FOR

}H SC

MACY

GIFT OF
Agricultural Educ.Div

BIOLOGY

LIBRARY

G

V

A GENERAL PHYSIOLOGY

FOR HIGH SCHOOLS

BASED UPON THE NERVOUS SYSTEM

BY

M. L. MACY, L.B.

Yy
ASSISTED BY

H. W. NORRIS, A.M.

PROFESSOR OF BIOLOGY, IOWA COLLEGE

" The physiology of the nervous system is emphatically the physiology
of the future." — MICHAEL FOSTER, M.D., F.R.S.

NEW YORK-:. CINCINNATI •:• CHICAGO

AMERICAN BOOK COMPANY

BIOLOGY
LIBRARY

G

CJOPYBIGHT, 1900, BT

M. L. MACY.

MACY'S PHYSIOLOOT.

E-P 7

PREFACE

THE effort has been made in this book to unify the study of the
parts and the functions of the human organism by the application of
approved pedagogical and scientific principles. The teaching of any
science proceeds logically from that which is known to that which is
not known. Physiology is one of the earliest of the natural sciences
to be presented for formal study in school. In respect to man's
organism the one sort of knowledge absolutely original and elemental
is consciousness — conscious motion and sensation. This it is that
forms the most apparent difference between the two kingdoms which
manifest the phenomena of life. It is characteristic of animals to
possess consciousness, volition, feeling. Plants are, to all appearance,
devoid of them all.

Hence this study of human physiology is made to begin with that
part of the body which is the organ of consciousness — the nervous
system. The pupil knows that he thinks and feels and wills and
moves, and he studies physiology in order to understand the appara-
tus by which these wonders are accomplished. He is here given first
(after a few preliminary definitions) a brief sketch of the parts com-
posing the nervous system. Next he studies those physical operations
into which consciousness enters as an essential quality, and becomes
familiar with the organs of motion and sensation. This leads natu-
rally to consideration of the provision for the sustenance of those
organs — nutrition in its comprehensive sense. Finally the student
comes to a more detailed examination of the mechanism for the
conscious activities of the human being.

Whatever may be true of philosophers, the infant begins the study
of physiology at the point here suggested, and follows a method in
harmony with this plan. More than one practical teacher has worked
out a similar method through years of experience in the class room.
By making the nervous system (the center and core of all animal
life) the leading thought throughout, a unity of impression is secured,

3

674621

4 PREFACE

the actual connection of every vital process with the one nervous
system becomes obvious, and the emphasis is placed where it properly
belongs. It is believed that this plan has advantages also for the
student of general biology. It emphasizes the one grand, obvious
distinction between plants and animals. To students of psychology
it will likewise commend itself. Because of prevalent ignorance of
the nervous system and its due predominance in the animal economy,
psychologists have been forced to become physiologists in order to
build across the gap, left by the ordinary manner of treatment,
between physiology and psychology.

Care has been taken to make no statements not in accord with
established science, but no effort is made to introduce the newest
conjectures. The necessary limitations of a school text-book have
been kept in mind as well as the degree of mental development of
those for whom the work is designed.

It is believed that the instruction respecting alcoholic drinks and
narcotics, while complying with the requirements of recent legislation
in the various states, will be found to be based upon rational and
scientific principles, and to be placed before the student in a manner
to win the assent of his reason rather than to create a mere prejudice
which further knowledge might overthrow. Nothing is gained by
overstatement, and it is always safe to tell the simple truth, for
nothing will so surely foster right living as a knowledge of the truth.

The writer has had much assistance from experienced and compe-
tent teachers and physicians. Dr. A. W. Alvord (M.D., University
of Michigan) of Battle Creek, Michigan, has kindly revised the
hygienic portions of the book. Mr. H. W. Norris, A. M., Professor of
Biology in Iowa College, has read and criticised the whole of the
manuscript. All of the experimental work has been prepared by him
and will be found of especial value. Many of the illustrations used
are such as are commonly found in schoolbooks treating the subject
of physiology, but a large number have been adapted from cuts in
recent advanced works, mainly those by Morris, Spalteholz, and Van
Gehuchten ; while numerous other drawings expressly for this work
have been made by Mr. E. W. Atherton under the direction of
Professor Norris.

CONTENTS

PART I
INTRODUCTION

CHAPTER PAGE

I. Matter and Cells 9

II. Tissues and Organs . . . 19

III. A General View of the Nervous System .... 27

PAET II

CONSCIOUS NERVOUS OPERATIONS: MOTION AND
SENSATION

IV. The Framework of the Body, or the Osseous System . 37

V. The Muscular System .59

VI. The Skin as an Organ of Sensation — Touch . . 82

VII. Taste and Smell 94

VIII. The Eye and the Sense of Sight . . . . . .101

IX. The Ear and the Sense of Hearing . . . . .126

X. The Vocal Apparatus . . . .... . 136

PAET III

NERVOUS OPERATIONS UNCONNECTED WITH
CONSCIOUSNESS

XL Blood, Lymph, and Chyle 147

XII. The Circulatory System 153

XIII. Nervous Control of the Circulation 176

XIV. Respiration . . .181

XV. Nervous Control of the Respiratory Apparatus . . . 198

5

6

CONTENTS

CHAPTER PACK

XVI. Food 201

XVII. The Digestive Apparatus and Nutrition .... 218

XVIII. The Ductless Glands 254

XIX. The Organs of Excretion . . 257

XX. The Heat of the Body 2CC

PART IV

THE NERVOUS SYSTEM.

XXI. Anatomical Description 275

XXII. Functions of the Nervous System ..... 297

XXIII. Hygiene of the Nervous System 314

PAKT V
THE PRESERVATION OF HEALTH

XXIV. Health and Disease . . .
XXV. Common Accidents and Injuries
XXVI. Public Hygiene, or General Sanitation

GLOSSARY
INDEX

335
344
300

395

PART I

INTRODUCTION

It is customary to divide the study of the human body
into three departments: (1) Anatomy, which is the science
that describes the structure of the body; (2) Physiology,
or the science of the functions, or uses, of. the various
parts of the body, and (3) Hygiene, or the science of
health, which treats of the care of the body and all its
parts for the purpose of maintaining the whole in its best
condition for usefulness and enjoyment. The term Physi-
ology, as applied to a schoolbook, however] "Js; o
to include all three of these lines of study.,

frig. 1. — The nervous system.

CHAPTER I

MATTER AND CELLS

1. Living and Lifeless Matter. — What matter is we are
not yet able to say, but as it exists in our world it may be
separated into two great divisions, — living matter and
lifeless matter. So far as present knowledge goes, these
two sorts of matter are wholly distinct the one from the
other, and lifeless matter never becomes living matter
except under the influence of matter already living. The
same substances are indeed found in the two sorts of
matter, and when living matter is killed, or becomes life-
less, no change can be discovered in its weight. That
mysterious something called life is therefore not material,
and living matter may be said to be only ordinary lifeless
matter existing in a different state or condition.

2. Chemical Elements. — A substance ;^}i£ch-8ajirjci;,b^
divided into two or more different kinds of matter is
called a chemical element, or a simple substance. All
others are called compound substances. Matter is sepa-
rated into its elements by processes which affect the mole-
cules or the atoms of which it is composed, that is, by
chemical analysis.

A molecule may be denned as the smallest particle of
matter which exists alone and retains most of the proper-
ties of the mass of the substance. An atom is one of the
ultimate particles of which a molecule is composed The

9

10

molecules of chemical elements are composed of atoms of
the same kind. Compound substances have atoms of dif-
ferent kinds. There are as many khjds of atoms as of
elements. Both atoms and molecules are too small to be
seen even with powerful microscopes.

A drop of water may be divided mechanically into
many small portions, and each part will retain all the
characteristics of the original drop. But when the chem-
ist separates the oxygen and hydrogen which together
make up the drop of water, he has no longer any matter
which resembles water, but instead two kinds of gaseous
matter of entirely different properties. The water has
been resolved by chemical analysis into its chemical
elements.

Chemical elements unite in different proportions with
one another to form a great variety of substances.
About seventy-five elements have been isolated by chem-
ists, but only a few of them are known to enter into the
structure of animal bodies. These are carbon, oxygen,
hydrogen, nitrogen, sulphur, phosphorus, chlorine, fluorine,
r; Silicon, potja^sjufmj sodium, lithium, calcium, magnesium,
'iro'n, afi(i ntahga'tfese. As a rule these elements exist in
, : *$e;Ucftty',i^ sofm?e;spri of combination with one another.

'3. * Protoplasm is a name given to living matter. It is
a clear, jellylike substance containing minute grains.
As protoplasm, it cannot be chemically analyzed, because
the process of analysis destroys its vitality so that it is no
longer protoplasm, but merely dead, lifeless matter. The
one essential thing about protoplasm is that it is alive;
dead protoplasm is a contradiction in terms. It has been
called " the physical basis of life," because without it life
does not exist, and with it there is always life. But the
material of which protoplasm is composed is found, when

MATTER AND CELLS 11

analyzed after it has ceased to live, to be highly complex.
A large part of its weight is water, while its solid portion
is chiefly composed of proteids. These are substances
found in many foods, white of egg being a familiar example.
They contain carbon, hydrogen, oxygen, and nitrogen-.

4. The Cell (Fig. 2). — All living bodies, both plants
and animals, are found to consist of cells. Cells are
the ultimate units of which living be-
ings are made up, just as bricks are

the units of which a brick wall is com-
posed. A cell is a microscopic bit of
protoplasm, with or without an inclos-
ing wall, having suspended within it a
rounded body of denser material called Fig. 2. — Diagram of

, , IT* u v • the Parts of a cel1-

the nucleus. It may be living apart, or

. - « nucleus.

may form one of the units of an organ- & cell body or proto-
ism. Plant cells have usually the cell v}*sm-

J c cell wall.

wall, but an animal cell may be only a
naked speck of living matter. Free cells tend to assume
a round shape, but under pressure they may take almost
any form.

5. The cells of the human body vary in size from -g^-
to -g-flVfr of an inch in diameter. All animals begin their
existence as single cells, and the life of any animal is the
sum of the activities of all its separate cells, while its
physical structure consists of the cells themselves and the
intercellular matter which they produce, together with
the various lifeless substances which they deposit within
themselves.

6. Essential Properties of Cells. — All living things pos-
sess two properties without which they cannot exist.

One of these properties is nutrition, — using the word in
its broader sense to include the double process of taking

12 INTRODUCTION

in material from outside and building it into the bodily
structure, — that is, the making of complex chemical com-
pounds out of simpler ones ; and the breaking down, or
reducing to simpler forms, of compounds already formed.
The former results in growth or repair of cell substance,
and is the storing up of energy ; the latter is the setting
free of energy, and the production of waste material to be
removed as no longer valuable. Nutrition includes all
the chemical changes which take place in living matter.

The other essential property of living bodies is the
power of reproduction, or of giving rise in some way to
living beings like themselves.

The first of these properties, nutrition, belongs to every
individual cell, to every plant, and every animal, as neces-
sary to its own continued existence. The second, repro-
duction, is needful only for the continued existence of the
race, and is in some cases possessed only by certain indi-
viduals of the race. Single cells are, however, capable of
giving rise by self-division to other cells like themselves.

Life is sustained by the ceaseless exercise of the two
powers of nutrition and reproduction.

7. Other Properties of Living Cells. — Certain other
properties are found to exist in most cells in the body,
for example, in the white corpuscles of human blood,
which are clearly defined nucleated cells.

These are contractility, or instability, that is, the power
of changing form without the application of pressure ;
irritability, or the power of vigorous action under stimulus,
as, for instance, when the blood cells contract under the
influence of electricity ; conductivity, or the power of pass-
ing on to distant parts of the cell the influence exerted
by a stimulus upon a single point; and coordination, or
the capacity in all the parts to work together in definite

MATTER AND CELLS 13

direction and with regulated strength to accomplish an
end, as when a particle of material suitable for building
up a cell is drawn in and used for that purpose.

8. Plants and Animals. — No naturalist can at the pres-
ent day place his finger upon a line of separation and
say: All living things upon this side are plants; all upon
that side, animals. It is, indeed, easy to distinguish the
higher forms of animal life from the higher forms of plant
life, and the most striking difference is that the animal
possesses the power of spontaneous movement, while the
plant is rooted to one spot. Other distinctions appear as
the two forms of life are studied. For example, both are
dependent for their continued life and growth upon the
food which is supplied from without themselves ; but
plants (the fungi excepted) subsist mainly upon carbon
dioxide, water, and mineral salts, while animals live upon
water and those chemical compounds which have formed
part of living bodies, that is, organic materials. Ani-
mals cannot use mineral substances as food except as they
are mixed with organic matter. But the simplest forms
of plant and animal life cannot be distinguished with
positiveness from each other. Both consist of single pro-
toplasmic cells, and it is not possible to show that the proto-
plasm of one is essentially different from that of the other.

As animals rise in the scale of being, however, they are
found to develop, as plants do not, a nervous system of
ever-increasing complexity and importance. Hence man,
as an animal, may be said to be distinguished from all
other animals by the superiority of his nervous system ;
and all the other parts of the human body may be consid-
ered as created simply to minister in some way to that
superior portion of the human frame which is the direct
agent or instrument of the highest manifestations of life.

14 INTRODUCTION

9. The Difference between Plants and Animals in Respect
to Stimulus. — Living animal cells possess the property of
irritability or excitability, that is, some change in their
composition results from the action of stimulus. Vegeta-
ble cells also possess this property in some degree. But it
is found that, as in the processes of development more and
more complex forms of plant life appear, the plant does
not develop special organs for the transmission of stimulus.
In the animal kingdom, on the other hand, a striking dif-
ference appears. In one of the lowest known representa-
tives of animal life — the amoeba (Fig. 3, p. 16), which
is a mere microscopic lump of naked protoplasm — each
minute particle of the protoplasm appears to respond to
a stimulus and to transmit it to the adjacent particles,
there being no distinction of parts or functions in the
single cell. But in the next higher division of ani-
mals, the corals, sea anemones, etc., the rudiments of a
nervous system are visible, and some division of sense
organs appears. It is probable that nervous impressions
are received first in but a single form, while a gradual
and uninterrupted development of the senses follows as
we rise in the scale. That is, one of the lower animals
may be said to have but one sense, touch, or a general sen-
sibility, — it receives but one kind of sense impression
from influences which higher animals recognize as diverse,
— while higher animals may distinguish two or more kinds
of impression, and so on. It should be noticed that the
common division of senses into touch, taste, smell, sight,
and hearing is somewhat arbitrary, even man not being
always able to discriminate, for instance, between taste
and smell, while certain sensations are recognized, such
as perception of temperature and of pain, which do not
strictly belong to any of the " five senses " so called.

MATTER AND CELLS 15

SUGGESTIONS REGARDING THE PRACTICAL WORK

The amount of illustrative experimental work in physi-
ology that can be done in a high school depends chiefly
upon two factors : the material equipment of the school
and the tact of the teacher.

Vivisection doubtless has its place, but not in the pub-
lic schools. Ordinary dissections sensibly performed can
be made a successful part of class work in most of our
high schools, but occasionally deference to public opinion
will require that the dissections be performed only by the
teacher, or possibly not at all.

No attempt is made in this book to give detailed direc-
tions for dissecting, nor for the preparation of material
for study with the compound microscope. It is assumed
that a teacher of advanced physiology has received some
preliminary training in anatomy and microscopical meth-
ods. If so, then suggestions will be far better than spe-
cific directions.

It is not expected that all the experiments will be per-
formed by a class. When a compound microscope is not
available, some of the exercises must necessarily be omit-
ted. It is believed, however, that all the demonstrations,
dissections, and experiments can be performed in any
school of moderate equipment. A great mistake is made
when much apparatus is interposed between the student
of elementary science and the objects of his study. The
teacher should make sure that the illustration is not sub-
stituted for the idea that it is intended to explain. In
some instances conditions will require that the teacher
perform most of the work* of an experiment, but as far
as possible the pupil should himself be responsible for
each detail.

16

INTRODUCTION

Fig. 3. — Amoeba in eight successive stages
of movement.

DEMONSTRATIONS AND EXPERIMENTS1

1. Amoeba. — The amoeba is not always easily obtained. If debris
of water plants be kept in shallow dishes of water for several days,
there can usually be found specimens of amoeba in the scum that

forms on the surface of
the water, or in the
ooze that collects at the
edges and bottoms of
the dishes. On mount-
ing some of the material
on a glass slide and ex-
amining with the com-
pound microscope, there
may be seen small, irreg-
ular, transparent masses
of a jellylike nature
moving along very slowly with a rolling or flowing motion (Fig. 3).
Attention should be given to the constantly changing form of the
animal, which thus exhibits a fundamental characteristic of proto-
plasm, instability. If, when an amoeba is fully extended, sending out
processes, pxeudopodia, from the main part of the body, the slide be
gently tapped, the animal will be seen to contract quickly into a
rounded mass, showing another characteristic of protoplasm, irritability,
or the capacity of response to stimulus.

2. White Blood Corpuscles. — If a drop of fresh human blood, or
preferably of frog's blood, be mount-
ed on a glass slide and examined

with the compound microscope,

among the numerous red corpuscles

may be seen a few transparent ones

(Fig. 4). On remaining undisturbed

for some time they change in shape, Rg 4._Blood ceiiB (corpuscles)

or even migrate, in a manner similar of frog.

1 Note to Teachers. — The demonstrations and experiments should
precede the recitation of the lessons which they illustrate. The pupil
should not be required to describe the brain, for example, until he has
studied the dissected organ itself.

MATTER AND CELLS

17

to that of the amoeba. Fresh blood may be obtained by pricking the
finger with a sterilized needle, and by decapitating or pithing a frog.

3. Movements of Protoplasm
in Plants. — The phenomena
of protoplasmic movements
can be observed in a variety
of plants. The Stoneworts,
Chara and Nitella, and the
stamen hairs of the Spider-
wort, Tradescantia, furnish
some of the best examples.
In all these the protoplasm is
inclosed in a cell wall, and
when observed with the com-
pound microscope is seen to
exhibit streaming movements
and circulation of particles in

Fig. 5. — Compound microscope with sim-
ple warming stage (W) attached.

the contents of the cell. The

response of protoplasm to

changes in temperature can

be very easily shown by placing the slide on a warming stage upon

the microscope stand as shown in Fig. 5. When the warming stage
is heated, the protoplasmic movements a,re seen to
increase in rapidity up to a certain point. As it
cools, the movements become slower.

4. Properties of Protoplasm in Muscle. — In some
animals the various tissues retain their vitality and
properties for a considerable time after the death
of the individual animal. The common frog fur-
nishes us one of the best examples of this. If a
frog's gastrocnemius muscle with sciatic nerve at-
tachments (Fig. 6) be dissected out (see Figs. 7
and 8) shortly after decapitation of the animal, it
will retain its properties for a considerable length
of time, if kept well moistened with normal salt
solution (0.75 per cent solution of common salt).
If the nerve be cut with sharp' scissors a contrac-
tion of the muscle occurs. Touching the nerve
with a red-hot needle produces a similar contraction

FLg. 6. — Nerve-
muscle prepara-
tion.

F femur.

G gastrocnemius

muscle.

S sciatic nerve.
T tendon (tendo

Achilles).

MACY'S PUYS. — 2

18

INTRODUCTION

in the muscle. Placing the fresh-cut end of the nerve in a saturated
solution of common salt brings about a series of contractions in the
muscle. The muscle also contracts when the nerve is stimulated with

a weak electric cur-
rent. If the nerve
muscle preparation
be placed on a copper
plate, and the tem-
perature of the latter
be raised above or
lowered below the
normal, there will oc-
cur variations in the
response of the mus-
cle to stimuli. (Elec-
trical stimulation will
be found most con-
venient.) The rela-
tion of muscular
action to temperature
will thus be striking-
ly represented. These
experiments with the
nerve-muscle prepa-
ration show that the
living substance is
irritable, unstable, and
conductive of stimuli.

M. biceps. sm M. semimembranosus. 5' Cells. — The

M. gastrocnemius. st M. semitendinosus. amoeba and the white

M. pyriformis. ta M. tibialis anticus. blood corpuscles al-

ready studied furnish
very good examples
of cells which have no fixed form nor definite shapes. The red blood
corpuscles of the frog are cells in which the nucleus can be easily dis-
cerned by aid of the microscope (Fig. 4, p. 16).

Fig. 7.

Muscles of the left leg of the frog. Fig. 8 shows
distribution of the sciatic nerve.

ad M. adductor magnus. sc sciatic nerve.

b

y

p

pe M. peroneus. tr M. triceps.

H M. rectus interims minor.

CHAPTER II

TISSUES AND ORGANS

10. The human body, beginning as a single cell, is
gradually built up by a process of division and subdivision
of that cell, so that the complete, adult man is but a
mass of cells with some cementive and connective matter.
It is found, however, that differences early appear in the
characteristics of different cells, and these differences
increase as development proceeds. A group of similar
cells having a similar function is called a tissue.

11. Differentiation of Tissues. — In the lowest animals,
composed of but a single cell, all the different parts of
the body are essentially alike (leaving the nucleus out of
consideration) and have the same functions. One part
may move as well as another. All parts share in the
process of nutrition, and one part responds as well as
another to stimulus. But the higher animals are found
to be made up of unlike parts, which minister in differ-
ent ways to the life of the whole being. As the cells
multiply, certain groups of cells become changed in
such a manner as to adapt them to the performance
of some special function, while other parts are adapted
to other functions. A number of cells lying together
become modified so as to make up a tissue adapted to
a certain purpose. Other cells become modified in a
different way to form a tissue adapted to a different

19

20 INTRODUCTION

purpose, and the whole body becomes a mass of many
different tissues, each having its definite and special char-
acteristics and structure. This process is known as dif-
ferentiation of the tissues, and is accompanied by what is
called physiological division of labor. One tissue is better
adapted to the performance of a certain office in the body
than are others, and that special work is given it to do, so
that the work of carrying on the operations of the body is
divided up among the tissues.

12. Organs. — A living being is often called an organism.
In order to secure the greatest efficiency in their labors,
the various tissues are built up into a multitude of mecha-
nisms called organs; for example, the eye, the hand, the
liver. Several different kinds of tissue often enter into
the structure of a single organ, and the same sort of tissue
appears in many different organs.

A number of organs so arranged and related to one
another as to cooperate in carrying on a special process
or series of processes, is called a system, — as the diges-
tive system, or the nervous system.

13. Classification of Tissues. — Tissues are variously clas-
sified by different authors, but one broad distinction may
be noted which divides them into two great classes :

(1) The tissues which have to do with the setting free of
energy. These are the muscular and nervous tissues.

(2) The tissues which have to do with renewing the sub-
stances and restoring the power of responding to stimulus.
In this second class are grouped all the remaining parts
of the body, which include tissues differing widely from
one another — from the solid, bony tissue of the skeleton,
and the still harder enamel which covers the teeth, to the
soft substance composing the brain, the elastic fat which
rounds out the figure, and the fluid which we call blood.

TISSUES AND ORGANS 21

14. The following table shows this classification : —

1. Tissues which have to do with liberating j Muscular
energy — Master Tissues j Nervous

a. Pavement

6. Cubical,

Sphe-

Simple Epi-

K^^A-IV
roidal,

thelium

and Co-

Epithelial

lumnar

2. Tissues which
have to do

Tissues

, c. Ciliated
Compound Transitkmal

Columnar
Ciliated

with the pro-
tection, sup-
port, and

Epithe- j Stratified
hum

Areolar f «• White

Squamous
or Scaly

renewal of

Fibrous .... 1 6- Yellow

the Master

Connective

Adipose or Elas-

Tissues

Tissues '

Cartilage I tic

Bone

Blood

15. The Master Tissues. — Muscular tissue liberates
energy which takes the form of motion attended by some
measure of heat. But the changes in muscular tissue
by which energy is liberated are guided, regulated, and
adapted to the purposes of human life by means of nervous
tissue; that is, the muscles are the instrument, but an
instrument motionless and useless until the nerves supply
the impulse which sets the muscles at work. A muscle
develops energy under the action of nervous stimulus con-
veyed to the muscle cell through nervous tissue. Energy
is set free in nervous tissue when the nervous organ
is stimulated by the influence adapted to it. The nerves
carry the impulse to the muscle, and energy is liber-
ated as motion and heat. Muscular and nervous tissues
possess irritability, that is, they respond to stimulus, in

22

INTRODUCTION

the one case by contraction, in the other by some
change not yet understood, giving rise to what is called a
" nervous impulse," and in the act they develop energy
by the breaking down of their own substance. Unless
that substance is renewed the tissue will cease to respond to
stimulus, — will die. The remaining tissues of the body,
therefore, are engaged in one way or another in preparing
the needful food, in conveying it to these " master tissues,"
in taking up the waste substances produced in the evolu-
tion of energy and preparing them for removal from the
body, or in furnishing mechanical support to the body and
its various parts. In these processes are involved all the
parts which are concerned in digestion, respiration, circu-
lation, and excretion. This varied and complex series of
operations implies a vast array of muscular movements,
and all are governed by the nervous system under the
action of its varied stimuli.

16. Epithelial Tissues. — The free surfaces of the body,
both within and without, are covered with a tissue called
epithelium. Simple epithelium is composed of but one

layer of cells, ar-
ranged like flat pav-
ing stones and fitted
together with a very
little cementing mate-
rial (Fig. 9, A). The
epithelium of this va-
riety found lining the
interior of the blood
vessels, and some other surfaces which are not exposed
to the outer air, is called endothelium.

The cubical, spheroidal, and columnar epithelial tissues
are named from the shape of their cells. In ciliated

Fig. 9.— Columnar epithelium.
A simple. B stratified.

TISSUES AND ORGANS

23

epithelium each of the cells is surmounted
by tapering, haiiiike filaments (Fig. 10).

Compound epithelium is composed of more
than one layer of cells (Fig. 11). Epithe-
lium contains no blood vessels, but is nour-
ished by lymph. It forms the external layer
of the skin and the mucous membrane.

17. Connective Tissues exist in many diverse
forms, but all are alike in origin, being devel-
oped from the same layer of the embryo ;
alike in structure, having a large amount
of intercellular material ; and alike in func-
tion, being devoted to supporting and connecting the
master tissues.

Fig. 10. — Cili-
ated epithe-
lium from a
small bron-
chial tube.

A B

Fig. 11. — Compound stratified epithelium.

A vertical section of the skin. B lateral view of the cells.

C flat side of scales like d, magnified 250 diameters, showing the nucleated
cells transformed into broad scales.

Areolar tissue is made up of cells, white and yellow
fibers, and some intercellular matter (Fig. 12). It is
found widely distributed through the body, appearing as
delicate, elastic, sheathing membrane for muscles, nerves,
glands, and other organs. It penetrates into the sub-
stance of the organs and connects and supports their
various parts.

24

INTRODUCTION

White fibrous tissue is found in ligaments and tendons,
the tough lining membranes of bones, brain, etc. (Fig. 13,
A). It is composed mainly of bundles of strong, white
fibers containing nucleated cells.

Bundle of White Fibers

Fig. 12. — Diagram of areolar
tissue.

Fig. 13. — Fibrous tissue.

A white fibrous tissue.

B elastic or yellow fibrous tissue.

Elastic or yelloiv fibrous tissue contains yellow, elastic
fibers (Fig. 13, B) bound into bundles by areolar tissue.
It appears in some ligaments, and in the walls of the
arteries, and in the air cells of the lungs.

Adipose tissue is the fat of the body, and is found in
nearly all parts, usually in connection with areolar tissue.
Adipose tissue consists of protoplasmic cell walls filled
with liquid fat.

18. Cartilage appears in two forms, — hyaline cartilage
(Fig. 14) and fibrocartilage (Fig. 15), the first being clear
and free from fibers, the second composed largely of white
or yellow fibers. Cells are found in all kinds of cartilage,
but there is always a proportionately large amount of inter-
cellular matter which is produced by the cells.

TISSUES AND ORGANS

25

Fig. 14. — Hyaline cartilage.

a group of four cartilage cells,
c a cell. n nucleus,

m matrix.

Fig. 15. — Fibrocartilage.

c cartilage cells surrounded by

hyaline matrix (m).
/ fibrous tissue.

19. Bone is more solid than the other tissues. It is
penetrated throughout by minute canals, called Haver-
sian canals, containing blood vessels (Fig. 16). The final

Fig. 16.— Cross section of bone.

a lacunae, spaces in living bone occupied by bone cells.
& Haversian canal.

INTRODUCTION

structure of bone is fibrous, and along with the fibers are
cells called bone corpuscles, while the cementing material
is earthy matter. In many situa-
tions, parts which are in early life
composed of cartilage become after-
ward replaced by bone, through the
process called ossification.

20. Blood is a fluid connective tis-
sue which conveys nutriment to all
parts of the body (Fig. 17). It
holds suspended in its liquid por-
tion, or plasma, large numbers of
cells called corpuscles. These are
of two sorts, named from their color the red or colored
corpuscles, and the white or colorless corpuscles. The
latter have one or more nuclei, while the red corpuscles
have none.

Fig. 17. — Human blood
corpuscles.

R red. W white.

CHAPTER III

A GENERAL VIEW OF THE NERVOUS SYSTEM

21. The great distinguishing feature separating man
as an animal from all other animals is, as we have seen,
his possession of a nervous system of more complex and
intricate structure than any other in the animal kingdom.
It is now fully recognized that the nervous system is the
central, unifying, coordinating element in the human
organism — that for which all other parts exist and to
which all are subordinate. In order, therefore, to under-
stand clearly the part which each portion of the body is
designed to play in the general plan, it is necessary to
have some general knowledge of the nervous system,
while a fuller study of its parts and their functions may
be postponed to a later period.

22. Divisions of the Nervous System. — Physiologists have
been accustomed to describe two great divisions of the
nervous system, called the central or cerebro- spinal sys-
tem, and the ganglionic or sympathetic system, the first
having control of sensation and voluntary motion, the
second presiding over those vital operations not under
voluntary control, its nerves being in general distributed
to the internal organs and the blood vessels. It has,
however, long been understood that there are not two
nervous systems, but one. Still, as a matter of conven-
ience in description, the well-known terms are generally

27

INTRODUCTION

retained, and the nervous system is
treated under its twofold aspect.

23. The Cerebro-spinal System is com-
posed of the brain and the spinal cord,
with the nerves passing from them to
the various parts of the body (see Fig.
1, p. 8, and Fig. 18).

24. The Brain fills the cavity of the
skull. It consists of five principal
parts : (1) the cerebrum, ; (2) the optic
thalami, which are so closely united to
the cerebrum as to seem to be a part of
it ; (3) the optic lobes, or corpora quad-
riff emina, and crura cerebri ; (4) the
cerebellum, and with it the pans Varolii ;
(5) the medulla oblong ata (Figs. 19 and
20). Looked at from above or from
the side, the only parts of the brain
that appear are the cerebrum, a part
of the cerebellum, and part of the
medulla oblongata.

25. Cranial Nerves. — From the un-
der surface of the brain arise twelve
pairs of nerves (Fig. 19), which pass
through openings in the cranial bones
and are distributed in a manner to be
described hereafter. They are of three
classes : (1) Nerves of special sensa-
tion ; (2) motor nerves, that is, nerves
which carry nervous impulses to the
muscles and cause them to contract;

Fig. 18.— Brain and and (3) mixed nerves, that is, both sen-
spinal cord, ventral •>
canterior) ^— sorV and motor.

A GENERAL VIEW OF THE NERVOUS SYSTEM

Olfactory Bulb

( to which j.s attached
the Olfactory Nerve)

Pituitary Body____^

Optic Ne rve

Optic Chiasma _

Oculomotor Nerve-—. __

Trochlear Nerve

Trigeminal Nerve- ___

Pons Faro/ft- _.__

Abducens Nerve- - _

Facial Nerve

Auditory Nerve- _

Glossopharyngeal Nerve _ _

Vagus Nerve —

Spinal- accessory Nerve —

Hypoglossal Nerve- -

Medulla Oblongata

First Spinal Nerve —
Cerebellum- -
Spinal Cord--
Second Spinal Nerve

Fig. 19. — Ventral (anterior) surface of the brain.

26. The Spinal Cord and Spinal Nerves. — The spinal
cord is a column of soft nervous matter, filling the long
channel in the spinal col-
umn (Fig. 18). Thirty-
one pairs of nerves arise
from the spinal cord,
each having two roots,
— a posterior and an
anterior root (Fig. 21).
Upon the posterior root,
just before it unites with

the anterior root, is a

,.,,, , „ Fig. 20.— Side view of brain.

little knot of nervous

a cerebrum, b cerebellum.

matter called a spinal c medulla obiongata.

30 INTRODUCTION

ganglion. The anterior roots of spinal nerves contain
what are called efferent nerve fibers, that is, fibers carry-
ing impulses from the nerve center. These are sometimes
called motor nerve fibers, because their stimulation usually

results in motion; but the
term is not strictly accurate,
since other than motor im-
pulses may pass over efferent
nerves. Posterior roots con-
Fig. 21. -Diagram of cross sec- tain afferent nerve fibers, that
tion of spinal cord, showing is, fibers carrying impulses
nerve roots. toward the nerve center. They

P posterior root of spinal nerve.

G ganglion. A anterior root. are also called sensory nerve
S spinal nerve. fibers, because when they are

stimulated feeling or sensation most often results, but other
impulses than sensory ones may be conveyed by them.

27. The Sympathetic System consists of a chain of ganglia
lying on each side and in front of the spinal column, of
three main plexuses (or nerve networks) in the cavities of
the chest and abdomen, of many small ganglia in all parts
of the body, and of an immense number of fine nerve fibers
(Fig. 22). Each ganglion of the chain is connected by
nerve fibers with the one above and the one below, as well
as with the spinal cord. In general, the number of pairs
of ganglia corresponds to the number of vertebrae, or seg-
ments of the backbone; but there are only three pairs of
ganglia in the neck, and in front of the coccyx, or last
segment of the backbone, there is only a single ganglion.

28. Gray and White Nervous Matter. — Two kinds of
nervous matter, easily distinguished by their color, are
found in the body. In the cerebrum and the cerebellum
the gray matter is mainly in the surface layer, called the
cortex, the deeper portions being of white matter ; while in

Cervical Spinal c'
Nerves

Dorsal Spinal /
Nerves \

Lumbar Spinal

Nerves f -r^

\

Fig. 22. —Diagram of the sympathetic nervous system.

G ganglion chain. Co coccygeal spinal nerve.

31

INTRODUCTION

the spinal cord the reverse is the case, a central column of
gray matter being surrounded by white matter (Figs. 23

and 24).
The gan-
glia are
composed

almost Fig. 24. — Cross see-
wholly of tjon of spinal cord,
showing arrange-
graymat- ment of gray and
white matter.

29. Nerve CeUs. — Gray
nervous matter is made

.7 ^""^ up mainly of nerve cells

Fig. 23.— Cross section of the hemispheres

of the brain, showing arrangement of (Fig. 25). These vary
gray and white matter. much in gize and ghape>

Each sends out one or more branches, or processes, one
of which forms the central core of a nerve fiber and
is called the axis cylinder process. A ganglion is a col-
lection of nerve cells imbedded in nerve fibers.

30. Nerve Fibers. — Every nerve fiber has connection
with at least one nerve cell, for its central strand, called

the axis cylinder, is al-
ways the axis cylinder
process of a nerve cell
(Fig. 26). This is the
essential, indispensable
part of the nerve fiber.
Surrounding the axis cyl-
inder there is usually a
layer of white, oily mat-
Fig. 25. -Nerve cells (mitral) from the ter called the medullary
olfactory bulb. , , , . , £

sheath, and outside of

that is a thin inclosing membrane called the neurilemma.

A GENERAL VIEW OF THE NERVOUS SYSTEM

33

The last is continuous for the whole length of the fiber,
but the medullary sheath is broken at short intervals by
little spaces called nodes. Some fibers
have only the neurilemma, and are there-
fore gray in color ; for it is the medullary
sheath which gives the characteristic shin-
ing white appearance to nerves and nerve
fibers. Those fibers possessing the sheath
are called medullated nerve fibers; those
without it are called nonmedullated.

>_ Node of
Kanvier

-Neurilemma

\--Nucleua

DEMONSTRATIONS

Neuraxon
~~ or Axis
Cylinder

Medullary
' 'Sheath

Fig. 26. -Por-
tion of a me-
dullated nerve
fiber.

6. The Brain. — The brain of the sheep will be
found to be very satisfactory in demonstrating to a
class the general structure of this portion of the cen-
tral nervous system. The brain of the cat, dog, or
ox may be used instead. The brain can be removed
from the skull by sawing away the roof of the latter
and with a scalpel cutting the attaching membranes
and nerves. The brain should be prepared some
days, or even weeks, before it is needed by the class,
and hardened and preserved in some suitable me-
dium. Strong alcohol, a 2 to 5 per cent solution of
formalin (formol) in water, and a 2 to 5 per cent
solution of bichromate of potash are very good hard-
ening and preserving reagents. But more satisfactory is the following
mixture : 95 per cent alcohol, six parts ; 2 per cent solution of formalin,
four parts. When specimens are preserved in a fluid containing for-
malin, they should be soaked in water a short time before using, to
avoid the irritating effects of formalin vapor on the eyes, etc. Where
possible, each student should be provided with one of the preserved
specimens. A brain recently removed should be at hand, but it will
be found to be too soft for much careful study. With care one pre-
served brain may be made to suffice for an entire class. After exami-
nation the specimens may be preserved for more detailed study later
on. In studying the brain follow the descriptions of the general text.
MACY'S PHYS. — 3

84 INTRODUCTION

7. The Spinal Cord. — Procure at a slaughterhouse a spinal cord of
an ox and examine it fresh, or preserve it in one of the fluids men-
tioned in the preceding section. Preserved portions can be used later
in a more careful study of the structure of the cord.

8. The Sympathetic Nervous System. — If the abdominal cavity of a
dog, cat, rat, or frog be opened and the viscera displaced, there may be
seen on each side of the backbone a white cord with grayish enlarge-
ments, ganglia. The two cords and their ganglia constitute the main
chains of the sympathetic system.

9. Nerve Fibers. — Tease out with needles in water on a glass slide
a small piece of a nerve. Even without the aid of a lens the nerve is
seen to be composed of small, threadlike fibers. Examined with the
compound microscope the fibrous structure will become more apparent.

PART II

CONSCIOUS NERVOUS OPERATIONS: MOTION
AND SENSATION

Of many of the processes which have to do with man's
life he is wholly or partly unconscious. The wonderful
operations of growth and development go on chiefly with-
out his knowledge. The nerve cells which order and
direct all the vital activities carry on their work so silently,
so regularly, so skillfully — without jar or confusion —
that neighboring cells may not even know that they are
busy.

Of other nervous activities a man is fully conscious, and
without his consciousness the object of those operations
is not accomplished. A large part of the nervous system
and a large part of the other tissues and organs of the
body have for their chief business the production of con-
scious motion. Other sets of nerves, nerve cells, and
special organs are employed in bringing about those
experiences called sensations. These two objects are
effected through what may be called conscious nervous
operations : motion being the result of the action of cer-
tain nervous impulses upon bones and muscles ; sensation,
the result of the action of other nervous impulses upon
the special organs for sensation.

In order to understand these conscious nervous opera-
tions it is necessary to study the skeleton and joints, the
muscular system, the skin as a sense organ, the senses
of taste, smell, sight, and hearing, and the apparatus for
speech.

35

PECTORAL GIRDLE

Fig. 27. — The skeleton.

CHAPTER IV

THE FRAMEWORK OF THE BODY, OR THE OSSEOUS SYSTEM

31. Functions of the Bones. — Certain parts of an animal
body are more essential to its existence than others, and
more important to its well-being. These portions are of
especial delicacy in substance and structure, and pecul-
iarly liable to injury. They therefore require protection.
For this purpose the more solid substances which make up
the body are arranged to inclose or shield the softer and
more delicate parts.

In one large group of animal forms, called invertebrates,
which includes insects, mollusks, crabs, lobsters, etc., the
outer portion of the body consists usually of a more or
less hard and tough crust called the exoskeleton, which
covers the softer parts. But the higher group of animals,
called vertebrates or backboned animals, to which man
belongs, possess an inner, bony framework, called the en-
doskeleton, so arranged as to form a support and a defense
to the more sensitive and more essential parts.

In all vertebrates the skeleton consists of a somewhat
firm but flexible bony column to which are attached the
bones of the head, the ribs, and the pectoral and pelvic
girdles, which connect respectively the upper and the
lower limbs with the trunk (Fig. 27).

The bones of the skeleton furnish the necessary levers
and points of support for the muscles which are the organs
of motion.

37

88 CONSCIOUS NERVOUS OPERATIONS

32. Provision for Movement in Different Classes of Ani-
mals.— A distinguishing feature of the animal kingdom
is the power of voluntary motion, and the ability at some
period of life to move about from place to place. For this
purpose the different classes and orders of animals are
provided with a great variety of mechanical devices.
Certain aquatic creatures propel themselves by means of
pulsations in the whole body. Snakes and worms swim
by the undulations of the body. The squid fills a certain
cavity within itself with water and then suddenly expels
it, and the force of the ejection moves the body in one
direction or another, according to the direction of the
current of water ejected. The jellyfish propels itself
by drawing in and expelling water from its bell-shaped
body. Animalcules move themselves by the rapid vibra-
tions of innumerable hairlike projections. But all the
higher forms of animals move by means of muscles and
ligaments attached to an internal solid framework, or
skeleton.

33. The Vertebrate Skeleton. — A careful study of any
vertebrate skeleton discloses marvelous adaptations for
accomplishing the two main objects of protection and
motion. Protection to the vital parts might have been
secured by means of a rigid, unyielding case, but in order
to allow motion in all parts of the body also, the skele-
ton is composed of many separate pieces united together
by elastic tissues. The whole number of bones in the
adult man is about 206, while in the child the number is
yet larger, because, as a child grows older, certain bones
which are at first distinct (and remain so in the lower ani-
mals) grow together to form one. For convenience in
study, the bony framework is divided into two parts called
the axial skeleton and the appendicular skeleton.

THE FRAMEWORK OF THE BODY

39

34. Axial Skeleton. — The bones of the head, neck, and
trunk compose the axial skeleton.

35. The Skull. — At the upper extremity of the vertebral
column appears the skull (Fig. 28), composed of (1) the
cranium, the strong

casket which in-
closes the most pre-
cious part of the
animal structure, —
the brain — and (2)
the various bones
forming the skeleton
of the face.

36. The Cranium.
— In the adult the
cranium consists of
eight bones, each
composed of two
firm, compact plates
with a spongy layer
between. The bones

which form the arch Fig. 28. — The skull,

of the head are
closely joined to-
gether by irregu-
larly notched edges,
the lines of union
being called sutures.

The cranial bones are named as follows: 1. The fron-
tal bone, forming the front of the skull and of especial solid-
ity and thickness, as most exposed to injury. 2. The
parietal bones, a pair of thin, flat bones meeting along the
top of the head. 3. The temporal bones, below the parietal

1 frontal bone. 6 occipital bone.

2 parietal bone. 7 superior maxillary

3 temporal bone. (upper jaw) bone-

4 sphenoid bone. 8 malar bone.

5 ethmoid bone. 9 lachrymal bone.

10 nasal bone.

11 inferior maxillary (lower jaw) bone.

40 CONSCIOUS NKKVnrs OPERATIONS

on each side, and having large openings leading into the
ear cavities. 4. The sphenoid* forming part of the floor
of the brain cavity. 5. The ethmoid, forming part of
the floor in front and joined to many of the facial bones.
It is perforated for the passage of the olfactory nerves.
6. The occipital, a large bone at the back of the head and
also a part of the floor of the skull. It is perforated by
small holes through which pass nerves, and by a large
opening called the foramen magnum for the passage of the
spinal cord to its union with the brain.

37. The Facial Skeleton consists of fourteen bones: 7. The
superior maxillary bones, or upper jaw bones, carrying
the upper teeth and forming most of the hard palate.
8. The malar bones, or cheek bones. 9. The lachrymal
bones, near the inner angle of the socket of the eye, and per-
forated for the tear ducts. 10. The nasal bones, forming
the roof of the nose. 11. The inferior maxillary or lower
jaw bone. 12. The inferior turbinate bones, one in each
nostril chamber. 13. The vomer, forming part of the par-
tition between the nostrils. 14. The palate bones, which
complete the skeleton of the hard palate.

38. The Hyoid. — A small U-shaped bone secured by
long ligaments to the base of the skull and lying in the
neck at the root of the tongue, is called the hyoid bone
(Figs. 79, 80, and 82, pp. 136, 138). It furnishes points
of attachment for many muscles.

39. Bones of the Ear. — Three minute bones in the middle
ear (Figs. 74 and 75), the malleus, the incus, and the stapes,
have to do with the conduction of sound.

40. The Vertebral Column. — In a man of average stature
the spinal column is about twenty-eight inches in length.
It consists of twenty-six separate bones (Fig. 29). The
upper part, which includes uiore than half the whole

THE FRAMEWORK OF THE BODY

41

length of the column,
is made up of twenty-
four separate bones,
each called a vertebra.

Of these the first
or upper seven lie in
the neck and are
called cervical verte-
brce.

The next twelve
bones of the spinal
column are those to
which the ribs are
attached. They are
called the thoracic or
dorsal vertebrce.

Next come the lum-
bar vertebrce, which
are larger than any
other of the movable
vertebrae. They sup-
port no ribs, but re-
ceive many large and
strong muscles.

Below these is seen
the sacrum, composed
in the infant of five
vertebrae, which in
the adult become one
bone. To the broad
spaces on its sides are
attached the bones of
the pelvic arch which

Fig. 29. — The vertebral column as seen
from left side (.4) and from behind (Li).

C 1-7, D 1-12, L 1-5 cervical, dorsal, and lum-
bar vertebrae.

S sacrum. sp spinous process.

Co coccyx. ' tr transverse process.

42

CONSCIOUS NERVOUS OPERATIONS

supports the lower limbs. It lias eight openings, which
communicate with the canal inclosing the spinal cord and
permit the passage of spinal nerves.

At the lower end of the spinal column is the coccyx,
formed by the union of four very small vertebrae into one
bone. It is that part of the skeleton which in the lower
vertebrate animals forms the tail.

41. The Vertebrae vary somewhat in form, but are all
constructed upon the same general plan (Fig. 30). There
is a stout bony cylinder, called the
body, or centrum. To this solid cen-
trum is attached an arch, called the
neural arch, which forms, with the
back of the centrum, an inclosed
space named the neural ring. The
successive neural rings form in the
spinal column a long tube in which
the spinal cord may safely lie.

From the back of the neural arch
extends a long bony projection
called the spinous process, and the
successive processes, or spines (Fig.
29), extending down the backbone,
give to it the name of spinal column.
Six other processes project from
vertebra: one on each side called transverse pro-
cesses; two called anterior articular processes, extending
forward ; and two called posterior articular processes,
extending backward, to meet the corresponding processes
of the neighboring vertebrae. These processes form, by
means of the intervening cushion of cartilage and con-
necting ligaments, a joint permitting a slight amount of
motion.

2

Fig. 30. — A dorsal verte-
bra shown in two posi-
tions.

1 centrum. 2 processes.
3 neural ring.

each

THE FRAMEWORK OF THE BODY 43

Two shallow depressions in the forward portion of the
centrum of each of the dorsal vertebrae, with correspond-
ing depressions in the adjoining vertebra, form pits which
receive the heads of the ribs. Similar depressions at the
ends of the transverse processes of the dorsal vertebrae
assist in securing the ribs to the spine (Fig. 31).

Fig. 31. — Articulation of a pair of ribs to a vertebra.

ce centrum of the vertebra. r rib.

tr transverse process. co costal cartilage.

st sternum.

Between each two adjoining vertebras are elastic cush-
ions of fibrocartilage, which assist in providing for motion
and flexibility in the spinal column and in preventing
injurious jarring of the brain and spinal cord.

42. The Atlas and Axis. — The first two cervical vertebras
have certain modifications of structure for the sake of
the freer motion needful in the neck. The atlas or first

44 CONSCIOUS NERVOUS OPERATIONS

vertebra (Fig. 32, A) supports the skull, being articulated
by two shallow hollows (a, J) with corresponding pro-
jections on the occipital bone above. This permits the
head to rock back and forth. The atlas has a very small
body or centrum, and a large neural ring subdivided by
the transverse ligament. Into the front portion of the
ring projects the odontoid process, a thick bony peg arising
from the axis or second cervical vertebra (Fig. 32, jB).
Around the odontoid process the atlas rotates, carrying
the head with it from side to side.

Fig.

A atlas. B atlas and axis, a, b articulations with occipital bone.
c transverse ligament, o odontoid process.

43. By means of the variations in the form of the ver-
tebrae, and by the four curvatures seen in the spinal
column, a considerable range of movement is provided for.
The vertebrae furnish strong support for the great mus-
cles of the trunk and a safe channel for the spinal cord,
while a firm but flexible and elastic column is secured for
the support of the whole frame.

44. The Ribs. — Attached by their heads to the tho-
racic vertebrae are the twelve pairs of slender curved bones
called ribs (Fig. 33). The upper seven pairs are attached
in front by costal cartilages to the sternum, or breastbone.
The next three pairs have their costal cartilages joined
each to the cartilage of the preceding rib ; while the last

THE FRAMEWORK OF THE BODY 45

two pairs have their front cartilage ends unattached, and
are therefore called floating ribs. All the ribs have a
downward slope, their front ends being lower than the
hinder ones. This per-
mits of a considerable
enlargement in the size
of the cavity of the
thorax, or chest, when,
by the contraction of
the muscles of the
chest, the front ends
of the ribs are raised.
The object of this will
be shown later.

45. The Sternum, or
breastbone (Figs. 27
and 33), supports the
forward ends of the
ribs (with the excep-
tion of the two lowest,
or floating ribs) by

means of the costal pig . 33._skeleton of thorax> showing ribs>
cartilages, which give costal cartilages, sternum, and some of the
more freedom of move- thoracic vertebr»-
ment than would be possible were the bones solid to the
end. The sternum is composed, in the adult, of three
pieces, the lowest being of cartilage.

46. The Appendicular Skeleton is composed of the pectoral
girdle, the pelvic girdle, and the bones of the limbs.

47. The Pectoral Girdle (Fig. 27) consists of four bones,
two on each side, — the scapula and the clavicle. The
scapula, or shoulder blade, is a triangular, nearly flat
bone lying at the back of the shoulder and not attached

46 CONSCIOUS NERVOUS OPERATIONS

directly to the spinal column. It has a shallow pit at one
of the upper corners for the end of the humerus, or upper
arm bone, and a projection to which the other bone of the
arch, the clavicle, or collar bone, is secured. The clavicle
is a round, slender bone, attached by its two ends to the
scapula and the sternum.

48. The Upper Limbs contain, each, thirty bones. They
are the humerus, or upper arm bone ; the radius and ulna,
side by side in the lower arm ; the eight small bones of
the carpus, or wrist ; the five cylindrical bones of the
metacarpus, or palm of the hand ; and the phalanges, or
finger bones, fourteen in number, two being in the thumb
and three in each other finger.

49. The Pelvic Girdle (Fig. 27) is formed by one large
spreading bone on each side, called the os innominatum, or
hip bone. On the outer side is a deep socket for the head
of the femur. The hip bones are made to support great
weight and to resist severe shocks. They sustain the
whole pressure of the trunk and of burdens carried, and
also receive the force of the various movements of the
lower limbs, as in running, jumping, cycling, etc.

50. The Lower Limbs are similar in structure to the
upper. The femur, or thigh bone, the largest bone in the
body, corresponds to the humerus ; the tibia and fibula,
to the radius and ulna. In the ankle are seven tarsal
bones, and in the arch of the foot five metatarsals, to which
are added the fourteen phalanges, or bones of the toes.
There is, besides, a bony disk, imbedded in the great liga-
ment over the knee, forming a protection to the knee-
joint, and called the patella, or kneepan.

51. Observe the provisions in the human skeleton for
securing firmness and strength to the upright figure. It
has been found that the arch is the strongest form of

THE FRAMEWORK OF THE BODY

47

structure for a given amount of material. The shoulder
arch of the skeleton furnishes support to the arms so
strong that those limbs may be used to lift great weights
and hurl them through the air, and to perform a great
variety of labors. The pelvic arch and the arches of the
foot are also designed to support securely the tall human
figure and to carry heavy loads.

52. Table of the Bones. —

1. Skull, 28

(.1) AXIAL SKELETON

Frontal

Parietal

Temporal

Occipital

Sphenoid

Ethmoid

Cranium, 8

Face, 14

Superior Maxillary

Inferior Maxillary

Palate

Nasal

Vomer

Inferior Turbinate

Lachrymal

Malar

Malleus

Bones of Ear, 6 \ Incus
Stapes

2. Hyoid, 1

3. Spinal Column, 26

4. Thorax, 25

Cervical Vertebrae
Dorsal Vertebr£e
Lumbar Vertebrae
Sacrum
Coccyx

Ribs

Sternum

1

2
2
1

1
1

2
1
2
2
1
2
2
2

2
2
2
1
7
12
5
1
1

24
1

48

CONSCIOUS NERVOUS OPERATIONS

(/?) APPENDIC'ULAH SKKLKTOX

1 Clavicle
Scapula

2

Humerus

Ulna

2

Radius

2

Carpals
Metacarpals
Phalanges

16
'10
28

Os Innoininatum

2

Femur

2

Fibula

2

Tibia

2

Patella

2

Tarsals

14

Metatarsals

10

Phalanges

28

1. Shoulder Girdle, 4

2. Upper Extremities, 60

3. Pelvic Girdle, 2

4. Lower Extremities, 60

53. Cartilage. — In infancy a considerable part of the
skeleton consists of cartilage, or gristle, which afterward
becomes ossified. But there are cartilages — such as the
external ear, the rings around the windpipe, and the ends
of various bones — which do not ossify, and are known as
permanent cartilages. Cartilage is a smooth white shining
tissue of close texture, rarely containing blood vessels.
It is made up, like the bones, of cells surrounded by the
intercellular substance which is the product of the living
cells. A thin layer of cartilage covers the surfaces of
the bones which come in contact with other bones. Car-
tilage also serves as padding in various parts of the body.

54. Connective Tissues of different varieties serve to com-
plete the skeleton. They form the strong cords and bands
and sheets called ligaments, for binding bones together,
and the tendons which fasten the muscles to the bones.

THE FRAMEWORK OF THE BODY

49

55. Articulations. — All unions between bones are called
articulations. Some of these allow of more or less move-
ment; others permit no movement at all. The bones of
the skull, with the exception of the lower jaw and the
minute bones belonging to the inner ear, have no motion.
In most cases their union is formed by means of toothed
edges which fit into each other, forming irregular lines
known as serrated sutures. They lessen jar and avert
injury to the brain. The different vertebrae of the spine
have a very slight motion upon one another, due to the
elasticity of the cartilage pads or cushions which sepa-
rate them.

56. Joints, — Where two bones are articulated in such
a way as to permit one bone to glide freely over the

Fig. 34. — Ball and socket joint at hip.
The parts are separated to show attachments of the round ligament.

other, the union is called a joint. Joints are of vari-
ous kinds and are adapted to various movements.
MACY'S PHVS. — 4

50

CONSCIOUS NERVOUS OPERATIONS

Fig. 35. — Hinge joint
of the elbow.

1 hum eras. 2 ulna.

The ball and socket joint seen in the shoulder and the
hip has the end of one bone fitted into the hollow of
another, and provides for motion in
any direction (Figs. 34 and 86).

The pivot joint is that in which one
bone rotates round another, as in the
atlas and axis joint (Fig. 32), already
described, and in the rotation of the
ulna on the radius at their junction
with the wrist.

The hinge joint permits of motion
in one plane only, as in the joints of
the fingers. Some hinge joints have
provision for additional movements, as
in the elbow (Fig. 35) and in the
articulation between the lower jaw
and the skull.

57. Synovial Membrane. — The broad, thin ligament sur-
rounding a joint forms a closed sac. This sac is lined
with the synovial membrane, which secretes a fluid whose
purpose is to lubricate the joint, as oil lubricates the parts
of a machine which move upon one another (Fig. 36).

58. Structure of Bone. — A living bone is tough, strong,
and slightly elastic. Burned in a fire it retains its size
and shape, but becomes brittle and easily crumbles to pow-
der. Soaked for a few days in dilute muriatic acid, it also
retains its shape, but becomes so flexible that, if one of the
long bones, it may be tied in a knot. The fire destroys
the 33 per cent of animal matter in the bone, leaving the
calcium phosphate, calcium carbonate, and the small quan-
tities of other salts which constitute the earthy or mineral
portion of bone. The acid dissolves out the earthy salts
and leaves the animal tissues.

THE FRAMEWORK OF THE BODY

51

On examination, one of the long bones in a fresh condi-
tion is seen to be covered at the two ends with smooth
white articular cartilage, while the shaft is inclosed in a
sheath of dense white fibrous membrane, called the peri-
osteum, closely adhering to it. It is on the inner side of
this membrane that the bone grows, and by it the nutri-

Pelvic Bone

Synovial Membrane

Head of Femur

-—Round Ligament

- Capsular Ligament

Fig. 36. — Section of hip joint.

tion of the bone throughout life is assisted. If the peri-
osteum is torn away, the bone dies. It covers every part
of the surface of a bone not covered by the articular car-
tilage, and into it the fibers of the ligaments extend, being
so interwoven as to make an indistinguishable and insep-
arable junction.

59. Inner Composition of Bone. — If the bone is sawn
through from end to end, the shaft is found to be hollow,
with the medullary cavity, as it is called, in the center,
filled with yellow marrow. The walls of the shaft are
of a dense, solid structure, except for a thin stratum of

52

CONSCIOUS NERVOUS OPERATIONS

spongy bone around the cavity which contains the mar-
row (lower end of Fig. 37).

In the enlarged articular extremities of the bone, how-
ever, the reverse is the case. The firm, compact part

forms only a thin
layer on the sur-
face, the rest being
a loose, spongy net-
work of bony mat-
ter, with the spaces
filled with a soft,
red substance called
red marrow.

Interlacing chan-
nels, called the Ha-
versian canals, run
through the whole
substance of a bone,
in the densest as
in the more porous
parts. The perios-
teum is richly sup-
plied with blood ves-
sels, and from them
minute branches en-
ter the bone itself
and run along the
Haversian canals.
Other blood vessels reach the solid portion of the bone
from within, through the medullary canal of the center of
the bone, and thus nutriment is conveyed to every part.

Each Haversian canal is surrounded by a set of hard
bony plates, and between the plates, or lamellce, are little

Fig 87.

Longitudinal section of the upper
end of the tibia.

THE FRAMEWORK OF THE BODY 53

cavities called lacunce, connected by minute canals with
one another (Fig. 16, p. 25). Within the lacunae and
their canals are found little masses of protoplasm called
bone cells, or bone corpuscles. These branching bone cells
communicate with one another and with the blood vessels
of the Haversian canals. They are the architects for
building up the bony fabric. Each cell constructs walls
which unite with those about them to form the solid mass.
Along with the arteries of the interior bony structure
very fine nerve fibers have been traced, and lymph vessels
are found in connection with the blood capillaries within
the substance of all bones.

60. Hygiene of Bones and Joints. — The science of hygiene
has to do with all that promotes normal action of the
various parts of the body and of the whole mechanism.
In respect to the bones we need to consider first the con-
ditions most favorable to their growth.

61. Bones of the Young. — As the skeleton grows it not
only becomes larger, but also becomes changed in the struc-
ture of its parts. The bones of an infant are almost wholly
composed of cartilage, having the form of the completed
bone, but the flexibility and elasticity of the cartilaginous
tissue. They become slowly more firm and hard by a
deposit of solid material furnished by the food, selected
from the blood and lymph by the living cells in the carti-
lage and the periosteum. As the bone is built up by the
deposit of the salts of lime (chiefly calcium phosphate),
which furnish nearly all the earthy part of bone, the carti-
lage cells waste away, and their dead matter is carried oft'
by the blood.

62. Importance of Proper Food. — It is evident that the
food suitable for young children must contain lime and
phosphorus in proper proportions for making bone. Milk

54 CONSCIOUS NERVOUS OPERATIONS

has been found to furnish, in most digestible form, those
substances and others needed by the human infant, and
is for early childhood the complete and perfect food. If
there is not a sufficient supply of earthy matter in the food,
the bones of a child remain soft and weak, and are easily
bent or deformed, as in the disease called rickets. For such
conditions an abundance of suitable food, with plenty of
fresh air and sunshine, supplies the cure.

Alcohol and tobacco are particularly to be avoided dur-
ing the time of growth, as they retard or prevent the full
development of the bone cells, making the figure stunted
and enfeebled. Cigarettes are especially harmful.

63. Deformity to be Guarded Against. — Children permitted
to walk too early, before the bones are sufficiently hardened,
may be made permanently bow-legged. They should be
allowed freedom of movement and plenty of exercise, but
should not be urged to walk too soon.

Long-continued pressure upon the bones of children
may result in deformity. Some tribes of Indians flatten
the heads of their children by fastening boards upon them.
Clothing should always be loose ; shoes especially should
allow room for movement and growth.

Care should be taken that a child should habitually
assume correct positions in sitting and standing, and fre-
quent changes of position are needful. The seat should
not be too high to permit the feet to rest easily and
squarely upon the floor, otherwise the bones of the thigh
may be bent by the weight of the legs. School children
should be taught to sit upright while writing or studying,
lest the spine become curved and diseased. Seats and
desks should be carefully adapted to the child's stature,
and round shoulders — the most common deformity —
should be especially guarded against

THE FRAMEWORK OF THE BODY 55

In standing, the weight should be supported evenly by
the two feet. One hip or one shoulder often becomes
higher than the other, upsetting the firm poise of the
figure by neglect of this precaution. A teacher should
see that a child is not kept standing till wearied.

64. Bones of the Aged. — As the bones of the young con-
tain an excess of animal matter, so those of the old have
an excess of mineral substances and are consequently
more brittle. The aged, therefore, need to guard espe-
cially against fractures of the bones. Not only are
their bones more easily broken, they are also healed with
greater difficulty. In the young and healthy the vital
processes are more actively carried on, and the busy bone
cells go swiftly to work to repair a breakage, throwing
out first around the injured parts a soft repairing material
in which bony matter is afterward deposited ; but in the
aged the bone cells work slowly, and a broken bone is
sometimes never fully restored.

65. Broken Bones. — The two ends of a broken bone
should be brought together into their correct position as
soon as possible, before inflammation and swelling render
this difficult. Of course a skillful surgeon should be
called to " set " a broken bone ; but there may be delay,
— the patient may have to be carried some distance. In
such cases care should be taken to prevent injury to the
surrounding parts from the fractured ends of the bone.
A limb should be bound to a strip of board or even an
umbrella as a temporary splint.

66. Injuries to Joints. — Dislocation of a joint stretches
or breaks the ligaments and other membranes around
it, producing inflammation. This renders examination
and putting in place difficult, and a dislocated joint
should therefore be restored to place as soon as the need-

56 CONSCIOUS NERVOUS OPERATIONS

ful skill can be procured. A sprain, which is a sudden
wrenching or straining of the ligaments not sufficient to
dislocate the joint, is often as serious as a dislocation.
Neither should be neglected or treated lightly. Inflamma-
tion, if not checked, sometimes results in the destruction
of the synovial fluid and the coverings of the ends of the
bones in the joints, and consequently in permanent stiff-
ness of the joint. Immediate and long-continued rest is
imperative, and competent surgical advice should usually
be secured.

DEMONSTRATIONS AND EXPERIMENTS

10. The Skeleton. — For the study of the osseous system there should
be accessible to the student a mounted human skeleton. In absence
of this, a mounted skeleton of a cat or dog may be used. Where the
school property does not include a skeleton of any kind, the enthusi-
astic teacher will provide one. This can be very quickly done as fol-
lows. Clean most of the flesh from the skeleton of a cat, dog, or
rabbit ; boil the partly cleaned skeleton in " liquid soap," one part,
and water, four parts, for forty minutes, then for thirty minutes in
liquid soap and water, equal parts ; cool the skeleton in cold water ;
clean with a brush and allow to dry. The liquid soap is made by
dissolving 12 grams of saltpeter and 75 grams of white soap in a mix-
ture of 2000 cubic centimeters of water and 150 cubic centimeters of
strong ammonia.

The skeleton may be studied without any attempt at mounting it.
The student should follow the text of this chapter, identifying each
bone as it is described. The teacher will find it profitable to have each
student " demonstrate " the whole or a certain part of the skeleton,
i.e. point out and name the various parts without any reference to the
text and without leading questions from the teacher.

11. Cartilage. — At a meat market, bones can be procured which
will show hyaline cartilage on their articular surfaces. At a slaughter-
house can be obtained the windpipe, ears, costal cartilages, etc., of
various animals, and the general appearance and purposes of the dif-
ferent varieties of cartilage can be shown from them. To show the

THE FRAMEWORK OF THE BODY 57

minute structure of cartilage, cut very thin sections with a razor from
the articular surface of a fresh bone of a young animal, mount in
normal salt solution, and examine with the compound microscope.

12. Structure of Bone. — Procure, at a meat market, a leg bone of
some animal and compare it in appearance with a similar bone that
has been exposed to the weather for months. Observe the pink color
of the fresh bone, and the fibrous periosteum that covers it. Saw
the two bones open lengthwise and observe the marrow cavity in each.
Notice the compact shaft of each, and the cartilage on the articular
surface of the fresh bone.

13. Minute Structure of Bone. — Mounted sections of bone may be
procured of dealers in microscopical supplies, or the teacher may pre-
pare them by sawing thin pieces from the shaft of a dry weathered
bone and then filing them down till they are extremely thin. They
may be mounted in water on a slide and examined with the micro-
scope. But a better way is to dry the sections thoroughly, after care-
fully washing them in alcohol, and then to mount them in Canada
balsam that has been evaporated until it solidifies on cooling. The
sections should be quickly placed in the hot balsam upon a clean slide,
covered with a cover glass, and cooled to harden the balsam.

14. Composition of Bone. — Two pieces of the same fresh bone or two
similar fresh bones should be obtained. Burn one piece in a fire for
several hours till it turns completely white. All the animal matter
has been removed. Place the other piece of bone in weak muriatic
acid (10-15 per cent strength) for several days to decalcify. It becomes
soft, owing to the removal of the mineral matter. Observe the brittle-
ness of the burned bone, and the toughness and flexibility of the other
piece. Place the burned bone in the muriatic acid, and burn the piece
of decalcified bone. What is left?

15. Joints. — The various kinds of joints can be demonstrated on a
skeleton. The actual movements that occur at those joints should be
performed by the student in corresponding joints of his own body.

16. Dissection of a Joint. — Procure a leg joint of a sheep and show
the possible movements of the bones that form the joints. Observe the
tendinous attachments of muscles, also the ligaments that hold the
bones together. Cut through the ligaments and open the joint cavity.
Notice the synovial fluid, and the cartilage on the articular surfaces
of the bones.

Fig. 38.— The muscular system.
68

CHAPTER V

THE MUSCULAR SYSTEM

67. Though the skeleton preserves the shape of the
body, the muscles with the surrounding fat fill out the
figure, giving roundness and grace of outline. Muscles
and bones, with the tendons and ligaments connecting
them, constitute the organs of motion and locomotion:
they are the apparatus by means of which the nervous
system acts when the object sought is movement; as the
stomach, liver, blood vessels, kidneys, and other parts
of the digestive system are the apparatus which the nerv-
ous system uses for the

purpose of nutrition.

68. The Muscles are the
lean part of meat. They
make up that part of the
body which we call flesh.
When a muscle is exam-
ined, it is found to consist
of small fibers bound to-
gether in bundles (Fig.
39), each bundle being
wrapped in a thin sheath

of areolar tissue, called perimysium, while each minute
fiber of which a bundle is composed has also its mem-
branous sheath, called the sarcolemma.

59

Fig. 39. — Bundles of striated

muscle cut across.
ff several bundles bound together into
larger bundles to make up the muscle.

60

CONSCIOUS NERVOUS OPERATIONS

HUH

Fig. 40. — Pieces of
striated muscle
fibers.

Showing the spin-
dle - shaped nuclei
and cross-striations.
At the left above is
the rounded end of a
fiber.

69. Classification. — The muscles are divided into two
classes, usually called the voluntary and the involuntary

muscles, the first being under the con-
trol of the will, while the second are not.
There is also a difference under the
microscope between the two classes of
muscles. Voluntary muscular tissue is
composed of fibers which are marked by
alternate dark and light stripes. They
are called striated or striped muscular
fibers (Fig. 40). The fibers which com-
pose the involuntary muscles are, as a
rule, destitute of these markings and
are called plain muscular fibers (Fig.
41).

Certain exceptions to the above rule
should be noted. The muscles of the heart, though not
under the control of the will, are made up of striped
muscular fibers ; and also the muscular fibers found in
the pharynx, part of the esophagus, and in the internal
ear, though involuntary, have the structure of voluntary
muscle fiber. On the other hand, the ciliary muscles,
by which the eye is accom-
modated for seeing objects
at different distances, are
under the control of the
will, though composed wholly of plain or unstriped
muscle fibers.

Some striped muscles, like those of respiration and of
the eyelids, are partly voluntary and partly involuntary.

70. Voluntary Muscles. — These are also called skeletal
muscles, because they constitute the muscular apparatus
attached to the bones. Each muscle is usually larger in

Fig. 41. — Plain muscle fiber.

N nucleus.

THE MUSCULAR SYSTEM

61

the middle than at the ends, and the swollen middle
portion is called the belly. The belly is usually unat-
tached, but the two ends are secured to the
bones by tendons which are continuous
with the connective tissue of the muscle
(Fig. 42).

Between the small fibers of the bundles
which make up a muscle is a little loose
areolar tissue in which are distributed the
blood vessels and nerves for the muscle.

71. Muscle Cells or Muscle Fibers. — It is in
the microscopic threads of the muscle that
the peculiar power of contraction lies.
These are variable in length and thick-
ness, but are said to average, in voluntary
muscles, -5^ of an inch in diameter and
about one inch in length. They are cylin-
drical in shape, with rounded ends (Fig.
40), and as a rule do not branch. In
the muscles of the face and tongue, how-
ever, the muscle fibers divide into many Fi 42 _Bice
branches. muscle.

Each muscle fiber, or cell, consists of the 1 tendinous ends.
sarcolemma and a soft, semifluid material of
alternate light and dark disks, called the contractile sub-
stance. Just beneath the sarcolemma are several long
oval nuclei.

72. Nerve Endings in Muscle Fiber. — It is impossible to
treat of muscles and their action without including some
study of the other sort of irritable tissue, nervous tissue,
upon which muscular action depends.

The sarcolemma of each muscle fiber is pierced by a
branch of a nerve fiber. The primitive sheath or neuri-

62

CONSCIOUS NERVOUS OPERATIONS

Nerve Fiber

lemma (the inclosing membrane of the nerve fiber) becomes
continuous with the sarcolemma, and the axis cylinder of

the nerve fiber branches many
times, the ramifications end-
ing in a flat or branched layer
°^ protoplasm containing nu-
clei. These terminal nerve
organs are called end plates
(Figs. 43 and 44).

73. How a Muscle Contracts.

Fig. 43. -Nerve endings in stri- ~ A muscle contracts or be-

ated muscle fibers. comes shorter in proportion to

its length, without change in

bulk, under the influence of stimulus. It is the office of
the nerves of the muscles to carry to them their natural
stimulus, but muscles also
contract under the action
of other stimuli; for in-
stance, in consequence of
a sudden blow or pinch,
when heat is applied sud-
denly, when certain chemi-
cal substances are dropped
upon them, or when an
electric shock is conducted
to them.

In living animals the
muscles are always more
or less contracted. This

Fig. 44. —Motor nerve endings in
striated muscle fibers.

is due to the nervous influence which they constantly
receive. If their nerves are cut or destroyed, the mus-
cles lengthen. This tension of the muscles keeps them
ready for immediate action. When a nervous impulse

THE MUSCULAR SYSTEM 68

reaches a muscle, the numerous branches of the nerve
— one for each individual muscle cell — distribute the
stimulus to all parts at practically the same instant.
The end plates are situated in each muscle fiber near
the middle between the two ends, and the fiber begins
there to contract. The two ends draw toward each
other ; the fiber becomes swollen and shorter. In the
muscle as a whole contraction is simply the sum of the con-
tractions of all the minute fibers which compose it. In
the muscle fiber contraction appears to be some compli-
cated movement of the molecules which produces a change
in the appearance of the stripes. It is found that in
those places where swift and rapid contraction is called
for, the muscular tissue has almost invariably the striped
fibers.

74. When a muscle is made to contract by a single
electric shock, or by other artificial means, the movement
is sudden and brief. Voluntary muscle, however, under
its natural nervous stimulus, never contracts with a
twitch. Its action is rather that of continued gentle
vibration, called tetanus, such as follows a rapid series
of electric shocks which leave no time for relaxation.
The nervous stimulus comes to the muscle in a quick
succession of impulses, — about twenty in a second, — so
that one vibration is succeeded by a second before the
first has ceased to agitate the muscle cell.

75. Internal Changes in Muscle under Stimulus. — Some of
the energy set free by a contracting muscle appears as work
done, weight lifted, etc., while a considerable amount
becomes heat, for the temperature of muscle always rises
under contraction. Certain chemical changes also ap-
pear. Variable amounts of carbonic acid and lactic acid
are set free, and oxygen is used up. Electric changes

64 CONSCIOUS NERVOUS OPERATIONS

lasting for some time are also produced in the muscle
by its contraction. These are shown by the use of a
delicate galvanometer.

76. Another important effect upon itself of a muscle's
contraction is what we call fatigue of the muscles, that is,
a lack of readiness to respond to stimulus. This is due
to the using up of the material in the muscles which was
available for the production of energy, and still more to
the accumulation of waste matter — the product of the
activity of the muscles. Experiments have shown that it
is not the muscle itself which first becomes too much
fatigued for contraction. Nor is the seat of fatigue in
the nerve, but in the end plate within the muscle cell. The
fatigue is relieved by even a brief rest, and such relief is
absolutely necessary to the health of the muscles. Even
the muscles of the heart, that organ which works cease-
lessly from the beginning of life to death, have a period
of rest after each beat.

77. External Effects of Muscular Contraction and Relaxation.
— The purpose of muscular contraction is the production
of motion. The contraction and relaxation of the muscular
walls of the heart keep the blood in constant movement ;
the various other vital processes are also dependent upon
more or less constant motion in the tissues and organs of
the body, and all our outward activities are likewise the
results of the shortening and lengthening of the innumer-
able strands of muscular tissue.

Muscular power, or the amount of force which a mus-
cle can supply, varies with its health and vigor, and with
its form. The thickest muscles can lift the heaviest
load. Those having the longest strands can move a
weight the greatest distance. Hence the human body
possesses both long, slender muscles, and short, stout ones,

. THE MUSCULAR SYSTEM 65

as well as those of all sizes and lengths between. Many
muscles which we might at first think to be long are
really short, but appear long because of the long tendons
by which they are attached to the bones. Many of the
muscles which move the fingers, for example, have their
bellies in the forearm, and are attached to the small bones
of the fingers by long, slender tendons. The force with
which muscles contract is sometimes very great. A human
muscle one square centimeter (.15 square inch) in section
can raise a weight of 5670 grams or 200 ounces.

When a muscle contracts, its two ends are drawn nearer
together, and hence draw toward each other the parts to
which the ends of the muscle or its tendons are attached ;
the belly of the muscle becomes swollen, and in strong
contraction the whole muscle becomes tense and hard.

78. Contraction is speedily followed* by relaxation. The
stimulating force ceases to be supplied, and the muscle
returns to a state of rest. If the hand has been raised by
the contraction of the biceps muscle on the inner side of
the humerus, it will fall under the action of gravitation
when that contraction ceases and the muscle becomes
passive. In order that the hand may be drawn down
with force the action of the triceps muscle at the back of
the humerus is needed. Muscles can give a powerful pull,
but they cannot push. Very generally, therefore, they
are arranged so that muscles which cause movement in
one direction are opposed by those which cause movement
in the opposite direction.

79. Dead Muscle. - - The muscles of a dead body, or
muscles which have been removed from a living body,
gradually undergo a marked change, which results in
the stiffening known as rigor mortis. That which was
translucent becomes more opaque, most of the natural

MACY'S PHYS. — 5

66 CONSCIOUS NERVOUS OPERATIONS

elasticity disappears, and a hard, rigid condition sets in,
accompanied by more or less contraction. This is due to
a coagulation of the protoplasm of the muscle cells, simi-
lar to the clotting of blood. Rigor mortis passes away
after a time, and the dead body becomes soft and flabby
— a sign of approaching decay.

80. Plain or Involuntary Muscles. — Though the plain
muscles are not under the control of the will, they still
have nervous connection with the central nervous system.
Most of the nerves supplying the organs having plain or
umtriped muscular tissue come from the sympathetic nerv-
ous system; but from every ganglion of the sympathetic
chain nerve fibers communicate with the brain and spinal
cord. The muscles of the blood vessels, lymphatics,
glands, and other internal organs, are of unstriped struc-
ture, and carry on their work without affecting conscious-
ness. Their action under stimulus is similar to that of
the skeletal muscles, but takes place much more slowly.

81. Plain Muscle Fibers. — Plain muscles are made up,
like skeletal muscles, of bundles of fibers, and these of
muscle cells. The cells, however, differ from those of the
voluntary muscles. They are long, spindle-shaped fibers,
having a rod-shaped nucleus in the center (Fig. 41). The
nerves of plain muscle fibers do not end in end plates, but
form plexuses, or networks, which ramify between and
around the muscle fibers. The nerves of the heart mus-
cles end as do those of the unstriped muscles.

82. Rhythmic and Peristaltic Movements of Involuntary Mus-
cle. — One of the characteristics of involuntary muscles is
a tendency to alternate regular periods of activity and
rest. The heart is the most familiar illustration of this
rhythmical tendency, but it is seen in some other organs,
and especially in some of the lower animals.

THE MUSCULAR SYSTEM 67

The peristaltic action of plain muscle is seen in the
small intestine and in other parts of the alimentary canal.
When any part of the tube is stimulated, a circular con-
traction results, which slowly passes along in a wavelike
manner through the length of the tube. In the diges-
tive tract this movement serves to drive the food onward.

83. Involuntary muscle, as a rule, contracts more slowly
than voluntary muscle. It contracts, not with a tetanus
like that of voluntary muscle, but with a single, much
prolonged contraction.

84. Mechanism of Movement. — The power of the muscles
to change their form carries with it the power to change
the positions of the bones and other parts of the body to
which they are attached, and hence to change the positions
of the different parts in respect to one another and to move
the whole frame from place to place.

When a part of the body is moved at a joint, the bone
which is moved acts as a lever. A lever is a stiff bar
which can be moved round a fixed point, or fulcrum.
Three classes of levers are known to the science of
mechanics, depending upon the position of the fulcrum
with reference to the weight to be moved and the power
which produces the motion. In the first class the fulcrum
is between the weight and the power, as in using a crowbar
to lift the edge of a stone. In the second class the ful-
crum is at one end, the power at the other, and the weight
between them. In the third class the fulcrum is at one
end, the weight at the other, and the power is applied
between the two. All three forms of levers are found in
the human body, though the levers of the third class are
the most numerous (Fig. 45).

85. Lever of the First Class. — The action of a lever of
the first class is seen in the straightening of the bent arm.

68 CONSCIOUS NERVOUS OPERATIONS

The muscle at the back of the humerus applies the power.
It is attached by tendons to the scapula and to the hinder
side of the humerus, while the tendon into which the lower
end of the muscle narrows is inserted into the end of the
ulna at the elbow, which is more than an inch above the
articulation of the ulna with the humerus. By its contrac-
tion the muscle pulls the upper end of the ulna upward, draw-
ing down the hand, which is the weight at the lower end of
the ulna, and straightening the joint. The fulcrum is at
the elbow joint, between the hand and the power at the
upper end of the ulna.

/ \ \ \ \ \

in
Fig. 45. —Diagram of the foot, illustrating levers of the three classes.

I tapping the toe on the floor. II rising on the toes.
Ill lifting a weight with the toes.

86. Lever of the Second Class. — When the body is raised
on the toes (Fig. 45, II) the action of a lever of the second
class is seen. The weight is that of the whole body sup-
ported by the foot at the ankle, while the power operates
through the muscles of the calf of the leg at the heel, the
toes acting as the fulcrum.

87. Lever of the Third Class. — When the body lying on
the ground is raised to a sitting posture, a lever of the
third class is used. The head and body are the weight,
the fulcrum is at the hip joints, and the power is applied

THE MUSCULAR SYSTEM

69

between the two by the muscles which pass from the front
of the thigh to the hip bones. The raising of the hand by
bending the elbow joint is perhaps a clearer example of
the lever of the third class. The weight is at the end of
the forearm, the fulcrum is at the elbow,
and the power is between, at the point
on the radius where is inserted the muscle
which lies on the front of the humerus.

88. Coordination of Muscular Action. —
Our ordinary movements involve the use
of many different muscles, and very com-
plicated action of levers and cords. Even
simply to stand erect requires strong ten-
sion of certain muscles and ligaments
pulling against one another. The mus-
cles on the front of the thigh contract to
keep the knee from bending, while the
ligaments of the joint prevent it from
bending the wrong way. The muscles
on the front of the leg contract to keep
the body from falling backward, and those
at the back contract to keep it from fall-
ing forward. In the same way the trunk
is balanced on the thigh bones by the
muscles passing from the body to the
thigh in front and back, while a particu- Fig. 46. — Diagram
larly strong ligament, crossing the hip £us'°™ °^
joint from the pelvis to the thigh bone, tend to keep the
keeps the extra backward weight of the body e
trunk from destroying the balance of the frame. At the
back of the neck are the muscles which give to the head
its erect and graceful poise, while many ligaments bind it
to the spinal column (Fig. 46).

70 CONSCIOUS NERVOUS OPERATIONS

89. In order to maintain all the nice adjustment and
balance of muscular force constantly demanded, the brain
and nerves must be continually at work. Just enough
stimulus must be supplied to each set of muscles and
supplied at exactly the right moment or something
will at once go wrong. This harmony of muscular ac-
tion and regulation of the complex relations between
the hundreds of muscles in the body is called coor-
dination. It is easy to show that it depends upon the
nervous system.

If one falls asleep or receives a blow which " stuns "
the brain, the muscles are relaxed, and, unless supported,
the body falls to the ground. Sudden nervous or emo-
tional excitement, as surprise, grief, or fear, may cause
the muscles of the heart to stop their action and the body
to fall in a " faint." In some cases the effect of sight
upon the brain is to destroy the power to control the
muscles, as when the sight of the moving waves of lake
or ocean renders one giddy. The perception of certain
odors may have the same effect, and in many other ways
the control of the muscles is affected by that which affects
the central nervous system.

The study of the brain has shown that the cerebellum
is the great center for the coordination of muscular move-
ment and especially of those muscular actions which have
to do with maintaining the equilibrium of the body.

90. Exhaustion of Muscles. — Even when we are quite
awake, and the brain is active, our muscles sometimes refuse
to act. Muscular fiber cannot contract continuously for a
long time. It must have periods of rest. That is the
reason we require frequent changes of position, one set
of muscles being thus allowed to rest while another set
is called into action. If a weight be held out at arm's

THE MUSCULAR SYSTEM

71

length from the shoulder, the muscles of the arm soon
become exhausted and incapable of sustaining the weight.
But a moment's rest restores the contractile power, and
the weight may again be held
out.

91 . Muscle Waste. — When a
muscle contracts certain chem-
ical changes take place in the
substance of its cells. Some
of the matter in the muscular
fiber becomes oxidized, and
new substances are formed
which are harmful to the body
if not removed. These are
called waste products, and that
which appears in largest quan-
tity is carbon dioxide. These
waste products are taken up
by the blood which flows along
the muscle cells and are finally
removed from the body by
means, mainly, of the lungs
and the kidneys. If the waste
matter is not removed, the
effect soon appears in the cen-
tral nervous system, to which
the poison is carried by the
blood.

92. Voluntary Movement. —
Let us suppose that a man

seeing an apple within reach puts forth his hand to take
it (Fig. 47). In such a case the light from the apple
enters the organ of sight and stimulates the nerve endings

Fig. 47. — Diagram of the path of
a nervous impulse which re-
sults in the hand reaching to
seize an object seen with the
eye.

G cerebrum.

Cb cerebellum.

M medulla oblongata.

MC motor center in brain.

OC optic center in brain.

P pons Varolii.

Q corpora quadrigemina.

S spinal cord.

T optic thalami.

72

CONSCIOUS NERVOUS OPERATIONS

appropriated to vision. The nervous irritation is con-
ducted by the optic nerve to that part of the brain con-
cerned in perception by means of the eye. The nervous
center is affected, and the nervous impulse is passed on,
by some unknown process which we speak of as the action
of the will, to the nerve fibers running down the white
columns of the spinal cord. These convey the impression
to the anterior horn of the gray matter of the cord, where
lie the motor cells from which arise the motor roots of the
spinal nerves. From the motor cells a new nervous
impulse goes forth to certain muscles of the arm and
hand. The muscular cells of such muscles contract, the
bones are moved at the joints, and the apple is seized.
This is voluntary muscular action.

93. Reflex Movement. — The voluntary muscles often act
without receiving any nervous impulse from the brain,

Fig. 48. — Diagram of the path of a simple nervous reflex action.

and without any conscious purpose. Suppose the man in
putting out his hand to take the apple is stung upon the
finger by a wasp not before perceived. The end organ
of sensation in the finger sends the impression of paiu

THE MUSCULAR SYSTEM 73

along the afferent sensory nerve through the posterior nerve
root to the cells of the spinal cord, and an impulse is at
once sent forth along efferent motor fibers to the muscles
of the hand and arm, which promptly jerk the hand away
(Fig. 48).

A great multitude of reflex actions are possible to the
muscles, and one of the chief functions of the spinal cord
is to act as a center of reflex action.

94. Automatic Movement. — Action of the muscles often
occurs without any obvious stimulation of the nerves from
without. That is, the nervous impulse may apparently
arise in the nerve center itself, and efferent, or outgoing
influences are not preceded by afferent, or incoming influ-
ences. Such changes often, occur rhythmically — activity
and rest, or diminished activity, following each other in
regular alternation — as in the movement of the muscles
of respiration ; and this characteristic is believed to be
due to certain rhythmic changes which take place in some
of the nervous material of the medulla oblongata.

95. The Muscular Sense. — It is not motor nerve fibers
only that are distributed to the muscles ; the muscles
receive sensory fibers also which pass to the posterior
roots of the spinal nerves and convey impressions from
the muscles to the spinal cord and thence to the brain.
These impressions are called the muscular sense. They
assist our judgments of weight, and inform the brain of
the general condition of the muscles.

96. Hygiene of the Muscles. — Muscles increase in size
and in strength by appropriating suitable material from
the food, and by use. If ill fed and inactive, they
become small and weak. If one limb is made useless from
disease or injury, — as when a bone is broken, — its
muscles shrink and grow soft, so that the unused limb

74 CONSCIOUS NERVOUS OP K RATIONS

becomes perceptibly smaller, and, of course, weaker than
its fellow.

97. Exercise is indispensable to health of muscles.
Growing children need much active exercise for develop-
ing and hardening the muscles, and all healthy children
crave it. Nothing is better than running and walking for
promoting the growth of the muscles, for developing the
power of the lungs and the heart, and so for aiding both
the free circulation of the blood and its purification, by
means of which the nutrition of the whole body is stimu-
lated. Those who exercise much in the open air (which
is always best) have, as a rule, good appetites, for food
is needed to repair the waste caused by the exercise.

Many diseases are prevented, and some are cured, by
suitable exercise. A brisk walk of several miles taken
regularly every day would alone do much to keep the
whole body in normal condition. If it is impossible to
go out of doors for the needful amount of exercise, the
indoor conditions should be as nearly as possible like
those without. Fresh air and light should be freely
admitted to the rooms used, additional clothing being
put on when necessary.

Rowing, swimming, boxing, horseback riding, climbing,
sweeping, cycling, etc. are of value in strengthening the
muscles of the limbs, chest, and back. A large, strong
chest, wherein the lungs have plenty of room for an abun-
dance of pure air, is not likely to belong to a consumptive
person.

It is desirable that exercise should be chosen which
develops both sides of the body. Throwing a ball with
one hand, if indulged in to excess or without sufficient
exercise of other sorts, sometimes causes irregular devel-
opment of the body, and curvature of the spine may fol-

THE MUSCULAR SYSTEM 75

low. Certain kinds of spinal curvature are cured by
wisely chosen exercise.

98. Exercise in the Cold. — For a healthy person nothing
so well develops the whole system and hardens the con-
stitution as regular, vigorous, and agreeable exercise in the
cold. Hence outdoor winter sports and occupations
should be encouraged. Skating, sliding, snowballing,
and swimming are excellent as promoters of health.

99. Time for Exercise. — Some times are better than
others for taking exercise. The morning is usually best
for the severer forms, because the whole system is then
refreshed and vigorous. In the evening one who has
been engaged in physical toil does not need exercise, but
rest ; while one whose occupation is mental labor or sed-
entary business will be rested and refreshed and prepared
for sound sleep by exercising judiciously in the open air
after the day's work is done.

When the muscles are called into use they require more
blood than when at rest, that the waste which results
from exercise may be repaired. This extra supply of
blood is drawn from other parts of the body, and the
demands of the muscles may retard the performance of
other physiological functions — since the total amount of
blood is practically invariable. This is why the muscles
should not be vigorously exercised for an hour or two, at
least, after meals, and not immediately before. Digestion
requires an increased flow of bloo.d to the alimentary canal
and digestive glands, and if the process is impeded by a
drain of the vital fluid to other parts, harm will result.

100. Training. — The scientific development of the mus-
cular system under " training " for particular purposes of
sport, or in a well-equipped gymnasium, may have excel-
lent results for those who are able to avail themselves of

76 CONSCIOUS NERVOUS OPERATIONS

such facilities. But the number of such persons is com-
paratively small, and as those who exercise in a gymna-
sium are usually, and ought always to be, under the guid-
ance of a qualified instructor, advice as to the use of the
gymnasium apparatus is not needed here.

101. The Healthf illness of Work. — While all due stress
should be laid upon the healthfulness of recreative exer-
cise, it should not be forgotten that the human machine
is the most skillfully designed and constructed apparatus
ever made for accomplishing an immense variety of differ-
ent kinds of work. The man whose daily employment
brings into play his various muscles under conditions of
reasonable comfort, and without overfatigue, may live a
healthful life without paying any attention to the preced-
ing suggestions. If that employment is carried on in the
open air, and is such that he finds interest and enjoyment
in it, he is still more fortunate. All the good effects of
the most carefully devised systems of physical culture
may be gained from a judiciously varied scheme of work,
and the pleasure of being able by one's own effort to
create some useful or beautiful or worthy product for the
enrichment of the world may be a tonic even more health-
fully stimulating than the most successful athletic con-
test. The varied round of household duties, sometimes
prescribed by a wise and skillful physician, has in many
cases brought health to a feeble, languid, ailing woman.
The effort which the idle rich man sometimes puts forth
in the way of exercise, that he may secure an appetite for
his dinner, would be still more promotive of health if
turned to some useful purpose.

The man whose business does not permit the proper
activity of all the muscles must necessarily give thought
and time to supply the deficiency. But to the great mass

THE MUSCULAR SYSTEM 77

of mankind it is happily possible to get all needful exer-
cise while doing useful work.

102. The Nervous System as involved in Muscular Exercise.
— We have already learned that contraction of voluntary
muscular tissue depends upon the stimulus brought to
each minute muscle cell by a nerve fiber. Without such
stimulus a man's limbs are motionless and the whole frame
a lifeless mass. If the nervous system is enfeebled by
disease or by exhaustion, the action of the muscles becomes
weakened or deranged. The disease called Saint Vitus's
dance, Avhich causes muscular movements beyond the con-
trol of the will, is not a disease of the muscles, but of the
nerves. So in other disorders which derange the action
of the muscles, the real trouble is seldom with the muscu-
lar tissue itself. The direct effect of muscular activity,
as suggested in section 91, is to poison the nervous cen-
ters. The greater the demand upon the muscle in the
way of rapid and frequent contraction, the greater the con-
sumption of living material and the greater the amount of
poisonous, dead, waste matter which passes into the circu-
lation. These waste products, if not promptly removed
from the system through the excretory organs, are found
to have a powerful injurious effect upon the central nerv-
ous system, an effect that is soon manifest in the weak-
ened action of the muscles themselves.

Anything, therefore, which affects injuriously the nerv-
ous system interferes with the free and easy play of the
muscles. And, conversely, anything which promotes a
high level of health in the nervous system is an aid to mus-
cular vigor also. Exercise undertaken for the carrying
out of some worthy purpose — a purpose in which the
mind is deeply interested and the whole man engaged —
is the most healthful exercise ; while that which is disliked

78 CONSCIOUS NERVOUS OPERATIONS

or entered upon indifferently and listlessly is found to
have little or no invigorating power.

103. Effect of Alcohol and Other Stimulants and Narcotics
upon Muscular Action. — The most serious effects of the
excessive use of alcoholic drinks, tobacco, opium, chloral,
and other narcotic drugs are felt by the nervous system
and will be most fully treated when we come to the special
study of that part of the human organism. But it is well
to notice here how those substances influence the organs
of motion.

No one who has ever seen a drunken man in the stage pre-
ceding that of stupor can have failed to observe the uncer-
tainty of his muscular movements : the shaking hand, the
staggering gait, the thick, indistinct utterance. These
effects are due to what is called the excessive use of alco-
holic drinks, and no one doubts that in large quantities
they act injuriously upon the system. Alcohol deranges
the action of the muscles by its influence upon the nervous
system, causing defective regulation of the supply of nerv-
ous force to the several muscles. As to whether it is pos-
sible to use alcohol in small amounts without impairing
the perfection and vigor of muscular action, there is one
very significant fact: that men in training for severe mus-
cular exertion in athletic contests are strictly forbidden
the use of alcohol in any form and in any quantity,
whether or not they have been previously accustomed to
such indulgence. As. the rules for such training are the
result of long and wide experience and most careful study,
it is safe to conclude that alcohol at least does not promote
strength, endurance, or precision of muscular movement.

It is very common for a person accustomed to a moder •
ate use of alcoholic beverages to suffer from tremor of the
hands, due to lack of control over the muscles, so that

THE MUSCULAK SYSTEM 79

he is disabled from manual work requiring dexterity or
skill. Sometimes an additional glass of liquor seems
to steady the hand for a time, but tne shakiness soon
returns.

104. Tobacco and other narcotics also affect muscular
activity through their effect upon the nerves. All nar-
cotics have as their natural, characteristic influence the
paralyzing of some of the nerve centers. As medicines
they may give relief from pain and so act beneficently
under skillful application. Tobacco has a special effect
upon the nerve centers regulating the action of the
muscles of the heart, making that action irregular and
less vigorous. This is particularly true of the young, and
it is not very uncommon for boys addicted to excessive
cigarette smoking to develop serious disease of the heart,
or even to die suddenly from " heart failure." Smoking
tobacco is found to interfere with work requiring fine and
delicate adjustment of muscular movement, as in watch
making and other delicate mechanical employments, in
scientific drawing, fine penmanship, etc. It is also for-
bidden to those persons in training for athletic contests,
and to all pupils in many schools, as well as to soldiers in
the armies of certain countries.

DEMONSTRATIONS AND EXPERIMENTS

17. General Structure and Properties of Muscles. — It is important
that the pupils see muscles in their natural positions and connections.
For this purpose the frog is convenient, since the animal is so small
that little dissection is necessary, and since entire muscles can be
observed and owing to their great vitality can be made to perform
their natural movements. The frog should be pithed or decapitated,
and the skin removed from one of the hind legs. The muscles of
the limb then stand out distinctly (Fig. 7, p. 18). The belly of a
muscle can be distinguished from its tendinous ends, and the origin

80 CONSCIOUS NERVOUS OPERATIONS

and the insertion can be made out. The respective share wnich each
muscle takes in the movements of the limb can be shown by touch-
ing the individual muscles with the electrodes of a weak galvanic
battery. The change in shape of the muscle during contraction will
also be very well shown.

18. Relaxation and Contraction of Muscles. — Extend one arm nearly
straight from the shoulder. Then bend the arm at the elbow, draw-
ing the hand up to the shoulder. With the other hand can be felt
the changes in the form of the biceps muscle, as it relaxes and con-
tracts. If the arm be bared the changes in form of the muscle can
be seen. The tendon of the biceps at the elbow can also be seen.

19. Gross Structure of Muscle. — Obtain a piece of boiled corned
beef, and dissect it with needles. The larger and smaller bundles of
muscle fibers can be easily differentiated. By aid of a lens even the
separate fibers can be isolated. Observe between the bundles and
fibers the whitish connective tissue, in life tough and fastening the
bundles and fibers together, but now softened in boiling.

20. Functional Difference between Voluntary and Involuntary Muscle.
— If the abdominal cavity of the frog experimented upon in a preced-
ing section be opened and the electrodes applied to the stomach and
intestines, the difference between the movements of voluntary and
involuntary muscle will be clearly demonstrated.

21. Fatigue of Muscle. — On applying repeated electric shocks
directly to a frog's muscle, or indirectly through its nerve, the re-
sponses are seen to become more and more feeble. But after a period
of rest, the muscle responds as vigorously as ever.

22. Nerve Endings in Muscle. — While the tracing out of the final
nerve ends in muscle must be left to the histological expert, yet
the general relations of motor nerves to muscles can be very easily
shown in the frog. Branches of the sciatic nerve can be traced out
to the muscles of the leg (Fig. 8, p. 18), and by electrical stimulation
the functional relation between nerve and muscle can be shown.

23. Rigor Mortis. — Observe in a frog, just after decapitation, that
the muscles are soft and relaxed. Shortly after the tissues have com-
pletely lost their vitality, the muscles will be found to be hard and
contracted. The limbs which may have been bent at the joints and
limp, are now straight and rigid. Death rigor or rigor mortis has set
in. After some time, the muscles again become flaccid and putrefac-
tion soon begins. Place fresh muscle in hot water, and observe that

THE MUSCULAH SYSTEM 81

heat rigor is at once manifest. In both cases, the rigor is due to
coagulation of the muscle substance.

24. Minute Structure of Voluntary or Striped Muxcle. — With needles
tease out, in normal salt solution, on a glass, a small piece of skeletal
muscle of a frog or other animal. Mount and examine with the com-
pound microscope. It will be seen to be composed of elongate thread-
like bodies, tapering (when not broken) at the ends. Some fibers will
show cross markings.

25. The Minute Structure of Involuntary or Plain Muscle. — Tease
out, as in the foregoing, a small piece of the outer wall of the intestine
of a frog or cat. Here the fibers are seen to be spindle-shaped cells,
much shorter than the striped muscle fibers.

The fibers of both striped and plain muscle can be much more
easily teased apart if the tissue be kept in a 20 per cent solution of
nitric acid one to two days.

26. Cross Section of Muscle. Minute Structure. — If a prepared
cross section of a small skeletal muscle can be obtained, the internal
structure of a muscle can be very well shown by aid of the compound
microscope.

27. Minute Structure of Tendon and Ligament. — Carefully tease
out in normal salt solution, on a slide, a small piece of a thin tendon
from the tail of a mouse. To obtain the tendon, cut off the tail from
the body, and then pull out the delicate tendinous threads from the
cut end. The tendon should be mounted immediately after removal,
to avoid drying. A convenient method of mounting is to stretch the
tendon across a slide, through a drop of normal salt solution in the
center, allowing the ends of the tendon to adhere to the dry edges of
the slide. On examining with the compound microscope the tendon
is seen to be composed of wavy bundles of fibers. If the preparation
be treated with a one per cent solution of acetic acid, the fibers will
swell and disappear from view, but there will appear, between the
bundles, rows of spindle-shaped cells.

MACT'S PHYS

CHAPTER VI

THE SKIN AS AN ORGAN OF SENSATION — TOUCH

105. Functions of the Skin. — The whole body is covered
with a flexible, elastic membrane of complex structure,
which serves several different purposes. It envelops
and protects the inner, soft parts, and especially the ends
of the nerves. It is one of the three principal channels
by which the waste products of the body are removed
— that is, it is an organ of excretion. It regulates the
temperature of the body by controlling the loss of heat
through general radiation and evaporation, as well a§ by
the direct action of the sweat glands in excretion. A
small amount of respiration, or exchange of gases, also
goes on in the skin, and it contributes by its general char-
acteristics and its various modifications to the ornamen-
tation of the body.

106. Structure of the Skin. — The present chapter has to
do with the skin as one of the organs by means of which
the nervous system is brought into direct communication
with the external world, that is, as the seat of the sense
of touch and of certain other allied nervous impressions.

Two distinct layers are found in the skin, called the
epidermis, or cuticle, and the dermis, corium, or true skin
(Fig. 49). The epidermis is composed of epithelial tis-
sue, or epithelium, and its cells lie in layers one above
another, the outer or horny layer of cells being flat,

82

THE SKIN AS AN ORGAN OF SENSATION

83

dry, and unnucleated, or dead. The epidermis contains
no blood vessels, but in the deepest layers are found
minute terminations of some of the nerve fibers; and in
the same layers are the fine granules called pigment which
give color to the skin. This coloring matter is power-
fully affected by sun and wind, causing tan and freckles.

Sweat-Duct

Sebaceous Gland

Horny layer <
Pigment layer

Epidermii

Dermis

Fig. 49.— Diagram of section of the skin.

107. Hair and Nails are peculiarly developed forms of
the cuticle. Each hair is a long filament growing obliquely
from a little bulb called a papilla, lying in a hollow called
the hair follicle, which reaches down below the skin into
the areolar tissue beneath (Fig. 49). The part of a hair
buried in the skin is called its root; the remainder, the
stem, which tapers to a point. The stem is covered with
scales overlapping like the scales of a fish and project-
ing toward the point. When a hair is pulled out by the
root, a new one will grow again so long as the papilla is
uninjured. Each hair contains pigment granules which

84 CONSCIOUS NERVOUS OPERATIONS

give its color. There are also cavities filled with air.
These small bodies of inclosed air are very abundant in
white hair, and, reflecting the / light, are the cause of its
color, just as the whiteness of snow is due to the many
reflections of light from the tiny bits of ice which compose
it.

In the nails the horny layer of the epidermis is greatly
developed. Each nail has its root firmly embedded in a
groove of the cuticle. The under side is fixed to the der-
mis except at the end of the tinger or toe, where there is
a free edge.

The hair preserves the temperature of the head and
is also a protection against injury. The nails protect
the sensitive ends of fingers and toes and aid in their
mechanical operations. Both hair and nails also help in
the ornamentation of the body.

108. Mucous Membrane. — Not only is the whole outer
surface of the body covered with the skin, but all the
inner cavities and passages which have an external com-
munication are also lined with it. These inner linings
are, however, of a modified form of skin called mucous
membrane, because it secretes a viscous fluid, or mucus.
This membrane is thinner, redder, and more sensitive and
delicate than the outer skin, but is of the same general
composition ; that is, it has the two layers, the outer
bloodless and insensible, the inner highly sensitive, soft,
fully supplied with blood vessels, glands, etc.

109. The Dermis, or True Skin, is a close network of
connective tissue fibers, forming a dense, tough, firm
envelope for the body, resting upon and gradually pass-
ing into the areolar tissue beneath, which is a loose
network of interlacing bands and cords with meshes
between. Ramifying through the derm is are nerves,

THE SKIN AS AN ORGAN OF SENSATION 85

blood vessels, and lymphatic vessels, and it contains great
numbers of sweat glands and oil glands.

The epidermis, lacking blood vessels, does not bleed,
and the horny layer, lacking nerves, has no feeling; but so
fine are the networks of blood vessels and nerves in the
dermis that the finest needle cannot pass between them.
The whole surface of the dermis is thrown into innumer-
able projections called papillce, many of them supplied
with capillary blood vessels and nerve fibers.

110. Sensation. — When we become conscious of receiv-
ing an impression, — that is, when we perceive that some
part of our nervous system is stimulated, — we have what
is called sensation. It has already been shown that nerv-
ous stimulation may affect parts of the nervous system
and reflex action may follow without conscious reception
by the brain of any influence — that is, without sensation.

In order that there may be sensation there must be (1)
a stimulus, (2) a nervous end organ suited to receive the
stimulus, (3) a path to the brain for the impulse excited by
the stimulus, (4) a part of the brain to receive the impulse.
Still another condition of a different sort seems essential
to sensation, and that is an attitude of the mind which
we call attention. A person absorbed in thought may look
upon an object without being conscious of perceiving it,
may hear music without knowing it. That is, all the con-
ditions of sight and hearing may be present save the one
of attention, for which we have as yet no physiologically
descriptive terms.

111. General and Special Sensations. — There are various
vague, indefinable feelings which are not referred to any
particular portion of the body or to any external influence,
and which we know as general sensibility. Sensations of
fatigue, of restlessness, languor, weakness, and the like,

86 CONSCIOUS NERVOUS OPERATIONS

are of this sort. It is supposed that these are associated
with the ramifying, interlacing plexuses of nerve fibrils in
many parts of the body, and are not due to the excitation
of specially constructed nerve endings.

Other sensations are more definite. We judge them to
be caused by some influence acting upon particular parts
of the body. What have long been known as the five
senses are of this sort. But we now recognize, in addi-
tion to touch, taste, smell, sight, and hearing, other sensa-
tions apparently distinct from them, for which, in some
cases at least, special nerve endings are provided, and spe-
cial brain centers. These are sensations of temperature,
of pain, of hunger, and of thirst, and the muscular sensa-
tions previously mentioned (§ 95).

112. The Sense of Touch. — Touch has been defined as a
sense of pressure referred to the surface of the body. It is
that sort of impression upon the nervous system which
gives information respecting certain properties of bodies
in contact with the skin or mucous membrane. Through
it we learn whether an object is hard or soft, rough or
smooth, and other particulars, some of which are also given
by the sense of sight.

The skin is supplied with a variety of special adapta-
tions which constitute it the organ of touch.

113. The Nervous Apparatus for Touch. — The thirty-one
pairs of spinal nerves contain the fibers for feeling for
the larger part of the body, as well as most of the motor
nerve fibers supplying the muscles. It will be remem-
bered that each spinal nerve arises by two roots from the
spinal cord, one root containing afferent or sensory fibers,
the other efferent or motor fibers. By the union of the
two roots the nerve is formed, which thence contains both
sorts of nerve fibers, as do its large branches.

THE SKIN AS AN ORGAN OF SENSATION 87

114. In the neck, loins, and pelvis adjacent nerves
interlace with one another to form a plexus, or network.
In a plexus nerve fibers from two or more nerves are
brought into connection in such a way that the parts of
the body which receive nervous fibers from the plexus
have communication with a greater number of nerve trunks
and nerve centers, and may receive more complex im-
pulses, than do those parts to which branches go from
but a single nerve trunk. This is why these plexuses
are so frequently found in connection with the nerves
going to the limbs, where great complexity of motion and
careful coordination are required.

The nerves of the skin form plexuses in the dermis.
In some parts of the body these contain fibers from spinal
nerves and also from certain of the cranial nerves. From
these plexuses minute nerve fibers pass to the papillse,
which contain the tactile end organs.

115. Tactile End Organs. — End organs are those pecul-
iarly formed nerve cells or groups of cells which receive
and pass on the stimulus to which

they are adapted. Tactile end organs
are of several different forms.

Pacinian corpuscles are found deep
in the dermis, scattered along the fine
nerve branches like buds on a plant.
Each corpuscle consists of layers of
delicate membrane within which is a
single minute nerve fiber (Fig. 50).
Another form of end organ, called the
touch corpuscle, appears especially in FlS- 50. — Pacmian
the papillae of fingers and toes, and is
much smaller than the Pacinian corpuscle. The touch
corpuscles are oblong masses, each containing a capsule

88

CONSCIOUS NERVOUS OPERATIONS

.V

Fig. 51. — Touch
corpuscle in pa-
pilla of the skin
of the hand.

C touch corpuscle.

N nerve fibers
winding around
the corpuscle.

which receives a nerve whose fibers wind round and
round the capsule before entering it (Fig. 51). Still
smaller end bulbs are found in the skin,
made up of nerve fibers ending in corpus-
cles in which the axis cylinder of the nerve
terminates. All the tactile end organs are
covered by the epidermis, so that the nerves
themselves are not brought into actual
contact with the external thing which they
feel. If the cuticle were stripped off arid
pressure applied to a naked nerve end-
ing, there would be, not a sense of touch
with ability to judge of the properties of
the body causing the sensation, but in-
stead a sense of pain. Certain portions
of the skin are more fully supplied with
end organs for touch than are others, and the epidermis
there is thinner, so that the sense of touch is more deli-
cate. The tip of the tongue, the skin of the face, and
the ends of the fingers are most sensitive. A pair of
blunt-pointed compasses applied to the end of the tongue
will be distinguished as two points even when they are
separated by only one twenty-fourth of an inch, while
they would be felt as but one point on the finger ; and
on the arm or back of the hand the two points much
further apart would seem but one.

116. Sensations of Heat and Cold. — Sensations of touch
arise from pressure, but through the skin we have, besides,
sensations of heat and cold ; that is, we perceive changes
of temperature. It is thought that experiments indicate
in the skin a separate set of end organs stimulated by
heat, and another set which is stimulated by cold.

117. The Muscular Sense. — Still another sensation asso-

THE SKIN AS AN ORGAN OF SENSATION 89

elated with the sense of touch is that called the muscular
sense (§ 95). By means of this sense we judge of the
weight of a body. When we hold an object in the hand we
feel its pressure upon the skin, and we also are conscious
of a muscular effort to support its weight. We lift it up,
move it from place to place, and by the amount of effort
put forth judge of the weight of the object. In this pro-
cess the muscles are involved as well as the cutaneous
organs of sensation.

Again, we are conscious, even with our eyes closed, of
the position of the whole body. (This we shall find to be
connected with a certain part of the internal ear, § 179.)
We are also conscious of the position of different parts of
the body in relation to one another, and when we come in
contact with external objects we perceive not only the
pressure from them affecting our organs of touch, but
also the pressure which we exert by muscular contrac-
tion upon them ; that is, the resistance to our movements
which is exerted by external things. It is sometimes
said that we have a "sense of effort" (or weight), a
" sense of position," and a " sense of movement," but
all these are included in the more general term, muscu-
lar sense.

118. Pain. — It is not yet fully determined whether the
sensation which we call pain is due merely to excessive
stimulation of the already known sensory organs, or is a
distinct sensation. Sometimes there is disease of sensory
tracts which destroys sensitiveness to pain, though the
sense of touch is unaffected. It may be that the nerve
fibers already referred to, which, distributed everywhere
through the body, constantly convey to the brain impres-
sions of which we are usually hardly conscious, and which
we call impressions of general sensibility, are the channels

90

CONSCIOUS NERVOUS OPERATIONS

by which a sense of pain is conveyed when they are more

strongly stimulated.

119. Path of a Touch Impression. — Let a touch corpuscle

be stimulated by pressure, and what follows ? (Fig. 52.)

The cells of the end
organ communicate
the impulse to the
afferent nerve fibers
passing from the
touch corpuscles to
the nerve distributed
to that part of the
skin. The sensory
nerve fibers may run
through more than
one nerve plexus and
through ganglionic
nerve centers. There
may be several breaks
in the path, where
the original impulse
is handed over from
one fiber to another,
or passes from cell
to cell, or from fiber

Fig. 52. — Diagram of the path of a touch
impression.

The dotted lines show the path when the im-
pulse ascends to the brain, exciting conscious- to Cell ; but the
ness, and through the motor center (MC),
producing voluntary motion.

pulse finally reaches
the spinal cord (ex-
cept when a cranial nerve conveys the impulse), through
a posterior nerve root, and the cells of the gray matter of
the cord are stimulated.

But there is yet no sensation, even though by the reflex
action of the cord a motor impulse may be sent out by an

THE SKIN AS AN ORGAN OF SENSATION 91

anterior root and certain muscles may be made to contract.
The brain must be stimulated before there can be percep-
tion of a nervous impulse. Through the nerve fibers
which run from cells of the gray column into and up the
white columns of the spinal cord, the nervous impression
must be carried on till it affects the special nerve cells in
the particular portion of the brain set apart for receiving
the particular kind, of nervous stimulus from the particu-
lar part of the body. Then sensation results, and through
the influence of the will, carried along the efferent motor
fibers, motion may be produced in the voluntary muscles,
and a great variety of acts may take place in consequence
of the stimulation of the sensory organs in the skin.

DEMONSTRATIONS AND EXPERIMENTS

28. Simple Epithelium. — In connection with the subject of the
skin, the general structure of epithelium may be profitably illus-
trated. Where frogs are kept in captivity, excellent examples of
simple epithelium can be obtained from the moulted skins, for
examination with the microscope.

29. Ciliated Epithelium. — If the roof of a living frog's mouth be
scraped with a scalpel and the debris thus obtained be mounted in
normal salt solution on a slide, there can be found, on examination
with the microscope, many cells which show cilia moving actively.

30. Squamous Epithelium. — Scrape the inside of the cheek with a
scalpel, mount the debris in water on a slide, and examine with the
microscope. Irregular flattened plates can be distinguished, singly
or in groups. In most of them the position of the nucleus can be
discerned.

31 . Epithelium in Section. — If possible, some prepared microscopi-
cal sections of various kinds of epithelium should be studied by
the class. Sections of the wall of the digestive tract, of the trachea,
of blood vessels, etc., furnish excellent examples.

32. Section of the Skin. — Specially prepared sections of human skin
can be purchased. Usually such sections contain hair follicles, sweat
glands, and oil glands.

92 CONSCIOUS NERVOUS OPE NATIONS

33. The Epidermis. — Observe that with a needle a portion of the
outer skin may be removed without pain or flow of blood. If the
hands be washed in warm water and then dried, on rubbing them
together briskly, portions of the dead scaly epidermis will be removed.

On the palm of the hand the epidermis is seen to be thrown up in a
series of curved parallel ridges. The latter are caused by the projec-
tions of the papillae of the underlying dermis. On examination with
a lens, large numbers of the minute openings of the sweat glands may
be seen on the ridges of the epidermis.

34. Discrimination in Touch. — Find the least distance at which the
points of a pair of blunt-pointed compasses can be distinguished as
two points when applied to the skin of the arm. Repeat the same
experiment on the back of the hand, the forehead, the finger tips, and
the tip of the tongue. In this way a region of greatest sensitiveness
can be distinguished.

35. Location of Touch. — Ask a person to close his eyes, touch some
part of his body with a pencil, and ask him to indicate the same point
with another pencil, immediately afterward. He will probably make
some errors. The experiment may be made more interesting by repeat-
ing the trials, taking the measure of each error and averaging the
errors. By repeating this experiment on a number of persons, some
very interesting results may be obtained and tabulated.

36. Aristotle's Experiment. — Cross the middle over the index finger
so that the tip of the middle finger is on the thumb side of the index
finger. Place between the two a marble or other small object. A
sensation of two objects will result, especially if the fingers be moved.

37. Delicacy of Touch. — With small weights of pith or cork, find
the least pressure that is perceptible on the skin of the arm and tips
of fingers. The weights may be applied by lowering them upon the
skin by means of delicate silk fibers attached to them. The surface
which is applied to the skin should have the same area in all the
weights, and care should be taken that the weights do not move after
touching the skin. The person experimented upon should keep the
eyes closed while the weights are being applied. The weights should
also be applied to the forehead, temples, lips, and tongue. The main
purpose of this experiment is to determine the regions of the skin
most sensitive to contact.

38. Hairs as Organs of Touch. — If the weights used in the preced-
ing experiment be applied to regions of the skin possessing hairs, it

THE SKIN AS AN ORGAN OF SENSATION 93

will be found that a weight touching a hair may be felt, even though
its contact is not perceived when it is applied directly to the skin.

39. Estimation of Weight by Sense of Pressure. — Rest the back of the
hand upon some easy support, and place on the pal in a small wooden
or pasteboard disk. Upon the latter place different weights. Find
the least difference in weight that can be detected. A great variety
of weights can be obtained by loading empty cartridges with shot to
any desired extent. If the cartridges are all of the same size, then the
person experimented upon can not estimate the weight by sight. Sev-
eral pupils should be experimented upon, to show variation in acute-
ness of pressure sense.

40. The Muscular Sense. — Modify the preceding experiment by
having the weights lifted instead of simply allowing them to press on
the hand. It will be found that smaller differences can be detected
than by pressure alone. Demonstrate that a weight lifted slowly
seems heavier than one lifted rapidly.

41. Sensations of Heat and Cold. — That there are in the skin two
distinct varieties of nerve endings of the temperature sense can be
very easily demonstrated by carefully stimulating any certain area of
the skin with hot and cold bodies. Let a square be marked off with
ink, on the forearm, and a pointed brass rod be heated and then care-
fully drawn across this square in parallel lines in various directions.
Here and there a sensation of heat will appear distinct from the sensa-
tion of contact. The hot spots should be marked with ink dots, as
they are recognized. Then in a similar way go over the square with
a cold brass rod. Cold spots will occasionally appear, in almost every
case distinct from the hot spots. The cold spots should be marked in
ink of a different color from that of the hot spots.

CHAPTER VII

TASTE AND SMELL

120. The mucous membrane of the mouth contains the
nerve endings which are affected by taste stimuli. The spe-
cial taste organs are
found chiefly in the
papillce of the tongue
and the palate.

121. The Tongue is
a mass of striped
muscular tissue, with
fibers running in va-
rious directions,
the whole organ
being covered
with mucous mem-
brane (Fig. 53). The
papillce of the tongue
are much larger than
those of the cuticle
and are plainly visi-
ble to the naked eye.
In some animals, as
the dog and cat, they
are very prominent

Fig. 53.

JT filiform papilla4.

The tongue.

7 funjfiform papilla.

L circumvallate papilla.

and have horny spines

TASTE AND SMELL

95

Fig. 54. — Section of circumvallate
papilla.

which give a marked roughness to the surface. On the
front and sides of the tongue the papillae are generally
long and slender, and are
therefore called filiform
papillce. Others with
broad, spreading, mush- Taste B
room-shaped tops are scat-
tered among the filiform
papillae and are called fun-
giform papillce. A third
variety, the largest of all, is
the circumvallate papillce (Fig. 54). These last are only
eight or ten in number, and are seen at the back of a man's
tongue, in two rows converging to a point backward.

122. Taste Buds. — In the walls of the circumvallate and
in some, at least, of the fungiform papillae the end organs
for taste have been found. These
consist of a number of overlapping
epithelial cells, like the leaves of a
bud (Fig. 55). The innermost core
of the bud is a number of slender,
closely packed cells terminating in
fine, stiff spikes which project at the
surface of the bud. These are the

Jc Iff* 00 •

A isolated taste bud, from taste ce^s and are tne essential part
whose upper free end of the taste buds. Around these

project the ends of the ,, ., ,.,

taste cells. CQLls the nerve filaments from cer-

B supporting or protect- tajn branches of the ninth pair of

ing cell. ,0.1 7 7

C taste cell. cranial nerves (the glossopharyn-

geal) end in brushlike expansions.

Branches from the fifth cranial nerve (the triyeminaT)
are also distributed to the tongue, and are believed by
many physiologists to be concerned in taste.

Taste Cells

upporting
Cells

96 CONSCIOUS NERVOUS OPERATIONS

Taste buds are affected so as to distinguish different
tastes only when the substances submitted to them are in
solution. The effect is increased by friction between the
mouth and the tongue.

123. Classification of Tastes. — Tastes are of four sorts :
(1) sweets, which are best appreciated by the tip of the
tongue ; (2) sour, or acid tastes, perceived best by the side
of the tongue ; (3) bitter tastes, most affecting the back
of the tongue ; (4) salts.

It is believed that separate taste buds are provided, one
sort being stimulated only by bitter substances, one by
sweet, one by sour, and one by salt. Some substances
taste sweet at the tip of the tongue and bitter at the back
of it, because they are able to stimulate two sorts of taste
buds, but one kind of buds recognizes only a sweet taste,
the other only a bitter taste.

124. Flavors. — We are accustomed to say and to think
that we taste a great variety of flavors in our food ; but
physiologists tell us that we really taste only the four
flavors mentioned above, while others are recognized by
the sense of smell. This may be tested by holding the
nostrils closed by the fingers while different kinds of food
are eaten. An onion will not taste different from a potato,
though one would be known from the other by its texture.

125. The Sense of Smell. — The organ for receiving im-
pressions from the minute particles called odors is the mu-
cous membrane lining the upper part of the nasal cavity.

126. The Olfactory Nerves are the first pair of cranial
nerves. They spring from the olfactory lobes, which are
prolongations of the hemispheres of the brain (Fig. 19,
p. 29) and extend forward from the base of the cere-
brum. Branches of the nerves of smell are distributed
from the olfactory bulbs, in which the olfactory lobes end,

TASTE AND SMELL

97

to the mucous membrane of the nasal passages (Fig. 56),
where the fine filaments of the nerve end in delicate

rod - shaped cells
crowded in among
the columnar cells
of the epithelium
lining the nasal
passages (Fig. 57).

Fig. 56. - Section of nose, showing outer wall Flf • 57 ~ Cells from ol-

of right nasal cavity factory membrane,

a, 6, c, d interior of nose. -# epithelial cell.

K olfactory bulb, below which are seen the nerve W nerve cell,
fibers spreading out in the mucous membrane.

127. An Olfactory Impression. — Odors are usually car-
ried to the membrane of the nose by means of the atmos-
phere, but they must be dissolved or suspended in liquid
before they can affect the end organs for smell. Hence
the glands of the olfactory membrane lining the nasal
passages, whose secretions keep the surface always moist,
are important subsidiary organs. As the air is brought
to the membrane in ordinary breathing, one is able to
perceive various odors when moderately strong. By
what is called " sniffing " the air is drawn into the upper
as well as the lower nasal chambers, and more of the
MACY'S PHYS. — 7

98 CONSCIOUS NERVOUS OPERATIONS

odoriferous particles reach the olfactory cells. Thus
one is able to examine more fully the odors of the air,
and several different " smells " may be sometimes distin-
guishable at once. Usually the odors reach both nostrils
at the same time and two impulses are conducted along
the two olfactory nerves ; they are, however, fused into
one sensation. If different odors are brought at one
time to the olfactory cells of the two nasal passages, one
sensation sometimes destroys the other ; sometimes first
one and then the other odor is perceived ; in any case
there is but one sensation.

128. Other afferent impulses than those of smell may
arise in the nasal membrane. A very pungent substance,
such as ammonia, causes sensation distinct from smell,
sensation which is found to belong both to parts of the
nasal membrane on which the olfactory nerves ramify
and also to other portions.

A very small quantity of odoriferous material is suffi-
cient to excite the sensation of smell. A very minute
particle of musk, for instance, will fill a large room with
its odor, and that for an indefinitely long time.

The end organs of the olfactory neryes are soon ex-
hausted, and sensation dies out. We soon cease to notice
the odors in a room, though we may have thought them
overpowering on entering. Many animals are much more
liberally endowed with the power of detecting and discrim-
inating odors than is man.

129. Path of an Olfactory Impulse. — The olfactory cells
in the epithelium of the nasal passages send a process
to the surface of the mucous membrane, and another
inward (Fig. 57). The latter process of each cell ends
in fine spreading fibrils which mingle with similar brush-
like fibrils from a deeper layer of nerve cells in the olfac-

TASTE AND SMELL

99

tory lobe. These deeper cells send axis cylinder processes
up and along the olfactory tract to different centers in
the gray matter of the cerebrum.
These centers lie in the temporal
lobe, back of the eye (Fig. 58).

The olfactory nerves have a
path exceptionally direct from
their external or peripheral end
to the brain center in which
they rise. Just what is the
connection between this fact
and the other often observed
fact that stronger mental asso-
ciations cling about sensations
of smell than about almost any
other external impressions, it is
not easy to say.

Strong reflex nervous action
often results from excessive stimulation of the olfactory
nerves, as when a person faints in consequence of inhal-
ing certain odors.

130. Effects of Alcohol upon Taste and Smell. — The ha-
bitual use of drinks containing alcohol, of tobacco, and of
very strongly flavored foods is found to dull the sense of
taste, and by alcohol, at least, the olfactories are rendered
less acute.

Fig. 58. — Diagram of the path
of an olfactory impulse.

The impulse passes from the
olfactory cells of the nose to the
olfactory bulb (01. B} , and thence
to the olfactory center (01. G) on
the inner side of the temporal
lobe of the cerebrum.

DEMONSTRATIONS AND EXPERIMENTS

42. The Tongue. — By the aid of a hand mirror the pupil can
easily distinguish the filiform and fungiform papillae, on his own
tongue. The circumvallate papillae lie so far back that it will be
found more convenient to demonstrate them on the tongue of one of
the domestic animals (dead).

100 CONSCIOUS NERVOUS OPERATIONS

43. Varieties of Tastes. — Wipe the tongue dry and place on its
tip a crystal of sugar. It is not tasted until it dissolves. Place a
crystal of sugar on the tip and another on the back of the tongue.
The sweet taste is more evident at the tip. Repeat the process, using
a strong solution of quinine sulphate dissolved in water by aid of
a little sulphuric acid. The bitter taste is most pronounced on the
back of the tongue. In a similar way determine where acids and
salts are tasted, using a 1 per cent solution of acetic acid and a 10 per
cent solution of common salt respectively.

44. Organs of Smell. — The turbiuated processes of the human
ethmoid and maxillary bones, or those of some of the domestic
animals, should be accessible to the pupil for examination, as they
show how a great deal of surface in a small space is provided for the
olfactory membrane. The teacher should perform such dissections
upon the head of some one of the domestic animals as to show the
olfactory epithelium, the exterior nasal passages, and the posterior
passages opening into the pharynx.

45. Combination of Taste with Smell. — Close the nostrils, shut the
eyes, and try to distinguish by taste alone between an apple, a potato,
and an onion. Chew a grain of roasted coffee and notice how nearly
tasteless it becomes when the nostrils are closed.

46. Fatigue of Smell. — For several minutes smell continuously of
a piece of camphor gum, breathing in through the nose and out through
the mouth. The intensity of the smell becomes much lessened. But
if some other odoriferous substance, as clove oil, is brought near the
nostrils, it will be found that the fatigue is only for the odor of
camphor.

CHAPTER

THE EYE AND THE SENSE OF SIGHT

131. By means of touch, taste, and smell the brain per-
ceives external objects through actual contact between
particles of matter from the objects perceived and the
human organism. But we need to be able to acquire
knowledge of the properties of objects at a distance from
ourselves. The sense of smell does indeed bring to us
limited information respecting some classes of objects at
no great distance; but it is by means of the eye and the
ear that we gain our most valuable knowledge of the uni-
verse, and through these that we enjoy the most refined
and elevated of all our pleasures.

132. Vision. — When rays of light fall upon a nervous
apparatus so made as to be affected by that stimulus, and
the impulse is carried by a nerve to the nerve center for
vision, there results the sensation of sight. Some animals
possess a simple arrangement for vision, consisting of only
three parts. Certain modified parts of the epidermis are
stimulated by the light, nerve fibers carry the impulse to
the nerve center, and light is perceived. Man, however,
is provided with organs of vision of elaborate and com-
plex structure.

133. Light. — All space is believed to be filled with an
extremely thin, perfectly elastic medium called ether, in
which atoms, molecules, and masses of matter are immersed

101

102

CONSCIOUS NERVOUS OPERATIONS

as fishes are immersed in the sea. Of this ether little- is
known, but it is supposed to transmit energy by waves.
The energy resident in vibrations of the ether is called
radiant energy, and it receives special names according to
its special, manifestations. For example, when it raises the
: temperature of objects^ which receive it, it is called radiant
<heat<; -wiier* it <oauses -chemical changes, it is called actinic
energy; in another form it is known as electricity; when it
affects the eye we call it light. All these forms of energy
extend in straight lines from the points of origin. Every
visible object sets up waves in the ether going in every
possible direction. Many millions of these waves are pro-
duced in a single second.

134. Color. — Some light waves give to the eye the sensa-
tion of red color; these are the longest of the light waves
perceived by the eye. Others give us the perception
of violet color; they are the shortest. Between them in
length are the waves of all the other colors. A union of
these many colors produces white light.

135. The Spectrum. — When a slender beam of sunlight
is allowed to pass through a small hole, and then through

a glass prism into a
darkened room, the rays
of light falling upon a
screen are seen in an
oblong band of light of
many colors arranged as
we see them in the rain-
bow. This band of col-
Fig. 59. — Separation of the rays of a . _. .

beam of light by a prism. ors is called a spectrum

(Fig. 59).

136. Refraction. — The separation of colors by the prism
is due to two facts. First, whenever a ray of light passes

THE EYE AND THE SENSE OF SIGHT 103

obliquely from one medium into another of different den-
sity, its direction is changed, the ray is bent, or refracted,
we may say. In passing from the atmosphere through the
prism, the ray of light is twice turned from its original
direction. Second, different colors are refracted in differ-
ent degrees; red rays, or those having the longest waves,
are bent least; the violet rays, those having the shortest
waves, most of all; and the colors between vary in this
respect in the order of their arrangement in the rainbow.

137. Images formed by Lenses. — A lens is a transparent
medium, having at least one curved surface. Rays of light
from any point pass-
ing through a lens

are bent either toward
each other or more
widely apart, accord-
ing to the arrange-
ment of the surfaces
of the lens. When Fig. 60.— Diagram of the formation of an
they are bent toward hnase with a lens-

parh nfhpr thpv mav a an object sending off light.

ney ] nay b leng c image of the object a

be brought together

at a point called the focus. If the focus is allowed to fall
upon a screen or other suitable surface, an accurate image
of the object from which the rays come is produced
(Fig. 60). By using a properly prepared plate the pho-
tographer fixes this image and produces a permanent
picture.

138. The Nervous Apparatus for Vision may be briefly said
to consist of : (1) the membrane of the eye, called the
retina, which receives the end filaments of the optic nerve ;
(2) the optic nerve; and (3) the visual center in the brain,
which receives the stimulus conveyed by the optic nerve

104

CONSCIOUS NERVOUS OPERATIONS

and gives rise to the consciousness of sight (Fig. 61).

Nerve fibers are also distributed to the numerous muscles

of the various parts of the
eye and its accessories.

139. Nerves of the Eye. —
The second pair of cranial
nerves are the optic nerves
(Fig. 19, p. 29). The third
pair go to four of the mus-
cles which move the eyeball,
and are called the oculomotor
nerves. The fourth and sixth
pairs also supply muscles of
the eyeball. From the fifth
pair of nerves (the trigemi-
nal) are sent branches to the
lachrymal glands and the
eyelids.

140. Course of the Visual
Impulse ( Fig . 01). — Rays of

light falling upon the retina produce certain changes
(chemical or other) in or about the peculiarly shaped
nerve cells called rods and cones. These changes excite a
nervous impulse which is conducted by the minute nerve
fibers from the rods and cones (the end organs of vision)
along the optic nerves which, after passing through the
opening in the back of each eye socket, unite at what is
called the opfic commissure. Here many of the nerve
fibers cross, but some from each eye pass on to the nervous
center of the same side ; so that if the centers of vision on
one side were destroyed, there would still be sight in both
eyes. This crossing of the optic nerve fibers is called the
optic chiasma (Fig. 62).

Fig. 61 . — Diagram of path
of optic impulse.

Three courses are possible : (1) di-
rectly from cells of retina to the
visual center (OG") ; (2) through a
relay in the optic thalamus (T);
(3) through a relay in the anterior
corpora quadrigemina (Q).

THE EYE AND THE SENSE OF SIGHT

105

Fig. 62. — Diagram of optic

chiasraa.

Rays from 0, falling on the
similar regions of the retina
(D, D'), give rise to impulses
passing to the same half of
the brain.

Beyond the junction of the optic nerves the course of a
visual impulse is called the optic tract. Some of the fibers
run directly to the visual center o^
from the retina, others pass to vX,

the corpora quadrigemina and
other centers before reaching the
cortex. The gray matter of the
brain is regarded as the seat of
sense perception, and the sense
of sight is believed to be located
in certain groups of cells in the
hinder part of the cerebrum.

141. The Eye. — Something
more than the nervous apparatus
above described is needed to
enable one to perceive a definite

image of a distant object. Light falling upon the general
surface of a retina with its conducting nerves and nerve
centers would result only in perception of light and of
color. But in the eye, lying in front of the retina, are cer-
tain refracting media which act as lenses to converge the
rays of light so that only points of the retina are affected
by them ; that is, the rays are brought to a focus, and
an image of the object from which the rays come is pro-
duced as in a photographer's camera. The eye lies in a
pyramidal cavity, called the orbit, having its apex directed
inward and backward.

142. The Coats of the Eye. — The eye is a nearly spherical
sac about one inch in diameter, made up of a firm wall of
tissues called the coats of the eye (Fig. 63). The outer of
these, composed of connective tissues, is opaque except at
the center of the front of the eye, where it becomes trans-
parent and is called the cornea; the remainder of this

106 CONSCIOUS NERVOUS OPERATIONS

outer coat is called the sclerotic coat, and forms the " white
of the eye." At the back of the eyeball the optic nerve
pierces through this coat to reach the retina. Both the
cornea and the sclerotic coat on the front of the ball are
covered with a thin layer of modified mucous membrane,
called the conjunctiva, which is folded back to form the
lining of the eyelids.

Sc

Fig. 63. —Cross section of the eye.

Sc sclerotic coat. Ch choroid. 0 optic nerve.

C cornea. / iris. B blind spot.

con conjunctiva. H retina. 1' yellow spot.

L lens. A anterior chamber, filled with aqueous humor.

V posterior chamber, filled with vitreous humor.

A second coat of the eyeball consists of the choroid,
made up largely of blood vessels and loose connective tis-
sue, and containing in the inner layers a dark pigment.
Just before it passes into the iris — which is that part
of the choroid forming the colored ring in the front of
the eyeball, pierced by the pupil — the choroid is laid

THE EYE AND THE SENSE OF SIGHT

107

in radiating folds called the ciliary processes, which are
also covered by the pigment.

143. The iris is a ring of plain, or involuntary, mus-
cular tissue. Its circular fibers by contracting narrow
the pupil, while its radi-
ating muscular or elastic

fibers by their contrac-
tion dilate the pupil
when the circular muscle
is relaxed. Fibers from
the third cranial nerve
are distributed to the
circular muscle, and oth-
ers from the sympa-
thetic nervous system
are also found in this
muscle of the iris. The
pigment of the iris gives
what we call the " color
of the eye." The pupil
is simply an opening
through the iris into the
dark chamber beyond.

144. The Retina.— The
third of the coats of the
eye is the retina. This
is composed essentially
of the end fibers of the
optic nerve and nerve

cells, which, with a supporting skeleton of connective tis-
sues, form a thin membrane lying loosely upon the choroid
and covering it as far as the ciliary processes. The retina
is too complex to admit of full description here. Though

Fig. 64. — Section of the retina.

A diagram of the structure of the retina
as seen with the compound microscope.

B the essential nervous elements of the
retina as demonstrated by the Golgi
method.

1 internal limiting membrane.

2 nerve-fiber layer.

3 nerve-cell or ganglion-cell layer.-

4 inner molecular layer.

5 inner granular layer.

6 outer molecular layer.

7 outer granular layer.

8 external limiting membrane.

9 rod-and-cone layer.
10 pigment-cell layer.

108

CONSCIOUS NERVOUS OPERATIONS

Direction of Light through Retina

only about one fiftieth of an inch in thickness at the point
opposite the pupil, where it is thickest, it consists of ten
different layers (Fig. 64). Beginning with the side toward
the center of the eyeball, the first layer, called the internal
limiting membrane, is in contact with the vitreous humor
which fills the largest cavity of the eye (§ 146), while the
tenth, or pigment-cell layer, is next the choroid.

In the second layer, that of the optic nerve fibers, the
minute filaments of the optic nerve are distributed. From
this second layer they turn backward to enter the deeper
layers of the retina.

The third layer is that of ganglion cells. They are

large nucleated cells,
whose axis cylinder
processes are con-
tinuous with the
optic nerve fibers
of the second layer.
In the ninth layer
are found nerve cells
of peculiar shapes,
called rods and cones.
There are more rods
than cones, three or
four .rods usually
lying between two
cones. It is under-
stood that in these cells arises the nervous impulse which
results in vision.

From the pigment-cell layer extends a thick fringe to
support the outer ends of the rods. Many of the rays of
light which fall upon the retina are absorbed by the pig-
ment, only a small part of the rays being reflected back

Direction of Optic Impulse
To Brain

Opti<rNerve

Fig. 65. — Diagram of a section of the retina.

Showing that the rays pass from the anterior
to the posterior parts of the retina to reach the
rods and cones. From the latter the optic im-
pulse passes to the anterior parts of the retina,
and thence by the optic nerve fibers through the
posterior parts to the brain.

THE EYE AND THE SENSE OF SIGHT 109

through the pupil. Hence the interior of the eye usually
looks black.

145. The Yellow Spot and the Blind Spot (Fig. 63). — The
retina is not equally sensitive to light over its whole
surface. Only upon a single spot, about one twenty-
fourth of an inch in diameter, are perfectly definite out-
lines of images formed. This is called, from its color,
the yellow spot.

About one tenth of an inch from the inner side of the
yellow spot is the optic disk, or blind spot, an elevated
surface where the optic nerve fibers enter the eye. These
are conducting nerve fibers only, not stimulated by light,
and that spot is therefore blind.

Delicate fibers from the optic nerve run straight to the
yellow spot. Here the layer of ganglion cells is much
thicker than elsewhere, and in the rod-and-cone layer of
the yellow spot no rods, but cones only, are found.

In the very center of the yellow spot is a colorless
depression, or pit, from which the various layers of the
retina have nearly disappeared, leaving only the rod and
cone layer. This is the point of most acute vision, the
spot upon which the image falls when, wishing to see with
the utmost distinctness, we look " straight at " an object.

146. The Lenses (Fig. 63). — The refracting media of the
eye are four in number. (1) The cornea has already been
defined. (2) The crystalline lens is a transparent, double-
convex body about one third of an inch in diameter and
one fourth of an inch thick, lying just back of the pupil
and kept in place by a sheet of transparent membrane
called the suspensory ligament attached to the circum-
ference of the lens and to the ciliary processes. (3) The
space between the iris and the cornea, called the anterior
chamber, is filled with a thin fluid like water, called the

110 CONSCIOUS NERVOUS OPERATIONS

aqueous humor. (4) The larger cavity of the eyeball,
behind the iris and the crystalline lens, called the posterior
chamber, is filled with a transparent, semifluid, jellylike
substance called the vitreous humor.

147. The Muscles of the Eyeball and their Nervous Supply
(Fig. 66). — Each eye is moved by six muscles, four of

which are straight and two ob-
lique. The straight, or rectus,
muscles have one end attached
to the margin of the opening in
the orbit through which the
optic nerve and accompanying
blood vessels pass, while the
Fig. 66. -Muscles of the other js inserted into the eye-
ball. The internal rectus muscle,

inserted on the nasal side of the eyeball, turns the ball
inward ; the external rectus, inserted on the outer or tem-
poral side, turns it outward. The superior rectus, inserted
on the upper and forward side, pulls the eye upward ; the
inferior rectus, inserted on the under and forward part of
the ball, draws it down.

The remaining muscles are called the superior and the
inferior oblique, and they unite with the straight muscles
to move the eyeballs inward and upward, inward and
downward, outward and upward, outward and downward,
and to produce a measure of rotation upon an axis. The
superior oblique muscle arises near the straight muscles in
the edge of .the orbit. Near its forward end it narrows
into a tendon which passes through a ring of fibrocartilage
attached to a notch in the frontal bone which bounds the
front and upper margin of the orbit ; the end of the tendon
is then inserted into the upper side of the eyeball. The
cartilage ring acts as a pulley to change the direction of

THE EYE AND THE SENSE OF SIGHT 111

the muscular action. The inferior oblique muscle arises
near the front of the orbit and at its inner side, whence it
passes under the ball and nearly halfway round it, to be
inserted into the back part on the temporal or outer side.

148. The muscles of the two eyes act simultaneously
so that the two retinas may receive images from the same
objects at the same time and upon corresponding portions
of their surfaces. The external rectus of the right eye
contracts at the same time as the internal rectus of the left
eye, turning both eyes to the right, and vice versa. All
these muscles are supplied with nerves from the third pair
of cranial nerves, except the superior oblique, which is
supplied by the fourth, and the external rectus, which is
supplied by the sixth.

149. The Ciliary Muscles and Nerves. — Besides the mus-
cles which move the eyeball as a whole, certain muscles
within the eyeball have to do with vision. These are the
muscles of the iris, which vary the area of the pupil, and
the ciliary muscles, which accommodate the eye for differ-
ent distances by altering the shape of the lens, as will be
explained a little later. The ciliary nerves supply these
muscles. They are composed of fibers from the third and
fifth cranial nerves with others from the sympathetic sys-
tem. Branches from the ciliary nerves are distributed
also to the cornea.

150. Other Appendages of the Eye ( Fig. 67). — Each
eyeball lies in its orbit upon a soft cushion of fat, and the
cavity also contains connective tissue, blood vessels, and
nerves. The front of the eye is protected by the eyelids,
which are two folds of skin stiffened by thin plates of
fibrous tissue. Along the edges of the lids arise rows of
curved hairs, called eyelashes, which serve to protect the
eye from dust, and furnish a slight shade. On the inner

112

CONSCIOUS NKK'Ynrs n]>K|{ ATK'NS

edges, in little grooves, are minute glands from which an
oily secretion flows to the free edges of the lids and

prevents their adhesion
when closed. Above
the orbits the thick
ridges set with hairs,
called eyebrows, also
serve to shield and
shade the eye.

In a depression in the
upper and outer part of
the orbit lies the lach-
rymal gland, with ducts
opening on the inner
surface of the upper
lid. It secretes a wa-
tery fluid designed to
lubricate the surface of
the eyeball. When stimulated by the irritation of the
mucous membrane of the eye, the nose, or the mouth, or
by strong mental emotion, the lachrymal fluid becomes
excessive, and is called tears. Canals or ducts placed at
the inner angle of the eye carry off the ordinary supply
of lachrymal fluid to the nasal passages. Branches from
the fifth (trigeminal) cranial nerve supply this gland and
send fibers also to the eyelids and to inner portions of the
eyeball.

151. The Eye as an Optical Instrument. — As has been
said, the eye is like a photographer's camera obscura, the
various parts of which all have to do with the produc-
tion of distinct images of external objects upon the back
portion of the box ; that is, in the camera upon the ground
glass screen, in the eye upon the nervous membrane called

Fig. 67. —Front view of the right eye,
showing the position of the lachrymal
apparatus.

G lachrymal gland.

CC upper and lower lachrymal ducts.

B naso-lachrymal duct.

THE EYE AND THE SENSE OF SIGHT

113

the retina (Fig. 68). In the camera a glass lens serves
to bring the rays of light to a focus upon the screen. In

Jig. 68.— Formation of an image on the retina.

the eye the cornea and the crystalline lens accomplish the
same object.

152. Accommodation (Fig. 69). — The camera is pro-
vided with an apparatus for changing the distance of the
lens from the sensitive plate or screen, so that light from
objects at different distances may be
focused. The eye is likewise supplied by
means of what is called accommodation,
which is the power of the eye to adjust
itself to objects at different distances.
This power is due primarily to the varia
ble shape of the crystalline lens. In the
camera, the lens and the screen which
receives the image are moved nearer to-
gether or farther apart in order to change
the focus. In the eye the same object is
gained by changing the convexity of the
lens itself. This is accomplished by the
contraction and relaxation of the ciliary muscle, which lies
just beyond the outer margin of the iris in the front part
IOCY'S PHYS. — 8

Fig. 69. — Dia-
gram show-
ing how the
lens changes
its form.

114 CONSCIOUS NERVOUS OPERATIONS

of the clioroid coat. It consists of plain muscle fibers,
whose nervous supply comes from the third cranial nerve.
The ciliary muscle is attached to the ciliary processes, and
these to a membrane called the suspensory ligament.
This ligament is secured also to the circumference of the
lens in such a way that when the eye is at rest it is in a
state of tension, which causes it to pull upon and slightly
flatten the lens. This keeps the eye at the focus neces-
sary for seeing clearly objects at a distance of perhaps
twenty or twenty-five feet. When the eye is directed to
a nearer object, the fibers of the ciliary muscle contract,
thereby drawing forward the ciliary processes, and thus
lessening the tension on the suspensory ligament, and the
elasticity of the lens causes it to push forward, or become
more convex on its front surface. This shortens the focal
distance, that is, causes the rays of light to converge more
rapidly. The cornea alone is capable of forming distinct
images, and the chief function of the crystalline lens seems
to be that of accommodation.

153. Function of the Iris. — The iris (Fig. 63) is an adjust-
able curtain, designed, by narrowing the pupil, to cut off
a portion of the light which might render the image con-
fused, and to prevent too strong a light from entering the
interior of the eye. This change in the size of the pupil
is effected by the contraction and relaxation of its mus-
cular tissue, under control of the ciliary nerves.

154. Inversion of Images (Figs. 60 and 68). — As in a
camera, so in the eye the image formed is inverted. The
rays of light cross in being brought to a focus, so that
the picture of a man, a house, or a tree on the retina is
upside down, and also much smaller than the object itself.
The reason why we do not see objects inverted and re-
duced in size is because it is not the picture on the retina

THE EYE AND THE SENSE OF SIGHT 115

that we see, but the object itself. Sensation is not in the
eye, but in the brain, or in the mind acting through the
brain. It is only by study and research that we learn
the fact of the inverted image in the eye, and meantime
we are accustomed to supplement our visual impressions
by the use of our muscles and our organs of touch. The
hand interprets the impression on the eye, and we learn
to see objects in their true positions. We judge of their
positions by the direction from which the light comes to the
eye, and of their size by a variety of experiences which
complete the impression given by sight. The figure on
the retina has little or nothing to do with those judgments.

155. Seeing with Two Eyes. — Two images of one object
are formed on the two retinas, and two optic nerves and
tracts convey the impression 'to the two opposite sides of
the brain. Why, then, do we not see two objects ? Here
again we must remember that our perceptions are never
simple, due to the action of a single organ and an isolated
set of nervous connections. Probably in every act of
perception the nervous system acts as a whole through
the intricate interlacing of nervous fibers and the close
connections of the cells in the various nerve centers. An
impression upon one set of end organs is supplemented
and corrected by a great number of familiar perceptions
of diverse sorts brought before the mind by memory, so
that the resulting judgment is an act too intricate and
complex to be disentangled. We come to think of the
object as we know it from all these combined impressions,
and not from a single one of them. Perception is the
result of association and experience combined with the
physical processes involved.

156. Advantages of Two Eyes. — For perfect vision the
retinal images must be formed upon corresponding portions

116 CONSCIOUS NERVOUS OPERATIONS

of the two retinas. The two pictures are not, however,
identical. The right eye will see more of one side of an
object than will the left, and the left eye will see more of
the opposite side. This enables us to form more accurate
judgments of form and distance than would be possible
with only one eye. Then, too, one eye may be wholly
destroyed and a person may still retain distinct vision.

157. Duration of Sight Sensation. — The impression made
upon the retina by a flash of light remains for about one
eighth of a second, so that if flashes of light follow one
another at a shorter interval than that they appear as
one continuous impression. Children make a circle of
fire by whirling rapidly a lighted stick, and the spokes of
a swiftly revolving wheel appear continuous. If one looks
at the sun or other bright object and then closes the eyes,
he will continue for an instant to see the object. These
delusive appearances are due to the fact that the nervous
impressions made by light upon the end organs in the ret-
ina remain after the removal of the rays which excite them.

158. Fatigue of the Retina. — While the retina is extremely
sensitive it is also easily fatigued. If one looks steadily
for a time at a bright object and then turns the eye away,
he will still see the outline of the bright object, but it will
be dark. This is because that part of the retina upon
which the light fell from the bright body has become wea-
ried and no longer responds to the stimulus of light. If
the body looked at is of a bright yellow color, the figure
seen when the eye is turned away will be blue, because
the retina is no longer able to respond to the stimulus of
yellow rays, but is affected by the rays of the complemen-
tary color.

159. Defects of Vision. — It is very common to see per-
sons wearing lenses, or " glasses," to correct what is called

THE EYE AND THE SENSE OF SIGHT 117

a shortsightedness," or "longsightedness." In short-
sighted persons the rays which in normal eyes come to a
focus exactly upon the retina meet at a point in front of
it, so that no distinct image is formed. The eye is too
long from front to back, and the difficulty must be cor-
rected by using lenses which will carry the focus back to
the surface of the retina (Fig. 70).

Fig. 70. — Diagram showing position of retina.
In natural sight (5). In far sight (£). In near sight (C7).

Those who habitually use their eyes for seeing only
objects near at hand are apt to become shortsighted. It
has been found that children who have grown up in
crowded parts of smoky London, with little opportunity
for looking off long distances, are very often nearsighted.
On the other hand, sailors and others accustomed to use
the eye constantly for distant vision grow longsighted.
Their eyes become shortened from front to back, so that
the focus for ordinary vision is beyond the retina.

As persons grow old the eye usually becomes flattened
on this axis, and glasses are needed to converge the rays
of light more rapidly.

160. Squinting, etc. — The muscles of the two eyes act
simultaneously so that the visual images are formed upon
corresponding parts of the two retinas. But if the internal
rectus muscle of one eye is paralyzed, or for some reason

118 CONSCIOUS NERVOUS OPERATIONS

the external rectus is too short, that eye will turn outward
and defective vision will result. If the external rectus is
paralyzed, the person will be cross-eyed, or squint-eyed.
Paralysis of either of the nerves distributed to the muscles
of the eye will result in abnormal action of those muscles.

161. Astigmatism. — Another defect, known as astigma-
tism, is due to the irregular curvature of the cornea or the
lens or both. The eye may be more convex on one merid-
ian than on others, so that rays of light falling upon one
part of the cornea (which is most frequently affected) are
brought to a focus at a different spot from the rays which
pass through other parts. Thus the image on the retina
is indistinct and the vision is blurred.

162. Color Blindness. — Some persons are unable to dis-
tinguish certain colors from certain other colors. They
are said to be color blind. Usually they differ from
persons of normal sight in their inability to distinguish
red from green. Sometimes only one eye is color blind,
the other being normal. The reasons for these phenom-
ena belong to the abstruse subject of color sensation,
which is beyond the scope of this work.

The power to distinguish colors accurately is of great
importance to those engaged in certain occupations, — for
example, to those employed upon railways, who are re-
quired to undergo examinations which test their eyes in
that particular.

163. Training of the Eye. — The eyes of the young may
be easily trained by practice under a teacher's guidance
to see quickly and accurately, and to judge correctly as to
the size of objects, distances, etc. Such training is of
great value in all circumstances of life. It is indeed
more strictly a training of the mind than of the eye,
but niay be fitly mentioned in this connection.

THE EYE AND THE SENSE OF SIGHT 119

164. Care of the Eye. — More than some other organs,
the eye depends for its healthy condition upon the gen-
eral health of the system. If that is impaired, the eye
is often weakened and liable to disease. The children of
the poor, who are ill-nourished and inadequately clothed,
oftener suffer from sore eyes and defective vision than
do those in better circumstances. Living in filthy sur-
roundings or rubbing the eyes with dirty hands often
provokes diseases of the eyes and eyelids. Some forms of
general disease — measles, diphtheria, scarlet fever, for ex-
ample— are apt to leave the eyes for some time in a
sensitive condition and in need of special care. Many
eyes, even those of young children, are abnormal in re-
spect to focalization, and the defect is often unsuspected
until a child has endured much inconvenience or even
suffering. Hence it is well for the eyes of every child
to be examined by a competent oculist, and to have any
defects corrected by suitable glasses. Children in school
often suffer from severe headaches and appear dull at
their studies simply because of easily remedied defects of
vision.

165. Very strong light should never be allowed to enter
the eye directly. When reading, sewing, writing, etc.,
one should sit so that the light will fall upon the work
from the left side without shining into the eyes. But
one should not read or write with direct sunlight falling
upon the paper. Lamps should be provided with shades
to shield the eyes, and the light should be steady, for a
flickering light is exceedingly trying to the eye.

Too faint a light also strains the eye. One should not
read or work by twilight, or by any light too dim to per-
mit the book or work to be clearly seen at about eighteen
inches from the eyes. Eyes may be made nearsighted

120 CONSCIOUS NERVOUS OPERATIONS

by carelessly acquiring a habit of holding books, etc.,
nearer than is necessary.

Reading while in a moving railway train or carriage
is bad for the eyes, as the motion necessitates constant
adjustment of the eyes to varying distance, and the power
of accommodation is overstrained.

It is well when using the eyes closely to raise them
often and look off to a distance, or to close them for a
moment of rest.

Warm or tepid water is better than cold water for bath-
ing the eyes. A compress wet in very hot water and laid
over the eyes a few minutes at a time, several times a day,
will cure slight inflammation, or relieve the weariness of
the eyes after close application.

166. Effects of Drinks containing Alcohol upon the Eye. —
Through its influence upon the nerves and the muscles,
the continued and too free use of alcohol renders the eye
unsteady and its adjustment uncertain ; the small blood
vessels become dilated, and the eyes are blood-shot and
often inflamed. The optic nerve is frequently affected,
causing dimness of vision, and specific diseases of parts
of the eye may result, such as cataract and disorders of
the retina. The confirmed inebriate is the victim of dis-
eased conditions in which the sight becomes untrust-
worthy. He sees horrible visions, frightful, venomous
creatures appear to threaten him, and he is haunted by
specters. Under his imaginary suffering he may become
a raving maniac, and repeated attacks of the disease are
likely to prove fatal.

DEMONSTRATIONS AND EXPERIMENTS

47. Dissection of the Eye. — The eye of the sheep or of the ox
should be studied. It may be examined fresh or after preservation

THE EYE AND THE SENSE OF SIGHT 121

in one of the fluids used in hardening and preserving the brain
(Ex. 6). First, the six muscles of the eyeball should be noticed and
identified. To examine the internal structures an equatorial incision
should be made about halfway between the cornea and the back part
of the eyeball, thus dividing the eye into two parts. The structures
thus made visible can be identified by reference to the corresponding
parts of the text. If the teacher has any knowledge of histological
methods, some excellent sections for study with the microscope can
be prepared by hardening the eye of a rat or frog in Perenyi's fluid
for two or three days, following with alcohols of increasing strength,
infiltrating and embedding in celloidin, and sectioning on a micro-
tome. Sections made horizontally through the entire eyeball, and
properly stained, show not only the different coats and inclosed
structures in situ, but the different layers of the retina, the entrance
of the optic nerve, or blind spot, and the yellow spot. Similar sec-
tions can be purchased.

48. Refract 'ng Media. — Refraction of light should be demonstrated
by means of lenses of various forms. Especial attention should be
given to the formation of images by convex lenses. The office of
the lens of the eye can be shown by removing it from the eye of a
recently killed animal and allowing the direct rays of the sun to be
focused by it.

49. Inversion of the Image on the Retina. — This can be very easily
shown by cutting away the posterior part of the sclerotic coat of a
fresh ox eye, leaving the retina intact. Then on turning the cornea
toward some bright object, as a candle flame, an inverted image
of the object may be seen shining through the retina. The image
appears much clearer if the eye is placed, cornea forward, in a tube
of blackened paper.

50. Model for demonstrating the Optical Properties of the Eye. — At
little labor and expense the teacher or pupil can construct simple appa-
ratus that will illustrate many of the optical features of the eye. Pre-
pare an oblong box from twelve to eighteen inches long, open on one
side, and blackened within (Fig. 71). One end should be perforated in
the center by an opening one half to one inch in diameter, to represent
the pupil of the eye. A watch crystal can be fastened over the open-
ing, outside, to represent the cornea. The amount of light admitted
through the opening in the box can be regulated by means of paper
diaphragms with different-sized perforations. Inside the box a reading

122

CONSCIOUS NERVOUS OPERATIONS

glass or other biconvex lens can be arranged on a support, so as to focus
the rays of light admitted through the pupil upon a movable screen at
the back part of the box. A serviceable ground glass screen can be made
by rubbing a piece of ordinary window glass with emery powder and
water. The box is left open on one side to permit observation and
manipulation ; but while experimenting the observer will find it neces-
sary to exclude all light, except that which enters through the end of
the box. This can be done by covering the box and the head of the ob-
server with a black cloth. While with this apparatus one can illustrate

Diap
\

ragm (Ir
J

/s
>•>

V

i Screen (Retina)
i»

Fig. 71. — Apparatus for illustrating the optical properties of the eye.

most of the characteristic optical features of the eye, yet obviously it
shows nothing regarding the functions of the aqueous and vitreous
humors. It must be borne in mind, also, that in the eye accommo-
dation for objects of different distances is brought about by changes
in the form of the lens ; here in the model by changes in the position
of the lens. Shortsightedness and longsightedness can be very easily
illustrated ; also the means of correcting them by spectacles. Astig-
matism can also be shown by holding in front of the artificial cornea
a bottle with sides of unequal curvature, filled with water.

51. Accommodation. — Hold up the forefinger six or eight inches
from the eye. Close one eye and look at the finger ; it appears dis-
tinct, while objects across the room seem blurred. Look at these
latter ; they become sharply outlined, but the outline of the finger
becomes indistinct. Notice that in accommodating for the near
object there is a feeling of effort. Cease looking at anything in par-
ticular, and allow the eyes to come to rest. They will be found to be
accommodated for distant vision.

52. Ask a person to accommodate his eye for distant objects. Then
look at his eye from the side, while he adapts his vision to a near

THE EYE AND THE SENSE OF SIGHT

123

object without moving the eyeball; the pupil and iris next the
observer will be seen to move forward, owing to the increased curva-
ture of the anterior surface of the lens.

53. Movements of the Iris. — In the preceding experiment the diame-
ter of the pupil was smaller when the eye was accommodated for near
objects, but dilated on changing to distant vision. Close one eye,
and by aid of a mirror observe the size of the pupil of the other eye.
Then open the closed eye ; the pupil of the othar eye contracts. Cover,
with the hands, another person's eyes. On suddenly removing the
hands, the pupils are seen to contract.

54. Astigmatism. — Close one eye and look at the radiating lines in
Fig. 72. Notice which lines, if any, appear with the greatest black-
ness and distinctness. Try the other eye ; do the two eyes agree ? Look
at the concentric circles of Fig. 72. In what portion of the figure, if

Fig. 72.

any, do the lines appear clearest ? The teacher should obtain, from
an optician, one of the charts commonly used in preliminary tests for
astigmatism. With this he can detect some of the more pronounced
cases of this optical defect among his pupils. It may happen, how-
ever, that very great defects cause little disturbance, since if the two
eyes are astigmatic on different axes, one eye may correct the defect
of the other.

55. Near sight and Farsight. — These are common defects, and
their causes should be illustrated by use of the apparatus described
in Ex. 50. If the teacher will perform some of the simpler tests
for optical defects of the eye (and almost any local optician will loan
the necessary apparatus, and give instructions), he may not only inter-

124 CONSCIOUS NERVOUS OPERATIONS

est and instruct his pupils, but confer lasting benefits upon some of
them in showing them their defects, and the means of correcting
them.

56. The Blind Spot. — Close the left eye and with the right look
intently at the cross in the following diagram (Fig. 73), holding the
book about fifteen inches in front of the eye. Both cross and circle

Fig. 73. — Diagram to demonstrate the existence of the blind spot.

are seen. Gradually bring the book nearer the eye; at a certain
distance the circle disappears because its image falls upon the
entrance of the optic nerve. Bring the book still nearer; the circle
reappears.

57. Field of Acute Vision. — Look at a printed page without moving
the eyes and observe how few words can be seen distinctly. The
diameter of this field of distinct view will probably be found to be
about one and one-half inches. Wherever the image of an object
falls outside the yellow spot, it is seen indistinctly.

58. Binocular Vision. — Hold before each eye a blackened tube of
pasteboard. Two distinct fields will be seen on looking through the
tubes. Cause the tubes to converge at their free ends, and the two
fields will finally fuse into one. This position of the two tubes repre-
sents approximately the normal convergence of the two optical axes.
Converge the tubes still more ; the two fields reappear, but they are
crossed. Look through the tubes at near and at far objects. It will
be found that, in order to have a single field of vision, the tubes must
be converged more for the near objects.

59. Close one eye, and, looking steadily ahead, note how much is
comprised in the field of view. On opening the eye the field is con-
siderably enlarged.

60. Holding the forefinger six or eight inches in front of the nose,
look at a distant object, as a tree. The forefinger appears double.
Now accommodate the eyes for the finger; the tree appears double.
An explanation of this can be deduced from Ex. 58.

61. Movements of the Eye. — Close one eye, and, holding the finger
tip on the lid, feel the movements of that eye as the other eye looks
about in various directions.

THE EYE AND THE SENSE OF SIGHT 125

62. Duration of Sight Sensations. — Cause a small wheel to revolve
rapidly ; the spokes no longer appear distinct, but seem to be thinned
out and fused together into a semitrausparent membrane. Spin a
top composed of an angular piece of card fastened to a suitable axis.
It appears circular instead of angular.

63. Look at a bright light for a moment. Then close the eyes;
the image persists for a short time.

64. Fatigue of the Retina. After Images. — Look steadily, for one or
two minutes, at a window, and then at a plain light-colored wall. An
image in which the light parts of the window are dark and the dark
parts are light will now be seen.

65. Complementary Colors. — Look steadily at a piece of red paper
and then at a light background ; a light green after image will be
seen. Repeat, using different colored papers. From dealers in kin-
dergarten supplies can be obtained packages of colored papers suitable
for this and other experiments on color.

66. Color Blindness. — The teacher frequently finds pupils unable to
name colors correctly. This may be due to color blindness, but in
most cases is caused by defective training. To make any accurate
tests of color blindness, the teacher should procure a set of Holm-
gren's test worsteds (price $2.50) and directions for experimenting.

CHAPTER IX

THE EAR AND THE SENSE OF HEARING

167. The ear is the mechanism by which we hear. It
has three main divisions, called the external, the middle,
and the internal ear (Fig. 74).

Endolymphatie
Duct

,'Saccule
'

"estibular Passage
^Tympanic Passage
Eustachian Tube Fenestra Rotunda

Fig. 74. — Diagram of the ear, showing relationship of its parts.

168. The External Ear. — The parts of the external ear
are formed to collect and conduct waves of sound to the
inner portions of the auditory apparatus. They are the
pinna, the external meatus, and the membrane of the tympa-
num. The pinna is a sheet of elastic cartilage covered
with skin, so folded as to direct the waves of sound
through the cartilaginous tube of the meatus, which is
continuous with it, to the membrane of the tympanum, or
eardrum, which closes the end of the passage. Along

126

THE EAR AND THE SENSE OF HEARING 127

the tube of the meatus are placed the wax glands with
their ducts.

169. The Middle Ear, or Tympanum, is an irregular cavity
in the temporal bone, lined with mucous membrane which
is supplied with small glands. By means of the Eusta-
chian tube, which passes from the lower back part to the
pharynx, or upper cavity of the throat, the tympanum
communicates with the external air, and so equalizes the
pressure upon the two sides of the membrane of the tym-
panum which separates the middle from the external ear.

Opposite the membrane of the tympanum are two
smaller openings into the chamber of the inner ear, called
the round window (fenestra
rotunda^), and the oval win-
dow (fenestra ovalis^). These
are closed, however, by thin
membranes. Three small
bones, called the auditory
ossicles, form a chain across
the middle ear (Figs. 74 and
75). The malleus, or hammer,
is attached by one end to the

membrane of the tvmpanum.

J ' Fig. 75. — The ossicles of the ear.

while the other end articu-
lates with the incus, or anvil bone. The incus articulates
with the third bone, the stapes, or stirrup bone, at the top
of its arch. The foot plate of the stapes fits into the open-
ing on the inner side of the tympanum called the oval
window, and is attached to the membrane which closes it.

170. The Internal Ear, or Labyrinth, is the essential part
of the organ of hearing, the others being merely con-
ductors of sound waves. The labyrinth is an irregular
chamber in the rocky part of the temporal bone (Figs. 74

128

CONSCIOUS NERVOUS OPERATIONS

Posterior
Canal

A ntertor
Canal

Fenestra Ovalia

Fenestra
Rotunda

and 76). Within it lies a closed membranous sac called
the membranous labyrinth, which follows the windings of
the bony cavity, and whose parts receive names corre-
sponding to the names given to the parts of the cavity.

The central part of the labyrinth is called the vestibule ;
it is about one eighth of an inch in diameter. In its walls

are the round and oval Avin-
dows already mentioned.
The membranous vestibule
is composed of two bags,
called the utricle and the
saccule, connected by a
roundabout passage.

171. From the utricle
arise three semicircular
canals, lying in the bony
passages of the same name.
One of these is horizontal
when a person stands up-
right; the others are vertical but at right angles to each
other. Two of these canals are united at one end, so that
there are but five openings from the canals into the vesti-
bule. Each canal has a swelling at one end called the
ampulla. At those swellings fibers from the eighth cranial
(auditory) nerve pass from the bony wall through the
membranes of the canals, firmly attaching one to the other.
For the rest of their course the membranous tubes are free,
or only loosely fastened by bands, of connective tissue to
the bony walls.

172. The Cochlea is the third and most complex division
of the inner ear. It has much the appearance of a snail
shell of two and a half coils. A bony tube is coiled spirally
round a central tapering pillar of bone. Into this tube

Fig. 76. — The bony labyrinth of the
right ear.

THE EAR AND THE SENSE OF HEARING

129

projects from the central pillar a thin shelf of bone partly
dividing the tube into two parts.

173. The Membranous Cochlea. — From the edge of the
bony shelf of the cochlea two membranes reach to the
opposite wall of the cochlea and divide the cavity into
three spiral tubes (Fig. 77). One of these, the vestibular

Fig. 77.— Diagram of a cross section of a single coil of the cochlea.

Showing the structures that compose the organ of Corti.

passage (scala vestibuliy, communicates with the vesti-
bule. A second, the tympanic passage (scala tympani),
has its base against the membrane of the round window.
At the apex of the coil of the cochlea the vestibular and
tympanic passages communicate with each other (Fig. 74).
The middle passage, the membranous cochlea, or cochlcar

MACY'S PHYS. — 9

130 CONSCIOUS NERVOUS OPERATIONS

canal, is closed at its apex, but opens near its base into the
saccule. In the cochlear canal is situated the most deli-
cate part of the ear, the organ of Corti.

174. Fluids of the Labyrinth. — The bony canal of the
inner ear is lined with a fine membrane which secretes a
thin fluid, filling all the spaces of the chamber. The
closed sac of the membranous labyrinth also secretes a
fluid similar in composition, but containing less solid
matter. When the membrane of the tympanum is
thrown into vibration, the movement is communicated to
the fluid filling the bony labyrinth, and then through
the thin wall of the membranous labyrinth to the fluid
inclosed, and so to the terminations of the auditory nerve.

175. The Auditory Nerve and the End Organs for Hearing. —
The eighth cranial nerve arises by two roots in certain
nerve centers of the medulla oblongata. Its two divi-
sions enter the labyrinth between the base of the cochlea
and the vestibule. One division, having several branches,
goes to the vestibule and semicircular canals ; the other
passes up through a channel in the bony axis of the coch-
lea, giving forth fibers on its way to the bony shelf
described above. These pass through, or come into rela-
tion with the spiral ganglion and reach the organ of Corti.

176. The Organ of Corti (Fig. 77), within the mem-
branous cochlea, is understood to contain the end organs
for the discrimination of degrees, variations, and qualities
of sound. It is composed of the rods of Corti with adja-
cent hair cells and supporting parts. The rods are pillar-
like cells attached by an expanded foot, or base, to one of
the membranes of the cochlea and ending in a swelling
called the head.

The pillars are arranged in pairs, of which there are
from three thousand to five thousand, separated at their

THE EAR AND THE SENSE OF HEARING 131

bases but leaning toward each other to form an arched
roof or tunnel. Toward the apex of the cochlea the rods
increase in length but are more widely separated at the
base, so that the tunnel becomes lower and wider.
Against the rods lean other cells called hair cells, which end
in many long, haiiiike processes. Between the hair cells
lie certain elongated supporting cells. The nerve fibers
end in fine branches between and around the hair cells.

177. Path of an Auditory Impression. — Sound waves pass
through the air and fall upon the membrane of the tym-
panum. In the middle ear they travel partly through
air and partly through solid bodies — membranes and
bones, — and in the inner ear through fluids and mem-
branes. Vibrations of the membrane of the tympanum
are u damped " by the ossicles of the middle ear, which
also receive and pass on the auditory tremors to the mem-
brane closing the oval window. These bones are so closely
bound together that they vibrate as if they were one, the
very slight amount of play at the articulations serving to
prevent jar and fracture.

From the middle ear vibrations pass to the inner ear
through the attachment of the stapes to the membrane of
the oval window. Movement of that membrane sets up
motion in the fluid filling the cavity. That, however,
would not be possible (since the fluid is inelastic and
incompressible) Avere not a vent provided at the round
window. When the stapes pushes in the membrane of
the oval window, that of the round window bulges out-
ward, and the action agitates the whole body of the fluid
which fills the bony labyrinth. But the vibrations in the
fluid are also communicated to the walls of the membra-
nous labyrinth which it bathes, and the fluid which the
latter contains is thereby set in motion.

132 CONSCIOUS NERVOUS OPERATIONS

Within the swollen ends of the semicircular canals, and
upon the walls of the utricle and the saccule, are project-
ing ridges composed of especially modified cells of the
lining, between which are spindle-shaped auditory cells
from which project auditory hairs into the fluid. At-
tached to these thickened disks, or ridges, are minute hard
particles, called otoliths, which serve to increase the effect
of the vibrations. The auditory vibrations in the fluid
and in the membranous walls of the labyrinth reach the
auditory hairs and give, according to the opinions of some
authors, the sensation of sound, or mere noise. A branch
of the vestibular division of the auditory nerve is distrib-
uted to the semicircular canals, and when its ends are
affected by the vibrations in the fluids of the labyrinth
there result, as is now believed, sensations other than
perception of sound.

178. The same vibrations pass at the same time up the
channel of the cochlea from below, affecting on their way
the walls of the membranous cochlea, and throwing into
vibration the fluid which they inclose. By the vibrations
of the fluid and the membrane the nerve endings in the
organ of Corti are acted upon in such a way as to give
rise to auditory impulses, resulting in perception of sound
quality — musical notes, harmony, etc. The cochlea alone
is now regarded as concerned with hearing, other parts
of the inner ear with equilibrium, etc. Sound waves may
also reach the auditory cells by transmission through the
bones of the head, as when one- hears the ticking of a
watch held between the teeth.

The auditory stimulus passes from the auditory cells
by the minute nerve fibers to that branch of the eighth
cranial, or auditory nerve, which passes through the coch-
lea and into the medulla obloiigata (Fig. 78), whence

THE EAR AND THE SENSE OF HEARING

certain fibers have been traced to the corpora quadri-
gemina, while others convey the impression to the gray
matter of certain convolutions
of the temporal lobe of the
cerebrum.

179. Function of the Vestibule
and Semicircular Canals. — Much
research has in recent years
been directed to the part played
by these portions of the inner
ear, but no investigator has yet
reached a conclusion which is
accepted in all its details by all
others. It is, however, gener-
ally believed that these parts Fig. 78.— Diagram of the path
have little, if any, direct con-
cern with the sense of hearing

and discriminating sounds.
The nerve branches distributed
here arise in the brain from a
root of the auditory nerve dif-
ferent from that which sends nerves to the cochlea. The
cerebellum, from which some of its fibers come, is well
known to be the great center for coordination of muscular
movement, and experiments seem to indicate that what is
called the vestibular branch of the auditory nerve, which
ends in the vestibule and semicircular canals, conveys to
the brain impressions of position and of movement in
space which have to do with the sense of equilibrium.

180. Hearing with Two Ears. — The two organs and two
nerves of hearing convey to the brain, not two sensations,
but one. By means of two ears we are able to some
extent to determine the locality from which sounds come,

of an auditory impulse.

The impulse passes from the
auditory cells in the ear to the cen-
ter of hearing (Au C) in the tem-
poral lobe of the cerebrum. Some
fibers pass to the anterior corpora
quadrigemina (Q).

134 CONSCIOUS NERVOUS OPERATIONS

but our judgment as to position in space of sound-pro-
ducing bodies, and of directions of sound, are indirect and
not always reliable.

181. Differences in Sound Perception. — The ears of differ-
ent persons vary greatly in power to distinguish differ-
ences in sound and in pitch, or the number of vibrations
in a given time. All are limited in the perception of
high-pitched notes. The ear may become wearied in
respect to sound of a particular pitch, much as the eye is
soon fatigued in respect to a particular color.

182. Care of the Ear. — A cold which causes inflamma-
tion of the throat often affects the lining membrane of
the Eustachian tube and that of the middle ear, causing
temporary partial deafness. If the cause often recurs,
one or both ears may be permanently impaired. Some-
times repeated attacks of inflammation in the ear — as
from abscesses — result in perforation of the membrane
of the tympanum and great injury to the hearing.

Generally the wax which is secreted in the external
canal of the ear needs no attention, and should not be
picked out. Occasionally, however, it accumulates and
hardens upon the membrane of the tympanum so as to
interfere with its vibrations and impair the hearing. In
such a case it should be removed by a surgeon.

Warm or tepid water should be used for washing the
ears — never very cold water. Before going to baths
in cold water or in salt water the ears should be filled
with soft absorbent cotton.

A sudden very loud noise, as from a gun or cannon,
has been known to rupture the eardrum, and a sudden
shout close to a child's ear has been known to make it
deaf. Insects sometimes crawl into the canal of the ear,
in spite of the wax and the hairs there which usually

THE EAR AND THE SENSE OF HEARING 135

prevent such accidents. They do not often do harm, and
may be removed by dropping warm water into the ear.

DEMONSTRATIONS AND EXPERIMENTS

67. Dissection of the Ear. — The external and the middle ear can be
fery easily studied by making a dissection of the head of a cat or
other domestic animal. Remove the lower jaw, expose and open the
temporal bulla. The latter is in many animals a conspicuous rounded
protuberance near the articulation of the jaw. The tympanic cavity
with the contained ossicles, etc., can then be studied. The internal ear
cannot be easily examined because of its smallness and well-nigh in-
accessible situation in the rocky portion of the temporal bone. The
bone which contains it can be dissected out, and the general outlines
of the cochlear region discerned. Or, this portion of the skull may
be treated with weak solution of muriatic acid for some days, after
which the parts may be partly dissected out.

68. Effect of Varying A ir Tension in the Tympanum. — While listening
to a ticking watch, close both nose and mouth, and expel as much air
as possible from the lungs, thus forcing the air through the Eustachian
tube into the middle ear. The ticking sounds fainter. Or under like
conditions inhale as much as possible. The result is as before.

69. Judgment of the Direction of Sounds. — Let a pupil, seated, keep
his eyes closed. Clink together two coins at varying distances and
directions from his head, and require him to indicate the direction of
the sound. Observe that while he rarely fails to distinguish between
right and left, he often errs in respect to other directions. Have him
hold his hands vertically one in front of each ear, and see if his judg-
ment of direction is thereby altered. Close one of his ears with
absorbent cotton, and try the effect upon his location of sounds.

70. A uditory Fatigue. — Strike a tuning fork, press the stem down
upon the crown of the head, and hold it there until the sound dies
away. Then remove it, and after a short interval replace it. The
sound will be heard again, but very faintly.

CHAPTER X

THE VOCAL APPARATUS

183. The Larynx, which contains the vocal cords, is the
special voice organ. It is a chamber made up of cartilages,
membranes, and muscles. Four cartilages compose the
framework. The thyroid is the largest, and forms a
prominent ridge in
front (called " Ad-
am's apple ") with
broad, flat sheets at
the sides, ending in
prolonged angles,
above and below
(Figs. 79 and 80).
It does not meet at
the back of the lar-
ynx. The cricoid car-
tilage, on the other

hand, is a complete
Fig. 79. -Front (ven- • ,1 i i hpino- Fig. 80. -Side view
tral) view of larynx. of larynx.

much wider than the

front. On top of the broad hinder portion of the cricoid
are the small, triangular arytenoid cartilages, which form
with the cricoid a true joint, having synovial membrane
and ligaments (Fig. 81).

Besides these four principal cartilages, which are of
hyaline, or nonfibrous cartilage, there are five others of

136

Trachea

Trachea

THE VOCAL APPARATUS

13T

Fig. 81.
larynx,
view.

Cartilages of
back (dorsal)

yellow fibrocartilage. They are the epiglottis, which is
attached to the upper front part of the larynx and
forms a lid to the chamber ; the
cartilages of Santorini, little horn-
shaped projections perched on top
of the arytenoids ; and the carti-
lages of Weisberg, which are still
smaller bits of cartilage lying in
folds of the mucous membrane in
the sides of the upper membranous
lining of the larynx.

A sheet of membrane connects
the thyroid cartilage with the hyoid
bone at the root of the tongue (Figs.
79 and 80). The thyroid is also joined to the cricoid by
joints with synovial membrane, and the lower projections,
or horns, of the thyroid clasp the cricoid closely, though
permitting movement between them. The cricoid is at-
tached by membrane to the upper cartilaginous ring of the
trachea, or windpipe. These parts, with the many small
muscles and ligaments attached, form the vocal apparatus.

184. The larynx is flattened behind, where it closely
adheres to the esophagus (Fig. 82). The esophagus is
the muscular tube which conveys food and drink from the
mouth to the stomach. Its enlarged upper portion is
called the pharynx, and lies back of the cavity of the
mouth. The larynx lies below and in front of the
pharynx. In ordinary respiration the epiglottis stands
nearly erect, leaving open the glottis^ or passage into the
larynx. In the process of swallowing, the epiglottis is
pressed backward and downward, closing the glottis and
permitting the food to slide down the esophagus instead
of dropping into the windpipe.

138

CONSCIOUS NERVOUS OPERATIONS

185. The Vocal Cords. — The larynx is smoothly lined
with mucous membrane except where it narrows at the
glottis. Here at the base of the epiglottis are seen, first,
on each side of the lining membrane, ridges called false
vocal cords, which are not concerned in speech (Fig. 82).
They play the chief part in closure of the glottis during
expiration. A little below them are the true vocal cords*

Opening of
Kustachian tube

Soft palate

Epiglottis

Glottis
Esophagus

Larynx —

Hani palate

Tongue

Hyoid bone
False vocal cords

. • True vocal cords

Thyroid carti-
lage

carti-
lage

Fig. 82. —Vertical section of the head and neck.

thickened bands of elastic tissue running in the mucous
membrane from the front angle of the thyroid cartilage
backward to their attachment at the base of the arytenoid
cartilages. Between the true and the false vocal cords is, on
each side, a recess called the ventricle. The true vocal cords
have fine, smooth edges, and are shining white in color.

186. The Glottis. — In ordinary respiration the glottis is
a triangular opening with its apex in front. In deep or

THE VOCAL APPARATUS 139

labored breathing it widens during inspiration and narrows
during expiration.

187. Vocalization. — There may be a sort of speech with-
out the action of the larynx or the vocal cords, when the
muscles of respiration, the lips, and what are called the
resonating cavities above the larynx are alone brought into
play. This produces whispering. But for vocalization
the vocal cords must be brought very near together, made
tense and parallel, and a current of air must be forced
swiftly through the narrow slit, throwing them into rapid
vibration. This is effected by means of a complicated
arrangement of muscles and ligaments attached to the
various cartilages. The two inner angles of the arytenoid
cartilages are drawn together by the contraction of certain
muscles, while others contract to stretch the vocal cords.
The thyroid and cricoid cartilages move upon each other
to assist in the process. The muscles of the thorax and
the abdomen are also brought into special action, and the
column of air in the air chamber composed of the trachea
and the bronchial system is thrown into vibration. Sound
is a result of the whole process.

188. The Resonating Cavities (Fig. 82). — The pharynx,
the mouth, and the nasal chambers are resonating cavities,
which, by very slight changes in form and size, are able
to bring into special prominence different parts of the
general tone produced in the larynx, and so modify the
resulting sound.

189. Speech is the enunciation of articulate sounds to
express thought, and is the result of the action of the vol-
untary muscles by which the vibrations produced in the
larynx are modified in the resonating cavities. The fac-
ulty of speech is a distinctive gift of man, and is possessed
by no other animal. It is a natural gift, but its use is the

140 CONSCIOUS NERVOUS OPERATIONS

result of training, and skill is acquired only by long years
of practice. The complex and greatly varied action
required in speech may take place with great rapidity,
and may be continued for hours without exhaustion, as in
the case of an accomplished singer or public speaker.

190. Vowels and Consonants. — Voice becomes speech
through the modifying action of the lips, tongue, throat,
etc. Those sounds of the spoken alphabet which require
the more open mouth, the more resonant and more pro-
longed tone, are called vowels; those which are uttered
with the closer position, and are less prolonged and less
resonant, are called consonants. Compare the position of
the parts of the mouth in enunciating the a in far with
that in sounding the b in cab, for example. Between
vowels and consonants there is no absolute division.
Sounds represented by some of the letters are more open
in some words or syllables than in others. Thus, I and
n are sometimes vowels and sometimes consonants.

191. Quality of Voice. — Voices are spoken of as "soft,"
" harsh," " rasping," " rough,'? " sweet," " low," " gentle,"
etc. An agreeable voice is a most attractive characteris-
tic and a most desirable possession. As the vocal appa-
ratus is wholly under the control of the will, and as its use
is chiefly a matter of imitation, it is of great importance
that while the habit of speech is forming the young should
be associated with those whose vocal habits are agreeable
and refined, and that the attention of children should be
early directed to the cultivation of -soft and pleasant tones
of voice. In this respect Americans are especially negli-
gent, and "the American voice" has become a byword
and a reproach in Europe.

192. Musical Sounds. — Sounds produced by regular vibra-
tions are musical. Irregular vibrations result in noise.

THE VOCAL APPARATUS 141

No sharp line of separation can, however, be drawn. The
sounds of ordinary speech are due to regular vibrations,
and are hence musical.

193. Pitch depends upon the rapidity of the vibrations,
and that varies with the length of the cords and with
their tension. In women the vocal cords are shorter than
in men, and the voice is an octave higher in pitch. Pitch
due to tension of the cords is a matter of voluntary con-
trol within the range of a voice. Loudness depends upon
the force of expiration. Stammering is due to lack of
coordination in the muscles of speech.

194. Nervous Mechanism of the Larynx. — A certain area
in the left hemisphere of the cerebrum is recognized as the
nervous center in which impulses resulting in speech origi-
nate. From the cells of this center nerve fibers run to
other cells in the wall of the fourth ventricle of the brain,
to the medulla oblongata, and on into the spinal cord. By
means of these communicating fibers the center for speech
is brought into connection with other groups of nerve
cells, from which arise the various nerves which are con-
cerned in vocalization. These are very numerous, for the
muscles of the face, the tongue, the thorax, and the abdo-
men, as well as those of the larynx, are called into action in
speaking, singing, etc. Those nerves distributed to the
muscles of the larynx are branches of the vagus, or pneu-
mogastric, which is the tenth cranial nerve and rises from
the medulla oblongata.

Suppose there arises in a man's mind a thought which
he desires to express in audible speech. He remembers
the sounds of the words which will serve his purpose, and
impulses arise in that part of the speech center called the
auditory word center, from which they pass to the motor
center. Thence the nerves of the various parts of the

142

CONSCIOUS NERVOUS OPERATIONS

vocal apparatus distribute the impulse to the necessary
muscles. In reading aloud it is the end organs for vision,
the eyes, which are first stimulated (Fig. 83); then the
impulse is carried to the visual center in the brain, from

which nervous influences travel
by connecting nerve fibers to
the auditory word center.
There, as before, the sound of
the words is revived and the
impulse follows the path previ-
ously described.

195. — When a person writes
from dictation, another course
is followed (Fig. 84). The
auditory end organs of the
inner ear are first stimulated;
the impression travels by the
auditory nerves to the audi-
tory word center, then across
to the visual word center,
reviving there the appearance
of the words. Impulses pass
thence to the motor centers
and by motor nerves to the
various muscles of the arm
and hand involved in writing.
If nerve fibers which connect
the two word centers, visual
and auditory, arc diseased, nei-

Fig. 83.— Diagram of path of
nervous impulses in reading
aloud.

Au C hearing center.

OC sight center.

Sp C speech center in left hemi-
sphere.

V, VII, X, XI, XII, Sp If nerves
supplying motor fibers to the
speech organs: lips, tongue,
chest, etc.

ther reading aloud nor writing from dictation is possible.
Vocalization may also be the result of reflex nervous
action, as when an involuntary scream follows sudden
fright.

THE VOCAL APPARATUS

148

196. Dumbness is most frequently due to deafness. The
auditory word center has never been stimulated. In
recent years it has been found
possible to stimulate the speech
center through its connection
with the visual center. Chil-
dren born deaf are taught to
imitate the movements of the
mouth, tongue, and throat of
one who speaks, and speech
results from these remembered
movements acting upon the
speech center.

197. . Care of Throat and Voice.
— If the delicate lining mem-
brane of the larynx becomes in-
flamed through " taking cold "
or from exposure to dust or
irritating gases or from over-
use or strain of the vocal
cords, the voice is injured and
its use may become painful
or impossible. These causes
should be avoided. When a
daily cold bath is not practi-
cable, a dash of cold water over the neck on rising in
the morning will prove a tonic for the throat and help
to avert colds, hoarseness, and sore throat. Breathing
should be through the nose, and not through the mouth,
and children should be trained in infancy to sleep with
the mouth closed. In going from the warm air of the
house into the cold outer air in winter the precaution
of closing the mouth is especially to be observed. Pass

Fig. 84. —Diagram of the path
of the nervous impulses in
writing from dictation.

Au C center of hearing.
MC motor center.
OC sight center.

144 CONSCIOUS NERVOUS OPERATIONS

ing through the winding nasal canal, the air becomes
tempered before reaching the sensitive membranes of
throat and lungs; also much of the dust always present in
the atmosphere is caught by the moist mucous lining of
the nostrils, and the deeper air passages are protected.

It is not necessary, in order to avoid cold, that the
throat should be thickly swathed in wraps of wool and
fur. Too much clothing about the neck causes excess of
perspiration there and makes the parts weak and tender.

198. Special Training of the voice for singing or public
speaking should not be begun by either boys or girls
before the age of sixteen or seventeen, and should always
be attended with judgment and care against overstrain.

199. Alcohol and Tobacco as affecting the Vocal Organs.
— As the perfect control of the voice depends upon the
healthy condition of all the muscles connected with the
vocal apparatus, and upon the accurate adjustment of
nervous force to their varying needs, anything which
affects those muscles or the nerves affects also the voice.
Alcohol and tobacco do affect both. The mucous mem-
brane of the larynx is often much inflamed by tobacco
smoking, and especially by the use of cigarettes. The
inflammation may extend through the Eustachian tubes,
impairing the hearing, and into the bronchial tubes, caus-
ing an annoying cough. A disease known as "smoker's
sore throat " may result. Alcoholic beverages irritate the
throat and are often forbidden to those cultivating the
voice for singing.

DEMONSTRATION

71. Dissection of the Larynx. — At a slaughterhouse can be obtained
a trachea of an ox with the larynx intact and a portion of the esoph-
agus ; the hyoid bone may be present also. With this material the
principal topics of this chapter can be illustrated.

PART III

NERVOUS OPERATIONS UNCONNECTED WITH
CONSCIOUSNESS

Those nervous operations of which man is necessarily
conscious and which are directly concerned in his useful-
ness and happiness, cannot continue to minister to his
higher nature without the assistance of another set of
actions of which he is in health almost wholly uncon-
scious. The complicated mechanisms for producing sen-
sation and voluntary motion are constantly worn away at
every point, and every tissue must- be as constantly re-
newed. Through the action, at every moment of life, of
nerves and nerve cells whose office it is to preside over
what are called the vital processes, the body is kept in
condition for the exercise of its conscious -powers. Those
vital processes are included under the general term nutri
tion, that is, the growth, waste, and repair of tissue.
Nutrition is effected by means of the circulation of the
blood, digestion (including absorption and assimilation),
respiration, and excretion. Because these operations are
wholly dependent upon nervous influences, and because
they go on through life without necessary connection
with consciousness, they are grouped here as unconscious
nervous operations.

145

Fig. 85. — The chief
blood vessels.

146

CHAPTER XI

BLOOD, LYMPH, AND CHYLE

200. Function of the Blood. — It will be remembered that
one of the essential properties of the living cell is its
power to incorporate into its own substance matter from
outside itself, a process which results in growth or in
repairing waste ; while another property, involved in
this, is the power to break down by oxidation, that is, to
resolve portions of its own body into simpler chemical
substances, thus producing waste matter.

In order that this double process may go on continually
(as it must while the cell is living), oxygen and oxidizable
substances, that is, food, must be brought to each cell, and
provision must be made for removing the waste products.
The blood is the medium for accomplishing this.

201. The Blood as a Tissue. — Blood is classed, for valid
reasons, among the connective tissues. While it does not
furnish support to the body or its parts in the same sense
as do more solid connective tissues, — such as bone or
cartilage, — it does support the whole body by conveying
nutriment to every part. It is like other connective
tissues also in that the cells make up a comparatively
small portion of its substance, the* intercellular material
being largely in excess. And, finally, it is formed in the
development of the embryo from the same layer as^ are
the other connective tissues.

MACY'S PHYS. — 10 147

148 UNCONSCIOUS NERVOUS OPERATIONS

202. Structure of the Blood. — Under the microscope the
blood is seen to consist of a nearly colorless fluid, the
plasma, in which float cells of two sorts, called from their
color the red and the white (or colorless) corpuscles (Fig.
17, p. 26). Ordinarily there are several hundreds of red
corpuscles to one of the white corpuscles, and to them the
color of the blood is due.

203. The Quantity of Blood in the human body is esti-
mated at about one thirteenth the body's total weight, or,
in a person of average size, about one and a quarter
gallons. Any deficiency of blood in the body (as from
hemorrhage), is soon supplied by the passage of water
from the tissues to the blood by means of the lymph
(§ 209), and an excess is removed by the transfer of
water to the tissues, and by the secretion of the kidneys.
Thus the quantity of blood in the system is practically
invariable.

204. The Red Corpuscles are unnucleated cells, all of
nearly the same size — about -$^$ of an inch in diameter,
and one fourth of that in thickness. They are round and
flat, but slightly thicker at the edge than in the middle.
Being flexible and elastic they are bent out of shape as
they are crowded together in the current, but resume
their usual form when the pressure is removed. They
have a close, colorless, spongy framework, — the stroma, —
while by far the larger part of their substance is a red
coloring matter in the meshes of the stroma, called hemo-
globin. This is the useful part of the corpuscle, the
stroma apparently having only the office of holding the
hemoglobin in convenient shape.

205. The Formation of the Red Corpuscles is found to take
place in the red marrow of the bones. The peculiar tissue
called red marrow is richly supplied with blood vessels

BLOOD, LYMPH, AND CHYLE 149

having very thin walls. Within these vessels are found
colored nucleated cells, some of which become changed in
the marrow into unnucleated red disks which are swept
into the blood current. It is the important function of
the red corpuscles to take in oxygen from the air which
reaches the blood in the lungs, and carry it to the other
tissues of the body. The red corpuscle lives in the blood
for an unknown time. When it dies, a new one takes
its place. The spleen also is believed to aid in the manu-
facture of both the red corpuscles and the white, but we
have little positive knowledge upon the subject.

206. The White Corpuscles are mostly larger than the
red, being generally about ^Vo .°^ an ^ncn *n diameter,
though some are smaller than the red. Some are globular
masses of granular protoplasm without cell walls and hav-
ing one or more nuclei. Others are of irregular and con-
stantly changing shape, less granular than the first and
with several nuclei. Many writers have remarked the
striking likeness of these corpuscles to the one-celled
animalcule, the amoeba. They have the same power as
the amoeba to change their shape spontaneously, sending
out processes from various parts of their circumference;
and they are able to take in and digest the bacilli which
are sometimes found in the blood, as the amo3ba digests
food. There are found in the blood some other small
bodies, whose nature and purpose are unknown.

207. Chemical Composition of Blood. — The blood is alka-
line, owing to the presence of small quantities of alkaline
salts. It contains chlorides, phosphates, and carbonates
of sodium and potassium, and smaller quantities of cal-
cium and magnesium.

208. Clotting of the Blood. — The blood in the blood ves-
sels is perfectly fluid, but if drawn out and allowed to

150 UNCONSCIOUS NERVOUS OPERATIONS

stand for a few minutes, it becomes a firm mass of jelly.
After an hour or more, a yellow fluid, called serum, begins
to ooze from the clot, which shrinks in size. The clotting
is caused by the formation, in the liquid blood, of a close
network of fine fibrils, called fibrin, in which the corpus-
cles of both kinds are entangled, while serum is the plasma
of the blood, minus an element in its composition called
fibrinogen, which changes into the solid fibrin in the coag-
ulation. It is thought that when the blood leaves the
blood vessel, or in some way comes in contact with foreign
matter, a portion of the white corpuscles are broken up,
and thus is set free a peculiar substance called fibrin fer-
ment. It is this which acts upon the fibrinogen, and
causes it to become fibrin. The fibrin may be gotten out
from a quantity of freshly drawn blood by quickly stir-
ring or whipping it with a bunch of twigs. The tiny
white threads cling to the sticks, and by washing in water
may be freed from the few entangled corpuscles which
remain, leaving the fibrin pure.

This power which the blood has to clot is of great
value, since by its means small breakages in or injuries to
the innumerable tubes conveying the blood throughout
the system are quickly stopped, and the serious hemor-
rhage which would otherwise result is quickly checked,
while the ruptured wall of the blood vessel is given time
to heal.

209. Lymph. — It is by the blood that nutriment is car-
ried to every part of the body; but the blood is always
inclosed within the walls of the tubes called blood vessels,
and, as blood, does not come in contact with the cells of
the tissues.

In the capillaries, which are the finest ramifications of
the blood vessels, some of the plasma passes from the

BLOOD, LYMPH, AND CHYLE 151

blood through the walls of the vessels into the spaces
between those walls and the substance of the tissues
around. This fluid is called lymph, and is that which
nourishes the tissue elements. It is clear, nearly trans-
parent, and contains more water with less solid matter
than the plasma of the blood. White corpuscles similar
to those in the blood are found in it, and, like the blood,
it coagulates by the formation of fibrin. Like the blood,
also, lymph is conveyed from the tissues in tubes, the
lymphatics or lymphatic vessels, which finally join the great
blood vessels, and so return to the blood the substances
drawn from it in the capillaries.

210. Lacteals and Chyle. — The lymphatics of the small
intestine are called lacteals ; after a meal containing fat,
they convey, instead of clear lymph, a milky fluid which
is called chyle, and is a product of digestion.

EXPERIMENTS

72. Blood Corpuscles. — Prick the finger with a sterilized needle,
mount the drop of blood thus obtained, and examine it with both low
and high powers of the compound microscope. There will be seen
large numbers of round bodies of a faint red tint — the red cor-
puscles. These are seen to be small disks, and appear dumb-bell
shaped when viewed on edge, owing to their being thinner in the
center than on the edges. Occasionally among the red corpuscles
may be seen slightly larger, transparent, sometimes irregular, bodies —
the white or colorless corpuscles. If watched for some time, they will
probably show slight changes in shape.

73. Clotting of Blood. — At a slaughterhouse fresh blood can be
obtained. If it be stirred vigorously immediately after being drawn
from the blood vessels, the fibrin can be separated from the blood
serum and corpuscles. Blood allowed to stand after being drawn
shows a firm clot. Both "whipped" blood and fibrin and the clotted
blood should be examined by the pupils.

The clotting of blood may be prevented by adding to it, as it is

152 UNCONSCIOUS NERVOUS OPERATIONS

drawn from the blood vessels, about one fourth its volume of a satu-
rated solution of sulphate of magnesia. This " salted " blood may be
kept in a cool place for several days without clotting. It may be
made to clot by diluting it with five to ten times its volume of water.

A more satisfactory method of preventing the clotting of blood, the
writer has found, consists in adding oxalate of potash in the propor-
tion of one part of a 5 per cent solution of oxalate of potash to
twenty-five parts of blood. The oxalate solution of the requisite
amount should be placed in a vessel and the blood be allowed to flow
into and mix with it. The mixing should be made thorough by
vigorous shaking. To produce a clot, add a few drops of a 2 per cent
solution of calcium chloride to some of the oxalate-blood. The potas-
sium oxalate prevents clotting by precipitating the calcium salts nec-
essary to coagulation. The addition of calcium chloride restores the
calcium and renders clotting possible.

74. The Minute Structure of the Fibrin Framework. — To a drop of
fresh blood on a slide add two drops of normal salt solution. Put on a
cover glass and set aside an hour or so to clot. Add 50 per cent alco-
hol at the edge of the cover glass (to wash out the corpuscles and
harden the fibrin). Observe with the microscope the network of
fibrin fibrils. Care must be taken not to move the cover glass during
the preparation for examination.

CHAPTER XII

THE CIRCULATORY SYSTEM

211. The apparatus distributing the blood throughout
the body and keeping it constantly in motion is composed
of the heart, the great central

pump; arteries, tubes to carry
blood from the heart ; veins, which
are tubes carrying blood to the
heart ; and capillaries, a network
of small tubes connecting arteries
and veins. These constitute the
vascular system (Fig. 85, p. 146).
In addition to them and forming
a part of the complete circulatory
system are the lymphatics and lac-
teals, sometimes called the lymph
vascular system. They are tubes
having walls thinner than those of
the blood vessels, running from
periphery to center, conve}dng
lymph and chyle.

212. The Heart is a hollow, cone- rp.

The heart is partly covered

shaped muscle, inclosed in a mem- by the lungs, hut its true out-
branous sac called the pericardium, line is shown by a dotted liue'
lying in the thorax between the right and left lungs (Fig.
86). Its base is directed backward and upward, while its

153

Fig. 86.— Front view of the
viscera in their natural
relations.

154

UNCONSCIOUS NERVOUS OPERATIONS

apex points downward ai}d forward a little to the left of
the sternum, or breastbone. The heart is divided longitu-
dinally irito two divisions wholly separate from each other.
Each of these is divided again into two chambers which
have free communication. The chambers at the base

Left Pulmonary
Artery

..Left Auricle

Fig. 87.— Front view of heart.
Coronary arteries and veins are injected, arteries red, veins blue.

of the cone are called the right and left auricles, while
the other two are called right and left ventricles (Figs. 87
and 88). Lying upon the outside of the auricles are two
flat earlike structures which are called the right and left
appendi'ces.

213. The Eight Auricle lies on the right side of the upper
part of the lieart. Its walls are thin, and are pierced by
openings for the two great veins, — the superior vena cava.

THE CIRCULATORY SYSTEM

155

entering from above, and the inferior vena cava, entering
from below. These two veins bring to the heart the blood
from all parts of the body, except from the lungs and the
heart itself. Close beside the inferior vena cava the coro-
nary vein opens into the right auricle. This brings to

Right Pulmonary Artery

Left Pulmonary
Artery"

Left Pulmonary

Left Auricle.

fij?/ /Supertor*
Vena Cava

Right Pulmonary
.--'•%'' Veins

iferior Vena Cava

Fig. 88.— Heart seen from behind.
Coronary arteries and veins are injected, arteries red, veins blue.

the auricle the blood from the capillaries of the heart
itself, which like all other organs of the body is supplied
with blood vessels and lymphatics for its own nutrition.

214. The Left Auricle lies at the left and back of the
upper part of the heart. Its walls are slightly thicker
than those of the right auricle. It receives four pulmo-
nary veins, two from each lung. The openings have no
valves.

156

UNCONSCIOUS NERVOUS OPERATIONS

215. The Right Ventricle occupies the principal part of
the forward surface of the heart, but is not a part of the
apex. The walls are thicker than those of the auricles
and less smooth. From the upper side of the cavity of
the ventricle a large opening leads to the great pulmonary
artery, while a still larger opening admits the blood from

Right Auricula-Ventricular
Aperture\

J^eft Auricula-Ventricular
\ Aperture

Aorta

Pulmonary
Artery

•Semilunar Valves

.Flaps of Tricuspid
Valve

Tendinous
- Cords

'--^Papillary
Muscles

89.— Eight ventricle, cut open to show the structures that
regulate the action of the tricuspid valve.

the right auricle (Fig. 89). The tricuspid valves prevent
the return of blood from the ventricle to the auricle. The
three main divisions of the valve and three smaller ones
are all triangular in shape, and are attached by their bases
to a tendinous ring surrounding the opening. The thin-
ner edges of the valves are flaps of transparent membrane

THE CIRCULATORY SYSTEM 157

hanging downward and held by .slender white tendinous
cords attached to little projecting columns in the walls of
the ventricle (papillary muscles). These cords and mus-
cles keep the valves from being pressed back into the
auricle further than is necessary to close the communica-
tion. Blood can thus flow from the auricle into the ven-
tricle, but not from the ventricle to the auricle. The
passage into the pulmonary artery is guarded by three
folds, or pockets, in the lining membrane, called semilunar
valves, which have their free edges turned upward, so that
when the blood is forced upward into the artery, the valves
lie flat against its walls, while if the blood should begin to
flow backward, the little pockets would at once be filled,
their edges crowded together in the center of the tube,
and the opening closed.

216. The Left Ventricle occupies the chief part of the
hinder surface of the heart, and includes the apex (Figs.
87 and 88). It opens at its upper side from the left auricle
and into the aorta, the great artery whose branches bear
the blood to the general system. The walls are much
thicker than in any other part of the heart because greater
force is required here to send the blood to the most dis-
tant parts of the body.

The mitral or bicuspid valves guard the opening into
the left auricle. They are similar to the tricuspids,
except that they have only two main divisions instead of
three. Tendinous cords and papillary muscles hold their
edges in place as in the case of the tricuspids. A strong
fibrous ring surrounds the end of the aorta, and within its
mouth are three semilunar valves, thicker and stronger
than those of the pulmonary artery. Their action is like
that of the other semilunar valves.

217. All the cavities of the heart are lined with a

158 UNCONSCIOUS NERVOUS OPERATIONS

smooth, shining membrane, the endocardium* which also
covers the valves, and is continuous with the lining of the
veins and arteries.

218. Cardiac Muscle. — As stated in the chapter on Mus-
cles, the muscular iibers of the heart form a class by them-
selves, being striped but involuntary (Fig. 90). The

fibers lie side by side, but send off at short
intervals branches which unite them. The
muscular fibers, moreover, are arranged in
the wall of the heart in bundles in such a
way that in contracting they draw the two
sides of the walls of the chambers together
until they meet. The muscle fibers of the
walls of the auricles are distinct from those
90 —TWO °^ ^e vehicles, so that thev contract sepa-
cardiacmus- rately, as we shall see. Each fiber, or muscle

cell, contains one nucleus.

Cardiac muscle fiber appears, to a large extent, to origi-
nate its own contraction, and is not so entirely as is a skel-
etal muscle fiber a mere instrument of a motor nerve
fiber. The action of cardiac muscle under stimulus is not
stronger or weaker in proportion to the strength of the
stimulus, as is the case with skeletal muscles. A weak
electric shock, if it causes any beat at all in the heart
muscles, causes as strong a beat as does a strong stimulus.

219. Arteries are the vessels which convey the blood
from the ventricles of the heart. The smallest of them
have a few plain muscular fibers wrapped round the tube
outside the endothelium. As the arteries grow larger,
the number of muscle fibers increases till they form a
definite muscular coat with a little connective tissue. In
the largest arteries the walls consist of three layers (Fig.
91) : (a) the inner coat, consisting of endothelium with a

THE CIRCULATORY SYSTEM

159

thin elastic layer on its outer side; (5) a muscular and
elastic coat; (<?) a connective tissue coat, forming the
outside of the vessel. The
very largest arteries have
more of the elastic in pro-
portion to the muscular
tissue. Owing to the pres-
ence of the elastic tissues,
arteries may be stretched
lengthwise, or distended
by pressure from within,
and will contract when
the stretching force dis
appears. Arteries have
no valves; those at the

Fig. 91. — Cross section of an artery.

, » , a smooth inner coat,

beginning Ot the aorta 6 middle or muscular coat.

c outer or connective tissue coat.

d small artery to nourish the large one.

and the pulmonary ar-
tery belong to the heart.
Branches of the smaller arteries often run into one
another, so that there is more than one path for the
blood from point to point; if, by any means, one becomes
closed, the blood can still pass round by another way.

220. Veins are the vessels which carry the blood toward
the heart. Great arteries open from the ventricles. The
great veins open into the auricles. Their walls are
thinner than those of the arteries, and collapse when the
veins are empty. They contain less of the elastic and
muscular tissues than arteries. Veins are supplied with
many semilunar valves, which prevent the blood from
flowing in the wrong direction.

221. Vascular and Nervous Supply of Blood Vessels.— The
coats of arteries and veins are supplied with their own
arteries, capillaries, lymphatics, and veins by means of

160 UNCONSCIOUS NERVOUS OPERATIONS

*

which they are nourished; and nerve fibers from sympa-
thetic nerves form plexuses around the blood vessels —
plexuses from which nerve fibers penetrate between the
muscle fibers of the muscular coat.

222. The Capillaries are the minute branches of veins
and arteries which form a connection and means of com-
munication between the two sets of vessels. Their walls
are formed of an extremely thin membrane which is easily
ruptured by unusual pressure. It is in the capillaries
that occur all the changes which take place in the blood.
In the web of a frog's foot, under the microscope, the
movement of the blood in the capillaries may be seen.

223. Osmosis is the term applied to the phenomena of
interchange between different fluids when in contact or
when separated by membranes or walls having minute
pores. By osmosis the blood inside the capillaries and the
tissue elements on the outside become intermingled, and
by the same means animal tissues live upon the lymph,
which is in turn replenished by the blood, while certain
elements pass from the protoplasmic cells of the tissues,
by means of the lymph, into the blood. It is not true,
however, that osmosis in living tissues is subject to the
same laws as that which takes place through dead animal
or vegetable membranes.

224. Course of the Blood in the Body. — In describing the
circulation of the blood it is customary to speak of the
general or systemic circulation, the pulmonary circulation,
and the portal circulation. These are convenient terms,
and are here retained for that reason. There is, however,
but one circulation, by which the blood leaving any one
part of the circulatory system returns to the same part
again. To do so it must pass through two sets of
capillaries and must be twice returned to the heart. The

THE CIRCULATORY SYSTEM

161

blood of the portal circulation passes in the liver through
a third set of capillaries.

Fig. 92. — Diagram of the course of the blood in the circulation.

225. The General or Systemic Circulation (Figs. 85 and
92). — The blood leaves the heart by the aorta, which
arises from the left ventricle and after forming a large

162

UNCONSCIOUS NERVOUS OPERATIONS

Sifbclavian Arteries^

arch over the root of the left lung passes downward near
the spinal column. Piercing the diaphragm, the aorta
enters the abdomen, and at the fourth lumbar vertebra
divides into the right and left common iliac arteries, and a
third small branch (the middle sacral) which continues on
to the end of the coccyx.

226. Branches of the Aorta (Figs. 85 and 93). — The
first branches of the aorta are the two coronary arteries
sent off just beyond the semilunar valves to supply the

Avails of the heart. The large
branches from near the top
of the arch are: (1) the in-
nominate artery, which soon
divides into two, the right sub-
clavian, running to the right
arm, and the right carotid, sup-
plying the right side of the
head and neck; (2) the left
common carotid for the left side
of the neck and head; and
(3) the left subclavian artery
for the left arm. Each sub-
clavian artery gives off at the
armpit the axillary and in the
arm the brachial artery. The
latter divides into the ulnar
and the radial arteries, named
from the bones along which they lie. They unite in the
hand to form the palmar arch.

The carotid arteries ascend the sides of the neck and
divide into two branches, which supply the head and face
and the brain.

The branches of the aorta within the thorax are (besides

iini.il- I'alvea

Fig. 93. — Arch of the aorta, dis-
sected free from the rest of
the heart.

THE CIRCULATORY SYSTEM

168

the coronary) the two bronchial, which go to the lungs;
the three or four esophageal, for the coats of the esopha-
gus; the pericardial, for the pericardium; and numerous
intercostal arteries.

Within the abdomen arise the phrenic, in the dia-
phragm ; the coeliac axis, with three branches, — the
hepatic, going mainly to the liver, the gastric, to the stom-
ach, and the splenic to the spleen (Fig. 94) ; the superior

R. Phrenic Artery
/Abdominal

/ Aorta
' ,CcKliac Axis
' /Gastric Artery

/Splenic Artery

Hepatic Artery

Fig. 94. — The coeliac axis and its branches.

and inferior mesenteric, which supply the intestine ; and
the renal, going to the kidneys.

The iliac arteries supply the walls and organs of the
pelvis and the legs. The artery on the front and inner
side of the thigh is called the femoral; above the knee
joint it passes to the back side of the leg, and is there
called the popliteal, while below the knee the main
branches are the tibial and the peroneal, which unite in

164 UNCONSCIOUS NERVOUS OPERATIONS

the foot in a palmar arch. All these arteries give off
numerous other branches all along their course.

227. The Principal Veins (Fig. 85). — The blood con-
veyed by the arteries to the capillaries of all parts of the
body passes there into the small veins, which unite into
larger ones, and, in general, run beside the arteries, and
often have corresponding names. They are gathered into
the superior vena cava, which collects the blood from the
head, arms, and portions of the chest ; the inferior vena
cava, by which the blood is returned from the remainder
of the body (the lungs and heart excepted) to the heart ;
and the coronary vein from the walls of the heart. All
these veins empty their contents into the right auricle.
Many of the veins are provided with valves to prevent
the reflow of the blood.

228. The Pulmonary Circulation (Fig. 92). — From the
right auricle the blood flows into the right ventricle, and
by its contraction is forced into the pulmonary artery,
which, dividing into two, one for each lung, carries the
blood to the capillaries of the lungs. It is then collected
by the pulmonary veins (two from each lung) and returned
to the left auricle, and passes thence to the left ventricle,
having completed the circuit of the body.

In the systemic circulation the arteries convey the pure,
oxidized, nutrient blood to the capillaries, while the veins
return the impure, deoxidized blood to the heart. In the
pulmonary circulation the reverse is true. Impure blood
flows through the pulmonary arteries to be oxidized in
the lungs, and returned pure by the pulmonary veins.

229. The Portal Circulation is an accessory and peculiar
circulation belonging to the liver. That organ not only
receives arterial blood through the hepatic artery, but is
also supplied by the portal vein with blood which has

THE CIRCULATORY SYSTEM

165

already circulated through the capillaries of the stomach,
spleen, intestines, and pancreas (Fig. 95). Unlike any
other vein, the portal vein ends in a second set of capil-

Gall Bladder-

Inferior
Vesenteric Vein

Inferior
"Mesenteric Artery

-Descending Colon

-Small Intestine

Fig. 95.— The portal vein and its chief branches.

The liver is turned back and the transverse colon and a part of the small
intestine are cut away.

laries around the cells of the liver, from which it is col-
lected into the hepatic veins, which open into the inferior
vena cava.

166

UNCONSCIOUS NERVOUS OPERATIONS

230. Action of the Heart in the Circulation (Fig. 96). — In
the beating of the heart, the contraction of the muscular
4 walls commences at the

mouths of the great
veins in the auricles,
runs through the two
auricles and then over
the two ventricles to-
gether, the auricles be-
ginning to dilate as the
ventricles begin to con-
tract. Then there is
an instant's pause, when
neither set of muscles
are contracting, but the
whole heart is expand-
ing, and its walls are
soft and flabby.

The impulse from the
heart's contraction is
felt in the arteries of
the wrist, the temples,
and some other parts of
the body, and is called
the pulse.

During the pause the
relaxed walls of the
heart yield to the blood
which flows into the
auricles from the pul-

Fig. 96. — Diagrams illustrating the ac- monary veins and the
tlooi of the valves of the heart. venffi ^^

A during the filling of the right ventricle. .

11 during the contraction of the ventricle. lunar valves

,
at tlie

THE CIRCULATORY SYSTEM 167

mouths of the great arteries are closed; the tricuspid and
mitral valves are open. The ventricles now begin to dilate,
and the blood flows freely into them from the auricles.
As they fill, currents in the blood along the walls carry up
the flaps of the valves till they are nearly closed. The
auricles now contract, the contraction beginning at the
mouths of the great veins, which narrows the openings,
and more blood is sent into the ventricles. 'This swifter
flow into the ventricles sets up stronger back currents
along their walls, and, the muscular walls beginning to
contract, the valves are completely closed. The blood
then has no escape but by the arteries issuing from the
ventricles. The strong walls of the ventricles press more
and more upon the imprisoned blood, it is forced swiftly
through the mouths of the arteries, pressing back the
semilunar valves, and the ventricles themselves are empty
before they begin to relax again. When relaxation sets
in, the return of arterial blood into the ventricles is pre-
vented by the semilunar valves.

231. Sounds of the Heart. — Two distinct sounds from the
heart may be detected by placing the ear over the region
of that organ. The first is dull and somewhat prolonged,
the second is shorter and sharper. The first may be heard
immediately before the pulse is felt at the wrist, the sec-
ond immediately after it. They are followed by a brief
silence. The exact cause of the first sound in not fully
determined, but it is thought that it may be partly due to
vibrations of the tendinous cords attached to the heart
valves themselves, and partly to a muscular sound pro-
duced by contraction in the mass of muscular fibers in
the ventricles. The second sound occurs at the moment
of closure of the semilunar valves, and is due to the strik-
ing together of those valves.

168 UNCONSCIOUS NERVOUS OPERATIONS

Action of the Arteries. — All the blood vessels are
always full of blood, — at the moment of the heart's pause,
as at every other. When, therefore, the contraction of
the left ventricle forces from four to six additional ounces
of blood into the aorta, that which already fills the vessels
must be crowded on. In the minute tubes of the capil-
laries there is, however, a very considerable amount of
friction to be overcome, and as beat follows beat, the
elastic walls of the arteries must stretch to receive the
flow. The elastic arteries also react upon the blood
between the beats to force it through the capillaries.
Thus the flow, which is intermittent in the arteries,
becomes continuous in the capillaries.

The muscular contraction in the arteries helps to regu-
late the amount of blood sent to different parts at different
times. Many familiar facts illustrate this. Blushing is
due to an increased flow of blood to the face ; a mustard
plaster draws more blood to the area which it covers ;
friction of the surface has a like effect. After death the
arteries are always found empty, their last contraction
having forced the blood into the veins.

233. Blood Pressure. — During life the elastic walls of
the arteries are always distended, and the pressure upon
their walls of the extra quantity of blood forced into
them by the beating of the heart is called blood pres-
sure. When an artery is cut, it is noticed that the blood
issues from it in jets corresponding to the beats of the
heart, and the nearer the cut is -to the heart, the stronger
is the spurt. When a vein is severed, on the other hand,
the flow is steady and with less force.

The difference in the amount of blood pressure in veins
and arteries is shown by experiments upon animals. If a
long glass tube be introduced into the carotid artery of

THE CIRCULATORY SYSTEM 169

a rabbit, for instance, the blood will rise in the tube to a
height of about three feet, and will be raised slightly
farther at each beat of the heart. If a similar tube be
placed in an opening in the jugular vein, the blood will
rise in the tube only very slightly, and the height will
not be affected by the heart beats.

234. Velocity of the Blood. — Of course the same quan-
tity of blood flows through the aorta as flows through all
the capillaries of the system and is returned to the right
auricle ; but all the capillaries together hold much more
blood than the aorta. The blood must, therefore, pass
more rapidly through the aorta than through the capil-
laries. Its rate is about fifteen inches a second in the
aorta, and about half that in the two venae cavie, while
in the capillaries it is thought to be less than one twenti-
eth of an inch in a second.

235. The Lymphatic Circulation. — We have seen (§ 209)
that the plasma of the blood which oozes through the thin
walls of the blood capillaries forms the fluid called lymph.
This fluid contains corpuscles apparently identical with the
white blood corpuscles, but no red ones. As it fills the
spaces between the cells of the tissues it conveys nutri-
ment directly to the cells themselves in all parts of the
body. A network of delicate vessels called lymph capil-
laries carries away the surplus fluid. The walls of these
tubes are extremely thin, being composed, like the blood
capillaries, of a single layer of flat cells with a little con-
nective tissue and a few plain muscular fibers. The small
vessels unite to make up larger ones, which are supplied
with valves, like the veins, and all finally pour their con-
tents into two large tubes. One of these is called the
thoracic duct, and runs upward in the thorax and abdomen
along the spinal column to empty into the angle of June-

170

UNCONSCIOUS NERVOUS OPERATIONS

Fig. 97. —The thoracic duct and right
lymphatic duct.

tion of the large jugular
vein in the neck with the
left subclavian (Fig. 97).
The other is the right
lymphatic duct, and opens
into the angle of junc-
tion of the right internal
jugular and subclavian
veins. The thoracic duct
receives on its way the
contents of the lacteals,
and the whole is poured
into the blood stream.
Lymph is an alkaline
fluid, and contains a
larger proportion of the
waste products of the
vital processes than does
the blood.

Nervous connection be-
tween the muscular.fibers
of the lymphatic vessels
and the nerve centers has
not been traced, though
from what is known of
nervous control over oth-
er organs and processes
in the body, it is believed
to exist.

236. Lymphatic Glands.
-Throughout the lym-
phatic system colorless
or white corpuscles are

THE CIRCULATORY SYSTEM 171

found. Some of these pass through the walls of the blood
capillaries with the plasma which forms the lymph, but
all along the course of the lymphatics are small -glands
made of networks of connective tissue which hold in their
meshes large numbers of small white corpuscles packed
sicle by side as closely as possible. The lymph, flowing
into these glands on one side and from them on the other
side, carries along with it some of these corpuscles and
thus keeps the blood supplied. These lymphatic glands,
or similar tissues in the body, are the source of the white
corpuscles of the blood.

237. Hygiene of the Circulation. — In perfect health the
blood circulates rapidly, because the heart beats strongly,
the muscular tone of arteries and veins is such as to pro-
mote the flow, the blood is purified in the lungs by an
abundant supply of pure air, plenty of fresh material is
supplied to it from suitable, well-digested food, the nerv-
ous centers are quickly responsive to their natural stimuli,
and furnish the needful impulse to the numerous parts of
the circulatory apparatus.

The blood cannot circulate freely unless the whole body
is so loosely clothed that there is no pressure upon any of
the blood vessels, no restriction of the breathing capacity,
no interference with the normal action of the stomach,
liver, and intestines. There must be exercise of all the
muscles, sleep sufficient to keep the nervous system in
good condition, and activity of the excretory organs.
The last is promoted by exercise, frequent bathing,
friction of the skin, and the wearing of woolen under-
garments.

238. Effects of Alcohol upon the Blood and the Circulation. —
The first effect of dilute alcohol taken into the stomach
appears to be to make the heart beat faster and with

172 UNCONSCIOUS NERVOUS OPERATIONS

more force, to expand the smaller blood vessels of the
skin, and to cause a more rapid flow of blood to the sur-
face. This produces a comfortable glow in the skin, and
the drinker thinks he has been warmed by his glass of wine
or beer or weak spirits. As a matter of fact, however,
most of the additional heat brought to the surface by the
increased flow of warm blood very soon passes off and is
followed by chilliness ; for the general bodily tempera-
ture, though at first raised by the oxidation of the alcohol,
is finally lowered by the increased radiation from the
surface.

Alcohol in the stomach is rapidly absorbed and passes
into the blood stream. There the strong affinity of alco-
hol for oxygen, which leads them to enter very rapidly
into chemical combination, causes the alcohol to appropri-
ate the oxygen of the red corpuscles of the blood, which,
as we have seen (§ 205), are the great oxygen carriers in
the body. This tends to impoverish the blood and render
it less valuable to the tissues.

The immediate stimulation to the heart's action soon
passes away and, like other muscles, the muscles of the
heart lose power and contract with less force after having
been excited by alcohol.

239. Effects of Tobacco upon the Circulation. — The fre-
quent use of cigars1 or cigarettes by the young seriously
affects the quality of the blood. The red blood corpus-
cles are not fully developed and charged with their nor-
mal supply of life-giving oxygen. This causes paleness
of the skin, often noticed in the face of the young smoker.
Palpitation of the heart is also a common result, followed
by permanent weakness, so that the whole system is
enfeebled, and mental vigor is impaired as well as physical
strength. Observant teachers can usually tell which of

THE CIRCULATORY SYSTEM 173

the boys under their care are addicted to smoking, simply
by the comparative inferiority of their appearance, and
by their intellectual and bodily indolence and feebleness.
After full maturity is attained the evil effects of com-
mencing the use of tobacco are less apparent ; but com-
petent physicians assert that it cannot be safely used by
those under the age of forty.

DEMONSTRATIONS AND EXPERIMENTS

75, Dissection of the Heart. — Order of a butcher the heart of a calf,
sheep, or pig. Explicit directions should be given that the entire
"pluck" be saved, i.e. heart, lungs, and larger blood vessels intact;
otherwise mutilated specimens will be received. By inflating the
lungs through the trachea their structure and general relationship
to the heart can be shown. Observe that the heart lies in a sac, the
pericardium. Cut open the latter and notice the pericardial fluid.
Before proceeding to cut open the heart identify as many as possible
of its parts and connected blood vessels. Observe the blood vessels
connecting the heart and the lungs, and distinguish between the
pulmonary artery and the pulmonary veins. The aorta and the two
venae cavae can be distinguished with very little trouble. After sever-
ing the vessels connecting the heart with the lungs, the course of the
blood through the heart can be shown, and a difference between
the arteries and the veins can be demonstrated by forcing water into
the vessels. Water injected through the venae cavse into the auricle
emerges from the pulmonary artery. Injected in the opposite direc-
tion the flow is retarded by the auriculo-ventricular valve. In this
way one can identify vessels of which he is in doubt, and demonstrate
the functions of the valves. Demonstrate the internal structure of
the Heart'by making incisions in the walls of the auricles and ventri-
cles, and identifying the parts as described in the text.

76. Demonstration of the Organs of Circulation. — The principal ves-
sels of the circulatory system can be readily dissected out in the body
of a cat, dog, or rabbit. If the teacher is familiar with methods of
injecting the circulatory system with some colored substance, the
vessels can be more easily traced out, and also preparations can be

MACY'S PHVS. — 11

174 UNCONSCIOUS NERVOUS OPERATIONS

made that will keep permanently in suitable preservative fluids. But
the larger blood vessels can be easily dissected out in iminjected
specimens.

77. Structure of Blood Vessels. — Prepared cross sections of the walls
of blood vessels can be purchased, or borrowed from some local
physician. The blood vessel is seen to be composed of three coats :
inner, epithelial; middle, largely muscular; and outer, fibrous.

78. Circulation in the Web of the Frog's Foot. — The frog should be
placed in a small cloth bag, one foot being allowed to protrude. The
animal should then be tied upon a board or wooden frame with the
web of its foot stretched over an opening in the board. The web
may be kept stretched by the aid of strings tied to the toes. The
apparatus should then be placed so that the web over the hole in the
frame lies directly under the objective of a compound microscope. If
the animal, and especially the web of the foot, be kept moist, and the
cords confining it are not too tight, the movements of the blood
corpuscles can be studied for a long time. The experiment may be
performed with little discomfort to the frog.

79. Valves in Veins can be shown by pressing firmly with the finger
upon one of the veins of the forearm, and then passing the finger
up along the vein toward the hand. The positions of the valves are
indicated by the temporary swellings that make their appearance as
the blood is forced back against the flaps of the valves.

80. Scheme of the Circulation. — The general features of the circu-
lation can be illustrated with the apparatus shown in Fig. 98. The
mechanism can be easily constructed, requiring only some rubber and
some glass tubing, a few glass Y-tubes, some pinchcocks, and a bulb
syringe.

81. To illustrate Arterial and Venous Pressure and Flow. — Remove
the clamp from tube C, and force water through the apparatus with
quick, regular strokes. The mercury in the manometers rises and falls
with each stroke, and the water issues in jets from E. Clamp C. and
continue as before. The mercury in manometer M oscillates out
rises higher than before, with a marked excess of rise over fall, so
that finally the mercury in one limb of the manometer stands at a
considerable height, showing vibrations with each stroke of the pump.
In manometer N the mercury rises slowly, with little or no oscillation,
but the pressure is not so great as in M. The water issues from E
in a steady stream. Open clamp at Z>; the water issues in jets corre-

THE CIRCULATORY SYSTEM

175

spending to the strokes of the pump. While working the pump press
lightly with the finger on the rubber tubing of the arterial side ; a
distinct pulsation is felt with each stroke. Repeat the same on the
venous side.

82. Osmosis. — Prepare a dialyzer by tying a thin animal membrane
(sausage skins, to be obtained of a butcher, furnish excellent mem-
branes for osmosis) over one end of a small lamp chimney. Partly
fill the dialyzer with a strong solution of sugar and place it in a larger
vessel of pure water, so that the liquids in the two vessels are at the
same level. In a short time the contents of the dialyzer begin to rise,
owing to the greater flow toward the denser liquid. It will also be
found that the water in the outer vessel becomes sweet as osmosis
goes on. If the membrane is allowed to become thoroughly dry after
being tied on the dialyzer, osmosis goes on more rapidly.

M N

Fig. 98. — Apparatus for illustrating the circulatory system.

A bulb syringe, by which water is forced through the apparatus.

B rubber tubing packed with bits of sponge to represent capillaries.

C rubber tube connecting arterial and venous regions. When C is closed with

the pinchcock the liquid must all pass through tubes B.
D small tube ending in capillary point and closed with a pinchcock. When

open it allows arterial " spurting " to be demonstrated.
E tube which shows venous flow. It ends in a tube of small caliber in order

to produce a venous pressure.
M, N manometers consisting of glass tubing bent in a U-shape and partly

filled with mercury. They show the pressure applied to the arterial and

venous sides respectively.

CHAPTER XIII
NERVOUS CONTROL OF THE CIRCULATION

240. Functions of the Nerves of the Circulatory System. —
When any special activity is required of one of the organs
of the body, an increased flow of blood is needful to that
part. There is not blood enough in the body to enable
all the muscles, all the organs of digestion, the brain, and
the organs of respiration, etc., to work in full activity at
the same time. There must therefore be some method of
regulating the activities of the different parts and organs,
so that some may rest while others work.

Then, too, some arrangement must exist for correlating
the action of the heart and the blood vessels, so that the
steady flow of nourishing blood may be kept up in all the
capillaries, with more powerful pressure applied when and
where it is needed, and not at the wrong place and the
wrong time.

As everywhere else, we find that in the circulatory
system the nerves furnish the controlling, coordinating,
and regulating force.

241. Nerves of the Heart (Fig. 99). — Three sources of
nervous control of the heart are usually mentioned. They
are the cardiac or heart branches of the tenth and eleventh
pairs of cranial nerves, — the vagus or pneumoyastric and
the spinal accessory; the cardiac branches of the sympa-
thetic^ from the ganglia of the neck ; and what have

NERVOUS CONTROL OF THE CIRCULATION

177

been called tlie intrinsic nerves of the heart, which were
formerly treated as independent of the other two sets
of nerve fibers. The intrin-
sic nerves are now known,
however, to be merely the
terminations of the other
nerves in the heart wall,
while the rhythmic beat of
the ventricles, which is
found to continue for some
time even after the heart
is removed from the body,
is believed to be a peculiar
property of the heart muscle
itself.

242. Path of the Nervous
Impulse. — • The roots of the
vagus and the spinal acces-
sory nerves rise near together /, kgp^

in the gray matter of the

medulla oblongata. A branch Fig. 99. — Diagram illustrating the
from the spinal accessory
soon joins the vagus, and
supplies some of its motor
or efferent fibers. Fibers
from the sympathetic nerves
of the neck also join the va-
gus. These have been traced
back into the spinal cord.
The cardiac nerves, there-
fore, are all connected with
the central nervous system,
and, since all parts of the

nervous control of the heart.

A cardiac accelerator center.

a accelerator fibers connected with
accelerator center through sym-
pathetic system (Sy), spinal
nerves (<S) , and spinal cord.

c fibers through which the cerebrum
exercises control over the car-
diac centers.

e fibers from the heart that excite
the inhibitory center.

I cardiac inhibitory center.

i inhibitory fibers whose action
slows the heart's beating.

s communicating fibers between
spinal nerves and sympathetic
system.

Sy sympathetic system.

178 UNCONSCIOUS NERVOUS OPERATIONS

spinal cord communicate with the brain, they are all con-
nected with the brain also. Certain fibers of the vagus
proper carry the afferent influences from the heart to the
brain, and by them the brain is kept informed of the
heart's condition. Fibers of the spinal accessory and
the sympathetic nerves convey motor impulses from the
brain to the heart.

243. Accelerator Fibers of Cardiac Nerves. — Experiments
have proved that it is the fibers from the sympathetic
ganglia which convey to the heart the impulse which
accelerates and strengthens its beat. They are supposed
to run up the spinal cord to an accelerator center in the
medulla oblongata (Fig. 99).

244. Inhibitory Fibers of Cardiac Nerves. — Stimulation of
the fibers of the motor branch of the vagus running to the
heart not only does not increase its action, but retards or
inhibits it, and may entirely stop its beating. By this
means the brain keeps a continual check upon the action
of the heart. It has been found that if the vagus nerves
of a dog are divided, the beat of the heart is quickened.

245. Reflex Inhibition. — A violent blow upon the stom-
ach or abdomen, as is well known, may cause fainting, due
to stoppage of the heart's action. The stimulus of the
blow is carried by the sympathetic nerves of the epigas-
tric plexus, situated around the pit of the stomach, to the
thoracic ganglia and thence to the medulla oblongata.
There the impulse is reflected along the efferent fibers of
the vagus to the heart muscles^ and their action is
checked. Fainting may be caused in a similar way by
the action of severe pain or strong emotion upon the nerve
cells of the brain. The impulse reaches the region of the
medulla oblongata from which the vagus arises, and is
sent on to the heart.

NERVOUS CONTROL OF THE CIRCULATION 179

246. Regulation of Blood Pressure in the Brain. — The

regulation of blood pressure in the brain is by means of
the inhibitory nerves. Excitement in the brain increases
blood pressure there, and that pressure gives rise to
inhibitory impulses by which the heart's action is re-
strained and danger to the brain is averted. Or, the
inhibition may be a reflex impulse originating in the heart
itself and sent up to the inhibitory center by the afferent
fibers of the vagus, and the heart may be thus enabled to
regulate its action according to its own necessities.

247. The Vasomotor Nervous System is that which regu-
lates muscular action in the blood vessels. It belongs to
the sympathetic system. The muscles of arteries and
veins are composed of plain muscular fibers, and the
nerves belonging to them appear to end in fine plexuses
round the fibers. Two sets of nerves for the blood vessels
have been made out, called the vasoconstrictor and the
vasodilator, whose influences correspond to the influences
of the accelerator and inhibitory fibers of the cardiac
nerves. It should be noted that in the vertebrate ani-
mals no inhibitory nerve fibers exist in the nerves supply-
ing the voluntary muscles, while the involuntary muscles
usually have both accelerator and inhibitory fibers.

248. The Vasoconstrictor Nerves have been traced to the
ganglia of the sympathetic chain and thence to the ante-
rior horns of the spinal cord. From there fibers pass up
to the vasomotor center in the gray matter of the medulla
oblongata.

249. Vasodilator Nerves accompany the vasoconstrictor
for a part of their course, and finally reach the same center
in the medulla. They carry inhibitory impulses, that is,
their action checks the contraction of the muscle fibers
in the blood vessels and permits them to dilate.

180 UNCONSCIOUS NERVOUS OPERATIONS

250. Effects of Vasomotor Action. — The muscular action
of the arteries gives its general tone to the arterial system
and regulates the flow of blood in the whole body, and
this general tone is influenced by the central nervous sys-
tem. For instance, certain kinds of mental excitement
which affect the brain result in dilation of the arteries of
the face, which permits a more ample flow of blood to that
part, causing what is called Hushing. An opposite effect
may be produced by emotion, causing pallor. The action
is mainly reflex. So also in the case of the vessels of the
skin. When the temperature is low, they are constricted
and the surface becomes pale. As the temperature rises
the vessels dilate and the skin becomes flushed. While
these changes occur upon the surface, changes of a reverse
order take place in the viscera, and the temperature of the
body is thus largely regulated. Certain poisons in the
blood circulating through the brain affect the vasomotor
center, as when the blood is imperfectly oxygenated and
therefore impure, resulting sometimes in suffocation.

251. Alcoholic beverages affect the delicate adjustment
of the vasoconstrictor arid vasodilator nervous forces
and may seriously interfere with the circulation. As pre-
viously stated, dilute alcohol causes the constrictor muscles
in the capillaries to relax so that the capillaries become
dilated, and by the continued use of alcoholic drinks they
may become permanently expanded.

CHAPTER XIV
RESPIRATION

252. Definition. — The lymph obtains from the blood in
the capillaries and conveys to the tissues all that they
need for sustaining their life. Their waste products are
returned to the blood. One important element which all
the tissues need, is oxygen, and one important element in
the waste is carbon dioxide, or carbonic acid gas.

Respiration is the process by which oxygen is supplied
to the blood and an excess of carbonic acid is removed from
it. As a general term, respiration includes also the inter-
change of these gases in the tissues, called internal respi-
ration, or tissue respiration, but the word is more com-
monly restricted to that part of the process which takes
place in the lungs.

253. The Respiratory Apparatus consists of the channels
through which air passes to reach the capillaries of the
lungs, viz. nostrils and mouth, pharynx, larynx, trachea,
bronchi, bronchial tubes, alveoli, and air cells ; together
with the muscles of the chest, of the diaphragm, and of
the abdomen.

254. Normally the air enters the pharynx through the
nostrils rather than the mouth. By passing through the
winding passages of the nose it acquires nearly the tem-
perature of the body, and is also relieved of some of the
particles of dust always floating in the atmosphere.

181

182

UNCONSCIOUS NERVOUS OPERATIONS

255. The Trachea is a large tube of from sixteen to
twenty incomplete cartilaginous rings (Fig. 100). It is
from four to four and a half inches in length, from the

Fig. 100. — Diagram of the respiratory organs.

cricoid cartilage, to which it is attached above, to its
lower extremity, where it divides into two bronchi, one
of which goes to each lung. At the back of the trachea,
between the ends of the cartilage rings, are bands of plain

RESPIRATION

183

muscular fiber, whose function is to draw the ends of the
rings together and reduce the caliber of the tube. The
whole tube is inclosed in a fibrous membrane, and lined,
like the rest of the passages, with mucous membrane. The
superficial layer of the epithelium of the trachea is ciliated,
that is, supplied with minute
hairlike prolongations.

256. The Bronchi resemble
the trachea in structure, but
have a distinct layer of plain
muscle running around them.

257. The Bronchial Tubes
and Alveoli. — The bronchi
have numerous branches called
bronchial tubes reaching to
all parts of the lungs, each
branch ending finally in a
wider, funnel-shaped passage,
the alveolus, surrounded by
clusters of short, somewhat

Fig. 101. — Two alveoli, show-
ing the clusters of air cells.

dilated sacs, the air cells (Fig. 101). All the tubes are lined,
like the trachea, with ciliated epithelium.
The cilia being continually in motion
drive out the mucus which is constantly
secreted, and along with it the dust
brought into the passages with the air.
258. The Air Cells are the hollow ex-
pansions of the alveolus (Fig. 102).
They have a lining of very fine epi-

Fi 102— s f f thelium, without cilia, and within that
an alveolus, show- a close network of capillaries. In these

mg air cells open- ^he arteries of the lungs make connec-

ing into the central

cavity. tion with the veins.

184 UNCONSCIOUS NERVOUS OPERATIONS

259. The Lungs are made up of collections of air cells
and the branches of the bronchial tubes. Their texture
is spongy and elastic, and a piece of a lung, unlike
any other tissue, will float in water. Each lung is envel-
oped in the pleura, which is a serous membrane folded
back to form the lining of the diaphragm and the chest
wall. The two layers of the pleura are in contact with
each other, with only enough of the fluid secretion to
enable them to glide smoothly over each other. Each
lung is partly divided into lobes, there being three lobes
in the right and two in the left lung (Fig. 86). Each lobe
is also made up of many small parts called lobules, each con-
taining a minute branch of a bronchial tube with air cells,
blood vessels, nerves, and lymphatics. The air cells in
the different lobules have no communication with one an-
other, so that if one of the bronchial tubes is obstructed
the cells opening into it are not supplied with air.

260. Blood supplied to the Lungs. — The blood conveyed
to the lungs is from two sources: (1) The pulmonary
artery from the right ventricle brings the impure blood,
collected by the veins throughout the body, to be purified,
or oxygenated. (2) The bronchial arteries bring pure
arterial blood for the nutrition of all parts of the organ.
This is returned through the bronchial veins, and in some
measure also through the pulmonary veins.

261. Inspiration and Expiration. — The thorax is a closed
cavity, and the air cannot reach the outside of the lungs,
hence the pressure of the weight of the atmosphere affects
the lungs only from the inside, and they are kept dis-
tended to fill the cavity. If the thorax is increased in
size, the air rushes in and distends the elastic cells of the
lungs still more. If the cavity of the thorax is reduced
in size, the air is forced out, and the lungs are contracted.

RESPIRATION

185

It is the pressure of the atmosphere which causes the air
to enter the lungs in what is called inspiration, and the
pressure upon the lungs by the walls of the thorax which
forces it out in expiration. These two acts together con-
stitute respiration.

262. The Respiratory Mechanism. — In respiration the size
of the thorax is increased in two ways: (1) by the de-
pression of the diaphragm, which forms the floor of the
cavity and separates it from the cavity of the abdomen;
(2) by the elevation of the forward ends of the ribs.

263. The Diaphragm is a sheet of muscle and tendon,
convex on its upper side, and attached by bands of striped
muscle to the lower ribs at

the side, to the sternum and
to the cartilages of the ribs
which join it in front, and
at the back by very strong
bands to the lumbar verte-
brae. Its center is a thin ex-
panse of tendon. When the
muscles about the circumfer-
ence contract, the arch is flat-
tened upon the contents of the
abdomen, which yield to its
pressure, and the thorax is en-
larged downward (Fig. 103).

264. Action of the Bibs and
Muscles of the Chest. — The

ribs are attached to the spinal column at an angle smaller
than a right angle (Fig. 33, p. 45), and slope downward
toward the breastbone, the lower ribs sloping more than
the upper. When, by the contraction of the chest mus-
cles, the sternum is drawn upward and outward, the ribs

\

Fig. 103. — Diagram illustrating
the varying position of the dia-
phragm during respiration.

186 UNCONSCIOUS NERVOUS OPERATIONS

are raised to a more nearly horizontal position, and the
cavity they inclose is enlarged toward the front. At the
same moment the ribs are rotated slightly at their articula-
tion with the vertebrae, and by their curvature they enlarge
the chest at the sides. Many muscles are involved in this
complex action. The external intercostal muscles (the
elevators of the ribs) and the muscles in the walls of the
abdomen are principally concerned, but certain muscles
of the head, neck, and back also assist, and in forced
breathing many others are brought into use. In ordinary,
quiet expiration, the elasticity of the chest walls, the
cartilages, and the lungs is sufficient to expel the air
inhaled without special muscular contraction. But in
special, extraordinary efforts of expiration, as in cough-
ing, sneezing, singing, etc., active muscular effort is
required. For this purpose the muscles of the abdominal
walls are chiefly brought into action, and by them the
diaphragm is forced upward, the cavity of the thorax is
made smaller, and the air is driven rapidly out of the
lungs. When those muscles again relax, the chest returns
to its normal size.

265. Effect of Respiration upon Air in the Lungs. — The
lungs are always full of air, about two hundred cubic
inches remaining in the lungs of an adult man after
expiration. He draws in and breathes out in ordinary
breathing from twenty to thirty cubic inches, and in
forced respiration may take in and expel one hundred
cubic inches more. By what is known as the diffusion of
gases the inspired air is equally mixed throughout with
that remaining in the air cells and tubes of the lungs, and
there is no accumulation anywhere of air which has been
deprived of oxygen. A similar interchange takes place
through the walls of the capillaries between the gases in

RESPIRATION 187

the air of the lungs and those in the blood; and in the
same way the oxygen passes from the blood to the tis-
sues, while the carbonic acid passes from the tissues into
the blood.

266. Atmospheric Air compared with Expired Air. — The
atmosphere is composed of five gases : oxygen, nitrogen,
argon, carbon dioxide, and watery vapor, the last varying
greatly in relative amount according as the atmosphere is
moist or dry. Helium and other recently discovered
gases exist in the air in very small traces, but may be left
out of consideration. Oxygen and nitrogen are the prin-
cipal elements in air. The amount of carbon dioxide in
outdoor air is very small.

Pure dry air contains in each one hundred parts 20.96
parts of oxygen, 78 parts of nitrogen, 1 part of argon, and
.04 part of carbon dioxide. Expired air (breathed once)
contains about 16 parts by volume of oxygen, 79 parts
nitrogen and argon, and 4 parts carbon dioxide. There is,
besides, in expired air, a considerable quantity of watery
vapor, and a variable amount of volatile organic matter,
not sufficient generally for chemical analysis to detect, but
often perceived in a close room by the sense of smell.

It appears from the above that more than four parts of
the oxygen is appropriated from the air in the lungs, and
that about four parts of carbon dioxide, besides a minute
amount of organic waste and some vapor of water, are
given back to the air. The temperature of the expired
air is very nearly the same as that of the body.

267. Effect of Respiration on the Blood. — The blood
brought to the lungs by the pulmonary artery is dark
purple in color, but that which is returned to the left
auricle of the heart, after circulating through the lungs,
is of a brilliant scarlet. The same difference is seen

188 UNCONSCIOUS NERVOUS OPERATIONS

between the bright arterial blood in the arteries and the
dark venous blood of the veins of the systemic circulation.
Chemical analysis shows that this difference in the blood
corresponds to the difference between the air inspired and
the air expired. The immense amount of capillary sur-
face which the air reaches in the air cells of the lungs has
taken from it a large amount of oxygen and has given up
to it carbon dioxide and organic waste, together with
some of the water in the venous blood of the capillaries.
That is, the blood has been arterialized in the lungs, for
(except in the pulmonary circulation, where the reverse is
the case) the arteries convey the oxygenated, or purified,
nourishing blood, while the veins are filled with the im-
pure, partly deoxidized, and poisonous blood. In health
both arterial and venous blood contain both oxygen and
carbon dioxide, the proportion of oxygen being much
larger in the arterialized blood.

268. Function of the Red Corpuscles. — It was stated in
the chapter on the Blood that the special function of the
red corpuscles is to take up and hold for a time a certain
amount of oxygen, and then to give it up to other tissues.
The red corpuscles, as we have seen, are chiefly made up
of a red substance called hemoglobin, and hemoglobin
which has absorbed a considerable amount of oxygen
becomes oxy 'hemoglobin, which is of a bright scarlet color.
Oxyhemoglobin becomes hemoglobin again and of a dark
purplish red when it is deprived of its oxygen. When
brought into contact with air in the lungs, the red cor-
puscles take up oxygen, while carbon dioxide is given
up in return. The oxygen is held b}^ the red corpuscles
in loose combination, that is, in such a chemical union
as is easily disturbed, the oxygen being readily given up
to form other combinations.

RESPIRATION 189

269. Tissue Respiration. — The lungs were once regarded
as the seat of the combustion of the body — as the fur-
nace to which the waste of the body was brought to be
burned up. It is now known that the tissues themselves
are the seat of combustion, or oxidation. The oxygen
given off to the tissues from the arterial blood in the cap-
illaries is not necessarily used at once in new chemical
combinations. In muscular tissue, and probably in other
varieties of tissue, it is stored for future use. This is
shown by the fact that severe muscular action, by which
the substance of the muscle fibers is broken down in the
production of energy, results in the elimination of carbon
dioxide which contains more oxygen than the whole
amount taken up by the lungs during the time of action.

It appears that the tissues are constantly taking oxygen
from the blood (or, strictly speaking, from the lymph)
and combining it in forms which are easily decomposed,
and thus the oxygen is ready when it is needed for the
liberation of energy. A man gives off from his lungs
more oxygen in the form of carbon dioxide during the
day, when his muscles, brain, and digestive organs are
at work, than the lungs take up during the same time.
The excess had been stored during his periods of rest.
Although oxygen is that element in the air which sup-
ports life, it has been established by experiments that an
animal uses no more oxygen in a given time when it
breathes the gas pure than when it breathes ordinary air,
that is, the amount of work done by the tissues is not de-
termined by the amount of oxygen supplied to them, but
the quantity of oxygen used is determined by the amount
of work done. An excess of oxygen above that amount
needful to prevent suffocation will not make the organs
work any more than extra food will make a man work.

MACY'S PHYS. — 12

190 UNCONSCIOUS NERVOUS OPERATIONS

270. Necessity of Ventilation. — In each ordinary expira-
tion of an adult man, from twenty to thirty cubic inches
of air issue from the lungs, or in one hour about twelve
cubic feet. This air has been deprived of a large pro-
portion of its oxygen, which has been replaced chiefly by
carbon dioxide. This carbonic acid, while not itself poi-
sonous, at least in small quantities, is always associated
in expired air with waste products of organic life which
are so, and is a measure of their amount. To be fit for
breathing, air should not contain more than one fifth of one
per cent of carbon dioxide. Some authorities say one tenth.

It is found that in quiet breathing a man gives out
something over 1000 cubic inches of carbon dioxide in an
hour. If hard at work, he will expire two or three times
as much. From 1000 to 3000 cubic feet of fresh air per
hour for each occupant of a closed room should be
supplied from outside the building, and in hospitals and
workshops the amount should often be much larger. Per-
sons vary greatly in their sensitiveness to impure air.
Many become accustomed by long usage to dwelling in
ill-ventilated rooms, and seem to suffer no immediate evil
effects ; when others coming from a purer atmosphere will
experience dizziness, headache, or nausea.

271. Ventilation is the regular and continuous removal
of the expired, vitiated air from a room and the admis-
sion of pure atmospheric air. To be adequate to human
needs, it must bring into a room enough external air to
dilute the poisonous products of respiration and of the
combustion of gas, oil, or candles, together with the exha-
lations from the skin, to such a degree that the air of the
room may remain pure enough for breathing.

The amount of air, by weight, inhaled by an average
person in twenty-four hours is from six to eight times

RESPIRATION 191

that of the food which he eats, and it is at least quite as
important that this air should be pure as that the food
consumed should be wholesome.

Every expiration of each pair of lungs in a closed room
reduces the quantity of oxygen in the room and increases
the carbonic acid gas and other impurities. Now, experi-
ence and experiment have proved that the relative propor-
tions of these gases in the air inhaled cannot be greatly
changed without injuriously affecting animal organisms.
The presence of 1 per cent of carbonic acid gas is harm-
ful, though 1 per cent may be endured for a time ; but it
is the impurities always present with the gas, other than
the carbonic acid gas itself, together with the increase of
moisture and heat and unpleasant odors , that produce the
bad effects. When the amount of carbon dioxide becomes
10 per cent death is only a matter of time.

A person may be suffocated to death in an ill-ventilated
room from lack of oxygen, from an excess of carbon
dioxide, or from the two causes combined, and he is also
exposed to other dangers whose effects are not manifest
at once. If several persons are present, germs of disease
are liable to be floating in the air or clinging to walls or
floor, and may easily be drawn into the lungs along with
other dust. The diseases most often communicated in
this way are consumption and pneumonia, each of which
is believed to be caused by a specific bacterium.

272. Methods of Warming and Ventilation. — In some mod-
ern buildings, provision for ventilation is made in connec-
tion with the heating apparatus. Hot air furnaces provide
for a constant flow of warm air into a room, with the removal
of that already present. The danger is lest the air brought
in should be taken not from pure outdoor sources but from
cellars, or from rooms where it has been already vitiated,

192 UNCONSCIOUS NERVOUS OPERATIONS

or from openings too near a cesspool or sewer pipe.
Houses warmed by the circulation of steam or hot water
must have independent arrangements for ventilation by
means of open fireplaces or chimney flues, and adequate
openings for admitting pure air. The same may be said
of houses heated by ordinary air-tight stoves, or by oil
and gas stoves. The latter, while making no provision for
ventilation, increase the need of it by their combustion.

When adequate provision for ventilation is not made in
the construction of a building, fresh air may be admitted,
without causing a direct draught, by fitting a board six
or eight inches wide under a raised window sash, so that
the exchange between internal and external air may take
place between the sashes. Such an arrangement is useful
in schoolrooms and other places of assembly. Care should
be taken to avoid a draught of cold air, which is some-
times more immediately dangerous than to breathe viti-
ated air for a little while. At the same time it should
not be forgotten that the worst effects of breathing im-
pure air do not appear at once. While it is a direct cause
of pulmonary consumption (the greatest scourge of the
human race) and other ills, it may be a long time before
disease appears. The vitality of the system is gradually
lowered, strength and vigor are undermined, so that some
slight overexertion or exposure to cold or to specific
germs of disease may result in serious or fatal conse-
quences. When the whole system is kept by correct
habits of life at a high level of health, when all the parts
work vigorously, easily, and in harmony, one is able to
endure unharmed exposure even to active germs of malig-
nant diseases.

273. Correct Breathing. — One can breathe properly only
when the clothing is loose enough to allow entirely free

RESPIRATION 193

movement of all the muscles concerned in respiration. It
has been noticed that men and infants use the abdominal
muscles and those of the lower part of the chest more
than women do. This is not because women have a
sort of breathing apparatus different from that of other
human beings, but because their clothing is too frequently
worn so tight that full and free respiration is impossible,
the various organs being displaced and deformed, and the
whole system weakened, while to the artistic eye the fig-
ure appears distorted and ugly.

One .should accustom himself to go often into the open
air and draw long, full, and deliberate breaths, followed
by slow expiration, in order that all the minute air cells
of the lungs may be filled and their walls expanded.
Those which are habitually unused may become perma-
nently collapsed and hardened, and the capacity of the
lungs be thus reduced, the whole system being weakened
and prepared to fall an easy prey to disease.

274. Temperature of Air for Breathing. — Man is able to
live a healthy life in the most torrid climates and in
regions where the air is many degrees below the freezing
point. He can even remain for some time unharmed in a
chamber heated far above the boiling point of water.
Such are the marvelous adjustments of which his organ-
ism is capable.

But in connection with the artificial warming of closed
rooms, it is necessary to inquire as to the most healthful
temperature of the air habitually breathed. Most people
in America live, in winter, in rooms too hot for health,
and thus render themselves unnecessarily liable to " take
cold " on going out. A living room for adults in ordinary
health should have a temperature of from 65° to 70° F,
(18° to 21° C.). For young children, the aged, or the

194 UNCONSCIOUS NERVOUS OPERATIONS

feeble the room may be a few degrees warmer. Sleep-
ing rooms should usually be much colder, but definite
rules cannot be given. Much depends upon habit, age,
and state of health. To live always in a warm atmos-
phere is enervating. Cold air, when pure, is far more
refreshing and invigorating. It is highly desirable to
accustom one's self to sleep with open windows in all
seasons.

275. Respiration as affected by the Use of Alcohol and
Tobacco. — The action of alcohol upon the muscular walls
of the arteries, which has been already more than once
referred to, is especially important in the capillaries of the
lungs. When they are dilated by the paralyzing effect
of alcohol, their expansion reduces the size of the air cells
in the lungs and leaves less room for the air which the
lungs need, so that less oxygen is supplied to the blood.
When the capillaries are often or continuously distended
in this way, their walls are likely to become permanently
thickened, and the interchange of gases which normally
takes place there, by which carbon dioxide passes from
the blood while the purifying oxygen is taken into the
blood, is impeded. Serious disease even may result, such
as a peculiar and quickly fatal form of consumption found
only among drinkers of alcoholic fluids.

The throat, bronchial tubes, and lungs of a tobacco
smoker are all liable to irritation by the poisonous smoke,
and chronic inflammation is often caused. The nicotine
of tobacco is a deadly poison, and" in cigarettes there are
often other poisons equally dangerous to health.

DEMONSTRATIONS AND EXPERIMENTS

83. Dissection of the Respiratory Organs. — The thorax of a rabbit,
cat, or dog will be found serviceable. Before cutting open the chest,

RESPIRATION

195

the arrangement of the ribs, intercostal muscles, and connected parts
should be noticed. When the thorax is cut open the lungs collapse.
Observe the relation of the heart to the lungs. Innate the latter
through a tube inserted in the trachea. Observe the diaphragm;
note its shape in contraction and relaxation. Cut open the lungs and
trace out in them the subdivisions of the bronchial tubes. The struc-
ture of the trachea and larynx should be carefully studied.

84. To illustrate the Action of the Diaphragm in Respiration. — Tie
over the large end of a stoppered bell jar, or of a large bottle whose

bottom has been removed, a
piece of thin rubber cloth
(Fig. 104). Close the smaller
opening of the jar with a
cork, through which runs a
glass tube, on whose inner end
a thin rubber bag is tied, as
shown in the figure. Then, if
the rubber bottom be pushed
in, the bag will collapse.
When the bottom is allowed
to return to its first position,
the bag expands. The rub-
ber bottom represents the dia-
phragm, and the small rubber
bag and the glass tubing the
lungs and trachea, while the /rflTi
jar itself represents the tho-
rax. If the lungs and trachea of a small animal be
carefully dissected out, they may be used to replace
the small rubber bag by tying the glass tube in the
trachea. In this way may be shown the movements
of the lungs themselves in respiration. Another form
of apparatus for demonstrating the action of the
diaphragm in respiration is shown in Fig. 105, in
which the bell jar and rubber cloth of Fig. 104 are
replaced by a lamp chimney and a piston. (The
piston can be made of a wooden stick with a piece
of wet cloth tied around the large end.)

85. To illustrate the Function of the Ribs in Respiration. — Construct a

Fig. 104.— Apparatus
to illustrate the
action of the dia-
phragm in respira-
tion.

Fig. 105.

Apparatus to de-
monstrate the
action of the
diaphragm in
respiration.

196

UNCONSCIOUS NERVOUS OPERATIONS

piece of apparatus as shown in Fig. 106. The standard A B repre-
sents the vertebral column ; the two pieces CD and EF represent two
of the ribs, with Z)F, a portion of the sternum, attached ; a and b are
rubber bands representing the external and internal intercostal muscles
respectively ; c is a rubber band of such strength that it Keeps the

Fig. 106. — Apparatus to illustrate the movements of the ribs and
sternum in respiration.

apparatus in position I when the rubber bands a and b are both on.
Remove the rubber band a ; Z>Fis lowered. Replace a and remove b ; DF
is raised. Observe that when DF is raised from position IT, the dis-
tance between DF and CE is increased, unless DF is raised too far.

86. To show the Moisture in Respired A ir. — Breathe upon a cool plate
of glass; some of the vapor in the breath will be condensed upon the
glass. To show that the presence of moisture is due to respiration,
blow upon the glass writh bellows.

87. To show that A ir is made Warmer in Respiration. — Notice the
reading of a thermometer, then breathe upon its bulb.

88. Some Properties of the Constituent Gases of A ir. — The teacher
should prepare oxygen, nitrogen, and carbon dioxide by methods
given in ordinary text-books of chemistry. Place a smoldering
splinter of wood in a vessel of oxygen ; the stick bursts into flame.
Place the flaming splinter in a vessel of carbon dioxide or nitrogen ;
the flame is at once extinguished. Place a blazing splinter in an
empty jar, i.e. containing only air; after burning some time it goes
out. Before the last trace of fire disappears, transfer the splinter to
a jar of oxygen; it burns actively again. Into a clean, empty jar put
a little limewater, prepared by dissolving lime in water. Cover the
jar and shake it well; if any considerable amount of carbon dioxide is
present, a white precipitate will form in the limewater. Now place
a burning splinter in the jar and allow it to burn out. Then shake

RESPIRATION 197

the jar ; the presence of carbon dioxide will be very evident. Repeat
the latter operation after allowing splinters to burn out in a jar of
oxygen. From these experiments it becomes evident that oxygen is
necessary in ordinary combustion, and that carbon dioxide is a
product of combustion.

89. To show that Respiration increases the Amount of Carbon Diox-
ide in the Air. — By means of a glass tube blow through lime water;
the white precipitate of carbonate of lime shows the presence of car-
bon dioxide in the breath. To show that most of this is a product of
respiration, pass some of the ordinary air of the room through lime
water ; the white precipitate is much smaller in amount.

90. To illustrate a Difference between "Arterial" and "Venous"
Blood. — Obtain some fresh ox blood at a slaughterhouse and "whip"
it to remove the fibrin and prevent clotting. By means of a carbon
dioxide generator, pass carbon dioxide gas through the blood; the
blood becomes darker. Now pass air through it, thus supplying
oxygen ; it becomes more scarlet in color.

CHAPTER XV
NERVOUS CONTROL OF THE RESPIRATORY APPARATUS

276. The movements of respiration may go on in ordi-
nary quiet breathing without consciousness and without
volition, but they are also, in a measure, under voluntary
control — not wholly so, for it is impossible to commit
suicide by holding the breath.

277. The Respiratory Center and Nerves (Fig. 107). — A
certain restricted area in the medulla oblongata is recog-
nized as the respiratory center, and there are believed to
be other such centers lower down in the spinal cord. Nerv-
ous impulses pass from the center down the spinal cord,
and thence by the anterior roots of many of the spinal
nerves to the plexuses which those nerves form. By com-
municating branches from these plexuses connection is
made with the spinal ganglia of the sympathetic system,
and with the tenth and eleventh cranial nerves. From
these various sources motor fibers pass on to the numerous
muscles concerned in respiration. That which supplies
the diaphragm is the phrenic nerve, which is traced back
to the three or four upper pairs of spinal nerves.

If the spinal cord be divided below the fourth pair of
spinal nerves, the diaphragm will continue to act, but the
intercostal muscles will be paralyzed. If the cord be cut
just below the medulla oblongata, all respiratory movement
of the chest ceases ; and if that small portion of the medulla

198

NERVOUS CONTROL OF RESPIRATORY APPARATUS 199

oblongata known as the respiratory center be removed, no
further respiratory movements will take place, and death
immediately follows.
On the other hand, the
whole of the brain for-
ward of the medulla
may be removed, and
breathing will not stop.
278". The Expiratory
Center. — It is now un-
derstood that the cen-
ter of respiration in
the medulla is in real-
ity double, — that there
is one center for inspir-
atory movement and
another beside it for
expiratory movement.
In ordinary quiet
breathing the first only
is excited, expiration
taking place by the re-
laxation of the muscles
contracted in inspira-
tion. But in violent or
forced expiration the
internal intercostal and
abdominal muscles are
brought into active use,
and the nervous influ-
ence stimulating them
to action comes from
the expiratory center.

Fig. 107. — Diagram of the nervous con-
trol of the respiratory organs.

ab motor spinal nerves going to muscles of
the abdominal walls.

E expiratory center.

ex sensory nerve fibers from the larynx ex-
citing the expiratory center.

ex' sensory fibers from the lungs exciting
the expiratory center.

ext motor spinal nerve fibers passing to
external intercostal muscles.

/ inspiratory center.

in sensory fibers from larynx inhibiting
the inspiratory center.

in' sensory fibers from the lungs that excite
the inspiratory center.

int motor spinal nerve fibers passing to in-
ternal intercostal muscles,
motor fibers of phrenic nerve going to
diaphragm.

ph

200 UNCONSCIOUS NERVOUS OPERATIONS

279. Reflex Action of Respiratory Center. — Though the
action of the breathing center in the medulla oblongata is
shown by experiment to originate efferent nervous impulses
independent of irritation conveyed to it by sensory fibers,
it is also largely under reflex control. For instance, when
the mucous membrane of the air passages is irritated by
foreign substances, a sudden sneeze or cough results. A
sudden dash of cold water upon the skin causes a quick,
long inspiration. So it appears that in normal respiration
the movements are not reflex, while reflex movements are
also possible.

280. The Normal Excitation of the Respiratory Center is due,
more than to any other cause, to the relative amounts of
oxygen and carbon dioxide in the blood which reaches it.
If the blood contains too little oxygen and too much carbon
dioxide, the center is stimulated, and the resulting respira-
tory movements tend to correct the evil.

Afferent nervous influences brought to the center along
the .vagus nerves also excite its action. The main trunk
of this tenth nerve contains fibers which excite inspiration,
and other fibers which inhibit, or check, inspiratory move-
ments. It is supposed that the expansion of the air cells
in the lungs, where many of the vagus fibers end, produces
impulses along those fibers which result in inhibitory or
expiratory impulses from the center in the medulla ; while,
on the other hand, collapse of the air cells excites along
other fibers contrary impulses which result in inspiration.
Thus the action of the lungs becomes that of a self-regulat-
ing pump. Other afferent impulses along branches of the
vagus, or from other nerve fibers connected with it, may
also affect respiration.

CHAPTER XVI
FOOD

281. Losses of the Body. — One effect of respiration is to
reduce the weight of the body. A man gives off from
the lungs, in the course of twenty-four hours, about eight
ounces of carbon and about half a pint of water, which
are taken from the tissues of the body as worn-out mate-
rials. There are also other sources of loss to the body in
the processes of excretion, by which the waste or used-up
matter of the body is cast off.

282. Sources of Restoration. — These losses must, of
course, be made good, or the body will waste away.
Through the lungs we get oxygen only, while we need
hydrogen, nitrogen, carbon, and other chemical elements
besides, which enter into the composition of our bodies.
These come to us in the food which we eat, and are pre-
pared for use within the body by the process called
digestion.

Food is that which, taken into the alimentary canal, sup-
plies material for the growth and repair of tissue, for the
generation of force, or for the regulation of force.

283. Nutrition. — Digestion is but one portion of a com-
plicated series of processes, called nutrition, which result
in the growth and repair of the constantly wasting tissues.
In its broad sense nutrition includes respiration, which
supplies the oxygen needed; digestion, or the conversion

201

202 UNCONSCIOUS NERVOUS OPERATIONS

of food by the chemical action of the digestive juices into
soluble substances ready to be acted upon by the absorb-
ents; absorption, or the passage of selected elements from
the digested food through the walls of the blood vessels
and lymphatics (lacteals); assimilation, or the conversion
of the new particles of food into the substance of the
tissues of the body; and the breaking down of the sub-
stance of the tissues to form waste. The building-up
processes constitute what is called anabolism, the break-
ing down of tissue Jcatabolism, while the whole double
operation receives the scientific name of metabolism. We
are now to study anabolism.

284. Object of Nutrition. — The various processes of nu-
trition take place in order to supply the human machine
with material in suitable form for the production of
energy. The oxidizable substances are distributed to
the tissues and are there submitted to the action of the
oxygen in the blood. Combustion then takes place, that
is, the substances in the tissue cells are burned. The
complex chemical compounds there found are decomposed,
and new and simpler compounds are formed, which being
of no further use to the body are removed from it by
mechanisms prepared for the purpose.

285. Forms of Energy in the Body. — The force set free
in the tissues by the combustion of their particles takes
many forms within the body, but as it leaves the body it
appears in two forms only : as heat or as work done by
the muscles. Just as matter may be changed from one
form to another, but cannot be destroyed, so energy, or
force, may be changed from one form to another, but can-
not be destroyed. The heat driven off in the combustion
of coal may be changed througli the agency of steam into
the motion of machinery, which may in turn be con-

FOOD 203

verted into electrical force or light, or again become heat.
A mechanic's blow upon an anvil converts muscular force
into motion, heat, and light. Any form of energy must
result from some other form of energy. It cannot come
from nothing.

286. Conservation of Energy and Correlation of Forces. —
These facts, in works upon the science of physics, are
stated as the laws of conservation of energy and of the
correlation of forces. The human body, like all other
matter, is subject to these laws.

As the power for a large proportion of our machines
comes from the heat of combustion, — that is, the union
of oxygen with other matter, — so does the energy of the
body come mainly from the same chemical action, and the
products of the slow combustion of food which takes place
within the body are much the same as they would be if
the food were burned in a furnace by swift combustion.
Those products are carbon dioxide, water, and a nitrogen-
containing substance which is discharged from the body
as urea, besides certain salts not oxidizable which would
appear in the furnace as ashes.

287. Food Elements. — The valuable parts of the matter
which we call food enter in varying proportions into many
different articles which we eat. Chemists divide these
elements, which are essential to the maintenance of the
body in health, into five classes, as follows : —

1. Proteids (Nitrogenous foods)

8 F^0^^68 [ (NonnitrogenoiiB)

4. Water )

5. Salts f Inorganic

Milk and eggs are examples of food containing all
these materials in proportions suitable for young, grow-

204 UNCONSCIOUS NERVOUS OPERATIONS

ing animals, and they are therefore spoken of as " perfect
foods."

288. Characteristics of a Healthful Diet. — (1) A health-
ful diet must contain all five chemical classes of food
elements in due proportion. (2) It must be adapted to
the climate, to the age of the individual, and to his mode
of life, that is, to the kind and amount of work which
he does. (3) Not only must the different kinds and
amounts of necessary food appear in the diet, but they
must appear in digestible form.

289. Classification of Foods. — With reference to the use
made of them, foods are divided into three classes : (1)
tissue builders ; (2) force generators ; (3) force regu-
lators. The proteids constitute the first class, though
we are not certain but that they may be sometimes oxi-
dized, yielding force without having entered into the
composition of living cells. In the second class are placed
the oxidizable substances, — the fats and carbohydrates.
They may also assist in forming tissue to some extent.
The third class includes the inorganic compounds,—
water, salts, etc., — and certain food accessories.

290. Proteids are the most important substances which en-
ter into the animal organism, being absolutely essential to
the phenomena of life. Plants are the great manufacturers
of proteids ; no process has yet been discovered for making
them artificially. Proteids are complex chemical com-
pounds and are characteristically represented by the
casein of milk and the albumin of egg. All are com-
posed of carbon, hydrogen, nitrogen, and oxygen in
various proportions, with a trace of sulphur. Proteids
are the only group of foods which contain nitrogen, and
whose chief if not sole purpose is the building of tissue.
Animals can live without carbohydrates and fats, but not

FOOD 205

without proteids. The chief proteids are the gluten
of all cereals, peas, potatoes, beans, and lentils; the albu-
min in white of egg, milk, and blood; globulin from yolk
of egg and blood; myosin found in lean meat; casein in
milk and cheese; fibrin in clotted blood. Though certain
vegetables (as beans and peas) contain more proteid than
does meat, they furnish it in a less digestible form, that
is, a considerable part of it passes from the body unaf-
fected by the digestive processes, and the proteid of these
vegetables is therefore less valuable as food.

Since only the proteids contain nitrogen, they are called
nitrogenous foods ; and carbohydrates and fats are called
nonnitrogenous.

A healthy, well-fed animal is found to lose by excretion
as much nitrogen daily as is supplied in his food. If the
food contains an insufficient amount of nitrogen, the quan-
tity excreted is greater than that received, and the tissues
waste away.

291. Fats are found in butter, milk, cheese, and meat,
in some of the grains, and in oils. They contain carbon,
hydrogen, and oxygen. They are oxidized in the body,
and furnish energy and heat.

292. The Carbohydrates, like the fats, contain carbon,
hydrogen, and oxygen; but the proportion of oxygen is
larger than in fats. The carbohydrates include (1) starch,
which is found in cereals, vegetables, nuts, etc. ; (2) sugars
of different kinds, — grape sugar, cane sugar, malt sugar,
and milk sugar, besides sugar manufactured from starch;
and (3) cellulose, found in fruits, cereals, and all vegetables.
Carbohydrates are very rapidly oxidized in the body, pro-
ducing heat, and it is they that are used up in the setting
free of energy when the muscles are vigorously exercised;
for it is found that the nitrogenous waste does not increase

MACY'S PHYS. — 13

206 UNCONSCIOUS NERVOUS OPERATIONS

in proportion to the increase of muscular effort. Carbo-
hydrates cannot alone form tissue, but under some circum-
stances may be used for that purpose with other elements.

293. Water, composed of oxygen and hydrogen, is found
in all foods, and has a variety of uses in connection with
nutrition, partly as a solvent for various elements in the
food, and partly as promoting osmosis, and as an aid to
the varied changes which take place in the tissues. Water
uncombined with food, introduced into the stomach as in
drinking, is all absorbed directly into the blood, of which
it forms about 80 per cent.

294. Salts. — The food elements that are salts are chiefly
the chlorides, phosphates, and carbonates of sodium and
potassium, and to a less extent those of calcium and mag-
nesium, with salts of iron and of some of the organic acids.
Common salt (chloride of sodium) appears in all animal
bodies, and to some extent in plants also. It helps to dis-
solve certain of the albumins of the body, promotes the flow
of the digestive fluids, and aids digestion in various ways.
About half an ounce each day is needed with the food.
That these saline matters are essential to health, is proved
by experiments upon animals. When they are eliminated
so far as possible from the diet, the central nervous sys-
tem soon suffers, and paralysis results, besides general
derangement of nutrition. When an animal body is
burned, the various salts which entered into its composi-
tion appear in the ashes which are left, while the other sub-
stances have been changed into gases.

295. Food Accessories. — These are the various drinks —
alcohol in different forms, tea, coffee, cocoa, etc. ; and condi-
ments — mustard, pepper, ginger, and other spices, and a
variety of other flavors added, not for their food value
(though of that they may have a small amount), but to give

FOOD 207

a pleasant taste which may assist digestion, and to stimulate
the secretion of digestive juices. Used to excess, how-
ever, all these drinks injuriously affect the nerves, and
the condiments may irritate the sensitive lining membrane
of the alimentary canal, besides impairing the delicacy of
the sense of taste.

296. Food Values. — The nutritive value of a diet lies
chiefly in the amount of nitrogen and carbon derived from
it. A man of moderately active life will give off, mainly
from the lungs as carbon dioxide, from eight to nine
ounces of carbon each day. If he is engaged in severe
muscular effort, he will give off much more carbon. The
amount of nitrogen passing from the body (chiefly as urea)
during a day is from .47 to .56 ounce, and with the
increase of muscular activity it does not increase to nearly
so great a degree as does the carbon.

In order to repair the daily waste of the tissues, the
proportions of carbon and nitrogen contained in the food
should be the same as in the excretions, viz. about 16.6 to
1. While the proteids contain carbon, they contain only
about 3.5 parts of carbon to 1 of nitrogen, hence other
groups of food elements must be depended upon to supply
the necessary carbon.

The oxygen contained in food, being already combined
with other elements, cannot be used in oxidation, so that
from the lungs alone comes the needful supply of that

Since the slow combustion within the body sets free the
same amount of energy as does the rapid combustion of
the same substances, by burning a quantity of food equal
to that which a man eats in a day and measuring the heat
given off, the amount of energy which that food can sup-
ply may be estimated. In that way it has been shown

208 UNCONSCIOUS NERVOUS OPERATIONS

that the energy from the fats is about equal to that from
proteids and carbohydrates together. It has been esti-
mated by a high authority that a healthful diet contains
from three and a half to four and a half times as much of
nonnitrogenous as of the nitrogenous foods.

297. The following table, from Landois and Stirling's
Physiology, gives approximately the relative amounts of
nitrogenous and nonnitrogenous elements in common
articles of food, and shows that, next to human milk,
wheat flour has most nearly the right proportion of the
two elements. Beef and other kinds of flesh have too
much proteid and should be eaten with potatoes or rice,
which supply the nonnitrogenous matter needed to make
the food complete. Vegetables contain too little nitro-
gen to be used alone as food.

Nitrogenous Nonnitrogenous

Veal 10 to 1

Rabbit's flesh . . . . ~ 10 to 2

Beef . . . . . '.10 to 17

Beans . . . . . . 10 to 22

Peas . .. . .'j . . 10 to 23

Mutton . r / .. . 10 to 27

Pork . . ' * . 10 to 30

Cow's milk . ... . 10 to 30

Human milk . . . . 10 to 37

Wheat flour ... . . 10 to 46

Oatmeal . . . . 10 to 50

Rye meal . . ;' . . 10 to 57

Barley . . . < . . 10 to 57

Potatoes * . . . " 10 to 115

Rice ....... 10 to 123

Buckwheat . . „ . > 10 to 130

298. Variation in the Amount of Food Required. — When
the body is at rest the amount of waste is much less than
it is when the muscles are engaged in active labor. Then

FOOD 209

the muscular tissue is rapidly broken down under the
strong contraction constantly called for, and the circula-
tion becomes swifter to supply material to rebuild the
decomposed cells. Respiration, too, must be quickened
to furnish a sufficient quantity of oxygen to arterialize
the blood flowing faster to the lungs, loaded with the
products of chemical changes in the tissue cells. Nerv-
ous tissue also is worn away by the constant demands
upon it for conveying impulses to the many muscles
engaged and in coordinating all their related actions.

If the body is exposed to a low temperature, a still
larger demand is made for food to supply the greater loss
of heat. During the period of growth a quantity of food
is needed in excess of the waste products to furnish mate-
rial for enlarging and strengthening all parts of the
body.

299. Undigested Food. — Some (an average of about one
tenth) of the food taken into the stomach, and especially
a part of our vegetable food, seems to play no part in sup-
plying nutrient material, but passes through the alimen-
tary canal to be expelled from the body unchanged. It
serves, however, as an aid to digestion by giving an
increase of bulk to the food, and so assists the action of
the digestive organs.

300. Cooking is the application of heat in one way or
another to articles used as food. Most of our diet comes
to the table after being submitted to this process, which
renders it more wholesome and more palatable. By cook-
ing, which lessens the cohesion of particles, the amount
of work required of the digestive organs is reduced, and
the chemical effects of heat prepare the various elements
in the food to receive more readily the action of the diges-
tive juices. Cooking also develops, especially in animal

210 UNCONSCIOUS NERVOUS OPERATIONS

foods, the agreeable flavors which stimulate not only the
appetite, but also the secretion of the digestive juices.

Another very important effect of the application of
heat in the cooking of food is the destruction of many of
the germs of disease which are sometimes introduced into
the human system with food. Certain diseases of animals
whose flesh is eaten by man may thus be communicated
to him if the meat is not first thoroughly cooked. Dis-
ease is often conveyed also by means of the water supplied
to a town or a dwelling, and in all cases where there is
reason for suspicion respecting the purity of the water
used for drinking, it should be boiled for at least half an
hour before using. This sterilizes it. Ice should never
be mixed with drinking water, on account of its impuri-
ties. Sterilized water may be cooled for drinking pur-
poses by inclosing it in tight cans of glass or metal and
placing the cans in contact with the ice.

Much of our food comes to the table badly prepared,
cooked too mucli or too little, or in an unhealthful man-
ner. The importance of good cooking cannot be overesti-
mated; the lack of it is a fruitful source of the widely
prevalent disease, dyspepsia, from which result innumer-
able physical and mental ills. In recent years much
attention has been paid to scientific cookery, and it is
now taught in many schools. Only a few hints can be
given here.

301. Cooking of Meats. — Fresh meat which is to be boiled
should be put at first into water which is already boiling
briskly. After fifteen minutes the kettle should be placed
where, for the rest of the time, the water will only bubble
slightly. By applying strong heat at first, the albumin
of the surface of the meat is hardened and forms a close
coating which retains the nutritive juices Avithin.

FOOD 211

When soup or broth is to be made, this process is
reversed — the object being to extract the soluble portion
of the meat from the fiber. The meat is cut into small
pieces and the bones are cracked. All is then placed in
cold water without salt, and heated slowly to a tempera-
ture just below the boiling point. It should be kept as
hot as possible, without actually boiling, for from six to
eight hours.

Salt meat may be placed in cold water and gradually
heated. Corned beef requires boiling for about five
hours.

Roasting and baking are done before an open fire or in
an oven. The meat should first be browned by exposure
to a very high temperature, in order to preserve the juices,
and the heat should then be reduced.

In broiling and frying the same principle applies.
Frying is regarded as the least healthful of the various
ways of preparing food, because the fat which coats the
surface is supposed to be indigestible. Anything cooked
by frying should be quickly and wholly immersed in fat
so hot that the surface browns at once and further
absorption of fat is prevented. Then the heat should be
lowered.

By stewing and braising, meats may be economically
cooked at a moderate temperature, but the process re-
quires several hours. In stewing, the temperature should
not quite reach the boiling point. In braising, which is
done in a closely covered pan in an oven, a higher degree
of heat is applied. By these two methods the tougher
and cheaper cuts of meat may be made entirely tender,
nutritious, and appetizing.

302. Fish. — Principles similar to those suggested above
apply to the cooking of fish.

212 UNCONSCIOUS NERVOUS OPERATIONS

303. Eggs. — Eggs are made most digestible by placing
them (in their shells) in cool water, applying heat, and
removing them from the water as soon as it boils. Or,
they may be put into water already boiling, the vessel
being covered and at once removed to where the water
will keep warm but will not boil. They will be " done "
in from ten to fifteen minutes, according to the weather
and the amount of water used. In eggs cooked in this
way, the albumen, which by boiling becomes hard and
difficult of digestion, remains soft, creamy, and nutritious,
while the yolk is partly solidified and rendered more
palatable.

304. Cooking of Vegetables. — Fresh vegetables should be
placed in boiling water only long enough to soften the
fiber and cause the starch granules to burst. Too much
cooking injures them.

Dried seeds require longer boiling, and it is often well
to soak them in water for several hours before cooking.

305. Bread is our most valuable food. It is made from
the various grains, also from the flour of certain nuts
and rootstocks. Salt, water, and yeast, in proper propor-
tions, and sometimes a small quantity of sugar to hasten
fermentation, are added to the flour or meal, and the mass
is allowed to become " light " by the fermentation of the
yeast before baking. Numerous chemical changes take
place in the process. The water dissolves the gluten and
sugar of the flour and swells the starch granules. If the
dough is at a temperature of 100° F., fermentation at
once sets in ; some of the starch becomes sugar ; sugar is
converted into alcohol and carbonic acid ; the gas formed
expands in little bubbles, which are surrounded by walls
of sticky gluten, and "raises" the bread. If the fer-
mentation is allowed to continue too long, a new chemical

FOOD 213

product, called acetic acid, appears, rendering the bread
sour and unwholesome.

A few things are indispensable to the making of good
bread. A good quality of flour must be used and good
yeast (Miss Parloa considers the " compressed yeast "
sold in the shops and bakeries the best procurable). The
dough should have at first a temperature of 100° F.,
which should later be reduced to 70°. The mass must
be kneaded sufficiently to distribute the yeast evenly
throughout, and again after it has " risen " to break the
bubbles of gas and force it to permeate every part, that
the loaf may be rendered light and spongy by innumera-
ble fine pores. After the final kneading and shaping into
loaves, they should be left to rise to about twice their
original size before baking. The oven should be heated
to about 400°, but for the last half of the baking the
temperature should be reduced to 300°. In baking, the
process of fermentation is checked as soon as the loaf is
raised to a temperature of 212°. The alcohol is vaporized
and driven off, the starch granules burst, and by the
transformation of starch into sugar and dextrine the
delightful sweetness of good wheat bread is developed.
Very large loaves are undesirable, as acetic acid may
be formed in their interior after they are placed in the
oven. Small loaves are better than large ones, also
because they have a larger proportion of crust, which is
the sweetest and most wholesome part of the loaf.

Bread made of whole-wheat flour is especially valuable
for children, because it contains more of the elements
which are needed for making teeth and bone than does
white flour. The same is true of what is called Graham
flour, but the coarse bran which such flour contains is to
some persons unwholesome.

214 UNCONSCIOUS NERVOUS OPERATIONS

EXPERIMENTS

Food Elements. — Some very interesting and easily performed
experiments may be made upon substances common in ordinary food.

91. Tests for Proleids. — To one fourth of a test tube of dilute white
of egg1 (a proteid) add a few drops of strong nitric acid and boil.
Cool and add a little ammonia; the yellow color changes to orange.
To show that the orange color is due to the presence of a proteid,
repeat the experiment, using pure water instead of white of egg.
Another test is as follows : To one fourth of a test tube of a 15 per
cent solution of caustic soda add two or three drops of a 1 per cent
solution of copper sulphate. Shake the mixture, and after warming
add a little white of egg or other solution of proteid ; the blue color
becomes violet. To show that these color changes are tests for pro-
teids, repeat the above experiments, using a solution of sugar and the
starch solution mentioned below, instead of the white of egg.

92. Coagulation of Albumin by Heat. — Boil dilute white of egg in a
test tube; it does not clot. Then add, drop by drop, dilute acetic
acid (2 per cent) ; a precipitate of coagulated albumin finally sepa-
rates. If the white of egg is not diluted, it coagulates, of course, on
boiling.

93. Solubility of Starch. — Stir some starch into cold water and
observe that it does not dissolve. Boil the mixture ; solution occurs,
but the liquid remains somewhat cloudy.

94. Test for Starch. — To some of the starch solution prepared
above, add a drop of iodine solution. The blue color resulting is the
characteristic reaction of iodine with starch. Dilute the starch solu-
tion and repeat the experiment. The dilution may be much pro-
longed before the blue color fails to appear on adding iodine. To
show that the blue color is related to the presence of starch, add
iodine to pure water or any liquid from which starch is known to be
absent.

95. Microscopical Examination of Starch. — Scrape the fresh cut -sur-
face of a potato, and mount in water on a slide some of the material
thus obtained. Examine with the compound microscope. Numerous

1 To prepare dilute white of egg, beat up the white of an egg with
about twenty volumes of water, filter through muslin, and pour off
gently to remove air bubbles present.

FOOD .-••- 215

small starch granules will be seen. Each granule shows concentric
markings. Add iodine solution ; the granules turn blue or blue black.
Examine other kinds of starch granules, of corn, oats, rice, etc.

96. Test for Sugar. — To one fourth test tube of a weak solution
of glucose, add an equal amount of a 15 per cent solution of caustic
soda. Shake, and after adding a few drops of a 1 per cent solution
of copper sulphate, boil for a few minutes. The liquid changes
from blue to yellow, or, if much sugar is present, to brown in color,
and a precipitate is formed. To show that the change in color is due
to the sugar present, repeat the preceding, using pure water, or any
solution known not to contain sugar, instead of the sugar solution.
This test is known as Trommer's test. It is not a test for cane sugar,
nor does it distinguish between glucose, malt sugar, and milk sugar.

97. Fats. — Put some melted butter, or olive oil, into a test tube
one fourth full of water. The fat rises to the top. Shake well ; a
whitish mixture, or emulsion, is the result, but the oil and water
quickly separate. To the contents of the test tube, add an equal
amount of 1 per cent solution of carbonate of soda (an alkali), and
shake. The emulsion with the alkali lasts much longer than that
with water alone. Add a drop or two of oleic acid (a fatty acid) to
the mixture, and shake well; the emulsion lasts longer than before.
It will be learned later that the fats are only slightly dissolved in
digestion, but are chiefly emulsified.

98. Examine with the microscope some of the emulsion prepared
above. The fat will be found to be broken up into innumerable fine
particles.

99. Shake some olive oil with dilute white of egg in a test tube ; an
emulsion results.

100. To one fourth test tube of water, add a few drops of oleic
acid, and shake. The oil rises to the surface as in the preceding-
experiments. To the contents of the test tube add carbonate of soda
as before. A white precipitate of soap is formed. An alkali and a
fatty acid form soap.

During digestion some of the fat is broken down into glycerin and
fatty acids. The latter unite with alkalis in the intestine to form sol-
uble soap.

101. Flour. — Boil a little flour in water and test with iodine for
starch.

102. Place a little flour in from five to ten times its bulk of water

216 UNCONSCIOUS NERVOUS OPERATIONS

in a flask and allow it to stand several hours, shaking it occasion-
ally. Filter and test the nitrate for proteids, as in Ex. 91, and for
sugar as in Ex. 96.

103. Shake some flour with ether in a test tube and allow it to
stand for an hour or two, keeping the tube tightly corked and shak-
ing it occasionally. Filter off the ether and place some of it on a clean
glass surface and allow it to evaporate. A greasy residue remains,
showing that the flour contained fat, some of which was dissolved out
by the ether.

104. Gluten. — Moisten flour with water till it forms a tenacious
dough. Tie it in muslin cloth and knead it in a vessel of water till
all the starch is separated. There remains in the cloth a sticky, elas-
tic mass of gluten, consisting of the insoluble albumins, some of the
ash, and the fats. Draw out some of the gluten into threads, and
notice its tenacity.

105. Milk. — Examine with the microscope a drop of fresh milk.
It is seen to be an emulsion of oil globules floating in a liquid.

106. Warm some milk in a flask, and add a few drops of acetic
acid. The mass clots and separates into a solid curd, consisting of
casein and fat, and a liquid, the whey. Caseinogen is the chief proteid
of milk. In curdling it is changed to casein.

107. Dilute milk with ten times its volume of water and slowly add
dilute acetic acid. As long as the liquid remains alkaline, or neutral,
— as can be tested with litmus paper, — no visible change occurs, but
on adding more and more of the acid there is finally formed a precipi-
tate of casein which, as in the preceding experiments, carries with it
most of the fat.

108. Filter the curd from the whey obtained in one of the preced-
ing experiments, and test the filtrate for sugar (milk sugar) and pro-
teids (see Exs. 96 and 91).

109. Test, with litmus paper, some perfectly fresh milk. It will
be found to be neutral, or alkaline. Allow it to stand in a warm place
till it becomes sour and curdles. It will be found to be acid in reac-
tion. In the souring of milk the milk sugar changes to lactic acid,
and curdling is finally produced by the acid, as was illustrated in
preceding experiments.

110. Lean Meat. — Mince finely some perfectly fresh muscles of a
cat, dog, or rabbit. Place them in a large jar of water and stir. Tn
about a quarter of an hour filter through muslin and place the muscle

FOOD 217

in a fresh jar of water. Test the nitrate for proteids (serum albumin)
as in Ex. 91. Repeat the washing till the nitrate gives no test of pro-
teids. An hour or two of washing will suffice. Then squeeze out the
water from the minced muscle, grind up the latter with clean sand,
and add ten times its volume of a 10 per cent solution of common
salt. Stir occasionally, and after an hour or more filter through mus-
lin. Add some of the nitrate, drop by drop, to a large vessel of pure
water ; there is formed a milky precipitate of myosin, the chief proteid
of muscle. In the living muscle the myosin exists as the soluble
myosinogen. Thus in muscle there are seen to be two kinds of pro-
teids : one, serum albumin, soluble in water, the other, myosin, in-
soluble in water, but soluble in weak salt solution.

CHAPTER XVII

THE DIGESTIVE APPARATUS AND NUTRITION

306. The apparatus for digestion consists of the alimen-
tary canal with its appendages. This is a long, irregular
tube having a continuous lining of raucous membrane.
It comprises the mouth, pharynx, esophagus, stomach, and
large and small intestines. Numerous glands along its
length furnish the digestive juices.

307. The Mouth (Fig. 108) is the chamber which re-
ceives the food through the opening and closing lips.
The soft palate at the back forms a curtain over the
opening at the back, while the hard palate of the roof,
the soft muscular walls of the cheeks, and the large muscle
of the tongue, together with the teeth, all assist in the
process of mastication to which the food is first subjected.
As in the skin, many minute papillce are found in the
mucous membrane, containing networks of nerves and
blood vessels. Some of these contain taste corpuscles.
Some have organs for touch.

308. The Teeth are the special organs for cutting and
grinding the food. Two sets" of teeth are provided.
The first, which appear in infancy and are only twenty
in number, are called temporary or milk teeth. They fall
out after a few years, to be replaced by the permanent
teeth, thirty -two in number.

The four front teeth on each jaw are called incisors.

218

THE DIGESTIVE APPARATUS AND NUTRITION 219

Next to them come the canines, one on each side, then the
two bicuspids, or premolars, and next to them three molars
on each side. The third pair of molars on each jaw are
called the wisdom teeth, and they sometimes fail to appear.

Opening of
Kustachiantube

Soft palate

Epiglottis

Glottis
Esophagus

Larynx

~~ Hard palate

— Tongue

Hyoid bone

False vocal cords

• True vocal cords

Thyroid carti-
lage

--"--==»•, Cricoid carti-
lage

Fig. 108. —Vertical section of the head and neck.

The teeth of different animals are adapted 'in form and
structure to the food upon which they subsist. Carnivo-
rous animals are provided with strong, sharp teeth for
seizing and tearing flesh, while the teeth of herbivorous
animals are broader and relatively shorter, with wide-
ridged surfaces for grinding grains and plant fiber. Man,
as requiring both animal and vegetable food, is provided
with teeth of both sorts.

309. Structure of a Tooth (Fig. 109). — A tooth has three
parts, — crown, neck, androote. The crown is the part which
projects beyond the gum, and is covered with the firm,

220

UNCONSCIOUS NERVOUS OPERATIONS

solid layer of enamel, the hardest tissue found in the body.

The neck is the narrowed portion just below the crown,

surrounded by the gum. The
root (one or more) is the re-
mainder of the tooth, which is
secured to the socket of the
jaw by means of the perios-
teum, through which it derives
nourishment. A tooth is com-
posed of a hard, close material
called dentine, much like bone,
but with less animal matter.
This is molded round the cen-
tral pulp cavity, which contains
the tooth pulp — a mass of loose
connective tissue, blood vessels,
nerves, and cells of different
shapes, one sort of which builds
the dentine. A layer of true
bone, called tooth cement, sur-
rounds the dentine of that part
of a tooth embedded in the gum,
as enamel caps the crown.

310. The Tonsils. — Between the arches of the soft palate
lies on each side a soft rounded body covered with mucous
membrane and containing many small glands which se-
crete mucus. They are called the tonsils (Fig. 108).
Their use is unknown except that they furnish some pro-
tection to the larynx and pharynx. Being sometimes
permanently enlarged and subject to frequent inflamma-
tion, they are occasionally removed by the surgeon with
apparent advantage to the patient.

311. The Pharynx (Fig. 108) lies behind the soft palate.

Fig. 109. - Diagram of the
structure of a tooth.

THE DIGESTIVE APPARATUS AND NUTRITION 221

It has muscular walls, mostly of voluntary fibers, which
contract upon the food to push it into the esophagus, or
may force it back into the mouth if desired. Seven
passages open into this cavity: the mouth, the two nasal
passages, the two Eustachian tubes, the larynx, and the
esophagus.

312. The Esophagus connects the pharynx with the stom-
ach (Figs. 108 and 110). It is a muscular tube lying
along the spinal column behind the trachea. The muscu-
lar coat of the wall of the esophagus contains an external
layer of fibers running lengthwise, while the second layer
is of circular fibers. They are mainly involuntary and
supplied by the vagus nerve, with fibers from sympathetic
ganglia also.

313. The Stomach lies in the cavity of the abdomen
immediately below the diaphragm (Fig. 86, p. 153).
It is a large sac, formed by the dilation of the alimentary
canal (Fig. 110), and its walls have the three coats of
the rest of that canal, — the inner mucous coat, the middle
connective tissue coat, and the external muscular coat, with
a fourth coat in addition, the peritoneum, which forms the
lining of the abdominal cavity and is reflected back over
the organs (or most of them) which it contains. The
peritoneum adheres to the walls of the abdominal cavity,
folds of it surround the blood vessels running to the
stomach, and a large pouch of the same forms a sling for
the stomach. From the lower side of the stomach another
large fold of the peritoneum, called the great omentum,
spreads over the rest of the abdomen. After middle life
it often holds a large accumulation of fat.

The muscular coat of the stomach is composed of layers
of unstriped muscular fibers. Its mucous lining is inelas-
tic, and as it lines the organ smoothly when it is distended,

MACY'S PHYS. — 14

222

UNCONSCIOUS NERVOUS OPERATIONS

it must lie in folds when the stomach is empty and
shrunken (Fig. 110). The blood supply of this mem-
brane is very large during digestion, and its appearance
is then much redder than at other times. The two open-

Fig. 110. — Stomach and duodenum.

The anterior walls are cut away to show the folds of the mucous membranes
rugne of stomach, and valvulae conniventes of intestine.

ings of the stomach are both upon the upper side. That
near the left end, the cardiac orifice, admits the food from
the esophagus; that on the right, the pyloric orifice, con-
nects with the small intestine. The latter is surrounded

THE DIGESTIVE APPARATUS AND NUTRITION 223

by a thick ring of circular muscular fiber, forming a
sphincter muscle, which keeps the opening closed except
when food is ready to pass from the stomach.

314. Nervous Supply of the Stomach. — Nerve fibers from
many centers reach the different coats, glands, and blood
vessels of the stomach and those of the large and small
intestines. They are gathered in large tangles of nervous
matter, called plexuses, which contain branches from the
vagus nerves, from many of the spinal nerves, and from
the ganglia of the sympathetic chain. The great solar
plexus, or epigastric plexus, is placed at the pit of the
stomach ( Fig. 22, p. 31) ; the hypogastric plexus lies
before the last of the lumbar vertebrae, and divides into
two parts, one lying on each side of the rectum. These
plexuses give rise to innumerable branches which control
the complicated processes of digestion, the precise path of
each different sort of nervous influence not having been
yet made out. It is easy to see, however, that this close
nervous connection of the digestive organs with all parts
of the system implies important relations between them.

Vagus nerve fibers appear to stimulate the peristaltic
or wavelike movement of the stomach and bowels, which
by the progressive narrowing of the tube forces on its
contents, while the sympathetic fibers are inhibitory and
bring the movements to an end. It is believed that the
walls of these organs possess some power of spontaneous
action such as appears in the walls of the heart.

315. The Small Intestine ( Fig. Ill ) is a tube with many
curves, about twenty feet in length, two inches in diameter
at its upper end and somewhat smaller in its lower por-
tion. Its coats are the same as those of the stomach, but
the peritoneum, a fold of .which forms the outer coat, does
not entirely surround the tube, but runs off to form a sup-

224

UNCONSCIOUS NERVOUS OPERATIONS

porting membrane for the intestine, called the mesentery.

This is gathered up and connected with the wall of the

abdominal cavity near the spinal
column. The blood vessels and
nerves pass through the mesen-
tery to reach the intestine, and
the absorbents also pass through
it from the intestine. The two
layers of muscular fibers, one
circular and one longitudinal,
in the intestinal wall, are of the
unstriped, involuntary kind.

316. Nerves of the Small Intes-
tine. — Between the muscular
layers is a plexus of nerve fibers

W^] lnany ganglia ;i11(l i]l tin;
layer beneath the mucous mem-
brane of the lining is another
nerve plexus, also gangliated.

317. The Mucous Membrane of
the Small Intestine has a very
important part in the function
of digestion, and is of peculiar
structure. Like the lining mem-
brane of the stomach, it has an
inner layer of columnar epithe-
lium, but unlike that of the
stomach the lining of the intes-
tine is for a large part of its
length laid in folds which do
not disappear when the canal is

are called valvulce conniventes
(Fig. 110). They lie around the inner surface of the

Fig. 111.— The stomach and
intestines.

1 stomach.

2 duodenum.

3 small intestine.

4 termination of the ileum.

5 caecum.

<5 vermiform appendix.

7 ascending colon.

8 transverse colon.

9 descending colon.

10 sigmoid flexure of the colon.

11 rectum.

12 spleen.

13 anus.

distended. These folds

THE DIGESTIVE APPARATUS AND NUTRITION 225

intestine, each separate valvula reaching about one half
or two thirds the way round. Their function is to fur-
nish a large amount of secreting and absorbing surface.

318. The Villi. — Still further to increase this surface,
the valvulse are covered with villi. These are minute
projections from one fiftieth to one eighth of an inch

Fig. 112. —Diagrammatic representation of a small area of the mucous
membrane of the small intestine.

1 cellular structure of the epithelium,

or outer layer.

2 a vein.

8 fibrous layer.

4 villi covered with epithelium.

5 a villus in section, showing its

covering of epithelium, and its
blood vessels and lymphatics.

6 a villus partly uncovered.

7 a villus stripped of its epithelium.

8 lymphatics or lacteals.

9 orifices of the glands opening be-

tween the villi.
10, 11, 12 glands.
13 capillaries surrounding the orifice

of a gland.

in length, and are found only in the small intestine (Fig.
112). They give to its mucous lining a peculiar velvety
appearance. Each vittus is covered with columnar epithe-
lium resting on a fine membrane. Within are blood vessels

226

UNCONSCIOUS NERVOUS OPERATIONS

(two or more arteries, a dense network of capillaries, and
one or two veins), connective tissue fibers, and a single

lymphatic or lacteal ves-
sel, which may be looped
or branched (Fig. 113).
Between blood vessels
and lymphatics is a very
thin layer of fine muscu-
lar fibers, which help to
propel the chyle along
the lacteals. Fine nerve
fibers are also found. In
the villi the digested
food passes through the
cells of the thin wall
into blood vessels and
lacteals.

319. The Large Intestine
(Fig. 111).— The small
intestine passes into the
large intestine, the ileo-
ccecal valve at the junc-
tion preventing any re-

Fig. 113. — Diagram of the essential
parts of a villus

a epithelium winch takes up food and

transports it to the tubes within.
b an artery, c capillaries. d a lactea^

flux of the contents from
the large to the small
tube. The large intestine has three parts, called the
caecum, the colon, and the rectum. The caecum is a large
sac on the right side, which receives the contents of
the small intestine. Attached to the lower side of the
cjecum is the small vermiform appendix, which has no
known function, but is regarded as a " survival " from
a previous type of animal structure. Continuous with
the ciecum is the colon, having ascend in; j, transverse, and

THE DIGESTIVE APPARATUS AND NUTRITION 227

descending parts. The rectum is the final portion of the
alimentary canal ; it opens externally at the anus.

The walls of the large intestine are like those of the
small intestine, except that the valvulse conniventes and the
villi are wanting. In the caecum and colon the longitudi-
nal muscular fibers are for the most part collected in three
bands, which, being shorter, from end to end, than the other
coats, draw up the intestinal wall into puckers, or folds.

The muscular coat of the rectum is much thicker than
elsewhere, and at the anus is a strong band called the
internal sphincter muscle.

320. Secretion. — All the living cells of the body are
engaged in taking from the blood certain substances suit-
able for their own special purposes, and returning to the
blood those particles of matter which have fulfilled their
mission and are no longer of use. Every cell requires
oxygen, and oxidation is now

understood to occur within
all the cells. But certain
cells or groups of cells take
up also other substances from
the blood, and manufacture
within themselves a new
product having a special
function. This process is
called secretion, and the or-
gans of secretion are called
glands.

321. Glands. — The sim-
plest glands are merely
minute tubes lined with cu-
bical cells (Fig. 114). Sometimes these tubes branch at
the inner end, all the branches being lined with the secret-

Fig. 114. — Structure of glands.

1 simple pit, surrounded by capillaries.

2 flask-shaped gland, with short duct.
3, 4 more complex glands, with longer

ducts.

228 UNCONSCIOUS NERVOUS OPERATIONS

ing cells, and all uniting in a single tube, or duct, through
which the secretions pass. Frequently a large number of
branches from a secreting tube are grouped together in
clusters to form an organ of considerable size, as the liver
or the pancreas.

The secreting surface is always composed of living
cells, and the processes carried on in them are similar to
those occurring in other cells. That is, secretion involves
building up, or growth, and breaking down, or waste, of
the cell substance, along with other changes. Under the
microscope the cells of the glands are seen to contain a
nucleus and many granules. These granules are products
of the cell itself. When the secreting process is going on,
water and other substances pass through the cells from
the blood, and at the same time the granules are dissolved
in the water and pass out along the secretory duct. Secre-
tion is a manufacturing process, and not merely a filter-
ing out of certain substances from the blood. In each
gland the chief or specific constituents of its peculiar juice
are formed in the cell and not simply extracted from the
blood.

The mucous membrane of the whole of the alimentary
canal is largely made up of glands.

322. Salivary Glands (Fig. 115). — There are three pairs
of salivary glands. Those lying in front of each ear are
the parotid glands; those under the lower jaw on each
side, the submaxillary glands; and those under the tongue,
the sublingual glands. They are large glands whose ducts
pour their watery secretions into the mouth.

323. Nervous Action upon the Salivary Glands. — Ordina-
rily the nervous action affecting the salivary glands is
reflex. The organs of taste are stimulated by food, or
the sight or odor of food stimulates the optic or olfactory

THE DIGESTIVE APPARATUS AND NUTRITION 229

nerves, the nervous center in the brain sends impulses to
the special center in the medulla oblongata from which
efferent secretory im-
pulses are reflected,
and they pass along
the fibers of a branch
of the seventh cranial
nerve, which probably
contains fibers from
the ninth nerve, with
which it communi-
cates. The impulse
finally reaches the
cells of the submaxil-
lary and sublingual
glands, and a flow of
saliva results. Even
the thought of food,
by stimulating a center in the brain, may produce nervous
impulses having the same effect. Nerve branches from
the sympathetic system also carry stimulus to these
glands.

For the parotid glands the chief secretory nerve fibers
arise in the glossopharyngeal nerves (ninth cranial).

324. Action of Saliva. — A part of the digestion of food
takes place in the mouth. Saliva is mixed with the food
by mastication, and serves to moisten the mass and lubri-
cate it for swallowing. It also causes a chemical action,
due to the presence of its active principle, ptyalin, which
affects the starch in food, converting it into malt sugar.
If one chews slowly a few grains of wheat, he will notice
that the paste becomes sweet. This is because some of the
starch in the wheat is changed by the saliva into sugar.

Fig. 115.

The salivary glands of the
right side.

230 UNCONSCIOUS NERVOUS OPERATIONS

325. Ferments. — The ptyalin belongs to a kind of sub-
stances called ferments. Of these there are two classes,
— the organized and the unorganized. The organized
ferments are living vegetable organisms. Yeast is one
of them, the vinegar plant is another, and the various
kinds of bacteria, some of which cause disease, are other
examples. The unorganized ferments are chemical sub-
stances resulting from the activity of living cells, and
capable of effecting certain changes in particular sub-
stances. The ptyalin is one of these. The ferments are
the agents for effecting most of the changes which the
food undergoes in digestion.

326. Gastric Juice. — The epithelium of the lining of the
stomach consists of a single layer of cells, and the mucous
membrane is almost entirely composed of simple tubelike
glands closely packed together. When food reaches the
stomach, more blood is sent into the dilated blood vessels,
and the glands make from the blood a colorless fluid called
gastric juice, which flows into the cavity of the stomach.

Chemical analysis shows that gastric juice contains,
besides water, a small amount of salts, a little free hydro-
chloric acid, and two of the ferments, called pepsin and
rennin. Rennin is that element in the gastric juice which
causes milk to curdle. The use of rennet (which is ob-
tained from the stomach of a calf) in the making of cheese
depends upon the presence of this ferment. Pepsin is
the ferment which is able to change proteids into soluble
form, and to make diffusible such as are not already so.
The ferments of the gastric juice act only in the presence
of an acid, and to assist their action seems to be the func-
tion of the hydrochloric acid. .

327. The Food in the Stomach. — The effect of the gastric
juice upon the food in the stomach is to make the whole

THE DIGESTIVE APPARATUS AND NUTRITION 231

mass acid. This destroys the ptyalin, and no more starch
is converted into sugar. As the saliva acts only upon
starch, so the gastric juice acts only upon the proteids.
By the muscular movements in the walls of the stomach
the food is moved from side to side and thoroughly mixed
with the gastric juice, and the mass becomes semifluid.
The fats and carbohydrates remain unchanged, except as
affected by the warmth of the stomach and by the removal
of the proteids which are dissolved out of the mass.

328. Digestion in the Small Intestine. — The food by re
maining in the stomach from one hour to three or four,
is converted into what is called chyme. The sphincter
muscle of the pyloric orifice relaxes at intervals, and the
chyme is then passed on into the small intestine by the
contractions of the wall of the stomach. Here it soon
encounters two other juices, the bile and the pancreatic
juice, *>y which it is still further changed.

329. The Pancreas is a long, slender gland, enlarged at
its right end, lying back of the stomach and along its
greater curvature, and supported by the mesentery (Fig.
94, p. 163). It is pinkish yellow in color, and resembles
the salivary glands in structure. A duct runs from one end
to the other, joins the common bile duct from the liver,
and passes with it obliquely through the wall of the small
intestine (Fig. 110).

330. The Pancreatic Juice. — The pancreas has reflex
nervous connection with the stomach, and as soon as food
enters the latter, secretion begins in the pancreas, and
the secreted fluid accumulates in the small intestine.

The pancreatic juice is a clear, somewhat viscid, alkaline
fluid, containing many different substances, the most im-
portant being the ferments. Of these there are four.

One, similar to pepsin, but able to act only in an

232 UNCONSCIOUS NERVOUS OPERATIONS

alkaline medium, affects the proteids more rapidly and
more powerfully than pepsin, and so digests those which
were not sufficiently changed by the gastric juice.

Another ferment in the pancreatic juice acts like the
saliva upon starch, converting it into malt sugar, but its
action is far more powerful. This ferment is not present
in the pancreatic juice of infants, and they are therefore
unable to digest starchy foods properly.

The pancreatic juice has two different effects upon the
fats, they having hitherto been unchanged. The first
effect is to separate them into exceedingly small particles,
which can pass through the walls of the intestine, that is,
the juice forms an emulsion with the fat. The second
effect is a chemical decomposition of fat into fatty acid
and glycerin by the action of the third of the pancreatic
ferments. The acids set free unite with the alkaline sub-
stances present to form soaps. •

The fourth ferment possesses the power of curdling
milk, as does rennin, though its action is not identical
with that of rennin. It is able to act upon any particles
of milk which have by any possibility escaped the influ-
ence of the gastric juice.

331. The Secretory Nerves of the Pancreas have been found
to be fibers of the vagus, or tenth cranial nerve, which, as
already mentioned, are stimulated by efferent impulses ex-
cited in the brain by afferent impulses from the stomach.

332. Other Functions of the Pancreas. — In addition to
its office in connection with digestion, experiments have
proved that this gland has some further influence upon
the general condition of the body ; but what that influ-
ence is, is as yet unknown.

333. The Liver, which weighs from fifty to sixty-four
ounces, is the largest gland in the body. It lies chiefly

THE DIGESTIVE APPARATUS AND NUTRITION 233

on the right side, immediately under the arch of the dia-
phragm (Fig. 86, p. 153). The peritoneum, without
entirely covering it, adheres closely to it and attaches it
to the diaphragm and other parts. By a deep fissure it
is separated into right and left lobes (Fig. 116). The
tissue elements of the liver are the hepatic cells, and all
the other parts contribute to their support, protection,

Fig. 116. — The liver seen from below.

and nutrition. The hepatic cells are grouped together in
little masses to form lobules, which are permeated by the
blood capillaries from the portal vein and the hepatic
artery. From these capillaries the blood passes to a small
vein which unites with those from other lobules to form the
hepatic veins, which empty into the inferior vena cava.

334. Blood Supply of the Liver. — The liver has an im-
mense supply of blood. That which is brought by the

234 UNCONSCIOUS NERVOUS OPERATIONS

portal vein has first circulated through the stomach, the
spleen, and the intestines (Fig. 95, p. 165), and has been
deprived of most of its oxygen. The supply of arterial
blood through the hepatic artery is relatively small.

335. Functions of the Liver. — One of the functions of
the liver is to store up sugar, or, rather, to form from the
sugar brought by the portal vein a substance called gly-
cogen, which is readily converted again into sugar. The
protoplasm of the hepatic cells possesses the power of
manufacturing glycogen from carbohydrates and of stor-
ing it up. This is effected by means of a ferment found
in the liver ; but what is the part played by glycogen in
the animal economy is not fully determined. Glycogen
is turned into sugar again and supplied by the liver to
the blood as it is needed. There is always sugar in the
blood, but more than a small amount seems undesirable.
There is much evidence that another function of the liver
is to act upon the nitrogenous foods in some manner
resulting in the production of the waste substance, urea,
which is eliminated by means of the kidneys. A third
and the most familiar office of the liver is the formation
of bile. This is stored in the gall bladder, lying between
the two lobes on the under side of the gland (Fig. 116).
Still another function of the liver is to protect the system
from the action of poisons produced by the processes of
digestion or by defective digestion. These are arrested or
transformed when they reach the liver.

336. The Bile is secreted from the portal blood as a yel-
lowish, reddish brown, or green fluid, according to the pre-
ponderance of different coloring matters which are formed
by the liver out of the hemoglobin of the red blood cor-
puscles. It is alkaline and is thought to have antiseptic
properties. Bile is a poison, and in one person enough is

THE DIGESTIVE APPARATUS AND NUTRITION 235

secreted in a day to kill three men ; but it is neutralized
in the intestines, in the liver, in the tissues, and in the
blood. Upon the food with which it mixes in the small
intestine bile seems to have little effect, and its function
there is supposed to be mainly to assist the pancreatic
juice in neutralizing the acid in the chyme, and in its
further action. Secretion of the bile goes on continu-
ally, but it passes into the intestine only when digestion
is proceeding. At other times it is carried by a side
branch of the bile duct to the gall bladder and there
stored. About two pints of bile is secreted daily.

337. The Intestinal Juice is a secretion of the mucous
membrane of the small intestine itself, and contains a
ferment which changes cane and malt sugars into glucose,
besides having possibly further action upon the food.

338. Bacterial Action. — There have been found to exist
in the alimentary canal certain microorganisms which
modify the digestive processes. Bacteria are especially
numerous in the intestines. The antiseptic gastric juice
destroys bacteria, or neutralizes their action in the stomach;
but some escape into the intestines, where they multiply.
Their presence is shown to be, under normal conditions,
beneficial, though certain forms of bacteria produce disease.

339. The Peristaltic Movements of the Intestines. — By suc-
cessive contractions and relaxations of the muscular fibers
in the two muscular layers of the intestinal wall, a wave-
like motion passes along the whole length of the organ and
forces the contents, from the constricted to the relaxed
portion, slowly on into the large intestine, bringing the
different substances in contact with the absorbing cells in
the mucous membrane.

340. Function of the Large Intestine. — Most of the food
which can be used in the body is absorbed in the stomach

236 UNCONSCIOUS NERVOUS OPERATIONS

and small intestine, so that what is left to pass into the
large intestine is indigestible matter and the remains of
the juices. The tubular glands in the mucous membrane
here absorb what is left of nutrient material and a con-
siderable amount of water, which is carried by the small
veins to the portal vein. The residuum, becoming more
solid as the water is absorbed, passes into the rectum and
is discharged as faces. The chief alteration in the con-
tents of the large intestine is due to the action of micro-
organisms which cause chemical changes, giving rise to
organic acids.

341. Absorption. — When the food has been digested it
is ready to be absorbed. It cannot be used for the sup-
port of the body until it reaches the blood, and there are
two ways by which it may reach the blood. First, it may
be absorbed directly into the blood. The mucous lining
of the alimentary canal is richly supplied with absorbing
cells. Little of the food, however, is taken up in the
mouth and esophagus, because of the thickness of the
epithelium in those cavities, and because the food passes
quickly through them. In the stomach, and especially in
the small intestine, the absorbents are very numerous, and
a large amount of digested food passes directly into the
blood stream by the capillaries through the columnar cells
of their epithelium ; while the walls of the large intestine
also absorb food, but to a less extent. This direct pas-
sage into the blood is now regarded as the more important
of the two channels of absorption. The living cells, while
allowing water and soluble salts to pass through them
unchanged, effect certain changes in the organic food
materials while in contact with them. The carbohydrates
and proteids are mainly absorbed into the blood in this
immediate way.

THE DIGESTIVE APPARATUS AND NUTRITION

342. The second agent of absorption is the lymph cells
in the tissues of the walls of the alimentary canal. It is
chiefly by the lymphatics that the fat of the food gets into
the circulation. Two changes are effected in the fats by
the digestive juices in the small intestine to prepare them
for absorption by the lymphatic vessels, which are in the
intestines called lacteals, because the presence of fat ren-
ders the fluid they contain milky. First, by the mixture
of the bile and pancreatic juice with the food an emulsion
is formed ; that is, the fat is broken up into minute
particles, which float in the liquid, giving it a milky
appearance. Secondly, a chemical union takes place
between some of the acid fats and the alkaline secretions
of the digestive organs, — a process called saponification,
which is the making of soap. The digested food in its
milky form is called chyle, and this is collected in larger and
larger tubes, and finally poured by the great thoracic duct
into the blood of the jugular vein. Being then carried to
the right auricle of the heart, it passes to the right ven-
tricle and thence to the lungs, in whose capillaries it
meets with the oxygen from the air, and having returned
to the left side of the heart is distributed throughout the
system.

343. The Lymphatic Vessels are delicate tubes which
drain the spaces between the cells of the tissues, gradu-
ally uniting to form the main lymphatic vessels, of which
the thoracic duct is the largest. These vessels are sup-
plied with numerous valves, like those of the veins, to
prevent the reflow of their contents, and the opening of
the thoracic duct is guarded by a valve. The flow of the
fluid is kept up by the pressure in the capillaries, which
is greater than is the pressure in the veins into which it
is emptied, and by the movements of the body, which

MACY'S PHYS. — 15

238 UNCONSCIOUS NERVOUS OPERATIONS

constantly cause pressure upon the tissues and so force
the lymph onward in the vessels, the valves preventing
any return.

344. Assimilation. — Though the food has been masti-
cated, digested, and absorbed, it has not yet nourished
the body. Still another process is needful before the
new material becomes part of the continually wasting
tissues. That process is called assimilation, and, though
we cannot pretend to understand it, it may be described
as the action of the living cells in choosing, appropriat-
ing, and building into their own substance the suitable
elements in the food-laden fluid which comes to them
from the alimentary canal and from the lungs.

Correlative to the process of assimilation is the destruc-
tive process by which the cells, by combustion and other
chemical changes, break up and send out as waste the
substances of their structure, to be expelled from the
body as excretions.

345. Hunger and Thirst. — We associate our feelings of
thirst with a dry ness of the mucous membrane of the
mouth and throat, and we say our throats are " parched "
when we are very thirsty. But under ordinary circum-
stances the feeling of thirst arises from a general con-
dition of the system, in which the throat shares, due to
a lack of water in the blood, or rather in the lymph.
Thirst may be temporarily relieved by moistening the
mucous membrane of the soft palate. Hence follows the
inference that the afferent nervous impulses originate
there, and are caused by a too great removal of water
from the lymph of the investing membrane.

Hunger is referred in our consciousness to the par-
ticular locality of the stomach, and that organ seems to
us to be empty when we are hungry. Indigestible mate-

THE DIGESTIVE APPARATUS AND NUTRITION 239

rial introduced into the stomach may for a time relieve
the hunger, as will a very small quantity of food. The
special sensation of hunger appears to be connected with
the state of the lining membrane of the stomach, while it
must be ascribed in a more general sense to a deficiency
of nutrient matter in the blood. Hunger may be alle-
viated by the introduction of soluble food into the circula-
tion, through the rectum, or through the absorbents of the
skin, but the relief comes more slowly thus than through
the stomach.

The nervous path of hunger sensations has not been
made out. The vagus is regarded as the sensory nerve
of the stomach, but it is said that both vagus nerves may
be cut and the sensation of hunger be unaffected. The
brain centers for thirst and hunger are believed to be in
the occipital lobes of the cortex, but they have not been
definitely located.

346. Some Practical Points connected with Nutrition. — In
order that the first of the digestive operations may be
properly performed, it is necessary to have a good set of
teeth and to chew thoroughly the food taken into the
mouth. The intensely hard enamel covering the exposed
portion of the teeth is a full protection to them against
all dangers .under proper conditions of life, and under
such conditions the teeth would last while life lasts.
That this is true is shown by the fact that nature makes
no provision for restoring or improving the enamel after
it is once formed. Here alone the special cells, whose
office it is to form the peculiar substance, entirely disap-
pear when their work is once completed. In all the other
tissues these formative cells remain to continue the nutri-
tion and repair of the tissues. But the tooth enamel,
whose growth, except in the wisdom teeth, is complete

240 UNCONSCIOUS NERVOUS OPERATIONS

when a child is ten or eleven years old, cannot be renewed
or improved after that time. It is therefore of the utmost
importance that young children should be fed upon food
which will build up perfect teeth. Milk should be largely
relied upon for the first three years, the diet to be varied
during the third and after years in accordance with sug-
gestions given in the chapter on Food. Great care should
be taken to guard children against attacks of what are
known as " infantile diseases," — measles, whooping cough,
etc., which sometimes suddenly arrest or disturb the gen-
eral nutrition, and especially that of the teeth, so that the
enamel becomes rough and irregular, and the teeth are
exposed to early decay. Another point should receive
special attention. It is observed that young children
who live a life of excessive nervous activity, with over-
stimulation of the brain, are particularly liable to defect-
ive development of the enamel of the teeth. This is one
among many reasons which make imperative a quiet, regu-
lar life for children, without excitement and without
undue mental activity.

347. But even perfect teeth may be injured by certain
bacteria, which multiply in the decaying particles of food
allowed to remain in the mouth. These minute organisms
form a corrosive acid which destroys the enamel and breaks
down the tooth substance. If the teeth are perfect and
are always kept perfectly clean, they will not decay.
They should be thoroughly brushed — the upper teeth
downward, the lower ones upward — after each meal, and
a thread of soft untwisted silk floss or fine strips of rubber
should be drawn back and forth between the teeth to cleanse
those parts which a brush cannot reach. In brushing the
teeth a powder or liquid should be used which contains
some safe germicide, — which is a substance destructive to

THE DIGESTIVE APPARATUS AND NUTRITION 241

the microorganisms mentioned above, — and the mouth
should be well rinsed with a solution of the same.

348. It is a mistake to suppose that a child should be
supplied with soft, pulpy food. Just as soon as the first
set of teeth are in place, he should have a fare which will
require vigorous mastication. He should not be allowed
to reject bread crusts and eat only the soft crumb, nor
should his bread be always soaked in milk or gravy.
Plenty of hard " chewing " is not only good for the teeth;
it also promotes the flow of the saliva necessary to diges-
tion and aids in the development of the jaws, and so
helps to provide room for the second set.

The teeth should be under the care of a competent den-
tist, who by yearly or seiniy early examination and repair
will be able to forestall and prevent the inroads of decay.

349. While a due action of the mechanism of mastica-
tion is to be sought, that overactivity which results from
the habit of chewing tobacco or gum is to be avoided. While
a sense of propriety and good taste should alone be suffi-
cient to condemn such a habit, there are hygienic rea-
sons for its avoidance. The constant stimulation of the
salivary glands leads finally to their weakness and defect-
ive action, thus laying a foundation for general derange-
ment of digestion. Many dentists also regard it as directly
injurious to the teeth.

350. Food is not ready for the action of the gastric
juice until it has been finely divided by the teeth and all
portions well moistened with saliva. Slow and thorough
mastication is therefore necessary to perfect digestion.
Too rapid eating not only shows bad manners, but also is
exceedingly bad for the health.

351. The temperature of our food should not be so hot
as to stimulate unduly the glands of the mucous mem-

242 UNCONSCIOUS NERVOUS OPERATIONS

brane of mouth and stomach, nor so cold as to retard the
digestive processes, which normally require a temperature
of about 100° F. (38° C. ). Ice water should never be
drunk, both because of the impurities usually found in
the ice, and because its coldness is injurious to the stom-
ach. Very large quantities of any liquid taken with the
food may dilute the gastric juice so much as to delay
digestion and weaken the organs.

352. It is well to establish and adhere to regular hours
for meals. The intervals between meals should be long
enough to permit the digestive organs to rest between
their periods of activity, and fresh food should not be
taken into the stomach to mix with that partly digested ;
that is, "eating between meals" is to be avoided. A
habit of continually nibbling at dainties is extremely per-
nicious, and may give rise to serious and perhaps incur-
able disease.

353. A considerable variety in diet is wholesome, but as
a rule one should adhere to the simpler and more easily
digested kinds of food. A person in health is scarcely
conscious of possessing a stomach, but injudicious indul-
gence may so disorder the natural processes that they will
be constantly attended with discomfort or suffering.

354. It is impossible to prescribe definite rules for the
quantity of food to be taken daily. A strictly natural
appetite is undoubtedly a safe guide ; but appetite is so
often and so early perverted that it is seldom reliable.
Food enough must be taken to supply the daily waste of
tissues. Continuous loss of weight is usually a seriously
unfavorable symptom. During the natural period of
growth the amount of food must be sufficient to supply
also what is needed for the full development of the body.
One living a life of physical activity requires, as a rule,

THE DIGESTIVE APPARATUS AND NUTRITION 243

more food than one engaged in sedentary occupations.
Brain workers, however, need a varied and generous diet,
and along with it gre"at care should be taken to secure
sufficient outdoor exercise. More food is called for in
winter than in summer, and more of the carbohydrates to
supply the demand for additional heat. Those who work
vigorously in the open air, and especially in cold climates,
often consume prodigious quantities of fats without injury
to digestion. With the coming of old age the vital proc-
esses in general are carried on more slowly ; digestion and
especially the power of assimilation are enfeebled. Less
energy is called for as the activities are lessened, and less
food is then required, with longer intervals between
meals. Foods rich in proteids are less needful and should
be diminished in quantity, while those which yield a large
amount of heat should be substituted.

355. What is Alcohol? — All organic bodies are subject
to decay ; the complex compounds of which they are
composed are broken up into simpler ones, and that
which was living, organized matter becomes lifeless and
inorganic. This destruction of organic tissue is due
under ordinary circumstances to the process called fer-
mentation in some one or more forms. This is the growth
and rapid multiplication of minute organisms, of which
yeast is the most familiar example. When the decom-
position of organic matter takes place under certain con-
ditions and reaches a certain stage, it is called putrefaction.
This is always attended by the multiplication of the low
forms of life known as bacteria, and by the production of
poisonous and ill-smelling gases. Another form of fer-
mentation is that which occurs in the juices of fruits,
grains, and vegetables which contain sugar; and is called
vinous fermentation. In this form of decomposition the

244 UNCONSCIOUS NERVOUS OPERATIONS

fungus known as the yeast plant is the active agent in
producing the changes which occur. The sugar of the
fruit or plant must be in solution, and the germs of the
yeast must in some way be introduced.

Alcohol is one of the products of vinous fermentation.
It is composed, like sugar, of carbon, hydrogen, and oxy-
gen, but in proportions different from their proportions
in sugar. The drinks which contain alcohol differ widely
in flavor according to their sources, and also vary in the
amount of alcohol which appears in them. In cider and
some kinds of beer the proportion may be as low as 2 per
cent. As alcohol is a very volatile fluid, it may be readily
separated from the other substances in the fermented
liquor by the process called distillation. This is the driv-
ing off of the alcohol in the form of vapor by the applica-
tion of heat, and its recondensation, by cooling, to liquid
again. In this way is obtained the strong alcohol which
is mixed with various coloring and flavoring matters to
form the spirituous liquors of commerce. Whether a
drink contains the 2 per cent of alcohol found in cider,
or the 50, or more, per cent found in whisky, or the
90 per cent of " cologne spirits," the alcohol is in all
cases identical in its nature and properties.

356. Properties of Alcohol. — Pure spirit, or "absolute
alcohol," is a colorless, volatile liquid with a strong affin-
ity for water, which it rapidly absorbs from the atmos-
phere or from any other substance containing water with
which it comes in contact. Alcohol burns readily in the
open air, that is, it is quickly oxidized and changed in its
chemical composition. It is a powerful solvent, dissolv-
ing many substances not soluble in water. Though itself
the product of fermentation, it is a preventive of putre-
faction.— that is, it preserves animal tissue from decay7

THE DIGESTIVE APPARATUS AND NUTRITION 245

— and introduced in sufficient amount into a liquid in a
state of vinous fermentation it destroys the power of the
yeast plant to multiply, while in smaller quantities it
retards the growth of the living cells in direct proportion
to its amount. When by the decomposition of sugar in
vinous fermentation the amount of alcohol produced has
reached 14 per cent, no further growth of the yeast takes
place. That proportion of alcohol destroys the vitality
of the living cells. It is thus useful as an antiseptic.
Brought in contact with food elements outside the body,
alcohol is found to harden them by abstracting the water
which they contain, and to coagulate the albumin, which
is thus rendered insoluble.

357. Is Alcohol a Food ? — Alcohol contributes nothing to
the formation of tissue, and cannot, therefore, be classed
in the first division of foods, according to the definition
given in § 289. As it is now proved that when taken
into the stomach in dilute form and in small quantities
it may be fully oxidized, producing energy, it must be
reckoned in the second class of foods, as a force generator.
For its stimulating effect it must also be included among
the force regulators. It acts upon the digestive glands,
causing them to pour out their special products more
rapidly, and so seems sometimes to assist digestion.

But, although alcoholic drinks in very small amounts
are found to come, strictly speaking, under the definition
of food, in that they may and do develop or regulate
force, they possess at the same time properties so peculiar
and so dangerous that it is wise to exclude them wholly
from our dietary, and use them, if at all, only under the
advice of a skillful physician in case of illness. In cer-
tain abnormal conditions of the system, when ordinary
food cannot be digested, it has sometimes been found that

246 UNCONSCIOUS NERVOUS OPERATIONS

an alcoholic drink, not requiring digestion, will supply
the necessary energy to sustain life until the diseased
organs have time to regain the power to assimilate better
food. But to the healthy body there is no need of such a
whip and spur, and the stimulus of alcohol upon the secre-
tions of the digestive tract, frequently applied, is likely to
result in overstimulation of the organs, and consequent
weakness, with a long train of evils to follow.

As a food, alcohol is of little value compared with other
substances. It is more expensive than almost anything
else that is ever used as food, and cannot by itself sustain
life ; for, while it does generate a certain amount of energy,
the body is really feeding upon the stored-up proteids,
and the cost of the few spoonfuls of whisky or brandy, or
the quart of beer which may perhaps be drunk without
immediate bad effects, would buy of wholesome bread and
meat enough to produce in the body many times the
amount of normal force which the alcohol imparts.

358. Alcohol as a Poison. — The beneficent use of alcoholic
drink seems to be wholly confined to its application as a
medicine to diseased conditions of the system, and with
that sort of use we have here nothing to do. It has been
demonstrated that a healthy man may consume drink, in
twenty-four hours, which contains from two to two and a
half ounces of alcohol without apparent injury, when all
circumstances are as favorable as possible for the perfect
action of all the bodily organs. But it by no means fol-
lows that it would be equally safe for a man in the varying
and uncertain conditions of ordinary life to incur the risk
of disturbing the nice balance of the physical adjustment
upon which vigorous health depends by introducing into
his organism an element which may, and more likely than
not will, disorder the action of some one or more of the

THE DIGESTIVE APPARATUS AND NUTRITION 247

delicate organs. Let him take just a little more than the
exact amount which can be at once oxidized in the blood
or other tissue, and it is carried on through the system as
alcohol, to work its characteristic effects. In the stomach
the alcohol may harden the albumin of the food, and so
prevent its complete digestion. If strong enough, it may
attack the albumin in the cells of the lining of the stomach
itself. This is the reason for the well-known fact that
alcoholic drinks do less harm if taken after a meal than if
taken on an empty stomach. A large quantity of strong
drink taken at once seems to paralyze the nerves control-
ling the absorbents in the stomach, and often results in
sudden death. Passing into the circulation, alcohol, as we
have already seen in respect to yeast, acts directly upon
the vitality of the living cells, hindering their growth and,
when strong enough, wholly destroying their vital power.
Any excess beyond the amount which can be oxidized at
once interferes with normal cell activity, and works vari-
ous physiological evils, as pointed out in different chapters
of this book. All these are the actions of a poison.

359. In the stomach alcoholic fluids of all sorts increase
very greatly the flow of gastric juice, and it would appear
that this stimulation might assist digestion. But since
the alcohol is found to disappear wholly from the alimen-
tary tract within half an hour, this direct influence upon
the secretion of gastric and other digestive juices can be
but slight. Moreover, excessive or abnormal stimulation
of any organ results ultimately in the weakening of its
functional power. In the healthy animal wholesome food
supplies all the stimulus needed by the various digestive
organs.

In the intestines alcohol is rapidly absorbed into the
blood. By dilution with the juices of the mouth and the

248 UNCONSCIOUS NERVOUS OPERATIONS

stomach its power for direct injury has already been re-
duced; but if the work of the stomach has been imper-
fectly done because of its presence, more labor remains
to the intestines, and that may disorder the whole system.

360. The portal vein carries the alcohol absorbed from
the stomach and the intestine directly to the liver. Here
its evil effects in developing disease are earliest and often-
est apparent. Alcohol in the liver, as in other places,
greedily uses up the oxygen needed for the necessary vital
operations. In that way it prevents the normal action of
the hepatic cells, for not enough oxygen remains for them
to do their work perfectly. Now the liver, as the largest
organ in the body, has a correspondingly important part to
play in the vital processes, and any interference with its
functions is extremely serious. It is well known to physi-
cians that a drunkard's liver presents a greatly modified
appearance, which is seen to a less degree in the liver of a
moderate drinker. Alcohol does not build useful tissue,
but instead it promotes the abnormal deposit of fat cells,
causing what is called " fatty degeneration." This is often
seen in the liver of alcohol users and causes enlargement
of the organ; the connective tissue, also, is sometimes
inflamed and hardened. Because of the imperfect action
of the liver, poisons which should have been neutralized
are allowed to circulate through the system and undermine
its health.

So it appears that throughout the digestive tract alco-
hol is liable to work harm to the organs more or less
serious in proportion to the frequency of its use and its
amount.

361 . Other Sources of Danger from Alcoholic Drinks. — Many
of the drinks containing alcohol contain also a mixture
of nutritious substances, such as unfermented sugar and

THE DIGESTIVE APPARATUS AND NUTRITION 249

other foods found in the vegetables used in the manu-
facture ; though no one drinks those beverages for the
sake of the trace of nourishing matter in them. But
there are formed along with the alcohol in fermentation
other products, some of which are known to be directly
poisonous, while others are at least probably injurious.
Fusel oil and various ethers are among these substances.
Another source of danger is found in the frequent adul-
teration of alcoholic beverages. The great expense attend-
ing their manufacture leads to the use of inferior
materials, impure sugars, defective fruits, etc., and to
the addition of poisonous coloring and flavoring matters.
In some cases even so virulent a poison as strychnine
has been found. These adulterations still further men-
ace the health of the users of such drinks.

362. The Most Dangerous Quality of Alcohol. — Bad as it is
to suffer from enfeebled physical conditions, it is yet worse
to become weak in mind and unstable in moral character.
No one will deny that such weakness and instability are
results of the excessive use of alcoholic liquors. But no
man ever lived who deliberately determined to make
himself a drunkard, when first beginning to taste the
exhilaration of the moderate use of such' beverages.
Every one thinks he will confine himself to the small
quantity which he believes will do him no harm. How
is it, then, that in all the great cities of the world certain
streets are by night full of the sounds of crazy drunken
revelry; that prisons are crowded with criminals made
such by involuntary acts when "in liquor"; that myriads
of human beings tumble every year into drunkards' graves,
dying as the beast dieth, all the beauty and dignity of
life wrecked long before, all hope, all possibility of rescue
long since abandoned ?

250 UNCONSCIOUS NERVOUS OPERATIONS

We class alcohol among the foods because it comes
within our definition of food, but in a higher degree than
any other substance used for food, it possesses a peculiar
power which is not characteristic of food. It is the power
of developing a progressive craving, an uncontrollable
appetite for itself, which is never satisfied, and which
leads the wine bibber to long ever for more and stronger
wine, or whisky, or gin, or brandy. It is easy to say, " I
will never drink any more alcohol in a day than the two
ounces and a half which science has proved can be wholly
oxidized in the body, yielding force and conserving to
the extent of its own service the physical powers." The
man who speaks thus may indeed be able so to regulate
his actions, but millions of his fellow-men have not been
able to do so. Men do not rightly estimate the full force
of the insidious power of alcohol to create an ever-grow-
ing appetite which demands ever more alcohol for its
satisfaction. Bread and meat and milk and fruit, which
build the tissues and supply the forces for vigorous and
worthy life, do not create an abnormal appetite for them-
selves. Sometimes a man or a woman indulges in the
excessive use of tea or coffee, and may possibly experi-
ence something of the unhealthy craving for those bev-
erages which the drunkard has for his liquor. But
harmful as the effect of such indulgence is upon the
physical system, it does not so undermine the mental and
moral health as does the alcoholic habit.

363. It is at least perfectly safe to avoid wholly the use of
alcoholic beverages. One who does so is certain to escape
the frightful danger of acquiring that overmastering appe-
tite for alcohol, to satisfy which he might become willing to
commit murder or arson, or any other crime, and for whose
indulgence he may be led to ruin all his hopes of happi-

THE DIGESTIVE APPARATUS AND NUTRITION 251

ness for this world and for the world to come, and crush
out all joy from the lives of those dear to him. What is
the wise course for a being endowed with reason ?

DEMONSTRATIONS AND EXPERIMENTS

111. A General Dissection of the Digestive Organs can be performed
on the body of a rat, cat, dog, or rabbit. In this dissection other
viscera besides the digestive organs should be examined. Just how
much of the dissection is to be done by pupils, if any at all, must be
left to the judgment of the teacher. Whether the actual class work
takes on the nature of a dissection or merely of a demonstration, the
attempt should be made to examine, as far as possible, every organ
described in the text. To show the villi, cut out a piece of the wall
of the small intestine, and after gently washing it examine the inner
surface with a hand lens. Teeth of various animals can be obtained
to show the arrangement in the jaws and the general structure and
materials of a tooth.

112. Minute Structure of Digestive Organs. — Some prepared micro-
scopical sections of various parts of the digestive tract will aid the
pupil greatly in understanding the structure and properties of the
alimentary organs. Very instructive are sections of the wall of
the esophagus; of the stomach, showing the three muscular coats;
of the small intestine ; and sections of a salivary gland and of the
liver. Tissues of any of the domestic animals can be used.

Experiments in Digestion. — It should be borne in mind that diges-
tion carried on in test tubes is not normal, and that these experi-
ments in digestion are merely illustrative.

113. Salivary Digestion. — To a test tube about half full of starch
solution * add a little saliva and place the tube where the temperature
can be kept at about 37° C. (98° F.). In a few minutes the starch
solution becomes clear, and while at first it gave the characteristic
reaction with iodine it now no longer turns blue, but if Trommer's
test (Ex. 96) be applied, turns yellow, showing presence of sugar. To

1 Rub a gram of laundry starch into a paste with a little cold water.
Then add a hundred cubic centimeters of boiling water, and boil for a few
minutes. Cool before using.

252 UNCONSCIOUS NERVOUS OPERATIONS

be sure that the sugar is a product of digestion, Trommer's test
should be applied to the solution before saliva is added, and also to
dilute saliva.

Prepare two other test tubes in a similar way, but boil the contents
of one, and place the other on ice, or in a very cool place. From this
conclusions may be drawn regarding the relation of temperature to
the activity of the ferment of saliva.

The saliva of some persons has little or no digestive effect, hence
this experiment will occasionally fail.

114. Gastric Digestion. — Fill three test tubes about half full of
artificial gastric juice,1 and three other test tubes with (1) water, (2)
water containing a little powdered pepsin, and (3) a ^ per cent
muriatic acid solution, respectively. Place in each test tube a few
shreds of fibrin. Fibrin is used because it is a solid proteid, and
the progress of its digestion can be followed with the eye, without
making special tests. Boiled white of egg may be used, but it
digests more slowly. Boil one test tube containing artificial gastric
juice, place a second on ice, and set away the other test tubes in a
warm (37° C.) place.

In a short time the fibrin in the tube of gastric juice kept in the
warm place is seen to be much swollen, and gradually it disappears
iii solution. Compare the test tube with the others. What effect
has temperature on gastric digestion? Is the presence of pepsin
necessary? \Does pepsin alone (in water) digest the fibrin?

115. Action of Gastric Juice on Milk. — To a test tube about half
full of fresh milk, add a little artificial gastric juice that has been
neutralized by the addition of dilute carbonate of soda. Keep at a
temperature of about 37° C. (98° F.). In a short time the milk
curdles. In previous experiments on milk, curdling was produced
by acids; here, since the gastric juice was neutralized, it is due to
some other cause. To the test tube add a little dilute muriatic acid to
acidulate the contents, and keep it in the warm place for several hours.
The casein is finally digested in the presence of acid, forming a straw-
colored fluid.

116. Action of Rennet on Milk. — To some fresh milk en a test
tube add a little commercial extract of rennet, and keep at a tempera-

1 Add a little powdered pepsin (to be obtained at a druggist's) to a
^a per cent solution of muriatic (hydrochloric) acid.

THE DIGESTIVE APPARATUS AND NUTRITION 253

ture of about 37° C. The milk curdles in a few minutes. In the
previous experiment the milk was curdled by the renuin ferment in
the artificial gastric juice.

117. Action of Pancreatic Juice on Starch. — Repeat Ex. 113, using,
instead of saliva, artificial pancreatic juice.1

118. Action of Pancreatic Juice on Proteids. — Repeat Ex. 114,
osing artificial pancreatic juice instead of gastric juice, and carbonate
of soda solution instead of muriatic acid.

119. The Emulsifying Effect of Pancreatic Juice. — Rub together,
in a mortar, some olive oil, or cod-liver oil, with pieces of fresh pan-
creas. An emulsion results. Shake together in a test tube some
olive oil and a little artificial pancreatic juice, as used in preceding
experiments. An emulsion occurs as before. Boil some artificial
pancreatic juice to destroy the ferment. It still forms an emulsion
with oil. In the experiments on fats (Exs. 97-100) it was seen that
an alkali, or a soluble proteid, forms an emulsion with fats. Natural
pancreatic juice contains both alkali and proteids. Hence, even when
boiled, pancreatic juice emulsifies fats.

120. Bile. — Obtain bile at a slaughterhouse. Observe its color.
Test with litmus paper. It is neutral or alkaline if fresh.

121. Action of Bile in Fats. — Shake some olive oil in a test tube,
with five times its bulk of bile. Make a similar mixture of olive oil
and water, and observe in which case the emulsion lasts longer.
Shake up bile with olive oil, to which a little oleic a'cid is added.
The emulsion lasts longer than before.

122. Action of Bile in Filtration and Absorption. — Into each of two
small funnels of exactly the same size, put a filter paper. Moisten
one with water and the other with bile. Pour into both equal
amounts of almond oil, and after covering to prevent evaporation, set
aside twelve to fourteen hours. The oil passes through the filter
moistened with bile, but scarcely at all through the other.

1 Add a little powdered pancreatine to a 1 per cent solution of car-
bonate of soda. Commercial pancreatine commonly contains both the
starch-digesting ferment, qmylopsin, and the proteid-digesting ferment,
trypsin.

MACY'S pnvs. — 16

CHAPTER XVIII
THE DUCTLESS GLANDS

364. The ductless glands are organs whose functions
are not yet well understood. Unlike other glands, they
do not form a definite secretion poured forth by means of
ducts. Some of what we call " true glands " have been
shown to send into. the lymph and blood, in addition to
the secretion passing through their ducts, material of great
importance to the healthy working of the body. This is
true of the liver and of the pancreas, though these addi-
tional functions are only partly understood. It is probable
that the ductless glands have similar offices in the economy
of the system.

365. The Spleen (Figs. 94 and 95, pp. 163 and 165). —
The largest of these peculiar glands is the spleen, a dark
purplish body of variable size and spongy texture, lying on
the left side of the abdominal cavity, just below the stom-
ach. In the meshes of the tissue of the spleen is a soft sub-
stance called spleen pulp. This consists largely of red
blood corpuscles and colorless cells, some of which are like
the white blood corpuscles.

366. The Blood Supply of the Spleen. — The splenic artery,
a branch from the aorta, carries an abundant supply of
blood to the gland (Fig. 94), and the smallest branches
of the artery open directly into the spleen pulp. This
is the only place in the body where the blood comes

264

THE DUCTLESS GLANDS

255

into actual contact with the cells and fibers of a tissue.
The veins of the spleen unite to form the splenic vein,
which carries the blood into the portal vein and so to the
liver.

367. Functions of the Spleen. — Little is yet positively
known as to the functions of the spleen. That the organ
has some connection with digestion is shown by its enlarge-
ment as soon as gastric digestion is completed. It has
also some close relation to the liver, and it is understood
to be engaged, like the lymphatic glands, in the manufac-
ture of white corpuscles. In some animals it forms the colored
corpuscles likewise, but we do not know whether that is
true of the human spleen. It is thought by some that the
spleen is the organ where the red corpuscles which are
worn out undergo disintegration, their coloring matter
being carried to the liver and there used to form the
coloring matter of the bile.

368. The Thyroid Gland is a body whose two lobes lie on
the sides of the trachea (Fig. 117). The disease called
goiter is an enlargement

and alteration of struc-
ture of the thyroid, and
the effects sometimes ex-
tend to the impairment
of muscular and nervous
activity and to a semi-
idiotic condition of mind,
resulting in death if the
whole gland is affected.
The diseased condition Fig. 117. — Thyroid and thymus glands
may be relieved or cured of an infant-

by grafting a portion of the thyroid gland from an
animal under the skin of the afflicted one, or by adding

— Thyroid Gland

... Carotid A.

-- Internal Jugular V.

Trachea

~ ~ Suspensory Ligament
-\--Innominate V.

Thymus Gland

— -Lung

256

UNCONSCIOUS NERVOUS OPERATIONS

Svpraren a I

Cortex

-Medulla

Pyramids

new thyroid tissue to the food, or even by subcutaneous
injection of the juice of a healthy gland. It is concluded
that the gland either forms, or helps to form, some sub-
stance needful to health, or has some place in the destruc-
tion of deleterious substances in the system, but positive
knowledge in respect to it is lacking.

369. The Thymus Gland lies in the thorax beneath the
sternum (Fig. 117). It is a small organ, weighing only

about half an ounce at birth.

< .1111

After growing with the body
until the second year it gradu-
ally shrinks away, and before
the age of sixteen usually
disappears. Its use is quite
unknown. The thymus of
calves and lambs forms an
article of food called sweet-
bread.

370. The Suprarenal Capsules
(Fig. 118) are small organs
Fig. 11 8. -^Longitudinal section of resting on the upper portion
kidney. of the kidneys. They are

supplied with an abundance of blood vessels and nerve
fibers and nerve cells. It has been found that their
removal from animals is invariably and quickly fatal.
All that can yet be said as to the function of these bodies
is that they appear to form something which is essential
to the healthy tone of the muscles.

— Ureter

CHAPTER XIX

THE ORGANS OF EXCRETION

371. We have already learned that a double vital proc-
ess is continually carried on by the living cells in the
tissues of the body. One side of this vital activity is the
taking up, from the blood, of oxygen and the nutrient
material which the blood receives from the food in the
alimentary canal, and it results in growth and repair.
The other side of cell activity is the oxidation, or decom-
position by burning in the tissues, of worn-out matter,
and its return to the blood to be expelled from the body.
This removal of waste matter from the blood is called ex-
cretion. The waste material from the tissues leaves the body
under three principal forms, — as carbon dioxide, water, and
urea. The lungs, as we have seen, not only supply oxygen
to the blood, but also give off' daily a large amount of water
and carbon dioxide. Two other organs also have the
function of excretion. They are the skin and the kidneys.
The skin gives off water and certain salts; the kidneys
remove urea and other nitrogenous waste, along with a
large amount of water.

372. The Skin as an Excretory Organ. — We have studied
the skin as an organ of sensation, and have learned some-
thing of its structure and its use as a sense organ and as
a protector of the more delicate parts. Now we are to
study it as a remover of waste.

257

258 UNCONSCIOUS NERVOUS OPERATIONS

373. Structure of the Skin. — It will be remembered that
the skin is composed of two layers: the epidermis, com-
posed of many layers of cells; and the dermis, or true
skin, in which are found the papillae, blood vessels, and
nerves, with the end organs for touch and glands of differ-
ent sorts (Fig. 49, p. 83).

374. Perspiration. — The excretion of the skin is called
perspiration, or sweat, and consists of water, a little dis-
solved salt, and some fat. When the perspiration is evapo-
rated from the skin as fast as it is secreted, it is called
insensible perspiration; but if the quantity is larger, so that
it collects upon the surface, we call it sensible perspiration.

When the amount of sweat produced is scanty, it is acid
in chemical composition; but when the discharge is profuse,
it is alkaline. This difference is understood to be due to
the mixture of the products of the sebaceous glands with
those of the sweat glands. The former are extremely
minute glands pouring their secretions into the hair
follicles. Their product is acid and fatty, and is constant,
or nearly so, in quantity, while that of the sweat glands is
alkaline and variable in amount.

375. The Sweat Glands are very abundant over the whole
skin. They consist of coiled tubes lying deep in the der-
mis, and the duct of each reaches the surface by a cork-
screwlike channel.

376. The Nerves controlling the Sweat Glands are of two or
three different sets. Those affecting the blood circulation,
vasomotor, diminish the secretion of sweat by narrowing
the size of the blood vessels, and increase it by dilating
them. The special secretory fibers, when stimulated,
cause production of perspiration. Still other nerve fibers
supply the plain muscle fibers of the glands and regulate
the expulsion of the fluid. All these nerve fibers are

THE ORGANS OF EXCRETION 259

found in the same nerve trunks. There are subsidi-
ary nervous centers for this secretion in different parts
of the spinal cord; but the chief center controlling the
others is the medulla oblongata, and the nerve fibers for
the sweat glands run in the nerve trunks supplying the
different parts of the body. For example, the sciatic
nerve, supplying the muscles of the leg, carries secretory
fibers to the swe'at glands of the leg.

377. Functions of Perspiration. — By means of the sweat
glands waste water taken from the blood continually
passes into the air. The amount varies greatly, but may
be said to average about one and a half pints daily. A
very little carbonic acid and solid matter are found in
the sweat, along with the fat from the sebaceous glands,
and a mere trace of urea.

Besides the removal of waste matter, another important
function belongs to the skin in connection with perspi-
ration. It is well known that as water passes from the
liquid to the gaseous state a large amount of heat becomes
latent, and this heat is supplied by adjacent bodies.
Hence it is clear that by the evaporation of the perspi-
ration the surface of the body is cooled, and the sweat thus
becomes a regulator of the temperature of the body, the
amount of evaporation depending upon the state of the
body and of the surrounding air.

The amount of sweat secreted is also affected by nerv-
ous impulses from the emotional centers in the brain.
Fear, for example, sometimes causes profuse sweating.
Strong muscular activity, developing heat and stimulating
the circulation, increases perspiration. A low temperature
in the surrounding air constricts the blood vessels of the
skin, and so diminishes the production of sweat and pre-
vents loss of heat from the surface.

260

UNCONSCIOUS NERVOUS OPERATIONS

378. The Kidneys (Fig. 118) are bean-shaped organs,
lying on each side of the lumbar portion of the backbone.

They are dark red in color,
about four inches long, two
and a half broad, and about
one inch in thickness. At
the center of the concave,
or inner edge, of each kid-
ney the arteries enter and
the veins leave the organ.
The arteries are branches of
the aorta ; the veins empty
into the inferior vena cava.
From the same portion of
each kidney passes another
tube, the ureter, which con-
veys the urine secreted by
the kidneys to the sac called
the bladder, in the lower
part of the abdomen, for
storage. The ureters pass
obliquely through the wall
of the bladder, so that return
of the contents of the latter
is prevented.

379. Structure of the Kidneys. — By dividing a kidney
lengthwise through the middle, two distinct parts may be
seen : an outer, granular portion, called the cortex, lying
next to the inclosing capsule, and an inner medullary por-
tion (Figs. 118 and 120). The latter consists of a number
of conical parts, called pyramids, with their bases toward
the cortex. In the cortical portion the tiny uriniferou*
tubules commence around tufts of blood capillaries {glo-

Fig 11 9. -The kidneys and bladder
viewed from behind.

A aorta, from which the renal arter-
ies extend to the kidneys.

V inferior vena cava, from which the
renal veins extend to the kidneys.

u ureters.

THE ORGANS OF EXCRETION

meruli) and are gathered by a complicated arrangement
into larger divisions, and finally empty into the enlarged
upper portion of the ureter. From the little bunches of
capillaries spreads throughout
the cortex a fine network of
capillary tubes, which gather
into veins and pour the blood
into the renal vein.

380. Nervous Supply of the
Kidneys. — The kidneys receive
nerves from the renal plexus
upon each side. This is com-
posed of both white and gray
nerve fibers and of nerve cells.
They come from many sources,
but mainly from the sympa-
thetic system by way of the Fie 12°- -Diagram of a longi-

. J ~/ J . , tudinal section of a kidney,

solar plexus. The renal plexus

a renal artery.

c capillaries.

g glomerulus.

t uriniferous tubule.

v renal vein.

has thus indirect connection
with the vagus and with other
nerves distributed to the inter-
nal organs. These nerves seem to have only vasomotor
functions. As yet, we are unable to trace the special
secretory nerves of the kidneys.

381. Functions of the Kidneys. — The food which we eat,
after rendering to the tissues of the body its proper serv-
ice, is converted into the waste products water, carbon
dioxide, small quantities of salts, and urea (or some sub-
stance closely allied). The first two excretions result
from decomposition of the carbohydrates and fats, while
from the proteids come certain salts and nitrogen. These
last are excreted almost wholly by the kidneys, along
with a large quantity of water and a very little carbon

262 UNCONSCIOUS NERVOUS OPERATIONS

dioxide. To the kidneys, then, belongs the important
function of removing from the body the waste product
of nitrogenous food in all the living tissues.

382. Urea. — The final result of the changes which
nitrogenous foods undergo is urea, and its chief ultimate
source is the most abundant tissue — muscular tissue.
There is, however, no urea in the muscles. Other steps
in its production lie between the muscles and the kidneys.
The spleen, lymphatic glands, and other glands have to do
with its formation, but the final and most distinctive changes
appear to occur in the liver. If the urea is not removed
from the system, it destroys life. The quantity daily
secreted by the human organism is about five hundred
grains, which is normally 2 per cent of the total excre-
tion from the kidneys.

383. Relation between the Kidneys and the Skin. — The
relation between the skin and the kidneys is such that if
one channel of excretion becomes clogged, extra labor
appears to be thrown upon the other. If perspiration is
checked, there is, along with diminished activity of the
sweat glands, constriction of the blood vessels of the sur-
face, followed by dilation of those of the viscera, which
permits an increased flow of blood in the internal organs,
including the kidneys. The secretion of the kidneys, there-
fore, becomes more abundant. When by warmth or exer-
cise the sweat glands are stimulated, the reverse is the case :
the vessels of the skin are dilated, while those of the abdo-
men are constricted, and the renal secretion becomes scanty.

384. The Kidneys and the Alimentary Canal. — Still more
important seems to be the connection between the amount
of the kidney secretion and the water absorbed by the
walls of the alimentary canal. When a large quantity of
water is drunk, it passes directly into the circulation, and,

THE ORGANS OF EXCRETION 263

though the general blood pressure is not raised, it does
appear to affect directly the action of the kidneys and to
increase the excretion.

385. The Kidneys and the Nervous System. — The state of
the central nervous system greatly affects the activity of
the kidneys. This may be by the passage of emotional
impulses, originating in the brain, along vasodilator fibers
to the kidneys. The blood vessels being thus dilated, the
activity of the glands would be stimulated. Very large
quantities of almost pure water are sometimes thus elimi-
nated under emotional excitement.

386. Excretion by the Alimentary Canal. — Portions of the
food taken into the stomach are unfit to enter into the
structure of the tissues, and are expelled unchanged
through the intestines. A small amount of true excretion
also takes place there, by which used-up matter is removed.

387. Autointoxication, or Self-poisoning. — Even under
normal conditions man's organism is " a receptacle and a
laboratory of poisons." They are taken in with the food
in the form of those minute bodies which cause putrefac-
tion. The process of katabolism (§ 283) is a manufacture
of poisons, and many of the secretions, such as the saliva
and the bile, are poisonous. A large number of poisonous
substances are formed in the intestines, and several forms
of deadly poison have been discovered in the urine. All
of the poisons made by the tissues, and some of those
manufactured in the digestive tube, are poured into the
blood, so that even normal blood contains poisons, though
an excessive amount of the same poisons threatens health
and life. Many diseases are now understood to result from
the self-poisoning due to disordered nutrition, along with
the opportunities for infection from specific germs which
are always present; and reabsorption of excrementitious

264 UNCONSCIOUS NERVOUS OPERATIONS

matter once separated from the blood for rejection is a
danger to be guarded against.

388. Attention has already been called to some of the
ways* by which man is protected from the injurious prod-
ucts of his own organism (§§ 335, 336, 338). The gastric
juice contains more than enough hydrochloric acid to
prevent all fermentation in the stomach ; but in the
intestines its action is neutralized by the alkalis of the
intestinal juices. In the intestines a variety of poisons
are found, and when digestion is disordered the num-
ber and quantity may be dangerously increased. Some
of these are excreted, while others are absorbed into the
blood. The liver is the great defense against the poisons
in the blood, many of which are caught by that gland,
and either transformed or passed on to be removed from
the body by means of the kidneys. By the lungs
enough carbon dioxide is removed from the body every
day to poison a man to death many times over ; but other
injurious matters are found in expired air, especially in
the case of persons suffering from defective nutrition.
The skin also plays its part in the elimination of poisons,
and the peculiar odor of the perspiration in certain abnor-
mal conditions is a guide to the physician as to the
internal state of the system.

All these facts show the immense importance of keep-
ing constantly open and in healthy condition the various
channels of excretion.

389. Influence of Alcohol upon Excretion. — If the waste
substances constantly formed in the body are not promptly
removed, they tend to poison the system. When the or-
ganism is at a high level of health, the breaking down of
tissue by oxidation, which produces waste, goes on rapidly
and vigorously. When this is retarded, as we have seen

THE ORGANS OF EXCRETION 266

it to be when alcohol is introduced into the circulation
and uses up the oxygen which should be applied to the
oxidation of food, then the weight may increase, but it
is by the retention of poisonous matter which ought to
be removed. No other one cause creates so much disease of
the kidneys as does the use of alcohol. Imperfect oxida-
tion of food develops poisons which the kidneys are
overtaxed to remove. This may be caused by eating too
much, or by eating unwholesome food, or too much of
certain kinds of food, as sugar especially; or it may be
caused by alcohol. " Fatty degeneration of the kidneys "
is a frequent result of the use of alcoholic drinks. The
cells of the tissues become so altered, also, that they fail
to act normally by removing only the poisonous sub-
stances, and they allow the valuable elements in the blood
to be drained off with the waste. This is seen in the
serious disease called " Bright's disease " in which the
albumin which is necessary to health is excreted by
the kidneys.

DEMONSTRATIONS

123. Dissection of the Kidney. — Procure a kidney of a sheep or of
a pig. As much as possible of the ureter should remain attached.
The kidney is seen to be inclosed in a capsule. Remove the latter,
and notice the shape of the kidney and the enlarged attachment of
the ureter. Split the kidney lengthwise parallel to the broad surface,
and observe on the outside of the section a layer, the cortical layer,
differing in color from the more internal, medullary, portions. Notice
the projections, pyramids, of the medullary portion into the sinus.
The latter is a cavity in the concave side of the organ, continuous
with the cavity of the ureter.

124. Minute Structure of the Kidney. — For this some prepared sec-
tions will be needed: (1) section showing general structure of cortex
and medulla, with uriniferous tubules plainly demonstrated ; (2) sec-
tion showing blood vessels injected ; (3) a cross section of the ureter.

CHAPTER XX

THE HEAT OF THE BODY

390. Inanimate bodies tend constantly to assume the
temperature of the air, water, or other objects near them.
An object which has been heated gives out heat to sur-
rounding objects until all are of the same temperature.
There is, as we say, a tendency to equilibrium in respect
to temperature.

391. Animal Heat. — Warm-blooded animals (birds and
mammals) maintain within their bodies, summer and win-
ter and indoors and out, with slight variations, the same
degree of heat, and are independent of their surroundings
in that respect.

392. Temperature of the Body. — In order that the vital
processes necessary to human health and comfort may go
on under the most favorable circumstances, it is necessary
that the body should maintain a temperature of from 98°
to 99° F. (from 36.6° to 37.2° C.). If it rises much above
or sinks much below this, it is an important indication of
abnormal condition in some part of the system. We may
be exposed to extreme heat and to severe cold without any
marked change in the bodily heat. The skin, it is true,
being in contact with external" objects, is usually cooler
than other parts. Some of the internal organs have in
health a temperature several degrees higher than the gen-
eral average, and any special activity of an organ develops

266

THE HEAT OF THE BODY 267

a local excess of heat. A group of muscles, for instance,
by their contraction, produce heat. A gland, by the act
of secretion, does the same. But the tide of blood, flow-
ing swiftly through the system and bathing every part,
tends to equalize the heat throughout.

393. The Sources of Animal Heat are of two sorts, — direct
and indirect. The great source of heat is the combustion
of food, that is, the oxidation which takes place in the
living cells in all parts of the body. This is equal to the
amount of heat which would be given off by the burning
in the open air of the same quantity of food which is con-
sumed in the body. The muscles and the glands are the
parts in which the greatest amount of oxidation takes
place. Some little heat is also received by the body in
hot foods and drinks.

Heat is produced indirectly by the transformation of
other forms of energy. Friction of one part upon another
— as of the blood along the walls of the blood vessels —
becomes heat. All mechanical work, all nervous activity,
and the slight manifestations of electricity within the
body liberate heat.

394. Regulation of Temperature is accomplished in two
ways; viz. by variation in the loss of heat and by varia-
tion in its production.

Variation in loss of heat. Everything which leaves the
body carries away a portion of its heat. The expired air,
the perspiration, the excretions, are sources of loss ; and
radiation and conduction of heat from the surface are con-
tinually going on, as well as evaporation from the skin and
the lungs. The skin is the chief regulator of loss. By
clothing the body a portion of the loss by radiation is pre-
vented, and we have already seen (§ 376) how the secre-
tion of sweat, and hence the cooling of the surface by

268 UNCONSCIOUS NERVOUS OPERATIONS

evaporation, is affected by the vasomotor and nervous
mechanisms of the skin.

Variation in production of heat. The processes of diges-
tion are attended by the setting free of heat. The
temperature rises after a meal, while a marked condition
in starvation is the fall of the bodily temperature. Mus-
cular contraction always going on develops heat, and the
more active the muscles are, the greater is the amount
of heat produced.

There is also evidence, from numerous experiments,
of direct nervous control over the production of heat.
Afferent impulses from the skin or other organs reach the
central nervous system and some restricted " heat center "
not yet anatomically made out in the central part of the
brain. The exact path of these impulses is not yet ascer-
tained. The stimulation of the heat center, wherever it
may be placed, gives rise to efferent impulses by which
activity in the tissues is increased and heat is produced.

395. Clothing. — Though the body is able to endure a
large amount of exposure to heat and cold without injury,
yet the mechanism for heat production may be overtaxed,
as well as the digestive, the muscular, or the nervous
system. Any such overtaxing interferes with the other
functions of the body. Excessive exposure to cold, or
insufficient clothing, forces the body to use an undue
amount of energy in manufacturing heat, and other parts
of the vital economy suffer ; growth in the young is inter-
fered with, and mental and muscular effort become diffi-
cult. The clothing worn should therefore be such as will
assist in preserving the natural' temperature of the body,
and the amount and the material will vary with climate
and season, as well as with the age, habits, and health
of the wearer.

THE HEAT OF THE BODY 269

While clothing is designed to prevent too rapid radia-
tion of heat from the surface, it should still permit the
evaporation of perspiration, for an accumulation of mois-
ture uf)on the skin may expose one to dangerous chills.

396. Fabrics of wool have been found to possess more
fully than any other materials the qualities desired for
clothing. They are so light and porous as to admit of
sufficiently free evaporation and the circulation of air ;
and as wool is a bad conductor of heat, it retains the heat
of the body, while it holds in its meshes a considerable
quantity of air, which is also a nonconductor of heat. In
variable climates, such as that of our Northern states, it is
wise, at least for those in delicate health or especially
sensitive to changes of temperature, to wear wool next
the skin at all seasons. The gentle friction of woolen
garments against the skin tends to prevent clogging of
the pores, to promote even circulation, and in general to
keep the surface in a healthy condition.

397. Silk is less valuable than wool in preserving heat
and permitting evaporation, though better than cotton oi-
lmen. It may be worn next the body when wool causes
irritation of the skin.

398. Linen is less useful than other materials for the
innermost garments, as it quickly becomes saturated with
moisture. Cotton, being more porous, answers the purpose
better. In respect to all these materials the weaving of
the fabric has much to do with its value for clothing.
Closely woven cloth of hard-twisted threads should not be
chosen for underwear, but rather that of soft, loosely
twisted fibers, loosely woven.

399. Fur is indispensable in the coldest climates, as it
retains better than anything else the bodily heat. But it
prevents the evaporation of perspiration, and should not

MACY'S PHYS. — 17

270 UNCONSCIOUS NERVOUS OPERATIONS

be worn in moderate weather ; nor should fur garments
be retained indoors — as when sitting in an assembly
room. The practice of muffling the throat in wraps of
fur should be avoided, as liable to render the larynx
unnecessarily sensitive to cold, and to cause the evil it
is intended to prevent.

400. Waterproof wraps, which prevent the escape of per-
spiration, should be worn only as a protection from rain or
snow.

401. Light-colored clothing reflects the rays of heat and
absorbs but little warmth, while dark colors absorb heat
and reflect little. Hence the common custom of wearing
light-colored garments in summer and dark ones in winter
is founded in reason.

402. Frequent changes of clothing, especially of that
which touches the skin, are needful. The pores of a
fabric soon become filled with the poisonous waste mat-
ters secreted by the skin. The clothing worn by day
should never be worn during the night also. If it is to
be resumed in the morning, it should be exposed to free
circulation of air during the night. Night clothes and
all bedding should be carefully sunned and aired each
day.

403. It is important that all clothing and bedding
should be thoroughly dry. Damp clothes do not retain
the natural heat of the body, but rapidly conduct it away,
leaving the surface chilled and the system exposed to
attacks of disease. Especially should shoes and stockings
which have become wet be removed as soon as possible.
Many a serious or fatal illness -has resulted from neglect
of this precaution. Damp bedding is especially dangerous
to health, as the relaxed condition of the body during
sleep renders it an easy prey to every cause of disease.

THE HEAT OF THE BODY 271

404. Care should be exercised in changing from the
warm clothing of winter to the thinner garments needed
in the spring. It is most prudent to make changes first
in the outer clothing, retaining the warm inner garments
until the mild weather is well established. Often in the
Northern states it is necessary to return to heavy winter
wraps after a season of high temperature.

In the early autumn, too, when cold, damp evenings
and nights follow hot, sunny days, judicious attention to
clothing will often ward off the intestinal and febrile
diseases prevalent in that season. It is frequently wise
to change the underclothing with the approach of night,
putting on the warm wool which was perhaps intolerable
at midday. Many physicians advise as a safeguard the
wearing of a broad woolen bandage over the abdomen
both by day and by night.

405. The Bodily Heat as affected by Alcohol. — The paralyz-
ing effect of the use of alcoholic drinks, upon the muscles
in the walls of the minute blood vessels, has been men-
tioned in connection with the muscles, the circulation,
and respiration. It should be referred to also in connec-
tion with the subject of this chapter.

Because alcohol is quickly oxidized, and because heat
is produced in the process, it was long believed to be of
value in maintaining the heat of the body. A different
view now prevails as the result of much observation and
experiment. Travelers in Arctic regions and others
exposed to intense cold agree that those who use no
alcohol whatever are far better able to resist the cold
than are those who indulge in it. Physiologists show by
careful experiments that though the temperature of the
body rises during digestion of food, it is lowered for some
hours when alcohol is taken. The flush which is felt

272 UNCONSCIOUS NERVOUS OPERATIONS

upon the skin after a drink of wine or spirits is due in
part to an increase of heat in the body, but also to the
paralyzing effect of the alcohol upon the capillary walls,
allowing them to dilate, and so permitting more of the
warm blood of the interior of the body to reach the sur-
face. There it is cooled by radiation, and the general tem-
perature is lowered.

PART IV

THE NERVOUS SYSTEM

All our previous study has had to do, directly or in-
directly, with the nervous system, with its methods of
action, its instruments, its nutrition, its arrangement and
functions. Now we are to examine its wonderful and
delicate mechanism more in detail, to inquire further into
the functions which the various parts fulfill, and into the
manner of life which study and experience have shown to
be most conducive to the preservation of the most impor-
tant part of the human organism in health and efficiency.

Even the limited amount of knowledge upon this great
subject which is within the reach of young students may
be made valuable in enforcing the necessity of hygienic
living, and also as a basis for a ready appreciation of that
larger revelation respecting the nervous system which
science will from time to time unfold.

In presenting this fuller description of the nervous
system some repetition of the statements given in Chap-
ter III is found necessary.

S78

Fig. 121.— The nervous system.

274

CHAPTER XXI
ANATOMICAL DESCRIPTION

406. Composition of the Nervous System. — The nervous
system is made up of nerve centers, nerves, and peripheral
end organs. These, though really constituting a single
system for the whole of man's organism, are commonly
described in two separate groups, or systems: the cerebro-
spinal or central and the sympathetic or ganglionic.

The nerve centers are the brain and spinal cord (often
called the cerebro -spinal axis), and little knots of nervous
matter found in different parts of the body, along the
course of the nerves, called ganglia. All nerve fibers
arise in the nerve centers.

407. Nervous Elements. — We have learned that nerv-
ous tissue exists in two forms : gray matter, which is
almost wholly composed of nerve cells, and white matter,
which is almost wholly composed of nerve fibers. Nerve
fibers and nerve cells constitute the nervous elements.

408. The Nerve Cell. — Nerve cells are microscopic, irreg-
ular bits of protoplasm like other cells. Each contains
a large nucleus, within which is a nucleolus, and usually
each cell sends off one or more fine branches, or proc-
esses (Fig. 122). Sometimes these are so numerous
as to give the cell a stellate appearance. Nerve cells
are found only in the central nervous system, in the

275

276 THE NERVOUS SYSTEM

ganglia, and in the peripheral terminations of certain
nerve fibers.

Fig. 122. — Nerve cells from the spinal cord.
A nerve cell with all its processes. B body of cell, showing nucleus (N).

409. The Axis Cylinder, or Neuraxon. — One of the proc-
esses of the nerve cell — and as a rule only one — becomes
what is called the axis cylinder of a nerve fiber. It is a
protoplasmic thread continuous with the substance of the
cell and usually inclosed within a sheath. Axis cylinder
processes give off, usually at right angles, fine side
branches which ramify in the adjacent nerve substance
(Fig. 123), and the final ending of the axis cylinder
itself is in many minute divisions. Many or most of the
nerve cells have other processes which do not become
axis cylinders, but end in fine twiglike divisions in the
gray matter around them.

410. The Nerve Fiber (Fig. 124).— The essential part
of every nerve fiber is the central protoplasmic core,
which is always the axis cylinder process of a nerve cell.
There is hence, after all, only one fundamental form of
nervous matter, viz. the protoplasm of the nerve cell.

ANATOMICAL DESCRIPTION

277

The central thread of a nerve fiber may have two inclos-
ing sheaths. A layer of white, oily matter immediately
surrounding the axis cylinder is called
the medullary sheath, or
sometimes the white sub-
stance of Schwann. Out-
side of this is a coat of
thin, elastic membrane
called the primitive sheath,
or neurilemma. The lat-
ter covers its fiber from
end to end, but the med-
ullary sheath is broken
at frequent intervals, and
between the breaks the
microscope shows along
the course of the axis lit-
tle nuclei buried in min-
ute masses of protoplasm.
Fig. 123. — Nerve In some nerve fibers
cells (pyramidal) the medullary sheath is
of the cortex of the .

cerebrum. wanting, leaving only the Fig. 124. — Por-

Ax axis cylinder proo neurilemma inclosing the duSated^erve

axis cylinder. These are fiber.

called nonmedullated nerve fibers. The medullary sheath
is brilliant, shining white in color, and gives to the nerve
its characteristic white appearance. The nonmedullated
fibers, therefore, are gray.

Nerve fibers may be very short or they may be many
feet in length. Every nerve fiber originates in a nerve
cell, but there are several ways in which it may end, as
has already been shown.

411. A Nerve is a bundle of nerve fibers bound together

l)_Nodeof
Ranvier

•Neurilemma

(--Nucleus

Neuraxon
" 'or Axis
Cylinder

Medullary
' 'Sheath

278

THE NERVOUS SYSTEM

by a little connective tissue in which run blood vessels
and lymphatics, the whole inclosed in a sheath called the
perineurium. The nerves from the central system are
composed chiefly of medullated fibers, with which are
bound up a few nonmedullated ones, while the nerves
of the sympathetic system are made up almost wholly of
the gray nonmedullated fibers.

412. A Ganglion is a little group of nerve cells forming
a nervous center. As a rule (to which the spinal ganglia
form an exception), the nerve fibers running from the cen-
tral system to a ganglion are medullated, while those
passing from the ganglion toward the periphery are non-
medullated and also more numerous.

413. Neuroglia. — The fibers and cells of both the gray
and the white nervous matter are supported by a tissue

called neuroglia (Fig. 125),
which is composed of ex-
tremely fine fibers and cells.
It differs chemically and in
origin from the connective
tissues, though like them in
function.

414. The Nerve Unit or Neu-
ron. — A nerve cell, with its
two sorts of processes, con-
stitutes a nerve unit^ or neuron
(Fig. 126). That is, the whole nervous system is built
up of an indefinite but enormous number of these units,
supported by neuroglia and connective tissue. A nerve
cell sends off one process (rarely more), which is pro-
longed into the axis cylinder, or neuraxon* while the
numerous other branches, called dendrons or dendrites,
almost immediately break up into fine twigs or brushlike

Fig. 125. — Neuroglia cells.

ANATOMICAL DESCRIPTION

279

£--', Dendrites

V™CteH Body

--------- Neuraxon

....... Medulla

\ ------ Node of Ranvier

--- -Neurilemma

divisions. The dendrons are thought by some to be con-
cerned only in absorbing nutriment for the nerve cell,
while other investigators believe them
to have also some part to play in the
conduction of nerve impulses. Each
neuron is anatomically independent
of every other. There is no continu-
ous path from one nerve cell to
another. The fine branches from
one cell mingle and interlace with
those of another cell, but do not
become connected with them to form
a continuous channel, any more than
do the interlacing branches of two
trees standing side by side form com-
municating channels for the passage
of the sap of one to the other.
Nervous influences do indeed pass
from one nerve unit to another by
some method not yet understood,
perhaps by a process similar to that
of electrical induction; but the old
idea of an uninterrupted channel for
the passage of a nervous impulse from center to periphery
and from periphery to center is now abandoned. There
may be several breaks in the course of transmission, as
there often are in the sending of a telegraphic message.
The two sorts of branches also preserve their identity
from beginning to end of each minutest filament. There
is no real network of nerve fibers in the nervous system.

415. The Spinal Cord (Fig. 18, p. 28) is a column of
nervous matter from fifteen to eighteen inches in length
in the adult, from the foramen magnum, through which

Nerve-ends

Fig. 126. —Diagram of a
neuron or nerve unit.

280

THE NERVOUS SYSTEM

Posterior Fissure

its fibers pass into the brain, to the fine gray filament
which forms its termination in the lumbar vertebrae.
A cross section shows it to be composed of white fibrous
matter, surrounding a central core of gray cellular matter
(Fig. 127). The gray matter presents in section a
rough outline of the letter H. In the middle of the
cross bar, or isthmus, connecting the two sides of the let-
ter, is a minute chan-
nel which extends the
whole length of the
cord and on into
the brain. The ends
of the letter H which
point forward are
club-shaped and are
known as the anterior
horns of the gray mat-
ter of the cord, while
those pointing back-
ward are pointed and
are called posterior
horns. The last cut
through the white
matter nearly to the
surface of the cord.
The white matter of the cord is composed of medullated
fibers, running for the most part longitudinally, together
with fibrous connective tissue and neuroglia. These fibers
are arranged in several different strands, or bundles, and
their areas have been carefully mapped out and named.
In each half of the cord is an anterior, a lateral, and a pos-
terior column, named from their positions and separated
from one another by the shallow depressions seen in the

Anterior Fissure

Fig. 127. — Diagram of a cross section of
the spinal cord, showing the divisions
of the white and gray matter.

The right half shows the threefold division
of the white matter commonly described ; the
left half shows the physiological divisions as
they are at present understood.

ANATOMICAL DESCRIPTION

281

surface of the cord. The gray matter consists largely of
nerve cells with many branching processes, but there are
also many delicate nerve fibers, together with the support-
ing neuroglia. The cord is divided into symmetrical
halves by fissures before and behind, the posterior fissure
being the deeper, and the anterior wider and more
distinct. Neither of the fissures cuts quite through the
white matter to the gray in the center.

416. Spinal Nerves. — From the grooves nearest the ante-
rior fissure spring, by many fine rootlets, the anterior roots

Fig. 128. — Diagrammatic cross section of the spinal cord, showing the
origin and the chief divisions of a spinal nerve.

A anterior column of white matter.
D posterior branch of nerve trunk.
Ga ganglion on the posterior root of the nerve, containing the cells from which

arise most of the fibers of the sensory root (<S).
Gr gray matter of the cord.
L lateral column of white matter.
M anterior or motor root of the nerve.
Me motor cells from which arise the motor nerve fibers.
N main trunk of the nerve.
P posterior column of white matter.
S posterior or sensory root of the nerve.
Sy ganglion of the sympathetic system which communicates with the spinal

nerve.
V anterior branch of nerve trunk.

of the spinal nerves, while the posterior roots of the same
nerves appear to rise near the other groove on the same
side (Fig. 128). The two roots soon unite; — but before

282 THE NERVOUS SYSTEM

their union the posterior root passes through a little knot
of gray matter, called the spinal ganglion.

The cells of the anterior horn of the gray matter of the
cord are large and branching, and each cell sends off an
axis cylinder process which passes out in an anterior nerve
root. Careful experiments have shown that the fibers in
the posterior nerve roots of spinal nerves arise in the spi-
nal ganglion. The nerve fibers which form this posterior
root are axis cylinder processes from nerve cells in the
spinal ganglion. As they pass out from the ganglion each
divides into two branches, one of which goes to form a
sensory nerve fiber in the spinal nerve. The other turns
back and enters the spinal cord, where it again divides,
its fibers ending variously. The main division of the
branch from the ganglion passes up to the brain, giving
off fine collaterals which end, by " arborizing " (as the
brushlike ending is called), round nerve cells at different
levels in the cord. In general, the posterior root fibers
travel upward mainly in the white columns of the cord,
while only a few fibers enter the gray matter of the cord.

417. Thirty-one pairs of spinal nerves issue from the
spinal cord (Fig. 18, p. 28), each nerve containing
both afferent, or sensory, nerve fibers from the posterior
root, and efferent, or motor, fibers from the anterior root.
These fibers remain distinct from each other for their
whole length. The spinal nerves are distributed by many
branches to the skin and skeletal muscles; they also form
connection, by what are called communicating branches,
with the ganglia of the sympathetic system (Figs. 128 and
136), and are afterward distributed to the viscera. The
whole of the sympathetic system may be regarded as
simply the development of these communicating branches
from certain spinal nerves.

ANATOMICAL DESCRIPTION 283

418. Plexuses. — We have already seen that in many
regions of the body, especially about the neck, loins, and
pelvis, adjacent nerves interlace to form a network, or
nervous plexus. Nerves passing outward from a plexus
contain fibers from several different nerves, and the parts
to which these nerves are distributed are thus sometimes
brought into connection with a considerable part of the
central nervous system. The nerves which supply the
limbs, where very complex muscular movements are re-
quired, and where nervous coordination of those move-
ments is necessary, come from large plexuses where fibers
from many nerves are intermingled. (It should be remem-
bered that the term " network " is here used subject to the
limitation given above [p. 279] and does not imply more
than is there stated.)

By means of the spinal nerves nearly all the nervous
impulses from the trunk and limbs pass through the spi-
nal cord to the brain.

419. Membranes of the Brain and Spinal Cord. — Three
membranes inclose the brain and spinal cord. The dura
mater is a tough, white fibrous and elastic membrane lin-
ing the bony cavity of the skull which contains the brain,
and the vertebral canal in which lies the spinal cord. It
also lies in folds between the divisions of the brain.

The arachnoid is a thin membrane of loose connective
tissue, forming a sort of closed sac (like the pericardium),
which secretes a serous fluid. It lies between the dura
mater and the pia mater.

The pia mater is an extremely delicate, highly vascular
membrane (that is, having many blood vessels), closely
investing the nervous matter of the spinal cord and the
brain. It follows all the curves and convolutions of the
brain, and carries to all its parts and to the spinal cord

284

THE NERVOUS SYSTEM

numerous blood vessels which assist in their nutrition.
The three membranes are sometimes called the cerebro-
spinal meninges, and the serious disease called cerebro-
spinal meningitis is due to inflammation of these lining
membranes.

Corpus Callos

Foramen of Monro

\ Third Ventricle

Pineal Body

i Cerebrum

Optic Chiasma

Pituitary Body /

Oculomotor' Nerve /

Pons Varolii / /

Aqueduct / /
Medulla Oblongat'a /
Fourth Ventricle

~ Corpora
O/uadrigemina

Cerebellum

Spinal Cord

Fig. 129.— The right half of a vertical median section of the brain.

420. The Brain (Figs. 129, 130, 131, and 134). — The
division of the brain into five principal parts is derived
from the manner of the development of those parts from
certain primary divisions of the embryo. Those parts
are : (1) the cerebrum, with its two hemispheres ; (2) the
optic thalami; (3) the corpora quadrigemina, or optic lobes,
with the crura cerebri; (4) the cerebellum and pans Varolii ;

ANATOMICAL DESCRIPTION

285

and finally (5) the medulla oblongata. More minute divi-
sions might be and often are given, but these are sufficient
for the present purpose.

Corpus Striatum
Fornix

Optic Thalamus
— Pineal Body
--•^-Corpora Quadrigemina
Trochlear Nerve

Fig. 130. — Brain viewed from above, with the cerebellum and a large
part of the cerebrum removed, exposing the structures hidden by
the cerebrum.

1, 2, 3 cut surfaces of the peduncles of the cerebellum.

421. The Cerebrum (Fig. 131). — More than two thirds
of the whole weight of the brain belongs to the two hemi-
spheres of the cerebrum. Its surface of gray matter,
called the- cortex, presents a characteristic folded appear-
ance, the convolutions being separated by fissures. The
deeper fissures divide each hemisphere into five lobes,
called, from their locations in the cranium, the frontal,
parietal, temporal, occipital, and central lobes, the last being
also called the insula or island of Reil. The insula is not
MACY'S PHYS. — 18

286

THE NERVOUS SYSTEM

visible from the surface, but lies deep within the Sylvian
fissure, which divides the frontal from the temporal lobe,
and is concealed by the convolutions of the upper lobes

Fissure of^
Rolando ~~

^.-Parietal Lobe

V"^>. Occipito-parietal

^ X / Fissure

Frontal Lobe

Occipital Lobe
^Sylvian Fissui
Temporal Lobe

Fig. 131.— Side view of the left cerebral hemisphere.

(Fig. 132). Other principal fissures are the deep lon-
gitudinal one separating the hemispheres ; the fissure of
Rolando, which lies between the frontal and parietal

lobes ; and the occipito-
parietal fissure, separat-
ing the parietal from
the occipital lobe. A
broad band of white
nerve fibers, the corpus
callosum, connects the
two hemispheres (Fig.
129). In the base of
- each frontal lobe is a
bulbous expansion of gray and white matter connected
by a stalk, or peduncle, called the olfactory tract, with the
mass of the hemisphere. These are the olfactory bulbs,

Fig. 132. —Side view of brain with tem-
poral lobe cut away so as to expose
the underlying insula.

ANATOMICAL DESCRIPTION 287

with which are connected the olfactory nerves (Fig. 134).
They are direct outgrowths of the brain substance. Lying
partly in the lateral ventricles (§ 426) and partly embedded
in white substance of the hemispheres, are the pear-shaped
corpora striata (Fig. 130), composed of white and gray
matter. They are ganglia on the path of motor nerves.

422. The Optic Thalami are masses of gray matter in the
base of the cerebrum (Fig. 130), and are closely con-
nected with the corpora striata, which belong to the cere-
brum. These two pairs of gray bodies are often called the
basal ganglia. From them nerve fibers radiate into the
convolutions of the cerebral hemispheres. The optic thai-
ami are ganglia on the path of sensory nerves ; the corpora
striata belong to the motor tract.

423. The Corpora Quadrigemina, or Optic Lobes, and the
Crura Cerebri. — The corpora quadrigendna, or optic lobes, lie
behind and between the optic thalami (Figs. 129 and 130).
They are masses of gray matter, or rather a single body
divided by shallow fissures into four hemispherical parts.
The optic tracts arise superficially from their surfaces.
The optic lobes rest upon the hinder face of the crura
cerebri. These latter are bundles of nerve fibers forming
peduncles, or stalks, which connect the cerebrum with
other parts of the brain.

424. The Cerebellum and Pons Varolii (Figs. 129 and
134). — The cerebellum is composed of gray and white
matter, and lies in two hemispheres across the back of the
cerebro-spinal axis. The hemispheres are connected by
bands of white matter, called peduncles, with each other
and with other parts of the brain. The white matter of
the cerebellum is arranged on each side in a central trunk,
which divides into many branches, around which the gra}^
matter is placed, the whole forming what is called, from

288 . THE NERVOUS SYSTEM

its likeness to a branching tree, uthe tree of life." The
gray surface is arranged in parallel ridges, or laminated
folds, differing from the irregular convolutions of the
cerebrum .

The pons Varolii also contains white and gray matter.
In it white fibers pass upward to connect the medulla ob-
longata with other parts of the brain. It contains, also,
the strands of white matter which form the middle
peduncle of the cerebellum. The pons is, therefore, as its
name implies, the passage, or bridge, by means of which
connection is made between all parts of the nervous
system.

425. The Medulla Oblongata, or Spinal Bulb, is the enlarged
upper portion of the spinal cord contained within the
cavity of the cranium (Figs. 129, 130, and 134). It is
conical in shape, about one inch in thickness at its broad-
est part, and about one inch arid a quarter in length, and
consists of two symmetrical halves. On the forward, or
anterior, surface is seen a deep groove, which is a con-
tinuation of the anterior fissure of the cord. A similar
but more shallow fissure forms the posterior division
between the halves. Just as the cord begins to expand
into the medulla, many of the fibers which compose the
lateral columns of the cord cross from one side to the
other. These bundles of white fibers are called, in
the medulla, the pyramids, and their crossing is called
the decussation of the pyramids. Other fibers of the
pyramidal tracts cross lower down at different levels in
the cord. In general, a rearrangement of the fibers of the
cord takes place in the medulla: What it is especially
important to notice is that each tract of fibers in the cord
has connection through the medulla with the centers in
both the cerebellum and the cerebrum.

ANATOMICAL DESCRIPTION

289

The gray matter of the medulla oblongata is partly
continuous with that of the cord, but is partly broken up
into independent groups of cells, or nuclei, which are the
deep origins of most of the cranial nerves.

426. The Ventricles of the Brain, and the Cerebro-spinal
Fluid. — The ventricles are irregular cavities in the brain,
communicating with one another and continuous with the
canal of the spinal cord (Fig. 133). The lateral ventricles
lie one in each hemisphere of the

cerebrum. They open into the
third ventricle, which is in the mid-
dle line. A narrow canal, called
the aqueduct of Sylvius, connects
the third with the fourth ventricle,
of which the back of the pons and
the medulla oblongata form the
floor, while the overhanging cere-
bellum forms part of its roof. A
small opening in the pia mater,
which completes the roof of the
fourth ventricle, makes connec-
tion between these interior cavities and the external sur-
face o*f brain and cord, so that the fluid which fills the
space beneath the arachnoid is continuous with that in
the inside.

The cerebro-spinal fluid is a thin, watery substance which
bathes the external surfaces of the brain and spinal cord,
and fills the ventricles and the spinal canal.

427. The Cranial, or Cerebral, Nerves (Figs. 134 and 135).
— Of the twelve pairs of nerves issuing from the brain,
ten have their deep origins in the floor of the fourth ven-
tricle or in adjacent gray matter. Each cranial nerve is
said to have a deep origin, which is that portion of gray

Fig. 133. — Cast of brain
cavities.

290

THE NERVOUS SYSTEM

matter where its fibers rise from nerve cells, and a super-
ficial origin, which is the region of the brain surface from
which the nerve, as a nerve, departs upon its mission.

1. The first pair of cranial nerves are the olfactory
nerves, distributed directly and wholly to the organ of
smell, and sensory in function.

Olfactory Bulb

(to which is attached
the Olfactory Nerve)

Pituitary Body — ___

Optic Nerve-
Optic Chiasma —
Oculomotor Nerve- — _

Trochlea r Nerve

Trigem inal Nerve — _

Pans Varolii
Abducena Nerve

Facial Nerve —
Auditory Nerve- ^ __
Glossopharyngeal Nerve __ J
Vagus Nerve---.
Spinal accessory Nerve- -
Hypoglossal Nerve- -
Medulla Oblongata--
First Spinal Nerve —

Cerebellum

Spinal Cord- -
Second Spinal Nerve —

fig. 134. — Ventral • anterior, surface of the brain.

2. The optic nerves go to the organs of sight. From
their deep origins to the point where a part of their
fibers cross they are called the ' optic tracts. They are
sensory.

3. The oculomotor nerve supplies all the muscles of the
eyeball except the superior oblique and external rectus,

ANATOMICAL DESCRIPTION

291

and communicates with a nerve plexus of the sympathetic
system.

4. The trochlear, the smallest of the cranial nerves, is
motor. It supplies the superior oblique muscle of the eye,
and communicates with the same plexus as does the third
nerve.

5. The trigeminal,
the largest cranial
nerve, is mixed in
function. Its motor
division goes to the
muscles of mastica-
tion. The larger
division is the great
sensory nerve of the
face and head.

6. The abducens
supplies the external
rectus muscle of the
eyeball as its motor
nerve.

7. The facial is
the great motor nerve

of the muscles of the face. One of its branches, the
chorda tympani, passes across the tympanum and joins the
lingual branch of the fifth nerve. It is purely motor.

8. The auditory; a sensory nerve, leaves the surface of
the brain in two roots : one, the cochlear branch, is the
auditory nerve proper, and goes to the cochlea ; the ves-
tibular branch ends in the semicircular canals, the utricle,
and the saccule.

9. The glossopharyngeal, after communicating with
several neighboring nerves and ganglia, separates into

\*t and -2nd

"Spinal Nerves

Fig. 135. — Diagram of the distribution of
the cranial nerves.

292 THE NERVOUS SYSTEM

two main divisions. One goes to the pharynx, the Eus-
tachian tube, the palate, and the tonsils, as a motor nerve
chiefly. The other is the nerve of taste for the back part
of the tongue.

10. The vagus, or pneumogastric, is the wandering nerve.
It is longer and has a more complicated distribution than
any other cranial nerve. It sends branches to pharynx,
larynx, esophagus, stomach, intestines, lungs, heart, liver,
and spleen. It is both sensory and motor.

11. The spinal accessory, a purely motor nerve, con-
tains fibers from a nervous center in the walls of the
fourth ventricle, and from the anterior horns of the spinal
cord. The latter fibers pass up into the cranium and join
the cerebral fibers of this nerve just before it passes out
of the skull. The nerve has two branches, one of which
joins the vagus, to which it supplies motor fibers and
inhibitory fibers for the heart, while the other supplies
certain muscles of the shoulder blade and neck.

12. The hypoglossal is connected with the vagus, Avith
a ganglion of the sympathetic system, and with some of
the upper spinal nerves. It is the motor nerve for the
muscles connected with the hyoid bone and the tongue,
and sends a branch to some muscles of the neck and chest.
It also contains vasomotor filaments.

428. The Nervous End Organs have been described in
previous chapters, and are mentioned here to complete
the anatomical view of the nervous system. They are in
man of three classes, viz. end plates of different forms
found in the muscles, organs of special sensation, and
secreting cells found in the various glands.

429. The Sympathetic System (Fig. 136). — What is
commonly called the sympathetic or ganglionic system con-
sists of a double chain of ganglia, twenty-four upon each

Cervical Spinal
Nerves

Dorsal Spinal /
<

Lumbar Spinal
Nerves

Fig. 136. — Diagram of the sympathetic nervous system=

Or ganglion chain. Co coccygeal spinal nerve.

294

THE NERVOUS SYSTEM

^ Solar Plexus

side, lying along the whole length of the spine. They
are connected by white fibers with the spinal cord, with
one another by gray or nonmedullated fibers, and with
the spinal nerves by both white and gray fibers. At their
upper extremities, and in other situations also, the great
sympathetic nerve trunks come into connection with all
the cranial nerves except the olfactory, auditory, and
optic.

The gray fibers issuing from the ganglia are usually
too minute to be visible to the naked eye, and they are

much more numerous than
those received by the ganglia
from the central system.
Most of these gray fibers
seem to convey efferent im-
pulses to the tissues, though
some are afferent, carrying
impulses from the viscera to
the central system. But a
certain number of the fibers
from the main sympathetic
chain turn back from the
ganglion toward the center,
some to reach the membranes
of the spinal cord, some to
follow the course of the prin-
cipal branch of the spinal
nerve which is distributed to
the skeletal muscles and the
skin. Nervous connection is
thus established between all these various parts. In their
distribution the sympathetic nerves follow closely the
course of the blood vessels, around which they form

L. Sympathetic

Chain
R.Sympathetic

Chain

Fig. 137 The solar and hypo-
gastric sympathetic plexuses.

ANATOMICAL DESCRIPTION 295

plexuses, fibers from which accompany the blood vessels
throughout the body, penetrating to all parts of the various
organs. In the abdomen is found also a great plexus of
nerve fiber called the solar plexus, because smaller plexuses
radiate from it like rays of light from the sun (Fig. 137).
From the solar plexus nerve filaments are distributed to all
the abdominal organs.

DEMONSTRATION

125. Dissection of the Brain. — The specimens used in Ex. 6 (p. 33)
should now be studied more in detail. The brain should be divided
into two symmetrical halves, and the longitudinal median section, thus
exposed, should be compared with Fig. 129. In this way all the parts
of special importance can be identified. Care should be taken that
the pupil makes this careful detailed comparison and identification.
Slice away the dorsal (upper) surface of the cerebrum till a cavity,
the lateral ventricle, is reached. By carefully removing the roof of
this cavity the latter is seen to extend forward and downward as the
anterior cornu, and downward and backward as the descending cornu.
The corpus striatum is an oval mass projecting into the cavity of the
anterior cornu. The hippocampus is an oval projection forming the floor
of the posterior part of the lateral ventricle, including the descending
cornu. Between the corpus striatum and the hippocampus extends
a fibrous band, the descending pillars of the fornix. This band can
be traced to the middle line and seen to be a part of the fornix
cut in the median section. Cut away the hippocampus and the band
of the fornix; the optic thalamus is exposed (see Fig. 130). Posterior
to the thalamus are the two corpora quadrigemina of that half of the
brain. Between the descending pillars of the fornix and the optic
thalamus is a narrow opening, the foramen of Munro, which commu-
nicates with the third ventricle and through the latter with its fellow
of the opposite half of the brain. By this means the two lateral ven-
tricles communicate with each other and with the other cavities of
the brain.

The cerebellum will be found on close examination to be attached
to the rest of the brain by three pairs of fibrous bands. One pair,

296 THE NERVOUS SYSTEM

the superior peduncles, connect the cerebellum with the corpora quad-
rigemina ; a second, the middle peduncles, form the lateral extensions
of the pons Varolii ; the third, inferior peduncles, connect with the
spinal cord. By severing the connections of the cerebellum the cut
ends of these peduncles may be seen. Other parts of the brain can
be identified by comparing with the illustrations of the human brain
given in the general text.

If the brain has been carefully removed from the skull, the twelve
pairs of cranial nerves can be identified by careful dissection and by
comparison with the figures of the human brain.

CHAPTER XXII

FUNCTIONS OF THE NERVOUS SYSTEM

430. In a broad sense, the functions of the nervous sys-
tem may be said to be to bring its possessor into due rela-
tion with the universe of which he is a part, and to enable
him to live that life to which his organism is adapted ; to
supply channels of communication between all parts of
the body ; to supervise, direct, and control all the con-
scious and unconscious activities of the organism. More
specifically they are, in the case of man, sensations, gen-
eral and special ; regulation of all motion ; control of all
vital processes ; and the manifestation of mental opera-
tions,— thought, will, and emotion.

431. Sources of Knowledge. — We have two sources of
information respecting the action of the various parts of
the nervous system. There is, first, observation upon
human subjects. Obviously few experiments can be made
upon man himself, but by careful study of man in health
and of symptoms shown in diseases which affect the brain
and nerves, much has been discovered. The second source
of knowledge is from experiments upon animals. Electri-
cal stimulation acts upon the nerves much as does the
natural nervous stimulus, and by its use in the physiologi-
cal laboratory, and by the destruction of one part or another
of the nervous system of an animal, the paths of transmis-
sion of impulses and the functions of the different parts

297

298 THE NERVOUS SYSTEM

have been gradually made out. While our knowledge of
the functions of the nervous system has thus been greatly
extended, especially during recent years, it is probable
that a much larger field still remains only partly explored,
and there is reason to expect that a much more accurate
and definite acquaintance with this most important portion
of the human organism will soon become possible.

432. Functions of the Nerves. — The nerves are the tele-
graph wires of the system. They transmit impulses
from all parts of the body to the central nervous system
and from the central system to all parts of the body.
Individual nerve fibers transmit impulses in only one
direction.

433. Afferent and Efferent Nerves. — Nerves or nerve
fibers which carry nervous impulses to the centers are
afferent; those which carry impulses from the centers are
efferent. The first are generally called sensory ; but im-
pulses which do not result in sensation, that is, which do
not affect consciousness, may be conveyed by afferent
nerves. The spinal cord may be cut or injured so that
its lower portion and the nerves issuing from it have no
connection with the brain. Still if the foot is pricked or
tickled, the afferent nerves carry the impulse to the cord,
efferent nerves bring back a motor impulse, and the foot
is drawn back, all without conscious sensation.

434. Classification of Nerves. — Afferent nerves have been
classed in two groups.

1. Nerves of special sense, viz. of sight, hearing, touch,
taste, and smell.

2. Nerves of general sensibility. These convey to the
brain those vague, indescribable feelings of comfort and
general well-being, or of discomfort, languor, and weari-
ness, which come from the interior of the body.

FUNCTIONS OF THE NERVOUS SYSTEM 299

Excessive stimulation of any of these nerves results in
pain.

435. Efferent Nerves carry impulses of many kinds be-
sides those of motion. Five classes of these nerves in the
human system have been described: —

1. Motor nerves, distributed to the voluntary and in-
voluntary muscles, and carrying impulses resulting in
movement.

2. Accelerator nerves, which increase the rate of rhyth-
mical action, as in the heart.

3. Inhibitory nerves, which retard or wholly check
rhythmical action, as in certain nerve fibers of the heart.

4. Secretory nerves, which convey from the central sys-
tem to the glands impulses resulting in the secretion of
their special products.

5. Trophic (from a Greek word meaning " nursing ")
nerves, which control the nutrition of the parts to which
they go.

Still other nerves exist which can be classed neither as
afferent nor efferent. They are those which connect dif-
ferent parts of the brain and cord with one another, and
in general form lines of communication between nerve
centers. They have been called intracentral nerves.

436. The Nervous Discharge. — When a nervous impulse
reaches a nerve cell, a remarkable change takes place.
Something similar to an explosion occurs, and a new,
different, and more powerful current issues from the cell.
An afferent impulse arrives at a nerve center; that change
which is called the nervous discharge takes place; energy
is set free which is conducted by efferent fibers to the
terminal plate in a muscle fiber, it may be. Here again
a second nervous discharge results, and a still larger
amount of force is liberated.

300 THE NERVOUS SYSTEM

437. Functions of the Spinal Cord. — A nerve center is a
group of nerve cells which join together in some particular
form of nervous action. The gray matter of the spinal
cord is a series of nerve centers, while the white matter
is arranged in bundles of nerve fibers whose function is,
like that of the nerves themselves, the transmission of
impulses.

Two sets of functions belong to the spinal cord. It is
the channel by which volitions of the brain are conveyed
to many of the muscles, and the channel by which many
sensory impulses reach the brain ; that is, by means of
the cord voluntary action takes place, and by means of it
sensory impulses are transmitted.

Another set of functions belonging to both the spinal
cord and the brain is the production of reflex action. Some
writers upon physiology maintain that all nervous action
is, in the final analysis, reflex, and due, more or less
remotely, to external stimulus, what is called mind not
being able to originate any nervous impulses whatever.
Others support the opposite view, that all nervous action
is voluntary in the beginning, and becomes reflex by prac-
tice, either on the part of the individual, or on that of
previous generations of ancestors, by whom the tendency
to act in certain ways has been transmitted to their de-
scendants. This is not the place for a discussion of such
a question, and we may accept the usual distinction
between voluntary and reflex action, the latter being
invariably the result of an impression received from
without.

438. Reflex Action. — By reference to Figs. 48 and 52,
on pp. 72 and 90, the course of a nervous impulse in
reflex action may be traced. A nerve is stimulated at
the surface, the impulse is conveyed by the afferent

FUNCTIONS OF THE NERVOUS SYSTEM 301

sensory fibers of the nerve through the posterior root to
the spinal cord. There it may pass up to the brain
(Fig. 52) in one of the white columns of the cord, and,
affecting certain cells in the cortex, result in conscious-
ness and sensation, followed by voluntary motion. Or
it may reach directly certain .cells in the posterior horn
of gray matter in the cord, and be thence transmitted by
communicating fibers across to other cells in the anterior
horn, from which a motor impulse is sent forth to certain
muscles, and they are called into action. By this shorter
path motion takes place without necessarily affecting con-
sciousness, and without the interference of the brain ;
that is, the nerve cells in the cord which receive the
stimulus reflect the impulse to other cells of the cord,
which then issue motor orders, without waiting for in-
structions from the overruling brain. It is as if the cap-
tain of a company of soldiers in a great army, having
received from incoming scouts news of an attack by hostile
forces, immediately orders his men, without waiting for
orders from his superior officers, to turn upon the enemy
and repulse them.

The medulla oblongata is also a great reflex center,
very many afferent-efferent circuits being completed there
without affecting the higher cerebral centers.

439. Examples of Reflex Action. — If a sudden flash of
light strikes the eyes, the lids are immediately closed.
Any part of the body touching a hot object is at once
drawn back. A person in sleep may raise his hand to
brush away a fly from his face, or he may start at a sud-
den noise whether awake or asleep. All these acts may
take place without conscious orders from the brain. Many
of the vital processes are wholly or mainly reflex acts.
Of most of them we are, in health, wholly unconscious.
MACY'S PHYS. — 19

302 THE NERVOUS SYSTEM

The spinal cord centers, or those of the medulla, send
efferent impulses to the glands that they may secrete the
digestive juices, when afferent impulses have been excited
by food taken into the mouth or the stomach. The mus-
cular movements of the alimentary canal, called peristal-
sis, are reflex. So are the contraction and dilation of
the blood vessels in response to sensations of temperature
conveyed by afferent nerves to the reflex centers. The
growth of the cells throughout the body is also presided
over by these centers.

The muscular movement of reflex action is often greatly
out of proportion to the strength of the stimulus received.
A slight irritation of the mucous membrane of the trachea
may result in a fit of coughing so violent as to bring into
action most of the muscles of the trunk and limbs. The
mere prick of a pin may cause a man to bound from his
chair and execute a series of movements involving hun-
dreds of muscles. It is as if the nervous irritation which
is brought by an afferent nerve to one of the nerve centers
overflowed the cells and fibers of that segment and stimu-
lated neighboring centers also.

440. Voluntary Movements may become Reflex. — When a
child begins to learn to walk, each separate movement is
slowly and carefully directed by the intelligence of the
brain. In time, however, the brain is relieved by the
spinal cord of nearly all attention to the locomotion of
the body, and action which was once voluntary is better
done under control of the reflex centers. If we undertake
to descend a stairway rapidly, watching and directing each
step by the will, we are far more likely to make a misstep
and fall than if we pay no attention to the separate move-
ments required. So in performing upon musical instru-
ments, in writing with a pen or a typewriter, or in riding

FUNCTIONS OF THE NERVOUS SYSTEM 303

a bicycle, the movements at first slow and toilsome become
rapid and unconscious as well as more accurate by prac-
tice, which places them under the direction of the spinal
cord instead of the brain. They become, as we say,
" automatic," instead of voluntary.

441. Advantages of Reflex Action. — By this provision for
independent action in the spinal nerve centers the brain is
relieved of a great amount of labor, and so given leisure
for the more important energies of life. Then, as the
spinal cord can act more promptly than the brain, it is
better able to protect us from sudden injury. If we had
to wait till the brain ordered the muscles of the arm to
pull the hand out of the fire, we might often be seriously
burned.

A thorough education of the spinal cord in respect to
a wide variety of reflex movements greatly extends a
man's useful and enjoyable activities.

442. Voluntary Control of Reflex Action. — Although
what are called reflex actions take place largely without
the interference of the will, it does not follow that any
distinct arbitrary line of demarkation can be drawn
between reflex and voluntary acts. In playing the
piano, for instance, the rapid and complex movements
required are to a certain extent voluntary as well as
reflex, though the cells of the nerve centers discharge
without waiting for the reception of orders from the
brain. In respect to a large number of reflex acts the
will is able to exercise a restraining influence if not entire
inhibition, and such overruling power constitutes self-
control. A child may, by reflex action, utter piercing
screams at sight of what he judges to be a dangerous
object, and may even be thrown into convulsions by terror ;
but when he has become a man — if he has received proper

304 THE NERVOUS SYSTEM

training — he will have acquired voluntary control over
his muscles, the scream will be restrained, and his muscles
will remain quiet, or will remove him from the dangerous
spot according to the direction of his brain. Many a sol-
dier has thrown down his gun and beat an inglorious
retreat from the scene of his first battle, and yet has after-
ward become the honored veteran of many a hard-fought
field. A child may roar with pain and clutch with all his
strength at the dentist's hand when his first tooth is drawn,
while men have been known to endure the amputation of
a limb without flinching. Important as it is to educate
the reflex nervous centers to the supervision of swift and
accurate useful movements, it is of even more importance
that the brain should still be able to exercise a superior
restraining power when needful in respect to even those
acts which may be ordinarily left to the reflex centers.

443. Functions of the Sympathetic System. — Experiments
have shown the functions of the sympathetic system to be
threefold.

(1) This system has control of the contractile coats of
the blood vessels. Certain fibers, called "vasoconstrictors,"
carry impulses by which the tone of the walls of arteries
and veins is maintained. If the sympathetic nerve is
divided in the neck, there is a general dilation of the
blood vessels on the same side, and a fall of blood pres-
sure in the arteries. Other fibers, called " vasodilators,"
seem to possess the power of inhibiting the action of the
44 constrictors," and so causing dilation of the vessels.
A large part of the action of the vital organs is controlled
by these vasomotor nerve fibers which regulate the amount
of blood distributed to those organs.

(2) Other fibers of the sympathetic nerves seem to stimu-
late directly the activity of secreting cells in the glands.

FUNCTIONS OF THE NERVOUS SYSTEM 305

(3) Still other fibers regulate the peristaltic action of
stomach and intestines, and so influence digestion, while
others influence, to some extent, the process of respiration.

The sympathetic nerves affect directly only involuntary
processes.

444. Functions of the Medulla Oblongata. — The whole of
the brain above the medulla may be removed from an
animal without killing it. Regular and rhythmical respi-
ration will go on, the heart will still beat, and the blood
will circulate, while reflex action will continue, and many
muscles will contract when the sensory nerves connected
with them are irritated. Still more complex movements
may take place. If food is placed on the back of the
tongue, the numerous muscles concerned in swallowing
will be excited and will act with their usual accuracy.
It is plain that all these reflex movements must be coor-
dinated in the medulla and the lower centers. An animal
living thus, by the action of the nervous centers connected
only with the spinal cord and the medulla, will exist by
means of purely reflex mechanism without sensation and
without intelligence.

But let the medulla be destroyed ; respiration will
cease (except in the case of the frog, which continues to
breathe by cutaneous respiration), and death will almost
instantly follow. The nervous center to which is com-
mitted the coordination of respiratory movement has
been located at the angle of the wall of the fourth ven-
tricle, and that point has been called the vital knot. The
medulla may be divided above the respiratory center, and
the action of the muscles of the chest and diaphragm will
be unaffected. Though the heart, as has been stated,
will continue its rhythmic beat for a time after all con-
nection with cerebro-spinal centers has been severed, still

306 THE NERVOUS SYSTEM

its movements are much modified through its nervous
communication with the medulla. Inhibitory fibers pass
from there in the vagus nerve, and if that is cut the
heart's motion is accelerated. Accelerator fibers from
the medulla pass to the heart through the spinal cord and
the sympathetic nerves. Their destruction or severance
from the center in the medulla slows the heart's beat. The
medulla oblongata, then, is a coordinating center for those
reflex actions upon which the maintenance of life depends.

445. Besides its great function as a center for the
reflex action connected with the vital processes, the
medulla oblongata also acts, like the cord, as a conductor
of sensory and motor impressions. Motor fibers from the
upper parts of the brain cross in the anterior pyramids
of the medulla and descend the cord, to pass out in the
anterior roots of spinal nerves. If they are destroyed on
the right side above the crossing, paralysis of motion of
the left side results ; while section of the fibers on the
right side below the crossing will cause paralysis on the
right side.

446. Functions of the Pons Varolii. — The pons, besides
serving as a passageway for afferent and efferent impulses
between the medulla and other parts of the brain, contains
imbedded in the bundles of white fibers a number of
nuclei of gray matter connected with the roots of cranial
nerves, some of the same nerves being also connected
with nuclei in the medulla. The pons is to be regarded
as both a conductor and a reflex center, and also as a
relay center between the cerebellum and the cerebrum.

447. Functions of the Cerebellum. — The cerebellum re-
ceives impressions through its three pairs of peduncles
by which its hemispheres are connected with other parts
of the brain, and so with the spinal cord, and with each

FUNCTIONS OF THE NERVOUS SYSTEM 307

other. It has long been regarded as established that its
special function is to act as a center — not the sole, but the
great center — for coordination of muscular movement, and
especially for that coordination of muscles necessary to
maintain the body in a position of equilibrium. This
harmonious adjustment of the working of so large a
number of muscles requires the action of a large and
complicated nervous mechanism, involving the eyes, por-
tions of the auditory apparatus, and the apparatus for
touch, as well as the muscular sense which tells us what
we are doing with our muscles. Sensory impulses from
these four sources reach the cerebellum by its peduncles
and keep it informed as to the position of the body in
space. Then, in order that all the numerous muscles
involved may act with regulated strength and in mutual
harmony to preserve the equilibrium, the nerve centers
in each half of the cerebellum send on afferent impulses
to the cerebral hemisphere of the opposite side. There
takes place the motor discharge which sends forth the
efferent impulse to the muscles. In the process of select-
ing the muscles which are to act, and arranging the order
and amount of their action, the gray matter of the higher
centers, of the basal ganglia, the cerebellum, and the
whole of the spinal cord is concerned.

The cerebellum is also especially involved in the pro-
duction of the finer and more delicate movements of the
hand.

448. Functions of the Corpora Quadrigemina and the Crura
Cerebri. — Of the functions of the crura cerebri, or pedun-
cles of the cerebrum, we know little except that they con-
duct nervous impulses. If one peduncle is destroyed, the
animal moves toward the opposite side, round and round
in circles. The corpora quadrigemina, or optic lobes, are the

308 THE NERVOUS SYSTEM

first portions of the brain to receive visual impressions
through the optic tracts; but just what share they have in
vision is still not fully determined. We know that they are
concerned in the movements of the iris and of the ciliary
muscle, and there are indications that they have much
to do with the consciousness of light and color. It may
be that these and other neighboring ganglia, having re-
ceived direct impressions from the retina, originate reflex
movements without waiting for voluntary, conscious action
of the higher centers. This would explain the uncon-
scious sight and movements of the somnambulist, who
sees, without knowing it, how to direct his steps along
dangerous and intricate paths. . Destruction of the cor-
pora quadrigemina causes immediate blindness.

449. Functions of the Optic Thalami. — The ganglia of the
optic thalami also have something to do with sight, as
serious injury to them invariably results in disturbance
or destruction of vision. There is also evidence that
they play a subordinate part in connection with sensa-
tion, and, with the corpora striata and conducting fibers,
establish a shorter afferent-efferent circle which does not
involve the higher centers of the brain, but whose action
results in consciousness and volition.

450. Functions of the Cerebrum. — If a frog be entirely
deprived of the cerebral hemispheres and left quite undis-
turbed, it will sit quietly in the same spot forever. Though
it breathes, it will be an insensible, immovable lump of
matter. It may be surrounded by food, but it will die
of starvation. No spontaneous movement is possible to
it. But let the frog be touched, and it will move. If
gently stroked, it will croak. If its foot be pinched, it will
hop. If thrown into water, it will swim to land. A sud-
den movement close to its eyes will cause it to draw back.

FUNCTIONS OF THE NERVOUS SYSTEM 309

A fish under similar conditions will continue to swim
in a straight line unless obstacles appear, and those it
will avoid as usual. Its movement will be kept up until
ended by exhaustion. It will never pause to eat, though
abundance is on every side. Like the frog, the fish de-
prived of its cerebrum is incapable of any action not the
result of immediate and direct external stimulus. It
swims because the contact of the water with the surface
furnishes constant irritation to the swimming mechanism.
Corresponding results follow experiments upon higher
animals and observations upon man himself. The lower
nerve centers act at once in response to present stimulus,
and act without necessarily affecting consciousness, with-
out sensation, and without will.

451. The frog or the fish retaining the whole of the
brain intact responds to external irritation, but the pre-
cise results of such irritation cannot be accurately pre-
dicted, and the action may be deferred for a longer time
than when the cerebrum is wanting.

In the higher animals the varieties of possible results
of stimulation are still more numerous. Strike a wild
cat over the nose with a club and he may turn and flee,
or he may plunge forward and bury his teeth in your
body. The nervous discharge in all these cases will,
however, be likely to take place with considerable prompt-
ness in one way or another.

But suppose a man to receive a severe injury or insult.
He may retaliate at once by shooting or knocking down
his assailant, or he may cherish a sense of wrong for many
years, seeking opportunity for revenge. He may even
inculcate the enmity upon the minds of his* children, to be
passed on from generation to generation as a family feud.
In man, therefore, and to some extent in the higher ani-

310 THE NERVOUS SYSTEM

mals also, we find the singular power of postponing, often
for an indefinite time, the reaction which in the lower
animals immediately follows stimulation. Because it is
impossible to trace all nervous reaction to an incoming
impulse, we must not thence conclude that none has been
received. To the higher cerebral centers alone, that is, to
the gray matter of the cortex, belongs this power of de-
ferred action. They are able to postpone the nervous
discharge which results from incoming impressions until
those impressions have been, as we may say, considered.
The nature and meaning of the efferent impulse to be
issued in consequence of the impulse received may then
be decided upon after long deliberation and in view of
very remote sensations.

452. The cerebrum, then, is the seat of those psychic or
mental processes which are called consciousness, perception,
volition, memory, thought, imagination, and emotion. These
are all terms which in the present state of knowledge
belong rather to psychology than to physiology. They
have an undeniable physical basis, but to what extent they
depend upon material facts and physical laws, we do not
know. Consciousness may be said to be the knowledge
which the mind has of its own operations and conditions.
Physiologically speaking, it has been called " the final
phase of sensory impressions." Perception is the recogni-
tion by the mind of impressions received through sensory
nervous tracts. Volition, so far as it is physiological, is
the impulse in the cerebral hemispheres which originates
motor activity. Memory may be called the power of stor-
ing up nervous impressions and making them at some
indefinite later period the cause of efferent influences.
Perhaps we need not go further in the attempt to give
physiological definitions to metaphysical terms.

FUNCTIONS OF THE NERVOUS SYSTEM 311

453. Localization of Functions in the Cortex. — The area
of the cortex, with all its convolutions, is in man about
four square feet. In the lowest vertebrate animals the
surface of the brain is smooth, but as animals rise in the
scale of intelligence fissures and folds appear, growing
more complex and more like those of man, till in the brain
of the highest apes a striking resemblance is seen to that
of man.

The whole Surface of the human cortex has now been
mapped out into tracts, or districts, to many of which it is
found that special functions are assigned. Post-mortem
examination of diseased human brains, together with close
study of the effects of disease during life, and numer-
ous experiments by vivisection upon animals, — especially
upon the monkey as possessed of a brain of the same
type as that of man, — have resulted in greatly extend-
ing our knowledge respecting this localization of func-
tions in the cortex. We cannot follow the method and
progress of discovery, but some of the conclusions have
been referred to in preceding chapters and others may
be mentioned here.

In respect to some of the highest mental operations
the brain probably acts as a whole through the immense
number of associational fibers connecting all parts of the
cortex, so that no physiologist is able to say that thought
is located in certain cells of that convolution, or memory
or imagination in another. But it is still correct to say
that certain groups of cortical cells are concerned in a
peculiar way with certain sensations or with certain
movements.

454. Motor Areas. — It has been found that when the
surface of an animal's brain is laid bare and an electric
surrent is applied to the convolutions, the stimulation of

312

THE NERVOUS SYSTEM

the same spot in the cortex is always followed by the
same movement in the same animal. Those portions of
the cortex, therefore, whose stimulation results in motion,
are called motor areas. Speaking generally, these motor
areas may be said to occupy the portion of the cortex
about the fissure of Rolando and along the middle surface,
or edge, of the hemispheres. Particular movements of
head, trunk, and limbs are associated with particular spots
in the surface of this region, as shown inf^ig. 138. The
area controlling articulate speech, that is, the movements

ii

fig. 138. — Diagrams illustrating localization of function in
the cerebrum.

I outer surface of left hemisphere.
II inner surface of right hemisphere.

Motor areas are shaded.
Cc corpus callosum.
Fr frontal lobe.

Oc occipital lobe.
Pa parietal lobe.
Ro fissure of Rolando.
Sy Sylvian fissure.
Te temporal lobe.

of tongue, lips, etc., in speech, lies adjacent to the Sylvian
fissure on the lowest frontal convolution. And, what is
peculiar to this cortical area for speech, it appears to be
confined to a single hemisphere — in most cases the left
— instead of being bilateral as are other parts of the
brain.

455. Sensory Areas in the cortex are less definitely
located than are the motor areas. Broadly speaking, they
lie behind the motor surfaces.

FUNCTIONS OF THE NERVOUS SYSTEM 313

The area for vision is in the occipital lobe. If this area
be diseased, blindness of half of each retina on the same
side results.

The auditory area is believed to lie in the upper
portion of the temporal lobe ; the areas for taste and
smell 011 the under and inner side of the same lobe.
Tactile sensations have been located in certain portions of
the under surface of the occipital lobe ; but most recent
experiments indicate that some, at least, of the sensory
fibers end in what has been called the motor area about
the fissure of Rolando. If that is established, it will
appear that the fibers connected with conscious sensation
are in close association with those which convey voluntary
motor impulses, and the Rolandic area will be more
properly termed the sensori-motor area.

456. It will be noticed that in the map of the cortex a
large portion of the front of the brain remains, like great
tracts of land in Central Africa upon old geographical
maps, without names and internal divisions. They are
unexplored or, at least, unknown regions. No specific
functions can be positively assigned to those frontal con-
volutions of the cerebrum. An animal deprived of them
appears to suffer little inconvenience in consequence, and
in one well-known case where a man lost the frontal por-
tion of his brain in an explosion of dynamite, full recovery
followed without any permanent noteworthy consequences.
It is a favorite theory with some that the frontal convolu-
tions are the seat of the intellectual faculties, but the
theory has not been confirmed.

CHAPTER XXIII

HYGIENE OF THE NERVOUS SYSTEM

457. It is often remarked in recent years, though per-
haps without sufficient evidence, that nervous diseases are
rapidly increasing. Cases of insanity, nervous prostra-
tion, insomnia, of mental and nervous weakness of various
kinds, are at any rate so numerous as to give occasion for
anxious inquiry as to the probable future of our race. It
is, then, of the utmost importance that we should know
how to order our lives so that our nervous systems may
be preserved in health and vigor. All the bodily actions
are dependent upon the reception of nervous stimulus at
the right time, the right place, and in due amount, and
when that fails, or is in any way deranged, the whole sys-
tem suffers.

458. Nervousness is not to be understood as a sign of a
particularly refined and delicate nervous constitution. It
is due to a lack of control by the higher nerve centers and
is always an indication of weakness or disease; always to
be fought against by all reasonable means, and never to be
accepted as a necessary feature of a sensitive organization.

459. Nutrition of the Nervous System. — Skillful and experi-
enced physicians tell us that true nervous diseases, that
is, disorders attended by actual degeneration or structural
changes in nervous matter, are comparatively rare, and
when they do occur are due to lack of nutrition rather

314

HYGIENE OF THE NERVOUS SYSTEM 315

than to excessive demands upon the nervous organism.
No part of the system is so carefully protected from
injury, so hedged about and guarded from evil influences
of every sort, as are the precious nerve centers. The nerv-
ous mechanism is the last to waste when the body dies
from starvation, and under such conditions it is probably
supported at the expense of other tissues as being more
important than they.

Recalling what we have learned from previous study we
shall see clearly the importance and the source of nour-
ishment for the nerve cells. It is by the blood alone that
they are fed. Every thriil of nervous influence destroys
tissue, and unless an abundance of pure arterial blood is
at hand for rebuilding the cells, weakness and decay will
follow. Diseases which lead to blood poisoning — as
pneumonia and typhoid fever — are accompanied with
delirium, weakening of the mental faculties, or other nerv-
ous symptoms.

460. In order that pure blood may be furnished, the
regular and perfect action of the digestive organs is in-
dispensable. Digestion is a slow process ; it cannot be
hastened. If we eat our food so rapidly that it is not
subjected to the action of the saliva, and is not properly
divided by the teeth, the gastric juice will not be able to
effect the necessary changes in the stomach, especially if
we hasten to call the blood away for other work too soon,
and the food will pass on into the intestines only half
ready for the work of the other juices. Even in a healthy
man the normal processes in the alimentary canal develop
an amount of poison sufficient to kill him if it is not neu-
tralized by the products of the liver, pancreas, and other
organs, which nature provides for that purpose. So, if
those secretions are interfered with, — as they are by the

316 THE NERVOUS SYSTEM

use of alcohol, for instance, — or fail of their due action
upon the food because the preceding processes are incom-
plete, the nutriment poured into the blood stream may
carry disease instead of health and vigor to brain and
nerve. It is just such inconsiderate habits in respect to
eating which, as physicians well know, have led to many
a serious case of " nervous prostration " among business
men or students.

461. But the blood cannot be kept pure without a con-
stant supply of pure air hi the lungs. If that is lacking,
there is at once defective nutrition of the nerve cells.
Undoubtedly the nervousness so common among women
is due, more than to any other one cause, to an insufficient
supply of pure air for the lungs. Tight clothing which
restricts the capacity of the chest, lack of outdoor exer-
cise, and the breathing of vitiated and usually (in winter)
too warm air are all direct causes of nerve weakness.

462. One more condition is necessary in order that the
blood may be pure, and that is a healthy activity of the ex-
cretory mechanisms. If the worn-out material from .the
wasting tissues is not removed, it will remain to clog and
poison the vital current. In a word, the condition of the
brain and spinal cord, and the vigor and readiness of nerv-
ous reaction, depend wholly upon the distribution and
quality of the blood, and those depend upon food, diges-
tion, respiration, and excretion. It is true that a man
does not die at once or become diseased because he has
eaten improper food or breathed foul air. The physical
organism has marvelous powers for contending against
unfavorable conditions, a wonderful way of throwing off
poison and rebounding from depression, so long as the
natural vigor of tissues is not impaired by persistent
abuse. But for each individual there is a point beyond

HfGlENE OK THE NERVOUS SYSTEM 317

which recuperation becomes doubtful, wholly impossible,
or only partial.

463. Fatigue of Nerve Cells. — A certain amount of activ-
ity in cells of all sorts is promotive of health. It causes
a more rapid flow of the blood and greater storage of
fresh matter to be afterward used in the liberation of
energy. But too prolonged exercise or stimulation leads
to exhaustion of the cells, and for every one there is a limit
to the power of restoration after exercise. In the last
stages of extreme fatigue it is the nerve cells and not the
muscles which succumb to exhaustion. Microscopic exam-
ination of animals shows that the cells of the nerve centers
gradually become shrunken and irregular in outline under
stimulation, while the nuclei within the cells and in the
inclosing wall are also seen to diminish. After refreshing
sleep the cells are at their full size, the blood current passes
at the normal rate through the nerve centers, and they
readily respond to stimulus. At the close of the day a
marked change has occurred in the cells of those centers.
The rate of blood circulation has declined, and the stream
is loaded with the accumulated products of the day's activ-
ities, while the diminished size of the nerve cells and their
nuclei proclaims a state of fatigue.

464. Sleep. — It is by means of sleep that the nerve cells
regain their form and their readiness to react on receiving
stimulus. During sleep the nervous activities are greatly
diminished. Afferent impulses do not set in motion the
complex cerebral processes of waking hours. Conscious-
ness is not excited, and memory fails to register the recep-
tion of impulses. Reflex movements may indeed result,
but in the deepest sleep even such action is mainly lack-
ing. Respiration and the circulation of the blood con-
tinue, but become slower, and a large amount of blood is

MACY'S PHYS. — 20

318 THE NERVOUS SYSTEM

withdrawn from the brain. Much of the internal muscu-
lar and secretory mechanism becomes comparatively inac-
tive. The whole body is affected by the changes brought
about by sleep. We may describe the effects of sleep,
though we are not able to tell what sleep is, or what are
its causes.

That sleep is essential to the life of all those animals
having a well-developed nervous system we know. Con-
tinued loss of sleep in man results in insanity and death
much sooner than death follows starvation. Regular
periods of sleep are needful, and nature provides for rest
to the brain by gradually reducing the amount of blood
circulating there when the accustomed hour for repose
draws near. Then, as we say, we become "sleepy."

465. Necessary Amount of Sleep. — Sleep, to be recupera-
tive, should continue uninterrupted for several hours. It
has been shown by experiments upon certain animals that
usually four hours or more are needed to reconstruct the
shrunken cells. Short " naps," even though the aggregate
be sufficient, do not restore and refresh the system as does
continuous sleep. If the nerve cells are forced to work
again before being fully restored, they do so under great
disadvantages. Growing children require more sleep
than adults, and a healthy, active child is not likely to
take more than is good for him. For adults who work
vigorously with mjiscles or brain, the old rule of eight
hours is a safe one, though many are satisfied with less.
Much depends upon habit and individual peculiarities.
The old usually need less sleep than others. The proc-
esses of growth are long since' completed, the activities
of life are less, vital processes go on more slowly, and
complete repair of the various tissues no longer takes
place.

HYGIENE OF THE NERVOUS SYSTEM 319

466 How to induce Sleep. — Insomnia has become so com-
mon of late that special attention should be paid to ways
of promoting sleep. A great variety of drugs are used
for the purpose, but some of them are extremely danger-
ous, and none of them should ever be taken except by the
advice of a competent physician. Any activity of cells, any
production of energy, — nervous energy as well as other
forms, — gives rise to certain substances harmful to the
body. By natural provision the presence of this waste
matter in the blood causes a feeling of fatigue which in-
clines to a lessening of activity and gives opportunity for
recuperation. To promote sleep, we cat off so far as possi-
ble the various sources of stimulus to the nerves. We
recline at full length that the trunk muscles may be relieved
from the effort to preserve the equilibrium. We remove all
burdensome or uncomfortable clothing which might con-
stantly excite the nerves of the skin. A warm bath just
before retiring tends to allay external irritation and helps
to withdraw the blood from the head. We darken the
room and close the door against noise. For some hours
before retiring our occupations should be free from excite-
ment. One who is inclined to sleeplessness should do no
evening brain work. A serene frame of mind conduces
to repose. Although late and heavy meals are not to be
recommended, it has been found that to eat moderately of
easily digested food at bedtime will sometimes withdraw
the blood from the brain and dispose to sound sleep.
Active physical exercise during the day, sufficient to cause
fatigue of the muscles, is usually followed by restful sleep.
For brain workers a short period of active exercise before
retiring — a quick walk or practice with dumb-bells or
Indian clubs — may promote sleep. So may a hot foot-
bath, or vigorous rubbing of the feet and legs, or other

320 THE NERVOUS SYSTEM

massage. Other means for accomplishing the object of
diverting the blood from the brain will occur to one who
gives t-he subject thought.

A sleeping room should be well ventilated, dark, and
quiet, the bed not too soft, nor the covering too abundant.
A habit of going to sleep may be cultivated by lying
down only at times when one wishes to sleep. By the
laws of association the reclining posture will come to aid
in inducing the cerebral condition desired.

467 " Overwork." — It is common to attribute most of
the nervous disorders of our time to the overtaxing of the
brain and nerves in business or study, or to excessive
strain of the nervous system from anxiety or care. No
doubt such cases occur, but other causes are far more
prolific than these. The nervous system seems to be
constructed to last as long as it receives nourishment
enough and is allowed sleep enough. Among students
there occur frequent cases of nervous derangement which
could be traced, if all the facts were known, to causes
other than overstudy. To keep a brain in health it must
be used. Even severe mental application is promotive of
health if practiced under healthful conditions. A student
may break down because he uses his brain without taking
sufficient sleep, exercise, and food to keep it in good con-
dition, or fails properly to vary the kind of mental effort ;
but if he follows the various suggestions upon these points
given in this book, he can hardly do so. There is no
patent "brain food" which will supply the nerve cells
with nutriment for their activities if it does not also build
up all the other organs. The human life is one life. If
one member suffers, all the members suffer. One cannot
cultivate the brain into vigorous health while neglecting
or abusing the stomach, the lungs, and other organs.

HYGIENE OF THE NERVOUS SYSTEM 321

Proper habits of study should be acquired. One should
learn to bring all his mental force to bear upon the work
in hand — to concentrate Ms thoughts, as we say ; that is,
to hold his attention firmly upon the subject before him,
and not dawdle over his book, letting his thoughts run
from one topic to another according to chance sugges
tions, coming back only now and then to his work. Such
practices weaken the brain and unfit it for effective labor.
Severe, intense mental effort for a short time should be
the rule, and then relaxation or complete change in the
form of labor. But bad mental habits, abuse of the
digestive organs, and the breathing of impure air are not
the only causes of injury to brain and nerves. A life
of overexcitement, which keeps the nerves continually
a quiver in response to incessant stimulation, has shattered
the nervous system of many a girl or young woman. Our
American customs leave to the young too little space
for the quiet, regular, uneventful living which promotes
health of mind and body, strengthens for future useful-
ness, and stores energy for the severe and sudden emer-
gencies of mature life. If a girl breaks down in health
during her school years, her teachers are usually blamed
as exacting too much brain work, whereas the mischief is,
in fact, far oftener due to unhygienic habits of life, to too
rich or otherwise unsuitable food, to lack of air and exer-
cise, and, especially, to too much social indulgence, along
with late hours which interfere with regular and abundant
sleep and use up the nervous force which should be given
to study or stored for the future.

468. Habit as connected with Nervous Action. — Something
was said upon this subject when reflex nervous action was
considered, but its importance is so great that it should
be further dwelt upon.

322 THE NERVOUS SYSTEM

Habit is a law or property of the material world, and
all our habits of life and action, mental as well as physical,
are now understood to have their basis in the physical
constitution of our bodies. The particles of matter which
compose inorganic bodies act and react upon one another
in a certain way, and ever after they act and react in that
same way more easily, that is, with less resistance than in
other ways, and by repetition of this action a habit is
established. In organic bodies this property is still more
marked. A pathway of discharge of nervous influence
in the brain, once formed, is afterward the channel by
which efferent nervous currents tend to pass outward.
All our activities are due to this streaming outward of
nervous currents excited by the constant streaming inward
of other nervous currents, or by stimulation originating
in the brain itself. A new channel once made for the out-
ward flow becomes the path of least resistance for the
next wave, which deepens the bed of the stream and de-
termines more surely the course of following impulses.
In course of time the nervous pathway becomes so deeply
cut that, given a certain incoming impulse, the resulting
nervous discharge can make its progress outward by that
course alone which has been prepared for it by permitting
previous impulses to pass that way. Then a habit has
become "fixed," and we all know how difficult it is to
change a fixed habit.

We have already seen how the possibility of acquiring
habits relieves the brain of the necessity of attention to
many of the movements of the muscles and vastly increases
the number of things which one can do. Most of us estab-
lish in time an order of proceeding for the daily processes
of dressing and undressing, for example, so that we go
through them, day after day, in a certain routine without

HYGIENE OF THE NERVOUS SYSTEM 323

giving any particular thought to them, and perhaps with-
out knowing that we do make the necessary movements
in the same succession, time after time. In such a case
the first muscular contraction (as, for instance, the first
voluntary motion after we have decided to retire to rest)
is the setting in motion of a chain of events, each of which
follows without thought from the sensation of the pre-
ceding muscular contraction. To change the order of the
movements costs a definite effort, as when we decide for
some reason to put on or off the left shoe first, when we
have formed a habit of putting on or off the right one
first.

469. Character. --It is the habits acquired which deter-
mine character. What a man has made himself by the
time he is twenty-five or thirty years of age, through the
pathways formed in the plastic substance of his brain,
such he is almost sure to remain to the end of life. In
many cases habits are by that time so strong that they
cannot be changed. The brain seems to have become har-
dened, " set," so that new channels for nervous impulses
can no longer be made. Even earlier in life many habits
of daily practice have usually become unchangeably
formed. The methods of speech, especially the idioms of
ordinary conversation, for one's whole life, are those ac-
quired in childhood. A man may become learned, pol-
ished, and scholarly in prepared or written productions
while still retaining in daily familiar speech rude and
uncultivated expressions learned in early years. It would
be too much to say that even fixed habits cannot be
changed, but to accomplish a change requires an amount
of determination and persistence not common among men.

470. To build into the material substance of the nerv-
ous system a tendency to do right and wise acts in the

324 THE NERVOUS SYSTEM

best way, to think pure and unselfish thoughts, to cherish
the loftiest and noblest aspirations, is the most important
business of youth. Manhood prepared by such training is
ready for grand achievements. The spinal cord and the
lower brain centers have been drilled to prompt and accu-
rate reflex action, and much of the mechanical labor of
life is left to their unconscious ordering. Not only are
the ordinary movements of the body in walking, riding,
and the various athletic sports thus directed, but facility
and correctness of speech, both oral and written, have be-
come no longer matter for cerebral care. Rapid writing,
attended by accuracy in respect to the accepted forms and
rules of composition, has been acquired by thorough train-
ing, and the brain is left free to concentrate all its powers
upon the higher activities of thought and imagination.
That the products of those activities shall be worthy is
determined by the abundant store of memories of worthy
and beautiful objects, acts, purposes, and thoughts. No-
ble deeds will be inevitable because of the constantly
repeated, voluntary turning of nervous impulses into
channels for such results. Acts demanded by great and
sudden emergencies, when deliberation and reason are
impossible, will be unselfish, wise, and every way worthy,
because previous voluntary action has habituated all the
nerve centers so to respond to stimuli received when judg-
ment and reason have had time to consider.

471 Heredity. — Did each individual come into the
world with all his powers in their normal condition, and
grow up in the most favorable surroundings, such sym-
metrical and perfect manhood might be the expected and
ordinary result. Unhappily that is not the case. Many
eminent men of science believe that the impressions made
upon the soft substance of a man's brain in early life are

HYGIENE OF THE NERVOUS SYSTEM 325

so deep and lasting that they not only persist through-
out the individual life, but also affect the brains and
nerves of his children, and his children's children, so
that they may have from their birth tendencies to act
as their parents or their grandparents have been accus-
tomed to act. They inherit a certain kind of nervous tem-
perament, we say, and their nerve cells have a natural
readiness to respond in certain ways to the influences
which come to them. This may be a powerful aid to the
development of upright and noble character, and it may
be an almost irresistible force urging in the opposite direc-
tion. It has been observed in many cases that the chil-
dren of criminals become criminal for generation after
generation. The inherited bent of their minds appears to
be evil, and as a rule their surroundings and associations
are also evil. The power of a bad inheritance may, how-
ever, be neutralized by a good environment.

472. Influence of Alcohol on the Nervous System. — While
the excessive use of alcoholic drinks works injury to every
part of the body, it is largely through the direct effect of
alcohol upon nervous tissue that the various evils are
accomplished.

We will consider the physiological influence of alcohol
on the nervous system under two heads : (1) acute dis-
eases caused by alcohol; (2) chronic diseased conditions.
Afterward the moral effects will receive attention.

473. Dipsomania (an acute disease) is the name given to
the morbid craving for alcohol which renders a person
utterly irresponsible for his acts while engaged in the mad
pursuit of that which he believes will satisfy his consuming
thirst. It is a distinctly diseased condition of the nervous
system, and may result from what is only a slightly ex-
cessive use of alcoholic liquors by the sufferer himself, or it

326 THE NERVOUS SYSTEM

may be due to a diseased state of nervous tissue inherited
from an ancestor accustomed to such use, though he may
never have indulged to the extent of intoxication. This
form of alcoholism is now considered and treated as a dis-
ease by medical rather than moral methods.

474. Another acute form of alcoholism is called delirium
tremens, and this is so terrible to witness, so frightful to
suffer, that men speak the very name with bated breath.
It occurs in persons whose nervous systems have been for
a considerable time under the poisonous influences of
excessive amounts of alcohol. At the height of the
attack the patient becomes a raving maniac, subject to
the most torturing illusions and sometimes, with the
unnatural strength of madness, overpowering and escap-
ing from several attendants. Repeated recurrence of the
disease is almost certain to be fatal, though the first attack
is rarely so. Permanent insanity may precede death.

475. Chronic Diseased Conditions arise from the gradual
poisoning of the system by the continued use of beverages
containing alcohol. Even though we admit that alcohol
in a definite small amount is, in some cases at least, fully
oxidized in the body, like other carbohydrates, and so
supplies energy as food, we must never forget that differ-
ent constitutions may be differently affected, and condi-
tions as to climate, temperament, and habits of life may
cause variations in its influence upon health and character.
We can never know perfectly the -nature of all the innu-
merable strains of hereditary tendency which unite to make
an individual what he is. Some one of these may have
impressed upon the nerve cells an instability, a weakness,
a peculiar susceptibility to the influence of alcohol, so that
the first taste may arouse the insatiable craving which
leads to dipsomania. In another case, the inherited weak-

HYGIENE OF THE NERVOUS SYSTEM 327

ness may render the child of an inebriate an epileptic, an
imbecile, or a consumptive. We can never foresee just
how the transmitted nervous weakness will manifest itself,
but as a rule the descendants of those whose systems
are poisoned by alcohol are enfeebled in body or mind or
both.

476. But suppose a man to have derived from his ances-
tors a sound constitution and to have become addicted
to the moderate use of alcohol; the insidious nature of
the dangerous substance may gradually lead him to con-
sume, insensibly perhaps, only a little more than the cells
can oxidize. Without realizing it, he may slowly poison
his system. The primary effect is upon the brain ; there
is congestion and overexcitement of the nerve cells there —
conditions which gradually extend to the nerve cells of the
spinal cord ; inflammation sets in, and there follows fibrous
degeneration of the tissues, substituting an inferior form
for the specialized tissues which do the work of the organs
in various parts of the body. Paralysis may result, or epi-
lepsy, or dyspepsia from lack of the due amount of nerv-
ous influence upon the digestive organs, or any one of a
thousand forms of disorder, some of which have been men-
tioned in preceding chapters. Though a man may never
drink to intoxication, and never realize that he is using
alcohol to excess, he may nevertheless become seriously
diseased in consequence of his moderate indulgence,
or what he believes to be such, while wondering why
he is not well and strong. Still less does he consider
the legacy of evil which he may be laying up for his
children.

Life insurance companies have gathered an immense
body of statistics respecting human life, with sole refer-
ence to their bearing upon the business of insurance, and

328 THE NERVOUS SYSTEM

it is well known that life insurance companies regard
policies upon the lives of drinking men — even " moder-
ate drinkers" — as involving "extra risk." Their figures
have convinced them that the man who uses no alcoholic
beverages is likely to live longer than one who does.

477. Many believe that climate has much to do with
the influence of alcohol on the nervous system. Our
American climate is peculiarly stimulating to the nerves,
and our systems are, in consequence, less able to bear the
additional stimulation of exciting beverages, while the
narcotic effects take place more readily than in other
climates, and self-control is more easily overthrown. This
is another reason, to us, for shunning the acquisition of
the alcohol habit.

The influence of race has also to do with the prevailing
use of strong drink and its evil effects. The Teutonic
peoples are recognized as "especially susceptible to the
taste for intoxicants, perhaps because of their eager crav-
ing for excitement, for action, for enterprise ; and because
of that very craving they can indulge with less safety the
appetite for stimulants.

478. The Moral Effects of Alcoholic Poisoning concern the
individual himself, his family and friends, and the whole
community of which he is a member.

The struggle of life grows more intense the world over ;
competition in all lines of effort is keener ; success is more
difficult. ' Every one has need of all his powers of mind
and body at their highest possible level of efficiency. A
man engaged in business needs every day and hour the
use of the very best and most careful judgment, lest a false
step — the buying of goods at the wrong time, the selling
at the wrong price, a mistake as to quality or style, a
wrong estimate of the tendency of the market — may

HYGIENE OF THE NERVOUS SYSTEM 329

give his competitors an advantage and lead to his own
ruin. In the professions it is no less true that no man
should dare run the risk of befogging his judgment. A
physician known to be a tippler will lose the best prac-
tice ; the lawyer whose legal advice is sometimes cloudy,
because of a trifle too much alcohol in his morning dram,
will not command the confidence of those wishing counsel.

A man seeking employment is likely to be met at every
turn by questions as to his habits respecting beverages
containing alcohol and his use of tobacco. Several of the
great railroad corporations employ only total abstainers
in any capacity. Purely from pecuniary considerations
they cannot afford to run the risk of accident upon their
roads, — involving destruction of the property of the road,
with also many thousands of dollars to pay for life and
limb destroyed, — because perhaps a brakeman, having
taken a " drop too much," was a little uncertain in his
vision and did not grasp as quickly as usual the meaning
of the signals ; or because a telegraph operator had fud-
dled his brain with beer and had forgotten to send the
dispatch which would have prevented a frightful wreck.
So in respect to positions in the great commercial houses
where trustworthiness, alertness, stability of character,
are required ; — it is those who drink neither brandy nor
beer who stand the best chance, other things being equal,
of securing desirable positions. In practically every walk
of life a man is handicapped in the race if he is believed
to be a drinking man.

All these facts clearly indicate the opinion of the world
in general that, considered merely as a piece of mecha-
nism for accomplishing various sorts of work, a man
who takes no alcohol into his machine is worth more than
one who does ; so that a man who drinks thereby deliber-

330 THE NERVOUS SYSTEM

ately lowers his own money value to the world and to
himself.

479. But there are higher considerations than these.
Alcohol in small quantities stimulates the cells to vig-
orous action for a time ; then reaction and weakness may
follow. In larger quantities alcohol produces, instead
of a stimulating effect, a narcotic poisoning which par-
alyzes the nerves. This is first apparent in the higher
cerebral centers, and if the poison is sufficient in amount,
the paralysis extends till the whole voluntary portion of
the nervous system is involved, leaving only the centers
controlling the vital functions unaffected. The first
glass of liquor may simply render a man unusually lively,
talkative, perhaps brilliant, eloquent, entertaining, con-
fidential, speaking freely of private affairs, revealing
secrets. This stage will pass away before long, and if
another glass is taken, and another, a progressive par-
alyzing of the mental faculties is seen. The ready flow
of language disappears, utterance becomes thick, and ideas
confused, stupor comes on, and the man falls to the floor
"dead drunk," though circulation and respiration still
go on. If he has taken alcohol enough, these too will
cease, from the paralysis of the vital centers, and the
victim will die. Occasionally a man runs through this
course in a single debauch, but such cases are rare.
Usually years of progressive deterioration precede the
great catastrophe. The man's friends look on in help-
less anguish. Noble manhood gradually sinks to the
level of the beast, and below even that. He who was
designed to be a mighty power- for good to himself and
to the world, becomes a curse to himself, a disgrace and
a terror to his family and a burden to the community,
which must employ police to watch him, build a hospital

HYGIENE OF THE NERVOUS SYSTEM 331

or a prison to receive him, and must finally bury him at
public expense and care for his unfortunate family.
How is it that a being endowed with reason can deliber-
ately put an enemy into his mouth to steal away his
brains, and ruin body and soul ?

Because one man whom we chance to know drinks
daily a small quantity of wine or beer, and does not
acquire that craving for more which leads to drunken-
ness, nor apparently injure himself in any way thereby,
it is never safe to conclude that another man can do like-
wise. Nothing is more uncertain. At the same time it
is a fact of common observation which no one will deny,
that multitudes make shipwreck of manhood every year
through the excessive use of alcohol ; yet no one of them
expected to be more than a " moderate drinker," not one
but would have scorned the suggestion that he might in
time become the vile drunkard of the gutter.

480. There is one infallible way of escaping these ills,
and there is but one. That is to abstain wholly from
alcoholic beverages. It is also a harmless way ; it can
do injury to no one. While it insures a man against the
frightful evils of drunkenness, this course also makes it
possible that by the force of his example he may help
many a weak, tempted fellow-man to escape the seduc-
tions of the wine cup.

It may be an admirable thing for a man to be able to
exercise the judgment, the self-restraint which permits
him to indulge his appetite for alcohol to exactly that
extent only which he believes to be harmless or helpful
to himself, never yielding to a temptation to exceed the
self-imposed limit. Is it not yet more admirable for a
man to recognize the weakness of human nature, and the
possibility — shown every year by thousands of sorrowful

332 THE NERVOUS SYSTEM

instances — that even the manhood which seems strongest
may be overcome, and so refuse to take the fearful risk of
placing himself within the power of so insidious a foe ?
Does not the truest courage lead a man to avoid ventur-
ing needlessly and recklessly into the presence of so terri-
ble a danger? And should not a man of really noble
character deliberately choose to make his influence help-
ful, rather than harmful, to those weaker than himself ?

481. Other Narcotics in Common Use. — Narcotics are very
widely used by the human family for the relief which
they give from pain or fatigue, or for the direct pleasur-
able sensations which they impart. All are deadly poisons
when taken in sufficient quantities. Those most common
(after alcohol) are tobacco and opium.

It has already been shown that tobacco may affect
unfavorably many parts of the system, and is especially
injurious to the young. It stimulates in small quantities
and narcotizes in larger ones, working its effects directly
upon the nervous system. Nicotine is a powerful poison
found in tobacco. It affects the nerve cells, injures the
brain, and leads especially to weakness of the heart by
interfering with its supply of nervous force. Many
cases of cancer of mouth and throat are believed to
have resulted from tobacco smoking.

Opium, for its benumbing influence upon the nerves, is
used by large numbers of persons, especially in Oriental
lands. Its continued use deranges all the digestive proc-
esses, disorders the brain, and weakens and degrades the
character. Like alcohol, it produces an intolerable crav-
ing for itself, and the strongest minds are not proof
against the deadly appetite.

482. Self-control versus Appetite. — Man is a bundle of
appetites. Every organ, every cell even, craves its appro-

HYGIENE OF THE NERVOUS SYSTEM 333

priate stimulus. Animals under natural conditions gratify
the appetites as they arise only to that extent which is
healthful for the whole body. Man alone, whose highly
developed brain is overlord to the rest of his system, per-
mits an unwholesome indulgence of appetite to interfere
with this general well-being. Alcohol, opium, and their
like are far from being the only substances whose excess-
ive use injures the organism and degrades character.
Children are often allowed to indulge a natural fondness
for sweets to an extent which is ruinous to digestion ;
for sugar, which is a useful and necessary food in suitable
quantities, becomes in larger ones a poison to the system.
Boys pampered with dainties from infancy logically infer
that a fancy for cigars or beer may be similarly gratified.
Appetite for even the most wholesome food may be in
excess of bodily needs, and the practice of gluttony is
certain to derange nutrition.

A child should bo early taught that because he " likes "
a certain article of food he should not therefore continue
to eat it after natural hunger is satisfied, or at times when
he does not need food ; while to persist in eating or
drinking that which experience, or the advice of those
competent to judge, has taught him to be harmful, should
be regarded as unworthy a rational being.

These are but illustrations of the manifold forms of
intemperance which work untold harm to the physical
and moral natures. There seems no possibility of im-
provement to our race except as the young are led to
recognize the manliness and dignity of controlling one's
appetites.

483. And it is not in respect to the delights of the
palate only that a foolish self-indulgence prevails. The
love of selfish pleasure in any form may be developed
MACY'S PHYS. — 21

334 THE NERVOUS SYSTEM

till it encroaches upon the general well-being. Man's
reason was designed to dominate all the appetites, to
gratify them only so far as will conduce to the best use
of the higher capacities. If the mind does not rule and
restrain the appetites by the dictates of reason, then the
body and not the mind is on the throne, and man sinks
to the level of the beasts that perish. Temperance in all
things, a wise moderation according to reason and expe-
rience, subordination of the appetites and passions of the
physical being to the nobler requirements of the spiritual
nature, and to the still finer sentiment of unselfish conse-
cration of all one's powers to the service of humanity —
these are the principles which dominate the highest type
of manhood.

PAET V

THE PRESERVATION OF HEALTH

CHAPTER XXIV
HEALTH AND DISEASE

484. Health, in man, is that condition of the organism
in which all the various parts composing it perform their
functions perfectly, so that the largest amount of the best
work of which the being is capable is performed easily
and without discomfort. Health is attended with a feel-
ing of buoyancy, vigor, and happiness. Disease is the
result of disordered action in some one or more parts of
the organism, usually long-continued and affecting more
and more the various vital processes.

Many of the ways in which persons are accustomed to
injure the health by inattention to hygienic rules, or by
violations of them, have been alluded to in preceding
chapters. Incorrect habits of life are the direct cause of
many diseases, and indirectly cause many more by weak-
ening the organs, and preparing the system to yield
readily when exposed to the influences of specific disease.

485. Bacteria. — It is now known that several forms of
disease arise from the growth and multiplication, within
the body, of certain microscopic forms of life called bac-
teria, or bacilli, or microbes, or germs. These are living

835

336 THE PRESERVATION OF HEALTH

cells belonging to the lowest orders of plants. They pos-
sess the power of rapid increase by repeated division of
the cells, so that many millions may be produced in a
short time from a single one. They are propagated also
by means of very minute spores, which may float in the
air, mix with the dust of a street or a room, or cling to
walls, clothing, or furniture. Only moisture, warmth,
and albumin for food are needed for their growth. Prob-
ably most (perhaps all) of these tiny organisms have some
useful part to play in the infinitely varied operations of
nature; but a few varieties are known to be enemies to
human life and health. Certain sorts of bacteria are
always concerned in the putrefaction of organic matter,
that is, as they multiply they break up the complex com-
pounds in vegetable and animal substances, and reduce
them to simpler chemical forms which may again be used
as food for plants. Thus dead animal and vegetable mat-
ter is being constantly oxidized by the bacteria found
everywhere in the soil, and rendered fit again to support
life. In this they of course minister to man's welfare,
although the process of decay is attended by the pro-
duction of deadly poisons, which may enter the body and
cause disease.

486. Bacteria within the Body. — The dry speck of dust
which is the spore, or germ, of a disease may, while it
remains dry, exist for an uncertain number of years as an
inert, harmless bit of matter. It may be subjected for
weeks to cold many degrees below zero, and even for a
short time to heat above that of boiling water, without
destruction of its vitality. It may then fall upon a moist
bit of albumin in the air passages of a man, or in the
alimentary canal, or in blood or lymph through a broken
surface, grow with wonderful rapidity, and swiftly poison

HEALTH AND DISEASE 337

the whole body. The dangerous germ may, indeed, be
caught by the moist surface of the mucous membrane and
removed before it has done harm; for it is one of the
functions of the moist lining of the winding nasal passages
to strain out the irritating and disease-bearing particles
from the air, and the ciliated epithelium of the lower
air passages also affords protection in the same way.
Expired air is practically free from germs and other dust.
What we call " taking cold " is now believed to be due to
the poisonous action of bacteria fastening upon the mucous
membrane where the cells have been injured by cold or
in some other manner. Finding food at the injured spot,
the bacteria multiply and cause inflammation of the air
passages and general discomfort, sometimes resulting in
disease.

487. It has been found that a large number of bacteria
of several varieties are always present in the human mouth.
The saliva has the power of destroying a limited number
of the harmful kinds, but others remain to multiply.
Certain sorts cause decay of the teeth (where the enamel
is defective). Others may make their way into the lungs
or the stomach. As they grow they manufacture from
the albumin which they decompose, certain poisons, called
toxins. These may enter the circulation and carry the
deadly influence to all parts of the system. If the stomach
is healthy and the gastric juice normal, many dangerous
germs will be destroyed in the stomach. It is even shown
by experiment that those of cholera and typhoid fever are
quickly killed by the gastric juice. Other germs have
greater resisting power and are able to multiply in the
stomach, causing dyspeptic symptoms or specific disease.
Some forms of bacteria feed upon and destroy other forms.
Many sorts escape the destructive action of other germs

338 THE PRESERVATION OF HEALTH

and of the digestive juices, and reach the intestines to
develop there. Still other kinds are always normally
present there. Immense numbers are always found in
the contents of the large intestine. The bile, which is
known to have the power of preventing putrefaction,
appears to be able to modify the action of the microbes and
to keep that action within certain limits which may render
it helpful to digestion.

Taken in through a wound in the epithelium, the noxious
germs cause inflammation and swelling, and their toxins
may circulate through the body. Or by the wonderful
power of the white corpuscles of the blood, which feed
upon the bacteria in the blood, the evil may be neutralized.
The plasma of blood and lymph seems also to possess the
property of destroying certain toxins, or of protecting
the system from their action.

488. Antitoxins. — In recent years some marvelous dis-
coveries have been made respecting nature's way of coun-
teracting in the body the effects of certain germs of
disease.

It has been shown that in the progress of certain in-
fectious or contagious diseases there is developed in the
serum of the blood or in the tissues a substance which
is a poison to the bacteria causing the disease, or a sub-
stance which neutralizes the toxins produced by them.
In course of time — it may be days or weeks — enough of
this substance, called antitoxin^ is manufactured to neu-
tralize the toxin or to destroy the germs of the particular
disease, and the patient recovers. In certain cases, as in
measles, smallpox, whooping cough, etc., this protecting
substance seems either to remain in the blood or to be
continually produced for the rest of life, giving perma-
nent security from the disease. In others, such as diph-

HEALTH AND DISEASE 339

theria and pneumonia, the security given by the antitoxin
is only temporary.

Certain animals are known to be subject to some of the
same diseases which attack human beings, or to be suscepti-
ble to them when the particular poisons are introduced into
their systems. Other animals cannot be made to " take "
certain infectious diseases, even when the specific germs
and toxins are injected into their circulations. They are
said to be " naturally immune " to those diseases, that is,
an antitoxin is supplied by nature in their blood serum
for the germs or toxins of those diseases. Other animals
are rendered immune to certain diseases by having experi-
enced them.

Advantage has been taken of this knowledge respecting
animals for the benefit of man. In several cases the anti-
toxic substances in the blood of animals immune to cer-
tain diseases have been separated out and injected in
minute quantities into the veins of human subjects suffer-
ing from- the particular infection. The proportion of
recoveries when the antitoxins are used under proper
safeguards is increasingly and encouragingly large.

489. Vaccination for smallpox was the first great dis-
covery in this direction. By means of it smallpox, which
was once the great scourge of the human race, — as com-
mon as measles or whooping cough is now, — has become
comparatively rare. The use of the diphtheria antitoxin,
which is derived from the blood serum of a horse which
has been innoculated with the diphtheria germ, is fast
becoming general, and we may hope to see diphtheria —
that terror of childhood — disappear with the advance
of beneficent science.

The greatest destroyer of human life which now remains
is consumption, — tuberculosis in its varied forms, — and

340 THE PRESERVATION OF HEALTH

there is reason to believe that it also is destined to be
overcome by the progress of scientific discovery, together
with a wider diffusion of sanitary knowledge. An anti-
toxin for consumption, called tuberculin, has been found by
cultivating the germ obtained from the mucus raised by
consumptive patients, in a substance found to favor its
development. This new remedy is yet so recent, and the
number of experiments made so few, that nothing positive
can be stated as to its value. But there is good reason to
hope that a trustworthy cure for tuberculosis will in time
be in common use.

490. Antiseptic Surgery is another result of the study of
the new science of bacteriology. (Antiseptic is derived
from two Greek words meaning "opposed to putrefac-
tion.") The great danger connected with wounds and
injuries has been found to be due to the opportunity
which they give for harmful germs and spores to enter
the system. This is .now guarded against by the practice
called sterilizing, applied to all instruments and appli-
ances used by the surgeon, and so far as possible to the
operating room itself. The object is the destruction of
all germs. The instruments used are previously boiled
for a sufficient time to kill all known forms of life.
Towels, operating gowns, all cloths, dressings, and other
things used are sterilized by heat or antiseptic chemicals,
and every possible precaution is taken to prevent the
access of any bacteria to the exposed surfaces. As a
consequence, the severest wounds often heal in a few
days, and the most astonishing operations are performed
with comparatively slight risk. -

491. How to avert Danger from Poisonous Germs. — To a
person in perfect health it is probable that bacteria of all
sorts are harmless. The healthy stomach seems able to

HEALTH AND DISEASE 341

\

digest typhoid-fever germs as well as its natural food.
To avoid disease, then, we have but to keep the whole
system at a high level of health and vigor. But few are
so fortunate as to possess and maintain perfect health, and
it is necessary to guard against the entrance of disease
germs into the body.

Careful attention to cleanliness of person and surround-
ings is of prime importance. The free use of soap and
water, and the daily cleansing of mouth and teeth, are
safeguards. Many thousands of bacteria have been
counted in the dirt lodged under a single finger nail,
and they swarm in soiled clothing. Some of them may
be germs of disease.

All excretions from diseased persons should be treated
as dangerous to health, and at once disinfected by fire or
by other methods under competent direction. In cases
of pulmonary consumption or other .diseases of lungs or
throat, all discharges from the respiratory passages should
be received upon pieces of soft paper or cloth and immedi-
ately burned. The unseemly practice of spitting in pub-
lic or in private places should be abolished. It has
undoubtedly been in past ages an active cause of the
spread of diseases of throat and lungs. The dried sputum
is carried hither and thither by the air, to be breathed in
by unconscious victims.

492. In respect to cleanliness of dwellings and their
surroundings we are becoming, year by year, more intelli-
gent. We know that oxygen and direct sunlight destroy
many harmful germs, and we are learning to banish from
our homes dark and heavy draperies which exclude sun
and air and harbor dust, as well as carpets nailed to the
floor and hence not easily and often cleaned. We burn
the sweepings from our rooms instead of scattering them

342 THE PRESERVATION OF HEALTH

upon the wind, and do not allow our washtubs to be
emptied upon the ground beside our door. We seek as
much light as possible for our cellars, and take care that
nothing is left there to decay. We look well to the source
of the water used. in our homes, lest it should bring to us
illness and death, and we have a wholesome fear of u sewer
gas," which leads us to keep all pipes and drains well
cleansed and in good repair.

All this is but putting in practice the rules of cleanli-
ness which have been known for ages to be necessary to
health. But we are now acquainted with many invisible
and deadly forms of filth unknown to our ancestors.

493. Dangers to Health in Rural Districts. — It would seem
that life in a country village or upon a farm, where every
house may be continually surrounded by pure air and
exposed to abundant sunshine, should be free from the
unfavorable influences which assail dwellers in towns and
cities. As a matter of fact, however, the same ignorance
and carelessness which are found in the city appear also
in the country. Sanitary precautions are needed upon the
farm no less than elsewhere. How often do we know of
farmers' families suffering from malarial or typhoid fevers,
and how many children have died upon farms from diph-
theria ! Because of their peculiar advantages country
dwellers are too often peculiarly careless. Wells for
family use are frequently placed where the leakage from
barnyard or cesspool will inevitably pollute the water
when the soil has become saturated. Even if the well
is at some distance from all apparent sources of con-
tamination, and upon higher ground, it is impossible to
tell what may be the underground conditions, what may
be the slope of the strata, and whether or not there is
poisonous leakage. In some cases the well is, for conven

HEALTH AND DISEASE 343

ience, very near the house, Avhile upon the ground around
it is poured all the liquid waste of the household, no pro-
vision being made for drainage. The soil then becomes
saturated with filth, which every shower washes into the
well. Sometimes a country dwelling is so closely sur-
rounded by trees as to shut out the sun and air and cause
unhealthful dampness. Convenient opportunities for fre-
quent bathing are often lacking, and in winter there is
apt to be too little attention to ventilation. With only
a moderate amount of intelligence and care, life in the
country might be made far more healthful.

CHAPTER XXV

COMMON ACCIDENTS AND INJURIES

494. Surface Wounds. — W hen the surface in any part
of the body is cut or torn, bacteria at once fasten upon the
moist parts and begin their harmful work. But for their
presence most injuries would quickly heal. Nature pro-
vides that the white cells in the blood shall multiply
about the wound to form a new tissue. They also have
the power of absorbing and destroying dead cells and for-
eign matter in the cut. New blood vessels grow in the
injured part and carry the material needed for building
the new tissue, while the cells of the cuticle also grow
from all sides to cover the exposed surface. But if
poisonous bacteria enter the wound, as they are almost
sure to do, they must be destroyed by the white blood
cells before healing can take place, and the process is
attended with inflammation, swelling, and pain, besides
being much prolonged. The edges of the wound should
be pressed together and kept in place by bandages or
plasters. Unless foreign matter, such as sand, glass, or
splinters, is believed to be in the cut, the blood should
not be washed away, but left -to clot and assist in the
restoration of the tissues. If nature is assisted by the
use of dressings and coverings which prevent the entrance
of bacteria, the cure will be much hastened.

344

COMMON ACCIDENTS AND INJURIES 345

495. Injuries to Blood Vessels. — If the capillaries merely
are hurt the blood only oozes slowly ; a clot will soon be
formed and the healing process begun. If a vein is opened,
the blood flows in a steady stream and is of a dark purple
color. But when an artery is divided, the blood from it
is bright scarlet and comes in spurts, corresponding to the
heart beats. Bleeding from an
artery is the most dangerous and
the most difficult to check. That
from capillaries and small veins
will ordinarily check itself by
the formation of clots, but the
flow from an artery may be so
fast as to prevent clotting. A
doctor is usually needed, but no
time must be lost in waiting for
him. Strong pressure must be
at once applied upon the artery,
either in the cut or between the
cut and the heart. If the injury
is to a limb, a handkerchief or
other bandage may be tied (in a
knot that will not slip) around Fig. 139. — Manner of com-
if alm^A fVia Tmrf tlia liarr! Vnnt pressing an artery with a

rt, t- L Knot handkerchief and stick,

placed over the artery, and a stick

inserted under the bandage (Fig. 139). By twisting the
stick the knot may be pressed upon the artery hard enough
to stop the bleeding. A firm hand may be able to effect
the same object with the thumb and finger, changing from
place to place till the right spot is found. Or a strong
rubber band or tube may be stretched, wound round and
round the whole limb, and tied.

A knowledge of the course of the principal arteries is

346

THE PRESERVATION OF HEALTH

desirable. That of the arm runs in the middle of the
inside of the elbow (Fig. 140) and along the middle of
the under side of the upper arm, just opposite the arm-

Fig. 140. — The left upper
arm.

The dotted line indicates the
course of the main artery (the
brachial) .

Fig. 141. -The right thigh.

The dotted line indicates the
course of the main artery (the
femoral) .

pit. Iii the leg the main artery is in the middle of the
hollow behind the knee and in the middle of the hollow
between the thigh and the trunk (Fig. 141).

496. To stop bleeding from a vein, apply pressure
between the cut and the extremity, that is, on the side
away from the heart.

Bleeding from the nose may often be stopped by apply-
ing cold water, snow, or ice to the back of the neck, the

COMMON ACCIDENTS AND INJURIES 347

forehead, and upper part of the nose. Other remedies are
to raise the arms high above the head, and to snuff up the
nostril a solution of alum or other astringent.

497. When blood comes from the stomach or the lungs,
it is usually a serious symptom, and calls for medical
attendance. The patient should be kept quiet in bed,
and small bits of ice should be swallowed frequently.

Broken Bones and Injuries to Joints. — See pp. 55, 56,
in Chap. IV.

498. Asphyxia, or Suffocation, may occur from various
causes, as strangulation, drowning, the breathing of cer-
tain gases, convulsions which close the throat, etc. The
immediate cause is always a lack of oxygen in the lungs,
and fresh air is always the remedy, though that alone is
not always a sufficient remedy. Artificial respiration is
sometimes necessary. (See §499.) Sometimes the heart
ceases to beat from an accumulation of venous blood in
the right side, because the unpurified blood will not circu-
late through the lungs. In such a case the physician
may draw a little blood from a vein, — after the air pas-
sages have been opened and fresh air supplied, — and so
start the circulation.

The most common cause of asphyxia, except drowning,
is probably the breathing of poisonous gas from a choked
or defective coal stove, from burning charcoal, or from a
gas burner. Fresh air, if supplied in time, will always
restore, though the system may show symptoms of de-
rangement for days or weeks afterward.

499. Apparent Drowning. — Efforts to restore persons
apparently dead from drowning should be persevered in,
even though no signs of life appear for several hours.
Quickly remove all clothing from the upper part of the
body. Turn the patient 011 his face, with a large, hard

348

THE PRESERVATION OF HEALTH

roll of clothing across the pit of the stomach. Let the
attendant throw his own weight heavily two or three
times for a moment upon the patient's back, to force all

the contents of
the stomach out
at the mouth.
Gently cleanse
the mouth with
a handkerchief
wrapped round a

Fig. 142. -Diagram of artificial respiration, finger- Then im'
showing inspiration. mediately set up

The arrows show that the arms are moved outward artificial breCLtJl-
from the sides of the chest. . rri

ing. Turn the

body upon the back, with the head slightly raised and
the roll of clothing placed under the chest. Kneel at
the head, grasp the arms above the elbows and gently
raise them above the head, holding them there two or
three seconds. Then bring them carefully down, pressing
them firmly for
the same length
of time against
the sides to expel
the air. Repeat
these movements
rhythmically
from twelve to
fourteen times a
minute. See that
the tongue is
drawn forward

Fig. 143. — Diagram of artificial respiration,
showing expiration.

The arrows show that the arms are carried di-
rectly forward until they are pressed hard against
the chest.

and not allowed to slip back to close the throat. Even
after signs of life appear — often only as a faint pinkish

COMMON ACCIDENTS AND INJURIES 349

color in finger nails or lips — continue the artificial res-
piration till natural breathing is well established. Keep
the patient cool, and in the open air if the weather is not
too cold. Do not use the galvanic batter}r. Dry, warm
clothing must be provided as soon as life appears ; warm
drinks should be given, and the patient will usually need
to be kept in bed for some days.

500. Other methods of artificial respiration are 'in use.
In one the patient is placed face down, with a roll under
the chest, the head on one arm. One person then gently
rolls the body upon the side for two or three seconds,
while an assistant supports the head. Then the body is
returned to the first position for two or three seconds, and
the movements are regularly alternated for hours, or until
natural breathing is set up.

Even the forcing of air into the patient's lungs from
the mouth of another has proved successful, and one well-
known method is to insert a tube into the trachea and
force in air from a bellows.

501. Burns and Scalds should be treated with great care
in a way to avoid chafing and to exclude the air. Cold
water may be applied immediately to relieve the pain.
Soft linen, wet in a very strong solution of common
baking soda, or a thick covering of wet soda, is good.
Carron oil, which is a mixture of equal parts of linseed or
olive oil and lime water, is an excellent remedy. Vase-
line is useful to exclude the air. Deep or extensive burns
or scalds should have immediate medical care.

502. A burn by lye, ammonia, or other alkali should be
treated at once with acid — dilute vinegar or lemon juice.
A burn by acid^ on the other hand, will be relieved by
applications of dilute alkali, such as ammonia or a solution
of soda.

MACY'S PHYS. — 22

350 THE PRESERVATION OF HEALTH

503. When Clothing takes Fire the sufferer should lie down
at once and roll over and over to smother the flame. Stand-
ing up allows the fire to reach the head and perhaps to be
breathed into the lungs, while running fans the flame and
makes it spread. A rug or any woolen garment at hand
should be thrown over the sufferer, care being taken to
cover neck and shoulders first, and so to force the fire
downward, away from the head and face.

504. Frost Bites. — Intense cold destroys the cells of the
surface, as does intense heat. Fingers, toes, nose, and ears
are the parts first "bitten." They become colorless and
insensible, showing that the circulation in the frozen part
has ceased. Every sort of warmth must be avoided till
the circulation has been gradually restored. Rub the
chilled parts hard with snow or with ice water until
sensibility and color return.

Parts which have been frozen generally remain particu
larly sensitive to cold. Chilblains often result from very
slight exposure and cause much discomfort. The parts
so affected should be bathed often, care being taken to
wipe them perfectly dry, and they should not be brought
near a fire, as heat increases the irritation.

505. Sunstroke, or Thermic Fever, results from exposure
to extreme heat from the direct rays of the sun or other
source. Anything which lowers the vitality of the body
— such as great fatigue, ill health, and the use of alcoholic
drinks — helps to render one susceptible to the effects of
high temperatures. When the air is stagnant and loaded
with moisture as well as very hot, as it may be in close,
confined rooms or streets, there is greater danger of sun-
stroke than when the atmosphere is dry and circulates
freely, though the thermometer may stand, higher.

A person suffering from heat fever is prostrated sud-

COMMON ACCIDENTS AND INJURIES 351

denly, and usually becomes unconscious. His blood tem-
perature may, in severe cases, rise to 112°, or even higher,
and death is likely to follow soon unless prompt relief is
given. The immediate cause of the alarming condition is
the effect of heat upon the nerve centers at the base of
the brain, which control respiration and the circulation.
Death is due to the paralysis of those centers.

Treatment consists in lowering the temperature of the
body as rapidly as possible, by the use of ice and very
cold water. No time must be lost in applying these to
the whole body, by means of wet sheets, by sprinkling
with the coldest water at hand, or by rubbing with ice.

Special sensitiveness to heat often remains long after
recovery from sunstroke.

506. Choking. — Small bodies often stick in the throat,
and jean neither be swallowed nor coughed up. Some-
times they can be reached with a finger or forced out by
sharp strokes upon the back between the shoulders, or by
tickling the inside of the throat to cause vomiting. If a
hard substance is lodged in the trachea a surgeon must be
called at once.

If hard objects are swallowed, they should usually be
left to pass off with rejected portions of the food, without
the use of physic. Bread, cheese and crackers may be
eaten freely, that the foreign body may be surrounded by
the stiff, pasty material, and pass easily through the ali-
mentary canal.

507. Foreign Bodies in the Eye. — Dust, cinders, etc., get
under the eyelids and cause much discomfort. As the
conjunctiva, or lining membrane covering the inside of
the lids and the front of the eyeball, is one continuous
sheet of tissue, these particles cannot get behind the ball
and can usually be seen and removed. Often the flow of

352 THE PRESERVATION OF HEALTH

tears caused by the irritation of the troublesome sub-
stance washes it away, or it may be wiped off by a fold of
soft linen. But it is sometimes lodged far under one of
the lids — usually the upper one — where it is not so eas-
ily reached. In that case let a friend take the lashes of
the lid in the fingers of one hand and turn the lid gently
up over a knitting needle or slender pencil held in the
other hand across the middle of the lid. Then if the ball
is rolled downward, and from side to side, the source of
irritation can be seen and removed. Care must be taken
not to increase the inflammation by rubbing the eye.
Applications of hot water will give relief in cases of slight
inflammation.

508. Foreign Bodies in the Ear are sometimes difficult to
remove. Syringe the passage gently with warm water ;
to drive out insects, drop warm salted water into the ear.
If such efforts do not avail, no violence must be used, but
a surgeon must be called in.

509. Foreign Bodies in the Nose. — Small buttons, cherry
stones, peas, beans, etc., are often crowded by children
so far up the nostrils that they cannot be reached. The
child can sometimes remove such an object by " blowing "
the nose hard, or it may be removed by slapping the
child's back. Occasionally a surgeon is needed.

510. Sudden Illnesses. — Fainting is directly caused by
a lack of blood in the brain. It should be treated by
placing the patient on his back with head and chest
slightly lower than the rest of the body. Plenty of fresh
air should be given ; cold water may be dashed over head
and neck. Clothing should be- loosened, and in severe
cases artificial respiration may be needed. Strong ammo-
nia or smelling salts applied to the nostrils is sometime
useful.

COMMON ACCIDENTS AND INJURIES 353

511. Epilepsy, or Fits, is an alarming nervous attack at-
tended by unconsciousness and sometimes by foaming
at the mouth. It is a chronic affection, and has been
known from very early ages. Julius Caesar and Napoleon
Bonaparte are both said to have been epileptics. Little
can be done during the paroxysm except to loosen the
clothing and see that the sufferer does not harm himself.
A pad of cloth crowded between the teeth will prevent
biting of the tongue.

512. Hysterical Fits occur oftenest in young women, and
usually follow emotional excitement. The patient laughs
and cries, sometimes drops to the floor, and disorderly,
almost convulsive movements may take place ; but the
tongue is never bitten, nor does the patient harm herself.
Dashes of cold water may cut short the attack. Calm,
firm, quiet remonstrance from a strong-minded friend
without much appearance of sympathy will be helpful.

513. Convulsions in young children sometimes occur
during teething, and at the outset of some serious
diseases — as scarlet fever and diphtheria. They may
also be a result of overeating or of deranged digestion.
If the muscles are not quickly relaxed by placing the
child in a warm bath, a physician should be called with-
out delay.

514. Poisons. — A poison is any substance which is capa-
ble, when taken into the body, of producing effects in-
jurious to health and life. Various substances in common
use in the household — such as ammonia, lye, ratsbane,
carbolic acid and other disinfectants — are poisons. Many
medicines (in sufficient quantities) are poisons, and all
medicines should be carefully labeled and used only at
such times and in such quantities as are prescribed by a
physician.

354 THE PRESERVATION OF HEALTH

515. Poisons are usually divided into two classes : cor-
rosive or irritant poisons, and narcotics.

Corrosive poisons cause great changes in the tissues.
In this class are included all those which affect the skin,
causing inflammation and sometimes destruction of the
tissues ; those which act upon the mucous membranes of
the alimentary canal, giving rise to inflammation, nau-
sea, vomiting, pain, and purging ; and those which act
upon the mucous lining of the respiratory organs. These
last are usually gases. A poison to affect the system must
be in liquid or gaseotis form, but solid poisons may be
quickly dissolved by the fluids of the mouth or the stom-
ach, or the exudations from the broken surface of the
skin, and the solution becomes dangerous. Some solid
poisons, however, dissolve so slowly that they may pass
through the alimentary canal and be expelled from the
body without doing harm. Those poisons which enter the
blood, and by causing alterations in it, or by circulating
in the blood, injuriously affect various organs, belong to
the class of irritants. The symptoms resulting differ as
one organ or another is most affected.

516. Narcotics do not produce marked tissue changes,
but affect chiefly the nervous system. The results vary
greatly. Sometimes convulsions, cramps, delirium ; some-
times depression, sleep, or stupor may be caused. Nar-
cotics work their effects more slowly than do the irritants,
and the particular symptoms which appear depend so much
upon the special susceptibility of the individual that diag-
nosis is often very difficult. Some poisons which produce
narcotic effects are also corrosive'to the tissues, so that the
classification into irritants and narcotics is not an absolute
and scientific one.

517. Treatment. — In case of poisoning, the object of

COMMON ACCIDENTS AND INJURIES

355

treatment is to prevent absorption of the dangerous
substance and local injury to the tissues. It is usually
desirable to cause vomiting. This may often be done
simply by thrusting a finger into the throat ; or a table-
spoonful of ground mustard, or of common salt, in a glass
of warm water, or even lukewarm water alone may act as
an emetic. Vomiting should be induced repeatedly, and
then the antidote for the poison, if known, should be given;
and, if the poison is an irritant, slimy fluids, such as white
of egg, mucilage, flaxseed tea, or barley water, should be
swallowed in order to protect the walls of the alimentary
canal from its action. In certain cases, however, emetics
should not be used.

518. Table of Common Poisons ; Symptoms and Antidotes. —

POISONS

Acids
Carbolic
Hydrochloric
Nitric
Oxalic

Sulphuric (the most
serious)

Alkalis
Ammonia
Caustic potash, or

soda
Lye
Saltpeter

SYMPTOMS

Blistering and burn-
ing of the surface ;
intense inflamma-
tion of stomach.
Carbolic acid causes
nervous symptoms
also — great weak-
ness.

Symptoms similar to
those caused by acid
poisoning.

TREATMENT

Weak alkalis, magne-
sia, common soda,
chalk, soap, dilute
ammonia, etc., after-
ward mucilaginous
drinks, white of egg,
milk, etc. For ox-
alic acid give lime ;
other alkalies are not
antidotes for it.

Treat corroded sur-
faces like burns.

Give no emetic.

Weak acids — vinegar,
or lemon juice ; olive
oil, melted butter,
cream. Give no
emetic. Soothing
applications to sur-
faces.

356

THE PRESERVATION OF HEALTH

POISONS

Arsenic

Paris green

Rat poison

Mercury, as corro-
sive sublimate

Lead, as sugar of
lead, or white
paint.

Phosphorus from
matches, rat poi-
sons, phospho-
rated oil.

SYMPTOMS

Vomiting, inflamma-
tion of stomach,
cramps in abdomen,
thirst; sometimes
abdominal symp-
toms almost absent,
and delirium, coma,
convulsions, lead to
speedy death.

Severe pain in stom-
ach, eructation and
vomiting: gases and
solids having phos-
phorescent odor.
Later, unconscious-
ness, collapse, con-
vulsions.

TREATMENT

Cause repeated vomit
ing (except in mer-
cury poisoning).
The antidote for ar-
senic is oxide of iron;
for lead, Epsom salts.
After the antidote
for arsenic, give
strong solution of
common salt; after
Epsom salts give oils,
flour and water ; for
mercury, give white
of egg, milk, or other
albuminous material.

Stomach must be emp-
tied thoroughly.
Give strong soap-
suds or magnesia
in water. Do not
give oils.

Strychnine

Chloral

Intense excitement of
spinal cord and gen-
eral nervous system,
causing cramps, con-
vulsions, lockjaw,
etc.

Deep sleep without
prev ious excitemen t,
passing into coma,
death resulting from
sudden heart failure.

Chloral, opium, and
bromide of potash
are antidotes ; empty
the stomach as
quickly as possible,
then give antidote.

Stomach must be
quickly emptied and
strong stimulants
given — such as
strychnine, atropiue,
etc.

COMMON ACCIDENTS AND INJURIES

357

POISONS

Opium
Morphine
Paregoric
Laudanum
Dover's powder
Soothing sirups, etc.

SYMPTOMS

First, state of mild,
mental excitement ;
later, drowsiness,
sleep, then complete
unconsciousness,
while pulse grows
weak and irregular,
skin cold and moist.
Pupils of the eyes
grow smaller and
smaller, respiration
becomes very slow,
and patient dies
from failure of
breathing.

TREATMENT

Stomach must be emp-
tied and repeatedly
washed out with
water. Patient must
be kept awake by
constant movement,
dashes of cold water,
strong coffee, or even
strychnine. The
muscles of respira-
tion may be stimu-
lated by electricity ;
and cases where
death has appar-
ently occurred may
be saved by forced
artificial respiration.

Aconite

r General numbness,^ ~ ,.

. ' Cause free vomiting,
weakness, and cold ~ . , . , , *

I Give stimulating
sweat : tingling in . . , „,.

drinks — coffee, etc.
throat. j

Belladonna

Eyes bright, pupils
dilated ; mouth and
throat dry. Some-
times convulsions.

Empty the stomach
thoroughly. Give
tannic acid or strong
bark tea.

Other Vegetable
Poisons

Wild parsley
Bitter sweet berries
Mountain ash ber-
ries

Indian tobacco
Toadstools
Hemlock
Tobacco, etc.

Nausea, weakness, stu-
por, etc.

Empty the siomacb
and intestines ; give
stimulants.

358

THE PRESERVATION OF HEALTH

POISONS

Putrefactive Poisons
Foods which have
begun t o decay
sometimes give
rise to deadly poi-
sons. These most
often appear in
meat, sausage, and
cheese; while a
particular poison
called tyrotoxicon
is developed in
milk, ice cream,
etc., which have
stood long in ves-
sels not kept per-
fectly clean, or
in rooms where
germs of decay
exist — as from
decaying wood.

SYMPTOMS

TREATMENT

Animal Poisons
Snake bites

Symptoms vary
greatly. There is,
usually, pain in the
digestive organs;
sometimes vomiting
and purging, fol-
lowed by weakness.

Local pain and swell-
ing, followed by
great weakness, diz-
ziness, blood poison-
ing; sometimes
death.

f Give mild emetic —
mustard or pow-
dered alum in warm
water — then vine--
gar and water.
Castor oil may be
given to empty the
intestines.

Apply tight ligature
between the wound
and the heart. Open
the wound and wash
with solution of
permanganate of
potassium; or the
poison may be
drawn out by suck-
ing with the mouth
or with a cupping
glass. In severe
cases the wound
should b e burned
with hot iron or
caustic. Give stimu-
lants to support the
system.

COMMON ACCIDENTS AND INJURIES

359

POISON

Insects' Stings
Wasps
Hornets
Bees
Mosquitoes, etc.

SYMPTOM

Swelling, pain; in se-
vere cases followed
by weakness.

TREATMENT

Generally little treat-
merit is needed.
Bathe with carbolic
acid, diluted with
water, to relieve
smarting. Some in-
sect stings are acid,
some alkaline. If
the application of
ammonia or wet soda
does not relieve, try
vinegar or lemoi?
juice.

CHAPTER XXVI

PUBLIC HYGIENE, OR GENERAL SANITATION

519. Definition. — As personal hygiene is the art and the
science of preserving the individual body in health, so
public hygiene is the art and science of promoting the
health of the community. A healthy man is one whose
body is sound and vigorous in all its parts, so that all the
functions of the system are performed perfectly, easily,
and without discomfort; no one of all the organs neglect-
ing or failing to do the work assigned it, and so deranging
or poisoning other organs.

A healthy village or city is one in which most of the
inhabitants are healthy, and especially one in which con-
tagious and infectious diseases do not pass from one per-
son to another.

We have learned that a man, in order to maintain his
health, must have pure air, pure water, and wholesome
food. But in crowded towns and cities even the wealth-
iest citizens are not able to procure these simple necessities
for themselves. The carelessness of some obscure and
ignorant person may poison the water supplied to rich
and poor alike ; germs of disease from the most squalid
part of a city may be borne by the air, by the gas of a
sewer pipe, or in any one of a thousand other ways to
carry death to a palace many miles away. A single filthy
dwelling may poison a whole town. It is not enough

PUBLIC HYGIENE, OR GENERAL SANITATION 361

that intelligent persons should themselves live according
to sanitary laws ; it is necessary to their health that the
ignorant and careless should also be obliged to do so.
This cannot be brought about by individual influence or
authority. Hence it has come to pass that in all civilized
communities some degree of control is exercised by the
officers of the government over the personal habits and
ways of life of private persons. Many of the laws given
by Moses to the Hebrews and preserved in the Scriptures
relate to sanitary matters connected with daily life, and
it is believed that obedience to those laws has had much
to do with the fact that the Jews, throughout their his-
tory, have been remarkably free from great epidemics of
disease. Neglect of sanitary precautions is, on the other
hand, understood to be responsible for the frightful
" plagues " which often swept over the earth in past
ages, destroying many thousands of lives. They arise
even yet in the filthy cities of Oriental countries, but are
now far less destructive and more easily kept within
bounds.

Our knowledge as to what the power of government
can do to promote the health of a community has been
increasing rapidly in recent years, but that knowledge is
far from being thoroughly applied, because the people in
general are not yet intelligent enough to demand it.

520, Knowledge of Sanitary Laws Essential to Good
Citizenship. — In a free, democratic government, such as
ours, proper attention to sanitary matters on the part of
public officers depends upon an intelligent and active
public sentiment. Since the people are the government,
it is the duty of the people — all the people — to see to it
that their servants, the officers appointed to protect them
against the dangers of unsanitary conditions in any part

3l)2 THE PRESERVATION OF HEALTH

of the town or city, shall do their duty. No man can
be a really good citizen who is ignorant of the condi-
tions which threaten the general health, or who neglects
to use his influence to keep the health officers watch-
ful and active. The subject of sanitation should there-
fore receive attention in our schools, and may properly
be considered briefly in connection with , the study of
physiology.

521. A Healthy Town or City is one in which the poorest
inhabitants have pure air to breathe, pure water to drink,
wholesome, unadulterated food to eat, and opportunities
for cleanliness in person and dwelling. These conditions
can be supplied only by the strong arm of a central power
supported by an enlightened public opinion. And having
provided these prime necessities, the central power of
government should require all citizens to make use of
them. A man should not be permitted to use the foul
water from a filthy well, even on his own premises; nor
to keep his own dwelling in so uncleanly a state as to
endanger the health of his own family and that of his
neighbors; if public washing conveniences are provided
he should even, if necessary, be obliged to have the cloth-
ing of his family cleansed and his own body bathed.

522. Cleanliness the One Essential. — The conditions of
general phvsical well-being may after all be reduced to
one, viz. cleanliness, taken in its broadest, fullest .sense.
That would include clean air, clean water, unadulterated
food, cleanliness of person and clothing, and adequate ex-
ercise by which purity of blood is promoted and removal
of the poisonous waste of the body is secured.

523. Pure Air. — A man can live for a considerable time
without food or water, and he may within certain limits
safely select what he will eat and drink. But he cannot

PUBLIC HYGIENE, OR GENERAL SANITATION 363

live for a single hour without air, and he is unable to
select what air he will use, for he must breathe that which
immediately surrounds him. Several things are needful
that the air of a dwelling or other building may be fit to
breathe.

(1) Drainage of the Ground on which a House stands. —
More or less of the air in a building comes from the ground
beneath and around it. A wet soil favors the multiplica-
tion of the bacteria always present in the ground, and
among them are often germs of specific disease. Water
is found at varying distances everywhere beneath the
earth's surface, and, in order that a spot may be fit for
building upon, what is called the ground water should be
not less than fifteen feet below the surface (some authori-
ties say thirty feet), and the level should not greatly vary
from time to time. That a house may be healthful, the
soil beneath it must be thoroughly drained by pipes laid
deep enough in the ground ; and public authorities should
have power to see that this is done.

(2) G-round Air should so far as possible be excluded from
a House. — The air in a house is usually warmer than that
outside, and so there is a tendency to suck up the air in
the porous ground below. Even if the soil is dry, there
are often gases from decaying vegetation or other sources,
which are more or less injurious to life, mixed with the
earth. These should be excluded from the house by cov-
ering cellar walls and floor with an impervious coating.
Care must also be taken that nothing is left to decay in
the cellar or any other part of a building.

(3) Sunshine is necessary to Health and to the purity of
the air in a house. No room is fit for human occupancy
if it does not at some time receive the direct rays of the
sun. Many dangerous germs are killed outright by direct

364 THE PRESERVATION OF HEALTH

sunlight. Those persons who live habitually shut out from
sunshine never have strong, buoyant health.

It is not yet common for public authorities to interfere
in respect to this matter. In our cities it is even permitted
to one citizen to cut off completely from his neighbor's
family this prime necessity to well-being.

524. The Air in Streets and Alleys is often rendered offen-
sive and dangerous by accumulations of filthy refuse from
dwellings, stables, factories, etc. Neglect of prompt and
thorough cleansing of all such passages by the officials
whose duty it is, should never be tolerated for a day, and
cleanliness of private premises should also be legally
enforced.

525. Pure Food. — Governmental inspection of the vari-
ous foods offered for sale is now recognized as an impor-
tant duty. Diseased meat, adulterated milk, butter, lard,
cheese, etc., are supposed to be excluded from the markets,
while adulterated sugars, baking powder, spices, etc., are
doubtless less common than formerly. But occasionally an
outbreak of typhoid fever or other fatal disease is traced
to the carelessness or ignorance or cupidity of some dealer
in dairy products, and hundreds of poor families are found
to be suffering in health from the adulterated bread or
flour or other necessary sold by an unscrupulous dealer.
The inspection of foods should be made much more strict,
and should be enforced in the smaller communities as well
as in the large cities.

526. Pure Water. — Nothing is more essential to the
health of a community than an abundant supply of whole-
some water for drinking, and good citizens look well to the
source of their drinking water. Water from small streams,
rivers, or lakes is seldom, in thickly settled parts of the
world, pure enough for drinking until it has been treated

PUBLIC HYGIENE, OR GENERAL SANITATION 365

by some of the various methods now in use for freeing it
from the unwholesome matters almost always present. It is
true that running streams and lakes exposed to the action
of sun and wind are purified to a considerable extent by
natural influences, and where they do not receive an
excessive amount of the waste of towns and factories,
may usually be safely used. But very often the filth of
a city or of several cities is poured continually into the
lake or river which supplies the inhabitants with drinking
water, the amount of poison being far more than nature is
able to destroy. In such cases many and complicated
devices are used for getting rid of the injurious sub-
stances. The water may be drawn off into large reser-
voirs and allowed to settle. Then, the coarser filth having
been deposited, the water may be drawn into other reser-
voirs and treated with certain chemicals which will cause
the precipitation of other substances as sediment. Some
chemical substances destroy organic matter by oxidizing
it, and sometimes the same result is obtained by forcing
air through the contaminated water.

Water is also partly purified by filtering through vari-
ous porous materials — large beds of sand, gravel, and
broken stone, for instance. The filtering body itself soon
becomes clogged with filth, and must be often renewed
or cleansed.

None of these processes destroys all the dangerous germs
to be found in impure water, and it is a wise precaution
for every family to boil for half an hour all water for
drinking which comes from a source liable to contamina-
tion. The water may then be placed in glass cans, tightly
closed, and cooled in a refrigerator, or in a cellar. By
this course much illness and death in large towns, where
typhoid fever and other water-borne diseases are always
MACY'S PHYS. — 23

THE PRESERVATION OF HEALTH

present, would be prevented. The same care should be
taken in the country, when the drinking water comes
from springs or shallow wells.

Probably the safest source of a water supply is from
deep welh, sunk far below any possible befoulment from
the surface. Many towns are now thus supplied. Ordi-
nary wells and cisterns are seldom safe, unless great care
is used. The leakage from a barnyard or cesspool many
rods away may find its way into a well through the layers
of earth, and poison the water. Rain water is mixed with
dust from the air and the roof, with bits of leaves and
other organic matter, and should be thoroughly filtered
and boiled for drinking.

Ice (unless manufactured from distilled water) contains
impurities, and should not be put into water used for
drinking.

527. Public Bathing and Washing Conveniences are now
provided by the most progressive cities, and contribute
much to the health of the people. They should be free,
or so nearly so that the poorest families may be able to
enjoy the luxury of cleanliness.

528. Disposal of Garbage and Sewage. — Not only must
the daily waste in towns and cities be gathered up and
removed from sight, but it must also be treated in some
way which shall destroy its dangerous character. It must
not be dumped upon vacant lots in the poorer quarters of
the town, and left to decay and poison the air. And it
is seldom safe to pour it into neighboring water ways or
lakes. Various devices have been tried for the better
disposal of the poisonous waste -of human life, no one of
which is absolutely best for all localities. That which is
most desirable for a particular community must be deter-
mined in view of all circumstances and surroundings.

PUBLIC HYGIENE, OR GENERAL SANITATION 367

No cheap and safe method has yet been discovered. All
are expensive, but any one is cheaper than the sacrifice of
life and health which is sure to result from unsanitary or
slipshod ways of dealing with this serious problem. Some
of the most satisfactory methods in use in the most pro-
gressive cities may be simply mentioned here.

Where a very large body of water is at hand, which
is not the source of the town's water supply, the sewage
may, for a time at least, be safely poured into it. This is
the cheapest way. But such pollution of streams and
lakes is now forbidden by law in many countries of
Europe, as it should be in the United States. In some
cities the sewage is collected in great vats, where the solid
portion is separated from the liquid, and sold for use as
a fertilizer. The liquid is by chemical treatment freed
from its harmful ingredients, and poured into the water-
courses. Some cities own large farms, to which the sewage
is conveyed in close tanks, and spread upon the soil as a
fertilizer. In other cases the soil is simply used as a
niter. The sewage is spread upon it, and the liquid
which filters through is received by drain tiles laid below
the surface, and carried into a natural stream. The solid
portion is decomposed by the action of air, sun, and bac-
teria, which render it harmless.

Garbage and the solid portion of sewage are frequently
consumed in great furnaces, that which remains inde-
structible by fire being safely used for filling up low
places about the city.

GLOSSARY

Ab-do'men (Lat.) : the cavity of the body lying below the diaphragm
and containing most of the digestive organs.

Ab-du'cens (Lat., leading away): the sixth pair of cranial nerves.

Ab-sorb'ents (Lat. absorbere, to suck in) : the vessels which take up
nutriment or waste matter.

Ab-sorp'tion : the process of taking up food from the alimentary canal
or other substances from the tissues.

Ac-cel'er-a-tor (Lat. accelerare, to hasten) : that which quickens, as an
accelerator nerve.

Ac-com-mo-da'tion of the eye (Lat. accommodare, to fit) : the adjust-
ment of the shape of the crystalline lens for distinct vision at dif-
ferent distances.

Ac'id (Lat. acidus, sour) : one of a class of chemical compounds usu-
ally sour to the taste, always soluble in water, capable of turning-
vegetable blue to red and of destroying the distinctive properties
of alkalis or bases. Acids combine with bases to form salts, and
then lose their own distinctive properties.

Ac-tin'ic energy (Gr. aktis, aktinos, ray) : that form of force in light
which produces chemical changes.

Ad'i-pose (Lat. adeps, fat) : that form of tissue which forms or con-
tains fat.

Affer-ent (Lat. ajferre, from ad, to, and ferre, to bear) : conducting
inward or toward a center ; opposed to efferent.

Al-bu'men (Lat. albus, white): white of egg.

Al-bu'min (Lat. albus, white) : a substance composed of carbon, ni-
trogen, hydrogen, and oxygen, found in animals and plants, and
an essential part of every living cell. It is found in its purest
natural form in the white of an egg.

Al-bu'mi-noid : one of the foods containing nitrogen ; a proteid.

Al'co-hol (Arabic al-kohl, fine powder of antimony, used in the East
to paint the eyebrows with) : the spirit.nous or intoxicating ele-
ment of fermented or distilled liquors ; or, in popular speech, any
liquid containing it in a considerable quantity.

370 GLOSSARY

Al-i-men'ta-ry (Lat. alimentum, food) : pertaining to food or concerned
with nutrition.

Alimentary canal: the passage for the food, in which digestion takes
place.

Al'ka-li (Arabic al-kali, al-qaliy, ashes of the plant saltwort) : one of
a group of caustic bases (such as soda and potash) which are solu-
ble in water, have the power of neutralizing acids and forming-
salts with them, of uniting with fats to form soaps, and of chan-
ging the tint of many vegetable colorings — as of litmus reddened
by acid — to blue.

Al-ve'o-lus (Lat., a small cavity) : a small sac or vesicle; one of the
air cells of the lungs.

A-mce'ba (Gr. amoibe, change, exchange) : one of the lowest forms of
animal life, consisting of a single cell which is capable of many
changes of form.

Am-pul'la (Lat., a narrow-necked vessel having two handles and
swelling out below) : one of the dilations of the semicircular canals
of the ear.

A-nab'o-lism (Gr. anabole, something heaped up) : the constructive
processes of the body ; opposed to katabolism.

A-nat'o-my (Gr. anatome, dissection, from anatemnein, to cut up) :
the science which treats of the structure of organic bodies.

An-te'ri-or : toward the head, or toward the front of the body.

An'ti-dote (Gr. anti, against, and didonai, to give) : a substance that
prevents a poison from injuring the tissues, when taken into the
body.

An-ti-sep'tic (Gr. anti, against, and septikos, septic, making putrid) :
having the power to prevent putrefaction.

An-ti-tox'in (Gr. anli, against, and toxikon, poison) : a substance which
neutralizes the action of a toxin, or animal poison.

A'nus (Lat.) : the opening at the lower end of the alimentary canal,
through which the excrements are discharged.

A-or'ta (Gr. aorte, from aeirein, to raise, to lift) : the great artery ris-
ing from the left ventricle of the heart.

Ap-pen-dic'u-lar skeleton : the pectoral girdle, the pelvic girdle, and the
bones of the limbs.

Ap-pen'dix; plural Ap-pen'di-ces (Lat., from appendere, to hang) : an
appendage. The vermiform appendix is a small portion of the
intestine, appended to the csecum. The term appendices is given
to the earlike projections from the auricles of the heart.

GLOSSARY. 371

Aq'ue-duct of Syl'vi-us : a channel connecting the third and fourth

ventricles of the brain. Named from the famous anatomist Dubois

or Sylvius (the latinized form of the name).

A'que-ous hu'mor : the fluid filling the anterior chamber of the eyeball.
A-rach'noid (Gr. arachnoeides, like a cobweb) : the middle one of the

three membranes of the brain and spinal cord.
A-re'o-lar tissue (Lat. areola, diminutive of area, a broad space of

level ground) : a fibrous connective tissue with loosely woven

fibers and many spaces.
Ar'gon (Gr. argos, lazy, inert) : a gas forming about one per cent of

the atmosphere ; first recognized in 1895.
Ar'ter-y (Gr. or Lat. arteria, windpipe) : one of the tubes conveying

blood from the heart. They were formerly thought to contain air

and to be branches of the windpipe.

Ar-tic-u-la'tion (Lat. articulatus, furnished with joints) : any junc-
tion between bones in the skeleton.
A-ryt'e-noid cartilages (Gr. arutainoeides, shaped like a ladle, from

arutaina, ladle, and eidos, form) : two small cartilages of the

larynx.
As-phyx'i-a (Gr. a-, without, and sphuzein, to throb, beat) : apparent

death from stoppage of respiration, as in suffocation from drowning

or the breathing of certain gases.
As-sim-i-la'tion (Lat. assimilatio, from assimilare, to make like) : the

final process of anabolism, by which nutritive material is converted

into the living substance of the body.
A-Stig'ma-tism (Gr. «-, without, and stigma, stigmatos, prick of a

pointed instrument, spot) : a defect of the eye due to irregular

curvature of the refractive media, by reason of which rays of light

from a point are not brought to a single focal point. It results

in indistinctness of vision.
At'las (Gr., one of the gods who bears up the pillars of heaven) : the,

first vertebra of the neck, supporting the weight of the head.
At'om (Gr. a-, without, and tomos, cut) : one of the ultimate indivisible

particles of matter.

Au'di-to-ry os'si-cles : the three small bones of the middle ear.
Au'ri-cle (Lat. auricula, diminutive of auris, ear) : a cavity at the base

(upper portion) of the heart.
Au-to-in-tox-i-ca'tion (Gr. auto, self, and Eng. intoxication, poisoning) :

a poisoning of the system from the products of physiological

processes or from the reabsorption of waste matter.'

372 GLOSSARY

Ax'i-al skeleton : the bones of the head, neck, and trunk.
Ax'il-la-ry (Lat. axilla, the armpit) : belonging to the armpit, as the

axillary arteries.

Ax'is (Lat., axle) : the second vertebra of the neck.
Ax'is cyl'in-der : the central core of a nerve fiber.

Ba-cil'li (plu. of mod. Lat. bacillus, diminutive of baculum, stick) :
microscopic, rod-shaped vegetable organisms; a variety of bac-
terium.

Bac-te'ri-a (plu. of bacterium, from Gr. bakterion, a staff) : microscopic
vegetable organisms, usually in the form of jointed rodlike threads.
They are found in connection with putrefying matter. Some sorts
cause disease.

Bi'ceps (Lat., having two heads, from bis, twice, and caput, head) :
the muscle on the inner side of the upper arm.

Bi-cus'pid valves (Lat. bi, two, and cuspis, a point) : the valves guard-
ing the opening from the left auricle of the heart into the left
ventricle ; the mitral valves.

Bicuspids : the two double-pointed teeth on each side of each jaw.

Bile (Lat. bills) : a greenish yellow fluid secreted by the liver. It
passes into the small intestine, where it assists in the digestion of
the food.

Bi-ol'o-gy (Gr. bios, life, and login, discourse) : the science of life.

Blind spot : an elevated surface on the retina where the optic nerve
fibers enter the eye.

Brach'i-al (Lat. brachium, arm): pertaining to the arm, — as the
brachial artery.

Bron'chi (Gr. brogchos, windpipe) : the subdivisions of the trachea.

Cae'cum (Lat. ccecus, blind) : the first division of the large intestine.
Cal'ci-um (Lat. calx, calcis, lime) : a chemical element found in lime,

gypsum, and other substances.
Ca-nines' (Lat. cam's, dog) : the sharp, pointed teeth next to the

incisors.
Cap'il-la-ry (Lat. capillus, hair) : one of the smallest blood vessels or

other minute tubes.
Car-bo-hy'drates (carbon and hydrate} : a class of foods which includes

starch, the sugars, and cellulose. They are composed of carbon,

oxygen, and hydrogen.
Car'bon (Lat. carbo, coal) : a chemical element found in all organic

compounds. Diamond and graphite are forms of carbon.

GLOSSARY 373

Carbon di-ox'ide : a gas composed of oxygen and carbon, always

present in expired air; also called carbonic acid gas.
Car'bon-ate : a salt of carbonic acid, as limestone.
Car'di-ac (Gr. kardia, the heart) : pertaining to the heart, as the

cardiac nerves.
Ca-rot'id arteries (Gr. karotides, from karos, heavy sleep. The early

Greeks believed these arteries in some way caused drowsiness) :

one of the two main arteries of the neck carrying blood from the

aorta to the head.
Car'pus (Gr. karpos) : the wrist.

Car'ti-lage (Lat. cartilago) : a translucent elastic tissue; gristle.
Cartilages of San-to-ri'ni : little horn-shaped projections on top of the

arytenoids in the larynx.
Cartilages of Weis'berg: small bits of cartilage in folds of the

mucous membrane of the larynx.

Cell: one of the ultimate units of which all living bodies are com-
posed.
Cel'lu-lose : the substance which constitutes the essential part of the

solid framework of plants. It is a carbohydrate.
Cen'trum (Lat., center) : the stout, bony body of a vertebra, to which

is attached the neural arch.
Cer-e-bel'lum (Lat., diminutive of cerebrum, brain) : the large lobe of

the hind brain between the cerebrum and the medulla oblongata.
Cer'e-bro-spi'nal fluid : the watery substance which fills the cavities

of the brain and the spinal canal, and bathes the outer surfaces of

the brain and spinal cord.
Cerebro-spinal me-nin'ges (Gr. menigx, a membrane) : the three

membranes of the brain and spinal cord.
Cerebro-spinal men-in-gi'tis : inflammation of the membranes of the

brain and spinal cord.
Cerebro-spinal system : the brain and spinal cord, with the nerves

arising from them.
Cer'e-brum (Lat., brain) : the anterior and principal part of the

brain.
Cer'vi-cal (Lat. cervix, neck) : of or belonging to the neck, as the

cervical vertebrae.
Chem'i-cal a-nal'y-sis : the separation of a compound substance, by

chemical processes, into its constituent elements.
Chemical element : a substance which cannot be decomposed by any

known means into two or more kinds of matter.

374 GLOSSARY

Chlo'ride: a compound of the element chlorine with some other ele

ment, as chloride of sodium (common salt).
Cho'roid: the second of the coats of the eye. It contains a dark

pigment.
Chyle (Gr. chulos, juice) : a milky fluid containing partly digested food,

and especially the fatty matter of the food in a state of emulsion.
Chyme (Gr. chumos, juice) : the partly digested food as it passes from

the stomach into the small intestine.
Cil'i-a (Lat. cilium, eyelid) : small hairlike appendages lining certain

organs, as the air passages.
Cil'ia-ry muscles : small muscles which help to adjust the eye for

seeing at different distances.
Ciliary processes: radiating folds of the choroid of the eye at the

outer edge of the iris.
Cir-cum-val'late pa-pil'lae (Lat. circum, around, and vallum, wall) :

a form of papillae found at the back of the tongue and containing

some of the taste end organs.

Clav'i-cle (Lat. clavicula, a little key) : the collar bone.
Co-ag-u-la'tion (Lat. coagulatio} : the change of a liquid to a thickened,

curdlike state because of some chemical change.

Coc'cyx (Gr. kokkux, cuckoo) : the end of the vertebral column be-
yond the sacrum.

Cochle-a (Lat., a snail) : a spiral bony tube of the internal ear.
Coe'li-ac axis (Gr. koilos, hollow, and Lat. axis, axle, pole) : a short,

thick branch of the abdominal aorta given off just below the

diaphragm.
Colon (Lat. and Gr.) : the middle and longest division of the large

intestine.

Color blindness : inability to distinguish colors.

Co'ma (Gr., lethargy) : deep stupor from which it is difficult or im-
possible to rouse a person.
Con-duc-tiv'i-ty (Lat. conducere, to bring together) : the power of

passing on a stimulus from one point to others.
Con-ges'tion (Lat. con, together, and gerere, to bring) : overfullness

of the blood vessels of a part of the body.
Con-junc-ti'va (Lat. conjunctivas, connective) : the mucous membrane

covering the external surface of the eyeball and forming the

lining of the lids.
Con-nect'ive tissues : tissues devoted to the support and connection

of the muscles and nerves.

GLOSSARY 375

Con'scious-ness (Lat. con, together, and scire, to know) : knowledge

of one's own mental operations.
Con-tract' ile substance (Lat. contrahere, to draw together) : the soft,

half-fluid material of light and dark disks composing the muscle

cells of voluntary muscles.
Con-trac-til'i-ty : the power possessed by living cells of changing

form independently of pressure.
Co-or-di-na'tion (Lat. co, together, and ordinare, arrange) : the act of

arranging in due order or relation.
Co'ri-um (Lat., a hide, leather) : the innermost layer of the skin ; the

true skin.
Cor'ne-a (Lat. corneus, horny) : the transparent part of the coat of

the eye which covers the iris and pupil.
Cor'o-na-ry arteries (Lat. corona, crown) : the arteries of the heart

itself.

Coronary veins : the veins of the wall of the heart.
Cor'po-ra quad-ri-gem'i-na (Lat., fourfold bodies) : one of the five

chief divisions of the brain ; called also the optic lobes.
Cor'pus-cle (Lat. corpusculum, diminutive of corpus, a body) : a minute

particle or cell, as a blood corpuscle, a lymph corpuscle.
Cor'pus cal-lo'sum (Lat., callous body) : the great white band of nerve

tissue connecting the hemispheres of the cerebrum.
Cor-re-late' (Lat. con, together, and relatus, referred) : to place in

mutual or reciprocal relations ; to establish a relation of inter-
dependence.
Cor'tex (Lat., bark) : an outer layer, as of the brain or the kidney.

The cortex of the brain consists mostly of gray matter.
Cos'tal (Lat. costa, rib) : pertaining to the ribs or side of the

body.
Cra'ni-al : belonging in any way to the cranium, as the cranial nerves

or arteries.

Cra'ni-um (Lat., from Gr. kranion, the skull) : the human skull.
Cri'coid (Gr. krikos, ring, and eidos, form) : a circular cartilage of the

larynx.
Cru'ra cer'e-bri (Lat., literally, the legs of the brain) : the bands of

nervous matter connecting the cerebrum with the medulla.
Crys'tal-line lens : the principal lens of the eye, lying just back of

the pupil.

Cu'ti-cle (Lat. cuticula, from cutis, the skin) : the epidermis 01 outer-
most layer of the skin.

376 GLOSSARY

De-cus-sa'tion of the pyramids ( Lat. decussatio, crossing) . the cross-
ing of the bundles of white nerve fibers called the pyramids, in the
medulla oblongata.

De-lir'i-um tre'mens (Lat. delirium, madness, and tremens, trembling) :
a disorder of the brain due to the excessive use of ardent spirits.

Den'tine (Lat. dens, dentis, tooth): the principal solid tissue of the
teeth.

Der'mis (Gr. derma, the skin) : the corium, or true skin.

Di'a-phragm ((Jr. diaphragma, a partition wall) : the membranous and
muscular division between the thorax and the abdomen.

Dif-fer-en-ti-a'tion of tissues (Lat. differentia, difference) : that modi-
fication in the structure of the tissues which adapts them to dif-
ferent functions.

Dif-fu'sion of gases : the homogeneous mixture which takes place in
two gases placed in contact.

Di-ges'tion (Lat. digestio) : conversion of food in the alimentary canal
into products which can be absorbed into the blood.

Dor'sal (Lat. dorsum, the back) : of or pertaining to the back, as
dorsal m uscles ; opposed to ventral.

Duct: a tube or canal; especially one conveying secretion from a
gland.

Du-o-de'num (Lat. duodeni, twelve each: because the length of the
duodenum is about twelve fingers' breadth) : the first division of
the small intestine, next the stomach.

Du'ra ma'ter (Lat., hard mother. The membrane was once thought
to give rise to every membrane of the body) : the tough, fibrous
membrane surrounding the brain and spinal cord and lining the
cavities of the skull and spinal column.

Em'bry-0 (Gr. embruori) : the early form of an animal in develop-
ment.

E-mul'sion (Lat. emulgere, emulsum, to milk out) : a mixture of
liquids which do not dissolve, the particles of one floating as small
globules in the other; as fat (butter) in milk.

En-am'el: the hard outer part of the tooth.

End bulbs : one form of touch end organs.

End organs : special nerve cells or groups of nerve cells which receive
and pass on the stimulus to which they are adapted.

End plate : the branching termination of a nerve fiber in a muscle
cell.

GLOSSARY 377

En-do-car'di-um (Gr. e.ndon, within, and kardia, the heart) : the mem-
brane lining1 the cavities of the heart.

En-do-skel'e-ton (Gr. endon, within, and Eng. skeleton) : the inner
bony framework possessed by vertebrate animals.

En-do-the'li-um (Gr. endon, within, and thele, nipple) : the thin epi-
thelium lining blood vessels, lymphatics, and serous cavities.

Ep-i-der'mis (Gr., epi, upon, and derma, skin) : the outer layer of the
skin, which is without blood vessels and nerves, and without sensa-
tion.

Ep-i-glot'tis (Gr., from epi, upon, and glotta, tongue) : a lidlike sheet
of cartilage which closes the glottis while food or drink passes
into the pharynx.

Ep-i-the'li-um (Gr. epi, upon, and thele, nipple): the superficial layer
of cells of the skin and mucous membrane, and of the blood vessels,
lymphatics, etc.

E-soph'a-gus (Gr. oisophagos, the gullet) : that part of the alimentary
canal between the pharynx and the stomach.

E'ther (Gr. aiiher,fromaithein,to burn, blaze) : a thin, elastic medium
supposed to pervade all space.

Eth'moid (Gr. ethmoeides, like a sieve) : the bone through which the
olfactory nerves pass out of the cranium.

Eu-sta'chi-an tube (named from Eustachi, an Italian physician) : the
small tube connecting the tympanum and the pharynx.

Ex-cre'tion (Lat. excernere, excretum, to sift out) : the act of discharg-
ing from the body useless or worn-out material.

Ex-0-skere-ton (Gr. exo, without, and Eng. skeleton) : the outer hard
crust or covering of many of the invertebrate animals.

Ex-pi-ra'tion (Lat. ex, out, and spirare, to breathe) : the act of breath-
ing out; opposed to inspiration.

Fau'ces (Lat., throat) : the narrow passage from the mouth to the
pharynx.

Fe'mur (Lat., thigh) : the thigh bone.

Fe-nes'tra (Lat.) : a window. The /enex/ra ovalis and fenestra rotunda
are the oval and round openings in the bone between the cavity of
the tympanum and the labyrinth of the ear.

Fer'ment (Lat. fermentum, tumult, agitation) : that which causes fer-
mentation, as yeast.

Fer-men-ta'tion : the transformation of an organic substance into ie\»
chemical compounds by the action o± a ferment.

378 GLOSSARY

Fi'brin (Lat./6ra, thread) : a white fibrous substance formed in the

clotting of the blood.
Fi-brin'o-gen : a substance in the blood which forms or helps to form

fibrin, and thus causes clotting.
Fib'u-la (Lat., clasp, buckle) : the outer and smaller of the two bones

of the leg.
Fill-form pa-pil'lae : one form of the papillae of the tongue, containing

end organs for taste.

Fissure of Ro-lan'do : the furrow separating the frontal from the pari-
etal lobe in the brain.
Floating ribs : the two lowest pairs of ribs, in man. They are not

connected with the others in front.
Food : that which, taken into the alimentary canal, supplies material

for the growth and repair of tissue, for the generation of force, or

for the regulation of force.
Food elements : the five classes of food substances necessary to the

health of the body, viz. proteids, carbohydrates, fats, water, salts.
Fo-ra'men mag'num (Lat. from/orare, to bore, pierce; magnus, great):

a large opening in the occipital bone of the skull, through which

the spinal cord passes.

Fron'tal bone : the bone forming the front of the skull.
Func'tion (L&t. functio, from fungi, to perform) : the appropriate action

of any organ or part of an organism.
Fun'gi-form pa-pil'lae : one form of the papillae of the tongue.

Gan'gli-on (Lat., a sort of swelling or excrescence, from Gr.) : a little
knot of nervous matter composed mainly of nerve cells.

Gas'tric (Gr. gaster, stomach) : pertaining to the stomach, or situated
near it; as the gastric juice, the gastric artery.

Gas-troc-ne'mi-us (Gr. gastroknemia, the calf of the leg) : the chief
muscle of the calf of the leg.

Gland (Lat. glans, glandis, acorn) : an organ for secreting something
to be used in or eliminated from the body.

Glo-mer'u-lus (Lat., diminutive of glomus, ball) : one of the little
bunches of looped capillary blood vessels in the cortex of the kid-
ney, from which the uriniferous tubules arise. »

Glos-so-phar-yn-ge'al nerves (Gr. glossa, tongue, and Eng. pharyngeal) :
the ninth pair of cranial nerves.

Glot'tis (Gr., from glotta, the tongue) : the opening from the pharynx
into the larynx.

GLOSSARY 379

Gly'co-gen (Gr. glukus, sweet, and -gen, producing) : a substance
belonging to the carbohydrates, found in animal tissues, and
especially in the liver. It is believed to be deposited as a reserve
material in the liver, and is converted into sugar as required. It
is sometimes called " animal starch."

Goi'ter (Fr., from Lat. guitur, throat): a disease which causes an
enlargement of the thyroid gland.

Hair f ol'li-cle (Lat. folliculus, a small bag) : a little pit or depression
in the skin, from the bottom of which a hair grows.

Ha-ver'sian canals (named from Havers, a London anatomist) : small
channels in the bones through which the blood vessels ramify.

He'li-um (Gr. helios, the sun) : a gaseous element identified in the
sun's corona (hence the name) long ago, and now proved to exist
in the earth's atmosphere, and in certain minerals of our planet.

Hem-o-glo'bin (Gr. haima, blood, and Lat. globus, a ball) : the coloring
matter of the red corpuscles of the blood.

He-pat'ic (Gr. hepatikos, of the liver) : pertaining in any way to the
liver, as the hepatic artery.

His-to-log'ic-al (Gr. histos, a web, and logia, speech) : pertaining to
histology, which is that branch of anatomy concerned with the
minute, especially the microscopic, structure of the tissues.

Hu'me-rus (Lat., the shoulder) : the bone of the upper arm.

Hy'a-line (Gr. hualos, glass) : resembling glass ; transparent, as hya-
line cartilage.

Hy'dro-gen (Gr. hudor, water, and -gen, producing) : one of the chemi-
cal elements ; a very light gas. It unites with oxygen to form
water.

Hy'gi-ene (Gr. hugieia, health) : that department of knowledge which
concerns the preservation of health.

Hy'oid bone (Gr. Y, the letter upsilon, and eidos, form ; from the shape
of the bone) : the bone at the root of the tongue.

Hy-po-gas'tric plexus (Gr. hupogastrion, the lower part of the abdo-
men) : a nervous network lying on each side of the rectum.

Hy-po-glos'sal (Gr. hupo, under, and glossa, tongue) : the twelfth pair
of cranial nerves.

Il-e-o-cae'cal valve (from ileum and ccecum) : the valve at the junction
of the small intestine with the large intestine. It prevents the
contents of the latter from flowing into the former.

380 GLOSSARY

Il'e-um (Lat., groin) : the last division of the small intestine.

Il'i-ac arteries (Lat. ilium, the flank) : the arteries supplying the pel-
vis and its organs and the legs.

Im-mune' (Lat. immunis, free, exempt) : exempt from a certain dis-
ease by nature, from inoculation, or from a previous attack.

In-ci'sors (Lat. incidere, to cut in) : the eight front teeth.

In'cus (Lat., anvil) : the middle one of the auditory ossicles, named
from its anvil-like shape.

In-flam-ma'tion (Lat. inftammatio) : a diseased condition of a part of
the body, shown by excess of blood, swelling, and extra heat.

In-hi-bi'tion (Lat. inhibere, to restrain) : the lowering or restraining
of the action of a nervous mechanism by nervous impulses from
a connected mechanism.

In-hib'i-to-ry : restraining.

In-nom'in-ate artery (Lat. innominatus, nameless) : one of the great
arteries rising from the arch of the aorta. It soon divides into the
right subclavian and the right common carotid artery.

In-OC-U-la'tion (Lat. inoculare, to ingraft) : the introduction of the
germs of a disease through the skin, so as to give the disease.

In-spi-ra'tion (Lat. in, in, and spirare, to breathe) : the act of breath-
ing in.

In'su-la (Lat., an island) : a portion of the cortex of the brain lying
beneath the Sylvian fissure ; also called the island of Reil.

In-ter-cos'tal (Lat. inter, between, and costa, rib) : between the ribs.

In-tes'tin-al juice : the fluid secreted by the glands of the intestine.
It plays some part in the digestive process.

In-tes'tine (Lat. intestinum) : the long tube leading from the stomach
to the anus ; the bowels.

In-tra-cen'tral nerves (Lat. intra, within) : those nerves which form
lines of communication between the various nerve centers, as dif-
ferent parts of the brain and spinal cord.

In-ver'te-brates (Lat. in-, without, and vertebratus, vertebrate): ani-
mals having no internal vertebral column.

I'ris (Gr. and Lat., the rainbow) : the colored portion of the eye, hav-
ing in its center the pupil.

Ir-ri-ta-bil'i-ty (Lat. irritare,to excite) : "the power possessed by living
cells of reacting under stimulus.

Je-ju'num (Lat., empty) : the middle portion of the small intestine,
between the duodenum and the ileum.

GLOSSARY 381

Ju'gu-lar vein (Lat. jugulum, collar bone, diminutive oi jugum, yoke) :
one of the two large veins of the throat.

Ka-tab'o-lism (Gr. kata, down, and ballein, to throw) : the destructive

processes of the body; opposed to anaboiism.
Kid'neys : glandular structures lying in the loins opposite the lumbar

vertebras. Their function is the purification of the blood by the

excretion of urine.

Lab'y-rinth (Lat. labyrinthus, a structure having many intricate pas-
sages) : the internal ear.

Lach'ry-mal gland (Lat. lacrima, tear) : the gland which secretes
the tears.

Lac'te-als (Lat. lacteus, milky): the lymphatic vessels which convey
the chyle from the alimentary canal to the thoracic duct ; so called
from the color of the chyle.

La-cu/nae (Sing, lacuna, Lat., a pit) : microscopic cavities in bone
occupied by the bone cells.

La-mel'lae (Sing, lamella, Lat., a small plate of metal) : layers of
bone tissue arranged around the Haversian canals.

Lar'ynx (Gr. larugx) : the enlarged upper end of the windpipe, con-
taining the vocal cords.

Lig'a-ment (Lat. ligare, to bind) ; a band of connective tissue bind-
ing one part to another.

Liv'er : a large gland lying below the diaphragm on the right side.
It secretes bile and performs other functions in metabolism.

Lum'bar (Lat,, lumbus, loin) : pertaining to or near the loins ; as the
lumbar arteries.

Lymph (Lat. lympha, clear water, a fountain) : a colorless fluid filling
the lymphatics and lymph spaces. It consists mostly of the fluid
part of blood.

lym-phat'ics : small transparent tubes arising in the tissues and con-
veying lymph.

Mag-ne'si-um : a light, silver-white metal.

Ma'lar bones (Lat. mala, the cheek bone, cheek) : the bones of the
cheek.

Mal'le-us (Lat., a hammer) : the outer of the three auditory ossicles,
named from its shape.

Mam'mal (Lat. mamma, the breast) : an animal of the class mam-
malia, the highest class1 of vertebrates, containing all those which
suckle their young.

MACY'S PHYS. — 24

382 GLOSSARY

Ma-nom'e-ter (Gr. memo*, thin, and metron, a measure) : an instru-
ment for measuring the pressure of gases and liquids.

Master tissues : those tissues of the body which have to do with the
liberation of energy, viz. the muscular and nervous tissues.

Mas-ti-ca'tion (Lat. masticare, to chew): the act of chewing the food.

Matter : that of which the sensible universe and all bodies are com-
posed; anything which occupies space or is perceptible to the
senses.

Max'il-la-ry bones (Lat. maxilla, jaw) : the bones of the jaws.

Me-a'tus (Lat., a passage, from meare, to go) : a natural passage or
canal. The auditory meatus is a tube of cartilage continuous with
the pinna of the ear, and leading to the membrane of the tym-
panum.

Me-dul'la (Lat., marrow) : a synonym for medulla oblongata. The
term is also applied to the marrow of bones, and to the deep inner
portions of the kidneys and other organs.

Medulla ob-lon-ga'ta (Lat.) : the hindmost segment of the brain,
continuous with the spinal cord.

Med'ul-la-ry cav-i-ty (Lat. medulla, marrow) : the cavity in a bone
which contains marrow.

Medullary sheath : the layer of white matter immediately surround-
ing the axis cylinder of a nerve.

Me-dul'la-ted : having the medullary sheath.

Mem'bra-nous coch'le-a: a membranous tube of the internal ear;
also called the cochlear canal.

Membranous lab'y-rinth: a closed sac of membrane lying in the
bony labyrinth of the ear.

Mes'en-ter-y (Gr. mesenterion, literally, the middle intestine) : the
membrane or one of the membranes which connect the intestines
and their appendages with the hinder wall of the abdominal
cavity.

Me-tab'o-lism ((Jr. metabole, change) : the processes by which living
cells transform into their own proper substance material brought
by the blood, and also break down and prepare for excretion
matter which has fulfilled its function ; anabolism and katabolism.

Met-a-car'pus (Gr. meta, beyond, and karpos, the wrist) : the part of
the skeleton between the wrist and the fingers, consisting of five
bones.

Met-a-tar'sus (Gr. meta, beyond, between, and torsos, the flat of the
foot) : that part of the skeleton between the ankle and the toes.

GLOSSARY 383

Mi'crobe (Gr. mikros, little, and bios, life) : a microscopic organism ;
especially one of those forms which produce disease.

Mi'tral valves: the bicuspid valves of the heart, which are shaped
like a miter.

Molars (Lat. molere, to grind) : the three back teeth on each side of
each jaw.

Mol'e-cule (Lat. molecula, diminutive of moles, a mass) : the smallest
part into which a substance can be divided without destroying its
chemical character.

Mo 'tor areas : those portions of the cortex of the brain whose stimu-
lation results in motion.

Motor nerves : nerves whose function it is to excite muscular contraction.

Mu'cous membrane (Lat. mucus, slime, and membrana, a skin, parch-
ment) : the lining membrane of all passages and cavities of the
body which have an external communication.

Mu'cus (Lat., slime) : a fluid secreted by the mucous membrane.

Mus'cu-lar sense: impressions conveyed by sensory nerve fibers
running from the muscles to the spinal cord and thence to the
brain, giving information of the general condition of the muscles,
and helping to form judgments of weight, pressure, etc.

Nar-cot'ic (Gr. narkotikos, making numb) : a substance which blunts
the sensibilities, induces sleep, and, in large quantities, complete
insensibility.

Nerv'ous impulse : the molecular disturbance which is conveyed by
the nerve fibers from the point of stimulation to the nervous center
in the brain or spinal cord, or from a nerve center to a muscle.

Neu'ral arch (Gr. neuron, nerve) : the arch of a vertebra which incloses
and protects the corresponding part of the spinal cord.

Neu-rax'on : the axis cylinder of a nerve fiber.

Neu-ri-lem'ma (Gr. neuron, nerve, and lemma, a husk) : the primitive
sheath, or inclosing membrane, of a nerve fiber.

Neu-rog'li-a (Gr. neuron, nerve, and glia, glue) : a peculiar supporting
tissue of the nervous system.

Neu'ron (Gr., nerve) : the nerve unit, consisting of a nerve cell with
its processes, one of which becomes the axis cylinder of a nerve
fiber. Of such units the whole nervous system is composed.

Ni'tro-gen (Lat. nitrum, natron, and -gen, producing) : a gaseous ele-
ment forming four fifths of the atmosphere, and found in many
important compounds.

384 GLOSSARY

Non-me-dulla-ted : without the medullary sheath, as nonmedullated

nerves.
Nu-cle-o'lus (Lat., diminutive of nucleus, a little nut) : the nucleus of

a nucleus.
Nu'cle-us (Lat., a little nut) : a central modified mass of protoplasm

found in nearly all cells.
Nu-tri'tion (Lat. nutrire, to nourish) : a term which, in its broad sense,

includes all the processes concerned in the growth, maintenance,

and repair of the living body and all its parts.

Oc-cip'i-tal (Lat. occiput, the back of the head) : pertaining to the
hinder part of the head, as the occipital lobe of the brain.

Oc-u-lo-mo'tor (Lat. oculus, the eye) : pertaining to the movements of
the eye ; applied especially to the third pair of cranial nerves.

0-don'toid process (Gr. odontoeides, tooth-shaped) : the tooth or peg of
the axis or second cervical vertebra.

01-fac'to-ry cells (Lat. olfnctu*, from olere, to have a smell, andfacere,
to make) : the cells which are affected by odors ; the end organs
for smell, in the lining membrane of the nasal passages.

Olfactory nerves : the nerves of smell, distributed from the olfactory
bulb over the membrane lining the nagal passages.

Olfactory tract : the band of nervous matter lying between the olfac-
tory bulbs (from which the olfactory nerves spread out) and the
roots of those nerves in the cerebrum.

O-men'tum (Lat.) : a fold of the peritoneum.

O'pi-um (Gr. opion, poppy juice) : the juice of the poppy, thick-
ened into a sticky brown mass of bitter taste and peculiar odor.
It is a stimulant narcotic, and powerfully affects the central nerv-
ous system.

Op'tic (Gr. optikos) : pertaining to sight.

Optic chi-as'ma (Gr., two lines crossed) : the crossing of the optic
nerves.

Optic com'mis-sure (Lat. con, with, and mittere, missus, to place) : the
union of the optic nerve fibers from the two eyes, after passing
through the openings in the eye sockets.

Optic thal'a-mus (Lat., chamber) : masses of gray matter at the base
of the cerebrum.

OrT)it (Lat. orbis, circle) : eye socket.

Or'gan ((Jr. organon, an instrument) : one of the parts or members
of a body which has some specific function ; as the organ of vision.

GLOSSAttY 385

Organ of Cor'ti (named from Corti, an Italian scientist) : an epithelial
structure within the membranous cochlea believed to contain the
end organs for hearing.

Os in-nom-i-na'tum (Lat., nameless bone) : the hip bone.

Os-mo'sis (Gr. osmos, impulsion, pushing) : the diffusion ot fluids
through membranes.

Os'se-ous (Lat. os, bone) : bony, made of bone; as osseous tissue.

Os-si-fi-ca'tion : the process of changing into bone.

O'to-liths (Gr. ous, otos, ear, and lithost stone) : minute hard particles
in the passages of the inner ear.

Ox-i-da'tion : the chemical union of oxygen with other substances, as
in combustion.

Ox-y-gen (Gr. oxus, sharp, acid, and -gen, producing, because errone-
ously supposed to be present in all acids) : a gaseous chemical ele-
ment found in the atmosphere and in many compounds.

Ox-y-hem-0-glo'bin : hemoglobin which has united with oxygen.

Pa-cin'i-an corpuscles (named from Pacini, an Italian physician) :

one of the forms of touch end organs.
Pal'ate (Lat. palatum) : the roof of the mouth and floor of the nose.

The soft palate is a fold of muscular membrane hanging between

the back part of the mouth and the upper part of the pharynx.
Pan'cre-as (Gr. pan, all, and krea*, flesh) : a gland in the abdomen

near the stomach. It pours its secretion into the duodenum. In

animals it is called sweetbread.
Pan-cre-at'ic juice : the secretion of the pancreas which acts upon the

fats and proteids in the food.
Pa-pilla (Lat., a nipple) : a minute, rounded projection ; as the papillae

of the tongue.
Pap'il-la-ry muscles : muscular bundles within the ventricles of the

heart, attached to the heart walls and, by the tendinous cords, to

the valves between the auricles and the ventricles.
Pa-ri'e-tal bones (Lat. paries, wall) : bones of the cranium forming a

part of the top and sides of the skull.
Pa-rot'id glands (Gr. para, near, and ous, otos, ear) : the salivary

glands near the ears.

Pa-tel'la (Lat., a small pan or dish) : the knee pan.
Pec'to-ral girdle (Lat. pectoralis, pertaining to the breast) : the clavi-
cle and scapula upon each side, to which are attached the bones of

the upper arms.

386 GLOSSARY

Pe-dun'cle: a band of nervous matter connecting different parts of
the brain.

Pel'vic girdle (Lat. pelvis, a basin) : the two bones, one upon each
side, called the os innominatura, to which are attached the bones of
the upper legs. •

Pel' vis (Lat., a basin) : the pelvic girdle and sacrum.

Pep'sin (Gr. pepsis, cooking, digestion) : a ferment found in the gas-
tric juice.

Per-i-car'di-um (Gr. pericardion, around the heart) : the serous mem-
brane which surrounds the heart.

Per-i-mys'i-um (Gr. peri, around, and mus, muscle) : the sheath of
areolar tissue which surrounds a bundle of muscle fibers.

Per-i-neu'ri-um (Gr. peri, around, and neuron, nerve) : the membra-
nous sheath surrounding a nerve.

Per-i-os'te-um (Gr. peri, around, and osteon, bone) : the membrane
surrounding a bone.

Pe-riph'er-al (Lat. peripheria, from Gr. peri, around, and pherein, to
bear, carry) : belonging to the outside or superficial portions of a
body.

Per-i-staTtic (Gr. peri, around, and stellein, to set, place) : pertaining
to the waves of contraction, called peristalsis, running down the
alimentary canal to force on the contents.

Per-i-to-ne'um (Gr. peri, around, and teinein, to stretch) : the serous
membrane lining the abdominal cavity.

Per-spi-ra'tion (Lat. per, through, and spirare, to breathe) : liquid
excretion from the skin, mainly from sweat glands.

Pha-lan'ges (Lat., plural of phalanx, a body of troops in ranks and
files, from Gr. phalagx) : the bones of the fingers and toes.

Phar'ynx (Gr. pharugx, the throat) : that part of the alimentary canal
between the cavity of the mouth and the esophagus.

Phos'phate : a chemical compound of phosphoric acid with a base.

Phos'pho-rus (Gr. phos, light, and pherein, to bring) : a chemical ele-
ment ; a white or yellowish waxy solid that gives off a faint glow.

Phre'nic (Gr. phren, the diaphragm) : belonging to the diaphragm ; as
the phrenic artery or nerve.

Phys-i-ol'o-gy (Gr. phusis, nature, and logia, discourse) : the science
which treats of the phenomena of living organisms. It is divided
into animal and vegetable physiology.

Pi'a ma'ter (Lat., kind, tender mother) : the delicate vascular mem-
brane immediately covering the brain and spinal cord.

GLOSSARY 387

Pi'ne-al body (Lat. pinea, a pine cone) : a glandlike body in the roof
of the third ventricle of the brain.

Pin'na (Lat., a feather) : the folded sheet of cartilage which forms
the principal part of the external ear.

Pithed : deprived of the central nervous system by the passing of a
wire or needle through the vertebral canal.

Plas'ma (Lat. and Gr., anything formed or molded) : the colorless
fluid of the blood.

Pleu'ra (Gr., a rib, the side) : the serous membrane which covers the
lungs and lines the cavity of the thorax.

Plex'us (Lat., a twining, braid, from plectere, to braid, twine) : a net-
work of vessels, nerves, or fibers.

Pons Va-ro'li-i (Lat., bridge of Varoli — an Italian anatomist): a
band of nervous tissue on the front or ventral side of the medulla
oblongata, connecting the two sides of the cerebellum.

Pop-lit'e-al (Lat. poples, the ham) : pertaining to the ham or back of
the knee, as the popliteal artery or ligament. .

Por'tal circulation (Lat. porta, gate) : the passage of venous blood
from the capillaries of one organ to those of another before reach-
ing the heart. In man, the circulation of the liver.

Portal vein : the large vein of the liver, bringing blood to its capil-
laries.

Pos-te'ri-or (Lat., coming after) : away from the head, or sometimes,
in human physiology, toward the back.

Po-tas'si-um (Lng. potash) : a chemical element, found only in com-
bination with acids.

Prim'i-tive sheath : the inclosing membrane of a nerve fiber.

Proc'ess (Lat. processus, a going forward) : an outgrowth ; a projec-
tion, as the spinous process of a vertebra.

Pro'te-ids (Gr. protos, first) : the food elements which form tissue.

Pro'to-plasm (Gr. protos, first, and plasma, anything formed) : an
albuminoid substance consisting of carbon, oxygen, nitrogen, and
hydrogen ; capable under proper conditions of manifesting certain
phenomena of life ; " the physical basis of life."

Pty'a-lin (Gr. ptualon, spittle) : the peculiar principle of saliva which
acts as a ferment on starch, converting it into dextrose, a variety
of sugar.

Pul'mo-na-ry (Lat. pulmo, a lung) : pertaining to the lungs, as the
pulmonary arteries, which carry blood from the heart to the
lungs.

388 GLOSSARY

Pulmonary circulation : the circulation of the blood from the right

ventricle of the heart through the pulmonary arteries, capillaries,

and veins back to the left auricle.

Pu'pil (Lat. pupilld) : the round opening in the center of the iris.
Pu-tre-fac'tion (Lat. putrefactio)i the offensive decay of albuminous

and other matter.
Py-lo'rus (Gr. puloros, gate keeper) : the opening from the stomach

into the intestine.

Ra'di-ant energy (Lat. radiare, to emit rays) : the force resident in
vibrations of the ether which fills all space.

Ra'di-us (Lat., a staff, rod, ray) : one of the bones of the forearm.

Rec'tum (Lat. rectus, straight) : the last division of the large intes-
tine, and hence of the alimentary canal.

Re'flex action (Lat. reflectere, reflexus, to bend back) : action in
which afferent impulses reach a nerve center and efferent impulses
are sent back without the higher brain centers having been stimu-
lated. Such action is involuntary and often unconscious.

Re-frac'tion (Lat. refranyere, refractus, to break) : the change in
the direction of a ray of light in passing from one medium to an-
other of a different density.

Re'nal (Lat. renes, kidneys) : pertaining to or in the region of the
kidneys, as the renal artery, the renal plexus.

Ren'nin (Anglo-Saxon rinnan, to run): that ferment in the gastric
juice which causes milk to curdle ; the element in rennet which
assists in the making of cheese.

Re-pro-duc'tion (Lat. reproduce re, to produce again) : the process by
which new organisms are produced from those already existing.

Res'o-na-ting cavities (Lat. resonare, to sound back, echo) : the
pharynx, mouth, and nasal cavities, slight changes in which
modify the sound of the voice.

Res-pi-ra'tion (Lat. respirare, to breathe) : the act of taking in and
giving out air.

Re-spir'a-to-ry center : that cluster of nerve cells in the medulla ob-
longata which controls and coordinates the movements of the
muscles concerned in breathing.

Ret'i-na (Lat. rete, a net) : that membrane of the eye in which the
fibers from the optic nerve terminate.

Rhyth'mic (Gr. rhuthmos, measured motion) : characterized by a regu
lar succession of movements, impulses, or sounds.

GLOSSARY 389

Rick'ets : a disease of early life characterized by defective nutrition
of the bones, and often due to a lack of proper food.

Ri'gor mor'tis (Lat., rigidity of death) : the condition in a dead ani-
mal body due to a coagulation of the protoplasm of the muscle
cells.

Rods of Cor'ti : pillarlike cells forming part of the organ of Corti in
the inner ear.

Sac'cule (Lat. sacculus, a little sac) : part of the membranous laby-
rinth of the ear.

Sa'crum (Lat. sacer, sacred) : the lower part of the spine, immedi-
ately above the coccyx.

Sa-li'va (Lat., spittle) : the mixed secretions of the salivary glands
and the mucous membrane of the mouth.

Sal'i-va-ry glands : the parotid, submaxillary, and sublingual glands
which pour their secretions into the mouth.

Salt : a chemical compound formed by uniting an acid with a base.
The salts which are food elements are chiefly chlorides, phosphates,
and carbonates of sodium, potassium, calcium, and magnesium,
with salts of iron and some organic acids.

Sar-co-lem'ma (Gr. sarx, flesh, and lemma, a husk) : the membrane
surrounding a striped muscular fiber.

Scap'u-la (Lat.) : the shoulder blade.

Sci-at'ic nerve (Lat. sciaticus) : the nerve of the hip and thigh.

Scle-rot'ic (Gr. skleros, hard) : the outer coat of the eye.

Se-ba'ceous glands (Lat. sebaceus, from sebum, tallow) : small glands
under the skin which secrete an oily matter which softens and
lubricates hair and skin.

Se-cre'tion (Lat. secretio, the act of secreting) : the process by which
the various glands separate material from the blood and elaborate
it into new substances so as to form the various secretions, as bile,
saliva, etc.

Se-cre'to-ry nerves : nerves that supply the organs of secretion.

Sem-i-cir'cu-lar canals : three half-circular canals of the internal ear.

Sem-i-lu'nar valves (Lat. semi-, half, and lunar is, from luna, the
moon) : valves of the heart, at the beginning of the aorta and of
the pulmonary artery, which prevent the blood from flowing back
into the ventricle.

Sen'so-ry areas: those portions of the brain whose stimulation re-
g ults in sensation.

390 GLOSSARY

Sensory nerves : nerves which carry impulses resulting in sensation.
Se'rous : pertaining to serum ; filled with, or secreting serum.
Se'rum (Lat., akin to Gr. oros, Skr. sara, curd) : the watery portion

of certain animal fluids, as blood, milk, etc.
Skull : the skeleton of the head.
So'di-um (Eng. soda) : a chemical element found in union with

various acids.
So'lar plexus: a network of nerves about the pit of the stomach,

containing fibers from many different nerves.
Spec'trum (Lat., an appearance, image) : the several rays of which

light is composed separated by refraction and spread out in a band

of colors and dark lines.
Sphe'noid (Gr. sphenoeides, wedge-shaped) : an irregularly shaped

bone in front of the occipital in the base of the skull.
Sphinc'ter (Gr. sphigkter, anything which binds tight) : a muscle

which surrounds and tends to close a natural opening.
Spi'nal (Lat. spina, the spine) : pertaining to the backbone.
Spinal ac-ces'so-ry nerves : the eleventh pair of cranial nerves.
Spinal cord : the cord of nervous matter lying in the channel of the

vertebral column, and continuous with the nervous matter of the

brain.

Spiral ganglion : a mass of nerve cells in the inner ear.
Spleen: one of the ductless glands, lying in the abdomen near the

stomach. Of its functions little is positively known.
Spleen pulp : a soft substance in the meshes of the tissue of the spleen.
Splen'ic : pertaining to the spleen ; as the splenic vein.
Spu'tum (Lat., from spuere, to spit): that which is expectorated or

discharged from the lungs.
Sta'pes (Lat., a stirrup) : the innermost of the auditory ossicles,

shaped like a stirrup.
Ster'il-ize (Lat. sterilis, barren) : to render incapable of germination ;

to make sterile ; to destroy the germs in food or water.
Ster'num (Gr. sternon, the breast) : the bone in the middle of the front

of the chest.
Stim'u-lus (Lat. for stigmulus, akin to instigare, to prick, to goad):

any substance or agent capable of arousing the activity of a nerve

or irritable muscle, or capable of producing an impression upon a

sensory organ.

Stro'ma (Gr., a couch) : the colorless framework of a red blood cor-
puscle or other cell.

GLOSSARY 391

Sub-cla'vi-an (Lat. sub, under, below) : situated below the clavicle, as
the subclavian arteries or veins.

Sub-lin'gual glands : the salivary glands under the tongue.

Sub-max'il-la-ry glands : the salivary glands under the jaw.

Su-pra-re'nal cap'sules (Lat. supra, above) : two small bodies situated
upon the kidneys. Their function is unknown.

Sus-pen'so-ry ligament (Lat. suspendere, suspensum, to suspend) : a
ligament attached to the crystalline lens and the ciliary processes
of the eye. It assists in accommodation.

Su'ture (Lat. sutura, a seam) : an immovable articulation, as one of
those between the bones of the skull.

Syl'vi-an fissure : the furrow which divides the frontal from the
temporal lobe of the brain; named from a famous anatomist
Dubois, or Sylvius (the Latin form of the name).

Sym-pa-thet'ic nervous system: the double chain of ganglia lying
on each side of the spinal column, with the nerves issuing there-
from, the plexuses which they form, and the small ganglia along
their course.

Syn-o'vi-al (Gr. sun, together, and Lat. ovum, egg) : of or pertaining
to synovia, the fluid secreted by a synovial membrane and named
from its resemblance to the white of egg.

Sys-tem'ic circulation : the general circulation of the blood through-
out the body ; opposed to the restricted pulmonary circulation.

Tar'sus (Gr. tarsos, the flat of the foot) : the ankle.

Taste buds : end organs for taste found in certain papillae of the tongue.

Tem'po-ral bones (Lat. tempora, the temples) : complex bones situated
in the side of the head, and containing the internal parts of the ear.

Temporal lobe: the part of the cerebrum lying on each side just
beneath the temporal bone.

Ten'don (Lat. tendere, to stretch) : a band or layer of dense fibrous
tissue at the end of a muscle, attaching it to a bone, or between
two muscular bellies ; a sinew.

Tet'a-nus (Gr. tetanos, spasm) : a gentle, continuous vibration, or pro-
longed contraction, as of a muscle or a nerve.

Tho-rac'ic duct (see Thorax} : a large lymphatic vessel running-
upward through the thorax to empty into the jugular vein.

Tho'rax (Lat. and Gr., a breastplate, or the part of the body covered
by a breastplate) : that part of the body between the neck and the
abdomen, and containing the heart and the lungs.

392 GLOSSARY

Thy'mus gland (Gr. thumos, the sweetbread) : a ductless gland in the
thorax behind the sternum. Its function is unknown.

Thy'roid cartilage (Gr. thureoeides, shield-shaped) : a sheet of carti-
lage on the front of the larynx.

Thyroid gland : a ductless gland of unknown function in the region
of the larynx.

Tib'i-a (Lat.) : the inner and larger of the two bones of the lower
leg.

Tis'sue : one of the materials of uniform structure forming the body,
as muscular tissue.

Ton'sil (Lat. tonsilla} : one of a pair of oval bodies situated in the
recesses on each side of the fauces.

Touch corpuscles: one form of touch end organs.

Tox'in (Gr. toxikon, poison) : a poisonous kind of the animal base
or alkaloid which is formed in the putrefaction of albuminous
matter.

Tra'che-a (Gr. trachus, rough) : the windpipe.

Trans'verse ligament: a band of strong tissue dividing the large
neural ring of the atlas into two parts, into one of which the odon-
toid process fits.

Tri'ceps (Lat., having three heads, from ires, three, and caput, head) :
the muscle at the back of the upper arm.

Tri-cus'pid valves (Lat. tres, three, and cuspis, point) : the valves
guarding the opening between the auricle and ventricle on the
right side of the heart.

Tri-gem'i-nal nerves (Lat. trigeminus, born three together) : the fifth
pair of cranial nerves.

Troch'le-ar nerves (Lat. trochlea, a pulley) : the fourth pair of cranial
nerves.

Troph'ic nerves (Gr. trophe, nourishment) : nerves which directly
influence the nutrition of the tissues to which they go.

Tu-ber'cu-lin : a liquid prepared from cultures of the tubercle-
bacillus, as a remedy for tuberculosis.

Tu-ber-cu-lo'sis (Lat. liiberculum, diminutive of tuber, tuber) : a disease
affecting most of the tissues, and characterized by the formation of
tubercles and the tubercle-bacillus.

Tur'bi-nate bones (Lat. turbinatus, shaped like a top or cone): two
small bones in the nostril chambers.

Tym'pa-num (Lat., a drum) : the middle ear. The membrane of the
tympanum is the eardrum.

GLOSSARY 393

Ul'na (Lat., the elbow) : the inner of the two bones of the fore arm.

U're-a (Gr. ouron, urine, originally water) : a crystalline solid, soluble
in water. It is the final product of proteid decomposition in the
body, and the chief solid constituent of the urine.

U-re'ter (Gr. oureter, from ouron, urine) : the excretory duct of the
kidney, conveying the renal excretion to the bladder.

U-ri-nif'er-ous tu'bules : small tubes which collect the urine secreted
in the cortex of the kidneys.

U'tri-cle (Lat. utriculus): a little sac; especially the little sac forming-
part of the membranous labyrinth of the ear.

Vac-ci-nartion (Lat. vacca, cow): inoculation with cowpox virus ob-
tained directly or indirectly from the cow.

Va'gus (Lat., wandering) : the tenth pair of cranial nerves.

Val'vu-lae con-ni-ven'tes (Lat. valva, the leaf of a double door; con-
nivere, to wink at, connive) : the semicircular folds in the lining
membrane of the small intestine, increasing the absorbing surface.

Vas'cu-lar (Lat. vasculum, diminutive of vas, vessel) : containing
small vessels or tubes, as the vascular system for the circulation of
the blood.

Vas-o-con-strict'or (Lat. vas, vessel, and Eng. constrictor, from Lat.
constringere, to draw together) : causing contraction of the blood
vessels.

Vas-0-di-lat'or : causing dilation or relaxation of the blood vessels.

Vas-o-mo'tor : regulating the tension of the muscular walls of the
blood vessels.

Vein (Lat. vena) : one of the tubes carrying blood to the heart.

Ve'na ca'va (Lat., hollow vein) : one of the great veins connected
directly with the heart.

Ven-ti-la'tion (Lat. ventilare, to air, ventilate) : the process of repla-
cing foul or vitiated air in any confined space with pure air.

Ven'tral (Lat. venter, belly) : toward the belly ; opposed to dorsal.

Ven'tri-cle (Lat. ventriculus, diminutive of venter, belly) : a cavity, as
the ventricles of the heart or the brain.

Ver'te-bra (Lat., a bone of the spine) : any segment of the backbone.

Ver'te-brates : animals having a backbone.

Ves'ti-bule (Lat. vestibulum, vestibule) : the central part of the laby-
rinth of the ear.

Vil'lus (Lat., shaggy hair) : one of the minute projections covering
the valvulae conniventes.

394 GLOSSARY

Vis'ce-ra (Lat., plu. of viscus, perhaps akin to Eng. viscid) : the organs
contained in the abdomen.

Vital knot : the nervous center in the medulla oblongata which pre-
sides over the coordination of the respiratory movements. If the
medulla be divided below this center respiration ceases and death
results.

Vit're-ous humor (Lat. vitreus, of glass) : the jellylike substance fill-
ing the posterior chamber of the eyeball.

Viv-i-sec'tion (Lat. vivus, living, and sectio, a cutting) : dissection of
a living body.

Vo'cal cords (Lat. vox, vocis, voice) : bands of elastic tissue in the
mucous membrane of the larynx which act upon the air like the
reeds of a musical instrument to produce musical sounds.

Vo'mer (Lat., a plowshare) : a small bone forming part of the parti-
tion between the nostrils.

Yellow Spot : an area about one twenty-fourth of an inch in diameter
in the retina of the eye, upon which the most definite images are
formed.

INDEX

Abdomen, 163, 186, 221, 224.

Abducens nerve, 291.

Absorbents, 224.

Absorption, 145, 202, 236, 237.

Accelerator nerves, 178, 299.

Accommodation of eye, 113, 114, 122.

Adam's apple, 136.

Adipose tissue, 24.

Afferent nerves, 30, 86, 298.

Air cells, 183, 184.

Air, composition of, 187.

expired, 187.

necessity for pure, 362-364.

temperature of, for breathing, 193,

194.

Albumin, 204, 205, 214.
Alcohol, as food, 245, 246.

as poison, 246-250.

effects on blood circulation, 171,
172, 180.

effects on bodily heat, 271, 272.

effects on character, 328-332.

effects on excretion, 264, 265.

effects on eye, 120.

effects on growth, 54.

effects on muscular action, 78.

effects on nervous system, 325-332.

effects on respiration, 194.

effects on taste and smell, 99.

effects on vocal organs, 144.

properties of, 244, 245.
Alimentary canal, 218-236.

excretion in, 263.

peristaltic movement in, 67.

relation to kidneys, 262.
Alveolus, 183.
Amoeba, 14, 16, 149.
Ampulla, 128.
Amylopsin, 253, note 1.
Anabolism, 202.

395

Anatomy, 7.

Animal heat, 266, 267.

Animals, cells of, 11.

distinguished from plants, 13, 14.
Ankle, bones of , 46.
Antidotes of poisons, 355-359.
Antiseptic surgery, 340.
Antitoxin, 338, 339.
Anus, 227.
Anvil bone, 127.
Aorta, 157, 161-163, 169.
Appendices, of heart, 154.
Appendicnlar skeleton, 38, 45-49.
Appendix, vermiform, 226.
Appetite, control of, 332-334.
Aqueduct of Sylvius, 289.
Aqueous humor, 110.
Arachnoid membrane, 283.
Areolar tissue, 23, 59.
Arm, bones of , 46.
Arterial blood, 174, 188, 197.
Arteries, 158, 162-164.

aorta, 157, 161-163, 169.

blood flow in, 168.

course of principal, 345, 346.

function of, 153, 164.

injury to, 168, 345, 346.

muscular action of, 179, 180.

pulmonary, 156, 164, 184.

splenic, 163, 254.

structure of, 158, 159.
Articular cartilage, 51.
Articular processes, anterior and pos-
terior, 42.

Articulations, defined, 49.
Arytenoid cartilages, 136.
Asphyxia, relief for, 347.
Assimilation, 145, 202, 238.
Astigmatism, 123.
Atlas vertebra, 43, 50.

396

INDEX

Atom, defined, 9, 10.
Auditory area, 313.
Aaditory cells, 132.
Auditory fatigue, 134, 135.
Auditory hairs, 132.
Auditory nerve, 128, 130, 291.
Auditory ossicles, 127.
Auditory word center, 141.
Auricle, left, 155.

right, 154.

Autointoxication, 263, 204.
Automatic movement, 73.
Axial skeleton, 38-47.
Axillary artery, 162.
Axis cylinder process, 32, 276.
Axis vertebra, 44, 50.

Bacilli, see bacteria.

Bacteria, action on body, 336-338.

function of, 335, 336.

in decomposition, 243.

in intestines, 235.
Ball and socket joint, 50.
Basal ganglia, 287.
Bathing, public, 366.
Belly of muscle, 61, 65.
Biceps muscle, 65.
Bicuspid valves, 157.
Bicuspids, 219.
Bile, 234, 237, 253, 338.
Bile duct, 231.
Binocular vision, 124.
Bladder, 260.

Blind spot of eye, 109, 124.
Blood, absorption in, 236.

arterial, 174, 188, 197.

as tissue, 147.

chemical composition of, 149.

circulation of, 145, 153-175.

clotting of, 149-152, 344, :u."i.

effect of respiration on, 187, 188.

function of, 26, 147.

quantity of, in body, 148.

structure of, 148.

supplied to lungs, 184.

velocity of, 168.

venous, 174, 197.
Blood corpuscles, 151.

red, 26, 148-151, 188.

white, 12, 16, 149, 151, 169-171, 255,
338.

Blood pressure, in arteries and veins,
168.

in brain, 179.
Blood vessels, for muscles, 61.

in bones, 52, 53.

in dermis, 85.

injuries to, 150, 345.

nerves for, 160, 179.

structure of, 174.

supply of, 159, 160.

vascular and nervous supply of s 159j
160, 179.

see arteries, veins, capillaries.
Blushing, 168, 180.
Bone cells, 53.
Bone corpuscles, 26, 53.
Bones, articulations of, 49.

broken, 55.

dissection of, 57.

function of, 37.

hygiene of, 53-55.

motion of, 49, 50.

number of, 38.

of appendicular skeleton, 45-47.

of axial skeleton , 39-45.

of children, 53,54.

of old people, 55.

structure of, 25, 26, 5<M52.

table of, 47, 48.
Brachial artery, 162.
Brain, blood pressure in, 179.

dissection of, 33, 295.

membranes of, 283.

nerve center, 239, 275.

parts of, 28, 284, 285.

stimulus for perception, 91.

ventricles of, 289.
Breastbone, 44, 45.
Bright's disease, 265.
Broken bones, 55.
Bronchi, 182, 183.
Bronchial arteries, 163, 184.
Bronchial tubes, 183.
Burns, remedies for, 349, 350.

Caecum; 226.
Canals in ear, 128, 133.
Canines, 219.
Capillaries, action of, 168.

bleeding from. 34"».

function of, 150, 151, 153, 160.

INDEX

397

Capillaries, lymph, 169.

velocity of blood in, 169.
Carbohydrates, 203, 205, 236.
Carbon, in food, 201, 204, 207.
Carbon dioxide, 181, 187-190, 257, 261;

see respiration.

Carbonic acid gas, see carbon dioxide.
Cardiac muscle, 158.
Cardiac nerves, 176-178.
Cardiac orifice of stomach, 222.
Carotid arteries, 162.
Carpus, 46.
Cartilage, articular, 51.

costal, 44, 45.

forms of, 24.

function of, 48.

of Santorini, 137.

of Weisberg, 137.

permanent, 48.

study of, 56.
Casein, 204, 205.
Casein ogen, 216.
Cells, 11.

air, 183, 184.

auditory, 132.

bone, 53.

forming tissue, 19.

motor, 72.

muscle, 61, 66.

nerve, 32, 275.

taste, 95.
Cellulose, 205.

Central lobe of cerebrum, 285.
Central nervous system, 27-30, 275,

279-292, 305-313.
Centrum of vertebra, 42.
Cerebellum, composition of, 287.

function of, 69, 70, 133, 306, 307.

nervous matter in, 30.
Cerebral nerves, see cranial nerves.
Cerebro-spinal fluid, 289.
Cerebro-spinal meninges, 284.
Cerebro-spinal nervous system, 27-30,

275, 279-292, 305-313.
Cerebrum, cortex of, 30, 285, 311-313.

functions of, 308-310.

nervous matter in, 30.

structure of, 285-287.
Cervical vertebrae, 41.
Character, formation of, 323-325.
Cheek bones, 40.

MACY'S PHYS. — 25

Chemical analysis, 9, 10.
Chemical element, 9, 10.
Chest, cavity of, 45.

muscles of, 185, 186.
Chiasma, optic, 104.
Chilblains, treatment for, 350.
Choking, treatment for, 351.
Chorda tympani, 291.
Choroid, 106.
Chyle, defined, 151.

tubes conveying, 153, 226, 237.
Chyme, 231.

Ciliary muscles, 60, 111, 113, 114.
Ciliary nerves, 111.
Ciliary processes, 107, 114.
Ciliated epithelium, 91, 183.
Circulation of blood, 153-175.

an unconscious nervous operation,
145.

effects of alcohol on, 180.

general or systemic, 160-164.

in frog's foot, 174.

nervous control of, 176-180.

portal, 160, 164, 165.

pulmonary, 160, 164.
Circumvallate papilla, 95.
Clavicle, 45, 46.
Cleanliness, 362.
Clothing, healthful, 268-271.
Clotting of blood, 149-152, 344, 345.
Coats of eye, 105, 106.
Coccyx, 30, 42.
Cochlea, 128, 129.
Coeliac axis, 163.
Cold, sensation of, 88, 93.
Colds, cause of, 337.
Collar bone, 46.
Colon, 226.
Color, complementary, 125.

production of, 102.
Color blindness, 118, 125.
Combustion, see oxidation.
Commissure, optic, 104.
Conductivity of cells, 12.
Cones and rods, 104, 108.
Conjunctiva, 106.

Connective tissues, 21, 23, 24, 48, 147.
Conscious nervous operations, 35-144.
Consciousness, 310.
Conservation of energy, 203.
Consumption, 339-341.

398

INDEX

Contractile substance, 61.
Contractility of cells, 12.
Contraction of muscle, 62-65, 80.
Convulsions, relief for, 353.
Cooking, principles of, 209-213.
Coordination of cells, 12.
Coordination of muscular movement,

69, 70, 133, 306, 307.
Coral, rudiments of nervous system in,

14.

Corium, 82.
Cornea, 105.
Coronary arteries, 162.
Coronary veins, 155, 164.
Corpora quadrigemina, 28, 284, 287,

307, 308.

Corpora striata, 287, 295.
Corpus callosum, 286.
Corpuscles, bone, 26, 53.

Pacinian, 87.

red blood, 26, 148-151, 188.

taste, 218.

touch, 87, 88.

white blood, 12, 16, 18, 26, 149, 151,

169-171, 255, 338.
Correlation of forces, 203.
Corrosive poisons, 354, 355.
Cortex, of cerebrum, 30, 285, 311-313.

of kidneys, 260.
Corti, organ of, 130.
Costal cartilages, 44, 45.
Cranial bones, 39, 40.
Cranial nerves, 28, 289-295; 40, 95, 96,
103, 104, 106, 108, 111, 112, 128,
130, 141, 142, 176-178, 229, 232.
Cranium, 39.
Cricoid cartilage, 136.
Crura cerebri, 28, 287, 307.
Crystalline lens, 109, 113, 114.
Cuticle, 82, 83, 88, 92.

Dead muscle, 65, 66.
Deafness, 143.

Decussation of pyramids, 288.
Deformity, causes of, 54, 55.
Delirium tremens, 326.
Dendrites, 278.
Dendrons, 278.
Dentine, 220.
Dermis, 82, 84, 85.
Dialyzer, 175.

Diaphragm, 185, 195.
Diffusion of gases, 186.
Digestion, defined, 201, 202.

experiments in, 251-253.
Digestive apparatus, 218-236.

dissection of, 251.
Dipsomania, 325, 326.
Disease, 335.

Dissection, in class work, 15.
Distillation, 244.
Dorsal vertebrae, 41.
Drainage, 363.

Drowning, treatment for, 347.
Ductless glands, 254-256.
Ducts, bile, 231.

of glands, 228.

thoracic, 169.
Dumbness, 143.
Dura mater, 283.

Ear, bones of, 40.

care of, 134.

dissection of, 135.

drum, 126, 127.

external, 126.

foreign bodies in, 352.

internal, 127-131.

middle, 127.

muscular fibers of, 60.

path of auditory impression, 131-

133.

Efferent nerves, 30, 86, 298, 299.
Eggs, as food, 203, 204.
Elements, chemical, 9, 10.

nervous, 275.
Emulsion, 232, 237.
Enamel of teeth, 220, 239, 240.
End bulbs, 88.
End organs, for hearing, 130.

for taste, 95.

nervous, 292.

of olfactory nerves, 98.

of vision, 104.

tactile, 87, 88.
End plates, 62, 63, 292.
Endocardium, 158.
Endoskeleton, 37.
Endothelium, 22.
Energy, conservation of, 203.

development of, 21, 22.

forms of, 202, 203.

INDEX

Energy, from foods, 207, 208.

radiant, 102.
Epidermis, 82, 83, 88, 92.
Epigastric plexus, 223.
Epiglottis, 137.
Epilepsy, relief for, 353.
Epithelium, 21-23, 82.

ciliated, 91, 183.
Equilibrium of body, 307.
Esophageal arteries, 163.
Esophagus, function of, 137.

muscular fibers of, 60.

structure of, 221.
Ether, 101, 102.
Ethmoid bone, 40.
Eustachian tube, 127.
Excretion, function of, 201, 238.

influence of alcohol on. 264, 265.

organs of, 82, 257-2(55.
Exercise, value of, 74-77.
Exoskeleton, 37.
Expiration, 184, 185.

center of, 199.
Eye, 101-125.

as optical instrument, 112, 113, 121
122.

care of, 119, 120.

coats of, 105, 106.

defects of vision, 116-118.

dissection of, 120, 121.

duration of sight sensation, 116.

fatigue of retina, 116.

foreign bodies in, 351, 352.

muscles of, 110, 111.

parts of, 105-109.

structure of, 103-105.
Eyeball, 104, 105.
Eyebrows, 112.
Eyelids, 60, 111.

Facial nerve, 291.

Facial skeleton, 40.

Faeces, 236.

Fainting, relief for, 178, 352.

Farsightedness, 124.

Fatigue, auditory, 134, 135.

of muscle, 64, 80.

of nerve cells, 317.

of retina, 116, 125.

of smell, 98, 100.
Fats, 203, 205, 215, 232.

Fatty degeneration, 248. 265.
Femoral artery, 163.
Femur, 46.
Fenestra ovalis, 127.
Fenestra rotunda, 127.
Fermentation, of organic tissue, 243.

vinous, 243, 244.
Ferments, action of, 230-232, 234,

fibrin, 150.
Fibers, muscle, 60, 61, 66.

nerve, see nerves.
Fibrin, 150, 152, 205.
Fibrin ferment, 150.
Fibrinogen, 150.
Fibrocartilage, 24, 43.
Fibrous tissue, 24.
Pibula, 46.
Filiform papilla?, 95.
Fingers, bones in, 46.
Fissures of cerebrum, 285, 266.
Flavors, 96.
Floating ribs, 45.
Focus of rays of light, 103.
Follicles, hair, 83, 258.
Food, 201-217.

alcohol as, 245.

classification of, 204.

cooking of, 209-213.

defined, 201.

effect of gastric juice on, 231,

for children, 53, 54, 240.

mastication of, 241.

necessity for, 147.

nitrogenous, 205, 208.

nonnitrogenous, 205, 208.

pure, 364.

quantity of, 242, 243.

undigested, 209.

values of, 207, 208.

variety in diet, 208, 209, 242.
Food accessories, 204, 206.
Food elements, 203-206.
Foramen magnum, 40, 279.
Foramen of Munro, 295.
Forces, correlation of, 203.
Fornix, 295.

Framework of body, see skeleton.
Frontal bone, 39.
Frontal lobe at cerebrum , 285.
Frost bites, treatment of, 350.
Fungiform papillae, 95.

400

INDEX

Gall bladder, 234.
Ganglia, basal, 287.

composition of, 32.

defined, 275, 278.

of sympathetic nervous system, 30,
292-295.

spinal, 29.
Ganglionic nervous system, 27, 30, 275,

292-295, 304, 305.
Garbage, disposal of, 366, 367.
Gastric artery, 163.
Gastric juice, 230, 252, 264.
General or systemic circulation, 160-

164.

Germs, see bacteria.
Glands, ductless, 254-256.

lachrymal, 112.

lymphatic, 169, 170.

of olfactory membrane, 97.

oil, 85.

salivary, 228, 229.

sebaceous, 258.

structure of, 227, 228.

sweat, 85, 95, 258.

wax, 127.
Globulin, 205.
Glomeruli, 260.

Glossopharyngeal nerve, 95, 221), 291.
Glottis, 137, 138.
Glucose, 235.
Gluten, 205, 216.
Glycerin, 232.
Glycogen, 234.
Goiter, 255.
Gray nervous matter, 30, 32, 275 ; see

nervous system.
Gristle, see cartilage.

Habit, 302, 321-324.

Hair, as organ of touch, 92.

function of, 84.

structure of, 83.
Hair cells of ear, 131.
Hair follicles, 83, 258.
Hammer bone, 40, 127.
Hand, bones of, 46.
Hard palate, 40.
Haversian canals, 25, 52.
Hearing, sense of, 126-135.
Heart, action of, in circulation, 166,
167.

Heart, dissection of, 173.

effects of stimulants on, 171, 172,

muscles of, 60.

nerves of, 176-178.

sounds of, 167.

structure of, 153-158.
Heat, of body, 266-272.

sensation of, 88, 93.
Hemoglobin, 148, 188.
Hepatic artery, 163, 164.
Hepatic cells, 233.
Hepatic veins, 165.
Heredity, 324-327.
Hinge joint, 50.
Hip bone, 46.
Hippocampus, 295.
Horns, anterior and posterior, of spinal

cord, 280.
Humerus,46.
Humor, aqueous, 110.

vitreous, 108, 110.
Hunger, sensation of, 86, 238, 239.
Hyaline cartilage, 24.
Hydrochloric acid, 230, 264.
Hydrogen in food, 201, 204, 205.
Hygiene, 7.

of bones and joints, 53-56.

of circulation, 171.

of clothing, 268-271.

of digestion, 239-243.

of ear, 134.

of exercise, 74-77.

of eye, 119, 120.

of food, 207-213.

of muscles, 73-76.

of nervous system, 314-334.

of respiration, 192, 193.

of vocal apparatus, 143, 144.

public, 360-367.
Hyoid bone, 40, 137.
Hypogastric plexus, 223.
Hypoglossal nerve, 292.
Hysterics, treatment for, 353.

Ileocsecal valve, 226.
Iliac arteries, 162, 163.
Images, formed by lenses, 103.

inverted, in eye, 114, 121.
Immunes, 339.
Incisors, 218.
Incus, 40, 127.

INDEX

401

Inhibitory nerves, 178, 299.

Innominate artery, 162.

Insomnia, 319.

Inspiration, 184, 185, 200.

Instability of protoplasm, 12, 16, 18.

Insula, 285, 286.

Intercellular substance, 23, 24, 48.

Intercostal arteries, 163.

Intestinal juice, 235.

Intestines, action of alcohol on, 247.

large, 226, 235, 236.

peristaltic movement of, 235.

small, 223, 224, 231, 235.
Intracentral nerves, 299.
Intrinsic nerves, of heart, 177.
Invertebrates, exoskeleton of, 37.
Inverted images, 114, 121.
Involuntary muscles, 60, 66, 67, 80, 81,

158.

Iris, 106, 107, 114.

Irritability of protoplasm, 12, 14, 16,
18.

of tissues, 21.
Irritant poisons, 354, 355.
Island of Reil, 285, 286.

Jaw bones, 40.

Joint, function of, 49, 50,

injuries to, 55, 56.

study of, 57.
Jugular vein, 169.

Katabolism, 202, 263.
Kidneys, 257, 260-265.
Kneepan, 46.

Labyrinth of ear, 127-131.
Lachrymal bones, 40.
Lachrymal gland, 112.
Lacteals, 151, 153, 170, 226, 237.
Lacunas, 25, 53.
Lamellae, 52.

Larynx, nervous mechanism of, 141,
142.

structure of, 136, 137.

study of, 144.
Lens, crystalline, 109, 113, 114.

image formed by, 103.
Levers, in human body, 67-69.
Ligaments, function of, 38, 48.

study of, 81.

Ligament, transverse, 44.
Limbs, bones of, 46, 47.
Liver, 232-234.

blood circulation in, 164, 165.

effects of alcohol on, 248.
Lobes of cerebrum, 96, 285.
Lobes, optic, 28, 284, 287, 307, 308.
Locomotion, organs of, 59.
Longsightedness, 117.
Lumbar vertebrae, 41.
Lungs, capacity of, 186.

excretory organs, 257.

structure of, 184.

see respiration.
Lymph, circulation of, 169.

function of, 23, 151.
Lymph capillaries, 169.
Lymph vascular system, 153.
Lymphatic duct, 170.
Lymphatic glands, 170.
Lymphatic vessels, 151, 153, 237.

Malar bones, 40.
Malleus, 40, 127.
Marrow, red, 52, 148.

yellow, 51.
Master tissues, 21.
Mastication, 218, 241.
Matter, intercellular, 23, 24, 48.

living and lifeless, 9.

nervous, 30, 32, 275; see nervous

system.

Maxillary bones, 40.
Meatus, external, 126.
Medulla oblongata, 28, 285.

reflex center, 301,306.

structure of, 288, 289.
Medullary cavity, 51.
Medullary portion of kidneys, 260.
Medullary sheath, 32, 33, 277.
Medullated nerve fiber, 33.
Membrane, mucous, see mucous mem-
brane.

Membranes, of brain and spinal cord,
283.

of tympanum, 126, 127.

synovial, 50.

Membranous labyrinth, 128.
Memory, 310.
Meninges, 284.
Mesenteric arteries, 163.

402

INDEX

Mesentery, 224.
Metabolism, 202.
Metacarpus, 46.
Metatarsals, 46.
Microbes, see bacteria.
Milk, as food, 203, 204, 216.
Milk teeth, 218.
Mitral valves, 157.
Molars, 219.
Molecule, 9, 10.
Motion, in animals, 38.

of bones, 49.

organs of, 59.

production of, 30, 35, 44.
Motor areas, 311, 312.
Motor cells, 72.
Motor center, 141.
Motor nerves, 28, 30, 86, 299.
Mouth, 218.
Movement, mechanism of, 67-69.

of involuntary muscles, 66, 67.

reflex, 72, 73.

voluntary, 71, 72.
Mucous membrane, of ear, 127.

of eye, 106.

of nose, 96, 97, 337.

of small intestine, 224.

of stomach, 221.

of tongue, 94.

of trachea, 183.

structure of, 84.
Mucus, 84.
Muscle waste, 71.
Muscles, cardiac, 158.

changes under stimulus, 63, 64.

classification, 60.

composition of, 59.

contraction of, (52-65.

coordination of muscular move-
ments, 69, 70, 133, 306, 307.

dead, 65, 66.

effects of stimulants on, 78.

fatigue of, 70.

function of, 37, 38.

hygiene of, 73, 76.

involuntary, 60, 66, 67, 81.

nerve endings in, 61.

nerves causing contraction of, 28.

nervous stimulus of, 21.

of blood vessels, 179.

of frog, 17, 18.

Muscles, papillary, 157.

plain, see involuntary.

properties of protoplasm in, 17, 18.

proteids in, 217.

reflex and automatic movements,
71-73.

relaxation, 65, 80.

skeletal, see voluntary.

study of, 79-81.

voluntary, 60, 61, 72, 73, 81.
Muscular fiber, of intestines, 224.

of stomach, 221, 222.

plain or unstriped, 60, 66, 81,

striated or striped, 60, 63, 81, 158.
Muscular movement, coordination of,

69, 70, 133, 306, 307.
Muscular power, 64, 05.
Muscular sense, 73, 86, 88, 89, 93.
Muscular system, 59-81.
Muscular tissues, 20, 21.
Musical sounds, 140.
Myosin, 205, 217.
Myosinogen, 217.

Nails, function of, 84.

structure of, 84.
Narcotics, effects of, 79, 332, 354; see

alcohol, tobacco.
Nasal bones, 40.
Nearsightedness, 123.
Nerve cells, fatigue of, 32, 275, 317.
Nerve center, 30, 239, 275, 300.
Nerve endings, in muscle, 80.
Nerve fiber, 30, 32-34, 276, 277.
Nerves, afferent, 30, 86, 298.

cerebral, see cranial.

controlling circulation, 176-180.

controlling heat production, 268.

controlling respiratory apparatus.
198-200.

controlling sweat glands, 258, 259.

cranial, 28, 289-295; 40, 95, 96, lo:;t
104, 106, 108, 111, 112, 128, 130,
141, 142, 176-178, 229, 232.

efferent, 30, 86, 298, 299.

end organs of, 61, 292.

for muscle, 61.

function of, 298.

motor, 28, 30, 86, 298, 299.

of blood vessels, 179.

of general sensibility, 298.

INDEX

403

Nerves, of heart, 176, 177.

of skin, 87.

of small intestines, 224.

of stomach, 223.

plexuses, 30, 66, 87, 223, 224, 261,
283, 295.

respiratory, 198.

sensory, 28, 30, 86, 298.

spinal, 29, 72, 86, 87, 281-283.

structure of, 277, 278.
Nervous discharge, 299.
Nervous disorders, 314, 316, 320, 321,

325-327.

Nervous elements, 275.
Nervous impulse, passage of, 22, 279.
Nervous operations, conscious, 35-145.

unconscious, 145-272.
Nervous prostration, 316.
Nervous system, anatomical descrip-
tion, 275-296.

cerebro-spinal or central, 27-30, 275,
278, 305-313.

controls muscular action, 70.

functions of, 22, 27, 35, 77, 297-313.

habit as connected with, 302, 321-
324.

hygiene of, 314-334.

influence of alcohol on, 325-332.

nutrition of, 314-317.

sympathetic or ganglionic, 27, 30,
275, 292-295, 304, 305.

vasomotor, 179, 180.
Nervous tissues, 20, 21, 30, 32, 275.
Nervousness, 314.
Neural arch, of vertebra, 42.
Neural ring, of vertebra, 42.
Neuraxon, 276, 278.
Neurilemma, 32, 33, 61, 277, 278.
Neuroglia, 278.
Nicotine, effects of, 332.
Nitrogen, in air, 187.

in food, 201, 204-208, 261.
Nodes, 33.
Noise, 141.

Nonmedullated nerve fibers, 33, 277.
Nonnitrogenous food, 205, 208.
Normal salt solution, 17.
Nose, bleeding of, 346, 347.

foreign bodies in, 352.
Nucleus of cell, 11.
Nutrition, 236-253.

Nutrition, defined, 201, 202.
function of, 11, 12.
how effected, 145.
of nervous system, 314-317.
organs for, 59.

Oblique muscles, 110, 111.

Occipital bone, 40.

Occipital lobe, 285.

Occipito-parietal fissure, 286.

Oculomotor nerve, 104, 290.

Odontoid process, 44.

Odors, 97.

Oil glands, 85.

Olfactory bulbs, 96, 286, 287.

Olfactory lobes, 96.

Olfactory nerves, 40, 9(5-98, 290.

Olfactory tract, 286.

Omeutum, great, 221.

Opium, effects of, 332.

Optic chiasma, 104.

Optic commissure, 104.

Optic lobes, 28, 284, 287, 307, 308.

Optic nerve, 103-106, 108, 290.

Optic thalami, 28, 284, 287, 308.

Optic tract, 105.

Orbit of eye, 105.

Organic matter, decomposition of, 243.

Organism, defined, 20.

Organs, defined, 20.

of Corti, 130, 131.

tissues forming, 20.
Os innominatum, 46.
Osmosis, 160, 175.
Ossicles, auditory, 127.
Ossification, process of, 26.
Otoliths, 132.
Oval window, of ear, 127.
Overwork, 320, 321.
Oxidation, 205-209, 227, 257, 267.
Oxygen, 147, 149, 201-209, 227, 257, 267 ;

see respiration.
Oxy hemoglobin, 188.

Pacinian corpuscles, 87.
Pain, sensation of, 86, 89, 90.
Palate, hard, 40, 218.

soft, 218.
Palate bones, 40.
Palmar arch, 162, 164.
Pancreas, 231.

404

INDEX

Pancreatic juice, 231, 237, 253.
Papillse, of hair, 83.

of mouth, 218.

of palate, 94.

of skin, 85.

of tongue, 94, 95.
Papillary muscles, 157.
Parietal bones, 39.
Parietal lobe, 285.
Parotid glands, 228.
Patella, 46.

Pectoral girdle, 37, 45, 46.
Peduncles, of cerebellum, 287, 296.

of cerebrum, 28, 287, 307.
Pelvic arch, 41.
Pelvic girdle, 37, 45, 46.
.Pepsin, 230.
Perception, 91, 310.
Pericardial arteries, 163.
Pericardium, 153.
Perimysium, 59.
Perineurium, 278.
Periosteum, 51, 52, 220.
Peristaltic movement, 66, 67, 223, 235,

302.

Peritoneum, 221, 224.
Permanent cartilage, 48.
Peroneal artery, 163.
Perspiration, 258, 259.
Phalanges, 46.
Pharynx, function of, 220, 221.

muscular fibers of, 60.

position of, 137.
Phrenic artery, 163.
Phrenic nerve, 198.
Physiology, 7.
Pia mater, 283.
Pigment, of eye, 106, 107.

of skin, 83, 84.
Pinna, 126.
Pitch, 141.
Pivot joint, 50.
Plain muscle, 60, 66, 67, 81.
Plants, cells of, 11.

distinguished from animals, 13, 14.

movements of protoplasm in, 17.

proteids manufactured by, 204.
Plasma, 26, 148, 338.
Pleura, 184.
Plexus, epigastric, 223, 295.

function of, 87, 283.

Plexus, hypogastric, 223.

of plain muscle fiber, 66.

of sympathetic system, 30.

renal, 261.

solar, 223, 295.
Pneumogastric nerve, 141, 176, 239,

292.
Poisons, and their antidotes, 353, 359.

in system, 263, 264.
Pons Varolii, 28, 284, 288, 306.
Popliteal artery, 163.
Portal circulation, 160, 164, 165.
Portal vein, 164, 165.
Premolars, 219.
Pressure sense, 93.
Primitive sheath, 61.
Process, axis cylinder, 32.

of nerve cells, 32, 275, 276.

spinous, 42.
Proteids, 203-205.

absorption of, 236.

action of gastric juice on, 230, 231.

action of pancreatic juice on, 231,
232.

defined, 11.

tests for, 214.
Protoplasm, defined, 10, 11.

in muscle, 17, 18.

in plants, 17.

properties of, 12, 14, 16, 18.
Pseudopodia, 16.
Ptyalin, 229, 230.
Pulmonary artery, 156, 164, 184.
Pulmonary circulation, 160, 164.
Pulmonary veins, 155, 164.
Pulse, 166.

Pupil of eye, 106, 107.
Putrefaction, 243.
Pylorus, 222.
Pyramids, in kidneys, 260.

in medulla oblongata, 288.

Radial artery, 162.

Radiant energy, 102.

Radius, 46, 50.

Rectum-, 226.

Rectus muscles, 110.

Red blood corpuscles, 26, 148-151, 188.

Reflex action, 72, 73, 178, 200, 300-304.

Refraction, 102, 103, 121.

Relaxation of muscles, 65, 80.

INDEX

405

Renal artery, 163.
Renal plexus, 261.
Kennet, 230, 252.
Rennin, 230, 253.
Reproduction, 12.
Resonating cavities, 139.
Respiration, 181-200.

artificial, 348, 349.

effects of alcohol and tobacco on,
194.

muscular action in, 60, 185, 186.

organs of, 181, 194, 195.
Respiratory apparatus, nervous control

of, 198-200.
Retina, 103, 106-108.

fatigue of, 116, 125.
Rhythmic movements of involuntary

muscles, 66, 67.

Ribs, action in respiration, 43, 185, 186,
195, 196.

attachment to spinal column, 41.

floating, 45.

structure of, 44, 45.
Rickets, 54.
Rigor mortis, 65, 80.
Rods and cones of eye, 104, 108.
Rods of Corti, 130, 131.
Round window, of ear, 127.

Saccule, 128.

Sacral arteries, 162.

Sacrum, 41.

Saint Vitus's dance, causes of, 77.

Saliva, action of, 229.

destroys bacteria, 337.

study of, 251, 252.
Salivary glands, 228, 229, 241.
Salts, as food elements, 203, 206, 261.

in gastric juice, 230.

skin excretes, 257, 258.
Sanitation, general, 360-367.
Santorini, cartilages of, 137.
Saponification, 232, 237.
Sarcolemma, 59, 61.
Scala tympani, 129.
Scala vestibuli, 129.
Scalds, treatment for, 349.
Scapula, 45.

Sclerotic coat of eye, 106.
Sea anemone, rudiments of nerve sys-
tem in, 14.

Sebaceous glands, 258.
Secreting cells, 292.
Secretion, 227-235.
Secretory nerves, 299.
Self-control, 303.
Semicircular canals, 128, 133.
Semilunar valves, 157, 159.
Sensation, conditions essential for, 85.

general, 85.

production of, 35.
Sense, muscular, 73, 86, 88, 89.

of hearing, 14, 86, 126-135.

of sight, 14, 86, 101-125.

of smell, 14, 86, 96-99.

of taste, 14, 86, 94-96.

of touch, 14, 86-91.
Sensory areas, 312.
Sensory nerves, 28, 30, 86, 298.
Serrated sutures, 49.
Serum, 150.
Serum albumin, 217.
Sewage, disposal of, 366, 367.
Sheath, primitive, 61.

medullary, 32, 33, 277.
Shortsightedness, 117.
Shoulder blade, 45.
Sight sensation, duration of, 116, 125
Sight, sense of, 14, 86, 101-125.
Sinus, 265.

Skeletal muscles, 60, 61, 72, 73, 81.
Skeleton, 38-57.

appendicular, 45-48.

axial, 47.

facial, 40.

study of, 56, 57.
Skin, function of, 82, 257-259.

organ of touch, 86.

regulator of heat loss, 267.

relation to kidneys, 262.

structure of, 82, 258.

study of, 91, 92.
Skull, parts of, 39, 49.
Sleep, 317-320.
Smell, area for, 313.

combination with taste, 100.

sense of, 14, 86, 96-99.
Sniffing, 97.
Solar plexus, 223, 295.
Sound, conduction of, 40.

direction of, 133-135.

production of, 139.

406

INDEX

Spectrum, 102.
Speech, 141. 312.
Sphenoid bone, 40.
Sphincter muscle, 223.
Spinal accessory nerve, 176, 177, 292.
Spinal bulb, see medulla oblonydta.
Spinal column, 40-44.
Spinal cord, center reflex action, 73,
302, 303.

function of, 300.

membranes of, 283.

nerve center, 275.

structure of, 29, 32, 279, 280.

study of, 34.
Spinal ganglion, 29, 282.
Spinal nerves, 29, 72, 86, 87, 281-283.
Spinous process, 42.
Spleen, 149, 254, 255.
Splenic artery, 163, 254.
Splenic vein, 255.
Sprain, treatment of, 56.
Squamous epithelium, 91.
Squinting, causes of, 117, 118.
Stammering, causes of, 141.
Stapes, 40, 127.
Starch, 205, 214.
Sterilizing, 340.
Sternum, 44, 45.
Stimulus, in plants and animals, 14.

nervous, 21.

of muscle, 21, 62-64.

results of, 309, 310.
Stirrup bone, 40, 127.
Stomach, absorbents in, 236.

action of alcohol in, 247.

action of gastric juice in, 230, 231.

structure of, 221-223.
Striped (striated) muscle fibers, 60,

63,81,158.
Stroma, 148.
Subclavian arteries, 162.
Snblingual glands, 228.
Submaxillary glands, 228.
Suffocation, treatment for, 347.
Sugar, 205.

conversion of starch into, 229, 232.

liver stores up, 234.

test for, LM5.

Sunstroke, treatment for, 350, 351.
Suprarenal capsules, 256.
Suspensory ligament, 109.

Sutures, 37, 49.
Sweat, 258, 259.
Sweat glands, 85, 92', 258.
Sylvian fissure, 280.
Sympathetic nervous system, compo-
sition of, 30, 292-29.">.

functions of, 27, 304, 305.

nerves from, 278.

study of, 34.
Synovial fluid, 56.
Synovial membrane, 50.
System, 20.
Systemic circulation, 160-164.

Tactile end organs, 87, 88.
Tactile sensations, area for, 313.
Tarsal bones, 46.
Taste, area for, 313.

combination with smell, 100.

sense of, 14, 86, 94-96.
Taste buds, 95, 96.
Taste cells, 95.
Taste corpuscles, 218.
Tear ducts, 40.
Tears, formation of, 112.
Teeth, 218-220.

care of, 240, 241.

enamel of, 239, 240.
Temperature, of air for breathing, 193,
194.

of body, 82, 266-268.

sensation of, 86, 93.
Temporal bones, 39.
Temporal lobe, 285.
Tendinous cords, 157.
Tendons, function of, 48.

study of, 81.
Tetanus, 63.
Thermic fever, 350, 351.
Thigh bone, 46.
Thirst, sensation of, 86, 238.
Thoracic duct, 169, 237.
Thoracic vertebrae, 41.
Thorax, arteries in, 162, 163.

contraction of muscles of, 45, 185.

in breathing, 184, 185.
Thymus gland, ii.">(».
Thyroid cartilage, 136, 137.
Thyroid gland, 255, 256.
Tibia, 4(5.
Tibial artery, 163.

INDEX

407

Tissue-forming foods, 204.
Tissues, classification of, 20-26.

connective, 48.

differentiation of, 19, 20.

nervous, 275.

organic, 243.
Tobacco, diseases from use of, 332.

effects on blood circulation, 172.

effects on growth, 54.

effects on muscular actions, 79.

effects on respiration, 194.

effects on vocal organs, 144.
Toes, bones of, 46.
Tongue, function of, 218.

structure of, 94, 95.

study of, 99.
Tonsils, 220.
Touch, Aristotle's experiment for, 92.

discrimination in, 88, 92.

path of touch impression, 90, 91.

sense of, 14, 82, 86-91.
Touch corpuscles, 87, 88.
Toxins, 337, 338.
Trachea, 182.
Transverse ligament, 44.
Transverse processes, 42.
" Tree of life," cerebellum called,

288.

Triceps muscle, 65.
Tricuspid valves, 156, 157.
Trigeminal nerve, 95, 104, 112, 291.
Trochlear nerve, 291.
Trommer's test for sugar, 215.
Trophic nerves, 299.
Trunk of body, 37.
Trypsin, 253, note 1.
Tuberculin, 340.
Tuberculosis, 339-341.
Turbinate bones, 40.
Tympanic passage, 129.
Tympanum, 126, 127.

Ulna, 46, 50.

Ulnar artery, 162.

Unconscious nervous operations, 145-

272.

Undigested food, 209.
Urea, 207, 234, 257, 261, 262.
Ureter, 260.
Urine, 260.
Utricle, 128.

Vaccination, 339.
Vagus nerve, 141, 176, 239, 292.
Valve, ileocaecal, 226.
Valves, in veins, 159, 174.

of heart, 156, 157, 159, 166, 167.

of lympathic vessels, 237.
Valvulae conniventes, 224, 225.
Vascular system, 153.
Vasoconstrictor nerves, 179, 304.
Vasodilator nerves, 179, 304.
Vasomotor nervous system, 179, 180.
Veins, continuous blood flow in, 168.

function of, 153.

in portal circulation, 164, 165.

injury to, 168,345,346.

muscular action of, 179.

principal, 164.

pulmonary, 155, 164.

splenic, 255.

structure of, 159.

valves in, 174.

Vena cava, 154, 155, 164, 169.
Venous blood, 188. 197.
Ventilation, 190-192.
Ventricles, of brain, 289.

of heart, 154, 156, 157.

of throat, 138.
Vermiform appendix, 226.
Vertebrae, 41-44.
Vertebral column, 40-44.
Vertebrate skeleton, 37-48.
Vestibular passage, 129.
Vestibule of ear, 128, 133.
Villi, 225.
Vision, area for, 313.

binocular, 124.

defects of, 116-118.

defined, 101.

nervous apparatus for, 103, 104.
Visual center, 103.
Vital knot, 305.
Vital processes, 145.
Vitreous humor, 108, 110.
Vivisection, 15.
Vocal apparatus, 136-145.
Vocal cords, 137, 138.
Vocalization, 139.
Voice, care of, 143, 144.
Volition, 310.
Voluntary action, 300-303.
Voluntary movement, 71, 72.

408

INDEX

Voluntary muscles, 60, 61, 63, 80, 81.
Vomer, 40.

Waste products, 71, 82, 181, 190, 207,

261 ; see excretion.
Water, excreted by the kidneys, 257,

261.

excreted by the skin, 257-259.
in gastric juice, 230.
necessity for pure, 364-366.
uses in nutrition, 206.
Wax glands, 127.
Weisberg, cartilages of, 137.
Whispering, 139.
White blood corpuscles, described, 149,

151.
function of, 338.

White blood corpuscles, in lymphatic
system, 169-171.

properties of, 12.

spleen manufactures, 255.

study of, 16.
White fibrous tissue, 24.
White light, production of, 102.
White nervous matter, 30, 32, 275 ; sec

nervous system.

White substance of Schwann, 277.
Wisdom teeth, 219.
Work, healthfulness of, 76.
Wounds, surface, 344.
Wrist, bones of, 46.

Yeast, 243-245.
Yellow spot of eye, 109.

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