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PHYS

HYGIENE

CONN

AMD

BUDIMGTOH

SILVER, BURDETT ^ COMI'^AOT

MEMCAL SCHOOL

>ard of
student

Digitized by the Internet Archive

in 2007 with funding from

IVIicrosoft Corporation

http://www.archive.org/details/advancedphysioloOOconnrich

ADVANCED PHYSIOLOGY
AND HYGIENE

FOR USE IN SECONDARY SCHOOLS

, t-?

HERBERT W.OCONN, Ph.D.,

FORMERLY PROFESSOR OF BIOLOGY IN WESLEYAN UNIVERSITY
AND

ROBERT A. BUDINGTON, A.M.,

PROFESSOR OF ZOOLOGY IN ©BERLIN COLLEGE

REVISED EDITION

SILVER, BURDETT AND COMPANY

BOSTON NEW YORK CHICAGO SAN FRANCISCO

THE CONN SERIES OF PHYSIOLOGIES

By H. W. Conn, Ph.D.
Formerly Professor of Biology, Wesleyan University

Physiology and Health, Book One
For Lower Grammar Grades
224 pages Illustrated

Physiology and Health, Book Two
For Upper Grammar Grades
384 pages Illustrated

Physiology and Health, One Book Course

448 pages Illustrated

Advanced Physiology and Hygiene

By II. W. CcNN AND R. A. Budington

For Secondary Schools

41 g Pages Illustrated

Advanced Physiology and Hygiene. Revised Edition
436 pages Illustrated

• • • «• 1

• • • •

a • • •

• • •• • • • '

■ • • • • • r t

••• • • » f

PREFACE

When the science of physiology was first introduced into
schools the texts offered for study treated largely of anat-
omy. As the subject developed and expanded it was
recognized that the study of anatomy should be made sub-
ordinate to that of function, and the text-books came to give
to function a place predominant over structure. Further ex-
perience emphasized the fact that the primary utility of the
study of physiology in schools consists in its bearing upon
health, and matters of personal hygiene came to occupy a
more and more prominent place. Still more recently problems
of public hygiene and general health have forced them-
selves to the front, and have been demonstrated to be an
important part of a person's education. With this broad-
ening scope and all these new aspects of life and health to
be considered, many phases of the subject of physiology
proper, themselves of scientific interest and importance,
have inevitably been given less and less attentioHf^ while the
more practical topics have been accorded fitting precedence.

Although perhaps no two teachers would agree as to the
relative importance of any specific topic, certain it is, how-
ever, that without some knowledge of anatomy, physiological
facts seem isolated and without foundation; while rules bear-
ing on hygiene, taken alone, are learned by the student mere-
ly as barren rules without any persuasive reason for them.
In this book the emphasis placed upon different subjects is
that which has seemed to the writers to be a close approxi-
mation to their relative importance in the present state
of the sciences of physiology and hygiene.

This book has one new feature which the authors feel

4 PREFACE

confident will commend it to physicians, health officers and
public spirited citizens generally. In connection with the
different systems of organs, the nature and causes of com-
mon diseases are discussed in simple terms with such sug-
gestions about the prevention of disease as may help ,to
make the high school student more intelligent in regard
to his own health and the health of the community.

In the treatment of the problems of the physiological effects
of alcohol it is assumed that students using this book are of
an age to appreciate that some of the many problems con-
nected with the use of this drug are still unsettled. Hence,
while some aspects of this subject have been introduced with-
out anticipating any final conclusion, the attempt is made
to point out the most important of the evil effects resulting
from the use of this drug.

The revised edition contains numerous additions to the
text embodying the results of the most recent scientific investi-
gations. Especial attention has been given the newer con-
ceptions of proteid digestion, carbon dioxid in respiration,
vitamines, the role of certain hormones, and the etiology of
numerous diseases. Since the last few years have offered
more convincing proof than ever before of the vital relation
between hygiene and health, sanitation and safety, especial
care has been taken to rewrite and to expand the chapter on
public control of health. The number of laboratory exercises
and demonstrations has been materially increased. These
have been assembled in a separate section and placed in the
back of the book with page reference to the portion of text
to which each applies.

Robert A. Budington.

CONTENTS

CHAPTER PAGE

I. The Living Material of the Body . . 9

Organs and Tissues. Microscopic Anatomy. Uni-
cellular and Multicellular Animals.

II. Chemical Composition of the Body . . 25

Elements. The Chief Chemical Compounds in the
Body, Metabolism.

III. Foods and Food Habits . . .37

Food Habits. The Value of Different Foods. Diet.
The Amount of Food Needed. Vegetarianism. In-
cidental Articles of Food. Cooking.

IV. Fermentation and Germ Diseases . . 62

Types of Fermentation. Yeasts. Bacteria. Im-
munity. Sterilization and Disinfection.

V. Digestion of Food — The Mouth and Throat 74
The Mouth. Digestion in the Mouth. The Throat.
Diseases of the Mouth and Throat.

VI. Digestion of Food — The Oesophagus and

Stomach ....... 88

The Oesophagus. Body Cavity and Sub-Divisions.
The Stomach. Composition and Action of the Gas-
tric Juice.

VII. Digestion of Food — The Intestine . . 98

The Small Intestine and Organs Connected with It.
The Large Intestine. Digestion of Different Foods.
Alcohol and Indigestion. Diseases of the Intestinal
Tract.

VIII. The Absorption of Foods . . .111

Structures Concerned in Absorption. Osmosis.
Changes in Food after Absorption. The Path
taken by the Absorbed Carbohydrates and Pro-
teids. Path taken by the Fats. Summary of
Digestion and Absorption.

PHYSIOLOGY AND HEALTH

CHAPTER I

THE LIVING MATERIAL OF THE BODY

''Know thyself" was a motto of the ancient Greeks. Wise
as such advice was in their day, it is far more necessary in
these modern times of complex civilization. The Greeks
knew less than we of the activities of the body organs, but
they needed such knowledge less because their mode of living
was simpler. Their lives were passed largely out of doors,
never in close houses; their food was plain, but nourishing
and abundant; their bodies were vigorous and active
because they exercised all their muscles.

But to-day people are so crowded into cities that there
is little time or opportunity for physical exercise and there is
every facility for the distribution of contagious diseases.
We shut ourselves up in close houses, thus depriving ourselves
of needed air; we use trolleys, carriages, automobiles, tel-
ephones and mails to save the time and trouble of walking,
we eat an endless variety of good and bad foods, variously
prepared and often adulterated; we live in the midst of
more or less constant and intense activity. Brain work
takes the place of muscle work with part of the race while
another part uses the brain very little.

Amid all these complexities the problem of retaining health
and vigor is increasingly difficult. In our crowded cities
people are living under unnatural conditions, and serious

10 ADVANCED PHYSIOLOGY

questions are constantly arising as to the proper means for
preserving health. Even country life is ceasing to be the
simple, natural life that it was once, and the smaller com-
munities are facing many of the problems of the large
cities. With each succeeding year we realize more fully the
need of understanding the laws of life in order to maintain
both individual and public health. All this makes a con-
stantly increasing demand for the study of those subjects
which teach us how to keep our bodies and minds in a
state of highest efficiency; and the study of physiology and
hygiene has come to be recognized as one of the necessities
of education.

Normal and Experimental Physiology. — Physiology is the
science of the activities of living things. It may refer to the
activities of animals or plants, of the whole animal or its
parts, of the whole plant or its parts, or even of whole
groups of animals or plants. If observations are made
upon animals under healthy, normal conditions, while they
are acting under their own ordinary impulses, the study
is called normal physiology. Sometimes, however, an animal
or a plant or parts of either may purposely be put under
unnatural conditions and the result noted. We may change
the food supply, the temperature or moisture of the sub-
stance in which it lives, we may try the effects upon it of
drugs and poisons, or we may artificially stimulate it to
action. In these cases the study is termed experimental
physiology.

The term physiology, as commonly understood, refers
to the study of the activities or functions of the different
parts of the human body under normal conditions. Although
thus primarily a study of activities, some attention must
also be paid to structure; for if one is to understand
thoroughly the working of any machine, he must know the
form and position of its parts. The study of the structure
of the body is called anatomy. Anatomy and physiology

THE LIVING MATERIAL OF THE BODY

are thus distinct subjects, yet so closely related that they
will be considered separately.

ORGANS AND TISSUES

There are several familiar fundamental facts concerning
living things; everyone knows that the commoner animals
feed, breathe, feel, give off waste material, have blood
circulating through their bodies and show many other points
of similarity. It may, however, surprise some people to learn
that these same functions are carried on in
plants, for they, too, must feed, breathe, give off
waste and have some kind of circulatory system,
although, to be sure, these life processes occur
differently in animals and plants. An organism
is anything which carries out the functions of
life.

Certain very important differences exist be-
tween the lower (i.e. microscopic) organisms and
the higher ones. In many of the lower types
of animal and plant Ufe all parts of the body
may perform the same office, e. g. of loco-
motion, sensation or feeding; but it is apparent
to anyone that different parts of the human
body — such as heart, stomach, brain or eye, per-
form each its own work or function ; and each is
therefore called an organ. An organ may be
defined as a part of the body which has one special
kind of work to do. This work as a rule contri-
butes to the sustaining of every other part of the
organism. The whole body, then, may be pictured as com-
posed of many separate and distinct organs, each cooperat-
ing with the other and thus constituting one organism.
Even the microscopic animals, hke those in Figure 1, have
some very simple organs, as for instance, the nucleus shown
at N,

FiQ. 1.— Hy-

ALODISCUS
LIMAX

A microscopic
animal resem-
bling amoeba,
which lives in
fresh water.
All parts of
the body are
nearly alike
and perform
the same
functions. A^
is the nucleus.

ADVANCED t>HYSIOLOGY

Muscle

This study of the parts of Hve organisms may be carried
still further; and just as the stairway, or the elevator, or the
windows of a house are not made entirely of wood, or of iron,
or of glass, so also the human body is not composed through-
out of the same kind of material. The nose, for example, is
covered with skin; is lined with a smooth, moist membrane;
contains a supporting framework, partly of
soft cartilage, partly of bone; blood vessels
are present in it; nerves make it sensitive to
odors and to touch; hairs are provided for
straining the air as one breathes; muscles
permit shght movements. Such parts as
these composing an organ are commoidy
called tissues. A tissue is a single kind of
living material with the 'power of doing a
single kind of work. Generally, several dif-
ferent kinds of tissue occur in the structure
of a single organ. The hand, for example,
contains bone tissue, muscle tissue, nerve
tissue and blood tissue, besides several
other kinds.

Kinds of Tissues. — The following are the
most important tissues of the human body.
Epithelium, or covering tissue, is a thin
layer covering the outer and inner sur-
faces of the body and of the different organs ; e. g. the
outer layers of the skin and the lining of the mouth and
throat.

Supporting tissues include bone, cartilage and connective
tissues. Bone forms the skeleton. Cartilage is found in many
different regions of the body. It is placed between each two
pieces of the 'back-bone'; it composes the principal part of the
voice-box; it makes the ears and the nose somewhat rigid; it
covers the ends of bones where they come together at moving

Tendon

Fig. 2. — The leg

Showing the bones,
mviscles and tendons
concerned in hfting
the body upon the
toes.

THE LIVING MATERIAL OF THE BODY

joints. Sometimes it connects the bones, e. g. as it joins the
front ends of the ribs to the breast bones. Connective tissue
occurs throughout the whole body, binding together the dif-
ferent parts. A simple kind of connective tissue is seen in
beefsteak, where it appears in fine lines or as thin, glistening
sheets holding together the small cord-like pieces of muscle
tissue. More evident kinds of connective tissue are the liga-
ments and tendons; Fig. 2. Ligaments hold bones together
at joints, as at the knee or the shoulder. Tendons connect
muscles to bones, and may
plainly be felt at the wrist
where they pass from the
muscles in the forearm to
the bones in the fingers;
Fig. 137. It is said that
if all the other materials
of the body were dissolved
away and the connective
tissue left, this tissue is so
abundant that the form of
the body would be per-
fectly retained.

Muscle tissue forms the
flesh and moves the differ-
ent parts of the body.

Gland tissue composes
organs and surfaces which
generally produce some
fluid secretion, hke the saliva in the mouth, the tears in
the eyes or the bile in the liver.

Blood forms the so-called "circulating tissue."

Nerve tissue is the material of which the brain and other
parts of the nervous system are composed.

Fat tissue, while not active, serves to store material for
future use.

Fig. 3. — Epithelial cells

a, flat, scale-like cells from the mouth;

b, from the membranes around the
intestine; c, from the intestine; d, cili-
ated epithelial cells from the wind pipe.

ADVANCED PHYSIOLOGY

A study of the organs and tissues of an organism as seen
with unaided eye is called a study of its macroscopic anatomy.
If a microscope is used, one is said to
be studying its microscopic anatomy.

MICROSCOPIC ANATOMY

After the invention of the micro-
scope by two Dutchmen, Hans and
ZachariasJanssen, about the year 1600,
curiosity gradually led to the examina-
tion of all kinds of animal and plant
substances under high magnification.
Of special interest to us here is a fact
established in 1838-1839, that all tis-
sues in plants and animals are made up of definitely formed
parts or units, somewhat in the manner in which the walls of
brick buildings are made up of separate bricks.

Bloodvessel^^ ^^

Fig. 4.— C a r t i l a gj e

CELLS

Embedded in an abundant

intercellular matrix.

Fig. 5. — The microscopic structure of bone
^, cross section; B, longitudinal section; C, a single young bone celi.

These small units had been seen two hundred years earlier and
at that time were called cells, since it was thought that they were
practically empty pockets. But to Schleiden and Schwann,
who first demonstrated that all tissues are made up of such

THE LIMNG MATERIAL OF THE BODY

Fig. 6, — Connective tissue

A bit of tendon highly magnified.
At C are shown some of the cells
which produced the fibres.

cells, is given the main credit of firmly establishing what has
since been known as the cell theory of tissue structure.

According to some students of the subject, these cells are
connected, each with its neighboring cells, by very tiny, hollow
tubes (''bridges''); but others are equally certain that each cell

acts by itself, save as fluids may
pass out from each cell and be
carried to otha? cells of the body
in tire blood stream.

Kinds of Cells. — The shape of
these cells is difTerent in differ-
ent kinds of tissues, just as bricks
used in the foundations of build-
ings differ from those employed
for fireplaces or ornamental work.
Epithelial cells are thin and disc-like or cylindrical in shape
(Fig. 3 a, 6; c and d) and usually have very little space be-
tween them.

Cartilage cells are round or hemi-
spherical and are usually more widely
separated; Fig. 4. The material be-
tween them, intercellular substance, has
been formed by the cells themselves
and secreted in large quantities, sep-
arating them as mortar does bricks.

Bone cells are close together in very
young bone, but later are separated by
a secretion which they deposit around
themselves. This deposit contains a
mineral matter, calcium phosphate, which
causes the mass to harden. As the bone
develops, this hard mineral matter be-
tween the cells becomes very abundant, and finally, in the fully
formed bone, the cells proper occupy very small spaces; Fig. 5.
Connective tissue shows almost no cells for it consists for
.e most part of numerous fine fibres, frequently arranged

Fig. 7. — Connective

TISSUE
The soft tissue that lies
between the skin and the
muscles. Fibres are
shown running irregu-
larly, and some cells, C.

ADVANCED PHYSIOLOGY

in bundles, as in tendons (Fig. 6) ; or in confused masses running
in all directions, as in the soft mass of connective tissue
beneath the skin; Fig. 7. But in each a few
genuine cells can be seen, and a study of the
growth of connective tissue shows that the fibres
are really produced by the cells.

Muscle tissue consists of fibres, sometimes
tapering at the ends; Fig. 8. When the muscle
contracts, these fibres diminish in length and
thicken in the middle. Such a fibre is some-
times a single muscle cell, and sometimes several
cells fused together, but in any case it is cellular.
Gland cells are frequently cylindrical, some-
times nearly spherical; Fig. 9. The material
they secrete collects in them and is later ex-
pelled, either continuously, as in some glands,
or at intervals, as in others.

Blood consists of many cells, called blood
<;orpuscles, floating in a liquid; Fig. 10. This
liquid is not formed like the mass of
material separating the cells in cartilage
and in bone, since it is not produced by
the blood cells themselves.

Nerve cells differ widely in shape; some
are nearly round, some are very long and
some are irregular in outline. A com-
mon type has an angular body with a
few much-branched prominences extend-
ing from the corners; Fig. 11.

Fat cells are like some of the other cells
of the body, but pick up bits of fat from
Showing ata the cells that the blood, holding it uutil it is wanted;
secrete, at 6 the duct that Fig. 12. These cells incidentally form

carries away the secretion j. r u* i • r

and at c the blood ves- ^ ^ort of cushiou or packmg for some

sels supplying the gland. of the SOft paits of the body.

Fig. 8.— Mus-
cle CELLS
FROM THE
WALL OF THE
INTESTINE

Fig. 9 — A portion of a

THE LIVING MATERIAL OF THE BODY

Although there is much diversity in the forms of cells in
the body, each tissue is made of only a single kind which
does a single kind of work. The size of cells varies widely.
Some of the smaller cells of animals are not more than
0.003 mm. (^^ in.) in

i^\*^s®^:?^2*^»^^>srt*,^^,

8 3 0 0

diameter, while the egg,
which is essentially a cell,
is sometimes several
inches in diameter. The
majority of cells in most
animals vary from 0.008
mm. to 0.01mm. (-g-yVTr to
Yzww i^-) ^^ diameter;
Fig. 13.

Structure of Cells. — In
recent years much atten-
tion has been paid to the
more minute details of
cell structure. As a re-
sult we now know that
all cells, while differing
in outward shape, are very much alike in their internal
organization. Each one is filled with a semifluid substance
called protoplasm, and this protoplasm is the part' of the
cell which is really alive. Protoplasm should not be thought
of as life itself but it is the only material in which life is
known to occur. When highly magnified, protoplasmic fluid
always seems to contain fine granules, or it may look like
a foam of extremely small bubbles or show a network
of excessively minute lines; Fig. 14. At all times, if the
cells under observation are alive and are not too much
disturbed, movement of the protoplasm is evident. No
one knows the cause of this motion; it can only be
accounted for by saying that protoplasm is alive.

Within each cell is a specially dense bit of protoplasm called

Fig. 10. — Blood

As it appears when put on a glass slide and
highly magnified. At a are shown red cor-
puscles and at 6 white corpuscles or leuco-
cytes.

ADVANCED PHYSIOLOGY

the nucleus. This nucleus seems to be the center of the

life and activity of the whole cell, for if deprived of it the

cell cannot long continue
to live. There are other
parts of the cell, as is
shown in Figure 14, for
the cell is really a com-
plicated bit of machinery.
The chemical composi-
tion of protoplasm is not
definitely known, but cer-
tain elements — carbon (C),
hydrogen (H), oxygen (0),
nitrogen (N), iron (Fe),
sulfur (S), calcium (Ca)
and phosphorus (P) — enter
into the composition of all
kinds of cell protoplasm;
other elements may occur
in smaller quantities.

Protoplasm, then,
should be remembered as
the only living substance
in the body. It cannot
live long without a nu-
cleus, neither can a nucleus
live without the support of
surrounding protoplasm.

The living protoplasm
may be surrounded by a
layer of greater consistency.
This may be very thick, as
in cartilage (Fig. 4) ; it may

be very thin, as in the nerve cell, or it may be entirely absent,

as in the white blood corpuscles; Fig. 10.

Fig. II. — A nerve cell or neuron

At o is shown the cell body; b, the nu-
cleus; c, the axon of a nerve fibre; d,
branching of the fibre; e, muscle fibres
within which the fibre ends: /, a node
in the fibre. (Barker)

THE LIVING MATERIAL OF THE BODY

Fig. 12. — Fat cells

a, representing young cells
just beginning to store fat;
h, fully developed cells
ailed with fat.

We may, therefore, define a cell in two ways. We may
say that it is one of the unit masses of which the tissues are
formed, or we may say that it is a
bit of protoplasm containing a nucleus
and generally surrounded by a cell wall.
In either case, the cell is the unit of
life.

The Life of Cells. — There are cer-
tain great differences between this
unit of living matter and a non-living
thing. Three distinguishing qualities
belong to the living cell: (1) growth,
(2) self-repair, (3) increase in num-
bers through self-division. These powers are possessed by
no other material in the world save protoplasm.

The growth of a cell is in all cases brought about by material
taken in from the outside. In the human body this material
is food, which after di-
gestion passes into the
blood and is then taken
in by the cells. This
process will be described
more fully later. In
some of the very lowest
organisms, where the
whole animal is a single
cell, solid particles may be taken into the cell through
definite openings or "mouths"; Fig. 15. In others, the
cell may change its shape so as to wrap itself about ths
particle to be taken in. But even in these instances the parti-
cles must be dissolved or digested before they can be built
up into the protoplasm of the cells.

A machine in motion wears out, and the worn out parts
must be replaced. Cells, too, wear out and new cells must be
formed or new protoplasm is required tO repair the old ones.

Fig. 13. — Showing the relative size

OF A pin head and A LARGE SIZED CELL
The small dot in the center represents the cell.

ADVANCED PHYSIOLOGY

Xl^ Nuct

Repair and growth are brougnt about by one and the same
process, the difference being that in repair, new material is
added only as fast as the old wears away, while in growth
new material is formed in excess of that which is worn out,,
the excess constituting the growth.

Cell Division. — Most living cells have the power of self
division as shown in Fig. 16. This results in two cells like the
original. In the human body, however, the cells do not
separate from each other, so that by continued repetition
of this process a large mass of cells
is produced.

Reproduction. — Every animal begins
its life as a single cell — an egg. This
cell repeatedly divides, the many cells
remaining attached to each other.
Thus the growth of an animal to
adult size is not due to the growth in
size of the individual cells making up
its body but to increase in their number.
The cells of the adult are not materially
larger than those of the young. In
time one or more of the cells from the
body of the adult may be set apart as
eggs, the process outhned above being
started over again. This derivation
of new individuals from single cells of
a preceding one is called reproduction.

The Cell as a Unit.— We have thus
seen that the body is made of organs,
that the organs are made of tissues and that the tissues are made
of cells. Is it possible to carry this division further? To this
question we must reply that, so far as yet known, the cell is
the final unit. It is true that the cell has parts — cell wall, nucleus,
cell substances etc. — ^but no one of them can live by itself,
while a complete cell may be an independent body and live an

PI.

...C.R.
CL.

Fig 14. — A cell showing

ITS INTERNAL STRUC-
TURE

C.W., cell wall; C.L., cell
liquid; C. R., cell reticulum;
Nuc, nucleus; Nucl., nucleo-
lus; Ch., chromatin; Cn.,
centrosome; Vac. vacuoles;
^l., plastida (pigment, chloro-
phyll, etc.); F. D., fat drops
(starch, gum etc. may be
eimilarly present in plant
ceU).

Fia. 15. — Showing a variety op animals, each op which is a

SINGLE CELL ClllGHLV MAUiNlFlEU;

ADVANCED PHYSIOLOGY

independent life. Although our own bodies are composed of
many millions of these cells, there are some organisms made
up of one cell only. These are usually microscopic and are
called unicellular animals and plants; although very tiny,
each lives an independent life. Some of these animals are
shown in Figure 15. They vary in shape and differ in struc-
ture. Some of them have ''mouths"; others simply take
their food in at any part of the body by allowing their pro-
toplasm to flow around it. Some of them have organs for
locomotion, others do not. Some have shells, while others
have no covering at all. But each is a single cell, and each
ijarries out its own life processes, such as respiration, secretion

Fig. 16. — Showing the method op cell division

and multiplication. The cell cannot be subdivided into
smaller units which would be able to sustain independent
life.

Since such cells are the simplest parts into which living
matter can be divided, we may call them the units of life
and may regard our bodies as a combination of a large num-
ber of such units, considering the life of the whole body
as the sum of the lives of its different cells. We should

THE LIVING MATERIAL OF THE BODY 23

constantly remember that it is really the cells which are the
active, living parts. The combined lives of all these millions
of cells make the life of the whole, much as the combined lives
of the persons within a city make up its life.

UNICELLULAR AND MULTICELLULAR ANIMALS

As we have seen, some animals are composed of a single
cell. But this cell is able to carry on all the functions of life :
it feeds, digests, respires, moves, multiplies and performs all
the necessary duties of complete, individual life. In our own
bodies there are many cells, but each is not capable of carrying
on all the functions of life, and if separated from the others,
would die. Each is able to do primarily only one thing;
hence each is dependent upon the others.

It may be asked why we should have so many kinds of
cells in our bodies, and why with us, too, one kind of cell
could not serve all purposes. The answer is easy to give.
A hermit can himself do everything needful to support
his life: he can prepare his own food, make his own clothes
and build his own shelter. But he can do this only be-
cause he lives very simply. When a family lives alone on
the frontier the members divide the work among themselves,
the husband doing the work out of doors, the wife that
indoors and the children contributing their different shares.
When several families come together, it will be found that
some members of the community are more skillful in
building houses, others in making shoes, others in dress-
making, still others in cooking and so on; so the people
agree to divide their tasks and share the results of their work.
In this way they may have better houses, better shoes, better
clothing and better food than before, because each man does
what he can do best. As the community grows this divi-
sion of labor becomes extended until, in a large city, each
person does only a very small part of the work necessary
to supply him with the things he needs. But he can do his

ADVANCED PHYSIOLOGY

own work well because he has only one thing to do. The
life of a city is of much higher grade than that of a pioneer
family; its population has many more luxuries and ac-
complishes much more, all because of this division of labor.
The people become more and more
dependent upon each other, but
for just that reason they are better
served.

So it is among organisms. Where one
cell does everything, the life is simple
and on a very low scale. Each cell can
feed itself and perform all the necessary
functions, but the whole life is only one
of growth and reproduction. As the
cells become more abundant, they also
become unlike. Each takes upon itself
certain duties, each contributes to the
good of the other cells, and each receives
aid from the others. In Figure 17, for
example, we have a simple animal in
which two kinds of cells are shown.
Those in the center take care of the
digestion of food, while those on the
outside protect the animal from ex-
ternal injuries. The entire organism
is thus much better served than it
would be if each cell had all the
varied duties to perform. The life of
any animal is the sum of the lives
of its cells, and with many kinds of
cells all working together for a common good, a higher
grade of activity is produced than with each working for
itself alone. Division of labor goes hand in hand with a
rise in the scale of accomplishment and results in a superior
type of life.

Fig. 17. — A multicel-
lular ANIMAL (Hy-
dra)

Showing its body to be
made of many cells that
are not all alike, B.base
for attachment ; M,
mouth; DC, digestive
cavity.

CHAPTER II
CHEMICAL COMPOSITION OF THE BODY

Everyone feels that he knows the difference between an
object that is ahve and one that is not ahve; and certainly
there is no difficulty in distinguishing between them when we
are considering such things as dogs and stones. But how can
we tell whether or not a dried pea is alive? We might find
out, perhaps, by planting it. If it sprouted, we should know
that it had life, but we could not tell by its appearance nor
by pulling it to pieces.

When it proves impossible to tell the nature of a material
from surface examination or by dissection, the chemist is
usually called in to settle the question. It would be natural
to suppose that living and non-living bodies are made of
different chemical materials; that the living body contains
some hidden, secret thing which the non-living lacks.

ELEMENTS

For a century or more chemists have been at work trying
to divide things into the simple materials of which they
are made. Those simple materials which cannot be further
divided are called elements. Out of one or more of them, all
the various kinds of material in the world are made. Rather
to our surprise we find that there are but a small number
of elements, only about eighty-one being known of which
less than twenty make up most of the common things.
This seems a remarkably small number until we learn how
many different things can be made from the same ele-

ADVANCED PHYSIOLOGY

merits. Think, for example, of sugar, alcohol, glycerine,
kerosene oil, starch, benzine, paraffin and fat. How unlike
they are! In spite of their apparent differences, all these
substances are made of carbon, hydrogen and oxygen; each
one contains these three and nothing more; they differ only
in the various proportions of the elements. In a similar
way, by varying the amount of each element put into
any combination, all the different substances in the world
are made from the eighty-one elements. This is true
of animals as well as of all other material things. The fact
that the body weighs just as much immediately after as it
does before death, shows that no substance is lost at death.
There is really no difference between dead-weight and live-
weight; clearly then the same elements enter into Uving and
dead bodies.

Oxt/qen

Fig. 18. — Diagram illustrating the relative amounts of some of

THE elements IN THE CHEMICAL COMPOSITION OF THE BODY.

CHEMICAL COMPOSITION OF THE BODY

Water, for example, as it leaves the body as perspiration,
is made of hydrogen and oxygen, the same as water from a
faucet. The juices formed in the stomach are partly made
of hydrochloric acid, the same as that used in various manu-
facturing processes. Much of the material in bones is lime;
some of the material in blood is iron, and it becomes red when
mixed with oxygen, the same as iron does when it rusts.
Salt is easily noticed in perspiration and tears, and has the
same composition as table salt.

! Living matter contains but a small number of the seventy-
seven elements referred to above; those commonest in the
body are carbon, hydrogen, oxygen, nitrogen, calcium, phos-
phorus, sulfur, sodium, chlorine, fluorine, potassium and
iron. The following table shows approximately the per-
centage in which each occurs:

CHEMICAL COMPOSITION OF THE BODY

Elements

Sym-
bol

Percent-
age

Elements

Sym-
bol

Percent-
age

Oxygen

Chlorine

.085

Carbon

13.2

Fluorine

.08

Hydrogen

9.1

Potassium

.026

Nitrogen

2.5

Iron

i^e

.01

Calcium

.25

Magnesium

.0012

Phosphorus

.15

Silicon

.0002

Sulfur

.02

Copper,Lead and

Sodium

Aluminium
in very small
quantities

These are the same chemical elements which we should
find if we analyzed materials all around us in nature; e.g.
air, water, soil or rocks. The Hving body is thus constructed
of the same materials as are found in non-living, inanimate
bodies. But there must be some difference. What is it?

28 ADVANCED PHYSIOLOGY

THE CHIEF CHEMICAL COMPOUNDS IN THE BODY

If the materials used in building a city block were chemi-
cally analyzed, many of the elements found would be the
same as those present in the body. But when we talk about
the construction of a building, we never mention the chemi-
cal elements of which it is composed; we speak rather of
the compounds of these elements. Beams, piping, windows,
chimneys, furnaces, flooring and doors are all parts of the
building, but they can be roughly classified as made of wood,
iron, brick or stone. Similarly, in speaking of our bodies,
mention is seldom made of the chemical elements in them,
but of the combinations in which the elements most fre-
quently occur.

There are three compounds that are of supreme import-
ance in living animals. They constitute almost all the
essential materials in our bodies. Since they are also the prin-
cipal constituents of our foods, they are called food stuffs.
These compounds are: (1) proteids, (2) carbohydrates and
(3) fats. Water and salts are also necessary.

Proteids (Albumen, Myosin, Gluten, Casein, Legumen,Fibrin).
— Proteid is made up chiefly of four elements: carbon, hydrogen,
oxygen and nitrogen, though sulfur and phosphorus are
present in small quantities. Proteid occurs in all animal and
vegetable organisms. For example, in the human body
proteid comprises 38.3% of the lens of the eye, 16% of the
muscles, 12% of the liver, 9% of the blood. These percent-
ages are not so small as they seem, since the greater part
of all tissues is water. The human body, taken as a whole,
is nearly 67% water, and the proteids form a large proportion
of the rest.

Proteids as Tissue Builders. — The proteid which the body
contains must either be obtained directly in foods or be made
from them. Now the body is quite unable to make proteid;

CHEMICAL COMPOSITION OF THE BODY 29

hence it follows that proteids form an absolutely necessary-
part of our food. We must eat a sufficient amount of
proteid or we shall starve, no matter how much other food
we eat. Proteid is needed in all the working parts of the
body. Muscle and blood are pre-eminently active. Perform-
ing absolutely vital functions every moment of our lives,
they are constantly exposed to "wear and tear" and unless
they were repaired would become exhausted and worn out.
The body must have new proteid for repair purposes and the
proteid must be provided by the use of proteid-containing food.
This food may be obtained from many sources. Some
proteids come from animal and some from vegetable materials.
That from meats is called myosin; that from eggs is albumen;
that from milk is casein; that from wheat is gluten; that
from beans is legumen. But although differently named and
differing in value to the body, all these forms of proteid serve
as a food which can replace and repair the worn-out parts of
the body. If we remember that proteids alone can thus re-
place worn-out tissue, we shall understand their fundamental
importance.

One naturally and correctly feels that proteids from animal
sources are probably most like that of the human body, and
so can be used with better results. Furthermore, as all sub-
stances taken as foods must be masticated, swallowed, digested,
absorbed into the blood, carried over the body and then re-
ceived into the living cells and made a part of the body sub-
stance, it is easy to imagine that some proteids undergo these
changes more readily than others, and so are more valuable.

In a later chapter dealing with foods the differing values
of various proteids will be discussed. Some kinds, taken
alone, will not support the growth of an animal at all; others
seem to furnish every needed substance, even when quite
small quantities are taken. Very extensive and expensive
studies have been made in recent years in the analysis of all
kinds of proteids and other food substances, together with

30 ADVANCED PHYSIOLOGY

their digestibility and final values. Human beings have been
used in these experiments so that the results are of great value.

Proteids as Fuel. — To keep an engine running it is not
enough that it be kept in repair; there must be a fire in
the fire-box. In one respect the body differs from an engine :
while the iron of which a locomotive is made cannot be used
as fuel, the proteids of which the body is made can be
burned. By being burned we mean here, united with oxygen,
a phenomenon which chemists call oxidation. Foods in the
body unite with oxygen and this may be called '' burning,"
though the oxidation is not so rapid in the body as in an
actual fire, and there is, of course, no flame: but the union
with oxygen is similar, heat is developed in a similar manner
and the final results are much alike. Proteids have a double
value: (1) they are burned in the body and (2) they build up
tissue. When all the proteid eaten is not needed to build up
or to repair the tissue, the rest may be burned to furnish heat
and force.

In using proteids for fuel there is, however, one disadvan-
tage which limits their value as food. After any fuel is
burned, certain waste products always remain. When a fire
burns in a locomotive, a vast amount of smoke and gas
arises and passes off through the smoke-stack, while ashes are
left to be raked down through the grate and thrown away.
The fire will not continue to burn unless these waste ashes
and gases are removed. In the body, too, as a result of the
burning, gases and other wastes arise. The gases pass off
readily enough through the lungs. But there is a more
troublesome residue that corresponds to the ashes. We have
noticed that proteids contain some of the chemical element,
nitrogen. After the burning of the proteid in the body,
this nitrogen becomes a waste product and can be disposed

CHEMICAL COMPOSITION OF THE BODY 31

of only as an excretion of the kidneys. The more proteid
we burn for fuel, the more of this waste there is, and hence
the greater the work of the kidneys. If, therefore, we eat
large amounts of proteid, the kidneys have extra work to do;
indeed, it is believed that some kidney troubles are produced
or at least aggravated by overtaxing those organs from the
consumption of too much proteid.

Nevertheless, the body must continue to burn fuel in
order to keep up its life; it can no more live without burn-
ing fuel than the locomotive can run without its fires. If
it is not wise to burn great amounts of proteid, what can the
body use as a source of the necessary heat and power? If
there is some kind of food that furnishes the required energy
without leaving behind nitrogen waste materials, it will
evidently be of much value. There are two such classes
of foods: carbohydrates and fats.

Carbohydrates. — Although starches and sugars seem very
different, they are really much alike in chemical composition
and may be converted, the one into the other. It is especially
easy to change starch into sugar. The similarity in their
chemical formulae is very noticeable. Fruit sugar is
Ce Hi2 Oe; starch is Ce Hio O5. Starches are always turned
into sugars and dissolved before they are taken from the
intestine into the blood. From the blood vessels the sugars
penetrate into all the tissues and are soon very widely
distributed.

Sugars and starches of various sorts are so commonly seen
that one should be warned against thinking of these sub-
stances, after their assimilation into the body, as having their
usual appearance. Both may be present in solid or crystalline
form in the cells of plant leaves, stems or roots; but not so in
the cells of any kind of animal. The nearest to it is a sub-
stance found especially in the cells of the liver and in muscles
and called glycogen. The chemical formula of glycogen is the

32 ADVANCED PHYSIOLOGY

same as that of starch (C6Hio05)n, though the two substances
have little else in common. Glycogen, too, varies much in the
amount stored up when an excess of sugar is eaten, and dis-
appears when one is hungry.

Fats. — Tallow, lard, cream, olive oil etc. furnish another
fuel that can be burned without giving a nitrogen waste.
These fats are derived from both animal and vegetable
foods and though made of the same elements as carbohy-
drates (C, O and H), they are more complex. Fat is plentiful
in the body in both fluid and semi-fluid condition. It is
absorbed by the blood from the intestine in a fluid condition,
is carried around the body in the blood and is eventually
taken from it and deposited in various parts of the body.

Fat occurs in masses among the muscles and just beneath
the skin; it forms a cushion for the eyeballs at the bottom
of the eye sockets; it is present among the folds of the
intestine; it fills up certain crevices in the exterior of the
heart muscle and is deposited in the central marrow of the
larger bones.

Evidence of these facts we have all seen many times in food
markets where meats are displayed. No meat is mingled
with so much fat as pork; hogs have famously large appe-
tites and, at the same time, sluggish habits. A result of this
is that only partial use of the fats is made for energy or heat
production, thus leaving excessive fat to be stored. A farmer
rather easily controls the degree of fatness of horses, cattle,
chickens, and other animals by attention to their food and
exercise; and their food does not necessarily contain fatty
substances, for many animals become fleshy though eating
nothing but the proteids and carbohydrates in hay and grain.

Uses of Carbohydrates and Fats. — The body must at all
times be kept warm and is constantly using power in
muscular activity. Heat and power may roughly be said to
constitute energy, and in order to live the body must have not

CHEMICAL COMPOSITION OF THE BODY 33

only material for growth and repair, but also a supply of
energy.

Fat is a form in which the body frequently stores fuel
food for future uses. If the body has an abundance of food
at one time, it need not all be used immediately but may be
laid aside as fat, to be called into use at some later time
when the body may not be able to secure or to take up the
necessary amount of food.

After a long sickness a patient's eyes are likely to be
sunken and the ribs to show through the skin. This is
due to the fact that during his illness he has not been able
properly to digest and assimilate food, and has been caUing
upon the stores of fat in his body to support life and furnish
him Vv^ith warmth and energy.

A tallow candle is made of fat and when it burns, gives
out heat. The Eskimo can warm his hands by holding them
over the burning candle; but he prefers to eat the candle and
let it warm his body through internal oxidation. In this way
he does not lose any of the heat. It would be perfectly
possible, though expensive, to warm our houses by burning
lard, olive oil or butter in our furnaces. So, too, we might
burn starches or sugars for the same purpose, or might run
an engine with the force they would furnish when burning.
Whenever these substances are oxidized, they liberate much
energy and if they are oxidized in the body, they liberate
this heat and force within it.

Carbohydrates and fats do not, however, yield equal
amounts of energy to the body, the carbohydrates giving
us, weight for weight, only about half as much as the fats.
Both are composed of the same elements, carbon, oxygen and
hydrogen, and it is natural as well as quite worth while to
ask why one yields so much more than the other. The
answer Ues in the relative amounts of carbon which these
foods contain; the chemical formula for starch is CeHioOs;
for sugar, C6H12O6; for fat, C61H104O9. Now, in the changes

34 ADVANCED PHYSIOLOGY

which these undergo in the body much of the hydrogen
may combine with the oxygen to form water, H2O, while
the carbon also unites with oxygen to form carbon dioxid,
CO2. It is this combining with oxygen, this oxidation of
materials, which results in heat, just as it is when the
carbon in burning wood unites with oxygen of the air, and
gives off heat in making the combination.

As will be noticed from the above formulae, fat contains
fifty-one parts of carbon, while sugar contains only six. Heat
is produced when the carbon combines with oxygen, as we
have said. In sugar the carbon already has six parts of
oxygen combined with it and cannot combine with very much
more. In fat, however, there are fifty-one parts of carbon,
and only nine parts of oxygen combined with it. In fat there
is therefore a much larger amount of carbon which can be com-
bined with the oxygen of the air than there is in sugar; when
fat is burned there is a large amount of oxidation and hence
a far greater amount of heat given off. Indeed, fat furnishes
a larger amount of heat than any other food.

Thus carbohydrates and fats furnish us with a quick and
profitable source of energy. It must be clearly understood,
however, that neither of them is of any value in tissue
building. Neither muscle nor brain nor gland nor any
other active tissue can be made or even repaired by them.

Gelatin. — Most meat foods contain another material known
as gelatin, which in its refined form causes the hardening of
most of our table jellies. It is obtained from connective
tissues (see page 13) by boiling. In its chemical nature it
resembles proteid, but it will not take the place of proteid
in tissue building. It may be used by the body as a source
of energy and hence has much the same function as carbo-
hydrates. In eating jellies one is likely to be deceived into
thinking that he is eating more than he is, since they contain
much water and are bulky, considering the small amount of
aetual food in them.

CHEMICAL COMPOSITION OF THE BODY 35

METABOLISM

All the materials of which living bodies are composed come
from the soil and from the air. All vegetable foods surely
come from these sources; animals eat plants or eat
other animals which, in turn, live on plants. After being
taken into the body the foods go through certain changes, the
final result of which is that part of the food, at least, is
transformed into living tissues. These changes constitute
what is generally spoken of as a " building up " process,
which means that complex substances are made of simple
ones. After these tissues have severally fulfilled their
functions, serving as muscle, brain, fat, bone or gland, as the
case may be, they gradually wear out; as this occurs they
are " broken down " from their complex condition into
simple forms again.

In living matter, there occur two types of changes — a
building up, or anabolism, and a breaking down, or kata-
bolism. As a result of this breaking down process the sub-
stances which have been alive and have acted at the bidding
of our wills become again inactive and non-living. Gradually
all parts of our bodies — heart, brain and everything else —
become once more a part of the soil and air, just as they were
before they were first taken up by plants. The changes are
long and complex. Some take place in the body and some
outside the body, for materials are sometimes excreted before
they are completely broken down. The changes that take
place in the body, the building up and the breaking down
taken together, are spoken of as metabolism. Metabolism
is thus a name for the chemical changes which are taking
place in living tissues.

Many factors combine to regulate each of these pro-
cesses. Katabolism (destructive change), for instance, is
increased by excessive work; by poor nuirition, by loss of

36 ADVANCED PHYSIOLOGY

sleep, by nervousness, by various diseases and by the action
of certain poisons and drugs, such as opium, chloral and
alcohol. It seems strange that men should consciously persist
in the use of some foods, and especially some drinks, which
inevitably bring about this increased katabolism in im-
portant organs; that they should continually expose them-
selves to weakening processes which the building up processes
can counterbalance with difficulty, if at all.

Growth. — The body is evidently a very active center into
which large amounts of material are constantly entering in
the form of food, drink and air, and from which, at the
same time, large amounts are constantly being eliminated.
Body substance is being constructed and destroyed at the
same time, and if these two processes are going on at the
same rate, the body neither increases nor diminishes either
in weight or efficiency. Such a condition is commonly
spoken of as one of metabolic equilibrium.

If, on the other hand, the destructive processes take
place more rapidly than those of construction, the body will
lose in weight or efficiency, and if this condition of things
continues long enough, death must result. When the con-
structive processes in the body go on faster than the de-
structive or wearing away processes, the result is an
crease in weight or in efficiency. The growth of the bod]
then, is the result of the excess of constructive changes ov^
destructive changes.

Anabolism exceeds katabolism during childhood and earj
youth; but after adult life is reached, under ordinal
circumstances the body maintains itself in metabolic eqi
librium. This latter condition constitutes what is general!
spoken of as healthy the maintenance of which should be a
matter of careful, serious attention as long as life lasts.

CHAPTER III
FOODS AND FOOD HABITS

It is important for us to know the real nutritive value
of the foods that we commonly eat. In this study it
should be constantly borne in mind that for the proper
support of life we must have a considerable amount of pro-
teid since this material alone builds up the tissues of the
body. Carbohydrates and fats can be used only as sources
of heat and force.

Scientific men who spend their time studying the fossils
of animals which lived ages ago, and which are known now
only by their imperfectly preserved skeletons, tell us that
they can determine what the animal ate and much about
the rest of its body if they can find the teeth. We cannot
say what it was originally intended that man should eat;
certainly it was not the kind of food which he eats now, for
many of our foods are recently discovered. But we can say
that his teeth are adapted for cutting, tearing and grinding,
and that his habits are omnivorous; i. e. he eats almost
all kinds of foods. In the preparation of foods, he has con-
trived methods which change their flavor, their appearance
and their smell. He is able to have summer foods in winter,
and spring foods in the autumn. Since he eats such a variety
of things under such different forms, the queries naturally
arise: W.hich are the best of these foods? Which kinds
are most easily digested? Which yield the most nutriment?

FOOD HABITS

We sometimes think that our foods are rather monoto-
nous and wish some new kinds might be found; yet it is

38 ADVANCED PHYSIOLOGY

interesting to note the great variety of foods on which people
live. Americans do not eat the same foods as Japanese,
and yet one nation thrives as well as the other. The Spar-
tans subsisted mainly on dried fruits and honey; the Chinese
employ rice as a staple article of diet, and many of the Italians
make a similar use of chestnuts. White caterpillars, seal
or whale blubber, tallow candles, leather, shark's fins, grass-
hoppers, earthworms, deer's sinews, dogs, cats, rats, are
choice articles of diet with different people. These seem odd
preferences, but are they more so than oysters or crabs in
their shells, and shrimps or frozen cream, all of which are
common with us?

The fact is that with the exception of the woody tissues
of plants, almost any part of an animal or plant may yield
nourishment, and under some conditions serve as food.
From an endless list, our selectioix depends chiefly upon
the customs of the community in which we live, on our
taste and on the cost. A person is always mistaken when
he thinks that any particular kind of food is a necessity.
We can all adapt ourselves to a wide variety and it is best to
become accustomed to the kinds of food most conveniently
obtained under the ordinary conditions of living in one's own
community.

Some foods are more useful than others; some are ex-
pensive, some difficult to digest and some dangerous to
health. It is fortunate for the majority of people that the
expensive foods are really no better than the cheaper ones;
indeed, expensive kinds are usually rich foods which, in
the end, are almost sure to produce digestive troubles.

THE VALUE OF DIFFERENT FOODS

Many things have to be considered in determining what
it is best to buy for the table. Certain very good foods do
not grow in some parts of the country, and this makes them
expensive. Other foods are expensive even where they

FOODS AND FOOD HABITS

2:;row because of the cost of raising and refining them. We
ike to have them on the table because they are ''choice."
Does their nutritive value, however, compensate for the
Additional cost? Some foods are attractive but not nutri-
:ious, and vice versa. To-day people are engaged in a wide
variety of occupations; their bodies are worn out in dif-
erent ways; then, too, some people can afford to pay twice
IS much, perhaps ten times as much as others for their food.
In considering these matters, we will take them up from
:he standpoint of the three primary food stuffs.

Proteid Yielding Foods. —

PERCENTAGE OF PROTEID IN SOME COMMON FOODS

Cheese, skim

Poultry

Egg, white

Beef, lean

Mutton, lean

Veal

Salmon

Egg, yolk

Beef, fat

Mutton, fat

Milk

Peas and Beans

Flour

Bread

44.8

21.

20.4

19.3

18.3

16.5

16.1

16.

14.8

12.4

3.
24.
10.8

8.1

—

From this table it will be seen that animal foods, in gen-
eral, furnish the largest amounts of proteid. Whenever we
3at meat, eggs, milk or cheese, we get a great deal of this
food stuff. We learn, too, that though we may eat the same
1 mount of food each day, we do not by any means always
3at the same amount of proteid. Fat pork often contains
much less than half the proteid per pound that lean beef

ADVANCED PHYSIOLOGY

does, and not more than three-fifths as much as fat beef.
Nevertheless, we eat one kind of meat for dinner one day
and another the next, and since we eat about the same
amount of each, we certainly obtain more proteid food with
some meals than with others.

Demonstration. — Boil an egg for ten minutes and remove the shell.
Cut in halves to show the coagulated albumen and the yolk.

The amounts of proteid in different vegetables also vary
greatly: peas and beans furnish an exceptionally large

Fig. 19. — Graphic representation of the food values of bread, beef

AND eggs

Fats are shown in black, carbohydrates in horizontal dotted lines, and proteids in
vertical dotted lines. Other parts are water.

amount of proteid; cereals, such as wheat, oatmeal and corn
meal have less, but still contain a large quantity; vege-
tables and fruits, such as cabbages, lettuce, tomatoes
and asparagus hold very small amounts, yet we often
substitute one of these foods for another. These vege-
tables and fruits are useful as promoters of digestion, or
because they have a pleasant flavor, but they must not be

FOODS AND FOOD HABITS

looked upon as furnishing any great amount of real food.

It is clear, then, that the common kinds of foods differ

much in their nutritive value, and though ordinarily we do

Wheat

Turnip

Fig.

20. — Showing the nutritive values of different foods

The shading as in Figure 19.

not think of this fact, we should bear it in mind if we would
properly regulate our diet. So far as proteid is concerned,
this is graphically shown by Figures 19 and 20.

Relative Expense of Proteid Foods. — Few things contribute
more to health and happiness than intelligence in choosing
foods. In the selection each person will be guided by a num-
l)er of considerations. Some nutritious foods can be obtained
at much smaller cost than others; for instance, a quarter of a
})Ound of cheese usually contains as much proteid as half a
pound of lean meat or three-quarters of a pound of fat meat;
half a pound of beans or bread contains as much of the needed
proteid as a pound of fatty meat, though its cost is much
'ess; Fig. 19. Skimmed milk contains as much proteid as whole
milk, the cream being chiefly fat and in some respects of

ADVANCED PHYSIOLOGY

much less value as nutriment than the casein in the skimmed
milk. Vegetables, in general, such as cabbage and lettuce,
contain extremely little nourishment of any kind. As a rule,
it is better to purchase foods which have large quantities of
the necessary substances in them than those which have
small amounts. If we should eat enough of the latter kind,
we could, of course, obtain all the food we need; but it
would compel the digestive organs to do a quite unnecessary
amount of work.

The following list, giving the amount of proteid which
can be bought in different forms for ten cents, will be of value
as a guide to an economical purchase of table supplies.

AMOUNT OF PROTEID PURCHASABLE FOR TEN CENTS

Beans

Oatmeal

Wheat flour

Corn meal

Cheese

Wheat bread

Potatoes

Wheat breakfast food

Beef, round

Milk

Mutton

Pork

Rice

Eggs

Beef, sirloin

Pork-fat, salt

Com, canned

Butter

1 1 1

1 1

1-350 of a pound

* Each division in this scale is one- tenth pound.

Carbohydrate Yielding Foods. — Carbohydrate yielding foods
are almost wholly vegetable, as animal substances furnish
only a small amount of starch or sugar. Milk, containing

FOODS AND FOOD HABITS

4% milk sugar, is the only important animal source. All
foods of vegetable origin, especially the cereals, wheat, corn,
oats, etc., furnish some starch. Peas, beans, and potatoes
all yield moderate amounts of starch only (Fig. 20.) This is
because potatoes contain much water, while peas, beans, etc.,
are composed one third to one fourth of proteid. Leafy vege-
tables, e.g., cabbage, and lettuce, yield almost no food proper.

Vegetable foods also contain sugars, though they are
not so common as starches and hence not so cheap. Sugar
cane and sugar beet provide us with the greatest quantity,
this sort of sugar being called saccharose. Fruits contain
considerable sugar of a type called fruit sugar, glucose or
dextrose. It is not so sweet as cane sugar, but its food value
is just as great. Chemists can easily make this form of sugar
from starch, and can produce it in this way quite cheaply.
This fact has caused it to be used frequently in the adultera-
tion of cane sugar and very clear, colorless syrups. The
fact that it has very little sweetening power makes it necessary
to use more of it to produce the desired sweet taste; it
is, therefore, an undesirable adulterant for cane or for beet
sugar.

PERCENTAGE OF CARBOHYDRATES IN COMMON FOODS

Sugar
Rice

Wheat flour
Corn meal
Oat meal
Peas or beans
Graham bread
Wheat bread
Potatoes
Green corn
Milk

Tomatoes
Meats

98
79
75
75
68
60
54
57
18
14
5
.2

ADVANCED PHYSIOLOGY

Fat Yielding Foods. — Fats are present in both animal and
vegetable foods, although the larger amounts come from
animal sources, and the most common fats are those in meats.
Lard is a fat from pork, and butter is simply the fat taken

ii I iiiKiii im[|ii iiiiililh; M!!; i!';
■|.|;!i;j!!!!!li!!!!l!ii|i!:;i!i!ii:!:!Ci!!i

Milk

duHer

esse

Fig. 21. — Showing the food value of milk, butter and cheese

The shading as in Figure 19.

from milk, which is an animal product; Fig. 21. From vege-
table products, e. g. olives, corn and nuts, more or less fat
is obtained, generally in the form of oil.

PERCENTAGE OF FATS IN COMMON FOODS

Butter
Salt pork
Mutton
Beef
Fish

Oatmeal
Milk

Corn meal
Rice
Beans
Wheat flour
Peas
Potatoes

85
60
22
20

10
8
3.5
2.2
.4
.2
.1
.1
.1

Varies from .2 to 20%

FOODS ANB FOOD HABITS 45

Some Characteristics of Fats. — Some fats, e. g. butter,
are very pleasant to taste, while others, like castor oil, are
decidedly unpleasant; some are easily swallowed, while others
can be swallowed only with difficulty. The reason for this
is that three different kinds of fatty materials are mixed
together in the ordinary fats of our foods; one of these,
called olein, melts at 23° F. (-5° C); a second, palmatin, melts
at 113° F. (45° C); and a third, stearin, melts at 140° F.
(60° C.)- It is easy to see that the more olein a fat contains
the more easily it can be melted. Olive oil is mostly olein
and is melted at ordinary temperatures, while beef tallow
contains much stearin and is solid even at the ordinary
temperature of the body. Butter and lard are quite soft
because they contain a large proportion of the easily melted
olein. It is well to remember also, that the easily melted fats
are the most readily digested.

Fats constitute an extremely important part of our food
since they are so easily digested and yield so much energy.
All fats, whatever their special natures or flavors, serve much
the same purpose.

Vitamines. — Until very recently it has been believed that
the three food materials above discussed, together with salts
and water, were all that is necessary for an ample diet, and
that new protoplasm is readily made from them alone. Cer-
tain diseases, e.g., a form of neuritis (''beri-beri"), an intestinal
disorder (scurvy), and rickets, were explained as due to the
use of incorrect proportions of the foods already mentioned.

It is now clearly proven that substances called vitamines
must also be eaten and when used, the illnesses referred to do
not occur, or if present, are cured.

Vitamines are found in the seed coats of most cereal grains,
in yeast, in whole milk and butter, in eggs, in leafy vegetables
(especially spinach), and in the juices of commonly eaten
fruits, e. g., oranges, apples, etc. These substances are
destroyed in boiled milk, and as fruits are heated when canned.

46 ADVANCED PHYSIOLOGY

such should not be considered as satisfactory substitutes for
fresh fruits. Again, in this connection, the necessity for a
varied diet is clearly emphasized.

COMPOSITION OF COMMON FOODS

Milk, taken alone, is a complete food, containing all nec-
essary materials. Its composition is approximately, — proteid,
2.5%; fat, 4%; sugar, 5%; water, 88%. Milk should be
considered a food and not a beverage; it contains a higher
percentage of solids than any of the commonly used vegetables
except peas and beans.

Butter is the fat of milk and little else. It contains prac-
tically no tissue building substances, but is useful to accom-
pany other foods, like bread, which are deficient in fat;
Fig. 21.

Cheese contains all the proteid in milk, together with
most of its fat. There is almost no carbohydrate in it, how-
ever, and while very nutritious because of its high percentage
of proteid (30% or more), it should be eaten only with
other foods containing sugars or starches, e. g. bread oj
crackers.

Meats always contain large amounts of proteid as well
considerable fat. They are among the most easily digestec
of the proteid foods. Meats contain no carbohydrates an<
should not be eaten alone, but should be accompanied h]
some starchy foods, such as bread or potatoes.

Eggs should be classed with meats since they contain aboi
the same kinds of material, and should be used in the sai
way.

Bread is one of the best foods. It contains considerable"
proteid and a large amount of starch. The fat present is not
sufficient to make bread a balanced food, but we commonly
eat it with butter. Bread and butter alone make an almost
perfect diet.

FOODS AND FOOD HABITS

Cereals — The various breakfast cereals are all excellent
foods and rank with bread in food value. They are made
mostly of wheat or oats, both of which contain much proteid
and starch; Fig. 22. They are somewhat lacking in fat,
but if eaten with cream
form an almost perfect
food.

Rice contains less pro-
teid than wheat and, like
it, very little fat. It
should, therefore, be eaten
with some food contain-
ing more proteid, e. g.
meats, cheese or beans. Fig. 22.— Showing the food values

Beans and peas contain of wheat flour and oatmeal

very large amounts of pro- Shading as in Figure 19.

teid, as much as meats or even more. Although they also
hold considerable starch, they are to be looked upon chiefly as a
source of proteid. To form a balanced diet they should be
accompanied by some food containing starch and fats, such
as bread and butter. Peas and beans are difficult to digest
and should be eaten somewhat sparingly.

Potatoes have a relatively small food value. They contain
only 1.8% of proteid, 14.7% of starch and little fat; Fig. 20
They are very poor foods if used alone, and must be eaten
in great quantities to supply the requisite amount of proteid.
They do, however, furnish a cheap source of starch and are,
therefore, valuable to accompany other foods such as meats,
cheese, beans etc.

Vegetables, as a rule, contain so little real nutriment that
we can scarcely consider them foods at all. They are valu-
able because of their pleasant flavors, which stimulate the
action of the digestive glands.

Fruits furnish about the same elements as vegetables.
They have pleasant flavors which excite proper activity in

IS ADVANCED PHYSIOLOGY

the digestive organs. It is, therefore, useful in regulating
digestion, but does not furnish much nutriment.

Nuts contain fat and in some cases much sugar and pro-
teid; Fig. 20. In spite of the fact that they are used
extensively by vegetarians, they are, unfortunately, hard to
digest.

Confectionery is a real food and not simply a luxury. It
furnishes fuel food only, but this in large amounts. A pound
of candy will yield about two-thirds of the fuel needed by
the body during a day.

THE AMOUNT OF FOOD NEEDED

Even when the body seems to be perfectly quiet it is doing
much work. The heart is beating, the blood is circulating,
the chest is moving. Much heat is constantly demanded to
maintain internal temperature and to counterbalance that
given off from the surface. The body, even when quiet in
sleep, is giving off heat about as fast as a sixteen- candle
power electric lamp; and when awake, but resting, as much
as a twenty-candle power lamp. The total amount of enerj
expended in various ways by the body may be better appn
ciated when it is noted that an ordinary person while remaii
ing quiet for a whole day uses up an amount of energy eqi
to that required in climbing a mountain five thousai
feet high. This measurement of energy is usually express(
in terms of heat units, called calories. A calorie* is tl
amount of heat required to raise the temperature of one kilc
gram (about one pint) of water about two degrees F. ; and tl
resting body uses from 2000 to 2300 of these units in twent]
four hours. If a man rises from his chair, walks about eighj
feet and returns, he uses about one unit. When a person is
working he liberates more heat and expends more energy than
when quiet; in order to do this he must oxidize more food. The
working man may use two to four times as much food as one

*This is the large calorie; not the small one, which is only y^^ as
great; i.e., the amount of heat required to raise the temperature ©f
<ir\e grain of water 1° C.

FOODS AND FOOD HABITS 49

resting, and a fair day's work would require an extra amount
of fuel food equal to about one pound of sugar or starch, or
I about one-half pound of fat. A working man's diet should
contain more carbohydrates and fats but little if any more
proteid than that of a person of sedentary occupation. A
large person needs more food than a small one and an adtdt
more than a child.

Hence no fixed amount of food would be the correct one
for every person. The amounts of some common foods in
either of the following rations represent approximately what
is required each day by an average adult person doing a moder-
ate amount of work:

A DAY'S RATION

I. — Lean meat, i lb. (a piece as big as a man's hand)
Potatoes, 1 lb.
One glass of milk
Bread, ^ lb. (^ of a small loaf)
Butter, sufficient to go with the bread

II.— Bread (with butter), 1 lb.
Milk, 1 pt.
Cheese, 2 oz.
Eggs, 2
Fruit

If one eats three meals a day, the amounts mentioned in
either list given above should, of course, be distributed through
the three meals. The rations outlined differ slightly in the
total amount of food they contain, but they are nearly equiv-
alent in nutriment. The amount of proteid in each is less
than some think necessary, and more than others advise.

Overeating. — Overeating may result from eating too much
at a meal or from eating too frequently. Undoubtedly
Americans suffer from eating too much. The difficulty of
saying just how much a person should eat makes it equally

60 ADVANCED PHYSIOLOGY

difficult to define what is meant by overeating. In general,
if one eats till he feels surfeited, or if he adds a dessert
after he has satisfied his appetite, he is overeating and will
probably suffer for it. A dessert is frequently a misfortune,
since it is added to a meal to please the sense of taste
rather than to satisfy the appetite. A growing boy or girl
needs more food than an adult, and overeating, though a
common fault with grown people, is not likely to occur with
children.

Frequency of meals. — Most Americans are in the habit of
taking three meals a day and regard this as necessary to health.
In reality frequency of eating is simply a matter of habit.
Some nations are in the habit of taking four or even five meals
in a day, others eat only two, while savage tribes eat very
irregularly, often only once in two or three days, without
suffering in health. No rule can be given as to the proper
time that should elapse betv/een meals. It is unwise, however,
to eat too frequently. Breakfast, if eaten immediately afte]
the long sleep, should ordinarily be the lightest meal of t
day, since the digestive organs are not ready to begin work
quickly as the brain. The hearty meal should be preferabl;
at the close of the day's work, and should be followed by rest for
an hour or more. Mental work immediately after eating seems
to interfere with digestion less than does muscular exercise.
A little food before going to bed may not be injurious, and is
frequently advantageous in enabling one to sleep more easily.
A hearty meal before retiring is, however, not advisable.
Among other bad effects it is likely to produce unpleasant
dreams.

The Appetite as a Guide in Eating. — The only guide which
nature has given us as to the amount and kind of food we
should eat and the liquid we should drink is the appetite.
Lack of food produces hunger which is felt in the stomach,
and lack of water produces thirst which is ipiii in the
throat.

POODS AND FOOD HABITS 51

When a person is in health the appetite is a tolerably safe
guide as to the amount he should eat. This is true only pro-
vided he distinguishes between a real desire for food and a
desire to please the taste, as for example, when eating candy.
If he should continue to eat and drink after his appetite is ap-
peased, he will do himself an injury. He who mistakes the pleas-
ure of gratifying his taste for that of satisfying his appetite be-
comes intemperate and is almost sure to lay the foundation for
digestive troubles.

Since the appetite is the guide that most people follow
each person should be particularly careful not to abuse
it by improper habits. If he Uves upon good, wholesome,
plain food and drinks water, he may rely on his appetite;
but if he pampers it with rich, highly seasoned foods, or
if he injures it by overeating or by so-called alcoholic
stimulants, he cannot depend upon it. If one leads a
sedentary Ufe, his appetite is likely to fail and he should
arouse it by exercise rather than tempt it with rich, highly
flavored dishes.

VEGETARIANISM

Some people believe that a meat diet should be avoided
and that a vegetable menu is conducive to better physical
health. These people are called vegetarians, although they
eat freely of eggs and drink milk. Most vegetables contain a
very limited percentage of proteid; some, like cabbage, lettuce,
tomatoes, beets, turnips, spinach and fruits, contain practically
no proteids, and while they are of value in stimulating the di-
gestive tract they do not furnish much nutriment.

The body is constantly demanding proteid, and while
some vegetable foods, such as potatoes and cereals, contain
large amounts of starch, they contain relatively smaller
amounts of proteid than do meats. Experiment, too, has shown
that the proteids of vegetables do not nourish the body as well
as equal amounts of animal proteids. One could in time gather

62 ADVANCED PHYSIOLOGY

a good deal of wheat by searching over the wheat fields and
picking up the stray stalks left by the reapers; but it would
be much simpler to take it from the wheat bins where large
quantities are stored. Likewise enough proteid will be obtained
if enough vegetable food is eaten; but this would usually in-
volve the consumption of too much starch. It is better,
therefore, to obtain proteid from the more concentrated foods.
Some of the cereals, especially wheat, contain large quantities,
as do beans and peas. Animal foods, as a whole, contain
large amounts, which are more easily digested and of more
value to the body than the proteids of vegetable foods.

Against the use of meats, on the other hand, several objec-
tions are urged. First is the claim that the frequent use of
meat involves the eating of too much proteid. This is especially
true of those who eat in restaurants and hotels, for with the
menu of the restaurant before him almost every one will choose
meat. It is believed that on-^ of the primary causes of the
kidney trouble prevalent among the American people is the
excessive amounts of meat which are eaten in a country where
that kind of food is comparatively cheap. Further it is urged
that by means of animal foods certain injurious parasites
such as tapeworms and trichinae are sometimes introduced
into the body; all these disastrous effects would be avoided
if we refrained from eating meats.

Whatever one may think of the matter, vegetarianism is
certainly a wholesome reaction against the food habits of
certain classes of people who make meat the basis of every
meal. There is, however, no good reason why meat should
not, in proper proportion, form a limited part of our diet each
day.

INCIDENTAL ARTICLES OF FOOD f

Condiments. — The spices — pepper, cinnamon, allspice, muS'
lard, nutmeg etc. — common table salt, the flavorings used in
foods, and the flavoring part of syrups used in drinks are all

FOODS AND FOOD HABITS 53

condiments. None of these is really a food, since.it con-
tains no nourishment; but they are all useful in one of two
ways: as agents for producing a .pleasanter taste in some
foods or as stimulants to provoke a more rapid flow of some
of the digestive juices. Common table salt seems to be a
necessity.

Other Materials Needed. — It will be seen from the figure on
page 26 that besides the constituents of the three chief food
substances the body contains a small but appreciable amount
of other materials. Compounds of iron, sulfur, potassium
and other elements, are all present in small amounts. One
of these, the necessity of which is easily appreciated, is the
mineral matter that forms the hard, resisting part of bones —
calcium phosphate, or phosphate of lime, as it is sometimes
called. Although one does not realize that he is consuming
lime in his food, many foods contain it. It is present in eggs,
as is shown by the fact that a chicken has bones when it is
hatched. It is in wheat, also, and in meats in small amounts.
In short, our common foods contain enough of this material
to supply all the lime we need for bone formation and
repair.

Sometimes a child whose bones are growing rapidly may
eat so much sugar-containing food, such as cake, pastry and
candy, that he gets too little of the more substantial foods
and fails to obtain the proper material for his bones and teeth.
This is occasionally shown by the rapid decay of the teeth
and in permanently crooked bones in the legs, a condition
called rickets. A more substantial diet of bread, eggs and meat
would be advisable in such cases.

COOKING

Everyone should know something about cooking. Cooking
always means the appHcation of heat in some form to a raw
food. Sometimes it is done by placing the food in dry, hot
air — baking or roasting; sometimes by putting the food in

ADVANCED PHYSIOLOGY

Fig. 23. — The cells of a potato

Showing the inclosed starch grains.

boiling water — boiling; sometimes by submerging the ma-
terial in hot or melted i&t— frying. Heat has a variety of

effects upon food and pro-
duces some decided chemical
changes.

Few foods except milk and
fruit are palatable in their
natural state. Cooking food
improves it in three differ-
ent ways: (1) in flavor, (2) in
digestibility, (3) in safety as
food.

1. The change in flavor is
very great, so great indeed,
that in some cases our taste
hardly recognizes the raw and
the cooked food as being the same material. The '^culj
tivated" tastes of the present day make people fastidioi
as to the flavors of foods. They seldom stop to question
the nutritive value of a particular dish, but select foo(

with reference to their flavoi
eating those that are palatabl
whether they are nutritious
not. An agreeable flavor
important, since it enables
more easily to digest our foo<

2. Exposure to heat and
the hot fluids in which foo(
are cooked does much towarc
softening food, ''making it tenj
der," so that later it readil]
falls to pieces under the actioi
of digestive ferments and the mechanical grinding of th^
mouth and stomach. Vegetable foods, especially, nee^
cooking. The walls of the plant cells resist digestive ageni

Fig. 24. — Showing how cooking
bursts the starch-holding

CELLS

FOODS AND FOOD HABITS

hut the heat of cooking breaks them, setting free the starch
granules which swell and burst under the influence of heat
and are thus more thoroughly and easily acted upon by the
saliva and other digestive juices; Figs. 23 and 24. Heat
acts upon starch much as it does upon grains of corn. We
can easily see that popped corn must be more readily digested

, than unpopped kernels. So far as ease

I of digestion is concerned the cooking
of animal foods is not so important,
since the connective tissue which holds
the muscle fibres together is easily dis-
solved by the digestive juices. Indeed,
most meats are more easily digested
uncooked, since the proteid in them
is coagulated by heat, and must be
turned back again to a liquid condition
before it can be absorbed. Frying, dur-
ing which process the food becomes
coated with fat, makes digestion diffi-
cult.

3. There is another entirely sufficient
reason for extreme care in the cooking
of meats; this is the liability that para-
sites of some kind may be present in the
meat fibres. Such parasites are found
more commonly in pork than in any
other kind of meat generally eaten. An
apparently excellent piece of pork may
contain in a single ounce as many as 85,000 of these little,
round worms, trichinae; Fig. 25. If these are swallowed
without being killed by thorough cooking, they wander out
through the walls of the human food canal and take up
their abode in the voluntary muscles of the body. As each
female trichina may produce a thousand or more young, it
10 evident that a serious disease, trichinosis, may result.

Fig. 25. — A, single

TRICHINA. B, A BIT OP
MUSCLE OF PORK
Showing trichina between
the fibres

66 ADVANCED PHYSIOLOGY

The young of the tapeworm also may be concealed in meats,
ready to attach themselves to the wall of the intestine as
soon as liberated from the meat by the digestive juices.
This animal never afterwards leaves the digestive tract, and its
presence there is by no means fatal, although it sometimes
attains great size and absorbs much of the nutrition which
should go to feed its human host.

The practice of wholly or partially cooking milk is becoming
more and more common. These processes are called steri-
lizing and pasteurizing. When milk is sterilized, it is heated
at least to the temperature of boiling water, 212° F.; when
it is pasteurized, it is not heated so much, usually to about
165° F. In either case the purpose is to destroy the micro-
scopic germs which it contains. Milk, since it is such a nutri-
tious food, furnishes an excellent abode for numerous bac-
teria. It is not uncommon to find 100,000 bacteria in a single
drop of city milk. Most of these are quite harmless and may
exist in the milk in great numbers without particularly
injuring it. But sometimes, unfortunately, germs of serious
diseases find their way into milk. Bacteria of typhoid fever,
tuberculosis, scarlet fever and diphtheria are sometimes thus
distributed. The germs that produce these diseases may
easily be killed by heat, even by the moderate heat of 165°
if it be rightly applied, and thus the milk may be rendered

Water. — "Do you drink plenty of water every day?" is
a question which a good physician often asks his patients;
and in giving medicine he may prescribe a whole glass of
water with a very small pill. It has been stated that three-
quarters of the "blues," ''gray days" and "east winds"
which come over people, discouraging and depressing them,
would be escaped if they would only drink a sufficient amount
of cold water.

All living matter, i.e. all protoplasm, contains water; and
while we cannot say that water is a food, we do know that it

FOODS AND FOOD HABITS 57

is vitally necessary to us. No solid matter can be absorbed
into the blood; everything must be dissolved and reduced to
a thin liquid in order to pass through the walls of the intes-
tine. The water necessary for this must be present, or ab-
sorption cannot take place.

If the food in the intestine is in a comparatively dry con-
dition, it is moved along with difficulty, and indigestion may
be the result. We are more likely to drink water too cold than
to drink it in too great quantities; if very cold, it may chill
the secreting surfaces, thus retarding their work and inter-
fering with digestion. The amount of water given off through
the lungs is about one pint per day, from the skin two pints,
and through the kidneys, in the case of an average person, a
little over three pints per day. Thus the demand for fresh
water is constant.

As a result of the life processes, broken down products of
body metabolism are continually produced. This material
must be eliminated, and for this purpose it must be dissolved
in the blood so as to be carried to the excreting organs. If
one drinks too little water, the blood may become overcharged
with such waste products, some of which are poisonous. These
substances, when too abundant in the blood, may dull the
nerve centers, giving one a disheartened feeling, and leaving
him in poor mental condition for meeting the demands of life.
By drinking plenty of water the body is kept constantly
"flushed," as it were, and one's whole life is more vigor-
ous and active. The Japanese soldiers have taught the
world a lesson in methods of preserving health, and
among other things have shown the beneficial results
arising from drinking large quantities of pure water without
''stimulants.""

There is no good reason why we should not drink water
freely during meals. The reason sometimes given for the
contrary view — that water dilutes the saliva and gastric
juice— has no great weight. Not only is water readily ab-

ADVANCED PHYSIOLOGY

sorbed, but digestion proceeds more rapidly when the Juices
are somewhat diluted.

Other Beverages. — In America, the most commonly used
beverages, other than water, are probably coffee, tea, cocoa
and chocolate. Cocoa and chocolate are foods, since they
contain some fatty material. Coffee and tea, on the other
hand, can be considered only as stimulants. The active ele-
ment in coffee is a substance called caffein; that in tea is
called thein, the two being practically identical. The degree
to which these affect different individuals is variable. As a
rule they excite the nerve centers to greater activity. This may
be of advantage in rare cases; but not when one is in bed,
trying to sleep. After the use of these drinks becomes a
habit, the nerve centers refuse to act well unless urged on
by this "whip" and it is better to live in the strength of one's,
own natural vigor.

The "soft drinks" sold at soda fountains are made of water'
into which carbon dioxid gas has been pressed. Flavors in
the form of syrups are added. Since carbon dioxid is reallyj
one of the waste products of the body, we might suppose that
in our drink it would be harmful; but it is of real injury only
when we breathe it. However, such drinks are no better
than water; they are expensive and the syrups may impair
digestion. Lemonade is used solely for its agreeable taste,
although the sugar which is usually in it serves to a small
degree as food. Some beverages are advertised as especially ^
''good for the nerves," but this claim is largely a pretense
used for the purpose of catching trade. If one finds any!
drink especially exhilarating, he is warranted in suspecting]
that it contains alcohol or a similar ingredient that produces
temporary excitement.

Alcohol. — Alcohol must be considered here because it has
so often been classed as a food, and has even been given the
unfortunate misnomer, "liquid bread". Alcohol is derived
from sugars by a process of fermentation. A large number

FOODS AND FOOD HABITS «>

of vegetable products contain considerable starch which can
easily be converted into sugar, and almost any of these may
serve as a source of alcohol. The fermenting agent in all
cases is yeast. This is sometimes intentionally added to the
fermentable mass; but sometimes fermentation is caused
simply by the action of the so-called wild yeasts, i. e. germs
which exist everywhere in nature, and which may get into the
material from the air, or more often from the skin of the fruit
or other substance which furnishes the sugar. In wine and
cider making, for instance, the yeasts are on the skius of the
fruits, having dropped there from the air. The yeasts ferment
the sugars, converting them into alcohol and carbon dioxid,
and the fermented product is used to form the basis of
alcoholic and fermented liquors.

Alcohol has a variety of undesirable effects upon the
different functions of the body, and they are sometimes even
disastrous, as will be pointed out from time to time in later
pages. Here a word is in place concerning its possible food
value.

Alcohol has no power to build up the body. It furnishes
no tissue-building material and neither makes nor repairs any
organ. Hence it does not nourish in the sense of building up
the body. When taken in any except the smallest quantities,
it is nearly all excreted from the body as alcohol; it is thus
not utilized by the body and simply taxes the excreting
organs.

A small amount of the alcohol taken, however, is not thus
excreted but is consumed in the body, and the effect of this
small portion must be considered. It is oxidized, and when
alcohol is oxidized, it yields heat. This will occur if the oxi-
dation takes place in a lamp and none the less surely if in the
body; hence to a certain extent, alcohol is a source of heat.
But only a small amount of our body heat can be derived from
alcohol, not enough to constitute any considerable part of the
supply needed for a day. Though a small quantity may fur-

60 ADVANCED PHYSIOLOGY

nish a little heat, a larger amount of alcohol does not furnish
more heat; it simply exerts a stronger and more clearly poison-
ous action. Moreover, the heat is not really utilized so effi-
ciently as is the heat that comes from the oxidation of sugars;
for one of the first effects of alcohol on the body is to enlarge the
blood vessels in the skin, producing a flushed condition. This
at once causes an increased loss of heat and in many cases,
if not in all, more heat is lost in this way than is gained from
the alcohol oxidized. The total result is, therefore, a loss rather
than a gain of heat.

When we consider its further effects on the body, we soon
find that it cannot properly be classed with the fuel foods
like starch and sugar. Gunpowder if placed in a stove will
yield plenty of heat, but notwithstanding this fact, it should
certainly not be classed with fuels like wood and coal. So
alcohol, even though it yields heat, has at the same time such
undesirable effects upon the body as to destroy its value
as a fuel food. The most exhaustive study has shown that
alcohol is certainly a poison, interfering with the normal
action of the cells of the body, and above all, with the nor-
mal action of the brain. This will be considered at length in
a later chapter.

Nor is there any difference of opinion as to the wisest
course to pursue in regard to the use of all forms of alcoholic
drinks. They are all injurious, tending to throw the organs
out of order, especially those ot the nervous system, and they
interfere with a healthful vigoroup life. Everyone who
indulges in them at all is occasionally or constantly under the
influence of their poisoning effect, and the onlr safe course
is to avoid their use entirely.

Concerning these facts there is no question- The dispuce
as to whether alcohol should or should not be called a fooa
has been due to a difference in opinion as to the definition
of the word food and need not concern us. The accepted
^^cts are clear and definite: alcohol is primarily a cellular

^^OODS AND FOOD HABITS 61

and nerve poison. If used in very small quantities it may
yield heat and energy but whatever value it might have in
this respect is usually quite nullified by its poisoning action.
For this reason it cannot be classed with fatty and carbo-
hydrate foods, and still less with proteid foods. The state-
ment sometimes made that it is ''liquid bread " is absolutely
false and misleading.

CHAPTER IV

FERMENTATION AND GERM DISEASES

Before food can be absorbed in the body it must be digested.
We shall study the details of digestion later, but before taking
them up, we must learn a little about the general process.

The changes in food during diges-
tion belong to a type of activities
known as fermentation. It is dif-
ficult to define the word fermen-
tation, and we can best learn its
meaning through illustrations.

TYPES OF FERMENTATION

Alcoholic Fermentation. — If to a

solution of sugar a little yeast is
added, an active change soon be-
gins. The sugar disintegrates and
turns into alcohol and carbon
dioxid gas. The sugar does not
change spontaneously but only
after the yeast is added, and the
process continues until the sugar is used up. The micro-
scope shows yeast to be a minute living plant; Fig. 27.
While the sugar is fermenting,
the yeast grows and multiplies,
fermentation being a result of
its growth. If the yeast is
boiled, it is killed and can
no longer excite fermentation.
Since this yeast is a Hving plant Fig. 27.— Growing yeast plants

.. 1 •!_ n J Showing the method of formation of

it can properly be called an buds on the sides of the ceils.

L'\n\e\JiicxVtT

flG. 26. A FERMENTING

SOLUTION

Showing the method of con-
ducting carbon dioxid gas into
lime water.

FERMENTATION AND GERM DISEASES 63

organism, and we speak of this kind of fermentation as due
to an organized ferment.

Later in this chapter, another group of organisms, the bac-
teria, are discussed and their intense fermentative powers are
pointed out. Being organisms, they too would be termed
organized ferments. While this designation is a convenient
one in some ways, there is valid objection to its use. It is not
the organisms themselves which are the ferments, but rather
the substances which they produce. But usage has, as a
rule, been that which is adopted in this text.

Fermentation of Starch. — The change of starch to sugar
is a very simple one and is due to the union of starch with a
little water, as follows:

C6H10O5 + H2O = C6Hl20«
Starch Water Sugar

If we mix starch with water alone, we get no such result;
but when we mix starch and water with saliva, the combina-
tion of starch with water begins, and sugar is formed. This
may continue until the starch is all converted into sugar.
If we boil the saliva it entirely loses this power; yet, if we^
study saliva with a microscope we find no living bodies in it
corresponding to the yeast plant. Nevertheless, there is some-
thing in the saliva that provokes this change. That something
can be separated from the saliva, and when so separated it
appears as a white, structureless powder. It does not grow,
multiply or increase like yeast during the fermentation pro-
cesses. Since it is not alive it cannot be called an organism,
and we speak of it as an unorganized ferment; it is more
commonly called an enzyme. It is clearly a ferment but quite
different from the yeast ferment. Moreover, when this enzyme
converts starch into sugar, the starch and some water arc
used up, but the enzyme remains unaltered.

64 • ADVANCED PHYSIOLOGY

Further than this, we should note that a substance which
has undergone one fermentative process and been broken up
chemically into two or more different substances, may be still
further subjected to changes by other ferments. As an illus-
tration: starch changes into sugar; sugar may be broken by
fermentation into alcohol and carbon dioxid; alcohol by
fermentation will yield acetic acid (the acid of vinegar) and
water; acetic acid by fermentation is resolved into carbon
dioxid and water.

It is noticeable that the change is always from what is com-
plex to things which are simpler; fermentation never produces
the opposite result, i. e., is never constructive. In other
words, to use a chemical term, ferments are catalytic agents.

These two examples are illustrations of different types
of fermentation, one produced by the growth of living, micro-
scopic plants; the other by non-living enzymes.

While these fermenting agents are unlike in many respects,
their activities agree in the following points, which are, there-
fore, characteristic of fermentations. 1. They are progres-
sive chemical changes which take place in organic bodies. By
^'progressive" is meant that when once begun they continue
until the fermenting body is used up or until something stops \
the action. 2. They never take place spontaneously, but
are brought about by the addition to the fermentable body
of substances called ferments. 3. They are stopped by the
influence of heat, and by the presence of some chemicals.
4. The substance which starts fermentation does not appear '
to be used up in the process.

When a substance ferments, its nature is totally changed;
alcohol and carbon dioxid are quite different from sugar,
and sugar is unlike starch. Fermentation always forms new
substances, and these new substances are sometimes good and
sometimes bad in their effects. Fermentations may produce
poisons from perfectly harmless substances. When starch
is turned into sugar, the product is a useful food, but when
sugar is turned into alcohol, the product is dangerous and

FERMENTATION AND GERM DISEASES 65

extremely harmful. When substances like meats are fer-
mented (or putrefied) deadly poisons are sometimes pro-
duced. Hence, materials that were originally wholesome and
harmless may, through fermentation, become unwholesome
or even poisonous.

In the study of physiology we are concerned with both
the organized and the unorganized types of ferments, but in
consideration of digestion we have to do especially with the
latter, or enzyme type. Several enzymes are formed in the
body. Saliva contains one, which is called ptyalin. The gas-
tric juice contains a second, called pepsin and another, called
rennet. The pancreatic fluid probably contains three, —
trypsin, amylopsin and steapsin, all of which contribute to
the digestion of food. They are all normal products and are
secreted by glands.

Organized ferments are living organisms, capable of growth
and multiplication. Because of their microscopic size they
are frequently called microbes; they are also called germs;
but neither of these terms is very satisfactory, and it is better
to call them by their proper name's, yeasts and bacteria.

Living ferments, save when taken in large numbers, are
invisible to the naked eye but are easily seen with a microscope.

They differ from each ^^^^^ -v/^-^

other chiefly in their Q Q QJ QQ
method of multiplica-
tion. Yeasts multiply
by the formation of
a small bud on the c i — Z)

side of the plant; Fig. Fig. 28.— Showing the method op

07 Tk^ U-^A «.„^^.o ;^ MULTIPLICATION OF BACTERIA, BY

Z7, ine bud grows in '

., _ ,f . . SIMPLY ELONGATING AND THEN DIVID-

size until finally it is ^^^
as large as the original

plant, when it may break away as a separate one. Bac-
teria, however, simply increase a little in length and then
break in two in the middle; Fig. 28. Both bacteria and

ADVANCED PHYSIOLOGY

yeasts bear very important relations to human health
and happiness.

YEASTS

Yeasts are abundant everywhere; they float in the air, are
found in water and are in and on the ground. Such yeasts

are sometimes called wild
yeasts. Scientists have learned
to cultivate them in labora-
tories, and they may be
grown in great masses. A cake
of compressed yeast is simply
a cake of millions of these
tiny plants, all alive and ready

Fig. 29 — Recently mixed dough,
inoculated with yeast, but
before the yeast has grown

(Conn, Bacteria, Yeasts and Molds).

to grow if given proper food.
These are called cultivated
yeasts; but in reality the culti-
vated yeasts and the wild yeasts
are the same kind of plants.
When a cook wishes the
dough " to rise," she puts a
yeast cake in it, and the yeast,
growing in the dough, ferments sugar in the starch of the
fiour, producing bubbles of gas, which make the cUugh

Fig. 30. — The same dough

AFTER yeast HAS GROWN AND
CAUSED THE DOUGH TO SWELL
BY THE ACCUMULATION OF GAS
(Conn, Bacteria, Yeasts and Molds),

FERMENTATION AND GERM DISEASES 67

''swell"; Figs 29 and 30. Alcohol also is produced, but passes
off when the bread is baked. The use of baking soda in pre-
paring food materials produces a lightness due to bubbles
also; but only the water in the mass is affected by its presence.
When a brewer makes beer, he makes a solution from certain
grains, containing starch which is changed into sugar, and
l^lants yeast in it. The yeast grows and destroys the sugar,
producing alcohol and carbonic acid gas. In the making of
cider or wine, when the sweet juice from apples or grapes is
squeezed out and placed in barrels, the wild yeasts from the
air grow in it, producing the same changes.

BACTERIA

Bacteria are more abundant than yeasts and are even
smaller (Fig. 31); they are so small that sometimes 50,00lr
of them, side by side,
would reach only an inch.
But small as they are,
they play a very impor-
tant part in our lives and
in the world. It may seem
strange that organisms as Fig. 31.— Showing the comparative
minute as these can have ^^"^^ ^^ '^^^ ^^™^ ^^ ^^^ ^^^^^'^

. - , „ ^ . CAMBRIC NEEDLE (a), A PARTICLE OF

an appreciable effect. A bust (6), bacteria (c), and yeasts (d)

single one, to be sure,

could do very little; but bacteria have such wonderful powers
of reproduction that they can accomplish much. So fast
do they multiply that, under favorable conditions, in twenty-
four hours a single one may have seventeen million offspring,
and in another twenty-four hours each of the first seventeen
millions may have seventeen million more. Most people
think of bacteria, germs or microbes as our deadly foes. While
this is partly true, it is likewise true that they are our friends.
Their distribution in the world shows clearly enough that they

ADVANCED PHYSIOLOGY

Fig. 32. — A bit of decaying meat

Highly magnified, showing the bacteria that
cause its decay.

cannot always be mischievous. They are found in the soil

under our feet, in the air we breathe, in the water and milkj

we drink, in much of the
food we eat; Fig. 32. They
are on our clothing, on our
skin, in our mouths and
stomachs (Fig. 33) ; there
are countless millions in
the intestine of every
healthy person.

Beneficial Bacteria. —
Although bacteria are
very small and are very_
simple organisms, then
are many different kinds
known; and while some
are injurious, the great
majority are harmless

and some are even beneficiaL One of the ways in which

tiiey are of value to us is through their power of causing

all sorts of putrefaction and decay.

This may not seem to be either

useful or desirable. Putrefying and

decaying material is disagreeable

and its odor is unpleasant, but

the process is really one of great

value, for it is nature's way of de-
stroying the dead bodies of animals

and plants, which would otherwise

accumulate, covering the ground

and fining the streams. The

bacteria of the air, ground and

water attack and consume all such

materials. As they consume them

they produce gases which give the unpleasant odors to the

Fig. 33. — Bacteria from a
healthy mouth, magni-
FIED

Bacteria

THE MICROSCOPE
Showing fat drops and bacteria.

FERMENTATION AND GERM DISEASES 69

decaying bodies. Nearly all kinds of decay are thus produced
by bacteria or closely allied organisms. The putrefaction of
meats and eggs, the souring of bread and milk, and hosts of
other processes by which
fooa is spoiled are instances
of bacterial action; Fig. 34.

Since the spoiling of food is
produced by bacteria, it fol-
lows that the preservation of
food for an indefinite length
of time is possible if bacteria
can be kept from it. This
is not an easy matter, how- Fig. 34.— A drop of milk under
ever, because of the wide
distribution of these plants.
They are sure to get into the foods in spite of all
ordinary caution. But many foods may be protected
from them by the process of canning. In canning, foods
are first subjected to a heat (commonly boiling) sufficient
to kill any bacteria in them, and then are sealed up in jars
or cans so tightly that no air or bacteria can reach them.
If this is done thoroughly and carefully, the food will keep
indefinitely. At any time afterward the cans may be opened
with the certainty that the food will be found in good condi-
tion. The discovery of the methods of canning has been of
extreme value, for it made it possible to preserve for winter
use vast quantities of food grown in the summer, which would
otherwise spoil before they could be consumed.

When such materials are decomposed by bacteria the prod-
i ucts that come from them pass into the soil and air in a form

I which can be used by subsequent generations of plants. In
this way soil is kept fertile, and we can depend upon getting,
rear after year, abundant harvests. Were it not for the
Iction of bacteria the soil would soon cease to yield crops,
knd we should eventually starve.
I

76 ABVANCED PHYSIOLOGY

The flavors of butter and, in part, of cheese are due to bac-
teria. Butter makers have learned that they can make
better butter if they put bacteria into the cream out of which
butter is to be made. They plant bacteria in cream, much as
cooks plant yeast in bread for bread raising, or farmers
plant grass in the fields. We must, therefore, look on bacteria
in many cases as our best friends. When we remember that
we have always carried millions of them in our mouths, and
still have enjoyed good health, we must not be alarmed if
we are told that there are bacteria in water, or milk, or in the
air we breathe.

Harmful Bacteria. — Unfortunately some kinds of harmful
bacteria live and grow in the \arious organs of our bodies.
It is easy to understand that when these minute parasites
are growing in great numbers in different parts of the body,
they may produce trouble. Such troubles are called diseases,
and to the bacteria which cause them is given the name of
disease germs, or pathogenic bacteria.

Not all kinds of disease are produced by bacteria. Some^
like malaria, are caused by tiny animals. The causes of some
diseases have not yet been determined, but probably many
are brought about independently of bacteria or parasitic
animals. Nevertheless, most of the common illnesses are pro-
duced by them, and none of the diseases caused by bacteria ever
make their appearance unless the germs that cause them
first get into the body and find opportunities for growth
there. Any disease caused by living germs is called infectious.

In most of these diseases the bacteria, after having developed
in the body for a while, begin to be given off in some way.
Sometimes this takes place through the mouth, sometimes
through the excreta, sometimes through the breath, sometimes
through special discharges of the skin. When bacteria are
thus given off from the body of a sick person, they are alive
and active, and are generally in condition to enter the body
vf another individual and produce the same trouble in him.

FERMENTATION AND GERM DISEASES 71

Hence one person can easily take a disease from another.
Such diseases are called contagious.

All contagious diseases such as diphtheriaj typhoid fever,
liiherculosis, measles, whooping cough, scarlet fever and small-
pox seem to be produced by living organisms, minute in size
but capable of living a parasitic Ufe in the body, and passing
readily from one person to another. The germs causing them
are not always of that class called bacteria, but they are always
minute, always parasitic and may all be properly classed
as disease germs. The methods by which these germs pass
from the patient to the healthy individual are various. The
bacteria themselves are not capable of any considerable
amount of motion, and are never able, of themselves, to travel
from person to person. They must be carried, and the various
kinds are carried by different means. Some are carried in the
air, some by water and some by insects.

Some diseases are very contagious, by which we mean
that they are very easily *' caught "; and others are slightly
contagious. This really refers to the ease with which the germs
can be carried from person to person and taken into the body.
In cases where the germs must pass into the water and be sub-
sequently drunk before they can enter the body of another
individual, it is evident that the liability of contagion is less
than in the cases where they simply pass into the air and are
breathed in by a second individual. All such diseases are
infectious, but not all are necessarily contagious. A study of
methods of transmission will give us valuable information as to
ways of preventing contagion.

IMMUNITY

Almost all kinds of bacteria are harmless even if they do
get into our bodies. This means that they are not able to
multiply in the body so extensively as to produce trouble.
We are immune against them. Moreover, certain kinds of
bacteria can grow in some of the lower animals and produce

72 ADVANCED PHYSIOLOGY

trouble there, though the same sort cannot injure man.
Further, it is well known that some people ''catch" diseases
more easily than others. Some people, indeed, although
again and again exposed to diseases, do not take them,
while others under the same conditions take them easily
enough. .

Lastly, in the case of some diseases, such as scarlet fever,
mumps and whooping cough, if a person has them once and
recovers, he is not likely to have them again even though
exposed to them. Such persons are immune against a second
attack of these diseases. Immunity is a condition which
enables a person to resist diseases when exposed to them. The
greater one's power to withstand diseases, the more secure
is his health.

There are various methods by which immunity can be
produced; one factor only need be mentioned here.

Resisting power varies with the physical condition of the per-
son. One in good health, with strong vitality, is less liable to
take the germ diseases than one who is less robust and vigorous.
Out-of-door life, and the eating of wholesome foods are, thus,
among our greatest safeguards against them. Especially
has it been shown that alcohol tends to lower this power of
resistance, and persons addicted to the use of alcoholic bever-
ages are more liable to yield to the attack of infectious dis-
eases than are those who refrain from their use. The reasons
for this are not wholly known. It is certain that alcohol
is primarily a poison, acting directly upon the living cells
so as to interfere with their normal functions. Resistance to
disease is dependent upon the activities of the cells, and it
is natural to conclude that if alcohol acts in any degree as a
cell poison it will interfere with this resisting power. At all
events, the facts are certain; and the more frequent the use
of alcohol, the less is one's power of resistance to harmful
bacteria.

FERMENTATION AND GERM DISEASES 73

STERILIZATION AND DISINFECTION

In connection with bacteria and germ diseases, we fre-
quently hear the terms, sterilization and disinfection. To
disinfect means to treat a thing in such a manner as to destroy
any micro-organisms that might produce infection or disease.
If there were harmful bacteria in water and we could kill them
mthout injuring the water, evidently the danger in drinking it
would be removed. If a room has been occupied for some time
by persons suffering with a germ disease, bacteria may be
distributed through the room, on the floor, ceihngs, curtains,
etc., and other people who come to live in the room later will
be likely to become infected. If we can treat the room in such
a way as to destroy the bacteria, it may be rendered safe. This
we call disinfection. To steriUze any object means to kill all
organisms -whether disease-producing or not.

Th^' simplest method of sterilizing is by the use of heat.
All bacteria are killed by sufficient heat, and nearly all that
are liable to produce disease in man are killed by the heat
of boiling water. Therefore anything that can be boiled,
like water or milk, or anything that can be treated in boiling
water, like towels or sheets, can be easily sterilized by this
means. Water and milk are frequently treated in this way
when there is any suspicion of their infection. When one is
uncertain as to how to sterilize or disinfect suspected articles
it is wisest to follow the advice of health officers, whose
duty it is to know these methods and their practical appli-
cations.

CHAPTER V
DIGESTION OF FOOD: THE MOUTH AND THROAT

In their original condition most of our foods are of no more
value to the body than are the trees of the forest or the stones
of the quarry to the builder, good as raw
material, but not immediately available.
Before they can be taken into the blood
they must be softened, ground up into
small bits and at least partially dissolved
into liquid form. This process is a long
Fig. 35.— Scale- ^^^ beginning, perhaps, when the food

LIKE CELLS FROM . . ,, , j r xl, u x T_ '11

THE LINING OF THE ^^ m the hauds of the butcher or miller,
MOUTH and carried further, by some process

of cooking. The chief part of this prep-
aration, however, is performed by the alimentary canal,
whose main function is to grind and dissolve the food masses
into readiness for absorption. This process of disintegra-
tion is partly mechanical and partly chemical, and we call
it digestion. The digestive canal is, in a sense, a chemical
laboratory.

THE MOUTH

The preparation of food for absorption begins in the mouth.
The whole mouth cavity is lined with a smooth, moist mem-
brane, consisting of cells (Fig. 35), which secrete a transparent
liquid somewhat thicker than water and called mucus.
Mucus is of no value as a factor in digestion, but it keeps the
lining membranes soft and flexible, and lubricates dry foods

DIGESTION OF FOOD: THE MOUTH

so that they can be pushed back toward the throat more
easily. This Hving mucous membrane and the outer skin
of the body come together at the Hps. They are much alike
in structure save that
the blood vessels
come nearer the sur-
face in the mucous
membrane and make
it look redder.

The Teeth.— Back of
the lips, which aid
slightly in holding and
directing the food, are
the teeth. These, by
catting, tearing and
grinding the food, pre-
{)are it for digestion.
Their shapes are ad-
mirably adapted for
this work, which is
called mastication.

The teeth of each
side of each jaw, begin-
ning at the middle in front, comprise two incisors, one canine^
t wo bicuspids and three molars, or grinders. The incisors (Fig.
06 /) with chisel edges are used almost exclusively for cutting
pieces from large morsels; in chewing they come into action
very little. The canines (Fig. 36 C), named from their similarity
to the tearing, tusk-Hke teeth of dogs, are of no great service
to civiUzed man, who, though he may eat fruits without first
cutting them, usually cuts his other foods with knife and
fork. The bicuspids (Fig. 36 B), so called from the two prom-
inences, or cusps, on their free ends, are of use partly for tear-
ing, and partly for grinding. The molars (Fig. 36 M), or heavy,
many-cusped " back teeth," are solely for grinding. Their

Fig. 36. — Showing the upper jaw of a
child and the lower jaw of an adult

In the upper figure Bu indicates the buds of
the permanent teeth nearly ready to push out
the first set, or milk teeth.

ADVANCED PHYSIOLOGY

position, far back near the hinge of the lower jaw, gives
great leverage; and being farthest from the mouth opening
and nearest the largest part of the cheek, room for their
grinding function is insured. The remarkable fitness of each
structure for its work is a striking fact which may be no-
ticed in all parts of the body. All of these are permanent teeth.
All except the molars are preceded in childhood by baby teeth
which are lost in early years. Permanent teeth may appear as
early as six years of age, and since this is so, particular pains
should be taken that they are properly cared for from the time
of their first * 'cutting through."

If a tooth is cut open, it proves to be made of four kinds
of material. The outside layer (see Fig. 37), an extremely

hard deposit of calcium phosphate,
is called the enamel. This is thick-
est on the exposed surface of the
tooth, or crown, and diminishes until,
as the tooth enters the gum, it gives
way entirely to a softer substance,
the cement. This cement covers
the roots and connects the teeth
firmly with their sockets in the jaw
bone. It is this substance which
yields when a tooth is extracted.

Inside the enamel and cement is a
uniform layer, the dentine. This,
too, is calcium phosphate in compo-
sition, but is less hard than the
enamel. Inside the dentine is a space occupying the
central part of the tooth, and extending down into the
tips of the roots. This central space is occupied by a soft,
pasty mass, like the marrow of a bone, filled with fatty and
connective tissues, blood vessels and nerves. These vessels
and nerves enter the tips of the roots, the former bringing

Decoued

Cement

'Nerve

Fig. 37. — A section

THROUGH A TOOTH

DIGESTION OF FOOD: THE MOUTH 77

nutritive materials for the tooth, the latter regulating the
use of these materials; Figs. 36 and 37.

Care of the Teeth. — Cleaning the teeth may seem to be

unnecessary, or merely a matter of good form; but this is a
wrong idea. In spite of the hard nature of the teeth, they
are very liable to decay, as almost everyone knows to his
misfortune. This decay is brought about by circumstances
which we can in great measure prevent if we understand
them. It is caused in part by the bacteria in the mouth.
These are not able to affect the uninjured teeth though they
can readily attack the softer foods that may lodge in or between
them. If, after eating, one chances to leave some of the food
in the crevices between the teeth, the bacteria at once begin
to feed upon it. The mouth is warm and moist and furnishes
the very best possible conditions for bacterial growth. In these
particles of food, therefore, bacteria flourish and, after a time,
turn them sour in much the same way that they turn milk
sour. The sourness is due to the production of an acid, which,
although not formed in very large amounts, always appears
if food is left between the teeth. Upon the hard substance
of the teeth this acid acts at once, dissolving the lime in such
a way as to produce soft spots or even cavities. Upon the
hard enamel the acid acts only with difficulty, but if this
is cracked or broken the acid acts easily upon the softer den-
tine within. As soon as these weak spots appear the teeth
decay rapidly; Fig. 37. Since our permanent teeth do not grow
and are never repaired or replaced by nature, it is very impor-
tant that they be kept in good condition.

It is becoming more and more certain that material from
decayed teeth, or from pus cavities in or above their roots,
may cause very unexpected and serious results, e. g. nervous-
ness, epilepsy, indigestion, blindness, or even insanity. **Mouth
cleanliness'* is of the greatest importance.

What is the use of toothache ? Though unpleasant, it certainly

ADVANCED PHYSIOLOGY

tells one that he is not treating his teeth properly since a tooth-
ache generally means decay. If one avoids injuring the en-
amel with hard substances, and if he does not allow food to
remain between the teeth for the bacteria to act upon, he can
thus check the pro'cess of decay. Carbohydrate foods are most
liable to be turned acid by bacteria, and hence bits of cracker
or bread are among the worst materials to leave lodged in
the mouth.

When a tooth begins to decay, the dentist removes the
decaying portion; he then closes the opening with gold or
silver or some other hard material. It is extremely important
to have a cavity attended to when it is very small so as to

save the tooth; hence the

Papiltoe with taste buds

Tbns'if

teeth should be examined
by a dentist at least twice
a year. This is not only
necessary as a means to uni-
form health, but, contrary to
the belief of some, is much
the most economical custom
for every one.

The Tongue. — The tongue
is a mass of muscles whose
fibres can move it in differ-
ent ways, either guiding
the food in the process
of chewing or carrying
the food back toward the
gullet. On the upper surfaces of this organ are numer-
ous minute projections, or papillse; Fig. 38. Everyone has
noticed the very rough tongues of dogs and cats. On the hu-
man tongue are three kinds of papillse. The largest, called
the circumvallate, are few in number and at the very back of
the tongue; Fig. 38. These papillae are short and blunt in

Tig.

-The surface

TONGUE

OF THE

DIGESTION OF FOOD: THE MOUTH

Openincj

To sM Cells

structure, growing up from shallow pits in the tongue^s surface-
More numerous than these and scattered over the remainder
of the tongue are two types, the filiform and the fungiform
papillae. As the terms indicate, the former are slender and
thread-like; the latter are short, pillar-like growths. In the
tissues of the circumvallate and fungiform papillae are located
the organs of taste, the so-called taste buds. The cells making
up these buds are elongate, arranged in a more or less spherical
mass. The cells in the middle of this mass come close to the
surface and are affected by the
food which touches them; Fig. 39.
From them the stimulus passes
through nerves to the brain.

There is a kind of taste geog-
raphy mapped out on the tongue's
surface. Bitter tastes are noticed
at the back of the tongue, acid on
the sides, salt and sweet toward
the front. None of these tastes can
be perceived if the tongue be wiped
dry. In other words, all material
to be tasted must be in solution.*
Electric stimuli applied to the
tongue produce the same impres-
sion as dissolved foods. Thus
arises the popular contention that

electricity is sweet, for the wires are usually applied to that
portion in which the sweet-perceiving nerve endings are
located.

The Palate. — The roof of the mouth toward the front is
called the hard palate and contains a bony partition between
the mouth and nose chambers. This bony partition, however,
soon ends, and the palate continues backward toward the
throat as a soft membrane; Fig. 40. This soft palate extends

* Students should prove these statements by experiments at home.

Fig. 39. — A taste bud from

THE TONGUE
Highly magnified, showing the
taste cella.

ADVANCED PHYSIOLOGY

to the place where the nose and mouth cavities come together
to form the throat or pharynx. From the back edges of the
soft palate, just in the middle, hangs down the uvula, a ver-
tically placed piece
of connective tissue
and muscle, half an
inch long and about
a quarter of an inch
thick. The uvula
sometimes becomes
swollen and elon-
gated until it hangs
down on the tongue
and even into the
throat. It then pro-
duces a slight tick-
ling which excites a
cough. A physician
sometimes cures dis-
eases of the throat

-^Tonsil
GloHis
Oesophagus

Sptn<JCord'-'''

Fig. 40. — A section through the head

Ehowingasurface view of the biain, and the mouth by removing a piece
and nasal cavities. ^f ^Jie UVUla.

In these days of hurry and stress, too much emphasis cannot
be placed on the necessity of thoroughly chewing the food.
If swallowed in large pieces, only the surface of these will
easily dissolved.

DIGESTION IN THE MOUTH

While food is being crushed into small pieces by the teeth
it is mixed with the liquids in the mouth until thoroughl;
moist. The membranes of the mouth are kept wet by
a mucous fluid that exudes from their surfaces and is
mixed with the food, upon which it really has no special
effect. As soon as the food enters the mouth and in-
deed, sometimes before — for the mere sight of food or

DIGESTION OF FOOD: THE MOUTH

Fig. 41.-

Arterif
Diagram

Showing the positions of the
parotid and submaxillary
glands.

even the thought of it produces the same effect — a watery
liquid, the saliva, begins to be poured into the mouth.
This comes from three pairs of
salivary glands. 1. The parotid,
j ust below and in front of each ear,
with long ducts opening through the
sides of the mouth opposite the
second molar teeth. 2. The sub-
lingual, beneath the tongue, with
numerous separate ducts. 3. The
submaxillary, beneath the tongue,
on each side, near the angle of the
jaw; Fig. 41. The ducts of these
last open under the tongue, on each
side of the middle, toward the front,
on slight elevations.

These salivary glands are com-
pact masses of varying sizes. The

parotids are fiat and of almost the same area as the ear;
the submaxillaries are about the size of. a walnut. Under a
microscope they are found to consist of many minute cavities.
If one imagines a cluster of extremely small grapes, which are
hollow, and discharge sap into their stems, he will get a good
picture of the structure of such a gland; Fig. 42. Each spher-
ical cavity (or each grape in the illustration) is called an
alveolus, and each has its walls made of cells. The cells
extract from the blood material out of which they make
saliva; this they pour into a little duct which drains the
alveolus. Each duct joins others from other alveoli, and all
finally unite to form a single duct which carries the secretion
into the mouth. These little clusters of hollow sacs are micro*
scopic, very numerous, and all bound together into a compact
mass. Several other glands in the body are constructed on
the same plan, and this pattern is called racemose from a
Latin word that means " full of clusters."

ADVAN€EB PHYSIOLO^IY

the

The salivary glands really receive stimuli from the brain.
The taste of food starts a nerve impulse that goes to the brain;
there certain nerve centers are excited and from them another
impulse passes to the salivary glands, causing them to se-
crete saliva. This passage of
the impulse from the brain
to the glands is an uncon-
scious one, and we certainly
do not secrete saliva by any
volition of our own. Such an
action is called a reflex action.

Saliva is more than
water. This moistens
food and makes it easy to
swallow. Indeed, this is one
of the most important func-
tions of saliva. One cannot
swallow a dry cracker until
he has thoroughly wet it with
saliva or water. When people are much frightened their sali-
vary glands sometimes refuse to secrete and at such times
they find it difficult or impossible to swallow.

While this is a very important function, saliva has also
a digestive action on the food. This is due to an enzyme called
ptyalin, present only in very minute quantity, but having
a powerful effect on starch, which it converts into sugar.
This change is absolutely necessary, since starch unchanged
cannot be absorbed from the digestive tract and hence cannot
be used in the body. The conversion of starch into sugar, as
we have already noticed, is brought about by the addition of
water to starch. (See page 63.) But this combination will not
occur except under the influence of some outside agent such
as ptyalin. Sugar is a substance that is easily absorbed
through the intestine while starch cannot be absorbed at all.
Hence this change from starch into sugar is true digestion.

Fig. 42. — Showing the structure
of a salivary gland

A , moderately magnified and represent-
ed as less compact than in reality, B,
two alveoli, highly magnified and show-
ing the connection with the duct.

DIGESTION OF FOOD: THE MOUTH 83

In eating, food is usually kept for so short a time in the
mouth, is so imperfectly chewed and broken up that the
ptyalin solution acts upon only a small portion of the starch.
Saliva does not at all affect other foods, i.e. fats or proteids.
In its chemical reaction it is slightly alkaline, due to traces
^of inorganic salts. Ptyalin will not act at all if the food mass
is acid, as when it is mixed with vinegar.

THE THROAT / 1 ;^

The Pharynx. — Back of the mouth and partly shut off
from it is a considerable cavity called the pharynx, or throat,
through which food must go before it reaches the gullet;
Fig. 40. In a person of average .*.

size this cavity is about four and fjif '^-c///^?

a half inches in length and of !-i'..v* '1

varying width.

It is partly shut off from the
mouth by the tongue below, by
the soft palate and uvula above,
and by the pillars of the fauces Fig. 43.— Ciliated cells that

, ,, ., rnt, 1 i. LINE THE PHARYNX

at the sides. These last are ver-
tically placed folds of tissue which can be easily seen by
opening the mouth widely before a mirror. They are
somewhat like thick curtains hanging down at the sides of
the opening into the throat.

The Tonsils. — To one who thinks that there is a use for
everything in the world, it is interesting to find that there
are several structures in the human body which are appar-
ently of no value. Among these are the tonsils, which are
frequently removed by a slight surgical operation. These
growths are located on each side of the passage from the
mouth to the throat, one between each pair of the pillars of
fauces; Fig. 40. They vary much in size, though in most
cases they are about as large as half a walnut. From their
position they are much exposed tQ currents of air taken iu

84 ADVANCED PHYSIOLOGY

through the nose or mouth, and thus easily become inflamed
by excessive cold, or by foreign particles in the air.

There are other openings into the pharynx besides that from
the mouth; of these, two open from the nose just above the
soft palate, near the mid-line. At this upper end where
the nasalpassages enter, the pharynx cavity is not very large
and is roofed over by the lower bone of the brain box, covered
by a soft membrane. Into this part of the pharynx project
innumerable hair-like structures, called cilia; Fig. 43. These
cilia are minute, transparent filaments which have the power
of lashing to and fro and creating a current in the mucus
on the surface of the cells. Particles of dust may thus be
moved along, and tears, which run down into the nose canals,
may also be hurried to the pharynx, where one becomes con-
scious of the liquid and spits it fiom the mouth or swallows it.

These dust particles in the air are generally covered with
bacteria; and since the tonsils are deeply wrinkled, these bacteria
easily lodge in the crevices and provoke inflammation. It has
even been proven that 80% of diseased tonsils harbor the
type of bacteria which causes tuberculosis, and may thus
act as an entrance point for this most serious malady.

In the upper part of the pharynx cavity on each side is a
minute opening through which a bristle can be thrust into a
canal leading to the ear. These small passages are called the
Eustachian tubes, and have much to do with hearing; Fig. 40.

If one closes the nose passages by holding the nose between
the fingers, and then swallows, the noise in the ears shows that
a passage exists between them and the throat. When the
pharynx wall is sore and swollen (pharyngitis) , this canal may
become closed and a disagreeable noise be constantly heard.

At the lower end of the pharynx are two comparatively
large openings. The front one is the glottis, which is the upper
end of the windpipe, and leads to the lungs; the one behind
that is in the gullet, or oesophagus opening, and leads to the
stomach. It is evident, then, that all food which leaves the

DIGESTION OF FOOD: THE MOUTH 85

mouth on the way to the stomach must pass over the upper
end of the windpipe.

There are, therefore, seven openings into, or out of the
pharynx, all of which may be closed. The large passage from
the mouth may be closed by the tongue, the soft palate and the
pillars of fauces, all of which contain muscles; the Eustachian
tubes can be closed by muscles going around the tubes and by
the pressure of surrounding tissues; the glottis, by a lid-like
door, the epiglottis, which drops back over the opening when
anything is swallowed; and the oesophagus may be closed
through the contraction of muscles which pass circularly
around it. The entrance from the nose passages is less per-
fectly shut off than the others and less often; but it can be
closed by the raising of the curtain-like soft palate and the
general contraction of the muscles in the upper part of the
pharynx. One or the other of these openings may be closed ac-
cording to whether food or air is passing through the cavity.

DISEASES OF THE MOUTH AND THROAT

Tonsilitis. — We have already noticed that the mouth usually
contains microscopic germs, called bacteria. Ordinarily these
do no harm, but occasionally bacteria of a more malignant
type get into the mouth and produce trouble.
They sometimes attack the tonsils or the* roof
and walls of the mouth and throat, causing
inflammation; the result is first noticed as a
sore throat, which may merely have an appear- Fig. 44. —
ance of redness that soon disappears. If the Bacteria
throat is covered with white patches, however, (Strepto-
and the tonsils are swollen and painful, the ?^^, .

Found m

trouble is called tonsilitis; Fig. 44. This is cases of ton-
accompanied by fever and a general feeling of ^^^'*^^-
illness; but it is not likely to be serious, and with proper treat-
ment will soon pass away. If the inflammation becomes still
greater, and the surrounding tissues are distended with pus,

Fig. 45.—

^ ADVANCED PHYSIOLOGY

making it almost impossible to swallow, it is called quinsy
sore-throat, which also yields to proper treatment.

Diphtheria. — Diphtheria has been one of the most serious
of human diseases and one which frequently results fatally.
It is produced by bacteria (Fig. 45.) which cause the formation
of white patches on the tonsils and near-by surfaces. These
• spread and grow together, finally forming a

js\ membrane over the throat which may extend

*^ ^ down into the windpipe and interfere with

breathing. Until recently no remedy for
diphtheria was known, and no disease excited
greater apprehension. Within the past feWj
(Bacterium 7^^^^, however, bacteriologists have found
diphtheria) method of treating it successfully by the us<
The cause of of a substance called antitoxin which neutral-
diphtheria. -^gg ^^^ g^g^^ Qf ^j^g bacteria. This anti-
toxin is prepared from the blood of horses which have previ-
ously been treated with diphtheria poisons. By its use, the
number of deaths from diphtheria has been much reduced.
It is better, however, to use the antitoxin in the early
stages of the disease. Therefore, it is important to attend
promptly to all cases of sore throat, and a physician should be
called whenever it becomes serious or when white spots appear.
Both tonsilitis and diphtheria are very contagious. The
bacteria in the throat pass out into the air when the patieni
coughs or speaks loudly, and they are also sure to get upoi
any object that the patient places in his mouth. Knives,^
forks and spoons used in eating, pencils which he may place^
in his mouth, books handled by the patient are all liable tc
be covered with the germs. Such articles will obviously be
a source of contagion to others who use them, but if the
articles are boiled, when possible, for ten minutes in water
this danger may be removed.

The serious nature of diphtheria and its frequency among
children has led to the custom of keeping from school those

DIGESTION OF FOOD: THE MOUTH 87

who have had the disease until the germs have disappeared
from their throats; sometimes other children from the same
family are kept at home, in quarantine as it is called, to pre-
vent them from carrying the germs to others in school. In
all cases the patient should be isolated; that is, he should be
kept in a room by himself and no one should be allowed to
see him except physicians and nurses. By such means the
spread of the germs can be prevented and many lives saved.
So dangerous is this disease that any precaution which will
prevent its dissemination is justifiable.

Mumps. — Mumps is another disease of the organs around
the mouth, being primarily a swollen condition of the parotid
glands. The face swells on one or both sides, swallowing is
painful, and for a day or tw^o the patient is very uncomfort-
able. The cause of the trouble is not known, and it usually soon
passes away. It is a contagious disease and can be avoided by
keeping away from those having it, but a person rarely has it
more than once.

Whooping Cough. — Whooping cough is a disease charac-
terized by violent paroxysms of coughing. It is believed to be
caused by a bacterium that clings in the air passage. The
disease is certainly contagious, and is easily caught by another
person when the patient is coughing. At such times the germs
are scattered from the patient and may find their way into
another person in the vicinity. The only method of avoid-
ing the germs is by keeping away from those who have the
disease, and especially by avoiding their breath at times of
coughing. The chance of. contagion by other means is slight
and, while the safest plan is to avoid patients entirely, a per-
son may frequently associate with one who has the disease
without catching it, if he is careful to avoid the breath. As long
as the coughing continues, usually several weeks, the danger
of contagion remains; although it decreases in the later stages
of the disease. Whooping cough is chiefly a disease of children
although adults frequently have it. Second attacks are rare.

CHAPTER VI

DIGESTION OF FOOD: THE (ESOPHAGUS AND STOMACH

Connecting the pharynx and the stomach cavities is a
tube about ten inches in length called the oesophagus.
This tube is lined throughout by an epithelium secreting
mucus, and for this reason it offers little resistance to the
swallowing of food.

Swallowing. — After food has been masticated and moist-
ened by the saliva it is rolled up by the tongue into a smooth,
moist mass. The tongue is then pushed up against the roof
of the mouth, first at its tip, and then moved backwards;
the food ball, being moist, slips along easily and is pushed
through the opening into the throat. Up to this point the
process of eating has been under one's control and could have
been stopped at any moment; but as soon as food goes into
the throat it passes beyond voluntary management. If one
should discover at this moment that the food contained
poison he could not refrain from swallowing it, for from this
point the action is involuntary, i.e. cannot be governed by
one's will power.

''How can a man standing on his head drink water, or a
cow drink out of a brook when her head is so much lower
than her stomach?" This question is easily answered as
soon as we understand the action of the oesophagus. Two
coats of muscle are found in the wall of the tube; next to
the lining is a layer of muscle going around it, and outside
this is a layer running lengthwise. By the combined action
of these a " swallow," or bolus, of food is pushed downward,
the muscles in front of the food mass continually letting the

DIGESTION OF FOOD: THE (ESOPHAGUS

passage open up, while those behind the mass contract and
thus push it along. The result is much the same as when one
forces a slippery ball
through a rubber
tube by squeezing
the tube between the
thumb and finger be-
hind the ball. This
action on the part of
the muscles would,
of course, carry food
along the tube, no
matter what the po-
sition of the body.
Even water does not
run down the gullet; it
is pushed down, grav-
ity having little or
nothing to do with the
process. This pecu-
liar method of move-
ment, called peristal-
sis, occurs through-
out the entire alimen-
tary canal. In man, a wave passes from the pharynx to the
stomach in about six seconds.

BODY CAVITY AND ITS SUB-DIVISIONS

All the space inside the ribs and the body wall, from the
hips to the shoulders, is called the body cavity. This is not
all in one large space, but is divided into an upper and a
lower part by a horizontal partition, called the diaphragm;
Fig. 46. At its center this is a thin sheet of tendinous material
from the edges of which muscles radiate to the body wall;
it extends across the body cavity betweeu the ribS; backbone

Abdomen

Fig. 46. — Showing the body cavity divided
by the diaphragm into thorax and ab-
DOMEN

90 ADVANCED I'HYSIOLOGY

and breast-bone, about one-third of the way down from the
shoulders; see Fig. 46. The upper and smaller cavity is called
the chest, or thorax, and its principal contents are the heart
and lungs. The lower, larger space is the abdominal cavity,
which contains the stomach and intestine, the large glands
connected with them, and the spleen, kidneys and bladder.

There are irregular crevices and spaces between these organs,
but these are" perfectly filled with the body cavity fluid
{coelomic fluid) .

Nearly all these organs have some muscular tissue in their
walls and are continually going through movements; or if
they are themselves quiet, they are being constantly rubbed
against by neighboring organs which are in motion. This
would result in a large amount of friction and irritation, if
it were not for the secretions of the serous membrane, which

forms a delicate lining to both
the thoracic and abdominal cav-
ities. This lining in the thoracic
cavity is called the pleura; that
of the abdominal cavity is known
as the peritoneum; Fig. 47. Along
certain lines, this lining is raised
into folds which hang out into the
cavities and in these folds the
Fig. 47.— Diagrammatic sec- organs are held. One particular
TioN ACROSS THE ABDOMEN fold of the perltoueum, called the
Showing the relation of the peri- mescntery, is especially large and

toneum and mesentery. •" ,i • . rm •

holds the small mtestme. This
complex lining is composed of one-celled glands, constantly
secreting a colorless fluid which allows the organs to glide easily
over one another or against the walls of the cavity.

THE STOMACH

The oesophagus extends down through the thorax as a
nearly straight tube, passing through the diaphragm, after

DIGESTION OF FOOD: tHE (ESOPHAGUS

tardioc Valve

which it enlarges into a good sized organ, the stomach, lying
a little to the left of the middle line; Fig. 46. The stomach
is pear-shaped and lies with the small end pointing obliquely
downward, and to the right. When moderately full it is
about ten inches long, by four wide and deep, and holds about
three pints. The entrance of the oesophagus is on the upper
side, about the middle of its length, and is commonly closed
by a muscular ring,
the cardiac valve; Fig.
48. This prevents the
food from going up
the oesophagus again,
while the stomach is
contracting about it.
Sometimes, when
there is too much
food in the stomach,
or when the food does
not digest well, this
valve opens and a re-
versal of the muscu-
lar action forces the
food back through
the oesophagus to the
mouth. This is vomiting and occurs most frequently in babies,
in which case the cause is, generally, too much food. With
adults, vomiting and nausea usually occur only when the
stomach is disturbed by food which does not properly digest.

From the small end of the stomach, called the pyloric end,
starts the first section of the intestine, the opening into it
being guarded by the strong, circular, muscular pyloric
valve; Fig. 48.

The cavity of the human stomach is one continuous space,
though in some lower animals which '' chew the cud," as we
3ay, there are four divisions in it; Fig. 49. In the camel,

Fig. 48. — Diagkam of the stomach and
intestine laid open

Showing the relation of ducts of liver and pancreas
to one another and to intestine.

ADVANCED PHYSIOLOGY

Fig. 49. — The stomach of a sheep

Showing the four compartments, (Huxley)

too, numbers of sac-like outgrowths from the stomach are
provided, in the cavities of which water is stored to be used

when the animal
Oetophoifus ^^^*^»T*^ needs it. On the ex-
terior of the human
stomach is a moist
covering which is,
in reality, continuous
with the mesentery
in which the intes-
tine is swung. Inside
this are three sets of muscle fibres, longitudinal, circular and
oblique, and separated from the lining of the
stomach by a thin layer of fat, the function of
which cannot be definitely stated.

Next comes the stomach lining proper. If this is
seen when the stomach is empty, there appears to
be a series of wrinkles or folds, going lengthwise
of the organ, from the pyloric to the cardiac
regions; these folds are spoken of as rugae;
Fig. 48. Furthermore, if any part of the inner
wall, on or between the folds, were to be
examined with a lens, the appearance would be
that of innumerable tiny pits, of polygonal
shape, giving to the whole the semblance of an
extremely fine celled honey-comb. These pits
are scarcely over one one-hundredth of an inch
in diameter, and in the bottom of each is a
minute opening through which gastric glands
pour a secretion. The glands are short and
cylindrical, thousands in number, and can be
compared to tiny tubes lying side by side, with
their mouths opening into the stomach cavity;
Fig. 50. Each of these glands is lined with
large cells which make gastric juice from the

Fig. 50.— a

SINGLE
GASTRIC
GLAND
Veiy highly
magnified

DIGESTION OF FOOD: THE (ESOPHAGUS 93

blood that flows around them, and pour it into the cavity
of the gland, whence it flows into the stomach.

COMPOSITION AND ACTION OF THE GASTRIC JUICE

Water makes up over 99% of the gastric secretion. Of
the remainder 0.3% is pepsin, 0.2% hydrochloric acid and
0.1% sodium chloride (common salt). Less in quantity, but
important, are the two ferments rennin and gastro-lipase ;
The work of the gastric juice is two-fold. 1. It softens
the solid foods, which are consequently easily broken up into
shreds by the active churning motion of the stomach. Meat,
for example, is made up of great numbers of little fibres
bound together into a solid mass by connective tissue. This
tissue is dissolved away by the gastric juice, thus setting
free the fibres and allowing the liquids to act further on
each separate fibre. The fat of the meat is also set free from
the masses in which it is swallowed, and is melted by the
heat of the body into oil. This softening action is performed
chiefly by the acid and water of the gastric secretion, not by
the pepsin.

We shall presently see that all foods are digested in the
intestine even more vigorously than in the stomach. But
stomach digestion is a very important factor, for while the
proteids themselves can be acted on in the intestine, the
connective tissue that holds the muscle fibres together, will
be less quickly dissolved there because of the absence of acid
in the intestinal secretions. Without the influence of the
gastric juice the muscle fibres will not be readily set loose
so that the juices may act upon them. '' Stomach digestion"
is thus an important preliminary to ** intestinal digestion. '^

2. Gastric juice produces a great chemical change in the
proteids. Strange as it may seem at first sight, these very
important foods, of which meats, milk and eggs are typical
examples, cannot be taken through the wall of the intestine,

ito the blood or be of any use to us unless they first cease

94 ADVANCED PHYSIOLOGY

to be proteids. They cannot he absorbed as proteid even though
our own muscles and blood are largely of proteid material.
The change which proteids must go through is a chemical
•"one, and the first step toward it is brought about by the
hydrochloric acid and the pepsin in the gastric juice. This
pepsin is one of the ferments, or enzymes, to which attention
was directed in an earlier chapter, and under its influence the
proteids, which are very complex bodies, are broken into simpler
ones. These new bodies, peptones, proteoses, and allied sub-
stances, are no longer real proteids but are far simpler chem-
ically, and may readily pass through the wall of the stomach.
It is probable, however, that a large part of the proteid eaten
is carried on into the intestine and still further modified
before absorption.

Milk cbntains much proteid in the form of casein. This
casein, however, is not readily acted on by pepsin until the
milk is curdled. Rennin, the second enzyme in gastric juice,
produces the curdling action on milk. It is from a similar
curd that cheese is made, cheese-makers adding to their
milk rennet which is usually obtained by a process of extrac-
tion and refinement from the stomachs of calves. Calves'
diet consists mainly of milk and their gastric glands contain
great quantities of rennin.

From these facts it is evident that milk taken into the
stomach is speedily soured by the acid in the gastric juice
and curdled by the rennin. If a baby vomits, and its milk
is found to be curdled and sour it may indicate that the child
has eaten more than it can comfortably hold in its stomach,
but the changes in its food only show that digestion is going
on properly.

On sugars and starches gastric enzymes have practically no
effect. Indeed, the digestion of starches which was begun
by the saliva in the mouth stops after the food has become
mixed with the gastric juice, because the salivary enzymes will
not act in an acid solution, and there is considerable acid in

DIGESTION OF FOOD: THE (ESOPHAGUS

Brain

the gastric juice. It takes some time, however, for the
swallowed food to become thoroughly mixed with the
gastric juice and therefore, for perhaps an hour after
reaching the stomach, the conversion of starch into sugar
continues.

For a long time it was held that fat undergoes only melt-
ing and emulsification in the stomach; but more recent
studies show the presence, in a Hmited way, of a third fer-
ment, gastro-lipase, which changes fats into glycerin and
fatty acids. Absorption of fats is now possible, but prob-
ably this does not occur till they have gone on into the in-
testinal division of the
alimentary canal.

The Flow of the Gastric
Juice ; — Between meals,
when the stomach is
practically empty, its
walls are of a pale pink
color, and the lining is
merely moist; very httle
secreting work is done by
the glands. But, on the
entrance of food, the
blood vessels in the
stomach walls expand,
and more blood flows
around the glands, the
cells of which begin a
copious secretion. Like
the case of the salivary
secretions, this response
of the blood vessels and
glands is a reflex action,

Spinal
■Cord

Fig. 51. — Diagram

Showing the method by which the stomach
receives its nerves from the brain and cord.
The nerves from the cord actually come
through the sympathetic system, not shown
in the figure. (Modified from Openchowski;

controlled by the central ner-

vous system. The actual contact of the mouth or stomach

96 ADVANCED PHYSIOLOGY

with food is not necessary since the mere sight or smell of
food is all that is required to produce the result. The stom-
ach does not regulate itself; it acts only at the command of
the brain; Fig. 51.

It is necessary, however, that the person be conscious,
or secretion will not occur. If food is put into the stomach
of a sleeping dog, no gastric secretion, and, therefore, no
digestion occurs. Again, more is secreted when one'is hungry
than when one swallows food though not hungry. Pleasani
tasting foods stimulate more active secretion than unpleasant,]
and thus we can conclude that pleasing flavors, althougl
they may have no food value, may have a decided use as
aids in digestion.

Sometimes when a person's digestion is poor, so-callec
predigested foods are taken. These are generally protei(
substances which have been treated artificially with pepsii
obtained from the stomachs of pigs. This predigested foo(
can be handled by the stomach more easily than ordinan
food; but its use should not become a habit, for constantly
aided in this way the stomach and other organs become
dependent on this assistance and lose their natural powers.

Cold, as a rule, retards the action of any gland, muscle
or other tissue in the body, while heat, within limits, is
favorable to their action. In the stomach the glands, togethei
with the nerves which control them, are so near the surface
that large quantities of cold food, like ice cream or ice watery
produce a shock which always delays their normal actioi
The distinct pain caused by too warm food or drink prevents
us from harming ourselves in this way. It is interesting
to note in this connection that heat as such, is not feli
when food is swallowed; the sensation is one of pain only.

The Passage of Food into the Intestine. — The length of time
that food remains in the stomach varies with the kind of foodj
but in the course of two to four hours after the average mealj
all foods have become a finely divided, sUmy mass callec

DIGESTION OF FOOD: THE (ESOPHAGUS 97

chyme. In this mass after an ordinary meal, there should be
water, saliva, mucus, gastric juice, peptones, unchanged
proteid, dissolved sugars, unmodified starches, curdled milk,
fat droplets, shreds of connective tissue and vegetable cellulose,
the woody substance in plant structures. Responding to the
presence of this chyme, the muscles in the pyloric valve
relax and allow the food to pass on into the small intestine.

The mere presence of chyme in the stomach does not pro-
voke the pyloric valve to open and let it pass through. This
would obviously be poor management should it happen
that the duodenum were already full, and completely busy
th its work on chyme previously received. It will be re-
embered that chyme is acid, as a result of hydrochloric
acid in the gastric juice. In contrast, the juices of the intestine
are alkaline; but it takes some time for the intestinal secre-
tions to overcome the acidity of material received from the
stomach. When this acidity is finally neutralized, however,
a message is sent from the intestine to the pylorus that all
is in readiness for a further installment of chyme from the
stomach, and the valve opens. Very unexpectedly this
message is sent, not through nerve fibres as most stimuli
are, but through the blood stream; this is a round-about
method, but it is the one used in this instance.

vjwi

CHAPTER VII
DIGESTION OF FOOD: THE INTESTINE

Fig. 52. — The digestive organs in
the abdomen

The stomach and liver are separated for
clearness' sake. They are really in close
contact.

A, appendix; B, large intestine; C, duodentim;
D, bile duct; E, liver; F, gall bladder; G, cys-
tic duct; H, hepatic duct; /, pancreas; J, sig-
moid flexure; K, rectum; L, anal aperture.

Many people have a
mistaken idea that the
stomach is the all-impor-
tant section of the food
canal, the chief organ of
digestion, and that almost
as soon as food is swal-
lowed it becomes trans-
formed by some marvel-
lous influence into energy,
heat, muscle or brain.
We frequently hear a
man say that he needs a
hearty dinner because he
is to work hard in the
afternoon, thus wrongly
assuming that the dinner
of the day furnishes him
with immediate muscular
power. But little if any
food is absorbed from the
mouth or gullet, and little
from the stomach. Food
is of no value until it has
left the stomach and, not
for many hours after eat-
ing does any portion of it
become a part of the bodv
itself. The power to do
each day's work comes
from the food eaten the
day before or, perhaps,

DIGESTION OF FOOD: THE INTESTINE

several days before. Food, after leaving the stomach, must
still pass through a long series of changes before it is of any
practical value.

The intestine may be considered in two sections: the small
intestine and the large. The former is about twenty feet in
length, and the latter about five; the total length below the
stomach affords, therefore, a large amount of surface for
absorption; Fig. 52.

THE SMALL INTESTINE AND ORGANS CONNECTED WITH IT

The small intestine commences at the pyloric valve of the
stomach and extends, coiling much on the way, to a point in
the right, lower part of the abdominal cavity, where it enters
the large intestine. Its average diameter is about one inch.
It occupies practi-

yf j mTftoratKDual

Ladiul

LtfrnphOhnd

cally all the space
in the lower half of
the abdominal cav-
ity, save that taken
by the large intes-
tine, the kidneys,
bladder and spleen.
Throughout its
length it is loosely
attached to the dor-
sal wall of the cav-
ity by a thin sheet
of tissue, the mesen-
tery. This mesentery
is traversed by a
multitude of arteries
and veins on their
way to and from the digestive tract; for it is solely through
these vessels that food is tak^n iip;frpm tbo^focd p^i\^l ^V^^
carried over the body; Fig^^^3/-;; V '^.^' T *^,^/'\ :,, ;■;

Fig. 53. — Diagram

Showing a piece of the intestine held in the meb^n-

tery and the blood and lymph vessels in it.

The mesenterj' is represented as narrower than it actr

ually is and hence the lymph glands as closer to the

intestine.

100 ADVANCED PHYSIOLOGY

After the food has been in the stomach for an hour and a
half or two hours, the valve which has kept it from going
into the intestine opens and allows a Uttle of it to pass out,
closing again quickly. Soon it opens again and more of the
digested food passes out, for this valve operates like a very-
sensitive mechanism which allows softened, partly dissolved
food to pass it, but closes at once if any solid, undigested
food touches it. The food thus passes out of the stomach,
a little at a time into this long tunnel, where it is to be still
further dissolved and changed for absorption. Through this
tube the food is slowly pushed along by peristaltic action of
muscles in its walls, similar to those in the oesophagus.
Almost at once after leaving the stomach the intestine makes
a bend downward and to the left, thus crossing the abdomen
below the stomach as the duodenum; Fig. 52. As the food
mass is carried around this bend it is mixed with a secretion
which enters the intestine by a duct shown in Figure 48, and
which comes from two large and very important organs, the
liver and the pancreas.

In many backboned animals these two organs connect with
the intestine through separate ducts, while in others their
ducts join as in man. The spleen, which is near by, has no
connection with the intestine physiologically.

The Liver and its Functions. — The liver is a large gland,
weighing in a person of average size about three pounds,
and located just below the diaphragm.

It is partially divided into a number of lobes. There is a
large right, a smaller left lobe, and other smaller divisions,
which easily adjust themselves to the neighboring organs.
The stomach over which its lobes hang is very active; the
body walls are constantly moving, and the diaphragm pulls the
organs up and down as one breathes. To all this environment,
the liver adjusts itself, its lobes gliding easily over one another,
^3 well as oVer tlie- OrgAns with which they come in contact.

'Everyone IS familiar wiill the dark red appearance of the

DIGESTION OF FOOD: THE INTESTINE 101

l:>eef' s liver as it hangs in the markets. This red color is partly
due to the fact that the organ is very full of blood; it has been
estimated that one-quarter of all the blood of the body may
be in the liver. Its surface shows
a mottled appearance, due to the
arrangement of tissues in the organ,
for it is really a large compound
gland; Fig. 54.

Beneath the right lobe is the
gall bladder, a pear-shaped sac,
about four inches in length, and
at its widest place an inch in
diameter. Its function is that of ^ig. 54.— The surface ot
a storage reservoir for holding the ^^^ liver

- ., X J 1, xu T 1, 'J. ' Slightly magnified

Dile secreted by the liver when it is

not needed in the intestine. From an examination of Figure
52, it will be seen that the bile does not run directly from the
liver into this sac, but that the only duct leading away from
the organ, the hepatic, goes in a fairly direct line to the first
loop of the intestine. A side branch from this, the cystic
duct, leads to the gall bladder; from their junction to the
intestine, is a tube called the common bile duct.

The liver keeps steadily secreting but the demand for bile
is not constant, as food conditions in the intestine are not
always the same. When bile is not needed in the intestine
the common bile duct closes, and the bile, then coming from
the liver, goes back and is stored in the gall bladder (Fig. 48);
there it accumulates until the opening into the intestine
again allows a free flow. The presence of chyme coming from
the stomach causes such an opening.

The large size of the liver and its abundant blood supply
suggest that the organ must have very important uses. The
amount of fluid which it secretes daily varies in different per-
sons from a pint to a pint and a half; it is a little thicker than
water, and of a golden brown color. Notwithstanding this

102

ADVANCED PHYSIOLOGY.

abundant secretion, which amounts to about one and one-
half pints per day in an adult, it is surprising to learn that
until recently little was known as to the value of bile as it
mixes with food materials in the intestine.

At least three uses for it are now recognized; of these the
most important is that it intensifies the action of pancreatic
juices about three-fold. Another function is the dissolving of
fatty acids and making them more absorbable; when its flow
is prevented, not only is fat only partially digested and
unabsorbed, but a fatty coating adheres to other kinds of
food and prevents digestive jui es having access to them, thus
letting them pass from the body unused. Bile also prevents
rapid growth of bacteria in the intestine with consequent
putrefaction and gas formation, though by itself it deteriorates
easily.

Other important functions of the liver will be pointed out
in their proper connections later.

The Pancreas and its Functions. — Unlike
bile, the fluid secreted by the pancreas
plays a necessary part in the digestive
process. As can be seen from Figure 48, a
duct from the pancreas joins the common
bile duct just before the latter enters the
intestine.

The pancreas is what the butcher calls
the "sweetbread." In the human being
it is about seven inches long by one and a
half broad, and one-half inch thick; not
a very large organ but of great impor-
tance. It is spongy in texture, and lies,
attached loosely, along the lower curved
border of the stomach. Its structure, as
shown in Figure 55, is very Uke that of the salivary glands.
The liquid output of its cells amounts to about one and one-
half pints a day, and is clear and watery in appearance. Zz

Fig. 55. — A highly

MAGNIFIED VIEW
OP A BIT OF THE
PANCREAS SHOW-
ING ALVEOLI

(Maziarski)

DIGESTION OF FOOD: THE INTESTINES 103

contrast to the acid secretions of the gastric glands, the
pancreatic secretion is strongly alkaline.

Food as it leaves the stomach is by no means completely-
digested. The starch is only partially changed to sugar; much
of the proteid passes through the stomach without change,
and the fats, though melted and emulsified in part, have been
only partially digested, if at all.

The fluid derived from the pancreas has the power to dis-
solve and change any kind of food, this being accomphshed f or
the most part by three different ferments (enzymes), as follows:

1. Trypsin, which starts the digestion of proteids by
changing many of them to peptones, thus supplementing the
work of the gastric juice.

2. Amyolopsin, which converts starches into sugars, thus
completing the action of the saliva.

3. Lipase (steapsin), under the action of which fats are
split up and made absorbable, i. e. digested.

The influence of trypsin is similar to that of pepsin although
more complete; it also acts upon the proteids which have
been partly changed into peptones, and breaks them up still
further chemically; this action continues till all proteid mat-
erial has been reduced to very simple substances called amino-
acids. These differ from proteids in that they are composed
of much smaller molecules, are soluble in water, do not
coagulate with heat, and easily pass through membranes.
Probably most, if not all, the peptones are changed into amino-
acids before absorption, this final step being brought about
by a ferment, erepsin, secreted by the intestinal wall glands.

About eighteen different amino-acids are now recognized as
resulting from the complete digestion of different sorts of pro-
teid foods. Some of these, e. g. arginine and glutaminic acid,
are abundant, i. e. derived from many proteid sources; others,
e.g. cystine, are seldom formed ;tryotophane (derived from milk
and wheat) and lysine (from milk and eggs) are very essential
to growth,, while glutaminic acid (from milk, eggs, wheat, peas.

104 ADVANCED PHYSIOLOGY

etc.) is a proteid product with very limited food value.

We thus see that there is a genuine basis for the arguments
which insist on a varied diet; for not all the substances in even
the so-called "best foods'* have real nutritional value.

The amylopsin acts upon starches much as does the ptyalin
of saliva and completes their change into sugar.

The steapsin acts upon the fats causing their digestion.

Two very different changes take place in ^

them. First, much of the fat is broken up in- c<§ip%Oo o
to extremely minute droplets, which float in '^o°o^^pO(5Co
the hquid of the food. In this condition it re- ^^2o^o^6
sembles the fat of milk and, indeed, the entire ^oo^°q^^S°^^
contents of the intestine, because of this con- ° o^°qO

dition of the fat, become more or less white Fig- 56. — Emulsi-
like milk. Such a condition of finely divided ^^^^ ^■^'^

fat droplets is called an emulsion; Fig. 56. 'Tghiy iTagnmet'^'
It was formerly thought that these fat drop-
lets were absorbed directly through the walls of the intestine
into the blood ; but it is now known that a second change takes
place in part of the fat, if not in all, before it is really absorbed.

This is a chemical change which results in splitting up the
fat molecules into two different substances called fatty acids
and glycerine — both of which are easily absorbed. Their
reformation into fat occurs very promptly, however, for true
fat droplets are found abundantly in the lining cells of the
intestine, immediately after fat digestion. See Fig. 64.

No digestive gland has such varied and efficient powers as
the pancreas. The pancreatic fluid digests any food that has not
been acted on by the other digestive juices. Some foods, espe-
cially complex sugars, may be simplified by enzymes, e. g.
maltose (which acts on starch-sugars) and lactose (which
ni odifies milk-sugar) occurring in juices which are added to
the food mass by cells in the intestinal lining.

After the food is completely digested, it is wholly changed
in nature and appearance. It was swallowed as meat, pota-
toes, bread and butter or milk; it has become dissolved into a

DIGESTION OF FOOD: THE INTESTINE

105

Villi.

GtandfoC,
Liebetkuhh

whitish, syrupy liquid, called chyle, in which there are but
few remnants of solid material. Its proteids have become
peptones or even simpler bodies; its starches are all sugars;
and its fats are either emulsified or are changed into fatty
acids and glycerine. It is not until the food has flowed
through a considerable section of the
intestine that digestion is complete.

The walls of the small intestine,
shown in Figure 57, are composed
of muscles that force the food along,
of glands, the secretion of which re-
sembles that of the pancreas, and of
viUi (described in the next chapter).

THE LARGE INTESTINE

The small intestine empties into
the large intestine in the lower right
side of the abdominal cavity. The
opening from one to the other is little
more than a slit, the sides of which
open easily in one direction but not
in the other; Fig. 58. Hence food
passes readily onward, but not back-
ward. The part of the large intestine
thus entered is the colon, and the
general shape of the course which
it takes is that of an inverted letter
U; i. e. beginning on the lower right side of the body cavity
I it passes up that side as far as the liver (ascending colon);

Iien it crosses to the left side of the body (transverse colon),
ad there passes downward (descending colon); Fig. 52.
The small intestine opens into the side of the large intes-
ne (see Figs. 52 and 58); about two and a half inches of
I the latter are thus left below the opening as a short section
ending blindly and called the coecum, a word meaning " blind."

Circulort-
tluscles

ilonfitudinhr^

tiusclej
Fig. 57. — A cross section

THROUGH THE WALL OP
THE SMALL INTESTINE
(Modified from Oppel).

106

ADVANCED PHYSIOLOGY

Coecum

tnfesfim

orm

From the lower end of the ccecum protrudes a short hollow
tube called the vermiform appendix; this varies in size in
different people but it is usually from
three to six inches long, and a quarter
of an inch or more in diameter. The
cavity opens into the coecum.

Beyond the lower end of the descend-
ing colon the intestine passes into an
S-shaped portion called the sigmoid
flexure; from this all intestinal contents
enter the final section of the digestive
tract, the rectum. This opens to the
exterior by the anal aperture; Fig. 52.
The walls of the large intestine are
constructed practically like those of the
small; but there seem to be no glands
opening into it which are concerned
with the digestion of food, though
mucous glands are numerous. The food may not be wholly
digested in the small intestine and so digestive processes,
to a small extent, go on here although not by virtue of
the glands of the large intestine itself. There is also very
rapid absorption from this region, particularly of water, and
this causes the intestinal contents to become more and more
hard. Much of this " undissolved food " performs a valuable
service, however, by mechanically stimulating the walls of
the intestine and thus causing more rapid peristaltic action.
A more certain passing along of food materials is thus ensured
and so the trouble called constipation is, in a measure, pre-
vented. If only very fine foods, e. g. those made from
finely powdered flours, are eaten, the water in them may be
absorbed quickly and then the mass becomes so dry and
unyielding that it is forced along the canal with great diffi-
culty. Coarse foods, which are sometimes refused by persons
who proudly consider thern too crude ^nd cheap for their

Verrnii
AppendtK

Fig. 58. — The begin-
mng of the large
intestine

Showing the opening
from the small intestine
at some distance from
its end.

DIGESTIOJVJ OF FOOD: THE INTESTINE 107

refined taste, are often not only very nutritious, but as a rule nec-
essary for uniformly good digestion and therefore good health.
Those materials which are not changed into a liquid condition
are never absorbed and never become parts of the body.

After the nutritive part of the intestinal contents has been
absorbed there remains a considerable portion of undigested
matter which is now useless and is passed to the exterior
as faeces. The elimination of these wastes once a day is of al-
most as much importance to health as the regular taking of
food. The intestinal contents after food absorption readily
undergo putrefaction from the growth of bacteria and soon
become filled with poisonous substances which injure the
body materially if the wastes are not regularly removed.
Their retention is apt to result in headaches or other bodily
derangements. Disturbances by which the wastes are re-
tained too long (constipation) or by which they are discharged
too frequently and in too liquid condition (diarrhea) are both
to be avoided. Such conditions are due as a rule to an error
in methods of living. One may be eating improper food;
he may be eating too much food or too often; he may be eating
too much fine food like wheat flour and not enough coarse
food or he may not be drinking enough water. He may
be living a too sedentary life; constipation especially is fre-
quently due to insufficient exercise and may be remedied by
various forms of bodily activity. The improper method of.
fighting these troubles is to use medicine ; for drugs only palUate
• and do not cure them. Regularity in expelling the waste large-
ly depends upon hahit. A little care and attention will enable
almost any one to acquire regular habits that will be of lasting
value to his general health. No one whose intestine is crowd-
ed with poisoning wastes can continue in good health.

DIGESTION OF DIFFERENT FOODS

Since no food can be absorbed into the body until it is
gested, the readiness with which a food can be digested is a

106 ADVANCED PHYSIOLOGY

factor in determining its value. Cheese is the most nutritious
of our foods, but it is such a condensed food that only a little
of it should be eaten at one time. Peas and beans are also
very nutritious foods, containing a large amount of proteid;
but these again are too difficult of digestion to be used
like bread, as a constant article of diet. The digestive
tract, however, can perfectly well handle a considerable amount
of foods that are difficult to digest and it is better to use some
of them rather than to give the digestive organs too easy a
task. But in choosing one's diet, it is well to bear in mind
that foods like milk, bread, rice, soft boiled beef, mutton and
broiled meats are more easily utilized than are beans, peas,
nuts, hard boiled eggs, pork, veal, fried foods and cheese.

ALCOHOL AND INDIGESTION

Various opinions have been held as to the effect of alcohol
on digestion. That it produces serious troubles whea used in
large amounts is questioned by no one, but it has been a popular
belief that when used in small quantities it aids digestion.
The most careful testing of this theory has shown that it is
a mistake. Alcohol has two opposite effects upon digestion.
It causes increased secretion of some of the digestive juices,
chiefly the saliva and gastric juice. To this extent it might
be supposed to promote digestion. But, on the other hand, its
presence in the stomach tends to weaken the action of the
digestive ferments and this serves to counteract the apparent
advantage of the increased secretion. As a result, when used
in small quantities alcohol neither hastens nor retards diges-
tion; when used in larger amounts, its retarding action is al-
ways certain.

With certain alcoholic drinks, the retarding action is
especially evident and, oddly enough, this is true of many
wines that are not infrequently taken as '^ appetizers " with
meals, under the false impression that they facilitate digestion.
Experiments with these wines show that they have a very

DIGESTION OF FOOD: THE INTESTINE 109

Itsonsiderable checking action upon digestion, greater than
■hat of pure alcohol. The effect is due in these cases to other
lubstances in the wines as well as to the alcohol.
I In short, it is an established fact that alcoholic drinks are,
m least to healthy persons, of no use in digestion and rarely
ft ever of value in illness. On the contrary they are usually,
and perhaps always, a direct detriment. It is not strange,
however, that persons who have used wine for a long time
think that it aids digestion since they have by its use brought
their bodies into a condition in which the digestive glands
will not act normally without it.

DISEASES OF THE INTESTINAL TRACT

Summer Complaint. — Very often something one has eaten
produces a quick and rather violent disturbance of the
digestive organs; a feeling of nausea, followed by vomiting,
frequently by pain in the stomach and bowels, occurs, and
perhaps also diarrhea. The cause is often hard to determine
exactly, but the trouble is practically always due to improper
food or drink. It is conamon in hot weather and therefore
has been called summer complaint While sometimes violent,
it is usually not serious, and under ordinary conditions will
pass away in a day or two if the person remains comparatively
quiet and is careful as to what he eats.

Peritonitis.^— We have noted that the abdominal cavity is
lined with a very delicate membrane in a fold of which the
intestine is held. These tissues sometimes become inflamed,
the many blood vessels in them becoming distended. At the
same time the sensitiveness of the parts becomes very great,
and much pain is felt in the abdomen. The condition is known
as peritonitis, a word derived from peritoneum, the name
of the abdominal lining. Peritonitis may be very serious and
even fatal; for in its severe form the blood vessels may burst,
causing exudation into the abdomen and other serious com-
plications. It is characterized by continued pain in the ab^

110 ADVANCED PHYSIOLOGY

domen which must not be confused with an ordinary stomach
ache due to improper eating.

Appendicitis. — We have already noticed the vermiform
appendix (Fig. 52) which opens into the large intestine
by a small aperture. It occasionally happens that an in-
flammation starts in the appendix; it becomes swollen, and
its blood vessels expand, causing pain and soreness on the
right side of the abdomen, which shows the presence of
appendicitis. This disease is a very serious one; for if pus
accumulates in the appendix and it is not drained off through the
lumen into the intestine, the appendix is likely to burst, the
pus escaping freely into the abdominal cavity. When this
occurs it is commonly followed by general peritonitis, with fatal
results. The serious nature of the trouble makes it advisable
to consult a physician when symptoms such as above described
are felt. The majority of cases may be cured by the removal
of the appendix, a surgical operation which, if
performed in time, involves little danger.

The real inciting causes of peritonitis and appen-
dicitis are not yet thoroughly imderstood and at
present we know of no rules for avoiding them.
Fig. 59.— Ty- Typhoid Fever. — Typhoid fever is caused by
PHoiD BA- ij^Q entrance into the intestine of a well known
^^^'^ , bacterium (Fig. 59) which grows abundantly there

The cause of . t - ^ re i i i •

typhoid fe- and excretes poisons which affect the body tissues.

^®^- There are certain definite symptoms of the disease,

one of which is a fever that may last several weeks. Doctors can
do little to cure it beyond maintaining the strength of the
body so that the person may have the power to drive off the
trouble himself. It is one of the most serious illnesses, and it
causes many deaths each year. About 10% of those taking the
disease die, and many others are incapacitated for work by
it for weeks or months, and sometimes permanently. It is
more common in th? fall than at any other season.

The sources from which one is liable to obtain typhoid

DIGESTION OF FOOD : THE INTESTINE 111

i)acteria are well known. Drinking water, if in any way
polluted with sewage, is almost certain to contain typhoid
germs. Hence, water from brooks, reservoirs, rivers, lakes
or wells that receive any sewage is unsafe to drink.

Milk is also a source of typhoid infection. If there is a
case of typhoid fever at a farm w^here milk is produced, the
genus are pretty sure to get into the milk. Oysters which
have been placed near the mouth of a river for the sake of
^'floating" them are also occasionally infected with the bac-
teria, and if eaten uncooked, cause the disease. Flies are apt
to carry the germs on their feet and deposit them on the food
upon which they feed.

i o avoid the dangers of typhoid fever one should drink none
except the purest water, be especially careful of the milk sup-
ply, and not allow flies to alight on food or dining tables. Both
water and milk can be made perfectly safe by boiling.

A very successful method of avoiding typhoid fever is by an
inoculation with anti-typhoid vaccine. This is injected uiider
a person's skin and thus renders him immune against typhoid
fever for two or three years. It is very widely used with
soldiers, and it is wise for persons who are to travel, where
they cannot properly control their food and water, to thus
protect themselves.

Hookworm. — This disease is caused by a small parasitic
worm. A person becomes infected sometimes by taking these
worms into the mouth with food or drink, but more com-
monly by getting dirt containing them onto the hands or feet.
They usually find their way to the intestine where they may
live for a long time. The symptoms of the disease are a dry or
yellow skin, anaemia (paleness), stupid facial expression, emacia-
tion, irregularities in appetite and breathing, weakness in the
muscles, headache, defective mentality, and some others. The
disease is quite easily cured by treatment with thymol. This
disease is very common in the South, especially among those who
go barefoot, since they are very easily infected through their feet.

CHAPTER VIII
THE ABSORPTION OF FOODS

It is very natural to compare the body to a factory and the
alimentary tract to the furnace room where fuel is being
burned. In both factory and furnace there is motion, work
is being done and heat is being produced.

This comparison is not, however, entirely applicable. In a
factory the fuel is burned in the furnace, only the heat from
the flames passing through the furnace walls. In our bodies,
on the contrary, the materials themselves in the digestive tract
pass through the intestinal walls and are transported around
the body. No heat at all comes from the digestive tract, for
the food gives up none of its stored-up properties until it has
passed out of this tract and been carried to its final destina-
tion in the hands, in the brain, in the liver or elsewhere. The
intestine is therefore not properly comparable to a furnace

A better analogy would be to compare the human body to a
city, from the gas plant of which gas is sent to different parts
of the city; some of it is to be used for cooking, some for
lighting, some for heating. Some of the heat is, perhaps,
employed for producing steam pressure in an engine, which_
in turn runs a sewing machine, a lathe or a water pump^
The material used in producing the heat is prepared in on(
part of the city, but it gives off neither heat nor power noi
light there, nor while going through the pipes. It is really
used only after it has reached some little nook or corner, ii
attic or basement, sleeping room, kitchen or shop; there 11
gives out its light, heat or power.

STRUCTURES CONCERNED IN ABSORPTION

We have traced the food to the intestine and noted it thei
in the form of chyle, ready to be absorbed. The small in-

\12

THE ABSORPTION OF FOODS

113

Fig. 60. — Appearance of the
interior of the intestine

Showing the folding of its lining.

oithelium

testine is practically a tube within a tube, the outer of which
is for the most part muscular. If we imagine the inner tube
to be longer than the outer, the
inner tube will consequently be
thrown into ridges which go trans-
versely around it, intruding on the
cavity more or less. Some but not
all of the ridges will pass entirely
around the tube; Fig 60. Further-
more the whole lining, ridges and
all, is covered with minute, flex-
ible projections, almost as if
there were tiny fingers protruding
mto the food mass of the intestine.
These fingers are called villi, and
they take the food from the intestine by a method of their
own. They are just long enough to be
seen with the naked eye; Fig. 61.

Into each villus extends a nerve and
also a tiny branch of one of the arteries

walls. This arteriole

the end of the villus

up into much smaller
blood vessels, which thus form a sort of
network; Fig. 62. After passing through
this network and picking up food in a
m anner to be described presently, the blood
returns again through veins to the intes-
tinal wall and is then carried off once more
into the body. Each villus contains
another tube also (Fig. 61), called a lacteal,
which receives the fats of the food. A
single layer of cells, the epithelium, covers
each villus and separates the blood vessels
and lacteals from the liquid contents

in the intestinal
extends nearly to
and there breaks

l/fe/W

^ _ Artery

Fig. 61. — A Single
Villus

Highly magnified.

of the intestine.

114

ADVANCED PHYSIOLOGY

OSMOSIS

Clands
of"

Uebtrkm

How is food actually absorbed through the intestinal walls?
Two liquids, the blood and the dissolved food, are separated

by a thin moistened membrane.
How is it possible for the liquid
to flow in one direction and not in
the other? In other words, why
does the liquid food go through
into the blood vessels, and the
blood at the same time not pass
out into the intestine? Physiol-
ogists are as yet able to give only
a partial answer to this rather
puzzling question.

Food absorption depends partly
upon a process called osmosis.
In the first place it is not quite
true that food passes from the
intestine, and that nothing passes
in the other direction; for a cer-
tain amount of liquid does pass
into the intestinal canal from
the blood. But the latter is
small in amount, perhaps chiefly
water, and more material passes
in the reverse direction. To
show how such a transfer could
take place, an illustration will be
useful. Procure a piece of mem-
branous tube, like that used for
the covering of sausages. Fill
this with a solution of pure grape sugar and suspend it in
a jar full of water, as shown in Figure 63. The tube may
thus represent the intestine full of digested food, and the

Muscles-

Fig. 62. — Showing the mi-
nute BLOOD VESSELS OF
THE VILLI AND INTESTINAL
WALLS

The arteries are striped, the veins
black and the capillaries open.
(Oppel)

THE ABSORPTION OF FOODS

116

water around it may represent the blood. Under these con-
ditions there would seem to be no special reason why there
should be a flow of liquid in either direction; but nevertheless,
as a matter of fact, the contents of the tube soon begin to
flow out through the wall of the tube into the jar and at the
same time water flows into the tube. They flow at different
rates of speed, however, in the two directions, the water, in
this particular case, flowing into the
tube much more rapidly than the
sugar solution flows out. This proc-
ess is called osmosis.

Since the membrane contains no
holes large enough to be seen with a
microscope, the condition in which
water or any other liquid could pass
through it must necessarily be that of
a very fine state of division, doubt-
less in what chemists call molecules.
Molecules are the smallest forms
which any substance can take and
yet maintain its own characteristics
and are, of course, invisible. It is

known, however, that molecules are of different sizes, a
sugar molecule containing practically eight times as many
parts (atoms) as a water molecule. If, then, sugar molecules
and water molecules are mingled inside the tube, and only
water molecules are on the outside, many more water mole-
cules are in contact with the membrane on the pure water side
than on the other; for each sugar molecule takes up much of
the space on the inside of the tube.

Physicists tell us that all molecules are in very rapid motion,
though each, in a general way, remains in its own "play-
ground." These molecules of water and sugar then are con-
stantly hitting against the walls of the membranous tube, and
some will pass through the infinitesimally small pores in it.

Fig. 63. — Diagram il-
lustrating OSMOSIS

116 ADVANCED PHYSIOLOGY

Both sugar and water molecules will pass through, but the
sugar molecules, since they are larger, will not pene-
trate as fast as water. Hence, there will be much
more water going into the tube than sugar going out.
Nevertheless, if we leave the tube in the jar long enough the
sugar will continue to pass out till the solution in the jar
becomes as sweet as that in the tube. After this, no noticeable
exchange occurs. But if we should then remove the water,
which by this time would contain some of the sugar,
and replace it with fresh water, once more putting the
tube in it, the sugar would then continue passing out. If we
continued to renew the water in the jar as fast as it became
charged with the sugar we could keep the sugar flowing
out of the tube into the water of the jar until all of
the sugar was gone from the tube, and only pure water
was left in it.

Food Absorption. — Now, this process of osmosis does not
fully explain the manner of food absorption, but it does ex-
plain certain phases of it. Physicists find that some sub-
stances will thus pass through membranes while others will
not. The former they call crystalloids, the latter colloids.
Most of our foods, when eaten, are of such a character that
they will not pass through membranes, and could not be
taken through the intestinal walls; but digestion changes
them, until finally they are in a form that will readily diffuse.
Starches and proteids, for example, will not diffuse, while
sugars and peptones will. Thus, digestion brings the food
into a condition in which it can be absorbed.

In the intestine digested food is on one side of the mem-
brane formed by the epithelium of the vilU, while on the other
side is blood; the membrane thus has different liquids moisten-
ing its two sides. Under these conditions the dissolved food
begins to flow through into the blood vessels, and as fast as
the blood present becomes filled with the absorbed food, it is
carried off and fresh blood takes its place. This continues

THE ABSORPTION OF FOODS

117

until nearly all the digested portion of the food has passed out
of the intestine into the blood.

But meantime, according to our illustration, water
has been passing from the blood into the intestine. Here,
however, the illustration partly fails; for while doubtless
some of the water of the blood does enter the intestine, it
does not do so as fast as it would in the illustration. Exactly
why this is so, physiologists do not fully know. So it must be
conceded that the real secret of food absorption is not entirely
understood, and we have merely to say that it occurs because
of the nature of the living cells in the intestinal walls. The
membrane of the villi is made of living cells and these cells,
when alive, act differently from those of non-living tubes.

CHANGES IN FOOD AFTER ABSORPTION

We can now understand that the
is to bring the foods into such a
pass through the intestinal walls.
Further changes occur in them,
however, after their absorption.
The proteids, for example, are
by digestion broken into very
simple compounds, but after these
are taken into the blood they are
built up into proteids again. Just
where and how this occurs is not
yet known; but it is known that
proteids are abundant in the
blood although only the simple
products of proteid digestion are
absorbed. Somewhere, therefore,
they are reconverted. A further

first purpose of digestion
condition that thej' can

Fig. 64. — A highly magni-
fied VIEW OP THE TIP OF
A VILLUS

Showing the absorption of fat.
The black dots are fat.

change also takes place

118

ADVANCED PHYSIOLOGY

These substances are also taken into the villi (Fig. 64), but
not into the blood vessels; they enter the single tube, the
lacteal, in the center of each villus, and during their absorption

appear to be again united into true
fat. Although physiologists do not
know just where or how this occurs,
the fact that true fat rapidly collects
in the lacteals during absorption
would seem to indicate that the fat is
broken up simply to enable it to be
absorbed through the intestinal walls.

Thoracic
Duct

THE PATH TAKEN BY THE ABSORBED
CARBOHYDRATES AND PROTEIDS

Proteid foods and carbohydrates
both pass directly into the blood ves-
sels. The veins carrying this blood
away from the viccera unite and
form one large vessel, called the
portal vein; this goes to the liver,
where it divides into very minute
branches; Fig. 65. After passing
through the liver, the blood collects
once more and flows to the heart.
This portal vein, which with these
same relations occurs in all back-
boned animals, is the only vein in
the body which breaks up into
branches in the liver on its way to
the heart. All the others run directly
to the heart.

Why should the blood from the
intestine be thus distributed through the Hver? It is evident
that soon after each meal the largest amount of food stuff is
present in the portal vein. If this should pass immedi-

FiG. 65. — Diagram of

THE VENOUS CIRCULA-
TION OF THE INTESTINE
AND LIVER

THE ABSORPTION OF FOODS

119

ately around the body, the various tissues would have an
over-supply of foods for a few hours, and after that, until
the next meal time, there would be a scarcity. This would
be a very faulty method of nutrition, since most of the
tissues are doing as much work at one time of the day as
at another, and so need food all the time.

The Liver as a Storehouse for Carbohydrates. — To prevent
this irregular supply of food to the tissues is one of the duties
of the hver. As the food-laden blood passes through it, a large
part of the sugar is changed into a compound called glycogen,
and left stored in the Hver cells; Fig. 66. Its chemical make-
up is the same as that of veg-
etable starch. The blood,
with a small load of sugar
leaves the organ, other food
substances having under-
gone no change. After
the food of one meal
has been absorbed from
the intestine, the liver
begins, little by little, to
dole out to the blood this
stored sugar so that the
latter, circulating about the body, contains at all times
about the same amount. This uniform supply is necessary
for the best health and most efficient activity of the body
organs. Too much or too little sugar in the blood is injurious.
Thus while the bile secreted by the liver is of little use in
digestion, the liver is itself a highly important organ, as a
regulator of the food supply to the blood.

PATH TAKEN BY THE FATS

The fats pass into the lacteals of the villi and these open
into larger vessels in the walls of the intestine, which in turn
unite with others to form still larger ones (of about the size of

Fig. 66. — Liver Cells

Loaded with glycogen which they have

made out of sugar taken from the blood-

(Modified from Frericha)

120 ' ADVANCED PHYSIOLOGY

blood vessels) and then pass up through the mesentery.
Thus there are three sets of vessels in the mesentery:
arteries bringing blood, veins carrying food-laden blood
away, and lacteals carrying off the fat; Fig. 65. The
lacteals finally empty into a duct which runs past the
liver and stomach, through the diaphragm, up through
the thorax into the neck region, a little above the heart.
This tube, which is called the thoracic duct, finally empties
into one of the large veins which bring blood bi:fck to the
heart; Fig. 65.

The contents of the thoracic duct are white and milky,
due to the fat in emulsion; in fact, the contained
materials are much the same as the chyle in the intestine.
The lacteals, then, and the ducts connected with them act as
a temporary storehouse for fats. The flow from the thoracic
duct into the large vein at the base of the neck is slow and
interrupted and it is only after several hours from the
time fat enters the lacteals, that it passes into the main
blood system.

The passage of the absorbed fats through the thoracic
duct is not produced by any heart-like organ. The simple
pressure of the surrounding organs, the peristaltic move-
ments of the intestine, the constant displacement of organs
by breathing muscles — these and other lesser influences
produce a slow flow. This movement can take place in
but one direction on account of valves which open only one
way* and are located at very frequent intervals throughout
the ducts.

Even the fat in time gets into the blood; but it seems as if
the thoracic duct and the lacteals were designed to switch
the fat around the liver and bring it to the blood without
flowing through that organ. The liver can readily store
sugars and is not injured by the proteids passing through it,
but apparently it is necessary for the fats to reach the blood
system by some other course.

■

1 w^.rp

THE ABSORPTION OF FOODS 12)

SUMMARY OF DIGESTION AND ABSORPTION

This finishes the story of the entrance of food into the body.
The brain begins the history by selecting the food through the
sense of taste; heat cooks and prepares it; the teeth grind it
I into fine pulp which, by means of the tongue, is thoroughly
mixed with water and saliva. Then begins a series of chemi-
I cal changes as the food is passed through that chemical lab-
I oratory, the alimentary canal. It is taken into this labora-
' tory as more or less solid material containing proteids, starches,
fats and other substances, but by the chemical action of the
ferments produced by the glands, these ingredients are soft-
ened and completely transformed until they are almost wholly
'' dissolved into a syrupy white mass, which does not bear the
slightest resemblance to the original food in appearance, and
I very little in chemical nature. As the food is forced along,
I the villi with which the intestine is lined begin to pick out of
I the mass the useful parts, leaving the rest in the canal to be
i ejected later as worthless. The sugars and proteids are handed
! over to the blood vessels which take them to the liver where
a part of the sugars is temporarily stored. The fats are passed
to the lacteals which likewise carry them to the blood, but by
a different track, a side track as it were, which switches them
around the liver. Finally all the nutriment gets into the
blood by which it is carried around the body to any part
that needs it. Digestion and absorption are thus finished
and we may turn our attention to the next process —
circulation.

CHAPTER IX
THE BLOOD AND ITS FUNCTIONS

Blood and blood vessels are entirely lacking in some of the
lower animals, as for example, in sponges, jelly fishes, corals
and the lowest of the worms, the so-called ''flat-worms." In
the insects, too, the blood system is present only in a weak,
poorly formed way. This seems particularly strange when
one considers how dependent a human being is on the blood
system; so dependent, indeed, that after a severe cut a person
may die from loss of blood. Blood, in fact, is considered the
symbol, if not the synonym, of life itself.

By studying these animals, however, we find the reason
why they do not need blood systems. The sponge has numer-
ous pores opening into the body; these lead to canals which
extend through the substance of the animal, thus carrying all
over the body the water and food substances, which enter
the canals. At the same time the sponge obtains oxygen from
the water circulating through the canals. The jelly-fishes,
corals and flat-worms .all have complex stomach cavities;
numerous pouches and ducts leading away from the stomach
carry the food particles to all parts of their bodies. So much
water is taken in with their food that these animals obtain
all the oxygen they need from the same water in which their
food floats. Insects have a tubular digestive tract going
almost straight through the animal; but besides this there is
a great network of air tubes all over the body, between the
muscles, passing into the legs, wings and, in fact, everywhere.
These bring air in through sets of pores in the ''skin," and
take it over the body. In the human being the digestive tract
is a tube, with no side branches of any sort; and all the air one
^akes in goes into two comparatively small sacs, the lungs.

122

THE BLOOD AND ITS FUNCTIONS 123

Thus animals in which there is some other means of dis-
tributing air and food lack the blood system. We may con-
clude, then, that one of the functions of that system is the
distribution of food and oxygen.

THE BLOOD

Blood makes up about one-thirteenth of the body weight.
It is really a very complex fluid, for it contains all of the food
materials from the intestine and also receives many waste
products from worn-out parts of the body. But leaving aside
these complexities of chemical composition, we may learn
by a study with the microscope that fresh blood consists
of a liquid almost as limpid as water, which has floating in
it an immense number of minute, solid bodies. The liquid
is called the plasma; the solid bodies are of three kinds: red
corpuscles or erythrocytes, white corpuscles or leucocytes, and
platelets; Fig. 10.

The relative proportion of these in the blood is approxi-
mately as follows: water 90%, sohds 10%. Of the soUds,
about 72% is proteid in character, the remainder consisting
of fats, acids, and salts. Some of these are unutilized food
materials, others the result of ''wear and tear" of body pro-
toplasm as it ceaselessly, day in and day out, performs its
vital work.

Blood Plasma. — The plasma is a transparent liquid of a
hght straw color. It is the plasma that gives the fluid char-
acter to the blood and enables it to flow through the vessels.
Its chemical composition varies. Into it are absorbed the
foods from the intestine, and into it also are passed the various
waste products from the body. Its composition will there-
fore be different after a meal from what it is after a period of
fasting. When one is resting, too, fewer waste products are
eUminated to make the blood impure than when one is actively
working. One of the constituents of the plasma will be no-
ticed later because of its important relation to blood clotting.

124 ADVANCED PHYSIOLOGY

This is a proteid kno^\Ti as fibrinogen which is so completely
dissolved as to Se quite invisible.

Red Blood Corpuscles. — Red blood corpuscles are minute
discs, having a diameter of about ^^Viy inch (.007 mm.), and a
thickness of 1-^77-0- inch (.0025 mm.) . There are about 5,000,-
000 of these in a drop of blood no larger than the head of an
ordinary pin. When freshly drawn from the body these loz-
enge-shaped discs appear concave on each side (Fig. 10),
but while circulating in the vessels they are frequently cup-
shaped. While, in some respects, they are like other cells in
the body they have no nucleus and no power of division.
This absence of a nucleus is found only in a group of animals
known as mammals; i. e. in those which have bodies covered
with hair, which suckle their young, and which have distinct
thoracic and abdominal cavities separated by a diaphragm.
Fishes, frogs, reptiles and birds are not mammals, and their
red blood corpuscles are nucleated.

Each corpuscle consists of two parts: (1) a spongy mass,
called the stroma; (2) a red liquid which is held in this stroma
somewhat as water is held in a sponge. The red color of the
corpuscle is due to this liquid, which is called haemoglobin.
It is the millions of these red corpuscles with their hsemiO-
globin that give the red color to the blood.

Haemoglobin is not always of the same color. If it is
mixed with plenty of air, it absorbs a great deal of oxygen,
becomes a bright, crimson red, and is then spoken of as
oxyhaemoglobin. This is its condition in the blood in the
arteries. If the oxygen is withdrawn, however, the hsemo-
globin assumes a darker color, and is called reduced haemo-
globin. This is its condition in the blood in the veins re-
turning from the body to the heart. Thus the corpuscles are
turned from a dark red to a bright red color as they com^e in
contact with the oxygen of the air in the lungs. This power
absorbing and giving up oxygen is the foundation of respin
tion and is dependent upon the presence of fresh air. Haei

THE BLOOD AND ITS FUNCTIONS 125

oglobin is a proteid, but it differs from most proteids, in
that it contains in addition to carbon, hydrogen, oxygen,
nitrogen and sulfur, a little iron.

While inside living corpuscles, haemo-
globin is in solution, but if a number of
corpuscles are treated with ether and the
ether evaporated, ha3moglobin will be left
behind in the shape of definitely formed
crystals; Fig. 67. Fig. 67.-Crystals

It will be easier to comprehend the rela- °^ hemoglobin

, . , , , , , . FROM RED BLOOD

tion which these corpuscles bear to a person corpuscles
if the facts are stated something as follows:
In the blood of a man weighing 150 pounds there are floating
about 25,000,000,000,000 red corpuscles. These contain about
one and one-half pounds of haemoglobin, and their surfaces
equal about 3,827 square yards or the area of a surface 225 feet
long by 150 feet wide. (Compare this with the area of your
school grounds.) The capillaries in the lungs are so small that
these corpuscles pass through them practically in single file. In
this way a great area is exposed for the absorption of oxygen.
Where does this great number of red corpuscles come from,
and what becomes of them? Do they live as long as the rest
of the body, or are they being constantly produced and de-
stroyed? Clearly, there must be some way in which they are
constantly produced, for a person may lose much blood from
a wound and recover completely in a few days. The answers
to these questions are rather unexpected; in a healthy person
blood corpuscles are constantly being produced in the red
marrow of the bones, and they are being as constantly destroyed
in the liver and perhaps in the spleen. Indeed, the bile from the
liver is, in part, the waste from broken down red corpuscles.
How long a red corpuscle lives we have no means of knowing;
but it starts in the bone marrow, does duty as an oxygen carrier
for 9, while, and finally ends its life in the liver or spleen.

126 ADVANCED PHYSIOLOGY

White Blood Corpuscles. — White blood corpuscles are of a
transparent, bluish white color and are considerably larger
than the red ones, although the latter are about five hundred
times as numerous; Fig. 10. White corpuscles are real
cells, since they contain a nucleus, but they are constantly
changing their shapes. They are active little bodies which
sometimes move of themselves, independently of the blood
flow. Any part of the white corpuscle may protrude, and the
entire substance of the body be allowed to flow into the pro-
trusion. By repeating this process indefinitely, the cor-
puscle moves from place to place. This method of locomo-
tion is called amoeboid, after the amoeba, a microscopic animal
which moves by the same method.

In function, too, the white corpuscles are different from
the red. One of their chief uses is to perform for the body
duties similar to those of street cleaners in our cities. They
are not confined inside the blood vessels, but may pass out
into the tissues, where they have many functions. If any
irritating or injurious substance gets into the body under the
skin, these white corpuscles collect around it in great numbers
for the purpose of removing it. If the irritating substance is
small, the white corpuscles may be able to surround it com-
pletely and then carry it off to be destroyed elsewhere in the
body.

Another useful function of the white corpuscles is to help
protect the body against invading disease germs. When
these tiny enemies make their entrance, the white corpuscles,
or leucocytes, assemble quickly to do battle with them. The
corpuscles attack the bacteria, and may even carry off their
dead bodies; Fig. 68. Many of the corpuscles, as well as
bacteria, are killed, however, and sometimes, indeed, the bac-
teria overcome the corpuscles. When this occurs, the bac-
teria spread through the body, and the person ''comes down"
with the disease. When the corpuscles are victors, and
succeed in overcoming the bacteria before they do harm,

THE BLOOD AND ITS FUNCTIONS

127

Fig. 68. — White blood corpuscles
or leucocytes that have engulfed
bacteria

In those at a may be seen chains of bacteria
such as cause blood poisoning and in those at
b are some rod shaped bacteria. (Metschni-
koff)

one may have absolutel)^ no knowledge that anything un-
usual has happened in the
body. Thus, many a time
in our lives, these little
defenders have guarded us
from dangers about which
we knew nothing. Some-
times when this battle is
near the surface, the skin
becomes painful and in-
flamed, and later it may
burst, allowing pus to es-
cape. This pus is largely
made up of white cor-
puscles; they themselves
have died and are dis-
charged, but they first
disposed of the foreign germs that would, perhaps, have done
us great injury.

When leucocytes are exhausted they merely go to pieces
i and dissolve in the blood, the residue
passing out of the body through the
different excretory organs.

Blood Platelets.— The third kind of
solid body in the blood is the platelet.
These platelets are ovoid bodies,
about one-third the diameter of the
led corpuscles, granular but color-
less; Fig. 69 c. They vary in number
Ijut are always very numerous in
unshed blood, 600,000 or so in a single
drop. These bodies disintegrate very
j quickly after blood is drawn; so quick-
I ly that by the time a drop can be
nlaced under a microscope for the purpose of studying themj

Fig. 69. — Various bodies

FOUND IN blood
a, red corpuscle; b, white cor
puscle with fibres of fibrin
radiating from it; c, platelets,
both separated and in clus-
ters.

128 ADVANCED PHYSIOLOGY

they have entirely disappeared. The only way to see them
at all is to draw the blood into some preserving fluid
which will prevent them from breaking to pieces. The
function of the blood platelets is not definitely known,
although they probably have something to do with blood
clotting.

BLOOD CLOTTING

Everyone is familiar with substances which may exist
either as liquids or solids. The most familiar example is
water, which becomes solid if the temperature falls below the
freezing point. The solidifying is dependent on temperature,
and the material can be changed from solid to liquid by
heating, or from liquid to solid by cooling.

So, too, blood has the property of existing in a liquid and ir
a solid form. When it becomes solid, we speak of it as
clotted. This clotting, however, differs decidedly from the
freezing of water, since it is not due to cooling, for blood will
clot even if kept warm. Indeed, the comparison of clotting
with the freezing of water is not a good one, for the blood
greatly changes its nature when clotting and can never be
brought back again into the condition of liquid blood. If
blood is drawn directly from the blood vessels into a small
dish, it will be found at first to be fluid, like water; if allowed
to stand a few minutes it becomes jelly-like. Presently it
forms such a firm jelly that the dish can be turned upsidf
down without displacing any of the blood. If it stands for
some time longer the jelly mass will shrink and a yellowish
liquid ooze out of it. This liquid is known as serum, and thr
contracted jelly, which holds most of the red corpuscles, is tht^
clot. If now the clot is taken out and thoroughly washed ii
water, all the corpuscles can be separated from it, and the
material left will be a tangled mass of white, elastic threads.
This substance is called fibrin. It must be understood thai
the fibrin does not exist while the blood is in the vessels, but

THE BLOOD AND ITS FUNCTIONS 129

is formed while the blood is clotting. Furthermore, it is known
that blood does not clot at all unless calcium is present in it.
The agents involved in the production of fibrin, and there-
fore of clotting, may be shown in relation to one another as
follows :
Thrombokinase (from tissue juice, white corpuscles or platelets)

+ Thrombogen (from plasma)
+ Calcium salts (from plasma)
= Thrombin = Fibrin ferment
Thrombin + Fibrinogen (in solution in blood)
= Fibrin (insoluble)

We have already noted that in the blood plasma there is a
proteid called fibrinogen (see page 124). This is dissolved in
the Hquid, and is no more visible than the sugar in a cup of
coffee. It is from this fibrinogen that the fibrin is produced.
Fibrinogen, however, will not give rise to fibrin if left to
itself, but if a certain amount of material called thrombin,
or fibrin ferment, is present, it at once breaks up into two
substances; one of these remains in solution in the blood, but
the other is not soluble, and appears at once as fibres form-
ing the fibrin. Hence blood clotting is due to the formation
of fibrin out of fibrinogen under the influence of fibrin ferment.

Whence comes this fibrin ferment? Since the blood will
not clot when flowing through the arteries and veins, we con-
clude that this ferment cannot be present in living blood. It
must be formed when the blood is drawn. Its source is not
certainly known but there are strong reasons for believing
that three different agents are involved:

(a) thrombokinase (from white corpuscles, platelets, or
the cut tissues) ;

(b) thrombogen (from the plasma) and

When these three factors are present at the same time, blood
clots quickly, and thus we conclude that they form the sub-
stance which changes fibrinogen into fibrin. At all

130 ADVANCED PHYSIOLOGY

events, it is an undisputed fact that while blood is flowing
through the vessels, it contains no fibrin ferment, and con-
sequently the fibrinogen remains unchanged; but as soon as
the blood comes into contact with any material other than
the regular lining of the blood vessels, fibrinogen at once
changes to fibrin and the blood clots. Even contact with
other tissues, e.g. muscle or skin of the same animal, pro-
duces a clot almost immediately; so, too, will an injury to a
blood vessel or simple exposure of blood to the air.

At times when it is desired to prevent blood from clotting,
this can be done by adding to it certain chemicals, e.g. sodium
sulfate or magnesium sulfate, pepsin, trypsin or peptones; the
extracts of the salivary glands of leeches or snake's venom will
very effectually prevent clotting. Rapid cooling will retard
and sometimes entirely check it. Blood can be made to clot
more rapidly by bringing it into contact with foreign sub-
stances, for example, by covering with cloth a wound from
which it is flowing.

Purpose of Blood Clotting. — Blood clotting is nature's
method of checking the flow of blood from wounds, thus pre-
venting possible fatal consequences. All our lives we are
thus guarded, not only from annoyance from small injuries,
but from the very serious results which would follow from bad
accidents or from surgical operations.

DISEASES OF THE BLOOD

It is often affirmed that a person's health is poor because
his blood is ''out of order" or needs "toning up." In most
cases, this is a mistake. Health is not determined by the con-
dition of the blood, but on the contrary the state of the blood
is determined by the rest of the body. The blood may not be
in good condition, it is true, but the reason is usually be-
cause the living cells of the rest of the body are out of order.
For example, a person is pale and white and suffers from lassi-
tude and other uncomfortable symptoms. The physician,

THE BLOOD AND ITS TTJNCTIONS 131

perhaps, makes an examination of the blood and finds that he
has ancemia, and that the blood contains too few red corpus-
cles. Now, while in this case it is true that the trouble shows
itself in the blood, the real cause is not there, but in those
parts of the body where the red corpuscles are formed,
and which for some reason are not making them rapidly
enough. Suppose again the paleness to be due to too many
white corpuscles. Here too, while the most noticeable
feature is in the blood, the real cause is in some of the other
organs whose impaired functions result in increasing the
numbers of white corpuscles until they are altogether too
numerous. The physician's treatment should be directed to
the real source of the trouble, not to the blood itself.

Blood Poisoning. — Blood poisoning is a name given to a
series of troubles caused by a certain kind of bacteria which
get into the body and multiply rapidly. The
poisoning agents are commonly in the skin, «— HJJN^
muscles, glands or some other active organ, not ^••'c.

often in the blood itself; but in some forms of \i*
the disease the blood carries them through the ^%kfLj^ ,
body and hence the name blood poisoning arises. ^^^H
The germs which cause the trouble (Fig. 70)
are abundant everywhere, in the air, in the soil, rp^^ g^*^_
on our clothes, on our skin, etc. They do no teria that
harm, unless they penetrate the skin by way of a produce
cut or bruise; and even then they do not often various
cause trouble, for our bodies are wonderfully ^^rms of

- 1 . , n . . 1 r^ blood POI-

endowed with power for resisting them. Com- g q n i n g
monly, therefore, they either do us no injury or boils etc.
produce simply a slight pimple, a little festering a, streptococci;
sore or a boil. If the body is in good condition, ^^. '°^ ^
the white corpuscles attack the bacteria in
these sores, and with the help of other resisting agencies the
germs are destroyed and the sore heals. But in other cases,
either where the resistance of the body is very weak or the

132 ADVANCED PHYSIOLOGY

germs are very strong, the germs are not checked in their
growth, but continue to multiply rapidly and are distributed
by the blood, producing serious and even fatal results. Blood
poisoning, as we call it, may thus be a very serious matter, but
it is similar in nature to the smaller troubles, e.g. festers, boils
and the soreness that follows skin woundSo

In endeavoring to avoid all forms of blood poisoning we
should remember a few simple facts: (1) The discharges
(pus) from sores or boils are sure to contain disease germs
and they should by every means be kept from coming in con-
tact with fresh cuts or bruises. (2) Whole, uninjured skin is
a sufficient protection for the parts underneath and germs
cannot penetrate it. But all points where the skin is broken,
cuts and bruises, should be carefully cleansed in boiled water.
(3) Various disinfecting ointments contain substances which
kill the germs. These ointments are of extreme value in
cases where the skin is broken. A wash of carbolic acid, one
part to twenty of water, is an excellent one to keep on hand, and
to use freely for washing all cuts, bruises or deep scratches.

Malaria. — Malaria, chills and fever, and fever and ague are
all practically the same disease. Here we have an actual dis-
ease of the blood, for it is due to a minute parasite that lives
upon the red corpuscles and in no other part of the body. These
parasites kill the corpuscle, which then breaks to pieces, and
the parasites come out into the blood plasma. At this time,
a little poison is let out into the blood from the broken cor-
puscle, producing a chill, followed by a fever. Soon after,
the parasites attack other corpuscles, grow forty-eight hours
and break up again. Thus, this peculiar disease is intermittent ;
i.e. comes with regularity at certain intervals. If there is a
small amount of quinine in the blood at the time the corpuscles
break up, the little parasites will be destroyed and the disease
checked. Hence quinine is almost always used as a medicine in
cases of malaria.

One of the most valuable discoveries of science has been

THE BLOOD AND ITS FUNCTIONS

133

the method by which these Uttle parasites find their way into
the blood. They cannot pass directly from person to person
and hence the disease is not contagious. It used to be sup-
posed that malaria came from bad air, especially from the air
of swamps, night air being thought particularly dangerous.

Surface ofWai-er

Fig. 71. — Mosquitoes

Figures a and 6 show the larvae in water, a being the harmless species (Culex) and
h (Anopheles) the species that carries malaria. At c is shown the position assumed
by the harmless type upon alighting, and at d the position of the dangerous one. In
the latter it will be seen that the body and head are in one straight line while in the
harmless species the body is bent at the neck. At e is shown the dangerous Anophe-
les with spotted wings and five hair-hke projections (or feelers) in front; at / the Cu-
lex with plain wings and three feelers.

P] But these theories have been disproved. It has been found
that these parasites live in a certain kind of mosquito. If

134

ADVANCED PHYSIOLOGY

a female mosquito bites a patient suffering from malaria
it will suck some of the red corpuscles containing the parasites
into its body. In the mosquito these parasites go through
some changes and finally come to lodge near its mouth. If
this mosquito later bites another person, the tiny parasites
are likely to be inoculated into the body where the skin is
pierced. Thus a second person is infected. This is the only
method by which malaria is known to be distributed. Hence
any means of getting rid of mosquitoes is a protection against
malaria. Mosquito netting at windows and doors is a very
efficient protection from this disease. Draining puddles and
pools and emptying all barrels of standing water where mos-
quitoes breed is another. Only one kind of mosquito dis-
tributes the disease and fortunately this
is not the most common kind. A method
of distinguishing it from the harmless species
is explained in Figures 7 1 and 72.

Yellow Fever. — Yellow fever is fortunately
uncommon in this country, occurring only
at rare intervals in the southern states. In
tropical countries, e.g. South America and
the West Indies, it is of more frequent
occurrence. Occasionally it does get into
our southern cities in the summer, and
in past years it has produced very serious
epidemics with thousands of deaths. Its
cause has recently been discovered to be
an extremely minute unicellular organism. It
is mentioned here because, like malaria, it is
known to be distributed by mosquitoes, though the species
carrying yellow fever germs, Stegomyia, is not the same as the
one which spreads malaria.

These facts show clearly that mosquitoes are among our
most deadly enemies. The different states of the Union are
showing appreciation of this fact by appropriating con-

FiG. 72. — Mos-
quitoes

g, Anopheles, h,
Oulex, as they
alight on the walla
of a room.

THE BLOOD AND ITS FUNCTIONS 135

siderable money for the warfare against mosquitoes. Since
mosquitoes breed in stagnant water, the draining of such
breeding pools or the pouring of kerosene on the surface is an
efficient method of kilUng the young. Everyone for his own
jood, as well as for the good of others, should give all the
5sistance he can to this work of mosquito extermination.

Influenza. — While this disease is doubtless acquired by
wreathing in the organisms causing it, it manifests itself prim-
rily as a disturbance of the blood in the form of a fever. As
well known, it is extremely contagious, and thus easily
ssumes the proportions of an epidemic. It differs from an
Ordinary cold by spreading even more rapidly, in causing a
)erson to feel suddenly weak, experience pain in the head,
)ack or eyes, develop a fever and ''feel sick'^ to a greater
degree. As to its cause, several bacteria have been recog-
nized as present, and the practice of inoculation against the
disease has been begun with fairly successful results. How-
ever, immunity is very transitory, and one may "catch'^
influenza repeatedly. Fatal results seldom accompany the
malady by itself, but it leaves the system weakened and
susceptible, so that other more serious diseases, e.g. pneu-
monia, are very liable to follow. Extreme care while con-
valescing should be observed.

Influenza is doubtless spread by the ''droplet method ;'*
i.e. a healthy person breathes in minute moisture droplets,
containing the germs, which have been expelled by a sick
or near-sick person while sneezing, coughing, talking, or sing-
ing. One should avoid crowded rooms, cars, public gather-
ings of all kinds, and contact with the sick; also spend as
much time as possible in the open air in recreative exercise.
If attending those sick with influenza, one should always
wear a gauze cloth over the nose and mouth as a precaution.

CHAPTER X

THE HEART AND THE BLOOD VESSELS

The heart has been recognized as an important organ for a
longer time than any other part of the body, and numerous
phrases in hterature show the fanciful, as well as mistaken,
ideas once held concerning its function. The expression '4ove
with all one's heart" is an example of the erroneous notion
that the heart has something to do with the emotions. In real-
ity the heart has but one function: it simply pumps the blood.
Location of the Heart. — The heart is located in the thorax,
between the lungs, just a little to the left of the mid-line, and
back of the ''breast bone." The rigidity of this bone prevents
one's feeling the heart under it, but the lower end of it pro-
duces a distinct ''beat" which can be felt and seen between
the fifth and sixth ribs. It is swung freely in the thoracic
cavity, attached to its upper wall by masses of connective

tissue, which also bind it
to the large arteries and
veins, and to the wind-
pipe.

The Coverings and
Structure of the Heart. —
The heart is completely
enveloped by a two-
layered bag, the pericar-
dium (Fig. 73), which is
pierced only by the large
arteries and veins leaving
and entering the organ.
The inner layer of the pericardium is grown fast to the heart
jDUScle^ and thus forms a firm, tou^h covering for it^ th§

Tracfi

f^ncarefionj

Fteura

Fig. 73. — Diagram

Showing the relations of heart, lungs and
membranes around them.

THE HEART AND THE BLOOD VESSELS 137

outer layer is loose, the two moving freely over each other.
These pericardial layers are covered by glandular epithelium
which secretes a fluid into the space between them, this liquid
being naturally called the pericardial fluid. Were it not for
this fluid, the ever-moving heart would rub against the sur-
rounding tissues, producing much friction and inflammation.

A person's heart is about the size of his fist. In shape it is
something Hke a strawberry and lies with the small end, or
apex, pointing downward and toward the left; the upper end
is called the base and here the large arteries leave and the
veins enter it. It is a hollow organ, the walls of which are com-
posed mainly of muscle; on the outside more or less fat is
usually deposited, especially in certain depressions where the
arteries and veins emerge, and along grooves which extend
lengthwise or obUquely on the organ over places whert par-
titions run in the interior.

The cavity of the heart is divided by a vertical wall into
right and left chambers; and each of these is again partially
divided into an upper portion, the auricle, and a lower, the
ventricle. Each of these four chambers is lined with a smooth
glistening sheet of membranous epithelium, which keeps the
blood from direct contact with the muscle tissues of its walls.
The walls of the auricles are very much thinner than those of
the ventricles and the wall of the left ventricle is thicker than
that of the right.

THE EVENTS OF A HEART BEAT

We can best learn the structure and action of the heart if
we trace the flow of blood through it, noticing how the valves
are closed and opened so that the blood always flows onward.
The blood is brought from the body to the heart through two
large veins, which open into the right auricle — the superior
vena cava, bringing the blood from the upper part of the body,
l^nd the other, the inferior vena cava, bringing it from the

138

ADVANCED PHYSIOLOGY

lower part; Fig. 74. If we begin our description at the rest
period of the heart, i.e. the period between any two beats, we
shall find that the blood flowing in these veins passes in a large

Inferior Vena
Coya

Superior Vena
Cava

Putmqnartf Arfertf

Tricuspid

Valve Oppn^^^

SemiLunar
v Vaiye • Closed

CAordaeTendin&

\Papillaru ffusdet T-

Tricutpid Yalye
Chsed

Fig. 74. — Diagram

Showing the mechanism of the heart. At A is shown the right side of the heart
at the period of rest, and at B the arrangement of the valves when the heart
contracts. The arrows show the direction of the blood flow.

stream directly into the right auricle (Fig. 74), whence it
flows freely through the wide opening from the auricle into the
ventricle. Thus the auricle and ventricle are both filling at
the same time.

The opening between the right auricle and right ventricle
is guarded by three flap-like membranes, attached at the top
of the ventricle; when the ventricle is empty, they hang down
loosely (Fig. 74 A), but as the entering blood collects in the
bottom, these flaps float on its surface. This condition lasts
only for a fraction of a second, when the muscles in the walls
of the auricle contract, forcing all the blood into the ventricle
with a rush. Carrying the flaps on its surface, the blood rises
rapidly until the ventricle is completely filled. At this time
the valves are lifted up directly across the opening from the
auricle; Fig. 74 B. They are of such size and shape that
when in this position they exactly fill the opening, completely

THE HEART AND THE BLOOD VESSELS

139

preventing the passage of any blood back into the auricle.
These valves between the chambers of the right side of the
heart are called the tricuspid valves.

Next, the muscles in the walls of the ventricle contract,
pressing upon the blood until the ventricle is emptied. In
what direction will the blood flow? It would go back into
the auricle if the tricuspid valve had not closed the opening
in that direction. These valves are only soft membranes,
and one would suppose that they might give way under the
pressure of blood in the ventricle and turn back into the
auricle. To prevent this, stout cords (chordae tendinae) are
attached to the edges of the valves (Fig. 74), their other
ends being fastened below to the walls of the ventricle.
These cords are of such lengths that when the valves are
stretched across the opening the cords are tight; Fig. 74 B,
It would not be possible to push the
valves up into the auricle without
breaking these cords; moreover they
can be drawn downward somewhat
by Uttle muscles attached to their
lower ends, the so-called papillary
muscles. As the ventricle contracts,
then, the blood must find another
outlet.

The only real outlet from the right
ventricle is a large artery shown in
Figure 74, and called the pulmonary
artery, since it leads to the lungs.
This artery is already filled with
blood, also under pressure, blood that
would readily flow back into the
heart were it not for a set of valves
preventing such a return; these, called the semilunar valves,
consist of three soft folds in the shape of half-cups or
pockets with their open ends directed away from the cavity

Fig. 75. — The pulmonary
artery cut open to
show the semilunar

VALVES.

140

ADVANCED PHYSIOLOGY

of the ventricle; Figs. 74 and 75. When the blood in the
pulmonary artery starts to run back into the empty ventricle,
it fills these little cups, causing them to swell until the three
stretch completely across the lumen of the artery, thus
wholly blocking the passage and preventing any backward
flow of blood. But when the ventricle contracts, blood is
pushed against the cups from below until it finally flattens
them against the walls of the artery so that blood can pass
them easily. These cup-like flaps remain flattened against
the walls of the pulmonary vessel as long as the contraction
3f the ventricle forces the blood onward.

After the ventricle has contracted as much as it can and
has squeezed out practically all the blood it contained, the

muscles in its walls relax, leav-
ing the cavity free to fill
once more. The blood which
has just been forced into the
artery starts to flow back but
immediately fills the semilunar
valves, which then block its
backward passage. This action
can be better understood, if
compared to the behavior of
an umbrella in a wind. When
pointing into the wind it offers
little or no resistance to the
currents of air, which would
tend to close it; but if turned
the other way, it is immediately
opened and filled, thus blocldng
the passage of the wind. The blood cannot flow back into
the ventricle but as the ventricle relaxes, the tricuspid
valves fall down loosely into the ventricle again, thus allow-
ing more blood to enter it from the auricle and reinstating
the condition with which we started.

Fig. 76.— Diagram

Showing the veins entering and the
arteries leaving the left side of the
heart. Broken line marks the aorta.

THE HEART AND THE BLOOD VESSELS 141

The blood that flows out of the right ventricle goes through
le pulmonary artery to the lungs, whence it goes through
mr vessels called the pulmonary veins to the left auricle of
le heart; Fig. 76. The left side of the heart, which the
ilood now enters, is almost exactly like the right side; there
a similar flap-like valve hanging down between the auricle
and ventricle. This mitral valve has two flaps instead of
three, but its action is precisely the same as that of the tricus-
pid. A large artery also leads out of the left ventricle, its
opening guarded by three semilunar valves, exactly like
those at the origin of the pulmonary artery. This artery
into which blood is pumped by the left ventricle is called the
aorta, and through branches of it, as we shall see, blood is
distributed over the entire body.

Rate of Heart Action^ — The beat of the heart is really very
rapid, a whole beat occupying less than a single second.
About seventy times a minute, day and night, the heart goes
through the entire act of opening and closing its several valves
and forcing along the blood. The two sides beat at exactly
the same time, so that with each beat a small cupful of blood
is forced into the pulmonary artery from the right ventricle and
a similar amount from the left ventricle into the aorta. The
actual beat of the heart, i. e. the contraction of the muscles
to force the blood along, takes only about 0.3 of a second.
After the beat, the heart rests during the time that the auri-
cles are filling from the veins. This time, which is the only
rest the heart has from its continual work, is about 0.5 of a
second. The beating period is called the systole, and the
resting period, the diastole.

Heart Sounds. — If one places his ear over a person's heart
when it is beating normally, or if an instrument constructed
for the purpose (the stethoscope) is applied to the area above
the heart, each beat seems to be accompanied by two sounds,
one longer than the other. When a he^rt beat begins and the

142 ADVANCED PHYSIOLOGY

blood rushes into the ventricle from the auricle, the curtain'
like valves lie in line with the current, just as a flag flies ou"
in the current of the wind. Although the wind may be steady,
the flag ''flaps" from side to side. So, in the heart, we ca:
imagine the mitral and tricuspid valves wavering in the cur
rent of blood, even if it is steady. This is thought to be th
cause of the first sound.

The second sound, following closely on the first, is sharper
and shorter. It is believed to be caused by the closing of the
semilunar valves in the large outgoing arteries. These, it is
thought, are thrown into their tense, filled condition so sud-
denly that they give rise to a distinct impact and noise, just
as doors do when they suddenly close in a current of wind,
even though they may be fitted with appliances for pre-
venting their actual "slamming."

The Throb at the Breast, and the Pulse. — When the heart
beats, the apex is turned distinctly forward with sufficient
force to lift the body wall between the fifth and sixth ribs,
and at this point a throb is easily felt. Every time the heart
beats a small amount of blood is forced into the arteries.
This fills those near the heart more full of blood than else-
where; consequently a wave of pressure travels rapidly along,
causing a slight swelhng of the arteries on its way. If the
fingers be placed on the artery of the wrist, where it comes
near the surface, this wave can be felt, and is called the pulse.
The pulse is due to a temporary increase in the diameter of
the artery, and is not as it seems to be, a little jet of blood
flowing through the artery at the point where the pulse is
felt. The pulse can be felt in any of the arteries which come
near the surface; but as arteries are commonly deeply im-
bedded in the muscles, there are only a few places aside from
the wrist where it is evident, e. g. the neck, and about the
temple, back of the eye. By feeling the pulse a physician
can determine the rate of the heart beat as well as its
force. The normal rate is 72 per minute.

THE HEART AND THE BLOOD VESSELS 143

The heart action, however, undergoes an interesting change
of rate with age, the average rate found in large numbers of
instances being as follows : In early babyhood, 140 beats per
minute. In childhood, 100 per minute. In youth, 90 per
minute. In adults, 75 per minute. In elderly persons, 70
per minute. In very aged persons, 75 to 80 per minute.

The Work Done by the Heart. — The muscular power of the
heart is very great. The work it does during one day is about
equal to the additional energy expended by a man in climbing

ito the top of a mountain 3600 feet high. Assuming that the
man weighs about 150 pounds, this would be equal to an
amount of energy sufficient to lift 90 tons to a height of
three feet. The work of the left side is greater than that of
the right, since the former has to drive the blood all over the
body, while the latter has only to force it through the lungs
which are near by. For this reason the muscle walls of the
right are much thinner than those of the left ventricle.

Defects in the Heart Mechanism. — We can readily see how
a very slight injury to the heart might result seriously. Sup-
pose, for example, that the valves should fail to close the pas-
sages over which they are placed as guards. In some cases of
heart disease, a bit of clotted blood collects on the edges of
the valves, preventing their perfect closure, causing a leakage
and seriously interfering with the action of the heart. It
appears that the serious disease, influenza, may frequently

j affect the heart muscles and valves, causing faulty action and
thus menace the general health. But one must not think

I that, because he has a pain around the heart, he is suffer-
ing from heart disease. Indeed, it often happens that those
who have some defect in the heart mechanism are quite
unconscious of the fact, since the effects are generally more

i noticeable elsewhere.

144

A.DVANCED PHYSIOLOGY

CAUSE AND REGULATION OF HEART BEAT

Brain

' Vaqus.
\5(pnpathetvs

What makes the heart beat? No one as yet understands
life sufficiently to give a satisfactory answer to this question,
but we do know that most activities are brought about at the
command of the brain; most of the muscles will not contract
at all unless it orders them to do so. How is it with the heart?
Does it need orders from the brain or can it direct its own
beating? That it can act independently of the brain has
been shown in the instances of many animals, where the
heart has been entirely removed from the body and has yet
continued to beat for a considerable length of time, even so

long as two days. Evidently then,
the heart contains in itself some
agency that causes it to beat.

The heart is thus automatic
and would of itself continue to
beat regularly through life; but
such regularity would be very
unsatisfactory, for the amount
of blood which the working or-
gans need varies at different
times. When the muscles are
active they need much blood,
when they are quiet they need
little. When one is asleep, the
organs need less blood than when
he is awake, and all through life
occasions are constantly occur-
ring where the body demands a
more or less rapid circulation
of blood than usual. To meet these varying demands, the
brain has the power of regulating the heart beat.

Two sets of nerves pass to the heart; one set arises in
the medulla of the brain, the other in the sympathetic

/fearf ,

Fig. 77. — Diagram

Showing the nerves controlling heart
beat.

THE HEART AND THE BLOOD VESSELS 146

nervous system. The nerves from the brain, the vagi (Fig. 77),
act as a brake on the heart; if they are artificially stimulated,
the beat of the heart is retarded; or if they are severely
irritated, heart action may stop altogether for a short time,
although after a little the heart escapes from its influence and
goes on beating again. The office, then, of the vagus nerves
is to keep the heart from beating too rapidly. In a healthy
body they would never stop the action as described above,
but the slowing influence is necessary when the body tissues
need but little blood, as when one is idle or asleep. The
vagus nerves, because they check the heart action, are called
the inhibitor nerves.

The second pair of nerves which affect the heart are called
the sympathetic nerves; Fig. 77. If these nerves are stimu-
lated, they make the heart beat faster and more forcibly, for
which reason they are sometimes called the accelerator nerves.

Thus we find that three influences are constantly affecting
and regulating the heart:

1. The impulse to beat, located within the heart itself.

2. The inhibitory influences, which reach it from the cen-
tral nervous system over the vagus nerves.

3. The accelerator influences, which come over fibres by
way of the sympathetic nerves.

All these actions take place unconsciously, for one has no
power voluntarily to modify the activity of the heart. If
the heart is thus made to beat more or less rapidly, it, of
course, affects the rate of circulation. The more rapidly the
heart beats, the more rapidly the blood circulates, and a
slowing of the heart beat will check the circulation of the blood.

THE BLOOD VESSELS

All vessels in the body which conduct blood, ''pure" or
"impure," away from the heart are called arteries; all which
carry blood to or toward the heart are called veins. Both
wre large in the region of the heart; but if one follows the ar-

146

ABVANCED PHYSIOLOGY

teries away from the heart, he finds that they branch re-
peatedly until at the ends of the arms, in the head, skin or
(ntestine, they are extremely small. The smallest subdivisions
of the blood vessels are called capillaries. Soon these minute
, , ^ ... tubes unite as veins,

Aorfa

which as they go to-
ward the heart are
joined by others and
finally are even larger
than the arteries.

The Arteries. —
From the right ventri-
cle, the blood enters
the pulmonary artery ;
Fig. 74. This artery
divides, sending one
branch to each lung,
and inside the lungs
each branch divides
into numerous small-
er branches; finally,
each minute twig
breaks up into a pro-
fusion of lung capil-
laries. In these capil-
laries the blood takes
up and gives off
gases. After passing
through the capilla-
ries, the blood collects
in veins which unite
to form large trunks, that finally leave the lungs, going
immediately into the left auricle; Fig. 76. From here, the
blood goes to the left ventricle, and thence out through
an artery, the aorta: Fig. 76.

Spleen
'uperioritlesenhric

Infesh

Fig. 78.— Diagram

Showing the aorta and its chief branches. The
broken line runs through the middle of the aorta.

THE HEART AND THE BLOOD VESSELS

147

Almost before this aorta emerges from the base of the

heart, it gives off two small arteries which supply blood to

the heart muscle itself. It may seem strange that the heart

with the great stream of blood flowing through it needs

special arteries to supply it with blood. But the blood

flowing through the heart does not nourish it any more than

the sap running up the tree nourishes the outer layers of the

bark. Hence the heart, ]/gjp

which works more con- . , \ v

Arferu \s

leucocyte
(Erythrocyte

stantlythan any other
organ, needs its own
blood supply, which
is received through
these coronary arteries.
The aorta goes up-
ward a couple of
inches, bends toward
the left, and then turns
downward through the Leucocifh
thorax and abdomen,
to the lower part of
the body, as shown in
Figure 78. Before
turning downward it
gives off branches, of
which the carotids pass
to the head on each
side (Fig. 78); while
others, the subclavians,
pass to each arm, thus supplying the upper extremities
with blood. The right carotid and right subclavian leave
the aorta as one trunk that soon divides. The main artery
(aorta) descends through the abdomen, side branches furnish
blood to the intestine and other organs in the abdomen, and
finally the aorta divides, one braftch extending into each leg.

Capillaries

Fig. 79. — The terminus of an artbkt

Showing its connection with a vein through the
capillaries. In the upper capillaries are shown
blood corpuscles flowing through them. Some
leucocytes are shown making their way through
the capillary walls, and others quite outside of the
blood vessels.

148

ADVANCED PHYSIOLOGY

The chief arteries and the organs to which they go are diagram-
matically shown in Figure 78.

The Capillaries.^ — Each artery divides and sub-divides into
smaller and smaller branches, and the smallest twigs are
distributed to the tissues in every part
of the body. If we follow a single one
of these branches, we find that each
ultimate twig finally breaks up into a
profusion of extremely minute vessels,
the capillaries, too small to be seen with
the naked eye; Fig. 79. They branch
abundantly and unite in the form of a
network, so that the blood which flows
into them has no definite course but.
may go through the network in an;
direction. These capillaries (Fig. 80.
are of great importance, for it is througl
them that the blood gives up its nu-
triment to the tissues and takes ii
turn the waste materials which ma^
have collected in them.

The Veins. — After passing througl
the capillaries the blood collects in ves-
sels, called veins. The smallest of these
join others from other sets of capilla-|
ries until they soon become vessels oi
good size. Every artery ends in a set
of capillaries, and each set of capillaries
empties into minute veins which unite
with others to form main trunks, carry-
ing the blood back toward the heart.
The blood from the head returns in two large veins on
each side of the neck, known as the jugular veins (Fig.j
81), and these join the large veins coming from eacl
^See Demonstration, Appendix, Section 14.

Fig. 80. — Showing the
distribution of cap-
illaries in muscles

The black irregular lines
are the capillaries. Their
minuteness and abundance
may be inferred from the
fact that the muscle fibres
themselves are only about
one five-hundredth of an
inch in diameter.

THE HEART AND THE BLOOD VESSELS

149

arm to form two trunks, wnich finally unite, forming
one large vessel, the superior vena cava;

This

Sub'^kj^tan

WStomach
\ 5pleen

\ Kidneif

empties directly into
the top of the right
auricle, as we have
already noticed. The
blood from the lower
part of the body
unites in large veins,
finally forming one
great trunk, the in-
ferior vena cava (Figs.
65 and 81), which
also empties into the
right auricle. By .
these two large veins
all of the blood car-
ried out from the left
ventricle, after pas-
sing through an im-
mense system of cap-
illaries, is brought
back to the right
ventricle to be sent
once more to the
lungs. In general,
one may say that the
blood vessels near the
surface of the body

are veins, while the arteries are imbedded deeply in the
tistsue; hence the wounding of the flesh is almost sure to cut a
vein, but will not, unless very deep, injure an artery.

I As a rule the arteries and veins going to and from a given
rea or organ lie closely parallel to one another, and often
ave the same names, e. g. subclavian artery, subclavian vein.

/ Infesiine

A \M///ac

Fig. 81. — Diagram

Showing the course of the chief veins.

160 ADVANCED PHYSIOLOGY

The Portal Blood System. — The portal blood system has
already been fully described (see page 118). Briefly sum-
marized, the portal vein begins in the capillaries of the in-
testine, stomach and spleen; the blood from all these organs
runs together to form the portal vein proper, which enters
the liver and there breaks up into capillaries, for purposes
already mentioned (shown also in Fig. 81). The liver, then,
receives venous blood from the portal vein, and arterial
blood from a branch of the aorta as it runs down through the
abdomen.

GENERAL SUMMARY OF THE CIRCULATION

The circulation of the blood is a double one, one half going
from the right ventricle through the lungs and back to the left
ventricle; the other half from the left ventricle through the
body and back to the right ventricle. The circulation through,
the lungs is called the pulmonary circulation; that through the!
rest of the body is the systemic circulation. During its entire]
passage around the body the blood as blood never leaves the
arteries, capillaries and veins (except in the spleen) . Remember-
ing that the right and left sides of the heart are entirely sepa-j
rated, it is plain that the blood after leaving the left ventricle]
of the heart, traverses the body, returns to the right side oi
the heart, goes thence to the lungs and so finally returns to]
the left side of the heart whence it started. It has however
traversed no area twice even though it has been twice to thej
heart.

STRUCTURE OF BLOOD VESSELS

If an artery be taken from an animal's body it will be found
that it is not a Ump tube, but rigid enough to keep its shape
even when empty. The tissues which make up an artery are;
arranged in three chief layers; Fig. 82. Next to the cavity

THE HEART AND THE BLOOD VESSELS

151

of the tube is a layer of thin, flat cells, making up a so-called
lining epithelium; outside this is a middle layer of involuntary,
smooth muscle, the fibres of which pass around the tube;
the outer coating is made of connective tissue disposed in a
dense, spongy mass of elastic fibres which thus gives the tube
its rigidity. If an artery is stretched it will return to its
fiormal length like a strip of rubber; if it is closed at one end
and air forced into the other, the artery will swell to two or
three times its first diameter.

Epithelial Lat/er

■Coffnecfiv^isue Latter

but will return to its normal
size when the pressure is
relieved.

Agents commonly causing
the contraction and relaxa-
tion of these muscles are dis-
cussed on pages 162-163.

Veins are made of the same
tissues as arteries ; they differ
in that the walls are very
much thinner so that the
tube collapses whenever it is
empty. The muscle and con-
nective tissue coats cannot be
easily distinguished as their
fibres are mixed together, and
both are thin as compared
with the same layers in arteries; Fig. 82 C. Veins are much
.jss elastic as well as less rigid than arteries. Some veins are also
provided with valves which prevent the blood from flowing
in any direction except toward the heart. These valves are
made of a thin, flexible layer of connective tissue and epithe-
um in the shape of half cups, fastened to the walls of the
veins by their edges; Fig. 83. Thus when the blood flows
in one direction the valves flatten against the side of the tube

(^ offer very Httl^ resistance; bi^t if the blood st^xta ba,clfr

Fig. 82. — Showing the structure
of a blood vessel.
At A is shown an artery with the different
layers removed at different levels. At
B is a cross section of an artery, and at
C of a vein. (Modified from Landois.)

152

ADVANCED PHYSIOLOGY

ward in the other direction, they fill and thus occupy the
whole calibre of the vein.

Capillaries are delicate, thin-walled tubes made of cells
which are continuous with the lining epithelium of the arteries
and veins; Fig. 84. The capillaries are essentially the same
as the arteries with the muscle and connective tissue layers
absent. Through their thin walls the fluids of the blood
easily pass, and thus come in contact with the surround-
ing tissues. In size, capillaries are, on the average, about 2X00
of an inch in diameter, and their numbers are countless.

The finest needle cannot
pass through the skin with-
out puncturing some of
them, and the deeper lying
organs are supplied in the
same way as those on the
surface.

Each of these blood tubes,
then, is especially fitted to
its place and function; the
arteries withstand the pow-
erful, unremitting driving
of blood into them by the
heart; the capillaries allow
the passage of the nutrient
fluids and gases into the
surrounding tissues, and also
take up waste fluids and
gases; the veins conduct
blood back to the heart,
open to their full diameter
all the time to permit the
easy flow of blood, yet col-
lapsible so as to prevent any tendency to the formation
of empty spaces. Of course, blood will not tend to flow

Fig. 83. — A vlix cut

OPEN

To show the irregular valves

within.

Fig. 84.—

A BIT OF
A CAPIL-
LARY
Showing it
to be made
of a single
layer of
epithelial
cells only.

THE HEART AND THE BLOOD VESSELS 15S

backward through the arteries since the heart pump is , con-
stantly pushing more blood along into them, thus keep-
ing the stream in one direction. Veins, however, which
do not feci this impulse from the heart, are provided with
valves so that a forward flow alone is possible.

Diseases of the Circulation. — Anything that impairs the
circulation will evidently interfere with normal bodily activity.
Irregularities in the action of the valves or muscles of the heart
will of course interfere with circulation. Slight imperfections
in heart action are not uncommon. They are commonly first
noticed by a shortness of breath rather than any trouble around
the heart. Persons with such defects must live a more quiet life
than is necessary for one whose heart is normal, and must avoid
all forms of athletics that produce excessive strain or ex-
haustion, e.g. running or football. With care in regard to over-
strain, these heart weaknesses need not cause especial alarm,
and those who have them are likely to live as long and useful
lives as others without such weakness.

In youth all the arteries are strong and elastic and capable
of adapting themselves to a large range of needs, so that vigorous
exercise, even of long distance running, is well endured. When
one passes middle life, however, the arteries become less elastic
and less able to respond to unusual demands upon them. When
this occurs a person should begin to live a more quiet life and
not subject his heart and arteries to such strains as would come
from running to catch a train, hurrying up stairs, or other
vigorous exercise. Later in life the trouble may become ex-
cessive, producing a disease called hardening of the arteries
(arterial sclerosis). This is commonly a sign of the approach o^v
old age and for it there is no known remedy.

CHAPTER XI

THE CIRCULATION OF THE BLOOD AND OF THE
LYMPH

Nearly every one has seen firemen handling hose, and has
noticed how, as the engine pumped, water spurted out at the
couplings or at some leak in the hose, showing that it was
under great pressure. This pressure is due both to the steady

pumping of the en-
gine and to the small
nozzle at the end of
the hose. If the noz-
zle were taken off, the
water would run in a
large stream but
would not be thrown
any great distance,
as there would be
nothing to prevent
the whole pipeful from escaping as fast as the water was
pumped into the hose. In such a case the water would be
under little or no pressure; Fig. 85.

BLOOD PRESSURE AND ITS CAUSE

The blood in our arteries is under pressure for similar rea-
sons, and the pressure is produced by two similar factors, (1)
the heart beat, and (2) the resistance offered by the capillaries
to onward flow. Since the heart contracts about seventy
times a minute and pushes fresh blood into the aorta, the
influence of its beat is evident. The narrower arteries and
capillaries offer great resistance to the blood flow, corr§-

Fig, 85, — Showing the effect upon pres-
sure OF DIFFERENT-SIZED NOZZLES
There is a leak in each hose and the height of the
stream of water shows the pressure.

CmcULATiON 01^ BLOOD AND OF LYMPH

spending roughly to the nozzle of the fireman's hose. When
a large artery is wounded, the force with which the blood
comes from the cut strikingly shows this pressure.

Naturally, the blood in all persons is under some pressure no
matter what their age. Age makes much difference, however,
and it has been found that in boys and girls of ten years of age
the pressure is only about one-half what it is at twenty-five
years and again that, in persons of fifty, it is about eighteen per
cent more than at twenty-five. Much of this is explained
by the decreasing elasticity of the arteries as one grows older.
In the aorta near the heart the pressure is very consider-
able, but it is slight where the blood flows into the capillaries.
It will be remembered that the cap-
illary walls are very thin, only the
thickness of one cell for the most
part; and this condition, which is
necessary for the ready exchange of
materials through their walls, would
make it impossible for them to
resist high pressure.

An idea of the amount of pressure
in the arteries has sometimes been
gained in the following way. If a
glass U-tube be inserted into a large
artery in the neck (Fig. 86) and if
this tube be open at the end, the
blood will, of course, flow out under
its pressure. But if the tube be

)laced in a vertical position and

lercury be put into it to hold the

>lood back, the more forcibly the

)lood presses, the more mercury will

)e required to hold it back and keep it from rising and

soming out. It takes about nine inches of mercury in the

tube to prevent the blood from rising. For this reason we

Fig. 86. — Showing method
of measuring blood
pressure

At 6 is a glass tube tied within
an artery of some animal ; c, a
flexible rubber tube;d, a glass
tube containing mercury. The
greater height of the mercury
in the open arm of the tube
shows the pressure.

156 ADVANCED PHYSIOLOGY

say that the pressure of blood in the artery is nine inches of mer-
cury. The pressure varies a Httle with each heart beat, being
greatest while the heart is contracting and least when the heart
is resting. The pressure decreases as the arteries become
smaller until it becomes very slight in the capillaries. This
should naturally be so, for, as seen on page 152, capillary walls
are extremely thin, and slight pressm*e would rupture them.
That they possess some elasticity, however, is evident from the
appearance of the face when blushing; it is also known that
the lymph passes through the walls of capillaries, sometimes
rapidly, sometimes slowly, and this seems to be due to a vary-
ing pressure within them as well as to a varying permeability
of capillary walls.

With the veins, into which the blood flows from the capil-
laries, the conditions are very different. They are wide open
where they end at the heart, so that there is nothing to keep the
blood from flowing freely imtil it reaches that organ. There is
nothing corresponding to the nozzle of the hose. For these
reasons the blood in the veins is under much less pressm^e than
that in the arteries, and varies much with the location and posi-
tion of the organ.

Bleeding from Arteries and Veins. — If an artery is cut, the
blood will come out in forcible jets, and prompt action is
necessary to prevent the person from bleeding to death. The
bleeding must be stopped by compressing the artery between
the cut and the heart. Such accidents are most common in
the legs and arms where they can easily be treated. Figures
87, 88 and 89 show the course of the chief arteries in an arm
and leg. The easiest and most effectual way to stop bleeding
is to put a ligature above the wound. A doctor should be
summoned and the ligature kept in position till he arrives.

Wounds in veins are generally less serious than in arteries,
but should a large vein be cut and the bleeding be so rapid
that clotting will not stop it, a ligature should be placed
beyond the wound.

CIRCULATION OF BLOOD AND OF LYMPH

157

The Pulse. — In an earlier section the real cause of the pulse,
I.e. the constantly alternating increase and decrease in size
of the arteries due to heart beat, has been
noted. There is, however, no pulse in the
capillaries. Such a constant
stretching and swelling
would break down their thin
walls. In the veins, too,
since they are formed by the
running together of the capil-
laries, no pulse is present.
Two agents have brought
about this disappearance of
pulse in the veins, (1) the
elasticity of the arterial
walls, and (2) the opposi-
tion which the small arter-
ies— arterioles — offer to on-
ward blood flow. If the
arteries had rigid walls, there
would be pulse in the capil-
laries and veins, in spite of
the small calibre of the arte-
rioles; and if the capillaries
and small arteries were large,
the pulse would be car-
ried over into the veins in
spite of the elasticity of the arterial walls.
We may note here also that the pulse is not
a simple throb, but consists of two parts; first,
"beat," and immediately following, a second
These cannot be felt as separate with the
aked finger, but are detected with a pulse recording apparatus.
The first part of the pulse wave is calused by the sudden rush of
lood into the arteries when the ventricle contracts, while the

Fig. 87.— The
abm from in

FRONT

Showing the chief
arteries. (Modi-
fied from Tiede-
mann)

Fig. 88.— The
thigh and
knee from
the inside

Showing arteries.
(Modified from
Tiedemann)

strong, abrupt
'weaker beat."

158

ADVANCED PHYSIOLOGY

less prominent beat is supposed to be caused by the closure of
the semilunar valves of the heart.

RATE OF BLOOD FLOW

With such a powerful organ as the heart
driving the blood about the body, the blood
current is fairly swift. The blood flows rapidly
in the large arteries, but as they branch, the
total area 'of arteries becomes greater, so that
it flows more and more slowly; just as a river
flows swiftly through a narrow gorge, but
more slowly when it spreads out into a
broad stream. In the large arteries near
the heart blood flows at the rate of about
sixteen inches per second. Farther from
the heart the rate is about nine inches per
second; in the smaller arteries it is much
slower; in the capillaries it flows not more
than -^\y inch per second. After passing into
the veins the rate increases and as the veins
merge into trunks and finally reach the
heart it is about as rapid as in the arteries
that leave the heart. It is in the capillaries
that the blood exchanges new food materials
for worn-out matter, and oxygen for carbon
dioxid; and to allow this to take place to ad-
vantage a very slow flow is necessary. The
length of time required for the blood to make
a complete circuit of the body is calculated at
twenty-eight seconds, requiring thirty-two to
thirty-four heart beats.

THE VASO-MOTOR SYSTEM
Regulation of the Size of the Blood Vessels.—
By changing the rapidity of the heart beat, the whole body
may be made to receive more or less blood than usual; but

Fig. 89.— The
lower leg

FROM BE-
HIND

Showing arter-
ies. Many of
the muscles
have been
removed .
(Modified
from Tiede-
mann)

CIRCULATION OF BLOOD AND OF LYMPH 159

there is another method of modifying the amount of blood
received by the separate organs. If the only method of
increasing the amount of blood sent to any organ were
by accelerating the rate of the heart beat, thus increasing the
circulation all over the body, it would be as inconvenient as
if the only way of regulating the gas in a house were by
turning it on or off at the gas factory. The body is
therefore, supplied with a more elaborate system so that
at any moment any single organ may receive a greater
or less supply of blood than usual.

All the small arteries, as well as the large ones, are en-
circled by muscles (Fig. 82), whose contraction causes a dimi-
nution in the size of the blood vessels. If the muscles relax, the
artery will become larger because of the pressure of the con-
tained blood. The capillaries also contract and expand in a
similar way. Certain parts of the brain and spinal cord are
connected by nerves with all of these muscles and thus con-
trol their size. These nerves are called the vaso-motor nerves,
and the muscles, the vaso-motor muscles. The muscles and
nerves, together with their nerve centers in the brain and
spinal cord, constitute the vaso-motor system.

Two sets of vaso-motor nerves are connected with the blood
vessels; one of them tends to constrict the vessels, and the
nerves composing it are called the vaso-constrictor nerves.
This set is acting all the time, keeping most of the vessels
sUghtly tightened; not sufficiently to shut off the flow of blood
but enough to prevent them from becoming loose and flabby;
this set supplies especially the vessels of the skin and intes-
tine. The other set of vaso-motor nerves causes the vessels to
enlarge; they are called the vaso-dilator nerves and arc found
especially supplying vessels of the muscles and glands.

Action of the Vaso-Motor System. — A few examples of the
work of this system may make its functions clearer. W3
often hear people say that one should not take severe or
rapid exercise soon after eating. Why is this so? 3ecft\«6^»

160

ADVANCED PHYSIOLOGY

when the muscles of the arms or legs are working they need
more blood than usual. Hence the vaso-motor nerves cause
the blood vessels of the muscles to relax and thus allow more
blood to be supplied to them. The consequence is that less

blood is at liberty to
go to the cells in the
stomach and intes-
tinal walls, when
these should be busi-
ly secreting diges-
tive juices or passing
along the food by
peristaltic contrac-
tions. Thus, witn
too little blood to
effect digestion the
food is sluggishly
handled, secretions
are less in amount
than they need be,
and the food is not
sufficiently changed
to allow of read}
absorption.

Blushing and
turning pale are evi-
dences of the work
of this system. These changes are due entirely to the differ-
ence in the size of the blood vessels of the face and are
brought about through the influence of nerves; Fig. 90.

Control of the Vaso-Motor System. — These messages to the
blood vessels go out from the brain without any consciousness
on our part, however; in fact we cannot control them, as is
shown by the vain struggles of people to keep from blushing
^hoD they are embarrassed. This is a most fortunate pro-

Fig. 90. — Apparatus for demonstrating
the function of the vaso-motor system

The arm is placed in the glass cylinder which is filled
ip-ith water. The tube a connects with the cyl-
inder also. Evidently any swelling of the arm will
cause the level of the water in the tube to rise.
Having noted, by the marker, the height of the
water, the person whose arm is in the cylinder is set
to studying hard. The marker quickly falls, show-
ing that blood has left his arm to go to the aid of
the hard working brain. If he stops studying the
marker rises again. (Fick)

CIRCULATION OF BLOOD AND OF LYMPH 161

vision, too; for the different organs of the body need different
amounts of blood at different times, and if this blood supply
were dependent on our conscious regulation of it, we could
accomplish very little else, and even that function would be
imperfectly performed.

The dilator influences, however, do not arise in the same
place as do the constrictor; the nerves which carry messages
causing constriction of blood vessels rise in the medulla, or
hind brain. From there they go down the spinal cord, and
are thence distributed in various directions. The vaso-con-
strictor center, therefore, is in the medulla, or hind portion of
the brain. No definite place can be determined, however, as
the centre from which messages go out to cause vessels to en-
large. Some fibres apparently arise in the vaso-constrictor
center, while others do not.

IMPORTANCE OF A VIGOROUS CIRCULATION

We seldom realize the fact that the whole body is traversed
in every direction by arteries, veins and capillaries and that
blood, a living stream under considerable pressure, is running
through it every minute of our fives.

A swift brook, dashing down a steep hifi, takes along with
it everything but the large pebbles and stones; all the loose
mud and dirt are carried along, and are left behind only when
the stream becomes sluggish and slow. Then the materials
in the muddy water catch on the grass and sticks in the stream,
and everything under the water is covered with dirt and refuse.
So when the blood flows strongly and steadily, it can pick up
many of the wastes of the body and carry them away. This,
however, is not due solely to the swiftness of .the stream, but
because, by means of this rapid flow, more blood is brought to
and carried away from every spot in the body; and the more
blood there is coming into contact with any tissue, the more
effectually that tissue is fed and the more perfectly it is
cleansed of its waste debris. In the business world there is

162 ADVANCED PHYSIOLOGY

usually a supply of those things for which there is a demand:
just so here, the ''law of supply and demand" is constantly
holding true; blood will flow rapidly and vigorously whenever
one does things which demand a plentiful flow. Vice versa,
a sluggish flow is the rule where the habits of the person are
sluggish.

This is the reason for the bracing effect produced through
the stimulation of the skin by rubbing, as after a bath; for
this affects surface capillaries, and their walls relax. The
inrush of blood reacts on all the contributing arteries, and a
readjustment of many vessels takes place, rousing them
from their inert condition. In the same way the skin is stimu-
lated by fresh air, with its accompanying changes of tempera-
ture, which produce a response in the vaso-motor system
creating a mild, though extensive effect on the whole body.
One single pursuit, one single kind of activity, mental or
physical, makes the supply and demand one-sided. Diver-
sity of exercise and interest is necessary to secure "a sound
mind in a sound body," an indispensable requisite, if one is
to meet life with thrill and enthusiasm. Exercise, either in
work or recreation, produces a demand for new materials, for
fresh blood. Change in one's train of thought, as in con-
genial, lively conversation, upsets the listlessness of the nerve
centers, affects the rate of blood flow, and tones up the whole
system.

The Influence of Heat and Cold upon Circulation. — Changes
in temperature cause great modification in the activities of all
organs in the body. As a rule all living tissues work with
greater readiness when warm than when cold. The influence
of heat is especially noticed in its effect on the blood vessels
in the skin; when the body is warm the walls of the arteries in
some areas relax more than usual, the capillaries become
over-full and one is said to be "flushed with heat."

On the other hand cold causes blood vessels to contract,
and all the muscles to act slowly. The first effect of going

CIRCULATION OF BLOOD AND OF LYMPH 163

out into the cold air may be a whitening of the skin; but later
an expansion of the capillaries causes the skin to become
flushed. The expansion and contraction of these vessels ex-
plain our feelings of warmth and cold. The blood in the interior
of the body is considerably warmer than that on the surface.
Since the nerve endings which perceive sensations of heat are
located in the skin, and not in the inside of the body, one has
no sensation of heat so long as the warm blood is in the in-
ternal organs. But if the body is exceptionally warm, from
vigorous exercise, for example, the blood vessels in the skin
relax for the purpose of allowing the hot blood to flow more
rapidly through the skin, that it may be cooled off. This
extra rush of warm blood to the skin produces a sensation of
heat. In other words, the feeling of warmth which one has
on a warm day or after exercising, is simply a sign that the
body is cooling off as rapidly as possible. On the other hand,
on a cool day, the body wishes to retain its heat, and the
blood vessels in the skin are consequently constricted. The
skin feels cold because there is so little warm blood flowing
through it. Thus the feeling of warmth does not necessarily
mean that the body is hotter than usual, but only that the
arterioles in the skin are relaxed and that warm blood is
flowing rapidly through them. If the skin is flushed, one
foels warm even though he is losing heat and so actually be-
coming colder.

Fainting. — The common and very unpleasant experience
of fainting is due to a smaller supply of blood than usual in
the brain. This condition may be brought about by many
causes, e.g. by the lack of a sufficient amount of oxygen in the
air, by the presence of a disagreeable odor, or by some dis-
order in the digestive functions. The last named cause is the
most frequent. In such cases the action of the heart may be
slower than usual or the vessels in the brain may contract so
that it is insufficiently supplied with blood. This causes a
^.topping of its regular activities, and the person becomes un-

164 ADVANCED PHYSIOLOGY

conscious. If he can be placed flat on his back with the head
lower, if possible, than the rest of the body, blood will run
into the brain again, and the person regain consciousness.
While a fainting person may seem to need immediate attention
and help, the common tendency for everyone who is near
to rush to his relief is unfortunate. There is usually no
especial danger, and if two or three are waiting on the
patient others may much better remain quietly away, and
thus not prevent free circulation of air, about the patient,
who will doubtless very quickly recover.

The Effect of Drugs upon the Circulation. — The whole cir-
culation may be more or less profoundly modified by various
drugs, some of which increase and others decrease its action.
Caffein, for example, the active principle in coffee causes the
heart to beat more forcibly and at the same time causes a con-
striction of the small arteries so as to raise blood pressure. J
For this reason it is called a stimulant. "

It has been frequently stated that alcohol increases the
activity of the heart. Careful experiment, however, shows
that not only is its effect not that of a stimulant, but that
when used in large amounts it very markedly weakens the
action of the heart. If taken in small amounts only, the
heart sometimes shows a slight increase in its rate of beating,
but this occurs only when the brain becomes excited, and if
the person is kept quiet no change in the heart beat is notice-
able. Its primary action is thus on the brain, as we shall
find later.

A second effect of alcohol is more evident. The small
blood vessels in the skin are enlarged, probably from the
partial paralysis of the vaso-motor center. This produces
a flushed skin, a feeling of warmth and a false feeling of
increased circulation. Its result is to send more blood through
the skin with a consequent extra loss of heat. This action is
evidently not due to stimulation but to the relaxation of the
muscles and is thus a decrease of activity rather than an in-

CIRCULATION OF BLOOD AND OF LYMPH

165

crease, even though the blood does flow a little more rapidly
through the skin. These facts make it clear that alcohol can-
not properly be called a stimulant of the circulatory organs.

THE LYMPH SYSTEM

Source of Lymph. — Blood in its usual condition occurs
only in blood vessels, and so long as it is in the vessels the
innumerable living cells of the body cannot profit by the
nourishment it contains. But while it is passing through the
capillaries, the liquid plasma, together with some of the white

/fflmph
//I'i Vessel

y^W

Arfeno<

Capillartf

Fig. 91. — Diagram

showing the origin of the lymph and the interchange of material between the living
cells and the lymph. Oxygen, various food materials, and water pass from the
capillaries to the cells via the lymph. The cells give up, e. g. carbon dioxid,
uric waste and water, which is carried away either through the veins or through the
lymph vessels.

but with none of the red corpuscles, oozes out through the
thin walls of these vessels. Outside (see arrows in Fig. 91),
this plasma flows irregularly in all directions among the liv-
ing parts of the body, actually bathing the cells. It is no
longer known as blood but as lymph and soon collects in
small vessels called lymph vessels; Fig. 92. This lymph is
a clear, watery fluid, containing in solution all of the food

166

ADVANCED PHYSIOLOGY

Arifni ,i^>5^^/

Fig. 92. — Diagram

Showing the beginning of the lymph vessels
and their relation to the capillaries.

materials which have entered the blood, and the body
cells take their nourishment from it. Moreover, the waste

products which arise in
the body are ejected from
the cells directly into the
same lymph. The lymph,
therefore, serves both to
supply the cells with their
nourishment, and to re-
ceive their waste pro-
ducts. It is thus an ex-
tremely complicated solu-
tion, containing all the
material which the body
absorbs, and all the excre-
tions which the body
produces.
Flow of the Lymph. — We may obtain a better idea of the
flow of the lymph and of the lymphatic vessels, by making a
comparison. Suppose a gravel walk extends from the top
to the bottom of a hillside. At the time of a heavy rainfall
all the pebbles in the walk will be bathed in the water that
runs over them. Let these pebbles correspond to the cells in
the extremities of the body, bathed in lymph. As we go
down the hill a little distance, we notice the water running
together in little shallow streams; no definite channels of any
depth will be formed, perhaps, but there will be little rills in
which the water runs. These correspond to the beginnings
of lymph ducts not as yet definitely walled in.

As we go farther on down the hill, we find streams of con-
siderable size made by the flowing together of the small rills.
These larger streams flow in very definite channels, and there
are banks on each side whicn keep the water in one route.
These definite streams may correspond to the larger lymph
ducts, with walls of their oviu. All along the course of these

CIRCULATION OF BLOOD AND OF LYMPH

167

Lym'ph
glands

larger streams, both on and away from its banks, the pebbles
continue to be wet with the rain, and the
tiny rills flow constantly to join the larger
current, until, at the foot of the hill, there
will be, perhaps, a single large stream car-
rying all the water that has fallen in the
path.

In a similar way the lymph collects, at
first in indefinite channels without walls,
but farther on in tubes with walls, which
are then called lymph vessels. Figure 92
shows the way in which these lymph ves-
sels originate, and Figure 93, which shows
their numbers in the superficial tissues of the
arm, only exemplifies the abundance with
which all parts of the body are supplied.

What Becomes of the Lymph? — Lymph
is primarily the liquid part of the blood
squeezed out of the capillaries. It must go
somewhere, for if it continued to accumu-
late, it would form pool-like masses among
the tissues. Sometimes lymph does gather
in certain spaces; e.g. the trouble called
water on the knee is caused by the accumu-
lation of lymph in that joint as the result
of an injury. Severe rubbing at any point
in the skin causes lymph to collect and
form a blister. A large gathering of lymph
produces the disease called dropsy. Ordina-
rily, however, lymph flows away as fast as it
appears.

The lymph vessels coming from all parts
of the body finally unite into two large
trunks. Lymph from the lower part of
the body flows into the large thoracic duct (Figs. 65 and 94) j

Fig. 93. — Ths
lymph vessels
in the superfi-
cial tissues of

THE ARM

168

ADVANCED PHYSIOLOGY

Ric/MLt/mpi
duci-

^.^ Vessel sum
■"^ Head

which, as we have already noticed, receives the lymph trom the
intestine and consequently the fat absorbed into the lacteals.

It is also joined by
subordinate vessels
from the left side of
the head and left arm,
and then empties into
the left sub-clavian
vein in the shoulder
region; Fig. 94. The
lymph from the right
arm and right side of
the head flow together
into a smaller vessel
which empties into
the right sub-clavian
vein. Thus the lymph,
which originally came
from the blood, after |
flowing through the
system of lymph
tubes, gets back again i
into the blood, pro-
ducing a continuous
circulation of lymph
from the blood to the
living cells and back
again to the blood.
Lymph transfers the
nutriment directly to the living cells and then brings back to
the blood the excreted products which are then carried to certain
organs for elimination.

.Thoracic
ducf

Li^mph
cflands

OF THE

Fig. 94. — Showing the course

thoracic duct

Its entrance into the vein in the neck and also the

right lymphatic duct.

DUCTLESS GLANDS

In different parts of the body are a number of organs, some-

CIRCULATION OF BLOOD AND OF LYMPH

169

Due / Secrefmq Cells

times called ductless glands,which do not seem to belong to any
of the general systems. Since one type of these is associated
with the lymph system, all of them will be mentioned here.

A gland (Fig. 95) is a collection of cells, the protoplasm
of which takes from the blood more fluid than is used in the
cell itself, and changes it chem-
ically, after which the extra
amount is secreted, or shed into
some cavity, (as the pericardial
cavity for example) , or into some
narrow passage or duct (as for
instance, those of the salivary
glands). There are, however,
some glands in the body which
do not empty their secretions
into any duct or cavity; they are
plentifully supplied with blood
vessels, and so have much ma-
terial at hand from which to
make quantities of a special kind
of secretion. Whatever fluid they
make is poured directly into the
blood vessels and the substances they furnish are called
hormones.

Lymph Glands. — The first of these ductless organs are the
so-called lymph glands. These are small, more or less round
masses of tissue, scattered along the course of the lymph
vessels; Fig. 93. They are found in many parts of the body,
particularly at such places as the shoulder and hip joints.
At present practically nothing is known of their functions,
although it is believed that they are the seat of white blood
corpuscle formation.

The Spleen. — The spleen is located near the lower wall of
the stomach and is supported there by folds of the mesentery;
Fig. 78, page 146. So plentiful is its blood supply that when

^em

Arfert^

95. — Diagram
simple gland

Showing the secreting cells and the

Fig.

blood vessels supplying them.

170 ADVANCED PHYSIOLOGY

seen in the living animal it shows distinct shrinking and en-
largement in size with each beat of the heart. The size of the
organ, too, would lead one to think that it must be of con-
siderable importance. In many animals it is as long as the
stomach itself, though not so broad. The use of the spleen is
not known. It can be entirely removed from the body without
fatal results. Various suggestions have been made as to its
functions; some think it concerned with the making of new
red blood corpuscles, while others take the opposite view,
that it is a place where old ^'.orpuscles are destroyed.

The Thyroid Glands. — The thyroid glands are located, one
lobe on each side of the oesophagus, a little below ''Adam's
apple,'* or the voice box of the trachea ; see Fig. 98, page 178.
Their influence on the living processes in the body is much
more evident than that of the spleen. The material which
they pour into the blood has a very definite effect upon the
manner in which the blood nourishes different parts of the
body. If a person is born lacking these glands, there is,
apparently, a case of badly regulated nutrition; the child
grows up with a stupid brain, weak Hmbs and a misshapen
body — a condition called cretinism. If such a child is given
a medicine containing the extract of the thyroid glands of
some animal, the trouble is frequently removed, the body
recovering its shape, and a normal development resulting.
The enlargement and disease of the thyroid glands sometimes
appears as great swellings on the neck, a trouble known as
goitre.

Adrenal Bodies. — Just above each kidney is located a small
gland, about the size of a walnut, called an adrenal body.
These bodies, too, empty their secretion into the blood as
it passes through them. While the amount of their secre-
tion in a given time is small, the fluid contributed is very
potent. Its main effect is to influence the muscles in the
walis of the arteries so that they contract and lessen the cali-
bre of the vessels. Under normal, healthy conditions, the

CIRCULATION OF BLOOD AND OF LYMPH 171

amount of this secretion is probably just enough to cause the
walls of the arteries to maintain a certain amount of contrac-
tion, thus preventing them from being too lax.

Other Ductless Glands. — There are several other ductless
glands, one connected with the thyroid called the parathyroid ;
one connected with the brain, pituitary body. The pancreas
also, besides furnishing digestive juices to the intestines through
its duct, gives other important substances to the body through
the blood. The exact and entire function of these ductless
glands is not fully understood.

One must not presume, however, that these glandular organs
just mentioned are the only ones which pass into the blood
as it goes through them substances which are essentially
hormones in character. Probably it is safe to say that every
tissue in the body makes its cordrihution and in this way sends
material to every other tissue, definitely influencing it in one
way or another.

In healthy then, each tissue gives out its own hormone in such
quantity and of such quality that all other tissues are benefited
by it. This fact should come to us as a suggestion that, by
careful eating, breathing, sleeping, and exercise, each tissue is
kept strong and healthy and so contributes to the strength and
health of the whole body.

CHAPTER XII
THE RESPIRATORY ORGANS

The daily distribution of food materials in a city seems
a wonderful accomplishment; delivery of milk and eggs, for
example, from thousands of farms to, perhaps, a million
inhabitants, scattered in thousands of houses, apartments
and flats is made at least every twenty-four hours. In the
body, however, there are more than a million times as many
cells as there are people in any city on earth; yet each cell re-
ceives its food much more often than once a day.

Besides food, another substance is delivered to the body
cells by the blood; this is oxygen.

THE FUNCTION OF RESPIRATION

No living thing, animal or plant (except a few bacteria) can
subsist without it. Unicellular and many other lower organ-
isms absorb it directly through the body surface; others (in-
sects) are provided with branching tubes which lead air from
the exterior to the internal cells; while others have special
breathing organs, such as lungs or gills, from which oxygen is
absorbed by the blood.

To understand why we need oxygen we have only to return
to the comparison of the body to a furnace. If all the dampers
in a stove are closed, the fire burns slowly, or else goes out. If
all the cracks and joints in the stove could be closed air-tight,
the fire would never burn. If the drafts are opened and air let
in, the fire burns rapidly. It is the union of the wood or coal
with oxygen which results in its ''burning,'' and giving off heat.

Of course there is no flame in the body; the food materials
inside it never glow like coals, but they do combine with
oxygen and give off heat, very slowly it may be, but none the
less certainly. The process is essentially the same as that

172

THE RESPIRATORY ORGANS

173

which takes place in the burning or oxidizing of fuel in a stove.
If all air (oxygen) were kept from entering the blood, i.e. if
the dampers were shut, the foods, even though digested and
in the blood, could not be oxidized, and would be only so much
dead weight and of no value. The stove is connected with a
chimney to carry off the smoke and other gases that are
formed in the burning fuel. Gases are also formed in the body
by the oxidizing of foods, and these Ukewise must be passed off.
The body needs to exchange gases with the air. Respiration
is the process of gas exchange in the tissues of living things.

THE NOSE AND PHARYNX

Figure 40 shows the structure of the nasal passages. Air
enters by the two nostrils into the nasal chambers, or canals
which are separated from one another by a partition made of
cartilage and connective tissue in front, and strengthened
farther back by a thin vertical sheet of bone. The canals
pass back through the nose, just above the hard palate, and
enter the upper por-

Olfaclvrtf
Nerve

Jurbma^ed^cjz
Bones

£usfacman
Tube

tion of the pharynx
by separate openings.
The bony and car-
tilaginous partition
between the two nasal
canals presents a fairly
smooth surface; but
the opposite wall of
each canal has, pro-
jecting into it, a much
folded, wrinkled,
spongy arrangement
of thin bones, the tur-
binated bones; Fig. 96.
The walls of the nose cavities are covered with a smooth
epithelium which contains innumerable mucous gland cells.

Tongue

FMe

Fig. 96. — Vertical section through the

NOSE
Showing the turbinated bonea and the olfactory
nerve entering from the brain into the upper nasal

passages.

174

ADVANCED PHYSIOLOGY

These keep the membranes always moist, even though the
air which is constantly going back and forth through the
nose would tend to dry them. In addition to the gland
cells of the nasal membranes, there are, mingled with them in
the deeper parts of the canals, many ciliated cells, whose
cilia are in constant motion, causing a current in the mucous
fluids. The turbinated bones might seem to be actual ob-
structions in the nasal passages, but they really serve a
double purpose.

1. They so fill up the passages that very coarse materials
taken in with the air are strained out by them, but a far
more effectual cleansing is obtained because the canals run-
ning between these bones are so crooked. Particles inhaled
through them lodge and stick on their moist surfaces, so that
they may be driven away by the cilia, which beat about in
such a way that they gradually push along any dust which
touches them, until it is driven from the air passages into the
throat, where it is swallowed with the saliva or expelled from
the mouth. In this way the dust particles of the air are
prevented, to a considerable extent, from reaching the lungs.

2. During cold weather, the position of the turbinated bones
in the nose passages and the warmth of the membranes which
cover them make them serve, almost precisely, the purpose of
a radiator. Just as air forced over steam pipes is warmed,
so air breathed through the meshes of the turbinated bones is
warmed and thus does not chill the delicate lung passages.

These facts explain, in part, the injury that may result
from mouth breathing. When the mouth is open, air rushes
rapidly into the throat and lungs, carrying dust particles
along with it. Moreover, such air is not properly warmed
and is taken into the lungs too cold. These two things make
a person more liable to diseases of the throat and lungs, and
because of the close connection between the ears and the
throat, sometimes produce deafness. For the benefit of his
future health, every young person should notice carefully

THE RESPIRATORY ORGANS 175

how he breathes. The pernicious habit of breathing through
the mouth is easily overcome, either by a Uttie care, or with
the aid of a surgeon; see page 177.

Lachrymal Canals. — Everyone has noticed that when tears
are running freely, they somehow get into the nose, whence
they may run out of the nostrils, but more often they pass
hack to the throat and are swallowed (a child is seen swallow-
ing frequently when crying hard). Two tiny, ciliated canals
leave the inner corner of each eye and carry the tears to the
tear sac, which is located very near the eye in the tissues of
the nose. From each tear sac a canal, about three-quarters
of an inch long, passes down to open into the nose chamber
of that side where the secretion is ordinarily discharged.

The Sense of Smell. — The sense of smell is extremely deli-
cate. Whatever the something is which passes from an
object to the cells lining the nose, it must be exceedingly
minute, otherwise the object giving off the odor would entirely
waste away in a very short time. Perfectly dry substances,
such as balsam needles and sachet powders, give out fragrance
for years and yet do not lose appreciably in weight. If a
bottle of peppermint oil be opened for a few minutes, its odor
will fill a house, and yet if weighed in delicate scales, no ap-
preciable amount will be found to have disappeared from the
bottle.

The upper passages in the nose, where the olfactory sense
is located, are separated from the brain by a very thin par-
tition, the ethmoid bone. This bone is perforated by numer-
ous short canals, through which olfactory nerves pass directly
from the front end of the brain. As soon as they enter the
nose they subdivide into numerous fine fibres which end
among the olfactory cells, both on the middle partition and on
the upper and middle turbinated surfaces; Fig. 96.

The main passages through which air is drawn in ordinary
l)reathing lie in the lower part of the nose and go nearly
straight back from the nostrils to the openings into the

176

ADVANCED PHYSIOLOGY

Nerrehfhe
"Brain

pharynx, or throat. The main current of air does not enter
the spaces high up in the nose, between and somewhat below
the level of the eyes, yet it is the lining of these upper passages
that is especially constructed for smelling. The two chief
kinds of cells in this lining are: mucous cells, which are cylin-
drical and rather large, and
the true olfactory cells, which
are slender and rod-like; Fig.
97.

Just what happens to the
olfactory cells when scented
air enters the nose, is not
known; but in some way they
are irritated and hand over
to nerve fibres connected with
them a message which is car-
ried to the brain; and this
message produces a sense of
smell.

The olfactory area is too
high in the nose for the main
currents of air to pass over
it. Consequently, when one
wishes to perceive very faint odors, the muscles of the nose
contract sUghtly, widening the passages, and one ''sniffs" the
air. By this we mean that one draws in the air in short,
quick breaths, which dislodge the air already in the smelling
region, and fill it with a new supply. These movements of
the nose and the sniffing process are seen most plainly in
animals, like dogs or foxes, which use this sense in locating
food.

Adenoid Growths. — Adenoids are unusual growths just
back of the nasal canals, in the region where these open
into the pharynx. Occasionally they occur as far down
as the tonsils, in which case the tonsils, too, are generally in-

Celli lininq iht[\ .„ , „r |,fv,rj. „ _ „

ror(/Ce//s

Fig. 97. — The nerves and cells
connected with the sense of

SMELL

The olfactory and mucous cells are on the
surface of the nasal passages, the rest of
the cells and fibres being within the
other soft tissues in the nose. (Schafer)

THE RESPIRATORY ORGANS 177

fiamed. They usually take the form of small bunches, vary-
ing from the size of a pea to that of an almond. Sometimes
they are stalked, and have the appearance of tiny mushroom-
like elevations. They occur most frequently in children
between the ages of ten and fifteen years, and are, apparently,
not induced by any particular exposure. They are growths
of useless tissue, sometimes rather tough and wart-Uke, but
more serious than warts, because they grow in the delicate
breathing passages. Their presence may make breathing
through the nose difficult and so induce mouth breathing.
They may impair hearing by closing the passages into the
ears and they prevent the perfect development of the whole
body. They should always be removed before they become
numerous. The operation is a simple one, easily performed
by a skilful surgeon. If one finds his nose constantly ''stopped
up " so that he cannot breath through it easily, he should have
it examined by a physician to see if the trouble is due to
adenoids.

THE TRACHEA

After passing through the nose and reaching the pharynx,
air is drawn to the lungs through the windpipe or trachea,
beginning with the enlarged portion, the larynx; Fig. 98.
The trachea is about five inches long and three-fourths of
an inch in diameter. It leaves the pharynx cavity just back
of the tongue; the opening into it, the glottis, is covered by a
lid called the epiglottis, made of connective tissue and muscle,
supported on a framework of cartilage; Fig. 40. During
ordinary breathing it is raised, leaving a free, open passage
for the entrance of air. When food is swallowed, it closes
down over the glottis, preventing particles from " going the
wrong way." If, by chance, a bit of food passes by it into
the windpipe, a violent spasm of coughing takes place. The
trachea is held open by a number of cartilaginous rings in its
walls, so that the air may pass freely through it; Fig. 98.

178

ADVANCED PHYSIOLOGY

Larunx

These rings are not complete but are in the form of irregular
horseshoes with the open part behind, where the windpipe
comes next to the oesophagus. The windpipe is, therefore,

soft and flexible next to the
oesphagus so that the swal-
lowing of food through the
latter is not hindered. As
long as the larynx is open
and the epiglottis is raised,
air drawn in either through
the nostrils or the mouth
passes with perfect freedom
down the windpipe into the
lungs.

THE LUNGS

Where the lower end of
the trachea enters the tho-
rax, it divides into right and
left bronchial tubes which
immediately enter the lungs.
Each lung is an elongated,
elastic bag of spongy tissue
and completely fills one half
of the thoracic cavity, if
we leave out of account the
part occupied by the heart
and large blood vessels. The shapes of the lungs cannot be
easily described, since each fits closely about the bordering
structures, the heart, the walls of the cavity and the dia-
phragm below. The right lung is a little larger, though shorter,
than the left; Fig. 73. The lungs are divided into lobes, aUke
in construction; the right lung has three and the left two
lobes, each lung thus being a compound structure.

Bronchioles ■

Lun^

Fig. 98. — The trachea and lungs

Showing the air passages. The position of
the thyroid glands is shown in dotted
lines. (Modified from Sappey)

THE RESPIRATORY ORGANS

179

Air Passages in the Lungs. — In the lungs each bronchial
tube, or bronchus, divides into smaller branches, called bron-
chioles, and these divide, until finally they become minute
twigs, as shown in Figure 98. At the end of every twig, the
air passage is swollen into a chamber, or series of chambers,
somewhat larger than the
passage itself. These little
air spaces are known as
alveoli, and each is partially
.subdivided into smaller
compartments, ''air-sacs''
or ''air-cells." There are
thousands of them in each
hmg, and they are the
places where blood and air
exchange gases. This con-
struction provides a very
large amount of surface, it
being estimated that the
area so provided amounts
to about 960 square feet;
this is over one hundred
times the skin surface of the
body. The walls of the alveoH are very thin and elastic, so that
they are expanded when filled with air, and would become
shrunken and nearly collapsed if emptied.

In spite of the filtering that the air receives in its passage
through the nose, much fine dust is constantly passing into
the windpipe and lungs. This would produce trouble were
there no means for its removal; but the whole series of pas-
sages, the trachea and all the bronchioles in the lungs, are
lined with the tiny, waving, hair-like bodies we have called
cilia; Fig. 3 d. These cilia are in constant motion, creatiiij^
a current upward toward the pharynx, and any dust taken in
with the air and caught on the moist surfaces is carried up-

Vesieb

Fig

99. Two OF THE AIR SACS IN

THE LUNGS
Highly magnified. The black lines are sec-
tions of the capillaries that fill the walls of
the air sacs. The arrows show the direc-
tion of the exchange of gas.

180 ADVANCED PHYSIOLOGY

ward toward the throat, to be finally expelled from the mouth
in the sputum, or to be swallowed. When working or riding
where it is very dusty, although one may have cleared the
throat of what mucus, sahva, or dust has collected there,
after waiting for a time he finds on clearing the throat again,
that more dust has accumulated. A service which can hardly
be overestimated is thus performed for us by these minute
ciliary projections from the cells in the air passages.

Blood Vessels in the Lungs. — A second set of passages in
the lungs is that of the blood vessels. We have already
noticed that the pulmonary artery from the right ventricle
divides, sending a branch into each lung. Each of these
branches separates in the lungs into smaller and smaller
divisions. These minute vessels finally break up into ex-
tremely complex sets of capillary vessels in the walls of the
alveoli; Fig. 99. The walls of these air sacs, as well as those
of the blood vessels, are extremely thin and the blood, flow-
ing in the capillaries, is brought into very close relation with
the air. There is, of course, no actual contact, for the blood
remains in the blood vessels and the air in the alveoli; but
the membranes that separate them are extremely thin, so
thin indeed, that they do not form any hindrance to gaseous
exchange between the air and the blood in the alveoli. In
other words, the gases in the alveoli pass with perfect
readiness into the blood, and gases that are dissolved in the
blood can with equal ease pass out of the vessels into th(
alveoU. It is while the blood is flowing through the capillaries]
in the walls of these alveoli that changes, which constitute]
an important part of the process of respiration, take place.

The Pleura. — On the outside of the lungs is a double fol(
of membrane called the pleura; Fig. 73, page 136. To under-
stand its relations, imagine a large, thin, flexible bag, com-
pletely closed at its top and bottom, to be wrapped around!
the lungs. One side of the bag would thus be in contact with

THE RESPIRATORY ORGANS 181

the lungs and the other side with the walls of the thorax.
Between the two would be the space that really is the cavity
of the bag. When the lungs move, these two layers of the sac
glide over each other. The layers themselves are made of
glandular cells which secrete a clear, watery liquid into the
space between them, keeping their surfaces moist and mak-
ing it possible for the lungs to move without friction or irrita-
tion.

DISEASES OF THE RESPIRATORY ORGANS

Colds. — The commonest ailment of the respiratory organs
is what is called a cold. This is primarily an inflammation of
the mucous membrane of the nose and throat. By the term
inflammation is meant an enlargement of the capillary blood
vessels, causing too abundant a supply of blood in the region
in question and bringing about a variety of other undesirable
effects, such as great sensitiveness, pain and, perhaps, fever.
In an ordinary cold the mucous membrane is very sensitive,
secretes an abundance of mucus and becomes swollen. This
state of things may interfere with the free passage of air,
since the nostrils may be so closed by the swollen membranes
that one can breathe only through the mouth. Soaking the
feet in hot water and drinking hot lemonade will sometimes
prevent the development of a cold and is usually effective
in the initial stages. •

Taking Cold. — Perhaps there is no way of avoiding colds
entirely, but it is possible to reduce their frequency. Oddly
enough, the method which most people adopt to prevent colds
frequently results in making them more, rather than less
susceptible to this ailment. To understand this seeming
paradox, we should find out first, what causes lead up to
a cold. The actual cause of colds is not known though they are
perhaps due to bacteria. It is quite certain that they are not
induced simply by exposure to cold, as the name would lead
one to believe, but are associated with the imperfect control

1S2 ADVANCED PHYSIOLOGY

exercised by the vaso-motor system over the small blood
vessels of the skin. Persons who live an out-of-door life,
although frequently exposed to extremely cold weather, rarely
suffer from colds. Those who regularly take cold baths, thereby
giving their skin repeated stimulation, are almost immune
against colds.

One is almost certain to take cold if he dresses very
warmly, never goes out without heavy wraps, bundles the neck
with a fur collar, or turns up the coat collar around the ears
when out of doors and, when in doors, lives in very warm
rooms. Such a method of caring for one's self will seldom
fail to bring on colds. The vaso-motor system of the skin
demands exercise just as much as the muscles of the legs or
arms. If we fail to use our muscles, they lose the power of
acting vigorously. So too, if we fail to give the vaso-motor
muscles their exercise, they become sluggish. If we should
wear less clothing, the skin would constantly be more or less
under the influence of the ever-changing temperature of the
air, so that the blood vessels would be kept vigorous and
active. We might then frequently feel cold, but we should
not " take cold."

As soon as one finds himself showing a tendency to colds,
he should begin at once to invigorate the skin by proper stimuli
and thus to tone up the vaso-motor system. A cold bath is
the best means of doing this, and if a person when young
accustoms himself to bathing every morning in cold water,
he will soon find himself almost proof against colds; see page
162. Especially is it necessary that the neck should be stimu-
lated by cold water, and not wrapped in furs, for this seems
to be the part of the body where there is the greatest trouble.

Colds in themselves are of comparatively little importance,
but they sometimes lead to more serious troubles. The in-
flammation which starts in the nose, as e.g. in a head cold,
may pass into the throat, and then down the trachea into the
lungs. A cold in the lungs or the chest is liable to produce

THE RESPIRATORY ORGANS 183

more trouble than one in the head. When serious inflani'
mation attacks the lungs, however, we no longer call it a cold.

Bronchitis. — Inflammation in the bronchi or their subdivi-
sions in the lungs is called bronchitis. It is really Uttle more
than a cold which has reached the smaller air passages of the
respiratory organs, but it produces much trouble there; for
many of the tubes are small and any inflammation or secretion
fills them more easily and quickly than the same amount would
the larger passages of the nose. In the case of a little child
or an old person bronchitis may cause severe illness, or even
death; but with those of middle age it is not much more
serious than a severe cold, although it produces more dis-
comfort and more distressing symptoms and is more lasting.

Pneumonia. — If the inflammation extends still farther into
the lungs, it is liable to develop into a far more serious disease,
called pneumonia. While this is a germ disease, and cannot
therefore be originated by a cold, a cold often prepares the
lungs for the ready implantation of the pneu-
monia bacteria. These bacteria are common in ($ £}'«y
the mouth and throat (Fig. 100 a), but if the •"•^

lungs are healthy, the germs may be inhaled '^//\*

without harm. When, however, the tiny air sacs h ;v'^"\^"»
in the lungs are inflamed by a cold, their sur- 'V'J^ft^

faces offer a place where these pneumonia germs „ .^^ __
can get a foothold. Developing there, they may ^^g g^^j
soon produce violent inflammation accompanied teria op
by high fever. Secretions accumulate in the air pneumonia
sacs, filling them partially or wholly, so that ^' thebac-
portions of the lungs may become practically

. r> J f J TUBERCU-

soUd and breathing sometimes be difficult. Of losis
course, if all the air sacs were thus filled, death
would at once result; but it generally happens that only cer-
tain places in the lungs are affected. After a time, if the
trouble is not too severe, the liquid mass in the lungs begins
-x) be absorbed, and eventually the lungs may clear up en-

184 ADVANCED PHYSIOLOGY

tirely and complete recovery take place. After recovery, how-
ever, the person may have a second attack, for this disease,
unlike such diseases as scarlet fever and measles, does not
render a person less susceptible to its return.

Pneumonia is one of the most dangerous of diseases and in
some localities more people die from the effects of it than
of any other common disease. There is no household remedy
which is especially beneficial in a case of pneumonia, and
every patient should be promptly placed in the hands of a
physician. Every precaution should be taken to avoid the
trouble, and the best way to prevent it is to guard against
colds.

Tuberculosis. — There is another little germ which may
seize the occasion of a cold to attack a person. It is called
the tvibercle bacillus (Fig. 100 h) and is one of man's most deadly
foes. It may enter the body in any of several ways, but its
chief method of entrance is through the mouth with food, or
through the nose with the air. We sometimes hear it said that
a person had a cold which developed into consumption. When
we remember that consumption is caused by a definite germ
and that a cold is something quite different, it is evident
that a cold cannot turn into consumption any more than a
worm can turn into a snake. But a cold in the lungs inflames
all the air passages and these, when inflamed, are much more
easily infected by bacteria than when in healthy condition.
If one is in good health, the tuberculosis bacilli may frequently
be inhaled without harming him. But if the walls of the
air passages are weakened in any way, the germs may find a
chance for growth.

This microscopic foe is far more dangerous than any of our
larger enemies. After it has once entered the body, i+ may
pass to almost any part of it and, stopping there, produce
trouble. It sometimes lodges in the abdomen and produces
serious and fatal diseases of the digestive organs. Sometimes
it grows in the skin, producing an ugly trouble, called lupus*

THE RESPIRATORY ORGANS I8f

Sometimes it is in the glands of the skin, causing them to swell
and thus producing scrofula. It grows in the kidneys, caus-
ing nephritis, or in the brain, occasioning some forms of
meningitis. It brings about joint troubles, one of which is
hip disease. But the most common trouble, and the most
serious of all, results when it attacks the lungs and brings on
consumption. Here it produces nodules, or tubercles (hence
the name, tuberculosis), causing the lung tissue to degenerate,
sometimes to the extent of breaking through into the blood
vessels, and producing bleeding in the lungs, or hemorrhages,
as they are called. Oftentimes these diseased places heal,
leaving the lungs more or less solid in the placed where the
germs have been working. But if the disease progresses suffi-
ciently, the person becomes more and more poisoned by the
germs, the lungs become more and more impaired in their
functions, until death occurs. In most communities this
disease causes more deaths than any other. In some,
pneumonia causes a higher death rate.

The War against Tuberculosis. — For centuries mankind
has known of this disease and has been helpless before it.
Its cause was not known, no cure had been discovered, and
nothing could be done to check its ravages. But in the
last thirty years great advances have been made, and to-day
we are armed with many means of fighting it. We have
learned that not all persons who contract the disease die,
as was formerly supposed. It has lately been shown that
most persons who have reached adult life have at some time
had an attack of this disease and have recovered without
even knowing that they had had it. In such cases the attack
probably appeared as a cold, which persisted for a time, but
finally disappeared. This shows that even when the germ
gets into the body, the body has strong powers of resisting
and overcoming it. When the trouble is discovered at the
outset, the chances for recovery are good, if the person at-
tacked will live out of doors, where he may breathe fresh air

186 ADVANCED PHYSIOLOGY

night and day, winter and summer. The sanatoria, where
consumptives are taken, rely for their cures upon Ufe in the
fresh air and good food, and their patients are kept out of
doors even in cold winter weather. No medicine has as yet
been found that is of any use, despite the many advertisements
with such claims.

The recent advance in the treatment of tuberculosis has
been not so much in curing as in preventing the disease. We
know enough to-day of the means of its distribution to stop it,
if we could only induce everyone to act intelligently in the
matter. The best way to fight it is to distribute information
concerning it, as a wide-spread knowledge of a few important
facts, which are becoming wellknown to-day, will do much
towards checking tuberculosis. Chief among these facts arej
the following:

1. The disease is not hereditary, and parents do not hanc
it down to their children.

2. It is contagious; that is, one person may give it to an-
other. The child may *' catch it " from Lis parents, but he
does not inherit it.

3. The germs may be carried in the air.

4. Dried sputum, or dried scrofulous discharges may con-
tain the germs of tuberculosis.

5. Every one has considerable power of resisting the disease]
this ability is increased by out-door life and good food; it is
decreased by in-door life, sedentary habits, poor food and h]
the use of alcoholic drinks.

6. Cows sometimes have tuberculosis, and their milk may]
contain the germs.

The forces which can be marshalled against this dread foej
may thus be easily deduced. Each individual should tak(
plenty of out-door exercise, he should eat good, but not to(
rich food, and should let alcoholic drinks alone. He should be
careful to use only such milk as comes from unquestionable
sources, unless he first sterilizes or pasteurizes it. When in

THE RESPIRATORY ORGANS 187

the presence of a consumptive, one should avoid breathing
air close to him while he is coughing and should take especial
care not to contaminate one's hands or clothing with the
sputum of the patient. To guard the public against the dis-
ease, there should be rigid insistence upon the carrying out of
certain rules to prevent the dissemination of infectious
material from the patient. The sputum should be burned.
Spitting should not be allowed in public places. The rules
given by the Charity Organization of New York are so valu-
able that they may be repeated here.

"Consumption can often be cured if its nature be recognized early and
if proper means be taken for its treatment. In a majority of cases it is not
a fatal disease.

"Consumptives are warned against the many widely advertised cures. ^
specifics and special methods of treatment of consumption. No cure can be
expected from any kind of medicine or method, except the regularly accepted
treatment, which depends upon pure air, an out-of-door life and nourishing
food.

"Consumption is a disease of the lungs, which is taken from others,
and is not simply caused by colds, although a cold may make it easier to
take the disease. It is caused by very minute germs, which usually enter
the body with the air breathed. The matter which consumptives cough
or spit up contains these germs in great numbers — frequently millions are
discharged in a single day. This matter, spit upon the floor, wall or else-
where, dries and is apt to become powdered and float in the air as dust.
The dust contains the germs, and thus they enter the body with the air
breathed. This dust is especially likely to be dangerous within doors.
The breath of a consumptive does not contain the germs and will not pro-
duce the disease. A well person catches the disease from a consumptive
only by in some way taking in the matter coughed up by the consumptive.

" It is not dangerous to live with a consumptive, if the matter coughed
up by him be promptly destroyed. This matter should not be spit upon
the floor, carpet, stove, wall or sidewalk, but always, if possible, iri a cup
kept for that purpose. The cup should contain water so that the matter
will not dry, or better, carbolic acid in a five per cent water solution (six
teaspoonfuls in a pint of water). This solution kills the germs. The cup
should be emptied into the water closet at least twice a day, and carefully
Washed with boiling water.

"Great care should be taken by consumptives to prevent their hands.

198 ADVANCED PHYSIOLOGY

face and clothing from becoming soiled with the matter coughed up. If
they do become thus soiled, they should at once be washed with soap and
hot water. Men with consumption should wear no beards at all, or only
closely cut mustaches. When consumptives are away from home, the
matter coughed up should be received in a pocket flask made for this pur-
pose. If cloths must be used, they should be immediately burned on re-
turning home. If handkerchiefs be used (worthless cloths, which can be
at once burned, are far better), they should be boiled at least half an hour
in water by themselves before being washed. When coughing or sneezing,
small particles of spittle containing germs are expelled, so that consump-
tives should always hold a handkerchief or cloth before the mouth during
these acts; otherwise, the use of cloths and handkerchiefs to receive the
matter coughed up should be avoided as much as possible, because it
readily dries on these, and becomes separated and scattered into the air.
Hence, when possible, the matter should be received into cups or flasks. Paper
cups are better than ordinary cups, as the former with their contents may
be burned after being used. A pocket flask of glass, metal, or pasteboard
is also a most convenient receptacle to spit in when away from home. Cheap
and convenient forms of flasks and cups may be purchased at many drug
stores. Patients too weak to use a cup should use moist rags, which shouk
at once be burned. If cloths are used they should not be carried loose
the pocket, but in a water-proof receptacle (tobacco pouch), which shoulc
be frequently boiled. A consumptive should never swallow his expectorf
tion.

"A consumptive should have his own bed, and if possible, his.oT
room. The room should always have an abundance of fresh air — tl
window should be open day and night. The patient's soiled wash-clothe
and bed linen should be handled as little as possible when dry, but shoi
be placed in water until ready for washing.

"If the matter coughed up be rendered harmless, a consumptive ma^
frequently not only do his usual work without giving the disease to other
but may also thus improve his own condition and increase his chances
getting well."

The simple discovery that a little parasite is the cause o|
this disease, has been the means of saving many thousanc
of lives. This seems hardly credible, for the discovery
the cause does not tell us of any cure. But it has shown
where the danger lies, and we can much better protect our-j
selves from a known than from an unknown danger. At al
events, since Prof. Koch discovered the cause of tuberculosisj

THE RESPIRA'IURY ORGANS 189

the number of deaths has been steadily decreasing. In Massa-
chusetts, for example, while in 1870 the number of deaths was
thirty-six in ten thousand, there are about eighteen in ten
thousand at the present time. Tuberculosis is largely a pre-
ventable disease, and if each person will do what he can to
pass along information as to its cause and the methods of
avoiding it, he will help to reduce the number of cases.

Pleurisy. — The ease of motion which we have noticed in
the lungs is dependent upon the free moving of the layers of
the pleura upon each other, and this in turn is dependent up-
on the presence of a watery liquid secreted by their glandular
surfaces. It sometimes happens that the pleura ceases to
perform its proper function, becomes inflamed, or adheres to
adjacent tissues. In all such cases the movements of the
lungs become difficult and, as a result, breathing is not so
free and sometimes becomes distinctly painful. The trouble
is called pleurisy, and may result from various causes, of
which a common cold is one. While painful, this trouble is
rarely dangerous, and usually passes off with proper treat-
ment at the hands of a physician.

CHAPTER XIII

THE MECHANISM AND CHEMISTRY OF RESPIRATION

txiernat
' Infercosfals

Iniernal
Infercosfals

In the preceding chapter we have been following the course
by which air passes from the exterior to the innermost cham-
bers of the lungs. But.
the reason air enters
and leaves the lungs
as we breathe is not
explained by merely
noting the construc-
tion of these passages;
for in spite of the va-
rious tissues compos-
ing them, these tubes
are of themselvei
powerless to inhale
even the smalles:
quantity of air. W«
often say "the lungd
fill with air'^; but w(
do not appreciate their^
entire helplessness,
their lack of ability to
make the least move-
ment of their own
accord. The lungs
because air is driven

Fig. 101. — The attachments of the ribs
to the back bone and sternum

To show their relations in breathing. Between one
pair of ribs is [shown the external intercostal
muscles and between a second pair the internal
intercostals, all other muscles being omitted.

never fill of
into them.

themselves; they fill

THE MECHANISM OF RESPmATION

Air is drawn into the lungs just as it is into a bellows.
When the space inside the bellows is increased air must rush

190

MECHANISM AND CHEMISTRY OF RESPIRATION 191

in through the openings left for that purpose or a vacuum is
formed. The thoracic cavity is absolutely air tight; there-
fore, any motion which will enlarge the cavity of the chest
will draw air into the lungs. The chest is so constructed
that it can be enlarged in two different ways, (1) by rib mo-
tion and (2) by diaphragm motion.

Rib Breathing. — The ribs in the body are inclined down-
ward and forward; Fig. 101. They are hinged to the back-
bone and if their outer ends are lifted, the sternum will be
Ufted and carried forward. This pushing forward of the
outer ends of the ribs increases the distance from the back-
bone to the sternum, and thus enlarges the cavity of the
thorax. The ribs are raised and lowered by two sets of
muscles, arranged between them, called the intercostals;
Fig. 101. When the external intercostals contract they lift up
the ribs, pushing forward the breastbone; when the internal
intercostals contract they pull the ribs down, thus drawing the
breastbone inward. But these same motions of the ribs cause
the chest cavity to enlarge and decrease in size laterally also.
This increase from side to side can be understood if we im-
agine a pail with two handles, one hanging down on either
side. If the handles are raised, each leaves the side of the
pail, and the distance between their outer curvatures is greater
than when hanging down. In precisely the same way, when
the external intercostal muscles raise the ribs the distance
between their curved sides is increased, for in their natural
position they lie inclined downward along the sides of the
body. When pulled back again to this position, the distance
between their sides is lessened and the thoracic cavity is made
smaller.

From the method of their attachment to the vertebrae the
libs can move only up and down. Bj^ looking at Fig. 123,
I)age 253, and imagining a rib attached to the centrum and then
tied by ligaments to the transverse process also, one sees that
the rib can move in but the one plane like a metal hinge joint.

It is evident then that whenever the external intercostals

192

ADVANCED PHYSIOLOGY

contract and lift the ribs, the chest cavity is enlarged and as
a result air will be drawn in to fill the enlarged space. This
forcing of the air into the lungs is called an inspiration. When
later the ribs fall downward again the chest cavity is con-
tracted and the air is forced out, producing an expiration*
It is a muscular effort to raise the ribs and inspire air, but they
fall back, in part at least, of their own weight.

Fig. 102, — Diagram

Illustrating the mechanism of diaphragm breathing. It represents the lungs of soi
small animal in a closed bell glass. As the rubber membrane below is pulled do\
enlarging the cavity, air rushes in through the tube that represents the trache
and the lungs enlarge. (Tigerstedt)

Diaphragm Breathing. — When at rest the diaphragm is noj
stretched across the bottom of the thoracic cavity in a flaj
plane, but arches upwards on all sides; Fig. 46, page
Its shape thus causes it to project into the thorax and decrease

MECHANISM AND CHEMISTRY OF RESPIRATION 193

the size of that cavity. The center of the diaphragm is a
tough membrane, from the edges of which muscles radiate
to the walls of the cavity. When these muscles contract,
the center of the diaphragm is drawn downward and the
whole structure takes a more nearly flat position. In doing
this the diaphragm presses upon the stomach and other ab-
dominal organs, forcing them downward and outward. Thus
the chest cavity is increased (Fig. 102), and air is sucked into
the lungs, which swell and fill the enlarged space.

At each expiration the muscles of the diaphragm relax,
and the muscles of the abdomen which were stretched some-
what when the organs in it were pressed downward, now
shorten, and the diaphragm is thus carried up into its former
dome-like shape; the room in the thoracic cavity is conse-
quently lessened, and air is forced out of the lungs. Breathing
may thus be accompanied by a rise and fall of the abdominal
walls, but this does not mean, of course, that air is taken into
that cavity; merely that the contained organs are displaced
at the descent of the diaphragm, and that the abdominal
muscles force them back again when the diaphragm relaxes.

The reason that air rushes into the lungs when the thoracic
cavity is enlarged is that air is constantly exerting a pressure
upon our bodies equivalent to fifteen pounds to the square
inch. As soon as the thoracic cavity is enlarged, air naturally
enters it, since otherwise there would be a vacuum.

EXTERNAL AND INTERNAL RESPIRATION

The alternate inflow and outflow of air through the passages
is the most superficial part of the breathing process. All the
air in these passages is still connected from the outside world,
and is not yet a part of the body in any sense whatever. This
tidal flow inward and outward is called external respiration .

Through the thin walls of the air sacs of the lungs the oxygen
of the air passes, following the law of osmosis of gases, and com-
bines with the haemoglobin of the red blood corpuscles, as de-

194 ADVANCED PHYSIOLOGY

scribed on page 124. From the lung region the blood hurries to
the innumerable cells of the body each of which is needing
its share of food and oxygen. From the capillaries these pass
into the lymph which surrounds the cells, and thence through
the cell walls into the protoplasm. This final step is the most
important of the entire respiratory process, and is naturally
called internal, or tissue respiration.

Up to this point the respiratory process has been described
as though serving only to carry oxygen to the cells; but this is
only half the story, for in the cell protoplasm numerous ele-
ments combine with oxygen, and among other things c^i'l^on
dioxid is thus formed. This passes out of the cells, into tn«
lymph, thence into the plasma of the blood (not into the hae-
moglobin save in very limited degree) and is carried to the lungs ;
here it dialyzes through into the air sacs, and then is expelled
during expiration.

NERVOUS CONTROL OF RESPIRATORY MOVEMENTS

That breathing is under the guidance of the nervous system!
is evident. One can breathe fast or slowly at will; one breathes)
faster when he is running than when he is still, and faster]
when he is excited than when he is calm. These changes in
the rate of breathing generally take place without any thought
whatever; but they are, nevertheless, brought about under
the direction of the brain. Unlike the heart, the breathing
muscles are not automatic, and unless stimuli come to them
from the central nervous system they will not act. The
source of these stimuli is in the lower part of the brain,
in the medulla, at the place known as the respiratory
center.

No nerves go directly from the respiratory center to the
intercostal muscles or diaphragm; they first go down in the
spinal cord for some distance and then pass out in nerves
which leave between the vertebrae. One set of nerve fibres
an each side of the body leaves the spinal cord in the neek

iMECIIANISM AND CHEMISTRY OF RESPIRATION 195

Head

\\f\Respiratoiy
Centre

\Nerve to
wiaphrqgm

W^^nfercostal

to Rib
'Muscfci

region (Fig 103); each set passes out of the cord by three
roots, i.e. by nerves between the second and third, third and
fourth, fourth and fifth vertebrae. These roots unite to
form a single nerve on each side which passes down through
the thorax behind the lungs and then spreads out in the
muscles of the diaphragm. Messages go over these phrenic
nerves from the respiratory center
to the diaphragm, but none go in
the opposite direction; Fig. 103.
The second set of fibres from the
respiratory center, the intercostal
nerves, go farther down the cord to
the region of the ribs to emerge
between the vertebrae and pass at
once into the intercostal muscles;
Fig. 103.

If these nerves which carry these
impulses from the respiratory center
to the various muscles concerned in
breathing are cut, or if that center
itself is destroyed, breathing stops
at once and death follows. As long
as the respiratory center is active, it
sends out stimuli to the breathing
muscles with perfect regularity. The
action of this center is partly in-
voluntary, i. e. goes on without any
action of the will, as is shown by the
fact that breathing continues while
one is asleep. At the same time, that
the center is partly voluntary is
demonstrated by the fact that one

can at any time breathe fast or slowly as he wishes.
During normal life the average rate at which respiratory
impulses are sent to the muscles concerned is fifteen to

Fig. 103. — Showing thb
origin of the nerves
controlling breathing

196 ADVANCED PHYSIOLOGY

twenty per minute. In case of sickness, especially in fevers,
this rate may be much more rapid.

Thus, although the stimuh for breathing all come from the
same general center, they go to the muscles by different
courses. Since all breathing impulses start from the brain
it is evident that if the neck be broken so as to cut off all con-
nection of these muscles with the brain, breathing will stop
at once. If, however, the neck should be broken below the
place where the phrenic nerves leave the cord, the diaphragm
would still be connected with the respiratory center and might
still be capable of making respiratory movements. Under
such circumstances persons have lived for years, although the
lower part of the body was cut off from the brain and of course
paralyzed.

The intercostal and phrenic nerves carry messages away
from the brain; probably never toward it.

One pair of nerves, however, carries messages from the
lungs to the brain; these are the respiratory branches of the
vagus nerves; Fig. 77, p. 144. The messages which go over
these respiratory branches are not for arousing movements,
but for informing the respiratory center of conditions in the
lungs, thus affecting the messages going to the muscles of the
diaphragm and ribs which are then modified to meet the
circumstances. I

The rate and nature of breathing are not only affected by
direct messages from the lungs, but by stimuli from the nose
lining. Fumes from ammonia or sulfur will practically stop
breathing processes for a short time. Moreover, sudden pain
in the abdomen may be followed by a cessation of breathing.
Dashes of cold water will set up more rapid breathing at first,
though later it may be followed by a slower respiration. None
of these influences on the body surface affects the breathing
muscles directly; sensations go from the surface to the
brain and then act indirectly through the respiratory
center.

MECHANISM AND CHEMISTRY OF RESPIRATION 197

THE CAPACITY OF THE LUNGS

Complemental Air

100 Cv in .

Air that can be taken
in with a deep breath

Tidal Air 3ocu in.
Taken in with each breath.

With each inspiration, a certain amount of air is drawn
into the lungs and with each expiration it is forced out. The
lungs, however, are never completely emptied in expiration
and never filled in an ordinary inspiration. At each inspira-
tion, the average person takes into his lungs about 30
cubic inches of new air. This is called the tidal air. With
some effort, about 100 cubic inches
of complemental air can be inhaled and
exhaled in addition to the tidal air.
After an expiration of the tidal air, one
can, by effort, expel an additional 100
cubic inches of so-called supplemental
air. Even after the greatest effort
of expiration there remain in the lungs
about 60 cubic inches of residual air
which cannot be expelled; Fig. 104.
These figures are only the average, and
different individuals have very differ-
ent breathing habits, i.e. some, even in
quiet breathing, inspire three times as
much air as others.

Thus with an ordinary breath only
about 30 cubic inches of the 190
cubic inches of air in the lungs of the
normal individual is changed. The
larger bronchi can hold 10 cubic
inches of air without much difficulty
and, therefore, much of the air
breathed in and out is merely used in ventilating these tubes.
Hence the air in the deepest parts of the lungs — that in
the alveoli, or air sacs — is not wholly changed. The lungs,
therefore, are never entirely filled with fresh air. The only
way that fresh air usually gets into the air sacs, where it

Supplemental Air

100 Cu. in

Air that can be expelled
with a deep expiration

/Residual Air

60 Cu. in.

Air that cannot be
driven from the lun^s

Fig. 104. — Diagram

Showing relative amoun*.
of air in lungs under dii-
ferent circumstances.

198 ADVANCED PHYSIOLOGY

comes in contact with the blood, is by gradual passage,
or by diffusion, from the larger air tubes into the smaller
sacs.

BREATHING HABITS

Certain practical lessons as to methods of breathing may
be drawn from these facts. Diaphragm breathing fills the
lungs at their lowest point, rib breathing tends to fill the
upper lobes. Either of these types alone will produce only
a partial action of the lungs, and if one accustoms himself to
only one type of breathing, parts of his lungs are liable to
become sluggish. This inactive condition produces a tendency
to lung diseases, e.g. consumption, which generally starts in
the least used lobes of the lungs. Breathing should, therefore,
involve the whole lung equally; neither rib nor diaphragm
breathing should predominate. Among people who are not
hampered by ill devised clothing, both ribs and diaphragm
act freely in natural breathing. Our methods of dress inter-
fere with this freedom. Corsets, tight bands around the
waist, and the custom of supporting the skirts from the hips,
interfere with women's abdominal breathing. Men have a
tendency to make the breathing too exclusively abdominal.
They should give particular attention to developing rib, or
chest breathing, while women should especially try to strength-
en their abdominal breathing. This can easily be done if a
little attention be given to the matter each day. Unneces-
sary or needlessly tight bands about the waist are used only
by those who see beauty in a weakened, misshapen form,
and who hold health a cheap possession.

In an active, out-of-door life, like that led by children,
soldiers or mountaineers, vigorous exercise causes very rapid
breathing and thus keeps the lungs active. But the quiet
life of adults in cities does not involve much exercise, and
the lungs are rarely filled with fresh air. For this reason it is
a very good practice for city-dwellers to take several long

MECHAJNISM AND CHEMISTRY OF RESPIRATION 199

breaths several times a day, filling and emptying the lungs as
completely as possible.

CAUSE OF RESPIRATORY MOVEMENTS

The Cause of Respiratory Movements. — None of these facts,
however, tell us much about the real purpose of respiration
or the actual cause of the respiratory movements; they
only describe how the movements are produced and
regulated.

The respiratory movements are started in the respiratory
center which sends regular, rhythmical messages down the
cord to the breathing muscles. What excites this center into
such regular activity? In answer to this question an interest-
ing experiment may be described. By a complicated method
it is possible to send through the brain, and thus through the
respiratory center, blood different from that which goes to the
rest of the body. If blood containing only a small amount
of oxygen is sent through it, the center begins to send out
messages very rapidly to the breathing muscles, even though
the rest of the body is receiving very pure blood. On the
other hand, if the blood sent through the respiratory center
contains an unusually large proportion of oxygen, the breath-
ing messages are sent out more slowly than usual. If blood
with an extremely large amount of oxygen be used, breathing
messages become very slow no matter what kind of blood the
rest of the body receives.

The logical conclusion is that the center in the brain, which
controls breathing, is influenced by the condition of the
blood which flows through it. When the body is doing more
work than usual, more oxygen is needed, and more carbon
dioxid is being formed. The blood rapidly loses the oxygen
and absorbs carbon dioxid; this impure blood affects the nerve
cells of the medulla, causing more rapid breathing. It is the
condition of the blood in the respiratory center that ordinarily
determines the rate of respiratory movements.

200 ADVANCED PHYSIOLOGY

THE CHEMISTRY OF RESPIRATION

Respiration is a process of the absorption and elimination
of gases which occurs in all animals. Not all animals, how-
ever, have lungs. Fishes have gills for this purpose; some ani-
mals (earthworms) can take sufficient amounts of these
gases through the skin and need no lungs, gills or any special
respiratory organs. Yet these same animals, if not allowed
to get rid of carbon dioxid and take in oxygen, shortly
die. To understand respiration we must, therefore, study
the relation of these gases to the blood.

Changes in the Air During Breathing. — 1. Inhaled air con-
tains about twenty per cent of oxygen, while exhaled air con-
tains only sixteen per cent, showing that oxygen is extracted
from the air while passing through the lungs.

2. Inhaled air contains no carbon dioxid, or only slight
traces of it, while exhaled air contains four per cent. Carbon
dioxid is, therefore, added to the air during respiration.

3. Inhaled air has a temperature which varies with the
conditions. On a cold winter day, it may be below zero; on
a hot summer day, it may be as high as one hundred degrees;
ordinarily it will be in the vicinity of seventy degrees, the
temperature at which our rooms are usually kept. Exhaled
air is found to be very nearly ninety-eight degrees, the body
temperature. Although there is some variation in the tem-
perature of exhaled air, it is never much below this point.
If the air is inhaled at 70° F., it will evidently be warmed
in its passage through the lungs, and the body become
cooled in consequence.

4. The amount of moisture in the inhaled air is variable.
On a dry day it is very slight, while on a wet day it is very
great; but exhaled air always contains nearly as much moist-
ure as it can hold. This can easily be seen by breathing upon
a piece of cold glass. The exhaled air, when cooled by the
glass, cannot hold as much moisture as when it was warm.

MECHANISM AND CHEMISTRY OF RESPIRATION 201

and moisture is deposited on the glass in the form of small
drops of water. This saturation of exhaled air shows that
it has extracted water from the body.

The lining of the lungs is the tissue through which these
exchanges are made; it is a membrane, moist because covered
with unicellular mucous glands, and thus always flexible and
not dried by the ever-changing air. Because of the nature of
its structure, gases diffuse through it even more readily than
they would go through a pure water film of the same thickness.
In the instance of carbon dioxid, diffusion is three times as fast
through lung tissue, as through a water membrane of equal
thickness. The actual thickness of the wall of a lung alveolus
is about 1-6250 of an inch (0.004 mm.)

Changes in the Blood. — The changes in the blood are, of
course, just the reverse of those in the air. What the air
absorbs, the blood has given up, and what the air has lost, the
blood has absorbed. From these simple facts we learn that
the blood takes oxygen from the air, but gives up to the air
carbon dioxid, heat and moisture.

How Oxygen Gets into the Blood. — When the blood flows
through the small capillaries in the walls of the alveoli of the
lungs (Fig. 99), it comes very close to the air, so close that
gases readily pass from the air to the blood. The air contains
oxygen in large amounts and under considerable pressure;
as a result some of it is at once absorbed by the liquid plasma
of the blood. There is nothing unusual in this fact, for water
or any other liquid will absorb gases from the air. Oxygen
is forced into water by the pressure of air (15 lbs. to the
sq. in.) on its surface. If water is placed in a closed chamber
from which all the air is then removed, this is very evident,
for the air dissolved in the liquid will come away from it in
bubbles. Contrariwise, if the pressure of air or other gases
above the water surface is increased, the gases are absorbed in
just the degree that the pressure is increased. So too, carbonic
9icid gas is forced into water^ to form soda or Seltzer water^ and

202 ADVANCED PHYSIOLOGY

the bubbles of gas can be seen coming out of such water when
the pressure is released.

The amount of oxygen which the blood absorbs in this way
is very small; by far the larger part is not simply absorbed
but chemically combined with the red coloring matter, or
haemoglobin.

Haemoglobin. — We have already seen that the blood con-
tains red corpuscles, which are like little sponges holding in
solution a material called haemoglobin; page 124. This sub-
stance has an affinity for oxygen, and provided the gas is
under slight pressure, will absorb it in large amounts when-
ever in contact with it. After haemoglobin has absorbed
oxygen, it is a bright crimson; but if then put in a place
where there is nO oxygen, or where the oxygen pressure is
very slight, it will release the oxygen it has absorbed and its
color will change to a bluish red. Hence arterial blood, which
has just taken on oxygen in the lungs, is bright crimson, while
venous blood, which contains less oxygen, is bluish red ii
color.

Oxygen can be absorbed by haemoglobin because of the iroi
element in it; by analysis it is found that a little over 0.3% ig
iron ; one molecule of oxygen will combine chemically with ever]
atom of iron. The oxygen capacity of the blood is thus Km-
ited ; but as each corpuscle hurries through the lung capillariesj
it seizes what it can absorb and hastens away to some part of
the body where the oxygen is needed. There is about nine-
teen per cent of oxygen in arterial blood, most of it being ii
the red corpuscles.

How the Blood Gives up its Oxygen. — Let us follow the bloodj
and see what becomes of its oxygen. After going back to th(
heart, from the lungs, and flowing out through the arteries, ii
finally comes to the capillaries in the muscles, glands, etc.J
somewhere in the body; for example, in the fingers; Fig. 91.
Although it spends only about one second in the capillaries itj
loses in that short time 35% of its oxygen. This is because]

MECHANISM AND CHEMISTRY OF RESPIRATION 203

no free oxygen is present in the tissues, since, as we shall see
later, the muscles are using up oxygen as fast as they can get
it. Here then, among the tissues where the oxygen is nearly
absent, or under very slight pressure, the corpuscles give up
the oxygen they are carrying and turn to a bluish red color
as they flow out from the capillaries into the veins and back
to the heart.

Nitrogen in Respiration. — Nitrogen composes about four-
fifths of the air we breathe, but so far as the respiratory pro-
cesses are concerned, it simply dilutes the oxygen of the air.
Some of it is doubtless absorbed by the blood plasma but none
of it is used in the body and practically none of it is given off
from the body in the form of gas. Hence the blood comes
back to the lungs from the tissues with just as much nitrogen
as it had originally.

Breathing Pure Oxygen. — The statement that nitrogen
dilutes the air is, however, open to a misapprehension. If
oxygen is as active a gas as we believe it to be, what will be
the effect if, instead of breathing an atmosphere which con-
tains only one-fifth oxygen, we breathe pure oxygen? We
might at first imagine that we should absorb much more
oxygen. Conversely, we might suppose that, if there were less
than the usual amount of oxygen in the air, we could not
obtain enough. We often think that the reason air in a
room becomes unpleasant and depressing is that it contains
so little oxygen. All of these impressions are mistakes. Since
the haemoglobin can absorb a certain quantity of oxygen
and no more, it can obtain this amount perfectly well from
ordinary air, or indeed from air containing less oxygen than
usual. If, therefore, one should breathe pure oxygen, the
blood would take on practically no more than it does from
ordinary air (a sHghtly greater amount might be taken in by
the blood plasma, for that combination is a mere mixture).
So far as the oxygen goes, there is probably enough in any air
we breathe to furnish the blood properly for effective working.

204 ADVANCED PH^SIOLOGV

Breathing Carbon Monoxid. — Carbon monoxid (CO) occurs
in all coal gas and all illuminating gas, sometimes escaping
from stoves which are badly constructed or have faulty
drafts. It is carbon monoxid which burns with the blue
flame often seen flickering over the surface of coal in a stove
or over burning charcoal. Haemoglobin will combine more
readily with carbon monoxid than with oxygen, so that if the
two are in the same air, carbon monoxid will unite with the
haemoglobin of the blood and oxygen will be excluded. If
this happens, the person concerned will die of suffocation
just as truly as if he had stopped breathing.

It is easy to see why leaking gas pipes and stoves are un-
healthful. Gas pipes which enter sleeping rooms should be
watched with especial care, for from a very sUght leak enough
escaping gas may accumulate during a night to suffocate a,
sleeping person. There is danger, too, in leaving illuminal
ing gas turned low, for the flame may go out, blown by a^
gust of wind, or because the pressure is temporarily lowered
at the central plant, and the room be filled with gas.

Carbon Dioxid in Respiration. — In oxidation some of thej
food products unite with oxygen and as a result another gasJ
carbon dioxid, is formed. When, for example, a candle is]
lighted, the tallow in it combines with oxygen, thus pro-
ducing carbon dioxid. If the tallow were eaten it would, inj
a similar way, be united with oxygen in the body and thej
same gas would result. Since this carbon dioxid is a waste
product, it must be removed from the body in some way and
the second phase of the respiratory process is concerned withj
this elimination.

Whenever any of the tissues of the body are active, some
food or tissue is combined with oxygen and a certain amount]
of carbon dioxid is formed. The blood, as it flows through]
the capillaries of these tissues, absorbs this gas very much as
it does oxygen in the lungs, and for the same reasons; i.e.
because the carbon dioxid pressure is high. By the time!

MECHANISM AND CHEMISTRY OF RESPIRATION 205

the blood has gone through the capillaries it has become loaded
with this gas. About 40% of what the blood carries is in loose
combination with the proteid materials in the corpuscles, but
this does not at all effect the freedom with which oxygen
combines with the iron of the haemoglobin. About 60% of
the carbon dioxid is carried in the plasma; a small part of this
(about 2%) is simply dissolved in the plasma, while the rest of
it is temporarily combined with other elements in the blood
stream.

When the blood comes to the air sacs in the lungs it finds con-
ditions opposite to those among the tissues; the amount of
carbon dioxid in the inhaled air is very small, and the pressure
is so low that the blood immediately lets go its hold on its
CO2, which thus passes at once into the air sacs. Thus carbon
dioxid gas is breathed out at every expiration, while new air is
breathed in. If this inhaled air should contain too much CO2,
the blood could not rid itself of its own quota of the gas, and
the person would soon die.

It has been found that air containing 8-9% of carbon
dioxid produces severe discomfort.

This gas, which is heavier than ordinary air, is sometimes
found in abundance in deep wells or mines where it accumu-
lates, making the air distinctly poisonous. Men who must
descend into such wells frequently first lower a lighted candle.
If it will burn, the air is safe to breathe; if not, no person can
safely enter.

BREATHING AND EXERCISE

Since without a supply of oxygen one cannot live, and since
one would soon be poisoned by carbon dioxid if he could not
dispose of it, the necessity of breathing is evident. We can
easily see, too, why breathing will increase in rapidity if one
exercises the muscles vigorously, as, for instance, in running.
Breathing must be accelerated ^0 ^s \g keep up a larger supply

206 ADVANCED PHYSIOLOGY

of air in the lungs, because (1) the blood needs more oxygen
for carrying on its extra activity during the running, and (2)
it is necessary to dispose of the extra carbon dioxid given off
by the muscles when they are contracting rapidly. But in-
creased breathing alone will not accomplish this end. A
more rapid circulation of the blood is needed to bring the
carbon dioxid to the lungs, so the heart begins to beat more
quickly and the blood to flow more swiftly. As soon as the
blood circulates more rapidly, however, and the gases are
carried off sufficiently, the necessity for quick breathing is in
part reduced. Every runner knows that after running a few
minutes, he gets what is called his '' second wind". Breathing
grows less rapid and he may keep on running for a consider-
able time without any trouble with respiration. This "second
wind" appears when the circulation of the blood has become
rapid enough to carry off properly the gases formed.

Evils of Indoor Life. — Nature, apparently, intended that
man should live out of doors. But we have adopted new
habits of life, and shut ourselves up for many hours of the
day in close rooms. Hence, we are forced to breathe air
which has, perhaps, been breathed by other people and thus
rendered unwholesome.

In spite of its advantages living indoors is unnatural, and is
conducive to certain diseases. People who live out of doors
are rarely attacked by lung diseases; while they do not entirely
escape them, they are affected much less often than house-
dwellers. Other diseases are rendered especially serious
because we live in more or less limited spaces. But since we
cannot, in the present state of civilization, pass all our time
out of doors, we should do our utmost to remedy these con-
ditions by furnishing our rooms with a proper supply of good
fresh air.

Ventilation. — More attention is paid to the proper ventila-
tion of buildings to-day than ever before. In the times when
rougher materials were used in their construction and when

MECHANISM AND CHEMISTRY OF RESPIRATION 207

open fireplaces were the rule, so many chances were left for
air to enter houses that special ventilating apparatus was
almost unnecessary. With more skilled workmanship, with
machine-made building materials and especially with improved
methods of heating, a necessity has arisen for fresh air radia-
tors, fans, transoms and the various ventilating devices.

The need for ventilating a room depends on the rate at
which the air is breathed by its occupants. The normal per-
son breathes from fifteen to twenty times a minute. When
quiet the muscles oxidize materials slowly and the breathing
rate is lowered, but any hurry or excitement causes an im-
mediate increase in the breathing rate. Since we know that
with each breath about thirty cubic inches of air is taken into
the lungs, it would be easy to calculate the amount of air
breathed in any given time, but this would not really tell us
how much air is needed. To know this it would be necessary
to find out to what degree air can be impure before it is not
properly respirable. Fresh air keeps one active and alert but
the air of a close room makes one feel stupid and sleepy, and
even produces headache. This is not, as sometimes supposed,
because there is not enough oxygen in the air, for all rooms
contain sufficisnt oxygen to furnish the haemoglobin with all
it can hold; nor is the reason to be found in the presence of
an unusually large amount of carbon dioxid. There may be
about three per cent of pure carbon dioxid in the air with-
out interfering in any degree with its wholesomeness. So long
as there is not enough to interfere with the elimination of this
gas from the lungs, it will do no injury, and the air of no or-
dinary room, however poorly ventilated, contains enough to
do this. The ill effects of breathing air already breathed by
other persons are partly due to the large amount of water it
contains and partly to its high temperature. Perhaps other
factors are concerned, but the trouble is generally neither lack
of oxygen nor the presence of too much carbon dioxid.

It is therefore evident that it is no simple matter to tell just

JOe ADVANCED PHYSIOLOGY

how much air a person needs. Taking everything into con-
sideration, those who have made a special study of ventila-'
tion tell us that each person should be allowed from 2000
to 3000 cubic feet of fresh air per hour. This amount would
be contained in a room ten feet high, twenty feet long, and
ten feet wide. Fortunately, doors and windows are always
loose enough to allow a free passage of air through the cracks
around them, for if churches, schoolrooms, theatres, etc., were
built with air-tight joints around windows and doors, they
would have to be made enormously large to meet the demands
of the crowds which gather in them.

In arranging for the ventilation of rooms, it is well to learn
and remember a few general principles:

1. A room may be well ventilated, but feel uncomfortable
because it is too hot. The temperature should never be
above 70° F, unless the room is occupied by very aged people.
Public halls and sleeping cars, for example, are often kept so
hot that they are very uncomfortable, even though there may
be good ventilation. On the other hand, the temperature
may be right, but the air may be poor. Too high a tempera-
ture with good ventilation is, however, the more common fault.

2. For proper ventilation, a constant motion of air is needed,
not simply around the room, but from the room to the out-
side. If proper means for the escape of air is provided,
plenty of air will come in around doors and cracks, to take
the place of that going out. An open fire place is one of the
best methods of ventilation. A fire in a stove will serve the
same purpose, for it is constantly sending heated gases up the
chimney, thus drawing fresh air into the room. The belief
that stoves are unhealthful, because they use up the oxygen
of a room, is a great mistake. They use oxygen, but they are
constantly drawing in fresh air to replace it. On the other
hand, gas stoves or gas burners in a room will use up oxygen;
for generally they are not connected with any chimney or
proper outlet, and therefore fill the air with the odor of burned

MECHANISM AND CHEMISTRY OF RESPIRATION 209

gas which is in itself undesirable. Such methods of warming a
room are hygienically bad. When heated air is sent into a
room from a furnace in the cellar it will produce good ventila-
tion provided there is some ready outlet for the air of the room.
Heating a room by a radiator, either hot water or steam,
simply warms the air already present and furnishes no proper
outlet for the stale air, often making the use of special venti-
lators a necessity.

3. The greater the difference in temperature between the
air in a room and that outside, the easier it is to produce
currents of air. In cold weather air comes in and goes out
through cracks around doors and windows much more rapidly
than it does in warm weather.

4. The rooms of an ordinary house are so large in pro-
portion to the few people living in them that no attention
need be given to ventilation except perhaps in very cold
weather when they are more closely shut.

5. Sleeping rooms should be more carefully ventilated
than living rooms. But most care is needed in schoolrooms
and similar places, where many people are gathered together.

6. Expired air is warmer than the ordinary air of a room,
and rises at first. As it cools, however, it sinks, because
it is heavier than the rest of the air on account of the
presence of carbon dioxid. Hence, while ventilators at the
top of a room will take away the warmed air, there should
also be ventilators low down to carry off the heavier gasep
after they have cooled and sunk to the floor.

Treatment in Cases of Suffocation. — There are many kinds
of accidents that result in the exclusion of air from the lungs,
or asphyxia as it is called, producing suffocation. In all cases
the first thing to be done is to remove the cause of the trouble.
If it be choking from compression at the throat, free the
throat from whatever constricts it; if it be breathing poison-
ous gases, remove the patient to fresh air; if it be water, as
in the most common cases of drowning, lift the patient by

210 ADVANCED PHYSIOLOGY

the middle of Iiis body and allow the water to run out of hig
moutL

Lay the patient on his stomach with the head turned to one
side so that his mouth and nose are away from the ground.
Either kneel at his side or sit on his hips and then place the
hands upon the small of his back, with the thumbs near the
spine and the fingers spread out over the lower ribs. Then
throw your weight onto the hands for about the time it takes to
count three slowly, and then slowly swing yourself backwards so
as to release the pressure. After three more counts repeat the
whole movement. The pressure when your weight is thrown
forward forces air out of the patient's lungs and the release of
the pressure causes them to fill again. This produces what is
called artificial breathing. Continue this process about twelvej
times a minute without any pauses. Do not be discouraged foi
an hour at least. Pause occasionally to see if natural respirj
tion has started, by holding some light object in front of the
nostrils. If there is any motion showing natural breathingj
cease the artificial respiration and wrap the patient warmly.^

THE VOICE

While the tongue is popularly associated with the voice]
it is really only an agent which modifies sounds made neai
the entrance to the windpipe. It would be possible for om
to make himself perfectly understood, even if his tongue were
removed. The words spoken by such an individual woul(
be badly pronounced, but just as loudly and nearly as intel-j
hgibly as those spoken by a normal person.

The Larynx. — The voice box, or larynx, as it is technically]
called, is located just below the glottis in the trachea; Fig.
The whole trachea is supported by incomplete rings of carti-j
lage, but in the larynx region they are especially formed toj

* If practical, demonstrate this process of artificial respiration upon sora€
person in the presence of the class.

MECHANISM AND CHEMISTRY OF RESPIRATION 211

lake the framework of the organ of voice. Their arrange-
ient there is as follows:

The uppermost cartilage, the thyroid, a broad U-shaped
irtilage, Hes horizontally with the opening at the back; its
mt curve protrudes and is
It through the skin as

"Adam's apple"; Fig. 105.

The tips of the sides of the

U at the back have short

vertical growths on them,

one extending upward and
L^f ne downward on each arm
IK the U.

^^m Below the thyroid is the
^Hricoid cartilage. This is a
P^omplete ring, narrow in
i front and broad behind.

Its lower hind border is

hinged on each side to the

lower prongs on the thyroid;

Fig. 105. On the upper edge

of the hind border of the

cricoid are located the two

small, triangular arytenoid

cartilages shown in Figure

106, which represents a view

looking into the larynx from

above. These four cartilages together with tendons, muscles

and connective tissue make up the voice box.

The passage through this structure will be seen in Figures

106 and 107, to be nearly closed by two transverse, curtain-

Uke membranes attached at the back (one to each arytenoid

cartilage) , along the sides, and at the front (to the thyroid) .

In front these two membranes come nearly together, while

they are separated at the back, thus leaving an approximately

Fig. 105. — The larynx as viewed

FROM THE LEFT SIDE
Slightly enlarged.

212

ADVANCED PHYSIOLOGY

trian;;^ular opening for air to go through in ordinary breathing.
The straight inner borders of these membranes next to the
triangular passages form the vocal cords.

Sound and Voice. — In making a sound the vocal cords are
drawn very near one another at their posterior ends, and are

stretched tightly; air is then

finffenot'd ^ Cricoid ^i'^^'

Fig

-Thijroid
Vocal Cords

forced through the slit between
them. In this stretching oi
the cords several muscles are
concerned. In Figure 106 the
muscles marked A and B open
and close the space between
the vocal cords by moving the
arytenoid cartilages to which
they are attached. The muscle
marked C will evidently loosen
the cords. One of the muscles
that tightens them is sliown
in the figure at D,

Essentially this same mech-
anism for voice production is
present in many lower animals,
e.g. frogs and toads, dogs,

106. T HE LARYNX

VIEWED FROM ABOVE
A part of the membranes and muscles
are removed so as to show the chief
muscles concerned in opening and
closing (Muscles A and B) as well as
those that loosen (Muscle C) the vocal
cords. Muscle D is one of those which
tighten the cords. (Carter)

sheep, seals, etc. The song of
birds is produced by a somewhat different structure.

Since sound is due to extremely rapid movements in the air,
how can the vocal cords be set in vibration when the air coming
from the lungs is passing them in a continuous and steady cur-
rent? The expiratory muscles, i.e. those of the ribs and
abdomen, certainly do not go through 2000 contractions per
second, and thus send air from the lungs in as many little
*'puffs"; yet 2000 per second is the rate of vibration in the air
which is required to produce some of the higher tones a person
can sing. We all do know, however, that a blade of grass
or a strip of paper drawn between the lips will vibrate very

MECHANISM AND CHEMISTRY OF RESPIRATION 213

rapidly even though one blows on it steadily. For similar
reasons the vocal cords, stretched across the trachea, will
vibrate when a strong, steady current of air is sent through
them, thus producing air waves which give rise to sound.

Pitch of Voice. — The short strings on a piano give out
higher tones than the longer ones; but the pitch of any of the
strings may be made higher by tightening them. In the

Cartilage

Vocal Cords

Talkinc]

Vocal Cords

Breaihinq

Fig. 107. — The larynx as viewed from above with the membranes

in position

The figure at the left shows the vocal cords tightened to produce a sound as in talking
and that at the right shows them slackened and widely open as in quiet breathing.

larynx, the length of the vocal cords cannot be changed, so
pitch must be modified by varying their tension. If the
muscles that tighten the vocal cords contract, the cords will
give out a high tone; if these muscles relax a little and the
opposite muscles (Fig. 106) shorten, the vocal cords will
loosen and a lower tone result. Under ordinary circum-
stances these differences in tension are brought about in-
voluntarily, but in singing, conscious determination of theii
tension occurs to a certain extent.

Difference in Voice in Women and Men. — The reason why
the voice in women is so much higher in pitch than it is in
men, is that a woman's larynx is actually smaller than a man's.
When a boy is about fifteen years of age, his larynx begins tc

214 ADVANCED PHYSIOLOGY

enlarge, and he goes through an experience called a ^'change
of voice"; at the close of this period the larynx assumes its
permanent shape and size, and the voice remains practically
the same thereafter.

Quality of Voice. — The difference in the " sound " of the
voice in different people is due to the shape and size of various
air spaces associated with the throat, mouth and nose. The
strings taken from the finest violin in the world and stretched
from one nail to another in a board would not give out pleas-
ing sound, however they were bowed. In like manner, air in
a barrel changes the " sound " of the natural voice when one
speaks into it; speaking into bottles of different sizes gives
rise to different sounds. The fine tone of an instrument is
due more to the vibration of the air inside it than to the
strings themselves.

In the same way the character of the voice is largely de-
termined by certain air spaces; by the columns of air in
the trachea, in the pharynx and in the nasal passages; by
certain air cavities in the bones between the pharynx and
the brain, and by others in the bones making up the parti-
tion between the nasal passages and the brain; Fig. 96.

These spaces are all of much consequence in determining the
finer characteristics of the singing voice, and much of voice
training consists in developing the habit of "placing" the voice
in such a way as to obtain the best use of these air chambers.

Loudness of Voice. — The loudness of the voice is due to
the amount of air and the force with which it is driven through
the slit between the vocal cords. A piano string which is set
in vibration by a very forcible stroke gives out a loud sound;
struck lightly, the same string, vibrating through lesser dis-
tances, gives out a fainter sound though of the same pitch.
In a similar way, the loudness of the voice depends upon the
amount of the vibration of the vocal cords, which in turn is
determined by the strength of the air current.

Pronunciation is effected almost entirely by the ishaping of

MECHANISM AND CHEMISTRY OF RESPIRATION 215

the mouth and by the use of the lips and tongue. The lips
govern all sounds involving m, b and p, the teeth and tongue
sounds involving d, I, n and t; while the tongue, by its
position at back or front, governs to some extent the pro-
nunciation of every word one utters.

The readiness with which one makes himself understood
is dependent more upon the clearness of his enunciation
than upon the loudness of his voice. Some public speakers
shout very loudly and yet are difficult to understand; others
speak quietly, but are heard easily. The difference is largely
due to the degree of distinctness with which they pronounce
the consonants at the beginnings and endings of words. The
loud shouting of the vowel sounds renders one's voice less,
rather than more inteUigible. If one pays a little attention
to the proper enunciation of the consonant sounds he will
have no difficulty in being understood either in public speak-
ing or private conversation.

CHAPTER XIV
THE EXCRETORY SYSTEM

No machine has ever yet been invented so perfect in con-
struction that it will not wear out. Often it is impossible to
see with the naked eye the material which wears away from
a machine, but we know that it does disappear. The axles of
wagon wheels grow smaller, the tires wear away, bolts get
loose; all these parts have to be renewed occasionally.

Furnaces do not show the same kind of friction as axles and
wheel tires but they require, at times, new piping, grates and
valves. In furnaces, too, there is another kind of material
which must constantly be removed: the ashes, which are the
waste from the burned fuel, must be raked out, or the fire-
box will become clogged so that the fire will not burn. From
the burning fire, too, a quantity of waste gas goes off up the
chimney.

In similar ways, wastes are produced in the human body.
The tissues are constantly wearing out, and the parts worn
away are useless and must be removed. . In the body, too,
the oxidation of food leaves waste material corresponding
in a way to ashes, and in this oxidation gases are produced,
and considerable water. All of this waste must be eliminated,
and the general process of getting rid of it is called ex-
cretion.

EXCRETORY ORGANS

These wastes are conveyed to the exterior by four main
paths: the lungs, intestine, kidneys and the skin. It is difficult
to say which is the most important, for interference with the
functions of any one produces serious consequences, Deaths

?I0

THE EXCRETORY SYSTEM 217

from lung and kidney troubles are frequent. Death from
skin troubles rarely occurs, since the skin is not apt to be
attacked over the whole body at once, but it has been dis-
covered that if a person's body is painted over with a varnish
that interferes with skin functions, death will inevitably
result. (See "Body Temperature," Chapter XV.)

When we speak of the portion of the waste material ex-
creted through the intestine, we do not refer to the undigested
parts of the food that simply pass through to be discharged,
but to materials actually excreted from the body into this
part of the digestive tract. Most of these come from the
hver, which, as we have seen, pours quantities of bile
into the intestine. This bile aids somewhat in digestion,
but is, after all, chiefly a waste product which passes from
the body with the faeces.

Agency of the Blood in Removing Wastes. — In the building
and economy of any great city two systems of piping are con-
nected with every house, and are at the service of every in-
dividual: the water pipes which supply the fresh water, and
the sewers which take away the waste and the polluted
water. To be sure, water could be taken from a well in the
cellar of each house, and the waste could be poured on the
ground outside; but these practices, sooner or later, would
almost certainly cause diseases, if not death, in the house or
community. All up-to-date houses are provided with special
water supplies and sewage outlets.

In the human body the same system of tubes serves to
bring in fresh food and water supplies and to take away the
wastes. The blood, which serves both these ends, is thus a
very complex liquid. It contains all of the food absorbed
from the intestine, and in its circulation it receives all the
wastes from the various parts of the body, carrying them
away to the organs that are to excrete them. Living involves
such constant activity that waste matters are continually
thrown into the blood. A certain amount of blood can ab-

218 ADVANCED PHYSIOLOGY

sorb only a certain amount of these wastes, but if they can
be constantly removed from it, the blood may go on absorb-
ing them continually. A part of these materials, we have
already learned, is excreted through the lungs, since there
carbon dioxid gas and water are being constantly ehminated,
respiration thus being in part an excretion. The wastes ex-
creted through the skin will be considered in a special chapter.
The portion secreted through the kidneys will be noticed here.

UREA: ITS SOURCE AND EXCRETION

Proteid food contains nitrogen; therefore, among the body
wastes there must be some which hold this element. The
main one is urea, which is essentially broken down proteid
material, with the chemical formula (N2H4) CO. Although
muscles are largely proteid this does not necessarily mean
that muscular work will result in a large amount of urea
formation, for the energy of muscular contraction comes
chiefly from the oxidation of starches, sugars and fats; since
these contain no nitrogen their oxidation, of course, produces
no urea. A considerable quantity of urea does come from
the muscles, but this happens whether they are working or
not; for the very act of living results in the breaking down of
proteid material, and consequently in nitrogenous waste.

The waste from muscles does not leave them as urea, but
in a slightly different form. It is probably carried by the blood
to the liver, where it is changed into urea. Thus we learn of
another function of the liver, viz. in converting this waste
from the form in which it leaves the muscles into a form ca-
pable of excretion. The proof of this fact is that an animal
from which the liver has been removed, or in which it is
diseased, gives off very little urea, though an unusual amount
of ammonia, which also contains nitrogen, is excreted in
such a case. From the liver the urea passes into the blood
again, to be carried to the kidneys whose function it is tp
remove urea from the blood.

Tiffi EXCRETORY SYSTEM

2id

The necessity for urea excretion is shown by the fact that
all animals, even microscopic ones, have organs for its
removal ; although these organs are known by different
names, in all cases they correspond in function to the
human kidneys.

THE KIDNEYS

The kidneys are located one on either side of the body, in
the "small" of the back, a little to each side of the backbone
and a trifle below the eleventh pair of ribs, the left kidney
lying somewhat higher up than
the right; Fig. 108. The peritoneal
hning of the body cavity, is
stretched tightly over them.
They are firm in texture and
dark red in color. Figure 108
shows each kidney to be oval in
general shape with a depression
on the side toward the backbone,
thus having a form known as
"kidney shape." From the de-
pression a tube, the ureter, leaves
the kidney and extends down-
ward to the bladder. Close by
the exit of the ureter the renal
artery enters the kidney and the
renal vein leaves it.

The internal structure of a kidney appears somewhat as
in Figure 109. The ureter is large like a funnel as it leaves
the organ and is continuous with a space, called the pelvis, in
he body of the kidney itself. Protruding from the kidney
substance into the mouth of this funnel are conical structures
of soft tissue, eight to eighteen in number, called the Mai-
pighian pyramids. On the apices of these are the openings

Bladder

.Urethra

Fig. 108. — Diagram

Showing the position of the kidneys
and their connections.

5!20

ADVANCED niYSIOLOGY

of numerous tubules, which come from the outer layer of the
kidney, the cortex. The outer ends of the tubules are the real
glands, which produce the kidney secretion; their inner ends

drain these glands,

Medulla

Corfei

^alpiqhian

Ureter

carrying their secre-
tion to the pyramids
and pouring it into
the funnel-like open-
ing of the ureter,
whence it runs to the
bladder. To under-
stand the structure
and action of the kid-
neys we must study
these tubules more
minutely.

A Urinary Tubule. —
In Figure 110 a dia-
gram of the arrange-
ment of two urinary
tubules is given. Each
begins at its outer
end, i.e. the end to-
ward the kidney surface, in the form of a bulb-like expansion, the
walls of which are only one cell thick. This bulb, the Malpighian
capsule, is deeply indented on one side, so as to form a pocket.
From this pocket, there arises a long tube which takes a some-
what irregular course. It turns toward the center of the kidney,
but almost at once becomes twisted into irregular coils,
called the convoluted part of the tube. Afterwards, it pro-
ceeds in a fairly straight line toward the pelvis of the kidney,
but goes only a short way, when it turns sharply on itself and
returns toward the outer surface of the kidney once more,
near where it started. Here it is joined by other tubules of
the same sort and together the united tubes now pass as «

Fig. 109. — Representing a kidney opened
lengthwise

(Sappey)

THE EXCRETORY SYSTEM

221

/vj lialplqhian
) Capsule

Convoluted portion
of Tube

single duct in a nearly straight line to the tip of one of the
pyramids. There the contents are emptied into the pelvis,
whence they immediately
enter the ureter. Cor-f-ex.

The Renal Blood Ves-
sels.— The distribution of
the blood vessels aids us in
understanding how these
tubules act. The artery
enters the kidney at the
pelvis, and breaks up into
many small vessels w^hich
run toward the surface or
cortex of the kidney. Here
a minute twig enters each
of the little pockets at the
beginnings of the tubules
(Fig. 110), inside which
it breaks up into a roundish
knot of capillaries called a
glomerulus. After flowing
through the capillaries the
blood emerges from the
pocket as a tiny vein, but
does not immediately flow
out of the kidney. A part of it enters at once another set of
capillaries that run among the convoluted kidney tubules.
After traversing this second set of capillaries, the blood enters
definite veins and flows out of the kidney by the renal vein;
Fig. 111.

The Separation of Urea from the Blood. — We must
keep in mind that the main nitrogenous waste, urea, is
made in the liver from materials in the blood and then
returned to the blood stream; and that it is only through
capillary walls that blood can expel its waste or absorb n3W

Outlet of
Tubule into'
Pelvis of Kidney

Fig. 110. — Diagram

Showing the course of two kidney tubules.
(Huxley)

222 ADVANCED PHYSIOLOGY

material. There are, then, two places where material from
the blood vessels can be set free into the tubule; through the
walls of the capsule which surrounds the glomerulus, and
through the walls of the convoluted part of the tubule. By
a series of delicate tests it has been found that water and
some common salts in solution leave the blood through the
walls of the capsule. Although this process is, doubtless,

Malpiqhian

Tubuk

Fig. 111. — Showing the distribution of the capillaries
around a single kidney tubule

The blood capillaries in the capsule form a glomerulus.

largely one of filtration, it is unlike ordinary filtering through
paper in that not all substances in solution will pass through.
The cells of a Malpighian capsule allow some substances to go
through, while they prevent others. This, like the absorption
of food through the intestinal walls, can only be explained
by saying that the cells making up the membranes are alive.

Where the capillary blood vessels spread out over the con-
voluted part of the tubule, the cells of the tubule are true
secreting cells, selecting from the blood waste organic ma-
terials, chiefly urea, but also some other substances {pig-
ment, 'phosphoric and sulfuric acids, sodium, chlorine, ammo-
nia, etc.). These pass into the tubule; there the water coming
down from the capsule dilutes the secretion and carries it
into the pelvis cavity.

The entire kidney is a compact mass of thousands of these
tubules, each having an irregular course and each opening
into the reservoir of the pelvis. Inasmuch as the cortex is
so richly supplied with blood capillaries, this surface layer is
redder in appearance than the deeper parts which border on

THE EXCRETORY SYSTEM 223

the pelvis. This latter medullary region is made up for the
most part of larger blood vessels, connective tissue and col-
lecting tubules.

The blood that flows out of the kidney by the renal vein is
the purest in the body. It is arterial blood containing con-
siderable urea when it enters, but in flowing through the
kidneys the urea and some other wastes are removed, so that
it flows out actually purer than when it entered.

Urine Excretion. — The rate at which the kidneys excrete
urine is very variable, depending largely upon conditions of
the air one breathes. More is excreted in cold weather than
in warm, and more in wet weather than in dry. In hot, dry
weather so much of the water waste of the body leaves it in
the form of perspiration that less is passed off through the
kidneys. Certain foods and drugs, the drinking of a great
quantity of water or other liquids, and nervousness are all
agents which may alter the rate of secretion. The rate at
which the urea is secreted is not, however, dependent upon
these factors. It is dependent simply upon the rate of its
formation in the body. If formed rapidly, it is excreted rapid-
ly, even though the total amount of urine is small." The rate
of urea formation is dependent upon the rate at which pro-
teid material is broken down in the body, and the kidneys
will eliminate this urea as fast as it is brought to them by the
blood. An average daily amount of kidney secretion is three
pints.

The Ureters. — The ureters, which receive the urine from
the kidneys, are small tubes of about the diameter of a good
sized quill. Internally, they are lined with a mucous mem-
brane, outside of which muscles are arranged, essentially
as in the intestinal walls. By their peristaltic contraction
these muscles force the urine downward into the bladder.

The Bladder.— The bladder, Fig. 108, is the reservoir for
the temporary storage of the urine, and is located in the
middle of the abdominal cavitv, in front of the rectum. It

224 ADVANCED PHYSIOLOGY

is an oval sac and when moderately full is about five inches
in vertical measurement and three inches across, hokUng
about two thirds of a pint. The muscle fibres of its
walls are smooth extending in every direction about it, so
that when they contract during the process of emptying, the
bladder shrinks in all its dimensions.

The Urethra. — The single tube which leads from the middle
of the lower end of the bladder to' the exterior, is called the
urethra. The opening from the bladder into it is ordinarily
closed by strong circular muscles passing around the tube at
its point of exit. These muscles stay in a condition of con-
stant, involuntary contraction most of the time, relaxing
only on receipt of a special message from the b^-ain.

The Need of Drinking Fresh Water. — In the chapter on foods
we learned that the body needs a constant and large supply
of water. The necessity for plenty of water in dissolving and
removing body wastes through the kidneys furnishes one of
the chief reasons for this. Most of the water that flows through
the kidney tubules must come originally from the water we
drink. If plenty is supplied, the whole liquid content of the
blood can be more easily kept in solution, and more water can
be given off in the urine to "flush" the system. The sewers
of a city must never be of too small capacity and they must
never become clogged; water must be kept running abun-
dantly in them to prevent solids from settling and decom-
posing; otherwise, pestilence and disease set in. Similarly,
every organ and cell in the body must have plenty of liquid
blood flowing through and past it to furnish fresh supplies,
and to receive all the wastes, liquid, solid or gaseous.

GENERAL SUMMARY OF METABOLISM

Since urea represents the form in which all the nitrogen of
the proteid material in our food leaves the body, the whole
process of metabolism may be appropriately mentioned here.
In an earlier chapter the definition of the term metabolism

THE EXCRETORY SYSTEM 225

showed it to be the series of changes by which simple inorganic
matter is built up into complex organic matter, and all the
consequent changes by which it is broken down again into
simple elements.

With the foregoing study of kidney excretion, the story of
metabolism is nearly complete. It begins with the life of
plants that take carbon, oxygen, hydrogen and nitrogen from
simple gaseous and mineral sources, and build them up into
proteid, carbohydrate and fatty compounds. Man, by eat-
ing plants, converts these into animal proteids, carbohydrates
and fats. To be sure, some of his foods come directly from
other animals, but even these come originally from plants.
After performing various functions as animal tissue in the
body, food is broken down and excreted. Much of it leaves
the body as carbon dioxid gas and water, reduced thus to the
condition in which plants originally obtained it. Part of the
food leaves the body as urea and part of it remains in
the body. Later, the urea secreted as well as the tissues of the
dead body undergo a further set of decomposition changes.
They are attacked by a host of microscopic organisms (bacteria
and molds) causing further and more complete breaking down.
These processes are colled fermentation, decay and putrefaction;
but it should be remembered that these are simply names
for the final steps in the decomposition of food materials.
At last they are brought once more into the same condition
as that from which they started, so that a new generation
of plants can feed upon them. The whole process is a cycle,
the same materials circulating around in an endless succession
from soil and air to plants, from plants to animals, from
animals back again to the soil or air, partially through the
agency of bacteria, to start again on their round of usefulness

DISEASES OF THE EXCRETORY ORGANS

Excretion of the wastes of the body is absolutely necessary,
anything interferes with the action of the kidneys, the

226 ADVANCED PHYSIOLOGY

body becomes rapidly poisoned by the accumulation of urea
in the blood.

Bright's Disease is a name which really covers a number of
different diseases but they are all characterized by an inter-
ference with the power of the kidneys to excrete urea and
other wastes. One of the earliest symptoms is usually the
appearance of considerable albumen in the urine. In a
healthy condition the urine contains no albumen and its
appearance is always an indication of faulty metabolism.
Although Bright's disease is dangerous, recovery from certain
forms of it is frequent.

Kidney Stones. — In another disease of the excretory organs,
hard, little nodules, called kidney stones or calculi, form in the
pelvis of the kidney and pass down into the bladder. They
are apt to cause severe pains as they go through the ureters
and sometimes cause alarming symptoms. Usually, if prop-
erly treated, they do not produce much trouble, and some-
times they pass away with the urine. In some severe
cases, however, a surgical operation is necessary for their
removal.

Diabetes is the name given to a disease in which sugar
appears in the urine, the normal urine containing none. It
is not, however, a disease of the kidneys, although the trouble
is detected in the secretion from these organs. It is due
rather to improper nutritive processes in the body, although
the exact seat of the trouble has not yet been determined.
An individual suffering from this disease is unable to assimi-
late his foods properly and there seems to be especial dif-
ficulty in the assimilation of sugar. This results in an
excessive amount of such material in the system and the
kidneys are obliged to excrete it. Diabetes is a very serious
disease, and recovery from it is rare.

Jaundice is a term used to denote symptoms of some
derangement of the liver, because of which it is failing to
carry on its proper functions in connection with excretion.

THE EXCRETORY SYSTEM 227

' The actual cause is not known, but the symptoms are
striking. The disease is characterized by a noticeable yellow
hue of the skin and very dark urine. The colors are some-
times so deep as to be alarming, but the trouble is not serious
as a rule, and soon disappears. The real cause of none of these
several diseases is as yet known. They do not seem to be
produced by disease germs, and none of them are contagious.
No methods of avoiding them are known beyond the general
one of maintaining good health by proper exercise and diet,
avoiding overeating and stimulants.

CHAPTER XV

THE SKIN

The skin is not ordinarily considered an organ of much
importance. It seems to be merely a covering for the body
and it is not at first easy to believe that the skin actively
functions. In reality, it is an important organ which performs
some of the most vital offices in the human body. There is
no part of the body which has more to do with one^s comfort
than the skin; and there is almost no part whose sluggish or
improper functioning leads to more general unpleasantness or
is more liable to induce illness.

STRUCTURE OF THE SKIN

The skin is a sheet of tissue covering every part of the
surface of the body, except the eyeballs, and even these when
the eyes are closed; there are a few large openings through it
for the entrance and exit of solid matter. The skin is about
j^ of an inch thick, but it varies considerably, being much,
thicker on the soles of the feet and palms of the hands than
elsewhere. If a thin section of the skin is examined under a
microscope it will be seen to consist of two distinct layers,
an outer called the epidermis, and an inner called the dermis.
The epidermis is lifeless, save for a thin layer on its inner
surface, and can be cut without pain or bleeding; the dermis
is extremely sensitive, full of nerves, blood vessels and glands;
Fig. 112.

The difference between a plump person and a slender one is
also manifest in the skin appearance generally, for m the former
much fat, called adipose tissue, is often present among the glands
and connective tissue of the dermis.

22§

THE SKIN

229

is necessary to cover the body. If it be seized by the fingers
almost anywhere, e.g. on the back of the hand, it can easily
be Ufted into a fold, but returns to its original place when

Flattentd
Cells

Epidcimk

Blood
Vessels

Dermis

Qrowlng
Cell6-
Blood
^sseh

Nerves

Fig. 112. — Section through the skin

Showing the layers of the epidermis and the sense organs and blood vessels of the

dermal papillae.

released. On account of this elasticity it readily accommo-
dates itself to the shape of the body, and is ordinarily stretched
smoothly over it. As a person grows older, it becomes less
elastic and is finally thrown into wrinkles.

THE EPIDERMIS

The inner surface of the epidermis is composed of a layer
of growing cells, somewhat rounded in shape; Fig. 112.
They are nourished by the blood from below, and are con-
stantly multiplying and growing. As they increase in num-
bers the new cells push the older ones toward the outer sur-
face of the skin, and the epidermis is thus made thicker by
growth in its deeper layers. As soon as the cells are pushed
away from the deep, growing layer, they cease to have life

280 ADVANCED PHYSIOLOGY

and gradually become flattened by pressure. The skin is
always wearing away at its surface because of the constant
friction it receives. Debris resulting from this wear is not
ordinarily noticed, but when it accumulates in the hair,
along with the dried secretion of certain skin glands, it is
called dandruff. After scarlet fever, measles, etc., the epider-
mis may come off in sizable flakes.

Some of the deeper cells of the epidermis contain pigment
matter which gives the skin its color. This pigment differs
in the skins of different races; in the negro it is abundant and
black; in the yellow races it is of a brownish yellow color; in
the skin of the white races there is very little, but here, too, it
varies slightly in amount, producing differences in complexion,
e.g. blonde and brunette. Freckles are due to the unequal
distribution of this pigment which may be especially dense
in spots; they are frequently produced in children by much
exposure to sunshine or cold winds.

Thickened Parts of the Epidermis. — Wherever there is
more than the usual amount of wear, the epidermis grows
more rapidly and becomes thicker than elsewhere; examples
of this growth are seen in the callouses on the hands and feet.
If the rubbing is not severe but long continued, the epidermis
grows into prominences called corns or bunions. Blisters
result from a sudden rubbing of the skin, the capillaries being
stretched and lymph collecting between the dermis and epi-
dermis in consequence.

Skin Grafting. — The only way in which epidermis grows
is by multiphcation of the cells in its deeper layers. When
these growing cells are destroyed over a large area, e.g. after
severe burns, it may be difficult for the epidermis to be
reproduced. If a bit of epidermis is taken from a healthy
part of the body, or from some other person, and firmly
placed upon the raw surface of such a wound, it will generally
grow there, extending rapidly and eventually covering the
surface which would not otherwise have healed. Such a

THE SKIN

231

procedure is called skin grafting and in modern surgery is a
common practice of dealing with slowly healing wounds,
especially wounds from burns.

Hair. — To the naked eye hair appears unlike any other part
of the skin. Throughout most of its length, hair is dead
and shows little structure; but* near the root where still
aUve it is made of cells like all other organic material. If a

\rferu \

HairPapiUa

Fig. 113.— Sec-
tion THROUGH
THE BASE OI- A
HAIR

Showing its differ-
ent layers, the
papilla upon which
it grows and the
blood vessel that
nourishes it.

'-ifZjiMusck

~]^aJt Ciand
Fig. 114. — Section through the skin

Showing the various organs in the dermis and
epidermis.

hair were split and examined under the microscope, its appear-
ance would be something as in Figure 113. In the center is
a kind of pith called the medulla of the hair; next this is a
horny layer, the so-called cortex, in the cells of which is the
pigment determining its color. Outside the cortical layer is
the cuticle of the hair, a transversely arranged series of horny
cells, each upper row overlapping the one below it like the
shingles of a roof. Each hair comes out of a sac, or hair

232 ADVANCED PHYSIOLOGY

follicle, a tiny canal of epidermal cells extending down into
the dermis; Figs. 113 and 114. The lower end of this folUcle
is enlarged and projecting upward into it is a papilla on which
the hair grows. Cells of this papilla are constantly multiply-
ing and turning into hair substance and thus the hair length-
ens. After a time (in the scalp, perhaps three years), the top
of the papilla ceases to form new cells, the hair dies and falls
out. Before this occurs, however, a new papilla has been
budded off the side of the old one and from it a new hair starts.
When a hair is pulled out the epidermal cells lining the
follicle may come away also, but the papilla usually remains
uninjured and a new hair soon grows from it. The straight-
ness or curliness of hair depends on its shape: kinky hair is
flat or oval in cross section; wavy hair is oval; while straight
hair is round and rod-like.

Emptying into each hair follicle is usually an oil or sebaceous
gland; Fig. 114. These glands secrete a substance which
moistens the surface of the hair and keeps it soft and flexible-
To the lower end of the follicle in most hair-bearing animals
is fastened a slender muscle, its other end being attached to
the lower layers of the epidermis; Fig. 114. The shortening
of this muscle pulls the follicle into a more vertical position,
making the hair "stand up straight," as a cat's fur frequently
does, for example.

All epidermal structures are disturbed and cast off to a
greater or less extent in the case of some fevers, and not in-
frequently the hair falls out after a long sickness.

Hair itself is not sensitive, though if it is stiff one may feel a
very slight touch upon it becauseof the presence of nerves in the
dermis at its base. The stiff hairs around the nostrils of a cat
are thus sense organs of touch. Over most of the human body,
hair remains so short as to be almost invisible and of only
slight protective value. The tendency for hair to fall out and
leave the head bald is probably due in part to the bad habit of
vvearing hot, heavy hats with stiff rims which bind the scalp.

THE SKIN

233

Nails. — The finger and toe nails are especially thickened
(parts of the epidermis. Figure 115 represents a lengthwise
[section through the tip of the finger, showing a nail. It
grows chiefly at its base, called the root, and as it grows
its free end is pushed out farther and farther. It also
grows thick by additions to its un-
der surface. The reason why a nail
appears whiter at its basal end is
that blood capillaries are less plentiful
in that region than elsewhere; this
*'white" of the nail is technically
called the lunula.

f^' ■l^oi'Mn

Fig. 115. — Section
through the end op

A FINGER

Showing the relation of

the nail to other parts.

THE DERMIS

Below the epidermis is a live layer
composed of connective tissue, nerves,
blood vessels and fat. It is largely
made of a dense mass of connective

tissue fibres like the material we have already noticed
in tendons and ligaments, except that in skin it is arranged
in a much looser mass; the fibres run in every direction, are
closely packed together near the epidermis, but below, near
the muscles, become quite loose; Fig. 114. In the spaces
between the fibres are masses of fat cells which fill out
the skin and make the body appear rounded. If these layers
of fat were not there, the skin would cling tightly to the
flesh so that muscles and tendons would show through it.
When a person is insufficiently nourished, as for example after
a long illness, the location of the separate muscles beneath
the skin is plainly seen because the fat stored in the dermis
has been used.

The dermis is full of blood vessels. This is most evident on
certain areas, e.g. the lips and inner surfaces of the eyelids,
where the epidermis is very thin and the capillaries of the
dermis show through, giving these areas their red appearance.

234

ADVANCED PHYSIOLOGY

Cold Perceimq Areas

The outer surface of the dermis, where it comes into con-
tact with the epidermis is not flat and smooth but shows
many small elevations, called papillae; the epidermis fits

over these so that the two
layers dovetail into each
other; Fig. 112. These
papillae on certain parts
of the body, e.g. on the
palms of the hands, are
arranged in parallel or
concentric rows so that
they show through the
epidermis and produce
the fine lines which appear
on the tips of the fingers
and toes.

Organs of Touch, Heat
and Cold. — In these pa-
pillae, nerve endings
and blood vessels are
abundant, though the
same papilla does not
usually contain both.
Some nerve endings as-
sociated with touch and
temperature changes are
shown in Figure 112. A
number of endings in the
same region will perceive
only cold, others only
warmth; so that in general we may say that the whole
body is mapped out into " cold and warm spots "; Fig. 116.
The ends of nerves which are sensitive to touch are called
tactile corpuscles or end bulbs; Figs. 117 and 118. They are
of different shapes and extremely small, varying for the most

Warmth Perceimq /trea$

Fig. 116. — Diagram

Showing the areas on the back of the hand
that perceive heat and cold. The two figures
represent the same area, one figure showing
the cold and the other the heat perceiving
areas. (Goldschneider)

£ncfBufb

Fig.

117. — One op the end
of touch in the eye

(Dogiel)

^ervc-

BULBS

THE SKIN

235

part from ^l-^j to -g-J-g- inch (0.04-0.08 mm.) in diameter.
The sense of touch may be one of mere pressure, or when
excessive may be that of pain. Naturally,
those parts of the body are most sensitive
where the papillae which contain these
nerve endings are most numerous. The
tip of the tongue has the most nerve
endings to a given area,, and the finger
tips are the next most sensitive organs.
Nerve endings are farthest apart on the
back, and on the back of the neck.
Two points one tenth of an inch (2.5
mm.) apart can be identified as two if
they are on the finger tips. In the middle
of the back, however, two points two
and a half inches (66 mm.) apart may
be felt as one.

Fig. 118. — A tactile

CORPUSCLE FROM

THE FINGER
(Ruffini)

The Skin as a Protecting Organ. — The skin is a protection
against the entrance of disease germs. The many over-
lapping layers of epidermis cells form such a thick mass that
bacteria cannot penetrate it and reach the living parts within.
If it is broken, however, bacteria can attack it at once. The
need of thoroughly cleansing skin wounds is thus manifest.

Any of the common antiseptic washes or lotions are of some
value, but especially those containing formalin (3-10% is very
effective), bichloride of mercury (1 part in 1000), or carbolic
acid (23^%), are effective, easily used, and inexpensive. If cer-
tain treatments cause sharp pain for a few minutes, this is a
good indication, for it probably means that the naked tissue is
being killed, with the bacteria on it.

THE SKIN AS AN EXCRETING ORGAN

The skin secretes perspiration at the rate of one to five
pints per day. This quantity varies according to the amount

236

ADVANCED PHYSIOLOGY

'^=-(^^^^idermii

of exercise a person takes and the condition of the air about
him. One perspires less on a wet day than on a dry one, and
less in cold weather than in warm. Ordinarily this secretion
is produced so slowly that it evaporates as fast as it is formed
and except for a realization that the
skin is kept moist and flexible, one is
unconscious of it. When the glands
secrete very rapidly, their output may
not evaporate as fast as it is formed,
and collects in small drops; this occurs
particularly when the weather is hot, or
when one is exercising vigorously. Phy-
siologists speak of this ''sweat" as sensi-
ble 'perspiration, while the ordinary slow
secretion is called insensible perspiration.
The amount of insensible perspiration
increases with a rise in temperature,
from a cold state up to about 92 °F; a
very sudden increase in the perspiration
rate then sets in, and sweat drops collect
on the skin; at the same time, CO2 is
eliminated in considerable amount
through the skin. In this connection it
is interesting to note that in some ani-
mals, e. g. the earthworm, frog, etc., the
skin is the principal breathing organ.

Sweat Glands. — There are about two
and a half million sweat glands scat-
tered through the dermis of the human
body. They occur in least numbers in the middle of the
back, where there are about four hundred per square inch,
while on the palm of the hand and sole of the foot there may
be two thousand five hundred in the same area. Each sweat
gland is a minute tube of uniform diameter, closed at its inner
end where much of its length is coiled into a knot; Fig. 119.

Fig. 119. — Diagram

Showing a sweat gland, its
duct and its blood supply^

THE SKIN 237

The cells which constitute this part of the tube are the true
secreting cells, and this glandular portion is surrounded by
a net-work of blood capillaries. The ducts from different
glands do not join one another, but each passes nearly straight
up through the dermis, then through the epidermis in a wavy
course, to open by a minute pore on the surface of the skin.
The pores are too small to be seen with the naked eye, but
are easily visible if the skin is examined with a good lens.

Like the other glands in the body sweat glands are under
the control of definite nerve fibres, called secretory nerves.
These are stimulated by various means; by reflex influences
when strenuous muscular work is being performed; by the
condition of the surrounding air; by fright or by special con-
ditions of the internal organs. Like other glands, too, their
action is not within control of the will.

Functions of the Sweat Glands.— The sweat glands have
two very important functions: (1) Excretion of water and
other materials. Large amounts of perspiration, which is
water in great measure, are secreted daily, thus making the
skin second only to the kidneys in regulating the amount ol
water in the blood. There are also small amounts of various
salts, traces of fat and other substances in perspiration. If
on account of a disease of the kidneys, urea cannot be properly
excreted from them, it may be partially disposed of through
the skin, which thus helps to purify the blood. (2) Regula-
tion of body temperature. This is a matter of such importance
that it must be discussed in considerable detail.

BODY TEMPERATURE

The life processes in all animals and plants are closely
related to temperature. At the freezing point all their
activities stop; at temperatures sHghtly above this they begin
and with increase of temperature become more vigorous.
For the human body 98° F. seems to be a very favorable tem-
perature. Even the simple functions of digestion are checked

238 ADVANCED PHYSIOLOGY

by temperatures markedly lower or higher than this; and it
follows, therefore, that the greatest vigor is possible only
when the body is warm.

Not only is the body warm but it is kept at an almost uni-
form temperature. This varies slightly in different persons,
and in the same person different parts of the body show slight
variations from the average of 98.6° F. The internal organs
are considerably warmer than those on the surface; the tem-
perature of the skin itself is not much over 90° F., while that
of the liver may be as high as 107° F. Moreover, the body
heat differs a little from hour to hour, being greatest between
1 P. M. and 4 P. M. and least between 1 A. M. and
4 A. M.

Health is so dependent upon the maintenance of proper
body temperature that if there is much departure from the
normal, illness results. If the temperature rises to over
100° F. we say that the individual concerned has a fever; a
slight fall of temperature below 98° F. is an equally sure
indication of illness, though we have no special name for this
condition and less commonly hear about it. During a high
fever a person's temperature may rise to 106 F. or even a
little higher, and recovery take place, but a rise to 107° F.
or 108° F. is usually followed by death.

The source of all body heat is the oxidation of foods. All body
activity involves the oxidation of food or tissues, and
thus is necessarily accompanied by heat production. This
explains why we get warm when exercising vigorously, why
we like to move around quickly on a cold day, and why we
need extra clothing when not exercising. We must not, how-
ever, confuse feeling cold with being cold. On a cold winter day
one feels much colder than on a warm summer one, and it is
hard to believe that the body temperature is practically the
same in the two instances. One's feeling of warmth is in
the skin; if the blood vessels in the skin are open so that
much warm blood can flow through them, one feels warm;

THE SKIN 239

if they are partly closed so that the blood is kept inside
[the body, one feels cold.

The larger part of the heat of the body is produced in the

[muscles when they contract, though a great deal seems to

)e formed in certain glands like the liver. This heat warms

ihe blood flowing through these organs. Then the blood

;oes to the cooler parts of the body, warming them in much

the same way as hot water warms the different rooms of a

house, as it goes to them through pipes from a heater. The

blood thus distributes, but does not produce heat.

Cold and Warm-Blooded Animals. — The cold-blooded an-
imals— frogs, alligators, lizards etc. — are never much warmer
than the air in which they live. While oxidation of course
takes place in them as in other animals, and heat is thus
produced, there seems to be no special regulation of body
heat, and they have a very low temperature on a cold day
and a high temperature on a hot day when lying in the sun.
They are apt to be sluggish at any time, but are sure to be so in
cold weather.

In warm-blooded animals, i. e. birds and mammals, the
amount of heat produced is always great, and the temperature
of the body does not change with the temperature of the air
but remains constant if the animal is in uniform health.
Such animals are called warm-blooded because their blood is
generally warmer than the air, although on a hot summer
day it may be cooler than the air. To maintain a constant,
high temperature a considerable amount of heat must be
produced and consequently a large amount of food must
be oxidized. Warm-blooded animals thus demand much
more food than cold-blooded. A turtle's activities are so
slight that the little energy stored in its body is sufficient to
keep it alive for six months without food while a warm-blooded
animal must have a large supply of food, and can live only
a comparatively short time if deprived of it.

The Regulation of Temperature. — The temperature of the

240 ADVANCED PHYSIOLOGY

body can evidently be modified either (1) by changing the
amount of heat produced, through an increase or decrease in
the amount of food oxidized; or (2) by varying the amount oj
heat lost. Each of these methods is adopted in part; but under
ordinary conditions it is by controlUng heat loss that this
regulation is chiefly effected. To appreciate this fact it
must be understood that the heat resulting from the ordinary
oxidation of food is more than enough to warm the body and
keep it at 98° F. To maintain the correct body temperature,
therefore, it is necessary that some heat be passed off.

Loss of Heat through the Lungs. — When the temperature
of the air is considerably lower than that of the body, as is
usually the case, one loses superfluous heat in breathing.
The inhaled air is cooler than the body, but when exhaled
its temperature has been raised. Of course, if the air has
thus been warmed the body has been correspondingly cooled.
The cooler the air breathed the more heat it will take from
the blood. On a cold day so much heat may be lost by this
means as to take away nearly all the surplus; but when the
air is warmer this loss is not sufficient for the purpose of keep-
ing the body temperature uniform.

Loss of Heat from the Skin. — The chief method of regulating
body heat is by the expansion and contraction of the blood
vessels in the skin. Since the air is almost always cooler
than the blood, blood will, of course, be cooled as it flows
through the skin; and the more rapidly the warm blood flows
through the skin, the more rapid will be the loss of heat.
But while this swift flow actually cools the body, it seems to
make it warmer. This is due to the fact that the skin is
very sensitive to temperature, and when an extra amount of
warm blood is flowing through it a feeling of extra warmth
will be experienced, though the body is actually cooling.

One often feels this to be true when a sore finger is bandaged
and a string tightly tied about it; the end of the finger feels cold
because free movement of the blood has been prevented by the

THE SKIN 241

ligature. A rubber band tightly wound on the finger gives
similar evidence of the same fact.

Expansion and Contraction of Blood Vessels in the Skin. —

We have already noticed how readily the small blood vessels
are expanded and contracted by the action of muscles in
them and that this action is controlled by nerves. In the
skin the muscles in the small arteries are especially well
developed and quickly relax or contract under the influence of
extra heat or cold. If the temperature of the air rises on a
warm day, if the body is warm, or if extra heat is being pro-
duced, the blood vessels in the skin relax. In short, when-
ever the heat being produced in the body is greater than that
required to maintain the proper temperature a relaxation of
the skin vessels allows more blood to come to the surface,
thus increasing the loss of heat. Whenever heat loss from
the skin is greater than heat production, so that the body is
cooling too rapidly, the skin vessels contract and allow less
blood to flow through them. This keeps the warm blood
inside, and, of course, prevents the body from cooling too
rapidly. The perfect control which the brain thus has over
these vessels enables it to regulate the amount of blood
flowing through the skin and, consequently, the amount of
heat lost through direct radiation from the body.

Perspiration as a Heat Regulator. — There is another means
by which loss of heat through the skin is regulated. The
sweat glands are constantly pouring their secretion upon the
skin, where it is as constantly evaporated. It is a simple
law of physics that heat is required to evaporate moisture.
Hence the larger the amount of sweat poured upon the skin
for evaporation, the greater will be the amount of heat re-
quired for evaporating it, and therefore any increase of per-
spiration increases the heat lost by this means. Everyone
knows that the amount of sweat increases with the tempera-
ture. On a hot day one perspires profusely, and on a cold
day imperceptibly. All these sweat glands are supplied with

242 ADVANCED PHYSIOLOGY

nerves in such a way that the brain can increase or decrease
the amount of their secretion. When the air becomes so warm
that it is difficult for the skin to lose by simple radiation an
amount of heat sufficient to keep the body temperature at
its proper point, the sweat glands increase their action. In
the evaporation of the extra moisture thus poured out on the
body surface so much heat is lost that the body temperature
is reduced to its proper level.

After a bath, even though the water used be warm, and the
room at more than usual temperature, this same sense of cool-
ness is felt. People often say while swimming in a river or the
ocean, ''The water is warm enough but the air is chilly.'*

The extent to which body heat may be reduced through
sv/eat evaporation is really very great. One experimenter
found that he could remain for some time in a room in which,
the air was warmer than 260° F. and in which the direcl
effect of the air would be, of course, to warm the blood rather'
than cool it. But evaporation of the profuse perspiration^
resulting took so much heat from his body that he found
perfectly possible to retain his normal temperature. Stokers]
on ocean steamers, living and working as they do in a tem-
perature of over 130° F., are evidence that this principle
admits of constant and daily application. The fact that
fever is accompanied by the lack of perspiration, partialb
explains the rise in the temperature of the body at such]
times.

SUMMARY OF METHODS OF HEAT REGULATION

As an illustration of heat regulation in the body, imagine]
a hot summer day with the temperature of the air over 100° F.
The air is actually warmer than the body; the sweat glands]
pour out an abundant secretion which rapidly evaporates.
This evaporation cools the skin and reduces the temperature ofj
the body to the desired point.

THE SKIJM 243

Hfeuppose the temperature of the air falls to 85° F. Profuse
I sweating ceases; perspiration does not stop, but the sweat is
1 less abundant, does not collect so profusely in drops, and a
! different method of controlling body heat comes into play. The
blood is now warmer than the air, and will be cooled as it
flows through the skin; owing to the heat, the skin vessels re-
main relaxed and large amounts of blood from the internal
organs are coming to the surface. The skin is thus filled
with warm blood and the person still feels warm, though
the blood is being cooled by the air. Heat thus passes off
I by direct radiation in sufficient quantities to keep body tem-
I perature at the proper point.

Suppose now that the temperature falls to about 70° F.
Sensible perspiration stops entirely; the blood vessels of the
! skin partly close so that less warm blood flows through them;
the body retains its heat in this way, and its general tem-
perature remains the same as before. If the external tempera-
ture falls still more, a different adjustment is necessary. The
skin vessels constrict still further, and the warm blood is
confined to the internal organs until they are almost over-
supplied with blood. Now since so little blood is flowing
through the skin, the person begins for the first time to feel
chilly, and it is at this temperature, i.e. between 70° and 60° F.,
that one is most liable to take cold. If the temperature falls
yet lower, more heat must be produced by increased oxida-
tion. Thus at temperatures above 70° F. regulation of body
heat is brought about by increasing or decreasing the loss of
1 heat; below this, chiefly by increasing heat production.

It is important to realize the significance of a constant
body temperature; man can exist only while warmth is as-
sured and if its supply were not regulated, he could live only
in certain climates. Because of this automatic control of
body temperature man can live in summer or winter, in the
cold regions of the north, or in the hot climate of the equator.
Animals with an abundance of hair do not perspire pro*

244 ADVANCED PHYSIOLOGY

fusely, and their skin has Httle power of regulating tempera-
ture. Such animals must depend largely upon respiration
to rid themselves of surplus heat. This explains the panting
of dogs, and their rapid breathing in hot weather or when
exercising rapidly.

CARE OF THE SKIN

To insure the healthful functioning of the skin, the pores
of the sweat glands must be kept free and open. The fat
glands connected with the hair follicles are constantly exuding
a certain amount of oil, and the sweat glands give out much
water, salts and other substances. The water will readily
evaporate, but the solid material will remain on the skin,
tend to clog the pores, check the ready action of the glands
and cause an offensive odor. Evidently the normal action
of the skin demands that this material be removed. To keep
the pores open, habitual bathing and washing of the skin is
a necessity. The frequency of the bath, however, is a matter
in regard to which no rule can be given. A daily bath is
certainly desirable, though doubtless not necessary to health.

It is a mistake to suppose that cleanliness is the primary
benefit to be derived from bathing, although it is an im-
portant one. The principal effect of the bath is in stimu- ;
lating the skin, and increasing its activity. The skin is a it
delicate organ, in which more blood is exposed to the air than »
in any other organ in the body. A large part of one's com- t
munications with the outer world are received through it. I

Cold Baths. — The first effect of a cold bath, whether it be a
plunge in cold water, a shower bath or merely a sponge bath,
is to stimulate the temperature nerves of the skin, producing n
decided sensation of cold. This acts through the brain and
causes (1) a contraction of the blood vessels in the skin; for
a short time the skin becomes white and cold, due to this
contraction. But this is presently followed by (2) a reaction;
almost immediately the brain withdraws its contracting in-

THE SKIN 245

fluence allowing the vessels to expand. More blood now
flows through the skin, it becomes flushed and warm, and
there is a feeling of exhilaration in the body. This '' after-
glow " may last a long time, and the person should leave the
water while still under its influence. If he stays in longer,
the blood vessels may again contract, making him chilly,
and since this time there is no subsequent reaction to warm
the body, he is Ukely to be cold and uncomfortable for many
hours. The length of time that the after-glow may continue
depends upon the person, the temperature of the water and
to a certain extent upon its character, lasting longer if the
water is salt, than if fresh.

The after-glow from a cold bath is increased if it is accom-
panied by a vigorous friction of the skin. Energetic rubbing
with a rough towel is of as much value as the bath as a stimu-
lant for the skin, and without it the bath accomplishes only
half its purpose. Rubbing with towels pulls to a slight degree
on every part of the surface, stretches the different tissues in
the dermis, dislodges any loose epidermis, and leaves the skin
alert and ready to perform its duties. In short, the cold
bath and the '' rub " are to the skin what the gymnasium is
to the skeletal muscles.

Since one of the chief objects of the cold bath is to shock
the skin, there is no reason why one should not take a plunge
into cold water, even when hot and sweaty, provided he
does not stay in long enough to become chilled. The shock
is an advantage, the cooling is refreshing. On the other hand
to take a cold plunge when one is already cold is neither
pleasant nor profitable, unless it is followed at once by a
vigorous friction which develops the proper aft6r-glow. Cold
baths should always be taken when one is warm, e.g. when
just out of bed or after vigorous exercise. After a night's
rest in a horizontal position, the heart is beating slowly, blood
is flowing sluggishly and nerves are stupid. A cold bath at
such a time is the best stimulant a person can take to get

246 ADVANCED PHYSIOLOGY

himself thoroughly awake, arouse his nerve centers and start
the human machine going for the day.

Hot Baths. — There are times when hot baths are desirable.
Warmth is sure to produce an expansion of the blood vessels
of the skin, and thus to a certain extent draw blood from the
internal organs. This may be very beneficial; for example,
it may enable one to get to sleep, or rest when restless, since
it draws blood from the brain. When one has the first symp-
toms of a cold, a hot bath, or even heating the feet in hot
water, may withdraw the blood from the inflamed throat or
nasal cavities and check the onset of the cold. This method
v^f causing the expansion of the vessels is not so good an
exercise for the skin as the cold bath, and is not really an in-
vigorating stimulant; it tends to leave the skin soft and deli-
cate, and the body should be warmly covered after such a
bath, and not exposed to any chill. Hot baths should never
be taken immediately after meals, for the blood rushing to
the skin to fill the relaxed capillaries is taken from the diges-
tive organs which then need it. Skin activity is the best
guard against the various skin diseases. A skin kept healthy
by bathing and friction will ward off many an attack of para-
sitic bacteria to which an unhealthful skin would yield.

CLOTHING

Much contradictory advice is given concerning the kind and
amount of clothing it is best to wear. Fortunately the body
so easily adapts itself to conditions that it can get along with
many differences in method of treatment. . While specific
rules for clothing cannot be given, certain principles are
involved.

Clothing serves two purposes: (1) to conserve warmth, and
(2) to absorb the perspiration of the body. The amount of
warmth that any fabric seems to give is dependent not only
on its thickness, or weight, but also upon the size and num-
ber of air spaces in the cloth. Air is a very poor conductor

|H| THE SKIJNT 247

V^Mf heat and cold. Coarse cloth in the meshes of which are
^^Bumerous air spaces is, therefore, warmer than closely woven
^^Rloth of equal weight. For the same reason, two or more
i thicknesses of cloth are warmer than one of equal weight,
I the air space between the two holding the heat.

If we were to live out of doors in the winter, much heavier
clothing would be needed than in warm weather; but most of
us spend the greater part of our time in rooms whose tempera-
ture is very little colder than that of summer and although we
do go out into the cold, a comparatively small amount of
our time is thus spent. For most people, therefore, it is plainly
a mistake to dress the body warmly all the time because of
the occasional minutes spent outside. The wiser method is
to wear the same amount of clothing that one would wear at
those seasons when the outside temperature is about the
same as that maintained in one's living rooms in the winter,
and then to add upon going out of doors such clothing as is
necessary for comfort. If one lives out of doors much of
the time in winter the case is different. The amount of cloth-
ing needed for very cold weather varies much with different
people, depending largely upon whether one has invigorated
his skin or has allowed it to become sluggish. One should
remember that the primary reason he wears heavy clothing
in winter is for comfort and not to prevent taking cold.
Indeed, an increase in exercise is a far more efficient means
of meeting an ordinary winter's cold than is the practice of
bundling the body heavily with wraps. Most people make
the mistake of wearing too much clothing in winter, thus
reducing their powers of resistance.

The clothing worn next the skin should be of a character to
absorb the water of perspiration readily. Cotton cloth is an
excellent absorbent and gives the water off again readily.
Woollen, which does not absorb water so readily and is apt to
hold it without allowing sufficient evaporation, should not be
worn next the skin at times when perspiration is abundant.

248 ADVANCED PHYSIOLOGY

In summer weather underclothing should be of cotton or of
tsome good absorbent material rather than of wool. In winter
when the amount of perspiration is less and its evaporation
from the skin a matter of much smaller consequence than in
summer, woollen underclothing is not unwise, although cotton
is entirely suitable. If one passes most of his time in winter
in highly heated rooms, he should wear the same kind of
underclothing that he wears in the spring and fall.

BURNS AND FROSTBITES

Although burns and frostbites are extremely common in-
juries to the skin, either of them may be serious if severe.
Ordinary burns may be simply treated. After the pain has
been relieved by plunging the burned part into cold water or
bathing it with water containing common baking soda, the
application of a little vaseline to exclude the air is all that is
necessary.

If the clothing catches fire, however, prompt action and
more careful treatment are required. Pick up anything at
hand which will serve as a wrapper; a rug, blanket, shawl,
or overcoat will serve. Wrap the person quickly to
smother the flames, throwing him down if necessary and
rolling him over and over in the wrapping material. After
the flames are extinguished remove the clothing from the
burned spots with great care and gentleness, cutting it and
softening it with water if it adheres to the skin. Be especially
careful not to break the blisters that have formed. Then
anoint the burned parts with vaseline, and in all severe cases
summon a physician at once.

Frostbites are generally confined to the fingers and toes,
ears and nose; in other words, to those parts where the blood
flow is least vigorous and where there is a large surface ex-
posed to the cold air. The muscles may, however, be con-
cerned as well as the skin. When a limb is frozen the water
in the blood and muscles is partly turned into ice. If it is

THE SKIN 249

I thawed slowly, the water may resume its former relations
and the body activities continue as before. But if thawed
out rapidly, the water will not return to its normal condition,
and inflammation, together with the final destruction of the
frozen part, may follow. For this reason the treatment of
frostbites or frozen parts, should be such as to cause them
to thaw slowly. Rubbing frozen parts with snow or cold
water is usually recommended, for this will slowly thaw them
with the least danger of injury. The preservation of the
frozen member depends largely upon prompt action although
the thawing must be very gradual. The person should be
warmly wrapped and after normal activities have been resumed,
some sort of hot drink should be administered.

Smallpox, Scarlet Fever, Measles. — These three diseases,
although distinct, are all characterized by skin eruptions.
They are all contagious and all occur as epidemics, many cases
appearing in a community at once. The ease with which one
person takes them from another makes it necessary to isolate
the patients and to quarantine the house they occupy. The
cause of none of these diseases is positively known, although
they are doubtless due to germs of some sort. The only methods
of preventing them are by avoiding association with patients,
and, in the case of small-pox, by vaccination.

Smallpox is the most serious of the three and, formerly pro-
duced frightful ravages. To-day it is largely controlled by
vaccination. It is probably distributed by particles discharged
through the skin. It is to be avoided by keeping away from
persons with the disease, and by vaccination (page 386).

Scarlet fever and measles are also serious. The infectious
material is certainly contained in the sputum and the dis-
charges from the nose of the patient and perhaps in the particles
given off from his skin. To avoid these diseases we must shun
those sick with them, and remember that the infectious material
is dangerous whether moist or dry, and that it may be carriQcJ
upon toys or clothing.

CHAPTER XVI
THE SKELETON

We have seen how foods furnish the body with heat and
act as a source of human energy in general; we may now give
attention to the more permanent forms which foods take as
body tissues, studying especially the skeleton and the mus-
cles, which form the largest part of the body in bulk.

The Functions of the Skeleton. — The function of the skele-
ton is two-fold.

1. It gives firmness to the body; without such a frame*
work, the other, softer tissues would form but a shapeless
mass, with no means of bracing itself for doing work.

2. It furnishes attachments for muscles, and thus makes
motions possible; muscles are so fastened to the bones as to
move them, thus producing movements of the body.

All large animals, except a few living in the ocean (jelly-
fishes, etc.), have skeletons of one sort or another; it is the
only method nature has devised for holding together large
masses of soft tissues and making it possible for them to
work to purposive ends. In some animals, e. g. lobsters, in-
sects, clams, etc., the skeleton is a mere crust on the outside,
and thus is called an exoskeleton ; but the circumstances are the
reverse with all ''backboned" animals, including man, which
are spoken of as possessing an endoskeleton. In the adult
human, the skeleton makes up about 16% of the weight of the
entire body, and comprises about two hundred separate bones;
the child's skeleton contains more because during the process
of growth some bones fuse together. In spite of their number,
the bones are so strongly bound together by tough, stringy
haments and by muscles that the whole skeleton forms a very

fiirm, solid unit; Fig. 120.

250

THE SKELETON

251

For convenience in study, the
skeleton may be considered as
consisting of two parts. (1) The
axial skeleton, made up of the
backbone, ribs and skull, forming
the main axis of the body and
the most rigid part of the whole;
(2) the appendicular skeleton,
or skeleton of the appendages
(arms and legs). In most
animals, e.g. dogs, cats and
horses, both arms and legs are
organs of locomotion; in birds
the front appendages are modified
as wings, while in man they are
not organs of motion, but grasp-
ing organs (organs of prehension).
In man alone the arm and hand
are used for this purpose only
though some of the monkeys use
them for prehension as well as
for locomotion.

AXIAL SKELETON

Spinal Column. — The central
part of the axial skeleton is
called the backbone, or spinal
column. This is not a single
bone but a series of vertebrae, ir-
regular bones placed one on top
of the other and firmly bound to-
gether; Fig. 121. Seven ring-like
vertebrae in the neck are called the
cervical vertebrae; twelve below
these are nearly alike and are

Fig. 120 — Human skeleton

A, Frontal; B, Clavicle; C,
Sternum; D, Scapula; E, Hu-
merus; F, Radius; G, Ulna; H
Carpals; /, Metacarpals; J,
Phalanges; K, Vertebrae; L,
Pelvis; M, Femur; N, Patella;
O, Fibula; P, Tibia; Q, Tarsals;
R, Metatarsals; S, Phalanges.

252

ADVANCED PHYSIOLOGY

)Cervicai

) Dorsal

termed the dorsal vertebrae; five heavier ones in the "small'*
of the back are the lumbar vertebrae.

Although the vertebrae differ in shape and size, each con-
sists of a rounded portion with flat
upper and lower surfaces, the centrum,
on the sides of which arise two pieces
of bone uniting to form the neural arch ;
where these two projections are joined,
they are prolonged into a spine, the
neural process; Figs. 122 and 123.
When the vertebrae are placed on top
of each other, with the spines pointing
backward, the arches are brought over
each other and the openings in the
successive vertebrae, i.e. the neural
foramina, together form a long tube
just in front of the row of spines. This
tube, completely surrounded by bone,
contains the spinal cord, an organ of
great importance and delicacy, which
is thus protected from all ordinary
injuries. When in position in the back
they do not actually touch one an-
other, for between each two is an
elastic pad of cartilage which serves
as a cushion to relieve jars. The
vertebrae are connected by ligaments,
running between every two vertebrae
and thus tightly binding all the parts
of the spinal column into a firm support.
Although the backbone is as a result a
strong structure, it possesses, never-
theless, a certain amount of flexibility. It has the greatest
amount of strength consistent with easy bending of the body
from side to side, or forwards and backwards. The verte-

^acral

(Coccyx
121. — The spinal

COLUMN
Showing the curves and
the separate vertebrae
(Thompson).

THE SKELETON

253

'Dj for Btood vessel

Centrum

Fig. 122. — One of the dorsal verta
br^ viewed from the side

brae are so united as to form a column of bones with graceful
curves (Fig. 121), an arrangement which in itself has more of
the qualities of a spring
than are possessed by a
straight column.

In order that the legs
may firmly support the
heavy body, strong con-
nection of the "hipbones"
to the spine is necessary.
To make this junction
solid, five of the vertebrse
in that region are enlarged
and grown together, form-
ing the sacrum; Figs. 121
and 124. Below this are
four much smaller ver-
tebrse, partially grown
together and called the
coccyx. It is the con-
tinuation of this which
forms the ' tail in some
animals.

The Ribs and Sternum.
— The ribs are a series
of slender arching bones,
attached at one end to
the twelve dorsal verte-
brse, and bending outward
and forward to enclose
the thorax or chest cav-
ity. The lower ribs afford
some protection to the
upper part of the abdo-
men also. After arching around the chest the ribs are

Neural Process

Centrum

Fig. 123. — One op the dorsal verte-
bra VIEWED FROM ABOVE

254

ADVANCED PHYSIOLOGY

Fig. 124. — The sacrum

Consisting of five fused vertebrae at the
lower end of the spinal column.

connected indirectly with the sternum by short pieces of
cartilage; Fig. 101. This material is more flexible and elastic

than bone, thus making it
possible for the ribs to move
freely without danger of
breaking. Two of the lower
ribs on each side, called float-
ing ribs, are very short and
are not attached to the
sternum at all. The thorax,
which contains the heart and
lungs, is thus protected on
all sides by a framework of
bones.

The sternum, or " breast
bone " (Fig. 120), is composed
of three flat, elongate bones, placed end to end; the uppermost
is roughly shield-shaped, the middle bone elongate rectangu-
lar, and the lower one triangular, with the point downward.
They are so closely joined that little movement occurs be-
tween them, and the three are generally spoken of as though
a single piece.

The Skull. — The skull is balanced on the spinal column and
is attached to the top vertebra in such a way that it may be
nodded backward and forward. The joint involved in
turning the head from side to side is that between the first
and second vertebrae. The skull is a complicated arrangement
of bones, twenty-two in all (Fig. 125), so rigidly fitted
together that there is no motion between them, except that
of the jaw bone. Teeth are not a part of the skeleton, since
they arise from the lining of the mouth and because this lining
is essentially the same as the outer skin.

We may consider the skull as made up of three parts.

1. The cranium, a large, rounded box of bones firmly

THE SKELETON

255

united (Figs. 120 and 125) and enclosing a large cavity, is filled
by the brain, the center of all mental activity. The cranium
is made of eight large bones, which in the adult are dove-
tailed together, the lines where they meet being called su-
tures. In childhood,
while the skull is grow-
ing, they are soft and
not so firmly joined,
though they touch each
other. If a young
baby's head be ex-
amined, there will be
found a soft spot in
the middle where the
bones have not yet
come together; Fig.
126.

2. The facial bones,
thirteen in number,
form the face. They
enclose the eyes and
comprise the cheek
bones and upper jaw.

3. The mandible,
forming the lower jaw,
is a single bone hinged to the temporal bone of the cranium,
Fig. 125. The only movable bone in the skull, it is acted
on by powerful muscles attached to each side of the cranium
and is provided with a blade-like extension of its surface, so
that there may be a larger area for the attachment of the
muscle.

It will be noticed that the skull is especially adapted to
the protection of several delicate organs of the nervous system.
The brain itself is entirely inclosed in bones which are so
thick that ordinary blows can not injure it. The eyes are

Fig. 125. — The skull disarticulated

,e. with the bones slightly pulled apart but
retaining their relative positions.

256

ADVANCED PHYSIOLOGY

Fig. 126.— Top of a
baby's skull

Showing the bones of the
cranium not yet grown
together. Upper side of
figure is posterior.

sunken in deep bony pits, formed by the bones in the eye-
brows, nose and cheek which thus ensures them against injuries.

The ears are best protected of all,
since the real hearing parts are
completely inclosed in hard bone
inside the skull, only narrow pass-
ages connecting them with the
exterior.

THE APPENDICULAR SKELETON

The Shoulder and the Arm. — Each
shoulder, or pectoral girdle, is made
of two bones. (1) The shoulder
blade is an oddly shaped, triangular
bone on the back of the shoulder
joint. To this scapula, the upper
bone of the arm is hinged (Fig.
127) and a shallow cavity
in it forms a part of the
shoulder joint. (2) The
collar bone or clavicle,
which is slender and in
such a position as to be
easily broken, extends
from the sternum to the
shoulder joint, thus brac-
ing the scapula; Fig.
120.

The first bone in the
arm is called the humer-
us and extends from the
shoulder to the elbov/,
Fig. 128. Between the
elbow and wrist are two bones, the radius and ulna, the
former on the same side as the thumb. The ulna alone

Seopula

Big. 127.

-The bones that form the

SHOULDER joint

THE SKELETON

257

Carpals

Meiacan

enters the elbow joint with the humerus and is large at that
end. The radius, which merely touches a
projection on the humerus, is large at the
other end and alone makes the real joint with
the small bones of the wrist, the ulna articulat-
ing with but one of these.

In the wrist are eight very small bones, the
carpals, between which very little movement
occurs. Following these is a series of five

Humerus iti elongate bones, the metacarpals, which form the

framework of the
body of the hand.
In Figure 129 these
are seen jointed to
the wrist bones; also
the phalanges, the
bones of the fingers,
two in the thumb
and three in each
finger.

The Hip and the
Leg. — On first ex-
amination, the
skeleton of the hip
or pelvic girdle
looks very unlike
that of the shoulder
girdle; Fig. 130.

One very large and irregular bone is on each
side; it is broad behind wnere it joins the
sacral portion of the backbone; and at the
point farthest from the midline, where the
body protrudes at the hip, it presents a cavity
into which fits the end of the upper bone of

the leg. It curves around to the front and meets the bone

Radius Wl

Uino

Fig. 128.— The
bones of the

ARM

The radius and
ulna are shown
in the position
they assume
when the hand
is held with the
palm down-
wards (in pro-
nation).

FhalaiKjes

Fig. 129. — ^The bones of
the wrist and hand

258

ADVANCED PHYSIOLOGY

■femur

Ilium

corresponding to it on the other side of the body at the
midline. These bones, each called the os innominatum, are
each made up of three bones which though separate in
childhood are fused into one in the adult. Since
the scapula in the young child also consists of
two bones (grown together in the adult), the
two girdles were originally made up of the same
number of parts.

In the leg proper, one long bone, the thigh
bone or femur, extends from the pelvis to the
knee: Fig. 131. Between the knee and the

ankle are two bones,
the tibia and fibula.
The tibia is large at
each end and enters
into the knee and
ankle j oints ; but the
fibula, which is
smaller and on the
outside, has no con-
nection with the
knee joint and little
to do with the ankle.
Indeed though
present in the hu-
man body, the
fibula is entirely lacking in some of the higher
animals.

The ankle is supported by seven small tarsal
bones; Fig. 132. In early childhood there are
eight of these as there are of the wrist carpals.
A series of five elongated bones, the metatarsals,
are joined to the tarsals and form the skeleton
of the body of the foot. The bones of the toes are of the same
number as those of the fingers and are also called phalanges.

ifi/ for
Femur
Pubis

Fig. 130. — The hip, or pelvic

GIRDLE
(The innominate bone) showing it
to be composed of three fixed
bones.

fibula'

Tibic

Fig. 131.—
The bones
OF the leg

From the thigh
to ankle

THE SKELETON

259

Torsaldoaep

STRUCTURE OF BONE

Shape and General Structure. — The shape of bones is de-
signed to render them as strong and yet as light as possible.
Upon the long bones of the arms and legs comes the heaviest
strain, and consequently they are the ones most frequently
broken. Every bone is covered on the exterior with a thin
connective tissue membrane called
the periosteum. This is full of
blood vessels and by means of the
material thus brought to the bone,
new matter is added to it so that
this membrane plays a very impor-
tant part in the growth of the
skeleton.

If a bone is cut open lengthwise,
it will be seen to be hollow through-
out most of its length, while the
bone itself, especially in the middle
of the shaft, is very hard and
tough. This arrangement in a
hollow cylinder is known to give the
greatest amount of strength possible
with the amount of material used.
The ends of the bone which are not
hollow are very much larger than
the shaft, in order to furnish suffi-
cient surface for the joint and also for the muscles, which
are attached to the bone near the end. The larger the surface
the more chance for the attachment of muscles and the
stronger their action. If a bone at its enlarged ends were of
the same dense structure as in the middle of the shaft, the
whole would be very heavy; to avoid this without materially
weakening it, the ends are spongy and porous.

Marrow. — The cavities in the middle of the long bones are

fldatanals

Phalofufef

Fig. 132. — The bones op

THE FOOT
(Thompson)

260 ADVANCED PHYSIOLOGY

not wasted spaces but are filled with a soft yellowish-red sub-
stance called marrow. In addition to much fat, this ma-
terial contains little bodies known as marrow cells, which, as
has been pointed out, produce red blood corpuscles.

Composition of Bone. — Bone itself is composed of two very
different substances: (1) mineral substance, chiefly phosphate
of Hme, which is hard and brittle, and gives rigidity; this is
secreted by cells called osteoblasts, and constitutes about 35%
of the entire body substance; (2) animal matter, a tougher
material than lime, and neither hard nor brittle. Being par-
tially made of organic materials, when a bone is placed in the
fire the animal matter is burned away, leaving the lime only.
The animal matter gives strength and toughness to the bone
so that it is not easily broken ; this substance is called collagen
and makes up about 16% of a bone. Collagen is more familiar
as the material which gives rise to gelatine when bones are
boiled. The rest of bone material (about 50%) is chiefly
water.

Bones of Children and Adults. — The relative amount of
animal matter in the bones of children is much greater than
in those of adults. Indeed, in very early childhood the
bones consist wholly of animal matter and it is not until
later that lime is gradually deposited in them; the bones of
children can therefore be bent considerably without breaking.
This is a manifest advantage, for the numerous falls and mis-
haps which a child suffers would produce many disastrous
results were the bones as brittle as in later life. But for this
very reason it is necessary that the child be taught habits of
holding the body erect and in proper position. If the body
is habitually allowed to stoop, or assume a position which
keeps the bones bent out of their proper form, they will be
almost certain to retain this shape when the lime is deposited
in them and they become hardened. A good straight form with
erect shoulders adds much, not only to a person's appear-
ance but also to his health and consequent happiness in life.

THE SKELETON 261

Any kind of dress which presses upon the bones is sure to
result in deformity. If one wishes health, he should let his
body grow as nature intended and not curb it by confining
it in tight garments. If the boy or girl stands erect and is
not hampered by constricting clothing, the bones will develop
properly. The deformity of bowed legs, however, is not due,
as frequently supposed, to the fact that a child has been
allowed to walk too early. ^'Bow legs" are found chiefly among
poor children, and are caused by a disease called rickets,
brought on by improper food and lack of air and sunhght.

Since so much in the way of body strength and usefulness
depends on the perfect condition of the skeleton, it is simply
a matter of common sense that care should be taken, espe-
cially with growing children, that the diet contain all mater-
ials necessary for bone making. Milk and its products, with
wheat and oat cereals, are valuable in this connection.

Repaii of Broken Bones. — The animal matter in a bone is
the only part of it which is alive, and it is this, therefore,
which effects its growth and repair. Each bone is provided
with tiny blood vessels which enter through small openings
and then branch into numerous vessels, running in every
direction inside the bone and furnishing the living parts with
materials for all necessary repairs. The bone is filled with
myriads of minute living cell bodies, called bone cells, which
have the power of making new bone material when necessary,
and thus of repairing broken bones. If a bone in the body is
broken and the ends are brought together, these living cells
begin at once to unite the two ends, and if allowed to continue
this work undisturbed for a few weeks, will completely join
them, making the bone as strong as ever.

The value of the periosteum, too, in this matter of bone
repair is very great, for, being filled with blood capillaries it
can furnish new material. It has even been shown that the
periosteum, if not disturbed when a bone is taken out of the
body, can replace all the hard parts of the bone.

262

ADVANCED PHYSIOLOGY

During a period when a bone is being repaired it must be
kept perfectly quiet, for any movement would easily tear
ap&rt the newly made materials. Consequently, the surgeon
always binds broken bones in such a way as to prevent motion
of the parts until they are well knit together. The setting of
a hone by a surgeon consists simply in bringing the two broken
ends nicely together and then binding them in proper position.
Since the animal matter in the bones of children is so much
more abundant than it is in adults, it follows that broken
bones are more easily mended in childhood than in later life.
In more advanced years when the amount of animal matter
is further decreased, the bones grow more brittle and are more
easily broken. At the same time they are not so easily re-
paired, because of the scarcity of living bone cells.

Microscopic Structure of Bone Tissue. — Figure 133 shows
a very thin piece of bone highly magnified.^ It consists of

Sfoodl/kyseL

Fig. 133. — Sections thbough bone

^, cross section; B, longitudinal section. Canaliculi are the minute canals radiating
from the elongate, black areas (lacunae). Lamellse are not shown.

groups of concentric rings, arranged around small openings.
These openings indicate the places where canals, running

THE SKELETON 263

lengthwise of the bone, and containing blood vessels have
been cut off; the concentric layers of bone tissue about
these are called bone lamellae. In the living bone these
central openings are occupied by blood vessels. Arranged
in rings around the vessels between the scale-like layers of
the lamellse, are a large number of small, lens-shaped spaces,
called lacunae, each of which shows numerous fine lines radia-
ting from it. Row after row of these little spaces appear
arranged around the central blood vessel, forming larger and
larger rings until they reach similar rings belonging to other
centers.

Each of the little spaces in the live bone is filled with living
matter, which is the remainder of what was originally a bone
cell. Because of the deposit of such mineral matter about it,
the original shape of the cell has become almost unrecogniz-
able. The radiating lines are really minute tubes, canaliculi,
passing from one row of spaces to the next. Since each row
is connected with the next, and since the inner row, by means
of the little tubes, is connected with the central space and
hence with the blood vessel, even the outer row of spaces is
supplied with nourishment derived from this vessel. It is be-
cause the bone possesses so many living cells, so well supplied
with nourishment, that it can be so easily repaired.

CARTILAGE

We have noticed that the ribs are not united directly to
the sternum, but that there is a short piece of softer material
at their front ends; this material is cartilage, a substance
which forms an important part of the skeleton. Early in
Ufe most of the bones are made of cartilage. Even in the
adult some cartilage still remains; e. g. the cushions between
the vertebrae, the supporting pieces around the windpipe
(Fig. 98), the pieces at the ends of the ribs (Fig. 101), in the
joints, and in the outer ear, which consists of cartilage covered
with skin. Cartilage, which is flexible but very tough, is

264 ADVANCED PHYSIOLOGY

much softer than bone and can be readily cut with a knife.
It differs from bone in that it is not suppHed with blood
vessels. Under the microscope a thin piece of cartilage
appears as in Figure 4, page 14. The cells composing it are
far apart, separated by much intercellular substance.

When, in early Ufe, certain cartilage masses begin to turn
into bone, the change does not take place throughout the
cartilage uniformly, but at certain points only, called centres
of ossification.

Cartilage is not so readily repaired as bone, but on the
other hand, it is not so easily broken. A broken rib is quickly
mended in a few weeks and is as good as ever, but if the injury
breaks or tears the cartilage, its mending may take a long
time.

JOINTS

When two bones are fitted together in such a way that
there is no movement between them, as for example, the
bones of the cranium, the line of joining is generally called
a suture joint; where movement is possible, a joint is said
occur. Of the true joints there are two kinds, imperfect and
perfect.

Imperfect joints are those in which the bones concerned do
not actually glide over one another although a certain amount
of movement is possible because of the flexibility of the elastic
cartilage between them. Such joints are noticed where the
front ends of the ribs approach the sternum; movement takes i
place at every breath, though it involves only bending the^
cartilages which occur there. The bending and slight torsion
which may take place between any two vertebrae also illus-
trate the action of imperfect joints. Perfect or movable
joints are the sort generally thought of as joints and occur j
where the end of one bone actually turns on some part of the]
surface of another.

THE SKELETON 265

As will be pointed out later (page 275), the muscles which
produce bending are not necessarily located near the joint
they operate; such an arrangement would often result in a
difficult and bungling sort of movement.

Since accidents at movable joints are always likely to be
serious because they are apt to cause stiffness, we shall ex-
amine one or two carefully in order to learn their mechanism.
Perfect joints are of several different kinds, but most of them
are modifications of three simple types: the hinge joint, the
ball-and-socket joint and the pivot joint.

The Hinge Joint. — In the hinge joint the bones are able to
move back and forth in one direction only, like a door on
hinges: the knee, the elbow and the joints of the fingers are
good examples. Since all hinge joints are very much alike
in structure, the description of one will show the salient
features of all.

The knee joint is made up of the femur and the tibia bones;
Fig. 131. The lower end of the femur is large and rounded
in one direction at the end, while the upper end of the tibia is
sHghtly hollowed on top; when the bones are placed together,
their shape permits movement only in one direction. The
rounded ends of both bones are covered with a thin layer of
cartilage, making movement easier. Two separate ring-like
cartilages, the semi-lunar fibro-cartilages, one on the outside
and one on the inside of the leg, furnish extra padding to
relieve the body of jars, and also fill up the spaces, making
the joint more compact. In the living joint, there is wrapped
around the ends of the bones the synovial membrane, which
secretes into the joint a liquid, the synovial fluid, the purpose of
which is to moisten the surfaces and prevent friction. The
free motion of the joint is dependent upon the presence of
this fluid and if for any reason the membrane ceases to secrete
it, friction develops, motion becomes difficult, inflammation
sets in, and eventually the bones are likely to grow together
aft4 the joint to become stiff. All of the parts are evidently

266

ADVANCED PHYSIOLOGY

designed to make the movements of the bones upon each
other smooth and free, with the least possible friction.

The bones are bound together by tough bands called liga-
ments. At the knee joints there are several (Fig. 134);
there is a pair of short ones, the crucial ligaments, run-
ning directly between the ends of the bones and crossing each
other like the parts of a letter X. More important are those
outside of the joint and extending over it from one bone to
the other. On either side there is a lateral ligament, attached

to the femur and
extending down to
the sides of the upper
parts of the tibia and
fibula. Another, the
posterior ligament, at
the back of the joint,
is attached to the
same bones. The
anterior ligament (in
front) is different
from the others in
having in the middle,
a rounded, flat disc
of bone, called the
knee cap, or patella,
strengthening the
joint and protecting
the more delicate
parts within from injury. There is another, rather irregular
ligament, called the capsular ligament, larger than the others
and partly covering them all, like a sac wrapped around the
bones and fastened to the lower end of the femur and the
upper end of the tibia.

The other hinge joints in the body differ from that at the
knee only in slight details. The exact position and number

Fig. 134. — The knee joint

A shows the exterior ligaments. B shows the joint

with the external parts removed. (Thompson)

THE SKELETON

267

Peht'c Girdle

of ligaments vary in them, and no other joint has a bone in
its ligaments like the knee cap. But they all have the same
smooth, rounded surfaces, the synovial membranes and
fluids, the ligaments and muscles to complete the joint,
and are all, of course, bound together on the outside by
the skin.

Ball-and-Socket Joints. — There are only two typical ex-
amples of ball-and-socket joints, one at the shoulder and the
other at the hip. As the name indicates, one bone in such a
joint ends in a rounded, ball-like head, while the other pre-
sents a concave socket
into which the ball fits.
In an arrangement of
this kind the motions
of the bones are not
confined to one direc-
tion, giving greater free-
dom of motion, but less
strength, than the hinge
joint.

Three bones enter in-
to the shoulder joint,
though only two of them
are of much importance.
The humerus, the upper
bone of the arm, has at
its upper end a good sized, rounded head fitting into a
socket made by a concave part of the scapula; Fig. .127
This cavity is very shallow but in the living body there is
a little rim of cartilage around its edge, making the socket
deeper, and the joint, therefore, somewhat more secure.

It will be noticed from the figure that two little projections
of the scapula hang over this socket: while these do not form
a part of the socket proper, they protect it from injury above
and in front. It is evident that when the arm bone is lifted,

Fig. 135. — The hip joint

%S ADVANCED PHYSIOLOGY

it will soon hit these projections, and its movement in that
direction will consequently be stopped. The round ends
of the bones are rendered smoother by being covered with
cartilage, as in the hinge joint, and a membrane around the
joint secretes a synovial fluid for moistening the joint and
reducing friction. The bones at the shoulder joint are bound
together by ligaments, but these are not so numerous as at
the knee joint. The only important one, the capsular liga-
ment, is attached to the scapula around the socket, and then
extends out over the head of the humerus in such a way that
it has a wide, extended fastening to that bone. It is so loose
as 'to make it possible for the bone to move in any direction
without hindrance. If it is cut the bones come apart at
once.

The ball-and-socket joint at the hip differs from that at the
shoulder, in that the muscles are much more massive and
powerful and the socket is much deeper. The joint is thus
firmer but has less freedom of movement; Fig. 135.

Pivot Joints. — In the case of a pivot joint, the two bones
concerned rotate on one another. In the movements of the
head, for example, all forward and backward tilting occurs
between the occipital bone of the skull, and the first, or atlas,
vertebra, the joint there being essentially a hinge joint. All
turning from right to left (not tilting from side to side) occurs
between the first, atlas, and second, or axis vertebra, one
bone rotating on top of the other and thus forming a pivot
joint. The turning of the radius bone of the lower arm on
the end of the humerus bone of the upper arm is another good
example of a pivot joint; Fig. 128.

INJURIES TO JOINTS

There are two kinds of accidents, not counting broken
bones, which occur, and frequently occur together, in joints.
These are sprains and dislocations.

Sprains. — A sprain is due to the stretching of some of the

THE SKELETON 269

ligaments in the joint to such an extent that they are more or
less torn, a condition followed by considerable pain and in-
flammation, accompanied by swelling. The injury may be
only a slight strain or it may be a severe rupture of the liga-
ments, more serious than a broken bone, requiring longer to
heal, and being more likely to result in permanent injury.
The best treatment is to place the joint in the most com-
fortable position and then apply, first, hot water (as hot as
endurable), then, cold water. The joint should then be tightly
bound in bandages. It is well to rest the joint, but the im-
pression that it should not be used until it is healed is a mis-
taken one, for this is likely to increase stiffness and make the
joint useless for a very long time. Indeed, a sprain heals
more quickly if the joint has some exercise, and after a day or
so, when the first inflammation has subsided, it should be
exercised frequently, and used as soon as possible. This
treatment is a little painful, but it results in making the joint
usable much sooner than the old method of completely
resting the joint until the sprain is healed.

Dislocations. — A dislocation occurs when the bones in a joint
are pulled out of position, as, for example, when the humerus is
pulled out of the socket at the shoulder, or the end of the femur
is pulled out of the depression in the tibia, in which it naturally
rests. The first thing to be done is to pull the bones back
into position. This usually requires the skill of a surgeon,
unless the dislocation should occur in one of the small joints
of the finger, which is easily put back into its proper place.
Since a dislocation is almost sure to be accompanied by a
strain and rupture of the ligaments, it should, after the bones
ire put back into position, be treated just like a sprain.

THE CARE OF THE FEET

That the feet may be a source of great discomfort many
iople are aware; but that health is closely connected with
16 condition of the feet is not so generally recognized. To

^270 ADVANCED PHYSIOLOGY

preserve one's health, exercise is necessary; no one can main-
tain his body in good condition for many years without it.
It is difficult to think of any real exercise in which the feet do
not take some part. Walking, which is about the mildest
form of exercise, is of course absolutely dependent on the con-
dition of the feet. If they are uncomfortable when one
stands or walks he will stay at home as much as possible, or
will use conveyances instead of his own muscles. He will
become more and more indisposed to exercise and out-door
life generally, and his health will inevitably suffer. As much
attention should therefore be paid to foot wear as to clothing
for other parts of the body, and there is no reason why one
should not retain through life feet which will be a comfort,
instead of a painful hindrance and an agent limiting him in
all his physical activities.

Climate and modern customs compel us to wear shoes,
but the barefooted child of summer time is still the one who

experiences the greatest
comfort, and whose feet
teach us what we all need
to know as to the shape
of shoes. Fashion, rather
than health or comfort,
has dictated the shapes
Fig. 136.— The bones and ligaments of our shoes, and there
OF THE FOOT are few people who do

To show the arch of the instep. (Modified from ^^^ ^^^^j. '^^ consequeUCe.
Thompson) *

Practically all defective
feet, save those improperly shaped from birth, are due to
badly patterned footwear.

All common troubles of the feet have to do either (1) with
the skin, or (2) with the bones and Hgaments in the foot skele-
ton. The most common skin deformities causing pain are
corns and bunions. Even though the shoe is properly
shaped, if it fits too loosely or too tightly, corns are the al-

THE SKELETON 271

most inevitable result. If the shoe is too tight, a slight
amount of rubbing will irritate the skin and provoke the
growth of corns; if the foot moves inside the shoe at each
step^ it of course rubs on the leather, and in nature's effort
to counteract this, a callous spot is formed which grows con-
stantly thicker. Tight and badly shaped shoes have a still
more unfortunate effect on the small bones of the toes and
ankle, forcing these into unnatural, strained positions. To
appreciate this, the free, unconfined foot should first be
studied. Between the heel and the ball (Fig. 136), the fool
does not touch the ground, save along its outer border and
there only slightly. Moreover, on the ball of the foot the
weight falls largely on the sides, i. e. just back of the grea
and little toes. There is, thus, one longitudinal and one
transverse arch in the foot. These act as springs: when one
steps, the weight of the body is first thrown on the long arch
(on the one between the heel and the ball); as one rises on
the toes in going forward, the weight is transferred to the
transverse arch; and as it flattens, the foot should be able to
spread a little, and all the toes, each separately, to take an
active part in pushing the load ahead.

It is thus very easy to see what high heeled shoes mean to
the long arch; they mean that the weight will be thrown for-
ward onto the ball, the Hgaments at A (Fig. 136) will be
strained, and all the bones in the ankle will be forced into
unnatural positions with consequent strain on those liga-
ments. In connection with the long arch it should also be
j noticed that if one " toes out '' excessively in walking, the
1 weight, as one leans forward, is thrown on the inner side of
i the long arch, which has no support at all, save that of the
muscles and ligaments. The weakening of the ligaments or
; muscles concerned in the long arch, whether through badly
j shaped or high heeled shoes, faulty position of the feet, oi*
I lack of exercise, leads to a very Dainful condition called

272 ADVANCED PHYSIOLOGY

foot down flat on the ground and causing the nerves and
muscles to suffer .much under unnatural strains.

To avoid the misfortune of a flat foot one needs to acquire
the habit of "toeing in" slightly. If a person practices rising
on the toes a few times each day, and in thus rising throws the
weight first on the little toes and then on the great toes, and
also learns a method of walking — like the Indians — with toes
pointed straight forward or a little inwards, he will generally
avoid ''flat foot" and broken arches. This method of walking
is best acquired by throwing the hips slightly forward with each
step.

Narrow-toed shoes affect the transverse arch in front. If
the toes forming this arch are crowded and confined, there is
nothing for them to do but to press mechanically upon one
another or be displaced; and when the weight is thrown for-
ward on the toes, if these cannot spread, they bind or are
forced to cross one another.

A tight shoe incidentally interferes with circulation in the
foot, which, of course, means the inadequate nourishing of
all the tissues concerned, and in winter especially makes
cold feet inevitable. Discomfort in any part of the body
signifies that there is nervous irritation there, and waste of
nerve energy in any one organ means that less will be avail-
able for the rest of the body.

A healthful shoe should, therefore, have low heels, should
conform to the shape of the foot, should not be so tight as
to pinch, should be made of yielding upper leather so that
the toes may be moved, and should fit in such a way that the
" breaking in " of the shoe will not be a necessary and dreaded
experience. Common sense and public sentiment are de-
manding that such shoes be manufactured more and more
extensively nowadays, and they can be obtained if one will
insist upon comfort and health, instead of fashion and false
notions of elegance.

CHAPTER XVII

MUSCLES

C/avK/e

While the skeleton is the hardest part of the body, it is not
the most abundant tissue and does not require so large a part
of the food materials for its building or maintenance as do
the muscles. The skeleton gives the body its general shape,
but the bones are of use only because of the muscles attached
to them. Life, of course, could not continue if we lacked
the abihty to move, and even though the internal organs of
breathing and circulation are in good condition, there is no
more pitiful sight than that of a person whose limbs are
withered or whose muscles are paralyzed.

Muscles make up the heaviest part of the arms and legs,
of the shoulders and hips. They occur in the trunk of
the body, both in
front and behind.
The heart, arteries
and veins are chiefly
composed of muscle
tissue; the tongue,
oesophagus, stomach
and intestine are also
largely muscular. In
short, about 44% of
the whole body is
made of muscle cells,
and most of the food
taken into the body
is used in building them up, and in furnishing them ma-

K rials on which they constantly draw while doing work.
„3

i//na
Fig. 137. — The arm (Semi-diagrammatic)

Showing the relations of the biceps muscle. From
the figure it is evident that if the muscle contracts
slightly the fore arm will be lifted over a great
distance.

274

ADVANCED PHYSIOLOGY

Although muscle is usually thought of merely as muscle,
there are three different kinds: striped, smooth or unstriped,
and cardiac. This division is made both on the basis of their

microscopic structure
and of their mode of
action.

Peci'oralis

STRUCTURE OF
STRIPED MUSCLE

"ijluhus

Striped muscles in-
clude aU those over
which we have con-
trol, and which are
attached to bones.
A good example for
study is the biceps
muscle in the upper
arm.

The biceps muscle
is shown in its natural
position in Figure
137. It is a long mass
of flesh, large and
reddish in the middle,
and tapering at the
two ends into a
dense, whitish band,
called a tendon. The
middle portion, the
muscle proper, is
alone capable of con-
traction; the tendon simply fastens the muscle to the bone.
A tendon is made of the same material as that of which
ligaments are composed; ligaments unite hones to hones, and
tendons unite muscles to hones. No muscle is united directly

Fig.

Sar^rius

T38. — The chief superficial muscles

ON THE UPPER PART OF THE BODY
(Thompson)

MUSCLES 275

to a bone; there is always a tendinous tissue between them,
although it may not be noticeable. On the other hand
the tendon may be very long; for example, some of the mus-
cles which move the fingers are near the elbow; Fig. 138.
The advantage of this is obvious; for if the muscles were lo-
cated in the parts used, these would be unwieldy and large.
Imagine the size and awkwardness of the fingers for example,
if all the muscles concerned in their work were located im-
mediately in them. The muscles which operate a bird's leg
and toes are placed high up on the leg among the feathers.
The leg of a wading bird, hke the flamingo, is a striking ex-
ample of this contrivance for obviating cumbersome mechan-
ism and allowing freedom of movement. The tendons are
popularly called cords. The wrist is little more than a bundle
of such cords around the bones.

As Figure 137 shows, the upper part of the biceps muscle
is attached at the shoulder by two tendons (whence the
name biceps), while the lower end is fastened by a tendon to
the radius bone below the elbow joint but not far from it.
A sHght shortening of the biceps will, therefore, lift the arm
through considerable distance.

Microscopic Structure of Striped Muscle. — If a muscle be
cut across, it will be found to consist of small parts, called
fasciculi, closely bound together, and giving a " grain " to
the muscle like that in a piece of raw steak. If one of these
fasciculi be pulled to pieces and examined with a microscope,
it will be found to consist of a large number of minute threads,
or fibres; Fig. 139.

These muscle fibres, which are too small to be seen with
the naked eye, always run lengthwise but do not usually
extend the whole length of a muscle. These fibres are cylin-
drical bodies, traversed by fine cross lines, or striae, which
gives rise to the name " striped muscle." Each fibre consists
of an outer tube, the sarcolemma, and a jelly-like substance
within. It is this soft material in the tube which is the

276

ADVANCED PHYSIOLOGY

Muscle Fibre

active part of the muscle, the sarcolemma itself having noth-
ing to do with its movement. A muscle, therefore, con-
sists of thousands of minute
fibres, each able to contract,
bound together in bundles to
form fasciculi.

Tendons, ligaments, sarcolem-
ma, periosteum — ■ all belong to
the body material called connec-
tive tissue. It is always fibrous
or membranous in structure, and
is so abundant that it has been
said that if all other tissues were
dissolved away, the shape of the
body would still be perfectly
preserved.

Blood Supply to Muscle. — Into
each muscle enter one or more
arteries which divide into minute
branches and finally end in a set
of capillaries (described in a pre
vious chapter; Fig. 80). In this
way each individual muscle fibre
is in contact with blood vessels
and from them obtains its nour-j
ishment — necessitated by the
activity of the muscles. If ai
muscle is soaked in water for a
while, the blood will filter out and
leave the muscle nearly white.
Contraction of Striped Muscle. — When a muscle contracts
the two ends are simply drawn toward one another, while a
corresponding swelling occurs at the middle of the fibre. The
muscle does not really become any smaller, but merely shorter
and larger around; Fig. 140. It is evident from Figure 137 that

NucUm i^

Tendon t, mi-

Fig. 139. — Two muscle fibres

With tendon fibres attached at their
ends.

MUSCLES

277

the shortening of the muscle will lift the arm. After the arm
J has been thus lifted, the muscle may remain contracted for
a time and the arm held up, but it requires a constant effort
to keep the muscle contracted, and just as soon as the effort
ceases, the arm falls of its own
weight. The muscle has no
power of forcibly lengthening
and pushing the arm down, but
as the arm falls, it pulls out the
muscle to its elongated form
again. On the back of the arm
is another muscle which acts in
opposition to the biceps, these
two muscles thus forming a pair,
each of which produces an
action opposed to that of the
other. They cannot both act
at once.

Nerve Control of Voluntary
Muscle Action. — While there are
some muscles in the body (the
heart, for example) which perform
very regular, apparently spon-
taneous contractions, all the body muscles are more or less
under the influence of nerves, and the striped muscles act
only when stimulated by the brain or spinal cord. It is
because they are under the control of the will that they are
called voluntary muscles. If a single muscle contracts, it
produces motion of a single bone in a single direction. The
motions of the body are, however, rarely simple, but
generally very compHcated. In the process of walking
nearly a hundred muscles are first contracted and then
relaxed in regular order. In throwing a baseball, nearly
all of the three hundred muscles of the body are brought
into use to some extent, and the remarkable thing is

Fig. 140.— Diagram

Showing that the muscle shortens
though it does not change its bulk
when it contracts.

278 ADVANCED PHYSIOLOGY

that each muscle must be contracted to just the right
amount at just the right moment, or the ball will go
wide of the mark. To insure the harmonious action of all
these muscles so that the ball will go exactly where it is in-
tended, requires a most wonderful control. One does not,
of course, have any consciousness that he is regulating all
these muscles. He simply decides to throw the ball, but the
brain unconsciously so regulates the stimuli sent to the
muscles that they act in the order to produce the desired
result. "Practice makes perfect," simply because the brain
has had the opportunity of learning to exercise this wonder-
ful control over the actions of the numerous muscles.

Tetanus of Striped Muscles. — The term tetanus, although
not so familiar, has much the same meaning as the word
"cramps." When one keeps a muscle contracted as, for
instance, when he holds a weight at arm's length, he does
this by sending stimuli into the muscles very rapidly, ten to
twenty per second — so rapidly that the muscle does not have
time to relax between the successive stimuli. As long as
these stimuli continue, the muscle remains contracted, i.e. in
a condition of tetanus. All of our muscle actions are really
of this character. Sometimes, when a muscle is tired and
perhaps quickly cooled by plunging into cold water, it is
thrown into a similar state of contraction or tetanus without
one's willing it or being able to stop the contraction. We
then call it " cramps," but it does not differ from ordinary
tetanus, except that it is not voluntary.

Effects of Heat and Cold on Muscle Action. — A jockey
drives his horse a couple of miles or so before putting him into
the race '^ to get him warmed up," and athletes for the same
reason take some gentle exercise before undertaking the
actual contest.

Whether the benefit of these preliminary exercises is
really due to the warming of the muscles or to an increased

MUSCLES 279

circulation may be open to question, but there is no doubt
that muscles function best when warm. Experiments with
cold blooded animals, like the frog, show that their muscles
will contract and relax five times as rapidly when warm as
when cold. When cooled to 40° F., they will not contract at
all, a condition known as cold rigor. On the other hand, if
raised to a temperature much above 104° F., they become
stiff and will not contract, a condition called heat rigor.
The effect of heat upon the muscles of warm blooded animals
is essentially the same. The numbness of the human muscles
when chilled excessively is an illustration of the effect of cold
which has come within the experience of almost everyone. The
muscles of warm blooded animals can contract at a somewhat
higher temperature than can those of the cold blooded variety,
and it does not take so low a temperature to stop their action.

Fatigue of Striped Muscles. — When one is tired and it be-
comes more and more of an effort to make the muscles of the
body contract and accomplish tasks, it is not primarily due
to the fatigue of the muscles themselves but to that of the
nerves. The muscle itself, however, on account of changes
which take place in it after doing a large amount of work may
become fatigued. The factors which enter into the phe-
nomena of fatigue are not all thoroughly understood, but a
common supposition that weariness in muscles is relieved by
merely feeding them, by stopping for a meal, for instance, is
certainly erroneous. Not only is the food not at the dis-
posal of the muscle for a period of several hours after it is
eaten, but it has been proved that a muscle can recover to
a considerable extent from fatigue, even when no blood at all
is flowing through it.

Main Voluntary Muscles in the Body. — Figure 138 shows
the distribution of some of the principal muscles on the ex-
terior of the body. There are more than three hundred
voluntary muscles, some large, some small, some short and
some long. They are commonly enlarged in the middle and

280 ADVANCED PHYSIOLOGY

fastened by tendons at the ends and generally extend between
two bones, moving one upon the other when they contract.
The muscles are generally arranged in pairs, one muscle of
the pair acting in opposition to the other. This is necessi-
tated by the fact that muscles cannot push the bones, their
sole power being that of contraction.

Muscles are usually so attached to bones that a short con-
traction of the muscle will produce a much larger movement
of the bone. For example, it has been seen (Fig. 137) that
the biceps, by shortening an inch, will lift the hand several
inches. This gives great freedom and quickness of motion.
A few muscles, however, are fastened in such a way that the
muscle contracts through a greater distance than that through
which the weight is moved; this gives greater strength, but less
movement. An example of this type of arrangement is seen in
the "calf^ muscle of the leg, when one rises on the toes; Fig. 2.

STRUCTURE OF UNSTRIPED MUSCLE

Unstriped muscles include all those in the walls of the
oesophagus, stomach and intestine, those in the arteries and
veins and in the contractile parts of the kidneys, ureters and
bladder. Unstriped or plain muscles are not attached to
bones and are always found in the walls of hollow organs.
Although, like striped muscles, they appear to act only when
stimulated by the nerves, they cannot be controlled through
the will and are, therefore, called involuntary muscles. Since
they are unattached and in sheets, e. g. those surrounding or
running lengthwise of the oesophagus, they have no tendons.

Plain muscle is composed of very small cells or fibres each
with a single nucleus; Fig. 8, page 16. One of the greatest
differences between plain and striped muscles is in their modes
of contraction. Smooth, or plain muscles contract very
slowly, several seconds often being required for a single con-
traction, and they may remain contracted for some time.
Voluntary muscles, on the other hand; act very quickly both

MUSCLES 281

when contracting and when relaxing. Because involuntary
muscles act so slowly they are very easily thrown into a con-
dition of tetanus. Indeed, so slow is their response to stimuli
that in some forms of smooth muscle, one stimulus in five
seconds is sufficient to prevent the muscle from relaxing at all.

It is a great gain to us that so many muscles as are present
in the entire digestive, blood, and excretory systems can perform
their daily and nightly work without any thought or bidding
on our part, and without error in time or rate.

Curiously, however, smooth muscle has a disposition to
act with apparent spontaneity. If a bit of the circular
muscle of the intestine of some animal be cut out, hung up
by one end and stretched by a light weight attached to the
other, it will very soon lift the weight and then relax again.
The muscle makes these movements over and over again
without any stimulus and they continue until the muscle is
exhausted or until its unusual exposure results in its death.

Isolated from the body in this way, the muscle can plainly
receive no stimulus from the brain, and, although different
kinds of smooth muscle act very differently in this respect,
they all have this power of spontaneous movement when en-
tirely disconnected from the central nervous system. Whether
or not there resides among the muscle cells some nerve in-
fluence which is the exciting agent is still an open question.

Although in many respects striped and unstriped muscles
act differently, yet in others their relations are the same.
Both seem to require the stimulus of nerves to make them
contract although in one case the contraction is voluntary and
in the other involuntary. Both can be thrown into tetanus
by repeated stimuli. Both are affected by heat and cold in
the same way. Both become fatigued from long action.

CARDIAC MUSCLE

The muscles of the heart are unUke any others, although in
structure as well as in action they have some points of simi-

ADVANCED PHYSIOLOGY

larity with striped and unstriped muscles. The cells com-
posing them are an elongate rectangular in form, and the
fibres made up of these cells show irregular striping; Fig. 141.
In its action cardiac muscle is unique in several ways; it
acts quickly, though not as rapidly as
the ordinary striped variety. Unlike
either striped or unstriped muscle, it
always contracts to its shortest possible
length, no matter how weak the stimulus
applied to it. It can ''beat" when un-
connected with the brain, but even then
it apparently depends for its impulse
upon nerve cells in its own tissue.

Cardiac tissue is unique in that it can-
not be thrown into tetanus. As has
already been noted, this condition is
usually provoked by the rapid recurrence
of some stimulus. In heart muscle, how-
ever, two succeeding stimuli do not pro-
duce any larger contraction than one,
and if another is applied just before
the muscle begins to relax, it has no effect. As soon as;
the muscle really begins to relax, it becomes open to stimu-
lation and if irritated will begin a second contraction before
it has fully relaxed from the first. Hence, no number of
repeated stimuli can induce tetanus in cardiac muscle; it
must begin to relax before it becomes responsive to any out-
side influence.

USE OF MUSCLES

Effect of Use. — It is a fact almost too trite for mention that
the activities of both work and play tend to strengthen the
body. But increased strength is only one of the benefits
derived from the use of the muscles. When muscles are
active, all the other organs of the body are affected, an(J

Fig, 141. — Cardiac
muscle cells

MUSCLES 283

while the size of the muscles is generally noted as proof ot
the beneficial effect of exercise, perhaps greater stress should
be laid on the toning up of all the internal organs, which re-
sults when they have been supplying the active muscles with
energy and clearing away the debris resulting from "wear
and tear."

Unlike inorganic substance, muscle increases instead of
diminishing in size with use. This is true of other living
matter also, e. g. brains, which grow with exercise. No one
can explain this characteristic of muscle fibre, though it is
inherent in the nature of the substance.

Effect of Disuse. — The result of failure to use muscles is
just the reverse of the effect of use, i. e. they grow smaller and
weaker, and less perfect control of them is possible. Some
of the peoples of India believe it a religious duty to hold
their arms still and have continued to hold them so until they
have become stiff and useless, the muscles losing absolutely
all power of contraction. Although in civilized countries,
one rarely sees such complete loss, a partial loss of power is
common among all classes of people. Children in their play
are pretty sure to use all their muscles and are likely to de-
velop them uniformly, but an adult is rarely as capable of
free action as a child. As one grows older and becomes
quieter, some of the muscles always suffer from disuse. If
he uses trolleys and elevators, the leg muscles suffer, and the
adult may lose the power to walk as far as the child. The
right hand is used so exclusively that the muscles of the left
become weak. The habit of sitting in comfortable reclining
chairs gives the back muscles too little exercise and they
often become so weak that it is really difficult for one to sit
upright for a very long time without some sort of support.
Some people use the laughing muscles so seldom that at last
they can scarcely be brought into action. Examples are
numerous, for few persons use their muscles in such a way as
to produce uniform development. Every one should re-

284 ADVANCED PHYSIOLOGY

member that each muscle he fails to use will become weak and
degenerate.

Need of Exercise. — The great value, indeed the necessity,
of exercising the muscles in order to retain good health is,
therefore, evident. It is hardly necessary to advise the
average school boy or girl to take exercise, for the plays of
childhood usually furnish plenty of it. But when the boy
or girl outgrows childish habits, and becomes a serious stu-
dent, or goes to work at some routine employment, there is
always the danger of poor bodily development. The time
between childhood and maturity is the period when sufficient
exercise is especially necessary to force all the muscles into
proper, harmonious growth. When a person has out-of-
door work to do, or indeed any work which requires con-
siderable muscular activity, he does not need to think of
exercise. But in modern city life, young people have com-
paratively little opportunity for muscular exercise and are
almost sure to suffer from the lack of it unless particular
attention is given to the matter. It is for this very reason
that gymnasiums have been established in schools and else-
where, and they should be patronized by every person whose
business is not such as naturally to involve exercise.

Exercise should not be violent. It is of no advantage toj
try to lift heavy weights, or to do difficult feats in the gym-
nasium. Indeed, such exercise is liable to injure youngj
people. We have noticed that the bones of children are not
all knitted together, and the severe strains from attempting]
difficult exercise and lifting heavy weights are apt to do per-
manent injury to the incompletely fused bones. Athletic
contests are certainly useful, but the tendency nowadays
toward excessive exercise in one line rather than the general]
use of all muscles results too often in unreasonably over-
taxing one's strength. Though the results of the straining
may not be evident until long after its occurrence, whenj
they do appear in later life, the person finds himself a per-'

MUSCLES

285

manent invalid. Exercise is useful and necessary, but ath-
letics are frequently harmful in their effect on the body.

Exercise for the Student. — The person who usually needs
the most emphatic advice as to exercise is the one who is
ambitious to become a scholar. He much prefers to remain
at his books, though he above all others should be the one
to take regular recreation. He who studies all the time is in
the end outstripped, even at his studies, by the one who plays
as well as studies. No one can become a scholar who neglects
to develop his body while cultivating his brain. He will be
likely to find in a few years that he must give up study al-
together because his body has been allowed to become we^k
while carrying out the dictates of his brain. Colleges have
been forced to make gymnasium practice a part of the stu-
dent's regular work in order to
counteract his tendency to shut
himself up with his books.

Kind of Exercise. — Exercise is
always most beneficial if it is
pleasant; exercise merely for the
sake of using muscles is sure to
become irksome. Hence, games
of base- ball or tennis, rowing or
bicycling in the country are
preferable to gymnastics or hard
work at a required occupation.
The mind needs its recreation,
as well as the body its exercise.
Out-of-door games are best.
Bicycling is an excellent ex-
ercise, although attempts to take long rides are mischievous,
and the habit of stooping over the handle bars and "scorch-
ing'^ is extremely bad. Horse-back riding and walking are
also good, but walking for exercise should be varied by some
running or rapid walking up hill, so as to make one somewhat

Fig. 142. — Diagram

Showing the effect upon the poise
of the body produced by improper
standing posture. The dotted line
represents the backbone.

286

ADVANCED PHYSIOLOGY

Fig. 143. — Diagram

Proper and improper sitting postures

breathless, for the lungs need exercise as well as the muscles,
and a quiet walk does not give them as much as they need.
The amount of exercise should be equivalent to at least a three-
mile walk each day. When it is possible, one should not take

it till two or three hours
after eating.

Everyone admires a
person with an erect car-
riage and a good form.
This always means grace
and easy motion, and it
also means good health.
A good figure is more de-
pendent upon the con-
tinued use of the muscles
of the whole body than
upon the actual shape of the body. It
is the constant exercise that they are
required to take that gives the West
Point cadets their splendid bearing.

One of the most common defects is
that of round shoulders; Fig. 142.
This results, primarily, from the mere
failure to keep the shoulders back and
the head erect. Nothing is more fatal
to grace and good general appearance
than this deformity and many a per-
son whose face is not handsome makes
a very pleasing impression because of
a graceful form due to a perfectly up-
right head. ''Head erect, shoulders
back and chin in" are three simple
directions for good carriage. Standing and sitting erect
are the means for developing a sound, handsome body, and
using hammocks, recUning chairs, and leaning against sup-

f iG. 144. — Diagram

Showing the curvature
produced by carrying a
parcel of books under the
arm. To avoid this result,
if books are carried under
the left arm one day,
t^ey should be carried
under the right arm on
the next, and vice versa.

MdSCLES 287

ports when standing are the common habits responsible for
many crooked, wrongly developed figures; Figs. 143 and 144.
All powers that are not used are soon lost, and a perfect body
requires the harmonious development of all its muscles, without
the excessive development of any at the expense of others.

DISEASES OF MUSCLES AND BONES

The tuberculosis bacillus sometimes attacks the bones,
especially at the joints, producing serious conditions such as
hip-disease. Frequently a trouble called rheumatism appears
around the joints and interferes with their ready action.
It is frequently an ailment of persons beyond middle age,
though it is not uncommonly found among young people.
Its cause is not yet known nor any method of preventing it,
except to avoid too rich a proteid diet.

Tetanus, commonly called lock-jaw, is an extremely serious
disease, which is characterized by a peculiar state of the muscles.
It is caused by a well known bacterium which
lives in the soil; Fig. 145. If a person receives ""^^^^
an injury from an instrument that has been ^jA
lying on the ground, a rusty nail, for example, '

some of these tetanus bacilli may enter through Fig. 145. —
the wound. Many cases of this disease have Tetanus
followed wounds from toy pistols and other fire- bacilli
works on the Fourth of July. If these bacilli that^To-
get into the body, they grow and multiply, ^^ce lock-
producing one of the most deadly poisons ^^^*
known, which is absorbed by the blood and carried over
the body. The most noticeable symptom is that the
jaw muscles contract so tightly that the mouth can-
not be opened, hence the name lock-jaw. The muscles
i in the rest of the body soon undergo a similar con-
traction. The disease is extremely painful, and prac-
tically always fatal. No sure remedy for tetanus is known,
though an antitoxin somewhat like that used for diphtheria

288 ADVANCED PHYSIOLOGY

is now used successfully in many cases. The best method of
combating this disease is by preventing it. If wounds are care-
fully cleaned so that no germs are left in them, the danger is
removed. A deep wound made by a dirty object should be
cleansed and disinfected with particular care. It is always a
risk not to put such a wound in the charge of a physician.
The deeper the wound and the more dirt which gets into it,
the greater the danger.

It is becoming common procedure nowadays to inject
with tetanus antitoxin those who have received deep wounds
made by dirty objects, or indeed any wounds that have not
been treated from the start with some disinfecting agent.
This plan prevents the development of tetanus from such wounds
and is far more likely to be successful than to try to cure a case
after it has developed. Enormous quantities of this antitoxin
have been used for this purpose with the soldiers who have been
wounded in the recent European war.

CHAPTER XVIil
THE NERVOUS SYSTEM

Without the nervous system, the human body would be in
the lamentable condition of a fully equipped factory with
plenty of willing workmen, which stands idle because of the
lack of a manager. Not a motion in the whole mechanism
would be possible and not an impulse or thought be experi-
enced. If the body were not alive, this want of power of
motion would be perfectly natural, but in the living body this
helplessness through lack of direction is one of the saddest of
sights. A yet sadder one is that of a living body showing a
large amount of activity, but not properly regulated. Such
a condition we sometimes see in idiots or insane people : life
in plenty, action in abundance, but all ill-applied and reach-
\Qg no useful end. It is as if the factory were running night
and day, burning coal and using up material, but turning out
no useful product.

The functions of the nervous system are numerous. It
must direct and control all visible movements; it must also
control many invisible activities lik^ the secretions of glands,
the movements of the intestine and the beating of the heart.
It is, moreover, concerned with higher functions, such as
feeling, thinking, remembering, willing and other mental
acts, many of which, though- frequently never apparent in
action, make up the most important part of our lives.

The central nervous system consists of the brain and spinal
cord, which are not separate organs but parts of the same
mass of tissue, and contain most of the nerve cells con-
cerned in the higher functions. The delicate structures of
the central nervous system are placed within strong protect-
ing bones, but that they may have communication with the

289

290 ADVANCED PHYSIOLOGY

rest of the body, they are connected with the individual
organs by a network of nerves and nerve endings, which make
up the peripheral nervous system. In addition to the central
and peripheral systems, there is a third, partially independent
collection of nerve fibres and cells, which is known as the
sympathetic nervous system.

THE CENTRAL NERVOUS SYSTEM

The Brain. — In all the higher animals, the brain is present
and is the seat of the mental life. One can scarcely say that it
is more important than the heart or the kidneys, for without
any one of them life could not continue; but it is the sole
directive agent of the higher functions.

The brain is inside the skull, the bones surrounding it and
making up the brain box being called the cranium. Where
the backbone joins the skull the spinal cord passes into the
cranium through a large opening, the foramen magnum.

Membranes about the Brain. — Apphed closely to the inner
surface of the cranium is a tough lining called the dura mater.
This serves at the same time both as a brain covering and a
sheath, which functions as the periosteum does in other bones.
Closely applied to the brain itself is a thin, rather delicate
covering, the pia mater. This follows the brain surface com-
pletely, dipping into every groove and covering every wrinkle.
The pia mater is very full of blood vessels, and thus forms
both a protecting and a nourishing agent.

Between the dura and the pia mater is a thin tubular mem-
brane, the arachnoid, the space within it being filled with the
arachnoid fluid. This serves the very apparent purpose of a
cushion. The brain is exposed to countless jars as one walks
or merely moves the head, and it is easy to see how much dif-
ference this fluid cushion must make in saving this delicate
nerve center from wear and tear.

Main Divisions of the Brain . — All animals with backbones
show the same brain parts as man. Assuming the brain to be

THE NERVOUS SYSTEM

291

Cerebrum

free from all its coverings and looked at from above, little is
seen but two large hemispherical masses, separated by a deep
fissure. These masses make up the cerebrum, and are called
the cerebral hemispheres. If the brain is tilted forward so
that the back part of the cerebrum is visible, there comes into
view the cerebellum, which also shows an open groove be-
tween its right and
left halves. Below
the cerebellum is the
medulla, which ex-
tends downward and
passes, without any-
special line of separa-
tion, into the spinal
cord. These parts
are shown in side
view in Figure 146.
Viewed from below
(Fig. 147), the same
structures can be
recognized, and the
olfactory or smelling
nerves should also
be noticed under the

front lobes of the cerebrum. Going from front to back,
observe next between the two cerebral hemispheres the
large optic nerves going to the eyes, the nerve from the
right side, and the one from the left meeting in the middle
line. The place where these fibres mingle forms an X-Uke
structure, called the optic chiasma, just beneath which is
the small, round pituitary body, whose function is not ex-
actly known. Behind this, notice on each side a length-
wise ridge. These two ridges, which are called the crura
cerebri, converge backward until they become the right
and left halves of the spinal cord. Back of the crura

Cerebelium

Fig. 146. — The human brain

Shown from the side with the cerebrum and cerebellum
separated from each other

292

ADVANCED PHYSIOLOGY

^P^'' Olfacfory

cerebri is a prominent transverse band of fibres, the pons
Varolii, which connects the right half of the cerebellum with

the left, going in
front of (ventral to)
the spinal cord as it
does so. Behind the
pons is the medulla.
The outer surface
of the brain in some
of the lower animals
is perfectly smooth,
but in man the cere-
brum and cerebellum
show many furrows
dipping into the sur-
face and separating
rounded ridges,
called convolutions.
If a number of dif-
ferent specimens of
the brain were ex-
amined, the main
convolutions would
be found to occur in
the same relative
positions in each.
The cerebellar con-
volutions are always
much narrower than
those of the cerebrum
and are more noticeably arranged in groups, with the ridges

^The cranial nerves are numbered; 1, Olfactory; 2, Optic (at their
place of crossing [optic chiasmal the pituitary body is shown); 3, Oculo-
motor; 4, Patheticus; 5, Trigeminal; 6, Abducens; 7, Facial; 8, Auditory;
9, Glossopharyngeal; 10, Vagus; 11, Spinal accessory; 12, Hypoglossal.

^^''"'1" ipmolCord

Fig. 147. — The brain as seen from below i

Cerebrum

Qraif matter or Corf en
Iffhiiernafkr

Cerebellum

Medulla

Fig. 148. — Diagram

Representing the divisions of the brain as lying in a
straight line and separated from each other and
showing the ventricles within.

THE NERVOUS SYSTEM . 293

approximately parallel or concentric, as is shown in Figure 147.

Cavities in the Interior of the Brain. — The interest which
anatomists have felt in the brain has led them to make minute
studies of its interior, but we shall notice only a few points.
If the cerebral hemispheres be forced apart at the
top, they are found to be joined together toward their
centers by a large cross band of fibres, called the corpus
callosum. There are also empty spaces in the brain. We
know that this is true of the larger bones but we seldom
think of cavities in the brain. If we assume the parts of the
brain to be arranged in a straight line, one part behind the
other, and the whole to be cut in a vertical plane near the
middle, the cavities or ventricles will appear as in Figure 148,
as a continuous series from the front through the brain and
down the cord. It must not be supposed that these passages
are open cavities, for the sides of the ventricles are in close
contact with one another. They are, however, cavities, just as
there is a cavity in a rubber water bottle when it is empty
even though its sides are collapsed. Just what purpose these
cavities serve is not known. The fluid in them is like that
between the dura and pia mater coverings, of a thin watery
consistency, and may act in connection with the blood from
which it is derived, as a means of nourishing the brain.

Gray and White Matter. — If a part of the brain be cut open,
its tissues will appear to be of two sorts: on the outside or
cortex, is gray matter, and inside this, white matter; Fig. 148.
This difference in color would be in itself of no consequence it
the microscope did not show these layers to be made up of es-
sentially different materials. The greater part of the graj
matter contains numerous nerve cells, while the white mattei
underlying the gray, appears to be made up almost entirely of
nerve fibres, which are, essentially, outgrowths from tha
nerve cells. This distribution of the white and gray matter
in the different parts of the brain will be noted as each divi-
sion is considered.

294.

ADVANCED PHYSIOLOGY

Surface- r yy..-;.
of Braim i\'ll,^.

THE CEREBRUM AND ITS FUNCTIONS

The cerebrum is by far the largest and most important
part of the brain and is the real center of thinking, perceiving,
willing and indeed of consciousness. Its
primary activities are carried on by the nerve
cells located in the gray matter or cortex.
The most important experiences in our lives
are carried on through the activities of these
cells. It is much easier to think of cells of
protoplasm as giving rise to materials like
iS;i\*/i saliva or bile, than to imagine them making
I '1m'i4* thoughts. The former process is called se-
IiVhA cretion; but shall we speak of the cells of the
brain as ^'secreting" or "making" thoughts,
or as "containing" memories, which may be
drawn on at will? We do not know; but we
do know that it is these cells that are the real
thinking part of the body.

Figure 149 shows a section of the cortex.
It will be noticed that the cells are of several
different kinds and shapes, though very few
are round and nearly all have several angles
or corners from which extend and branch
thread-Hke outgrowths, called dendrites; Fig.
11, page 18). There is always one process
from each cell that extends much farther
than the others and finally ends, either near
dendrites of other cells, or else passes down the
spinal cord. This long outgrowth becomes the
central axis of a nerve fibre, over which
messages are either sent or received as the case
may be, sometimes for as great a distance asj
two or three feet. Further description of these]
nerve cells will be made later (page 310).

F I G. 149.— A

SECTION O F
THE CEREBRAL
CORTEX
To show the nu-
merous cells that
it contains. The
surface of the
brain is at the
top and the white
matter would be
at the bottom of
the figure.

THE NERVOUS SYSTEM

Since the white matter consists of fibres and the g;ray of
cells, the conclusion is that in general the white central
layers of the brain are
made up of fibres
arising from the cells
that lie near its sur-
face. Every nerve
fibre is really a part
of a nerve cell, how-
ever far from the cell
it may extend. This
relation of the white
to the gray matter
should be kept in
mind during all our
discussion of brain
structure and func-
tion. If the cells of
the cerebrum were in-
active the heart beat
and breathing might
continue; but there
would be no powers of
sensation, of thought,
of judgment or of vo-
lition, no emotions, no
anticipation nor mem-
ory; lacking the cells
of the cortex one could not consciously move any muscle of
the body. Thus, in the cells of the gray matter of the cerebrum
reside all 'powers of sensation, of voluntary motion and what
we call intellect.

One other very important fact should be mentioned here;
the cells in the right half of the cerebrum are, to quite an extent,
connected by fibres with the left side of the body, and those

Fig. 150. — Diagram

To show the courses of fibres through thebrain. It
will be seen that all paths to or from the spinal
cord cross, those from the brain crossing at the
base of the brain, and those to the brain crossing
lower down. Outer shaded area represents the
cortex of the cerebrum; inner shaded areas are
subordinate nerve centers. (Landois)

296 ADVANCED PHYSIOLOGY

of the left half with the right side of the body. Doubtless the
student has known of a case where some part of a person's
body is paralyzed. As a rule, whichever side of the body
is affected, the trouble is on the opposite side of the
brain. As a proof of this, if the brain of an animal is laid
bare and then stimulated in spots with electricity, the move-
ments which result are always on the side of the body oppo-
site to that on which the brain is stimulated. Paralysis
sometimes results when a blood vessel has broken and a clot
causes pressure on some part of the cortex; if the clot can be
removed, the patient may entirely recover. Other causes
of paralysis will be noted in connection with the spinal
nerves.

The jSbres in the center of the cerebrum are concerned
wholly with carrying nerve messages or impulses, never in
originating or receiving them. Figure 150 shows the courses
of some of these fibres of white matter. In the performance
of one's varied motions, it is evident that the most intimate
connection between the two sides of the brain must be es-
tablished. The right and left sides of the body, and both
arms and legs are doing things which must be directed toward
the same end in an orderly manner. The figure shows that
some fibres put the two halves of the cerebrum into com-
plete communication with one another. The different cells
of the same side are also connected since they govern such
different muscles and must be completely harmonized in their
actions. No picture can represent accurately all of these
fibres, nor would it be possible to follow them all, so numerous
are they. It is necessary merely to keep in mind that these
cells are all in ready communication with one another, and
thus work together in the control of the thousands of muscle
movements in the body.

Cerebral Localization. — The use of these fibres becomes
very easy to understand when we note that certain parts of
the brain have special work to do. The functions of the cells

THE NERVOUS SYSTEM

297

Fig. 151 — The brain of a monkey

Showing the parts of the brain that control
movements of different parts of the body.
(Horsley and Schafer)

of the middle, superficial part of the cerebrum have been par-
ticularly investigated and it has been shown that some of these
control the muscles of the
arm, others those of the
leg, those of the neck,
those of the eye and so
on. The whole surface of
the cerebrum can not be
mapped out in this way.
Figure 151 shows the main
areas of the brain and the
parts of the body which
they control. All parts of
the brain cortex have not
yet been proved to have
clearly defined uses. In-
deed, there are on record
instances in which, through
accidents, parts of the
human brain have been
removed, and yet the in-
jured person showed no
unfavorable effects, in fact,
almost entirely- recovered.

THE CEREBELLUM AND
ITS FUNCTIONS

We have already noticed
that the external surface
of the cerebellum shows

great complex of nar-

*row ridges, separated by

grooves. If this organ is

cut open, the cut surface shows, as does the cerebrum, the

white and gray matter, but it is arranged somewhat

Fig. 152. — A section of the cere-
bellum

Highly magnified. Some cells in this organ
have especially long and nimaerous den-
drites. (ObeBsteiner)

298 ADVANCED PHYSIOLOGY

differently. Cells and fibres are also the main materials of
which the cerebellum is made. Figure 152 shows their
arrangement diagrammatically. The nerve cells are of
several kinds, some showing very complex and some very
simple bunches of dendrites. In every case, the cells are
located near the surface, while the fibres make up the
centre of each lobe.

The real use of this part of the brain is not thoroughly
understood, but there are two main functions which are
usually ascribed to it: first, that of a co-ordinating centre.
Messages starting from cells in the cerebrum, on their way to
the different parts of the body, go to the cerebellum and are
there brought together in such a way that the movements
which they produce take place in an orderly, related manner.

In every human being several activities are going on at the
same time. In ordinary walking, for example, the muscles in
one leg are contracting while corresponding muscles of the other
are relaxing. While a person is walking it is entirely possible
for the muscles of the neck to turn the head, for those of the
tongue and mouth to be concerned in speaking, and for those
of one hand to be contracted about a package or umbrella.
Thus, although one does not frequently think about it, all our
habitual activities involve a very complicated nervous mech-
anism. This direction of movements so that many muscles
may work together toward a single end is called co-ordina-
tion, and is one of the functions of the cerebellum. Impulses
provoking movements start in the cerebrum, but are regulated
in the cerebellum. An animal from which the cerebellum has
been removed is unable to control or direct the movements
of the various body muscles and cannot perform even the
slightest action in an orderly, straightforward manner.

A second function of the cerebellum which has been em-
phasized by some physiologists is that of a relay station for
outgoing impulses from the cerebrum, strengthening the force
of nerve messages on their way to the lower muscles of the

THE NERVOUS SYSTEM SM

body. Acts of thinking, too, seem to be somewhat weakened,
becoming less virile and positive, in the cases where the
cerebellum has been impaired by disease or some other cause.
However, this function of the cerebellum as a message-
strengthening organ cannot be regarded as so important, or
so certainly known, as its co-ordinating influence.

THE MEDULLA

The medulla is connected with the control of respiratory
and circulatory organs. It lies beneath the cerebellum and
its lower end is continuous with the spinal cord from which
it is not distinctly separate. Large bundles of fibres, crura
cerebri, extend from its upper end into the cerebrum.

If the tissues of the medulla were carefully examined, it
would show a complex mixture of nerve fibres and nerve cells,
whose arrangement would differ very much, depending on
whether the cut were made through the anterior, middle or
posterior portion of the structure. We need merely note
that among these fibres there are patches of cells, sometimes
called '' nuclei," from which most of the cranial nerves take
their origin. The fibres themselves come from cells which
are either in the cerebrum or lower down, in the cord; so that
the medulla becomes a great complex of paths for messages
passing in either direction.

So far as its fibres are concerned, the medulla simply trans-
mits messages from the brain down to the spinal cord, and in
the reverse direction, but its nerve cells give it some other
functions. The particular activities which are controlled
by the nerve cells of the medulla have been determined by
removing from some animal the other parts of the brain and
then noting carefully what powers have been taken away and
what powers are left. Such an animal keeps on breathing, and
the blood vessels still continue to expand and contract, so we
say that the medulla contains respiratory and vaso-motor
centers. In the medulla is also the cardio-inhibitory center,

300

ADVANCED PHYSIOLOGY

rachial
P/exus

from which messages go over the vagus nerves to check the
beating of the heart; see page 145. Although the above are

the most important, there are other
centers located in the medulla; but,
in general we may say that the
medulla is the seat of all involuntary
activities.

THE CONNECTIONS BETWEEN THE
BRAIN AND THE BODY

The brain, shut up as it is within
the bony walled cranium, may be
compared to a telegraph operator in
his small office. It is quite remote
from many important organs of the
body, but by means of innumerable
nerve fibres, corresponding to tele-
graph wires, it is connected with
them all, as the telegraph operator
may be in communication with the
rest of the world. The next step
in our discussion, then, is to study
the spinal cord, which is the main
cable, as it were, of nerve fibres.

THE SPINAL CORD

Fig. 153. — The spinal

Since the term spine is commonly

appHed to the backbone, the large

nerve which passes down through

it is naturally called the spinal cord.

Notwithstanding the innumerable

twists and bends which the body

makes, the cord is perfectly protected from strain and injury.

Figure 123 shows that each vertebra is essentially an irregular

ring of bone encircHng an opening; when a number of vertebrae

CORD
With the spinal nerves at-
tached. Upon one side is
shown the sympathetic
system. (Thompson)

THE NERVOUS SYSTEM

301

are arranged one on top of the other, these openings form a
long tube, the spinal canal. In this is the spinal cord, con-
tinuous with the brain above and terminating by dividing into
branches in the lumbar vertebrae. Fig. 121. It is nearly uni-
form in size throughout its length, though it enlarges somewhat
as it merges into the brain and is somewhat larger than else-
where in the region between the shoulders and in the lumbar
region, or " small of the back.'* Its average diameter is about
three-quarters of an inch.

Like the brain the cord is protected by two sheaths, the
dura mater and the pia mater, which are continuous with

rPoshnor Rool^

lama

ier

Merve
fibres

Nerve

Cells

Orat/

flatter

AhferiorRoof

Fig. 154. — A cross section of the spinal cord

The white matter is really filled with nerve fibres but in the figure these are shown

at only one point.

those of the brain, and like them in every way, save
that the dura mater is not grown to the vertebrae as it is to
the inner side of the cranial bones. Arachnoid fluid is present
and forms a cushion about the cord as it does about the brain.
Structure of the Cord. — The cord is cylindrical in shape
and divided into right and left halves by deep grooves, one

302

ADVANCED PHYSIOLOGY

on its anterior and one on its posterior surface, the anterior
being more open and more shallow than the posterior. The
two halves, which are clearly shown in Figure 153, are held
together by a central connecting portion, about one third of
the diameter in width.

The grooves of the cord are still better appreciated by a
study of a cross section; Fig. 154. Such a section, too, shows
that the cord, like the brain, is made up of two kinds of
material, nerve fibres and nerve cells, though in reversed re-
lations, the outer layers of the cord being of white, fibrous
matter, and the inner of gray, cellular matter. Recognizing
that the nerve fibres simply conduct impulses, while the nerve
cells have other more complex functions, it will be evident
that the cord has these two different classes of activities.
Since the process of conduction is the simpler matter, we shall
study it first.

The Cord as a Conductor of Impulses. — Messages sent

through the cord pass

Pojferior Roof

Anierio.
Hoof

either up or down in the
white matter; but do im-
pulses going up the cord
follow the same paths as
those going down? This
question has been answered
by experiments on some of
the lower animals which are
constructed essentially like
man, and also by observa-
tion of the results in human
beings in which the cord is
diseased or has been injured
by accident. These observa-
tions have shown that if a
part of the cord is disabled, sometimes sensation and some-

Fig. 155. — Diagram of a cross
section of the spinal cord

Showing the parts that carry messages
up (ascending) and those that carry
messages down the cord (descending).
(Modified from Flint and Landois)

THE NERVOUS SYSTEM

303

times the power of motion is lost below the injured point.

If the power of motion is lost, e.g. the motion of the leg, then

the injury must be in a descending tract, where the messages

that pass from the brain down to the leg have been interfered

with. If the person

loses the sensation of

feeling so that he has no

consciousness of anything

that may touch a given

part of the body below

the injured spot, then it

is assumed that an

ascending tract has been

severed.

By these studies the
areas which are devoted
to impulses going in one
direction or the other
have been determined
approximately as in
Figure 155. Roughly
speaking, all ascending
impulses go up to the
brain either on the poste-
rior side or on the right'
and left lateral regions
near the surface; while
the descending impulses
pass downward on the anterior side or in the deeper layers
of the lateral regions.

One unexpected fact, however, comes to light in studying
the nerve paths in the spinal cord. An injury on one side
of the cord is, as a rule, accompanied by loss of sensation on
the other side of the body but not on the same side as the
injury. The conclusion is that messages brought into the

Fig. 156. — Diagram

Showing the course of the ingoing and outgoing
impulses in the cord.

$04

ADVANCED PHYSIOLOGY

spinal cord pass immediately to the other side and ascend
there. Curiously enough, however, an injury destroys the
power of voluntary motion on the same side as the injury,
but not on the other. Hence messages from the brain pass
down the cord on the same side as that to which they finally
go. Figure 156 shoWs these facts diagrammatically. These
messages from the brain going down the cord cross over from
left to right and vice versa, higher up, mainly in the me-
dulla, so that all messages going to either side of the body
start from the other side of the brain. Thus, the sensations
and motions of each side of the body are connected with and

controlled by the cells in

the cerebral hemisphere of
the other side. Although
there are a few exceptions
to this arrangement, this
is, in the main, the rela-
tion of the spinal cord to
the rest of the body.

THE PERn>HERAL NER-
VOUS SYSTEM

The nerves over which
messages are brought to
the spinal cord or the
brain and those over
which messages are sent
out compose the periph-
eral nervous system.
These nerves are classed
in two groups: (1) the
cranial nerves which go to
or leave the brain directly without entering the cord; (2)
the spinal nerves which enter and leave the cord.
The Cranial Nerves. — The cranial nerves are twelve in

' Vagus
*^"' fotfearf&Lungt

Fig. 157. — Diagram

Showing the distribution of the different cranial
nerves. The numbers indicate the number
of each nerve, and the arrows show whether
each is afferent or efferent.

[
I

THE NERVOUS SYSTEM 305

number, arising directly from the brain and passing out of
the cranium to supply, chiefly, the organs of the head; Fig. 157.
The muscles of the head are controlled by them, sensations
from the face, the nose, the eye, the ear and the tongue are
received through them. Some of the more important of these
we shall consider in the following chapter.

The Spinal Nerves, i — Between the neural arches of each
two vertebrse enough space is left for a nerve of considerable
size to pass from the spinal cord on each side. There are
thirty-one of these spinal nerves on PosiaiorJioot

each side of the cord. Five of them
unite to make up the brachial plexus,
i.e. the nerve combination which
supplies the arm; four form the lumbar
plexus and thence pass down each leg AmemTRoot

as one nerve; Fig. 153. The rest supply Fig. 158.— A bit of
the numerous organs of the neck and ™^ ^^^^^^ ^^^^

, -^. icrou ±u 4. Showing the method of

trunk proper. Figure 158 shows that a origin, of the spinal nerves
spinal nerve does not leave or enter the ^y *^o ™°*s-
cord in one place as a branch grows out of a tree, but arises
by two roots, one being continuous with the gray matter in
the anterior part of the cord and the other with that in the
posterior part. These two roots join to form one nerve;
before their junction, however, a swelling, a nerve ganglion,
occurs on the posterior root.

The precise function of these two roots has been ascertained
by experiments upon animals. If, for example, the posterior
roots of all the nerves going to some one organ, e.g. the leg,
have been cut, it is found that nothing touching the leg, not
even a burn, is felt in the least, but it is still possible for the
animal to move the leg or any part of it. This result shows
that all sensory impulses, all messages having to do with
feeling, as we say, pass from the leg into the spinal cord over
the posterior roots of the spinal nerves. The function of the

306

ADVANCED PHYSIOLOGY

posterior roots of all the spinal nerves of the bod}^, therefore,
is to carry sensory messages or impulses which are always
passing into the cord or brain, and are frequently called
afferent impulses, and the nerves concerned, afferent nerves.
If, on the other hand, the ventral or anterior roots are cut
and the posterior left intact, the animal so injured is unable
to move its leg, but can feel perfectly anything in contact
with it. From this, one decides that the impulses from the

brain or cord which go
to the muscles of the leg
leave the cord by the
anterior roots. The ante-
rior roots of all spinal
nerves, then, carry motor
impulses. Motor im-
pulses always pass from
the cord or brain; they
are called efferent im-
pulses and the nerves
concerned in carrying
them, the efferent nerves.
After the dorsal and
ventral roots (afferent
and efferent) unite into

Fig. 159. — Three nerve cells

In two of them is shown the axon, or axis
cylinder, of the nerve connected with the cell.

a single trunk, the spinal nerve resulting is a mixture of both
kinds of fibres, though their functions remain distinct. In
the various figures in this chapter the direction of the arrows
indicates the direction of the impulses that pass through the
various nerves. The number of nerve fibres that thus enter
or find exit through the cord is very large. There are many
hundreds of thousands of them in the thirty-one pairs of spinal
nerves and by means of them every part of the body is brought
under the direct influence of the spinal cord and brain.

Structure of Nerve Fibres. — In the opening chapter the
mmute cells which make up the bodv were described. These

THE NERVOUS SYSTEM 307

cells are essentially alike, in that each consists of a bit of proto
plasm, containing a nucleus. Nerve cells differ from others,
of course, in their pecuHar function, and it would be interest-
ing indeed to know how they do their work of thinking,
memorizing, inventing, etc., but this no one can tell. They
also frequently differ from others in their very irregular shape
(Fig. 159) and in the outgi'owth from most of them of a long
process, the axon, or axis cylinder, the work of no other cells
requiring such connection with parts of the body at a dis-
tance from them.

A portion of a nerve fibre is represented in Figure 160. It
consists of a very fine central thread, the above-mentioned

^ Primitive Sh«ath__ fledulfant^

Fig. 160. — A short piece of a nerve jtibrb

Very highly magniiiecL

axis cylinder, which is continuous from its point of exit from
a cell in the brain or spinal cord, to its end, e. g. in some
muscle, gland or skin cell. Covering this axis cylinder, which
is the real conducting fibre of the nerve, is the medullary
sheath, which is of material different from that of the fibre and
contains considerable fat. It seems to act as a covering to
prevent impulses which are passing along the fibre from
jumping across into other fibres lying close by, thus serving
something the same purpose as does the insulating covering
of gutta percha around an electric wire. This medullary
sheath is interrupted at short intervals called nodes (Fig.
160) and between every two nodes there occurs a nucleus
showing the medullary sheath to be made up of many cells.
Outside the whole is a thin covering, the primitive sheath.

On the other hand, since this sheath contains fats, the
nutrition of the nerve fibre has been regarded as its main
ction. There is little to support this view, however.

308

ADVANCED PHYSIOLOGY

Sheath

Fig. 161. — A cross section of a

NERVE

Showing it to be a bundle of fibres held

in a sheath of connective tissue.

In the spinal nerves and every nerve leaving or entering
the brain or cord there are very many of these minute fibres
running together in a bundle. It is this bundle of nerve fibres

which is meant when the term
Fibre nerve is popularly used; Fig.

161. Even in the bundle,
each fibre has its medullary
and primitive sheaths; only
after the fibre has entered or
before it leaves the brain or
spinal cord is the primitive
sheath left off. In the white
matter of the central nervous
system the fibres have unin-
terrupted medullary sheaths,
i. e. not divided into nodes
and internodes, and there are no external sheaths. In
very exceptional cases, as for example, the nerves going to
the nose, which is so near the brain, both medullary and
primitive sheaths are wanting.

Replacement of Nerves after their Injury. — Whenever a per-
son cuts or otherwise injures the skin or any muscle just
beneath it, healing begins almost at once and soon there is
enough new tissue formed to repair the wound completely.
When, however, one of the long nerve fibres which pass from
the cord or brain to the surface of the body is cut off, repair
takes place in a very different way. The two ends of the cut
nerve will never come together again and mend, but the part
of the fibre between the point of injury and the organ to which
it goes dies. The stump between the injured place and the
cord or brain often does not deteriorate at all, or only for a
very short distance.

A new nerve to replace the portion of the nerve peripheral
to the injury is formed from material made by the cells of
the old primitive sheath. These increase in number along

THE NERVOUS SYSTEM

the line of the old fibre, become changed at first into a jelly-
like material and later into nerve-fibre substance. This new
nerve fibre makes connections with the stump of the old one,
and communication is again possible between the cell in the
cord or brain and the old nerve ending.

Nerve Endings. — As has been pointed out, nerves are divided
into two classes: (1) the afferent nerves, which bring in im-
pulses from the outside world or from internal organs to the
spinal cord or brain; and (2) the efferent nerves, which take
impulses out from the cord or brain to the organs which they
supply.

Several kinds of afferent nerve endings, or more properly
beginnings, in the skin or elsewhere have already been re-
ferred to and shown in Figures 112, 117 and 118. In general,
they may be said to start in very minute spheres or oblong
bodies called corpuscles. The nerve fibrils begin here as fine
branches either on the sx ..Nerve

exterior or in the in-
terior of these organs.
These skin end-organs
receive mainly impres-
sions of touch and tem-
perature, an extreme of
either taking the form
of pain.

The efferent nerves
are distributed almost
entirely to muscles and
glands and excite these to action. The manner in which
nerves end in muscles is diagrammatically shown in Figure
162. It is not possible to say just what happens in a muscle
or gland when a message is delivered to it. The muscle
contracts or the gland secretes, but just what change in their
protoplasm excites these activities is not known.

Fig. 162. — The ending of a nerve in

MUSCLE fibres

The end organ of a motor nerve. (Bohn «&

Davidofif)

CHAPTER XIX

THE NERVOUS SYSTEM— NEURONS, NERVE
IMPULSES AND REFLEX ACTION

It has already been noted that the whole nervous system is
made up of nerve cells and nerve fibres, which indeed form
the basis of the gray and white matter, respectively. The
fibres and cells are not separate structures but each fibre is
a part of some cell; and thus it comes about that the whole
nervous system is composed of these units, each consisting
of a cell with its connected fibre or fibres. These units are
called neurons (one of these is pictured in Figure 11). Each
consists of a nerve cell with its nucleus; extending from the
ceil are dendrites and one axis cylinder, at the distal or
outer end of which is a nerve ending.

A neuron may receive an impulse through its axis cylinder
and send it out through its dendrites, or it may receive the
impulse through its dendrites and send it out through its axis
cylinder. In either case it is as the neurons act, each by itself,
and each in connection with the other neurons, that the func-
tions of the nervous system are performed. Some of them
constitute the thinking and willing part of the brain; others
^in the cord and elsewhere are the servants of those in the brain,
since they carry messages to and from the brain, though the}^
have, besides, important functions in connection with reflex
actions. We shall consider first those which carry impulses
to the brain, then those that carry impulses away from it
and finally those concerned in reflexes.

NERVE IMPULSES AND REFLEX ACTION

311

THE NEURONS AS TRANSMITTERS OF IMPULSES

Ingoing Paths. — We have already learned that the pos-
terior roots of the spinal nerves carry messages inward and
that upon each posterior root
there is a swelling, the so-called
spinal gangUon; Fig. 158.

Inside this spinal ganglion are
the cell bodies of a large
number of neurons. From each
ceil body extends a single pro-
jection or axis cylinder, which
soon divides, one branch passing
inward to the spinal cord, the
other outward in the nerve trunk
into the body, finally ending in
some sensitive part, e.g. the skin;
Fig. 163. If the skin is touched
in any way at that point, an
impulse will start and go rapidly
inv/ard on the fibre, pass the
neuron cell body in the ganglion
and continue into the cord. In
the cord, as shown also in Figure
164, the fibre again divides, one
fibre going upward and the other
downward. The branch passing
up the cord soon divides into a
number of twigs, forming at c
a brush of fibrils called arboriza-
tions. Close to these arborizations
begin similar divisions of another
fibre whose cell body is higher up, possibly in the brain itself:
Fig. 164d The imDulse which enters the cord mav thus

Fig. 163. — Diagram illustrat-
ing A SIMPLE REFLEX ACTION
The impulse from the sense organ
oasses in over the nerve fibre, a,
and may pass up to the brain over
a-c. But a part may be switched
off through e down the fibre / to
the muscle, causing it to contra-ct
without the aid of the brain.

312

ADVANCED PHYSIOLOGY

jump from one of these fibres to the other through their

tuft-like endings and then go to the brain.

But there is another direction which the impulse from the

skin may take after its arrival in
the cord. The branch in the
cord marked a in Figure 164 also
has side branches ending in arbo-
rations e. If the ingoing impulse
passes out into these, it may jump
across into the fibrils of another
neuron whose fibre,/, does not lead
to the brain at all, but passes out
through the anterior motor root
of the spinal nerve to some muscle.
The result will be movement at
the end of the motor fibres. From
the course which the impulse in
this last instance took, it is evi-
dent that the resulting motion
must have occurred without the
mediation of any conscious centers
in the brain, since only the cells of
the gray matter of the spinal cord
were concerned in the process.
This production of movement in
a muscle without the ''consent"
of any conscious centers of the
brain is called a reflex action. In-
voluntary movements of both vol-
untary and involuntary muscles
occur very frequently in the body

and play an important part in life processes. They will be

considered at greater length a little later.

From an examination of Figure 164 it is easy to see that

two results might follow the arrival in the cord of an impulse

Fig. 164. — Diagram
Illustrating the course of messages
to and from the brain through
the spinal cord.

{

NERVE IMPULSES AND REFLEX ACTION - 313

from the skin: a part of the impulse might go into the side
branch, e, and give rise to a reflex movement, while the rest of
the impulse could take the path, a, leading to the brain and
there produce sensation. Influenced by this sensation, the
brain might send down a message through the fibre, g, which
would result in conscious movement, in addition to the re-
flex response. Suppose, for example, a barefooted boy steps
on a thistle. He jumps off quickly (a reflex action). In
a fraction of a second he feels the prick and acts accordingly,
but he jumped before he was conscious of the pain.

The neurons described are those in the spinal cord and
spinal ganglia, but there are a large number in the brain it-
self. The details of their structure are slightly different, but
their general relation and method of working is the same.

Outgoing Paths. — Although the gray and white materials
of the brain cortex have been previously referred to merely
as cells and fibres respectively, it is necessary to realize that
the brain material is a mass of neurons and that the whole
nervous system is made up of these same units. The white
material is not independent of the gray ; it merely consists of
the axis cylinder fibres of the neuron cell bodies of the gray
matter.

The cell bodies of these brain neurons receive all messages
brought to them, and are the centers of the thinking pro-
cesses. Decisions are made in them and they start impulses
outward to any part of the body which they have decided to
move or influence. These impulses pass directly downward
over an axis cylinder (Fig. 164 g) or nerve fibre, which finally
ends somewhere in the cord in a bimch of arborizations, like
those already described; Fig. 164 h. Very near these fine
endings are the dendrites of another neuron body, i, and into
these the descending impulses pass. The long axis cylinder
of this last neuron (Fig. 164 /) passes out through the anterior
or ventral root of a spinal nerve, and extends directly, with
no further interruptions or * 'relay neurons", to the special

314 ADVANCED PHYSIOLOGY

organ which it is to supply. In this way, impulses started
by the brain neurons eventually reach the muscles to be
moved or the tissue to be innervated.

REFLEX ACTIONS

We have already noted that a message coming into the cord
from the body may, on occasion, be switched off onto side
branches of the fibre it was traversing, jump from its terminal
arborations to the dendrites of a neighboring neuron, and go
outward over the anterior root of a spinal nerve without
immediately going to the brain. There are some further
aspects of these reflex actions which should be noted, for an
almost infinite number of movements and minor functions
of the body, as well as many very important ones, are thus
performed.

Probably every person makes more movements uncon-
sciously than consciously. If his attention were especially
called to each one of his actions, they would immediately
become matters of all-absorbing concern to him, and would
take so much of his time that he would be able to attend to
nothing but the simplest activities. Suppose, for example,
that one had to think definitely about the contraction of each
muscle concerned in walking, whenever he took a step; sup-
pose he had to deliberate about the contraction of every
muscle concerned in winking every time he moved his eyelids;
suppose that every time his clothing touched him at any
point, a message were sent to his centre of consciousness in
the brain. The nervous energy required would be almost
incalculable, and the maintenance and regulation of life
would be impossible.

We have already found that the essential peculiarity of a
reflex movement is that it is performed without the media-
tion of any of the conscious centers of the brain. These re-
sponses can indeed be obtained in animals from which the

NERVE IMPULSES AND REFLEX ACTION 315

brain has been entirely removed. The fact that the brain of
a frog can be taken out, and yet the tissues of the body remain
alive for a considerable time (even the heart may go on beat-
ing) makes the frog an especially favorable animal for this
study. Of course, such a frog has no sensations and no
ability to make voluntary motions, still it shows some most
interesting reactions. If its toe be pinched, it is pulled away
quickly; if the tip of the toe be dipped in acid, it will be pulled
out promptly. The frog acts as though it had sensations of
pain, though, with the brain wanting, we know that it can
have none. It moves because the impulses excited in its
nerve endings, after reaching the cord, cannot go to the brain,
and therefore take one of the side tracks leading across arbora-
tions to other neuron bodies, whose axis cylinders pass im-
mediately out to muscles in the part of the body whence the
incoming impulse started.

If the frog has its brain, a different result may follow, for
the conscious centers will become aware of the pinch in
the toe and the animal may decide to jump, instead of simply
pulling its foot away. In this case, the stimulus has of course
gone all the way to the brain and back down again, finally
passing into the motor cells of the cord, fibres of which extend
to the jumping muscles. Thus we see that the same muscles
are under the control of two different centers, the conscious
center of the brain and one in some other part of the central
nervous system, probably in the cord (as we have assumed
in the foregoing instances). Save that reflexes are usually
quicker, there is no appreciable difference between reflex and
conscious movements.

Reflex movements msLj involve the brain, as well as the
cord. This would seem an impossibility; i. e. the unconscious
action of a conscious center. We get this impression, however,
merely because as a rule the brain is thought of as an organ
in which only conscious activity occurs. This is a mistake, for
not all the cells of the brain are by any means conscious ce^ters.

316 ADVANCED PHYSIOLOGY

It is not difficult to cite instances of brain reflexes. If a
sudden light flashes in front of the eyes, or if another person
shakes a handkerchief or other solid object toward the face,
one shuts the eyes instantly. Now a person does not stop
to think whether or not he will shut his eyes under these cir-
cumstances. They are closed before he realizes it and he
himself is opening them carefully, lest the danger is not yet
passed. Yet all the nerves controlling the eye muscles come
directly from the brain, and the centers from which they
arise have acted without the person's conscious vohtion.
Ordinary winking is carried on unconsciously, as we know.
The surface of the eye becomes sUghtly dry, and this condi-
tion irritates it. Messages go to the centers controUing the
winking muscles, they act and the eyes wink, but the whole
process takes place without one's being aware of it. In tak-
ing food into the mouth, the movements of the tongue and
jaw, while under one's control, nevertheless occur without
conscious thought about it. One does not say to himself,
"I will now shut my mouth," and afterwards, '' I will now
open my mouth." These are only two of the innumerable
instances of unconscious action on the part of brain
centers.

In the above illustrations of reflex actions we have con-
fined ourselves to visible movements. There are innumerable
muscular and glandular activities in the body of which one
has absolutely no intimation, which also come under this
head; e. g. respiratory movements and the movements of the
stomach and intestinal walls. Before any of these occur,
messages first go from the organ concerned to the central
nervous system. For example, when the stomach is empty
it lies perfectly passive, but if food is swallowed, the ends of
nerves in the stomach are stimulated. They carry the mes-
sage to some center in the gray matter of the cord or brain, or]
both, and immediately impulses are sent out over motor nerves
to the muscles of the stomach walls, which then begin their!

NERVE IMPULSES AND REFLEX ACTION 317

churning action. In the same way, when the food commences
to pass on into the intestine, it too begins its complicated
movements. One should always remember that these occur
only because certain nerve centers are acting.

Reflex Centers as Servants of Conscious Centers. — It is
hardly possible to overestimate the value of the reflex centers;
it is only through them that the conscious centers can carry
on the multitude of duties which devolve upon them. One's
attention cannot possibly be given to all the little details ot
living, so these are turned over to the lower parts of the brain
and cord, which thus act as a great coterie of servants. To
them the whole control of many activities is given after the
decision has been made in the conscious centers. Take the
common act of walking: one simply directs the lower center
to put the walking muscles into proper motion, and then his
attention may be wholly devoted to thinking or talking,
while the reflex center will superintend the walking move-
ments until he tells it to stop.

That the reflex centers are servants and not independent
units is plain when we notice that the higher centers always
keep the upper hand, so to speak. With adults, walking be-
comes a reflex. Still, by an interference, the conscious
centers can interrupt the reflex centers at any time, and one
can stand in one place as long as he wishes, starting the walk-
ing reflex again when he chooses. The eyes may be getting
dry, for example, and the tendency of the neurons in reflex
centers is to make the winking muscles contract; neverthe-
less, by giving the matter conscious thought, one can inhibit
the winking muscles even until he really suffers pain in the
eyeballs. One can also stop the breathing reflex center from
acting for a considerable period. Some impulses going out
from the brain may, therefore, be negative, or inhibitory as
we say, and a great many reflex centers, while acting with
partial independence of higher control, are yet constantly liable
to its dictates. Others, however, like the involuntary

318 ADVANCED PHYSIOLOGY

movements of internal organs, may be practically beyond any
control of even the highest centers.

Relation of Reflex Actions to Training and Habits. — The
reflex centers in all cases consist of the nerve cells, the central
parts of some of the neurons or of groups of such cells. But
the interesting and important fact is that at the beginning of
one's life most of these servants are untrained and cannot
perform at all the duties assigned to them in later life. Ex-
actly how these nerve centers are trained, it is impossible to
say; but we do know that by being made to do the same thing
over and over again they finally learn to do it well, and
at last almost without one's consciousness. When a child
first learns to walk, for example, his muscles do not readily
work out his will, but after some years of practice he no longer
thinks of the motions, for the reflex centers take charge of
them. Practice makes 'perfect, simply because by constant
use the reflex centers may be so trained that they do their
work perfectly. When we learned to write we were obliged
to attend carefully to the motions of the fingers, to see that
all the up-strokes and down-strokes came in the right order.
But now, if we are good writers, we do not have to think of
up-strokes or down-strokes, hardly of the letters. We think
out the ideas we wish to put on the paper, and reflex
centers take charge of most of the movements. One
becomes aware of this fact when he tries to disguise his hand-
writing. He finds such a procedure as difficult as he did
learning to write, for the muscles and nerve centers are
trained to do a thing one way, and continue to do so.

Most of the activities of the child's life have for their pur-
pose the training of these useful nervous centers. His work,
his play and his study all have the same end in view; i. e.
training for his use a set of faithful servants who will con-
tinue for the rest of his life to work in just the way they have
been taught in youth. The saying, ''It is hard to teach an
old dog new tricks," merely expresses the difficulty of training

NERVE IMPULSES AND REFLEX ACTION 316

these nerve centers in any new way after a person has grown
up. Education of the body and the mind is thus first of all
the training of reflexes. Since one must employ these ser-
vants all the rest of his life, it is of the greatest importance
that they be trained aright. This is the reason why it is
necessary to give so much attention to education, to physical
training and to all discipline that develops useful habits of
thought or action.

THE NERVE IMPULSE

We have mentioned the fact that nerve impulses pass over
the nerve fibres, and considering the differences in the re-
sults they produce, one would naturally suppose that there
would be corresponding differences in the impulses; e. g. that
the impulse which produces a sensation of light must be very
different from one producing a sensation of sound. This is
not the case, however. An electric current through a wire
may produce different results according to the different kinds
of apparatus employed at the end of the wire: it may ring a
bell, or produce light in a bulb, or sound in a telephone; but
though the results are various, the electric current is essen-
tially the same in all cases. So in the body, the impulse
which travels over a nerve is always essentially the same.

No one need be told that nerve messages travel over the
nerves very rapidly. One can appreciate no lapse of time
between willing to move the fingers and their actual motion,
and yet the message must meantime have passed from the
brain to the muscles concerned. The rate at which messages
pass into the central nervous system, i. e. the rate over sen-
sory nerves, is greater than that at which messages pass out
over motor nerves. The former travel inward about 140
feet per second, while the latter travel outward at a rate of
about 110 feet per second.

But what is the impulse which travels over nerves? The
old idea was that the nerves were hollow and filled with a

320 ADVANCED PHYSIOLOGi:

fluid, but we know now that this is false. Among other
ideas which have been held concerning this question are the
following:

1. The chemical theory maintains that when a nerve is
stimulated, a chemical disturbance passes along the axis cylin-
der of the neuron involved. This may be compared to the
change which takes place in a tiny trail of gunpowder when
one end of the line is ignited. The difficulty in accepting
this theory is that we should have to imagine the train of
material in a nerve to be instantaneously replaced, so that
the nerve would be ready to transmit another message at
once.

2. The mechanical theory assumes that the molecules
of the nerve fibres are in close contact, and that any
unusual movement of them at one end of a nerve is
transmitted through the whole line until it is felt at the
other end. Suppose the molecules are compared to croquet
balls placed in contact, in a long, straight line. If one at
the end is struck the one at the opposite end bounds away
from the others, though the intervening balls do not move
appreciably.

3. The electrical theory looks upon the nerve impulse as
an electrical phenomenon. It can easily be excited by an
electric shock, it travels very rapidly over the nerve without
seeming to produce any changes in it, and in these respects
resembles electricity. Then, too, careful study shows that
there are electric changes in the nerve when the impulse
passes over it. Sometimes an impulse is supposed to jump
from one fibre to another as an electric current may jump
from one wire to another. On the other hand, the nerve
impulse differs from electricity in several important respects.
It travels too slowly, 100 feet per second being too slow for
electricity. If a string is tied tightly around a nerve it will
stop the passage of the nerve impulse, but such treatment of
an electric wire will not stop an electric current over it. If

NERVE IMPULSES AND REFLEX ACTION 321

a nerve is cut and the ends put together ever so carefully, still
no impulse will pass over the break. Cutting electric wires
in no way impairs them; even though the ends be put to-
gether carelessly the current will pass along perfectly, if only
there is good contact. Lastly, the nerve fibre is a poor
conductor of electricity.

Taking all these facts together, it would seem that the
nerve impulse is not exactly Uke any other kind of force with
which we are acquainted. Although it certainly resembles
electricity in many respects, at present it is regarded as a
special kind of impulse that travels rapidly through the nerve
fibre from any point where it may be started to the other
end.

Nerve impulses may be instituted by many different
methods. In the body they usually start from some part of a
neuron, but we do not yet know the method by which this
is brought about. Impulses may also be started artificially.
If an electric shock is sent into a nerve, an impulse is excited
and travels to the nerve ending; if the nerve is pinched or cut,
an impulse starts from the point of injury. If a hot body
touches the nerve, or certain chemicals are dropped upon it,
these will also give rise to a nerve impulse. In some nerves
an impulse is started by light, in others by sound etc.

CARE OF THE BRAIN

Under the conditions of modern life to a far greater extent
than in earlier centuries it has become necessary for each in-
dividual to use his brain. While some occupations require
this more than others, there is none in which one is not helped
in the achievement of success by having a well-trained and
active brain. Education gives this training. As the years
of school life pass, the brain not only obtains information,
but it learns how to act; it grows stronger by use just as
muscles do.

We sometimes hear of persons whose health has broken

322 ADVANCED PHYSIOLOGY

down because of excessive mental work resulting in nervous
strain. Since such a condition is very unfortunate and very
serious, it is important to learn what causes contribute to it.

In the first place we may be confident that only in very
rare cases is the trouble due to overwork, or to excessive study.
The brain gains strength by use, and even a very hard student
is not likely to use it too severely, if he is otherwise in proper
health. If the brain is treated reasonably, and the whole
body kept in a state of health, the brain may work very
hard and grow stronger all the time. But the person who is
fond of study is apt to neglect entirely the other functions of
his body, and allow his muscles and other organs to lack
proper exercise. Exercise, especially in fresh air to produce
vigorous respiration, helps to keep the brain alert. The
student perhaps fails to use proper discretion in his diet;
overeating, irregular eating and too rich foods throw his
body out of condition. The brain needs good wholesome
food to keep it active, and it is well to remember that there
are no special " brain foods," this term being used simply to
catch trade for certain food products. The student neglecting
some of these plain laws of health, becomes ill and his break-
down is apt to be considered due to over-study.

It is working the brain under improper conditions rather
than working it too hard that produces nerve strain. Using
the brain excessively without sufficient outdoor exercise,
studying late at night when one needs sleep, using it too long
upon the same kind of work, are all likely to injure it. Rest
and sleep are necessary for an active brain. The amount of
sleep needed is not the same for all persons, and growing^
people require more than adults. In general about eight|
hours sleep in a day should be taken by every one, and more
than this by children. The attempt to study after one has
become sleepy is always a mistake; in the first place it is the
hardest tax on the brain, and in the second place it is often
useless. The brain is not in condition to receive and remem-

NERVE IMPULSES AND REFLEX ACITON 323

ber, and it will be found the next day that almost nothing is
retained of that which was studied the night before, so that
the hard work was of no value. The bad habit of cramming
should be particularly avoided. To accomplish the most in
the way of learning, one should do a proper amount of work
regularly each day. If this is done, it will be found that
when the time comes for examinations, cramming will not be
necessary. The poorest way to prepare for an examination
is to sit up late the night before, vainly trying to crowd into a
tired brain the information which should have been previously
acquired. Too long continued attention given to one sub-
ject is also a mistake. A change of occupation is sometimes
just as much of a rest as to stop work entirely. To work
with the muscles is a rest from study, and reading is a rest
from muscular work; to study algebra is also a rest from the
study of language, although both of these require brain
work.

The condition of the body is largely modified by the con-
dition of the mind. We know, for example, that one's
emotions affect the beating of the heart. Worry and anxiety
are matters which have their origin in the mind; but their
actual effect may take very unfortunate forms; e. g. loss of
appetite, inability to sleep, super-sensitiveness, lack of in-
terest in things in general. These and many other of our little
ills are made worse by continually thinking of them. On
the other hand, health is augmented by cheerfulness and
mental buoyancy. Muscular fatigue, or even headache and
toothache often disappear before a game of tennis or baseball,
or during an evening of music. Digestive juices are more
readily secreted when one is in good spirits, than when one
is nervous or worrying. All of these things show that the
mind has a decided effect upon the condition and general
health of the body, — a fact which imposes upon one the
possibility and duty of cheerfulness, not only because of the
advantage to himself but for the sake of others.

324 ADVANCED PHYSIOLOGY

SYMPATHETIC SYSTEM OF NERVES

The term sympathetic system has been applied to a series
of nerve cells and fibres which connect all the spinal
nerves and, to a certain extent, bind them together,
not only anatomically, but to a limited extent in their
functional work also. Just how far there is any co-
operation of this kind is uncertain, and the term ''sym-
pathetic," is not well applied.

This system comprises two strands of nerve tissue lying in
the body cavity, one on each side of the back bone; Fig. 153.
Each line of fibres makes connections with each of the spinal
nerves on its side of the body, and at the junction with each
spinal nerve a ganglionic collection of nerve cells is formed.
Of course, no impulses really originate in the cords of the
sympathetic system, but the fibres in them take up impulses
which have come out over spinal nerves, from the spinal cord
or from the brain.

The majority of branches from the sympathetic system go
to the blood vessels in the abdominal region, and exercise con-
strictor effects on them. Some go to the heart, others branch
and make an extensive network of fibres which here and
there fuse together forming, with the addition of nerve cells,
ganglia. Such ganglia are seen in the walls of the stomach,
in the body cavity, in the " small of the back " and also in
the neck, and from these ganglia, nerves pass out to near-by
organs. The secretion of some of the large glands like the
liver is controlled by impulses reaching them over the sym-
pathetic fibres. As a rule, the impulses which pass through
the sympathetic system are not under the control of the will,
and furthermore they generally provoke responses from the
organ to which they go of the very opposite character to that
produced by impulses over the ordinary spinal or cranial
nerves. For instance, the sympathetic nerves going to the
laeart carry messages that stimulate it to more rapid action.

^' NERVE IMPULSES AND REFLEX ACTION 325

while those going over the vagus nerves, direct from the brain,
produce a slowing effect.

DISEASES OF THE NERVOUS SYSTEM

If there is trouble in the brain it is liable to affect the whole
life of the individual and especially his intelligence.

Idiocy. — Sometimes a person is born with the brain only
partially developed, and even as he grows, it never becomes
as large as it should. The skull, too, is usually small and
peculiarly shaped. With an abnormally small brain there
is sure to be found imperfect intelligence, and such a person
is called an idiot. Idiocy is thus a lack of normal intelligence,
due usually to the failure of the brain to reach its full size.
Size alone may not determine the degree of intelligence in an
individual. Frequently abnormal conditions in other organs
(especially the thyroid) may produce defective mentality.

Insanity. — On the other hand, a person may have a well
developed brain, but something may occur to interfere with
its proper functioning. Sometimes, for example, an abscess
grows inside the skull and presses on the brain; or after cer-
tain accidents, a bit of bone may press in upon it. In all such
cases the mental powers of the person are thrown out of
balance; he may imagine all sorts of strange things, e.g. that
he is another person, or he may become violent and dangerous.
Indeed, it is never possible to tell what he may do or think,
and we call a person whose mind is so affected, insane. In-
sanity is very different from idiocy, for it is due to the de-
rangement of brain functions which were originally normal.
Insanity varies from a very mild type in which the person is
perfectly sane on alinost all subjects, but cannot think clearly
on some one topic, to that in which the person is violent, and
his thinking powers are completely upset.

Inasmuch as insanity is due, sometimes, to some pressure
on the brain, it is occasionally possible to cure it by a surgical
operation; in many cases, however, there is no cure. When a

§26 ADVANCED PHYSIOLOGY

person is born with the skull or some other part so improperly
shaped, that the brain does not have the chance to develop
rightly, a pecuHar disposition may result. The person may
be excessively irritable, he may be subject to fits, or quite
lacking in any ideas of right and wrong, and thus apt to be-
come a criminal. In some instances a slight operation has
completely relieved these conditions, and a decided change
in the person been produced.

Paralysis, or Shock. — The breaking of a blood vessel is one
of the most serious accidents which may occur in the nervous
system. It rarely happens in young people, although it
occurs frequently in older ones. The breaking of a vessel
usually produces a clot which may then press upon nerves
and cause the trouble commonly called nervous shock. The
kind of trouble produced, however, varies with the location
of the clot. If this should be in the spinal cord, it may more
or less completely cut off communication between the brain
and the parts of the body below it. This of course would
mean that both sensation and power of movement might be
lost in these lower organs, i.e. the person would be paralyzed.
If the clot is in the brain, and that organ is hindered in its
functions, this also may produce paralysis. In sensory
paralysis, only sensations are lost, the person can move the
body but cannot feel; in motor paralysis he retains the power
of sensation, but cannot move; in complete paralysis, both 1
movement and sensation are wanting.

Recovery from this trouble is not very common. If it is
due to a broken blood vessel and the clot is not too large, itj
may be dissolved and more or less completely disappear. If
it is on the surface of the brain it may be removed by a surgi-
cal operation, but another break of the same kind is always]
apt to occur. Paralysis is an indication of the weaken-]
ing of bodily vigor, and usually a sign of approaching
old age.

XTervous Prostration. — Nervous prostration is the common]

NERVE IMPULSES AND REFLEX ACTION 327

name for an affection of the nervous system, concerning
the cause of which httle is known. It sometimes occurs
when one has been living for a long time under great nervous
tension, such as comes from continued excitement, too little
sleep or constant anxiety. It occurs more frequently in
civilized life and the highly complex conditions of modern
society than in the simpler life of the country. The symp-
toms of this trouble are too varied to be described here, but
very often the person imagines himself ill from troubles which
do not exist, and is in a constant state of worry about his own
health. The remedy for nervous prostration is a complete
change of life to relieve the body from the kind of strains
which have been producing t^e trouble. If one lives simply,
takes life as calmly as possible, does not allow himself to
worry nor live too highly, he is well protected against this
illness. Nervous prostration does not usually result from
overwork, as has been frequently supposed. It is more
likely to follow wrong habits as regards food, sleep, recreation
etc. If one breaks the monotony of work occasionally with
a brief period of real recreation, he may work very hard and
long without serious consequences.

Cerebro-spinal Meningitis. — Meningitis is one of the very
serious diseases, frequently fatal, and is caused by a certain
bacterium which attacks the brain. It is more common
among children than adults and sometimes occurs in epidemics.
Its method of passing from individual to individual is not
known, nor its means of entering the body. It is certainly
not very contagious, rarely more than one case occurring in a
family. Our lack of knowledge as to its method of distribu-
tion has prevented the devising of efficient rules for avoiding
it, and the only suggestions now possible are to keep up the
general health and to avoid contact with those suffering from
the disease, and with secretions from their mouths. A method
of combatting it by inoculation has been devised that is fre-
quently successful in producing a cure.

CHAPTER XX*
A CLEAR MIND THE NEED OF THE DAY

Every living being must contend with enemies for its own
existence. In the early periods man counted among his foes
wild animals, storms, floods, famines and droughts. Against
these he has in a large measure ceased to contend; he has
overcome wild animals, and with fires, houses and various
other devices can defend himself against the elements of
nature. It is due to the wonderful power of his mind that he
has been able to master these enemies, and it certainly be-
hooves him to keep this, his greatest treasure, in as efficient
condition as possible.

Man is still engaged in a struggle for existence with certain
foes which his changed conditions have brought prominently
forward, and the struggle is all the more severe because he
does not always recognize his worst foes as foes at all. Among
the most dangerous of his remaining enemies is the micro-
scopic, parasitic germ. Doubtless, germs existed in the early
periods of man's existence, but they were not especially
serious until people came to live in crowded communities.
The larger the community the greater becomes the danger
from microbes. An epidemic may kill thousands and other
diseases, like tuberculosis, which do not produce violent
epidemics, are quietly at work destroying the lives of hundreds
of thousands each year. Germs are particularly dangerous
because they are invisible, because people do not know where
they are nor how to avoid them, and because they are capable
of multiplying so fast that no matter how many of them are
destroyed, their numbers can in a few days be fully replaced
^ This chapter is entirely the work of the senior author.
328

A CLEAR MIND THE NEED OF THE DAY 32&

by the rapid multiplication of those which remain. Man is,
however, learning to fight them, more and more successfully.
Microscopes are discovering where they are, and careful
scientific studies are showing how in a measure they may be
avoided. Indeed, through modern sanitation, which has
driven them backward and has reduced the number and
violence of epidemics, men have succeeded in making the city
almost as secure against microbes as the country. We shall
notice in another chapter some of the methods adopted today
in fighting this worst enemy in our struggle for existence.

THE USE OF DRUGS THAT AFFECT THE BRAIN

Another enemy against which man has to contend is
especially dangerous because it also is not commonly recog-
nized as a foe. Indeed, many people look upon it as a friend,
while others regard it as a luxury, which may be indulged in
more or less frequently without thought of danger. The
nervous system controls the whole body, and everything that
affects the activities of the brain has a profound influence upon
the whole life. But some men have unfortunately developed
the habit of using certain substances which have a direct
action on that organ and interfere with its normal functions.
There are two classes of brain drugs: stimulants, and nar-
cotics— each of which has pernicious effects.

Stimulants. — There is great difference of opinion as to the
proper definition of the word stimulant. This term usually,
however, denotes a drug that will excite an organ to increased
activity. The effect is temporary and does not indicate in-
creased strength, but only enables the body to call upon its
reserve power a little more quickly. In most cases, if not in
all, the stimulating action is followed by a corresponding
depression so that there is no gain in the end. A whip gives
no power to a jaded horse, though it may excite him for a
short time to more exertion. The constant use of a stimu-
lant, too, acts somewhat like the constant use of a whip on a

330 ADVANCED PHYSIOLOGY

horse; the animal soon ceases to mind the whip, or refuses to
go without its constant application. The only substances in
common use which act in this way are coffee and tea (caffein
and thein). Persons who have become accustomed to these
stimulants are no longer normal individuals, they cannot
readily work without them and really suffer if deprived of
them. Sometimes the effect of tea and coffee is so great as
to cause positive ill health.

Strychnin, which is a deadly poison when taken in con-
siderable quantity, will, when given in small amounts, quicken
the heart beat. For this reason it has been prescribed by
physicians in cases of critical illness where it is necessary to
accelerate the action of the heart, and it has therefore been
called a heart stimulant. The habit of using even mild stimu-
lants like tea and coffee is, however, a useless and very un-
wise one for young people to acquire.

Narcotics. — Narcotics have an effect the reverse of that of
stimulants. Instead of producing an increase of activity,
they lessen it; instead of making the organs work more vigor-
ously, they dull and render them less efficient. In particular
they have the effect of causing the brain to become sluggish
and finally of putting it to sleep. Just as fast as the brain
comes under their influence, it loses its unique pov/ers. The
use of a narcotic thus deprives the individual of his most
valuable possession.

The commonest narcotics are opiates; e.g. laudanum, pare-
goric, morphine, soothing syrup. Cocaine, chloral, chloroform,
ether and the like also produce a deadening effect, though
their action is different from the opium products. When
one of these drugs has an action on the brain strong enough
to cause unconsciousness, it is said to act as a general anes-
thetic, and if it produces insensibility to pain in only one
particular part of the body without causing unconsciousness,]
it is called a local anesthetic.

Narcotics have their useS;, and as a means of relieving P^iil'

A CLEAR MIND THE NEED OF THE DAY 331

in emergencies they have been of incalculable benefit. But
most of them have an unfortunate tendency to create an
appetite, before which in the end the user becomes helpless.
A person begins with a small dose, perhaps at the advice of a
physician to relieve pain, and continues to repeat it either
for the same purpose or for some other reason, until the habit
of frequently using the narcotic is formed. The small doses
cease to have the desired effect, the more it is used the more it
is craved and the larger are the amounts taken. Surely and
even rapidly this undermines the health and destroys the will
power until the man becomes a wreck. Usually he does not
appreciate the fact that he is coming under the influence of
the drug until he becomes its slave, and when he does recog-
nize that he is being ruined he is usually too far gone to wish
to reform, or his will power is too much shattered to enable
him to do so.

There are few more difficult habits to conquer than the
opium habit and the only safe way to escape this great danger
is by avoiding the use of this narcotic entirely. The same
applies to the use of cocaine and chloral. The amount of in-
jury done to children by the ignorant use of soothing syrups
by their mothers or nurses cannot be calculated, and it is
doubtless true that many a child's death is due to the use of
such drugs, most of which contain opium or a similar narcotic.
One should hesitate about the continued use of any drugs
which rapidly relieve pain or induce sleep, though some ere
more injurious than others.

Alcohol. — The most commonly used drug belonging to the
class of narcotics is alcohol. The dispute about the food value
of alcohol has already been mentioned, but there is no ques-
tion about classing alcohol as a drug which provokes the
brain to abnormal action. If it is used constantly and in
large amounts, it not only affects the brain but other organs.
An inflammation in the form of chronic catarrh is produced
ID the stomach, and the functional activities of that organ are

332 ADVANCED PHYSIOLOGY

decidedly impaired. In the liver a peculiar disease called
cirrhosis sometimes appears, the liver becoming hardened and
enlarged. The kidneys become enlarged by the formation of
useless connective tissue which encroaches upon the kidney
proper and weakens its action. The heart is sometimes en-
larged and weakened. The blood vessels are permanently
dilated, producing for example, the red nose which often
marks those addicted to alcohol. Accompanying indulgence
in some forms of alcoholic drinks there is a tendency to the
formation of an abnormal amount of fat, which is only an
incumbrance and tends to interfere with the normal func-
tioning of certain organs. It is usually deposited in the
abdomen but may be stored around the heart, tending to
check its free action and produce heart troubles. All of
these phenomena are abnormal, and indicate that alcohol
deranges the body functions. Physicians recognize alcohol-
ism as a very real and very serious disease brought on by the
use of alcoholic drinks. When small amounts only are taken
derangements are less evident, although the difference is
probably in degree rather than in kind.

In all cases alcohol has some action on the brain, and the
nervous system as a whole is the one most affected by it.
Here its influence seems to be from the first that of a narcotic,
since it always tends to dull the brain activities. One of its
first effects is to stupefy the vaso-motor center. We have
learned that this center governs circulation in general, al-
ways acting in such a way as to keep the small arteries parti v
closed, and thus regulating the amount of blood sent to dif-
ferent parts of the body. When this center is dulled the
small arteries relax and the blood rushes through them faster
than usual, the cheeks become flushed and the skin warmed;
thus what appears to be an increased activity is really an
effect of the narcotic action of alcohol on the brain. This
increase of blood flow also affects the brain itself, causing a
feeling of excitement, a certain hilarity of spirits which is

A CLEAR MIND THE NEED OF THE DAY 333

commonly mistaken for increased mental activity. Hence
the stimulating effect oi alcohol is only apparent and is really
due to the partial paralyzing of the vaso-motor center.

The question whether alcohol is to be regarded as a narcotic
or a stimulant has been very much debated, due partially to
the difficulty of defining the word stimulant, and partly to
the pseudo-stimulating action of alcohol. It is certainly
true that many people have believed and still believe that it
"gives strength." Indeed there is little doubt that many
persons have learned to use it under a genuine conviction
that it makes them stronger and even that it makes them
think more quickly. But these beliefs are wholly unfounded.
Alcohol does not give strength. At the risk of direct in-
jury to many internal organs, it will furnish an extremely
small amount of heat, although sugar and fat will do this
much better. No one who understands the facts would ever
use it when he has any hard work to do under the impres-
sion that it can under any conditions make him more effi-
cient.

Effects of Alcohol on the Brain. — The most noticeable effect
of alcohol is that upon the brain. Its use is followed by a
feeling of excitement and flow of spirits that resembles very
much the result of a stimulant. But this, too, is really due
to the fact that its narcotic action has dulled the person's
feeling of reserve and self control. He is apt to do anything
that comes into his mind or say anything that impulse sug-
gests, whereas ordinarily he would think further before speak-
ing. Hence he speaks and laughs more easily, and in general
acts as if stimulated, when the fact is that he has merely lost
; the valuable power of self restraint. The man who keeps his
I brain clear and uninfluenced by alcohol is usually more than
a match for the one who has ^'stimulated" his mind by wine
I or other alcoholic drink.

The action of alcohol does not stop here, however. From
the first it dulls the powers of perception and makes one less

334

ADVANCED PHYSIOLOGY

quick to see and understand; one does less work or does it not
so well, although oddly enough he thinks that he is doing better
than usual. If more than a very small quantity of alcohol is
used, its narcotic action becomes extremely apparent. Even
before the person has any appreciation of the fact that the
alcohol has influenced him at all, it has begun its effects. He
becomes sleepy, loses control of his muscles, and staggers if
he tries to walk; finally he may become totally intoxicated,
in which condition his brain has become so completely para-
lyzed that it no longer has control over his body. In these
extreme cases the narcotic action of alcohol is evident, but
between the intoxication and the action of smaller amounts
(as in the case of the moderate drinker), the differences are
of degree rather than of kind.

One physiologist found after a dinner at which he had
taken light wines, in amount not sufficient to have any ap-
preciable effect upon him, that either his senses or his muscle
control had become dulled, as shown by the fact that, if he
went shooting at such a time, he always shot behind the birds,
not being quick enough in his judgment or action to allow
for their flight.

The German physicist, Helmholtz, found that if he had a
difficult problem to think out, he must let alcohol entirely
alone, for even the smallest quantity destroyed the keen edge
of his thinking powers, and prevented him from doing his best.

Careful observations have shown further that in work re-
quiring accuracy, e. g. adding figures or setting type, the use
of a very small amount of any kind of alcoholic drink impairs
a person's efficiency, making it impossible for him either to do
so rapid or so exact work as usual. These illustrations are
sufficient to show that even from the first the use of alcohol
acts as a narcotic upon brain functions and that its apparent
stimulating action is misleading, due to results which are the
direct outcome of its narcotic action, e. g. dulling sensibility^
relaxing the blood vessels and withdrawing self restraint.

A CLEAR MIND THE NEED OF THE DAY 335

Insurance companies have found by recent carefully col-
lected statistics that, on the average, drinkers are shorter lived
than abstainers. It is not surprising that these companies
will not insure the lives of hard drinkers, but they have also
found that the moderate drinker has a shorter life than the
total abstainer.

The great business enterprises of this country have realized
the sapping influence and dangerous tendencies of the use of
alcohol. Of seven thousand industrial concerns questioned
in this respect, 75% when engaging employees take into con-
sideration the question of their use of alcoholic drinks. Over
half refuse to employ persons in certain positions if they use
alcohol. The large railroads exclude from places of respon-
sibility those addicted to it, and banks will generally dis-
charge an employee if they find him frequenting saloons. In
short, a person is now seriously handicapped in getting a
good start in life if he is accustomed to use alcohol in any
form. He must frequently cease to strive for good, respon-
sible positions and be content with those below the grade he
could otherwise reach. Moreover, physicians in recent years
are prescribing alcohol less and less as a medicine, many of
them being convinced that its use for most purposes is futile.
According to a report of the British Medical Society, with
those persons over twenty-five years of age who use alcohol
habitually, life is shortened on an average of about ten years,
and the injury to the young is still greater.

'The best bred man indulging in wine with permissible
moderation no more escapes the minor psychical changes
induced by it than does the meaner slave fail of its sense-
destroying power when he drinks till he remembers his misery
no more. In the case of the former the mental changes in-
duced will never attain the degree when self respect and social
conduct are outraged, and they will pass unnoticed by all
except those who are keen observers of their own mental
states.'' (Abd)

336

ADVANCED PHYSIOLOGY

It may seem a little strange to class disease germs and
alcohol together as man's greatest foes, but it is really stranger
that while we all agree to fight the one persistently, a con-
siderable portion of mankind prefers to play with or indulge
the other. Everyone who understands the nature of disease
recognizes the need of fighting its agents or germs, but vast
numbers of people welcome rather than struggle against the
dangers of alcoholism. The reasons for this attitude are
many, but one of them is that many fail to realize that the
microscopic germs and the alcohol appetite are equally
menaces to health and happiness.

Yet any one who will open his eyes to the conditions around
him will see clearly enough that alcholism is, in the majority
of cases, associated with disease, for the reason that it lowers
one's powers of resistance. Besides shortening his own exis-
tence, the man who drinks much is living only part of his
normal life, for his mind is constantly in a state of partial
stupefaction brought on by the influence of this paralyzing
drug. The old toper has lost the use of his most valuable
possession, while the moderate drinker is endeavoring to
meet life with slightly impaired mental capacity and physical
powers. Many a youth begins with a little beer or wine in]
the desire to be ''social," to do as others are doing, and in-
advertently develops a habit which places him upon a lowei
plane of possibility and action than he would otherwise have]
attained. Probably there is no drunkard who, in youth, did!
not have his good intentions, his resolutions and ambitions t(
be and to do good, but he trifled with them. It is never pos-
sible to predict whether or not one will become a victim of]
this appetite, for persons with apparently the strongest will
are often those who yield most readily. The desire for alcohol
is an insidious one which grows slowly, usually without the]
consciousness of the individual, until it becomes too stronj
for him or until he ceases to care whether he masters it or notJ
Whole families are wiped out by the evils which come fromJ

A CLEAR MIND THE NEED OF THE DAY 337

its use, and hundreds of thousands of individuals are de-
prived of one or more years of useful and enjoyable life by
imprisonment for crime committed while under the influence
of alcohol.

There are other foes with which we have to contend in our
efforts to make life a success, but none is greater than these
two. The person who does achieve success, both in his outer
and in his inner life, is the one who learns to keep his body in
health and his mind clear. The intellect is man's most pre-
cious possession, and in weakening it, alcohol is attacking
him at the very point on which he must place his dependence
if he is to carry on a successful ^'struggle for existence."

Tobacco. — The formation of the tobacco habit also pre-
sents a question difficult for some young people to settle.
The action of tobacco upon the body is a more or less com-
pUcated one, and is not the same in all individuals. Tobacco
contains a poison, nicotine, which has a powerful influence on
nerve cells.

The physical effect of the use of tobacco depends upon the
quantity used, and, as we have just said, upon the individual
user. If very small amounts are used it is doubtful whether
there is an appreciable result, and the injury may not be
recognized. Whatever influence it does have is bad, es-
pecially for young people. If large quantities are consumed,
the effect is frequently noticeable in an abnormal heart action
and in the stupefying of the brain. The "tobacco heart,"
the "cigarette heart," have become well known terms which
the physician appUes to certain symptoms due to the exten-
sive use of tobacco.

The effect of tobacco upon those who have not attained
their full growth is probably always injurious. The evidence
is complete that its use by such persons prevents the full and
proper development of the body, and that a boy who smokes
constantly is stunted in his growth. In intellectual power,
too, young people seem to be injured by the tobacco habit

838

ADVANCED PHYSIOLOGY

A careful study of the records made by college students shows
that those who habitually use tobacco are, on the average,
mentally inferior to those who do not have that habit. The
brightest and most independent are most likely to avoid it.
After one reaches maturity, i. e. after twenty-five years or so,
the effect of tobacco smoking is not so noticeable, but for all
persons of student age the habit is very unwise, and some-
times disastrous. Moreover, employers of boys find the cigar-
ette smoker decidedly inferior to his cleaner companions, and
this inferiority, generally speaking, may be said to persist in
later life. The smoker is often incapacitated for fine work.

MEDICINES

In spite of all one's attempts to keep himself in proper
health, he does not always succeed, and almost everyone is
occasionally ill. There is a very general feeling that if one
is ill the necessary thing is to take a dose of medicine. People
have a notion that medicine in some mysterious way will cure
disease no matter what its cause, and sometimes no matter
what the medicine. Much evil results from this ignorant
idea. For ordinary ills there is always a cause, and the proper
course is to remove the cause rather than to take medicine. If,
for example, one suffers from indigestion, he should endeavor
to change his food habits or his food, or to take more exercise
rather than to continue in the old way and rely upon medicine
to cure. Indeed, most of the little ills in life can be readily
mastered by a change of habit, without medicine. Medicine i
has its uses, beyond doubt, but it is very unwise and unsafe]
for the untrained person to administer it.

Especially is it a mistake to buy and use the numerous!
so-called ^^ patent medicines, ^^ extensively advertised and
claiming to cure a long list of troubles. This does not mean]
that none of them has any value, but that many contain]
powerful drugs, alcohol or opium, which cannot be safely]
used by anyone and certainly not without the advice of aj

A CLEAR MIND THE NEED OF THE DAY 339

physician. Beyond a few simple remedies we should leave
the giving of medicines to a physician who understands that
they are merely a help and not a cure for disease and that
the patient is frequently better off without them.

If one recovers from disease it is often because the body
cures itself by its own vitality. Medicines may assist, but
a person really cures himself. The taking of too much medi-
cine without the advice of a physician is one of the great
faults of the American people. Every young person in prep-
aration for life should make up his mind that, if properly
treated, his body can take care of itself without the use of
drugs. If it is ill, except when the trouble is a germ disease,
the difficulty usually lies in an improper mode of living, and
this cannot be cured by medicine. Medicines, properly
administered by one who understands them, are useful, but
miscellaneously used by others, they are productive of a vast
deal of harm and an incalculable waste of money.

CHAPTER XXI

ORGANS OF SPECIAL SENSE— THE EYE

In a preceding chapter we noted that every sensory nerve
ends in a special bulb, or corpuscle, and some of these were
shown in Figures 117, 118 and 162. The endings there rep-
resented were very simple, having only simple functions to
perform, like that of receiving touch, heat or pain stimuli.
There are other sensory nerves, particularly some of those
coming out of the brain directly, which have very elaborate
endings, usually spoken of as organs of special sense. The
most important of these are the eye and the ear.

EXTERNAL PARTS OF THE EYE

The eye (Fig. 165) is set into a cavity in the skull, the eye
socket, which is lined with a layer of fatty tissue serving as a
cushion. The eyeball is not perfectly round, since over the
colored portion at the front the sphere bulges slightly, although
not enough to be noticed ordinarily.

Externally the eyes are protected by the lids, which are
folds of the skin of the face supplied with muscles to permit
movement in winking; Fig. 166. In the process of moving
the lids two muscles especially are concerned: one, the so-
called orbicular, is a circular muscle running around in both the
upper and the lower lids; the other, the levator, is in the
upper lid, and runs upward from the edge and raises it after
the orbicular has closed the eye. The lower lid moves very
little, and is not drawn downward by any sp«^al muscle.

At the inner corner of each eye is a little whitish mass of
tissue which is of doubtful value in man; in birds and some rep-
tiles, a corresponding structure is a third eyelid, which is trans-
parent and can be closed while the others remain motionless.

ii40

ORGANS OF SPECIAL SENSE— THE EYE 341

The lashes on the edges of the Uds protect the eyes some-
what from dust. The inner surface of the Hds is really nothing
but the external skin folded back underneath, but it is pro-
vided with special glands which are not present in the ordinary
surface of the skin. These Meibomian glands are arranged in
little clusters, with their openings near the edges of the hds
(Fig. 166) and are more abundant in the upper than in the
lower lid. Their secretion is oily and by mixing with the
more watery product of the tear glands prevents the rapid
drying of the latter as it is spread over the eye in a thin
layer when one winks.

A tear, or lachrymal, gland is located just above the
outer corner of each eye. It is about three-quarters of an
inch long, one-quarter of an inch wide, and the material which
it secretes is poured under the upper lid through six or seven
tiny canals. This lachrymal secretion is largely water, with
a little salt, and the smearing of the secretion over the eye-
balls in winking prevents the delicate membranes of the eye
from becoming dry, and consequently more or less opaque.

The liquid material secreted by the several glands about
the eye runs away through two tiny openings in the inner
corner of each eye into canals, which unite into the lachrymal
duct, leading to the nose chamber. A downward current is
produced in these canals by cilia which project into them on
all sides.

Muscles which Move the Eye. — The movement of the eye is
effected by six different muscles, all of which are attached to
the eyeball at different points back of the lids: Fig, 165. Four
of these, one above, one below, one outside and one inside, are
called rectus muscles and pass from their attachments to the
eyeball directly back to a point in the deepest part of the
socket. The one next the nose is called the internal rectus;
the outer, the external rectus; the upper is the superior, and the
lower the inferior rectus. The other two muscles are called the
obHques. The inferior oblique is attached to the lower sur-

342

ADVANCED PHYSIOLOGY

face of the eyeball and to the bones on the side of the nose.
The superior oblique muscle on the upper surface of the eye
passes inward toward the hose, but on reaching it, its tendon

Inferior
Oblique muscle

Superior
Oblique muscle

Opfic ,..

ner'ye
infer. Reef us

/^ExtenRecfus
Super: •

Fig. 165. — Diagram

Showing the eyes in position in their sockets, the muscles that move them and
the optic nerves. (Fox)

goes through a loop, which acts as a pulley, and then passing
backward is attached near the same place as the rectus muscles.

Demonstration. — The muscles which move the eye can be well shown
by use of the eye of a dog-fish. The skull is cartilaginous and easily cut
away, and the muscles are diagrammatically plain. Appendix, Section 30.

All movements either in a vertical or a horizontal plane
must be made by the rectus muscles, and movements not ex-
actly in either of these planes may be produced by the com-
bined action of two or more of them. It would seem that
their contraction would produce all movements the eyes ever
make. As a matter of fact, however, the oblique muscles are

ORGANS OF SPECIAL SENSE— THE EYE

343

'uscIp

constantly used, not alone, but to adjust the movements of
the rectus muscles more accurately.

The extreme delicacy with which these muscles work is
not usually appreciated.
Especially remarkable is
the accuracy with which
they move when one is
reading a printed page.
The eye is perfectly di-
rected to a certain letter,
to comma or period, and
then as suddenly turned,
it may be only a hair's
breadth, and the process
repeated thousands of
times in an hour, yet
always with the most re-
markable precision.

tluscle

Olancf

Fig. 166. — A section through the

UPPER EYELID
Highly magnified. (Fuchs)

STRUCTURE
OF THE EYE PROPER -- — >-y^ tashcs

The Sclerotic and Cho-
roid Coats. — On the ex-
terior of the front of the
eye is an extremely thin
layer of tissue called the conjunctiva. This is continuous
with the lining of the eyelids, and its transparency
makes it imperceptible. Beneath the conjunctiva is a
thicker layer which extends over the whole eyeball,
serving to protect it and keep it in shape. In front,
this also is perfectly transparent; but beginning with the
"white" and passing about the rest of the sphere, it is tough
and opaque. The transparent portion in front is called the
cornea, the rest the sclerotic coat; Fig. 167,

344

ADV.\XCED PHYSIOLOGY

Beneath the sclerotic and cornea is the choroid coat; Fig.
167. It contains a large number of blood vessels and is the
principal nourishing layer of the eye. The choroid covers
the whole ball save a small spot exactly in front, the pupil.
Around the pupil is a colored area, blue, brown or black, as
the case may be, called the iris. The pigment area of the iris
is for the purjxxse of shutting out all Ught except an amount
sufficient to stimulate properly the nerves of sight. When the
light is dim, more must be admitted to produce the requisite
degree of stimulation; consequent!}' the iris is provided with
muscles by whose contraction and relaxation the aperture of the

pupil is made smaller
or larger. Certain other
muscles belonging to
the choroid coat will
be mentioned in a
later paragraph in con-
nection with the focus-
ing mechanism of the
eyes.

The Retina. — Inside
the choroid covering
is the retina, the only
layer of tissue in the
eye which is sensitive
to lights This does not go entirely about the eye, being
absent in front in the region of the iris and pupil.

The Vitreous and Aqueous Humors. — Filling up the center
of the eye, and making the whole organ spherical, is a mass of
clear, jelly-Uke material, the vitreous humor. In front in the
space between the iris and the cornea is also a mass of clear,
faansparent material, the aqueous humor, which causes the
cornea to protrude slightly; Fig. 167.

The Lens. — The lens also is made of perfectly clear, trans-
parent material of the consistency of thick jelly. In shape it

Fig. 167. — Diagsam
a section throq^ ikm vyAaB

ORGANS OF SPECIAL SENSE— THE EYE 346

is like ordinary glass lenses, though more convex on both sides.
If taken out of the eye, the lens still has enough rigidity of its
own to keep its shape. It is in the same cavity with the vitre-
ous humor in a vertical plane just back of the iris. Note in
Figure 167 that the lens is more convex on the back than on
the front side, and that at its edges it is held in place by slender
ligaments which run outward into the choroid layer. These are
collectively called the suspensory ligament, which must be
thought of as a thin sheet of ligamentous tissue going entirely
about the lens border, rather than as a cord attached to any
one or several points. It swings the lens into position, by
tension on its edges in every direction.

THE FORMATION OF IMAGES

When one's eyes are open, there is formed upon the retina
a picture or image of the object in front of the eye. The
secret of this picture formation lies entirely in the lens and
the cornea, more especially in the former.

Everyone knows that light, reflected from trees, buildings,
people or other objects, on passing through the lens of a photo-
grapher's camera produces an impression on the sensitive
plate within. If we compare this plate to the retina of the
eye, and the lens to the lens of the eye, the similarity between
the eye and the camera is very striking. In Figure 167 is
shown the arrangement of the lens and the retina. Straight
lines show the direction which rays of light take in the eye.
In this case it is supposed that the object seen is a point and
that the rays of light entering the eye are parallel. It will
be seen that these rays after passing through the lens bend
from their parallel direction and come together. It is plain
that they must meet, otherwise they would strike many
different parts of the retina at the same time, and a large
number of points instead of one would be seen. Each would
be seen indistinctly, too, since the light would be so sub-
divided as not to be intense at any one place on the retina.

346

ADVANCED PHYSIOLOGY

v. Glass

The law which makes the rays bend as they go through
the lens, and causes them to form an image on the other side
is very simple. When a ray of light passes from any point
through air, it always passes in a straight line; but if it enters
a transparent substance like glass, which is denser than air,
it is usually turned to one side. If it enters the glass per-
pendicularly, it still goes on in a
straight line (Fig. 168 C-c); but
if it enters at an angle it is always
bent to one side, and the greater
the angle at which it enters the
more it is bent (Fig. 168 A-a,
B-h) . After it has passed through
the glass and as it comes out on
the other side, it is bent again.

So it happens that rays of light
in passing through glass at an
acute angle to its surface are sure
to change their direction. One
often sees this principle illustrated when he looks out of
doors through a window. If the light from the objects thus
seen comes to him through a more or less irregular piece of
ordinary window glass, and especially if it comes through
slantwise, the object seems to be very much distorted. If
one sees things through a piece of plate glass there appears
to be far less disturbance of the image than in the case of un-
even glass, yet when the plate glass is bevelled along the edge,
objects which can be seen through the general surface plainly,
cannot be seen at all, or only in a distorted manner through
the bevelled area. Light from the object in going through the
bevelled surface has been thrown out of its path.

Let us now notice the effect of a lens upon rays of hght.'
The surfaces of the lens are curved, i. e. parts of spheres.
From Figure 169 it will be seen that if parallel rays enter the
^ For demonstration see Appendix, Sections 32 and 33,

Air

Fig. 168. — Diagram

Showing the refraction of light
while passing through a piece of
glass with parallel surfaces.

ORGANS OP SPECIAL SENSE— THE EYE

347

lens, they enter it at different angles, and are consequently
bent in different directions and that when they emerge they
are bent again, each differently from the others. Now when
the surfaces of the spheres are perfect curves, the angles at
which the rays enter and leave it are such that after passing
through they are bent toward one point where all of the rays
meet; Fig. 169. If a

sheet of paper is held at 7^

this focus, a point of /— V

light will show upon it.
Figure 170 shows a
slightly different con-
dition. Here A is a
point of light near the
lens, and from it light

rays pass outward in all directions. The rays are not parallel
as in the former instance but diverging; yet they are bent as
before, as they are passing through the lens and are also
brought toward one point a, at which they focus. But it will
be noticed that this focus is farther from the lens than the

Fig. 169. — Diagram

Showing the manner in which a lens bends
rays of light so as to bring them to a focus.

r::^^

Fig. 170. — ^Diagram

Showing the relative position of the foci formed by parallel rays of light and by
diverging rays of light coming from objects near the lens.

focus of parallel rays, /. If the point of light is brought nearer
the lens, at B, its focus, h, will be still farther away.

There is a way in which the image can be brought nearer
to the lens and the focal distance not be lengthened. If the
lens be replaced by one of greater curvature, i. e. more bulging,
it will bring the rays to a focus sooner. If on the other

348

ADVANCED PHYSIOLOGY

Fig. 171. — Diagram

Showing the method of the formation of an image

by a lens.

hand it is replaced by one of less curvature, it will bend them
less sharply and bring them to a focus at a greater distance
from the lens. If, however, the lens be concave, the rays
will be scattered instead of being brought to a focus. It is
important that these points be clearly seen, in order that one
may understand the accommodation of the eye.

If, instead of a single point giving out light, there is an
object of some size, the action of the lens is essentially the

same. Suppose that
the object is a candle
flame (Fig. 171); the
tip of the Hght, A, is
a point and the rays
passing from it will,
of course, be focused
at a point, a. The
base of the light isi
another point, BA
which will be focused at b. In the center of the candle we]
might select another point which would then be focused]
between a and b. The whole candle and its flame arej
made up of points, each of which will be focused at a cor-
responding point. If, therefore, a piece of paper or a screen,
be placed at the line, a-b, we shall find an image of the candle]
flame upon it. The image, however, will be upside down,
is evident from the figure.

In the human eye an image is formed in exactly the same|
manner. The lens focuses the light that passes through it]
and produces an image at a certain distance behind it. Inj
a normal eye the retina is at just the proper distance so that]
the rays of Hght are focused upon it, and the image thus
formed; Fig. 172. Since this image is, of course, up side!
down, one naturally asks, why do we not see things in in-j
verted positions. This question arises from the false im-!
pression that one's brain pictures things just as they occur on'

ORGANS OF SPECIAL SENSE— THE EYE

348

the retina, as if the brain were looking at the image on the
retina. The exact process by which the brain perceives the
image is compHcated, and not entirely known. For our pur-
pose it is sufficient to say that
although the image is certainly
inverted on the retina, after the
impression has reached the brain,
it is interpreted so that we see
things as they are.

Accommodation. — Every one
knows that it is perfectly pos-
sible to look at a spot on the
window glass and see it clearly,
and at the same time see indis-
tinctly whatever there may be beyond the glass, trees, build-
ings etc. If one chooses he can give all his attention to the
trees and see them very clearly, at the same time seeing very

Fig. 172. — Diagram

Showing the formation of an im-
age upon the retina.

Fig. 173. — Diagram

Showing the effect of different lenses in changing the position of the focus of light'
and illustrating how a change of the lens is necessary if objects at different dis-
tances are to be focused upon a screen.

indistinctly the window glass and frame. When he changes
his attention from one to the other he is conscious that some-
thing is taking place in his eyes, and that it requires part of

350 ADVANCED PHYSIOLOGY

a second, at least, for the change to be made. This process
is called accommodation, and occurs almost entirely in the
lens, although the front of the cornea is also sUghtly
modified.

The form which a lens must take when the object viewed
is near at hand, as compared with its form when the object is
far away, is shown in Figure 173. When a point is near the
lens, as at A, the rays of light going from it will diverge
rapidly. In order to bring them to a focus at the distance
of the screen or retina, they must be bent very decidedly
inward. It is also evident that if a point is farther away from
the lens, as at B, the rays will not be diverging as rapidly
when they reach the lens, and not being turned from their
course as much as those from A, will come to a focal point in
front of the screen or retina at h. Moreover, we have already
noticed that the more bulging or convex the lens, the more
sharply the light rays going through it will be bent from their
paths. If, therefore, a flatter lens is substituted, like the one
marked I, which has a curvature only suflacient to bring rays
from point B' to a focus at 6', the rays from point A^ will not be
sufficiently bent and will be focused behind the screen at a\
But if a more convex lens is substituted, like the one at l\
the rays from both A^ and B^ will be focused in front of the
screen at a'' and 6''. Thus a lens of a definite curvature is
necessary for properly focusing light from anj^ particular point.
If one wishes to look at a distant point after examining a
near one, the lens must be flattened; and when the attention is
turned from a distant point to a near one, a more convex
lens is necessary.

Mechanism of Accommodation. — In the eye it is not neces-
sary to replace one lens with another, for the lens of the eye
is not rigid like glass, but can change its shape from a thin,
flattish to a very convex form. Attached to the edge of the
lens and holding it to the choroid layer, we have noticed the
suspensory ligament. This is under tension, and as a result

ORGANS OF SPECIAL SENSE— THE EYE

351

is pulling outwards on the edge of the lens in every direction;
Fig. 167. Since the lens is somewhat soft, this outward pull
tends to flatten it. In this shape, the lens is in condition for
focusing on the retina rays of light coming from a dis-
tance.

If the object viewed is near, as it is in reading or writing,
the lens must be more convex. All that is needed to make it
so is to loosen the ligament, when the lens of its own elasticity
will bulge, and assume the necessary convexity. For every
different distance the tension of the Ugament must be changed
accurately and almost instantaneously, so that the convexity
of the lens may be exactly correct.
This regulation of the suspensory lig-
ament is accomphshed by the so-called
ciliary muscle, (Fig. 174), one end of
which is attached to the choroid coat
behind the point where the suspensory
Ugament arises, the other end fusing
with the iris and the inner layers of the
cornea. When this muscle contracts,
it is easy to see that the choroid layer
will be pulled forward, the ligament
will become loose and the lens will
"bulge," taking the shape of the dotted
line in Figure 174. The more the muscle
contracts, the more convex the lens
will become, and consequently the

nearer objects may be held and yet be seen. There is, however,
a limit to the nearness at which objects may be seen. The
ciliary muscles can contract only a certain amount, and the
lens can become convex only within certain limits. When
an object is held too near the eyes, everything becomes blurred
since its light is not focused on the retina. The chief reason
that one's eyes become tired from reading is that the ciliary
muscles are weary from staying contracted during the prt?-

Ciliortf Muscle..

Suspensory
li^ameirf

Fig. 174. — Diagram

Showing the method by whici:
the lens is held by the sus-
pensory ligament, and the
ciliary muscle whose con-
traction will loosen the liga-
ment and allow the lenf
to bulge.

352

ADVANCED PHYSIOLOGY

^A=-«

Fig. 175. — Diagram
Showing that when parallel rays of light are
focused on the retina, rays from near objects
will be focused back of the retina.

longed period that one has been looking at the book held neai
the eyes.

Figures 175 and 176 show what the result would be if the
lens of the eye could not be accommodated to different dis-
tances. There would be
only one point at which
objects could be seen
clearly. If parallel rays
of light are focused on
the retina as in Figure
175, rays from points
near by, as at A, will
be focused behind it.
If, however, rays from
an object near the eye are
properly focused, as in
Figure 176, objects farther away would be indistinct because
light from them would come to a focus in front of the retina.
The power of changing the shape of the lens allows objects

at any distance (not too
near) to be seen clearly.

Near- and Farsightedness.
— The normal eye is of such
shape that parallel rays of
light are focused exactly on
the retina; Fig. 175. Often,
however, a person's eyeballs
are a little too long or the
lenses a little too convex
(Fig. 176), so that enter-
ing rays of light coming from a distance are not focused
on the retina but in front of it, and to be focused ex-
actly on the retina, an object must be held close to the eyes.
Nearsightedness, or myopia, may result from either of these
causes, and in either case the difficulty may be remedied by

Fig. 176. — Diagram

Showing that when near objects are
focused on the retina, parallel rays of
light will be focused in front of it.

ORGANS OF SPECIAL SENSE— THE EYE

353

Fig. 177. — Diagram

Showing a nearsighted eye with a proper
lens for correcting the defect.

glasses. The reason that the nearsighted person finds it hard to
see distant objects distinctly is that the rays forming the image
come to a focus too quickly after entering the eye; if lenses of
just the right curvature be
placed in front of his eyes, so
that the rays are caused to
diverge a little before reach-
ing the eyes (Fig. 177, dotted
lines), the rays will be brought
to a focus at exactly the right
place. By '^fitting a person
with glasses" we simply mean
that extra lenses are chosen
of just the right curvature to correct his particular trouble.
Myopia is common among those who read very much or
use their eyes for other work at close range. To avoid devel-
oping nearsightedness, one should acquire the habit of hold-
ing books at least eighteen inches from the eyes.

In farsightedness, or hyperopia, the conditions are just the
reverse of those in nearsightedness. The person cannot see a
near-by object clearly because
the lens is too flat or the eye-
ball too short. The rays of
light going into the eye come
together behind the retina, as
shown in Figure 178. In such
an eye even the full contraction
of the ciliary muscle may be
unable to make the lens convex
enough to bend the light rays
to a point by the time they reach

the retina, and consequently the image is blurred. If, how-
ever, a sHghtly convex spectacle lens be used, which will
turn the rays and start them to a point, the lens of the eye
can do the rest; Fig. 178.

Fig. 178. — Diagram

Showing a farsighted eye with proper
correcting lens.

354

ADVANCED PHYSIOLOGY

Astigmatism. — We have assumed that the surface of the cor-
nea in front and of the lens behind it were parts of true spheres,
curving equally in all directions. The majority of eyes, how-
ever, are astigmatic, i. e. there is somewhere, either in the
cornea or lens, an irregularity so that the combined shape of
these bodies is more like that of a football than like a true
sphere, curving in a circle in one direction, but in an oval in
the other. As a rule there is one plane in which persons
with astigmatic eyes can see well, but in all other planes the
image will be blurred; Fig. 179. To remedy this very serious
defect it is plain that neither a perfectly convex nor a per-

FiG. 179. — Diagram of defects in an astigmatic eye

Showing that rays from a point are not properly focused. A, source of light;
B, C, retinal surface; D, lens. Rays in one plane come to a focus at a point; in
the other plane they are distributed over B C in a line.

fectly concave lens will suffice. The need, then, is for a lens
ground at two different curvatures, the opposites of those in
the eye lens.

THE RETINA AND ITS FUNCTIONS

We have seen that the images of objects in the external
world are focused upon the retina, a fact which suggests that
this is the sensitive, i. e. the real seeing part of the eye.

The actual thickness of the retina at its thickest part, at
the back, is only about one seventy-fifth of an inch and it is
much thinner than that on the sides of the eye. Its border

ORGANS OF SPECIAL SENSE— THE EYE

355

near the sides of the iris is a mere frayed edge of tissue. Yet
this thin layer is a very compHcated structure, a microscopic
section showing eight well defined layers or strata. Next to
the choroid coat is a pigment layer. At first glance this
usually appears black, but when more carefully examined it
proves to be made up of granules of a purplish hue, a fact
which explains why this material is sometimes called the
"visual purple." This pigment is not laid down in an even
coating next the

choroid, but is ar- -^°^^ ^°"^'

ranged in a kind of
mosaic of six-sided
patches.

Next the pigment
is a layer of cells of
very peculiar shape.
Each contains a nu-
cleus like any other
cell, but has two
outgrowths on op-
posite sides; Fig.
180. On one side
a fibre extends and
ends in numerous
small branches or
arborations; on the
other side opposite
the fibre, in some a
rod-like, in others a cone-like structure is found. These rods
and cones are all arranged parallel with one another, their ends
pointed toward the pigment layer, the rods in many cases
reaching into the pigment. At the back of the eye the cones are
much more abundant than on the sides of the eyeball, where the
rods predominate. In the very center of the back of the eye
directly behind the pupil, is a minute area in which there are

■ Nerve Fibns
Fig. 180. — Section through the retina

Very highly magnified. The lower edge is the om
toward the center of the eye. The rods and cone?
are indirectly connected with the nerves. (Cajal)

850 ADVANCED PHYSIOLOGY

only cones, and which lacks nearly all the other layers of the
retina. It is plain from its situation that light coming directly
into the eye falls on this spot. This is the area of clearest
vision, or in scientific terms, the fovea centralis, Fig. 167.

The other layers of the retina are represented in Figure 180,
but no special description of them will be given. From the
figure it will be noticed that from the inner ends of the rod and
cone cells other nerve cells arise, which extend toward the inner
portion of the retina, and are there connected or closely as-
sociated with nerve fibres. Any impulse, then, which starts
from the rods and cones may pass up through these connec-
tions until it reaches the nerve fibres, and goes through them
to the brain.

The nerve fibres thus arise on the innermost side of the
retina next to the vitreous humor. They all pass toward the
back of the eyeball and finally unite to form the large optic
nerve. This nerve passes through the various coats of the
eyeball and then goes to the brain. It does not leave the eye
directly at the back, in the line of entering light, but on the
side of the eye toward the nose. At the point where the
nerve leaves the eye there is a small area which, having no rods
or cones and no pigment (these structures alone are really
sensitive to light), is blind and is therefore called the blind
Spot. In the ordinary use of the eyes, however, we do not
notice the presence of any such area.

EFFECT OF LIGHT IN THE EYE

How does light act on the parts of the eye which are sen-
sitive to it — the pigment and the rod and cone layers of thej
retina? No one has any precise knowledge of this matter,]
but there are two interesting theories as to its effect.

The Chemical Theory. — The chemical theory supposes thai
the chemical composition of the pigment layer is changed by]
light, somewhat as is the sensitive plate in a camera whenj
ilie abutter is opened. The theory rests upon these facts :j

ORGANS OF SPECIAL SENSE— THE EYE 357

(1) that the amount of pigment increases when the eye is
closed, and decreases when Hght enters it; (2) that if the eye
of an animal be closed, the animal then immediately killed
and the eye first opened in a solution of alum in a dark room,
the image of the last thing seen by the eye can thus be pre-
served in the pigment layer. (Such a picture is called an
optogram). A difficulty in the way of accepting this theory
is that it supposes the pigment to be constantly broken down
by light and again restored. In reading, for example, the
shapes of thousands of letters and the spaces between them
and between the lines are continually appearing and forming
rapidly changing pictures on the retina. In the ordinary use
of the eyes, hundreds of different images are being formed and
changed every minute. In order to be continually in con-
dition to receive new light rays, i.e. receive new images, the
pigment would have to undergo repairs at a rate of which we
can hardly conceive.

The Mechanical Theory. — The mechanical theory supposes
that light falling on the retina disturbs or shakes the rods and
cones, and thus starts in them impulses which travel
through their connections to the optic nerve and thence go
to the brain. How can this be possible? In answering this
question we have to remember that light itself is in the form
of very short, wave-like movements. The rapidity of these
vibrations is almost beyond our powers of appreciation; but
the theory is that they pass into the eye and thus stir the rods
and cones to the same rapid movement, the disturbance
being interpreted in the brain as *'Ught."

The main reason for doubting that the effect of light in the
eye is so simple is that the light waves take place at such very
rapid rates. For instance,' the slowest movements which we
interpret as hght at all occur at the rate of 107,000,000,000,000
per second; the fastest rate which we can perceive at all is
40,000,000,000,000,000 per second. Red hght vibrates at
392,000,000,000,000, and violet at 757,000,000,000,000 per

358 ADVANCED PHYSIOLOGY

second; the other colors which we can see are caused by
vibrations at rates between those of red and violet. Although
these figures really mean very little to us, it is certainly im-
probable that the material particles which we call rods and
cones can be thrown into such rapid movement, and especially
hard is it to see how their rates of vibration could be changed
from one frequency to another with such accuracy as they
must be when one suddenly looks from red to violet, or from
yellow to green, for example.

In spite of the reasons which make it seem hard to believe
the action of light on the retina of the eye to be either chemical
or mechanical, we can hardly avoid the conclusion that it
must be one of these two, or a combination of them. We are
practically forced to say that we do not know what light
really does in the eye.

COLOR VISION AND COLOR BLINDNESS

We have already noted that in the back of the eye cones
are especially abundant and diminish toward the sides of the
retinal area, while rods are few at the back and plenty on the
sides. Hence light entering the eye from the side would
strike mainly on rods, while that going straight toward the
back would disturb chiefly cones.' If we keep this fact in
mind, and reflect that the color of an object is most plainly
seen when the object is straight in front of us, we must con-
clude that the cones are the more sensitive of the two to color
changes. Rods seem to be sensitive to light and shade, but
not to color, while cones are sensitive to both. It can be
proved by experiment, too, that a larger area of the retina
is sensitive to one color than to another; for example, one can
see violet objects as they are brought around slowly from the
side to the front sooner than he can identify a green object so
brought before him. Consequently we conclude that the area
of the eye which can see violet is larger than that which can
perceive green. The area which can see red is also larger than

ORGANS OF SPECIAL SENSE— THE EYE 359

that which is sensitive to green, but smaller than that which is
sensitive to violet. Physiologists claim that red, green and
violet are the only colors perceived by the eye, and that other
colors are seen when two or more of these colors are stimulated
at the same time, in different degrees.

Color blindness is a more common defect than is supposed.
It consists in inability to see any difference between two
colors which seem to most people very unlike and distinct.
The most common kind is that in which a person is unable to

I distinguish between red and green. To such a person the
only difference between red apples and green leaves on the
same tree would be merely a difference in shape and brightness.
If one accepts the theory that the eye perceives only red,
green and violet, then red color blindness would be explained
by supposing that the red sensations were only imperfectly
developed, or perhaps altogether lacking.

Persons who are colcfr blind cannot obtain employment on
railroads or ships, for in such positions it is absolutely neces-
sary that one see clearly both red and green, since flags,
lights etc., used as signals are generally of these colors.
There is no known remedy for this defect.

CARE OF THE EYES

Probably no defects are so apt to escape attention and
proper treatment as imperfections in the eyes. Even in
cases where the eye is very defective, one may see fairly well
and so neglect to attend to the matter. The result is that
some part of the eye may be in a condition of strain, trying to
force the refractive surfaces into shape to produce a proper
focus upon the retina. This strain brings on fatigue of the
delicate muscles themselves and exhaustion of the nerves
that may lead to serious results, e. g. headaches, indigestion,
nausea and various nervous diseases. Any one of these out-
comes is sufficient practically to disable a person for hard
work and to cloud living with continuous pain. The mental

380 ADVANCED PHYSIOLOGY

and physical disturbances which follow in the wake of eye
defects should lead one to the most jealous care of these
priceless organs. Glasses should be fitted by a skillful
oculist as soon as it is discovered that the eyes are unable
easily to meet the demands upon them. The cost of this
sort of care should not be allowed to influence one in the matter
of procuring and following the most expert advice.

If one has to hold a book nearer to the eye than 12 inches,
the indication is that he is nearsighted. On the other hana,
if he finds it necessary to hold a book 20 inches or more from
the eyes to read it easily, the probability is that he is farsighted.
In either case he should consult an occuUst.

Some troubles due to imperfect eyes, such as headaches
and nervousness, are not always recognized as associated
with those organs. Sometimes a child in school is thought
stupid when the trouble is that he cannot see what is written
on the blackboard. A wise plan has been adopted in many
schools in recent years, undei* which the eyes of each scholar
are tested to determine whether or not he needs glasses.
Properly adjusted glasses not only bring relief to strained
eyes but so improve general health that everyone ought to
welcome an examination of his eyes, and if necessary the
adoption of proper glasses.

In ordinary life, through ignorance and carelessness we
frequently use our eyes unwisely and in such a way as to
invite or increase a tendency to eye trouble. A few general
suggestions, therefore, may be profitably remembered by
everyone.

Illumination. — By changes in the size of the pupil consider-
able variation in intensity of illumination can be met, since
the pupil opens in dim light and closes in bright. Too dim
light, as for instance that at twilight, taxes the eyes severely
if one tries to use them for exacting work, like reading. On
the other hand, very bright light is equally injurious, so that
one should not allow sunlight to fall upon a page he is reading.

ORGANS OF SPECIAL SENSE-THE EYE 361

Flickering Light. — A light whose intensity is constantly
changing is very tiresome. It is injurious to read by candle-
light, not so much because it is dim, as because it is not
steady. Reading in the cars is very taxing because the im-
ages on the retina are those of an object which is constantly
shaken by the motion of the car.

Resting the Eyes. — Eyes are made for use and if properly
treated will grow stronger, but if overtaxed they will
suffer quickly. Reading fine print or looking intently and
constantly at small objects is always severe on the eyes.
Everyone whose work requires such application should
appreciate the need of giving the eyes an occasional rest by
looking off at distant objects, or by ceasing to use them at all.
If rested in this way xhey may be used for exacting work for
years without injury.

Injuries. — The eyes are too delicate to be carelessly treated
and injuries to them usually need the attention of a physician.
A particle of dust or a cinder in one's eye can usually be re-
moved with ease, however. In most cases tears will quickly
wash it over the surface to the tear duct. This process may
be assisted by seizing the lids with the fingers and lifting them
away from the eyeball, when the tears that accumulate will
ordinarily dispose of the dust. The eye should not be rubbed.
If the dust particle is under the lower lid, this can easily be
lifted and the particles be removed on the corner of a hand-
kerchief; if it is under the upper lid, this can be rolled up
gently over a lead pencil. A physician should, however, take
care of any serious eye trouble.

CHAPTER XXII

THE EAR

Although externally the ear does not appear to be so
delicate an organ as the eye, yet as a sense organ it is scarcely
less iiiiricate m structure, or necessary in daily life. It has
been noted that the eye is quite protected in its rather deep
socket; but the ear is yet more secure, being set deeply into
and almost surrounded by the temporal bone of the cranium.
For convenience in description it is treated as though in three
parts, the outer, the middle, and the inner ear.

The Outer Ear. — The portion of the ear which protrudes
on the side of the head is made up largely of skin, containing
several small pieces of cartilage which give it shape. In many
animals the outer ear is large and acts as an organ for gathering
sound waves and leading them against the ear drum inside;
in man, however, this use of the outer ear is practically gone,
and it has no special function. Muscles for moving it, which
are highly developed in many and especially in four-footed
animals, are present in man also, but have degenerated
through lack of use. The old-fashioned ear trumpet was
merely an auxiliary contrivance for collecting more sound
waves and conducting them into the ear.

The canal leading into the head is called the external
auditory meatus; Fig. 181. This comes to an abrupt ending
against a thin membrane, the ear drum, or tympanic mem-
brane. The canal dips downward a little as it goes inward,
and this fact explains how it is that water may get into the
ear when one has the head under water when swimming, and
why it can only be gotten out by tipping the head to one side

362

THE EAR

363

and j arring it. In the skin which lines this canal are numerous
glands that secrete a substance which partially evaporates
and leaves what is called ear wax. This seems to have little
function, but it should never be interfered with except by a
competent physician.

The Middle Ear. — The middle ear is a space just inside the
ear drum (Fig. 181) and is scientifically called the tym-
panum. The cavity
is not large and is
surrounded by bone
on all sides save at
a few points, which
will be especially
noticed later. On the
lower side of this cav-
ity is an opening lead-
ing into the Eusta-
chian tube, which
passes down to the
throat. On the inner

the inner ear is shown natural size. In the upper sidQ of the tvmpaUUm
figure the external ear is shown much too small

Fig. 181. — Diagram

Showing the structure of the ear. In the lower figure

relatively to the size of the internal structures.
The oblique shading represents bone. A, external
meatus; B, utricle; C, saccule; D, semi-circular
canal; £^, nerve; i^, cochlea; G, Eustachian tube;
H, tympanic membrane; /, cochlea.

are two small open-
ings, which lead to the
inner 'ear, but which
are closed by mem-
branes; the upper one is the foramen ovale, the lower,
the foramen rotimdum. At the upper part of the tympanum
are some minute pores leading into spaces, called the mastoid
cavities, in the surrounding bone. Reaching across the tym-
panic cavity is a chain of three httle bones; Fig. 181.

The Eustachian Tube. — The Eustachian tube serves two
very important functions. First, it allows air to go in and
out, between the ear and the pharynx. At first thought it
seems odd that there should be any connection between the
ear and the throat, but such connection is necessary to keep

364 ADVANCED PHYSIOLOGY

the air in the middle ear at the same pressure as that outside,
so that the ear drum may be kept flat. The Eustachian tube
is, therefore, of especial use in enabling one to adapt himself
to different altitudes. At the sea-level, atmospheric pressure
is much greater than on the tops of mountains; if the Eu-
stachian tube did not thus regulate internal pressure in the ear,
the drum would sometimes be pressed inward or again out-
ward, perhaps to the breaking point. The Eustachian tube
is also useful as a drainage way for the middle ear; its lining is
ciliated, and mucus which is formed in small quantities in the
tympanum is thus carried to the pharynx.

The Eustachian tube is not generally open; it is rather in
the condition of a thin rubber tube, with its sides collapsed.
Its closing prevents the voice, which is produced in the voice
box just below the opening of the tube into the pharynx, from
passing up the tube and creating a loud disturbance during
ordinary conversation. Moreover, if the tube were con-
stantly open, air would be continually passing in and out of
the middle ear as one breathes. This would keep the thin
membrane of the drum and the partition between the middle
and inner ear cavities under constantly changing pressures,
and irritate the hearing organ seriously.

Mastoid Cavities. — Whether or not the mastoid cavities are
of any value is not clear; but they are sometimes the cause of
serious trouble. When there is inflammation in this region
and the cavities become filled with pus, producing a disease
called mastoiditis, the most skilled physician or surgeon
should be given charge of the case. The distance from the
mastoid region to the brain is so short that inflammation can
easily spread through the thin, bony walls of the brain cavity,
and if the brain becomes involved the trouble may be fatal.

The Ear Bones. — There are three tiny bones stretching in
a zigzag course across the middle ear cavity, from the ear
drum to the foramen ovale; Fig. 182. The first is the malleus
(hammer), and is fastened to the drum at one end. From

THE EAR

365

Jncus

tlalleus

there it extends upward, where it is attached to the second
bone, the incus. This bone has something the shape of a
blacksmith's anvil (hence the name incus) and one projection
from it extends downward into the cavity again, connecting
with the third bone, the stapes (stirrup), which ends in a broad,
flat area, fitting into the
opening mentioned above
as the foramen ovale; Fig.
182. """'^^^iiis^ 7"'W/-i /^^^

The three bones are con-
nected by ligaments, and
there is practically no
hinge action except be-
tween the incus and
stapes. Two tiny muscles
are connected with these
bones; one, the tensor tym-
pani, leads from the wall of
the Eustachian tube to the
malleus bone. When it
shortens, it pulls on the
malleus and thus indirectly
tightens the drum. The other muscle, the stapedius, runs
from the wall of the cavity to the neck of the stapes, and
when it contracts pulls the stapes to one side, thus changing
the position of the membrane over the foramen ovale. The
value of these muscles will be discussed later.

The Inner Ear. — The foramen ovale is a short passage in
the bone and leads into a series of cavities which constitute
the inner ear. As shown in Figure 181, this cavity is com-
plicated and difficult to understand. Altogether it is no
larger than the end joint of the Uttle finger, but it is the loca-
tion of the whole organ of hearing and of balancing. Inside
the foramen ovale membrane is a cavity called the vestibule,
filled with a thin watery fluid, the perilymph. The cavity ia

Tqmpamc tJembrane

Fig. 182. — The ear bones
Stretching across the middle ear from the
tympanic membrane to the foramen orvale.
(Hensen)

366

ADVANCED PHYSIOLOGY

not a simple one, but from its main central portion (Fig. 181)
three tubes lead out into the surrounding bone in different
directions, make half circle turns and come around into the
central cavity again. On the posterior side of this cavity a
longer canal, twisted into a spiral form, goes out into the bone.
In this curiously shaped cavity and floating in its fluid are
two thin-walled sacs; the larger is called the utricle and is
connected with the smaller, the saccule, by a slender canal.
From the utricle membranous tubes, called the semicircular
canals, run through the three half circular canals noted above.
Extending from the other sac, i.e. the saccule, and following
the course of the spix-al tube in the bone, is another mem-
branous canal. This spiral bony canal and its contained
membranous canal are together called the cochlea. The
utricle, the saccule and all the tubes in connection with them
are filled with a clear, watery fluid, the endolymph.

FUNCTION OF THE SEMICIRCULAR CANALS

■Posterior Semicircular Canal
.-External » » "

Superior^

Cochlea

'Saccule
Utricle

The ear is usually thought of
as an organ of hearing rather
than one of balancing, but the
semicircular canals are con-
cerned with the latter function.
Figure 182A shows that each
canal has a swelling, an am-
pulla, at one end near where it
leaves the utricle. The inner
structure of an ampulla is
shown in Figure 183.
On one side of the ampulla is a ridge, and on top of the
ridge are a number of hair-Uke projections, among which are
lime granules. The direction in which the canals run should
also be noted. No two pass around through the bone in the
same plane; one lies approximately in a horizontal plane,
another in a vertical plane, in a right-to-left direction, and the

Ampulla
Fig. 182 A. Diagram

OF BAR PARTS

THE EAR

367

third in a vertical plane, in a front-to-back direction. Thus,
one of these canals is located in each of the three planes of
space, in each of the maia directions in which the body can be
inclined.

If the location and structure of the canals is clear, their
manner of functioning can be readily understood. They are
filled with endolymph, and when the head is rotated, this
fluid acts as water does in a pail or glass jar when the latter
is turned around in

the hands. The liquid lime, qranules

scarcely moves, but
the pail or jar slips
around outside the
liquid. If there were
threads attached to
the sides of the pail,
these would be bent
back and forth by the
water slipping over
them as the pail was
turned first one way
and then the other; in

like manner, if the head is tipped from side to side, or forward
and backward, the endolymph in the canals tends to stay in its
original position, while the canals slip around it. This makes
the hair-like projections on the crests in the ampullae bend to
and fro, and since nerve fibres end in these ampullae, this sway-
ing of the threads creates a message which is carried to the
brain. In tipping in any direction, the lime granules will set-
tle on different parts of the ampullae. This will irritate
nerves ending in these regions, and the result is that one has
a sensation of inclining from side to side, of falling or of rolling
over, as the case may be.

Of course all the movements one makes are not in the exact
planes in which the semicircular canals lie, but they are at

Fig. 183. — ^^A section of one of the ampulla

OF THE SEMI-CIRCULAR CANALS (Kolliker)

368 ADVANCED PHYSIOLOGY

least somewhere between them, in which case the endolymph
in two of the canals is moved, and from the resulting sensation
one judges the direction of the body motion. These facts, too,
explain why children who have been whirling about on their
feet in one direction for some time become dizzy. If a pail
of water is whirled long enough in one direction the water
will finally get to whirHng with the pail; and if then the pail
is suddenly stopped the water will keep on moving for some
time. In the same way, a whirling child sets the endolymph
moving in the direction in which the canals go, so that the
latter no longer slip around outside the endolymph; when the
child stops whirling the endolymph keeps on moving in the
canals, and though the body is quite erect, messages continue
to go to the brain, and the resulting sensation makes the nerve
center feel that some other position of the body must be sought.
Messages are consequently sent out to some muscles to relax
and to others to contract. As a result the child makes stagger-
ing movements, or falls over. Relief can be obtained quickly
by whirling in the opposite direction for a moment, thus com-
pelling the endolymph to overcome more friction and sooner
become quiet.

THE STRUCTURE AND FUNCTION OF THE COCHLEA

The shape of the cochlea tube, as it winds into the bone of
this region, has already been described as that of a spiraL
The diagram in Figure 184, which represents the cochlea as
unwound and straightened out, makes this matter of the con-
nection between the cochlea and vestibule clear. The part of j
the structure "which has to do with hearing is the dottec
horizontal tube, in the walls of which the auditory nerves
end. The cochlea is large where it leaves the vestibule, but]
grows smaller as it coils. It has often been likened to aj
snail's shell, and indeed takes its name from that fact.

Extending through the membranous tube (marked cochlea!
in Figure 184) is a pecuUar organ, a sketch of which (highly!

THE EAR

369

magnified) is shown in Figure 185. This is called the organ
of Corti, and in it are the endings of the auditory nerve fibres.
It is the real organ of hearing, just as the retina is the organ
of sight. The manner

in which it is affected .,/^. ^^i^.. .VesHbule

by sound is not fully
known, but it is prob-
ably something as

ollows : —
Sound is produced

y vibrations or waves
of the air. When
waves reach the body
they pass into the

Coc hleo UincoHed)

Fig. 184. — Diagram

Showing the relation of the cochlea (uncoiled) tc

the vestibule and other parts of the ear.

external auditory meatus until they come against the tympanic
membrane or drum. As the waves fall upon this they set it to
moving at the rate at which they strike it. This movement of
the drum will evidently be transmitted to the ear bones attached

Haircelh

Fig. 185. — Section of the organ of corti

Highly magnified. Showing the real hearing part of the ear. (Retzius)

to it and by their motion the end of the stapes is pulled back
and forth in the foramen ovale. This motion will in turn
produce a similar set of little waves in the liquids of the in-
ternal ear, with the result that the whole mass of liquid will
vibrate just as rapidly as the air outside the head. As a re-

370 ADVANCED PHYSIOLOGY

suit, the organ of Corti, which Hes quite freely in the Hquid,
will also be thrown into vibration. In this organ, as we
have learned, are the ends of the nerves of hearing, and it is
supposed that the slight shaking they thus receive is sufficient
to stimulate them so that they transmit impulses to the brain,
which are then interpreted as sound.

Perception of Pitch. — The method by which the ear recog-
nizes high and low tones is not fully understood, but it ap-
pears to be in part based upon a very simple fact. Sound is
the result of air waves, and the different pitches are due to
waves of different degrees of rapidity. In high sounds the
rate is very rapid, in low sounds it is slow; the longest strings
of a piano vibrate about thirty-three times per second, the
shortest strings about four thousand two hundred times. If
one stands close to a piano and plays a loud note upon a flute,
for example, and then stops, he will notice that he can hear
the same note sounding in the piano for several seconds.
The waves of air starting from the flute have passed into the
piano and strike upon the various strings. There is one
string in the instrument that naturally vibrates just as
rapidly as the waves which come from the flute, and these
wave motions from the flute set that particular wire into
vibration, so that even after the flute is silent, one can hear a
faint sound from the piano string. If two notes were played
near the piano at the same time, two wires would be set into
vibration, etc. This phenomenon takes place according to
a principle known as that of sympathetic vibration.

By reference to Fig. 185 it is noted that the rods of Corti and
the ^'hair cells" seem to stand on a straight, basal membrane;
this is really a shelf-like curtain which is attached to the core
of the spiral cochlea along one edge, and to the outer curve of
the tube on the other, dividing it into two spaces lengthwise.
This basilar membrane is made up of about 24,000 threads
(Retzius) of practically as many lengths. These basilar mem- j
brane threads, it is thought, vibrate at different rates,

THE EAK an

much as do the various wires of a piano. When, therefore,
the liquids in the inner ear are thrown into vibration, it is
evident that some part of the organ of Corti will naturally
vibrate with exactly the same rapidity as the movements of
the liquid, according to the laws of sympathetic vibration.
Thus for every different sound a nerve fibre will be stimulated,
and the brain recognizes the different pitches. While this
general theory of tone perception seems to be reasonable and
correct, we must admit that as yet no one knows precisely
what part the organ of Corti plays in the appreciation of
sounds.

Loudness of Sound. — Loudness of sound depends, not on
the rate at which air is moving in waves, but on the size of
the waves; not on the rapidity of vibrations, but on their
amount. This we know from the simple fact that a piano
string struck heavily will give out a loud sound; if struck
gently, a low sound, though of the same pitch as when struck
heavily. Violent movements in the air are set up when the
string is vibrating back and forth through considerable dis-
tance after being struck hard, and these start large waves
in the surrounding air, which however vibrate at the same
rate as if the wire had been struck gently. These violent
movements are finally transferred to the inner ear over paths
we have already discussed, and thus the nerve endings in the
organ of Corti are greatly irritated. One interprets this
strong stimulation as loudness of sound; faint sounds are con-
versely due to very slight air waves and slight nerve stimula-
tion.

When listening intently to catch some faint sound, almost
everyone strikes the same instinctive attitude. The body is
held very quietly, the ear turned in the direction from which
the sound is expected, and the whole attention is focused on
the ear. In the perception of faint sounds, slight changes
occur in the middle ear, and the purpose of these changes may
be understood from the analogous action of a drumhead.

372 ADVANCED PHYSIOLOGY

When a drum head is loosely drawn, the drum will sound
very well if struck hard enough with the sticks, but if
the drummer merely touches the head or hits it very gently,
no sound of consequence comes from it. If, on the other hand,
the drum head is drawn tight by shoving down the straps on
the cords at the sides of the drum, the merest movement of
the sticks on the head produces a very distinct noise.

In the middle ear the two tiny muscles, mentioned on
page 365, are so placed that they can tighten the membranes
bordering on the middle ear, so that the least movement of
sound waves in the air can be detected. The tensor tympani
draws the ear drum tight, and the stapedius pulls on the stapes
and adjusts the membrane over the foramen ovale; the
ear is thus put into condition for perceiving very faint sounds

Quality of Sound. — As has already been pointed out, the
quality of one's voice is determined not entirely by the nature
of the vocal cords, but by the size and shape of the cavities of
the trachea, the pharynx, the nose and some smaller cavities
in the bones of the upper part of the nose. The air in these
cavities is set in vibration by sound waves, and the people
who are listening to one's voice get the effect of all the inci-
dental influences of the cavities upon the sound. How
marked the influence of these centers is may be proved by
merely closing the nasal passages — grasping the nose between
the fingers while talking.

DEAFIiESS

Defective hearing is due to a variety of circumstances. In
elderly people it is generally caused by the stiffening of the
ear drum or other delicate membranes so that they are not
so sensitive to slight sound waves as formerly, or it may be
due to the fact that the bones of the middle ear have become
more or less rigid and do not move readily.

In younger people, and in those who become temporarily
deaf, the trouble usually is that the Eustachian tubes have

THE EAR 373

become closed by some inflammation of the tissues about them.
This often happens to a person who has catarrhal troubles.
A bad "sore throat" may produce deafness or '^ringing
sounds" in the head for this simple reason. The result of
the closure of the Eustachian tubes is that the pressure of air
in the tympanic cavity, or middle ear, becomes different from
that outside (whether greater or less, the result is the same)
and the membranes involved will not act well under these
strained conditions. Such circumstances impose a kind of
stress on the fluids of the inner ear, so that they can move
very little, if at all. ''Ringing noises" may be due to the
fact that the fluids cannot move in the normal way, and these
being under extra stress, a large proportion of the nerve end-
ings in the ear feel the strain, and innumerable mild messages
go to the hearing center in the brain. These may be so con-
tinuous and disturbing as to induce headaches and generally
disagreeable results. One should not allow the trouble to
continue long without submitting it to skilled treatment. If
a ''buzzing in the ears'' or temporary deafness occurs as the
result of a cold, a physician should be consulted, since such
troubles, left unattended, may result in permanent deafness.
The other so-called special senses are taste, smell and the
sense of feeling, including touch, heat and cold. Each of
these has been considered in previous chapters and need not
be discussed here.

CHAPTER XXIII
THE CONTROL OF HEALTH

Personal Hygiene. — As one's usefulness in the world
depends directly on the quantity and quality of mental and
physical energy he has to spend, it is necessary to know the
important factors which contribute to personal health and
efficiency such as in food, exercise, sleep, etc. We cannot
exercise too great care in the selection, preparation and eating
of our food, or we shall yet condemn ourselves to ill-health by
our unwisdom.

Foods. — Our food should be selected with reference to a
proper balance of elements as outlined in Chapter III. Pro-
teids, carbohydrates, and fats are all vitally necessary, as well
as certain constituents (vitamines) found in vegetables and
milk. The action of vitamines is not yet thoroughly under-
stood, but it is known they play a very important role.

Excess of any food qualities to the exclusion of others will
finally, though not immediately, reduce the body to weakness;
this must never be forgotten.

Constipation, or the failure of food materials to be steadily
carried through the digestive tube, results in abnormal decom-
position and the formation of poisons which, absorbed, cir-
culate through and injure the whole body. This condition
can be avoided in most cases (a) by the use of coarse breads,
bran, graham, and the like; (6) by the use of leafy vegetables,
the larger part of which are never absorbed but become a
"roughage" which, in contact with the intestinal wall, pro-
vokes peristalsis; (c) by the right use of fats and oils; (d) by
the use of fruits. The old saying, **An apple a day keeps the

374

THE CONTROL OF HEALTH 375

doctor away", may be taken seriously, (e) Temporary laxa-
tives, such as drugs, must not be employed frequently, or the
system will come to depend upon them. Paraffin oil (Amer-
ican oil) is one of the safest and best laxatives and is not
unpleasant to the taste. (/) By the use of plenty of water.
Two quarts per day is not too much for a person weighing
150 pounds. Water taken in Hquid foods is needed in addition
to this amount, (g) Exercise, by which the body is repeatedly
bent into various positions, subjects the abdominal organs to
various pressures, the nerves are awakened, and the blood
flow quickened.

Salt and condiments : The fact that salt (NaC) leaves the
body in the same form as it enters makes it no less a necessity.
In 1000 parts of blood there are 5.5 parts of salt. Its intimate
role in the body is not entirely understood. Spices have no
food value, and should as a rule be eaten sparingly. Flavors
make foods more palatable, and in themselves are generally
harmless.

Beverages: Coffee and tea are the commonest table bever-
ages exclusive of water. In using them one must remember
that their food value is nil, save for the cream and sugar
usually taken with them. Caffein, in coffee, excites certain
nerve centres, and hastens kidney excretion, necessitating
abnormal demands on the organs involved. Thein, an
ingredient in tea, seems to prevent free digestive action of
saliva on starch. The use of either tea or coffee cannot be
commended, and must be strictly limited. Cocoa and choco-
late have decided food value, but contain also theo-bromine
which has the same properties in general as caffein.

The so-called **soft drinks," soda waters, etc., may have
small sugar value, but as generally taken, interfere with the
appetite for wholesome food, and besides the purchase of them
is a waste of money.

Irregular Eating. — The habit of eating between meals is a
specially vicious one if the regular meals are the proper time

376 ADVANCED PHYSIOLOGY

* apart, and are adequate for the kind of work being done.
If one feels faint or nauseated before a meal, the probability
is that his last meal was deficient and a lunch would have been
very wisely taken. The stomach, digestive organs and glands
must be given rest, just as we know muscles and nerves
demand it. The appetite may suggest irregular and frequent
eating, but its suggestions may not always be followed. See
page 51.

Alcoholic Beverages. ^ — ^The effect of alcoholic beverages
upon the nervous system has already been discussed.

Exercise. — Muscles comprise fully 40 %of the body weight,
and their condition, healthful or otherwise, affects the body
as a whole. The blood, going to and from every tissue,
carries away materials from muscle of a nature unlike that
taken from any other part of the body. As the blood stream
hurries on, every other tissue, e. g. nerves, glands, etc., is
influenced by what has gone into the blood stream from
muscles.

These changes which take place when a resting muscle
begins to act are as follows: (a) Sarco-lactic acid is produced
and replaces the alkaline character of resting muscle. (6)
Loosely combined oxygen is speedily associated with carbon
forming CO2. (c) Glycogen already stored in the muscle is
transformed and poured into the blood as dextrose, (d) The
temperature of the muscle is raised.

These changes, happening in the muscle itself, are, through
the blood stream, felt throughout the body, with many accom-
panying results, some of which are: (a) The respiration is
quickened and as a result the air is rapidly changed in the
lung recesses and the respiratory muscles are exercised and
given new **tone." (6) The heart beats faster, all blood tubeS'
are thus flushed and their own muscular walls called into
action, (c) The mechanism which regulates the temperature
of the whole body is roused and put to work, (d) Blood and
lymph are forced away from points where they may have

THE CONTROL OF HEALTH 377

become sluggish in their flow, (e) The digestive system
receives a reflex stimulus and is much benefited.

Exercise which comes through physical work directed to
some useful, productive end, brings its most genuine and
cheerful satisfaction. Play differs from most work in its
excess of mental exhilaration, its spirit of winning, its call for
particular skill, its social companionship. Exercise, to be of
value, should be vigorous, though not to the point of strain;
it should call for repeated moderate action of the same set of
muscles rather than a few severe or sustained contractions.
Gymnasia offer opport»unities for varied exercises which have
been selected with the advice of trained directors to meet the
individual need for the correction of faulty physique.

Sleep. — Sleep is the great restorer of the nervous system.
One should sleep with wide-open windows or in sleeping
porches. The hygienic reasons for sleep are these : (a) Every
other system of organs except the nervous system can secure
rebuilding during waking hours, if it is deliberately excused
from action; but unconsciousness is the only condition which
permits nerves to *'let go." (b) Sleep gives the time necessary
for the more complete elimination of wastes. A thorough
freeing from katabolic products cannot occur while new ones
are constantly added to those in the blood and lymph. This
purification can, however, be largely accomplished in eight
consecutive hours of total inactivity in sleep, (c) Sleep
permits that relaxation which cannot occur when one is active
mentally. A kind of tone or tension pervades the entire
system normally when awake and this needs to be excluded
regularly.

Hygiene of Particular Organs: Eyes. — No organ of the
entire body is more intricate than the eye. Its defects, if
any, have a far reaching influence on other organs, e. g.,
serious digestive irregularities, headache and nervousness
often result from eye-strain. If these symptoms are present,
or if it is difficult to see objects clearly unless held very near

378 ADVANCED PHYSIOLOGY

(6 or 8 inches) or very far away, or if the image of the object
is blurred in any way whatever, a skilled ocuUst should be
consulted to remedy the defect. When reading book or paper
of average sized type, it should not be held nearer the eye than
sixteen inches; nor should the focussing muscles be obliged to
act for that distance for long periods without rest. To obtain
a change in the focussing requirement when reading, look
about the room or out of the window occasionally.

Too intense light is apt to be used. It is only by actual
strain that the eye can function in our customary brilUant
illumination and if a gUstening paper or picture is being
examined the result is all the worse.

Ears. — To preserve good hearing, nothing must interfere
with any portion of the hearing apparatus. No small object
should be allowed to touch the ear-drum, much less puncture
it. Ear *Vax" should be removed with much care, and not
permitted to collect.

The greatest danger to the ear lies in its relation, via the
Eustachian tube, to the throat. Inflammation of the pharynx
can thus spread to the middle ear, and cause pus formation
either there or in the nearby mastoid cells (page 364) . It is
difficult to cure such a condition without endangering the
hearing function.

Social Hygiene. — By this term is meant the relation which
the mingling of people in numbers has upon the health of
each one, and of all collectively. In a general way, the
health of a community is the sum total of the health of its
individuals.

Ever since the germ theory of disease was established by
Pasteur, it has been well known that the health of a home or
the health of a whole community may be determined by the
health or the sickness of a single individual. The process of
the transfer of a disease from one person to another is termed
a process of infection.

Infection. — Quite a contrast with the days of long ago.

THE CONTROL OF HEALTH 379

we now know that many diseases are definitely passed from
one person to another either (1) by contact, or (2) by taking
into the body * 'particles'* given off from the body of the sick
individual. Other diseases are caused by the body being
invaded by certain of the lower animals (e. g. malarial organism,
trichina), or by bacteria.

* 'Contagious** and ''infectious'* diseases are now considered
essentially identical, being communicable. Among these
are typhoid fever, cholera, measles, mumps, whooping cough,
smallpox, — communicable from man to man. From the
lower animals man "catches'* tuberculosis, anthrax (splenic
fever) from cattle, malta fever from goats, malaria from
mosquitoes, plague from rats, and tapeworms from various
meats.

The main problem in avoidance of disease concerns those
which, in bacterial form, are passed from man to man. These
organisms secure an entrance generally in one of three ways:
(1) in the food we eat; (2) in the air we breathe; (3) by way
of the skin, through natural pores or through injured surfaces.

Two fundamental facts of bacteriology must be kept in
mind ; bacteria thrive either when in moist substances or when
dry or semi-dry so that they may float in the air, either free,
or attached to dust. Dust blows about and settles every-
where, e. g. on clothing, hands and face, on solid and liquid
foods if exposed, eating and cooking utensils, furniture of all
sorts, curtains and floor coverings. These are mentioned
that we may not forget what may be sources of bacterial
infection, and how thoroughly all the articles in a room with
a sick person may be the lodging places of disease bacteria.
Such articles as are nearest him are most liable to carry them,
e. g. personal clothing, bedding, handkerchiefs, knives, forks,
spoons, dishes, and all containers of waste material.

After handling such articles as these just mentioned, if one
is to safely guard against infection, the hands should be
thoroughly disinfected by using germ-killing washes, such

380 Advanced I'hysiology

as 2% carbolic acid solution, or a very weak (0.1%) solution
of corrosive sublimate. Some of the germ-laden dust from
clothing or bedding may have been breathed in, and an
antiseptic solution should be used as a mouth wash and
gargle, as well as nasal spray.

As a rule, washes for the skin should never be used for
mouth or nasal disinfection.

Recently opinion has inclined to the belief that many
diseases are spread by the droplet method; e.g. when the
patient, or carrier of the disease germs, coughs, sneezes, or
even talks, he expels into the air minute droplets of the
mucuous fluids of the mouth or near-by breathing passages.
These droplets float about in the air and may be breathed in,
or fall on utensils or foods which may later be put into the
mouth, and thus the well person be infected by the bacteria
which are in these droplets.

Any person who is ill, even with a cold, should never fail
to use a handkerchief over the nose and mouth when coughing
or sneezing and should never face toward a nearby person
when talking, laughing,singing, or the like.

The period of time which usually elapses between infection
and the actual on-coming of the disease (called the incubation
period) varies much even with exposures to the same disease.
This is because the body is in better physiological condition
at one time than another, or, in other words, possesses more
resistance. Persons differ greatly in their susceptibility to
disease and some may even be immune while others are very
liable to a given disease. The following table is given to
indicate the time during which a person, knowing of his
exposure to some disease, should avoid close association with
others :

Small-pox 14 days

Measles 10 "

Scarlet fever 3 "

Diphtheria 3 "

THE CONTROL OF HEALTH 381

Chicken-pox 20 days

Whooping cough 21 "

Cholera 10 "

Typhoid fever ........ 14 "

Mumps 24 **

Infantile Paralysis 28 "

Immunity. — In a previous chapter (page 72) we have
defined immunity as a condition of the body such that it is
not susceptible to a communicable disease even when inti-
mately exposed to it. For example, the same mosquito
(genus Anopheles, and carrying malarial germs) biting a man
and a bird, conveys malarial fever to the man but not to the
bird. Another genus of mosquito (Culex) biting both, causes
malaria in the bird but not in man. Each organism is naturally
immune to the bacteria which cause a disease in the other.

Immunity cannot in any way be secured against some
maladies, e. g. tuberculosis. Immunity is being secured
against an increasing number of diseases by artificial and
harmless means. The discoveries made by Louis Pasteur
marked what may justly be considered the most important
epoch in the history of medicine, and what may almost be
called the physical salvation of mankind.

To understand how immunity may be brought about
requires attention to the relation which exists between the
invading bacteria and the person invaded.

When disease bacteria from any source obtain entrance to
the human body, they soon become vigorous and multiply
very rapidly because of the warm temperature and of the
nutrition they so easily absorb from the body fluids. Under
favorable circumstances a single bacterium of certain kinds
may give rise to as many as 17,000,000 descendants in twenty-
four hours. Passing from the respiratory or digestive organs
into the blood or lymph, they give from their bodies substances
called toxins, which are often very poisonous, and cause the
discomfort and symptoms of th^ (disease. / The cells of the

382 ADVANCED PHYSIOLOGY

body (probably those of the blood vessels in particular) being
irritated by these toxins, endeavor to defend themselves by
giving off materials which nullify the poisons. These sub-
stances are called antitoxins. If the body cells can create
sufficient antitoxin rapidly enough, the bacteria as well as their
products are overcome, and the person will soon be well again.
It is quite obvious that the blood of a person so recovering
contains antitoxin substances which will make him safe from
similar attack so long as they last. He is then said to be
actively immune to that special disease.

One may secure immunity against some diseases by means
other than first going through a period of sickness with it.
The commoner means are by vaccination and by serum
inoculations or injections. The principle on which both these
procedures work is this: if, instead of virile disease bacteria,
very weak (attenuated) germs, or the toxin secreted by them,
are introduced into the human body through a shallow abrasure
or cut in the skin (vaccination) or by hypodermic injection
(injection or innoculation) , enough antitoxin is immediately
produced by the body so that the weak germs are killed off
and the toxin made of no effect. With antitoxin thus on
hand, the body has a * 'running start" and can successfully
compete against the invasions of strong, vicious bacteria of
the same sort. This is the manner of procedure against
typhoid and small-pox. The wide use of vaccination for
small-pox and innoculation for typhoid fever has thoroughly
established their reliability and safety. Persons so rendered
safe from a certain disease are said to be artificially immune.

Instead of injecting weak and dying bacteria or the toxin
characteristic of them, the body can be fortified against some
diseases by injecting antitoxin taken from some animal which
has had the disease and recovered from it; this is the case
when serums are injected to ward off diphtheria. Curiously
enough, the body cells can be deceived in this way, and on
becoming * 'conscious" of the presence of some antitoxin will

THE CONTROL OF HEALTH 38?.

busily begin to make more like it. A quantity is thus soon
on hand sufficient to combat successfully the heaviest infections.

Home and School Hygiene. — Since at least one half the
life of each person is spent indoors, it is very essential that
homes, school buildings, etc., should be as conducive as pos-
sible to the health and general welfare of mind and body.
Many matters of building hygiene apply equally to dwellings
and school-houses, so, unless specially designated, the following
considerations pertain to both.

Primarily a home should be located with reference to its
water suppljs drainage, air supply, and light. Beauty of
surroundings, freedom from noise, relation to markets and
transportation conveniences, and congeniality of neighbors
are likewise considerations of real importance.

Location and Water Supply. — Wherever one is, he cannot
live unless provided with pure water in unfaihng quantity.
If wells are the only source of water, they must be carefully
isolated from contamination by house or barn drainage.
A knowledge of **the lay of the land" where the well is dug
should be obtained so that underlying layers of rock or imper-
vious earth (clay) may not lead impure water into the well
from a distance. The area immediately about such a well
should be raised decidedly above the general level, and
cemented over for a distance of at least six feet on all sides
of the opening, to prevent rains from washing surface debris
either directly or indirectly into the well. It should be
covered tightly to prevent leaves, dust, foreign matter, or
small animals from getting into the water.

If one is contemplating living in any given city or village,
the source of its water supply, its treatment, the manner of
its storage and method of delivery should be investigated.
No portion of a water-shed affecting a supply should be a place
of human habitation unless all the circumstances of such a
house are known, and its drainage prohibited from entering
the waters destined for household use.

384 ADVANCED PHYSIOLOGY

In case a town supply must be taken from a river, pond,
or lake, the science of sterilizing, softening and clearing water
is so highly developed there is no reason why wholesome
waters should not be secured. Clearness, ''softness," and lack
of odor do not insure pure water. Its bacterial content is
of more significance than any other single factor; and the
number of bacteria is of little consequence as compared with
their kind. Bacteria which thrive in decomposing organic
material should not be present, particularly such as are found
in the human digestive canal. If such are found, it is obvious
that insanitary drainage from human dwellings is somehow
entering the supply, and the health of every person using this
water is in imminent danger.

The temperature, except for affecting its palatableness, has
nothing to do with its desirableness. If ice is used in water,
one should be certain that it, in turn, is made from pure water,
and in its use one should remember the physiological fact that
cold temporarily slows or even stops the action of life pro-
cesses.

Location and Drainage. ^ — Formerly, if the basement of a
house kept dry, little was thought of other drainage. The
water wastes were thrown on the near-by ground, and either
allowed to sink in, or to run into an open ditch. Solid matters
were allowed to collect wherever they might.

In modern times, large amounts of water are used in washing,
rinsing, house-cleaning, and the like. Lavatories, bathtubs,
and the sanitary water-flushed toilet have become necessities
of civilization. Rainwater should be conducted away and
not be allowed to fall from the eaves, as this undermines the
foundations and creates a damp, unwholesome basement.

Houses should be so located that all waste water can be
conducted away to a safe distance; in order to do this the
house should stand above the general level so this drainage
may be easily and surely secured.

House Construction.^ — A dry basement is very essential.

THE CONTROL OF HEALTH 385

It is secured by keeping surface water away from foundation
walls by tight bottom construction, and by a drainage exit
for any water which may enter in unanticipated ways.

The side walls of a building are much warmer if made in at
least two thicknesses (preferably three) with an air space
between. This same method of insulation against a tempera-
ture change is used in the construction of refrigerators and
incubators, where maximum uniformity in temperature is
wanted. Windows should be numerous, both for purposes of
light entrance and for ventilation. The doors as well as the
windows should be fitted with screens so that insects may be
kept out, as some of these are now well known carriers of
numerous kinds of disease * 'germs" (bacteria).

Walls and floors of rooms should be so finished as to be
easily kept free from dirt and dust. Fancy wood-work in
which dust collects and which is cleaned with difficulty, is
unhygienic.

Location with Reference to Light and Air. — Whether
in city or country, one should keep in mind the need of adequate
hght and the vital necessity of plenty of pure air when deciding
on a place of residence. Dense shade from trees or an environ-
ment of high buildings makes the eyes work under difficulties,
necessitates the expense of artificial light, and constitutes a
condition of general unwholesomeness. This is because sun-
light is one of the most effective agents in the destruction of
bacteria. Sunny rooms are not merely well lighted, but are
healthful. This germicidal action of light should be utiUzed
by putting clothing, rugs, and house-furnishings in the open
air on sunny days.

Artificial Light. — Of the modern methods of artificial
lighting, electricity is by far the most convenient and hygienic.
Its convenience is obvious, and its use is hygienic because
there is no leakage or odor as with gas or oil lighting. Electric
lighting systems have now been developed so that a home in
the country may be lighted by electricity.

386 ADVANCED PHYSIOLOGY

Tn the use of gas, care should be taken to prevent an^^
leakage, to adjust the mixture of gas and air at each burner,
so as to obtain the most light, and to obviate vitiating the air
with unoxidized gas.

Acetylene gas plants are often placed in private houses,
especially in the country; here again leakage should be par-
ticularly guarded against, and users should clearly understand
its explosive qualities. Kerosene oil may be burned where
other artificial illumination is not available, but extreme
cleanliness is necessary to prevent bad odors and to secure
maximum light.

In all kinds of illumination, our tendency is to employ too
brilliant Hght and to use too little care in preventing light
from shining or being reflected directly into the eyes. From
whatever source, light should come from over the shoulder,
not from the front or side.

Artificial Heat.- — Stoves are still used for heating houses,
even though they are somewhat unsatisfactory for this pur-
pose. They are unsatisfactory for several reasons: Dust and
dirt accumulate about them; the distribution of the heat in
the room is uneven; the floors remain cold above the basement;
poisonous gases may escape (from coal stoves) ; and the danger
of fires from a number of stoves in one house is increased.
Central heating from a furnace obviates all these objections.
Each of the different sorts of central heating systems, hot air,
steam and hot water, has points in its favor as well as against it.

Hot Air Furnace: The hot air system brings fresh air into
the house, at such temperatures as to obviate cold drafts,
and in this respect is a most desirable method of heating;
but dust is almost certain to collect in the furnace and delivery
pipes, and be brought up in the air current. As winds greatly
modify the dehvery of hot air to different rooms in the house,
the equable distribution of the hot air on cold, windy days
is not always possible.

Steam System: In this system, the steam pressure can be

THE CONTROl. OF HEALTH 387

raised to such a degree that the radiators can be made very
hot in severe weather and every room thoroughly warmed.
The objections to steam heat are: The air of a room is heated
over and over with no ventilation unless such is specially
provided; the radiators may become over-hot and "burn up"
the air; and no heat is obtained from the fire till the water is
near the boiling point.

Hot Water System: This has the advantage of delivering
some heat to the radiators as soon as the water is slightly
warm. The heat is steady, and the radiators remain warm a
long time after the fire is low. The disadvantages of this
heating plan are that the radiators never get so warm as with
steam, and must therefore be much larger for the same service;
furthermore, ventilation must be secured in ways not related
to the heating system.

Ventilation. • — ■ Ventilation is necessary for several reasons :
breathed air contains too little oxygen, too much CO2, too
much moisture and too many organic compounds in small
amounts. Each person vitiates about 1,800 cubic feet of
air per hour, and provision must be made for its renewal or the
individual becomes inefficient in working power and in resis-
tance to disease, and is reduced to poor health generally.

Of all the many ways of letting fresh air into rooms, the
old-time method by way of windows and doors is one of "the
best; forced ventilation with flues and fans is seldom entirely
satisfactory and is very expensive. A good way to ventilate
a room is to let fresh air enter near the top of the room, and to
let the stale air escape at the bottom as through a fireplace or
some similar exit. Fresh air is bound to enter around loose
windows and doors.

Especial provision must be made for all buildings where
many people congregate as in schools, churches, and theatres.
Sufficient air space cannot be secured for such rooms unless
they are made very large, or with high ceilings. No drafts,
either warm or cold, should be allowed during cold weather;

388 ADVANCED PHYSIOLCC'A'

temperature should not vary more than 2° from 68° F., and
the air should be neither too dry nor too moist. In buildings
heated with steam or hot water, special consideration should
be given the matter of humidity, as very dry air is irritating to
the lung membranes and is thus a menace to health. Moisture
should be provided in the form of steam, and the supply
regulated by an automatic humidometer.

Furnishings. ~ Whatever the use of the building, its fur-
nishings must be such as may easily be kept clean. Fancy
wood furniture or iron desks are kept free from dust with great
difficulty. Carpets fastened down so that dirt cannot be
removed from under them are now little used; only such rugs
as can be easily and thoroughly cleaned should be considered
practical or desirable. Window hangings and upholstery
should also be selected primarily with reference to healthful-
ness.

Cleaning of Buildings. — In performing any cleaning the
one prime rule to insist upon is NO DUST, whatever the
method used. If the dust is removed and not scattered in
the process, the method is excellent. Cloths used in dusting
should be oiled to entangle and remove dust, not scatter it as
was the case with the old-fashioned feather duster. Prepara-
tions for entangling the dust and dirt should be scattered on
floors before sweeping them, and unless a vacuum cleaner is
used, rugs should be taken out of doors to be cisaned.

In school-houses chalk dust should be wiped from black-
boards with a damp cloth or some other dust absorber. The
chalk trough below the board should be covered with wire
screening to keep hands and erasers from the dust. Slate
boards are cleaner than wooden ones, besides largely doing
away with the glare from reflected light.

Disinfection of Rooms and their Contents. — • This pro-
cedure as a preventive against the spread of disease is of very
much less value than was once supposed. For instance, there
seems very little virtue in disinfection after cases of measles.

THE CONTROL OF HEALTH 389

whooping cough, influenza, pneumonia, diphtheria, or men-
ingitis.

Clothing and bedding which may have been stained by
fluids from the body of a sick person should be thoroughly
boiled and other articles from the sick room hung in the air
and sunshine for several hours to free them from bacteria.
Thin clothing hanging in a closet can be disinfected by placing
a small sheet, sprayed with strong formalin, in the closet and
closing the door tightly for some hours.

If a room is to be disinfected, the permanganate-formalin
method is considered the best. The method of procedure is
as follows: After sealing the room air-tight (strips of paper
can be pasted over cracks), place potassium permanganate
(250 grams^ — 9 ounces for each 100 cubic feet of space) in a
very deep pail near the middle of the room; the pail should
stand on a couple of bricks or similar support as the bottom
will become hot. When all is ready, pour onto the perman-
ganate 500 cc. (about 1 pint) of formalin, full strength. The
gas from this has poor penetrating power, so that thick cloth-
ing, bedding, etc., should be given special treatment, i. e.
steamed, boiled or soaked in 5% solution of formahn.

Special Home Problems: Sewage Disposal. ^ — In most
municipalities refuse from kitchen sinks, lavatories, and
toilets is carried away by the sewage system. In smaller
villages and country places, private cess-pools, with un-
cemented walls will, with little attention, take care of the
needs of an ordinary house for some years. Such a cess-pool
must never be located so that seepage from it will enter any
supply of water.

In the country, if privy vaults are necessary, they should

be perfectly isolated from flies or vermin and be so closed and

treated as to be free from odor. The container should be a

I removable, water-tight can, the contents of which should be

I frequently buried, never thrown on top of the ground.

IK Special School Problems: {a) Sanitation of Public

S90 ADVAisrCED 1>HYSI0L0GY

Buildings.- — -Schools, theatres, and churches are the com-
monest meeting places of the people of a neighborhood.
These meetings afford an ideal opportunity for the spread of
disease. Close personal contact is almost inevitable, rebreath-
ing of air is certain, common water faucets and toilets are the
rule.

The proper management of a schoolhouse or any other
pubhc building is one of its greatest educational influences,
as its sanitary arrangements and general cleanliness will no
doubt affect those benefited by them.

Too great emphasis cannot be laid on the importance of
extreme sanitation in school lavatories and toilets. Any part
of the equipment of these rooms which has been touched by
the diseased surface of a person suffering from a communicable
disease is very hable to be a source from which the disease
may be transferred to others.

Drinking fountains, paper towels, and laws compelling the
use of only new books are among the most recent developments
of sanitary science.

(b) School Nurses and Physical Examinations. • — As
children are compelled by law to attend school, it is the duty
of the school officials to see that their health is safeguarded
in every way. For this purpose school doctors and nurses are
employed who inspect the children's health. Their throats,
teeth, eyes and ears are examined by experts who either give
or suggest skilled treatment for physical defects, thereby

removing conditions which might later on seriously interfere

with health and usefulness.

Specific results of tonsil and adenoid infections, decayed

teeth, eye strain, and ear diseases have already been pointed

out in the sections dealing with the physiology of the throat,

mouth, and special senses.

Quarantine Laws. ■ — By the term quarantine is meant the

isolation of a person or persons having, or suspected of having,

a communicable disease. This procedure prevents the spread

THE CONTROL OF HEALTH 391

of communicable diseases. The quarantine period may
involve:

1. The time elapsing between exposure and onset of disease.

2. Time of actual sickness with the disease.

3. A detention period after active sickness is past but during

which the person may be a "carrier," i. e., be a source
of infection to others.

r We have already called attention to the "incubation"
period of several common diseases in Chapter XXIII. The
second period mentioned will differ much with the physio-
logical condition and care given the patient, so that Httle may
be said about it in advance. The period of detention also
varies but in no case should a person recovering from a com-
municable disease be allowed to return to the company of
others without permission from a physician. The quarantine
law for some minor maladies often reads thus: "Persons
suffering from measles, whooping-cough, mumps, German
measles, and chicken-pox shall be barred from school for
twenty-one days from the onset of the disease." Lessening
or lengthening of this period is left to the physician or health
officer having jurisdiction.

Houses in which there are communicable diseases should
bear a placard so stating; and the Board of Health should
furnish a list of communicable diseases, with the quarantine
rules applying to them, to all parents who have children in
school.

Municipal Health and Hygiene. • — From the standpoint
of health, the city has many of the characteristics of the
single home. As the ill health of one or two members of a
family may endanger the health of the rest, in precisely similar
fashion unhealthful conditions in any section of a city are a
menace to the whole city. Therefore authority must be
given special groups of men who shall act toward affairs of a '
city as parents do in the affairs of families.

392 ADVANCED PHYSIOLOGY

Public Commissions and Boards for Safeguarding
Public Health.- — The Board of Health, with the co-operation
of other Commissioners and Committees, keeps vigil over the
health of the entire city. Other bodies which act with them
or under their direction are the Water Commissioners, Street
Commissioners, Milk and Food Inspectors, and School Nurses.
Among the larger responsibilities of such pubHc officials are
the prevention of carelessness as to food and water supplies,
condition of streets, garbage disposal, the prevalence of noise
and smoke, the ventilation of stores, factories, and public
buildings, the quarantine of infectious diseases, and provision
of opportunities for securing recreation and fresh air for all
classes. Their work is said to be that of securing public
hygiene in contrast to that science and observance which
makes for the health of the individual and is called personal
hygiene.

It is very apparent that only scientifically trained men
should be chosen members of Boards of Health, for the lives
of hundreds, or hundreds of thousands, are in their hands.

Public Water Supplies. ■ — • The greatest care should be
exercised to secure pure water for towns and cities. Public
reservoirs must be filled from sources entirely uncontaminated
by refuse from human habitations and must be kept pure.
Leaves and dying plants should not be allowed to collect in
them, as they become breeding places for bacteria and other
unicellular organisms injurious to health.

Conduit pipes and faucets must be of materials which will
not vitiate the water. If a water supply is taken from lakes
or rivers which are unavoidably contaminated, it should be
sterilized chemically or otherwise, and thoroughly filtered.
No dependence should be placed on the ordinary small faucet
* 'filters'* sold for private use.

Public Food Supplies: Markets. — The fitness of foods
cannot be determined unless they are traced to their sources,
and the method of gathering, packing, shipping, selling, and

THE CONTROL OF HEALTH 393

delivering is known. Uncleanness at any point in this process
unfits the article for use. Contact with human hands always
brings in a source of danger; exposure in stores or on sidewalks
gives opportunity for infection from many sources. Many
foods deteriorate if left at temperatures which permit bacteria
to increase rapidly; some containers have surfaces which, under
action of the air and acids, will poison the contents. All fruits
and vegetables which are not cooked before eating should be
thoroughly washed.

The United States Government and the various State
Governments, as well as municipalities, have passed laws and
regulations governing the production and sale of food stuffs,
such as the seeding of raisins, the packing of figs and meat, the
wrapping of bread, the canning of vegetables and fruits, and
the milling of flour. Inspectors are appointed to see that
foods offered for sale comply with these regulations.

Highly nutritious foods like milk are especial breeding places
for bacteria and must be handled with extreme cleanliness
from source to consumer. Cows must be healthy (no tuber-
culous condition), stables sanitary, milking men and machines
clean (and men healthy), cans and bottles sterile. With the
best of care milk receives bacteria from the air; but Grade A
milk (for infants) should not contain over 60,000 bacteria
per cCo (if Pasteurized, not over 30,000 per cc). Grade B
not over 100,000 per cc, and Grade C (used only for cooking)
not over 300,000 per cc.

To be on the safe side, one should always remember that
thorough cooking (boiling temperatures or higher) destroys all
living matter. Thus, danger from infected food may be
avoided; but food free from infection is safer and better yet.

Purity also impUes freedom from adulterants; coffee, tea,
spices, syrups, milk, powdered and dry * 'foods "are not
infrequently increased in bulk and weight with cheap sub-
stitute articles.

Pork should be free from trichina worms, oysters from

394 ADVANCED PHYSIOLOGY

typhoid bactena, cereals and meals from insect eggs and the
maggots which hatch from them, vinegar from 'Vinegar eels."

Public Disposal of Garbage. • — At each of the many
homes in a city there accumulates daily an unavoidable quan-
tity of debris; garbage from the kitchen, waste paper, empty
food containers, ashes, etc. Such material cannot be disposed
of on the premises, save by use of costly incinerators or by
burial. A system of collection at pubhc expense is the only
safe and sure way of securing sanitary disposal of such material.
"Filth breeds disease" as one often reads, and one protects
not only himself but all about him when he insists on sanita-
tion in the matter just mentioned. Garbage, if not burned
immediately, must always be kept, until collected, in covered
containers which will keep out insects and vermin.

Street Cleaning. • — The sources of dirt and filth in a city
are innumerable. To some extent this dirt adheres to every
one. Air currents stir it up and carry it everywhere. The
accumulation of dirt and filth in a city should either be washed
away, or carried to stations especially fitted for burning it or
to places where it may be buried. The city's example of
cleanliness or lack of it is one which influences the practices of
all the inhabitants. To compel this public cleanliness by
law should be the willing procedure of the people. DisraeU,
the famous Englishman, once said: * 'Public health is the foun-
dation on which reposes the happiness of the people and the
power of the country. The care of the public health is the
first duty of a statesman."

Public Playgrounds and Parks. — The providing of play-
grounds and parks is necessary, as we now appreciate the vital
relation between recreation, fresh air, and rest on the one
hand, and effectiveness, health, and readiness for action on
the other. These pubhc playgrounds and parks, with the
opportunities they afford to leave the crowded sections of the
city with their barren walls, their din, smoke, fatigue, and
monotony, are the oases in the city desert. Parks ^xe urmec-

THE CONTROL OF HEALTH 395

essary for those who can afford their own ample yards, or can
quickly reach the country in automobiles; but for the vast
majority who have no other source of out-door relief, they are
indispensable. For many children they undoubtedly mean
the difference between living and not living.

Medical Inspectors and the Control of Epidemics. ^ —
The real nature of communicable diseases, their symptoms, the
sources of infection, the method of treatment, the liability and
manner of spreading, and the seriousness of the disease to the
patient is known only by those well trained in the science of
medicine. Medical inspectors are given legal permission and
the assigned duty of keeping track of the pubHc health. They
give the sick prompt attention and protect others from infec-
tion. Without them communicable diseases would be uncon-
trolled and without proper attention one case might easily
spread to thousands. It is the duty of every physician to
report cases of communicable disease to the public health
officers and to co-operate with them in every possible manner.
The people, in turn, should give their willing support to the
decisions of these men.

COMMON EPIDEMICS AND THEIR PREVENTION.

Influenza. — The nature of this disease has been already
discussed. A person sick with influenza expels the infecting
organisms in minute droplets of mucus when sneezing, cough-
ing, laughing, or shouting. The fingers of a patient are
probably constantly infected. These minute droplets con-
taining the infecting organisms are inhaled by others and
infection may take place.

An ordinary infection will produce illness in from one to
four days. The patient should be isolated and the case
reported to the Board of Health.

396 ADVANCED PHYSIOLOGY

The best known measures to avoid the spread of influenza
are the following:

1. Prevent the crowding of people together in homes,
schools, churches, theatres, cars, etc.

2. Provide plenty of ventilation.

3. Avoid extremes of temperature.

4. Provide ample nourishment and take recreative exercise
out of doors.

Measles. — The ca-use of this disease is unknown. The
incubation period is from five to ten days (average seven).
A patient may **give" the disease to others, however, five days
before he is aware that he has the disease. The most infective
stage is when the patient is first * 'breaking out."

To prevent epidemics the following precautions should be
observed :

1. All cases should be reported and isolated for five days
after ** breaking out."

2. Those exposed should refrain from contact with others
for fifteen or eighteen days. Exceptions to this are those who
have had measles earlier, as they are permanently immune.

3. Avoid contact with people by keeping away from crowds,
particularly indoor gatherings.

Disinfection of rooms recently occupied by measles patients
seems to be unnecessary. Middle-ear infection is the most
common consequence of measles, while diphtheria and pneu-
monia following measles are often fatal.

Cerebro-spinal meningitis. — Epidemics of this disease
occur in late winter and spring, and among children below five
years, or young people between sixteen and twenty-four
years of age. This disease is spread by discharges from the
mouth and nose ; and many carry the disease germs and infect
others, without themselves being sick. Such people are
called ''carriers."

THE CONTROL OF HEALTH 397

The incubation period is unknown. Protective measures
are:

1. Isolation.

2. Extreme care to disinfect and destroy all materials
expelled from the mouth and nose; these should be collected
in gauze cloths and burned.

Typhoid Fever. ^ — This disease is known to spread in no
wa}^ except through the swallowing of bacteria from the
excreta of a previous case. Sickness sets in from eight to
fourteen days after infection.

Epidemics are prevented, or if under way, may be controlled
in these ways :

L Rigid examination of all foods and drinks, to insure
purity and sterility.

2. Prohibition of sale of food and drink by peddlers.

3. Prevention of transmission by flies, by screening houses
and destroying breeding places of flies.

4. ''Carriers" should be identified, isolated, and "cured."

5. Careful sterilization of all dishes used by patient.

6. Insistence upon general use of typhoid serum.

Mumps. ^ — The cause of this disease is unknown. Its
manner of spreading is by the saliva which is often on fingers
which have been purposely or thoughtlessly put into the
mouth. Anything they touch is then infected, and passes
on germs to any other person who may touch it.

The incubation period is from one to three weeks.

Epidemics of mumps are partially avoided at least by:

1. Isolating patients.
L 2. Guarding against infection of anything with saliva.
F 3. Avoiding infection droplets from a patient.

Scarlet Fever. • — This disease is not as epidemic as many
others and concerns chiefly young people. The cause is
unknown; the incubation period is from one to seven days.

398 ADVANCED PHYSIOLOGY

Transmission is through droplets or smears from the mem-
branes of the mouth and air passages. * 'Carriers" are respons-
ible for many cases. However, many epidemics are believed
to have been caused by milk which had become infected during
handling.

Its spread may be hindered or stopped by:

1. Avoiding crowding of people together.

2. Pasteurizing all milk supphes.

3. Isolation of patients.

4. Disinfection of all discharges from the mouth or nose. -

Scales from the skin probably have no special infective
power, and rooms once occupied by patients may be dis-
infected with formaldehyde if desired; this precaution is
probably unnecessary.

If, after learning and perhaps experiencing some of the
modern methods of health conservation, some are tempted to
feel that such procedures interfere with personal liberties,
they should remember that, in the long run, personal, family,
neighborhood, school, and municipal health and hygiene are
so closely interdependent that authority must be present at
every point ; also that observance of legislation looking toward
the greatest common good should be accorded, not grudgingly,
but eagerly and sympathetically by all.

DEMONSTRATIONS OR LABORATORY EXERCISES

The following directions are made on the supposition that no teacher
will be giving instruction in Physiology who has not had specific prepara-
tion for it, and will therefore be able to comprehend the significance of
each suggestion, and know, in a general way at least, how to proceed with it.

A hst of firms, from whom many materials called for can be obtained, is
here given, as also formula? for the making of necessary gases and reagents,
and a table of equivalents between the English- American units of measure
and those of the metric system. By anticipating the class or laboratory
in a reasonable manner no difficulty will be found in making nearly every
page of the text vivid and scientific in its presentation.

The chapter and page numbers refer to the relevant chapter and page
in the body of the text.

CHAPTER I

Page 12. — Numerous forms of protozoa can be easily obtained from
dishes containing decaying pond plants, barely covered with water, which
have been standing quietly a couple of weeks, and may be studied by
placing them in a drop of water under a microscope.

Page 15. — Cells are easily shown by use of prepared slides. (See sources
of material and apparatus, page 421.)

Fresh cells can be shown under a microscope as follows : in very thin
cross sections of plant stem, e.g. corn stalk, lily ; blood cells from frog,
or in blood from finger prick ; in thin bit of cartilage from upper end of
femur bone of frog ; in the thin tail of tadpole of frog, toad, or salamander.

Page 17. — Living protoplasm can be «een easily in live Amoebae, gen-
erally found in dishes of decaying pond plants; in cells of pond weed
Nitella, or Chara ; or in hair cells from leaf of Tradescantia (" Wandering
Jew ") ; high powers of microscope required.

Page 23. — Set aside (1) pond scum and weeds in dish with just enough
water to cover, for 2 weeks ; (2) hay in water (preferably in water in
which other hay has been boiled, and then cooled).

Many unicellular animals will be found in a drop of this material under
microscope. See also addresses of firms who sell this material.

399

400 ADVANCED PHYSIOLOGY

CHAPTER n

Page 27. — Show the class some charcoal, graphite (" lead " of a lead
pencil), and some lampblack, caUing attention to the fact that they are
the same chemical element, carbon. Light a bit of candle and cover with
a bell glass. The candle soon goes out. Explain that the carbon has
combined with the oxygen in the air to form a new compound, CO2 or
carbon dioxid.

Show the class specimens of phosphorus, sodium, potassium, iron and
sulfur. Place a little sulfur in an earthen dish and ignite it. It burns
with a blue flame and gives off a suffocating gas. It has combined with
the oxygen of the air, forming by oxidation a new compound, SO2 or sulf ar
dioxid.

Page 29. — Tests should be made on a variety of common foods to
prove the presence of proteid. White of egg, meat juice, ground oat-
meal, show the test readily. With a solution of any one of them in water
in a test tube (use 10 cc. or so) add a little strong nitric acid and heat to
boiling; note the yellow color. Add ammonia, and note the orange
color (Xanthoproteic reaction).

With rather weak solution of same material in test tube, add a little
1 % sol. copper sulfate, then a little caustic potash ; a violet color shows
presence of proteid.

Try same reagents with starch and sugar solutions, and show that the
tests are negative.

The gluten content of flour can be shown by putting a quantity of
flour in a mushn bag and thoroughly kneading it in a pail of water. Much
of the bulk will wash out into the water ; the gluten will be left as a sticky,
undissolved mass in the bag.

Pour a Uttle hydrochloric acid into a small amount of milk. The
curd which forms is largely casein.

Fibrin can be obtained from perfectly fresh blood by stirring it. The
fibers which catch on the object used in stirring are fibrin.

Myosin can be shown in finely minced lean meat by soaking it in a
little water for a few hours, and then pouring strong acid (nitric) into some
of the juice. The material which coagulates is myosin.

Page 31. — (a) Shake up a little corn or potato starch with water in
test tube and add a few drops of an iodine solution. A typical blue-
color reaction will appear. Ground rice, flour, and cereal also respond
readily. Use the same test on white of egg or sugar solution to prove
validity of test.

LABORATORY EXERCISES 401

(h) Put a few drops of 1% copper sulfate solution in test tube, and
add solution of grape sugar (dextrose) ; then add a few drops of strong
caustic potash solution and boil ; a rust-red precipitate is formed in bot-
tom of tube (cuprous hydrate or oxide).

If cane sugar is used, the above result will not follow unless the sugar
solution is first treated with a few drops of 25% solution of sulfuric acid
and then boiled ; after this treatment, proceed as in case of dextrose and
same result follows. Unmodified cane sugar does not contain dextrose.

Test starch or white of egg in the same way and show that the reaction is
negative.

Page 32. — Put a small bit of fat meat (of size of pea is sufficient) in
test tube and then pour in a little 1% solution of osmic acid. The fat
turns black.

Place a few drops of olive oil in a test tube with a little water and shake
vigorously. The oil forms a milky white emulsion. Examine a drop of
milk with a microscope, and note the fat globules forming an emulsion.
Put a small bit of fat meat on a perfectly clean slide, pour on a little ether
and allow to evaporate; the ether dissolves the fat ahd on evaporation
leaves a scum on the glass.

Tests of same sort with proteids or carbohydrates give negative
results.

Page 34. — Boil tough, gristly pieces of meat and cut bones in a little
water. A jelly will form as the solution cools, which illustrates the
nature of gelatin.

CHAPTER III

Page 37. — Since the character of the teeth is an indication of what an
animal eats, it will be instructive to show different sorts of skulls with
teeth in position ; e.g. the human teeth indicate omnivorous diet ; the rab-
bit teeth indicate herbivorous diet ; the cat or dog teeth indicate carnivo-
rous diet.

Page 40. — Boil an egg for ten minutes and remove the shell. Cut in
halves to show the coagulated albumen and the yolk. Put some of the
coagulated white in water and heat to prove that it will not dissolve.
The white of raw egg coagulates in strong acid the same as in boiling
water.

Page 42. — The proteid value of foods will be made more vivid if a
considerable list of foods is on hand in quantities which can be used in
connection with the table.

402 ADVANCED PHYSIOLOGY

Page 43. — Cut a raw potato and place some iodine upon the cut
surface. Treat a bean that has been soaked in water for a day in the same
way. Which shows the more starch?

By definite trials, prove that egg albumen, meat, flour, and sugar do not
react in uniform ways to this treatment. The test is specific for starch.

Page 45. — With a thermometer it will be easy to ascertain the melting
point of some fats, e.g. butter, lard, pork fat, and mutton fat ; then com-
pare with temperature of the body.

Page 54. — With very sharp razor prepare very thin sections of raw and
cooked potato; place under a microscope and demonstrate the points
here mentioned.

Page 55. — Prepared slides of pork muscle infected with trichina are
obtainable from nearly any dealer in microscopical preparations. Con-
sult address list in another part of Appendix for partial Ust of dealers.

CHAPTER IV

Page 63. — Fill a test tube half full of a solution of molasses (better
than this is Pasteur's solution) and to it add a little yeast from an ordinary
yeast cake. Let the mixture stand in a warm place for several hours.
CO2 gas, due to fermentation, will appear as bubbles. To prove the nature
of this gas, take a larger amount of the fermenting mixture in a flask, and
conduct the gas by a tube, as shown in Figure 26, into limewater; a
white precipitate in the latter proves the presence of CO2. After a time,
the formation of alcohol in the sugar mixture can be detected by its odor.

To make this demonstration more vivid and complete, the fermenting
solution should be put into flask, over opening of which a rubber tube is
fitted, this in turn being connected to glass tube which can be led through
a stream of water ; then boil the liquid, and the vapor will be condensed
in the cold glass tube and thus alcohol can be collected in liquid form.
This carries out the principle of a still.

Page 64. — Mix starch and water in a small beaker. Heat, stirring
constantly, and note how the mixture thickens owing to the bursting of
the starch grains and the absorption of water.

Place a little of the mixture in a test tube and by the method used in
the demonstration for page 31 determine that it contains no sugar. In
another test tube mix a small portion of the starch solution with plenty
of saliva. Be very sure that the test tube is perfectly clean ; a trace of
acid in it will prevent the desired result in this experiment. Place the
saliva and starch mixture in a beaker of water. Heat the latter to about

LABORATORY EXERCISES [403

le temperature of the body and let it stand for about ten minutes.
Then test for sugar. A typical reaction should appear. The sweet taste
of bread (a starchy food), after being in the mouth for a while is well
known.

Examine saliva under a microscope to note the absence of any fermenting
bodies, like yeast.

Page 67. — 1. To see yeast cells, examine a mixture of yeast and water
with a microscope (high power).

2. Set aside, in a warm place, any food material such as piece of meat,
in small receptacle ; barely cover with water, and leave for two or three
days. Then examine a drop, covered, under microscope with high powers,
for numerous forms of bacteria. They have almost no color, and much
care must be used in having just the right degree of illumination.

With a dull edged instrument (e.g. spoon handle) scrape a little material
from inside lining of the cheek, or take a little material from between the
teeth with tooth-pick; place this in a little water under cover-sUp and
examine as above. Bacteria will be numerous, perhaps loose epithelial
cells also.

Page 73. — Fill four test tubes one-third full of water. Place in two
of them a small bit of meat and in the other two a little white of egg.
Plug all four with cotton. Place one of each set of two in a beaker of
water and boil briskly for ten minutes. Set all four aside. Examine after
two days and again after four days.

Many bacteria will appear in the unboiled tubes, with characteristic
decomposition odors ; the boiled tubes will show no deterioration.

CHAPTER V

Page 76. — 1. A human skull should be at hand for direct reference
to the teeth. Separate teeth to show roots, etc., can usually be obtained
from a dentist. Other skulls containing teeth are useful to show differ-
ent shapes in animals of different habits. Teeth of a rabbit or horse are
very different from those of a carnivorous animal, e.g. cat or dog.

2. The layers of a tooth can be easily shown by use of prepared sections.
See list of dealers in shdes.

A model of a tooth can be rather easily cut from piece of hard soap.

Page 77. — Dip a bit of blue litmus paper into a little dilute hydro-
chloric acid, and note that it turns red. In the same way test vinegar,
lemon juice, and sour milk. Dip a bit of red Utmus paper into an alkaline
liquid, like ammonia. Test soapsuds in the same way. Determine whether
saliva is acid or alkaline.

404 ADVANCED PHYSIOLOGY

Page 78, — To illustrate the action of an acid on the teeth, show the
result of putting hydrochloric acid on an egg shell. Rapid corrosion
follows.

Page 79. — The correctness of the text figure can be easily proved by use
of prepared slides of taste buds. See list of dealers.

Page 80. — The connection between the nose and mouth cavities
through the pharynx is easily shown by merely noting that any breath
drawn in through the mouth can be expelled through the nose, or vice
versa.

This point may also bs illustrated by use of human skull, or if this is
not at hand, by the skull of cat, dog, rabbit, etc.

Page 81. — The salivary glands of a cat show readily as soon as the
skin is removed from the head, and in same location as in man. The
duct from the parotid gland passes across the cheek region and no dissec-
tion is required to show most of its length.

Page 84. — Ciliary action can be easily shown under high powers of
a compound microscope by mounting on a glass slide (in 0.6% salt solu-
tion) some ciliated cells scraped from roof of a frog's mouth, or a piece of a
clam's gill. A correct idea of cilia cannot be obtained otherwise.

The surprising power of cili.. to move objects is demonstrated by remov-
ing the lower jaw and floor of mouth complete from frog after brain has
been destroyed. Keeping the surface of roof of mouth moist with normal
saline solution (0.6%) place on it a small wooden block, size of pea. It
will be moved along by the cilia.

Page 84. — 1. If one closes the nose passages by holding the nose between
the fingers, and then swallows, the noise in the ears shows that a passage
exists between them and the throat.

A model of the human pharynx should be used in this connection.

2. The several openings into the pharynx described in Chapter V
can easily be shown in a recently chloroformed frog. The glottis is a
longitudinal slit on a slight prominence at the back of the tongue. The
gullet is immediately back of the glottis. The posterior openings of the
nostrils are just back of the upper jaw, at the very front of the mouth.
The Eustachian tubes can be seen as wide openings at the junction of
upper and lower jaws ; a bristle can easily be passed into them co as to
demonstrate that the passage leads to the ear.

LABORATORY EXERCISES 405

CHAPTER VI

Page 90. — The body cavity, its divisions and contained organs, should
be made plain by use of a manikin.

If some animal such as cat, rabbit, white rat, or the like can be dissected,
the entire teaching of the body cavity and contained organs can be very
easily made clear.

Page 94. — Coagulate some white of egg in boiling water in a beaker.
Note that water alone will not dissolve such proteid. Put a piece of egg
as large as the end of one's little finger (mincing it first) into a test tube
half full of artificial gastric juice (see formula). Stand the test tube in a
beaker of water kept at about body temperature (98°) and note that the
egg slowly dissolves. When it has gone into solution, add copper sulfate
and caustic potash ; a rose-red color instead of violet shows that the pro-
[ teid has been changed into peptone.

Page 94. — A solution of rennet can be obtained from any druggist,
and its action on milk shown by merely adding a little to a tube of warm
milk and allowing it to stand for about | hour.

CHAPTER VII

Page 99. — A very useful demonstration of the intestine with arteries
and veins injected, and the whole made translucent, can be obtained from
the W. H. Welsh Manufacturing Company, 1516 Orleans St., Chicago.

Page 100. — The teacher should demonstrate all the organs described
in this chapter, as well as details like the mesentery, gall bladder, etc.,
by use of a manikin of the human body, or by the dissection of some small
mammal. Even a fish shows much of interest in this connection, but
has no diaphragm and is unlike the human in numerous ways.

Page 101. — The bile duct, gall bladder, and liver lobes are very easily
dissected in the dog-fish.

Page 103. — Artificial pancreatic juice should be placed in a test tube
with coagulated white of egg, kept at body temperature, and the test for
peptones made. Starch should be treated in the same way, and after its
digestion, tests made for sugar.

To show action of pancreatic secretion on fats it is best to imitate the
conditions present in the intestine by mixing with the artificial pancreatic
juice a little white of egg, as other things besides fat are always present.
Pour into such a mixture some olive oil and shake vigorously. The emul-
sion thus formed will not separate as does a mixture of oil and water,

406 ADVANCED l>HYglOLOGY

and a drop of it should be examined under a microscope and coinpared
with milk.

CHAPTER VIII

Page 115. — Cover the bulb end of a thistle tube with some membrane
like the lining of an egg shell or a piece of goldbeater's skin, tying it tightly.
Fill the bulb with solution of glucose, holding the bulb in dish* of water
while doing so to avoid breaking the membrane, which is very thin. Then
lower bulb into the water till glucose and external water show the same
level. Fasten the tube in this position ; the water will pass into the glucose
solution through the membrane, till glucose level is much the highest.
This occurs against the force of gravity, under no compulsion except that
of osmotic pressure.

Page 120. — The lacteal branches of the lymphatic system which arise
in the walls of the intestine may be plainly shown in the mesentery of a
cat or dog, if the animal is chloroformed about three hours after it has
eaten freely of fatty meat and milk. On opening the abdomen imme-
diately after death, the mesentery holding the intestine will be seen filled
with numerous tiny ducts full of white, fatty emulsion.

CHAPTER IX

Page 123. — The plasma and corpuscles in blood can be shown by put-
ting a drop of fresh blood from a prick in the tip of the finger on a glass
slide, with a little 0.6% solution of common salt. It is not possible to
demonstrate the platelets except by special methods. Frog's blood is
also easily obtained. For permanent mounts of the blood see address
list of dealers.

Page 125. — 1. Defibrinated blood may be procured from a butcher,
by catching blood directly from some animal and stirring it immediately,
thus removing the fibrin as it forms. Blood so treated will not clot and
will keep for some time. Put some in a large test tube, and by means of
a glass tube opening into the bottom of the test tube run oxygen gas
through the blood. The bubbles which will be thus formed will be of
bright red color (oxyha3moglobin) . For methods of making this gas,
see Appendix, " Formulae and Methods."

2. The blood of a guinea pig, rat, or dog is best for showing oxyhaemoglo-
bin crystals. It is not so readily shown in human blood. The amount
of ether used should be only a fraction of that of the blood. If blood
is merely mounted in water and allowed to stand some time, crystals
form to some extent.

LABORATORY EXERCISES 407

Page 127. — Prepared slides of blood are very useful here ; see address
list of dealers.

Page 129. — Arrangements may be made with a butcher to fill a pint
glass container with fresh blood; this should be set aside immediately
and left undisturbed until the blood has completely clotted. The less
the specimen is disturbed before being shown in a classroom, the better.
The serum will appear as a clear fluid about the clot; the latter will
shrink, but will retain the shape of the container. Clean fibrin can be
obtained by kneading a clot in water ; the longer it is washed the better.
It can then be preserved in 4% formalin, for use at any future time.

Page 131. — Dealers will furnish prepared slides of numerous sorts of
bacteria, including the types here mentioned. They also furnish sUdes
of blood showing the malarial organism, Plasmodium malariae.

Page 133. — It will be worth while to procure and show " wrigglers "
and pupae of mosquitoes, as well as adults, or parts of them, under low
power lenses. The young are easily obtainable, as a rule, from any woods
pond in early spring. Prepared slides of mosquito mouth parts are pur-
chasable.

CHAPTER X

Page 137. — Obtain a turtle if possible, as it will show more satisfactorily
than any other animal the external events of a heart-beat. Action con-
tinues a long time after the head is removed.

Page 138. — If time and opportunity permit, the teacher may show the
heart of a beef or calf to the class, demonstrating the structure and action
of this organ. Instructions should be given the butcher to leave the blood
vessels connected with the heart long, i. e. the pulmonary artery and the
aorta should be severed not less than five inches from their exit from the
heart. The pericardium should be left on.

Before class period the specimen should be trimmed of all rough ends of
tissues ; the blood vessels should be nicely dissected out from the mass of
tissue which surrounds them ; in doing this the pericardium will be cut
away in part, but should be left cs perfect as possible. The external
appearance of auricles and ventricles, the elasticity of the blood vessels,
• the contrast between arteries and veins, will be easily noted. If the follow-
ing order of procedure is observed, practically every feature of anatomy
and function of the internal parts can be readily shown.

Cut away the pericardium. Shut off the pulmonary artery with a
strong clamp, as far from the heart as possible. Cut through the wall of
the right ventricle toward the apex of the heart j carry this cut forward

408 ADVANCED PHYSIOLOGY

carefully and remove most of the right ventricular wall, but do not get
within an inch of the semilunar valves of the pulmonary artery. At this
point the tricuspid valve, chordae tendinae, and papillary muscles of this
side of the heart are fully exposed. If the conveniences of a water faucet
and sink are at hand, slip over the faucet opening a rubber tube (about a
yard long) in the end of which is a piece of glass tubing, both ends of which
have been made smooth by heating. Insert the tube between the semilunar
valves and fill the artery with water till it swells under the pressure ; when
very full, quickly draw out the tube ; the semilunar valves will completely
close and prevent the escape of water. If the specimen is held up to the
light, the position of the valves and their perfect closure of the aperture
can be clearly shown.

The action of the other type of heart valve can be shown as follows :
First follow the aorta downward into the substance of the base of the heart,
till the two coronary arteries are found; these must be tied off (with a
broad cord, as the tissues are soft and easily cut by a small ligature) or the
rest of the experiment will not succeed. Now cut off the top of the left
auricle ; the peculiar internal structure of an auricle is thus seen. Clamp
off the aorta, as near its end as possible. Thrust the water tube down
through the auriculo- ventricular opening, and fill with water. The left
ventricle will first fill, and from there the water will go into the aorta and
fill that. In the meantime, the two flaps of the mitral valve have risen
and perfectly closed the entrance to the ventricle. When the internal
pressure of the water has become considerable, draw out the tube, and the
heart can then be manipulated to show better the valves in their closed
position. After this, the ventricle can be cut open, the thickness of its
walls compared with that of the right ventricle, the extreme thinness
of the wall at the apex of the heart shown, and any other points which
the instructor wishes to bring out.

Do not fail to cut out the semilunar valves and place in formalin for
future use.

Pages 143. — To one end of a piece of thin rubber tubing about three
feet long attach a syringe bulb by means of which water can be forced
through the tube. Into the other end of the tube insert a glass cannula,
drawn fine, in imitation of a capiUary. As the bulb is pressed rhythmi-
cally a regular pulse can be felt in the tube by holding it between the thumb ■
and finger. It can be shown a large class by connecting the short arm of a
horizontal lever with the tube by means of an upright strip of wood, or
other material ; see figure on opposite page. The amount of " pulse " or
change in diameter of the tube will be increased in proportion to the
differences between the lengths of the arms of the lever.

LABORATORY EXERCISES

409

Page 145. — Count the pulse rate ; then run up stairs and down, or
50 yards and back, and make recount of the rate. Try effect of holding
the breath.

Page 147. — A permanent preparation of a frog with arteries injected
is purchasable, and very suggestive for the study given here. If laboratory
work is given, fill arteries with starch mass (see formula), by injecting
forward through the truncus arteriosus (big vessel leaving the heart),
tying off both toward the heart before injecting, and beyond injection
point after injecting. See addresses of firms selling injection syringes, etc.

Page 148. — Circulation may be shown as follows : Bore a hole one-
half inch in diameter through one end of a piece of thin, softwood board.
The cover of an ordinary chalk box will serve. Etherize a frog till wholly
unconscious ; wrap it in cheesecloth (to aid in handling) except one hind
leg. Bind the frog to the board, letting the web of the free foot lie over
the hole. Pin out the web so that it will be lightly stretched over the
hole, and then place on stage of compound microscope, so that light will
shine through the web. Capillaries of various sizes will be seen, with
blood flowing in them.

Page 149. — These large blood vessels have probably been seen in
the course of the demonstration for page 137, but can be further shown
by use of a model of the heart.

Page 151. — Prepared sections of arteries and veins should be shown
under the microscope.

CHAPTER XI

Page 155. — Arrange a rubber tube in horizontal position, with a
capillary glass tube in one end and syringe bulb at the other. In the
middle of the tube insert a glass T, and from this side branch let a glass
tube lead vertically ; its upper end should be open. On pumping in water
with the syringe the pressure will be evident from the height to which
water rises in the vertical branch. If the capillary at the end of the hori-
zontal tube be removed, scarcely any pressure will be produced.

410

ADVANCED PHYSIOLOGY

Page 156. — The conditions described here can be imitated by using the
same apparatus as above, connecting a U-tube on the side branch, and
fining it half full of mercury. The open end of the U-tube should be long
enough so that subsequent rise of the mercury during the pressure on the
syringe bulb will not throw the mercury out. All air must be taken out
of the tubes between the water and mercury, as such an air cushion will
practically counteract the effect of rhythmical pressure on the water.
The capillary end must be used on the horizontal tube in this experiment.

Page 157. — Connect a syringe bulb with a Y-tube, and to the branches
of the Y connect a glass and a rubber tube respectively ; these should be
of equal caliber and about four feet long; the rubber tubing should be
thin and elastic. A removable glass capillary should be fitted to the
free end of each tube. By having a clamp, or valve, in each tube near
the arms of the Y, water can be sent through either tube separately. A
continuous stream can be obtained when the bulb is pressed rhythmically,
only when water is running through the rubber tube and then only when
the capillary is attached to it. See figure below.

'Rubber

Glass

Page 170. — It will add to the interest of the class to show them thyroid
tablets, adrenaUn tablets, and powdered pancreatin such as is used medici-
nally and obtainable at any drug store, or from physicians.

Page 172. — The ready combination of oxygen with carbon in wood is
strikingly shown by making oxygen and thrusting into it a glowing splinter.
Fine wire taken from a piece of picture cord, loaded with a bit of flaming
sulfur, will burn if plunged into a jar of oxygen.

CHAPTER XII

Page 178. — If a large class is being taught, the trachea and lungs of a
sheep or calf should be used to show the structure of those organs. In
the case of a small class it is better to show these organs in position m a
cat; the glottis, epiglottis and voice-box, as well as the arrangement of
the lungs in the thoracic cavity, can be shown in such a small animal to
advantage. The lungs should be inflated by inserting a tube into the
trachea aud blowing them full gf air. The bronchi aud bronchioles can be

LASOMTORY l:3tERCl§T3S

411

dissected readily. A prepared section of an injected lung should be shown
under the microscope.

Page 179. — The moving of particles of cork or bits of wood, etc., by-
cilia may be shown by pithing a frog, cutting away the lower jaw, and
then, with the frog on its back, putting such particles on the roof of the
mouth. If this be kept moist with 0.6% salt solution, these bits of mate-
rial may be slowly but visibly moved backward to the opening of the gullet.

In pithing a frog the brain is destroyed, and thus consciousness of any
pain, while the rest of the body is left entirely uninjured. Hold the frog
in one hand, ventral side against the palm ; put the first finger over top of
head and hold against middle finger which, with the other two, grasps the
body of the frog. With the back side of the blade of a scalpel placed
transversely to the skull, find the groove between the skull itself and the
first vertebra. Drive the point of the scalpel into this groove and sever
the cord ; then thrust a needle forward through the foramen magnum into
the brain box and mix up the brain. In this condition the frog may give
reflex movements, but these are from the cord alone. If it is desired to
do away with these also, pass a long needle or stiff wire backward from the
wound through the neural canal of the spine.

Page 183. — Prepared slides of many forms of pathogenic (disease
causing) bacteria can be obtained from dealers in same, and will greatly
interest a class if shown under highest powers of the microscope.

CHAPTER XIII

Page 191. — Prepare the piece of apparatus shown in figure below.
By the use of rubber bands as shown, demonstrate to the class how the
internal and external intercostals raise and lower the ribs, and thus in-
crease and decrease the size of the thorax.

412 ADVANCED PHYSIOLOGY

Page 193. — Arrange a bell jar of the type shown In Figure 102; or
let the long stem of a Y-tube pass through the cork and represent the
trachea, the two short branches representing the bronchi. Attach to
each " bronchus " a small rubber bulb, such as is on the mouth-piece affair
used by small boys as a " squawker." Close the lower end of the bell
jar with a sheet of rubber (obtainable from any dentist). By pushing the
rubber " diaphragm " upward, its position when the breath is expelled
is imitated, and the " lungs " collapse ; when drawn down, air fills the
" lungs." The leakages around the cork can be stopped by use of melted
paraffin.

Page 197. — The capacity of the lungs, amounts of tidal air, comple-
mental air, etc., can be effectually shown by use of thin wooden or paste-
board boxes of sizes to represent the different volumes referred to.

Page 201. — Show changes in air enumerated here as follows :
a. With air pump, syringe bulb, or bicycle pump, force the ordinary air
of the room through a large test tube of limewater, by conducting the air
through a tube to bottom of water so that the bubbles rise through it.

6. With a glass tube in the mouth blow through limewater. The cal-
cium carbonate formed can be dissolved with a little hydrochloric acid.

c. Breathe on the thermometer bulb.

d. Moisture is left on clean, cold glass when it is breathed upon.

e. Exhale through a glass tube into strong sulfuric acid for some time ;
the acid turns black on account of organic matter in the breath. Extreme
care should be taken not to draw the acid into the mouth.

Page 205. — That COo is heavy and will not support combustion can
be shown by leading that gas from a generator into the bottom of a pint
fruit jar, for instance ; it will drive out the air by collecting under it, thus
showing its weight. A lighted splinter thrust into it will go out. If a
piece of candle be placed in the bottom of a beaker and lighted, CO2 can
be poured into the beaker and the flame extinguished. See Appendix
list of formulae and methods.

Page 206. — To prove the fact of adjustment of breathing to different
circumstances, have students count rate of breathing when quietly sitting,
just after running up stairs and back, and before getting up in the morning.
Averages struck from a large number of such reports will be interesting.

Page 210. — If possible, the larynx of a sheep, calf, or dog should be
shown and dissected. This organ in a smaller animal is not large enough to
be of any value. Models of this organ can be bought (see list of dealers in
models) or one may be made from modeling wax, or carved from a

LABORATORY EXERCISES 413

piece of hard soap. See list of dealers for source of modeling wax ; such
material is often used in grade schools or kindergartens.

Page 214. — Use can be made here of a tuning fork. If it is struck
and the stem of it placed on the side of a hollow wooden box open at one
end (or on a regular resonator), the combined effect of the vibration of
the tuning fork and of the air chamber will be marked. The text sugges-
tion of talking into different sizes of air containers should be carried out.

CHAPTER XIV

Page 219. — The kidney of a sheep or pig is best adapted to show
structure; that of calf or beef is not similarlj^ constructed. Show the
capsule about the kidney, and then split it open by cutting from the
[convex side toward the ureter. The cortex and medullary regions, pyra-
mids, etc., are readily noted.

By use of a cat, or rabbit, the ureters, bladder, and urethra can be
plainly demonstrated.

Page 221. — Prepared slides of injected kidney should be examined
and Malpighian capsules containing glomeruli noted. The tubules will
be seen in cross and longitudinal section, though none will be found com-
iplete.

CHAPTER XV

Page 228. — Prepared slides of skin show practically all the points
mentioned. A student should prove that a needle thrust into the epider-
mis causes no pain or bleeding.

The subcutaneous tissue holding the skin to the outer muscle layers
of the body is easily demonstrable in any small animal, e.g. cat, rat,
white mice, or any which may be obtainable.

Page 235. — Examine the skin with a simple magnifier and compare
the markings of different fingers. Let one pupil be blindfolded and various
parts of his skin tested with points of dividers. Scissors, firmly gripped,
may very well be used in same way. Determine how near together they
may be and yet be felt as two. Test the fingers, the back of the hand,
the arm, the forehead, and back of the neck.

The determination of hot and cold spots requires too much apparatus
for class use. However, interesting results are secured in the following
manner : Have at hand two bowls, one containing quite warm water, the
other cool water. Put finger of one hand into the warm water, a finger
of other hand into the cool water. Is there a difference in sensations ?
After holding thus for a. minute, place both in lukewarm water ; what
is the result? Try to explain why.

414 ADVANCED PHYSIOLOGY

Page 236. — 1. If one holds the hand very near a piece of cold glass,
e.g. the window glass, moisture collects on the latter. This is insensible
perspiration.

When the opportunity presents itself, each student should very carefully
weigh himself, follow this with very vigorous exercise during which per-
spiration is sensibly produced, and then weigh himself again. The amount
of loss will be the amount perspired, most of which was sensible perspira-
tion.

2. The arrangement of the dermal papillae in rows, resulting in the fine
parallel lines on the hand, with special patterns particularly well seen
on the finger and thumb tips, is emphasized by use of a hand lens ; the
sweat glands open along the tops of these ridges. A class would be much
interested in making a series of " finger prints," obtained simply by press-
ing the finger or thumb tip on to a paper or glass which has been smoked
in gas or camphor flame.

Page 242. — Wet the finger and blow upon it gently. In spite of the
fact that the breath is warm, it will feel cool. This is because the air
current evaporates the water, and this uses up the heat of the finger.

CHAPTER XVI

Page 250. — Throughout this study of the bones constant use should
be made of a good human skeleton and of as many separate bones as can
be procured. Interesting comparisons can be made with the skeletons of
the fish, frog, and bird.

Page 254. — A disarticulated skull, like that shown in Figure 125, should
be on hand for examination.

Page 260. — A fresh bone of some size, e.g. the humerus or femur
of a sheep or calf, should be examined in class. Cross and longitudinal
sections made with hand saw show essential structure. Dried bones do
not show periosteum or marrow to advantage.

Rib bones of a sheep or pig show bone composition well. Either burn
in fire to remove animal matter, or place in hydrochloric acid (15-20%)
to remove mineral matter.

Page 262. — Microscopic sections of bone, cross and longitudinal, should
be shown through medium powers of compound microscope.

Page 264. — Any fresh bone from a joint is good for showing carti-
lage. Microscopic sections can be conveniently made from fresh material
(end of femur of frog, if none other is at hand) with hand razor ; mount on
slide in water or 1% acetic acid.

LABORATORY EXERCISES

415

Page 265. — The leg of a sheep or pig, with muscles removed, is good
for showing essential features of a joint. An articulated human skele- ,
ton should be referred to constantly in connection with discussion of various
sorts of joints.

Page 271. — In discussing and illustrating the matter of shoes, reference
may well be made to the Munson last, after which pattern all U. S. Army
shoes are made. Aside from allowing plenty of room for the small toes,
the inner side of the shoe should be
so shaped that a line drawn lengthwise
through the middle of the big toe and
continued backward will pass through
the middle of the heel. Plenty of space
in front of the toes is also provided.

The endeavor to make the foot seem
short and small by wearing high heels
can be shown by the use of board
drawings. The following line drawings
are easily made :

Line A-B = apparent length of foot.
Line A-C= actual length of foot.

The lines should pass through the long,
mid-axes of the big toes and the middle
of the heels.

CHAPTER XVII

*Page 276. — Preparations of striped muscle make satisfactory material
under high powers of the microscope. If fresh muscle can be separated
into fine enough shreds, striae show fairly well. Muscles of an insect.

I e.g. grasshopper, are especially good for this. If a section of tongue is
available, it can be used in this connection ; the muscle fibers running in
different directions are strongly striped.

416

ADVANCED PHYSIOLOGY

Page 278. — To show the relation of muscle to nerve, tetanus, etc.,
destroy the brain of a frog, remove the skin of the upper part of the hind
leg, and by pulling apart the muscles locate the large sciatic nerve. By
stimulating the nerve the muscles of the leg will contract. For more
careful study proceed as follows : Follow the nerve carefully without
stretching or even touching it any more than necessary through the hip
joint to its exit from the spinal cord in the middle of the back; cut it
there, carefully get it free from the surrounding tissues, and coil it up
(two inches or so in length) on the muscle at the knee joint. Do not allow
it to lie on the skin of the lower leg. Now remove the muscles from the
thigh region, reserving the femur bone ; cut the latter off near the hip,
and clamp in a holder supported on a standard. Place the nerve on a
pair of electrodes which are connected with a key and cells in an electric
battery circuit, taking care all the time not to let the nerve get dry ; mois-
ten with 0.6% salt (NaCl) solution, with camel's hair brush. By opening
and closing the key, a single or often repeated stimulus can be sent into
the nerve, and the characteristic effect on the muscle noted.

Figure showing simplest possible scheme of apparatus for using
nerve-muscle preparation.
B = battery E = electrodes

K = key iV= nerve X A T

w = circuit wires Af = muscle W

PF= weight

Pi^e 281. — Microscopic preparations of smooth muscle which have
been properly stained are most satisfactory for examination. Unless
there is at hand special apparatus, it is not easy to show the normal reac-
tion to stimuli of smooth muscle. So, too, its involuntary rhythmic con-
tractions cannot be easily demonstrated unless, if taken from intestine of
warm-blooded animal, it be maintained at the full body temperature in

LABORATORY EXERCISES 417

specially devised chamber. It is not a practical experiment to attempt
with limited time and apparatus.

Page 282. — To try out the point that heart muscle is apparently not
susceptible of tetanus, lay bare the heart of a frog of which the brain is
destroyed, and bend the electrodes of such an apparatus as is shown on
opposite page so that the heart may be placed between them. Rapid
making and breaking of the current can then be secured by use of the key.

CHAPTER XVIII

Page 290. — The bones of the head of a cat are sufficiently thin so
that they dissect easily. The brain coverings, fluids present, main divi-
sions of the brain, and distribution of blood vessels can be admirably
shown in such a dissection. If it is desired to show the distribution of
gray and white matter, take such a brain (or preferably that of a sheep)
and wrap it in cotton to prevent flattening against side of jar, and place
for two weeks or so in potassium bichromate solution (see Formula 10).
Sections can then be made through it with a razor and internal structures
shown to any desired extent. The brain can be hardened immediately
in formalin (5%), but will not show above differentiation.

While the brains of fishes have their parts developed to sizes which differ
from those of the cat's brain, their general relations and order of arrange-
ment are the same. The cartilage skull of the shore dogfish (Mustelus or
Squalus) permits very easy and beautiful demonstration of all brain parts
and nerves. See address Ust of dealers.

Page 293. — In order to demonstrate the so-called gray and white
regions of the central nervous system, the parts must be prepared in spe-
cific ways. See formula for this purpose. Even free-hand sections of such
material make clear demonstrations.

Page 294. — Prepared sections of the cortex of the brain show cells
well, though the student will get but a limited idea of the brain as a whole
from any one section which may be studied.

Page 301. — The general appearance and structure of the spinal cord
can be well learned by obtaining at a market a piece of the spinal cord of
some animal {e.g. the sheep or ox) still in its coverings. If this is hardened
in equal parts of 5% formalin and 70% alcohol, it is easily handled. If the
potassium bichromate method is followed the results will be better yet.

Prepared sections of the spinal cord will also be interesting.

Page 302. — That the cord is the path through which nerve impulses
are sent out from the brain can be shown on the body of a freshly beheaded

418 ADVANCED PHYSIOLOGY

frog. If electrodes are pliced on the exposed anterior end of the cord,
and a stimulus given from a battery current, or from an induction coil,
the effect on the whole posterior part of the body will prove that the cord
is the conductor of the shock. The above method is the neatest; but
essentially the same result is obtained by probing the exposed cord with
a needle.

Page 305. — Spinal nerves can be easily shown by removing the organs
in the body cavity of a frog, after which the spinal nerves, including the
brachial and lumbar plexuses, show without further dissection. Their
number is less than in man, being ten only ; it will also be easy to notice
that two go to the arm (fore-foot) and are called the brachial plexus.
Four pass to the hind leg, and together are called the sciatic plexus. The
same terms are used in human anatomy.

Page 307. — The features of a nerve fiber as described here can be made
out by separating a spinal nerve of a frog into its component fibers, and
mounting them on a slide in salt solution under the microscope.

CHAPTER XIX

Page 314. — Simple reflexes may be shown upon a frog whose head has
been removed or whose brain is destroyed. The latter method is neater,
while the former more evidently shows that the brain is absent. Suspend
the frog so that its body hangs downward, and then gently pinch the toe
or dip it into weak hydrochloric acid.

Touch a minute spot on the flank with strong acid and note that the
hind leg will scratch it even with brain lacking. This weU illustrates a
spinal reflex.

Page 324. — The main components of the sympathetic system of
nerves in a large frog show quite clearly as soon as the digestive tract and
reproductive organs are carefully removed. Do not tear out the mesen-
teries or the sympathetic chain will probably be ruined. It is delicate
but appears lying parallel to the back-bone, some of the way against it.
The sympathetic system can be better shown in a cat if dissected by a
person knowing the anatomy well.

CHAPTER XXI

Page 340. — The parts of the eye mentioned in the next few paragraphs
can be best shown in a model : the external muscles are generally shown
on the head of a manikin.

Have pupils note how rapidly the muscles closing the eyes operate;
only about .05 of a second is required to close the lid.

LABORATORY EXERCISES 419

Page 341. — The muscles which move the eye can be well shown
by use of the eye of a dog-fish. The skull is cartilaginous and easily cut
away, and the muscles are diagrammatically plain. The nerves control-
ling them can also be identified if sufficient care is taken.

Page 343. — The eye of an ox can be easily dissected to show practi-
cally all the parts mentioned here. In taking off the choroid coat the
pigment layer of the retina usually comes away also, but the cell layers
will be left in position. Material should be perfectly fresh.

Page 344. — Let one student face a bright light while keeping one eye
covered with the hand; others should notice difference in size of pupils
when the hand is removed. This makes clear the function of the iris.

Page 348. — 1. A very convincing way of showing the image on the retina
to be inverted is to mount the perfectly fresh eye of a chloroformed albino
rabbit in one end of a stiff paper tube, the cornea looking outward. A
person looking through the tube at the back of the eye sees the inverted
image of whatever is in front of it. Always look at something brightly
illuminated, e.g. anything out of doors on a sunny day, or an electric
bulb, or candle flame.

2. A great many of the principles involved in the passage of light into
the eye can be well shown by use of an artificial eye apparatus. The
ordinary defects in the eye, as well as their correction, can also be shown
with it. Ordinary loose lenses can also be used as shown in the diagrams ;
the source of the light should be confined in a dark box, with a single hole
in its side, through which light rays can emerge and strike the lenses.
A darkened room is imperative for all experimental work with light.

Permanent models of lenses and rays of light can easily be made. A
lens of any shape, regular or deformed, can be made of modeUng wax.
This can be supported on brass rods above the middle of a board base.
The source of light can be represented by a point on an upright piece of
wood a foot or two from the lens, and the retina by a flat piece of board a
foot or two from the other side of the lens. String or thread can be used
as rays of light, and strung from source of light to lens, where they can be
fastened with pins as the wax is soft. The exit of rays on the other side
can be set up in a similar way, and their distribution on the retina shown
by fastening the " rays " with tacks.

Page 361. — Adaptation of the eyes to different distances is easily
felt by the pupil if he holds up a finger of one hand about a foot from his
eyes, with finger of other hand in same line two feet away. Give atten-
tion first to one and then to the other. Board diagrams of what happens

420 ADVANCED PHYSIOLOGY

in changing the angle of convergence of light entering the pupil will assist
in making the facts clear.

Page 353. — If possible, arrange with some ociihst, or physician with
a knowledge of optics and of eye troubles, to bring into class pieces of
testing apparatus and charts and to explain the commoner eye defects
and method of correction.

Page 355. — Prepared sections of the retina will prove very fascinat-
ing if shown in this discussion, not for comment on its details, but in
proof that it is a comphcated, delicate structure.

Page 358. — Sets of differently colored worsted yarns can be obtained
for testing for color-blindness. Require pupils to place together such
samples as seem to be of the same color. It is quite probable that some
student will show defective color vision.

CHAPTER XXII

Page 362. — A large model of the entire ear must be on hand in order
that the student may get a clear idea of it. A separate preparation of
the temporal bone of the human skull, sawed open to show the ear struc-
tures, is also desirable.

Page 366. — In no other animal can the semicircular canals be so well
shown as in the dog-fish, in which they occupy a large area just back of the
eye and can be easily dissected out of the cartilaginous skull.

Page 370. — If stringed instruments are not at hand to show sym-
pathetic vibration, two tuning forks, vibrating at the same rate, can be
used. One should be struck and its stem placed upon a table top, while
the other is held near it. Then smother the one struck and place the
stem of the second on the table top. The second will be found to give
out sound.

APPENDIX

Address List of a Few Firms Dealing in Materials for
Demonstrations or Laboratory Work

Zoological material, e.g. dog-fish, flies, mosquito adults or larvoe, etc. :

(a) Supply Department, Marine Biological Laboratory, Woods Hole,
Mass.

(6) The Chicago Biological Supply House, 5505 Kimbark Avenue,
Chicago, 111.

Microscopic slides:

(a) Powers and Powers, Sta. A, Lincoln, Neb.

(&) The Chicago Biological Supply House, 5505 Kimbark Avenue,
Chicago, 111.

{d) The Cambridge Botanical Supply Company, Waverley, Mass.

Living unicellular animals:
(a) Powers and Powers, Sta. A, Lincoln, Neb.

(6) The Chicago Biological Supply House, 5505 Kimbark Avenue, Chi-
cago, 111.

(d) Cambridge Botanical Supply Company, Waverley, Mass.

Microscopes and dissecting instruments:

(a) The Spencer Lens Company, Buffalo, N. Y.

(6) Bausch and Lomb Optical Company, Rochester, N. Y.

{d) Arthur H. Thomas Company, Philadelphia, Pa.

For physiological apparatus:

(a) The Harvard Apparatus Company, Back Bay P. O., Boston, Mass.

(b) Wilham Gaertner and Company, 5345 Lake Avenue, Chicago, 111.

For skeletons and models:

(a) Ward's Natural Science Establishment, Rochester, N. Y.

(h) The Kny-Scheerer Company, 404 West 27th Street, New York City.

421

422 ADVANCED PHYSIOLOGY

Modeling wax:

(a) Any dealer in art goods.

(6) Devoe and Reynolds, Fulton Street, New York City,

General laboratory supplies, not named above:

(a) Arthur H. Thomas Company, Philadelphia, Pa.

(6) Central Scientific Company, Chicago, 111.

Formulae and Methods of Making Various Substances
Mentioned in This Book

1. Formula for iodine solution for use in testing for starch :

4 parts potassium iodide
1 " iodine
40 " water

Dissolve above and add 960 parts water. Smaller amounts may be
made using same proportions.

2. Formula for Pasteur's solution :

10 parts potassium phosphate
1 " calcium phosphate
1 " magnesium sulfate
50 " ammonium tartrate
750 " cane sugar
4188 " water

3. Formula for artificial gastric juice :

0.2 parts hydrochloric acid
0.1 " pepsin
0.05 " calcium chloride
0.05 " potassium phosphate
100 " water

The above is a precise formula, but for ordinary experiments for ele-
mentary classes the calcium and potassium compounds may be omitted and
the other two used in greater strength.

4. Formula for artificial pancreatic juice:

0.6 part common salt 0.2 part pancreatin

0.2 " sodium carbonate 0.2 *' potassium phosphate

0.2 " diastase 0.2 " lipase

100 parts water

For elementary work the potassium, diastase, and lipase maybe omitted.

APPENDIX

423

W^O

H,0

JVa/k^

5. Formula for lime water :

Add calcium hydrate to water till saturation is reached ; then filter.

6. Formula for normal salt solution :

0.6-0.75%. This solution is merely sodium chloride in distilled water.

7. Fehling's solution for sugar tests :

A quantity sufficient for convenient use can be made up as follows:
Solution 1 : dissolve 17 grams (about 1^ teaspoonfuls) of pure copper sulfate
in 100 cc. (a quarter pint) of water. Solution 2 : dissolve 75 grams (about
6 teaspoonfuls) of Rochelle salt and 25 grams (about 1^ 5-inch sticks)
caustic soda in 250 cc. (about \ pint) of water. Mix the two solutions
thoroughly. This solution keeps in usable shape only for short time and it
is more convenient to procure
tablets ready for dissolving
from a druggist. Whether the
solution is correct or not can
be ascertained by boiling a
little ; if it loses its color, the
solution is useless.

8. The following is a con-
venient method of making
oxygen gas :

Put some spdium peroxid
powder into a medium sized
flask. This should be fitted
with a rubber cork, through
which runs a glass tube for leading off the gas, and a separatory funnel
by means of which water can be slowly dropped on to the peroxid at will.
The gas forms immediately and in large quantity. It can be most easily

O collected in jars over water by

^_^ downward displacement; see

figure.

9. To make carbon dioxid

Put into a medium sized flask
some broken bits of marble.
Cover with water. Through the
rubber cork in the neck pass a
glass tube through which to
lead off the gas ; also a thistle
tube, letting the lower eod qi the

\. ^^^m:

Illustrating the method of making oxygen gas.

M&H^O

Illustrating the method of making carbon dioxid

424 ADVANCED PHYSIOLOGY

latter reach below the water level. Pour hydrochloric acid into the thistle
tube ; CO2 is immediately formed, though slowly, and can be collected by
merely letting the gas run into the bottom of a jar ; the weight of the gas
will force out the air above it. Too free diffusion into the air should be
prevented by covering the jar with a glass plate ; see figure.

10. Formula for fluid in which to preserve parts of central nervous
system so as to show white and gray regions :

10 parts potassium bichromate
15-20 " formaldehyde (40%)
500 " water

Let material stand in above mixture two weeks or so ; if not hard then,
place overnight in :

2 parts 5% formalin

1 " 95% alcohol (ethyl)

A fresh brain placed in the last named mixture alone will harden in two
days ; but the regions of gray and white matter will not be differentiated.

Chemical Composition of Various Substances Mentioned
in This Book

Acetic Acid

C.H4O.

Alcohol

C2H6OH

Ammonia

NH3

Caffein

05H(CH3)3N40a

Carbon Dioxid

C02

Fat (stearin)

CsvHiioOe

Glycogen

CeHioOs

Glycerin

C3H5(OH)3

Hydrochloric Acid

HCl

Milk Sugar

C12H22O11

Proteid (egg albumin)

C204H322O66N52S2

Starch

CeHioOa

Sugar (grape sugar,

glucose,

etc.)

CeHizOe

Urea

CO(NH2)2

Uric Acid

CaH403N4

APPENDIX

425

A Comparison of the Units of Measure Commonly Employed
in America with Those of the Metric System

Length

Weight

Capacity . .

Work . .

Heat . .

1 meter (m.) =1000 millimeters (mm.).
1 " =100 centimeters (cm.) =39.37 inches.

1 inch =25.4 millimeters.

1 foot =30.5 centimeters.

. 1 M = TojHj millimeter =5^055 inch (nearly).

1 kilogram (kg.) =1000 grama (g.) =2.2 lb. Avoirdupois.

1 gram (g.) =1000 milligrams (mg.) =15.4 grains,

1 pound (Avoir.) =453.6 grams, or about 5 kilogram.

1 ounce " =28.35 grams =437.5 grains.

1 liter (1.) =1000 cubic centimeters (cc.) =2.1 pints.

1 fluid ounce =29.57 cubic centimeters.

1 pint =16 fluid oz. =473.1 cubic centimeters.

1 gallon =3.78 liters.

1 cubic inch =16.38 cubic centimeters.

1 cubic foot =28.3 liters.

1 kilogram-meter (kg.m.) =7.23 foot-pounds.
1 foot-pound =.138 kilogram-meter.

1 foot-ton =276 kilogram-meters.

1 unit of heat =heat necessary to raise 1 pound of water through

1° F.
1 calorie (Metric) = " " " " 1 gram " '*

1° C.
Mechanical equivalent of heat unit =778 foot-pounds.

" " " calorie =427 gram-meters.

INDEX

Abdominal cavity, 90
Absorption of food, 112, 116

summary of digestion and, 121
Accommodation, process of, 349

mechanism of, 350
Adenoids, 176
Adipose tissue, 228
Adrenal bodies, 170
Ague, fever and, 132
Air changes in,during breathing,200

and house location, 385

in lungs, 197

in middle ear, 364
Albumen, 28

in Bright's disease, 226
Alcohol and brain, 333

and length of life, 335

and indigestion, 108

as food, 59

formation of, through fermenta-
tion, 62

influence of, on circulation, 164

oxidation of, in body, 59

users and railroad companies, 335
Alveolus, of gland, 81

of lung,179
Amino-acids, 201
Ampullae of ear, 366
Amylopsin, 103
Anabolism, 35
Anatomy, definition of, 10
Anesthetics, 330
Animals, multicellular, 23

unicellular, 22, 23

warm and cold blooded, 239
Antiseptic lotions, 235
Antitoxin, 86, 287
Aorta, 141

Apoplexy — see Paralysis, 326
Appendicitis, 110
Appendix, vermiform, 106
Appetite as guide in eating, 51
Aqueous humor, 344
Arachnoid fluid, 290, 301

Arborizations,

(see Dendrites)
Arm, 256

blood in, 157

bones of, 256

nerves to, 305
Arteries, main, in body, 145, 146

pulmonary, 139

structure of, 151
Astigmatism, 354
Auricle, 137
Axis cylinder (axon) of nerves, 307

Backbonej the, 251
Bacteria, 67

and white corpuscles, 126

beneficial, 68

distribution of, 68

harmful, 70

immunity against, 71

in milk, 393

multiplication of, 65

of blood poisoning, 131

of diphtheria, 86

of pneumonia, 183

of tonsilitis, 85

of tuberculosis, 184-189

relation of, to disease, 70
Ball and socket, 267
Basilar membrane, 370
Baths, cold, 244

hot, 246

in general, 244
Beans, 40, 47
Beef, 40, 46
Beverages, 375
Bicuspid teeth, 75
Bile, 101, 102
Bladder, gall, 101

stones, 226

urinary, 223
Bleeding, 156
Blind spot, 356
Blisters, 167, 230

427

428

INDEX

Blood, amount of, 123

cells, 16, 124, 126

clotting, 128

composition of, 123

demonstration of, 406

diseases of, 130

in excretion, 217

lack of, in some animals, 122

part played by, in paralysis, 326

platelets, 127

poisoning, 131

pressure, 154

rate of flow of, 158

tissue, 13

vessels, 145

in dermis, 233, 241
in kidneys, 221 .
in lungs, 180
regulation of size of, 158
structure of, 150
to legs, 158
Blushing, 160
Body, cavity, 89

chemical composition of, 27, 28
Boils, 131
Bone cells, 15, 261, 263

composition of, 260

material used in making, 53

repair of, 261

structure of, 259

tissue, 12, 262
Bones, carpal, 257

dislocation of, 269

of children and adults, 260

of ear, 3,64

of face, 255

of feet, 258

of jaw, 255

of leg and hip, 257

of skull, 254

of spine, 251

patella, 266

rib, 253

setting of, 262
Brain, 290-293

alcohol and, 333

care of, 321

cortex of, 293

demonstration of, 417

drugs affecting, 329

dura mater of, 290

ventricles of. 293

Bread, composition of, 46
proteid in, 39

Breathing and exercise, 205

carbon dioxid, 204

diaphragm, 192
Breathing, habits, 198

pure oxygen, 203

rib, 191

through mouth, 174
Bright's disease, 226
Bronchial tubes, 178
Bronchitis, 183
Bunions, 230
Burns, 248
Butter, 46

Caffein, 58. 164

Calculi in bladder, 226

Callouses, 230

Calories produced* in a day, 48

Canaliculi, 263

Canals, external ear, 362

semicircular, 366
Canine teeth, 75
Capillaries, 146, 148, 409

structure of, 152
Carbohydrates, 31

after absorption, 118

compared with fats, 33

kinds of, 31

per cent of, in foods, 43

tests for, 400

uses of, 32
Carbon dioxid and ventilation, 207

in respired air, 200, 204

method of making, 423
Cardiac, muscle, 281

nerves, 145

valve, 91
Carpal bones, 257
Cartilage, 12, 263

ends of ribs, 253

of larynx, 211

rings of trachea, 177
Casein, 29
Cavity abdominal, 90

mastoid, 363

thoracic, 90

INDEX

429

Cell, definition of, 19

division of, 20

growth, 20

repair, 2G

structure, 17

theory, 15

wall, 18
Cells, division of labor among, 24

gland, 16
Cells, repair of, 20
Cement of teeth, 76
Center, circulatory, 161

coordinating, 298

respiratory, 194
Cereals, composition of, 47
Cerebellum, 291

functions of, 298

structure of, 297
Cerebrum, 291

functions of, 295

localization in, 296

structure of, 294
Charity Organization Society of
New York, rules of, as to tuber-
culosis, 187
Cheese, 39, 46
Chemical compounds, 28
Chills, 132

Chordae tendinae, 139
Choroid, 344
Chyle, 105
Chyme, 97
Cilia, in Eustachian tubes, 364

demonstration of, 411

in nose, 174

in pharynx, 84

in trachea, 179

movement of, 403
CUiary muscle, 351
Circulation, apparatus illustrating,
408; diseases of, 153

importance of vigor of, 161

influence of drugs on, 164

influence of heat and cold, 162

pulmonary, 140, 141, 150

summary of, 150

systemic, 147, 150
Clavicle, 256

Cleaning of buildings, 388
Clothing, 246

and colds, 182

Clotting, of blood, 128

purpose of, 130
Coccyx, 253
Cochlea, 366
Coecum, 105
Coelomic fluid, 90
Coffee, 58, 330
Cold baths, 244

influence of, on circulation, 162

nerve endings perceiving, 234

rigor of muscle, 279
Colds, 181
Colloids, 116
Collagen, 260
Colon, 105
Color blindness, 359

vision, 358
Condiments, 52
Cones in retina, 355
Confectionery, 48
Conjunctiva of eye, 343
Connective tissue, 12, 15, 276
Constipation, 106
Consumption, 184, 381
Cooking, 53

relation of, to digestibility of

food, 55
Coordination, 298
Cornea, 343
Corns, 230
Corpus callosum, 293
Corpuscles, nerve ending, 309

red blood, 124

white, 126
Cortex of brain, 293

of hair, 231

of kidney, 220
Cramming, 323
Cranium, 254, 290
Cretinism, 170
Crura cerebri, 291
Crystalloids, 116
Cystic duct, 101

Dandruff, 230
Deafness, 372
Deficiency diseases, 45
Dendrites, 294, 310
Dentine, 76
Dermis, 228, 233
papillae of, 234
Diabetes, 226

430

INDEX

Diaphragm, location and structure
of, 89

manner of functioning, 193

nerves to, 195
Diastole, 141
Digestion, in general, 74

in intestine, 101

in mouth, 80

in stomach, 93

summary of, 121
Digestive system, 74, 88, 98
Diphtheria, 71, 86, 380
Diseases, associated with blood, 130,

163
Diseases, hip, 185, 287

of blood, 130

of excretory organs, 225

of intestinal tract, 109

of mastoid cavities, 364

of mouth and throat, 85, 176

of muscles and bones, 287

of nervous system, 325

of respiratory system, 181

of thyroid glands, 170

relation of, to imagination, 323

struggle against germs of, 328
Disinfection, 73
Dislocation of bones, 269
Division of cells, 20

of labor in body, 24
Dropsy, 167
Drowning, 209
Drugs, 164

affecting brain, 333
Drum, ear, 362
Duct, cystic, 101

hepatic, 101

pancreatic, 102

salivary, 81

thoracic, 120
Ductless glands, 168
Duodenum, 100
Dura mater, of brain, 290

of cord, 301

Ear, 362-365

air in middle, 364

ampullae of, 366
Eggs, 39, 46,
Elements, chemical,in living matter,

25,27
Emulsion of fats, 104

Enamel of teeth, 76

Endolymph, 366

Energy, carbohydrate sources of, 32

fat sources of, 32

proteid sources of, 30
Enunciation, 215
Enzymes, 63
Epidemics, 395
Epidermis, 228
Epiglottis, 85
Epithelium, 12, 15
Ethmoid bone, 175
Eustachian tubes, 363, 372

and deafness, 84
Excretion, of urea, 218, 221

organs of, 216

through skin, 235
Exercise, and breathing, 205

for student, 285

kinds of, 285

need of, 284

walking as, 285
Expiration, 192
Eye, 340

apparatus illustrating, 418

conjunctiva of, 343

formation of images in, 345
Eyelids, 340
Eyesight, 354

Faeces, 107
Fainting, 163
Farsightedness, 353
Fat, after absorption, 119

as body component, 28

cells, 16

characteristics of, 45

comparison with carbohydrates,
33

kinds and distribution of, 32

per cent of, in common foods, 44

tests for, 401

tissue, 13
Fatigue, 279
Fats, carbohydrates compared with,

34
Feet, bones of, 258

care of, 269

defective, 270
Fehling's solution, 423
Femur, 258

INDEX

431

Fermentation, alcoholic, 62

of starch, 62

demonstration of, 402
Ferments, characteristics of, 64

kinds formed in the body, 65

organized, 63

unorganized, 63
Fever, and ague, 132

scarlet, 71

typhoid, 71, 110

yellow, 134
Fibres, muscle, 275

nerve, 307
Fibrin, 129

ferment, 129
Fibrinogen, 129
Fibula, 258
Finger nails, 233
Fingers, bones of, 257
Flatfoot, 271, 272
Flavorings, 53
Flour, 39
Fluid, arachnoid, 290, 301

synovial, 265
Focus of light, 347
Food, absorption of, 112, 116

alcohol as, 59

amount needed, 48

changes in, after absorption, 117

composition of common, 46

digestion and absorption of, 121

habits, 37

inspectors, 393

parasites in, 55

predigested, 96

purity of, 393

relation of, to work, 98

salt in, 53

supplies, sanitary handling, 393

value of, 38
Foramen, magnum, 290

ovale, 363

rotundum, 363
Form of body, factors influencing,

260, 285
Fovea centralis, 356
Frostbites, 248
Furnishings, hygienic, 388

Gall bladder, 101
Ganglion, spinal, 305
sympathetic, 324

Garbage disposal, 394
Gastric, glands, 92

juice, 93

formula for arti cial, 422
nervous control of, 95
secretion, 93
Gastrolipase, 93, 95
Gelatin, 34

source of, 401
Girdle, pectoral, 256

pelvic, 257
Gland, alveolus of, 81

cells, 16

ductless, 168

gastric, 92

liver, 100

pancreatic, 102

racemose type of, 81

salivary, 81

tissue, 13
Glomerulus, 221
Glottis, 84, 404
Glucose, 43
Gluten, 29

Glycerin from fats, 104
Glycogen, 31, 119
Goitre, 170
Grafting, skin, 231
Growth, of cells, 19

in general, 36
Gullet, 84, 404
Gymnastics, 285

Habits, reflex action and, 318
Haemoglobin, 124

in respiration, 202
Hair, 231
Health, municipal, 391

officers, 392

problems, public control of, 395
Hearing, sense of, 369
Heart, cause of beat, 144

defects in, 143

demonstration of action of, 407

events of beat, 137

location and structure of, 136

muscle, 281

rate of beat, 141, 143

regulation of beat, 145

sounds, 141

ventricles of , 137

work done by, 143

432

INDEX

Heat, amount used in a day, 48

artificial, 386

and cold, sense of, 234

influence of, on circulation, 162

loss of, 240

nerves perceiving, 234

regulation of, 239, 242

rigor of muscle, 279
Hemorrhage, 185
Hepatic duct, 101
Hip, 257

disease, 185, 287

joint at, 267
Hookworm, 111
Hormones, 169
Hot and cold spots, 413
House construction, 384
Humerus, 256
Humor, aqueous, 344

vitreous, 344
Hydrochloric acid in gastric juice,

93
Hygiene, municipal, 391

personal, 374

social, 378
Hyperopia, 353

Idiocy, 325

Images, formation of, in eye, 345
Illumination, intensity of, 360
Immunity against bacteria, 71

active, 382

artificial, 382
Impulse, theories of nerve, 319
Incisor teeth, 75
Incus, 365

Indigestion, alcohol and, 108
Infection, 378 i

Influenza, 135, 143
Inoculation, 382
Insanity, 325
Inspiration, 192
Insurance companies, and users of

alcohol, 335
Intercostal muscles, 191

nerves, 195
Intestinal tract, diseases of, 109
Intestine, large, 105

small, 99
Involuntary muscle, 280
Iodine, for ^tarch tests, 422
Iris, 344

Iron in blood, 202
Isolation periods, 380

Jaundice, 226

urine in, 227
Joints, 264

ball and socket, 267

hinge, 265

imperfect, 264

injuries to, 268

pivot, 268

Katabolism, 35
Kidney, cortex of, 220

of a sheep, 413

pelvis of, 219
Kidneys, excretion of, in relation
to proteid, 32

structure of, 219
Knee joint, 265

Lachrymal canals, 175, 341

glands, 341
Lactase, 104
Lacteals, 113, 119

demonstration of, 406
Lacunae of bone, 263
Lamellae of bone, 263
Larynx, 177, 210

cartilage of, 211

of a sheep, 412
Lashes of eyes, 341
Laxatives, 374
Leg, blood vessels to, 158

bones of, 257

nerves to, 305
Legumen, 29
Lens, the, 344

change of form in, of eye, 351
Lens, p&,ssage of light through, 347
Leucocytes, 126
Lids of eyes, 340
Life, indoor, 206

length of, and alcohol, ,336

outdoor, 182
Ligaments, 266, 274

capsular, 266

crucial, 266

suspensory, 345, 351
Light, effect of flickering, 360

effect of, in cy^, 356

focus of, 347

kinds of artificial,, 385

INDEX

433

Lime water, formula, 423

Lipase, 103

Liver, function of, 101

secretion of, 101

storage of sugar in, 119

structure of, 101

urea formation in, 218
Living and non-li\ing matter, 19, 27
Location of houses, 383
Lockjaw, 287

(see tetanus)
Lung, alveolus of, 179
Lungs, air in, 197

capacity of, 197

coverings of, 180

demonstration of, 412

structure of, 179
Lupus, 184
Lymph, ducts, 120

flow of, 166

glands, 169

system, 165

vessels, 167, 403
Lysine, 104

Malaria, 132

and mosquitoes, 133
Malleus, 364
Malpighian, capsule, 220

pyramids, 219
Maltose, 104
Mandible, 255
Marrow, 259
Mastication, 75
Mastoid cavities, 363

disease of, 364, 373
Matter, living and non-living, 19,

27
Meals, frequency of, 50

water during, 57
Measles, 71, 385
Meat, composition of, 46
Meatus of ear, 362
Medicines, 338
Medulla, of brain, 292

of hair, 231

respiratory center in, 194

seat of involuntary activities, 300

structure of, 299

vaso-constrictor centre in, 161

Medullary sheath of nerves, 307
Meibomian glands, 341
Meningitis, 185, 327
Mesentery, 90
Metabolism, 35

summary of, 224
Metacarpal bones, 257
Metatarsal bones, 258
Microbes, 65
Milk, action of rennin on, 94

calcium in, 260

composition of, 46

proteid in, 39

source of typhoid. Ill
Mind, need of clear, 328
Molar teeth, 75
Mosquitoes and malaria, 133

and yellow fever, 134
Mouth, 74

breathing through, 174

digestion in, 80

diseases of, 85, 176
Mucous cells, 173, 176
Mucus, 74, 180
Multicellular organism, 23
Mumps, 87
Muscle, cardiac, 281

cells, 15

ciliary, 351

distribution of, 273

effect of use and disuse of, 282

external, of eye, 340

fibres, 275

internal, of eye, 341

kinds of, 274

papillary, 139

relation to nerve, 416

stapedius, 365, 372

striped, 274-279

unstriped, 280
Muscles in body, main, 279
Muscular system, 275
Mutton, 39
Myopia, 352
Myosin, 29

Nails, finger, 233
Narcotics, 330
Nearsightedness, 352
Nephritis, 185

434

INDEX

Nerve, accelerator, to heart, 145

auditory, 367, 371

cells, 16

control over muscle, 416

cranial, 304

endings, 309

fibres, 307

impulse, 319

inhibitor, to heart, 145

olfactorv, 175, 291

:)ptic, 291, 356

iecretory, 82, 95, 237

spinal, 305

tissue, 13
Nerves, afferent, 306, 310

axon of, 307

cardiac, 145

efferent, 306, 313

ganglia, 305, 311

intercostal, 195

sympathetic, 145, 324

to diaphragm, 195
Nervous system, preservation of,
377

prostration, 326

system, 289, 310, 340, 362
central, 289
peripheral, 304
Neural foramina, 252
Neurons, 310
Nitrogen, in body, 26

in respiration, 203

in proteid, 30

in urea, 31, 218
Nodes of nerve fibres, 307
Nose, 173

cilia in, 174
Nucleus of cells, 18

Oesophagus, 84, 88
Olein, 45
Olfactory, cells, 176

nerves, 175
Opiates, use of, 330
Optic, chiasma, 291

nerves, 291, 356
Organ of Corti, 369
Organism, definition of, 11

multicellular, 23

unicellular, 22
Os innominatum, 258

Osmosis, 114

demonstration of, 406
Osteoblasts, 260
Osteoclasts, 260
Ossification, 264
Oxidation, 30, 34, 238
Oxygen, breathing, 203

in body, 27

method of making, 423

relations of, to blood, 201
Oysters source of typhoid, 111, 393

Pain, sense of, 96, 235

Palate, 79

Palmatin, 45

Pancreas, secretion of, 103, 171

structure of, 102
Pancreatic juice, artificial, 422

secretion, 103
Papillae of dermis, 234

on tongue, 78
Papillary muscles, 139
Paralysis, 326
Parasites in food, 52
Parotid gland, 81

Pasteur's solution, formula for, 422
Patella, 266
Peas, 40, 47
Pelvis, bones of, 257, 267

of kidney, 219
Pepsin, 93
Peptone, 94, 103
Pericardium, 136
Perilymph, 365
Periosteum, 258, 261
Peristalsis, in intestine, 100

in oesophagus, 89

in ureters, 223
Peritoneum, 90
Peritonitis, 109
Perspiration, 235

and heat regulation, 241

salt in, 237
Physiology, definition of, 10
Phalanges, 257
Pharynx, 83, 85

ciUa, in 84

demonstration of, 404
Pia mater of brain, 290

of cord, 301

INDEX

435

Pigment, in hair, 231

in retina, 355

in skin, 230
Pillars of fauces, 83
Pimples, cause of, 131
Pitch, of voice, 213

perception of, 370
Pituitary body, 291
Plasma, 123
Playgrounds, 394
Pleura, 90, 180

inflammation of, 189
Pleurisy, 189

Plexus, brachial and lumbar, 305
Pneumonia, 183
Poisoning, blood, 131
Pons VaroUi, 292
Portal blood system, 118, 150
Potatoes, 47
Poultry as food, 39
Pressure, blood, 154
Primitive sheath of nerves, 307
Pronunciation, 214
Prostration, nervous, 326
Proteid, as fuel, 30

as tissue builder, 28

disadvantages of, 30

elements in, 28

expense of, 42

in bread, 39

in milk, 39

kinds of, 29

nitrogen in, 30

per cent of, in foods, 39

relation of kidneys to, 31

tests for, 400
Protoplasm, 17

demonstration of living, 399
Protozoa, cultures of, 399
Ptyalin, 82
Pulmonary, arteries, 139

veins, 141
Pulse, 142, 157

demonstration of, 408
Pupil of eye, 344
Purple, visual in eye, 355
Pyloric valve, 91
Pyramids, Malpighian, 219

Quarantine laws, 390

Racemose type of gland, 81

Radius, 256

Railroad companies and users of

alcohol, 335
Ration for a day, 49
Rectum, 106
Reflex action, 312, 314

and gastric secretion, 95

and habits, 318

and salivary secretion, 82
Reflex action, relation to conscio'

centers, 317
Renal blood vessels, 221 ■*

organs, 219
Rennin, 93

action of, on milk, 94
Repair of cells, 20
Respiration, cause of movements of,
199

center of, 194

chemistry of, 200

diseases of organs of, 181

external, 193

function of, 172

internal, 193

mechanism of, 190

nitrogen in, 203

rate of movements in, 196
Retina, 344, 354, 355

pigment in, 355
Rheumatism, 287
Ribs, 253
Rice, 47
Rickets, 53
Rods in retina, 355
Rugae in stomach, 92

Saccharose, 43
Saccule, 366
Sacrum, 253
Saliva, 63, 81
Salivary glands, 81

demonstration of, 404
Salt in food, 53

and condiments, 375

in perspiration, 237

in urine, 222
Salt solution, formula, 423
Sarcolemma, 275
Scapula, 256
Scarlet fever, 71
School, hygiene, 383

nurses, 390

436

INDEX

Sclerotic, 343
Scrofula, 185
Secretion, gastric, 93

lachrymal, 341

liver, 101

pancreatic, 103, 171

salivary, 81
Semicircular canals, 366
Sense, of hearing, 368

heat and cold, 234

pain, 96, 235

sight, 354

smell, 175

taste, 79
Serum, 128
Sewage, 389
Shock, nervous, 326
Shoes, 270

proper fitting of, 415
Shoulder, 256
Sight, 354

Sigmoid flexure, 106
Sinuses, air, 214
Skeleton, 250

parts of, where obtainable, 421
Skin, care of, 244

excretion through, 235

grafting, 230-231

pigment in, 230

protection from germs, 235

structure of, 228
Sleep, 322

as hygienic measure, 377
Smallpox, 71,249
Smell, 175
Socket of eyes, 340
Soimd, loudness of, 371

perception of, 369

quaUty of, 372
Spinal column, 251
Spinal cord, 291

as conductor, 405

as conductor of impulses, 302

ganglion, 305

method of preparing sheep's, 417

nerves, 418
structure of, 301
demonstration of, 417
Spleen, 100, 169
Sprains, 268

Stapedius muscle, 365, 372
Stapes, 365

Starchy solution for testing, 422

Steapsm, 103

Stearin, 45

Sterilization, 73

Sternum, 253

Stimulants and the brain, 329

Stomach, 91

Striae of muscle, 275

Street cleaning, 394

Strychnin, 330

Sublingual gland, 81

Submaxillary gland, 81

Suffocation, 209

Sugar, 31

and diabetes, 226

stored in liver^ 119
Summer complamt, 109
Sutures between bones, 255
Swallowing, 88
Sweat, evaporation of, 241

glands, 237
Sympathetic ganglia, 324

nerves, 145, 324

demonstration of, 418
Synovial fluid, 265
System, blood, 122, 136, 154

digestive, 74, 88, 98

excretory, 216

muscular, 273

nervous, 289, 310, 340, 362

respiratory, 172, 190

sympathetic nervous, 324
Systole, 141

Tapeworms, 52
Tarsal bones, 258
Taste buds, 79
Tea, 58, 330
Teeth, 75-77, 254
Temperature, body, 237

regulation of, 239
Temporal bone, 362
Tendon, function of, 274

Tetanus' 278, 281, 282, 287, 288
Thein, 58
Thoracic duct, 120
Thorax, 90
Throat, 83, 85, 176
Thrombin, 129
Thyroid cartilage, 211
glands, 170

INDEX

437

Tibia, 258

Tissue, bone, 12,262

builder, proteid as, 28

connective, 13

definition of, 12

kinds of, 12
Tissues, permanent preparation of,

399
Tobacco, 337
Tongue, 78
Tonsilitis, 85
Tonsils, 83
Toothache, 77
Touch, 234
Toxin, 381
Trachea, 177

demonstration of, 410
Tract, alimentary, 74

ascending nerve in cord, 303

descending nerve in cord, 303
Trichina, 52
Trypsin, 103
Tryptophane, 104
Tuberculosis, 71, 184-189
Tubules, urinary, 220, 222
Turbinated bones in nose, 173
Tympanic, cavity, 363

membrane, 362

tensor muscle of, 365, 372
Tympanum, 363
Typhoid fever, 71, 110

milk, oysters, water, sources of,
111

Ulna, 256

Unioellular organism, 22

Urea, excretion of, 221

formula of, 218

making of, 218

nitrogen in, 31,218
Ureters, 219, 223
Urethra, 224
Urine, 222

in jaundice, 226

salt in, 222
Utricle, 366
Uvula. 80

Vagus nerves, relation to heart,
145

relation to lungs, 196
Value of food, 38
Valves, cardiac, 139, 141

in lymph ducts, 120

in veins, 151
Vaso-motor system, 159
Veal, 39

Vegetables, 43, 47
Vegetarianism, 51
Veins, 145

main, in body, 148

portal, 118, 150

pulmonary, 141

structure of, 151
Venae cavae, 137, 149
VentQation, 206, 387
Ventricles of brain, 293

of heart, 137
Vertebrae, 251
Vestibule of ear, 365
Vmi, 113
Vitamines, 45
Vitreous humor, 344
Vocal cords, 212
Voice, 210-214
Voluntary muscles, 275-279
Vomiting, 91

Walking, and good feet, 269

as exercise, 285
Water, ice, and, 384

during meals, 57

excretion of, in kidneys, 222

excretion of, in perspiration, 237

excretion of, in respiration, 200

necessity for, 57, 224

source of t5T)hoid, 111

supplies, 383
Wax in ears, 363
Whooping cough, 71, 87, 381
Wounds, danger from, 288

ligaturing after, 156

Yeasts, 62, 66

Yellow fever and mosquitoes, 134

20.

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Advanced physiology and
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