Physiology and[-[ygiene 
TAUGHT OBJECTIVELY. 
INTRODUCED BY 
ELEMENTARY LESSONS ON SCIENCE. 
by h. CORNER, PH. D., 
M 
Principal, Milwaukee Public Schools. 
SUGGESTIVE, NOT EXHAUSTIVE 
Copyrighted 1893 by H. Dorner, 
PUBT.ISHED BY THE AUTHOR 
1922 Cedar Street, 
MILWAUKEE. 
PRESS OF 
WESTLAKE, DELAHUNT & SMITH COMPj 
BROADWAY, MILWAUKEE PREFACE. 
This book is the direct outcome of work done in the school- 
room. It has been tested for years, both by the author and by 
other teachers whose work could easily be supervised. 
It is objective in its methods, wherever possible and practica- 
ble, leads up from observations and experiments to theories and 
laws, and aims to teach as nature might teach a bright child 
under happy influences. 
The so-called “New Education”, which advocates objective teaching, 
has found numerous adversaries, because inexperienced teachers, full of 
idealistic views on the value of objective methods, have made shocking 
blunders in applying them in large classes. Some, for instance, have 
tried to teach classes of fifty or sixty pupils as they would a few bright 
children supplied with all modern appliances. But when, toward the end 
of the term or school year, principals or superintendents have asked for 
results, the misapplications of the teachers’ methods have become pain- 
fully evident. 
In order to satisfy the claims of both—the advocates of the principles 
of sound, objective teaching and the supervising educators looking for 
results—this book proceeds on the following plan; First, it either recalls 
to pupils former experiences or introduces them to new observations; 
second, it incites them to express the facts deduced in correct language; 
and third, it presents, for memorizing, a concise statement of the facts, 
laws, or theories in question. 
To avoid an undue extension of the book, the introductory, method- 
ical work required for each paragraph has been condensed into a few 
leading questions or statements ; pmly in the first six paragraphs have 
the methods herein recommended'been exemplified in all their fullness, in 
order to serve as a guide for the teacher. 
It teaches Science in connection with Physiology and Hygiene. 
The latter two are the principal topics; the chapters on Science 
are auxiliary. 
Before learning of respiration the pupil is taught to observe the 
properties of air (expansibility and pressure) ; before finishing this 
chapter, combustion is treated and the products of respiration and 
combustion compared. Similarly levers and bones, pumps and the heart, 
electric wires and the nerves, sound and the ear, light and the eye, are 
taught together. Chapters on water and heat precede the study of 
Physiology proper. 
It is not a scientific book in the common sense of the word, 
that is, it does not commence with the basis or the elements of 
a scientific system in accordance with the present comprehensive 
ideas about the universe. The elements here presented are 
selected with a view to didactic or pedagogical principles, the 
foremost of which are: proceed from the easy to the difficult, 
from the simple to the compound, from the known to the un- 
known. 
There are numerous excellent books written in the deductive, strictly 
scientific style and suited to the intellect of mature pupils. This book, 
however, is intended for children, who, for the first time, receive elemen- PREFACE 
tary lessons in natural sciences, together with tn _.ig, 
and arithmetic. Children of this age (11 to 14 _ require 
the strictly logical, systematic lectures of the college or university pro- 
fessor. What they need is a live teacher able to interest them in the 
work, able to ask proper questions and elicit correct and complete ans- 
wers, and a book containing the most important and most useful facts 
arranged in a manner facilitating reviews. 
It is written in simple language, adapted to the understand- 
ing of children of average capacity. 
Many books on physiology contain a great number of scientific terms 
that children learn with a great expenditure of energy and retain with 
difficulty. Whenever opportunity has offered, the pupil has been assured 
that mere names, dates, numbers, and unintelligible statements are worth 
less than nothing, burdening, as they do, the mental storehouse, obscur- 
ing the intelligence and weakening the energy. 
It throws the main work on the pupil; the teacher’s task is 
to guide and direct. Thus the pupil, learning through his own 
exertions, becomes interested in the work and strives for progress. 
All children are eager for knowledge and desirous of exerting their 
faculties in the investigation of nature. They know they cannot do this 
without labor; they desire and need early and continued effort; never- 
theless, they feel the need of guidance in their first attempts, and it is 
one of the most important duties of the teacher to save the waste of 
time in blundering into needless toils. 
A suggestive, not an exhaustive treatment of the subject, has 
been the author’s aim. 
As a consequence, pupils using this book intelligently are likely to 
apply for themselves laws and theories they have learned to understand, 
and to classify facts which they know with those named in this book. 
The subject matter is divided into paragraphs, in each of 
which the main thought or fact is expressed in concise language. 
This allows teachers to omit those parts which they consider of 
minor importance, and to select the most suitable work for individual 
needs. At the same time it facilitates reviews. 
The author would take this occasion to acknowledge most 
gratefully his indebtedness, for valuable assistance during the 
progress of the work, to: Miss Mary Maher, Miss Lutie 
Stearns, Mrs. E. Rissmann, Mr. Sanford A. Hooper, Mr. Wm, 
E. Anderson, and, especially, to Miss Julia A. Koerner, who has 
given much time to the correction of the proof and the designing 
of the illustrations. CONTENTS 
WATER. 
Air in Water; Vapor; Singing Water 1— 
Boiling Point; Vapor in Breath; Steam; Fog s—lo 
Moisture; Clouds; Rain 11—14 
Solutions; Evaporation; Crystallization 15—19 
Distillation; Rainwater; Springs ; Wells 30—34 
Circulation of Water; Value of Forests... 35—31 
HEAT. 
How Rooms are Heated; Rays of Heat 33—37 
Dew ; Frost; Insular and Continental Climate 38—39 
Expansion of Solids, of Liquids, and of Air ; Thermo- 
meter 40—45 
Convection in Air and Water; Winds 46—48 
How Animals are Protected from the Cold ; Conductors 49—53 
DIGESTION. 
Changes of Weight; Course of our Food 54—56 
Organs; the Mouth ; Teeth.. 57—68 
Saliva; Starch; Salivary Glands 64—67 
Poodpipe; Stomach; Proteids... 68—73 
Intestinal Digestion; Change of Food into Blood. 74—79 
Hygiene of Digestion 80—84 
Bread; Vegetables; Sugar 85—87 
Boast Beef, Salting and Smoking 88—89 
Baw Meat; Parasites; Meat Generally 90—91 
Eggs; Milk; Milktester ; Fat; Cheese. 93—95 
Spices and Condiments; Tea and Coffee 96—97 
RESPIRATION AND CONDUCTION 
Expansion and Pressure of Air. 98—101 
Pair of Bellows; the Chest; Breathing 103—104 
Lungs and Rubber Balloons 105—107 VI 
CONTENTS. 
A Burning Candle; Yapor and Carbonic Acid *iT 108—110 
Composition of Air; Changes during Combustion 111—113 
Respiration and Combustion Compared 113—116 
Confined and Fresh Air 117—121 
Admission of Fresh Air 133—124 
CIRCULATION. 
Hero’s Fountains ; Syringe; Pumps 125—128 
Rubber Syringe and Heart 129—131 
Two Hearts; Three Kinds of Blood Vessels 133—135 
Necessity of the Blood ; its Composition.. 136—137 
Need of Motion; Function of Capillaries 138—139 
Two Kinds of Blood ; Substances Found in Blood 140—143 
Dissection of a Heart 143—144 
How to Treat Wounds 145 
THE SKIN 
Qualities; What is Found in the Skin. 146—148 
Two Layers; Scarf Skin; Nails; Hair; Glands 149—153 
Papillae; the Daily Sponge Bath. 154—157 
EXCRETION. 
Lungs and Skin ; Kidneys ; the Renal Organs 158—160 
Urine; Hygiene of the Kidneys. 161—162 
MUSCLES. 
Contraction ; Tendons ; Connective Tissue ; Fibers 163—167 
Attachment; Substances Moved ; Two Kinds 168—170 
Exercise; Value of Strong Muscles 171—173 
Work and Sleep ; Improper Exercise 173—174 
LEVERS AND BONES. 
Scales; Steelyard; Effect of a Weight. 175—177 
Law of the Lever; Kinds of Levers; their Work 178—180 
Forearm, Foot, and Head as Levers 181—183 
Joints; Three Kinds of Joints; Ligaments 184—190 
Parts and Substances of Bones. 191—192 CONTENTS. 
VII 
Hollow Bones ; Skeleton; Backbone *[[ 193—197 
Bones of the Arm and Leg ; Chest 198—200 
Skull; Four Uses of Bones 201—202 
Broken Bones; Crooked Legs; Round Shoulders. 203—205 
Tight Lacing ; Tight Shoes 206—207 
THE THREE LOWER SENSES 
Sense of Feeling; the Nose 208—209 
Smell; Sense of Taste 210—211 
SOUND AND THE EAR. 
Production of Sound; Sound-Waves; Pitch 212—214 
Structure of the Ear 215—218 
ORGANS OF VOICE. 
Voice-Box; Voice-Cords 219—220 
The Mouth ; Care of the Voice 221—222 
THE EYE AND LIGHT. 
Parts Outside; Surface of Eyeball 228—227 
Eyeball, its Membranes 228—230 
Pupil; Iris; Interior of the Eyeball 231—233 
Lens; Camera Obscura; Opera Glasses 234—236 
Short-Sight; Long-Sight 237—238 
Self-Luminous Objects; Rays of Light . 239—241 
Shadows; Reflection; Diffusion 242—245 
Looking Glass; Refraction. 246—247 
Projection and Duration of Impressions 248—250 
Use of Two Eyes; Stereoscope 251—252 
MAGNETISM. 
Magnets; Induction; Magnetic Needle. 253—255 
North and South-Magnetism.. 256 
ELECTRICITY. 
Amber, Attraction, Repulsion ' 257—259 
Conductors and Insulators; Electropborus 260—261 
Two Electricities ; Induction; Electric Phenomena 262—264 
Lightning ; Thunder; Lightning Conductor 265—267 CONTENTS. 
GALVANISM. 
Telegraph Wires; an Electric Cell 268—269 
Electric Currents ; Electro-Magnetism... 270—272 
The Electro-Magnetic Telegraph 273 
Appearance and Distribution of Nerves... 274—275 
Nerves and Blood Vessels ; Nervous Elements 276—277 
The Brain; the Spinal Cord 278—280 
Sensory and Motory Nerves 281—282 
The Seat of Feeling; Sensations 288—284 
The Sympathetic System; Reflex Actions; Instincts... 285—286 
Brain and Mind ; Mental Health 287—288 
Sleep; Rest; Exercise 289—290 
THE NERVOUS SYSTEM. 
ALCOHOL. 
Effects Generally; Bones; Muscles 291—298 
Arteries; Heart; Blood; Digestion... 294—297 
Respiration ; Kidneys ; the Nervous System 298—300 
TOBACCO. 
Nicotine; Respiration 301—302 
Stomach; Blood. 303—304 METHODICAL TREATMENT OF INTRODUCTORY 
LESSONS. 
It will now be shown how to teach in accordance with the 
methods recommended in this book. 
Tl. USE OP THERMOMETER. The teacher places on a suit- 
able table an alcohol lamp, a tripod, a piece of wire netting, a flask, 
and a thermometer. 
Teacher (holding up a flask ). “ What is this ? ” 
Pupil. “That is a glass bottle.” 
T. “Is it such a bottle as you have at home ? ” 
P. “It is a bottle made of thin glass.” 
T. “We call it a flask. What is this ( holding up the lamp )? ” 
P. “That is an alcohol lamp.” 
T. “ What are the parts of an alcohol lamp ? ” (Teacher assists by 
holding up the separate parts. ) 
P. “The parts of an alcohol lamp are a glass vessel, a wick of cot- 
ton, a wick holder, a cap or cover, and alcohol.” 
T. “ What is this ? ” 
P. “ That is a three-legged iron stand, a tripod.” 
T. “This?” 
P. “That is a piece of wire netting.” 
T. “ What am I doing? ” 
P. “You pour water into the flask, you place the flask upon the wire 
netting, which rests upon the tripod, and put the alcohol lamp below.” 
T. “I want you to observe what happens when water is heated. 
You might have performed the same experiment in your kitchen. Why 
did I not use the same materials that are used there ? ” 
P. “We can see the water in a flask better than in a kettle. Glass 
is transparent, iron is not.” 
T. “That you may know how warm the water is, I will place this 
thermometer inside.” ( See figure. The thermometer is thrust through 
a flat piece of cork, which rests lightly on the neck of the bottle.) 
“What does the thermometer hanging there tell us ? ” 
P. “That thermometer tells us how warm the room is.” 
T. “ Does it tell how warm the wall, or the chair, or the floor is ? ” 
P. “It does not; it tells us how warm the air in the room is.” 
T. “ How do you know ?” 
P. “It is surrounded by air.” 
T. “What surrounds this thermometer ?” 
P. “ Water surrounds it.” 
T. “At least it surrounds the lower part where you find the sub- 
stance that indicates how warm anything is. When does a thermometer 
tell how warm the air is, and when does it tell how warm the water is?” 
P. “A thermometer tells how warm the air is when it is surrounded 
hy air; it tells how warm the water is when it is surrounded by water.” 
T. “You may say: A thermometer tells the temperature of the 
surrounding air, water, or other substances. By temperature we mean 
the degree of heat which a substance has.” 
“ Write the words ‘thermometer, temperature, degree’, on the black- 
board. Spell them.” 
While some of the pupils are engaged in writing and spelling these 
words, others are invited to come to the table and tell ho w many degrees 
the thermometer shows. Their attention is called to the fact that the 
eye must be at the same height as the top of the mercury in the thermo- 
meter is. The teacher must give plenty of time to the introductory 
exercises, in order that pupils may thoroughly understand how all the 
objects are used in combination. X 
INTRODUCTORY LESSONS. 
If 2. AIR IN WATER. The lamp is lighted. Pupils are invited 
to come to the table, one by one, notice the rise of temperature and make 
the result of their observation known to the class. 
T. “What change do you see in the water ?” 
P. “Bubbles appear atthe bottom and sides, and rise to the surface.” 
T. “Of what do the bubbles consist?” 
P. “Bubbles consist of air.” 
T. “What makes the bubbles appear ?” 
P. “ The heat does.” 
T. “Then what does the water contain ?” 
P. “Water contains air, and the heat drives the air out.” 
T. “Why does air rise in water, why does it not sink there ?” 
P. “ Air is lighter than water; water is heavier than air.” 
T. “Suppose there were no air in water, how would that affect the 
fishes ?” 
P. “They would die if there were no air in water.” 
T. “Which contains more air, cold or warm water?” 
P. “Cold water contains more air than warm water, because heat 
drives the air out.” 
T. “Let somebody at home give you a cup of boiling water and 
place it where it will cool off. You will then have water like this, which 
I have prepared for you. How does it taste ?” 
P. “It tastes flat.” 
T. “What gives a fresh taste to water.” 
P. “Air does.” 
T. “See what a great quantity of air is driven out. How many 
degrees does the thermometer show ?” 
13. VAPOR. 
T. “ What is this ?” (pointing to the upper part of the bottle.) 
P. “ That is moisture.” 
T. “Is moisture air or water ?” 
P. “ Moisture is water.” 
T. “Prom what place did this moisture come ?” 
P. “This moisture came from the water below.” 
T. “Did the water run up there ?” 
P. “It cannot run up ; water always runs down.” 
T. “ But how came it up there ?” 
P. “It came up with the air.” 
T. “ Can you see it coming up with the air ?” 
P. “We can not.” 
T. “ What substance in this room cannot be seen ?’’ 
P. “Air cannot be seen.” 
T. “ What do we call substances which cannot be seen ?” # 
P. “Substances that cannot be seen are called invisible.” 
T. “As, for instance, what substance ?” 
P. “ Air is invisible. ’ ’ 
T. “ What substance came up with the air ?” 
P. “ Water came up with the air.” 
T. “As you cannot see this water, what kind of water must it be ?” 
P. “It must be invisible water.” 
T. “We call this invisible water vapor.” 
T. “Now, I want you to be very quiet, and listen to the water. 
What do you hear?” 
P. “The water grows noisy; it is singing.” 
T. “ And what do you see ?” 
P. “There are bubbles at the bottom of the bottle, which do not 
come to the surface, but disappear.” 
T. “You see the air rising to the surface in a great many small 
bubbles, which look almost like dust or smoke, but the large bubbles at 
the bottom look different. These bubbles cannot be air. What are they?” 
P. “ They consist of steam.” 
T. “ Where is the water warmer, near the bottom, or near the sur- 
face ?” 
P. “The water is warmer near the bottom.” 
T. “Why?” 
P. “ Because it is nearer the fire.” 
T. “ Where must the first steam bubbles appear ?” 
14. SINGING WATER. INTRODUCTORY LESSONS. 
P. “ Near the bottom.” 
T. “Into what water do the steam bubbles come when they rise?” 
P. “ They come into colder water.” 
T. “And” the colder water changes the steam back to water. Where 
does the steam appear, and where does it disappear?” 
P. “The steam appears near the bottom, in the warmer water, and 
disappears near the surface, in the colder water.” 
T. “Where does the water change into steam, and where does the 
steam change into water?” 
P. “Near the bottom the water changes into steam; near the 
surface the steam changes into water,” 
T. “So the steam appears below, and disappears above. There is a 
conflict between the warm water below and the cold water above; the 
warm water will change into steam, and the cold water will not; there- 
fore the noise. 
I want you to watch the warm water in your kitchen, and tell me 
next time whether you heard it singing.” 
T. “Now the steam bubbles grow larger, they rise higher, and the 
singing becomes louder. How warm is the water now ? 
After some time, the steam rises to the surface, and there are billows 
and waves. Now the whole mass of water is hot enough to change into 
steam, and you tell me that the thermometer shows 212 degrees. 
We will leave it boiling, and after some time you may again notice 
how warm it is. It is always 212 degrees. It remains at 212 degrees as 
long as the water boils. 
212 degrees is the temperature of boiling water. We call this tem- 
perature the boiling point of water. How is boiling water affected when 
the heat of the fire is increased?” 
15. BOILING POINT. 
16. VAPOR IN BREATH. 
T. “Does the air in this room contain vapor?” 
P. “It does.” 
T. “ How do yon know ?” 
P. “We know it, because we breathe it out.” 
T. “If somebody should say that we do not breathe out vapor, how 
could you prove that we do ? Can you show the water breathed out by 
you?” 
P. “Yes, we can; when we breathe into our hands, we feel the 
moisture, and this moisture was contained in our breath.” 
T. “How can you quickly show the moisture in your breath to the 
whole class ?” 
P. “By breathing' against the blackboard.” 
T. “One cold day in winter I heard a boy say that he had seen 
horses smoking. He said the smoke camefrom the nostrils of the horses. 
What did he mean?” 
P. “ The horses breathed out vapor, and the vapor changed to fog— 
not smoke—in the cold air.” 
T. “Correct. You see the fog escaping from the nostrils of horses, 
from your own nostrils, and from those of other animals during winter. 
In what countries might a person detect the presence of large animals by 
the fog they breathe out ?” 
P. “In cold countries.” 
T. “ As, for instance, in King Williams Land. There the Esquimaux 
are able to detect the presence of reindeer at a distance of six miles. 
They see a cloud rising at a distance, a little cloud in the clear and cold 
atmosphere, and presently they know that this cloud arises from a herd 
of reindeer. Some Esquimaux are able to distinguish reindeer and musk- 
oxen by the fog or cloud rising from them, and this cloud enables them 
to pursue the path of the animals without looking at their tracks. 
What other large animal, living in the ocean, is detected by the water 
and fog thrown out ?” 
P. “The whale.” 
T. “High up on the mast of a whaling vessel, in a place called the 
crows-nest, is a sailor always watching for the little fountain of water 
and fog arising from the head of a whale. As soon as he sees this, he 
calls “spout!” boats are made ready, and the hunting commences in 
earnest. Thus the reindeer, the musk-ox, and the whale are detected by 
their breath.” ERRATA. 
Page 1, *T 2, line 7, read retains for may contain ; 
“ 3, “ 12, “ 1, “ retains for may contain; 
“ 4, “ 15, “ 3, “ it for is; 
• “ 8, “ 26, “ 5, “ river water for rain water; 
“ 8, “ 27, “12, “ remains for remain; 
“ 16, “ 47, last line, insert “the” between “of” and “cold”; 
“ 20, “ 55, line 5, omit “a” between “what” and “large”; 
“ 25, “ 67, “ 11, read globes for tubes; 
“ 87, “ 91, “ 10, “ than for then; 
“ 43, “104, “ 10, omit the question; 
“ 71, “161,. “ 9, read exclusively for conclusively; 
“ 113, “ 235, last line, read 'pictures for picures. ELEMENTARY SCIENCE AND PHYSIOLOGY. 
CHAPTER I 
WATER. 
Section I. 
VAPOR, STEAM, FOG. 
1. USE OF THE THERMOMETER. A Thermometer shows 
the temperature of the surrounding air, water and other sub- 
stances. 
a thermometer kept in the room. It may 
tell us that the air has a temperature of 60 
or 70 degrees. The degree of heat in the 
air is called its temperature. 
The temperature of water is the num- 
ber of degrees which a thermometer shows 
when placed in it. 
2. AIR IN WATER. Describe Fig. 
1. What change do you see in the water 
after the lamp is lighted ? What causes 
the bubbles to appear ? Of what do the 
bubbles consist ? 
WATER contains air. Heat drives 
out the air (expels it). Cold water may 
If we wish to know how warm the air in a room is, we look at 
contain more air than warm water. Cold water containing no 
air tastes flat or insipid. 
Fig. 1. 
3. VAPOR. When the water is heated, the upper part of the 
flask grows wet, or is covered with moisture. Whence does this 
moisture come ? Can you see it coming up ? Where was it before 
it settled on the flask ? 2 
WATER 
YAPOR is invisible water forming part of the air. 
A bottle half filled with water contains vapor in the other half. 
This vapor cannot be seen. 
4. SINGHNG WATER. Where do the first steam bubbles 
appear ? Why ? Where do they disappear ? Why ? Into what 
does the water near the bottom change? Into what does the steam 
change when it comes near the surface ? 
Water produces a singing noise when the lower portions are 
warm enough to change into steam and the upper portions are 
not. 
5. BOILINH POINT. When the heating is continued, the 
steam-bubbles grow larger and rise higher. At last they rise to the 
surface, and there are billows and waves. 
212 degrees is the temperature of boiling water. This tem- 
perature is called the boiling point of water. 
The temperature of boiling water does not change. If we 
increase the heat, the water will boil more vigorously and change 
into steam more rapidly. 
6. OUR BREATH. How can you prove that the air in this 
room contains vapor ? One cold day in winter a boy said that he 
had seen horses smoking. What did he mean ? 
In winter you see fog passing from your nostrils and from those 
of horses, dogs and other animals. 
In King Williams Land the Esquimaux are able to detect the 
presence of reindeer at a distance of six miles. When they see a 
cloud rising at a distance, a little cloud in a clear and cold atmo- 
sphere, they know that it rises from a herd of reindeer. 
What large animal living in the ocean is detected by the water 
and fog thrown out ? 
Our breath contains vapor. Some of this vapor changes into 
moisture when it touches a cold object and to fog when in cold 
air. 
7. STEAM. Fill a flask half with water and boil it. What 
is above the boiling water ? Is steam visible or invisible ? 
Steam and vapor are invisible and aeriform. 
Aeriform substances are substances having the form of air. VAPOR, STEAM, FOG. 
3 
8. STEAM AND FOG. What do you see above the opening 
of a bottle or kettle containing boiling water ? Does this fog remain 
visible ? What becomes of it ? What change do you observe in 
the fog that rises from the steam-escape of locomotives, steam- 
vessels or fire-engines ? or from the chimneys of houses in winter ? 
Steam changes into fog when it enters the atmosphere ; fog 
changes into vapor in clear air. 
9. STEAM AND YAPOR. What qualities are common to 
steam and vapor ? What difference is there between the two ? 
Steam rises from boiling water; vapor rises from water 
not boiling. 
Steam and vapor are essentially the same, both being aeriform 
water. Steam is hot, vapor is cold. Vapor is the aeriform water 
that forms part of the atmosphere. 
10. FOG. Sometimes fog collects in enormous masses, fills 
the air as far as we can see, and surrounds us everywhere. It 
gathers in the meadows as if great masses of smoke were collected. 
At what times of the day do you see the greatest amount of fog ? 
At what times during the year ? 
Fog appears when the air grows colder and disappears 
when it grows warmer. 
11. MOISTURE. Bring a cold, dry glass into a warm room. 
What change do you observe? Whence did the moisture come? 
What causes vapor to change into moisture ? What parts of your 
sleeping room are covered with moisture early in the morning? 
Explain. 
Moisture appears on cold objects and disappears when 
they grow warm. 
12. YAPOR AND AIR. Warm air may contain more vapor 
than cold air. 
We seldom see fog when the air is very warm because the heat 
changes the fog into vapor, and warm air may contain a great 
amount of vapor. 
13. FOG AND CLOUDS. To learn the relation between 
fog and clouds, we should observe the atmosphere in mountainous 
countries or hear what is said about them by persons who have 4 
WATER 
gone up in a balloon. The moment a rising balloon seems to 
disappear in a cloud, the persons in it find themselves surrounded 
by fog. 
A cloud consists of fog high up in the air. Fog is a cloud 
near the surface of the earth. 
14. RAIN. As long as the particles of fog are few and small, 
they float in the air as dust does—the slightest wind carries them 
along. But when they increase in size and number, and there is 
not much wind, they will meet, form drops, and fall. 
Rain is caused by increased fogginess. 
Section 11. 
THE CIRCULATION OF WATER. 
15. SOLUTIONS. Prepare a clear solution of salt-water and 
ask a school-mate of yours what it is. If he is thoughtless or 
ignorant, he will call is water, because he cannot see the salt. What 
must he do to ascertain the nature of the liquid ? What is a liquid 
called in which something is dissolved ? Sugar, salt, saltpeter, alum, 
slaked lime, potash, green vitriol and blue vitriol are some of the 
substances that dissolve in water. Most of these solutions can not 
be distinguished by their looks, but may be, by their taste. 
A solution of a white substance is transparent, that of a 
blue substance, bluish. 
16. TO DISSOLVE AND TO MELT. Name substances that 
melt. What is needed to melt a substance? What is needed to 
dissolve a substance ? Does sugar dissolve or melt in coffee ? 
To dissolve means to unite with a liquid; to melt means to 
become liquid by heat. 
17. SATURATION. What will take place if we take too 
much blue vitriol, or too much salt? We may help the substance 
dissolve by shaking or stirring the water, but at last we must give 
it up, as the water becomes completely tilled with the substance. 
A liquid is saturated with a substance when it can not 
dissolve any more of it. CIRCULATION OF WATER. 
5 
18. EVAPORATION. How can I change a glass of water to 
vapor (not to steam) before school closes to-day? Instead of 
“change to vapor” we may use the word “evaporate.” Where 
does water evaporate more quickly—in an open bottle or on the 
floor? In what kind of weather does the washing dry quickly? 
When do wet sidewalks dry quickly? Name three causes of quick 
evaporation. 
Water evaporates quickly, when it has a great surface, 
when it is exposed to wind, or when the air is warm and dry. 
For the next lesson you may prepare solutions of salt, alum, 
and blue vitriol, put them in flat dishes, and keep them open in a 
moderately warm place. We will see what becomes of them. 
19. CRYSTALLIZATION. What do you see in the three 
dishes in which we had the solutions of salt, alum and blue vitriol? 
Compare the little regular bodies with each other. Would you 
recognize the little bodies of salt and alum, if they were brought 
to you from another place? Look at the table salt, which was 
obtained from the grocery. Do you recognize the form of the 
little bodies which we obtained by evaporation? 
Crystals are the regular forms that substances tend to assume 
when changing into solids. Crystallization is the process by 
which a substance assumes the form of crystals. 
The more slowly crystallization proceeds, the larger will the 
crystals become. Druggists sometimes exhibit beautiful large 
crystals of colored salts. Large 
mineral collections also contain a 
variety of fine crystals, such as 
rock crystal, topaz, ruby, emerald, 
sapphire, amethyst, diamond, etc. 
In winter you may see beautiful 
crystals in many places. They 
cover the windows; they fall from 
the sky; they hang on boughs and 
branches, and form pretty cover- 
ings on exposed metal. Rivers and 
lakes are even full of them. If 
you measure the angles formed by 
Fig. 2. 
SNOW CRYSTALS. 
the lines of these crystals, you will find them to be of the same size 6 
WATER. 
always; they never show a right angle, only such angles as occur 
in a regular hexagon and a regular triangle. 
20. DISTILLATION. Distillation is the process of sepa- 
rating a liquid from substances held in solution, by changing 
the liquid into steam and the steam into a liquid. 
The glass vessel a is called a retort; the glass vessel b, a receiver. 
The water in ais changed into steam. The steam passing into bis 
Fig-. 3. 
cooled off by means of cold water and changes back into water. 
Water thus obtained is called distilled water. Shorten the defini- 
tion of distillation by using the words evaporation (change of a 
liquid to steam or vapor) and condensation (change of steamer 
vapor to a liquid). 
21. DISTILLED WATER is used by druggists in the pre- 
paration of medicines, which are often solutions of certain sub- 
stances. Why do not the druggists use common water, such as we 
get from a river or lake? What makes this water impure? 
Distilled water contains no substances in solution; drinking 
water usually does. 
22, RAIN-WATER. Compare the appearance of rain-water 
with that of our drinking water. What makes it impure? How 
can we purify it ? May druggists substitute filtered rain-water for 
distilled water? Why is it that rain-water is free from dissolved 
substances, while the water of rivers and lakes is not? CIRCULATION OF WATER. 
7 
Rain-water is condensed vapor; distilled water is condensed 
steam. 
23. SPRINGS. What becomes of the rain-water that falls 
upon the surface of the earth? Does it remain in the ground? 
Where are there the greater number of springs, in level or in hilly 
places ? Are they in low places or in high places ? 
Springs are streams of water issuing from the ground. 
How does spring-water taste? Some spring-water is called 
hard water j it contains lime, gypsum, and other substances. 
Where did these substances enter the water? 
24. WELLS. Describe a well that you have seen. On what 
does it depend whether the well-water contains dissolved substances 
or not? Many times it has happened that persons have been 
poisoned by drinking well-water, though no one had purposely 
thrown poison into the well. Many fatal cases of typhoid fever 
are occasioned in this way. How this may happen the accomp- 
anying figure, which represents facts, will tell. Describe it. 
Fig. 4. 
The lesson to be learned from this picture is, that every dairy 
furnishing milk for sale, ought, by law, to be under sanitary 8 
WATER 
inspection. Not long ago a well was found in a cemetery, in close 
proximity to the ground in which dead bodies were deposited. 
The water in wells in the neighborhood of decaying animal 
substances is poisonous. 
25. RIYERS AND LAKES. What becomes of the water of 
springs ? Whence does all the water of rivers and lakes come ? 
At what times are the rivers low ? When do rivers overflow ? 
All the water of rivers and lakes descends from the atmo- 
sphere. 
26. SUBSTANCES DISSOLVED IN RIYER-WATER. Sup 
pose there is a great quantity of salt not far below the surface. 
What kind of river-water may you expect in the neighborhood ? 
Give a similar instance. 
Salt, lime, and other substances dissolved in rain-water are 
obtained from the soil through which the water soaks before it 
enters the river. 
27. CIRCULATION OP WATER. What becomes of all the 
substances held in solution by the water of springs and rivers ? Do 
they ever leave the ocean again? Does the water (without the 
dissolved substances) ever leave the oceans again? What be- 
comes of the vapor that rises from the surface of the oceans? 
The vapor in the atmosphere changes into water, which 
descends to the earth. This forms springs, brooks, streams, and 
rivers, that And their way to the ocean. The water of the ocean 
evaporates and returns to the atmosphere. Thus water is in con- 
tinuous circulation. 
Nearly the whole of the substances (lime, salt, etc.) that the 
river-water carries into the ocean remain there. A small quantity 
of salt is taken out by men, but a much greater quantity of lime is 
taken up by such animals as corals, shell-fish, and minute beings 
whose skeletons build up great masses of chalk. But all this is little 
compared with the enormous quantity of dissolved substances 
remaining. About of the whole watery mass that fills the ocean 
consists of substances held in solution. THE VALUE OF FORESTS. 
9 
Section 111. 
THE VALUE OF FORESTS. 
28. FORESTS AND RAIN. What changes occur in coun- 
tries in which the amount of rain becomes less from year to year ? 
How does this affect farmers ? How the inhabitants of cities? 
Countries with few forests have hut little rain. 
In former years the forests of Spain, Greece, France, Palestine, 
Egypt, Switzerland, and other countries covered more ground than 
they do now. The disappearance of forests was accompanied by 
the disappearance of rain. The greater the forests that were de- 
stroyed, the greater were the droughts in the countries thus made 
bare. Some states in the Union are having this experience. 
29. THE SOIL. It is not difficult to see why the amount of 
rain must depend upon the extent of forests. You have been in 
forests in summer—in the months of July and August. How did 
you find the ground, as compared with that of open fields ? What 
is the cause of this difference ? What covers the soil of forests ? 
Is the soil itself the same as that of open fields ? 
The soil in forests retains much water; in open fields it does 
not. 
The soil in forests consists of loose, porous earth, covered 
with fallen leaves, moss, and decaying wood, and is moist the year 
round. The soil of open fields is not protected from the heat of the 
sun; the water evaporates quickly. In the month of July, the for- 
est soil was found to contain to the depth of three feet 3| times 
as much water as that of open fields. 
80. THE RIVERS. Where does the water run off more 
rapidly, in forests or in open fields ? In what season do springs 
and brooks carry the greatest amount of water ? In what countries 
do rivers overflow in spring, in those where the forests are exten- 
sive, or in those where they are scarce? 
In countries having few forests the rivers overflow in spring 
and the open fields suffer from droughts in summer. 
After a heavy rain the water of open fields reaches the rivers 
in a very little while. The highest water-mark of the Seine in 
France is at present thirty feet above the lowest, while in former 
centuries there was hardly any difference between the two. The 10 
HEAT 
Ohio sometimes becomes so high that hundreds of people lose their 
property or their lives. 
81. FORMATION OF CLOUDS. The water contained in 
the soil of forests enters the roots of the trees and ascends the 
trunks and branches to the leaves, where it evaporates. The 
vapor rising from forests forms clouds. 
Without forests, rivers overflow and rains become scarce. With 
forests, rivers keep their height the year round, and there is sufficient 
rain to make the crops grow. 
This is not the only benefit forests confer. They equalize the 
temperature; they protect the country from excessive heat; they 
break the power of hurricanes and cyclones, and protect the valleys 
of mountainous countries from avalanches and earth-slides. 
CHAPTER 11. 
HEAT. 
Section I. 
RADIATION. 
32. HOW ROOMS ARE HEATED. The amount of heat 
varies at different times and places. Sometimes a place is warm, 
sometimes it is cold. This room was colder last night than it is now. 
Whence did the heat come into this room? 
We are sitting at different distances from the stove. Do all 
of us receive the same amount of heat? How do we protect our- 
selves from too much heat? How do ladies walking in the sunshine 
protect themselves from the light and heat of the sun? What 
similarity is there between a parasol and a screen ? 
Rooms receive heat from the stove and from the sun. 
33. RAYS OF HEAT. How does the sun heat the room? 
What are those brilliant lines sent by the sun called ? How do the 
rays sent by the stove differ from the rays sent by the sun ? 
Rays of heat are straight lines in which the heat mores. 
The rays of the sun contain heat and light; those of the stove 
contain heat only. RADIATION. 
11 
34. HEAT OF OBJECTS. Objects are distinguished as hot, 
warm, or cold. What objects are called hot? What, warm? What, 
cold? Sometimes one person calls a room cold, while another at 
the same time pronounces it to be very warm. How is this differ- 
ence of opinion caused? What is the real difference between a 
warm and a cold body ? May a cold object become colder ? What 
does an object lose when it becomes colder ? 
All objects have beat, because all objects may become colder. 
They become colder by losing beat. Hot objects bave much 
beat; warm objects, some; cold objects, little. 
There is onty the difference of more and less among hot, warm, 
and cold objects. It is about the same as the difference between 
great and small things. Both possess size or volume, the one much, 
the other little. 
35. EXCHANGE OF RAYS. We have learned that stoves 
send out rays of heat. At what times do they send them out ? 
Is it probable that they do this at all times? May they grow 
colder at all times ? There is no reason to doubt that stoves, like all 
other objects, throw out rays of heat at all times. Our own bodies 
throw out rays of heat. Perhaps you have felt the heat given out 
by persons near you. or have seen how the ice on a window7-pane is 
affected by a finger or hand in its neighborhood. 
All objects throw out rays of beat. A hot object throws 
ont more beat than a warm object; a warm object more than a 
cold object. All objects receive rays of beat. 
The more rays an object throws out, the colder it grows. The 
more rays an object receives, the warmer it grows. If an object 
receives more rays of heat than it throws out, it grows warmer ; if 
it receives fewTer rays of heat than it throws out, it grows colder. 
To radiate is to throw out rays; to absorb is to take up rays. 
Radiation is the process of radiating; absorption is the process of 
absorbing. 
36. REFLECTION OF RAYS. Hold a piece of glass before 
the face, and go near a fire. What do you observe? Why is your 
face not struck by the radiated heat of the fire? Feel the glass. Is 
it very warm? Did the glass take in (absorb) all the rays? 
Some of the rays falling on objects are absorbed; some are 
reflected. 12 
HEAT 
To reflect is to throw back. Rays of heat are reflected from 
glass as marbles rebound when thrown against a wall. 
37. INFLUENCE OF CLOUDS. Does our earth radiate heat 
or does it keep all the heat that it receives from the sun ? Where 
do the rays radiated by the earth go? How is the earth affected by 
the radiation of heat? At what times of the day is the cold resulting 
from radiation felt most? Why? 
Sometimes we have clear nights, sometimes cloudy nights. 
Which are generally colder? What have the clouds to do with the 
rays of heat sent forth from the ground below? 
Clouds reflect the heat radiated by the earth. 
88. DEW AND FROST. What do we sometimes notice 
early in the morning, when we look at the grass and other plants? 
At what times does the dew cover plants and other objects, when 
the air is clear or when it is cloudy? When do plants lose more 
heat, in clear air or in cloudy air? At what times is the air surround- 
ing the plants colder, when the sky is clear or when it is full of 
clouds? Which air is unable to hold much moisture, the cold or 
the warm? 
Grass, leaves, wooden sidewalks, and iron railings radiate a 
great deal of heat during clear nights. The air surrounding 
them grows cold and is unahle to hold much vapor. The vapor 
thrown out (ejected) by the air condenses and covers the objects 
in the form of dew or frost. 
Grass directly under benches or tables is not usually covered 
with dew; the lower surface of the benches and tables has reflected 
the rays of heat. There is no dew or frost when the sky is cloudy. 
When does dew change to frost? 
Dew is beneficial to the growth of plants, as it comes when 
the weather is clear and rain is scarce. There are countries, for 
instance, those west of the Andes in South America, where vegeta- 
tion would not exist if it were not for the dew. Name those 
countries. 
39. INSULAR AND CONTINENTAL CLIMATE. There is 
a great difference between the climate of islands and that of regions 
far from oceans, as, for instance, England and the North Central 
Plain of America. Where is the air generally clearer ? What sub- 
stance impairs the clearness of the air ? Where does the greater 
number of fogs occur? EXPANSION. 
13 
Countries in which the air is usually clear have a changeable 
climate ; countries in which the air is usually full of vapor and 
fog, have a temperate climate, without extremes of heat or cold. 
The former climate is called continental, the latter, insular. 
The rays of the sun do not freely penetrate the moist air of 
islands ; they cannot heat the ground excessively, and the summers 
are moderately warm. The rays of the earth cannot pass freely 
beyond the air ; the ground does not cool off excessively, and the 
winters are mild. 
In countries having a dry, clear atmosphere, the heat of the sun 
is not checked, the ground becomes immoderately warm and the 
summers are torrid. The heat of the earth radiates without much 
obstruction, the ground cools off excessively, and the winters are 
very cold. 
In some parts of Australia, where the air is excessively dry, the 
daily range of temperature is sometimes from 70 to 80 degrees. 
In the desert of Sahara, where “the ground is fire and the wind is 
flame” the nights are often cold enough to cause a thin sheet of ice 
to form on the surface of water. 
Section 11. 
EXPANSION. 
40. IRON. 
Examine the 
effect of heat 
upon an iron 
ball just large 
enough to slip 
through a metal 
ring. (See Fig. 
5.) Heat the ball 
over the flame of 
an alcohol lamp. 
What effect has 
the heat upon 
the iron ? Let 
cold water run 
over the ball. 
How is it chang- 
ed ? 
Fig 5. 14 
HEAT 
Iron is expanded by heat and contracted by cold. 
In what season are things made of iron large? In what, small? 
How are nails in stone walls affected by heat and cold? 
41. SOLIDS. Not only iron, but also copper, silver, lead, 
gold, platinum, and all other metals are expanded by heat, and 
contracted by cold. What is the cause of the cracks or fissures 
sometimes seen in the ice of skating rinks and rivers ? 
All solid substances expand while growing warmer and con- 
tract while growing colder. 
A thick piece of glass held over a flame cracks because the 
heat does not readily pass through the glass, and the lower surface 
expands while the upper does not. A thin piece of glass held over 
a flame does not crack, because the upper surface has nearly the 
same temperature as the lower. 
42. LIQUIDS. Connect a glass tube by means of a perfor- 
ated cork with the neck of a flask completely filled with water. (See 
Fig. 6.) Mark the height at which the water stands, 
and heat the flask over an alcohol lamp. What do you 
observe ? Surround the flask with very cold water. 
What do you expect to see now ? State how the water 
is changed by different temperatures. 
Liquid substances expand when their tempera- 
ture rises and contract when it falls. 
Use the word “volume,” which means “the 
size of the occupied space ” in expressing the same 
law. Suppose you buy alcohol by the gallon ; when 
do you get more, in winter or in summer, and why ? 
Fig. 6. 
48. AIR. Heat a flask filled with air over the flame of an 
alcohol lamp. Can you see whether the air expands? Why not? 
Once you noticed bubbles of air escaping from the water. Where 
was that? What must you do, if you want to see the escape of air 
from the flask? 
Air expands considerably more than either solids or fluids. 
The expansion of air may easily be proved with an empty 
flask. If its opening is kept in water and the flask heated, bubbles EXPANSION. 
15 
will be found to escape from it. What happens if the lamp is taken 
away and the flask remains in its place? 
Why does wood make a crackling noise after it becomes 
heated? What makes chestnuts jump off the pan, when they are 
roasted ? 
44. THE THERMOMETER. What three parts has a ther- 
mometer? Describe the glass-tube. What fluids are used? What 
causes the fluid to rise or to fall ? AThy must there be a globe or 
bulb at the lower end of the tube? Why is the upper end of the 
tube closed? 
A thermometer consists of a glass tube, a fluid, and a scale. 
The tube has the same width throughout, is closed at the upper 
end, and is connected with a globe at the lower. The fluid is 
usually mercury. The scale consists of a series of numbers. 
Sometimes colored alcohol is used instead of mercury. 
45. THE SCALE. Suppose you have a thermometer whose 
scale is lost. How could you restore it with the help of another? 
How many times would you have to compare the two thermometers 
and mark the height of the mercury in the incomplete one? 
But suppose you could not get hold of another thermometer, or 
were, like Robinson Crusoe, on a desolate island with a thermo- 
meter whose scale was lost. What would you do to prepare a new 
scale? 
You have learned that water under certain conditions always 
shows the same temperature ; so you can mark one point of the 
scale and you need but one other definite temperature in order to 
get the whole scale. This is the temperature of melting snow or 
ice. 
The scale lias two definite points, the freezing point and the 
boiling point. The freezing point is the temperature of freezing- 
water or melting ice. It is marked 82 degrees. The boiling point 
is the temperature of boiling water. It is marked 212 degrees. 
One degree is rJa of the difference between the temperatures of 
boiling water and melting snow. 16 
HEAT 
Section 111. 
CONVECTION. 
46. CONVECTION IN AIR. What is repre- 
sented by Fig. 7 ? How can you make such a piece of 
paper revolve on its axis ? Is there a difference in the 
motion of the paper, when blown at from above or 
from below? Hold the paper above a heated stove or 
a warm pipe. Explain the motion. How does the 
heat cause the air to rise ? What takes the place of 
the air rising from the stove? Show this in a drawing. 
Convection is the transmission of heat by means 
of currents. The air above a hot stove (or steam- 
pipe) rises, because the heat expands it and makes it 
lighter than the surrounding air. It ascends to the ceiling, 
where it spreads, cools off, and descends to the stove. 
The air in heated rooms is in constant motion. There are 
upward currents of warm air and downward currents of cold air. 
Describe how a furnace heats rooms. 
Fig. 7. 
47. WINDS. Open the door of your room slightly and place 
a lighted candle in the opening, first near the bottom, then near the 
top and lastly in the middle. What 
do you notice? What pushes the 
flame in different directions ? 
Where do you feel the draughts 
when a door leading to a cold hall 
is opened, at the head or at the 
feet ? 
Wind is air in motion. An 
open connection between a cold 
space and a warm space produces 
a cold current entering the lower 
part of the warm space, and a 
warm current entering the upper 
part of cold space. 
Fig. 8. CONDUCTION. 
17 
48. CONVECTION IN WATER. Put saw- 
dust or indigo into a tiask filled with water and 
heat the water by means of an alcohol lamp. 
What do you observe? (See Fig. 9.) What 
causes the water to 
move in this way ? 
What is accomplished 
by this motion? Fill 
a test tube with water 
and hold its upper part 
in the flame of an alco- 
hol lamp. (See Fig. 10.) 
Water heated from 
below shows convec- 
tion ; water heated 
from above does not. 
Fig. 9 
Fig. 10. 
Section IY. 
CONDUCTION. 
49. PROTECTION FROM COLD. As winters are quite 
severe in the northern part of the United States, the people use 
various means to protect themselves and their property from the 
cold. Name some of these means of protection. Name substances 
we use to keep things warm. Which of these substances are 
warmer than their surroundings? Describe how a hot-bed is made 
and how it works. Does the manure used in a hot-bed change 
while it is warm? Does fuel change while it heats? Does fur 
change while it keeps our bodies warm? 
Suppose you feel both surfaces of a fur coat worn by a person 
in winter. Is the outer surface just as warm as the inner? What 
makes the inner surface of the coat warm? Does the fur coat pro- 
duce heat like fuel, which burns, or manure, which 'crumbles to 
pieces? If it does not produce heat, how can it keep us warm? 
To keep things warm we use fuel, clothes, fur, straw, 
manure, etc. 
Burning fuel and decaying manure keep their surroundings 
warm, because they are warmer than those; they produce heat. 
Fur, clothes and straw are not warmer than their surroundings; 18 
HEAT 
they do not produce heat. The former change while they produce 
heat; the latter do not change while they keep things warm. 
50. MAMMALS. What animals yield the best fur ? In 
what climate do these animals live? What benefit do they derive 
from their fur? Of what does fur consist? 
Animals having hair in the skin are called mammals. Our 
blood, and that of all other mammals, has a temperature of about 
99 degrees. If, from any cause the temperature rises or falls a few 
degrees, disease or death is the consequence. What is the disease 
when the blood becomes too warm? When it becomes too cold? If 
we had no means of protecting ourselves from the cold we should 
die. Is the same true of all animals living in the Frigid Zone? 
Can any mammal that is not very well protected from the cold live 
in the Frigid Zone? Is the whale a mammal or a fish, and why? 
How is it protected from the coldness of the surrounding water? 
Mammals are warm-blooded animals having hair in the skin. 
Their blood has a temperature of about 1)9 degrees. They are 
protected from the cold by fur or fat, or both. 
Seals, otters, beavers, foxes, bears, reindeer, musk-oxen and 
other mammals living in a cold climate yield the best fur. 
51. BIRDS. What birds live in cold climates? What is the 
difference between mammals and birds? How are geese, ducks, and 
gulls protected? How penguins and auks? Does the great amount 
of fat in the bodies of the latter prevent them from flying? How 
do their wings look? 
Birds are warm-blooded animals covered with feathers. 
Their blood has a temperature of 100 to 104 degrees. They are 
protected from the cold by feathers or fat, or by both. 
52. OTHER ANIMALS. All animals need protection from 
cold and die when their blood grows colder than water changing 
to ice. 
Reptiles and amphibians protect themselves by burrowing into 
the earth or mud. Fish are protected by the ice at the surface. 
Flies live in warm rooms or hide in cow-sheds and stables, between 
straw and manure; fallen leaves in the woods protect beetles, 
spiders, centipedes, wood-lice, caterpillars and others; earth worms 
go deep below the surface; mosquitoes hide in mud; bees crowd CONDUCTION. 
19 
together and the heat of their bodies is generally sufficient to keep 
the temperature in the hive at about 80 degrees. 
58. CONDUCTORS. Poor conductors are those substances 
which do not allow the heat to pass through them; good con- 
ductors are those which allow the heat to pass. 
Fur, hair, feathers, fat, straw, wool, cotton, linen, wood, glass 
and paper are poor conductors ; metals are good conductors. 
Water is a poor conductor, because it may be heated at one place 
and remain cold at another (see TT 48). Airis a poor conductor, 
and may be used to protect us from the cold. (Notice this in the case 
of double windows, doors or walls, and air between our clothes.) 
Suppose we put a piece of ice into a feather bed, or wrap a 
woolen sheet about it. Will it melt or remain solid, and why ? 
CHAPTER 111. 
DIGESTION. 
Section I. 
INTRODUCTION. 
54. OUR WEIGHT. Why must we eat and drink ? What 
would be the consequence if we should not eat or drink for a week 
or a fortnight ? What do you call such a death ? How does a 
starved person look ? How does a person change in appearance 
when he does not eat or drink for three days ? ’ How does his 
weight change during that time ? In what way could he regain his 
weight ? 
The weight of a person increases during his meals and de- 
creases in the times between his meals. 
The loss of weight is caused by loss of substance. The body 
is constantly losing some of its substance. 20 
DIGESTION. 
55. WHY THE WEIGHT OF THE BODY CHANGES. Sin ce 
the loss of substance is continuous, it must be caused by some 
continuous action or movement of the body. Try to find this 
movement. Sit quietly, do not speak or think of anything else, but 
observe attentively what a large part of your body is moving. Try 
to stop these movements. Do not breathe for five minutes. Can 
you do it ? Do you breathe while you are asleep ? Are there any 
persons who can stop breathing for an hour or so ? 
We have now learned two facts: first, we continually lose 
some of the substance of our bodies ; second, we are continually 
breathing. The coincidence of these two facts suggests the thought 
that they belong together, that the loss of substance is caused by 
breathing. 
What two opposite actions do you perform while you are 
breathing ? Is the air taken in the same as that breathed out ? 
We lose weight because we breathe out more air than we 
breathe in. We must eat and drink to make up for the loss of 
substance caused by breathing. 
It follows that our food changes to the substance that we lose 
by breathing—changes to air. This is a wonderful, nevertheless 
true fact; most (not all) of the food we eat and drink is Anally 
changed into air. 
56. THE COURSE OF THE FOOD. The first place to 
which the food is taken is the mouth. From here it moves to the 
stomach, then enters the intestines, and from the intestines is 
sent through the whole body till it Anally changes to the air that 
we breathe out. 
Our work will be to follow the food in its course, learn what 
changes it undergoes everywhere, by what means the changes are 
made and how we may help or hinder the changes. The knowl- 
edge of all this is useful, because it teaches us how to remain 
healthy. Ignorant persons become the victims of humbugs and 
quacks. 
57. ORGANS. The tongue, the teeth, and the stomach are 
organs. Name the organs of plants. Animals and plants have 
organs, while stones have not. Stones consist of parts, but these 
parts are not called organs. THE TEETH. 
21 
Organs are parts that perform functions. Animals and 
plants are organisms or organized beings, while stones are 
Inorganic substances. 
Functions are actions peculiar to organs. Name the functions 
of some organs of animals and plants. It is a very interesting and 
important work to investigate the functions. 
58. THE MOUTH. The parts of the month are the lips 
(upper and lower), cheeks (right and left), teeth (upper and 
lower), jaws (upper and lower), tongue, palate. 
The lips are at the entrance of the mouth—one above, one 
below ; the cheeks are at its sides; the jaws are the bones covered 
by the soft parts of the mouth; the teeth are partly in the jaws, 
partly above or below them; the tongue is in the middle of the 
mouth; the palate is at its upper end. For what are these organs 
used, or what actions are assisted by them? 
Section 11. 
THE TEETH. 
59. KINDS. Examine a collection of human teeth.* How do 
they look and feel ? Are they all of the same form ? How many 
have a single root and how many have more than one root ? How 
Fig. 11 c. 
Fig. 11 a. 
Fig. 11 b. 
many have a cutting edge, and how many are pointed at both ends? 
Into how many classes may we separate the thirty-two teeth 
properly, and how many belong to each class ? 
A full-grown person who lias lost none of his teeth, usually 
has thirty-two of them—eight cutting teeth (incisors), four eye 
* A collection of teeth may be obtained from an obliging dentist. 22 
DIGESTION. 
teeth (canines), and twenty grinding teeth (premolars and 
molars). 
The cutting teeth have single roots and sharp cutting crowns ; 
the eye teeth have single roots and pointed crowns; the grinding 
teeth have more than one root and round crowns. 
60. USE. Why would it not he just as well, if all our teeth 
were of the same size and form ? What work have they to perform 
when, for instance, you eat an apple ? Are these two actions 
performed by the same teeth ? What is the use of the eye teeth ? 
Let us compare our teeth with instruments used for similar 
purposes. Biting is similar to cutting. What instruments are used 
for cutting ? Are our cutting teeth similar to knives or scissors, 
and why ? Close and open your mouth several times and observe 
how the cutting teeth move. Do the grinding teeth move in a 
similar way, when you open and close your mouth ? How do the 
grinding teeth move when you chew ? What tools or instruments 
move in the same way ? 
The cutting teeth are used to cut off pieces of food—they 
resemble a pair of scissors; the eye teeth are used to fasten them- 
selves into pieces of food—they resemble nails; the grinders are 
used to grind the food—they resemble mill-stones. 
Rabbits, squirrels, and other gnawing animals have large 
cutting-teeth, which they use for gnawing; cats and other flesh- 
eating animals have large eye-teeth, which they use for tearing; 
cows, sheep and other hoofed animals have large grinders, which 
they use for crushing and grinding. 
61. PARTS. Each tooth has a root, a neck, and a crown. 
The root is in the jaw-bone; the neck is covered by the gum; 
the crown projects into the mouth. 
02. SUBSTANCES. Look at the surface of the parts of a 
tooth. Touch them. Is there a difference? Try to cut them with 
a knife. The smooth, shiny, hard substance of the crown is called 
enamel. The dull and less resistant substance of the root and 
neck is bony and called cement. 
Enamel is the hardest of all the substances in our body, so 
hard that it will strike a spark with steel. Try it. THE TEETH. 
23 
The accompanying figure shows a 
longitudinal section of a cutting tooth. 
Describe it. The white substance that 
forms the largest part of the tooth (o') is 
called dentine or ivory. By what is it 
covered? The cavity of a dead tooth is 
empty; in a living tooth it is filled with 
a soft pulp, full of blood-vessels and 
nerves. Examine the end of the root- 
What do you notice? Why must there 
be au opening? 
Each tooth is composed of enamel, 
cement, dentine, and pulp, the latter 
consisting of blood-vessels and nerves. 
The enamel is the covering of the 
crown; the cement is the covering of the 
root and neck; the dentine is below 
the surface of the tooth. The blood- 
vessels and nerves enter the tooth through 
a small opening at the end of the root. 
63. CAUSE OF HOLLOW TEETH. 
What have your parents told you about 
the treatment of your teeth ? Why is it 
necessary to clean them twice a day? 
Fig. 12. 
What makes the teeth unclean? Sometimes when cleaning your 
teeth you find little pieces of meat or other food between them. 
How do these pieces smell? This putrid smell it caused by deca}r. 
The pieces of food have changed, have become sour and coiTosive, 
and in this state dissolve that part of the tooth with which they are 
in contact. 
To find out the effect of a sour substance upon teeth, put a 
tooth into vinegar. When it has been there for two days, you can 
easily scratch off some of the enamel with your pocket knife. In 
a week it will become as soft as lime-stone. 
I knew a little girl one of whose upper cutting teeth had a 
little cavity in the middle of the cutting edge. This was not caused 
by remnants of food, but by biting thread. We learn from this 
instance that it is not well to bite hard substances; cracking nuts 
may seriously injure the teeth. 24 
DIGESTION. 
Teeth not properly cleaned become hollow; cutting teeth and 
eye teeth become hollow at the sides, grinders, at the sides and 
on the grinding surfaces. 
Children who visit a dentist twice or three times a year, will 
very seldom, if ever, have toothache ; neither need they have a tooth 
pulled nor will they have bad teeth. The teeth may be injured 
otherwise, nevertheless out of a hundred hollow teeth, eighty have 
become hollow from insufficient cleaning. 
CHANGES OF FOOD. 
Section 111. 
64. SALIVA. Which is better, to eat quickly or slowly? 
Why ? What is there in the mouth that mixes with whatever we 
chew ? 
Once, when I was very hungry, a person near me took out a 
sweet, juicy orange, peeled it, and deliberately put one piece after 
another into his mouth. He did not offer me any of it, although I 
expected him to do so. Now, something remarkable took place in 
my mouth. What was it? We learn from this that our mouths 
fill with saliva at particular times, or on particular occasions ; that 
there is not a constant, even flow of saliva, but that it comes when- 
ever we think we need it. 
When food is eaten or chewed, the mouth tills with saliva. 
Saliva mixes with the food and thus enables us to swallow dry 
food. 
65. STARCH.* Saliva is necessary for the digestion of 
bread or anything containing starch. Starch is an important 
article of food ; it is contained in nearly all plants. 
Rice, wheat, Indian corn, and rye contain a great amount of 
starch, more than half of their weight; buckwheat, pea- and bean- 
meal about two-fifths of their weight; potatoes about one-third. 
* How to obtain starch. Scrape a potato, mix the pulp with water, 
and squeeze it through a piece of clean linen cloth. Let the liquid that 
passes through the cloth stand in the glass till a white powder has 
settled. Pour the water oft' and dry the sediment. It is starch. How 
does it look ? Touch it with your fingers and rub them against each 
other. How do they feel ? 
Any kind of flour will yield starch when mixed with water and 
treated in the same way as the pulp of potatoes. Beans, pease, and 
seeds of similar plants, after having been soaked in water for several 
days, may be crushed or pounded in a mortar to a fine pulp and then 
made to give up their starch. CHANGES OF FOOD, 
25 
When you consider that all kinds of bread and all root crops 
contain starch, you will call starch an almost indispensable article 
of food. It is for the digestion of this substance that saliva is 
necessary. 
66. CHANGE OF STARCH. Does starch dissolve in water ? 
It is necessary that food be dissolved, in order to be digested. 
Whatever is to be digested must be liquid; changes do not take 
place as long as a substance is solid. We can not even taste a 
substance when it is solid. Try it. Wipe your tongue dry and put 
a piece of loaf sugar on it. What do you observe ? 
The change of starch into a soluble substance is accomplished 
by saliva. 
Starch surrounded hy saliva changes into sugar. 
67. SALIVARY GLANDS. Saliva is made (or secreted) 
by organs called salivary glands. Two of them are placed in 
front of and a little below the ears; others lie between the halves 
of the lower jaw-bone. 
Salivary glands re- 
semble grapes in their 
structure. They consist 
of numerous little globes, 
each of them at the end 
of a little tube. The 
walls of the tubes contain 
blood-vessels. The sa- 
liva is drawn from the 
blood and fills the globes; 
from there it is sent into 
the little tubes. The little 
tubes connect with larger 
Fig. 13. 
tubes, and the last and largest of them sends the saliva into the 
mouth. What parts of the grapes correspond to the tubes? 
A BRANCH OF A SALIVARY GLAND. 
68. THE FOOD-PIPE. Through what tube does the food 
pass when it moves from the mouth to the stomach? Is the large 
tube whose hard walls we feel in the front of our neck, the food- 
pipe? Which of the two tubes is nearer to the mouth? Where is 
the upper opening of the wind-pipe? The back part of the mouth 26 
DIGESTION. 
is a spacious cavity into which several tubes or other cavities open. 
It is called the throat (pharynx). Name these tubes and cavities. 
One day some one at our dinner table told a funny stoiy, which 
made every one laugh. Suddenly my neighbor was seized with a 
coughing fit. When he had recovered from it, he said that some- 
thing had “gone the wrong way,” and that he had to send it the 
right way by coughing. What did he mean? 
The act of swallowing, or the process of sending food or drink 
into the stomach, is quite complicated and must not be disturbed. 
While we swallow, the opening of the wind pipe is closed by a 
cover or lid (the epiglottis), the nasal cavities, by a fleshy mem- 
brane (the soft palate,) and the opening between the throat and 
mouth, by all the soft surrounding parts. The only way food can 
go now, is into the food-pipe. 
Examine the food-pipe of a calf, pig, or sheep. Is it a wide open 
channel, like the wind-pipe, or is it a narrow passage? Of what 
Fig. 14. 
do the walls consist? The flesh (muscles) of this tube pushes the 
morsels of food along, toward the stomach. 
What animals swallow food while their heads are near the 
ground, lower than the stomach ? What can you learn from this 
fact? Then it must also be possible to push the food the other 
way from the stomach to the mouth. What animals do this 
regularly ? 
The food-pipe ( oesophagus) is a narrow, fleshy tube, 
through which the morsels of food are pushed toward the 
stomach. It is located close behind the wind-pipe. 
Fig. 15. CHANGES OF FOOD. 
27 
69. THE TRUNK contains two cavities, the chest and the 
abdomen. They are separated by the midriff (diaphragm.) The 
chest is the cavity above the midriff: the abdomen is the cavity 
belowr the midriff. 
The diaphragm is stretched across the trunk. It has the form 
of an inverted wash-basin. Where is the uppermost part of the 
diaphragm? Where is the lowest? In which of the two cavities is 
the food-pipe. 
70. THE STOMACH is a somewhat conical or oval bag 
placed transversely in the upper part of the abdominal cavity. 
Its widest part is at the left side. It has two openings, one 
through which the food enters, and one through which it passes 
out. 
The opening on the left side is connected with the food-pipe 
the opening at the 
right side with the 
intestines. The “pit 
of the stomach” is 
a slight depression 
in the skin over the 
lower end of the 
breast bone, direct- 
ly in front of the 
stomach. 
71. THE FOOD. When food enters the stomach, the open- 
ing at the right side is closed and remains closed for more than 
an hour. This is necessary that the food may be changed in the 
stomach. 
Substances may be changed in three different ways : they may 
be reduced to smaller pieces; they may be dissolved; they may be 
affected by heat. Is all this done with the food in our body ? 
Fig. 16. 
72. THE THREE COATS OF THE STOMACH. When the 
stomach is empty, the inner surface is pale and slightly mqist, but 
on the entrance of food it becomes very red, and over all the surface 
the gastric juice, a clear, sour, and colorless liquid, trickles out like 
sweat on the skin of a perspiring person. At the same time the 
walls of the stomach commence to move in and out. Why ? 28 
DIGESTION. 
The stomach has three coats, or layers: an outer coat, a 
middle coat, and an inner coat. The outer coat is smooth and 
moist, in order that friction with neighboring organs may be 
prevented; the middle coat consists of muscles, by which the 
movements of the stomach are performed; the inner coat lies in 
little ridges, or folds, and contains the gastric glands, which 
secrete the gastric juice. 
The outer coat is called the serous coat; the middle, the 
muscular coat; the inner, the mucous coat. 
73. PROTEIDS.* Gastric juice dissolves the substances, 
called proteids or albuminous substances. There are four kinds 
of proteids : albumen, gluten, fibrine, and casein. 
Albumen is found in the white of eggs, gluten in flour, fibrine in 
meat and blood, casein in cheese and milk. 
74. THE INTESTINES consist of a tube having a length 
of about twenty-five feet in an adult person. They are sep- 
arated into the small and large intestines. The former, which 
commence at the end of the stomach, are about twenty feet long, 
and an inch and a half wide ; the latter arc about five feet long 
and two or three times as wide as the small intestines. (See 
Fig. 17 on next page). 
The length of the intestines shows that an important part of 
the work of digestion is reserved for them ; other liquids, secreted 
by the liver, the pancreas, and numerous small glands situated in 
the walls of the intestines, are poured upon the food as soon as 
it leaves the stomach. 
75. THE LITER is an abdominal organ lying near the 
diaphragm, at the right side of the body. It is large and of a 
reddish-brown color. It consists of a substance softer than meat. 
All animals with bones (vertebrate animals) have a liver. The 
human liver weighs from three to four pounds and contains num- 
erous blood-vessels. 
* How to obtain albumen and gluten. Rub raw potatoes on a 
grater, so as to get a line pulp, inclose the pulp in a piece of linen, place 
it in water and squeeze it. Pour the turbid water in a glass, let the 
starch settle at the bottom, and heat the clear upper water in a test 
tube, The albumen coagulates in the form of loose, flaky particles of 
grayish color. 
Mix a spoonful of wheat flour with enough water to make a thick 
dough, enclose the dough in a piece of linen, place it in water, and squeeze 
or knead it. Continue the squeezing or kneading till the water, which 
you may renew several times, no longer appears milky (from starch). 
The substance remaining in the linen is gluten. CHANGES OF FOOD 
29 
76. THE GALL-BLAD- 
DER is a pear-shaped hag 
fastened to the under side of 
the liver; it contains the bile, 
or gall, a dark-greenish 
liquid of bitter taste. 
Bile is the secretion of the 
liver. It accumulates in the 
gall-bladder and is emptied 
into the small intestines when 
food enters them. From 
what substance of the body is 
the bile secreted? Why are 
there numerous blood-vessels 
in the liver? 
77, THE PANCREAS or 
sweet-bread is an elongated, 
sott organ, about as large 
as a hand. It is situated 
close behind the stomach, 
and secretes the pancreatic 
juice, a watery looking liquid. 
Fig. 17. 
The pancreatic juice, together with the bile, is emptied into 
the small intestines, at a place about two inches from the end of 
the stomach. (See Fig. 16, i.) 
78. INTESTINAL DIGESTION. When the food leaves the 
stomach, it consists of a soft, half digested mass, called chyme. 
Bile, pancreatic juice, and intestinal juice now begin their work 
and complete the changes. Any particles of starch or of albumi- 
nous substances that have escaped the action of saliva and gastric 
juice, are finally digested. Fat and oily substances are prepared 
for absorption. The latter are acted upon in a double way; a small 
part of the fat is changed into a kind of soap, which is easily dis- 
solved and the remainder is separated into very minute particles, 
which float in the liquid contents of the intestines. 
The result of the combined action of all the digestive juices is 
a liquid of a creamy color, called chyle. 30 
DIGESTION. 
Bile, pancreatic juice, ami intestinal juice are mixed with 
the soft, half digested mass of food that enters the intestines. 
The mass of food contained in the stomach is called chyme; that 
contained in the small intestines is called chyle. 
79. CHANGE OF FOOD INTO BLOOD. It is necessary for 
the food to become liquid (to liquefy) 
in the organs of digestion. Why? The 
liquefied food is taken up (absorbed) by 
narrow tubes. Where do they begin ? 
Do they begin at the inner or outer sur- 
face of the intestines? Get a piece of 
the small intestines of an animal (a sheep 
or calf) and open it lengthwise, that you 
may examine the inner surface. After 
having opened the piece with a pair of 
scissors, gently move it through water, 
so as to remove all particles of chyle. 
Then keep a small piece floating and 
notice the tassels (villi.) The tassels are 
thread-like or hair-like appendages which 
contain the beginnings of the tubes that 
receive the liquid food. You can not see 
the liquid tubes because they are too 
small, but Fig. 18 shows how they look 
when sufficiently magnified. 
Fig. 18. 
a. lining membrane built 
of cells; b, small blood- 
vessel; d, narrow tube 
absorbing chyle. 
The chyle is taken up (absorbed) by 
milk tubes* located in the tassels of the 
intestines. The milk tubes unite into wider tubes and these 
finally empty into one of the blood vessels, where the chyle 
undergoes further changes, and is soon converted into blood. 
The contents of the milk tubes are white and milky looking. 
What parts of plants resemble the vessels and milk-tubes of the 
body—take up liquid food and carry it along? What is the name 
of the fluid that moves in plants? What fluids in plants and 
animals have the same functions, resemble each other, and why? 
*Milk tubes, or lacteals, from a latin word (lac) meaning milk. 
These and other terms are omitted in the text, because children do not 
easily remember them, frequently confuse them with other scientific terms, 
and because they do not necessarily help the understanding of the pro- 
cesses of digestion and assimilation. HYGIENE OF DIGESTION. 
31 
We may notice this important distinction between most animals and 
plants ; the former have the tubes which absorb the food inside of 
their bodies, while the latter have the absorbing organs (cells) 
outside. Plants must therefore be stationary, while animals may 
move from place to place. 
Section IY. 
HYGIENE OF DIGESTION. 
80. DISORDERS. What changes did you notice in your 
condition, when your digestive organs were out of order? What 
caused these disorders? What ought you to learn from these 
experiences? 
Nearly all disorders of our digestive organs are caused by 
some imprudence of our own. 
If we eat too much, or eat of food that does not agree with us, 
have too much candy or pie, or too many figs, or rich cakes, etc., 
we are made sick. 
81. CHEWING. Suppose you bolt lumps of bread; why 
may that be a cause of disorder? Or you swallow big pieces of 
meat; why is that hurtful? Upon what part of a piece of bread or 
meat do saliva or gastric juice act ? Upon what part do they 
not act? Which has a greater surface one whole piece or the 
same piece cut into several pieces ? How is your food usually 
reduced to small pieces ? 
Name some articles of food that are reduced to small pieces 
before they are eaten. Is it better to have this grinding and chopp- 
ing done outside of the mouth, or inside? Is anything wanting, if 
the chewing of the food is done away with? 
What food should not be eaten without chewing? What food 
might, without much loss? How will it affect our health, if the 
teeth are unfit to chew the food, or if we have lost them, so that 
wre are obliged to eat soft substances only? Is there a way to avoid 
these evil consequences? What benefits are derived from a set of 
artificial teeth ? 
The food must be sufficiently chewed ; otherwise it will not 
be well digested. 32 
DIGESTION. 
The digestive fluids act only upon the surfaces of solid food ; 
the saliva does not penetrate through lumps of bread which are 
bolted (swallowed without having been chewed); the gastric juice 
does not reach the interior of large pieces of meat. 
82. EATINGI TOO MUCH causes an unnatural enlargement 
of the stomach. 
We should not continue to eat when we feel that we have had 
enough. If we do so, we feel uncomfortable, and lose strength. 
If we do it often, the enlargement of the stomach becomes perman- 
ent, and we lose not only the power to tell how much food we 
need, but also, in time, may become the prey of dyspepsia, which, 
in many cases, begins with an unnaturally enlarged stomach. 
88. THE INTERVAL between meals should be at least 
three hours. 
A ring of muscle at the outlet of the stomach prevents the 
passage of food before it is fit to enter the intestines. About an 
hour after a meal this muscular ring commences to relax a little and 
allows portions of the food to pass. It then closes again, opens in 
another half hour, and thus continues, till in three or three and a 
half hours the stomach is empty. 
81. NOURISHING! FOOD. You mentioned that you had 
eaten food that did not agree with you, such as rich cakes, hot 
bread, a great quantity of raisins, figs, candy, ice-cream, etc. It is 
true that experience will in time teach us what to avoid and what 
to use ; but in most cases this experience is bought at too great an 
expense. It is better to know beforehand the consequences of 
eating improper food. For this purpose we shall have to study the 
various articles of food systematically, to learn whether they are 
valuable or not. 
Nourishing food is food that is nutritious aud digestible. 
Nutritious food is food containing a great number of substances 
that the body needs. Digestible food is food that is easily dissolved 
in the stomach and easily prepared to enter the blood. VEGETABLE FOOD. 
33 
Section Y. 
VEGETABLE FOOD. 
85. BREAD. Wheat is the most nourishing food. It 
contains from ten to fifteen per cent, of gluten, from sixty to 
seventy per cent, of starchy substances, a small quantity of fat, 
and useful minerals. Rye, rice, Indian-corn, and other grains 
are not quite so nourishing as wheat. 
Wheat ranks first among all vegetable food-stuffs; it is highly 
nutritious and easily digestible. With the exception of milk, there 
is no single article of food that approaches more closely an ideal, or 
normal, diet than wheat. Bread is made from wheat or other grains. 
Valuable as wheat is, it may be the means of weakening the 
stomach, if prepared or used improperly. It is improperly prepared 
if, in the form of dough, it is mixed with too much fat or too much 
sugar, as in fried cakes, tarts, or sweetmeats; it is improperly used as 
bread, if it is eaten either too fresh or too old, or if taken in too 
great quantities. 
Bread fresh from the oven frequently forms big lumps in the 
stomach, which are almost impenetrable to the digestive fluids, and 
may, therefore, cause serious consequences, particularly to per- 
sons with a weakened stomach. Old bread is unwholesome when 
it is moldy; the mold may cause dysenterjr or dyspepsia. 
8(5. VEGETABLES are built up of cells containing starch, 
albuminous substances, and other materials. The walls of the 
cells must be crushed and the cells opened to give up their con- 
tents. 
Cells are found in all the parts of plants ; they constitute the 
elements (the building-stones) of all plant-structures. Every part 
Fig. 19. 
CELLS OF PLANTS 
Fig. 20. 34 
DIGESTION. 
of a plant is built up of cells. What difference do you see in the 
walls of the various cells represented ? Which substances are more 
easily digested those made up of cells with thick walls, or those 
made up of cells with thin walls? Give the reason why. What do 
we do to open the cells ? How do we assist the work of the teeth ? 
When vegetables are boiled, the cell walls are affected in two 
ways. Name them. 
87. SUBAR is a healthful, nutritious, and easily digestible 
substance, particularly when forming a part of other dishes. 
Persons eating too much sugar have bad teeth, and become weak- 
ened in health. 
Put sugared water or a sweet juice in a warm place for a few 
days. What change will occur? How do the remnants of sweet 
substances change in the mouth? How do sour substances affect 
the teeth? 
If the stomach is overloaded with sugar, as in persons who 
daily indulge in candy and other sweet substances, it will become 
diseased and the appetite for simpler, more wholesome food will 
lessen. 
Section YI. 
ANIMAL FOOD. 
88. ROAST BEEF is more digestible and nutritions than 
Boiled beef as usually prepared. The quality of beef depends, 
firstly, on the condition of the animal from which the meat is 
taken; secondly, on the piece obtained; thirdly, on the skill of 
the cook. 
In the selection and preparation of beef we should be guided 
by the following rules: 
1. Good, healthy beef is of a pale, reddish color, feels firm, 
and hardly moistens the touching finger; diseased beef is soft and 
slimy. 
2. Beef of a deep purple color is taken from an animal not 
killed by man, but by disease. 
8. A marbled appearance, caused by interspersed fat, is found 
in beef obtained from well fattened cattle; it is healthy and nutri- 
tious. 
4. Fat of healthy cattle is white and hard; fat of diseased 
beef is yellow, Avatery, or gelatinous. ANIMAL FOOD., 
35 
5. Good beef has little odor; diseased beef has a rank smell. 
6. Before roasting or boiling beef or any other kind of meat, 
do not wash it, because water removes good juices from near the 
surface—it is sufficient to wipe it with a clean linen cloth. 
How long a roast should be on the fire depends on its size. 
Thus pieces of tender beefsteak should remain on the fire but a 
few minutes, while roasts weighing from ten to fifteen pounds 
should be on the fire till a crust is formed, which may take from 
ten to fifteen minutes, and after this be kept in an oven for about 
three hours. The inside of the roast should remain red and con- 
tain blood. If the roast is overdone, it is hard, tasteless, and indi- 
gestible. 
89. SALTING AND SMOKING. Salt beef and salt pork 
have less nutritive value than roast beef or pork, and are less 
digestible. Smoking makes the fibres hard and dry. 
The brine in which meat is salted extracts most of the valuable 
juices. Smoked beef can be well digested by a healthy stomach. 
90. RAW MEAT is less digestible than roasted meat, and 
may be the means of bringing parasites into the body. 
Parasites are animals living in or upon the body of others 
—feeding on the substance of the animals they inhabit. 
The most frequent parasites introduced by raw meat 
are the tape-worm and the trichina. 
Tape-worms are introduced by beef and pork, 
mostly by pork. The pig is sometimes infested by a 
small animal called the tailed bladder worm. Its body 
consists of a small head, a short neck, and a trunk 
formed of a yellowish-white bladder filled with a fluid 
Fig. 21. 
Bladder 
worm. 
substance. If the head of 
this worm be introduced 
into the human stomach, 
it will soon lodge a tape- 
worm. 
The tape-worm in- 
habits the intestines. Its 
head, which is quite simi- 
lar to that of the bladder 
worm, fastens itself, by 
means of a tiny ring of 
hard, strong hooks, to 
Fig. 22. 
Tape-worm. 36 
DIGESTION. 
some place on the soft inner surface of the intestines. Its body 
consists of hundreds of joints, the last of which contain numerous 
eggs. They detach themselves and are ejected from the body with 
the waste products of digestion. 
The tape-worm, though troublesome, and disturbing the health 
of persons infested by it, seldom causes serious consequences. 
The trichina, however, is dangerous, and has frequently 
caused death. It is dangerous for two reasons; first, because the 
parasite is so small and transparent that it can be detected only 
with the microscope ; and secondly, because it is usually intro- 
duced in great numbers, which further increase in the human body. 
Figure 23 represents the 
parasite as seen in pork. 
Describe its appearance. 
The pouch, or bag, consists 
of a membrane containing 
lime. If introduced into 
the stomach, the sour gas- 
tric juice dissolves the mem- 
brane, and the parasite is 
set free. It now feeds on 
the contents of the stomach 
and intestines, and soon 
brings forth about 300 living 
young, which are carried by 
the blood to every part of the body. They finally lodge in the 
muscles, where they form coils like those represented in figure 23. 
Fig. 23. Trichinae. 
A few days after eating meat infested by trichinae a person is 
annoyed by slight disturbances of the digestive organs, such as 
catarrh and diarrhoea. At this time the trichinae may be ejected 
by purgatives. But if the young have commenced to wander, 
nothing can be done except to uphold and strengthen the vital 
powers of the patient, who suffers intense pain in various parts of 
the body and, in many cases, dies of paralysis of the muscles of 
inspiration. 
How may we protect ourselves from this danger? We should 
avoid eating pork that is not thoroughly cooked. The intense 
heat to which all parts of the pork are subjected, is the only sure 
method of destroying the trichinae. Roast pork that is still red ANIMAL FOOD. 
37 
inside, may contain living trichinae. Salting and smoking does not 
kill them—sausages made of smoked pork may contain them alive. 
91. MEAT GENERALLY. The flesh of mammals is more 
nutritive titan that of most birds. The flesh of flsh contains 
more water than that of mammals or birds, but is easily digested, 
and should not be left out of our diet. 
Yeal is not so nutritive as beef, but is more tender, and, when 
of good quality, more easily digested. Good mutton is nearly as 
good as beef, but harder to digest. Pork has less nutritive value 
than beef or mutton, and is harder to digest than either. The flesh 
of deer, rabbits, hares, and squirrels is less nutritive than beef or 
mutton, but more easily digested then these. The meat of chickens, 
turkeys, and pigeons is more easily digested than that of geese or 
ducks. Crabs and lobsters are not easily digested. Oysters are 
considered wholesome, and are most easily digested when eaten 
raw. 
92. EGJCJS. Can you give a reason why eggs must contain 
most or all of the substances that the bodies of animals contain ? 
Eggs are nutritious food, because they contain much albumen 
and fat. 
In what condition are eggs most easily digested ? It is not 
advisable to eat hard boiled eggs. The white is almost indigestible, 
though the yolk offers no difficulty in this state. 
93. MILK. In what respect do eggs and milk re- 
semble each other ? 
Milk contains albumen (casein), sugar, fat (butter), 
salts, and water. For children it is the healthiest, 
cheapest, and most suitable food. 
Unfortunately milk is often adulterated ; the cream, 
which contains the wholesome fat, is skimmed, and the 
milk mixed with water, flour, rice-water, starch, or other 
substances. A fraudulent addition of water may be de- 
tected. 
Which fluid has a greater weight milk or water? 
In what does an object float better —in a heavy or in a 
light fluid ? In what fluid will an object sink deeper—in 
a heavy or in a light one ? If we mix milk with water, 
Fig. 24. 
Milk Tester, 38 
DIGESTION. 
does it become heavier or lighter, and will an object sink deeper or 
less deep in it than in pure milk ? 
A milk tester (lactometer) consists of a short, upright glass 
tube with a heavy globe attached to the lower end and a very 
narrow glass tube above. When using the instrument one must 
be careful in his judgment, because different cows give different 
milk and the weight of different kinds of milk is not always the 
same. But when the tester shows as much as one-third or one- 
fourth of water added, one may be sure it is an intentional mixture. 
94. FAT. How do persons look who are fond of eating fat, 
and how is their health ? Sometimes a physician tells parents to 
have their children take cod-liver oil daily. Why ? In what 
climate do persons eat great quantities of fat ? How do those 
persons look ? Do they suffer much 
from colds ? Is it healthful to eat 
fat ? 
You should make it a rule to eat 
some fat daily. You are doing so 
when you eat bread with butter, 
which is the most digestible of all 
fats. It is a fact that persons who 
eat and digest a sufficient quantity 
of fat very seldom suffer from cold, 
and are less liable to fall victims to 
the dreadful disease, consumption. 
What is the use of fat in our 
bodies ? At what place in em- 
bodies will the fat, as a protection 
from the cold outside, be of great- 
est use ? What effect has it upon 
the looks of persons ? 
A third use of fat is seen when, 
after a long sickness, in which most 
of the fat has disappeared, a person 
tries for the first time to stand on 
his feet. The weight of the body 
resting upon the soles produces 
pain. In a normal state, the fat 
cells between the skin and the inner 
part of the soles act like a number 
Fig. 25. 
Fat cells in loose connective 
tissue. ARTICLES OF RELISH. 
39 
of rubber balls, which, while being px-essed together, lessen the 
pressure of the body upon the sensitive parts of the skin. 
Suppose a person grows too fat; how can he rid himself of 
the superfluous quantity ? Nature does not allow an excess of 
wealth without punishing the offender. A person who is too fat is 
weak in manj7' respects and may easily sicken. 
The cause of this inconvenience is, sometimes, a hereditary 
disposition ; in other cases, it is the habit of eating too much and 
too rich food, and not exercising enough. Indulgence in alcoholic 
drinks is likewise a frequent cause of an unhealthy accumulation 
of fat. 
Persons foml of eating fat and able to digest it well, are 
strong and healthy. Fat protects ns from colds; it improves our 
looks; and it lessens the pressure of the body upon the sensitive 
parts of the skin. 
95. CHEESE contains casein, fat (butter), fatty acids, 
and salt. It is very nutritious, but exceedingly hard to digest. 
There are but few articles of food so hard to digest as cheese. 
A person with a weak stomach should avoid its use entirely. Dry 
cheese should he grated before being eaten. 
Section YII. 
ARTICLES OF RELISH. 
96. -SPICES AND CONDIMENTS. Name the spices and 
condiments. What do your parents tell you about the use of 
pepper, mustard, pickles,-vinegar, etc.? How do you feel if you 
take much of them ? Mustard is sometimes used as a poultice. 
What effect has it upon the skin ? What effect, therefore, must it 
have upon the inner, sensitive membrane of the stomach, if taken 
in great quantities ? 
Spices and condiments are injurious to health, if taken daily 
or in great quantities. A small quantity, just enough to give 
relish to other dishes, is sufficient to stimulate the digestive 
organs. 
Vinegar, in small quantities, may assist the work of the gastric 
juice in promoting the digestion of albuminoids. Pepper increases 
the flow of saliva and gastric juice in a marked degree. Mustard is 
a gentle stimulant, but none of these substances should be taken 40 
RESPIRATION AND COMBUSTION. 
every day. If that is done, their effect is lessened, and if, to 
produce the usual effect, their quantity is increased, various 
disturbances constipation, indigestion, dyspepsia —are the in- 
evitable consequences. Spices are to the digestive organs what the 
whip is to the horse ; the less you use the whip, the more sensitive 
is the horse ; the more you use it, the more callous and obdurate 
the horse becomes. 
97. TEA AND COFFEE are not articles of food; they are 
stimulants. Stimulants are substances that excite the organs, 
and increase their vigor and activity. 
What was mentioned in regard to spices is true of coffee and 
tea; they are beneficial when used in moderate quantities, but 
destructive to health, if used to excess. Both contain a deadly 
poison. Chocolate is similar to tea and coffee in its effect upon the 
system, but preferable to them on account of its high nutritive 
value. Coffee and tea, as generally prepared, contain no nourish- 
ing substances except the sugar and milk that aremdded. * 
CHAPTER IV. 
RESPIRATION AND COMBUSTION. 
Section I. 
PROPERTIES OF AIR. 
98. AIR SPREADS (expands) in every direction—it tries 
to till all the spaces it can reach. Air has. the quality of 
expansion. 
Air is found in all the places where we are; it comes and it 
goes out through every little opening; it is in the earth into which 
we dig; it finds its way into substances like a sponge or a powder; 
it surrounds the whole earth. The whole mass of air surrounding 
the earth is called the atmosphere. 
*An exposition of the dangerous effects of alcohol and tobacco will 
be found in 302-315. PROPERTIES OF AIR. 
41 
99. HEIGHT OF THE ATMOSPHERE. Is there a limit 
to this expansion? Does the air spread from the earth to the moon, 
and the sun, and the stars? Is the whole universe filled with air? 
What have you heard about the air on high mountains? 
It is believed that the air does not extend beyond the solid 
earth higher than one hundred miles. 
100. PRESSURE OF AIR. The air accompanies the earth 
in its course through space, just as we do ourselves, and as all 
objects found on the earth do. Air is attracted by the earth, as 
everything else is; it follows that it must press upon other bodies. 
Immerse a glass in water, turn it, and lift it, upside down, so 
that the bottom is above the surface. Why does the water not fall 
out? Put one end of a glass tube in water; can you take away the 
air in the glass tube and make the water rise ? 
What causes the water to rise? Fill a glass with 
water, cover it with a piece of paper, turn the glass 
upside down, and slowly remove your hand. Does 
the paper hold the water in its place by its own 
force? In what direction does the air press? Roll 
a piece of paper into the form of a tube, close one 
end by pressing the tube together, take the other 
end in your mouth, and exhaust the air. What 
happens? What is the cause of this motion ? 
Fig. 26. 
Air presses in all directions. 
101. WHY THE LOWER 
AIR IS DENSE. Suppose our 
room, or a very high hall, were 
tilled with loose cotton; would 
the upper cotton differ from the 
lower? Why? 
The lower air is denser 
than the upper, because it is 
pressed upon by the latter. 
The air near the surface of 
the earth is dense and heavy, 
while the air in the upper 
regions is rare and light. 
Fig. 27. 42 
RESPIRATION AND COMBUSTION. 
102. A PAIR OF BELLOWS consists of two boards of 
equal size, connected at their edges by a wide piece of leather. 
At one end there is a tube leading from the outside to the inside; 
at the opposite side there are two handles. 
There is, besides, a valve in one of the boards, 
but we will not consider the valve for the present. 
How is the inner space changed, if you separate the 
boards from each other ? How does that change 
the air inside ? Where is now the dense air, inside 
or outside ? What takes place if you push the 
boards towards each other ? How does that change 
the inner space ? The inner air ? What motion 
of the air is caused by the approach of the boards 
toward each other ? 
Fig. 28. 
Section 11. 
RESPIRATION 
103. THE CHEST. Place your two hands flat upon your 
chest, draw a breath, and forcibly breathe out again. A pupil may 
put the bellows before you with the tube pointing upwards, the 
movable board in front, and set it in motion. 
The chest acts like a pair of bellows. The windpipe corre- 
sponds to the tube of the bellows, the movable wall of the chest 
to the movable board of the bellows. 
When a person moves the front wall of the chest forward and 
upward, the space inside the chest grows larger, and the air 
contained there, thinner. The air outside has more pressure and 
forces its way in through the windpipe. 
When the front wall of the chest moves back, the space inside 
becomes smaller and the air contained there, denser. This dense 
air has more pressure than the air outside; it therefore forces its 
way out. 
104. BREATHING. Sit straight for a few moments and 
direct your attention to the act of breathing. Try to keep the 
front wall of the chest perfectly quiet; what other part of your 
body is moving instead ? You will understand what this part has 
to do with breathing, if you remember what you learned about the 
two cavities in the trunk. What is the name of the partition 
between the two cavities ? We can not feel the movements of the RESPIRATION. 
43 
midriff, as we can those of the front wall of the chest, but we must 
take it as a fact that the midriff moves down when the front wail 
of the abdomen moves forward. Why does it move in this way ? 
We can breathe in two ways; either by moving the front 
wall of the chest, or by moving the front wall of the abdomen. 
The latter movement is caused by the movement of the midriff 
(diaphragm). 
There is nowhere an empty space in the cavity of the abdomen. 
When the diaphragm moves down, it presses upon the soft organs 
contained in the abdomen, and these affect the movable front wall. 
105. LUNGS AND RUBBER BALLOONS. For this lesson 
we need a rubber balloon attached to a wooden 
tube. Blow air through the tube. What takes 
place? What takes place when you stop blow- 
ing? What widens the balloon? What causes 
the balloon to collapse ? What two forces change 
the form of the rubber balloon ? Suppose several 
of these rubber balloons were connected in such 
a way that the air could freely move from the 
inside of one balloon to that of any other; 
would the same two forces be able to make the 
same two changes ? 
Our lungs consist of a number of such bal- 
loons. It is true that their walls do not consist 
of rubber, but the substance of the walls has the 
essential quality of rubber elas- 
ticity. A great number of balloons 
with elastic walls, in fact, several 
millions of them, are connected in 
such a way that the air contained 
in one may freely pass to all the 
others. They are not nearly so 
large as a rubber balloon, but their 
size does not change their quality; 
they act exactly like a number of 
large balloons connected in the 
same way. 
Fig. 29. 
A rubber balloon is widened 
by the pressure of air and nar- 
rowed by the elasticity of the 
Fig. 30 
Air Cells of the Lungs. RESPIRATION AND COMBUSTION. 
rubber walls. Our lungs are composed of a great number of 
similar balloons, which are called air cells. Their walls consist 
of elastic tissue. 
Examine the lungs of a rabbit. You can not see the air cells, 
because they are very minute, but you can see them act. Blow 
into the windpipe. What change do you see in the lungs? Stop 
blowing. What change do you now see in the lungs ? What pro- 
duces these changes? • 
10G. COLOR OF THE LUNOS. The lungs of a rabbit are 
of a roseate color, which they take from the blood they contain. 
The lungs of human beings are of a darker color. 
The dark color of our lungs is due to dust, the great enemy of 
health, which we can not keep out of the- houses and streets 
of cities and towns. If you had lived in fresh air all your life, your 
lungs would be as beautiful as those of animals, and you would be 
free from many serious diseases. 
-107. STRUCTURE OF THE LUNGS. Our lungs are sep- 
arated into the right and left lung, each of which has several 
lobes. The two 
lungs are 
connected by 
the windpipe, 
which is first 
divided into 
two, then into 
many smaller 
branches. The 
sub-divisions of 
the windpipe 
are called bron- 
chi (singular; 
bronchus.) The 
windpipe and 
bronchi consist 
of cartilaginous 
rings, counect- 
Ed by membranous tissues. * 
Lungs and Heart. 
Pig. 31. 
* Do not study this lesson without having seen and touched the 
objects mentioned. COMBUSTION. 
45 
When you have an opportunity, compare the rings in the wind- 
pipe of a turkey or chicken with those of a rabbit or squirrel. 
Compare the structure of the lungs with that of a tree, or with that 
of a bunch of grapes. 
Section 111. 
COMBUSTION. 
108. A BURNING CANDLE. To learn more about the 
nature of air, we will examine it in connection with a burning 
candle. Place a short caudle upon the table, light it, and put a 
glass chimney over it. What 
happens ? What is the cause of 
the extinction ? It can not be 
that air is wanting, because 
there is air all around the light— 
the chimney is tilled with air. 
Why are the flames in lamps 
with chimneys not extinguished? 
Arrange your candle and chim- 
ney in such a way that the light 
will not be extinguished. 
A burning1 caudle needs a 
constant supply of fresh air. 
The fresh air enters the flame 
from below and from the sides; 
the hot air escapes upward. 
A candle or a lamp burns 
brightly when enclosed by a 
chimney, because then the hot, 
light air forms a column which moves quickly upward. The 
chimney of a stove or a fireplace acts in the same way. The 
greater the draft, the greater the amount of fresh air that reaches 
the burning substance, and the brighter the fire. 
Fig. 32. 
109. WATERY YAPOR IN THE AIR ESCAPING FROM 
FLAMES. Place a glass chimney over a light and closely observe 
whether it changes its appearance. What do you see ? What 
substance makes it dim ? Place a flask filled with cold water over a 
flame and watch its lower surface. What do you see ? 46 
RESPIRATION AND COMBUSTION. 
The air escaping from a flame contains watery vapor. 
A kettle shows big drops of water on its lower surface shortly 
after being placed on the fire. A chimney grows dim from moisture 
shortly after it is placed over a light. When the kettle or the 
chimney becomes hot, the moisture evaporates. 
110. CARBONIC ACID IN AIR ESCAPING! FROM 
FLAMES. We shall now try to find another substance in air escap- 
ing from flames, but it is somewhat difficult and you would 
probably never learn anything about it without being told. A 
hundred years ago or longer, it was not known to anyone that this 
substance is contained in air. 
The detection of it is difficult, because the substance resembles 
common air so closely that artificial means must be used to find a 
difference between the two. For this purpose we make use of a 
liquid called limewater.* Buy a small quantity of it at the drug- 
store and describe its appearance and taste. Its peculiar taste is 
called alkaline. It is produced by dissolving a small quantity of 
slaked lime in water. 
Pour some limewater into a wide-necked bottle, close the 
bottle, and shake it. Does the limewater change its appearance ? 
Pour the limewater out and hold the bottle upside down over a 
burning candle for about half a minute, pour a small quantity of 
limewater into the bottle, close it, and shake. Does it change its 
appearance now? Whence did the substance come that makes the 
limewater milky? 
The air escaping from a flame contains carbonic acid. Car- 
bonic acid is an aeriform, invisible substance, which is detected 
by limewater. 
111. AIR A MIXTURE OF OXYGEN AND NITROGEN. 
For this experiment we need a plate with water, a tumbler, and a 
piece of tissue-paper. Light the paper, throw it quickly into the 
tumbler, and place the tumbler upside down on the plate, in the 
water. What happens? With what was the glass filled before it 
was placed in the water? With what is it filled now? Measure the 
quantity of air and water in the tumbler. 
*How to make limewater; Throw a spoonful of slaked lime (the 
white substance that masons mix with sand to form mortar) into a 
bottle of water, shake well, and let it stand a few hours. When the 
upper water is clear, pour it off carefully. RESPIRATION AND COMBUSTION COMPARED. 
47 
Not taking into account a few bubbles that escaped through 
the effect of heat, we find that one fifth of the air disappeared while 
the paper burned. You learned some time ago that a burning, 
substance needs fresh air. This experiment teaches the same, and 
at the same time shows us that about one fifth of the air is used up 
by a burning substance. Does the remaining air support the 
burning of the substance ? 
Suppose I place some substance in the manger of a hungry 
horse, and I find that the horse eats but one fifth, though I know 
he is still hungry; what must I think about the nature of the sub- 
stance placed in the manger? Did it consist of equal parts or of 
unequal parts? Apply this to air. 
Air consists of two substances, one which supports com- 
bustion, and one which does not. The former is called oxygen, 
the latter, nitrogen. 100 measures of air contain 20.8 meas- 
ures of oxygen, and 79.2 measures of nitrogen. 
112. A REMARKABLE CHANGE. We have learned that a 
flame consumes oxygen and produces watery vapor and carbonic 
acid. Nitrogen is not changed while passing through the flame; 
it is neither consumed nor produced. Two questions must arise 
from these facts: 1. Where does the oxygen go? 2. Whence do 
the watery vapor and the carbonic acid come? Oxygen can not be 
destroyed, that is, changed to nothing ; vapor and carbonic acid 
can not be created, this is, arise from nothing. We should add 
another fact to be explained at the same time: the consumption of 
the candle itself. 
When a candle burns, the substance of the candle and the 
oxygen disappear, while carbonic acid and watery vapor appear. 
This shows that the substance of the candle and the oxygen 
CHANGE into carbonic acid and watery vapor. 
Section IV. 
RESPIRATION AND COMBUSTION 
COMPARED. 
113. TEMPERATURE. In studying the process of respira- 
tion more thoroughly, we may now make use of what we have 
learned. How warm is the air expired ? Hold the bulb of a 48 
RESPIRATION AND COMBUSTION. 
thermometer in the hollow of your hands and breathe against it. 
Where does the air increase its temperature ? 
The interior of our bodies has a temperature of about 100 
degrees, and the air we expire, or breathe out, is nearly as 
warm. 
114. VAPOR. What substance do you notice when you 
breathe into the hollow of your hands ? Which air will hold more 
vapor, warm or cold (see *[[ 13)? This tells very clearly which 
air contains more vapor, the inspired or the expired air. 
The air which we expire is usually saturated with vapor. 
115. CARBONIC ACID. You have learned how to detect 
carbonic acid; see whether or not the breath contains it. 
The air which we expire contains the same amount of 
nitrogen as the air which we inspire, but has lost a considerable 
quantity (4.782 percent.) of oxygen, and gained almost as 
much (4.85 per cent.) of carbonic acid. 
116. RESPIRATION AND COMBUSTION. What do our 
bodies lose through the process of respiration ? What other process 
produces heat, vapor, and carbonic acid ? Is the air which supports 
a flame the same as that which enters our bodies when we breathe ? 
The inspired air is identical with the air which moves toward 
a burning candle; the expired air is similar to the air which 
leaves a burning candle. 
This makes it probable that a process similar to the burning of 
a candle takes place in our own bodies. 
Section V. 
VENTILATION. 
117. CONFINED AIR. Recall the time when you were 
present at a lecture or an entertainment, when a large hall was 
crowded with several hundred people. How did you feel toward 
the end of the lecture or entertainment ? 
The air in a room occupied by persons loses oxygen, grows 
warmer, and takes up vapor and carbonic acid. Hot air filled 
with vapor and carbonic acid is unhealthful. VENTILATION. 
49 
Type-setters and printers, tailors and shoemakers, persons in 
factories, and others who live indoors almost constantly, look pale 
and are weak. “The air of closed rooms brings about the great- 
est part of human misery that is the result of disease.” 
118. FRESH AIR. What persons live in fresh air most of 
their time ? How do most of them look and how is their health ? 
What makes them strong, and what makes those living indoors, 
weak ? 
Fresh air is the chief preserver of good cheer and health; it 
lessens the danger of nearly all diseases. 
Farmers, hunters, sailors, and others who live in fresh air 
almost constantly look fresh and are strong. 
The effect of fresh air is very great indeed, greater than most 
persons think. Animals that live in fresh air all their lives, are 
seldom sick; but if we house them or imprison them in cages, they 
are attacked by numerous diseases, just as we are. 
The mere desire to breathe fresh air is not sufficient; the 
fulfillment of this wish is difficult and requires knowledge and 
energy. We must first learn what makes the air impure, secondly, 
what impurities are the most dangerous, and thirdly, what are the 
best means of purifying the air. 
119. VAPOR. What do we call air containing much vapor ? 
Is the air on small islands dry or moist ? What kind of air do 
sailors and fishermen usually breathe ? Are sailors and fishermen 
strong and healthy or not ? 
In summer the air is sometimes exceedingly moist and warm, 
and has hardly any motion there is scarcely any wind. We do 
not like to move about then. Why not ? In which air does the 
sweat evaporate more freely, in dry or in moist air ? What air do 
we call close and sultry ? 
A moderate amount of vapor in the air which we breathe is 
healthful; a great amount is unhealthful. 
120. CARBONIC ACID. This is a poisonous gas. Fresh 
air contains f^o per cent, of it, or ten thousand measures of fresh 
air contain four measures. Two measures in one thousand 
measures of air ( | per cent.) cause headache and dizziness. Four 
per cent, of carbonic acid in the air (or the amount contained in 
our breath) is dangerous. 50 
RESPIRATION AND COMBUSTION. 
In fresh air carbonic acid is found in a greatly diluted state, 
and does not affect onr health. When its amount increases, it 
injures the health. 
121. ORGANIC SUBSTANCES CONTAINED IN EXHALED 
AIR. Until now we have mentioned vapor and carbonic acid as 
the only substances our bodies give out. Can we detect their 
presence by the sense of smell? Is the air of a closed room in 
which many persons breathe, inodorous? In view of these facts 
exhaled air must contain other substances. 
The air exhaled by persons contains organic substances. 
These substances have a musty or fetid smell. Infectious dis- 
eases (small-pox, scarlet fever, measles, diphtheria,) spread from 
one person to another by means of exhaled organic substances. 
Organic vapors and minute solid particles are thrown off from 
the lungs and skin. When we are sick, or when the body is very 
active, as during vigorous muscular exercise, the amount of these 
substances is greatly increased. You will have noticed a peculiar 
sour smell near persons exercising vigorously. The air of sick- 
rooms or hospitals is very offensive to the smell, if nothing is done 
to improve it. 
Think of the smell of your own sleeping room. You do not 
observe it in the morning, when you rise and dress; but if you 
return to the room after having been outside for a few minutes, what 
do you notice? If you send this air through pure water by means 
of a pair of bellows, the water will soon become highly disgusting. 
Or simply blow your breath through a glass of pure water, and 
you will have the same result. Do you consider such water fit to 
drink? If you stop to think of if, you do not care to take this highly 
disgusting air into your lungs, perhaps over and over again; or you 
do not care to breathe in what your neighbor has breathed out. 
What is done with the bed-clothes during day-time, and why? 
Wool, feathers, articles of dress, bed-clothes, wall-paper, and damp 
walls absorbe these organic substances very readily and keep the 
peculiar fetid smell for a long time. 
Sometimes the same disgusting, musty smell is noticed in a 
school-room, partly caused by the clothes of some boys who are not 
well cared for at home, or are too lazy to attend to their personal 
neatness. What have these boys neglected to do? How should the VENTILATION. 
51 
clothes be cleaned? On what day of the week should the clothes 
be thoroughly dusted and aired? 
Are there any decaying substances in your own house? It is 
frequently the case that vegetables kept in the cellar, such as pota- 
toes, cabbage, carrots, or bulbs of garden plants (dahlias, begonias, 
cannas) decay without the knowledge of the inmates of the house; 
or that the remains of the meals are kept in some corner of the 
dwelling-house where they exhale a putrid smell. 
The belief that this foul air does not affect the health of the 
inmates of the house, because they seldom enter the basement, is 
wrong. It is true that they do not often go there, but the air 
comes to them. Air is a very movable and penetrating substance, 
easily passing through the ceilings and floors, particularly in 
winter, when the heat expands it and causes it to rise. Dangerous 
fevers have frequently been caused by the foul air of basements. 
122. AMOUNT OF FRESH AIR NEEDED. We must find 
means to supply our rooms with fresh air, and to expel the bad air; 
in other words, we must find means to ventilate our rooms. 
A comparison will make the nature of this work clearer. 
Suppose a large barrel or cask filled with water is blackened by a 
thin but steady stream of ink. We want to purify the water. If 
we could empty the cask, and fill it anew, we should need a 
comparatively small amount of water. But this can not be done. 
The cask has to remain full at all times, and the stream of ink can 
not be checked. What are we to do ? We must throw in a large 
and steady stream of pure water, and provide for the overflow. In 
this way we shall not rid ourselves of all the ink, but we shall keep 
its amount within certain bounds or limits. The greater the supply 
of pure water, the less ink that remains. 
The purification of the air in a room is a similar process. In 
order to estimate the amount of fresh air that should be brought in, 
we should compare the amount of carbonic acid in the air we breathe 
out with the amount of carbonic acid in fresh air. (See 115). 
How much carbonic acid is contained in a mixture of one measure of 
exhaled air and 100 measures of fresh air ? The correct answer to 
this question proves that even this great amount of fresh air would 
keep the air of a room only about half as pure as the air outside. 
Practical experiments have shown that a sufficient purification of 52 
RESPIRATION AND COMBUSTION. 
the air can not be obtained unless the amount of fresh air brought 
in is from 130 to 140 times as great as the air exhaled. 
At least 2000 cubic feet of fresh air per hour and person 
must be sent into a dwelling-room to counteract the evil effects of 
exhaled air. 
2000 cubic feet is a great amount. At first sight it seems 
almost impossible to comply with this demand without expensive 
machinery. But nature will assist us, if we only understand its 
laws. 
123. VENTILATING FLUES. The opening of windows or 
doors for the purpose of ventilation is accompanied by two evils: 
firstly, it causes draughts, which are injurious to health; secondly, 
it requires constant attention. 
A perfect ventilation should, firstly, cause no dangerous 
draughts; secondly, work without requiring much attention ; 
thirdly, be inexpensive. All these requirements may be fulfilled. 
Since most rooms are heated by stoves, we will consider how 
the latter can be used for the purpose of ventilation. The fire in a 
stove is similar to the light of a lamp. How many and what 
currents of hot air does the light of a lamp produce ? How many 
and what currents does the heat of a stove produce ? Of what do 
the walls of a chimney consist ? What is the temperature of the 
walls? This heat may be used to produce another outward current 
of air. It is only necessary to double the chimney, that is, to build 
two passages for the out-going air, one for the smoke and the other 
products of combustion, and one for the foul air of the room; or the 
chimney may be built of double width, and divided by a partition- 
wall. Should this partition-wall be thick or thin, and why ? 
A flue separated from the chimney by a thin partition affords 
an excellent means of producing an outward current of air in a 
room. The inner surface of the flue should be smooth, so as not 
to impede the air current. 
If the inner surface of the ventilating flue is rough, or clogged 
with mortar or pieces of brick, it will not work well. The cost of 
this arrangement is slight, if made at the time of building the house. 
The opening of the ventilating flue should be near the floor and pro- 
vided with a register. One ventilating flue may be used for several 
adjoining rooms on each floor, in the same way that the chimney 
may be used. VENTILATION 
53 
Since only a few houses are 
ventilated in this way, it will be 
useful to show how the chimney 
itself may be utilized for the pur- 
pose of carrying out the foul air. 
Explain Fig. 38. 
The ventilating flue (v.f.) should 
consist of a tin or sheet-iron pipe, 
from six to ten inches in diameter, 
according to the size of the room. 
The arrangement is cheap and use- 
ful and should not be omitted in 
any room heated by a stove. 
Fig. 33. 
124. ADMISSION OF FRESH AIR. A well ventilated 
room has special arrangements for the admission of fresh air. 
A wooden tube, six or eight indies in diameter, commencing on 
the outside of the building, extending under the floor and ending 
in an opening behind the stove, affords an excellent means for 
that purpose. 
How will the air of this tube move when the stove is heated ? 
How is this current of air produced ? 
A simple mode of admitting fresh air without causing draught 
is to raise the lower window sash from four to eight inches, and to 
close up the space below with a board. By this means a draught in 
the lower part of the room is avoided, and through the opening thus 
made between the upper and lower sash, a current of air is directed 
upward, toward the ceiling, where it diffuses throughout the room ; 
or several small elbow-tubes may be fitted into the wall and turned 
upward in the room. 
Some persons may object to these means of ventilation on 
account of the cost. They will find, however, that the cost is much 
lower then they upon first thought suppose. The stove may need 
a little more coal, but good ventilation will improve the health of 
all the inmates of the house, and money will be saved that other- 
wise might be spent for drugs and the doctor. 54 
CIRCULATION. 
CHAPTER V. 
CIRCULATION 
Section I. 
MACHINES FOR MOVING WATER. 
126. HERO’S FOUNTAIN. Fill a glass bottle half full with 
water, perforate a cork and pass a clay pipe or glass tube through 
the opening. Connect the cork and the neck of the 
bottle air-tight. How can you test whether or not the 
two are connected air-tight ? 
A Hero’s fountain consists of a bottle partly filled 
with water and a tube whose lower end reaches into 
the water. The neck of the bottle and the tube are 
connected air-tight by means of a perforated cork. 
Blow very forcibly through the pipe or tube, which 
reaches nearly to the bottom of the bottle. What 
happens when you stop blowing ? 
126. THE SYRINGE consists of a tube terminating in a 
small orifice and a piston. A piston is a short cylinder that fits 
air-tight into a tube. 
When the narrow end of the syringe is dipped into water, and 
the piston moved upward, the space below the piston becomes 
Fig. 34. 
greater and the 
air,thinner. The 
outer air, being 
denser, forces 
Fig. 35 
some of the water into the tube. When the piston is pushed in, the 
air inside grows denser and throws the water out. (Compare with 
1[ 103-3.) 
Use the word volume, which means “the space which a thing 
occupies” in the above explanation. MACHINES FOR MOVING WATER. 
55 
127. THE SUCTION-PUMP. Suppose I hold the syringe 
vertically, with the opening turned downward, and raise the piston 
so as to get some water into the tube. If I press the 
piston back, the water will squirt out. I want to pre- 
vent this. I want near the opening an arrangement 
that will allow the water to come in, but prevent it 
from flowing out; that opens when pressed upward, 
and closes when pressed downward. This is accom- 
plished by a heavy round object that fits exactly where 
the tube begins to get narrow. We call such an 
arrangement a valve. 
The suction-pump consists of a barrel (or cylinder) 
with a piston, a suction-pipe, and two valves. One 
valve (b) is in the piston, the other (a) at the upper 
end of the suction-pipe. Both valves allow the water 
to move upwards, not downwards. 
A valve is an arrangement that allows a fluid to flow 
in one direction only. How do the valves of the 
suction-pump act when the piston is raised ? When it 
is lowered ? What is the use of the side-tube ? 
Fig. 36. 
Suction-Pump. 
128. THE FORCE-PUMP consists of a barrel (or cylinder) 
with a piston, a suction-pipe, a side-tube 
near the lower end of the barrel, and two 
valves. One valve is at the upper end of 
the suction-pipe, the other in the side-tube. 
Both valves allow the water to move away 
from the suction-pipe, not toward it. 
How do the valves act when the piston is 
raised ? When it is lowered ? 
129. THE RUBBER SYRINGE consists 
of an oval rubber bag, with two rubber 
tubes attached. Each tube contains a valve, 
one of them allowing a fluid to flow towards 
the bag, the other, from the bag. 
Place the end of one tube into water (do 
not take the wrong tube), and periodically 
press the bag. What takes place ? What 
makes the bag assume its former shape, after 
Fig. 37. 
Force-Pump. 56 
CIRCULATION. 
the pressure ceases ? What prevents the water from squirting out 
from the same tube through which it entered ? Give a full descrip- 
tion of the work of the rubber 
syringe. Pumps or syringes 
of this description are used 
by physicians. We have a 
similar arrangement in our 
bodies, an arrangement by 
whose action a very useful 
fluid is set in motion. What 
is it's name ? 
Fig. 38. Rubber Syringe. 
Section II 
THE BLOOD. 
130. THE HEART consists of a barrel, or bag, made of 
muscle, and tubes leading to and from it. (See Fig. 31.) 
Muscle, or muscular substance, is what we usually call flesh. It 
has a power peculiarly its own, the power to become shorter or to 
contract. You can feel that, if you place your right hand upon the 
inner side of the left upper arm and move the left hand toward the 
shoulder. What do you notice ? 
The greater thickness is caused by the contraction of the arm- 
muscle. Now suppose an oval bag, like the barrel of a rubber 
syringe, were built of muscular substance, and this substance con- 
tracted ; how would the inner space be changed ? 
181. MOVEMENTS OF THE HEART. The heart becomes 
narrow by the contraction of its muscular walls, and is widened 
(not by its own action but by a power outside of itself ) when the 
contraction ceases and the blood rushes in. 
The hag of a rubber syringe becomes narrow by pressure from 
without and widens by its own elasticity ; the heart becomes narrow 
by its own activity, which is the power of contraction, and widens 
when discontinuing to contract. 
132. TWO HEARTS. Our body contains two hearts, which 
are grown together, and which contract and are expanded 
simultaneously. THE BLOOD. 
57 
It is a general mistake to speak of one heart, when, in fact, all 
men, all mammals, and all birds, have two distinct hearts, just as 
distinct as the two lungs. It is true that the two hearts are grown 
together, and that they contract and expand in unison, but their 
interiors are entirely separated from each other by a complete parti- 
tion, and the blood in one part is widely different from that in the 
other. 
188. LEFT AND RIGHT HEART. Our hearts are force- 
pumps that drive the blood through the body. The left heart 
forces the blood through the body (with the exception of the 
lungs ) ; the right heart forces the blood to the lungs only. 
The left heart is sometimes called the body heart, the right 
heart, the lung heart. Which of the two has more work to do ? 
How does a muscle that works much, differ from one that works 
less ? What difference, therefore, is there between the two hearts ? 
The two hearts have equal capacities, but the left heart weighs 
twice as much as the right heart. 
134 THE BLOOD-VESSELS. All the blood of our bodies 
is contained in blood-vessels. Blood-vessels are tubes carrying 
blood. 
You can see or feel blood-vessels on the back of your bands 
and arms, at the wrist, at the sides of the lower jaw, at the temples, 
in the arm-pits, at the back of the foot. 
The red blood shines through the skin on the cheeks, the lips, 
in the mouth, in the tongue, and at other places. Here the blood- 
vessels are too small to be seen without the use of the microscope. 
Nails, hair, the outer skin, the hard substance of our teeth, and the 
cartilage are without blood. All the other parts of the body are 
tilled with blood, so that a person can not stick a pin into any part 
of his body without drawing blood at once. 
135. THREE KINDS OF BLOOD-VESSELS. Put your 
finger on a blood-vessel at the inner side of your wrist. What do 
you notice ? You can feel the same at several other places—at the 
sides of the lower jaw, at the temples, at the back of the foot, etc. 
Feel the blood-vessels on the back of the hand or arm. Try to press 
them. Do you feel the difference between those in wffiich the 
blood beats and those in which it does not ? Examine a blood-vessel 
that you take from a piece of veal, from a liver, or from a piece of 
roast. Describe it. 58 
CIRCULATION. 
Arteries are blood-vessels with stiff, elastic walls ; veins are 
blood-vessels with thinner .and inelastic walls. Capillaries are 
the narrow blood-vessels between the two. 
The blood in the arteries beats or pulsates, that is, the arteries 
grow periodically wider and longer. This is caused by the action of 
the heart, which presses blood into the full arteries. The veins are 
the blood-vessels in which the blood returns to the heart; they do 
not beat or pulsate. The capillaries connect the ends of the arteries 
with the beginnings of the veins. 
136. NECESSITY OF THE BLOOD. Why is it necessary 
to have blood everywhere in our bodies ? What becomes of the old 
substances in our bodies? What two duties has the blood to per- 
form ? Suppose a muscle has been working continuously for some 
time, till it has become tired ; what important service will now be 
done by the blood ? 
Blood is necessary in all parts of the body, because it brings 
them fresh substances and carries away the old. Every active 
organ throws off waste material and needs fresh material to work 
with. 
A working muscle is similar to a steam engine, which uses fuel, 
throws off ashes, and produces motion. Muscles are not the only 
parts of the body that work and, consequently, need blood. 
187. COMPOSITION OF THE BLOOD. Does the blood con- 
tain everything that is contained in a muscle ? How do you know? 
The same is true of other parts of the body ; consequently, blood 
contains all the substances of the bones, eyes, tongue, skin, lungs, 
stomach, liver, heart, throat, teeth, brains, nerves, tendons, hair, in- 
testines, etc. You may shorten the list by using one word. 
Blood contains every substance or material in our bodies; it 
is the liquefied body. 
Suppose you visit a large factory, consisting of many rooms 
containing a great variety of tools. Suppose the factory produces 
red cloth, white cloth, porcelain knives, stone pillars, shovels made 
of horn, photographic apparatus, musical instruments, soft brushes, 
sieves, drop curtains, and many other things. You ask where the 
laborers are, and are told that there are none, but that there is a 
curious red fluid carried to every single article, and that this curious 
red fluid has manufactured all the articles. It is further asserted THE BLOOD. 
59 
that not only the articles, but the tubes in which the fluid runs, 
nay, the factory itself, with all the splendid large rooms, are the 
work of nothing but this fluid. 
You think this is a story from fairy-land, and yet it tells only 
what may be said of our blood. The factory with its rooms is 
what ? And what are the various articles mentioned ? 
188. SEED OF MOTION. Put your finger on one of tlie 
arteries at your wrist and feel your pulse. Try to count tfie beats 
in exactly one minute. Try again. Spend some time in obtaining 
this number as exactly as you possibly can. Rise. Count again. 
What is the average this time ? How many more than at first ? 
March in place. Count again. How many more this time ? 
Suppose you should count while you are running; what would 
be the result ? And if you should lie down on a lounge; what would 
be the number of beats ? What do we learn from these observa- 
tions ? 
The blood runs slowly in persons lying down, and gradually 
increases its speed when they sit, stand, walk, or run. Rapidly 
flowing blood carries off the old material more thoroughly and 
brings more fresh material in its place. 
Which persons have more blood, are stronger, and enjoy better 
health, those who lie down and sit much, or those who stand, 
walk and run more ? What causes their better health ? Do you 
really believe that running is healthful ? If you train yourselves, 
you will be able to run a long while without being exhausted. 
In ancient Greece every one—man, woman, and child—was regu- 
larly trained in gymnasia, and daily exercise was taken in rapid 
running. Now most persons exercise running only when they want 
to board a street car. Name a few animals remarkable for their 
speed. How about elephants, hippopotami, fat hogs, bears, and 
other heavy animals ? What does that teach about fat persons ? 
What do you think about walking matches ? 
189. FUNCTIONS OF CAPILLARIES. We have heard that 
blood may be called the “liquefied body”, that it carries away old 
material from, and brings new material to, all the organs of the body. 
Where may this exchange of material between the blood and the 
organs take place most successfully—in the arteries, in the veins, or 
in the small blood-vessels between the two ? Why ? Will this ex- 60 
CIRCULATION. 
change of material take place more successfully in vessels with 
thick walls or in vessels with thin walls? 
The exchange of substances between the blood and the organs 
of the body takes place through the walls of the capillaries, 
which are extremely thin. 
All organs containing blood have numerous capillaries. The 
heart, arteries, and veins have no other purpose than to provide the 
capillaries with the necessary material. 
140. THE TWO KINDS OF BLOOD. An important ex 
change occurs in the capillaries of the lungs ; the air changes and 
and the blood changes. State the changes of the air. The oxygen 
lost by the air is taken up by the blood, and the carbonic acid and 
vapor, which are taken up by the air, are lost by the blood. Accord- 
ingly there are two kinds of blood. 
The light-colored hlood is loaded with oxygen, which is taken 
from the air; the dark blood is loaded with carbonic acid and 
water, which are taken from the various organs of the body. 
How does the color of the blood change in the lungs ? The 
opposite change occurs in the capillaries of the body. Name the 
two systems of capillaries and state the change of the blood in each 
of them. 
141. SUBSTANCES FOUND IN BLOOD. Blood consists of 
a fluid called plasma and billions of solid blood cells. The blood 
cells have the form of circular 
discs thin in the middle and thick 
at the margin or edge. 
Fig. 39 shows how the blood cells 
look when greatly magnified. A 
piece of money pressed together in 
Pig. 39. 
Blood Cells. 
the middle and thickened at the margin, would be a fair repre- 
sentation of their form. 
It is remarkable that they are so numerous. There are thou- 
sands in every single drop, and thousands of millions in the body of 
every person. 
In a healthy person about one-half of the blood consists of 
blood cells ; the other half is plasma. But the quantities vary. A 
person who is poorly fed, or one who suffers from want of sleep, 
has a small number of blood cells. They increase after a meal, 
after a sound and healthy sleep, and after a long stay in fresh air THE BLOOD. 
61 
and sunshine. A look into a person’s face usually shows whether 
he has a sufficient number of blood cells or not. How ? 
142. PLASMA consists of fibrin and serum. Plasma is 
blood less the blood cells ; serum is plasma less the fibrin. 
Blood forms a clot over a healing wound. The clot consists of 
coagulated fibrin and encloses a great number of blood cells. 
Blood taken from a living body separates itself into a clot contain- 
ing fibrin and blood cells, and a watexy liquid, the serum. 
143. THE HEART. We have compared the heart with a 
rubber syringe. Is there a pulsation in the water which is pressed 
out of the syringe ? Does the water run in continually, or in suc- 
cessive impulses ? 
The heart, too, forces the blood out in successive impulses, just 
as the rubber syringe does with the water, but it receives the blood 
in a continuous stream. 
I wish you to clearly understand this peculiarity of the heart. 
The blood is forced out in successive beats or impulses, and it flows 
in without interruptions. 
Suppose we had the same 
in a rubber syringe; what 
would become of the water 
which runs into ®, while h 
contracts, (see Fig. 40)? 
If the water collects in v, the walls have to extend, so that a 
Fig. 40. 
kind of reservoir or receptacle is formed 
there. Such an arrangement is found in 
the heart at the place where the veins dis- 
charge their blood. Here it collects while the 
heart contracts. 
Each of the two hearts has a receptacle 
where the blood collects while the heart 
contracts. 
How many valves are there in the rubber 
syringe, and where ? The heart has two 
valves at the same places and for the same 
purposes; a valve at the outlet, to prevent 
the return of the blood from the artery when 
the heart expands, and one at the inlet, to 
prevent the return of the blood into the 
receptacle when the heart contracts. 
Scheme of a single 
heart. 
A,receptacle; B,heart; 
C, vein ; D, artery. 
Fig. 41. 62 
CIRCULATION. 
Each heart has two sets of valves, one where the receptacle 
opens into it, and one where the artery commences. 
144. DISSECTION OF A HEART. You may now examine 
a real heart. Each pupil must bring a heart from a butcher and do 
his own dissecting. It does not help you much, if some one else 
does the work for you. You will have to find and describe the 
following: the left heart and the right heart; the left receptacle 
and the right receptacle; the two sets of valves between the 
receptacles and the hearts ; the two sets of valves at the outlet of 
each heart. 
Examine the size of the receptacle; it holds nearly as much 
blood as the heart itself, but its walls are much thinner. This 
is because it has less work to do. What is its work ? The 
Fig. 4.2. The three membranous pockets, the artery being opened. 
work of the heart is to send the 
blood a great distance through 
a system of arteries. Con- 
sequently the walls of the heart 
must be stronger and more 
muscular then those of the re- 
ceptacle. 
The outlet of the right heart is 
in front of that of the left heart. 
The valves at the outlets con- 
sist of sets of three membra- 
Fig. 4.3. 
The same when filled with blood. 
nous pockets. * 
* Those who are interested in scientific names may learn the follow- 
ing. The two parts that we called hearts are the ventricles; what we 
called receptacles are the auricles; the flap-valves between the ventricles 
and auricles are called the bicuspid valve (left heart) and the tricuspid 
valve (right heart); the sets of membranous pocket-valves are called 
semi-lunar valves; the artery into which the right heart sends its blood, 
is the pulmonary artery, that of the left heart, the aorta. THE BLOOD. 
63 
145. HOW TO TREAT WOUNDS. A wound may heal 
quickly without causing much pain, or the same wound may annoy 
a person for a long time. Why is this ? 
Wounds properly attended to heal quickly, without causing 
much pain ; wounds not properly cleansed and cared for become 
inflamed and cause pain. 
The first step in the treatment of a wound is to stop the bleeding. 
The bleeding of wounds in which the blood is furnished by 
capillaries only will either soon stop of itself, or it will do so if cold 
water or ice be applied. Bleeding from a vein is not usually serious 
and may also be stopped by the application of iced water or band- 
ages kept cool by ice or soaked with a solution of alum. 
But if a larger artery should be cut or torn and the light-colored 
blood continue to flow in spite of pressure upon the wound, there 
is danger of bleeding to death. In such a case a physician should 
be called at once, that he may tie up the artery. Meanwhile some 
person present should try to press upon the trunk of the artery at a 
place above the wound. If, for instance, the artery at the wrist 
should be severed, where should you try to press ? At the same 
time raise the injured arm so that the hand will be above the head. 
Why? If the artery in the elbow-joint be cut, the sleeves should 
be cut open at once, and the upper arm be firmly compressed. 
There are many ways of doing this. If you have a long piece 
of rubber, tie it firmly around the arm several times. If you have 
a bandage, use it in the same way, always placing one turn directly 
over the other, then tying the ends together, and pouring water on 
it in order to make it tighter. Elastic suspenders make very suitable 
compressors; soldiers and travelers should have no other kind. 
If you have only a handkerchief or a towel, tie it around the arm, 
put a cane, a stick, or a key under it, and twist it around several 
times; or tie your bandage over a suitable piece of wmod laid across 
the artery,' and do not cease your endeavors, till the bleeding is 
stopped. 
If afterwards a clot of coagulated blood is formed over the 
wound, do not remove it; it is the best possible covering. 
Remember that dust or dirt in a wound is very hurtful. Use 
neither shreds of cotton nor linen (char pie or lint)*, nor court - 
* Except the antiseptic preparations sold by druggists. 64 
THE SKIN. 
plaster, nor old sponges, dirty linen, spider-web, nor any other possi- 
bly dirty object, nor touch the wound with unwashed fingers. 
The least amount of dirt or dust, even the invisible dust of the 
air, may cause inflammation, putrefaction, or the production of pus. 
Everything that touches the wound should be scrupulously clean. 
CHAPTER VI. 
THE SKIN. 
146, (QUALITIES. Where is the skin ? Can you lift the 
skin from the organs underneath ? What kind of covering, there- 
fore, is the skin ? 
The skin is a loose, elastic covering of the whole body. 
147. THICKNESS. Compare the thickness of the skin on 
the neck, the throat, and on one of the eye-lids. 
As a rule the skin is thin on the front of the body and on the 
inner side of joints and limbs ; it is thick on the back of the body 
and on the outer side of joints .and limbs. On the neck it is about 
as thick as on a calf— of an inch. 
Examine the skin of the hand, the inner side of the fingers, the 
palm, the outer side of the fingers, the back of the hand. Where 
do you find numerous folds ? Where are they curved, where 
straight, concentric, parallel, or crossing each other ? Where flat ? 
Where deep ? 
148. WHAT IS FOUND IN THE SKIN. Lift your hand as 
high as your eyes. What do you find at its surface ? The whole 
skin, except at the palms and soles, is covered with hair. What is 
found in the skin of the fingers and toes, but not in the skin of 
other parts of the body ? What fluid substance is occasionally 
found upon the skin ? What is the name of the organs secreting 
sweat or perspiration ? Another substance, occasionally found 
upon the skin, is a kind of oil or fat. You can prove the existence 
of this substance by touching tissue paper when your fingers are 
moist with sweat. How does the appearance of the paper change ? 
What is the name of the organs secreting oil ? What causes the red THE SKIN. 
65 
color of the skin ? How can you prove that there are nerves in the 
skin ? 
In the skin, or attached to it, are hairs, nails, sweat-glands, 
oil-glands, blood-vessels, and nerves. 
Blood causes the red color of the skin ; nerves cause its 
sensibility. 
149. THE TWO LAYERS OF THE SKIN. The skin con- 
sists of two parts, or layers—one outside, the other inside. The 
layer outside is called the scarf-skin (epidermis); the layer 
inside, the true skin (dermis). The scarf-skin has neither 
blood-vessels nor nerves; the true skin contains blood-vessels, 
nerves, .and the bases of hairs, nails, sweat-glands, and oil- 
glands. 
We may cut into the scarf-skin with a sharp or pointed knife, 
or we may tear off a piece with a pin without causing pain. A 
separation of the two layers is caused by a blister, such as appears 
after the skin has been scalded or burned. 
150. THE-SCARF SKIN. Where is the scarf-skin thick? 
What persons have a thick and hard scarf-skin on their hands ? 
What persons have a thick scarf-skin on their soles ? What causes 
the scarf-skin to become hard and thick? 
We say of persons having a hard skin that their hands are 
horny—we speak of a horny list. An accurate comparison between 
horn and the substance of the scarf-skin shows that the two are 
closely allied. The whole body is enclosed by a true horny cover- 
ing, which, through suitable training, may become an effective 
protection from blows and similar injuries. 
When you tear off a piece, what difference do you observe 
between the inner and the outer surface of the scarf-skin ? How 
does it affect the outer part of the skin, if you rub it with a rough 
towel, particularly after a warm bath ? 
The scarf-skin becomes hard and horny hy frequent pressure. 
Its inner surface is soft and moist; its outer surface is dry and 
hard. 
The scarf-skin continually peels off. The more active the skin 
is, the greater is the quantity of surface material that may be rubbed 
off. 66 
THE SKIN. 
151. THE NAILS. Where are the nails ? What two parts 
may be distinguished in a nail ? Press that part of the finger that 
is directly under the nail, on a desk, and try to trace the inner end 
of a nail. What appendages of cats, cows, and horses correspond 
to our nails ? In what respect are nails similar to claws and hoofs ? 
We may distinguish two parts in a nail,—the part outside 
and the part inside (the base.) 
152. HAIR. The hair is similar to the nail in having two 
parts—one longer part outside, and one shorter part inside. In 
what part of the nails and hair are there nerves and blood-vessels ? 
What is the use of blood-vessels in the bases ? 
The function of the nerves is to regulate the 
secretion of the material necessary for the 
growth. Examine Fig. 44 to see how the inner 
end of a hair is connected with the skin. 
The longer part of a hair, outside of the 
skin, is called the SHAFT, the shorter part 
inside, the ROOT or BASE. The root is en- 
closed in a kind of hag formed by the true skin 
and called the hair-sac. From the bottom of 
this bag a PAPILLA arises. The papilla is 
full of blood-vessels and nerves. 
Usually two oil-glands open into the hair- 
sac near its upper end and supply the hair 
with oil, a kind of natural pomatum. 
Baldness may be caused in various ways, 
and, sometimes, can not be prevented. To avoid 
it, cleanse the skin of your head carefully, and 
Fig. 44. 
be temperate in all your habits. Every morning cleanse the scalp 
with a fine toothed comb. If the hair be dry, use a small amount 
of oil or fat (pure vaseline is excellent), and occasionally wash the 
head with soap and water. Do not wear a cap or hat when you 
can avoid it; the head needs fresh air. Do not have the hair cut 
too short. 
158. THE SWEAT GLANDS. They are found over all the 
skin. They are very numerous in the palms, where their outlets 
(the pores) may barely be distinguished with the naked eye. THE SKIN. 
67 
Examine those at the tips of your fingers with an ordinary lens or 
burning-glass. 
A sweat-gland (see Fig. 45) is a narrow tube that commences 
at the surface and penetrates the skin to a depth of about one 
fourth of an inch. There it coils up into a small bundle, or 
knot. This is surrounded by a net work of capillaries. 
Why are the capillaries close to the coils of the sweat-glands ? 
What is the use of nerves in the same places? On what occasion 
do we perspire much ? A slight perspiration goes on continually, 
even when the sweat is not visible. The amount of sweat that we 
lose in one day varies between one and three and a half pounds. 
Suppression of perspir- 
ation is unhealthful. 
154. THE PA- 
PILLA. What or- 
gans of the skin are 
connected with nerves? 
Besides, the skin con- 
tains numerous other 
nerves which are the 
true organs of touch 
and feeling. To under- 
stand how these are 
arranged you may ex- 
amine Fig. 45, which 
represents an enlarged 
view of a vertical sec- 
tion of the skin. Show 
the scarf-skin, the true 
skin, the sweat-glands, 
the blood-vessels and 
the nerves. Describe 
a, outer part of scarf-skin; 6, inner part of the 
same; c, papillae; h, fat cells; g, sweat glands; 
d, blood-vessels, i, nerves. 
Fig. 45. 
the surface in which the scarf-skin and the true skin touch each 
other. 
The surface in which the true skin and the scarf-skin touch 
each other has a great many small elevations called papillae. * 
Some papillse contain blood-vessels, some, nerves. 
Are there more papillae with blood-vessels or more with nerves ? 
* The Latin name for warts. 68 
THE SKIN. 
155. THE NERYE-PAPILLiE are the organs of touch and 
feeling. 
By means of the nerves in the papilla} we discover whether sub- 
stances are rough or smooth, hard or soft, warm or cold. 
156. BLOOB-PAPILL-E. What is the use of blood-vessels 
in the skin ? What takes place when blood and air are separated by 
a thin membrane ? Why have some persons a fresh, ruddy, healthy- 
looking skin, while in others the skin looks faded and sallow ? 
When does the skin look healthier, in summer or in winter ? In 
winter we can not have as much air and sunshine as we desire, but 
we can bring plenty of blood into the skin, if we are not too lazy. 
How do you warm your fingers when they feel cold and you have 
no fire ? How do you feel after you have thoroughly rubbed your 
skin with a coarse towel ? Why not have this comfortable feeling 
of health and strength every day ? 
The blood-papillae allow the blood to come close to the out- 
side of the body where it may interchange its gases with the 
atmosphere. The skin takes an active part in respiration. 
157. THE DAILY SPONGE-BATH. Many of you have not 
the means of bathing every day. Then you may learn of a method 
that will give you the benefit of a daily bath without any cost worth 
mentioning. All you need is a wash-basin with water, a piece of 
soap, a big sponge, and a rough towel. 
Early in the morning first wash your face and ears, then undress 
the upper half of your body, and use water, soap, and towel to 
wash and rub it, then undress the lower half of your body, and 
sponge first, the lower part of your trunk, then one leg, then the 
other. 
The rubbing with a coarse towel is necessary and should not be 
hurried. Even in a cold room you will not catch cold or even feel 
cold, if you take a sponge-bath; on the contrary, you will feel 
warm and comfortable, and, what is still better, will harden your 
body and protect yourself from colds. 
What effect has the rubbing upon the scarf-skin ? What effect 
has it upon respiration, if the scarf-skin is thin ? What upon the 
acuteness of touch ? Upon perspiration ? Upon the amount of 
blood in the skin ? EXCRETION. 
69 
The daily sponge-bath produces an increase of respiration, 
perspiration, and warmth, a greater acuteness of the sense of 
touch, and a healthier look. 
Nothing so simple and inexpensive is of equal benefit to your 
health and energy as a daily sponge-bath of the entire skin. Those 
who unfailingly take a daily sponge-bath are best protected from 
colds and infectious diseases. 
CHAPTER VII. 
EXCRETION. 
158. LUNGS AND SKIN. To excrete means to throw off 
what is useless. What two substances are excreted by both the 
lungs and the skin ? The skin excretes a small quantity of carbonic 
acid and a considerable quantity of water. Does the skin excrete 
the same quantity of water daily, or does it lose much on some days 
and little on others ? 
Lungs and skin excrete carbonic acid and water. The 
amount of water excreted by the skin varies greatly; we lose 
much water when it is hot or when we sweat; we lose little 
water when it is cold or when we do not move about much. 
Since there are great variations in the quantity of water that 
the skin excretes, our bodies need organs for the discharge of the 
surplus water, or of that amount of water which is prevented from 
leaving through the skin. These organs are the kidneys and the 
bladder. 
159. KIDNEYS. Examine a pig’s or sheep’s kidney. What 
is its shape ? The human kidney has the same shape. What can 
you say of its appearance and its other qualities ? At what place is 
it connected with other organs ? What organs can you distinguish 
at the concave side ? 70 
EXCRETION. 
Examine the interior ; cut through the kidney with a sharp 
knife; lead the knife all around the margin. The white substance 
is fat. Try to take away as 
much of it as you can with- 
out injuring the surrounding 
parts. Notice that there is a 
small cavity, or basin. Look 
at the brown substance. Do 
you see any lines indicating 
a special arrangement of this 
substance ? Find out what 
part of the outside is attached 
to this cavity. 
The kidneys lie in the 
hack of the abdominal cav- 
ity, one on each side of the 
hack-bone. Each is of the 
size of about one half of its 
owner’s list, has the shape 
of a bean, is brown in color, 
smooth, and softer than 
meat. The interior con- 
Fig, 46. 
Section through the Kidney of a Child. 
tains a small cavity or basin located near the concave side. 
The light brown substance is separated into a darker part near 
the outside and a lighter part further on the inside. The latter 
is again divided into seven or eight conical pieces with the points, or 
apices, directed toward the cavity. The cavity is continued in a 
long tube called the ureter. 
IGO. THE RENAL* ORGANS. Examine Fig. 47, and name 
Hie objects, or organs, represented. 
What organs are connected by the ureters ? At what place 
do the ureters unite with the bladder ? What is the use of the 
blood-vessels represented in Fig. 47 ? It is not pure water which 
the kidneys excrete, it is urine, a liquid containing about 95 per 
cent, of water. 
The renal organs consist of the two kidneys, several blood- 
vessels, the two ureters, the bladder, and the urethra. 
* Renal means pertaining to kidneys (renes). EXCRETION 
71 
The kidneys excrete urine 
from the blood which the blood 
vessels bring to them ; the urine 
Hows through the ureters into 
the bladder; and the bladder- 
discharges the same through the 
urethra. 
A muscular ring at the base 
of the urethra keeps the bladder 
closed when no urine is being 
discharged. 
161. UKINE contains 95 
per cent, of water and 5 per 
cent, of dissolved substances. 
The most important of the 
latter is urea, a substance con- 
taining nitrogen. 
Substances containingnitro- 
g'en are excreted by the kidneys 
almost conclusively. If the kid- 
Fig. 47. The Renal Organs. 
neys are disordered, if their function is obstructed, and the urea 
retained, serious consequences follow. If this condition lasts, the 
person can not live. 
162. HYGIENE OF THE KIDNEYS. Why can the kidneys 
not be spared from the body ? If both kidneys be cut from a living 
animal, it dies in a few hours from blood-poisoning. What has 
poisoned the blood ? Is the work of the kidneys the same every 
day or is it sometimes great and sometimes small ? When does the 
skin excrete a very small amount of water ? Does moi-e water 
leave the skin of a person who takes a daily sponge-bath, or of one 
who does not ? How does dirt prevent the excretion of water from 
the skin ? Whose kidneys have more work, those of a cleanly or 
those of an uncleanly person ? Whose skin contains more blood ? 
Whatever increases the amount of blood in the skin increases 
respiration and relieves the kidneys; whatever decreases the 
amount of blood in the skin decreases respiration and throws 
work on the kidneys. Imprudent exposure to cold, particularly 
in the early stages of recovery from measles or scarlet fever, 
may cause incurable kidney diseases. 72 
MUSCLES. 
If a person imprudently exposes his skin to the cold, it grows 
pale, because the blood is driven out. Then the work of excreting 
a sufficient quantity of water is thrown upon the kidneys, which, 
consequently, are overworked. In this way a severe cold may re- 
sult in a serious disease of the kidneys. 
Children having just recovered from measles or scarlet fever 
must be careful, because their kidneys are still in a weak condition. 
Some children suffer from a weakness of the renal system and 
often feel the need of discharging urine. They should not hesitate 
to do so, but comply with the demands of nature at once. If in 
school, they should ask permission to leave. It is true that the class 
is disturbed, and that careless children ask more than is necessary. 
Yet it is better to suffer these inconveniences than to endanger the 
health of any one. 
Children should be reminded that in every school-session there 
are three distinct times when they may relieve themselves without 
disturbing the class : before commencement of lessons, at recess, 
and at the close of the session. Children who make a habit of 
leaving between times, without being obliged by their state of 
health to do so, are careless and disorderly. 
CHAPTER VIII. 
MUSCLES. 
Section I. 
STRUCTURE AND FUNCTION. 
163. CONTRACTION. What name is given to muscles by 
the butcher and the housekeeper ? Place your right hand at the 
inner or front side of your left arm and raise your left hand toward 
the shoulder. How does the muscle change ? 
The muscle at the front of the upper arm grows thicker ami 
shorter when the hand is raised toward the shoulder. Muscles 
contract. STRUCTURE AND FUNCTION. 
73 
The contraction of the above-named muscle is caused by the 
will, or energy, which has its seat in the brain. If the will, hav- 
ing its seat in the brain, causes the contraction of muscles situated 
in the arm, there must be a connection between the brain and the 
arm. Of what does this connection consist ? 
It is just as if there were telegraph wires between the two. 
The will, acting upon one end of a nerve, gives a command. The 
command is carried through the nerve to the muscle, and the 
muscle contracts. 
164. TENDONS. How far does the arm-muscle extend ? 
Where does it commence and where does it end ? Is the muscle of 
equal thickness throughout, or is it thick in some places, and thin 
in others ? Feel it while it is slowly contracting. The middle of 
the muscle consists of flesh ; the two ends are made of a tough, 
white substance called a tendon. To what are the ends of a tendon 
attached ? For what purpose ? 
Look at the white glistening pieces sticking out from the 
severed feet of chickens, geese, and turkeys. They are tendons. 
Pull one of them. What takes place ? Stretch your fingers forci- 
bly, what do you feel near the bases of the fingers ? These pieces, 
too, are tendons; they resemble the white glistening ribbons in the 
chickens’ feet. We may compare the tendons with ropes fastened 
to a heavy body and pulled by some power placed at the other end. 
What is the load, and what is the power, when the forearm is 
bent ? 
The two ends of the arm-muscle (and of many other muscles) 
consist of a tough white substance and are called tendons. The 
tendons connect the muscles with bones. When the muscles con- 
tract, the tendons pull the bones. 
165. CONNECTIVE TISSUE. (See Fig. 25.) Get the leg of 
a rabbit, squirrel, or any other small animal. Carefully remove the 
skin. The substance found close under the same is called the con- 
nective tissue. What does it connect ? It is also found between 
the muscles. It forms a sheath, or envelope, for every muscle. 
Connective tissue is a loose, white substance found throughout 
the body. Not only the muscles, but also the nerves, hones, and 
blood-vessels, the heart, lungs, and all other interior organs are MUSCLES. 
surrounded by membranes consisting of connective tissue. At 
other places it has the office of packing material, filling out the 
spaces between adjoining organs. 
Without connective tissue, the relative position of our organs 
would change continually. It keeps the organs and the various 
parts of each organ in their places, and prevents a dislocation of 
any part inside of our body. 
Muscles, nerves, blood-vessels, and the other parts of our 
body are kept together and in their places by a white, loose sub- 
stance called connective tissue. 
166. FIBRES. To see a muscle in its whole extent, tear 
the connective tissue all around it, or cut and remove it. What 
shape has the muscle ? How does it look and feel at the surface ? 
The elements of a muscle extend lengthwise. They are 
called fibres. 
Fibres are from a half to one and one half inches long, and 
are placed regularly alongside of and behind one another. 
167. CONTRACTION AND EXPANSION. Let us return to 
the above-mentioned muscle of the upper arm. Suppose it has 
contracted and the fore-arm is bent; how is the arm made to take 
its former position ? You may discover it by slowly bending and 
forcibly stretching your lower arm about twenty times. At what 
place do you feel your upper arm grow tired ? How is that caused? 
How is the upper arm made to perform the two opposite motions of 
bending and stretching ? 
The only active work of the muscles is their contraction; 
their expansion is passive. Muscles contract and are expanded. 
What adjective may we use to denote the ability of muscles to 
contract ? Change this word to a noun. 
168. ATTACHMENT OF MUSCLES. To what are the 
muscles of the fore-arm attached ? Those of the neck ? Are the 
two ends of a muscle attached to the same bone or to two bones, 
and why ? Are bones the only parts of the body moved by muscles, 
or can you name other parts moved by them, while the nearest 
bones remain in their places ? STRUCTURE AND FUNCTION. 
75 
Fig. 48. 
Muscles and Nerves of the Head. 
Many muscles are attached to two bones and move one bone 
toward or away from the other. A few muscles connect two 
places in the skin, or they reach from an underlying bone to 
the upper soft parts. 76 
MUSCLES. 
Muscles of the first kind are those of the limbs ; muscles of the 
second kind are those around the mouth and the eyes. The eyeballs 
are moved by muscles reaching from an underlying bone to the 
surface of the eyeball. 
169. SUBSTANCES MOVED BY MUSCLES. Not only 
bones and skin are moved by muscles, but also foreign substances 
introduced into our body from without are moved by them. 
Our body contains a number of tubes and hollow organs 
(esophagus, stomach, intestines, heart, tubes connected with 
glands, etc.) in which various substances are moved along. 
This motion is caused by the contraction of muscles in the walls 
of the organs. 
170. TWO KINDS OF MUSCLES. W'hen do the muscles 
of the esophagus contract ? Food widens the esophagus ; it exerts 
a pressure on its walls. The muscles ©f the stomach contract when 
food enters ; the heart contracts when it is filled with blood. In all 
these cases the contraction of muscles is caused by the pressure of 
substances. What two causes for the contraction of muscles have 
we mentioned ? 
Muscles that contract when directed by the will are called 
voluntary muscles ; muscles that contract when they are pressed 
against are called involuntary muscles. 
Section 11. 
HYGIENE. 
171. EXERCISE. Do old persons have a larger number of 
muscles than young persons ? Does the number of muscles increase 
as we grow older ? Do all persons of the same age have muscles of 
the same size ? Which of your arms is usually stronger, and why ? 
What change takes place if one is obliged to carry an arm in a 
sling ? Name some tradesmen who habitually have large muscles 
in their arms. What is the cause of the large size of their muscles? 
Why have storekeepers, teachers, merchants, and others smaller 
muscles ? 
Muscles grow large and hard when they are used frequently 
and forcibly. HYGIENE. 
77 
172. YALUE OF STRONG! MUSCLES. Why is it well to 
have large and strong muscles in every part of the body ? What 
must we do to have strong muscles everywhere ? When is the best 
time to develop our muscles, when we are young or when we are 
old, and why ? Name some exercises that you like and often per- 
form, and the parts of the body they strengthen. 
Do you perform any exercises that tend to strengthen your 
chest, your back, or your sides ? 
In most children the muscles of the neck and back are too 
weak to carry the head erect and to keep the shoulders and arms 
back. They need suitable exercises to strengthen these muscles. 
A strong and wide chest is not the only benefit to be gained by 
daily exercise. What effect has exercise upon the current of blood? 
What functions of the blood are performed more thoroughly, if it 
runs quickly through the whole body ? 
How does exercise affect respiration ? How does it affect the 
skin ? How does it affect the appetite ? 
Persons with large muscles are stronger ami healthier than 
those with smaller muscles. They feel better, are not easily 
tired, have sound sleep, enjoy their food, digest it well, and are 
not easily affected by cold. 
Proper exercises increase our health and our well-being. The 
blood carries off the waste more thoroughly and brings more fresh 
substances to the organs; the breathing is deeper and quicker; 
more carbonic acid is thrown off, and more oxygen taken in ; the 
skin becomes warm and ruddy ; the appetite increases. 
173. WORK AND SLEEP. When did your sleep bring more 
energy and vigor, when it followed a day of writing and studying 
indoors, or a day of lively exercise outside ? You know children 
who are seldom allowed to enjoy play and fresh air, and others who 
spend every spare moment out-doors, or who have to work in the 
fields, which of them sleep longer, and which are the stronger 
and healthier ? 
Persons who use their muscles vigorously do with less sleep, 
and are more refreshed hy it than persons whose muscles are 
usually inactive. 
Laborers, farmers, tradesmen, housemaids, and others who are 
used to hard labor, usually do not sleep so long as persons who 78 
LEVERS AND BONES. 
have little muscular exercise. The less a person is used to hard 
labor, the more easily he is tired. 
174:. IMPROPER EXERCISE. A word of caution is neces- 
sary before we close this chapter. Some of you may think that, as 
exercise increases a person’s strength and well-being, you should 
take it on every occasion and as much of it as you possibly can. 
But there is such a thing as over-work. Nature has put a limit to 
the amount of work that each person can do, and it is well to re- 
spect this limit. How do you feel after vigorous work ? 
If you feel exhausted, it is but natural that you should rest. 
Exhaustion is the warning sign of nature. Stop your work and 
rest till you feel strong again. If you exercise regularly every day, 
you will soon be able to work a long while without feeling ex- 
hausted. Persons who do not stop when it is necessary, may be 
affected by valvular diseases of the heart. If they do it often, the 
whole body may prematurely decay. 
Furthermore, the time immediately after a hearty meal is not 
suitable for muscular exercise; we feel disinclined to work then. 
If we overcome our disinclination, and work on, our food will be 
imperfectly digested. 
Do not exercise when you are exhausted ; do not exercise 
immediately after a hearty meal. 
CHAPTER IX. 
LEVERS AND BONES. 
Section I. 
LEVERS. 
175. THE SCALES. Examine a pair of scales, such as a 
grocer or a druggist uses. Show its essential parts. Which of 
these parts are movable ? Describe the motion of the iron beam. LEVERS. 
79 
The essential parts of a pair of scales are : the TWO 
SCALES ; the IRON BEAM that supports the scales; the BASE, 
which supports the iron beam. The two halves of the beam are 
Fig. 49. 
called the ARMS ; the middle of the beam is called the ELL 
CRUM; the beam itself is called a lever. 
When is the beam or lever in a horizontal position ? 
176. THE STEELYARD is a lever with two unequal arms. 
Its fulcrum is the point about which it turns. 
Butchers use a steelyard to find the weight of a pig or calf. 
The animal is hung on the short arm, and a ring to which an iron 
ball is attached, is placed over the long arm. The iron ball is put at 
the place where it balances the weight of the animal, and the 
number at this place tells its weight. LEVERS AND BONES. 
In what order are the numbers arranged on the long arm ? 
Where are the lower numbers ? What increases with the distance 
from the fulcrum ? 
Fig. 50. 
177. EFFECT OF A WEIGHT. You will easily understand 
why the numbers must be arranged in this way, if you remember 
how a see saw is arranged when a little child and a big boy balance 
each other. Where is the support, or fulcrum, of the see saw in 
such a case ? 
A weight has more effect ou a long arm of the lever than on 
the short arm. 
178. THE LAW OF THE LEVER. We shall be better able 
to express the law of the lever, if 
we distinguish the two weights as 
power and weight. Suppose we 
have a lever whose arms have a 
respective length of four and eight 
inches; what power will balance 
a weight of ten pounds at the end 
of the shorter arm ? Show this in 
a drawing. Demonstrate it with a 
Fig. 51. LEVERS. 
81 
few small weights and a strong ruler supported by the top of a 
chair. What two pairs of these numbers must be multiplied 
together to obtain equal results ? Substitute words for the numbers 
of the equation which you obtained. Which of the two arms may 
be called the power-arm ? Which, the weight-arm ? What takes 
place if the product of the weight and the weight-arm is equal to 
the product of the power and the power-arm ? 
The lever IS IN EQUILIBRIUM (at rest), if the product of 
the power and the power-arm is equal to the product of the 
weight and the weight-arm. 
179. THREE KINDS OF LEVERS. The balance, the steel- 
yard, and the see-saw represent what are called levers of the first 
kind. What is the respective position of the power, weight, and 
fulcrum in levers of this kind ? 
There are other levers 
in which the weight is 
between the power and 
fulcrum, or the power is 
between the weight and 
fulcrum. We will try to 
find applications of these 
levers. 
How may a work- 
man raise a heavy stone 
by means of an iron bar ? 
(See figures). In which 
of these cases have we a 
lever of the first kind ? 
Fig. 52. 
Fig. 53. 
The other case represents a lever of the second kind. Define it. 
What, then, is a lever of the third kind ? An example of the last 
kind is a fishing rod held as the following figure shows. 
Describe it. Suppose 
the fish weighs five 
pounds, the weight arm is 
eight feet, and the power- 
arm, two feet; how great 
must the power be to 
balance the weight of the 
fish ? 
Fig. 54. 82 
LEVERS AND BONES. 
Twenty pounds will balance the fish in the air. While in the 
water, the fish uses its muscular power to pull with a much greater 
force. Anyone who has had a big fish on a line will remember that 
it took both power and skill to overcome the resistance. 
A lever of the first kind is one with the fulcrum between the 
power and the weight; in a lever of the second kind, the weight 
is between the fulcrum and the power; in a lever of the third 
kind, the power is between the fulcrum and the weight. 
What kind of lever is represented by a ladder raised by taking 
hold of one of the rounds while placing the foot against the end ? 
What kinds are represented by a door pushed very near the hinges ? 
By a door taken hold of at its edge ? By a spade ? A wheel- 
barrow ? A chopping-knife ? An oar ? A sling for throwing 
stones ? A pump-handle ? 
Definition. A lever is an inflexible bar capable of being 
freely moved about a fixed point or line. 
180. WORK OF LEYERS. Levers do not lessen the work 
that is to be done, because they do not perform work themselves; 
but they change the work of moving a great weight through a 
short distance into the work of moving a small weight through a 
great distance, or they change the work of moving a small weight 
through a great distance into the work of moving a great weight 
through a short distance. 
You cannot lift a weight of 250 pounds as a whole, but if you 
use a suitable lever (a crowbar), it is as if you divided the 250 
pounds into 10 weights of 25 pounds each and lifted one after 
another to the required height. 
You cannot move a stone lying in your hand with great 
rapidity, but by the use of a suitable lever (a sling) you increase 
the rapidity of the stone while exerting more muscular power. The 
same amount of muscular power would move a heavier stone lying 
in the hand. 
Section 11. 
BONES. 
181. THE FORE-ARM AS A LEVER. Our bodies and those 
of animals contain numerous levers. Which of our organs may act 
as such, and why ? Name some bones and tell about what points BONES 
83 
they may be moved. Suppose the fore arm and hand are in a 
horizontal position, at a right angle to the upper arm, and that they 
carry a weight of 25 pounds. Where is the fulcrum and where the 
weight-arm ? 
Fig. 55. 
What organ holds the fore-arm in its place ? Where is the 
tendon of this muscle (the biceps) attached ? What is the power- 
arm of the fore-arm ? What kind of lever is the fore-arm, and why ? 
The weight-arm is about six times as long as the power-arm. 
How great a power must be exercised by the contracting muscle in 
balancing 35 pounds ? 
If we substitute a mechanical arrangement for a muscle, we 
should need this weight. 
The fore-arm and hand held in a horizontal position, at a 
right angle to the upper arm, and carrying a weight, represent 
a lever of the third kind. 
The fulcrum is at the elbow ; the weight-arm is the distance 
between the elbow and the hand ; the power-arm is the distance 
between the elbow and the space where a muscle (the biceps muscle) 
is attached to the bone. The muscle contracts with a power of 
about 150 pounds to balance a weight of 25 pounds. 84 
LEVERS AND BONES. 
182. THE FOOT AS A LEVER. Another instance of the 
use of a bone as a lever is found in the act of 
rising on the toes of one foot. What repre- 
sents the lever, its fulcrum, weight-arm, and 
power-arm ? 
M\lieu we stand upon the toes of one 
foot, the foot represents a lever of the 
second kind. 
The fulcrum is the place where the foot 
rests ; the weight is that of the body acting 
down through the ankle, and the power is 
the great muscle at the calf acting by its 
tendon inserted into the heel bone. 
In the act of walking, the muscle at the 
calf contracts with a power of more than 100 
pounds, and as this is done many times during 
the day, it must be considerably larger than 
that of the upper arm. 
183. THE HEAD AS A LEVER. 
What position does the head take when no 
active, or muscular, power is exerted, as, for 
instance, when a person falls asleep in a 
sitting position? How is it brought back 
into its erect position ? 
In the movement of nodding, the head 
represents a lever of the first kind. 
The fulcrum is the place where the head 
rests on the back-bone; the weight is the 
fore part of the head (or the excess of its 
weight over that of the part behind the 
fulcrum); the power is the muscle of the neck acting by its tendon 
inserted into the back of the head. 
Fig. 56. 
What kind of levers are represented by the parts of our upper 
and lower limbs ? By the lower jaw ? Which teeth exert a greater 
pressure, the cutting teeth or the grinders, and why ? Why have 
cats and lions shorter jaws than oxen and horses ? 
184. JOINTS. We will now examine the places that we have 
recognized as the fulcra of bones. Name those places. What name BONES 
85 
is applied to all of them? Name other joints in the body. What 
office, or function, have joints ? 
Joints are the pla- 
ces where two hones 
meet and where they 
can be moved about 
each other. 
The elbow-joint, the 
ankle-joint, the place 
where the head rests 
upon the back-bone, 
the joint of the jaw- 
bone, the shoulder- 
joint, the finger-joints, 
the joints at the hips, 
knees, wrists, and toes, 
are examples of differ- 
ent joints. 
185. HIShE- 
JOINTS. Examine 
the movements of the 
fore-arm. Name other 
joints that allow the 
bones to be moved like 
the fore-arm —in one 
plane only. What 
movable objects in 
your room are moved 
in the same way —in 
one plane only ? What 
is the name of the 
mechanical appliance 
that allows these move- 
ments ? 
Hinge-joints are 
joints that allow move- 
ments in one plane 
only. 
Fig. 57. 
The fore-arm moves 86 
LEVERS AND BONES. 
in one plane only —in that of the upper arm ; the elbow-joint is a 
hinge-joint. Other hinge-joints are the knee-joints, the finger- 
joints, and the joints between the bones of the toes. The bones 
move in the joints like a door in its hinges. 
186. BALL-AND-SOCKET-JOINTS. Name bones that move 
in many directions. The joints in which these bones move are 
called ball-and-socket-joints. You have heard the name “socket” 
in connection with the teeth. The eyes are in sockets. Define 
socket. 
Examine the hip-joint in Fig. 57, and tell why it receives the 
name of ball-and-socket-joint. The same arrangement is found in 
the joint connecting the bone of the upper-arm with the shoulder- 
blade. Enumerate and perform the motions of the upper-arm in 
this joint. What parts of your hands may be moved in many 
directions ? In what directions may the jaw-bones be moved ? 
Ball-and-socket-joints are joints allowing the bones to move 
in many directions. 
The shoulder-joint, the hip-joint, the joint of the jaw-bones are 
ball-and-socket-joints. A socket is a hollow space that receives and 
holds something. What joints are those at the bases of the fingers? 
187. SLIDING AND COMPOUND 
JOINTS. Examine the figures repre- 
senting the hones of the wrist and 
ankle. What do you observe ? 
Wherever two of the little bones 
face each other, they are connected by 
joints. These joints are called sliding 
joints, because they allow the bones to 
slide over each other a little, when 
subjected to pressure or pulling. If 
Fig. 58. 
Fig. 59. BONES, 
87 
we consider the wrist or the ankle as one joint, we call it a com- 
pound joint. 
Sliding joints are joints allowing the bones to slide over 
each other through a small space; compound joints are joints 
composed of many sliding joints. 
What similarity is there between a ball-and-socket-joint and a 
compound joint ? Why are there any compound joints ? Would 
it be better if there were ball-and-socket-joints instead ? 
An arrangement that is perfect at one place in our body, may 
be unsuitable in another. This is the reason why there is such a 
great variety of joints. Even the joints that are classified under 
one head, as, for instance, hinge-joints, are not exactly the same 
everywhere. If you should examine them more closely, you would 
find peculiarities in each. 
Enumerate the kinds of joints. Name the places where these 
joints are found. What movements do they allow ? 
188. OUTER STRUCTURE OF JOINTS. From the leg of 
a rabbit ( or the foot of a pig or calf,) cut away the skin, the mus- 
cles, and most of the connective tissue, and examine how the bones 
are united in a joint. * 
Each joint is surrounded by a short, air-tight cylinder, 
consisting of a flexible, but tough membrane, called a capsule. 
There is uo air below the capsule. The union of bones in joints 
is accomplished by the pressure of air. 
Rise and lift one foot from the ground. The leg which now 
hangs down from your trunk has a Aveight of 15 to 35 pounds. Do 
you feel this weight ? The leg is carried by the air—the air presses 
the leg into the hip-joint and carries it. This is also the reason 
why we do not feel the weight of our arms and legs when we are 
walking. 
189. STRUCTURE OF JOINTS INSIDE. Open the capsule 
and examine the inside. Touch the surface of the bones there and 
cut into one of the ends. Do you find bone or another substance ? 
Why do you put a cushion of cloth under your hand when you play 
at marbles ? Why are the bones in joints covered with cartilage ? 
Why is the cartilage in joints oily ? 
* The class will learn better and show more interest and enthusiasm 
if each pupil can be induced to bring' to school a suitable piece of a mam- 
mal or bird, further, a plate, a towel, and a sharp knife, and to prepare 
and examine the joint under the direction of the teacher. Knowledge 
gained in this way is indelibly impressed on the mind. 88 
LEVERS AND BONES. 
The ends of the bones, or the places where the bones meet, 
are covered by a layer of cartilage, which is lubricated with an 
oily or greasy substance, the synovia. The synovia is secreted 
by glands in the capsule. 
The cartilage in joints acts like a cushion ; as it contains neither 
nerves nor blood-vessels (See 184), it is not hurt by pressure. 
190. LIGAMENTS. Look at the joint once more. Try to 
find some thicker pieces of a tough, tendon-like substance reaching 
from one bone to another. 
Ligaments are strong bands of an elastic, tendinous 
substance reaching from one bone to another. Their 
function is to prevent any too extensive movements. 
Ligaments keep the movements within certain limits. 
Without them the muscles would often perform move- 
ments which would bring the bones out of joint. 
191. PARTS OF BONES. Compare a fresh bone 
with an old one, such as you sometimes find in the fields. 
Feel the surfaces of the two bones and tell how they differ. 
Try to pull off something from the surface of the fresh 
bone. This membrane is called periosteum. It covers 
each bone, excepting where another bone touches it. 
The periosteum contains blood-vessels, which send 
numerous small branches into the bone itself. You can 
not plainly see these blood-vessels in a fresh bone. But 
look at the old bone. What do you find on its surface? 
There are the places where the blood-vessels enter the bone. 
Fig. 60. 
ligaments in 
the joints of 
a finger. 
The fresh bone is a solid piece, a piece without hollow spaces ; 
the old bone is porous ; it contains large cavities whose beginnings 
you can see at the surface, and many small cavities, which may be 
seen with a magnifying glass. 
If you touch a piece of paper with a fresh bone, it becomes 
transparent. What causes the transparency ? If a butcher saws a 
fresh bone, the surfaces of the saw and of the sections are covered 
with a fatty liquid. 
A fresh bone is a solid piece without any pores or cavities. 
It contains blood-vessels and a fatty liquid and is covered with a 
thin membrane, called periosteum. BONES, 
89 
192. SUBSTANCES OF BONES. Prepare two bones in 
the following way: place one in the bright fire of a stove or 
furnace ; keep the other in diluted muriatic acid for several days. 
What qualities do the bones show ? 
The two methods produce diverse results with the bones. The 
substances burned by the fire are preserved by the acid, and the 
substances dissolved by the acid are preserved by the fire. 
Bones consist of a hard and a soft, flexible substance. The 
former is called the mineral substance; the latter, the animal 
substance.* The mineral substance makes the bones hard and 
strong; the animal substance makes them flexible and elastic. 
The bones of old persons contain a great quantity of mineral 
substance and a small quantity of animal substance. The con- 
sequence is that shocks or concussions that do not seriously affect 
the bones of young persons, result in broken bones in the aged. 
The opposite is true of the bones of very young children. Their 
bones abound in animal substances and lack mineral substances. 
What takes place if they walk at too early an age ? 
198. WHY LONG BONES ARE HOLLOW. Break a long 
bone or ask the butcher to saw across the leg of a sheep. Look at 
the section. What do you see ? 
Long bones must support the upper body, just as the legs of 
tables and chairs must support the upper parts. What quality must 
the legs have that they may be able to support, and not break 
down ? 
You probably have seen houses whose ground-floor is used for 
stores. The fronts of these stores have large show-windows. 
Directly over these show-windows are the w’alls and windows of 
two, three, or four upper stories. How is the front of such a build- 
ing supported ? Are the iron pillars solid or hollow ? What 
resemblances are there between the iron pillars and the long bones 
of our body ? Why do the contractors and builders not use solid 
iron pillars ? 
Suppose I have 250 pounds of iron of which I want a pillar 
made, 16 feet high, and as strong as possible; should it be a solid or 
a hollow one ? 
* The mineral substance is mainly phosphate of lime and carbonate 
of lime ; the animal substance is cartilage. 90 
LEVERS AND BONES. 
The long bones in our arms ami legs are filled with a kind of 
fat called marrow. Hollow columns are stronger than solid 
columns of the same length and weight. 
It is easier to break a solid stick than a hollow stick of the same 
length and weight. Iron pillars that are used to support great 
weights are hollow. If they were solid and had the same size, they 
would be unnecessarily heavy and expensive; if they had the same 
weight, they would not be strong. 
191. THE SKELETON consists of the 
united bones of our body. Its three main 
parts are the head, the trunk, and the limbs. 
Its central part is the back-bone. (See Fig. 
57.) 
Where do you see long bones ? Where, 
flat bones ? Where are the most massive bones? 
Where do you see a number of small bones 
lying close together ? 
195. THE BACK-BONE. The back-bone, 
or vertebral column, consists of many bones 
placed one upon another. Each of these 
bones is called a vertebra ; it consists of a ring 
with a body in front and projections at the 
sides and back. 
The upper part of the vertebral column con- 
sists of twenty-four vertebrae, seven of which 
are in the neck, twelve back of the chest, and 
five between the loins. 
The spaces between the front bodies of the 
vertebrae are filled up by cartilaginous cushions 
which have the essential quality of India rubber 
—elasticity. They are pressed together if a 
weight rests upon them, and expand if this is 
not the case. Measure your height early in the 
morning just after rising, and late at night 
just before going to bed. What do you find ? 
196. CURVES IN THE BACK-BONE. 
Draw a line parallel with the axis of the back 
bone. Describe this line. What part of the 
Vertebral Column. 
Fig. 61. BONES 
91 
body is in front of the upper convexity ? Of the upper concavity ? 
What inconvenience would it be to the chest if these curves were 
turned in the opposite directions ? 
There is still another benefit derived from these curves. Tell 
why the head is jarred when you jump upon the heels while your 
legs are straight. Do the curves change when you jump or fall 
upon the feet ? 
The hack-bone has four curves. It is bent forward in the 
neck and between the loins, backward in the chest and in the 
lower parts. 
The curves in the chest and in the lower part enlarge the size 
of the cavities in the trunk. The elastic cushions between the 
bodies of the vertebrae allow slight movements of the back-bone to 
all sides. When we jump or fall, they cause an increase of the 
curves. In this way the head is protected from violent shocks. 
197. USE OF THE BACK-BONE. Each of the vertebrae 
has a cylindrical opening. What do all these openings, lying 
directly one over another, form together ? What fills this cylinder 
in a living person ? 
The back-bone forms a long hollow cylinder for the protection 
of the spinal cord. The spines of the back-bone serve for the 
attachment of muscles. 
Fig. 62. 
Second Lumbar Verte- 
bra. Upper View. 
Fig. 63. 
First and Second Lumbar 
Vertebrae. Side View. 
Fig. 64. 
First and Second Lumbar 
Vertebrae. Back View. 
The back bone is sometimes called the spinal column. Why is 
it called spinal ? Is there anything in a back-bone resembling 
spines ? Where can you feel the projections, or spines, of your 
backbone. 92 
LEVERS AND BONES. 
Sit very straight and feel the swelling of muscles on your back. 
Hold your hand at the loins and feel how the muscles at the two 
sides alternately swell when you walk. 
Remember that the meat taken from the loins of rabbits, deer, 
oxen, and other animals is very rich and tender, doubtless because 
the frequent use of these muscles in walking and running draws 
much blood and nourishment to them. 
198. THE BONES OF THE ARM. How many bones can 
you count in your hand ? Furthermore there are eight bones in 
the wrist, two in the fore-arm, and one in 
the upper arm. (Show these bones in 
Fig. 57.) 
Hold your right hand at the upper 
left side of your chest and move the left 
upper arm up and down. What do you 
feel ? This bone is called the collar-bone. 
Its use is that of a brace ; it holds the arm 
away from the middle of the chest. 
What other bone moves when we raise or 
lower the arm or shoulder ? 
Describe the form of the shoulder- 
blade. What part of the body does it 
cover ? In what persons does it project ? 
It is used as a place of attachment for the 
large muscles that move the upper arm. 
There are fourteen bones in the An- 
gers and thumb, Ave at their bases, eight 
in the wrist, two in the fore-arm, one 
in the upper arm. The bone of the 
upper arm is connected with the trunk 
by means of the collar-bone and shoul- 
der-blade. 
Pig 65. 
Shoulder-blade, with its 
muscles. 
199. THE BONES OF THE LEO. There are fourteen 
bones in the toes, Ave in the foot, seven in the ankle, two in the 
lower leg, one in the upper leg. The bone of the upper leg is 
joined to the hip-bone. A round Aat bone on the front side of the 
knee-joint is called the knee-pan. BONES 
93 
How many bones altogether ? Which of 
these bones are smaller and which larger than 
the corresponding bones of the arm ? Is the 
arm less protected at the elbow-joint than the 
leg is at the knee-joint ? Which bone of the 
leg corresponds to the bone of the upper arm? 
The bone of the upper arm is joined to the 
shoulder-blade ; the shoulder-blade connects 
it with the trunk. What bone corresponding 
to the shoulder-blade connects the upper leg 
to the trunk ? 
The two hip-bones and the lower part 
of the hack-hone form the largest hony 
structure of the body; it supports the 
entire upper body and is itself supported 
hy the legs. 
200. THE CHEST. Fig. 67 represents 
all the bones of the chest. It looks some- 
what like a basket. How many ribs do you 
count on each side ? Which ribs are long 
and which are short ? Notice that the front 
parts of the ribs differ from the main parts. 
These front parts are pieces of elastic cartilage 
connecting the bony ribs with the breast bone. 
Is there a piece of cartilage to each rib ? 
What shape has the 
breast-bone ? With what 
are the ribs connected in 
the back part of the 
chest ? Name all the 
parts of the skeleton con- 
tained in the chest. 
The hones of the chest consist of twelve pairs of ribs, the 
breast-hone, and a part of the hack-hone. The upper ten pairs of 
ribs are connected with the breast-hone hy means of elastic 
cartilages. The two lower pairs of ribs are called floating ribs. 
Fig. 66. 
201. THE SKULL. Examine a skull and compare it with 
Fig. 68. Which bone of the skull is movable ? Does the remaining 94 
LEVERS AND BONES. 
part of the skull consist of one bone or of many bones ? How are 
these bones united with each other ? 
Look at the upper surface 
of the skull. The connection 
of the bones made by the 
edges fitting one into another 
is called a suture. It reminds 
us of the manner of connect- 
ing wood-work known as 
dovetailing. Two boards 
have their edges notched, 
and the projecting pieces of 
one fit accurately into the 
receding places of the other. 
One part of the skull is a 
bony box containing the 
brain. As the brain is very 
tender, any pressure, shock, or injury being followed by serious 
consequences, this bony box is exceedingly firm and strong. 
These qualities are the result of both form and structure. What is 
the form of that part of the skull which contains the brain? You 
may call it the brain case. 
How strong an oval case is, an egg may show you. Take its 
ends between your thumb and finger and try to crush it. Even a 
Fig. 67. 
strong man would not 
succeed. Perhaps you 
can crush it, if you 
put the ends in your 
two palms. Try it. 
The second cause of 
the strength of the 
brain-case is its struc- 
ture. Each bone con- 
sists of a smooth layer 
outside and a smooth 
layer inside, with a 
spongy mass between 
them. 
the head is received by the tough outer layer ; if this should he 
Fig. 68. 
A heavy blow upon HYGIENE OF BONES. 
95 
crushed, the softer middle layer moderates the jar, and the very 
hard inner layer will seldom be seriously affected. A tender object 
is well protected if placed in a tight box which is itself packed in 
hay or cotton and surrounded by a second, larger box. The brain 
is protected in a similar way. 
The remaining bones of the skull form several cavities whose 
function is to receive and protect the organs of sense. Which are 
the uppermost of these cavities ? Show the cavities of the ears and 
nose. The jaw-bones surround the seventh cavity of the skull. 
The skull consists of the hrain-hox, the cavities of the eyes, 
ears, nose, and the jaw-boue. The brain-case has an oval form 
and is exceedingly firm and strong. 
202. FOUR USES OF BONES. Which quality of the 
bones of the skull is the most valuable, and why ? Are long limbs 
more valuable than short ones ? What is the use of the bones in 
the limbs ? What is the use of the spines of the back-bone ? 
What is the main use of the bony structure of our foot ? 
Bones protect; they allow movements; they serve for the 
attachment of muscles; they carry the weight of the body. 
What bones protect the brain ? The eyes ? The inner ears ? 
The organs of the mouth ? The spinal-cord ? The lungs and the 
heart ? The lower intestines ? What bones are used for the most 
extensive movements ? What bones carry the greatest weight ? 
The largest muscles are located at the base of our limbs. To 
give them sufficient space where they may attach themselves, there 
are flat bones with great surfaces. Name them. 
Write a composition about all the bones of your body. Name 
them in groups or singly, tell what is the main use of each, whether 
or not they serve more than one purpose, and how their form and 
structure aid them in the accomplishment of their functions. 
Arrange them as long bones, flat bones, and round bones, and 
tell of what use their form is. In this arrangement consider the 
ribs as parts of one extended flat bone. 
Section 111. 
HYGIENE OF BONES. 
203. BROKEN BONES. Perhaps there are children in your 
school whose arms or legs have been broken. They may tell you 
how it happened, what the doctor did, and how long it took till the 96 
LEVERS AND BONES. 
limb could be used again. Have you seen a person whose fore-arm 
had recently been broken ? How had he to keep his arm, and why? 
If a person breaks a bone, a surgeon should be called at 
once. Meanwhile the sufferer should be kept as quiet as possible, 
and bandages soaked in cold water put around the injured part. 
If often renewed, they will prevent swelling and inflammation. 
When the broken bones are “set”, they must be kept per- 
fectly quiet till the pieces are grown together. 
An unskilled person, in trying to set a bone, usually does more 
harm than good, increases the suffering of the person injured, and 
delays the healing. 
204. CROOKED LEGS may be caused in two ways; either 
by standing or walking at too early an age —before the bones 
have attained the necessary strength—or by eating food lacking 
mineral substances. 
Suitable appliances ( splints and straps) should be used as soon 
as possible. In some cases such children should be given a more 
generous diet should eat more meat and eggs than usual, drink 
good milk, have plenty of fresh air, and take a daily (sponge) bath. 
205. ROUND SHOULDERS AND A CROOKED BACK. 
What is the cause of a crooked back ? At what age is the back 
most liable to grow crooked ? Sometimes before the children go to 
school they have acquired a crooked figure. Why do older persons 
not grow crooked ? 
Most persons of seventy years and over have a round upper 
back and keep their shoulders bent forward. Both—the danger of 
a humpback for children, and the round shoulders of old persons— 
show that the back needs strengthening and protection. Suitable 
exercises for strengthening the back (swinging the arms, rowing, 
sawing wood, mowing with a scythe, pulling a rope, mounting a 
rope) should frequently be taken, and a suitable rest for the small 
of the back should be used when persons are obliged to sit a long 
while. This will enable them to sit straight. 
Compare the looks of a person carrying himself straight, with 
his shoulders kept back, with those of a person bending forward. 
Are round shoulders a detriment to the health ? 
Round shoulders and a crooked back make a narrow chest. 
A narrow chest is accompanied by weakness and debility. A 
broad, capacious chest is the sign of health and strength. HYGIENE OF BONES. 
97 
The ancient statues of gods show physical perfection in the 
enormous capacity of their chests. Courage, intrepidity, and 
heroism are said to dwell in the strong chests of warriors. 
We should be desirous 
of developing strong 
chests and backs at the 
right time, in youth. 
206. TIGHT LACING. 
Look at Fig. 69. It repre- 
sents the bony chest of 
a woman twenty-three 
years of age, deformed 
by tight lacing. What 
organs are injured by a 
continuous pressure of the 
lower ribs ? 
Tight lacing injures 
the lungs, the heart, the 
liver, and the stomach. 
Tight lacing makes all 
healthful exercise im- 
possible. Women indulg- 
ing in it “get out of breath” easily, the least exertion fatigues them; 
Fig. 69. 
the heart is pressed against 
the stomach, the liver is 
crushed, and weakness of 
circulation and digestion are 
the inevitable consequences. 
No part of the body can 
be continually compressed by 
tight garments without caus- 
ing lasting injuries. 
207. TIGHT SHOES. 
Look at Figs. 70 and 71, and 
tell what they represent. 
What injuries are done by 
the wearing of tight shoes ? 
How is the ability to walk 
affected, if the great toe is 
Pig. to. 
Fig. ti. 98 
THE THREE LOWER SENSES. 
turned out of its place, or if one toe is pressed over the other ? 
What painful excrescences of the skin are caused by the pressure 
of tight shoes ? Which is easier and more natural—to walk on the 
toes, or on the whole sole ? 
Tight shoes and shoes with high heels injure the feet, make 
walking painful, lead to the avoidance of healthful exercises, 
and prevent ns from enjoying many innocent pleasures. 
A tight shoe turns the great toe out of place, and causes corns 
and bunions. Corns are horn-like excrescences of the skin. 
Bunions are painful inflammations of interior parts at the base of 
the great toe. High heels produce an awkward, unnatural gait, 
and induce fatigue. They cause a person to walk mainly on his 
toes. 
CHAPTER X. 
THE THREE LOWER SENSES. 
208. THE SENSE OF FEELINH enables us to perceive, 
firstly, that an object touches the skin; secondly, that an object 
is warm or cold; thirdly, that something causes pain. 
As a rule, the skin is more delicate on the front parts of the 
body, and on the inside of joints and limbs, and less delicate on the 
back of the body, and on the outer side of joints and limbs. The 
sense of feeling is most acute where the nerve-papillse (U 154) are 
most numerous. 
209. THE NOSE consists of two symmetrical halves. Its 
partition is bony at the base and cartilaginous in the front part. 
It contains two cavities, whose openings are called nostrils. 
These cavities are lined with mucous membrane. 
Do we usually breathe through the nose or through the mouth ? 
Do we derive any benefit from this manner of breathing ? One 
benefit is that the air, by passing through the long and intricate 
passages of the nose, is properly warmed before entering the lungs. 
Furthermore, it is, to a considerable extent, freed from dust. SOUND 
99 
210. SMELL is the sensation we experience by means of 
the nerves distributed throughout the nasal cavities. 
Since the nose is situated just above the mouth, it most conven- 
iently allows us to smell articles of food before taking them in. 
211. THE SENSE OF TASTE. The nerves of taste are 
distributed over the tongue and the back of the mouth. 
In a certain signification the sense of taste is called the lowest, 
yet it affords pleasant sensations and renders the daily act of eating 
agreeable. 
What danger follows the thoughtless gratification of this sense?* 
CHAPTER XI. 
SOUND AND THE EAR. 
Section I. 
SOUND. 
212. HOW SOUND IS PRODUCED. Attach one end of a 
knitting needle to a table and move the other in such a way that it 
will produce a sound. What organs give us knowledge of this 
sound ? 
As your ears are at a distance from the needle, there must be 
some connection between them. What substance is there between 
them ? 
Something must travel through the air from the needle to 
your ears. What is it ? What is sound, or noise, that it can travel 
from one place to another, through the air ? Is it a substance ? 
If it is no substance, and yet travels from one place to another, 
through the air, what is it? 
* The senses of taste and smell are closely connected and often con- 
founded. Many so-called tastes are actually smells, as, for instance, the 
sensations produced by_ spices, such as pepper, cinnamon, or onions. 
When the nose is held tightly closed, or when the nasal chambers are 
blocked or inflamed by a cold in the head, the “taste ’’ of these spices is 
not perceived. Normal tastes are: sweetness, sourness, saltness, and 
bitterness. 100 
SOUND AND THE EAR. 
If you can not find out, tell what takes place with the needle 
when we hear the sound. What takes place with the air which 
surrounds the needle ? There is a motion of the air near the needle, 
a motion called vibration. Can you tell now what travels through 
the air ? 
Our ears give us a knowledge of noises and sounds. Sounds 
are produced by vibrating objects. The motion travels through 
the air from the vibrating objects to the ears. 
How can you prove that the vibrations of the air travel in all 
directions ? 
218. SOUND-WAVES. As we can not see the motions or 
vibrations of the air, it is difficult to get a correct idea of the same. 
But vibrations similar to those of the air are seen in water when a 
stone is thrown into it. Describe these vibrations. 
The air vibrates in a similar way, except that the waves do not 
spread in one plane, or over one surface, as those of the water do, 
but in all directions, up and down, right and left, forward and 
back, and in all intermediate directions. 
Vibrating objects produce sound-waves in the air. Sound- 
waves spread in all directions. They form spheres; they are 
spherical. 
Fig. 72. THE EAR. 
101 
214. PITCH. How may we produce different sounds with a 
knitting needle ? What difference is there in the tones when 
longer or shorter portions vibrate ? What difference is there in the 
vibrations themselves when the vibrating pieces are short or long ? 
What can you tell of the vibrating strings of violins, guitars, 
pianos, etc. ? 
You saw a musician tune his violin. How did he do it ? Does 
a tone depend on the tightness, or tension, of a vibrating string ? 
What three qualities of vibrating objects decide the height or depth 
(pitch) of a tone ? 
Pitch is the degree of height or depth of a tone. It depends 
on the length, the thickness, and the tightness (tension) of the 
vibrating object. 
Long portions of knitting needles vibrate slowly and produce 
low tones ; short portions vibrate quickly and produce high tones. 
Long and thick strings produce low tones ; short and thin 
strings, high tones. 
A musician tunes his instrument by tightening or loosening 
the strings; the tighter a string, the higher the tone. 
Section 11. 
THE EAR. 
215. STRUCTURE OF THE EAR. The ear is composed 
of three parts, the outer ear , the middle ear, and the inner ear. 
The outer ear consists of the CARTILAGINOUS PIECE outside 
of the head and the 
PASSAGE leading into 
the head; the middle ear 
is an irregular cavity 
called the DRUM OF 
THE EAR; the inner 
ear is an irregularly 
shaped piece called the 
LABYRINTH. The 
outer and the middle ear 
are separated by a mem- 
branous partition called 
the DRUM MEMBRANE. 
Fig. 73. 102 
SOUND AND THE EAR. 
The outer and the middle ear are filled with air ; the inner ear 
is filled with a watery liquid. 
There is great difficulty in studying the structure of the ear 
from nature; it would he well for you to examine an enlarged 
model of an ear. 
216. THE OUTER EAR. Compare your ear with the ears 
of other animals. Of what benefit is it to animals to be able to 
move their ears ? What has the size of the ears to do with the 
acuteness of hearing ? What, then, is the use of the outer ear ? 
The outer ear catches the vibrations of the air and leads 
them to the middle ear, in a way similar to that in which a 
funnel carries water in one direction. 
Animals able to move their ears bring them into a position 
where they can best catch the sound; they turn the opening in the 
direction from which the sound comes. 
217. THE MIDDLE EAR is a cavity through which a series 
of little bones (the hammer, anvil, and stirrup) extends. The 
bones are made to vibrate by the drum membrane; they carry 
the vibrations further, to the inner ear. 
The middle ear is connected with the throat by means of a 
little tube called the Eustachian tube. (See Fig. 73.) 
The outer ear catches the vibrations of the air ; the inner ear is 
a box for the nerves; the middle ear, or the part between the 
catcher and the nerve-box, is especially adapted to the conduction 
of the vibrations of air, enabling them to assume a form, or condi- 
tion, in which they will most readily affect or irritate the nerves. 
The drum membrane, at the beginning of the middle ear, is a 
tightly stretched thin membrane. It is moved by the vibrations of 
the air contained in the air-passage. 
What is the use of the series of bones ? What substance, or 
medium, surrounds the series of bones in the middle ear ? 
The presence of air in the middle of the ear necessitates an 
open connection with the outside, with the atmosphere. If there were 
no connection with the outside, the inner air would be more or 
less dense than the air outside. How would that affect the drum 
membrane ? How would it affect the acuteness of hearing ? 
The connection is effected by a narrow tube, about an inch in 
length, which extends from the middle ear to the throat. It is THE EAR. 
103 
called the Eustachian tube. You may convince yourselves of the 
fact that you have two of these tubes in your head. Close your 
nostrils with your fingers, keep the mouth closed too, and fill your 
mouth with air ; inflate your checks. What do you feel ? Make 
the movements of swallowing. 
The disagreeable sensation in your ears is caused by the dense 
air in your mouth, which penetrates through the narrow tube into 
your middle ear and presses the drum membrane outwards, thereby 
hindering the free movements of the membrane and the series of 
bones. When you make the movement of swallowing, you open 
the throat-ends of the tubes, and the surplus air escapes. 
218. THE INNER EAR. The inner ear is the most peculiarly 
shaped part of the entire ear. Look at the piece resembling a 
snail’s shell, at the three tubes 
curved in various ways, and at 
the wider piece connecting the 
shell and the tubes. What is 
the substance of which these 
pieces are made ? What is 
inside? What part of the middle 
ear touches the inner ear ? 
The flat part of the stirrup, its 
footplate, is inserted into the 
wall of the inner ear, in such a 
way that its surface touches the 
fluid. To what part of the inner 
ear are the vibrations of the stir- 
rup transferred ? 
The inner ear, or labyrinth, 
consists of a peculiarly shaped, 
Fig. 74. 
hollow hone tilled with a watery fluid and hundreds of nerves. 
Each shake, swing, or vibration of the fluid affects or stimulates 
the nerves, and each stimulation of any of these nerves is 
perceived as sound. 
The function of the outer ear, the drum membrane, and the 
series of little bones, is to conduct the vibrations of the air to the 
liquid and the nerves occupying the inner ear. 104 
THE ORGANS OF VOICE. 
CHAPTER XII. 
THE ORGANS OF VOICE. 
219. THE VOICE-BOX (larynx) is the uppermost part of 
the windpipe. It is felt just below the skin, has a projection in 
its front and upper part, and is smooth at the sides. 
In what direction does the voice-box move ? Is there a differ- 
ence in the voice-boxes of different persons ? What difference is 
there in the voices of different persons ? Is there any connection 
between the size of the voice-box and the height and depth (pitch) 
of the voice ? 
220. THE VOICE-CORDS (or vocal cords) are two delicate 
bands of elastic tissue. Their bases are at the right and left in- 
ner sides of the voice-box. Their upper edges extend from the 
prominent point of the voice-box to a place directly opposite. 
The narrow slit between the edges is called the glottis. 
The voice-cords are neither drums nor strings, but partake of 
the nature of both 
Fig. 76 represents a model 
which may give you an idea of 
their shape and action. A strip 
of rubber cloth is laid around 
the end of a glass tube in such 
a way that about one inch of the 
rubber extends beyond the end 
of the tube. 
Fig. 75. 
Vocal Cords and Glottis. 
Fig. 76. 
Take two opposite portions 
of the projecting rubber between the fingers of your right and left 
hand, and slightly stretch the rubber. Now blow through the tube. 
What happens ? 
At what place has the air the greatest power, and where, there- 
fore, does it cause the rubber to vibrate ? 
The air sent through the vocal cords has its greatest power in 
the glottis ; it causes the edges, which are thick and round, to vi- 
brate more or less forcibly. Suitable muscles tighten the vocal 
cords more or less, according to the pitch of the sound which is to 
be produced. THE ORGANS OF VOICE. 
105 
221. THE MOUTH takes an active part in the production 
of the voice. Its cavity forms an air-chamber, which has a note 
of its own ; the lips, teeth, tongue, and palate vary the sound in 
many ways. 
Open your mouth wide and utter the sound of “a” as in 
“father”; then gradually narrow the mouth and protrude the lips. 
The sound “a” will change to “o” as in “more” and “oo” as in 
“food”. This proves the activity of the mouth in the production of 
the voice. 
If you desire to learn what organs of the mouth are active in 
the production of the various sounds, you must carefully observe 
these organs while you utter the simple sounds. Probably your 
grammar contains some statements regarding the same. 
222. CARE OF THE VOICE. Most good voices are spoiled 
in early childhood. Children produce load noises before their 
vocal organs are strong enough to permit such exertions. 
Many persons do not pay proper attention to the preservation 
of their voices, though the possession of a pleasant voice is a source 
of much pleasure and benefit, and but little care is needed to preserve 
its power and beauty. It is true that an excellent singing voice is 
the gift of nature, but many persons ruin, by improper treatment, 
what nature has bestowed upon them. 
The improper way in which many children scream rather than 
sing, in school and out, tends to impair the character of their vocal 
cords, hardens them, destroys their smoothness and uniformity, 
and makes their voices coarse and disagreeable. Whoever wishes 
to have a pleasant voice must not scream, wrangle, or sing boister- 
ously at any time, and when the throat is sore from any cause, 
must exert it as little as possible. 
Which persons have larger and stronger vocal organs—women 
or men ? Which, as a rule, have more pleasant voices ? How is 
that caused ? 
The purity of the voice is further endangered by some gaseous 
substances. How does it affect you if you accidently inhale the 
smoke of burning sulphur ? How does tobacco smoke affect you ? 
. Habitual smokers seldom possess a clear and pleasant voice. 
The constant irritation of the pungent tobacco smoke has an inju- 
rious effect upon the vocal cords. 106 
THE EYE AND LIGHT. 
CHAPTER XIII. 
THE EYE AND LIGHT. 
Section I. 
STRUCTURE OF THE EYE. 
228. PARTS OUTSIDE. 
There are numerous organs in 
connection with the eyeball. Place a finger on your 
forehead, just above one eye, and move it downward. 
What does the finger touch ? Draw the line which 
your finger describes. Compare it with the line in 
Fig. 77. Name the various parts of this line. Point 
to the outer surface of the upper eyelid; the upper 
surface of the lower eyelid ; the inner surface of the 
upper eyelid. 
A line drawn from the forehead to one of the 
cheeks, across the eye, touches the eyebrow, the 
upper eyelid with its eyelashes, the eyeball, and the 
lower eyelid with its eyelashes. 
Fig. 77. 
221. EYEBROWS, EYELIDS, AND EYELASHES. What 
is the use of the eyebrows ? Of the eyelids ? Whence does the 
light generally come into the eyes ? Which lids are used more, the 
upper or the lower? What arrangement that may be compared 
with the upper eyelids is used to protect rooms from too much sun- 
light ? Lift your upper eyelids between your thumb and fore-finger. 
What do you feel in the interior of the lid ? 
The eyelids and eyelashes shade and close the eyes and protect 
them from dust. 
The eyebrows prevent the sweat from running into the eyes. 
225. THE EYEBROW-ARCH, Place three fingers on one 
eyebrow; move them up and down. What do you feel? This 
bone is somewhat like an over-hanging roof. Is it of benefit to us? 
In what way does it protect the eye? STRUCTURE OF THE EYE. 
107 
We compared our eyelids to awnings or shades. Is there any- 
thing near the windows which might be compared to the eyebrow- 
arch ? 
The eyebrow-arch (superciliary arch) forms a projection 
over the eyeball, and serves to guard it from blows and bruises. 
The eyebrow-arches of monkeys, bears, lions, and other animals 
are larger and more prominent than those of men. Persons with 
large and prominent eyebrow-arches have a savage, ferocious look. 
226. GLANDS OF THE EYE. How does the surface of the 
eyeball look, compared with that of the surrounding skin ? How 
does the surface feel ? What is spread over the surface of the 
eyeball ? 
Is tear-water secreted in the eyes of all persons ? Is it secreted 
daily ? Is it secreted in the eyes of animals ? Whence does the 
tear-water come, or by what organs is it secreted ? 
The tear-glands are situated below the outer ends of the 
eyebrows ; the oil-glands are situated inside of the lids. Their 
joint secretion keeps the surface of the eyeball smooth and 
shining. 
If you handle the lid carefully, you can see the outlets of the 
oil-glands with a small magnifying glass in the following manner: 
Lift the lower lid of a person by gently pressing your finger upon 
it, and moving it downward ; then look at the internal edge. What 
is at the external edge of the eyelids ? 
Sometimes the little oil-glands, whose outlets you have seen, 
become conspicuous in a disagreeable way. They swell, inflame, 
and form what is called a sty. 
When you tried to see the little openings, or outlets, of the oil- 
glands, you should have seen one larger opening. Where? Find 
something similar in the upper eyelid. These two large openings 
are the mouths of two canals, through which the surplus tear-water 
is carried off toward the nose and throat. 
In addition, the inner corner of the eye contains a cluster of 
little glands which secrete a slimy substance. This substance 
collects during the night; in the morning we find it dried and 
hardened. 
227. THE SURFACE OP THE EYEBALL. Look at the 
dark center of the eyeball of your neighbor. What do you see 108 
THE EYE AND LIGHT. 
there ? Tell him to look toward a window and move a book up and 
down before his eyes. What do you notice ? Of what else may 
you see an image in his eyes ? Where have you seen similar 
images ? What do you call objects in which you see images ? Why 
is it that our eyeballs act like mirrors ? Do all smooth or highly 
polished surfaces act as mirrors ? 
The surface of the eyeball acts like a mirror, because it is 
smooth and shining. 
228. THE EYEBALL. Bring the eyeball of a calf. It is 
very similar to our own. What is its shape? We often hear 
persons speak of oval eyes, or of eyes shaped like almonds. Are 
they different from such as this ? 
What is the size of the eyeball ? What do you see outside of 
the eyeball, attached to its enclosing membrane ? These flat pieces 
are portions of muscles. The butcher has cut through them, and 
we see only those parts that are near the eyeball. Why must there 
be muscles ? 
At what place do you see a short white cylinder ? Do you 
think it was longer when the calf was alive ? What is its name? 
Examine it once more. How thick 
is it, and what is its consistence ? 
Do you know a similar substance ? 
The eyeball has the shape of a 
sphere; its diameter is nearly an 
inch. Several muscles are at- 
tached to its surface. The optic 
nerve enters the eyeball at a place 
near the center of the back 
surface. 
The muscles move the eyeball 
in many directions. The optic 
nerve reaches from the eye to the 
brain. If it were cut, or its con- 
nection were severed, we should 
be blind. By means of the optic 
nerve the brain obtains knowledge 
of what is going on in the eye. 
229. MEMBRANES. Instead 
of the word eyeball, some persons 
use the term bulb of the eye. The 
Fig. 78. Left eyeball; a, b, c, d, g 
muscles; f, optic nerve. STRUCTURE OF THE EYE 
109 
structure of the eyeball is similar to that of a bulb ; both consist of 
several thin pieces, or enclosing membranes, and a large central 
piece. 
The eyeball is enclosed by three membranes called the white 
membrane, the blood-membrane, and the net-membrane. The 
white membrane protects the eye; the blood-membrane nourishes 
the eye; the net membrane is affected by the light. 
Where is the proper place for the protecting membrane ? What 
qualities are expected from a protecting membrane ? Press a 
knife against the eyeball. Try to cut it, What makes the knife 
glide off ? In this way you will find that it serves its purpose well. 
The white membrane (sclerotica)* is seen at the surface of the 
eyeball; it is tough, thick, and strong. The blood-membrane 
(choroid) is the membrane next below the white membrane ; it is full 
of blood-vessels. The net-membrane (retina) is the internal mem- 
brane ; it is very delicate. 
ball and look at the membranes, we will try to find out more by 
observing our own eyes or those of our neighbors. Does the white 
membrane surround the whole eyeball ? Why must there be a 
transparent piece in front ? This transparent piece is just as hard 
and strong as the white membrane. 
280. THE HORN-MEMBRANE. Before we open an eye- 
Close one of your eyes. Place one or two of your fingers 
gently upon the eyelid, and move the eyeball in different directions. 
What do you feel ? 
The horn-membrane (cornea) is the transparent front part 
of the white membrane; its outline is circular. 
The horn-membrane is fastened to the white membrane in 
nearly the same way that a glass is fastened on a watch. 
The exterior surface of the horn-membrane is more prominent 
than the rest of the eye. 
281. THE PUPIL is a circular opening in a colored ring 
below the horn-membrane. It looks like a black spot. 
Pupil is the name for yourself. Why has this black spot been 
given your name ? Suppose your father looks at the pupil of your 
* It should be understood that there is no particular knowledge con- 
veyed bv these scientific names, and that correct ideas about shape and 
nature are worth more than scientific names. Popular names are prefer- 
able, because their meaning is more generally understood. 110 
THE EYE AND LIGHT. 
eye, how does he appear there? Everybody looks small in the eye 
of another. Can you guess at the reason now? A similar word 
is puppet, a doll, or a small person. 
282. THE RAINBOW-MEMBRANE is the colored ring sur 
rounding the pupil. What color has it ? Observe the eyes of some- 
one whom you first ask to direct his looks toward a distant object, 
and then, to read from a book close by. What changes occur in his 
rainbow-membrane and pupil ? Observe that the outline of the 
rainbow-membrane remains the same. 
What is the size of the pupil in a glaring light ? When is it 
very large ? What causes the rainbow-membrane to expand ? Is 
this arrangement useful ? What animals change the size of their 
pupils more remarkedly than we do ? What advantage does this 
give them? Can cats and owls see in a place which is entirely 
dark ? 
Look at the rainbow-membrane once more. Is it convex or 
flat ? Draw a picture representing the shape of the rainbow-mem- 
brane. How many and what lines do you need ? 
There is a cavity between the horn-membrane and the rainbow- 
membrane. What form has this cavity? Do you observe any 
substance in this cavity ? 
The rainbow-membrane (iris) is a colored ring surrounding 
the pupil. In strong light the pupil becomes smaller by the 
extension of the rainbow-membrane. 
The space between the horn-membrane and the rainbow- 
membrane is rounded in front and flat behind. It is filled with 
a transparent fluid called the eye-water (humor aqueus.) 
You are now ready to open an eyeball and examine its parts. 
Any butcher will oblige you by cutting an eyeball from the head 
of a calf or sheep. Bring it to the next lesson, and, besides, pro- 
vide yourselves with a sharp knife, a pair of scissors, a plate, and a 
towel. 
283. THE INTERIOR OF THE EYEBALL. Before you 
open the eyeball, cut off the fat, the connective tissue, and the 
portions of muscles. 
Try to cut through the white membrane in a direction parallel 
with the rainbow-membrane. Is it easily cut through ? STRUCTURE OF THE EYE. 
After you have succeeded in making a small opening, cut all 
around with your scissors, thus dividing the white membrane into 
a front and a back half. What do you see of the interior ? 
Turn the white membrane hack. What do you see now ? This 
gelatinous substance is called the jelly of the eye (humor vitreus). 
Separate the membranes from the jelly, and put the jelly on the 
plate. What special piece do you notice in the jelly ? Find the 
lens of the eye. Loosen it with your scissors by cutting all around 
the margin. What quality is most prominent in the lens and the 
jelly ? 
Place the jelly in water. How does it look there ? What 
forms have the two sides, or surfaces, of the lens? Which substance 
is harder, the lens or the jelly ? Squeeze the lens between your 
fingers. What do you notice ? 
Try to find the blood-membrane, the rainbow-membrane, and 
the net-membrane. What do you find on both surfaces of the 
blood-membrane ? Show the circular opening of the rainbow- 
membrane. What is it called ? Is it still black ? 
What peculiarity of the net-membrane do you notice ? Look 
at the outside. What is exactly opposite the place where the net- 
membrane is fastened ? The net-membrane is the continuation of 
the optic nerve; it is the optic nerve spread in the form of a mem- 
brane. 
You may now draw a figure to rep- 
resent the section of the eyeball 
obtained by dividing it into a right 
and left half. Compare your draw- 
ing with Fig. 79. 
A longitudinal section of the 
eyeball (Fig. 79.) shows the 
white membrane in connection 
with the horn-membrane, the 
blood-membrane in connection 
with the rainbow membrane, the 
optic nerve in connection with the 
net membrane; furthermore, the lens that separates the eye 
water from the jelly of the eye. 
Fig. 79. 112 
THE EYE AND LIGHT. 
Section 11. 
LIGHT. 
234. THE LENS. What part of the eye is similar to the 
object represented by Fig. 80? In what respect do the two differ 
from each other ? Both are called lenses and are essentially the 
same in regard to light. They may differ in size and material, 
but all (optical) lenses are transparent and have a similar form. 
Hold a (double-convex) lens in the rays of the sun, and find a 
very brilliant and hot spot, not far from the glass. How does this 
spot become brilliant and 
hot ? What is the direc- 
tion of the rays before 
they Dgo through the 
glass? And afterwards ? 
Hold the lense near a 
piece of white paper, till 
an image of the window 
Fig. 80. Convex Lens. 
appears. Compare the image with the window itself 
Close the shutters, in order to exclude the bright day-light, 
and hold the lens near a lighted candle. Find a large inverted 
image of the flame on an opposite white wall. 
Lastly, hold the lens near your hand while you look through 
it. How do your fingers appear ? How does this image differ 
from the image on the wall? 
A double-convex lens (a burning-glass) may produce three 
kinds of images; a small and inverted image, a large and in- 
verted image, and a large and upright image. 
A picture is something painted or drawn and consists of material 
substances. An image is not painted or drawn; it consists of light. 
235. THE CAMERA OBSCURA is an apparatus made for 
the purpose of showing the small inverted images which are pro- 
duced by means of a lens. 
Usually it is a rectangular box whose inside is painted black or 
is covered with black paper. There is a lens in front and a piece of 
ground glass in the rear on which the image appears. The distance 
between the lens and the ground glass can be regulated. LIGHT 
113 
Such a box is not complicated ; you can easily construct one 
yourselves. A lens can be bought for 25 cents. The rest is card- 
board, paper, and thin board. A piece of looking-glass placed at an 
angle of 45 degrees (half of a right angle) against the back wall will 
Fig. 81. 
change the inverted image to an upright one, appearing on the 
upper wall which should then be made of ground glass. In this 
shape the camera obscura affords an excellent aid for drawing pic- 
ures of landscapes or other views. 
286. OPERA GLASSES consist of two tubes, each contain- 
ing a convex and a concave lens. They are made for the purpose 
of showing large, upright images of distant objects. 
Unscrew the lenses from one of the tubes and find out what 
images they give. 
Fig. 82. Concave Lens. 
Look at a near object first with one, then with the other lens. 
Why might you have expected that convex and concave lenses 
would produce opposite effects ? 114 
THE EYE AND LIGHT. 
A convex lens collects parallel rays. What may you expect a 
concave lens to do with the same ? Try it. Let parallel rays of the 
sun fall on a concave lens and observe the light spot on the other 
side. Try it at different distances. 
Represent the divergence of rays through a convex lens in a 
drawing. Continue the diverging lines backward. What do you 
find ? 
A convex lens concentrates the light in almost a single brilliant 
point; it causes parallel rays to converge. A concave lens spreads 
the light; it causes parallel rays to diverge. A convex lens is also 
called a converging lens ; a concave lens, a diverging lens. 
What change do you see in the appearance of distant objects if 
you look at them through opera glasses ? Can you use the opera 
glasses in such a way as to make the objects appear smaller and 
farther off ? 
287. SHORT-SIGHT. There are some who are obliged to 
wear spectacles because they are near-sighted. See what kind of 
glasses they have. 
Where are there more near-sighted persons, in cities or in the 
country ? Why ? Does short-sight (near-sightedness) depend only 
on the length of time during which we read or write, or have the 
kinds of books we read anything to do with it ? 
Not only should the use of small print be avoided, but also the 
use of tracing books in penmanship lessons, of paper with narrow 
lines for drawing exercises, as often found in kindergartens, and 
the use of everything else that necessitates a strain of the eyes. 
Short-sight is usually caused by immoderately exerting the eyes 
during school days. 
If we lean forward and keep our eyes too near the book, we 
hurt them in two ways : firstly, too much blood enters the eyes when 
the head is bent down ; secondly, we accustom them to short 
distances. Both causes tend to increase the convexity of the lens 
and to create short-sightedness. 
We should not only look at near objects, but often direct our 
looks toward distant ones, that we train our eyes in both direc- 
tions, and improve their power of accommodation. 
Short-sighted persons wear concave spectacles. Short-sight 
is caused hy reading and writing too much, by using small print LIGHT 
115 
oi’ narrow lines, or by working in unsuitable light, or in improper 
positions. 
Remember the following rules ; 
3. Do not read or write when you can not plainly see the 
letters or lines. 
1. Do not read or write when the sun shines on your book. 
3. Let the light enter from the left side or from the rear (not 
from the right side or from the front). 
4. Do not bend your head down when you are reading or 
writing. 
5. Often direct your looks to distant objects. 
Near-sighted persons, particularly. children, should not use 
spectacles at all times, but try to recover part of the lost power by 
moderate training, and, above all, should observe the foregoing rules. 
288. LONG-SIGHT. In what persons have you observed 
far-sightedness ? How did you find this out ? 
Many persons grow far-sighted in old age. This is caused by a 
flattening of the horn-membrane and lens, which do not receive as 
much nourishment as formerly. Others become far-sighted 
because they are not used to reading, writing, or looking sharply at 
near objects; they are persons who live mostly outdoors. Name 
them. 
Long-sighted persons use convex glasses. 
Old persons who have grown far-sighted should not hesitate to 
use suitable spectacles when looking at near objects. If they 
strain their eyes, they will increase their defect. 
289. SELF-LUMINOUS OBJECTS. We have learned about 
the eye, about lenses and images produced by them, and about 
apparatus in which lenses are used. It is now time to study that 
which gives real value to all these appliances, without which 
they would be useless. What is it that enters the eyes, that passes 
through lenses and is changed by them in different ways ? 
All around you are objects. You close your eyes and the objects 
disappear; you open them and the objects stand out clearly. 
Whence does the eye receive the light which shows this table, this 116 
THE EYE AND LIGHT. 
wall, and this chair ? Do all visible objects throw out light ? Is 
the table visible at all times ? What two classes of visible objects 
can you distinguish ? 
Self-luminous objects are those which send out their own 
light. Objects that are not self-luminous can not be seen unless 
the sun or another self-luminous object throws light on them. 
Give a list of self-luminous objects ? Have you seen self- 
luminous objects darting through space high above your heads ? 
Have you observed or heard of self-luminous animals ? What is 
meant by the phosphorescence of the sea ? 
240. TRANSPARENT, TRANSLUCENT, AND OPAQUE 
OBJECTS. Transparent bodies transmit rays of light, so that 
objects can be distinctly seen through them ; translucent bodies 
transmit rays of light without permitting objects to be distinctly 
seen through them; opaque bodies do not transmit rays of light. 
Name objects belonging to each of the three classes. Is water 
transparent or translucent ? Can you look through fifty feet of 
water ? If it were very pure, you could, but as it is in our rivers 
and lakes, you can not. 
May water be transparent or opaque ? Is air absolutely trans- 
parent ? Is the air in valleys as transparent as the air on 
mountains ? How can jmu prove that glass is not absolutely 
transparent ? 
241. RAYS OF LIGHT. All visible objects radiate light. 
Can you prove that they do this in all directions ? Can you also 
prove that light is radiated in straight lines ? What are the straight 
lines in which the light moves, called ? 
Visible objects radiate light in straight lines and in all di- 
rections. These straight lines are called rays of light. 
Construct two paper tubes, one to fit closely over the other. 
Cover the outer end of one with an opaque piece of paper that has 
a small opening in the middle, and the outer end of the other with 
a piece of tissue paper. Hold the tube opposite a window or a 
lighted candle, with the opaque paper directed toward the same, 
and move the other tube in and out till you see an image of the 
window or lighted candle on the tissue paper. LIGHT 
117 
This apparatus is called an optic chamber or a camera optica. 
Compare the image with the object. Why is the image inverted ? 
What quality of the rays is proved by the inversion of the image ? 
In summer time you may sometimes observe numerous bright 
circles in the shadow of a tree. Whence does the light come which 
forms the circle? Of what are the bright circles images ? Under 
which trees do these circles appear large, under which, small ? 
When may you expect the bright circles to change to the form of 
sickles or crescents ? 
Sometimes the bright images of the sun on the ground partly 
over-lap each other. What will be the final result, if we constantly 
increase the number of openings between the leaves ? 
242. SHADOWS. When does a shadow appear ? Compare 
the two sides of an opaque object placed in the sunlight. Is the 
darkness only at the surface of the opaque object, or does it extend 
into the space behind the object ? What is the name of this dark 
space ? Define shadow. 
What difference is there between your own shadow in the 
morning, at noon, and in the afternoon ? What changes do you 
notice in your shadow when you pass a street lantern ? When is 
the shadow darkest ? 
Let the shadow of the bars of a window through which the sun 
shines fall on a piece of white paper. Is it of equal intensity every- 
where ? 
Represent the sun, the earth, and the shadow of the latter in a 
drawing. Compare the size of the shadow nearer the earth with 
the size of the shadow farther off. Imagine the whole shadow to 
be a body having height, width, and length. What is the form of 
this body ? 
In what position is the moon in relation to the sun and earth 
when struck by this shadow ? What phenomenon will then be 
observed ? Such an eclipse may last If hours. 
What are the conditions of 
a total eclipse of the sun ? 
The diameter of the shadow 
which in such a case falls 
upon the earth, averages 
about 150 miles, and the 
longest time an eclipse of 
Fig. 83. 118 
THE EYE AND LIGHT. 
the sun can be total at any place on the surface of tbe earth, is a 
little less than eight minutes. 
A shadow is the dark space behind an opaque and lighted 
object. It has two parts the full shadow and the half shadow 
(umbra and penumbra.) 
The full shadow of the earth has the form of a cone. If the 
moon passes through this shadow, there is a total eclipse of the 
moon. The full shadow of the moon has likewise the form of a 
cone. If a part of the earth’s surface passes through this 
shadow, it will be totally eclipsed ; if it passes through the half 
shadow of the moon, it will be partially eclipsed. 
248. REFLECTION. Put a piece of glass where it will 
reflect a ray of sunlight. Hold a string in the ray of reflected 
light. Where does the reflected ray commence ? Where does it 
end ? Hold a string in the original or direct ray of sun-light. 
Where does this ray commence and 
end ? Represent the direct ray, the 
piece of glass, and the reflected ray 
n a drawing. 
A ray of light falling on a piece 
i)f glass is thrown hack or reflected. 
The reflected ray and the direct ray 
form equal angles with a perpendic- 
ular (b d) erected at the lighted point. 
Fig. 84,. 
244. DIFFUSION. Put a piece of white paper in the place 
where the glass has reflected the sunlight. Does the paper reflect 
the light which the sun sends upon it ? How do you know ? 
Where does the paper send the light which it reflects ? What 
difference is there between the direction of the light reflected by the 
glass and that reflected by the paper ? This difference is caused by 
a difference between the reflecting surfaces. Feel the surface of 
the glass and of the paper. What difference is there between the 
two? Look at both with a magnifying glass. 
There are thousands of rays falling on the little piece of paper. 
Each little elevation and each little depression is struck by many 
rays. LIGHT 
119 
Sunlight falling on surfaces 
which are not perfectly smooth is 
scattered in all directions. Light 
scattered by reflection is called 
diffused light, the reflection itself, 
diffusion. 
Name objects that diffuse light 
as paper does. Whence do we 
Fig. 85. 
receive the diffused light shortly after sunset and before sunrise ? 
245. NECESSITY OF DIRECT SUNLIGHT. In winter 
and spring we like to be in direct sunlight; in summer we seek the 
shade. In this particular, children should imitate the good example 
of almost all animals, which like to bask in the sun. 
You raise the objection that the direct sunlight burns the skin, 
causes freckles and sun-strokes, hurts the eyes, and lessens our 
energy ; we soon become tired when working in the sunshine. 
You are right; we should use it intelligently. We do not, when 
we exclude it altogether from our dwelling rooms, fearing, perhaps, 
the bright colors of carpets or curtains might fade. The sun is our 
friend, when we understand how to use it, 
Direct sunlight, when intelligently used, gives us a healthy 
complexion, makes us cheerful, and heightens our energy. It 
should not be entirely excluded from our dwelling rooms. 
246. THE LOOKING-GLASS. Compare the image in a 
looking-glass with the object itself. Do the image and the object 
look perfectly alike ? Open your reader, hold it in front of a 
looking-glass, and read from the image. How do the object and 
the image differ ? In what are they alike ? Should you look in a 
glass while raising your right arm, what arm is raised by your 
image ? 
An object and its image in a looking-glass are alike in size, 
color, and distance from the glass, but are changed in regard to 
sides; what is right in the object, is left in the image, and vice 
versa. The object and its image are said to be symmetrical. 
247. REFRACTION. Put a stone into a washbasin. One 
of the pupils may go near the washbasin, look at the stone and 
then move backwards till the stone is out of sight and hid- 120 
THE EYE AND LIGHT. 
den by the side of the washbasin. Now pour water into the 
washbasin, but do not let the stone change its place. When there 
is a sufficient quantity of water in the basin, the pupil, without 
having changed his place, will again see the stone. 
Whence does the light come which shows him the stone ? 
Stretch a string between the stone and the eye of the pupil. This 
shows that the light does not 
move in a straight line. It 
does so in the water, but 
when it changes water for 
air, it changes its direction 
too. 
In the direction of what 
light does the pupil see the 
stone ? It is a general law 
that we see everything in 
the direction of the light that 
Fig. 86. 
enters the eye. We do not assume that we can look around a 
corner, though in fact we do it daily, The pupil has looked around 
the corner of the washbasin. We can look at things behind our 
back, if we use a looking-glass. 
Does the stone appear in the same place in the basin filled with 
water as it does in the dry basin ? Does the bottom of the wash- 
basin seem to have changed its position ? Does the depth of the 
washbasin seem to be the same as before ? If you look at pebbles 
or other objects in the water of a brook or pond, where do they 
seem to be ? Why does a cane or an oar appear to be broken 
when partly immersed in water ? 
Rays of light are refracted when changing their medium. * 
To refract means to break or change the direction. The 
medium is the substance through which the light moves. An 
object lying in water appears to be in a higher place than that in 
which it really is. This is caused by the refraction of the light 
at the boundary of water and air, and by the fact that everything 
is seen in the direction of the light which enters the eye. 
* There is but one exception ; that is, when the rays of light pass the 
boundary at right angles. FUNCTIONS OF THE EYE. 
121 
Section 11. 
FUNCTIONS OF THE EYE. 
248. THE EYE is similar to a camera obscura. Each has a 
lens, is dark inside, and excludes all the light not entering 
through the lens. Each is filled with a highly transparent 
substance; the hack wall of each presents a suitable surface for 
the reception of the image; in each, the image is small and 
inverted. 
The highly transparent substance in the eye is the jelly of the 
eye (vitreous humor), that of a camera obscura is air; the back 
wall of the eye is the net-membrane (retina), that of the camera 
obscura is the ground glass. 
249. PROJECTIONS OF IMPRESSIONS. About eighty 
years ago a curious case was brought before an English Judge. 
A man had been assaulted and robbed on a dark night, and a certain 
person of bad repute was suspected of being the evil doer. 
He denied the charge, and as no third person had been present 
when the robbery took place, conviction seemed impossible. But 
the man robbed asserted that he recognized the culprit “because he 
had seen his features by the light rushing from his own eyes when 
they were struck by the robber”. The Judge did not know whether 
to admit this evidence or to reject it. How would you have decided ? 
Do you believe the story of Baron Muenchhausen, who, finding 
that he had forgotten his matches, lighted his pipe with the sparks 
that flew from his eye when he struck it with his fist ? 
Close you eyes and thrust a finger between an eyebrow arch and 
the adjoining eye. What do you observe ? Thrust a finger between 
the cheek-bone and the adjoining eye. What do you observe ? 
What is proved by these experiences ? Direct your attention to the 
places where you perceive the light. 
Every impression that the net-membrane receives is projected 
outside. We do not perceive the image on the net-membrane, 
but the objects that produce the image. 
If a spot in the upper half of the net-membrane is irritated, we 122 
THE EYE AND LIGHT. 
perceive light below the eye ; if a spot in the lower half of the net- 
membrane is irritated, we perceive light above the eye. The 
inverted image on the net-membrane causes the perception of 
upright objects outside. 
250. DURATION OF IMPRESSIONS. A live coal moved in 
a circle appears as a bright line. How can this be explained ? Name 
similar phenomena. Draw the picture of a bird on a piece of card- 
board, and that of a cage on the opposite side. Fasten two strings 
at opposite places, and whirl the cardboard around this string. 
What do you see ? 
Impressions made on the net-membrane last longer than the 
time during which the corresponding objects are in their places. 
251. USE OF TWO EYES. Put a thick book upright before 
you with its back opposite your nose, close one eye, and notice how 
much of the book you can see. Close the other, and notice the 
same. What do you find ? 
Look at the objects in your room with but one eye, then with 
both eyes. In which case do you see the objects more correctly ? 
A near object produces two unequal images in our two eyes— 
one representing more of the left side, the other more of the 
right side. The inequality of the two images is the reason why 
we see the object as a body, not as a picture. 
Fig-. 87. The images of a cube in the two eyes. FUNCTIONS OF THE EYE. 
123 
The two eyes enable us to see more of an object than could be 
represented in a drawing. 
252. THE STEREOSCOPE is an instrument with two pris- 
matic glasses at one end and a place for two well lighted photo- 
graphs at the other. A partition extends from between the two 
glasses towards the middle of the photographs. 
Hold a printed sheet in the place for one of the photographs, 
letting it extend over the upper margin of this place ; then look 
with one eye through the glass on this side, and notice how the 
print is changed in place and 
appearance. 
Close the eye with which 
you have just looked and 
find out whether you can see 
the printed sheet (whose 
place must remain unchang- 
ed ) with the other eye. Try 
the same with the other side. 
Now look with both eyes at 
the printed sheet, this time 
placed under both glasses. 
If you take two photo- 
graphs instead, they will also 
Fig. 88. 
overlap each other, and as they are nearly alike, you will not notice 
that you look at two photographs ; they will appear as one object. 
In the same way you do not usually notice that you get two impres- 
sions of one object before you, one from each eye. 
The two photographs resemble the two views of an object 
which we get with twro eyes. The photographer took them from 
two different places. He photographed an object or landscape 
twice at the same time, with a double camera obscura, just as if the 
two eyes had fixed the images of their net-membranes. 
Sometimes the objectivity produced by photographs in stereo 
scopes appears greater than in nature, and the distances between 
things nearer and farther off, magnified and unnatural. In this 
case the two camerse obscurse were not arranged correctly ; they 
gave views that would be seen with eyes half a foot apart from 
each other. This inequality may be increased so far as to make 124 
MAGNETISM. 
it impossible for us to unite the two views into the appearance of 
one object. 
It is interesting to notice that in certain cases our eyes, similarly, 
show us two pictures instead of one object. Hold one finger at a 
distance of about eight inches in front of your face, a finger of 
the other hand eight inches further off, and then look steadily 
at one of the fingers. How does the other appear ? 
This concludes our studies in optics. I hope you have gained 
some knowledge of this beautiful and highly interesting branch of 
science, but the object aimed at in teaching you would be very im- 
perfectly attained indeed, if you should now cease to think and 
study. You have seen on previous occasions that there is much 
that you may find out, either by your own observations and 
thoughts, by consulting books, or by conversing with educated 
persons. 
CHAPTER XIV. 
MAGNETISM. 
250. MAGNETS. Of what substance or material are magnets 
made ? Show what they can do. Find out whether all parts of the 
surface attract 
iron and steel. 
Fasten a small 
iron ball to a 
string, hold a bar 
magnet upright, 
and move the 
iron ball along 
the magnet, 
without touch- 
ing it. What do 
you observe ? 
Cover the magnet with a sheet of paper, and find out whether 
it attracts through the paper. Strew iron filings on a sheet of paper 
covering a magnet. What do you see ? 
Fig. 89. MAGNETISM. 
125 
Magnets are pieces of steel which have the power of attract- 
ing iron and steel. The places having the greatest attractive 
power are called the poles. 
How many poles has a magnet, and where are they ? 
254. INDUCTION. Get a knitting needle and find out 
whether it is magnetic. If it is not, place the two poles of a horse- 
shoe magnet upon the middle of the knitting needle, move them to 
one end of the needle, then to the other, then again to the first, 
repeat this motion twenty times each way, without lifting the 
magnet off the needle, and at last lift it from the middle. See 
whether the needle has grown magnetic. What use have we made 
of the horseshoe magnet ? 
A magnet may be used to develop (induce) magnetism in a 
piece of unmagnetic steel. 
255. MAGNETIC NEEDLE. Try to balance the magnetic 
knitting needle on the nail of your thumb. Notice in what position 
it rests. Take it off the nail and try again. Suspend a double wire 
loop (Fig. 90.) from a string and balance the needle 
in it. Watch the position and direction of the 
needle each time. Do you notice anything remark- 
able ? 
A magnetic needle, capable of freely turning 
on its center, points with one end to the north and 
with the other to the south. 
The end of the magnet pointing to the north is 
called the north pole ; the end pointing to the south 
is called the south pole. 
In what other way can we find north and south? 
What persons must know at all times where north 
and south are ? What do they use for this purpose? 
A compass consists of a box with a magnetic 
needle. The magnetic needle is capable of freely 
Fig. 90. 
Wire loop. 
turning on its center. The bottom of the box contains the names 
of directions, or the points of the compass. 
256. NORTH-MAGNETISM AND SOUTH-MAGNETISM. 
Hold the north pole of a bar magnet near the north pole of the 
magnetic needle. What do you observe ? Suspend the bar magnet 126 
ELECTRICITY. 
in the wire loop and hold the north pole of the needle near the 
north pole of the bar. What do you observe ? Learn how the 
south poles of two mag- 
nets act towards each 
other. Learn how the 
south pole of one magnet 
acts toward the north 
pole of another and vice 
versa. 
The magnetism of the 
north pole is called north- 
magnetism ; the magnet- 
ism of the south pole is 
called sonth-magnetisin. 
Like poles of magnets 
repel, unlike poles at- 
tract each other. 
Fl®-91- 
The north pole of a 
magnet attracts what the south pole repels; the north-magnetism 
and the south-magnetism are of opposite qualities. 
CHAPTER XV. 
ELECTRICITY. 
257. AMBER OR ELECTRON. The substance we must 
use is called amber. It is found on the shores of the Baltic Sea 
especially after 
a storm. Large 
pieces are highly 
prized. Describe 
its appearance. 
Rub a piece of 
amber with a 
woolen cloth and 
hold it over small 
pieces of paper, 
(shreds of cotton 
Fig. -92. ELECTRICITY. 
127 
or silk, feathers, gold-foil, bran, saw-dust, or any other light 
object). What do you observe ? 
A piece of amber, after having been rubbed with a woolen 
cloth, attracts light objects. The Greek name for amber is 
electron. Electricity is the attractive power of amber. 
258. ATTRACTION. Heat a piece of writing paper over a 
lamp, place the paper on a table, rub it a few times with India 
rubber, lift it carefully, and place it near a wall. 
Suspend a wire loop from a narrow ribbon, and balance a walk- 
ing stick in the loop. Rub a rubber comb with a piece of flannel 
and try to pull the stick around with the comb. Place the comb 
in the loop and try to pull it around with the stick. 
Instead of the comb and flannel use a glass tube about 18 inches 
long and | of an inch thick, (not thinner, lest it should break in 
your hands and injure you), and a silken pad composed of three or 
four layers of silk, and repeat the former experiments. 
Place an egg in an egg cup and balance a lath of about four 
feet in length upon the egg. Let it follow the glass, comb, or a piece 
of sealing wax. Attract soap bubbles with electrified bodies, let 
empty egg shells, paper hoops, and other light objects roll after 
them. 
Electrified and unelectrifled bodies attract each other. 
Electrified bodies are those having the power of rubbed amber. 
259. REPULSION. Suspend a wire loop from a narrow 
silken ribbon, place an electrified comb in the loop, and approach 
it with another electrified comb. Bring an electrified glass tube 
near the electrified comb. Suspend an electrified glass lube and 
approach it with another electrified glass tube. What conclusions 
do you draw from your observations ? 
There are two kinds of electricity (as there are two kinds 
of magnetism); the one electricity is called the positive (glass) 
electricity, designated by the sign +. The other is the negative 
(rubber) electricity, designated by the sign—. 
Objects having the same electricity repel each other; objects 
having opposite electricities attract each other. 
Determine what kinds of electricity are developed in sealing 
wax, rock crystal, paper, shellac, and other substances. 128 
ELECTRICITY. 
260. CONDUCTORS AND INSULATORS. Attach a piece 
of hard rubber (a comb) to one end, and a cork to the other end of 
a stiff wire. Hold the rubber with two or three fingers of your left 
band, electrify it with the other, and find out whether the cork is 
electrified. Substitute a silken thread for the wire and repeat the 
same experiment. What do you observe ? 
Substances that conduct electricity from one object to another 
are called conductors of electricity ; those which do not conduct 
the electricity are called insulators of electricity. 
Metals, moist objects, and the human body are conductors of 
electricity; silk, rubber, glass, wax are insulators of electricity. 
261. THE ELECTROPHORUS consists of a plate of hard 
rubber (about one foot square,) a disk of zinc * to which are 
attached three silken strings, and a fox-tail. 
Brush or beat the rubber with the 
fox-tail, place the disk, which is held 
by the strings, upon the rubber plate, 
lift it by the strings, and bring it near 
some light objects. The light objects 
are not attracted the disk is not 
electrified. Repeat the experiment 
with thefollowing modification ; After 
Fig. 93. 
having placed the disk upon the plate, touch it for a moment with a 
finger, then lift it by the strings, and bring it near the light objects. 
They are attracted the disk is electrified. 
An explanation of the last experiment, or rather, the theory, 
by means of which we try to understand this and other electric 
phenomena, is at follows : 
262. THE TWO ELECTRICITIES. The two kinds of 
electricity are present in every object, be it electrified or uuelec- 
trifled. In an nnelectrifled object the quantities of the two elec- 
tricities are equal; in an electrified object the quantity of one 
electricity exceeds that of the other. 
At first it seems strange that an unelectrified object should have 
electricity, but after consideration you will become familiar with 
the idea. We will illustrate it in the following simple way. 
* The disk is made of two circular pieces of sheet zinc connected by 
means of a rounded edge of zinc about half an inch in height. ELECTRICITY. 
129 
Suppose two boys of equal strength take hold of each other. 
In this state neither of the two boys is able to do anything except 
to hold the other; neither is able to write, to throw a ball, or to pick 
up a pen. Though each of them has a certain power, he is unable 
to exercise this power otherwise than in balancing that of the other. 
The two electricities in an unelectrified object hold similar 
relations to each other they hold or bind each other, and are 
unable to exercise their power on anything outside. 
263. INDUCTION. Now suppose that a third person uses 
his power to tear one of the boys away. How does that affect 
the other ? 
Something similar occurs when an electrified object comes 
near an unelectrified conductor; for instance, when the metallic 
disk is placed upon the electrified plate of hard rubber. The 
plate has an abundance of free negative electricity and the disk 
has the two electricities united with each other, bound up in 
each other. How does the free negative electricity of the plate 
act upon the two united electricities of the disk? Which elec- 
tricity is at the upper, which at the lower side of the disk? 
Which of the two is held captive, which is free ? 
What happens when a person touches the disk while it 
rests on the plate ? What happens if the disk, after having been 
touched, is separated from the plate by means of the silken 
strings ? 
The separation of the two electricities in a conductor (as, for 
instance, the metallic disk) by the free electricity of an object 
near by is called induction. 
If an electrified object (A.) conies near an unelectrifled Con- 
Fig. 94 
ductor (BC), the two electricities of the latter are separated— 
the opposite electricity is attracted toward the electrified object, 130 
ELECTRICITY. 
and the like electricity is repulsed. The opposite electricity is 
held captive; the like electricity is repulsed and free. 
If we place the unelectrified disk of the electrophorus on the 
electrified plate, the two electricities of the disk are separated ; the 
opposite electricity is attracted and held captive, the like electricity 
is repulsed and free. If we touch the disk with a finger, we allow 
the repulsed electricity to escape through our bodies. If we then 
lift the disk by means of the silken threads, the disk is filled with 
free electricity. 
It is essential that you have a clear idea of this process ; other- 
wise you will be unable to understand any of the electrical phe- 
nomena. Induction is the key to the understanding of the whole 
subject. 
264. ELECTRIC PHENOMENA. Repeat the experiment 
with the electrophorus. Touch the disk, lift it by means of the 
strings, and bring a knuckle of your hand near the round edge. 
What happens ? With what electricity is the disk charged when it 
is suspended by the silken strings ? What takes place in the 
knuckle or hand held near the electric disk ? Hold the electric 
disk over the head of a child. What happens ? Hold it close to 
your face. What sensation does it produce ? 
If we place a finger near the electric disk, a spark flies out 
and a crackling noise is heard. If we hold it close to the head 
of a person, his hair rises on end. If we hold it near the face, 
we have a sensation as if we were touched by spiderwebs. 
The electric spark appears when the two opposite electricities 
break through the separating air and join each other. The singular 
sensation in the face is caused by the rising of the numerous little 
hairs on its surface. 
265. LIGHTNING. I wonder whether you thought of light- 
ning and thunder when you saw the electric spark and heard the 
accompanying noise. It would not be astonishing if you did, as 
the resemblances are very marked indeed. 
The famous philosopher Franklin was satisfied that the 
electricity of the clouds and the electricity of the electrophorus 
were identical. He, therefore, boldly set out to experiment with 
the electricity of the clouds. For this purpose he constructed a 
kite with a pointed metal rod attached to it, and, when an oppor- ELECTRICITY. 
131 
tunity offered, flew his kite directly toward a thunder cloud. 
The electricity descended by means of the hempen string which 
held the kite, so that if Franklin had held the end of the string in 
his hand, he would most assuredly have been killed by lightning. 
But he was careful. He fastened a key to the end of the hempen 
string, and held in his hand a silken string, which had been tied 
to the other. In this way he insulated himself from the kite and 
drew the sparks from the key. 
Lightning is a discharge of atmospheric electricity, accom- 
panied by a vivid flash of light. The electric spark and light- 
ning are essentially the same, only different in their intensity. 
266. THUNDER. What happens if lightning strikes a frame 
house or a tree ? This proves that lightning communicates heat to 
substances which it strikes or through which it passes. So it does 
with the air. The air occupying the path which lightning takes is 
immediately and intensely heated. What effect has heat upon air 
and upon other substances ? See Tf 43. 
Consequently the air occupying the path of lightning suddenly 
expands. We may take it for granted that this air suddenly expands 
to more than ten times its former volume. How will that affect the 
surrounding air ? 
The motion caused by the expanding air will be communicated 
to the air all around. In a short time the motion will reach the air 
surrounding ourselves. What part of the body is most sensitive to 
the motion of air ? What shall we hear ? 
Thunder is the noise caused by the vibration of air follow- 
ing lightning. The air vibrates, because the electric spark 
suddenly heats and expands the air through which it passes. 
Thunder is not caused by the concussion of clouds. Clouds 
are like fog, and two bodies of fog moving against each other 
can not produce a loud noise. 
267. THE LIGHTNING CONDUCTOR. * Explain Fig. 95. 
From what place does the electricity come when lightning passes 
between the cloud and the earth from the cloud, from the earth, 
or from both ? Does all the lightning pass between the cloud and 
the earth ? 
In which class of objects may the two electricities be separated 
* Invented by Benjamin Franklin in 1749. 132 
GALVANISM. 
more easily —in conductors or in insulators ? What parts on the 
outside of houses, particularly on the roofs, are conductors of elec- 
tricity ? Suppose a cloud charged with electricity is near a house. 
What parts of the house may be struck more easily the con- 
ductors or the insulators, and why ? It was a consideration like the 
above that suggested to Franklin the advisability of preparing a 
path for lightning, a pathway by which lightning can be con- 
ducted harmlessly into the ground. 
Fig. 95. 
The lightning conductor is composed of three parts : one 
above the roof, one in the ground, and a conductor between the 
two. The part above the roof consists of an iron or copper rod 
with a gilded point; the part in the ground is another metal rod 
ending in water or moist earth; the conductor consists of any 
metal forming an unbroken connection between the two. 
A rainpipe may be used as such a conductor, excepting that 
care must be taken that there is no interruption. Why ? 
CHAPTER XVI 
GALVANISM. * 
268. TELEGRAPH WIRES. In many streets and country 
roads, and everywhere along the railroads, you see high poles with 
numerous wires. What is the name of these poles ? Why ? Of 
* Galvani was a professor in Bologna, Italy, who, in the year 1789, 
discovered the peculiar kind of electricity that is made use of in tele- 
graphs and telephones. To distinguish it from the electricity caused by 
friction it is called Galvanism. GALVANISM. 
133 
what do the wires consist ? Other wires, which are placed in the 
ground or laid at the bottom of lakes and oceans, consist mainly of 
copper. Ask your teacher to show you samples of these wires. 
Describe them. 
Telegraph wires are suspended in the air and conducted 
through the ground or the water. The first consist of iron, the 
second and third of copper. 
Fig. 96. (a) 
Copper wire used underground is usually 
covered with gutta-percha. Submarine wires 
are protected by various substances ; they are 
called cables. 
Fig. 96 represents a portion of the Atlantic 
cable laid in 1866. Its copper center is pro- 
tected first by a stout layer of gutta-percha, 
then by a woven coating of jute, and, out- 
side of all, by a sheath made of ten iron wires, each of them covered 
with hemp. Give two reasons why the copper wires are covered. 
Fig. 96. (b) 
269. AN ELECTRIC CELL. The electric or galvanic cell 
consists of a glass tumbler, a cylindrical piece of zinc, a porous 
cup of earthenware, and a piece of carbon. The carbon is 
placed in the porous cup and surrounded with nitric acid*; the 
zinc is placed outside of the cup and inside the tumbler, and 
surrounded with dilute sulphuric acid**. The contact of car- 
bon and zinc with the acid produces electricity. 
The fluids do not quite cover the carbon and zinc, a short piece 
of both is outside and dry. The outside or free part of the carbon 
* Nitric acid, or a liquid composed of a saturated solution of potas- 
sium bichromate, or (better) sodium bichromate, mixed with one sixth 
of its volume of sulphuric acid. 
** The mixture, or rather the combination, of sulphuric acid and 
water, must by prepared by pouring the former into the latter. If done 
the opposite way, the acid may be thrown out and may injure the sur- 
rounding objects. 134 
GALVANISM. 
shows positive electricity, the free part of the zinc, negative elec- 
tricity. 
Besides this hind of electric 
cell there are many others in 
use. 
The combination of several 
electric cells is called an elec- 
trie battery. 
270. THE ELECTRIC 
SPARK. Use metal clasps 
to connect both the carbon 
and the zinc with a copper 
wire each. Now hold the 
free ends of the two wires 
close together. What do you 
notice ? Connect a file with 
one of the copper wires and 
scrape over its surface with the end of the other. 
An electric spark appears whenever the free ends of the 
carbon and zinc of the electric cell are connected or discon- 
nected. 
Fig. 97. 
271. THE ELECTRIC CURRENT. The discharges and 
the new charges follow each other so rapidly that a wire con- 
necting the pieces of carbon and zinc is said to contain a con- 
stant double current of electricity : the positive electricity of 
the carbon flows continually towards the zinc, and the negative 
electricity of the zinc flows continually towards the carbon. 
The continuity of the electric current is the most marked and 
most valuable quality of galvanic electricity. 
The power of the galvanic or electric current depends on the 
power and number of the galvanic cells. To produce a strong cur- 
rent, several galvanic cells are properly connected with each other. 
The combined electricity of three or four cells is sufficient to melt 
a thin iron wire, and the heat may be used to explode gunpowder 
in a mine or to discharge a cannon at a distance. The power of 
sixty of these cells is sufficient to produce a bright electric light, 
which consists of carbon made incandescent by a strong galvanic 
current. But the most important effect of the current is the one 
described in the following paragraph. GALVANISM. 
135 
273. ELECTRO-MAGNETISM. Fig. 98 represents a bar of 
soft iron having the form of a horseshoe and an insulated wire 
coiled around it. Prepare such an instrument and find out 
whether it is a magnet. What substance is used for magnets ? Now 
send a current of electricity through the coil of wire, not through 
the iron horseshoe. What remarkable change takes place ? Inter- 
nipt the current of electricity by separating 
the wires. What is the consequence ? When is 
the iron magnetic and when unmagnetic ? 
The electro-magnet is a piece of soft iron 
placed within a coil of insulated wire. The 
electro-magnet is magnetic when a current of 
electricity passes through the coil; it is un- 
magnetic when there is no current. 
It is a very valuable circumstance in this 
phenomenon that, though the cell and the elec- 
Fig. 98. 
Electro-magnet. 
tro-magnet may be at a very great distance from each other—may 
be thousands of miles apart the one may still be affected by 
the other. 
273. THE ELECTRO MAGNETIC TELEGRAPH. Fig. 99 
represents the receiver of telegraphic despatches. Show the elec- 
Fig. 99. 
tro magnet in it. What takes place when an electric current is sent 
through its coil of wire ? Is there anything near the electro- 136 
THE NERVOUS SYSTEM. 
magnet which may be attracted ? Do you see the part that 
moves this piece of iron away from the electro-magnet, if the 
electro-magnet loses its power ? Both the pieces of iron and the 
spring are attached to a bar capable of being moved about a fixed 
point or line. What is this bar called ? See 179. 
The receiver of the telegraph* consists of a lever of the first 
kind, moved to and fro by an electro-magnet and a spring. 
When a current is sent to the receiver, one side of the lever 
moves towards the electro-magnet; when the current is inter- 
rupted, the spring draws it the opposite way. Short currents 
produce short sounds; long currents produce long sounds. 
The following table contains the telegraphic signs of all the 
letters, short sounds being represented by points, long sounds by 
lines: 
A H O --- Y 
B I - - P W 
C J Q X 
D K R Y 
E- L S Z 
FM T 
G N U 
Full stop Repetition - - - - Hyphen 
Apostrophe 
CHAPTER XVII. 
THE NERVOUS SYSTEM. 
274. APPEARANCE. Several times in our studies we have 
had occasion to mention nerves; we have seen and examined 
some of them. How do they look ? You have seen optic nerves. 
To see dental nerves examine a sheep’s head. You will find 
that there is not much difference between the two kinds of nerves. 
All the nerves have the same qualities. Even the thickness of 
nerves does not differ in such a degree as the two kinds of nerves 
might indicate, for neither of them is a single nerve, but a nerve 
trunk or a bundle of single nerves closely packed together. The 
optic nerve, for instance, consists of more than one thousand single 
* Invented by Samuel Morse 1832. THE NERVOUS SYSTEM. 
137 
nerves or nerve fibers lying closely side by side, any one of them 
not thicker than about 1-2000 (.0005) of an inch. 
Nerves are white, solid cylinders, smooth and shining at the 
surface, harder than meat, but somewhat compressible between 
the fingers. Each nerve that is visible without the aid of a mi- 
croscope consists of numerous nerve fibers, and is more properly 
called a nerve trunk. 
275. DISTRIBUTION. Fig. 48 (p. 75) shows the distribu- 
tion of the nerves in the human face. Look at the white lines. 
Are they nerve trunks or nerve fibers ? Follow some of the nerve 
trunks to the surface. What do you notice ? Follow the nerve 
trunks in the opposite direction. What becomes of them ? 
The nerve trunks break up into finer and still finer bran- 
ches until the subdivisions become too small to be seen without 
the aid of a microscope. Traced the other way the nerve 
trunks unite with others, finally forming large masses called 
nerve-centers. 
276. NERVES COMPARED WITH BLOOD-VESSELS. 
All the blood-vessels are intimately connected with each other, and 
form one coherent system of tubes in such a way that a drop of 
blood may pass from one place to any other; while the nerves are 
not intimately connected with each other, each of them commenc- 
ing by itself, independently of other nerves, and terminating by 
itself. When two blood-vessels connect with each other, they 
form one single tube, while the nerve fibers remain independent 
of each other, even when they lie close together. 
Fig. 100. Nerve fibers. 138 
THE NERVOUS SYSTEM. 
Nerves and blood vessels resemble each other in their dis- 
tribution through the human body; both are found in nearly 
all the organs. But all the blood-vessels form one coherent 
system, while the nerve fibers usually remain independent of 
each other. 
Considering the functions of nerves and blood-vessels this 
point of contrast should be noticed; for blood-vessels carry the 
same fluid throughout the body, while nerves conduct a variety 
of impressions to the brain and to other organs. 
277. THE NEHYOUS ELEMENTS. Where are the external 
ends of the fibers of the optic nerve ? Where, those of the nerves 
of touch ? The external ends of the nerves of smell are in the lin- 
ing membrane of the nose; those of 
the nerves of taste in the lining mem- 
brane of the tongue and the soft palate. 
By what are the external ends of 
the optic nerves affected or stim- 
ulated ? By what, those of the au- 
ditory nerves ? Those of the skin are 
affected by pressure and temperature, 
those of the nose and tongue, by the 
qualities of substances entering the 
nose or the mouth. 
Most of these agencies, in order to 
make impressions, need peculiarly 
constructed bodies that are very 
easily iufluenced ; they are extremely 
slender and delicate, hair-like organs 
which are found attached to the ex- 
ternal ends of the nerves mentioned. 
Fig. 101 shows the slender and deli- 
cate bodies that form the external 
ends of the optic nerve. 
Fig. 101. 
Elements of retina. 
The internal ends of the nerve fibers 
are occupied by rounded, soft bodies called nerve cells. Their 
diameter is about eight times as large as that of the nerve fibers. 
Many thousands of them are found in the brain and spinal cord. 
The nervous system is built up of three elements: the 
hair-like organs, the nerve fibers and the nerve cells. The THE NERVOUS SYSTEM. 
139 
hair-like organs are external or peripheral, the nerve cells are 
internal, or central, the nerve fibers are intermediate. 
Fig-. 102. Nerve cells and nerve fibers. 
278. THE BRAIN. We will examine a calf’s or sheep’s 
brain. What shape has it ? Describe the upper surface. 
The folds, or convolutions, which you see at the upper sur- 
face are more or less numerous in different persons and animals ; 
they are deeper and more numerous in the brain of man than 
in that of any animal. 
Find the deep cut passing from the front to the back, sep- 
arating the brain into a right and a left half. The two halves 
are called hemispheres of the brain. Find also a small piece 
with parallel folds located in the lower part. This piece, whose 
weight is about one eighth of that of the main part of the brain, 
is called the small brain, the two hemispheres, the large brain. 
A third part is distinguished as the continuation of the spinal 
cord. It is located below the large brain, in front of and near 
the small brain. It was partly cut away when the brain was 
taken from the skull. Perhaps you are also able to distinguish 
some nerve trunks entering the brain at its lower side. There 
are twelve pairs of them. 
The hrain is the nerve-center located in the skull. It has 
three parts; the large brain (cerebrum), the small hrain 
(cerebellum), and the continuation of the spinal cord (medulla 
oblongata). (Fig. 103. See next page.) 
What are the characteristics of the large brain ? What are 
the characteristics of the small brain ? 140 
THE NERVOUS SYSTEM. 
279. STRUCTURE OF THE BRAIN. In order to examine 
the interior of the brain, pass a long knife in a perpendicular 
Pig. 103. Lower surface of the brain of a baby. 
direction through its front half. In this way you will obtain a 
transverse section. What do you see ? Is there any regularity 
in the distribution of the gray and the white matter ? Now cut 
through the cerebellum. How are the gray and the white matter 
distributed here ? The figure which you see in the section is called 
the tree of life (arbor vitae). THE NERVOUS SYSTEM. 
141 
What two nervous elements are found in the brain ? As there 
are two differently colored substances, you may easily suppose that 
one of them is made up of 
cells, the other of fibers. 
By microscopic investi- 
gations it has been found 
that the gray matter is 
Fig. 104. 
Transverse section of the brain. 
almost entirely made up of cells, while 
the white matter contains the fibers. 
The brain contains two substances 
called the gray matter and the white 
matter. The gray matter forms the 
outer part of the brain, and contains 
the nerve cells, the 
white matter forms 
the inner part and 
contains the fibers. 
280. THE SPINAL 
C0R1). Fig. 105 gives 
you an idea of the 
shape of the spinal 
cord when taken from 
the interior of the 
spinal column. Fig. 
106 shows cross sec- 
tions through the cord. 
Describe the figures. 
The cross section of 
the interior gray mat- 
ter shows a resem- 
blance in form to one 
Fig. 106. 
Fig. 105. 
of the capital letters. To which ? 142 
THE NERVOUS SYSTEM. 
At what place do the nerve trunks commence ? There are 
thirty-one pairs of nerves commencing in the spinal cord. Name 
the resemblances and the differences between the brain and the 
spinal cord. 
The spinal cord is the nerve-center located in the spinal 
column. It is separated into a right and left half, which are 
united in the middle. The gray matter is inside, the white mat- 
ter, outside. 
281. SENSORY NERVES. Often we do not realize the 
value of our possessions until we have lost them. In former 
times people had a similar experience with their nerves ; they 
did not understand their value and necessity in the living body, 
until, by accident, they had injured or destroyed them. 
Injuries to nerves are not very frequent, because, as a rule, 
they are well protected. Perhaps the most common instance of this 
kind is the loss of vitality in certain dental nerves. If this has 
taken place, the dentist may scratch, file, or drill into the tooth 
whose nerve has been destroyed, without causing pain. 
Let us consider another case. A nerve connecting the skin of 
a finger with the brain is cut somewhere in its course, as, for 
instance, in the elbow. What takes place ? Just what takes place 
in the case of a tooth the skin loses its sensibility. Now, we 
might put a red hot iron on the skin of this finger, or cut into the 
skin until blood flows, or pour boiling water on it; no pain 
would be felt. 
What will follow if the optic nerve be cut ? Name similar 
cases. Where is the proper beginning of these nerves—in the 
various organs we have mentioned, or in the brain ? In which 
direction does the impression or stimulus travel in these nerves 
in the direction to the brain or from the brain ? 
Sensory nerves are nerves in which impressions travel 
toward a nerve-center. 
282. MOTORY NERVES. Motory nerves are those in 
which an impulse travels from a nerve-center. 
The word motory has a meaning similar to that of motion or 
movement. Why did the motory nerves receive this name ? Where 
do they begin ? Where do they end ? THE NERVOUS SYSTEM. 
143 
Our will emanating from the brain, sends the message through 
the motory nerves. What happens if a motory nerve be cut ? 
What ability have the muscles lost, if the nerves connecting the 
brain with them are cut ? Most of the motory nerves carry im- 
pulses to muscles, some, to glands. 
283. THE SEAT OF FEELING. If your finger be burnt 
where do you feel the pain ? Why does a person, whose sen- 
sory nerve of the finger is cut through, not feel pain, if his finger 
be burnt ? His finger is not changed if the nerve is cut through 
at the elbow. His finger has all the substances our fingers have, 
is just as sound and healthy as ours, and the burning must, there- 
fore, produce the same effect on his finger as on ours. Either 
pain is felt in the fingers of both or of neither of us. 
One of the two statements must be wrong and one must be 
right. Is it possible that a person may feel pain, when he does not 
know anything about it ? Then it must be wrong to say that a 
person feels the pain in his finger. It certainly can not be denied 
that a person feels pain, but it is not true that he feels it in his fin- 
ger—he feels the pain in his brain. 
Strange as it may seem at first thought it is nevertheless 
perfectly true that all our feelings are perceived in the brain, 
and that the sensations are erroneously ascribed to different parts 
of the body. 
Remember that we imagine we feel witb the end of a long 
stick, or with the end of a long line, when we are angling or 
trolling. When we have a bite, it seems as if we felt with the 
end of the line. This error is caused in the same way as the 
error of locating pain or feeling in various parts of the body. 
There are other facts that point to the same error. If we 
strike the elbow at a certain spot (called the funny bone), we feel 
a tingling pain in our fingers. The fingers themselves were not 
touched, only the nerve that passes from the fingers to the brain. 
When a limb is amputated and pressure is exerted upon the end 
of the stump, it seems as if there were a sensation in the missing 
part. Pain or pressure is felt in a foot or arm that no longer 
exists! 
The seat of feeling is the brain. It is a common error to 
locate feelings or sensations in any other part of the body. 144 
THE NERVOUS SYSTEM. 
284. SENSATIONS. When we plunge our hands into cold 
water, the sensation of cold is produced in the following way: first, 
the cold water stimulates the sensory nerves of the hand; second, 
the stimulation is carried along the sensory nerves from the hand 
to the brain; third, the mind becomes conscious of the feeling of 
coldness. 
Objects within our field of vision produce a sensation in the 
following way: the objects send light into our eyes; an image of 
the object is produced on the net-membrane; the net-membrane 
is stimulated by the light ; the stimulation is carried to the brain ; 
the mind becomes conscious of a sensation. 
The sensation of sound is produced in the following way: 
external objects vibrate; the vibration is carried through the air 
to the drum-membrane and conducted through a series of little 
bones to the fluid filling the labyrinth ; nerves in contact with the 
watery fluid are stimulated by the vibration ; the stimulation of 
the nerves is carried to the brain ; the mind becomes conscious of 
a sensation. 
How may a hollow tooth produce the sensation of pain ? How 
may a heavy book produce the sensation of pressure ? 
To produce a sensation it is necessary, first, that an ex- 
ternal object should stimulate a nerve ; second, that a nerve 
should carry the stimulation to the brain; third, that the mind 
should become conscious of the stimulation. 
285. THE SYMPATHETIC SYSTEM. Are the stomach, 
the heart, intestines, blood-vessels, etc. supplied with nerves ? 
Under ordinary circumstances we do not feel these organs; we 
neither receive sensations from them, nor do we move them. 
Nevertheless, their functions can not be performed without the 
regulating influence of nerves. 
Nerves stimulate the glands of the stomach to secrete gastric 
juice ; nerves stimulate the muscles of the stomach to move the 
walls in and out. In fact all the organs of the body, except those 
in which blood-vessels are also missing, are supplied with nerves. 
Nerves, like blood-vessels, are present in every active organ of the 
body, some for nutrition, others for order and regularity. 
The nerves regulating the processes of digestion, circulation, 
secretion, and nutrition are not primarily or immediately con- 
nected with the brain or spinal cord. There is a third nerve- THE NERVOUS SYSTEM. 
145 
center, which administers to the needs of the heart, the liver, 
the stomach, and the glands. This nerve-center is the sympathetic 
system. 
The sympathetic system consists principally of a double chain 
of ganglions (small groups of nerve cells) which lie in front 
of the spinal column, one on each side. The ganglions are 
connected by strings composed of nerve fibers. 
The sympathetic system regulates the processes of diges- 
tion, circulation, secretion, nutrition, and others that are per- 
formed without the activity of the mind. 
The sympathetic system is a kind of assistant, to whom are 
entrusted those functions of the body, whose regulation would be 
onerous and annoying to the headmaster residing in the brain. 
It would be extremely troublesome, nay, impossible, for the mind 
to regulate the secretion of every gland, the motion of every morsel 
of food, and the nutrition of every organ. 
Only in extreme cases, as when one of the processes of nutri- 
tion or secretion is disturbed, does the mind become conscious 
of it. This is accomplished by a special nervous connection 
between the sympathetic system and the brain. Such cases are 
the following: we feel pain at the stomach; our hearts beat too 
fast; our perspiration is excessive, etc. 
Certain states of the mind may also affect the work of organs 
usually under the control of the sympathetic system. Fright, ter- 
ror, or expectation cause a quicker beating of the heart; shame or 
embarrassment dilate certain blood-vessels, thus producing a rush 
of blood into the face ; fear contracts the same blood-vessels, 
thus producing paleness of the face, etc. 
286. REFLEX ACTIONS AND INSTINCTS. That we may 
better understand the functions of nerves, we will consider the part 
they take in some of the common occurrences of daily life : 
1. Someone asks me to cut a rose from one of my bushes; I 
perform the action. Here the sensation of sound is carried by 
sensory (receiving) nerves to my mind, and by means of motory 
( sending) nerves I direct certain muscles of the arm to do the work. 
2. I rest my head upon my arm. The pressure of the hard 
support becoming unpleasant, after some time I change my posi- 
tion. In this case the sensation of pressure is carried to the mind 146 
THE NERVOUS SYSTEM. 
by means of receiving nerves, tbe sensation gradually becomes 
disagreeable and painful, an impulse is sent through sending 
nerves, and muscles affected by them effect a change of position. 
8. My hand accidentally touches a hot object. I instantly 
remove it. In this case the sensation of heat is carried to the 
brain by means of receiving nerves and the contraction of muscles 
is caused by an impulse sent through sending nerves. 
4. When I smell the juice of oranges, saliva collects in my 
mouth. The sensation of smell is caused by receiving nerves, the 
secretion of saliva, by sending nerves. 
If we compare the four instances, we find that the mind is not 
equally active in all of them. It is active in the first case, because 
I become conscious of the request, and the will directs the action of 
cutting. In the second instance, I gradually become conscious of 
the pressure. I deliberately change my position, or I do it with- 
out a conscious direction of my will. In the third and fourth 
Cases, the removal of the hand, and the secretion of saliva, are 
done without the direction of the mind. 
Involuntary actions of the body, such as sneezing, winking, the 
removing of the hand from a hot spot, etc., are called reflex 
actions. It is as if the irritation or impulse of a receiving nerve 
were reflected through a sending nerve. 
Some actions require the direction of the mind when first per- 
formed. but become unconscious and change to reflex actions after 
a sufficient number of repetitions, as for instance, walking—it takes 
a child a long time to learn it. Reading, performing on instru- 
ments, knitting, embroidering, in fact every kind of mechanical 
work becomes unconscious after a certain number of repetitions. 
All the actions of the body are the consequences of previous 
impressions. The nervous centers are thrown into activity only by 
effects of changes that have taken place in receiving nerves; the 
activity of the sending nerves follows. The more highly organized 
a being is, the more it will influence the activity of sending nerves, 
will place its mind or will between the actions of receiving and 
sending nerves, invent new combinations, and acquire abilities that 
other beings do not possess. 
Most of the actions of the lower animals are reflex actions. 
Some have been repeated a great number of times, in exactly the 
same way, so that no activity of the mind is required to perform THE NERVOUS SYSTEM. 
147 
them in the best possible manner ; the offspring inherit the bodily 
organizations allowing the repetition of the same actions with the 
least possible mental activity, and thus instincts are developed. 
REFLEX ACTIONS are actions of our organs which are 
performed without the consciousness of the mind. 
287. BRAIN AND MIND. The brain is the seat of the 
mind. Disturbances or injuries of the brain are accompanied by 
disturbances of the mind. Permanent abnormities of the brain 
are accompanied by permanent insanity, imbecility, madness, or 
other diseases of the mind. 
The principal mental actions are thinking, willing, and feeling. 
A temporary injury to the brain, such as is caused by a blow on the 
head, deprives us of consciousness—makes us unable to think, to 
will, or to feel. If the heart is prevented from sending a sufficient 
supply of blood to the brain, the person faints becomes uncon- 
scious. If the brain is flooded with a great quantity of blood, as 
happens when a blood-vessel of the head bursts, the person is 
seized by an apoplectic fit* 
288. MENTAL HEALTH. The health of the mind and 
of the brain depend on each other. Sorrow, anger, an excitable 
temper, worry, and similar mental conditions have a depressing 
effect upon the mind and, through the mind, upon the brain. A 
brave heart and a cheerful disposition are conducive to a healthy 
brain. 
Nothing wears upon the nervous system more than constant 
worry. If the heart is depressed, if a person has lost his courage, 
if he constantly dreads failure, he can not do half the work of 
which he otherwise Would be capable. 
289. SLEEP. How long does your baby-brother sleep during 
the day ? How long do your parents sleep ? What do your parents 
tell you about going to bed and rising ? Is it healthful for a girl 
of fifteen or sixteen to study till midnight and rise at six or seven 
in the morning ? 
* To restore to consciousness a person who has fainted, he should at 
once be laid flat on the back, that the blood may more easily be pumped 
into the head. His face should be briskly sprinkled with cold water, and 
some strong smelling substance, as hartshorn, be held to his nostrils. 
A person seized with an apoplectic fit should be moved as little as 
possible, and a physician be called at once. Meanwhile apply cold ban- 
dages or bags of ice to the head. 148 
ALCOHOL. 
During sleep the brain has a complete rest, which is as 
necessary for its health as periods of rest are for the muscles or 
the stomach. Children should have plenty of sleep ; they should 
go to bed in season and not rise too early. 
Children who habitually go to bed late and have only a small 
amount of sleep are incapable of vigorous work—they grow feeble in 
mind and body. Girls who study till midnight sulfer from anaemia 
(bloodlessness) and muscular debility ; they endanger their present 
and future health greatly. 
290. REST AND EXERCISE. To keep the brain in a 
healthy condition, it must be treated similarly to our muscles. 
What promotes the strength and capability of our muscles ? The 
same is true of the brain and mind. 
Regular, moderate, and varied mental exercise and sufficient 
rest are necessary to the health and strength of the mind. 
In early youth children are soon overworked and tired, their 
attention is easily diverted, and concentration of mind upon one 
subject is hardly possible. After a few years the mind is better 
able to concentrate itself and the reasoning powers begin to de- 
velop. Still they easily tire and must not be kept too long upon 
one subject. The desire for knowledge must still be encouraged 
and strengthened by interesting, stimulating methods of teaching. 
Adults (businessmen or scientists) who have to contend with 
others for remunerative and pleasant positions in life, usually keep 
their thoughts busy in only a few directions and easily become one- 
sided and narrow-minded in their mental aspirations. Variety of 
mental work and exercise is as necessary for their mental health as 
varied muscular exercise is necessary for their bodily health. 
CHAPTER XVIII. 
ALCOHOL. 
291. ITS EFFECTS. Alcohol is contained in wine, beer, 
cider, whisky, and all kinds of intoxicating drinks. It is alcohol 
that causes intoxication. 
The enormous extent to which these beverages are used 
throughout the civilized and uncivilized world, and the destructive ALCOHOL. 
149 
effects consequent upon their use, have awakened the interest of 
physicians, lawmakers, and people in general. Many persons con- 
sider this question as one of the utmost importance to the welfare 
of individuals and of the entire commonwealth. 
There is hardly an organ or system in the body whose 
composition is not changed or whose function is not disturbed by 
the continued use of alcohol. 
It will be proper to take up, in regular order, one system after 
the other, and hear what experienced persons have found out. 
292. THE BONES. A lady having received as a present a 
young and very tiny King Charles’ dog which she wished to keep 
small, was advised to feed him a certain amount of alcohol daily, 
in order to check his growth. She did it with the result that the 
poor little dog stopped growing entirely. At the same time he lost 
his former liveliness and activity, became fretful and lazy, and 
died before he was a year older. 
It is seldom that the same experiment is made with children, 
because the state would punish anyone who assisted in such a 
crime. Yet, in rare cases, it has been made, the result having been 
the same with the poor children as with the dog their growth 
was stunted, they lost their natural liveliness and cheerfulness, 
became peevish and irritable, behaved and moved like old men, 
and died before they reached maturity. 
What parts determine the height of the body and the length of 
the limbs ? What, therefore, is the influence of alcohol upon the 
bones ? 
Alcohol checks the growth of bones. 
298. THE MUSCLES. To learn whether or not the strength 
of the muscles is impaired by the use of alcohol, it will be best to 
consider the experience of persons who, like soldiers, travelers, or 
athletes, have to do very hard work, or perform especial feats of 
strength. 
The experience repeatedly gained by them is that alcoholic 
drinks lessen the strength. A number of soldiers bear the fatigue 
of along march better when they have received no alcohol. Many 
arctic travelers have stated that alcohol weakens the power to 
endure both bodily labor and cold. It is now generally conceded 
to be a serious blunder for anyone to depend upon alcohol as a 150 
ALCOHOL. 
means of increasing his strength or endurance. Just the contrary 
effect of alcohol has been proved. 
The above is not the only proof of the injurious influence of 
alcohol on muscles. When persons have been used to alcoholic 
drinks, the number of fibers in their muscles is found to be fewer 
and the connective tissue to have increased. 
Persons used to alcoholic drinks have lost part of their mus- 
cular power— the number of muscular fibers has decreased and 
that of the connective tissue has increased. 
294. ARTERIES. The arteries are injured in several ways. 
How does the face, particularly the nose, of a hard drinker look ? 
Red cheeks are considered an indicator of health. Is that the 
impression made by the face of a drunkard ? 
The healthy red is spread evenly over the face or it makes a 
handsome spot on the cheeks, but the red of the drinker looks 
loathsome, his face is blotched. These red blotches are caused by 
dilated blood-vessels. The walls of the arteries contain a number 
of circular or ring-shaped muscles that help, to a certain degree, to 
keep the arteries in proper width. By the use of alcohol the 
nervous control over these ring-muscles is weakened, and the con- 
sequence is an extreme dilatation of the arteries and a flushing of 
certain parts of the skin. 
A second injury is to the walls of the arteries, which lose some 
of the strong elastic tissue that, in a healthy person, is of the 
greatest importance to a well regulated circulation. The place of 
the tough elastic tissue is taken up by oil-drops. Then the blood 
gradually distends the weakest places and a so-called aneurism 
is caused, which usually ends in the bursting of arteries. 
In drunkards the ring-muscles of the arteries are expanded 
and certain parts of their faces are flushed. Part of the elastic 
tissue is replaced by oil-drops, and the walls of the arteries 
are weakened so that they easily burst. 
295. THE HEART. Through the use of alcohol, the muscu- 
lar elements of the heart decrease and the fat cells increase ; in other 
words, the fat cells take the place of the muscular tissue. Which 
is stronger a heart containing very few fat cells or one in which 
they abound ? ALCOHOL. 
151 
Through the use of alcohol, the muscular elements of the 
heart decrease iu quantity and the fat increases. A tatty heart 
can not pump a sufficient quantity of blood through the body. 
A post-mortem examination discloses the fatty heart as the 
cause of death. Fatty degeneration of the heart is so often due to 
indulgence in alcoholic drinks that physicians call a fatty heart a 
“whisky heart/' 
296. THE BLOOD. The influence of alcohol upon the 
blood shows itself plainly in a gradual disappearance of fibrin. 
Why must a defective composition of blood affect the compo- 
sition and function of other organs ? What is the use of fibrin 
when we are wounded ? What must happen if the blood of a 
wounded person does not contain enough fibrin ? 
Hence all wounds and all surgical operations on persons indulg- 
ing in alcoholic drinks are attended with danger. 
297. DIGESTION. The digestive organs being the first to 
come in contact with alcohol, it is easily understood that they are 
the first to suffer from it. 
In what part of the digestive system does alcohol remain for a 
long time ? What may we, therefore, expect ? Upon the entrance 
of alcohol, the internal membrane of the stomach becomes over- 
charged with blood, and presents the same appearance that a part 
of the skin does when it is inflamed. 
This unnatural condition of the stomach causes a loss of appe- 
tite. If a person drinks beer or wine just before dinner, he is un- 
able to eat the usual quantity of food. If he continues to drink, 
the function of the stomach is disturbed for a longer time. 
Persons dying from the use of alcohol show a frightfully dis- 
torted stomach, with ugly ulcers and deformities that caused 
great pain before resulting in death. 
The “gin drinker’s liver”, as the physicians call a liver 
degenerated through the effects of alcohol, presents a shrunken, 
hard, rough mass, unable to do efficient work. 
298. RESPIRATION. Alcohol sometimes causes slight 
inflammations of the air-passages, thus increasing the tendency 
to colds. Furthermore, it weakens the muscles of respiration, 
thus lessening the amount of air breathed in. 152 
ALCOHOL. 
The injurious effect of alcohol upon the lungs themselves has 
also been demonstrated to be the cause of consumption, This 
consumption is known as “ alcoholic phthisis.” 
299. THE KIDNEYS. Excessive drinking often produces 
a kidney disease known as “Bright’s disease”.* The working 
substance of the kidneys gradually disappears, .and is replaced by 
an excess of connective tissue. At last the organ is unable to do 
its work, and death ensues. 
Alcoholic drinks being fluid, it is to he expected that they will 
affect the organs most active in excreting fluids. The injury is 
done in several ways; first, they throw too much work on the 
kidneys; secondly, they interfere with the proper preparation of 
the nitrogenous waste which it is the function of the kidneys to 
excrete ; thirdly, part of these substances passes through the 
kidneys unchanged. 
300. THE NERVOUS SYSTEM. The most direct effect of 
alcohol is upon the brain and the nervous system generally. 
A small quantity of wine or spirits causes an increased flow of 
blood to the head. The blood brings more nourishment than 
usual, more than is wanted—the brain is overfed, and the person 
becomes irritable and excited, talkative, dizzy, and unable to think 
clearly. 
If the quantity is increased, the person behaves in a manner 
that is painful to behold, losing control over himself and com- 
mitting deeds that are hurtful to himself and others. If let alone, 
he is soon overcome by sleep, and on awakening is troubled with a 
sick headache and nausea. 
A repetition and further increase of the dose is followed by 
more serious and troublesome consequences. The talkativeness is 
accompanied by indistinct speech, and the dizziness, by trembling 
limbs and reeling steps. This shows that the nervous system has 
lost control of the muscles. At the same time, the sensations become 
indistinct, hearing and touch are dulled, the vision is obscured, the 
eyeballs do not move together, and objects appear double. A person 
in this state is like one insane his mind is wandering and his 
memory, uncertain. At last he loses consciousness entirely, can 
* Sometimes Bright’s disease follows scarlet fever, typhoid fever, or 
cholera. TOBACCO. 
153 
not hold himself upright, and falls into a heavy sleep, from which 
he can not be awakened. In this condition he may suffer a sudden 
death from paralysis of the heart or apoplexy of the brain. 
When at last the person has slept off his “drunken fit”, he 
awakens in a state of health that is almost unbearable his digest- 
ive organs are quite out of order ; his head is heavy and painful, 
and his moral sense, weakened. 
Drunkards are subject to numerous and serious diseases of the 
nervous system. Congestion (accumulation of blood) of the brain 
and its membranes, apoplexy caused by the bursting of blood- 
vessels, inflammation of the brain followed by its gradual consump- 
tion, and analagous diseases of the spinal column and the organs 
of sense are not infrequent. 
These bodily disorders are accompanied by a variety of mental 
derangements, such as hallucinations, delirium tremens (trembling 
madness), dipsomania ( a mad passion for alcohol), loss of memory, 
and imbecility. 
Intemperate persons not only destroy their own health and 
happiness, but also that of their families. Their children inherit 
certain physical, mental, and moral imperfections; they grow 
weak in body, mind, and will. The children of drunkards show a 
tendency toward epilepsy, St. Vitus dance, rickets, insanity, or 
imbecility. 
CHAPTER XIX. 
TOBACCO. 
801. Tobacco contains a highly poisonous substance called 
nicotine. 
Do you know a boy who smokes ? How does he look ? Is he 
an attractive boy ? Is he clean and neat in person and dress ? Is 
he well-behaved and a kind playmate ? 
The answers to these questions will show that in the majority 
of cases a boy who smokes is rude, associates with a low class of 
society, and is dirty in his person and dress. He has coarse 
manners; he is not fair in his dealings with other children, but 
abuses them or imposes upon them. 154 
TOBACCO. 
On the other hand think of a boy who is well cared for, 
and is kind and obliging to others, neat in person and attire, who 
is refined in his manners, and liked by his parents, teachers, and 
schoolmates. Is he found smoking cigars or cigarettes ? 
The desire of boys or young men to smoke or chew originates 
from the example given by older persons. It is the natural desire 
of young persons to imitate their elders in behavior and looks. 
When the first shadow of a coming mustache begins to show, the 
young man enjoys a touch of his upper lip or a look in the glass 
he is proud of the appearance of this token of manliness and 
imagines himself to be at the threshold of a new life. This is an 
innocent pleasure, which may be enjoyed without harm to anyone. 
But the use of tobacco, in any form, is not harmless. There is 
no difference of opinion about its injurious character. The ex- 
perience of every country shows that boys and young men in- 
variably injure their health by smoking or chewing tobacco. 
Look at a youngster who believes that he is doing a coura- 
geous act in puffing the smoke of his first cigar, or in chewing the 
nasty stuff for which he has spent his money. You can plainly 
see that it produces very disagreeable sensations a copious flow 
of saliva, giddiness, headache, great paleness of the face, cold 
sweat, trembling limbs, nausea, diarrhoea, and, sometimes, a gen- 
eral breakdown, showing itself in nervous exhaustion and faint- 
ing fits. 
These symptoms are produced by a poisonous substance called 
nicotine, contained in tobacco. A few drops of pure nicotine 
will bring about a rapid death through paralysis of the heart. 
It belongs to the class of poisonous substances called narcotics, 
some of which are used as medicines. Nicotine, however, is so 
powerful in its effects that it is regarded as too dangerous to be 
used as medicine. 
302. RESPIRATION. The inhalation of smoke containing 
poisonous substances is injurious. Persons suffering from lung 
diseases should avoid places filled with tobacco smoke. A dis- 
ease peculiar to habitual smokers is “smokers’ sore throat.” 
Everywhere we hear the demand for fresh air. We try to 
thoroughly ventilate our dwelling and sleeping rooms, our schools, 
and our assembly halls ; yet we suffer our friends and visitors to TOBACCO. 
155 
fill the room with the injurious smoke of tobacco, or to enjoy 
themselves in places filled with a smoking multitude. 
If fresh air is necessary to health, foul air or air filled with 
a poisonous smoke must be injurious. What do you think of a 
person suffering from a lung complaint, and either smoking him- 
self, or sitting in a place filled with smoke ? What good advice 
should be given him ? 
It is worthy of special remark that the smoking of cigarettes 
is more injurious to the throat or lungs than the smoking of 
cigars or pipes. 
303. THE STOMACH. The smoke and the juice of chewed 
tobacco interfere with the secretion of saliva and disturb the 
work of the stomach. 
The first advice a person suffering from dyspepsia receives 
from his physician is to give up smoking or chewing. 
304. THE BLOOD. Tobacco interferes with the proper 
development of the blood cells. The skin of an habitual smoker 
looks yellowish-white. His muscles are feeble. 
Indulgence in tobacco causes a feeling of lassitude and indis- 
position to exertion of any kind. If a person is not yet suffi- 
ciently warned by these symptoms, attacks of palpitation of the 
heart, trembling limbs, sleeplessness, melancholy, even a gradual- 
ly increasing paralysis of the body, and the loss of eyesight may 
be experienced. QUESTIONS FOR REVIEW. 
WATER. 
What does the thermometer show ? What is vapor ? What 
is the boiling point of water ? How may you prove that our 
breath contains vapor ? What qualities are common to steam and 
vapor ? What difference is there between steam and fog ? When 
does fog appear ? What air can hold much vapor ? 
What difference is there between dissolving and melting ? 
When does water evaporate quickly ? Wrhat are crystals ? What 
is distillation ? What are springs ? What well-water is poisonous ? 
Describe the circulation of water. 
What countries have but little rain ? How do forests improve 
the climate of countries ? 
HEAT. 
What are rays or heat ? What difference is there between 
hot, warm, and cold objects ? Why are cloudy nights warmer 
than cold nights ? Describe the formation of dew. What differ- 
ence is there between a continental and an insular climate ? 
Describe the effect of heat upon solid, liquid, and aeriform 
substances. Describe a thermometer. What is convection ? De- 
scribe how a stove heats a room. What is wind ? How is wind 
caused ? 
How are mammals protected from the cold ? How, birds ? 
How, other animals ? What are poor conductors of heat ? 
DIGESTION. 
When does the weight of a person decrease ? How is the 
loss of substance caused ? Describe the course of food through 
the body. 
Describe the three kinds of teeth. Name the parts of a tooth. 
Name the substances of which a tooth is composed. What causes 
hollow teeth ? 
What is the use of saliva ? Describe starch. Where is it 
found ? Locate and describe the salivary glands ; the food-pipe; 
the stomach ; the three coats of the stomach. Name the kinds 
of proteids and state where they are found. Describe the intes- 
tines; the bile; the liver. What fluids are mixed with food in 
the intestines ? What are chyme and chyle ? Describe the milk- 
tubes. QUESTIONS FOR REVIEW. 
157 
What is the usual cause of disorders of the digestive organs ? 
Why must food be well chewed ? What is nourishing food ? 
State the amount of nourishing substances contained in 
wheat. What is the value of sugar as an article of food ? 
On what does the value of beef as an article of food depend ? 
Describe two parasites found in raw meat. Compare the value 
of flesh of mammals, birds, and fish. What valuable substances 
are contained in eggs ? In milk ? Describe a lactometer and 
state how it is used. State three uses of fat in the body. 
What qualities has air ? Prove that air presses in all direc- 
tions. Describe a pair of bellows. 
RESPIRATION AND COMBUSTION. 
Compare the chest with a pair of bellows. Describe the two 
ways of breathing. Describe the motions of the air cells. What 
is the color of the lungs ? Describe the structure of the lungs. 
What two substances escape from a burning candle and how 
are they detected ? What is the composition of fresh air ? What 
changes occur during the burning of a candle ? 
Compare the inhaled air with the exhaled air. Compare the 
changes of air in respiration with those in combustion. 
What changes are observed in the air of a room occupied by 
persons ? How does carbonic acid affect our health ? From 
what sources do organic substances enter the air of dwelling 
rooms? How do we counteract the evil effects of foul air in a 
room ? How much fresh air in needed for this purpose ? De- 
scribe a ventilating flue. Describe a means of admitting fresh air 
into a room without causing draught. 
Describe a Hero’s Fountain ; a syringe. What is a piston ? 
What does the word volume mean ? What are the parts of a 
suction-pump ? Of a force-pump ? What is a valve ? Describe 
a rubber syringe. 
CIRCULATION. 
Of what does the heart consist ? How is the heart widened ? 
What is the work of the left heart ? Of the right heart ? Name 
the three kinds of blood-vessels. Describe each. Prove that 
blood contains the elements of every substance in our bodies. 
Of what benefit is rapidly flowing blood ? What is the function 
of the capillaries ? Describe the two kinds of blood. Of what 
substances does blood consist? Name the parts of the heart. 
How should wounds be treated ? 158 
QUESTIONS FOR REVIEW. 
THE SKIN. 
What qualities has the skin ? What organs and appendages 
are found in the skin ? Describe the two layers. Name the parts 
of a hair. Describe the sweat-gland. Describe two kinds of 
papillaß. Of what use is a daily sponge-bath ? 
EXCRETION. 
What is excreted by the lungs and the skin ? Describe the 
kidneys. Name the renal organs. What does urine contain ? 
What effect has an increased amount of blood in the skin ? How 
are serious kidney diseases often caused ? 
What can muscles do ? Of what do the two ends of many 
muscles consist ? How are the parts of our body kept in their 
places ? What are fibers ? How is the expansion of muscles 
caused ? How are substances moved through tubes and hollow 
organs of the body ? Describe the two kinds of muscles. How 
do muscles grow large and hard ? Of what benefit are large and 
hard muscles ? How is our sleep modified by the work previously 
done ? When may exercise become injurious ? 
MUSCLES. 
LEVERS AND BONES. 
What is a lever ? Describe the three kinds of levers. When 
is a lever in equilibrium ? What is the use of levers ? 
Name three bones each representing a lever. What are 
joints ? Describe three kinds of joints. How is the union of 
bones in joints accomplished ? Describe the ends of the bones 
in a joint. What is the function of ligaments ? Describe a fresh 
bone. Of what two main substances do bones consist ? What 
effect has each of these substances upon the condition of bones? 
Why are long bones hollow ? Describe one of the bones in the 
vertebral column. Name the curves in the backbone. What 
is the use of the backbone? Name the bones of the arm and 
of the leg. What bones form the largest bony structure of the 
body ? Describe the bones of the chest. Describe the structure 
of the skull. What is a suture ? Name four uses of bones. 
What should be done in case of broken bones ? How are 
crooked legs caused ? How may round shoulders be avoided ? 
What organs are injured by tight lacing ? What injuries are 
done by tight shoes ? QUESTIONS FOR REVIEW. 
159 
THE LOWER SENSES. 
What does the sense of feeling enable us to perceive ? De- 
scribe the nose. What is smell ? Where do the nerves of taste 
commence ? What two senses are closely connected ? 
SOUND AND THE EAR. 
How are sounds produced ? Describe the sound waves. 
What is pitch ? On what does pitch depend ? Describe the 
structure of the ear. Of what use is the outer ear ? 
Name the parts of the middle ear. Of what does the inner 
ear consist? 
THE ORGANS OF VOICE. 
Describe the voice-box. Describe the voice-cords. Describe 
the part the mouth takes in the production of the voice. How 
are good voices spoiled ? 
THE EYE AND LIGHT. 
Of what use are the eyebrows, the eyelids, the eyelashes, and 
the eyebrow-arches ? Locate the glands of the eye. Describe 
the outside of the eyeball. Locate its three membranes. Describe 
the horn-membrane, the pupil, and the rainbow-membrane. What 
does a longitudinal section of the eyeball show ? 
Name the three kinds of images which a convex lens may 
produce. What is a camera obscura ? How does a concave lens 
change the direction of parallel rays falling upon it ? How is 
short-sight caused ? How, long sight ? What are self-luminous 
objects ? What are transparent, translucent, and opaque objects ? 
What are rays of light ? What is a shadow ? When does a 
total eclipse of the- sun occur ? What is the law of reflection ? 
What is diffused light ? What benefit do we derive from direct 
sunlight? Compare an object and its image in a looking-glass. 
State why objects immersed in water appear in a higher position 
than they really are. 
Compare the eye with a camera obscura. What is done with 
every impression that the net-membrane receives ? What is stated 
about the duration of impressions on the net-membrane ? What 
difference is there between the views we obtain with one eye and 
those wTe obtain with two eyes ? Describe the stereoscope. 
MAGNETISM. 
What are magnets ? Describe the induction of magnetism 
in a piece of unmagnetic steel. What peculiar power has a 160 
QUESTIONS FOR REVIEW. 
magnetic needle ? State the law of magnetic attraction and re- 
pulsion. 
ELECTRICITY. 
What are electrified bodies ? State the law of electric attraction 
and repulsion. What are conductors of electricity ? What, insu- 
lators ? Describe an electrophorus. Where are the two kinds of 
electricity found ? What is the difference between electrified and 
unelectrifled objects ? What is induction ? What is lightning ? 
What is thunder ? Describe a lightning conductor. 
Describe an electric cell. When does an electric spark appear ? 
What is an electro-magnet ? Describe the receiver of the telegraph. 
GALVANISM. 
Describe a nerve. Describe the distribution of nerves. Com- 
pare nerves with blood-vessels. Name the three elements of the 
nervous system. Describe the brain. Describe the two essential 
substances found in the brain. Describe the spinal column. 
What are sensory nerves ? What are motory nerves ? What is 
the seat of feeling ? How is a sensation produced ? Of what 
does the sympathetic system consist ? What does it regulate ? 
Describe a reflex action. How are instincts developed ? What 
connection is there between the brain and the mind ? When does 
the brain rest ? What kind of exercise does the mind need ? 
THE NERVOUS SYSTEM. 
What organs or systems of the body are changed or dis- 
turbed by the continued use of alcohol ? Prove that alcohol 
checks the growth of bones. How are the muscles affected? What 
effect has alcohol upon the arteries ? Upon the heart ? Upon 
the blood ? What appearance has the stomach of persons dying 
from the use of alcohol? How does the “gin drinker’s liver” 
look ? What kidney disease is often caused by excessive drink- 
ing? Describe the effect of alcohol upon the nervous system. 
ALCOHOL. 
TOBACCO. 
What poison is contained in tobacco ? What effect has the 
smoke of tobacco upon respiration ? How does smoking or chew- 
ing affect the stomach ? What effect has the use of tobacco 
upon the blood ? In what other ways may the use of tobacco 
be hurtful ? OPINIONS OF TEACHERS. 
From Hon. Henry Raab, State Superintendent of Illinois. 
T have examined your “ Elementary Science and Physiology” and 
do not hesitate in saying that I consider it a valuable contribution 
to popular science teaching. The arrangement of the subject matter 
is excellent, the language is simple, and all experiments are so easy 
that it cannot but interest and instruct both old and young. I like 
the plan of the work, and am confident that even inexperienced, con- 
scientious teachers will find it a desirable means of instruction. 
From F. Louis Soldan, Principal Normal and High School, St. Louis, 
Mo. 
I have examined with some care the plan, arrangement, and method 
of your work “Elementary Science and Physiology” and I am most 
favorably impressed. The method of presentation, as outlined by you, 
proceeds inductively, and will tend to stimulate the self-activity of the 
pupil, and rouse his interest in scientific work. I am confident that 
your book will be appreciated by every teacher. 
From H. O. R. SiEEERT, Ass’t Superintendent Public Schools, Milwau- 
kee, Wis. 
Your “Elementary Science and Physiology” has impressed me very 
favorably. If used correctly it will make the study of physiology a 
delightful occupation to pupil and teacher. Your plan of basing the 
teaching of the functions of the several organs on scientific principles 
is well conceived, and will help to make the learner an active student. 
I do not hesitate to say that I consider your book far above the 
average text-book on physiology. 
From Emil Dapprich, Director of German-American Teacher’s Sem- 
inary, Milwaukee, Wis. 
I have carefully read the manuscript of your “Elementary Science 
and Physiology” and its perusal has given me a great deal of pleasure. 
If physiology is taught as you propose it in this book, it will be 
taught well. The arrangement of the topics, the methods of present- 
ing them, the experiments proposed, and illustrations used will make 
the yvork a valuable help to teachers. 
From M. P. Weymann, M. D., Professor High School, Council Bluffs, la. 
While we are well aware of the vast importance of physiological 
teaching in the Public Schools, we know equally well that many parts 
of tha»t science and often the most important are memorized by the 
pupils without a full appreciation of the facts. This is due to a lack 
of knowledge in such auxiliary branches as physics and chemistry. 
Dr. Dorner has tried to avoid this difficulty by giving, along with the 
regular work, instruction in those branches, and, although this may 
seem a difficult task, has succeeded remarkably well. 
The whole work is based on object lessons so that the pupil de- 
duces and formulates in his own language the scientific truths, in my 
opinion the only correct way. A feature of particular merit is the 
ingenious application of scientific principles to facts and occurrences 
within our daily observation. The number of such examples is so 
great as to make the little book to a certain extent unique, even with- 
out the other points of excellence.