THE HUMAN BODY AND 
ITS ENEMIES 
A TEXTBOOK OF HYGIENE SANITATION 
AND PHYSIOLOGY 
BY 
CARL HARTMAN, B.A., M.A. 
Adjunct Professor of Zoology, University of Texas 
AND 
.EWIS BRADLEY BIBB, B.A., M.D. 
Attending Physician, Austin Sanitarium 
WITH TWO HUNDRED AND FORTY-SIX 
ILLUSTRATIONS 
YONKERS-ON-HUDSON, NEW YORK 
WORLD BOOK COMPANY 
1914 BY THE SAME AUTHORS 
First Book of Health; a textbook of 
personal hygiene for pupils in the lower 
grades. Cloth, one hundred and sixty 
pages, one hundred and twenty-two il- 
lustrations. 
Copyright, 1912, by Carl Hartman and Lewis Bradley Bibb 
Copyright, 1913, by World Book Company hbhb — a PREFACE 
An examination of school physiologies published within 
the last four or five decades discloses the changing viewpoints 
of teachers of this subject. First anatomy was emphasized, 
then physiology became prominent, while in recent years, 
leaders in educational thought are agreed that hygiene is 
of paramount importance. Within this recent period there 
has been a shifting of accent from dress and diet to the 
prevention of germ diseases. The most generally accepted 
course of today, for elementary physiology, is one which does 
not minimize any of the phases of the subject, but preserves 
a correct proportion among them. 
The essential principle of hygiene has ever been clean- 
liness. The race has developed an instinctive horror of 
the unclean. Since the discovery of microorganisms as the 
causative agents of disease, however, our adherence to clean- 
liness has become specific and intelligent. There are, for 
example, many harmless substances far more revolting than 
human blood containing malarial parasites. But modern 
hygiene teaches that the blood of a malarial patient, taken in 
conjunction with a certain species of mosquito, makes a 
combination which is, from a health standpoint, very unclean. 
There is, therefore, a well-founded demand that children 
be taught the essentials of germ diseases and their preven- 
tion. The authors of the present volume have placed this 
material first, believing that its importance justifies this order 
of treatment. 
In some quarters a certain timidity prevails in dealing with 
the topics of health and disease, on the ground that increased 
knowledge along these lines will lead to a more pessimistic 
point of view. The important role of optimism in the preser- 
vation of health is well recognized. Yet, in view of our pres- 
ent knowledge of the wonderful defenses of the human body, IV 
PREFACE 
it must be conceded that an understanding of them gives an 
increased confidence and renewed optimism based on fact and 
not merely on sentiment. 
The discussion of the anatomy of the human body has been 
in this book reduced to a minimum, and the physiology 
has been subordinated to the principles of hygiene. Such a 
treatment is believed to appeal to the reason of the child, for 
persuasion is more effective than arbitrary command. 
The fact has been borne in mind that physiology and 
hygiene are practically the only natural sciences that the great 
bulk of our people ever have an opportunity of studying. The 
scientific treatment has, therefore, been adhered to as closely 
as the intellectual advancement of the pupil for whom this 
work is intended, would seem to allow. 
Aids to the memory, however, have not been omitted. A 
summary of the important points together with carefully 
selected questions, at the end of each chapter, will be found 
of help to the pupil in liis study. Frequent review questions 
and cross references in the text afford ample opportunities 
for repetition. 
Experience in teaching science soon convinces one that 
poor thinking is largely due to vague mental concepts of 
things and relations. The laboratory method of seeing for 
one's self has been followed in these pages. The numerous 
experiments introduced throughout the book are all simple 
and can be performed easily with very little outlay for appa- 
ratus and material. 
Illustrations are considered a necessity in a modern scien- 
tific book, particularly in one intended for the young. Many 
of the illustrations in this book were drawn expressly for it, 
and for most of them a distinct pedagogical value is claimed. 
In adapting the work to present conditions in Texas, the 
authors have received valuable assistance from the State Medi- PREFACE 
cal Association, acting through its Textbook Committee; while 
the chapters on the care of the teeth were written with the 
cooperation and advice of the State Dental Association, act- 
ing through Us Textbook Committee. The authors' grateful 
thanks and expressions of appreciation are due to them and 
to their many friends of the leaching and medical professions 
in Texas and other slates, for kind assistance and suggestions 
in the preparation of the volume. 
CARL HARTMAN 
LEWIS BRADLEY BIBB 
Austin, Texas. CONTENTS 
PAGE 
Preface vi 
Introduction i 
Bacteria or Germs 4 
Diseases that are Catching io 
Our Protection Against Disease Germs 15 
Practical Value of Artificial Immunity 22 
Typhoid Fever 29 
Consumption or Tuberculosis 40 
Colds, Grip, and Pneumonia 48 
Diphtheria and Meningitis 52 
Malaria, Yellow Fever and Dengue 57 
Quarantinable and Reportable Diseases 63 
Pellagra and Hookworm Disease 70 
Bubonic Plague 75 
Disease Carriers 78 
Insects which Carry or Scatter Disease 81 
The House, or Typhoid, Fly 84 
Mosquitoes 89 
ELeeping Germs out of Our Drinking Water 96 
Disinfection, or How to Kill Bacteria 106 
Keeping Account of Our Treasure 113 
The Body a House of Many Parts 118 
Why We Eat 124 
What We Eat 128 
Pure Food 134 
The Meaning of Digestion 144 
Where Digestion Begins: The Mouth and the Teeth . 149 
Other Digestive Organs: Gullet, Stomach, and 
Intestines 158 
The Digestive Glands 166 
How the Food is Taken up by the Blood and Lymph: 
Absorption 170 
The Making of Living Substance: Assimilation . . . .178 
Why We Breathe . 183 
The Air Passages 187 
The Lungs 192 PAGE 
Ventilation 197 
The Circulation of the Blood 202 
The Blood and the Lymph 210 
Hygiene of the Circulation 217 
Excretion 222 
The Skin 226 
The Regulation of Heat in the Body 232 
Hints on Clothing and Bathing 237 
Locomotion: Bones and Joints 241 
Hygiene of the Skeleton . . . . 249 
Locomotion: Muscles 253 
Hygiene of the Muscles 258 
The Nervous System: General 262 
The Brain 266 
The Spinal Cord and Sympathetic System 272 
Training of the Nervous System : 281 
The Care of the Nervous System 285 
Alcohol, Narcotics, and Stimulants 291 
The Special Senses: Touch 299 
Taste and Smell 302 
Hearing 306 
Sight 312 
How We See 318 
Hygiene of the Eyes 325 
Accidents and Emergencies 329 
APPENDICES 
A. Poisoning 337 
B. The Sanitary Code for Texas 339 
C. Sanitary and Unsanitary Outhouses 347 
Index 351 
CONTENTS The 
Human Body and its Enemies 
CHAPTER I. INTRODUCTION 
The rider of a motorcycle must study his machine. He 
must know its various parts, understand how they are put 
together, and have a clear idea of the work each part 
performs. Without knowing these things he cannot hope 
to keep the machine in good order or to feel the pleasure 
of its smooth motion. 
The Human Body a Living Machine. It is the duty of 
each one of you to care for and operate a machine much 
Figure i. — The rider of a motorcycle should understand his machine. 
more interesting than the motorcycle; namely, the human 
body. Did you ever stop to think what a wonderful machine 
your body is? Think of the brain, with which we know 
and remember things, feel emotions, and control our acts; 
and the eye, which is a little camera in itself. Think 
how wonderfully all the parts of our body are connected 
by the nerves, which act as telegraph wires, carrying 
messages from the various parts to the brain, which is like 
the central office. 
The human body is certainly the most marvelous, the 
most delicately balanced and the most sensitive machine THE HUMAN BODY AND ITS ENEMIES 
2 
in existence, surpassing any invention of man, and if we 
are to operate it without doing it harm, we should certainly 
understand something about it, so that we may take proper 
care of it and see that it does its work aright. 
Dangers which Threaten the Body. The rider of a motor- 
cycle, however, must know more than the parts of his ma- 
chine; he must know also what kind 
of dangers are to be met in the road. 
He must know the whereabouts of 
cactus thorns, sharp stones, and deep 
sands, in order to avoid them. Just 
so the driver of the human machine 
must know what dangers beset him 
on his life journey. The habit of 
drinking alcohol, for instance, is a 
danger that besets some of us. Im- 
pure foods are very harmful to the 
body, and they are one of the dangers that may befall any 
of us. One of the commonest dangers, however, is disease 
or sickness due to germs. 
Disease Germs and the Body. Disease germs not 
only cause more than one third of all deaths that occur in 
the state, but also cause a large part of the blindness and 
other ills that afflict our citizens. And yet we cannot be 
Figure 2. — A camera. 
Figure 3. — The eye, a human camera. 
harmed by disease germs unless they enter our sys- 
tem. In order, then, to protect ourselves against these 
enemies, we must study them and learn where they come INTRODUCTION 
from and how they gain entrance into the human body. 
We shall then be in a position to avoid them, and thus 
steer our human machine 
clear of this danger. 
If we understand our 
bodies, and also under- 
stand just what dangers 
threaten them and how 
to avoid these dangers, 
we shall be more likely 
to succeed in keeping 
ourselves in that pleasant condition which we call health. 
3 
Figure 4. — A few of our germ enemies. 
IMPORTANT POINTS 
1. The human body is more complex than any machine or 
instrument made by man. 
2. We should understand this machine in order to keep its 
various parts in order. 
3. We should also know how best to avoid certain dangers 
which threaten us, such as typhoid fever, tuberculosis or 
consumption, and other diseases due to germs. 
QUESTIONS 
i. Why should we study the human body? 2. Name some 
things which can injure the body. 3. Name one important cause 
of blindness. 4. What proportion of all deaths in Texas is due to 
germs? 5. Name several things we should know about disease 
germs in order to avoid them. CHAPTER II. BACTERIA OR GERMS 
What are Bacteria? The word bacteria comes from a 
Greek word meaning little rods. Scientists reserve the 
word for those germs that are shaped like little rods, but in 
this book we shall use the word bacteria and the word germs as 
though they meant the same. Bacteria are such wonderful 
little beings, and they are so different from the creatures 
which you know, that it is very hard to get an idea of what 
they really are. All of you have read in the fairy tales 
about certain fairies that were invisible. The story of 
Figure 5. — This shows bacteria on the 
point of a needle, highly magnified. 
bacteria is like a fairy tale, because for many centuries 
we were surrounded by bacteria, and yet they were invisi- 
ble to us, and in fact we never guessed or dreamed that 
they existed until long after Columbus discovered America. 
And bacteria are invisible to this day, unless we use a 
microscope to aid the human eye, or unless we look at a 
great many of the bacteria in a clump or colony. 
Size of Bacteria. To begin with, then, bacteria are 
very small. If you took a colony of them and picked it 
out with a needle till you had little pieces that you could 
barely see with the naked eye, each one of these little 
pieces would contain hundreds and probably thousands of 
bacteria. Many of them are so small that it would take 
twenty-five thousand of them placed side by side to occupy 
the space of an inch. As small as they are, however, each 
one has a definite shape. Bacteria are generally found in 
one of three different shapes, the rod-shaped, the round- 
shaped, and the spiral-shaped. You can see examples of 
each of these in Figure 4. 
4 BACTERIA OR GERMS 
5 
Motion of Bacteria. Some bacteria can swim about 
from one place to another, and others never move unless 
they are washed about or jostled in the fluid they live in. 
Those that move, either do so by squirming along like a 
Figures 6 and 7. — The rod-shaped germs cannot move about rapidly like 
the ones with the little lashes on them. 
snake swimming, or else they have, growing out from their 
bodies, tiny hairs with which they whip the water. Of 
course the perfectly round ones cannot squirm, and unless 
they have little hairs on them, they cannot move. 
Food of Bacteria. The bacterium (for this is the word 
we use in speaking of a single one) needs food, and it may 
even need oxygen just as we do. But it is 
so small that the food can soak in from the 
outside, and so it • does not need a mouth. 
Practically all of its active life is spent in 
a liquid, and the food simply dissolves in 
the liquid and passes through its very thin 
skin into its inside. For you know the 
entire bacterium is not nearly so thick as a 
sheet of tissue paper, and its skin must be 
really so thin that we cannot realize its true 
thinness. But some bacteria (here we use 
the plural word again) seem to secrete a 
juice of some kind that digests meat. The 
difference between their digestion and ours, 
however, is that they pour the juice over the 
meat or other food while it is still outside 
Figure 8.—Pic- 
ture of a glass 
tube containing 
bacteria grow- 
ing on gelatine. 6 
THE HUMAN BODY AND ITS ENEMIES 
their bodies. They let the digestion occur outside their 
bodies, and then absorb or soak up the food in a liquid 
form. 
Toxins. Whatever of waste matter there is in the body 
of a bacterium can soak or ooze out, just as its food soaks 
in. This is one way that some bacteria injure us. Some 
kinds of bacteria live in our bodies and there pour, or ooze 
out, their waste material. If this waste material is poison- 
ous to us, the bacteria make us sick. The poisonous 
material is called toxin, which means poison. Other 
bacteria form a waste material which is not poisonous, and 
these bacteria do not make us sick, unless they multiply 
fast enough to stop up some passageway, such as a blood 
vessel, in the body. 
Multiplication of Bacteria. Bacteria can multiply very 
rapidly indeed. They seem to multiply by simply dividing 
in two. Each one thus divides, and you have two bacteria 
where only one was in the first place. Starting with one 
bacterium, we may have many millions in a day or two. 
Ultra-microscopic Bacteria. In studying bacteria we 
must not lose sight of the fact that some are too small to 
be seen even with the most powerful microscope. No one 
has ever seen these germs. The word ultra means beyond, 
and these bacteria are called ultra-microscopic because 
they are beyond the power of the microscope. You may 
well ask how, then, we know that they exist. We know 
only from their effects. For instance, we know that foot 
and mouth disease in cattle is caused by a germ, and the 
blood of an animal sick of this disease, if injected into 
another animal, will cause the second animal to catch 
the disease. Even if we filter the blood from the sick 
animal, so as to remove all particles large enough for us 
to see with the most powerful microscope, it will still 
cause foot and mouth disease when injected into another 
animal. Our filters are fine enough to strain out all germs 
that are visible, and since the filtered blood still causes BACTERIA OR GERMS 
7 
disease, we must conclude that it contains invisible germs. 
These germs are so small that they pass easily through the 
filter and set up foot and mouth disease as soon as they 
reach their natural living place, which is the body of the 
cow. Possibly some pupil, at present busy in one of our 
schools, may some day invent a microscope powerful enough 
to reveal these ultra-microscopic bacteria to our sight. 
Smallpox, yellow fever, and measles may be due to 
small bacteria which we call ultra-microscopic. Certain 
diseases which attack the lower animals have been 
proved beyond a doubt to be due to these ultra-microscopic 
germs. 
Where Bacteria Live. We have said nothing yet about 
where the bacteria live. They live almost everywhere, 
— in water, in milk, in the ground, in dust, in decaying 
fruits, — almost everywhere except where they have been 
removed in some way. The most important place that 
bacteria inhabit is certain parts of our bodies. Some harm- 
less bacteria are always present in the mouth. There are 
always a great many harmless bacteria in the intestines 
and in the outer horny layer of the skin. Certain kinds 
cause milk to sour. Certain others cause milk to curdle 
into cheese. Still other bacteria live on the roots of clover 
and peas and help to enrich the soil. 
Harmless Germs and Disease Germs. There are thou- 
sands of different kinds of germs or bacteria, and probably 
not over one hundred different kinds that are harmful to 
man. There are some that do not multiply anywhere 
except in the human body, and there make poisons causing 
sickness or death. These bacteria are dangerous. Ty- 
phoid fever, meningitis, tuberculosis, grip, and diphtheria 
are all caused by bacteria. These germs are visible with 
the microscope, but are so small that they could not harm 
us except for the poisons which they make in our bodies. 
Disease Germs Multiply Only in the Body. It is very 
important to remember that very few of the bacteria which 8 
THE HUMAN BODY AND ITS ENEMIES 
cause disease can live more than a few weeks or months 
outside the human body. These harmful bacteria do not 
as a rule multiply at all except in the human body. It is 
therefore much easier to keep free from them, because all 
we have to do is to see that none of the bacteria from sick 
people enter the body. Think how hard it would be to 
avoid typhoid fever, for instance, if the germs were found 
naturally in the ground. It is hard enough to keep free 
from them when we know that they exist only where they 
have been thrown. 
How Bacteria are Scattered. The germs seem to have 
great success in getting themselves scattered. Diphtheria 
germs can be carried from one individual to another on 
such a little thing as the point of a pencil, especially if 
the users of the pencil place it in their mouths. Waving 
a soiled handkerchief in the air may set the germs 
floating in the air, and they may be taken into the body 
with the breath. The fingers which have touched such a 
handkerchief may grasp a door knob and leave many germs 
there. The next fingers that grasp the door knob will 
take away some of the germs. The washerwoman by han- 
dling the soiled linen is especially likely to get the germs 
into her system. Every solid or liquid particle that leaves 
the body of any one suffering from a germ disease may carry 
the germs of that disease. Whether it be saliva, tears, 
perspiration, bath water, or any other thing of this kind, 
it is dangerous, because it may have germs in it. 
Careless People. Since we now know the exact germ 
that causes each one of the diseases mentioned, and since 
we know just how the germs are carried from one person 
to another, it is only a question of time until we shall get 
the diseases under control. This knowledge is so new that 
the majority of people either do not possess it or cannot 
realize the truth about it. You will see men and women 
with sweet character who nevertheless go about spreading 
disease germs and causing sickness and death. Have you BACTERIA OR GERMS 
not seen consumptives spit on the floor? It would be 
kinder if the consumptive would set a steel trap to catch 
little children by the foot, instead of setting this disease 
trap for them. Boys and girls in school now should learn 
a great deal more about disease germs than their parents 
could when they were in school. The spitting nuisance is 
dying out. People sometimes need to expectorate, but 
they should expectorate into the toilet, or into a cuspidor 
or spittoon containing water or else something that will 
kill the germs. It is also permissible to expectorate into 
rags or paper napkins which can be promptly burned. 
9 
1. Bacteria are too small to be seen with the naked eye, and 
some of them are so small that we have never even seen them 
with the microscope. 
2. Bacteria live almost everywhere, especially in decaying 
food and dirty places. 
3. Many bacteria live in our bodies, and a few are harmful 
to us. Most of the harmful ones produce toxins which make 
us sick. 
4. Many people have never learned the importance of not 
spitting on the floor. 
5. The pocket handkerchief becomes dangerous as soon as 
it has been soiled, and it becomes soiled as soon as it has been 
used. 
IMPORTANT POINTS 
i. How small are bacteria? 2. Can they all move about? 3. 
How do bacteria multiply? 4. Name some places where bacteria 
live. 5. Are all bacteria harmful to man? 6. How do they injure 
us? 7. Name some of the ways in which disease germs are carried 
from one person to another. 8. What should persons suffering 
from any communicable disease use, instead of the ordinary pocket 
handkerchief? 
QUESTIONS CHAPTER III. DISEASES THAT ARE CATCHING 
Did you ever have measles or mumps? If so, you may 
be able to tell just from whom you caught the disease. 
In other words, you could trace the source of contagion 
or infection. Some diseases, like measles and smallpox, 
are understood to be contagious, or catching. A better 
word to use is communicable. A communicable disease is 
one that can be communicated or given to another. 
Communicable Diseases. There are a great many 
diseases that are communicable; for instance, typhoid 
fever. We have always known that leprosy, cholera, 
smallpox, plague, measles, scarlet fever, hydrophobia, 
diphtheria, and others were communicable; but we have 
learned only in our own generation that consumption, 
typhoid fever, malarial chills and fever, yellow fever, 
meningitis, infantile paralysis, erysipelas, and dengue are 
also communicable. A great many well-informed and 
educated people today do not realize this fact. 
Scientists who Gave up their Lives. Many scientists 
have given up their lives in the effort to find exactly how 
communicable diseases are spread. In 1900, Dr. Lazear 
and Dr. Carroll, both United States Army surgeons, will- 
ingly contracted yellow fever in order to find the exact 
method by which it is spread. Dr. Lazear died after a 
few days; Dr. Carroll lived for several years, but finally 
died as a result of the yellow fever. Dr. Ricketts, a young 
physician of Chicago, went to Mexico in 1909 to study 
jail fever. During his experience he was attacked by the 
disease and died. 
How Diseases are Communicated. By exposing them- 
selves to danger these scientists have found out just how 
most of the communicable diseases are spread. These dis- 
eases are not all spread in the same way, although all of 
them are conveyed by solid or fluid particles which leave 
our bodies. Water spreads disease only when the particles 
of solid or liquid material that leave our bodies are in the 
water. Even the mosquito cannot carry disease except DISEASES THAT ARE CATCHING 
Figure 9. — This picture shows almost all the different ways by which 
germs or contagion can leave or enter the body. There is not one solid or 
liquid particle cast off from the human body which may not, under certain 
conditions, carry or convey disease. Beginning at the top, you will note 
that dandruff is cast off from the scalp. Dandruff is in all probability a 
contagious disease spread largely by combs and brushes in barber shops. 
Pus from the eye conveys sore eyes of several kinds, some of which can 
cause blindness. Secretion from the nose and mouth is the medium for 
spreading consumption, diphtheria, tonsillitis, acute rheumatism, certain 
forms of meningitis and other diseases. Dead skin from the surface of the 
body is believed to spread smallpox, scarlet fever, measles, and other dis- 
eases. Waste matter from the kidneys and bowels undoubtedly conveys 
typhoid fever, dysentery, Asiatic cholera, hookworm disease, and others. 
The mosquito is the only insect pictured here, but many other insects carry 
disease from one person to another. You will learn more about these in 
Chapter XV. From this page, learn one lesson: All contagion is due to solid 
or liquid particles which leave the body of the sick, while absolutely all such 
particles are capable of carrying disease. 12 
THE HUMAN BODY AND ITS ENEMIES 
when it has sucked some of the blood of a person who is ill. 
The fly is powerless to carry disease except when it has 
been walking over some of the waste that is cast off from 
our bodies. The air spreads disease germs only by means 
of the small particles of dry or liquid material which leave 
the body of a sick person and float in the air. 
The Dangers of the Pocket Handkerchief. The clean 
handkerchief can serve a good purpose, but as soon as a 
handkerchief has been used to remove secretion from the 
nose or mouth, it becomes a source of danger. The hand- 
kerchief is really a dangerous article, for it may be carried 
in the pocket long after it has become soiled with disease 
germs. 
Such an unclean handkerchief may be flirted in the air 
so as to distribute its germs; it may also scatter the germs 
over the face and hands; and it may carry disease germs 
into the pocket, where they may soil the hands or soil other 
articles in the pocket. It would be much safer to use paper 
napkins, which can be destroyed after they have once been 
used. Invalids and sick persons generally should by all 
means use paper napkins or cloths that can be burned, 
and should carry a waxed paper or oil cloth wallet to con- 
tain the soiled napkins or cloths until they can be burned. 
Those who use handkerchiefs should have a new or clean 
handkerchief at least once daily when in health, and 
oftener when the nose is giving off secretion. 
How Disease Germs Leave the Body. Try to rid your 
mind of that old, hazy, indefinite idea that contagion 
may be in the air, or due to bad weather or an unhealth- 
ful climate. Instead, think of contagion as something 
definite, that you can see and weigh and feel. Let us take 
note of the different ways in which particles leave the body. 
We have first the waste materials, which are thrown off 
by the kidneys, the alimentary canal, and the skin. Then 
we have the dried skin, which peels off from every part of 
the body; these little particles are believed in some cases DISEASES THAT ARE CATCHING 
to carry the germ of smallpox. The hair may spread a 
very troublesome disease of the scalp called ringworm. 
Then there are the sputum and saliva from the mouth, 
and the nasal secretion, both of which may spread many 
different diseases, such as measles, scarlet fever, diphtheria, 
consumption, meningitis, leprosy, and smallpox. The 
secretion from the eye is responsible for the spread of 
trachoma, or granulated lids, and conjunctivitis, or sore 
eyes. All the discharges mentioned leave the body natu- 
rally. In addition, certain insects take from the body 
blood, which may convey malaria. There are, then, many 
different ways by which solid and liquid particles leave 
our bodies, and some kind of disease germ may be carried 
by almost every one of these particles. To get a clear 
idea of how communicable diseases are spread, let us take 
certain examples. 
Typhoid Fever. Typhoid fever is spread especially by 
the body wastes, which are thrown out from the sick 
room on the ground. Flies light upon the wastes, dip 
their feet in them, and may fly into the dining room and 
walk over our food. Then, too, the rain may wash these 
body wastes into the well or spring, and we may drink the 
water containing the typhoid germs. 
Tuberculosis. This disease is spread especially by dust 
from dried sputum, or spittle. For instance, a consumptive 
spits on the floor; the sputum dries; and when the floor 
is swept, the dried sputum is thrown up in the air with 
the dust, and is inhaled by all the persons in the room. 
Malaria, Yellow Fever and Dengue. Malaria, yellow 
fever, and dengue are not spread by body wastes, but by 
the mosquito which gets a drop of blood from a patient 
suffering from the disease and then bites a well man; 
and thus the malaria or other germs are injected into the 
well man. 
Diphtheria. A person suffering from diphtheria may 
soil the handkerchief with secretion from his nose. In 
13 THE HUMAN BODY AND ITS ENEMIES 
14 
handling the handkerchief, the secretion and germs get on 
his fingers. He then handles knife and fork, and door 
knobs, or shakes hands with some one. The germs are 
thus passed on to the hands of others, who in turn pick 
their noses or use a pocket handkerchief, and thus place 
the germs in the nose. From the nose they easily get 
into the throat and cause diphtheria. 
Granulated Lids, or Sore Eyes. These diseases are 
spread by the secretion from diseased eyes. The secretion, 
or pus, is collected on a handkerchief, and some of it reaches 
the fingers. From the fingers it contaminates pencils, 
towels, door knobs, etc. 
Every person sick with a communicable disease has been 
given the disease by some secretion or excretion from the body 
of another person who has the same disease, and the newly 
sick person may communicate the disease to others. 
IMPORTANT POINTS 
1. All disease germs are carried from the body by some solid 
or liquid particles thrown off from the body. 
2. Sputum and body wastes are especially likely to contain 
disease germs. 
3. No disease can spread if we prevent the solid and liquid 
particles which leave the patient from getting into or on some 
other person. 
i. Name all the solid and liquid particles which leave the body. 
(For example, body wastes, perspiration, etc.) 2. What is meant 
by communicable diseases? 3. Name ten communicable diseases. 
4. Name three diseases spread by sputum. 5. Describe how disease 
germs from body wastes can get from the ground into a new patient. 
6. Name some careless habit by which disease is spread by sick 
people. 
QUESTIONS CHAPTER IV. OUR PROTECTION AGAINST 
DISEASE GERMS 
From previous chapters you have learned something 
of the enemies which attack our bodies from without, 
and it now remains for us to learn how wonderfully we are 
protected against these germ enemies. Let us not think 
for one instant that the germs have an easy fight even after 
they get into our bodies. Before any germs can cause 
disease, they must fight the battle of their life, and the 
human body wins out in the vast majority of cases, for 
it has a wonderful system of defenses against disease 
germs. 
The Skin as a Protective Covering. To begin with, 
our skin has on the outside a thin horny layer, which 
few bacteria can penetrate, if it is kept 
healthy and whole. The best way to 
keep the skin healthy is to keep it clean 
with soap and water. People who take 
a bath every day are more likely to avoid 
disease than those who bathe less fre- 
quently. Those who bathe no oftener 
than once a week are dirty. We ought 
to take at least two or three baths a 
week, and one of them should be a warm 
bath. In addition the face, neck, and hands should be 
washed when we think they are soiled. We should wash 
our hands when we have been to the 
toilet, and whenever we have been in 
contact with the sources of contagion of 
which we are learning. 
How the Gastric Juice Kills Germs. 
The stomach, too, is well protected. It 
is the first stopping place of everything 
we swallow. The stomach always con- 
tains some gastric juice, which is the 
digestive fluid formed by the stomach. It is fatal to germs, 
because of the strong acid, called hydrochloric acid, which 
Figure io. — The 
skin, showing its pro- 
tective horny layer. 
Figure n. — The 
gastric juice in the 
stomach is fatal to 
most germs. 16 
THE HUMAN BODY AND ITS ENEMIES 
it contains. Gastric juice also contains a substance called 
pepsin, which will digest germs; hence if our digestion is 
good, not many germs will pass through the stomach. 
White Blood Cells. Whenever germs get into the body, 
as for instance when a wound is washed with unboiled 
water, they are almost immediately attacked by the white 
cells of the blood. On later pages you will learn that the 
blood contains many little round bodies, soft like jelly. 
Most of them are red, but some are colorless. The color- 
less ones are called the white cells of the blood, and they 
Figure 12. — White cell of the blood 
swallowing and digesting germs. 
take up or swallow germs, as shown in Figure 3. These 
white cells might be compared to policemen, as they cap- 
ture the germ enemies that have invaded the body. Some- 
times the white cells digest the germs, but sometimes the 
germs kill the white cells. When a person is in good 
health, however, his white cells can usually destroy the few 
germs which get into the body. 
Immunity, Another Protection against Germs. It is 
generally true that after a person has recovered from an 
attack of measles, he cannot be affected by this disease 
again. The body has become changed in some way. It is 
hard to understand just how the body undergoes this 
change, but we can easily see that during the course of the 
illness, the body gains a protective power which it did not 
have in the beginning. A person who is protected against 
measles in this way is said to possess an immunity toward 
measles. Immunity, then, means the power to resist a 
particular kind of disease germ. A person may, however, 
possess a complete immunity toward measles without pos- 
sessing any immunity toward other contagious diseases, PROTECTION AGAINST GERMS 
such as whooping cough or scarlet fever. Measles is not 
the only disease that is followed by immunity. Smallpox 
is followed by immunity toward smallpox; scarlet fever is 
followed by immunity toward scarlet fever. A number 
of other contagious diseases are followed by immunity. 
An attack of one disease, however, does not cause a person 
to become immune to any other disease. 
Changes in the Blood. The blood of persons recovering 
from typhoid fever has the power to injure or kill the 
typhoid germ. This can be seen by mixing a drop of the 
blood with a few drops of water and placing a number of 
typhoid germs in the mixture. If observed through the 
microscope, the germs are seen to lose their active motions 
and to lie still in groups or clusters. Blood from persons 
who have never had typhoid fever does not thus injure 
typhoid germs. We can therefore understand, at least in 
part, how immunity is produced. When germs produce 
disease by multiplying in the body, certain protective 
substances are formed and under certain favorable condi- 
tions can be found in the blood. The blood of persons re- 
covering from some other germ diseases, produces a similar 
effect upon the particular germs concerned. This experi- 
ment shows that the substances which protect us against 
certain diseases are found in the blood. 
Artificial Immunity. After you grasp the fact that the 
power to resist diseases depends in certain instances on 
protective substances formed in the blood, you will see 
how helpful it would be to cause the body to form these 
protective substances when desired. This can be done. 
Scientists have discovered that killed germs injected under 
the skin may cause the body to make these protective 
substances. If typhoid germs are killed by heat and 
injected properly, they cause a person’s blood to become 
partly filled with substances which protect against typhoid. 
If living typhoid germs are added to a drop of blood from 
such a person, the germs are injured or killed just as if the 
17 18 
THE HUMAN BODY AND ITS ENEMIES 
blood were taken from a person recovering from typhoid. 
It is thus seen that the injection of killed typhoid germs 
causes immunity toward typhoid fever. 
Explanation of Immunity. When disease germs of any 
kind multiply in the body, or when killed disease germs of 
any kind are injected into the body, the body usually makes 
substances which are injurious or fatal to that particular 
kind of germ. These substances are injurious to germs, 
and therefore protective to the body. Such protective 
substances are probably not actually made in the blood 
itself, but they soon pass into the blood and travel all over 
the entire body, thus protecting the body. 
Kinds of Immunity. When we possess immunity by 
reason of having suffered an attack of the actual disease, 
we call it an actual immunity. When we possess immunity 
due to our having received injections of killed germs, we 
call it an artificial immunity. Artificial immunity can be 
produced by the injection of killed germs, and also by the 
injection of weakened germs. The germs, when killed, 
are usually killed by heat; if weakened germs are used 
they are weakened in various ways, — by heating, by 
chilling, by drying, by allowing them to live and multiply 
in the body of certain animals, and in other ways. 
Artificial Immunity against Smallpox. The most im- 
portant effect of artificial immunity is the prevention of 
smallpox. To produce immunity against this disease, 
physicians inject smallpox germs that have been weakened 
in a peculiar way; that is, by living in the bodies of cattle. 
Whenever smallpox germs live and multiply in the body 
of a cow, they become weakened and cause a very mild 
disease called cowpox. Germs taken from the cow and 
injected into persons do not cause smallpox, but cause 
a slight inconvenience, resulting in artificial immunity 
against smallpox. The weakened germs are called vaccine, 
from a Latin word meaning cowpox. To apply or inject 
these weakened germs is to vaccinate. Nearly all who PROTECTION AGAINST GERMS 
study this book already possess an artificial immunity 
against smallpox because they have been vaccinated. 
Vaccines. Vaccine had been used to produce an artifi- 
cial immunity against smallpox for over half a century 
before artificial immunity was produced against any other 
disease. Today there are a number of diseases against 
which we can produce an artificial immunity, and we have 
come to use the word vaccine to refer to the various killed 
or weakened germs used for this purpose. A vaccine, 
then, is a preparation of killed or weakened germs used to 
produce artificial immunity. 
Another Way to Produce Artificial Immunity. To 
immunize a person against any disease is to cause him to 
become immune to that disease. Scientists have found 
in certain instances that it is possible to immunize a horse 
against a disease and then take a part of his blood for 
immunizing persons. When this method is used to im- 
munize persons against diphtheria, a horse is caused to 
receive injections of diphtheria toxin or poison until his 
blood becomes charged with protective substances. In 
this instance the protective substances are called anti- 
toxin, meaning against or opposed to toxin. The blood 
of the horse is then removed in a very cleanly way (See 
Fig. 13), and is allowed to clot. The clear, straw-col- 
ored fluid that is formed when the clot separates is called 
serum. If this serum, containing the antitoxin, is injected 
into persons, it immunizes them against diphtheria. 
Difference between Antitoxin and Vaccine. Whenever 
a vaccine or preparation containing killed or weakened 
germs is injected into a person, it usually takes one to 
three weeks for the protective substances to be formed. 
If the vaccine is injected after the person is actually ill 
from the disease, the protective substances are not usually 
formed in time to do any good. For this reason the 
vaccines are found more useful to prevent disease than to 
cure it. The protective substances in serum, however, are 
19 20 
THE HUMAN BODY AND ITS ENEMIES 
already made, and the injection of such serum often pro- 
duces almost immediately a complete cure of diphtheria. 
Artificial Immunity against Different Diseases. We 
have in artificial immunity a safe and efficient method of 
preventing smallpox, hydrophobia, Asiatic cholera, bubonic 
plague, typhoid fever, diphtheria, tetanus or lockjaw, and 
meningitis. Vaccines and serums for the treatment of 
other diseases are still imperfect, but are being improved. 
The practical value of artificial immunity will be discussed 
in the following chapter. 
IMPORTANT POINTS 
1. The skin acts as a barrier to keep disease germs out of 
the body. 
2. Germs that are swallowed are usually killed and digested 
in the stomach by the gastric juice. 
3. Germs that get into the body are usually attacked by the 
white cells of the blood. 
4. When germs multiply in the body, they cause the forma- 
tion of protective substances which circulate in the blood. 
. 5. The presence of the protective substances in the blood of 
immune persons can be shown by placing disease germs in' a 
drop of blood: the disease germs are injured or killed. 
6. By the injection of vaccines, we can cause the formation 
of these protective substances. 
7. Immunity is the power of the body to resist a particular 
disease. 
8. Actual immunity is the immunity that follows an attack 
of a particular disease. 
9. Artificial immunity is the immunity which follows the 
injection of vaccines or serums. 
QUESTIONS 
i. How does the skin protect the body? 2. How does the stomach 
protect the body? 3. How do the white cells of the blood protect 
the body? 4. What is immunity? 5. Name two kinds of im- 
munity and tell the difference between them. 6. How can we 
prove that the blood of immune persons contains protective sub- PROTECTION AGAINST GERMS 
21 
stances? 7. How can we cause the body to form protective sub- 
stances? 8. How may the germs be weakened for preparing vaccines? 
9. Describe the method of preparing diphtheria antitoxin. 10. 
Explain the difference in the effect of vaccines and serums (anti- 
toxins). 11. Name all the diseases against which we can produce 
an artificial immunity. 12. Need the careful and cleanly person be 
alarmed on account of disease germs? 13. What are toxins? 14. 
What are antitoxins and of what use are they to the body? CHAPTER V. PRACTICAL VALUE OF ARTIFICIAL 
IMMUNITY 
It would be fortunate indeed if we could immunize 
persons against all the communicable diseases as described 
in the preceding chapter. Only a few diseases, however, 
can be prevented in this way, and a list of them was given 
at the end of the last chapter. The present chapter deals 
with the need of artificial immunity and its value in each 
of these diseases. 
Vaccination against Smallpox. The value of smallpox 
vaccination was recognized and proved about 1797 by an 
English physician named Edward Jenner. He found his 
vaccine ready-made, for the germs of smallpox are weakened 
by living in the bodies of cattle. Jenner’s method, which 
is still in use, was to place some of these weakened germs 
in or under the skin of persons, and thus cause im- 
munity against smallpox. Vaccination against smallpox is 
practically harmless, but it should be done in the most 
cleanly manner. 
Importance and Need of Vaccination. The importance 
and need of preventing a disease depend upon two things: 
first, whether the disease is dangerous, and second, whether 
it is easily communicated or carried from one person to 
another. Smallpox is a dangerous disease, and kills from 
twenty to sixty per cent of those whom it attacks. It is 
also extremely contagious. From fifty to ninety per cent 
of all unvaccinated persons who are exposed to the disease 
are affected by it. Persons just becoming ill from small- 
pox can convey the disease to others before the dangerous 
character of this illness can be recognized. When we add 
the fact that the germ of smallpox can live for months in 
clothing and on furniture, we see that without vaccination 
it would be practically impossible to control this disease. 
Hence vaccination against smallpox is of great importance 
and value. 
Effectiveness of Vaccination against Smallpox. Vacci- 
nation against smallpox practically always prevents the 
22 VALUE OF ARTIFICIAL IMMUNITY 
23 
disease for several years. Afterward the protective power 
is gradually lost. Ninety-eight persons had the disease in 
a Texas city. Of these, only two had been vaccinated — 
one fifteen years before, the other sixty years before — 
and both recovered. In May, 1904, the United States 
Army ship Liscom left Manila with two hundred and 
ninety-two persons on board. During the first week at sea 
an unvaccinated child became ill with smallpox. Every 
one on board except three persons had been vaccinated. 
Within fourteen days all three of these persons developed 
smallpox, while not a single one of the two hundred and 
eighty-nine vaccinated ones took the disease. The medical 
officers of the United States Government strongly recom- 
mend vaccination, because they know it is the only safe 
and efficient way to prevent smallpox. 
Vaccination after Exposure. If you are exposed to 
smallpox and are vaccinated at once, the vaccination will 
develop in time to prevent the disease. This is due to the 
fact that vaccination develops more rapidly than smallpox. 
It is believed that smallpox enters the body through the 
nose, and it takes a few days for the germs to multiply and 
pass on into the blood, skin, and other organs. In vac- 
cination, the germs are placed in the skin, so that they 
multiply more rapidly, thus heading off the smallpox. 
Our Duty to be Vaccinated. We not only owe it to 
ourselves to be vaccinated for our own protection, but 
we also owe it to our fellow-citizens to be vaccinated, in 
order to protect them. In no other way can we affect 
our neighbors more than by our own health; if we take a 
communicable disease, we are very likely to cause some 
one else to take it. 
When and How Often to Vaccinate. Every child should 
be vaccinated before beginning to go to school. If this 
vaccination does not take, it gives no protection and should 
be repeated until it does take. After one good scar has 
been formed, there will be complete immunity for several  THE HUMAN BODY AND ITS ENEMIES 
24 
years and partial immunity all through life. It is well to 
vaccinate again about ten years after the first vaccination, 
and if this takes, the immunity is generally complete for 
life. 
Pasteur Treatment of Hydrophobia. Hydrophobia is 
caused by germs introduced into the body by the bite 
of a mad or rabid animal. The word hydrophobia comes 
from two Greek words meaning fear of water. Persons 
suffering from this disease are thrown into spasms by the 
attempt to swallow any fluid or solid substance, and it was 
formerly believed that they were afraid of water: hence 
the name hydrophobia. Animals that have become mad 
are said to be rabid; the disease is sometimes called rabies, 
from a Latin word meaning madness. Hydrophobia, 
when it occurs, always follows the bite of a rabid animal. 
The bite of the animal is therefore a warning that hydro- 
phobia may develop. By prompt action, the disease may 
be headed off, for there is a way of immunizing against 
this disease. The method employed was discovered by the 
famous French scientist, named Louis Pasteur. 
Today the Pasteur Institutes in Texas, at Austin and at 
El Paso, use the method that Pasteur worked out for 
protecting human beings against hydrophobia. At these 
institutes, the germs of hydrophobia are allowed to grow 
in the spinal cord of rabbits. These spinal cords, con- 
taining the hydrophobia germs, are removed in a very 
cleanly manner, placed in dry jars, and kept in a refrigerator 
until the germs lose their power to cause hydrophobia. 
This takes about fourteen days. Small pieces of these 
spinal cords are injected into persons who have been bitten 
by mad dogs or other animals believed to have hydro- 
phobia. These persons become immune toward hydro- 
phobia within three to five weeks, and unless they have 
been so badly bitten that they develop the disease within 
this length of time, they almost invariably escape. 
The following animals are capable of having hydro- VALUE OF ARTIFICIAL IMMUNITY 
25 
phobia: dogs, cats, wolves, skunks, rats, mice, rabbits, 
horses, mules, cattle, goats, chickens, geese, and others. 
The first four mentioned are the cause of nearly all hydro- 
phobia in Texas. When a person is bitten by an animal 
believed to be rabid, the animal should by all means be 
watched long enough to see if it is healthy. If the animal 
dies or is killed, its head should be removed, packed in 
ice, and shipped by express or parcel post to the nearest 
Pasteur Institute for examination. If the examination 
proves that the animal was rabid, no time should be lost 
in giving the bitten person the Pasteur treatment for 
preventing hydrophobia. 
All hydrophobia due to the bites of dogs could be pre- 
vented by the muzzling of dogs. 
Artificial Immunity against Typhoid Fever. Typhoid 
fever is common in Texas, as in other agricultural states, 
but it can be prevented by the injection of killed typhoid 
germs. The injection of these germs does not usually 
cause very much inconvenience. It takes about three 
weeks for the body to form the protective substances in 
the blood. A remarkable example of the value of artificial 
immunity against typhoid was shown by the experience of 
the United States Army at San Antonio in 1911. Many 
thousands of soldiers were encamped in San Antonio for 
several months during the summer season. Most of the 
soldiers had been injected with dead typhoid germs, and 
were immune. Not one single soldier that had been thus 
treated developed typhoid fever. Physicians and trained 
nurses often protect themselves against the disease by the 
injection of killed typhoid germs. Epidemics of typhoid 
fever in certain communities have been stopped by im- 
munizing all persons under forty-five years of age in these 
communities. The killed typhoid germs have usually 
been furnished by the Public Health Service at Washington 
or by the Texas State Board of Health at Austin. 
Asiatic Cholera and Bubonic Plague. Artificial im- 26 
THE HUMAN BODY AND ITS ENEMIES 
munity against each of these diseases can be produced by 
injecting a vaccine containing the killed cholera germs or 
plague germs. Cholera and bubonic plague are described 
on later pages. 
Diphtheria Antitoxin. It takes three weeks to immunize 
a person against smallpox, hydrophobia, or typhoid fever. 
It takes only a day, however, to immunize a person against 
diphtheria, because the protective substances have been 
prepared beforehand in the blood of the horse. Hence 
diphtheria antitoxin will almost always cause an immedi- 
ate improvement in the condition of a person suffering 
from diphtheria. Diphtheria antitoxin, therefore, is of 
value not only as a preventive, but also as a cure, of diph- 
theria. Children who have unquestionably been exposed 
to diphtheria should be immunized by receiving an injec- 
tion of diphtheria antitoxin. 
Figure 13. — Injecting the horse with diphtheria toxin in order to form 
diphtheria antitoxin in his blood. 
Immunizing against Diphtheria. In the United States, 
the annual number of case's of diphtheria has not dimin- ished since the discovery of diphtheria antitoxin, because 
antitoxin has not been used often enough for immunizing those 
exposed to the disease. The percentage of deaths, however, 
among persons suffering from diphtheria has decreased to 
about one fourth or one fifth of what it was formerly, 
because antitoxin is nearly always used to cure the disease. 
It is safer to prevent it than to cure it. Antitoxin should 
never be injected except under the supervision of a physi- 
cian, especially if the person to receive it has ever had 
asthma or has ever received any kind of horse serum 
before. 
Tetanus Antitoxin. Tetanus or lockjaw is a disease 
caused by germs introduced into a small, deep wound such 
as a nail thrust. Other facts about the disease will be 
mentioned later. Tetanus can be prevented by the use 
of horse serum containing tetanus antitoxin, but the serum 
must be used before the disease develops. After tetanus 
once develops, and the dreadful spasms begin, the serum 
does much less good. Tetanus is always the result of a 
wound of some kind, and hence persons have warning. 
Every nail puncture should be treated thoroughly, and 
in doubtful cases tetanus antitoxin should be administered. 
Meningitis Serum. Meningitis is the dreadful disease 
described in Chapter IX. The serum from horses that have 
been immunized against this disease is the best known 
remedy for curing it. The disease rarely attacks more 
than one per cent of the inhabitants of a community, and 
for this reason it is extremely difficult to collect evidence 
as to the possibility of immunizing against the disease. 
VALUE OF ARTIFICIAL IMMUNITY 
27 
IMPORTANT POINTS 
1. Vaccination against smallpox is the oldest as well as the 
most important method that we know of producing artificial 
immunity. 
2. Vaccination against smallpox is safe and effective. 
3. Smallpox cannot be controlled without vaccination. 28 
THE HUMAN BODY AND ITS ENEMIES 
4- Vaccination should be repeated after seven to ten years. 
5. Vaccination after exposure to smallpox prevents the 
development of the disease. 
6. It is a public duty of every citizen to be vaccinated. 
7. Hydrophobia can be prevented by the Pasteur treat- 
ment, which should be administered promptly. 
8. Typhoid fever can be prevented by the use of killed 
typhoid germs. 
9. Diphtheria antitoxin cures diphtheria. 
10. Diphtheria antitoxin should also be used as a preventive. 
11. Tetanus or lockjaw can always be prevented by the 
prompt use of tetanus antitoxin. 
QUESTIONS 
i. Why is it so hard to prevent the spread of smallpox? 2. Who 
discovered the first method of producing artificial immunity, and 
where did he get the vaccine? 3. How often should the average 
citizen be vaccinated? 4. Explain why it is a duty to be vaccinated. 
5. Give two ways of finding out whether a dog is mad. 6. Where 
in Texas are Pasteur Institutes located? 7. Which is more impor- 
tant, the cure or the prevention of diphtheria? 8. What kind of 
wounds cause tetanus? 9. How can tetanus be prevented? CHAPTER VI. TYPHOID FEVER 
Typhoid fever is somewhat like measles. It causes a 
breaking out or rose rash, like the rash seen in measles, 
although there are generally only one or two dozen spots 
on the skin at one time. It is like measles 
in that each typhoid patient catches the 
disease from a previous typhoid patient. It 
is like measles in that it seems to affect 
young people especially; old people are 
less often affected. It is important to 
remember that each typhoid patient must 
be carefully handled to avoid giving the 
fever to some one else. 
Importance of Typhoid Fever. Typhoid 
fever is a disease that is very common in 
nearly all parts of Texas. It is common in town and city. 
Every year there are about nine hundred deaths from typhoid 
fever reported in our state; and yet it is a disease that can be 
prevented more easily than most other diseases. We can do 
more in preventing sickness and death by studying typhoid 
fever and its prevention, than in any other way. Typhoid 
fever is a contagious disease; see Rule 3, Sanitary Code. 
Germs of Typhoid Fever. Now, typhoid fever is due 
to a germ. The germ is a little rod-shaped bacterium 
that lives in certain parts of the intestines. It also lives 
in the blood and travels over every part of the body. 
It injures the entire body, but is especially harmful to the 
intestines. The germs sometimes cause raw ulcers in the 
intestines; the ulcers may be so deep that they cause a 
hole in the intestinal wall, and the patient may die. The 
hole through the intestinal wall is called a perforation. 
If the ulcer does not eat out a hole entirely through the 
wall of the intestines, it may cause the patient’s death by 
bleeding. Such a bleeding is called a hemorrhage, — in 
this case a hemorrhage of the intestines. 
Where Typhoid Germs Multiply. You have learned 
that the germ lives and multiplies in the human body. 
Figure 14.— 
Typhoid bacteria, 
showing the little 
lashes by which 
they move. 
29 THE HUMAN BODY AND ITS ENEMIES 
30 
With the exception of milk, the human body is the only 
place in nature where the germ can multiply. The typhoid 
germ does not live in the lower animals, and therefore they 
never can have typhoid fever. But the typhoid germ can 
live for a few days in water or milk, or it can live for 
a longer time in filth. It can live long enough to be carried 
to a new patient and cause the disease in him. 
Typhoid Germs in Waste Matter. No doubt you are 
wondering how the germ can get into the mouth of the new 
patient, to be swallowed by him. There are several ways 
by which the germ can pass from the sick to the healthy 
person. For instance, the germs are swarming by millions 
in the unclean waste matter that is thrown off by the 
intestines. When we eat any food, the digestible portion 
of it is dissolved and absorbed by the stomach and intes- 
tines; but there always remains a certain quantity that is 
not digestible, and hence is useless to the body. This 
passes entirely through the intestines and is cast off from 
the body as body waste. This body waste from a typhoid 
patient is alive with typhoid germs. If you could see 
them, you would see that they are more numerous than 
blackbirds in the biggest flock of blackbirds you ever saw. 
How Flies Carry Typhoid Germs. One single fly can 
carry enough of this unclean and dangerous material on 
one foot to cause a person to take typhoid fever. The fly 
acts as a messenger between the typhoid patient and the 
well person and causes the latter to become sick. The 
fly goes out into the back yard, where the unclean body 
waste from the sick room has been poured on the ground 
by careless people. He lights on it and puts his feet in 
it. The feet of the fly are covered with hair, to which 
the unclean material clings. The fly may then pass into 
the dining room or kitchen and walk over the butter or the 
jelly. Can you imagine how the fly leaves a trail of germs 
behind? Figure 15 shows a flat dish of jelly that a fly has 
crawled over. The germs have multiplied for twenty-four TYPHOID FEVER 
hours and have caused the spots which you see. Any one 
eating this jelly now would swallow more germs than there 
are people inhabiting the United States. If some little boy 
had eaten the jelly just after the fly squirmed across it, 
Figure 15. — Tracks made when a fly walked across a plate of gelatine. 
Each dot is a colony of germs. 
he would have been unable to see any trail, but would 
nevertheless even then have swallowed more germs than 
the number of inhabitants in your county. 
Do you see how easy it is for the germs to pass from a 
sick to a well person? 
Typhoid Germs in Drinking Water. The germs can 
also reach us by another route, and that is in the drinking 
water. Suppose there is a family living on a hillside, with 
the back yard higher than the front. The well will prob- 
ably be near the house. A great many unclean things are 
thrown on the ground near the well, and as the back yard 
slopes up the hill, any rain that falls will tend to wash 
these unclean things back toward the well. A great many 
wells are cased in at the top with rocks or pieces of stone. 
Water can easily trickle through the cracks between the 
pieces of stone. In a loose soil the germs can soak through 32 
THE HUMAN BODY AND ITS ENEMIES 
without being filtered out. The water may contain 
millions of typhoid germs that came from the body waste 
of a typhoid patient. If any one drinks the water of this 
well, he is likely to become ill with typhoid fever in about 
twelve or fourteen days; for it takes about that time for 
typhoid fever to develop after the first germs enter the 
Figure 16. — Showing a well located in the wrong place. The drainage 
either seeps or overflows into the well. 
body. Hence, in trying to trace the source of a case of 
typhoid, we always inquire particularly where the patient 
was, about two weeks before his illness began. 
Typhoid Germs in Milk. Most typhoid is spread by flies, 
or by drinking water, but there is another way by which 
these dangerous and active little germs are frequently 
passed on from one person to another; namely, in milk. 
Dozens of epidemics have occurred in which practically 
all the sick people had been using milk from the same milk 
dealer. Typhoid germs multiply very rapidly in milk, 
and if milk cans are washed in water containing typhoid 
germs, or if a single fly lights on the milk, it can poison the 
whole can of milk. If this is mixed with other milk it will TYPHOID FEVER 
poison that, and there is thus no limit to the harm that 
may come from germs in milk. 
There are several other ways in which germs can get 
into milk. One of the men or women handling the milk 
may be a typhoid carrier. 
Typhoid Carriers. A typhoid carrier is a person who 
has the typhoid germs in his system, but who is not sick. 
Usually a typhoid carrier has had typhoid fever at some 
previous time, and although he has recovered his health, 
the germs of the disease have never left his body. This 
seems hard to believe, but is absolutely true. It is easy 
to see how a man could have a few germs in his body after 
he began to get well, but the typhoid carrier actually has 
many germs in his body for months or years after he has 
recovered. Look at Figure 43 and observe that the typhoid 
carrier is usually a healthy person. 
When you studied the chapter on immunity, you learned 
how it is possible for a deadly disease germ to be harmless 
to individuals who are immune. In the case of a typhoid 
carrier, he is immune to the typhoid germ and cannot be 
injured by it; and yet the germ has the power to live in 
his body. 
Dangers from Typhoid Carriers. Just think what 
terrible damage a typhoid carrier can do! Without know- 
ing it, he can give this disease to those he holds most dear, 
as well as to strangers. The United States Army will not 
allow a known typhoid carrier to enlist in the army. He 
would be too dangerous to his comrades. Not many 
typhoid patients develop into typhoid carriers, however, 
and this is fortunate. 
Necessity for Washing the Hands Frequently. A great 
many people get the typhoid fever germs by shaking hands 
with a typhoid patient or by handling his bed or clothing. 
Anything a typhoid patient has touched is likely to be 
soiled with the germs. In order to avoid getting the dis- 
ease in this way, always, after having touched a typhoid 
33  THE HUMAN BODY AND ITS ENEMIES 
34 
fever patient or the things that he has touched, rinse the 
hands carefully in soap and water, or better in an antiseptic 
solution. No one who waits on or nurses a typhoid patient 
should cook for the family. If it is necessary for any one 
to do so, the hands should be thoroughly disinfecteckbefore 
entering the kitchen. 
Now you have learned the most important ways in 
which typhoid fever is spread. There are many other 
ways also, as for instance by oysters, lettuce, radishes, and 
other articles of food, commonly eaten raw. Raw vege- 
Figure 17. — Plate, knife, and 
fork. The patient should keep 
his own separate from those of 
the rest of the family. 
Figure 18. — Hole dug to re- 
ceive typhoid wastes. The lid 
is to keep out flies. Disinfectant 
should be poured into the hole. 
tables are positively dangerous wherever the soil in which 
they grow has been enriched with human waste matter. 
Finding the Cause of Epidemics. There are certain 
ways in which we can form an idea as to how an epidemic 
is spread. It is important to ascertain the exact way in 
which a disease is spread in order to take steps to stop the 
infection. 
(i) The epidemic of typhoid fever spread by the fly always 
occurs at a time when flies are plentiful; that is, in warm 
weather. An epidemic spread by the fly usually occurs 
in those parts of a town where there are most flies. An 
epidemic spread by flies is never sudden or explosive in its 
nature, but drags along through the summer, getting a 
little worse as August and September approach, and dying 
away after the first frost. In an epidemic spread by 
flies each case is usually near some other case. TYPHOID FEVER 
35 
(2) The epidemic spread by drinking water, if in a town 
with a public water supply, is usually explosive or sudden, 
and a dozen or possibly a hundred people will become ill 
in the same week. In an epidemic spread by drink- 
ing water, cases occur in widely separated parts of a town. 
An epidemic spread by drinking water usually follows 
certain cases of typhoid which have occurred upstream 
along the banks of the river supplying the town. 
(3) The epidemic of typhoid spread by milk is likely to 
affect persons who take milk from a certain dairyman; 
the persons affected are all on one milk route. In an 
epidemic spread by milk, children and old people are 
especially affected, because they use most milk. Such an 
epidemic is likely to affect well-to-do people in cities, 
because they use more milk than poor people; but this 
poipl is not noticeable in small towns in Texas, where 
almost all citizens are able to get milk. 
Disinfectants Used to Kill Typhoid Germs. Now comes 
the great question how to prevent typhoid fever. The 
most important thing is to kill all the germs as fast as they 
leave the body of the patient. This is best done by chemi- 
cals or drugs that are poisonous to germs. We call these 
chemicals disinfectants. In Chapter XIX, you will learn 
more about how to use disinfectants. Most disinfectants 
are poisonous to human beings as well as to germs, hence 
they should be applied only by grown people. 
All body wastes, discharges, secretions, excretions, and 
all slops from the typhoid sick room, should be disinfected 
thoroughly. This may be done cheaply with chlorid of 
lime, or with pure or crude carbolic acid, or with corrosive 
sublimate, or by patented preparations made from coal 
tar. These are mentioned and described in Chapter XIX. 
Method of Disinfection for Country Districts. Dig a 
hole two feet square and two or three feet deep in the back 
yard, at least one hundred feet from the well. First, 
disinfect the slops, then pour them into the hole, and have 36 
THE HUMAN BODY AND ITS ENEMIES 
a closely fitted wooden or wire gauze lid to cover the 
hole to keep out the flies (Fig. 18). The method used had 
best be determined by the physician caring for the case. 
Dangers of Carelessness. If you do not disinfect the 
body wastes from the patient, you are scattering sickness 
and death among your neighbors. It would be far better 
Figure 19. — The slop bucket 
is the stronghold of typhoid 
fever. Always disinfect it. 
Figure 20. — Disinfecting the 
linen. The bundle is dropped into 
the water without being undone. 
to set free a dozen rattlesnakes in your back yard than 
to pour out on its surface the body wastes containing the 
living typhoid germs. 
How to Handle the Laundry of a Typhoid Patient. It is 
not right to turn a lot of soiled linen from a typhoid patient 
over to a washerwoman or laundry without warning. In 
handling the soiled linen, the washerwoman or one of the 
laundry workers may get the disease. All soiled linen TYPHOID FEVER 
from the sick room should either be soaked in a disinfectant 
solution before being sent to the laundry, or should be 
wrapped in a clean sheet or pillow case, so that the washer- 
woman can drop it into the boiling water without touching 
the soiled linen. 
The plates, knives and forks, and other utensils used by 
a typhoid patient should be kept separate from those of 
the family, and should either be soaked in a disinfectant 
solution or placed in a dishpan of water and boiled. These 
points will naturally be looked after by the physician, and 
in case a trained nurse is in attendance the physician will 
probably entrust all these things to her. 
Length of Time Contagion Lasts. These precautions 
should be kept up until the physician declares the patient 
to be free from typhoid germs. At the present time it is 
impossible for a bacteriological examination to be made in 
each case, but Texas will not be free of typhoid fever until 
these tests are made regularly in all cases. 
How to Avoid Catching Typhoid from Neighbors. But 
suppose that the case of typhoid fever is in a neighbor’s 
family, how can we escape catching it? There are several 
practical things we can do. The most important is to 
use screens and sticky fly paper, and wage war on the flies 
of the neighborhood, in every possible way. We must also 
notice the lay of the land, to see if there is any drainage 
from our neighbor’s premises on to our own. If he is on 
the uphill side of us, we must be extremely careful, because 
a rain may wash his back yard, and the washings may 
trickle into our well. If there is a reasonable doubt as to 
this point, we must boil the drinking water. The patented 
household filters are as a rule worthless. Those who 
object to the flat taste of boiled water can restore the taste 
by pouring it through the air a few times from one pitcher 
to another. 
When Cistern Water is Dangerous. If a cistern is used 
on the premises, it is well to be careful about English 
37 38 
THE HUMAN BODY AND ITS ENEMIES 
sparrows and pigeons, which may carry typhoid germs on 
their feet and soil the roof. The germs thus left on the 
roof may wash into the cistern. Whenever possible the 
sunny side of the roof should be used as a watershed to 
collect water for cisterns, because the sun kills the germs 
on the roof. 
When typhoid is occurring all around you, it is well to 
see first that your dwelling is free from flies; then convince 
yourself as to the purity of the drinking water. Then 
inquire as to your milk supply and your supply of raw 
vegetables and oysters. Persons who fear they have been 
exposed to typhoid fever will probably desire in some cases 
to be made immune by anti-typhoid vaccination. 
Asiatic Cholera. This is a fatal disease, due to a little 
comma-shaped germ which, like the typhoid germ, is 
spread by unclean drinking water. It is not likely to enter 
Texas, unless brought in by ships passing through the 
Panama Canal. The way to prevent cholera is to quaran- 
tine those who are sick and to use drinking water which is 
free from germs. 
IMPORTANT POINTS 
1. Typhoid fever is a definite disease, and one attack is 
usually followed by immunity. 
2. There are over nine hundred deaths reported in Texas 
from this cause each year. 
3. At this time there is no better way to improve the health 
of the people of Texas than by directing our efforts against 
typhoid fever. 
4. The typhoid germ does not multiply anywhere outside 
the human body except in milk. 
5. Typhoid germs always come from the solid and liquid 
material thrown off from the body. 
6. The fly is the cause of more epidemics of typhoid fever 
in Texas than has been realized in the past. 
7. Drinking water is usually polluted by drainage water 
which runs into the well from the top. 
8. By carefully observing certain facts it is possible to TYPHOID FEVER 
39 
decide with some accuracy whether a given epidemic is due to 
the fly, the water, or the milk of the community. 
9. Typhoid germs can live in the body of a healthy man, 
and other people can catch the disease from him. 
10. No person recovering from typhoid fever should handle 
the public milk or food supply of a city unless tested by a com- 
petent bacteriologist and found free from typhoid fever germs. 
11. No person nursing a case of typhoid fever should handle 
the milk or food of a family. 
12. A slop bucket is the stronghold of typhoid fever. 
13. Typhoid vaccination is harmless and is valuable in pre- 
venting typhoid fever. 
QUESTIONS 
i. What are the two most common causes of the spread of typhoid 
fever in Texas? 2. How many deaths are reported in Texas from 
typhoid fever each year? 3. Can we accomplish anything by trying 
to prevent typhoid fever? 4. What kind of unclean material does 
the typhoid germ live in? 5. Suppose a large mass of decaying 
vegetables and small animals were left near a house, if there were 
no human waste material in it could it cause typhoid fever? 6. 
What part of a well is most likely to let the typhoid germs get in, — 
the top, the sides, or the bottom? 7. What part of the fly is espe- 
cially likely to carry germs? 8. Why is it dangerous for a person 
just getting over typhoid fever to sell milk? 9. How [do the 
typhoid germs get into milk? 10. Why should the nurse not make 
the bread for the family in case of typhoid fever? n. After com- 
ing from the typhoid sick room, what should you do before eating? 
12. What is a typhoid carrier? 13. When does a person become 
immune to typhoid fever? CHAPTER VII. CONSUMPTION OR TUBERCULOSIS 
Consumption is such a common disease that some boys 
and girls think they already know all about it. But com- 
mon as it is, there are a great many interesting things about 
consumption that will surprise 
you when you hear them. For in- 
stance, there are about six people 
that get entirely well from con- 
sumption for every one that dies. 
Majority of People have Con- 
sumption. Almost everybody 
who lives to be fifty years old has 
had consumption at some time 
during his lifetime. At least 
three out of every four men have 
consumption before they die. You wonder how we know 
they have consumption if they do not know it themselves. 
We know it because thousands and thousands of bodies 
have been examined after death, and a large majority of 
them have shown scars made by consumption germs. 
Many of these people — indeed, most of them — never 
dreamed they had ever had this disease. 
The organs most often damaged by consumption are the 
lungs. The usual signs are a cough that lasts a long time, 
and loss of weight. Most people who cough constantly are 
consumptives. 
The Lungs are Especially the Seat of Consumption. The 
lungs are so important in the spread of consumption that 
we shall not study consumption in the other organs to any 
extent; yet it is well to know that the consumption germ 
can live in the skin, in the intestines, in the bones, in the 
kidneys, in the coverings of the brain and spinal cord, and 
in fact anywhere in the body. By far the greater number 
of cases of consumption, however, are cases of consumption 
of the lungs. We have almost given up the use of the word 
consumption except in speaking of the lungs. When we 
Figure 21.—The germ of con- 
sumption, called the tubercle 
bacterium. 
40 CONSUMPTION OR TUBERCULOSIS 
41 
mention the disease in the other organs we give it the longer 
name tuberculosis. We then mention the organ affected, 
as for instance, tuberculosis of the bones or of the hip. 
The Germ of Tuberculosis. The germ of tuberculosis 
is a little rod-shaped bacterium. It cannot move, but 
remains still until something blows it or washes it along to 
a new place. This bacterium can live but a few hours if 
placed on a pane of glass in the sun; it can live a few days 
on the surface of the ground in a sunny place; but it can 
live for weeks and possibly months where it is dark and 
moist. It does not multiply, however, after it leaves the 
human body. A house that has been occupied by a care- 
less consumptive who has spit on the floor is dangerous for 
months afterward. 
Method of Spread of Consumption. It is easy to account 
for the spread of consumption, but the remarkable thing 
Figure 22.— The careless consumptive spits on the floor; the spit dries 
and is swept up into the air with the dust; everybody in the room then 
inhales the dust and the germs. 
is that so many escape the disease. Some people have 
consumption for years, and go about spitting on the floor, 
on the sidewalks, on the floor of street cars, and even on 42 
THE HUMAN BODY AND ITS ENEMIES 
carpets. The sputum dries up, and people walk over it 
and grind it into dust; the wind blows it up into the air, 
and men breathe it into their lungs. 
Evils of Dry Sweeping. There is nothing that spreads 
consumption germs so thoroughly as dry sweeping. One 
can take a broom and go into a room and raise a dust in 
three minutes that will float in the air for at least an hour 
or two, and will place germs, first in the nose of the sweeper, 
and then in the noses of all who enter the room, for a long 
time after the sweeping is finished. After the dust settles, 
it is there to be stirred up again, perhaps with the feather 
duster. 
There is a remedy for this: we have plenty of water 
with which to sprinkle the floor, and we can stop spread- 
ing consumption in our homes at any rate. It is against 
the law in Texas for any porter or janitor to sweep a 
public building without sprinkling. (See Sanitary Code 
for Texas, in this book, Rule 54.) * * 
How to Avoid Raising a Dust. There are several ways 
of avoiding a dust when we sweep our homes. We should 
have a floor as smooth as possible. It can be cleansed in 
several ways. If it is a hall, the floor may be oiled once 
a month and brushed up daily with a brush instead of a 
broom. In the case of a bedroom with a common pine 
floor, such as we find in the majority of Texas homes, 
dampened sawdust may be scattered over the floor before 
sweeping. In some places sawdust is scarce, and there 
pieces of newspaper can be dampened and scattered on 
the floor before sweeping. In all cases a brush is better 
than a broom. Rugs which can be taken out and shaken 
or beaten are not dangerous. Heavy carpets should be 
avoided, but if a carpet is in use, it should be swept with 
a carpet sweeper, or, better still, with a vacuum cleaner. 
In dusting, a rag or cloth should be used, and it should 
be dampened with water or greased with raw linseed oil, 
so that the dust will stick to the cloth. It is not necessary CONSUMPTION OR TUBERCULOSIS 
to use any drug or chemical in the water. (See also Sani- 
tary Code for Texas, Rule 54.) 
Feather Dusters. Feather dusters are too dangerous 
to have in a dwelling occupied by human beings. It is 
all right to use them out in the open air to brush the dust 
off a buggy or an automobile, 
but dust in houses is dangerous. 
House dust is more dangerous 
than street dust, for two reasons: 
first, the sunlight of the street 
will kill any germ in a few days; 
and second, almost all disease 
germs come from human beings, 
and in and around the house there 
are more human beings and hence 
more disease germs. 
Consumption Spread by Cough- 
ing. When a consumptive coughs, 
he blows out a number of little 
fine drops of sputum. These droplets are so small that 
some of them float in the air like fog on a misty day. For 
this reason it is dangerous to have your face close to a con- 
sumptive when he is coughing or even when he is talking. 
Have you not noticed the saliva leap out of a man’s mouth 
when he was talking? There are a great many droplets 
which, although invisible, may contain germs and are 
therefore dangerous. For this reason it is dangerous to 
sleep in the same room with a consumptive. 
Outdoor Sleeping. No consumptive ought to sleep in a 
room. He ought to sleep in the open air, and this can 
always be arranged, especially in our Southern climate, 
where bitter cold weather seldom comes. 
Kissing. A consumptive should never be kissed early 
in the morning until he has washed his face, and even 
then not on the mouth. Kissing him on the cheek is not 
dangerous immediately after he has washed his face. It 
43 
Figure 23. — The feather dus- 
ter is dangerous and should be 
replaced by the moist cloth. 
(Compare Figure 26.) 44 
THE HUMAN BODY AND ITS ENEMIES 
is the dust and uncleanliness that are dangerous. It is 
always very wrong for a consumptive to fondle another 
person or to kiss any one on the mouth, especially a baby 
or a little child. 
Consumption is Not Inherited. No child ever comes 
into the world with this disease upon him. But we can 
inherit a set of lungs that will develop consumption if the 
germs ever get into them. Even then we cannot possibly 
have consumption unless we get the germs into our lungs. 
Some are so fortunate, it seems, that even a fair number 
of germs can get into their lungs without remaining there. 
In some way the lungs are proof against consumption. 
Others are not so lucky, and as soon as the germ gets into 
their lungs, it multiplies and causes consumption. These 
germ-proof men and women are in good health and their 
strength is up to the standard. In general, it can be truly 
said that a person who is run down or overworked catches 
the disease more readily than one who is strong and in 
good condition. 
Avoiding Tuberculosis from Milk. Cows have con- 
sumption, and their milk often contains the germs. Babies 
and small children using this milk are likely to get tuber- 
culosis of the bones, of the intestines, or of the kernels 
along the side of the neck. The cow that has tuberculosis 
may look well. You have probably known people who 
were the picture of health and yet had consumption. 
It is the same with cattle; it is impossible to tell by out- 
ward appearances whether or not a cow is diseased. The 
veterinary surgeon can tell, however, by testing the cow. 
All cows that furnish milk for children’s use should be 
tested by a good veterinary surgeon to find out if they 
have tuberculosis. 
Consumption is* Curable. Consumption is so common 
in Texas that every one ought to know something about the 
treatment of the disease. Consumption is curable. There 
are hundreds of healthy persons in Texas who have had it CONSUMPTION OR TUBERCULOSIS 
and have recovered, among them some of our most promi- 
nent men. Almost every man can point to some friend 
who has had the disease and has recovered. 
There are four things to do in order to recover from 
consumption: first, sleep and live out of doors; second, 
eat plenty of good food, such as milk, eggs, light bread, 
45 
Figure 24. — The careful consumptive sleeps alone, and if possible he 
sleeps in the open air or in a window tent. 
chicken, fish, and things of that kind; third, rest and save 
your strength, especially if you have fever; and fourth, 
keep in touch with a good physician to advise you about 
any special things that may be needed in your particular 
case. 
How to Prevent Consumption. If we wish to prevent 
consumption, we must be sure that the rented houses which 
we move into are free from tuberculosis germs. Careful 
inquiry should be made in all cases before moving into a 
rented house. Find out if anybody has died there in the 
last year. If there has been any case of sickness in the 
house within twelve months, the house should be disin- 
fected. A description of the best method of disinfecting a 
room will be found in another chapter. 
Spitting. We should .all be careful where we spit. 
Every one has to spit sometimes, and it is safe to spit into 46 
THE HUMAN BODY AND ITS ENEMIES 
the toilet, into a spittoon containing water or disinfectant 
substance, on the ground in a sunny place, provided it is 
not on the sidewalk, or in a special paper handkerchief or 
cloth carried for the purpose. Those who have tuber- 
culosis should carry cloths or paper handkerchiefs at all 
times, and after spitting in them should burn them. (See 
Sanitary Code for Texas, Rule 62.) 
Duty of the Family. The most important thing a family 
can do to prevent the spread of tuberculosis is to stop the 
dry method of sweeping and dusting. 
The Duty of the Government. The health department 
in every city should have a map showing where each case 
Figure 25. — The consumptive should spit in a rag or paper; the rag 
should be burned to destroy the germs in the spit. 
of consumption occurs. When the house of a consumptive 
person is vacated, it should be disinfected before any one 
else moves into it. The city should also furnish free 
printed matter to the poor who have consumption, so that 
they may learn how to get well and how to keep from 
giving the disease to others. The city should have an out- 
door hospital, or pavilion, for poor consumptives, as this CONSUMPTION OR TUBERCULOSIS 
47 
would prevent them from spreading the germs. Only the 
larger cities can afford to have a visiting nurse to go into 
the homes of the poorer consumptives and actually teach 
them how to take care of themselves and others. All 
towns should have an inspector to see that the milk sold 
in the towns is pure. This is especially to protect the 
babies. 
IMPORTANT POINTS 
1. Consumption is the commonest disease on earth. A 
large percentage of all people who live to be fifty years old 
have had consumption at some time in life. 
2. Consumption is curable, and a great majority of those 
who have it recover. 
3. Consumption is not hereditary, but is catching; it is 
spread by a rod-shaped bacterium that is cast off from the body 
in the sputum. 
4. The germs of tuberculosis can live for months in dark 
corners of dwellings, and all rented houses should be disinfected 
before being occupied. 
5. Dusting and sweeping by the dry method is one of the 
best ways to spread consumption. 
6. Babies and small children should never drink the milk 
from a tuberculous cow; the only way to be sure a cow is free 
from tuberculosis is to have her tested. 
7. Careless spitting is dangerous. 
8. The city government should keep a record of all consump- 
tives, and should disinfect all houses that have been vacated 
by them. 
QUESTIONS 
i. What percentage of all persons have consumption? 2. Is 
consumption curable? 3. How is consumption spread? 4. De- 
scribe the germ of consumption. 5. Describe the proper method of 
sweeping a room; of dusting. 6. Give several precautions which 
tend to prevent consumption. 7. How long can the germ of con- 
sumption live in sunlight? In dark corners? 8. What is the 
danger in moving into rented houses? 9. Where should a consump- 
tive spit? 10. Where should we spit? n. Is consumption spread 
by milk? 12. Name some things the city government should do 
to limit the spread of consumption. CHAPTER VIII. COLDS, GRIP AND PNEUMONIA 
A great many disease germs are so harmful to the body 
that they cause disease as soon as they enter it. Con- 
sumption germs are of this kind. You never find consump- 
tion germs in a healthy person. But some other disease 
germs are not quite so harmful to a strong, healthy man, 
and they can live in his body without harming him. The 
man is too healthy and strong for the germs to injure him. 
But if this same man gets wet and chilled, especially when 
he is hungry and tired, the germs begin at once to do him 
harm. 
The Germs of Colds, Grip and Pneumonia. The 
germs which cause colds, grip and pneumonia are all of 
this kind. They are very common, and almost every one 
has some of them in his nose and throat all the time. But 
Figure 26. — A moist rag should 
be used to remove dust. 
Figure 27. — The germs of grip or 
influenza, very highly magnified. 
they cannot harm us as long as we are in good condition. 
If we stay out in the open air a great deal, eat plenty of 
plain, nourishing food, and do not expose ourselves to the 
weather without proper, warm clothing, the germs are 
powerless. But if we go hunting in rainy, windy weather 
and stay all day without eating or resting, or if we get our 
feet wet, especially when we are tired, the germs may 
cause a cold or something worse. 
Pneumonia Dangerous to Drunkards. In no other 
disease does alcohol show its damaging effects so plainly 
48 as in pneumonia. It is a fact well known to physicians 
that a drunkard cannot withstand pneumonia as well as a 
person who does not drink.. This is one proof that alcohol 
acts as a poison to the entire system, because pneumonia 
is a disease of the system and not of the stomach. 
Alcohol does not therefore limit its harmful effects to 
organs with which it comes in direct contact, but it 
weakens the entire system. 
How to Avoid these Diseases. There are two ways to 
avoid grip and pneumonia. The first is to keep ourselves 
in good condition all the time. We can do this by regular 
habits of eating and sleeping, working and playing. We 
can also make ourselves hardy by spending a great deal of 
time in the open air and by taking cool baths regularly. 
We should start taking the cool baths in the summer time, 
not in the winter. We should also start the habit of re- 
maining in the open air in the summer time. Then, as 
the winter wears on, we can keep it up, within reasonable 
limits. 
The other way to avoid these diseases is to try to keep 
from getting germs from any one who is ill. Pneumonia 
germs from a severe case are more likely to cause the 
disease than pneumonia germs from the throat of a healthy 
person. You know, the pneumonia germ does occur in 
the noses and throats of healthy people. But these do not 
seem to be so harmful as the germs from an actual case of 
pneumonia. The same is true of grip. Many people who 
appeared to be strong and well have caught pneumonia 
and grip by going into a sick room; these people have not 
done anything to weaken themselves, and yet the germs 
overcame them. Therefore, no one should enter the sick 
room except for some good reason, and the hands should 
always be washed afterward. 
The Value of Fresh Air. Plenty of fresh air in our 
living and sleeping rooms helps a great deal in keeping our 
strength up to the standard. Air is never bad because it 
COLDS, GRIP AND PNEUMONIA 
49 THE HUMAN BODY AND ITS ENEMIES 
is cold, but because we are not properly clothed to with- 
stand cold. We can enjoy living an outdoor life if we wear 
enough clothing and use enough blankets. 
The Sick Room. Everybody should know that certain 
precautions should be taken in every sick room. For 
instance, the linen from the patient and his bed should not 
be handled or flirted in the air, but should be carefully 
bundled up and dropped into boiling water or into a dis- 
infectant solution, as already described. Those who have 
to care for the patient should always wash their hands 
carefully after leaving the room, especially before eating. 
Dusting and sweeping by the dry method should not be 
done in the sick room, nor indeed in any room. The 
plate, knife and fork should be kept separate from those 
used by other members of the family. 
IMPORTANT POINTS 
1. The germs of colds, grip, and pneumonia are frequently 
found in the air passages of healthy persons. 
2. Exposure to wet and cold weather upsets the body of 
these persons slightly and enables the germs to multiply and 
produce toxins and so cause disease. 
3. The germs of any of these three diseases sometimes 
attack strong, healthy persons who have not been exposed to 
cold weather. 
4. We can avoid these diseases in two ways: first, by 
keeping ourselves strong, so that the germs cannot overcome us; 
and second, by keeping away from persons sick with these 
diseases. 
5. In the sick room the usual precautions should be taken as 
follows: a separate set of eating utensils should be kept for the 
patient; the linen should be handled cautiously; dusting and 
sweeping should be done by the moist method; all persons 
entering the sick room should wash their hands after leaving. 
QUESTIONS 
i. Name some germs that cause disease whenever they enter 
the human body. 2. Name some germs which sometimes live in COLDS, GRIP AND PNEUMONIA 
the human body without causing disease. 3. Suppose you have the 
germs of grip living in your nose and mouth; tell how you could 
bring on an attack of grip. 4. Does the germ of pneumonia or grip 
ever act like the typhoid germ and cause illness in a strong, healthy 
person? 5. Give three precautions to remember concerning the 
sick room. 6. What proof have we that alcohol does harm to the 
entire system? CHAPTER IX. DIPHTHERIA AND MENINGITIS 
The germs of diphtheria and meningitis can live in the 
nose or throat without causing disease. It is more usual, 
however, for them to cause dangerous illness. Both 
diphtheria and meningitis are dangerous and contagious. 
Diphtheria, a Dangerous Disease. Diphtheria caused 
almost as many deaths in the United States in 1910 as 
typhoid fever, but in Texas it causes only about one fourth 
as many deaths each year as typhoid fever. In 1911, 
diphtheria caused two hundred and eighty-one deaths in 
this state; diphtheria stood sixth among the communicable 
diseases as a cause of death. 
How the Diphtheria Germ Injures the Human Body. 
The diphtheria germ lives in the nose and throat. It may 
Figure 28. — The germ of diphtheria is cast off from the body in spit; 
, also found in the pocket handkerchief. 
cause the lining of these passages, called mucous membrane, 
to swell and stop up the throat so that the patient cannot 
get his breath; the germ may also do harm by the poisons 
or toxins formed in the patient’s body. These toxins are 
absorbed into the blood and may be carried to the brain 
and cause death. The toxins made by diphtheria germs 
cause the patient to have fever and flushed cheeks. 
Diphtheria Antitoxin. It is indeed fortunate that we 
have an excellent remedy against diphtheria. You have 
learned already something about how antitoxin is made. 
This antitoxin or serum almost always cures the cases in 
which it is given early, and for this reason it is well to have 
all sore throats examined, so that if diphtheria is present, 
no time will be lost. While the death rate from the disease 
52 DIPHTHERIA AND MENINGITIS 
53 
has been lowered by the treatment with serum, there are 
still far too many cases. It would be much better to prevent 
the disease than to have to cure it. 
How to Prevent Diphtheria. The most effective way to 
prevent diphtheria is to isolate every case until the 
person is well and the germs have left the throat, and 
to give a small dose of antitoxin to every one who has 
been exposed to the disease. A person who has received 
a small dose of antitoxin cannot catch the disease for 
several weeks. It has been found that the germs live for 
some time in the throats of patients after recovery. For 
Figure 29.—All public towels should 
be of paper and should be used only 
once before being thrown away. 
Figure 30. — White blood 
cells containing meningitis 
germs, highly magnified. 
this reason, wherever possible, an examination of the throat 
should be made before allowing a patient to go about in 
public. It is not always practicable to do this, however, 
and the doctor will have to use judgment in letting the 
patient go. 
Seeing that healthy boys and girls can carry the germs 
in their noses and throats without knowing it, it is wise to 
avoid using the public drinking cup and the public towel. 
One should avoid borrowing pencils and things of that kind 
from others, for many people have the foolish habit of 
moistening their pencils in their mouths. 
The diphtheria germs do not multiply outside the body,  THE HUMAN BODY AND ITS ENEMIES 
54 
except when some careless person allows them to get into 
milk. They always come from the human body. 
Epidemic Meningitis. This disease is an inflammation of 
the coverings of the spinal cord, and is due to a little oval 
germ which lives in the nose and throat and spinal canal 
of those who are sick. We call this little germ the menin- 
gococcus, and as you can see in Figure 30, it occurs in pairs. 
The picture shows that the white cells of the blood have 
swallowed some of the meningitis germs. 
The spinal cord is composed of nerves and nerve cells, 
and is almost like a part of the brain, as you will learn later. 
It is well protected by tough coverings, and it is on these 
coverings that the meningitis germ especially lives. The 
germ causes inflammation of the coverings of the cord. 
It is not the only germ that can live in this position and 
cause inflammation, but it is the only germ that causes 
these symptoms in epidemics. When other germs attack 
the coverings of the spinal cord, it is almost always in the 
course of an illness in which other parts of the body are 
also affected; the typhoid germ, for instance, can affect 
the coverings of the spinal cord and, in a sense, cause 
meningitis, but the typhoid germ never causes epidemics 
of meningitis. 
Meningitis Carriers. It seems altogether probable that 
the germ of meningitis can live in the nose and throat of 
a healthy individual without causing any inconvenience. 
From this person’s throat the germ can spread to other 
people and cause meningitis. 
How the Meningitis Germs Enter our Body. These 
germs enter through the nose and mouth. For this reason 
all those who have been close to a meningitis patient 
should be very careful, for they may be carriers of menin- 
gitis, although they are not sick. 
Value of the Serum Treatment of Meningitis. Before 
the introduction of the serum treatment of meningitis, 
almost all persons who had it died; and those who did DIPHTHERIA AND MENINGITIS 
55 
not die were usually blind, crippled, or otherwise injured. 
Since the use of this treatment, more than half the patients 
have recovered, and it is rare to find any serious defects 
as a result of the disease. Even now, however, meningitis 
is one of the most dangerous diseases known. Probably 
it is the most dangerous epidemic disease that ever affects 
our country. 
How to Prevent Meningitis. The best things to do to 
prevent meningitis from spreading are to isolate the sick 
and to use sprays in the nose and throat to destroy the 
germs. All who have been near a meningitis patient should 
keep their throats sprayed, to protect themselves as well 
as others; for one who feels entirely well can carry the 
germs and may spread the disease. Only a mild solution 
should be used for spraying the nose and throat. 
1. Diphtheria is a dangerous contagious disease of the nose 
and throat, and is due to the diphtheria germ. 
2. The diphtheria germ itself does not live all through the 
body; the toxins cause fever and other symptoms of diphtheria. 
3. Diphtheria can be cured by antitoxin, if it is used early. 
4. The secretions from the nose and throat contain the diph- 
theria germ, and therefore public drinking cups and public 
towels are dangerous. 
5. Meningitis is the most dangerous epidemic disease that 
occurs in our State. 
6. It is due to a germ that lives in the coverings of the 
spinal cord, and also in the nose and throat. 
7. Meningitis is spread in the same manner as diphtheria, 
by secretions from the nose and throat. 
8. In both diphtheria and meningitis, the germs can live in 
the nose or throat of a healthy person, without causing incon- 
venience. 
9. The serum treatment of meningitis has cut in half the 
death rate from this disease. 
10. Diphtheria and meningitis are prevented in the same 
ways: isolate the sick; avoid handling articles such as public 
IMPORTANT POINTS 56 
THE HUMAN BODY AND ITS ENEMIES 
drinking cups and public towels; and remember that healthy 
persons may be disease carriers. 
QUESTIONS 
i. Where do the germs that cause diphtheria and meningitis enter 
our body? 2. How does the diphtheria germ injure us? 3. What is 
a diphtheria carrier? 4. What is the cure for diphtheria? 5. Ex- 
plain how the public drinking cup spreads diphtheria. 6. What is 
the most dangerous epidemic disease that occurs in Texas? 7. 
Where does the meningitis germ enter the human body? 8. What 
is the cure for meningitis? 9. What symptoms formerly followed 
meningitis if the patient recovered? 10. Would it be dangerous for 
the nurse in charge of a meningitis patient to mingle in a crowd of 
people? Why? CHAPTER X. MALARIA, YELLOW FEVER, AND 
DENGUE 
Malaria, or Chills and Fever. This is just as definite a 
disease as measles, and we know more about it than we 
know about measles. We know the little germ that lives 
in our bodies and multiplies, causing malaria; its name 
is the malarial parasite, or plasmodium, of malaria. The 
germ cannot live anywhere in the world except in two 
places: first, in certain parts of the human body, especially 
in the blood; and second, in a certain species of mosquito. 
The germs of malaria cannot live in all parts of the 
human body. For instance, if we accidentally swallowed 
or breathed in some of the germs they would not live, but 
would die in our bodies and do us no harm. If we drank 
water containing the wiggle tails, which are only young 
mosquitoes, they could not cause malaria. In order to 
live in the body, the germ must enter it in one particular 
way. 
How the Germ Enters our Bodies. How, then, does 
the germ of malaria get into our body? It comes in through 
the bill of the mosquito when it bites us.- That is the only 
way it ever enters our bodies. Now, it is strange, but true, 
that a malarial patient cannot give malaria to any one else 
unless the mosquito acts as a messenger or carrier to others. 
In other words, if one member of the family has malaria, 
it is perfectly safe for him to remain in the same room with 
the others, so long as he uses a mosquito bar or net to keep 
the mosquitoes from reaching him. 
How Malaria Is Spread. The first man to prove that 
the germs of malaria grow and develop in the mosquito 
was Dr. Ronald Ross of England, who made this discovery 
on August 20, 1897. Two years later the United States 
Army Commission proved at Havana that yellow fever 
also is spread by the mosquito, and in no other way. In 
Chapter III you have already learned that Dr. Carroll 
and Dr. Lazear lost their lives while making these investi- 
gations. This was in 1900. The same year Dr. William 
57 58 
THE HUMAN BODY AND ITS ENEMIES 
Thayer of Baltimore and Dr. Albert Woldert of Texas 
demonstrated that in this country the Anopheles mosquito 
harbors malarial germs, which it injects into persons, thus 
spreading chills and fever. 
While our American scientists were making these brilliant 
discoveries, Dr. Sambon and Dr. Low of London spent 
Figure 31. — Observe that the malarial mosquito 
stands out from the wall. 
the summer in the Italian Campagna swamp, near Rome, 
where almost every one had malaria during the summer. 
These physicians, however, slept behind mosquito-proof 
screens, and, as you will imagine, they remained free from 
malaria. 
Where the Mosquito Gets the Germs. We must not 
forget that the mosquito is harmless unless it has previously 
bitten a patient sick with malaria. We say mosquitoes 
carry malaria from one man to another. If the mosquito 
could think and talk, it might say, “Human beings carry 
malaria from one mosquito to another.” One man cannot 
give malaria to another without the mosquito, which acts 
as a messenger or carrier. The mosquito sucks human 
blood. It thrusts its bill down into the skin of a malarial 
patient deep enough to suck out some of the blood, together 
with the malarial germs present in this little drop of blood. 
The malarial germs multiply in the body of the mosquito. 
Later, when it bites some other human being, the germs 
pass through the bill of the mosquito and enter the body MALARIA AND YELLOW FEVER 
59 
of the unfortunate person, who then becomes sick with 
malaria. 
Prevention of Malaria. When we get rid of mosquitoes, 
we prevent malaria. The best method of getting rid of the 
mosquitoes is to kill the wigglers by pouring oil over the 
water in which they live. Wherever possible, we should 
do away with all standing water, a point fully discussed 
in Chapter XVII. 
Screens Prevent Malaria. There is something, how- 
ever, which we can all do that will almost surely protect 
us from malaria; that is, screen our homes. In Texas 
we have so delightful a climate, and so little really cold 
weather, that we need screens all the year round to protect 
us from insects. Copper or brass wire screens are most 
durable, but they are expensive. Galvanized iron wire 
screens are next best. Ordinary wire screens do not last 
long. All the screens should be 
fine-meshed, so as to keep out 
all mosquitoes. The variety of 
screen that has sixteen meshes 
to the inch is best. Mosquitoes 
easily crawl through the twelve- 
mesh screens, or through bars 
with coarse mesh. 
Mosquitoes may be driven 
out of the house by burning cer- 
tain things in a room, so as to 
cause a dense smoke, as for 
instance chips, leaves, or pieces 
of old cotton cloth. The fumes 
from burning sulphur or insect powder kill mosquitoes. 
Whenever sulphur is burned indoors, it should be remem- 
bered that the fumes, if inhaled, are irritating and 
dangerous. Burning sulphur has a tendency to sputter, 
and pieces of it may leap out of the bucket or tub and set 
fire to the house. The fumes of sulphur will tarnish metals, 
Figure 32. — Note that all doors 
and windows are screened and 
that the porch is also screened 
in. This house is safe from 
malaria in any climate. 60 
THE HUMAN BODY AND ITS ENEMIES 
and therefore metal articles should be taken from a room 
before fumigating it with sulphur. 
Old-fashioned Ideas. Malaria cannot be spread by 
damp air or by the beautiful mists that may be seen 
early in the morning rising over the swamps. A home in 
Figure 33. — A mosquito bar can always be procured, and it is the next 
best thing to a screened room. 
the swamps or river bottoms can be made perfectly safe 
from malaria by screens and mosquito bars or netting; 
for malaria is a disease that is spread in one way, only, 
and that is by the mosquito. 
Other Diseases Spread by the Mosquito. There are 
two other diseases which are carried by the mosquito; 
namely, yellow fever and dengue fever. 
Each Disease Spread by a Separate Kind of Mosquito. 
It is remarkable that only certain kinds of mosquitoes can 
carry these diseases, and a particular kind of mosquito 
carries each separate disease. One kind of mosquito, 
called Anopheles, carries malaria; another kind, called 
Stegomyia, carries yellow fever; and another kind, called 
Culex, carries dengue. Figures 53, 54, and 55 show the 
three kinds. But, remember, the mosquito cannot carry 
the disease unless it has bitten some one who is sick 
with it. 
Yellow Fever. This is a very fatal disease, and in olden 
times it was much dreaded in Texas, because when it MALARIA AND YELLOW FEVER 
61 
occurred in epidemics it killed many people. The people 
thought it was due to “ something in the atmosphere,” 
or “something that blows up from the swamps.” They 
were right, for that “something” was simply a mosquito. 
Nowadays we know how to stamp out the disease because 
we know that it cannot be carried in any way except by 
the mosquito. Yellow fever is not so much dreaded now 
as formerly. And yet we are so close to Mexico and Cuba 
and Brazil that once in a while some ship will sail into 
our Texas ports with yellow fever on board. When this 
occurs, we can prevent the spread of the disease by killing 
all mosquitoes on board. It does no good to quarantine 
against the mosquito. If a yellow fever patient entered 
a town, he could not give the disease to any one if he tried, 
except by mosquitoes. Of course, if a town does not rid 
itself of mosquitoes, a quarantine is needed. 
Dengue. This is an unpleasant disease to have, but 
not a dangerous one. About every ten years it appears 
in Texas, and sometimes it sweeps all over those parts 
of the state where mosquitoes are most abundant. It has 
occurred so many times while there was also an epidemic 
of yellow fever that some people formerly thought it was 
related to yellow fever. It is really an entirely different 
disease, and an attack of yellow fever does not protect one 
from dengue. There were thousands of cases of dengue 
in Texas in the late summer and fall of 1907, and the dis- 
ease did a great deal of harm by leaving people weak and 
nervous, and also by frightening them. To prevent another 
epidemic, each city and town should have a health depart- 
ment to destroy the breeding places of mosquitoes. In 
addition, all homes in Texas should be screened. 
IMPORTANT POINTS 
i. Malaria is due to a germ that lives half its life in the 
blood of a malarial patient, and the other half in the body of a 
certain kind of mosquito. 62 
THE HUMAN BODY AND ITS ENEMIES 
2. Malaria will disappear from Texas when all our people 
use screens and mosquito bars. 
3. Yellow fever and dengue fever are also spread by the 
mosquito, but each one by a different kind of mosquito. 
4. By doing away with all breeding places for the mosquito, 
and by screening the sick, we do away with yellow fever, malaria, 
and dengue. 
i. What connection has malaria with the location of a house? 
2. Name two places where the malarial germ lives. Does it live 
anywhere else? 3. Suppose you should swallow the eggs of a mos- 
quito, would you be likely to have malaria? 4. If you drink water 
from a cistern in which there are wigglers, will it give you malaria? 
5. Suppose you were bitten by a hundred mosquitoes, none of 
which had bitten a malarial patient, would you contract malaria? 
6. Name two other diseases that are carried from the sick to the 
well by mosquitoes. 
QUESTIONS CHAPTER XI. QUARANTINABLE AND REPORT- 
ABLE DISEASES 
One very old method of limiting the spread of a com- 
municable disease is by quarantine. The word quarantine 
is from an old Italian word meaning forty, because 
people with contagious disease on board a ship were 
not allowed to leave the vessel for forty days. Today the 
word quarantine usually means confining people to certain 
premises or places in order to stop the spread of communi- 
cable diseases. 
Modern Quarantine. Our ideas of quarantine have 
changed as we have learned more about the cause and 
spread of diseases. For instance, in cases of smallpox the 
patient is held in quarantine a certain number of days after 
he recovers; but in diphtheria, since the germ can live in 
the throat for some time after the patient recovers, the 
patient is not kept for a definite number of days, but until 
his throat is free from diphtheria germs. Sometimes this 
is a few days after the attack is over, and sometimes it is 
six months. For this reason many people are allowed to 
go free sooner than they otherwise would, because their 
throats contain no germs; but other patients are kept 
much longer than formerly, because if permitted to go 
about in public, they would be dangerous to the public 
health. 
We still have to rely on a definite time limit, however, 
in many diseases. The following are declared by the laws 
of Texas to be quarantinable: Asiatic cholera, plague, 
typhus fever, yellow fever, leprosy, smallpox, scarlet fever, 
diphtheria (membranous croup), epidemic cerebro-spinal 
meningitis, dengue, typhoid fever, epidemic dysentery, 
trachoma, tuberculosis, and anthrax (charbon). (See 
Sanitary Code, Appendix B.) 
The length of time patients are held in quarantine varies 
with the different diseases and depends on the length of 
time during which patients may communicate the disease 
after recovery from the illness. 
63 64 
THE HUMAN BODY AND ITS ENEMIES 
Quarantine of Exposed Persons. Sometimes people in 
health are quarantined because they have been exposed to 
a disease and it is feared they may develop it. In this 
case the length of time they are kept in quarantine depends 
on how long it takes the disease to develop after one 
has been exposed to it. This period, while the disease is 
developing, is called the incubation period, from the fact 
that the germs are being incubated in the body. After 
Figure 34. — Nurse under quaran- 
tine. Note the sheet over door. 
Figure 35.—This code is the law 
in Texas. (See Appendix B.) 
the germs are introduced it usually takes them several 
days to multiply sufficiently to cause symptoms of disease. 
Even before symptoms develop, however, such patients 
can convey the disease to other people. 
Reportable Diseases. We should especially note that 
the law requires reports to be made and complete records 
to be kept of all quarantinable diseases, including typhoid 
fever and tuberculosis. The physician in attendance on 
these cases is required by law to report them to the State 
Board of Health, and both the local and the state health REPORTABLE DISEASES 
officers keep a record. The records of cases of tuber- 
culosis are required by law to be kept privately, and no 
one except the proper authorities has the right to see them. 
This is done because no person has a right to know from 
what a patient is suffering except the officers of the law 
who are protecting the public health. At present there 
are so few cases of these diseases in many communities in 
Texas that complete records are not kept. As our state 
grows, however, it will be more necessary to observe the 
law, and we need improvement in this regard even now. 
Investigate and see if these diseases are reported in your 
community. If they are not, make up your mind to do 
your part in future and get them reported. 
How to Get the Sanitary Code. The State Board of 
Health at Austin will take pleasure in sending to your 
school a copy of the Sanitary Code, containing many of 
the legal rules concerning quarantine and health matters 
generally. It would be well for each class to get a copy 
of this, as it is the law of the land. Is it well enforced in 
your county or town? Good citizens should be willing to 
submit to quarantine whenever they have a communicable 
disease, even though it is in a mild form, because fatal 
cases may arise from very mild ones. The Sanitary Code 
for Texas is given in abbreviated form in Appendix B. 
Flagging the House. As a rule, quarantine consists in 
keeping the sick individuals in a certain room or house 
and preventing any one from entering or leaving this room 
or house, except the nurse and physician, who know how 
to avoid carrying the disease to others. A placard is tacked 
outside' warning the public not to enter, or a yellow flag is 
placed on the house. 
Elsewhere in this book you have learned what the follow- 
ing diseases are and how they are carried from one patient 
to another: Asiatic cholera, plague, yellow fever, diph- 
theria, dengue, meningitis, typhoid fever, tuberculosis, 
and trachoma. We will take up in order the following 
65 66 
THE HUMAN BODY AND ITS ENEMIES 
communicable diseases: typhus fever, leprosy, smallpox, 
and scarlet fever. 
Typhus Fever. This is another name for jail fever, or 
ship fever, and it is not closely related to typhoid fever. 
It exists at all times in Mexico, and is found in unclean 
Figure 36. — A house under quarantine. The sign on the porch is 
usually omitted. The flag is yellow or red. 
houses. It is carried by certain insects that live in the 
clothing or hair of uncleanly people. These insects are 
called body lice, or head lice. It is not likely that this 
disease will gain much foothold in Texas. 
Leprosy. This is a very old disease and one that is 
very terrifying to most people. It is due to a germ that 
resembles the tuberculosis germ. The germ of leprosy is 
found in the sores and in the secretions from the nose of 
lepers. It is not likely to attack many people in Texas. 
Smallpox. This is a dangerous disease that causes fever 
and pustules or little pockets of pus over the skin of the 
body. It is one of the most contagious diseases known, 
and a high percentage of those exposed take the disease. REPORTABLE DISEASES 
67 
Fortunately this is one disease which we know how to pre- 
vent. Vaccination is a certain preventive of smallpox, as 
you have learned in Chapter V. 
Scarlet Fever. This is simply another name for scarlatina. 
There is no difference between the two. It is a very con- 
tagious disease, and the germs can live in the garments of 
a scarlet fever patient for many months. Up to this time 
we do not know the nature of the germ that causes scarlet 
fever, and so can do very little to prevent its spread except 
to quarantine all scarlet fever patients. The greatest care 
is necessary in the way of destroying or disinfecting all 
toys, clothing and other things of the kind, that have been 
in the room with a scarlet fever patient. 
Diseases which Exclude Children from School. There 
are several diseases that affect children especially, in which 
quarantine is not usually enforced. These diseases are 
measles, mumps, whooping cough, and chicken pox. They 
are alike in that they attack a large percentage of all children 
in this country. If one escapes these diseases, however, 
as a child, he may have them after he is grown up. Pupils 
with any of the four diseases mentioned are debarred from 
school. 
Measles. This is by far the most important of these 
diseases. It causes about six thousand deaths in the United 
States every year. In Texas alone two hundred and 
twenty-two deaths from measles were reported in 1911. 
Measles is more fatal among infants and children under 
five years old than among boys and girls from five to fifteen 
years old. This should lead mothers to be careful to pre- 
vent their children from having measles before they reach 
the age of five or ten. It is not uncommon to hear mothers 
say that they want their children to have measles and get 
through with it. But this is not wise, for measles is a 
serious disease, especially among little children. 
Whooping Cough. This is also a serious disease when 
it attacks babies and very young children. It is due to a 68 
THE HUMAN BODY AND ITS ENEMIES 
germ that resembles the grip germ. The whooping cough 
germ cannot easily be carried in the clothing, but is usually 
spread from one child to another by direct contact. That 
is, the germs pass from the hand or face of one child to the 
hands of another; or from the hands or lips of one child, 
to some toy, and from it to the hands or lips of another 
child. It is not hard to ward off whooping cough. All 
Figure 37. — Little children should not be allowed to mingle on the street 
with other children, as whooping cough and other diseases are caught in 
this way. 
that is needed is to keep babies away from other children, 
except those known to be healthy. Whooping cough, 
measles, and scarlet fever each cause about the same 
number of deaths each year in the United States. Whoop- 
ing cough is fatal in one fourth of the cases occurring among 
infants under two years of age. 
How these Diseases Are Spread. To spread either of 
these diseases, some solid or liquid particles must pass 
from the body of the sick into the body of the well. The 
particles which spread the diseases are especially the 
droplets of saliva that fly out of the mouth when the 
patient coughs or speaks. In measles and scarlet fever it REPORTABLE DISEASES 
69 
may be that the dried particles of skin that scale off are 
concerned in the spread of the disease, although this is not 
proved. The germ of measles and that of scarlet fever 
have' not been found, and it is possible that they are so 
small that they are invisible with our strongest micro- 
scopes. You have already learned that some germs are 
so small that they cannot be seen at all, as for instance the 
germ of rabies or hydrophobia. 
1. Quarantine is one method of preventing the spread of 
disease, but in some cases we have learned a better way; in 
many cases we still resort to quarantine because we do not know 
a better way of preventing the spread of the disease. 
2. The laws of Texas declare that the following diseases are 
quarantinable: typhus fever (not typhoid), Asiatic cholera, 
plague, yellow fever, smallpox, scarlet fever, diphtheria (mem- 
branous croup), dengue, and leprosy. 
3. The following diseases are quarantinable only to the 
extent that they debar pupils from school: measles, mumps, 
whooping cough, and chicken pox. 
4. The germs of smallpox and scarlet fever live for many 
months in garments and on toys and furniture, and retain their 
power to cause the disease. 
5. The risk of contagion of measles and of whooping cough 
does not last over two weeks, as a rule; these diseases are danger- 
ous to small children and babies. 
IMPORTANT POINTS 
QUESTIONS 
i. What is the old or original meaning of the word quarantine? 
2. Why do we not hold all dangerous contagious cases exactly forty 
days now? 3. Name two quarantinable diseases in which the con- 
tagion will last a long while in clothing. 4. Is it wise for mothers 
purposely to expose little children to the measles? 5. Name three 
diseases that should exclude pupils from school, but which are not 
of sufficient importance to require a full quarantine. 6. What is 
the best way to prevent whooping cough in babies? 7. Why is it 
important to prevent infants and young children from getting whoop- 
ing cough? 8. How can you get a copy of the Sanitary Code for 
Texas? CHAPTER XII. PELLAGRA AND HOOKWORM 
DISEASE 
Much attention has been paid in recent years to hook- 
worm disease and pellagra, two diseases that may be called 
new in the United States. 
The Cause of Pellagra Disease Unknown. In Texas more 
attention has been paid to pellagra than to hookworm, 
although hookworm disease is more prevalent and more 
easily curable than pellagra. Not knowing positively the 
cause of pellagra, we can do nothing to prevent it. It is 
not very catching, if at all, and yet we ought to be careful 
about stating that it is not catching till we know more 
about the cause. No precautions have usually been taken 
to prevent its spread, and yet in this state no case has ever 
caused a second case among the nurses or physicians and 
others who have cared for the patients. At the same time, 
there have been several families in which more than one 
case has occurred. The main symptoms of pellagra are: 
a redness resembling sunburn on the back of the hands, 
face and neck, diarrhoea, and nervousness. Many pellagra 
sufferers get well, and if medical attention is sought early 
no one should be discouraged on account of this disease. 
A change to a cool climate is probably beneficial. 
Hookworm Disease in Texas. Hookworm disease is 
not uncommon in the thickly settled parts of Texas, espe- 
Figure 38. — Male and female hookworm. 
dally in the sandy soils of East Texas. From one fourth 
to one half of the first three thousand school children 
and citizens examined in Texas by the Rockefeller Hook- PELLAGRA AND HOOKWORM 
worm Commission were found to have hookworms. It is 
a preventable and curable disease. 
Where the Hookworm Lives. The hookworm that 
causes this disease lives in the small intestines and sucks 
blood from the intestinal wall. The disease shows itself 
especially by lack of blood in the patient. People who 
have hookworm disease are usually pale and weakly. 
They lack energy and strength. They are often nervous 
and have fickle appetites. But, after all, no especial 
symptom is caused by the hookworm that is not caused 
also by other diseases. 
Diagnosis of the Disease. The only way surely to know 
whether anybody has hookworm is by the use of the micro- 
Figure 39. — The hookworm eggs hatch into little worms which pene- 
trate the human skin, enter a blood vessel, pass to the lungs, enter a 
bronchus, crawl up the windpipe, are swallowed and thus reach the small 
intestines. 
scope. The worm lays eggs, and these eggs leave the 
intestines in the waste matter that is thrown off from 
the body. The eggs are too small to be seen without a 
microscope. 
The Hookworm. This is a small worm about half an 
inch long, and it remains in the intestines. The eggs, 
however, pass out, and are dangerous, as they cause the 72 
THE HUMAN BODY AND ITS ENEMIES 
spread of the disease. Just how the eggs hatch out and 
get into man’s body is a wonderful story. It almost sur- 
passes belief, but we qre forced to believe it, because there 
are actual photographs showing the worm in all the stages 
of its journey from one person to another. 
The egg hatches soon after it leaves the body or in- 
testines of the patient. A little worm is formed from the 
egg. This worm gets on the skin of children, especially 
those who go barefooted, and goes into the skin, causing 
a little blister where it enters. This blister is known as 
the “ground itch.” We know now that ground itch is 
nothing but one stage in hookworm disease. The worm 
passes through the skin and gets into a blood vessel. It 
passes up the blood vessel to the lungs. Here it eats its 
way through the wall of the blood vessel and gets into a 
bronchus, or bronchial tube. The worm squirms along 
the bronchial tube and gets to the windpipe and then to 
the throat. It then turns back down the throat and passes 
through the stomach into the intestines, where it begins its 
usual life. It is probable that some hookworm eggs 
are swallowed directly and are hatched in the stomach or 
intestines. 
Dangers of Soil Pollution. When unclean wastes from 
the body are allowed to be poured out on the soil, the 
ground is not only unclean, but is dangerous, because a 
child walking along barefooted is likely to develop ground 
itch, which is the beginning of hookworm disease. Such 
children are backward in their growth, stunted, and weakly. 
They are not well, and do not play and study like healthy 
children. 
Need of Sewers and Sanitary Outhouses. The best 
preventive of soil pollution is a good sewer system, but 
this cannot be had on the average farm. The next best 
thing is well-built outhouses. Pictures near the end of 
this book show a poor and a good kind of outhouse. 
No wastes from the human body should ever be allowed PELLAGRA AND HOOKWORM 
73 
to be thrown on the ground, as there are too many diseases 
which may be spread in this way. People who do not 
know they have any disease may be disease carriers. 
Tapeworms and Round Worms. Other intestinal worms 
that cause disease in man are tapeworms and round worms. 
The eggs of the tapeworm leave the body as in the case of 
hookworm. The eggs of the tapeworm then get into the 
body of the hog or beef or fish, where they hatch into young 
worms. When we eat the flesh of these animals, if it is 
not well cooked, the young worms begin their life in our 
intestines. All meat should be inspected carefully by a 
meat inspector, and it should be well cooked to prevent 
the spread of tapeworms and of other diseases. 
Thymol. This is the remedy for hookworm, but as it 
is not a harmless drug, it should be employed under the 
advice of a physician. No oil of any kind or butter should 
be eaten after taking thymol. 
IMPORTANT POINTS 
1. Pellagra is a disease somewhat new in America, but 
fairly well distributed over the Middle and Southern parts of 
the United States. 
2. We do not know the cause of the disease. 
3. Pellagra is often curable, and a cold climate seems to have 
a beneficial action, both in the prevention and in the cure of 
this disease. 
4. Hookworm disease is due to the presence in the small 
intestines of small worms about half an inch long, which attach 
themselves to the wall of the intestines and suck blood. 
5. We know how to prevent and cure hookworm disease: 
it can be prevented by avoiding soil pollution from body wastes, 
and it can be cured by small doses of thymol. 
6. The small hookworms, just after they are hatched, can 
pass through the skin and find their way, by a complicated route, 
to the small intestine, which is their home. 
7. The sanitary outhouse, built according to the directions 74 
THE HUMAN BODY AND ITS ENEMIES 
given near the end of this book, will prevent the spread of hook- 
worm disease. 
i. Do we know the cause of pellagra? 2. What is the cause of 
hookworm disease? 3. Where do the hookworms live in the body? 
4. What symptoms do they cause? 5. Where do the worms enter 
the body? 6. Describe their journey from the skin of the feet to 
their final home. 7. What is the most effective way to prevent the 
spread of hookworm disease? 8. Is there a cure for the disease? 
9. In what kinds of meat are we likely to find tapeworms? 
QUESTIONS CHAPTER XIH. BUBONIC PLAGUE 
The Panama Canal brings Texas into much closer con- 
nection than ever before with China, India, and the Eastern 
countries generally. It is possible that persons suffering 
from bubonic plague may land in one of our ports and start 
Figure 40. — Ships from foreign countries might 
bring bubonic plague into our seaports. 
a focus of the plague in our state. We should know that 
the disease is spread by fleas from animals such as rats 
and squirrels, so that we can protect ourselves intelligently. 
Animals Also Have Plague. Plague, or bubonic plague, 
as it is called, is one disease that man shares with lower 
animals. It is due to a germ that lives in the lymph 
nodes, in the lungs, and in the blood. The disease kills a 
high percentage of those who have it and it also kills many 
rats and ground squirrels. There was a plague center in 
California not long ago. Only squirrels and rats were 
affected there, but now and then some hunter catches 
the disease from squirrels. Plague is also found in some 
of the South American countries. 
How Plague Is Spread. Fleas from gnawing animals, 
such as squirrels and rats, carry plague to human beings. 
The huntsman kills a squirrel and picks it up. The fleas 
leave the dead squirrel, get on the man, and bite him. 
The man develops the disease. 
Why Rats Are Objectionable. Rats are dangerous, 
since they carry other diseases as well as plague; and they 
75 76 
THE HUMAN BODY AND ITS ENEMIES 
are very expensive, because of the quantities of grain which 
they destroy. 
It is wise to make all premises as nearly rat proof as 
possible. This can be done in the following way: Wooden 
walks should be torn up and replaced by concrete or gravel. 
The residence should be at least eighteen inches above the 
Figure 41. — Plague affects 
squirrels. 
Figure 42. — Rats spread 
plague. 
ground, measuring from the lowest joist. The barn and 
chicken yard should have concrete floors, and chicken wire 
of small mesh (f inch) should be used. The woodshed 
should have no floor, and the wood should be piled on 
platforms at least two feet high. Garbage should be kept 
in an iron can with close-fitting lid. All grain should be 
stored in a metal container. If the premises are rat proof, 
a little poison exposed on cheese or meat will kill all the 
rats, because the rats will be driven by hunger to eat the 
poisonous bait. 
Plague Also Spread by Particles Thrown off from the 
Body. The germs of plague, called plague bacilli, may be 
spread by sputum and discharges from the body of those 
who have the disease. Hence the same precautions should 
be taken as in the case of pneumonia, tuberculosis, 
diphtheria, and other dangerous communicable diseases. 
IMPORTANT POINTS 
i. Plague is epidemic in the Far East, and hence it may 
enter Texas. BUBONIC PLAGUE 
77 
2. Plague is spread principally by the fleas which are found 
on rats and ground squirrels. 
3. In case plague should break out, we could probably soon 
get it under control by quarantine, but after it gets a start 
among the rats and squirrels it is a very difficult matter to 
exterminate it. 
4. The proper way to guard against plague is to quarantine 
the sick; and also to exterminate the rat, and if necessary the 
ground squirrel and all the animals that harbor fleas and are 
subject to plague. 
QUESTIONS 
i. How is bubonic plague spread? 2. What countries are afflicted 
with plague today? 3. In what state of the United States has plague 
existed and among what animals? 4. How could we prevent the 
spread of plague if it should appear in one of our seaports? 5. Why 
is quarantine against plague necessary? CHAPTER XIV. DISEASE CARRIERS 
You have learned that it is possible for a healthy person 
to have disease germs in his throat or elsewhere in his 
body. This is particularly true of typhoid fever, diph- 
theria, meningitis, pneumonia, and grip. We call people 
who walk about carrying these dangerous germs, germ 
carriers, or disease carriers. It is hard to realise that this kind 
of thing is possible, but we must believe it, for many reli- 
able men, and men of good judgment, 
have investigated the matter and proved 
it to be true. 
Typhoid Carriers. In the case of 
typhoid fever, the carriers are usually 
people who have had the disease a year 
or two before. By carefully examining 
all who have had typhoid fever, certain 
scientists have found that some healthy 
men have the typhoid germ in their in- 
testines, or in their kidneys. Many 
people have caught typhoid fever from 
these carriers, who were proved to have 
typhoid germs in their bodies. 
Dr. Robert Koch, the great scientist 
who discovered the bacterium of tuber- 
culosis, said that if the typhoid carriers 
could be prevented from spreading 
typhoid fever, the disease could be 
stamped out. The particular danger 
with typhoid carriers is that many of 
them are cooks, bakers, dairymen, and the like. One 
typhoid carrier in New York was a cook and caused 
twenty-six cases of typhoid in seven different families. 
Diphtheria Carriers. It was a surprise to many doctors 
when it was discovered that the diphtheria germ could be 
found in the throat of healthy boys and girls. This 
fact, however, is well proved. The right way to apply 
quarantine to a family that has had diphtheria is to 
Figure 43. — A 
typhoid carrier 
handling milk is 
very dangerous. 
Ty p h o i d carriers 
are usually in good 
health, but are dan- 
gerous to others. 
78 DISEASE CARRIERS 
examine their throats and let the persons go free as soon 
as their throats are found free from the diphtheria germ. 
The same is true of meningitis. 
Meningitis Carriers. Meningitis is such a deadly 
disease, especially when not treated by serum, that it 
seems almost unbelievable that 
the meningitis germ should live 
in any one’s throat without 
making him sick. But this is 
most certainly true, and it ex- 
plains why people fall sick with 
meningitis when they have never 
been near a meningitis patient. 
Without knowing it they have 
been near a meningitis carrier. 
How to Avoid Carriers. Ev- 
ery applicant for employment 
in a bakery, kitchen, restaurant, 
or other place where food is 
handled should be asked if he 
has had any contagious disease, 
especially typhoid fever, within 
two years. If he has had such a 
disease, he should be required to 
show by a certificate from the local health officer that he is 
not a disease carrier. 
Care of Convalescents. Every person recovering from 
typhoid fever should consider himself a possible carrier, 
until proper bacteriological examinations have proved 
otherwise. If there is no laboratory in the town they live 
in, persons who have to handle food for others should 
communicate with the State Bacteriologist at Austin in 
order to get the proper tests made. 
Uncleanly Habits Dangerous. Uncleanly habits are 
always dangerous, because persons who appear healthy 
may be disease carriers. Such habits as putting pencils or 
79 
Figure 44. — A diphtheria 
carrier. Diphtheria carriers 
are usually in good health, 
but are dangerous to others. 80 
THE HUMAN BODY AND ITS ENEMIES 
coins in the mouth, eating without washing the hands, or 
spitting on the floor, sooner or later surely lead to disease. 
IMPORTANT POINTS 
1. Some disease germs, such as the germs of consumption, 
are so harmful that they invariably cause disease whenever 
they live in the human body. 
2. Other disease germs usually cause disease when they 
live in the body, but can live in the bodies of certain persons 
without causing disease. 
3. A healthy person who has disease germs living in his 
body is called a disease carrier. 
4. Other people may be killed by the disease germs which 
are harmless to the disease carrier. 
5. Typhoid fever, diphtheria, and meningitis are spread by 
carriers. 
6. Persons have been known to carry the typhoid germs for 
years after recovering from the fever. 
7. Typhoid carriers are especially dangerous when they 
work in dairies, kitchens, bakeries, restaurants, or other places 
where food is handled. 
8. It is impossible to tell whether a typhoid convalescent is 
a carrier except by a laboratory examination for the bacteria. 
QUESTIONS 
i. Name three diseases spread by carriers. 2. Can you tell a 
typhoid carrier by his appearance? 3. How do you explain the fact 
that the germs in a disease carrier do not make him sick? (See 
Chapter IV.) 4. In what occupations are disease carriers most 
dangerous to the public? 5. How can disease carriers be discovered? 
6. Suppose you catch typhoid fever from a carrier or from a mild 
case, is your case likely to be mild? 7. How can we avoid danger 
from disease carriers? 8. Why are uncleanly habits dangerous 
even when no sick persons are near? 9. To whom may those persons 
apply who desire to be treated to see if they are carriers? CHAPTER XV. INSECTS WHICH CARRY OR 
SCATTER DISEASE 
The important fact has many times been pointed out in 
these pages that disease germs are derived from the bodies 
of persons who are sick. The germs of disease are carried 
from the sick to the healthy in various ways: in the air, 
in clothing, by insects, by means of drinking cups and 
towels, by contact, in our food, and in our drinking water. 
The house fly carries typhoid and other germs to our food, 
and blood-sucking insects transfer the germs of certain 
diseases from the blood of the sick to the blood of the 
well, thereby causing disease. Mosquitoes are responsible 
for distributing yellow fever, malaria, dengue fever, and 
several other diseases. Ticks spread disease among men, 
among cattle, and among chickens. We now consider it 
almost a rule that any insect which lives on the blood of 
any animal is likely to convey disease from one of those 
animals to another. 
The Stable Fly. The common stable fly is often mis- 
taken for the commoner house fly, but, unlike the latter, 
Figure 45. — Stable fly in its various 
stages of growth. 
Figure 46. — Feeler, eye and 
proboscis of stable fly. 
it is able to pierce the skin and suck blood. Facts have 
recently been brought to light which seem to prove that 
the stable fly is the active agent in the spread of infantile 
paralysis, a dreaded disease of children. This discovery was 82 
THE HUMAN BODY AND ITS ENEMIES 
made by* Professor C. T. Brues of Harvard University, who 
is a graduate of the University of Texas, and Dr. P. A. E. 
Shepard of the Massachusetts State Board of Health; and 
it has been confirmed by Dr. M. J. Rosenau of Harvard 
Medical School. Other observers have failed to confirm it. 
The Tsetse Fly. In East Africa there is a terrible disease 
known as the sleeping sickness. This disease is trans- 
mitted by the tsetse fly, another blood-sucking insect about 
the size of a house fly. It is thus seen that flies are among 
the most dangerous enemies of the human race. 
Fleas. Fleas are insects that have no wings and have 
hind legs adapted for hopping. They live on all kinds of 
warm-blooded animals. The fleas that live on rats and 
ground squirrels are most dangerous to man, because 
these animals may become infected with plague, the germs 
of which- are carried from the living or dead rat to man. 
To fight plague, therefore, we 
must make war on the rat and 
the ground squirrel, as has been 
done in California in recent 
years. We have not had plague 
in Texas, but it may come from 
Asia on ships passing through 
the Panama Canal, or from South America. 
Lice. Body lice transfer typhus fever or jail fever from 
the sick to the well. This disease occurs in Mexico. 
Proper sanitary measures are almost sure to prevent its 
introduction into Texas. 
Ticks. Ticks are not strictly insects, but are much like 
them. How many legs has a tick? A spider? An insect? 
Ticks have been proved to carry tick fever from cattle to 
cattle. The disease is deadly to imported cattle unless 
they are made immune by a special kind of vaccination, 
such as that described in Chapter IV. Cattle shipped out 
of Texas have to be dipped in a solution that kills ticks. 
Another kind of tick is responsible for carrying Rocky 
Figure 47. — Flea. INSECTS WHICH CARRY DISEASE 
83 
Mountain spotted fever to people. This disease originated 
in the Bitter Root Valley of Montana, where it causes 
about a dozen deaths annually. It also occurs now in 
other states. 
IMPORTANT POINTS 
1. Any insect that has the habit of sucking the blood of an 
animal is likely to carry or spread disease from one animal to 
another. 
2. The stable fly bites persons and thus transfers from one 
person to another the germs of the disease known as paralysis 
of children. 
3. The tsetse fly of Africa, also a biting fly, carries from one 
person to another the germs of a dangerous disease known as 
sleeping sickness. 
4. Fleas from rats and ground squirrels carry the germs of 
plague and thus spread the disease. 
5. Lice are responsible for the spread of typhus or jail fever. 
6. Ticks spread disease among persons, among animals, and 
among chickens. 
QUESTIONS 
i. What kind of insects are especially likely to carry disease? 
2. Name five insects known to carry disease. 3. What insect 
causes the spread of plague? 4. What disease does the stable fly 
spread? 5. What disease do lice spread? 6. What diseases are 
spread by ticks? CHAPTER XVI. THE HOUSE OR TYPHOID FLY 
Description of the House Fly. The house fly may be 
called one of our domestic animals, for it is found almost 
exclusively about the habitations of man. Since it cannot 
bite like its cousin the stable fly, it has until recently 
been considered perfectly harmless. It is a pretty creature, 
with a pair of gauzy wings, compound eyes, and lively 
habits. 
Parts of the Fly. Studying the different parts of the 
fly will enable us to understand how the fly carries disease 
germs. All parts of the body of the fly, especially the 
feet (Fig. 49), arc covered with stiff hairs well adapted for 
catching up filth particles containing disease germs. The 
Figure 48. — This picture (after Howard) shows 
the eggs of the fly, and then the larva and pupa 
which the egg changes into before it finally be- 
comes a grown fly. The larva is called a maggot. 
Figure 49. — The 
foot of the house 
fly. Very highly 
magnified. 
last joint of each leg of the fly carries, first, a pair of claws 
fitted for holding on to rough surfaces, and second, a pair 
of pads between the claws. The pads have short knobbed 
and sticky hairs, by which the fly is enabled to walk on 
smooth surfaces such as a window pane, or upon the ceil- 
ing. No doubt these acrobatic feats have all seemed 
wonderful to you. Would you not suppose that these 
sticky hairs could also take up dust and dirt containing 
germs of typhoid or diphtheria? The proboscis is the 
84 HOUSE OR TYPHOID FLY 
85 
name we give to the tongue or sucking tube of the fly, and 
on account of the presence of numerous hairs and bristles, 
this also is a good collector of filth and disease germs. 
(See Figure 50.) 
How the House Fly Scatters Disease Germs. Thus 
we see that we should look with fear and disgust upon this 
pretty creature. It is really the poisoner of millions of 
persons. The house fly has fitly 
earned its new name of typhoid fly. 
It likes filth. It visits the back yard 
or the sick room of a typhoid patient, 
where careless people have placed 
the patient’s body wastes. It cov- 
ers the bristles and sticky hairs of 
its feet with filth and germs, and 
then flies into the kitchen or dining 
room and crawls over the bread and 
meat and jelly. If the typhoid- 
laden fly drops into a can of milk at 
a dairy, the germs multiply therein 
and may infect dozens of consumers 
of the milk. The fly may carry 
germs from the body wastes of one baby sick with sum- 
mer complaint to the milk bottle with which another 
baby is fed, causing another case of sickness and perhaps 
death. If a consumptive spits upon the sidewalk, it is 
possible for flies to carry the germs from the sputum to 
the candy eaten by a boy or girl living close by. The fly 
frequently carries filth several hundred feet. Figure 15 
shows a plate of gelatin over which a fly had been allowed 
to walk. At first no tracks could' be seen, because the 
germs left by the feet of the fly were too small. But in 
twenty-four hours each germ had multiplied into a colony 
of thousands of germs. These colonies of germs are shown 
in the picture. 
Life History of the Fly. The female fly usually lays her 
Figure 50. — The pro- 
boscis or “tongue” of 
the house fly. 86 
THE HUMAN BODY AND ITS ENEMIES 
eggs, about one hundred in number, in the manure of ani- 
mals, especially in that of horses. The egg hatches in less 
than a day into a legless, wormlike larva or maggot. Each 
larva feeds upon the manure until full grown, when its 
outer shell turns hard and brown. The insect is then 
said to be in the pupa or resting stage. In the shell a 
wonderful change takes place, for soon this breaks open at 
one end and out slips the mature or adult fly. In about 
ten days, during average weather, the fly passes through 
the egg, larva, and pupal, to the adult, stage. 
How to Reduce the Number of Flies. Flies are plentiful 
wherever filth or excrement is plentiful. If we remove the 
barnyard manure once a week, we 
remove with it all the young flies 
in the larval or egg stage. A 
good plan is to have a box or bin 
(Fig. 51) in which to keep the 
rakings from the stable and barn- 
yard. The bin should be fly 
proof and its contents should be 
hauled off once a week or oftener. 
It is much easier to prevent the 
hatching of flies than to catch them in the adult or winged 
stage. Fly traps are often useful for catching adult flies. 
There are several good patterns on the market. 
Figure 51. — A fly-proof 
manure-bin with lid. 
Observation Work. Secure a number of fly traps and 
place them in good situations. Use different bait (moist bread, 
molasses, sugar-water, meat, etc.) in the different traps, so as 
to find out which is most attractive. It is also interesting to 
capture a fly and study the parts (eyes, wings, proboscis, feet, 
feelers, balancers, etc.) with a magnifying glass. Disinfect 
the fly by rolling it in formaldehyd or hydrogen peroxid, and 
wash the hands in soap and water after handling it. 
When the flies get into the house in spite of all we can 
do to prevent it, they should be killed. Liquid poisons HOUSE OR TYPHOID FLY 
87 
in sweetened water are sometimes used, but they are not 
to be recommended for the reason that the poisoned flies 
are likely to fall into the food and thus do as much damage 
as living ones. Sticky fly paper is the best means of killing 
the flies. The flail (Fig. 52) can be used to kill 
flies as well as mosquitoes that gather on the 
inside of our screen doors and windows. If we 
darken a room, with the exception of one win- 
dow, the flies will gather at this window, 
where they may be killed. 
Avoiding Disease. To prevent the carrying 
of germs to our food we should first try to 
keep down the number of flies by removing 
their breeding places, and second, screen our 
houses so as to keep the flies out of our 
kitchens and dining rooms. If you doubt the 
need of screens, take some lime and throw it 
on to the flies out near the stable or closet. 
Within an hour you will probably find flies with lime 
on their backs on your dining-room table. The best 
screens that can be obtained at reasonable cost are 
those made of galvanized wire. To keep out mosquitoes 
as well as flies, the wire gauze should have no less than 
sixteen meshes to the inch. 
Disinfection of Body Wastes. After taking all the pre- 
cautions mentioned, we still have not done the most impor- 
tant thing to prevent the spread of disease. If we do not 
expose germ-laden filth to the fly, there will he no germs for 
1 T?c fly to carry. The most important thing to do to pre- 
mt the scattering of typhoid and other diseases is to 
iisinfect the body wastes of the sick, as described in Chap- 
ter VI. Typhoid fever is a filth disease. Flies can scatter 
the germs only when the germs are placed where the flies 
can get to them. 
Figure 52.— 
Fly killer. 88 
THE HUMAN BODY AND ITS ENEMIES 
IMPORTANT POINTS 
1. The foot and the proboscis of the fly are centered with 
hairs, so that filth clings to them. 
2. The fly alights on filth, and then carries germs on its 
dirty feet into unscreened dining rooms and kitchens. 
3. The egg of the fly hatches to form a maggot; the maggot 
eats and grows until at length it becomes a pupa; the pupa 
rests a few days and hatches to form a full-sized adult fly. 
4. The egg can pass through all the stages and form an adult 
fly in ten days. 
5. Hauling off manure from the barnyard is the most effect- 
ive way of preventing flies. 
6. Screens should be used to keep flies out of the house. 
i. How is the house fly adapted to gathering germs? 2. Explain 
how the fly places dangerous germs on butter, jelly, or other articles 
of food. 3. Give the different steps in the development of the fly 
from the egg. 4. How long does it take the egg to develop into a 
full-grown fly? 5. What are two important things to do in pre- 
venting flies from spreading typhoid fever? 
QUESTIONS CHAPTER XVII. MOSQUITOES 
In Texas mosquitoes cause hundreds of deaths, which 
are chiefly the result of malarial fever, or what is more 
commonly known as chills and fever, malaria, or simply 
chills. In all cases it is the mosquito that takes the 
germ of malarial fever from a person sick with chills and 
fever and injects these germs through its proboscis into the 
Figure 53. — Yellow fever mosquito (Stegomyia). 
Figure 54. — Ordinary, or 
dengue, mosquito (Culex). 
Figure 55. — Malaria mos- ’ 
quito (Anopheles). 
blood of a healthy person, thus producing malaria. The 
germ of malarial fever is known as the malarial parasite. 
Dengue fever makes its appearance in Texas from time 
to time; and when cases do come in from Mexico and 
elsewhere, mosquitoes are here to spread the disease. 
Yellow fever threatens to slip in from South America every 
summer, but this will probably be prevented by the watch- 
fulness of our quarantine officers. Yellow fever is not THE HUMAN BODY AND ITS ENEMIES 
likely to become epidemic in Texas again in the present 
advanced state of scientific knowledge. The study of the 
mosquito is important mainly from the standpoint of 
preventing malarial and dengue fevers. 
Description of a Mosquito. The mosquito is an insect 
with a single pair of wings and a pair of balancers. For our 
present purpose the most interesting part of the animal is 
the proboscis, or bill. This is not a simple affair, but a 
whole set of instruments in itself. There are six sharp- 
pointed pieces in the proboscis for piercing the skin and 
making the blood flow. There is also a tube with which 
to suck up the blood; this tube is the duct through which 
the mosquito injects its saliva into the human skin. This 
saliva carries with it the germs of the particular disease of 
which the mosquito is a carrier. 
How the Mosquito Scatters Disease Germs. The germs 
of malaria are sucked up through the proboscis of the 
mosquito and carried into its stomach. Here the germs 
cause knots or cysts in the stomach wall and multiply 
in countless numbers. In fourteen days the germs are 
mature and break out of the stomach wall of the mosquito 
and enter its salivary glands. If the mosquito then bites 
a person, the germs pass into the blood with the saliva 
which the mosquito injects into the wound. 
Kinds of Mosquitoes. Yellow fever, malaria, and 
dengue are each carried by a particular kind of mosquito. 
Figures 53, 54, and 55 show the three kinds, all of which 
are found in Texas. 
Observation Work. Secure a number of mosquitoes and 
try to identify them. This is not easy, even after looking at 
the pictures. The yellow fever mosquito (Stegomyia) has 
white markings in the shape of a lyre on the thorax and has 
striped legs. The malarial mosquito (Anopheles) has spotted 
wings, and when at rest stands at an angle from the wall (Fig. 
31). The common mosquito (Culex; Fig. 31) holds its body 
parallel to the surface on which it rests. MOSQUITOES 
Breeding Places of the Mosquito. To destroy these 
insect enemies of ours we must learn their breeding places 
and the habits of the young mosquito. We can keep the 
adult insects out of our houses, but we cannot kill them 
after they have grown wings and 
flown away. We may, however, 
easily keep down their numbers by 
filling up or draining their breed- 
ing places, and so getting rid of 
their young. 
Everybody knows that the wig- 
gler of our ponds and puddles is 
the young stage of the mosquito, 
but not everybody realizes what 
large numbers of mosquitoes may 
grow up in a small quantity of 
water. A tin can may catch enough 
rain water to raise a thousand 
mosquitoes in a summer. The rain 
barrel or the overground cistern is 
often a source of a continuous 
stream of mosquitoes throughout 
the season. Roof gutters may be- 
come clogged and hold water after 
every rain. Water troughs, hoof 
prints of cattle in wet ground, urns in cemeteries, and 
even a neglected vase inside the house may harbor mos- 
quito wigglers. 
The remedy for all this, and the easiest way to get rid 
of mosquitoes, is to destroy their breeding places. City 
and county authorities should see to it that useless accumu- 
lations of stagnant water are drained. Necessary ponds 
and tanks should be stocked with fish which eat the 
wigglers. Tin cans should have holes punched in them 
and should be carried off, and other such breeding places 
of the mosquito should be removed. The rain barrel 
Figure 56. — Rain barrel 
with lid. 92 
THE HUMAN BODY AND ITS ENEMIES 
and cistern should be made absolutely mosquito proof 
with screen covers (Fig. 56) and strips tacked over 
cracks. 
By referring to Figure 60 you will see a cistern with the 
top open and exposed to mosquitoes. This cistern could 
be made more sanitary by covering it with boards, or, 
better still, with boards and cloth. 
Life History of the Mosquito. Before laying a batch of 
eggs the mosquito must gorge itself with food, such as the 
blood of animals or man. It then 
deposits its eggs on the surface 
of the water, where they swell 
up and float. The eggs of the 
dengue mosquito are in a raft- 
like mass of two hundred to four 
hundred (Fig. 58); those of other 
mosquitoes are scattered singly 
on the surface of the water (Fig. 57). The eggs hatch in 
half a day, and come out wigglers, or larvae. These feed on 
tiny particles of organic material. It is interesting to 
watch the brushlike mouth parts as they rake in the food. 
The larvae of the Anopheles or malarial mosquito lie flat 
upon the surface of the water (Fig. 58); larvae of other 
kinds feed at various levels and float with the head down- 
ward in the water. 
When the larva becomes full grown, it stops eating and 
becomes a pupa (Fig. 58), on the inside of which the adult 
insect develops. When the adult is ready to emerge, the 
pupa splits open at the back, and slowly the mosquito 
comes forth, pulling out its legs, feelers, and wings. It 
uses the skin it leaves behind as a raft until the wings are 
quite dry. After this it flies away. 
How could one witness this magic transformation from 
worm to winged insect without thinking of the butterfly 
and the beautiful Greek story of Psyche, typifying the 
soul? 
Figure 57. — Eggs-and larva 
of the ordinary, or dengue, 
mosquito. MOSQUITOES 
93 
Observation Work. It is easy to rear mosquitoes in the 
school room. You may go down to the pond and find eggs, 
larvae, and pupae, and bring them to school in a glass jar. It is 
best to use the water in which they are found. Study all the 
stages. See if the larvae change their skins. Watch the adults 
emerge. You may also set out a jar of rain water where mos- 
quitoes abound, and the next morning you will probably find 
eggs on the surface of the water. Drop a single cooked bean 
or bread crumb into the rain water for the larvae. If you wish 
to keep some adult mosquitoes in a cage, capture a dozen or 
so, place them in a cage, and feed them a slice of banana. Let 
the mosquitoes also have a tumbler of rain water in which to 
lay their eggs. 
Destroying Mosquitoes. Besides removing the water 
in which the larvae and pupae live, there is another way 
of killing them. In Figure 58 both pupae and larvae are 
shown at the surface of the water, with the breathing 
tubes protruding into the air. If we pour oil on the water, 
the oil will spread over the surface in a thin film. The 
wiggler, therefore, dies for want of air. 
Observation Work. Every school should organize an 
anti-mosquito brigade. Let the pupils look up and report all 
of the breeding places of mosquitoes in the school ward or school 
district. 
Experiment. Place a few wigglers in each of two tumblers 
of water. To one tumbler add one drop of kerosene oil. Keep 
the other tumbler entirely free from oil. Note result. 
Adult mosquitoes that succeed in getting into our houses 
can be killed with the flail (Fig. 52), on the inside of our 
screens, where they gather about dusk. 
Screens. Some of the worst yellow fever and malarial 
districts of the world (Havana and Panama) have been 
made habitable to man by draining pools of water and 
by the use of screens, thus doing away with mosquitoes. 
Screens are necessary in all parts of Texas, both against 94 
THE HUMAN BODY AND ITS ENEMIES 
flies and against mosquitoes. The river bottoms of the 
state can be made quite safe for white people by the use 
of screens on doors and windows of dwellings. If a person 
Figure 58. — Showing eggs, larva, and pupa, or the different stages in the 
development of the malaria mosquito. 
has malaria, he should be carefully screened off from the 
other members of the family, and every precaution taken to 
prevent the access of mosquitoes, which might carry the 
disease to others. 
1. Malaria is spread by the Anopheles mosquito and in no 
other way. 
2. Dengue is spread by the Culex mosquito and in no other 
way. 
3. Yellow fever is spread by the Stegomyia mosquito and in 
no other way. 
4. The proboscis of the mosquito is sharp pointed and con- 
tains a tube for sucking blood. 
5. The germs of malaria are sucked up from a malarial 
patient, and after multiplying in the wall of the stomach of 
the mosquito, are injected beneath the skin of other persons, 
causing malaria. 
6. Mosquitoes breed in ponds, tin cans, rain barrels, cis- 
terns, roof gutters, water troughs, and wherever there is stag- 
nant water. 
IMPORTANT POINTS MOSQUITOES 
7. The egg of the mosquito hatches into a larva (called a 
wiggler); the larva leads an active life for a few days and goes 
into the resting stage, when it is called a pupa; the full-grown 
mosquito comes out of the pupa. 
8. We can prevent the multiplication of mosquitoes by drain- 
ing ponds and by preventing water from standing. 
9. Screening gives immediate protection against mosquitoes. 
95 
QUESTIONS 
i. Can malaria or dengue be spread without mosquitoes? 2. 
Describe the proboscis of the mosquito. 3. Explain how the 
mosquito gets the germs of malaria from a patient. 4. Name six 
common breeding places of the mosquito. 5. In what way can we 
get immediate protection against mosquitoes? 6. Why is it more 
necessary to screen a patient with malaria than one sick with men- 
ingitis? 7. Point out the eggs, larva, and adult of the malarial 
mosquito; also the adult in resting position. CHAPTER XVIII. KEEPING GERMS OUT OF 
OUR DRINKING WATER 
The most harmful things in drinking water are not the 
mineral matter, but the germs of disease which the water 
may contain. Of course there are poisonous waters, such 
as the strong gypsum waters found in certain parts of 
Texas, and there are some stagnant pools that are so full 
of filth that they would not serve as drinking water; but, 
on the whole, the only dangers that lurk in drinking water 
are in the form of disease germs, and in this country typhoid 
germs are the most to be feared. 
Appearance of Water Not a Good Test. Disease germs 
are not visible except when placed under a microscope or 
Figure 59. — Lad drinking from artesian well. 
viewed in large numbers, and it is impossible to tell, by 
looking at water or tasting it, whether it is free from danger- 
ous germs or not. There are many wells and springs which 
furnish water of a pleasant taste; such water may seem to 
be perfectly clean, and yet it may contain hundreds of 
typhoid germs in each drop. It is important to realize 
how impossible it is to judge a specimen of water by its GERMS IN DRINKING WATER 
appearance and taste. A much better way to form an 
opinion as to the purity of water is to examine into the 
source of the water. 
Kinds of Water Used in Texas. In general there are 
five kinds of drinking water used in Texas, as follows: 
rain water, shallow well water, spring water, river water, 
and deep well water. 
Rain Water. This is perfectly pure when it falls, but 
after it has fallen on a roof that has been soiled by English 
97 
Figure 60. — The uncovered cistern is a breeding place for mosquitoes, 
sparrows and pigeons, it may become polluted from disease 
germs. Underground cisterns subject to either overflow 
or seepage may contain germs of typhoid fever. Water 
should be gathered in a cistern from the sunny side of the 
roof only, as sunlight destroys germs. The gutters should 
be cleaned as often as necessary. Water from winter rains 
only should be allowed to flow into the cistern. Open 
cisterns may serve as breeding places for mosquitoes and 
thus do great harm, as you have learned in Chapter VI. 98 
THE HUMAN BODY AND ITS ENEMIES 
The Shallow Well. This is the source of most of the 
drinking water used in many parts of Texas. A well of 
this kind is usually less than a hundred feet deep. Practi- 
cally all wells, except the deep or artesian wells, are shallow. 
The shallow well is one of the most dangerous sources of 
Figure 61. — This 
well is poorly con- 
structed; water can 
leak through the 
platform or through 
the sides of the well. 
A rope and bucket 
should not be used. 
Figure 62. — This 
well is properly con- 
structed. The plat- 
form is watertight. 
The sides of the well 
are watertight. The 
pump is better than 
the bucket and rope. 
Figure 63. — The 
concrete curb should 
be prolonged down- 
ward to the layer of 
clay, which does not 
allow germs to pass 
through. The water 
in gravel is good. 
water, but it can be made reasonably safe in most instances. 
In nine cases out of ten, the fault is not in the lay of the 
land, but in the way the well is cased in, the method of 
drawing the water, or other conditions that can be cor- 
rected. When we take into account the fact that usually 
the water in a shallow well has filtered or seeped through 
at least twenty feet of closely packed earth, we must con- 
clude that most of the germs would be filtered out. It is 
certainly true, however, that if a well is placed close to a 
cesspool, especially on the downhill side, and if this cess- 
pool is filled with unclean material month after month, 
sooner or later some disease germs will pass through the 
soil and into the well. A well is seldom placed, however, 
in such a dangerous position. We may therefore conclude 
that the germs which seep into the bottom of a well with 
the water are not so important as the germs that spill in GERMS IN DRINKING WATER 
99 
over the top of the well or those that trickle in through 
leaks in the sides. Not only should the well be cased in, 
but the platform or cover should be watertight, in order to 
prevent the well from being soiled with material dropping 
off the shoes of the persons drawing water. 
Casing of Wells. Figure 61 shows a typical faulty 
shallow well. Point out four errors in the construction 
of this well. Figure 62 shows the same well with the faults 
corrected. The model well shown in the picture is cased 
from bottom to top with concrete rings, which are fitted 
together with cement so as to make a perfectly watertight 
joint. These rings are usually molded to fit a standard 
well, three feet in diameter, and it takes about thirty 
dollars to pay for the casing in of a well thirty feet deep. 
The concrete rings are superior to brick or stone, because 
they have fewer joints. The model well shows the concrete 
rings built up two feet or so above the surface of the ground, 
and when this is done, the mound around the surface of 
the well is unnecessary. It is a good rule, however, to 
hill up the soil around every well to prevent surface water 
from running in at the top. To make a still better well, 
a two-inch cap of concrete can be placed over the mound 
for a distance of three feet from the well in every direction, 
as shown in Figure 63. 
Many wells in Texas could be made comparatively safe 
in the manner shown in Figure 63. Here the upper layers 
of the earth are porous and admit surface drainage into 
the well. By continuing the cement wall into the layer of 
clay, all chance of seepage into the well would be cut off 
and the well thus made safe, because germs cannot pass 
through clay. 
Dangers from Rope and Bucket. The model well is 
fitted with a pump. This delivers the water into the 
bucket in a pure state. If the water is drawn with a rope 
and bucket, the drippings from the hands fall into the 
bucket. From what you have learned about typhoid  THE HUMAN BODY AND ITS ENEMIES 
fever you can readily see how easy it would be for a person 
nursing a case of typhoid fever to transfer the germs from 
the hands to the water. 
Spring Water. This is not a safe water supply if we take 
it year in and year out. A spring gets its supply of water 
from the surface also, but is not usually dangerous if it 
is protected so that no water can get in except through 
the fountain head of the spring. A spring should have a 
concrete curb around it to keep water from the near-by 
surface from draining into it. If a spring is on the down- 
hill side of a house, it is dangerous, especially if it has not 
a watertight curb or rim around it. 
River Water. This is the main source of the water of 
most of our cities, and it is usually so dangerous that it 
must be treated in some way before it is safe to use at all. 
It is easy to see that many filthy things get into a river, 
and were it not for the purifying action of the sunlight and 
air, and the filtering of the sand, river water would be 
entirely unusable. River water is especially dangerous just 
below a city or town. Some cities keep an account of all 
cases of illness that occur along the banks of the river for 
miles and miles above the pipe which takes in their water 
supply from the river. 
In case of an epidemic of typhoid in any city or town, 
it is well to ask your local health officer about the water 
supply. As far as communicable diseases are concerned, 
all water may be made safe for drinking by boiling. The 
taste may be restored to boiled water by pouring it through 
the air from one vessel to another. 
Deep Well Water. This is absolutely safe, provided no 
surface water can leak in from the top. If the casing is 
watertight, no leakage can occur. The casing is usually 
made of iron pipe. 
Importance of Water Supply of Summer Camps. The 
pleasant climate of Texas, and the excellent facilities for 
enjoying camp life, entice many campers out into the groves GERMS IN DRINKING WATER 
101 
and prairies each year. It is not at all uncommon for 
these campers to contract typhoid fever while on their 
vacation, and as the fever requires two weeks to develop, 
these attacks of fever usually come on after the campers 
Figure 64. — Boys out hunting should not drink from streams. 
have returned to the town or city. We should learn from 
this the necessity for being careful about selecting drink- 
ing water even when out for a few days’ trip. The picture 
shows a lad drinking from a brook. Streams are often 
poisoned by the germs that have washed into them from 
the premises of farmers up the stream. 
Contamination after Water is Drawn. Even if we have 
a good water supply, bacteria may get into the water after 
it is drawn, unless we take certain precautions in the han- 
dling of it. The public drinking cup is a great danger. 
You have learned that the secretions from our bodies are 
likely to contain the bacteria which cause disease. Each 
time that we put a drinking cup to our mouth, some of 
the saliva that has dried on our lips is removed by the cup. 
Needless to say, any germs that are in our system are likely 
to be spread in this way. We have every reason to believe 
that the germs of diphtheria, tuberculosis, typhoid fever, 
and other dangerous diseases have been distributed by the 
public drinking cup. (See Sanitary Code, Rule 61.) 102 
THE HUMAN BODY AND ITS ENEMIES 
How to Make a Sanitary Drinking Cup. This is shown 
in Figure 65. In making these cups, use a clean sheet of 
paper, and do not put the fingers inside to pull the cup open 
after it is made. 
Figure 65. — This picture shows how to make a sanitary drinking cup 
The Sanitary Drinking Fountain. In public places the 
sanitary fountain is coming to be used. One of these is 
shown in Figure 66. Before drinking from such a fountain, 
a person should make sure that the water is spurting up 
high enough to enable one to drink without touching the 
lips to the metal or rubber mouthpiece of the fountain 
itself. If the lips touch the mouthpiece, an exchange of GERMS IN DRINKING WATER 
103 
germs might take place which would defeat the object of 
the sanitary fountain. 
Typhoid Fever. This is without doubt the disease we 
should think of when we study the water supply. We 
should not, however, forget that the fly may cause as 
much typhoid fever in Texas as the drinking water. You 
Figure 66. — Sanitary fountain in one of the Houston schools. 
have learned on another page how to tell whether a given 
epidemic is due to drinking water. In towns, if the epi- 
demic is due to water, it is likely that a great many persons 
will be affected at the same time, and all parts of the town 
using water from the same source will be equally affected. 
If the epidemic comes up in springtime, and grows gradu- 
ally worse as the summer wears on and as the flies increase, 
it is not likely to be due to the water. It is more likely 
to be due to the fly, especially if certain unsanitary parts 
of the town are affected more than others. 
Asiatic Cholera. This disease is spread by drinking 
water also, but is not likely to attack us. It has been 
almost stamped out in the greater part of the civilized 
world. 104 
THE HUMAN BODY AND ITS ENEMIES 
Other Diseases Spread by Water. Hookworm disease 
may be spread to some extent by drinking water, and 
this is probably the case in the older parts of the state, 
especially in the sandy regions. Amebic dysentery is 
spread by drinking water, but there is not a great deal of 
it in Texas. It is likely to be brought in at any time from 
Mexico, but it is not an epidemic disease. 
All Typhoid Germs Come from the Bodies of the Sick. 
Probably the most important thing to remember in con- 
nection with the spread of disease by drinking water, is the 
fact that the germs have to originate in the body of some 
one sick with typhoid or other disease. If the germs are 
not poured out on the ground, they cannot be washed 
into the well or river. The best place to attack a disease is 
in the sick room, and the best method of attacking it is to 
disinfect all body wastes so that the germs are done away with 
forever. You will learn in Chapter XIX how to disinfect. 
When we disinfect the body wastes, we are heading the 
germs off from our drinking water. 
IMPORTANT POINTS 
1. It is not the chemical or mineral contents of water, but 
the bacteria, which make it unsafe. 
2. Water may be clear and palatable and yet be dangerous. 
3. Cistern water may be contaminated by bacteria carried 
to the roof by pigeons and sparrows, or it may be contaminated 
by surface water wrhich overflows or leaks into the underground 
cistern; owing, however, to the mosquitoes which breed in 
them, cisterns are concerned more in the spread of malaria than 
in the spread of typhoid. 
4. The shallow well is dangerous, but it can be made a reason- 
ably safe source of drinking water by observing the situation 
of the well, by casing it in and covering it properly, and by 
having a pump to raise the water. 
5. River water is risky and usually has to be treated by 
filtration when used as a public water supply; in time of an GERMS IN DRINKING WATER 
105 
epidemic in towns and cities the water should be boiled before 
it is used. 
6. A deep well, when properly cased in, supplies a perfectly 
pure water. 
7. Bacteria are frequently introduced into drinking water 
after it leaves the well, as for instance by the public drinking 
cup. 
8. Typhoid fever is the disease which drinking water most 
often spreads, although this disease is spread in other ways 
also. 
9. Hunters, campers, and persons out in the country should 
not drink from creeks, “tanks,” or streams, as these may con- 
tain the germs of typhoid fever or other disease. 
QUESTIONS 
i. Why must we be careful in selecting drinking water? 2. Of 
all diseases spread in Texas by drinking water, which one causes the 
most deaths? 3. Do you understand this to mean that water is 
the only cause, or the most important cause of the spread of this 
disease? 4. What are the dangers of the uncovered cistern? 5. 
What is the object of casing the well in, and how should this be done? 
6. Why is a pump safer than a bucket and rope? 7. What is the 
object of having a watertight platform or cover for the well? 
8. Why should the earth be piled up around the well? 9. What 
diseases can be spread by the public drinking cup? 10. What is 
the danger in placing one’s mouth over the outlet of a sanitary 
fountain before the water begins to flow? n. Fold a sanitary drink- 
ing cup. 12. Where do the disease germs come from that are in 
drinking water? 13. Where is the best place to kill these germs? CHAPTER XIX. DISINFECTION, OR HOW TO 
KILL BACTERIA 
In this chapter we shall learn how to kill bacteria in 
various ways. They are easy to kill if one knows how, 
but they are not all alike, and what will kill one variety 
of bacterium may not kill another. So the question is 
an important one to study. Remedies that kill germs, 
or prevent them from multiplying, are called germicides, 
disinfectants, or antiseptics. 
Sunlight and Fresh Air. These kill germs better than 
any other remedies. Wherever we can get a supply of 
bright sunlight, we shall not have many germs. There 
are some things, however, that we need to notice about 
Figure 67. — Sunlight is a good disinfectant. 
the action of the sun on bacteria; for instance, the sun 
must shine directly on and against the body of the bac- 
terium before it can kill it. If you place some tuberculosis 
germs in a thin layer on a pane of glass, and then put this 
in the sunlight, the germs will be dead in a few hours. 
But if you throw the germs on the ground, some of them 
will remain on top of the ground and can be readily reached 
and killed by the sunlight, while others may sift down 
into the dirt so that the sun cannot shine upon them. 
These will not be killed by sunlight. In dark corners, 
inside the house, the germs of tuberculosis can live for 
months. DISINFECTION, TO KILL BACTERIA 
107 
Soap and Water. Next to sunshine, soap and water 
are the best disinfectants for everyday use. If we use 
plenty of water and plenty of good soap, the skin will be 
kept almost free of germs. If we keep the hands clean, 
Figure 68. — Soap and water, another good disinfectant, 
we shall escape those diseases spread by fingers, such as 
typhoid fever. 
Difficulties of Disinfection. But there are times when 
we wish to destroy all germs in a certain place, and to do 
it at once. In these cases we can use heat, or we can use 
certain powerful chemicals or drugs. These disinfectants 
are powerful enough to kill any germ, and, if they are not 
used properly, they may kill human beings. Germs are to a 
certain extent like human beings, because they are living; 108 
THE HUMAN BODY AND ITS ENEMIES 
and whatever tends to kill the germ, might also tend to 
kill the human being. This will make clear to you the 
difficulty of killing germs when they are in our bodies. 
Unfortunately, we have no chemical that will kill the 
tuberculosis germ in the human body without injuring 
the body itself. 
Boiling Kills Germs. In case the bacteria we wish to 
kill are not in the human body, our task is much easier. 
Boiling will kill any bacterium known. One minute’s 
boiling will kill almost all bacteria. There are certain 
bacteria, however, which can withstand boiling for several 
minutes. These bacteria are encased in a hard shell in 
which they are safely shut up like a turtle in its shell. It 
is only certain kinds of bacteria that form these shells, and 
we call the bacterium with its shell around the outside, 
a spore. The tetanus or lockjaw germ, and the germ of 
anthrax or charbon, which attacks cattle, are two germs 
which form spores. You will see that our worst diseases, 
such as tuberculosis and typhoid fever, are caused by 
germs that are very easy to kill, when we can get at them. 
The meningitis germ is very easy to kill. 
Chemical Disinfectants. It is not always convenient 
to boil things, and there are certain chemical disinfectants 
that will kill germs just as certainly as heat. Probably 
carbolic acid is the commonest one of these. A solution 
of carbolic acid, made by adding one tablespoonful of the 
acid to a quart of water, will kill any one of the germs, 
except the spore-forming ones, in five minutes. This is a 
strong solution, and yet it takes five long minutes to kill 
the germs. A mistaken idea exists that a saucer of car- 
bolic acid placed under the bed will disinfect the entire 
room. 
Some people believe that by removing bad odors they 
disinfect a room. Some even go so far as to believe it is 
sufficient to cover up these bad odors with other stronger 
ones. This is not only useless, but it is dangerous, because DISINFECTION, TO KILL BACTERIA 
109 
it gives a sense of false security or safety. In the toilet 
rooms of many public buildings, hotels and the like, are to 
be found little metal cylinders which give off a peculiar 
odor. These do not destroy disease germs. It would be 
just as sensible for us to use perfume instead of bathing 
as it is to place these strong-smelling cylinders in our 
buildings. Another mistake is that of confusing disinfect- 
ants with insecticides. Some remedies are sure death to 
insects but harmless to germs; some remedies which kill 
germs do not harm insects. The gasoline mixtures which 
do such good service as insecticides are usually ineffective 
as disinfectants. 
The following table shows how the various disinfectants 
should be diluted for use, and tells which are most effec- 
tive. All things considered, the coal-tar disinfectants are 
the most effective and the cheapest. There are several 
of these preparations on the market, and the State Bac- 
teriologist has prepared a list giving the exact strength of 
each. This list will be furnished upon request to the State 
Board of Health at Austin. 
In buying a disinfectant, always take into consideration 
how much diluting is required. It is best to rely upon 
reports made by the Marine Hospital service at Washing- 
ton or the State Board of Health at Austin, as to the 
strength of a given disinfectant. Of two disinfectants at 
the same price, buy the one of the greater strength, which 
will require greater dilution and go farther. 
Fumigation. So far, the chemical disinfectants men- 
tioned are useful only when we can place the thing to be 
disinfected in the solution. But when we come to disinfect 
an entire room, as for instance when we move into a rented 
house, we cannot do this, and so we have to use a gase- 
ous disinfectant, such as formaldehyd. The formaldehyd 
method of disinfecting a room is very effective, is not 
difficult, and does not damage any of the furnishings 
usually found in a living room. The following directions  THE HUMAN BODY AND ITS ENEMIES 
Table Showing How Long It Takes Certain Disinfectants of 
Given Strength to Destroy Germs 
Name of Disinfectant 
Name of Germ 
How to Make 
Solution 
Length of Time 
Needed to Destroy 
Germs Mentioned 
Boric Acid 
Typhoid 
All that will dissolve 
in water 
Does not destroy all 
of the germs even 
in a week’s time 
Boric Acid 
Pus Germs 
All that will dis- 
solve in water 
Has very little 
effect on germs 
Carbolic Acid 
Typhoid 
Tablespoonful to 
quart of water 
Five minutes 
Carbolic Acid 
Pus Germs 
Tablespoonful to 
quart of water 
Five minutes 
Carbolic Acid 
Anthrax 
Spores 
Two tablespoonfuls 
to pint of water 
Spores live four to 
forty-five minutes 
Corrosive Subli- 
mate; Bichlorid of 
Mercury 
Typhoid 
Three grains to pint 
of water 
Five minutes 
Corrosive Subli- 
mate; Bichlorid of 
Mercury 
Pus Germs 
Seven grains to pint 
of water 
Five minutes 
Corrosive Subli- 
mate; Bichlorid of 
Mercury 
Anthrax 
Spores 
Three grains to pint 
of water 
Twenty-six hours 
Coal-tar disinfect- 
ants 
Typhoid 
Teaspoonful to pint 
of water 
From one-half to 
five minutes 
are taken from the book of instructions of the Texas State 
Board of Health: 
To fumigate an average-sized room the only utensils 
needed are an old three-gallon scrub bucket made of zinc 
(not wood), and three bricks. Secure from the drug store DISINFECTION, TO KILL BACTERIA 
13-2 ounces of potassium permanganate and a quart of 
formaldehyd. Place the bricks in the center of the room 
on the carpet or the floor, and the bucket on the bricks. 
Close the doors and windows tight and place strips of wet 
paper over all cracks and openings. It is a good plan 
to stretch all linen, quilts, etc., on a line so as to expose 
as much surface as possible to the disinfectant gas. They 
should not be thrown in a heap. Put the permanganate 
Figure 69. — Fumigating a room in a rent house. This should always be 
done except in a house that is new, or one in which the family moving out 
were in perfect health. 
into the bucket and pour the formaldehyd over it. Leave 
the room at once, closing the door tightly, and do not 
open the room for at least six hours. (See also Sanitary 
Code for Texas, Rules 55-60.) 
Mixed Disinfectants Are Not Good. It is almost always 
unwise to mix disinfectants, because when two disinfect- 
ants are mixed, the resulting mixture does not usually 
possess a disinfectant value equal to the sum of the disin- 
fectant values of the two ingredients. For this reason the 
patented antiseptic solutions alleged to contain boric acid  THE HUMAN BODY AND ITS ENEMIES 
112 
and several other antiseptic substances are often expensive 
and inefficient. 
IMPORTANT POINTS 
1. Soap and water and sunshine have a great influence on 
your daily life. Keeping your hands clean and cleansing them 
especially before eating, is a health-saving habit for you to form. 
2. It takes strong chemicals and a considerable length of 
time to kill bacteria, hence we should not rely upon any dis- 
infectants except those approved by the proper authorities. 
3. Every family should fumigate or disinfect a house before 
moving into it, unless they know something of the history of 
the house and its occupants for the previous twelve months. 
QUESTIONS 
i. Name three ways of killing germs. 2. Is it easy to kill germs 
in the human body? 3. How long can disease germs live in boiling 
water? 4. What are spores? 5. Name one disease germ that 
forms spores. 6. What two things are of importance in killing 
germs with carbolic acid in water? 7. When should we disinfect a 
room by fumigation? CHAPTER XX. KEEPING ACCOUNT OF OUR 
TREASURE 
What is the most valuable thing on earth? Some of you 
may answer friendship, gold, radium, platinum, diamonds. 
There is one thing, however, which we must have before 
we can use or enjoy any of these things, and that is life 
itself; the most valuable thing in the world, then, is human 
life. 
Bookkeeping. Every merchant keeps a set of books 
showing the money he takes in and pays out. He does 
this because the money is worth a great deal. Every 
civilized government keeps a set of books dealing with 
lives, as well as dollars. This set of books shows the 
number of lives received each day, or, in other words, the 
1911 VITAL STATISTICS 
TUBERCULOSIS 
3137 
TYPHOID 
992 
MALARIA 
349 
DIPHTHERIA 
289 
MEASLES 
222 
SCARLET FEVER 
105 
PNEUMONIA 
1756 
MENINGITIS 
259 
GRIP 
133 
WHOOPING COUGH 
120 
TETANUS 
86 
SMALLPOX 
47 
Figure 70. — These figures show the deaths from certain 
preventable diseases in Texas during 1911. 
number of babies born. It shows also the number of lives 
paid out each day, and what they were paid out for; that 
is, the number of deaths and by what the deaths were 
caused. If a merchant finds that he is paying out a great 
deal of money for coal, he will try to find some way to stop 
the expense, because money is valuable to him. If the 
government finds it is paying out a great many lives each 
day on account of typhoid fever, for example, the govern- 
ment will try to stop the disease, because the, lives are  THE HUMAN BODY AND ITS ENEMIES 
114 
valuable. Now, this set of books kept by the government 
we call Vital Statistics. 
Usefulness of Vital Statistics. There is no use in keep- 
ing this list of deaths unless it is studied with a view to 
saving life. On the other hand, it is hard to try to save 
people from sickness unless there is a list showing which 
diseases are killing the most people. Suppose the pupils 
in your school wished to help in the prevention of disease 
and started in by studying the plague. There has not 
been a case of plague in Texas, however, for many years; 
probably there has never been any here. You could not 
help Texas people much in that direction, could you? 
But by observing the records of vital statistics you will see 
that typhoid fever kills a hundred people or more in Texas 
each month; you might, then, do some good by trying to 
prevent typhoid fever. After you had been at work a 
year or two, and found that typhoid was killing only fifty 
people in a month, you would feel that you were going 
at the business of life-saving in the right way, would you 
not? It would be foolish to try to prevent disease without 
keeping a complete record, so as to see where prevention 
was needed, and to see whether your attempts at preven- 
tion were a success. 
Other Purposes of Vital Statistics. It has been found 
that vital statistics can be made to serve other good pur- 
poses besides protecting the public health. The official 
records of births and deaths, for instance, are useful in 
settling disputes as to age and inheritance. Most states 
which have a system of vital statistics require a death cer- 
tificate to be signed and filed with the proper officer before 
allowing a burial to take place. Murderers and poisoners 
find it impossible to get a death certificate signed for their 
victims, because there is no physician who knows the cause 
of death, and hence the body of the victim of the crime 
cannot be buried legally. When the murderer tries to 
get a physician to sign the certificate, or tries secretly to KEEPING OUR ACCOUNTS 
115 
bury the body of the victim, he is frequently detected and 
brought to justice. 
Death Certificates. It has been found most practical 
to require the undertaker to fill out and prepare the death 
certificate, for the physician rarely goes back to the 
house after a person is dead. The undertaker always has 
dealings with the family just after the death occurs, and 
hence he is best situated to get the information required 
on the death certificate. The physician, however, is the 
only person to pass on the question of the cause of death, 
and so the law in Texas requires him to sign the death 
certificate, giving the cause of death. The report of the 
death is filed with the city physician in case the death 
occurs in a town or city; if it occurs in the country, or 
outside of an incorporated town, the report of the death 
is sent by the undertaker to the county clerk. The officer 
who first receives the death report sends it to the State 
Registrar of Vital Statistics at Austin, and once each month 
the State Registrar publishes a statement of the causes of 
all deaths reported during the month. (Study in this 
connection the Sanitary Code for Texas, Rules 34-50.) 
Texas Statistics. Not much more than half of the 
United States preserves complete and accurate vital statis- 
tics. In the thinly settled parts of the country it is hard to 
get the deaths and births reported. Texas has not yet 
succeeded in getting complete reports of all its deaths, but 
it has been making rapid improvements in this regard, and 
no doubt will have a complete set of returns before a great 
while. We cannot compare our Texas vital statistics with 
those of other parts of the United States without making 
certain changes to make up for the incompleteness of our 
reports. But we can make these changes and in that way, 
with a fair degree of accuracy, compare our health condi- 
tions with the conditions in other states. 
Comparison of Texas with Other States. We will begin 
by assuming that Texas has about the same annual death 116 
THE HUMAN BODY AND ITS ENEMIES 
rate as Indiana, or 13.5 per thousand living inhabitants. 
In order to make comparison easy, it is customary for all 
death rates to be calculated on a basis of so many per thou- 
sand inhabitants, or so many per hundred thousand inhab- 
itants. When this is done, it saves us the trouble of taking 
into account the number of inhabitants of each place. The 
following table shows the death rates of several states from 
some of the prevalent diseases. The figures from the 
United States as a whole are given in order to give us 
an idea of the average death rate over the entire country. 
The rates from Massachusetts are given because this is an 
old and thickly settled state and has an especially good set 
of health laws. The rate from Indiana is given because 
this state is largely agricultural, like Texas, and hence the 
conditions in the two states are more or less similar. 
The first column of figures in the table refers to the 
annual death rate per thousand of population; all the other 
columns refer to the annual death rate per hundred thou- 
sand of population. 
All 
Causes 
Typhoid 
Fever 
Tuber- 
culosis 
Measles 
Scarlet 
Fever 
Small- 
pox 
United States 
I5-° 
23-5 
139-7 
12.3 
11.6 
0.4 
Massachusetts 
16.1 
12.4 
137.6 
11.6 
8.0 
0.0 
Indiana 
13-5 
34-o 
144.9 
16.6 
7-5 
0.1 
Texas 
Paris, France 
13-5 
16.7 
48.3 
7.0 
136.1 
4.6 
1.9 
2.0 
From this table we learn that Texas makes a favorable 
showing so far as the more contagious diseases are con- 
cerned, but makes a very poor showing in the case of 
typhoid fever. In proportion to her population, Texas 
loses almost four times as many citizens from typhoid 
fever as Massachusetts, over twice as many as the United 
States as a whole, and over six times as many as Paris, 
France. KEEPING OUR ACCOUNTS 
117 
1. A good system of vital statistics is necessary as the first 
step toward intelligently attempting to improve the public 
health. 
2. Our Texas system is not perfect, but is very valuable, and 
we should make every effort to improve it. 
3. It can easily be seen that we have in Texas more than our 
share of typhoid fever. 
IMPORTANT POINTS 
QUESTIONS 
i. What are vital statistics? 2. Why do we keep accounts of 
births and deaths? 3. Have we valuable statistics of deaths in 
Texas? 4. Are they perfect? 5. Who should report deaths? 6. 
To whom should he report them? 7. Compare the death rate from 
typhoid fever in Texas with that in Massachusetts. 8. Compare 
the death rate from measles in Texas with that in Massachusetts or 
Indiana. 9. Consult the table of vital statistics, but do not memo- 
rize it. CHAPTER XXI. THE BODY A HOUSE 
OF MANY PARTS 
Up to this time you have learned of the microscopic 
bacteria which sometimes invade the body in countless 
swarms, and you have learned that some of them 
tend to destroy our health by the poisons they give 
Figure 7T. — Diagram of a section 
through the body to show the loca- 
tion of the principal organs. 
Figure 72. — Diagram show- 
ing the principal cavities of 
the body. 
off into the blood. It is truly wonderful how our 
bodies can defend themselves against their enemies, the 
germs of disease, in the ways described in the preceding 
pages. We shall now learn many other wonderful things 
that the various organs of the human body have to do. 
We shall study the physiology of the organs; that is, their A HOUSE OF MANY PARTS 
119 
functions or duties, and how these are performed. To 
understand their functions we must first learn the structure 
of the organs; this study is called anatomy. After we have 
learned the function and the structure of an organ or a 
system of organs, we shall be told how to keep the organs 
in a condition favorable for doing their duty properly. 
The last study is called hygiene, or the science of health. 
Review and Observation Work. Review Chapter I; 
draw an outline sketch of Figure 73, and in the drawing name 
the organs mentioned in the chapter. Secure a manikin, or 
model of the human body, and with the aid of this, study the 
organs. 
Organs. From the study of the figures you are led to 
conclude that an organ is a particular part of the body; and 
when you recall what you already know of the work of the 
organs, like the heart, you will come to the conclusion that 
each organ has a particular duty to perform. Thus, the 
heart is an organ that pumps blood. Mention some other 
organs and tell what you think their duties are. Now, 
define organ in your own words. 
The situation of the chief organs of the body may be 
learned by a study of Figures 71, 72, and 73. The word 
dorsal is the scientific term for the back and ventral for the 
front of the human body. Dorsal and ventral are also used 
in speaking of the corresponding regions of the bodies of 
animals. 
The brain and the spinal cord are seen to occupy the 
dorsal cavity. The ventral cavity is separated by a partition, 
called the diaphragm, into the thoracic and the abdominal 
cavities. Above this partition are the heart, which pumps 
the blood, and the lungs, with which we breathe. Below 
the diaphragm are the organs of digestion, the organs of 
excretion, and others. 
Finer Structure of the Organs. Each organ is composed 
of parts called tissues. There are different kinds of 120 
THE HUMAN BODY AND ITS ENEMIES 
tissues, and each kind has a particular work to do in the 
organ. Take, for example, a piece of beef. The soft red 
part is muscle tissue; it is the main tissue that goes to make 
up the organs called muscles. Its work is to contract and 
expand, and thus cause motion. 
Muscle tissue is very tender, however, and would not 
hold together by itself. The tissue that binds muscle 
Figure 73. — Ventral view of the principal 
organs in the thoracic and abdominal cavities. 
Figure 74. — Muscle 
attached to the bone. 
tissue together is tough and pliable, and is found in all 
muscles; it is called connective tissue. This may be seen 
as glistening white strands in beef or other lean meat. 
It also serves to bind muscles to bones and bones to each 
other. The sinews or leaders in the legs of deer were 
used by the Indians for bow-strings on account of their 
toughness, for they consist of connective tissue. In the 
muscle shown in Figure 74 the part at B consists mainly of 
connective tissue; at A, mainly of muscle tissue; at C, of 
about equal quantities of each. A HOUSE OF MANY PARTS 
121 
Other white strands often seen in a piece of meat are 
nerves, which consist of nerve tissue. Thus a muscle is 
an organ consisting of muscle tissue, connective tissue, 
nerve tissue, and other tissues not so easily seen. 
Observation Work. Secure a piece of soup meat or 
other tough meat from around a bone, and let several pupils 
each take a small piece and dissect it. To do this, lay the 
specimen on a board or an old newspaper and pick it to pieces 
with a knife or sharp sticks. How many kinds of tissue can 
you find? Let all the pupils see them. Describe the kinds 
of tissue that can readily be seen. 
Cells. Our study does not end here, however. With 
the unaided eye we cannot find out anything more about 
Figure 75.—Different kinds of cells: A and B, muscle cells; C, fat cells; 
D, connective tissue cells; E and F, epithelial cells; e, a single cell; a, end 
view of flat cells. 
the tissues; but with the aid of the microscope men have 
been able to discover that the tissues are themselves com- 
posed of very tiny parts called cells. A number of cells 
are shown in Figure 75. Muscle cells are long and slender. 
One kind of muscle cell, shown at A, Figure 75, is very 
long and extremely slender; the other kind is spindle- 
shaped and shorter (B). A very long cell, like a muscle 
cell, is often called a fiber. Connective tissue consists of 
long fiberlike strands and scattered rounded cells (D). 
A collection of connective tissue cells filled with fat, as at 
C, is called fatty tissue. 122 
THE HUMAN BODY AND ITS ENEMIES 
Epithelial tissue is another important kind of tissue. 
In this the cells are shaped rather like grains of rice or 
corn, or are flat and thin like shingles. They stand or lie 
side by side, like the bricks of a pavement, and cover 
surfaces. For this reason the tissue is sometimes called 
pavement tissue. The skin consists of connective tissue 
covered over with epithelial tissue. Flat cells, like those 
pictured at F, can be scraped from the lining of the cheek 
and studied under the microscope. 
Observation Work. To get an idea of what a fiber looks 
like, take a sheet of good smooth writing paper. Tear off a 
corner and examine the torn edge, holding it between the eye 
and the light. The frazzled edge shows tiny fibers similar to 
the fibers of muscle and connective tissue^ 
Again, if each tiny cell is studied carefully under the 
microscope, it is found to consist of definite parts. These 
parts are (i) the body of the cell, and within 
that (2) a denser portion, the nucleus, as shown 
in Figure 76. 
The body is thus a colony of cells and may be 
compared to a brick building made up of an 
immense number of individual bricks. Just as 
from a distance we cannot distinguish the indi- 
vidual bricks of a house, so also we cannot 
distinguish the cells of the body, until we examine its 
tissues with the aid of a microscope. Without this instru- 
ment we should still be ignorant of much that we now 
know of the wonderful structure and work of our bodies. 
Figure 76.— 
A cell, show- 
ing nucleus. 
SUMMARY 
The body consists of myriads of tiny cells that cannot be 
seen without the aid of a microscope. Cells are of different 
kinds; a collection of similar cells is called a tissue. Tissues 
are combined to form organs. Each tissue has a particular 
duty to perform in the organ: muscle tissue to contract and A HOUSE OF MANY PARTS 
123 
expand and thus move the body, connective tissue to bind parts 
together, epithelial tissue to cover surfaces. Other kinds of 
tissues will be studied in later chapters. 
QUESTIONS 
i. When I say, “The heart pumps blood,” does the statement 
concern the physiology or the anatomy of the heart? 2. What is 
meant by Physiology? 3. Anatomy? 4. Hygiene? 5. Sanita- 
tion? 6. What is an organ? 7. Name the cavities of the body. 
8. Name and locate the important organs of the body shown in 
Figures 71 and 73. 9. Tell how the microscope has been of service 
to mankind. 10. Describe muscle tissue; connective tissue; a 
cell. 11. Draw pictures of several kinds of cells. CHAPTER XXII. WHY WE EAT 
All Animals Need Food. Have you ever observed a 
mother bird feeding her little ones in her nest? How wide 
the young birds open their hungry mouths while the de- 
voted mother brings one worm, insect, or seed after another 
to appease their appetites! All animals must have food. 
You who eat your daily meals with regularity have perhaps 
not thought of the way animals have to struggle for a 
living. Consider how the following animals secure their 
food: cats, wolves, deer, fish, birds, spiders, boll weevils, 
mosquitoes, bees, owls. Discuss them in class. 
A large part of an animal’s time is spent in securing food. 
The same is true of man. In order that you may eat, the 
food for you is secured by your parents or guardians. They 
supply you with food while you are in school in order that 
you may learn useful things, which will better enable you 
later to earn your bread for yourself. A reference to your 
textbook of geography will show you what a large part 
of man’s time is spent in raising, distributing, and selling 
plants and animals for food. 
Why we Need Food. When asked why we need food, 
different persons give different answers. “To nourish the 
body,” “To give us strength,” “To keep us alive,” are 
among the answers often given. Perhaps we may find more 
simple answers to the question why we eat. 
If, in the first place, you consider that you must feed 
your horse more when he works than when he is idle 
and that you are usually hungry after vigorous exercise, 
you must come to the conclusion that food has something 
to do with our power to work. We may answer the ques- 
tion why we eat by saying first, that food furnishes us with 
energy for work. 
You have also noticed another thing about the living 
body; namely, that it is always warm. Food is used up 
in the body all the time. It is the source of heat as well 
as of energy for work in the body. We need food, in the 
second place, for warmth. 
124 WHY WE EAT 
125 
To make clear just how food furnishes us energy and heat, 
the body has been compared to an engine. Let us take for 
example a steam engine, under the boiler of which wood is 
burned to get up steam. It is plain that the energy that 
makes the engine run comes from the wood that is burned 
under the boiler. Before we explain just what happens to 
the wood when it burns, it will be well for you to perform 
the following experiment: 
Experiment with Carbon. You have all seen carbon in 
the form of charcoal or of coal. You are also acquainted with 
it in the form of graphite, the so-called lead of your pencil. Strike 
a match and let it burn until it is well scorched. The black 
you now see is carbon that has separated out from the wood and 
that has not yet burned. Now light another match and let it 
burn. Note that it becomes smaller and smaller; the match is 
being used up. Note the current of air passing off from the 
flame. Something is passing off from the burning match into 
the air. In burning, then, the fuel is used up and matter is 
given off into the air. Strike a third match and hold it in a 
small bottle. It will soon go out for want of air. 
In the process of burning, as was noted in the experi- 
ment just performed, two things are needed: fuel and air. 
In the case of the fire under the boiler of the engine, fuel 
and a draft of air into the furnace of the boiler are both 
necessary for the fire. Now, air contains a gas called 
oxygen (O). It is this oxygen that takes part in the burn- 
ing. It does so by uniting with the carbon (C) of the fuel 
and forming a new substance, carbon dioxid (C02). This is 
also a gas, and passes off into the air with the smoke. 
Burning is, therefore, sometimes spoken of as oxidation. 
Oxidation results in forming carbon dioxid as a waste 
substance and, most important of all, in giving off heat 
in the process. 
The same thing happens in the body-engine. Food is 
the fuel of the body. Oxygen is taken from the air we 
breathe. Oxidation of the foods takes place in the tissues 126 
THE HUMAN BODY AND ITS ENEMIES 
of the body. By this process heat is produced and the 
body does work. Wastes are also produced, especially 
carbon dioxid. This gas is given off into the air breathed 
out by the lungs. 
Can you tell why you must breathe faster when you 
exercise? Can you tell why you grow warmer from such 
exercise? It is plain, then, that we must eat that our bodies 
may be supplied with energy for work and with heat to keep 
them warm. 
We also need food for other reasons. Consider that the 
nestling bird is small and featherless, the puppy is not 
nearly so large as the grown dog, and you are not as large 
as you expect to be. Young animals and boys and girls 
eat to grow. Not all the food is oxidized in the body, for 
some of it must be changed into flesh and blood and added 
to the growing body. In this respect the body differs 
from an engine made of iron and steel. 
Our bodies differ from an engine in another respect. The 
engine cannot repair itself. If a part breaks or wears out, 
a new part must be supplied. Every part of the body is 
constantly wearing out, but the body repairs itself. In 
case of injury to the skin, new skin soon covers the wound. 
If a bone is broken, the pieces will grow together again. 
Hair and nails and skin, are continually growing to take 
the place of cells worn off. We need food, therefore, to 
repair worn-out parts of the body. 
How Plants Serve Man. Plants are living things just 
as animals are, and they, too, need food. Plants, however, 
manufacture their food themselves out of mineral sub- 
stances; whereas animals and man must make use of the 
starch and other substances prepared for them by the 
plants. 
SUMMARY 
Green plants manufacture foods for animals and man. This 
food furnishes energy, enabling us to move about in work and 
play and keeping our bodies warm. The food containing car- WHY WE EAT 
127 
bon will burn like wood or coal by uniting with oxygen from the 
air. Food also furnishes material for growth and for the repair 
of injured or worn-out parts of the body. 
i. Make a list of the names of animals and place opposite each 
the name of the chief kind of food the animal lives on. 2. Name 
four reasons why we need food. 3. Do we need more food in winter 
or in summer? 4. Why do we need more food when we exercise 
than when we rest? 5. What kind of substance is carbon? 6. 
Name some substances that contain carbon. 7. What is the use 
of carbon in our foods? 8. What part do plants play in nature? 
QUESTIONS CHAPTER XXIII. WHAT WE EAT 
All animals depend directly or indirectly upon green 
plants for food. Most animals live upon plants directly, 
as cattle, potato beetles, and plant lice. (Mention five 
others.) Some animals prey upon other animals, as wolves 
upon sheep and cats upon mice; but in each case the prey 
gets its food from green plants, and so the wolf and the 
cat are dependent indirectly upon plants. Man eats both 
plant and animal food. Do you know of animals that do 
the same? Consulting your geographies, make a list of 
five important animals used by man for food, and ten 
important plants. Tell where each of these is raised. 
Make a list of twenty-five food products that you can 
buy at the grocery store. These studies will show you that 
there are many kinds of food. Even the same animal may 
produce various kinds; cattle, for instance, furnish meat, 
milk, and cheese. All food of man, therefore, comes from 
living things. 
All these kinds of food are really made up of five 
classes of food substances. That is, all the foods placed 
on the table before us to eat, or that we feed to our domestic 
animals, are mixtures of these classes: carbohydrates, fats, 
proteins, mineral salts, and water. These five classes of 
substances are called the foodstuffs. 
The Carbohydrates. The carbohydrates include starch 
and the sugars. They come almost altogether from 
plants and are the cheapest of the foodstuffs. Starch is 
found in large quantities in most seeds, such as corn, rice, 
wheat, beans, and peas; in the stem of the sago palm 
(sago); in roots and underground stems of manioc (tapioca), 
in the tubers of the sweet potato and the Irish potato. 
Sugars are of different kinds: cane sugar, secured from sugar 
cane and sugar beet; and glucose or grape sugar, found 
naturally in grapes and other fruits, but also manufac- 
tured from cornstarch in large quantities. Cane sirup 
(molasses) and corn sirup contain chiefly sugar and 
water. Honey and the sap of maple trees are also sources 
128 WHAT WE EAT 
129 
of sugar. Sweet corn and milk and most fruits contain 
some sugar. 
Experiment with Starch. One can easily find out whether 
a substance contains starch or not. Iodin turns starch blue. 
Make a thin starch paste by boiling a little starch in water. 
Add one drop of tincture of iodin (to be secured from any drug 
store) to a little starch paste in a test-tube or a small bottle. 
Try this on crumbs of bread shaken up in water. Place a drop 
of the solution on a cooked potato; on a raw potato; on an 
apple, or on any other food you want to test for starch. 
Experiment with Sugar. If food is sweet, it contains 
either cane sugar or glucose. The latter is easily found if 
present, because it causes a red color to appear when heated 
with Fehling’s solution. Fehling’s solution is a mixture of two 
Figure 77. — Showing two methods of heating liquids, 
solutions: A, a solution of bluestone, and B, a solution of caus- 
tic soda. The solutions should be kept separate until they are 
used. They can be secured at the drug store and should be 
fresh. Glucose is found in corn sirup and cheap stick candy. 
Dissolve some of either in water. When ready to make the 
test, make up a quantity of Fehling’s solution, by using equal 
parts of A and B. Pour the mixed solution into a test-tube to 
the depth of an inch. Bring it to a boil, using an alcohol lamp 
and applying the flame to the top of the liquid, as shown in 
Figure 77. Now add about fifteen drops of a solution of stick 
candy. The red color which will appear indicates glucose; 
for cane sugar will not cause the red color. Try this also 
on cheap cakes, to find out what kind of sugar was used in their 
manufacture. 
Experiment to Show how Glucose is Made from Starch. 
Add ten drops of ten per cent hydrochloric acid to thin starch 130 
THE HUMAN BODY AND ITS ENEMIES 
paste in a test-tube (to the depth of one inch) and heat it for ten 
or fifteen minutes. Note that the liquid becomes clear. Test 
for sugar as in the last experiment. The acid has turned the 
starch into glucose. 
Some Foods Rich in Fat. Animals produce fats in their 
bodies. Meat, therefore, contains more or less fat, such as 
tallow and lard. The cream of milk is fat; cheese, being 
made from milk, contains much fat. Nuts are usually 
rich in fat, as are also the seeds of the cotton plant and 
peanut and the fruit of the olive. There is not much 
oil in grain, but corn contains more than the other grains. 
A fat that is liquid at ordinary temperatures is called an 
oil. Thus cottonseed oil is an oil; tallow is a fat. 
Some Foods Rich in Proteins. A few plants furnish 
food rich in protein, as for example peas, beans, and pea- 
nuts. Among the common grains, wheat contains the 
most protein, rice the least. The chief source of protein, 
however, is animal foods. The white of an egg, called 
albumen, is almost pure protein, as are also lean meat and 
the curd of milk. 
Experiment with Protein. Shake up a very little white 
of egg in a test-tube with about twenty drops of wrater. Add 
ten drops of concentrated nitric acid and warm the mixture 
over an alcohol flame. A yellow color appears. Add ammonia 
until effervescence ceases. The orange color that appears indi- 
cates the presence of protein, — in this case, the white of egg. 
Try this on bread crumbs or other food. 
Observations on Grains of Rice, Wheat, and Corn. 
Soak in water for twenty-four hours enough grains of rice, 
wheat, and Indian corn to supply one or two of each kind to each 
pupil in the class. If needed at once, the seed may be boiled 
for a short time. Note the germ or embryo (E) as shown in 
the outline sketches in Figure 78. With a sharp knife cut the 
grain lengthwise through the germs along the straight lines 
indicated in the drawings. Study the cut side; make out 
the germ in the corner and the protein and starch portions WHAT WE EAT 
131 
of the grain. The starch will be found white and softer than 
the more shiny and horny protein portion of the seed. What 
kind of corn is it more profitable to raise, corn with seeds rich 
in starch or corn with seeds rich in protein? 
Figure 78. — Sections through seeds of rice (I), wheat (II), and corn 
(III), showing the protein (P) and the starch (S) of the seeds, and their 
germ (E); 1,2, and 3, the seeds as seen from the outside, natural size. 
Mineral Salts. All our food, even most drinking 
water, contains mineral salts. If we eat a variety of food 
we get all the mineral salts we need, except table salt, 
without adding them to the food in cooking. 
Experiment. To show that foods contain mineral matter, 
take a piece of bread or meat, place it on a piece of tin, or 
Figure 79. — When bread or other food is burned the ash or mineral part 
of the food is left. 
better, in an iron spoon (Fig. 79), and burn it over a fire. Ex- 
amine the ashes. They are the mineral matter in the food. 132 
THE HUMAN BODY AND ITS ENEMIES 
Water. From one standpoint oxygen is the greatest 
need of the body, for we could live only a few minutes 
without breathing. Water comes next in importance; 
for while we may be able to live for forty days or more 
without food other than water, we cannot live much more 
than one fourth as long without water. Almost three 
fourths of the body is water. We not only drink water, 
but we get a great deal of it in our food. Over eighty 
per cent of potatoes, for example, and fifty per cent of beef 
consists of water. 
Experiment. Weigh an apple or a potato. Then chop it 
up and dry it with slow, gentle heat. Now weigh it again and 
calculate the per cent of water in the food. 
Uses of the Foodstuffs in the Body. In the last chapter 
it was stated that foods (i) furnish energy for heat and 
work and (2) furnish material for growth and repair. All 
the foodstuffs, except water and mineral salts, serve the 
first purpose, because they have carbon that burns up in 
the body.1 The carbohydrates and fats can serve only to 
produce heat and energy and are therefore called the 
fuel foods. Proteins can serve this purpose also; but in 
addition to this they build up the body and repair the 
tissues. The proteins are therefore the only building 
foods. Some mineral salts help to build up the body to 
some extent, as lime to help form bone; but they are 
chiefly needed to keep all parts of the body in good working 
condition. 
There are many kinds of food that serve for man and beast 
the world over, some derived from plants and some from 
animals. These contain only five classes of foodstuffs: carbo- 
hydrates (sugars and starch), fats, proteins, mineral salts, and 
SUMMARY 
1 You may easily prove that there is carbon in protein and in starch 
and sugar by scorching them (in frying an egg or baking bread, for ex- 
ample). The black substance is carbon. WHAT WE EAT 
133 
water. Carbohydrates and fats are called the fuel foods, since 
they serve only to be oxidized or burned in the body for the 
production of heat and energy. Fats are the best heat-pro- 
ducing foodstuffs. Proteins also are of use as a fuel food, but 
in addition they build up the tissues, being used in the body 
for growth and repair. Certain mineral salts and water must 
also be taken with the food for the maintenance of health. 
QUESTIONS 
i. Mention ten common foods. 2. Mention the main foodstuffs. 
3. Are animal or vegetable foods the richer in carbohydrates? 4. 
Mention four foods rich in fats; six rich in protein; eight rich in 
carbohydrates. 5. How can you test a food to find out if it contains 
starch? 6. What is the test for protein? 7. Which foodstuff is 
the only tissue builder? 8. Why can all the foodstuffs furnish work- 
ing energy and heat? 9. Which is the best fuel food? 10. Mention 
some important mineral salts, n. How can you prove the presence 
of mineral in food? CHAPTER XXIV. PURE FOOD 
To select foods wisely we should remember several 
important things: what foodstuffs the foods contain, for 
whom they are intended, how to get the greatest food value 
at least expense, and we should see that all foods are free 
from disease germs. 
A Mixed Diet. Every one knows that a person cannot 
live on eggs alone, and you now know that the reason is 
that eggs do not contain carbohydrates. All of you like 
Figure 80. — Refrigerator: food should be 
kept cold to prevent decay. 
candy; but you would soon grow tired of candy if you had 
nothing else to eat, and would ask for plain bread and 
butter and meat. It is not a good plan to live on any one 
kind of food. We need a mixed diet. As a rule, we need 
nine times as much carbohydrates as fats and twice as 
much protein as fats. 
Starch and sugar are useful to furnish working energy 
and warmth. They should make up the bulk of what we 
eat. Protein is especially useful for building up our bodies, 
and growing children need plenty of protein food. One 
134 PURE FOOD 
who is recovering from an illness needs much protein. 
Of fats we should eat more in cold weather than in warm, 
for the reason that fats are the best fuel foods. 
Eating Habits. It is important for the health that one 
should eat regularly. Although eating between meals is a 
bad practise, a sandwich or the like on returning home from 
school may be permitted. Too often candy is indulged in 
between meals. Candy is harmless in moderate quan- 
tities, but it should be eaten at the end of the regular 
meal. Colored candy, however, is harmful in many cases. 
A warning is also needed in the matter of school lunches. 
Many children buy candies and pastry instead of providing 
themselves with lunches consisting of good food. School 
lunches, as indeed all meals, should be eaten slowly and 
the food well chewed; children should not rush out on 
the playground and engage in violent exercise immediately 
after the meal. 
The Cost of Foods. The foods that cost least per pound 
are not necessarily the cheapest; thus corn meal is cheaper 
than wheat flour, but it contains less protein. The costliest 
is not always the best, for oysters are costlier but have less 
food value than either cheese or round steak. In pur- 
chasing food, we must take into consideration the quan- 
tity and proportion of the foodstuffs as well as the price 
per pound. Peas and beans are very cheap and nutri- 
tious articles of food. It is necessary also to take into 
consideration the individual tastes in the matter of select- 
ing foods, as foods must be appetizing and must agree 
with a person to be of the greatest value. 
Buying Food in the Market. The best way to buy food 
is to make a personal visit to the market. In this way one 
can secure the best of any kind of food and can find things 
that he would otherwise not think of. In buying always 
say, “Let me see it first.” 
If you are too busy to go to market and must order the 
food over the telephone, always inspect it as soon as it is 
135  THE HUMAN BODY AND ITS ENEMIES 
136 
received and return that which is not fresh and good. 
The market man will furnish just as good food as we ask 
Figure 81. — Cooking is so important that the subject is taught 
in many schools. 
for. There is plenty of good food material to be had in 
Texas, and if our housekeepers pay attention to the food 
as it is bought, they can get good food. In buying fish and 
meats especially, great care is necessary; also in buying 
fruits and vegetables. Think of the number of over-ripe 
tomatoes that are placed on the table in Texas in the 
course of a year. The only way to avoid this is by looking 
Figure 82. — The cuts of beef: x, neck; 2, 
chuck; 3, ribs; 4, shoulder clod; 5, fore 
shank; 6, brisket; 7, cross ribs; 8, plate; 
9, navel; 10, loin; 11, flank; 12, rump; 13, 
round; 14, second cut round; 15, hind shank. 
at the tomatoes closely, and this should be done at the 
time they are bought. Those who are interested in mar- PURE FOOD 
137 
keting may learn the names of the cuts of beef from the 
numbered diagram (Fig. 82). 
Canned Goods. Canned fish and canned meats are 
dangerous, because a pinhole in the can, too small to be 
seen, may allow germs to get in and cause the decay of 
the meat. Canned vegetables are not dangerous as a rule 
but canned fish and canned meats are always subject to 
suspicion. A young man in Austin ate some canned 
salmon at three o’clock one afternoon and died of ptomain 
poisoning the next morning. Many people are thus made 
sick but do not die. Sometimes canned goods in putrefy- 
ing form a gas which presses out the top and bottom of 
Figure 83.—Swell head. Bacteria sometimes 
cause decay of canned foods, especially meats; 
the can may “swell” from gases on the inside. 
the can, causing what is known as swell head (Fig. 83).. 
It is unnecessary to say that such a can should be strictly 
avoided. 
We should likewise reject old rusty cans. On opening 
the can, see if it is rusted on the inside; also taste and 
smell the contents and make sure that they have not 
begun to decay. Canned vegetables are more of a neces- 
sity in the North than they are here. Texas needs some 
progressive men to develop the various vegetable indus- 
tries, just as the onion industry has been developed in and 
around Laredo. 
Ptomain Poisoning. Through ignorance and careless- 
ness in selecting food, more serious consequences may result 
than mere loss of food. We sometimes poison people by- 138 
THE HUMAN BODY AND ITS ENEMIES 
giving them poisoned food. Have you not heard of the 
dreadful ptomain poisoning which kills so many people, 
especially after they have eaten fish? Many cases of 
ptomain poisoning could have been prevented by a little 
care in inspecting the fish when it was bought. Many of 
you may say that you do not know how to tell good fish or 
meat when you see it. But if you try, you will find that 
you can do so. There is a fresh fishy odor about all fresh 
fish, but there is a putrid odor, an odor of decay, which 
comes from decaying fish. 
Another source of poisoning is ice-cream. When once 
allowed to melt, ice-cream should never be refrozen. 
Cooking. Most foods are improved by cooking (baking, 
boiling, broiling, stewing, etc.) for the following reasons: 
Figure 84. — A 
trichina from a 
muscle. 
Figure 85. — Portions of a tapeworm with 
its “head” enlarged. 
i. Heat may destroy the bacteria. Bacteria you know 
are likely to be present in food, but heat does not always 
destroy the poisons or toxins formed by bacteria in decayed 
or decaying food. Heat also destroys certain worm para- 
sites, like trichina in pork (Fig. 84), or tapeworm larvae in 
pork and beef (Fig. 85). PURE FOOD 
2. Cooking makes most foods more appetizing. Appetiz- 
ing appearance and pleasant flavor in foods are important 
aids to digestion. 
3. Cooking usually renders foods more easily digestible. 
In the case of vegetable foods we find that the plant cells 
have very thick and indigestible walls, and that the starch 
and protein grains (Fig. 86) have tough skins around 
them. Heat breaks up the starch grains and the plant 
cells (Fig. 86), so that the digestive juices can get to the 
food material. In the case of meats, heat causes the con- 
nective tissue to swell and soften, thus making it easy for 
the muscle tissue to be broken apart. 
It should be remembered that heat hardens such pro- 
teins as muscle tissue and the white of eggs and makes 
139 
Figure 86. — Uncooked and cooked potato cells, magnified. 
them harder to digest. White of eggs is more easily 
digested soft boiled than hard boiled. It is important to 
note that grease renders foods less digestible. Frying in 
grease is the worst way to cook. The grease soaks into 
the mass of the food, covering the minute particles so that 
these become very hard to digest. 
Milk as a Food. Milk is one of the most nourishing of 
all foods. Cow’s milk is the milk commonly sold on the 
market, and it forms an especially large part of the food of 
young children, old people, and invalids. When intended 
for babies under two years old, milk should be prepared 140 
THE HUMAN BODY AND ITS ENEMIES 
by adding certain foodstuffs to it to make the proportions 
exactly right; that is, the same as those of human milk. 
This should be done under the advice of a physician. 
Babies usually do better on cow’s milk than on patented 
baby foods when these are fed alone. Since, then, milk is 
so important as a food, we ought to see to it that our milk 
supply is clean and pure. 
Bacteria in Milk. Because milk is very nourishing, 
bacteria will thrive and multiply in it. There are still a 
few dishonest people who add preservatives to milk; but 
the most dangerous things we find in the milk are the 
Figure 87. — This cow, though healthy in appearance, was 
found to have tuberculosis. 
harmful bacteria. More epidemics of disease have been 
spread by milk than by any other food. Hundreds of 
different outbreaks of disease have been definitely traced 
to germs scattered in milk. Most of these epidemics were 
of typhoid fever, but scarlet fever and diphtheria also 
have occurred in epidemic form because of the presence of 
disease germs in milk. Milk is especially connected with 
tuberculosis, because cattle are affected by that disease, 
and tuberculosis is one of the commonest diseases in the 
world. In view of these facts it is well to learn how milk 
can be kept free from dangerous germs. PURE FOOD 
How to Get Clean Milk: the Cow. First, the cow her- 
self must be healthy. In many states, one fourth of all 
milch cows are affected with tuberculosis. In Texas, 
however, the tests made by the Dairy and Food Com- 
missioner show that only one cow in about one hundred 
is affected. Children can contract bone and gland tuber- 
culosis from germs in milk, and hence they should never 
drink milk from cows that have not been tested and found 
to be free from tuberculosis. The most healthy-looking 
cow may have the disease. Figure 87 shows a cow in 
apparently good condition, but when tested she was found 
to have tuberculosis. 
141 
Figure 88. — A bad and a good kind of milk pail. 
Milking. In milking we should do all we can to prevent 
bacteria, from getting into the milk. If carelessly handled, 
especially about the cowsheds, the milk contains swarms of 
bacteria at the very beginning. As harmless and harmful 
bacteria alike multiply in milk, it is important to keep them 
from getting into it. There are several important points 
to remember in milking: 
(i) No person who has had typhoid fever within twelve 
months should be allowed to handle the milk, unless a 
physician has made a test and pronounced the patient free 
from dangerous germs. A typhoid carrier infects the 
milk with his hands or by coughing over the milk bucket. 142 
THE HUMAN BODY AND ITS ENEMIES 
Every milker should wash his hands with soap and water 
before milking. , 
(2) Dust carries many bacteria into milk. To prevent 
this the cow’s udder should be washed before milking. A 
milk bucket with a small opening, as shown on the right of 
Figure 88, should be used. If the milk is intended for 
the baby, it is well to milk through a scalded cheesecloth 
stretched over the bucket. The cloth should be scalded 
before each using. It is, of course, needless to add that 
flies should be kept from wiping their feet on any of the 
milk vessels. 
Figure 89. — A home-made ice box for keeping 
milk cold and sweet. 
Care of the Milk. Germs will not grow and multiply 
rapidly in the cold. The warm milk from the cow should 
be cooled at once after straining and should be kept on 
ice. In case ample cooling facilities are not at hand, at 
least milk intended for the baby should be kept cold until 
it is to be used, when it can be quickly warmed. Figure 
89 shows a simple, inexpensive form of home-made ice box. 
The milk room should be screened and free from flies. 
Dairy Inspection. When a person has his own cattle, 
it is a comparatively simple matter to have everything 
connected with the care of the milk clean and sanitary. 
Those who get their milk from a dairy, however, find it 
hard to get absolutely clean milk. It is well to patronize PURE FOOD 
a dairy that you know is sanitary, and it is well to pay the 
dairy an occasional visit. Every one should try to secure 
proper laws for the regulation of the milk supply and to 
see to it that these laws are enforced. 
Remember particularly the following points: 
1. Care should be taken in the selection of food. In plan- 
ning a meal we should select a variety of foods so that all of 
the foodstuffs are represented. 
2. Canned goods should be examined carefully before using, 
for they occasionally contain poisonous germs. 
3. Above all, we should select food free from disease germs. 
4. Cooking kills germs and makes many foods, particularly 
most vegetable foods, more digestible and more palatable. 
5. Milk is so important a food and so often contains danger- 
ous germs that every care should be taken to secure pure milk. 
6. Milk may be infected with dangerous germs from dust, 
from flies, and from the milker’s hands and throat. 
7. Milk should be drawn into a bucket covered with a 
scalded cheesecloth, and should be strained and put on ice at 
once. 
SUMMARY 
QUESTIONS 
i. What is meant by a mixed diet? 2. Select for a dinner five 
foods that will together constitute a mixed diet. 3. Why is it 
better to eat a sandwich and fruit for a school lunch than candy 
and pie? 4. Discuss the danger from canned foods. 5. What are 
the most harmful things that get into food? 6. State three 
advantages of cooking food. 7. What foods should be cooked long 
and at a high heat? 8. Why is milk an important food? 9. Why 
may milk be also a dangerous food? 10. What diseases are known 
to be scattered by infected milk? n. Why should milch cows be 
tested for disease? 12. Discuss fully how we can prevent bacteria 
from getting into milk. 13. Why should milk be kept cold? 14. 
How could you make a cheap ice box sufficiently large for keeping 
several bottles of milk? 15. What does Figure 86 illustrate? Figure 
87? CHAPTER XXV. THE MEANING OF DIGESTION 
The proper selection of food in the market and its prepa- 
ration in the kitchen are important; but the food is even 
then not ready for the blood. In the mouth, stomach, 
and intestines the food is changed very much. It is ground 
up, mixed with juices, and becomes liquid before the blood 
receives it to carry it to all parts of the body. The follow- 
ing experiments should be performed to illustrate the 
changes the food undergoes in the body: 
Preliminary Experiments, (i) Take two tumblers half 
full of water. In one place a lump of salt (table salt); into the 
other drop the same quantity of salt that has first been pow- 
dered by grinding in a mortar or with a hammer on a smooth 
board. In which tumbler does the salt dissolve faster, and 
why? To another tumbler add a little starch. Does this dis- 
solve like the salt? The salt is said to be soluble; the starch 
insoluble. 
(2) Procure three tumblers with water, a quantity of hy- 
drochloric (muriatic) acid, and three small pieces of lime- 
stone or marble about the size of a pea. Drop 
one piece of limestone into tumbler No. 1. To 
both the other tumblers add a few drops of acid. 
To tumbler No. 2 add a piece of marble in 
a lump; pound the other piece of marble to 
pieces and add them to tumbler No. 3. Tum- 
bler No. 1 has water and a lump of marble 
only. Tumbler No. 2 has water and a lump 
of marble with acid. Tumbler No. 3 has water 
and fragments of marble with acid. Now ob- 
serve the results. (Add more acid to Nos. 2 
and 3, if bubbling should cease before the lime- 
stone is dissolved.) 
Figure 90. — 
Limestone dis- 
solving in acid. 
Putting together the results of the foregoing experi- 
ments, we reach the following conclusions: 
1. That salt is soluble. 
2. That starch is insoluble. 
3. That limestone or marble is insoluble. 
144 THE MEANING OF DIGESTION 
145 
4. That acid will change limestone into a form that is 
soluble in water. 
5. That salt in small particles is more readily dissolved 
than when in lumps. 
6. That limestone is acted on more quickly when in small 
particles than when in a lump. 
Digestion Defined. Digestion of food in the body 
consists of changing it and rendering it soluble, so that it 
may be taken up by the blood. There are two sides to the 
digestive process: first the mechanical and second the 
chemical. The mechanical changes consist mainly of 
breaking up the food into small particles, and its purpose 
is, as noted in the experiments above (conclusion 6), to 
make the chemical changes take place faster. In the 
chemical changes the food is changed into entirely new 
substances, just as starch is changed to glucose by acid 
and heat. 
Mechanical Digestion. Mechanical digestion is per- 
formed mainly by the teeth, which in the process of chew- 
Figure 91. — Well chewed and poorly chewed 
food, magnified. 
ing cut, tear, and grind the food into very small particles 
(Fig. 91 A). Chewing the food is extremely important. 
To eat a meal in a hurry, swallowing the food in large 
lumps (Fig. 91 B), is injurious and may cause various ail- 
ments. If food is improperly chewed, it is likely to decay 
or sour before it can be fully digested. Chewing is also 146 
THE HUMAN BODY AND ITS ENEMIES 
good for the teeth, for unless they are used sufficiently 
they will decay. 
In the mouth the food is also moistened with saliva, 
which aids in swallowing. To show how hard it is to 
swallow dry food, crush a small cracker and try to swallow 
it quickly. Then try one that has been soaked in water. 
The movements of the stomach and intestine are also 
important parts of mechanical digestion. 
Chemical Digestion. When acid acts on limestone, it 
brings about a chemical change; the insoluble limestone 
is changed into a new substance which is soluble. Simi- 
larly, when starch is heated with an acid it is starch no 
longer, but is changed to glucose. In the body starch is 
not changed to sugar by strong acid or great heat, but by 
a certain substance in the saliva of the mouth and by 
another juice found in the intestines. The action of saliva 
on'starch is almost the same as that of acid and heat; 
saliva changes starch to sugar. Such a change is called 
a chemical change, and the process in the body is called 
chemical digestion. 
The active agents of The digestive juices that bring about 
chemical digestion are called enzymes. There are a number 
of enzymes in the mouth, stomach, and intestine, and 
each enzyme acts on a single kind of foodstuff. For ex- 
ample, amylase is the enzyme that changes starch to sugar. 
The most important enzymes are given in the table at the 
end of this chapter. The chemical digestion of starch by 
saliva can be studied in the following experiments: 
Experiments to Prove that Starch is Changed to Sugar 
by Saliva, (i) Taste a piece of clean wood; chew it a little. 
Has it a sweet taste? Take a piece of cracker soaked in water 
and note whether it has a sweet taste the moment it is taken into 
the mouth; or does it at first taste like wood? Chew it and 
note the result. Why does not the wood taste sweet just as 
the cracker does after it is chewed awhile? (2) Let one of the 
pupils chew half a cracker for a few minutes. Have a small THE MEANING OF DIGESTION 
147 
portion of the now nearly liquid contents of his mouth placed 
in a test-tube. Add Fehling’s solution and boil as in the exper- 
iment given elsewhere. The red color proves that a consider- 
able quantity of sugar is present. 
Starch must be changed to sugar before the blood can 
take it up. Proteins are changed to soluble substances, 
which we may call animal acids. Fats 
are also digested. The first step in the 
digestion of fats is similar to the making 
of soap. In making soap, fat and an alkali 
are put into a pot and boiled. In the 
human intestines there is an enzyme that 
digests fat by changing it, with the aid 
of an alkali from the glands, to a kind of 
soap. Glycerin is formed out of the fat 
in addition to the soap. 
Figure 92.— Oil glob- 
ules in milk. 
SUMMARY 
Digestion of food in the body consists of changing insol- 
uble into soluble foodstuffs: first, by the thorough chewing of 
the food, or mechanical digestion and next by chemical digestion 
due to the various juices called digestive juices: by means of 
which starch is changed to sugar, proteins to animal acids, 
and fats to soap and glycerin. 
The following table shows the juices and enzymes that act 
upon the different kinds of food, and the digestive organ in 
which the action takes place in the process of chemical digestion: 
Digestive Organs 
Juice 
Enzyme 
Digests 
Mouth 
Saliva 
Amylase 
Starch 
Stomach 
Gastric Juice 
| Pepsin 
1 (Rennin) 
Protein 
(Curdles Milk) 
Small Intestine 
[■ Pancreatic Juice 
1 Intestinal Juice 
[ Trypsin 
j Amylase 
L Lipase 
(Invertin) 
Protein 
Starch 
Fats 
(Cane Sugar) 148 
THE HUMAN BODY AND ITS ENEMIES 
• 
i. Define soluble; insoluble. 2. Mention several soluble and 
several insoluble substances. 3. What does Figure 90 illustrate? 
4. Describe an experiment illustrating digestion. 5. Define me- 
chanical digestion. 6. Describe an experiment that shows the 
value of chewing our food. 7. What is meant by a chemical change? 
Illustrate. 8. In the experiment with saliva, how can you prove 
that the starch has been changed to sugar? 9. Where are enzymes 
found, and what work do they do? 10. Name the digestive juices. 
11. How are fats digested? 12. Mention the foodstuffs that have 
to be digested, and tell into what each is changed in the processes of 
digestion. 
QUESTIONS CHAPTER XXVI. WHERE DIGESTION BEGINS 
The Mouth 
Where Digestion begins. The organs of digestion are 
the various parts of the food-tube 
or alimentary canal and the several 
organs called glands that commu- 
nicate with the alimentary canal. 
The food-tube begins at the mouth. 
The other organs can be seen in 
Figure 94. Draw Figure 94 on 
paper or on the blackboard, and 
after comparing it with Figure 73 
name the digestive organs on your 
drawing. 
The Mouth. Name the organs 
found in the mouth. What bounds 
the mouth on the sides? in front? 
The roof of the mouth is called the 
palate (Fig. 93); the hard palate, 
nearer the front, can be touched by 
the tongue pressed upward; the 
soft palate passes backward and 
ends in a flap called the uvula. 
The mouth communicates behind 
with the throat or pharynx and is 
partly separated from this by the 
soft palate. Stand before a mir- 
ror facing the light, and study in 
your mouth the organs shown in 
Figure 93. 
Mechanical Digestion. Before 
being swallowed, the food is me- 
chanically reduced to very small 
pieces. What organs in the mouth 
do this work? How is digestion 
hindered when food is swallowed in 
lumps? 
Figure 93. — The mouth 
cavity. 
Figure 94.— Outline of the 
principal digestive organs. 
(Compare with Figs. 71 and 
73-) 
149 150 
THE HUMAN BODY AND ITS ENEMIES 
Chemical Digestion in the Mouth. Review the chemical 
action of saliva on starch. The saliva is produced by three 
pairs of salivary glands, placed as shown in Figure 95. 
These glands empty their juice, the saliva, through open- 
ings on the inside of the cheek {DP) and under the tongue 
(DS). A further use of sa- 
liva is to moisten the food 
so that we may swallow it. 
Saliva also keeps the in- 
side of the mouth continu- 
ally moist. 
The tongue is a muscular 
organ attached behind to 
the tongue bone (Fig. 121). 
Chew a mouthful of food 
and note exactly how the 
tongue handles it. Place 
a little salt on the tip of 
your tongue; can you taste 
it without drawing back the 
tongue? What letters 
of the alphabet are made 
in speech mainly by the tongue? By the lips? By the 
teeth? State three functions of the tongue suggested by 
these questions. 
Figure 95. — The salivary glands 
of the left side. 
The Teeth 
Structure of a Tooth. A tooth is composed of a crown, 
a neck, and one or more roots. The crown is the only 
part of the tooth that is visible. It is covered with enamel, 
the hardest material in the body. This enamel protects 
the rest of the tooth. The roots stand in sockets in the 
jaw-bones (Figs. 96 and 97) and are covered with cement, 
a bony substance not so hard as enamel. Under enamel 
and cement is the bonelike dentine, which forms the bulk 
of the tooth. A cavity, the pulp-cavity, is the hollow in WHERE DIGESTION BEGINS 
151 
the middle of the tooth running up into the dentine. The 
pulp-cavity is filled with connective tissue, nerves, and 
blood vessels. The relation of these parts can be better 
understood by reference to Figure 96, or still better by 
studying a section of a real 
tooth as instructed in the 
next paragraph. 
Observation Work on a 
Tooth. Secure a molar tooth 
of a horse or a cow (as these 
are large) or ask a dentist for 
a human tooth. A tooth not 
too old and dry is to be pre- 
ferred. Have a blacksmith 
saw this in two with a hack 
saw. Then for a few minutes 
vigorously rub the surface of 
each half on a whetstone, using 
plenty of water. The two 
halves should now clearly show 
the parts of the tooth. 
Different Forms of Teeth 
and their Functions. The 
adult human being has thir- 
ty-two teeth. Figure 97 
gives the outlines of the teeth 
of one half of the upper and one half of the lower jaw. 
In each half-jaw there are two incisors, one canine, two 
pre-molars (bicuspids), and three molars. The incisors are 
flat and sharp; the canines are cone-shaped. These teeth 
are for biting and tearing the food. The bicuspids and 
the molars have wide surfaces for crushing and grinding 
the food and mixing it thoroughly with the saliva. 
The Two Sets of Teeth, Temporary and Permanent. 
Every person has in his lifetime two sets of teeth. Why is 
this? It is because the jaws in childhood are too small 
Figure 96.— Section of a tooth 
showing its parts. E, surface 
view of the enamel, highly mag- 
nified. 152 
THE HUMAN BODY AND ITS ENEMIES 
to hold the large teeth we need in later life; the first teeth 
must make room for the new teeth that push up under 
them. In early life, we have a set of twenty small temporary 
teeth (Fig. 98), five to each half-jaw. The first teeth of 
this set appear at about the age of six months, and the set 
is completed at about the age of two years. 
Figure 97. — The permanent teeth. A, the teeth 
in the lower jaw; B, upper and lower teeth of one 
side. 
Figure 98.— Child’s 
lower jaw with tem- 
porary teeth. (Com- 
pare with Fig. 97.) 
The First Permanent Molars. The earliest permanent 
teeth to appear are the first molars, which come behind 
the temporary molars about the sixth year. The perma- 
nent set is complete at the twelfth or thirteenth year of 
age, with the exception of the third molars, the so-called 
wisdom teeth, which appear about the eighteenth year or 
later. 
Observation Work and Experiments on the Teeth. 
With a mirror study the shape of each of your teeth and from 
their shape judge what is the function of each kind: whether 
cutting, tearing, or grinding. Imagine yourself biting off a 
piece of bread and note how the incisors of the lower jaw move 
over those of the upper. Observe how the jaw moves during 
this process. Now, note the cusps or points on the back 
teeth. Observe how the cusps of the upper and the lower 
back teeth fit into each other when the jaws are tightly closed. 
Move the jaw as if chewing. How does the lower jaw move WHERE DIGESTION BEGINS 
in the grinding, as compared with the biting, movement? You 
can now understand how the food is crushed and ground to 
pieces as the lower teeth slide across the upper. You can also 
understand how important it is that the teeth should be reg- 
ular, so that the upper and the lower shall fit together properly. 
Count your teeth. How many have you? Name each 
tooth. Look at the teeth of a boy or girl six or seven years 
old. If there are three double teeth on one side of the jaw, 
the back one is the first permanent molar. 
If possible, examine the incisors of a gnawing animal, as a 
rabbit, a squirrel or a mouse; the teeth of a dog or a cat; the 
molars of a horse or a cow. What is the relation of the shape 
of the teeth to flesh-eating or plant-eating habits of animals? 
Judging from his teeth, what kinds of food is it natural for man 
to eat? 
Importance of the First Permanent Molars. These 
teeth are so important that they have been called the 
keystone of the arch of the teeth. They should never 
be pulled or allowed to decay, for if they are missing, the 
jaws and other teeth cannot grow properly and the power 
of chewing properly will be lost. On account of the early 
appearance of the first permanent molars, parents fre- 
quently mistake these teeth for temporary teeth and 
allow them to decay, thinking that other teeth will come 
in their places. It is important, therefore, to learn to 
recognize these teeth when they appear. 
Importance of the First or Temporary Teeth. The firsts 
or temporary teeth, perform the same functions for the 
child that the permanent teeth perform for the adult, and 
it is important to care for them and to keep them sound 
until they are ready to be shed. If these little teeth decay 
and ache, the child suffers from toothache just as a grown 
person suffers. Besides, if the temporary teeth are ex- 
tracted before they are ready to be shed, the jaws contract 
or do not grow large enough to hold the next set of teeth, 
which will then come in crooked.  THE HUMAN BODY AND ITS ENEMIES 
154 
Causes of Irregular Teeth. The main cause of irregular 
teeth is the premature loss of the temporary teeth. Cer- 
tain habits of babyhood or childhood, such as sucking the 
thumb, biting the lips, or breathing through the mouth, 
may cause the upper teeth to protrude. If the teeth 
are not used enough in chewing good solid food, the 
teeth and jaws do not develop well, for they need exercise 
just as the arms do. If the teeth are not regular, they 
should be straightened. It is easier to do this when a 
person is young than later on in life. 
There are three reasons why a crooked set of teeth should 
be straightened: (i) They can do their work better, and 
when the teeth chew the food well, the whole body is 
more healthy. (2) The teeth do not decay so easily when 
they are regular. (3) Straight teeth improve one’s per- 
sonal appearance. 
The Unclean Mouth. Decay of the teeth is the com- 
monest disease in the world, and it is due to uncleanli- 
ness. The reasons for this statement are as follows: A 
tooth consists largely of limestone. From the experiment 
described on another page you learned that limestone is dis- 
solved by acids. Strong acids decay the teeth rapidly, 
and weak acids do so in time. Now, there are many 
bacteria in the mouth that live in food substances left 
there after eating. The bacteria form acids from the food. 
It is now thought that tartar, a dark, hard substance that 
collects on neglected teeth, is also caused by a germ. Decay 
often occurs under this tartar. When decay once begins, 
it spreads rapidly. Every decaying spot in a tooth 
should be repaired without delay. Indeed, it is a good 
plan to visit a dentist once or twice a year to have the 
teeth examined for any decay that may have started or 
for the removal of any tartar that may have formed on 
them. 
Other Diseases of the Teeth. Among other germ 
diseases of the unclean mouth may be mentioned inflamed WHERE DIGESTION BEGINS 
155 
gums, abscesses of the teeth, blood poisoning, and pyorrhea 
or Rigg’s disease. The last-mentioned is caused by pus- 
forming germs that lodge under the gums and around the 
roots under tartar or other hard deposits. The membranes 
of the roots and their bony sockets become infected, the 
teeth become loose, and pus flows from under the gums. 
This often causes foul odors to come from the mouth. 
Thorough cleanliness is a preventive of Rigg’s disease as 
well as of ottier diseases of the mouth and teeth. 
Effect on the Stomach. A further argument for mouth 
hygiene is the effect of germs on the stomach. Many of 
the germs in the mouth are swallowed and enter and infect 
the stomach. Furthermore, if the teeth are defective, a 
person will not chew his food well; the food is swallowed 
in large lumps and the stomach is burdened with addi- 
tional work. An unhealthy mouth is sure, sooner or later, 
to result in an unhealthy stomach. Poorly chewed and 
poorly digested food are both likely to decay in the stom- 
ach and intestines. When the products of such decay 
are absorbed by the blood, they cause general harm to 
the body and indirectly affect the teeth, causing early 
decay. 
Care of the Mouth and Teeth. It is, of course, important 
that the enamel should be preserved from mechanical 
injury. Such injury is likely to result from biting a hard 
object, such as a nut, or from picking the teeth with a hard 
instrument, such as a knife or a pin. The enamel is not one 
solid piece, but it consists of thousands of six-sided prism- 
shaped pieces set close together, like the bricks of a pave- 
ment. The prisms are shown in surface view at E, Figure 
96. If some of these prisms are broken, others will break 
soon after. Extremely hot or cold food or drink should 
be avoided, because rapid changes of temperature are likely 
to crack the enamel. 
The secret of mouth hygiene, however, is cleanliness, — 
the avoidance of germs in the mouth. The best way to 156 
THE HUMAN BODY AND ITS ENEMIES 
avoid germs is to remove their food, the remnants of the 
meals that are left in the mouth. 
Brushing the Teeth. The things most needed to clean 
the teeth are a tooth-brush of suitable size and shape, waxed 
dental floss or silk floss, a tooth powder, and pure soap 
and water. The brush should be moderately stiff. If the 
gums bleed from brushing, it shows that the mouth has 
been neglected. As you persist in the regular use of 
the brush, the gums will become hard, firm, and healthy. 
The brushing of the gums promotes circulation and pre- 
vents them from becoming soft or spongy. 
In brushing the teeth the brush should be moved up and 
down on the gums and teeth, on the inside as well as on the 
outside. This allows the bristles to pass between the teeth 
to remove food particles lodged there. After this, the teeth 
should be brushed crosswise. After the teeth have been 
brushed, the top of the tongue should be brushed as far 
back as possible. The teeth and tongue should be well 
brushed before breakfast and after each meal. 
Precipitated chalk is a good tooth powder for occasional 
use and is useful as a polisher. Waxed silk floss is better 
for cleaning between the teeth than toothpicks and should 
be used after each meal. 
SUMMARY 
In the mouth starch is partly digested by the amylase of 
the saliva. The mechanical work of tearing and grinding the 
food is still more important, for this prepares the food for 
all the chemical changes in the process of digestion. The 
teeth are so important as organs of mechanical digestion that no 
pains should be spared to preserve them. The teeth can be pre- 
served only by strict cleanliness, and especially by the removal 
of remnants of food left in the mouth after meals; for decay is 
brought about by the agency of acid forming bacteria living on 
food remaining in the mouth. All defects of the teeth, such 
as decay and irregularities, should be promptly corrected 
by the dentist. WHERE DIGESTION BEGINS 
157 
QUESTIONS 
i. Name and locate the digestive organs. 2. Mention the organs 
that can be seen by looking into the open mouth. 3. Describe 
the process of digestion in the mouth. 4. What are the uses of the 
tongue? 5. Locate the salivary glands and tell where the duct of 
each opens in the mouth. 6. Describe the structure of a tooth from 
an outline figure placed on the blackboard. 7. Point out the dif- 
ferent kinds of teeth in the mouth. 8. Why are the first permanent 
molars important? 9. Give reasons why the temporary teeth should 
be preserved. 10. Name causes of irregular teeth, n. What 
causes the decay of teeth? 12. State the harmful effects of the 
unclean mouth. 13. Describe fully how to clean the teeth. CHAPTER XXVII. OTHER DIGESTIVE ORGANS 
The Gullet, Stomach, and Intestines 
As the food is swallowed, it passes through the pharynx 
or throat (Fig. 121) into the gullet or esophagus. This 
organ is nearly straight and leads directly to the stomach. 
The stomach has a greater diameter than the other parts 
of the alimentary canal and its walls are thicker. Joining 
the stomach at its lower end is the small intestine. This 
is by far the longest part of the canal, measuring from 
twenty to thirty feet in length. This length necessitates 
its being coiled up in the abdominal cavity. The small 
intestine joins the large intestine in such a way as to 
leave a blind sac (13, Fig. 93). To this is attached the 
vermiform appendix (14), a useless organ. When this 
becomes diseased, the patient is said to have appendicitis. 
Thus from the throat downward the alimentary canal 
is a hollow tube having muscular walls and lined with 
smooth epithelial tissue called mucous membrane. This is 
only one cell thick in the stomach and intestine (A, Figs. 
108 and 109) but it is much thicker in the mouth and 
gullet. It is red from the presence of much blood so close 
to the surface. 
The Gullet. The gullet is the passageway by which the 
food passes from the throat to the stomach. Liquid food 
passes down the gullet very quickly, but solid food is forced 
down by a movement of the muscles of which the wall of the 
gullet is largely composed. These muscles are in two layers. 
In the outer, thinner layer the muscles run lengthwise; in 
the inner, thicker layer they run in rings around the 
canal as shown in the upper portion of Figure 102. These 
ring muscles successively contract behind each lump of 
food, so that a wavelike motion passes along the canal, 
pushing the food before it. This can be seen by observing 
the throat of a horse drinking water. The waves running 
along the neck of the horse indicate the passage of each 
swallow of water down the gullet (Fig. 99). This wave- 
158 STOMACH AND INTESTINES 
like motion is called peristalsis, and it is made by the 
intestines and part of the stomach as well as by the 
gullet. The action of a ring muscle may be further illus- 
trated by puckering up the mouth as in the act of whistling, 
Figure 99. — Ring muscles carry swallows 
of water up the horse’s throat. 
for there is just such a muscle around the mouth. Such 
ring muscles, controlling openings, are called sphincter 
muscles. 
The gullet is not very likely to become injured or diseased. 
The commonest disease of the gullet is scarring from con- 
centrated lye swallowed by mistake. The scars contract 
and make the gullet so narrow that not even water can 
trickle through. 
The Stomach. The stomach is a large, baglike organ 
situated under the diaphragm (Fig. 71). It possesses a 
layer of oblique muscle fibers as well as ring and longi- 160 
THE HUMAN BODY AND ITS ENEMIES 
tudinal muscle layers. In the walls of the stomach are 
found organs not present in the gullet. The mucous 
membrane of the stomach dips down into the wall, forming 
Figure 100. — A, a spool; B, half of a spool cut longitudinally; C, manner 
of cutting spool to get D and E; D, a longitudinal section; E, a cross section. 
tiny sacs or pockets. These are the gastric glands. They 
can be seen in section in Figure 102.1 The gastric glands 
secrete gastric juice. Each gland is very tiny, but there 
are so many that when all act together a large quantity of 
gastric juice is secreted. 
When the muscles in the walls of the stomach contract, 
the food is thoroughly mixed with gastric juice. But only 
the lower, smaller half of the stomach engages in this 
movement, the food remaining more or less quiet in the 
large end of the stomach for some time after it is swallowed. 
The Pylorus. At the point where the stomach passes 
into the intestines, there is a ring muscle which is unusually 
thick. When this contracts it closes the opening so as to 
keep the food in the stomach, just as a lady’s handbag is 
closed by pulling the strings. When the muscle relaxes 
the food may pass from the stomach to the intestines. 
This muscle, then, acts like a valve. It is called the 
pylorus (Fig. 102), or gateway to the stomach. 
1 In describing the structure of organs the terms “ longitudinal section ” 
and “ cross section” are frequently used. With the aid of Figure ioo 
these terms should be explained and applied to illustrations representing 
such sections. STOMACH AND INTESTINES 
161 
Figure ioi. — A portion of the wall of the stomach, much enlarged; 
i, peritoneum; 2 and 3, muscle layers; 4, lining of stomach; 5, mouths of 
glands. 
Figure 102. — Gullet, stomach, and small intestine, partly laid open. 
Numbers same as in Figure 101. 
Figure 103. —A portion of the wall of the small intestine, more enlarged 
than Figure 101; 6, villi containing blood capillaries; 7, villi containing 
lymph capillaries; other numbers as in Figure 101. 162 
THE HUMAN BODY AND ITS ENEMIES 
The Small Intestine. The small intestine has also 
a wall of muscle, both circular and longitudinal. The 
motion of the muscles results in moving the food forward 
along the intestine and in thoroughly mixing the food with 
the various juices that are poured into the canal. The 
mucous membrane lining the small intestine is more 
uneven than that of the stomach. Pocketlike glands, 
similar to the gastric glands of the stomach, extend back 
into the wall of the intestines and open by tiny mouths all 
over the inner lining shown in Figure 103. These are called 
the intestinal glands, and they secrete intestinal juice. But 
in addition to these glands there are fingerlike outpushings 
of the mucous membrane called villi (singular villus). 
That is, whereas the glands lead down from the surface 
into the wall, the villi extend up into the hollow of the 
intestine. In this connection carefully study Figures 102 
and 103. The large intestine has no villi. 
The Liver and the Pancreas. We have thus far learned 
of three kinds of digestive glands; that is, glands that make 
Figure 104. — Some of the important digestive 
organs of the abdomen. 
or secrete digestive juices. These are the salivary glands, 
that pour saliva into the mouth; the gastric glands in the STOMACH AND INTESTINES 
163 
walls of the stomach; and the intestinal glands in the walls 
of the small intestine. Besides these there are two others, 
the largest and most important of all: the liver and the 
pancreas. The liver is a very large gland occupying the 
space just under the diaphragm, especially on the right 
side. The liver secretes bile. It does this all the time, 
and when the bile is not being used it is stored in a bag, 
called the gall bladder. The pancreas is a long gland lying 
behind and below the stomach (Fig. 73). It secretes the 
pancreatic juice. Bile and pancreatic juice are carried to 
the intestines by ducts which join and empty the juices 
into the intestines together (Fig. 104). 
Digestion in the Stomach. In the large part of the 
stomach the digestion of starch by the action of amylase 
continues for some time. In the lower part of the stomach 
the gastric juice is mixed with portions of the food. Here 
proteins are acted upon and changed by an enzyme called 
pepsin. 
Digestion in the Small Intestine. In the small intestine 
all the food (except glucose) undergoes chemical change. 
The intestinal juice contains enzymes that digest cane 
sugar. The pancreatic juice has enzymes capable of 
digesting proteins, starch, and fats. It is the most power- 
ful digestive juice in the body. The bile has no enzyme, 
but it is useful in aiding the pancreatic juice to do its work 
and in keeping the mucous membrane of the intestines in 
good condition. The liver and the pancreas have other 
functions besides that of producing digestive juices. 
The Hygiene of Cheerfulness. Saliva and gastric juice 
are found to secrete best when the food is attractive in 
appearance and pleasing to the taste. They have been 
called the appetite juices. They secrete better, too, and 
the intestine also carries on its peristaltic movement better 
when a person is in a cheerful mood. Anger, fear, sorrow, 
worry — all interfere with the secretion of the appetite 
juices and with the proper mixing of the foods with them. 164 
THE HUMAN BODY AND ITS ENEMIES 
Skilful preparation of food and a clean and attractive 
appearance of the table and the dining room add to the 
value of the food. Meal time, too, should be the pleas- 
antest time of the day. 
Summary and review of the chemical action of the digestive 
juices to show what juices digest the various foodstuffs and 
where: 
Juice 
Produced in 
Emptied into 
Digests 
Saliva 
Salivary glands 
Mouth 
Starch 2 
Gastric1 
Gastric glands 
Stomach 
Proteins 2 
Intestinal 
Intestinal glands 
Small intestine 
Cane sugar 
| Starch 2 
Pancreatic 
Pancreas 
Small intestine 
| Proteins2 
(Fats2 
Bile 
Liver 
Small intestine 
Aids other juices 
The alimentary canal is a long tube which begins at the 
mouth and includes the throat, the gullet, the stomach, and the 
small and the large intestines. The tube is lined with mucous 
membrane. The wall of the canal is made mainly of muscles 
which, by contracting and expanding, mix the food with the 
juices and move it along. In the walls of the stomach and 
the small intestine are many small glands; other glands (salivary 
glands, pancreas, and liver) are outside the canal but pour their 
juices into it through ducts. 
The small intestine is the most important organ of chemical 
digestion. It is the only organ where sugar and fats are digested, 
and in it the digestion of the proteins and starch is completed. 
SUMMARY 
1 Gastric juice also contains an acid (hydrochloric acid) which helps to 
destroy germs that get into the stomach. The acid also aids in digestion. 
Gastric juice will also curdle milk. 
2 See Chapter XXVII for digestion of starch, proteins, and fats. STOMACH AND INTESTINES 
165 
QUESTIONS 
i. Mention the parts of the alimentary canal numbered in Figure 
93. 2. With a spool before you, draw a cross section and a longi- 
tudinal section of the spool. 3. Do the same for a top. 4. Sketch 
cross sections of the gullet, the stomach, and the small intestine. 
5. What is the use of the muscle layers of the alimentary canal? 
6. How is this use illustrated in Figure 99? 7. Describe the pylorus. 
8. Draw a longitudinal section through the pylorus (Fig. 102). 
9. Where is the mucous membrane found? 10. Locate the gastric 
glands. 11. Compare these glands with the intestinal glands. 
12. Where are the villi found? 13. From what part of Figure 102 
is Figure 101 supposed to be taken? 14. In what organs is starch 
acted on? Proteins? 13. What is the only juice that can digest 
fats? 16. What foods are digested in the intestines? 17. Where 
is the chemical digestion of proteins begun? Of starch? Of fats? 
Of cane sugar? 18. Why does pleasant conversation at the table 
and cheerful company add to the value of food? 19. How does 
tasteful preparation of food conduce to health? CHAPTER XXVIII. THE DIGESTIVE GLANDS 
Definition of a Gland. You know by this time what is 
the function of a gland; that it produces or secretes, 
that is, takes up from the blood, a fluid or a juice. You 
could make a list of at least four digestive juices and tell 
by what glands they are secreted. 
The mouth is always moist because the salivary glands 
secrete saliva and pour it into the mouth. There are 
many different kinds of glands in the body besides those 
already mentioned, as for example the tear glands and the 
sweat glands. 
How the Gland Cells Are Arranged. Let us point out 
the kinds of cells that glands are composed of and how 
Figure 105. — Diagrams of various types of glands. E, 'epithelial layer 
consisting of gland cells; H, blood capillaries; M, mouth of gland; D, 
duct. 1, gland with flat epithelial layer; 2 and 3, pocket-shaped glands; 
4 and 5, tubular glands, the one at 5 having tube so long as to necessitate 
its being coiled up at the lower end; 6, gland with blood vessels coiled up 
inside of epithelial layer; 7, compound gland with many pockets and ducts. 
these cells are arranged. Gland cells are epithelial (E, Fig. 
105); that is, they are arranged side by side so as to make 
a layer, as shown in the diagrams in the figure. This THE DIGESTIVE GLANDS 
167 
layer has one surface lying against the connective tissue, 
in which there is a rich supply of blood vessels. Where 
these come close to the gland cells they are thin-walled, 
so that the substances may readily be taken out of the 
blood by the cells. These sub- 
stances are changed by the cells 
into juices which ooze through 
the cells and are given off on the 
free side of the epithelial layer. 
Diagram i of Figure 105 rep- 
resents the glandular layer as 
flat. A gland of this kind, if 
extended, takes up a great deal 
of space; therefore most glands 
have the secreting surface pushed 
down into pockets and tubes, as 
figured in longitudinal sections 
in diagrams 3-7, Figure 105. 
Blood vessels surround these 
glands and come close to the 
gland cells; the hollow of the 
gland serves to catch the secreted 
fluid and to give it off at the open- 
ing, the mouth of the gland (M). 
The relation of blood vessels and gland cells is again 
shown in Figure 106. Just such glands are found in the 
walls of the stomach and the intestines. They may be 
simple, as shown in Figure 106, or compound, that is, with 
several branches, as in diagram 4, Figure 105. Their 
exact position is seen in Figure 102, where the walls of the 
stomach and the intestines are represented as cut away, 
exposing sections of the walls. These glands are very 
small,—much smaller than shown in Figure 102, which 
has the stomach about one fourth natural size, but shows 
the glands enlarged five or more times. Figure 101 
represents a block of the stomach wall more enlarged; 
Figure 106. — A gastric gland 
from Figure 101, highly mag- 
nified. GL, gland cells; M, 
mouths of other glands. 168 
THE HUMAN BODY AND ITS ENEMIES 
it shows how numerous are the gastric glands in the 
stomach. 
The intestinal glands are similar, usually simple, like 
the gastric gland shown in Figure 106. Study them also 
in Figure 103. Among the glands are projections, the 
villi, which project out from the walls while the glands 
extend down into them. The duty of the villi we shall 
study in the next chapter. 
Other Glands. The glands just described occupy all 
the space available in the stomach and the intestines, but 
Figure 107. — Details of tiny portion of pancreas. A, a number of 
pockets that empty their juice into duct (partly cut open); 8, a pocket in 
longitudinal section, more highly magnified at B; 3, a pocket in cross sec- 
tion, more highly magnified at C; 1, large duct, more highly magnified at 
D; 4, small duct; BV, blood vessel; 5, appearance of gland cells before a 
meal; 7, after a meal. 
they are not sufficient to supply the alimentary canal with 
all the digestive juices needed. There are, therefore, 
other glands of large size outside the canal, but communi- 
cating with it by ducts or tubes, to carry the juice from the 
gland to the proper organ. As already noted, these glands 
are: six salivary glands, whose ducts lead to the mouth, 
and the liver and the pancreas, whose ducts lead to the 
small intestines. The salivary glands, the liver, and the THE DIGESTIVE GLANDS 
169 
pancreas are complex, not simple, glands, as are the gastric 
glands. But when carefully studied, each smallest part or 
unit of a large gland is found to be a little pocket of epithe- 
lial tissue. Each pocket corresponds exactly to a simple 
gland. A large gland, then, is a large collection of simple 
pockets, all of which empty their fluid into ducts or tubes 
that combine into one or more large ducts to carry off the 
fluid to the mouth or the intestines. As in all glands, the 
epithelial cells of each pocket get material from the blood 
wherewith to make their secretions. Study in this con- 
nection Figure 107. 
SUMMARY 
There are many different kinds of glands in the body, but 
they are all alike in having the cells that do the work arranged 
as an epithelial tissue which lies upon connective tissue very rich 
in blood. The cells secrete fluids; that is, they take materials 
out of the blood and make them over into various fluids. The 
digestive glands are of five kinds: (1) the gastric glands in the 
walls of the stomach; (2) the intestinal glands in the wTalls of 
the intestines, — these are very simple and numerous. Out- 
side the alimentary canal, but communicating with it, are: 
(3) six salivary glands, (4) the pancreas, and (5) the liver. 
i. What is a gland? 2. What is the principal kind of tissue in 
a gland? 3. What letter marks the layer of gland cells in Figure 
105? 4. Where do the cells get the material from which to make 
their juices? 5. Which has more gland cells, 3 or 4 of Figure 105? 
6. Describe a gastric gland. 7. Where are glands like this shown 
in Figure 101? 8. Locate them also in Figure 102. 9. Compare 
the glands of Figure 103 with the gastric glands. 10. What part of 
Figure 107 is like a gastric gland? n. Why does the blood have to 
come near the working cells of a gland? 12. Where are the gland 
cells of Figure 106? Of Figure 107? 
QUESTIONS CHAPTER XXIX. HOW THE FOOD IS TAKEN UP 
BY THE BLOOD AND LYMPH: ABSORPTION 
We have now considered digestion as the process of 
making insoluble food soluble. Only water and soluble 
substances can be taken up out of the digestive organs. 
Water, salt, and some sugars are taken up without change, 
but other foodstuffs, as we have learned, must be digested 
before they can be taken up. So long as the food remains 
within the alimentary canal, however, even after it has 
been digested, it does the body no good. Of what use can 
the food be to the cells of the hand, head, or other parts so 
long as it remains in the stomach or intestines? To be 
of use to any part it must be carried to that part. The 
food is carried to the distant parts of the body by the 
blood. From the stomach and the intestines the blood 
and lymph take the digested food. The process by which 
the food soaks through the wall of the alimentary canal is 
called absorption. 
The Blood as a Carrier. The blood is the carrying agent 
of the body. The heart pumps the blood; and in order 
that the blood may flow quickly and surely to all parts of 
the body, it flows in definite tubes, called the blood vessels. 
Arteries are blood vessels that carry the blood away from 
the heart. These divide again and again and grow smaller 
and smaller the farther they pass from the heart, until they 
become so tiny that they cannot be seen without a micro- 
scope. The smallest vessels are called capillaries. They 
have walls so thin that substances can pass in and out 
through them. These capillaries combine again to form 
veins, which return the blood to the heart. 
Thus the arteries carry blood to the capillaries in the 
walls of the stomach and intestines; the blood while passing 
through the capillaries absorbs food; and then, flowing 
into veins, the blood carries the food to the right side of 
the heart. It then flows through the lungs and back to 
the left side of the heart, from which, rich in the different 
kinds of food, it is pumped to all parts of the body. 
170 ABSORPTION OF FOOD 
The Lymph. You must also learn at this point that 
there is another fluid in the body, called the lymph. This 
absorbs some foods from the intestines and carries them 
into the blood. The lymph begins in the lymph capillaries, 
in the walls of the intestines. 
Where the Food is Absorbed. The entire inner surface 
of the stomach and the small and large intestines is covered,. 
171 
Figure 108. — Diagram of 
portion of wall of stom- 
ach, showing three gastric 
glands; A, absorbing cells; 
B, gland cells. 
Figure 109. — Diagram of 
portion of wall of intestine, 
showing a villus (1) and 
three intestinal glands (2). 
The rest as in Figure 108. 
as we have learned, with mucous membrane (i, Figs, ioi 
—103). The whole mucous membrane is a soft, moist 
material, very much like a soft jelly. Just below this 
layer of mucous membrane lie an enormous number of 
tiny blood and lymph capillaries, so closely laid together 
that they almost touch one another. The dissolved food 
particles soak through the jelly like mucous membrane 
into the streams of blood and lymph. As these move 
along under the mucous membrane they continue to absorb 
from the mucous membrane the various foods, until all 
are absorbed from the inside of the stomach and intestines.. THE HUMAN BODY AND ITS ENEMIES 
172 
The insoluble part only is left behind to be cast off from 
the body. 
In the stomach and the small and large intestines are 
various glands, gastric and intestinal glands (Figs, ioi 
and 103), which secrete digestive juices. These glands are 
lined with mucous membrane. The cells of the glands 
do not absorb food and pass it on to the blood, but on the 
contrary they take substances out of the blood and make 
juices of them, which they pass into the stomach and 
intestines. These glands are shown at B, Figures 108 and 
109. The arrows indicate the direction in which sub- 
stances pass out of the blood through the gland cells. 
The Stomach and Intestines as Absorptive Organs. 
The stomach plays a very important part in the digestion 
of food, but a comparatively unimportant part in absorp- 
tion. Most of the food is absorbed in the small intestine; 
some in the large intestine. The small intestine is the 
most important absorptive organ because it contains the 
most powerful digestive juices and because the digestion 
of all the foodstuffs is completed in it. Other reasons 
will be stated presently. 
The Absorption of Water. Very little if any water is 
absorbed in the stomach; water is passed on at once to the 
small intestine, in which the greater part of it is absorbed. 
Most of what is left is absorbed in the large intestine. 
When the water is taken up too thoroughly in the large 
intestine, constipation results. To avoid this, water should 
be drunk just before going to bed at night and on getting 
up in the morning. 
The Small Intestine as an Absorptive Organ. The 
lining of the small intestine is seen on examination with 
the naked eye to have a soft, velvety appearance. If 
examined with a hand lens, the velvety surface looks like 
the rough surface of a coarse bath towel. This is due to 
the presence of the tiny projections called villi which 
project up into the inside of the intestines. Figure 103 ABSORPTION OF FOOD 
173 
shows that the villi are scattered over the surface of the 
intestine among the intestinal glands. 
The villi are covered with mucous membrane. Their 
function is to increase the extent of surface of the mucous 
membrane, for the greater the extent of the surface the 
greater will be the quantity of food absorbed. As there 
are several thousand villi to the square inch of surface, one 
can readily understand the advantage the small intes- 
tine has as an absorptive organ. Figure 109 represents 
a diagram of a portion of the wall of the small intestine. 
A villus is shown at 1. The cells at A are absorptive cells 
of the mucous membrane. A study of Figure 108, which 
shows the absorptive cells of the mucous membrane of the 
stomach at A, shows how little space the stomach has for 
absorption of food as compared with the small intestine. 
The surface of the small intestine is further increased by 
the great length of that organ. 
Structure of the Villi. As noted above, the villi are 
covered over with mucous membrane through which the 
food is absorbed. To carry off the absorbed food, each 
villus has a fine meshwork of blood capillaries and one 
or more lymph capillaries (the latter are called lacteals). 
Three villi are shown in Figure no, page 174. In II blood 
capillaries only are shown; III shows only a lacteal. 
Course of the Absorbed Food. The blood capillaries 
and the lacteals divide the work of carrying off the ab- 
sorbed food substances. The carbohydrates and proteins 
are carried off by the blood capillaries, the fats by the 
lacteals. Lacteals means “milk vessels,” for after a meal 
they can be seen to be white as milk on account of the fat 
droplets they have absorbed. 
By the time the blood reaches the heart, all of the ab- 
sorbed food is mixed together, for the lymph carrying the fat 
is returned to the blood at a point above the heart. Figure 
in, page 175, shows the course of the fats; the vein called 
the portal vein carries the carbohydrates and proteins to the 174 
THE HUMAN BODY AND ITS ENEMIES 
liver, through which these foodstuffs must pass before being 
taken to the heart and pumped to all parts of the body. 
Figure no. — Three villi of the small intestine: I, with blood capillaries 
(C) and lacteal (L); II, with blood capillaries only; III, with lacteal (L) 
only; G, intestinal gland. 
How the Food is Absorbed: Diffusion. You have 
noticed that the food must pass through the jellylike 
mucous membrane to get into the blood; also through the 
walls of the blood vessels. We say it does this by diffu- 
sion, by which we mean that substances pass from the part 
of a solution where they are abundant to the part where 
they are less abundant. Thus food substances pass from 
the inside of the intestines into the blood and lymph, for 
there is less foodstuff in the blood and lymph, since the 
supply is continuously being carried away by the circu- 
lating liquids. ABSORPTION OF FOOD 
175 
How gases diffuse is familiar to most people. Thus in a 
closed room in which there are no currents of air, gas in one 
part of the room will soon diffuse into all parts. How 
substances diffuse in liquids can 
be seen in the following experiment: 
Experiment. Put some crystals 
of bluestone (copper sulphate) in the 
bottom of a tall glass jar, and pour 
water over them very carefully and 
slowly so that no mixing occurs. Set 
the jar aside in a perfectly quiet place, 
and from day to day look at the solu- 
tion. The blue color gradually spreads 
to the top, showing that the blue- 
stone diffuses into the water. 
Diffusion through a Membrane. 
The part played by the membrane 
in diffusion is to keep out undesir- 
able substances; it serves to allow 
only certain substances to pass 
through. Thus water, salts, animal 
acids, etc., will pass readily through 
the mucous membrane. Substances 
such as gelatin or the white of an 
egg do not diffuse to any extent. 
These must, therefore, be digested 
before they can pass through the 
mucous membrane and enter the 
blood. The following experiment illustrates how a mem- 
brane allows water, but not protein, to pass through. 
Figure in.—Diagram to 
show the course of food- 
stuffs to the heart. Fats 
are carried in lymph ves- 
sels. The portal vein car- 
ries the other foodstuffs. 
Experiment. Take an egg, a glass tube or a straw about 
a foot long, a bottle to hold the egg, and a vessel to hold the 
bottle and the egg, as shown in the accompanying figure. With 
great care crack the shell at the large end of the egg and pick 176 
THE HUMAN BODY AND ITS ENEMIES 
off the bits of shell with the finger nails, being careful not to 
injure the membrane under the shell. Or better, dissolve away 
the shell by immersing the egg in dilute hydrochloric acid; this 
can be done by placing the egg in a cloth bag and hanging the 
bag in the acid to the required depth. Now, 
punch a hole in the other end of the egg, and 
into this thrust a straw as far as the center of 
the yolk of the egg. With melted beeswax or 
paraffin or tallow seal the joint of the straw to 
the egg. Set up the apparatus, as in Figure 
112, and add water, immersing half of the egg, 
and await results. If the membrane of the 
egg is not broken where it touches the water, 
the water will pass into the egg but the contents 
of the egg will not pass out. This causes the 
contents of the egg to rise in the tube. Watch 
the experiment and explain what you see. 
Figure 112.—Ex- 
periment in dif- 
fusion. B, bottle; 
/,jar; both con- 
taining water; E, 
egg; T, glass tube 
or straw sealed 
to egg with wax 
(T). 
SUMMARY 
After the food is digested it is worthless to 
the body unless absorbed by the blood and 
lymph and carried to the hungry cells of the 
body. The digested, or soluble food, is absorbed 
by diffusion through the thin mucous membrane 
lining the stomach and the intestines. The 
small intestine is the chief absorptive organ; its absorptive 
surface is very great and in it the digestion of all the foodstuffs 
is completed. The area of the inner surface of the small intestine 
is enormously increased by the great length of the canal and 
especially by the villi. The villi number thousands to the 
square inch, and each villus contains blood capillaries and lac- 
teals, which carry the foods to the veins and through these to 
the pumping station, the heart. 
i. Why must food get into the blood? 2. How does the food 
pass in? 3. Why must food be soluble in order to be absorbed by the 
blood? 4. What membranes must the food pass through to get into 
the blood (Figs. 108 and 109)? 5. Describe an experiment to 
QUESTIONS ABSORPTION OF FOOD 
illustrate diffusion. 6. What is the principal use of the mucous 
membrane (M, Fig. no)? 7. Describe a villus. 8. What 
membrane in Figure no corresponds to the membrane around the 
egg in Figure 112? 9. What organ in a villus takes up fats? Pro- 
teins and carbohydrates? 10. What foodstuffs pass through the 
liver before going to the heart? n. What cells in Figure no are 
touched by the nearly liquid contents of the small intestine? CHAPTER XXX. THE MAKING OF LIVING 
SUBSTANCE: ASSIMILATION 
In the last few chapters we have discussed: (i) the kinds 
of food that are eaten; (2) how these foods are digested, 
or prepared for absorption; (3) how they are absorbed or 
taken into the blood to be pumped by the heart to all 
the cells of the body. We shall now consider how the 
food passes out of the blood to supply the cells. 
Blood as the Carrier. It was noted in the last chapter 
that the blood 
vessels are every- 
where closed and 
that food substances 
pass into the thin- 
walled capillaries of 
the villi by diffusion. 
Just so, after the 
blood has reached 
the hungry working 
cells in distant parts 
of the body, the 
food which the blood 
carries passes out 
through the capillary walls to the cells. The blood does 
not actually touch the cells, but stays in the blood vessels; 
it merely passes close enough to the cells so that, by 
diffusion, the food may pass to the cells, just as water 
passes into the egg through the membrane in the experi- 
ment described above. Figure 113 shows this relation of 
capillaries and cells of the body. 
The Lymph. Some cells of the body lie loosely together 
in such a way that there are spaces among them. This is 
especially true of connective tissue. Such spaces are filled 
with a thin, colorless fluid called lymph. It may be said 
that we — that is, our cells —■ live in a fluid just as fish 
live in water. You will note by studying the diagram 
(Fig. 113) that substances which pass from the blood to 
Figure 113. — Diagram to illustrate the relation 
of cells, lymph and blood. C02 = carbon dioxid. ASSIMILATION OF FOOD 
the cells must first pass through the lymph that fills all 
the spaces among the cells. 
Assimilation. The question now is: What becomes of 
the food after it reaches the cell? This is the climax of 
the subject, — the food becomes in part living substance. 
Living substance makes dead matter over into living matter 
like itself. This is called assimilation (Latin ad, to, 
and similis, like). Living matter, found in all living 
cells, is called protoplasm. A cell, therefore, represents 
a definite mass of protoplasm (Fig. 76). In doing work 
a cell uses up some of its protoplasm, but it creates new 
protoplasm out of food brought to it; it repairs and adds to 
itself. No machine can perform such work as the living 
body can. As explained elsewhere, however, proteins only 
can serve to form protoplasm. Indeed, it has been found 
that only certain kinds of protein can form it. Foods 
not used for assimilation are mostly used to furnish heat 
and energy for work. 
Growth of Cells. It is easy to see from this how cells 
grow and multiply. As the body grows, more cells are 
179 
developed from those already there. The cell reaches its 
full growth and then divides in two (Fig. 114); then there 
are two cells to grow again and multiply as before. When 
the skin is injured it grows from around the edge of the 
wound, for the skin is formed only from skin cells already 
present. The material for growth is furnished by the 
blood under and in the skin. Assimilation, growth, and 
multiplication are processes that are performed only by 
protoplasm or living substance contained in the cells of 
animals and plants. 
Figure 114. — Cell growth and division. 180 
THE HUMAN BODY AND ITS ENEMIES 
Wastes. In burning or oxidizing the tissues and food 
in the body, waste substances are produced by the cells. 
The chief waste substances 1 are carbon dioxid, water, and 
urea. Excessive quantities of these are harmful to the 
cells and must be carried away by the blood. So without 
end, from birth till death, protoplasm is built up out of 
food and torn down by oxidation (burned) that life may 
go on. It is truly life by death. 
Food Storage. But some substances can be stored in 
the body, to be used in case of need when food cannot 
Figure 115. — Growth of a fat cell by the accumulation of drops of oil. 
be eaten or secured. How long can a person live without 
eating? A kind of starch (animal starch) is prepared by 
the liver and stored in that organ and in muscles. Other 
foodstuffs are made into fat by the cells of the body and 
stored in certain cells. These cells grow larger and larger 
until filled with large drops of fat, as shown in Figure 115. 
How Disease Germs Feed in the Body. Sometimes 
some of the food that is digested in the alimentary canal 
and made ready for absorption goes to support plants 
and animals called parasites, which get into the body. 
Such a parasite is the tapeworm, which lives in the 
intestines. (See page 138.) It has no eyes, limbs, mouth, 
or digestive organs of any kind; it simply lies in the food 
substance in the intestines and soaks up the food through 
the walls of its body, just as a cell of the body does. 
Besides large parasites like tapeworms, hookworms, etc., 
there are millions of germs that live in the body. Many 
1 Here are not included the indigestible wastes passed from the small 
intestine into the large intestine. These wastes are not produced by the 
cells of the body, never having been absorbed by the villi. ASSIMILATION OF FOOD 
181 
of these are harmless, especially the kinds found in the 
alimentary canal. Others are very harmful. These, and 
the harmful effects of their toxins, have already been 
described. 
Why Parasites Thrive in the Body. A moment’s reflec- 
tion will show you why it is that parasites often thrive 
in our bodies. There are three things living beings need 
in order to live: food, water, and oxygen. In the body 
parasites find these things: (1) food in the mouth, the 
mucous membrane, the stomach and intestines, the blood 
Figure 116. — Diagram to show how a disease germ 
gives off toxin which is destroyed by antitoxin pro- 
duced by the cells of the body. 
and the cells; (2) water, for seventy-five per cent of the 
body is water; (3) oxygen, which is constantly being 
carried from the lungs to the tissues. Most parasites also 
need warmth, and this we also furnish, for our bodies are 
always at a temperature of about 98.8° Fahrenheit. No 
wonder that many kinds of bacteria and other parasites 
make our bodies their home, since we take good care of 
such visitors. 
Toxins and Antitoxins. A study of Figure 116 will 
help us to understand the work of disease germs in the 
body. Suppose we take a bacterium living in the blood. 
From the blood it takes food and oxygen and water, and 
into the blood it pours its waste substances. With the 182 
THE HUMAN BODY AND ITS ENEMIES 
waste substance it gives off poisons called toxins. The 
toxins circulate with the blood and are carried to all the 
cells of the body, working them injury. A small patch of 
diphtheria germs in the throat may, for example, give off 
enough toxins to cause the whole body to become sick. 
When toxins are present the cells of our body begin at once 
to produce antitoxins, which pass into the blood and lymph. 
The antitoxin destroys the toxin and sometimes also the 
germs, and in this way often protects us against the harmful 
effects of disease germs. 
SUMMARY 
The living substance of which the cells of our bodies are 
composed is called protoplasm. The most wonderful thing 
this protoplasm can do is to change the food we eat into sub- 
stance like itself. This process is called assimilation. The cells 
of the body are surrounded by lymph. Food passes out of the 
blood capillaries into the lymph and then into the cells, and 
waste matter passes back into the blood. Disease germs feed 
in the body just as the cells of the body themselves do. They 
give off toxins or waste substances, which injure the body. 
Often the cells of the body give off antitoxins, which destroy the 
toxins or the germs or both and thus protect us from disease. 
i. What is the chief work of the blood? 2. Define arteries, 
capillaries, and veins. 3. In which of these does the blood take on 
and give off its loads? 4. Why do the capillary walls have to be 
thin? 5. Does the blood touch all the cells of the body? 6. 
What is the use of lymph and where is it found? 7. What is assimi- 
lation? 8. What is the most wonderful work of protoplasm? 9. 
Where is protoplasm found? 10. How are waste substances pro- 
duced? 11. What are the chief wastes made by protoplasm? 12. 
What foodstuffs are of use in building up the cells? 13. How do 
wastes get into the blood? 14. What does the blood do with them? 
15. Draw Figure 113 on the board and discuss the work of the cells. 
16. Show how disease germs feed in the body just as the cells of 
the body do. 17. How do germs harm the body? 18. What is 
produced by the cells of the body to counteract the germs of disease? 
QUESTIONS CHAPTER XXXI. WHY WE BREATHE 
Review. In the previous chapters it was pointed out 
that the cells of the body are continually in need of food 
and that this food is needed by the cells for growth and 
repair, to keep them warm, and to enable them to 
work. It was also shown that it is not the food itself 
that produces heat, but the burning of the food, or the 
burning of cell substance itself, that causes us to be warm 
and enables us to move. We might compare the body to 
a stove. The stove is not heated merely by laying the 
wood in it, but by the burning of the wood. To burn the 
wood, a draft through the stove is necessary; cut off 
the draft and the fire goes out. This simply means that 
oxygen from the air is needed to combine with the wood 
to produce heat. The same is true of the body. What 
the draft is to the stove the breath is to the body. Oxygen 
is needed by the cells to burn up the food and to keep up 
the activities of life; stop breathing, and the body grows 
cold and life ceases. 
In the present chapter we shall see how the air contain- 
ing the oxygen we need reaches the lungs, how the oxygen 
gets very close to the blood, and how it is absorbed by the 
blood so as to be carried where it can be of use to the cells 
of the body. 
How Carbon Dioxid is Produced. In the burning of 
wood in the stove some of the waste, products that result 
from the burning are given off into the stove-pipe and 
chimney as smoke and gas. Just so the waste products 
of burning food are given off into the blood and are carried 
to the organs that throw them off from the body. One of 
the chief wastes is carbon dioxid. Starch and other food- 
stuffs contain carbon, and when this is burned the carbon 
unites with the oxygen to form carbon dioxid. 
Respiration Defined. Respiration includes not only 
the taking in and giving out of air by the lungs, usually 
called breathing, but also the absorption of oxygen and the 
giving off of carbon dioxid by the cells of the body. Res- 184 
THE HUMAN BODY AND ITS ENEMIES 
piration means, in brief, a taking in of oxygen and a giving 
off of carbon dioxid. Every cell does this (see Fig. 117); 
therefore every cell respires. But the cells are so far from 
the outside world that the blood must carry the oxygen to 
the cells and the carbon dioxid away from them. In the 
Figure 117. — Diagram illustrating respiration of the 
cell of the body. C02 = carbon dioxid. 
earthworm the carbon dioxid is given off and oxygen taken 
in through the whole skin. In the fish' the gills are the 
organs of respiration. The gills are covered with a thin 
membrane and filled with blood; it is through this mem- 
brane that the fish takes oxygen out of the water and gives 
off carbon dioxid into the water. In man and the higher 
animals the air containing oxygen must be taken into the 
lungs (inspiration) and breathed out again (expiration). 
While in the lungs the blood takes up oxygen and gives off 
carbon dioxid. Just how the exchange of carbon dioxid 
for oxygen takes place through the thin membrane of the 
lungs and how the blood comes close to this thin mem- 
brane, we shall see later. WHY WE BREATHE 
185 
Observation and Experiments, (i) Bring earthworms to 
school and place them in shallow dishes or plates with a little 
water. Earthworms must be kept moist, for if their skin 
dries they cannot breathe through it, and therefore they die. 
Note the red blood vessels that can be seen through the skin of 
the animals. Why is it that fish and men cannot 
have skin delicate enough for oxygen to pass 
through? (2) Keep a goldfish, minnow, or other 
fish in a clear glass jar of water. Where are the 
gills of the fish? Note that the water goes into 
the mouth and out of the gill slits on the side just 
behind the head. Boys who have strung fish can 
tell all about this. How does the fish take up 
oxygen dissolved in water and give off carbon 
dioxid into the water? (3) Watch your desk- 
mate breathe; that is, inspire and expire air. 
Watch him when he is not aware of it and count 
the number of breathing movements he makes in 
a minute. (4) Take a short candle and light it. In- 
vert a fruit jar over the candle and note what 
happens (Fig. 118). Why does the candle go out? Air contains 
four parts of nitrogen to one part of oxygen. But not all the 
oxygen can be burned out of the air with a candle, for the candle 
goes out before all the oxygen is used up. (5) To show more 
plainly that some of the oxygen disappears, burn a match-head 
under a quart jar, with the jar inverted over water, as shown in 
Figure 119. To do this the match must stand upright and be 
surrounded by an inch or two of water in a broad vessel. The 
match can be stuck into a block of potato to hold it up. 
Now, with another match light the match that is to burn out 
the oxygen from the jar. As soon as the match begins to 
burn, quickly place the jar over it and into the water. Watch 
the water rise in the jar. Some of the oxygen has been used 
up out of the air in the jar, and the water has taken its place 
(Fig. 119). (6) That expired air contains large quantities 
of carbon dioxid can be demonstrated easily. Dissolve a 
little fresh lime (such as masons use to make mortar) in some 
water and either filter it to get it clear or allow it to stand cov- 
ered a day or two until the undissolved particles settle to the 
bottom; then pour off the perfectly clear liquid on top. Now, 
Figure 118.— 
A candle will 
go out for lack 
of oxygen if 
covered with 
a jar. 186 
THE HUMAN BODY AND ITS ENEMIES 
with a straw or a glass tube blow your breath through this clear 
liquid (Fig. 120). The milky condition of the liquid indicates 
that carbon dioxid has been added to it. 
Figure 1x9.— Burning the oxygen 
out of a jar (/) of air; M, match 
stuck into a piece of potato in a 
dish (D) of water. A, level of 
water after removal of oxygen by 
burning of match-head. 
Figure 120. — Experiment to show 
that clear lime water made with fresh 
lime will become milky from carbon 
dioxid breathed into it. 
SUMMARY 
Respiration is the taking in of oxygen and the giving off of 
carbon dioxid. The oxygen is taken from the air and is used 
in the body for oxidation. The oxygen unites with the carbon 
of our food and tissues, producing carbon dioxid, a waste sub- 
stance, injurious to the body. Every cell in the body uses 
oxygen and gives off carbon dioxid. The blood carries the 
oxygen to the cell and the carbon dioxid away from it. The 
carbon dioxid leaves the body in the breath, as can easily be 
seen by experiment. 
i. Define respiration. 2. How is carbon dioxid formed in the 
body? 3. In a stove? 4. Why is oxygen needed? 5. Why do 
we need more oxygen when running than when sitting? 6. What 
common observation seems to prove this? 7. How does each cell 
secure oxygen and get rid of carbon dioxid (Figs. 113 and 117)? 
8. How does the whole body get rid of carbon dioxid and take on 
oxygen? 9. How can you prove that about one fifth of air is oxygen? 
10. How can you show that carbon dioxid is given off in the breath? 
QUESTIONS CHAPTER XXXII. THE AIR PASSAGES 
In the last chapter it was shown how the cells of the 
body take oxygen out of the blood and give off carbon 
dioxid into it. This is called internal respiration. In the 
lungs the blood exchanges carbon dioxid for oxygen with 
the air that is breathed in and out. The breathing of air 
in and out of the lungs is called 
external respiration. How ex- 
ternal respiration is carried on 
will be explained in this chapter. 
The Breathing Organs. The 
breathing organs, or the organs 
of respiration, are the lungs 
and the air passages carrying 
the air to and from the lungs. 
The bones of the chest and 
the muscles attached to them 
cause the air to enter the lung 
through the air passages. 
The air passages are the 
nasal passages leading from the 
nostrils back to the throat or 
pharynx, where the air passage 
and the food passage cross; 
the larynx, or voice box; and 
the trachea, or windpipe and 
its branches. The trachea 
divides opposite the lungs into 
two bronchi, and these, after 
entering the lungs, divide into 
smaller and smaller bronchial 
tubes or bronchioles, as the 
branches of a tree divide until 
the smallest twigs are reached, 
in the figures. 
The Nasal Passages. The nasal passages are lined 
with mucous membrane. Here end the nerves of smell, 
Figure 121. — Diagram of the air 
passages; arrows show crossing 
of food and air passages in the 
throat. Air sacs of lungs and 
pleura; shown. 
All of these are illustrated 188 
THE HUMAN BODY AND ITS ENEMIES 
which can detect odors in tiny particles coming in with 
the air we breathe. We say the nose is the organ of smell. 
The mucous membrane is, furthermore, richly supplied 
with blood; and as the passage is very crooked because of 
passing between and around the irregular bones (Fig. 122) 
of the skull, the air is warmed as it passes through. The 
nostrils are guarded by hairs which prevent coarse particles 
of dust from passing farther into the air passage. Mention 
two reasons why we should breathe through the nose and 
not through the mouth. Very often children (and rarely 
Figure 122.— The turbinated 
bones, showing the irregular 
nasal passage in which the air is 
warmed as it passes through it 
to the lungs. 
Figure 123. — Adenoids are 
spongy growths in the nose 
that tend to stop up the nasal 
passages. (Compare with 
Fig. 121.) 
grown persons) have spongy growths called adenoids just 
behind the nose (Fig. 123). These growths stop up this 
passage and force the patient to breathe through the mouth. 
Children who are mouth breathers are not healthy, and 
when they attend school they do not do well in their studies. 
Since a large number of children have adenoids, it is im- 
portant that all children be examined for nose and throat 
troubles as early as possible. If adenoids are discovered 
they should be removed by a physician without delay. The THE AIR PASSAGES 
189 
removal of adenoids is a simple operation and affords a 
wonderful relief to the sufferer. 
The Larynx. The larynx or voice box leads off from the 
pharynx. As the air crosses in the pharynx the path taken 
by the food (Fig. 121), there is danger of food as well 
as air going down into the larynx. To prevent this there 
is a flap, the epiglottis (Fig. 127), that fits down over the 
top of the larynx while swallowing. Point out this organ 
in Figure 121. The epiglottis itself does not move up and 
down, but the larynx is pulled up against it in swallow- 
Figure 125. — Diagram to 
illustrate the vibration of the 
vocal cords. The breath is 
blown upon a slip of paper 
between the thumbs. 
Figure 124. — Cartilage tissue showing 
the cells and the tough tissue between 
them. 
ing, as you can readily determine by feeling your throat 
while swallowing. The larynx is a box of cartilage 
tissue, commonly known as gristle, which is strong and 
somewhat elastic. The Adam’s apple at your throat is 
the front of the larynx. Feel it and press it. 
The larynx is made largely of cartilage so as to keep the 
passage always open for the air; for cartilage, while elastic, 
is stiff enough to support organs. The outer ear and tip 
of the nose are supported by cartilage. Feel them. If 
the larynx were made of softer tissue instead of cartilage, 
what would happen during inspiration? Cartilage tissue, 190 
THE HUMAN BODY AND ITS ENEMIES 
shown in Figure 124, consists of cells with tough and 
elastic substance between them. It is another of the 
tissues of the body and finds a variety of uses. 
Experiments on the Voice. Take a strip of paper about 
three fourths of an inch wide and two inches long, or as wide 
a blade of grass as possible, and place it between the thumbs, as 
shown in Figure 125, page 189. Now blow hard against the 
edge of the paper or grass. Stretched across the larynx are 
two flaps of connective tissue, each of which corresponds to the 
strip of paper you used in the experiment. (2) To prove that 
the vocal cords are situated in the larynx, sing a note, and as 
you sing, alternately press and let go of the Adam’s apple. (3) 
As sound is produced by the vocal cords, the hollows of the 
throat, mouth, and nose increase it. To illustrate this, hold 
up a tin bucket horizontally to one side of the mouth and speak 
into the bucket, noting the effect. 
The Trachea and its Lining. The trachea and its 
branches are simply tubes the walls of which are held open 
Figure 126. — Ciliated cells of the air 
passages have it as their duty to sweep 
dust back into the throat. 
by rings of cartilage (A and B, Fig. 127, page 192). You can 
feel these rings in the trachea by rubbing the front of the 
trachea up and down. The breathing tubes are, of course, 
lined with mucous membrane. The cells of this mem- 
brane are peculiar in that they are supplied with tiny 
hairlike projections called cilia (Fig. 126). These cilia THE AIR PASSAGES 
stand out from the membrane and are constantly in motion 
like a field of waving grass. 
The cilia act like tiny brushes, sweeping mucous contain- 
ing fine dust particles out of the lungs toward the throat, 
where it gathers to be coughed up. In this way nature 
provides means to keep dust out of the lungs. Of course, 
if the air passages are overloaded with dust the cilia cannot 
take care of it all. We should avoid dust. When we are 
unavoidably in a very dusty place, a handkerchief tied 
over the nostrils and mouth will keep out most of the 
dust. 
Respiration consists of internal respiration and external 
respiration. Internal respiration is the respiration of the cells. 
The organs of external respiration consist of the air passages 
and the lungs. Through the air passages the air enters the 
lungs, being warmed and freed from dust on the way. Hairs 
in the nose filter out the large particles of dust, and cilia in the 
air passages sweep finer dust particles back to the throat. But 
dust should be avoided as much as possible. 
SUMMARY 
QUESTIONS 
i. Where does the air enter the body? 2. Where does oxygen 
get into the blood and carbon dioxid leave it? 3. Name the air 
passages leading to the lungs. 4. Give reasons why we should 
breathe through the nose. 5. With a ruler held to your own face, 
indicate how the skull would have to be cut so that one might see 
the irregular bones of the nose shown in Figure 122. 6. Where 
do adenoids sometimes develop? 7. If affected by adenoids, why 
should we have them removed? 8. Why is cartilage tissue needed 
in the windpipe and air tubes? 9. How is voice produced? 10. 
How does the cavity of the mouth and throat help the voice? ix. 
Point out the cilia in Figure 127. 12. What is the function of the 
cilia? CHAPTER XXXIII. THE LUNGS 
Review. Study Figures 71 and 73 and the figures in 
this chapter. How many lungs are there? What is their 
location with reference to the heart? How are they con- 
nected with the bronchi? In what cavity do they lie? 
What organ do they touch below? How are they and the 
heart protected from injury? 
The Lungs. The lungs are made up largely of air tubes, 
air spaces, connective tissue, and blood vessels. The air 
Figure 127. — The lungs and air passages (/l); B, a small part of the 
trachea or windpipe, magnified, showing cilia and cartilage in the wall; 
air sacs in upper right hand corner are a portion of A enlarged; D, the 
tiniest air sacs still more enlarged. 
spaces make them light and spongy, so that they expand 
and contract readily with each inspiration and expiration. 
In their movements the lungs rub against each other, 
against the diaphragm, against the heart, and against the 
walls of the thorax. To reduce friction they are covered 
with a double bag, two pleura (singular pleura), between 
the two layers of which is secreted a liquid, the pleural 
192 THE LUNGS 
193 
fluid. One pleura thus covers the lungs, while the other 
lines the thorax, as shown in Figure 121. When one’s 
pleurae become inflamed and hot, one is said to have 
pleurisy. 
How we Breathe. We breathe by making the cavity 
of the chest alternately larger and smaller. When it is 
Figure 128. — The 
chest and abdomen 
in inspiration. AB, 
horizontal diame- 
ter; CD, vertical 
diameter of chest; 
D, diaphragm. 
Figure 129. — The 
chest and abdomen 
in expiration. A, 
B horizontal di- 
ameter decreased, 
D, diaphragm elev- 
ated by expiration. 
Figure 130. — Inspiration is 
due partly to the raising of 
the ribs. Solid lines, posi- 
tion of organs in expiration; 
dotted lines, in inspiration. 
Muscles between two of 
the ribs are shown at M. 
made larger there is more room for air, and air comes in to 
till the space. The question “How we breathe” becomes 
u How do we make the cavity of the chest larger or smaller? ” 
A study of Figures 128-130 will illustrate the two ways of 
increasing the capacity of the chest; namely, by raising 
the ribs and by lowering the diaphragm. This is done by 194 
THE HUMAN BODY AND ITS ENEMIES 
the action of the muscles of the chest and by the contrac- 
tion of the diaphragm, which is really a large, flat muscle. 
When the ribs are lowered, the capacity of the chest is 
lessened and air is forced out of the lungs. Figure 128 
shows the ribs raised and the diaphragm lowered in inspira- 
tion. Figure 129 shows the ribs lowered and the diaphragm 
raised in expiration. Figure 130 shows both positions. 
The Air Sacs of the Lungs. Thus by breathing move- 
ments the air is drawn into the lungs through the air 
passages. The oxygen finally is carried down into the finest 
Figure 131.—Diagram illus- 
trating respiration in the air 
sac of the lung. C02 = car- 
bon dioxid. O = oxygen. 
Figure 132. — An 
air sac in the lungs, 
surrounded by 
blood capillaries. 
Figure 133. — Diagram 
illustrating respiration 
of a cell at a distance 
from the lungs. 
air tubes (Fig. 127). At the ends of these there are air 
spaces or air sacs surrounded with extremely thin walls. 
(See lower part of Figure 121 and also C and D, Figure 
127.) Around the air sacs, very close to these thin walls, 
are many blood capillaries. Just as the food passes through 
the villi of the small intestine into the blood, so in the 
lungs oxygen passes from the air sacs of the lungs into 
the surrounding blood capillaries and carbon dioxid passes 
from the blood vessels into the air sacs by diffusion, as 
indicated in Figure 131. At the cells in other parts of the 
body the exchange of oxygen for carbon dioxid again takes 
place, as discussed in chapter XXXI and again shown in the THE LUNGS 
195 
diagram (Fig. 133). The intimate relation of the blood 
vessels and air sacs is shown in Figure 132. 
Hygiene of the Lungs. In pneumonia, the disease 
germs cause an inflammation of the lining of the air sacs. 
In asthma, the smaller bronchial tubes become partially 
stopped up, rendering it difficult for the patient to get 
oxygen to the air sacs. How do the germs of pneumonia 
reach the lungs? 
The linings of the air sacs are also injured by alcohol. 
This gets into the blood in the stomach and the intes- 
tine and comes out into the breath through the air sacs, 
as proved by the odor of the drinker’s breath. The 
air sacs become inflamed, and therefore more liable to 
become diseased and incapacitated for the work they have 
to do. 
The use of cigarettes is so injurious that many states 
have laws against their sale. Their worst damage is to 
the lungs, for much of the poison in cigarettes is inhaled 
and reaches the air sacs. 
Exercise is an important means of increasing the capacity 
of the lungs and the power of the chest to expand. Breath- 
ing movements or breathing exercises are helpful, but the 
best way to develop the lungs is by playing vigorous games 
in the open air. 
The lungs contain the air sacs, or hollows at the ends of the air 
tubes. The air sacs have very thin walls and are surrounded 
by meshes of blood capillaries. It is here that the blood gives 
off the carbon dioxid and takes on the oxygen. The air in the 
lungs is renewed by the breathing movements of expiration and 
inspiration, due to the action of the diaphragm and the muscles 
that raise and lower the ribs. The air sacs may be injured by 
alcohol and tobacco, the use of which should be avoided. Games 
in the open air are for most people highly beneficial to the 
lungs. How to prevent disease germs from harming the res- 
piratory organs is fully treated in the first part of this book. 
SUMMARY 196 
THE HUMAN BODY AND ITS ENEMIES 
QUESTIONS 
i. How are the lungs protected from injury? 2. What are the 
pleurae? 3. How is friction of the lungs against the wall of the 
chest prevented? 4. C, Figure 127, is an enlarged portion of what 
part of A? 5. Similarly, explain the relation of D to C and A. 
6. Draw D, Figure 127, placing the blood capillaries about it properly 
(See Fig. 132). 7. Describe how the blood gets rid of carbon 
dioxid and gives up oxygen. 8. Explain two ways by which we 
breathe. 9. Explain the meaning of Figures 117 and 133. 10. 
How are the lungs often injured? 11. Name several diseases of the 
lungs and air passages, and state in each case how the disease may be 
avoided. CHAPTER XXXIV. VENTILATION 
How Air is Made Foul. Abundant reasons have already 
been given why we need oxygen. Outside air consists of 
about 21 per cent oxygen and about 79 per cent nitrogen, 
with only a very slight trace of carbon dioxid. But the 
air expired from our lungs has only 16 per cent of oxygen, 
4.4 per cent of carbon dioxid, and some water vapor; the 
nitrogen remains the same. 
Other poisonous matter is given off from the lungs in 
addition to carbon dioxid. When many persons remain 
in a room for some time, the organic matter from the 
lungs, and from the skin as well, makes the air of the room 
smell bad. The nose, therefore, is a good guide to detect 
bad air in rooms, provided one has first been in the open 
air; for after any one has been in foul air for a while, he 
can no longer detect the bad odor with his nose. In any 
case, however, he can often tell that the air is bad from 
his sick and drowsy feeling and headache. Carbon dioxid, 
organic substances from the lungs and the skin, and disease 
germs, therefore, poison the air that people breathe. 
They cause sickness, and, in extreme cases, death. 
Ventilation. The foul air about us should be removed 
constantly. In the open air the wind carries our foul 
breath away, but we must remove the foul air from the 
buildings we live and work in and bring in fresh air artifi- 
cially. This process is called ventilation. In what sense 
is breathing a ventilation of the lungs? Just as we ven- 
tilate the lungs, so, if we build houses around us, we must 
ventilate these houses. 
Every person needs 3000 cubic feet of fresh air per hour. 
On a cold day the air cannot be changed over five times in 
an hour. Every person should, therefore, be surrounded 
by 600 cubic feet of space in the room in which he stays. 
Figure out how far your school room falls short of this 
standard. 
Principles of Ventilation. To supply this fresh air, 
such buildings as theaters, large churches, office buildings, 
197 198 
THE HUMAN BODY AND ITS ENEMIES 
and some large schools have electric blow-fans that cause 
drafts of air, previously heated, to blow through the rooms 
and hallways. But in our homes, and in most churches 
and schools, we must heat and ventilate without any spe- 
Figure 134. — Experi- 
ment with box and 
candle. 
Figure 135. — Experiment to show out- 
going current of warm air and incoming 
current of cold air at a window. 
cial fans or airshafts. Ventilation as ordinarily applied 
with stoves and furnaces depends upon the fact that heated 
air rises, because it expands, becomes lighter, and is pushed 
up by cold air coming in from all sides, as can easily be 
seen from the following experiments: 
Experiments, (i) Take a plain wooden box, set it on end, 
and cut two holes in it, as shown in Figure 134. Place a lighted 
candle on the inside. After ventilation has begun, hold a 
smoldering match or small rag at each hole and note the direc- VENTILATION 
tion of the current as indicated by the smoke. (2) Now try 
the same experiment on the school room, if this is heated and the 
wind is not blowing too hard on the outside. Hold a burning 
match or a candle at the top of an open doorway or window and 
then at the bottom, and note the direction of the current in 
each case (Fig. 135). 
Prevention of Draft. From your observations in the 
experiments with the box and the candle, how would 
you ventilate by means of win- 
dows only? You would lower the 
top sash and raise the bottom sash. 
If the stove stands at one end of the 
room, you should ventilate by the 
windows nearest the stove. Why? 
Ventilating by this method is 
imperfect because the warm air 
passes out of the top of the win- 
dow without doing the occupants 
of the room any good; and the 
cold air comes in at the bottom, 
causing a draft. A better way 
is to leave the top sash in place, 
raise the lower one, and place a board in front of the 
open space, as shown in Figure 136. 
Ventilation of School Rooms. All these methods may 
do fairly well for homes during the day, for there are not 
many persons in a room at a time, and fresh air comes in 
through the doors, which are opened and closed frequently. 
For the school room, where thirty to sixty pupils are 
breathing for some hours at a time, the methods given are 
absolutely inadequate. It is not too much to say that 
more children die from the indirect effects of foul air in the 
school room than from exposure on the way to and 
from school. There is absolutely no excuse for building 
a school house that cannot be ventilated properly. The 
following points should be kept in mind: 
Figure 136. — A simple 
means of ventilating in 
very cold weather. 200 
THE HUMAN BODY AND ITS ENEMIES 
1. Heated air rises. The arrows in Figure 137 indicate 
the directions of air currents. Discuss the ventilation of 
this school room in class. 
2. Fresh air should be furnished, but this should first 
be warmed. Where should the inlet therefore be? Study 
Figure 137. — A schoolroom equipped with jacketed stove and venti- 
lating flue. Arrows indicate direction of air currents. Fresh air comes 
through a grate in the floor, passes up between the hot stove and the jacket 
and supplies the room with warm, fresh air. The foul cool air passes through 
a grate in the wall behind the stove, into the foul-air vent of the chimney 
and thence to the outside. 
Figure 137 and note that the warm fresh air circulates 
about the room. 
3. This warm fresh air should not be allowed to mix with 
the foul air of the room. The stove should, therefore, be sur- 
rounded by an iron jacket reaching to the floor (Fig. 137). 
4. There should be an outlet for the foul air. This is 
in connection with the chimney, which should have two 
compartments, as shown: one for the smoke, the other for 
the foul air. The outlet should be near the floor, as it is in 
the illustration. Why? Draw a picture with an outlet at 
the top of the room and show by arrows how the air would VENTILATION 
pass out. A small fireplace instead of a mere opening is 
desirable. Other details can be gathered from the picture.1 
Outdoor Sleeping. Many people in Texas, as well as in 
all other parts of the civilized world, are sleeping out- 
of-doors. Indeed, patients suffering from such terrible 
diseases as tuberculosis and pneumonia are treated by the 
fresh-air method. If oxygen is good for one who is sick,, 
it ought to be good for one who is healthy. How much 
time do we spend sleeping each day? How many years 
in a lifetime of seventy is this? If all this time were spent 
in fresh air, you can readily see how much healthier we 
should be. Figure 32 represents a sleeping porch con- 
structed for outdoor sleeping. If any one cannot have 
this, it is important that one sleep with windows open, of 
course keeping well covered and avoiding direct drafts. 
The rooms we live in should be well ventilated to keep the 
air relatively pure. This is almost as important as breathing 
itself. Where many persons stay in a room for a long time, as 
pupils in a school room, there should be means of ventilating 
the room without cold drafts. This is best accomplished by 
means of a jacketed stove so arranged as to furnish warm fresh 
air and remove cold foul air continuously. 
SUMMARY 
i. Why is oxygen needed by the body? 2. How does expired 
air differ from inspired air? 3. What are the harmful substances 
given off by the breath? 4. Define ventilation. 5. How can you 
tell if your school room is poorly ventilated? 6. Explain Figures 
134 and 135. 7. Mention some rules for ventilating an ordinary 
room. 8. Explain in full the circulation of air in Figure 137. 9. 
Where does the fresh air come in? 10. Where does the foul air pass 
out? 11. How is the foul air of the room kept from mixing with the 
fresh air coming in under the stove? 12. What are the special 
advantages of sleeping out-of-doors? 
QUESTIONS 
1 Any school board in Texas desiring literature and expert advice on 
the subject of building school houses may obtain both free by addressing 
the Department of Extension, University of Texas, or the State Superinten- 
dent of Public Instruction, Austin, Texas. CHAPTER XXXV. THE CIRCULATION OF THE 
BLOOD 
A good deal has already been said about the blood and 
the lymph and their functions. At this stage of your 
study, it is perfectly plain to you that the main function 
of the blood is to carry the useful materials of food and 
the oxygen to the cells of the body and to take away the 
harmful waste substances. The blood flows in a system 
of closed tubes. It is the thinnest and smallest of these, 
the capillaries, that carry the blood close 
enough to the cells of the body so that 
the food and waste substances may be 
exchanged between the blood and the 
cell. The lymph surrounding cells and 
the capillaries together form the medium 
through which the food and waste mate- 
rials pass to and from the cells; see Figure 
113. Capillaries also come close to the 
cells of the glands (Fig. 105), the villi 
(Fig. no), and the air sacs of the lungs 
(Fig. 132), as has been shown. In short, 
the capillaries of the blood come close to 
each and every living and working cell 
of the body. 
The Blood as a Carrier. To take on 
a load of food or oxygen the blood must 
go to the proper organ to get it, just as 
your grocer must go to the freight depot 
to get the groceries before he can supply 
you with them. The blood is pumped 
by the heart to the supplying organs: first to the lungs, 
where it receives its load of oxygen. Here the arteries 
break up into capillaries which surround the air sacs. 
Through the thin capillary wall and the thin walls of the 
air sacs the blood takes in oxygen and gives off carbon 
dioxid. The purified blood then goes back to the heart 
to be pumped out again to all parts of the body. In the 
Figure 138.—The 
lesser circulation 
(through the lungs) 
and the greater cir- 
culation (through 
the body). 
202 CIRCULATION OF THE BLOOD 
203 
same way the blood passes through the stomach and 
the small intestine and takes on food, which is carried by 
the blood to the heart to be pumped out to all the cells. 
The Lesser and the Greater Circulation. It is to be 
noted that a special trip is made to the lungs; the blood 
goes to them and then straight back to the heart. This is 
the lesser circulation (Fig. 138). When the blood starts out 
again from the heart it goes to all parts of the body, passes 
through the capillaries among the cells, and returns again 
to the heart. This is the greater circulation (Fig. 138). 
In short, the heart pumps blood into arteries; these 
divide again and again into finer and still finer arteries, 
which finally become capillaries in the lungs and other 
parts of the body. The capillaries combine to form 
veins, which return the blood to the heart. The blood is 
Figure 139. — Showing manner of mounting a tadpole to observe the 
circulation of blood in arteries, veins, and capillaries. (See p. 204.) 
forced out by the pumping action of the heart. It returns 
partly by this force and partly by other forces, as will be 
described later. 
Observation on the Circulation of the Blood. If you 
hold your hand up to a bright light, you see the red color plainly  THE HUMAN BODY AND ITS ENEMIES 
204 
through the skin. But you cannot see the blood flow. If you 
chop a chicken’s head off, the blood will run out and the blood 
will flow, but this is not circulation. Very favorable subjects 
for studying the circulation are the thin web of a frog’s foot 
and the thin membrane at the sides of the tail of a tadpole. 
To see the latter a compound microscope is needed. But the 
sight is so beautiful that it is well worth while to go to some 
trouble to have a high school teacher or a local physician bring 
his microscope and show you the sight. 
Tadpoles can be found in standing pools of water at almost 
any season in Texas. Secure one and put it in place, as in Fig- 
ure 139. To do this the tadpole 
should be lightly covered with 
cotton (C) kept wet with water. 
The piece of tin is bent at right 
angles and has a hole (H) through 
which the tail of the tadpole pro- 
trudes. This hole should not be 
so large as to allow the whole 
animal to slip through. The tail 
is laid over the slit (S) in the 
shingle so as to let the light 
through in viewing a thin part of 
the tail, as at point X, with a 
microscope. Here the circulation 
of the blood can be well seen. 
A thread may be strung over the 
tail to keep it from flapping dur- 
ing observation. If you are fortunate enough to view this 
sight, note that the blood flows through the capillaries in a 
steady stream and not in jerks. 
Figure 140. — A network of blood 
capillaries connecting an artery 
with a vein. 
How the Blood Circulates. The word circulate means 
to travel in a circle. When we say the blood circulates 
we mean that it continues to return to its starting point. 
We noted above that this is what happens. The blood is 
forced on its journey by the heart. From the heart the 
blood travels in the arteries. These arteries divide into 
smaller and smaller branches, until the finest hairlike CIRCULATION OF THE BLOOD 
205 
arteries become capillaries (Fig. 140). The blood now starts 
on its journey back to the heart again. The capillaries com- 
bine to form veins, which continue to unite as they proceed 
to the heart. The blood passes through two sets of capilla- 
ries on one complete round through the body: through the 
capillaries of the lungs, and through the capillaries in 
different parts of the body, but the blood goes each time to 
the heart to be pumped out again, as shown in Figure 138. 
In what sense are there two circulations? In what sense 
is there really but one complete circulation? 
The Heart. The heart has a single duty to perform, and 
that is to pump blood. It is, therefore, composed largely 
of muscle and connective tissue. It is located in the 
thorax, between the lungs, just a little to the left of the 
middle line, with the point directed to the left (Fig. 73 
and Fig. 141). We can feel the beat of the heart between 
the fifth and sixth ribs. As this organ is in motion a large 
part of the time, we should expect it to be protected against 
friction. How are the lungs protected against friction? 
Name the coverings of the lungs. The heart is in the 
same way covered by a two-layered bag, the pericardium, 
with a lubricating liquid between the layers. 
The heart is divided into two halves by a solid partition 
wall. No blood can pass from one side of the heart to 
the other except by going around through the capillaries. 
The blood must pass through the capillaries of the lungs to 
go from the right side to the left side, and through other 
parts of the body in passing from the left to the right side 
(Fig. 138). Each half of the heart consists of a thin- 
walled upper chamber called the auricle, to receive the 
blood, and a thick-walled lower chamber called the ven- 
tricle, to pump the blood out into the arteries. How many 
chambers has the heart? Name them. 
Two large veins bring the blood back to the heart from 
all parts of the body: the descending vena cava, from the 
upper part of the body (7, Fig. 141), and the ascending 206 
vena cava, from the lower part (8). One pulmonary artery 
(5) leaves the right ventricle for the lungs, and four pul- 
monary veins (20) carry the blood back to the left auricle. 
One large artery, the aorta (6), takes the blood out of the 
THE HUMAN BODY AND ITS ENEMIES 
Figure 141. — A view of the principal arteries and veins. 1, right ven- 
tricle; 2, right auricle; 3, part of left ventricle; 4, corner of left auricle; 
5, pulmonary artery (to lungs); 6, aorta; 7, vena cava, descending; 8, 
vena cava, ascending; 9, renal artery (to kidney); 10, renal vein (from kid- 
ney); 11, right and left subclavian veins; 13 and 16, left and right subcla- 
vian arteries; 12, jugular veins; 14 and 15, left and right carotid arteries 
18, veins from abdominal organs; 19, arteries to abdominal organs. 
Figure 142. — Left side heart, with left ventricle (3) and auricle (4) cut 
open; 20, two of the four pulmonary veins, from lungs; 21, valves of pul- 
monary artery (5) almost closed; 24, similar valves of the aorta (6), with 
part of the aorta cut away; 22, valve between auricle and ventricle; 23, 
cords and muscles holding the valves. 
left ventricle to all parts of the body. How many veins 
come back to the heart? How many arteries leave the 
heart? 
The Action of the Heart. After the blood has come into 
both of the auricles, these contract and push the blood CIRCULATION OF THE BLOOD 
207 
into the ventricles. Then the ventricles contract, pushing 
the blood into the arteries. The contraction of the ven- 
Figure 143. — Diagrams of heart, showing action of valves; A, at expan- 
sion of heart; B, at the beginning of contraction. Diagrams a and b 
illustrate action of valves between auricle and ventricle. 
tricles constitutes the heart-beat. Since the arteries 
are already full, pumping more blood into them makes 
them expand; this expansion is called the pulse. Since 
Figure 144. — Valves in 
aorta. (Compare with 
Fig. 142, in which part of 
the aorta is shown cut 
away.) 
Figure 145 — 
The valves in 
Fig. 144, closed, 
as seen from with- 
in the aorta. 
Figure 146. — A vein with 
several branches laid open, 
showing valves that pre- 
vent the blood from flowing 
back. 
this happens at every heart-beat, you can count the heart- 
beat by feeling the pulse. The blood is kept from going 208 
THE HUMAN BODY AND ITS ENEMIES 
back into the auricles from the ventricles by flaps of con- 
nective tissue, so placed and held by cords (Fig. 142) that 
the blood catches under the flaps and closes them after the 
manner of Figure 143, B. This is illustrated further by 
diagrams a and b of the same 
figure. So, too, when the ventri- 
cles expand and rest between beats, 
the blood, under pressure in the 
arteries, tends to gush into the 
ventricles. It is kept from return- 
ing, however, by pockets fastened 
to the walls of the arteries (shown 
at 24 in Fig. 142, and again, 
more enlarged, in Figs. 144 and 
145). Such flaps or pockets that 
prevent the blood from going in 
the wrong direction are called 
valves. Point out the valves of 
the heart in the illustrations, and 
explain how each acts. How many 
sets are there? 
Observation Work, (i) Find the 
pulse on your wrist and count the 
number of heart-beats per minute. 
(2) Listen to the heart-beat of some 
person by pressing your ear against 
the chest or back on the level of the 
heart. You will hear two sounds at 
each beat. These are partially due 
to the closing of the valves, or as it 
might be called the slamming of the doors. Which valves 
close to make the first sound? (Remember that the right and 
left ventricles contract and expand together.) (3) Study 
Figures 141 and 147 and trace the blood in a circuit through 
the body. Trace it from the head back to the head; from 
the lungs back to the lungs; from the liver back to the liver. 
Figure 147. — Diagram of 
the circulation of the blood. 
Compare with Figure 138. CIRCULATION OF THE BLOOD 
209 
There is one vein that deserves special mention. It is 
the portal vein. It carries proteins and sugar from the 
small intestine to the liver. 
SUMMARY 
The blood is the carrying agent of the food to all parts of 
the body. It is pumped by the heart into the arteries, which 
branch and gradually become capillaries. The walls of the 
capillaries are extremely thin, and the blood in the capillaries 
comes so near the cells of the body that it can give off food to 
the cells and take on waste products from the cells. Blood is 
returned to the heart by the veins. The blood passes through 
the capillaries of the lungs, back to the heart, and through the 
capillaries of the rest of the body in one complete circulation. 
The heart consists of four chambers: the right auricle, to 
receive the blood from all parts of the body; the right ventricle, 
to pump the blood to the lungs; the left auricle, to receive the 
blood from the lungs; and the left‘ventricle, to pump the blood 
to all parts of the body. Valves are so arranged as to direct 
the flow of blood in the right direction. 
QUESTIONS 
i. What is the chief function of the blood? 2. Define artery, 
vein, and capillary. 3. In which of these blood vessels does the 
blood come nearest the muscle and gland cells of the body? 4. 
Why have the capillaries thin walls? 5. What does the blood take 
up in the lungs? In the small intestine? From the various working 
cells of the body? 6. What does the blood give off to these cells? 
7. What does it give off in the lungs? 8. Name the chambers of 
the heart. 9. From Figure 143 describe the action of the heart in 
pumping blood. 10. What is the use of the valves between the 
auricles and the ventricles? n. What is the use of those at the 
openings of the arteries? 12. How many times does the heart beat 
each minute? 13. Trace the course of blood from the right auricle 
to the left ventricle. 14. Trace the course of blood around to other 
parts of the body as the teacher may direct. CHAPTER XXXVI. THE BLOOD AND THE 
LYMPH 
What the Blood is. We have seen that the blood is 
the great carrier of the body, taking food and oxygen to 
the cells and carrying waste matter away. Most of these 
substances are carried simply in solution, that is in a liquid 
condition. Blood is largely water containing dissolved 
substances. 
Review Work. Make a list of all the substances you would 
expect to find dissolved in the blood. 
Blood contains certain cells called corpuscles: red and 
white. They are extremely small; one small drop the size 
of a pinhead contains several million red corpuscles and 
many thousands of white ones. In the left of Figure 148 
Figure 148. — Blood corpuscles, highly magnified. 
A, red, and B, white blood corpuscles. 
are shown two masses of red corpuscles as often seen 
under the microscope. Above these one corpuscle is 
shown in end view and, in the middle of the figure, three 
corpuscles in flat view. Describe the shape of a red 
blood corpuscle. White corpuscles are shown at B. The 
blood is easily studied with a large microscope, and this 
should be done if possible. This sight through the micro- 
scope will certainly be a revelation to you, for who would 
think, after looking at a drop of blood with the naked eye, 
that it is made up of so many different things? 
210 THE BLOOD AND THE LYMPH 
211 
The Red Blood Corpuscles. The red corpuscles are of 
just the right size to pass through the capillaries in single 
file, as can be plainly seen in the tail of the tadpole. 
Now, when you are told that it is the duty of these little 
cells to carry oxygen from the air sacs of the lungs, you will 
readily see why they must pass in single file. At a circus 
the crowd passes in single file by the ticket window to 
get the tickets, and each person deposits his ticket at 
the entrance. Copy Figures 131 and 133, and add to your 
drawing red corpuscles in the capillaries. 
How the Red Blood Corpuscles Carry Oxygen. Just 
how the corpuscles carry oxygen is not easy to understand. 
Oxygen in the air is a gas, and in 
that condition a little oxygen takes up 
a great deal of room. The oxygen makes 
itself small by uniting with a substance 
called hemoglobin, which is found in 
the red blood corpuscles. When there 
is much oxygen present, as in the air sacs 
of the lungs (Fig. 131), the hemoglobin 
causes the oxygen to unite with it, and 
in this condition the oxygen takes up 
almost no room. But the oxygen will 
easily let go of the hemoglobin when 
the blood reaches a place where oxygen 
is scarce, as it is out among the working 
cells of the body (Fig. 133). 
The White Blood Corpuscles. The 
white corpuscles differ from the red ones 
for they can change their shape, and 
they have also quite a different work to 
do. They are the soldiers and scaven- 
gers of the body. What is a soldier’s 
duty? A scavenger’s? . The white 
corpuscles fight for ns, swallowing and digesting the 
disease germs of the body (Fig. 12, page 16). They also 
Figure 149.— Blood ves- 
sel of frog, showing how 
white blood corpuscles 
pass out of the blood 
vessel. A, corpuscle 
within the vessel; B, 
partly, and C, entirely 
outside the vessel. R, 
red corpuscle.  THE HUMAN BODY AND ITS ENEMIES 
212 
take up fragments of worn-out protoplasm among the 
cells. If you stick a splinter in your finger, the white 
corpuscles travel to the spot and try to surround the 
splinter and protect the body. These corpuscles can 
get out of the capillaries by squeezing through them 
between the cells, just as you would squeeze a large- 
sized rubber ball through a small crack in a fence 
(Fig. 149). 
Where the Corpuscles are Produced. Both kinds 
of corpuscles are continually being worn out and new 
ones produced. The red ones are made by certain 
cells in the red marrow of flat bones and in the spleen; 
the white ones by certain cells in the spleen and lymph 
glands. 
What happens to the body if we have too few white 
blood corpuscles? What do the cells lack if the blood has 
too few red ones? If the red ones are scarce in the blood 
of a person, he is said to suffer with anemia. In malarial 
fever the germs destroy the 
red corpuscles. A patient 
suffering with this disease 
is anemic and shows it by a 
pale or sallow complexion. 
Hookworm patients, too, are 
anemic, owing to the loss 
of blood that is sucked from 
the wall of the intestines by 
the worms. It is important 
that we should do everything 
to help the body produce 
many corpuscles. Plenty of 
fresh air, good food, sleep, 
and exercise are conducive to the production of blood 
corpuscles. 
Clotting of Blood. How does the blood act when it 
runs out of- a cut or other wound? It clots, you say. 
Figure 150.— Clotted blood, show- 
ing fibrin strands; RC, red, and 
WC, white blood corpuscles. THE BLOOD AND THE LYMPH 
213 
This is due to the strands of fibrin that the blood contains 
(Fig. 150). Fibrin is a kind of protein, which separates out 
or coagulates, just as the white of an egg, another kind of 
protein, coagulates when it is heated. There is a protein 
in the blood that coagulates and changes to fibrin when it 
is exposed to the air. 
Observation Work. Leave a bottle at 
the butcher’s and ask him to have it filled 
with ox blood. 
When you call for the bottle and take it 
to school, a dark red clot will have formed 
(Fig. 151). Of what does this clot consist? 
The straw-colored liquid on top is serum; 
this contains water, foodstuffs, and wastes 
in solution. It also contains antitoxins when 
these are present in the blood (Fig. 116). 
Figure 151.— Clotted 
blood in a tumbler. 
The Lymph. There is another fluid in the body very 
much like the blood; namely, the lymph. Read again 
what has been said of lymph and describe where it is found. 
Lymph differs from the blood, for it lacks red blood cor- 
puscles and clots more slowly than the blood does. Per- 
haps you remember when you last had a blister from 
a burn. The blister was filled with thin lymph. The 
fluids contained in the pericardium, between the pleurae, 
and around the abdominal organs are kinds of lymph. 
After studying Figure 113 you will understand that the 
function of the lymph is to fill the spaces among the cells 
of the body and to form the means of communication 
between the cells and capillaries. Which substances are 
given to and which taken from the cells in Figure 113? 
A little thought will also tell you where all the lymph 
probably comes from: it oozes out of the blood capillaries 
and is, we might say, the liquid part of the blood. The 
cells also add their waste substances to the lymph. The 
lymph helps the blood to carry off these waste substances. 214 
THE HUMAN BODY AND ITS ENEMIES 
The Lymphatics. Now the lymph must be constantly 
renewed and therefore constantly drawn off. It does not 
pass back into the blood directly, but it has vessels of its 
own, the lymph capillaries and lymph vessels, that carry the 
Figure 152. — Lymphatic capillaries (L) beginning 
in the lymph spaces among cells of the body. 
lymph away. The lymph capillaries start in the lymph 
spaces (Fig. 152) and unite into veins just as the blood 
capillaries do. The lymph veins all finally unite in two 
large lymphatic ducts, the larger of which, on the left 
side, is called the thoracic duct. Figure 153 shows where the 
two ducts are situated. Note that they empty into large 
veins above the heart, where the lymph again mixes with 
the blood. The liquid portion of the blood that comes out 
of the capillaries thus runs back into the blood. 
There is another special starting point for the lymph. 
Review what was said about the lacteals and tell where 
they are and what these lymph vessels carry into the blood. 
The lacteals unite and empty into the thoracic duct (Figs. 
hi and 153). 
Lymph Glands. On their way the lymph tubes pass 
through knots of spongy tissue, called lymph glands, or 
lymph nodes. Ftere certain changes occur in the lymph; 
disease germs are stopped here and kept from going into 
the blood. The lymph glands also produce corpuscles, 
as mentioned above. The spleen is a large gland very 
much like lymph glands. Figure 153 shows the location THE BLOOD AND THE LYMPH 
of some of the lymph glands of the body. Figure 154 
represents a single one cut open. Note that the lymph 
vessels have cross lines 
on them. These show 
where the valves are, the 
use of which is exactly 
that of the valves in the 
215 
Figure 153. — The lymphatic 
system. LA C, lacteals. 
Figure 154. — A lymph node, 
with lymph vessels. 
veins. How blood is forced along in the veins and lymph 
in the lymph vessels will be described in the next chapter. 
SUMMARY 
The blood contains red and white corpuscles. The red 
blood corpuscles have to do with interior respiration, for they 
carry oxygen from the lungs to the cells of the body. The 
white corpuscles have to do with the fighting of disease germs 
in the body. The number of both kinds of corpuscles is in- 
creased by correct habits of living. The blood also contains 
a protein that forms fibers of fibrin, which cause the blood to 
clot. The lymph surrounds the cells of the body. It is moved 216 
THE HUMAN BODY AND ITS ENEMIES 
along and collected in lymph vessels, which empty into the 
blood vessels above the heart. 
QUESTIONS 
i. What have the red corpuscles to do with respiration? 2. 
What is the work of the white corpuscles? 3. In what organ of 
the body is each kind of corpuscle made? 4. What is anemia? 
5. How do hookworm and malaria cause anemia? 6. What is the 
value of the clotting of blood? 7. What is serum? 8. What parts 
of the blood does the clot (Fig. 151) contain? 9. Where is lymph 
found in the body? 10. Describe a lymph vessel, n. Is it more 
like a vein or more like an artery? Why? 12. What does the 
thoracic duct carry? 13. Where does it empty its contents? 14. 
What are the lymph glands? 15. How does exercise help the flow 
of lymph? CHAPTER XXXVII. HYGIENE OF THE 
CIRCULATION 
Differences between Arteries and Veins. Arteries and 
veins differ, as has been seen, in the direction in which the 
blood flows in them. In which does the blood flow away 
from the heart? They differ also in the thickness of their 
wails (Fig. 155). The veins have less elastic connective 
Figure 155. — Cross section of artery, vein, and two capillaries. 
E, epithelial lining (the only tissue in the capillaries); M, muscle 
tissue; C, connective tissue. 
tissue and muscle than the arteries. The veins, further- 
more, have valves throughout their course, as shown in 
Figure 146. Where are the only valves in the arteries? 
In the arteries the blood is under pressure. When an 
artery is cut, therefore, the wound stands open, blood 
spurts out, and a person is in great danger of bleeding to 
death. The arteries are protected by being placed deeper 
under the skin and muscles than the veins. When an 
artery is cut, pressure should be applied between the cut 
and the heart, to stop the bleeding, as will be described 
in Chapter LVIII. 
How the Blood Gets Back to the Heart. Contraction of 
the heart is the main force that sends the blood coursing 
toward the capillaries, where the blood does its main work. 
Now, let us see how the blood is forced back to the heart. 
First, the pressure from the arteries pushes the blood 
through the capillaries into the veins. Second, the blood is 
sucked toward the heart. The suction occurs in the chest 218 
THE HUMAN BODY AND ITS ENEMIES 
when we breathe in air. Third, the blood is squeezed on 
its way toward the heart every time any muscle contracts. 
When the muscle becomes hard and firm it presses against 
the blood vessels and thus tends to drive the blood out of 
them. To prevent the blood from flowing away from the 
heart, there are valves all along the veins, set as illustrated 
in the diagrams (Figs. 156 and 157). The suction action 
of breathing and the contraction of the muscles force the 
lymph along exactly as the blood is forced along the veins. 
Observation Work. You can easily locate the valves in 
a vein on the back of your hand or on your wrist. Hold your 
Figure 156. — Valves in 
vein, open. 
Figure 157. — Valves in vein, 
closed. 
hand down and press the muscles of your forearm on the edge 
of the desk. This will make the veins of the back of your 
hand stand out. Now, with the blunt end of your pencil, 
press along a vein toward the fingers (away from the heart) 
and note that the vein does not fill from the end toward the 
heart. 
How Exercise Helps the Circulation. From what has 
been said in this chapter it stands to reason that exercise 
improves the circulation in a number of ways: 
First, exercise causes a stronger beating of the heart, 
which strengthens this organ as it does any other muscle. 
We should take enough exercise every day to make the 
heart beat strongly for a while. Such exercise will enable 
the heart to endure hard work. 
Second, exercise causes deep breathing, which increases 
the suction of the blood and lymph toward the heart. 
Third, exercise helps the flow of blood through the 
muscles. That is the reason why muscles that are used a HYGIENE OF THE CIRCULATION 
great deal are darker than others.1 Since it is hardest for 
the blood to pass back to the heart from the lower limbs,, 
walking and running are very important forms of exercise. 
It should also be noted that rubbing a part of the body 
helps to improve the circulation of the blood and the 
lymph. 
Experiment to Show the Effect of Exercise on the 
Heart. Count the pulse after you have remained quiet for 
fifteen minutes. Stand up and after one minute count the 
pulse; walk a minute and count again; run or hop a minute 
and make another count. Why does exercise make the heart 
beat faster? Review previous lessons before trying to answer 
fully. 
Over Exercise. While it is true that the heart should beat 
strongly for a while each day, we must guard against too 
severe exercise, such as boys and girls in the grammar 
grades are likely to indulge in. At this age the heart 
grows very fast. The valves of the heart have not grown 
strong enough to stand the great pressure which its too 
vigorous beating may cause. Foot-racing, bicycle riding, 
football, and even tennis may easily be overdone. Gram- 
mar school boys should not attempt to run more than a 
fifty-yard dash or a quarter-mile relay race. 
Changes in the Quantity of Blood in the Arteries. You 
have noticed that after exercise your skin is red. This 
shows that more blood has been sent to the skin. When 
the body is warm, the skin is red; when the body is cold, 
the skin is pale. Embarrassment often causes blushing, 
and fear causes pallor. These are examples of change in 
the quantity of blood that is sent to the skin. Now the 
quantity of blood in an organ at any time depends upon 
the size of the blood vessels in that organ. When the 
arteries of the skin are expanded, they allow more blood 
to come in, and this is shown in the redder color of the 
skin after exercise and when one is embarrassed. 
219 
1 Compare, for example, the breast and the leg muscles of a chicken. 220 
THE HUMAN BODY AND ITS ENEMIES 
Alcohol. Alcohol causes the blood vessels of the skin to 
enlarge, For this reason a person feels warmer after a 
drink of whisky and some people think that this warmth is 
real. Since there is more blood in the skin, however, the 
actual effect is that the body cools off faster. It is, there- 
fore, a mistake to take whisky when starting out on a trip 
in cold weather. No one who uses alcohol could ever 
reach the North or the South Pole. A good quantity of 
fuel food and not alcohol is the real producer of heat and 
energy in the body. 
Other Effects of Alcohol on the Circulation. Alcohol 
makes the heart beat faster and so interferes with nature’s 
way of regulating the beat. The heart is thus overworked. 
It is said that alcohol in small quantities makes a person 
fat. But this fat is unhealthy, and if the fat is deposited 
about the heart, it becomes dangerous. Many deaths 
occur from diseases, because the heart fails to do its duty. 
This is specially true of pneumonia. You have heard it 
said of a sick person, “Tomorrow will come a turning point 
in the disease,” or “If he lives until tomorrow he will get 
well.” How necessary it sometimes is to have a heart that 
will hold out just one day longer! We cannot afford to 
do anything that will injure this wonderful organ, the 
heart. 
Tobacco. Doctors speak of an “alcohol heart” and a 
“tobacco heart”: an unsteady, palpitating, fluttering, 
unreliable heart. Tobacco is particularly harmful to the 
young boy of grammar or high school age. At that time 
the heart grows rapidly and any interference with its 
proper development is sure to lead to permanent injury. 
SUMMARY 
Arteries are not as easily cut as veins, because they lie deeper 
under the skin and muscles; but when cut it is more difficult 
to stop them from bleeding, since the blood in them is under 
pressure. Blood is returned through the veins to the heart by HYGIENE OF THE CIRCULATION 
221 
pressure transferred through the capillaries from the arteries 
by the sucking action of the breathing movements and by the 
squeezing action of the muscles of the body during exercise. The 
valves all along the veins keep the blood from flowing backward. 
The lymph is forced on its way by similar means. Exercise 
is necessary to the proper circulation of the blood and lymph, 
and to the strengthening of the heart. Alcohol has a decidedly 
harmful effect because it causes a faster beating of the heart 
and an increased flow of blood to the skin when these things 
are not necessary. Tobacco causes interference with the ner- 
vous control of the heart-beat. 
QUESTIONS 
i. Name some of the differences between veins and arteries. 
2. Where should pressure be applied to stop bleeding from an artery 
that is cut? 3. How does deep breathing help the circulation? 
4. Discuss the action of valves in the veins. 5. How does exercise 
help the flow of blood? 6. How does exercise strengthen the heart? 
7. What is the danger of overexercise? 8. How does alcohol injure 
the heart? Tobacco? 9. Why does alcohol really cause the body 
to lose heat? CHAPTER XXXVIII. EXCRETION 
The Meaning of Excretion. We have thus far con- 
sidered a number of activities of living cells: the taking of 
food, assimilation, growth, respiration, and other activities. 
You should be able to tell in your own words what each of 
these means. Digestion, absorption, assimilation, and 
growth are all building-up processes, which end in the mak- 
ing of protoplasm by the cells of the body. Then oxygen 
comes to the cell and burns up the protoplasm and the 
foods, and thus tears down or breaks up the protoplasm. 
Oxidation is a tearing-down process, but it is necessary in 
order that energy for warmth and motion may be produced. 
Oxidation not only produces energy, but also forms 
waste substances. The production of waste substances is 
called excretion. Every cell excretes waste substances 
(Fig. 113), and the blood carries them to the organs by 
which they are removed. The organs that remove waste 
substances from the blood are called excretory organs. 
The Waste Materials of the Cell. We have already 
studied one set of excretory organs,1 the lungs, which 
remove carbon dioxid from the body. Respiration thus 
includes two phases: the taking in of oxygen and the 
removing of carbon dioxid (Fig. 117). The lungs are, 
therefore, in a sense, organs of excretion which remove 
most of the used-up carbon from the body. 
Another important waste substance is that containing 
nitrogen and is called urea. This is removed by the kidneys 
and by the sweat glands of the skin. 
Thus it is seen that there are two main kinds of waste 
substances: carbon dioxid, which contains most of the 
carbon and is removed from the blood by the lungs; and 
urea, which contains all the nitrogen and is removed from 
the blood by the kidneys and skin. 
1 We shall not include here the large intestine, which removes indiges- 
tible and undigested foods, unabsorbed portions of the digestive juices, 
and bacteria from the alimentary canal. It is, of course, of extreme impor- 
tance to health that decaying remnants of the food should be removed 
-daily from the body. 
222 EXCRETION 
223 
The liver is sometimes included with the excretory organs,, 
but this is only partly correct. The liver does not remove: 
waste substances, but changes them to a form that is more 
easily removed by the kidneys and skin. 
The Kidneys. The situation and shape of the two 
kidneys can be seen in Figure 71; also at 16, in Figure 
Figure 158. — Vertical section of a kidney; II, hollow of kidney, com- 
municating with ureter. T, tubules (much enlarged) beginning in pockets 
and emptying in hollow, H. PY, masses of tubules beginning in pockets in 
region C. 
Figure 159. — Tubule and pocket of kidney, much enlarged; X, epi- 
thelial tissue of pocket, F and Z of tubule. Cap. 1, blood capillaries of 
pocket; Cap. 2, capillaries of tubule. 
Figure 160. — A portion of tubule much more enlarged. F, cells of: 
tubule. 
141. Figure 158 represents one kidney, opened, showing 
the internal structure. As the urea is carried to the kidney 
by the blood there are, as we would expect, a large artery 
(renal artery) leading to the organ, and a large vein (renal 
vein) carrying the blood away (9 and 10, Fig. 141). Which 
of these, artery or vein, has the smaller amount of im- 
purities in it? So you see that arteries do not always carry 224 
THE HUMAN BODY AND ITS ENEMIES 
purer blood than the corresponding vein. Give another 
example of this occurrence. 
Structure of the Kidney. The kidney is made up of a 
very large number of fine tubes or tubules that begin near 
the outer surface as little pockets of epithelial tissue. The 
pockets are indicated in the figure by dots (C, Fig. 158) 
and the tubules by lines (FT). These tubules pass toward 
the hollow of the kidney at H. Four tubules, enlarged, 
are shown at T in the same figure, two near the top and 
two near the middle of the section represented. From 
Figure 160 the course of the capillaries of the blood can be 
seen. A bunch of capillaries (Cap. 1) enters the pocket 
at the head of the tubule itself (Cap. 2). The cells that 
take water and waste substances out of the blood are the 
cells shown at X, F, and Z. The kidney is in a sense a 
gland. By comparing Figure 160 (a part of a tubule much 
magnified) with the gland shown in Figure 106, you may 
easily see how much the tubule of the kidney is like a gland. 
We have here another example of the close relation of 
working cells to the blood capillaries. The waste sub- 
stances here removed by the kidney cells are emptied into 
the hollow of the kidney at H, Figure 158, thence through 
the ureter into the bladder. 
Hygiene of the Kidneys. There are not many points 
to be remembered in the hygiene of the kidneys. A large 
percentage of the kidney diseases that occur are due in- 
directly to germ diseases such as scarlet fever and diphtheria. 
The kidneys have to filter out the poisons which the germs 
of such diseases as scarlet fever, diphtheria, smallpox and 
others form in our bodies, and this work is damaging to the 
kidney cells (X, Y, and Z, Fig. 160). The best way to 
take care of the kidneys is to take care of the body itself. 
It is wise to drink a great deal of water at all times, as 
this dilutes the poisons which are thrown off by the kid- 
neys. It seems reasonable to believe that all irritating 
substances which pass out through the kidneys, like alcohol EXCRETION 
225 
and the oils from hot condiments and spices, such as 
mustard or horse radish, will irritate the kidneys and in 
the long run damage them. Fried food contains certain 
irritating substances which are the result of the burning of 
the grease, and these substances must be thrown off by the 
kidneys. Lastly, sudden and extreme changes in tempera- 
ture may injure the kidneys. 
SUMMARY 
The pair of kidneys are the chief excretory organs of the 
body for the removal of urea. They are richly supplied with 
blood vessels. A study of the finer structure of the kidneys 
shows them to be true glands, for the capillaries of the blood 
enter pockets of gland tissue and surround tubules of the same 
kind of tissue. The gland cells take the waste material out 
of the blood and pass it on to larger tubes emptying into the 
hollow' of the kidney. Alcohol and toxins of disease germs are 
especially injurious to the gland cells of these organs. 
QUESTIONS 
i. Why do the cells of the body form waste substances? 2. Name 
the two chief kinds of waste substances produced and the organs that 
remove them from the blood. 3. Why has the renal vein purer 
blood than the renal artery? 4. What cells in Figure 160 take 
waste substances out of the blood? 5. In what regard are the 
pocket and tubule (Fig. 160) like glands shown in Figure 105? CHAPTER XXXIX. THE SKIN 
Description of the Skin. The skin is a double covering 
of the body. The thinner outer skin, the scarf-skin or 
epidermis (Fig. 161), is made up of dead, flattened cells, 
with the exception of the lowest layer. This lowest layer 
produces the cells in the outer layer of the skin as fast as 
Figure 161. — A block of skin about the size of a small grain of corn, 
magnified. All below the living layer of epidermis is dermis, PD, 
papillae of dermis; TB, touch buds in papilla; N, nerve; CAP, blood 
capillary; E, coil of sweat glands; EG, portion of duct of sweat gland more 
enlarged; CS, cross section of sweat duct; F, hair follicle; 06', oil glands; 
M, muscle of hair; C, connective tissue of dermis. 
they are ordinarily worn away. The epidermis contains 
few nerves and no blood vessels. 
The inner or true skin, the dermis, is made largely of 
connective tissue (C); this is, therefore, the part of the 
skin of animals that is made into leather. It is richly 
226 THE SKIN 
227 
supplied with blood vessels and there are many fat cells 
scattered through it. The fat helps to keep animals warm; 
the whale, for example, has a thick layer of fat under 
the skin so as to keep warm in the icy waters of the cold 
seas. 
The skin is the organ of touch. It contains nerves that 
end in certain cells placed where the dermis projects up 
into the epidermis; these projections, or papilla, contain 
the nerves of touch with which we feel things, — that 
is, distinguish hard and soft, wet and dry, sharp and 
dull, etc. With other nerves in the skin we distinguish 
heat and cold. 
The blood vessels in the skin perform their usual duty of 
serving the wants of the living cells. They must, in the 
first place, bring material with which the living layer of 
the epidermis can grow and multiply and produce more 
cells to take the place of those that wear off. The mass 
of cells worn off in the course of a year would, if they could 
be collected, fill a basket of considerable size. Dandruff 
is simply masses of skin cells from the scalp. To furnish 
materials to renew the worn-off cells, the blood comes 
through the dermis close to the living layer of the epidermis. 
(Compare Fig. 161; also C, Fig. 211). The blood also 
carries material for the hair and the sweat glands, that 
reach down from the epidermis into the dermis. 
The Hair. The hair is made up of the same substance as 
the epidermis; indeed, it is produced by epidermal cells 
that extend down into the dermis like a kind of socket. 
In this socket, called the hair follicle (F, Fig. 161), the root 
of hair stands. At the bottom of the follicle is a mass of 
cells that grow and multiply rapidly, adding to the hair 
and pushing it out as it grows. Hair thus grows from the 
bottom, or “root,” which is richly supplied with blood. 
Hair has attached to it two organs; first, a muscle (M), 
which by contracting can make the hair stand on end. 
A dog or a cat when angry uses these muscles to make the 228 
THE HUMAN BODY AND ITS ENEMIES 
hairs on its back stand up. Each hair is also provided 
with one or more oil glands (OG), which empty oil into the 
hair follicle. You have noticed how a leather harness 
cracks and breaks when not kept oiled; the skin and hair, 
too, must be oiled to keep them fresh and pliable. 
The Nails. The finger nails and the toe nails are also 
horny like the epidermis, but they are much thicker. 
They are produced from cells at 
the base or root of the nail, and 
are pushed forward as they grow 
(Fig. 162). The nails should be 
trimmed even with the fingers, but 
no farther. Dirt that collects 
under the nail should be removed 
with a dull instrument, — not with 
a sharp knife, for this roughens 
the under surface of the nail and 
makes dirt gather still more easily. Stains on the surface 
may often be removed with vinegar. 
Structure of the Sweat Glands. Other extremely im- 
portant organs of the skin are the sweat glands. These 
are simply tubes running down from the surface, through 
the epidermis, and for some distance into the dermis. 
They are coiled up at their lower ends. The coil (B, Fig. 
161) is surrounded by a network of blood capillaries as seen 
in diagram 5, Figure 105, and again in Figure 163. The 
epithelial tissue of the sweat gland comes in close contact 
with blood capillaries, as is the case with all glands. The 
sweat gland is coiled up in the dermis (B) because it is so 
long; there would not be room in the skin if all the sweat 
glands were stretched out straight. The sweat glands are 
long so that there may be much surface for excreting. 
Functions of the Sweat Glands. The sweat glands 
remove from the blood sweat or perspiration, which con- 
sists of water with salt and some waste substances dis- 
solved in the water. They are thus in part excretory, and 
Figure 162. — Longitudinal 
section of end-joint of finger. THE SKIN 
229 
each sweat gland may be compared to a single tubule of the 
kidney. Compare Duct, Figure 161, with Figure 159. 
How is a sweat gland similar to a tubule of the kidney in 
structure? But excretion is not the chief function of the 
sweat glands, for the perspiration is of great use to the 
body in helping to keep it from getting too hot, as will be 
explained below. Each gland 1 opens on the surface of the 
skin by a pore (Fig. 161). 
Figure 163. — Coiled end of sweat gland; the 
network of capillaries removed from its natural 
position around the coil. (Compare with 5, 
Figure 105, and B, Fig. 161.) 
Hygiene of the Skin. The skin must be frequently 
washed to keep it clean. Dirt, disease germs, the solid sub- 
stances dissolved in sweat, dead epidermal cells, and oils 
are continuously being given off by the skin. Good pure 
soap should be used in washing, for soap dissolves oil by 
breaking it up into tiny particles. The ease with which 
grease is removed by soap is familiar to every one. Soap 
is a good disinfectant and should be used for this reason 
also. 
1 The number of sweat glands in the adult has been estimated 
at 2,500,000. 230 
THE HUMAN BODY AND ITS ENEMIES 
Wounds. Disease germs cannot easily get into the 
blood through the unbroken skin. Hookworm larvae on 
the bare feet of children get into the blood vessels of the 
dermis by way of the hair follicles. Lockjaw germs 
usually live in the soil, especially around horse lots, they 
may, if present on the skin, be driven into and under the 
skin by a nail (Figs. 239-241) or a piece of firecracker or 
a cap of a toy pistol. When this happens a person may 
have lockjaw and die. If the skin is wounded and the 
blood runs freely and then dries well over the wound, 
remove the excess of blood with a dry, clean white cloth 
and tie the wound up without washing, for blood itself is 
a good cleanser. But if the wound is open, and dirt and 
bacteria are likely to get in, the wound should be washed 
with a disinfecting solution and bound up in a clean white 
cloth. 
Warts and Moles. Oftentimes you have noticed on 
the skin little tumors known as warts or moles. The 
warts are usually only temporary and harmless. The 
moles are usually harmless also, but may last a lifetime. 
Either wart or mole may degenerate or change into a 
dangerous tumor like a cancer, especially if it is in an 
exposed place where it is likely to be irritated. For this 
reason these warts or moles should not be allowed to be- 
come irritated. If they are in a place where irritation 
cannot be prevented, they should be thoroughly removed 
by a physician. Any sign of inflammation in a mole 
should be heeded, as it sometimes takes on a rapid growth. 
Pimples. All young people are interested in having a 
good complexion, and without doubt pimples on the face 
are the commonest cause of poor complexions. We do 
not know all the facts as to the cause of these pimples, 
and until we do we cannot do much toward preventing 
them. After the pimples appear, they are usually slow 
and stubborn to leave; but patience and care will drive 
them away. The problem of how to get rid of them is THE SKIN 
231 
too difficult to explain here, but it is best to make it a rule 
to get the entire body in as perfect health as possible, 
and not try plans of cure except those recommended by 
reliable persons. 
SUMMARY 
The skin consists of a thin outer layer, the epidermis, and a 
thicker inner layer, the dermis. The dermis is well furnished 
with blood vessels, which supply the sweat glands and the 
growing cells of the epidermis, the hair, and other organs of 
the skin. The functions of the skin may be summarized as 
follows: 
1. To form the covering for the body. (Both layers.) 
2. To protect the more delicate parts (a) from injury and 
(b) from disease germs. (Epidermis, hair, and nails.) 
3. To excrete waste. (Sweat glands.) 
4. To cool the body. (Sweat glands.) 
5. To act as the organ of touch. (Touch buds and nerves.) 
QUESTIONS 
i. What are the functions of the skin? 2. Name the organs 
found in the skin. 3. Point out (Figure 161) the living cells 
of the epidermis. 4. Wherein do the dermis and epidermis 
differ? 5. With Figure 161 before you, describe the skin. 6. De- 
scribe a hair. 7. Why do blood capillaries come close to the root 
of the hair? 8. To what part of a kidney does duct (Figure 161) 
correspond? 9. Wherein are the tubule of a kidney and a sweat 
gland alike? 10. Why may warts or moles become dangerous? 
11. How should we treat an open wound in the skin? 12. A closed 
wound, as a nail thrust? CHAPTER XL. THE REGULATION OF HEAT 
IN THE BODY 
If the temperature of a healthy person is taken, winter 
or summer, day or night, at rest or at work, it is always 
found to be near 98.6° Fahrenheit. The body is constantly 
giving off heat into the surrounding atmosphere. To make 
good this loss, foodstuffs are burned or oxidized in the 
body. The temperature of the body is the balance between 
the heat formed in the body and the heat lost. We have 
previously studied the use of food and oxygen in causing 
heat in the body. In this chapter we shall discuss how the 
body-engine is kept from becoming too hot or growing too 
cold. 
Distribution of Heat in the Body. When heat is pro- 
duced by exercising a muscle in one part of the body, the 
whole body becomes warmer. For example, if you work 
the right arm you will soon feel warm all over. If the 
extra heat is produced only in the arm, why does the arm 
not become hot? Why do all parts of the body feel warmer? 
The blood distributes heat over the body, drawing it away 
from the part being exercised. The blood, therefore, carries 
away from the working cells not only waste material, but 
also heat. 
It is now easy to answer the question, “What does the 
blood do with the heat brought away from the muscle 
cells?” The heat is carried to the skin, where the body 
comes in contact with the outside world. Here the heat 
leaves the body and passes into the surrounding air. This 
occurs all the time, but faster in cold than in warm weather. 
In winter, therefore, more heat must be generated by 
oxidation; for that reason it is well to eat more fats in the 
cold season. Alcohol is of no use and is positively harmful 
when taken for the purpose of increasing body heat. 
How the Body Gets Rid of Excessive Heat. During 
exercise the body must use special means of getting rid of 
excessive heat. Note the color of the faces of boys and 
girls coming in after recess from a frolic on the playground. 
232 HEAT IN THE BODY 
Their faces are flushed because more blood flows into the 
skin. This is brought about in the following manner: 
In the arteries of the skin, as 
in all arteries, there are muscles 
and nerves. When the muscles 
contract the artery becomes 
smaller and contains less blood. 
When they relax, the artery is 
dilated (made larger) and more 
blood rushes into the blood ves- 
sel. Heat stimulates the nerves 
that make the arteries expand. 
Therefore, when the body is 
warm the skin is red. 
In case there is much heat to 
be removed another thing hap- 
pens: the sweat glands begin to 
work faster, stimulated by the 
presence of warm blood around 
them. Sweat is poured onto 
the surface of the body, and 
there evaporates, carrying away 
much heat. When water evap- 
orates it absorbs heat, as can 
be seen by either of the follow- 
ing experiments: 
Experiments. (i) Take two 
thermometers. Set one in a vessel 
of water. Around the bulb of the other tie a cloth wet with 
water taken from the vessel in which the first thermometer is 
standing. Now fan the thermometers and note the drop in 
temperature of the one with the wet cloth (Fig. 164). (2) If 
the thermometers are not available, tie a dry handkerchief 
about one hand and a handkerchief wrung out of tepid water 
about the other. Wave both through the air vigorously. 
Which feels the colder, and why? Tell why a person feels colder 
in wet than in dry clothes. 
Figure 164. — Experiment to 
show effect of evaporation 
on temperature. A, ther- 
mometer in water (little 
evaporation); B, thermom- 
eter with wet rag, which is 
fanned to hasten evapora- 
tion. 234 
THE HUMAN BODY AND ITS ENEMIES 
In case of fever, the body becomes hotter than it is when 
in health, partly because the sweat glands fail to do their 
duty. The temperature of the body in fever rises above 
98.6° Fahrenheit. 
How the Heat of the Body is Retained. We have just 
learned how the body gets rid of excessive heat. In cold 
weather it is necessary to prevent loss of heat, for too 
low a temperature is- as dangerous to health as too high a 
temperature. 
If you recognize the fact that cold makes the arteries 
of the skin contract, you will readily understand Nature’s 
way of keeping necessary heat in the body: in just the 
opposite way from getting rid of it; namely, by driving 
the blood out of the skin into the body and away from the 
cold. The less blood brought to the skin, the less heat 
will escape from it. 
Catching Colds. Keeping the blood out of the skin is a 
safeguard within limits only. You must know that the 
skin may hold much blood. This is driven out of the skin 
by cold. When the body is cold for some time, causing 
great loss of heat, the germs of cold or grip present may 
get a foothold in the body, causing disease. Without the 
germs one cannot catch cold. Travelers in the icy North 
do not have colds, since there are no sick persons to scatter 
germs. On the other hand, even if germs are present, 
they are not likely to gain entrance into the blood unless 
the body is exposed to the cold. Thus, for example, it is 
dangerous for a person to sit in a cold room below 65° 
Fahrenheit or to wear wet clothing or too little clothing. 
Wet shoes and stockings are especial sources of danger. 
Cold fresh air is wholesome, however, when one is warmly 
clad. 
Alcohol and Body Heat. Alcohol is a drug that has the 
power of dilating the arteries of the skin, causing a rushing 
of blood to the skin, as indicated by the red face of the 
drinker. This makes a person feel warm for a while, but HEAT IN THE BODY 
235 
it does not make him warm. It really makes him cool, 
for the presence of so much blood so near the surface of the 
body results in a rapid loss of heat. To take a drink of 
whisky before venturing out into the cold is one of the 
worst things a person can do. Arctic explorers found out 
from experience long ago that alcohol is a great hindrance 
to feats of daring and endurance in the polar regions. 
But it need not be supposed that alcohol is a good thing 
in hot climates. It is a well-known fact that the death 
rate of those who use alcohol is even greater in the tropics 
than in our own temperate climate. 
Shelter. Food and oxygen to make us warm, and well- 
trained blood vessels in the skin, to regulate the heat, are 
not sufficient for man: he needs also clothing and shelter. 
Man’s life is largely spent in getting food, clothing, and 
shelter. 
The rooms of our houses should not only be well venti- 
lated, but should also be kept at the right temperature, 
68-72° Fahrenheit. If a school room is heated and venti- 
lated correctly, all parts of the room will be comfortable; 
none will be too hot or too cold, as in the case of many 
schools in Texas as well as elsewhere. A room should also 
have moisture enough, for if the air is too dry, the nose 
and throat will become parched and irritated. The 
moisture can be supplied by placing a pan of water on the 
stove. The effects of sitting in a room that is too cold 
have been explained. If the room is too warm, the blood 
vessels of the skin become dilated, and on going into the 
cold air the body loses too much heat from the rich supply 
of blood in the skin. 
SUMMARY 
The body is kept warm by the oxidation of the food and 
tissues. Fats are the best fuel food and are relished in cold 
weather. Alcohol is doubly harmful in the cold. The body 
must be kept at a nearly constant temperature not exceeding  THE HUMAN BODY AND ITS ENEMIES 
236 
98.6° Fahrenheit. The quantity of heat given off from the 
body is greater when the quantity of blood in the skin is greater, 
as during exercise or after drinking alcohol. Evaporation of 
sweat from the body is the most important means of removing 
the excessive heat from the body during exercise or in warm 
weather. In cold weather the skin has less blood, and less heat 
is consequently lost. When one’s body loses too much heat 
for a long period, one is likely to become sick with colds, grip, 
etc. It is important that our rooms be heated to the right 
temperature for health and comfort, and that the air in them 
should not be too dry. 
QUESTIONS 
i. What are the functions of the skin? 2. How is body heat 
produced? 3. What becomes of the heat produced in a working 
muscle? 4. What is the effect of heat on the arteries of the skin? 
Of cold? 5. Is much or little heat lost when there is much blood in 
the skin? Why? 6. Why is the skin red when we are exercising? 
7. Why is the skin pale when we are cold? 8. Why does a person 
actually cool off faster after drinking alcohol? 9. What are the 
harmful effects of prolonged chilling of the skin? 10. Why is too 
warm a room harmful to a person? n. Why should the air in a 
room have a certain degree of moisture? CHAPTER XLI. HINTS ON CLOTHING AND 
BATHING 
What animals do you see abroad in the winter time? 
Frogs? Snakes? Insects? You see only birds, covered 
with feathers; mammals, covered with hair; and man, 
who uses clothing to retain the heat of the body. In warm 
weather clothing serves also to protect the body from 
injury and from the heat and light of the sun> 
Kinds of Clothing. Clothing owes its power to retain 
heat to the fact that heat will not readily pass through dry 
air. Find out how an ice box (used to keep heat out) or a 
fireless cooker (used to keep heat in) is made, and you will 
learn how clothing keeps one warm. Furs hold more air 
than hair. When a horse or a cow gets wet in winter it 
suffers much from the cold, for in that case water takes the 
place of air in the fur. Fur is the best material for clothing 
to keep one warm in extremely cold climates. Of wool, 
silk, cotton, and linen cloth, wool is the best for winter and 
linen for summer wear, for wool holds the most, and linen the 
least, air in the meshes of the fibers. Clothing should not 
fit too tightly, for in that case the circulation of the blood 
is hindered and the heat of the body cannot be well 
distributed. 
Clothing for the Climate of Texas. In Texas “ northers ” 
often sweep down, causing a sudden drop in temperature. 
When it becomes suddenly colder, we should change cloth- 
ing to suit the change in the weather. Many persons 
change to woolen or other kinds of heavy underwear in the 
fall and wear this all the winter, regardless of the weather. 
This is not the best plan to follow. It is best to have at 
least three weights of underwear for use at different times. 
If one has on heavy underwear and the weather suddenly 
becomes colder, he can increase the underwear by using 
a light-weight underneath a layer of heavy underwear. 
Some persons find that they catch cold in changing to light 
underwear in the spring, but this is usually due to too great 
difference in the thickness of the underwear. A good rule 
237 238 
THE HUMAN BODY AND ITS ENEMIES 
to follow in changing from winter to summer underwear 
is to have a medium weight of winter underwear, or two 
thicknesses of summer underwear, so as to make the 
change more gradually. These, and many other rules of 
health that stand the test today, were well known to 
Benjamin Franklin, who was a keen observer as well as a 
great statesman. 
Our long, hot summers can be made more pleasant for 
us if we wear light, washable outer clothing. Suits of 
duck, cottonade, mohair, and the like are light and cool, 
and in summer they enable us to endure the warmth of the 
climate better. It is to be noted also that light-colored 
clothing is, in the sunshine, cooler than dark-colored cloth- 
ing of the same material. 
Need of Bathing. In the study of the skin we learned 
that various secretions are poured upon its surface by the 
sweat glands and the oil glands. 
We also learned that disease 
germs are likely to be present in 
the dust and dirt that gather on 
the skin. From these facts it is 
apparent that frequent bathing is 
necessary for cleanliness. 
Washing the Hands. To pre- 
vent disease it is especially impor- 
tant that the fingers be washed 
thoroughly with soap, and rinsed 
off with clean water, as often as 
the hands are soiled. The fingers 
become soiled in many ways, 
especially by touching such things as door knobs that are 
handled a great deal. The fingers and hands should be 
washed well with soap before each meal. It is wise to 
keep the fingers from touching articles of food as much 
as possible. The hands should always be washed after 
touching the body or clothing of any one who is sick and 
Figure 165. — A soap-book, 
containing sheets of soap. 
Avoid the common box of 
soap at public places. CLOTHING AND BATHING 
after each visit to the toilet. Avoid using the common 
towel at public places; use the paper towel wherever it is 
supplied (Fig. 29). 
The Shower Bath. Up to this time most households 
have been supplied with bathtubs instead of shower baths. 
This has been due to the fact that 
the advantages of the shower bath 
have not been realized, and also to 
the fact that home makers have 
not known a practical way to install 
a shower bath in an ordinary room 
wdth a pine floor. Figure 166 shows 
a* simple and cheap shower bath 
that can be substituted for a bath- 
tub in an ordinary bathroom. 
Under the shower is a porcelain 
basin, into which the water runs 
after trickling off the bather. A 
curtain is provided to keep the 
water from splashing on the wall 
or floor. This shower bath is more 
sanitary than the tub bath. 
Hot and Cold Baths. Since 
people go to extremes on the sub- 
ject of bathing, a word of caution 
is necessary concerning the tem- 
perature of the water used. It may 
be said that water about the temperature of the body 
or slightly warmer is always a safe temperature. Water 
much warmer than this should not be used except for some 
special reason and under the advice of a physician. The 
water may be cooler, or even quite cold, so long as it leaves 
a pleasant after-effect on the bather. This applies to 
those who are well and strong. No one who is at all sick 
should take cold baths except under the direction of a 
physician. It is not unusual for persons to be found dead 
239 
Figure 166. —-A shower 
bath is the most sanitary 
because the water runs off 
of the body and away. 240 
THE HUMAN BODY AND ITS ENEMIES 
in a bathtub. This shows that a person in delicate health 
should use some judgment in the matter of bathing. It is 
never well to bathe immediately after a meal. 
Swimming. Swimming is an excellent way to combine 
recreation and exercise with bathing. It is better than 
bathing in a tub or a shower bath, as it brings a person 
out into the open air and gives opportunity for pleasant 
and healthful exercise. A plunge into the water of a 
lake, river, or the ocean is very invigorating. 
Hot Applications. The curative value of hot applica- 
tions should be learned. When a person sprains an ankle 
or a wrist, an inflammation begins there and the part be- 
comes hot and red. This is caused by the flow of blood to 
the part to effect a cure. In case of sprains, therefore, we 
can hasten the cure by increasing the flow of blood to the 
injured part. This is done by the application of hot cloths. 
Ventilation of the Bathroom. Bathrooms should be 
ventilated. When gas is used to heat the water, great care 
should be taken to prevent suffocation from escaping gas. 
The heaters should have a hood and flue to carry off to the 
outside the carbon dioxid and other poisonous products of 
burning gas. 
Clothing serves to prevent loss of heat. Excessive loss of 
heat is prevented by the use of extra clothing when out-of- 
doors and by keeping the living rooms comfortable when 
indoors. One should wear clothing to suit the climate and the 
weather. Bathing is necessary for cleanliness. Excessively 
hot or cold baths should be indulged in with judgment and 
only in case the after-effects prove to be agreeable. 
SUMMARY 
i. Mention some helpful points with regard to clothing for winter 
in Texas. For summer. 2. Why must the hands be washed very 
■often? 3. Why is bathing necessary? 4. What should be the 
temperature of the bath water? 5. When should a person not take 
a bath? Why? 6. Why is a shower bath more hygienic than a 
tub bath? 7. How would you treat a sprain? 
QUESTIONS CHAPTER XLII. LOCOMOTION: BONES AND 
JOINTS 
Review. Different tissues or collections of cells have 
different duties to perform. Glands, mucous membrane, 
and epidermis are made largely of epithelial tissue. 
Muscles are muscle fibers bound together by connective 
tissue. The muscle fibers can shorten or contract. Wher- 
ever in the body a strong, flexible cord or flap is needed, 
it is made of connective tissue. Thus the valves of the 
heart and of the veins are made largely of connective 
tissue. Muscles are attached to bones by strands of con- 
nective tissue called tendons, and bones are bound to each 
other by similar strands called ligaments. Connective tis- 
sue is thus an important supporting tissue of the body. 
Cartilage tissue (or gristle) is a supporting tissue for the 
framework of the trachea, windpipe, and bronchi, the 
outer ear, and the nose (Fig. 124). Many bones have at 
their ends caps of cartilage, for these caps must be smooth, 
so as to glide upon each other without friction, and tough, 
so as not to break when struck together. Cartilage serves 
as packing between the vertebrae of the backbone; for, 
being elastic, it helps to deaden jars that might otherwise 
injure the brain. 
Observation Work, (i) Study all that can be made out 
from the end of a muscle with the tendon still attached to the 
bone. Ligaments are best studied when studying the joints. 
(2) Measure your height at bedtime; and on rising next day. 
What do the results prove about the cartilage between the 
vertebrae of the backbone? 
Uses of Bones. With cartilage and connective tissue 
alone, however, the body would lack support and rigidity. 
Support to the body is furnished by bones of many shapes 
and sizes, joined together and built up into the skeleton 
(Fig. 167). The skeleton is the framework of the body. 
With muscles fastened to this, and all covered by the skin, 
the shape of the body is completed. 
241 Figure 167. — The human skeleton. BONES AND JOINTS 
243 
The Use of Bones for Support. Bones serve for pro- 
tection and for support; some of them form boxes to 
protect the vital organs. The skull is a tight fitting box 
(Fig. 167). The spinal cord lies in a tube (the vertebral 
canal) made by the hole running through the vertebrae 
(Fig. 168). The patella, or knee-cap, protects the delicate 
knee joint from injury. The 
heart and lungs in the chest 
are protected by the shoulder 
blades, the breastbone, and the 
ribs. These bones are mainly 
flat and contain red marrow, as 
you can see by studying the sawed 
end of a rib. This red marrow 
is of special interest because most 
of the red blood corpuscles are 
manufactured in it. There are 
many flat or irregular bones with 
red marrow that serve other pur- 
poses than protection alone; for 
example, the shoulder blades and 
the hip bones. 
The Use of Bones for Motion. 
Bones are also used as attach- 
ment for the powerful muscles 
that move the body. Many flat bones are movable to 
some extent, the lower jaw and the shoulder blade 
serving as good examples. The bones of the hand and 
the wrist are short and irregular, containing red marrow, 
and are movable. For rapid and powerful motion there 
are certain long bones of the limbs with muscles to move 
them. These bones are light and thick enough to do their 
work. The femur or thigh bone is an example of such a 
long bone. It is enlarged at both ends, where it joins 
other bones, and has projections to which muscles are 
attached by their tendons. Inside, the enlarged end of the 
Figure 168. — Three vertebrae 
with portion of spinal cord in 
place. FR, hollows for attach- 
ment of ribs; FV, surface for 
attachment of next lower ver- 
tebra.  THE HUMAN BODY AND ITS ENEMIES 
244 
bone has a spongy appearance; that is, it is full of hollows 
scattered among the bone tissue (ST, Fig. 169). The hollow 
between the spongy ends is filled with fatty marrow. 
Bone Tissue. In a cross section of a long bone, such as 
appears in the center of a piece of round steak, the bone 
tissue seems perfectly solid and impenetrable. Under the 
microscope, however, it has quite a different appearance. 
Figure 169. — Femur, one half in longitudinal section, show- 
ing spongy tissue (ST) in end and compact tissue around the 
marrow cavity in shaft. P, periosteum. Cut end, A, en- 
larged in Figure 170. 
Figure 170. — End A of Figure 169 enlarged, showing bone 
tissue in shaft of femur. 
Figure 171. — Bone tissue (block B of Figure 170) still 
more enlarged. This shows the arrangement of bone cells (black dots) 
about the canals. Still finer canals run out from the cells. 
The apparently solid part of the bone is seen to be trav- 
ersed by fine canals containing blood vessels and nerves, 
and about these canals living bone cells are arranged, as 
shown in Figures 170 and 171. The cells themselves are 
connected with the canals and with one another by still 
finer tubes. Thus it is seen that even the solid part of 
bone is porous and supplied with blood, which carries food 
and oxygen to the bone cells, as it does to other parts of 
the body. Figures 169-171 should be carefully studied to 
make this point clear. BONES AND JOINTS 
245 
All bones are surrounded by the periosteum (P), which 
holds many blood vessels and nerves that pass through it 
on their way into the bone. 
Experiments to Show the Composition of 
Bones. (i) Examine a bone that has been 
burned thoroughly. Compare it with pieces of 
limestone. It is the mineral part of the bone, 
made up largely of limestone and phosphate of 
lime. It is the part that makes bone hard. (2) 
Soak a bone of convenient size, say a chicken 
drumstick, in strong 
vinegar or weak hydro- 
chloric acid, and note 
the result. Tie the bone 
into a knot (Fig. 172). 
State what has been re- 
moved from the bone. 
What is left is animal 
matter, which gives 
toughness and a certain 
amount of elasticity or springiness to 
the bones. 
Figure 172.— 
Bone tied into 
a knot. 
Joints. The place where two 
bones are joined together is called 
a joint. Some joints, as those of 
the skull bones, are immovable. 
The bones of the wrist and ankle 
glide over one another; their joints 
are therefore called gliding joints. 
The elbow and the knee joints 
allow a greater freedom of motion 
to the arms and legs, which move 
like a hinged door; they are called 
hinge joints (Fig. 173). 
The upper arm is attached to the shoulder blade by a 
ball-and-socket joint, allowing the arm to be moved in 
almost any direction. By a similar joint, but with a 
Figure 173. — Diagrams, 
showing how the hand may 
be turned around by means 
of the pivot joint of the 
radius. (For use of hinge 
joint see Figure 182.) 246 
THE HUMAN BODY AND ITS ENEMIES 
deeper socket, the femur or thigh bone is attached to the 
hip bone. At the elbow there are two joints. Here the 
humerus, or bone of the upper arm, joins the two bones of 
the forearm, — the radius on the thumb side and the ulna 
on the side of the little finger. The ulna is attached to the 
humerus by a hinge joint, the radius by a pivot joint. 
This arrangement allows the latter bone to twist around 
Figure 174. — Hip joint; I, innominate bone; CL, outer ligament. 
Figure 175. — Hip joint with outer ligament (CL) cut to show the inner 
or round ligament (RL). 
Figure 176. — Section of hip joint. CL and RL, ligaments; S, synovial 
membrane over cartilage of joint; SF, synovial fluid. 
and enables us to turn the hand palm up or palm down 
(Fig. 173), in a way in which we cannot turn the foot. 
Study other joints in your own body and try to tell what 
kind of joint each is. 
At the joints the bones are fastened together with liga- 
ments or strands of connective tissue, which extend across 
the joint from one bone to the other. Two kinds of liga- 
ments holding the thigh bone in place can be seen at RL BONES AND JOINTS 
247 
and CL, Figures 174-176. The ends of the bones form 
smooth surfaces covered with smooth, tough cartilage. 
To reduce friction still further a lymphlike fluid, the 
synovial fluid, is present in the joint. Further details of 
the joint can be studied in these pictures and also in an 
actual joint of some animal. 
Observation Work. Secure a ball-and-socket joint from 
the butcher, first having him saw it in two lengthwise. The 
hip joint of a pig or calf would answer best. Study the solid 
and the spongy parts of the bones, the smooth cartilage tip of 
the ball, and the lining of the socket and the ligaments. 
Bones with connective tissue and cartilage form the frame- 
work of the body. Bones also protect delicate organs from 
injury, and, having muscles attached to them, act as levers 
to move the body. The two hundred or more bones of the 
body are of many different shapes, according to the function 
each performs. The long bones are hollow, so as to combine 
strength with lightness of weight. The flat bones contain 
red marrow, where the red blood corpuscles are manufac- 
tured. Even the solid part of the bone is porous, being trav- 
ersed by fine canals containing blood vessels and nerves. The 
bone cells are arranged around the canals within the bone 
substance. Bone tissue contains animal matter for toughness 
and mineral matter for firmness. 
Bones are bound together by ligaments at the joints. 
Smooth cartilage and synovial fluid in the joint prevent fric- 
tion as the bones rub upon each other. 
SUMMARY 
QUESTIONS 
i. Name some organs of which cartilage tissue forms a part. 
2. What is a tendon? A ligament? 3. Point out each in two differ- 
ent pictures. 4. Of what kind of tissue are tendons and ligaments 
chiefly composed? 5. State the uses of bones. 6. In what direc- 
tion do the canals run through the long bone? 7. What are the  THE HUMAN BODY AND ITS ENEMIES 
248 
canals for? 8. How are the bone cells arranged with reference to 
the canals? 9. Give the chief uses of each bone that may easily 
be seen in Figure 167. 10. Name the kinds of joints and give 
examples, n. Name the two joints in the elbow. 12. State the 
use of each. (Study Figs. 173 and 182.) 13. How are bone 
cells supplied with blood? 14. How can we prove that bones con- 
tain mineral matter? Animal matter? CHAPTER XLHI. HYGIENE OF THE SKELETON 
The skeleton may be injured by strong blows or heavy 
falls, but it will be shown in this chapter that the bones 
are more usually misshapen by tight clothing or by habits 
of keeping the parts of the body in improper position. 
Hygiene of Joints. Sometimes a joint becomes dislo- 
cated or sprained; when it is dislocated the bones become 
separated at the joints so that they will not return to their 
proper place unless pressed back by force. When a finger 
is dislocated, as sometimes happens when playing base 
ball, it should be pulled until it goes back into place. When 
a joint is sprained the ligaments are strained, or they may 
be torn loose from their attachment to the bone. Hot 
applications to the sprained spot will help to effect a cure. 
A severe dislocation or sprain should receive the immediate 
attention of a physician. 
Hygiene of Bones. It is very important to recognize 
the fact that children’s bones contain a small proportion of 
mineral matter, and are therefore soft and flexible. Since 
this is true, it is easy to see that children’s bones are easily 
bent out of shape and permanently deformed. A baby 
may bend his legs out of shape by beginning to learn to 
walk too early, or by walking too much. Children who 
are improperly fed do not develop their bones properly. 
Proper Position. It is important for old and young, 
but especially for the young, to stand and sit up straight. 
The chest should be raised and the shoulders thrown back. 
This is better not only for the bones, but for the lungs and 
other organs, and it also improves the personal appearance. 
Many persons are one-sided from always carrying things, 
school books for example, on the same side of the body. 
Observation Work. Measure carefully the height of each 
shoulder from the ground. Compare the two measurements 
to find out whether or not you are one-sided. 
Tight Clothing. Tight clothing is very harmful for 
young and old. The habit of lacing the waist tightly is 
249  THE HUMAN BODY AND ITS ENEMIES 
250 
very common and is most dangerous. The feet, too, are 
often harmed by wearing tight and ill-fitting shoes. Shoes 
should fit well and should not have high heels. The foot 
naturally acts like a spring in deadening the shocks as 
we walk. This protects the 
brain and other organs of 
the body. There are three 
structures in the skeleton 
which help to prevent the 
jarring of the brain: the 
elastic cartilages between 
the vertebrae, the curvature 
of the spinal column, and 
the arch of the foot (Fig. 
179). Of these the spring- 
iness of the foot is perhaps 
the most important. But 
when French or very high 
heels are worn, the foot 
tends to slide down into the 
toe of the shoe, the foot is pinched still more, and corns and 
other painful ailments of the feet are caused thereby. 
School Desks. Young peo- 
ple spend a great deal of their 
time sitting at their desks in 
school. It is essential to their 
health that they learn to sit 
up straight and that they 
make it a habit to do so. 
This is, of course, impossible when the desk is too high or 
the seat too low. If the seat is too low, the position of the 
pupil is sure to be cramped. If it is too high, the feet 
dangle in the air, the pressure on the muscles of the thigh 
cuts off the circulation, and the weight of the feet bends the 
thigh bone out of shape. If the desk is too high, the arm 
and shoulders are raised too much when writing; if it is too 
Figure 177. — A deformed foot. 
Figure 178. — Natural shape of foot 
and shape of ill-fitting shoe. 
Figure 179/— Bones of foot, 
to show arched shape. HYGIENE OF THE SKELETON 
251 
low, it is necessary to stoop when working over the desk, 
and round shoulders and hollow chests are the result. The 
desk should also be at the right distance from the seat, not 
so close as to press against the chest, nor so far away as 
to make it necessary to lean forward. 
By neglecting to supply proper desks, many school 
authorities are causing physical defects in children, 
Figure 180. — A school desk and seat 
adjustable to size of pupil. 
defects that often last through life. In case the school 
does not possess comfortable and hygienic school desks, 
the teacher can often make a child comfortable with a box 
as a foot rest or with some other device, or she can relieve 
the situation for the time, particularly with the youngest 
children, by giving frequent short recesses and by dismiss- 
ing early in the afternoon. It is important that desks of 
right size and shape should be furnished. 
SUMMARY 
Serious dislocations and sprains should have the prompt 
attention of a physician. Hot applications are helpful to a 
sprained joint. 
Mineral matter is deposited in bones throughout life. The 
bones of children are soft and therefore easily bent out of shape. 252 
THE HUMAN BODY AND ITS ENEMIES 
Correct positions in sitting and standing, and avoidance of 
tight clothing, are essential to the proper growth of the bones. 
As children at school must sit at their desks many hours each 
week, it is important that the desks be of correct size and shape 
and that the pupils adopt the habit of sitting erect. 
QUESTIONS 
i. Why may children’s bones be easily bent out of shape? 2. 
How may you develop an erect, strong framework of your body? 
3. What can you say as to the fit of shoes? 4. Mention some harm- 
ful effects of tight clothing. 5. State the importance of having the 
right kind and size of school desk. CHAPTER XLIV. LOCOMOTION: MUSCLES 
When a boy is large in stature, his size is due mainly 
to the size of his bones; when we say he is strong, we refer 
to the power of his muscles to contract. When a boy 
Figure 181. — The muscles. 
wishes to show his strength he holds out his arm and says, 
“Feel my muscle,” and is proud to show the size and hard- 
ness of the biceps muscle. 
Primary Use of Muscles. Throughout this book the 
chief use of the muscle has been described as producing 
253 254 
THE HUMAN BODY AND ITS ENEMIES 
locomotion. But muscles have other uses in the body 
than those just described. They are used in swallowing 
and in performing the movements of the digestive organs, 
such as peristaltic movements. A large number of muscles 
are used in breathing. The tongue is a mass of muscles. 
We noted that the heart is a muscular sac, the work of which 
is to pump blood, and that the arteries and veins contain 
muscles. As long as we live there must be more or less 
continual motion of organs in the body. 
The larger motions of the body are performed by strong 
muscles attached to bones. Each muscle runs across the 
Figure 182. — Muscles are attached to bones 
for the larger motions of the body. 
joint, from one bone to the other; and thus, when the 
muscle contracts, one bone is moved toward the other. 
For example, when the biceps muscle (Fig. 182) contracts, 
the forearm is pulled up at an angle toward the upper arm. 
In this way the fingers, arms, legs, etc., are moved and the 
whole body is carried from place to place, as in walking, 
running, and jumping. Even when standing many muscles 
are in use (Fig. 183). About two fifths of the weight of 
the body, or more than one half of the soft parts of the 
body, consist of muscle (Fig. 181). An inspection of the 
meat in a butcher’s shop will convince one of the quarn- THE MUSCLES 
255 
tity of muscle it takes to carry on the work of an animal’s 
body, for all the lean meat sold by the butcher is muscle. 
Secondary Uses of Muscles. Muscles serve 
other purposes than that of producing motion 
either within the body or for taking the body 
from place to place. First, they cover the 
skeleton. Thus, with the skin as a covering for 
all, muscles complete the shape of the body. 
To secure a graceful development of the body 
it is first of all necessary to develop the muscles 
properly. Second, muscles form the walls of 
cavities. The cheek, for example, is made of 
muscles which form the sides of the mouth, and 
the wall of the abdomen is a muscular structure 
that protects the intestines. 
Two Kinds of Muscles. A little reflection 
and experiment will show that there are two 
kinds of muscles. You can move your finger, 
your eyelids, or your arm at will. But you 
cannot make your heart beat, nor cause your 
stomach to begin its movements, and after food 
has passed into your throat, you cannot stop 
it from going down the gullet. There must, 
therefore, be two kinds of muscles: those that 
are under the control of the will and those that 
are not. The muscles used in the large move- 
ments of the body, as those of the limbs, are 
under the control of the will and are called 
voluntary muscles. Muscles that are not under 
the control of the will are called involuntary 
muscles. Mention organs that appear to you 
likely to contain involuntary muscles. 
There is a great difference in the cells of which the two 
kinds of muscles are made up, as shown in Figure 184. 
The voluntary muscle cells or fibers are striped crosswise 
(I); the involuntary muscle cells are smooth or unstriped 
Figure 183. 
— The large 
muscles used 
in standing. 256 
THE HUMAN BODY AND ITS ENEMIES 
(III). The striped muscle fibers have to contract quickly 
and forcefully; the smooth fibers act slowly. The heart 
Figure 184. — Muscle fibers: I, striped, voluntary; II, striped of heart; 
III, smooth. C, connective tissue; .4, cut ends of fibrils, better shown at 
F; P, process of heart muscle fibers; S, a single smooth muscle cell. 
muscle is therefore an exception, in being involuntary but 
striped (II), for the contraction of the heart must be rapid 
like that of the limb muscles. 
Figures 185-187. — Structure of a muscle. Figure 185, biceps muscle of 
arm, with portion cut away exposing the bone (IT). Figure 186, lower por- 
tion of Figure 185 more enlarged, showing the larger bundles; F, smaller 
bundles within larger bundle. Figure 187, a smaller bundle containing 
muscle fibers (MF) bound together by connective tissue (C). THE MUSCLES 
257 
Structure of a Muscle. Muscle fibers are connected 
together into a whole organ, a muscle, with connective 
tissue fibers, which extend all through the muscle and come 
out at the ends to form the tendon (Fig. 185). The func- 
tion of the tendon is to bind the muscles to the bones. 
Often the bone that is to be moved is some distance from 
the muscle that moves it. In the hands and feet, for 
example, the tendons are long and slender. 
Observation Work. Study your forearm, hand, and fin- 
gers for the parts mentioned above. Move your fingers freely 
and at the same time watch all parts of the arm and hand to 
determine the relation of muscles, tendons, bones, etc. 
Muscles, by contraction, produce all motion of the body. 
Some muscles are involuntary and are made up of smooth 
muscle fibers. Such muscles carry on the movement of the 
internal organs. The voluntary muscles, made of striped fibers, 
are attached to bones, and with them as levers, move the limbs. 
SUMMARY 
i. What are the uses of muscles? 2. How do the two main kinds 
of muscles differ? 3. How do the heart muscles differ from these? 
4. How are muscles fastened to bones? 5. Place your biceps 
muscle in position B, Figure 182; what joint does the lower tendon 
of the biceps cross? 
QUESTIONS CHAPTER XLV. HYGIENE OF THE MUSCLES 
Review. State in your own words whence the muscles 
derive the energy with which to do work. 
Food must be brought to the muscles to repair them as 
they are wasted by use and to furnish them with energy. 
Blood vessels course through the muscles, 
and the blood capillaries come close to 
the muscle fibers or cells as they do to 
all the cells of the body (Fig. 188). This 
is, of course, what you would expect from 
what you have already learned about the 
relation of the capillaries to the cells. 
To nourish the muscles properly, good 
and properly varied food must be eaten. 
An athlete training for a contest is very 
careful about his diet, selecting the 
wholesome foods and avoiding greasy 
foods and pastry. 
Alcohol and Tobacco. Alcohol and 
tobacco are strictly avoided by athletes, 
as they have uniformly found that these 
drugs reduce their strength. If a boy 
will abstain from alcohol and tobacco in 
order to win a foot-race or help win a 
football game, does it not pay to avoid 
these drugs in order to have a healthy body for the battle 
of life? Some persons believe that they can do harder work 
under the stimulus of alcohol; but they are mistaken in 
this, for experiment after experiment has proved that 
alcohol actually lessens the power of the muscles to con- 
tract. This is another fact which Benjamin Franklin knew 
from observation, and it has been later proved by scientific 
experiment over and over again. 
Fresh Air. An ample supply of fresh air is another 
essential to the health of the muscles, as it is to the health 
of the whole body. 
Exercise. Another thing that is absolutely essential to 
Figure 188. — Blood 
capillaries supplying 
muscle fibers. 
258 HYGIENE OF THE MUSCLES 
the health of the muscles is exercise. Its most important 
advantage is the effect on the circulation of the blood and 
lymph, as described in Chapter XXXVII. By exercise 
the heart is made to beat faster, and is thus itself exercised; 
the breathing movements are increased; the veins are 
squeezed with each contraction of a muscle, and the blood 
is forced on toward the heart. All these activities help 
259 
Figure 189. — A healthful form of recreation. 
the circulation of the blood and the lymph. Exercise also 
makes the muscles harder and stronger. 
Play. To be of the greatest value to the body, exercise 
must be pleasant. Play is, therefore, an essential element 
in one’s training. All young animals play; it is nature’s 
way of developing their muscles. Children should be 
allowed their right to a reasonable amount of play. Games, 
moreover, develop the social instinct, teach children to 
work together (team work), to be honest, to tye consid- 
erate of one another, to stand up for one’s rights, and to 
understand human nature. Older persons should engage 
in outdoor sports as circumstances will allow. Name ten 
good games that require some exercise out of doors. 
Gymnastics. Gymnastic exercises are valuable princi- 
pally because by means of them deformities may be cor- 
rected or undeveloped muscles brought out. Exercises 
for almost every voluntary muscle of the body have been 
invented, so that a person may take a scientific course 
in physical culture by the gymnastic method. Gymnastic 
exercises are of great importance in the bodily devel- 
opment of boys and girls in crowded cities, where there 260 
THE HUMAN BODY AND ITS ENEMIES 
are fewer opportunities for other forms of exercise. But 
gymnastic exercises usually lack interest and are, in 
general, not so good for the health as enjoyable games. 
A five or ten minute drill with movement of the trunk and 
limbs may, however, be very beneficial in school, where 
the pupils have to sit still a long time. A brisk walk into 
the open air for five minutes, however, is better. 
Figure 190. — A playground is a valuable part of a school equipment. 
Work. Boys need a great deal of play and also an 
equal amount of good hard work. A good combination 
for boys would be splitting wood, digging bait, and going 
fishing. Some hard work is good for girls too, for example, 
sweeping (but not by the dry method) and washing dishes; 
but girls also need an equal amount of play. 
Fatigue. There is a limit to the exercise one ought to 
take. Have you ever been on a picnic or a day’s tramp 
and come home very tired? And did you not feel sore 
the next day, the very muscles hurting when you touched 
them? Why did they hurt you? Study Figure 113 
and try to tell the reason. Waste products from the 
muscle cells themselves accumulate during continued heavy HYGIENE OF THE MUSCLES 
261 
exercise faster than they can be carried off by the blood, 
and they then act as a toxin on the cells of the body. 
This condition is called fatigue. 
Rest. Rest, therefore, is a necessity. Rest gives the 
muscle and nerve cells a chance to get rid of waste sub- 
stances and to rebuild worn-out protoplasm. During rest 
the building-up process is greater than that of the tearing- 
down. A person who does not rest sufficiently cannot do 
his best work, does not enjoy life fully, and may finally 
become a prey to disease germs. 
SUMMARY 
Blood capillaries supply all the muscle fibers with food and 
oxygen and carry away waste products produced by exercise. 
They also carry alcohol and the poisons of tobacco to the fibers, 
weakening the muscles. 
Exercise, if pleasant and enjoyable, is highly beneficial to 
the muscles. Outdoor games are the best form of exercise, 
except for special purposes. We should never exercise to the 
point of being dead tired, but should stop and rest when the 
point of pleasant fatigue is reached. 
i. How do the muscle cells secure their nourishment (Fig. 
188)? 2. How can the poison in tobacco reach the muscle cells? 
3. What part of Figure 186 is the bundle shown enlarged in Figure 
187? 4. What are some of the needs of muscle cells (Fig. 113)? 
5. What drugs weaken the muscles? 6. Discuss the value of exer- 
cise to the muscle. 7. What is the chief value of play? 8. Discuss 
the use of gymnastics. 9. Why is rest necessary? 10. How is 
fatigue produced? 
QUESTIONS CHAPTER XLVI. THE NERVOUS SYSTEM: 
GENERAL 
Thus far we have considered the body as being made 
up of myriads of separate cells, each with its own work 
to perform. These cells 
multiply and unite to 
form tissue, and tissues 
are united to make up 
organs. We have con- 
sidered the different 
organs chiefly as sep- 
arate parts of the body, 
without especially no- 
ticing how one part 
acts upon another. We 
have studied the oper- 
ation, or work, of the 
cells, tissues and organs. 
In this chapter we shall 
see how the parts of 
the body cooperate or 
work together. 
Examples of Cooper- 
ation. Every one is 
familiar with examples 
of the cooperation of 
the organs for the good 
of the whole body. The 
blood serves every cell 
in a very important 
way, as has often been 
pointed out in previous 
chapters. The stomach 
and intestines digest 
food, not for themselves 
alone, but for the whole body. Even the presence of small 
quantities of waste substances is useful to the body, 
Figure 191. — The nervous system. 
262 THE NERVOUS SYSTEM 
263 
because they cause fatigue and induce sleep. When we 
consider the body as made up of many cooperating parts, 
we may liken it to a perfect baseball team, each one of 
whose members does the right thing at the right moment, 
all working together so that the team may win. 
Review Work. Make a list of the most important organs 
you have studied and state what each does for the good of the 
whole body. 
The more you think about it the more you will realize 
how perfectly this machine, the body, works. If some one 
strikes at you, you wink your eyes, throw up your hands, 
and perhaps step back. If a particle of food goes the wrong 
way on passing down the throat (Fig. 121), you cough; 
or if dust enters the nose, you sneeze. As you taste food 
and begin to chew, the digestive glands begin to secrete. 
If you prick your finger with a pin a message is sent to 
the brain and spinal cord, and in an instant a message is 
sent back to the proper muscle to remove the finger from 
the place of danger. Or I may say, “Move your right 
thumb”; you hear what I say and do as I request. My 
voice, your ear, and your thumb have perfect means of 
communication between themselves. 
Review Work. Tell at least a half-dozen things that 
happen in as many of the organs of the body when you 
begin to exercise, — for instance, to run. Review Chapter 
XL and explain how heat and cold affect the blood vessels 
of the skin. 
Nerve Cells. We have already learned how communi- 
cation between all the cells of the body is brought about 
by the blood. We shall now learn of another system of 
communication; namely, the nervous system. The nervous 
system is made up of cells, as is every other part of the body. 
A little reflection would lead us to suppose that nerve cells 264 
THE HUMAN BODY AND ITS ENEMIES 
are longer and more slender than any other cells, even than 
muscle and connective tissue fibers, and this is true. 
Figure 192 is a diagram of a nerve cell. The body of 
the cell (called simply nerve cell for the sake of brevity) 
contains the nucleus, and has running off 
from it one or more long projections or 
processes and usually many short ones. 
The short processes are of use in com- 
municating with adjoining cells; the long 
ones, the nerve fibers, run to the various 
cells of the body or to other nerve cells. 
The nerve fibers may be very long; for 
example, those running into the feet from 
the small of the back are a yard or more 
in length. A single nerve fiber cannot be 
seen by the naked eye, but when many 
are bundled together they form a nervey 
and a nerve can be seen as a white 
strand of greater or less thickness running 
through the flesh. 
The Function of Nerves. If you were 
asked what the brain is for, you would 
probably say, “To know and feel with/'' 
by which you would mean that the brain 
is the organ of the mind. If asked the 
function of nerves, you would now readily 
answer that nerves carry messages or 
impulses from one part of the body to 
another, and so keep the parts cooperat- 
ing for the good of the whole. These two answers are as 
nearly correct as most people can state them. 
We might compare our system of nerves with a telephone 
system. The nerves correspond to the wires which con- 
nect homes, stores, and offices in a city. There are, also, 
nerve centers, and the brain and the spinal cord correspond 
to the central office or exchange of the telephone system. 
Figure 192. — A 
nerve cell. THE NERVOUS SYSTEM 
265 
When you wish to telephone, you first call central and give 
the number you want. Likewise, when you touch the 
point of a pin with your finger, a call is sent to the central 
of the body. Again, the central operator of the telephone 
gives you the number you call for and rings that number. 
So, too, in the brain or in the spinal cord, the message, 
“Sharp object at finger,” is changed to “Move finger 
away,” and this message is sent to the proper muscles of 
the arm and hand. There are, therefore, nerves running 
in from the skin, which bring us in touch with the 
outside; and there are nerves running out to the muscles, 
controlling their action. 
The organs of the nervous system might be said to con- 
sist of the central nervous system, the brain and the spinal 
cord, containing most of the nerve cells; and the peripheral 
nervous system, consisting of nerves and containing mainly 
nerve fibers that carry messages to and from the central 
nervous system and the other parts of the body. 
SUMMARY 
The functions of the nervous system are to act as the organ 
of the mind and to control all the organs of the body. The 
nerve cells receive or send on impulses or messages, and their 
nerve fibers carry the impulses from one part of the body to 
another. 
i. Do you think the various parts of the body are independent 
of one another? 2. Give reasons for your answer. 3. Give examples 
of cooperation of organs. 4. How are parts brought into com- 
munication? 5. Wherein is the nervous system like a telephone 
system? 6. Name the parts of the central nervous system. 7. 
Of what does the peripheral nervous, system consist? 8. Find these 
parts on Figure 191. 
QUESTIONS CHAPTER XLVII. THE BRAIN 
Since the brain plays so important a part in the body, 
it is often pointed to as the most important organ of the 
nervous system. We must bear in mind, however, that 
all parts of the nervous system are of importance. The 
organs of the nervous system are: 
1. The brain (Fig. 199). 
2. Twelve pairs of nerves arising from the brain and 
running out mainly to the head and shoulders and to the 
Figure 193. — The brain and upper part of the spinal cord. 
heart, stomach, and other important organs of the thorax 
and abdomen. 
3. The spinal cord (Fig. 199). 
4. Thirty-one pairs of nerves arising from the spinal 
cord and sending out branches into the trunk and the 
limbs (Figs. 191 and 199). 
5. The sympathetic ganglia and their nerves (Fig. 199). 
1 and 3 make up the central nervous system; 2 and 4, the 
peripheral nervous system. 
The Brain. The brain lies in the hollow of the skull, 
and the spinal cord lies in the canal running through the 
266 THE BRAIN 
267 
spinal column (Figs. 72 and 193). Besides the bony 
covering, both have three double protective coverings.1 
All hollow spaces between the coverings are filled with a 
kind of lymph. The coverings and the lymph cause the 
brain and the cord to fit snugly into their cavities. The 
brain is also protected from jars by the springy arch of 
the foot, by the curves of the backbone, and by the cushions 
of cartilage between the vertebrae. 
Ganglia. The nerve cells are all contained in certain 
definite parts of the brain and spinal cord and in certain 
Figure 194. — Section of portion of the brain; gray 
matter near the surface. 
Figure 195. — Section of spinal cord; gray matter 
on the inside. 
small collections of nerve cells called ganglia. A ganglion 
is simply a collection of nerve cells. In this sense the 
brain and spinal cord may be considered enormous ganglia. 
Figure 203 shows a number of ganglia. One region of the 
brain and of the spinal cord is, then, composed mainly of 
nerve cells, and this is called gray matter because of its 
color. The region of fibers is white and is called white 
matter. In the brain the gray matter is on the outer sur- 
face and forms the cortex of the brain (Fig. 194); in the 
spinal cord the gray matter is on the inside (Fig. 195). 
The brain consists of three main parts: the cerebrum, 
the cerebellum, and the medulla.2 
1 The three together are called the meninges (M, Fjg. 209). The disease 
of the nervous system called cerebrospinal meningitis derives its name 
from these membranes, which are inflamed by the disease. 
2 The medulla is also called the “ bulb.” 268 
THE HUMAN BODY AND ITS ENEMIES 
The Cerebrum. Cerebrum is the Latin word for 
brain. The cerebrum consists of two halves, the cere- 
bral hemispheres (Fig. 196), connected by a mass of fibers. 
In a man it is the largest organ of the nervous system, 
though this is not the case in some of the lower animals; 
the more intelligent animals have a large cerebrum. 
The larger the organ is, 
the more nerve cells it 
may contain, since the 
larger size increases the 
extent of the cortex or 
gray matter. In man 
and in several of the more 
intelligent animals, as the 
dog and the horse, the 
extent of the surface of 
the cortex is further in- 
creased by folds or convolu- 
tions (Figs. 193 and 196). 
A great number of fibers 
connect the different parts 
of each hemisphere of the 
cerebrum (Fig. 197), con- 
nect the hemispheres with 
each other, and run out 
from the cells to the spinal 
cord and to various parts of the body. These fibers pass- 
ing from the cerebrum into the spinal cord cross in the 
medulla; if the left side of the brain were injured, the 
right side of the body (except the head) would be paralyzed. 
Functions of the Cerebrum. The cerebrum is the organ 
of the mind. Without it we could not know, think, im- 
agine, remember, or do anything which we commonly 
associate with the activities of the mind. The cerebrum 
receives impulses from sense organs (ear, eye, nose, tongue, 
and skin) by means of fibers starting in the sense organs 
Figure 196. — The brain from above; 
only the cerebrum is seen in this view. 
(Compare Figure 198.) THE BRAIN 
269 
and ending in cells in the cerebrum. The cerebrum thus 
receives sensations. Without the cells of the cerebrum we 
would have no sensations of hearing, sight, smell, taste, or 
touch, nor would we feel hungry, tired, cold, or warm. 
In the cerebrum are other cells, from which fibers run to 
the voluntary muscles. These cells send impulses to the 
muscles that cause them to contract. Without these cells 
we could not cause our muscles to obey our will. 
Figure 197. — Nerve fibers connect the parts of the cerebral 
cortex with one another. 
The Cerebellum. Cerebellum means little brain. It 
lies behind the medulla and below the dorsal part of the 
cerebrum. The cerebrum is so large in man that it covers 
the cerebellum, which cannot be seen from above (Fig. 
196). A frog whose cerebellum has been injured cannot 
sit up; or, if it falls into the water, it makes an effort to 
swim, but with irregular and ill-controlled movements. 
A man whose cerebellum has been injured staggers in his 
walk as though intoxicated. One function of the cere- 
bellum, therefore, is to keep the muscles ready for action 
and to make the muscles used in walking, standing, and 
running act together in an orderly manner, or, in other 
words, to coordinate their action. It probably has other 
functions not yet understood. 270 
THE HUMAN BODY AND ITS ENEMIES 
The Medulla. With both the cerebrum and the cere- 
bellum injured, an animal still lives. If this animal is a 
pigeon, for example, grains of corn placed on the ground 
beside it will awaken no response, for without the cerebrum 
the animal cannot see, nor can it will to act; and without 
the cerebellum it cannot even maintain an upright posture. 
However, if a grain of corn is 
placed in the pigeon’s mouth, 
the muscles that are used in 
swallowing will act and the 
grain of corn will pass down 
the throat. As the grain touches 
the mouth, it starts impulses 
that pass along nerves leading 
to cells in the medulla. The 
word medulla means pith. From 
the medulla, fibers then carry 
impulses back to muscles en- 
gaged in swallowing. Such 
action is called reflex action, 
and will be more thoroughly 
explained below. 
If the animal has lost the 
entire brain, including the medulla, the heart stops beating, 
the breathing movements cease, and death occurs. This 
proves that these vital movements are under the control 
of the medulla, which is therefore sometimes called the 
vital knot. All the fibers connecting the higher parts of 
the brain with the spinal cord and the various parts of 
the body pass through the medulla. 
Figure 198. — The brain from 
below; 1 to 12, cranial nerves. 
SUMMARY 
The brain contains millions of nerve cells in the cortex, or 
gray matter, and has many fibers running in and out. The 
brain consists.of the cerebrum, the cerebellum, and the me- 
dulla. The cerebrum performs the functions of the mind, as THE BRAIN 
271 
the will, reason, memory, etc. The cerebrum of man is larger 
than that of any of the lower animals. The cerebellum serves 
chiefly to coordinate the movements of the muscles. The 
medulla controls the breathing movements, the heart-beat, 
and other vital processes. It is the center of reflex action for 
parts of the body and also contains nerve fibers leading from 
the brain into the spinal cord. 
QUESTIONS 
i. Name the parts of the nervous system. 2. How many pairs 
of nerves run out from the central nervous system? 3. What, are 
these together called? 4. What do the flaps at M, Figure 200, 
represent? 5. What is a ganglion? Point out ganglia in at least 
one picture. 6. What are the functions of the cerebrum? 7. 
How would a person with an injured cerebellum act? 8. What is 
the work of the medulla? 9. What fibers pass through the medulla? CHAPTER XLVIII. THE SPINAL CORD AND 
SYMPATHETIC SYSTEM 
From a study of the functions of the 
brain, as described in the preceding chap- 
ter, one might conclude that it controls 
all the actions of the organs. The differ- 
ent parts of the brain have, indeed, a 
variety of duties. But we shall learn in 
this chapter that the spinal cord has 
important duties of its own, and that 
the sympathetic system plays an im- 
portant part in the control of certain 
organs. 
Description of the Spinal Cord. The 
brain ends and the spinal cord begins at 
the place where the cranial cavity (Fig. 
72) communicates with the vertebral 
canal. An inspection of Figure 199 
discloses the fact that the spinal cord is 
a continuation downward of the medulla. 
The cord is about eighteen inches in 
length. Like the brain, it is covered by 
the meninges {M, Fig. 200). It is further 
protected by a bony covering, the ver- 
tebrae of the spinal column, shown in 
Figure 168. 
The gray matter of the spinal cord, 
containing the nerve cells, is on the 
inside. The shape and position of the 
gray matter can best be understood by 
a study of Figure 200. A cross section 
of the gray matter (G, Fig. 200) resem- 
bles the letter II. The four points of 
the letter represent the four ridges (R) 
of the gray matter. In Figure 200 the 
white matter (IF) has been cut away, exposing a portion 
of the two dorsal ridges (R) of the gray matter. 
Figure 199. — The 
brain; the spinal cord 
with beginnings of 
its nerves; the sym- 
pathetic nerve gan- 
glia of the right side. 
272 THE SPINAL CORD 
273 
The Spinal Nerves. There are thirty-one pairs of nerves, 
called the spinal nerves, that start off from the spinal cord 
to supply the trunk and the limbs with nerve fibers. (Study 
Figure 199.) The spinal nerves leave the cavity of the back- 
bone through openings between the vertebrae, as can be 
seen in Figure 168. 
Each spinal nerve is attached to the spinal cord by two 
roots, one on the dorsal side (the dorsal root) and one on 
Figure 200. — Spinal cord; cut end with portion of white matter (W) 
cut away, exposing the dorsal ridges (R) of gray matter. D, dorsal; V, 
ventral; WL, nerve fibers of white matter cut lengthwise; G, cross section 
of gray matter; M, meninges or covering membranes; N, spinal nerve; 
DR, VR, dorsal and ventral roots; DG, dorsal or sensory ganglia. 
the ventral side (the ventral root). The nerve fibers run- 
ning out through the ventral root begin in the cells of the 
ventral ridge of the gray matter. The nerve fibers coming 
in through the dorsal root come from a special ganglion of 
nerve cells. Study Figure 200 very carefully. 274 
THE HUMAN BODY AND ITS ENEMIES 
The Spinal Cord in Reflex Action. If we take a frog 
that has just been killed by the removal of the whole brain, 
we find that the spinal cord can act as the medulla does in 
completing certain nerve circuits. If we irritate the chest 
of the brainless frog, the front legs move to scratch at the 
irritated part; or if the skin of the toe is irritated, the foot 
is jerked away. It appears, then, that nerve impulses 
pass into the spinal cord from the outside (from the chest 
or the foot, for example), and that impulses pass out again 
from it to the muscles to relieve the irritated part. Such a 
response to impulses from the outside is called reflex action. 
If, now, the spinal cord of the dead frog is also destroyed, 
there is no response to irritation of the chest or the foot. 
This proves that the spinal cord is the necessary central 
station that receives incoming messages and sends the 
proper message back down the outgoing nerve to the 
muscles. In other words, the spinal cord is the center of 
reflex action. 
Two Kinds of Nerve Fibers. When you will to move 
your first finger, you send an impulse to the muscles that 
move it, and the finger moves. When you touch an object 
with the finger, you feel the object; this time a different 
impulse passes along the nerve. One kind of impulse goes 
out from the center to a muscle and results in motion. It 
is called a motor impulse, and it uses a special set of nerve 
cells and their fibers, which are therefore called motor cells 
and motor fibers. The other kind of impulse comes from 
outside to the center; and if carried as far as the brain causes 
us to feel, this is called a sensory impulse. It begins in 
sensory fibers and ends in relay cells located in the spinal 
cord, which sent it on to the brain. 
Most nerves consist of motor and sensory fibers bundled 
up together. In reflex action the sensory impulse does not 
pass all the way to the cerebrum, but after entering the 
spinal cord (or medulla) is at once returned as a motor 
impulse running along motor fibers to the proper muscle. THE SPINAL CORD 
275 
An Example of Reflex Action. You have noticed that 
when you touch the point of a tack unawares, your finger 
is withdrawn by reflex action before you think. The 
paths along which the impulses travel to bring about this 
Figure 201. — Diagram illustrating path of nerve impulses 
in reflex action involving voluntary muscles. 
reflex action are as follows (study Fig. 201): The sensory 
impulse started by the tack passes along sensory fibers to 
the spinal nerve, then through the dorsal root and the 
dorsal ganglion to sensory or receiving nerve cells in the 
gray matter of the spinal cord. Immediately the impulse 
passes to motor cells in the ventral ridge of the gray matter 
and then out through the ventral root of the spinal nerve 
along motor fibers to the muscles of the arm or hand. 
This is the simplest machinery of reflex action. 
It works so perfectly that the impulses are always sent 
back to the muscles that are best suited to remove the 
part in danger of being injured. This perfection of reflex 
action we must attribute to the wonderful power of the 
cells in the gray matter to select the particular nerve fibers 
that carry the motor impulses to the proper muscles. 
Quickness of Reflex Action. When the sensory impulse, 
caused by touching the point of a tack, reaches the spinal 
cord, it is also passed on to fibers leading to the brain 
(cerebrum). Here it causes conscious sensation; that is, it 
makes you feel. After thinking it over, you would will to 
remove the finger from the tack. But this far-around 276 
THE HUMAN BODY AND ITS ENEMIES 
way takes so long that much harm would be done to the 
finger by the tack before you could think it over. The 
circuit through the spinal cord, as described in the preced- 
ing paragraph, is more rapid. We may say, then, that 
the principal purpose of reflex action is to protect the 
body. 
The Cranial Nerves. The head is supplied with nerves 
that start off from the brain. They are called the cranial 
nerves and correspond in many ways to the spinal nerves, 
Figure 202. — Diagram showing the twelve cranial nerves. 
which supply the trunk and the limbs. The cranial nerves 
contain sensory or motor fibers or both. The nerves of 
smell, taste, sight, and hearing are sensory cranial nerves. 
Three pairs of nerves control the movements of the eye- 
ball. When you have toothache, impulses pass to the 
brain along a cranial nerve. When you move the jaw in 
chewing, or wink the eye or use the tongue, motor impulses 
pass out through other cranial nerves. One pair of cranial 
nerves, however, passes out of the head into the trunk and THE SPINAL CORD 
277 
controls the vital organs the heart, lungs, stomach, and 
intestines (see Figure 202). 
The Sympathetic Nervous System. Besides the brain 
and the spinal cord and the cranial and the spinal nerves, 
there are other nerves and ganglia. These make up the 
sympathetic nervous system. 
This consists of two chains 
of ganglia on the dorsal 
wall of the chest and abdo- 
men, one chain on each side 
of the spinal cord and close 
to the backbone. The left 
one is shown in Figure 203, 
the right one in Figure 199. 
There are, in addition to 
the chains of ganglia, scat- 
tered ganglia and bunches 
of nerve fibers called plex- 
uses near and even within 
the organs of the chest and 
abdomen, especially the 
heart and the stomach. A 
blow over the stomach, 
where the solar plexus is 
situated, paralyzes the 
nerves there and may 
cause sudden death. 
Function of the Sympa- 
thetic Nerves. The sym- 
pathetic nerves are closely 
connected by fibers with 
the central nervous system. 
They are like the fibers of 
the spinal nerves in that 
they carry impulses in and out of the spinal cord. They 
take part in reflex action which involves the involuntary 
Figure 203. — The sympathetic 
ganglia and nerves of the left side of 
the body. 278 
THE HUMAN BODY AND ITS ENEMIES 
muscles; that is, the heart and all muscles composed of 
smooth fibers. The sympathetic nerves, therefore, help to 
regulate the heart-beat, cause movements of the alimentary 
canal, etc. In short, they aid in the control of what we 
might call the vital functions, or those processes in the 
body on which life depends. 
Further Examples. When we begin to exercise, our 
heart-beat and breathing become more rapid. Soon the 
skin becomes red and the sweat glands begin to secrete. 
After we have exercised a while, impulses of heat are sent 
from the skin along sensory fibers to the central nervous 
system. Then impulses are sent out through the sym- 
pathetic system, which brings about the events that happen 
in the body on account of exercise. 
Another example of such a reflex act, which you may 
readily observe for yourself, is the change in size of the 
pupil of the eye. There are smooth muscle fibers in the 
colored ring, or iris, around the pupil of the eye. When 
these muscles contract, the pupil becomes smaller. This 
happens by reflex action when a bright light shines into 
the eye. In the dark the pupil is larger, for then the 
muscles of the iris relax. This action may be observed in 
the following experiment: 
Experiment. Hold a mirror before you and examine the 
pupil of the eye. Note its size. Now close the eye a moment 
and open it suddenly. As you raise the eyelid, note that the 
pupil is larger than when at first observed, and that it very 
quickly becomes smaller. Explain the reflex action. 
Reflex Action of the Glands. Besides controlling the 
involuntary muscles, the sympathetic system controls 
the work of the glands. During exercise, for example, the 
sweat glands secrete without our willing them to do so. 
We have also learned that taste and chewing of food cause 
the secretion of saliva and gastric juice, the “appetite” 
juices. Secretion and excretion are, therefore, also 
reflex acts. THE SPINAL CORD 
279 
SUMMARY 
The spinal cord has two main functions. First, it carries 
sensory impulses from the outside to the brain and motor 
impulses from the brain to the outside. It is a cable of fibers, 
and there are relay stations on the way. The fibers are located 
in the white matter of the cord and in thirty-one pairs of spinal 
nerves and their roots; the nerve cells are the relay stations 
and are found in the gray matter of the cord and in the dorsal 
ganglia of the spinal nerves. 
Second, the spinal cord, acts as a reflex center; that is, 
it is able to receive sensory impulses and translate them into 
motor impulses. This may be called the short circuit of reflex 
and unconscious action, as distinguished from the long circuit 
through the cord and the brain, which results in conscious 
action. 
There are twelve pairs of cranial nerves starting off directly 
from the brain. These nerves include among others the impor- 
tant nerves of sight, hearing, taste and smell, and one pair of 
nerves that help the sympathetic system in the control of the 
heart-beat and the work of the digestive organs. 
The heart and all the organs having smooth muscle fibers 
are controlled mainly by the sympathetic nervous system. 
This consists of ganglia and nerve fibers that communicate 
with the central nervous system. The sympathetic nerves 
carry stimuli that cause the glands to secrete and also cause 
the reflex action of the involuntary muscles. The sympathetic 
nerves therefore control those acts on which at every moment 
the very life depends. 
QUESTIONS 
i. Where in the body are the organs pictured in Figure 199 located? 
2. With Figure 200 before you, describe the structure of the spinal 
cord. 3. In what direction do impulses pass along motor fibers? 
Along sensory fibers? 4. Draw Figure 201 on the blackboard and 
explain the course of sensory and motor impulses in and out of the 
spinal cord. 5. Explain how it is that a frog with its head cut off 
will still draw up its leg when its foot is irritated. 6. Give three 
examples of reflex action. 7. What is meant by reflex action? 8. 
Why is reflex action quicker than conscious action? 9. What two 280 
THE HUMAN BODY AND ITS ENEMIES 
kinds of muscles are there? io. Which of these is controlled by 
the sympathetic nerves? n. Where are the sympathetic ganglia 
situated? 12. What nerves cause the salivary glands to act? 13. 
What are the cranial nerves and what parts of the body do they 
control? 14. Give an example of reflex action in which the nerve 
impulses must pass along cranial nerves. SYSTEM 
In Chapter XLVII we learned that the cerebrum is the 
part of the brain with which we remember, think, will, and 
feel. The lower nerve centers (sympathetic, spinal cord, 
medulla, and cerebellum) control many actions, thus 
leaving the cerebrum free to carry on the higher functions 
of the mind. We shall see how the cerebrum is naturally 
relieved from attention to reflex acts, and how we can train 
the different parts of the nervous system to become the 
ready servants of our will. 
Advantages of Reflex Acts of Involuntary Muscles and 
Glands. It is very plain that it would be impossible for a 
person to regulate the heart-beat, the breathing move- 
ments, the movements of the intestines, and the secretion 
of sweat and of the digestive juices, by acts of the will, 
all at the right time and in the right degree. If the cere- 
brum had to regulate all these acts necessary for life, we 
could not do or think about anything else. As it is actually 
arranged, the cerebrum is free to perform the higher 
functions, leaving automatic acts to be performed in part 
by the sympathetic system and in part by the medulla. 
Such reflex acts are more perfectly performed for the 
very reason that they are automatic. They are as 
perfect in babies and in animals as they are in grown 
people. 
Advantages of Reflex Action of the Voluntary Muscles. 
One of the advantages of ordinary reflex action of the 
voluntary muscles was pointed out in the last chapter. 
You can move the muscles of the arm at will; yet in reflex 
action the arm is moved without your willing to do so, as 
when you touch the point of a pin or a hot stove. Reflex 
action is more rapid than voluntary action and is, therefore, 
of value to the body in protecting it against sudden 
harm. 
Observation Work. Name six ways in which reflex action 
has been a protection to you during the past week. 282 
THE HUMAN BODY AND ITS ENEMIES 
The movement of voluntary muscles by reflex action 
also spares the cerebrum. Many acts are done reflexly 
and without the necessity of conscious attention. Thus, 
when we eat, we swallow our food without thinking about 
swallowing. The act of swallowing is a reflex act. 
Habit. There are many acts in life that are very hard 
to do at first but become easy later on. The child learning 
to walk must give his whole attention to the act. Later, 
walking becomes so easy that we walk without even think- 
ing about it. So it is with many other acts. The oftener 
any act is repeated, the easier it becomes and the more one 
tends to do the act. We say it becomes a habit. 
Value of Habit. Before the habit is formed we must 
give our whole attention to the act. Washing, dressing, 
eating, writing, and a thousand other things that we do 
every day are difficult until we have done them often. 
In other words, the cerebrum has hard work at first in 
training the muscles to do the right thing at the right time. 
Later, the cerebrum has less and less to do with the act, 
the lower centers taking charge of the business. Finally 
we perform habitual movements without even knowing 
that we are moving. 
For these reasons habit is a great aid to the mind. The 
more habits we form, the less work the cerebrum has to do 
with the petty acts of life and the more attention can be 
given to thinking about things more worth while. 
Practise. Practise makes perfect. When you first 
try to tie your necktie, you can do it neither easily nor 
neatly. With practise, however, come ease and skill. 
It is important early in life to learn to do well as many 
useful things as possible. Thus, when the multiplication 
table is once learned, that much of life’s work is laid aside. 
We should learn to read, write, spell, think accurately, 
develop skill in using the hands, and do as many other 
things as possible while we are young. When we are 
grown these things can be performed unconsciously, leav- TRAINING OF NERVOUS SYSTEM 
283 
ing the cerebrum free to give attention to more difficult 
acts. 
Education. The formation of right habits of thinking 
and acting is a large part of the work of education. This 
fact makes education in the home and the school very 
important. Every day possible should be spent at school. 
The person who has many good habits and who has the 
ability to do many things easily and well is the person who 
is most likely to be successful in life. 
Experiment. Write the word Practice on a white sheet 
of paper. You write it easily and without thinking how each 
letter is made or how the word is 
spelled. Now copy immediately below 
the word just written the characters 
in Figure 204, turn the sheet around, 
and hold it up to the light. Why did 
you write the first more easily than 
the second? A child who has never 
written a word would find it more difficult to write the word 
Practice than you find it to write the characters in Figure 
204, which is a mirror image of the word Practice. 
Figure 204. 
Breaking Bad Habits. It is as easy to form a bad habit 
as a good one. Biting the finger nails, speaking evil of 
others, and neglecting the teeth are bad habits. Habits 
are hard to break. It is difficult, the first time we try, to 
keep from doing any act that has become habitual; but 
the second time we abstain from doing the act it is easier, 
and so on until it becomes a habit to abstain from the act. 
It is best to acquire good habits and never to form bad 
ones. A person with many good habits will be more 
successful in life than a person with bad habits or too few 
good ones. 
The reflex acts of secretion and of the movements of smooth 
muscles are involuntary and the cerebrum is freed from giving 
SUMMARY 284 
THE HUMAN BODY AND ITS ENEMIES 
attention to them. Such acts are not subject to education and 
are as perfect in babies and in animals as they are in grown 
people. Ordinary reflex acts of the voluntary muscles are 
quicker than voluntary acts and therefore are protective to 
the body. All reflex acts that are performed unconsciously 
(as swallowing, for example) relieve the cerebrum from the 
work of controlling them. 
Many complicated acts of life, that call into action many 
voluntary muscles, such as walking, are difficult at first and 
require much work on the part of the cerebrum. With prac- 
tise these acts become more like reflex acts and require the 
attention of the cerebrum less and less the oftener they are 
performed. 
Such acts of life, that have to be learned by the training of 
the nervous system, are habits. There are good habits and 
bad habits. Education is intended to increase the number of 
good habits and keep down the number of bad ones. A per- 
son is likely to be successful and happy if he has formed many 
good, and few bad, habits in youth. 
QUESTIONS 
i. What are the functions of the cerebrum? 2. What are the 
acts not controlled by the cerebrum? 3. Why would it not be well 
for us to have to control our heart-beat consciously? 4. Describe 
an experiment illustrating the action of an involuntary muscle. 5. 
Why does the cerebrum have no direct control over the secretion of 
the glands? 6. Do you think of swallowing all the time that you 
are eating? Why not? 7. State two advantages of reflex action. 
8. What is a habit? 9. Name five good habits. Three bad habits. 
10. What is the value of habit? n. Why does practise make 
perfect? 12. Why should education be obtained in youth? 13. 
How can we train the nervous system? 14. How are bad habits 
broken? CHAPTER L. THE CARE OF THE NERVOUS 
SYSTEM 
The nervous system is the most wonderful and the 
most delicate part of the human body. It is also more 
closely connected with our real selves than any other part. 
The nervous system not only coordinates all our organs, 
as has been pointed out in Chapter XLVI, but also regu- 
lates our relations with the world around us. The care of 
the nervous system, therefore, becomes the most important 
problem of hygiene. The man who solves the problem of 
how to keep an active efficient nervous system has largely 
solved the problem of correct living. 
This is a difficult task, and you cannot expect to learn 
all about it in a single year. Indeed, you must learn a 
great deal from experience. In this book we can only 
hint at some of the important points to bear in mind with 
reference to the nervous system. These points we may 
summarize in the following rules: (i) Keep the body in 
general good health according to the rules of hygiene thus 
far learned; (2) avoid all stimulants except when they are 
prescribed by a physician in case of sickness; (3) form good 
habits; (4) avoid the poisoning which results from germ 
diseases such as typhoid fever, scarlet fever, grip, and 
others; (5) keep the stomach in good order; (6) avoid 
worry, overwork, and mental strain; (7) sleep sufficiently; 
(8) take enough recreation. 
Habits. We shall take up first the subject of habits, as 
stimulants are discussed in the next chapter. Habits are 
physical as well as mental and moral. Among bad habits 
may be mentioned that of spitting on the floor, which is, 
of course, a physical habit. A bad mental habit is that of 
giving poor attention to one’s studies. Giving way to fits 
of anger is a bad habit, both from a moral and a physical 
standpoint. The sum total of a man’s habits forms his 
character. Most people have more good habits than bad 
ones, and would have fewer bad habits if they realized 
how easy it is to prevent a habit if one begins in time. 
285 286 
THE HUMAN BODY AND ITS ENEMIES 
People desire the best habits, even from a selfish point of 
view, as soon as they come to realize how much more of 
joy in this world good habits bring. 
Effect of Germ Diseases on the Nervous System. We 
often see young people so weakened by an attack of disease, 
such as typhoid fever for 
instance, that it is years be- 
fore they can perform their 
ordinary duties with comfort. 
All the germ diseases set 
poisons free in our blood. 
These poisons injure the del- 
icate nerve cells. While it 
is not an everyday occurrence 
to see insanity as a result of 
smallpox or typhoid fever, 
such things do occur. You 
can imagine, then, the ter- 
rible harm that can result 
to the nervous system, when 
a patient lies for weeks in a 
delirium due to the poisons 
of typhoid fever. Many nervous diseases are caused by 
germ diseases, and if we prevent the germ diseases, we 
prevent the nervous diseases which follow. 
Effect of the Stomach on the Nervous System. The 
stomach is very richly supplied with nerves, both from the 
brain and from the sympathetic system. The solar plexus 
(Fig. 203) supplies many nerves to the stomach. The 
close connection between the stomach and the nervous 
system is shown by the fact that fright can make some 
people sick at the stomach, or nauseate them. Strong ex- 
citement or anger interferes with appetite and digestion. 
For this reason only pleasant topics should be discussed at 
meal time. If we are careless in our eating habits, and 
swallow food hurriedly, or eat at irregular hours, or fail to 
Figure 205.— All the catching 
diseases leave the nervous sys- 
tem weakened to a greater or 
less degree. CARE OF THE NERVOUS SYSTEM 
masticate our food properly, it is very likely to upset the 
stomach and make us nervous and miserable. There 
is one kind of dyspepsia that is called nervous dyspepsia; 
few people are so miserable as those who suffer in this way. 
Overwork. A reasonable amount of work helps to keep 
the body in good condition and makes a person enjoy his 
leisure and his sleep. But this work must be regulated 
according to the strength of the worker. One man can 
stand twice as much work as some other man. It is said 
of some men that they can work eighteen hours a day for 
many days at a time. This is prob- 
ably not true. It is certain that such 
a practise would wear out an average 
man in a short time. Some people 
of delicate constitution can work 
only an hour or two at a time with- 
out being fatigued. When one works 
too long or too hard, he notices that 
he cannot do quite as good work as 
usual, and that he does not enjoy his 
work as much. If he keeps on try- 
ing to drive himself to work as hard 
as ever, he finds that he is depressed 
and becomes discouraged easily. He 
gets what is called the blues, and 
becomes more irritable than is his habit. He is likely to 
become nervous and sleepless, and may lose weight. He 
feels tired, even on rising in the morning, and spends a 
very miserable existence indeed. 
It is often difficult to say whether a boy is overworked or 
whether he is merely lazy. One indication of laziness is 
that the individual is interested in something outside of 
his work, a thing not likely to be the case with an over- 
worked boy. We should remember, however, that people 
of an enthusiastic, eager disposition are more likely to 
overwork themselves than those of a reserved, smooth 
287 
Figure 206. — This repre- 
sents a man who has been 
overworked. 288 
THE HUMAN BODY AND ITS ENEMIES 
temperament. If you are of an enthusiastic disposition, 
there may be times when you feel overworked, and in 
these times you should talk with some older person, such 
as a parent, sister, or guardian. Oftentimes an outsider 
can plainly see what we ourselves overlook. 
A nervous breakdown resulting from overwork is a serious 
matter. The cure for it is a change of scene and habits, 
which is expensive. Hence it is 
wise to avoid a breakdown. 
Longer hours for sleep and rec- 
reation, and more cautious use 
of exercise, should be begun as 
soon as signs of a nervous break- 
down occur. 
Sleep. One who sleeps enough 
is not likely to suffer a nervous 
breakdown. Sleep is the cure for 
worry and overwork. A child of 
twelve should sleep from nine to 
eleven hours a day. A man 
doing hard physical labor should sleep at least eight hours 
a day. Intellectual laborers should sleep an hour more. 
Those who have a delicate constitution should take a nap 
in the middle of the day, especially in warm weather. 
Recreation. This is next to sleep in importance. Every 
man needs some exercise which he can take with so much 
pleasure that he forgets himself. The true test of recrea- 
tion is, that it cause the player to forget himself in the 
enjoyment. Men who perform hard physical labor usually 
like some recreation which employs the mind more than 
the body, such as music or reading. Intellectual workers 
usually prefer some form of recreation which calls the mus- 
cles into play, such as tennis, golf, or hunting. Exercise 
for the sole purpose of building up the body, especially if it 
is unpleasant, is not true recreation. To get the most 
good out of recreation, it must be enjoyable. In Texas 
Figure 207. — Sleep is the 
greatest restorer of worn-out 
nervous systems. CARE OF THE NERVOUS SYSTEM 
289 
the climate is such that outdoor exercise can be enjoyed 
all the year round, and all persons who have a nervous 
tendency should try to spend a large part of the time out- 
of-doors. It is nearly always possible to find a congenial 
occupation out-of-doors. 
The Nerve Cells. The nerve cells are the seat of those 
nervous changes which go to make up our conscious 
life. When the nerve cells are well nourished and fresh, 
we feel well; when the nerve cells are tired, exhausted, or 
starved, we feel ill. The nerve cells are so delicate that 
we cannot handle them after death without destroying 
Figure 208. — The picture to the left is a fresh, unfatigued nerve-cell. 
The middle picture is a moderately fatigued nerve-cell. The picture to 
the right is a nerve-cell poisoned by alcohol or disease. 
them, and so, up to this time, we have never seen many 
of the changes which occur in them as a result of fatigue 
or of poisoning. 
The results of fatigue are best seen in the cells of animals 
which are hard at work all day, such as the bee or the 
swallow. If the nerve cells of these little beings are ex- 
amined at night, they appear shrunken and irregular in 
outline. In the morning, while the little creatures are 
fresh and strong, the nerve cells seem to be well rounded 
out. This is shown in Figure 208. We know, then, that 290 
THE HUMAN BODY AND ITS ENEMIES 
we cannot do good work with worn-out or poisoned nerve 
cells. Disease germs, alcohol, or morphin cause poisoning 
of the nerve cells. Rest, recreation, and sleep restore the 
cells to their proper strength and vigor. 
Just as the mind is the highest function of the nervous 
system, so the judgment is the highest faculty of the mind. 
At no point do we need good minds and good judgment 
more than in the regulation of our lives so as to keep our 
nervous system in good order. 
IMPORTANT POINTS 
The enemies of a good nervous system are as follows: 
1. General poor health from other causes. 
2. Stimulants, such as alcohol, tea, and coffee. 
3. Bad habits, and excesses of all kinds. 
4. Germ diseases such as typhoid fever. 
5. Improper habits of eating, causing imperfect digestion. 
6. Worry, overwork, and mental strain. 
7. Lack of sleep and lack of recreation. 
QUESTIONS 
i. Name some stimulants which may cause nervous disease. 2. 
Name all the germ diseases you know. 3. Name some bad habits. 
4. Explain why the stomach is concerned in nervous disorders. 
5. Explain the importance of sleep. 6. Explain what is meant by 
recreation. 7. If a man practises with dumb-bells in order to gain 
muscle, is this recreation? 8. How, then, can you tell whether an 
exercise is true recreation or not? 9. What is the difference between 
the nerve cells of a bee early in the morning and at the close of a busy 
day? 10. What kind of persons are likely to be overworked? CHAPTER LI. ALCOHOL, NARCOTICS, AND 
STIMULANTS 
We have already learned that the poisonous liquid or drug 
called alcohol can injure the various organs of the body; 
but this poison acts in such a stealthy and peculiar way 
that we shall devote some time now to the study of the 
poison itself, of its effects on the human body, and of how 
to avoid it. 
Alcohol. Pure alcohol is a clear, colorless liquid, some- 
what lighter than water. It mixes with water very readily. 
Alcohol evaporates rapidly, and for this reason, when 
placed on the skin, the skin feels cool as it evaporates into 
the air. If it is placed on the skin and then covered, 
however, it feels hot and causes reddening of the skin. 
Alcohol is made from fermenting sugars. In the process 
of making alcohol, the yeast germs change the sugar to 
alcohol, and in so doing they cause carbon dioxid to bubble 
out of the fluid. If the yeast germs are allowed to remain 
in the water and sugar solution, there comes a time when 
they have formed so much alcohol that they can no longer 
live in the mixture, and they die. Other germs are less 
able to live in the alcohol solution than the yeast germs. 
From this it might be supposed that alcohol is good for 
us, because it kills germs. But in the chapter on disin- 
fectants we have learned that if we desire to kill germs in 
the human body we must use something that is more 
poisonous for the germs than for our bodies. Alcohol is 
just as poisonous for us as it is for the germs, and indeed 
it gives the germs the advantage by upsetting our system. 
So it is not a useful drug for killing germs in the human 
body. 
Percentage of Alcohol in Whisky, Beer, and Wine. We 
have learned that pure alcohol is a clear liquid; but the 
drinks sold to the public do not usually contain more than 
fifty per cent of pure alcohol. Whisky and brandy contain 
about fifty per cent, the wines from seven to twenty per 
cent, and beer from one to five per cent of alcohol. Prac- 
291 292 
THE HUMAN BODY AND ITS ENEMIES 
tically all that any of these liquors contains in addition 
to the alcohol is some sugar and flavoring and coloring 
matter. The picture shows that the quantity of pure 
alcohol contained in an ordinary drink of whisky is about 
the same as that contained in a drink of beer or wine. 
It is most remarkable how this alcohol attacks every 
organ of the body with which it comes in contact. 
Figure 209. — Although beer and wine contain a lower percentage of 
alcohol than whisky, a drink of beer contains about the same amount of 
alcohol as a drink of whisky. The tall graduated glasses represent the 
amount of absolute alcohol in a single drink of beer, whisky, and wine. 
Effects of Alcohol on the Stomach and Liver. The 
stomach is very badly affected by alcohol, and it becomes 
inflamed from the irritating action of liquors containing 
this poison. Indigestion, loss of weight, and a general 
condition of invalidism, are signs of the bad effects which 
the alcohol has on this particular organ. The liver also 
feels the presence of alcohol, and shows it by becoming tough 
and fibrous from the scar tissue or connective tissue which 
is caused by alcohol. When this has once developed, 
there is no hope that the patient will ever recover. As a 
rule the drinker does not know he is threatened with this 
trouble until it is too late. 
Effects of Alcohol on the Respiratory System. The 
fumes or odor of alcohol can be detected in the breath, 
which means that the lungs are doing their part to throw 
the poison out of the system. Alcohol makes people 
susceptible to the inflammations of the lungs, such as ALCOHOL, NARCOTICS, STIMULANTS 
293 
pneumonia. Persons who drink alcohol succumb more 
easily to pneumonia than persons who drink no alcohol. 
Whenever physicians are called in to treat a case of 
pneumonia, they always inquire if the patient is a user 
of alcohol. This disease is dangerous at any time, but 
especially so when it occurs in drinkers. 
Effect of Alcohol on the Kidneys. The kidneys help the 
lungs to rid the system of alcohol, and in throwing this 
poison off, the kidneys are somewhat injured. They are 
often so injured that they can never be repaired; usually 
when a drinker has caused nephritis, or kidney disease, by his 
bad habits, it is too late to remedy the matter. Nephritis 
means an injury of the little kidney cells (XYZ, Fig. 158). 
Like the liver cells, the kidney cells, when they are in- 
flamed, are replaced to some extent by connective tissue. 
Effect of Alcohol on the Heart. Drinking alcoholic 
liquors injures the heart, because the liquid has to be 
pumped to the lungs and to the kidneys, to be thrown off 
from the body. The heart is thus made to pump more 
blood than the needs of the body demand; and it seems 
reasonable to suppose that a heart is overloaded when one 
drinks much liquor. The alcohol in the blood also hardens 
the arteries and causes the growth of scar tissue, which can 
be seen in spots in the arteries after death. Hardened 
arteries sometimes burst, and when such a vessel ruptures 
in the brain, it causes the disease known as apoplexy. 
Effect of Alcohol on Muscles and Bones. The muscles 
and bones are injured by alcohol, because they suffer from 
want of food. If the stomach is inflamed, it cannot pre- 
pare food for the needs of the body, and for this reason 
persons who drink large quantities of alcohol are usually 
weak and feeble. 
Effect of Alcohol on the Nervous System. The nervous 
system is so delicate that it must be taken care of properly 
or it will certainly get out of order. The most wonderful 
watch that was ever made, when compared with the 294 
THE HUMAN BODY AND ITS ENEMIES 
human nervous system, is as clumsy and awkward as an 
ox wagon. The delicate machinery of brain, spinal cord, 
and nerves has to do with the proper control of our organs 
and also with our thoughts. Think what dreadful conse- 
quences must follow the injury to these little cells which 
form our thoughts. More cases of insanity are caused by 
alcohol than by anything else except heredity. Probably 
about twenty per cent of all insanity is due entirely to 
alcohol. 
How the Drink Habit is Formed. It is not stated any- 
where in this book that all persons who use alcohol will 
develop any of the diseases mentioned. Indeed, there are 
some people who do not seem to be injured by alcohol, so 
far as we can tell. Such persons are to be compared with 
typhoid carriers. You remember that some persons have 
the typhoid germs in their bodies without showing any 
symptoms of the disease. These persons are well and 
strong, and so far as they are concerned, are none the 
worse off for having the germs; but they spread the 
disease to others. So it is with drinkers: some of them 
take the alcohol into their systems without showing any 
immediate ill effects on themselves, but they spread the 
drink habit. Young men and boys see them drink and 
follow their example. In the case of germ diseases, a 
person who has a mild case may give the disease in its 
worst form to another person; so a man who drinks just 
a little can give the germs of the habit to another man, 
who may drink himself into his grave or into the asylum. 
Possible Effects of the First Drink. Probably all of 
you know now how alcohol can drug its victim. You have 
no doubt heard of, or possibly seen, a drunkard, with his 
staggering gait, his unkempt hair, and his bleary eyes. 
Such a poor drunkard goes about exposing himself to the 
weather, and leaves his family to look out for themselves. 
He is not himself, and that marvelously beautiful instru- 
ment, the brain, is in such poor working order that he is ALCOHOL, NARCOTICS, STIMULANTS 
295 
little better than an idiot. A drunkard may scowl at his 
best friend as though he hated him, or may speak roughly 
to a little child; on the other hand, he may look on a scene 
of sadness and chuckle as if it were a joke. You may be 
sure that no man ever expected to be anything like this 
Figure 210. — The first drink is almost always taken to accommodate a 
friend. Have your mind made up beforehand never to take the first drink. 
when he took his first drink. And yet it is impossible to 
tell beforehand just who will develop into a drunkard. 
Since, then, alcoholic drinks are absolutely worthless to 
the user, and may cause irreparable harm to body and 
mind, it is best never to begin to drink. When invited by 
a friend to drink with him, it takes strength of mind and 
force of character to refuse to be led into so dangerous 296 
THE HUMAN BODY AND ITS ENEMIES 
a habit. Make up your mind that, when you are in the 
situation of the young man shown in Figure 210, you will 
decline. 
Effect of Alcohol on Business Success. For business 
reasons it is wise to leave alcohol absolutely alone, for 
many firms will not employ any one who drinks. This 
is true especially of banks, railways, and other business 
concerns which are entrusted with people’s property or 
people’s lives. Athletes who are ambitious to excel always 
leave alcohol alone when preparing for a contest. Loco- 
motive engineers must not drink, for the lives of the pas- 
sengers are in their hands. Lawyers must work hard at 
times, and sometimes an innocent man’s life depends on 
the good work of the lawyer who is defending him; in a 
case of this kind alcohol is a hindrance. The physician 
fighting disease cannot afford to drink, as it would make 
him unfit to give advice to the patient depending on him. 
The machinist cannot afford to drink, for if his nerve is 
unsteady he may lose a finger or suffer some other painful 
and mutilating accident. The salesman in a 'store cannot 
afford to drink, for he must receive money and return the 
change quickly and accurately. The stenographer dares 
not drink, for he may write an error into an important 
letter. Indeed, it may be said that any good work demands 
of a man that he leave alcohol alone. Drinking is out of 
place in the life of any man. 
Tea and Coffee. Somewhat akin to the alcohol question, 
but of less importance, is the tea and coffee problem. 
Both tea and coffee contain a substance which in its pure 
form exists as white crystals, called thein or cajjein. This 
substance acts as a powerful stimulant to the muscles, the 
nerves, and the mind. After the first effect passes off, the 
drug causes depression and discomfort. In mild doses it 
is not very harmful to some people, but it is always risky to 
tamper with stimulants. In the long run, any man can 
do more work without stimulants than with them. It is ALCOHOL, NARCOTICS, STIMULANTS 
297 
rather cowardly to take stimulants in order to stand up 
under a special strain. A man should face his trials man- 
fully, whether they are an extra hard day’s work, a tedious 
examination, or some other hard task. The use of stim- 
ulants to give a man temporary strength to perform his 
duty undermines his self-reliance. 
Opiates. There is a drug that affects another part of 
the brain, and this drug is opium or morphin. Opium 
is the dried juice of the poppy, and morphin is a white 
crystalline substance which represents the strength of 
opium. Opium and morphin do not increase the intel- 
lectual powers, but they stimulate the imagination and 
relieve pain. These drugs are even more deadly than 
alcohol, because they almost invariably cause the opium or 
morphin habit. You can have no idea how these drugs 
cause one to long for them after one has taken them a few 
times. When the first effect wears off and the dreadful 
after-effect comes on, the user of the morphin is nervous 
and miserable, and frequently takes his own life. 
The morphin habit is very hard to shake off. It is 
against the law for such drugs as morphin to be sold in 
Texas except on a physician’s prescription, and all con- 
scientious physicians take precautions in the use of these 
deadly drugs, in order to prevent their patients from 
forming the habit. Laudanum, paregoric, Dover’s powder, 
cocain, and some headache powders or capsules, belong 
in the same class. It would be well for you to make it 
a rule never to take any medicine to relieve pain except 
on the advice of a competent physician. 
IMPORTANT POINTS 
1. There was never a drunkard who believed at the time 
he took his first drink that he would become a drunkard. 
2. Alcohol injures all the organs of the human body, but 
does its greatest harm to character. 
3. The first drink is usually taken to please a friend. 298 
THE HUMAN BODY AND ITS ENEMIES 
4. Tea and coffee act as stimulants, but in the long run do 
not increase one’s ability to perform work. 
5. We should avoid taking morphin, opium, soothing sirups, 
and headache powders or capsules for the relief of pain. 
QUESTIONS 
i. What is alcohol? 2. Alcohol does not help the body destroy 
germs, although alcohol itself will kill germs. Why is this? 3. In 
what way does alcohol do its greatest harm to the body? 4. Since 
beer contains a smaller percentage of alcohol than whisky, explain 
why it is that a drink of beer contains as much alcohol as a drink 
of whisky. 5. Why should physicians let alcohol alone? 6. Why 
should a salesman let alcohol alone? 7. Name three other types of 
persons who cannot afford to drink alcohol in any form. 8. Is there 
any business in which a drunkard is likely to succeed? 9. Why is 
it dangerous to take medicine freely to relieve pain? CHAPTER LII. THE SPECIAL SENSES: TOUCH 
General Sensations. We have learned (Chapter 
XLVIII) that there are two kinds of nerve fibers: sensory 
fibers, carrying impulses in to the central nervous system, 
and motor fibers, carrying impulses out to the muscles. 
In reflex action, sensory impulses may pass only to the 
spinal cord, and be there changed to motor impulses that 
pass out to the muscles. If the sensory impulses reach 
the cerebrum, they result in sensations. When meal time 
arrives we are hungry; if water is needed, we are thirsty. 
Hunger and thirst are sensations due to impulses that 
arise from all parts of the body. They are, therefore, 
called general sensations. Feelings of fatigue and of 
nausea are other general sensations. General sensations 
are useful in serving as a guide to the general condition of 
the body. 
The Special Senses. The special senses (touch, taste, 
smell, sight, hearing) differ from the general sensations in 
that each has a special organ that produces a particular 
kind of sensation. Thus the skin is the organ of touch, 
the nose of smell, the eyes of sight, and the ears of hearing. 
These organs are called the organs of the special senses, by 
which we feel, taste, smell, see, and hear. Through the 
special senses we learn all we know about the things around 
us. Since this is true, it is very important that we train 
the senses so that they may, through practise and habit, 
become our skilful servants. 
Four Conditions Needed for Sensations. In studying 
the special senses we must remember that a number of 
things are necessary in order that a sensation may be pro- 
duced. (i) There must be a proper stimulus, for without 
something touching the skin we could not feel, or without 
light we could not see. (2) There must be cells (the end 
cells) in the sense organ to catch up these stimuli, magnify 
them, and translate them into nerve language and pass 
them on. (3) From the end cells sensory nerve fibers must 
take the nerve impulse to the brain. (4) The cortex of the 
299 300 
THE HUMAN BODY AND ITS ENEMIES 
cerebrum must be active, so as to receive the impulse and 
produce the sensation. If any one of these four is absent 
or injured, there can be no sensation. In studying the 
sense organs we shall make it a point to study the situation 
of the end cells and to 
discover how the various 
stimuli reach them. 
Touch. The skin is the 
organ of touch. As shown 
in Figure 161, and again in 
B, Figure 211, there are 
groups of cells called touch 
buds, among the cells in 
which the sensory nerve 
fibers end. When an ob- 
ject touches the skin, it 
presses against the touch 
buds and stimulates the 
nerve fibers; the impulses 
are then carried to the brain and we have the sensation of 
touch. If the pressure is even over the skin, we feel the 
object as smooth; if the pressure is greater in spots, we 
feel the object as rough. Hard, soft, sharp, dull, etc., are 
words that describe how objects feel from the way they 
press against the skin. 
Experiments on the Sense or Touch, (i) Some parts 
of the skin are more sensitive to pressure than others, as can 
be readily observed by experiment. Take a bristle from a 
whisk-broom or clothes-brush and press it against the skin of 
the nose, forehead, lips, back of neck, tips of fingers, etc. (2) 
Another test for sensitiveness of touch can be made by finding 
out the greatest distance apart two points, pressing on the skin 
at the same time, will be felt as one point. Take a pair of 
blunt scissors and place the two points, separated one sixteenth 
of an inch, on the tips of the fingers of a person, who should 
have his eyes shut or be looking away. Are they felt as one 
point or as two? Repeat the experiment for different regions 
Figure 211. — Papillae of the skin; A, 
epidermis; 1 and 3, papillae with blood 
vessels; 2, papilla with touch bud. THE SPECIAL SENSES: TOUCH 
of the skin, separating the points more or less; on the back of 
the neck the points may be several inches apart and still felt 
as one point. Try this on different persons, but try to con- 
fuse the person experimented upon by alternating the applica- 
tion of a single point and of two points. 
The Temperature Sense. At some places in the skin 
certain nerve fibers end in cells that are not a part of touch 
buds. Many of these fibers carry sense impulses of heat 
and cold. The ability to feel differences in temperature 
is known as the temperature sense. 
A person is capable of feeling general and special sensations. 
Hunger and fatigue are general sensations which do not come 
from special organs. The special senses are those of touch, 
taste, smell, hearing, and sight. Certain organs can be desig- 
nated as the organs of the special senses: the skin, the tongue, 
the nose, the ears, and the eyes. In these organs are special 
cells, the end cells, whose duty it is to take up the stimuli. 
Objects striking or touching the skin, for example, stimulate 
the end cells of touch in the touch buds of the skin. These 
end cells pass the stimuli on to the sensory nerve fibers (the 
nerves of touch) leading to the cerebrum. Here the stimuli 
are translated into sensations, and thus we feel. A similar 
process takes place in all the special senses, as will be seen in 
the following chapters. 
SUMMARY 
i. Mention some general sensations. 2. What is the use of 
these? 3. Why can you not designate organs of general sensations? 
4. Name the special senses and give the organ of each. 5. What 
is the function of the end cells in the sense organs? 6. What other 
conditions besides end cells must there be before we can experience 
sensations? 7. Illustrate this in the case of touch. 8. Where are 
the end cells of touch situated? 9. What parts of the skin have 
you found to be most sensitive to touch? 10. What is meant by the 
temperature sense? 11. Tell the different events that must happen 
in order that you may have a sensation of touch. 
QUESTIONS CHAPTER LIII. TASTE AND SMELL 
The senses of taste and smell are very much alike. In- 
deed, many things which we think we taste, we really smell. 
Thus vanilla flavoring is not tasted but smelled. Sweet, 
sour, bitter, and salty substances only can be tasted. 
We distinguish flavors by the sense of smell. 
Experiment. Close your eyes and hold your nose. Now 
let some one lay on your tongue successively a slice of apple, 
of potato, and of onion. Can you distinguish them by taste 
alone? 
Organ of Taste. Just as the skin is the organ of touch, 
the tongue is the organ of taste. Just as there are touch 
buds in the skin, so there are 
taste buds in the tongue. They 
are situated on the sides of the 
elevations or papilla of the 
tongue. The largest of these 
papillae occur in two rows near 
the back of the tongue, and 
other smaller ones are scattered 
over the tongue (Fig. 212). A 
cross section of one of the large 
papillae is shown in Figure 213. 
The taste buds are seen to con- 
sist of long, spindle-shaped cells 
(1 and 2, Fig. 214), with their 
points coming together at the 
taste pores (P). Among some 
of these cells (2) arise fibers of 
the nerves of taste (N), which are branches from certain 
cranial nerves. 
How we Taste. Substances are tasted by being taken 
up by the taste cells of the taste buds and a few other 
taste cells scattered over the tongue. These taste cells 
in turn stimulate the nerves of taste. Only liquid sub- 
stances, that is, substances dissolved in water, can be 
Figure 212. — The tongue. 
302 TASTE AND SMELL 
303 
tasted, because only these can be absorbed by the taste 
cells. The sense of taste is useful in helping to guide 
Figure 213. — Section of large papilla of the tongue, showing taste buds 
(B) and nerve of taste (N). 
Figure 214. — A taste bud of 213 more enlarged; P, taste pore; 2, end cell 
of taste; 1, supporting cell. 
animals in the selection of their food and to stimulate the 
digestive glands to secrete juices. How does saliva help 
us to taste starchy food? 
Organ of Smell. The nose is the organ of smell. In 
order that the nerves of smell may be excited, gases or 
tiny particles floating in the air must enter the nasal 
passages. Study Figure 121, and note two ways by which 
odors may pass into the nasal passages. The nerves of 
smell make up the pair of first cranial or olfactory nerves 
(1, Figs. 198 and 202). The branches of this nerve are 
spread out over the irregular inner surface of the nose 
(Fig. 215) and pass through holes in the base of the skull. 
The end cells of smell are situated in the mucous mem- 
brane of the nasal cavities. Here are two kinds of cells: 
long epithelial cells (Fig. 216) and spindle-shaped cells 
with a long projection at one end and nerve fibers at the 
other. The cells with the nerve fibers are the smelling 
cells. 
How we Smell. Particles of matter are sniffed in with 
the air and, striking the ends of the smelling cells, stimulate 
them. The impulses are passed on to fibers of the olfac- 304 
THE HUMAN BODY AND ITS ENEMIES 
tory nerves, and thence to the brain. The sense of smell is 
extremely acute, especially in some animals, such as dogs, 
and some birds, fishes, and insects. The tiniest particles 
passing into the nose can stimulate the nerves of smell. 
Figure 215. — The nerve of smell at the base of the brain and the branches 
in the upper part of the left nasal passage. 
Figure 216. — The cells of smell from the mucous membrane of the 
nasal passage. 
Use of the Sense of Smell. Smell is a useful sense for 
it enables us to detect harmful gases in the air, such as fuel 
gas and odors that indicate disease-breeding objects in 
our vicinity. Foul odors are disagreeable and warn us 
when human beings are not cleanly and healthy. The 
nose is a good detector of impure air in a school room, 
when a person comes into the room from out-of-doors. 
The end cells of taste are situated chiefly in the papillae 
that occur scattered over the tongue. The end cells of smell 
are special cells among the epithelial cells of the upper part of 
the nasal passage. The end cells of taste are stimulated by 
substances in solution in water. The smelling cells are stimu- 
lated by the presence of minute particles carried in by the air 
we breathe. Both of these senses are useful to us in the choice 
of our food. The sense of smell also enables us to avoid foul 
and unhealthful places. 
SUMMARY TASTE AND SMELL 
QUESTIONS 
i. What kind of substances can be tasted only? 2. What sub- 
stances are smelled? 3. Where are the end cells of taste? Of smell? 
4. How does saliva help us to taste? 5. How does taste help to 
make the saliva flow? 6. How are smell and taste of service to us? 
7. Describe how we smell. CHAPTER LIV. HEARING 
Taste is a more delicate sense than touch, and smell is 
more delicate than taste. Hearing is still more delicate. 
What is it we hear? Sound, you say. When two objects 
are struck together, as when a bell is rung, invisible waves 
of air are produced, called sound waves, which radiate out 
from the center in all directions as waves of water radiate on 
the surface of a quiet pool when a pebble is thrown into it. 
The sound waves are caught up and transmitted to cer- 
tain cells in the ear where the nerve of hearing (auditory 
nerve) ends. Since the hearing organ is so complicated and 
easily injured, it is encased for protection in the bones of 
the skull. 
The Outer Ear. The ear consists of three parts or 
regions: the outer, the middle, and the inner ear. The 
Figure 217. — Diagram of a section of the ear, 
showing outer, middle and inner ear. 
outer ear consists of the shell-shaped outer part which 
serves to collect the sound waves; and a canal, the audi- 
tory canal (Fig. 217), which conducts the sound waves to 
a membrane, the tympanum or ear-drum, at its bottom. 
The tympanum may be likened to a drum-head: when the 
drum-head is beaten it vibrates; so, too, the tympanum HEARING 
307 
vibrates when the sound waves strike it. Hearing would 
be imperfect without the tympanum. 
Hygiene of the Outer Ear. For protection the ear-drum 
is set back at the bottom of the auditory canal. For 
further protection the canal is crooked. There are also 
glands in it that secrete yellow, bitter wax which keeps 
insects away from the tympanum. Under no circum- 
stances should any one try to remove objects from the 
depths of the canal with any hard instrument, for fear of 
injury to the tympanum. Warm water and a soft cloth are 
all that is needed in washing out the ears. Should an insect 
get into one of them, a little warm water poured into the 
upturned ear is usually sufficient to remove the intruder. 
The Middle Ear. The middle ear is likewise hollow, 
and communicates below through the Eustachian tube 
(Figs. 215 and 217) with the pharynx and through this 
with the outside world. Thus air can get to the tympanum 
from both sides. Do you see why this is? Your physical 
geography teaches that atmospheric pressure varies with 
the weather. If the pressure were greater or less on the 
outer, than on the inner, surface of the tympanum, this 
organ would be stretched, causing pain. Sometimes an 
ear-drum is broken by air waves caused by a very loud 
sound, as the report of a cannon. If the Eustachian tube 
is in good condition, such an accident may probably be 
prevented by simply opening the mouth when the cannon 
is discharged. 
The Ear-bones. How, then, do the sound waves cross 
the middle ear? Attached to the tympanum is a bridge 
of three bones, named from their shape, hammer, anvil, and 
stirrup (Fig. 217). The hammer is attached to the tym- 
panum, the anvil is in the middle, and the stirrup is next 
to the inner wall of the middle ear. These bones vibrate 
with the vibrations of the tympanum, and as they do so 
the stirrup knocks at the door of the inner ear, causing 
corresponding vibrations in this organ. 308 
THE HUMAN BODY AND ITS ENEMIES 
Hygiene of the Middle Ear. Since the cavity of the 
middle ear communicates with the throat by the Eusta- 
chian tube, you can readily see that germs may get into 
the middle ear from the nose and throat. Diseased tonsils, 
catarrh, and severe colds may affect the middle ear. Ade- 
Figure 218. — The inner ear, A, as removed from the skull; B, same, 
natural size; C, section of cochlea, through line 1-2; D, a canal (c) of C, 
more enlarged, showing end cells of hearing. 
noids in the throat are also frequently the cause of inflam- 
mation in the ear. Colds sometimes result in earaches, 
because the Eustachian tube may become stopped up. 
This prevents the middle ear from being properly supplied 
with air. 
The Inner Ear. The inner ear is made up of two parts: 
the cochlea and the semicircular canals. Of these only the 
cochlea functions in hearing, for therein are the nerve 
endings that take up the sound waves. 
The Cochlea. Cochlea means snail-shell (Fig. 218). 
As in a snail-shell the hollow winds round and round to the 
top, so in the cochlea a canal winds round two and one half 
times to the top and then turns back. There are really 
two canals, communicating at the top and separated all 
the way by a partition. The canals are filled with a liquid, 
a kind of lymph. Now, on the partition between the two 
canals, there are cells with tiny hair-like projections: 
these are the end cells of the auditory nerve, the cells HEARING 
that catch up sound waves and transmit the impulse to 
the auditory nerve, which carries it to the cerebrum as 
the sensation of sound. 
How we Hear. How, then, do sound waves from the 
air about us, reach the hearing cells in the cochlea? First, 
the air waves strike the tympanum and set it in vibration; 
this then causes the hammer, anvil, and stirrup to vibrate. 
The stirrup in turn knocks against the oval window 
(O, Fig. 218) of the cochlea, setting in vibration the lymph 
309 
Figure 219. — Diagram showing passage of waves of sound through the 
ear; AC, auditory canal; T, ear drum; ET, Eustachian tube. 
in the canals; the waves of this liquid pass through one 
canal to the top of the cochlea, then down the other, and 
finally die out when reaching the end of the canal at the 
round window of the cochlea (R, Fig. 218). This prin- 
ciple is shown in Figure 219, which represents the cochlea 
uncoiled and stretched out. The arrows indicate the path 
of the waves. When the lymph is in motion in the canals, 
it rubs over the hair-like projections of the hearing cells 
(D, Fig. 218) and starts impulses that are carried to the 
brain by the auditory nerve fibers and produces the sensation 
of sound. 
The Semicircular Canals. The semicircular canals are 
not used in hearing, but they have an important use in 
that they act as spirit levels and inform us (unconsciously,  THE HUMAN BODY AND ITS ENEMIES 
310 
however) when we are about to fall over. They, too, are 
filled with a liquid, and their walls contain cells with hair- 
like projections. In these cells end certain fibers of the 
auditory nerve. When the body or the head is moved in 
any direction, the liquid moves in one or the other of the 
canals. Of course, in the daytime a person can see with 
his eyes what position he is in, or he can see when he is 
about to fall over; but with the semicircular canals he 
feels it much more quickly, and by reflex action he rights 
himself at once. 
The stimuli from the outside that cause us to hear are waves 
or vibrations of air. These are collected by the outer ear and 
directed to the ear-drum, which is thus made to vibrate. The 
sound waves are carried across the middle ear by a series of 
three bones, the inner one of which, the stirrup, knocks against 
the opening of the inner ear. It is in the cochlea of the inner 
ear that the auditory nerve reaches the end cells that catch up 
the waves of sound. These cells are upon the partition of the 
spiral canal which winds up through the cochlea. The wave 
travels in the liquid with which the cochlea is filled to the top 
of the cochlea on one side of the partition and comes back on 
the other side. As it travels through the cochlea, it stimulates 
the end cells to which the auditory nerve fibers are attached. 
The impulse is carried to the brain, and thus we hear. 
The semicircular canals also contain a liquid and end cells 
with nerve fibers. The canals are so placed that whenever 
we change our position the liquid in one or the other of them 
moves. The canals thus help us to maintain the balance or 
equilibrium of the body. 
SUMMARY 
i. What is air composed of (Chapter XXXI)? 2. How are 
sound waves produced? 3. Name the divisions of the ear. 4. 
Name the parts of the outer ear and tell the function of each part. 
5. What separates the outer ear from the middle ear? 6. How 
may the ear-drum be injured? 7. How is it protected? 8. How 
does the middle ear communicate with the outside air? 9. Why 
QUESTIONS HEARING 
311 
is this so? io. How do sound waves cross the middle ear? n. 
How may diseases of the nose and throat cause diseases of the middle 
ear? 12. Name the two parts of the inner ear. Which of these 
is used in hearing? 13. Where are the end cells of hearing? 14. 
How do the sound waves reach these cells? 15. How are impulses 
carried from these cells to the brain? 16. What is the use of the 
semicircular canals? CHAPTER LV. SIGHT 
As the ears are the organs of hearing, the eyes are the 
organs of sight. As the ears are constructed to receive 
stimulations of sound waves and start these stimulations 
to the cerebrum, so the eyes are built to receive from light 
waves stimulations that are passed on to nerves going to 
the cerebrum. 
Sound waves are vibrations of air, and without air there 
could be no sound. But light travels far beyond the limit 
of the atmosphere, for it comes to us from the sun, moon, 
Figure 220. — The muscles that move the eyeball. 
and stars. Air seems to us to be very light and thin, but 
it is really very heavy and dense when compared with the 
substance that carries light. This substance is called 
ether. It pervades all space, and waves of ether are light 
waves. Although we cannot see the waves of ether, we 
must imagine them to be like the waves rippling across the 
surface of a pond of water. The eye has end cells, sensitive 
to these delicate waves of ether, and branches of the nerve 
of sight {the optic nerve) to carry the impulse to the brain. 
Protection of the Eye. The eye cannot be put away 
inside the bones like parts of the ear, but it, too, is pro- 
tected. It is set back in an orbit or hollow of the skull 
(Fig. 167), so that a fall or a blow on the face will not be 
very likely to injure the eye. Again, two flaps of muscle, 
the eyelids, can be pulled over the eye to protect it against 
312 SIGHT 
313 
objects flying toward the face. (Study the action of the 
eyelids from the standpoint of reflex action.) The eye- 
lids are aided in their work of keeping out dust and dirt by 
protruding hairs on their edges, the eyelashes. 
The Tear Glands. You have noticed that persons and 
animals wink at intervals. The purpose of this is to dis- 
tribute over the eyeball a fluid secreted by the tear glands, 
for the surface of the eyeball must be kept moist. The 
Figure 221. — The tear gland of the eye. 
tear glands lie along the outer side of the eye, and the tear 
is emptied on the under side of the upper eyelid (Fig. 221). 
The tear is usually carried off by certain tear ducts that 
lead to the nose; when one weeps the glands form tears 
faster than the ducts can carry them away. 
The secretion of the tear glands is regulated by nerve 
fibers from the cranial nerves and, as you would expect, 
from the sympathetic system. One of the two openings 
of the tear duct can be seen in the center of a little eleva- 
tion or papilla on the edge of the lower eyelid, near the 
inner corner of the eye. That the tears do not always run 
over the edge of the eyelid is due to the fact that there is a 314 
THE HUMAN BODY AND ITS ENEMIES 
row of oil glands which empty their fatty secretion on the 
edge of the lid, thus preventing the tears from running 
over. In certain diseases these glands secrete too large a 
quantity of oil, which on drying becomes hard and yellow. 
When this happens during sleep, it is often difficult to open 
the eyes on awaking. 
Observation and Practise Work. Using a mirror, find 
the papilla on the lower eyelid as described above. Pull the 
eyelid down a little and the papilla with the opening to the 
tear-duct will come to view. Make a drawing of the eye, with 
the eyebrows, lids, eyelashes, and other parts. Name them in 
the drawing. 
How the Eyeballs are Moved. Looking at a sheet of 
paper, you will notice that, without turning the head, you 
Figure 222. — Section of the eyeball with parts named. 
Figure 223. — A part of Figure 222 enlarged, to show attachment of 
lens. 
Figure 224. — The part A of the retina in Figure 222, much enlarged 
to show the seeing cells of the retina. 
can glance from the center to the right and left edges, to 
the top and bottom edges, and to the corners of the paper. 
It takes six muscles (three pairs, Fig. 220) to move each SIGHT 
eye, and it takes three pairs of cranial nerves to govern 
these muscles and to regulate their action. The two eyes 
move together, since the motor nerves send branches to 
corresponding muscles of each eye. 
The Form and Inner Structure of the Eyeball. The 
eyeball is almost spherical in shape, bulging a little in front, 
as shown in Figure 222. The wall of the eyeball has three 
coats: the outer, or sclerotic coat, the middle, or choroid 
coat, and the inner, or retina. 
The white of the eye is a part of the sclerotic, as is 
also the transparent cornea, through which the black 
pupil and the colored iris can be seen. The choroid con- 
tains dark pigment or coloring matter so as to darken the 
inside of the eye; for the eye is a miniature camera, a 
315 
Figures 225 and 226. — The pupils of the eye, large and small. 
dark box with only a small opening in front for the light 
to enter. This opening is the pupil, which is surrounded 
by a colored ring, the iris, a part of the choroid coat. A 
person’s eye is said to be blue or brown if the iris is blue 
or brown. In bright light the pupil is small (Fig. 226); 
in the dark the pupil is large (Fig. 225). There are smooth 
muscles in the iris that regulate the size of the pupil, and 
these muscles are regulated by cranial and sympathetic 
nerves. Their action is reflex and involuntary, as de- 
scribed in Chapter XLIV. 
Observation Work. Repeat the experiment on the reflex 
action of the iris muscles.  THE HUMAN BODY AND ITS ENEMIES 
316 
The Lens. Immediately behind the iris is the lens. 
This is a most important organ; it enables us to see clearly 
and is to the eye what the glass lens is to the camera. The 
eyeball is filled with a clear, watery fluid, the aqueous 
humor (Fig. 222), in front of the iris, and with a clear, 
jelly-like mass, the vitreous humor, behind the lens. 
The Retina. Waves of light enter the pupil, pass 
through the lens, and are distributed over the inside wall 
of the eye. Where, then, are the sensitive cells and their 
nerve fibers, that catch up the light waves? These cells 
are found in the coat of the eye called the retina, inside of 
the choroid layer (Fig. 222). This layer of sensitive cells 
occupies a position similar to that of the sensitive film or 
plate in a camera. The retina is, therefore, the sensitive 
coat of the eye. 
Figure 224 represents a section of the retina, much 
enlarged. The sensitive cells are rods and cones (so called 
from their shape) and stand pointing toward the choroid 
layer. More or less closely connected with these are nerve 
fibers from the optic nerve. Light waves, strike the rods 
and cones and cause nerve impulses in the fibers of the 
optic nerve. These, on reaching the nerve cells of the 
cerebrum, cause the sensation of sight. 
SUMMARY 
The eye, or seeing organ of the body, may be likened to a 
camera. Like the camera, the eye is a dark box, the choroid 
coat serving the purpose of the black paint on the inside of the 
camera. There is an opening, the pupil of the eye, to admit the 
light. The size of this, and consequently the intensity of the 
light entering the eye, is regulated by the iris. The sensitive 
film is the retina, containing the rods and cones, which are the 
sensitive end cells, or seeing cells, connected with fibers of the 
optic nerve. These end cells are sensitive to waves of ether, 
called light waves. There is, too, a clear convex lens, which 
serves the eye in a manner to be described in the next chapter. SIGHT 
i. What are sound waves? Light waves? 2. Why cannot the 
eye be put away in the skull bones as is the inner ear? 3. How is 
the eye protected against blows? Against dust? Against drying? 
4. How are tears ordinarily kept from flowing over the edge of the 
eyelids? 5. Point to your own tear glands. 6. Why do we have to 
blow the nose when we begin to cry? 7. How many muscles move 
the eyeball? 8. How many nerves are represented in Figure 202 
as passing to the eyeball? 9. From a section drawn on the black- 
board after Figure 222, point out the three coats of the eye. 10. 
What is the function of each coat? n. Of what part of Figure 222 
is Figure 224 an enlargement? 12. How does the pupil grow larger 
and smaller? 13. Why does it change in size? 14. Why cannot 
owls see well in daylight? 15. Where is the cornea? The lens? 
The iris? 
QUESTIONS CHAPTER LVI. HOW WE SEE 
In the last chapter we learned the parts of the eye and 
described where the cells sensitive to light waves are situ- 
ated. ' In this chapter we shall learn how we see clearly; 
that is, how the rays of light are made to fall upon the 
cells of the retina in the right way. 
The Refraction of Light. Rays of light tend to travel 
in a straight line. But when, after passing through air, 
they strike the surface of water or glass or the transparent 
parts of the eye, the rays are bent sud- 
denly out of their course. We say they 
are broken or refracted. This refraction 
can be illustrated by the following ex- 
periments : 
Experiments on Refraction, (i) Put 
a pencil in a tumbler of water and note that 
the pencil looks broken, as shown in Figure 
227. (2) Place a coin in a tin cup and have 
ready a quantity of clear water. Stand so 
that the eye is in the position shown in Fig- 
ure 228 and the coin is just out of view. 
Now pour water into the cup gently. Note 
that the coin gradually comes into view as the water level 
rises. Figure 229 gives the explanation of this. Rays of light 
between the bottom of the cup and the eye (£) are refracted 
Figure 227. — A 
pencil looks bent 
or broken when 
immersed in water. 
Figures 228 and 229. — An experiment in refraction. (See text.) 
at the surface of the water where water and air meet. There- 
fore the coin is in full view, although not in direct line, 
and seems to be raised above the bottom of the cup, as at B. 
(3) To show how a lens refracts the rays of light, hold a 
318 HOW WE SEE 
magnifying glass or a convex lens from a pair of spectacles, in 
the sun, using it as a burning glass. The rays of sunlight are 
refracted by the lens and turned together to a focus, or central 
point. 
How the Image Is Thrown upon the Retina. The rods 
and cones that catch up the rays of light are very small. 
In order to see sharply and clearly, a single rod or cone 
Figure 230. — The rays of light from a single point would be scattered 
over the retina if there were no cornea or lens. 
must receive the light from a single point of an object. 
To make it clear how an image is formed on the retina, we 
may begin with a simple thing, for instance a small spark 
the size of the period used in punctuation. The spark gives 
off rays of light in every direction, for it can be seen from 
all sides. But only those rays which pass through the pupil 
Figure 231. — The cornea and the lens focus rays of light. 
would reach the retina. Thus, of all the rays of light 
represented in Figure 230 which radiate from the spark, 
(S), only A, B, and C reach the retina. Now, if the light 
rays would enter the eye unobstructed, as represented in 320 
THE HUMAN BODY AND ITS ENEMIES 
Figure 230, the rays A, B, and C would strike the retina at 
a, b, and c. So with all other rays between them. There 
would be so many images that we should see the spark as 
a large, round spot. Of course, if the pupil were so small 
that only ray C could enter, there would be but one image, 
c; but this would not be bright and strong. It is, there- 
fore, desirable that all the rays that strike the eye in 
front of the pupil {A, B, and C) should fall on the point c, 
as in Figure 231. This is brought about by the convex 
surfaces of the cornea and the lens, which refract the rays 
and turn them together to a point or focus on the retina 
{(c, Fig. 231). Collecting the rays of light and bringing 
them to a focus is called focusing. 
So it is with all the many rays of light that pass out from 
every object. In Figure 232 the rays from the points, 
Figure 232.—'Every ray of light from any one point of an object is 
focused on the retina. This causes a clear image of the object to form on 
the rods and cones of the retina. Two points, A and B, are taken as 
examples. 
on the head of the arrow, are focused on point a of the 
retina; those from point B, on the feather of the arrow, are 
focused at b on the retina. Each part of the arrow is thus 
clearly cut on the retina. The images of objects are thrown 
on the retina inverted. In order, then, that the image of 
the object may be clear, the cornea, the lens, and the entire 
eyeball must be of the right shape. Such is the case in 
the normal eye. 
Observation Work. Look out of the window into the dis- 
tance. Now hold up your hand in front of your face and con- HOW WE SEE 
tinue looking into the distance between the fingers. The hand 
is not seen clearly; it is blurred. Again, hold your finger one 
foot from your face, between your eyes and the landscape. 
Look at your finger. If you see the finger in clear outline, the 
objects of the landscape are blurred. This is due to the action 
of muscles changing the shape of the lens, as will be noted 
below. 
Accommodation. As shown in the experiment just 
made, there must be something in the eye which must be 
set for seeing far or near. That something is the lens, 
which accommodates the eye for far or near sight. For 
seeing near objects, the lens must bulge out in front; that 
is, it must be more convex. It is made so by muscular 
Figure 233. — Diagram to show how the lens is changed for far or near 
vision. (Compare with Fig. 222.) 
effort. Figure 233, which is part of Figure 222 enlarged, 
shows that the lens is attached by a ligament (Lig) to a pro- 
cess called a ciliary process in the wall of the eyeball. The 
ligament is a complete circle of ciliary processes. Muscles 
called ciliary muscles, are so attached that when they con- 
tract, the ciliary processes are pulled toward the lens and the 
ligament holding the lens slackens. The result is that the 
lens, being elastic, assumes a more convex form (B, Fig. 
233). The lens is not stretched and flattened by muscular 
effort, as is sometimes thought, but is made to bulge or 
thicken. When the ciliary muscles relax, the ligament of 
the lens resumes its pull and the lens again takes on the  THE HUMAN BODY AND ITS ENEMIES 
322 
flatter shape for seeing at a distance. It is important to 
note that it requires muscular effort for seeing close by, 
as for example in reading and sewing. Study carefully 
A and B, Figure 233. 
Experiment. To feel that muscular effort is needed for 
near vision, look into the distance. The lenses of your eye 
are now accommodated for far vision. The ciliary muscles are 
at rest. Now bring the finger up rather closely before the 
eyes and remove the attention from the distance to the finger, 
noting carefully the feeling in the eyeball as the accommoda- 
tion to near vision is being made. 
The Normal Eye. In a normal eye the eyeball is of 
the right shape; the iris properly regulates the amount 
of light that enters the eye; all the parts through 
which light has to pass are transparent (name them); 
the lens and cornea have a smooth, regular surface, 
without irregularities; the lens is elastic, responding readily 
to the effect of the ciliary muscles, or springing back into the 
resting position; and the ciliary muscles act perfectly in 
accommodation for far and near vision. 
The Defective Eye. Common imperfections in vision 
are due to defects in regard to one or more of the points 
just enumerated. The image must come to a focus ex- 
actly on the retina (Fig. 232), or the image will not be 
distinct. 
In near-sightedness the image comes to a focus before 
reaching the retina (Fig. 234), and the same rods and cones 
Figures 234 and 235. — In short-sightedness the eyeball is too long. This 
may be corrected by glasses with concave lenses. 
receive rays of light from different parts of the object, 
thus confusing the image and making it dim and blurred. HOW WE SEE 
323 
Such an eye would be helped by spectacles with concave 
lenses, for such lenses would spread the rays of light 
and prevent their coming to a focus too soon (Fig. 235). 
Near-sightedness is usually due to the fact that the eye is 
too deep; that is, the distance from cornea to retina is too 
great (Fig. 234). 
Far-sightedness is due to the opposite cause from that of 
near-sightedness; the eye is too short from cornea to 
Figures 236 and 237. — In far-sightedness the eyeball is too short. This 
defect is corrected by wearing glasses with convex lenses. 
retina (Fig. 236). In such an eye the image reaches the 
retina before the rays of light have been brought to a focus. 
A person suffering with far-sightedness should wear glasses 
with convex lenses, for these bring the rays of light together 
and help the lens of the eye to focus the rays on the retina 
(Fig. 237). Many headaches are due to imperfect eyesight 
that might easily be corrected with glasses or spectacles.1 
Astigmatism is a defect of the cornea or the lens, in 
which either or both have irregularities or uneven places in 
their curved surfaces. This is a common cause of imper- 
fect vision with children, and should receive prompt atten- 
tion. A pupil poor in reading, but good in other studies, 
probably has something wrong with the eyes. 
SUMMARY 
Rays of light tend to travel in a straight line. When they 
pass from the air into a denser medium, as water or the cornea 
or the lens of the eye, the rays are broken or refracted. In 
1 Most old persons are far-sighted. The tissues of the lens become 
hardened and cannot be accommodated for near vision. This is the 
reason why most old persons can use one another’s glasses. 324 
THE HUMAN BODY AND ITS ENEMIES 
the normal eye all rays of light are thus made to fall upon the 
right places on the retina, so that we see clearly and sharply. 
For far and for near vision a different focus is required. 
This change of focus is brought about by a change in the con- 
vexity of the lens. When the ciliary muscles contract, they 
bring the ciliary processes nearer the lens, thus allowing the 
elastic lens to bulge out. When the muscles relax, the lens is 
brought back to the flatter shape. We can rest the eye from 
continued close work by occasionally looking off into the dis- 
tance. Short-sightedness, far-sightedness, and astigmatism are 
common defects in vision, due mainly to the imperfection of 
the focusing apparatus of the eye. They may be corrected by 
wearing the glasses with the right kind of lenses. 
QUESTIONS 
i. Why can we not see all the rays of light coming from a given 
point? 2. What is meant by refraction? 3. Describe two experi- 
ments to illustrate refraction. 4. How is the lens held in place? 
5. Describe focusing. 6. Why do rays of light have to be focused 
on the retina? 7. How are they focused? 8. How is the eye 
accommodated for seeing near objects? 9. Draw Figure 222 on the 
board and explain the use of all the parts shown. 10. How can 
you prove that it requires muscular effort to accommodate the eye 
for seeing a near object? n. How can you rest your eyes at inter- 
vals when engaged in close work? 12. Mention the common defects 
of the eye. 13. Describe the near-sighted eye. The far-sighted 
eye. 14. Why do people usually become far-sighted with age? 
15. What is astigmatism? 16. What can we do for these common 
optical defects? CHAPTER LVII. HYGIENE OF THE EYES 
A study of the anatomy of the eye and the pysiology 
of its parts enables us to study intelligently its hygiene. 
Rest. Since the ciliary muscles contract to accommodate 
the lens for near work, such as reading or sewing, it is 
necessary that they be rested from time to time. This is, 
of course, easy to do by simply looking into the distance. 
This relaxes the muscles and has the same effect on them as 
relaxation has on the muscles of the arms and legs. 
Rest is necessary for the optic nerve as well as for the 
muscle of the eye. Overworking the nerve of sight not 
only affects this nerve, but often causes inflammation of 
the eyes, which can best be cured by rest. 
The Size of Type. The size of type used in printing 
the matter you read is an important consideration. If 
the type is too small, the strain on the eyes is very great. 
It does not pay to buy a cheap book wifh poor type. The 
size of the letters in the Primer and First Reader used 
in your school is probably the best size for a beginner. 
This book is printed in clear type of the right size for 
most people. 
Direction of the Light. The best rule to follow is to 
have the light pass over the left shoulder on to the printed 
page. The light should never come from the front. In a 
school room, the front windows, if there are any thus 
wrongly placed, should be darkened. The main light 
should come from the left. The windows should be placed 
high, even touching the ceiling, for it is the light from above 
falling on the desks which is best in the school room. 
When reading by artificial light, do not allow the light 
to shine directly into the eyes. It is well to shade the 
light or to place a shade over the eyes to protect them. 
Intensity of Light. For reading or other close work 
the light should be neither dim nor very bright. If too 
dim, the pupil of the eye becomes so large as to cause the 
letters of the printed page to be less clear and distinct. It 
is a great mistake to read at dusk without artificial light. 
325 326 
THE HUMAN BODY AND ITS ENEMIES 
If window shades are needed to keep out the direct 
rays of the sun, they should be of the adjustable kind, so 
as to allow some light to enter from the top if possible. 
Window shades that pull up from the bottom are often 
more advantageous than those that pull down from the 
top. Shades pulled down on a sunny day should be raised 
on a cloudy day. 
Steady Light. A flickering light, such as that of a 
candle, or a simple gas jet without a mantle, is hard on the 
eyes. Reading on trains should also be avoided. It is 
also a mistake to read while lying in bed. 
Eye Strain. The eyes are strained in various ways 
even when not worked excessively. The strain is usually 
due to defects in particular parts of the eye or eyes. In 
the far-sighted eye, the ciliary muscles are under the 
greatest possible strain when close work is attempted. 
Astigmatism is a source of much worry and causes 
great strain. Sometimes the muscles that move the 
eyeball do not move in orderly fashion, so that focusing 
both eyes on a given object becomes difficult. All these 
defects cause eye strain, which usually becomes more 
and more serious the longer the eyes are neglected. 
Such strain not only affects the eyes, but in time causes 
sick headaches, nervousness, and even indigestion. Many 
children, otherwise bright and capable, are backward in 
school for no other reason than that their eyesight is 
defective. 
Spectacles. All these defects in vision may be greatly 
relieved, and often permanently cured, by the fitting and 
wearing of proper glasses or spectacles. One should, of 
course, be careful to have the eyes fitted by a trained 
oculist, as wrong glasses do more harm than good. Teachers 
should be on the lookout for cases of defective eyesight, and 
parents should consult a competent oculist concerning the 
child’s eyes when there is the slightest suspicion of anything 
wrong with them. HYGIENE OF THE EYES 
327 
Cinders in the Eye. The eyeball is covered, and the 
eyelids are lined, with a very delicate membrane. The 
presence of hard, sharp particles, such as cinders or sand 
grains, irritates this membrane and causes inflammation 
of the eyeball and of the lid. The foreign particles should 
be removed with the corner of a clean pocket handkerchief. 
Disease germs are also likely to enter the eye and cause 
inflammation. The eye should not be rubbed with the 
fingers, as by this means germs are often transferred to 
the eyes. 
Trachoma. The disease called granulated lids (properly 
called trachoma) is the worst communicable disease that 
affects the eyes. It is not very common in this state, and 
yet it is fairly well distributed over the different counties. 
It causes sore eyes, and later scarring under the lids, so 
that they pucker up and do not fit the eyeball. The cause 
of trachoma is not known, but we do know positively that 
it is contagious. It is communicated by the matter or 
secretion from the eyes of persons suffering with the disease. 
The secretion in some way or other gets into the eyes 
of the new victim. The disease may be spread by pub- 
lic towels or by pencils borrowed from children who 
have sore eyes. Gnats and flies are also responsible for 
the spread of the disease. These insects light on the eyes 
of one person, pick up a drop of the infected fluid, and 
carry it to the eyes of another. For this reason, as well as 
for many others, our houses should be screened to keep 
out insects. 
Sore Eyes. The ordinary sore eyes is another con- 
tagious disease which is called pink eye. This is carried 
from one child to another in the same way as trachoma. 
In 1902 there occurred in Texas an epidemic of this disease, 
due to the gnats and flies. We do not often have so many 
insects as we had in 1902, but we /have the public towel 
with us at all times, and we should be on our guard against 
that. A good substitute for it is the sanitary paper towel, 328 
THE HUMAN BODY AND ITS ENEMIES 
which can be bought at about a quarter of a cent apiece 
(Fig. 29). 
A very dangerous eye disease sometimes affects new-born 
infants. If not treated at once, the child will become 
quickly and permanently blind. 
Sore eyes are also caused by eye strain, by smoking, 
and by other causes easily avoided. 
SUMMARY 
On account of the great usefulness of the eyes and their 
delicacy, we should take the utmost care of them. 
The eyes may be spared in many ways. They should not 
be overworked. Both the ciliary muscles of the eye and the 
optic nerve should be given sufficient rest. We should always be 
careful about the size of type of the books and papers that we 
read and of the character and direction of the light. 
The light should be steady and of the right strength. We 
should avoid reading in dim light and, by using the right kind 
of shades, should keep out strong light. Light should never 
come from the front, nor should it shine directly into the eyes. 
The membrane covering the eye is easily injured by foreign 
particles. These should be removed with great care. The 
eyes should never be rubbed. Disease germs often attack the 
eyes. Among the common contagious diseases of the eye are 
trachoma, sore eyes of infants, and pink eye. These diseases 
may be spread by towels, gnats, and in other ways and may be 
avoided by appropriate means. Sore eyes of any kind should 
receive prompt treatment. 
QUESTIONS 
i. Why is the care of the eyes important? 2. How may you rest 
the ciliary muscles during reading? 3. Discuss the size of type 
for reading. 4. What is the best and what the worst direction for 
the light to come into a school room? 5. How can we regulate the 
intensity of light? 6. Make five suggestions for the hygiene of the 
eyes at home. 7. Tell why you think that the wearing of glasses is 
not a mere fad. 8. How should a cinder be removed from the eye? 
9. Name several germ diseases of the eye. 10. How are these 
diseases scattered and how may they be avoided? n. Find out 
what the state law requires as to the lighting of school houses. CHAPTER LVm. ACCIDENTS AND EMERGENCIES 
When persons are accidentally injured, a physician 
should be called immediately. The following paragraphs 
are to teach what should be done while the physician is 
on the way. 
Examination of the Injured Person. The first thing 
to do when any one is injured is to look him over and 
see whether he is losing blood and whether he is getting 
his breath. If he is not bleeding very much, and is 
breathing, there is little that can be done until a physician 
arrives. 
• Severe Hemorrhage or Bleeding. If, however, the in- 
jured person is bleeding profusely, something must be done 
at once. In case of a severe hemorrhage, that is, if the 
patient is bleeding as much as a teacupful every minute 
or two, it is absolutely necessary to stop the hemor- 
rhage at once. There is no time to hunt up medicines or 
clean bandages. In these circumstances the cleanest cloth 
that can be found must be pressed into and around the 
wound. If it is pressed tightly, with all one’s strength, it 
will stanch almost any hemorrhage. 
After the bleeding is hurriedly stopped, or at least 
diminished in this way, it is time to look around for some 
more satisfactory method of preventing bleeding till 
assistance can arrive. Sometimes it is necessary to hold 
the fingers pressed into a wound for an hour till the surgeon 
can reach the patient. If the hemorrhage is from an 
extremity, — that is, from an arm or leg, — a tight band- 
age, which can be made with a handkerchief, wrapped 
around the limb between the wound and the heart, will stop 
the bleeding. A tight bandage should not be left on a limb 
for more than half an hour or it may cause gangrene, which 
will result in death and putrefaction of the limb. 
A slight hemorrhage should be stopped by placing a 
clean white cloth over the wound and making gentle 
pressure. Usually, binding the cloth on to the wound 
will prevent a return of the hemorrhage. 
329 330 
THE HUMAN BODY AND ITS ENEMIES 
Cuts and Other Open Wounds. These should not be 
washed with water unless the water is pure. Boiled water 
is always free from germs, A reliable antiseptic or disin. 
fectant should be applied to wounds of this character, and 
they should be covered with clean white cloths, preferably 
cloths that have been boiled and dried without being 
handled. Disinfectants have been described in Chapter 
XIX. It is never wise to employ a solution of carbolic 
acid as a permanent dressing. Gangrene has been pro- 
duced in numerous instances by dressing wounds in moist 
carbolic bandages. 
Fracture of Bones. Broken bones may in certain cases 
be dangerous. The worst thing that can happen after a 
Figure 238. — A pillow and two boards make a good temporary brace 
or splint for a broken limb. The pillow is made into a trough, the limb is 
placed in this trough, and the boards are adjusted and held in place by 
several bandages. 
fracture has occurred is for the bones to protrude or stick 
out through the skin. When they do so, they are likely 
to become infected by germs, especially the tetanus or 
lockjaw germ. The bones should therefore be handled 
carefully to avoid pushing them through the skin. The 
picture shows a pillow-splint that can be applied when no 
surgeon is at hand. This splint is suitable for fracture of 
arm or leg. 
Tetanus or Lockjaw. The tetanus, or lockjaw, germ is 
one of the worst germ enemies we have. This germ more 
frequently lives outside the body than inside. It is not 
like the typhoid germ, which multiplies only in the human 
body. The tetanus germ lives in the ground, especially ACCIDENTS AND EMERGENCIES 
331 
around gardens and horse lots. It practically never harms 
the human body except when introduced through an open 
wound. So far as we know, swallowing the tetanus germ 
never hurts any one. The tetanus germ cannot live in the 
air; it has to he shut off from the air. Supposing that a 
wound has been made by a rusty nail, after the skin swells 
a little and closes the hole made by the nail, the germ is 
down under the skin and is shut off from the air. You 
have noticed that healing of the skin often occurs, even 
though there are germs and pus deep down under it. 
Tetanus is Almost Incurable. After this disease once 
develops, the doctors have great difficulty in healing or 
curing it. Lockjaw causes terrible spasms all over the 
body. The locked jaws are the least part of the disease. 
If we are to save one's life after he has thrust a nail into his 
foot, we must act before the disease develops. 
Usually tetanus develops about a week or ten days 
after the wound is received. The proper treatment is 
to open up the wound and let the air get down into 
the depths of it. This is shown in Figures 239-241. If 
there is any doubt about the air getting into the deepest 
Figures 239-241. — A lockjaw wound: Figure 239, a nail thrust; Figure 
240, the lockjaw germs are shut off from the air when the skin over the 
wound heals. The only safe thing to do is to open the abscess and let in 
the air (Fig. 241). 
part of the wound, tetanus antitoxin should be given. 
If these precautions are neglected, and if tetanus once 
appears, all the powers on earth cannot with any certainty 
prevent death. Over three fourths of all cases of tetanus 
die. The antitoxin is good for prevention, but cannot be 
relied upon to cure after the disease once develops. 332 
THE HUMAN BODY AND ITS ENEMIES 
Narrow and Deep Wounds. All narrow, deep wounds 
are especially dangerous, because the skin closes up and 
shuts out the air, making it possible for the tetanus bac- 
terium to live. The burns made by powder from little toy 
pistols and from firecrackers are deep wounds, and often 
cause lockjaw. These wounds should be carefully treated 
at once, or it will be too late. Splinters also make narrow, 
deep wounds and are likely to cause lockjaw. 
Snake-bites. The number of deaths occurring in Texas 
from snake-bites is very small. In case one is bitten by 
a snake, unless he knows that the bite was inflicted by a 
harmless variety, it is well to proceed as follows: If the 
wound is on a leg or an arm, as is likely, quickly wind a 
bandage that can be twisted tight around the limb between 
the wound and the heart. A handkerchief serves well for 
a bandage; out in the woods, twigs of some tough plant 
will do. After bandaging, to prevent the blood from 
carrying the poison toward the heart, take a knife and 
sterilize the blade of it by heating it in the flame of a match. 
Then make an incision over the wound made by the fangs of 
the snake, cutting two cross marks each a quarter of an inch 
deep. If available, crystals of permanganate of potash may 
be rubbed on the open cut. Squeeze out as much blood as 
possible up to the amount of a wineglassful, but no more. 
You can always tell whether your treatment is effective 
or not, for if ineffective the patient will become weak and 
pale in less than half an hour. Mere fainting, which lasts 
only a few minutes, is not to be mistaken for this. A 
teaspoonful of spirits of camphor in half a teacupful of 
water may be given to prevent fainting. The tight bandage 
need not be kept on longer than thirty minutes in case 
no symptoms of weakness arise; but if they do, and the 
bandage is kept on longer, it should be removed for one 
minute every twenty minutes. 
A word of caution is here needed about the use of alcohol. 
Whisky should not be used in case of snake-bite. The ACCIDENTS AND EMERGENCIES 
333 
medicine to take along for snake-bites, when on hunting 
and camping trips, is potassium permanganate. A strong 
solution of this in water is to be poured into the crossed 
incision described above. 
There are only a few poisonous snakes in Texas. The 
worst and most common are: the rattlesnake, which is 
familiar to most people the world over; the copperhead, 
which is a dull-mottled snake, with a blunt tail, and is 
found in dry upland fields; and the cotton-mouth moccasin, 
which has a blunt tail, is white under the chin, and lives in 
streams and ponds. The prairie runner or “coachwhip,” 
the chicken snake, and the garter snake are harmless. 
Fainting. There are few accidents that excite the by- 
stander more than fainting. When the fainting person 
falls, let him he, but see to it that he has plenty of fresh 
air. Fanning the person is helpful, as is also the inhala- 
tion of a little ammonia. A dash of cold water in the face 
is also good. Recovery from a fainting spell usually takes 
place in a few minutes. 
Burns. Women and girls are especially in danger of 
getting burned because of their loose clothing, and also 
because of their duties in the house and around the fire. 
In 1911 there were thirty-nine women accidentally burned 
to death in Texas. 
Burning is a form of accident for which very little can 
be done before the physician arrives. Clean cloths greased 
with olive oil, linseed oil, or petroleum jelly may be laid 
over the burned surface. It is well to keep unclean articles 
from touching the raw surfaces of the burn. It is not well 
to put water on large burns. The dead skin should be 
left in place until the doctor comes. 
Common Causes of Burns. Bums are usually, though 
not always, the result of carelessness or ignorance with 
regard to the nature of coal-oil or kerosene. Never start 
a fire with kerosene oil. The oil so easily bursts into flame 
that the slightest spark is sufficient to cause it to do so. 334 
THE HUMAN BODY AND ITS ENEMIES 
Furthermore, when oil once starts to burn in an open place, 
it burns with such violence as to spatter burning particles 
all around. 
Smothering Flames. Every one knows that when 
flames are fanned they burn more strongly. Therefore, 
when a person has caught fire, he or she should be prevented 
from running wildly about. If there is not enough water 
at hand, the flames may be smothered by throwing the 
burning person to the ground and piling on him rugs, 
blankets, and similar articles that may be handy. 
Artificial Respiration. This means making a person 
breathe when for any cause his natural breathing move- 
ments have stopped, as for instance when one has been 
Figure 242. — Position in giving artificial respiration. 
shocked badly by electricity or has been almost drowned. 
The best method of causing artificial respiration may 
be used by one person alone, and is illustrated in 
Figure 242. The injured person is placed face down, 
with his head turned slightly to one side to keep the 
mouth out of the dirt. If possible, the head should be 
turned downhill. The person who gives this artificial 
respiration sits across the hips of the injured one, as shown 
in the picture, and places his hands on the other’s back and 
lower ribs. By alternately pressing and releasing pressure 
with the hands, fifteen times to the minute, air is first 
pressed out and then drawn into the lungs. This method ACCIDENTS AND EMERGENCIES 
335 
of artificial respiration is especially good for the reason that 
the patient is lying on his face and the tongue does not 
fall back and stop up the throat. In the older methods 
two persons were required, because the patient was on his 
back and his tongue had to be held forward by a second 
person. The movements in artificial respiration should 
never be forcible enough to injure the lungs, and as soon 
as the patient shows signs of gasping, an attempt should 
be made to cause exhalation when he is trying to exhale. 
It would, of course, be unwise to exert pressure on his chest 
if he were trying to inhale. 
IMPORTANT POINTS 
If the injured one is breathing, and if he is not bleeding; 
there will not be any need for very special haste. 
If he is bleeding very rapidly, anything clean pressed into 
and around the wound will stop the bleeding till you can dp 
something further. 
Do not wash cuts with water unless the water has been 
boiled, and do not touch the cut with anything except a clean 
cloth. 
Nail thrusts are dangerous and should be opened up thor- 
oughly to let in air and prevent the growth of the tetanus or 
lockjaw germ. 
To avoid burns, do not take kerosene, gasoline, naphtha, or 
alcohol near a stove; do not pour oil into a warm stove; and do 
not try to fill a lamp or oil stove while it is lighted. 
To put out clothing that has caught fire, throw the burning 
person to the ground and smother the flames with a wet or dry 
blanket, rug, carpet, or other cloth. 
QUESTIONS 
i. When is bleeding dangerous? 2. What is one sure way to 
stop bleeding? 3. Why is it unwise to wash a fresh cut? 4. Give 
two common causes of burns. 5. What accidents are likely to pro- 
duce lockjaw? 6. Out on a ranch, what would you do if a friend 
were bitten by a large rattlesnake? 7. Would you prop up a per- 
son who has fainted, or let him lie horizontally? 8. How do you give 
artificial respiration? APPENDIX A. POISONING 
When a person has taken poison, there are certain general rules 
to follow, whether the nature of the poison be known or not. These 
general rules are given below, together with special reference to the 
commoner poisons. 
To Produce Vomiting. A tablespoonful of mustard in a pint of 
warm water is immediately effective. Warm, salt water in large 
quantities is also good. The stomach tube is good in the hands of 
a physician or nurse. 
To Counteract Acids. If an acid has been swallowed (carbolic 
acid is not here included), alkaline substances should be given, such 
as cooking soda, prepared chalk, whiting, magnesia, and limewater. 
Follow with raw eggs or olive oil. 
To Counteract Alkalies. If a strong alkali has been taken, such 
as concentrated lye, acids such as vinegar or lemon juice should be 
given. Follow with raw eggs or olive oil. 
Carbolic Acid Poisoning. This must be treated within twenty 
minutes or death may result. The treatment is undiluted whisky, 
or pure grain alcohol diluted half and half with water. If this is 
not at hand, Epsom salts in the usual doses is almost as good. If 
the alcohol is used, Epsom salts should be used a little later. 
For Arsenic Poisoning. Poisoning from “ Rough on Rats” or 
other forms of arsenic should be treated by remedies to cause vom- 
iting as described above. These should be followed or accompanied 
by raw eggs or cooked starch paste. The druggists prepare a regular 
antidote to arsenic, which should be given as soon as it can be 
obtained. 
For Phosphorus Poisoning. Phosphorus poisoning should be 
treated by remedies to cause vomiting, and by stimulants and raw 
eggs. No oil should be given under any circumstances. 
For Opium Poisoning. Morphin, paregoric, laudanum, and other 
forms of opium all act alike, and should be treated by remedies which 
cause vomiting, by tannic acid, one teaspoonful, or by potassium 
permanganate, five grains repeated in ten minutes. In addition, 
the patient should be kept awake by strong coffee, cold water, and 
attempts at rousing. 
For Faintness. If the patient seems faint, let him lie down; 
then give him stimulants, such as a cup or two of strong coffee, a 
teaspoonful of aromatic spirits of ammonia, or a teaspoonful of 
Hoffman’s anodyne. 
For Sleepiness. If a patient seems sleepy, keep him awake by 
bathing his face with cold water and fanning him, but do not wear 
him out by walking him around. 
For Coldness of Hands and Feet. If the extremities are cold, 
warm them with hot-water bottles, warm bricks, or warm flatirons. 338 
THE HUMAN BODY AND ITS ENEMIES 
To Avoid Poisoning. Medicines and poisons should be kept 
out of the reach of children and medicine should never be given in 
the dark. When concentrated lye is used in scrubbing the floor, 
the open can should never be left on the floor or in reach of 
children. 
Figure 243. — Medicines 
and poisons should be 
locked up out of reach 
of children. APPENDIX B. ABSTRACT OF THE SANITARY 
CODE FOR TEXAS 
Note. — The Sanitary Code for Texas is important; it not only has a 
bearing on the everyday life of each citizen, in that it must be obeyed, but 
it also has great educational value, for it expresses the judgment of Texas 
sanitarians and legislators as to the wisest method of combating prevent- 
able disease. There are many valuable rules in the Sanitary Code which 
are not familiar to the citizens; some of these rules need to be invoked 
in time of epidemic, but others should be enforced every day to protect 
the public against such common dangers as tuberculosis and typhoid fever, 
which in Texas, as elsewhere, are prevalent at all times. Again, some of 
the rules of the Code relate to schools. These have been printed in black- 
faced type, and will be of service to teachers and trustees. 
Rule i. Any physician in Texas who is called in to treat a person 
sick with any contagious disease is required to notify immediately 
the local health authority. 
Rule 2. By “local health authority” is meant the city or county 
health officer or the local board of health. 
Rule 3. The following are considered as contagious diseases: 
Asiatic cholera, bubonic plague, typhus fever, yellow fever, leprosy, 
smallpox, scarlet fever (scarlatina), diphtheria (membranous croup), 
epidemic cerebrospinal meningitis, dengue, typhoid fever, epidemic 
dysentery, trachoma, tuberculosis, and anthrax. 
Rule 4. The local health officer is required to keep a record of all 
contagious diseases reported to him, and to make a monthly report 
of these cases to the State Board of Health. The records of tubercu- 
losis are to be kept private. 
Rule 5. School trustees and health authorities are required to 
regulate their quarantine in a certain way, as follows: 
a. Absolute quarantine contemplates that no persons shall enter 
or leave the premises, guards being used to enforce this rule if neces- 
sary; the premises shall be placarded; no articles shall be allowed 
to pass out of the premises; food shall be furnished by the proper 
authorities under restrictions. 
b. Modified quarantine contemplates that the same restrictions 
shall apply as in absolute quarantine, except that certain members 
of the family can enter and leave the premises if they take precau- 
tions, while the sick person is required to be isolated in a certain 
part of the premises. 
c. Absolute isolation includes certain special measures of techni- 
cal interest. 
d. Modified isolation includes confinement of the patient and 
attendant in certain rooms, while the other members of the house- 
hold are allowed to enter and leave as they please. 
339 340 
THE HUMAN BODY AND ITS ENEMIES 
e. Special isolation includes prohibiting the patient from attend- 
ing any public assemblage, providing separate sleeping apartments, 
eating utensils, towels, and napkins for the patient. 
/. Complete disinfection includes the disinfection during illness, 
under the physician, of patient’s body, of all excretions or discharges, 
of all clothing and utensils used by patient; after illness is over, the 
disinfection of walls, woodwork, furniture, bedding, etc. 
g. Partial disinfection includes disinfection of discharges or ex- 
cretions of patient, the clothing, and the room occupied by patient 
during illness. 
Rule 6. All disinfection required by these rules shall be done 
according to the method recommended by the Texas State Board of 
Health. 
Rule 7.. When he receives information to the effect that a con- 
tagious disease exists in his territory, the local health officer is 
required to placard the house with a flag or a card of a certain size 
and bearing the inscription “ Contagious Disease.” 
Rule 8. After a house is placarded, and placed under quaran- 
tine, no person except those authorized to do so by the local health 
authority is allowed to enter or leave the premises or carry away 
from the premises any article by which the disease might be spread. 
This rule holds until the premises have been disinfected and released 
from quarantine. 
Rule 9. When any person is exposed to a contagious disease, 
it is his duty to follow the instructions of the health officer, in order 
to avoid the spread of the disease. 
Rule 10. No person affected with any contagious or quaran- 
tinable disease shall be allowed to ride in any public conveyance, 
or to be present in any public assemblage, or to travel any public 
thoroughfare. 
Rule ii. It is unlawful for any person to remove or destroy the 
quarantine placard, and if it is removed, the owner of the premises 
shall report this fact to the local health authority within twenty- 
four hours. 
Rule 12. The following diseases are not only quarantinable, 
but are pestilential, and persons suffering from any of them are to 
be kept in absolute isolation, and the premises are to be absolutely 
quarantined as described in Rule 5, and complete disinfection must 
be performed after the termination of the illness: Asiatic cholera, 
plague, typhus fever, yellow fever. 
Rule 13. The following diseases are dangerous contagious 
diseases, and persons suffering from any of them are to be placed in 
modified isolation, under modified quarantine, and complete dis- 
infection must be performed after the termination of the illness: SANITARY CODE FOR TEXAS 
341 
leprosy, smallpox, scarlet fever (scarlatina), diphtheria (membra- 
nous croup), and dengue. 
Rule 14. The following diseases are to be treated by special 
isolation and partial disinfection: typhoid fever, cerebrospinal men- 
ingitis, epidemic dysentery, trachoma, tuberculosis, and anthrax. 
Rule 15. The following diseases are quarantinable for school 
purposes, and persons suffering from these diseases are barred from 
school for twenty-one days: Persons suffering from measles, whoop- 
ing cough, German measles (roetheln), and chicken-pox shall be 
required to be barred from school for twenty-one days (at the dis- 
cretion of the local health officer) from date of onset of the disease, 
with such additional time as may be deemed necessary, and may 
be readmitted on a certificate by him attesting to their recovery and 
non-inf ectiousness. 
Rule 16. Minor diseases are to be excluded during illness. 
Those actually suffering from tonsillitis, itch (scabies), impetigo 
contagiosa, and favus shall be excluded from school during such 
illness and be readmitted on the certificate of the attending physician 
attesting to their recovery and non-infectiousness. 
Rule 17. Additional precautionary measures may be instituted 
at the discretion of the local health authority. 
Rule 18. When the local health officer hears of the existence 
of any contagious disease within the territory over which he has 
jurisdiction, it is his duty to investigate and if necessary declare a 
quarantine. 
Rule 19. The local health officer is required to see that all quar- 
antine in his territory is properly enforced, and that disinfection, 
when required by law, is properly done. Persons exposed to small- 
pox, if unvaccinated, are required to be held for eighteen days from 
date of last exposure. 
Rule 20. No person shall offer for rent any building in which a 
case of any quarantinable disease has occurred, without previously 
having the building disinfected. This refers especially to houses 
which have been occupied by consumptives. 
Rule 21. If disinfection is not performed as required, the house 
in which the contagious disease has occurred shall be placarded by 
the local health officer. 
Rule 22. Nurses and midwives are required to report within 
twelve hours the presence of so-e eyes or inflamed lids in the newly 
born; this report is made to the local health officer or to any reputable 
physician. 
Rule 23. When any quarantinable disease occurs, it shall be 
the duty of the householder in charge of the premises to report the 
presence of the disease to the local health officer. In the presence 342 
THE HUMAN BODY AND ITS ENEMIES 
of a quarantinable disease, before quarantine is established, it is 
unlawful for any person to move out of the infected house or to 
remove any articles from the house. 
Rule 24. No person suffering with any reportable disease, or 
who resides in a house in which there exists a case of smallpox, scarlet 
fever, diphtheria, or typhoid fever, shall work or be permitted in or 
about any dairy or any establishment for the manufacture of food 
products, until the local health authority has given such a person a 
written certificate to the effect that no danger to the public will 
result from his or her employment or presence in such establishment. 
Rule 25. When he is notified of the presence of smallpox or 
other quarantinable disease, the local health officer shall send im- 
mediately to the physician, or with his approval, to the patient, 
printed matter published by the State Board of Health relating to 
such cases. 
Rule 26. Persons suffering from trachoma (granulated lids, 
contagious catarrhal conjunctivitis) are to be excluded from the 
schools unless they are under the strict supervision of a physician and 
hold a certificate to the effect that active inflammation has subsided; 
and this certificate must also be signed by the local health officer. 
Rule 27. When any person suffering from smallpox, scarlet 
fever, or diphtheria is found to have been in a school room, the 
school must be closed until the building has been properly disinfected 
under the supervision of the local health officer. 
Rule 28. In the event that the disease causing the closing of the 
school shall have been smallpox, the school must remain closed for 
eighteen days, unless the trustees require the vaccination of all un- 
vaccinated pupils and teachers. In the latter case, the school may 
be reopened at once after disinfection. 
Rule 29. The local health authority shall notify the superin- 
tendent or principal of any school of the locations of quarantinable 
diseases, and if the superintendent or principal finds any attendants 
in such schools who live in said houses, he shall deny them admission 
to the said schools, only admitting them again upon the presenta- 
tion of a certificate from the attending physician, countersigned by 
the local health authority, attesting that there is no danger from 
contagion. 
Rule 30. No superintendent, principal, or teacher of any school, 
and no parent, master, or guardian of any child or minor, having the 
authority and power to prevent, shall permit any such child or minor, 
having any quarantinable disease, or any child residing in any house 
in which any such disease exists or has recently existed, to attend 
any public, private, parochial, church, or Sunday school until the 
requirements of these rules have been complied with. SANITARY CODE FOR TEXAS 
Rule 31. In cities and incorporated towns, the city health* 
authorities shall assume control of quarantine, isolation, and dis- 
infection; in districts outside of cities and towns, the county health 
officer shall assume control. 
Rule 32. Cities, counties, and towns have the privilege of de- 
claring quarantines independently of the State Health Authorities, 
so long as the additional quarantine is consistent with and subordi- 
nate to the quarantines established by the Governor and State Board 
of Health. In case any local health authorities declare a quarantine, 
they are required to notify the State Board of Health. 
Rule 33. All health authorities have the privilege of passing 
through quarantine lines, provided they announce that they are 
acquainted with the disease they are visiting and will take pre- 
cautions to prevent its spread. 
343 
Vital Statistics 
Rule 34. Each birth occurring in Texas shall be reported by the 
physician, surgeon, or midwife, or in the absence of these, by the 
parent, to the city or county registrar. 
Rule 35. Undertakers shall report each death to the local regis- 
trar, and the individual or firm selling the coffin is considered the 
undertaker. 
Rule 36. All births and deaths, except those occurring in a city 
or incorporated town, shall be reported to the clerk of the county 
court; in cities and incorporated towns, births and deaths are re- 
ported to the city registrar. 
Rule 37. Each city or incorporated town is a primary registra- 
tion district. The city health officer shall be the local registrar. 
Each local registrar shall appoint a deputy to serve during his absence 
or disability, and both registrar and deputy are subject to the rules 
of this Code; provided, that in cities or towns where the secretary 
or other official is serving as local registrar, and where a burial or 
removal certificate is required before allowing any dead body to be 
buried within or removed from the city limits, such city secretary 
shall continue as the local registrar, but shall be subject to the regu- 
lations of this Code. No body must be removed from or interred 
in any local registration district until the local registrar has issued a 
burial or removal certificate, and such certificate shall not be issued 
by the local registrar until he has received and filed the death cer- 
tificate as described later; but a death or removal certificate issued in 
accordance with the law of the place the death occurred, whether in 
Texas or not, shall be sufficient authority for the local registrar to 
grant a burial permit; in this case, the local registrar shall write 344 
THE HUMAN BODY AND ITS ENEMIES 
plainly across the face of the copy of the record which he sends in to 
the State Registrar the fact that the body was shipped in for burial. 
The city registrar is required to record in a permanently bound book 
all births and deaths, with the statistical data required by law, and 
at the end of each month the city registrar shall forward to the 
State Registrar a copy of each birth or death certificate filed with him 
during the month. 
Rule 38. All certificates of births and deaths shall be made accord- 
ing to the form prescribed by the State Board of Health. 
Rule 39. For each dead body for which he provides a coffin, the 
undertaker shall fill out the death certificate, and shall turn the 
certificate over to the physician for the latter to give a signed state- 
ment as to the cause of death. The undertaker or physician shall 
then send the death certificate to the local registrar. 
Rule 40. It is the physician’s duty to be prompt in filling in the 
medical particulars of the death certificate. 
Rule 41. In rural districts, where no undertaker officiates, the 
last attending physician shall hand in the death report. 
Rule 42. Where a person dies without medical attendance, the 
coroner, if one is called in, shall file the death report; if no coroner 
is called in, the householder on whose premises the death occurred 
shall report the death to the local health officer; the latter shall issue 
the death certificate, after holding an autopsy if necessary. 
Rule 43. If a death occurs in a hospital, certain statistical facts 
are required to be given by the superintendent of the hospital before 
the undertaker sends in the report. 
Rule 44. If any physician, coroner, or superintendent of any 
hospital refuses to fill in the medical particulars on the death report, 
the undertaker shall report such person to the State Registrar for 
prosecution. 
Rule 45. This relates to stillbirths, which shall be reported as 
both deaths and births. 
Rule 46. The county clerk in each county shall preserve a bound 
record of all data contained in death and birth reports, and shall 
report monthly to the State Registrar of Vital Statistics. 
Rule 47. Each sexton of a cemetery is required to file all burial 
permits received, and to send in a monthly report of all bodies in- 
terred to the State Registrar of Vital Statistics. 
Rule 48. The State Registrar is required to have printed all 
death and birth certificates, while the city and county governments 
are required to have printed the permanently bound book for pre- 
serving birth and death records. The State Registrar has authority 
to require additional information about any birth or death from any 
person in possession of the facts. SANITARY CODE FOR TEXAS 
345 
Rule 49. The city and county registrars are required to furnish 
the birth and death certificate blanks to all persons using or requiring 
them. 
Rule 50. The city or county registrar shall examine certificates 
of birth and death to see that they are complete. He shall number 
the births and deaths in separate series, commencing anew at the 
beginning of each year. 
Depots, Railway Coaches, and Sleeping Cars 
Rule 51. No person known to be suffering from smallpox, diph- 
theria, measles, scarlet fever, or whooping cough shall be allowed to 
enter or ride in any railway coach or street car, and in case any such 
person is discovered in such car, it shall be the duty of the conductor 
to notify the nearest health officer, who shall remove and isolate the 
patient as required by law. 
Rule 52. All depots, railway coaches, interurban cars, and street 
cars must be properly ventilated and, in cold weather, heated. 
Rule 53. Cuspidors in adequate numbers must be provided in 
all depots and waiting rooms, as well as in railway coaches; these 
cuspidors must contain at least one third pint each of some approved 
disinfectant solution, and must be cleaned out every twenty-four 
hours. 
Rule 54. Dry dusting and sweeping are prohibited at all times in 
waiting rooms of depots and railway stations, and in railway coaches, 
interurban cars, and street cars. 
Rule 55. Railway day coaches shall be thoroughly cleaned accord- 
ing to the method described by law at the end of each trip, or at least 
as often as once in forty-eight hours, when in use. 
Rule 56. Railway waiting rooms shall also be cleaned in a sani- 
tary manner once in each twenty-four hours. 
Rule 57. Parlor, buffet, and dining cars must be thoroughly 
cleaned at each terminal; food-boxes, refrigerators, closets, drawers, 
and cupboards must be cleansed, scalded, and disinfected with an 
approved disinfectant. 
Rule 58. Interurban and street cars must be washed with a 
hose and scrubbed thoroughly once every twenty-four hours; any 
such car must be fumigated immediately after any case of contagious 
disease has been discovered therein. 
Rule 59. Sleeping cars must be cleansed thoroughly and dis- 
infected at least twice in -each week, except that on certain lines 
designated by the President of the State Board of Health, one cleans- 
ing and one disinfection per week may suffice; any such car must 346 
THE HUMAN BODY AND ITS ENEMIES 
always be disinfected, however, immediately after any one suffer- 
ing from any contagious or infectious disease is discovered therein. 
Rule 6o. In each passenger car operated in Texas, a signed record 
must be kept showing the place and date of each disinfection, the 
length of time devoted to such disinfection, and the name of the 
person doing the disinfecting. 
Rule 6i. All depots, railway coaches, interurban cars, and sleep- 
ing cars must be provided with a water cooler for the use of patrons; 
these coolers must be kept sanitary, must be cleansed once in each 
twenty-four hours, and the ice used therein mtist be handled with 
tongs, and not dumped on floors, sidewalks, or car platforms. 
Rule 62. Expectorating or spitting on the floors, walls, or furni- 
ture of any depot, waiting room, platform, or any street car, rail- 
way coach, or interurban car is prohibited, and placards must be 
displayed calling the attention of the public to this fact. 
Rule 63. Brushing of teeth or expectorating in basins used for 
lavatory purposes is prohibited, and placards announcing this fact 
shall be hung in proper places. 
Rule 64. Sleeping-car companies shall provide separate compart- 
ments for their negro porters. 
Rule 65. Negro porters shall not sleep in sleeping berths nor 
use bedding intended for white passengers. 
Rule 66. No waiting room in any railway station or depot shall 
be floored in part or entirely with burlap or cocoa matting. 
Rule 67. All depots and railway stations shall be provided with 
water closets which shall be so constructed as to exclude flies; these 
water closets shall be kept in sanitary condition, and shall be cleaned, 
emptied, and disinfected at least once in each thirty days. 
Rule 68. The premises of all railway stations shall be thoroughly 
drained, sp that no stagnant water shall collect thereon. 
Rule 69. All cisterns, fire water-barrels, or other water con- 
tainers upon the premises of any depot or railway station shall be 
screened with not less than 16-mesh wire gauze. 
Note. — The rules governing the transportation of dead bodies are 
omitted. They are of technical interest, and can be obtained from any 
railway or express agent. APPENDIX C. SANITARY AND UNSANITARY 
OUTHOUSES 
In the state of Texas there are a great many sensible boys 
who believe in carrying into effect what they learn. Many of these 
boys are Boy Scouts. For these energetic and intelligent young 
men the following directions for making a sanitary privy, such as 
the one shown in Figures 245, 246 and 247, are given. 
The three things necessary in closets are as follows: First, flies 
must be absolutely excluded; second the closet must not overflow 
and drain into the well; third, 
the waste must not flow out 
where it can be stepped on 
by barefooted boys, who might 
in this way get hookworm. 
Many boys will find that they 
Figure 244. — When the lid is dropped, flies cannot reach the receptacle. 
Figure 245. — Notice the screened windows or ventilators, and the trap- 
door on the seat. The building should be neatly painted. 
can modify the water closet which they already have so as to make 
it fulfil all these three requirements. For instance, a few yards of 
wire screen well placed will exclude flies with absolute certainty. A 
watertight tub or other vessel can be placed underneath to catch the 
waste materials, and this tub must be emptied at intervals of a week 
or two. It should be treated with some disinfectant each day or 
two; probably the coal-tar disinfectants referred to in Chapter XIX 
are the best. Quicklime (unslacked) is also good. 
For making an entirely new closet (and this would better be done 
347 348 
THE HUMAN BODY AND ITS ENEMIES 
where there is any doubt at all about the possibility of fixing up the 
old one), order the following materials: One piece 6X6 inches, 
8 ft. long. One piece 4X4 inches, 16 ft. long. Five pieces 2X4 
inches, 16 ft. long. Three pieces 1X6 inches, 16 ft. long. Two 
pieces 1X9 inches, 9 ft. long. Three pieces 1 X 10 inches, 7 ft. 
long. Fifteen pieces 1 X 12 inches, 12 ft. long. Twelve pieces i X 
3 inches, 16 ft. long. Two pounds 20-penny spikes. Six pounds 10- 
penny nails. Seven-feet screen, 15-mesh, galvanized or copper, 12 
inches wide. Four hinges, six-inch strap. Two hinges, six-inch, 
“ T ” or three-inch butts for cover. One coil spring for front door. 
Having secured this material, cut up the wood as follows: 
A — Two pieces of lumber 4 feet long and 6 inches square at ends. 
B — One piece of lumber 3 feet 10 inches long, 4 inches square at 
ends. 
C — Two pieces of lumber 3 feet 4 inches long, 4 inches square 
at ends. 
D — Two pieces of lumber 7 feet 9 inches long, 2X4 inches at 
ends. 
E — Two pieces of lumber 6 feet 7 inches long, 2X4 inches at 
ends. 
F — Two pieces of lumber 6 feet 3 inches long, 2X4 inches at 
ends. 
G — Two pieces of lumber 5 feet long, 2X4 inches at ends. 
H — One piece of lumber 3 feet 10 inches long, 2X4 inches at 
ends. 
I — Two pieces of lumber 3 feet 4 inches long, 2X4 inches at 
ends. 
J — Two pieces of lumber 3 inches long, 2X4 inches at ends. 
K — Two pieces of lumber 4 feet 7 inches long, 6 inches wide, 
and 1 inch thick. The ends of K should be trimmed after being 
nailed in place. 
L — Two pieces of lumber 4 feet long, 6 inches wide, and 1 inch 
thick. 
Having sawed the lumber into the right sizes, put it together as 
follows, referring to Figure 247 as a model: 
First lay down the sills marked A and join them with the joist 
marked B; then nail in position the two joists marked C, with their 
ends 3 inches from the outer edge of A; raise the corner posts (D 
and F), spiking them at bottom to A and C and joining them with 
L, I, G, and K\ raise door posts E, fastening them at I, and then 
spike / in position; H is fastened to K. 
After the frame is erected, the sides, floor, roof, seat, windows, 
and doors can be built as shown in Figures 245 and 246. These 
pictures and directions are borrowed from Public Health Bulletin SANITARY AND UNSANITARY OUTHOUSES 
349 
37, written by Dr. C. W. Stiles and issued by the U. S. Public Health 
Service. The bulletin may be had by writing to the Service at 
Washington, D. C. Somewhat fuller 
instructions will be found in the bul- 
letin than in this chapter. 
It might be further suggested that 
the school grounds should not only be 
sanitary but also beautiful. The out- 
buildings should be rendered as inoffen- 
sive to good taste as possible. They 
should be painted, both for the sake 
of appearance and for durability. The 
privies should be screened from gen- 
eral view. This screen should consist, 
not of an ugly board fence, but of an 
arbor of plants. A trellis of lattice 
work covered with a hardy, perennial 
climber, such as the Cherokee rose or 
honeysuckle, would be very pretty. A 
hedge of shubbery would be still 
better and more permanent. Georgia 
cane makes a good background against 
which such evergreens as California 
privet, youpon, cedar, or wild peach 
could be grown. For full directions 
on beautifying the school grounds con- 
sult Farmers’ Bulletins Nos. 134 and 185 of the U. S. Department 
of Agriculture, Washington, D. C., and Bulletins of the Department 
of Extensions, University of Texas. 
Figure 246.— This shows how 
to erect the frame for a sani- 
tary closet. (See instructions 
on this and the preceding 
pages.) INDEX 
A star (*) after a page number indicates that the subject is illustrated. 
Abdomen, the, ?nd breathing, 193*. 
Abdominal cavity, the, 119*. 
Abscesses of the teeth, 155. 
Absorption, 170; of water, 172; of food, 172. 
Accidents and emergencies, 329. * 
Accommodation of the eye, 321*. 
Acids, to counteract, 337. 
Adam’s apple, 189. 
Adenoids, 188*. 
Air, composition of, 197; dryness of, harm- 
ful, 229; foul, how made, 197; fresh, and 
the muscles, 258; passages, the, 187*; 
quantity of fresh required, 197; sacs of 
the lungs, 194*; value of fresh, 49. 
Alcohol, 291; and the body heat, 234; and 
the circulation, 220; and the heart, 220; 
and the muscles, 258; effect of on busi- 
ness success, 296; on the heart, 293; on 
kidneys, 293; on muscles and bones, 293; 
on nervous system, 293; on respiratory 
system, 292; on the stomach, 292; injures 
the lungs, 195. 
Alimentary canal, the, 149*. 
Alkalies, to counteract, 337. 
Amylase, 147. 
Anatomy, defined, 119. 
Anemia, causes of, 212. 
Anopheles, the mosquito of malaria, 58, 60, 
89*. 
Anthrax (charbon), germ, the, 108; spores, 
disinfectant for, no; quarantinable, 63. 
Anti-mosquito brigades, 93. 
Antiseptics, 106. 
Antitoxin, 19; diphtheria, 26*, 52, 62; for 
tetanus, 27, 331. 
Antitoxins and toxins, 181*. 
Anvil bone in ear, 307. 
Aorta, the, 206*. 
Appendicitis, 158. 
Aqueous humor, the, 316*. 
Arch of the foot, 250*. 
Arsenic poisoning, 337. 
Arteries, the, 170; and veins, difference 
between, 217*. 
Artery, effect of cutting a, 217; the renal, 
223*. 
Artificial, immunity, 17; respiration, 334. 
Asiatic cholera, 38; and artificial immunity, 
20, 25; quarantinable, 63. 
Assimilation, 178-179*. 
Asthma, 195. 
Astigmatism, 323. 
Auditory, canal, the, 306; nerves, the, 308*. 
Auricles of the heart, 205*. 
Austin Pasteur Institute, 24. 
Bacteria, 4*; destroyed by cooking, 138; 
food of, 5; growing on gelatin, 5; how to 
kill, 106*; in milk, 140; motion of, 5*: 
multiplication of, 6; shapes of, 4*; size of, 
4*; ultra microscopic, 6. 
Bacterial diseases, 7, 
Bacterium and bacteria, 5*. 
Baking food, 138. 
Bathroom, ventilation of, 240. 
Baths and bathing, 237-238; hot and cold, 
239; the shower, 239; water, germs in, 8. 
Beef, the cuts of, 136. 
Beer, 29*. 
Bichlorid of mercury, no. 
Bicuspid teeth, the, 151-152*. 
Bile, 163; use of the, 164. 
Births and deaths, registration of, 343. 
Bleeding, 329. 
Blood, and the lymph, 210*; as the carrier, 
170*, 178, 202; cells and meningitis 
germs, 53; changes in the arteries, 219; 
circulation of the, 202; clotting of, 212; 
composition of, 210*; lymph and cells, 
relation of, 178*; observation on clotting 
of, 213*; vessels and gland cells, 167. 
Body, the, a house, 118*; a machine, 1*; a 
steam engine, 125; disease germs in the, 
180, 181*; distribution of heat in the, 
232; heat, alcohol and, 234; parasites in 
the, 180-181*; position of the, 249*; regu- 
lation of heat in the, 232*; wastes and 
the house fly, 87; wastes, typhoid germs 
in, 30. 
Boiling food, 138; kills germs, 108. 
Bone tissue, 244*. 
Bones, the, 241*; effects of alcohol on, 293; 
experiments to show composition of, 245*; 
fracture of, 330*; hygiene of, 249; uses 
of the, 242, 273. 
Boric acid, no. 
Brain, the, 266*. 
Breathing, 183*, 193*; observation and 
experiments, 185*; organs, the, 187*. 
Broken bones, 330*. 
Bronchi, the, 187*. 
Bronchioles, 187. 
Brues, Prof. C. T., 82. 
Brushing the teeth, 155. 
Bubonic plague, the. (See Plague.) 
Building foods, 132. 
Burns, 333. 
Burying typhoid wastes, 34. 
Business success, effect of alcohol on, 296. 
Buying food, 135. 
Caffein, 296. 
Candy, 135. 
Cane sugar, where digested, 164. 
Canine teeth, the, 151, 152*. 
Canned food, dangers of, 137*. 
Capillaries, the, 170; and the cells, 202; in 
the lungs, 194*; of the sweat glands, 229*. 
Carbohydrates, 128. 
Carbolic acid, 35, 108, no; poisoning, 337. 
Carbon dioxid, how produced, 183. 
Carrier, the blood as a, 202. 
Carriers of disease germs, 78. 
Carroll, Dr., 10, 57. 352 
INDEX 
Cartilage, 242; observation work on, 242; 
tissue, 189*. 
Cell and its nucleus, 122*; waste materials 
of the, 222. 
Cells, 121; and the capillaries, 202; growth 
and division of, 179*; lymph and blood 
relation of, 178*; the gland, 166. 
Cement of the teeth, 150*. 
Cerebellum, the, 269. 
Cerebrospinal meningitis, quarantinable, 
63. 
Cerebrum, the, 268*. 
Certificates of death, 115. 
Cheerfulness, the hygiene of, 163. 
Chemical disinfectants, 108. 
Chest cavity, the, and breathing, 193*. 
Chills and fever, 37. 
Chlorid of lime, 33. 
Cholera, a communicable disease, 10, 38; 
and the water supply, 103. 
Choroid, coat, of the eye, 315*. 
Cigarettes, injure the lungs, 195. 
Cilia, in the trachea, 190*. 
Ciliary, muscles, the, 321*; process, the, 
321*- 
Cinders in the eye, 327. 
Circulation, effects of alcohol on, 220; 
hygiene of the, 217*; meaning of, 204*; 
of the blood, 202*; observation on, 203*; 
the, and exercise, 218; experiment on, 219; 
the greater and the lesser, 203*. 
Clothing, and bathing, 237; tight, 249. 
Clotting of blood, 212. 
Coal tar disinfectants, 33, 109, no. 
Cocain, 297. 
Cochlea, the, 308*. 
Coffee, effects of, 296. 
Cold, baths, 239; feet, 337; hands, 337; 
weather, ventilating in, 199. 
Colds, germs of, 48; how to avoid, 49; 
catching, 234. 
Communicable diseases, to, 66. 
Connective tissue, 120*, 242; cells, 121*. 
Consumption or tuberculosis, 40-47; a com- 
municable disease, 10; causes of, 44; 
curable, 44; duty of the family, 46; of 
the Government, 46; germs of, 41; how 
spread, 41*, 43; how to cure, 43; lungs 
the seat of, 40; majority of people have 
it, 40; prevention of, 45. 
Contagion, modes of, 11*; duration of 
danger, 36; what is it?, 12. 
Contagious diseases, 10, 339. 
Convalescents, care, of, 79. 
Cooking, effects of, 137; importance of, 
136*. 
Cooperation of organs of the body, 262*. 
Cornea, the, 313*. 
Corpuscles, the blood, 210*; where produced, 
212*. 
Corrosive sublimate, 33, no. 
Cortex, the, 267*. 
Cotton clothing, 237. 
Cottonade, 238. 
Cowpox, 18. , 
Cows, care of, 141. 
Cranial nerves, the, 266, 276*. 
Crown of the tooth, 150*. 
Culex, the mosquito of dengue, 60-89*. 
Cup, a sanitary drinking, 102*. 
Cups, public drinking dangers of, tor. 
Curability of consumption, 44, 45*. 
Cuts, 330; of beef, the, 136. 
Dairy and Food Commission, 141; inspection, 
142. 
Dangers, of cistern water, 37; that threaten 
the body, 2. 
Dark and light colored clothing, 238. 
Death, certificates, 115; rate, Texas com- 
pared with other States, ri6. 
Deaths, registration of, 343. 
Dengue fever, a communicable disease, 10, 
89; and mosquitoes, 60; how spread, 13; 
quarantinable, 63; spread by mosquitoes, 
61; unpleasant but not dangerous, 61. 
Dental Association, the State, viii. 
Dental floss, 156. 
Dentine, 130*. 
Depots, sanitary regulations for, 345 
Dermis, the, 226*. 
Desks, school, 250*. 
Diaphragm, the, and breathing, 193*. 
Diet, a mixed, 134. 
Diffusion, 174; experiment in, 175, 176*. 
Digestibility, of food increased by cooking, 
139- 
Digestion, chemical, 146, 150; defined, 14s; 
in the small intestine, 163; in the stomach, 
163; the meaning of, 144; mechanical, 
145; where it begins, 149. 
Digestive, glands, the, 166; juices, chemical 
action of the, 164. 
Diphtheria, a germ disease, 7; a communi- 
cable disease, 10; and artificial immunity, 
20; antitoxin, 26*; carriers, 78*; deaths 
from, 113; germs, the, 52*. 
Direction of light, 323. 
Disease, carriers, 78; how to avoid, 79; 
germs scattered by house fly, 83*; spread 
by insects, 8r. 
Disease germs, 7; and the body, 2*; how 
carried by mosquitoes, go; in the body, 180, 
181*. 
Diseases, how communicated, 10; how 
spread, 13, 63; immunity against, 26; 
prevention of, 53; quarantinable, 63; 
spread by milk, 140; that are catching, 
10; that keep children from school, 67. 
Disinfectants, 106; chemical, 108; for 
typhoid germs, 35; mixed are no good, 
hi; table of, no. 
Disinfecting body wastes, 87; the linen, 36*; 
the slop bucket, 36*. 
Disinfection, 106*, 340; country districts, 
33; difficulties of, 107. 
Dislocations, 249. 
Dorsal cavity, the, 119*. 
Dover’s powder, 297. 
Draft, prevention of, 199*. 
Drink, effects of the first, 294*; habit, how 
formed, 294*. INDEX 
353 
Drum of the ear, 306.* 
Drunkards, pneumonia dangerous to, 48. 
Dry sweeping, evils of, 42. 
Duck clothing, 238. 
Dust and milk, 142; how to avoid, 42; im- 
portance of avoiding, 191. 
Dusters, feather, 43*. 
Dusting furniture, etc., 42. 
Dysentery and water supply, 104; epidemic, 
quarantinable, 63. 
Ear, bones of the, 306*, 307. 
Eating habits, 135. 
Education, 283. 
El Paso, Pasteur Institute, 24. 
Emergencies and accidents, 329. 
Enamel of the tooth, 150*. 
End cells, 297. 
Energy for work from food, 124. 
Enzymes, 146-147; the, in the intestinal 
juices, 163; of the pancreatic juice, 163. 
Epidemics, causes of, 34. 
Epidermis, the, 226*, 227. 
Epiglottis, the, 189. 
Epithelial, cells, 121*; gland cells, 166*; 
tissue, 122. 
Erysipelas, a communicable disease, 10. 
Esophagus, the, 158. 
Ether, 312. 
Eustachian tube, the, 307. 
Evaporation, experiment in, 233*. 
Eye, a human camera, 2*; cinder in the, 327; 
defective, 322; observation work on, 320; 
protection of the, 312*; reflex action of 
the, 278; strain, 326; the normal, 322. 
Eyeball muscles that move, 312*; how 
moved, 314*. 
Eyes, experiments with the, 322; granulated 
eyelids, 312*; how spread, 14; hygiene of 
the, 325. 
Excretion, 222*. 
Excretory organs, the, 222*. 
Exercise and the circulation, 218; effects of, 
219; on the lungs, 195; on muscles, 238*. 
Experiment in diffusion, 175, 176*; in 
digestion, 144; in habit, 283; on exercise 
and the circulation, 219; on oxidation, 
125; on reflex action, 278; on refraction, 
318*; on sense of touch, 300; on the 
teeth, 152; on ventilation, 198*; on the 
voice, 190; to show composition of bones, 
245*; to show effect of evaporation, 233*; 
with carbon in foods, 132; with the eye, 
322; with protein, 130; with mineral 
salts, 131; with starch, 129; with starch 
and sugar, 146. 
Expiration, 184. 
Exposed persons, quarantine of, 64. 
External respiration, 187. 
Fainting, 333. 
Faintness, remedy against, 337. 
Far-sightedness, 323*. 
Fat cells, 126*, 180*. 
Fat foods, 130. 
Fatigue, 260-261; digestion of, 147, 164. 
Fatty tissue, 121*. 
Feather dusters, 43. 
Femur or thigh bone, 246*. 
Fiber, the study of, 121, 122. 
Fibrin, 213*. 
Fish, care in buying, 136. 
Flagging the house, 65*. 
Flames, how to smother, 334. 
Flavors, produced by cooking, 139. 
Fleas and the plague, 82. 
Flies, 84; and typhoid germs, 30; and the 
body wastes, 87; epidemics caused by 
34; how to kill, 86*; how to study, 86; 
life history of, 85; tracks on gelatin 
plates, 31. 
Floors, how to sweep, 42. 
Fly, the stable, 81*. 
Focusing, 320*. 
Food, buying of, 13s; cost of, 135; for 
growth, 126; for repair of body, 126; 
how affected by cooking, 138; of bac- 
teria, s; storage of in the body, 180; 
taken up by blood and lymph, 170; the, 
we eat, 128; the need of, 124; where 
absorbed, 172. 
Foods, canned, 137; rich in fat, 130; rich in 
protein, 130. 
Foodstuffs, uses of the, 132. 
Food tube, the, 149*. 
Foot, and mouth disease, 6; bones of, 250*. 
Formaldehyd, fumigation, 109. 
Fountain, sanitary drinking, 102*. 
Fracture of bones, 330*. 
Franklin, B., on clothing, 238. 
Fresh air and sunlight, 106*; value of, 49. 
Fruits, care in buying, 136. 
Frying food objectionable, 139. 
Fuel foods, 132. 
Fumigation, 109*, in*. 
Fur, clothing, 237. 
Gall bladder, the, 162*, 163*. 
Ganglia, 267. 
Gastric glands, the, 160; a, 167*; juice, 
147, 160; juice and germs, is*. 
Gelatin, bacteria growing on, 5*; plate, fly 
tracks on, 31. 
Germ carriers, 78; how to avoid, 79; disease, 
7; and nervous system, 286; enemies, 
our, 3*; of tuberculosis, 41. 
Germicides, 106. 
Germs, 4*; and drinking water, 96; multi- 
plication of, 7; of tetanus, 330; protec- 
tion against, 15. 
Gland, a gastric, 167*; cells, the, 166; func- 
tion of the, 166; gastric and intestinal, 
167*, 172; reflex action of the, 278; the 
digestive, 166, 149; the lymph, 214, 215*. 
Glycerin, 147. 
Granulated eyelids, 327. 
Gray matter, the, 267*; of spinal cord, 272*. 
Greater circulation, the, 203*. 
Grip, a germ disease, 7; germs of, 48*; 
deaths from, 113; how to avoid, 49. 
Gullet, the, 138, 159, 162*. 
Gums, inflamed, 155. INDEX 
354 
Gymnastics, effect of on the muscles, 259*, 
260*. 
Habit, 282; the drink, 294*; value of, 282. 
Habits, 285; breaking bad, 283; danger of 
unclean, 79; eating, 135. 
Hair, the, 227*; follicles, the, 227*. 
Hand, bones of the, 245*. 
Handkerchief, dangers of the, 12. 
Hands, washing the, 238. 
Hammer bone in ear, 307. 
Harmless germs, 7. 
Headache powders, 297. 
Health officers, duties of, 341. 
Hearing, 306*, 309*. 
Heart, action of the, 206; contraction of 
the, 217; effect of alcohol on, 220, 293; 
effect of tobacco on, 220; how the blood 
gets back to the, 217; the function of, 
205; observation work on the, 208. 
Heat, alcohol and the body, 234; distribu- 
tion of, 232; how retained, 234*; regula- 
tion of, 232*. 
Hemoglobin, 211. 
Hemorrhage, 329. 
Hookworm, 71; and soil pollution, 72; dis- 
ease, 70*; and water supply, 104; symp- 
toms and progress of, 71*. 
Hot baths, 239. 
House or typhoid fly. (Sec Flies.) 
House under quarantine, 66; ventilation, 
198. 
Houston schools, sanitary fountain in, 103*. 
Humerus, the, 245*. 
Hydrochloric acid in the stomach. 164. 
Hydrophobia, a communicable disease, 10; 
animals liable to, 25; artificial immunity, 
20; Pasteur treatment of, 24. 
Hygiene defined, 119; of bones, 249; of 
cheerfulness, 163; of joints, 249; of the 
circulation, 217; of the eyes, 325; of the 
kidneys, 223*; of the lungs, 195; of the 
middle ear, 308; of the muscles, 258*; 
of the outer ear, 307; of the skeleton, 
249*; of the skin, 229. 
Ice, box for milk, 142; cream, danger of, 138. 
Immunity, 16-20, 22. 
Incisor teeth, the, isi*-i52. 
Incubation period, the, 64. 
Infantile paralysis, 10. 
Inner ear, the, 308*. 
Innominate bone, the, 246. 
Insecticides and disinfectants, 109, 
Insects and spread of disease, 71. 
Inspiration, 184. 
Internal respiration, 187*. 
Intestinal glands, the, 162, 168*. 
Intestinal juice, 147, 162, 163. 
Intestine, digestion in the small, 163; the 
small, 158, 162; bacteria in the, 7; wastes 
in the large, 222. 
Invertin, 147. 
Invisible germs, 6. 
Involuntary muscles, 255, 281. 
Iris, the, 315*. 
Irregular teeth, 154. * 
Isolation, 339. 
Jenner, Dr. E., and vaccination, 23. 
Joint, ball and socket, 245; the hip, 246*. 
Joints, 245*; hygiene of, 249; observation 
work on, 247. 
Kidney, structure of the, 224*; effect of 
alcohol on, 293; hygiene of the, 223*; the 
function of the 222 . 
Kissing, dangers of, 43. 
Knee cap, 243. 
Koch, D. R., on disease carriers, 78. 
Lacteals, the, 173, 214. 
Larynx, the, 187*, 189. 
Laudanum, 297; poisoning, 337. 
Laundry of typhoid cases, disinfecting, 36*. 
Lazear, D., 10, 57. 
Laziness, 287. 
Lens of the eye, 315. 
Leprosy, a communicable disease, 10, 66; 
quarantinable, 63. 
Lesser circulation, the, 203*. 
Lice, and typhus fever, 82. 
Ligaments, 242. 
Light, and dark colored clothing, 238; 
direction of, 32s; intensity of, 325; re- 
fraction of, 318; should be steady, 326; 
waves, 312. 
Lime in the bones, 245*. 
Linen clothing, 237. 
Lipase, 147. 
Liscom, smallpox on board the, 23. 
Liver, the, 162*, 163*, 168; the function of 
the, 223. 
Living substance, making of, 178*. 
Lockjaw (See Tetanus), 330. 
Locomotion, 241*; muscles, 253*. 
Low, Dr., 58. 
Lungs, the, 192*; air sacs of the, 194*; 
hygiene of the, 195; the seat of consump- 
tion, 40. 
Lymph, the, 171; and the blood, 210; blood 
and cells relation of, 178*; capillaries, 
214*; defined, 178; distribution of, 213*; 
glands, 214*, 215; nodes, 214*, 215*; 
vessels, 214*. 
Lymphatics, and the lymphatic system, 
2I4*-2I5. 
Malaria, or chills and fever, 57; a com- 
municable disease, 10; deaths from, 113; 
and mosquitoes, 58*; how spread, 13, 
57; the mosquito, 89*; prevention, 59. 
Malarial parasite, the, 57. 
Marine Hospital service, 109. 
Marketing, 135. 
Marrow, 243*. 
Materials for clothing, 237, 238. 
Measles, 7; a communicable disease, 10; 
deaths from, 113; death rate compared, 
116; a reportable disease, 67. 
Medical Association, the State, vii. 
Medicines and poisons, 338, INDEX 
Medulla, the, 270*. 
Membrane, diffusion through a, 175*. 
Membranous cronp, quarantinable, 63. 
Meninges, the, 272*. 
Meningitis, a communicable disease, 10; 
deaths from, 113; a germ disease, 7; 
carriers, 54, 78; and artificial immunity 
from, 20; germs, 53*, 54; prevention of, 
55; quarantinable, 63; serum, 27; serum 
treatment of, 54. 
Meningococcus, the, 54*. 
Middle ear, hygiene of the, 308. 
Milk and bacteria., 7; and disease, 140; and 
tuberculosis, 44,140; and typhoid carriers 
141; and typhoid germs, 32; how to get 
clean, 141; pails bad and good, 141*; 
typhoid germs in, 30. 
Milking, care in, 141. 
Mineral salts, 128, 131; experiment with, 
131; uses of, 132. 
Mixed diet, 134. 
Mohair, 238. 
Molar teeth, the, 151*, 152; the first perma- 
nent, 153. 
Moles and warts, 230. 
Morphine, 297; poisoning, 337. 
Mosquitoes and disease germs, 90; and 
malaria, 58*; bar, a, 60*; breeding places 
of the, 91*; description of, 90; how to 
destroy, 93; how to rear, 93; life history 
of the, 92*; malarial, the, 58; smoking 
out, 59; spread of disease by, 10. 
Motion, of bacteria, 5*; use of bones for, 243. 
Motor cells and fibers, 274. 
Mouth and teeth, 149; care of, 155; bac- 
teria in the, 7; breathers, 188; the un- 
clean, 154. 
Multiplication of bacteria, 6-8. 
Muscle cells, 121*; structure of a, 256*; 
tissue, 120*. 
Muscles, the, 241, 253*; the ciliary, 321*; 
contraction of, 254; effect of alcohol on, 
293; fibers, 256*; hygiene of the, 258*; 
involuntary, 255*; primary use of, 253*; 
voluntary, 255*. 
Nails, the, 228*. 
Nasal passages, the, 187*. 
Near-sightedness, 322*. 
Nerve, cells, 263*; and fatigue, 289*; tissue, 
121. 
Nerves, function of the, 264; of hearing, 
306*, 309*; of sight, 312*; of smell, 304*; 
the spinal, 273*; of taste, 302*. 
Nervous system, the, 262*; and the stom- 
ach, 286; care of, 285; the central, 265; 
compared to a telephone system, 264; 
effects of alcohol on, 293; and germ dis- 
eases, 286; the peripheral, 265; training 
the, 281. 
Nodes, the lymph, 2i4*-2i5. 
Nose, the, 313*. 
Nurse, duties of, under quarantine, 64. 
Observation, and experiments, 185*; work 
on body position, 249; on cartilage, etc., 
242; circulation of the blood, 203*; on 
clotting blood, 213; on the eye, 320; with 
flies, 86, 93; on the heart, 208; on joints, 
247; with mosquitoes, 90-93; on rice, 
wheat and corn, 130; on a tooth, 151*, 
152; on veins, 218*. 
Opiates, effects of, 297. 
Opium, 297; poisoning, 337. 
Optic nerve, the, 312. 
Organs of the body, the, 119. 
Outdoor sleeping, 43, 201. 
Outer ear, hygiene of the, 307. 
Outhouses, sanitary need of, 72; sanitary 
and unsanitary, 347*. 
Overexercise, 219. 
Overwork, 287*. 
Oxidation, experiments in, 125. 
Palate, the, 149*. 
Pancreas, the, 162*, 163*, 168*. 
Pancreatic juice, 147, 163. 
Paper towels, 53, 327. 
Papillae, the, 227, 302*. 
Parasites, 180-181*. 
Paregoric, 297; poisoning, 337. 
Pasteur Institutes in Texas, 24. 
Pasteur, Louis, 24; treatment of vaccina- 
tion, 24. 
Patella, the, 243. 
Pellagra, cause of unknown, 70; symptoms 
of, 70. 
Pencils and bacteria, 8. 
Pepsin, 147, 163; digests germs, *6. 
Pericardium, the, 203*. 
Periosteum, the 245. 
Peristalsis in the gullet, 158, 159*. 
Permanent teeth, the, 151*, 152. 
Perspiration, germs in, 8. 
Pestilential diseases, 340. 
Pharynx, the, 149*, 187*. 
Phosphorus poisoning, 337. 
Physiology defined, 118. 
Pimples, 239. 
Pink eye, 327. 
Plague, the, 75*; a communicable disease, 
10; artificial immunity against, 20*, 2,3; 
and fleas, 82; how spread, 75, 76; quaran- 
tinable, 63. 
Plants, how they serve man, 126. 
Plasmodium, of malaria, the, 57- 
Pleura, the, 192. 
Pleural fluid, the, 192. 
Pleurisy, 193. 
Plexuses, the, 277*. 
Pneumonia, 175; deaths from, 113; germs 
of, 48; how to avoid, 49. 
Poisoning, 337; ptomain, 137. 
Portal vein, the, 173*, 209. 
Position of the body, 249*. 
Practise, 282. 
Pre-molar teeth, the, I5i*-i52. 
Preventable diseases, 113. 
Prevention of consumption, 45; of diph- 
theria, 53; of draft, 199*; of malaria, 59; 
of meningitis, 55; of typhoid fever, 29. 
Protection against germs, 15. 
355 356 
INDEX 
Proteins, 128; where digested, 164; experi- 
ment with, 130; foods, 130. 
Protoplasm, 179. 
Ptomain poisoning, 137. 
Pulmonary artery, the, 206*; veins, 206*. 
Pulp cavity of the teeth, 130*. 
Pulse, the, 207*. 
Pupil, the, of the eye, 313. 
Pure food, 134*. 
Pus germs, disinfectant for, no. 
Pylorus, the, 160*. 
Pyorrhea or Rigg’s disease, 133. 
Quarantinable diseases, 63. 
Quarantine, 339; a house under, 66*; mean- 
ing of, 63; nurse under, 64*. 
Rabies. (See Hydrophobia.) 
Radius, the, 245*. 
Railway coaches, sanitary regulations for, 
345- 
Rain water, 97*. 
Rat-proof buildings, 76. 
Rats and the plague, 75*. 
Raw food and typhoid fever, 34. 
Recreation, 288; the need of, 2s8*-26i. 
Red blood corpuscles, 210*. 
Reflex action, 270, 278; example of, 273*; 
experiment in, 278; of the eye, 278; of 
the glands, 278; in the spinal cord, 2741 
Refraction of light, 318. 
Refrigerator, a, 134 . 
Registration of births and deaths, 343. 
Rennin, 147. _ 
Reportable diseases, 64, 67. 
Respiration, artificial, 334; defined, 183; 
external, 187; internal, 187. 
Respiratory system, effect of alcohol on, 292. 
Rest for the eyes, 323; the need of, 261. 
Retina, the, 313*, 316*; image thrown on 
the, 319*. 
Ricketts, Dr., 10. 
Rigg's disease or pyorrhea, 133. 
Rocky Mountain spotted fever, 83. 
Rods and cones, the, 316*. 
Rod-shaped bacteria, 4*. 
Rosenau, Dr. J. M., 82. 
Ross, Dr. Ronald, 37. 
“Rough on Rats,” 337. 
Round worms, 73. 
Round-shaped bacteria, 4*. 
Saliva and digestion, 146; germs in, 8. 
Salivary glands, 168; the function of, 130*. 
Sambon, Dr., 58. 
Sanitary Code of Texas, 339; how to get 
the, 65; drinking cup, 102*; drinking 
fountain, 102*; outhouses, 347*; out- 
houses, need of, 72. 
Scarlatina, 67. 
Scarlet fever, a communicable disease, 10, 
67; death rate compared, 116; deaths 
from, 113; quarantinable, 63. 
School, lunches, 133; room ventilation, 198*, 
199*. 
Sclerotic coat, the, 313*. 
Screens, prevent malaria, 59*; the use of, 93. 
Semicircular canals, the, 308*, 3og. 
Sensations, general, 299. 
Sensory cells and fibers, 274; nerve fibers, 
299- 
Serum, 213*; against meningitis, 27; treat- 
ment of meningitis, 54. 
Sewers, need of, 72. 
Shelter, 235. 
Shepard, Dr. P. A. E., 82. 
Shoes, ill fitting, 250*. 
Shower bath, the, 239*. 
Sickroom, care of the, 50. 
Sight, 312*. 
Silk for clothing, 237. 
Size of bacteria, 4*; of type, 323. 
Skeleton, the human, 241*; hygiene of the, 
249*. 
Skin, the, 226*; care of the, 15*; hygiene of 
the, 229. 
Sleep, 288*. 
Sleepiness, 337. 
Sleeping, cars, sanitary regulations for, 34s; 
out of doors, 43, 201. 
Smallpox, a communicable disease, 10, 66; 
a germ disease, 7; artificial immunity 
against, 18-20; deaths from, 22; 113; 
death rate compared, 116; quarantinable, 
63; vaccination against, 22. 
Smell, the organ of, 303*; use of the sense 
of, 304. 
Snake bites, 332. 
Soap and water, 106*. 
Soil pollution and hookworm, 72. 
Solar plexus, the, 277*. 
Sore eyes, 327. 
Special senses, the, 299*. 
Spectacles, 326. 
Sphincter muscles of the gullet, 139. 
Spinal cord, the, 243*, 272*; nerves, the, 273*. 
Spiral shaped bacteria, 4*. 
Spitting, 4S*-46; nuisance, the, 9. 
Spore bacteria, 108. 
Sprains, 240, 249. 
Squirrels and the plague, 75*. 
Stable fly, the, 81*. 
Starch, experiment with, 129; where digested, 
164. 
Stegomyia, the mosquito of yellow fever, 
60*, 89*. 
Stewing food, 138. 
Stimulus, 299. 
Stirrup bone in ear, 307. 
Stomach, the, 139, 162*; affected by bad 
teeth, 155; and intestines, i6r*; and the 
nervous system, 286; digestion in the, 
163; effect of alcohol on, 292; lining of 
the, 171. 
Straining the eyes, 326. 
Sunlight and fresh air, 106*. 
Sweat glands, function in structure of the, 
228*, 229*. 
Sweating, effect of, 233. 
Sweeping a floor, 42. 
Swell head, canned goods, 137*. 
Swimming, 240. INDEX 
357 
Sympathetic nervous system, the, 277*. 
Synovial fluid, the, 247. 
Tadpole, circulation of the blood in, 204*. 
Tapeworms, 73, 138*, 180. 
Tartar, on the teeth, 154. 
Taste, 302*; and smell, 302; buds, the, 302. 
Tea, effects of, 296. 
Tear ducts, 313*; glands, the, 313*. 
Tears, germs in, 8. 
Teeth, the, 150; abscesses on, 135; action 
of in digestion, 146; and their functions, 
131; and mouth, 149; brushing the, 156; 
care of the, 135; decaying, 134; a struc- 
ture of the, 130*; tartar on, 154. 
Temperature of rooms, 23s; sense, the, 301. 
Temporary, teeth, the, 131 *; importance of 
the, 133. 
Tendons, 241. 
Tetanus, 330; antitoxin, 27; artificial im- 
munity, 20; deaths from, 113. 
Texas, accidental burning in, 333; clothing 
for climate of, 237; death rate compared 
with other States, 116; hookworm disease 
in, 70; pink eye in, 327; preventable 
diseases in, 113; Sanitary Code, 339; 
snake bites in, 331; State Dental Asso- 
ciation, the, viii; State Medical Associa- 
tion, vii; Vital Statistics, 113, 116; water 
used in, 97. 
Thayer, Dr. W., 38. 
Them, 296. 
Thoracic cavity, the, 119*; duct, the, and 
the lymph, 214. 
Thymol, how to use, 73. 
Ticks, fever carriers to animals, 82. 
Tissues, the, 119*; bone tissue, 244*. 
Tobacco and the muscles, 258; effect of on 
the heart, 220. 
Tomatoes, care in buying, 136. 
Tongue, the, 302*; the use of, in digestion, 
ISO. 
Toothpicks, 156; powder, 136. 
Touch, 300*; buds, 300*; experiments on 
sense of, 300. 
Towels, public, 53. 
Toxins, 6; and antitoxins, 181*. 
Trachea, the, 187*; the, 190*. 
Trachoma, 327; how spread, 14; quaran- 
tinable, 63. 
Training the nervous system, 281. 
Trichina, 138*. 
Trypsin, 147. 
Tsetse fly, the, 82. 
Tuberculosis, 4*, 47; and milk, 44, 140; 
deaths from, 113; death rate compared, 
116; a germ disease, 7; how spread, 13; 
quarantinable, 63. 
Tuberculosis cow, a, 140*. 
Tubules of the kidneys, 226*, 229. 
Tympanum, the, 306. 
Type size of, 325. 
Typhoid bacteria, 29; and water supply, 
104; carriers, 78*; carried by flies, 30; 
and milk, 32, 141; deaths from, 113; dis- 
infectant for, 33, no; disinfection of 
laundry, 36*; fever, 2g*-38; a communi- 
cable disease, io; and water supply, 103; 
and artificial immunity, 16, 25; death rate 
compared, 116; effects of, 29; germ of, 
29; a germ disease, 7; how spread, 13; 
how to avoid catching, 37; in drinking 
water, 31; in waste matter, 30; impor- 
tance of, 29; length of time contagion 
lasts, 37; prevalence of, 29; quarantinable, 
63; spread by raw food, 34; symptoms of, 
29; where they multiply, 29, 30. 
Typhoid fly, or house fly, the, 84*. (See 
Flies.) 
Typhus fever, a communicable disease, 66; 
quarantinable, 63; spread .by lice, 82. 
Ulna, the, 245*. 
Ultra-microscopic bacteria, 6. 
Unclean habits, dangers of, 79; mouth, the, 
154. 
Underwear, advice on, 237. 
Unsanitary outhouses, 347*. 
Urea, removed by the kidneys, 222. 
Uvula, the, 149. 
Vaccination, 18; after exposure, 23; against 
smallpox, 22; importance and need of, 
22, 23; when and how often, 23. 
Vaccines, 19. 
Valves in aorta, 207*; of the veins, 207*, 
218*. 
Vegetables, care in buying, 136. 
Vejn, the renal, 223*. 
Veins and arteries, difference between, 217*; 
observation work on, 218*: valves of the, 
218*. 
Vena cava, the ascending, 205*; the de- 
scending, 205*. 
Ventilation, 197*; and temperature, 235; 
experiments in, 198; of the bathroom, 
240; of the home, 197*; of the school- 
room, 199*. 
Ventral cavity, the, 119*. 
Ventricles of the heart the, 205*. 
Vermiform appendix, the, 158. 
Vertebra;, the, 243*. 
Villi, the, 162*,. 168; of the intestine, 174; 
of the small intestine, 172*; structure of 
the, 173*. 
Vital Statistics, 113, 343; in Texas, 115; 
State Registrar of, 115; use and purpose 
of, 114. 
Vitreous humor, the, 316*. 
Vocal cords, the, 189*. 
Voice experiments on the, 190. 
Voluntary muscles, 255, 281. 
Vomiting, to produce, 337. 
Warmth from food, 124. 
Warts and moles, 230. 
Washing the hands, 238*. 
Waste materials of the cell, 222. 
Wastes of the body, 180. 
Water, 128; appearance of, 96; absorption 
of, 172; and cholera, 103; cistern dangers 
of, 37; and germs, 96; dysentery, 104; 358 
INDEX 
and hookworm disease, 104; and the 
spread of disease, 10; and typhoid germs, 
31, 104; well water, 99*, 100; as food, 
132; epidemics caused by, 33; supply 
and typhoid fever, 103; supply of summer 
camps, 100*; used in Texas, 97. 
Wax in the ear, 307. 
Well, rope and bucket, 99; water, 98; deep, 
100. 
Wells, casing of, 99; danger from, 31*; 
good and bad, 98*. 
Whisky, 2gr*. 
White, blood cells, the, 16*; corpuscles, 
2i x*; matter, 267*. 
Whooping cough, deaths from, 113; a re- 
portable disease, 67*. 
Wigglers, how to destroy, 91. 
Wine, 291*. 
Winter underwear, 238. 
Woldert, Dr. Albert, 58. 
Woolen clothing, 237. 
Work, effect of, on muscles, 260. 
Wounds, 230; deep, 332; open, 330. 
Yellow fever, 89; a communicable disease, 
10; a germ disease, 7; how spread, 13; 
mosquito, the, 89*; quarantinable, 63; 
spread by mosquito, 50. BY THE SAME AUTHOR 
Laboratory Manual for 
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Experimental Studies in 
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