the fingers, on the back of the hand, by the mouth, and in
other ways.
These experiments, showing how the bones serve as levers, may be
multiplied and varied as circumstances may require.
75. The Erect Position. The erect position is peculiar to man. No
other animal naturally assumes it or is able to keep it long. It is the
result of a somewhat complex arrangement of muscles which balance each
other, some pulling backwards and some forwards. Although the whole
skeleton is formed with reference to the erect position, yet this attitude
is slowly learned in infancy.
In the erect position the center of gravity lies in the joint between the
sacrum and the last lumbar vertebra. A line dropped from this point would
fall between the feet, just in front of the ankle joints. We rarely stand
with the feet close together, because that basis of support is too small
for a firm position. Hence, in all efforts requiring vigorous muscular
movements the feet are kept more or less apart to enlarge the basis of
support.
Now, on account of the large number and flexibility of the joints, the
body could not be kept in an upright position without the cooperation of
certain groups of muscles. The muscles of the calf of the leg, acting on
the thigh bone, above the knee, keep the body from falling forward, while
another set in front of the thigh helps hold the leg straight. These thigh
muscles also tend to pull the trunk forward, but in turn are balanced by
the powerful muscles of the lower back, which help keep the body straight
and braced.
The head is kept balanced on the neck partly by the central position of
the joint between the atlas and axis, and partly by means of strong
muscles. Thus, the combined action of these and other muscles serves to
balance the body and keep it erect. A blow on the head, or a sudden shock
to the nervous system, causes the body to fall in a heap, because the
brain has for the time lost its power over the muscles, and they cease to
contract.
[Illustration: Fig. 36.--Diagram showing the Action of the Chief Muscles
which keep the Body Erect. (The arrows indicate the direction in which
these muscles act, the feet serving as a fixed basis.) [After Huxley.]
_Muscles which tend to keep the body from falling forward._
A, muscles of the calf;
B, of the back of the thigh;
C, of the spinal column.
_Muscles which tend to keep the body from falling backward._
D, muscles of the front of the leg;
E, of the front of the thigh;
F, of the front of the abdomen;
G, of the front of the neck.
]
76. Important Muscles. There are scores of tiny muscles about the
head, face, and eyes, which, by their alternate contractions and
relaxations, impart to the countenance those expressions which reflect the
feelings and passions of the individual. Two important muscles, the
temporal, near the temples, and the masseter, or chewing muscle,
are the chief agents in moving the lower jaw. They are very large in the
lion, tiger, and other flesh-eating animals. On the inner side of each
cheek is the buccinator, or trumpeter's muscle, which is largely
developed in those who play on wind instruments. Easily seen and felt
under the skin in thin persons, on turning the head to one side, is the
sterno-cleido-mastoid muscle, which passes obliquely down on each
side of the neck to the collar bone--prominent in sculpture and painting.
The chest is supplied with numerous muscles which move the ribs up and
down in the act of breathing. A great, fan-shaped muscle, called the
pectoralis major, lies on the chest. It extends from the chest to the
arm and helps draw the arm inward and forward. The arm is raised from the
side by a large triangular muscle on the shoulder, the deltoid, so
called from its resemblance to the Greek letter delta, [Greek: D]. The
biceps, or two-headed muscle, forms a large part of the fleshy mass
in front of the arm. Its use is to bend the forearm on the arm, an act
familiarly known as "trying your muscle." Its direct antagonist is the
three-headed muscle called the triceps. It forms the fleshy mass on
the back of the arm, its use being to draw the flexed forearm into a right
line.
On the back and outside of the forearm are the extensors, which
straighten the wrist, the hand, and the fingers. On the front and inside
of the forearm are the flexors, which bend the hand, the wrist, and
the fingers. If these muscles are worked vigorously, their tendons can be
readily seen and felt under the skin. At the back of the shoulder a large,
spread-out muscle passes upward from the back to the humerus. From its
wide expanse on the back it is known as the latissimus dorsi
(broadest of the back). When in action it draws the arm downward and
backward, or, if one hangs by the hands, it helps to raise the body. It is
familiarly known as the "climbing muscle."
[Illustration: Fig. 37.--A Few of the Important Muscles of the Back.]
Passing to the lower extremity, the thigh muscles are the largest and the
most powerful in the body. In front a great, four-headed muscle,
quadriceps extensor, unites into a single tendon in which the
knee-cap is set, and serves to straighten the knee, or when rising from a
sitting posture helps elevate the body. On the back of the thigh are
several large muscles which bend the knee, and whose tendons, known as the
"hamstrings," are readily felt just behind the knee. On the back of the
leg the most important muscles, forming what is known as the calf, are the
gastrocnemius and the soleus. The first forms the largest part
of the calf. The soleus, so named from resembling a sole-fish, is a muscle
of broad, flattened shape, lying beneath the gastrocnemius. The tendons of
these two muscles unite to form the tendon of Achilles, as that hero
is said to have been invulnerable except at this point. The muscles of the
calf have great power, and are constantly called into use in walking,
cycling, dancing, and leaping.
77. The Effect of Alcoholic Drinks upon the Muscles. It is found that
a man can do more work without alcohol than with it. After taking it there
may be a momentary increase of activity, but this lasts only ten or
fifteen minutes at the most. It is followed by a rapid reduction of power
that more than outweighs the momentary gain, while the quality of the work
is decidedly impaired from the time the alcohol is taken.
Even in the case of hard work that must be speedily done, alcohol does not
help, but hinders its execution. The tired man who does not understand the
effects of alcohol often supposes that it increases his strength, when in
fact it only deadens his sense of fatigue by paralyzing his nerves. When
put to the test he is surprised at his self-deception.
Full intoxication produces, by its peculiar depression of the brain and
nervous system, an artificial and temporary paralysis of the muscles, as
is obvious in the pitifully helpless condition of a man fully intoxicated.
But even partial approach to intoxication involves its proportionate
impairment of nervous integrity, and therefore just so much diminution of
muscular force. All athletes recognize this fact, as while training for a
contest, rigid abstinence is the rule, both from liquors and tobacco. This
muscular weakness is shown also in the unsteady hand, the trembling limbs
of the inebriate, his thick speech, wandering eye, and lolling head.
78. Destructive Effect of Alcoholic Liquors upon Muscular Tissue.
Alcoholic liquors retard the natural chemical changes so essential to good
health, by which is meant the oxidation of the nutritious elements of
food. Careful demonstration has proved also that the amount of carbon
dioxide escaping from the lungs of intoxicated persons is from thirty to
fifty per cent less than normal. This shut-in carbon stifles the nervous
energy, and cuts off the power that controls muscular force. This lost
force is in close ratio to the retained carbon: so much perverted chemical
change, so much loss of muscular power. Not only the strength but the fine
delicacy of muscular action is lost, the power of nice control of the hand
and fingers, as in neat penmanship, or the use of musical instruments.
To this perverted chemical action is also due the fatty degeneration so
common in inebriates, affecting the muscles, the heart, and the liver.
These organs are encroached upon by globules of fat (a hydrocarbon),
which, while very good in their proper place and quantity, become a
source of disorder and even of death when they abnormally invade vital
structures. Other poisons, as phosphorus, produce this fatty decay more
rapidly; but alcohol causes it in a much more general way.
This is proved by the microscope, which plainly shows the condition
mentioned, and the difference between the healthy tissues and those thus
diseased.
[Illustration: Fig. 38.--Principal Muscles on the Left Side of Neck.
A, buccinator;
B, masseter;
C, depressor anguli oris;
D, anterior portion of the digastric;
E, mylo-hyoid;
F, tendon of the digastric;
G, sterno-hyoid;
H, sterno-thyroid;
K, omo-hyoid;
L, sternal origin of sterno-cleido-mastoid muscle;
M, superior fibers of deltoid;
N, posterior scalenus;
O, clavicular origin of sterno-cleido-mastoid;
P, sterno-cleido-mastoid;
R, trapezius;
S, anterior constrictor;
T, splenius capitis;
V, stylo-hyoid;
W, posterior portion of the digastric;
X, fasciculi of ear muscles;
Z, occipital.
]
[NOTE. It was proposed during the Civil War to give each soldier in a
certain army one gill of whiskey a day, because of great hardship and
exposure. The eminent surgeon, Dr. Frank H. Hamilton of New York, thus
expressed his views of the question: "It is earnestly desired that no
such experiment will ever be repeated in the armies of the United
States. In our own mind, the conviction is established, by the
experience and observation of a life, that the regular routine
employment of alcoholic stimulants by man in health is never, under
any circumstances, useful. We make no exceptions in favor of cold or
heat or rain."
"It seems to me to follow from these Arctic experiences that the
regular use of spirits, even in moderation, under conditions of great
physical hardship, continued and exhausting labor, or exposure to
severe cold cannot be too strongly deprecated."
A. W. Greely, retired Brigadier General, U.S.A., and formerly leader
of the Greely Expedition.]
79. Effect of Tobacco on the Muscles. That other prominent narcotic,
tobacco, impairs the energy of the muscles somewhat as alcohol does, by
its paralyzing effect upon the nervous system. As all muscular action
depends on the integrity of the nervous system, whatever lays its
deadening hand upon that, saps the vigor and growth of the entire frame,
dwarfs the body, and retards mental development. This applies especially
to the young, in the growing age between twelve or fourteen and twenty,
the very time when the healthy body is being well knit and compacted.
Hence many public schools, as well as our national naval and military
academies, rigidly prohibit the use of tobacco by their pupils. So also
young men in athletic training are strictly forbidden to use it.[12] This
loss of muscular vigor is shown by the unsteady condition of the muscles,
the trembling hand, and the inability to do with precision and accuracy
any fine work, as in drawing or nice penmanship.
Additional Experiments.
Experiment 23. _ To examine the minute structure of voluntary
muscular fiber._ Tease, with two needles set in small handles, a bit of
raw, lean meat, on a slip of glass, in a little water. Continue until
the pieces are almost invisible to the naked eye.
Experiment 24. Place a clean, dry cover-glass of about the width of
the slip, over the water containing the torn fragments. Absorb the
excess of moisture at the edge of the cover, by pressing a bit of
blotting-paper against it for a moment. Place it on the stage of a
microscope and examine with highest obtainable power, by light reflected
upward from the mirror beneath the stage. Note the apparent size of the
finest fibers; the striation of the fibers, or their markings,
consisting of alternate dim and bright cross bands. Note the arrangement
of the fibers in bundles, each thread running parallel with its
neighbor.
Experiment 25. _To examine the minute structure of involuntary
muscular fiber, a tendon, or a ligament._ Obtain a very small portion of
the muscular coat of a cow's or a pig's stomach. Put it to soak in a
solution of one dram of bichromate of potash in a pint of water. Take
out a morsel on the slip of glass, and tease as directed for the
voluntary muscle. Examine with a high power of the microscope and note:
(1) the isolated cells, long and spindle-shaped, that they are much
flattened; (2) the arrangement of the cells, or fibers, in sheets, or
layers, from the torn ends of which they project like palisades.
Experiment 26. Tease out a small portion of the tendon or ligament
in water, and examine with a glass of high power. Note the large fibers
in the ligament, which branch and interlace.
Experiment 27. With the head slightly bent forwards, grasp between
the fingers of the right hand the edge of the left
sterno-cleido-mastoid, just above the collar bone. Raise the head and
turn it from left to right, and the action of this important muscle is
readily seen and felt. In some persons it stands out in bold relief.
Experiment 28. The tendons which bound the space (popliteal) behind
the knee can be distinctly felt when the muscles which bend the knee are
in action. On the outer side note the tendons of the biceps of the leg,
running down to the head of the fibula. On the inside we feel three
tendons of important muscles on the back of the thigh which flex the leg
upon the thigh.
Experiment 29. _To show the ligamentous action of the muscles._
Standing with the back fixed against a wall to steady the pelvis, the
knee can be flexed so as to almost touch the abdomen. Take the same
position and keep the knee rigid. When the heel has been but slightly
raised a sharp pain in the back of the thigh follows any effort to carry
it higher. Flexion of the leg to a right angle, increases the distance
from the lines of insertion on the pelvic bones to the tuberosities of
the tibia by two or three inches--an amount of stretching these muscle
cannot undergo. Hence the knee must be flexed in flexion of the hip.
Experiment 30. A similar experiment may be tried at the wrist. Flex the
wrist with the fingers extended, and again with the fingers in the fist.
The first movement can be carried to 90 degrees, the second only to 30
degrees, or in some persons up to 60 degrees. Making a fist had already
stretched the extensor muscles of the arm, and they can be stretched but
little farther. Hence, needless pain will be avoided by working a stiff
wrist with the parts loose, or the fingers extended, and not with a
clenched fist.
Review Analysis: Important Muscles.
Location.
Name. Chief Function.
Head and Neck.
Occipito-frontalis. moves scalp and raises eye brow.
Orbicularis palpebrarum. shuts the eyes.
Levator palpebrarum. opens the eyes.
Temporal. raise the lower jaw.
Masseter. " " " "
Sterno-cleido-mastoid. depresses head upon neck and neck upon chest.
Platysma myoides. depresses lower jaw and lower lip.
Trunk.
Pectoralis major. draws arm across front of chest.
Pectoralis minor. depresses point of shoulder,
Latissimus dorsi. draws arm downwards and backwards.
Serratus magnus. assists in raising ribs.
Trapezius. Rhomboideus. backward movements of head and shoulder,
Intercostals. raise and depress the ribs.
External oblique. /various forward movements
Internal oblique. \ of trunk
Rectus abdominis. compresses abdominal viscera and acts upon
pelvis.
Upper Limbs.
Deltoid. carries arm outwards and upwards.
Biceps. flexes elbow and raises arm.
Triceps. extends the forearm.
Brachialis anticus. flexor of elbow.
Supinator longus. flexes the forearm.
Flexor carpi radialis. flexors of wrist.
Flexor carpi ulnaris. " " "
Lower Limbs.
Gluteus maximus. adducts the thigh.
Adductors of thigh. draw the leg inwards.
Sartorius. crosses the legs.
Rectus femoris. flexes the thigh.
Vastus externus. extensor of leg.
Vastus internus. extensor of leg upon thigh.
Biceps femoris. flexes leg upon thigh.
Gracilis. flexes the leg and adducts thigh.
Tibialis anticus. draws up inner border of foot.
Peroneus longus. raises outer edge of foot,
Gastrocnemius. keep the body erect, and
Soleus. aid in walking and running.
Chapter IV.
Physical Exercise.
80. Importance of Bodily Exercise. Nothing is so essential to success
in life as sound physical health. It enables us to work with energy and
comfort, and better to endure unusual physical and mental strains. While
others suffer the penalties of feebleness, a lower standard of functional
activities, and premature decay, the fortunate possessor of a sound mind
in a sound body is better prepared, with proper application, to endure the
hardships and win the triumphs of life[13].
This element of physical capacity is as necessary to a useful and
energetic life, as are mental endowment and intellectual acquirement.
Instinct impels us to seek health and pleasure in muscular exercise. A
healthy and vigorous child is never still except during sleep. The
restless limbs and muscles of school children pent up for several hours,
feel the need of movement, as a hungry man craves food. This natural
desire for exercise, although too often overlooked, is really one of the
necessities of life. One must be in ill health or of an imperfect nature,
when he ceases to feel this impulse. Indeed, motion within proper bounds
is essential to the full development and perfect maintenance of the bodily
health. Unlike other machines, the human body becomes within reasonable
limits, stronger and more capable the more it is used.
As our tenure of life at best is short, it is our duty to strive to live
as free as possible from bodily ills. It is, therefore, of paramount
importance to rightly exercise every part of the body, and this without
undue effort or injurious strain.
Strictly speaking, physical exercise refers to the functional
activity of each and every tissue, and properly includes the regulation of
the functions and movements of the entire body. The word exercise,
however, is used usually in a narrower sense as applied to those movements
that are effected by the contraction of the voluntary muscles.
Brief reference will be made in this chapter only to such natural and
systematic physical training as should enter into the life of every
healthy person.
81. Muscular Activity. The body, as we have learned, is built up of
certain elementary tissues which are combined to make bones, muscles,
nerves, and other structures. The tissues, in turn, are made up of
countless minute cells, each of which has its birth, lives its brief
moment to do its work in the animal economy, is separated from the tissue
of which it was a part, and is in due time eliminated by the organs of
excretion,--the lungs, the skin, or the kidneys. Thus there is a
continuous process of growth, of decay, and removal, among the individual
cells of each tissue.
[NOTE. The Incessant Changes in Muscular Tissue. "In every tiny
block of muscle there is a part which is really alive, there are parts
which are becoming alive, there are parts which have been alive, and
are now dying or dead; there is an upward rush from the lifeless to
the living, a downward rush from the living to the dead. This is
always going on, whether the muscle be quiet and at rest, or whether
it be active and moving,--some of the capital of living material is
being spent, changed into dead waste; some of the new food is always
being raised into living capital. But when the muscle is called upon
to do work, when it is put into movement, the expenditure is
quickened, there is a run upon the living capital, the greater, the
more urgent the call for action."--Professor Michael Foster.]
These ceaseless processes are greatly modified by the activity of the
bodily functions. Every movement of a muscle, for instance, involves
change in its component cells. And since the loss of every atom of the
body is in direct relation to its activity, a second process is necessary
to repair this constant waste; else the body would rapidly diminish in
size and strength, and life itself would soon end. This process of repair
is accomplished, as we shall learn in Chapters VI. and VII., by the organs
of nutrition, which convert the food into blood.
[Illustration: Fig. 39.--Showing how the Muscles of the Back may be
developed by a Moderate Amount of Dumb-Bell Exercise at Home. (From a
photograph.)]
82. Effect of Exercise upon the Muscles. Systematic exercise
influences the growth and structure of the muscles of the body in a manner
somewhat remarkable. Muscular exercise makes muscular tissue; from the
lack of it, muscles become soft and wasted. Muscles properly exercised not
only increase in size, both as a whole and in their individual structure,
but are better enabled to get rid of material which tends to hamper their
movements. Thus muscular exercise helps to remove any needless
accumulation of fat, as well as useless waste matters, which may exist in
the tissues. As fat forms no permanent structural part of the organism,
its removal is, within limits, effected with no inconvenience.
Muscular strength provides the joints with more powerful ligaments and
better developed bony parts. After long confinement to the bed from
disease, the joints have wasted ligaments, thin cartilages, and the bones
are of smaller proportions. Duly exercised muscles influence the size of
the bones upon which they act. Thus the bones of a well-developed man are
stronger, firmer, and larger than those of a feeble person.
He who has been physically well trained, has both a more complete and a
more intelligent use of his muscles. He has acquired the art of causing
his muscles to act in concert. Movements once difficult are now carried on
with ease. The power of coordination is increased, so that a desired end
is attained with the least amount of physical force and nervous energy. In
learning to row, play baseball, ride the bicycle, or in any other
exercises, the beginner makes his movements in a stiff and awkward manner.
He will use and waste more muscular force in playing one game of ball, or
in riding a mile on his wheel, than an expert would in doing ten times the
work. He has not yet learned to balance one set of muscles against their
antagonists.
[Illustration: Fig. 40.--The Standard Special Chest Weight.
A convenient machine by means of which all the muscles of the body may be
easily and pleasantly exercised with sufficient variations in the
movements to relieve it of monotony.
A space 6 ft wide, 6 ft deep, and 7 ft high nearly in front of the machine
is required for exercise.]
In time, however, acts which were first done only with effort and by a
conscious will, become automatic. The will ceases to concern itself. By
what is called reflex action, memory is developed in the spinal cord and
the muscular centers (sec. 273). There is thus a great saving of actual
brain work, and one important cause of fatigue is removed.
83. Effect of Exercise on Important Organs. The importance of
regular exercise is best understood by noting its effects upon the
principal organs of the body. As the action of the heart is increased both
in force and frequency during exercise, the flow of blood throughout the
body is augmented. This results from the force of the muscular
contractions which play their part in pressing the blood in the veins
onward towards the heart. Exercise also induces a more vigorous
respiration, and under increased breathing efforts the lung capacity is
increased and the size of the chest is enlarged. The amount of air
inspired and expired in a given time is much larger than if the body were
at rest. The blood is thus supplied with a much larger amount of oxygen
from the air inhaled, and gives off to the air a corresponding excess of
carbon dioxid and water.
Again, exercise stimulates and strengthens the organs of digestion. The
appetite is improved, as is especially noted after exercise in the open
air. The digestion is more complete, absorption becomes more rapid, the
peristaltic movements of the bowels are promoted, and the circulation
through the liver is more vigorous. More food is taken to supply the force
necessary for the maintenance of the mechanical movements. Ample exercise
also checks the tendency towards a torpid circulation in the larger
digestive organs, as the stomach and the liver, so common with those who
eat heartily, but lead sedentary lives. In short, exercise may be regarded
as a great regulator of nutrition.
Exercise increases the flow of blood through the small vessels of the
skin, and thus increases the radiation of heat from the surface. If the
exercise be vigorous and the weather hot, a profuse sweat ensues, the
rapid evaporation of which cools the body. The skin is thus a most
important regulator of the bodily temperature, and prevents any rise above
the normal which would otherwise result from vigorous exercise. (See secs.
226 and 241).
84. Effect of Exercise upon the Personal Appearance. Judicious and
systematic exercise, if moderately employed, soon gives a more upright and
symmetrical figure, and an easier and more graceful carriage. Rounded
shoulders become square, the awkward gait disappears, and there is seen a
graceful poise to the head and a bearing of the body which mark those
whose muscles have been well trained. A perfectly formed skeleton and
well-developed muscles give the graceful contour and perfect outline to
the human body. The lean, soft limbs of those who have never had any
physical education, often look as if they belonged to persons recovering
from sickness. The effects of sound physical exercise are well exhibited
in the aspect of the neck, shoulders, and chest of one who has been well
trained. This is noticeable in gymnasts and others who practice upon the
horizontal bar, with chest weights, dumb-bells, and other apparatus which
develop more especially the muscles of the upper half of the trunk.
[Illustration: Fig. 41.--Young Woman practicing at Home with the "Whitely
Exerciser." (From a photograph)]
Exercise improves the condition of the tissues generally. They become more
elastic, and in all respects sounder. The skin becomes firm, clear, and
wholesome. Hence, every part of the surface of the body rapidly takes on a
change in contour, and soon assumes that appearance of vigor and soundness
which marks those of firm physical condition. The delicate, ruddy aspect
of the complexion, the swing about the body and the bearing of the head
and shoulders, of young women whose physical training has been efficient,
are in marked contrast with those characteristics in persons whose
education in this respect has been neglected.
85. Effect of Unsuitable or Excessive Exercise. But exercise, like
everything else which contributes to our welfare, may be carried to
excess. The words excessive and unsuitable, when applied to muscular
exertion, are relative terms, and apply to the individual rather than to
amount of work done. Thus what may be excessive for one person, might be
suitable and beneficial to another. Then the condition of the individual,
rather than the character of the muscular work, is always a most important
factor.
Breathlessness is, perhaps, the most common effect of undue exertion. Let
a middle-aged person, who is out of practice, run a certain distance, and
he is soon troubled with his breathing. The respirations become irregular,
and there is a sense of oppression in his chest. He pants, and his
strength gives out. His chest, and not his legs, has failed him. He is
said to be "out of breath." He might have practiced dumb-bells or rowed
for some time without inconvenience.
The heart is often overstrained, and at times has been ruptured during
violent exertion, as in lifting an immense weight. The various forms of
heart-disease are common with those whose occupations involve severe
muscular effort, as professional athletes and oarsmen. Haemorrhages of
various kinds, especially from the lungs, or rupture of blood-vessels in
the brain, are not uncommon results of over-exertion.
Excessive repetition of muscular movements may lead to permanent
contractions of the parts involved. Thus sailors, mechanics, and others
frequently develop a rigidity of the tendons of the hand which prevents
the full extension of the fingers. So stenographers, telegraphers and
writers occasionally suffer from permanent contractions of certain muscles
of the arm, known as writer's cramp, due to their excessive use. But the
accidents which now and then may result from severe physical exertion,
should discourage no one from securing the benefits which accrue from
moderate and reasonable exercise.
86. Muscular Fatigue. We all know how tiresome it is to hold the arm
outstretched horizontally even for a few moments. A single muscle, the
deltoid, in this case does most of the work. Even in a vigorous man, this
muscle can act no longer than four to six minutes before the arm drops
helpless. We may prolong the period by a strong effort of the will, but a
time soon comes when by no possible effort are we able to hold out the
arm. The muscle is said to be fatigued. It has by no means lost its
contractile power, for if we apply a strong electric stimulus to it, the
fatigue seems to disappear. Thus we see the functional power of a muscle
has a definite limit, and in fatigue that limit is reached.
[Illustration: Fig. 42.--A Well-Equipped Gymnasium. (From a photograph.)]
The strength of the muscle, its physical condition, the work it has done,
and the mental condition of the individual, all modify the state of
fatigue. In those difficult acts which involve a special effort of the
will, the matter of nerve exhaustion is largely concerned. Thus, the
incessant movements in St. Vitus' dance result in comparatively little
fatigue, because there is no association of the brain with the muscular
action. If a strong man should attempt to perform voluntarily the same
movements, he would soon have to rest. None of the movements which are
performed independently of the will, as the heart-beats and breathing
movements, ever involve the sensation of fatigue. As a result of fatigue
the normal irritability of muscular tissue becomes weakened, and its force
of contraction is lessened. There is, also, often noticed in fatigue a
peculiar tremor of the muscles, rendering their movements uncertain. The
stiffness of the muscles which comes on during severe exercise, or the day
after, are familiar results of fatigue.
This sense of fatigue should put us on guard against danger. It is a kind
of regulator which serves in the ordinary actions of life to warn us not
to exceed the limits of useful exercise. Fatigue summons us to rest long
before all the force of the motor organs has been expended, just as the
sensation of hunger warns us that we need food, long before the body has
become weak from the lack of nourishment.
We should never forget that it is highly essential to maintain an unused
reserve of power, just as a cautious merchant always keeps at the bank an
unexpended balance of money. If he overspends his money he is bankrupt,
and the person who overspends his strength is for the time physically
bankrupt. In each case the process of recovery is slow and painful.
87. Rest for the Muscles. Rest is necessary for the tissues, that
they may repair the losses sustained by work; that is, a period of rest
must alternate with a period of activity. Even the heart, beating
ceaselessly, has its periods of absolute rest to alternate with those of
work. A steam-engine is always slowly, but surely, losing its fitness for
work. At last it stops from the need of repair. Unlike the engine, the
body is constantly renewing itself and undergoing continual repair. Were
it not for this power to repair and renew its various tissues, the body
would soon be worn out.
This repair is really a renovation of the structure. Rest and work are
relative terms, directly opposed to each other. Work quickens the pulse
and the respiration, while rest slows both. During sleep the voluntary
muscles are relaxed, and those of organic life work with less energy. The
pulse and the respiration are less frequent, and the temperature lower
than when awake. Hence sleep, "tired Nature's sweet restorer," may be
regarded as a complete rest.
The periods of rest should vary with the kind of exercise. Thus exercise
which produces breathlessness requires frequent but short rests. The
trained runner, finding his respiration embarrassed, stops a moment to
regain his breath. Exercises of endurance cause fatigue less quickly than
those of speed, but require longer rest. Thus a man not used to long
distances may walk a number of hours without stopping, but while fatigue
is slow to result, it is also slow to disappear. Hence a lengthy period of
rest is necessary before he is able to renew his journey.
88. Amount of Physical Exercise Required. The amount of physical
exercise that can be safely performed by each person, is a most important
and practical question. No rule can be laid down, for what one person
bears well, may prove very injurious to another. To a certain extent, each
must be guided by his own judgment. If, after taking exercise, we feel
fatigued and irritable, are subject to headache and sleeplessness, or find
it difficult to apply the mind to its work, it is plain that we have been
taxing our strength unduly, and the warnings should be heeded.
Age is an important factor in the problem, as a young man may do with
ease and safety, what might be injurious to an older person. In youth,
when the body is making its most active development, the judicious use of
games, sports, and gymnastics is most beneficial. In advanced life, both
the power and the inclination for exercise fail, but even then effort
should be made to take a certain reasonable amount of exercise.
Abundant evidence shows that physical development is most active from
thirteen to seventeen years of age; this manifests itself clearly by
increase in weight. Hence this period of life is of great consequence. If
at this age a boy or girl is subjected to undue physical strain, the
development may suffer, the growth be retarded, and the foundation laid
for future ill health.
[Illustration: Fig. 43.--Student exercising in the School Gymnasium on the
Rowing Machine. (From a photograph.)]
The proper amount of exercise must vary greatly with circumstances. It may
be laid down as a fairly safe rule, that a person of average height and
weight, engaged in study or in any indoor or sedentary occupation, should
take an amount of exercise equivalent to walking five or six miles a day.
Growing children, as a rule, take more exercise than this, while most men
working indoors take far less, and many women take less exercise than men.
Exercise may be varied in many ways, the more the better; but for the most
part it should always be taken in the open air.
89. Time for Exercise. It is not prudent to do hard work or take
severe exercise, just before or just after a full meal. The best time is
one or two hours after a meal. Vigorous exercise while the stomach is
busily digesting food, may prove injurious, and is apt to result sooner or
later in dyspepsia. On the other hand, severe exercise should not be taken
on an empty stomach. Those who do much work or study before breakfast,
should first take a light lunch, just enough to prevent any faint feeling.
With this precaution, there is no better time for moderate exercise than
the early morning.
In the case of children, physical exercises should not be undertaken when
they are overtired or hungry. Neither is it judicious for adults to take
vigorous exercise in the evening, after a long and arduous day's work.
90. Walking, Running, and Jumping. Walking is generally regarded as
the simplest and most convenient mode of taking exercise. Man is
essentially a walking animal. When taken with a special object in view, it
is the best and most pleasant of all physical activities. It is suited for
individuals of all ages and occupations, and for residents of every
climate. The child, the athlete, and the aged are all able to indulge in
this simple and effective means of keeping the body in health.
In walking, the muscles of the entire body are brought into action,
and the movements of breathing and the circulation of the blood are
increased. The body should be erect, the chest thrown out, the head and
shoulders held back, and the stride long and elastic. It is an excellent
custom to add to the usefulness of this fine exercise, by deep, voluntary
inhalations of pure air.
Running is an excellent exercise for children and young people, but
should be sparingly indulged in after the age of thirty-five. If it be
accompanied with a feeling of faintness, breathlessness, and palpitation
of the heart, the exercise is too severe, and its continuance may do
serious harm. Running as an exercise is beneficial to those who have kept
themselves in practice and in sound condition. It brings into play nearly
every muscle of the body, and thus serves to develop the power of
endurance, as well as strength and capacity for rapid movement.
Jumping may well be left to boys and young men under twenty, but
skipping with a rope, allied to jumping, is an admirable and beneficial
form of exercise. It brings into action many muscles without putting undue
strain upon any particular group.
91. Skating, Swimming, and Rowing. Skating is a delightful and
invigorating exercise. It calls into play a great variety of muscles, and
is admirably adapted for almost all ages. It strengthens the ankles and
helps give an easy and graceful carriage to the body. Skating is
especially valuable, as it can be enjoyed when other out-door exercises
are not convenient.
Every child above ten years of age should be taught to swim. The art,
once mastered, is never forgotten. It calls into use a wide combination of
muscles. This accomplishment, so easily learned, should be a part of our
education, as well as baseball or bicycling, as it may chance to any one
to save his own life or that of a companion.
In many respects rowing is one of the most perfect exercises at our
command. It expands the chest, strengthens the body, and gives tone to the
muscles of the abdomen. It is very suitable for girls and women, as no
other exercise is so well adapted to remedy the muscular defects so marked
in their sex. Even elderly persons can row day after day without
difficulty. The degree of muscular effort required, can be regulated so
that those with weak hearts and weak lungs can adjust themselves to the
exercise.
92. Bicycling as an Exercise. The bicycle as a means of taking
exercise has come into popular use with remarkable rapidity. Sharp
competition bids fair to make the wheel more popular and less expensive
than ever. Its phenomenal use by persons of all ages and in all stations
of life, is proof of the enthusiasm with which this athletic exercise is
employed by women as well as by men.
Mechanical skill has removed most of the risks to health and person which
once existed. A good machine, used by its owner with judgment, is the most
convenient, the safest, and the least expensive means of traveling for
pleasure or exercise. It is doing more than any other form of exercise to
improve the bodily condition of thousands whose occupations confine them
all day to sedentary work. Dependent upon no one but himself, the cyclist
has his means of exercise always at hand. No preparation is necessary to
take a spin of ten miles or so on the road, during a summer evening or
before breakfast.
Bicycling brings into active use the muscles of the legs as well as those
of the trunk and arms. It seems to benefit those who suffer from
dyspepsia, constipation, and functional disorders of the liver.
A special caution must be used against overdoing in cycling, for the
temptation by rivalry, making a record, by social competition on the road,
is stronger in this form of exercise than in any other, especially for
young folks. Many cases have occurred of permanent injury, and even loss
of life, from collapse simply by excessive exertion and exhaustion.
93. Outdoor Games and Physical Education. While outdoor games
are not necessary to maintain health, yet we can scarcely overestimate the
part that the great games of baseball, football, tennis, golf, and
croquet, play in the physical development of young people. When played in
moderation and under suitable conditions, they are most useful and
beneficial exercises. They are played in the open air, and demand a great
variety of vigorous muscular movement, with a considerable amount of skill
and adroitness of action. These games not only involve healthful exercise,
but develop all those manly and wholesome qualities so essential to
success in life.
A vigorous body is well-nigh essential to success, but equally important
are readiness of action, sound judgment, good temper, personal courage, a
sense of fair play, and above all, a spirit of honor. Outdoor games, when
played in a reasonable and honorable manner, are most efficient and
practical means to develop these qualities in young people.
94. The School and Physical Education. The advantages to be derived,
during the school period, from the proper care and development of the
body, should be understood and appreciated by school officials, teachers,
and parents. The school period is the best time to shape the lives of
pupils, not mentally or morally alone, but physically as well. This is the
time, by the use of a few daily exercises at school, to draw back the
rounding shoulders, to form the habit of sitting and standing erect, to
build up strong and comely arms and chests, and otherwise to train pupils
to those methods which will serve to ripen them into vigorous and
well-knit men and women.
Teachers can by a little effort gain the knowledge requisite properly to
instruct their pupils in a few systematic exercises. Gratifying results
will follow just as the teacher and pupils evince interest and judgment in
the work. It is found by experience that pupils are not only quick to
learn, but look forward eagerly to the physical exercises as an
interesting change from the routine of school life.
There should be a stated time for these school exercises, as for any other
duty. There can be practiced in the schoolroom a great variety of
interesting and useful exercises, which call for little or no expense for
apparatus. Such exercises should no more interfere with the children's
usual games than any other study does. Under no circumstances should the
play hours be curtailed.
95. Physical Exercises in School. Physical exercises of some sort,
then, should be provided for pupils in our schools, especially in large
towns and cities, where there is little opportunity for outdoor games, and
they should form a part of the regular course of study. The object should
be the promotion of sound health rather than the development of muscle, or
performing feats of agility or strength. Exercises with dumb-bells and
wands, or even without any apparatus, practiced a few times a day, for
five minutes at a time, do a great deal of good. They relax the tension of
body and mind, and introduce an element of pleasure into the routine of
school life. They increase the breathing power and quicken the action of
the heart.
[Illustration: Fig. 44.--Physical Exercises as carried on in Schools.
(From photographs.)]
[NOTE. "In early boyhood and youth nothing can replace the active
sports so much enjoyed at this period; and while no needless
restrictions should be placed upon them, consideration should be paid
to the amount, and especially to the character, of the games pursued
by delicate youth. For these it would be better to develop the
weakened parts by means of systematic physical exercises and by
lighter sports."--Dr. John M. Keating on "Physical Development" in
Pepper's _Cyclopaedia of the Diseases of Children_.]
If vigorously and systematically carried out, these exercises invigorate
all the tissues and organs of the body, and stimulate them to renewed
activity. They serve to offset the lack of proper ventilation, faulty
positions at the desks, and the prolonged inaction of the muscles. To
secure the greatest benefit from physical training in school, it is
important that the pupils be interested in these exercises, and consider
them a recreation, and not a task[14].
96. Practical Points about Physical Exercise. The main object in
undertaking systematic and graduated physical exercises is not to learn to
do mere feats of strength and skill, but the better to fit the individual
for the duties and the work of life. Exercises should be considered with
reference to their availability from the learner's standpoint. The most
beneficial exercises ordinarily are the gentle ones, in which no strain is
put upon the heart and the respiration. The special aim is to secure the
equal use of all the muscles, not the development of a few. The
performance of feats of strength should never come within the scope of any
educational scheme. Exercises which call for sustained effort, violent
exertion, or sudden strain are best avoided by those who have had no
preparation or training.
Regular exercise, not sudden and occasional prolonged exertion, is
necessary for health. The man or woman who works in an office or store all
the week, and on Sunday or a holiday indulges in a long spin on the
bicycle, often receives more harm than good from the exertion. Exercise
should be taken, so far as is convenient, in the open air, or in a large
and well-ventilated room.[15]
After the more violent exercises, as baseball, football, a long ride on
the bicycle, or even after a prolonged walk, a warm bath should be taken
at the first convenient opportunity. Care should be taken to rub down
thoroughly, and to change a part or all of the clothing. Exercise is
comparatively valueless until the idea of taking it for health is quite
forgotten in the interest and pleasure excited by the occasion. No
exercise should be carried to such a degree as to cause fatigue or
exhaustion. Keep warmly clad after exercise, avoid chills, and always stop
exercising as soon as fatigue is felt.
Wear clothing which allows free play to all the muscles of the body. The
clothing should be light, loose, and made of wool. Care should be taken
not to take cold by standing about in clothes which are damp with
perspiration. In brisk walking and climbing hills keep the mouth shut,
especially in cold weather, and breathe through the nose, regulating the
pace so that it can be done without discomfort.
97. Effect of Alcoholic Liquors and Tobacco upon Physical Culture. As
a result of the unusual attention given to physical culture in the last
few years, hundreds of special instructors are now employed in training
young people in the theory and practice of physical exercise. These expert
teachers, to do their work with thoroughness and discipline, recognize the
necessity of looking after the daily living of their students. The time of
rising and retiring, the hours of sleep, the dress, the care of the diet,
and many other details of personal health become an important part of the
training.
Recognizing the fact that alcoholic drink and tobacco are so disastrous to
efficiency in any system of physical training, these instructors rigidly
forbid the use of these drugs under all circumstances. While this
principle is perhaps more rigorously enforced in training for athletic
contests, it applies equally to those who have in view only the
maintenance of health.
Books on Physical Education. There are many excellent books on
physical education, which are easily obtained for reading or for
reference. Among these one of the most useful and suggestive is Blackie's
well-known book, "How to Get Strong and how to Stay so." This little book
is full of kindly advice and practical suggestions to those who may wish
to begin to practice health exercises at home with inexpensive apparatus.
For more advanced work, Lagrange's "Physiology of Bodily Exercise" and the
Introduction to Maclaren's "Physical Education" may be consulted. A
notable article on "Physical Training" by Joseph H. Sears, an Ex-Captain
of the Harvard Football Team, may be found in Roosevelt's "In Sickness and
in Health."
Price lists and catalogues of all kinds of gymnastic apparatus are easily
obtained on application to firms handling such goods.
Various Systems of Physical Exercises. The recent revival of popular
interest in physical education has done much to call the attention of the
public to the usefulness and importance of a more thorough and systematic
use of physical exercises, both at home and in the schools. It is not
within the scope of this book to describe the various systems of gymnastic
and calisthenic exercises now in common use in this country. For the most
part they have been modified and rearranged from other sources, notably
from the two great systems, i.e., Swedish and German.
For a most comprehensive work on the Swedish system, the teacher is
referred to the "Swedish System of Educational Gymnastics," with 264
illustrations, by Baron Nils Posse. There is also a small manual for
teachers, called "Handbook of School Gymnastics of the Swedish Systems,"
by the same author.
Chapter V.
Food and Drink.
98. Why we need Food. The body is often compared to a steam-engine in
good working order. An engine uses up fuel and water to obtain from them
the energy necessary to do its work. So, we consume within our bodies
certain nutritious substances to obtain from them the energy necessary for
our activities. Just as the energy for the working of the engine is
obtained from steam by the combustion of fuel, so the energy possessed by
our bodies results from the combustion or oxidation within us of the food
we eat. Unless this energy is provided for the body it will have but
little power of doing work, and like an engine without steam, must soon
become motionless.
99. Waste and Repair. A steam-engine from the first stroke of its
piston-rod begins to wear out, and before long needs repair. All work
involves waste. The engine, unless kept in thorough repair, would soon
stop. So with our bodies. In their living cells chemical changes are
constantly going on; energy, on the whole, is running down; complex
substances are being broken up into simpler combinations. So long as life
lasts, food must be brought to the tissues, and waste products carried
away from them. It is impossible to move a single muscle, or even to think
for one moment, without some minute part of the muscular or brain tissue
becoming of no further use in the body. The transformation of dead matter
into living tissue is the ever-present miracle which life presents even in
its lowest forms.
In childhood the waste is small, and the amount of food taken is more
than sufficient to repair the loss. Some of the extra food is used in
building up the body, especially the muscles. As we shall learn in Chapter
VIII., food is also required to maintain the bodily heat. Food, then,
is necessary for the production of energy, for the repair of the body, for
the building up of the tissues, and for the maintenance of bodily heat.
100. Nature of the Waste Material. An ordinarily healthy person
passes daily, on an average, by the kidneys about 50 ounces of waste
material, of which 96 per cent is water, and from the intestines, on an
average, 5-1/2 ounces, a large proportion of which is water. By the skin,
in the shape of sweat and insensible perspiration, there is cast out about
23 ounces, of which 99 per cent is water; and by the lungs about 34
ounces, 10 of which are water and the remainder carbon dioxid.
Now if we omit an estimate of the undigestible remains of the food, we
find that the main bulk of what daily leaves the body consists of water,
carbon dioxid, and certain solid matters contained in solution in
the renal secretion and the sweat. The chief of these solid matters is
urea, a complex product made up of four elements,--carbon, hydrogen,
oxygen, and nitrogen. Water contains only two elements, hydrogen and
oxygen; and carbon dioxid also has only two, carbon and oxygen. Hence,
what we daily cast out of our bodies consists essentially of these four
elements in the form mainly of water, carbon dioxid, and urea.
These waste products represent the oxidation that has taken place in
the tissues in producing the energy necessary for the bodily activities,
just as the smoke, ashes, clinkers, and steam represent the consumption of
fuel and water in the engine. Plainly, therefore, if we could restore to
the body a supply of these four elements equivalent to that cast out, we
could make up for the waste. The object of food, then, is to restore to
the body an amount of the four elements equal to that consumed. In other
words, and briefly: The purpose of food is to supply the waste of the
tissues and to maintain the normal composition of the blood.
101. Classification of Foods. Foods may be conveniently divided into
four great classes, to which the name food-stuffs or alimentary
principles has been given. They correspond to the chief "proximate
principles" of which the body consists. To one or the other of these
classes all available foods belong[16]. The classification of food-stuffs
usually given is as follows:
I. Proteids, or Nitrogenous Foods.
II. Starches and Sugars, or Carbohydrates.
III. Fats and Oils.
IV. Inorganic or Mineral Foods,--Water, Salt.
102. Proteids; or Nitrogenous Foods. The proteids, frequently
spoken of as the nitrogenous foods, are rich in one or more of the
following organic substances: albumen, casein, fibrin, gelatine, myosin,
gluten, and legumin.
The type of this class of foods is albumen, well known as the white of an
egg. The serum of the blood is very rich in albumen, as is lean meat. The
curd of milk consists mainly of casein. Fibrin exists largely in blood and
flesh foods. Gelatine is obtained from the animal parts of bones and
connective tissue by prolonged boiling. One of the chief constituents of
muscular fiber is myosin. Gluten exists largely in the cereals wheat,
barley, oats, and rye. The proteid principle of peas and beans is legumin,
a substance resembling casein.
As the name implies, the proteids, or nitrogenous foods, contain nitrogen;
carbohydrates and fats, on the contrary, do not contain nitrogen. The
principal proteid food-stuffs are milk, eggs, flesh foods of all kinds,
fish, and the cereals among vegetable foods. Peas and beans are rich in
proteids. The essential use of the proteids to the tissues is to supply
the material from which the new proteid tissue is made or the old proteid
tissue is repaired. They are also valuable as sources of energy to the
body. Now, as the proteid part of its molecule is the most important
constituent of living matter, it is evident that proteid food is an
absolute necessity. If our diet contained no proteids, the tissues of
the body would gradually waste away, and death from starvation would
result. All the food-stuffs are necessary in one way or another to the
preservation of perfect health, but proteids, together with a certain
proportion of water and inorganic salts, are absolutely necessary for the
bare maintenance of animal life--that is, for the formation and
preservation of living protoplasm.
103. Starches and Sugars. The starches, sugars, and gums, also known
as carbohydrates, enter largely into the composition of foods of
vegetable origin. They contain no nitrogen, but the three elements,
carbon, hydrogen, and oxygen, the last two in the same proportion as in
water. The starches are widely distributed throughout the vegetable
kingdom. They are abundant in potatoes and the cereals, and in arrowroot,
rice, sago, and tapioca. Starch probably stands first in importance among
the various vegetable foods.
The sugars are also widely distributed substances, and include the
cane, grape, malt, maple, and milk sugars. Here also belong the gums and
cellulose found in fruit, cereals, and all vegetables which form the
basis of the plant cells and fibers. Honey, molasses, and manna are
included in this class.
The physiological value of the starches and sugars lies in the fact that
they are oxidized in the body, and a certain amount of energy is thereby
liberated. The energy of muscular work and of the heat of the body comes
largely from the oxidation, or destruction, of this class of foods. Now,
inasmuch as we are continually giving off energy from the body, chiefly in
the form of muscular work and heat, it is evident that material for the
production of this energy must be taken in the food. The carbohydrates
constitute the bulk of our ordinary food.
104. Fats and Oils. These include not only the ordinary fats of
meat, but many animal and vegetable oils. They are alike in
chemical composition, consisting of carbon and hydrogen, with a little
oxygen and no nitrogen. The principal kinds of fat used as food are the
fat of meat, butter, suet, and lard; but in many parts of the world
various vegetable oils are largely used, as the olive, palm, cotton seed,
cocoanut, and almond.
The use of the fats in the body is essentially the same as that of the
starches and sugars. Weight for weight they are more valuable than the
carbohydrates as sources of energy, but the latter are more easily
digested, and more easily oxidized in the body. An important use of fatty
foods is for the maintenance of the bodily heat. The inhabitants of Arctic
regions are thus enabled, by large use of the fat and oil from the animals
they devour, to endure safely the severe cold. Then there is reason to
believe that fat helps the digestion of other foods, for it is found that
the body is better nourished when the fats are used as food. When more fat
is consumed than is required to keep up the bodily heat and to yield
working power, the excess is stored up in various parts of the body,
making a sort of reserve fuel, which may be drawn upon at any future time.
105. Saline or Mineral Foods. All food contains, besides the
substances having potential energy, as described, certain saline
matters. Water and salts are not usually considered foods, but the results
of scientific research, as well as the experience of life, show that these
substances are absolutely necessary to the body. The principal mineral
foods are salt, lime, iron, magnesia, phosphorus, potash, and water.
Except common salt and water, these substances are usually taken only in
combination with other foods.
These saline matters are essential to health, and when not present in due
proportion nutrition is disturbed. If a dog be fed on food freed from all
salines, but otherwise containing proper nutrients, he soon suffers from
weakness, after a time amounting to paralysis, and often dies in
convulsions.
About 200 grains of common salt are required daily by an adult, but a
large proportion of this is in our food. Phosphate of lime is obtained
from milk and meats, and carbonate of lime from the hard water we drink.
Both are required for the bones and teeth. The salts of potash, which
assist in purifying the blood, are obtained from vegetables and fruits. An
iron salt is found in most foods, and sulphur in the yolk of eggs.
106. Water. Water is of use chiefly as a solvent, and while not
strictly a food, is necessary to life. It enters into the construction of
every tissue and is constantly being removed from the body by every
channel of waste[17].
As a solvent water aids digestion, and as it forms about 80 per cent
of the blood, it serves as a carrier of nutrient material to all the
tissues of the body.
Important Articles of Diet.
107. Milk. The value of milk as a food cannot be overestimated.
It affords nourishment in a very simple, convenient, and perfect form. It
is the sole food provided for the young of all animals which nourish their
young. It is an ideal food containing, in excellent proportions, all the
four elements necessary for growth and health in earlier youth.
[Table: Composition of Food Materials. Careful analyses have been
made of the different articles of food, mostly of the raw, or uncooked
foods. As might be expected, the analyses on record differ more or less in
the percentages assigned to the various constituents, but the following
table will give a fair idea of the fundamental nutritive value of the more
common foods:
In 100 parts Water Proteid Fat Carbohydrate Ash
Digestible Cellulose
Meat 76.7 20.8 1.5 0.3 -- 1.3
Eggs 73.7 12.6 12.1 -- -- 1.1
Cheese 36-60 25-33 7-30 3-7 -- 3.4
Cow's Milk 87.7 3.4 3.2 4.8 -- 0.7
Wheat Flour 13.3 10.2 0.9 74.8 0.3 0.5
Wheat Bread 35.6 7.1 0.2 55.5 0.3 1.1
Rye Flour 13.7 11.5 2.1 69.7 1.6 1.4
Rye bread 42.3 6.1 0.4 49.2 0.5 1.5
Rice 13.1 7.0 0.9 77.4 0.6 1.0
Corn 13.1 9.9 4.6 68.4 2.5 1.5
Macaroni 10.1 9.0 0.3 79.0 0.3 0.5
Peas and Beans 12-15 23-26 1-1/2-2 49-54 4.7 2-3
Potatoes 75.5 2.0 0.2 20.6 0.7 1.0
Carrots 87.1 1.0 0.2 9.3 1.4 0.9
Cabbage 90 2.3 0.5 4-6 1-2 1.3
Fruit 84 0.5 -- 10 4 0.5
]
Cheese is the nitrogenous part of milk, which has been coagulated by the
use of rennet. The curd is then carefully dried, salted, and pressed.
Cheese is sometimes difficult of digestion, as on account of its solid
form it is not easily acted upon by the digestive fluids.
108. Meats. The flesh of animals is one of our main sources of food.
Containing a large amount of proteid, it is admirably adapted for building
up and repairing the tissues of the body. The proportion of water is also
high, varying from 50 to 75 per cent. The most common meats used in
this country are beef, mutton, veal, pork, poultry, and game.
Beef contains less fat and is more nutritious than either mutton or pork.
Mutton has a fine flavor and is easily digested. Veal and lamb, though
more tender, are less easily digested. Pork contains much fat, and its
fiber is hard, so that it is the most difficult to digest of all the
meats. Poultry and game have usually a small proportion of fat, but are
rich in phosphates and are valued for their flavor.
109. Eggs. Consisting of about two-thirds water and the rest albumen
and fat, eggs are often spoken of as typical natural food. The white
of an egg is chiefly albumen, with traces of fat and salt; the yolk is
largely fat and salts. The yellow color is due partly to sulphur. It is
this which blackens a silver spoon. Eggs furnish a convenient and
concentrated food, and if properly cooked are readily digested.
110. Fish. Fish forms an important and a most nutritious article of
diet, as it contains almost as much nourishment as butcher's meat. The
fish-eating races and classes are remarkably strong and healthy. Fish
is less stimulating than meat, and is thus valuable as a food for invalids
and dyspeptics. To be at its best, fish should be eaten in its season. As
a rule shell-fish, except oysters, are not very digestible. Some persons
are unable to eat certain kinds of fish, especially shell-fish, without
eruptions on the skin and other symptoms of mild poisoning.
111. Vegetable Foods. This is a large and important group of foods,
and embraces a remarkable number of different kinds of diet. Vegetable
foods include the cereals, garden vegetables, the fruits, and other less
important articles. These foods supply a certain quantity of albumen and
fat, but their chief use is to furnish starches, sugars, acids, and salts.
The vegetable foods indirectly supply the body with a large amount of
water, which they absorb in cooking.
112. Proteid Vegetable Foods. The most important proteid vegetable
foods are those derived from the grains of cereals and certain
leguminous seeds, as peas and beans. The grains when ground make the
various flours or meals. They contain a large quantity of starch, a
proteid substance peculiar to them called gluten, and mineral salts,
especially phosphate of lime. Peas and beans contain a smaller proportion
of starch, but more proteid matter, called legumin, or vegetable casein.
Of the cereal foods, wheat is that most generally useful. Wheat, and corn
and oatmeal form most important articles of diet. Wheat flour has starch,
sugar, and gluten--nearly everything to support life except fat.
Oatmeal is rich in proteids. In some countries, as Scotland, it forms an
important article of diet, in the form of porridge or oatmeal cakes.
Corn meal is not only rich in nitrogen, but the proportion of fat is also
large; hence it is a most important and nutritious article of food. Rice,
on the other hand, contains less proteids than any other cereal grain, and
is the least nutritious. Where used as a staple article of food, as in
India, it is commonly mixed with milk, cheese, or other nutritious
substances. Peas and beans, distinguished from all other vegetables by
their large amount of proteids--excel in this respect even beef, mutton,
and fish. They take the place of meats with those who believe in a
vegetable diet.
113. Non-proteid Vegetable Foods. The common potato is the best type
of non-proteid vegetable food. When properly cooked it is easily
digested and makes an excellent food. It contains about 75 per cent of
water, about 20 per cent of carbohydrates, chiefly starch, 2 per cent of
proteids, and a little fat and saline matters. But being deficient in
flesh-forming materials, it is unfit for an exclusive food, but is best
used with milk, meat, and other foods richer in proteid substances. Sweet
potatoes, of late years extensively used as food, are rich in starch and
sugar. Arrowroot, sago, tapioca, and similar foods are nutritious, and
easily digested, and with milk furnish excellent articles of diet,
especially for invalids and children.
Explanation of the Graphic Chart. The graphic chart, on the next
page, presents in a succinct and easily understood form the composition of
food materials as they are bought in the market, including the edible and
non-edible portions. It has been condensed from Dr. W. O. Atwater's
valuable monograph on "Foods and Diet." This work is known as the Yearbook
of the U.S. Department of Agriculture for 1894.
KEY: 1, percentage of nutrients; 2, fuel value of 1 pound in calories. The
unit of heat, called a _calorie_, or gramme-degree, is the amount of heat
which is necessary to raise one gramme (15.43 grains) of water one degree
centigrade (1.8 degrees Fahr.). A, round beef; B, sirloin beef; C, rib
beef; D, leg of mutton; E, spare rib of pork; F, salt pork; G, smoked ham;
H, fresh codfish; I, oysters; J, milk; K, butter; L, cheese; M, eggs; N,
wheat bread; O, corn meal; P, oatmeal; Q, dried beans; R, rice; S,
potatoes; T, sugar.
This table, among other things, shows that the flesh of fish contains more
water than that of warm-blooded animals. It may also be seen that animal
foods contain the most water; and vegetable foods, except potatoes, the
most nutrients. Proteids and fats exist only in small proportions in most
vegetables, except beans and oatmeal. Vegetable foods are rich in
carbohydrates while meats contain none. The fatter the meat the less the
amount of water. Thus very lean meat may be almost four-fifths water, and
fat pork almost one-tenth water.
[Illustration: Fig. 45.--Graphic Chart of the Composition of Food
Materials. Composition of Food Materials. Nutritive ingredients, refuse,
and fuel value. ]
114. Non-proteid Animal Foods. Butter is one of the most digestible
of animal fats, agreeable and delicate in flavor, and is on this account
much used as a wholesome food. Various substitutes have recently come into
use. These are all made from animal fat, chiefly that of beef, and are
known as butterine, oleomargarine, and by other trade names. These
preparations, if properly made, are wholesome, and may be useful
substitutes for butter, from which they differ but little in composition.
115. Garden Vegetables. Various green, fresh, and succulent
vegetables form an essential part of our diet. They are of importance
not so much on account of their nutritious elements, which are usually
small, as for the salts they supply, especially the salts of potash. It is
a well-known fact that the continued use of a diet from which fresh
vegetables are excluded leads to a disease known as scurvy. They are also
used for the agreeable flavor possessed by many, and the pleasant variety
and relish they give to the food. The undigested residue left by all green
vegetables affords a useful stimulus to intestinal contraction, and tends
to promote the regular action of the bowels.
116. Fruits. A great variety of fruits, both fresh and dry, is
used as food, or as luxuries. They are of little nutritive value,
containing, as they do, much water and only a small amount of proteid, but
are of use chiefly for the sugar, vegetable acids, and salts they contain.
In moderate quantity, fruits are a useful addition to our regular diet.
They are cooling and refreshing, of agreeable flavor, and tend to prevent
constipation. Their flavor and juiciness serve to stimulate a weak
appetite and to give variety to an otherwise heavy diet. If eaten in
excess, especially in an unripe or an overripe state, fruits may occasion
a disturbance of the stomach and bowels, often of a severe form.
117. Condiments. The refinements of cookery as well as the craving
of the appetite, demand many articles which cannot be classed strictly as
foods. They are called condiments, and as such may be used in
moderation. They give flavor and relish to food, excite appetite and
promote digestion. Condiments increase the pleasure of eating, and by
their stimulating properties promote secretions of the digestive fluids
and excite the muscular contractions of the alimentary canal.
The well-known condiments are salt, vinegar, pepper, ginger, nutmeg,
cloves, and various substances containing ethereal oils and aromatics.
Their excessive use is calculated to excite irritation and disorder of the
digestive organs.
118. Salt The most important and extensively used of the condiments
is common salt. It exists in all ordinary articles of diet, but in
quantities not sufficient to meet the wants of the bodily tissues. Hence
it is added to many articles of food. It improves their flavor, promotes
certain digestive secretions, and meets the nutritive demands of the body.
The use of salt seems based upon an instinctive demand of the system for
something necessary for the full performance of its functions. Food
without salt, however nutritious in other respects, is taken with
reluctance and digested with difficulty.
Salt has always played an important and picturesque part in the history of
dietetics. Reference to its worth and necessity abounds in sacred and
profane history. In ancient times, salt was the first thing placed on the
table and the last removed. The place at the long table, above or below
the salt, indicated rank. It was everywhere the emblem of hospitality. In
parts of Africa it is so scarce that it is worth its weight in gold, and
is actually used as money. Torture was inflicted upon prisoners of state
in olden times by limiting the food to water and bread, without salt. So
intense may this craving for salt become, that men have often risked their
liberty and even their lives to obtain it.
119. Water. The most important natural beverage is pure water; in
fact it is the only one required. Man has, however, from the earliest
times preferred and daily used a variety of artificial drinks, among which
are tea, coffee, and cocoa.
All beverages except certain strong alcoholic liquors, consist almost
entirely of water. It is a large element of solid foods, and our
bodies are made up to a great extent of water. Everything taken into the
circulating fluids of the body, or eliminated from them, is done through
the agency of water. As a solvent it is indispensable in all the
activities of the body.
It has been estimated that an average-sized adult loses by means of the
lungs, skin, and kidneys about eighty ounces of water every twenty-four
hours. To restore this loss about four pints must be taken daily. About
one pint of this is obtained from the food we eat, the remaining three
pints being taken as drink. One of the best ways of supplying water to the
body is by drinking it in its pure state, when its solvent properties can
be completely utilized. The amount of water consumed depends largely upon
the amount of work performed by the body, and upon the temperature.
Being one of the essential elements of the body, it is highly important
that water should be free from harmful impurities. If it contain the germs
of disease, sickness may follow its use. Without doubt the most important
factor in the spread of disease is, with the exception of impure air,
impure water. The chief agent in the spread of typhoid fever is
impure water. So with cholera, the evidence is overwhelming that filthy
water is an all-powerful agent in the spread of this terrible disease.
120. Tea, Coffee, and Cocoa. The active principle of tea is called
theine; that of coffee, caffeine, and of cocoa, theobromine. They also
contain an aromatic, volatile oil, to which they owe their distinctive
flavor. Tea and coffee also contain an astringent called tannin, which
gives the peculiar bitter taste to the infusions when steeped too long. In
cocoa, the fat known as cocoa butter amounts to fifty per cent.
121. Tea. It has been estimated that one-half of the human race now
use tea, either habitually or occasionally. Its use is a prolific source
of indigestion, palpitation of the heart, persistent wakefulness, and of
other disorders. When used at all it should be only in moderation. Persons
who cannot use it without feeling its hurtful effects, should leave it
alone. It should not be taken on an empty stomach, nor sipped after every
mouthful of food.
122. Coffee. Coffee often disturbs the rhythm of the heart and causes
palpitation. Taken at night, coffee often causes wakefulness. This effect
is so well known that it is often employed to prevent sleep. Immoderate
use of strong coffee may produce other toxic effects, such as muscular
tremors, nervous anxiety, sick-headache, palpitation, and various
uncomfortable feelings in the cardiac region. Some persons cannot drink
even a small amount of tea or coffee without these unpleasant effects.
These favorite beverages are unsuitable for young people.
123. Cocoa. The beverage known as cocoa comes from the seeds of the
cocoa-tree, which are roasted like the coffee berries to develop the
aroma. Chocolate is manufactured cocoa,--sugar and flavors being added to
the prepared seeds. Chocolate is a convenient and palatable form of highly
nutritious food. For those with whom tea and coffee disagree, it may be an
agreeable beverage. The large quantity of fat which it contains, however,
often causes it to be somewhat indigestible.
124. Alcoholic Beverages. There is a class of liquids which are
certainly not properly food or drink, but being so commonly used as
beverages, they seem to require special notice in this chapter. In view
of the great variety of alcoholic beverages, the prevalence of their
use, and the very remarkable deleterious effects they produce upon the
bodily organism, they imperatively demand our most careful attention, both
from a physiological and an hygienic point of view.
125. Nature of Alcohol. The ceaseless action of minute forms of plant
life, in bringing about the decomposition of the elaborated products of
organized plant or animal structures, will be described in more detail
(secs. 394-398).
All such work of vegetable organisms, whether going on in the moulding
cheese, in the souring of milk, in putrefying meat, in rotting fruit, or
in decomposing fruit juice, is essentially one of fermentation,
caused by these minute forms of plant life. There are many kinds of
fermentation, each with its own special form of minute plant life or
micro-organism.
In this section we are more especially concerned about that fermentation
which results from the decomposition of sweet fruit, plant, or other
vegetable, juices which are composed largely of water containing sugar and
flavoring matters.
This special form of fermentation is known as alcoholic or vinous
fermentation, and the micro-organisms that cause it are familiarly termed
alcoholic ferments. The botanist classes them as _Saccharomycetes_, of
which there are several varieties. Germs of _Saccharomycetes_ are found on
the surfaces and stems of fruit as it is ripening. While the fruit remains
whole these germs have no power to invade the juice, and even when the
skins are broken the conditions are less favorable for their work than for
that of the moulds,[18] which are the cause of the rotting of fruit.
But when fruit is crushed and its juice pressed out, the
_Saccharomycetes_ are carried into it where they cannot get the oxygen
they need from the air. They are then able to obtain oxygen by taking it
from the sugar of the juice. By so doing they cause a breaking up of the
sugar and a rearrangement of its elements. Two new substances are formed
in this decomposition of sugar, viz., carbon dioxid, which arises
from the liquid in tiny bubbles, and alcohol, a poison which
remains in the fermenting fluid.
Now we must remember that fermentation entirely changes the nature of the
substance fermented. For all forms of decomposition this one law holds
good. Before alcoholic fermentation, the fruit juice was wholesome and
beneficial; after fermentation, it becomes, by the action of the minute
germs, a poisonous liquid known as alcohol, and which forms an essential
part of all intoxicating beverages.
Taking advantage of this great law of fermentation which dominates the
realm of nature, man has devised means to manufacture various alcoholic
beverages from a great variety of plant structures, as ripe grapes, pears,
apples, and other fruits, cane juices, corn, the malt of barley, rye,
wheat, and other cereals.
The process differs according to the substance used and the manner in
which it is treated, but the ultimate outcome is always the same,
viz., the manufacture of a beverage containing a greater or less
proportion of alcoholic poison. By the process of _distillation_, new and
stronger liquor is made. Beverages thus distilled are known as ardent
spirits. Brandy is distilled from wine, rum from fermented molasses, and
commercial alcohol mostly from whiskey.
The poisonous element in all forms of intoxicating drinks, and the one so
fraught with danger to the bodily tissues, is the alcohol they
contain. The proportion of the alcoholic ingredient varies, being about 50
per cent in brandy, whiskey, and rum, about 20 to 15 per cent in wines,
down to 5 per cent, or less, in the various beers and cider; but whether
the proportion of alcohol be more or less, the same element of danger is
always present.
126. Effects of Alcoholic Beverages upon the Human System. One of the
most common alcoholic beverages is wine, made from the juice of grapes. As
the juice flows from the crushed fruit the ferments are washed from the
skins and stems into the vat. Here they bud and multiply rapidly,
producing alcohol. In a few hours the juice that was sweet and wholesome
while in the grape is changed to a poisonous liquid, capable of injuring
whoever drinks it. One of the gravest dangers of wine-drinking is the
power which the alcohol in it has to create a thirst which demands more
alcohol. The spread of alcoholism in wine-making countries is an
illustration of this fact.
Another alcoholic beverage, common in apple-growing districts, is cider.
Until the microscope revealed the ferment germ on the "bloom" of the
apple-skin, very little was known of the changes produced in cider during
the mysterious process of "working." Now, when we see the bubbles of gas
in the glass of cider we know what has produced them, and we know too that
a poison which we do not see is there also in corresponding amounts. We
have learned, too, to trace the wrecked hopes of many a farmer's family to
the alcohol in the cider which he provided so freely, supposing it
harmless.
Beer and other malt liquors are made from grain. By sprouting the grain,
which changes its starch to sugar, and then dissolving out the sugar with
water, a sweet liquid is obtained which is fermented with yeast, one kind
of alcoholic ferment. Some kinds of beer contain only a small percentage
of alcohol, but these are usually drunk in proportionately large amounts.
The life insurance company finds the beer drinker a precarious risk; the
surgeon finds him an unpromising subject; the criminal court finds him
conspicuous in its proceedings. The united testimony from all these
sources is that beer is demoralizing, mentally, morally, and physically.
127. Cooking. The process through which nearly all food used by
civilized man has to pass before it is eaten is known as cooking.
Very few articles indeed are consumed in their natural state, the
exceptions being eggs, milk, oysters, fruit and a few vegetables. Man is
the only animal that cooks his food. Although there are savage races that
have no knowledge of cooking, civilized man invariably cooks most of his
food. It seems to be true that as nations advance in civilization they
make a proportionate advance in the art of cooking.
Cooking answers most important purposes in connection with our food,
especially from its influence upon health. It enables food to be more
readily chewed, and more easily digested. Thus, a piece of meat when raw
is tough and tenacious, but if cooked the fibers lose much of their
toughness, while the connective tissues are changed into a soft and
jelly-like mass. Besides, the meat is much more readily masticated and
acted upon by the digestive fluids. So cooking makes vegetables and grains
softer, loosens their structure, and enables the digestive juices readily
to penetrate their substance.
Cooking also improves or develops flavors in food, especially in animal
foods, and thus makes them attractive and pleasant to the palate. The
appearance of uncooked meat, for example, is repulsive to our taste, but
by the process of cooking, agreeable flavors are developed which stimulate
the appetite and the flow of digestive fluids.
Another important use of cooking is that it kills any minute parasites or
germs in the raw food. The safeguard of cooking thus effectually removes
some important causes of disease. The warmth that cooking imparts to food
is a matter of no slight importance; for warm food is more readily
digested, and therefore nourishes the body more quickly.
The art of cooking plays a very important part in the matter of health,
and thus of comfort and happiness. Badly cooked and ill-assorted foods are
often the cause of serious disorders. Mere cooking is not enough, but good
cooking is essential.
Experiments.
Experiments with the Proteids.
Experiment 31. As a type of the group of proteids we take the white
of egg, egg-white or egg-albumen. Break an egg carefully, so as not to mix
the white with the yolk. Drop about half a teaspoonful of the raw white of
egg into half a pint of distilled water. Beat the mixture vigorously with
a glass rod until it froths freely. Filter through several folds of muslin
until a fairly clear solution is obtained.
Experiment 32. To a small quantity of this solution in a test tube
add strong nitric acid, and boil. Note the formation of a white
precipitate, which turns yellow. After cooling, add ammonia, and note that
the precipitate becomes orange.
Experiment 33. Add to the solution of egg-albumen, excess of strong
solution of caustic soda (or potash), and then a drop or two of very
dilute solution (one per cent) of copper sulphate. A violet color is
obtained which deepens on boiling.
Experiment 34. Boil a small portion of the albumen solution in a test
tube, adding drop by drop dilute acetic acid (two per cent) until a flaky
coagulum of insoluble albumen separates.
Experiments with Starch.
Experiment 35. Wash a potato and peel it. Grate it on a nutmeg grater
into a tall cylindrical glass full of water. Allow the suspended particles
to subside, and after a time note the deposit. The lowest layer consists
of a white powder, or starch, and above it lie coarser fragments of
cellulose and other matters.
Experiment 36. Examine under the microscope a bit of the above white
deposit. Note that each starch granule shows an eccentric hilum with
concentric markings. Add a few drops of very dilute solution of iodine.
Each granule becomes blue, while the markings become more distinct.
Experiment 37. Examine a few of the many varieties of other kinds of
starch granules, as in rice, arrowroot, etc. Press some dry starch powder
between the thumb and forefinger, and note the peculiar crepitation.
Experiment 38. Rub a few bits of starch in a little cold water. Put a
little of the mixture in a large test tube, and then fill with boiling
water. Boil until an imperfect opalescent solution is obtained.
Experiment 39. Add powdered dry starch to cold water. It is
insoluble. Filter and test the filtrate with iodine. It gives no blue
color.
Experiment 40. Boil a little starch with water; if there is enough
starch it sets on cooling and a paste results.
Experiment 41. Moisten some flour with water until it forms a tough,
tenacious dough; tie it in a piece of cotton cloth, and knead it in a
vessel containing water until all the starch is separated. There remains
on the cloth a grayish white, sticky, elastic "gluten," made up of
albumen, some of the ash, and fats. Draw out some of the gluten into
threads, and observe its tenacious character.
Experiment 42. Shake up a little flour with ether in a test tube,
with a tight-fitting cork. Allow the mixture to stand for an hour, shaking
it from time to time. Filter off the ether, and place some of it on a
perfectly clean watch glass. Allow the ether to evaporate, when a greasy
stain will be left, thus showing the presence of fats in the flour.
Experiment 43. Secure a specimen of the various kinds of flour, and
meal, peas, beans, rice, tapioca, potato, etc. Boil a small quantity of
each in a test tube for some minutes. Put a bit of each thus cooked on a
white plate, and pour on it two or three drops of the tincture of iodine.
Note the various changes of color,--blue, greenish, orange, or yellowish.
Experiments with Milk.
Experiment 44. Use fresh cow's milk. Examine the naked-eye character
of the milk. Test its reaction with litmus paper. It is usually neutral or
slightly alkaline.
Experiment 45. Examine with the microscope a drop of milk, noting
numerous small, highly refractive oil globules floating in a fluid.
Experiment 46. Dilute one ounce of milk with ten times its volume of
water. Add cautiously dilute acetic acid until there is a copious,
granular-looking precipitate of the chief proteid of milk (caseinogen),
formerly regarded as a derived albumen. This action is hastened by
heating.
Experiment 47. Saturate milk with Epsom salts, or common salt. The
proteid and fat separate, rise to the surface, and leave a clear fluid
beneath.
Experiment 48. Place some milk in a basin; heat it to about 100 degrees
F., and add a few drops of acetic acid. The mass curdles and separates
into a solid curd (proteid and fat) and a clear fluid (the whey), which
contains the lactose.
Experiment 49. Take one or two teaspoonfuls of fresh milk in a test
tube; heat it, and add a small quantity of extract of rennet. Note that
the whole mass curdles in a few minutes, so that the tube can be inverted
without the curd falling out. Soon the curd shrinks, and squeezes out a
clear, slightly yellowish fluid, the whey.
Experiment 50. Boil the milk as before, and allow it to cool; then
add rennet. No coagulation will probably take place. It is more difficult
to coagulate boiled milk with rennet than unboiled milk.
Experiment 51. Test fresh milk with red litmus paper; it should turn
the paper pale blue, showing that it is slightly alkaline. Place aside for
a day or two, and then test with blue litmus paper; it will be found to be
acid. This is due to the fact that lactose undergoes the lactic acid
fermentation. The lactose is converted into lactic acid by means of a
special ferment.
Experiment 52. Evaporate a small quantity of milk to dryness in an
open dish. After the dry residue is obtained, continue to apply heat;
observe that it chars and gives off pungent gases. Raise the temperature
until it is red hot; allow the dish then to cool; a fine white ash will be
left behind. This represents the _inorganic matter_ of the milk.
Experiments with the Sugars.
Experiment 53. Cane sugar is familiar as cooking and table sugar. The
little white grains found with raisins are grape sugar, or glucose. Milk
sugar is readily obtained of the druggist. Prepare a solution of the
various sugars by dissolving a small quantity of each in water. Heat each
solution with sulphuric acid, and it is seen to darken or char slowly.
Experiment 54. Place some Fehling solution (which can be readily
obtained at the drug store as a solution, or tablets may be bought which
answer the same purpose) in a test tube, and boil. If no yellow
discoloration takes place, it is in good condition. Add a few drops of the
grape sugar solution and boil, when the mixture suddenly turns to an
opaque yellow or red color.
Experiment 55. Repeat same experiment with milk sugar.
Chapter VI.
Digestion.
128. The Purpose of Digestion. As we have learned, our bodies are
subject to continual waste, due both to the wear and tear of their
substance, and to the consumption of material for the production of their
heat and energy. The waste occurs in no one part alone, but in all the
tissues.
Now, the blood comes into direct contact with every one of these tissues.
The ultimate cells which form the tissues are constantly being bathed by
the myriads of minute blood-vessels which bring to the cells the raw
material needed for their continued renewal. These cells are able to
select from the nutritive fluid whatever they require to repair their
waste, and to provide for their renewed activity. At the same time, the
blood, as it bathes the tissues, sweeps into its current and bears away
the products of waste.
Thus the waste occurs in the tissues and the means of repair are obtained
from the blood. The blood is thus continually being impoverished by having
its nourishment drained away. How, then, is the efficiency of the blood
maintained? The answer is that while the ultimate purpose of the food is
for the repair of the waste, its immediate destination is the blood.[19]
129. Absorption of Food by the Blood. How does the food pass from the
cavity of the stomach and intestinal canal into the blood-vessels? There
are no visible openings which permit communication. It is done by what in
physics is known as _endosmotic_ and _exosmotic_ action. That is, whenever
there are two solutions of different densities, separated only by an
animal membrane, an interchange will take place between them through the
membrane.
To illustrate: in the walls of the stomach and intestines there is a
network of minute vessels filled with blood,--a liquid containing many
substances in solution. The stomach and intestinal canal also contain
liquid food, holding many substances in solution. A membrane, made up of
the extremely thin walls of the blood-vessels and intestines, separates
the liquids. An exchange takes place between the blood and the contents of
the stomach and bowels, by which the dissolved substances of food pass
through the separating membranes into the blood.
[Illustration: Fig. 46.--Cavities of the Mouth, Pharynx, etc. (Section in
the middle line designed to show the mouth in its relations to the nasal
fossae, the pharynx, and the larynx.)
A, sphenoidal sinus;
B, internal orifice of Eustachian tube;
C, velum palati;
D, anterior pillar of soft palate;
E, posterior pillar of soft palate;
F, tonsil;
H, lingual portion of the pharynx;
K, lower portion of the pharynx;
L, larynx;
M, section of hyoid bone;
N, epiglottis;
O, palatine arch
]
This change, by which food is made ready to pass into the blood,
constitutes food-digestion, and the organs concerned in bringing
about this change in the food are the digestive organs.
130. The General Plan of Digestion. It is evident that the digestive
organs will be simple or complex, according to the amount of change which
is necessary to prepare the food to be taken up by the blood. If the
requisite change is slight, the digestive organs will be few, and their
structure simple. But if the food is varied and complex in composition,
the digestive apparatus will be complex. This condition applies to the
food and the digestion of man.
[Illustration: Fig. 47.--Diagram of the Structure of Secreting Glands.
A, simple tubular gland;
B, gland with mouth shut and sac formed;
C, gland with a coiled tube;
D, plan of part of a racemose gland
]
The digestive apparatus of the human body consists of the alimentary canal
and tributary organs which, although outside of this canal, communicate
with it by ducts. The alimentary canal consists of the mouth, the pharynx,
the oesophagus, the stomach, and the intestines. Other digestive organs
which are tributary to this canal, and discharge their secretions into it,
are the salivary glands,[20] the liver, and the pancreas.
The digestive process is subdivided into three steps, which take place in
the mouth, in the stomach, and in the intestines.
131. The Mouth. The mouth is the cavity formed by the lips, the
cheeks, the palate, and the tongue. Its bony roof is made up of the upper
jawbone on each side, and the palate bones behind. This is the _hard
palate_, and forms only the front portion of the roof. The continuation of
the roof is called the _soft palate_, and is made up of muscular tissue
covered with mucous membrane.
The mouth continues behind into the throat, the separation between the two
being marked by fleshy pillars which arch up from the sides to form the
soft palate. In the middle of this arch there hangs from its free edge a
little lobe called the uvula. On each side where the pillars begin to
arch is an almond-shaped body known as the tonsil. When we take cold,
one or both of the tonsils may become inflamed, and so swollen as to
obstruct the passage into the throat. The mouth is lined with mucous
membrane, which is continuous with that of the throat, oesophagus,
stomach, and intestines (Fig. 51).
132. Mastication, or Chewing. The first step of the process of
digestion is mastication, the cutting and grinding of the food by the
teeth, effected by the vertical and lateral movements of the lower jaw.
While the food is thus being crushed, it is moved to and fro by the varied
movements of the tongue, that every part of it may be acted upon by the
teeth. The advantage of this is obvious. The more finely the food is
divided, the more easily will the digestive fluids reach every part of it,
and the more thoroughly and speedily will digestion ensue.
The act of chewing is simple and yet important, for if hurriedly or
imperfectly done, the food is in a condition to cause disturbance in the
digestive process. Thorough mastication is a necessary introduction to the
more complicated changes which occur in the later digestion.
133. The Teeth. The teeth are attached to the upper and lower
maxillary bones by roots which sink into the sockets of the jaws. Each
tooth consists of a _crown_, the visible part, and one or more fangs,
buried in the sockets. There are in adults 32 teeth, 16 in each jaw.
Teeth differ in name according to their form and the uses to which they
are specially adapted. Thus, at the front of the jaws, the incisors,
or cutting teeth, number eight, two on each side. They have a single root
and the crown is beveled behind, presenting a chisel-like edge. The
incisors divide the food, and are well developed in rodents, as squirrels,
rats, and beavers.
Next come the canine teeth, or cuspids, two in each jaw, so called
from their resemblance to the teeth of dogs and other flesh-eating
animals. These teeth have single roots, but their crowns are more pointed
than in the incisors. The upper two are often called eye teeth, and the
lower two, stomach teeth. Next behind the canines follow, on each side,
two bicuspids. Their crowns are broad, and they have two roots. The
three hindmost teeth in each jaw are the molars, or grinders. These
are broad teeth with four or five points on each, and usually each molar
has three roots.
The last molars are known as the wisdom teeth, as they do not usually
appear until the person has reached the "years of discretion." All animals
that live on grass, hay, corn, and the cereals generally, have large
grinding teeth, as the horse, ox, sheep, and elephant.
The following table shows the teeth in their order:
Mo. Bi. Ca. In. In. Ca. Bi. Mo.
Upper 3 2 1 2 | 2 1 2 3 = 16
| } = 32
Lower 3 2 1 2 | 2 1 2 3 = 16
The vertical line indicates the middle of the jaw, and shows that on each
side of each jaw there are eight teeth.
134. Development of the Teeth. The teeth just described are the
permanent set, which succeeds the temporary or milk teeth.
The latter are twenty in number, ten in each jaw, of which the four in the
middle are incisors. The tooth beyond on each side is an eye tooth, and
the next two on each side are bicuspids, or premolars.
The milk teeth appear during the first and second years, and last until
about the sixth or seventh year, from which time until the twelfth or
thirteenth year, they are gradually pushed out, one by one, by the
permanent teeth. The roots of the milk teeth are much smaller than those
of the second set.
[Illustration: Fig. 48.--Temporary and Permanent Teeth together.
_Temporary teeth:_
A, central incisors;
B lateral incisors;
C, canines;
D, anterior molars;
E, posterior molars
_Permanent teeth:_
F, central incisors;
H, lateral incisors;
K, canines;
L, first bicuspids;
M, second biscuspids;
N, first molars
]
The plan of a gradual succession of teeth is a beautiful provision of
nature, permitting the jaws to increase in size, and preserving the
relative position and regularity of the successive teeth.
[Illustration: Fig. 49.--Showing the Principal Organs of the Thorax and
Abdomen _in situ_. (The principal muscles are seen on the left, and
superficial veins on the right.)]
135. Structure of the Teeth. If we should saw a tooth down through
its center we would find in the interior a cavity. This is the pulp
cavity, which is filled with the dental pulp, a delicate substance
richly supplied with nerves and blood-vessels, which enter the tooth by
small openings at the point of the root. The teeth are thus nourished like
other parts of the body. The exposure of the delicate pulp to the air, due
to the decay of the dentine, gives rise to the pain of toothache.
Surrounding the cavity on all sides is the hard substance known as the
dentine, or tooth ivory. Outside the dentine of the root is a
substance closely resembling bone, called cement. In fact, it is true
bone, but lacks the Haversian canals. The root is held in its socket
by a dense fibrous membrane which surrounds the cement as the periosteum
does bone.
[Illustration: Fig. 50.--Section of Face. (Showing the parotid and
submaxillary glands.)]
The crown of the tooth is not covered by cement, but by the hard
enamel, which forms a strong protection for the exposed part. When
the teeth are first "cut," the surface of the enamel is coated with a
delicate membrane which answers to the Scriptural phrase "the skin of the
teeth." This is worn off in adult life.
136. Insalivation. The thorough mixture of the saliva with the food
is called insalivation. While the food is being chewed, it is
moistened with a fluid called saliva, which flows into the mouth from
six little glands. There are on each side of the mouth three salivary
glands, which secrete the saliva from the blood. The parotid is
situated on the side of the face in front of the ear. The disease, common
in childhood, during which this gland becomes inflamed and swollen, is
known as the "mumps." The submaxillary gland is placed below and to
the inner side of the lower jaw, and the sublingual is on the floor
of the mouth, between the tongue and the gums. Each gland opens into the
mouth by a little duct. These glands somewhat resemble a bunch of grapes
with a tube for a stalk.
The saliva is a colorless liquid without taste or smell. Its
principal element, besides water, is a ferment called _ptyalin_, which has
the remarkable property of being able to change starch into a form of
cane-sugar, known as maltose.
Thus, while the food is being chewed, another process is going on by which
starch is changed into sugar. The saliva also moistens the food into a
mass for swallowing, and aids in speech by keeping the mouth moist.
The activity of the salivary glands is largely regulated by their abundant
supply of nerves. Thus, the saliva flows into the mouth, even at the
sight, smell, or thought of food. This is popularly known as "making the
mouth water." The flow of saliva may be checked by nervous influences, as
sudden terror and undue anxiety.
Experiment 56. _To show the action of saliva on starch_. Saliva for
experiment may be obtained by chewing a piece of India rubber and
collecting the saliva in a test tube. Observe that it is colorless and
either transparent or translucent, and when poured from one vessel to
another is glairy and more or less adhesive. Its reaction is alkaline to
litmus paper.
Experiment 57. Make a thin paste from pure starch or arrowroot.
Dilute a little of the saliva with five volumes of water, and filter it.
This is best done through a filter perforated at its apex by a pin-hole.
In this way all air-bubbles are avoided. Label three test tubes _A, B_,
and _C_. In _A_, place starch paste; in _B_, saliva; and in _C_ one
volume of saliva and three volumes of starch paste. Place them for ten
minutes in a water bath at about 104 degrees Fahrenheit.
Test portions of all three for a reducing sugar, by means of Fehling's
solution or tablets.[21] _A_ and _B_ give no evidence of sugar, while
_C_ reduces the Fehling, giving a yellow or red deposit of cuprous
oxide. Therefore, starch is converted into a reducing sugar by the
saliva. This is done by the ferment ptyalin contained in saliva.
137. The Pharynx and OEsophagus. The dilated upper part of the
alimentary canal is called the pharynx. It forms a blind sac above
the level of the mouth. The mouth opens directly into the pharynx, and
just above it are two openings leading into the posterior passages of the
nose. There are also little openings, one on each side, from which begin
the Eustachian tubes, which lead upward to the ear cavities.
The windpipe opens downward from the pharynx, but this communication can
be shut off by a little plate or lid of cartilage, the epiglottis.
During the act of swallowing, this closes down over the entrance to the
windpipe, like a lid, and prevents the food from passing into the
air-passages. This tiny trap-door can be seen, by the aid of a mirror, if
we open the mouth wide and press down the back of the tongue with the
handle of a spoon (Figs. 46, 84, and 85).
Thus, there are six openings from the pharynx; the oesophagus being
the direct continuation from it to the stomach. If we open the mouth
before a mirror we see through the fauces the rear wall of the pharynx. In
its lining membrane is a large number of glands, the secretion from which
during a severe cold may be quite troublesome.
The oesophagus, or gullet, is a tube about nine inches long,
reaching from the throat to the stomach. It lies behind the windpipe,
pierces the diaphragm between the chest and abdomen, and opens into the
stomach. It has in its walls muscular fibers, which, by their worm-like
contractions, grasp the successive masses of food swallowed, and pass them
along downwards into the stomach.
138. Deglutition, or Swallowing. The food, having been well chewed
and mixed with saliva, is now ready to be swallowed as a soft, pasty mass.
The tongue gathers it up and forces it backwards between the pillars of
the fauces into the pharynx.
If we place the fingers on the "Adam's apple," and then pretend to
swallow something, we can feel the upper part of the windpipe and the
closing of its lid (epiglottis), so as to cover the entrance and prevent
the passage of food into the trachea.
There is only one pathway for the food to travel, and that is down the
oesophagus. The slow descent of the food may be seen if a horse or
dog be watched while swallowing. Even liquids do not fall or flow down the
food passage. Hence, acrobats can drink while standing on their heads, or
a horse with its mouth below the level of the oesophagus. The food is
under the control of the will until it has entered the pharynx; all the
later movements are involuntary.
[Illustration: Fig. 51.--A View into the Back Part of the Adult Mouth.
(The head is represented as having been thrown back, and the tongue drawn
forward.)
A, B, incisors;
C, canine;
D, E, bicuspids;
F, H, K, molars;
M, anterior pillar of the fauces;
N, tonsil;
L, uvula;
O, upper part of the pharynx;
P, tongue drawn forward;
R, linear ridge, or raphe.
]
139. The Stomach. The stomach is the most dilated portion of the
alimentary canal and the principal organ of digestion. Its form is not
easily described. It has been compared to a bagpipe, which it resembles
somewhat, when moderately distended. When empty it is flattened, and in
some parts its opposite walls are in contact.
We may describe the stomach as a pear-shaped bag, with the large end to
the left and the small end to the right. It lies chiefly on the left side
of the abdomen, under the diaphragm, and protected by the lower ribs. The
fact that the large end of the stomach lies just beneath the diaphragm and
the heart, and is sometimes greatly distended on account of indigestion or
gas, may cause feelings of heaviness in the chest or palpitation of the
heart. The stomach is subject to greater variations in size than any other
organ of the body, depending on its contents. Just after a moderate meal
it averages about twelve inches in length and four in diameter, with a
capacity of about four pints.
[Illustration: Fig. 52.--The Stomach. A, cardiac end; B, pyloric end, C,
lesser curvature, D, greater curvature]
The orifice by which the food enters is called the cardiac opening,
because it is near the heart. The other opening, by which the food leaves
the stomach, and where the small intestine begins, is the pyloric
orifice, and is guarded by a kind of valve, known as the pylorus, or
gatekeeper. The concave border between the two orifices is called the
_small curvature_, and the convex as the _great curvature_, of the
stomach.
140. Coats of Stomach. The walls of the stomach are formed by four
coats, known successively from without as serous, muscular,
sub-mucous, and mucous. The outer coat is the serous membrane
which lines the abdomen,--the peritoneum (note, p. 135). The second
coat is muscular, having three sets of involuntary muscular fibers. The
outer set runs lengthwise from the cardiac orifice to the pylorus. The
middle set encircles all parts of the stomach, while the inner set
consists of oblique fibers. The third coat is the sub-mucous, made up of
loose connective tissues, and binds the mucous to the muscular coat.
Lastly there is the mucous coat, a moist, pink, inelastic membrane, which
completely lines the stomach. When the stomach is not distended, the
mucous layer is thrown into folds presenting a corrugated appearance.
[Illustration: Fig. 53.--Pits in the Mucous Membrane of the Stomach, and
Openings of the Gastric Glands. (Magnified 20 diameters.)]
141. The Gastric Glands. If we were to examine with a hand lens the
inner surface of the stomach, we would find it covered with little pits,
or depressions, at the bottom of which would be seen dark dots. These dots
are the openings of the gastric glands. In the form of fine, wavy
tubes, the gastric glands are buried in the mucous membrane, their mouths
opening on the surface. When the stomach is empty the mucous membrane is
pale, but when food enters, it at once takes on a rosy tint. This is due
to the influx of blood from the large number of very minute blood-vessels
which are in the tissue between the rows of glands.
The cells of the gastric glands are thrown into a state of greater
activity by the increased quantity of blood supply. As a result, soon
after food enters the stomach, drops of fluid collect at the mouths of the
glands and trickle down its walls to mix with the food. Thus these glands
produce a large quantity of gastric juice, to aid in the digestion of
food.
142. Digestion in the Stomach. When the food, thoroughly mixed with
saliva, reaches the stomach, the cardiac end of that organ is closed as
well as the pyloric valve, and the muscular walls contract on the
contents. A spiral wave of motion begins, becoming more rapid as digestion
goes on. Every particle of food is thus constantly churned about in the
stomach and thoroughly mixed with the gastric juice. The action of the
juice is aided by the heat of the parts, a temperature of about 99 degrees
Fahrenheit.
The gastric juice is a thin almost colorless fluid with a sour taste
and odor. The reaction is distinctly acid, normally due to free
hydrochloric acid. Its chief constituents are two ferments called pepsin
and rennin, free hydrochloric acid, mineral salts, and 95 per cent of
water.
[Illustration: Fig. 54.--A highly magnified view of a peptic or gastric
gland, which is represented as giving off branches. It shows the columnar
epithelium of the surface dipping down into the duct D of the gland, from
which two tubes branch off. Each tube is lined with columnar epithelial
cells, and there is a minute central passage with the "neck" at N. Here
and there are seen other special cells called parietal cells, P, which are
supposed to produce the acid of the gastric juice. The principal cells are
represented at C.]
Pepsin the important constituent of the gastric juice, has the
power, in the presence of an acid, of dissolving the proteid food-stuffs.
Some of which is converted into what are called _peptones_, both soluble
and capable of filtering through membranes. The gastric juice has no
action on starchy foods, neither does it act on fats, except to dissolve
the albuminous walls of the fat cells. The fat itself is thus set free in
the form of minute globules. The whole contents of the stomach now assume
the appearance and the consistency of a thick soup, usually of a grayish
color, known as chyme.
It is well known that "rennet" prepared from the calf's stomach has a
remarkable effect in rapidly curdling milk, and this property is utilized
in the manufacture of cheese. Now, a similar ferment is abundant in the
gastric juice, and may be called _rennin_. It causes milk to clot, and
does this by so acting on the casein as to make the milk set into a jelly.
Mothers are sometimes frightened when their children, seemingly in perfect
health, vomit masses of curdled milk. This curdling of the milk is,
however, a normal process, and the only noteworthy thing is its rejection,
usually due to overfeeding.
Experiment 58. _To show that pepsin and acid are necessary for
gastric digestion._ Take three beakers, or large test tubes; label them
_A_, _B_, _C_. Put into _A_ water and a few grains of powdered pepsin.
Fill _B_ two-thirds full of dilute hydrochloric acid (one teaspoonful to
a pint), and fill _C_ two-thirds full of hydrochloric acid and a few
grains of pepsin. Put into each a small quantity of well-washed fibrin,
and place them all in a water bath at 104 degrees Fahrenheit for half an
hour.
Examine them. In _A_, the fibrin is unchanged; in _B_, the fibrin is
clear and swollen up; in _C_, it has disappeared, having first become
swollen and clear, and completely dissolved, being finally converted
into peptones. Therefore, both acid and ferment are required for gastric
digestion.
Experiment 59. Half fill with dilute hydrochloric acid three large
test tubes, labelled _A_, _B_, _C_. Add to each a few grains of pepsin.
Boil _B_, and make _C_ faintly alkaline with sodic carbonate. The
alkalinity may be noted by adding previously some neutral litmus
solution. Add to each an equal amount--a few threads--of well-washed
fibrin which has been previously steeped for some time in dilute
hydrochloric acid, so that it is swollen and transparent. Keep the tubes
in a water-bath at about 104 degrees Fahrenheit for an hour and examine
them at intervals of twenty minutes.
After five to ten minutes the fibrin in _A_ is dissolved and the fluid
begins to be turbid. In _B_ and _C_ there is no change. Even after long
exposure to 100 degrees Fahrenheit there is no change in _B_ and _C_.
After a variable time, from one to four hours, the contents of the
stomach, which are now called chyme, begin to move on in successive
portions into the next part of the intestinal canal. The ring-like
muscles of the pylorus relax at intervals to allow the muscles of the
stomach to force the partly digested mass into the small intestines.
This action is frequently repeated, until even the indigestible masses
which the gastric juice cannot break down are crowded out of the stomach
into the intestines. From three to four hours after a meal the stomach
is again quite emptied.
A certain amount of this semi-liquid mass, especially the peptones, with
any saccharine fluids, resulting from the partial conversion of starch or
otherwise, is at once absorbed, making its way through the delicate
vessels of the stomach into the blood current, which is flowing through
the gastric veins to the portal vein of the liver.
[Illustration: Fig. 55.--A Small Portion of the Mucous Membrane of the
Small Intestine. (Villi are seen surrounded with the openings of the
tubular glands.) [Magnified 20 diameters.]]
143. The Small Intestine. At the pyloric end of the stomach the
alimentary canal becomes again a slender tube called the small
intestine. This is about twenty feet long and one inch in diameter,
and is divided, for the convenience of description, into three parts.
The first 12 inches is called the duodenum. Into this portion opens
the bile duct from the liver with the duct from the pancreas, these having
been first united and then entering the intestine as a common duct.
The next portion of the intestine is called the jejunum, because it
is usually empty after death.
The remaining portion is named the ileum, because of the many folds
into which it is thrown. It is the longest part of the small intestine,
and terminates in the right iliac region, opening into the large
intestine. This opening is guarded by the folds of the membrane forming
the ileo-caecal valve, which permits the passage of material from the
small to the large intestine, but prevents its backward movement.
144. The Coats of the Small Intestine. Like the stomach, the small
intestine has four coats, the serous, muscular, sub-mucous,
and mucous. The serous is the peritoneum.[22] The muscular consists
of an outer layer of longitudinal, and an inner layer of circular fibers,
by contraction of which the food is forced along the bowel. The sub-mucous
coat is made up of a loose layer of tissue in which the blood-vessels and
nerves are distributed. The inner, or mucous, surface has a fine, velvety
feeling, due to a countless number of tiny, thread-like projections,
called villi. They stand up somewhat like the "pile" of velvet. It is
through these villi that the digested food passes into the blood.
[Illustration: Fig. 56.--Sectional View of Intestinal Villi. (Black dots
represent the glandular openings.)]
The inner coat of a large part of the small intestine is thrown into
numerous transverse folds called _valvulae conniventes_. These seem to
serve two purposes, to increase the extent of the surface of the bowels
and to delay mechanically the progress of the intestinal contents. Buried
in the mucous layer throughout the length, both of the small and large
intestines, are other glands which secrete intestinal fluids. Thus, in the
lower part of the ileum there are numerous glands in oval patches known as
_Peyer's patches_. These are very prone to become inflamed and to ulcerate
during the course of typhoid fever.
145. The Large Intestine. The large intestine begins in the
right iliac region and is about five or six feet long. It is much larger
than the small intestine, joining it obliquely at short distance from its
end. A blind pouch, or dilated pocket is thus formed at the place of
junction, called the caecum. A valvular arrangement called the
ileo-caecal valve, which is provided with a button-hole slit, forms a kind
of movable partition between this part of the large intestine and the
small intestine.
[Illustration: Fig. 57.--Tubular Glands of the Small Intestines.
A, B, tubular glands seen in vertical section with their orifices at C,
opening upon the membrane between the villi, D, villus (Magnified 40
diameters)]
Attached to the caecum is a worm-shaped tube, about the size of a lead
pencil, and from three to four inches long, called the _vermiform
appendix_. Its use is unknown. This tube is of great surgical importance,
from the fact that it is subject to severe inflammation, often resulting
in an internal abscess, which is always dangerous and may prove fatal.
Inflammation of the appendix is known as _appendicitis_,--a name quite
familiar on account of the many surgical operations performed of late
years for its relief.
The large intestine passes upwards on the right side as the ascending
colon, until the under side of the liver is reached, where it passes
to the left side, as the transverse colon, below the stomach. It
there turns downward, as the descending colon, and making an S-shaped
curve, ends in the rectum. Thus the large intestine encircles, in the
form of a horseshoe, the convoluted mass of small intestines.
Like the small intestine, the large has four coats. The mucous coat,
however, has no folds, or villi, but numerous closely set glands, like
some of those of the small intestine. The longitudinal muscular fibers of
the large intestine are arranged in three bands, or bundles, which, being
shorter than the canal itself, produce a series of bulgings or pouches in
its walls. This sacculation of the large bowel is supposed to be designed
for delaying the onward flow of its contents, thus allowing more time for
the absorption of the liquid material. The blood-vessels and nerves of
this part of the digestive canal are very numerous, and are derived from
the same sources as those of the small intestine.
146. The Liver. The liver is a part of the digestive apparatus,
since it forms the bile, one of the digestive fluids. It is a large
reddish-brown organ, situated just below the diaphragm, and on the right
side. The liver is the largest gland in the body, and weighs from 50 to 60
ounces. It consists of two lobes, the right and the left, the right being
much the larger. The upper, convex surface of the liver is very smooth and
even; but the under surface is irregular, broken by the entrance and exit
of the various vessels which belong to the organ. It is held in its place
by five ligaments, four of which are formed by double folds of the
peritoneum.
The thin front edge of the liver reaches just below the bony edge of the
ribs; but the dome-shaped diaphragm rises slightly in a horizontal
position, and the liver passes up and is almost wholly covered by the
ribs. In tight lacing, the liver is often forced downward out from the
cover of the ribs, and thus becomes permanently displaced. As a result,
other organs in the abdomen and pelvis are crowded together, and also
become displaced.
147. Minute Structure of the Liver. When a small piece of the liver
is examined under a microscope it is found to be made up of masses of
many-sided cells, each about 1/1000 of an inch in diameter. Each group of
cells is called a _lobule_. When a single lobule is examined under the
microscope it appears to be of an irregular, circular shape, with its
cells arranged in rows, radiating from the center to the circumference.
Minute, hair-like channels separate the cells one from another, and unite
in one main duct leading from the lobule. It is the lobules which give to
the liver its coarse, granular appearance, when torn across.
[Illustration: Fig. 58.--Diagrammatic Section of a Villus
A, layer of columnar epithelium covering the villus;
B, central lacteal of villus;
C, unstriped muscular fibers;
D, goblet cell
]
Now there is a large vessel called the portal vein that brings to the
liver blood full of nourishing material obtained from the stomach and
intestines. On entering the liver this great vein conducts itself as if it
were an artery. It divides and subdivides into smaller and smaller
branches, until, in the form of the tiniest vessels, called capillaries,
it passes inward among the cells to the very center of the hepatic
lobules.
148. The Bile. We have in the liver, on a grand scale, exactly the
same conditions as obtain in the smaller and simpler glands. The
thin-walled liver cells take from the blood certain materials which they
elaborate into an important digestive fluid, called the bile.[23]
This newly manufactured fluid is carried away in little canals, called
_bile ducts_. These minute ducts gradually unite and form at last one main
duct, which carries the bile from the liver. This is known as the hepatic
duct. It passes out on the under side of the liver, and as it
approaches the intestine, it meets at an acute angle the cystic duct which
proceeds from the gall bladder and forms with it the common bile
duct. The common duct opens obliquely into the horseshoe bend of the
duodenum.
The cystic duct leads back to the under surface of the liver, where
it expands into a sac capable of holding about two ounces of fluid, and is
known as the gall bladder. Thus the bile, prepared in the depths of
the liver by the liver cells, is carried away by the bile ducts, and may
pass directly into the intestines to mix with the food. If, however,
digestion is not going on, the mouth of the bile duct is closed, and in
that case the bile is carried by the cystic duct to the gall bladder. Here
it remains until such time as it is needed.
149. Blood Supply of the Liver. We must not forget that the liver
itself, being a large and important organ, requires constant nourishment
for the work assigned to it. The blood which is brought to it by the
portal vein, being venous, is not fit to nourish it. The work is done by
the arterial blood brought to it by a great branch direct from the aorta,
known as the hepatic artery, minute branches of which in the form of
capillaries, spread themselves around the hepatic lobules.
The blood, having done its work and now laden with impurities, is picked
up by minute veinlets, which unite again and again till they at last form
one great trunk called the hepatic vein. This carries the impure
blood from the liver, and finally empties it into one of the large veins
of the body.
After the blood has been robbed of its bile-making materials, it is
collected by the veinlets that surround the lobules, and finds its way
with other venous blood into the hepatic vein. In brief, blood is brought
to the liver and distributed through its substance by two distinct
channels,--the portal vein and the hepatic artery, but it leaves
the liver by one distinct channel,--the hepatic vein.
[Illustration: Fig. 59--Showing the Relations of the Duodenum and Other
Intestinal Organs. (A portion of the stomach has been cut away.)]
150. Functions of the Liver. We have thus far studied the liver only
as an organ of secretion, whose work is to elaborate bile for future use
in the process of digestion. This is, however, only one of its functions,
and perhaps not the most important. In fact, the functions of the liver
are not single, but several. The bile is not wholly a digestive fluid, but
it contains, also, materials which are separated from the blood to be
cast out of the body before they work mischief. Thus, the liver ranks
above all others as an organ of excretion, that is, it separates
material of no further use to the body.
Of the various ingredients of the bile, only the bile salts are of use in
the work of digestion, for they act upon the fats in the alimentary canal,
and aid somehow in their emulsion and absorption. They appear to be
themselves split up into other substances, and absorbed with the dissolved
fats into the blood stream again.
The third function of the liver is very different from those already
described. It is found that the liver of an animal well and regularly fed,
when examined soon after death, contains a quantity of a carbohydrate
substance not unlike starch. This substance, extracted in the form of a
white powder, is really an animal starch. It is called glycogen, or
liver sugar, and is easily converted into grape sugar.
The hepatic cells appear to manufacture this glycogen and to store it up
from the food brought by the portal blood. It is also thought the glycogen
thus deposited and stored up in the liver is little by little changed into
sugar. Then, as it is wanted, the liver disposes of this stored-up
material, by pouring it, in a state of solution, into the hepatic vein. It
is thus steadily carried to the tissues, as their needs demand, to supply
them with material to be transformed into heat and energy.
151. The Pancreas. The pancreas, or sweetbread, is much smaller
than the liver. It is a tongue-like mass from six to eight inches long,
weighing from three to four ounces, and is often compared in appearance to
a dog's tongue. It is somewhat the shape of a hammer with the handle
running to a point.
The pancreas lies behind the stomach, across the body, from right to left,
with its large head embraced in the horseshoe bend of the duodenum. It
closely resembles the salivary glands in structure, with its main duct
running from one end to the other. This duct at last enters the duodenum
in company with the common bile duct.
The pancreatic juice, the most powerful in the body, is clear,
somewhat viscid, fluid. It has a decided alkaline reaction and is not
unlike saliva in many respects. Combined with the bile, this juice acts
upon the large drops of fat which pass from the stomach into the duodenum
and emulsifies them. This process consists partly in producing a fine
subdivision of the particles of fat, called an emulsion, and partly in a
chemical decomposition by which a kind of soap is formed. In this way the
oils and fats are divided into particles sufficiently minute to permit of
their being absorbed into the blood.
Again, this most important digestive fluid produces on starch an action
similar to that of saliva, but much more powerful. During its short stay
in the mouth, very little starch is changed into sugar, and in the
stomach, as we have seen, the action of the saliva is arrested. Now, the
pancreatic juice takes up the work in the small intestine and changes the
greater part of the starch into sugar. Nor is this all, for it also acts
powerfully upon the proteids not acted upon in the stomach, and changes
them into peptones that do not differ materially from those resulting from
gastric digestion. The remarkable power which the pancreatic juice
possesses of acting on all the food-stuffs appears to be due mainly to the
presence of a specific element or ferment, known as _trypsin_.
Experiment 60. _To show the action of pancreatic juice upon oils or
fats._ Put two grains of Fairchild's extract of pancreas into a
four-ounce bottle. Add half a teaspoonful of warm water, and shake well
for a few minutes; then add a tablespoonful of cod liver oil; shake
vigorously.
A creamy, opaque mixture of the oil and water, called an emulsion, will
result. This will gradually separate upon standing, the pancreatic
extract settling in the water at the bottom. When shaken it will again
form an emulsion.
Experiment 61. _To show the action of pancreatic juice on starch_.
Put two tablespoonfuls of _smooth_ starch paste into a goblet, and while
still so warm as just to be borne by the mouth, stir into it two grains
of the extract of pancreas. The starch paste will rapidly become
thinner, and gradually change into soluble starch, in a perfectly fluid
solution. Within a few minutes some of the starch is converted through
intermediary stages into maltose. Use the Fehling test for sugar.
152. Digestion in the Small Intestines. After digestion in the
stomach has been going on for some time, successive portions of the
semi-digested food begin to pass into the duodenum. The pancreas now takes
on new activity, and a copious flow of pancreatic juice is poured along
its duct into the intestines. As the food is pushed along over the common
opening of the bile and pancreatic ducts, a great quantity of bile from
this reservoir, the gall bladder, is poured into the intestines. These two
digestive fluids are now mixed with the chyme, and act upon it in the
remarkable manner just described.
[Illustration: Fig. 60.--Diagrammatic Scheme of Intestinal Absorption.
A, mesentery;
B, lacteals and mesentery glands;
C, veins of intestines;
R.C, receptacle of the chyle (receptaculum chyli);
P V, portal vein;
H V, hepatic veins;
S.V.C, superior vena cava;
R.A, right auricle of the heart;
I.V.C, inferior vena cava.
]
The inner surface of the small intestine also secretes a liquid called
intestinal juice, the precise functions of which are not known. The
chyme, thus acted upon by the different digestive fluids, resembles a
thick cream, and is now called chyle. The chyle is propelled along
the intestine by the worm-like contractions of its muscular walls. A
function of the bile, not yet mentioned, is to stimulate these movements,
and at the same time by its antiseptic properties to prevent putrefaction
of the contents of the intestine.
153. Digestion in the Large Intestines. Digestion does not occur to
any great extent in the large intestines. The food enters this portion of
the digestive canal through the ileo-caecal valve, and travels through it
slowly. Time is thus given for the fluid materials to be taken up by the
blood-vessels of the mucous membrane. The remains of the food now become
less fluid, and consist of undigested matter which has escaped the action
of the several digestive juices, or withstood their influence. Driven
onward by the contractions of the muscular walls, the refuse materials at
last reach the rectum, from which they are voluntarily expelled from the
body.
Absorption.
154. Absorption. While food remains within the alimentary canal it is as
much outside of the body, so far as nutrition is concerned, as if it had
never been taken inside. To be of any service the food must enter the
blood; it must be absorbed. The efficient agents in absorption are the
blood-vessels, the lacteals, and the lymphatics. The process through which
the nutritious material is fitted to enter the blood, is called
absorption. It is a process not confined, as we shall see, simply to the
alimentary canal, but one that is going on in every tissue.
The vessels by which the process of absorption is carried on are called
absorbents. The story, briefly told, is this: certain food materials
that have been prepared to enter the blood, filter through the mucous
membrane of the intestinal canal, and also the thin walls of minute
blood-vessels and lymphatics, and are carried by these to larger vessels,
and at last reach the heart, thence to be distributed to the tissues.
155. Absorption from the Mouth and Stomach. The lining of the mouth
and oesophagus is not well adapted for absorption. That this does
occur is shown by the fact that certain poisonous chemicals, like cyanide
of potash, if kept in the mouth for a few moments will cause death. While
we are chewing and swallowing our food, no doubt a certain amount of water
and common salt, together with sugar which has been changed from starch by
the action of the saliva, gains entrance to the blood.
In the stomach, however, absorption takes place with great activity. The
semi-liquid food is separated from the enormous supply of blood-vessels in
the mucous membrane only by a thin porous partition. There is, therefore,
nothing to prevent the exchange taking place between the blood and the
food. Water, along with any substances in the food that have become
dissolved, will pass through the partition and enter the blood-current.
Thus it is that a certain amount of starch that has been changed into
sugar, of salts in solution, of proteids converted into peptones, is taken
up directly by the blood-vessels of the stomach.
156. Absorption by the Intestines. Absorption by the intestines is a
most active and complicated process. The stomach is really an organ more
for the digestion than the absorption of food, while the small intestines
are especially constructed for absorption. In fact, the greatest part of
absorption is accomplished by the small intestines. They have not only a
very large area of absorbing surface, but also structures especially
adapted to do this work.
157. The Lacteals. We have learned in Section 144 that the mucous
lining of the small intestines is crowded with millions of little
appendages called villi, meaning "tufts of hair." These are only
about 1/30 of an inch long, and a dime will cover more than five hundred
of them. Each villus contains a loop of blood-vessels, and another vessel,
the lacteal, so called from the Latin word _lac_, milk, because of the
milky appearance of the fluid it contains. The villi are adapted
especially for the absorption of fat. They dip like the tiniest fingers
into the chyle, and the minute particles of fat pass through their
cellular covering and gain entrance to the lacteals. The milky material
sucked up by the lacteals is not in a proper condition to be poured at
once into the blood current. It is, as it were, in too crude a state, and
needs some special preparation.
The intestines are suspended to the posterior wall of the abdomen by a
double fold of peritoneum called the mesentery. In this membrane are
some 150 glands about the size of an almond, called mesenteric
glands. Now the lacteals join these glands and pour in their fluid
contents to undergo some important changes. It is not unlikely that the
mesenteric glands may intercept, like a filter, material which, if allowed
to enter the blood, would disturb the whole body. Thus, while the glands
might suffer, the rest of the body might escape. This may account for the
fact that these glands and the lymphatics may be easily irritated and
inflamed, thus becoming enlarged and sensitive, as often occurs in the
axilla.
Having been acted upon by the mesenteric glands, and passed through them,
the chyle flows onward until it is poured into a dilated reservoir for the
chyle, known as the receptaculum chyli. This is a sac-like expansion
of the lower end of the thoracic duct. Into this receptacle, situated at
the level of the upper lumbar vertebrae, in front of the spinal column, are
poured, not only the contents of the lacteals, but also of the lymphatic
vessels of the lower limbs.
158. The Thoracic Duct. This duct is a tube from fifteen to eighteen
inches long, which passes upwards in front of the spine to reach the base
of the neck, where it opens at the junction of the great veins of the left
side of the head with those of the left arm. Thus the thoracic duct
acts as a kind of feeding pipe to carry along the nutritive material
obtained from the food and to pour it into the blood current. It is to be
remembered that the lacteals are in reality lymphatics--the
lymphatics of the intestines.
[Illustration: Fig. 61.--Section of a Lymphatic Gland.
A, strong fibrous capsule sending partitions into the gland;
B, partitions between the follicles or pouches of the _cortical_ or
outer portion;
C, partitions of the _medullary_ or central portion;
D, E, masses of protoplasmic matter in the pouches of the gland;
F, lymph-vessels which bring lymph _to_ the gland, passing into its
center;
G, confluence of those leading to the efferent vessel;
H, vessel which carries the lymph away _from_ the gland.
]
159. The Lymphatics. In nearly every tissue and organ of the body
there is a marvelous network of vessels, precisely like the lacteals,
called the lymphatics. These are busily at work taking up and making
over anew waste fluids or surplus materials derived from the blood and
tissues generally. It is estimated that the quantity of fluid picked up
from the tissues by the lymphatics and restored daily to the circulation
is equal to the bulk of the blood in the body. The lymphatics seem to
start out from the part in which they are found, like the rootlets of a
plant in the soil. They carry a turbid, slightly yellowish fluid, called
lymph, very much like blood without the red corpuscles.
Now, just as the chyle was not fit to be immediately taken up by the
blood, but was passed through the mesenteric glands to be properly worked
over, so the lymph is carried to the lymphatic glands, where it
undergoes certain changes to fit it for being poured into the blood.
Nature, like a careful housekeeper, allows nothing to be wasted that can
be of any further service in the animal economy (Figs. 63 and 64).
The lymphatics unite to form larger and larger vessels, and at last join
the thoracic duct, except the lymphatics of the right side of the head and
chest and right arm. These open by the right lymphatic duct into the
venous system on the right side of the neck.
The whole lymphatic system may be regarded as a necessary appendage to the
vascular system (Chapter VII.). It is convenient, however, to treat it
under the general topic of absorption, in order to complete the history of
food digestion.
160. The Spleen and Other Ductless Glands. With the lymphatics may be
classified, for convenience, a number of organs called ductless or
blood glands. Although they apparently prepare materials for use in
the body, they have no ducts or canals along which may be carried the
result of their work. Again, they are called blood glands because it is
supposed they serve some purpose in preparing material for the blood.
The spleen is the largest of these glands. It lies beneath the
diaphragm, and upon the left side of the stomach. It is of a deep red
color, full of blood, and is about the size and shape of the palm of the
hand.
The spleen has a fibrous capsule from which partitions pass inwards,
dividing it into spaces by a framework of elastic tissue, with plain
muscular fibers. These spaces are filled with what is called the spleen
pulp, through which the blood filters from its artery, just as a fluid
would pass through a sponge. The functions of the spleen are not known. It
appears to take some part in the formation of blood corpuscles. In certain
diseases, like malarial fever, it may become remarkably enlarged. It may
be wholly removed from an animal without apparent injury. During digestion
it seems to act as a muscular pump, drawing the blood onwards with
increased vigor along its large vein to the liver.
The thyroid is another ductless gland. It is situated beneath the
muscles of the neck on the sides of "Adam's apple" and below it. It
undergoes great enlargement in the disease called goitre.
The thymus is also a blood gland. It is situated around the windpipe,
behind the upper part of the breastbone. Until about the end of the second
year it increases in size, and then it begins gradually to shrivel away.
Like the spleen, the thyroid and thymus glands are supposed to work some
change in the blood, but what is not clearly known.
The suprarenal capsules are two little bodies, one perched on the top
of each kidney, in shape not unlike that of a conical hat. Of their
functions nothing definite is known.
Experiments.
The action produced by the tendency of fluids to mix, or become equally
diffused in contact with each other, is known as _osmosis_, a form of
molecular attraction allied to that of adhesion. The various physical
processes by which the products of digestion are transferred from the
digestive canal to the blood may be illustrated in a general way by the
following simple experiments.
The student must, however, understand that the necessarily crude
experiments of the classroom may not conform in certain essentials to
these great processes conducted in the living body, which they are
intended to illustrate and explain.
[Illustration: Fig. 62.]
Experiment 62. _Simple Apparatus for Illustrating Endosmotic
Action._ "Remove carefully a circular portion, about an inch in
diameter, of the shell from one end of an egg, which may be done without
injuring the membranes, by cracking the shell in small pieces, which are
picked off with forceps. A small glass tube is then introduced through
an opening in the shell and membranes of the other end of the egg, and
is secured in a vertical position by wax or plaster of Paris, the tube
penetrating the yelk. The egg is then placed in a wine-glass partly
filled with water. In the course of a few minutes, the water will have
penetrated the exposed membrane, and the yelk will rise in the
tube."--Flint's _Human Physiology_, page 293.
Experiment 63. Stretch a piece of moist bladder across a glass
tube,--a common lamp-chimney will do. Into this put a strong saline
solution. Now suspend the tube in a wide mouthed vessel of water. After
a short time it will be found that a part of the salt solution has
passed through into the water, while a larger amount of water has passed
into the tube and raised the height of the liquid within it.
161. The Quantity of Food as Affected by Age. The quantity of food
required to keep the body in proper condition is modified to a great
extent by circumstances. Age, occupation, place of residence, climate, and
season, as well as individual conditions of health and disease, are always
important factors in the problem. In youth the body is not only growing,
but the tissue changes are active. The restless energy and necessary
growth at this time of life cannot be maintained without an abundance of
wholesome food. This food supply for young people should be ample enough
to answer the demands of their keen appetite and vigorous digestion.
In adult life, when the processes of digestion and assimilation are
active, the amount of food may without harm, be in excess of the actual
needs of the body. This is true, however, only so long as active muscular
exercise is taken.
In advanced life the tissue changes are slow, digestion is less active,
and the ability to assimilate food is greatly diminished. Growth has
ceased, the energy which induced activity is gone, and the proteids are no
longer required to build up worn-out tissues. Hence, as old age
approaches, the quantity of nitrogenous foods should be steadily
diminished.
Experiment 64. Obtain a sheep's bladder and pour into it a heavy
solution of sugar or some colored simple elixir, found at any drug
store. Tie the bladder carefully and place it in a vessel containing
water. After a while it will be found that an interchange has occurred,
water having passed into the bladder and the water outside having become
sweet.
Experiment 65. Make a hole about as big as a five-cent piece in the
large end of an egg. That is, break the shell carefully and snip the
outer shell membrane, thus opening the space between the outer and inner
membranes. Now put the egg into a glass of water, keeping it in an
upright position by resting on a napkin-ring. There is only the inner
shell membrane between the liquid white of the egg (albumen) and the
water.
An interchange takes place, and the water passes towards the albumen. As
the albumen does not pass out freely towards the water, the membrane
becomes distended, like a little bag at the top of the egg.
162. Ill Effects of a too Generous Diet. A generous diet, even of
those who take active muscular exercise, should be indulged in only with
vigilance and discretion. Frequent sick or nervous headaches, a sense of
fullness, bilious attacks, and dyspepsia are some of the after-effects of
eating more food than the body actually requires. The excess of food is
not properly acted upon by the digestive juices, and is liable to undergo
fermentation, and thus to become a source of irritation to the stomach and
the intestines. If too much and too rich food be persistently indulged in,
the complexion is apt to become muddy, the skin, especially of the face,
pale and sallow, and more or less covered with blotches and pimples; the
breath has an unpleasant odor, and the general appearance of the body is
unwholesome.
An excess of any one of the different classes of foods may lead to serious
results. Thus a diet habitually too rich in proteids, as with those who
eat meat in excess, often over-taxes the kidneys to get rid of the excess
of nitrogenous waste, and the organs of excretion are not able to rid the
tissues of waste products which accumulate in the system. From the blood,
thus imperfectly purified, may result kidney troubles and various diseases
of the liver and the stomach.
163. Effect of Occupation. Occupation has an important influence upon
the quantity of food demanded for the bodily support. Those who work long
and hard at physical labor, need a generous amount of nutritious food. A
liberal diet of the cereals and lean meat, especially beef, gives that
vigor to the muscles which enables one to undergo laborious and prolonged
physical exertion. On the other hand, those who follow a sedentary
occupation do not need so large a quantity of food. Brain-workers who
would work well and live long, should not indulge in too generous a diet.
The digestion of heavy meals involves a great expenditure of nervous
force. Hence, the forces of the brain-worker, being required for mental
exertion, should not be expended to an unwarranted extent on the task of
digestion.
164. Effect of Climate. Climate also has a marked influence on the
quantity of food demanded by the system. Much more food of all kinds is
consumed in cold than in warm climates. The accounts by travelers of the
quantity of food used by the inhabitants of the frigid zone are almost
beyond belief. A Russian admiral gives an instance of a man who, in his
presence, ate at a single meal 28 pounds of rice and butter. Dr. Hayes,
the Arctic traveler, states from personal observation that the daily
ration of the Eskimos is 12 to 15 pounds of meat. With the thermometer
ranging from 60 to 70 degrees F. below zero, there was a persistent
craving for strong animal diet, especially fatty foods.[24]
[Illustration: Fig. 63.--Lymphatics and Lymphatic Glands of the Axilla.]
The intense cold makes such a drain upon the heat-producing power of the
body that only food containing the largest proportion of carbon is capable
of making up for the loss. In tropical countries, on the other hand, the
natives crave and subsist mainly upon fruits and vegetables.
165. The Kinds of Food Required. An appetite for plain, well-cooked
food is a safe guide to follow. Every person in good health, taking a
moderate amount of daily exercise, should have a keen appetite for three
meals a day and enjoy them. Food should be both nutritious and digestible.
It is nutritious in proportion to the amount of material it furnishes for
the nourishment of the tissues. It is digestible in a greater or less
degree in respect to the readiness with which it yields to the action of
the digestive fluids, and is prepared to be taken up by the blood. This
digestibility depends partly upon the nature of the food in its raw state,
partly upon the effect produced upon it by cooking, and to some extent
upon its admixture with other foods. Certain foods, as the vegetable
albumens, are both nutritious and digestible. A hard-working man may grow
strong and maintain vigorous health on most of them, even if deprived of
animal food.
While it is true that the vegetable albumens furnish all that is really
needed for the bodily health, animal food of some kind is an economical
and useful addition to the diet. Races of men who endure prolonged
physical exertion have discovered for themselves, without the teaching of
science, the great value of meat. Hence the common custom of eating meat
with bread and vegetables is a sound one. It is undoubtedly true that the
people of this country, as a rule, eat meat too often and too much at a
time. The judicious admixture of different classes of foods greatly aids
their digestibility.
The great abundance and variety of food in this country, permit this
principle to be put into practice. A variety of mixed foods, as milk,
eggs, bread, and meat, are almost invariably associated to a greater or
less extent at every meal.
Oftentimes where there is of necessity a sameness of diet, there arises a
craving for special articles of food. Thus on long voyages, and during
long campaigns in war, there is an almost universal craving for onions,
raw potatoes, and other vegetables.
166. Hints about Meals. On an average, three meals each day, from
five to six hours apart, is the proper number for adults. Five hours is by
no means too long a time to intervene between consecutive meals, for it is
not desirable to introduce new food into the stomach, until the gastric
digestion of the preceding meal has been completed, and until the stomach
has had time to rest, and is in condition to receive fresh material. The
stomach, like other organs, does its work best at regular periods.[25]
Eating out of mealtimes should be strictly avoided, for it robs the
stomach of its needed rest. Food eaten when the body and mind are wearied
is not well digested. Rest, even for a few minutes, should be taken before
eating a full meal. It is well to lie down, or sit quietly and read,
fifteen minutes before eating, and directly afterwards, if possible.
Severe exercise and hard study just after a full meal, are very apt to
delay or actually arrest digestion, for after eating heartily, the vital
forces of the body are called upon to help the stomach digest its food. If
our bodily energies are compelled, in addition to this, to help the
muscles or brain, digestion is retarded, and a feeling of dullness and
heaviness follows. Fermentative changes, instead of the normal digestive
changes, are apt to take place in the food.
167. Practical Points about Eating. We should not eat for at least
two or three hours before going to bed. When we are asleep, the vital
forces are at a low ebb, the process of digestion is for the time nearly
suspended, and the retention of incompletely digested food in the stomach
may cause bad dreams and troubled sleep. But in many cases of
sleeplessness, a trifle of some simple food, especially if the stomach
seems to feel exhausted, often appears to promote sleep and rest.
[NOTE. The table on the next page shows the results of many
experiments to illustrate the time taken for the gastric digestion of
a number of the more common solid foods. There are a good many factors
of which the table takes no account, such as the interval since the
last meal, state of the appetite, amount of work and exercise, method
of cooking, and especially the quantity of food.]
Table Showing the Digestibility of the More Common Solid Foods.
Food How Time in
Cooked Stomach,
Hours
-------------------------------------------------
Apples, sweet and mellow Raw 1-1/2
Apples, sour and hard " 2-1/2
Apple Dumpling Boiled 3
Bass, striped, fresh Broiled 3
Beans, pod Boiled 2-1/2
Beef, with salt only " 2-3/4
" fresh, lean Raw 3
" " " Fried 4
" " " Roasted 3-1/2
" old, hard, salted Boiled 4-1/4
Beefsteak Broiled 3
Beets Boiled 3-3/4
Bread, corn Baked 3-1/4
" wheat, fresh " 3-1/2
Butter Melted 3-1/2
Cabbage, with vinegar Raw 2
" " " Boiled 4-1/2
" heads Raw 2-1/2
Carrots Boiled 3-1/4
Cheese, old, strong Raw 3-1/2
Chicken, full-grown Fricassee 2-3/4
" soup Boiled 3
Codfish, cured, dried " 2
Corncake Baked 2-3/4
Custard " 2-3/4
Duck, domestic Roasted 4
" wild " 4-1/2
Eggs, fresh, whipped Raw 1-1/2
" " 2
" soft-boiled Boiled 3
" hard-boiled " 3-1/2
" Fried 3-1/2
Fowl, domestic Boiled 4
" " Roasted 4
Gelatin Boiled 2-1/2
Goose Roasted 2-1/2
Green corn and beans Boiled 3-3/4
Hash, meat and vegetables Warmed 2-1/2
Lamb Broiled 2-1/2
Liver " 2
Milk Boiled 2
" Raw 2-1/4
Mutton, fresh Broiled 3
" " Boiled 3
" " Roasted 3-1/4
Oysters, fresh Raw 2-1/2
" " Roasted 3-1/4
" " Stewed 3-1/2
Parsnips Boiled 2-1/2
Pig Roasted 2-1/2
Pig's feet, soused Boiled 1
Pork, recently salted " 4-1/2
" Fried 4-1/4
" Raw 3
" steaks Fried 3-1/4
" Stewed 3
" fat or lean Roasted 5-1/4
Potatoes Baked 2-1/2
" Boiled 3-1/2
" Roasted 2-1/2
Rice Boiled 1
Sago " 1-3/4
Salmon, salted " 4
Soup, barley " 1-1/2
" beans " 3
" beef, vegetables, bread " 4
" marrow bone " 4-1/2
" mutton " 3-1/2
Sponge Cake Baked 2-1/2
Suet, beef, fresh Boiled 5-1/3
" mutton " 4-1/2
Tapioca " 2
Tripe, soused " 1
Trout, salmon, fresh " 1-1/2
" " " Fried 1-1/2
Turkey, wild Roasted 2-1/4
" domestic Boiled 2-1/4
" " Roasted 2-1/2
Turnips Boiled 3-1/2
Veal Roasted 4
" Fried 4-1/2
Venison, steaks Broiled 1-1/2
The state of mind has much to do with digestion. Sudden fear or joy, or
unexpected news, may destroy the appetite at once. Let a hungry person be
anxiously awaiting a hearty meal, when suddenly a disastrous telegram is
brought him; all appetite instantly disappears, and the tempting food is
refused. Hence we should laugh and talk at our meals, and drive away
anxious thoughts and unpleasant topics of discussion.
The proper chewing of the food is an important element in digestion.
Hence, eat slowly, and do not "bolt" large fragments of food. If
imperfectly chewed, it is not readily acted upon by the gastric juice, and
often undergoes fermentative changes which result in sour stomach, gastric
pain, and other digestive disturbance.
If we take too much drink with our meals, the flow of the saliva is
checked, and digestion is hindered. It is not desireable to dilute the
gastric juice, nor to chill the stomach with large amount of cold liquid.
Do not take food and drink too hot or too cold. If they are taken too
cold, the stomach is chilled, and digestion delayed. If we drink freely of
ice-water, it may require half an hour or more for the stomach to regain
its natural heat.
It is a poor plan to stimulate a flagging appetite with highly spiced food
and bitter drinks. An undue amount of pepper, mustard, horseradish,
pickles, and highly seasoned meat-sauces may stimulate digestion for the
time, but they soon impair it.
[NOTE. The process of gastric digestion was studied many years ago by
Dr. Beaumont and others, in the remarkable case of Alexis St. Martin,
a French-Canadian, who met with a gun-shot wound which left a
permanent opening into his stomach, guarded by a little valve of
mucous membrane. Through this opening the lining of the stomach could
be seen, the temperature ascertained, and numerous experiments made as
to the digestibility of various kinds of food.
It was by these careful and convincing experiments that the foundation
of our exact knowledge of the composition and action of gastric juice
was laid. The modest book in which Dr. Beaumont published his results
is still counted among the classics of physiology. The production of
artificial fistulae in animals, a method that has since proved so
fruitful, was first suggested by his work.]
It cannot be too strongly stated that food of a simple character, well
cooked and neatly served, is more productive of healthful living than a
great variety of fancy dishes which unduly stimulate the digestive organs,
and create a craving for food in excess of the bodily needs.
168. The Proper Care of the Teeth. It is our duty not only to take
the very best care of our teeth, but to retain them as long as possible.
Teeth, as we well know, are prone to decay. We may inherit poor and soft
teeth: our mode of living may make bad teeth worse. If an ounce of
prevention is ever worth a pound of cure, it is in keeping the teeth in
good order. Bad teeth and toothless gums mean imperfect chewing of the
food and, hence, impaired digestion. To attain a healthful old age, the
power of vigorous mastication must be preserved.
One of the most frequent causes of decay of the teeth is the retention of
fragments of food between and around them. The warmth and moisture of the
mouth make these matters decompose quickly. The acid thus generated
attacks the enamel of the teeth, causing decay of the dentine. Decayed
teeth are often the cause of an offensive breath and a foul stomach.
[Illustration: Fig. 64.--Lymphatics on the Inside of the Right Hand.]
To keep the teeth clean and wholesome, they should be thoroughly cleansed
at bedtime and in the morning with a soft brush and warm water. Castile
soap, and some prepared tooth-powder without grit, should be used, and the
brush should be applied on both sides of the teeth.
The enamel, once broken through, is never renewed. The tooth decays,
slowly but surely: hence we must guard against certain habits which injure
the enamel, as picking the teeth with pins and needles. We should never
crack nuts, crush hard candy, or bite off stout thread with the teeth.
Stiff tooth-brushes, gritty and cheap tooth-powders, and hot food and
drink, often injure the enamel.
To remove fragments of food which have lodged between adjacent teeth, a
quill or wooden toothpick should be used. Even better than these is the
use of surgeon's floss, or silk, which when drawn between the teeth,
effectually dislodges retained particles. If the teeth are not regularly
cleansed they become discolored, and a hard coating known as _tartar_
accumulates on them and tends to loosen them. It is said that after the
age of thirty more teeth are lost from this deposit than from all other
causes combined. In fact decay and tartar are the two great agents that
furnish work for the dentist.[26]
169. Hints about Saving Teeth. We should exercise the greatest care
in saving the teeth. The last resort of all is to lose a tooth by
extraction. The skilled dentist will save almost anything in the shape of
a tooth.
People are often urged and consent to have a number of teeth extracted
which, with but little trouble and expense, might be kept and do good
service for years. The object is to replace the teeth with an artificial
set. Very few plates, either partial or entire, are worn with real
comfort. They should always be removed before going to sleep, as there is
danger of their being swallowed.
The great majority of drugs have no injurious effect upon the teeth. Some
medicines, however, must be used with great care. The acids used in the
tincture of iron have a great affinity for the lime salts of the teeth. As
this form of iron is often used, it is not unusual to see teeth very badly
stained or decayed from the effects of this drug. The acid used in the
liquid preparations of quinine may destroy the teeth in a comparatively
short time. After taking such medicines the mouth should be thoroughly
rinsed with a weak solution of common soda, and the teeth cleansed.
170. Alcohol and Digestion. The influence of alcoholic drinks upon
digestion is of the utmost importance. Alcohol is not, and cannot be
regarded from a physiological point of view as a true food. The reception
given to it by the stomach proves this very plainly. It is obviously an
unwelcome intruder. It cannot, like proper foods, be transformed into any
element or component of the human body, but passes on, innutritious and
for the most part unappropriated. Taken even into the mouth, by any person
not hardened to its use, its effect is so pungent and burning as at once
to demand its rejection. But if allowed to pass into the stomach, that
organ immediately rebels against its intrusion, and not unfrequently
ejects it with indignant emphasis. The burning sensation it produces
there, is only an appeal for water to dilute it.
The stomach meanwhile, in response to this fiery invitation, secretes from
its myriad pores its juices and watery fluids, to protect itself as much
as possible from the invading liquid. It does not digest alcoholic drinks;
we might say it does not attempt to, because they are not material
suitable for digestion, and also because no organ can perform its normal
work while smarting under an unnatural irritation.
Even if the stomach does not at once eject the poison, it refuses to
adopt it as food, for it does not pass along with the other food material,
as chyme, into the intestines, but is seized by the absorbents, borne into
the veins, which convey it to the heart, whence the pulmonary artery
conveys it to the lungs, where its presence is announced in the breath.
But wherever alcohol is carried in the tissues, it is always an irritant,
every organ in turn endeavoring to rid itself of the noxious material.
171. Effect of Alcoholic Liquor upon the Stomach. The methods by
which intoxicating drinks impair and often ruin digestion are various. We
know that a piece of animal food, as beef, if soaked in alcohol for a few
hours, becomes hard and tough, the fibers having been compacted together
because of the abstraction of their moisture by the alcohol, which has a
marvelous affinity for water. In the same way alcohol hardens and toughens
animal food in the stomach, condensing its fibers, and rendering it
indigestible, thus preventing the healthful nutrition of the body. So, if
alcohol be added to the clear, liquid white of an egg, it is instantly
coagulated and transformed into hard albumen. As a result of this
hardening action, animal food in contact with alcoholic liquids in the
stomach remains undigested, and must either be detained there so long as
to become a source of gastric disturbance, or else be allowed to pass
undigested through the pyloric gate, and then may become a cause of
serious intestinal disturbance.[27]
This peculiar property of alcohol, its greedy absorption of water from
objects in contact with it, acts also by absorbing liquids from the
surface of the stomach itself, thus hardening the delicate glands,
impairing their ability to absorb the food-liquids, and so inducing
gastric dyspepsia. This local injury inflicted upon the stomach by all
forms of intoxicants, is serious and protracted. This organ is, with
admirable wisdom, so constructed as to endure a surprising amount of
abuse, but it was plainly not intended to thrive on alcoholic liquids. The
application of fiery drinks to its tender surface produces at first a
marked congestion of its blood-vessels, changing the natural pink color,
as in the mouth, to a bright or deep red.
If the irritation be not repeated, the lining membrane soon recovers its
natural appearance. But if repeated and continued, the congestion becomes
more intense, the red color deeper and darker; the entire surface is the
subject of chronic inflammation, its walls are thickened, and sometimes
ulcerated. In this deplorable state, the organ is quite unable to perform
its normal work of digestion.[28]
172. Alcohol and the Gastric Juice. But still another destructive
influence upon digestion appears in the singular fact that alcohol
diminishes the power of the gastric juice to do its proper work. Alcohol
coagulates the pepsin, which is the dissolving element in this important
gastric fluid. A very simple experiment will prove this. Obtain a small
quantity of gastric juice from the fresh stomach of a calf or pig, by
gently pressing it in a very little water. Pour the milky juice into a
clear glass vessel, add a little alcohol, and a white deposit will
presently settle to the bottom. This deposit contains the pepsin of the
gastric juice, the potent element by which it does its special work of
digestion. The ill effect of alcohol upon it is one of the prime factors
in the long series of evil results from the use of intoxicants.
173. The Final Results upon Digestion. We have thus explained three
different methods by which alcoholic drinks exercise a terrible power for
harm; they act upon the food so as to render it less digestible; they
injure the stomach so as seriously to impair its power of digestion; and
they deprive the gastric juice of the one principal ingredient essential
to its usefulness.
Alcoholic drinks forced upon the stomach are a foreign substance; the
stomach treats them as such, and refuses to go on with the process of
digestion till it first gets rid of the poison. This irritating presence
and delay weaken the stomach, so that when proper food follows, the
enfeebled organ is ill prepared for its work. After intoxication, there
occurs an obvious reaction of the stomach, and digestive organs, against
the violent and unnatural disturbance. The appetite is extinguished or
depraved, and intense headache racks the frame, the whole system is
prostrated, as from a partial paralysis (all these results being the voice
of Nature's sharp warning of this great wrong), and a rest of some days
is needed before the system fully recovers from the injury inflicted.
It is altogether an error to suppose the use of intoxicants is necessary
or even desirable to promote appetite or digestion. In health, good food
and a stomach undisturbed by artificial interference furnish all the
conditions required. More than these is harmful. If it may sometimes seem
as if alcoholic drinks arouse the appetite and invigorate digestion, we
must not shut our eyes to the fact that this is only a seeming, and that
their continued use will inevitably ruin both. In brief, there is no more
sure foe to good appetite and normal digestion than the habitual use of
alcoholic liquors.
174. Effect of Alcoholic Drinks upon the Liver. It is to be noted
that the circulation of the liver is peculiar; that the capillaries of the
hepatic artery unite in the lobule with those of the portal vein, and thus
the blood from both sources is combined; and that the portal vein brings
to the liver the blood from the stomach, the intestines, and the spleen.
From the fact that alcohol absorbed from the stomach enters the portal
vein, and is borne directly to the liver, we would expect to find this
organ suffering the full effects of its presence. And all the more would
this be true, because we have just learned that the liver acts as a sort
of filter to strain from the blood its impurities. So the liver is
especially liable to diseases produced by alcoholics. Post mortems of
those who have died while intoxicated show a larger amount of alcohol in
the liver than in any other organ. Next to the stomach the liver is an
early and late sufferer, and this is especially the case with hard
drinkers, and even more moderate drinkers in hot climates. Yellow fever
occurring in inebriates is always fatal.
The effects produced in the liver are not so much functional as organic;
that is, not merely a disturbed mode of action, but a destruction of the
fabric of the organ itself. From the use of intoxicants, the liver
becomes at first irritated, then inflamed, and finally seriously diseased.
The fine bands, or septa, which serve as partitions between the hepatic
lobules, and so maintain the form and consistency of the organ, are the
special subjects of the inflammation. Though the liver is at first
enlarged, it soon becomes contracted; the secreting cells are compressed,
and are quite unable to perform their proper work, which indeed is a very
important one in the round of the digestion of food and the purification
of the blood. This contraction of the septa in time gives the whole organ
an irregularly puckered appearance, called from this fact a hob-nail liver
or, popularly, gin liver. The yellowish discoloration, usually from
retained or perverted bile, gives the disease the medical name of
cirrhosis.[29] It is usually accompanied with dropsy in the lower
extremities, caused by obstruction to the return of the circulation from
the parts below the liver. This disease is always fatal.
175. Fatty Degeneration Due to Alcohol. Another form of destructive
disease often occurs. There is an increase of fat globules deposited in
the liver, causing notable enlargement and destroying its function. This
is called fatty degeneration, and is not limited to the liver, but other
organs are likely to be similarly affected. In truth, this deposition of
fat is a most significant occurrence, as it means actual destruction of
the liver tissues,--nothing less than progressive death of the organ. This
condition always leads to a fatal issue. Still other forms of alcoholic
disease of the liver are produced, one being the excessive formation of
sugar, constituting what is known as a form of diabetes.
176. Effect of Tobacco on Digestion. The noxious influence of
tobacco upon the process of digestion is nearly parallel to the effects of
alcohol, which it resembles in its irritant and narcotic character.
Locally, it stimulates the secretion of saliva to an unnatural extent, and
this excess of secretion diminishes the amount available for normal
digestion.
Tobacco also poisons the saliva furnished for the digestion of food, and
thus at the very outset impairs, in both of these particulars, the general
digestion, and especially the digestion of the starchy portions of the
food. For this reason the amount of food taken, fails to nourish as it
should, and either more food must be taken, or the body becomes gradually
impoverished.
The poisonous _nicotine_, the active element of tobacco, exerts a
destructive influence upon the stomach digestion, enfeebling the vigor of
the muscular walls of that organ. These effects combined produce
dyspepsia, with its weary train of baneful results.
The tobacco tongue never presents the natural, clear, pink color, but
rather a dirty yellow, and is usually heavily coated, showing a disordered
stomach and impaired digestion. Then, too, there is dryness of the mouth,
an unnatural thirst that demands drink. But pure water is stale and flat
to such a mouth: something more emphatic is needed. Thus comes the
unnatural craving for alcoholic liquors, and thus are taken the first
steps on the downward grade.
"There is no doubt that tobacco predisposes to neuralgia, vertigo,
indigestion, and other affections of the nervous, circulatory and
digestive organs."--W. H. Hammond, the eminent surgeon of New York city
and formerly Surgeon General, U.S.A.
Drs. Seaver of Yale University and Hitchcock of Amherst College,
instructors of physical education in these two colleges, have clearly
demonstrated by personal examination and recorded statistics that the use
of tobacco among college students checks growth in weight, height,
chest-girth, and, most of all, in lung capacity.
Additional Experiments.
Experiment 66. Test a portion of _C_ (Experiment 57) with solution
of iodine; no blue color is obtained, as all the starch has disappeared,
having been converted into a reducing sugar, or maltose.
Experiment 67. Make a thick starch paste; place some in test tubes,
labeled _A_ and _B_. Keep _A_ for comparison, and to _B_ add saliva, and
expose both to about 104 degrees F. _A_ is unaffected, while _B_ soon
becomes fluid--within two minutes--and loses its opalescence; this
liquefaction is a process quite antecedent to the saccharifying process
which follows.
Experiment 68. _To show the action of gastric juice on milk_. Mix two
teaspoonfuls of fresh milk in a test tube with a few drops of neutral
artificial gastric juice;[30] keep at about 100 degrees F. In a short
time the milk curdles, so that the tube can be inverted without the curd
falling out. By and by _whey_ is squeezed out of the clot. The curdling
of milk by the rennet ferment present in the gastric juice, is quite
different from that produced by the "souring of milk," or by the
precipitation of caseinogen by acids. Here the casein (carrying with it
most of the fats) is precipitated in a neutral fluid.
Experiment 69. To the test tube in the preceding experiment, add two
teaspoonfuls of dilute hydrochloric acid, and keep at 100 degrees F. for
two hours. The pepsin in the presence of the acid digests the casein,
gradually dissolving it, forming a straw-colored fluid containing
peptones. The peptonized milk has a peculiar odor and bitter taste.
Experiment 70. _To show the action of rennet on milk_. Place milk in a
test tube, add a drop or two of commercial rennet, and place the tube in
a water-bath at about 100 degrees F. The milk becomes solid in a few
minutes, forming a _curd_, and by and by the curd of casein contracts,
and presses out a fluid,--the _whey_.
Experiment 71. Repeat the experiment, but previously boil the rennet. No
such result is obtained as in the preceding experiment, because the
rennet ferment is destroyed by heat.
Experiment 72. _To show the effect of the pancreatic ferment (trypsin)
upon albuminous matter_. Half fill three test tubes, _A, B, C_, with
one-per-cent solution of sodium carbonate, and add 5 drops of liquor
pancreaticus, or a few grains of Fairchild's extract of pancreas, in
each. Boil _B_, and make _C_ acid with dilute hydrochloric acid. Place
in each tube an equal amount of well-washed fibrin, plug the tubes with
absorbent cotton, and place all in a water-bath at about 100 degrees F.
Experiment 73. Examine from time to time the three test tubes in the
preceding experiment. At the end of one, two, or three hours, there is
no change in _B_ and _C_, while in _A_ the fibrin is gradually being
eroded, and finally disappears; but it does not swell up, and the
solution at the same time becomes slightly turbid. After three hours,
still no change is observable in _B_ and _C_.
Experiment 74. Filter _A_, and carefully neutralize the filtrate with
very dilute hydrochloric or acetic acid, equal to a precipitate of
alkali-albumen. Filter off the precipitate, and on testing the filtrate,
peptones are found. The intermediate bodies, the albumoses, are not
nearly so readily obtained from pancreatic as from gastric digests.
Experiment 75. Filter _B_ and _C_, and carefully neutralize the
filtrates. They give no precipitate. No peptones are found.
Experiment 76. _To show the action of pancreatic juice upon the
albuminous ingredients (casein) of milk_. Into a four-ounce bottle put
two tablespoonfuls of cold water; add one grain of Fairchild's extract
of pancreas, and as much baking soda as can be taken up on the point of
a penknife. Shake well, and add four tablespoonfuls of cold, fresh milk.
Shake again.
Now set the bottle into a basin of hot water (as hot as one can bear the
hand in), and let it stand for about forty-five minutes. While the milk
is digesting, take a small quantity of milk in a goblet, and stir in ten
drops or more of vinegar. A thick curd of casein will be seen.
Upon applying the same test to the digested milk, no curd will be made.
This is because the pancreatic ferment (trypsin) has digested the casein
into "peptone," which does not curdle. This digested milk is therefore
called "peptonized milk."
Experiment 77. _To show the action of bile_. Obtain from the butcher
some ox bile. Note its bitter taste, peculiar odor, and greenish color.
It is alkaline or neutral to litmus paper. Pour it from one vessel to
another, and note that strings of mucin (from the lining membrane of the
gall bladder) connect one vessel with the other. It is best to
precipitate the mucin by acetic acid before making experiments; and to
dilute the clear liquid with a little distilled water.
Experiment 78. _Test for bile pigments_. Place a few drops of bile on a
white porcelain slab. With a glass rod place a drop or two of strong
nitric acid containing nitrous acid near the drop of bile; bring the
acid and bile into contact. Notice the succession of colors, beginning
with green and passing into blue, red, and yellow.
Experiment 79. _To show the action of bile on fats_. Mix three
teaspoonfuls of bile with one-half a teaspoonful of almond oil, to which
some oleic acid is added. Shake well, and keep the tube in a water-bath
at about 100 degrees F. A very good emulsion is obtained.
Experiment 80. _To show that bile favors filtration and the absorption
of fats_. Place two small funnels of exactly the same size in a filter
stand, and under each a beaker. Into each funnel put a filter paper;
moisten the one with water (_A_) and the other with bile (_B_). Pour
into each an equal volume of almond oil; cover with a slip of glass to
prevent evaporation. Set aside for twelve hours, and note that the oil
passes through _B_, but scarcely any through _A_. The oil filters much
more readily through the one moistened with bile, than through the one
moistened with water.
Experiments with the Fats.
Experiment 81. Use olive oil or lard. Show by experiment that they
are soluble in ether, chloroform and hot water, but insoluble in water
alone.
Experiment 82. Dissolve a few drops of oil or fat in a teaspoonful
of ether. Let a drop of the solution fall on a piece of tissue or rice
paper. Note the greasy stain, which does not disappear with the heat.
Experiment 83. Pour a little cod-liver oil into a test tube; add a
few drops of a dilute solution of sodium carbonate. The whole mass
becomes white, making an emulsion.
Experiment 84. Shake up olive oil with a solution of albumen in a
test tube. Note that an emulsion is formed.
Chapter VII.
The Blood and Its Circulation.
177. The Circulation. All the tissues of the body are traversed by
exceedingly minute tubes called capillaries, which receive the blood from
the arteries, and convey it to the veins. These capillaries form a great
system of networks, the meshes of which are filled with the elements of
the various tissues. That is, the capillaries are closed vessels, and the
tissues lie outside of them, as asbestos packing may be used to envelop
hot-water pipes. The space between the walls of the capillaries and the
cells of the tissues is filled with lymph. As the blood flows along
the capillaries, certain parts of the plasma of the blood filter through
their walls into the lymph, and certain parts of the lymph filter through
the cell walls of the tissues and mingle with the blood current. The lymph
thus acts as a medium of exchange, in which a transfer of material takes
place between the blood in the capillaries and the lymph around them. A
similar exchange of material is constantly going on between the lymph and
the tissues themselves.
This, then, we must remember,--that in every tissue, so long as the blood
flows, and life lasts, this exchange takes place between the blood within
the capillaries and the tissues without.
The stream of blood _to_ the tissues carries to them the material,
including the all-important oxygen, with which they build themselves up
and do their work. The stream _from_ the tissues carries into the blood
the products of certain chemical changes which have taken place in these
tissues. These products may represent simple waste matter to be cast out
or material which may be of use to some other tissue.
In brief, the tissues by the help of the lymph live on the blood.
Just as our bodies, as a whole, live on the things around us, the food and
the air, so do the bodily tissues live on the blood which bathes them in
an unceasing current, and which is their immediate air and food.
178. Physical Properties of Blood. The blood has been called the
life of the body from the fact that upon it depends our bodily existence.
The blood is so essentially the nutrient element that it is called
sometimes very aptly "liquid flesh." It is a red, warm, heavy, alkaline
fluid, slightly salt in taste, and has a somewhat fetid odor. Its color
varies from bright red in the arteries and when exposed to the air, to
various tints from dark purple to red in the veins. The color of the blood
is due to the coloring constituent of the red corpuscles, _haemoglobin_,
which is brighter or darker as it contains more or less oxygen.
[Illustration: Fig. 65.--Blood Corpuscles of Various Animals. (Magnified
to the same scale.)
A, from proteus, a kind of newt;
B, salamander;
C, frog;
D, frog after addition of acetic acid, showing the central nucleus;
E, bird;
F, camel;
G, fish;
H, crab or other invertebrate animal
]
The temperature of the blood varies slightly in different parts of the
circulation. Its average heat near the surface is in health about the
same, _viz_. 98-1/2 degrees F. Blood is alkaline, but outside of the body
it soon becomes neutral, then acid. The chloride of sodium, or common
salt, which the blood contains, gives it a salty taste. In a hemorrhage
from the lungs, the sufferer is quick to notice in the mouth the warm and
saltish taste. The total amount of the blood in the body was formerly
greatly overestimated. It is about 1/13 of the total weight of the body,
and in a person weighing 156 pounds would amount to about 12 pounds.
179. Blood Corpuscles. If we put a drop of blood upon a glass slide,
and place upon it a cover of thin glass, we can flatten it out until the
color almost disappears. If we examine this thin film with a microscope,
we see that the blood is not altogether fluid. We find that the liquid
part, or plasma, is of a light straw color, and has floating in it a
multitude of very minute bodies, called corpuscles. These are of two
kinds, the red and the colorless. The former are much more
numerous, and have been compared somewhat fancifully to countless myriads
of tiny fishes in a swiftly flowing stream.
180. Red Corpuscles. The red corpuscles are circular disks about
1/3200 of an inch in diameter, and double concave in shape. They tend to
adhere in long rolls like piles of coins. They are soft, flexible, and
elastic, readily squeezing through openings and passages narrower than
their own diameter, then at once resuming their own shape.
The red corpuscles are so very small, that rather more than ten millions
of them will lie on a surface one inch square. Their number is so enormous
that, if all the red corpuscles in a healthy person could be arranged in a
continuous line, it is estimated that they would reach four times around
the earth! The principal constituent of these corpuscles, next to water,
and that which gives them color is _haemoglobin_, a compound containing
iron. As all the tissues are constantly absorbing oxygen, and giving off
carbon dioxid, a very important office of the red corpuscles is to carry
oxygen to all parts of the body.
181. Colorless Corpuscles. The colorless corpuscles are larger
than the red, their average diameter being about 1/2500 of an inch. While
the red corpuscles are regular in shape, and float about, and tumble
freely over one another, the colorless are of irregular shape, and stick
close to the glass slide on which they are placed. Again, while the red
corpuscles are changed only by some influence from without, as pressure
and the like, the colorless corpuscles spontaneously undergo active and
very curious changes of form, resembling those of the amoeba, a very
minute organism found in stagnant water (Fig. 2).
The number of both red and colorless corpuscles varies a great deal from
time to time. For instance, the number of the latter increases after
meals, and quickly diminishes. There is reason to think both kinds of
corpuscles are continually being destroyed, their place being supplied by
new ones. While the action of the colorless corpuscles is important to the
lymph and the chyle, and in the coagulation of the blood, their real
function has not been ascertained.
[Illustration: Fig. 66.--Blood Corpuscles of Man.
A, red corpuscles;
B, the same seen edgeways;
C, the same arranged in rows;
D, white corpuscles with nuclei.
]
Experiment 85. _To show the blood corpuscles_. A moderately
powerful microscope is necessary to examine blood corpuscles. Let a
small drop of blood (easily obtained by pricking the finger with a
needle) be placed upon a clean slip of glass, and covered with thin
glass, such as is ordinarily used for microscopic purposes.
The blood is thus spread out into a film and may be readily examined. At
first the red corpuscles will be seen as pale, disk-like bodies floating
in the clear fluid. Soon they will be observed to stick to each other by
their flattened faces, so as to form rows. The colorless corpuscles are
to be seen among the red ones, but are much less numerous.
182. The Coagulation of the Blood. Blood when shed from the living
body is as fluid as water. But it soon becomes viscid, and flows less
readily from one vessel to another. Soon the whole mass becomes a nearly
solid jelly called a clot. The vessel containing it even can be
turned upside down, without a drop of blood being spilled. If carefully
shaken out, the mass will form a complete mould of the vessel.
At first the clot includes the whole mass of blood, takes the shape of
the vessel in which it is contained, and is of a uniform color. But in a
short time a pale yellowish fluid begins to ooze out, and to collect on
the surface. The clot gradually shrinks, until at the end of a few hours
it is much firmer, and floats in the yellowish fluid. The white corpuscles
become entangled in the upper portion of clot, giving it a pale yellow
look on the top, known as the _buffy coat_. As the clot is attached to the
sides of the vessel, the shrinkage is more pronounced toward the center,
and thus the surface of the clot is hollowed or _cupped_, as it is called.
This remarkable process is known as coagulation, or the clotting of
blood; and the liquid which separates from the clot is called serum.
The serum is almost entirely free from corpuscles, these being entangled
in the fibrin.
[Illustration: Fig. 67.--Diagram of Clot with Buffy Coat.
A, serum;
B, cupped upper surface of clot;
C, white corpuscles in upper layer of clot;
D, lower portion of clot with red corpuscles.
]
This clotting of the blood is due to the formation in the blood, after it
is withdrawn from the living body, of a substance called fibrin.[31] It is
made up of a network of fine white threads, running in every direction
through the plasma, and is a proteid substance. The coagulation of the
blood may be retarded, and even prevented, by a temperature below 40
degrees F., or a temperature above 120 degrees F. The addition of common
salt also prevents coagulation. The clotting of the blood may be hastened
by free access to air, by contact with roughened surfaces, or by keeping
it at perfect rest.
This power of coagulation is of the most vital importance. But for this,
a very small cut might cause bleeding sufficient to empty the
blood-vessels, and death would speedily follow. In slight cuts, Nature
plugs up the wound with clots of blood, and thus prevents excessive
bleeding. The unfavorable effects of the want of clotting are illustrated
in some persons in whom bleeding from even the slightest wounds continues
till life is in danger. Such persons are called "bleeders," and surgeons
hesitate to perform on them any operation, however trivial, even the
extraction of a tooth being often followed by an alarming loss of blood.
Experiment 86. A few drops of fresh blood may be easily obtained to
illustrate important points in the physiology of blood, by tying a
string tight around the finger, and piercing it with a clean needle. The
blood runs freely, is red and opaque. Put two or three drops of fresh
blood on a sheet of white paper, and observe that it looks yellowish.
Experiment 87. Put two or three drops of fresh blood on a white
individual butter plate inverted in a saucer of water. Cover it with an
inverted goblet. Take off the cover in five minutes, and the drop has
set into a jelly-like mass. Take it off in half an hour, and a little
clot will be seen in the watery serum.
Experiment 88. _To show the blood-clot._ Carry to the slaughter
house a clean, six or eight ounce, wide-mouthed bottle. Fill it with
fresh blood. Carry it home with great care, and let it stand over night.
The next day the clot will be seen floating in the nearly colorless
serum.
Experiment 89. Obtain a pint of fresh blood; put it into a bowl,
and whip it briskly for five minutes, with a bunch of dry twigs. Fine
white threads of fibrin collect on the twigs, the blood remaining fluid.
This is "whipped" or defibrinated blood, which has lost the power of
coagulating spontaneously.
183. General Plan of Circulation. All the tissues of the body depend
upon the blood for their nourishment. It is evident then that this vital
fluid must be continually renewed, else it would speedily lose all of its
life-giving material. Some provision, then, is necessary not only to have
the blood renewed in quantity and quality, but also to enable it to carry
away impurities.
So we must have an apparatus of circulation. We need first a central
pump from which branch off large pipes, which divide into smaller and
smaller branches until they reach the remotest tissues. Through these
pipes the blood must be pumped and distributed to the whole body. Then we
must have a set of return pipes by which the blood, after it has carried
nourishment to the tissues, and received waste matters from them, shall be
brought back to the central pumping station, to be used again. We must
have also some apparatus to purify the blood from the waste matter it has
collected.
[Illustration: Fig. 68.--Anterior View of the Heart.
A, superior vena cava;
B, right auricle;
C, right ventricle;
D, left ventricle;
E, left auricle;
F, pulmonary vein;
H, pulmonary artery;
K, aorta;
L, right subclavian artery;
M, right common carotid artery;
N, left common carotid artery.
]
This central pump is the heart. The pipes leading from it and
gradually growing smaller and smaller are the arteries. The very
minute vessels into which they are at last subdivided are
capillaries. The pipes which convey the blood back to the heart are
the veins. Thus, the arteries end in the tissues in fine, hair-like
vessels, the capillaries; and the veins begin in the tissues in
exceedingly small tubes,--the capillaries. Of course, there can be no
break in the continuity between the arteries and the vein. The apparatus
of circulation is thus formed by the heart, the arteries, the
capillaries, and the veins.
184. The Heart. The heart is a pear-shaped, muscular organ
roughly estimated as about the size of the persons closed fist. It lies in
the chest behind the breastbone, and is, lodged between the lobes of the
lungs, which partly cover it. In shape the heart resembles a cone, the
base of which is directed upwards, a little backwards, and to the right
side, while the apex is pointed downwards, forwards, and to the left side.
During life, the apex of the heart beats against the chest wall in
the space between the fifth and sixth ribs, and about an inch and a half
to the left of the middle line of the body. The beating of the heart can
be readily felt, heard, and often seen moving the chest wall as it strikes
against it.
[Illustration: Fig. 69.--Diagram illustrating the Structure of a Serous
Membrane.
A, the viscus, or organ, enveloped by serous membrane;
B, layer of membrane lining cavity;
C, membrane reflected to envelop viscus;
D, outer layer of viscus, with blood-vessels at
E communicating with the general circulation.
]
The heart does not hang free in the chest, but is suspended and kept in
position to some extent by the great vessels connected with it. It is
enclosed in a bell-shaped covering called the pericardium. This is
really double, with two layers, one over another. The inner or serous
layer covers the external surface of the heart, and is reflected back upon
itself in order to form, like all membranes of this kind, a sac without an
opening.[32] The heart is thus covered by the pericardial sac, but
is not contained inside its cavity. The space between the two membranes is
filled with serous fluid. This fluid permits the heart and the pericardium
to glide upon one another with the least possible amount of friction.[33]
The heart is a hollow organ, but the cavity is divided into two parts by a
muscular partition forming a left and a right side, between which there is
no communication. These two cavities are each divided by a horizontal
partition into an upper and a lower chamber. These partitions, however,
include a set of valves which open like folding doors between the two
rooms. If these doors are closed there are two separate rooms, but if open
there is practically only one room. The heart thus has four chambers, two
on each side. The two upper chambers are called auricles from their
supposed resemblance to the ear. The two lower chambers are called
ventricles, and their walls form the chief portion of the muscular
substance of the organ. There are, therefore, the right and left auricles,
with their thin, soft walls, and the right and left ventricles, with their
thick and strong walls.
185. The Valves of the Heart. The heart is a valvular pump, which
works on mechanical principles, the motive power being supplied by the
contraction of its muscular fibers. Regarding the heart as a pump, its
valves assume great importance. They consist of thin, but strong,
triangular folds of tough membrane which hang down from the edges of the
passages into the ventricles. They may be compared to swinging curtains
which, by opening only one way, allow the blood to flow from the auricles
to the ventricles, but by instantly folding back prevent its return.
[Illustration: Fig. 70.--Lateral Section of the Right Chest. (Showing the
relative position of the heart and its great vessels, the oesophagus
and trachea.)
A, inferior constrictor muscle (aids in conveying food down the
oesophagus);
B, oesophagus;
C, section of the right bronchus;
D, two right pulmonary veins;
E, great azygos vein crossing oesophagus and right bronchus to empty
into the superior vena cava;
F, thoracic duct;
H, thoracic aorta;
K, lower portion of oesophagus passing through the diaphragm;
L, diaphragm as it appears in sectional view, enveloping the heart;
M, inferior vena cava passing through diaphragm and emptying into
auricle;
N, right auricle;
O, section of right branch of the pulmonary artery;
P, aorta;
R, superior vena cava;
S, trachea.
]
The valve on the right side is called the tricuspid, because it
consists of three little folds which fall over the opening and close it,
being kept from falling too far by a number of slender threads called
chordae tendinae. The valve on the left side, called the mitral,
from its fancied resemblance to a bishop's mitre, consists of two folds
which close together as do those of the tricuspid valve.
The slender cords which regulate the valves are only just long enough to
allow the folds to close together, and no force of the blood pushing
against the valves can send them farther back, as the cords will not
stretch The harder the blood in the ventricles pushes back against the
valves, the tighter the cords become and the closer the folds are brought
together, until the way is completely closed.
From the right ventricle a large vessel called the pulmonary artery
passes to the lungs, and from the left ventricle a large vessel called the
aorta arches out to the general circulation of the body. The openings
from the ventricles into these vessels are guarded by the semilunar
valves. Each valve has three folds, each half-moon-shaped, hence the
name semilunar. These valves, when shut, prevent any backward flow of the
blood on the right side between the pulmonary artery and the right
ventricle, and on the left side between the aorta and the left ventricle.
[Illustration: Fig. 71.--Right Cavities of the Heart.
A, aorta;
B, superior vena cava;
C, C, right pulmonary veins;
D, inferior vena cava;
E, section of coronary vein;
F, right ventricular cavity;
H, posterior curtain of the tricuspid valve;
K, right auricular cavity;
M, fossa ovalis, oval depression, partition between the auricles formed
after birth.
]
186. General Plan of the Blood-vessels Connected with the Heart.
There are numerous blood-vessels connected with the heart, the relative
position and the use of which must be understood. The two largest veins in
the body, the superior vena cava and the inferior vena cava,
open into the right auricle. These two veins bring venous blood from all
parts of the body, and pour it into the right auricle, whence it passes
into the right ventricle.
From the right ventricle arises one large vessel, the pulmonary
artery, which soon divides into two branches of nearly equal size, one
for the right lung, the other for the left. Each branch, having reached
its lung, divides and subdivides again and again, until it ends in
hair-like capillaries, which form a very fine network in every part of the
lung. Thus the blood is pumped from the right ventricle into the pulmonary
artery and distributed throughout the two lungs (Figs. 86 and 88).
We will now turn to the left side of the heart, and notice the general
arrangement of its great vessels. Four veins, called the pulmonary
veins, open into the left auricle, two from each lung. These veins
start from very minute vessels the continuation of the capillaries of the
pulmonary artery. They form larger and larger vessels until they become
two large veins in each lung, and pour their contents into the left
auricle. Thus the pulmonary artery carries venous blood from the right
ventricle _to_ the lungs, as the pulmonary veins carry arterial blood
_from_ the lungs to the left auricle.
From the left ventricle springs the largest arterial trunk in the body,
over one-half of an inch in diameter, called the aorta. From the
aorta other arteries branch off to carry the blood to all parts of the
body, only to be again brought back by the veins to the right side,
through the cavities of the ventricles. We shall learn in Chapter VIII.
that the main object of pumping the blood into the lungs is to have it
purified from certain waste matters which it has taken up in its course
through the body, before it is again sent on its journey from the left
ventricle.
187. The Arteries. The blood-vessels are flexible tubes through which
the blood is borne through the body. There are three kinds,--the
arteries, the veins, and the capillaries, and these differ
from one another in various ways.
The arteries are the highly elastic and extensible tubes which carry
the pure, fresh blood outwards from the heart to all parts of the body.
They may all be regarded as branches of the aorta. After the aorta leaves
the left ventricle it rises towards the neck, but soon turns downwards,
making a curve known as the arch of the aorta.
From the arch are given off the arteries which supply the head and arms
with blood. These are the two carotid arteries, which run up on each
side of the neck to the head, and the two subclavian arteries, which
pass beneath the collar bone to the arms. This great arterial trunk now
passes down in front of the spine to the pelvis, where it divides into two
main branches, which supply the pelvis and the lower limbs.
The descending aorta, while passing downwards, gives off arteries to the
different tissues and organs. Of these branches the chief are the
coeliac artery, which subdivides into three great branches,--one
each to supply the stomach, the liver, and the spleen; then the renal
arteries, one to each kidney; and next two others, the mesenteric
arteries, to the intestines. The aorta at last divides into two main
branches, the common iliac arteries, which, by their subdivisions,
furnish the arterial vessels for the pelvis and the lower limbs.
[Illustration: Fig. 72.--Left Cavities of the Heart.
A, B, right pulmonary veins;
with S, openings of the veins;
E, D, C, aortic valves;
R, aorta;
P, pulmonary artery;
O, pulmonic valves;
H, mitral valve;
K, columnae carnoeae;
M, right ventricular cavity;
N, interventricular septum.
]
The flow of blood in the arteries is caused by the muscular force of the
heart, aided by the elastic tissues and muscular fibers of the arterial
walls, and to a certain extent by the muscles themselves. Most of the
great arterial trunks lie deep in the fleshy parts of the body; but their
branches are so numerous and become so minute that, with a few exceptions,
they penetrate all the tissues of the body,--so much so, that the point
of the finest needle cannot be thrust into the flesh anywhere without
wounding one or more little arteries and thus drawing blood.
188. The Veins. The veins are the blood-vessels which carry the
impure blood from the various tissues of the body to the heart. They begin
in the minute capillaries at the extremities of the four limbs, and
everywhere throughout the body, and passing onwards toward the heart,
receive constantly fresh accessions on the way from myriad other veins
bringing blood from other wayside capillaries, till the central veins
gradually unite into larger and larger vessels until at length they form
the two great vessels which open into the right auricle of the heart.
These two great venous trunks are the inferior vena cava, bringing
the blood from the trunk and the lower limbs, and the superior vena
cava, bringing the blood from the head and the upper limbs. These two
large trunks meet as they enter the right auricle. The four pulmonary
veins, as we have learned, carry the arterial blood from the lungs to
the left auricle.
[Illustration: Fig. 73.
A, part of a vein laid open, with two pairs of valves;
B, longitudinal section of a vein, showing the valves closed.
]
A large vein generally accompanies its corresponding artery, but most
veins lie near the surface of the body, just beneath the skin. They may be
easily seen under the skin of the hand and forearm, especially in aged
persons. If the arm of a young person is allowed to hang down a few
moments, and then tightly bandaged above the elbow to retard the return of
the blood, the veins become large and prominent.
The walls of the larger veins, unlike arteries, contain but little of
either elastic or muscular tissue; hence they are thin, and when empty
collapse. The inner surfaces of many of the veins are supplied with
pouch-like folds, or pockets, which act as valves to impede the backward
flow of the blood, while they do not obstruct blood flowing forward toward
the heart. These valves can be shown by letting the forearm hang down, and
sliding the finger upwards over the veins (Fig. 73).
The veins have no force-pump, like the arteries, to propel their contents
towards their destination. The onward flow of the blood in them is due to
various causes, the chief being the pressure behind of the blood pumped
into the capillaries. Then as the pocket-like valves prevent the backward
flow of the blood, the pressure of the various muscles of the body urges
along the blood, and thus promotes the onward flow.
The forces which drive the blood through the arteries are sufficient to
carry the blood on through the capillaries. It is calculated that the
onward flow in the capillaries is about 1/50 to 1/33 of an inch in a
second, while in the arteries the blood current flows about 16 inches in a
second, and in the great veins about 4 inches every second.
[Illustration: Fig. 74.--The Structure of Capillaries.
Capillaries of various sizes, showing cells with nuclei]
189. The Capillaries. The capillaries are the minute, hair-like
tubes, with very thin walls, which form the connection between the ending
of the finest arteries and the beginning of the smallest veins. They are
distributed through every tissue of the body, except the epidermis and its
products, the epithelium, the cartilages, and the substance of the teeth.
In fact, the capillaries form a network of the tiniest blood-vessels, so
minute as to be quite invisible, at least one-fourth smaller than the
finest line visible to the naked eye.
The capillaries serve as a medium to transmit the blood from the arteries
to the veins; and it is through them that the blood brings nourishment to
the surrounding tissues. In brief, we may regard the whole body as
consisting of countless groups of little islands surrounded by
ever-flowing streams of blood. The walls of the capillaries are of the
most delicate structure, consisting of a single layer of cells loosely
connected. Thus there is allowed the most free interchange between the
blood and the tissues, through the medium of the lymph.
The number of the capillaries is inconceivable. Those in the lungs alone,
placed in a continuous line, would reach thousands of miles. The thin
walls of the capillaries are admirably adapted for the important
interchanges that take place between the blood and the tissues.
190. The Circulation of the Blood. It is now well to study the
circulation as a whole, tracing the course of the blood from a
certain point until it returns to the same point. We may conveniently
begin with the portion of blood contained at any moment in the right
auricle. The superior and inferior venae cavae are busily filling the
auricle with dark, impure blood. When it is full, it contracts. The
passage leading to the right ventricle lies open, and through it the blood
pours till the ventricle is full. Instantly this begins, in its turn, to
contract. The tricuspid valve at once closes, and blocks the way backward.
The blood is now forced through the open semilunar valves into the
pulmonary artery.
The pulmonary artery, bringing venous blood, by its alternate expansion
and recoil, draws the blood along until it reaches the pulmonary
capillaries. These tiny tubes surround the air cells of the lungs, and
here an exchange takes place. The impure, venous blood here gives up its
_debris_ in the shape of carbon dioxid and water, and in return takes up a
large amount of oxygen. Thus the blood brought to the lungs by the
pulmonary arteries leaves the lungs entirely different in character and
appearance. This part of the circulation is often called the lesser or
pulmonic circulation.
The four pulmonary veins bring back bright, scarlet blood, and pour it
into the left auricle of the heart, whence it passes through the mitral
valve into the left ventricle. As soon as the left ventricle is full, it
contracts. The mitral valve instantly closes and blocks the passage
backward into the auricle; the blood, having no other way open, is forced
through the semilunar valves into the aorta. Now red in color from its
fresh oxygen, and laden with nutritive materials, it is distributed by the
arteries to the various tissues of the body. Here it gives up its oxygen,
and certain nutritive materials to build up the tissues, and receives
certain products of waste, and, changed to a purple color, passes from the
capillaries into the veins.
[Illustration: Fig. 75.--Diagram illustrating the Circulation.
1, right auricle;
2, left auricle;
3, right ventricle;
4, left ventricle;
5, vena cava superior;
6, vena cava inferior;
7, pulmonary arteries;
8, lungs;
9, pulmonary veins;
10, aorta;
11, alimentary canal;
12, liver;
13, hepatic artery;
14, portal vein;
15, hepatic vein.
]
All the veins of the body, except those from the lungs and the heart
itself, unite into two large veins, as already described, which pour their
contents into the right auricle of the heart, and thus the grand round of
circulation is continually maintained. This is called the systemic
circulation. The whole circuit of the blood is thus divided into two
portions, very distinct from each other.
191. The Portal Circulation. A certain part of the systemic or
greater circulation is often called the portal circulation, which
consists of the flow of the blood from the abdominal viscera through the
portal vein and liver to the hepatic vein. The blood brought to the
capillaries of the stomach, intestines, spleen, and pancreas is gathered
into veins which unite into a single trunk called the portal vein.
The blood, thus laden with certain products of digestion, is carried to
the liver by the portal vein, mingling with that supplied to the
capillaries of the same organ by the hepatic artery. From these
capillaries the blood is carried by small veins which unite into a large
trunk, the hepatic vein, which opens into the inferior vena cava. The
portal circulation is thus not an independent system, but forms a kind of
loop on the systemic circulation.
The lymph-current is in a sense a slow and stagnant side stream of
the blood circulation; for substances are constantly passing from the
blood-vessels into the lymph spaces, and returning, although after a
comparatively long interval, into the blood by the great lymphatic trunks.
Experiment 90. _To illustrate the action of the heart, and how it
pumps the blood in only one direction_. Take a Davidson or Household
rubber syringe. Sink the suction end into water, and press the bulb. As
you let the bulb expand, it fills with water; as you press it again, a
valve prevents the water from flowing back, and it is driven out in a
jet along the other pipe. The suction pipe represents the veins; the
bulb, the heart; and the tube end, out of which the water flows, the
arteries.
[NOTE. The heart is not nourished by the blood which passes through
it. The muscular substance of the heart itself is supplied with
nourishment by two little arteries called the _coronary arteries_,
which start from the aorta just above two of the semilunar valves. The
blood is returned to the right auricle (not to either of the venae
cavae) by the _coronary vein_.]
The longest route a portion of blood may take from the moment it leaves
the left ventricle to the moment it returns to it, is through the portal
circulation. The shortest possible route is through the substance of the
heart itself. The mean time which the blood requires to make a complete
circuit is about 23 seconds.
192. The Rhythmic Action of the Heart. To maintain a steady flow of
blood throughout the body the action of the heart must be regular and
methodical. The heart does not contract as a whole. The two auricles
contract at the same time, and this is followed at once by the contraction
of the two ventricles. While the ventricles are contracting, the auricles
begin to relax, and after the ventricles contract they also relax. Now
comes a pause, or rest, after which the auricles and ventricles contract
again in the same order as before, and their contractions are followed by
the same pause as before. These contractions and relaxations of the
various parts of the heart follow one another so regularly that the result
is called the rhythmic action of the heart.
The average number of beats of the heart, under normal conditions, is from
65 to 75 per minute. Now the time occupied from the instant the auricles
begin to contract until after the contraction of the ventricles and the
pause, is less than a second. Of this time one-fifth is occupied by the
contraction of the auricles, two-fifths by the contraction of the
ventricles, and the time during which the whole heart is at rest is
two-fifths of the period.
193. Impulse and Sounds of the Heart. The rhythmic action of the
heart is attended with various occurrences worthy of note. If the hand be
laid flat over the chest wall on the left, between the fifth and sixth
ribs, the heart will be felt beating. This movement is known as the
beat or impulse of the heart, and can be both seen and felt on
the left side. The heart-beat is unusually strong during active bodily
exertion, and under mental excitement.
The impulse of the heart is due to the striking of the lower, tense part
of the ventricles--the apex of the heart--against the chest wall at the
moment of their vigorous contraction. It is important for the physician to
know the exact place where the heart-beat should be felt, for the heart
may be displaced by disease, and its impulse would indicate its new
position.
Sounds also accompany the heart's action. If the ear be applied over the
region of the heart, two distinct sounds will be heard following one
another with perfect regularity. Their character may be tolerably imitated
by pronouncing the syllables _lubb_, _dup_. One sound is heard immediately
after the other, then there is a pause, then come the two sounds again.
The first is a dull, muffled sound, known as the "first sound," followed
at once by a short and sharper sound, known as the "second sound" of the
heart.
The precise cause of the first sound is still doubtful, but it is made at
the moment the ventricles contract. The second sound is, without doubt,
caused by the sudden closure of the semilunar valves of the pulmonary
artery and the aorta, at the moment when the contraction of the ventricles
is completed.
[Illustration: Fig. 76.--Muscular Fibers of the Ventricles.
A, superficial fibers common to both ventricles;
B, fibers of the left ventricle;
C, deep fibers passing upwards toward the base of the heart;
D, fibers penetrating the left ventricle
]
The sounds of the heart are modified or masked by blowing "murmurs" when
the cardiac orifices or valves are roughened, dilated, or otherwise
affected as the result of disease. Hence these new sounds may often afford
indications of the greatest importance to physicians in the diagnosis of
heart-disease.
194. The Nervous Control of the Heart. The regular, rhythmic movement
of the heart is maintained by the action of certain nerves. In various
places in the substance of the heart are masses of nerve matter, called
ganglia. From these ganglia there proceed, at regular intervals,
discharges of nerve energy, some of which excite movement, while others
seem to restrain it. The heart would quickly become exhausted if the
exciting ganglia had it all their own way, while it would stand still if
the restraining ganglia had full sway. The influence of one, however,
modifies the other, and the result is a moderate and regular activity of
the heart.
The heart is also subject to other nerve influences, but from outside of
itself. Two nerves are connected with the heart, the pneumogastric
and the sympathetic (secs. 271 and 265). The former appears to be
connected with the restraining ganglia; the latter with the exciting
ganglia. Thus, if a person were the subject of some emotion which caused
fainting, the explanation would be that the impression had been conveyed
to the brain, and from the brain to the heart by the pneumogastric nerves.
The result would be that the heart for an instant ceases to beat. Death
would be the result if the nerve influence were so great as to restrain
the movements of the heart for any appreciable time.
Again, if the person were the subject of some emotion by which the heart
were beating faster than usual, it would mean that there was sent from the
brain to the heart by the sympathetic nerves the impression which
stimulated it to increased activity.
195. The Nervous Control of the Blood-vessels. The tone and caliber
of the blood-vessels are controlled by certain vaso-motor nerves,
which are distributed among the muscular fibers of the walls. These nerves
are governed from a center in the medulla oblongata, a part of the brain
(sec. 270). If the nerves are stimulated more than usual, the muscular
walls contract, and the quantity of the blood flowing through them and the
supply to the part are diminished. Again, if the stimulus is less than
usual, the vessels dilate, and the supply to the part is increased.
Now the vaso-motor center may be excited to increased activity by
influences reaching it from various parts of the body, or even from the
brain itself. As a result, the nerves are stimulated, and the vessels
contract. Again, the normal influence of the vaso-motor center may be
suspended for a time by what is known as the inhibitory or
restraining effect. The result is that the tone of the blood-vessels
becomes diminished, and their channels widen.
The effect of this power of the nervous system is to give it a certain
control over the circulation in particular parts. Thus, though the force
of the heart and the general average blood-pressure remain the same, the
state of the circulation may be very different in different parts of the
body. The importance of this local control over the circulation is of the
utmost significance. Thus an organ at work needs to be more richly
supplied with blood than when at rest. For example, when the salivary
glands need to secrete saliva, and the stomach to pour out gastric juice,
the arteries that supply these organs are dilated, and so the parts are
flushed with an extra supply of blood, and thus are aroused to greater
activity.
Again, the ordinary supply of blood to a part may be lessened, so that the
organ is reduced to a state of inactivity, as occurs in the case of the
brain during sleep. We have in the act of blushing a visible example of
sudden enlargement of the smaller arteries of the face and neck, called
forth by some mental emotion which acts on the vaso-motor center and
diminishes its activity. The reverse condition occurs in the act of
turning pale. Then the result of the mental emotion is to cause the
vaso-motor nerves to exercise a more powerful control over the
capillaries, thereby closing them, and thus shutting off the flow of
blood.
Experiment 91. Hold up the ear of a white rabbit against the light
while the animal is kept quiet and not alarmed. The red central artery
can be seen coursing along the translucent organ, giving off branches
which by subdivision become too small to be separately visible, and the
whole ear has a pink color and is warm from the abundant blood flowing
through it. Attentive observation will show also that the caliber of the
main artery is not constant; at somewhat irregular periods of a minute
or more it dilates and contracts a little.
[Illustration: Fig. 77.--Some of the Principal Organs of the Chest and
Abdomen. (Blood vessels on the left, muscles on the right.)]
In brief, all over the body, the nervous system, by its vaso-motor
centers, is always supervising and regulating the distribution of blood in
the body, sending now more and now less to this or that part.
[Illustration: Fig. 78.--Capillary Blood-Vessels in the Web of a Frog's
Foot, as seen with the Microscope.]
196. The Pulse. When the finger is placed on any part of the body
where an artery is located near the surface, as, for example, on the
radial artery near the wrist, there is felt an intermittent pressure,
throbbing with every beat of the heart. This movement, frequently visible
to the eye, is the result of the alternate expansion of the artery by the
wave of blood, and the recoil of the arterial walls by their elasticity.
In other words, it is the wave produced by throwing a mass of blood into
the arteries already full. The blood-wave strikes upon the elastic walls
of the arteries, causing an increased distention, followed at once by
contraction. This regular dilatation and rigidity of the elastic artery
answering to the beats of the heart, is known as the pulse.
The pulse may be easily found at the wrist, the temple, and the inner side
of the ankle. The throb of the two carotid arteries may be plainly felt by
pressing the thumb and finger backwards on each side of the larynx. The
progress of the pulse-wave must not be confused with the actual current of
the blood itself. For instance, the pulse-wave travels at the rate of
about 30 feet a second, and takes about 1/10 of a second to reach the
wrist, while the blood itself is from 3 to 5 seconds in reaching the same
place.
The pulse-wave may be compared to the wave produced by a stiff breeze on
the surface of a slowly moving stream, or the jerking throb sent along a
rope when shaken. The rate of the pulse is modified by age, fatigue,
posture, exercise, stimulants, disease, and many other circumstances. At
birth the rate is about 140 times a minute, in early infancy, 120 or
upwards, in the healthy adult between 65 and 75, the most common number
being 72. In the same individual, the pulse is quicker when standing than
when lying down, is quickened by excitement, is faster in the morning, and
is slowest at midnight. In old age the pulse is faster than in middle
life; in children it is quicker than in adults.
[Illustration: Fig. 79.--Circulation in the Capillaries, as seen with the
Microscope.]
As the pulse varies much in its rate and character in disease, it is to
the skilled touch of the physician an invaluable help in the diagnosis of
the physical condition of his patient.
Experiment 92. _To find the pulse_. Grasp the wrist of a friend,
pressing with three fingers over the radius. Press three fingers over
the radius in your own wrist, to feel the pulse.
Count by a watch the rate of your pulse per minute, and do the same with
a friend's pulse. Compare its characters with your own pulse.
Observe how the character and frequency of the pulse are altered by
posture, muscular exercise, a prolonged, sustained, deep inspiration,
prolonged expiration, and other conditions.
197. Effect of Alcoholic Liquors upon the Organs of Circulation.
Alcoholic drinks exercise a destructive influence upon the heart, the
circulation, and the blood itself. These vicious liquids can reach the
heart only indirectly, either from the stomach by the portal vein to the
liver, and thence to the heart, or else by way of the lacteals, and so to
the blood through the thoracic duct. But by either course the route is
direct enough, and speedy enough to accomplish a vast amount of ruinous
work.
The influence of alcohol upon the heart and circulation is produced mainly
through the nervous system. The inhibitory nerves, as we have seen, hold
the heart in check, exercise a restraining control over it, very much as
the reins control an active horse. In health this inhibitory influence is
protective and sustaining. But now comes the narcotic invasion of
alcoholic drinks, which paralyze the inhibitory nerves, with the others,
and at once the uncontrolled heart, like the unchecked steed, plunges on
to violent and often destructive results.
[Illustration: Fig. 80.--Two Principal Arteries of the Front of the Leg
(Anterior Tibial and Dorsalis Pedis).]
This action, because it is quicker, has been considered also a stronger
action, and the alcohol has therefore been supposed to produce a
stimulating effect. But later researches lead to the conclusion that the
effect of alcoholic liquors is not properly that of a stimulant, but of a
narcotic paralyzant, and that while it indeed quickens, it also really
weakens the heart's action. This view would seem sustained by the fact
that the more the intoxicants are pushed, the deeper are the narcotic and
paralyzing effects. After having obstructed the nutritive and reparative
functions of the vital fluid for many years, their effects at last may
become fatal.
This relaxing effect involves not only the heart, but also the capillary
system, as is shown in the complexion of the face and the color of the
hands. In moderate drinkers the face is only flushed, but in drunkards it
is purplish. The flush attending the early stages of drinking is, of
course, not the flush of health, but an indication of disease.[34]
198. Effect upon the Heart. This forced overworking of the heart
which drives it at a reckless rate, cuts short its periods of rest and
inevitably produces serious heart-exhaustion. If repeated and continued,
it involves grave changes of the structure of the heart. The heart muscle,
endeavoring to compensate for the over-exertion, may become much
thickened, making the ventricles smaller, and so fail to do its duty in
properly pumping forward the blood which rushes in from the auricle. Or
the heart wall may by exhaustion become thinner, making the ventricles
much too large, and unable to send on the current. In still other cases,
the heart degenerates with minute particles of fat deposited in its
structures, and thus loses its power to propel the nutritive fluid. All
three of these conditions involve organic disease of the valves, and all
three often produce fatal results.
199. Effect of Alcohol on the Blood-vessels. Alcoholic liquors injure
not only the heart, but often destroy the blood-vessels, chiefly the
larger arteries, as the arch of the aorta or the basilar artery of the
brain. In the walls of these vessels may be gradually deposited a morbid
product, the result of disordered nutrition, sometimes chalky, sometimes
bony, with usually a dangerous dilatation of the tube.
In other cases the vessels are weakened by an unnatural fatty deposit.
Though these disordered conditions differ somewhat, the morbid results in
all are the same. The weakened and stiffened arterial walls lose the
elastic spring of the pulsing current. The blood fails to sweep on with
its accustomed vigor. At last, owing perhaps to the pressure, against the
obstruction of a clot of blood, or perhaps to some unusual strain of work
or passion, the enfeebled vessel bursts, and death speedily ensues from a
form of apoplexy.
[Illustration: Fig. 81.--Showing the Carotid Artery and Jugular Vein on
the Right Side, with Some of their Main Branches. (Some branches of the
cervical plexus, and the hypoglossal nerve are also shown.)]
[NOTE. "An alcoholic heart loses its contractile and resisting power,
both through morbid changes in its nerve ganglia and in its muscle
fibers. In typhoid fever, muscle changes are evidently the cause of
the heart-enfeeblement; while in diphtheria, disturbances in
innervation cause the heart insufficiency. 'If the habitual use of
alcohol causes the loss of contractile and resisting power by
impairment of both the nerve ganglia and muscle fibers of the heart,
how can it act as a heart tonic?'"--Dr. Alfred L. Loomis, Professor of
Medicine in the Medical Department of the University of the City of
New York.]
200. Other Results from the Use of Intoxicants. Other disastrous
consequences follow the use of intoxicants, and these upon the blood. When
any alcohol is present in the circulation, its greed for water induces the
absorption of moisture from the red globules of the blood, the
oxygen-carriers. In consequence they contract and harden, thus becoming
unable to absorb, as theretofore, the oxygen in the lungs. Then, in turn,
the oxidation of the waste matter in the tissues is prevented; thus the
corpuscles cannot convey carbon dioxid from the capillaries, and this fact
means that some portion of refuse material, not being thus changed and
eliminated, must remain in the blood, rendering it impure and unfit for
its proper use in nutrition. Thus, step by step, the use of alcoholics
impairs the functions of the blood corpuscles, perverts nutrition, and
slowly poisons the blood.
[Illustration: Fig. 82.--The Right Axillary and Brachial Arteries, with
Some of their Main Branches.]
[NOTE. "Destroy or paralyze the inhibitory nerve center, and instantly
its controlling effect on the heart mechanism is lost, and the
accelerating agent, being no longer under its normal restraint, runs
riot. The heart's action is increased, the pulse is quickened, an
excess of blood is forced into the vessels, and from their becoming
engorged and dilated the face gets flushed, all the usual concomitants
of a general engorgement of the circulation being the result."--Dr.
George Harley, F.R.S., an eminent English medical author.
"The habitual use of alcohol produces a deleterious influence upon the
whole economy. The digestive powers are weakened, the appetite is
impaired, and the muscular system is enfeebled. The blood is
impoverished, and nutrition is imperfect and disordered, as shown by
the flabbiness of the skin and muscles, emaciation, or an abnormal
accumulation of fat."--Dr. Austin Flint, Senior, formerly Professor of
the Practice of Medicine in Bellevue Medical College, and author of
many standard medical works.
"The immoderate use of the strong kind of tobacco, which soldiers
affect, is often very injurious to them, especially to very young
soldiers. It renders them nervous and shaky, gives rise to
palpitation, and is a factor in the production of the irritable or
so-called "trotting-heart" and tends to impair the appetite and
digestion."--London _Lancet_.
"I never smoke because I have seen the most efficient proofs of the
injurious effects of tobacco on the nervous system."--Dr.
Brown-Sequard, the eminent French physiologist.
"Tobacco, and especially cigarettes, being a depressant upon the
heart, should be positively forbidden."--Dr. J. M. Keating, on
"Physical Development," in _Cyclopoedia of the Diseases of
Children_.]
201. Effect of Tobacco upon the Heart. While tobacco poisons more or
less almost every organ of the body, it is upon the heart that it
works its most serious wrong. Upon this most important organ its
destructive effect is to depress and paralyze. Especially does this apply
to the young, whose bodies are not yet knit into the vigor that can brave
invasion.
The _nicotine_ of tobacco acts through the nerves that control the heart's
action. Under its baneful influence the motions of the heart are
irregular, now feeble and fluttering, now thumping with apparently much
force: but both these forms of disturbed action indicate an abnormal
condition. Frequently there is severe pain in the heart, often dizziness
with gasping breath, extreme pallor, and fainting.
The condition of the pulse is a guide to this state of the heart. In this
the physician reads plainly the existence of the "tobacco heart," an
affection as clearly known among medical men as croup or measles. There
are few conditions more distressing than the constant and impending
suffering attending a tumultuous and fluttering heart. It is stated that
one in every four of tobacco-users is subject, in some degree, to this
disturbance. Test examinations of a large number of lads who had used
cigarettes showed that only a very small percentage escaped cardiac
trouble. Of older tobacco-users there are very few but have some warning
of the hazard they invoke. Generally they suffer more or less from the
tobacco heart, and if the nervous system or the heart be naturally feeble,
they suffer all the more speedily and intensely.
Additional Experiments.
Experiment 93. Touch a few drops of blood fresh from the finger,
with a strip of dry, smooth, neutral litmus paper, highly glazed to
prevent the red corpuscles from penetrating into the test paper. Allow
the blood to remain a short time; then wash it off with a stream of
distilled water, when a blue spot upon a red or violet ground will be
seen, indicating its _alkaline_ reaction, due chiefly to the sodium
phosphate and sodium carbonate.
Experiment 94. Place on a glass slide a thin layer of defibrinated
blood; try to read printed matter through it. This cannot be done.
Experiment 95. _To make blood transparent or laky_. Place in each
of three test tubes two or three teaspoonfuls of defibrinated blood,
obtained from Experiment 89, labeled _A, B_, and _C. A_ is for
comparison. To _B_ add five volumes of water, and warm slightly, noting
the change of color by reflected and transmitted light. By reflected
light it is much darker,--it looks almost black; but by transmitted
light it is transparent. Test this by looking at printed matter as in
Experiment 94.
Experiment 96. To fifteen or twenty drops of defibrinated blood in
a test tube (labeled _D_) add five volumes of a 10-per-cent solution of
common salt. It changes to a very bright, florid, brick-red color.
Compare its color with _A, B_, and _C_. It is opaque.
Experiment 97. Wash away the coloring matter from the twigs (see
Experiment 89) with a stream of water until the fibrin becomes quite
white. It is white, fibrous, and elastic. Stretch some of the fibers to
show their extensibility; on freeing them, they regain their elasticity.
Experiment 98. Take some of the serum saved from Experiment 88 and
note that it does not coagulate spontaneously. Boil a little in a test
tube over a spirit lamp, and the albumen will coagulate.
Experiment 99. _To illustrate in a general way that blood is
really a mass of red bodies which give the red color to the fluid in
which they float._ Fill a clean white glass bottle two-thirds full of
little red beads, and then fill the bottle full of water. At a short
distance the bottle appears to be rilled with a uniformly red liquid.
Experiment 100. _To show how blood holds a mineral substance in
solution_. Put an egg-shell crushed fine, into a glass of water made
acid by a teaspoonful of muriatic acid. After an hour or so the
egg-shell will disappear, having been dissolved in the acid water. In
like manner the blood holds various minerals in solution.
Experiment 101. _To hear the sounds of the heart_. Locate the heart
exactly. Note its beat. Borrow a stethoscope from some physician. Listen
to the heart-beat of some friend. Note the sounds of your own heart in
the same way.
Experiment 102. _To show how the pulse may be studied_. "The
movements of the artery in the human body as the pulse-wave passes
through it may be shown to consist in a sudden dilatation, followed by a
slow contraction, interrupted by one or more secondary dilatations. This
demonstration may be made by pressing a small piece of looking-glass
about one centimeter square (2/3 of an inch) upon the wrist over the
radial artery, in such a way that with each pulse beat the mirror may be
slightly tilted. If the wrist be now held in such a position that
sunlight will fall upon the mirror, a spot of light will be reflected on
the opposite side of the room, and its motion upon the wall will show
that the expansion of the artery is a sudden movement, while the
subsequent contraction is slow and interrupted."--Bowditch's _Hints for
Teachers of Physiology_.
[Illustration: Fig. 83.--How the Pulse may be studied by Pressing a
Mirror over the Radial Artery.]
Experiment 103. _To illustrate the effect of muscular exercise in
quickening the pulse_. Run up and down stairs several times. Count the
pulse both before and after. Note the effect upon the rate.
Experiment 104. _To show the action of the elastic walls of the
arteries._ Take a long glass or metal tube of small caliber. Fasten one
end to the faucet of a water-pipe (one in a set bowl preferred) by a
very short piece of rubber tube. Turn the water on and off alternately
and rapidly, to imitate the intermittent discharge of the ventricles.
The water will flow from the other end of the rubber pipe in jets, each
jet ceasing the moment the water is shut off.
The experiment will be more successful if the rubber bulb attached to an
ordinary medicine-dropper be removed, and the tapering glass tube be
slipped on to the outer end of the rubber tube attached to the faucet.
Experiment 105. Substitute a piece of rubber tube for the glass
tube, and repeat the preceding experiment. Now it will be found that a
continuous stream flows from the tube. The pressure of water stretches
the elastic tube, and when the stream is turned off, the rubber recoils
on the water, and the intermittent flow is changed into a continuous
stream.
Experiment 106. _To illustrate some of the phenomena of
circulation._ Take a common rubber bulb syringe, of the Davidson,
Household, or any other standard make. Attach a piece of rubber tube
about six or eight feet long to the delivery end of the syringe.
To represent the resistance made by the capillaries to the flow of
blood, slip the large end of a common glass medicine-dropper into the
outer end of the rubber tube. This dropper has one end tapered to a fine
point.
Place the syringe flat, without kinks or bends, on a desk or table.
Press the bulb slowly and regularly. The water is thus pumped into the
tube in an intermittent manner, and yet it is forced out of the tapering
end of the glass tube in a steady flow.
Experiment 107. Take off the tapering glass tube, or, in the place
of one long piece of rubber tube, substitute several pieces of glass
tubing connected together by short pieces of rubber tubes. The obstacle
to the flow has thus been greatly lessened, and the water flows out in
intermittent jets to correspond to the compression of the bulb.
Chapter VIII.
Respiration.
202. Nature and Object of Respiration. The blood, as we have learned,
not only provides material for the growth and activity of all the tissues
of the body, but also serves as a means of removing from them the products
of their activity. These are waste products, which if allowed to remain,
would impair the health of the tissues. Thus the blood becomes
impoverished both by the addition of waste material, and from the loss of
its nutritive matter.
We have shown, in the preceding chapter, how the blood carries to the
tissues the nourishment it has absorbed from the food. We have now to
consider a new source of nourishment to the blood, _viz._, that which it
receives from the oxygen of the air. We are also to learn one of the
methods by which the blood gets rid of poisonous waste matters. In brief,
we are to study the set of processes known as respiration, by which
oxygen is supplied to the various tissues, and by which the principal
waste matters, or chief products of oxidation, are removed.
Now, the tissues are continually feeding on the life-giving oxygen, and at
the same time are continually producing carbon dioxid and other waste
products. In fact, the life of the tissues is dependent upon a continual
succession of oxidations and deoxidations. When the blood leaves the
tissues, it is poorer in oxygen, is burdened with carbon dioxid, and has
had its color changed from bright scarlet to purple red. This is the
change from the arterial to venous conditions which has been described in
the preceding chapter.
Now, as we have seen, the change from venous to arterial blood occurs in
the capillaries of the lungs, the only means of communication between the
pulmonary arteries and the pulmonary veins. The blood in the pulmonary
capillaries is separated from the air only by a delicate tissue formed of
its own wall and the pulmonary membrane. Hence a gaseous interchange,
the essential step in respiration, very readily takes place between the
blood and the air, by which the latter gains moisture and carbon dioxid,
and loses its oxygen. These changes in the lungs also restore to the dark
blood its rosy tint.
The only condition absolutely necessary to the purification of the blood
is an organ having a delicate membrane, on one side of which is a thin
sheet of blood, while the other side is in such contact with the air that
an interchange of gases can readily take place. The demand for oxygen is,
however, so incessant, and the accumulation of carbon dioxid is so rapid
in every tissue of the human body, that an All-Wise Creator has provided a
most perfect but complicated set of machinery to effect this wonderful
purification of the blood.
We are now ready to begin the study of the arrangement and working of the
respiratory apparatus. With its consideration, we complete our view of the
sources of supply to the blood, and begin our study of its purification.
[Illustration: Fig. 84.--The Epiglottis.]
203. The Trachea, or Windpipe. If we look into the mouth of a friend,
or into our own with a mirror, we see at the back part an arch which is
the boundary line of the mouth proper. There is just behind this a similar
limit for the back part of the nostrils. The funnel-shaped cavity beyond,
into which both the mouth and the posterior nasal passages open, is
called the pharynx. In its lower part are two openings; the
trachea, or windpipe, in front, and the oesophagus behind.
The trachea is surmounted by a box-like structure of cartilage, about
four and one-half inches long, called the larynx. The upper end of
the larynx opens into the pharynx or throat, and is provided with a lid,--
the epiglottis,--which closes under certain circumstances (secs. 137
and 349). The larynx contains the organ of voice, and is more fully
described in Chapter XII.
The continuation of the larynx is the trachea, a tube about three-fourths
of an inch in diameter, and about four inches long. It extends downwards
along the middle line of the neck, where it may readily be felt in front,
below the Adam's apple.
[Illustration: Fig. 85.--Larynx, Trachea, and the Bronchi. (Front view.)
A, epiglottis;
B, thyroid cartilage;
C, cricoid-thyroid membrane, connecting with the cricoid cartilage below,
all forming the larynx;
D, one of the rings of the trachea.
]
The walls of the windpipe are strengthened by a series of cartilaginous
rings, each somewhat the shape of a horseshoe or like the letter C, being
incomplete behind, where they come in contact with the oesophagus.
Thus the trachea, while always open for the passage of air, admits of the
distention of the food-passage.
204. The Bronchial Tubes. The lower end of the windpipe is just
behind the upper part of the sternum, and there it divides into two
branches, called bronchi. Each branch enters the lung of its own
side, and breaks up into a great number of smaller branches, called
bronchial tubes. These divide into smaller tubes, which continue
subdividing till the whole lung is penetrated by the branches, the
extremities of which are extremely minute. To all these branches the
general name of bronchial tubes is given. The smallest are only about
one-fiftieth of an inch in diameter.
[Illustration: Fig. 86.--Relative Position of the Lungs, Heart, and its
Great Vessels.
A, left ventricle;
B, right ventricle;
C, left auricle;
D, right auricle;
E, superior vena cava;
F, pulmonary artery;
G, aorta;
H, arch of the aorta;
K, innominate artery;
L, right common carotid artery;
M, right subclavian artery;
N, thyroid cartilage forming upper portion of the larynx;
O, trachea.
]
Now the walls of the windpipe, and of the larger bronchial tubes would
readily collapse, and close the passage for air, but for a wise
precaution. The horseshoe-shaped rings of cartilage in the trachea and the
plates of cartilage in the bronchial tubes keep these passages open.
Again, these air passages have elastic fibers running the length of the
tubes, which allow them to stretch and bend readily with the movements of
the neck.
205. The Cilia of the Air Passages. The inner surfaces of the
windpipe and bronchial tubes are lined with mucous membrane, continuous
with that of the throat, the mouth, and the nostrils, the secretion from
which serves to keep the parts moist.
Delicate, hair-like filaments, not unlike the pile on velvet, called
cilia, spring from the epithelial lining of the air tubes. Their
constant wavy movement is always upwards and outwards, towards the mouth.
Thus any excessive secretion, as of bronchitis or catarrh, is carried
upwards, and finally expelled by coughing. In this way, the lungs are kept
quite free from particles of foreign matter derived from the air.
Otherwise we should suffer, and often be in danger from the accumulation
of mucus and dust in the air passages. Thus these tiny cilia act as
dusters which Nature uses to keep the air tubes free and clean (Fig. 5).
[Illustration: Fig. 87.--Bronchial tube, with its Divisions and
Subdivisions. (Showing groups of air cells at the termination of minute
bronchial tubes.)]
206. The Lungs. The lungs, the organs of respiration, are two
pinkish gray structures of a light, spongy appearance, that fill the chest
cavity, except the space taken up by the heart and large vessels. Between
the lungs are situated the large bronchi, the oesophagus, the heart
in its pericardium, and the great blood-vessels. The base of the lungs
rests on the dome-like diaphragm, which separates the chest from the
abdomen. This partly muscular and partly tendinous partition is a most
important factor in breathing.
Each lung is covered, except at one point, with an elastic serous membrane
in a double layer, called the pleura. One layer closely envelops the
lung, at the apex of which it is reflected to the wall of the chest cavity
of its own side, which it lines. The two layers thus form between them a
Closed Sac a serous cavity (see Fig. 69, also note, p. 176).
[Illustration: Fig. 88.--The Lungs with the Trachea, Bronchi, and Larger
Bronchial Tubes exposed. (Posterior view.)
A, division of left bronchus to upper lobe;
B, left branch of the Pulmonary artery;
C, left bronchus;
D, left superior pulmonary vein;
E, left inferior pulmonary vein;
F, left auricle;
K, inferior vena cava;
L, division of right bronchus to lower lobe;
M, right inferior pulmonary vein;
N, right superior pulmonary vein;
O, right branch of the pulmonary artery;
P, division of right bronchus to upper lobe;
R, left ventricle;
S, right ventricle.
]
In health the two pleural surfaces of the lungs are always in contact, and
they secrete just enough serous fluid to allow the surfaces to glide
smoothly upon each other. Inflammation of this membrane is called
_pleurisy_. In this disease the breathing becomes very painful, as the
secretion of glairy serum is suspended, and the dry and inflamed surfaces
rub harshly upon each other.
The root of the lung, as it is called, is formed by the bronchi, two
pulmonary arteries, and two pulmonary veins. The nerves and lymphatic
vessels of the lung also enter at the root. If we only remember that all
the bronchial tubes, great and small, are hollow, we may compare the whole
system to a short bush or tree growing upside down in the chest, of which
the trachea is the trunk, and the bronchial tubes the branches of various
sizes.
207. Minute Structure of the Lungs. If one of the smallest bronchial
tubes be traced in its tree-like ramifications, it will be found to end in
an irregular funnel-shaped passage wider than itself. Around this passage
are grouped a number of honeycomb-like sacs, the air cells[35] or
alveoli of the lungs. These communicate freely with the passage, and
through it with the bronchial branches, but have no other openings. The
whole arrangement of passages and air cells springing from the end of a
bronchial tube, is called an ultimate lobule. Now each lobule is a
very small miniature of a whole lung, for by the grouping together of
these lobules another set of larger lobules is formed.
[Illustration: Fig. 89.
A, diagrammatic representation of the ending of a bronchial tube in air
sacs or alveoli;
B, termination of two bronchial tubes in enlargement beset with air sacs
(_Huxley_);
C, diagrammatic view of an air sac.
a lies within sac and points to epithelium lining wall;
b, partition between two adjacent sacs, in which run capillaries;
c, elastic connective tissue (_Huxley_).
]
In like manner countless numbers of these lobules, bound together by
connective tissue, are grouped after the same fashion to form by their
aggregation the lobes of the lung. The right lung has three such
lobes; and the left, two. Each lobule has a branch of the pulmonary artery
entering it, and a similar rootlet of the pulmonary vein leaving it. It
also receives lymphatic vessels, and minute twigs of the pulmonary plexus
of nerves.
[Illustration: Fig. 90.--Diagram to illustrate the Amounts of Air
contained by the Lungs in Various Phases of Ordinary and of Forced
Respiration.]
The walls of the air cells are of extreme thinness, consisting of delicate
elastic and connective tissue, and lined inside by a single layer of thin
epithelial cells. In the connective tissue run capillary vessels belonging
to the pulmonary artery and veins. Now these delicate vessels running in
the connective tissue are surrounded on all sides by air cells. It is
evident, then, that the blood flowing through these capillaries is
separated from the air within the cells only by the thin walls of the
vessels, and the delicate tissues of the air cells.
This arrangement is perfectly adapted for an interchange between the
blood in the capillaries and the air in the air cells. This will be more
fully explained in sec. 214.
208. Capacity of the Lungs. In breathing we alternately take into and
expel from the lungs a certain quantity of air. With each quiet
inspiration about 30 cubic inches of air enter the lungs, and 30 cubic
inches pass out with each expiration. The air thus passing into and out of
the lungs is called tidal air. After an ordinary inspiration, the
lungs contain about 230 cubic inches of air. By taking a deep inspiration,
about 100 cubic inches more can be taken in. This extra amount is called
complemental air.
After an ordinary expiration, about 200 cubic inches are left in the
lungs, but by forced expiration about one-half of this may be driven out.
This is known as supplemental air. The lungs can never be entirely
emptied of air, about 75 to 100 cubic inches always remaining. This is
known as the residual air.
The air that the lungs of an adult man are capable of containing is thus
composed:
Complemental air 100 cubic inches.
Tidal " 30 " "
Supplemental " 100 " "
Residual " 100 " "
----
Total capacity of lungs 330 " "
If, then, a person proceeds, after taking the deepest possible breath, to
breath out as much as he can, he expels:
Complemental air 100 cubic inches.
Tidal " 30 " "
Supplemental " 100 " "
----
230
This total of 230 cubic inches forms what is called the vital
capacity of the chest (Fig. 90).
209. The Movements of Breathing. The act of breathing consists of a
series of rhythmical movements, succeeding one another in regular order.
In the first movement, inspiration, the chest rises, and there is an
inrush of fresh air; this is at once followed by expiration, the
falling of the chest walls, and the output of air. A pause now occurs, and
the same breathing movements are repeated.
The entrance and the exit of air into the respiratory passages are
accompanied with peculiar sounds which are readily heard on placing the
ear at the chest wall. These sounds are greatly modified in various
pulmonary diseases, and hence are of great value to the physician in
making a correct diagnosis.
In a healthy adult, the number of respirations should be from 16 to 18 per
minute, but they vary with age, that of a newly born child being 44 for
the same time. Exercise increases the number, while rest diminishes it. In
standing, the rate is more than when lying at rest. Mental emotion and
excitement quicken the rate. The number is smallest during sleep. Disease
has a notable effect upon the frequency of respirations. In diseases
involving the lungs, bronchial tubes, and the pleura, the rate may be
alarmingly increased, and the pulse is quickened in proportion.
210. The Mechanism of Breathing. The chest is a chamber with bony
walls, the ribs connecting in front with the breastbone, and behind with
the spine. The spaces between the ribs are occupied by the intercostal
muscles, while large muscles clothe the entire chest. The diaphragm serves
as a movable floor to the chest, which is an air-tight chamber with
movable walls and floor. In this chamber are suspended the lungs, the air
cells of which communicate with the outside through the bronchial
passages, but have no connection with the chest cavity. The thin space
between the lungs and the rib walls, called the pleural cavity, is in
health a vacuum.
Now, when the diaphragm contracts, it descends and thus increases the
depth of the chest cavity. A quantity of air is now drawn into the lungs
and causes them to expand, thus filling up the increased space. As soon as
the diaphragm relaxes, returning to its arched position and reducing the
size of the chest cavity, the air is driven from the lungs, which then
diminish in size. After a short pause, the diaphragm again contracts, and
the same round of operation is constantly repeated.
The walls of the chest being movable, by the contractions of the
intercostals and other muscles, the ribs are raised and the breastbone
pushed forward. The chest cavity is thus enlarged from side to side and
from behind forwards. Thus, by the simultaneous descent of the diaphragm
and the elevation of the ribs, the cavity of the chest is increased in
three directions,--downwards, side-ways, and from behind forwards.
It is thus evident that inspiration is due to a series of muscular
contractions. As soon as the contractions cease, the elastic lung
tissue resumes its original position, just as an extended rubber band
recovers itself. As a result, the original size of the chest cavity is
restored, and the inhaled air is driven from the lungs. Expiration may
then be regarded as the result of an elastic recoil, and not of active
muscular contractions.
[Illustration: Fig. 91.--Diagrammatic Section of the Trunk. (Showing the
expansion of the chest and the movement of the ribs by action of the
lungs.) [The dotted lines indicate the position during inspiration.]]
211. Varieties of Breathing. This is the mechanism of quiet, normal
respiration. When the respiration is difficult, additional forces are
brought into play. Thus when the windpipe and bronchial tubes are
obstructed, as in croup, asthma, or consumption, many additional muscles
are made use of to help the lungs to expand. The position which asthmatics
often assume, with arms raised to grasp something for support, is from the
need of the sufferer to get a fixed point from which the muscles of the
arm and chest may act forcibly in raising the ribs, and thus securing more
comfortable breathing.
The visible movements of breathing vary according to circumstances. In
infants the action of the diaphragm is marked, and the movements of the
abdomen are especially obvious. This is called abdominal breathing. In
women the action of the ribs as they rise and fall, is emphasized more
than in men, and this we call costal breathing. In young persons and in
men, the respiration not usually being impeded by tight clothing, the
breathing is normal, being deep and abdominal.
Disease has a marked effect upon the mode of breathing. Thus, when
children suffer from some serious chest disease, the increased movements
of the abdominal walls seem distressing. So in fracture of the ribs, the
surgeon envelops the overlying part of the chest with long strips of firm
adhesive plaster to restrain the motions of chest respiration, that they
may not disturb the jagged ends of the broken bones. Again, in painful
diseases of the abdomen, the sufferer instinctively suspends the abdominal
action and relies upon the chest breathing. These deviations from the
natural movements of respiration are useful to the physician in
ascertaining the seat of disease.
212. The Nervous Control of Respiration. It is a matter of common
experience that one's breath may be held for a short time, but the need of
fresh air speedily gets the mastery, and a long, deep breath is drawn.
Hence the efforts of criminals to commit suicide by persistent restraint
of their breathing, are always a failure. At the very worst,
unconsciousness ensues, and then respiration is automatically resumed.
Thus a wise Providence defeats the purpose of crime. The movements of
breathing go on without our attention. In sleep the regularity of
respiration is even greater than when awake. There is a particular part of
the nervous system that presides over the breathing function. It is
situated in that part of the brain called the medulla oblongata, and is
fancifully called the "vital knot" (sec. 270). It is injury to this
respiratory center which proves fatal in cases of broken neck.
From this nerve center there is sent out to the nerves that supply the
diaphragm and other muscles of breathing, a force which stimulates them to
regular contraction. This breathing center is affected by the condition of
the blood. It is stimulated by an excess of carbon dioxid in the blood,
and is quieted by the presence of oxygen.
Experiment 108. _To locate the lungs_. Mark out the boundaries of
the lungs by "sounding" them; that is, by _percussion_, as it is called.
This means to put the forefinger of the left hand across the chest or
back, and to give it a quick, sharp rap with two or three fingers. Note
where it sounds hollow, resonant. This experiment can be done by the
student with only imperfect success, until practice brings some skill.
Experiment 109. Borrow a stethoscope, and listen to the respiration
over the chest on the right side. This is known as _auscultation_. Note
the difference of the sounds in inspiration and in expiration. Do not
confuse the heart sounds with those of respiration. The respiratory
murmurs may be heard fairly well by applying the ear flat to the chest,
with only one garment interposed.
Experiment 110. Get a sheep's lungs, with the windpipe attached.
Ask for the heart and lungs all in one mass. Take pains to examine the
specimen first, and accept only a good one. Parts are apt to be hastily
snipped or mangled. Examine the windpipe. Note the horseshoe-shaped
rings of cartilage in front, which serve to keep it open.
Experiment 111. Examine one bronchus, carefully dissecting away the
lung tissue with curved scissors. Follow along until small branches of
the bronchial tubes are reached. Take time for the dissection, and save
the specimen in dilute alcohol. Put pieces of the lung tissue in a basin
of water, and note that they float.
The labored breathing of suffocation and of lung diseases is due to the
excessive stimulation of this center, caused by the excess of carbon
dioxid in the blood. Various mental influences from the brain itself, as
the emotions of alarm or joy or distress, modify the action of the
respiratory center.
Again, nerves of sensation on the surface of the body convey influences to
this nerve center and lead to its stimulation, resulting in a vigorous
breathing movement. Thus a dash of cold water on the face or neck of a
fainting person instantly produces a deep, long-drawn breath. Certain
drugs, as opium, act to reduce the activity of this nerve center. Hence,
in opium poisoning, special attention should be paid to keeping up the
respiration. The condition of the lungs themselves is made known to the
breathing center, by messages sent along the branches of the great
pneumogastric nerve (page 276), leading from the lungs to the medulla
oblongata.
213. Effects of Respiration upon the Blood. The blood contains three
gases, partly dissolved in it and partly in chemical union with certain of
its constituents. These are oxygen, carbon dioxid, and nitrogen.
The latter need not be taken into account. The oxygen is the
nourishing material which the tissues require to carry on their work. The
carbon dioxid is a waste substance which the tissues produce by their
activity, and which the blood carries away from them.
As before shown, the blood as it flows through the tissues loses most of
its oxygen, and carbon dioxid takes its place. Now if the blood is to
maintain its efficiency in this respect, it must always be receiving new
supplies of oxygen, and also have some mode of throwing off its excess of
carbon dioxid. This, then, is the double function of the process of
respiration. Again, the blood sent out from the left side of the heart is
of a bright scarlet color. After its work is done, and the blood returns
to the right side of the heart, it is of a dark purple color. This change
in color takes place in the capillaries, and is due to the fact that there
the blood gives up most of its oxygen to the tissues and receives from
them a great deal of carbon dioxid.
In brief, while passing through the capillaries of the lungs the blood has
been changed from the venous to the arterial blood. That is to say, the
blood in its progress through the lungs has rid itself of its excess of
carbon dioxid and obtained a fresh supply of oxygen.[36]
214. Effects of Respiration upon the Air in the Lungs. It is well
known that if two different liquids be placed in a vessel in contact with
each other and left undisturbed, they do not remain separate, but
gradually mix, and in time will be perfectly combined. This is called
diffusion of liquids. The same thing occurs with gases, though the process
is not visible. This is known as the diffusion of gases. It is also true
that two liquids will mingle when separated from each other by a membrane
(sec. 129). In a similar manner two gases, especially if of different
densities, may mingle even when separated from each other by a membrane.
In a general way this explains the respiratory changes that occur in the
blood in the lungs. Blood containing oxygen and carbon dioxid is flowing
in countless tiny streams through the walls of the air cells of the lungs.
The air cells themselves contain a mixture of the same two gases. A thin,
moist membrane, well adapted to allow gaseous diffusion, separates the
blood from the air. This membrane is the delicate wall of the capillaries
and the epithelium of the air cells. By experiment it has been found that
the pressure of oxygen in the blood is less than that in the air cells,
and that the pressure of carbon dioxid gas in the blood is greater than
that in the air cells. As a result, a diffusion of gases ensues. The
blood gains oxygen and loses carbon dioxid, while the air cells lose
oxygen and gain the latter gas.
[Illustration: Fig. 92.--Capillary Network of the Air Cells and Origin of
the Pulmonary Veins.
A, small branch of pulmonary artery;
B, twigs of the pulmonary artery anastomosing to form peripheral network
of the primitive air cells;
C, capillary network around the walls of the air sacs;
D, branches of network converging for form the veinlets of the pulmonary
veins.
]
The blood thus becomes purified and reinvigorated, and at the same time is
changed in color from purple to scarlet, from venous to arterial. It is
now evident that if this interchange is to continue, the air in the cells
must be constantly renewed, its oxygen restored, and its excess of carbon
dioxid removed. Otherwise the process just described would be reversed,
making the blood still more unfit to nourish the tissues, and more
poisonous to them than before.
215. Change in the Air in Breathing. The air which we exhale during
respiration differs in several important particulars from the air we
inhale. Both contain chiefly the three gases, though in different
quantities, as the following table shows.
Oxygen. Nitrogen. Carbon Dioxid.
Inspired air contains 20.81 79.15 .04
Expired air contains 16.03 79.58 4.38
That is, expired air contains about five per cent less oxygen and five per
cent more carbon dioxid than inspired air.
The temperature of expired air is variable, but generally is higher than
that of inspired air, it having been in contact with the warm air
passages. It is also loaded with aqueous vapor, imparted to it like
the heat, not in the depth of the lungs, but in the upper air passages.
Expired air contains, besides carbon dioxid, various impurities, many of
an unknown nature, and all in small amounts. When the expired air is
condensed in a cold receiver, the aqueous product is found to contain
organic matter, which, from the presence of _micro-organisms_,
introduced in the inspired air, is apt to putrefy rapidly. Some of these
organic substances are probably poisonous, either so in themselves, as
produced in some manner in the breathing apparatus, or poisonous as being
the products of decomposition. For it is known that various animal
substances give rise, by decomposition, to distinct poisonous products
known as _ptomaines_. It is possible that some of the constituents of the
expired air are of an allied nature. See under "Bacteria" (Chapter XIV).
At all events, these substances have an injurious action, for an
atmosphere containing simply one per cent of pure carbon dioxid has very
little hurtful effect on the animal economy, but an atmosphere in which
the carbon dioxid has been raised one per cent by breathing is highly
injurious.
The quantity of oxygen removed from the air by the breathing of an adult
person at rest amounts daily to about 18 cubic feet. About the same amount
of carbon dioxid is expelled, and this could be represented by a piece of
pure charcoal weighing 9 ounces. The quantity of carbon dioxid, however,
varies with the age, and is increased also by external cold and by
exercise, and is affected by the kind of food. The amount of water,
exhaled as vapor, varies from 6 to 20 ounces daily. The average daily
quantity is about one-half a pint.
216. Modified Respiratory Movements. The respiratory column of air is
often used in a mechanical way to expel bodies from the upper air
passages. There are also, in order to secure special ends, a number of
modified movements not distinctly respiratory. The following peculiar
respiratory acts call for a few words of explanation.
A sigh is a rapid and generally audible expiration, due to the
elastic recoil of the lungs and chest walls. It is often caused by
depressing emotions. Yawning is a deep inspiration with a stretching
of the muscles of the face and mouth, and is usually excited by fatigue or
drowsiness, but often occurs from a sort of contagion.
Hiccough is a sudden jerking inspiration due to the spasmodic
contraction of the diaphragm and of the glottis, causing the air to rush
suddenly through the larynx, and produce this peculiar sound. Snoring
is caused by vibration of the soft palate during sleep, and is habitual
with some, although it occurs with many when the system is unusually
exhausted and relaxed.
Laughing consists of a series of short, rapid, spasmodic expirations
which cause the peculiar sounds, with characteristic movements of the
facial muscles. Crying, caused by emotional states, consists of
sudden jerky expirations with long inspirations, with facial movements
indicative of distress. In sobbing, which often follows
long-continued crying, there is a rapid series of convulsive inspirations,
with sudden involuntary contractions of the diaphragm. Laughter, and
sometimes sobbing, like yawning, may be the result of involuntary
imitation.
Experiment 112. _Simple Apparatus to Illustrate the Movements of
the Lungs in the Chest_.--T is a bottle from which the bottom has been
removed; D, a flexible and elastic membrane tied on the bottle, and
capable of being pulled out by the string S, so as to increase the
capacity of the bottle. L is a thin elastic bag representing the lungs.
It communicates with the external air by a glass tube fitted air-tight
through a cork in the neck of the bottle. When D is drawn down, the
pressure of the external air causes L to expand. When the string is let
go, L contracts again, by virtue of its elasticity.
[Illustration: Fig. 93.]
Coughing is produced by irritation in the upper part of the windpipe
and larynx. A deep breath is drawn, the opening of the windpipe is closed,
and immediately is burst open with a violent effort which sends a blast of
air through the upper air passages. The object is to dislodge and expel
any mucus or foreign matter that is irritating the air passages.
Sneezing is like coughing; the tongue is raised against the soft
palate, so the air is forced through the nasal passages. It is caused by
an irritation of the nostrils or eyes. In the beginning of a cold in the
head, for instance, the cold air irritates the inflamed mucous membrane of
the nose, and causes repeated attacks of sneezing.
217. How the Atmosphere is Made Impure. The air around us is
constantly being made impure in a great variety of ways. The combustion of
fuel, the respiration of men and animals, the exhalations from their
bodies, the noxious gases and effluvia of the various industries, together
with the changes of fermentation and decomposition to which all organized
matter is liable,--all tend to pollute the atmosphere.
The necessity of external ventilation has been foreseen for us. The
forces of nature,--the winds, sunlight, rain, and growing vegetation,--all
of great power and universal distribution and application, restore the
balance, and purify the air. As to the principal gases, the air of the
city does not differ materially from that of rural sections. There is,
however, a vastly greater quantity of dust and smoke in the air of towns.
The breathing of this dust, to a greater or less extent laden with
bacteria, fungi, and the germs of disease, is an ever-present and most
potent menace to public and personal health. It is one of the main causes
of the excess of mortality in towns and cities over that of country
districts.
This is best shown in the overcrowded streets and houses of great cities,
which are deprived of the purifying influence of sun and air. The fatal
effect of living in vitiated air is especially marked in the mortality
among infants and children living in the squalid and overcrowded sections
of our great cities. The salutary effect of sunshine is shown by the fact
that mortality is usually greater on the shady side of the street.
218. How the Air is Made Impure by Breathing. It is not the carbon
dioxid alone that causes injurious results to health, it is more
especially the organic matter thrown off in the expired air. The
carbon dioxid which accompanies the organic matter is only the index. In
testing the purity of air it is not difficult to ascertain the amount of
carbon dioxid present, but it is no easy problem to measure the amount of
organic matter. Hence it is the former that is looked for in factories,
churches, schoolrooms, and when it is found to exceed .07 per cent it is
known that there is a hurtful amount of organic matter present.
The air as expelled from the lungs contains, not only a certain amount of
organic matter in the form of vapor, but minute solid particles of
_debris_ and bacterial micro-organisms (Chap. XIV). The air thus
already vitiated, after it leaves the mouth, putrefies very rapidly. It is
at once absorbed by clothing, curtains, carpets, porous walls, and by many
other objects. It is difficult to dislodge these enemies of health even by
free ventilation. The close and disagreeable odor of a filthy or
overcrowded room is due to these organic exhalations from the lungs, the
skin, and the unclean clothing of the occupants.
The necessity of having a proper supply of fresh air in enclosed
places, and the need of removal of impure air are thus evident. If a
man were shut up in a tightly sealed room containing 425 cubic feet of
air, he would be found dead or nearly so at the end of twenty-four hours.
Long before this time he would have suffered from nausea, headache,
dizziness, and other proofs of blood-poisoning. These symptoms are often
felt by those who are confined for an hour or more in a room where the
atmosphere has been polluted by a crowd of people. The unpleasant effects
rapidly disappear on breathing fresh air.
219. The Effect on the Health of Breathing Foul Air. People are often
compelled to remain indoors for many hours, day after day, in shops,
factories, or offices, breathing air perhaps only slightly vitiated, but
still recognized as "stuffy." Such persons often suffer from ill health.
The exact form of the disturbance of health depends much upon the
hereditary proclivity and physical make-up of the individual. Loss of
appetite, dull headache, fretfulness, persistent weariness, despondency,
followed by a general weakness and an impoverished state of blood, often
result.
Persons in this lowered state of health are much more prone to surfer from
colds, catarrhs, bronchitis, and pneumonia than if they were living in the
open air, or breathing only pure air. Thus, in the Crimean War, the
soldiers who lived in tents in the coldest weather were far more free from
colds and lung troubles than those who lived in tight and ill-ventilated
huts. In the early fall when typhoid fever is prevalent, the grounds of
large hospitals are dotted with canvas tents, in which patients suffering
from this fever do much better than in the wards.
This tendency to inflammatory diseases of the air passages is aggravated
by the overheated and overdried condition of the air in the room occupied.
This may result from burning gas, from overheated furnaces and stoves,
hot-water pipes, and other causes. Serious lung diseases, such as
consumption, are more common among those who live in damp, overcrowded, or
poorly ventilated homes.
220. The Danger from Pulmonary Infection. The germ of pulmonary
consumption, known as the bacillus tuberculosis, is contained in the
breath and the sputa from the lungs of its victims. It is not difficult to
understand how these bacilli may be conveyed through the air from the
lungs of the sick to those of apparently healthy people. Such persons may,
however, be predisposed, either constitutionally or by defective hygienic
surroundings, to fall victims to this dreaded disease. Overcrowding, poor
ventilation, and dampness all tend to increase the risk of pulmonary
infection.
It must not be supposed that the tubercle bacillus is necessarily
transmitted directly through the air from the lungs of the sick to be
implanted in the lungs of the healthy. The germs may remain for a time in
the dust turn and _debris_ of damp, filthy, and overcrowded houses. In
this congenial soil they retain their vitality for a long time, and
possibly may take on more virulent infective properties than they
possessed when expelled from the diseased lungs.[37]
[Illustration: Fig. 94. Example of a Micro-Organism--Bacillus Tuberculosis
in Spotum. (Magnified about 500 diameters.)]
221. Ventilation. The question of a practicable and economical system
of ventilation for our homes, schoolrooms, workshops, and public
places presents many difficult and perplexing problems. It is perhaps due
to the complex nature of the subject, that ventilation, as an ordinary
condition of daily health, has been so much neglected. The matter is
practically ignored in building ordinary houses. The continuous renewal of
air receives little if any consideration, compared with the provision made
to furnish our homes with heat, light, and water. When the windows are
closed we usually depend for ventilation upon mere chance,--on the
chimney, the fireplace, and the crevices of doors and windows. The proper
ventilation of a house and its surroundings should form as prominent a
consideration in the plans of builders and architects as do the grading of
the land, the size of the rooms, and the cost of heating.
The object of ventilation is twofold: First, to provide for the removal
of the impure air; second, for a supply of pure air. This must
include a plan to provide fresh air in such a manner that there shall be
no draughts or exposure of the occupants of the rooms to undue
temperature. Hence, what at first might seem an easy thing to do, is, in
fact, one of the most difficult of sanitary problems.
222. Conditions of Efficient Ventilation. To secure proper
ventilation certain conditions must be observed. The pure air introduced
should not be far below the temperature of the room, or if so, the
entering current should be introduced towards the ceiling, that it may mix
with the warm air.
Draughts must be avoided. If the circuit from entrance to exit is short,
draughts are likely to be produced, and impure air has less chance of
mixing by diffusion with the pure air. The current of air introduced
should be constant, otherwise the balance may occasionally be in favor of
vitiated air. If a mode of ventilation prove successful, it should not be
interfered with by other means of entrance. Thus, an open door may prevent
the incoming air from passing through its proper channels. It is desirable
that the inlet be so arranged that it can be diminished in size or closed
altogether. For instance, when the outer air is very cold, or the wind
blows directly into the inlet, the amount of cold air entering it may
lower the temperature of the room to an undesirable degree.
In brief, it is necessary to have a thorough mixing of pure and impure
air, so that the combination at different parts of the room may be fairly
uniform. To secure these results, the inlets and outlets should be
arranged upon principles of ventilation generally accepted by authorities
on public health. It seems hardly necessary to say that due attention must
be paid to the source from which the introduced air is drawn. If it be
taken from foul cellars, or from dirty streets, it may be as impure as
that which it is designed to replace.
Animal Heat.
223. Animal or Vital Heat. If a thermometer, made for the purpose, be
placed for five minutes in the armpit, or under the tongue, it will
indicate a temperature of about 98-1/2 degrees F., whether the surrounding
atmosphere be warm or cold. This is the natural heat of a healthy person,
and in health it rarely varies more than a degree or two. But as the body
is constantly losing heat by radiation and conduction, it is evident that
if the standard temperature be maintained, a certain amount of heat must
be generated within the body to make up for the loss externally. The heat
thus produced is known as animal or vital heat.
This generation of heat is common to all living organisms. When the mass
of the body is large, its heat is readily perceptible to the touch and by
its effect upon the thermometer. In mammals and birds the heat-production
is more active than in fishes and reptiles, and their temperatures differ
in degree even in different species of the same class, according to the
special organization of the animal and the general activity of its
functions. The temperature of the frog may be 85 degrees F. in June and 41
degrees F. in January. The structure of its tissues is unaltered and their
vitality unimpaired by such violent fluctuations. But in man it is
necessary not only for health, but even for life, that the temperature
should vary only within narrow limits around the mean of 98-1/2 degrees F.
We are ignorant of the precise significance of this constancy of
temperature in warm-blooded animals, which is as important and peculiar as
their average height, Man, undoubtedly, must possess a superior delicacy
of organization, hardly revealed by structure, which makes it necessary
that he should be shielded from the shocks and jars of varying
temperature, that less highly endowed organisms endure with impunity.
224. Sources of Bodily Heat. The heat of the body is generated by the
chemical changes, generally spoken of as those of oxidation, which are
constantly going on in the tissues. Indeed, whenever protoplasmic
materials are being oxidized (the process referred to in sec. 15 as
katabolism) heat is being set free. These chemical changes are of
various kinds, but the great source of heat is the katabolic process,
known as oxidation.
The vital part of the tissues, built up from the complex classes of food,
is oxidized by means of the oxygen carried by the arterial blood, and
broken down into simpler bodies which at last result in urea, carbon
dioxid, and water. Wherever there is life, this process of oxidation is
going on, but more energetically in some tissues and organs than in
others. In other words, the minutest tissue in the body is a source of
heat in proportion to the activity of its chemical changes. The more
active the changes, the greater is the heat produced, and the greater the
amount of urea, carbon dioxid, and water eliminated. The waste caused by
this oxidation must be made good by a due supply of food to be built up
into protoplasmic material. For the production of heat, therefore, food is
necessary. But the oxidation process is not as simple and direct as the
statement of it might seem to indicate. Though complicated in its various
stages, the ultimate result is as simple as in ordinary combustion outside
of the body, and the products are the same.
The continual chemical changes, then, chiefly by oxidation of combustible
materials in the tissues, produce an amount of heat which is efficient to
maintain the temperature of the living body at about 98-1/2 degrees F. This
process of oxidation provides not only for the heat of the body, but also
for the energy required to carry on the muscular work of the animal
organism.
225. Regulation of the Bodily Temperature. While bodily heat is being
continually produced, it is also as continually being lost by the lungs,
by the skin, and to some extent, by certain excretions. The blood, in its
swiftly flowing current, carries warmth from the tissues where heat is
being rapidly generated, to the tissues or organs in which it is being
lost by radiation, conduction, or evaporation. Were there no arrangement
by which heat could be distributed and regulated, the temperature of the
body would be very unequal in different parts, and would vary at different
times.
The normal temperature is maintained with slight variations throughout
life. Indeed a change of more than a degree above or below the average,
indicates some failure in the organism, or some unusual influence. It is
evident, then, that the mechanisms which regulate the temperature of the
body must be exceedingly sensitive.
The two chief means of regulating the temperature of the body are the
lungs and the skin. As a means of lowering the temperature, the
lungs and air passages are very inferior to the skin; although, by giving
heat to the air we breathe, they stand next to the skin in importance. As
a regulating power they are altogether subordinate to the skin.
Experiment 113. _To show the natural temperature of the body_.
Borrow a physician's clinical thermometer, and take your own
temperature, and that of several friends, by placing the instrument
under the tongue, closing the mouth, and holding it there for five
minutes. It should be thoroughly cleansed after each use.
226. The Skin as a Heat-regulator. The great regulator of the bodily
temperature is, undoubtedly, the skin, which performs this function
by means of a self-regulating apparatus with a more or less double action.
First, the skin regulates the loss of heat by means of the vaso-motor
mechanism. The more blood passes through the skin, the greater will be
the loss of heat by conduction, radiation, and evaporation. Hence, any
action of the vaso-motor mechanism which causes dilatation of the
cutaneous capillaries, leads to a larger flow of blood through the skin,
and will tend to cool the body. On the other hand, when by the same
mechanism the cutaneous vessels are constricted, there will be a smaller
flow of blood through the skin, which will serve to check the loss of heat
from the body (secs. 195 and 270).
Again, the special nerves of perspiration act directly as regulators
of temperature. They increase the loss of heat when they promote the
secretion of the skin, and diminish the loss when they cease to promote
it.
The practical working of this heat-regulating mechanism is well shown by
exercise. The bodily temperature rarely rises so much as a degree during
vigorous exercise. The respiration is increased, the cutaneous capillaries
become dilated from the quickened circulation, and a larger amount of
blood is circulating through the skin. Besides this, the skin perspires
freely. A large amount of heat is thus lost to the body, sufficient to
offset the addition caused by the muscular contractions.
It is owing to the wonderful elasticity of the sweat-secreting mechanism,
and to the increase in respiratory activity, and the consequent increase
in the amount of watery vapor given off by the lungs, that men are able to
endure for days an atmosphere warmer than the blood, and even for a short
time at a temperature above that of boiling water. The temperature of a
Turkish bath may be as high as 150 degrees to 175 degrees F. But an
atmospheric temperature may be considerably below this, and yet if long
continued becomes dangerous to life. In August, 1896, for instance,
hundreds of persons died in this country, within a few days, from the
effects of the excessive heat.
A much higher temperature may be borne in dry air than in humid air, or
that which is saturated with watery vapor. Thus, a shade temperature of
100 degrees F. in the dry air of a high plain may be quite tolerable,
while a temperature of 80 degrees F. in the moisture-laden atmosphere of
less elevated regions, is oppressive. The reason is that in dry air the
sweat evaporates freely, and cools the skin. In saturated air at the
bodily temperature there is little loss of heat by perspiration, or by
evaporation from the bodily surface.
This topic is again discussed in the description of the skin as a
regulator of the bodily temperature (sec. 241).
227. Voluntary Means of Regulating the Temperature. The voluntary
factor, as a means of regulating the heat loss in man, is one of great
importance. Clothing retards the loss of heat by keeping in contact with
it a layer of still air, which is an exceedingly bad conductor. When a man
feels too warm and throws off his coat, he removes one of the badly
conducting layers of air, and increases the heat loss by radiation and
conduction. The vapor next the skin is thus allowed a freer access to the
surface, and the loss of heat by evaporation of the sweat becomes greater.
This voluntary factor by which the equilibrium is maintained must be
regarded as of great importance. This power also exists in the lower
animals, but to a much smaller extent. Thus a dog, on a hot day, runs out
his tongue and stretches his limbs so as to increase the surface from
which heat is radiated and conducted.
The production, like the loss, of heat is to a certain extent under the
control of the will. Work increases the production of heat, and rest,
especially sleep, lessens it. Thus the inhabitants of very hot countries
seek relief during the hottest part of the day by a siesta. The quantity
and quality of food also influence the production of heat. A larger
quantity of food is taken in winter than in summer. Among the inhabitants
of the northern and Arctic regions, the daily consumption of food is far
greater than in temperate and tropical climates.
228. Effect of Alcohol upon the Lungs. It is a well recognized fact
that alcohol when taken into the stomach is carried from that organ to the
liver, where, by the baneful directness of its presence, it produces a
speedy and often disastrous effect. But the trail of its malign power does
not disappear there. From the liver it passes to the right side of the
heart, and thence to the lungs, where its influence is still for harm.
In the lungs, alcohol tends to check and diminish the breathing capacity
of these organs. This effect follows from the partial paralyzing influence
of the stupefying agent upon the sympathetic nervous system, diminishing
its sensibility to the impulse of healthful respiration. This diminished
capacity for respiration is clearly shown by the use of the _spirometer_,
a simple instrument which accurately records the cubic measure of the
lungs, and proves beyond denial the decrease of the lung space.
"Most familiar and most dangerous is the drinking man's inability to
resist lung diseases."--Dr. Adoph Frick, the eminent German physiologist
of Zurich.
"Alcohol, instead of preventing consumption, as was once believed,
reduces the vitality so much as to render the system unusually
susceptible to that fatal disease."--R. S. Tracy, M.D., Sanitary
Inspector of the N. Y. City Health Dept.
"In thirty cases in which alcoholic phthisis was present a dense,
fibroid, pigmented change was almost invariably present in some portion
of the lung far more frequently than in other cases of
phthisis."--_Annual of Medical Sciences_.
"There is no form of consumption so fatal as that from alcohol.
Medicines affect the disease but little, the most judicious diet fails,
and change of air accomplishes but slight real good.... In plain terms,
there is no remedy whatever for alcoholic phthisis. It may be delayed in
its course, but it is never stopped; and not infrequently, instead of
being delayed, it runs on to a fatal termination more rapidly than is
common in any other type of the disorder."--Dr. B. W. Richardson in
_Diseases of Modern Life_.
229. Other Results of Intoxicants upon the Lungs. But a more potent
injury to the lungs comes from another cause. The lungs are the arena
where is carried on the ceaseless interchange of elements that is
necessary to the processes of life. Here the dark venous blood, loaded
with effete material, lays down its carbon burden and, with the
brightening company of oxygen, begins again its circuit. But the enemy
intrudes, and the use of alcohol tends to prevent this benign interchange.
The continued congestion of the lung tissue results in its becoming
thickened and hardened, thus obstructing the absorption of oxygen, and the
escape of carbon dioxid. Besides this, alcohol destroys the integrity of
the red globules, causing them to shrink and harden, and impairing their
power to receive oxygen. Thus the blood that leaves the lungs conveys an
excess of the poisonous carbon dioxid, and a deficiency of the needful
oxygen. This is plainly shown in the purplish countenance of the
inebriate, crowded with enlarged veins. This discoloration of the face is
in a measure reproduced upon the congested mucous membrane of the lungs.
It is also proved beyond question by the decreased amount of carbon dioxid
thrown off in the expired breath of any person who has used alcoholics.
The enfeebled respiration explains (though it is only one of the reasons)
why inebriates cannot endure vigorous and prolonged exertion as can a
healthy person. The hurried circulation produced by intoxicants involves
in turn quickened respiration, which means more rapid exhaustion of the
life forces. The use of intoxicants involves a repeated dilatation of the
capillaries, which steadily diminishes their defensive power, rendering
the person more liable to yield to the invasion of pulmonary diseases.[38]
230. Effect of Alcoholics upon Disease. A theory has prevailed, to a
limited extent, that the use of intoxicants may act as a preventive of
consumption. The records of medical science fail to show any proof
whatever to support this impression. No error could be more serious or
more misleading, for the truth is in precisely the opposite direction.
Instead of preventing, alcohol tends to develop consumption. Many
physicians of large experience record the existence of a distinctly
recognized alcoholic consumption, attacking those constitutions broken
down by dissipation. This form of consumption is steadily progressive, and
always fatal.
The constitutional debility produced by the habit of using alcoholic
beverages tends to render one a prompt victim to the more severe diseases,
as pneumonia, and especially epidemical diseases, which sweep away vast
numbers of victims every year.
231. Effect of Tobacco upon the Respiratory Passages. The effects of
tobacco upon the throat and lungs are frequently very marked and
persistent. The hot smoke must very naturally be an irritant, as the mouth
and nostrils were not made as a chimney for heated and narcotic vapors.
The smoke is an irritant, both by its temperature and from its destructive
ingredients, the carbon soot and the ammonia which it conveys. It
irritates and dries the mucous membrane of the mouth and throat, producing
an unnatural thirst which becomes an enticement to the use of intoxicating
liquors. The inflammation of the mouth and throat is apt to extend up the
Eustachian tube, thus impairing the sense of hearing.
But even these are not all the bad effects of tobacco. The inhalation of
the poisonous smoke produces unhealthful effects upon the delicate mucous
membrane of the bronchial tubes and of the lungs. Upon the former the
effect is to produce an irritating cough, with short breath and chronic
bronchial catarrh. The pulmonary membrane is congested, taking cold
becomes easy, and recovery from it tedious. Frequently the respiration is
seriously disturbed, thus the blood is imperfectly aerated, and so in turn
the nutrition of the entire system is impaired. The cigarette is the
defiling medium through which these direful results frequently invade the
system, and the easily moulded condition of youth yields readily to the
destructive snare.
"The first effect of a cigar upon any one demonstrates that tobacco can
poison by its smoke and through the lungs."--London _Lancet_.
"The action of the heart and lungs is impaired by the influence of the
narcotic on the nervous system, but a morbid state of the larynx, trachea,
and lungs results from the direct action of the smoke."--Dr. Laycock,
Professor of Medicine in the University of Edinburgh.
Additional Experiments.
Experiment 114. _To illustrate the arrangement of the lungs and the
two pleurae._ Place a large sponge which will represent the lungs in a
thin paper bag which just fits it; this will represent the pulmonary
layer of the pleura. Place the sponge and paper bag inside a second
paper bag, which will represent the parietal layer of the pleura. Join
the mouths of the two bags. The two surfaces of the bags which are now
in contact will represent the two moistened surfaces of the pleurae,
which rub together in breathing.
Experiment 115. _To show how the lungs may be filled with air._
Take one of the lungs saved from Experiment 110. Tie a glass tube six
inches long into the larynx. Attach a piece of rubber to one end of the
glass tube. Now inflate the lung several times, and let it collapse.
When distended, examine every part of it.
Experiment 116. _To take your own bodily temperature or that of a
friend._ If you cannot obtain the use of a physician's clinical
thermometer, unfasten one of the little thermometers found on so many
calendars and advertising sheets. Hold it for five minutes under the
tongue with the lips closed. Read it while in position or the instant it
is removed. The natural temperature of the mouth is about 98-1/2 degrees
F.
Experiment 117. _To show the vocal cords._ Get a pig's windpipe in
perfect order, from the butcher, to show the vocal cords. Once secured,
it can be kept for an indefinite time in glycerine and water or dilute
alcohol.
Experiment 118. _To show that the air we expire is warm._ Breathe
on a thermometer for a few minutes. The mercury will rise rapidly.
Experiment 119. _To show that expired air is moist_. Breathe on a
mirror, or a knife blade, or any polished metallic surface, and note the
deposit of moisture.
Experiment 120. _To show that the expired air contains carbon
dioxid_. Put a glass tube into a bottle of lime water and breathe
through the tube. The A liquid will soon become cloudy, because the
carbon dioxid of the expired air throws down the lime held in solution.
Experiment 121. "A substitute for a clinical thermometer may be readily
contrived by taking an ordinary house thermometer from its tin case, and
cutting off the lower part of the scale so that the bulb may project
freely. With this instrument the pupils may take their own and each
other's temperatures, and it will be found that whatever the season of
the year or the temperature of the room, the thermometer in the mouth
will record about 99 degrees F. Care must, of course, be taken to keep
the thermometer in the mouth till it ceases to rise, and to read while
it is still in position."--Professor H. P. Bowditch.
Experiment 122. _To illustrate the manner in which the movements of
inspiration cause the air to enter the lungs._ Fit up an apparatus, as
represented in Fig. 95, in which a stout glass tube is provided with a
sound cork, B, and also an air-tight piston, D, resembling that of an
ordinary syringe. A short tube, A, passing through the cork, has a small
India-rubber bag, C, tied to it. Fit the cork in the tube while the
piston is near the top. Now, by lowering the piston we increase the
capacity of the cavity containing the bag. The pressure outside the bag
is thus lowered, and air rushes into it through the tube, A, till a
balance is restored. The bag is thus stretched. As soon as we let go the
piston, the elasticity of the bag, being free to act, Movements of
drives out the air just taken in, and the piston returns to its former
place.
[Illustration: Fig. 95. Apparatus for Illustrating the Movements of
Respiration.]
It will be noticed that in this experiment the elastic bag and its tube
represent the lungs and trachea; and the glass vessel enclosing it, the
thorax.
For additional experiments on the mechanics of respiration, see Chapter
XV.
Chapter IX.
The Skin and the Kidneys.
232. The Elimination of Waste Products. We have traced the food from
the alimentary canal into the blood. We have learned that various food
materials, prepared by the digestive processes, are taken up by the
branches of the portal vein, or by the lymphatics, and carried into the
blood current. The nutritive material thus absorbed is conveyed by the
blood plasma and the lymph to the various tissues to provide them with
nourishment.
We have learned also that oxygen, taken up in the air cells of the lungs,
is being continually carried to the tissues, and that the blood is
purified by being deprived in the lungs of its excess of carbon dioxid.
From this tissue activity, which is mainly oxidation, are formed certain
waste products which, as we have seen, are absorbed by the capillaries and
lymphatics and carried into the venous circulation.
In their passage through the blood and tissues, the albumens, sugars,
starches, and fats are converted into carbon dioxid, water, and urea, or
some closely allied body. Certain articles of food also contain small
amounts of sulphur and phosphorus, which undergo oxidation into sulphates
and phosphates. We speak, then, of carbon dioxid, salts, and water as
waste products of the animal economy. These leave the body by one of
the three main channels,--the lungs, the skin, or the kidneys.
The elimination of these products is brought about by a special apparatus
called organs of excretion. The worn-out substances themselves
are called excretions, as opposed to secretions, which are
elaborated for use in the body. (See note, p. 121.) As already shown, the
lungs are the main channels for the elimination of carbon dioxid, and
of a portion of water as vapor. By the skin the body gets rid of a
small portion of salts, a little carbon dioxid, and a large
amount of water in the form of perspiration. From the kidneys
are eliminated nearly all the urea and allied bodies, the main
portion of the salts, and a large amount of water. In fact,
practically all the nitrogenous waste leaves the body by the kidneys.
[Illustration: Fig. 96.--Diagrammatic Scheme to illustrate in a very
General Way Absorption and Excretion.
A, represents the alimentary canal;
L, the pulmonary surface;
K, the surface of the renal epithelium;
S, the skin;
o, oxygen;
h, hydrogen,;
n, nitrogen.
]
233. The Skin. The skin is an important and unique organ of the
body. It is a blood-purifying organ as truly as are the lungs and the
kidneys, while it also performs other and complex duties. It is not merely
a protective covering for the surface of the body. This is indeed the most
apparent, but in some respectes, the lest important, of its functions.
This protective duty is necessary and efficient, as is proved by the
familiar experience of the pain when a portion of the outer skin has been
removed.
The skin, being richly supplied with nerves, is an important organ of
sensibility and touch. In some parts it is closely attached to
the structures beneath, while in others it is less firmly adherent and
rests upon a variable amount of fatty tissue. It thus assists in relieving
the abrupt projections and depressions of the general surface, and in
giving roundness and symmetry to the entire body. The thickness of the
skin varies in different parts of the body. Where exposed to pressure and
friction, as on the soles of the feet and in the palms of the hands, it is
much thickened.
The true skin is 1/12 to 1/8 of an inch in thickness, but in certain
parts, as in the lips and ear passages, it is often not more than 1/100 of
an inch thick. At the orifices of the body, as at the mouth, ears, and
nose, the skin gradually passes into mucous membrane, the structure of the
two being practically identical. As the skin is an outside covering, so is
the mucous membrane a more delicate inside lining for all cavities into
which the apertures open, as the alimentary canal and the lungs.
[Illustration: Fig. 97.--A Layer of the Cuticle from the Palm of the Hand.
(Detached by maceration.)]
The skin ranks as an important organ of excretion, its product being
sweat, excreted by the sweat glands. The amount of this excretion
evaporated from the general surface is very considerable, and is modified
as becomes necessary from the varied conditions of the temperature. The
skin also plays an important part in regulating the bodily
temperature(sec. 241).
234. The Cutis Vera, or True Skin. The skin is remarkably complex in
its structure, and is divided into two distinct layers, which may be
readily separated: the deeper layer,--the true skin, dermis, or
corium; and the superficial layer, or outer skin,--the epidermis,
cuticle, or scarf skin.
The true skin consists of elastic and white fibrous tissue, the
bundles of which interlace in every direction. Throughout this feltwork
structure which gradually passes into areolar tissue are numerous muscular
fibers, as about the hair-follicles and the oil glands. When these tiny
muscles contract from cold or by mental emotion, the follicles project
upon the surface, producing what is called "goose flesh."
The true skin is richly supplied with blood-vessels and nerves, as when
cut it bleeds freely, and is very sensitive. The surface of the true skin
is thrown into a series of minute elevations called the papillae, upon
which the outer skin is moulded. These abound in blood-vessels,
lymphatics, and peculiar nerve-endings, which will be described in
connection with the organ of touch (sec. 314). The papillae are large
and numerous in sensitive places, as the palms of the hands, the soles of
the feet, and the fingers. They are arranged in parallel curved lines, and
form the elevated ridges seen on the surface of the outer skin (Fig. 103).
235. The Epidermis, or Cuticle. Above the true skin is the epidermis.
It is semi-transparent, and under the microscope resembles the scales of a
fish. It is this layer that is raised by a blister.
As the epidermis has neither blood-vessels, nerves, nor lymphatics,
it may be cut without bleeding or pain. Its outer surface is marked with
shallow grooves which correspond to the deep furrows between the papillae
of the true skin. The inner surface is applied directly to the papillary
layer of the true skin, and follows closely its inequalities. The outer
skin is made up of several layers of cells, which next to the true skin
are soft and active, but gradually become harder towards the surface,
where they are flattened and scale-like. The upper scales are continually
being rubbed off, and are replaced by deeper cells from beneath. There are
new cells continually being produced in the deeper layer, which push
upward the cells already existing, then gradually become dry, and are cast
off as fine, white dust. Rubbing with a coarse towel after a hot bath
removes countless numbers of these dead cells of the outer skin. During
and after an attack of scarlet fever the patient "peels," that is, sheds
an unusual amount of the seal; cells of the cuticle.
The deeper and more active layer of the epidermis, the _mucosum_, is made
up of cells some of which contain minute granules of pigment, or coloring
matter, that give color to the skin. The differences in the tint, as
brunette, fair, and blond, are due mainly to the amount of coloring matter
in these pigment cells. In the European this amount is generally small,
while in other peoples the color cells may be brown, yellow, or even
black. The pinkish tint of healthy skin, and the rosy-red after a bath are
due, not to the pigment cells, but to the pressure of capillaries in the
true skin, the color of the blood being seen through the semi-transparent
outer skin.
[Illustration: Fig. 98.--Surface of the Palm of the Hand, showing the
Openings of the Sweat Glands and the Grooves between the Papillae of the
Skin. (Magnified 4 diameters.) [In the smaller figure the same epidermal
surface is shown, as seen with the naked eye.]]
Experiment 123. Of course the living skin can be examined only in a
general way. Stretch and pull it, and notice that it is elastic. Note
any liver spots, white scars, moles, warts, etc. Examine the outer skin
carefully with a strong magnifying glass. Study the papillae on the
palms. Scrape off with a sharp knife a few bits of the scarf skin, and
examine them with the microscope.
236. The Hair. Hairs varying in size cover nearly the entire body,
except a few portions, as the upper eyelids, the palms of the hands, and
the soles of the feet.
The length and diameter of the hairs vary in different persons, especially
in the long, soft hairs of the head and beard. The average number of hairs
upon a square inch of the scalp is about 1000, and the number upon the
entire head is estimated as about 120,000.
Healthy hair is quite elastic, and may be stretched from one-fifth to
one-third more than its original length. An ordinary hair from the head
will support a weight of six to seven ounces. The hair may become strongly
electrified by friction, especially when brushed vigorously in cold, dry
weather. Another peculiarity of the hair is that it readily absorbs
moisture.
237. Structure of the Hair. The hair and the nails are structures
connected with the skin, being modified forms of the epidermis. A hair is
formed by a depression, or furrow, the inner walls of which consist of the
infolded outer skin. This depression takes the form of a sac and is called
the hair-follicle, in which the roots of the hair are embedded. At
the bottom of the follicle there is an upward projection of the true skin,
a papilla, which contains blood-vessels and nerves. It is covered
with epidermic cells which multiply rapidly, thus accounting for the rapid
growth of the hair. Around each papilla is a bulbous expansion, the hair
bulb, from which the hair begins to grow.
[Illustration: Fig. 99.--Epidermis of the Foot.
It will be noticed that there are only a few orifices of the sweat glands
in this region. (Magnified 8 diameters.)]
The cells on the papillae are the means by which the hairs grow. As these
are pushed upwards by new ones formed beneath, they are compressed, and
the shape of the follicle determines their cylindrical growth, the shaft
of the hair. So closely are these cells welded to form the cylinder, that
even under a microscope the hair presents only a fibrous appearance,
except in the center, where the cells are larger, forming the
medulla, or pith (Fig. 106).
The medulla of the hair contains the pigment granules or coloring matter,
which may be of any shade between a light yellow and an intense black. It
is this that gives the great variety in color. Generally with old people
the pigment is absent, the cells being occupied by air; hence the hair
becomes gray or white. The thin, flat scales on the surface of the hair
overlap like shingles. Connected with the hair-follicles are small bundles
of muscular fibers, which run obliquely in the skin and which, on
shortening, may cause the hairs to become more upright, and thus are made
to "stand on end." The bristling back of an angry cat furnishes a familiar
illustration of this muscular action.
[Illustration: Fig. 100.--Hair and Hair-Follicle.
A, root of hair;
B, bulb of the hair;
C, internal root sheath;
D, external root sheath;
E, external membrane of follicle;
F, muscular fibers attached to the follicle;
H, compound sebaceous gland with its duct;
K, L, simple sebaceous gland;
M, opening of the hair-follicle.
]
Opening into each hair-follicle are usually one or more sebaceous, or
oil, glands. These consist of groups of minute pouches lined with
cells producing an oily material which serves to oil the hair and keep the
skin moist and pliant.
238. The Nails. The nails are also formed of epidermis cells
which have undergone compression, much like those forming the shaft of a
hair. In other words, a nail is simply a thick layer of horny scales built
from the outer part of the scarf skin. The nail lies upon very fine and
closely set papillae, forming its matrix, or bed. It is covered at its
base with a fold of the true skin, called its root, from beneath
which it seems to grow.
The growth of the nail, like that of the hair and the outer skin, is
effected by the production of new cells at the root and under surface. The
growth of each hair is limited; in time it falls out and is replaced by a
new one. But the nail is kept of proper size simply by the removal of its
free edge.
239. The Sweat Glands. Deep in the substance of the true skin, or in
the fatty tissue beneath it, are the sweat glands. Each gland
consists of a single tube with a blind end, coiled in a sort of ball about
1/60 of an inch in diameter. From this coil the tube passes upwards
through the dermis in a wavy course until it reaches the cuticle, which it
penetrates with a number of spiral turns, at last opening on the surface.
The tubes consist of delicate walls of membrane lined with cells. The coil
of the gland is enveloped by minute blood-vessels. The cells of the glands
are separated from the blood only by a fine partition, and draw from it
whatever supplies they need for their special work.
[Illustration: Fig. 101.--Concave or Adherent Surface of the Nail.
A, border of the root;
B, whitish portion of semilunar shape (the lunula);
C, body of nail. The continuous line around border represents the free
edge.
]
[Illustration: Fig. 102.--Nail in Position.
A, section of cutaneous fold (B) turned back to show the root of the
nail;
B, cutaneous fold covering the root of the nail;
C, semi lunar whitish portion (lunula);
D, free border.
]
With few exceptions every portion of the skin is provided with sweat
glands, but they are not equally distributed over the body. They are
fewest in the back and neck, where it is estimated they average 400 to the
square inch. They are thickest in the palms of the hands, where they
amount to nearly 3000 to each square inch. These minute openings occur in
the ridges of the skin, and may be easily seen with a hand lens. The
length of a tube when straightened is about 1/4 of an inch. The total
number in the body is estimated at about 2,500,000, thus making the entire
length of the tubes devoted to the secretion of sweat about 10 miles.
240. Nature and Properties of Sweat. The sweat is a turbid, saltish
fluid with a feeble but characteristic odor due to certain volatile fatty
acids. Urea is always present in small quantities, and its proportion may
be largely increased when there is deficiency of elimination by the
kidneys. Thus it is often observed that the sweat is more abundant when
the kidneys are inactive, and the reverse is true. This explains the
increased excretion of the kidneys in cold weather. Of the inorganic
constituents of sweat, common salt is the largest and most important. Some
carbon dioxid passes out through the skin, but not more than 1/50 as much
as escapes by the lungs.
The sweat ordinarily passes off as vapor. If there is no obvious
perspiration we must not infer that the skin is inactive, since sweat is
continually passing from the surface, though often it may not be apparent.
On an average from 1-1/2 to 4 pounds of sweat are eliminated daily from
the skin in the form of vapor. This is double the amount excreted by the
lungs, and averages about 1/67 of the weight of the body.
The visible sweat, or sensible perspiration, becomes abundant during
active exercise, after copious drinking of cold water, on taking certain
drugs, and when the body is exposed to excessive warmth. Forming more
rapidly than it evaporates it collects in drops on the surface. The
disagreeable sensations produced by humid weather result from the fact
that the atmosphere is so loaded with vapor that the moisture of the skin
is slowly removed by evaporation.
Experiment 124. Study the openings of the sweat glands with the aid
of a strong magnifying glass. They are conveniently examined on the
palms.
A man's weight may be considerably reduced within a short time by loss
through the perspiration alone. This may explain to some extent the
weakening effect of profuse perspiration, as from night sweats of
consumption, convalescence from typhoid fever, or the artificial sweating
from taking certain drugs.
241. The Skin as a Regulator of the Temperature of the Body. We thus
learn that the skin covers and protects the more delicate structures
beneath it; and that it also serves as an important organ of excretion. By
means of the sweat the skin performs a third and a most important
function, _viz_., that of regulating the temperature of the body.
The blood-vessels of the skin, like those of other parts of the body, are
under the control of the nervous system, which regulates their diameter.
If the nervous control be relaxed, the blood-vessels dilate, more blood
flows through them, and more material is brought to the glands of the skin
to be acted upon. External warmth relaxes the skin and its blood-vessels.
There results an increased flow of blood to the skin, with increased
perspiration. External cold, on the other hand, contracts the skin and its
blood-vessels, producing a diminished supply of blood and a diminished
amount of sweat.
Now, it is a law of physics that the change from liquid to vapor involves
a loss of heat. A few drops of ether or of any volatile liquid placed on
the skin, produce a marked sense of coldness, because the heat necessary
to change the liquid into vapor has been drawn rapidly from the skin. This
principle holds good for every particle of sweat that reaches the mouth of
a sweat gland. As the sweat evaporates, it absorbs a certain amount of
heat, and cools the body to that extent.
242. How the Action of the Skin may be Modified. After profuse
sweating we feel chilly from the evaporation of a large amount of
moisture, which rapidly cools the surface. When the weather is very warm
the evaporation tends to prevent the bodily temperature from rising. On
the other hand, if the weather be cold, much less sweat is produced, the
loss of heat from the body is greatly lessened, and its temperature
prevented from falling. Thus it is plain why medicine is given and other
efforts are made to sweat the fever patient. The increased activity of the
skin helps to reduce the bodily heat.
The sweat glands are under the control of certain nerve fibers originating
in the spinal cord, and are not necessarily excited to action by an
increased flow of blood through the skin. In other words, the sweat glands
may be stimulated to increased action both by an increased flow of blood,
and also by reflex action upon the vaso-dilator nerves of the parts. These
two agencies, while working in harmony through the vaso-dilators, produce
phenomena which are essentially independent of each other. Thus a strong
emotion, like fear, may cause a profuse sweat to break out, with cold,
pallid skin. During a fever the skin may be hot, and its vessels full of
blood, and yet there may be no perspiration.
[Illustration: Fig. 103.--Papillae of the Skin of the Palm of the Hand.
In each papilla are seen vascular loops (dark lines) running up from the
vascular network below, the tactile corpuscles with their nerve branches
(white lines) which supply the papillae.]
The skin may have important uses with which we are not yet acquainted.
Death ensues when the heat of the body has been reduced to about 70
degrees F., and suppression of the action of the skin always produces a
lowering of the temperature. Warm-blooded animals usually die when more
than half of the general surface has been varnished. Superficial burns
which involve a large part of the surface of the body, generally have a
fatal result due to shock.
If the skin be covered with some air-tight substance like a coating of
varnish, its functions are completely arrested. The bodily heat falls very
rapidly. Symptoms of blood-poisoning arise, and death soon ensues. The
reason is not clearly known, unless it be from the sudden retention of
poisonous exhalations.
243. The Skin and the Kidneys. There is a close relationship between
the skin and the kidneys, as both excrete organic and saline matter. In
hot weather, or in conditions producing great activity of the skin, the
amount of water excreted by the kidneys is diminished. This is shown in
the case of firemen, stokers, bakers, and others who are exposed to great
heat, and drink heavily and sweat profusely, but do not have a relative
increase in the functions of the kidneys. In cool weather, when the skin
is less active, a large amount of water is excreted by the kidneys, as is
shown by the experience of those who drive a long distance in severe
weather, or who have caught a sudden cold.
[Illustration: Fig. 104.--Magnified View of a Sweat Gland with its Duct.
The convoluted gland is seen surrounded with big fat-cells, and may be
traced through the dermis to its outlet in the horny layers of the
epidermis.]
244. Absorbent Powers of the Skin. The skin serves to some extent as
an organ for absorption. It is capable of absorbing certain
substances to which it is freely exposed. Ointments rubbed in, are
absorbed by the lymphatics in those parts where the skin is thin, as in
the bend of the elbow or knee, and in the armpits. Physicians use
medicated ointments in this way, when they wish to secure prompt and
efficient results. Feeble infants often grow more vigorous by having their
skin rubbed vigorously daily with olive oil.
A slight amount of water is absorbed in bathing. Sailors deprived of
fresh water have been able to allay partially their intense thirst by
soaking their clothing in salt water. The extent to which absorption
occurs through the healthy skin is, however, quite limited. If the outer
skin be removed from parts of the body, the exposed surface absorbs
rapidly. Various substances may thus be absorbed, and rapidly passed into
the blood. When the physician wishes remedies to act through the skin, he
sometimes raises a small blister, and dusts over the surface some drug, a
fine powder, like morphine.
The part played by the skin as an organ of touch will be considered
in sections 314 and 315.
Experiment 125. _To illustrate the sense of temperature_. Ask the
person to close his eyes. Use two test tubes, one filled with cold and
the other with hot water, or two spoons, one hot and one cold. Apply
each to different parts of the surface, and ask the person whether the
touching body is hot or cold. Test roughly the sensibility of different
parts of the body with cold and warm metallic-pointed rods.
Experiment 126. Touch fur, wood, and metal. The metal feels
coldest, although all the objects are at the same temperature. Why?
Experiment 127. Plunge the hand into water at about 97 degrees F. One
experiences a feeling of heat. Then plunge it into water at about 86
degrees F.; at first it feels cold, because heat is abstracted from the
hand. Plunge the other hand direct into water at 86 degrees F. without
previously placing it in water at 97 degrees F.,--it will feel pleasantly
warm.
Experiment 128. _To illustrate warm and cold spots_. With a blunt
metallic point, touch different parts of the skin. Certain points excite
the sensation of warmth, others of cold, although the temperatures of
the skin and of the instrument remain constant.
245. Necessity for Personal Cleanliness. It is evident that the skin,
with its myriads of blood-vessels, nerves, and sweat and oil glands, is an
exceedingly complicated and important structure. The surface is
continually casting off perspiration, oily material, and dead scales. By
friction and regular bathing we get rid of these waste materials. If this
be not thoroughly done, the oily secretion holds the particles of waste
substances to the surface of the body, while dust and dirt collect, and
form a layer upon the skin. When we remember that this dirt consists of a
great variety of dust particles, poisonous matters, and sometimes germs of
disease, we may well be impressed with the necessity of personal
cleanliness.
This layer of foreign matter on the skin is in several ways injurious to
health. It clogs the pores and retards perspiration, thus checking the
proper action of the skin as one of the chief means of getting rid of the
waste matters of the body. Hence additional work is thrown upon other
organs, chiefly the lungs and the kidneys, which already have enough to
do. This extra work they can do for only a short time. Sooner or later
they become disordered, and illness follows. Moreover, as this unwholesome
layer is a fertile soil in which bacteria may develop, many skin diseases
may result from this neglect. It is also highly probable that germs of
disease thus adherent to the skin may then be absorbed into the system.
Parasitic skin diseases are thus greatly favored by the presence of an
unclean skin. It is also a fact that uncleanly people are more liable to
take cold than those who bathe often.
The importance of cleanliness would thus seem too apparent to need special
mention, were it not that the habit is so much neglected. The old and
excellent definition that dirt is suitable matter, but in the wrong place,
suggests that the place should be changed. This can be done only by
regular habits of personal cleanliness, not only of the skin, the hair,
the teeth, the nails, and the clothing, but also by the rigid observance
of a proper system in daily living.
246. Baths and Bathing. In bathing we have two distinct objects in
view,--to keep the skin clean and to impart vigor. These are closely
related, for to remove from the body worn-out material, which tends to
injure it, is a direct means of giving vigor to all the tissues. Thus a
cold bath acts upon the nervous system, and calls out, in response to the
temporary abstraction of heat, a freer play of the general vital powers.
Bathing is so useful, both locally and constitutionally, that it
should be practiced to such an extent as experience proves to be
beneficial. For the general surface, the use of hot water once a week
fulfills the demands of cleanliness, unless in special occupations.
Whether we should bathe in hot or cold water depends upon circumstances.
Most persons, especially the young and vigorous, soon become accustomed to
cool, and even cold water baths, at all seasons of the year.
The hot bath should be taken at night before going to bed, as in the
morning there is usually more risk of taking cold. The body is readily
chilled, if exposed to cold when the blood-vessels of the skin have been
relaxed by heat. Hot baths, besides their use for the purposes of
cleanliness, have a sedative influence upon the nervous system, tending to
allay restlessness and weariness. They are excellent after severe physical
or mental work, and give a feeling of restful comfort like that of sleep.
[Illustration: Fig. 105.--Epithelial Cells from the Sweat Glands. The
cells are very distinct, with nuclei enclosing pigmentary granulations
(Magnified 350 times)]
Cold baths are less cleansing than hot, but serve as an excellent
tonic and stimulant to the bodily functions. The best and most convenient
time for a cold bath is in the morning, immediately after rising. To the
healthy and vigorous, it is, if taken at this time, with proper
precautions, a most agreeable and healthful luxury. The sensation of
chilliness first felt is caused by the contraction of the skin and its
blood-vessels, so that the blood is forced back, as it were, into the
deeper parts of the body. This stimulates the nervous system, the
breathing becomes quicker and deeper, the heart beats more vigorously,
and, as a consequence, the warm blood is sent back to the skin with
increased force. This is known as the stage of reaction, which is best
increased by friction with a rough towel. This should produce the pleasant
feeling of a warm glow all over the body.
A cold bath which is not followed by reaction is likely to do more harm
than good. The lack of this reaction may be due to the water being too
cold, the bath too prolonged, or to the bather being in a low condition of
health. In brief, the ruddy glow which follows a cold bath is the main
secret of its favorable influence.
The temperature of the water should be adapted to the age and strength of
the bather. The young and robust can safely endure cold baths, that would
be of no benefit but indeed an injury to those of greater age or of less
vigorous conditions of health. After taking a bath the skin should be
rapidly and vigorously rubbed dry with a rough towel, and the clothing at
once put on.
247. Rules and Precautions in Bathing. Bathing in cold water should
not be indulged in after severe exercise or great fatigue, whether we are
heated or not. Serious results have ensued from cold baths when the body
is in a state of exhaustion or of profuse perspiration. A daily cold bath
when the body is comfortably warm, is a safe tonic for almost all persons
during the summer months, and tends especially to restore the appetite.
Cold baths, taken regularly, render persons who are susceptible to
colds much less liable to them, and less likely to be disturbed by sudden
changes of temperature. Persons suffering from heart disease or from
chronic disease of an important organ should not indulge in frequent cold
bathing except by medical advice. Owing to the relaxing nature of hot
baths, persons with weak hearts or suffering from debility may faint while
taking them.
Outdoor bathing should not be taken for at least an hour after a
full meal, and except for the robust it is not prudent to bathe with the
stomach empty, especially before breakfast. It is a wise rule, in outdoor
or sea bathing, to come out of the water as soon as the glow of reaction
is felt. It is often advisable not to apply cold water very freely to the
head. Tepid or even hot water is preferable, especially by those subject
to severe mental strain. But it is often a source of great relief during
mental strain to bathe the face, neck, and chest freely at bedtime with
cold water. It often proves efficient at night in calming the
sleeplessness which results from mental labor.
Hot baths, if taken at bedtime, are often serviceable in preventing a
threatened cold or cutting it short, the patient going immediately to bed,
with extra clothing and hot drinks. The free perspiration induced helps to
break up the cold.
Salt water acts more as a stimulant to the skin than fresh water.
Salt-water bathing is refreshing and invigorating for those who are
healthy, but the bather should come out of the water the moment there is
the slightest feeling of chilliness. The practice of bathing in salt water
more than once a day is unhealthful, and even dangerous. Only the
strongest can sustain so severe a tax on their power of endurance. Sea
bathing is beneficial in many ways for children, as their skin reacts well
after it. In all cases, brisk rubbing with a rough towel should be had
afterwards.
[Illustration: Fig. 106.--Magnified Section of the Lower Portion of a Hair
and Hair-Follicle.
A, membrane of the hair-follicle, cells with nuclei and pigmentary
granules;
B, external lining of the root sheath;
C, internal lining of the root sheath;
D, cortical or fibrous portion of the hair shaft;
E, medullary portion (pith) of shaft;
F, hair-bulb, showing its development from cells from A.
]
The golden rule of all bathing is that it must never be followed by a
chill. If even a chilliness occur after bathing, it must immediately
be broken up by some appropriate methods, as lively exercise, brisk
friction, hot drinks, and the application of heat.
Swimming is a most valuable accomplishment, combining bathing and
exercise. Bathing of the feet should never be neglected. Cleanliness of
the hair is also another matter requiring strict attention, especially in
children.
248. Care of the Hair and Nails. The hair brush should not be too
stiff, as this increases the tendency towards scurfiness of the head. If,
however, the hair is brushed too long or too hard, the scalp is greatly
stimulated, and an increased production of scurf may result. If the head
be washed too often with soap its natural secretion is checked, and the
scalp becomes dry and scaly. The various hair pomades are as a rule
undesirable and unnecessary.
The nails should be kept in proper condition, else they are not only
unsightly, but may serve as carriers of germs of disease. The nails are
often injured by too much interference, and should never be trimmed to the
quick. The upper surfaces should on no account be scraped. The nail-brush
is sufficient to cleanse them without impairing their smooth and polished
surfaces.
[Illustration: Fig. 107.--Longitudinal Section of a Finger-Nail.
A, last phalanx of the fingers;
B, true skin on the dorsal surface of the finger;
C, epidermis;
D, true skin;
E, bed of the nail;
F, superficial layer of the nail;
H, true skin of the pulp of the finger.
]
249. Use of Clothing. The chief use of clothing, from a hygienic
point of view, is to assist in keeping the body at a uniform temperature.
It also serves for protection against injury, and for personal adornment.
The heat of the body, as we have learned, is normally about 98-1/2 degrees
F. This varies but slightly in health. A rise of temperature of more than
one degree is a symptom of disturbance. The normal temperature does not
vary with the season. In summer it is kept down by the perspiration and its
rapid evaporation. In winter it is maintained by more active oxidation, by
extra clothing, and by artificial heat.
The whole matter of clothing is modified to a great extent by climatic
conditions and local environments,--topics which do not come
within the scope of this book.
250. Material Used for Clothing. It is evident that if clothing is to
do double duty in preventing the loss of heat by radiation, and in
protecting us from the hot rays of the sun, some material must be used
that will allow the passage of heat in either direction. The ideal
clothing should be both a bad conductor and a radiator of heat. At the
same time it must not interfere with the free evaporation of the
perspiration, otherwise chills may result from the accumulation of
moisture on the surface of the body.
Wool is a bad conductor, and should be worn next the skin, both in
summer and winter, especially in variable climates. It prevents, better
than any other material, the loss of heat from the body, and allows free
ventilation and evaporation. Its fibers are so lightly woven that they
make innumerable meshes enclosing air, which is one of the best of
non-conductors.
Silk ranks next to wool in warmth and porosity. It is much softer and
less irritating than flannel or merino, and is very useful for summer
wear. The practical objection to its general use is the expense. Fur
ranks with wool as a bad conductor of heat. It does not, however, like
wool, allow of free evaporation. Its use in cold countries is universal,
but in milder climates it is not much worn.
Cotton and linen are good conductors of heat, but are not
absorbents of moisture, and should not be worn next the skin. They are,
however, very durable and easily cleansed. As an intermediate clothing
they may be worn at all seasons, especially over wool or silk. Waterproof
clothing is also useful as a protection, but should not be worn a longer
time than necessary, as it shuts in the perspiration, and causes a sense
of great heat and discomfort.
The color of clothing is of some importance, especially if exposed
directly to the sun's rays. The best reflectors, such as white and light
gray clothing, absorb comparatively little heat and are the coolest, while
black or dark-colored materials, being poor reflectors and good
absorbents, become very warm.
251. Suggestions for the Use of Clothing. Prudence and good sense
should guide us in the spring, in changing winter flannels or clothing for
fabrics of lighter weight. With the fickle climate in most sections of
this country, there are great risks of severe colds, pneumonia, and other
pulmonary diseases from carelessness or neglect in this matter. A change
from heavy to lighter clothing should be made first in the outer garments,
the underclothing being changed very cautiously.
The two essentials of healthful clothing are cleanliness and
dryness. To wear garments that are daily being soiled by perspiration
and other cutaneous excretions, is a most uncleanly and unhealthful
practice. Clothing, especially woolen underclothing, should be frequently
changed. One of the objections to the use of this clothing is that it does
not show soiling to the same extent as do cotton and linen.
Infectious and contagious diseases may be conveyed by the clothing. Hence,
special care must be taken that all clothing in contact with sick people
is burned or properly disinfected. Children especially are susceptible to
scarlet fever, diphtheria, and measles, and the greatest care must be
exercised to prevent their exposure to infection through the clothing.
We should never sleep in a damp bed, or between damp sheets. The vital
powers are enfeebled during sleep, and there is always risk of pneumonia
or rheumatism. The practice of sitting with wet feet and damp clothing is
highly injurious to health. The surface of the body thus chilled may be
small, yet there is a grave risk of serious, if not of fatal, disease. No
harm may be done, even with clothing wet with water or damp with
perspiration, so long as exercise is maintained, but the failure or
inability to change into dry garments as soon as the body is at rest is
fraught with danger.
Woolen comforters, scarfs, and fur mufflers, so commonly worn around the
neck, are more likely to produce throat troubles and local chill than to
have any useful effect. Harm ensues from the fact that the extra covering
induces local perspiration, which enfeebles the natural defensive power of
the parts; and when the warmer covering is removed, the perspiring surface
is readily chilled. Those who never bundle their throats are least liable
to suffer from throat ailments.
252. Ill Effects of Wearing Tightly Fitting Clothing. The injury to
health caused by tight lacing, when carried to an extreme, is due to the
compression and displacement of various organs by the pressure exerted on
them. Thus the lungs and the heart may be compressed, causing short breath
on exertion, palpitation of the heart, and other painful and dangerous
symptoms. The stomach, the liver, and other abdominal organs are often
displaced, causing dyspepsia and all its attendant evils. The improper use
of corsets, especially by young women, is injurious, as they interfere
with the proper development of the chest and abdominal organs. The use of
tight elastics below the knee is often injurious. They obstruct the local
venous circulation and are a fruitful source of cold feet and of enlarged
or varicose veins.
Tightly fitting boots and shoes often cause corns, bunions, and ingrowing
nails; on the other hand, if too loosely worn, they cause corns from
friction. Boots too narrow in front crowd the toes together, make them
overlap, and render walking difficult and painful. High-heeled boots throw
the weight of the body forwards, so that the body rests too much on the
toes instead of on the heels, as it should, thus placing an undue strain
upon certain groups of muscles of the leg, in order to maintain the
balance, while other groups are not sufficiently exercised. Locomotion is
never easy and graceful, and a firm, even tread cannot be expected.
The compression of the scalp by a tight-fitting hat interferes with the
local circulation, and may cause headaches, neuralgia, or baldness, the
nutrition of the hair-follicles being diminished by the impaired
circulation. The compression of the chest and abdomen by a tight belt and
various binders interferes with the action of the diaphragm,--the most
important muscle of respiration.
253. Miscellaneous Hints on the Use of Clothing. Children and old
people are less able to resist the extreme changes of temperature than are
adults of an average age. Special care should be taken to provide children
with woolen underclothing, and to keep them warm and in well-ventilated
rooms. Neither the chest nor limbs of young children should be unduly
exposed, as is often done, to the cold blasts of winter or the fickle
weather of early spring. Very young children should not be taken out in
extremely cold weather, unless quite warmly clad and able to run about.
The absurd notion is often entertained that children should be hardened by
exposure to the cold. Judicious "hardening" means ample exposure of
well-fed and well-clothed children. Exposure of children not thus cared
for is simple cruelty. The many sicknesses of children, especially
diseases of the throat and lungs, may often be traced directly to gross
carelessness, ignorance, or neglect with reference to undue exposure. The
delicate feet of children should not be injured by wearing ill-fitting or
clumsy boots or shoes. Many deformities of the feet, which cause much
vexation and trouble in after years, are acquired in early life.
No one should sleep in any of the clothes worn during the day, not even in
the same underclothing. All bed clothing should be properly aired, by free
exposure to the light and air every morning. Never wear wet or damp
clothing one moment longer than necessary. After it is removed rub the
body thoroughly, put on at once dry, warm clothing, and then exercise
vigorously for a few minutes, until a genial glow is felt. Neglect of
these precautions often results in rheumatism, neuralgia, and diseases of
the chest, especially among delicate people and young women.
Pupils should not be allowed to sit in the schoolroom with any outer
garments on. A person who has become heated in a warm room should not
expose himself to cold without extra clothing. We must not be in a hurry
to put on heavy clothes for winter, but having once worn them, they must
not be left off until milder weather renders the change safe. The cheaper
articles of clothing are often dyed with lead or arsenic. Hence such
garments, like stockings and colored underclothing, worn next the skin
have been known to produce severe symptoms of poisoning. As a precaution,
all such articles should be carefully washed and thoroughly rinsed before
they are worn.
The Kidneys.
254. The Kidneys. The kidneys are two important organs in the
abdomen, one on each side of the spine. They are of a reddish-brown color,
and are enveloped by a transparent capsule made up of a fold of the
peritoneum. Em |
