Title: A Practical Physiology: A Text-Book for Higher Schools
Author: Blaisdell, Albert F. (Albert Franklin)
Language: English
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[Illustration]


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 ¾ of the weight of the
whole human body. Carbon, which exists in an impure state in charcoal,
forms more than ⅕ 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 ⅔ 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:


Proteids, or albuminous substances.

Carbohydrates (starches, sugars, and gums).

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 amœba 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 amœba
begins its life as a cell split off from its parent. This divides in
its turn, and each half is a complete amœba. When we come a little
higher than the amœba, 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 amœba (Fig. 2). Even
such dense structures as bone, cartilage, and the teeth are formed from
cells.

Illustration: Fig. 2.—Amœboid 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:

Connective Tissues Proper:
White Fibrous Tissue.
Yellow Elastic Tissue.
Areolar or Cellular Tissue.
Adipose or Fatty Tissue.
Adenoid or Retiform Tissue.

Cartilage (Gristle):
Hyaline.
White Fibro-cartilage.
Yellow Fibro-cartilage.

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 fasciæ 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
vertebræ together (Fig. 26), in the true vocal cords, and in certain
ligaments of the larynx. In the skin and fasciæ, 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
vertebræ, 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 _lacunæ_, while the fine lines are
very minute canals, _canaliculi_, which connect the lacunæ and the
Haversian canals. These Haversian canals are supplied with tiny
blood-vessels, while the lacunæ 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 (lacunæ),
  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:

Spinal Column, 26 bones:

7 Cervical Vertebræ.
    12 Dorsal Vertebræ.
     5 Lumbar Vertebræ.
     1 Sacrum.
     1 Coccyx.

Ribs, 24 bones:

14 True Ribs.
     6 False Ribs.
     4 Floating Ribs.

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 vertebræ. The
seven upper ones belong to the neck, and are called cervical vertebræ.
The next twelve are the dorsal vertebræ; these belong to the back and
support the ribs. The remaining five belong to the loins, and are
called lumbar vertebræ. On looking at the diagram of the backbone (Fig.
9) it will be seen that the vertebræ 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 vertebræ 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 vertebræ 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 vertebræ 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 vertebræ 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° or 70°. Now bend forwards, so as
to let the dorsal and lumbar vertebræ come into play, and the head can
be turned 30° more.

Experiment 9. _To show how the spinal vertebræ 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 vertebræ. 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 vertebræ, 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 vertebræ 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 (Υ). 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.    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 vertebræ 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 vertebræ (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 Vertebræ.
                 /                         /  12 Dorsal Vertebræ,
                /       I. Spinal Column  |    5 Lumbar Vertebræ,
               |           (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, fibrillæ (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 fibrillæ.
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 fibrillæ, 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_ (Δ, 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 bursæ, similarly lined and
containing fluid, are also found in special places between two surfaces
where much motion is required. There are two of these bursæ 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, Δ. 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°, the second only to 30°,
or in some persons up to 60°. 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 of trunk
Internal oblique.
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 coördination 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. Hæmorrhages 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 _Cyclopædia 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,
5½ 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:

     Proteids, or Nitrogenous Foods.
    Starches and Sugars, or Carbohydrates.
   Fats and Oils.
    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.

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     1½-2     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° 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.

COMPOSITION OF FOOD MATERIALS
Nutritive ingredients, refuse, and fuel value.

Illustration: Fig. 45.—Graphic Chart of the Composition of Food
Materials.


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° 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 fossæ, 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 œsophagus, 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,
œsophagus, 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° 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 Œsophagus. 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 œsophagus 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 œsophagus, 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
œsophagus. 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 œsophagus. 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 raphé.


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° 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° 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° 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° 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-cæcal 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 _valvulæ 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 cæcum. A valvular arrangement called the ileo-cæcal 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 cæcum 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-cæcal 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
œsophagus 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 vertebræ, 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° 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 below 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 Cooked     Time in Stomach, Hours
Apples, sweet and mellow     Raw     1½
Apples, sour and hard     ”     2½
Apple Dumpling     Boiled     3
Bass, striped, fresh     Broiled     3
Beans, pod     Boiled     2½
Beef, with salt only     ”     2¾
”    fresh, lean     Raw     3
”    ”    ”     Fried     4
”    ”    ”     Roasted     3½
”    old, hard, salted     Boiled     4¼
Beefsteak     Broiled     3
Beets     Boiled     3¾
Bread, corn     Baked     3¼
”    wheat, fresh     ”     3½
Butter     Melted     3½
Cabbage, with vinegar     Raw     2
”    ”    ”     Boiled     4½
”    heads     Raw     2½
Carrots     Boiled     3¼
Cheese, old, strong     Raw     3½
Chicken, full-grown     Fricassee     2¾
”    soup     Boiled     3
Codfish, cured, dried     ”     2
Corncake     Baked     2¾
Custard     ”     2¾
Duck, domestic     Roasted     4
”    wild     ”     4½
Eggs, fresh, whipped     Raw     1½
”     ”     2
”    soft-boiled     Boiled     3
”    hard-boiled     ”     3½
”     Fried     3½
Fowl, domestic     Boiled     4
”    ”     Roasted     4
Gelatin     Boiled     2½
Goose     Roasted     2½
Green corn and beans     Boiled     3¾
Hash, meat and vegetables     Warmed     2½
Lamb     Broiled     2½
Liver     ”     2
Milk     Boiled     2
”     Raw     2¼
Mutton, fresh     Broiled     3
”    ”     Boiled     3
”    ”     Roasted     3¼
Oysters, fresh     Raw     2½
”    ”     Roasted     3¼
”    ”     Stewed     3½
Parsnips     Boiled     2½
Pig     Roasted     2½
Pig’s feet, soused     Boiled     1
Pork, recently salted     ”     4½
”     Fried     4¼
”     Raw     3
”    steaks     Fried     3¼
”     Stewed     3
”    fat or lean     Roasted     5¼
Potatoes     Baked     2½
”     Boiled     3½
”     Roasted     2½
Rice     Boiled     1
Sago     ”     1¾
Salmon, salted     ”     4
Soup, barley     ”     1½
”    beans     ”     3
”    beef, vegetables, bread     ”     4
”    marrow bone     ”     4½
”    mutton     ”     3½
Sponge Cake     Baked     2½
Suet, beef, fresh     Boiled     5⅓
”    mutton     ”     4½
Tapioca     ”     2
Tripe, soused     ”     1
Trout, salmon, fresh     ”     1½
”    ”    ”     Fried     1½
Turkey, wild     Roasted     2¼
”    domestic     Boiled     2¼
”    ”     Roasted     2½
Turnips     Boiled     3½
Veal     Roasted     4
”     Fried     4½
Venison, steaks     Broiled     1½

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 fistulæ 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° 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° 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° 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° 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° 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° 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,
_hæmoglobin_, 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_. 98½° 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
_hæmoglobin_, 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 amœba, 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° F., or a temperature above 120° 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 œsophagus and
trachea.)


A,  inferior constrictor muscle (aids in conveying food down the
œsophagus);
  B, œsophagus;
  C, section of the right bronchus;
  D, two right pulmonary veins;
  E, great azygos vein crossing œsophagus and right bronchus to empty
  into the superior vena cava;
  F, thoracic duct;
  H, thoracic aorta;
  K, lower portion of œsophagus 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 chordæ tendinæ. 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
cœliac 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, columnæ carnoeæ;
  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 venæ cavæ 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 _débris_ 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 venæ cavæ) 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_, _dŭp_. 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 _Cyclopœdia 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 (⅔ 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 œsophagus 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 œsophagus.
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 œsophagus, 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     

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
_débris_ 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 _débris_ 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 Sputum. (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 98½° 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° F. in June and 41° 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 98½° 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
98½° 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°
to 175° 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° F. in the dry air of a high plain may be quite tolerable, while a
temperature of 80° 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
aërated, 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
pleuræ._ 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 pleuræ, 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 98½° 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° 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 ⅛ 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 papillæ,
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 papillæ 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
papillæ 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 Papillæ 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 papillæ 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 papillæ 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 papillæ, 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 1½ 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.—Papillæ 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 papillæ.

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°
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°F. One
experiences a feeling of heat. Then plunge it into water at about
86°F.; at first it feels cold, because heat is abstracted from the
hand. Plunge the other hand direct into water at 86°F. without
previously placing it in water at 97°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 98½° 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. Embedded in fat, the kidneys lie between the upper lumbar
vertebræ, and the crest of the hip bone. The liver is above the right
kidney, and the spleen above the left, while both lie close against the
rear wall of the abdomen, with the intestines in front of them. The
human kidneys, though somewhat larger, are exactly of the same shape,
color, and general appearance as those of the sheep, so commonly seen
in the markets.

The kidneys are about four inches long, two inches across, one inch
thick, and weigh from 41/2 to 51/2 ounces each. The hollow or concave
side of the kidneys is turned inwards, and the deep fissure of this
side, known as the hilus, widens out to form the pelvis. Through the
hilus the renal artery passes into each kidney, and from each hilus
passes outwards the renal vein, a branch of the inferior vena cava.

A tube, called the ureter, passes out from the concave border of each
kidney, turns downwards, and enters the bladder in the basin of the
pelvis. This tube is from 12 to 14 inches long, about as large as a
goose quill, and conveys the secretion of the kidneys to the bladder.

255. Structure of the Kidneys. The pelvis is surrounded by reddish
cones, about twelve in number, projecting into it, called the pyramids
of Malpighi. The apices of these cones, known as the _papillæ_, are
crowded with minute openings, the mouths of the uriniferous tubules,
which form the substance of the kidney. These lie parallel in the
medullary or central structure, but On reaching the cortical or outer
layer, they wind about and interlace, ending, at last, in dilated
closed sacs called Malpighian capsules.

Illustration: Fig. 108.—Vertical Section of the Kidney.


A,  pyramids of Malpighi;
  B, apices, or papillæ, of the pyramids, surrounded by subdivisions of
  the pelvis known as cups or calices;
  C, pelvis of the kidney;
  D, upper end of ureter.


256. Function of the Kidneys. The Malpighian capsules are really the
beginning of the tubules, for here the work of excretion begins. The
thin wall of the capillaries within each capsule separates the blood
from the cavity of the tubule. The blood-pressure on the delicate
capillary walls causes the exudation of the watery portions of the
blood through the cell walls into the capsule. The epithelial cell
membrane allows the water of the blood with certain salts in solution
to pass, but rejects the albumen. From the capsules, the excretion
passes through the tubules into the pelvis, and on through the ureters
to the bladder. But the delicate epithelial walls of the tubules
through which it passes permit the inflow of urea and other waste
products from the surrounding capillaries. By this twofold process are
separated from the blood the fluid portions of the renal secretion with
soluble salts, and the urea with other waste material.

257. How the Action of the Kidneys may be Modified. The action of the
kidneys is subject to very marked and sudden modifications, especially
those operating through the nervous system. Thus whatever raises the
blood-pressure in the capillaries of the capsules, will increase the
quantity of fluid filtering through them. That is, the watery portion
of the secretion will be increased without necessarily adding to its
solids. So anything which lowers the blood-pressure will diminish the
watery portion of the secretion, that is, the secretion will be scanty,
but concentrated.

The Renal Secretion.—The function of the kidneys is to secrete a fluid
commonly known as the urine. The average quantity passed in 24 hours by
an adult varies from 40 to 60 fluid ounces. Normal urine consists of
about 96 per cent of water and 4 per cent of solids. The latter consist
chiefly of certain nitrogenous substances known as urea and uric acid,
a considerable quantity of mineral salts, and some coloring matter.
Urea, the most important and most abundant constituent of urine,
contains the four elements, but nitrogen forms one-half its weight.
While, therefore, the lungs expel carbon dioxid chiefly, the kidneys
expel nitrogen. Both of these substances express the result of
oxidations going on in the body. The urea and uric acids represent the
final result of the breaking down in the body of nitrogenous
substances, of which albumen is the type.

Unusual constituents of the urine are _albumen, sugar_, and _bile_.
When albumen is present in urine, it often indicates some disease of
the kidneys, to which the term _albuminuria_ or Bright’s Disease is
applied. The presence of grape sugar or glucose indicates the disease
known as diabetes. Bile is another unusual constituent of the urine,
appearing in _jaundice_.

The bladder is situated in the pelvic cavity or in the lowest part of
the abdomen. When full, the bladder is pear-shaped; when empty, it is
collapsed and lies low in the pelvis. The functions of the bladder are
to collect and retain the urine, which has reached it drop by drop from
the kidneys through the ureters, until a certain quantity accumulates,
and then to expel it from the body.

Illustration: Fig. 109.—Vertical Section of the Back. (Showing kidneys
_in situ_ and the relative position of adjacent organs and vessels.)
[Posterior view.]


A,  12th dorsal vertebra;
  B, diaphragm;
  C, receptaculum chyli;
  D, small intestines

In the kidneys, as elsewhere, the vaso-motor nerves are distributed to
the walls of the blood-vessels, and modify the quantity and the
pressure of blood in these organs. Thus, some strong emotion, like fear
or undue anxiety, increases the blood-pressure, drives more blood to
the kidneys, and causes a larger flow of watery secretion. When the
atmosphere is hot, there is a relaxation of the vessels of the skin,
with a more than ordinary flow of blood, which is thus withdrawn from
the deeper organs. The blood-pressure in the kidneys is not only
diminished, but the total quantity passing through them in a given time
is much lessened. As a result, the secretion of the kidneys is scanty,
but it contains an unusual percentage of solids.

When the atmosphere is cold, the reverse is true. The cutaneous vessels
contract, the blood is driven to the deeper organs with increased
pressure, and there is a less amount of sweat, but an increased renal
secretion, containing a smaller proportion of solids. Certain drugs
have the power of increasing or diminishing the renal secretion. As the
waste matters eliminated by the kidneys are being constantly produced
in the tissues, the action of the renal organs is continuous, in marked
contrast with the intermittent flow of most of the secretions proper,
as distinguished from the excretions.

258. Effects of Alcoholic Drinks upon the Kidneys. The kidneys differ
from some of the other organs in this: those can rest a while without
any harm to themselves, or to the body. We can keep the eyes closed for
a few days, if necessary, without injury, and in fact often with
benefit; or, we can abstain from food for some days, if need be, and
let the stomach rest. But the kidneys cannot, with safety, cease their
work. Their duty in ridding the blood of waste products, and of any
foreign or poisonous material introduced, must be done not only
faithfully, but continually, or the whole body at once suffers from the
evil effects of the retained waste matters.
This vital fact is the key to the injurious results developed in the
kidneys by the use of alcoholic drinks. These two organs have large
blood-vessels conveying full amounts of blood to and from their
structures, and they feel very quickly the presence of alcohol.
Alcoholic liquors excite and irritate the delicate renal membranes, and
speedily disturb and eventually destroy their capacity to excrete the
proper materials from the blood.

The continued congestion of the minute structure of the kidney cuts off
the needed nutrition of the organ, and forms the primary step in the
series of disasters. Sometimes from this continued irritation, with the
resulting inflammation, and sometimes from change of structure of the
kidney by fatty degeneration, comes the failure to perform its proper
function. Then, with this two-edged sword of disaster, the urea, which
becomes a poisonous element, and should be removed, is retained in the
system, while the albumen, which is essential to healthy blood, is
filtered away through the diseased kidney.

259. Alcoholic Liquors as a Cause of Bright’s Disease. The unfortunate
presence of albumen in the urine is often a symptom of that insidious
and fatal malady known as _albuminuria_ or Bright’s disease, often
accompanied with dropsy and convulsions. One of the most constant
causes of this disease is the use of intoxicants. It is not at all
necessary to this fatal result that a person be a heavy drinker.
Steady, moderate drinking will often accomplish the work. Kidney
diseases produced by alcoholic drinks, are less responsive to medical
treatment and more fatal than those arising from any other known
cause.[39]

Experiment 129. Obtain a sheep’s kidney in good order. Observe that its
shape is something like that of a bean, and note that the concave part
(hilus), when in its normal position, is turned towards the backbone.
Notice that all the vessels leave and enter the kidney at the hilus.
Observe a small thick-walled vessel with open mouth from which may be
pressed a few drops of blood. This is the renal artery. Pass a bristle
down it. With the forceps, or even with a penknife, lift from the
kidney the fine membrane enclosing it. This is the kidney capsule.
Divide the kidney in halves by a section from its outer to near its
inner border. Do not cut directly through the hilus. Note on the cut
surfaces, on the outer side, the darker cortical portion, and on the
inner side, the smooth, pale, medullary portion. Note also the pyramids
of Malpighi.



Chapter X.
The Nervous System.


260. General View of the Nervous System. Thus far we have learned
something of the various organs and the manner in which they do their
work. Regarding our bodily structure as a kind of living machine, we
have studied its various parts, and found that each is designed to
perform some special work essential to the well-being of the whole. As
yet we have learned of no means by which these organs are enabled to
adjust their activities to the needs of other tissues and other organs.
We are now prepared to study a higher, a more wonderful and complex
agency,—the nervous system, the master tissue, which controls,
regulates, and directs every other tissue of the human body.

The nervous system, in its properties and mode of action, is distinct
from all the other systems and organs, and it shares with no other
organ or tissue the power to do its special work. It is the medium
through which all impressions are received. It connects all the parts
of the body into an organism in which each acts in harmony with every
other part for the good of the whole. It animates and governs all
movements, voluntary or involuntary,—secretion, excretion, nutrition;
in fact all the processes of organic life are subject to its regulating
power. The different organs of the body are united by a common sympathy
which regulates their action: this harmonious result is secured by
means of the nervous system.

This system, in certain of its parts, receives impressions, and
generates a force peculiar to itself. We shall learn that there can be
no physical communication between or coördination of the various parts
of organs, or harmonious acts for a desire result, without the nerves.
General impressions, as in ordinary sensation, or special impressions,
as in sight, smell, taste, or hearing,—every instinct, every act of the
will, and every thought are possible only through the action of the
nerve centers.

261. Nerve Cells. However complicated the structure of nerve tissue in
man seems to be, it is found to consist of only two different elements,
nerve cells and nerve fibers. These are associated and combined in many
ways. They are arranged in distinct masses called nerve centers, or in
the form of cords known as nerves. The former are made up of nerve
fibers; the latter of both cells and fibers.

Illustration: Fig. 110.—Nerve Cells from the Spinal Cord.

Nerve cells, which may be regarded as the central organs of the nerve
fibers, consist of masses of cell protoplasm, with a large _nucleus_
and _nucleolus_. They bear a general resemblance to other cells, but
vary much in size and shape. Nerve cells grow, become active, and die,
as do other cells. A number of processes branch off from them, some
cells giving one or two, others many. The various kinds of nerve cells
differ much in the shape and number of processes. One of the processes
is a strand which becomes continuous with the axis cylinder of the
nerve fibers; that is, the axis cylinders of all nerve fibers are
joined in one place or another with at least one cell.

Each part of this system has its own characteristic cell. Thus we have
in the spinal cord the large, irregular cells with many processes, and
in the brain proper the three-sided cells with a process jutting out
from each corner. So characteristic are these forms of cells, that any
particular part of nerve structure may be identified by the kind of
cells seen under the microscope. Nerve cells and nerve fibers are often
arranged in groups, the various cells of the groups communicating with
one another. This clustered arrangement is called a nerve center.

262. Nerve Fibers. The nerve fibers, the essential elements of the
nerves, somewhat resemble tubes filled with a clear, jelly-like
substance. They consist of a rod, or central core, continuous
throughout the whole length of the nerve, called the axis cylinder.
This core is surrounded by the white substance of Schwann, or medullary
sheath, which gives the nerve its characteristic ivory-white
appearance. The whole is enclosed in a thin, delicate sheath, known as
neurilemma.

Illustration: Fig. 111.—Nerve Cells from the Gray Matter of the Brain.


The axis cylinder generally passes without any break from the nerve
centers to the end of the fibers.[40] The outer sheath (neurilemma) is
also continuous throughout the length of the fibers. The medullary
sheath, on the other hand, is broken at intervals of about 1/25 of an
inch, and at the same intervals nuclei are found along the fiber,
around each of which is a minute protoplasmic mass. Between each pair
of nuclei the sheath is interrupted. This point is known as the _node
of Ranvier_.

Some nerve fibers have no inner sheath (medullary), the outer alone
protecting the axis cylinder. These are known as the non-medullary
fibers. They are gray, while the ordinary medullary fibers are white in
appearance. The white nerve fibers form the white part of the brain and
of the spinal cord, and the greater part of the cerebro-spinal nerves.
The gray fibers occur chiefly in branches from the sympathetic ganglia,
though found to some extent in the nerves of the cerebro-spinal system.

In a general way, the nerve fibers resemble an electric cable wire with
its central rod of copper, and its outer non-conducting layer of silk
or gutta percha. Like the copper rod, the axis cylinder along which the
nerve impulse travels is the essential part of a nerve fiber. In a cut
nerve this cylinder projects like the wick of a candle. It is really
the continuation of a process of a nerve cell. Thus the nerve cells and
nerve fibers are related, in that the process of one is the axis
cylinder and essential part of the other.

The separate microscopic threads or fibers, bound together in cords of
variable size, form the nerves. Each strand or cord is surrounded and
protected by its own sheath of connective tissue, made up of nerves.
According to its size a nerve may have one or many of these strands.
The whole nerve, not unlike a minute tendon in appearance, is covered
by a dense sheath of fibrous tissue, in which the blood-vessels and
lymphatics are distributed to the nerve fibers.

Illustration: Fig. 112.—Medullated Nerve Fibers.


A,  a medullated nerve fiber, showing the subdivision of the medullary
sheath into cylindrical sections imbricated with their ends, a nerve
corpuscle with an oval nucleus is seen between the neurilemma and the
medullary sheath;
  B, a medullated nerve fiber at a node or constriction of Ranvier, the
  axis cylinder passes uninterruptedly from one segment into the other,
  but the medullary sheath is interrupted.


263. The Functions of the Nerve Cells and Nerve Fibers. The nerve cells
are a highly active mass of living material. They find their
nourishment in the blood, which is supplied to them in abundance. The
blood not only serves as nourishment, but also supplies new material,
as it were, for the cells to work over for their own force or energy.
Thus we may think of the nerve cells as a sort of a miniature
manufactory, deriving their material from the blood, and developing
from it nervous energy.

The nerve fibers, on the other hand, are conductors of nervous energy.
They furnish a pathway along which the nerve energy generated by the
cells may travel. Made up as they are of living nerve substance, the
fibers can also generate energy, yet it is their special function to
conduct influences to and from the cells.

Illustration: Fig. 113.—Non-Medullated Fibers.
Two nerve fibers, showing the nodes or constrictions of Ranvier and the
axis cylinder. The medullary sheath has been dissolved away. The deeply
stained oblong nuclei indicate the nerve corpuscles within the
neurilemma.


264. The Nervous System Compared to a Telegraphic System. In men and
other highly organized animals, nerves are found in nearly every tissue
and organ of the body. They penetrate the most minute muscular fibers;
they are closely connected with the cells of the glands, and are found
in the coats of even the smallest blood-vessels. They are among the
chief factors of the structure of the sense organs, and ramify through
the skin. Thus the nervous system is the system of organs through the
functions of which we are brought into relation with the world around
us. When we hear, our ears are bringing us into relation with the outer
world. So sight opens up to us another gateway of knowledge.

It will help us the better to understand the complicated functions of
the nervous system, if we compare it to a telegraph line. The brain is
the main office, and the multitudes of nerve fibers branching off to
all parts of the body are the wires. By means of these, nerve messages
are constantly being sent to the brain to inform it of what is going on
in various parts of the body, and asking what is to be done in each
case. The brain, on receiving the intelligence, at once sends back the
required instructions. Countless messages are sent to and fro with
unerring accuracy and marvelous rapidity.

Thus, when we accidentally pick up something hot, it is instantly
dropped. A nerve impulse passes from the nerves of touch in the fingers
to the brain, which at once hurries off its order along another set of
nerves for the hand to drop the burning object. These examples, so
common in daily life, may be multiplied to any extent. Almost every
voluntary act we perform is executed under the direction of the nervous
system, although the time occupied is so small that it is beyond our
power to estimate it. The very frequency with which the nerves act
tends to make us forget their beneficent work.

265. Divisions of the Nervous System. This system in man consists of
two great divisions. The first is the great nerve center of the body,
the cerebro-spinal system, which rules the organs of animal life. This
includes the brain, the spinal cord, and the cerebro-spinal nerves.
Nerves are given off from the brain and the cord, and form the mediums
of communication between the external parts of the body, the muscles or
the sense organs, and the brain.

The second part is the sympathetic system, which regulates the organic
life. This consists of numerous small nerve centers arranged in oval
masses varying greatly in size, called ganglia or knots. These are
either scattered irregularly through the body, or arranged in a double
chain of knots lying on the front of the spine, within the chest and
abdomen. From this chain large numbers of nerves are given off, which
end chiefly in the organs of digestion, circulation, and respiration.
The sympathetic system serves to bring all portions of the animal
economy into direct sympathy with one another.

266. The Brain as a Whole. The brain is the seat of the intellect, the
will, the affections, the emotions, the memory, and sensation. It has
also many other and complex functions. In it are established many
reflex, automatic, and coordinating centers, which are as independent
of consciousness as are those of the spinal cord.

The brain is the largest and most complex mass of nerve tissue in the
body, made up of an enormous collection of gray cells and nerve fibers.
This organ consists of a vast number of distinct ganglia, or separate
masses of nerve matter, each capable of performing separate functions,
but united through the cerebral action into a harmonious whole.

Illustration: Fig. 114.—The Upper Surface of the Cerebrum. (Showing its
division into two hemispheres, and also the convolutions)

The average weight of the adult human brain is about 50 ounces for men
and 45 ounces for women. Other things being equal, the size and weight
of the brain bear a general relation to the mental power of the
individual. As a rule, a large, healthy brain stands for a vigorous and
superior intellect. The brains of many eminent men have been found to
be 8 to 12 ounces above the average weight, but there are notable
exceptions. The brains of idiots are small; indeed, any weight under a
certain size, about 30 ounces, seems to be invariably associated with
an imbecile mind.

The human brain is absolutely heavier than that of any other animal,
except the whale and elephant. Comparing the size of these animals with
that of man, it is instructive to notice how much larger in proportion
to the body is man’s brain. The average proportion of the weight of the
brain to the weight of the body is greater in man than in most animals,
being about 1 to 36. In some small birds, in the smaller monkeys, and
in some rodents, the proportional weight of the brain to that of the
body is even greater than in man.

267. The Cerebrum. The three principal masses which make up the brain
when viewed as a whole are:

The cerebrum, or brain proper.

The cerebellum, or lesser brain.

The medulla oblongata.

The cerebrum comprises nearly seven-eighths of the entire mass, and
fills the upper part of the skull. It consists of two halves, the right
and left cerebral hemispheres. These are almost separated from each
other by a deep median fissure. The hemispheres are united at the
bottom of the fissure by a mass of white fibers passing from side to
side. Each of these hemispheres is subdivided into three lobes, so that
the entire cerebrum is made up of six distinct lobes.

The cerebrum has a peculiar convoluted appearance, its deep folds being
separated by fissures, some of them nearly an inch in depth.

It is composed of both white and gray matter. The former comprises the
greater part of the mass, while the latter is spread over the surface
in a layer of about ⅛ of an inch thick. The gray matter is the portion
having the highest functions, and its apparent quantity is largely
increased by being formed in convolutions.

The convolutions of the cerebrum are without doubt associated with all
those higher actions which distinguish man’s life; but all the
convolutions are not of equal importance. Thus it is probable that only
the frontal part of the brain is the intellectual region, while certain
convolutions are devoted to the service of the senses.

The cerebrum is the chief seat of the sensations, the intellect, the
will, and the emotions. A study of cerebral injuries and diseases, and
experiments upon the lower animals, prove that the hemispheres, and
more especially the gray matter, are connected with mental states. The
convolutions in the human brain are more prominent than in that of the
higher animals, most nearly allied to man, although some species of
animals, not especially intelligent, have marked cerebral convolutions.
The higher races of men have more marked convolutions than those less
civilized.

A view of the under surface of the brain, which rests on the floor of
the skull, shows the origin of important nerves, called the cranial
nerves, the cerebellum, the structure connecting the optic nerves
(optic commissure), the bridge of nervous matter (pons Varolii)
connecting the two hemispheres of the cerebellum, and lastly numerous
and well-marked convolutions.

268. The Cerebellum. The cerebellum, or lesser brain, lies in the back
of the cranium, and is covered over in man by the posterior lobe of the
cerebrum. It is, at it were, astride of the back of the cerebro-spinal
axis, and consists of two hemispheres joined by a central mass. On its
under surface is a depression which receives the medulla oblongata. The
cerebellum is separated from the cerebrum by a horizontal partition of
membrane, a portion of the dura mater. In some animals, as in the cat,
this partition is partly bone.

The cerebellum is connected with other parts of the nervous system by
strands of white matter on each side, radiating from the center and
divided into numerous branches. Around these branches the gray matter
is arranged in a beautiful manner, suggesting the leaves of a tree:
hence its name, arbor vitæ, or the tree of life.

The functions of the cerebellum are not certainly known. It appears to
influence the muscles of the body so as to regulate their movements;
that is, it serves to bring the various muscular movements into
harmonious action. The mechanism by which it does this has not yet been
clearly explained. In an animal from which the cerebellum has been
removed, the functions of life do not appear to be destroyed, but all
power of either walking or flying straight is lost.

Illustration: Fig. 115.—A Vertical Section of the Brain.


A,  frontal lobe of the cerebrum;
  B, parietal lobe;
  C, parieto occipital lobe with fissure between this lobe and
  D, the occipital lobe;
  E, cerebellum;
  F, arbor vitæ;
  H, pons Varolu;
  K, medulla oblongata;
  L, portion of lobe on the opposite side of brain.

The white curved band above H represents the corpus callosum.

Disease or injury of the cerebellum usually produces blindness,
giddiness, a tendency to move backwards, a staggering, irregular gait,
and a feeling of insecurity in maintaining various positions. There is
no loss of consciousness, or other disturbance of the mental functions.

269. The Membranes of the Brain. The brain and spinal cord are
protected by three important membranes, known as the meninges,—the dura
mater, the arachnoid, and the pia mater.

The outer membrane, the dura mater, is much thicker and stronger than
the others, and is composed of white fibrous and elastic connective
tissue. It closely lines the inner surface of the skull, and forms a
protective covering for the brain. Folds of it pass between the several
divisions of the brain and serve to protect them.

The arachnoid is a thin membrane which lies beneath the dura mater. It
secretes a serous fluid which keeps the inner surfaces moist.

The pia mater is a very delicate, vascular membrane which covers the
convolutions, dips into all the fissures, and even penetrates into the
interior of the brain. It is crowded with blood-vessels, which divide
and subdivide very minutely before they penetrate the brain. The
membranes of the brain are sometimes the seat of inflammation, a
serious and painful disease, commonly known as brain fever.

270. The Medulla Oblongata. This is the thick upper part of the spinal
cord, lying within the cavity of the skull. It is immediately under the
cerebellum, and forms the connecting link between the brain and the
spinal cord. It is about an inch and a quarter long, and from one-half
to three-fourths of an inch wide at its upper part. The medulla
oblongata consists, like the spinal cord, of columns of white fibers
and masses of gray matter, but differently arranged. The gray matter is
broken up into masses which serve as centers of origin for various
nerves. The functions of the medulla oblongata are closely connected
with the vital processes. It is a great nerve tract for transmitting
sensory and motor impressions, and also the seat of a number of centers
for reflex actions of the highest importance to life. Through the
posterior part of the medulla the sensory impressions pass, that is,
impressions from below upwards to the brain resulting in sensation or
feeling. In the anterior part of the medulla, pass the nerves for motor
transmission, that is, nerve influences from above downwards that shall
result in muscular contractions in some part of the body.

The medulla is also the seat of a number of reflex centers connected
with the influence of the nervous system on the blood-vessels, the
movements of the heart, of respiration, and of swallowing, and on the
secretion of saliva. This spot has been called the “vital knot.” In the
medulla also are centers for coughing, vomiting, swallowing, and the
dilatation of the pupil of the eye. It is also in part the deep origin
of many of the important cranial nerves.

Illustration: Fig. 116.—Illustrating the General Arrangement of the
Nervous System. (Posterior view.)


271. The Cranial Nerves. The cranial or cerebral nerves consist of
twelve pairs of nerves which pass from the brain through different
openings in the base of the skull, and are distributed over the head
and face, also to some parts of the trunk and certain internal organs.
These nerves proceed in pairs from the corresponding parts of each side
of the brain, chiefly to the organs of smell, taste, hearing, and
sight.

The cranial nerves are of three kinds: sensory, motor, and both
combined, _viz_., mixed.

Distribution and Functions of the Cranial Nerves. The cranial nerves
are thus arranged in pairs:

The first pair are the olfactory nerves, which pass down through the
ethmoid bone into the nasal cavities, and are spread over the inner
surface of the nose. They are sensory, and are the special nerves of
smell.

The second pair are the optic nerves, which, under the name of the
_optic tracts_, run down to the base of the brain, from which an optic
nerve passes to each eyeball. These are sensory nerves, and are devoted
to sight.

The third, fourth, and sixth pairs proceed to the muscles of the eyes
and control their movements. These are motor nerves, the movers of the
eye.

Each of the fifth pair of nerves is in three branches, and proceeds
mainly to the face. They are called tri-facial, and are mixed nerves,
partly sensory and partly motor. The first branch is purely sensory,
and gives sensibility to the eyeball. The second gives sensibility to
the nose, gums, and cheeks. The third (mixed) gives the special
sensation of taste on the front part of the tongue, and ordinary
sensation on the inner side of the cheek, on the teeth, and also on the
scalp in front of the ear. The motor branches supply the chewing
muscles.

The seventh pair, the facial, proceed to the face, where they spread
over the facial muscles and control their movements. The eighth pair
are the auditory, or nerves of hearing, and are distributed to the
special organs of hearing.

The next three pairs of nerves all arise from the medulla, and escape
from the cavity of the skull through the same foramen. They are
sometimes described as one pair, namely, the eighth, but it is more
convenient to consider them separately.

The ninth pair, the glosso-pharyngeal, are partly sensory and partly
motor. Each nerve contains two roots: one a nerve of taste, which
spreads over the back part of the tongue; the other a motor nerve,
which controls the muscles engaged in swallowing.

The tenth pair, the pneumogastric, also known as the vagus or wandering
nerves, are the longest and most complex of all the cranial nerves.
They are both motor and sensory, and are some of the most important
nerves in the body. Passing from the medulla they descend near the
œsophagus to the stomach, sending off, on their way, branches to the
throat, the larynx, the lungs, and the heart. Some of their branches
restrain the movements of the heart, others convey impressions to the
brain, which result in quickening or slowing the movements of
breathing. Other branches pass to the stomach, and convey to the brain
impressions which inform us of the condition of that organ. These are
the nerves by which we experience the feelings of pain in the stomach,
hunger, nausea, and many other vague impressions which we often
associate with that organ.

Illustration: Fig. 117.—Anterior View of the Medulla Oblongata.


A,  chiasm of the optic nerves;
  B, optic tracts;
  C, motor oculi communis;
  D, fifth nerve;
  E, motor oculi externus;
  F, facial nerve;
  H, auditory nerve;
  I, glosso-pharyngeal nerve;
  K, pneumogastric;
  L, spinal accessory;
  M, cervical nerves;
  N, upper extremity of spinal cord;
  O, decussation of the anterior pyramids;
  R, anterior pyramids of the medulla oblongata;
  S, pons Varolii.

The eleventh pair, the spinal accessory, are strictly motor, and supply
the muscles of the neck and the back.

The twelfth pair, the hypoglossal, are also motor, pass to the muscles
of the tongue, and help control the delicate movements in the act of
speech.

272. The Spinal Cord. This is a long, rod-like mass of white nerve
fibers, surrounding a central mass of gray matter. It is a continuation
of the medulla oblongata, and is lodged in the canal of the spinal
column. It extends from the base of the skull to the lower border of
the first lumbar vertebra, where it narrows off to a slender filament
of gray substance.

The spinal cord is from 16 to 18 inches long, and has about the
thickness of one’s little finger, weighing about 1½ ounces. Like the
brain, it is enclosed in three membranes, which in fact are the
continuation of those within the skull. They protect the delicate cord,
and convey vessels for its nourishment. The space between the two inner
membranes contains a small quantity of fluid, supporting the cord, as
it were in a water-bath. It is thus guarded against shocks.

The cord is suspended and kept in position in the canal by delicate
ligaments at regular intervals between the inner and outer membranes.
Finally, between the canal, enclosed by its three membranes, and the
bony walls of the spinal canal, there is considerable fatty tissue, a
sort of packing material, imbedded in which are some large
blood-vessels.

273. Structure of the Spinal Cord. The arrangement of the parts of the
spinal cord is best understood by a transverse section. Two fissures,
one behind, the other in front, penetrate deeply into the cord, very
nearly dividing it into lateral halves. In the middle of the isthmus
which joins the two halves, is a very minute opening, the _central
canal_ of the cord. This tiny channel, just visible to the naked eye,
is connected with one of the openings of the medulla oblongata, and
extends, as do the anterior and posterior fissures, the entire length
of the cord.

The spinal cord, like the brain, consists of gray and white matter, but
the arrangement differs. In the brain the white matter is within, and
the gray matter is on the surface. In the cord the gray matter is
arranged in two half-moon-shaped masses, the backs of which are
connected at the central part. The white matter, consisting mainly of
fibers, running for the most part in the direction of the length of the
cord, is outside of and surrounds the gray crescents. Thus each half or
side of the cord has its own gray crescent, the horns of which point
one forwards and the other backwards, called respectively the anterior
and posterior cornua or horns.

It will also be seen that the white substance itself, in each half of
the cord, is divided by the horns of the gray matter and by fibers
passing from them into three parts, which are known as the anterior,
posterior, and lateral columns.

Experiment 130. Procure at the market an uninjured piece of the spinal
cord from the loin of mutton or the sirloin or the rib of beef. After
noting its general character while fresh, put it to soak in dilute
alcohol, until it is sufficiently hard to be cut in sections.

274. The Spinal Nerves. From the gray matter on each side of the spinal
cord 31 spinal nerves are given off and distributed chiefly to the
muscles and the skin. They pass out at regular intervals on each side
of the canal, by small openings between the vertebræ. Having escaped
from the spine, they pass backwards and forwards, ramifying in the soft
parts of the body. The first pair pass out between the skull and the
atlas, the next between the atlas and the axis, and so on down the
canal. The eighth pair, called _cervical_, pass out in the region of
the neck; twelve, called _dorsal_, in the region of the ribs; five are
_lumbar_, and five _sacral_, while the last pair leave the cord near
the coccyx.

Each spinal nerve has two roots, one from the anterior, the other from
the posterior portion of the cord. These unite and run side by side,
forming as they pass between the vertebræ one silvery thread, or nerve
trunk. Although bound up in one bundle, the nerve fibers of the two
roots remain quite distinct, and perform two entirely different
functions.

After leaving the spinal cord, each nerve divides again and again into
finer and finer threads. These minute branches are distributed through
the muscles, and terminate on the surface of the body. The anterior
roots become motor nerves, their branches being distributed to certain
muscles of the body, to control their movements. The posterior roots
develop into sensory nerves, their branches being distributed through
the skin and over the surface of the body to become nerves of touch. In
brief, the spinal nerves divide and subdivide, to reach with their
twigs all parts of the body, and provide every tissue with a nerve
center, a station from which messages may be sent to the brain.

Illustration: Fig. 118.—Side View of the Spinal Cord. (Showing the
fissures and columns.)


A,  anterior median fissure;
  B, posterior median fissure;
  C, anterior lateral fissure;
  D, posterior lateral fissure;
  E, lateral column;
  F, anterior column;
  G, posterior column;
  H, posterior median column;
  K, anterior root;
  L, posterior root;
  M, ganglion of
  N, a spinal nerve.


275. The Functions of the Spinal Nerves. The messages which pass along
the spinal nerves to and from the brain are transmitted mostly through
the gray matter of the cord, but some pass along the white matter on
the outer part. As in the brain, however, all the active powers of the
cord are confined to the gray matter. The spinal nerves themselves have
nothing to do with sensation or will. They are merely conductors to
carry messages to and fro. They neither issue commands nor feel a
sensation. Hence, they consist entirely of white matter.

276. Functions of the Spinal Cord. The spinal cord is the principal
channel through which all impulses from the trunk and extremities pass
to the brain, and all impulses to the trunk and extremities pass from
the brain. That is, the spinal cord receives from various parts of the
body by means of its sensory nerves certain impressions, and conveys
them to the brain, where they are interpreted.

The cord also transmits by means of its motor nerves the commands of
the brain to the voluntary muscles, and so causes movement. Thus, when
the cord is divided at any point, compressed, as by a tumor or broken
bone, or disorganized by disease, the result is a complete loss of
sensation and voluntary movement below the point of injury. If by
accident a man has his spinal cord injured at some point, he finds he
has lost all sensation and power of motion below that spot. The impulse
to movement started in his brain by the will does not reach the muscles
he wishes to move, because traveling _down_ the spinal cord, it cannot
pass the seat of injury.

So the impression produced by pricking the leg with a pin, which,
before pain can be felt, must travel up the spinal cord to the brain,
cannot reach the brain because the injury obstructs the path. The
telegraph wire has been cut, and the current can no longer pass.

277. The Spinal Cord as a Conductor of Impulses. The identity in
structure of the spinal nerves, whether motor or sensory, and the vast
number of nerves in the cord make it impossible to trace for any
distance with the eye, even aided by the microscope and the most
skillful dissection, the course of nerve fibers. The paths by which the
motor impulses travel down the cord are fairly well known. These
impulses originate in the brain, and passing down keep to the same side
of the cord, and go out by nerves to the same side of the body.

The sensory impulses, however, soon after they enter the cord by the
nerve of one side, cross in the cord to the opposite side, up which
they travel to the brain. Thus the destruction of one lateral half of
the cord causes paralysis of motion on the _same side_ as the injury,
but loss of sensation on the _opposite side_, because the posterior
portion destroyed consists of fibers which have crossed from the
opposite side.

Experiment proves that if both roots of a spinal nerve be cut, all
those parts of the body to which they send branches become paralyzed,
and have neither sense of pain nor power of voluntary movement. The
parts might even be cut or burned without pain. It is precisely like
cutting a telegraph wire and stopping the current.

Illustration: Fig. 119.—The Base of the Brain.


A,  anterior lobe of the cerebrum;
  B, olfactory nerve;
  C, sphenoid portion of the posterior lobe;
  D, optic chiasm;
  E, optic tract;
  F, abducens;
  H, M, hemispheres of the cerebellum;
  K, occipital portion of the occipital lobe;
  L, fissure separating the hemispheres;
  N, medulla oblongata;
  O, olivary body;
  P, antenor pyramids;
  R, pons Valoru;
  S, section of olfactory nerve, with the trunk removed to show sulcus
  in which it is lodged;
  T, anterior extremity of median fissure

Experiment also proves that if only the posterior root of a spinal
nerve be cut, all sensation is lost in the parts to which the nerve
passes, but the power of moving these parts is retained. But if the
anterior root alone be divided, all power of motion in the parts
supplied by that nerve is lost, but sensation remains. From these and
many other experiments, it is evident that those fibers of a nerve
which are derived from the anterior root are motor, and those from the
posterior root sensory, fibers. Impulses sent _from_ the brain and
spinal cord to muscles will, therefore, pass along the anterior roots
through those fibers of the nerves which are derived from these (motor)
roots. On the other hand, impressions or sensations passing _to_ the
brain will enter the spinal cord and reach the brain through the
posterior or sensory roots.

278. The Spinal Cord as a Reflex Center. Besides this function of the
spinal cord as a great nerve conductor to carry sensations to the
brain, and bring back its orders, it is also an independent center for
what is called reflex action. By means of its sensory nerves it
receives impressions from certain parts of the body, and on its own
authority sends back instructions to the muscles by its motor nerves,
without consulting the brain. This constitutes reflex action, so called
because the impulse sent to the spinal cord by certain sensory nerves
is at once reflected or sent back as a motor impulse to the muscles.

This reflex action is a most important function of the spinal cord.
This power is possessed only by the gray matter of the cord, the white
substance being simply a conductor.

The cells of gray matter are found all along the cord, but are grouped
together in certain parts, notably in the cervical and lumbar regions.
The cells of the anterior horns are in relation with the muscles by
means of nerve fibers, and are also brought into connection with the
skin and other sensory surfaces, by means of nerve fibers running in
the posterior part of the cord. Thus there is established in the spinal
cord, without reference to the brain at all, a reflex mechanism.

279. Reflex Centers. For the purpose of illustration, we might consider
the body as made up of so many segments piled one on another, each
segment presided over by a similar segment of spinal cord. Each bodily
segment would have sensory and motor nerves corresponding to its
connection with the spinal cord. The group of cells in each spinal
segment is intimately connected with the cells of the segments above
and below. Thus an impression reaching the cells of one spinal segment
might be so strong as to overflow into the cells of other segments, and
thus cause other parts of the body to be affected.

Take as an example the case of a child who has eaten improper food,
which irritates its bowels. Sensory nerves of the bowels are disturbed,
and powerful impressions are carried up to a center in the spinal cord.
These impressions may now overflow into other centers, from which
spasmodic discharges of nerve energy may be liberated, which passing to
the muscles, throw them into violent and spasmodic contraction. In
other words, the child has a fit, or convulsion. All this disturbance
being the result of reflex action (the spasmodic motions being quite
involuntary, as the brain takes no part in them), the child meanwhile
is, of course, entirely unconscious and, however it may seem to be
distressed, really suffers no pain.

Scattered along the entire length of the spinal cord, especially in the
upper part, are groups of nerve cells which preside over certain
specific functions of animal life; that is, definite collections of
cells which control definite functions. Thus there are certain centers
for maintaining the action of the heart, and the movements of
breathing; and low down in the cord, in the lumbar regions, are centers
for the control of the various abdominal organs.

Numerous other reflex centers are described by physiologists, but
enough has been said to emphasize the great importance of the spinal
cord as an independent nerve center, besides its function as a
conductor of nervous impulses to and from the brain.

280. The Brain as a Reflex Center. The brain, as we have just stated,
is the seat of consciousness and intelligence. It is also the seat of
many reflex, automatic, and coordinating centers. These give rise to
certain reflex actions which are as entirely independent of
consciousness as are those of the spinal cord. These acts take place
independently of the will, and often without the consciousness of the
individual. Thus, a sudden flash of light causes the eyes to blink, as
the result of reflex action. The optic nerves serve as the sensory, and
the facial nerves as the motor, conductors. The sudden start of the
whole body at some loud noise, the instinctive dodging a threatened
blow, and the springing back from sudden danger, are the results of
reflex action. The result ensues in these and in many other instances,
without the consciousness of the individual, and indeed beyond his
power of control.

281. The Importance of Reflex Action. Reflex action is thus a marvelous
provision of nature for our comfort, health, and safety. Its vast
influence is not realized, as its numberless acts are so continually
going on without our knowledge. In fact, the greater part of nerve
power is expended to produce reflex action. The brain is thus relieved
of a vast amount of work. It would be impossible for the brain to serve
as a “thinking center” to control every act of our daily life. If we
had to plan and to will every heart-beat or every respiration, the
struggle for life would soon be given up.

The fact that the gray cells of the spinal cord can originate a
countless number of reflex and automatic activities is not only of
great importance in protecting the body from injury, but increases
vastly the range of the activities of our daily life.

Even walking, riding the bicycle, playing on a piano, and numberless
other such acts may be reflex movements. To learn how, requires, of
course, the action of the brain, but with frequent repetition the
muscles become so accustomed to certain successive movements, that they
are continued by the cord without the control of the brain. Thus we may
acquire a sort of artificial reflex action, which in time becomes in a
way a part of our organization, and is carried on without will power or
even consciousness.

So, while the hands are busily doing one thing, the brain can be
intently thinking of another. In fact, any attempt to control reflex
action is more apt to hinder than to help. In coming rapidly down
stairs, the descent will be made with ease and safety if the spinal
cord is allowed entire charge of the act, but the chances of stumbling
or of tripping are very much increased if each step be taken as the
result of the will power. The reflex action of the cord may be
diminished, or inhibited as it is called, but this power is limited.
Thus, we can by an effort of the will stop breathing for a certain
time, but beyond that the reflex mechanism overcomes our will and we
could not, if we would, commit suicide by holding our breath. When we
are asleep, if the palm of the hand be tickled, it closes; when we are
awake we can prevent it.

Illustration: Fig. 120.—Dr. Waller’s Diagrammatic Illustration of the
Reflex Process.

From the sentient surface (1) an afferent impulse passes along (2) to
the posterior root of the spinal cord, the nerve fibers of the
posterior root ending in minute filaments among the small cells of this
part of the cord (3). In some unknown way this impulse passes across
the gray part of the cord to the large cells of the anterior root (5),
the cells of this part being connected by their axis-cylinder with the
efferent fibers (6). These convey the stimulus to the fibers of the
muscle (7), which accordingly contract. Where the brain is concerned in
the action the circuit is longer through S and M.

Experiment 131. _To illustrate reflex action by what is called
knee-jerk._ Sit on a chair, and cross the right leg over the left one.
With the tips of the fingers or the back of a book, strike the right
ligamentum patellæ. The right leg will be raised and thrown forward
with a jerk, owing to the contraction of the quadriceps muscles. An
appreciable time elapses between the striking of the tendon and the
jerk. The presence or absence of the knee-jerk may be a most
significant symptom to the physician.

282. The Sympathetic System. Running along each side of the spine, from
the base of the skull to the coccyx, is a chain of nerve knots, or
ganglia. These ganglia, twenty-four on each side, and their branches
form the sympathetic system, as distinguished from the cerebro-spinal
system consisting of the brain and spinal cord and the nerves springing
from them. The ganglia of the sympathetic system are connected with
each other and with the sensory roots of the spinal nerves by a network
of gray nerve fibers.

At the upper end the chain of each side passes up into the cranium and
is closely connected with the cranial nerves. In the neck, branches
pass to the lungs and the heart. From the ganglia in the chest three
nerves form a complicated network of fibers, from which branches pass
to the stomach, the liver, the intestines, the kidneys, and other
abdominal organs. A similar network of fibers is situated lower down in
the pelvis, from which branches are distributed to the pelvic organs.
At the coccyx the two chains unite into a single ganglion.

Thus, in general, the sympathetic system, while intimately connected
with the cerebro-spinal, forms a close network of nerves which
specially accompany the minute blood-vessels, and are distributed to
the muscles of the heart, the lungs, the stomach, the liver, the
intestines, and the kidneys—that is, the hollow organs of the body.

283. The Functions of the Sympathetic System. This system exercises a
superintending influence over the greater part of the internal organs
of the body, controlling to a certain extent the functions of
digestion, nutrition, circulation, and respiration. The influence thus
especially connected with the processes of organic life is generally
different from, or even opposed to, that conveyed to the same organs by
fibers running in the spinal or cranial nerves. These impulses are
beyond the control of the will.

Illustration: Fig. 121.—The Cervical and Thoracic Portion of the
Sympathetic Nerve and its Main Branches.


A,  right pneumogastric;
  B, spinal accessory;
  C, glosso-pharyngeal;
  D, right bronchus;
  E, right branch of pulmonary artery;
  F, one of the intercostal nerves;
  H, great splanchnic nerve;
  K, solar plexus;
  L, left pneumogastric;
  M, stomach branches of right pneumogastric;
  N, right ventricle;
  O, right auricle;
  P, trunk of pulmonary artery;
  R, aorta; S, cardiac nerves;
  T, recurrent laryngeal nerve;
  U, superior laryngeal nerve;
  V, submaxillary ganglion;
  W, lingual branch of the 5th nerve;
  X, ophthalmic ganglion;
  Y, motor oculi externus.

Hence, all these actions of the internal organs just mentioned that are
necessary to the maintenance of the animal life, and of the harmony
which must exist between them, are controlled by the sympathetic
system. But for this control, the heart would stop beating during
sleep, digestion would cease, and breathing would be suspended. Gentle
irritation of these nerves, induced by contact of food in the stomach,
causes that organ to begin the churning motion needed for digestion.
Various mental emotions also have a reflex action upon the sympathetic
system. Thus, terror dilates the pupils, fear acts upon the nerves of
the small blood-vessels of the face to produce pallor, and the sight of
an accident, or even the emotions produced by hearing of one, may
excite nausea and vomiting.

The control of the blood-vessels, as has been stated (sec. 195), is one
of the special functions of the sympathetic system. Through the nerves
distributed to the muscular coats of the arteries, the caliber of these
vessels can be varied, so that at one moment they permit a large
quantity of blood to pass, and at another will contract so as to
diminish the supply. This, too, is beyond the control of the will, and
is brought about by the vaso-motor nerves of the sympathetic system
through a reflex arrangement, the center for which is the medulla
oblongata.

284. Need of Rest. The life of the body, as has been emphasized in the
preceding chapters, is subject to constant waste going on every moment,
from the first breath of infancy to the last hour of old age. We should
speedily exhaust our life from this continual loss, but for its
constant renewal with fresh material. This exhaustion of life is
increased by exertion, and the process of repair is vastly promoted by
rest. Thus, while exercise is a duty, rest is equally imperative.

The eye, when exactingly used in fine work, should have frequent
intervals of rest in a few moments of darkness by closing the lids. The
brain, when urged by strenuous study, should have occasional seasons of
rest by a dash of cold water upon the forehead, and a brief walk with
slow and deep inspirations of fresh air. The muscles, long cramped in a
painful attitude, should be rested as often as may be, by change of
posture or by a few steps around the room.

It is not entirely the amount of work done, but the continuity of
strain that wears upon the body. Even a brief rest interrupts this
strain; it unclogs the wheels of action. Our bodies are not designed
for continuous toil. An alternation of labor and rest diminishes the
waste of life. The benign process of repair cannot go on, to any
extent, during strenuous labor, but by interposing frequent though
brief periods of rest, we lessen the amount of exhaustion, refresh the
jaded nerves, and the remaining labor is more easily endured.

285. Benefits of Rest. There is too little repose in our American
nature and in our modes of life. A sense of fatigue is the mute appeal
of the body for a brief respite from labor, and the appeal should, if
possible, be heeded. If this appeal be not met, the future exertion
exhausts far more than if the body had been even slightly refreshed. If
the appeal be met, the brief mid-labor rest eases the friction of toil,
and the remaining labor is more easily borne. The feeling that a
five-minute rest is so much time lost is quite an error. It is a gain
of physical strength, of mental vigor, and of the total amount of work
done.

The merchant burdened with the cares of business life, the soldier on
the long march, the ambitious student over-anxious to win success in
his studies, the housewife wearied with her many hours of exacting
toil, each would make the task lighter, and would get through it with
less loss of vital force, by occasionally devoting a few minutes to
absolute rest in entire relaxation of the strained muscles and
overtaxed nerves.

286. The Sabbath as a Day of Physiological Rest. The divine institution
of a Sabbath of rest, one day in seven, is based upon the highest needs
of our nature. Rest, to be most effective, should alternate in brief
periods with labor.

It is sound physiology, as well as good morals and manners, to cease
from the usual routine of six days of mental or physical work, and rest
both the mind and the body on the seventh. Those who have succeeded
best in what they have undertaken, and who have enjoyed sound health
during a long and useful life, have studiously lived up to the mandates
of this great physiological law. It is by no means certain that the
tendency nowadays to devote the Sabbath to long trips on the bicycle,
tiresome excursions by land and sea, and sight-seeing generally,
affords that real rest from a physiological point of view which nature
demands after six days of well-directed manual or mental labor.

287. The Significance of Sleep as a Periodical Rest. Of the chief
characteristics of all living beings none is so significant as their
periodicity. Plants as well as animals exhibit this periodic character.
Thus plants have their annual as well as daily periods of activity and
inactivity. Hibernating animals pass the winter in a condition of
unconsciousness only to have their functions of activity restored in
early spring. Human beings also present many instances of a periodic
character, many of which have been mentioned in the preceding pages.
Thus we have learned that the heart has its regular alternating periods
of work and rest. After every expiration from the lungs there is a
pause before the next inspiration begins.

Now sleep is just another manifestation of this periodic and
physiological rest by which Nature refreshes us. It is during the
periods of sleep that the energy expended in the activities of the
waking hours is mainly renewed. In our waking moments the mind is kept
incessantly active by the demands made on it through the senses. There
is a never-ceasing expenditure of energy and a consequent waste which
must be repaired. A time soon comes when the brain cells fail to
respond to the demand, and sleep must supervene. However resolutely we
may resist this demand, Nature, in her relentless way, puts us to
sleep, no matter what objects are brought before the mind with a view
to retain its attention.[41]

288. Effect of Sleep upon the Bodily Functions. In all the higher
animals, the central nervous system enters once at least in the
twenty-four hours into the condition of rest which we call sleep.
Inasmuch as the most important modifications of this function are
observed in connection with the cerebro-spinal system, a brief
consideration of the subject is properly studied in this chapter. In
Chapter IV. we learned that repose was as necessary as exercise to
maintain muscular vigor. So after prolonged mental exertion, or in fact
any effort which involves an expenditure of what is often called
nerve-force, sleep becomes a necessity. The need of such a rest is
self-evident, and the loss of it is a common cause of the impairment of
health. While we are awake and active, the waste of the body exceeds
the repair; but when asleep, the waste is diminished, and the cells are
more actively rebuilding the structure for to-morrow’s labor. The
organic functions, such as are under the direct control of the
sympathetic nervous system,—circulation, respiration, and
digestion,—are diminished in activity during sleep. The pulsations of
the heart and the respiratory movements are less frequent, and the
circulation is slower. The bodily temperature is reduced, and the
cerebral circulation is diminished. The eyes are turned upward and
inward, and the pupils are contracted.

The senses do not all fall to sleep at once, but drop off successively:
first the sight, then the smell, the taste, the hearing and lastly the
touch. The sleep ended, they awake in an inverse order, touch, hearing,
taste, smell, and sight.

289. The Amount of Sleep Required. No precise rule can be laid down
concerning the amount of sleep required. It varies with age,
occupation, temperament, and climate to a certain extent. An infant
whose main business it is to grow spends the greater part of its time
in sound sleep. Adults of average age who work hard with their hands or
brain, under perfectly normal physiological conditions, usually require
at least eight hours of sleep. Some need less, but few require more.
Personal peculiarities, and perhaps habit to a great extent, exert a
marked influence. Some of the greatest men, as Napoleon I., have been
very sparing sleepers. Throughout his long and active life, Frederick
the Great never slept more than five or six hours in the twenty-four.
On the other hand, some of the busiest brain-workers who lived to old
age, as William Cullen Bryant and Henry Ward Beecher, required and took
care to secure at least eight or nine hours of sound sleep every night.

In old age, less sleep is usually required than in adult life, while
the aged may pass much of their time in sleep. In fact, each person
learns by experience how much sleep is necessary. There is no one thing
which more unfits one for prolonged mental or physical effort than the
loss of natural rest.

290. Practical Rules about Sleep. Children should not be played with
boisterously just before the bedtime hour, nor their minds excited with
weird goblin stories, or a long time may pass before the wide-open eyes
and agitated nerves become composed to slumber. Disturbed or
insufficient sleep is a potent factor towards producing a fretful,
irritable child.

At all ages the last hour before sleep should, if possible, be spent
quietly, to smooth the way towards sound and refreshing rest. The sleep
induced by medicine is very often troubled and unsatisfactory.
Medicines of this sort should not be taken except on the advice of a
physician.

While a hearty meal should not usually be taken just before bedtime, it
is not well to go to bed with a sense of positive faintness and hunger.
Rather, one should take a very light lunch of quite simple food as a
support for the next eight hours.

Illustration: Fig. 122.—Trunk of the Left Pneumogastric.
(Showing its distribution by its branches and ganglia to the larynx,
pharynx, heart, lungs, and other parts.)

It is better, as a rule, not to engage in severe study during the hours
just before bedtime. Neither body nor mind being at its best after the
fatigues of the day, study at that time wears upon the system more, and
the progress is less than at earlier hours. One hour of morning or day
study is worth a much longer time late at night. It is, therefore, an
economy both of time and of nerve force to use the day hours and the
early evening for study.

The so-called “cat naps” should never be made to serve as a substitute
for a full night’s sleep. They are largely a matter of habit, and are
detrimental to some as well as beneficial to others. Late hours are
usually associated with exposure, excitement, and various other drains
upon the nerve force, and hence are injurious.

It is better to sleep on one or other side than on the back. The head
should be somewhat raised, and a mattress is better than a feather bed.
The bedclothes should be sufficient, but not too heavy. Light tends to
prevent sleep, as do loud or abrupt sounds, but monotonous sounds aid
it.

291. Alcohol and the Brain. The unfortunate effects which alcoholic
drinks produce upon the brain and nervous system differ from the
destructive results upon other parts of the body in this respect, that
elsewhere the consequences are usually both less speedy and less
obvious. The stomach, the liver, and even the heart may endure for a
while the trespass of the narcotic poison, and not betray the invasion.
But the nervous system cannot, like them, suffer in silence.

In the other parts of the body the victim may (to a certain extent)
conceal from others the suffering of which he himself is painfully
conscious. But the tortured brain instantly reveals the calamity and
the shame, while the only one who may not fully realize it is the
victim himself. Besides this, the injuries inflicted upon other organs
affect only the body, but here they drag down the mind, ruin the
morals, and destroy the character.

The brain is indeed the most important organ of the body, as it
presides over all the others. It is the lofty seat of power and
authority. Here the king is on his throne. But if, by this malignant
adversary, the king himself be dethroned, his whole empire falls to
ruins.

292. How Alcohol Injures the Brain. The brain, the nerve centers, and
the nerves are all made up of nerve pulp, the softest and most delicate
tissue in the whole bodily structure. Wherever this fragile material
occurs in our bodies,—in the skull, the spine, the trunk, or the
limbs,—the all-wise Architect has carefully protected it from violence,
for a rough touch would injure it, or even tender pressure would
disturb its function.

It is a further indication of the supreme importance of the brain, that
about one-fifth of the entire blood of the body is furnished to it.
Manifestly, then, this vital organ must be tenderly cared for. It must
indeed be well nourished, and therefore the blood sent to it must be
highly nutrient, capable of supplying oxygen freely. This condition is
essential to successful brain action. But intoxicants bring to it blood
surcharged with a poisonous liquid, and bearing only a limited supply
of oxygen.

Another condition of a healthy brain is that the supply of blood to it
shall be equable and uniform. But under the influence of strong drink,
the blood pours into the paralyzed arteries a surging tide that floods
the head, and hinders and may destroy the use of the brain and the
senses. Still another requirement is that whatever is introduced into
the cerebral tissues, having first passed through the stomach walls and
thence into the blood, shall be bland, not irritating. But in the brain
of the inebriate are found not only the distinct odor but the actual
presence of alcohol. Thus we plainly see how all these three vital
conditions of a healthy brain are grossly violated by the use of
intoxicants.

“I think there is a great deal of injury being done by the use of
alcohol in what is supposed by the consumer to be a most moderate
quantity, to persons who are not in the least intemperate, and to
people supposed to be fairly well. It leads to degeneration of the
tissues; it damages the health; it injures the intellect. Short of
drunkenness, that is, in those effects of it which stop short of
drunkenness, I should say from my experience that alcohol is the most
destructive agent we are aware of in this country.”—Sir William Gull,
the most eminent English physician of our time.


293. Why the Brain Suffers from the Alcoholic Habit. We do not find
that the alcoholic habit has produced in the brain the same coarse
injuries that we see in other organs, as in the stomach, the liver, or
the heart. Nor should we expect to find them; for so delicate and so
sensitive is the structure of this organ, that a very slight injury
here goes a great way,—a disturbance may be overwhelming to the brain
that would be only a trifle to some of the less delicate organs.

Alcohol has different degrees of affinity for different organs of the
body, but much the strongest for the cerebral tissues. Therefore the
brain feels more keenly the presence of alcohol than does any other
organ. Almost the moment that the poison is brought into the stomach,
the nerves send up the alarm that an invading foe has come. At once
there follows a shock to the brain, and very soon its paralyzed
blood-vessels are distended with the rush of blood. This first effect
is, in a certain sense, exhilarating, and from this arousing influence
alcohol has been erroneously considered a stimulant; but the falsity of
this view is pointed out elsewhere in this book.

294. Alcohol, the Enemy of Brain Work. The healthy brain contains a
larger proportion of water than does any other organ. Now alcohol, with
its intense affinity for water, absorbs it from the brain, and thus
condenses and hardens its structure. One of the important elements of
the brain is its albumen; this also is contracted by alcohol. The nerve
cells and fibers gradually become shriveled and their activity is
lowered, the elasticity of the arteries is diminished, the membranes
enveloping the brain are thickened, and thus all proper brain nutrition
is impaired. The entire organ is slowly hardened, and becomes unfitted
for the proper performance of its delicate duties. In brief, alcohol in
any and every form is the enemy of successful and long-continued brain
work.

Illustration: Fig. 123.—Nerve Trunks of the Right Arm.


295. Other Physical Results of Intoxicants. What are some of the
physical results observed? First, we note the failure of the vaso-motor
nerves to maintain the proper tone of the blood-vessels, as in the
turgid face and the congested cornea of the eye. Again, we observe the
loss of muscular control, as is shown by the drop of the lower lip, the
thickened speech, and the wandering eye. The spinal cord, too, is often
affected and becomes unable to respond to the demand for reflex action,
as appears from the trembling hands, the staggering legs, the swaying
body, and the general muscular uncertainty. All these are varied
results of the temporary paralysis of the great nerve centers.

Besides, the sensibility of the nerves is deadened. The inebriate may
seize a hot iron and hardly know it, or wound his hand painfully and
never feel the injury. The numbness is not of the skin, but of the
brain, for the drunken man may be frozen or burned to death without
pain. The senses, too, are invaded and dulled. Double vision is
produced, the eyes not being so controlled as to bring the image upon
corresponding points of the retina.

296. Diseases Produced by Alcohol. The diseases that follow in the
train of the alcoholic habit are numerous and fatal. It lays its
paralyzing hand upon the brain itself, and soon permanently destroys
the integrity of its functions. In some the paralysis is local only,
perhaps in one of the limbs, or on one side of the body; in others
there is a general muscular failure. The vitality of the nerve centers
is so thoroughly impaired that general paralysis often ensues. A
condition of insomnia, or sleeplessness, often follows, or when sleep
does come, it is in fragments, and is far from refreshing to the jaded
body.

In time follows another and a terrible disease known as _delirium
tremens_; and this may occur in those who claim to be only moderate
drinkers, rarely if ever intoxicated. It accompanies an utter breakdown
of the nervous system. Here reason is for the time dethroned, while at
some times wild and frantic, or at others a low, mumbling delirium
occurs, with a marked trembling from terror and exhaustion.

There is still another depth of ruin in this downward course, and that
is _insanity_. In fact, every instance of complete intoxication is a
case of temporary insanity, that is, of mental unsoundness with loss of
self-control. Permanent insanity may be one of the last results of
intemperance. Alcoholism sends to our insane asylums a large proportion
of their inmates, as ample records testify.

297. Mental and Moral Ruin Caused by Alcoholism. Alcoholism, the evil
prince of destroyers, also hastens to lay waste man’s mental and moral
nature. Just as the inebriate’s senses, sight, hearing, and touch, fail
to report correctly of the outer world, so the mind fails to preside
properly over the inner realm. Mental perceptions are dulled. The
stupefied faculties can hardly be aroused by any appeal. Memory fails.
Thus the man is disqualified for any responsible labor. No railroad
company, no mercantile house, will employ any one addicted to drinking.
The mind of the drunkard is unable to retain a single chain of thought,
but gropes about with idle questionings. The intellect is debased.
Judgment is impossible, for the unstable mind cannot think, compare, or
decide.

The once active power of the will is prostrate, and the victim can no
longer resist the feeblest impulse of temptation. The grand faculty of
self-control is lost; and as a result, the baser instincts of our lower
nature are now uppermost; greed and appetite rule unrestrained.

But the moral power is also dragged down to the lowest depths. All the
finer sensibilities of character are deadened; all pride of personal
appearance, all nice self-respect and proper regard for the good
opinion of others, every sense of decorum, and at last every pretence
of decency. Dignity of behavior yields to clownish silliness, and the
person lately respected is now an object of pity and loathing. The
great central convictions of right and wrong now find no place in his
nature; conscience is quenched, dishonesty prevails. This is true both
as to the solemn promises, which prove mere idle tales, and also as to
property, for he resorts to any form of fraud or theft to feed the
consuming craving for more drink.

298. Evil Results of Alcoholism Inherited. But the calamity does not
end with the offender. It may follow down the family line, and fasten
itself upon the unoffending children. These often inherit the craving
for drink, with the enfeebled nature that cannot resist the craving,
and so are almost inevitably doomed to follow the appalling career of
their parents before them.

Nor does this cruel taint stop with the children. Even their
descendants are often prone to become perverse. As one example, careful
statistics of a large number of families, more than two hundred
descended from drunkards, show that a very large portion of them gave
undoubted proof of well-marked degeneration. This was plain in the
unusual prevalence of infant mortality, convulsions, epilepsy,
hysteria, fatal brain diseases, and actual imbecility.[42]

It is found that the long-continued habitual user of alcoholic drinks,
the man who is never intoxicated, but who will tell you that he has
drunk whiskey all his life without being harmed by it, is more likely
to transmit the evil effects to his children than the man who has
occasional drunken outbreaks with intervals of perfect sobriety
between. By his frequently repeated small drams he keeps his tissues
constantly “alcoholized” to such an extent that they are seldom free
from some of the more or less serious consequences. His children are
born with organisms which have received a certain bias from which they
cannot escape; they are freighted with some heredity, or predisposition
to particular forms of degeneration, to some morbid tendency, to an
enfeebled constitution, to various defective conditions of mind and
body. Let the children of such a man attempt to imitate the drinking
habits of the father and they quickly show the effects. Moderate
drinking brings them down.

Among other consequences of an alcoholic inheritance which have been
traced by careful observers are: Morbid changes in the nerve centers,
consisting of inflammatory lesions, which vary according to the age in
which they occur; alcoholic insanity; congenital malformations; and a
much higher infant death rate, owing to lack of vitality, than among
the children of normal parents.

Where the alcoholic inheritance does not manifest itself in some
definite disease or disorder, it can still be traced in the limitations
to be found in the drinking man’s descendants. They seem to reach a
level from which they cannot ascend, and where from slight causes they
deteriorate. The parents, by alcoholic poisoning, have lowered the race
stock of vitality beyond the power of ascent or possibility to rise
above or overcome the downward tendency.

Of course these effects of alcoholics differ widely according to the
degree of intoxication. Yet, we must not forget that the real nature of
inebriety is always the same. The end differs from the beginning only
in degree. He who would avoid a life of sorrow, disgrace, and shame
must carefully shun the very first glass of intoxicants.

299. Opium. Opium is a gum-like substance, the dried juice of the
unripe capsule of the poppy. The head of the plant is slit with fine
incisions, and the exuding white juice is collected. When it thickens
and is moulded in mass, it becomes dark with exposure. _Morphine_, a
white powder, is a very condensed form of opiate; _laudanum_, an
alcoholic solution of marked strength; and _paregoric_, a diluted and
flavored form of alcoholic tincture.

300. Poisonous Effects of Opium. Some persons are drawn into the use of
opium, solely for its narcotic and intoxicating influence. Every early
consent to its use involves a lurking pledge to repeat the poison, till
soon strong cords of the intoxicant appetite bind the now yielding
victim.

Opium thus used lays its benumbing hand upon the brain, the mind is
befogged, thought and reasoning are impossible. The secretions of the
stomach are suspended, digestion is notably impaired, and the gastric
nerves are so deadened that the body is rendered unconscious of its
needs.

The moral sense is extinguished, persons once honest resort to fraud
and theft, if need be, to obtain the drug, till at last health,
character, and life itself all become a pitiful wreck.

301. The Use of Opium in Patent Medicines. Some forms of this drug are
found in nearly all the various patent medicines so freely sold as a
cure-all for every mortal disease. Opiates are an ingredient in
different forms and proportions in almost all the soothing-syrups,
cough medicines, cholera mixtures, pain cures, and consumption
remedies, so widely and unwisely used. Many deaths occur from the use
of these opiates, which at first seem indeed to bring relief, but
really only smother the prominent symptoms, while the disease goes on
unchecked, and at last proves fatal.

These patent medicines may appear to help one person and be fraught
with danger to the next, so widely different are the effects of opiates
upon different ages and temperaments. But it is upon children that
these fatal results oftenest fall. Beyond doubt, thousands of children
have been soothed and soothed out of existence.[43]

302. The Victim of the Opium Habit. Occasionally persons convalescing
from serious sickness where anodynes were taken, unwisely cling to them
long after recovery. Other persons, jaded with business or with worry,
and unable to sleep, unwisely resort to some narcotic mixture to
procure rest. In these and other similar cases, the use of opiates is
always most pernicious. The amount must be steadily increased to obtain
the elusive repose, and at best the phantom too often escapes.

Even if the desired sleep is procured, it is hardly the coveted rest,
but a troubled and dreamy slumber, leaving in the morning the body
quite unrefreshed, the head aching, the mouth dry, and the stomach
utterly devoid of appetite. But far worse than even this condition is
the slavish yielding to the habit, which soon becomes a bondage in
which life is shorn of its wholesome pleasures, and existence becomes a
burden.

303. Chloral. There are other preparations which have become
instruments of direful and often fatal injury. Chloral is a powerful
drug that has been much resorted to by unthinking persons to produce
sleep. Others, yielding to a morbid reluctance to face the problems of
life, have timidly sought shelter in artificial forgetfulness. To all
such it is a false friend. Its promises are treason. It degrades the
mind, tramples upon the morals, overpowers the will, and destroys life
itself.

304. Cocaine, Ether, Chloroform, and Other Powerful Drugs. Another
dangerous drug is Cocaine. Ether and chloroform, those priceless
blessings to the human race if properly controlled, become instruments
of death when carelessly trifled with. Persons who have been accustomed
to inhale the vapor in slight whiffs for neuralgia or similar troubles
do so at imminent hazard, especially if lying down. They are liable to
become slowly unconscious, and so to continue the inhalation till life
is ended.

There is still another class of drugs often carelessly used, whose
effect, while less directly serious than those mentioned, is yet far
from harmless. These drugs, which have sprung into popular use since
the disease _la grippe_ began its dreaded career, include
_phenacetine_, _antipyrine_, _antifebrine_, and other similar
preparations. These drugs have been seized by the public and taken
freely and carelessly for all sorts and conditions of trouble. The
random arrow may yet do serious harm. These drugs, products of coal-oil
distillation, are powerful depressants. They lower the action of the
heart and the tone of the nervous centers. Thus the effect of their
continued use is to so diminish the vigor of the system as to aggravate
the very disorder they are taken to relieve.

305. Effect of Tobacco on the Nervous System. That the use of tobacco
produces a pernicious effect upon the nervous system is obvious from
the indignant protest of the entire body against it when it is first
used. Its poisonous character is amply shown by the distressing
prostration and pallor, the dizziness and faintness, with extreme
nausea and vomiting, which follow its employment by a novice.

The morbid effects of tobacco upon the nervous system of those who
habitually use it are shown in the irregular and enfeebled action of
the heart, with dizziness and muscular tremor. The character of the
pulse shows plainly the unsteady heart action, caused by partial
paralysis of the nerves controlling this organ. Old, habitual smokers
often show an irritable and nervous condition, with sleeplessness, due
doubtless to lack of proper brain nutrition.

All these results tend to prove that tobacco is really a nerve poison,
and there is reason to suspect that the nervous breakdown of many men
in mature life is often due to the continued use of this depressing
agent. This is shown more especially in men of sedentary life and
habits, as men of active habits and out-door life, experience less of
the ill effects of tobacco.

Few, if any, habitual users of tobacco ever themselves approve of it.
They all regret the habit, and many lament they are so enslaved to it
that they cannot throw it off. They very rarely advise any one to
follow their example.

306. Effects of Tobacco on the Mind. With this continuously depressing
effect of tobacco upon the brain, it is little wonder that the mind may
become enfeebled and lose its capacity for study or successful effort.
This is especially true of the young. The growth and development of the
brain having been once retarded, the youthful user of tobacco
(especially the foolish cigarette-smoker) has established a permanent
drawback which may hamper him all his life.

The young man addicted to the use of tobacco is often through its use
retarded in his career by mental languor or weakening will power, and
by mental incapacity. The keenness of mental perception is dulled, and
the ability to seize and hold an abstract thought is impaired. True,
these effects are not sharply obvious, as it would be impossible to
contrast the present condition of any one person with what it might
have been. But the comparison of large numbers conveys an instructive
lesson. Scholars who start well and give promise of a good future fail
by the way. The honors of the great schools, academies, and colleges
are very largely taken by the tobacco abstainers. This is proved by the
result of repeated and extensive comparisons of the advanced classes in
a great number of institutions in this country and in Europe. So true
is this that any young man who aspires to a noble career should bid
farewell either to his honorable ambition or to his tobacco, for the
two very rarely travel together. Consequently our military and naval
academies and very many seminaries and colleges prohibit the use of
tobacco by their students. For the same reasons the laws of many states
very properly forbid the sale to boys of tobacco, and especially of
cigarettes.

307. Effect of Tobacco upon Character. Nor does tobacco spare the
morals. The tobacco-user is apt to manifest a selfish disregard of the
courtesies due to others. He brings to the presence of others a
repulsive breath, and clothing tainted with offensive odors. He poisons
the atmosphere that others must inhale, and disputes their rights to
breathe a pure, untainted air. The free use of tobacco by young people
dulls the acuteness of the moral senses, often leads to prevarication
and deceit in the indulgence, and is apt to draw one downward to bad
associates. It is not the speed but the direction that tells on the
future character and destiny of young men.

Additional Experiments.

Experiment 132. _To illustrate the cooperation of certain parts of the
body._ Tickle the inside of the nose with a feather. This does not
interfere with the muscles of breathing, but they come to the help of
the irritated part, and provoke sneezing to clear and protect the nose.

Experiment 133. Pretend to aim a blow at a person’s eye. Even if he is
warned beforehand, the lids will close in spite of his effort to
prevent them.

Experiment 134. _To illustrate how sensations are referred to the ends
of the nerves_. Strike the elbow end of the ulna against anything hard
(commonly called “hitting the crazy bone”) where the ulna nerve is
exposed, and the little finger and the ring finger will tingle and
become numb.

Experiment 135. _To show that every nerve is independent of any other._
Press two fingers closely together. Let the point of the finest needle
be carried ever so lightly across from one finger to another, and we
can easily tell just when the needle leaves one finger and touches the
other.

Experiment 136. _To paralyze a nerve temporarily_. Throw one arm over
the sharp edge of a chair-back, bringing the inner edge of the biceps
directly over the edge of the chair. Press deep and hard for a few
minutes. The deep pressure on the nerve of the arm will put the arm
“asleep,” causing numbness and tingling. The leg and foot often “get
asleep” by deep pressure on the nerves of the thigh.

Experiment 137. Press the ulnar nerve at the elbow, the prickling
sensation is referred to the skin on the ulnar side of the hand.

Experiment 138. Dip the elbow in ice-cold water; at first one feels the
sensation of cold, owing to the effect on the cutaneous nerve-endings.
Afterwards, when the trunk of the ulnar nerve is affected, pain is felt
in the skin of the ulnar side of the hand, where the nerve terminates.



Chapter XI.
The Special Senses.


308. The Special Senses. In man certain special organs are set apart
the particular duty of which is to give information of the nature of
the relations which he sustains to the great world of things, and of
which he is but a mere speck. The special senses are the avenues by
which we obtain this information as to our bodily condition, the world
around us, and the manner in which it affects us.

Animals high in the scale are affected in so many different ways, and
by so many agencies, that a subdivision of labor becomes necessary that
the sense avenues may be rigidly guarded. One person alone may be a
sufficient watch on the deck of a sloop, but an ocean steamer needs a
score or more on guard, each with his special duty and at his own post.
Or the senses are like a series of disciplined picket-guards, along the
outposts of the mind, to take note of events, and to report to
headquarters any information which may be within the range of their
duty.

Thus it is that we are provided with a number of special senses, by
means of which information is supplied regarding outward forces and
objects. These are touch, taste, smell, seeing, and hearing, to which
may be added the muscular sense and a sense of temperature.

309. General Sensations. The body, as we have learned, is made up of a
great number of complicated organs, each doing its own part of the
general work required for the life and vigor of the human organism.
These organs should all work in harmony for the good of the whole. We
must have some means of knowing whether this harmony is maintained, and
of receiving timely warning if any organ fails to do its particular
duty.

Such information is supplied by the common or general sensations. Thus
we have a feeling of hunger or thirst indicating the need of food, and
a feeling of discomfort when imperfectly clad, informing us of the need
of more clothing.

To these may be added the sensation of pain, tickling, itching, and so
on, the needs of which arise from the complicated structure of the
human body. The great majority of sensations result from some stimulus
or outward agency; and yet some sensations, such as those of faintness,
restlessness, and fatigue seem to spring up within us in some
mysterious way, without any obvious cause.

310. Essentials of a Sense Organ. Certain essentials are necessary for
a sensation. First, there is a special structure adapted to a
particular kind of influence. Thus the ear is formed specially for
being stimulated by the waves of sound, while the eye is not influenced
by sound, but responds to the action of light. These special structures
are called terminal organs.

Again, a nerve proceeds from the special structure, which is in direct
communication with nerve cells in the brain at the region of
consciousness. This last point is important to remember, for if on some
account the impression is arrested in the connecting nerve, no
sensation will result. Thus a man whose spine has been injured may not
feel a severe pinch on either leg. The impression may be quite
sufficient to stimulate a nerve center in a healthy cord, so as to
produce a marked reflex act, but he has no sensation, because the
injury has prevented the impression from being carried up the cord to
the higher centers in the brain.

311. The Condition of Sensation. It is thus evident that while an
impression may be made upon a terminal organ, it cannot strictly be
called a sensation until the person becomes conscious of it. The
consciousness of an impression is, therefore, the essential element of
a sensation.

It follows that sensation may be prevented in various ways. In the
sense of sight, for example, one person may be blind because the
terminal organ, or eye, is defective or diseased. Another may have
perfect eyes and yet have no sight, because a tumor presses on the
nerve between the eye and the brain. In this case, the impression fails
because of the break in the communication. Once more, the eye may be
perfect and the nerve connection unbroken, and yet the person cannot
see, because the center in the brain itself is injured from disease or
accident, and cannot receive the impression.

312. The Functions of the Brain Center in the Perception of an
Impression. Sensation is really the result of a change which occurs in
a nerve center in the brain, and yet we refer impressions to the
various terminal organs. Thus, when the skin is pinched, the sensation
is referred to the skin, although the perception is in the brain. We
may think it is the eyes that see objects; in reality, it is only the
brain that takes note of them.

This is largely the result of education and habit. From a blow on the
head one sees flashes of light as vividly as if torches actually dance
before the eyes. Impressions have reached the seeing-center in the
brain from irritation of the optic nerve, producing the same effect as
real lights would cause. In this case, however, knowing the cause of
the colors, the person is able to correct the erroneous conclusion.

As a result of a depraved condition of blood, the seeing-center itself
may be unduly stimulated, and a person may see objects which appear
real. Thus in an attack of delirium tremens, the victim of alcoholic
poisoning sees horrible and fantastic creatures. The diseased brain
refers them as usual to the external world; hence they appear real. As
the sufferer’s judgment is warped by the alcoholic liquor, he cannot
correct the impressions, and is therefore deceived by them.

313. Organs of Special Sense. The organs of special sense, the means by
which we are brought into relation with surrounding objects, are
usually classed as five in number. They are sometimes fancifully called
“the five gateways of knowledge”—the skin, the organ of touch; the
tongue, of taste; the nose, of smell; the eye, of sight; and the ear,
of hearing.

Illustration: Fig. 124.—Magnified View of a Papilla of the Skin, with a
Touch Corpuscle.


314. The Organ of Touch. The organ of touch, or tactile sensibility, is
the most widely extended of all the special senses, and perhaps the
simplest. It is certainly the most precise and certain in its results.
It is this sense to which we instinctively appeal to escape from the
illusions into which the other senses may mislead us. It has its seat
in the skin all over the body, and in the mucous membrane of the
nostrils. All parts of the body, however, do not have this sense in an
equal degree.

In Chapter IX. we learned that the superficial layers of the skin
covers and dips in between the papillæ. We also learned that these
papillæ are richly provided with blood-vessels and sensory nerve fibers
(sec. 234). Now these nerve fibers terminate in a peculiar way in those
parts of the body which are endowed with a very delicate sense of
touch. In every papilla are oval-shaped bodies about 1/300 of an inch
long, around which the nerve fibers wind, and which they finally enter.
These are called touch-bodies, or tactile corpuscles, and are found in
great numbers on the feet and toes, and more scantily in other places,
as on the edges of the eyelids.

Again, many of the nerve fibers terminate in corpuscles, the largest
about 1/20 of an inch long, called Pacinian corpuscles. These are most
numerous in the palm of the hand and the sole of the foot. In the
papillæ of the red border of the lips the nerves end in capsules which
enclose one or more fibers, and are called end-bulbs.

The great majority of the nerve fibers which supply the skin do not end
in such well-defined organs. They oftener divide into exceedingly
delicate filaments, the terminations of which are traced with the
greatest difficulty.

315. The Sense of Touch. Touch is a sensation of contact referred to
the surface of the body. It includes three things,—the sense of
contact, the sense of pressure, and the sense of heat and cold.

The sense of contact is the most important element in touch. By it we
learn of the form, size, and other properties of objects, as their
smoothness and hardness. As we all know, the sense of touch varies in
different parts of the skin. It is most acute where the outer skin is
thinnest. The tips of the fingers, the edges of the lips, and the tip
of the tongue are the most sensitive parts.

Even the nails, the teeth, and the hair have the sense of touch in a
slight degree. When the scarf skin is removed, the part is not more
sensitive to sense of contact. In fact, direct contact with the
unprotected true skin occasions pain, which effectually masks the
feeling of touch. The sense of touch is capable of education, and is
generally developed to an extraordinary degree in persons who are
deprived of some other special sense, as sight or hearing. We read of
the famous blind sculptor who was said to model excellent likenesses,
guided entirely by the sense of touch. An eminent authority on botany
was a blind man, able to distinguish rare plants by the fingers, and by
the tip of the tongue. The blind learn to read with facility by passing
their fingers over raised letters of a coarse type. It is impossible to
contemplate, even for a moment, the prominence assigned to the sense of
touch in the physical organism, without being impressed with the
manifestations of design—the work of an all-wise Creator.

316. Muscular Sense; Sense of Temperature; Pain. When a heavy object is
laid upon certain parts of the body, it produces a sensation of
pressure. By it we are enabled to estimate differences of weight. If an
attempt be made to raise this object, it offers resistance which the
muscles must overcome. This is known as the muscular sense. It depends
on sensory nerves originating in the muscles and carrying impressions
from them to the nerve centers.

The skin also judges, to a certain extent, of heat and cold. These
sensations can be felt only by the skin. Direct irritation of a nerve
does not give rise to them. Thus, the exposed pulp of a diseased tooth,
when irritated by cold fluids, gives rise to pain, and not to a
sensation of temperature. Various portions of the body have different
degrees of sensibility in this respect. The hand will bear a degree of
heat which would cause pain to some other parts of the body. Then,
again, the sensibility of the outer skin seems to affect the
sensibility to heat, for parts with a thin skin can bear less heat than
portions with a thick cuticle.

Experiment 139. _To illustrate how the sense of touch is a matter of
habit or education_. Shut both eyes, and let a friend run the tips of
your fingers first lightly over a hard plane surface; then press hard,
then lightly again, and the surface will seem to be concave.

Experiment 140. Cross the middle over the index finger, roll a small
marble between the fingers; one has a distinct impression of two
marbles. Cross the fingers in the same way, and rub them against the
point of the nose. A similar illusion is experienced.

Experiment 141. _To test the sense of locality_. Ask a person to shut
his eyes, touch some part of his body lightly with the point of a pin,
and ask him to indicate the part touched.
    As to the general temperature, this sense is relative and is much
    modified by habit, for what is cold to an inhabitant of the torrid
    zone would be warm to one accustomed to a very cold climate.
    Pain is an excessive stimulation of the sensory nerves, and in it
    all finer sensations are lost. Thus, when a piece of hot iron burns
    the hand, the sensation is the same as when the iron is very cold,
    and extreme cold feels like intense heat.

317. The Organ of Taste. The sense of taste is located chiefly in the
tongue, but may also be referred even to the regions of the fauces.
Taste, like touch, consists in a particular mode of nerve termination.

The tongue is a muscular organ covered with mucous membrane, and is
richly supplied with blood-vessels and nerves. By its complicated
movements it is an important factor in chewing, in swallowing, and in
articulate speech. The surface of the tongue is covered with irregular
projections, called papillæ,—fine hair-like processes, about 1/12 of an
inch high. Interspersed with these are the fungiform papillæ. These are
shaped something like a mushroom, and may often be detected by their
bright red points when the rest of the tongue is coated.

Towards the root of the tongue is another kind of papillæ, the
circumvallate, eight to fifteen in number, arranged in the form of the
letter V, with the apex directed backwards. These are so called because
they consist of a fungiform papilla surrounded by a fold of mucous
membrane, presenting the appearance of being walled around.

In many of the fungiform and most of the circumvallate papillæ are
peculiar structures called taste buds or taste goblets. These exist in
great numbers, and are believed to be connected with nerve fibers.
These taste buds are readily excited by savory substances, and transmit
the impression along the connected nerve.

The tongue is supplied with sensory fibers by branches from the fifth
and eighth pairs of cranial nerves. The former confers taste on the
front part of the tongue, and the latter on the back part. Branches of
the latter also pass to the soft palate and neighboring parts and
confer taste on them. The motor nerve of the tongue is the ninth pair,
the hypoglossal.

Illustration: Fig. 125.—The Tongue.


A,  epiglottis;
  B, glands at the base of tongue;
  C, tonsil;
  D, median circumvallate papilla,
  E, circumvallate papillæ;
  F, filiform papillæ;
  H, furrows on border of the tongue;
  K, fungiform papillæ.


318. The Sense of Taste. The sense of taste is excited by stimulation
of the mucous membrane of the tongue and of the palate, affecting the
ends of the nerve fibers. Taste is most acute in or near the
circumvallate papillæ. The middle of the tongue is scarcely sensitive
to taste, while the edges and the tip are, as a rule, highly sensitive.

Certain conditions are necessary that the sense of taste may be
exercised. First, the substance to be tasted must be in _solution_, or
be soluble in the fluids of the mouth. Insoluble substances are
tasteless. If we touch our tongue to a piece of rock crystal, there is
a sensation of contact or cold, but no sense of taste. On the other
hand, when we bring the tongue in contact with a piece of rock salt, we
experience the sensations of contact, coolness, and saline taste.

Again, the mucous membrane of the mouth must be _moist_. When the mouth
is dry, and receives substances not already in solution, there is no
saliva ready to dissolve them; hence, they are tasteless. This absence
of taste is common with the parched mouth during a fever.

The tongue assists in bringing the food in contact with the nerves, by
pressing it against the roof of the mouth and the soft palate, and thus
is produced the fullest sense of taste.

319. Physiological Conditions of Taste. The tongue is the seat of
sensations which are quite unlike each other. Thus, besides the sense
of taste, there is the sensation of touch, pressure, heat and cold,
burning or acrid feelings, and those produced by the application of the
tongue to an interrupted electric current. These are distinct
sensations, due to some chemical action excited probably in the touch
cells, although the true tastes may be excited by causes not strictly
chemical. Thus a smart tap on the tongue may excite the sensation of
taste.

In the majority of persons the back of the tongue is most sensitive to
bitters, and the tip to sweets. Saline matters are perceived most
distinctly at the tip, and acid substances at the sides. The nerves of
taste are sensitive in an extraordinary degree to some articles of food
and certain drugs. For example, the taste of the various preparations
of quinine, peppermint, and wild cherry is got rid of with difficulty.

Like the other special senses, that of taste may become fatigued. The
repeated tasting of one substance rapidly deadens the sensibility,
probably by over-stimulation. Some savors so impress the nerves of
taste that others fail to make any impression. This principle is used
to make disagreeable medicine somewhat tasteless. Thus a few cloves, or
grains of coffee, or a bit of pepper, eaten before a dose of castor
oil, renders it less nauseous.

Flavor is something more than taste. It is in reality a mixed
sensation, in which smell and taste are both concerned, as is shown by
the common observation that one suffering from a cold in the head,
which blunts his sense of smell, loses the proper flavor of his food.
So if a person be blindfolded, and the nose pinched, he will be unable
to distinguish between an apple and an onion, if one be rubbed on the
tongue after the other. As soon as the nostrils are opened the
difference is at once perceived.

Experiment 142. Put a drop of vinegar on a friend’s tongue, or on your
own. Notice how the papillæ of the tongue start up.

Experiment 143. Rub different parts of the tongue with the pointed end
of a piece of salt or gum-aloes, to show that the _back_ of the tongue
is most sensitive to salt and bitter substances.

Experiment 144. Repeat the same with some sweet or sour substances, to
show that the _edges_ of the tongue are the most sensitive to these
substances.

Experiment 145. We often fail to distinguish between the sense of taste
and that of smell. Chew some pure, roasted coffee, and it seems to have
a distinct taste. Pinch the nose hard, and there is little taste.
Coffee has a powerful odor, but only a feeble taste. The same is true
of garlic, onions, and various spices.

Experiment 146. Light helps the sense of taste. Shut the eyes, and
palatable foods taste insipid. Pinch the nose, close the eyes, and see
how palatable one half of a teaspoonful of cod-liver oil becomes.

Experiment 147. Close the nostrils, shut the eyes, and attempt to
distinguish by taste alone between a slice of an apple and one of a
potato.

320. Modifications of the Sense of Taste. Taste is modified to a great
extent by habit, education, and other circumstances. Articles of food
that are unpleasant in early life often become agreeable in later
years. There is occasionally a craving, especially with people of a
peculiar nervous organization, for certain unnatural articles (as chalk
and laundry starch) which are eaten without the least repugnance.
Again, the most savory dishes may excite disgust, while the simplest
articles may have a delicious flavor to one long deprived of them. The
taste for certain articles is certainly acquired. This is often true of
raw tomatoes, olives, and especially of tobacco.

The organs of taste and smell may be regarded as necessary accessories
of the general apparatus of nutrition, and are, therefore, more or less
essential to the maintenance of animal life. While taste and smell are
generally maintained until the close of life, sight and hearing are
often impaired by time, and may be altogether destroyed, the other
vital functions remaining unimpaired.

321. Effect of Tobacco and Alcohol upon Taste. It would be remarkable
if tobacco should fail to injure the sense of taste. The effect
produced upon the tender papillæ of the tongue by the nicotine-loaded
juices and the acrid smoke tends to impair the delicate sensibility of
the entire surface. The keen appreciation of fine flavors is destroyed.
The once clear and enjoyable tastes of simple objects become dull and
vapid; thus highly spiced and seasoned articles of food are in demand,
and then follows continued indigestion, with all its suffering.

Again, the burning, almost caustic effect of the stronger alcoholic
drinks, and the acrid pungency of tobacco smoke, are disastrous to the
finer perceptions of both taste and odors.

322. Smell. The sense of smell is lodged in the delicate membrane which
lines the nasal cavities. The floor, sides, and roof of these cavities
are formed by certain bones of the cranium and the face. Man, in common
with all air-breathing animals, has two nasal cavities. They
communicate with the outer air by two nostrils opening in front, while
two other passages open into the pharynx behind.

To increase the area of the air passages, the two light, spongy
turbinated bones, one on each side, form narrow, winding channels. The
mucous membrane, with the branches of the olfactory nerve, lines the
dividing wall and the inner surfaces of these winding passages. Below
all these bones the lower turbinated bones may be said to divide the
olfactory chamber above from the ordinary air passages.

Illustration: Fig. 126.—Distribution of Nerves over the Interior of the
Nostrils. (Outer wall.)


A,  branches of the nerves of smell—olfactory nerve, or ganglion;
  B, nerves of common sensation to the nostril;
  E, F, G, nerves to the, palate springing from a ganglion at C;
  H, vidian nerve, from which branches
  D, I, and J spring to be distributed to the nostrils.

The nerves which supply the nasal mucous membrane are derived from the
branches of the fifth and the first pair of cranial nerves,—the
olfactory. The latter, however, are the nerves of smell proper, and are
spread out in a kind of thick brush of minute nerve filaments. It is in
the mucous membrane of the uppermost part of the cavity of the nostril
that the nerve endings of smell proper reside. The other nerves which
supply the nostrils are those of common sensation (sec. 271).

323. The Sense of Smell. The sense of smell is excited by the contact
of odorous particles contained in the air, with the fibers of the
olfactory nerves, which are distributed over the delicate surface of
the upper parts of the nasal cavities. In the lower parts are the
endings of nerves of ordinary sensation. These latter nerves may be
irritated by some substance like ammonia, resulting in a powerfully
pungent sensation. This is not a true sensation of smell, but merely an
irritation of a nerve of general sensation.

In ordinary quiet breathing, the air simply flows along the lower nasal
passages into the pharynx, scarcely entering the olfactory chamber at
all. This is the reason why, when we wish to perceive a faint odor, we
sniff up the air sharply. By so doing, the air which is forcibly drawn
into the nostrils passes up even into the higher olfactory chamber,
where some of the floating particles of the odorous material come into
contact with the nerves of smell.

One of the most essential conditions of the sense of smell is that the
nasal passages be kept well bathed in the fluid secreted by the lining
membrane. At the beginning of a cold in the head, this membrane becomes
dry and swollen, thus preventing the entrance of air into the upper
chamber, deadening the sensibility of the nerves, and thus the sense of
smell is greatly diminished.

The delicacy of the sense of smell varies greatly in different
individuals and in different animals. It is generally more acute in
savage races. It is highly developed in both the carnivora and the
herbivora. Many animals are more highly endowed with this sense than is
man. The dog, for example, appears to depend on the sense of smell
almost as much as on sight. It is well known, also, that fishes have a
sense of smell. Fragments of bait thrown into the water soon attract
them to a fishing ground, and at depths which little or no light can
penetrate. Deer, wild horses, and antelopes probably surpass all other
animals in having a vivid sense of smell.

Smell has been defined as “taste at a distance,” and it is obvious that
these two senses not only form a natural group, but are clearly
associated in their physical action, especially in connection with the
perception of the flavor of food. The sense of odor gives us
information as to the quality of food and drink, and more especially as
to the quality of the air we breathe. Taste is at the gateway of the
alimentary canal, while smell acts as the sentinel of the respiratory
tract. Just as taste and flavor influence nutrition by affecting the
digestive process, so the agreeable odors about us, even those of the
perfumes, play an important part in the economy of life.

324. The Sense of Sight. The sight is well regarded as the highest and
the most perfect of all our senses. It plays so common and so
beneficent a part in the animal economy that we scarcely appreciate
this marvelous gift. Sight is essential not only to the simplest
matters of daily comfort and necessity, but is also of prime importance
in the culture of the mind and in the higher forms of pleasure. It
opens to us the widest and the most varied range of observation and
enjoyment. The pleasures and advantages it affords, directly and
indirectly, have neither cessation nor bounds.

Apart from its uses, the eye itself is an interesting and instructive
object of study. It presents beyond comparison the most beautiful
example of design and artistic workmanship to be found in the bodily
structure. It is the watchful sentinel and investigator of the external
world. Unlike the senses of taste and smell we seem, by the sense of
vision, to become aware of the existence of objects which are entirely
apart from us, and which have no direct or material link connecting
them with our bodies. And yet we are told that in vision the eye is
affected by something which is as material as any substance we taste or
smell.

Note. “The higher intelligence of man is intimately associated with the
perfection of the eye. Crystalline in its transparency, sensitive in
receptivity, delicate in its adjustments, quick in its motions, the eye
is a fitting servant for the eager soul, and, at times, the truest
interpreter between man and man of the spirit’s inmost workings. The
rainbow’s vivid hues and the pallor of the lily, the fair creations of
art and the glance of mutual affection, all are pictured in its
translucent depths, and transformed and glorified by the mind within.
Banish vision, and the material universe shrinks for us to that which
we may touch; sight alone sets us free to pierce the limitless abyss of
space.”—M’Kendrick and Snodgrass’s _Physiology of the Senses_.

Physicists tell us that this material, known as the _luminiferous
ether_, permeates the universe, and by its vibrations transmits
movements which affect the eye, giving rise to the sensation of light,
and the perception of even the most distant objects. Our eyes are so
constructed as to respond to the vibrations of this medium for the
transmission of light.

325. The Eye. The eye, the outer instrument of vision, is a most
beautiful and ingenious machine. All its parts are arranged with such a
delicate adjustment to one another, and such an exquisite adaptation of
every part to the great object of the whole, that the eye is properly
regarded as one of the wonders of nature.

The eyeball is nearly spherical in shape, but is slightly elongated
from before backwards. The front part is clear and transparent, and
bulges somewhat prominently to allow the entrance of the rays of light.
The eye rests in a bowl-shaped socket, called the orbit, formed by
parts of various bones of the head and face. The margins of this cavity
are formed of strong bone which can withstand heavy blows. The socket
is padded with loose, fatty tissue, and certain membranes, which serve
as a soft and yielding bed in which the eyeball can rest and move
without injury. In a severe sickness this fatty tissue is absorbed, and
this fact explains the sunken appearance of the eyes.

The orbit is pierced through its posterior surface by an opening
through which the nerve of sight, the optic, passes to the eyeball. We
may think of the optic nerve holding the eyeball much as the stem holds
the apple. It is the function of this most important nerve to transmit
retinal impressions to the seat of consciousness in the brain, where
they are interpreted.

The eye is bathed with a watery fluid, and protected by the eyelids and
the eyebrows; it is moved in various directions, by muscles, all of
which will soon be described.

Illustration: Fig. 127.—Section of the Human Eye.


326. The Coats of the Eyeball. The eyeball proper is elastic but firm,
and is composed of three coats, or layers, each of which performs
important functions. These coats are the sclerotic, the choroid, and
the retina.

The sclerotic coat is the outside layer and enclosing membrane of the
eyeball. It is a tough, fibrous coat for the protection and maintenance
of the shape of the eye. It is white and glistening in appearance, and
is in part visible, to which the phrase, “the white of the eye,” is
applied. To this coat, which serves as a kind of framework for the eye,
are attached the muscles which move the eyeball. In front of the globe,
the sclerotic passes into a transparent circular portion forming a
window through which one can see into the interior. This is the cornea.

The cornea, a clear, transparent, circular disk, fits into the
sclerotic, somewhat as the crystal fits into the metallic case of a
watch, forming a covering for its dial. It projects from the general
contour of the eyeball, not unlike a rounded bay-window, and is often
spoken of as the “window of the eye.”

Lining the inner surface of the sclerotic is the second coat, the
choroid. It is dark in color and fragile in structure, and is made up
almost entirely of blood-vessels and nerves. As the choroid approaches
the front part of the eyeball, its parts become folded upon themselves
into a series of ridges, called ciliary processes. These folds
gradually become larger, and at last merge into the ciliary or
accommodation muscle of the eye. The circular space thus left in front
by the termination of the choroid is occupied by the iris, a thin,
circular curtain, suspended in the aqueous humor behind the cornea and
in front of the crystalline lens. In its center is a round opening for
the admission of light.

This is the pupil, which appears as if it were a black spot. The back
of the iris is lined with dark pigment, and as the coloring matter is
more or less abundant, we may have a variety of colors. This pigment
layer and that of the choroid and retina absorb the light entering the
eye, so that little is reflected.

The pupil appears black, just as the open doorway to a dark closet
seems black. The margin of the iris is firmly connected with the
eyeball all round, at the junction of the sclerotic and the cornea.

327. The Retina. The third and innermost coat of the eyeball is the
retina. This is the perceptive coat, without which it would be
impossible to see, and upon which the images of external objects are
received. It lines nearly the whole of the inner surface of the
posterior chamber, resting on the inner surface of the choroid. It is
with the retina, therefore, that the vitreous humor is in contact.

The retina is a very thin, delicate membrane. Although very thin, it is
made up of ten distinct layers, and is so complicated in structure that
not even a general description will be attempted in this book. It does
not extend quite to the front limits of the posterior chamber, but
stops short in a scalloped border, a little behind the ciliary
processes. This is the nerve coat of the eye, and forms the terminal
organ of vision. It is really an expansion of the ultimate fibers of
the optic nerve, by means of which impressions are sent to the brain.

The retina contains curious structures which can be seen only with the
aid of the microscope. For instance, a layer near the choroid is made
up of nerve cells arranged in innumerable cylinders called “rods and
cones,” and packed together not unlike the seeds of a sunflower. These
rods and cones are to be regarded as the peculiar modes of termination
of the nerve filaments of the eye, just as the taste buds are the modes
of termination of the nerve of taste in the tongue, and just as the
touch corpuscles are the terminations of the nerves in the skin.

Experiment 148. Close one eye and look steadily at the small a in the
figure below. The other letters will also be visible at the same time.
If now the page be brought slowly nearer to the eye while the eye is
kept steadily looking at the small a, the large A will disappear at a
certain point, reappearing when the book is brought still nearer.

Illustration:

On the reappearance of the A it will be noted that it comes into view
from the inner side, the x being seen before it. If now we move the
book towards its original place, the A will again disappear, coming
again into view from the outer side when the o is seen before it.

328. Inner Structure of the Eye. Let us imagine an eyeball divided
through the middle from above downwards. Let us now start in front and
observe its parts (Fig. 127). We come first to the cornea, which has
just been described. The iris forms a sort of vertical partition,
dividing the cavity of the eyeball into two chambers.

Illustration: Fig. 128.—Diagram illustrating the Manner in which the
Image of an Object is brought to a Focus on the Retina.

The anterior chamber occupies the space between the cornea and the
iris, and is filled with a thin, watery fluid called the aqueous humor.

The portion behind the iris forms the posterior chamber, and contains
the crystalline lens and a transparent, jelly-like fluid, the vitreous
humor. This fluid is never renewed, and its loss is popularly described
by the phrase, “when the eye runs out.”

Experiment 149. The retina is not sensitive where the optic nerve
enters the eyeball. This is called the “blind spot.” Put two
ink-bottles about two feet apart, on a table covered with white paper.
Close the left eye, and fix the right steadily on the left-hand
inkstand, gradually varying the distance from the eye to the
ink-bottle. At a certain distance the right-hand bottle will disappear;
but nearer or farther than that, it will be plainly seen.

The vitreous humor fills about four-fifths of the eyeball and prevents
it from falling into a shapeless mass. It also serves to hold the
choroid and the retina in position, and to maintain the proper
relations of the inner structures of the eye.

The iris consists of a framework of connective tissue, the surface of
which is lined by cells containing pigment, which gives color to the
eye.

Bundles of involuntary muscular fibers are found in the substance of
the iris. Some are arranged in a ring round the margin of the pupil;
others radiate from it like the spokes of a wheel. When the circular
fibers contract, the pupil is made smaller, but if these fibers relax,
the radiating fibers cause the pupil to dilate more or less widely.

329. The Crystalline Lens. Just behind the pupil and close to the iris
is a semi-solid, double-convex body, called the crystalline lens. It is
shaped like a magnifying glass, convex

Illustration: Fig. 129.—Diagram showing the Change in the Lens during
Accommodation.

On the right the lens is arranged for distant vision, the ciliary
muscle is relaxed and the ligament D is tense, so flattening by its
compression the front of the lens C; on the left the muscle A is
acting, and this relaxes the ligament and allows the lens B to become
more convex, and so fitted for the vision of near objects]

on each side, but with the posterior surface more convex than the
anterior. In health it is perfectly clear and transparent, and highly
elastic. When the lens becomes opaque, from change in old age, or from
ulcers or wounds, we have the disease known as _cataract_.

The lens is not placed loosely in the eyeball, but is enclosed in a
transparent and elastic capsule suspended throughout its circumference
by a ligament called the suspensory ligament. This ligament not only
retains the lens in place, but is capable of altering its shape. In
ordinary conditions of the eye, this ligament is kept tense so that the
front part of the lens is flattened somewhat by the pressure on it.

All around the edge, where the cornea, sclerotic, and choroid meet, is
a ring of involuntary muscular fibers, forming the ciliary muscle. When
these fibers contract, they draw forwards the attachment of the
suspensory ligament of the lens, the pressure of which on the lens is
consequently diminished. The elasticity of the lens causes it at once
to bulge forwards, and it becomes more convex.

The ciliary muscle is thus known as the muscle of accommodation,
because it has the power to accommodate the eye to near and distant
objects. In this respect it corresponds in its use to the adjusting
screw in the opera-glass and the microscope.

330. The Eye Compared to the Photographic Camera. As an optical
instrument, the eye may be aptly compared, in many particulars, to the
photographic camera. The latter, of course, is much simpler in
structure. The eyelid forms the cap, which being removed, the light
from the object streams through the eye and passes across the dark
chamber to the retina behind, which corresponds to the sensitive plate
of the camera. The transparent structures through which the rays of
light pass represent the lenses. To prevent any reflected light from
striking the plate and interfering with the sharpness of the picture,
the interior of the photographic camera box is darkened. The pigmented
layer of the choroid coat represents this blackened lining.

In the camera, the artist uses a thumb-screw to bring to a focus on the
sensitive plate the rays of light coming from objects at different
distances. Thus the lens of the camera may be moved nearer to or
farther from the object. In order to obtain clear images, the same
result must be accomplished by the eye. When the eye is focused for
near objects, those at a distance are blurred, and when focused for
distant objects, those near at hand are indistinct. Now, in the eye
there is no arrangement to alter the position of the lenses, as in the
camera, but the same result is obtained by what is called
“accommodation.”

Again, every camera has an arrangement of diaphragms regulating the
amount of light. This is a rude contrivance compared with the iris,
which by means of its muscular fibers can in a moment alter the size of
the pupil, thus serving a similar purpose.

Illustration: Fig. 130.—Illustrating the manner in which the Image of
an Object is brought to a Focus in a Photographer’s Camera.


331. The Refractive Media of the Eye. The eye is a closed chamber into
which no light can pass but through the cornea. All the rays that enter
the eye must also pass through the crystalline lens, which brings them
to a focus, as any ordinary lens would do.

Now, if the media through which the light from an object passes to
reach the retina were all of the same density as the air, and were also
plane surfaces, an impression would be produced, but the image would
not be distinct. The action of the lens is aided by several refractive
media in the eye. These media are the cornea, the aqueous humor, and
the vitreous humor. By reason of their shape and density these media
refract the rays of light, and bring them to a focus upon the retina,
thus aiding in producing a sharp and distinct image of the object. Each
point of the image being the focus or meeting-place of a vast number of
rays coming from the corresponding point of the object is sufficiently
bright to stimulate the retina to action.[44]

Thus, the moment rays of light enter the eye they are bent out of their
course. By the action of the crystalline lens, aided by the refractive
media, the rays of light that are parallel when they fall upon the
normal eye are brought to a focus on the retina.

If the entire optical apparatus of the eye were rigid and immovable,
one of three things would be necessary, in order to obtain a clear
image of an object; for only parallel rays (that is, rays coming from
objects distant about thirty feet or more), are brought to a focus in
the average normal eye, unless some change is brought about in the
refractive media. First, the posterior wall of the eye must be moved
further back, or the lens would have to be capable of movement, or
there must be some way of increasing the focusing power of the lens. In
the eye it is the convexity of the lens that is altered so that the eye
is capable of adjusting itself to different distances.[45]

Illustration: Fig. 131.—The Actual Size of the Test-Type, which should
be seen by the Normal Eye at a Distance of Twenty Feet.


332. The More Common Defects of Vision. The eye may be free from
disease and perfectly sound, and yet vision be indistinct, because the
rays of light are not accurately brought to a focus on the retina. “Old
sight,” known as presbyopia, is a common defect of vision in advancing
years. This is a partial loss of the power to accommodate the eye to
different distances. This defect is caused by an increase in the
density of the crystalline lens, and an accompanying diminution in the
ability to change its form. The far point of vision is not changed, but
the near point is removed so far from the eye, that small objects are
no longer visible.

Illustration: Fig. 132.—Diagram illustrating the Hypermetropic
(far-sighted) Eye.

The image P′ of a point P falls behind the retina in the unaccommodated
eye. By means of a convex lens it may be focused on the retina without
accommodation (dotted lines). (To save space P is placed much too near
the eye.)

Hence, when a person about forty-five years of age complains of dim
light, poor print, and tired eyes, the time has come to seek the advice
of an optician. A convex lens may be needed to aid the failing power to
increase the convexity of the lens, and to assist it in bringing the
divergent rays of light to a focus.

In “long sight,” or hypermetropia both the near and far point of vision
are concerned, and there is no distinct vision at any distance without
a strain. It is a defect in the focus, dependent upon the form of the
eyes, and exists in childhood. The axis of the eyeball is too short,
and the focus falls beyond the retina, which is too near the cornea. In
childhood this strain may pass unnoticed, but, sooner or later it
manifests itself by a sense of fatigue, dizziness, and a blurred and
indistinct vision. The remedy is in the use of convex glasses to
converge parallel rays of light before they enter the eye. The muscles
of accommodation are thus relieved of their extra work.

“Short sight,” known as myopia, is one of the commonest defects of
vision. In this defect the axis of the eye, or the distance between the
cornea and the retina, is too long and the rays of light are brought to
a focus in front of the retina. The tendency to short-sightedness
exists in many cases at birth, and is largely hereditary. It is
alarmingly common with those who make a severe demand upon the eyes.
During childhood there is a marked increase of near-sightedness. The
results of imprudence and abuse, in matters of eyesight, are so
disastrous, especially during school life, that the question of short
sight becomes one of paramount importance.

Experiment 150. With a hand-mirror reflect the sunlight on a white
wall. Look steadily at the spot for a full minute, and then let the
mirror suddenly be removed. The “complementary” color—a dark spot—will
appear.

Experiment 151. _To show that impressions made upon the retina do not
disappear at once_. Look steadily at a bright light for a moment or
two, and then turn away suddenly, or shut the eyes. A gleam of light
will be seen for a second or two.
    Look steadily at a well-lighted window for a few seconds, and then
    turn the eyes suddenly to a darkened wall. The window frame may be
    plainly seen for a moment.
    Glance at the sun for a moment, close the eyes and the image of the
    sun may be seen for a few seconds.

Experiment 152. Take a round piece of white cardboard the size of a
saucer, and paint it in alternate rings of red and yellow,—two primary
colors. Thrust a pin through the center and rotate it rapidly. The eye
perceives neither color, but orange,—the secondary color.

Experiment 153. To note the shadows cast upon the retina by opaque
matters in the vitreous humor (popularly known as floating specks, or
gossamer threads), look through a small pin-hole in a card at a bright
light covered by a ground-glass shade.

Experiment 154. _To illustrate accommodation_. Standing near a source
of light, close one eye, hold up both forefingers not quite in a line,
keeping one finger about six or seven inches from the other eye, and
the other forefinger about sixteen to eighteen inches from the eye.
Look at the _near_ finger; a distinct image is obtained of it, while
the far one is blurred or indistinct. Look at the far image; it becomes
distinct, while the near one becomes blurred. Observe that in
accommodating for the near object, one is conscious of a distinct
effort.

In many cases near-sightedness becomes a serious matter and demands
skillful advice and careful treatment. To remedy this defect, something
must be done to throw farther back the rays proceeding from an object
so that they will come to a focus exactly on the retina. This is done
by means of concave glasses, properly adjusted to meet the conditions
of the eyes. The selection of suitable glasses calls for great care, as
much harm may be done by using glasses not properly fitted to the eye.

Illustration: Fig. 133.—Diagram illustrating the Myopic (near-sighted)
Eye.

The image P′ of a distant object P falls in front of the retina even
without accommodation. By means of a concave lens (L) the image may be
made to fall on the retina (dotted lines). (To save space P is placed
much too near the eye).

There is an optical condition of the eye known as astigmatism, in which
the cornea is usually at fault. In this defect of vision the curvature
of the cornea is greater in one meridian than in another. As a result
the rays from an object are not all brought to the same focus. Objects
appear distorted or are seen with unequal clearness. Glasses of a
peculiar shape are required to counteract this defect.

333. The Movements of the Eyes. In order that our eyes may be efficient
instruments of vision, it is necessary that they have the power of
moving independently of the head. The mechanical arrangement by which
the eyeballs are moved in different directions is quite simple. It is
done by six little muscles, arranged in three pairs, which, with one
exception, originate in the back of the cavity in which the eye rests.
Four of these muscles run a straight course and are called the _recti_.
The remaining two muscles bend in their course and are called
_oblique_. The coördination of these tiny muscles is marvellous in its
delicacy, accuracy, and rapidity of action.

When, for any cause, the coördination is faulty, “cross eye,”
technically called strabismus, is produced. Thus, if the internal
rectus is shortened, the eye turns in; if the external rectus, the eye
turns out, producing what is known as “wall eye.” It is thus evident
that the beauty of the internal mechanism of the eye has its fitting
complement in the precision, delicacy, and range of movement conferred
upon it by its muscles.

334. The Eyelids and Eyebrows. The eye is adorned and protected by the
eyelids, eyelashes, and eyebrows.

Illustration: Fig. 134.—Muscles of the Eyeball.


A,  attachment of tendon connected with the three recti muscles;
  B, external rectus, divided and turned downward, to expose the
  internus rectus;
  C, inferior rectus;
  D, internal rectus;
  E, superior rectus;
  F, superior oblique;
  H, pulley and reflected portion of the superior oblique;
  K, inferior oblique; L, levator palpebri superioris;
  M, middle portion of the same muscle (L);
  N, optic nerve.

The eyelids, two in number, move over the front of the eyeball and
protect it from injury. They consist of folds of skin lined with mucous
membrane, kept in shape by a layer of fibrous material. Near the inner
surface of the lids is a row of twenty or thirty glands, known as the
_Meibomian glands_, which open on the free edges of each lid. When one
of these glands is blocked by its own secretion, the inflammation which
results is called a “sty.”

The inner lining membrane of the eyelids is known as the conjunctiva;
it is richly supplied with blood-vessels and nerves. After lining the
lids it is reflected on to the eyeballs. It is this membrane which is
occasionally inflamed from taking cold.

The free edges of the lids are bordered with two or more rows of hairs
called the eyelashes, which serve both for ornament and for use. They
help to protect the eyes from dust, and to a certain extent to shade
them. Their loss gives a peculiar, unsightly look to the face.

The upper border of the orbit is provided with a fringe of short, stiff
hairs, the eyebrows. They help to shade the eyes from excessive light,
and to protect the eyelids from perspiration, which would otherwise
cause serious discomfort.

335. The Lacrymal Apparatus. Nature provides a special secretion, the
tears, to moisten and protect the eye. The apparatus producing this
secretion consists of the lacrymal or tear gland and lacrymal canals or
tear passages (Fig. 136).

Outside of the eyeball, in the loose, fatty tissue of the orbit, in the
upper and outer corner is the lacrymal or tear gland. It is about the
size of a small almond and from it lead several little canals which
open on the inner surface of the upper lid. The fluid from the gland
flows out by these openings over the eyeball, and is collected at the
inner or nasal corner. Here in each lid is a little reddish elevation,
or _lacrymal caruncle_, in which is an opening, communicating with a
small canal in the lid which joins the lacrymal sac, lodged between the
orbit and the bridge of the nose (Fig. 137).

From this sac there passes a channel, the nasal duct, about one-half of
an inch long, leading into the lower portion of the nostril. The fluid
which has flowed over the eye is drained off by these canals into the
nose. During sleep this secretion is much diminished. When the eyes are
open the quantity is sufficient to moisten the eyeball, the excess
being carried into the nose so gradually that the attention is not
attracted to it.

The lacrymal canals are at times blocked by inflammation of the nasal
duct, and the fluid collects in the corners of the eyelids and
overflows down the cheeks, producing much inconvenience. The lining
membrane of the eyelids through these canals is continuous with that of
the nostrils. Hence, when the lining membrane of the eye is red and
swollen, as during a cold, the nasal passages are also irritated, and
when the nasal membrane is inflamed, the irritation is apt to pass
upwards and affect the eyelids.

336. The Tears. The lacrymal or tear gland is under the control of the
nervous system. Thus, if anything irritates the eyelids, the sensory
nerves are stimulated and the impression is carried to the brain.
Thence the nerve impulses travel to the lacrymal glands, leading to an
increased flow of their secretion. The irritation of the sensory nerves
in the nasal passages by smelling such substances as onions, or pungent
salts, often causes a copious flow of tears.

Illustration: Fig. 135.—Lacrymal Gland and Ducts.


A lachrymal gland, the size of a small almond lodged in a shallow
depression in the bones of the orbit;

B, lachrymal ducts (usually seven), which form a row of openings into
the conjunctival fold.

Various mental emotions, as joy and grief, may produce similar results.
In these cases the glands secrete the fluid in such quantities that it
cannot escape by the lacrymal canals, and the excess rolls over the
cheeks as tears. Excessive grief sometimes acts on the nerve centers in
exactly the opposite manner, so that the activity of the glands is
arrested and less fluid is secreted. This explains why some people do
not shed tears in times of deep grief.

Experiment 155. Gently turn the inner part of your lower eyelid down.
Look in a mirror, and the small lacrymal point, or opening into the
nasal duct, may be observed.

337. Color-blindness. There is an abnormal condition of vision called
color-blindness, in which the power of discrimination between different
colors is impaired. Experiment shows that ninety-six out of every one
hundred men agree as to the identity or the difference of color, while
the remaining four show a defective perception of color.

The first may be said to have _normal vision_; the second are called
_color-blind_. It is a curious fact that ten times more men than women
are color-blind.

In its true sense, color-blindness is always congenital, often
hereditary. This condition of abnormal vision is totally incurable. A
person may be color-blind and not know it until the defect is
accidentally revealed. The common form of defective color-vision is the
inability to distinguish between _red_ and _green_. As green lights
mean safety, and red lights danger, on railroads, on shipboard, and
elsewhere, it becomes of paramount importance that no one who is
color-blind should be employed in such service. Various tests are now
required by statute law in many states to be used for the detection of
such defects of vision among employees in certain occupations.

338. School Life and the Eyesight. The eyes of children need more care
than those of adults, because their eyes are still in the course of
development. The eyes, like any other organ which is yet to attain its
full growth, require more care in their use than one which has already
reached its full size. They are peculiarly liable to be affected by
improper or defective light. Hence the care of the eyes during school
life is a matter of the most practical importance.

In no matter of health can the teacher do a more distinct service than
in looking after the eyesight of the pupils. Children suffering from
defective vision are sometimes punished by teachers for supposed
stupidity. Such pupils, as well as the deaf, are peculiarly sensitive
to their defects. Every schoolroom should have plenty of light; it
should come from either side or the rear, and should be regulated with
suitable shades and curtains.

Pupils should not be allowed to form the bad habit of reading with the
book held close to the eyes. The long search on maps for obscure names
printed in letters of bad and trying type should be discouraged.
Straining the eyes in trying to read from slates and blackboards, in
the last hour of the afternoon session, or in cloudy weather, may do a
lifelong injury to the eyesight. Avoid the use, so far as possible,
especially in a defective light, of text-books which are printed on
battered type and worn plates.

The seat and desk of each scholar should be carefully arranged to suit
the eyesight, as well as the bones and muscles. Special pains should be
taken with the near-sighted pupils, and those who return to school
after an attack of scarlet fever, measles, or diphtheria.

Experiment 156. _To test color-blindness._ On no account is the person
being tested to be asked to name a color. In a large class of students
one is pretty sure to find some who are more or less color-blind. The
common defects are for red and green.

Place worsteds on a white background in a good light. Select, as a test
color, a skein of light green color, such as would be obtained by
mixing a pure green with white. Ask the examinee to select and pick out
from the heap all those skeins which appear to him to be of the same
color, whether of lighter or darker shades. A color-blind person will
select amongst others some of the confusion-colors, _e.g._, pink,
yellow. A colored plate showing these should be hung up in the room.
Any one who selects all the greens and no confusion-colors has normal
color vision. If, however, one or more confusion-colors be selected,
proceed as follows: select as a test color a skein of pale rose. If the
person be red-blind, he will choose blue and violet; if green-blind,
gray and green.

Select a bright red skein. The red-blind will select green and brown;
the green-blind picks out reds or lighter brown.

339. Practical Hints on the Care of the Eyes. The eye is an exceedingly
delicate and sensitive organ. While it is long-suffering, its endurance
has a limit. Like all the other organs of the body, the eyes are better
for moderate and rational use. More than any other organ they require
attention to the general health, as the condition of the skin, exercise
in the open air, good food, and proper habits of daily living.

The tissues of the eyes are peculiarly sensitive to any general
influence. Certain constitutional diseases, like rheumatism,
lead-poisoning, diphtheria, and measles often affect the eyes. Special
care should be taken with children’s eyes during and after an attack of
measles and scarlet fever. The eyes of young infants should not be
exposed to glaring lights or to the direct rays of the sun, as when
taken out in baby carriages.

Illustration: Fig. 136.—Showing the Relative Position of the Lacrymal
Apparatus, the Eyeball, and the Eyelids.


A,  lacrymal canals, with the minute orifices represented as two black
dots (puncta lacrymalia) to the right;
  B, tendon of the orbicularis palpebrarum muscle; apparently under B
  is seen the lacrymal sac. The minute openings of the Meibomian glands
  are seen on the free margins of the eyelids.

Below A is seen a small conical elevation, with black dots (the
lacrymal papilla or caruncle).

Glasses should be worn when they are needed. A failure to do this
ususally causes much unnecessary suffering. It is far from wise to
postpone as long as possible the first use of glasses. The selection
and proper fitting of glasses call for the combined skill of both the
physician and the optician. Obstinate headaches are often caused by
defective vision, and may disappear after discontinuing improper
glasses.

The habit of reading, in the cars or elsewhere, the daily paper and
poorly printed books, with their blurred and indistinct type, is a
severe strain on the accommodation apparatus of the eyes. It is a
dangerous practice to read in bed at night, or while lying down in a
darkened or shaded room. This is especially true during recovery from
illness. The muscles of the eyes undergo excessive strain in
accommodating themselves to the unnatural position. The battered type,
wood-pulp paper, and poor presswork, now so commonly used in the cheap
editions of books and periodicals, are often injurious to the eyesight.

Reading-matter should not be held nearer to the eyes than is necessary
to make the print appear perfectly sharp and distinct. No print should
be read continuously that cannot be seen clearly at about eighteen
inches. Those who read music are especially liable to strain the eyes,
because exact vision is required to follow the notes. Persons who wear
glasses for reading should be careful to use them while reading music,
and good light is necessary to avoid any undue strain.

After reading steadily for some time, the eyes should be rested by
closing them a short period or by looking at some distant object, even
if only for a few moments. The book, the sewing, and work generally,
should be held as far from the eyes as is compatible with good vision.
The natural tendency is to reverse this rule. We should never read,
write, sew, stitch, or otherwise use the eyes when they smart or
tingle, or when the sight is dim or blurred. The eyes are then tired
and need a rest. Much injury may be done by reading in twilight, or by
artificial light in the early morning, and by reading and working in
badly lighted and ill-ventilated rooms.

Good artificial light is much to be preferred to insufficient sunlight.
The artificial light should be sufficiently bright and steady; a
fickering light is always bad. Riding against a strong wind, especially
on a bicycle, may prove hurtful, at least for eyes that are inclined to
any kind of inflammation. The light reflected from snow is a common
source of injury to the eyes. It is a wise caution in passing from a
dark room to avoid looking immediately at the sun, an incandescent
light, the glistening snow, or other bright objects.

The eyes should never be rubbed, or the fingers thrust into them,[46]
and much less when they are irritated by any foreign substance. The
sooner the offending substance is removed the better.

Illustration: Fig. 137.—Lacrymal Canals, Lacrymal Sac, and Nasal ducts,
opened by their Anterior Portion.


340. Effect of Alcohol upon the Eye. The earlier and slighter forms of
injury done to the eye by the use of intoxicants are quite familiar:
the watery condition of the eye and of the lids, and the red and
bleared aspect of the organ. Both are the result of chronic
inflammation, which crowds the blood into the vessels of the cornea,
making them bloodshot and visible. The nerves controlling the
circulation of the eye are partially paralyzed, and thus the relaxed
vessels become distended.

But more serious results ensue. Long use of intoxicants produces
diseases of the retina, involving in many cases marked diminution of
acuteness as well as quickness of vision, and at times distorted images
upon the surface of the retina. In other instances, the congestion of
the optic nerve is so serious as to involve a progressive wasting of
that organ, producing at first a hazy dimness of vision which gradually
becomes worse and worse, till total blindness may ensue.

It is beyond question that a wide comparison of cases by careful
observers proves that a large fraction of those who indulge in strong
drink suffer from some form of disease of the eye.

341. Effect of Tobacco upon Vision. Tobacco, in its distribution of
evil effects, does not neglect the senses and especially the eye. A
variety of vicious results is produced. The pungent smoke inflames the
lids. The narcotic dilates the pupil, causing dimness and confusion of
vision. A diseased condition occurs with severe pain in the eye
followed by impaired vision.

Oculists speak impressively of the ill effects of tobacco, and
especially of cigarettes, upon the eyes of the young. They mention a
well-known disease, tobacco blindness, usually beginning with
color-blindness, and progressing occasionally with increasing dimness
of vision to entire loss of sight.[47]

342. The Sense of Hearing. The structure of the human ear is much more
complicated than is generally supposed. It is an apparatus constructed
to respond to the waves of sound. As a whole, it may be considered a
peculiar form of nerve-ending.

The external ear forms only a part of a most elaborate apparatus
whereby sound waves may be transmitted inwards to the real organ of
hearing. The really sensitive part of the ear, in which the auditory
nerve ends, is buried for protection deep out of sight in the bones of
the head; so deep that sounds cannot directly affect it. Some
arrangement, therefore, is required for conducting the sounds inwards
to this true organ.

Illustration: Fig. 138.—The Pinna, or Auricle.

In studying the structure of the ear, and how it is fitted to respond
to sonorous vibrations, we may divide it into three parts: the
sound-conducting part, known as the external ear, the middle ear, and
the deeply placed nerve portion, the inner ear.

343. The External Ear. The external ear consists of an expanded portion
known as the pinna or _auricle_, and of a passage, the auditory canal
or _meatus_, leading inwards from it. The surface of the auricle is
convoluted to collect and transmit the vibrations of air by which sound
is produced the auditory canal conducts these vibrations to the
tympanic membrane. Many animals move the auricle in the direction of
the sound. Thus the horse pricks up its ears when it hears a noise, the
better to judge of the direction of sounds.[48]

The external auditory meatus, the passage to the middle ear, is curved
and is about an inch and a quarter long. Near its outer portion are a
number of fine hairs slanting outwards to prevent the entrance of
insects. Embedded in the deeper parts of the canal are glands which
secrete the _cerumen_, or ear-wax, which keeps the canal moist, and
helps to protect it against foreign bodies and insects. As the result
of a cold, this wax may collect in sufficient quantities to block the
passage, and to diminish to a considerable extent the power of hearing.

344. The Middle Ear. At the inner end of the outer ear passage is the
tympanum, known as “the drum of the ear.” It is a thin, oval membrane,
stretched at an angle across the deep end of the passage, which it
completely closes. The tympanum is thus a partition between the passage
of the outer ear and the cavity of the middle ear. On its inner side is
a small air chamber in the petrous portion of the temporal bone, called
the cavity of the tympanum. Its bony walls are lined with mucous
membrane similar to that lining the nose, mouth, and throat. On the
inner wall of the tympanum are two openings, the round window, or
_foramen rotundum_, and the oval window, or _foramen ovale_.

The tympanic cavity communicates with the back part of the throat, by
the Eustachian tube. This tube is about one and a half inches long and
lined with mucous membrane similar to that of the tympanic chamber and
the throat. This passage is usually closed, but is opened in the act of
swallowing. In health there is no communication between the chamber of
the middle ear and the outside, except by the Eustachian tube. Thus a
throat cold, with redness and swelling of the mucous membrane, is
usually accompanied with some degree of deafness, because the swelling
may block the lumen of the tube, and thus prevent the free passage of
air to and fro.

Illustration: Fig. 139.—General View of the Organ of Hearing.


A,  pinna;
  B, cavity of the concha, showing the orifices of a great number of
  sebaceous glands;
  C, external auditory meatus;
  D, membrana tympani;
  F, incus;
  H, malleus;
  K, handle of malleus applied to the internal surface of the membrana
  tympani;
  L, tensor tympani muscle;
  between M and K is the tympanic cavity;
  N, Eustachian tube;
  O, P, semicircular canals;
  R, internal auditory canal;
  S, large nerve given off from the facial ganglion;
  T, facial and auditory nerves.

A most curious feature of the ear is the chain of tiny movable bones
which stretch across the cavity of the middle ear. They connect the
tympanic membrane with the labyrinth, and serve to convey the
vibrations communicated to the membrane across the cavity of the
tympanum to the internal ear. These bones are three in number, and from
their shape are called the malleus, or _hammer_, incus, or _anvil_; and
stapes, or _stirrup_.

The hammer is attached by its long handle to the inner surface of the
drum of the ear. The round head is connected with the anvil by a
movable joint, while the long projection of the anvil is similarly
connected with the stirrup bone. The plate of the stirrup is fixed by a
membrane into the oval window of the inner wall of the tympanic
chamber.

These little bones are connected with each other and the tympanum by
ligaments and moved by three tiny muscles. Two are attached to the
hammer, and tighten and relax the drum; the other is attached to the
stirrup, and prevents it from being pushed too deeply into the oval
window.

Illustration: Fig. 140.—Ear-Bones. (Anterior View.)


1, malleus, or hammer;
  2, incus, or anvil;
  3, stapes, or stirrup.


345. The Internal Ear. This forms one of the most delicate and complex
pieces of mechanism in the whole body. It is that portion of the organ
which receives the impression of sound, and carries it directly to the
seat of consciousness in the brain. We are then able to say that we
hear.

The internal ear, or bony labyrinth, consists of three distinct parts,
or variously shaped chambers, hollowed out in the temporal bone,—the
vestibule, the semicircular canals, and the cochlea, or snail’s shell.

Illustration: Fig. 141.—A Cast of the External Auditory Canal.
(Posterior view)

The vestibule is the common cavity with which all the other portions of
the labyrinth connect. It is an oval-shaped chamber, about ⅓ of an inch
in diameter, occupying the middle part of the internal ear. It is on
the inner side of the oval window, which was closed, as we have seen,
by the stirrup bone. From one side of this vestibule, or central hall,
the three semicircular canals pass off, and from the other side, the
cochlea.

The three semicircular canals, so called from their shape, are simply
bony tubes about 1/20 of an inch in width, making a curve of about 1/4
of an inch in diameter. They pass out from the vestibule, and after
bending around somewhat like a hoop, they return again to the
vestibule. Each bony canal contains within it a membranous canal, at
the end of which it is dilated to form an _ampulla_.

Experiment 157. _To vibrate the tympanic membrane and the little
ear-bones._ Shut the mouth, and pinch the nose tightly. Try to force
air through the nose. The air dilates the Eustachian tube, and is
forced into the ear-drum. The distinct crackle, or clicking sound, is
due to the movement of the ear-bones and the tympanic membrane.

The cochlea, or snail’s shell, is another chamber hollowed out in the
solid bone. It is coiled on itself somewhat like a snail’s shell. There
is a central pillar, around which winds a long spiral canal. One
passage from the cochlea opens directly into the vestibule; the other
leads to the chamber of the middle ear, and is separated from it by the
little round window already described.

The cochlea contains thousands of the most minute cords, known as the
fibers or _organ of Corti_.[49] Under the microscope they present the
appearance of the keyboard of a piano. These fibers appear to vibrate
in sympathy with the countless shades of sounds which daily penetrate
the ear. From the hair-like processes on these tightly stretched
fibers, auditory impulses appear to be transmitted to the brain.

The tubes and chambers of the inner ear enclose and protect a delicate
membranous sac of exactly the same shape as themselves. Between the
bony walls of the passages and the membranous bag inside is a thin,
clear fluid, the _perilymph_. The membranous bag itself contains a
similar fluid, the _endolymph_. In this fluid are found some minute
crystals of lime like tiny particles of sand, called _otoliths_, or
ear-stones. Every movement of the fluid itself throws these grains from
side to side.

Illustration: Fig. 142.—Bony internal Ear of Right Side. (Magnified;
the upper figure of the natural size.)


A,  oval window (foramen ovale);
  B, C, D, semicircular canals;
  * represents the bulging part (ampulla) of each canal;
  E, F, G cochlea, H, round window (foramen rotundum).

The auditory nerve, or nerve of hearing, passes to the inner ear,
through a passage in the solid bone of the skull. Its minute filaments
spread at last over the inner walls of the membranous labyrinth in two
branches,—one going to the vestibule and the ampullæ at the ends of the
semicircular canals, the other leading to the cochlea.

346. Mechanism of Hearing. Waves of sound reach the ear, and are
directed by the concha to the external passage, at the end of which
they reach the tympanic membrane. When the sound-waves beat upon this
thin membrane, it is thrown into vibration, reproducing in its
movements the character of the air-vibrations that have fallen upon it.

Now the vibrations of the tympanic membrane are passed along the chain
of bones attached to its inner surface and reach the stirrup bone. The
stirrup now performs a to-and-fro movement at the oval window, passing
the auditory impulse inwards to the internal ear.

Every time the stirrup bone is pushed in and drawn out of the oval
window, the watery fluid (the perilymph) in the vestibule and inner ear
is set in motion more or less violently, according to the intensity of
the sound. The membranous labyrinth occupies the central portion of the
vestibule and the passages leading from it. When, therefore, the
perilymph is shaken it communicates the impulse to the fluid
(endolymph) contained in the inner membranous bag. The endolymph and
the tiny grains of ear-sand now perform their part in this marvelous
and complex mechanism. They are driven against the sides of the
membranous bag, and so strike the ends of the nerves of hearing, which
transmit the auditory impulses to the seat of sensation in the brain.

It is in the seat of sensation in the brain called the _sensorium_ that
the various auditory impulses received from different parts of the
inner ear are fused into one, and interpreted as sounds. It is the
extent of the vibrations that determines the loudness of the sound; the
number of them that determines the pitch.

Experiment 158. Hold a ticking watch between the teeth, or touch the
upper incisors with a vibrating tuning-fork; close both ears, and
observe that the ticking or vibration is heard louder. Unstop one ear,
and observe that the ticking or vibration is heard loudest in the
stopped ear.

Experiment 159. Hold a vibrating tuning-fork on the incisor teeth until
you cannot hear it sounding. Close one or both ears, and you will hear
it.

Experiment 160. Listen to a ticking watch or a tuning-fork kept
vibrating electrically. Close the mouth and nostrils, and take either a
deep inspiration or deep expiration, so as to alter the tension of the
air in the tympanum; in both cases the sound is diminished.

Experiment 161. With a blindfolded person test his sense of the
direction of sound, _e.g._, by clicking two coins together. It is very
imperfect. Let a person press both auricles against the side of the
head, and hold both hands vertically in front of each meatus. On a
person making a sound in front, the observed person will refer it to a
position behind him.

347. Practical Hints on the Care of the Ear. This very delicate and
complicated organ is often neglected when skilled treatment is urgently
needed, and it is often ignorantly and carelessly tampered with when it
should be let alone.

Never insert into the ear canal the corners of towels, ear spoons, the
ends of toothpicks, hairpins, or any other pointed instruments. It is a
needless and dangerous practice, usually causing, in time, some form of
inflammation. The abrasion of the skin in the canal thus produced
affords a favorable soil for the growth of vegetable parasites.

Illustration: Fig. 143.—Diagram of the Middle and Internal Ear.

This, in turn, may lead to a chronic inflammation of the canal and of
the tympanic membrane. Again, there is always risk that the elbow may
be jogged and the instrument pushed through the drum-head. There is, of
course, a natural impulse to relieve the itching of the ear. This
should be done with the tips of the fingers or not at all.

The popular notion that something should be put into the ear to cure
toothache is erroneous. This treatment does not cure a toothache, and
may lead to an injury to the delicate parts of the ear. A piece of
absorbent cotton, carefully inserted into the ear, may be worn out of
doors, when the cold air causes pain, but should be removed on coming
into the house.

Frequent bathing in the cold water of ponds and rivers is liable to
injure both the ears and the general health. In salt-water bathing, the
force of the waves striking against the ears often leads to earache,
long-continued inflammation, or defective hearing; to diminish this
risk, insert into the ears a small plug of absorbent cotton.

The ears are often carelessly exposed to cold water and inclement
weather. Very cold water should never be used to bathe the ears and
nostrils. Bathe moderately and gently in lukewarm water, using a
wash-rag in preference to a sponge; dry gently and thoroughly.
Children’s ears are often rudely washed, especially in the auditory
canal. This is not at all necessary to cleanliness, and may result in a
local inflammation.

Never shout suddenly in a person’s ear. The ear is not prepared for the
shock, and deafness has occasionally resulted. A sudden explosion, the
noise of a cannon, may burst the drum-head, especially if the
Eustachian tube be closed at the time. During heavy cannonading,
soldiers are taught to keep the mouth open to allow an equal tension of
air.

Illustration: Fig. 144.—Section of Cochlea.

From A straight downwards is the direction of the central column, to
which E points. B points to the projecting ridge, almost dividing the
canal of the tube into an upper compartment (D), and a lower (C).]

Insects may gain entrance to the ears and occasion annoyance, pain, and
fright, perhaps leading to vomiting, even to convulsions, with nervous
children. A lighted lamp held at the entrance of the ear will often
induce the offending insect to crawl out towards the light. A few drops
of warm water, sweet oil, or molasses, dropped into the ear, will help
remove the intruder.

When a discharge occurs from the ears, it is not best to plug them with
cotton wads. It only keeps in what should be got rid of. Do not go to
sleep with the head on a window sill or in any position, with the ears
exposed to draughts of cold or damp air.

No effort should be made to remove the ear wax unless it accumulates
unduly. The skin of the canal grows outward, and the extra wax and dust
will be naturally carried out, if let alone. Never employ any of the
many articles or “drops,” advertised to cure deafness. Neuralgic pain
in the canal, usually classed as earache, may be due to decayed or
improperly filled teeth.

Quinine, so generally used in its many preparations for malaria, causes
a peculiar ringing or buzzing in the ears. This is a warning that it
should be taken in smaller doses, or perhaps stopped for a time. In
some cases quinine may produce temporary deafness.

The practice of snuffing up cold water into the nostrils is
occasionally followed by an acute inflammation of the middle ear, some
of the water finding its way through the Eustachian tube into this part
of the organ of hearing. The nasal douche, so often advised as a home
remedy for nasal catarrh, should be used only with great caution, and
always in accordance with detailed directions from a physician.

348. Effect of Tobacco upon the Hearing. The sense of hearing is often
injured by the use of tobacco. The irritating smoke filling all the
inner cavity of the mouth and throat, readily finds its way up the
Eustachian tube, dries the membrane, and irritates or inflames the
delicate mechanism of the inner ear. Thus may be produced a variety of
serious aural disturbances, such as unnatural noises, whistling, and
roaring, followed oftentimes by a partial loss of hearing.

Hearing may be impaired by the use of alcoholic beverages. Alcohol
inflames the mucous membrane of the throat, then by its nearness the
lining of the Eustachian tube, and finally may injure the delicate
apparatus of the internal ear.

Additional Experiments.

Experiment 162. Use a small pair of wooden compasses, or an ordinary
pair of dividers with their points guarded by a small piece of cork.
Apply the points of the compasses lightly and simultaneously to
different parts of the body, and ascertain at what distance apart the
points are felt as two. The following is the order of sensibility: tip
of tongue, tip of the middle finger, palm, forehead, and back of hand.

Experiment 163. Test as in preceding experiment the skin of the arm,
beginning at the shoulder and passing downwards. Observe that the
sensibility is greater as one tests towards the fingers, and also in
the transverse than in the long axis of the limb. In all cases compare
the results obtained on both sides of the body.

Experiment 164. By means of a spray-producer, spray the back of the
hand with ether, and observe how the sensibility is abolished.

Experiment 165. Touch your forehead with your forefinger; the finger
appears to feel the contact, but on rubbing the forefinger rapidly over
the forehead, it is the latter which is interpreted as “feeling” the
finger.

Experiment 166. Generally speaking, the sensation of touch is referred
to the cutaneous surfaces. In certain cases, however, it is referred
even beyond this. Holding firmly in one hand a cane or a pencil, touch
an object therewith; the sensation is referred to the extremity of the
cane or pencil.
    If, however, the cane or pencil be held loosely in one’s hand, one
    experiences two sensations: one corresponding to the object
    touched, and the other due to the contact of the rod with the skin.
    The process of mastication affords a good example of the reference
    of sensations to and beyond the periphery of the body.

Experiment 167. Prepare a strong solution of sulphate of quinine with
the aid of a little sulphuric acid to dissolve it (_bitter_), a
five-per-cent solution of sugar (_sweet_), a ten-per-cent solution of
common salt (_saline_), and a one-per-cent solution of acetic acid
(_acid_). Wipe the tongue dry, and lay on its tip a crystal of sugar.
It is not tasted until it is dissolved.

Experiment 168. Apply a crystal of sugar to the tip, and another to the
back of the tongue. The sweet taste is more pronounced at the tip.

Experiment 169. Repeat the process with sulphate of quinine in
solution. It is scarcely tasted on the tip, but is tasted immediately
on the back part of the tongue. Test where salines and acids are tasted
most acutely.

Experiment 170. _To illustrate the muscular sense_. Take two equal iron
or lead weights; heat one and leave the other cold. The cold weight
will feel the heavier.

Experiment 171. Place a thin disk of _cold_ lead, the size of a silver
dollar, on the forehead of a person whose eyes are closed; remove the
disk, and on the same spot place two warm disks of equal size. The
person will judge the latter to be about the same weight, or lighter,
than the single cold disk.

Experiment 172. Compare two similar wooden disks, and let the diameter
of one be slightly greater than that of the other. Heat the smaller one
to over 120° F., and it will be judged heavier than the larger cold
one.

Experiment 173. _To illustrate the influence of excitation of one sense
organ on the other sense organs_. Small colored patches the shape and
color of which are not distinctly visible may become so when a
tuning-fork is kept vibrating near the ears. In other individuals the
visual impressions are diminished by the same process.
    On listening to the ticking of a watch, the ticking sounds feebler
    or louder on looking at a source of light through glasses of
    different colors.
    If the finger be placed in cold or warm water the temperature
    appears to rise when a red glass is held in front of the eyes.

Experiment 174. _Formation of an inverted image on the retina_. Take a
freshly removed ox-eye; dissect the sclerotic from that part of its
posterior segment near the optic nerve. Roll up a piece of blackened
paper in the form of a tube, black surface innermost, and place the eye
in it with the cornea directed forward. Look at an object—_e.g._, a
candle-flame—and observe the inverted image of the flame shining
through the retina and choroid, and notice how the image moves when the
candle is moved.

Experiment 175. Focus a candle-flame or other object on the
ground-glass plate of an ordinary photographic camera, and observe the
small inverted image.

Experiment 176. _To illustrate spherical aberration_. Make a pin-hole
in a blackened piece of cardboard; look at a light placed at a greater
distance than the normal distance of accommodation. One will see a
radiate figure with four to eight radii. The figures obtained from
opposite eyes will probably differ in shape.

Experiment 177. Hold a thin wooden rod or pencil about a foot from the
eyes and look at a distant object. Note that the object appears double.
Close the right eye; the left image disappears, and _vice versa_.

Experiment 178. _To show the movements of the iris_. It is an extremely
beautiful experiment, and one that can easily be made. Look through a
pin-hole in a card at a uniform white surface as the white shade of an
ordinary reading-lamp. With the right eye look through the pin-hole,
the left eye being closed. Note the size of the (slightly dull)
circular visual field. Open the left eye, the field becomes brighter
and smaller (contraction of pupil); close the left eye, after an
appreciable time, the field (now slightly dull) is seen gradually to
expand. One can thus see and observe the rate of movements of his own
iris.

Illustration: Fig. 145.


Experiment 179. _To show the blind spot_. The left eye being shut, let
the right eye be fixed upon the cross as in Fig. 145. When the book is
held at arm’s length, both cross and round spot will be visible; but if
the book be brought to about 8 inches from the eye, the gaze being kept
steadily upon the cross, the round spot will at first disappear, but as
the book, is brought still nearer both cross and round spot will again
be seen.

Experiment 180. _To illustrate the duration of retinal impressions_. On
a circular white disk, about halfway between the center and
circumference, fix a small, black, oblong disk, and rapidly rotate it
by means of a rotating wheel. There appears a ring of gray on the
black, showing that the impression on the retina lasts a certain time.

Illustration: Fig. 146.—Optic Disks.
The disk A, having black and white sectors, when rotated rapidly gives
an even gray tint as in B.


Experiment 181. Mark off a round piece of cardboard into black and
white sectors as in A (Fig. 146). Attach it so as to rotate it rapidly,
as on a sewing machine. An even gray tint will be produced as in B.

Experiment 182._To illustrate imperfect visual judgments_. Make three
round black dots, A, B, C, of the same size, in the same line, and let
A and C be equidistant from B. Between A and B make several more dots
of the same size. A and B will then appear to be farther apart than B
and C.

Illustration:

For the same reason, of two squares absolutely identical in size, one
marked with alternately clear and dark cross-bands, and the other with
alternately clear and dark upright markings, the former will appear
broader and the latter higher than the other.

Experiment 183. Make on a white card two squares of equal size. Across
the one draw _horizontal_ lines at equal distances, and in the other
make similar _vertical_ lines. Hold them at some distance. The one with
horizontal lines appears higher than it really is, while the one with
vertical lines appears broader, _i.e._, both appear oblong.

Experiment 184. Look at the row of letters (S) and figures (8). To some
the upper halves of the letters and figures may appear to be of the
same size as the lower halves, to others the lower halves may appear
larger. Hold the figure upside down, and observe that there is a
considerable difference between the two, the lower halves being
considerably larger.

S S S S S S S S                    8 8 8 8 8 8 8 8


Experiment 185. _To illustrate imperfect visual judgment_. The length
of a line appears to vary according to the angle and direction of
certain other lines in relation to it (Fig. 147). The length of the two
vertical lines is the same, yet B appears much longer than A.

Illustration: Fig. 147.—To show False Estimate of Size.


Experiment 186. In indirect vision the appreciation of direction is
still more imperfect. While leaning on a large table, fix a point on
the table, and then try to arrange three small pieces of colored paper
in a straight line. Invariably, the papers, being at a distance from
the fixation-point, and being seen by indirect vision, are arranged,
not in a straight line, but in the arc of a circle with a long radius.



Chapter XII.
The Throat and the Voice.


349. The Throat. The throat is a double highway, as it were, through
which the air we breathe traverses the larynx on its way to the lungs,
and through which the food we swallow reaches the œsophagus on its
passage to the stomach. It is, therefore, a very important region of
the body, being concerned in the great acts of respiration and
digestion.

The throat is enclosed and protected by various muscles and bony
structures, along which run the great blood-vessels that supply the
head, and the great nerve trunks that pass from the brain to the parts
below.

We have already described the food passages (Chapter VI.) and the air
passages (Chapter VIII.).

To get a correct idea of the throat we should look into the wide-open
mouth of some friend. Depressing the tongue we can readily see the back
wall of the pharynx, which is common to the two main avenues leading to
the lungs and the stomach. Above, we notice the air passages, which
lead to the posterior cavities of the nose. We have already described
the hard palate, the soft palate, the uvula, and the tonsils (Fig. 46).

On looking directly beyond these organs, we see the beginning of the
downward passage,—the pharynx. If now the tongue be forcibly drawn
forward, a curved ridge may be seen behind it. This is the epiglottis,
which, as we have already learned shuts down, like the lid of a box,
over the top of the larynx (secs. 137 and 203).

The throat is lined with mucous membrane covered with ciliated
epithelium, which secretes a lubricating fluid which keeps the parts
moist and pliable. An excess of this secretion forms a thick, tenacious
mass of mucus, which irritates the passages and gives rise to efforts
of hawking and coughing to get rid of it.

350. The Larynx. The larynx, the essential organ of voice, forms the
box-like top of the windpipe. It is built of variously shaped
cartilages, connected by ligaments. It is clothed on the outside with
muscles; on the inside it is lined with mucous membrane, continuous
with that of the other air passages.

Illustration: Fig. 148.—View of the Cartilages in front project and
form the lages and Ligaments of the “Adam’s apple,” plainly seen and
Larynx. (Anterior view.)


A,  hyoid bone;
  B, thyro-hyoid membrane;
  C, thyroid cartilage;
  D, erico-thyroid membrane;
  E, cricoid cartilage, lateral ligaments seen on each side;
  F, upper ring of the trachea.
  (“Adam’s apple” is in the V-shaped groove on a line with B and C.)

The larynx has for a framework two cartilages, the thyroid and the
cricoid, one above the other. The larger of these, called the thyroid,
from a supposed resemblance to a shield, consists of two extended wings
which join in front, but are separated by a wide interval behind. The
united edges in front project and form the “Adam’s apple” plainly seen
and easily felt on most people, especially on very lean men.

Above and from the sides rise two horns connected by bands to the hyoid
bone from which the larynx is suspended. This bone is attached by
muscles and ligaments to the skull. It lies at the base of the tongue,
and can be readily felt by the finger behind the chin at the angle of
the jaw and the neck (sec. 41 and Fig. 46). From the under side of the
thyroid two horns project downwards to become jointed to the cricoid.
The thyroid thus rests upon, and is movable on, the cricoid cartilage.

The cricoid cartilage, so called from its fancied resemblance to a
signet-ring, is smaller but thicker and stronger than the thyroid, and
forms the lower and back part of the cavity of the larynx. This
cartilage is quite sensitive to pressure from the fingers, and is the
cause of the sharp pain felt when we try to swallow a large and hard
piece of food not properly chewed.

Illustration: Fig. 149.—Diagram of a Sectional of Nasal and Throat
Passages.

  C, nasal cavities;
  T, tongue;
  L, lower jaw;
  M, mouth;
  U, uvula;
  E, epiglottis;
  G, larynx;
  O, œsophagus.

On the upper edge of the cricoid cartilage are perched a pair of very
singular cartilages, pyramidal in shape, called the arytenoid, which
are of great importance in the production of the voice. These
cartilages are capped with little horn-like projections, and give
attachment at their anterior angles to the true vocal cords, and at
their posterior angles to the muscles which open and close the glottis,
or upper opening of the windpipe. When in their natural position the
arytenoid cartilages resemble somewhat the mouth of a pitcher, hence
their name.

351. The Vocal Cords. The mucous membrane which lines the various
cartilages of the larynx is thrown into several folds. Thus, one fold,
the free edge of which is formed of a band of elastic fibers, passes
horizontally outwards from each side towards the middle line, at the
level of the base of the arytenoid cartilages. These folds are called
the true vocal cords, by the movements of which the voice is produced.

Above them are other folds of mucous membrane called the false vocal
cords, which take no part in the production of the voice. The
arrangement of the true vocal cords, projecting as they do towards the
middle line, reduces to a mere chink the space between the part of the
larynx above them and the part below them. This constriction of the
larynx is called the glottis.

Illustration: Fig. 150.—View of the Cartilages and Ligaments of Larynx.
(Posterior view.)


A,  epiglottis;
  B, thyroid cartilage;
  C, arytenoid cartilage;
  D, ligament connecting lower cornu of the thyroid with the back of
  the cricoid cartilage;
  E, cricoid cartilage;
  F, upper ring of the trachea.


352. The Mechanism of the Voice. The mechanism of the voice may be more
easily understood by a study of Fig. 150. We have here the larynx,
viewed from behind, with all the soft parts in connection with it. On
looking down, the folds forming the true vocal cords are seen enclosing
a V-shaped aperture (the glottis), the narrow part being in front.

The form of this aperture may be changed by the delicately coordinate
activities of the muscles of the larynx. For instance, the vocal cords
may be brought so closely together that the space becomes a mere slit.
Air forced through the slit will throw the edges of the folds into
vibration and a sound will be produced.

The Variations in the form of the opening will determine the variations
in the sound. Now, if the various muscles of the larynx be relaxed, the
opening of the glottis is wider. Thus the air enters and leaves the
larynx during breathing, without throwing the cords into vibration
enough to produce any sound.

We may say that the production of the voice is effected by an
arrangement like that of some musical instruments, the sounds produced
by the vibrations of the vocal cords being modified by the tubes above
and below. All musical sounds are due to movements or vibrations
occurring with a certain regularity, and they differ in loudness,
pitch, and quality. Loudness of the sound depends upon the extent of
the vibrations, pitch on the rapidity of the vibrations, and quality on
the admixture of tones produced by vibrations of varying rates of
rapidity, related to one another.

Illustration: Fig. 151.—Longitudinal Section of the Larynx. (Showing
the vocal cords.)


A,  epiglottis;
  B, section of hyoid bone;
  C, superior vocal cord;
  D, ventricle of the larynx;
  E, inferior vocal cord;
  F, section of the thyroid cartilage;
  H, section of anterior portion of the cricoid cartilage;
  K, trachea;
  L, section of the posterior portion of the cricoid cartilage;
  M, arytenoid cartilage;
  N, section of the arytenoid muscle.


353. Factors in the Production of the Voice. Muscles which pass from
the cricoid cartilage to the outer angle of the arytenoids act to bring
the vocal cords close together, and parallel to one another, so that
the space between them is narrowed to a slit. A strong expiration now
drives the air from the lungs through the slit, between the cords, and
throws them into vibration. The vibration is small in amount, but very
rapid. Other muscles are connected with the arytenoid cartilages which
serve to seperate the vocal cords and to widely open the glottis. The
force of the outgoing current of air determines the extent of the
movement of the cords, and thus the loudness of the sound will increase
with greater force of expiration.

We have just learned that the pitch of sound depends on the rapidity of
the vibrations. This depends on the length of cords and their tightness
for the shorter and tighter a string is, the higher is the note which
its vibration produces. The vocal cords of women are about one-third
shorter than those of men, hence the higher pitch of the notes they
produce. In children the vocal cords are shorter than in adults.[50]
The cords of tenor singers are also shorter than those of basses and
baritones. The muscles within the larynx, of course, play a very
important part in altering the tension of the vocal cords. Those
qualities of the voice which we speak of as sweet, harsh, and
sympathetic depend to a great extent upon the peculiar structure of the
vocal cords of the individual.

Besides the physical condition of the vocal cords, as their degree of
smoothness, elasticity, thickness, and so on, other factors determine
the quality of an individual’s voice. Thus, the general shape and
structure of the trachea, the larynx, the throat, and mouth all
influence the quality of voice. In fact, the air passages, both below
and above the vibrating cords, act as resonators, or resounding
chambers, and intensify and modify the sounds produced by the cords. It
is this fact that prompts skillful teachers of music and elocution to
urge upon their pupils the necessity of the mouth being properly opened
during speech, and especially during singing.

Experiment 187. _To show the anatomy of the throat_. Study the general
construction of the throat by the help of a hand mirror. Repeat the
same on the throat of some friend.

Experiment 188. _To show the construction of the vocal organs_. Get a
butcher to furnish two windpipes from a sheep or a calf. They differ
somewhat from the vocal organs of the human body, but will enable us to
recognize the different parts which have been described, and thus to
get a good idea of the gross anatomy.

  One specimen should be cut open lengthwise in the middle line in
  front, and the other cut in the same way from behind.

354. Speech. Speech is to be distinguished from voice. It may exist
without voice, as in a whisper. Speech consists of articulated sounds,
produced by the action of various parts of the mouth, throat, and nose.
Voice is common to most animals, but speech is the peculiar privilege
of man.

Illustration: Fig. 152.—Diagramatic Horizontal Section of Larynx to
show the Direction of Pull of the Posterior Crico-Arytenoid Muscles,
which abduct the Vocal Cords. (Dotted lines show position in
abduction.)]

The organ of speech is perhaps the most delicate and perfect _motor_
apparatus in the whole body. It has been calculated that upwards of 900
movements per minute can be made by the movable organs of speech during
reading, speaking, and singing. It is said that no less than a hundred
different muscles are called into action in talking. Each part of this
delicate apparatus is so admirably adjusted to every other that all
parts of this most complex machinery act in perfect harmony.

There are certain articulate sounds called vowel or vocal, from the
fact that they are produced by the vocal cords, and are but slightly
modified as they pass out of the mouth. The true vowels, _a, e, i, o,
u_, can all be sounded alone, and may be prolonged in expiration. These
are the sounds chiefly used in singing. The differences in their
characters are produced by changes in the position of the tongue,
mouth, and lips.

Consonants are sounds produced by interruptions of the outgoing current
of air, but in some cases have no sound in themselves, and serve merely
to modify vowel sounds. Thus, when the interruption to the outgoing
current takes place by movements of the lips, we have the _labial_
consonants, _p_, _b_, _f_, and _v_. When the tongue, in relation with
the teeth or hard palate, obstructs the air, the _dental_ consonants,
_d_, _t_, _l_, and _s_ are produced. _Gutturals_, such as _k_, _g_,
_ch_, _gh_, and _r_, are due to the movements of the root of the tongue
in connection with the soft palate or pharynx.

To secure an easy and proper production of articulate sounds, the
mouth, teeth, lips, tongue, and palate should be in perfect order. The
modifications in articulation occasioned by a defect in the palate, or
in the uvula, by the loss of teeth, from disease, and from congenital
defects, are sufficiently familiar. We have seen that speech consists
essentially in a modification of the vocal sounds by the accessory
organs, or by parts above the larynx, the latter being the essential
vocal instrument.

Many animals have the power of making articulated sounds; a few have
risen, like man, to the dignity of sentences, but these are only by
imitation of the human voice. Both vowels and consonants can be
distinguished in the notes of birds, the vocal powers of which are
generally higher than those of mammals. The latter, as a rule, produce
only vowels, though some are also able to form consonants.

Persons idiotic from birth are incapable of producing any other vocal
sounds than inarticulate cries, although supplied with all the internal
means of articulation. Persons deaf and dumb are in the same situation,
though from a different cause; the one being incapable of imitating,
and the other being deprived of hearing the sounds to be imitated.

Illustration: Fig. 153.—Direction of Pull of the Lateral
Crico-Arytenoids, which adduct the Vocal Cords. (Dotted lines show
position in adduction.)

In _whispering_, the larynx takes scarcely any part in the production
of the sounds; the vocal cords remain apart and comparatively slack,
and the expiratory blast rushes through without setting them in
vibration.

In _stammering_, spasmodic contraction of the diaphragm interrupts the
effort of expiration. The stammerer has full control of the mechanism
of articulation, but not of the expiratory blast. His larynx and his
lips are at his command, but not his diaphragm. To conquer this defect
he must train his muscles of respiration to calm and steady action
during speech. The _stutterer_, on the other hand, has full control of
the muscles of expiration. His diaphragm is well drilled, but his lips
and tongue are insubordinate.

355. The Care of the Throat and Voice. The throat, exposed as it is to
unwholesome and overheated air, irritating dust of the street,
factories, and workshops, is often inflamed, resulting in that common
ailment, _sore throat_. The parts are red, swollen, and quite painful
on swallowing. Speech is often indistinct, but there is no hoarseness
or cough unless the uvula is lengthened and tickles the back part of
the tongue. Slight sore throat rarely requires any special treatment,
aside from simple nursing.

The most frequent cause of throat trouble is the action of cold upon
the heated body, especially during active perspiration. For this reason
a cold bath should not be taken while a person is perspiring freely.
The muscles of the throat are frequently overstrained by loud talking,
screaming, shouting, or by reading aloud too much. People who strain or
misuse the voice often suffer from what is called “clergyman’s sore
throat.” Attacks of sore throat due to improper methods of breathing
and of using the voice should be treated by judicious elocutionary
exercises and a system of vocal gymnastics, under the direction of
proper teachers.

Persons subject to throat disease should take special care to wear
suitable underclothing, adapted to the changes of the seasons. Frequent
baths are excellent tonics to the skin, and serve indirectly to protect
one liable to throat ailments from changes in the weather. It is not
prudent to muffle the neck in scarfs, furs, and wraps, unless perhaps
during an unusual exposure to cold. Such a dress for the neck only
makes the parts tender, and increases the liability to a sore throat.

Every teacher of elocution or of vocal music, entrusted with the
training of a voice of some value to its possessor, should have a good,
practical knowledge of the mechanism of the voice. Good voices are
often injured by injudicious management on the part of some incompetent
instructor. It is always prudent to cease speaking or singing in public
the moment there is any hoarseness or sore throat.

The voice should not be exercised just after a full meal, for a full
stomach interferes with the free play of the diaphragm. A sip of water
taken at convenient intervals, and held in the mouth for a moment or
two, will relieve the dryness of the throat during the use of the
voice.

356. Effect of Alcohol upon the Throat and Voice. Alcoholic beverages
seriously injure the throat, and consequently the voice, by causing a
chronic inflammation of the membrane lining the larynx and the vocal
cords. The color is changed from the healthful pink to red, and the
natural smooth surface becomes roughened and swollen, and secretes a
tough phlegm.

The vocal cords usually suffer from this condition. They are thickened,
roughened, and enfeebled, the delicate vibration of the cords is
impaired, the clearness and purity of the vocal tones are gone, and
instead the voice has become rough and husky. So well known is this
result that vocalists, whose fortune is the purity and compass of their
tones, are scrupulously careful not to impair these fine qualities by
convivial indulgences.

357. Effect of Tobacco upon the Throat and Voice. The effect of tobacco
is often specially serious upon the throat, producing a disease well
known to physicians as “the smoker’s sore throat.” Still further, it
produces inflammation of the larynx, and thus entails disorders of the
vocal cords, involving rough voice and harsh tones. For this reason
vocalists rarely allow themselves to come under the narcotic influence
of tobacco smoke. It is stated that habitual smokers rarely have a
normal condition of the throat.

Additional Experiments.

Experiment 189. _To illustrate the importance of the resonating cavity
of the nose in articulation_. Pinch the nostrils, and try to pronounce
slowly the words “Lincoln,” “something,” or any other words which
require the sound of _m_, _ln_, or _ng_.

Illustration: Fig. 154.


Experiment 190. _To illustrate the passage of air through the glottis._
Take two strips of India rubber, and stretch them over the open end of
a boy’s “bean-blower,” or any kind of a tube. Tie them tightly with
thread, so that a chink will be left between them, as shown in Fig.
154. Force the air through such a tube by blowing hard, and if the
strips are not too far apart a sound will be produced. The sound will
vary in character, just as the bands are made tight or loose.

Experiment 191. “A very good illustration of the action of the vocal
bands in the production of the voice may be given by means of a piece
of bamboo or any hollow wooden tube, and a strip of rubber, about an
inch or an inch and a half wide, cut from the pure sheet rubber used by
dentists.
    “One end of the tube is to be cut sloping in two directions, and
    the strip of sheet rubber is then to be wrapped round the tube, so
    as to leave a narrow slit terminating at the upper corners of the
    tube.
    “By blowing into the other end of the tube the edges of the rubber
    bands will be set in vibration, and by touching the vibrating
    membrane at different points so as to check its movements it may be
    shown that the pitch of the note emitted depends upon the length
    and breadth of the vibrating portion of the vocal bands.”[51]—Dr.
    H. P. Bowditch.

Note. The limitations of a text-book on physiology for schools do not
permit so full a description of the voice as the subject deserves. For
additional details, the student is referred to Cohen’s _The Throat and
the Voice_, a volume in the “American Health Primer Series.” Price 40
cents.



Chapter XIII.
Accidents and Emergencies.


358. Prompt Aid to the Injured. A large proportion of the accidents,
emergencies, and sudden sicknesses that happen do not call for medical
or surgical attention. For those that do require the services of a
physician or surgeon, much can be often done before the arrival of
professional help. Many a life has been saved and much suffering and
anxiety prevented by the prompt and efficient help of some person with
a cool head, a steady hand, and a practical knowledge of what to do
first. Many of us can recall with mingled admiration and gratitude the
prompt services rendered our families by some neighbor or friend in the
presence of an emergency or sudden illness.

In fact, what we have studied in the preceding chapters becomes tenfold
more interesting, instructive, and of value to us, if we are able to
supplement such study with its practical application to the treatment
of the more common and less serious accidents and emergencies.

While no book can teach one to have presence of mind, a cool head, or
to restrain a more or less excitable temperament in the midst of sudden
danger, yet assuredly with proper knowledge for a foundation, a certain
self-confidence may be acquired which will do much to prevent hasty
action, and to maintain a useful amount of self-control.

Space allows us to describe briefly in this chapter only a few of the
simplest helps in the more common accidents and emergencies which are
met with in everyday life.[52]

 359. Hints as to what to Do First. Retain so far as possible your
 presence of mind, or, in other words, keep cool. This is an
 all-important direction. Act promptly and quietly, but not with haste.
 Whatever you do, do in earnest; and never act in a half-hearted manner
 in the presence of danger. Of course, a knowledge of what to-do and
 how to do it will contribute much towards that self-control and
 confidence that command success. Be sure and send for a doctor at once
 if the emergency calls for skilled service. All that is expected of
 you under such circumstances is to tide over matters until the doctor
 comes.

Illustration: Fig. 155.—Showing how Digital Compression should be
applied to the Brachial Artery.

Do not presume upon any smattering of knowledge you have, to assume any
risk that might lead to serious results. Make the sufferer comfortable
by giving him an abundance of fresh air and placing him in a restful
position. Do all that is possible to keep back the crowd of curious
lookers-on, whom a morbid curiosity has gathered about the injured
person. Loosen all tight articles of clothing, as belts, collars,
corsets, and elastics. Avoid the use of alcoholic liquors. They are
rarely of any real service, and in many instances, as in bleeding, may
do much harm.

360. Incised and Lacerated Wounds. An incised or cut wound is one made
by a sharp instrument, as when the finger is cut with a knife. Such a
wound bleeds freely because the clean-cut edges do not favor the
clotting of blood. In slight cuts the bleeding readily ceases, and the
wound heals by primary union, or by “first intention,” as surgeons call
it.

Lacerated and contused wounds are made by a tearing or bruising
instrument, for example, catching the finger on a nail. Such wounds
bleed but little, and the edges and surfaces are rough and ragged.

If the incised wound is deep or extensive, a physician is necessary to
bring the cut edges together by stitches in order to get primary union.
Oftentimes, in severe cuts, and generally in lacerations, there is a
loss of tissue, so that the wound heals by “second intention”; that is,
the wound heals from the bottom by a deposit of new cells called
_granulations_, which gradually fill it up. The skin begins to grow
from the edges to the center, covering the new tissue and leaving a
cicatrix or scar with which every one is familiar.

361. Contusion and Bruises. An injury to the soft tissues, caused by a
blow from some blunt instrument, or a fall, is a contusion, or bruise.
It is more or less painful, followed by discoloration due to the escape
of blood under the skin, which often may not be torn through. A black
eye, a knee injured by a fall from a bicycle, and a finger hurt by a
baseball, are familiar examples of this sort of injury. Such injuries
ordinarily require very simple treatment.

The blood which has escaped from the capillaries is slowly absorbed,
changing color in the process, from blue black to green, and fading
into a light yellow. Wring out old towels or pieces of flannel in hot
water, and apply to the parts, changing as they become cool. For cold
applications, cloths wet with equal parts of water and alcohol,
vinegar, and witch-hazel may be used. Even if the injury is apparently
slight it is always safe to rest the parts for a few days.

When wounds are made with ragged edges, such as those made by broken
glass and splinters, more skill is called for. Remove every bit of
foreign substance. Wash the parts clean with one of the many antiseptic
solutions, bring the torn edges together, and hold them in place with
strips of plaster. Do not cover such an injury all over with plaster,
but leave room for the escape of the wound discharges. For an outside
dressing, use compresses made of clean cheese-cloth or strips of any
clean linen cloth. The antiseptic _corrosive-sublimate gauze_ on sale
at any drug store should be used if it can be had.

Wounds made by toy pistols, percussion-caps, and rusty nails and tools,
if neglected, often lead to serious results from blood-poisoning. A hot
flaxseed poultice may be needed for several days. Keep such wounds
clean by washing or syringing them twice a day with hot _antiseptics_,
which are poisons to _bacteria_ and kill them or prevent their growth.
Bacteria are widely distributed, and hence the utmost care should be
taken to have everything which is to come in contact with a wounded
surface free from the germs of inflammation. In brief, such injuries
must be kept _scrupulously neat_ and _surgically clean_.

Illustration: Fig. 156.—Dotted Line showing the Course of the Brachial
Artery.

The injured parts should be kept at rest. Movement and disturbance
hinder the healing process.

362. Bites of Mad Dogs. Remove the clothing at once, if only from the
bitten part, and apply a temporary ligature _above_ the wound. This
interrupts the activity of the circulation of the part, and to that
extent delays the absorption of the poisonous saliva by the
blood-vessels of the wound. A dog bite is really a lacerated and
contused wound, and lying in the little roughnesses, and between the
shreds, is the poisonous saliva. If by any means these projections and
depressions affording the lodgment can be removed, the poison cannot do
much harm. If done with a knife, the wound would be converted,
practically, into an incised wound, and would require treatment for
such.

If a surgeon is at hand he would probably cut out the injured portion,
or cauterize it thoroughly. Professional aid is not always at our
command, and in such a case it would be well to take a poker, or other
suitable piece of iron, heat it _red_ hot in the fire, wipe off and
destroy the entire surface of the wound. As fast as destroyed, the
tissue becomes white. An iron, even at a white heat, gives less pain
and at once destroys the vitality of the part with which it comes in
contact.

If the wound is at once well wiped out, and a stick of solid nitrate of
silver (lunar caustic) rapidly applied to the entire surface of the
wound, little danger is to be apprehended. Poultices and warm
fomentations should be applied to the injury to hasten the sloughing
away of the part whose vitality has been intentionally destroyed.

Any dog, after having bitten a person, is apt, under a mistaken belief,
to be at once killed. This should not be done. There is no more danger
from a dog-bite, unless the dog is suffering from the disease called
_rabies_ or is “mad,” than from any other lacerated wound. The
suspected animal should be at once placed in confinement and watched,
under proper safeguards, for the appearance of any symptoms that
indicate rabies.

Should no pronounced symptoms indicate this disease in the dog, a great
deal of unnecessary mental distress and worry can be saved both on the
part of the person bitten and his friends.

363. Injuries to the Blood-vessels. It is very important to know the
difference between the bleeding from an artery and that from a vein.

If an artery bleeds, the blood leaps in spurts, and is of a bright
scarlet color.

If a vein bleeds, the blood flows in a steady stream, and is of a dark
purple color.

If the capillaries are injured the blood merely oozes.

Bleeding from an artery is a dangerous matter in proportion to the size
of the vessel, and life itself may be speedily lost. Hemorrhage from a
vein or from the capillaries is rarely troublesome, and is ordinarily
easily checked, aided, if need be, by hot water, deep pressure, the
application of some form of iron styptic, or even powdered alum. When
an artery is bleeding, always remember to make deep pressure between
the wound and the heart. In all such cases send at once for the doctor.

Illustration: Fig. 157.—Showing how Digital Compression should be
applied to the Femoral Artery.


Do not be afraid to act at once. A resolute grip in the right place
with firm fingers will do well enough, until a twisted handkerchief,
stout cord, shoestring, suspender, or an improvised tourniquet[53] is
ready to take its place. If the flow of blood does not stop, change the
pressure until the right spot is found.

Sometimes it will do to seize a handful of dry earth and crowd it down
into the bleeding wound, with a firm pressure. Strips of an old
handkerchief, underclothing, or cotton wadding may also be used as a
compress, provided pressure is not neglected.

In the after-treatment it is of great importance that the wound and the
dressing should be kept free from bacteria by keeping everything
surgically clean.

364. Where and how to Apply Pressure. The principal places in which to
apply pressure when arteries are injured and bleeding should always be
kept in mind.

Experiment 192. _How to tie a square knot_. If the student would render
efficient help in accidents and emergencies, to say nothing of service
on scores of other occasions, he must learn how to tie a square or
“reef” knot. This knot is secure and does not slip as does the “granny”
knot. The square knot is the one used by surgeons in ligating vessels
and securing bandages. Unless one knew the difference, the insecure
“granny” knot might be substituted.
    A square knot is tied by holding an end of a bandage or cord in
    each hand, and then passing the end in the _right_ hand over the
    one in the left and tying; the end now in the _left_ hand is passed
    over the one in the right and again tied.

Illustration: Fig. 158.—Showing how a Square Knot may be tied with a
Cord and a Handkerchief.

If in the finger, grasp it with the thumb and forefinger, and pinch it
firmly on each side; if in the hand, press on the bleeding spot, or
press with the thumb just above and in front of the wrist.

For injuries below the elbow, grasp the upper part of the arm with the
hands, and squeeze hard. The main artery runs in the middle line of the
bend of the elbow. Tie the knotted cord here, and bend the forearm so
as to press hard against the knot.

For the upper arm, press with the fingers against the bone on the inner
side, and just on the edge of the swell of the biceps muscle. Now we
are ready for the knotted cord. Take a stout stick of wood, about a
foot long, and twist the cord hard with it, bringing the knot firmly
over the artery.

For the foot or leg, pressure as before, in the hollow behind the knee,
just above the calf of the leg. Bend the thigh towards the abdomen and
bring the leg up against the thigh, with the knot in the bend of the
knee.

365. Bleeding from the Stomach and Lungs. Blood that comes from the
lungs is bright red, frothy, or “soapy.” There is rarely much; it
usually follows coughing, feels warm, and has a salty taste. This is a
grave symptom. Perfect rest on the back in bed and quiet must be
insisted upon. Bits of ice should be eaten freely. Loosen the clothing,
keep the shoulders well raised, and the body in a reclining position
and absolutely at rest. Do not give alcoholic drinks.

Blood from the stomach is not frothy, has a sour taste, and is usually
dark colored, looking somewhat like coffee grounds. It is more in
quantity than from the lungs, and is apt to be mixed with food. Employ
the same treatment, except that the person should be kept flat on the
back.

366. Bleeding from the Nose. This is the most frequent and the least
dangerous of the various forms of bleeding. Let the patient sit
upright; leaning forward with the head low only increases the
hemorrhage. Raise the arm on the bleeding side; do not blow the nose.
Wring two towels out of cold water; wrap one around the neck and the
other properly folded over the forehead and upper part of the nose.

Add a teaspoonful of powdered _alum_ to a cup of water, and snuff it up
from the hand. If necessary, soak in alum water a piece of absorbent
cotton, which has been wound around the pointed end of a pencil or
penholder; plug the nostril by pushing it up with a twisting motion
until firmly lodged.

367. Burns or Scalds. Burns or scalds are dangerous in proportion to
their extent and depth. A child may have one of his fingers burned off
with less danger to life than an extensive scald of his back and legs.
A deep or extensive burn or scald should always have prompt medical
attendance.

In burns by acids, bathe the parts with an alkaline fluid, as diluted
ammonia, or strong soda in solution, and afterwards dress the burn.

In burns caused by lime, caustic potash, and other alkalies, soak the
parts with vinegar diluted with water; lemon juice, or any other
diluted acid.

Remove the clothing with the greatest care. Do not pull, but carefully
cut and coax the clothes away from the burned places. Save the skin
unbroken if possible, taking care not to break the blisters. The secret
of treatment is to prevent friction, and to keep out the air. If the
burn is slight, put on strips of soft linen soaked in a strong solution
of baking-soda and water, one heaping table spoonful to a cupful of
water. This is especially good for scalds.

Illustration: Fig. 159.—Dotted Line showing the Course of the Femoral
Artery.

_Carron oil_ is one of the best applications. It is simply half
linseed-oil and half lime-water shaken together. A few tablespoonfuls
of carbolic acid solution to one pint may be added to this mixture to
help deaden the pain. Soak strips of old linen or absorbent cotton in
this time-honored remedy, and gently apply.

If carbolized or even plain _vaseline_ is at hand, spread it freely on
strips of old linen, and cover well the burnt parts, keeping out the
air with other strips carefully laid on. Simple cold water is better
than flour, starch, toilet powder, cotton batting, and other things
which are apt to stick, and make an after-examination very painful.

Illustration: Fig. 160.—Showing how Hemorrhage from the Femoral Artery
may be arrested by the Use of an Improvised Apparatus (technically
called a _Tourniquet_).


368. Frost Bites. The ears, toes, nose, and fingers are occasionally
frozen, or frost-bitten. No warm air, warm water, or fire should be
allowed near the frozen parts until the natural temperature is nearly
restored. Rub the frozen part vigorously with snow or snow-water in a
cold room. Continue this until a burning, tingling pain is felt, when
all active treatment should cease.

Pain shows that warmth and circulation are beginning to return. The
after effects of a frost bite are precisely like those of a burn, and
require similar treatment. Poultices made from scraped raw potatoes
afford much comfort for an after treatment.

369. Catching the Clothing on Fire. When the clothing catches fire,
throw the person down on the ground or floor, as the flames will tend
less to rise toward the mouth and nostrils. Then without a moment’s
delay, roll the person in a carpet or hearth-rug, so as to stifle the
flames, leaving only the head out for breathing.

If no carpet or rug can be had, then take off your coat, shawl, or
cloak and use it instead. Keep the flame as much as possible from the
face, so as to prevent the entrance of the hot air into the lungs. This
can be done by beginning at the neck and shoulders with the wrapping.

370. Foreign Bodies in the Throat. Bits of food or other small objects
sometimes get lodged in the throat, and are easily extracted by the
forefinger, by sharp slaps on the back, or expelled by vomiting. If it
is a sliver from a toothpick, match, or fishbone, it is no easy matter
to remove it; for it generally sticks into the lining of the passage.
If the object has actually passed into the windpipe, and is followed by
sudden fits of spasmodic coughing, with a dusky hue to the face and
fingers, surgical help must be called without delay.

If a foreign body, like coins, pencils, keys, fruit-stones, etc., is
swallowed, it is not wise to give a physic. Give plenty of hard-boiled
eggs, cheese, and crackers, so that the intruding substance maybe
enfolded in a mass of solid food and allowed to pass off in the natural
way.

371. Foreign Bodies in the Nose. Children are apt to push beans, peas,
fruit-stones, buttons, and other small objects, into the nose.
Sometimes we can get the child to help by blowing the nose hard. At
other times, a sharp blow between the shoulders will cause the
substance to fall out. If it is a pea or bean, which is apt to swell
with the warmth and moisture, call in medical help at once.

372. Foreign Bodies in the Ear. It is a much more difficult matter to
get foreign bodies out of the ear than from the nose. Syringe in a
little warm water, which will often wash out the substance. If live
insects get into the ear, drop in a little sweet oil, melted vaseline,
salt and water, or even warm molasses.

If the tip of the ear is pulled up gently, the liquid will flow in more
readily. If a light is held close to the outside ear, the insect may be
coaxed to crawl out towards the outer opening of the ear, being
attracted by the bright flame.

373. Foreign Bodies in the Eye. Cinders, particles of dust, and other
small substances, often get into the eye, and cause much pain. It will
only make bad matters worse to rub the eye. Often the copious flow of
tears will wash the substance away. It is sometimes seen, and removed
simply by the twisted corner of a handkerchief carefully used. If it is
not removed, or even found, in this way, the upper lid must be turned
back.

Illustration: Fig. 161.—Showing how the Upper Eyelid may be everted
with a Pencil or Penholder.

This is done usually as follows: Seize the lashes between the thumb and
forefinger, and draw the edge of the lid away from the eyeball. Now,
telling the patient to look down, press a slender lead-pencil or
penholder against the lid, parallel to and above the edge, and then
pull the edge up, and turn it over the pencil by means of the lashes.

The eye is now readily examined, and usually the foreign body is easily
seen and removed. Do not increase the trouble by rubbing the eye after
you fail, but get at once skilled help. After the substance has been
removed, bathe the eye for a time with hot water.

If lime gets into the eye, it may do a great amount of mischief, and
generally requires medical advice, or permanent injury will result.
Until such advice can be had, bathe the injured parts freely with a
weak solution of vinegar and hot water.

374. Broken Bones. Loss of power, pain, and swelling are symptoms of a
broken bone that may be easily recognized. Broken limbs should always
be handled with great care and tenderness. If the accident happens in
the woods, the limb should be bound with handkerchiefs, suspenders, or
strips of clothing, to a piece of board, pasteboard, or bark, padded
with moss or grass, which will do well enough for a temporary splint.
Always put a broken arm into a sling after the splints are on.

Illustration: Fig. 162.—Showing how an Umbrella may be used as a
Temporary Splint in Fracture of the Leg.


Never move the injured person until the limb is made safe from further
injuries by putting on temporary splints. If you do not need to move
the person, keep the limb in a natural, easy position, until the doctor
comes.

Remember that this treatment for broken bones is only to enable the
patient to be moved without further injury. A surgeon is needed at once
to set the broken bone.

Illustration: Fig. 163.—Showing how a Pillow may be used as a Temporary
Splint in Fracture of the Leg.


375. Fainting. A fainting person should be laid flat at once. Give
plenty of fresh air, and dash cold water, if necessary, on the head and
neck. Loosen all tight clothing. Smelling-salts may be held to the
nose, to excite the nerves of sensation.

376. Epileptic and Hysterical Fits, Convulsions of Children. Sufferers
from “fits” are more or less common. In _epilepsy_, the sufferer falls
with a peculiar cry; a loss of consciousness, a moment of rigidity, and
violent convulsions follow. There is foaming at the mouth, the eyes are
rolled up, and the tongue or lips are often bitten. When the fit is
over the patient remains in a dazed, stupid state for some time. It is
a mistake to struggle with such patients, or to hold them down and keep
them quiet. It does more harm than good.

See that the person does not injure himself; crowd a pad made from a
folded handkerchief or towel between the teeth, to prevent biting of
the lips or tongue. Do not try to make the sufferer swallow any drink.
Unfasten the clothes, especially about the neck and chest. Persons who
are subject to such fits should rarely go out alone, and never into
crowded or excited gatherings of any kind.

_Hysterical fits_ almost always occur in young women. Such patients
never bite their tongue nor hurt themselves. Placing a towel wrung out
in cold water across the face, or dashing a little cold water on the
face or neck, will usually cut short the fit, speaking firmly to the
patient at the same time. Never sympathize too much with such patients;
it will only make them a great deal worse.

377. Asphyxia. Asphyxia is from the Greek, and means an “absence of
pulse.” This states a fact, but not the cause. The word is now commonly
used to mean _suspended animation_. When for any reason the proper
supply of oxygen is cut off, the tissues rapidly load up with carbon
dioxid. The blood turns dark, and does not circulate. The healthy red
or pink look of the lips and finger-nails becomes a dusky purple. The
person is suffering from a lack of oxygen; that is, from asphyxia, or
suffocation. It is evident there can be several varieties of asphyxia,
as in apparent drowning, strangulation and hanging, inhalation of
gases, etc.

The first and essential thing to do is to give fresh air. Remove the
person to the open air and place him on his back. Remove tight clothing
about the throat and waist, dash on cold water, give a few drops of
ammonia in hot water or hot ginger tea. Friction applied to the limbs
should be kept up. If necessary, use artificial respiration by the
Sylvester method (sec. 380).

The chief dangers from poisoning by noxious gases come from the fumes
of burning coal in the furnace, stove, or range; from “blowing out”
gas, turning it down, and having it blown out by a draught; from the
foul air often found in old wells; from the fumes of charcoal and the
foul air of mines.

378. Apparent Drowning. Remove all tight clothing from the neck, chest,
and waist. Sweep the forefinger, covered with a handkerchief or towel,
round the mouth, to free it from froth and mucus. Turn the body on the
face, raising it a little, with the hands under the hips, to allow any
water to run out from the air passages. Take only a moment for this.

Lay the person flat upon the back, with a folded coat, or pad of any
kind, to keep the shoulders raised a little. Remove all the wet,
clinging clothing that is convenient. If in a room or sheltered place,
strip the body, and wrap it in blankets, overcoats, etc. If at hand,
use bottles of hot water, hot flats, or bags of hot sand round the
limbs and feet. Watch the tongue: it generally tends to slip back, and
to shut off the air from the glottis. Wrap a coarse towel round the tip
of the tongue, and keep it well pulled forward.

The main thing to do is to keep up artificial respiration until the
natural breathing comes, or all hope is lost. This is the simplest way
to do it: The person lies on the back; let some one kneel behind the
head. Grasp both arms near the elbows, and sweep them upward above the
head until they nearly touch. Make a firm pull for a moment. This tends
to fill the lungs with air by drawing the ribs up, and making the chest
cavity larger. Now return the arms to the sides of the body until they
press hard against the ribs. This tends to force out the air. This
makes artificially a complete act of respiration. Repeat this act about
fifteen times every minute.

Illustration: Fig. 164.—The Sylvester Method. (First
movement—inspiration.)

All this may be kept up for several hours. The first sign of recovery
is often seen in the slight pinkish tinge of the lips or finger-nails.
That the pulse cannot be felt at the wrist is of little value in itself
as a sign of death. Life may be present when only the most experienced
ear can detect the faintest heart-beat.

When a person can breathe, even a little, he can swallow. Hold
smelling-salts or hartshorn to the nose. Put one teaspoonful of the
aromatic spirits of ammonia, or even of ammonia water, into a
half-glass of hot water, and give a few teaspoonfuls of this mixture
every few minutes. Meanwhile do not fail to keep up artificial warmth
in the most vigorous manner.

379. Methods of Artificial Respiration. There are several
well-established methods of artificial respiration. The two known as
the Sylvester and the Marshall Hall methods are generally accepted as
efficient and practical.

Illustration: Fig. 165.—The Sylvester Method. (Second
movement—expiration.)


380. The Sylvester Method. The water and mucus are supposed to have
been removed from the interior of the body by the means above described
(sec. 378).

The patient is to be placed on his back, with a roll made of a coat or
a shawl under the shoulders; the tongue should then be drawn forward
and retained by a handkerchief which is placed across the extended
organ and carried under the chin, then crossed and tied at the back of
the neck. An elastic band or small rubber tube or a suspender may be
used for the same purpose.

The attendant should kneel at the head and grasp the elbows of the
patient and draw them upward until the hands are carried above the head
and kept in this position until one, two, three, can be slowly counted.
This movement elevates the ribs, expands the chest, and creates a
vacuum in the lungs into which the air rushes, or in other words, the
movement produces _inspiration_. The elbows are then slowly carried
downward, placed by the side, and pressed inward against the chest,
thereby diminishing the size of the latter and producing _expiration_.

These movements should be repeated about fifteen times each minute for
at least two hours, provided no signs of animation show themselves.

381. The Marshall Hall Method. The patient should be placed face
downwards, the head resting on the forearm with a roll or pillow placed
under the chest; he should then be turned on his side, an assistant
supporting the head and keeping the mouth open; after an interval of
two or three seconds, the patient should again be placed face downward
and allowed to remain in this position the same length of time. This
operation should be repeated fifteen or sixteen times each minute, and
continued (unless the patient recovers) for at least two hours.

Illustration: Fig. 166.—The Marshall Hall Method. (First position.)


If, after using one of the above methods, evidence of recovery appears,
such as an occasional gasp or muscular movement, the efforts to produce
artificial respiration must not be discontinued, but kept up until
respiration is fully established. All wet clothing should then be
removed, the patient rubbed dry, and if possible placed in bed, where
warmth and warm drinks can be properly administered. A small amount of
nourishment, in the form of hot milk or beef tea, should be given, and
the patient kept quiet for two or three days.

Illustration: Fig. 167.—The Marshall Hall Method. (Second position.)


382. Sunstroke or Heatstroke. This serious accident, so far-reaching
oftentimes in its result, is due to an unnatural elevation of the
bodily temperature by exposure to the direct rays of the sun, or from
the extreme heat of close and confined rooms, as in the cook-rooms and
laundries of hotel basements, from overheated workshops, etc.

There is sudden loss of consciousness, with deep, labored breathing, an
intense burning heat of the skin, and a marked absence of sweat. The
main thing is to lower the temperature. Strip off the clothing; apply
chopped ice, wrapped in flannel to the head. Rub ice over the chest,
and place pieces under the armpits and at the sides. If there is no
ice, use sheets or cloths wet with cold water. The body may be
stripped, and sprinkled with ice-water from a common watering-pot.

If the skin is cold, moist, or clammy, the trouble is due to heat
exhaustion. Give plenty of fresh air, but apply no cold to the body.
Apply heat, and give hot drinks, like hot ginger tea. Sunstroke or
heatstroke is a dangerous affliction. It is often followed by serious
and permanent results. Persons who have once suffered in this way
should carefully avoid any risk in the future.



Chapter XIV.
In Sickness and in Health.


383. Arrangement of the Sick-room. This room, if possible, should be on
the quiet and sunny side of the house. Pure, fresh air, sunshine, and
freedom from noise and odor are almost indispensable. A fireplace as a
means of ventilation is invaluable. The bed should be so placed that
the air may get to it on all sides and the nurse move easily around it.
Screens should be placed, if necessary, so as to exclude superfluous
light and draughts.

The sick-room should be kept free from all odors which affect the sick
unpleasantly, as perfumery, highly scented soaps, and certain flowers.
Remove all useless ornaments and articles likely to collect dust, as
unnecessary pieces of furniture and heavy draperies. A clean floor,
with a few rugs to deaden the footsteps, is much better than a woolen
carpet. Rocking-chairs should be banished from the sick-room, as they
are almost sure to disturb the sick.

A daily supply of fresh flowers tends to brighten the room. Keep the
medicines close at hand, but all poisonous drugs should be kept
carefully by themselves and ordinarily under lock and key. A small
table should be placed at the bedside, and on it the bell, food tray,
flowers and other small things which promote the comfort of the
patient.

The nurse should not sleep with the patient. Sofas and couches are not
commonly comfortable enough to secure needed rest. A cot bed is at once
convenient and inexpensive, and can be readily folded and put out of
sight in the daytime. It can also be used by the patient occasionally,
especially during convalescence.

384. Ventilation of the Sick-room. Proper ventilation is most essential
to the sick-room, but little provision is ordinarily made for so
important a matter. It is seldom that one of the windows cannot be let
down an inch or more at the top, a screen being arranged to avoid any
draught on the patient. Remove all odors by ventilation and not by
spraying perfumery, or burning pastilles, which merely conceal
offensive odors without purifying the air. During cold weather and in
certain diseases, the patient may be covered entirely with blankets and
the windows opened wide for a few minutes.

Avoid ventilation by means of doors, for the stale air of the house,
kitchen smells, and noises made by the occupants of the house, are apt
to reach the sick-room. The entire air of the room should be changed at
least two or three times a day, in addition to the introduction of a
constant supply of fresh air in small quantities.

385. Hints for the Sick-room. Always strive to look cheerful and
pleasant before the patient. Whatever may happen, do not appear to be
annoyed, discouraged, or despondent. Do your best to keep up the
courage of sick persons under all circumstances. In all things keep in
constant mind the comfort and ease of the patient.

Do not worry the sick with unnecessary questions, idle talk, or silly
gossip. It is cruel to whisper in the sick-room, for patients are
always annoyed by it. They are usually suspicious that something is
wrong and generally imagine that their condition has changed for the
worse.

Symptoms of the disease should never be discussed before the patient,
especially if he is thought to be asleep. He may be only dozing, and
any such talk would then be gross cruelty. Loud talking must, of
course, be avoided. The directions of the physician must be rigidly
carried out in regard to visitors in the sick-room. This is always a
matter of foremost importance, for an hour or even a night of needed
sleep and rest may be lost from the untimely call of some thoughtless
visitor. A competent nurse, who has good sense and tact, should be able
to relieve the family of any embarrassment under such circumstances.

Do not ever allow a kerosene light with the flame turned down to remain
in the sick-room. Use the lamp with the flame carefully shaded, or in
an adjoining room, or better still, use a sperm candle for a night
light.

Keep, so far as possible, the various bottles of medicine, spoons,
glasses, and so on in an adjoining room, rather than to make a
formidable array of them on a bureau or table near the sick-bed. A few
simple things, as an orange, a tiny bouquet, one or two playthings, or
even a pretty book, may well take their place.

The ideal bed is single, made of iron or brass, and provided with woven
wire springs and a hair mattress. Feather-beds are always objectionable
in the sick-room for many and obvious reasons. The proper making of a
sick-bed, with the forethought and skill demanded in certain diseases,
is of great importance and an art learned only after long experience.
The same principle obtains in all that concerns the lifting and the
moving of the sick.

Sick people take great comfort in the use of fresh linen and fresh
pillows. Two sets should be used, letting one be aired while the other
is in use. In making changes the fresh linen should be thoroughly aired
and warmed and everything in readiness before the patient is disturbed.

386. Rules for Sick-room. Do not deceive sick people. Tell what is
proper or safe to be told, promptly and plainly. If a physician is
employed, carry out his orders to the very letter, as long as he visits
you. Make on a slip of paper a note of his directions. Make a brief
record of exactly what to do, the precise time of giving medicines,
etc. This should always be done in serious cases, and by night
watchers. Then there is no guesswork. You have the record before you
for easy reference. All such things are valuable helps to the doctor.

Whatever must be said in the sick-room, say it openly and aloud. How
often a sudden turn in bed, or a quick glance of inquiry, shows that
whispering is doing harm! If the patient is in his right mind, answer
his questions plainly and squarely. It may not be best to tell all the
truth, but nothing is gained in trying to avoid a straightforward
reply.

Noises that are liable to disturb the patient, in other parts of the
house than the sick-room, should be avoided. Sounds of a startling
character, especially those not easily explained, as the rattling or
slamming of distant blinds and doors, are always irritating to the
sick.

Always attract the attention of a patient before addressing him,
otherwise he may be startled and a nervous spell be induced. The same
hint applies equally to leaning or sitting upon the sick-bed, or
running against furniture in moving about the sick-room.

387. Rest of Mind and Body. The great importance of rest for the sick
is not so generally recognized as its value warrants. If it is worry
and not work that breaks down the mental and physical health of the
well, how much more important is it that the minds and bodies of the
sick should be kept at rest, free from worry and excitement! Hence the
skilled nurse does her best to aid in restoring the sick to a condition
of health by securing for her patient complete rest both of mind and
body. To this end, she skillfully removes all minor causes of alarm,
irritation, or worry. There are numberless ways in which this may be
done of which space does not allow even mention. Details apparently
trifling, as noiseless shoes, quietness, wearing garments that do not
rustle, use of small pillows of different sizes, and countless other
small things that make up the refinement of modern nursing, play an
important part in building up the impaired tissues of the sick.

388. Care of Infectious and Contagious Diseases. There are certain
diseases which are known to be infectious and can be communicated from
one person to another, either by direct contact, through the medium of
the atmosphere, or otherwise.

Of the more prevalent infectious and contagious diseases are _scarlet
fever, diphtheria, erysipelas, measles_, and _typhoid fever_.

Considerations of health demand that a person suffering from any one of
these diseases should be thoroughly isolated from all other members of
the family. All that has been stated in regard to general nursing in
previous sections of this chapter, applies, of course, to nursing
infectious and contagious diseases. In addition to these certain
special directions must be always kept in mind.

Upon the nurse, or the person having the immediate charge of the
patient, rests the responsibility of preventing the spread of
infectious diseases. The importance must be fully understood of
carrying out in every detail the measures calculated to check the
spread or compass the destruction of the germs of disease.

389. Hints on Nursing Infectious and Contagious Diseases. Strip the
room of superfluous rugs, carpets, furniture, etc. Isolate two rooms,
if possible, and have these, if convenient, at the top of the house.
Tack sheets, wet in some proper disinfectant, to the outer frame of the
sick-room door. Boil these sheets every third day. In case of diseases
to which young folks are very susceptible, send the children away, if
possible, to other houses where there are no children.

Most scrupulous care should be taken in regard to cleanliness and
neatness in every detail. Old pieces of linen, cheese-cloth, paper
napkins, should be used wherever convenient or necessary and then at
once burnt. All soiled clothing that cannot well be burnt should be put
to soak at once in disinfectants, and afterward boiled apart from the
family wash. Dishes and all utensils should be kept scrupulously clean
by frequent boiling. For the bed and person old and worn articles of
clothing that can be destroyed should be worn so far as possible.

During convalescence, or when ready to leave isolation, the patient
should be thoroughly bathed in water properly disinfected, the hair and
nails especially being carefully treated.

Many details of the after treatment depend upon the special disease, as
the rubbing of the body with carbolized vaseline after scarlet fever,
the care of the eyes after measles, and other particulars of which
space does not admit mention here.

Poisons and Their Antidotes.

390. Poisons. A poison is a substance which, if taken into the system
in sufficient amounts, will cause serious trouble or death. For
convenience poisons may be divided into two classes, irritants and
narcotics.

The effects of irritant poisons are evident immediately after being
taken. They burn and corrode the skin or membrane or other parts with
which they come in contact. There are burning pains in the mouth,
throat, stomach, and abdomen, with nausea and vomiting. A certain
amount of faintness and shock is also present.

With narcotic poisoning, the symptoms come on more slowly. After a time
there is drowsiness, which gradually increases until there is a
profound sleep or stupor, from which the patient can be aroused only
with great difficulty. There are some substances which possess both the
irritant and narcotic properties and in which the symptoms are of a
mixed character.

391. Treatment of Poisoning. An antidote is a substance which will
either combine with a poison to render it harmless, or which will have
a directly opposite effect upon the body, thus neutralizing the effect
of the poison. Hence in treatment of poisoning the first thing to do,
if you know the special poison, is to give its antidote at once.

If the poison is unknown, and there is any delay in obtaining the
antidote, the first thing to do is to remove the poison from the
stomach. Therefore cause vomiting as quickly as possible. This may be
done by an emetic given as follows: Stir a tablespoonful of mustard or
of common salt in a glass of warm water and make the patient swallow
the whole. It will usually be vomited in a few moments. If mustard or
salt is not at hand, compel the patient to drink lukewarm water very
freely until vomiting occurs.

Vomiting may be hastened by thrusting the forefinger down the throat.
Two teaspoonfuls of the syrup of ipecac, or a heaping teaspoonful of
powdered ipecac taken in a cup of warm water, make an efficient emetic,
especially if followed with large amounts of warm water.

It is to be remembered that in some poisons, as certain acids and
alkalies, no emetic should be given. Again, for certain poisons (except
in case of arsenic) causing local irritation, but which also affect the
system at large, no emetic should be given.

392. Reference Table of Common Poisons; Prominent Symptoms; Antidotes
and Treatment. The common poisons with their leading symptoms,
treatment, and antidotes, may be conveniently arranged for easy
reference in the form of a table.

It is to be remembered, of course, that a complete mastery of the table
of poisons, as set forth on the two following pages, is really a
physician’s business. At the same time, no one of fair education should
neglect to learn a few of the essential things to do in accidental or
intentional poisoning.

                  A Table of the More Common Poisons,

       With their prominent symptoms, antidotes, and treatment.
       Poison Prominent Symptoms Antidotes and Treatment _Strong
       Acids:_

Muriatic,

Nitric,

Sulphuric (vitriol),

Oxalic.
Burning sensation in mouth, throat, and stomach; blisters about mouth;
vomiting; great weakness _No emetic_ Saleratus; chalk; soap; plaster
from the wall; lime; magnesia; baking soda (3 or 4 teaspoonfuls in a
glass of water). _Alkalies_:

Caustic potash and soda,

Ammonia,

Lye,

Pearlash,

Saltpeter.
Burning sensation in the parts; severe pain in stomach; vomiting;
difficulty in swallowing; cold skin; weak pulse. _No emetic_ Olive
oil freely; lemon juice, vinegar; melted butter and vaseline; thick
cream. _Arsenic:_

Paris green,
Rough on rats,
White arsenic,
Fowler’s solution,
Scheele’s green. Intense pains in stomach and bowels; thirst; vomiting,
perhaps with blood; cold and clammy skin. Vomit patient repeatedly,
give hydrated oxide of iron with magnesia, usually kept by druggists
for emergencies; follow with strong solution of common salt and water.
_Other Metallic Poisons_:
Blue vitriol,
Copperas,
Green vitriol,
Sugar of lead,
Corrosive sublimate,
Bedbug poison. Symptoms in general, same as in arsenical poisoning. 
With lead and mercury there may be a metallic taste in the
mouth. Emetic with lead; none with copper and iron; white of eggs in
abundance with copper; with iron and lead give epsom salts freely;
afterwards, oils, flour, and water. _No emetic with mercury;_ raw eggs;
milk, or flour, and water. _Phosphorus from_
Matches, rat poisons, etc. Pain in the stomach; vomiting; purging;
general collapse. _Cause vomiting_. Strong soapsuds; magnesia in
water. Never give oils. _Opium:_

Morphine,
Laudanum,
Paregoric,
Dover’s powder,
Soothing syrups,
Cholera and diarrhœa mixtures Sleepiness; dullness; stupor; “pin-hole”
pupils; slow breathing; profuse sweat. _Cause vomiting_. Keep
patient awake by any means, especially by vigorous walking; give strong
coffee freely; dash cold water on face and chest. _Carbolic Acid:_
Creasote. Severe pain in abdomen; odor of carbolic acid, mucous
membrane in around mouth white and benumbed; cold and clammy
skin. _No emetic._ Milk or flour and water; white of  eggs.
_Aconite:_
Wolfsbane Monkshood Numbness everywhere, great weakness; cold
sweat. _Vomit patient freely._ Stimulating drinks. _Belladonna_
Deadly Nightshade Atropia Eyes bright, with pupil enlarged; dry mouth
and throat. _Vomit patient freely._ _Various Vegetable Poisons_

Wild parsley,
Indian tobacco,
Toadstools,
Tobacco plant,
Hemlock,
Berries of the Mountain Ash,
Bitter sweet, etc. Stupor, nausea, great weakness and other symptoms
according to the poison. _Cause brisk vomiting_. Stimulating drinks.

393. Practical Points about Poisons. Poisons should never be kept in
the same place with medicines or other preparations used in the
household. They should always be put in some secure place under lock
and key. Never use internally or externally any part of the contents of
any package or bottle unless its exact nature is known. If there is the
least doubt about the substance, do not assume the least risk, but
destroy it at once. Many times the unknown contents of some bottle or
package has been carelessly taken and found to be poison.

Careless and stupid people often take, by mistake, with serious, and
often fatal, results, poisonous doses of carbolic acid, bed-bug poison,
horse-liniment, oxalic acid, and other poisons. A safe rule is to keep
all bottles and boxes containing poisonous substances securely bottled
or packed, and carefully labeled with the word POISON plainly written
in large letters across the label. Fasten the cork of a bottle
containing poison to the bottle itself with copper or iron wire twisted
into a knot at the top. This is an effective means of preventing any
mistakes, especially in the night.

This subject of poisons assumes nowadays great importance, as it is a
common custom to keep about stables, workshops, bathrooms, and living
rooms generally a more or less formidable array of germicides,
disinfectants, horse-liniments, insect-poisons, and other preparations
of a similar character. For the most part they contain poisonous
ingredients.

Bacteria.

394. Nature Of Bacteria. The word bacteria is the name applied to very
low forms of plant life of microscopic size. Thus, if hay be soaked in
water for some time, and a few drops of the liquid are examined under a
high power of the microscope, the water is found to be swarming with
various forms of living vegetable organisms, or bacteria. These
microscopic plants belong to the great fungus division, and consist of
many varieties, which may be roughly divided into groups, according as
they are spherical, rod-like, spiral, or otherwise in shape.

Each plant consists of a mass of protoplasm surrounded by an
ill-defined cell wall. The bacteria vary considerably in size. Some of
the rod-shaped varieties are from 1/12,000 to 1/8,000 of an inch in
length, and average about 1/50,000 of an inch in diameter. It has been
calculated that a space of one cubic millimeter would contain
250,000,000 of these minute organisms, and that they would not weigh
more than a milligram.

Illustration: Fig. 168.—Examples of Micro-Organisms called Bacteria.
(Drawn from photographs.)


A,  spheroidal bacteria (called _cocci_) in pairs;
  B, same kind of bacteria in chains;
  C, bacteria found in pus (grouped in masses like a bunch of grapes).
     [Bacteria in A, B, and C magnified about 1000 diameters].
  D, bacteria found in pus (tendency to grow in the form of chains).
     [Magnified about 500 diameters.]

Bacteria are propagated in a very simple manner. The parent cell
divides into two; these two into two others, and so on. The rapidity
with which these organisms multiply under favorable conditions, makes
them, in some cases, most dangerous enemies. It has been calculated
that if all of the organisms survived, one bacterium would lead to the
production of several billions of others in twenty-four hours.

395. The Struggle of Bacteria for Existence. Like all kinds of living
things, many species of bacteria are destroyed if exposed to boiling
water or steam, but seem able to endure prolonged cold, far below the
freezing-point. Thus ice from ponds and rivers may contain numerous
germs which resume their activity when the ice is melted. Typhoid fever
germs have been known to take an active and vigorous growth after they
have been kept for weeks exposed in ice to a temperature below zero.

The bacteria of consumption (bacillus tuberculosis) may retain their
vitality for months, and then the dried expectoration of the invalids
may become a source of danger to those who inhale air laden with such
impurities (sec. 220 and Fig. 94).

Like other living organisms, bacteria need warmth, moisture, and some
chemical compound which answers for food, in order to maintain the
phenomena of life. Some species grow only in contact with air, others
need no more oxygen than they can obtain in the fluid or semi-fluid
which they inhabit.

396. Importance of Bacteria in Nature. We might well ask why the
myriads of bacteria do not devastate the earth with their marvelous
rapidity of propagation. So indeed they might, were it not for the
winds, rains, melting snow and ice which scatter them far and wide, and
destroy them.

Again, as in countless other species of living organisms, bacteria are
subject to the relentless law which allows only the fittest to survive.
The bacteria of higher and more complex types devour those of a lower
type. Myriads perish in the digestive tract of man and other animals.
The excreta of some species of bacteria act as poison to destroy other
species.

It is true from the strictest scientific point of view that all living
things literally return to the dust whence they came. While living they
borrow a few elementary substances and arrange them in new
combinations, by aid of the energy given them by the sun, and after a
time die and leave behind all they had borrowed both of energy and
matter.

Countless myriads of bacteria are silently at work changing dead animal
and vegetable matter into useful substances. In brief, bacteria prepare
food for all the rest of the world. Were they all destroyed, life upon
the earth would be impossible, for the elements necessary to maintain
it would be embalmed in the bodies of the dead.

397. Action of Bacteria. In certain well-known processes bacteria have
the power of bringing about decomposition of various kinds. Thus a
highly organized fungus, like the yeast plant, growing in the presence
of sugar, has the power of breaking down this complex body into simpler
ones, _viz._, alcohol and carbon dioxid.

In the same way, various forms of bacteria have the power of breaking
down complex bodies in their immediate neighborhood, the products
depending upon the substance, the kind of bacteria, and the conditions
under which they act. Thus the _bacteria lactis_ act upon the milk
sugar present in milk, and convert it into lactic acid, thus bringing
about the souring of milk.

Illustration: Fig. 169.—Examples of Pathogenic Bacteria. (Drawn from
photographs.)


A,  spiral form of bacteria found in cholera (Magnified about 1000
diameters)
  B, rod-shaped bacteria (called _bacilli_) from a culture obtained in
  _anthrax_ or malignant fustule of the face. Diseased hides carry this
  micro-organism, and thus may occasion disease among those who handle
  hides and wool. (Magnified about 1000 diameters)

Now, while most species of bacteria are harmless, some are the cause of
sickness and death when they gain admittance to the body under certain
conditions. These disease-producing bacteria (known as _pathogenic_),
when established in the blood and tissues of the body, bring about
important chemical changes, depending upon the species of bacteria, and
also produce a particular form of disease. The production of certain
diseases by the agency of bacteria has now been proved beyond all
doubt. In yellow fever, erysipelas, diphtheria, typhoid fever,
consumption and other diseases, the connection has been definitely
established.

The evil results these germs of disease produce vary greatly in kind
and severity. Thus the bacteria of Asiatic cholera and diphtheria may
destroy life in a few hours, while those of consumption may take years
to produce a fatal result. Again, the bacteria may attack some
particular organ, or group of organs, and produce mostly local
symptoms. Thus in a boil there is painful swelling due to the local
effect of the bacteria, with slight general disturbance.

398. The Battle against Bacteria. When we reflect upon the terrible
ravages made by infectious diseases, and all their attendant evils for
these many years, we can the better appreciate the work done of late
years by tireless scientists in their efforts to modify the activity of
disease-producing bacteria. It is now possible to cultivate certain
pathogenic bacteria, and by modifying the conditions under which they
are grown, to destroy their violence.

In brief, science has taught us, within certain limitations, how to
change the virulent germs of a few diseases into harmless microbes.

399. Alcoholic Fermentation and Bacteria. Men of the lowest, as well as
of the highest, type of civilization have always known that when the
sugary juice of any fruit is left to itself for a time, at a moderately
warm temperature, a change takes place under certain conditions, and
the result is a liquid which, when drank, produces a pronounced effect
upon the body. In brief, man has long known how to make for himself
alcoholic beverages, by means of which he may become intoxicated with
their poisonous ingredients.

Whether it is a degraded South Sea Islander making a crude intoxicant
from a sugary plant, a Japanese preparing his favorite alcoholic
beverage from the fermentation of rice by means of a fungus plant grown
for the purpose, a farmer of this country making cider from fermenting
apple juice, or a French expert manufacturing costly champagne by a
complicated process, the outcome and the intent are one and the same.
The essential thing is to produce an alcoholic beverage which will have
a marked physiological effect. This effect is poisonous, and is due
solely to the alcoholic ingredient, without which man would have little
or no use for the otherwise harmless liquid.

While the practical process of making some form of alcoholic beverage
has been understood for these many centuries, the real reason of this
remarkable change in a wholesome fruit juice was not known until
revealed by recent progress in chemistry, and by the use of the
microscope. We know now that the change is due to fermentation, brought
about from the influence, and by the action, of bacteria (sec. 125).

In other words, fermentation is the result of the growth of low form of
vegetable life known as an organised ferment. The ferment, whether it
be the commonly used brewer’s yeast, or any other species of alcoholic
ferment, has the power to decompose or break down a large part of the
sugar present in the liquid into alcohol, which remains as a poison,
and _carbon dioxid_, which escapes more or less completely.

Thus man, ever prone to do evil, was once obliged, in his ignorance, to
make his alcoholic drinks in the crudest manner; but now he has forced
into his service the latest discoveries in science, more especially in
bacteriology, that he may manufacture more scientifically and more
economically alcoholic beverages of all sorts and kinds, and distribute
them broadcast all over God’s earth for the physical and moral ruin of
the people.

Disinfectants.

400. Disinfectants, Antiseptics, and Deodorants. The word disinfectant
is synonymous with the term _bactericide_ or _germicide_. A
disinfectant is a substance which destroys infectious material. An
antiseptic is an agent which may hinder the growth, but does not
destroy the vitality, of bacteria. A deodorant is not necessarily a
disinfectant, or even an antiseptic, but refers to a substance that
destroys or masks offensive odors.

401. Air and Water as Disinfectants. Nature has provided for our
protection two most efficient means of disinfection,—pure air (sec.
218) and pure water (sec. 119). The air of crowded rooms contains large
quantities of bacteria, whereas in pure air there are comparatively
few, especially after rain, which carries them to the earth. Living
micro-organisms have never been detected in breezes coming from the
sea, but in those blowing out from the shore large numbers may be
found.

In water tainted with organic matter putrefactive bacteria will
flourish, whereas pure water is fatal to their existence. Surface
water, because it comes from that part of the soil where bacteria are
most active, and where there is most organic matter, generally contains
great quantities of these organisms. In the deeper strata of the soil
there is practically no decomposition of organic matter going on,
hence, water taken from deep sources is comparatively free from
bacteria. For this reason, deep well water is greatly to be preferred
for drinking purposes to that from surface wells.

402. Disinfectants. It is evident that air and water are not always
sufficient to secure disinfection, and this must be accomplished by
other means. The destruction of infected material by fire is, of
course, a sure but costly means of disinfection. Dry heat, steam, and
boiling water are valuable disinfectants and do not injure most
fabrics. These agents are generally used in combination with various
chemical disinfectants.

Certain chemical agents that are capable of destroying micro-organisms
and their spores have come, of late years, into general use. A form of
mercury, called _corrosive sublimate_, is a most efficacious and
powerful germicide, but is exceedingly poisonous and can be bought only
under restrictions.[54] _Carbolic acid, chloride of lime, permanganate
of potash_, and various other preparations made from zinc, iron, and
petroleum, are the chemical disinfectants most commonly and
successfully used at the present time. There are also numerous
varieties of commercial disinfectants now in popular use, such as
Platt’s chlorides, bromo-chloral, sanitas, etc., which have proved
efficient germicides.

Instructions for the Management of Contagious Diseases.

The following instructions for the management of contagious diseases
were prepared for the National Board of Health by an able corps of
scientists and experienced physicians.

403. Instructions for Disinfection. Disinfection is the destruction of
the poisons of infectious and contagious diseases. Deodorizers, or
substances which destroy smells, are not necessarily disinfectants, and
disinfectants do not necessarily have an odor. Disinfection cannot
compensate for want of cleanliness nor of ventilation.

404. Disinfectants to be Employed. 1. Roll sulphur (brimstone); for
fumigation.

2. Sulphate of iron (copperas) dissolved in water in the proportion of
one and a half pounds to the gallon; for soil, sewers, etc.

Note. A most useful little manual to consult in connection with this
chapter is the _Hand-Book of Sanitary Information_, written by Roger S.
Tracy, Sanitary Inspector of the New York City Health Department.
Price, 50 cents.]

3. Sulphate of zinc and common salt, dissolved together in water in the
proportion of four ounces sulphate and two ounces salt to the gallon;
for clothing, bed-linen, etc.

405. How to Use Disinfectants. 1. _In the sick-room._ The most
available agents are fresh air and cleanliness. The clothing, towels,
bed-linen, etc., should, on removal from the patient, and before they
are taken from the room, be placed in a pail or tub of the zinc
solution, boiling-hot, if possible.

All discharges should either be received in vessels containing copperas
solution, or, when this is impracticable, should be immediately covered
with copperas solution. All vessels used about the patient should be
cleansed with the same solution.

Unnecessary furniture, especially that which is stuffed, carpets, and
hangings, should, when possible, be removed from the room at the
outset; otherwise they should remain for subsequent fumigation and
treatment.

2. _Fumigation_. Fumigation with sulphur is the only practicable method
for disinfecting the house. For this purpose, the rooms to be
disinfected must be vacated. Heavy clothing, blankets, bedding, and
other articles which cannot be treated with zinc solution, should be
opened and exposed during fumigation, as directed below. Close the
rooms as tightly as possible, place the sulphur in iron pans supported
upon bricks placed in washtubs containing a little water, set it on
fire by hot coals or with the aid of a spoonful of alcohol, and allow
the room to remain closed for twenty-four hours. For a room about ten
feet square, at least two pounds of sulphur should be used; for larger
rooms, proportionally increased quantities.[55]

3. _Premises_. Cellars, yards, stables, gutters, privies, cesspools,
water-closets, drains, sewers, etc., should be frequently and liberally
treated with copperas solution. The copperas solution is easily
prepared by hanging a basket containing about sixty pounds of copperas
in a barrel of water.[56]

4. _Body and bed clothing, etc_. It is best to burn all articles which
have been in contact with persons sick with contagious or infectious
diseases. Articles too valuable to be destroyed should be treated as
follows:

_(a)_ Cotton, linen, flannels, blankets, etc., should be treated with
the boiling-hot zinc solution; introduce piece by piece, secure
thorough wetting, and boil for at least half an hour.

_(b)_ Heavy woolen clothing, silks, furs, stuffed bed-covers, beds, and
other articles which cannot be treated with the zinc solution, should
be hung in the room during fumigation, their surfaces thoroughly
exposed and pockets turned inside out. Afterward they should be hung in
the open air, beaten, and shaken. Pillows, beds, stuffed mattresses,
upholstered furniture, etc., should be cut open, the contents spread
out and thoroughly fumigated. Carpets are best fumigated on the floor,
but should afterward be removed to the open air and thoroughly beaten.

Books for Collateral Study. Among the many works which may be consulted
with profit, the following are recommended as among those most useful:
Parkes _Elements of Health_; Canfield’s _Hygiene of the Sick-Room;_
Coplin & Bevan’s _Practical Hygiene;_ Lincoln’s _School Hygiene_;
Edward Smith’s _Health_; McSherrys _Health; American Health Primers_
(12 little volumes, edited by Dr. Keen of Philadelphia); Reynold’s
_Primer of Health_; Corfield’s _Health_; Appleton’s _Health Primers;_
Clara S. Weeks’ _Nursing_; Church’s _Food_; Yeo’s _Food in Health and
Disease;_ Hampton’s _Nursing, its Principles and Practice_; Price’s
_Nurses and Nursing;_ Cullinworth’s _Manual of Nursing_; Wise’s
_Text-Book of Nursing_ (2 vols.); and Humphrey’s _Manual of Nursing_.



Chapter XV.
Experimental Work in Physiology.


406. The Limitations of Experimental Work in Physiology in Schools.
Unlike other branches of science taught in the schools from the
experimental point of view, the study of physiology has its
limitations. The scope and range of such experiments is necessarily
extremely limited compared with what may be done with the costly and
elaborate apparatus of the medical laboratory. Again, the foundation of
physiology rests upon systematic and painstaking dissection of the dead
human body and the lower animals, which mode of study very properly is
not permitted in ordinary school work. Experiments upon the living
human body and the lower animals, now so generally depended upon in our
medical and more advanced scientific schools, for obvious reasons can
be performed only in a crude and quite superficial manner in secondary
schools.

Hence in the study of physiology in schools many things must be taken
for granted. The observation and experience of medical men, and the
experiments of the physiologist in his laboratory must be depended upon
for data which cannot be well obtained at first hand by young students.

407. Value of Experiments in Physiology in Secondary Schools. While
circumstances and regard for certain proprieties of social life forbid
the use of a range of experiments, in anatomy and physiology, such as
are permitted in other branches of science in secondary schools, it by
no means follows that we are shut out altogether from this most
important and interesting part of the study. However simple and crude
the apparatus, the skillful and enthusiastic teacher has at his command
a wide series of materials which can be profitably utilized for
experimental instruction. As every experienced teacher knows, pupils
gain a far better knowledge, and keep up a livelier interest in any
branch of science, if they see with their own eyes and do with their
own hands that which serves to illuminate and illustrate the
subject-matter.

Note. For additional suggestions and practical helps on the subject of
experimental work in physiology the reader is referred to Blaisdell’s
_How to Teach Physiology_, a handbook for teachers. A copy of this
pamphlet will be sent postpaid to any address by the publishers of this
book on receipt of ten cents.


The experimental method of instruction rivets the attention and arouses
and keeps alive the interest of the young student; in fact, it is the
only true method of cultivating a scientific habit of study[57]. The
subject-matter as set forth on the printed pages of this book should be
mastered, of course, but at the same time the topics discussed should
be illuminated and made more interesting and practical by a
well-arranged series of experiments, a goodly show of specimens, and a
certain amount of microscopical work.

408. The Question of Apparatus. The author well understands from
personal experience the many practical difficulties in the way of
providing a suitable amount of apparatus for classroom use. If there
are ample funds for this purpose, there need be no excuse or delay in
providing all that is necessary from dealers in apparatus in the larger
towns, from the drug store, markets, and elsewhere. In schools where
both the funds and the time for such purposes are limited, the zeal and
ingenuity of teachers and students are often put to a severe test.
Fortunately a very little money and a great deal of ingenuity and
patience will do apparent wonders towards providing a working supply of
apparatus.

It will be noticed that many of the experiments in the preceding
chapters of this book can be performed with very simple, and often a
crude and home-made sort of apparatus. This plan has been rigidly
followed by the author, first, because he fully realizes the
limitations and restrictions of the subject; and secondly, because he
wishes to emphasize the fact that expensive and complicated apparatus
is by no means necessary to illustrate the great principles of anatomy
and physiology.

409. Use of the Microscope. To do thorough and satisfactory work in
physiology in our higher schools a compound microscope is almost
indispensable. Inasmuch as many of our best secondary schools are
equipped with one or more microscopes for use in other studies, notably
botany, it is much less difficult than it was a few years ago to obtain
this important help for the classes in physiology.

Illustration: Fig. 170.—A Compound Microscope

For elementary class work a moderate-priced, but well-made and strong,
instrument should be provided. If the school does not own a microscope,
the loan of an instrument should be obtained for at least a few weeks
from some person in the neighborhood.

The appearance of the various structures and tissues of the human body
as revealed by the microscope possesses a curious fascination for every
observer, especially for young people. No one ever forgets the first
look at a drop of blood, or the circulation of blood in a frog’s foot
as shown by the microscope.

Note. For detailed suggestions in regard to the manipulation and use of
the microscope the student is referred to any of the standard works on
the subject. The catalogues of scientific-instrument makers of our
larger cities generally furnish a list of the requisite materials or
handbooks which describe the use of the various microscopes of standard
make.
    The author is indebted to Bergen’s _Elements of Botany_ for the
    following information concerning the different firms which deal in
    microscopes. “Several of the German makers furnish excellent
    instruments for use in such a course as that here outlined. The
    author is most familar with the Leitz microscopes, which are
    furnished by Wm. Krafft, 411 West 59th St., New York city, or by
    the Franklin Educational Co., 15 and 17 Harcourt St., Boston. The
    Leitz Stand, No. IV., can be furnished duty free (for schools
    only), with objectives 1, 3, and 5, eye-pieces I. and III., for
    $24.50. If several instruments are being provided, it would be well
    to have part of them equipped with objectives 3 and 7, and
    eye-pieces I. and III.
    “The American manufacturers, Bausch & Lomb Optical Company,
    Rochester, N.Y., and No. 130 Fulton St., New York city, have this
    year produced a microscope of the Continental type which is
    especially designed to meet the requirements of the secondary
    schools for an instrument with rack and pinion coarse adjustment
    and serviceable fine adjustment, at a low price. They furnish this
    new stand, ‘AAB,’ to schools and teachers at ‘duty-free’ rates, the
    prices being for the stand with two eye-pieces (any desired power),
    ⅔-inch and ¼-inch objectives, $25.60, or with 2-inch, ⅔-inch, and
    ¼-inch objectives, and two eye-pieces, $29.20. Stand ‘A,’ the same
    stand as the ‘AAB,’ without joint and with sliding tube coarse
    adjustment (as in the Leitz Stand IV.), and with three eye-pieces
    and ⅔-inch and ¼-inch objectives, is furnished for $20.40. Stand
    ‘A,’ with two eye-pieces, ⅔-inch and ⅙-inch objectives, $20.40.”


410. The Use of the Skeleton and Manikin. The study of the bones by the
help of a skeleton is almost a necessity. To this intent, schools of a
higher grade should be provided both with a skeleton and a manikin. If
the former is not owned by the school, oftentimes a loan of one can be
secured of some medical man in the vicinity. Separate bones will also
prove useful. In fact, there is no other way to study properly the
structure and use of the bones and joints than by the bones themselves.
A good manikin is also equally serviceable, although not so commonly
provided for schools on account of its cost.

411. The Question of Vivisection and Dissection. There should be no
question at all concerning vivisection. _In no shape or form should it
be allowed in any grade of our schools._ Nor is there any need of much
dissection in the grammar-school grades. A few simple dissections to be
performed with fresh beef-joints, tendons of turkey legs, and so on,
will never engender cruel or brutal feelings toward living things. In
the lower grades a discreet teacher will rarely advise his pupils to
dissect a dead cat, dog, frog, or any other animal. Instead of actual
dissection, the pupils should examine specimens or certain parts
previously dissected by the teacher,—as the muscles and tendons of a
sheep, the heart of an ox, the eye of a codfish, and so on. Even under
these restrictions the teacher should not use the knife or scissors
before the class to open up any part of the specimen. In brief, avoid
everything that can possibly arouse any cruel or brutal feeling on the
part of young students.

In the higher schools, in normal and other training schools, different
conditions prevail. Never allow vivisection in any form whatever,
either in school or at home. Under the most exact restrictions students
in these schools may be taught to make a few simple dissections.

Most teachers will find, however, even in schools of a higher grade,
that the whole subject is fraught with many difficulties. It will not
require much oftentimes to provoke in a community a deal of unjust
criticism. A teacher’s good sense and discretion are often put to a
severe test.

Additional Experiments.

To the somewhat extended list of experiments as described in the
preceding chapters a few more are herewith presented which may be used
as opportunity allows to supplement those already given.

Experiment 193. _To examine white fibrous tissue._ Snip off a very
minute portion from the muscle of a rabbit, or any small animal
recently dead. Tease the specimen with needles, mount in salt solution
and examine under a high power. Note the course and characters of the
fibers.

Experiment 194. _To examine elastic tissue._ Tease out a small piece of
ligament from a rabbit’s leg in salt solution; mount in the same, and
examine as before. Note the curled elastic fibers.

Experiment 195. _To examine areolar tissue._ Gently tease apart some
muscular fibers, noting that they are attached to each other by
connective tissue. Remove a little of this tissue to a slide and
examine as before. Examine the matrix with curled elastic fiber mixed
with straight white fibers.

Experiment 196. _To examine adipose tissue._ Take a bit of fat from the
mesentery of a rabbit. Tease the specimen in salt solution and mount in
the same. Note the fat cells lying in a vascular meshwork.

Experiment 197. _To examine connective tissues._ Take a very small
portion from one of the tendons of a rabbit, or any animal recently
dead; place upon a glass slide with a drop of salt solution; tease it
apart with needles, cover with thin glass and examine with microscope.
The fine wavy filaments will be seen. Allow a drop of dilute acetic
acid to run under the cover glass; the filaments will swell and become
transparent.

Experiment 198. Tease out a small piece of ligament from the rabbit’s
leg in salt solution; mount in the same, and examine under a high
power. Note the curled elastic fibers.

Experiment 199. _A crude experiment to represent the way in which a
person’s neck is broken._ Bring the ends of the left thumb and the left
second finger together in the form of a ring. Place a piece of a wooden
toothpick across it from the middle of the finger to the middle of the
thumb. Put the right forefinger of the other hand up through the front
part to represent the odontoid process of the axis, and place some
absorbent cotton through the other part to represent the spinal cord.
Push backwards with the forefinger with just enough force to break the
toothpick and drive its fragments on to the cotton.

Experiment 200. _To illustrate how the pulse-wave is transmitted along
an artery._ Use the same apparatus as in Experiment 106, p. 201. Take
several thin, narrow strips of pine wood. Make little flags by
fastening a small piece of tissue paper on one end of a wooden
toothpick. Wedge the other end of the toothpick into one end of the
strips of pine wood. Use these strips like levers by placing them
across the long rubber tube at different points. Let each lever
compress the tube a little by weighting one end of it with a blackboard
eraser or book of convenient size.
    As the pulse-wave passes along under the levers they will be
    successively raised, causing a slight movement of the tissue-paper
    flags.

Experiment 201. _The dissection of a sheep’s heart._ Get a sheep’s
heart with the lungs attached, as the position of the heart will be
better understood. Let the lungs be laid upon a dish so that the heart
is uppermost, with its apex turned toward the observer.
    The line of fat which extends from the upper and left side of the
    heart downwards and across towards the right side, indicates the
    division between the right and left ventricles.
    Examine the large vessels, and, by reference to the text and
    illustrations, make quite certain which are the _aorta_, the
    _pulmonary artery_, the _superior_ and _inferior venæ cavæ_, and
    the _pulmonary veins_.
    Tie variously colored yarns to the vessels, so that they may be
    distinguished when separated from the surrounding parts.
    Having separated the heart from the lungs, cut out a portion of the
    wall of the _right ventricle_ towards its lower part, so as to lay
    the cavity open. Gradually enlarge the opening until the _chordæ
    tendineæ_ and the flaps of the _tricuspid valve_ are seen. Continue
    to lay open the ventricle towards the pulmonary artery until the
    _semilunar valves_ come into view.
    The pulmonary artery may now be opened from above so as to display
    the upper surfaces of the semilunar valves. Remove part of the wall
    of the right auricle, and examine the right auriculo-ventricular
    opening.
    The heart may now be turned over, and the _left ventricle_ laid
    open in a similar manner. Notice that the mitral valve has only two
    flaps. The form of the valves is better seen if they are placed
    under water, and allowed to float out. Observe that the walls of
    the _left_ ventricle are much thicker than those of the _right_.
    Open the left auricle, and notice the entrance of the _pulmonary
    veins_, and the passage into the ventricle.
    The ventricular cavity should now be opened up as far as the aorta,
    and the semilunar valves examined. Cut open the aorta, and notice
    the form of the _semilunar valves_.

Experiment 202. _To show the circulation in a frog’s foot_ (see Fig.
78, p. 192). In order to see the blood circulating in the membrane of a
frog’s foot it is necessary to firmly hold the frog. For this purpose
obtain a piece of soft wood, about six inches long and three wide, and
half an inch thick. At about two inches from one end of this, cut a
hole three-quarters of an inch in diameter and cover it with a piece of
glass, which should be let into the wood, so as to be level with the
surface. Then tie up the frog in a wet cloth, leaving one of the hind
legs outside. Next, fasten a piece of cotton to each of the two longest
toes, but not too tightly, or the circulation will be stopped and you
may hurt the frog.
    Tie the frog upon the board in such a way that the foot will just
    come over the glass in the aperture. Pull carefully the pieces of
    cotton tied to the toes, so as to spread out the membrane between
    them over the glass. Fasten the threads by drawing them into
    notches cut in the sides of the board. The board should now be
    fixed by elastic bands, or by any other convenient means, upon the
    stage of the microscope, so as to bring the membrane of the foot
    under the object glass.
    The flow of blood thus shown is indeed a wonderful sight, and never
    to be forgotten. The membrane should be occasionally moistened with
    water.
    Care should be taken not to occasion any pain to the frog.

Experiment 203. _To illustrate the mechanics of respiration_[58] (see
Experiment 122, p. 234). “In a large lamp-chimney, the top of which is
closed by a tightly fitting perforated cork (A), is arranged a pair of
rubber bags (C) which are attached to a Y connecting tube (B), to be
had of any dealer in chemical apparatus or which can be made by a
teacher having a bunsen burner and a little practice in the
manipulation of glass (Fig. 171). From the center of the cork is
attached a rubber band by means of a staple driven through the cork,
the other end of which (D) is attached to the center of a disk of
rubber (E) such as dentists use. This disk is held to the edge of the
chimney by a wide elastic band (F). There is a string (G) also attached
to the center of the rubber disk by means of which the diaphragm may be
lowered. Such is a description of the essentials of the model. The
difficulties encountered in its construction are few and easily
overcome. In the first place, the cork must be air-tight, and it is
best made so by pouring a little melted paraffin over it, care being
taken not to close the tube. The rubber bags were taken from toy
balloon-whistles. In the construction of the diaphragm, it is to be
remembered that it also must be air-tight, and in order to resemble the
human diaphragm, it must have a conical appearance when at rest. In
order to avoid making any holes in the rubber, the two attachments (one
of the rubber band, and the other of the string) were made in this
wise: the rubber was stretched over a button having an eye, then under
the button was placed a smaller ring from an old umbrella; to this ring
was attached the rubber band, and to the eye of the button was fastened
the operating string. When not in use the diaphragm should be taken off
to relieve the strain on the rubber band.”

Illustration: Fig. 171.


Experiment 204. _To illustrate the action of the intercostal muscles_
(see sec. 210). The action of the intercostal muscles is not at first
easy to understand; but it will be readily comprehended by reference to
a model such as that represented in Fig. 172. This maybe easily made by
the student himself with four laths of wood, fastened together at the
corners, A, B, C, D, with pins or small screws, so as to be movable. At
the points E, F, G, H, pins are placed, to which elastic bands may be
attached (A). B D represents the vertebral column; A C, the sternum;
and A B and C D, the ribs. The elastic band F G represents the
_external_ intercostal muscles, and E H, the _internal_ intercostals.
    If now the elastic band E H be removed, the remaining band, F G,
    will tend to bring the two points to which it is attached, nearer
    together, and the result will be that the bars A B and C D will be
    drawn upwards (B), that is, in the same direction as the ribs in
    the act of _inspiration_. When the elastic band E H is allowed to
    exert its force, the opposite effect will be produced (C); in this
    case representing the position of the ribs in an act of
    _expiration_.

Illustration: Fig. 172.


Experiment 205. Pin a round piece of bright red paper (large as a
dinner-plate) to a white wall, with a single pin. Fasten a long piece
of thread to it, so it can be pulled down in a moment. Gaze steadily at
the red paper. Have it removed while looking at it intently, and a
greenish spot takes its place.

Experiment 206. Lay on different parts of the skin a small, square
piece of paper with a small central hole in it. Let the person close
his eyes, while another person gently touches the uncovered piece of
skin with cotton wool, or brings near it a hot body. In each case ask
the observed person to distinguish between them. He will always succeed
on the volar side of the hand, but occasionally fail on the dorsal
surface of the hand, the extensor surface of the arm, and very
frequently on the skin of the back.

Experiment 207. _Wheatstone’s fluttering hearts_. Make a drawing of a
red heart on a bright blue ground. In a dark room lighted by a candle
hold the picture below the level of the eyes and give it a gentle
to-and-fro motion. On continuing to look at the heart it will appear to
move or flutter over the blue background.

Experiment 208. At a distance of six inches from the eyes hold a veil
or thin gauze in front of some printed matter placed at a distance of
about two feet. Close one eye, and with the other we soon see either
the letters distinctly or the fine threads of the veil, but we cannot
see both equally distinct at the same time. The eye, therefore, can
form a distinct image of a near or distant object, but not of both at
the same time; hence the necessity for accommodation.

Experiment 209. Place a person in front of a bright light opposite a
window, and let him look at the light; or place one’s self opposite a
well-illuminated mirror. Close one eye with the hand and observe the
diameter of the other pupil. Then suddenly remove the hand from the
closed eye: light falls upon it; at the same time the pupil of the
other eye contracts.

Experiment 210. _To illustrate the blind spot. Marriott’s experiment_.
On a white card make a cross and a large dot, either black or colored.
Hold the card vertically about ten inches from the right eye, the left
being closed. Look steadily at the cross with the right eye, when both
the cross and the circle will be seen. Gradually approach the card
toward the eye, keeping the axis of vision fixed on the cross. At a
certain distance the circle will disappear, _i.e._, when its image
falls on the entrance of the optic nerve. On bringing the card nearer,
the circle reappears, the cross, of course, being visible all the time
(see Experiment 180, p. 355).

Experiment 211. _To map out the field of vision_. A crude method is to
place the person with his back to a window, ask him to close one eye,
stand in front of him about two feet distant, hold up the forefingers
of both hands in front of and in the plane of your own face. Ask the
person to look steadily at your nose, and as he does so observe to what
extent the fingers can be separated horizontally, vertically, and in
oblique directions before they disappear from his field of vision.

Experiment 212. _To illustrate imperfect judgment of distance_. Close
one eye and hold the left forefinger vertically in front of the other
eye, at arm’s length, and try to strike it with the right forefinger.
    On the first trial one will probably fall short of the mark, and
    fail to touch it. Close one eye, and rapidly try to dip a pen into
    an inkstand, or put a finger into the mouth of a bottle placed at a
    convenient distance. In both cases one will not succeed at first.
    In these cases one loses the impressions produced by the
    convergence of the optic axes, which are important factors in
    judging of distance.

Experiment 213. Hold a pencil vertically about twelve inches from the
nose, fix it with both eyes, close the left eye, and then hold the
right index finger vertically, so as to cover the lower part of the
pencil. With a sudden move, try to strike the pencil with the finger.
In every case one misses the pencil and sweeps to the right of it.

Experiment 214. _To illustrate imperfect judgment of direction_. As the
retina is spherical, a line beyond a certain length when looked at
always shows an appreciable curvature.
    Hold a straight edge just below the level of the eyes. Its upper
    margin shows a slight concavity.

Surface Anatomy and Landmarks.

In all of our leading medical colleges the students are carefully and
thoroughly drilled on a study of certain persons selected as models.
The object is to master by observation and manipulation the details of
what is known as surface anatomy and landmarks. Now while detailed work
of this kind is not necessary in secondary schools, yet a limited
amount of study along these lines is deeply interesting and profitable.
The habit of looking at the living body with anatomical eyes and with
eyes at our fingers’ ends, during the course in physiology, cannot be
too highly estimated.

In elementary work it is only fair to state that many points of surface
anatomy and many of the landmarks cannot always be defined or located
with precision. A great deal in this direction can, however, be done in
higher schools with ingenuity, patience, and a due regard for the
feelings of all concerned. Students should be taught to examine their
own bodies for this purpose. Two friends may thus work together, each
serving as a “model” to the other.

To the following syllabus may be added such other similar exercises as
ingenuity may suggest or time permit.

Syllabus.

I. Bony Landmarks.

1. The _occipital protuberance_ can be distinctly felt at the back of
the head. This is always the thickest part (often three-quarters of an
inch or more) of the skull-cap, and is more prominent in some than in
others. The thinnest part is over the temples, where it may be almost
as thin as parchment.

2. The working of the _condyle of the lower jaw_ vertically and from
side to side can be distinctly felt and seen in front of the ear. When
the mouth is opened wide, the condyle advances out of the glenoid
cavity, and returns to its socket when the mouth is shut. In front of
the ear, lies the zygoma, one of the most marked and important
landmarks to the touch, and in lean persons to the eye.

3. The sliding movement of the _scapula_ on the chest can be properly
understood only on the living subject. It can move not only upwards and
downwards, as in shrugging the shoulders, backwards and forwards, as in
throwing back the shoulders, but it has a rotary movement round a
movable center. This rotation is seen while the arm is being raised
from the horizontal to the vertical position, and is effected by the
cooperation of the trapezius with the serratus magnus muscles.

4. The _patella_, or knee-pan, the _two condyles of the tibia_, the
_tubercle on the tibia_ for the attachment of the ligament of the
patella, and the _head of the fibula_ are the chief bony landmarks of
the knee. The head of the fibula lies at the outer and back part of the
tibia. In extension of the knee, the patella is nearly all above the
condyles. The inner border of the patella is thicker and more prominent
than the outer, which slopes down toward its condyle.

5. The short, front edge of the _tibia_, called the “shin,” and the
broad, flat, subcutaneous surface of the bone can be felt all the way
down. The inner edge can be felt, but not so plainly.

6. The head of the _fibula_ is a good landmark on the outer side of the
leg, about one inch below the top of the tibia. Note that it is placed
well back, and that it forms no part of the knee joint, and takes no
share in supporting the weight. The shaft of the fibula arches
backwards and is buried deep among the muscles, except at the lower
fourth, which can be distinctly felt.

7. The _malleoli_ form the great landmarks of the ankle. The outer
malleolus descends lower than the inner. The inner malleolus advances
more to the front and does not descend so low as the outer.

8. The line of the _clavicle_, or collar bone, and the projection of
the joint at either end of it can always be felt. Its direction is not
perfectly horizontal, but slightly inclined downwards. We can
distinctly feel the _spine_ of the scapula and its highest point, the
_acromion_.

9. Projecting beyond the acromion (the arm hanging by the side), we can
feel, through the fibers of the _deltoid_, the upper part of the
humerus. It distinctly moves under the hand when the arm is rotated. It
is not the head of the bone which is felt, but its prominences (the
tuberosities). The greater, externally; the lesser in front.

10. The _tuberosities of the humerus_ form the convexity of the
shoulder. When the arm is raised, the convexity disappears,—there is a
slight depression in its place. The head of the bone can be felt by
pressing the fingers high up in the axilla.

11. The _humerus_ ends at the elbow in two bony prominences (internal
and external condyles). The internal is more prominent. We can always
feel the _olecranon_. Between this bony projection of the ulna and the
internal condyle is a deep depression along which runs the ulna nerve
(commonly called the “funny” or “crazy” bone).

12. Turn the hand over with the palm upwards, and the edge of the
_ulna_ can be felt from the olecranon to the prominent knob (styloid
process) at the wrist. Turn the forearm over with the palm down, and
the head of the ulna can be plainly felt and seen projecting at the
back of the wrist.

13. The upper half of the _radius_ cannot be felt because it is so
covered by muscles; the lower half is more accessible to the touch.

14. The three rows of projections called the “knuckles” are formed by
the proximal bones of the several joints. Thus the first row is formed
by the ends of the metacarpals, the second by the ends of the first
phalanges, and the third by the ends of the second phalanges. That is,
in all cases the line of the joints is a little in advance of the
knuckles and nearer the ends of the fingers.

II. Muscular Landmarks.

1. The position of the _sterno-mastoid_ muscle as an important and
interesting landmark of the neck has already been described (p. 70).

2. If the left arm be raised to a vertical position and dropped to a
horizontal, somewhat vigorously, the tapering ends of the _pectoralis
major_ and the tendons of the _biceps_ and _deltoid_ may be felt by
pressing the parts in the axilla between the fingers and thumb of the
right hand.

3. The appearance of the _biceps_ as a landmark of the arm has already
been described (p. 70). The action of its antagonist, the _triceps_,
may be studied in the same manner.

4. The _sartorius_ is one of the fleshy landmarks of the thigh, as the
biceps is of the arm, and the sterno-cleido-mastoid of the neck. Its
direction and borders may be easily traced by raising the leg,—a
movement which puts the muscle in action.

5. If the model be directed to stand on tiptoe, both of the large
muscles of the calf, the _gastrocnemius_ and _soleus_, can be
distinguished.

6. Direct the model, while sitting upright, to cross one leg over the
other, using his utmost strength. The great muscles of the inner thigh
are fully contracted. Note the force required to pull the legs to the
ordinary position.

7. With the model lying in a horizontal position with both legs firmly
held together, note the force required to pull the feet apart while the
great muscles of the thigh are fully contracted.

8. In forcible and resisted flexion of the wrist two tendons come up in
relief. On the outer side of one we feel the pulse at the wrist, the
radial artery here lying close to the radius.

9. On the outer side of the wrist we can distinctly see and feel when
in action, the three extensor tendons of the thumbs. Between two of
them is a deep depression at the base of the thumb, which the French
call the “anatomical tobacco box.”

10. The relative position of the several extensor tendons on the back
of the wrist and fingers as they play in their grooves over the back of
the radius and ulna can be distinctly traced when the several muscles
are put in action.

11. There are several strong tendons to be seen and felt about the
ankle. Behind is the _tendo Achillis_. It forms a high relief with a
shallow depression on each side of it. Behind both the inner and outer
ankle several tendons can be felt. Over the front of the ankle, when
the muscles are in action, we can see and feel several tendons. They
start up like cords when the action is resisted. They are kept in their
proper relative position by strong pulleys formed by the annular
ligament. Most of these tendons can be best seen by stand a model on
one foot, _i.e._ in unstable equilibrium.

III. Landmarks of the Heart.

To have a general idea of the form and position of the _heart_, map its
outline with colored pencils or crayon on the chest wall itself, or on
some piece of clean, white cloth, tightly pinned over the clothing. A
pattern of the heart may be cut out of pasteboard, painted red, or
papered with red paper, and pinned in position outside the clothing.
The apex of the heart is at a point about two inches below the left
nipple and one inch to its sternal side. This point will be between the
fifth and sixth ribs, and can generally be determined by feeling the
apex beat.

IV. Landmarks of a Few Arteries.

The pulsation of the _temporal_ artery can be felt in front of the ear,
between the zygoma and the ear. The _facial_ artery can be distinctly
felt as it passes over the upper jaw at the front edge of the masseter
muscle. The pulse of a sleeping child can often be counted at the
anterior fontanelle by the eye alone.

About one inch above the clavicle, near the outer border of the
sterno-mastoid, we can feel the pulsation of the great _subclavian_
artery. At the back of the knee the _popliteal_ artery can be felt
beating. The _dorsal_ artery of the foot can be felt beating on a line
from the middle of the ankle to the interval between the first and
second metatarsal bones.

When the arm is raised to a right angle with the body, the _axillary_
artery can be plainly felt beating in the axilla. Extend the arm with
palm upwards and the _brachial_ artery can be felt close to the inner
side of the biceps. The position of the _radial_ artery is described in
Experiment 102.



Glossary.


Abdomen (Lat. _abdo_, _abdere_, to conceal). The largest cavity of the
body, containing the liver, stomach, intestines, and other organs.

Abductor (Lat. _abduco_, to draw from). A muscle which draws a limb
from the middle line of the body, or a finger or toe from the middle
line of the foot or hand.

Absorbents (Lat. _absorbere_, to suck up). The vessels which take part
in the process of absorption.

Absorption. The process of sucking up nutritive or waste matters by the
blood-vessels or lymphatics.

Accommodation of the Eye. The alteration in the shape of the
crystalline lens, which accommodates, or adjusts, the eye for near or
remote vision.

Acetabulum (Lat. _acetabulum_, a small vinegar-cup). The cup-shaped
cavity of the innominate bone for receiving the head of the femur.

Acid (Lat. _acidus_, from _acere_, to be sour). A substance usually
sour, sharp, or biting to the taste.

Acromion (Gr. ἀκρον the tip, and ᾧμος, the shoulder). The part of the
scapula forming the tip of the shoulder.

Adam’s Apple. An angular projection of cartilage in the front of the
neck. It may be particularly prominent in men.

Adductor (Lat. _adduco_, to draw to). A muscle which draws towards the
middle line of the body, or of the hand or foot.

Adenoid (Gr. ἀδήν, a gland). Tissue resembling gland tissue.

Afferent (Lat. _ad_, to, and _fero_, to convey). Vessels or nerves
carrying the contents or impulses from the periphery to the center.

Albumen, or Albumin (Lat. _albus_, white). An animal substance
resembling the white of an egg.

Albuminuria. A combination of the words “albumin” and “urine.” Presence
of _albumen_ in the _urine_.

Aliment (Lat. _alo_, to nourish). That which affords nourishment; food.

Alimentary (Lat. _alimentum_, food). Pertaining to _aliment_, or food.

Alimentary Canal (Lat. _alimentum_). The tube in which the food is
digested or prepared for reception into the blood.

Alkali (Arabic _al kali_, the soda plant). A name given to certain
substances, such as soda, potash, and the like, which have the power of
combining with acids.

Alveolar (Lat. _alveolus_, a little hollow). Pertaining to the alveoli,
the _cavities_ for the reception of the teeth.

Amœba (Gr. ἀμείβω, to change). A single-celled, protoplasmic organism,
which is constantly changing its form by protrusions and withdrawals of
its substance.

Amœboid. Like an _amœba_.

Ampulla (Lat. _ampulla_, a wine-flask). The dilated part of the
semicircular canals of the internal ear.

Anabolism (Gr. ἀναβάλλω, to throw or build up). The process by means of
which simpler elements are _built up_ into more complex.

Anæsthetics (Gr. ἀν, without, and αἰσθησία, feeling). Those medicinal
agents which prevent the feeling of pain, such as chloroform, ether,
laughing-gas, etc.

Anastomosis (Gr. ἀνά, by, and στόμα, a mouth). The intercommunication
of vessels.

Anatomy (Gr. ἀνατέμνω, to cut up). The science which describes the
structure of living things. The word literally means dissection.

Antiseptic (Lat. _anti_, against, and _sepsis_, poison). Opposing or
counter-acting putrefaction.

Antrum (Lat. _antrum_, a cave). The cavity in the upper jaw.

Aorta (Gr. ἀορτή, from ἀείρο, to raise up). The great artery that
_rises up_ from the left ventricle of the heart.

Aponeurosis (Gr. ἀπό, from, and νεῦρον, a nerve). A fibrous membranous
expansion of a tendon; the nerves and tendons were formerly thought to
be identical structures, both appearing as white cords.

Apoplexy (Gr. ἀποπληξία, a sudden stroke). The escape of blood from a
ruptured blood-vessel into the substance of the brain.

Apparatus. A number of organs of various sizes and structures working
together for some special object.

Appendages (Lat. _ad_ and _pendeo_, to hang from). Something connected
with a part.

Aqueous Humor (Lat. _aqua_, water). The watery fluid occupying the
space between the cornea and crystalline lens of the eye.

Arachnoid Membrane (Gr. ἀράχνη, a spider, and εἰδώς, like). The thin
covering of the brain and spinal cord, between the dura mater and the
pia mater.

Arbor Vitæ. Literally, “the tree of life”; a name given to the peculiar
appearance presented by a section of the cerebellum.

Areolar (Lat. _areola_, a small space, dim. of _area_). A term applied
to a connective tissue containing _small spaces_.

Artery (Gr. ἀήρ, air, and τερέω, to contain). A vessel by which blood
is carried away from the heart. It was supposed by the ancients to
contain only air, hence the name.

Articulation (Lat. _articulo_, to form a joint). The more or less
movable union of bones, etc.; a joint.

Arytenoid Cartilages (Gr. ἀρύταινα, a ladle). Two small cartilages of
the larynx, resembling the mouth of a pitcher.

Asphyxia (Gr. ἀ, without, and σφίξις, the pulse). Literally, “without
pulse.” Condition caused by non-oxygenation of the blood.

Assimilation (Lat. _ad_, to, and _similis_, like). The conversion of
food into living tissue.

Asthma (Gr. ἆσθμα, a gasping). Spasmodic affection of the bronchial
tubes in which free respiration is interfered with, owing to their
diminished caliber.

Astigmatism (Gr. ἀ, without, and στίγμα, a point). Irregular refraction
of the eye, producing a blurred image.

Atrophy (Gr. ἀ, without, and τροφή, nourishment). Wasting of a part
from lack of nutrition.

Auditory Nerve (Lat. _audio_, to hear). The special nerve of hearing.

Auricle (Lat. _auricula_, a little ear). A cavity of the heart.

Azygos (Gr. ἀ, without, and ζυγός, a yoke). Without fellow; not paired.

Bacteria (βακτήριον, a staff). A microscopic, vegetable organism;
certain species are active agents in fermentation, while others appear
to be the cause of infectious diseases.

Bactericide (_Bacterium_ and Lat. _caedere_, to kill). Same as
_germicide_.

Bile. The gall, or peculiar secretion of the liver; a viscid, yellowish
fluid, and very bitter to the taste.

Biology (Gr. βίος, life, and λόγος, discourse). The science which
treats of living bodies.

Bladder (Saxon _bleddra_, a bladder, a goblet). A bag, or sac, serving
as a receptacle of some secreted fluid, as the _gall bladder_, etc. The
receptacle of the urine in man and other animals.

Bright’s Disease. A group of diseases of the kidney, first described by
Dr. Bright, an English physician.

Bronchi (Gr. βρόγχος, windpipe). The first two divisions, or branches,
of the trachea; one enters each lung.

Bronchial Tubes. The smaller branches of the trachea within the
substance of the lungs terminating in the air cells.

Bronchitis. Inflammation of the larger bronchial tubes; a “cold”
affecting the air passages.

Bunion. An enlargement and inflammation of the first joint of the great
toe.

Bursa. A pouch; a membranous sac interposed between parts which are
subject to movement, one on the other, to allow them to glide smoothly.

Callus (Lat. _calleo_, to be thick-skinned). Any excessive hardness of
the skin caused by friction or pressure.

Canal (Lat. _canalis_, a canal). A tube or passage.

Capillary (Lat. _capillus_, hair). The smallest blood-vessels, so
called because they are so minute.

Capsule (Lat. _capsula_, a little chest). A membranous bag enclosing a
part.

Carbon Dioxid, often called _carbonic acid_. The gas which is present
in the air breathed out from the lungs; a waste product of the animal
kingdom and a food of the vegetable kingdom.

Cardiac (Gr. καρδία, the heart). The cardiac orifice of the stomach is
the upper one, and is near the heart; hence its name.

Carnivorous (Lat. _caro_, flesh, and _voro_, to devour). Subsisting
upon flesh.

Carron Oil. A mixture of equal parts of linseed oil and lime-water, so
called because first used at the Carron Iron Works in Scotland.

Cartilage. A tough but flexible material forming a part of the joints,
air passages, nostrils, ear; gristle, etc.

Caruncle (Lat. _caro_, flesh). The small, red, conical-shaped body at
the inner angle of the eye, consisting of a cluster of follicles.

Casein (Lat. _caseus_, cheese). The albuminoid substance of milk; it
forms the basis of cheese.

Catarrh. An inflammation of a mucous membrane, usually attended with an
increased secretion of mucus. The word is often limited to _nasal_
catarrh.

Cauda Equina (Lat., horse’s tail). The collection of large nerves
descending from the lower end of the spinal cord.

Cell (Lat. _cella_, a storeroom). The name of the tiny miscroscopic
elements, which, with slender threads or fibers, make up most of the
body; they were once believed to be little hollow chambers; hence the
name.

Cement. The substance which forms the outer part of the fang of a
tooth.

Cerebellum (dim. for _cerebrum_, the brain). The little brain, situated
beneath the posterior third of the cerebrum.

Cerebrum. The brain proper, occupying the upper portion of the skull.

Ceruminous (Lat. _cerumen_, ear wax). A term applied to the glands
secreting cerumen, or _ear wax_.

Chloral. A powerful drug and narcotic poison used to produce sleep.

Chloroform. A narcotic poison generally used by inhalation; of
extensive use in surgical operations. It produces anæsthesia.

Chondrin (Gr. χονδρός, cartilage). A kind of gelatine obtained by
boiling _cartilage_.

Chordæ Tendineæ. Tendinous cords.

Choroid (Gr. χορίον, skin, and εἶδος, form). The middle coat of the
eyeball.

Chyle (Gr. χυλός, juice). The milk-like fluid formed by the digestion
of fatty articles of food in the intestines.

Chyme (Gr. χυμός, juice). The pulpy liquid formed by digestion in the
stomach.

Cilia (pl. of _cilium_, an eyelash). Minute hair-like processes found
upon the cells of the air passages and other parts.

Ciliary Muscle. A small muscle of the eye which assists in
accommodation.

Circumvallate (Lat. _circum_, around, and _vallum_, a rampart).
Surrounded by a rampart, as are certain papillæ of the tongue.

Coagulation (Lat. _coagulo_, to curdle). Applied to the process by
which the blood clots or solidifies.

Cochlea (Lat. _cochlea_, a snail shell). The spiral cavity of the
internal ear.

Columnæ Carneæ. Fleshy projections in the ventricles of the heart.

Commissure (Lat. _con_, together, and _mitto_, _missum_, to put). A
joining or uniting together.

Compress. A pad or bandage applied directly to an injury to compress
it.

Concha (Gr. κόγχη, a mussel shell). The shell-shaped portion of the
external ear.

Congestion (Lat. _con_, together, and _gero_, to bring). Abnormal
gathering of blood in any part of the body.

Conjunctiva (Lat. _con_, together, and _jungo_, to join). A thin layer
of mucous membrane which lines the eyelids and covers the front of the
eyeball, thus joining the latter to the lids.

Connective Tissue. The network which connects the minute parts of most
of the structures of the body.

Constipation (Lat. _con_, together, and _stipo_, to crowd close).
Costiveness.

Consumption (Lat. _consumo_, to consume). A disease of the lungs,
attended with fever and cough, and causing a decay of the bodily
powers. The medical name is _phthisis_.

Contagion (Lat. _con_, with, and _tango_ or _tago_, to touch). The
communication of disease by contact, or by the inhalation of the
effluvia of a sick person.

Contractility (Lat. _con_, together, and _traho_, to draw). The
property of a muscle which enables it to contract, or draw its
extremities closer together.

Convolutions (Lat. _con_, together, and _volvo_, to roll). The tortuous
foldings of the external surface of the brain.

Convulsion (Lat. _convello_, to pull together). A more or less violent
agitation of the limbs or body.

Coördination. The manner in which several different organs of the body
are brought into such relations with one another that their functions
are performed in harmony.

Coracoid (Gr. κόραξ, a crow, εἶδος, form). Shaped like a crow’s beak.

Cornea (Lat. _cornu_, a horn). The transparent horn-like substance
which covers a part of the front of the eyeball.

Coronary (Lat. _corona_, a crown). A term applied to vessels and nerves
which encircle parts, as the _coronary_ arteries of the heart.

Coronoid (Gr. κορώνη, a crow). Like a crow’s beak; thus the _coronoid_
process of the ulna.

Cricoid (Gr. κρίκος, a ring, and εἶδος, form). A cartilage of the
larynx resembling a seal ring in shape.

Crystalline Lens (Lat. _crystallum_, a crystal). One of the humors of
the eye; a double-convex body situated in the front part of the
eyeball.

Cumulative. A term applied to the violent action from drugs which
supervenes after the taking of several doses with little or no effect.

Cuticle (Lat. dim. of _cutis_, the skin). Scarf skin; the epidermis.

Cutis (Gr. σκῦτος, a skin or hide). The true skin, also called the
_dermis_.

Decussation (Lat. _decusso_, _decussatum_, to cross). The _crossing_ or
running of one portion athwart another.

Degeneration (Lat. _degenerare_, to grow worse, to deteriorate). A
change in the structure of any organ which makes it less fit to perform
its duty.

Deglutition (Lat. _deglutire_, to swallow). The process of swallowing.

Deltoid. Having a triangular shape; resembling the Greek letter Δ
(_delta_).

Dentine (Lat. _dens_, _dentis_, a tooth). The hard substance which
forms the greater part of a tooth; ivory.

Deodorizer. An agent which corrects any foul or unwholesome odor.

Dextrin. A soluble substance obtained from starch.

Diabetes Mellitus (Gr. διά, through, βαίνω, to go, and μέλι, honey).
Excessive flow of sugar-containing urine.

Diaphragm (Gr. διαφράσσω, to divide by a partition). A large, thin
muscle which separates the cavity of the chest from the abdomen.

Diastole (Gr. διαστέλλω, to dilate). The _dilatation_ of the heart.

Dietetics. That part of medicine which relates to diet, or food.

Diffusion of Gases. The power of gases to become intimately mingled.

Diplöe (Gr. διπλόω, to double, to fold). The osseous tissue between the
tables of the skull.

Dipsomania (Gr. δίψα, thirst, and μανία, madness). An insatiable desire
for intoxicants.

Disinfectants. Agents used to destroy the germs or particles of living
matter that are believed to be the causes of infection.

Dislocation (Lat. _dislocare_, to put out of place). An injury to a
joint in which the bones are displaced or forced out of their sockets.

Dissection (Lat. _dis_, apart, and _seco_, to cut). The cutting up of
an animal in order to learn its structure.

Distal (Lat. _dis_, apart, and _sto_, to stand). Away from the center.

Duct (Lat. _duco_, to lead). A narrow tube.

Duodenum (Lat. _duodeni_, twelve). The first division of the small
intestines, about twelve fingers’ breadth long.

Dyspepsia (Gr. -δύς, ill, and πέπτειν, to digest). A condition of the
alimentary canal in which it digests imperfectly. Indigestion.

Dyspnœa (Gr. δύς, difficult, and πνέω, to breathe). Difficult
breathing.

Efferent (Lat. _effero_, to carry out). _Bearing_ or _carrying
outwards_, as from the center to the periphery.

Effluvia (Lat. _effluo_, to flow out). Exhalations or vapors coming
from the body, and from decaying animal or vegetable substances.

Element. One of the simplest parts of which anything consists.

Elimination (Lat. _e_, out of, and _limen, liminis_, a threshold). The
act of _expelling_ waste matters. Signifies, literally, “to throw out
of doors.”

Emetic (Gr. ἐμέω, to vomit). A medicine which causes vomiting.

Emulsion (Lat. _emulgere_, to milk). Oil in a finely divided state,
suspended in water.

Enamel (Fr. _émail_). Dense material covering the crown of a tooth.

Endolymph (Gr. ἔνδον, within, and Lat. _lympha_, water). The fluid in
the membranous labyrinth of the ear.

Endosmosis (Gr. ἔνδον, within, and ὠθέω, to push). The current from
without _inwards_ when diffusion of fluids takes place through a
membrane.

Epidemic (Gr. ἐπί, upon, and δέμος, the people). An extensively
prevalent disease.

Epiglottis (Gr. ἐπί, upon, and γλόττις, the entrance to the windpipe).
A leaf-shaped piece of cartilage which covers the top of the larynx
during the act of swallowing.

Epilepsy (Gr. ἐπίληψις, a seizure). A nervous disease accompanied by
fits in which consciousness is lost; the falling sickness.

Ether (Gr. αἰθήρ, the pure, upper air). A narcotic poison. Used as an
anæsthetic in surgical operations.

Eustachian (from an Italian anatomist named Eustachi). The tube which
leads from the throat to the middle ear, or tympanum.

Excretion (Lat. _excerno_, to separate). The separation from the blood
of the waste matters of the body; also the materials excreted.

Exosmosis (Gr. ἔξω, without, and ᾀθέω, to push). The current from
within _outwards_ when diffusion of fluids takes place through a
membrane.

Expiration (Lat. _expiro_, to breathe out). The act of forcing air out
of the lungs.

Extension (Lat. _ex_, out, and _tendo_, to stretch). The act of
restoring a limb, etc., to its natural position after it has been
flexed or bent; the opposite of _flexion_.

Fauces. The part of the mouth which opens into the pharynx.

Fenestra (Lat.). Literally, “a window.” Fenestra ovalis and fenestra
rotunda, the oval and the round window; two apertures in the bone
between the tympanic cavity and the labyrinth of the ear.

Ferment. That which causes fermentation, as yeast.

Fermentation (Lat. _fermentum_, boiling). The process of undergoing an
effervescent change, as by the action of yeast; in a wider sense, the
change of organized substances into new compounds by the action of a
ferment. It differs in kind according to the nature of the ferment.

Fiber (Lat. _fibra_, a filament). One of the tiny threads of which many
parts of the body are composed.

Fibrilla. A little fiber; one of the longitudinal threads into which a
striped muscular fiber can be divided.

Fibrin (Lat. _fibra_, a fiber). An albuminoid substance contained in
the flesh of animals, and also produced by the coagulation of blood.

Flexion (Lat. _flecto_, to bend). The act of bending a limb, etc.

Follicle (Lat. dim. of _follis_, a money bag). A little pouch or
depression.

Fomentation (Lat. _foveo_, to keep warm). The application of any warm,
medicinal substance to the body, by which the vessels are relaxed.

Foramen. A hole, or aperture.

Frontal Sinus. A blind or closed cavity in the bones of the skull just
over the eyebrows.

Fumigation (Lat. _fumigo_, to perfume a place). The use of certain
fumes to counteract contagious effluvia.

Function (Lat. _functio_, a doing). The special duty of any organ.

Ganglion (Gr. γάγγλιν, a knot). A knot-like swelling in a nerve; a
smaller nerve center.

Gastric (Gr. γαστήρ, stomach). Pertaining to the stomach.

Gelatine (Lat. _gelo_, to congeal). An animal substance which dissolves
in hot water and forms a jelly on cooling.

Germ (Lat. _germen_, a sprout, bud). Disease germ; a name applied to
certain tiny bacterial organisms which have been demonstrated to be the
cause of disease.

Germicide (_Germ_, and Lat. _caedere_, to kill). Any agent which has a
destructive action upon living germs, especially _bacteria_.

Gland (Lat. _glans_, an acorn). An organ consisting of follicles and
ducts, with numerous blood-vessels interwoven.

Glottis (Gr. γλόττα, the tongue). The narrow opening between the vocal
cords.

Glucose. A kind of sugar found in fruits, also known as grape sugar.

Gluten. The glutinous albuminoid ingredient of cereals.

Glycogen. Literally, “producing glucose.” Animal starch found in liver,
which may be changed into glucose.

Gram. Unit of metric system, 15.43 grains troy.

Groin. The lower part of the abdomen, just above each thigh.

Gustatory (Lat. _gusto_, _gustatum_, to taste). Belonging to the sense
of _taste_.

Gymnastics (Gr. γυμνάξω, to exercise). The practice of athletic
exercises.

Hæmoglobin (Gr. αἷμα, blood, and Lat. _globus_, a globe or globule). A
complex substance which forms the principal coloring constituent of the
red corpuscles of the blood.

Hemispheres (Gr. ἡμί, half, and σφαῖρα, a sphere). Half a sphere, the
lateral halves of the cerebrum, or brain proper.

Hemorrhage (Gr. αἷμα, blood, and ῥήγνυμι, to burst). Bleeding, or the
loss of blood.

Hepatic (Gr. ἧπαρ, the liver). Pertaining to the liver.

Herbivorous (Lat. _herba_, an herb, and _voro_, to devour). Applied to
animals that subsist upon vegetable food.

Heredity. The predisposition or tendency derived from one’s ancestors
to definite physiological actions.

Hiccough. A convulsive motion of some of the muscles used in breathing,
accompanied by a shutting of the glottis.

Hilum, sometimes written Hilus. A small fissure, notch, or depression.
A term applied to the concave part of the kidney.

Homogeneous (Gr. ὁμός, the same, and γένος, kind). Of the _same kind_
or quality throughout; uniform in nature,—the reverse of heterogeneous.

Humor. The transparent contents of the eyeball.

Hyaline (Gr. ὕαλος, glass). Glass-like, resembling glass in
transparency.

Hydrogen. An elementary gaseous substance, which, in combination with
oxygen, produces water.

Hydrophobia (Gr. ὕδωρ, water, and φοβέομαι, to fear). A disease caused
by the bite of a rabid dog or other animal.

Hygiene (Gr. ὑγἰεια health). The art of preserving health and
preventing disease.

Hyoid (Gr. letter υ, and εἰδος, form, resemblance). The bone at the
root of the tongue, shaped like the Greek letter υ.

Hypermetropia (Gr. ὑπέρ over, beyond, μέτρον, measure, and ώ̓ψ, the
eye). Far-sightedness.

Hypertrophy (Gr. ὑπέρ, over, and τροφή, nourishment). Excessive growth;
thickening or enlargement of any part or organ.

Incisor (Lat. _incido_, to cut). Applied to the four front teeth of
both jaws, which have sharp, cutting edges.

Incus. An anvil; the name of one of the bones of the middle ear.

Indian Hemp. The common name of _Cannabis Indica_, an intoxicating drug
known as _hasheesh_ and by other names in Eastern countries.

Inferior Vena Cava. The chief vein of the lower part of the body.

Inflammation (Lat. prefix _in_ and _flammo_, to flame). A redness or
swelling of any part of the body with heat and pain.

Insalivation (Lat. _in_ and _saliva_, the fluid of the mouth). The
mingling of the saliva with the food during the act of chewing.

Inspiration (Lat. _inspiro, spiratum_, to breathe in). The act of
drawing in the breath.

Intestine (Lat. _intus_, within). The part of the alimentary canal
which is continuous with the lower end of the stomach; also called the
bowels.

Iris (Lat. _iris_, the rainbow). The thin, muscular ring which lies
between the cornea and crystalline lens, giving the eye its special
color.

Jaundice (Fr. _jaunisse_, yellow). A disorder in which the skin and
eyes assume a yellowish tint.

Katabolism (Gr. καταβάλλω, to throw down). The process by means of
which the more complex elements are rendered more simple and less
complex. The opposite of _anabolism_.

Labyrinth. The internal ear, so named from its many windings.

Lacrymal Apparatus (Lat. _lacryma_, a tear). The organs for forming and
carrying away the tears.

Lacteals (Lat. _lac, lactis_, milk). The absorbent vessels of the small
intestines.

Laryngoscope (Gr. λάρυγξ, larynx, and σκοπέω, to behold). An instrument
consisting of a mirror held in the throat, and a reflector to throw
light on it, by which the interior of the larynx is brought into view.

Larynx. The cartilaginous tube situated at the top of the windpipe.

Lens. Literally, a lentil; a piece of transparent glass or other
substance so shaped as either to converge or disperse the rays of
light.

Ligament (Lat. _ligo_, to bind). A strong, fibrous material binding
bones or other solid parts together.

Ligature (Lat. _ligo_, to bind). A thread of some material used in
tying a cut or injured artery.

Lobe. A round, projecting part of an organ, as of the liver, lungs, or
brain.

Lymph (Lat. _lympha_, pure water). The watery fluid conveyed by the
lymphatic vessels.

Lymphatic Vessels. A system of absorbent vessels.

Malleus. Literally, the mallet; one of the small bones of the middle
ear.

Marrow. The soft, fatty substance contained in the cavities of bones.

Mastication (Lat. _mastico_, to chew). The act of cutting and grinding
the food to pieces by means of the teeth.

Meatus (Lat. _meo_, _meatum_, to pass). A _passage_ or canal.

Medulla Oblongata. The “oblong marrow”; that portion of the brain which
lies upon the basilar process of the occipital bone.

Meibomian. A term applied to the small glands between the conjunctiva
and tarsal cartilages, discovered by _Meibomius_.

Membrana Tympani. Literally, the membrane of the drum; a delicate
partition separating the outer from the middle ear; it is sometimes
popularly called “the drum of the ear.”

Membrane. A thin layer of tissue serving to cover some part of the
body.

Mesentery (Gr. μέσος, middle, and ἔντερον, the intestine). A
duplicature of the peritoneum covering the small _intestine_, which
occupies the _middle_ or center of the abdominal cavity.

Metabolism (Gr. μεταβολή, change). The _changes_ taking place in cells,
whereby they become more complex and contain more force, or less
complex and contain less force. The former is constructive metabolism,
or _anabolism_; the latter, destructive metabolism, or _katabolism_.

Microbe (Gr. μικρός, little, and βίος, life). A microscopic organism,
particularly applied to bacteria.

Microscope (Gr. μικρός, small, and σκοπέω, to look at). An optical
instrument which assists in the examination of minute objects.

Molar (Lat. _mola_, a mill). The name applied to the three back teeth
at each side of the jaw; the grinders, or mill-like teeth.

Molecule (dim. of Lat. _moles_, a mass). The smallest quantity into
which the mass of any substance can physically be divided. A molecule
may be chemically separated into two or more atoms.

Morphology (Gr. μόρφη, form, and λόγος, discourse). The study of the
laws of form or structure in living beings.

Motor (Lat. _moveo_, _motum_, to move). The name of the nerves which
conduct to the muscles the stimulus which causes them to contract.

Mucous Membrane. The thin layer of tissue which covers those internal
cavities or passages which communicate with the external air.

Mucus. The glairy fluid secreted by mucous membranes.

Myopia (Gr. μύω, to shut, and ὤψ, the eye). A defect of vision
dependent upon an eyeball that is too long, rendering distant objects
indistinct; _near sight_.

Myosin (Gr. μῶς, muscle). Chief proteid substance of muscle.

Narcotic (Gr. ναρκάω, to benumb). A medicine which, in poisonous doses,
produces stupor, convulsions, and sometimes death.

Nerve Cell. A minute round and ashen-gray cell found in the brain and
other nervous centers.

Nerve Fiber. An exceedingly slender thread of nervous tissue.

Nicotine. The poisonous and stupefying oil extracted from tobacco.

Nostril (Anglo-Saxon _nosu_, nose, and _thyrl_, a hole). One of the two
outer openings of the nose.

Nucleolus (dim. of _nucleus_). A little nucleus.

Nucleus (Lat. _nux_, a nut). A central part of any body, or that about
which matter is collected. In anatomy, a cell within a cell.

Nutrition (Lat. _nutrio_, to nourish). The processes by which the
nourishment of the body is accomplished.

Odontoid (Gr. ὀδούς, a tooth, εἶδσ, shape). The name of the bony peg of
the second vertebra, around which the first turns.

Œsophagus. Literally, that which carries food. The tube leading from
the throat to the stomach; the gullet.

Olecranon (Gr. ὠλένη, the elbow, and κρανίον, the top of the head). A
curved eminence at the upper and back part of the ulna.

Olfactory (Lat. _olfacio_, to smell). Pertaining to the sense of smell.

Optic (Gr. ὀπτεύω, to see). Pertaining to the sense of sight.

Orbit (Lat. _orbis_, a circle). The bony socket or cavity in which the
eyeball is situated.

Organ (Lat. _organum_, an instrument or implement). A portion of the
body having some special function or duty.

Osmosis (Gr. ὠσμός, impulsion). Diffusion of liquids through membranes.

Ossa Innominata, pl. of Os Innominatum (Lat.). “Unnamed bones.” The
irregular bones of the pelvis, unnamed on account of their
non-resemblance to any known object.

Otoconia (Gr. οὖς, an ear, and κονία, dust). Minute crystals of lime in
the vestibule of the ear; also known as _otoliths_.

Palate (Lat. _palatum_, the palate). The roof of the mouth, consisting
of the hard and soft palate.

Palpitation (Lat. _palpitatio_, a frequent or throbbing motion). A
violent and irregular beating of the heart.

Papilla. The small elevations found on the skin and mucous membranes.

Paralysis (Gr. παραλύω, to loosen; also, to disable). Loss of function,
especially of motion or feeling. Palsy.

Parasite. A plant or animal that grows or lives on another.

Pelvis. Literally, a basin. The bony cavity at the lower part of the
trunk.

Pepsin (Gr. πέπτω, to digest). The active principle of the gastric
juice.

Pericardium (Gr. περί, about, and καρδία, heart). The sac enclosing the
heart.

Periosteum (Gr. περί, around, ὀστέον, a bone). A delicate fibrous
membrane which invests the bones.

Peristaltic Movements (Gr. περί, round, and στέλλω, to send). The slow,
wave-like movements of the stomach and intestines.

Peritoneum (Gr. περιτείνω, to stretch around). The investing membrane
of the stomach, intestines, and other abdominal organs.

Perspiration (Lat. _perspiro_, to breathe through). The sweat.

Petrous (Gr. πέτρα, a rock). The name of the hard portion of the
temporal bone, in which are situated the drum of the ear and labyrinth.

Phalanges (Gr. φάλαγξ, a body of soldiers closely arranged in ranks and
files). The bones of the fingers and toes.

Pharynx (Gr. φάρμγξ, the throat). The cavity between the back of the
mouth and the gullet.

Physiology (Gr. φύσις, nature, and λόγος, a discourse). The science of
the functions of living, organized beings.

Pia Mater (Lat.). Literally, the tender mother; the innermost of the
three coverings of the brain. It is thin and delicate; hence the name.

Pinna (Lat. a feather or wing). External cartilaginous flap of the ear.

Plasma (Gr. πλάσσω, to mould). Anything formed or moulded. The liquid
part of the blood.

Pleura (Gr. πλευρά, the side, also a rib). A membrane covering the
lung, and lining the chest.

Pleurisy. An inflammation affecting the pleura.

Pneumogastric (Gr. πνεύμων, the lungs, and γαστήρ, the stomach). The
chief nerve of respiration; also called the _vagus_, or wandering
nerve.

Pneumonia. An inflammation affecting the air cells of the lungs.

Poison (Fr. _poison_). Any substance, which, when applied externally,
or taken into the stomach or the blood, works such a change in the
animal economy as to produce disease or death.

Pons Varolii. Bridge of Varolius. The white fibers which form a
_bridge_ connecting the different parts of the brain, first described
by _Varolius_.

Popliteal (Lat. _poples_, _poplitis_, the ham, the back part of the
knee). The space _behind the knee joint_ is called the _popliteal_
space.

Portal Vein (Lat. _porta_, a gate). The venous trunk formed by the
veins coming from the intestines. It carries the blood to the liver.

Presbyopia (Gr. πρέσβυς, old, and ὤψ, the eye). A defect of the
accommodation of the eye, caused by the hardening of the crystalline
lens; the “far sight” of adults and aged persons.

Process (Lat. _procedo_, _processus_, to proceed, to go forth). Any
projection from a surface; also, a method of performance; a procedure.

Pronation (Lat. _pronus_, inclined forwards). The turning of the hand
with the palm downwards.

Pronator. The group of muscles which turn the hand palm downwards.

Proteids (Gr. πρῶτος, first, and εἶδος, form). A general term for the
albuminoid constitutents of the body.

Protoplasm (Gr. πρῶτος, first, and πλάσσω, to form). A _first-formed_
organized substance; primitive organic cell matter.

Pterygoid (Gr. πτέρων, a wing, and εἶδος, form, resemblance).
Wing-like.

Ptomaine (Gr. πτῶμα, a dead body). One of a class of animal bases or
alkaloids formed in the putrefaction of various kinds of albuminous
matter.

Ptyalin (Gr. σίαλον, saliva). A ferment principle in _saliva_, having
power to convert starch into sugar.

Pulse (Lat. _pello, pulsum_, to beat). The throbbing of an artery
against the finger, occasioned by the contraction of the heart.
Commonly felt at the _wrist_.

Pupil (Lat. _pupilla_). The central, round opening in the iris, through
which light passes into the interior of the eye.

Pylorus (Gr. πυλουρός, a gatekeeper). The lower opening of the stomach,
at the beginning of the small intestine.

Reflex (Lat. _reflexus_, turned back). The name given to involuntary
movements produced by an excitation traveling along a sensory nerve to
a center, where it is turned back or reflected along motor nerves.

Renal (Lat. _ren_, _renis_, the kidney). Pertaining to the _kidneys_.

Respiration (Lat. _respiro_, to breathe frequently). The function of
breathing, comprising two acts,—_inspiration_, or breathing in, and
_expiration_, or breathing out.

Retina (Lat. _rete_, a net). The innermost of the three tunics, or
coats, of the eyeball, being an expansion of the optic nerve.

Rima Glottidis (Lat. _rima_, a chink or cleft). The _opening_ of the
glottis.

Saccharine (Lat. _saccharum_, sugar). The group of food substances
which embraces the different varieties of sugar, starch, and gum.

Saliva. The moisture, or fluids, of the mouth, secreted by the salivary
glands; the spittle.

Sarcolemma (Gr. σάρξ, flesh, and λέμμα, a husk). The membrane which
surrounds the contractile substance of a striped muscular fiber.

Sclerotic (Gr. σκληρός, hard). The tough, fibrous, outer coat of the
eyeball.

Scurvy. Scorbutus,—a disease of the general system, having prominent
skin symptoms.

Sebaceous (Lat. _sebum_, fat). Resembling fat; the name of the oily
secretion by which the skin is kept flexible and soft.

Secretion (Lat. _secerno_, _secretum_, to separate). The process of
separating from the blood some essential, important fluid; which fluid
is also called a _secretion_.

Semicircular Canals. Three canals in the internal ear.

Sensation. The perception of an external impression by the nervous
system.

Serum. The clear, watery fluid which separates from the clot of the
blood.

Spasm (Gr. σπασμός, convulsion). A sudden, violent, and involuntary
contraction of one or more muscles.

Special Sense. A sense by which we receive particular sensations, such
as those of sight, hearing, taste, and smell.

Sputum, pi. Sputa (Lat. _spuo_, _sputum_, to _spit_). The matter which
is coughed up from the air passages.

Stapes. Literally, a stirrup; one of the small bones of the middle ear.

Stimulant (Lat. _stimulo_, to prick or goad on). An agent which causes
an increase of vital activity in the body or in any of its parts.

Striated (Lat. _strio_, to furnish with channels). Marked with fine
lines.

Styptics (Gr. στυπτικός astringent). Substances used to produce a
contraction or shrinking of living tissues.

Subclavian Vein (Lat. _sub_, under, and _clavis_, a key). The great
vein bringing back the blood from the arm and side of the head; so
called because it is situated underneath the _clavicle_, or collar
bone.

Superior Vena Cava (Lat., upper hollow vein). The great vein of the
upper part of the body.

Suture (Lat. _sutura_, a seam). The union of certain bones of the skull
by the interlocking of jagged edges.

Sympathetic System of Nerves. A double chain of nervous ganglia,
situated chiefly in front of, and on each side of, the spinal column.

Symptom (Gr. σύν, with, and πίπτω, to fall). A sign or token of
disease.

Synovial (Gr. σύν, with, and ὠόν, an egg). The liquid which lubricates
the joints; joint-oil. It resembles the white of a raw egg.

System. A number of different organs, of similar structures,
distributed throughout the body and performing similar functions.

Systemic. Belonging to the system, or body, as a whole.

Systole (Gr. συστέλλω, to contract). The contraction of the heart, by
which the blood is expelled from that organ.

Tactile (Lat. _tactus_, touch). Relating to the sense of touch.

Tartar. A hard crust which forms on the teeth, and is composed of
salivary mucus, animal matter, and a compound of lime.

Temporal (Lat. _tempus_, time, and _tempora_, the temples). Pertaining
to the temples; so called because the hair begins to turn white with
age in that portion of the scalp.

Tendon (Lat. _tendo_, to stretch). The white, fibrous cord, or band, by
which a muscle is attached to a bone; a sinew.

Tetanus (Gr. τείνω, to stretch). A disease marked by persistent
contractions of all or some of the voluntary muscles; those of the jaw
are sometimes solely affected; the disorder is then termed lockjaw.

Thorax (Gr. θώραξ, a breast-plate). The upper cavity of the trunk of
the body, containing the lungs, heart, etc.; the chest.

Thyroid (Gr. εἶδος, a shield, and εἶ̓δος, form). The largest of the
cartilages of the larynx: its projection in front is called “Adam’s
Apple.”

Tissue. Any substance or texture in the body formed of various
elements, such as cells, fibers, blood-vessels, etc., interwoven with
each other.

Tobacco (Indian _tabaco_, the tube, or pipe, in which the Indians
smoked the plant). A plant used for smoking and chewing, and in snuff.

Trachea (Gr. τραχύς, rough). The windpipe.

Tragus (Gr. τράγος, a goat). The eminence in front of the opening of
the ear; sometimes hairy, like a goat’s beard.

Transfusion (Lat. _transfundo_, to pour from one vessel to another).
The operation of injecting blood taken from one person into the veins
of another.

Trichina Spiralis. (A twisted hair). A minute species of parasite, or
worm, which infests the flesh of the hog: may be introduced into the
human system by eating pork not thoroughly cooked.

Trochanter (Gr. τροχάω, to turn, to revolve). Name given to two
projections on the upper extremities of the femur, which give
attachment to the _rotator_ muscles of the thigh.

Trypsin. The ferment principle in pancreatic juice, which converts
proteid material into peptones.

Tubercle (Lat. _tuber_, a bunch). A pimple, swelling, or tumor. A
morbid product occurring in certain lung diseases.

Tuberosity (Lat. _tuber, tuberis_, a swelling). A protuberance.

Turbinated (Lat. _turbinatus_, from _turbo, turbinis_, a top). Formed
like a _top_; a name given to the bones in the outer wall of the nasal
fossæ.

Tympanum (Gr. τύμπανον, a drum). The cavity of the middle ear,
resembling a drum in being closed by two membranes.

Umbilicus (Lat., the navel.) A round cicatrix or scar in the median
line of the abdomen.

Urea (Lat. _urina_, urine). Chief solid constitutent of _urine_.
Nitrogenous product of tissue decomposition.

Ureter (Gr. οὐρέω, to pass urine). The tube through which the _urine_
is conveyed from the kidneys to the bladder.

Uvula (Lat. _uva_, a grape). The small, pendulous body attached to the
back part of the palate.

Vaccine Virus (Lat. _vacca_, a cow, and _virus_, poison). The material
derived from heifers for the purpose of vaccination,—the great
preventive of smallpox.

Valvulae Conniventes. A name given to transverse folds of the mucous
membrane in the small intestine.

Varicose (Lat. _varix_, a dilated vein). A distended or enlarged vein.

Vascular (Lat. _vasculum_, a little vessel). Pertaining to or
possessing blood or lymph vessels.

Vaso-motor (Lat. _vas_, a vessel, and _moveo, motum_, to move). Causing
_motion_ to the _vessels_. Vaso-motor nerves cause contraction and
relaxation of the blood-vessels.

Venæ Cavæ, pl. of Vena Cava. “Hollow veins.” A name given to the two
great veins of the body which meet at the right auricle of the heart

Venous (Lat. _vena_, a vein). Pertaining to, or contained within, a
vein.
Ventilation. The introduction of fresh air into a room or building in
such a manner as to keep the air within it in a pure condition.

Ventral (Lat. _venter, ventris_, the belly). Belonging to the abdominal
or belly cavity.

Ventricles of the Heart. The two largest cavities of the heart.

Vermiform (Lat. _vermis_, a worm, and _forma_, form). Worm-shaped.

Vertebral Column (Lat. _vertebra_, a joint). The backbone; also called
the spinal column and spine.

Vestibule. A portion of the internal ear, communicating with the
semicircular canals and the cochlea, so called from its fancied
resemblance to the vestibule, or porch, of a house.

Villi (Lat. _villus_, shaggy hair). Minute, thread-like projections
upon the internal surface of the small intestine, giving it a velvety
appearance.

Virus (Lat., poison). Foul matter of an ulcer; poison.

Vital Knot. A part of the medulla oblongata, the destruction of which
causes instant death.

Vitreous (Lat. _vitrum_, glass). Having the appearance of glass;
applied to the humor occupying the largest part of the cavity of the
eyeball.

Vivisection (Lat. _vivus_, alive, and _seco_, to cut). The practice of
operating upon living animals, for the purpose of studying some
physiological process.

Vocal Cords. Two elastic bands or ridges situated in the larynx; the
essential parts of the organ of voice.

Zygoma (Gr. ζυγώς, a yoke). The arch formed by the malar bone and the
zygomatic process of the temporal bone.



Index.


Absorption
  from mouth and stomach
  by the intestines
Accident and emergencies
Achilles, Tendon of
Air, made impure by breathing
  Foul, effect of, on health
Alcohol, Effect of, on bones
  Effect of, on muscles
  Effect of, on muscular tissue
  Effect of, on physical culture
  Nature of
  Effects of, on human system
    and digestion
  Effect of, on the stomach
    and the gastric juice
  Final results on digestion
  Effects of, on the liver
  Fatty degeneration due to
  Effect of, on the circulation
  Effect of, on the heart
  Effect of, on the blood-vessels
  Effect of, on the lungs
  Other results of, on lungs
  Effect of, on disease
  Effect of, on kidneys
Alcohol
  as cause of Bright’s disease
  and the brain
  How, injures the brain
  Why brain suffers from
  the enemy of brain work
  Other physical results of
  Diseases produced by
  Mental and moral ruin by
  Evil results of, inherited
  Effect of, on taste
  Effect of, on the eye
  Effect of, on throat and voice
Alcoholic beverages
Alcoholic fermentation and Bacteria
Anabolism defined
Anatomy defined
Antidotes for poisons
Antiseptics
Apparatus, Question of
Arm, Upper
Arteries
Astigmatism
Asphyxia
Atlas and axis
Atmosphere, how made impure

Bacteria, Nature of
Bacteria, Struggle for existence of
  Importance of, in Nature
  Action of
  Battle against
Baths and bathing
Bathing, Rules and precautions
Bicycling
Bile
Biology defined
Bladder
Bleeding, from stomach
  from lungs
  from nose
  How to stop
Blood, Circulation of
  Physical properties of
  corpuscles
  Coagulation of
  General plan of circulation
Blood-vessels, Nervous control of
  connected with heart
  Effect of alcohol on
  Injuries to
Bodies, living, Characters of
Body, General plan of
Bone, Chemical composition of
  Physical properties of
  Microscopic structure of
Bones, uses of, The
  Kinds of
  in infancy and childhood
  positions at school
  in after life
  Broken
  broken, Treatment for
  Effect of alcohol on
  Effect of tobacco on
Breathing, Movements of
Breathing, Mechanism of
  Varieties of
  Nervous control of
  change in the air
  Air, made impure by
Brain, as a whole
  Membranes of
  as a reflex center
  Effects of alcohol on
Brain center, Functions of, in perception of impressions
Bright’s disease caused by alcohol
Bronchial tubes
Burns or scalds

Capillaries
Carbohydrates
Carpus
Cartilage
  Hyaline
  White fibro-
  Yellow fibro-
  Thyroid
  Arytenoid
  Cricoid
Cells
  and the human organism
  Kinds of
  Vital properties of
  Epithelial
  Nerve
Cerebrum
Cerebellum
Chemical compounds in the body
Chloral
Chyle
Chyme
Cilia of air passages
Circulation
  General plan of
  Portal
  Pulmonic
  Systemic
  Effect of alcohol on
Clavicle
Cleanliness, Necessity for
Clothing, Use of
  Material used for
  Suggestions for use of
  Effects of tight-fitting
  Miscellaneous hints on use of
  Catching, on fire
Coagulation of blood
Cocaine, ether, and chloroform
Cochlea of ear
Cocoa
Coffee
Colon
Color-blindness
Complemental air
Compounds, Chemical
  Organic
Condiments
Conjunctiva
Connective tissue
Consonants
Contagious diseases
Contraction, Object of
Contusions and bruises
Convulsions
Cooking
Coughing
Cornea
Corpuscles, Blood
  Red
  Colorless
Corti, Organ of
Cranial Nerves
Cranium, Bones of
Crying
Crystalline lens
Cuticle
Cutis vera, or true skin

Degeneration, Fatty, due to alcohol
Deglutition, or swallowing
Deodorants
Diet, Important articles of
  Effect of occupation on
  Too generous
  Effect of climate on
Digestion, Purpose of
  General plan of
  in small intestines
  in large intestines
  Effect of alcohol on
Disease, Effect of alcoholics upon
Diseases, infectious and contagious, Management of
  Care of
  Hints on nursing
Disinfectants
  Air and water as
  How to use
Dislocations
Dogs, mad, Bites of
Drowning, Apparent
  Methods of treating
  Sylvester method
  Marshall Hall method
Duct, Hepatic
  Cystic
  Common bile
  Thoracic
  Nasal
Duodenum
Dura mater

Ear, External
  Middle
  Bones of the
  Internal
  Practical hints on care of
  Foreign bodies in
Eating, Practical points about
Eggs as food
Elements, Chemical, in the body
Epidermis, or cuticle
Epiglottis
Epithelium
  Squamous
  Columnar
  Glandular
  Ciliated
Epithelial tissues, Functions of
Erect position
Ethmoid bone
Eustachian tube
Excretion
Exercise, Physical
  Importance of
  Effect of, on muscles
  Effect of, on important organs
  Effect of, on personal appearance
  Effect of excessive
  Amount of, required
  Time for
  Physical, in school
  Practical points about
  Effect of alcohol and tobacco on
Experiments, Limitations of
  Value of
Eye
  Inner structure of
  Compared to camera
  Refractive media of
  Movements of
  Foreign bodies in
  Practical hints on care of
  Effect of alcohol on
  Effect of tobacco on
Eyeball, Coats of
Eyelids and eyebrows
Eyesight in schools

Face
  Bones of the
Fainting
Fats
  and oils
Femur
Fibrin
Fibula
Fish as food
Food and drink
Food, why we need it
  Absorption of, by the blood
  Quantity of, as affected by age
  Kinds of, required
Foods, Classification of
  Nitrogenous
  Proteid
  Saline or mineral
  Vegetable
  Proteid vegetable
  Non-proteid vegetable
  Non-proteid animal
  Table of
Food materials, Table of
  Composition of
Foot
Foul air, Effect of, on health
Frontal bone
Frost bites
Fruits as food

Gall bladder
Garden vegetables
Gastric glands
Gastric juice, Effect of alcohol on
Glands
  Mesenteric
  Lymphatic
  Ductless
  Thyroid
  Thymus
  Suprarenal
  Lacrymal
Glottis

Hair
  Structure of
Hair and nails, Care of
Hall, Marshall, method for apparent drowning
Hand
Haversian canals
Head and spine, how joined
Head, Bones of
Hearing, Sense of
  Mechanism of
  Effect of tobacco on
Heart
  Valves of
  General plan of blood-vessels connected with
  Rhythmic action of
  Impulse and sounds of
  Nervous control of
  Effect of alcohol on
  Effect of tobacco on
Heat, Animal
  Sources of
Hiccough
Hip bones
Histology defined
Humerus
Hygiene defined
Hyoid bone
Hypermetropia

Ileum
Injured, Prompt aid to
Insalivation
Intestine, Small
  Coats of small
  Large
Intoxicants, Physical results of
Iris of the eye

Jejunum
Joints
  Imperfect
  Perfect
  Hinge
  Ball-and-socket
  Pivot

Katabolism defined
Kidneys
  Structure of
  Function of
  Action if, how modified
  Effect of alcohol on
Kidneys and skin

Lacrymal apparatus
  gland
Lacteals
Landmarks, Bony
  Muscular
  heart
  arteries
Larynx
Laughing
Lens, Crystalline
Levers in the body
Life, The process of
Ligaments
Limbs, Upper
  Lower
Liver
  Minute structure of
  Blood supply of
  Functions of
  Effect of alcohol on
Lungs
  Minute structure of
  Capacity of
  Effect of alcohol on
  Bleeding from
Lymph
Lymphatics

Mad dogs, Bites of
Malar bone
Mastication
Maxillary, Superior
  Inferior
Meals, Hints about
Meats as food
Medulla oblongata
Membrane, Synovial
  Serous
  Arachnoid
Membranes, Brain
Mesentery
Metabolism defined
Metacarpal bones
Metatarsal bones
Microscope, Use of
Milk
Mineral foods
Morphology defined
Motion in animals
Mouth
Movement, Mechanism of
Muscles, Kinds of
  voluntary, Structure of
  involuntary, Structure of
  Arrangement of
  Important
  Effect of alcohol on
  Effect of tobacco on
  Review analysis of
  Rest for
Muscular tissue, Effect of alcohol on
  Changes in
  Properties of
  activity
  contraction
  fatigue
  sense
Myopia

Nails
  Care of
Nasal bones
Nerve cells
  fibers
  cells and fibers, Function of
Nerves, Cranial
  Spinal
  Motor
  Sensory
  spinal, Functions of
Nervous system, General view of
  compared to telegraph system
  Divisions of
  Effect of alcohol on
  Effect of tobacco on
Nitrogenous foods.
Non-proteid vegetable foods
  animal foods
Nose, Bleeding from
  Foreign bodies in

Occipital bone
Œsophagus
Opium
  Poisonous effects of
  In patent medicines
  Victim of the, habit
Organic compounds
Outdoor games
Oxidation

Pain, Sense of
Palate bones
Pancreas
Pancreatic juice
Parietal bones
Patella
Pepsin
Pericardium
Periosteum
Peritoneum
Phalanges
Pharynx and œsophagus
Physical exercise
Physical education in school
Physical exercises in school
Physiology defined
  Study of
  what it should teach
  Main problems of, briefly stated.
Physiological knowledge, Value of
Pia mater
Pneumogastric nerve
Poisons
Poisons, Table of
  Antidotes for
  Practical points about
Poisoning, Treatment of
Portal circulation
Portal vein
Presbyopia
Pressure, Where to apply
Proteids
Proteid vegetable foods
Protoplasm
Pulmonary artery
  veins
Pulmonary infection
Pulse
Pupil of the eye

Radius
Receptaculum chyli
Rectum
Reflex centers
  in the brain
Reflex action, Importance of
Renal secretion
Residual air
Respiration, Nature and object of
  Nervous control of
  Effect of, on the blood
  Effect of, on the air
  Modified movements of
  Effect of alcohol on
  Effect of tobacco on
  artificial, Methods of
Rest, for the muscles
  Need of
  Benefits of
  The Sabbath, a day of
  of mind and body
Retina
Ribs and sternum

Saline or mineral foods
Saliva
Salt as food
Salts, Inorganic, in the body
Scalds or burns
Scapula
School, Physical education in
  Positions at
School and physical education
Secretion
Semicircular canals
Sensations, General
Sensation, Conditions of
Sense, Organs of
Sense organ, The essentials of
Serous membranes
Sick-room, Arrangement of
  Ventilation of
  Hints for
  Rules for
Sighing
Sight, Sense of
Skating, swimming, and rowing
Skeleton
  Review analysis of
Skeleton and manikin, Use of
Skin, The
  regulating temperature
  Action of, how modified
  Absorbent powers of
  and the kidneys
Skull
  Sutures of
Sleep, a periodical rest
  Effect of, on bodily functions
  Amount of, required
  Practical rules about
Smell
  Sense of
Sneezing
Snoring
Sobbing
Special senses
Speech
Sphenoid bone
Spinal column
Spinal cord
  Structure of
  Functions of
  conductor of impulses
  as a reflex center
Spinal nerves
  Functions of
Spleen
Sprains and dislocations
Stammering
Starches and sugars
Sternum
Stomach
  Coats of
  Digestion in
  Effect of alcohol on
  Bleeding from
Strabismus
Stuttering
Sunstroke
Supplemental air
Suprarenal capsules
Sutures of skull
Sweat glands
Sweat, Nature of
Sylvester method for apparent drowning
Sympathetic system
  Functions of
Synovial membrane
  sheaths and sacs

Taste, Organ of
  Sense of
Taste, Physiological conditions of
  Modifications of the sense
  Effect of alcohol on
  Effect of tobacco on
Tea
Tear gland and tear passages
Tears
Technical terms defined
Teeth
  Development of
  Structure of
  Proper care of
  Hints about saving
Temperature, Regulation of bodily
  Skin as a regulator of
  Voluntary regulation of
  Sense of
Temporal bones
Tendon of Achilles
Tendons
Thigh
Thoracic duct
Throat
  Care of
  Effect of alcohol on
  Effect of tobacco on
  Foreign bodies in
Thymus gland
Thyroid gland
Tibia
Tidal air
Tissue, White fibrous
  Connective
  Yellow elastic
  Areolar
  Adipose
  Adenoid
  Muscular
Tissues, Epithelial
Tissues, epithelial, Varieties of
  Functions of
  Connective
Tobacco, Effect of, on bones
  Effect of, on muscles
  Effect of, on physical culture
  Effect of, on digestion
  Effect of, on the heart
  Effect of, on the lungs
  Effect of, on the nervous system
  Effect of, on the mind
  Effect of, on the character
  Effect of, on taste
  Effect of, on hearing
  Effect of, on throat and voice
Touch, Organ of
  Sense of
Trachea
Trunk, Bones of
Tympanum, Cavity of

Ulna
Urine

Valve, Mitral
Valves of the heart
Valves, Tricuspid
  Semilunar
Vegetable foods
Veins
Ventilation
  Conditions of efficient
  of sick-room
Vestibule of ear
Vermiform appendix
Vision, Common defects of
  Effect of tobacco on
Vivisection and dissection
Vocal cords
Voice, Mechanism of
  Factors in the production of
  Care of
  Effect of alcohol on
  Effect of tobacco on
Vowel sounds

Walking, jumping, and running
Waste and repair
Waste material, Nature of
Waste products, Elimination of
Water as food
Whispering
Wounds, Incised and lacerated

Yawning



Footnotes

 [1] The Value of Physiological Knowledge. “If any one doubts the
 importance of an acquaintance with the fundamental principles of
 physiology as a means to complete living, let him look around and see
 how many men and women he can find in middle life, or later, who are
 thoroughly well. Occasionally only do we meet with an example of
 vigorous health continued to old age; hourly do we meet with examples
 of acute disorder, chronic ailment, general debility, premature
 decrepitude. Scarcely is there one to whom you put the question, who
 has not, in the course of his life, brought upon himself illness from
 which a little knowledge would have saved him. Here is a case of heart
 disease consequent on a rheumatic fever that followed a reckless
 exposure. There is a case of eyes spoiled for life by overstudy.
    “Not to dwell on the natural pain, the gloom, and the waste of time
    and money thus entailed, only consider how greatly ill health
    hinders the discharge of all duties,—makes business often
    impossible, and always more difficult; produces irritability fatal
    to the right management of children, puts the functions of
    citizenship out of the question, and makes amusement a bore. Is it
    not clear that the physical sins—partly our ancestors’ and partly
    our own—which produce this ill health deduct more from complete
    living than anything else, and to a great extent make life a
    failure and a burden, instead of a benefaction and a
    pleasure?”—Herbert Spencer.

 [2] The word protoplasm must not be misunderstood to mean a substance
 of a definite chemical nature, or of an invariable morphological
 structure; it is applied to any part of a cell which shows the
 properties of life, and is therefore only a convenient abbreviation
 for the phrase “mass of living matter.”

 [3] “Did we possess some optic aid which should overcome the grossness
 of our vision, so that we might watch the dance of atoms in the double
 process of making and unmaking in the living body, we should see the
 commonplace, lifeless things which are brought by the blood, and which
 we call food, caught up into and made part of the molecular whorls of
 the living muscle, linked together for a while in the intricate
 figures of the dance of life, giving and taking energy as they dance,
 and then we should see how, loosing hands, they slipped back into the
 blood as dead, inert, used-up matter.”—Michael Foster, Professor of
 Physiology in the University of Cambridge, England.

 [4] “Our material frame is composed of innumerable atoms, and each
 separate and individual atom has its birth, life, and death, and then
 its removal from the ‘place of the living.’ Thus there is going on a
 continuous process of decay and death among the individual atoms which
 make up each tissue. Each tissue preserves its vitality for a limited
 space only, is then separated from the tissue of which it has formed a
 part, and is resolved into its inorganic elements, to be in due course
 eliminated from the body by the organs of excretion.”—Maclaren’s
 _Physical Education_.

 [5] The periosteum is often of great practical importance to the
 surgeon. Instances are on record where bones have been removed,
 leaving the periosteum, within which the entire bone has grown again.
 The importance of this remarkable tissue is still farther illustrated
 by experiments upon the transplantation of this membrane in the
 different tissues of living animals, which has been followed by the
 formation of bone in these situations. Some years ago a famous surgeon
 in New York removed the whole lower jawbone from a young woman,
 leaving the periosteum and even retaining in position the teeth by a
 special apparatus. The entire jawbone grew again, and the teeth
 resumed their original places as it grew.

 [6] The mechanism of this remarkable effect is clearly shown by an
 experiment which the late Dr. Oliver Wendell Holmes used to take
 delight in performing in his anatomical lectures at the Harvard
 Medical College. He had a strong iron bar made into a ring of some
 eight inches in diameter, with a space left between the ends just
 large enough to be filled by an English walnut. The ring was then
 dropped to the floor so as to strike on the convexity just opposite to
 the walnut, which invariably was broken to pieces.

 [7] For the treatment of accidents and emergencies which may occur
 with reference to the bones, see Chapter XIII.

 [8] “Besides the danger connected with the use of alcoholic drinks
 which is common to them with other narcotic poisons, alcohol retards
 the growth of young cells and prevents their proper development. Now,
 the bodies of all animals are made up largely of cells, ... and the
 cells being the living part of the animal, it is especially important
 that they should not be injured or badly nourished while they are
 growing. So that alcohol in all its forms is particularly injurious to
 young persons, as it retards their growth, and stunts both body and
 mind. This is the theory of Dr. Lionel S. Beale, a celebrated
 microscopist and thinker, and is quite generally accepted.”—Dr. Roger
 S. Tracy, of the New York Board of Health.

 [9] “In its action on the system nicotine is one of the most powerful
 poisons known. A drop of it in a concentrated form was found
 sufficient to kill a dog, and small birds perished at the approach of
 a tube containing it.”—Wood’s _Materia Medica_.
    “Tobacco appears to chiefly affect the heart and brain, and I have
    therefore placed it among cerebral and cardiac poisons.”—Taylor’s
    _Treatise on Poisons_.

 [10] “Certain events occur in the brain; these give rise to other
 events, to changes which travel along certain bundles of fibers called
 nerves, and so reach certain muscles. Arrived at the muscles, these
 changes in the nerves, which physiologists call nervous impulses,
 induce changes in the muscles, by virtue of which these shorten
 contract, bring their ends together, and so, working upon bony levers,
 bend the arm or hand, or lift the weight.”—Professor Michael Foster.

 [11] The synovial membranes are almost identical in structure with
 serous membranes (page 176), but the secretion is thicker and more
 like the white of egg.

 [12] “Smoking among students or men training for contests is a
 mistake. It not only affects the wind, but relaxes the nerves in a way
 to make them less vigorous for the coming contest. It shows its
 results at once, and when the athlete is trying to do his best to win
 he will do well to avoid it.” Joseph Hamblen Sears, Harvard Coach, and
 Ex-Captain of the Harvard Football Team, Article in _In Sickness and
 in Health_.

 [13] “There is no profession, there is no calling or occupation in
 which men can be engaged, there is no position in life, no state in
 which a man can be placed, in which a fairly developed frame will not
 be valuable to him; there are many of these, even the most purely and
 highly intellectual, in which it is essential to success—essential
 simply as a means, material, but none the less imperative, to enable
 the mind to do its work. Year by year, almost day by day, we see men
 (and women) falter and fail in the midst of their labors; ... and all
 for want of a little bodily stamina—a little bodily power and bodily
 capacity for the endurance of fatigue, or protracted unrest, or
 anxiety, or grief.”—Maclaren’s _Physical Education_.

 [14] “One half the struggle of physical training has been won when a
 boy can be induced to take a genuine interest in his bodily
 condition,—to want to remedy its defects, and to pride himself on the
 purity of his skin, the firmness of his muscles, and the uprightness
 of his figure. Whether the young man chooses afterwards to use the
 gymnasium, to run, to row, to play ball, or to saw wood, for the
 purpose of improving his physical condition, matters little, provided
 he accomplishes that object.”—Dr. D. A. Sargent, Director of the
 Hemenway Gymnasium at Harvard University.

 [15] “It is _health_ rather than _strength_ that is the great
 requirement of modern men at modern occupations; it is not the power
 to travel great distances, carry great burdens, lift great weights, or
 overcome great material obstructions; it is simply that condition of
 body, and that amount of vital capacity, which shall enable each man
 in his place to pursue his calling, and work on in his working life,
 with the greatest amount of comfort to himself and usefulness to his
 fellowmen.”—Maclaren’s _Physical Education_.

 [16] To this classification may be added what are called albuminoids,
 a group of bodies resembling proteids, but having in some respects a
 different nutritive value. Gelatine, such as is found in soups or
 table gelatine is a familiar example of the albuminoids. They are not
 found to any important extent in our raw foods, and do not therefore
 usually appear in the analyses of the composition of foods. The
 albuminoids closely resemble the proteids, but cannot be used like
 them to build up protoplasm.

 [17] The amount of water in various tissues of the body is given by
 the following table in parts of 1000:

         Solids.                   Liquids.
         Enamel, 2 Blood, 791 Dentine, 100 Bile, 864
         Bone, 486 Blood plasma, 901
         Fat, 299 Chyle, 928
         Cartilage, 550 Lymph, 958
         Liver, 693 Serum, 959 Skin, 720 Gastric
         juice,  973 Brain, 750 Tears, 982
         Muscle, 757 Saliva, 995
         Spleen, 758 Sweat, 995 Kidney, 827 Vitreous
         humor, 987

 [18] The work of some kinds of moulds may be apparent to the eye, as
 in the growths that form on old leather and stale bread and cheese.
 That of others goes on unseen, as when acids are formed in stewed
 fruits. Concerning the work of the different kinds of moulds.
 Troussart says: “_Mucor mucedo_ devours our preserves; _Ascophora
 mucedo_ turns our bread mouldy; _Molinia_ is nourished at the expense
 of our fruits; _Mucor herbarium_ destroys the herbarium of the
 botanist; and _Choetonium chartatum_ develops itself on paper, on the
 insides of books and on their bindings, when they come in contact with
 a damp wall.”—Troussart’s _Microbes, Ferments, and Moulds_.

 [19] “The physiological wear of the organism is constantly being
 repaired by the blood; but in order to keep the great nutritive fluid
 from becoming impoverished, the matters which it is constantly losing
 must be supplied from some source out of the body, and this
 necessitates the ingestion of articles which are known as
 food.”—Flint’s _Text-book of Human Physiology_.

 [20] Glands. Glands are organs of various shapes and sizes, whose
 special work it is to separate materials from the blood for further
 use in the body, the products being known as secretion and excretion.
 The means by which secretion and excretion are effected are, however,
 identical. The essential parts of a gland consist of a basement
 membrane, on one side of which are found actively growing cells, on
 the other is the blood current, flowing in exceedingly thin-walled
 vessels known as the capillaries. The cells are able to select from
 the blood whatever material they require and which they elaborate into
 the particular secretion. In Fig. 47 is illustrated, diagrammatically,
 the structure of a few typical secreting glands. The continuous line
 represents the basement membrane. The dotted line represents the
 position of the cells on one side of the basement membrane. The
 irregular lines show the position of the blood-vessels.

 [21] Tablets and other material for Fehling and additional tests for
 sugar can be purchased at a drug store. The practical details of these
 and other tests which assume some knowledge of chemistry, should be
 learned from some manual on the subject.

 [22] The Peritoneum. The intestines do not lie in a loose mass in the
 abdominal cavity. Lining the walls of this cavity, just as in a
 general way, a paper lines the walls of a room, is a delicate serous
 membrane, called the peritoneum. It envelops, in a greater or less
 degree, all the viscera in the cavity and forms folds by which they
 are connected with each other, or are attached to the posterior wall.
 Its arrangement is therefore very complicated. When the peritoneum
 comes in contact with the large intestine, it passes over it just as
 the paper of a room would pass over a gas pipe which ran along the
 surface of the wall, and in passing over it binds it down to the wall
 of the cavity. The small intestines are suspended from the back wall
 of the cavity by a double fold of the peritoneum, called the
 mesentery. The bowels are also protected from external cold by several
 folds of this membrane loaded with fat. This is known as the _great
 omentum_.
    The peritoneum, when in health, secretes only enough fluid to keep
    its surface lubricated so that the bowels may move freely and
    smoothly on each other and on the other viscera. In disease this
    fluid may increase in amount, and the abdominal cavity may become
    greatly distended. This is known as _ascites_ or dropsy.

 [23] The human bile when fresh is generally of a bright golden red,
 sometimes of a greenish yellow color. It becomes quite green when
 kept, and is alkaline in reaction. When it has been omited it is
 distinctly yellow, because of its action on the gastric juice. The
 bile contains a great deal of coloring matter, and its chief
 ingiedients are two salts of soda, sodium taurocholate and
 glycocholate.

 [24] Nansen emphasizes this point in his recently published work,
 _Farthest North_.

 [25] We should make it a point not to omit a meal unless forced to do
 so. Children, and even adults, often have the habit of going to school
 or to work in a hurry, without eating any breakfast. There is almost
 sure to be a fainting, or “all-gone” feeling at the stomach before
 another mealtime. This habit is injurious, and sure to produce
 pernicious results.

 [26] The teeth of children should be often examined by the dentist,
 especially from the beginning of the second dentition, at about the
 sixth year, until growth is completed. In infancy the mother should
 make it a part of her daily care of the child to secure perfect
 cleanliness of the teeth. The child thus trained will not, when old
 enough to rinse the mouth properly or to use the brush, feel
 comfortable after a meal until the teeth have been cleansed. The habit
 thus formed is almost sure to be continued through life.

 [27] “If the amount of alcohol be increased, or the repetition become
 frequent, some part of it undergoes acid fermentation in the stomach,
 and acid eructations or vomitings occur. With these phenomena are
 associated catarrh of the stomach and liver with its characteristic
 symptoms,—loss of appetite, feeble digestion, sallowness, mental
 depression, and headache.”—James C. Wilson, Professor in the Jefferson
 Medical College, Philadelphia.
    “Man has recourse to alcohol, not for the minute quantity of energy
    which may be supplied by itself, but for its powerful influence on
    the distribution of the energy furnished by other things. That
    influence is a very complex one.”—Professor Michael Foster.

 [28] “When constantly irritated by the direct action of alcoholic
 drinks, the stomach gradually undergoes lasting structural changes.
 Its vessels remain dilated and congested, its connective tissue
 becomes excessive, its power of secreting gastric juice diminishes,
 and its mucous secretions abnormally abundant.”—H. Newell Martin, late
 Professor of Physiology in Johns Hopkins University.
    “Chemical experiments have demonstrated that the action of alcohol
    on the digestive fluids is to destroy its active principle, the
    pepsin, thus confirming the observations of physiologists that its
    use gives ride to the most serious disorders of the stomach and the
    most malignant aberrations of the entire economy.”—Professor E. C.
    Youmans, author of standard scientific works.
    “The structural changes induced by habitual use of alcohol and the
    action of this agent on the pepsin, seriously impair the digestive
    power. Hence it is, that those who are habitual consumers of
    alcoholic fluids suffer from disorders o digestion.”—Robert
    Bartholow, recently Professor of Materia Medica in the University
    of Pennsylvania.
    “Alcohol in any appreciable quantity diminishes the solvent power
    of the gastric fluid so as to interfere with the process of
    digestion instead of aiding it.”—Professor W. B. Carpenter, the
    eminent English physiologist.

 [29] “Cirrhosis of the liver is notoriously frequent among drunkards,
 and is in fact almost, though not absolutely, confined to
 them.”—Robert T. Edes, formerly Professor of Materia Medica in Harvard
 Medical College.
    “Alcohol acts on the liver by producing enlargement of that organ,
    and a fat deposit, or ‘hob-nailed’ liver mentioned by the English
    writers.”—Professor W. B. Carpenter.

 [30] Preparation of Artificial Gastric Juice. _(a)_ Take part of the
 cardiac end of the pig’s stomach, which has been previously opened and
 washed rapidly in cold water, and spread it, mucous surface upwards,
 on the convex surface of an inverted capsule. Scrape the mucous
 surface firmly with the back of a knife blade, and rub up the
 scrapings in a mortar with fine sand. Add water, and rub up the whole
 vigorously for some time, and filter. The filtrate is an artificial
 gastric juice.
    _(b)_ From the cardiac end of a pig’s stomach detach the mucous
    membrane in shreds, dry them between folds of blotting-paper, place
    them in a bottle, and cover them with strong glycerine for several
    days. The glycerine dissolves the pepsin, and on filtering, a
    glycerine extract with high digestive properties is obtained.
    These artificial juices, when added to hydrochloric acid of the
    proper strength, have high digestive powers.
    Instead of _(a)_ or _(b)_ use the artificial pepsin prepared for
    the market by the wholesale manufacturers of such goods.

 [31] The cause of the clotting of blood is not yet fully understood.
 Although the process has been thoroughly investigated we have not yet
 a satisfactory explanation why the circulating blood does not clot in
 healthy blood-vessels. The ablest physiologists of our day do not, as
 formerly, regard the process as a so-called vital, but a purely
 chemical one.

 [32] Serous Membranes.—The serous membranes form shut sacs, of which
 one portion is applied to the walls of the cavity which it lines; the
 other is reflected over the surface of the organ or organs contained
 in the cavity. The sac is completely closed, so that no communication
 exists between the serous cavity and the parts in its neighborhood.
 The various serous membranes are the _pleura_ which envelops the
 lungs; the _pericardium_ which surrounds the heart; the _peritoneum_
 which invests the viscera of the abdomen, and the _arachnoid_ in the
 spinal canal and cranial cavity. In health the serous membranes
 secrete only sufficient fluid to lubricate and keep soft and smooth
 the opposing surfaces.

 [33] A correct idea may be formed of the arrangement of the
 pericardium around the heart by recalling how a boy puts on and wears
 his toboggan cap. The pericardium encloses the heart exactly as this
 cap covers the boy’s head.

 [34] “Alcohol taken in small and single doses, acts almost exclusively
 on the brain and the blood-vessels of the brain, whereas taken in
 large and repeated doses its chief effects are always nervous effects.
 The first effects of alcohol on the function of inhibition are to
 paralyze the controlling nerves, so that the blood-centers are
 dilated, and more blood is let into the brain. In consequence of this
 flushing of the brain, its nerve centers are asked to do more
 work.”—Dr. T. S. Clouston, Medical Superintendent of the Royal Asylum,
 Edinburgh.
    “Alcoholic drinks prevent the natural changes going on in the
    blood, and obstruct the nutritive and reparative
    functions.”—Professor E. L. Youmans, well-known scientist and
    author of _Class Book of Chemistry_.

 [35] The word “cell” is not used in this connection in its technical
 signification of a histological unit of the body (sec. 12), but merely
 in its primary sense of a small cavity.

 [36] “The student must guard himself against the idea that arterial
 blood contains no carbonic acid, and venous blood no oxygen. In
 passing through the lungs venous blood loses only a part of its
 carbonic acid; and arterial blood, in passing through the tissues,
 loses only a part of its oxygen. In blood, however venous, there is in
 health always some oxygen; and in even the brightest arterial blood
 there is actually more carbonic acid than oxygen.”—T. H. Huxley.

 [37] “Consumption is a disease which can be taken from others, and is
 not simply caused by colds. A cold may make it easier to take the
 disease. It is usually caused by germs which enter the body with the
 air breathed. The matter which consumptives cough or spit up contains
 these germs in great numbers—frequently millions are discharged in a
 single day. This matter spit upon the floor, wall, or elsewhere is apt
 to dry, become pulverized, and float in the air as dust. The dust
 contains the germs, and thus they enter the body with the air
 breathed. The breath of a consumptive does not contain the germs and
 will not produce the disease. A well person catches the disease from a
 consumptive only by in some way taking in the matter coughed up by the
 consumptive.”—Extract from a circular issued by the Board of Health of
 New York City.

 [38] “The lungs from the congested state of their vessels produced by
 alcohol are more subject to the influence of cold, the result being
 frequent attacks of bronchitis. It has been recognized of late years
 that there is a peculiar form of consumption of the lungs which is
 very rapidly fatal and found only in alcohol drinkers.”—Professor H.
 Newell Martin.

 [39] “The relation to Bright’s Disease is not so clearly made out as
 is assumed by some writers, though I must confess to myself sharing
 the popular belief that alcohol is one among its most important
 factors.”—Robert T. Edes, M.D.

 [40] Thus the fibers which pass out from the sacral plexus in the
 loins, and extend by means of the great sciatic nerve and its branches
 to the ends of the toes, may be more than a yard long.

 [41] Remarkable instances are cited to illustrate the imperative
 demand for sleep. Gunner boys have been known to fall asleep during
 the height of a naval battle, owing to the fatigue occasioned by the
 arduous labor in carrying ammunition for the gunner. A case is
 reported of a captain of a British frigate who fell asleep and
 remained so for two hours beside one of the largest guns of his
 vessel, the gun being served vigorously all the time. Whole companies
 of men have been known to sleep while on the march during an arduous
 campaign. Cavalrymen and frontiersmen have slept soundly in the saddle
 during the exhausting campaigns against the Indians.

 [42] According to the Annual Report of New York State Reformatory, for
 1896, drunkenness among the inmates can be clearly traced to no less
 than 38 per cent of the fathers and mothers only.
    Drunkenness among the parents of 38 per cent of the prisoners in a
    reformatory of this kind is a high and a serious percentage. It
    shows that the demoralizing influence of drink is apt to destroy
    the future of the child as well as the character of the parent.
    “There is a marked tendency in nature to transmit all diseased
    conditions. Thus the children of consumptive parents are apt to be
    consumptive. But, of all agents, alcohol is the most potent in
    establishing a heredity that exhibits itself in the destruction of
    mind and body. There is not only a propensity transmitted, but an
    actual disease of the nervous system.”—Dr. Willard Parker.

 [43] “It is very certain that many infants annually perish from this
 single cause.”—Reese’s _Manual of Toxicology_.

 [44] If an eye removed from its socket be stripped posteriorly of the
 sclerotic coat, an inverted image or the field of view will be seen on
 the retina; but if the lens or other part of the refractive media be
 removed, the image will become blurred or disappear altogether.

 [45] This change in the convexity of the lens is only a slight one, as
 the difference in the focal point between rays from an object twenty
 feet distant and one four inches distant is only one-tenth of an inch.
 While this muscular action is taking place, the pupil contracts and
 the eyeballs converge by the action of the internal rectus muscles.
 These three acts are due to the third nerve (the motor oculi). This is
 necessary in order that each part should he imprinted on the same
 portion of the retina, otherwise there would be double vision.

 [46] The Germans have a quaint proverb that one should never rub his
 eyes, except with his elbows!

 [47] “The deleterious effect of tobacco upon eyesight is an
 acknowledged fact. The Belgian government instituted an investigation
 into the cause of the prevalence of color-blindness. The unanimous
 verdict of the experts making the examination was that the use of
 tobacco was one of the principal causes of this defect of vision.
    “The dimness of sight caused by alcohol or tobacco has long been
    clinically recognized, although not until recently accurately
    understood. The main facts can now be stated with much assurance,
    since the publication of an article by Uhthoff which leaves little
    more to be said. He examined one thousand patients who were
    detained in hospital because of alcoholic excess, and out of these
    found a total of eye diseases of about thirty per cent.
    “Commonly both eyes are affected, and the progress of the disease
    is slow, both in culmination and in recovery.... Treatment demands
    entire abstinence.”—Henry D. Noyes, Professor of Otology in the
    Bellevue Hospital Medical College, New York.

 [48] “The student who will take a little trouble in noticing the ears
 of the persons whom he meets from day to day will be greatly
 interested and surprised to see how much the auricle varies. It may be
 a thick and clumsy ear or a beautifully delicate one; long and narrow
 or short and broad, may have a neatly formed and distinct lobule, or
 one that is heavy, ungainly, and united to the cheek so as hardly to
 form a separate part of the auricle, may hug the head closely or flare
 outward so as to form almost two wings to the head. In art, and
 especially in medallion portraits, in which the ear is a marked
 (because central) feature, the auricle is of great importance”—William
 W. Keen, M.D., editor of Gray’s _Anatomy_.

 [49] The organ of Corti is a very complicated structure which it is
 needless to describe in this connection. It consists essentially of
 modified ephithelial cells floated upon the auditory epithelium, or
 basilar membrane, of the cochlea. There is a series of fibers, each
 made of two parts sloped against each other like the rafters of a
 roof. It is estimated that there are no less than 3000 of these arches
 in the human ear, placed side by side in a continuous series along the
 whole length of the basilar membrane. Resting on these arches are
 numbers of conical epithelial cells, from the free surface of which
 bundles of stiff hairs (cilia) project. The fact that these hair-cells
 are connected with the fibers of the cochlear division of the auditory
 nerve suggests that they must play an important part in auditory
 sensation.

 [50] The voices of boys “break,” or “change,” because of the sudden
 growth or enlargement of the larynx, and consequent increase in length
 of the vocal cords, at from fourteen to sixteen years of age. No such
 enlargement takes place in the larynxes of girls: therefore their
 voices undergo no such sudden change.

 [51] This experiment and several others in this book, are taken from
 Professor Bowditch’s little book called _Hints for Teachers of
 Physiology_, a work which should be mastered by every teacher of
 physiology in higher schools.

 [52] The teacher or student who is disposed to study the subject more
 thoroughly and in more detail than is possible in a class text-book,
 will find all that is needed in the following excellent books, which
 are readily obtained by purchase, or may be found in the public
 libraries of larger towns: Dulles’ _Accidents and Emergencies;_
 Pilcher’s _First Aid in Illness and Injury_; Doty’s _Prompt Aid to the
 Injured;_ and Johnston’s “Surgical Injuries and Surgical Diseases,” a
 special article in Roosevelt’s _In Sickness and in Health_.

 [53] “A tourniquet is a bandage, handkerchief, or strap of webbing,
 into the middle of which a stone, a potato, a small block of wood, or
 any hard, smooth body is tied. The band is tied loosely about the
 limb, the hard body is held over the artery to be constricted, and a
 stick is inserted beneath the band on the opposite side of the limb
 and used to twist the band in such a way that the limb is tightly
 constricted thereby, and the hard body thus made to compress the
 artery (Fig. 160).
    “The entire circumference of the limb may be constricted by any
    sort of elastic band or rubber tube, or any other strong elastic
    material passed around the limb several times on a stretch, drawn
    tight and tied in a knot. In this way, bleeding may be stopped at
    once from the largest arteries. The longer and softer the tube the
    better. It requires no skill and but little knowledge of anatomy to
    apply it efficiently.” Alexander B. Johnson, Surgeon to Roosevelt
    Hospital, New York City.

 [54] Corrosive sublimate is probably the most powerful disinfectant
 known. A solution of one part in 2000 will destroy microscopic
 organisms. Two teaspoonfuls of this substance will make a solution
 strong enough to kill all disease germs.

 [55] The burning of sulphur produces sulphurous acid, which is an
 irrespirable gas. The person who lights the sulphur must, therefore,
 immediately leave the room, and after the lapse of the proper time,
 must hold his breath as he enters the room to open the windows and let
 out the gas. After fumigation, plastered walls should be white-washed,
 the woodwork well scrubbed with carbolic soap, and painted portions
 repainted.

 [56] Put copperas in a pail of water, in such quantity that some may
 constantly remain undissolved at the bottom. This makes a saturated
 solution. To every privy or water-closet, allow one pint of the
 solution for every four persons when cholera is about. To keep privies
 from being offensive, pour one pint into each seat, night and morning.

 [57] “While physiology is one of the biological sciences, it should be
 clearly recognized that it is not, like botany or zoology, a science
 of observation and description; but rather, like physics or chemistry,
 a science of experiment. While the amount of experimental instruction
 (not involving vivisection or experiment otherwise unsuitable) that
 may with propriety be given in the high school is neither small nor
 unimportant, the limitations to such experimental teaching, both as to
 kind and as to amount, are plainly indicated.
    “The obvious limitations to experimental work in physiology in the
    high school, already referred to, make it necessary for the student
    to acquire much of the desired knowledge from the text-book only.
    Nevertheless, much may be done by a thoughtful and ingenious
    teacher to make such knowledge real, by the aid of suitable
    practical exercises and demonstrations.”—_Report of the Committee
    of Ten on Secondary School Studies_.

 [58] This ingenious and excellent experiment is taken from the _New
 York School Journal_ for May, 1897, for which paper it was prepared by
 Charles D. Nason, of Philadelphia.





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