CIRCULATION THROUGH THE HEART AND LUNGS. A TREATISE 
ON 
PHYSIOLOGY AND HYGIENE; 
FOR 
SCHOOLS, FAMILIES, AND COLLEGES. 
By J. C. DALTON, M.D., 
PROFESSOR OF PHYSIOLOGY IN THE COLLEGE OF PHYSICIANS AND SURGEONS, N. Y. 
LOitl) illustrations. 
NEW YORK: 
HARPER & BROTHERS, PUBLISHERS. 
FRANKLIN SQUARE. 
1 875. Entered, according to Act of Congress, in the year one thousand eight hundred and 
sixty-eight, by 
HARPER & BROTHERS, 
In the Clerk’s Office of the District Court of the Southern District of New York. 
Copyright also secured in Great Britain, and entered at Stationers’ Hall, London, 
and Translation reserved. PREFACE. 
This book is intended as a means of instruction in 
Physiology and Hygiene for pupils and general read- 
ers who have no previous knowledge on medical sub- 
jects. The writer has endeavored to arrange the 
statements and descriptions in such a way that no an- 
atomical or physiological term should be employed, 
the meaning of which has not been already explained 
in the text. For convenience of reference, however, 
in cases where this explanation may have been over- 
looked or forgotten, a Glossary is added in the latter 
part of the book, which contains the meaning of all 
professional terms employed in the body of the work. 
A large proportion of the complicated names and 
phrases required for the complete study of Anatomy 
and Physiology are entirely unnecessary for those 
who pursue it simply as a part of their general edu- 
cation—that is, in the same way as they study Geog- 
raphy, Astronomy, or Mathematics. The most im- 
portant, and, at the same time, the most interesting 
facts of Physiology may be taught with success in a 
perfectly simple manner, provided they be given in 
the proper order and in their natural relation to each 
other. It has been the aim of the present work to 
accomplish this object; and if it be found to have 
succeeded in that respect, it is hoped that it will be 
an assistance to the teachers, parents, and pupils for 
whose use it was designed. 
New York, 1868. CONTENTS. 
CHAPTER I. 
The Bones.—Their Composition.—Their Structure.—The Skeleton. 
—Spinal Column.—The Skull.—Pelvis.—Tibia.—Bones of the 
Foot.—Curvatures of the Skeleton.—Elastic Ligaments. 
The Muscles.—Their Contraction.—Relaxation.—Flexor and Ex- 
tensor Muscles.—Tendons.—Movement of Joints.—Walking.— 
Running.—Leaping.—Elasticity of the Skeleton.—Exercise of the 
Muscular System.—Its Repose Page 19 
general structure and mechanism of the animal frame. 
CHAPTER II. 
THE FOOD AND ITS INGREDIENTS. 
Inorganic Substances.—Water.— Salt.—Lime.—Other Inorganic 
Matters.—Starch.—Its different Varieties.—Properties of Starch. 
—Its conversion into Sugar.—Sugar.—Whence obtained.—Propor- 
tion in the Food.—Fermentation of Sugar.—Fats.—Stearine.— 
Margarine.—Oleine.—Crystallization of Fat.—Emulsions.—Con- 
dition of Fat in Animal and Vegetable Tissues.—How extracted.— 
Adipose Tissue.—Proportion of Fat in the Food.—Albuminous 
Matters.—Different kinds.—Coagulation. —Ferments. —Putrefac- 
tion.—Proportion of Albuminous Matters in Food.—All the nutri- 
tious substances necessary to Life 45 
CHAPTER III. 
THE DIFFERENT KINDS OF FOOD, AND THEIR MODE OF PREPARA- 
Meat—its Composition.—Effect of Cooking.—Eggs.—Composition 
of the White and Yolk.—Milk—its Composition.—Butter—how 
obtained. — Cheese — its Preparation. — Bread — how made. — 
Yeast.—Fermentation of Bread.—Baking.—Wine—its Fermenta- 
tion.—Beer.—Vegetables.—Effect of Cooking on Vegetables.— 
Essential Qualities of Food.—Necessary Quantity 72 
TION. viii 
CONTENTS. 
CHAPTER IV. 
Necessity for Food. — Nature of Digestion.—Alimentary Canal — 
its different Parts.—Digestive Fluids.—Mastication.—The Teeth. 
—Incisors.—Canines.—Molars.—Their different Functions.—Sali- 
va.—Salivary Glands.—Composition of Saliva—its double Func- 
tion.—Action of the Tongue.—(Esophagus—its Peristaltic Action. 
—Deglutition.—The Stomach—its lining Membrane.—Gastric Tu- 
bules.—Gastric Juice—its Secretion.—Peristaltic Movements of the 
Stomach.—Composition of the Gastric Juice.—Pepsine.—Lactic 
Acid.—Action of Gastric Juice on the Food.—It is a Ferment.— 
Digestibility of Food.—Food should be properly cooked—should be 
taken in moderate quantity—with regularity.—The small Intestine. 
—Follicles of Lieberkiihn.—Intestinal Juice—its action on Starch. 
—Pancreatic Juice — its Composition — its action on Fat.—The 
Chyle.—Peristaltic Movement of Intestine.—Changes of Food in 
the Alimentary Canal.—End of Digestion Page 83 
DIGESTION. 
CHAPTER V. 
ABSORPTION. 
Lining Membrane of Intestine.—Valvulas Conniventes.—Villi.—En- 
dosmosis.—Absorption by Living Membranes.—Influence of the 
Circulation.—Blood-vessels of the Intestine.—Portal Vein.—Blood 
of the Portal Vein during Digestion contains Albuminose, Sugar, 
and Chyle.—Change in its appearance owing to Chyle.—Distribu- 
tion of Portal Vein in the Liver.—Reabsorption of the Digestive 
Fluids. —Lymphatic Vessels. —Lacteal Vessels. —Appearance of 
Lacteals during Digestion.—Receptaculum Chyli.—Thoracic Duct. 
—Discharge of Digested Matters into the Blood.—Their Transfor- 
mation and Disappearance.—Nutrition of the Blood 119 
CHAPTER VI. 
Situation and Structure of the Liver—its Lobules.—Biliary Ducts.— 
Secretion of the Bile.—Gall-bladder.—Accumulation of Bile in the 
Gall-bladder—its discharge into the Intestine.—Appearance and 
Composition of the Bile.—Biliary Salts.—Mode of extracting them 
from the Bile.—Their Crystallization.—Changes of the Bile in the 
Intestine—its absorption by the Blood.—Function of the Bile.— 
Formation of Sugar in the Liver—its absorption by the Blood-ves- 
sels.—Sugar finally decomposed in the Circulation 134 
THE DIVER AND ITS FUNCTIONS. CONTENTS. 
IX 
CHAPTER VII. 
THE BLOOD. 
Ingredients of the Blood.—Water. — Salt. — Lime.—Albumen.— 
Properties of Albumen.—Fibrine—its Properties.—Blood Globules 
—their Form—Size—Color—Consistency.—White Globules.— 
Quantity of different Ingredients in the Blood.—Coagulation of the 
Blood.—Clot.—Serum.—Coagulation dependent on the Fibrine.— 
Use of Coagulation in stoppage of Bleeding.—Why Blood does not 
Coagulate in the Vessels.—Daily Production and Decomposition 
of Fibrine.—Entire Quantity of Blood in the Body—its Variation.— 
Variation in Composition of the Blood.—Two different Kinds of 
Blood in the Body Page 145 
CHAPTER VIII. 
RESPIRATION. 
The Oxygen of the Air—its Necessity to Life.—Nature of Respiration. 
—The Lungs—their Structure.—Larynx.—Trachea.—Bronchial 
Tubes.—Lobules.—Air Vesicles. — Movement of Inspiration.— 
The Diaphragm—its Contraction.—Entrance of the Air.—Inter- 
costal Muscles.—Motion of the Ribs.—Movement of Expiration.— 
Elasticity of the Lungs.—Quantity of Air used in Respiration.— 
Movements of Respiration involuntary.—Effect of Respiration on 
the Blood.—Its Change of Color.—Venous Blood.—Arterial Blood. 
—Absorption of Oxygen in the Lungs.—Loss of Oxygen in the 
Tissues.—Carbonic Acid—where formed.—Discharged with the 
Breath.—Animal Vapor.—Watery Vapor.—Ventilation.—Ventila- 
tion by Doors and Windows—by Fires and Chimneys—by other 
Means.—Necessity for complete Ventilation 158 
CHAPTER IX. 
The Organs of Circulation. —The Heart—its Muscular Fibres.— 
Auricles.—Ventricles. —Pulmonary Artery.—Aorta. —Movement 
of the Blood through the Heart.—Contraction of the Heart—its 
Relaxation.—Valves of the Heart.—Ventricular Valves.—Semilu- 
nar Valves.—Action of the Heart involuntary.—The Arteries.— 
Arch of the Aorta.—Distribution of the Arteries—their Elasticity. 
—The Pulse—how felt.—Rapidity of the Pulse.—Pressure on the 
Blood in the Arteries. — The Capillaries.—Capillary Network.— 
Circulation of the Blood in the Capillaries.—The Veins—their 
Valves.—Movement of the Blood in the Veins.—Obstruction of the 
THE CIRCULATION. X 
CONTENTS. 
Circulation by compressing the Veins.—Rapidity of the Circula- 
tion.—Its local Variations Page 182 
CHAPTER X. 
ANIMAL HEAT. 
Warmth of Living Bodies—how preserved.—Production of Animal 
Heat.—Warm-blooded Animals. —Cold-blooded Animals.—Tem- 
perature of the Human Body.—Source of Animal Heat.—Differ- 
ence in Temperature of the Internal Organs.—Animal Heat neces- 
sary to Life.—Effects of cooling the Blood and Internal Organs.— 
Regulation of Heat by Perspiration.—Perspiratory Glands.—Com- 
position of the Perspiration.—Insensible Transpiration.—Increase 
of Perspiration by Heat.—Effect of its Evaporation.—Effect of heat- 
ing the Blood above 100° Fahrenheit.—Solid Ingredients of the 
Perspiration.—Sebaceous Secretion.—Necessity for frequent Bath- 
ing 200 
CHAPTER XI. 
NUTRITION. 
Definition of Nutrition.—Its three different Parts.-—Assimilation.— 
Absorption of Inorganic Ingredients.—Their different Proportions 
in the Tissues and the Blood.—Different kinds of Albuminous In- 
gredients.—Transformation of the Albumen.—Secretion.—Struc- 
ture of a Gland.—Follicles.—Lobules.—Ducts.—Inorganic Ingre- 
dients of a Secretion.—Its Albuminous Ingredient.—Increase of 
Secretion with excitement of the Circulation.—Excretion.—Altera- 
tion of Animal Tissues during Life.—A necessary consequence of 
Activity.—New Substances so produced.—Carbonic Acid.—Ani- 
mal Vapors. —Urea. — Creatine. —Creatinine. —Urate of Soda. — 
Double Movement of Nutrition.—Supply and Discharge.—Quanti- 
ty of Material absorbed and discharged in twenty-four hours... 210 
GENERAL STRUCTURE AND FUNCTIONS OF THE NERVOUS SYSTEM. 
CHAPTER Xir. 
United Action of the Organs.—System of Telegraphs.—Nervous Fila- 
ments.—Nerves.—Spinal Cord. — Spinal Nerves.—Brain.—Cere- 
brum.— Cerebellum.—Medulla Oblongata. — Cranial Nerves.— 
Nervous Fibres are Organs of Communication.—Irritability of 
Nerves.—Sensitive Fibres.—Motor Fibres.—Nerve Cells.—Nerv- 
ous Centres.—Reflex Action of the Nervous System 227 CONTENTS. 
XI 
CHAPTER XIII. 
THE SPINAL NERVES AND SPINAL CORD. 
Function of the Spinal Nerves.—Sensation and Motion.—Paralysis 
from injury of Nerve.—Restoration of a divided Nerve.—Anterior 
and Posterior Roots of Spinal Nerves.—Anterior Roots motor.— 
Posterior Roots sensitive.—Anterior and Posterior Columns of the 
Cord.—Anterior Columns motor.—Posterior Columns sensitive.— 
Connection of Spinal Cord with Brain.—Paralysis from injury of 
Spinal Cord.—Paraplegia.—Crossed Action of the Spinal Cord.— 
Hemiplegia.—Intercostal Nerves.—Phrenic Nerve.—Sensibility of 
the Skin—its Variation in different Parts.—Ordinary Sensibility.— 
Sensibility to Pain.—Sensibility to Heat and Cold.—Spinal Cord as 
a Nervous Centre.—Its Gray Matter.—Reflex Action of the Spinal 
Cord.—Its Character and Function Page 238 
CHAPTER XIV. 
Character of the Cranial Nerves.—Sensibility of the Face.—Fifth 
Pair of Cranial Nerves—its three Branches—their Distribution— 
their Sensibility.—Neuralgia.—Tic Douloureux.—Motor Branch 
of the Fifth Pair.—Muscles of Mastication.—Temporal.—Masse- 
ter.—Pterygoids.—Movements of Expression.—Facial Nerve—its 
Distribution—its Motive Power.—Paralysis of the Face.—Hypo- 
glossal Nerve.—Movements of the Tongue.—Pneumogastric Nerve 
—its Origin and Distribution.—Pharyngeal Branch.—Act of Deg- 
lutition.—Sensibility of the Pharynx.—Protection of the Nostrils 
in Deglutition.—Laryngeal Branches of the Pneumogastric.—The 
Glottis—its Movements in Respiration.—Protection of the Glot- 
tis in Deglutition.—Formation of the Voice.—Action of the Lar- 
ynx 256 
THE CRANIAL NERVES. 
CHAPTER XV. 
THE BRAIN. 
Form of the Brain—its Anatomical Divisions.—Medulla Oblongata. 
— Cerebellum.—Pons Yarolii.—Tuber Annulare.—Cerebrum.— 
Functions of the Cerebrum.—Memory.—Judgment.—Reason.— 
Effects of Injury to the Cerebrum.—Functions of the Tuber An- 
nulare.—Sensation and Volition.—Instinctive Movements.—Func- 
tions of the Medulla Oblongata.—Movements of Respiration—how 
performed.—Reflex Action of Medulla Oblongata.—Effects of In- 
jury to Medulla Oblongata.—Different kinds of Reflex Action in 
the Brain 282 xii 
CONTENTS, 
CHAPTER XVI. 
General Structure of the great Sympathetic—its Ganglia—its Nerves. 
—Arterial Plexus—their Distribution—connection with the Cere- 
bro-spinal System.—Slow operation of Sympathetic Nerves.—Effect 
of Cold and Wet.—Inflammation of the Internal Organs.—How to 
avoid the effects of Exposure.—Different kinds of Reflex Action 
through Sympathetic and Cerebro-spinal Systems Page 297 
STSTEM OF THE GREAT SYMPATHETIC. 
CHAPTER XVII. 
THE SPECIAL SENSES. 
Definition of the Special Senses.—Nerves of Special Sense.—Organs 
of Special Sense.—The Sense of Sight.—Optic Nerve.—The Eye- 
ball—its different Parts.—Field ofVision.—Line of distinct Vision. 
—Estimation of Distance.—Solidity and Projection.—Stereoscope. 
—Thaumatrope.—Internal Impressions.—Muscles of the Eyeball. 
—Eyelids.—The Tears.—Winking.—Meibomean Glands.—Lach- 
rymal Canal.—Practices injurious to the Sight.—Sense of Hear- 
ing.— Auditory Nerve. — Labyrinth.—Tympanum or Drum.— 
Chain of Bones.—Eustachian Tube.—External Ear.—Direction, 
Contrast, and Pitch of Sounds. — Sense of Smell. — Olfactory 
Nerves.—Nasal Passages.—Turbinated Bones.—Two kinds of Sen- 
sibility in Nose.—Uses of the Sense of Smell.—Sense of Taste. 
—Papillae of Tongue.—Two kinds of Sensibility in Tongue.—Glos- 
so-pharyngeal Nerve.—Uses of the Sense of Taste 305 
CHAPTER XVIII. 
DEVELOPMENT. 
Definition of Development.—Newly-born Infant—its Weight—con- 
dition of its Skeleton.—Ossification of the Skeleton.—Spinal Col- 
umn.— Skull.—Fontanelles. —Pelvis.—Long Bones.—Respiration 
of the Infant — its Digestion and Nutrition — its Nervous Sys- 
tem. — Reflex Actions. —Formation of the Teeth. —First Set. — 
Childhood.—Muscular System of the Child.—Nervous and Mental 
Functions.—Preponderance of the Instincts.—Formation of new 
Set of Teeth.—Youth.—Continued Ossification of the Skeleton.— 
Union of the Bones.—Completion of Development 359 INTRODUCTION. 
Physiology is the science which teaches us the 
natural actions of the living body, and the manner in 
which they are performed. It is very important for 
us to know what these actions are, and how they take 
place, for two reasons: 
First, because we learn in this way what kind of 
work the living body is capable of accomplishing, and 
to what uses it is adapted, so that we may be enabled 
to employ our natural powers to the best advantage, 
and not waste them by attempting what is useless or 
impracticable. 
Secondly, by understanding the natural actions of 
our bodies, and how they are maintained in a healthy 
condition, we are enabled to avoid injuring them by 
improper treatment, and thus actually diminishing our 
vital powers, or exposing them to debility and disease. 
Nothing can be more important than this either to 
our comfort, our usefulness, or even our mental im- 
provement. For the bodily frame is the organization 
by which our animal life is maintained, through 
which all our knowledge of the world about us is ac- 
quired, and by means of which alone all our designs 
are carried into execution. The knowledge of the 
mode in which health is to be maintained, and the 
bodily and mental powers kept unimpaired, consti- 
tutes the science of Hygiene. XIV 
INTRODUCTION. 
The study of physiology, therefore, leads directly 
to that of hygiene, and the two are necessarily asso- 
ciated with each other. 
In examining the bodily frame, we easily see that it 
is composed of various parts, which differ from each 
other in size, appearance, texture, and location. In 
one region, for example, there is the heart, in another 
the liver, in another the brain; while the surface is 
every where enveloped by the sensitive expansion of 
the skin. These different parts or portions of the 
body are called its Organs. They are connected in 
such a way as to give to each other a mutual support, 
and to form by their union a complete bodily organi- 
zation. 
Now eacli one of tliese organs is intended for a 
particular use, which is necessary in some way to the 
maintenance of life. Thus the heart circulates the 
blood, the lungs breathe, the liver produces the bile, 
the stomach digests the food, and the brain directs 
the movement of the limbs. The particular act or 
duty which eacli organ performs in this wTay is called 
its Function. Each function is different from every 
other, just as the organ which performs it is different 
from the rest; but they are all necessary to the 
healthy action of the whole body. For the different 
functions are associated together like the different or- 
gans that perform them, and are in the same way 
mutually dependent. Thus the liver can not pro- 
duce bile unless it be properly supplied with blood, 
and the blood will soon become poor and useless un- 
less the stomach continues to digest the food. introduction. 
XV 
The whole body, accordingly, is made up of differ- 
ent organs, united with each other, and performing at 
the same time a variety of functions. It is a kind of 
workshop in which various duties are performed by 
different workmen, while all combine to produce the 
final result. This result is the* complete and healthy 
activity of the entire frame. 
While studying, accordingly, in their regular order, 
the various animal functions, we find that they are 
naturally arranged in certain groups, which are dis- 
tinguished from each other by the nature of the acts 
performed and the object to be accomplished by 
them. Some of these acts are comparatively simple, 
others more peculiar and complicated. We shall find 
that their study is facilitated by taking up first the 
more simple of the animal functions, and afterward 
in succession those which are more complex. 
These functions will accordingly be described in 
four different groups or sections. 
Section I.—The animal functions belonging to the 
first group are entirely Mechanical in their nature. 
They are those by which the body is held together 
by the articulation of its various parts; by which the 
internal organs are protected from mechanical in- 
jury ; and by which the voluntary movements of the 
limbs and trunk are performed. This group com- 
prises the functions of the bones, the cartilages, the 
ligaments, the tendons, and the muscles. 
Section II.—The second group of functions are 
those which are physical or chemical in their nature, 
and which provide for the nourishment or Nutrition xvi 
introduction. 
of the body. This group includes a great variety of 
functions, which all tend, however, to the accomplish- 
ment of a single object, viz., the maintenance of the 
animal frame in its proper condition of flesh, strength, 
and activity. We shall study, in this division of the 
subject, the ingredients and qualities of the food, its 
preparation, digestion, and absorption, the blood and 
its circulation, respiration, secretion, and the nutri- 
tion of the animal tissues. 
Section III.—The third group includes the actions 
of the Nervous System. These actions are quite dif- 
ferent in their nature from any of the preceding, and 
have for their ultimate object the guidance or regu- 
lation of the other functions. It is in the study of 
this group that we shall learn the action of the senses, 
of the will, of the instincts, of many involuntary 
movements, and of the various operations of the 
mind. 
Section IV.—Finally, an important division of the 
subject is that which relates to the changes in the 
functions of the body at different ages, to its growth, 
adolescence, maturity, and Development. For the 
history of the animal functions is not entirely the 
same at different ages, hut undergoes various modifi- 
cations, like the external appearance of the frame, 
and the capacity of the mental and bodily powers. 
The entire organization, therefore, is adapted to dif- 
ferent purposes at different ages, somewhat in the 
same way as the various organs are permanently de- 
voted to particular functions. Section I. 
MECHANICAL FUNCTIONS. PHYSIOLOGY AND HYGIENE. 
CHAPTER I. 
GENERAL STRUCTURE AND MECHANISM OF THE ANIMAL 
FRAME. 
The Bones.—Their Composition.—Their Structure.—The Skeleton. 
—Spinal Column.—The Skull.—Pelvis.—Tibia.—Bones of the 
Boot.—Curvatures of the Skeleton.—Elastic Ligaments. 
The Muscles.—Their Contraction.—Relaxation.—Flexor and Ex- 
tensor Muscles.—Tendons.—Movement of Joints.—Walking.— 
Running.—Leaping.—Elasticity of the Skeleton.—Exercise of the 
Muscular System.—Its Repose. 
1. Structure and Composition of the Bones—The body 
depends for its general form and solidity upon the bones. 
The bones are of various sizes and shapes in different 
parts of the frame, but they are distinguished from the 
other organs by being hard and rigid, instead of soft 
and yielding; so that they are adapted to sustain the 
other tissues which are attached to them, and to pro- 
tect the internal organs which they inclose more or 
less perfectly in interior cavities. Now the bones have 
this important quality of hardness and rigidity because 
they contain, among other substances, a large propor- 
tion of a mineral ingredient. This ingredient is Lime, 
which, in certain forms of combination, is united with 
the animal matter of the bones, and makes them firm 
and resisting. If the bones were composed entirely of 20 
PHYSIOLOGY AND HYGIENE. 
this mineral ingredient, they would be stony and brit- 
tle, like limestone or marble; but, in reality, they con- 
sist partly of animal matter and partly of lime. The 
lime gives them their stifihess and resistance, while the 
animal matter makes them, at the same time, some- 
what tough and elastic; so that they combine, to a cer- 
tain extent, the two qualities of stiffness and elasticity. 
They are hard enough to sustain the weight of the 
body, and yet are not so brittle as to be easily broken. 
As a general rule, the bones are composed of about one 
half animal matter and one half mineral substance. 
Another important quality of the hones is their light- 
ness, which is combined in a proper degree with firm- 
ness and resistance. If they were en- 
tirely dense and solid, they would be 
too heavy for motion, and would be 
rather a load and impediment to the 
animal body than a support and assist- 
ance. But, in point of fact, the bones 
are hollow (Figs. 1 and 2). They are 
covered every where on their exterior 
with a layer of very compact bony tis- 
sue, which acts as a firm and resisting 
shell, while in their interior there are 
cavities occupying a large portion of 
the bony mass. In the middle of the 
bones of the limbs these cavities are 
elongated and cylindrical, and are filled 
with a soft vascidar substance termed 
the Marrow / but their rounded ends 
contain a multitude of small bony nee- 
dles and filaments, which branch and unite in various 
directions, dividing the principal cavity into a great 
Fig. 1. 
Thigh-bone, sawn 
open lengthwise. 21 
number of smaller spaces, and giving to the bone in 
this situation a very finely reticulated or honey-combed 
THE BONES. 
Fig. 2. 
Lower end of the thigh-bone, sawn across, showing its central cavity. 
structure. By this means the bones are made lighter, 
while they also preserve their firmness and resistance, 
and at the same time give a secure fastening to the 
muscles and tendons which are attached to their sur- 
face. 
2. General arrangement of the Skeleton.—The hones 
are united to each other, by strong fibres or ligaments, 
into a connected series or system, which is called the 
Skeleton. The skeleton is therefore a bony scaffolding 
or frame-work, which sustains by its physical solidity 
the other organs, and which gives its general configu- 
ration to the entire body. It consists, first of all, of the 
“ spinal column,” or Back-bone (Fig. 3), which runs up 
and down along the middle line of the back, and which 
can be readily felt in that situation, like a bony ridge, 
extending from the back of the neck to the region of 
the hips. This ridge is formed by a line of sharp 
prominences or “ spines,” each of which belongs to a 
separate bone; and as these bones are placed one upon 22 
PHYSIOLOGY AND HYGIENE, 
another, like a pile or column, the en- 
tire series has accordingly received 
the name of the “ spinal column.” 
The bones of the spinal column, twen- 
ty-six in number, are articulated and 
locked together by various projec- 
tions, and fastened by ligaments in 
such a way that it is capable of being 
maintained with security in the erect 
position. It stands, therefore, as a 
kind of central upright pillar, around 
which the other organs of the body 
are grouped, and upon which they 
depend for their support. It is the 
most important part of the whole 
skeleton. 
The spinal column sustains upon 
its upper extremity the “ cranium,” 
or Skull, which is a hollow bony case 
containing the brain, and having at- 
tached to it the jaws and other parts 
of the frame-work of the face. Its 
lower extremity rests upon the “ pel- 
vis,” or Hip-bone, between the two 
halves of which it is fastened like a 
wedge, and secured by strong liga- 
ments. The pelvis is a bony expansion, very much like 
a basin in shape, and is intended to receive and sup- 
port the organs of the lower part of the abdomen. By 
placing the hands upon the hips, we can easily feel the 
flaring edges of this basin-like bone, and can readily 
understand Iioav it serves to support the intestines and 
other organs placed above it. 
Fig. 3. 
Diagram of the skele- 
ton, etc., in profile. 
The clotted lines 
show the direction 
of the principal 
muscles. PHYSIOLOGY. 
January, 1874. 
1 How axe the bones fastened together? De- 
scribe the contraction of a muscle. What joints 
move in a circle? Why is exercise of the muscles 
necessary to health? 
2 Name four inorganic ingredients of the food. 
What is a ferment? Why is bread fermented 
with yeast? Name the necessary qualities of 
wholesome food. 
3 What is mastication? Describe the act of 
swallowing. 
•1 Name two conditions requisite for healthy di- 
gestion. What are the lacteals ? What is chyle ? 
liy what two routes is the chyle conveyed into the 
(Circulation? 
5 Detine coagulation. Why is it an important 
property of the blood? 
6 Describe the larynx. Duringrespiration what 
change takes place in the air? What in the 
blood? What is necessary for good ventilation? 
7 Which division of the heart is strongest and 
why? Explain the use of the valves of the 
heart. Describe the course of the blood in the 
circulation. 
8 How is the heat of the body produced? How 
is it regulated? 
9 Name the divisions of the brain. Which is 
most important and why? Why are the internal 
■organs affected by exposure of the body to cold 
and wet? 
10 Describe the iris. Explain the use of the 
conjunctiva. 23 
The pelvis, in its turn, rests upon the “femur,” or 
great Thigh-bone ; the largest and strongest single bone 
in the whole body. It is placed nearly straight up and 
down, and is surrounded by the thick muscles of the 
thigh. It is itself supported by the Tibia, or leg-bone, 
upon which it is placed, end for end. The tibia is some- 
what triangular in shape, and forms the sharp ridge 
which may be felt on the front part of the leg below 
the knee. Lastly, the lower end of the tibia rests upon 
the bones of the Foot. These bones are arranged very 
much in the form of an arch; for while the foot touches 
the ground by the point of the heel behind and the ball 
of the toes in front, the bones between them rise into a 
curved figure, forming at this part an arch or vault, 
called the “ hollow of the foot.” 
THE BONES. 
Now the bones of the foot are not fastened immova- 
bly to each other, but are so connected by elastic bands 
and ligaments that they yield a little when pressed 
upon, and again resume their usual position when the 
pressure is taken off*. We can perceive this very dis- 
tinctly by bearing down upon the foot forcibly from 
above, when it spreads out a little, and afterward re- 
covers itself and returns to its original shape. 
The principal internal organs, such as the heart, 
lungs, liver, stomach, and intestines, are contained in 
the cavities of the chest and abdomen, being situated 
in front and on the sides of the spinal column. 
3. Balancing of the different parts of the Skeleton.— 
The entire skeleton, therefore, forms a connected series 
or vertical frame of hones, which is so balanced that it 
may be kept in an upright position. 
The different parts of the skeleton are not placed ex- 
actly in a straight line, one above another, but, on the 24 
PHYSIOLOGY AND HYGIENE. 
contrary, vary somewhat both in a backward and for- 
ward direction. The bones of the foot are placed very 
obliquely, as we have already seen, forming an arch. 
The tibia, which rests upon this arch, is the only bone 
which is exactly vertical. The femur is somewhat 
curved in shape, and is also tipped forward, so that its 
upper extremity is articulated with the pelvis a little 
in front of the junction of the pelvis with the spinal 
column above. And the spinal column itself has no 
less than three different curvatures, which are turned 
alternately in the backward and forward direction. 
Nevertheless, if we look at the diagram of the skele- 
ton in Fig. 3, we shall see that all these variations com- 
pensate for each other; so that, although the skeleton 
is thus curved in its different parts, its general direc- 
tion is a straight one, and the weight of the head and 
upper part of the body rests almost exactly above the 
ankle-joint. 
But, as the different parts of the skeleton are movable 
at the joints or articulations, they must be fixed or 
steadied in some way, in order to keep the body in an 
upright position. This is accomplished by the follow- 
ing means. 
4. Action of the Elastic Ligaments.—First of all, the 
body is held erect by a series of Elastic ligaments, 
which are attached to the back part of the spinal col- 
umn. This jointed column is so arranged that it is ca- 
pable of moving in various directions, and especially 
of bending forward; and as the principal internal or- 
gans are situated in front of it, their weight would nat- 
urally cause it to bend over in this direction. But the 
spinal column is also provided throughout its entire 
length with bony eminences, projecting backward from THE MUSCLES. 
25 
its posterior surface. Now between these eminences 
there are attached, from one end to the other, a succes- 
sion of strong ligaments or bands, called the “ elastic 
ligaments of the spinal column,” because they are ex- 
tensible and elastic like India-rubber. These ligaments 
are sufficient to prevent the spinal column from yield- 
ing to the weight of the organs situated in front. 
When the back bone is bent forward by the action of 
the muscles, the bony eminences on its posterior sur- 
face, of course, are opened and separated from each oth- 
er like the sticks of a fan; but afterward they are 
drawn together as before by the elastic force of their 
ligaments, and the spinal column is again straightened. 
5. Structure and Action of the Muscles.—Secondly, 
the skeleton is maintained in its upright position by 
the action of the Muscles. These are the organs which 
are attached to the different parts of the skeleton in 
such a way as to control its movements. They form a 
large proportion of the whole mass 
of the body, and constitute the firm 
and ruddy fibrous Flesh, which is 
found every where underneath the 
skin, which clothes the bones, and 
which envelops in a kind of mus- 
cular sac the cavities of the chest 
and abdomen. 
If the muscles be examined by 
the microscope (Fig. 4), they are 
seen to be composed of a great 
number of very small fibres, too mi- 
nute to be seen by the naked eye, 
placed side by side, and all run- 
ning in nearly the same direction. 
Fig. 4. 
Muscular fibres highly 
magnified. 26 
These fibres are ruddy in color, and very elegantly 
marked by transverse line's or stripes, which run around 
them in a circular direction. The fibl-es themselves are 
united into small bundles, of from 100 to 200 each, which 
are placed side by side with other similar bundles, but 
separated from them by a thin layer of loose interven- 
ing tissue, called Cellular Tissue. A number of these 
bundles are also united into larger bundles writh cellu- 
lar tissue between them, and these again into still 
larger. Thus the entire muscle is made up of many 
bundles of parallel fibres, which can be separated from 
each other by careful dissection, and reduced to finer 
and finer divisions, until they become too small for the 
naked eye. It is this which gives to the muscular flesh 
its fibrous appearance on close examination. 
PHYSIOLOGY AND HYGIENE. 
Now the muscles, as we have described them above, 
are endowed with the power of Contraction. By this 
it is meant that the muscular fibres, when they are ex- 
cited by the influence of the -will, can shorten them- 
selves, so as to draw together any two points to which 
their ends are attached. Both ends of a muscle are 
never attached to one and the same bone, but between 
their two attachments there is always an articulation 
or joint, which allows of motion between one bone and 
the other. 
In contracting, therefore, the muscle draws the two 
bones to which it is attached nearer to each other. 
Whenever a muscle contracts, it swells from side to 
side at the same time that its fibres are shortened; and 
very accurate experiments have shown that it increases 
in thickness in exactly the same proportion that it di- 
minishes in length. It does not become, therefore, 
either larger or smaller during contraction, and only 
changes its shape, but not its size. THE MUSCLES. 
27 
If we grasp with the fingers the muscles on the front 
part of the arm above the elbow, we can perceive their 
contraction whenever we bend the elbow forcibly up- 
ward. At this time two changes in the muscle are dis- 
tinctly felt. First, it swells, as we have already said, 
and becomes prominent under the skin ; and, secondly, 
it becomes at the same moment harder and more resist- 
ing to the touch. This increased hardness of the mus- 
cle during contraction is caused by the forcible tension 
of its fibres, which continues as long as they remain in 
activity. 
The action of a muscle, accordingly, during contrac- 
tion is as follows: it shortens in the direction of its 
length, enlarges in the direction of its thickness, and be- 
comes more tense and firm in consistency. 
A muscle can remain in contraction only for a short 
time. After a few instants it returns to its former 
condition, becomes comparatively soft and yielding, 
and ceases to exert its force, so that it may be easily 
drawn out to its former length. This state of the mus- 
cle is called its Relaxation ; and when completely re- 
laxed, its fibres no longer exert any active effect upon 
the parts to which they are attached. 
Every muscle, accordingly, is alternately in one of 
two different states, viz., the state of active contrac- 
tion or that of passive relaxation. 
6. Arrangement and Action of the Flexors and Exten- 
sors.—Nearly all the muscles of the body and limbs 
are so arranged in two different sets as to act alter- 
nately with each other. One of these two sets is placed 
on the anterior, or front part, the other on the posteri- 
or, or back part; and w’hen thrown into activity, they 
serve to move the limb in two opposite directions. 28 
Those which bend the joint are called the Flexor mus 
cles; those which straighten it are called the Extensor 
muscles. Thus the muscles on the back part of the 
thigh draw the leg backward and bend the knee; they 
are therefore the flexor muscles. Those on the anterior 
part of the thigh draw the leg forward and straighten 
the knee; they are therefore the extensor muscles. On 
the other hand, the muscles on the front part of the 
arm, above the elbow, bend the arm at the elbow, and 
are flexors; those on the back part straighten the el- 
bow, and are extensors. 
PHYSIOLOGY AND HYGIENE. 
In this manner the movements of the body are ac- 
complished by the alternate contraction and relaxation 
of the two sets of muscles operating in different direc- 
tions; for when the flexors contract, they bend the 
limb without any resistance from the extensors; and 
when the flexors become relaxed, the extensors again 
straighten the limb as before. When both flexors and 
extensors are thrown into activity at the same moment, 
they make the limb rigid, and prevent its moving in 
either direction. 
But, as we have already seen, a muscle can remain in 
constant action for only a few seconds at a time. Aft- 
er a short period it must again become relaxed, not 
only to allow the opposite muscle to bend the limb in 
a different direction, but also to gain for itself new 
strength for another movement; for the force of the 
muscular fibres is more or less exhausted during con- 
traction, and again restored during relaxation. The 
muscles, therefore, alternately expend their power while 
contracted, and regain it in the state of relaxation. It 
is on this account that it is so exhausting to hold the 
arm or the leg outstretched in the same position for THE MUSCLES. 
29 
several minutes together, while the same limb may be 
moved backward and forward during an equal period 
without any sense of fatigue. For the same reason, it 
is more tiresome to stand upright and motionless for a 
quarter of an hour, than to walk about for the same 
length of time. 
In the ordinary movements of the body, therefore, 
the different muscles are constantly changing from con- 
traction to relaxation, and their natural vigor is thus 
kept unimpaired. 
Accordingly, it is easy to see how the skeleton is 
held erect by the action of the muscles. The effect of 
this action is not that of a rigid and unyielding stiff- 
ness, hut a delicate and graceful balancing, which al- 
lows of constant changes and inclinations of the body, 
without its being thrown out of the upright position. 
Those muscles which are situated in front prevent the 
joints from bending backward, and those which are at- 
tached behind prevent their yielding in a forward di- 
rection. In the same manner, those which are placed 
upon the right and left sides of the body prevent its 
falling in either direction laterally. The muscles are 
like the stays which support the masts of a ship, only 
they are not inanimate and passive, but active and 
movable in controlling the different parts of the skele- 
ton. The body can not remain upright for a single in- 
stant without their aid; for, if the muscles be para- 
lyzed at any time, as by an apoplexy, or a sudden blow 
upon the head, the power of standing erect is instantly 
lost. The head falls down upon the chest, the spinal 
column bends forward, the thighs bend at the hip-joints, 
the legs give way at the knees, and the entire frame 
falls together in a collapsed and shapeless mass. But 30 
PHYSIOLOGY AND HYGIENE. 
while the muscles retain their natural action by con- 
stantly drawing upon the different parts of the limbs 
and trunk, alternately backward and forward and from 
side to side, they prevent any undue deviation, and 
maintain the body in the erect posture. 
7. Attachment and Mechanism of the Muscles.—The 
muscles of the limbs are usually rather elongated in 
shape, and somewhat thinner at their two extremities 
than in the middle. At their upper extremities, as a 
general rule, they are quite closely attached to the 
bones; but at their lower extremities they become 
more slender and tapering, and run into somewhat long 
and narrow rounded cords of white fibrous tissue, which 
are called “ sinews,” or Tendons. These tendons have 
no power of contraction like that of the muscular fibres, 
nor can they be stretched like the elastic ligaments of 
the spinal column; they are simply very strong and 
unyielding fibrous cords, by which the muscles are at- 
tached to the bones upon which they are to act. When 
a muscle contracts, accordingly, it draws upon the bone 
below, by means of the tendon which is inserted into 
it, exactly as a horse draws a loaded wagon by means 
of the leathern tugs and couplings of his harness. 
The tendons are usually inserted into the movable 
part of a limb, at a short distance below the joint. Ac- 
cordingly, when the muscles contract, they act upon the 
limb with great rapidity; and a small amount of con- 
traction in the muscle will move the farther extremity 
of the limb over a considerable distance. Thus the 
hand and arm are raised, in bending the elbow-joint, by 
the action of the flexor muscles situated on the front 
of the upper arm, above the elbow, called the Biceps 
flexor and the Brachialis anticus (Figure 5). They THE MUSCLES. 
31 
rig. 5. 
Diagram of the arm bent at the elbow, showing the 
action of the flexor muscles. 
arise from the bones of the shoulder and upper arm, 
whence their fibres pass in a downward direction, their 
tendons being finally inserted into the bones of the fore- 
arm just below the elbow-joint. When these muscles 
contract they draw the fore-arm upward, moving it 
upon the elbow-joint like a door upon its hinges, and 
thus raising any weight which is supported upon the 
hand or wrist. The greater the weight which is to be 
lifted in this way, the greater the force which is ex- 
erted by the muscles; and they may be felt, according- 
ly, on the front of the upper arm, swelling and harden- 
ing at the moment of contraction exactly in proportion 
to the amount of strength put forth. The tendon of 
the biceps may also be felt at the same time, just in 
front of the elbow-joint, made tense and rigid like a 
bowstring by the action of the muscle above. 
Nearly all the movements of the body and limbs are 
performed by a mechanism like that just described. 
Whatever variations occur are mainly due to the dif- 
ferent construction of the joints ; for, while some of 32 
PHYSIOLOGY AND HYGIENE. 
them, as the elbow-joint and the knee-joint, are so ar- 
ranged that they can move only backward and forward 
like hinges, others, such as the shoulder and hip joints, 
can be turned in various directions, or even carried 
round and round in a circle, or rotated by a kind of 
twisting motion, like the hand and fore-ann. But in all 
cases this is accomplished by the action of muscles, 
whose tendons are inserted into the bones in various di- 
rections, and which thus produce by their contraction 
the corresponding movements. 
8. Movements of Walking, Running, and Leaping.— 
The movements of Walking, Running, Leaping, etc., 
are performed as follows: When the body stands up- 
right, as in Fig. 3, the feet are planted flat upon the 
ground, bearing at once upon the heels behind and the 
ball of the toes in front, the weight of the body resting 
between the two, upon the middle of the arch of the 
foot. The body is maintained in this position, as we 
have seen, by the various muscles, which act in such a 
way as to keep its different parts carefully balanced, 
and to retain the weight of the whole suspended exact- 
ly over the ankle-joint. 
Now in walking, when a movement is to be executed 
in advance, the body is first made to lean a little for- 
ward, so that its weight no longer remains above the 
ankle, but is thrown forward so as to rest entirely upon 
the toes. The heel is then lifted from the ground by 
the action of the very strong muscles situated on the 
back part of the leg, called the Gastrocnemius and Soleus 
muscles. These muscles, which come doAvn from above, 
form the fleshy mass which is known as the “ Calf of the 
leg.” They terminate in a strong cord-like tendon, 
called the “ Tendon of Achilles,” which is easily felt at 33 
THE MUSCLES, 
the back part of the ankle-joint, 
and which is attached to the 
projecting bone of the heel, 
termed the Calcaneum (Fig. 6), 
When these muscles contract, 
they draw the heel upward b} 
means of the tendon inserted 
into it, and lift in this way the 
ankle-joint and the whole body, 
carrying it upward and forward, 
its principal weight resting, as 
already mentioned, over the ball 
of the toes. 
The action of the leg and foot, in this movement, is 
the same with that by which we might lift a weight 
from the ground with the aid of a lever. Suppose one 
end of a strong stick to rest upon the ground, and that 
this stick bears upon its middle a heavy weight (Fig. 7). 
Fig. 6. 
Diagram of the foot and ankle, 
with the heel drawn up by the 
“ Tendon of Achilles." 
Fig. 7, 
Then, by taking in the hand the other end of the stick, 
we may lift the wreight exactly as the body is lifted, in 
walking, by the muscles of the leg and the ankle-bones. 
At the moment that the body is raised and tilted 
forward in this way, the other foot is lifted entirely 
from the ground and swung forward, so as to take a 
step in advance. As soon as the body has been carried 
far enough in an onward direction, the second foot is 34 
PHYSIOLOGY AND HYGIENE. 
also raised in the same manner as before, while the 
first is swung forward in its turn to take another step. 
In this way the two legs act alternately, the weight of 
the body being carried forward first by one and then 
by the other; all the muscles, however, upon the two 
side3 combining harmoniously in their action, so as to 
produce an easy, graceful, and continuous movement. 
In the act of walking, as above described, one foot is 
always upon the ground, and the weight of the body is 
mainly supported in this way by bearing upon the toes; 
it is only lifted forward alternately on the two sides by 
the leverage of the bones of the foot. Consequently no 
violent muscular exertion is required, and the move- 
ment can be kept up for a long time without fatigue. 
The act of Running, however, instead of being a 
series of steps, is performed by a succession of leaps 
or springs, in ’each of which the whole body is thrown 
clear of the ground, and carried forward by the im- 
petus which it has received. In order to accomplish 
this, at the moment the heel is about to be raised by 
the action of the muscles above described, the knee and 
hip joints are first bent, and then instantly straightened 
by the sudden contraction of their extensor muscles. 
The whole limb thus acts like a powerful spring, which, 
by its sudden extension, throws the entire body off the 
ground and carries it through the air in an onward di- 
rection. The opposite limb is at the same time thrown 
forward to receive the weight of the body, and to per- 
form, in its turn, and with a similar rapidity, the same 
movements. The speed of the runner depends on the 
vigor of the muscular contractions, and the swiftness 
with which the successive motions are performed. 
The act of Jumping is accomplished in a similar way THE MUSCLES. 
35 
with that of running, except that the same motions are 
executed by both limbs together, so that each leap is 
performed by itself, and is not combined with the oth- 
ers into a continuous movement. 
9. Elasticity of the Skeleton. — In all these various 
movements, the body is protected from the. effect of 
sudden shocks and jars by important peculiarities of 
structure and function. 
First of all, the bones themselves are elastic. This 
elasticity is not very marked in degree for any single 
bone, but still it exists every wThere, and is a quality of 
considerable importance for the entire skeleton. It is 
owing to the fact which has already been mentioned, 
viz., that the bones are formed of an animal substance 
united with a combination of lime. The elasticity of 
the animal substance is much diminished in conse- 
quence of its union with the mineral ingredient; but 
still it does not disappear altogether, and the entire 
bone therefore retains the property to a certain degree. 
In children and very young persons the quantity of 
lime in proportion to the animal substance is smaller 
than in adults, and their bones are consequently more 
flexible and elastic than at a later period. It is for this 
reason that the bones of young children are very sel- 
dom broken by falls or other accidents, Avhile those of 
adults are more liable to injury from this cause. 
Secondly, the articulating ends of the hones are cov- 
ered with a layer of firm, India-rubber-like substance, 
called Cartilage. In most of the movable joints there 
are two of these cartilages, firmly attached to the cor- 
responding bones, and moving smoothly and easily 
upon each other by their opposite surfaces, which are 
lubricated with a transparent fluid. In the spinal col< PHYSIOLOGY AND HYGIENE. 
umn the principal cartilages are quite thick and pulpy, 
lying, like so many elastic cushions, between the differ- 
ent bones of which the column is composed. All these 
cartilages serve to receive the shock of sudden blows 
or falls, and to dissipate their injurious effects. 
Thirdly, the Curvatures of the different parts of the 
skeleton have also an important influence in this re- 
spect. These curvatures are especially marked in the 
spinal column, which, in its natural position, is bent al- 
ternately in three different directions (Figure 3), thus 
presenting a wavy or serpentine figure instead of a 
straight vertical line. The consequence of this is that, 
when it receives a sudden shock or impulse, it yields 
momentarily by increasing its curvatures, like a bow or 
spiral spring, and then recovers itself when the press- 
ure is relieved. All the bones of the limbs are also 
slightly curved in their figure, and therefore contrib- 
ute, in some degree, to the same effect. 
10. Protective Action of the Muscles.—Lastly, an im- 
portant protecting influence is exerted by the action of 
the muscles; for in leaping, running, or jumping from 
a high place, the body is never abandoned entirely to 
its own unassisted weight. The muscles are always 
employed in holding the limbs in the required position, 
and keeping them in readiness for other movements. 
When the body reaches the ground, the limbs bend at 
the joints, still controlled, however, by the extensor 
muscles; and these muscles immediately afterward 
react, again bringing the body into an erect position. 
In this manner a certain kind of elasticity, dependent 
upon muscular vigor, is communicated to the motions 
of the whole frame, and protects it from the effect of 
sudden concussions. THE MUSCLES. 
37 
11. Exercise.—The natural force of the muscular sys- 
tem requires to be maintained by constant and regular 
Exercise. If all the muscles, or those of any particular 
part, be allowed to remain for a long time unused, they 
diminish in size, grow softer, and finally become slug- 
gish and debilitated. By use and exercise, on the con- 
trary, they maintain their vigor, continue plump and 
firm to the touch, and retain all the characters of their 
healthy organization. It is very important, therefore, 
that the muscles should be trained and exercised by 
sufficient daily use. Too much confinement by seden- 
tary occupations, in study, or by simple indulgence in 
indolent habits, will certainly impair the strength of 
the body and injuriously affect the health. Every one 
who is in a healthy condition should provide for the 
free use of the muscles by at least two hours’ exercise 
each day; and this exercise can not be neglected with 
impunity, any more than the due provision of clothing 
and food. 
The muscular exercise of the body, in order to pro- 
duce its proper effect, should be regular and moderate 
in degree. It will not do for any person to remain in- 
active during the greater part of the week, and then 
take an excessive amount of exercise on a single day. 
An unnatural deficiency of this kind can not be com- 
pensated by an occasional excess. It is only a uniform 
and healthy action of the parts which stimulates the 
muscles, and provides for their nourishment and growth. 
Exercise which is so violent and long-continued as to 
produce exhaustion or unnatural fatigue is an injury 
instead of an advantage, and creates a waste and ex- 
penditure of the muscular force instead of its healthy 
increase. 38 
PHYSIOLOGY AND HYGIENE. 
Walking is therefore one of the most useful kinds of 
exercise, since it calls into easy and moderate action 
nearly all the muscles of the body, and may be con- 
tinued for a long time without fatigue. Riding on 
horseback is also exceedingly efficacious, particularly 
as it is accompanied by a certain amount of excitement 
and interest which acts as an agreeable and healthy 
stimulus to the nervous system. Running and leaping, 
being more violent, should be used more sparingly. 
For children, the rapid and continuous exercise which 
they spontaneously take in their various games and 
amusements in the open air is the best. The exact 
quantity of exercise to be taken is not precisely the 
same for different persons, but should be measured by 
its effect. It is always beneficial when it has fully 
employed the muscular powers without producing any 
sense of excessive fatigue or exhaustion. 
It should be remembered, also, that the object of ex- 
ercise is not the mere acquisition or increase of muscu- 
lar strength, but the proper maintenance of the general 
health. A special increase of strength may be produced 
to a very great extent by the constant practice or train- 
ing of particular muscles. Thus the arms of the black- 
smith and the legs of the dancer become developed in 
excessive proportions; and by the continued practice, 
in a gymnasium, of raising weights, or carrying loads, 
the muscular system generally maybe greatly increased 
in force. But this unusual muscular development is not 
necessary tq health, and is not even particularly bene- 
ficial to it. The best condition is that in which all the 
different organs and systems of the body have their full 
and complete development, no one of them prepondera- 
ting excessively over the others. The most useful kind THE MUSCLES. 
39 
of exercise, accordingly, is that which employs equal- 
ly all the limbs, and cultivates agility and freedom of 
movement, as well as simple muscular strength. 
In all cases, also, the exercise which is taken should 
be regular and uniform in degree, and should be re- 
peated as nearly as possible for the same time every 
day. 
12. Repose.—The muscular system requires, further- 
more, a daily period of Repose. This is not only the 
interval between the periods of active exercise; for 
even while sitting, or standing, or engaged in ordinary 
quiescent occupations, we constantly employ some de- 
gree of muscular exertion. It is also necessary that all 
muscular activity be entirely suspended for a time, dur- 
ing the period of sleep; for it is during sleep that the 
main part of the nourishment of the tissues takes place, 
and the renovation of their active powers is accomplish- 
ed. We feel, accordingly, a sense of refreshment and 
renewed vigor after sleep, which is owing in great meas- 
ure to the nourishment and repair of the muscular sys- 
tem. A privation of this necessary repose will inevita- 
bly show its effect, after a day or two, in diminished 
strength and the failure of the powers generally. The 
requisite amount of sleep, therefore, should always be 
taken at night with the same regularity that exercise 
is employed during the day; for it is by the uniform 
and alternate influence of both that the muscular sys- 
tem is kept in the highest condition, and the general 
health most effectually secured. 40 
PHYSIOLOGY AND HYGIENE. 
QUESTIONS FOR CHAPTER I. 
1. What is the use of the bones ? 
2. How do they differ in consistency from the other organs ? 
3. What ingredient gives them their hardness ? 
4. What ingredient gives them their elasticity ? 
5. Are the bones solid or hollow ? 
6. What are their hollow parts filled with ? 
7. How are the bones fastened to each other ? 
8. What name is given to the whole series of bones united to- 
gether ? 
9. What is the most important part of the skeleton ? 
10. Why is it called the “ spinal column ?” 
11. Wtyit is supported upon the upper end of the spinal column ? 
12. What is contained within the cranium? 
13. What does the lower extremity of the spinal column rest upon ? 
14. What is the shape of the pelvis ? 
15. What organs does the pelvis serve to support? 
16. What is the bone of the thigh ? 
17. What is the bone of the leg? 
18. What is the form of the bony framework of the foot? 
19. How does the foot move when pressed upon ? 
20. Are the different parts of the skeleton straight or curved ? 
21. How is the skeleton held upright? 
22. What are the “ elastic ligaments,” and where are they situated ? 
23. What are the muscles ? 
24. Of what are they composed ? 
25. What is the appearance of the muscular fibres ? 
26. What peculiar property is possessed by the muscles ? 
27. What effect is produced on the bones by the contraction of the 
muscles ? 
28. When a muscle contracts, how is its shape altered ? 
29. How is it changed in consistency ? 
30. What is the relaxation of a muscle ? 
31. What is the difference between a flexor muscle and an exten- 
sor muscle ? 
32. When the flexor muscles and extensor muscles both contract at 
the same time, what effect do they have on the limb ? 
33. When is the force of a muscle expended ? QUESTIONS. 
41 
34. When is it restored ? 
35. Why is it tiresome to hold the arm or leg continuously in one 
position ? 
36. How do the muscles serve to balance the different parts of the 
skeleton ? 
37. By what are the muscles attached to the movable hones? 
38. Where are the muscles situated which bend the elbow ? 
39. Where are their tendons inserted ? 
40. What joints move like a hinge ? 
41. What joints can be moved round in a circle ? 
42. How is the motion of walking performed ? 
43. How is the motion of running performed ? 
44. How are the motions of leaping and jumping performed ? 
45. How is the body protected from shocks and jars ? 
46. Why are the bones of children more elastic than those of 
adults ? 
47. What are the ends of the hones covered with ? 
48. What is the use of the cartilages ? 
49. What is the use of the curvatures of the skeleton ? 
50. How do the muscles protect the body from injury ? 
51. Why is exercise of the muscles necessary to health? 
52. How should the exercise be taken ? 
53. What are the most useful kinds of exercise ? 
54. Why is repose necessary to health ? 
55. What effect is produced by a want of natural sleep ? Section II. 
FUNCTIONS of NUTRITION. CHAPTER II. 
THE FOOD AXD ITS INGREDIENTS. 
Inorganic Substances.—Water. — Salt.—Lime. — Other Inorganic 
Matters.—Starch.—Its different Varieties.—Properties of Starch. 
—Its conversion into Sugar.—Sugar.—Whence obtained.—Propor- 
tion in the Food.—Fermentation of Sugar.—Fats.—Stearine.— 
Margarine.—Oleine.—Crystallization of Fat.—Emulsions.—Con- 
dition of Fat in Animal and Vegetable Tissues.—How extracted.— 
Adipose Tissue.—Proportion of Fat in the Food.—Albuminous 
Matters.—Different kinds.—Coagulation.—Ferments.—Putrefac- 
tion.—Proportion of Albuminous Matters in Food.—All the nutri- 
tious substances necessary to Life. 
13. Nature and Necessity of Food.—Under the term 
“ food” are included all those substances, both solid and 
liquid, which are necessary for the nutrition of the body. 
The constant action of the different organs in the liv- 
ing body requires a regular supply of nourishment, by 
which their strength and activity may be maintained; 
for these organs can not perform their allotted func- 
tions without undergoing a corresponding waste of ma- 
terial, and this waste must be made good by an appro- 
priate supply, if the organs are to retain their powers, 
and the functions of life continue. 
The expenditure of material which thus takes place 
in the living body is not a simple physical disintegra- 
tion, as when the wheels and axles of a carriage wear 
out by mechanical friction; it is a kind of internal de- 
composition, which pervades every part of the animal 46 
PHYSIOLOGY AND HYGIENE. 
frame, and which is very nearly proportionate in amount 
to the activity of the organs themselves. It is some- 
what like the consumption of water and fuel by a loco- 
motive engine, the water and fuel being used up and con- 
verted into smoke and steam, in order to enable the ma- 
chine to do its work. Somewhat in a similar way the 
active functions of the living body create a constant de- 
mand for nutritious food, which must be supplied with 
regularity in order to preserve them in continued action. 
It is important to know, therefore, what are the nec- 
essary ingredients of the food, how they are prepared 
and combined, and in what manner they are absorbed 
and consumed by the living body. 
14. Inorganic Substances.—In the first place, the food 
contains a large proportion of materials which are call- 
ed Inorganic Substances. They are substances which 
are found every where in external nature, and wThich 
form a portion of the rocks, earth, and running streams. 
It is on this account that they are termed inorganic 
substances, because they occur in unorganized bodies, 
and are not peculiar to animated beings. They are 
found, however, also in the bodies of living animals, 
and therefore they must be present in similar propor- 
tions in the food, for it is from this source alone that 
all the materials of the animal frame are necessarily de- 
rived. 
The first and most abundant of these inorganic sub- 
stances is Water. Water is universally present in all 
the solids and fluids of the body. It is especially abun- 
dant in the blood and secretions, for it gives them their 
necessary fluidity, and enables them to dissolve all the 
important materials which they contain. 
But it is also an ingredient of the solid tissues; for FOOD AND ITS INGREDIENTS. 
47 
if we take a muscle or a cartilage, and expose it to a gen- 
tle heat in dry air, it loses water by evaporation, dimin- 
ishes in size and weight, and becomes dense and stiff. 
Even the bones and teeth lose water by evaporation in 
this way, though in smaller quantity. In all these 
more solid parts of the body, the water which they con- 
tain is useful by giving them a certain degree of soft- 
ness and flexibility, which is necessary to their useful- 
ness. Thus a tendon, in its natural condition, is white, 
glistening, and opaque; and, though very strong, per- 
fectly flexible. If its water be expelled by evapora- 
tion it becomes yellowish in color, shriveled, semi- 
transparent, inflexible, and totally unfit for performing 
its mechanical functions. The same thing is true of 
the skin, muscles, cartilages, and other soft parts. 
The following list shows the proportion of water in 
different solids and fluids: 
Quantity of Water in 1000 parts in 
Teeth 100 
Bones 130 
Cartilage 550 
Muscles '. 750 
Ligaments 768 
Brain 789 
Blood 795 
Bile 880 
Milk 887 
Pancreatic juice 900 
Lymph 960 
Gastric juice 975 
Perspiration 986 
Saliva 995 
According to the best calculations, water constitutes, 
in the human subject, between two thirds and three 
quarters of the entire weight of the body. 
Accordingly, water is also a very important element 
of the food. We require every day nearly three pounds 
and a half as drink, either in the form of pure water, or 
in that of tea, coffee, milk, or other fluids. Beside this, 
however, tne different kinds of solid food, such as bread, 48 
meat, etc., all contain water as part of their substance; 
so that, counting all that is taken in both solid and liq- 
uid food, we find that the entire quantity of water con- 
sumed every day by a healthy adult is not less than 
about four pounds and a half. 
PHYSIOLOGY AND HYGIENE. 
After being once introduced into the body and ab- 
sorbed by the tissues, the water is again discharged; 
for its usefulness in the animal frame, like that of the 
other ingredients of the body, is not permanent, but 
temporary. It does its work while passing through 
the animal organism; and, having accomplished this 
purpose, it then makes its exit by various ways. A 
large proportion is discharged with the perspiration by 
the skin; another quantity is exhaled from the lungs 
with the breath; while the remainder is discharged by 
the kidneys. 
Another inorganic ingredient of the food is common 
Salt. This substance exists in all parts of the body, 
though usually in much less abundance than the water; 
and the animal frame, therefore, could not be properly 
nourished without it. It is found in the different solids 
and fluids in the following proportions: 
Quantity of Common Salt in 1000 parts in the 
Muscles 2 
Bones 2.5 
Cartilages 2.8 
Milk 1 
Saliva 1.5 
Bile 3.5 
Blood 4.5 
Mucus 6 
In the blood it is more abundant than all the other in- 
organic ingredients excepting water. 
Salt, accordingly, is not only a natural ingredient in 
most kinds of food, but we almost always take it in ad- 
dition, as a condiment, to increase the relish of many ar- 
ticles of diet. This desire for salt is instinctive, and in- FOOD AND ITS INGREDIENTS. 
49 
dicates the natural craving of the system for something 
which is essential to its organization. In many in- 
stances it must be given also to the lower animals, in 
order to provide fully for their nourishment. Farmers 
and stock-bi eeders, for this reason, habitually give it to 
horses, cattle, and sheep; and experience has shown 
that animals, when regularly supplied with a proper al- 
lowance of salt, are kept in much better condition than 
when they are fed only with hay, grain, and other veg- 
etable substances. 
Salt is also useful by exciting the action of the di- 
gestive secretions, and assisting in this way the solution 
of the food; for food which is tasteless, however nu- 
tritious its qualities may be, is taken with reluctance 
and digested with difficulty; while the attractive fla- 
vor which is developed by cooking, and by the addition 
of salt and other proper condiments, excites the secre- 
tion of the saliva and the gastric juice, and therefore 
facilitates digestion. The salt, introduced in this man- 
ner, is afterward absorbed by the blood-vessels from the 
intestine, and is deposited in the different tissues of the 
body. It is finally discharged in the mucus, perspira- 
tion, and other secreted fluids. 
The most important mineral ingredient of the food, 
next to common salt, is Lime. We have already seen 
how abundant this substance is in the bones. It is also 
found in still larger quantity in the teeth. It exists 
beside, in smaller proportions, in all the other tissues 
and fluids of the body. It occurs principally in the 
form of two different combinations, called “ phosphate 
of lime” and “ carbonate of lime.” The first of these 
is usually the most abundant. Its proportion is shown 
in the following list: 50 
PHYSIOLOGY AND HYGIENE. 
Quantity of Phosphate of Lime in 1000 parts in the 
Teeth 650 
Bones 550 
Cartilages 40 
Muscles 2.5 
Blood 0.3 
Gastric juice 0.4 
In the blood, secretions, etc., the lime is in the liquid 
form, being dissolved by the watery parts of the animal 
fluids. In the bones, teeth, cartilages, and other firm 
tissues, it is solid, and intimately united with the ani- 
mal matters of these parts. It is useful here by giving 
to the tissues their proper consistence and solidity. In 
the enamel of the teeth, which is almost entirely com- 
posed of phosphate and carbonate of lime, we have a 
substance capable of grinding down by mastication all 
the harder materials of the food, and of 
resisting unharmed the greatest amount 
of mechanical friction. In the remain- 
ing portion of the teeth, or “ ivory,” the 
lime is in smaller proportion, but still 
very abundant; and in the bones it con- 
tinues to form more than one half the en- 
tire substance of the tissue. 
Its importance in communicating to 
the bones their natural stiffness and con- 
sistency may easily be seen from the ef- 
fect produced by its removal. If any one 
of the long bones be soaked for a consid- 
erable time in a mixture of water and 
muriatic acid, the lime will be dissolved 
out, and the bone, which thus loses its 
rigidity, may then be bent or twisted in 
any direction without breaking (Fig. 8). 
If the bones of the skeleton, therefore, 
were destitute of mineral ingredients, they would bend 
Fig. 8. 
Fibula (small bone 
of the leg), tied in 
a knot after being 
macerated in a di- 
lute acid. 51 
under the action of the muscles, and would be entirely 
incapable of sustaining the weight of the body. 
FOOD AND ITS INGREDIENTS. 
Lime is contained, in suflicient quantity, in various 
kinds of food, particularly in muscular flesh, in milk, 
and in the vegetable grains. 
The other inorganic substances existing in the food 
are combinations of Soda, Potash, Magnesia, and Iron. 
They are in much smaller quantity than those already 
mentioned, but serve by their presence, though in mi- 
nute proportion, to complete the constitution of the 
food, and provide for all the mineral ingredients neces- 
sary to the formation of the tissues. 
The inorganic substances, as a general rule, do not un- 
dergo any chemical change or decomposition in the in- 
terior of the body. They are absorbed with the food, 
and form, for a time, a part of the animal tissues; after 
which they are again discharged with the secretions, 
and replaced, in turn, by a fresh supply of similar ma- 
terials. Nevertheless, they are absolutely indispensa- 
ble to the proper nourishment of the body; and if the 
food were entirely deprived of mineral ingredients, the 
system would soon become seriously disordered and 
weakened by their absence. 
15. Starch. — The next important ingredient of the 
food is /Starch. 
This substance is familiar to all in the form of a light 
white powder, which is used for various purposes in the 
arts and in manufactures. When it is rubbed between 
the fingers it gives a peculiar crackling sensation to the 
touch, by which it can almost always be recognized. 
But it is much more certainly distinguished by its ap- 
pearance when examined under the microscope. It is 
then seen to be composed of minute solid grains, which 52 
PHYSIOLOGY AND HYGIENE. 
are too small to be seen by the naked eye, but which 
have a very peculiar appearance when magnified. Dif- 
ferent kinds of starch can be distinguished from each 
other by the size,and aspect 
of their grains. In potato 
starch, for example (Fig. 9), 
the grains vary in size from 
ruoTTcr to w of an inch in 
diameter. They are irregu- 
larly pear-shaped in form, 
and are marked by fine con- 
centric lines, as if the sub- 
stance of the starch-grain 
had been deposited in layers. 
At one spot on the surface of each there is a minute 
point, and the circular lines are arranged round this 
point as a centre. 
In wheat starch (Fig. 10) 
the grains are not so large 
as in that from the potato. 
They vary from T6 to 
of an inch in diameter. 
They are also nearly circm 
lar in shape, but do not 
show any distinct concen- 
tric lines. Many of them 
are compressed or flattened 
from side to side, so that 
they present a broad surface in one direction, and a 
narrow edge in the other. 
The starch grains of Indian corn (Fig. 11) are of 
nearly the same size with those of wheat flour; but 
they are usually more angular and irregular in form, 
Pig. 9. 
Pig. 10. 
Starch grains of Wheat flour. FOOD AND ITS INGREDIENTS. 
53 
and are often marked with 
crossing or radiating lines, 
as if they had been par- 
tially broken by pressure. 
Now all the starch which 
is used for food, for the arts, 
or in manufactures, is ob- 
tained from plants. It is 
not an inorganic substance, 
therefore, like water, salt, 
or lime, but is a product of 
vegetable growth. Its minute grains are found packed 
away in the tissues of the plants, among their fibres, 
and in the interior of vegetable cells; and are accumu- 
lated in various quantities in their tuberous roots, in 
the pith of their stems, or in their seeds and fruit. It 
forms at least one seventh of the whole substance of 
the potato, about one third of peas and beans, over one 
half of wheat, rye, and oats, and at least three quarters 
of rice and Indian corn. Arrow-root is nothing but the 
starch from the tuberous roots of a West Indian plant; 
Tapioca is starch from the root of another plant, also 
from the West Indies; and Sago is nearly pure starch 
from the pith of various kinds of palms. 
Fig. 11. 
Starch grains of Indian corn. 
The exact quantity of starch in the more ordinary 
articles of food is shown in the following list: 
Quantity of Starch in 100 parts in 
Kice 85.07 
Maize 80.92 
Barley-meal 67.18 
Ryemeal 61.07 
Oatmeal .59.00 
Wheat flour 72.00 
Iceland moss 41.60 
Kidney-bean 35.94 
Peas 32.45 
Potato 15.70 
It is obtained in a pure form by grinding up some 54 
PHYSIOLOGY AND HYGIENE. 
vegetable matter which contains it in abundance, and 
mixing it with cold water. The water is then strained 
and allowed to stand, when the starch after a time set- 
tles to the bottom, and is finally dried and powdered. 
Starch is not affected by cold water; but if it be 
boiled for a short time, its grains swell up, become 
transparent, absorb a large quantity of water, and at 
last melt away into a thin, grayish-looking fluid. When 
this fluid is allowed to cool, it sets or stiffens into a 
kind of pasty mass, which is quite solid if the starch 
have been used in large quantity. But after this cook- 
ing process the separate grains are no longer to be dis- 
tinguished, and the whole is changed into a uniform 
homogeneous material, because the water has been per- 
manently absorbed by the starch, and is therefore re- 
tained in combination with its substance. 
Another very curious fact about starch is that by 
various means it may be entirely altered in its quali- 
ties and converted into sugar. 
One mode of accomplishing this singular transforma- 
tion is the following: If starch be mingled with a very- 
thin watery solution containing an acid, and boiled for 
a short time, it soon loses its grayish color, and becomes 
quite clear and transparent; and if the boiling be con- 
tinued for a longer period, all the starch finally disap- 
pears, and the solution is then found to have a sweet 
taste and to contain sugar. The starch, in fact, lias been 
consumed or altered, and sugar has taken its place. 
Some animal and vegetable substances have the pow- 
er of causing the same change. Thus, if a little saliva 
from the mouth be mixed with a solution of starch and 
then kept in a warm place, after a time the starch will 
be found to have disappeared and sugar to have been FOOD AND ITS INGREDIENTS. 
55 
produced instead. Something of this kind happens in 
certain vegetable tissues, especially in seeds during the 
first process of their growth or “ germination,” when a 
part of the starch which has been stored up in their 
substance becomes changed spontaneously into sugar. 
We shall also find hereafter that the starch which is 
taken with the food is entirely changed in the process 
of digestion. None of it, therefore, is to be found after- 
ward in any of the circulating fluids or secretions of 
the body. 
16. Sugar.—The next ingredient of the food is Sugar, 
which, as we have already seen, is closely related to 
starch. Sugar is always readily distinguished by its 
sweet taste, a character which forms its most attract- 
ive quality. It is found in many animal and vegetable 
juices, being obtained principally from the juices of the 
sugar-cane, the rock maple, and the beet root; but of 
these, the sugar-cane supplies much the largest quanti- 
ty. In its natural condition the sugar is dissolved in 
the vegetable fluids, where it is mingled with many 
other different substances. 
It is extracted in the following manner: 
The vegetable juices are first collected by crushing 
the fresh sugar-canes between iron rollers. The fluids 
obtained in this way are then heated with a solution of 
lime, which causes many of their impurities to separate 
and rise in a kind of scum upon the surface. This is 
carefully removed, and the purified juice is then boiled 
down until the sugar solidifies as a brownish colored 
granular deposit. This brown sugar is again dissolved 
and farther separated from its impurities by boiling and 
crystallizing, until it is at last obtained in a pure, white, 
granular crystalline mass. PHYSIOLOGY AND HYGIENE. 
Beet-root sugar, which is manufactured very exten- 
sively in France, is prepared from the juices of the beet 
by a similar process to that just described, and is very 
pure, white, and crystalline in appearance. 
Maple sugar is prepared from the sap of the maple- 
tree, which runs freely, in the early part of the spring, 
from punctures made in the wood, and which is after- 
ward boiled down until the sugar solidifies. This sug- 
ar, however, can not be completely purified, and there- 
fore remains comparatively moist and brownish in color. 
Molasses is the sweet residue of the vegetable juices 
which can not be crystallized, and which also contains, 
mingled with it, various flavoring and coloring matters, 
which impart to it a peculiar taste. 
Sugar also exists in considerable quantity in milk, in 
honey, and in all the sweetly-flavored fruits and vege- 
tables, such as apples, pears, grapes, corn, flour, etc. 
The following list shows the quantity which is contain 
ed in various art icles of food : 
Figs 62.50 
Cherries 18.12 
Peaches 16.48 
Tamarinds 12.50 
Pears 11.52 
Beets 9.00 
Sweet almonds 6.00 
Quantity op Sugar in 100 parts in 
Wheat flour 5.40 
Kyemeal 3.28 
Indian-meal 1.45 
Peas 2.00 
Cow’s milk 4.77 
Ass’s milk 6.08 
Human milk 6.50 
One of the most remarkable properties of sugar is 
that it is capable of being decomposed in a peculiar 
manner, and converted into other substances by Fer- 
mentation. Fermentation sometimes takes place spon- 
taneously, in warm weather, in molasses, honey, and 
other liquids containing sugar; when they swell up,be- come frothy, and acquire a different taste and odor. It 
is also produced artificially for the purpose of manufac- 
turing wines and spirituous liquors. This process will 
be more fully explained hereafter. 
FOOD AND ITS INGREDIENTS. 
The sugar which is taken with the food is destroyed, 
like starch, in the interior of the body, and, excepting 
that contained in the milk, is never discharged during 
health with the secreted fluids. 
IV. Fats, or Oleaginous Substances.—The food also 
contains a considerable quantity of Fats or Oleaginous 
substances. The fats are obtained from both animal 
and vegetable tissues. They are exceedingly valuable, 
not only as articles of food, but also for frequent use in 
the arts and manufactures. 
We can readily distinguish fats and oleaginous mat- 
ters by their appearance to the eye, by their unctuous 
feel, and especially by their “ lubricating” property, on 
account of which they are extensively used to facilitate 
the action of machinery, and prevent its being injured 
by friction. if any of these fats or oils be closely 
examined, they are usually found to contain, mingled 
together, three different oleaginous substances, which 
are known by the names of Stearine, Margarine, and 
Oleine. These substances resemble each other very 
closely in most respects, but are principally distinguish- 
ed by their consistency. Stearine is the most solid sub- 
stance of the three, margarine rather less so, and oleine 
is the most fluid. In their natural condition they are 
usually mingled with each other in the animal and veg- 
etable tissues in different quantities. When the mix- 
ture contains a larger proportion of stearine or marga- 
rine, it is more firm in consistency, like the various kinds 
of “ fat,” such as lard, tallow, wax, butter, etc.; and 58 
PHYSIOLOGY AND HYGIENE. 
when it contains a greater abundance of oleine it is 
more liquid, and we therefore call it an “ oil.” 
But when these substances are completely separated 
from each other and purified, the difference in their con- 
sistency is very marked. Thus stearine is often made 
up by itself into candles, and remains perfectly solid 
until melted by the heat of the burning wick. On the 
other hand, olive oil, which consists mostly of oleine, is 
quite liquid at all ordinary temperatures. 
Generally speaking, however, these mixtures of the 
oleaginous substances in the human body are fluid, or 
nearly so, during life; for the margarine and stearine 
which they contain are dissolved in the oleine by the 
warmth of the living body. But after death, when the 
body cools, the stearine and margarine sometimes sep- 
arate from the mixture in a crystalline form, since the 
oleine can no longer retain in solution so large a quan- 
tity as it had dissolved while warm. 
The oleaginous substan- 
ces crystallize in very slen- 
der needles, w'hich are al- 
ways more or less radia- 
ted, sometimes straight, 
and sometimes curved and 
wavy in their outline. 
They frequently have a 
very elegantly branched or 
arborescent arrangement 
(Fig. 12). 
When they are in a fluid 
state, the oleaginous matters show themselves under the 
form of rounded drops or globules, which vary exceed- 
ingly in size, but which may be easily recognized by 
Fig. 12. 
Stearine crystallized from a warm so- 
lution in oleine; magnified. FOOD AND ITS INGREDIENTS 
59 
tlieir appearance under the 
microscope. They have a 
faint amber color, and a 
very sharp, well - defined 
outline, showing a brilliant 
centre surrounded by a dark 
border. In Figure 13 these 
fluid oil-drops are seen min- 
gled with radiating crystals 
of the more solid fat. 
One of the most import- 
ant characters of oil, and of 
all oleaginous matters, is that they will not dissolve in 
water, nor remain in any way intimately mingled with 
it, so that it is even proverbial that “ oil and water will 
not mix.” For if the two liquids be violently shaken 
up together in a bottle so as to mingle them as thor- 
oughly as possible by mechanical agitation, as soon as 
the mixture is allowed to remain at rest the oil at once 
begins to separate from the water, and, being lighter, 
rises to the surface; and after a short time all the oil 
will be collected by itself at the top, and all the water 
will remain by itself at the bottom. So strong is the 
repulsion between these two liquids in their natural 
condition. 
Fig. 13. 
Oleaginous principles of human fat. 
Stearine and margarine crystal- 
lized ; oleine fluid. 
But it is very different when certain other substances 
are added at the same time; for if some alkaline sub- 
stance, such as potash or soda, be first dissolved in the 
water, and the oil then gently shaken up with it, it im- 
mediately becomes separated into very fine particles, 
and uniformly disseminated through the whole mix- 
ture. The oil is no longer liable to separate from the 
watery parts, even when left at rest, but the whole re- 60 
PHYSIOLOGY AND HYGIENE. 
mains as a uniform, white, opaque, milky-looking fluid. 
Such a mixture of oily granules uniformly suspended in 
a watery liquid is termed an Emulsion. 
The same effect may be produced by some of the an- 
imal matters; for if we take a fresh white of egg in its 
fluid condition, and shake it up thoroughly with a lit- 
tle oil, the whole becomes white and turbid, and re- 
mains permanently in the state of an emulsion. This 
property is often found useful in reducing oily sub- 
stances to a state of minute subdivision. 
The oleaginous matters exist in the animal and vege- 
table tissues under a peculiar form. For while they are 
ahvays mutually dissolved and united with each other, 
as we have already seen, they do not dissolve in water, 
nor do they combine with other substances, such as 
salt, starch, or sugar. On the contrary, they are depos- 
ited separately in drops and granules in the interstices 
of the fibres, or in little caATities which are intended for 
their reception. Even in the animal fluids and secre- 
tions, such as milk, they are not dissolved in the watery 
parts, but are suspended in them in the condition of mi- 
nute granules, forming an emulsion, as above described. 
Owing to this fact, the oils can he easily extracted 
from the organized tissues, for the most part, by simple 
mechanical means. The animal or vegetable tissues con- 
taining them are merely cut into small pieces, and then 
subjected to pressure, by -which the oil is forced out 
from the parts in which it was entangled, and collected 
in a state of purity. Sometimes the operation is assist- 
ed by heating the substances, and thus making the oily 
matters more liquid; and sometimes they are boiled 
with water, -when the oils rise to the top, and may be 
skimmed olf by themselves. No chemical change or decomposition, therefore, is required, but the oils are 
simply separated mechanically from the parts with 
which they were naturally entangled. 
FOOD AND ITS INGREDIENTS. 
The tissue in which the oleaginous matters are most 
abundantly found in the animal body is called the 
“ Fat,” or the “ Adipose tissue.” It consists of a great 
number of little sacs or vesi- 
cles, each one composed of a 
thin transparent membrane 
forming a closed cavity, in 
Avhich the oily matter is 
contained (Fig. 14). These 
ATesicles are associated to- 
gether into masses or lob- 
ules, surrounded by cellular 
tissue, and supplied with 
blood-vessels and nerves. 
Neither the blood-vessels nor the nerves, hoAvever, are 
very abundant; so that the adipose tissue is not very 
sensitive, nor does it bleed freely when wounded. It 
acts as a soft and delicate cushion, placed underneath 
the skin to protect the neighboring parts from injury; 
and it also serves to retain the warmth of the internal 
organs, and prevents its being too rapidly dissipated. 
Consequently, those persons who are well provided with 
fat are much less readily chilled by exposure to cold 
than those who are thin and emaciated. 
Fig. 14. 
Human adipose tissue. 
In some of the internal organs oily matters are de- 
posited in their tissue in the form of drops and glob- 
ules. Thus, in the glandular cells of the liver (Fig. 15), 
oil is always found in more or less abundance, forming 
a natural part of their constitution. It is also found 
in the cartilages of the ribs, and in some other situa- 62 
PHYSIOLOGY AND HYGIENE. 
tions; but always in separate globules and granules, 
which may readily be distinguished by their appear- 
ance under the microscope. 
Fig. 15. 
Fisr. 16. 
Glandular cells of the liver, contain- 
ing oil globules; magnified. 
Milk globules, as seen under the mi- 
croscope. 
Iii the milk, which is a kind of natural emulsion, the 
oily matters also exist in the form of little masses or 
globules, called the “milk globules” (Fig. 16). They 
constitute the Butter of the milk, which, in its natural 
condition, is suspended in the watery liquid, and gives 
it its white and opaque appearance. By churning, 
these globules may he separated from the other ingre- 
dients of the milk, and collected into a uniform mass. 
Oleaginous matters are taken in large quantity with 
the food, mostly in butter, in milk, in the fat of meat, 
and in some vegetable substances, such as olive oil, etc. 
The following list shows the proportion of oily matters 
in various kinds of food: 
Quantity of Fat in 100 parts in 
Filberts 60.00 
Cocoanuts 47.00 
Olives 32.00 
Yolk of eggs 28.00 
Indian com 9.00 
Ordinary meat 14.30 
Liver of the ox 3.89 
Cow’s milk 3.13 
Human milk 3.55 
Goat’s milk 3.32 FOOD AND ITS INGREDIENTS. 
The fat which is taken with the food disappears for 
the most part in the interior of the body, like starch 
and sugar. A very little is secreted by certain glands 
in the skin and about the roots of the hair, which 
serves to keep these parts soft and pliable. But this 
forms only a small portion of the whole; the greater 
part of the oleaginous matters, except what is stored 
away in the adipose tissue, being used up and consumed 
for the nutrition of the body. 
18. Albuminous Matters.—The last class of substan- 
ces contained in the food are the Albuminous matters. 
These substances are peculiar in many respects, and 
very important; for of all the solid ingredients of the 
body, they constitute considerably the largest part of 
its mass. They are not composed of grains, like starch, 
nor are they ever crystalline in form, like sugar and 
fat; but, even when solid, they are smooth and uniform 
in texture. They have also a peculiar consistency, 
which combines in a remarkable degree the two quali- 
ties of softness and solidity. We may form an idea 
of this peculiar consistency by feeling of any of the in- 
ternal organs, such as the liver or heart of an ox, or a 
piece of muscular flesh. These organs are firm enough 
to retain their form and texture, and yet they are soft 
to the touch. They have these qualities because they 
are composed in so large a proportion of the albumi- 
nous matters. 
The albuminous matters are derived both from ani- 
mal and vegetable sources, but they are most abundant, 
as a general rule, in animal substances. It is for this 
reason that animal food is, for the most part, richer 
and more nutritious than that which is composed of 
vegetables. PHYSIOLOGY AND HYGIENE. 
The albuminous matters are of various kinds, some 
of them being liquid in their natural condition, some of 
them solid, and some of them having a consistency in- 
termediate between the two. That which is most fa- 
miliar to us, and which has given its name to the whole 
class, is Albumen, which is the principal ingredient in 
the white of egg. Another kind of albumen is also 
found in the blood, and is the most abundant of its ani- 
mal ingredients. Fibrine is also found in the blood, 
though in smaller quantity than albumen. Caseine is 
the albuminous substance of milk, and -when solidified 
forms the principal ingredient of cheese. Gluten is the 
albuminous matter of wheat flour, and is an important 
element in the making of bread. 
There are other albuminous substances found in va- 
rious kinds of food and the different parts of the body; 
but those which we have already mentioned are the 
most familiarly known, and will serve to represent the 
peculiarities of the entire class. 
One of these peculiarities is the property of Coagu- 
lation. The albuminous matters which are naturally 
liquid may be suddenly solidified in various ways, after 
which they are said to be “ coagulated.” Some of them 
may be coagulated by one method, others by a differ- 
ent one; and we may often distinguish one albuminous 
substance from another by the particular method re- 
quired for its coagulation. 
Thus white of egg, in its natural state, is transparent, 
of a light amber color, and very nearly liquid; but if 
it be heated to the temperature of boiling water, it co- 
agulates, and becomes solid, white, and opaque. 
Milk, on the other hand, may he boiled without coag- 
ulating; but if a little acid be added to it, such as vin- 65 
egar or lemon-juice, its caseine at once solidifies, and it 
assumes the coagulated form. 
FOOD AND ITS INGREDIENTS. 
The fibrine of the blood, again, coagulates without 
either boiling or the addition of an acid. If a little 
blood be drawn from the veins and received into a cup, 
it becomes clotted in a few moments by a spontaneous 
change which takes place in its own substance. 
Nothing similar to this property of coagulation be- 
longs to any other than the albuminous substances. 
Another peculiarity of the albuminous matters is 
that they become Ferments. This property is so im- 
portant that it will require a particular description. 
A “ ferment” is a material which, on being added in 
small quantity to other substances, causes in them a re- 
markable change and decomposition, often accompanied 
by the production of bubbles of gas and the formation 
of entirely new ingredients. This change is called “ fer- 
mentation.” Thus, if a little yeast be added to a mix- 
ture of flour and water, and the whole kept in a warm 
place, the influence of the yeast disseminates itself 
throughout the whole, and causes the entire mass to 
ferment. If milk be allowed to remain two or three 
days in a warm place, the caseine is partially altered, 
and then becomes a ferment, which changes the sugar 
of the milk into an acid substance called “ lactic acid;” 
when the acid thus produced reacts upon the rest of 
the caseine and coagulates it, as any other acid would 
do. This is the manner in which the ordinary souring 
and curdling of milk takes place. The souring of the 
milk is caused by the change or decomposition of the 
sugar of the milk, and the curdling or coagulation is 
caused by its acidity. 
Now a “ferment” is always composed of an albumi- 66 
PHYSIOLOGY AND HYGIENE, 
nous substance. This substance may not be perfectly 
fresh; indeed, it is very often the case that the ferments 
most in use are albuminous matters which are them- 
selves beginning to suffer decomposition. But wThen 
the ferment is introduced, in ever so small a quantity, 
into another mixture, it seems to act by contagion, and 
excites by its mere presence an extensive change, which 
often pervades the entire mass. 
A ferment always requires for its action two things: 
first, the presence of moisture; and, secondly, a mod- 
erately warm temperature, between the two extremes 
of heat and cold. None of the ferments, therefore, will 
act if they are perfectly dry, and they are also inactive 
so long as they are kept at a freezing temperature; 
but if supplied with moisture, they begin to act when 
the temperature rises, and become more energetic as 
the warmth increases. Their activity is usually great- 
est about the temperature of the living body, or 100 de- 
grees Fahrenheit. Above this point they again become 
less active, and cease altogether when the temperature 
approaches that of boiling water. 
Lastly, the albuminous matters are the only ones 
liable to Putrefaction. This is a peculiar kind of de- 
composition, which resembles, in many respects, that 
of fermentation. For example, one substance which is 
already partially decomposed will excite putrefaction 
in others of the same kind more quickly than if they 
were left to themselves; and decayed fruit, as it is 
well known, will rapidly contaminate sound fruit of the 
same kind, if left in contact with it. But still all sub- 
stances of an albuminous nature, if exposed to the air 
and moisture at warm temperatures, will after a time 
become putrefied; that is, they decompose and liquefy, 67 
with the production of a variety of gases, of a pecul- 
iarly disagreeable odor, which are called “ putrefactive 
gases.” Thus, whenever we perceive the odor of putre- 
faction, we know that some substance composed of al- 
buminous matter is undergoing decomposition. 
FOOD AND ITS INGREDIENTS. 
Like fermentation, putrefaction will not take place 
without moisture; for meat or vegetable matters, if 
thoroughly dried, will keep unchanged for an indefinite 
period. Neither will it go on at a low temperature; 
and dead substances kept at the freezing point will not 
putrefy. The most complete preservation takes place 
wdien the two conditions of cold and dryness are com- 
bined. At the Hospice of the Great St. Bernard, in 
Switzerland, a little over 8000 feet above the level of the 
sea, the bodies of travelers found frozen in the snow are 
sometimes preserved for over twenty years. For, while 
still at a freezing temperature, they become thoroughly 
dried; and though after a long time they slowly crum- 
ble and become disintegrated, there is no putrefaction, 
nor any evolution of putrefactive gases. 
Finally, animal substances are also incapable of pu- 
trefaction at a very high temperature. Meat which 
has once been boiled changes much less rapidly than 
if exposed to the air when fresh; and if kept at the 
temperature of 200 or 300 degrees Fahrenheit, either 
dries up altogether, or suffers a change entirely different 
from putrefaction. 
The following list shows the proportion of albumi- 
nous matter in various kinds of food: 
Quantity of Albuminous Matter in 100 parts in 
Muscular flesh 22.00 
White of egg 15.28 
Yolk of egg 12.75 
Wheat flour 7.30 
Oatmeal 4.30 
Milk 4.48 68 
Albuminous matters, like starch, sugar, and oil, are 
almost entirely consumed and altered in the process of 
nutrition, only a small portion of them being discharged 
with the perspiration and other secreted fluids. By far 
the greater part disappears in the interior of the body. 
PHYSIOLOGY AND HYGIENE. 
19. Necessity for all these Substances in the Food.— 
From what has already been said, it will easily be un- 
derstood that the food must contain, in some form or 
other, all the different classes of substances above emir 
merated. Food, from which either one of the sub- 
stances necessary to nutrition is absent, although it 
may be nutritious for a time, will certainly fail, sooner 
or later, to keep up the proper organization of the 
body, and its deficiency will be inevitably felt. This 
is true even of the inorganic substances. A man might 
be starved to death by keeping him on food which con- 
tains no lime or no salt; that is, after a time he Avould 
become so feeble that slight causes would be sufficient 
to produce a fatal result. This would not happen so 
soon as if he were deprived of the more nutritious mat- 
ters, because they are required in larger quantity. But 
it would certainly take place at last; for the mineral in- 
gredients of the body, though small in amount, are still 
indispensable to health. We have already seen that 
they are usually present in sufficient quantity in the 
substances used as food. 
Neither will any of the proper ingredients of the food 
be sufficient by themselves. The experiment has been 
tried of feeding animals upon food containing only 
starch and sugar; and although such food is consumed 
with relish for a time, the animals soon become feeble 
and emaciated, and finally die of imperfect nutrition. 
In some instances this experiment has been tried by FOOD AND ITS INGREDIENTS. 
69 
medical men upon themselves, who have always found 
their health to suffer after a few days of such diet, and 
who have never been able to continue it indefinitely, 
owing to increasing debility and general disturbance 
of the system. 
A diet exclusively composed of fatty substances is 
equally incapable of supporting life. This has been 
tried at various times on quadrupeds and birds ; and it 
has been found that after a short time, usually about 
three weeks, these animals, though abundantly fed with 
fat, die with all the symptoms of inanition. 
Lastly, the same thing is true even of the albumi- 
nous matters. These substances are usually consider- 
ed more nutritious than the others. But this is only 
because they are required in greater quantity than the 
rest, since they form so large a proportion of the animal 
tissues. The albuminous matters, if taken alone, are no 
more capable of supporting life indefinitely than starch, 
sugar, or oil; and animals, when fed on pure fibrine or 
pure albumen, become emaciated and at last die of in- 
anition, as in the cases mentioned above. 
All these substances, therefore, must be combined, in 
order to make the food which contains them capable 
of sustaining life. 
Now it is found that every article of food which has 
been universally recognized by the instinct of man as es- 
pecially valuable, does in reality contain these different 
ingredients, viz., 1st, water and mineral substances; 2d, 
oleaginous or starchy materials, or both ; and, 3d, some 
form of albuminous matter. This will be distinctly 
shown when we come to examine more particularly the 
different kinds of alimentary substances. PHYSIOLOGY AND HYGIENE. 
1. What is the definition of ‘ ‘ food ?” 
2. What is the food intended to supply ? 
3. What are the “inorganic substances?” 
4. Which is the most abundant of the inorganic ingredients of the 
food? 
5. What parts of the body contain water ? 
6. What is the use of water in the animal fluids ? In the solids ? 
7. What proportion of the whole body consists of water ? 
8. How much water is consumed per day by a healthy adult ? 
9. Does the water remain in the body, or is it again discharged 
from the system ? 
10. By what channels is the water discharged from the body ? 
11. What is the next most important inorganic ingredient? 
12. In what animal fluid is salt most abundant ? 
13. Why is salt useful as an article of food ? 
14. In what organs of the body is lime most abundant ? 
15. What effect is produced on the bones by depriving them of 
their lime ? 
16. In what articles of food is lime contained? 
17. What are the other inorganic ingredients of the body and the 
food? 
18. Are they decomposed in the body, or discharged with the se- 
cretions ? 
19. What is the physical appearance of starch ? 
20. From what sources is it obtained ? 
21. What kinds of food contain the largest quantities of starch ? 
22. What is the mode of obtaining starch from vegetables ? 
23. What is the effect of boiling starch with Avater ? 
24. Is starch discharged again with the secretions, or decomposed 
within the body ? 
25. How may starch be converted into sugar ? 
26. What is the characteristic property of sugar ? 
27. From \Adiat sources is sugar obtained ? 
28. What is the process of extracting sugar from cane-juice? 
From the beet-root ? From the maple-tree ? 
29. What is molasses ? 
30. What other articles of food contain sugar ? 
31. Is the sugar discharged Avith the secretions, or decomposed 
aa ithin the body ? 
QUESTIONS FOR CHAPTER II. QUESTIONS. 
71 
32. How are the fats or oleaginous substances distinguished ? 
33. What are the three varieties of fats ? 
34. How do they differ from each other ? 
35. What is the appearance of their crystals ? 
3G. What is the appearance of fluid oil-drops ? 
37. Can oil he dissolved in water ? 
38. What happens if you shake up oil and water together ? 
39. What is an emulsion ? 
40. What substances will convert oil into an emulsion ? 
41. How do the fats exist in the interior of the body? United 
with the other ingredients, or separate ? 
42. How can fats he extracted from animal and vegetable tissues ? 
43. In what tissues of the body are the oleaginous matters most 
abundant ? 
44. What is the structure of fat, or adipose tissue ? 
45. What is its use in the animal body ? 
46. What is the appearance of the oleaginous matters in milk ? 
47. What other kinds of food contain fat ? 
48. Is fat discharged with the secretions, or decomposed within the 
body? 
49. What is the last class of ingredients of the body and the food? 
50. What is the peculiar consistency of the albuminous matters ? 
51. Are the albuminous matters more abundant in animal or in 
vegetable food ? 
52. What are the four principal kinds of albuminous matters, and 
where are they found ? 
53. What is the process of coagulation ? 
54. How can albumen be coagulated ? Howcaseine? Howfibrine? 
55. What is a ferment ? 
56. What is the process of the souring of milk ? 
57. At what temperature does fermentation take place ? 
58. What is putrefaction ? 
59. Is putrefaction communicated from one substance to another ? 
60. How may putrefaction be prevented ? 
61. What kinds of food contain the greatest abundance of albumi- 
nous matters ? 
62. Are the albuminous matters discharged from the body, or de- 
composed in the animal system ? 
63. Can life be sustained upon starch or sugar alone ? Upon fat 
alone ? Upon albuminous matter alone ? 
64. Does the natural food contain all these different ingredients ? 72 
PHYSIOLOGY AND HYGIENE. 
CHAPTER HI. 
THE DIFFERENT KINDS OF FOOD, AND THEIR MODE OF 
PREPARATION. 
Meat—its Composition.—Effect of Cooking.—Eggs.—Composition 
of the White and Yolk.—Milk—its Composition.—Butter—how 
obtained. — Cheese — its Preparation. — Bread — how made. — 
Yeast.—Fermentation of Bread.—Baking.—Wine—its Fermenta- 
tion.—Beer.—Vegetables. — Effect of Cooking on Vegetables.— 
Essential Qualities of Food.—Necessary Quantity. 
20. Meat. — Meat consists of the muscular flesh of 
various animals, mingled with more or less of fat or 
adipose tissue. Of all the different varieties, beef is 
undoubtedly the most valuable and the most exten- 
sively used. Mutton and venison hold the next place; 
then the flesh of fowls, the various kinds of game birds, 
and, lastly, fish. 
In ordinary meat we have the albuminous substance 
of the muscular fibres and cellular tissue, and the ole- 
aginous matter of the fat, in about the following pro- 
portions : 
Composition of Ordinary Butcher’s Meat. 
Muscular parts 85.70 
Water 63.42 
Solid matter 22.28 
Fat, cellular tissue, etc .. 14.30 
100.00 
The preparation of meat for food consists in exposing 
it to a high temperature, usually by roasting or boiling. 
In roasting, the meat is simply cooked in its own juices; 
in boiling, it is cooked by the aid of the boiling water. 
The effect of the heat thus applied is as follows: DIFFERENT KINDS OF FOOD, ETC. 
73 
First, the albumen which is present in the muscular 
tissue is coagulated, and the muscular fibres therefore 
become rather firmer and more consistent than in the 
fresh meat. 
Secondly, the cellular tissue between the muscular 
fibres is softened and gelatinized, so that the fibres are 
more easily separated from each other, and the whole 
mass becomes more tender and easily digestible; and, 
thirdly, the high temperature develops in the albumi- 
nous ingredients of the meat a peculiar and attractive 
flavor, which they did not possess before, and which 
excites in a healthy manner the digestive secretions, 
thus serving not only to please the taste, but also to 
assist in the digestion of the food. Raw meat, accord- 
ingly, is usually insipid and unattractive. It is only 
after it has been subjected to a certain amount of cook- 
ing that the desired flavor makes its appearance, by 
which the appetite is stimulated, and the nutritious 
qualities of the food consequently improved. 
The preparation of meat in cooking should be care- 
fully managed, so as to accomplish the results above 
described. For if the heat be insufficient, the proper 
flavor will not be developed; and if it be excessive, 
the meat, instead of being cooked, will be burned and 
decomposed, and thus rendered useless for the purposes 
of nutrition. 
21. Eggs.—Eggs consist of the “ white,” which is al- 
most entirely composed of albumen and mineral ingre- 
dients ; and the “ yolk,” in which a large proportion of 
oleaginous substance in a granular form is mingled 
with the albuminous matter, giving it an opaque yel- 
low color. The exact composition of the two parts is 
as follows: PHYSIOLOGY AND HYGIENE. 
White of Egg. Yolk of Egg. 
Water 80.00 53.78 
Albumen and mucus 15.28 12.75 
Yellow oil — 28.75 
Salts 4.72 4.72 
100.00 100.00 
Composition of Eggs. 
When eggs are boiled or otherwise cooked, the albu- 
men, of course, is coagulated, and becomes white and 
opaque. The yolk also becomes firmer than before, but 
still remains less solid than the white, owing to the 
large proportion of oily matter mingled with it. 
22. Milk.—Milk, which is the first food of the infant, 
represents more fully than any other single substance 
a complete collection of all the alimentary materials. 
It contains water; a full supply of mineral ingredients; 
caseine, which is its albuminous substance; the milk 
globules, which are oleaginous, and held in suspension; 
and sugar, which is dissolved in the watery parts. The 
proportion of these substances is as follows: 
Composition of Cows’ Milk. 
Water 87.02 
Caseine 4.48 
Butter 3.13 
Sugar of Milk 4.77 
Mineral ingredients 0.60 
100.00 
The Butter of the milk, as we have already seen, is in 
the form of minute globules. The whole mixture is an 
“ emulsion,” in which the oleaginous matter is held in 
suspension, and disseminated through the watery fluid 
by the action of the albuminous caseine. The milk glob- 
ules are not perfectly fluid like oil, but have a pasty or 
semi-solid consistency. Accordingly, they can be col- 
lected and separated from the other ingredients in the 
form of butter. DIFFERENT KINDS OF FOOD, ETC. 
75 
For this purpose the fresh milk is placed in shallow 
pans, and allowed to remain undisturbed for twenty- 
four hours. During this time the surplus quantity of 
the milk globules rise to the top, owing to their being 
lighter than the watery parts, and collect in a thick, 
densely white layer upon the surface. This upper layer 
of fluid, which is richer than the rest in milk globules, 
is the “ cream.” When a sufficient quantity of cream 
has been collected, it is removed and placed in churns, 
where it is subjected to continuous beating with wood- 
en ladles. By this process the milk globules are beaten 
together and made to cohere into a uniform, consistent, 
yellowish mass. This mass is the butter. 
The butter, however, when obtained in this way, still 
retains entangled with it some of the watery portions 
of the milk containing caseine, sugar, etc., in solution. 
These must be carefully removed; for if the be 
allowed to remain, it soon begins to be altered, acts as 
a ferment, and then produces a change in the butter by 
which it becomes rancid. • To guard against this, the 
butter is thoroughly worked over, and the liquid im- 
purities washed out or absorbed by appropriate means, 
until they are entirely removed. 
When the butter is completely purified in this way. 
it has the following composition: 
Composition of the Butter of Cows’ Milk. 
Margarine 68 
Oleine 30 
Butyrine 2 
100 
The last of these ingredients, the “ butyrine,” is the 
substance which gives to the butter of cows’ milk its 
peculiar flavor. 76 
PHYSIOLOGY AND HYGIENE. 
Cheese is composed principally of the solidified albu- 
minous matter of the milk, or “ caseine.” Caseine, as 
we have seen, may be coagulated by any acid sub- 
stance ; but the material usually employed for this 
purpose is derived from the fourth stomach of the calf. 
The juices of this stomach contain a substance which 
will be more fully described hereafter, and which has 
the property of coagulating milk in a very gentle and 
uniform manner. When the calf has been fed with 
milk, the stomach is taken out, cut into strips, and 
dried for future use. The whole mass thus contains 
the coagulating principle disseminated through its sub- 
stance, and is then called “ rennet.” 
When a little rennet, previously softened in water, is 
added to fresh milk, it produces a coagulation of its 
caseine. The coagulated mass is then subjected to 
strong pressure, by which the watery parts of the milk 
are driven out, and the whole reduced to the consisten- 
cy of cheese. A considerable portion of the butter of 
the milk still remains entangled with the caseine, and 
communicates to it a rich flavor and a yellowish color. 
The very gradual change which the caseine undergoes 
on exposure to the air produces also a certain alteration 
in the buttery ingredients, by which the cheese, after 
being kept for a time, usually assumes a sharper and 
rather aromatic flavor. Cheese accordingly contains 
the nutritious elements of the milk in a condensed but 
somewhat indigestible form. 
23. Bread.—Bread is made of various kinds of grain, 
but by far the best and most nutritious is that made 
from wheat. Wheat flour contains the following in- 
gredients : DIFFERENT KINDS OF FOOD, ETC. 
77 
Composition of Wheat Flour. 
Gluten 7.30 
Starch 72.00 
Sugar 5.40 
Gum 3.30 
Water 12.00 
100.00 
In the making of bread, the flour is first thoroughly 
mixed with water and worked up into a pasty mass, 
to which is then added a little yeast. 
Yeast consists of an albu- 
minous matter containing an 
abundance of a fungous veg- 
etable growth, in the form 
of minute globules or cells 
(Fig. 17), which rapidly mul- 
tiply by a process of bud- 
ding whenever placed in a 
favorable condition. It is 
one of the most energetic 
kinds of ferment,**and is es- 
pecially liable to act upon all substances containing 
sugar. 
The mixture of flour and water, with the yeast add- 
ed, is then placed in a warm temperature, and allowed 
to remain for some hours. During this time the yeast 
excites a fermentation, by which the sugar of the flour is 
decomposed, and converted into alcohol and carbonic 
acid. The carbonic acid is a gas; and, being produced 
in the form of small air-bubbles, attempts to rise and 
escape from the dough, just as it would from a watery 
mixture. But the gluten of the wheat, being some- 
what viscid in consistency, entangles and retains the 
bubbles of gas as they are developed in its substance, 
and the whole mass of the dough is thus distended and 
puffed up by the gaseous matter contained within it. 
Pig. IT. 
Vegetable fungus of yeast; magnified. 78 
The dough, thus distended, is then baked at a high 
temperature. The effect of this is to fix and solidify 
the gluten, and cause it to retain the form which it has 
already assumed. When the baked loaf, accordingly, 
is afterward cut through, it is seen to be every where 
perforated with a multitude of little cavities, which 
were formerly occupied by the gas developed in fer- 
mentation. This gives the bread a light,and honey- 
combed or spongy texture throughout the interior of 
its mass. 
PHYSIOLOGY AND HYGIENE. 
It is this spongy texture, given to bread in the man- 
ner above described, which is the main object of the 
process of fermentation. For if the flour were simply 
mixed with water and baked, the solid and consistent 
mass thus produced, though abundantly nutritious, 
would be tough and difficult of digestion; but, owing 
to the light texture which it acquires in fermentation, 
it is aftemard easily masticated, and becomes readily 
penetrated and acted on by the digestive fluids. 
The small quantity of alcohol produced during the 
fermentation of bread is dissipated by the heat of the 
oven, and carried off* by evaporation. 
The starch of the flour, during this process, absorbs 
water under the influence of the heat, and its grains be- 
come amalgamated with each other. The whole amount 
of water which is absorbed and retained by the dough 
is rather more than twenty-five per cent, of its original 
weight; so that one pound of flour, after being mixed 
with water and made into bread, weighs a little over 
one pound and a quarter. 
24. Wine.—Wine is produced from the juices of the 
grape after undergoing fermentation. 
The juices of the ripe grape, in their natural condi- DIFFERENT KINDS OF FOOD, ETC. 
tion, contain water, a little albuminous matter, sugar, 
various coloring and flavoring substances, and a small 
quantity of mineral ingredients. For the purpose of 
making wine, the ju ice is first expelled by crushing the 
grapes, and then exposed to the air in vats at a moder- 
ately warm temperature. After a short exposure, the 
albuihinous matter suffers a certain alteration by con- 
tact with the air, and becomes a ferment; and this fer- 
ment then acts upon the sugar of the grape-juice, con- 
verting it into alcohol and carbonic acid, as in the fer- 
mentation of bread. The fermentation of the grape- 
juice, however, is a slow and gradual process, often re- 
quiring several months for its completion. During this 
time the carbonic acid gas which is produced rises to 
the surface in bubbles, and escapes from the fermenting 
liquid; but the alcohol remains behind, giving to the 
liquid a vinous or alcoholic taste. 
When the fermentation of the wine is completed, it 
forms a clear and transparent liquid, containing wa- 
ter, alcohol, coloring matter, and various flavoring sub- 
stances ; some of which are derived directly from the 
original ingredients of the grape-juice, while others 
are formed from their alteration during the ferment- 
ing process. 
In some wines all the sugar of the grape-juice is not 
completely decomposed by the process of fermentation; 
they therefore retain a sweet taste, in addition to the 
alcoholic flavor. 
. In some instances the wine is bottled before the fer 
mentation is finished; and, the process continuing to go 
on, the carbonic acid gas afterward produced is accm 
mulated and confined in the imprisoned liquid. When 
the bottles are then opened and the pressure taken off, the superabundant gas escapes in bubbles, sometimes 
with considerable force. Such wines are called “ spark- 
ling,” or “ effervescent” wines. 
PHYSIOLOGY AND HYGIENE. 
The strength of any particular wine depends on the 
quantity of alcohol produced in its fermentation. Still, 
wine is not simply a mixture of alcohol and water, but 
it contains many other ingredients furnished by the 
juices of the fruit from which it is made; and the al- 
cohol, produced by a slow fermentation, is united with 
various other vegetable substances also undergoing pe- 
culiar modifications. 
Consequently, wine can not be artificially manufact- 
ured by mixing together alcohol, water, sugar, etc. 
Such a mixture is simply a crude imitation, generally 
hurtful in its effects, and, for the most part, wanting in 
the peculiar properties of the wine which it is intend- 
ed to imitate. 
25. Beer. — Beer is a liquid prepared from barley, 
somewhat in the same way as wine is made from 
grapes. We have already mentioned that in the first 
sprouting or “ germination” of many seeds, the starch 
which they contain is transformed spontaneously into 
sugar. This happens with the grains of barley. In or- 
der to make beer, the barley is kept warm and moist 
until germination has taken place, and a sufficient quan- 
tity of sugar has thus been produced in their substance. 
The barley is then ground up, mixed wdth warm water, 
and an infusion of hops, with a little yeast, added to the 
mixture. The hops serve as a flavoring ingredient; and 
the yeast, acting as a ferment, causes the fermentation 
of the sugar, producing alcohol and an abundant evolu- 
tion of carbonic acid gas. The liquid finally produced 
is beer. It contains much less alcohol than wine, but a DIFFERENT KINDS OF FOOD, ETC. 
large proportion of flavoring and nutritious substances 
are also derived from the grain used in its preparation. 
26. Preparation of Vegetables.—Of the different Vege- 
tables used for food, such as potatoes, beans, peas, tur- 
nips, etc., the greater part contain principally starch, 
mingled with various proportions of albuminous mat- 
ter, sugar, water, and mineral substances. The effect 
of cooking upon these vegetables is mainly to soften 
and disintegrate them, since in their raw state they are 
usually so hard as to be entirely indigestible. It is 
very essential, therefore, in the preparation of vege- 
tables, that their cooking should be thorough and com- 
plete, as otherwise they are liable to produce injurious 
effects. An agreeable taste is also developed in vege- 
tables by the process of cooking, though not to so great 
an extent as in the case of animal substances. 
27. Necessary Qualities of wholesome Food.—In order 
to maintain health, the food which is consumed should 
he simple, hut, at the same time, nutritious in quality, 
and the very best of its hind. The meat should be that 
of well-fed animals, of good color, and abundantly sup- 
plied with the natural juices. The bread should be 
made from well-ground and properly-dried flour; and 
the vegetables should be of natural color and consist- 
ency, and free from excrescences or other imperfections. 
Particularly the preparation- of the food by cooking 
should in all cases be carefully performed; since im- 
proper cooking will often vitiate or destroy the nutri- 
tious qualities of the most valuable kinds of food. 
28. Quantity of Food required.—The entire quantity 
of food required during twenty-four hours varies with 
the age, sex, and habits of the individual. Children re- 
quire more food, in proportion to their size, than adults; 82 
PHYSIOLOGY AND HYGIENE. 
and those who take much physical exercise need more 
than those who remain comparatively inactive. As a 
general rule, however, it is a valuable indication of 
health when the full average quantity of food is re- 
quired and consumed every day. The result of inves- 
tigation on this point shows that for a healthy adult 
man, taking free exercise in the open air, and living 
upon plain but substantial food, the average quantity 
required during twenty-four hours is as follows: 
Meat 16 ounces, or 1.00 lb. avoirdupois. 
Bread 19 “ “ 1.19 “ “ 
Butter or fat . 3J “ “ 0.22 “ “ 
Water 52fluid oz. “ 3.38 “ “ 
Average Daily Quantity op Food. 
that is to say, rather less than two and a half pounds 
of solid food, and rather over three pints of liquid food. 
QUESTIONS FOR CHAPTER III. 
1. Of what does meat consist ? 
2. What kinds of animal food are most nutritious ? 
3. What is the effect of cooking upon meat ? 
4. What is the composition of eggs ? 
5. What effect is produced upon eggs by boiling ? 
6. What is the composition of milk ? 
7. How is the butter extracted from milk ? 
8. Why should it be carefully purified ? 
9. What is cheese, and how is it made ? 
10. What are the ingredients of wheat flour ? 
11. Describe the making of bread. 
12. What is the use of fermenting bread with yeast ? 
13. What is the process of making wine f 
14. What is beer, and how is it made ? 
15. What are the vegetables principally used for food? 
16. What is the effect of cooking upon vegetables ? 
17. What are necessary qualities of wholesome food ? 
18. How much meat is required per day by a healthy man ? how 
much bread ? how much fat ? how much liquid ? DIGESTION. 
83 
CHAPTER IY. 
DIGESTION. 
Necessity for Food. — Nature of Digestion.-—Alimentary Canal — 
its different Parts.—Digestive Fluids.—Mastication.—The Teeth. 
—Incisors.—Canines.—Molars.—Their different Functions.—Sali- 
va.—Salivary Glands.—Composition of Saliva—its double Func- 
tion.—Action of the Tongue.—(Esophagus—its Peristaltic Action. 
—Deglutition.—The Stomach—its lining Membrane.—Gastric Tu- 
bules.—Gastric Juice—its Secretion.—Peristaltic Movements of the 
Stomach.—Composition of the Gastric Juice.—Pepsine.—Lactic 
Acid.—Action of Gastric Juice on the Food.—It is a Ferment.— 
Digestibility of Food.—Food should be properly cooked—should he 
taken in moderate quantity—with regularity.—The small Intestine. 
—Follicles of Lieberkiihn.—Intestinal Juice—its action on Starch. 
—Pancreatic Juice — its Composition — its action on Fat.—The 
Chyle.—Peristaltic Movement of Intestine.—Changes of Food in 
the Alimentary Canal.—End of Digestion. 
29. The demand for Food.—Why is it that we require 
food? 
It is because the human body is not an inert and 
senseless machine, hut a collection of living organs, in- 
cessantly active, and constantly employed in perform- 
ing their allotted functions. Corresponding with this 
activity a continuous change goes on in the substance 
of the organs, by which their materials are constantly 
decomposed and constantly renewed. Throughout the 
interior of the frame nature is incessantly engaged in 
taking apart the tissues of which the body is composed, 
and in making them over again of new and fresh ma- 84 
PHYSIOLOGY AND HYGIENE. 
terials. We shall hereafter see in what manner this 
process of the unraveling and recomposition of the an- 
imal frame is accomplished, and what peculiar sub- 
stances are produced in consequence. For the present 
it is sufficient to know that it is continually going on, 
and that the healthy tissues of the body are according- 
ly always renewed and always ready to perform their 
work. 
This requires a constant supply of new material from 
without. 
But, beside this, in young children a provision is 
also necessary for their growth and development. The 
newly-born infant weighs from six to seven pounds; at 
the end of a year his weight has increased to twenty 
pounds; and at twenty-five years of age it has reached 
one hundred and forty pounds. During all this time 
new material has been added to the body, not only 
sufficient to compensate for its waste of tissue, but also 
in surplus quantity to provide for its increasing size. 
This new material has been taken with the food, has 
been distributed over the body, and disseminated every 
where throughout the substance of the tissues. 
30. Nature of the Digestive Process.—But the food 
itself will not serve directly for the nourishment of the 
animal frame. First of all, because the ingredients of 
our food are for the most part solid, and they must be 
liquefied before they can be absorbed by the mem- 
branes and circulate with the blood ; and, secondly, 
because the ingredients of the food, the animal and 
vegetable juices, the starch, fat, albumen, etc., are not 
the same with the ingredients of the human body. 
They are nutritious, but only because they are capable 
of being converted into other substances, which are DIGESTION. 
85 
then appropriated by the internal organs. All the 
substances used as food, therefore, are subjected to a 
kind of preliminary disintegration and metamorphosis. 
Meat, bread, fruits, vegetables, must all be first reduced 
to a new condition before they can finally take part in 
the nutrition of the body. Their ingredients are com- 
pelled to undergo a transformation, which fits them at 
last to be absorbed by the living tissues. 
This liquefaction and transformation of the ingredi- 
ents of the food is the process of Digestion. 
31. General Structure and Arrangement of the Diges- 
tive Apparatus.—The digestion of the food is perform- 
ed in a long tube or canal, called the “ Alimentary Ca- 
nal,” which commences at the mouth, and runs contin- 
uously from one end of the body to the other. If we 
examine its different parts, we shall see, first, that they 
differ from each other in size, form, and structure, and 
are accordingly known by different names, such as the 
“ pharynx,” the “ oesophagus,” the “ stomach,” and the 
“ intestine;” and, secondly, that there are different ani- 
mal fluids, called the “ digestive secretions,” which are 
poured into the alimentary canal at different points, 
and there come into contact with the ingredients of the 
food. It is these secretions which have the power of 
acting upon the food, so as to dissolve it and transform 
its materials in the manner described above. 
Now the mode in which this action is performed is 
very remarkable. Each one of the digestive secretions 
contains a peculiar albuminous matter, different from 
those of all the rest, and having the power of acting 
like a ferment. When this ferment comes into con- 
tact with certain ingredients of the food, it at once 
produces a change in their condition, so that they are 86 
PHYSIOLOGY AND HYGIENE. 
transformed, and become capable of being used for the 
nourishment of the body. Thus the different ingredi- 
ents of the food are acted upon, in the different parts 
of the alimentary canal, by different digestive fluids ; 
and as the food gradually passes from above down- 
ward, its various elements are successively transformed, 
and the digestion of the whole is finally accomplished. 
At the commencement of the alimentary canal (Fig. 
18) we find, as already mentioned, the cavity of the 
Mouth. This cavity is guarded in front by the open- 
ing of the lips, and behind by the muscular walls of the 
throat, or Pharynx, which can close at will, so as to pre- 
vent the passage of substances from the mouth back- 
ward. Beyond the pharynx comes a long and narrow 
tube, the gullet or (Esophagus (a), which runs nearly 
straight downward along the back part of the neck 
and chest until it reaches the abdomen. Here it term- 
inates in the Stomach (b), which is a large, flask-shaped 
expansion, lying across the cavity of the abdomen, just 
beneath the lower extremity of the breast-bone. Like 
the mouth, the stomach is guarded at each end by mus- 
cular bands, which sometimes shut up its orifices, and 
sometimes open to allow the passage of the food. The 
first of these orifices, situated on the left side, and com- 
municating with the oesophagus (c), is called the “ car- 
diathe second, situated on the right side (cl), is called 
the “pylorus.” 
Beyond the pylorus the alimentary canal becomes a 
long and very narrow tube, not more than an inch and 
a half in width, but nearly twenty-five feet in length, 
called the Small intestine (e). The small intestine is 
folded upon itself with many different turns, so that it 
forms a convoluted mass, occupying a large part of the DIGESTION. 
Pig. IS. 
Human Alimentary Canal.—a. (Esophagus; b. Stomach ; c. Cardiac orifice : 
d. Pylorus ; e. Small intestine; /. Biliary duct; g. Pancreatic duct; h. Ascend- 
ing colon ; i. Transverse colon; j. Descending colon; k. Rectum. 88 
PHYSIOLOGY AND HYGIENE. 
space within the abdomen. At its upper portion, a few 
inches below the pylorus, two slender tubes open into 
its cavity, coming one from the liver, the other from 
the pancreas, called the Biliary and Pancreatic ducts 
{ft 9)' They serve to convey into the intestine at this 
point two important secretions, viz., the bile and the 
pancreatic juice. The small intestine itself is provided 
with a lining membrane, which varies somewhat in 
structure in different parts of the tube. It terminates 
in the lower part of the abdomen, near the right side, 
where it opens by a narrow orifice into the last divis- 
ion of the alimentary canal, viz., the Large intestine 
(A, ij, k). 
The large intestine, so called because it is wider than 
the rest, is the receptacle for the refuse parts of the 
food which have not been digested. It passes upward 
along the right side of the abdomen, where it is called 
the “ ascending colon” (h); then to the left side, as the 
“ transverse colon” (i); then descends along the left 
side of the abdomen as the “ descending colon” (J); 
and finally passes into the pelvis, where it terminates 
under the name of the “ rectum” (&). 
In order to understand the process of digestion, we 
must examine the changes which the food undergoes in 
each successive division of the alimentary canal. 
The first of these divisions is the mouth. When first 
introduced into this cavity, the food is subjected to 
two processes, which are very simple, but very impor- 
tant. It is masticated’, and at the same time mingled 
with the saliva. 
32. Mastication.—The mastication of the food con- 
sists in its grinding np or comminution by the action * 
of the teeth. The digestive fluids, which are to dis- DIGESTION. 
89 
solve the food in the stomach and intestine, could not 
readily act upon it if it were swallowed in a crude and 
solid mass. It must first be triturated and reduced to 
a state of fine subdivision, in order to prepare it for the 
digestive process; in the same way as a piece of loaf- 
sugar if simply placed in water dissolves slowly and 
with difficulty, but if first crushed into fine grains is 
rapidly attacked and liquefied by the solvent fluid. 
The organs of mastication are the Teeth. They are 
composed of a strong bony substance, and are firmly 
fixed in their places by strong “ roots,” which penetrate 
into the substance of the jaws. The projecting part of 
each, which is called the “ crown” of the tooth, is cov- 
ered with a layer of exceedingly dense material, the 
“ enamel,” which, as we have already seen, is the hard- 
est substance in the body, and capable of resisting the 
strongest pressure. 
The teeth are thirty-two in number, viz., sixteen in 
each jaw (Fig. 19). They vary somewhat in size and 
Fig. 19. 
Human Teeth—Upper Jaw.—a. Incisors; b. Canines; c. Anterior molars; 
d. Posterior molars. 90 
PHYSIOLOGY AND HYGIENE. 
shape, and are adapted, in different parts of the jaw, to 
somewhat different uses. The four teeth in the front 
part of each jaw are the Incisors, or “ cutting teeth.” 
They are rather flat, with a thin, chisel-like edge run- 
ning from side to side. As their name indicates, these 
teeth are adapted to cutting the food, so far as this is 
required; as in biting off the stems of juicy plants and 
certain kinds of vegetables and fruits. They corre- 
spond to the gnawing teeth of mice, squirrels, rabbits, 
and other similar species, in which they are very highly 
developed, and capable of cutting through the hardest 
substances. * 
Immediately outside the incisors are the Canine teeth 
(b), one on each side of each jaw. They are somewhat 
pointed in form, and correspond to the large and prom- 
inent “ tusks” of the carnivorous animals, which are so 
formidable as weapons of offense for wounding and 
seizing their prey. In the human species they do not 
differ very much in their function from the incisors. 
Behind the canine teeth, and occupying all the rest 
of the jaw, are the Molars (c, f/), five in number on each 
side, viz., two anterior and three posterior. They are 
very thick and strong, and have rather flat surfaces 
covered with conical elevations. Most of them are 
provided with two or more spreading roots, which fix 
them more firmly in the jaws, and enable them to re- 
sist the pressure from side to side. These are the most 
powerful and important teeth for the comminution of 
the food. The incisors and canines have less force, be- 
cause they are situated in the front part of the jaws, 
and are adapted only for cutting or piercing substances 
which offer but little resistance. But when the food is 
once taken into the mouth we carry it backward, be- DIGESTION. 
91 
tween the strong molar teeth, which are situated just 
within the muscles upon the sides of the jaws. Then, 
by repeated lateral movements of the jaws from right 
to left, the food is ground and comminuted between 
their hard surfaces, as it would be between two mill- 
stones, until its different parts are reduced to a fine 
homogeneous mixture. 
We can readily appreciate the greater power of the 
molar teeth by attempting to use them upon different 
substances. We can easily bite off a slender thread or 
a juicy vegetable by placing it between the incisors. 
But when the substance is more resisting, like a hard 
crust or a woody stem, wTe instinctively place it be- 
tween the molars in the back part of the mouth, when 
it is seized and crushed with all the power of the strong 
muscles situated on the sides of the jaws. 
In the movements of mastication it is the lower jaw 
only which moves. The upper remains stationary, as 
we can easily convince ourselves by placing the fingers 
upon the sides of the face while mastication is going on. 
We can also feel in the same way the strong muscles 
in this situation, which swell and become rigid when- 
ever the lower jaw is pressed firmly against the upper. 
33. Saliva.—But the mastication of the food is very 
much assisted, and at the same time rendered more ef- 
ficacious, by the Saliva which is mingled with it in the 
cavity of the mouth. 
The saliva is produced by various glandular organs 
situated in and near the mouth. These organs are of 
four different kinds. First, the Parotid gland, situated 
beneath the skin immediately in front of the ear; sec- 
ond, the Submaxillary gland, just within the angle of 
the lower jaw; third, the Sublingual gland,beneath the 92 
PHYSIOLOGY AND HYGIENE. 
side of the tongue; and, fourth, the Mucous 
situated in the lining membrane of the mouth, particu- 
larly on the inside of the lips and cheeks. These vari- 
ous glandular organs produce four different kinds of 
fluid, which vary in consistency, some of them being 
more watery, others more viscid ; but they are all final- 
ly mingled together to form the saliva. 
The saliva is constantly secreted in moderate quan- 
tity, sufficiently to lubricate the lining membrane of 
the mouth, and to keep it moist and pliable. Its flow 
is excited, however, in greater abundance by any thing 
which stimulates the sense of taste, such as sweet, 
sour, or bitter substances. This effect is produced 
through the action of the nervous system. Even the 
sight or sometimes the thought of attractive articles 
of food, when the appetite is excited, will stimulate the 
discharge of saliva, and, as it is commonly expressed, 
“bring the water to the mouth.” The movement of 
the jaws, as in speaking, and more especially in masti- 
cation, will also increase the quantity of saliva; and 
the action of swallowing lias, for the moment, a similar 
effect. 
But the flow of saliva is stimulated, most of all, by 
the ordinary mastication of the food in eating; when 
the excitement of the taste, the movement of the jaws, 
and the action of swallowing all combine to excite the 
activity of the glandular organs. It is then poured out 
in the greatest abundance, to perform its office in the 
preparation of the food. 
The saliva is a thin, colorless, slightly viscid, and al- 
kaline fluid. When first discharged it is somewhat 
frothy and opaline in appearance, hut after it has re- 
mained at rest for a short time its upper portion be- DIGESTION. 
comes nearly clear, while a fine white flocculent sub- 
stance is deposited at the bottom. This deposit, when 
examined by the micro- 
scope (Fig. 20), is seen to 
be composed of minute 
granules, a few oil globules, 
and a quantity of thin, fiat, 
scale-like bodies, or cells, 
called “ epithelium cells,” 
which have been separated 
from the surface of the lin- 
ing membrane of the mouth. 
There are also a few small- 
er rounded cells mingled 
with the rest, which are derived from the mucous glan- 
dules of the mouth. 
Fig. 20. 
Deposit from the saliva, showing epi- 
thelium cells, etc.; highly magnified. 
The saliva lias the following composition in 1000 
parts: 
Water *. 995.16 
Albuminous matter 1.34 
Mineral ingredients 1.88 
Mixture of epithelium 1.62 
1000.00 
Composition op Saliva in 1000 parts. 
Tt is accordingly a very thin fluid, containing but a 
small quantity of solid substances in proportion to its 
watery parts. 
The albuminous matter of the saliva is called Ptya- 
line. It is owing to the presence of this albuminous 
matter that the saliva is somewhat viscid, and that it 
readily becomes frothy when mixed with air. 
The entire quantity of the saliva produced in twenty- 
four hours has been calculated by ascertaining how 94 
PHYSIOLOGY AND HYGIENE. 
much is naturally absorbed by the food during masti- 
cation, and adding this quantity to that gradually se- 
creted in the intervals between the meals. It is thus 
found that in an adult man very nearly three pounds 
of saliva are secreted every day. This quantity, how- 
ever, is not all discharged from the mouth. By far the 
larger portion is secreted during mastication, and min- 
gled with the food which is taken into the stomach. 
34. Function of the Saliva.—The function of the saliva 
is twofold. 
First of all, it assists mastication. This can easily 
be seen by noticing the difficulty of masticating per- 
fectly dry substances. Pounded crackers, for example, 
or dry meal, are masticated with extreme difficulty 
until they have become moistened wTith a certain quan- 
tity of saliva. After this the process is much easier. 
The act of swallowing is also assisted to an important 
degree by the presence of the saliva. It is almost im- 
possible to swallow a perfectly dry mouthful until it 
has been moistened and lubricated by the saliva. The 
same thing happens in animals when the saliva can no 
longer find its way into the cavity of the mouth. In 
the horse, for example, it lias been found that when the 
saliva of the parotid glands alone has been prevented 
from passing into the mouth, the animal is nearly four 
times as long in masticating and swallowing a given 
quantity of grain as when the natural flow of the secre- 
tion is undisturbed. 
The saliva is also useful by assisting in digestion. It 
does this simply by moistening the food and preparing 
it for the action of the other digestive fluids, particu- 
larly those of the stomach. For the juices of the stom- 
ach, which, as we shall hereafter see, are very important DIGESTION. 
95 
in digestion, require to penetrate readily all parts of the 
alimentary mass in order'to produce their proper effect. 
This they can do much more readily if the food be al- 
ready moistened than if it be dry and resisting. This is 
true of almost any fluid that requires to be absorbed by 
a solid substance. If a perfectly dry sponge be thrown 
upon the water, it will float upon the surface for a long 
tirUe almost untouched. But if it be first made damp 
or slightly moistened throughout, it then rapidly ab- 
sorbs the water as soon as it touches the surface, and 
sinks at once to the bottom. 
It will be easily understood, therefore, how impor- 
tant it is that the process of mastication be regularly 
and thoroughly accomplished. It must never be neg- 
lected, nor performed in a hurried and imperfect man- 
ner ; for if so, the subsequent digestion of the food will 
certainly be delayed and obstructed, and perhaps pre- 
vented altogether. And if the food which is taken into 
the stomach be not digested as it should be within the 
natural period, it then becomes a source of irritation, 
and is liable to produce a variety of injurious effects be- 
fore it is finally discharged from the alimentary canal. 
35. Action of the Tongue in Mastication.—In the mas- 
tication of the food an important office is also perform- 
ed by the Tongue. 
First, because this organ is the principal seat of the 
sense of taste; and it is by this sense that we judge of 
the fitness of certain substances to be used as food. 
Those substances which are sound, nutritious, and well 
cooked are usually agreeable to the taste and are ad- 
mitted without delay; while such as are decayed, of 
inferior quality, or improperly prepared, are at once de- 
tected by a more or less disagreeable flavor. This dis- 96 
PHYSIOLOGY AND HYGIENE. 
agreeable flavor notifies us of the presence of some sub- 
stance in the food which is unfit for digestion, and 
accordingly it may be rejected before it has been con- 
veyed to the cavity of the stomach. 
Secondly, the tongue possesses, in a very exquisite 
degree, the sensibility of touch. By this means it can 
appreciate all the physical qualities of the food intro- 
duced into the mouth, and can ascertain at once wheth- 
er it has been sufficiently masticated, or whether there 
yet remain any portions which are still crude and re- 
sisting. Endowed also by its muscular apparatus with 
a powder of varied and flexible motion, it carries the 
food about from one part of the mouth to another, so 
that the whole is finally subjected to the action of the 
teeth. 
36. Combined Effect of the Saliva and Mastication.— 
The preparation, accordingly, which the food under- 
goes in the mouth is the combined effect of its mas- 
tication and its mixture with the saliva. None of its 
ingredients are as yet changed or decomposed, but they 
are all present in the masticated mass, though no longer 
distinguishable by the eye. The food is simply tritu- 
rated and disintegrated by the teeth ; and at the same 
time, by the movements of the jaws, cheeks, and tongue, 
it is intimately mingled with the saliva, which is work- 
ed into its substance until the whole is reduced to a 
soft, pasty material, of uniform consistency, and ready 
to be penetrated by the digestive fluids. 
This softened material is then brought together by 
the movements of the tongue, which penetrates into 
every part of the mouth, searching busily in all its cor- 
ners and cavities until it has collected the masticated 
food into a single mass upon its upper surface. The DIGESTION. 
97 
mass is then pressed backward by the muscular force 
of the organ, and carried through the opening of the 
pharynx into the upper part of the oesophagus. 
Here it passes beyond the control of the will. All 
the movements of the mouth, the jaws, and the tongue 
which we have heretofore described are voluntary in 
their character, and may be set in motion or arrested, 
hastened or retarded, at will. But from the moment 
the food passes the pharynx and enters the oesophagus it 
is no longer under our control, and is received by anoth- 
er set of organs, whose action is entirely involuntary. 
37. Deglutition.—The oesophagus, as we have already- 
mentioned, is a narrow tube, extending from the phar- 
ynx downward to the stomach. It is provided through- 
out its length with a double layer of muscular fibres, 
some of which are placed longitudinally in its walls, 
while others run round it in a circular direction, thus 
clasping the tube like the fingers of a closed hand. 
When the food enters the upper part of the oesopha- 
gus, these circular fibres contract upon it from above 
and force it onward; while the longitudinal fibres at 
the same time draw the lower part of the tube upward, 
and open a passage for the food in a downward direc- 
tion. The same action is repeated successively in ev- 
ery part of the oesophagus, so that a continuous undu- 
lating or wave-like contraction moves steadily from 
above downward through the whole length of the 
oesophagus, carrying the food before it in a rapid but 
gentle and uniform manner. 
This movement of the oesophagus is called the “ peri- 
staltic,” or vermicular action, because it resembles the 
motion of a worm in crawling over the ground. It at 
last reaches the cardia at the lower end of the tube; 98 
PHYSIOLOGY AND HYGIENE. 
when this orifice yields to the pressure from above, and 
the food, passing through it, is finally conveyed into the 
cavity of the stomach. The whole process by which 
the food is thus carried from the mouth to the stomach 
is called the act of swallowing, or “Deglutition.” 
38. The Stomach and its Lining Membrane.—The stom- 
ach, as we have already seen, is an enlargement of the 
alimentary canal, forming a rounded cavity or sac. It 
is here that the most important part of the digestive 
process is performed; so that the food, which has al- 
ready been triturated and softened by mastication, 
now begins to be actually liquefied and dissolved, 
and at the same time transformed and altered in its 
properties. 
The stomach consists of two principal parts, viz., 
first, a lining membrane, and, secondly, a muscular coat. 
Its lining membrane is thick, soft, and abundantly 
supplied with blood-vessels. Its inner surface is not 
perfectly smooth, but is raised into little ridges and 
projecting eminences (Fig. 
21). In the middle portions 
of the stomach, and toward 
the pylorus, these elevations 
are rather pointed in form, 
and generally flattened from 
side to side. Each one con- 
tains a small blood-vessel, 
which turns upon itself in a 
loop at the extremity of the 
projection, and communi- 
cates freely with the sur- 
rounding vessels. 
The substance of the lining membrane forms an act- 
Fig. 21. 
Inner surface of the lining membrane 
of the pig’s stomach, as seen in ver- 
tical section, magnified 420 times; 
showing its conical elevations, and 
the blood-vessels contained in them. DIGESTION. 
99 
ive and peculiar glandular 
apparatus. Its whole thick- 
ness is filled with little cy- 
lindrical or tubular organs, 
called the “gastric tubules” 
(Fig. 22). These little tubes 
terminate by rounded ends 
beneath, and open upon the 
upper surface of the mem- 
brane by minute orifices, 
situated between the point- 
ed elevations already de- 
scribed. The small blood- 
vessels penetrate every where between the tubules, and 
form an abundant net-work about their sides. 
Fig. 22. 
Lining membrane of me pig’s stom- 
ach, showing its whole thickness, 
with the gastric tubules; magnified 
70 times. 
39. The Gastric Juice.—The stomach exerts its action 
upon the food by means of a liquid secretion, which is 
produced by its lining membrane. This fluid is the 
Gastric Juice. 
The gastric juice is poured out from the lining mem- 
brane of the stomach at the moment when the food en- 
ters its cavity. The lining membrane is sensitive to 
the contact of the food, and is excited to pour out its 
secretion, just as the glands in the neighborhood of the 
mouth pour out their saliva when the food is undergo- 
ing mastication. But the action of the stomach takes 
place without our consciousness. The excitement of its 
lining membrane is not communicated to us by any sen- 
sation, and takes place as one of the involuntary actions 
of the interior of the body. 
During the intervals of digestion, therefore, the stom- 
ach is quiescent and empty. But no sooner does the 
food pass the cardiac orifice and enter its cavity than 100 
PHYSIOLOGY AND HYGIENE. 
an influx of blood takes place into its vessels, its lining 
membrane becomes swollen and congested, and of a 
bright red color, and its tubules begin to secrete a 
clear, watery, acid fluid. This fluid exudes from the 
lining membrane in a multitude of minute drops like 
the perspiration from the surface of the skin, and, com- 
ing in contact with the food, begins at once to act upon 
its ingredients. 
40. Peristaltic Action of the Stomach. — At the same 
time another action is excited in the stomach of a dif- 
ferent nature. This is the action of its muscular coat. 
The muscular fibres of the stomach, like those of the 
(esophagus, are partly longitudinal and partly circular. 
When the food is introduced, and the flow of the gastric 
juice begins, they are also stimulated to contraction, 
and commence a series of movements from side to side, 
and from one end of the organ to the other. These are 
the peristaltic movements of the stomach. They pro- 
duce a kind of gentle kneading or continuous churning 
of the food, by which it is moved slowly about in the 
interior of the organ. They are like the movements of 
mastication performed in the mouth, except that they 
are involuntary, like the peristaltic action of the oesoph- 
agus, and are performed without knowledge. Their 
effect is to work the gastric juice, as fast as it is se- 
creted, into the interior of the masticated food, until it 
penetrates the mass equally throughout. 
These movements have occasionally been seen, both 
in men and animals, in cases where an opening has been 
made into the stomach either accidentally or by a sur- 
gical operation. At the same time, the gastric juice has 
been obtained and subjected to examination. 
41. Ingredients of the Gastric Juice.—When the gas- DIGESTION. 
101 
trie juice is thus collected from the cavity of the stom- 
ach, it is found to be clear, transparent, of a light amber 
color, and very distinctly acid. It contains the follow- 
ing ingredients: 
Composition op the Gasteic Juice in 1000 parts. 
Water 975.00 
Albuminous matter 15.00 
Lactic acid 4.78 
Mineral ingredients 5.22 
1000.00 
The albuminous matter of the gastric juice is termed 
Pepsine, owing to its active properties in the digestion 
of the food. It may be coagulated by boiling, and also 
by the addition of a large quantity of alcohol. When 
separated by either of these means and dried, it appears 
as a fine white powder, which may be again dissolved 
in water. This is the most important ingredient of the 
gastric juice. 
The Lactic acid is the same substance which is pro- 
duced from sugar in the souring of milk. It is in a 
very dilute form in the gastric juice, but is necessary 
to its digestive properties; for the pepsine will not act 
upon the food unless it be dissolved in an acid fluid. 
The Mineral ingredients of the secretion are also 
present in small quantity. They consist of common 
salt, together with combinations of potash, lime, mag- 
nesia, and iron. 
42. Action of Gastric Juice upon the Food.—The gas- 
tric juice, constituted as above, has a very remarkable 
effect upon the food. For if a small portion of meat, 
bread, boiled white of egg, or cheese, be cut into thin 
slices, placed in gastric juice, and kept at a warm tem- 
perature, the alimentary substance soon begins to be 102 
disintegrated and liquefied by the action of the fluid. 
This effect first shows itself upon the outer surface of 
the substances acted on, which become more transpar- 
ent and softer, and thus gradually melt away. If the 
mixture be gently agitated, so as to shake off the soft- 
ened parts, the process goes on more rapidly. The gas- 
tric juice penetrates deeper and deeper into the interi- 
or, softening and dissolving as it goes, until the whole 
mass is finally reduced to the form of a fluid mixture. 
PHYSIOLOGY AND HYGIENE. 
But if the fluid mixture thus produced be examined 
more closely, it will be found that all the ingredients 
of the food have not been equally affected. In fact, it 
is only the albuminous constituents which are dissolved 
by the gastric juice, while the starchy and oleaginous 
matters are not altered. But as the food, when taken, 
consists of starchy and oleaginous substances united 
and enveloped by albuminous matters, the solution of 
the latter sets free the other ingredients from their 
combination. 
Thus bread consists of starch entangled with the so- 
lidified glutinous matter of the flour. When the glu- 
tinous matter is dissolved by the action of the gastric 
juice, the starch is consequently disintegrated at the 
same time, though it still retains its other peculiar 
properties. 
Again, cheese consists of the solidified caseine of the 
milk, with the oily or buttery milk globules imbedded 
in its substance. The caseine is dissolved and lique- 
fied by the gastric juice, but the oily parts remain un- 
changed, and simply rise to the top and float upon the 
surface of the watery fluid. 
The gastric juice accordingly appears to act upon 
the whole mass of the food, but in reality it is only by DIGESTION. 
103 
dissolving that large portion of its ingredients which 
consist of albuminous matter. 
Now the action of the gastric juice in this process is 
a very peculiar one, and depends upon the properties 
of the pepsine which it contains. This substance acts 
as a ferment, and, simply by coming in contact with 
the albuminous matter, changes its nature and reduces 
it to the liquid form. For albumen, after being digest- 
ed by the gastric juice, is no longer albumen, but has 
been transformed and converted into something else. 
This new substance is termed Albuminose, and is dis- 
tinguished by peculiar properties. Thus white of egg, 
in its natural condition, is coagulated by boiling, and 
is usually taken as food in this solid and coagulated 
form ; but after it has been liquefied in the manner 
above described, and converted into albuminose, it can 
not again be coagulated by heat, but remains fluid, and 
is ready to be absorbed by the blood-vessels. 
Like the other ferments which have been already de- 
scribed, the pepsine of the gastric juice, in order to pro- 
duce its effect, must have a moderately warm tempera- 
ture, neither too hot nor too cold. The gastric juice 
will not act upon the food when near the freezing point 
of water, neither will it have any effect if raised to the 
neighborhood of a boiling temperature. It must be in- 
termediate between the two; and its greatest activity 
is about 100 degrees Fahrenheit, which is exactly the 
temperature of the interior of the living stomach. 
In some instances the action of the gastric juice is 
very curious. Thus milk, if taken in a fluid form, is 
first coagulated by the fluids of the stomach. It is ow- 
ing to this property that rennet, which is nothing else 
than the dried fluids of the calf’s stomach, causes the 104 
PHYSIOLOGY AND HYGIENE. 
coagulation of milk in the manufacture of cheese. In 
digestion this effect is instantaneous, or nearly so. But 
soon afterward the pepsine begins to act upon the co- 
agulated caseine, and finally reduces it again to the liq- 
uid form. Thus the same substance, during digestion, 
is first solidified, and afterward dissolved by the gastric 
juice. This proves that the act of digestion does not 
consist in a simple solution, but is an actual transforma- 
tion of the albuminous substances. 
The gastric juice is the most abundant of all the di- 
gestive fluids. It continues to be produced by the lin- 
ing membrane so long as any food remains undigested 
in the stomach. The quantity which is first secreted 
acts upon a corresponding portion of the albuminous 
matters. The liquefaction of these albuminous matters 
causes, as we have already seen, a disintegration of the 
food previously combined and agglutinated by their 
substance, and these disintegrated portions pass at 
once through the pylorus into the cavity of the small 
intestine. A fresh quantity of gastric juice is at the 
same time secreted, does its work in a similar manner, 
and is carried with another portion of the debris of the 
food into the intestine. This process goes on until the 
whole of the food, thus successively broken down and 
disintegrated by the solution of its albuminous portions, 
has been removed from the cavity of the stomach, and 
carried downward into the channel of the small intes- 
tine. 
When this is accomplished, the secretion of gastric 
juice by the stomach conies to an end, the congestion 
of its lining membrane disappears, its peristaltic action 
ceases, and the entire organ returns to its ordinary qui- 
escent condition. DIGESTION. 
105 
The stomach, accordingly, is alternately in two differ 
ent conditions, corresponding to the digestive process, 
viz., a condition of rest and a condition of activity 
While digestion is going on, it is in active secretion; 
during the intervals of digestion it remains quiescent. 
43. Digestibility of Food.—The digestibility of differ- 
ent kinds of food varies considerably. Some of them 
are disposed of in a comparatively short time; others 
take a longer period. This difference is, to a certain 
extent, a matter of common experience, since every one 
is conscious that certain articles of food require a lon- 
ger time for digestion than others. Dr. William Beau- 
mont had an opportunity, many years ago, of examin- 
ing this point in a patient who had a permanent open- 
ing in the stomach, the result of a gun-shot wound. 
He compared the time required for the digestion of 
many different kinds of food, some of which are enu- 
merated in the following list: 
Hrs. Min. 
Pig’s feet 1 00 
Tripe 1 00 
Trout (broiled) 1 30 
Venison steak 1 35 
Boiled milk 2 00 
Roasted turkey 2 / 30 
Time Required for Digestion according to Dr. Beaumont. 
Hrs. Min. 
Roasted beef 3 00 
“ mutton 3 15 
Veal (broiled) 4 00 
Salt beef (boiled) 4 15 
Roasted pork 5 15 
These results would not always be precisely the same 
for different persons, since there are variations in this 
respect according to age and temperament. Thus, in 
most instances, mutton would probably be equally di- 
gestible with beef, or perhaps more so; and milk, which 
in some persons is easily digested, in others is disposed 
of with considerable difficulty. But, as a general rule, 106 
PHYSIOLOGY AND HYGIENE. 
the comparative digestibility of different substances is 
no doubt correctly expressed by the above list. 
44. Conditions requisite for healthy Digestion.—The 
healthy action of the digestive process must be pro- 
vided for by careful attention to various particulars. 
First of all, the food should be of good quality and 
properly cooked. The best methods of preparation by 
cooking are the simplest, such as roasting, broiling, or 
boiling. Articles of food which are fried are very apt 
to be indigestible and hurtful, because the fat used in 
this method of cooking is infiltrated by the heat, and 
made to penetrate through the whole mass of the food. 
Now we have seen that fatty substances are not digest- 
ed in the stomach, as the gastric juice has no action 
upon them. In their natural condition they are simply 
mixed loosely with the albuminous matters, as butter 
when taken with bread or vegetables, or the adipose 
tissue which is mingled with the muscular flesh of 
meat; and the solution of the albuminous matters in 
the stomach, therefore, easily sets them free, to pass 
into the small intestine. But when imbibed and thor- 
oughly infiltrated through the alimentary substances, 
they present an obstacle to the access of the watery 
gastric juice, and not only remain undigested them- 
selves, but also interfere with the digestion of the albu- 
minous matters. It is for this reason that all kinds of 
food in which butter or other oleaginous matters are 
used as an ingredient, so as to be absorbed into their 
substance in cooking, are more indigestible than if pre- 
pared in a simple manner. 
It is also important, more particularly in all kinds of 
vegetable food, that the cooking should be thorough 
and complete. This is necessary in order that their DIGESTION. 
107 
texture may be sufficiently softened and their starchy 
ingredients properly prepared. For raw starch is ex- 
ceedingly difficult of digestion, while that which has 
been boiled, or heated in any way in contact with wa- 
ter, absorbs moisture, as we have seen, so that its grains 
become softened, and are then easily acted on by the 
digestive fluid. 
Secondly, the food should be taken in moderate quan- 
tity at a time. If an excessive amount be swallowed at 
once, it appears to exert a paralyzing influence upon the 
stomach, which is overpowered by the unaccustomed 
load, and fails to act with energy upon the alimentary 
materials. This danger is especially to be avoided 
when the appetite is voracious, after an unusually long 
abstinence. The excessive desire for food at such times 
is an unnatural one, and should not be immediately 
gratified to its fullest extent, since it is liable to over- 
tax the capacity of the stomach, and thus produce a 
disturbance in the digestive function. 
Thirdly, the food should he taken with regularity, 
and about the same time each day. The digestive or- 
gans are subjected to the influence of habit in this re- 
spect, for some reason which we do not fully under- 
stand. They accomplish their work more promptly 
and thoroughly when the food is taken at the accus- 
tomed time and in the accustomed manner than if it be 
taken irregularly and out of season. This fact was no- 
ticed so long ago as the time o£ Hippocrates, who says 
in his Treatise on Regimen that if a man who has not 
been accustomed to take food in the middle of the day 
should do so, he is liable to be oppressed and disturbed 
by it; while those who are in the habit of dining at this 
time, if they omit the usual meal, are equally affected, 108 
and perhaps lose their appetite for the rest of the day. 
In some persons the system is exceedingly sensitive to 
any such irregularity, and in all the process of diges- 
tion is more or less liable to be affected by it. 
PHYSIOLOGY AND HYGIENE. 
Lastly, the secretion of the gastric juice and the di- 
gestion of the food are much influenced by the condi- 
tion of the nervous system. It has been found, by the 
experiments of Dr. Beaumont and others, that irritation 
of the temper and other moral causes will frequently 
diminish or altogether suspend the natural flow of the 
gastric fluids. Any feverish action in the system or 
any excessive fatigue is liable to produce the same ef- 
fect. Every one is aware how readily any mental dis- 
turbance, such as anxiety, anger, or vexation, will take 
away the appetite and interfere with digestion. Any 
injurious nervous impression, occurring especially at 
the comme7icement of digestion, seems to produce an 
effect which lasts for a considerable period; for it is 
often noticed that when any annoyance, hurry, or anx- 
iety occurs soon after the food has been taken, though 
it may last but for a few moments, the digestive process 
is not only endangered for the time, but is liable to be 
permanently disturbed during the entire day. 
In order, therefore, that digestion may go on proper- 
ly in the stomach, food should he taken only when the 
appetite demands it, and as nearly as possible at regu- 
lar intervals; it should be properly prepared by cook- 
ing, and thoroughly masticated at the outset; and, 
finally, both mind and body, particularly during the 
commencement of the process, should be free from any 
unusual or disagreeable excitement. 
45. Entrance of Food into the small Intestine. — As 
the disintegrated and partly liquefied food passes out DIGESTION. 
109 
through the pylorus into the small intestine, it consists, 
first, of the gastric juice, together with the albuminous 
matters which it holds in solution; second, of the 
starchy substances which have been set free from the 
other ingredients of the food, but not otherwise alter- 
ed ; and, third, of the oleaginous matters which are 
also unchanged by the gastric juice. The last two 
substances, however, are now digested by the action 
of the fluids which are poured into the cavity of the 
small intestine. 
46. The Intestinal Juice and Digestion of Starch.—The 
first of these fluids is the Intestinal Juice. The intes- 
tinal juice is secreted by a vast number of small tubu- 
lar glands called the “Follicles of Lieberkiihn,” which 
are thickly set throughout the whole extent of the lin- 
ing membrane of the intestine 
(Fig. 23). Like the tubules of 
the stomach, these bodies are 
cylindrical in form, with round- 
ed ends below, and opening by 
little mouths upon the inner sur- 
face of the intestine. Owing to 
the great length of this part of 
the alimentary canal, and con- 
sequently the extent of its lin- 
ing membrane, these follicles are 
exceedingly numerous. The in- 
testinal juice which they secrete is colorless, slightly 
alkaline, and of a viscid consistency. It contains an 
albuminous ingredient, somewhat similar to that pro- 
duced by the mucous glandules of the mouth. 
Now the intestinal juice, thus secreted, has the pow- 
er of acting upon starch with great rapidity at the 
Fig. 23. 
Follicles of Lieberkiihn, from 
the small intestine. 110 
PHYSIOLOGY AND HYGIENE. 
temperature of the living body, and of converting it 
into sugar. If a little of the fresh intestinal juice be 
mingled with boiled starch and kept in warm water for 
a few seconds, the stai’ch begins to disappear from the 
mixture, and sugar to take its place; and in a short 
time the whole of the starch will have undergone the 
same transformation. 
This change is accomplished by the action of the al- 
buminous ingredient of the intestinal juice. Like the 
pepsine of the gastric juice, it acts as a ferment; and 
by simply coming in contact with the starchy matters 
of the food at a warm temperature, it causes them to 
change their properties, and transforms them into sugar. 
When the starchy substances have thus been converted 
into sugar, their digestion is accomplished; for they 
have then become liquefied, and accordingly may be 
readily dissolved by the fluids of the intestine. 
When the food passes into the small intestine, there- 
fore, it meets with the intestinal juice, which is secreted 
with activity at that time ; and by the contact of this 
fluid, its starch is rapidly transformed into sugar, and 
then held in solution by the intestinal fluids. 
47. Pancreatic Juice.—There is still another secretion 
which is mingled with the food in the cavity of the in- 
testine, viz., the Pancreatic Juice. As its name indi- 
cates, this fluid is the production of the “ pancreas,” a 
gland situated near and a little behind the lower bor- 
der of the stomach. The pancreas discharges its secre- 
tion into the upper part of the small intestine, a few 
inches below the situation of the pylorus (Fig. 18, g). 
The pancreatic juice, as it enters the intestine, is a 
clear, colorless, alkaline and rather viscid fluid, some- 
what similar in appearance to the intestinal juice. It 
contains the following ingredients : DIGESTION. 
Composition of the Pancreatic Juice in 1000 parts. 
Water 900.76 
Albuminous matter 90.38 
Mineral ingredients 8.86 
1000.00 
It contains, therefore, a much larger proportion of 
albuminous matter than either saliva or the gastric 
juice; and, accordingly, it is more viscid than either of 
these secretions, sometimes almost resembling white of 
egg in consistency. 
This albuminous matter is termed “ Pancreatine.” It 
may be coagulated by boiling, by the addition of an ex- 
cess of alcohol, and by various other chemical means. 
It is the principal and most active ingredient of the 
pancreatic juice. 
48. Action of the Pancreatic Juice on Fat. — The most 
important property of this secretion is its action upon 
the oleaginous matters. These substances, as we have 
seen, are not digested in the stomach. They are only 
melted by the warmth of the body, or by the solution 
of the albuminous matters are set free from the tissues 
in which they were entangled. In the stomach, there- 
fore, they are always easily recognized, floating in the 
form of oily drops and globules among the other ingre- 
dients of the food. 
But in the intestine these oily drops are no longer to 
be seen. In place of them there appears a white milky- 
looking fluid, mingled with the other substances in this 
part of the alimentary canal, which smears over its in- 
ternal surface, and collects in the little folds and hol- 
lows of its lining membrane. This white fluid is the 
Chyle. It contains all the oleaginous matters of the 
food, but so changed in their condition that they are no 112 
longer distinguishable by the naked eye. If we ex- 
amine it by the microscope, we see that it is filled with 
excessively minute granules of fat, so fine that they can 
hardly be measured, and suspended in the albuminous 
liquids like an emulsion. 
PHYSIOLOGY AND HYGIENE. 
The chyle is, in fact, an emulsion, which has been 
produced by the action of the pancreatic juice upon the 
oily particles of the food. 
If we take a quantity of fresh pancreatic juice, and 
shake up with it a little olive oil or other fatty sub- 
stance, the same effect is immediately produced. The 
oil is at once disintegrated and broken into minute par- 
ticles, which are then disseminated through the mix- 
ture, forming a perfectly white, opaque, milky-looking 
fluid. This action is accomplished by the albuminous 
ingredient of the pancreatic juice, which is known as 
“pancreatine.” We have already seen, in a former 
chapter (p. 60), that fresh white of egg will produce 
this effect upon oil when shaken up with it in a glass 
vessel. Now pancreatine is very similar in its proper- 
ties to the white of egg, and especially resembles it in 
this action which it exerts upon the oily parts of the 
food, by which they are converted into an emulsion. 
This change, when accomplished, is sufficient to com- 
plete the digestion of the fat; for in the emulsioned form 
it is capable of being absorbed by the vessels, and thus 
received into the general current of the circulation. 
49. Peristaltic Movement of the Intestine.—At the 
same time that the changes which have now been de- 
scribed take place, the elements of the food, mingled 
with the various digestive fluids, are carried from above 
downward by the peristaltic action of the intestine. 
For the intestine, like the oesophagus and the stomach, DIGESTION. 
113 
is provided with a double muscular coat, consisting of 
longitudinal and circular fibres. The action of these 
fibres may be seen very plainly in the intestines of the 
ox or sheep, immediately after they are removed from 
the body of the slaughtered animal. Indeed, it is in 
this part of the alimentary canal that the peristaltic ac- 
tion is most active and most distinct. A contraction 
takes place at a particular spot, by which the intestine 
is reduced in diameter, its sides drawn together, and its 
contents forced onward into the next portion of the ali- 
mentary canal. This contraction then extends to the 
neighboring parts, while the portion originally con- 
tracted becomes enlarged; so that a slow, continuous, 
creeping motion of the intestine is produced, by suc- 
cessive waves of contraction and relaxation, which in- 
cessantly follow each other from above downward. 
The effect of this is to produce a peculiar writhing, 
worm-like movement among the coils of the intestine, 
by which the food, while undergoing digestion, is stead- 
ily carried forward, so as to traverse the entire length 
of the small intestine, and to come in contact success- 
ively with the whole extent of its lining membrane. 
50. Complete Digestion of Food in the Intestine.—In 
this way the complete digestion of the food, and at the 
same time its absorption, are provided for. For, as the 
food moves slowly from above downward, those por- 
tions which are already digested are removed by ab- 
sorption through the lining membrane. This leaves 
the remaining portion of the food more fully exposed 
to the contact of the digestive fluids, until, toward the 
lower part of the small intestine, the whole has been 
thoroughly liquefied and converted into materials fitted 
for absorption. 114 
PHYSIOLOGY AMD HYGIEME. 
Thus, in different parts of the small intestine, the ap- 
pearance of the alimentary mass is different, according 
to the stage of the digestive function; and its progress 
may be seen by examining the alimentary canal during 
digestion in some of the 
lower animals. The turbid 
mixture which passes out 
of the stomach into the in- 
testine when the animal 
has been fed upon meat 
(Fig. 24), contains muscu- 
lar fibres, separated from 
each other and more or less 
disintegrated by the action 
of the gastric juice. The fat 
vesicles are but little alter- 
ed, and there are only a few 
free oil globules to be seen 
floating among the other ingredients. 
In the upper part of the 
intestine the muscular fibres 
are farther disintegrated. 
They become very much 
broken up, pale and trans- 
parent, but can still be rec- 
ognized by the granular 
markings and striations 
which distinguish their 
structure (Fig. 25). The 
fat vesicles also begin to 
become altered. The solid 
granular fat of beef becomes 
liquefied and emulsioned, 
Fig. 24. 
Contents of Stomach during Digestion 
of Meat.—a. Fat vesicle tilled with 
opaque, solid, granular fat; b, b. Bits 
of partially disintegrated muscular 
fibre; c. Oil globules. 
Fig. 25. 
From upper part of Small Intestine.— 
a, Fat vesicle, with its contents di- 
minishing. The vesicle is beginning 
to shrivel and the fat breaking up; 
b, b. Disintegrated muscular fibre; 
c, c. Oil globules. DIGESTION. 
115 
and appears under the form of oil-drops and fatty mol- 
ecules, and milky chyle shows itself in greater or less 
abundance; while the fat vesicles themselves are par- 
tially emptied, and become, accordingly, collapsed and 
shriveled. 
In the middle and lower parts of the intestine (Figs. 
26 and 27) these changes continue. The muscular fibres 
Fisr. 26. 
Pig. 2T. 
From middle of Small Intestine.—a, a. 
Fat vesicles, nearly emptied of their 
contents. 
From last quarter of Small Intestine. 
—a, a. Fat vesicles, quite empty and 
shriveled. 
become constantly more and more disintegrated, and a 
large quantity of granular debris is produced. The fat 
at the same time progressively disappears, and the ves- 
icles may at last be seen entirely collapsed and empty. 
In this way the digestion of the different ingredients 
of the food goes on in a continuous manner, from the 
stomach throughout the entire length of the small in- 
testine. At the same time, it results in the production 
of three different materials, viz.: 1 st. A solution of al- 
buminous matters, produced by the action of the gas- 
tric juice; 2d. An oily emulsion, produced by the action 
of the pancreatic juice on fat; and, 3d. Sugar, produced 
from the transformation of starch by the mixed intes- 116 
PHYSIOLOGY AND HYGIENE. 
tinal juices. These substances are then ready to be 
taken up into the circulation; and as the mingled in- 
gredients of the intestinal contents pass successively 
downward through the alimentary canal, the products 
of digestion, together with the digestive secretions 
themselves, are gradually removed and absorbed by 
the vessels of the lining membrane. 
Thus the food, which is taken into the mouth in the 
form of bread, meat, fruits, and vegetables, is reduced 
and transformed by the action of the digestive fluids, 
until its nutritious ingredients are separated from each 
other and converted into new materials. The refuse 
matters which are not digestible, and which can serve 
no purpose in the nourishment of the body, are at the 
same time eliminated and rejected. They pass into 
the large intestine; while the nutritious portions re- 
main behind, ready to be taken up into the current of 
the circulation. 
QUESTIONS FOR CHAPTER IV. 
1. What is the object of digestion? 
2. What is the alimentary canal? 
3. By what is the food digested in the alimentary canal ? 
4. In what way is it digested ? 
5. Name and describe the different parts of the alimentary canal. 
6. To what two processes is the food subjected in the mouth ? 
7. WThat is mastication ? 
8. What are the organs of mastication ? What are they composed 
of, and what are their different parts ? 
9. How many different kinds of teeth are there, and how many of 
each in each jaw ? 
10. What is the situation, form, and use of the incisors? of the ca- 
nines ? of the molars ? 
11. How are the movements of mastication performed? 
12. By what glands is the saliva produced ? 
13. At what time is it most abundantly secreted ? QUESTIONS. 
117 
14. What is its appearance, and what are its ingredients ? 
15. How much saliva is produced in twenty-four hours ? 
16. What are the uses of the saliva ? 
17. How does the tongue assist in mastication? 
18. What is the combined effect of the saliva and mastication ? 
19. At what point does the food pass beyond the control of the 
will? 
20. What is the structure of the oesophagus ? 
21. How is the food swallowed into the stomach? 
22. What is the structure of the stomach ? of its lining membrane ? 
23. What digestive fluid is produced in the stomach ? 
24. At what time is the gastric juice secreted ? 
25. What is the action of the muscular coat of the stomach ? 
26. What is the appearance of the gastric juice, and what are its 
ingredients ? Which is the most important ? 
27. What effect does the gastric juice have upon the food ? 
28. Which of the ingredients of the food are dissolved by the gas- 
tric juice ? 
29. In what way does the pepsine act in digesting the food ? 
30. What temperature is required for the action of the gastric juice? 
31. What effect does the gastric juice have upon milk ? 
32. Where does the food pass after leaving the cavity of the 
stomach ? 
33. What kinds of food are most easily digestible ? 
34. What are the best methods of cooking food ? 
35. Why is fried food apt to be difficult of digestion ? 
36. Why should vegetables be very thoroughly cooked ? 
37. Why should the food be taken in moderate quantity ? 
38. Why should it be taken at regular times ? 
39. What effect does nervous irritation have on the process of di- 
gestion ? 
40. What digestive fluid is produced by the small intestine ? 
41. What are the Follicles of Lieherkiihn? 
42. What is the appearance of the intestinal juice ? 
43. What effect does it have upon the food ? 
44. What is the appearance of the pancreatic juice? 
45. By what organ is it produced, and where is it poured into the 
intestine ? 
46. What are its ingredients ? 
47. What effect does it have upon the food ? PHYSIOLOGY AND HYGIENE. 
48. What is the fluid called which is produced by the digestion of 
the fats ? 
49. What is its appearance ? 
50. What is the “peristaltic action” of the intestine? 
51. What effect does it have upon the food ? ABSORPTION. 
119 
CHAPTER V. 
ABSORPTION. 
Lining Membrane of Intestine.—Valvulas Conniventes.—Villi.—En- 
dosmosis.—Absorption by Living Membranes.—Influence of the 
Circulation.—Blood-vessels of the Intestine.—Portal Vein.—Blood 
. of the Portal Vein during Digestion contains Albuminose, Sugar, 
and Chyle.—Change in its appearance owing to Chyle.—Distribu- 
tion of Portal Vein in the Liver.—Beabsorption of the Digestive 
Pluids. —Lymphatic Vessels. —Lacteal Vessels. —Appearance of 
Lacteals during Digestion.—Receptaculum Chyli.—Thoracic Duct. 
—Discharge of Digested Matters into the Blood.—Their Transfor- 
mation and Disappearance.—Nutrition of the Blood. 
51. Absorption of the Food. — We now enter upon a 
new chapter in the history of the materials of nutrition. 
The first stage in their progress toward the nourish- 
ment of the body has been passed, and they are now 
ready to undergo a different action ; for all the changes 
and modifications which we have thus far studied in 
the digestion of the food have been simply a kind of 
preparation for that which is to follow. The digested 
and nutritious elements of the food are still inclosed in 
the alimentary canal; and, before they can reach their 
destination and arrive at the tissues which they are to 
nourish, they must first pass through its walls and gain 
entrance into the blood. This process is known by the 
name of Absorption. 
How is this passage from the intestine into the blood- 
vessels accomplished? 
52. Lining Membrane of the Intestine.—The lining 120 
PHYSIOLOGY AND HYGIENE. 
membrane of the alimentary canal, as we have already 
said, is of great extent. For not only does it follow 
the whole length of the tube itself, but in the small in- 
testine it is thrown into a great number of transverse 
folds or valves, called the Valvuloe conniventes. Each 
valve is formed of a double layer of the lining mem- 
brane, folded upon itself at its inner edge like the 
plaiting of a ruffle; so that all of them, taken together, 
increase very much its extent of surface. As the small 
intestine itself measures twenty-five feet in length, the 
entire extent of its lining membrane, owing to the folcfs 
just described, is at least doubled, or not less than fifty 
feet in all. 
This membrane, however, is exceedingly thin, soft, 
and flexible, so that it is easily contained within the 
limits of the intestine. 
53. Villi of the Small Intestine.—But beside this, the 
lining membrane of the small intestine is beset through- 
out with a multitude of still more minute elevations, in 
the form of delicate flattened, conical, or thread-like 
filaments projecting from its inner surface, which are 
called the Villi (Fig. 28). 
They resemble the pointed 
elevations in the pyloric 
portion of the stomach (p. 
98), except that they are 
longer and more slender in 
shape. They are so closely 
set that they give to the 
surface of the lining mem- 
brane a fine velvety ap- 
pearance, and an exceeding 
softness to the touch. Each 
Fig. 28. 
Villi of the Small Intestine, with their 
blood-vessels; highly magnified. ABSORPTION. 
121 
villus is provided with a network of minute vessels, 
through which the blood circulates in a multitude of 
inosculating currents. 
These villi are the principal agents of absorption. 
They hang out freely in the cavity of the intestine, and 
penetrate every where into the digested material which 
it contains. They are the rootlets by which the lining 
membrane absorbs the nutritious elements of the food, 
just as the roots of a plant absorb nourishment from 
the soil in which they are imbedded. 
54. The Nature and Method of Absorption.—But there 
are no openings in the substance of the villi, which on 
the contrary present every where a continuous and un- 
broken surface. How is it, therefore, that the nutri- 
tious fluids can find an entrance ? 
It is owing to a peculiar action manifested by the 
animal membranes, which enables certain fluids to pass 
directly through their substance by a kind of transuda- 
tion or imbibition. This action is known by the name 
of Midosmosis. 
Every animal membrane will absorb certain fluids 
with greater or less facility. If you take a dried blad- 
der and place it in warm water, it will gradually ab- 
sorb the liquid, and become thickened, moist, and pli- 
able, until it recovers nearly its original appearance 
and consistency. This will take place usually with 
any substance formed of an animal tissue, but it does 
not always happen in exactly the same way. Each 
animal membrane will absorb some fluids more read- 
ily than others. Thus some of them will absorb pure 
water more abundantly than a solution of salt, or a 
solution of sugar more readily than one of gum; and 
the same liquid will be absorbed more readily by one 122 
PHYSIOLOGY AND HYGIENE. 
membrane, and less so by others. Thus every animal 
membrane has a special power of absorption for certain 
liquids, which it will take up in greater or smaller quan- 
tity, according to their nature and composition. In all 
cases, however, there is a natural limit to this quantity, 
beyond which absorption will not continue. 
55. Absorption by the Blood-vessels.—Now this power 
is exhibited by the animal membranes much more ac- 
tively during life than after death; because, first of all, 
the living membranes are perfectly fresh and unchanged 
in their structure, and, second, because they are filled 
with the circulating blood moving incessantly through 
their vessels. This increases very much the quantity 
of fluid taken up; because the blood absorbs the new 
materials from the animal membrane, just as the mem- 
brane has absorbed them from the external liquid, and 
this blood, passing immediately away with the current 
of the circulation, is followed by a new supply, which 
takes up in its turn what has accumulated since. Thus 
the animal membrane is constantly relieved of the fluid 
which it has already absorbed, and is then enabled to 
receive a fresh supply; just as a reservoir, which re' 
ceives water at one extremity and discharges it by a 
waste-pipe at the other, may be kept constantly full 
but never running over. Accordingly, the absorbing 
power of the living membrane is not easily exhausted, 
but remains in full activity so long as the blood con- 
tinues to perform its work. 
It is in this way that the digested fluids are conveyed 
from the intestine into the blood-vessels. The liquid 
albuminose from the stomach, and the sugar produced 
from the digestion of starch, are both dissolved in the 
fluids of the alimentary canal, and are thus made ready ABSORPTION. 
123 
for absorption. Even the oily substances of the chyle 
are capable, in their minutely disintegrated form, of 
penetrating the substance of the villi, and of entering 
their blood-vessels. For it is found that the fine parti- 
cles of a milky emulsion may be absorbed by an animal 
membrane, although the oil in its natural condition can 
not pass through its substance. And, in point of fact, 
if the villi from the small intestine, during digestion, be 
examined by the microscope, they are found to be tur- 
gid with chyle, and penetrated every where with its 
minute oily particles. Thus all the materials of the di- 
gested food are taken up by the villi of the alimentary 
canal. From the villi they pass directly onward into 
the blood. 
56. The Portal Vein and Circulation through the Liver. 
*—The course of the blood-vessels, which after passing 
through the walls of the intestine return from them to 
the heart, is a peculiar one, and merits a particular de- 
scription. We have already seen that each one of the 
intestinal villi is filled with a network of minute vessels. 
These vessels terminate at the base of each villus in a 
little vein, which receives the blood coming from it, and 
unites with other similar veins returning from the adja- 
cent parts of the intestine. The branches so formed 
unite with still others coming from more distant re- 
gions, like so many different roads all joining a com- 
mon highway. In this manner, the veins, returning 
from all parts of the intestine, are at last collected into 
a single great trunk, which is known by the name of 
the Portal Vein. The portal vein therefore contains 
all the blood which has traversed the lining membrane 
of the intestinal canal, together with the substances 
which it has absorbed from the intestinal cavity. 124 
PHYSIOLOGY AND HYGIENE. 
Accordingly, the blood circulating in the portal vein, 
while digestion and absorption are going on, is charged 
with the nutritious materials of the food. It contains 
the digested albuminous matters under the form of al- 
buminose, and the sugar produced by the digestion of 
starch. It contains also the oily substances of the chyle 
mingled with its other ingredients. This gives to the 
blood of the portal vein, during digestion, a peculiar as- 
pect. For wdiile the sugar and albuminous matters, be- 
ing in a state of solution, can not be distinguished by 
the eye and are only to be recognized by their chem- 
ical tests, the oily granules of the chyle, being simply 
suspended in the blood, consequently alter its color and 
appearance, and may be easily distinguished by the mi- 
croscope. The blood of the portal vein, therefore, at 
this time is rich in oleaginous granules; and when it 
coagulates, its watery parts are turbid and whitish in 
color, and a thin milky pellicle rises to the surface. In 
the intervals of digestion, on the contrary, the watery 
parts of the portal blood are clear and transparent, like 
that from any other region of the body. 
The portal vein, conveying the blood thus loaded 
with nutritious materials, passes upward through the 
cavity of the abdomen until it reaches the situation of 
the liver. 
Here, however, instead of continuing its course di- 
rectly toward the heart, it passes into the substance of 
the liver, where it undergoes a very singular distri- 
bution. It is on this account that it has received the 
name of the “ portal” vein, because it enters the liver 
by a kind of fissure or “ gate way” upon its under sur- 
face. Once within the substance of the organ, it divides 
right and left into two great branches, which penetrate ABSOEPTION. 
125 
the two opposite sides of the liver; and then, dividing 
still into smaller and more numerous ramifications, its 
branches at last reach the little glandular lobules of 
which the whole organ is composed. Here they finally 
break up into a plexus of minute vessels, as fine as those 
which originally occupied the substance of the intesti- 
nal villi, and which fill the entire substance of the liver 
with a similar vascular network. 
Beyond the glandular lobules of the liver, the blood- 
vessels again collect into little veins, and those from the 
neighboring lobules unite into larger branches, like 
those from the adjacent villi of the intestine. Now, 
however, the veins so formed are called the “ hepatic 
veinsand by repeated junction, those coming from all 
parts of the liver are at last united into one common 
Hepatic Vein. This vein soon afterward discharges its 
blood into the great venous current returning directly 
to the heart. 
Thus the blood which has circulated through the lin- 
ing membrane of the intestine, and which has there ab- 
sorbed the digested materials of the food, is compelled to 
pass through another set of inosculating vessels before 
returning to the heart. Arriving at the liver by the 
portal vein, it is there distributed through all the vas- 
cular channels of the organ, and comes into contact ev- 
ery where with the substance of its lobules. We shall 
see hereafter what important changes take place while 
the blood is thus pursuing its course through the depths 
of the glandular tissue. Having accomplished this pas- 
sage, however, and still bringing with it the nutritious 
materials of digestion, it arrives at the heart by the 
great veins of the abdomen. Here it finally discharges 
its load into the general mass of the circulating blood. 126 
PHYSIOLOGY AND HYGIENE. 
57. Reabsorption of the Digestive Fluids.—But at the 
same time that the elements of the food are thus taken 
up from the intestine and conveyed into the blood, the 
intestinal juices themselves are also absorbed and re- 
turned to the blood from which they came. For it is 
the blood which originally furnished all the materials 
for the digestive fluids. The saliva, the gastric juice, 
the intestinal juice, the pancreatic juice, are produced 
by the glandular organs and the lining membrane of 
the alimentary canal, as we have already described; 
but they are produced at the expense of the blood, 
which necessarily supplies the requisite nourishment 
for all the organs of the body. 
Now these digestive fluids are secreted in large quan- 
tity. Taken altogether, not less than twenty pounds 
of animal juices are poured into the alimentary canal 
every day for the digestion of the food. If this quan- 
tity were simply drained away from the blood, it would 
prove utterly exhausting to the animal frame. The di- 
gestion of the food would cost more, so to speak, in the 
waste of the digestive fluids, than it would return to 
the body in the form of nourishment. 
But none of these fluids are lost. They are all taken 
up again by the vessels of the lining membrane, to- 
gether with the elements of the food which they have 
served to digest. What the blood-vessels absorb, there- 
fore, is not simply the nutritious elements of the food, 
but these nutritious elements dissolved in the digestive 
fluids. The albuminous matters, when transformed by 
the pepsine, are at once liquefied in the abundant gas- 
tric juice; the sugar is dissolved also in the intestinal 
fluids; and the chyle, as we have seen, is really an 
emulsion of the fatty particles in the albuminous liquid ABSORPTION. 
127 
of the pancreatic juice. All these substances, digest- 
ors and digested, are finally absorbed at the same time 
by the blood-vessels of the alimentary canal. 
The digestive fluids, accordingly, perform a sort of 
circulation; passing from the blood to the intestine, and 
from the intestine back again to the blood. They are 
the messengers, sent out by the blood to collect the nu- 
tritious elements in the alimentary canal, and then to 
return with them into the current of the circulation. 
58. Absorption by the Lacteals.—But the absorption 
of the food is also accomplished in part by another set 
of vessels, differing from those which we have hereto- 
fore described. These vessels are the Lacteals. 
The lacteals are simply part of a great system of vas- 
cular channels distributed throughout the body, which 
are called the “Lymphatic” or “Absorbent” vessels. 
In the skin, the muscles, the internal organs, the lining 
membranes, they begin by a fine network, imbedded in 
the tissues, and then collect into small branches which 
run upward and inward toward the great cavities of 
the chest and abdomen. They finally terminate in the 
veins. Those coming from the right arm and the right 
side of the head and neck empty into the veins of this 
part of the body. Those from the legs and thighs pass 
into the cavity of the abdomen, where they are joined 
by others coming from the loins, the kidneys, the spleen, 
the liver, stomach, and intestine. All these collect into 
a single tube or duct, not more than a quarter of an 
inch in diameter, which then mounts from the abdomen 
into the chest, and runs upward along the spinal col- 
umn. This tube is called the “ Thoracic Duct.” It at 
last rises from the chest into the lower part of the 
neck, and then, curving forward, terminates in the 128 
great subclavian vein, not far from the region of the 
heart (Fig. 29). 
PHYSIOLOGY AND HYGIENE. 
Now these vessels are incessantly engaged in absorp- 
tion. They take up constantly, from all parts of the 
body where they are distributed, a transparent and 
colorless liquid, which is termed the “ lymph.” It is 
on this account that they have received the name of 
lymphatics. The lymph represents a portion of those 
ingredients of the tissues which have become useless, 
and which must be restored or renovated before they 
can again take part in the functions of life. They are 
therefore taken up by the lymphatic vessels and con- 
veyed back toward the heart, there to be mingled with 
the current of the venous blood. 
The lymphatic vessels are not readily distinguished 
by the eye. First, because they are very small in size, 
and their walls exceedingly thin and delicate; and, sec- 
ondly, because the lymph which they contain is colorless 
and transparent. The blood-vessels we can easily see, 
even when their walls are thin, owing to the red color 
of the blood which they contain; but there is nothing to 
distinguish the course of the lymphatics, since both their 
walls and their contents are equally colorless. They 
are therefore easily overlooked, unless we take especial 
pains to search for them among the other tissues. 
The lymphatics of the intestine are exactly like those 
of other parts of the body. They commence in the villi 
and in the substance of the lining membrane, and then 
pass inward to join those coming from other organs. 
Usually they are almost invisible like the rest, for they 
contain only the transparent lymph, as we have already 
described. But when the digestion of the food is in full 
activity they also begin to take up the oily particles ABSORPTION. 
129 
from the cavity of the intestine. They become turgid 
with chyle, and then, enlarged and distended with this 
milky fluid, they at once become visible to the eye as 
white rounded filaments, showing through the trans- 
parent coverings of the intestine. They are then called 
the “ lacteals,” from their white color and the milk-like 
appearance of the fluid which they contain. 
The intestines, folded upon themselves in many turns, 
as we have already described them, are loosely attach- 
ed to the spinal column by a broad sheet of thin mem- 
brane, like the band of a ruffle, which is called the 
“ mesentery.” Through this sheet the lacteals pass 
from the intestine toward the back part of the abdo- 
men; and there, just before mounting into the chest, 
they unite into a little cavity or sac, which is called the 
“ receptaculum chyli,” or “ receptacle of the chyle,” sit- 
uated just at the commencement of the thoracic duct 
(Fig. 29). 
Accordingly, the absorbent vessels of the abdomen 
have a very different appearance at different times. In 
the intervals of digestion they are nearly invisible, for 
they are then merely lymphatics, and contain only a col- 
orless fluid. But during digestion they present them- 
selves as an abundance of fine white glistening ducts, 
converging every where from the folds of the small in- 
testine, and uniting with each other at the receptaculum 
chyli. Thence the chyle is carried onward through the 
thoracic duct and is discharged at last into the blood 
of the subclavian vein. When the process of digestion 
is terminated, and all the chyle has been exhausted 
from the cavity of the intestine, the lymphatics of the 
abdomen return to their former condition, and become 
again colorless and invisible as before. 130 
PHYSIOLOGY AND HYGIENE. 
Thus the chyle 
produced during di- 
gestion is conveyed 
into the circulation 
by two different 
routes. First,by the 
blood-vessels of the 
intestine, through 
the portal vein and 
the liver, to the he- 
patic vein; and, sec- 
ondly, by the lacte- 
als and the thoracic 
duct to the subcla- 
vian vein. It is, ac- 
cordingly, all finally 
mingled with the 
blood returning to 
the heart. 
59. Changes in the 
Food after it is Ab- 
sorbed.—The history 
of absorption is not 
yet finished. 
Thus far w*e have 
seen how the sub- 
stances produced by 
digestion are taken 
up from the intes- 
tinal canal and min- 
gled with the circulation. But they are not yet ready 
for nutrition, since they are still different from the nat- 
ural ingredients of the blood. The albuminous matter 
Fig. 29. 
Lacteals and Lymphatics. ABSOEPTION. 
131 
formed in digestion is not the same with the albumen 
of the blood. Sugar also is a substance which is not 
to be found in the blood-vessels generally; and the 
milky chyle, so abundant in the portal vein during di- 
gestion, is not an ordinary ingredient of the circulating 
fluid. These substances, therefore, must be still farther 
modified and transformed before the nutrition of the 
blood is complete. 
This transformation is accomplished in the blood-ves- 
sels. Soon after entering the circulation, the albumi- 
nose, which was absorbed by the intestinal veins, disap- 
pears and is replaced by the natural albumen of the 
blood. This is a metamorphosis or conversion, similar 
to that by which the albuminose was itself produced by 
the gastric juice in digestion. The other ingredients of 
the circulating fluid act upon it by catalysis, and change 
it into the substance necessary for the composition of 
the blood. 
Thus the albumen of the blood is finally recruited 
from the nutritious elements of the food. But it is only 
after these have undergone a double transfoi-mation; 
first into albuminose by the influence of the gastric juice 
in the stomach, and secondly into albumen by the influ- 
ence of the blood itself in the interior of the vessels. 
The sugar and the oily matters also disappear soon 
after they are received into the circulation. We do 
not know exactly what becomes of them; but they are 
amalgamated in some way with the natural ingredients 
of the blood, and thus serve at last for its nutrition. 
60. Periodical Excitement of the Digestive Apparatus. 
—Finally, the whole process of digestion and absorption 
is accompanied by a remarkable excitement and conges- 
tion of the alimentary canal. We have already seen 132 
PHYSIOLOGY AND HYGIENE. 
how the lining membrane of the stomach becomes filled 
with blood when the food is taken into its cavity. The 
same thing happens with the small intestine. During 
the act of digestion its lining membrane becomes thick- 
ened and more vascular, at the same time that the pe- 
ristaltic movement of its walls is called into activity. 
While absorption is going on, also, its vessels are loaded 
with the nutritious fluids absorbed from its cavity, and 
return to the heart a larger quantity of blood than at 
other times. This continues until the process of diges- 
tion is complete, and until all its new materials have 
been distributed throughout the circulation. Then the 
unusual excitement and act ivity of the aliment ary canal 
gradually subsides. Its walls become paler and softer; 
its muscular contractions grow less frequent and active; 
and, finally, the whole intestine is restored to its ordina- 
ry condition of repose. 
QUESTIONS FOR CHAPTER V. 
1. What is absorption ? 
2. What are the valvulce conniventes of the small intestine ? 
3. What are the villi of the small intestine ? 
4. What is the function of the villi ? 
5. What is endosmosis, and how is it regulated ? 
6. How does the circulation of the blood assist in absorption ? 
7. How are the blood-vessels arranged in the villi? 
8. Into what vein do they empty ? 
9. What does the blood of the portal vein contain during the di- 
gestion of the food ? 
10. To what organ is the blood conveyed by the portal vein ? 
11. After passing through the liver, whither is the blood conveyed r 
12. What becomes of the digestive fluids during the digestion an i 
absorption of the food ? 
13. What are the lymphatic or absorbent, vessels ? 
14. Where do they originate and where do they terminate ? 
15. In what duct do the lymphatics of the abdomen terminate? QUESTIONS. 
133 
16. Where does the thoracic duct communicate with the veins ? 
17. What is the general appearance of the lymphatic vessels, and 
of the lymph which they contain ? 
18. What is the appearance of the lymphatics of the intestine dur- 
ing digestion, and why are they then called “ lacteals?” 
19. By what two routes is the chyle conveyed into the circulation ? 
20. What changes take place in the elements of the food after their 
absorption ? 
21. How is the circulation in the alimentary canal changed during 
digestion, and what is its condition after digestion is finished ? 134 
PHYSIOLOGY AND HYGIENE. 
CHAPTER VI. 
THE LIVER AND ITS FUNCTIONS. 
Situation and Structure of the Liver—its Lobules.—Biliary Ducts.— 
Secretion of the Bile.—Gall-bladder.—Accumulation of Bile in the 
Gall-bladder—its discharge into the Intestine. — Appearance and 
Composition of the Bile.—Biliary Salts.—Mode of extracting them 
from the Bile.—Their Crystallization.—Changes of the Bile in the 
Intestine—its absorption by the Blood.—Function of the Bile.— 
Formation of Sugar in the Liver—its absorption by the Blood-ves- 
sels.—Sugar finally decomposed in the Circulation. 
From what we have already learned, it is evident 
that the liver plays a prominent part in regard to the 
process of absorption. Placed in the immediate neigh- 
borhood of the digestive organs, and united with them 
by various anatomical connections, it is, to some extent, 
associated with them in function. ’It is also the great 
highway through which the blood passes in its course 
from the intestine to the heart, and where it undergoes 
certain changes of the greatest importance. 
61. Situation and Vascularity of the Liver.—The liver 
is a large and solid organ, placed in the upper part and 
on the right side of the abdomen, a little above the 
level of the stomach. If we place the open hand over 
the lowermost ribs of the right side of the body, it will 
almost exactly cover the situation of this organ. It re- 
ceives, as we have seen, the portal vein, which ramifies 
extensively in its substance. It is also supplied with 
an artery; but this artery is comparatively of small THE LIVER AND ITS FUNCTIONS. 
135 
size, and by far the larger portion of the blood which 
circulates in the liver comes from the branches of the 
portal vein. 
The first and most well known function performed 
by the liver is the production of the Bile. 
62. Structure and Secretive Function of the Liver.—If 
we examine the minute structure of the organ, we find 
that it is composed of a great number of small rounded 
granular masses, closely packed together, which are 
called its “ lobules.” It is into the substance of these 
lobules that the minute blood-vessels penetrate, and 
form there a fine vascular network. 
But beside these blood-vessels there is another set of 
tubes, equally delicate, which commence in the sub- 
stance of the lobules and join each other in the spaces 
between them. They then unite into branches like those 
of the veins, and, continuing their course from the deep- 
er parts of the organ, finally emerge at the great fissure 
or gateway at its under surface. These little tubes are 
called the “biliary ducts.” 
The liver is accordingly drained throughout its sub- 
stance by a multitude of fine ducts or canals, like the 
ditches of a cultivated field; only these ducts are of 
minute size and disseminated every where throughout 
the organ, collecting at last into a main tube or sluice- 
way at its surface. 
Now in the interior of these ducts there appears a 
watery fluid, of a rich brownish-yellow color and a bit- 
ter taste, containing many different ingredients of a 
peculiar nature. This fluid is the Bile. It is formed in 
the interior of the lobules, and is taken up from them by 
the little canals in their tissue. As it accumulates in the 
smaller ducts it fills the larger branches also, and is thus 136 
PHYSIOLOGY AND HYGIENE. 
conducted into the main channel at the under surface of 
the organ. 
How is it that the bile is formed in the substance of 
the lobules ? 
This is another example of that singular transforma- 
tion of which we have already seen so many instances. 
None of the more important ingredients of the bile are 
to be found in the blood; and yet the blood is the only 
source from which the liver derives its nourishment. 
But, as the lobules absorb from the blood its nutritious 
elements, and fix them in their own substance, they at 
the same time transform or change some of them into 
other materials. We can not explain more fully the 
manner in which this takes place; we only know that 
this is a propert y belonging to the tissue of the lobules, 
just as it is the property of the gastric juice to change 
the albuminous substances in digestion. It is thus that 
the peculiar ingredients of the bile, giving it ks bitter 
flavor, its yellow color, and its other important proper- 
ties, make their appearance in the interior of the liver. 
The liver is therefore a kind of manufactory in which 
a new fluid is produced, differing from the blood by 
which its materials are supplied. 
From the great fissure upon the under surface of the 
organ the main biliary duct passes downward to the 
small intestine, which it reaches at the distance of a 
few inches from the pylorus (Fig. 18,/). Here it pene- 
trates the wall of the intestine, and opens into its cav- 
ity by a small orifice on the inner surface of the lin- 
ing membrane. 
Thus the bile, first produced in the liver, is conveyed 
downward by the biliary duct, and finally discharged 
into the upper part of the small intestine. THE LIVER AND ITS FUNCTIONS. 
137 
But about midway between the liver and the intes- 
tine the biliary duct communicates with a membranous 
sac or bag, which is called the Gall-bladder. It is a 
rounded, pear-shaped bag, about three inches in length, 
attached to the under surface of the liver. It can be 
easily recognized, both in man and in most of the ani- 
mals used as food, by its form and situation, and by its 
being filled with dark liquid bile. The bile, in fact, ac- 
cumulates in the gall-bladder as in a kind of reservoir. 
A portion of it always passes downward through the 
biliary duct, and is discharged at once into the intes- 
tine; but a portion is also turned back into the gall- 
bladder, especially in the intervals of digestion, and 
is there stored away for future use. The longer the 
time which has elapsed since digestion, the greater the 
quantity of bile which accumulates in the gall-bladder. 
Consequently, this organ varies very much in size at 
different times. Immediately after digestion it is small 
and collapsed; but if examined after one, two, or three 
days of fasting, it is found full of bile, and increased to 
two or three times its former dimensions. 
Beside, the bile which is contained in the gall-bladder 
is somewhat different from that which is still in the bil- 
iary ducts. In the ducts within the substance of the liv- 
er it is thin, watery, and yellowish. In the gall-bladder 
it is thicker, darker colored, and viscid in consistency. 
While retained in the gall-bladder, therefore, it suffers 
a certain change; and this change is principally due 
to a viscid substance or “mucus,” which is secreted 
by the gall-bladder, and mingled with the bile which 
it contains. 
63. Physical Appearance and Ingredients of the Bile.— 
Owing to the accumulation of the bile in the reservoir 138 
of the gall-bladder, wre can easily obtain it for examina- 
tion. 
PHYSIOLOGY AND HYGIENE. 
As it comes from the gall-bladder, the bile is a rather 
viscid fluid of a golden-brown color, which often varies 
through many different shades of yellow and green. If 
we shake it up in a closed vessel with air, it becomes 
very frothy and soapy in appearance, entangling the 
bubbles of air, which adhere closely to each other and 
to the surface of the fluid. 
The ingredients of the bile are, first, water; secondly, 
certain substances of an animal nature, combined with 
soda, which are its most peculiar elements, and wrhich are 
therefore called the “ Biliary saltsthirdly, a coloring 
matter, which gives to the bile its greenish or brownish 
hue; fourthly, substances of a fatty nature; and, lastly, 
mineral ingredients. Mingled with these, as vre havb 
already mentioned, there is usually a small quantity of 
mucus from the lining membrane of the gall-bladder. 
The proportion of these ingredients is as follows: 
Water 880.00 
Biliary salts 90.00 
Coloring aiul fatty matters 13.42 
Mineral ingredients 15.24 
Mucus of the gall-bladder 1.34 
1000.00 
Composition or the Bile in 1000 parts. 
Of all these ingredients, those which are called the 
“ Biliary salts” are the most important. They may be 
extracted from the dried bile by pure alcohol, since 
they are soluble in this fluid, and are thus separated 
from other impurities which remain behind. But if 
ether be afterward added to the alcoholic solution, the 
biliary salts separate from the mixture, and are then THE LIVER AND ITS FUNCTIONS. 
139 
slowly deposited in a crystalline form. The crystals 
are at first very minute and of various shapes. After- 
ward they gradually increase in size, until they some- 
times become visible to the naked eye 
(Fig. 30). 
The entire quantity of the bile which 
is secreted during the day varies in dif- 
ferent kinds of animals. As a general 
rule, it is more abundant in those which 
live upon vegetable food than in those 
which are carnivorous. In man, the 
best calculations show that the daily 
quantity of bile is about two pounds 
and a half. 
64. Function of the Bile in the Intes- 
tine.—What purpose does the bile serve 
in the alimentary canal ? 
This is not an easy matter to decide; 
for, notwithstanding the abundance of 
the bile and its remarkable characters, 
its ingredients are so different from those 
of the other secretions, and its functions 
are so obscure, that this has been found one of the most 
difficult of all the questions connected with the diges- 
tion and absorption of the food. What has been really 
learned in regard to it is as follows: 
First of all, the bile is secreted and poured into the 
alimentary canal at all times. It is not like the gastric 
juice, which is produced only during the period of di- 
gestion ; but it is incessantly formed by the liver, and 
is continually discharged into the intestine by the bilia- 
ry duct. It is always to be found, therefore, in greater 
or less quantity, in the cavity of the alimentary canal, 
Fiff. 30. 
Crystals of the Bilia- 
ry Salts, from hu- 
man bile; magni- 
fied 25 times. 140 
PHYSIOLOGY • AND HYGIENE. 
where it can be easily recognized by its yellow color, 
and by the chemical tests which are employed to de- 
tect it. 
Nevertheless, it is poured into the intestine more 
abundantly at the beginning of digestion. At this 
time, and within a few minutes after the food is taken 
into the stomach, the commencing excitement of the 
whole digestive apparatus is communicated to the gall- 
bladder. Its muscular fibres contract, and it thus dis- 
charges the bile which has accumulated within it into 
the upper part of the small intestine. It is for this rea- 
son that the gall-bladder is found empty soon after di- 
gestion, and again distended with bile when a long in- 
terval has elapsed. 
But, after the gall-bladder is emptied, the liver still 
continues its activity of secretion, and the bile which it 
produces is still conveyed into the intestinal cavity. 
Here, however, it gradually disappears. Abundant 
in the upper part of the small intestine, it is less so in 
the middle and lower parts, and, finally, it is no longer 
to be recognized either by its color or by its chemical 
tests. These tests also show that it is not discharged 
from the body. It is therefore withdrawn from the ali- 
mentary canal, and taken up by the blood-vessels at the 
same time with the digested element s of the food. 
But before being absorbed from the cavity of the in- 
testine it is changed. Its peculiar ingredients, the bilia- 
ry salts, are transformed into other materials by the in- 
fluence of the intestinal fluids, and are then conveyed 
into the current of the circulation. 
We do not know what these new materials are, but 
we know that they are necessary to life; for if the bile 
be not secreted, or if it be prevented from entering the THE LIVER AND ITS FUNCTIONS. 
141 
intestine, the animals so affected die enfeebled and 
emaciated. 
Thus the bile passes through the alimentary canal, 
not for the purpose of assisting in the digestion of the 
food, but in order that its own ingredients may be 
changed and converted into other substances. The 
blood needs these substances for its nutrition, and they 
are accordingly produced by means of the biliary secre- 
tion. 
This is accomplished, again, by a double transforma- 
tion. As the muscular flesh of our food is converted 
first into albuminose by the stomach and afterward into 
albumen in the blood-vessels, so certain of the elements 
of the blood are transformed by the liver into the salts 
of the bile, and these again are changed in the intestine 
into new materials, which are finally absorbed by the 
blood-vessels of its lining membrane. 
65. Formation of Sugar in the Liver.—Beside the for- 
mation of the bile, the liver performs also another and 
very important office ; that is, the production of sugar. 
We have seen that when starch is taken with the 
food it is changed into sugar by digestion, and this 
sugar is absorbed by the blood-vessels and thus carried 
into the circulation. But there are many animals who 
never take any starch or sugar with their food. Such 
are all the carnivorous animals—that is, those who live 
entirely upon the flesh of other animals. Their food 
contains no vegetable substances, and consequently has 
no starchy ingredient. 
Now it is a very curious fact that in these animals 
the substance of the liver always contains sugar. Even 
Avhen they have kept for many weeks or months upon 
no other food than animal flesh, sugar is still found in 142 
PHYSIOLOGY AND HYGIENE. 
the tissue of the liver. Furthermore, no other organ 
in the body contains this substance, and even the 
blood with which the liver is supplied is equally desti- 
tute of it. 
Therefore it is the liver itself which forms the sugar, 
in these cases, out of other materials. It would be too 
long a history to describe all the ingenious and careful 
experiments by which physiologists have arrived at 
this conclusion; but there is now no doubt that in the 
carnivorous animals sugar really makes its appearance 
in the liver, when no such material has been taken with 
the food. 
The same thing is true of man, and of the herbivo- 
rous or vegetable-feeding animals. For in them also the 
liver contains a certain proportion of sugar, no matter 
what may be the nature of the food consumed; and 
this proportion is often greater than that which could 
be produced in the digestive process. 
The sugar thus produced is formed in the solid tissue 
of the organ itself. This tissue absorbs the nutritious 
materials from the blood, and then transforms a part 
of them into a saccharine ingredient. The same tissue, 
as we have already seen, also contains the elements of 
the bile ; and it is for this reason that the livers of cer- 
tain animals, when cooked for food, have at the same 
time a bitter and a sweet taste. 
66. Absorption and Decomposition of the Liver-sugar. 
—But the sugar, when once formed, does not remain 
in the liver. It at once begins to be absorbed by the 
blood-vessels of the organ, and so, entering the circu- 
lation, passes onward with the blood of the hepatic 
veins toward the heart. Thus, in many cases, the 
blood of the portal vein coming to the liver contains THE LIVER AMD ITS FUNCTIONS. 
143 
no sugar; while the blood of the hepatic veins, going 
away from it, is charged with this substance which it 
has absorbed from the tissue of the organ in its pas- 
sage. 
Soon afterward, the sugar disappears entirely. We 
have already seen how that which is produced by di- 
gestion is finally decomposed in the circulation; the 
same thing happens with that which is absorbed from 
the liver. None of it is to be found in the blood of the 
general circulation. 
In the liver, therefore, there are produced two differ- 
ent substances, which pass away in two opposite direc- 
tions : First, the bile, which is absorbed by the biliary 
ducts, and conveyed downward to the intestine; and. 
secondly, the sugar, which is absorbed by the blood- 
vessels, and passes upward to the heart. In either case, 
these secretions are afterward decomposed into new 
substances, which finally take their place as ingredi- 
ents of the circulating blood. 
QUESTIONS EOR CHAPTER VI. 
1. What is the situation of the liver ? 
2. What is the principal vessel which supplies it with blood ? 
3. What is the principal secretion produced by the liver ? 
4. What are the lobules of the liver ? 
5. WThat ducts originate from the substance of the lobules ? 
6. Where does the bile first make its appearance in the liver ? 
7. How do the lobules produce the ingredients of the bile ? 
8. Where is the bile conveyed by the main biliary duct ? 
9. What is the situation and form of the gall-bladder ? 
10. What is its use ? 
11. At what time does the bile accumulate in the gall-bladder ? 
12. How is it changed while remaining in the gall-bladder? 
13. What is the consistency of the bile? its color? 
14. What are its ingredients ? which are the most important ? 
15. How may the biliary salts be extracted from the bile ? PHYSIOLOGY AND HYGIENE. 
16. Is the bile more abundant in carnivorous or in herbivorous an- 
imals ? 
17. How much is produced in man during twenty-four hours ? 
18. Is the bile secreted occasionally or constantly ? 
19. At what time is it poured into the intestine most abundantly ? 
20. What becomes of the bile after it is poured into the intestine ? 
21. What other substance is produced in the liver beside the bile? 
22. How do we know that sugar is formed in the liver ? 
23. What becomes of the sugar produced by the liver ? THE BLOOD, 
145 
CHAPTER VH. 
THE BLOOD. 
Ingredients of the Blood. —W.ter. — Salt. — Lime. —Albumen. — 
Properties of Albumen.—Pibrine—its Properties.—Blood Globules 
—tbeir Form—Size—Color— Consistency. — White Globules. — 
Quantity of different Ingredients in the Blood.—Coagulation of the 
Blood.—Clot.—Serum. Coagulat' n dependent on the Fibrine.— 
Use of Coagulation in stoppage of Bleeding.—Why Blood does not 
Coagulate in the Vessels.—Daily Production and Decomposition 
of Fibrine.—Entire Quantity of Blood in the Body—its Variation.—• 
Variation in Composition of the Blood.—Two different Kinds of 
Blood in the Body. 
We now come to the study of that remarkable fluid 
which contains all the materials necessary for nutrition, 
and provides for the common support of the whole 
body. Nourished itself by the elements of the digest- 
ed food which it has absorbed from the intestine, it 
compels them to assume a new form on entering the 
blood-vessels, and converts them into its own ingredi- 
ents. Thus it is constantly maintained in a healthy 
condition by the incessant supply of new materials. 
All the processes, therefore, of digestion and absorp- 
tion are subservient to the nutrition of the blood. 
67. Physical Appearance and Composition of the Blood. 
—The blood is a thick opaque fluid, of a rich deep red 
hue, so peculiar that it may usually be distinguished 
by its color alone. It contains many different ingredi- 
ents, of which the most important are, first, Water; 146 
PHYSIOLOGY AND HYGIENE. 
second, Mineral substances / and, third, Albuminous 
matters. 
The water of the blood is what gives it its fluidity. 
For if the water be driven off by evaporation, the other 
ingredients remain behind in the form of a dry mass, 
which would be entirely useless for the purpose of nu- 
trition. But in its natural condition the water of the 
blood unites all its other ingredients into a uniform 
liquid, which easily moves through the blood-vessels, 
and dissolves the new substances which are absorbed 
from without. Taken altogether, the water forms rath- 
er more than three fourths of the whole mass of the 
blood. 
The mineral ingredients are in much smaller propor- 
tion. The most abundant is common salt, which we 
know is taken with the food, and is a necessary ingre- 
dient of all the tissues. It forms, however, only about 
four parts in a thousand of the whole blood. The com- 
binations of Lime, which the bones and teeth require 
for their nourishment, are found in still smaller quan- 
tity, dissolved in the animal fluids of the blood. Other 
mineral substances of various kinds are also present in 
their requisite quantity. 
But the most remarkable of all the ingredients of the 
blood are its albuminous matters. It is these sub- 
stances which give to it its thick and animal consist- 
ency, and which also act the most important part in the 
nutrition of the body. They are of two different kinds, 
which are naturally mingled together in the blood in a 
liquid form. 
The first of these is the Albumen. We can obtain a 
tolerably correct idea of the characters of albumen 
from the fresh white of egg, which has received a simi- THE BLOOD. 
147 
lar name. This is not exactly the same thing with the 
albumen of the blood, but still the two resemble each 
other very closely. They may both be coagulated by 
boiling, when they become solid, white, and opaque. 
The principal difference between them is, that the fresh 
white of egg is partly gelatinous in consistency, while 
the albumen of the blood is perfectly fluid, and may 
readily be made to flow through the veins, or to run 
from one glass vessel into another. 
The albumen is about forty parts in a thousand, or 
one twenty-fifth of the whole blood. It represents, in 
great part, the concentrated nourishment derived from 
the food, for it is probably into this substance that 
most of the albuminose is converted after being ab- 
sorbed from the intestine in the digestive process. It 
is the material out of which the tissues of the body are 
afterward formed. 
The other animal matter in the blood is the Fibrine. 
Although this is in very small quantity, viz., only two 
parts in a thousand, it is an exceedingly curious and 
important ingredient. For it possesses a property 
which does not belong to any other animal substance, 
viz., the property of “ spontaneous coagulation”—that 
is, it will coagulate by itself, without being boiled or 
brought in contact with an acid, or treated by any 
other chemical substance. We shall see hereafter what 
an important character this property gives to the 
blood. 
But these substances are only the liquid portions of 
the blood. They are all dissolved in each other, and 
form a perfectly transparent and almost colorless fluid. 
Beside them there are a multitude of little rounded 
bodies contained in the liquid mixture, which make the 148 
PHYSIOLOGY AND HYGIENE. 
blood opaque, and give to it its red color. They are so 
abundant that they are crowded together by thousands 
in each drop of blood, and so minute that they are only 
visible by the aid of the microscope. They are called 
the Blood Globules. 
68. Globules of the Blood.—If we examine a drop of 
blood under the microscope, 
we see the blood globules 
floating in profusion in the 
fluid parts. Each one is a 
delicate circular plate or 
disk, somewhat like a piece 
of money in form, only with 
the edges rounded and rath- 
er thicker than the central 
part. In human blood they 
are about of an inch in 
diameter when measured across their flat surfaces, and 
about of an inch in thickness (Fig. 31). 
Fig. 31. 
Blood-globules; highly magnified. 
The blood globules are exceedingly soft and flexible 
in consistency. In fact they are nearly fluid, like drops 
of very thick oil or honey, only they do not dissolve in 
the other parts of the blood, but retain their own form 
and substance. Consequently, when moving about in 
the fluid, as they often do under the microscope, follow- 
ing accidental currents in the blood, passing through 
narrow channels, and turning corners among the other 
globules, they may be seen to twist about, and bend 
over, and elongate in various ways, and then resume 
their natural figure as before. This peculiar semi-fluid 
and flexible consistency is one of their greatest pecul- 
iarities. 
When seen by transmitted light and in thin layers, THE BLOOD. 
149 
they are of a very pale amber color and nearly trans- 
parent. Nevertheless they contain all the red color of 
the blood; and when seen heaped together in layers 
only five or six deep, they show distinctly the ruddy 
color which belongs to them. Beside, if they are sep- 
arated by filtration or any other means, or if they are 
not formed in their natural quantity, the blood be- 
comes paler, exactly in proportion as its globules are 
deficient. 
They also communicate to the blood its opacity. Al- 
though each globule by itself is transparent, yet, when 
they are crowded together and mingled with the fluid 
parts of the blood, the whole becomes opaque and ap- 
parently impenetrable to light. This is because the 
globules of the blood and its fluid parts are of a differ- 
ent nature and composition. The same thing will hap- 
pen when oil is emulsioned by a watery alkaline solu- 
tion. The oil is transparent by itself, and the alkaline 
liquid is transparent by itself; but if you mix the two 
together, the whole becomes white and opaque like 
milk. So the globules of the blood and its fluid parts, 
mingled together, produce a thick red and opaque liq- 
uid. 
The red globules are the vivifying elements of the 
blood. They communicate to it its animating and 
stimulating properties, by which all the organs are 
maintained in a condition of vital activity. We shall 
understand their action more fully when we come to 
study the whole subject of respiration and circulation. 
We shall then see what is the precise function of these 
globules, and bow important an office they perform. 
Beside the red globules, the blood contains other 
little bodies of a different form and aspect. These are 150 
PHYSIOLOGY AND HYGIENE. 
the white globules. They are very much less numerous 
than the red, as there are not more than three or four 
of them for every thousand of the others. They are of 
a little larger size, measuring about -g-ga-g- of an inch in 
diameter, of a rounded form and a finely granulated 
texture. They are usually concealed, for the most part, 
in the greater abundance of the red globules. 
When the ingredients of the blood are examined by 
analysis, they are found to be mingled together in the 
following proportions: 
Composition of the Blood in 1000 parts. 
Water 795 
Globules 150 
Albumen 40 
Fibrine . 2 
Other animal matters 5 
Mineral substances 8 
1000 
69. Coagulation of the Blood.—Such are the proper- 
ties and constitution of the blood while circulating in 
the interior of the body. But if it be withdra wn from 
the vessels, a very remarkable change takes place, which 
alters its whole appearance. 
This change is its Coagulation. 
When a patient is bled from the arm, or is accident ■ 
ally wounded, the blood runs from the opened vein in a 
perfectly liquid stream; but soon afterward it begins to 
appear thicker than before, and will not run in drops, 
nor moisten the fingers so easily when touched. When 
this alteration has once commenced, it goes on rapidly 
increasing, the blood growing thicker amd thicker, until 
it finally sets into a uniform, firm, elastic, jelly-like mass. 
It is then said to be “ coagulated” or “ clotted.” This THE BLOOD. 
151 
change is usually complete in about twenty minutes 
after the blood has been withdrawn from the veins. 
Now this coagulation of the blood is entirely de- 
pendent upon its fibrine. This substance alone has the 
property of coagulating spontaneously. None of the 
other ingredients can solidify in this way, and if the 
fibrine be taken out, the blood loses altogether its 
power of coagulation. 
But how is it that the whole blood becomes clotted 
in a single mass, if this power belongs only to the 
fibrine ? 
It is because the fibrine, though in very small quanti- 
ty, as compared with the other substances in the blood, 
is diffused uniformly throughout the whole; and when 
it coagulates, therefore, on being withdrawn from the 
vessels, it entangles all the other ingredients with it, 
and holds them imprisoned in its own substance. The 
water of the blood, accordingly, the albumen, the glob- 
ules, etc., are all mechanically retained by the coagu- 
lating fibrine. 
But not long afterward a partial separation takes 
place between them. The fibrine solidifies still more; 
and, by contracting upon itself, squeezes out the liq- 
uid portions of the blood from between its meshes. 
Drops of a clear, amber-colored fluid begin to exude 
from its surface, and these drops, growing larger and 
larger, run together into little pools, which still in- 
crease in size until the entire surface is covered with 
the transparent liquid. The remainder grows at'the 
same time smaller and firmer, until at last the whole 
is permanently separated into two parts, a solid and a 
liquid. The solid part is called the Clot; the liquid 
part is the Serum. 152 
PHYSIOLOGY AND HYGIENE. 
If you examine, therefore, a cupful of blood at the end 
of twelve hours after it has been drawn from the veins, 
you will see that it is no longer a uniform mass, but ap- 
pears as a solid clot floating in the transparent serum. 
The clot, at this time, is still firm, red, and opaque, 
since it contains all the globules of the blood as well as 
the fibrine. For these globules can not escape from the 
clot, owing to their form and size, and are therefore re- 
tained by the meshes of the coagulated fibrine. The 
serum, on the other hand, is transparent, and nearly 
colorless. It contains all the albumen, the water, and 
other substances dissolved in them. 
70. Importance of Coagulation. — Now this coagula- 
tion of the blood is a property of the greatest impor- 
tance ; for it is the only thing which prevents our 
bleeding to death after the slightest incision or injury 
to the blood-vessels. Whenever these vessels are 
opened by an accidental cut in the skin or in the mus- 
cles, the blood at first flows with great freedom, ac- 
cording to the size of the wound. But if we press firm- 
ly upon the injured part with a bandage or with the 
fingers, and then, after a short time, remove the press- 
ure, we find that the bleeding has stopped altogether. 
This is because the thin layer of blood between the 
edges of the wounded vessels has coagulated and 
blocked up the opening. No matter how thin this 
layer may be, it still coagulates; for every particle of 
the blood, however small, contains its due proportion 
of fibrine, and consequently solidifies at the proper 
time. The clot thus formed adheres to the edges of 
the wounded parts, and so acts as a continuous band- 
age or plug, until the tissues have again grown togeth- 
er and become permanently united. THE BLOOD. 
153 
It is in this way that the bleeding from all ordinary 
wounds is usually arrested by nature. No matter how 
freely the blood may flow at first, if you keep the parts 
steadily compressed for twenty minutes or half an 
hour, the fibrine will then be coagulated and the bleed- 
ing will stop. 
But when the wound is very deep, or when any of the 
principal arteries have been severed, this means will not 
succeed; for the blood comes wdth so much force from 
these larger vessels that it can not be kept back by or- 
dinary pressure, and no time is allowed for its perma- 
nent coagulation. Then we must call for the assist- 
ance of the surgeon, who is often compelled to search 
for the blood-vessels in the deeper parts of the wound, 
and to tie up their open mouths with a fine cord or lig- 
ature. Why this operation is successful requires a far- 
ther explanation. 
VI. Coagulation in the Interior of the Body.—It is a 
curious fact that the blood will coagulate, not only 
when it is discharged externally, but also even in the 
interior of the body, whenever it is withdrawn from the 
ordinary course of the circulation. Thus, if we receive 
a bruise, and the little vessels beneath the skin are 
torn, the blood which flows from them coagulates in 
the neighborhood of the injury. Any internal bleed- 
ing produces, after a time, a clot in the corresponding 
situation where the blood is effused. After death, also, 
coagulation takes place in the cavities of the heart and 
in the great veins near it; and whenever any part of 
the body is so injured as to stop its circulation, the 
blood necessarily coagulates in its vessels. 
Accordingly, when the surgeon places a ligature upon 
a wounded vessel, he stops the circulation through it. 154 
PHYSIOLOGY AND HYGIENE. 
The blood is imprisoned in the neighborhood of the lig- 
ature, and soon afterwrard coagulates and blocks up the 
cavity of the vessel with its solidified fibrine. After a 
time the ligature separates and is thrown off, and the 
wounded parts unite" by the healing of the tissues. 
We see, therefore, that the coagulation of the blood is 
a property that belongs to the fibrine, and that it is spon- 
taneous. As soon as the fibrine is formed it possess- 
es this property, by which it is distinguished from all 
other substances. It is not manifested immediately, for 
it requires a certain time for its completion; but, owing 
to the very nature of the fibrine, wherever it may be, 
within a short period after it is shut off from the circu- 
lation it exhibits this peculiar character, and coagulates 
inevitably. 
Why, then, does it not coagulate in the vessels, and 
thus stop the circulation of the blood ? 
To understand this, we must remember that the his- 
tory of all the animal substances in the living body is 
one of incessant change. None of them remain the 
same, but all undergo successive transformations. The 
albuminose formed in digestion is no sooner taken up 
by the blood-vessels than it is converted into albumen. 
The oily matters absorbed with the chyle, and the sug- 
ar produced in the liver, are also rapidly decomposed, 
as we have seen, and disappear in the circulation. What 
is destroyed in this way for the purposes of nutrition is 
constantly replaced by a fresh quantity formed in the 
same organs. 
This is also true of the fibrine. That which is circu- 
lating in the blood-vessels to-day is not the same fibrine 
which was there yesterday, but a new supply, freshly 
produced in the process of daily nutrition. It is esti- THE BLOOD. 
155 
mated by physiologists that all the fibrine which exists 
in the blood is destroyed and reproduced at least three 
times over in the course of a single day. What the 
new substances are which are formed by its decomposi- 
tion is still unknown, for we can not yet follow out 
all the details of these changes which take place so rap- 
idly in the living body. But there is every reason to 
believe that the renovation of the fibrine in the blood 
takes place as constantly and rapidly as that of its oth- 
er ingredients. 
The blood, therefore, does not coagulate while the 
circulation is going on, because its fibrine is being in- 
cessantly altered and converted into new substances. 
It has been found that in certain of the internal organs, 
especially in the liver and kidneys, the fibrine disap- 
pears, and that little or none of it is contained in the 
blood returning from them. When we come to learn 
with what rapidity the circulation is carried on, we 
shall easily understand how coagulation may thus be 
prevented. But if the blood be withdrawn from the 
circulation altogether, or confined in any part by a lig- 
ature, then its fibrine can no longer go through with 
the natural changes of its decomposition, and it accord- 
ingly coagulates, as we have above described. 
/ 72. Quantity of the Blood. — The entire quantity of 
blood in the vessels is about one eighth part, by weight, 
of the whole body; so that in a man weighing 140 
pounds, the quantity of blood is very nearly 18 pounds. 
The quantity of blood, however, as well as its composi- 
tion, varies somewhat at different times. Soon after 
digestion it is considerably increased; for it has ab- 
sorbed all the nutritious materials taken with the food, 
and these materials must necessarily pass through the 156 
PHYSIOLOGY AND HYGIENE. 
blood in order to reach the tissues. After long absti- 
nence it is diminished in quantity to a corresponding 
degree. For the same reason, its composition varies to 
a certain extent, since its different ingredients will di- 
minish or increase, according as they have been dis- 
charged or absorbed in greater or less abundance. 
73. Effects produced by Loss of Blood.—Only a small 
proportion of the blood in the body can be lost without 
causing a serious effect upon the system. Generally 
speaking, the loss of one pound of blood causes faint- 
ness, and that of a pound and a half or two pounds is 
followed by complete unconsciousness. If the bleeding 
be then stopped, the patient usually recovers; but if a 
still larger quantity of blood be lost, recovery becomes 
impossible. 
When the strength, however, has been very much re- 
duced by excessive bleeding, it may sometimes be re- 
stored by injecting into the blood-vessels healthy blood 
from another person. This is called the “ Transfusion 
of the Blood.” In several instances where the vital 
powers were nearly exhausted, life has been restored by 
this operation. 
74. Two different kinds of Blood in the Body.—Finally, 
there is a most remarkable difference in the appearance 
of the blood in different parts of the body. In one half 
of the circulation, that is, in all those vessels which are 
called “ arteries,” it is of a brilliant scarlet hue; while 
in the “ veins” it is of a deep bluish-purple, almost black 
color. These two kinds of blood follow each other in 
the circulation, changing alternately from one color to 
the other; so that, although there is always red blood 
in the arteries, and always blue blood in the veins, yet 
the same blood is alternately scarlet and purple, as it QUESTIONS. 
157 
passes from one set of vessels into the other. This leads 
us, in the next place, to the subject of Respiration. 
QUESTIONS FOE CHAPTER VII. 
1. What fluid provides for the nourishment of the whole body? 
2. What is the physical appearance of the blood ? 
3. What are its ingredients ? 
4. What is the use of the water of the blood ? 
5. What is the proportion of water in the blood ? 
6. What are the most important mineral ingredients of the blood ? 
7. What are the properties of the albumen of the blood, and how 
does it differ from the white of egg ? 
8. What is the proportion of albumen in the blood ? 
9. What is its use ? 
10. What is the distinguishing peculiarity of jibrine ? 
11. What is the appearance of the blood globules ? their consistency? 
12. Does the color of the blood reside in the liquid parts, or in the 
blood globules ? 
13. What change takes place in the blood when it is withdrawn 
from the vessels ? 
14. Which of the ingredients of the blood causes its coagulation ? 
15. Describe the separation of the blood into clot and serum. 
16. What does the clot contain ? What does the serum contain ? 
17. How does the coagulation of the blood control bleeding ? 
18. What should be done to check the bleeding from a wound ot 
moderate size ? 
19. What must be done when a large artery is wounded ? 
20. Why does not the blood coagulate while circulating in the ves- 
sels ? 
21. How rapidly is the fibrine of the blood destroyed and repro- 
duced ? 
22. In which of the internal organs does it disappear ? 
23. Why does it coagulate when shut off from the circulation ? 
24. What is the quantity of blood contained in the whole body ? 
25. What effect is produced by an excessive loss of blood ? 
26. What is the operation of “ transfusion ?" 
27. What two different kinds of blood are there in the body? 158 
PHYSIOLOGY AND HYGIENE. 
CHAPTER Yin. 
The Oxygen of the Air—its Necessity to Life.—Nature of Respiration. 
—The Lungs—their Structures—Larynx.—Trachea.—Bronchial 
Tubes.—Lobules.—Air Vesicles. — Movement of Inspiration.— 
The Diaphragm—its Contraction.—Entrance of the Air.—Inter- 
costal Muscles.—Motion of the Ribs.—Movement of Expiration.— 
Elasticity of the Lungs.—Quantity of Air used in Respiration.— 
Movements of Respiration involuntary.—Effect of Respiration on 
the Blood.—Its Change of Color.—Venous Blood.—Arterial Blood. 
—Absorption of Oxygen in the Lungs.—Loss of Oxygen in the 
Tissues.—Carbonic Acid—where formed.—Discharged with the 
Breath.—Animal Vapor.—Watery Vapor.—Ventilation.—Ventila- 
tion by Doors and Windows—by Fires and Chimneys—by other 
Means.—Necessity for complete Ventilation. 
RESPIRATION. 
75. Oxygen.—In the air which surrounds us, pene- 
trating into the minutest crevices, and distributed ev- 
ery where over the surface of the globe, dissolved in 
the water, and diffused throughout the atmosphere, in- 
visible but omnipresent, there is a substance of singular 
activity, and endowed with a most prominent part in 
the operations of nature. It forms and destroys odor- 
iferous vapors, it corrodes the metals, it crumbles the 
texture of woody plants, it decomposes all dead and de- 
caying materials, and it devours the substance of burn- 
ing bodies. It is every where active, and every where 
ready to produce some new change in the materials of 
the inorganic world. This substance is Oxygen. 
Oxygen is equally important in the organic world. RESPIRATION. 
159 
No animal can live without it; and it is incessantly in 
operation, uniting with the tissues, and forming a mul- 
titude of internal combinations which are necessary to 
existence. Furthermore, the activity of life in differ- 
ent kinds of animals is in exact proportion to the in- 
tensity with which they receive the influence of oxy- 
gen. The more sluggish of them, such as worms, shell- 
fish, and reptiles, require but little of it, and will still 
survive when deprived of it for a short time. But the 
more perfect the organization of the animal, and the 
more active its temperament, the more constant and 
imperative is its demand for oxygen. In the quadru- 
peds, in the birds, and in the human species, where the 
circulation is rapid and the movements vigorous, and 
where all the functions of life are in active operation, 
this substance is the first and most indispensable req- 
uisite to existence. With them oxygen is a food which 
must be incessantly supplied, for if it be withheld for 
only a few minutes together life inevitably comes to 
an end. 
16. The Atmosphere and Respiration.—Now the great 
reservoir of oxygen, and the source from which it is 
constantly derived for our use, is the atmosphere. 
Oxygen does not exist, however, in the atmosphere 
by itself. On the contrary, it is mingled there with 
another substance which is more abundant than it, but 
which does not possess its active properties. This sub- 
stance is termed “Nitrogen.” The quantities of the two 
are in such proportion that there is one part of oxygen 
to about four parts of nitrogen. The atmosphere, there- 
fore, is a mixture of these two gases, in which the oxy- 
gen, which is active and powerful, is diluted with the 
nitrogen, which is mild and inert. PHYSIOLOGY AND HYGIENE. 
Consequently we depend directly upon the atmos- 
phere for the maintenance of life. If it be withdrawn 
or shut out from us in any way, we die within a short 
time, because we are deprived of the oxygen which is 
essential to our existence. 
The manner in which the air serves to support life is 
by penetrating into the interior of the body, into cer- 
tain organs which are adapted for its reception. These 
organs are called the “ Lungs.” The air is drawn into 
them with the breath, and immediately after exhaled 
again, to give place to a fresh supply. This action, by 
which the air is introduced into the lungs, and there 
used for the maintenance of life, is the process of 
Respiration. 
Let us see, first, how it is that the movements of 
respiration are accomplished; and, secondly, what are 
the changes thus produced in the interior of the body. 
77. The Organs of Respiration.—The lungs are two 
large and exceedingly vascular organs, situated in the 
cavity of the chest, one on each side, and extending 
from about the level of the collar-bone to just below 
the region of the heart. They are “spongy” in their 
texture—that is, they are filled every where with little 
cavities, imperfectly separated from each other by slen- 
der partitions, like the tissue of a sponge. Each one 
of these cavities is filled with air; and so minute are 
they, and so closely packed together, that the whole 
substance of the lung is thus filled with small air-bub- 
bles, disseminated every where through its tissue. If 
you take a piece of the lung, therefore, such as that 
of an ox or a sheep, and press it between the fingers, 
you will perceive a fine crackling sensation, owing to 
the partial dislodgment of these minute bubbles of air. RESPIRATION. 
161 
For the same reason, the tissue of the lung, unlike 
that of any of the other organs, will float in water. 
The substance of other organs, being solid and heav- 
ier than wrnter, sinks at once to the bottom; but that 
of the lungs, every where infiltrated with air, is buoyed 
up by it, and floats lightly upon the surface. 
These minute cavities, containing the air-bubbles just 
described, are called the “ air vesicles” of the lungs. 
Now the air which is thus disseminated through the 
lung has been derived from the external atmosphere. 
For the cavities of the lungs communicate with the ex- 
terior through certain channels or air passages, called 
respectively the Larynx, the Trachea, and the Bron- 
chial Tubes. 
The larynx is a firm cartilaginous box or framework, 
situated directly at the front of the upper part of the 
neck, where it forms an angular prominence which is 
easily felt by the fingers. Internally the larynx is hol- 
low, and communicates with the back part of the throat 
by a narrow chink or crevice, which is termed the 
“ glottis.” Through this chink the air passes from the 
nostrils and back part of the throat into the larynx. 
From the larynx it passes downward into the trachea. 
This is a straight rounded tube, about an inch in di- 
ameter, which runs from the lower end of the larynx 
directly downward along the middle of the neck to the 
upper part of the chest. It is formed of membranous 
walls; but these are held apart, so as to secure a free 
passage for the air, by a series of elastic cartilaginous 
rings imbedded in their substance. 
As the trachea enters the cavity of the chest it di- 
vides, right and left, into two tubes or “ bronchi,” one 
of which goes to each lung. Arrived at the lungs, the PHYSIOLOGY AND HYGIENE. 
bronchi themselves break up into smaller divisions, 
which are the “ bronchial tubesand these tubes con- 
tinue to separate into still smaller branches and ramifi- 
cations. Each ramification of the bronchial tubes term- 
inates at last in an oval sac or bag, separated in its in- 
terior into various divisions or compartments, into which 
the air penetrates from the end of the bronchial tube. 
Fig. 32. 
Human Larynx, Trachea, Bronchi, and Lungs; showing the ramifi- 
cation of the bronchi, and the division of the lungs into lobules. 
These oval-shaped sacs are called the “ lobules” of the 
lung, and, united together, make up its entire substance 
(Fig. 32). RESPIRATION. 
163 
Finally, each lobule is itself 
composed of a group of small 
rounded cavities, called the “ air 
vesicles,” formed by the divis- 
ions or partitions which project 
from the inner surface of the 
lobule. Thus all the air vesicles 
contained in a lobule communi- 
cate with the central cavity of 
the lobule itself, and through it 
with the end of the bronchial 
tube (Fig. 33). 
Now these divisions and ram- 
ifications of the interior of the 
lung produce a very large ex- 
tent of surface, over which the air comes in contact 
with its tissue. Each air vesicle is only about of an 
inch in diameter; and we can easily understand, there- 
fore, how many of them may be contained in an or- 
gan of the size of the lung. But each one of these air 
vesicles is in contact with the air over its whole inter- 
nal surface, and all these surfaces combined must be 
very extensive. It is estimated by anatomists that the 
whole internal surface of the lungs, if spread out, would 
be many times greater than the whole external surface 
of the skin. 
Fig. 33. 
Lobule of Human Lung.—a. Ul- 
timate bronchial tube; 6. Cav- 
ity of lobule; c,c,c,c. Air ves- 
icles. 
No doubt this is true. The page of an ordinary book, 
of the octavo form, represents about one third of a 
square foot. Such a book, one inch thick, will contain 
at least 400 pages, and will accordingly represent, alto- 
gether, a surface of 133 square feet. If you take out of 
the book every alternate leaf, so as to leave a layer of 
air of the same thickness between all the rest, there 164 
will still be remaining, in contact with the air, a com- 
bined surface of square feet, which is very nearly 
four times the whole external surface of the human 
body. 
The tissue of the lung, however, is much more deli- 
cate and complicated than the pages of a book, and is 
capable of much greater extension within the limits of 
the same space. 
Thus the air passes from without through the larynx, 
trachea, and bronchi; and, following the successive di- 
visions of the bronchial tubes, arrives at last in the 
cavities of the lobules and air vesicles. It thus pene- 
trates throughout the tissue of the lung, and is dissemi- 
nated over the immense extent of its internal surface. 
PHYSIOLOGY AND HYGIENE. 
78. Movements of Respiration.—But what is the mech- 
anism of respiration, and how is the air constantly re- 
newed in the interior of the chest ? 
It is by a double movement, by which the air is alter- 
nately drawn into the lungs and again expelled from 
them. These two acts are called the movements of In- 
spiration and the movements of Expiration. 
First, the movements of Inspiration. 
The lungs, as we have seen, are inclosed in the cavity 
of the chest, and communicate with the exterior only 
through the bronchial tubes and the trachea. Now the 
chest is separated from the abdomen by a strong mus- 
cular floor or partition, which is attached to the edges 
of the lower ribs in front and at the sides, and to the 
spinal column behind. This partition is the Diaphragm. 
It has an arched or vaulted form, so that its middle 
portion is higher than its edges, and projects upward 
like a dome into the chest. Above this arched portion, 
in the chest, are placed the lungs; beneath it, in the RESPIRATION. 
165 
abdomen, are the stomach and liver. When the dia- 
phragm is at rest, these organs remain undisturbed in 
their position. 
But the diaphragm is a muscle. Its fibres radiate 
every where from its central portion outward and down- 
ward, to be inserted into the firm edges of the ribs 
and the spinal column. When they contract, therefore, 
they draw the central part of the diaphragm down- 
ward, and the arched floor of the chest descends toward 
the abdomen. In its descent the diaphragm pushes be- 
fore it the liver and the stomach; and at the same time 
the lungs follow its movement from above, and expand 
with the air which flows into them through the trachea. 
This is the movement of inspiration. 
Accordingly, at the time of inspiration, we can feel 
that the abdomen protrudes, while the air passes in by 
the mouth and nostrils. 
Now the air is drawn into the lungs at this time by 
the force of suction. It is not a violent action, how- 
ever, but is accomplished by a gentle and easy move- 
ment, owing to the elasticity of the atmosphere, Avhich 
enables it to penetrate every where where there is a 
space open to receive it. A little explanation will 
make this evident. 
If you move a book from one end of a table to the 
other, it displaces the air from the spot in which it is 
deposited; but, on the other hand, the air at the same 
time occupies the space which the book has left. If 
you walk a few steps in any direction, the air, displaced 
by the movements of the body, fills at once the spot 
left vacant by the body itself. The air is so movable 
and elastic that, so long as suflicient space is allowed 
it, it takes indifferently either position. 166 
In the same way, if you take an empty syringe, hold- 
ing it upright, with the nozzle pointing upward, and 
then draw down the handle of the piston, as the piston 
descends the air follows it from above, entering through 
the nozzle into the interior of the syringe, just as it 
passes into the lungs through the the 
descent of the diaphragm. 
PHYSIOLOGY AND HYGIENE. 
But, in order that this may happen, a space must be 
open for the air to move freely, both inside and outside 
the cavity which is to be filled; for if this space be not 
open to it, its resistance will be re-enforced by the press- 
ure and elasticity of the entire atmosphere. When the 
lungs are full, close the mouth and nostrils firmly with 
one hand, and then try to compress the chest by the 
strength of the muscles. You can not; because the 
air within the chest has no exit, and resists, therefore, 
with the whole force of its elastic pressure. When the 
lungs are empty, on the other hand, close the mouth 
and nostrils as before, and endeavor to expand the 
chest. You can not; for the air outside the chest is 
unable to find an entrance, and resists with a pressure 
which is greater than the entire force of the muscles. 
But when there is no obstacle to the free movement 
of the air, no resistance is offered by its pressure. The 
muscles have only to overcome the weight and elastic- 
ity of the organs set in motion, and the air then follows 
the movements of the diaphragm as gently and easily 
as a door swings upon its hinges. 
The action of the diaphragm in inspiration is aid- 
ed, at the same time, by the movements of the ribs. 
The ribs are of a curved form, and encircle the chest 
with a kind of bony cuirass or framework (Figure 34). 
They slant outward and downward, and overlap each RESPIRATION. 
167 
other from above down- 
ward, somewhat like the 
shingles on the roof of a 
house; only the adjacent 
ribs do not touch each oth- 
er, but are separated by a 
narrow space which is fill- 
ed by so many intervening 
muscles. These muscles, 
being situated between the 
ribs, are called the “ inter- 
costal muscles.” They 
contract at the same time 
with the diaphragm, and, 
by shortening their fibres, 
they lift the ribs and ex- 
pand the cavity of the 
chest from side to side. 
Thus during the act of 
respiration we can feel the chest rise and fall, as the 
air moves inward and outward through the passage of 
the lungs (Fig. 35). 
The movement of Inspiration is immediately follow- 
ed by the movement of Expiration. 
As soon as the lungs are filled with air by the ac- 
tion of the intercostal muscles and the diaphragm, 
these muscles are relaxed, and the air is again expelled 
through the same channels by which it entered. 
This is accomplished- principally by the elastic reac- 
tion of the lungs. For throughout the tissue of these 
organs there are disseminated a great number of mi- 
nute fibres, which have the property of elasticity in a 
high degree, and which therefore communicate this 
Fig. 34. 
Part of the Spinal Column, with the 
ribs attached, inclosing the cavity of 
the chest. 168 
PHYSIOLOGY AND HYGIENE, 
Fig. 35. 
A. Figure with the chest collapsed; B. Figure with the chest expanded; 
c. Cavity of the chest; d. Diaphragm. 
property to the lungs themselves. The air vesicles 
and lobules are in this respect like so many little Indiar 
rubber bags; and after being filled with air they react 
upon it at the moment of expiration, and exj>el it by 
their own elasticity. 
Beside this, the walls of the abdomen, pushed for- 
ward by the descent of the diaphragm, return to their 
places when this muscle is relaxed, and the liver and 
the stomach rise again to their former situations. RESPIRATION. 
169 
Thus the movement of inspiration is an active move- 
ment, produced by the contraction of the diaphragm 
and the intercostal muscles; that of expiration is a 
passive movement, caused by the elastic reaction of 
the lungs and the walls of the abdomen. These two 
movements follow each other alternately, with the suc- 
cessive contraction and relaxation of the respiratory 
muscles. 
The movements of respiration are performed slowly 
but constantly. Under ordinary circumstances, a man 
breathes naturally about twenty times per minute. 
These motions are increased in frequency by any mus- 
cular exertion, but afterward return to their former 
regularity. 
79. Quantity of Air used in Respiration.—At every 
respiration twenty cubic inches of air (-£ of a pint) are 
taken into the lungs. If we count the entire number of 
respirations in a day, including those caused by mus- 
cular exertion, this will give about 600,000 cubic 
inches, or 350 cubic feet of air which passes and re- 
passes through the lungs in every twenty-four hours. 
This is nearly eighty times the bulk of the whole 
body. 
4 80. Character of the Respiratory Movements. — The 
movements of respiration are involuntary. The dia- 
phragm descends and the chest expands without any 
exertion of the will, and even without our knowledge. 
From the instant of our birth to the last moment of 
existence, during the activity of our waking hours and 
in the unconsciousness of sleep, they continue in untir- 
ing and ceaseless operation. For the necessity of respi- 
ration is not occasional, but incessant; and the perform- 
ance of this function, therefore, is not confided to the 170 
PHYSIOLOGY AND HYGIENE. 
will, but is provided for by an involuntary action, which 
requires no attention and produces no fatigue. 
It is true that we can exercise a partial control over 
the movements of respiration; that is, we can hasten 
or retard them at will. But this is only for a very 
short time. If we try to breathe much more rapidly 
than is natural, say one hundred times a minute, we 
shall soon find how laborious and exhausting the move- 
ments become. On the other hand, if we stop respira- 
tion altogether, we at once feel an internal impulse 
which calls for its renewal, and which grows rapidly 
stronger and more imperative, until it becomes at last 
irresistible. There are few persons who can voluntari- 
ly suspend the breath for more than thirty or forty 
seconds at a time. 
Such is the manner in which the movements of respi- 
ration are performed. Now let us see what happens 
while the air is thus taken into the cavity of the chest. 
81. Change in the Air during Respiration.—In the first 
place, as the air penetrates into the lungs it is robbed 
of its oxygen. This substance disappears, so that the 
air which has once been drawn into the chest, and again 
expelled with the breath, no longer contains it in due 
proportion. 
What has become of the oxygen which thus disap- 
pears from the air in respiration ? 
It is absorbed by the blood. For the blood-vessels 
coming to the lungs are distributed every where in the 
minute spaces between the air vesicles, and envelop 
their walls with an abundant vascular network. If we 
recollect the great extent of surface represented by the 
tissue of the lungs, we shall see that the blood circulat- 
ing in their vessels is spread out over a corresponding RESPIRATION. 
171 
surface; and that, in a thousand minute currents, it 
moves through the lungs almost in contact with the 
air contained in the vesicles. It is as if the blood were 
sprinkled through the air in a fine shower; so that ev- 
ery particle of the blood and every particle of the air are 
brought into the closest proximity. At this moment 
the oxygen leaves the air and enters the blood over the 
whole internal surface of the pulmonary tissue. 
82. Change in the Blood during Respiration.—At the 
same time a most remarkable change takes place in the 
blood itself. 
The blood which is distributed to the lungs is venous 
blood. It is that which has already circulated through 
the organs and tissues of the body, and has served for 
their nutrition. From them it is collected by the veins, 
brought back to the heart, and from the heart distribu- 
ted to the lungs. At this time it is of a dark blue or 
purple color, approaching to black. 
Now, as this venous blood enters the lungs and takes 
possession of the oxygen contained in the air vesicles, 
it changes from a dark blue to a brilliant scarlet color. 
This change is instantaneous and complete; so that the 
blood, as it leaves the lungs on one side, is entirely dif- 
ferent in appearance from that which is entering them 
on the other (Fig. 36). 
After the blood has passed through the lungs and 
has changed its color from blue to red, it returns to the 
heart, and is again distributed throughout the body by 
another set of vessels, which are called the “ arteries.” 
Accordingly, there are always two kinds of blood in 
the general circulation, of different colors and occupy- 
ing two different sets of vessels. The blood in the veins 
is blue, and is called Venous blood; that in the arteries 172 
PHYSIOLOGY AND HYGIENE. 
Fig. 36. 
Cumulation through the Lungs.—a, b. .Right side of heart, containing venous 
blood; g, f. Left side of heart, containing arterial blood; c. Blood-vessel 
conveying the blood to the lungs; e. Blood-vessel bringing it back from 
the lungs; d. Blood-vessels distributed in the lungs; h. Great artery going 
off from the heart. 
is red, and is called Arterial blood. The blood is also 
constantly changed from venous to arterial while pass- 
ing through the vessels of the lungs. 
It is for this reason that the lij)s turn purple and the 
face assumes a dark ashen color w'henever the breath- 
ing is sei’iously obstructed. For the blood, no longer 
becoming arterialized, retains its venous hue and com- 
municates a dark color to all the transparent and vas- 
cular tissues. 
But the change in color is not the only difference be- 
tween these two kinds of blood. The venous blood, 
which has already circulated through the body, has 
lost its vital properties. It has expended a part of its 
substance in the nourishment of the tissues, and is no 
longer fit for the maintenance of life. RESPIRATION. 
173 
What is it that the blood has thus lost in passing 
through the tissues which is necessary to its vitality ? 
It is its oxygen. 
For the arterial blood, as it passes out from the heart 
to be distributed throughout the body, carries with it 
the oxygen which it has absorbed in the lungs. It ar 
rives at the tissues charged with this vivifying princi 
pie, and the tissues immediately seize upon it and ap- 
propriate it to themselves. Thus the blood, as it passes 
through the circulation, gives up its oxygen and returns 
to the venous condition. There is, therefore, a double 
change going on incessantly in the blood in the differ- 
ent parts of the body. In the tissues it loses oxygen, 
and changes from red to blue; in the lungs it absorbs 
oxygen, and changes from blue to red. 
83. Action of the Blood Globules in Respiration.—Now 
the ingredients of the blood which are most active in 
producing this change are the Blood globules. It is 
these little bodies which take the oxygen from the air, 
and fix it in their own substance for the renovation of 
the blood. They are the carriers, which load them- 
selves with oxygen in the lungs, to transport it after- 
ward to distant parts in the current of the circulation. 
As all the color of the blood resides in them, we easily 
see why this color should change with the changing 
constitution of the globules themselves. 
It is by the process of respiration, accordingly, that 
the blood is kept constantly renovated and restored to 
the arterial condition. 
84. Quantity of Oxygen Consumed.—The importance 
of oxygen to the living body is shown by the quantity 
which is consumed. At every inspiration one cubic 
inch of oxygen is withdrawn from the air and absorbed 174 
PHYSIOLOGY AND HYGIENE. 
by the blood. This amounts in the course of an entire 
day to about 17£ cubic feet, or by weight a little over 
one pound. 
85. Evolution of Carbonic Acid. — But, at the same 
time that oxygen is absorbed from the air in respira- 
tion, another substance makes its appearance in the 
lungs, and is expelled with the breath. This is Car- 
bonic acid. It is a gas, like oxygen, but differing from 
it in its properties. It is the same gas which is formed 
in the fermentation of bread, wine, beer, and all sub- 
stances containing sugar. It is produced from burning 
coal and candles, and many other combustible bodies. 
It is sometimes exhaled from the surface of marshy 
pools, and often collects at the bottom of old wells. It 
is not fit for respiration; and when a man is accidental- 
ly caught in an atmosphere composed of carbonic acid, 
as sometimes happens in cleaning beer-vats or in repair- 
ing old wells, he at once becomes insensible, and soon 
dies by suffocation. 
This gas, as we have said, is found in the breath. No 
less than one twenty-fifth part of the air passing out of 
the lungs consists of carbonic acid. This is immediate- 
ly diffused through the atmosphere, or carried away by 
it‘s movements; and the fresh air then taken into the 
lungs is again loaded with carbonic acid and expelled 
in its turn. This process goes on with every successive 
respiration; so that in the course of an entire day the 
amount of this gas discharged with the breath is near- 
ly 15£ cubic feet, or by weight about one pound and a 
half. 
Now the carbonic acid so produced is formed in the 
tissues. It is absorbed from them by the blood, carried 
by the blood to the lungs, there exhaled into the pul- RESPIRATION. 
175 
monary vesicles, and finally discharged with the breath. 
It is a useless and exhausted material which the tissues 
have rejected, and which is therefore expelled from the 
body in the process of respiration. 
86. Exhalation of Water and Animal Vapors with the 
Breath.—Beside carbonic acid, the breath also contains 
a peculiar animal vapor, which is produced in the inte- 
rior of the body. Though this vapor is in very small 
quantity, it is sufficient to give to the breath a faint 
but perceptible odor. There is also some water dis- 
charged from the lungs in a gaseous form. The breath 
therefore is damp; and if we breathe upon a mirror, its 
polished surface becomes dimmed from the deposit of 
the watery parts of the expired air. In warm weather 
the moisture thus exhaled with the breath is imper- 
ceptible, because it is perfectly gaseous and transpar- 
ent ; but if the outer air be cold it is immediately con- 
densed and becomes visible. Thus, on a winter’s day, 
when the temperature of the air is low, the breath may 
be seen as a white cloudy vapor, issuing from the mouth 
and nostrils and diffusing itself in the atmosphere. 
87. Necessity for Fresh. Air and Ventilation.—From 
all that has been said, we see that the first and most in- 
dispensable requisite of health, and even of existence, 
is a constant supply of fresh air. Nature has provi- 
ded for this, so far as the mechanism of the body is 
concerned, by the unceasing play of the movements of 
respiration, by which the air within the chest is renew- 
ed with every breath. If the air were not thus re- 
newed, it would at once become altered and contami- 
nated, and consequently incapable of supporting life. 
The same thing, of course, would take place outside 
the chest. If we remain shut up in a close apartment, 176 
PHYSIOLOGY AND HYGIENE. 
breathing the same air over and over again, with every 
respiration it loses a part of its oxygen and becomes 
contaminated with carbonic acid. As we know how 
much oxygen is consumed with each respiration, we can 
easily calculate how long it will be before the whole of 
it in the atmosphere will be exhausted. At the same 
time the carbonic acid continues to accumulate, and 
thus the air confined in the apartment is constantly 
degenerating, until it becomes totally unfit to support 
respiration. 
We must therefore renew the air in our houses and 
apartments, as carefully and thoroughly as it is renew- 
ed in the lungs by the movements of respiration. 
The method by which this is accomplished is called 
Ventilation. 
The ventilation of an apartment or of a house con- 
sists, like the respiratory movements, of a double pro- 
cess, viz., the introduction of fresh air from without, and 
the discharge of the contaminated air from within. It 
is effected by means of doors, windows, and chimneys. 
In order that ventilation may he effectual, every 
apartment should have doors or windows upon two op- 
posite sides, in order that the frgsh air may pass com- 
pletely through it, and thus remove every vestige of 
foul atmosphere. In the warm summer weather, and 
in ordinary apartments, this is nearly always sufficient, 
since both doors and windows are usually opened often 
enough to secure an abundant supply of air. But in 
winter, when the doors and windows are closed for a 
great part of the time to exclude the cold, other means 
are necessary. Ventilation is then aided by means of 
fires and chimneys. 
Chimneys produce ventilation in this way. The air, heated by the burning fuel in the fire-place, rises in the 
chimney, and the chimney itself becomes warmer than 
the rest of the building. A permanent current of 
heated air is thus established, which constantly rises 
through the chimney and is discharged from its upper 
extremity. This is the “ draft” of the chimney. The 
hotter the fire, the more rapid and powerful is the draft, 
and the more complete the ventilation. For fresh air 
at the same time finds its way into the apartment 
through all the minute openings and crevices of the 
doors and windows. We can not seal up these open- 
ings sufficiently to exclude the air, so long as a heated 
current is constantly driven upward through the fire- 
place and the chimney. 
RESPIRATION. 
A fire, burning in an open fire-place, is therefore the 
best and most effectual means of ventilation. Other 
methods of warming an apartment, such as close stoves, 
or iron pipes filled with hot water or steam, have no 
such good effect, for they produce no current. The at- 
mosphere is warmed by them, but it does not move; 
and the air consequently remains in the apartment, im- 
perfectly renewed and consequently vitiated by respi- 
ration. Such contrivances frequently economize fuel, 
but they economize it at the expense of something 
which is much more valuable, viz., the air and its oxy- 
gen, which are necessary to life. 
But, beside this, in every inhabited dwelling-house, 
ventilation should be further secured by free opening 
of the doors and windows, and liberal admission of the 
external air at least once every day. For in every such 
house there are other sources of contamination for the 
atmosphere beside respiration. The preparation of the 
food by cooking, the cleansing of the apartments, and 178 
PHYSIOLOGY AND HYGIENE. 
the unavoidable daily accumulation of refuse of various 
kinds, produce emanations which are harmless when 
fresh, but which become offensive and injurious if al- 
lowed to remain and stagnate. We may be sure that 
no atmosphere is wholesome where any of'these stagna- 
ting odors are perceptible. A house should therefore be 
swept throughout, each day, by a current of fresh air 
sufficient to maintain the cleanliness and salubrity of 
its atmosphere. 
Still farther means are requisite in apartments where 
large numbers of persons are collected together; as in 
school-rooms, lecture-rooms, theatres, and manufacto- 
ries. Here the contamination of the atmosphere is 
more rapid, being in proportion to the number of per- 
sons present. For the respiration of ten men will ex- 
haust the atmosphere ten times as rapidly as that of 
one; and the quantity of air which would last a single 
person for five hours, in an audience of three hundred 
would be consumed in exactly one minute. The means 
of ventilation in these cases, accordingly, must be very 
much greater, in proportion to the size of the apart- 
ment, than in those used for ordinary habitation. Large 
openings are usually made in the walls or ceiling, lead- 
ing into flues or passages which rise to the roof. These 
flues should be conducted alongside the chimneys, in 
the walls of the building; so that, being warmed by 
their contact, they may serve as so many additional 
chimneys to carry off the vitiated air of the apartment. 
In addition to this, a rotary fan, driven by machinery, 
is often employed to secure a constant supply of fresh 
air from without. 
Whatever means of ventilation are employed, we 
may judge of their success by a very simple criterion. RESPIRATION. 
179 
After the apartment has been occupied for an hour, its 
atmosphere sh ould be as pure as it was at first. Any 
ventilation which is less than this is insufficient; for 
every impurity which has collected in the air must 
necessarily be breathed by the occupants, and accord- 
ingly must vitiate their respiration to a corresponding 
degree. 
The function of respiration, as we have seen, is a 
double process of absorption* and discharge. It sup- 
plies incessantly to the body the oxygen which is nec- 
essary to life, and expels front it at the same time the 
carbonic acid produced in its tissues. It is by this pro- 
cess that the arterial blood is constantly renewed, and 
enabled to perform its natural office in the circulation. 
1. What natural substance is the most indispensable to life? 
2. From wh$t source is oxygen most abundantly obtained ? 
3. What other substance does the atmosphere contain beside oxy- 
gen? 
4. Which of these two gases is most abundant in the atmosphere, 
oxygen or nitrogen ? 
5. Which of them is the active ingredient, and which is compara- 
tively inert ? 
6. Why is it fatal to an animal to deprive it of atmospheric air ? 
7. What is the function of respiration ? 
8. What are the organs of respiration ? 
9. What is the structure of the lungs ? 
10. What is contained in the minute cavities of the lungs ? 
11. Through what passages is the air introduced into the lungs ? 
12. What is the larynx, and where is it situated ? 
13. What is the narrow opening called through which the air pass- 
es into the larynx ? 
14. What is the form and structure of the trachea ? 
15. What is the use of the cartilaginous rings of the trachea? 
16. What are the bronchi ? the bronchial tubes ? the lobules ? and 
the air vesicles of the lungs ? 
QUESTIONS FOR CHAPTER VIII. 180 
PHYSIOLOGY AND HYGIENE. 
17. What is the object of the division and multiplication of the 
bronchial tubes and air vesicles ? 
18. What are the two movements by which the air is drawn into 
and expelled from the lungs ? 
19. What muscle forms the floor of the chest ? 
20. What is the form of the diaphragm ? 
21. When the diaphragm contracts, how is its form altered ? 
22. What effect does this have upon the lungs ? what upon the or- 
gans of the abdomen ? 
23. By what force is the air drawn into the lungs when the dia- 
phragm descends? * 
24. Is this a violent or a gentle action ? 
25. How do the ribs move at the time of inspiration ? 
26. What muscles serve to lift the ribs in inspiration ? 
27. What follows when the movement of inspiration comes to an 
end? 
28. By what force is the air expelled from the cavity of the lungs ? 
29. Which of the movements of respiration is an active, and which 
a passive movement ? 
30. How many respirations are usually performed per minute ? 
31. By what are the movements of respiration accelerated ? 
32. How much air is introduced and expelled at each respira- 
tion? 
33. What is the average quantity of air used in twenty-four hours ? 
34. Are the movements of respiration voluntary or involuntary ? 
35. What substance disappears from the air in respiration ? 
36. What becomes of the oxygen which disappears in the lungs ? 
37. What effect does this have upon the color of the blood ? 
38. What is venous blood ? and what is arterial blood ? 
39. Why do the lips turn purple when respiration is obstructed ? 
40. What change takes place in the blood while circulating through 
the tissues ? what is the function of the blood globules ? 
41. How much oxygen is consumed by respiration in twenty-four 
hours ? 
42. What substance is exhaled from the lungs in respiration ? 
43. From what other sources is carbonic acid produced ? 
44. Is carbonic acid capable of sustaining life ? 
45. What proportion of carbonic acid is contained in the breath at 
each expiration? 
46. How much is discharged from the body in twenty-four hours ? QUESTIONS. 
181 
47. Where does the carbonic acid come from which is exhaled with 
the breath ? 
48. What other substances are exhaled with the breath beside car- 
bonic acid ? 
49. What gives the breath its odor ? 
60. What makes it cloudy upon a cold day ? 
51. What effect is produced upon the air by continued respiration 
in a confined space ? 
52. What is ventilation ? 
53. What is the most effectual means of ventilation ? 
54. Why are close stoves, hot water, or steam-pipes bad means for 
warming an apartment ? 
55. Why should a house be also ventilated every day by opening 
the doors and windows ? 
56. Why should the means of ventilation be increased in school- 
rooms, lecture-rooms, etc. ? 
57. What is the necessary rule or criterion for sufficient ventilation ? 182 
PHYSIOLOGY AND HYGIENE. 
CHAPTER IX. 
THE CIRCULATION. 
The Organs of Circulation. — The Heart—its Muscular Fibres.— 
Auricles.—Ventricles.—Pulmonary Artery. —Aorta.—Movement 
of the Blood through the Heart.—Contraction of the Heart—its 
Relaxation.—Valves of the Heart.—Ventricular Valves.—Semilu- 
nar Valves.—Action of the Heart involuntary.—The Arteries.— 
Arch of the Aorta.—Distribution of the Arteries—their Elasticity. 
—The Pulse—how felt.—Rapidity of the Pulse.—Pressure on the 
Blood in the Arteries.—The Capillaries.—Capillary Network.— 
Circulation of the Blood in the Capillaries. — The Veins—their 
Valves.—Movement of the Blood in the Veins.—Obstruction of the 
Circulation by compressing the Veins.—Rapidity of the Circula- 
tion.—Its local Variations. 
88. Circulation of the Blood.—The blood, enriched by 
the products of digestion, and arterialized by the influ- 
ence of the air, is the medium through which the nour- 
ishment of the whole body is accomplished. It is des- 
tined to visit every part of the system, and to supply 
the necessary materials of life, which it carries with it 
in the current of the circulation. By the circulation, 
accordingly, we mean that continuous round or circuit 
of the blood by which it passes from the heart outward 
for the nutrition of the tissues, and from the tissues 
back again to the heart, to be renewed by respiration 
in the lungs. 
The organs of the circulation are, first, the Heart, 
and, secondly, the Blood-vessels. The blood-vessels are 
the tubes which convey the blood in its movement 183 
throughout the body; the heart is the organ which im- 
pels it onward in its course. 
THE CIRCULATION. 
89. The Heart.— The heart is a muscle. Like the 
stomach, it is a hollow organ with two openings, one 
of entrance and one of exit, and provided with muscu- 
lar walls, so that its contractions force every thing 
which enters it at one extremity to pass outward by 
the other. Only, in the heart these muscular layers are 
exceedingly abundant and powerful, and its contrac- 
tions accordingly are rapid and energetic. While, 
therefore, the food during digestion passes but slowly 
and gradually through the stomach, the blood is pro- 
pelled by the contractions of the heart in a forcible and 
impetuous stream. 
The heart is situated in the middle of the chest, be- 
tween the two lungs, and almost directly behind the 
breast-bone. It is a little larger than the clenched fist. 
It is somewhat conical in form, being wide at its upper 
part, and narrower and rather pointed below. The up- 
per and wider portion of the heart is placed exactly in 
the middle of the chest, but its lower part is turned 
obliquely to the left. If we place the fingers in the 
space between the fifth and sixth ribs, a little to the 
left of the breast-bone, we can feel the point of the heart 
at each muscular contraction striking the side of the 
chest from within. 
The heart consists of four different cavities, two on 
each side, called respectively the Auricles and the Ven- 
tricles. In each case the “ auricle” receives the blood 
coming into the heart by the veins, and the “ ventricle” 
drives it out by the other extremity into the arteries. 
As this is done at the same time on both sides of the 
organ, right and left, there are accordingly, first, a 184 
PHYSIOLOGY AND HYGIENE. 
“ right auricle” and a “ left auricle;” and, secondly, a, 
“ right ventricle” and a “ left ventricle.” We shall be- 
gin by describing the auricle and ventricle of the right 
side. 
The right auricle is the receptacle of all the venous 
blood returning from the body. This blood is collected 
from the different veins into two great venous trunks, 
which meet on the right side of the heart and open into 
the cavity of the auricle. The auricle itself is a kind 
of muscular bag which receives the blood through this 
opening of the veins, and then urges it onward through 
another rounded opening, situated near by. This sec- 
ond orifice leads into the ventricle; and because it 
forms the entrance into this cavity, it is known by the 
name of the “ ventricular orifice.” 
The ventricle is much larger than the auricle, and its 
muscular walls are thicker and stronger. As it con- 
tracts, it sends the blood through an opening at its far- 
ther extremity into a large artery, which is called the 
“pulmonary artery.” This artery leads to the lungs. 
As it reaches the lungs it divides into numberless 
branches and ramifications, which penetrate, as we have 
said, into all the minute spaces between and around the 
air vesicles. It is while passing through these channels 
that the blood is arterialized by the influence of the air. 
The bright red arterial blood is then collected from the 
lungs and returned to the heart by corresponding veins, 
called the “ pulmonary veins,” which open into the left 
auricle. 
The left auricle is similar in its structure to the right 
auricle. It opens by a corresponding orifice into the 
left ventricle. 
The left ventricle is by far the thickest and strongest THE CIRCULATION. 
185 
portion of the heart. Its muscular walls are three quar- 
ters of an inch in thickness; and they require this ad- 
ditional force, for they are intended to propel the blood, 
by their muscular contractions, all over the body. The 
left ventricle opens by its farther extremity into the 
commencement of a large and strong artery, which re- 
ceives all the blood coming from its cavity. This ar- 
tery is termed the Aorta. From the heart it rises up- 
ward for a short distance, and then, curving over in an 
arched form, it passes downward through the chest and 
abdomen, sending off, right and left, all the branches 
which distribute its blood to the different regions of 
the body. 
In Fig. 37 the two sides of the heart are shown, to- 
gether with the course of the blood, from the right cav- 
ities through the pulmonary artery to the lungs, thence 
by the pulmonary vein to the left auricle, and finally 
from the left ventricle through the arch of the aorta 
into the commencement of the arterial system. 
In studying this part of the circulation, two things 
especially claim our attention. First, the movements 
of the heart; and, secondly, the action of its valves. 
rt 90. Movements of the Heart.—In the movements of 
the heart the two auricles first contract together, and 
then the two ventricles follow, also simultaneously with 
each other. The contraction of the ventricles is much 
more powerful than that of the auricles, owing to the 
greater thickness of their walls. The two sides of the 
heart therefore move exactly together, the contraction 
beginning with the auricles and finishing with the ven- 
tricles. The whole, taken together, forms one entire 
act or movement of the heart, which is called its “ pul- 
sation.” It is this movement which can be felt, as we 186 
PHYSIOLOGY AND HYGIENE. 
Fig. 37. 
Circulation through the Heart and Lungs.—1. Right Auricle; 2. Right Ven- 
tricle ; 3. Pulmonary Artery and its Branches; 4. Pulmonary Veins; 5. Left 
Auricle; 6. Left Ventricle; 7. Arch of the Aorta ; 8. Branches of the Aorta. 
have said, immediately below the fifth rib on the left 
side of the chest. 
The contraction of the heart is immediately followed 
by its relaxation. In this respect it is like all other 
muscles, which require that intervals of repose should 
alternate with their periods of,activity. But in the 
heart these alternating contractions and relaxations 
follow each other with a continuous and almost uniform 
rapidity. PHYSIOLOGY 
1. By what two means is the body held erect ? 
. Describe the manner in which the hand and arm 
are raised. Describe one means by which the 
body is protected from sudden jars. 
~ 2. Show the importance of lime as an ingredi- 
, ent of food. Which of the necessary ingredients 
j is acted upon by the gastric juice? .Name two 
conditions requisite for healthy digestion. 
3. Describe the lining membrane of the 
. stomach. Trace the course of the food through 
r, the digestive organs, and state briefly the change 
it undergoes in each. 
4. Describe the Thoracic Duct. When are the 
lymphatics called lacteals and why? What two 
substances are produced in the liver and what 
becomes of them? 
o. When will the blood coagulate in the in- 
terior of the body? Name the organs of respira- 
tion and describe two of them. 
6. The difference between arterial and venous 
blood. The office of the blood globules. 
7. Describe the arrangement and distribution 
of the arteries; the manner in which the blood is 
moved through the arte Hies. 
8. What is the source of animal heat? How 
do the tissues of the body obtain materials for 
their nourishment? Name the two kinds of 
nerve fibres and describe the office of each. 
9. What is the effect of an injury to the spinal 
. chord? Describe the reflex action of the spinal 
chord and show why it is important? What is 
the office of the retina? 
10. Describe the manner in which sounds are 
transmitted from the tympanum to the auditory 
nerve. Name two conditions requisite for the 
sense of taste; one use of this sense. 
Januaey, 1876. 187 
THE CIRCULATION. 
91. Action of the Valves.— But how is it that these 
movements cause the blood to flow onward in its nat- 
ural direction ? Why do they not expel it from the 
heart altogether, or drive it backward into the veins ? 
This brings us to the consideration of the Valves. 
A valve is simply a movable partition or obstacle, 
which swings open in one direction and closes in the 
other. A door is a valve. You can open it freely from 
without inward; but when you shut it, it closes firmly 
against the framework of the doorway, and can not 
pass beyond. The same office is performed by the 
valves of a pump, or those of a steam-engine. They 
are made of different materials, hut they all act in a 
similar way. Before one of them was ever construct- 
ed, there were valves in the interior of the heart. 
At the edges of the narrow opening between the 
auricles and ventricles, on each side of the heart, there 
are placed broad sheets of a thin but strong fibrous 
membrane, which are called the “ ventricular valves.” 
These valves hang loosely into the cavity of the ven- 
tricle, and are easily pushed aside by the current of 
blood entering from the auricle (Fig. 38). They do not, 
therefore, offer any obstacle to the movement of the 
blood in this direction. 
But when the ventricle contracts, in order to expel 
the blood from its cavity, the valves are lifted by the 
impulse of the blood, their edges come together, and 
they close completely the ventricular orifice. They 
would then he forced backward through this orifice 
into the auricle, but for a number of strong fibrous 
cords which sustain them in their places. These cords 
are attached to the edges and under surface of the 
valves, and, passing downward, are attached to little 188 
PHYSIOLOGY AND HYGIENE. 
Pig. 38. 
Right Auricle and Ventricle.—Ventricular valves open; Semilunar 
valves closed. 
muscular eminences, or columns, on the sides of the 
ventricle. These muscular columns contract at the 
same time with the walls of the ventricle, and by the 
aid of their tendinous cords hold the valves in position, 
and prevent the regurgitation of the blood (Fig. 39). 
The blood, therefore, which can not return into the 
auricle, is forced to find exit in the opposite direction, 
and escapes into the orifice of the corresponding ar- 
tery. 
There are also valves at the entrance of the great 
arteries. They are in the form of semicircular bags 
or festoons, and are therefore called the “ semilunar” 
valves. They open into the artery to admit the cur- 
rent of blood (Fig. 39), and again shut back to close 
its orifice when the ventricle is relaxed (Fig. 38). 
Thus these valves move backward and forward, and TIIE CIRCULATION. 
189 
Fi<?. SO. 
Right Auricle and Ventricle.—Ventricular valves closed; Semilunar 
valves open. 
alternately open and shut with each pulsation of the 
heart. The blood, accordingly, can never go backward, 
but is carried in a continuous circuit from the right 
side of the heart to the left, through the successive 
channels of the circulation. 
92. Character of the Heart’s Action.—Lastly, the move- 
ment of the heart is involuntary. It is still more inde- 
pendent of our control than the movements of respira- 
tion ; and we can not hasten or retard it in the least 
degree, much less arrest it for even a single pulsation. 
It is kept up by the operation of an internal stimulus, 
which is entirely withdrawn from the influence of the 
will. 
Nevertheless, it is aflected by many involuntary emo- 
tions. Joy or sorrow, anger or excitement, will disturb 190 
PHYSIOLOGY AND HYGIENE. 
the regularity of its motions, and increase or diminish 
their rapidity. Disagreeable sights or sounds, and va- 
rious moral emotions, will sometimes affect its action 
to such an extent as to produce faintness; but after 
the disturbing cause has passed away, the heart recov- 
ers its force and resumes the natural regularity of its 
movements. 
We now pass from the study of the heart to that of 
the blood-vessels. 
93. Arrangement and Distribution of the Arteries.— 
The first set of vessels into which the blood passes on 
leaving the heart are the Arteries. The arteries begin, 
as we have already said, with the aorta. This vessel 
rises from the left ventricle for a short distance behind 
the breast-bone, and then curves downward, forming a 
semicircular bend near the top of the chest, which is 
called the “arch of the aorta.” From the arch of the 
aorta there are given oft' several large branches (Fig. 37 
[8]), which supply the blood for the two arms and the 
two sides of the head. The aorta then passes downward 
parallel with the spinal column, through the chest and 
abdomen, giving otf every where branches to the vari- 
ous internal organs. In the lower part of the abdo- 
men it finally separates into two equal divisions, one of 
which supplies the right lower extremity, the other the 
left. Thus all the different parts of the body are pro- 
vided with branches coming from the aorta. 
When the arterial branches arrive at the organs to 
which they belong, they break up into innumerable sub- 
divisions. These divisions grow smaller and smaller at 
the same time that they become more numerous; until 
the whole substance of the organ is penetrated by their 
ramifications, and every part of it is provided with a 
due supply of arterial blood. THE CIRCULATION. 
191 
The arterial system is therefore like a great tree, of 
which the aorta is the trunk, and the smaller arterial 
branches are the twigs and ramifications; only this ar- 
terial tree is every where hollow, forming a connected 
series of vascular canals. 
94. Elasticity of the Arteries.—Now the arteries are 
elastic. If we take a piece of the aorta of an ox or a 
sheep, we shall find that we can stretch it, and that aft- 
erward it will retract and recover itself like so much 
India-rubber. The same property belongs to the arter- 
ies of the human body in a nearly equal degree. This 
quality is due to the presence of elastic fibres in the 
walls of the arteries similar to those which we have al- 
ready spoken of in the lungs; only in the arteries these 
fibres are much more abundant than in the lungs, and 
their elastic reaction is therefore more rapid and pow- 
erful. 
The elasticity of the arteries has a most important 
share in the circulation of the blood. 
95. Pulsation of the Arteries.—At each movement of 
the heart, the left ventricle throws the blood into the 
aorta with the whole power of its muscular contraction. 
This distends the aorta and its branches, with an im- 
pulse which is felt throughout the arterial system. The 
heart is like a force-pump, driving the blood into the 
elastic arterial tubes; and the arteries open to receive 
it, because the strength of the heart is greater than 
their resistance. This expansion of the arteries, pro- 
duced at each stroke of the heart, is called the Pulse. 
The pulse may be felt wherever an artery can be ex- 
amined. If we press the fingers firmly upon the upper 
and front part of the neck, just alongside the situation 
of the larynx, we shall feel the pulsation of the great 192 
PHYSIOLOGY AND HYGIENE. 
arteries which supply the head, and which are called 
the “ carotid” arteries. It is still better when the ar- 
tery crosses a bone near the under surface of the skin. 
Immediately in front of the middle of the ear is a small 
artery passing upward to the temples and the outside 
of the head, called the “ temporal” artery, which we can 
easily feel by pressing lightly upon the skin in this sit- 
uation. Just above the wrist, in front of the outer 
bone of the arm, is another artery supplying the hand 
and fingers, called the “ radial” artery. This is the ar- 
tery which the physician selects for feeling the pulse, 
simply because its situation is a convenient one for that 
purpose. 
For the pulse is a valuable guide in learning the con- 
dition of the heart. As each stroke of the pulse repre- 
sents a contraction of the heart, by counting the one 
Ave know the rapidity of the other. In grown-up 
persons, during health, the pulse beats about seventy- 
five times per minute. In fevers and inflammations, 
when the irritability of the heart is excited, it rises to 
eighty, ninety, one hundred, or even more than this. 
Many other peculiarities of the pulse, such as its 
strength, its fullness, its regularity or irregularity, 
show corresponding variations in the action of the 
heart, and indicate the condition of the circulatory 
system. 
96. Movement of the Blood through the Arteries.—But 
at the moment when the heart is relaxed, the arteries 
still exert their elastic force. The blood is prevented 
from returning into the ventricle by the closure of the 
semilunar valves, and is thus forced onward through 
the arterial system. 
The blood in the arteries is therefore under an inces- TIIE CIRCULATION. 
193 
sant pressure. It is always compressed by the elastic 
reaction of the arterial walls, and at each stroke of the 
heart it is urged by an additional pressure, derivecj. 
from the muscular contraction. It thus moves through 
the arteries in successive waves or impulses, passing 
rapidly from the heart toward the ramifications of the 
arterial system. 
97. The Capillary Blood-vessels.—The arteries termi- 
nate in another set of blood-vessels, still finer and more 
minutely subdivided, which are termed the Capillaries. 
The capillaries are invisible to the naked eye. They 
are so small that they require the aid of the microscope 
for their examination, and yet they are the most im- 
portant part of the whole circulating system, for it is 
in them that the blood comes into intimate contact 
with the substance of the tissues. 
These vessels are formed of an exceedingly thin 
and delicate membrane. They penetrate every where 
among the cells and fibres of the different organs, and 
form so many minute channels by which the blood 
makes its way through the 
tissues. Their great pecul- 
iarity is that they constant- 
ly unite and communicate 
with each other in every di- 
rection like the meshes of a 
net, so that they form what 
is called the “ capillary net- 
work” (Figure 40). The 
meshes of this network have 
different forms in different 
organs, but they every 
where present the essential characters above described. 
Fig. 40. 
Capillary Network in the web of the 
Frog’s foot, magnified. 194 
PHYSIOLOGY AND HYGIENE. 
In some cases the circulation of the blood in the 
capillaries can be seen. In the transparent web of 
the frog’s foot, when placed 
under the microscope, the 
blood globules can be per- 
ceived shooting along 
through the smaller arter- 
ies and penetrating into 
the capillary network (Fig. 
41).. Here the currents of- 
ten turn and wind in va- 
rious directions, passing 
through the various com- 
munications between the 
different capillary vessels, and penetrating in this way, 
in a multitude of different streams, the various tissues 
of the part. As the red globules in the frog are larger 
than those of human blood, and of an oval form, they 
are readily seen while carried along with the current 
of the blood. 
Fig. 41. 
Capillary Circulation in the web of 
the Frog’s foot. 
The movement of the blood in the capillaries is 
steady and incessant. There is no pulsation here sim- 
ilar to what takes place in the arteries. For, by the suc- 
cessive division and multiplication of the smaller ves- 
sels and the combined influence of their elastic walls, 
the arterial pulsation has been equalized and converted 
into a continuous pressure; and under this pressure the 
blood moves through the capillaries in a uniform and 
uninterrupted stream. It is in this part of the cir- 
culation that the blood loses its oxygen, and becomes 
changed from the arterial to the venous condition. 
98. The Veins and the Venous Circulation.—From the 
capillaries the blood is collected into larger channels, 
and so returned to the heart by means of the Veins, THE CIRCULATION. 
195 
We have already studied the structure of the veins 
in different organs. We know how they are formed 
by the union of the smaller branches into larger and 
larger trunks. The arrangement of the veins, there- 
fore, is exactly the opposite to that of the arteries. The 
arteries divide and separate as they pass from the heart 
outward; the veins unite and coalesce as they pass 
from the capillaries inward. In this way the continu- 
ous circuit of the blood is effected from the arteries to 
the veins, through the capillaries, which are the chan- 
nels of communication between them; so that the same 
blood which passes from the left side of the heart into 
the arteries, is returned at last to the right side of the 
heart by the veins. 
We can easily convince ourselves that the blood 
moves in the veins from without inward. If we clasp 
tightly the lower part of the arm, a little above the 
wrist, we shall soon see the veins on the back of the 
hand enlarge and become turgid, until we can almost 
see the blue color of their blood through the semi- 
transparent skin. This is because the blood accumu- 
lating from behind can no longer find its way back to 
the heart, and consequently distends the veins below 
the situation of the pressure ; but as soon as the press- 
ure is taken off, the veins empty themselves toward the 
heart, and again disappear beneath the skin. 
Now as many of the veins are situated very near the 
surface, they are often liable to be partially compressed 
and obstructed, as above, by the pressure of the cloth- 
ing and the accidental contact of foreign bodies. But 
this does not stop the circulation of the blood; because, 
in the first place, the veins communicate with each 
other by frequent lateral branches, and, secondly, they 196 
PHYSIOLOGY AND HYGIENE. 
are provided at many points with valves, resembling 
the semilunar valves of the heart, which prevent the 
blood from being forced backward into the capillaries. 
When the circulation is obstructed, therefore, in a sin- 
gle vein, the blood passes off by a lateral channel, and 
thus still finds its way back to the heart. In order to 
check the venous current effectually, it is necessary to 
encircle the whole limb with a simultaneous pressure, 
as in the experiment on the veins of the arm above de- 
scribed. 
But we should take the greatest care that no such 
pressure is left upon any part of the body as to inter- 
fere in this way with the venous circulation; for a lig- 
ature which compresses an entire limb, however lightly, 
is liable to obstruct the movement of blood in the veins, 
and thus interfere with the entire circulation in that re- 
gion. This injurious effect is indicated by the swell' 
ing of the parts below the ligature; and if continued 
habitually, it will at last cause a permanent injury to 
the limb by preventing the due nutrition of its tissues. 
In young children, where the process of growth and de- 
velopment is constantly going on, these bad effects are 
especially injurious. No such pressure, therefore, should 
be left upon any part of the body as will interfere with 
the venous circulation; but the blood should be left 
every where free to find its way back to the heart 
through the natural passages of the vascular system. 
Two other important points remain to be noticed in 
the phenomena of the circulation. 
99. Rapidity of the Circulation—In the first place, 
the circulation of the blood is exceedingly rapid. This 
rapidity is so great that it would he incredible, were it 
not for abundant experiments which have established it THE CIRCULATION. 
beyond a doubt. The time required for the blood to 
circulate over the body and return again to the heart 
is not more than from twenty-five to thirty seconds. 
During this period it passes through the arteries, trav- 
erses the capillary network, returns by the veins, and is 
again transported through the lungs to the left side of 
the heart. We can understand, therefore, how rapidly 
the changes in the tissues may go on, and how soon an 
impurity in the blood, from deficient respiration or 
otherwise, will be felt in the remotest parts of the cir- 
culation. 
100. Variations of the Circulation.—Secondly, the cir- 
culation exhibits, from time to time, local variations of 
an important character. Sometimes these variations 
are occasional and irregular, as where the face becomes 
flushed from mental emotion, or where any part of the 
skin is reddened by some accidental irritation, like a 
blister or a burn. But most of them are regular and 
periodical. Thus the stomach and intestine are flushed 
and congested during the digestion of the food, and this 
excitement passes off when digestion is finished. The 
salivary glands become reddened with blood while the 
secretion of saliva is going on, and afterward return to 
their ordinary pallid condition. Nearly all the inter- 
nal organs have their periods of rest and their periods 
of activity; and their periods of activity are accom- 
panied by a local excitement of the vessels, by which 
they are supplied at that time with an increased amount 
of blood. These temporary variations in the circula- 
tion of the blood are under the involuntary control of 
the nervous system, by which the necessary stimulus is 
conveyed to the different organs. 198 
PHYSIOLOGY AND HYGIENE. 
1. What is the circulation of the blood? 
2. What are the organs of the circulation ? 
3. Of what is the tissue of the heart composed ? 
4. What is the situation of the heart ? its size ? its form ? 
5. Where can the point of the heart be felt ? 
6. How many cavities are there in the heart ? their names ? 
7. Whence does the right auricle receive its blood ? 
8. Whither does the blood go from the right auricle ? 
9. How does the right ventricle differ from the auricle ? 
10. Into what vessel does the blood go from the right ventricle ? 
11. Whither is the blood conveyed by the pulmonary artery? 
12. What vessels bring the blood back from the lungs? and into 
what cavity do they empty ? 
13. Whither does the blood pass from the left auricle? 
14. Why is the left ventricle stronger than the other portions of the 
heart? 
15. Into what vessel does the blood pass after leaving the left ven- 
tricle ? and whither does this vessel carry it ? 
16. Which of the cavities of the heart contract simultaneously with 
each other ? 
17. What is the movement of the heart in contraction called? 
18. What follows after each contraction of the heart ? 
19. What is a valve ? 
20. What is the situation of the ventricular valves ? 
21. What is their structure ? 
22. Which way do they open, and which way do they shut ? 
23. What prevents the valves from being forced back into the auri- 
cle at the time of the heart’s pulsation ? 
24. What is the situation of the semilunar valves ? their form ? 
25. Which way do they open, and which way do they shut ? 
26. What effect do the valves have upon the movement of the blood ? 
27. Is the action of the heart voluntary or involuntary? 
' 28. How may it be accelerated or retarded ? 
29. What are the first set of blood-vessels which convey the blood 
outward from the heart ? 
30. Describe the aorta and its branches. 
31. What becomes of the arteries when they arrive at the different 
organs ? 
QUESTIONS FOR CHAPTER IX. QUESTIONS. 
199 
32. What is the principal physical peculiarity of the arteries ? 
33. What is the arterial pulse ? 
34. In what situations may the arterial pulse be felt ? 
35. What is the average rapidity of the pulse in health ? 
36. By what may it be accelerated or disturbed ? 
37. At the relaxation of the heart, what effect is produced on the 
blood by the elastic pressure of the arteries ? 
38. How does the blood move through the arterial system, steadily 
or in waves ? 
39. What is the next set of blood-vessels in which the arteries ter- 
minate ? 
40. What is the size and structure of the capillary vessels ? 
41. What is the capillary network ? 
42. How can the circulation of the blood in the capillaries be seen ? 
43. How does the movement of blood in the capillaries differ from 
that in the arteries ? 
44. Into what vessels does the blood pass after leaving the capil- 
laries ? 
45. What is the general arrangement of the veins, and what is the 
course of the blood through them ? 
46. What is the effect of compressing the veins by bandages or 
otherwise ? 
47. What permanent injury may be produced by obstructing the 
venous circulation ? 
48. How long a time is required for the blood to pass throughout 
the whole body ? 
49. What are the local variations of the circulation in particular 
parts ? 200 
PHYSIOLOGY AND HYGIENE. 
CHAPTER X. 
Warmth of Living Bodies—how preserved.—Production of Animal 
Heat.—Warm-blooded Animals.—Cold-blooded Animals.—Tem- 
perature of the Human Body.—Source of Animal Heat.—Differ- 
ence in Temperature of the Internal Organs.—Animal Heat neces- 
sary to Life.—Effects of cooling the Blood and Internal Organs.— 
Regulation of Heat by Perspiration.—Perspiratory Glands.—Com- 
position of the Perspiration.—Insensible Transpiration.—Increase 
of Perspiration by Heat.—Effect of its Evaporation.—Effect of heat- 
ing the Blood above 100° Fahrenheit.—Solid Ingredients of the 
Perspiration.—Sebaceous Secretion.—Necessity for frequent Bath- 
ing. 
101. Animal Heat.—One of the most remarkable qual- 
ities of animal bodies is their heat. Place your hand 
upon any part of the skin, and you feel that it is warm 
to the touch; that is, it is warmer than the atmosphere, 
or than surrounding bodies at ordinary temperatures. 
Animals, when exposed to cold, crowd together to pro- 
tect themselves from its influence, and endeavor to pre- 
serve their warmth by mutual contact. Even the 
breath which is expelled from the lungs in respiration 
is warmer than the fresh air which entered a moment 
before. So general and characteristic is this quality 
in living animals that we instinctively regard their 
warmth as an indication of vitality, and its absence as 
a sign of death. 
Furthermore, if we measure the warmth of the living 
body by the thermometer, we shall find that it is al- 
ANIMAL HEAT. ANIMAL HEAT. 
201 
ways very nearly the same. Take the bulb of the ther- 
mometer between the fingers of the closed hand, and it 
already rises to 90 or 95 degrees. But place it in the 
interior of the mouth, beneath the tongue, and keep it 
there for a few moments protected from the air, and it 
will stand at 100 degrees of Fahrenheit. This, accord- 
ingly, is the temperature of the internal parts. 
Now this internal temperature is nearly invariable. 
In winter and in summer, in the arctic regions as well 
as in the torrid zone, even though the external parts be 
chilled or frostbitten, the internal temperature of the 
body is still 100 degrees of Fahrenheit, or thereabout. 
But as the temperature of the air is nearly always far 
below this point, the living body must be constantly 
losing heat by contact with the cooler atmosphere. 
How, then, does it keep up its own temperature at this 
elevated standard, notwithstanding a continual loss of 
heat from the external surface ? 
102. Internal Production of Heat.—There is only one 
way in which this is possible. The living body pro- 
duces or generates heat in its interior, and thus con- 
stantly replaces what is lost from without. The inter- 
nal heat, so produced, is known by the name of Vital 
or Animal heat. 
All animals produce heat with more or less rapidity. 
In birds and quadrupeds, as well as in the human spe- 
cies, this production is so active that their blood and 
internal organs are nearly always considerably above 
the external temperature; they are therefore called 
“ warm-blooded” animals. In reptiles and fish, on the 
contrary, the production of heat, like most of the oth- 
er internal functions, is sluggish and feeble, and their 
temperature varies but little from that of the air or 202 
PHYSIOLOGY AND HYGIENE. 
water in which they live. Their temperature is so 
much below our own that we call them “ cold-blood- 
ed” animals. 
Accordingly, it is by its own internal heat that the 
living body is warmed. When we cover ourselves with 
clothing for protection from the cold, it is not that this 
clothing has any warmth in itself; it simply prevents 
the internal heat of the body from being dissipated. 
Even when we warm our houses with furnaces and 
fires, we only prevent, in a similar way, the body from 
being too rapidly cooled. For the atmosphere, even in 
the warmest apartment, never rises to the heat of the 
living body, which is still the only source of its own 
vital temperature. 
103. Animal Heat necessary to Life.—This elevated 
temperature of the animal body is essential to life. The 
external parts of the frame, especially those which are 
thinner and more exposed, such as the ears and the 
fingers, may be chilled by the external cold, and again 
recover themselves; but if the internal organs and the 
blood be cooled down a few degrees below their natu- 
ral standard, death inevitably results. The muscular 
power is diminished, the sensations become dull, the 
circulation of the blood is enfeebled; and the torpidity 
of the system gradually increases, until life is finally 
extinguished. 
104. Source of Animal Heat.—The source of the ani- 
mal heat is in the nutritive changes going on within 
the body. We know that heat may he produced in a 
variety of different ways—by the rays of the sun, the 
friction of solid substances, the compression of air, the 
passage of electric currents, and the burning of com- 
bustible bodies. It is also produced by many different 203 
chemical changes, by solutions, combinations, and de- 
compositions of various kinds. Every one knows how 
much heat is evolved by the combination of lime with 
water; and a mixture of water with sulphuric acid will 
produce a similar effect. Now, in the interior of the 
animal frame, an innumerable variety of these chemical 
changes are constantly going on. They are not all 
similar to those which take place outside the body, 
and the details of many of them are still unknown to 
us; but they are in incessant operation, and are suffi- 
cient to produce, for their final result, the elevated tem- 
perature of the living body. 
ANIMAT. HEAT. 
105. Variations and Equalization of Animal Heat in 
different Organs.—Accordingly, the temperature of the 
different internal organs is not exactly the same, since 
the chemical changes which go on in their tissues are 
different. Careful experiments have shown that this 
difference in temperature sometimes amounts to nearly 
degree of Fahrenheit. Thus far the liver has been 
found to be the warmest of all the internal organs; but 
the blood, which also, no doubt, generates heat of its 
own, passes so rapidly through the circulation that it 
distributes the warmth of the internal organs, and thus 
tends to equalize the temperature of the whole. The 
external surface, therefore, which is in contact with the 
atmosphere, is kept constantly warmed by the blood 
coming from within; and the different parts of the 
body, when carefully examined, show but little varia- 
tion from the standard temperature. 
106. Regulation of Animal Heat by Perspiration.—But 
it is also remarkable that the temperature of the body 
is not only thus kept up to a natural standard, hut 
that it never rises above this standard in any appre- 204 
PHYSIOLOGY AND HYGIENE. 
ciable degree. If the same amount of heat were gen- 
erated in summer as in winter, we should expect the 
body to become warmer; since less heat is lost by con- 
tact with the atmosphere. But no such variation oc- 
curs. As in winter the internal temperature of the 
body never falls below 100 degrees, so in summer it 
never rises above that point. How is it that the 
warmth of the body is thus regulated ? 
It is by means of the Perspiration. 
Immediately beneath the skin, over the whole sur- 
face of the body, but more abundantly on the palms of 
the hands, the soles of the feet, and the front parts gen- 
erally, there are a multitude of little glandular bodies 
which are called the “ Perspiratory glands.” Each one 
consists of a slender tube, about of an inch in di- 
ameter, which penetrates from the surface through the 
whole thickness of the skin, and there terminates in a 
globular coil, very much like a mass of small intestines 
in miniature. The capillary blood-vessels distributed 
to these glands are interwoven with their coils, and 
cover their surface with a fine vascular network. 
Now, although these glands are so small, yet they 
are also so numerous that, when taken together, they 
form an important glandular system. Each one of them, 
when its coil is carefully unraveled, is about of an 
inch in length. According to the best calculations, the 
whole number of perspiratory glands in the body is 
about 2,300,000. The combined length of their glandu- 
lar tubing is therefore not less than 153,000 inches, or 
about two miles and a half. 
Throughout this extent of the glandular tubes the 
blood of the capillary vessels comes in contact with 
their tissue. It there supplies a watery fluid, which is 205 
poured into their cavities and finally discharged upon 
the surface of the skin. This fluid is the perspiration. 
If the perspiration be examined by chemical analysis, 
it is found to have the following composition: 
ANIMAL HEAT. 
Composition of the Perspiration. 
Water 995.00 
Animal matters, with lime 10 
Sulphates, and substances soluble in water 1.05 
Chlorides of sodium and potassium, and spirit-extract 2.40 
Acetic acid, acetates, lactates, and alcohol-extract 1.45 
1000.00 
We see, therefore, that the perspiration is composed 
principally of water. The animal matters which it con- 
tains produce in it a faint and peculiar odor, and its 
acetic acid gives it a slightly acid reaction; but more 
than ninety-nine one hundredths of its materials consist 
of water. 
Now the perspiration is secreted all the time. The 
minute blood-vessels pour out its ingredients into the 
slender cavities of the glandular tubes; and, as these 
become filled, they discharge their contents through 
their external ppenings upon the skin, so that the skin 
is constantly exuding a watery fluid upon its surface. 
Nevertheless, we do not see this fluid; indeed, it does 
not remain, usually, for one instant upon the skin, but 
is at once taken up by the atmosphere and dissipated 
by evaporation. This is what is called the “ insensible 
transpiration” of the skin. 
The surface of the body, therefore, though constantly 
supplied with moisture from its glands, is constantly 
dry, because all the moisture is at once carried off by 
evaporation. The effect of this evaporation is to cool 
the surface. 206 
PHYSIOLOGY AND HYGIENE. 
Evaporation is one of the most effectual means of pro- 
ducing cold. If you moisten the hand with any fluid 
which evaporates rapidly, you will at once feel the sen- 
sation of cold produced. If you move the hand about 
briskly in the air, so as to hasten the evaporation, the 
sense of coolness will be increased in proportion. The 
more rapid the evaporation, the greater the feeling of 
cold which is caused by it; and chemists even employ 
this means to produce the freezing of water or other 
liquids. 
The surface of the skin, accordingly, is constantly 
cooled; first, by contact with the atmosphere, and, sec- 
ondly, by the evaporation of its own fluids. In cold 
weather, however, the perspiration is in exceedingly 
small quantity. Its evaporation is not sufficient to chill 
the surface, and the temperature of the body is there- 
fore kept up to its natural standard. 
But in warm weather the perspiration is more abun- 
dant. The skin becomes active under the stimulus of 
the heat, the blood circulates more freely in the per- 
spiratory glands, and a larger quantity of fluid is ex- 
uded upon the skin. Now, therefore, tjhe perspiration 
sometimes becomes visible, because it is secreted more 
rapidly than it can be carried olf by evaporation. The 
evaporation of this increased quantity of fluid pro- 
duces, of course, a greater cooling effect. Consequent- 
ly, in the sensibility of the skin and its perspiratory 
glands, the body possesses an apparatus for regulating 
its own temperature, notwithstanding the variations of 
the external atmosphere. 
The regulation of the heat of the body by the skin is 
nearly as important as its production. For if the blood 
be actually heated much above its natural temperature, 207 
ANIMAL HEAT. 
death follows as certainly as if it had been cooled down 
below it. There are only a few degrees of variation 
above and below 100 Fahrenheit within which life can 
be maintained. Now whenever we make any unusual 
muscular exertion the body becomes warmer, probably 
because all the vital changes which produce heat then 
go on with greater rapidity. But, at the same time, the 
circulation in the skin is excited, and an abundant flow 
of perspiration thus prevents the heat from becoming 
excessive. 
"r 107. Quantity of the Perspiration.—The skin, there 
fore, is in constant activity; and whenever the temper- 
ature rises beyond a certain point, this activity is in- 
creased, and the cutaneous exhalation becomes more 
abundant. The average quantity of water discharged 
in this way with the perspiration is very nearly two 
pounds per day. 
108. Solid Matter secreted by the Skin.—The watery 
parts of the perspiration, as we have seen, are carried 
otf by evaporation. But its solid ingredients remain 
behind, and are deposited upon the surface of the skin. 
There is also another cutaneous secretion which is less 
abundant than the perspiration, and which serves to 
keep the skin soft and pliable. It is called the “ seba- 
ceous” matter. It is to a great extent oleaginous in its 
nature; and its solid ingredients, like those of the per- 
spiration, remain deposited upon the surface. 
109. Necessity for general Ablution.—Accordingly, it 
is of the greatest importance to keep the skin cleansed 
of these accumulations by frequent ablution. Not only 
those parts which are exposed to the contact of exter- 
nal impurities, but the whole surface of the body, should 
be frequently washed, in order to remove the debris of 208 
PHYSIOLOGY AND HYGIENE. 
its own secretions. The contact of cold water also acts 
as a healthy stimulus to the skin itself, and tends to 
preserve it in a vigorous condition, ready at all times 
to perform its natural functions. 
QUESTIONS FOR CHAPTER X. 
1. What is the temperature of the internal parts of the body? 
2. Does this temperature vary with different climates, or remain 
the same ? 
3. How is the temperature maintained independently of the exter- 
nal air ? 
4. Do all animals produce heat more or less ? 
5. Which are called “warm-blooded” and which “cold-blooded” 
animals ? and what is the difference between them ? 
6. Is the body kept warm by external temperature or by its own 
internal heat ? 
7. How does clothing, etc., sene to maintain the warmth of the 
body? 
8. Is animal heat necessary to life ? 
9. What follows when the blood and internal organs are cooled 
down below their natural temperature ? 
10. How is the internal heat of the body produced ? 
11. Is it exactly the same in the different internal organs ? 
12. If not, how much does it vary? 
13. How is the animal heat disseminated and equalized throughout 
the body ? 
14. Is the interior of the body any warmer in summer than in 
winter ? 
15. By what is the heat of the body moderated in warm weather ? 
16. What are the glands which produce the perspiration, and what 
is their structure ? 
17. What is the length of each glandular tube? 
18. What is the combined length of all the perspiratory glands ? 
19. What are the ingredients of the perspiration ? 
20. Is the perspiration secreted occasionally or constantly ? 
21. What becomes of it after it is exuded upon the skin ? 
22. What is the effect of evaporation upon the warmth of the 
skin? QUESTIONS. 
209 
23. When is the perspiration 11 insensible," and when does it be- 
come visible ? 
24. What becomes of the solid parts of the perspiration when its 
watery portions are evaporated ? 
- 25. What is the sebaceous matter of the skin, and what is its use ? 
26. Why is frequent washing of the body necessary to health ? 210 
PHYSIOLOGY AND HYGIENE. 
CHAPTER XI. 
Definition of Nutrition.—Its three different Parts.—Assimilation.— 
Absorption of Inorganic Ingredients.—Their different Proportions 
in the Tissues and the Blood.—Different kinds of Albuminous In- 
gredients.—Transformation of the Albumen.—Secretion.—Struc- 
ture of a Gland.—Follicles.—Lobules.—Ducts.—Inorganic Ingre- 
dients of a Secretion.—Its Albuminous Ingredient.—Increase of 
Secretion with excitement of the Circulation.—Excretion.—Altera- 
tion of Animal Tissues during Life.—A necessary consequence of 
Activity.—New Substances so produced.—Carbonic Acid.-—Ani- 
mal Vapors. —Urea.—Creatine. —Creatinine. —Urate of Soda. — 
Double Movement of Nutrition.—Supply and Discharge.—Quanti- 
ty of Material absorbed and discharged in twenty-four hours. 
NUTRITION. 
By the term Nutrition we mean more especially all 
those secret and varied changes of substance which are 
constantly going on in the interior of the body, and 
which are essential to its life and organization. We 
shall find that these changes are of three different kinds, 
each of them necessary, in a different way, to the con- 
tinued operation of the whole. They are, 1 st, Assimi- 
lation ; 2d, Secretion; and, 3d, Excretion. 
110. Assimilation.—Assimilation is the formation of 
the tissues from the elements of the food. For the tis- 
sues of the body are all different in their composition 
from the substances which we take as food, and can 
only be formed when the elements of the food are made 
like, or “ assimilated” to them. It is this process which 
we shall study in the first place. NUTRITION. 
211 
We have already seen how the ingredients of the 
food are changed in the process of digestion, and how 
these substances, again, are converted into the materials 
of the blood. We may then say that they have been 
assimilated to the blood; for this fluid has now its par- 
ticular ingredients, produced by the absorption and 
transformation of the digested food. 
But this food is not yet converted into the tissues. 
None of the tissues have the same composition as the 
blood, and they are all different from each other; and 
yet they all depend exclusively for their materials upon 
the blood, which must supply them with every thing 
needed for their growth and organization. How is 
their nourishment, therefore, to be accomplished ? 
The fluid parts of the blood consist, as we remember, 
first, of water, with mineral substances in solution, which 
form its inorganic ingredients ; and, secondly, of albu- 
men and fibrine, which are its organic elements. Now 
all the inorganic substances have been derived from the 
food. They were absorbed from without, and now, con- 
sequently, form a part of the blood. They also exist in 
all the solid tissues. Some of them, like the chloride of 
sodium, or common salt, are every where in the body, 
no tissue being without them. Others, like the phos- 
phate of lime, are sometimes in great abundance, as in 
the bones and teeth, where this substance forms more 
than half the entire tissue. When the blood, according- 
ly, freighted with these inorganic materials, arrives at 
the capillary circulation, penetrating every where into 
the interstices of the tissues, it gives up to them the 
substances necessary for their growth, by exuding them 
through the walls of the blood-vessels. 
But here we meet with a singular phenomenon. 212 
ill. Deposit of Ingredients in different Proportions.— 
These inorganic substances are present in all the tissues 
in different proportions. The lime, for example, which 
in the bones constitutes over five hundred parts in a 
thousand of their tissue, in the cartilages forms only 
forty parts, and in the muscles only two parts and a 
half. Water, which in the teeth is only ten per cent, 
of their substance, in the brain is more than seventy- 
eight per cent. Each tissue also must contain these 
substances in its own proper proportion. If the lime, 
for example, were deficient in the bones, they would 
yield and bend under the weight of the body; and if it 
were in excess in the substance of the heart, the organ 
could not perform its function, and the circulation 
would come to an end. 
PHYSIOLOGY AND HYGIENE. 
Each tissue, accordingly, selects from the blood its 
own due proportion of inorganic matters and appropri- 
ates them to itself. It is as if each one were endowed 
with a kind of instinct, by which it should take no more 
and no less than is useful for its organization. This 
property resides in the substance of the tissues them- 
selves. We found, while studying in a former chapter 
the subject of “Absorption” and “ Endosmosis,” that 
each animal tissue will absorb certain fluids and solu- 
tions more readily than others, and that the same sub- 
stance will be taken up in greater quantity by one mem- 
brane than by a different one. The same thing happens 
during the circulation in the living body. Thus each tis- 
sue absorbs from the blood its proper quantity of mate- 
rial, and preserves continuously its special composition. 
Furthermore, many of these ingredients are in much 
larger proportion in the tissues than in the blood. The 
lime, again, which is over five hundred parts per thou- NUTKITIOIST. 
213 
sand in the bones, in the blood is only three parts in 
ten thousand. How can the blood, therefore, in which 
it is so scanty, supply it to the bones, in which it is so 
abundant ? 
It is owing to the rapidity of the circulation. The 
blood which has passed through the capillaries of an 
organ and given up to it its ingredients, is at once fol- 
lowed by a fresh and unexhausted supply; and as it 
moves through the rapid course of the circulation, it in- 
cessantly revisits the different parts of the body, and 
continues, little by little, the contributions necessary 
for their support. 
112. Transformation of the Albuminous Matter.—But 
we now come to the organic or “ albuminous” ingredi- 
ents of the body. 
These are of the most varied character. In the mus- 
cular fibres the albuminous ingredient is termed “ Mus- 
culine,” and has peculiar chemical qualities. In the 
bones it is called “ Osteine,” in the cartilages “ Chon- 
drine,” in the hair and nails “Keratine,” and in the 
transparent lens of the eyeball “Crystalline.” These 
substances are all solid in consistency, and nearly every 
tissue contains one peculiar to itself. And yet they are 
all supplied from the blood, which contains only two, 
namely, albumen and fibrine, neither of which forms the 
substance of any of the tissues. 
Here, then, we have a phenomenon of transformation. 
As the albumen of the blood passes through the capil- 
laries of each tissue, it is transuded and absorbed like 
the inorganic materials. But, unlike them, it is at the 
same time changed in character. In one tissue it be- 
comes osteine, in another musculine, in another ehon- 
drine, and the like. This transformation is effected by 214 
PHYSIOLOGY AND HYGIENE. 
catalysis ; that is, the constituent of each tissue has the 
power, simply by its contact, of converting the albumen 
of the blood into its own substance, and thus providing 
for its own regeneration. 
It is in this way that the various tissues preserve 
their natural constitution. It is by this miraculous 
transformation, which is daily going on in the interior 
of our frame, and by which the gluten of bread, the 
caseine of milk, and the albumen of eggs are at last con- 
verted into the flesh, the bones, the membranes, and the 
nervous tissues of the human body. Through the in- 
termediate action, therefore, of digestion and the blood, 
all the ingredients of the food are finally assimilated to 
the substance of the various tissues. 
113. Secretion.—The second part of the nutritive pro- 
cess is Secretion. 
A secretion is a fluid prepared from the blood by va- 
rious internal organs, in order to accomplish a certain 
purpose in the animal economy. We have already had 
occasion to speak of several of these secretions, and to 
describe the office which they perform. Thus the gas- 
tric juice, secreted in the stomach, assists in the diges- 
tion of the food. The bile, formed by the liver, goes 
through certain changes in the intestine for the produc- 
tion of other materials. The perspiration is poured out 
upon the skin to regulate its temperature by evapora- 
tion. There are vai’ious other secretions which have 
not yet been mentioned, such as the tears, which moist- 
en and protect the transparent surface of the eye; the 
milk, which serves for food to the young infant; and 
the mucus, which lubricates the internal passages of the 
body. Each one of these fluids serves for some definite 
and useful end in the vital operations. NUTRITION. 
215 
114. Structure and action of the Secreting Organs.— 
The secretions are formed in certain organs, which con- 
sist of little cavities or “ follicles,” each one opening by 
an external orifice. 
Several follicles are 
usually grouped to- 
gether, with all 
their mouths open- 
ing into a little 
tube, thus forming 
a “ lobuleand a 
number of lobules 
are also united into 
a compact mass, 
with their various 
tubes all joining 
into one common 
tube or “ duct” (Fig. 42). Such an organ is called a 
Gland. 
Sometimes the little cavities or follicles have the form 
of slender tubes, which open separately, each one by 
itself, as in the tubules of the stomach, the follicles of 
the intestine, and the perspiratory glands of the skin; 
but all the larger glandular organs, such as the parotid 
gland, the pancreas, and the milk glands, have the struc- 
ture above described. 
The capillary blood-vessels penetrate between these 
follicles, and bring the blood into minute contact with 
every part of the gland. 
Now a change takes place in the glandular organ 
somewhat like that which we have described in the tis- 
sues. The blood, under the pressure of the circulation, 
parts with its water and its inorganic ingredients, which 
Fis*. 42. 
Structure of a Gland. 216 
transude through the blood-vessels into the cavities of 
the glandular follicles. Thus a fluid is produced from 
the ingredients of the blood, which is withdrawn or 
separated from the circulation, and is therefore called a 
“ Secretion.” 
But each gland separates the ingredients of the blood 
in especial proportions, which are different for each se- 
cretion. Thus some secretions have a large quantity 
of water, like the perspiration; others a large propor- 
tion of solid material, like the pancreatic juice. For 
this peculiar constitution they depend upon the power 
of the gland to appropriate their materials in the prop- 
er quantity. 
But in each secretion there is also a peculiar animal 
substance which does not exist in the blood, and it is 
usually upon this that the especial character of the se- 
cretion depends. Thus in the gastric juice there is pep- 
sine, which serves to dissolve the food; in the saliva, 
the viscid substance which assists in mastication; in 
the milk, the caseine which gives it its nourishing quali- 
ty. Now all these substances are produced in the gland 
itself. This is again a transformation, by which the al- 
bumen of the blood assumes a new form in the cavities 
of the glandular organ. The secretion, therefore, con- 
sists of this new substance, manufactured in the gland, 
together with the water and mineral ingredients which 
have been supplied directly by the blood. 
The peculiar fluid thus produced is poured into the 
glandular follicles, and fills their cavities. It then ap- 
pears in the tubes leading from the follicles, and, ac- 
cumulating constantly in this way from behind, is final- 
ly discharged from the main duct or outlet of the gland. 
We see, accordingly, how it is that these secretions 
PHYSIOLOGY AND HYGIENE. 217 
NUTRITION. 
are produced more abundantly at particular times. 
When the circulation in the gland is excited, more 
blood is admitted to its capillaries, and its materials 
are supplied in greater quantity. They then exude 
rapidly into the glandular follicles, and pass out by its 
tubes and ducts in an abundant flow. When the cir- 
culatory excitement subsides, the production of fluid is 
again checked, and the gland is restored to a condition 
of repose. 
115. Excretion.—Lastly, we have to study the pro- 
cess of Excretion. 
In all our machines and mechanical contrivances we 
can make use of power only by the expenditure of ma- 
terial. Every mill must not only have a canal to sup- 
ply it with water from above, but a sluice-way to car- 
ry off the waste water from below. The fuel of a fur- 
nace is constantly consumed, and afterward discharged 
in the form of smoke and ashes. The piston of a steam- 
engine is driven by the expansive force of the steam ; 
but when the steam has once acted in this way, it has 
lost its power. In expanding it has changed its form, 
and must then be expelled from the cylinders to make 
room for a fresh supply. 
The same thing happens in the living body. Every 
animal organ and tissue is altered and decomposed by 
its own activity. At every pulsation of the heart a 
portion of its vital power is expended, and the sub- 
stance of its fibi-es changed. Every time the nerves 
feel, at the same moment their tissue is wasted and 
their sensibility more or less impaired. 
This is not, however, a destructive or injurious ac- 
tion ; it is the natural and healthy operation of the liv- 
ing organs. For it is by this very alteration of their 218 
PHYSIOLOGY AND HYGIENE. 
substance that they perform their work; and fresh ma- 
terial is at the same time constantly supplied for their 
renovation. It is as if nature were incessantly employ- 
ed in unweaving and reconstructing the texture of the 
body, so that it may be always new, and always endow- 
ed with undiminished vitality. 
116. Substances produced by Excretion.—But in this 
process new substances make their appearance in the 
body. As the changes which we have just described 
go on in the depths of the tissues, their ingredients are 
decomposed and appear under other forms. These sub- 
stances represent the used or exhausted elements of the 
frame, and accordingly, from the first moment of their 
production, they are destined to be expelled. Their 
evacuation or elimination from the body is no less im- 
portant than the other changes of nutrition; for by re- 
maining, they would interfere with the vital powers and 
obstruct the activity of the system. It would be of lit- 
tle use to supply a furnace with fresh fuel, if it were to 
remain clogged with the ashes and cinders of the old. 
Excretion is the process by which these waste ma- 
terials are eliminated, and the substances so eliminated 
are termed the “ excretions.” 
The most important and abundant of them all is Car- 
bonic acid. We have already seen how constantly this 
substance is formed in the body, and how rapidly it is 
discharged by the lungs. It passes to the lungs with 
the liquid ingredient s of the blood, and is there exhaled 
in a gaseous form by the breath. 
At the same time, there is a small quantity of Ani- 
mal vapor discharged in respiration. This vapor has 
no name, but it is that which gives a peculiar odor to 
the breath. So long as the breathing is unconfined and NUTRITION. 
219 
ventilation free, we do not perceive it to any great ex- 
tent ; but in the confined atmosphere of a crowded and 
ill-ventilated room it at once becomes perceptible by 
its stifling and offensive odor. Though in compara- 
tively small quantity, there is reason to believe that 
this substance is even more deleterious to health than 
the carbonic acid which accumulates at the same time. 
It is undoubtedly through this vapor of the respiration 
that contagious diseases are communicated, when the 
two persons who are affected have never been in actual 
contact, but have only breathed the air of the same 
apartment. 
An odoriferous matter of similar nature is also ex- 
haled with the perspiration. Like the former, it is in 
minute quantity, and is only injurious when allowed to 
accumulate and stagnate in the atmosphere. If carried 
away by ventilation, it is soon destroyed by the oxygen 
of the air, or decomposed by vegetables for their own 
nutrition. 
11V. Urea.—Another very important and abundant 
material of excretion is Urea. 
Urea is a crystallizable substance which is produced 
in the body usually to the amount of rather over one 
ounce per day. We do not yet know in what particu- 
lar parts of the system it is formed, but it makes its 
appearance every where in the blood, dissolved in its 
liquid ingredients. The quantity of urea produced va-> 
ries somewhat with the activity of the body; for ex- 
periments have shown that it is increased by muscular 
exertion, and diminished during the periods of repose. 
Even mental application alone, without bodily effort, 
will be indicated by the increased amount of this sub- 
stance formed in the system. 220 
In some diseases the urea accumulates in the blood 
beyond its natural proportion. It then produces very 
injurious effects, and acts upon the system like a poi- 
son. The senses become deranged, and the circulation 
is impeded; and if the accumulation continues, it at 
last produces convulsions, insensibility, and death. 
But in health the urea is constantly discharged from 
the blood by the kidneys. As the blood passes through 
the capillaries of these organs, its urea filters away, 
and it returns cleansed and purified to the circulation. 
Thus, as the carbonic acid produced in the body is ex- 
pelled from the lungs, so the urea is expelled by the 
kidneys. It accumulates in their passages together 
with other watery and inorganic ingredients of the 
blood, and is finally discharged altogether from the 
system. 
There are various other substances of a similar na- 
ture which pass out from the blood by the same chan- 
nels with the urea. Two of them are termed Creatine 
and Creatinine. They are formed first in the muscles, 
and are absorbed from them by the blood. Another is 
termed TJrate of soda, because its peculiar animal ingre- 
dient is combined with soda at the time of its forma- 
tion. All these substances are expelled from the body, 
during health, nearly as fast as they are formed. 
Next to the lungs, therefore, the kidneys are the 
great organs of purifica tion for the blood. By them its 
waste and exhausted materials are incessantly removed, 
while its other ingredients are retained in their due pro- 
portion. 
118. Renovation of the Materials of the Body.—We see, 
then, that the nutrition of the body is accompanied by 
a double movement of supply and discharge ; and neither 
PHYSIOLOGY AND HYGIENE. NUTRITION. 
221 
of these two processes can go on independently of the 
other. Intermediate between the two is a third move- 
ment, namely, that of secretion/ but most of the secre- 
ted fluids, after being once separated from the blood, 
are again absorbed by the blood-vessels, and so re-enter 
the circulation. 
Now, if we examine the entire quantity of the mate- 
rials thus absorbed and discharged every twenty-four 
hours, we can form an estimate of the rapidity with 
which the vital operations go on. We have already 
given the daily quantities of many of these substances; 
those of the remainder are added in the following list. 
The numbers are all given for a man of ordinary stat- 
ure, weighing 140 pounds. In the first column is placed 
the quantity of material absorbed, in the second that 
of the material discharged. 
Absorbed during 24 hours. 
Oxygen 1.02 lbs. 
Water 4.73 “ 
Albuminous matter 40 “ 
Starch G6 “ 
Fat 22 “ 
Mineral Salts 04 “ 
7.07 
Discharged during 24 hours. 
Carbonic Acid 1.53 lbs. 
Vapor from tbe lungs...1.15 “ 
Perspiration 1.93 “ 
Water of the Urine 2.02 “ 
Urea and other excretions .40 “ 
Mineral Salts 04 “ 
7.07 
Rather more than seven pounds of material, there- 
fore, are absorbed and discharged daily by a healthy 
full-grown man; and, for one having the average 
weight of 140 pounds, a quantity equal to the weight 
of the whole body is thus taken into the system and 
expelled from it in the course of twenty days. 
It is plain, also, that this material does not simply 
pass through the system, like water through a sieve. 
On the contrary, it actually combines during its pas- 222 
PHYSIOLOGY AND HYGIENE. 
sage with the ingredients of the tissues, and forms for 
the time a part of their substance. A large portion of 
it also suffers chemical transformations two or three 
times over, under the influence of the vital actions, 
passing successively through different forms, until it is 
finally discharged in the process of excretion. 
Thus the history of nutrition is one of incessant 
change; by which the various ingredients of the body 
are continuously destroyed and renewed, while the 
body itself remains always vigorous and unaltered. 
QUESTIONS FOR CHAPTER XI. 
1. What are the three processes of nutrition ? 
2. What is assimilation ? 
3. Upon what fluid do the tissues depend for their nourishment ? 
4. Does the blood contain all the watery and mineral ingredients 
of the tissues ? 
5. Does it contain them in the same proportion as they exist in the 
tissues ? 
6. Do these substances exist in the various tissues in the same pro- 
portion or in different proportions ? 
7. Name some instances of the varying proportion of inorganic in- 
gredients in the different tissues. 
8. How are these substances deposited in their proper proportion in 
each tissue ? 
9. How can the blood supply more water or lime to a tissue than it 
contains itself? 
10. Does the blood contain any of the “ albuminous” ingredients 
of the tissues ? 
11. What are the albuminous ingredients of the blood? 
12. Name some of the albuminous ingredients of the tissues. 
13. How are the albuminous ingredients of the blood converted into 
those of the tissues ? 
14. What is a secretion ? 
15. Name some of the secretions and their uses. 
16. Describe the structure of a gland. 
17- What arc its follicles ? its lobules? its duct? QUESTIONS. 
223 
18. What is the arrangement of the capillary blood-vessels in a 
gland ? 
19. From what source are the watery and mineral ingredients of a 
secretion supplied ? 
20. How is its animal substance produced ? 
21. How are the secretions produced more abundantly at particular 
times ? 
22. What is the last of the processes of nutrition ? 
23. Do the organs of the body remain the same, or are they changed 
by the performance of their functions ? 
24. Is this change a destructive or a healthy process ? 
25. How are the organs maintained in a healthy condition ? 
26. What is an excretion ? 
27. Why must the excretions be discharged from the system ? 
28. What is the most abundant and important of all the excretions? 
29. How is it discharged ? 
30. What other excretion is discharged with the breath beside car- 
bonic acid? 
31. When do the odoriferous matters of the breath and perspiration 
become deleterious ? 
32. What is urea ? 
33. How much urea is produced in the body per day ? 
34. When urea accumulates in the blood in disease, what effect 
does it produce ? 
35. By what organs is it discharged from the system during health ? 
36. What other excretions are discharged by the kidneys ? 
37. What is the entire quantity of materials absorbed and dis- 
charged by the body in twenty-four hours ? 
38. Does this material simply pass through the body, or is it com- 
bined with the tissues and again decomposed ? 
39. How long would it take for the whole substance of the body to 
be renovated by nutrition ? Section III. 
THE NERVOUS SYSTEM. CHAPTER Xn. 
GENERAL STRUCTURE AND FUNCTIONS OF THE NERVOUS 
SYSTEM. 
United Action of the Organs.—System of Telegraphs.—Nervous Fila- 
ments.—Nerves.—Spinal Cord.—Spinal Nerves.—Brain.—Cere- 
brum.— Cerebellum.—Medulla Oblongata. — Cranial Nerves.— 
Nervous Fibres are Organs of Communication. — Irritability of 
Nerves.—Sensitive Fibres.—Motor Fibres.—Nerve Cells.—Nerv- 
ous Centres.—Reflex Action of the Nervous System. 
119. Object and Use of the Nervous System.—In the 
foregoing chapters we have studied the manner in 
which each different organ of the body performs its 
work. We are now about to see how they are made 
to act in harmony with each other, for the benefit and 
support of the whole. 
For it is not enough that an organ be made capable 
of performing a certain function; it must also act at a 
particular time and in a particular manner. How is it 
that the diaphragm moves upward and downward just 
often enough to supply the lungs with the air needed 
in respiration ? The stomach, as we have seen, secretes 
its gastric juice precisely when this is required for the 
digestion of the food, and not at other times. The 
varying currents of the circulation, the action of the 
glandular organs, and even the movement of the limbs, 
must all work together, or alternately, in such a way as 
not to interfere with each other, but to assist harmoni- 
ously in the general functions of the bodily frame. 
This harmonious action of the different organs is se- 228 
PHYSIOLOGY AND HYGIENE. 
cured by the aid of the JVervous System. What is the 
structure of the nervous system, and how does it per- 
form its work ? 
120. General Arrangement of the Nervous System.— 
Imagine a series of telegraph wires running from all 
the police stations of a great city to the central office 
or head-quarters of the department. These wires form 
a communication between every street, lane, and ave- 
nue of each district and the central office, and again be- 
tween the central office and all parts of the city. Any 
thing which happens in one district may be telegraphed 
to head-quarters, and an answer at once returned, giving 
the necessary orders or sending the required assistance. 
If a man is found sick or wounded, surgical aid is dis- 
patched to his relief. If a larger number of policemen 
are required to quell a disturbance, or to perform any 
unusual duty, they are ordered from other districts and 
collected at the proper point by the same means of com- 
munication. Thus the whole machinery of the depart- 
ment acts together or separately, as occasion demands, 
and its different parts move constantly in harmony 
with each other. 
The nervous system is such a means of communica- 
tion between the different parts of the animal frame. 
121. Nervous Fibres or Filaments.—Throughout the 
body there are distributed a multitude of slender white 
threads or filaments, which run in every direction, in- 
terlacing themselves with the various tissues, and 
reaching every part of the skin, the muscles, and the 
glandular organs. These filaments are of extreme del- 
icacy, the smallest of them measuring only t oo'gp °f an 
inch in diameter, and the largest not more than 70tct>- of 
an inch. Each one is composed of a fine gray ribbon- 229 
like thread in the centre, which is surrounded by a 
white, soft material, very nearly like thickened cream 
in consistency (Figure 43), the whole being inclosed 
in a thin, transparent covering, or tubular membrane. 
The filaments so formed are called the Nervous fila- 
ments. 
At their commencement, the nervous filaments, as we 
have said, are disseminated among the tissues of the va- 
rious organs. From 
these points they ap- 
proach each other, 
uniting, side by side, 
into little bundles. 
As these bundles 
emerge from the dif- 
ferent parts of an or- 
gan they also join 
each other, and form 
larger cords by the 
continued association 
of other filaments. 
When such a collec- 
tion has become large 
enough to be seen by 
the naked eye, it is 
called a Nerve. 
Each nerve, accord- 
ing is a bundle of 
such filaments, col- 
lected from different 
parts, and all running 
in the same direction. These filaments do not unite or 
become confounded with each other in the substance of 
STKUCTUKE, ETC., OF THE NEKVOUS SYSTEM. 
Fig. 43. 
Different Nervous Filaments uniting to form 
a nerve; highly magnified: a. portion of 
nerve; b, c, d, e. Nervous filaments. 230 
PHYSIOLOGY AND HYGIENE. 
the nerve, but remain distinct, like the separate threads 
in a skein of silk (Fig. 43). 
When a nerve has thus disengaged itself from the 
deeper textures, and begins to run in the interstices be- 
tween the adjacent parts, it becomes invested with a 
thin but strong covering of white fibrous tissue, which 
binds together and protects its separate filaments. For 
these filaments, composed of the soft and delicate mate- 
rial which we have described, would be liable to injury 
or laceration by the movement of the limbs and the 
pressure of more solid organs, were they not protected 
by such an investment. This fibrous covering of the 
nerve is called its “ neurilemma,” or Sheath. It gives to 
the nerves that white and glistening color by which 
they are recognized by the surgeon in his dissection of 
the various parts. 
The nerves originating in the skin and muscles of the 
different regions of the body, and from the upper and 
lower limbs, pass inward, from the right side and the 
left, toward the situation of the median line and the 
spinal column. Arrived in this neighborhood, they form 
thirty-one distinct pairs, each pair consisting of two 
symmetrical nerves, one right and one left, coming from 
the corresponding sides of the body. They then pass 
through certain openings in the sides and back part of 
the spinal column, and thus penetrate into the cavity of 
the spinal canal. Here they unite into a long, white, cy- 
lindrical nervous mass, running from below upward di- 
rectly along the middle line of the back, in the cavity of 
the spinal canal. This nervous mass is the Spinal cord. 
The spinal cord, therefore, contains within itself the 
filaments derived from all the nerves of the external 
parts of the body and limbs. As these nerves unite STRUCTURE, ETC., OF THE NERVOUS SYSTEM. 
231 
with the spinal cord in the manner above described, 
they are called the Spinal nerves. 
The substance of the spinal cord is soft and delicate; 
but it is defended by the solid mass of the spinal col- 
umn in front, and by its bony prominences, which arch 
over and embrace the spinal cord at the sides and be- 
hind. It is thus inclosed 
in a long cavity or canal, 
which we have already 
mentioned under the 
name of the “ spinal ca- 
nal.” The spinal cord 
passes through this ca- 
nal from below upward 
until it reaches the up- 
per extremity of the spi- 
nal column. Here it en- 
ters the cavity of the 
cranium, and at once ex- 
pands into a large round- 
ed nervous mass, which 
is the Brain (Fig. 44). 
The brain itself con- 
sists of three parts, viz., 
1st, an upper, larger, 
and more rounded mass, 
covered with sinuosities 
or convolutions, which 
fills all the upper, mid- 
dle, and anterior portion 
of the skull, called the Cerebrum ; 2d, a smaller and 
more flattened portion, also convoluted upon its sur- 
face, situated at the lower and back part of the skull, 
Fig. 44. 
The Brain, Spinal Cord, and Spinal Nerves, 
seen from behind.—1,2. Brain, consist- 
ing of, (1), the Cerebrum, and, (2), the 
Cerebellum; 3. the Spinal Cord and 
Nerves; 4. Nerves of upper limbs; 5. 
Nerves of lower limbs. 232 
called the Cerebellum / and, 3d, a still smaller portion, 
placed at the junction of the spinal cord with the brain, 
and called the Medulla oblongata. In the preceding 
figure the medulla oblongata is not shown, because it 
is concealed by the larger masses of the cerebrum and 
cerebellum. 
Both the brain and the spinal cord, furthermore, are 
divided by a deep furrow into two equal parts, right and 
left. These portions are joined to each other beneath 
by connecting masses of nervous substance; but upon 
their surface, especially when seen from behind, as in 
Fig. 44, they pi’esent the appearance of two separate 
halves, corresponding to the two sets of nerves coming 
from the opposite sides of the body. 
Beside the nerves connected with the spinal cord, 
there are various other pairs, supplying the pai'ts about 
the head and neck, which reach the brain by passing 
through openings in the lower part of the cranium. 
They are called the Cranial nerves. They are not rep- 
resented in the preceding diagram, as they pass, for the 
most part, in a direction from behind forward, and from 
before backward. 
Thus the main part of the nervous system, as above 
described, consists of, 1st, the Nerves coming from the 
various parts of the body ; and, 2d, the Brain and Spi- 
nal cord, with which these nerves are united. 
Now the nervous filaments are the fibres of communi- 
cation of the nervous system. They are the telegraphic 
wires through which its secret messages are sent from 
one part of the bodily frame to another. How is it 
that they perform this otfice ? 
) 122. Irritability of the Nervous Fibres.—Each nervous 
fibre is endowed with a peculiar power, which is called 
PHYSIOLOGY AND IIY'GIENE. STRUCTURE, ETC., OF THE NERVOUS SYSTEM. 
233 
its Irritability. By this we mean that whenever it re- 
ceives a certain impression, every portion of it is roused 
into a peculiar state of activity or excitement. What 
is the precise nature of this activity of the nervous 
filament we do not know; hut we know that it is in- 
stantly propagated through its substance from one ex- 
tremity to the other. If you strike one end of a bar 
of iron, the metal vibrates throughout its entire length. 
Somewhat in a similar way, when the proper stimulus 
is applied to one extremity or any part of a nervous 
fibre, the whole of it is thrown into simultaneous ex- 
citement. 
Now this activity of a nervous fibre does not pro- 
duce any visible effect in the nerve itself. Its peculiar 
quality is that it calls into activity some other organ. 
Thus the muscles are made to contract, or the glands 
are excited to secretion by the stimulus of the nerves; 
and yet the nerves which convey this excitement do 
not themselves show any change in their appearance. 
They serve to communicate the stimulus which is to 
produce its effect elsewhere. 
123. Two different kinds of Nervous Fibres.—But when 
we closely examine the nervous fibres, they are found 
to be of two different kinds, endowed with two different 
functions. 
The first are the sensitive fibres. They are distrib- 
uted throughout the skin, the lining membranes, and 
other organs of the body. They are so called because 
they are sensitive to the impressions made upon these 
organs; and they communicate the impressions thus re- 
ceived to the central parts of the nervous system. They 
transmit the nervous excitement, therefore, in a direc- 
tion from without inward. 234 
The others are the motor fibres. They are so called 
because they call into motion or activity the muscles 
or other organs to which they are distributed. They 
act, accordingly, in a direction exactly contrary to the 
former, and transmit the nervous stimulus from within 
outward. 
124. Nervous Centres, or Ganglia.—But the wires of a 
telegraphic system would be useless in themselves un- 
less they were connected with a telegraph oflice or sta- 
tion, where their messages could be received, and from 
which the necessary answers could be returned. There 
are such telegraphic stations in the nervous system. 
Beside the white nervous matter, formed of the fila- 
ments or fibres already described, there is another kind 
of nervous tissue, called the “ gray” or “ cineritious” 
matter. As its name indicates, it is of a gray or ashy 
color; and it contains, beside nervous fibres and blood- 
vessels, a great abundance of microscopic bodies, of va- 
rious forms, which are called the “ nerve-cells.” These 
cells are the peculiar elements of the gray nervous mat- 
ter, and are not found elsewhere. They are generally 
more or less rounded in form, 
with an oval spot upon each, 
which is called its “ nucle- 
us.” Many of them have 
slender projections or elon- 
gations running out from 
the surface in various direc- 
tions (Fig. 45). The nerve- 
fibres are abundantly min- 
gled and interwoven with 
the cells, and often, if not 
always, communicate with 
PHYSIOLOGY AND HYGIENE. 
Fig. 45. 
Nerve-cells; highly magnified. From 
a ganglion. STRUCTURE, ETC., OP THE NERVOUS SYSTEM. 
235 
them by means of the slender prolongations above spo- 
ken of. Such a collection of gray nervous matter is 
said to he a “ ganglion.” 
The gray matter forms a large part of the structure 
of the nervous system. It is found in the interior of 
the spinal cord, running in a double tract through its 
central parts, from one extremity to the other, being 
covered by the white fibres on its exterior. In the 
brain, on the contrary, it is spread out upon the surface, 
forming the folds and convolutions; and it.is also dis- 
tributed in several different masses in the deeper and 
inferior parts. The brain and spinal cord may there- 
fore be considered as a collection of ganglia, added to 
the mass of white fibres coming from the nerves. 
Now the ganglia are what are called the Nervous 
Centres. That is, the sensitive fibres terminate in them, 
and the motor fibres originate in them. We have al- 
ready said that these fibres are only organs of commu- 
nication. But the nervous centres are the organs which 
receive the sensitive impressions from without, and 
which originate the nervous action from within. They 
receive intelligence by the sensitive fibres from the dis- 
tant membranes; and by the motor fibres they send 
out in return the stimulus which calls into activity the 
muscles or the glands. 
125. Reflex Action of the Nervous System.—Thus the 
nervous centres are intermediate in their function be- 
tween the sensitive and motor fibres. The stimulus 
conveyed from without inward is received by them, 
and then returned or reflected in the opposite direc- 
tion. This action is called the Reflex Action of the nerv- 
ous system. 
This term expresses the whole secret of the nervous 
functions. 236 
PHYSIOLOGY AND HYGIENE. 
We see, accordingly, how it is that the nervous sys- 
tem acts as a means of communication between differ- 
ent organs. This communication is not direct, but cir- 
cuitous in its action. It passes first inward to the 
nervous centres, and again outward by reflection to the 
external organs. 
By the operation of the nervous system, also, we find 
that a stimulus applied to one organ excites the activity 
of another. Thus cold applied to the skin produces a 
contraction of the muscles; food introduced into the 
stomach causes the evacuation of the gall-bladder; and 
an irritating substance in the throat excites coughing 
by the muscles of the abdomen. 
Thus the different organs are associated in their func- 
tion, and made to act together, separately or in succes- 
sion, as the requirements of the system may dictate. 
There are a considerable number of nervous centres, 
which preside over different functions, and which re- 
ceive and communicate stimulus of different kinds. We 
shall now proceed to study in succession these various 
departments of the nervous system. 
QUESTIONS FOE CIIAPTEK XII. 
1. Why must the different organs act in harmony with each other? 
2. By what system is the harmonious action of the organs secured ? 
3. What is the structure, size, and appearance of the nervous fila- 
ments ? 
4. What is a nerve ? 
5. By what are the filaments of a nerve bound together and pro- 
tected ? 
6. In what part of the nervous system do the nerves of the body 
and limbs terminate ? 
7. What is the situation and form of the spinal cord ? 
8. With what is the spinal cord connected at its upper extremity ? 
9. In what cavity is the brain contained ? QUESTIONS. 
237 
10. What are the three principal parts of the brain ? 
11. By what are the two lateral halves of the brain and spinal cord 
separated from each other ? 
12. What are the spinal nerves ? what are the cranial nerves ? 
13. What is the general function of the nerves and nervous fila- 
ments ? 
14. What is the irritability of a nerve ? 
15. Where is the effect of nervous irritability manifested—in the 
nerve itself, or in some other organ ? 
16. What two kinds of nervous fibres are there in the nervous sys- 
tem ? 
17. What is the property of the sensitive fibres? 
18. What is the property of the motor fibres ? 
19. What is the structure of the gray nervous matter ? 
20. What is the name given to a collection of gray nervous matter ? 
21. Where is the gray matter situated in the spinal cord? in the 
brain ? 
22. What is the function of a ganglion ? 
23. What is the reflex action of the nervous system ? 
24. Name some instances of reflex action. 238 
PHYSIOLOGY AND HYGIENE. 
CHAPTER Xffl. 
Function of the Spinal Nerves.—Sensation and Motion.—Paralysis 
from injury of Nerve.—Restoration of a divided Nerve.—Anterior 
and Posterior Roots of Spinal Nerves.—Anterior Roots motor.— 
Posterior Roots sensitive.—Anterior and Posterior Columns of the 
Cord.—Anterior Columns motor.—Posterior Columns sensitive.— 
Connection of Spinal Cord with Brain.—Paralysis from injury of 
Spinal Cord.—Paraplegia.—Crossed Action of the Spinal Cord.— 
Hemiplegia.—Intercostal Nerves.—Phrenic Nerve.—Sensibility of 
the Skin—its Variation in different Parts.—Ordinary Sensibility.— 
Sensibility to Pain.—Sensibility to Heat and Cold.—Spinal Cord as 
a Nervous Centre.—Its Gray Matter.—Reflex Action of the Spinal 
Cord.—Its Character and Function. 
THE SPINAL NERVES AND SPINAL CORD. 
126. Distribution of the Spinal Nerves.—The spinal 
nerves, as we have seen, which are distributed to the 
external surface and muscles of the body and limbs, 
place these organs in communication with the spinal 
cord, and, through the spinal cord, also with the brain. 
Now these nerves are the organs of the two great 
functions of Sensation and Motion. If we touch any 
part of the external surface we feel the contact, because 
it is transmitted to the nervous centres by the nerve 
coming from the part. Whenever we move a limb, we 
do so by means of the nerve which calls into action the 
muscles to which it is distributed. These two func- 
tions, therefore, of sensation and motion, are confided to 
each nerve for that part of the body to which it be- 
longs. 239 
127. Effects of injury to a Spinal Nerve.—Consequent- 
ly, when a spinal nerve is injured or destroyed, these 
functions can not continue. Such an effect is produced 
whenever the principal nerves of the arm or the leg are 
accidentally compressed so that their vitality is suspend- 
ed. The limb is then said to be “ asleep.” It is numb 
and powerless, and seems like a dead weight attached 
to the body. When the pressure is taken off, the nerve 
gradually recovers itself, and sensibility and movement 
return in the affected limb. 
The same effect is still more complete when a nerve 
is actually cut or torn apart. Then all communication 
is severed between the central parts and the injured 
limb. The muscles may be sound, but we can not use 
them, since the necessary stimulus can no longer reach 
them through the divided nerve. The skin may be un- 
injured, but we can not feel, because the nervous com- 
munication stops short before it arrives at the spinal 
cord. This affection is called Paralysis. 
In such cases the paralysis, of course, is confined to 
that part supplied by the injured nerve. Thus, if the 
nerve going to one leg be cut off, that leg alone is par- 
alyzed. If the nerve belonging to the right arm be db 
vided, the right arm alone is affected. Any portion of 
the limb, such as the hand or even one finger, may be 
separately paralyzed, if the nerve distributed to it be 
severed while the others remain uninjured. 
In such a paralysis it is evident that there are two 
different affections combined, namely, & paralysis of mo- 
tion and a paralysis of sensation. Both kinds of paral- 
ysis are produced at once, because the nerve contains 
both motor and sensitive fibres, and because all these 
fibres have been cut off at the same time. 
THE SPINAL NEEVES AND SPINAL COED. 240 
PHYSIOLOGY AND HYGIENE. 
128. Reunion of divided Nerves.—Now, does an acci- 
dent like this destroy all hope of cure, and entail a per- 
manent loss of motion and sensibility in the injured 
parts? Fortunately it does not. If it were so, every 
surgical operation would produce more or less paraly- 
sis, and even every accidental cut upon the fingers 
would destroy the sensibility and action of some por- 
tion of them. For the smaller nerves are so finely dis- 
tributed that some fibres are necessarily severed by any 
incision of the tissues, and after a time a repetition of 
such accidents would paralyze a considerable portion 
of the surface. 
But these fibres, when cut, grow together again. They 
heal, like the muscles or the skin, and thus re-establish 
their communication. This healing of the nerves is 
slower and more difficult than that of other tissues, and 
therefore the surgeon avoids them in his operations. 
But after a long interval, sometimes several months or 
even a year, according to the size of the nerve, the 
wounded fibres gradually reunite, and sensibility re- 
turns to the surrounding parts. 
In the spinal nerves of the limbs and trunk the sensi- 
tive and motor fibres are inextricably mingled togeth- 
er. They also have precisely the same structure, and 
we can not distinguish one kind from the other by any 
difference in their appearance. We only know that the 
nerve serves at the same time both for sensation and 
motion, and therefore that it contains both motor and 
sensitive fibres. 
129. Distinction of Sensitive and Motor Roots in the 
Spinal Nerves.—But as the nerve enters the cavity of 
the spinal canal, a curious change becomes manifest in its 
anatomical arrangement. There the two kinds of fibres THE SPINAL NEEVES AND SPINAL COED. 
241 
part company. The sensitive fibres pass backward in a 
separate bundle, and join the spinal cord toward its pos- 
terior part; the motor fibres disengage themselves from 
the others, and unite with the spinal cord toward its 
front part. Thus every spinal nerve, on each side the 
body, has two separate roots, by which it is connected 
with the spinal cord, viz., a posterior root, composed of 
sensitive fibres, and an anterior root, composed of mo- 
tor fibres (Fig. 46). 
Pig. 46. 
Transverse oeouon oi me bpiinu Void.—re, o. Spinal nerves of right and left 
side, showing their two roots: d. Anterior root; e. Posterior root; c. Ganglion 
of posterior root. 
In the accompanying diagram, the spinal cord is 
shown in transverse section; that is, as if it were cut 
across horizontally at the level of one pair of spinal 
nerves. The lower part of the drawing represents the 
front of the spinal cord, and the upper part its posterior 
portion. The two roots of each nerve, anterior and pos- 
terior, are seen separating from each other, and uniting 
with the corresponding parts of the spinal cord. The 
posterior root has upon it a small swelling or ganglion 
(marked c), which is the only particular in which its 
appearance differs materially from that of the anterior 
root. The longitudinal fissure is also shown, by which 242 
PHYSIOLOGY AND HYGIENE. 
the spinal cord is partially divided into right and left 
halves. This fissure is rather wide and shallow at the 
front, but narrow and deep behind. Finally, the gray 
matter is seen in the central part of the spinal cord, 
showing the singular cross-like form in which it is ar* 
ranged. 
While in the nerves of the exterior, accordingly, the 
functions of motion and sensibility are mingled togeth- 
er by the interlacing of their fibres, in the central parts 
of the nervous system they are separated from each 
other and occupy distinct situations. 
What becomes of the fibres of the nerves after they 
have been united with the spinal cord ? 
130. Passage of Sensitive and Motor Fibres through 
the Spinal Cord.—On arriving at the corresponding por- 
tions of the cord, they change their direction and pass 
from below upward. The sensitive fibres of the poste- 
rior roots then form a part of those two vertical bun- 
dles of white nervous matter which run up and down 
on the back of the spinal cord, on each side the central 
fissure. (See Fig. 44.) These are called the Posterior 
columns of the cord. The motor fibres of the anterior 
roots join two similar bundles of white matter in front; 
these are called the Anterior columns of the cord. 
The posterior columns of the cord are sensitive, like 
the fibres of the posterior roots; and the anterior col- 
umns are motor, like the fibres of the anterior roots. 
131. Termination of Nervous Fibres in the Brain.— 
From this point the anterior and posterior columns of 
the cord pursue their course to the upper part of the 
spinal canal. Here they enter the great opening or 
foramen in the base of the skull, and then, enlarging 
and spreading their fibres in various directions, termi- THE SPINAL NEKVES AND SPINAL COED. 
243 
nate, as we have already said, in the substance of the 
brain. 
Throughout this distance the nervous fibres of the spi- 
nal cord maintain an undisturbed connection. Anato- 
mists can not yet determine whether each filament by 
itself runs a continuous and uninterrupted course from 
the nerve to the brain throughout the spinal cord, or 
whether successive fibres connect with each other the 
nerve, the spinal cord, and the brain. For these fila- 
ments are so innumerable and so delicate that it is im- 
possible to follow the same one under the microscope 
long enough to be sure of its exact destination. But, 
whatever may be their precise anatomical arrangement, 
the physiological connections of the anterior and pos- 
terior columns are continuous and complete up to the 
point of their termination in the brain. 
Now the brain is the seat of the consciousness and 
the will. No sensation can be perceived until it arrives 
at the brain, and no voluntary motion can be performed 
unless the nervous stimulus, starting from the brain, 
can reach the nerve through the spinal cord. 
The spinal cord, therefore, as thus far considered, is a 
medium of communication between the brain and the 
spinal nerves. It may be regarded itself as a great 
nerve, inclosed in the spinal canal and giving off the 
successive pairs of spinal nerves as branches from its 
own trunk. 
132. Paralysis from Injury of the Spinal Cord.—Ac- 
cordingly, any injury to the spinal cord will produce 
paralysis of the parts below. This happens where any 
severe accident has broken and displaced the bony 
arches of the spinal column which inclose and protect 
the cord. The broken pieces of bone, pressing upon 244 
PHYSIOLOGY AND HYGIENE. 
the cord and lacerating its substance, cut off the com- 
munication between the brain and the inferior parts. 
When such an injury has produced paralysis of the 
lower part of the body, we say of the paralyzed person 
that his “ back is broken.” The fracture of the bones, 
however, would not be, by itself, of much consequence, 
since it is only the projections on the back of the spi- 
nal column which are usually broken; but it becomes 
important and dangerous on account of the injury in- 
flicted at the same time upon the spinal cord. 
When such a fracture of the spine happens in the 
middle of the back, the legs are paralyzed, while the 
arms remain unaffected. This form of paralysis, which 
is confined to the lower half of the body, is termed 
Paraplegia. If the injury be in the middle of the neck, 
the arms are also paralyzed, since the spinal cord is 
then severed above the point at which the nerves to 
these limbs are given off. 
In all such cases as the above, the powers of motion 
and of sensibility are usually paralyzed together. The 
skin becomes insensible, and the voluntary muscles pow- 
erless over the whole extent of the paralyzed parts; be- 
cause so rude an injury to the spinal cord will general- 
ly reach all parts of its thickness, and tear off at the 
same time its sensitive and motor fibres. But some- 
times it happens that the accident affects only the an- 
terior or only the posterior portion of the cord. In 
such instances the power of motion is suspended while 
sensibility remains; or, on the other hand, the sensi- 
bility of the skin is lost while the muscles retain their 
power. 
133. Decussation of the Motor and Sensitive Fibres of 
the Spinal Cord.—A singular feature in the connection THE SPINAL NERVES AND SPINAL CORD. 
245 
of the spinal nerves with the brain through the spinal 
cord is that this connection is a crossed one; that is, 
that the nerves of the right side of the body are connect- 
ed icith the left side of the brain, and those of the left 
side of the body with the right side of the brain. 
The anterior columns of the cord pass upward, as we 
have seen, their fibres running nearly parallel with each 
other until they reach the entrance to the skull. Im- 
mediately above this point, and before joining the brain 
proper, the spinal cord enlarges into a somewhat wider 
and thicker oblong-shaped mass, which has been already 
mentioned, called the il medulla oblongata.” At this 
situation the fibres of the two columns cross over ob- 
liquely from side to side, those of the left anterior col 
umn passing to the right side, and those of the right 
anterior column passing to the left side. This is called 
the “Decussation of the anterior columns of the cord.” 
Their fibres then terminate respectively in the corre- 
sponding sides of the brain. 
Thus each side of the brain holds under its control 
the voluntary movements of the opposite side of the 
body. 
134. Paralysis from injury of the Brain.—The conse- 
quence of this is, that when a serious injury is inflicted 
upon the brain at the point where these motor fibres of 
the nerves take their origin, a singular kind of paralysis 
is produced, which is exactly confined to one side of the 
body. The right arm and the right leg, for instance, 
will be paralyzed, while the two limbs of the left side 
will remain uninjured. This kind of paralysis is known 
as Heyniplegia. It is situated on the opposite side of 
the body to that on which the injury to the brain has 
been inflicted. 246 
PHYSIOLOGY AND HYGIENE. 
The sensitive fibres of the spinal cord also pass from 
one side to the other. Their crossing, however, takes 
place, not in a particular spot, but throughout the whole 
length of the cord. As the sensitive root of each nerve 
joins the posterior column, its fibres soon pass over 
through the central portions of the cord, and then form 
a part of the posterior column of the opposite side. In 
hemiplegia, therefore, produced by injury of one side 
of the brain, the powder of sensation is lost on the oppo- 
site side of the body, at the same time with the power 
of motion. 
135. Intercostal and Phrenic Nerves.—Among the spi- 
nal nerves there are certain ones that deserve particu- 
lar attention. 
The first of these are the Intercostal nerves. As their 
name indicates, they are situated between the ribs, and 
are distributed to the intercostal muscles in the same 
situation. They are united with the spinal cord in the 
middle region of the back, from the level of the first rib 
to that of the last. It is these nerves, therefore, which 
enable the intercostal muscles to move in the act of in- 
spiration. 
Now, if we recall the mechanism of inspiration, we 
shall remember that this mechanism consists of two as- 
sociated actions: first, the movement of the diaphragm, 
by which the abdomen is protruded below, and, second- 
ly, the movement of the intercostal muscles, by which 
the chest is raised and expanded above. Both these 
sets of muscles are animated by nerves which come 
from the spinal cord; and the intercostal nerves, as we 
have seen, are given off from it in the middle region of 
the back. 
Accordingly, if the spinal cord be injured at the level THE SPINAL NERVES AND SPINAL COED. 
247 
of the first rib or at the lower part of the neck, the in- 
tercostal muscles are at once paralyzed. The chest no 
longer expands in respiration, but remains quiescent 
and motionless. It is for this reason that a fracture of 
the spine at the upper part of the back is more danger- 
ous than when situated lower down. Nevertheless, the 
breathing does not stop altogether, since it is still par- 
tially kept up by the action of the diaphragm. 
The other important pair of spinal nerves are the 
Phrenic nerves, which belong to the diaphragm itself. 
This nerve springs from the spinal cord by branches 
from two or three of the spinal nerves, just above the 
middle of the neck. Thence it passes downward as a 
single trunk on each side, and, entering the cavity of 
the chest, is distributed to the muscular fibres of the 
diaphragm. Upon the phrenic nerve depends the whole 
power of motion of this important muscle. 
When the spinal cord, therefore, is severed above the 
middle of the neck, both the intercostal muscles and the 
diaphragm are paralyzed together. All the movements 
of respiration accordingly cease, and death is necessa- 
rily produced. 
136. Acuteness of Sensibility in different parts.—Sev- 
eral facts remain to be noticed in regard to the sensibil- 
ity conferred by the fibres of the spinal nerves. 
This sensibility is extended throughout the skin or 
general integument of the body, and is therefore called 
the “ General sensibility.” It is not, however, distrib- 
uted every where in an equal degree, but is much more 
acute in some situations than in others; being more 
highly developed than elsewhere in the tips of the fin- 
gers. Physiologists have sometimes measured the de- 
gree of sensibility of different parts; and have found 248 
PHYSIOLOGY AND HYGIENE. 
that at the tips of the fingers it is twice as great as at 
the middle of their under surface, five times as great as 
on the back of the fingers, nine times as great as on the 
back of the hand, seventeen times as great as on the 
top of the foot, and more than thirty times as great as 
in the middle of the back. It is for this reason that we 
generally use the fingers as the organs of touch; and 
also because by their varied movements we can easily 
adapt them to the different surfaces which wTe may 
wish to examine. 
The sensibility of the skin is called into action by the 
contact of foreign bodies, and gives us information of 
their softness or resistance, their external shape, the 
smoothness or roughness of their surface, their fluidity 
or solidity, of cold and heat, and of all the physical 
qualities which can be ascertained by the touch. 
The internal tissues, siich as the muscles and some 
of the lining membranes, are also endowed with sensi- 
bility, but it is much less acute in them than in the 
skin. 
137. Sensibility to Pain.—It is through the sensibility 
of these parts that we are capable of feeling pain. But 
it is a curious fact that the sensibility to pain is entire- 
ly distinct from ordinary sensation, and even interferes 
with it exactly in proportion as it becomes more acute. 
Thus, if we place the hand upon a piece of iron at or- 
dinary temperatures, we can tell whether it is cool or 
warm, and can form a good idea of the exact degree of 
its cold or heat. But if it be hot enough to burn the 
skin, we no longer estimate the degree of its tempera- 
ture, but only feel the pain which it occasions. It is 
for this reason, as it is commonly said, that bodies which 
are excessively hot or excessively cold produce the same THE SPINAL NERVES AND SPINAL CORD. 
249 
sensation. The truth is, they do not produce any sen- 
sation of cold or heat, properly speaking, but only a 
sensation of pain, which is different from either. 
138. Sensibility to Heat and Cold.—Finally, the sensi- 
bility to heat and cold is different also from the ordina- 
ry sensibility of the touch; and instances hare been 
known where persons have lost the power of distin- 
guishing temperatures, while they have retained both 
the sensibility of touch and the sensibility to pain. 
All these different kinds of sensation are communi- 
cated to the brain through the medium of the spinal 
nerves and the spinal cord. 
So far, then, we have found the spinal cord to be an 
organ of communication between the spinal nerves and 
the brain; serving to conduct the power of sensation 
and voluntary motion by means of its anterior and pos- 
terior columns. 
' 139. The Spinal Cord -as a Nervous Centre.—But the 
spinal cord is also a Nervous centre. For it contains in 
its deeper parts a double band of gray nervous matter, 
in the form of a long ganglion running through its en- 
tire length. The form and situation of this gray mat- 
ter may be seen in a transverse section of the cord, as 
in Fig. 46. The motor and sensitive fibres of the spinal 
nerves not only join its anterior and posterior columns, 
as already described, but they also communicate with 
the gray matter in its central parts. The spinal cord 
may therefore act independently, as a distinct ganglion. 
When the cord is severed in the region of the neck 
or the upper part of the back, communication with the 
brain being cut off, all voluntary motion is lost in the 
muscles of the limbs below. But still these muscles 
may act; and they may act in response to a stimulus 250 
PHYSIOLOGY AND HYGIENE. 
applied to the skin of the paralyzed parts. This is 
sometimes seen in persons affected with complete pa- 
ralysis of the lower half of the body. Such persons are 
entirely helpless and insensible in the lower limbs. And 
yet touching the legs or the soles of the feet, the impres- 
sion of cold air, or the contact of the clothes, will often 
produce very evident twitching of the muscles, and even 
bending or straightening of the knees and ankles. 
In these cases the patient has no feeling in the pai’a- 
lyzed parts, and no knowledge of the movements which 
they execute. The brain, therefore, has nothing to do 
with these movements. They are performed by the in- 
dependent action of the spinal cord. Such movements, 
however, are reflex in their nature. That is, the action 
of the muscles is excited by a stimulus applied to the 
skin. The nervous stimulus is first conveyed inward 
by the sensitive fibres of the skin, and again reflected 
outward through the motor fibres to the muscles. This 
is called the Reflex Action of the spinal cord. How is 
this action accomplished ? 
When the stimulus applied to the skin is conveyed 
inward by the nerves, it arrives at the spinal cord by 
the posterior roots, and reaches the gray matter in its 
central parts. Here the gray matter receives the nerv- 
ous impression, and instantly converts it into a motor 
impulse, which is reflected outward along the motor 
fibres of the anterior roots. As these fibres are final- 
ly distributed to the muscles, they stimulate these or- 
gans to contraction, and thus the reflex movement is 
finally produced (Fig. 47). In the accompanying dia- 
gram the spinal cord is shown in vertical section ; that 
is, as if it were split longitudinally from above down- 
ward. The gray matter in its centre, therefore, ap- THE SPIRAL NERVES AND SP1NAE CORD. 
251 
pears as a vertical band 
or ribbon, still covered 
with the white substance 
on its exterior. The di- 
rection of the nervous 
stimulus is also shown, as 
it passes inward by the 
posterior root to the gray 
matter, and is there turn- 
ed or reflected back, to 
pass outward again along 
the motor fibres of the 
anterior root. 
Now the peculiarity of this action of the spinal cord 
is that it is a perfectly simple reflex action; that is, 
it is not accompanied by any sensation, consciousness, 
or volition. These properties reside altogether in the 
brain, and do not belong to the spinal cord. Conse- 
quently, when the communication with the brain is cut 
off, it is only the simple blind operation of the cord 
itself which is called into activity. 
140. Importance of the Reflex Action of the Spinal Cord. 
—But this independent action of the spinal cord takes 
place also in health, only we do not usually notice it, 
because our attention is not attracted by any conscious 
sensation. Nevertheless, it is very important in pro- 
tecting the body from sudden injuries, and in regula- 
ting the action of some of the internal organs. 
When the skin of any part is unexpectedly brought 
in contact with a foreign body, such as a heated iron or 
a rough surface, we often withdraw the limb by an in- 
stantaneous and involuntary motion before we are fair- 
ly conscious of any injury. This is the reflex action of 
Fig. 47. 
Diagram of Spinal Cord in Vertical Sec- 
tion, showing Reflex Action.—a. Pos- 
terior root of spinal nerve; b. Ante- 
rior root of spinal nerve. 252 
PHYSIOLOGY AND HYGIENE. 
the spinal cord. In falling from a height, the limbs are 
instinctively thrown into such a position as to defend 
the most important parts of the body, and break as 
much as possible the force of the shock. This is the 
reflex action of the spinal cord. Certain of the internal 
muscles which guard the natural passages of the body 
are maintained in continuous contraction without vol- 
untary effort and without fatigue, and are moved in va- 
rious directions at the proper time, to provide for the 
healthy operation of the internal functions. This is 
also accomplished by the reflex action of the spinal 
cord. 
When the sensibility or reflex power of the spinal 
cord is unnaturally increased, it produces diseases of a 
terrible character. These are the various affections 
which are accompanied by Convulsions; in which all 
the muscles of the body are thrown into involuntary 
spasms, and the limbs are bent and distorted by irre- 
sistible contractions. In the convulsions of infants, 
these movements are usually caused by indigestion. In 
the more fatal diseases of “ Tetanus” and “ Hydropho- 
bia,” in grown-up persons, the least external excitement, 
such as the openipg of the doors, the contact of the 
dress, or a breath of air, is sufficient to call out the un- 
natural irritability of the cord, and throws the whole 
muscular system into spasmodic rigidity. 
During health, accordingly, wrn are not conscious how 
much we owe to the spinal cord and its reflex power. 
Quiet and unnoticed, it keeps watch over the safety of 
the body, ready to act at an instant’s warning, and per- 
forms its work without ever causing us fatigue, or re- 
quiring any effort of attention or of the will. But when, 
irritated by disease, it loses its character of moderation THE SPINAL NEKVES AND SPINAL COED. 
253 
and regularity, and from the servant of the body be- 
comes its master, then it rapidly exhausts the muscular 
force and destroys life by the uncontrolled violence of 
its action. 
The spinal cord, therefore, is not only a medium of 
communication between the brain and the external 
parts. It is also a nervous centre, which presides by 
itself over the involuntary movements of the body and 
limbs. It acts as such without our consciousness and 
independently of our will; and its function is to pro- 
vide for certain muscular actions in the interior, and to. 
protect the body against unforeseen dangers from with- 
out. 
1. How are the different parts of the body and limbs placed in com- 
munication with the spinal cord and the brain ? 
2. What are the two great functions of the spinal nerves ? 
3. What is the effect of compressing or cutting off a spinal nerve ? 
4. What is paralysis ? 
5. What two kinds of paralysis exist together after cutting off a 
spinal nerve ? 
6. May the nerve grow together again after it has been once di- 
vided ? What effect does this have on the paralyzed parts ? 
7. What two kinds of fibres are contained in the spinal nerves ? 
8. How are the sensitive and motor fibres separated within the spi- 
nal canal ? 
9. How and where do they unite with the spinal cord ? 
10. Of what fibres is the anterior root of a spinal nerve composed ? 
11. Of what is the posterior root composed ? 
12. In what direction do the nervous fibres pass after joining the 
spinal cord ? 
13. What are the anterior and posterior columns of the cord, and 
what is the difference in their function ? 
14. What is the effect of injury of the spinal cord upon the parts 
below ? 
15. Why is fracture of the spine liable to produce paralysis ? 
QUESTIONS FOR CHAPTER XIII. 254 
PHYSIOLOGY AND HYGIENE. 
16. What is paraplegia ? 
17. What part of the spinal cord must be injured to produce para- 
plegia ? 
18. What part of the spinal cord must be injured to produce paral- 
ysis of both arms and legs ? 
19. Are motion and sensation both suspended together in ordinary 
cases of paralysis ? 
20. Are they ever affected separately ? Under what circumstances ? 
21. How are the two opposite sides of the body and brain connect- 
ed with each other ? 
22. Where do the fibres of the anterior columns cross to the oppo- 
site side ? 
23. What is hemiplegia ? 
24. If the right side of the brain be injured, which side of the body 
will be paralyzed ? 
25. If the left side of the brain be injured, which side of the body 
will be paralyzed ? 
26. Where do the sensitive fibres of the spinal cord cross from side 
to side ? 
27. Where are the intercostal nerves united with the spinal cord ? 
28. What effect is produced on respiration by fracture of the spine 
at the upper part of the back ? 
29. By what nerves is the diaphragm supplied ? 
30. Where are the phrenic nerves united with the spinal cord ? 
31. What effect is produced on respiration by injury to the spinal 
cord above the origin of the phrenic nerves ? 
32. What is 11 general sensibility ?” 
33. In what parts is the sensibility of the integument most acute ? 
34. Is the sensibility of the internal organs more or less acute than 
that of the skin ? 
35. What information do we acquire by means of the general sen- 
sibility ? 
36. What is the difference between general sensibility and sensi- 
bility to pain ? 
37. May general sensibility exist without sensibility to pain, and 
vice versa ? 
38. Why is the spinal cord a nervous centre as well as an organ of 
communication ? 
39. What is the reflex action of the spinal cord? 
40. How is this reflex action seen in paralyzed persons ? 41. How is the nervous stimulus conveyed in reflex action of the 
spinal cord? 
42. Is this action accompanied hy sensation ? by consciousness ? 
by volition ? Why not ? 
43. Name instances of the involuntary reflex action of the spinal 
cord in health—in disease. 
44. What is the effect of excessive irritability of the spinal cord in 
disease ? 
QUESTIONS. 
255 256 
PHYSIOLOGY AND HYGIENE. 
CHAPTER XIV. 
Character of the Cranial Nerves.—Sensibility of the Face.—Fifth 
Pair of Cranial Nerves—its three Branches—their Distribution— 
their Sensibility.—Neuralgia.—Tic Douloureux.—Motor Branch 
of the Fifth Pair.—Muscles of Mastication.—Temporal.—Masse- 
ter.—Pterygoids.—Movements of Expression.—Facial Nerve—its 
Distribution—its Motive Power.—Paralysis of the Face.—Hypo- 
glossal Nerve.—Movements of the Tongue.—Pneumogastric Nerve 
—its Origin and Distribution.—Pharyngeal Branch.—Act of Deg- 
lutition.—Sensibility of the Pharynx.—Protection of the Nostrils 
in Deglutition.—Laryngeal Branches of the Pneumogastric.—The 
Glottis—its Movements in Respiration.—Protection of the Glottis 
in Deglutition.—Formation of the Voice.—Action of the Larynx. 
In the study of the spinal nerves we have seen that 
these nerves by their sensitive fibres supply sensibility 
to the skin of the body and limbs, and by their motor 
fibres communicate the power of motion to the corre- 
sponding parts. 
141. Functions of the Cranial Nerves.—Now the same 
powers reside in the external portions of the head and 
face. The skin of these parts is also sensitive, and their 
movements are varied and important. Accordingly, 
they are supplied with nerves similar in many respects 
to those connected with the spinal cord. But as the 
nerves of the head and face pass directly from the brain 
through openings in the bony floor of the cranium, they 
are distinguished by the name of the Cranial nerves. 
In all there are twelve pairs of cranial nerves. But 
THE CRANIAL NERVES. 257 
as some of these nerves are very peculiar in their na- 
ture, and have no relation with the external parts but 
only with the organs of the special senses, we shall ex- 
amine for the present only those which are connected 
with the simpler and more ordinary nervous functions 
of this part of the body. 
The first of these functions is that of Sensibility. This 
power is highly developed in all parts of the face, and 
at the tip of the tongue is more acute than in any other 
part of the body, being twice as great as in the ends 
of the fingers. The lips are also highly sensitive, and 
the eyelids, the nose, and the surface of the cheeks pos- 
sess the same property in a somewhat less degree. The 
most insensible part of the head is that portion of the 
scalp which is covered with hair; but even here the 
surface is sufficiently sensitive to perceive readily the 
contact of foreign substances. 
142. Fifth Pair of Cranial Nerves.—The sensibility of 
the face is supplied by a large and very interesting 
nerve, which is called the Fifth pair. Anatomists have 
given it this name because, in counting all the cranial 
nerves from before backward, it comes the fifth one in 
the series. It is also called the “ trigeminal” nerve, be- 
cause, after emerging from the base of the brain, and 
while still contained within the cavity of the skull, it 
divides into three great and nearly equal branches. 
Just at the level of this division the nerve has upon it 
a rounded swelling or ganglion of gray matter, which 
is called the “Gasserian ganglion,” from the name of the 
anatomist who first described it. Its threefold branches 
then pass through three separate openings in the base 
of the skull, and, running thence from behind forward, 
are distributed to the skin of the three different regions 
TIIE CRANIAL NERVES. 258 
PIIYSIOLOGY AND HYGIENE. 
of the face. The first branch passes upward to the fore- 
head and the top of the head, the second to the middle 
portion of the face, the nose, cheeks, and upper lip, and 
the third to the lower lip, the chin, and the adjacent 
parts. During their passage through the deeper tex- 
tures, the second and 
third branches also send 
filaments respectively to 
all the teeth of the up- 
per and lower jaw; and 
nervous fibres are also 
sent to the tongue and 
the inside of the mouth 
and nostrils (Fig. 48). 
Thus all the different 
parts of this region are 
supplied with sensibili- 
ty. The fifth pair, there- 
fore, is the great sensi- 
tive nerve of the face; 
and it is on account of 
the delicate organiza- 
tion and minute ramification of this nerve that the skin 
is here endowed with the sense of touch in such un- 
usual perfection. 
But when the fifth pair is exposed to irritation from 
disease, its sensibility is the source of exquisite pain. 
If a tooth, for example, be attacked by caries or decay 
of its hard substance, the suffering which it occasions is 
of extreme severity. For every tooth is provided with 
a filament coming from the fifth pair, which penetrates 
its root from below, and there lies concealed and defend- 
ed by the hard covering of its crown. But when this 
Fig. 48. 
Distribution of the Fifth Pair upon the 
Face.—a. Gasserian ganglion ; 1, 2, and 
3. First, second, and" third branches of 
the Fifth Pair. THE CRANIAL NERVES. 
259 
covering becomes wasted or destroyed from any cause, 
then the slightest touch of the food in mastication, or 
even the contact of the air, produces an irritation which 
penetrates to the nervous tissue below. Every one 
knows how intolerable is the pain of toothache from 
this cause. When the injury to the tooth is excessive, 
the only remedy is to extract it from its socket in the 
jaw. The nerve is then torn olf at its root, and the sen- 
sibility of the tooth destroyed. Afterward the wound- 
ed tissues heal over, and the pain is permanently re- 
lieved. 
The fifth pair is also the seat of an extremely painful 
affection termed Neuralgia. This is simply an irrita- 
tion of the nerve from some disease of its tissue. All 
the sensitive nerves are liable to this affection; but 
when seated in the nerves of the face, it is so much 
more severe than elsewhere that it has received a dis- 
tinct name, and is called “ tic douloureux,” or the “ pain- 
ful spasmbecause it seizes the patient in sudden twin- 
ges or paroxysms. The best protection against these 
troublesome affections is to preserve the general func- 
tions of the body in a sound and healthy condition. 
143. Motor portion of the Fifth Pair.—But there is one 
part of the fifth pair which presents a remarkable differ- 
ence from those which we have thus far examined. This 
is a portion of the third branch, which accompanies it 
through its opening in the skull, but which has a differ- 
ent destination and different properties. All the other 
parts of the fifth pair are sensitive in their character, 
and are distributed to the skin and lining membranes 
of the face. This portion, on the contrary, is motor in 
character, and is distributed to muscles. Moreover, it 
belongs to a set of muscles which are all associated in 260 
one function, viz., that of mastication. The nervous 
branch which supplies these muscles with motive power 
is therefore called the Masticator nerve. 
The muscles of mastication are four in number on 
each side. The two larger and more powerful are, 1st, 
the Temporal, and, 2d, the Masseter muscles. 
The temporal muscle is so called because it is situ- 
ated in the temples. Its fibres run upward from their 
attachment to the lower jaw, and are spread out in a 
fan-like form upon each side of the head in front of and 
above the ear. Place the fingers upon the temple, and 
then move the lower jaw upward and downward, and 
you will feel this muscle swelling and hardening at 
every alternate movement. It serves to press the low- 
er jaw against the upper, and thus to bring the teeth 
firmly in contact with each other. 
The masseter is a thick and strong muscle, situated 
at the back part of the side of the jaw. We can easily 
feel its movement in this situation during the process 
of mastication. Both these muscles act together, and 
in the same direction ; and they accordingly move the 
lower jaw from below upward with great rapidity and 
force. 
But, during mastication, the lower jaw is also moved 
from side to side, in order to produce the grinding ac- 
tion which is so essential for the comminution of the 
food. This lateral movement is performed by two in- 
ternal muscles on each side, called the Pterygoid mus- 
cles, which are concealed between the inner part of the 
jaw and the base of the skull. They are rather smaller 
than the others, but share with them the work of mov- 
ing the jaw in mastication. 
All these muscles are exclusively animated by the 
PIIYSIOLOGY AND HYGIENE. THE CRANIAL NERVES. 
261 
motor branch of the Fifth pair. This branch is there- 
fore justly named the masticator nerve. 
144. Seventh Pair, or Facial Nerve.—But, beside the 
acts concerned in mastication, the face itself has very 
numerous and important movements. Its whole sur- 
face is endowed with a mobility by which its expres- 
sion is constantly changed, and the varying emotions 
of the mind portrayed upon its exterior. The eyelids 
may be opened or closed ; the nostrils expanded or con- 
tracted ; the lips drawn upward or downward, and their 
opening enlarged or narrowed. These movements may 
also be combined with each other in a multitude of va- 
rious ways, so as to change in a corresponding degree 
the external appearance and configuration of the face. 
They are therefore called the Movements of Expression. 
By their aid the face speaks a language of its own, 
and a language which is easily understood, for every 
one comprehends its meaning by instinct. 
The muscles of expression are animated by a nerve 
which is called the Facial nerve. 
The facial nerve originates from the side of the me- 
dulla oblongata, and, after passing through a long and 
tortuous canal in the floor of the skull, emerges from a 
small orifice in the bone a little behind the external 
opening of the ear. It then curves forward beneath 
the ear, passes by several branches through the sub- 
stance of the parotid gland which occupies this situa- 
tion, and then, spreading out in various directions, is 
distributed to the muscles which move the different 
parts of the face (Fig. 49). 
The natural function of this nerve has already 
been explained. It is the nerve of expression, and en- 
ables the countenance to assume those varied appear- 262 
PHYSIOLOGY AND HYGIENE. 
ances which indicate the 
changes of mental emo- 
tion. Like the fifth pair, 
however, it is also sub- 
ject to disease; and, 
when affected in this 
way, its natm*al func- 
tion is consequently dis- 
turbed. As irritation 
of the fifth pair pro- 
duces pain, so irritation 
of the facial nerve 
produces convulsive 
twitchings of the face, 
and an unnatural change 
in its expression. The 
facial nerve may also be injured, either by accidental 
violence or by swellings pressing upon it in its bony 
canal. The result of this injury is a singular kind of 
paralysis, known as “ paralysis of the face.” This is al- 
most always confined to one side; but on this side the 
face becomes devoid of animation, and remains passive 
and motionless. The feelings have no longer any in- 
fiuence upon its action, and the features cease to exhibit 
their natural changes of expression. 
145. Motor Nerves of the Eyeball.—Beside the facial, 
there are three small motor nerves belonging to the 
cranium which do not appear externally, but go to ani- 
mate the muscles of the eyeball, within the orbit of the 
eye. They are the third, fourth, and sixth pairs of cra- 
nial nerves. They provide for the movement of the 
eyes from right to left, or upward and downward, or 
for turning obliquely in their orbits. They assist in 
Fig. 49. 
The Facial Nerve. 263 
this way, to a certain extent, in the expression of the 
face. 
" 146. Motor Nerve of the Tongue.—There is still an- 
other motor nerve which is distributed to the muscles 
of the tongue. It is therefore called the “ hypoglossal 
nerve.” It comes from the front part and side of the 
medulla oblongata, passes through an opening in the ad- 
jacent portion of the skull, and then runs forward, deep- 
ly concealed among the tissues of the neck, until it ar- 
rives beneath the tongue. It then passes upward into 
the substance of the organ, sending out branches and 
ramifications to all the muscular bundles of which its 
mass is composed. It provides for all the varied move- 
ments which the tongue is required to perform, both in 
breaking and in the mastication of the food. 
The tongue, accordingly, like the other parts about 
the face, is supplied with a sensitive nerve and a mo- 
tor nerve. Its sensitive nerve is the branch which it 
receives from the fifth pair; and its motor nerve is 
the hypoglossal, which is distributed to its muscular 
fibres. 
But there are other nerves coming from the brain 
beside those which are devoted to sensation and volun- 
tary motion. The most remarkable of these is a long 
and very important nerve, termed the Pneumogastric. 
147. Pneumogastric Nerve.—The pneumogastric nerve 
is so called because its final branches are distributed to 
the lungs and to the stomach. To reach these organs, 
however, it traverses a long distance from its origin at 
the base of the brain, and passes successively through 
the neck, the chest, and the upper part of the abdomen. 
On account of this extended and varied course, so dif- 
ferent from that of the other cranial nerves, the older 
THE CRANIAL NERVES. 264 
anatomists called it the Par vagum, or the “ wandering 
pair.” The name was well deserved. 
The pneumogastric takes its origin from the side of 
the medulla oblongata, by ten or fifteen separate fila- 
ments, which soon unite into a single nervous cord, and 
pass, in this form, through a bony canal in the floor of 
the skull. It has an abundance of sensitive fibres of 
its own, and receives, beside, motor fibres by branches 
which join it from the facial nerve, the hypoglossal 
nerve, and others in its neighborhood. At a short dis- 
tance from its origin it has also a small swelling or 
ganglion, like the Gasserian ganglion of the fifth pair. 
After emerging from the skull, it pursues its course 
downward through the neck, deeply imbedded in the 
tissues, and in close company with the great blood-ves- 
sels of the part, and thus enters the cavity of the chest. 
During this passage it gives off three important 
branches. 
The first of these is the Pharyngeal branch. 
As its name implies, this nerve is distributed to the 
“ pharynx,” or the funnel-shaped muscular tube which 
receives the food from the back part of the mouth and 
conducts it to the (Esophagus. The fibres of the nerve 
penetrate its muscular layers and lining membrane, and 
supply them both with sensibility and motive power. 
The second is the Superior laryngeal branch. This 
is distributed to the lining membrane of the larynx, 
and communicates to it, as we shall hereafter see, a sen- 
sibility of an important character. 
The third branch follows a remarkable course. It is 
given off from the main trunk of the nerve in the lower 
part of the neck or just at its entrance into the chest. 
It then, after continuing a very short distance down- 
PHYSIOLOGY AND HYGIENE. THE CRANIAL NERVES. 
ward, returns upon itself, and, curving round the great 
vessels at the top of the chest, mounts upward again 
along the neck until it arrives 
at the level of the larynx, when 
it is distributed to the various 
muscles of this organ. It is 
therefore called the Inferior 
laryngeal branch. 
This nerve has a singular 
historical interest; for it was 
especially studied by Galen, 
the most eminent physician of 
the Roman Empire in the sec- 
ond century, who examined 
its properties, and discovered 
its physiological connection 
with the function of the voice. 
He called it the “ recurrent” 
nerve, owing to its peculiar 
course in returning, as we have 
described, from below upward. 
It still retains this name, by 
which it is often designated at 
the present day. 
Thus the larynx is supplied 
with two separate nerves, both 
branches of the pneumogas- 
tric, viz., the superior laryn- 
geal, which gives sensibility 
to its lining membrane, and 
the inferior laryngeal, which 
communicates to its muscles 
the power of motion. 
Fig. 50. 
Diagram of the Pneumogastiic 
Nerve, with its principal branch- 
es.—1. Pharyngeal branch; 2. Su- 
perior laryngeal; 3. Inferior la- 
ryngeal; 4. Branches to the 
lungs ; 5. Stomach; 6. Liver. PHYSIOLOGY AND HYGIENE. 
The inferior laryngeal branch also gives filaments to 
the oesophagus in the region of the neck. 
The pneumogastric nerve, in its passage through the 
chest, sends off numerous filaments, which penetrate the 
lungs, and follow the ramification of the bronchial tubes 
to their termination in the air vesicles. To these or- 
gans it communicates a peculiar sensibility, the impor- 
tance of which we shall learn hereafter. It then en- 
ters the abdomen, and is there finally distributed to 
the walls of the stomach (Fig. 50). 
The upper branches of the pneumogastric nerve are 
connected with the mechanism of two most important 
functions, viz., that of Swallowing and that of Respira- 
tion. 
148. Action of the Pneumogastric Nerve in Swallowing. 
—As we have already seen, both the lining membrane 
of the mouth and the surface of the tongue are en- 
dowed with ordinary sensibility of a high degree by 
the fibres of the fifth pair. But as the food passes to- 
ward the back part of the throat and into the pharynx, 
it meets with another sensibility of a peculiar kind. 
This sensibility no longer gives rise to the sensations 
of ordinary touch, but it excites at once, by a reflex ac- 
tion, the whole muscular apparatus of deglutition. Of 
these muscles the three most active are those which are 
called the Constrictors of the pharynx, because they 
are wrapped round this canal in such a way as to con- 
strict or compress it successively from above down- 
ward, and thus to carry the food through it in the same 
direction. 
This reflex action takes place through the pharyn- 
geal branch of the pneumogastric nerve; its sensitive 
fibres receive the impression of the food, and its motor 
fibres excite the muscles to contraction. TIIE CRANIAL NERVES. 
267 
It is for this reason that the action of the pharynx 
in swallowing is involuntary. So long as mastication 
is going on, we can vary or arrest its movements at 
will; but when once the food has passed the isthmus 
of the throat, and is fairly within the grasp of the phar- 
ynx, these muscles close upon it by reflex action, and 
carry it with a kind of spasmodic movement downward 
to the oesophagus. 
But when foreign substances not fit for deglutition 
are brought in contact with the lining membrane of 
the pharynx, the opposite effect is produced. If the 
feather of a quill or the ends of the fingers be thrust 
backward into the throat, the impression so produced 
upon its lining membrane no longer excites the move- 
ment of swallowing, but a resistance and reaction of 
tiie muscles of the pharynx; and if the irritation be 
continued, the oesophagus and stomach at last sympa- 
thize with the reaction, and may even be excited to 
vomiting. Thus all the reflex actions are so arranged 
that they provide for the natural and regular operation 
of the animal functions. When the proper stimulus of 
the lining membrane is presented to it, the nervous 
system responds by an easy and natural movement; 
but it revolts against an unnatural stimulus, and re- 
jects the offending substance by a spasmodic effort of 
the muscles. 
149. Protection of the Nostrils during Deglutition.— 
There is still another point in the mechanism of deglu- 
tition which requires attention. 
If you look into the back part of the throat when it 
is illuminated by the sunshine or a strong gas-light, 
you will see that the cavity of the mouth is partially 
separated from the pharynx by a sort of muscular cur- 268 
PHYSIOLOGY AND HYGIENE. 
tain or partition hanging downward from above, and 
attached on each side by double folds of the lining 
membrane. This is the Hanging Palate. Beneath it 
is the arched passage or doorway which leads from the 
mouth into the pharynx, and from the middle of the 
arch hangs a soft conical fleshy appendage called the 
“ uvula.” 
Now behind this hanging curtain of the palate the 
upper part of the pharynx communicates with the nos- 
trils, and it is through this passage that the air enters 
in respiration when the mouth is closed. When we in- 
hale any pungent odors by the nostrils, we often feel 
them penetrate into the back of the throat by passing 
in this way with the inspired air through the posterior 
part of the nostrils and behind the hanging palate. 
Accordingly, when the food is carried backward from 
the mouth to the pharynx, it would escape upward into 
the passage of the nostrils if there were not some pro- 
vision to prevent it. 
But at the moment of deglutition the muscles on the 
two sides of the palate contract and draw together the 
arched sides of the passage, as the two halves of a cur- 
tain might be drawn together to close the opening of a 
window. At the same time, the palate itself is stretch- 
ed backward like an awning, and shuts olf in this way 
the communication between the pharynx below and the 
nostrils above; and the food, urged by the tongue from 
the mouth into the pharynx, and finding no passage 
open into the nostrils, necessarily turns downward, and 
is carried into the oesophagus. 
All these movements are excited at the same time by 
the reflex action of swallowing. 
Secondly, the laryngeal branches of the pneumogas- THE CRANIAL NERVES. 
trie nerve play a very important part in the act of res- 
piration. 
150. Structure of the Glottis and its Movements in Res- 
piration.—The larynx, which is the commencement of 
the trachea and bronchial tubes, communicates with the 
front part of the pharynx by a narrow opening or crev- 
ice, which we have already spoken of as the “ glottis.'’ 
Accordingly, the air, in respiration, enters by the mouth 
and nostrils into the back part of the throat, and thence 
passes into the larynx by the opening of the glottis. 
The structure of the glottis is as follows: The larynx, 
as we have already seen, is a kind of cartilaginous box, 
formed of various pieces connected with each other by 
articulations and ligaments. Its internal cavity is, for 
the most part, as spacious as that of the trachea; but 
just at its upper portion it is partly obstructed by two 
elastic bands of fibrous tissue, which are termed the 
Vocal chords. 
We shall hereafter see how important a function 
these chords perform in the production of the voice, 
from which their name is derived. The vocal chords 
are attached, side by side, at the front of the larynx, 
and thence run backward nearly parallel with each oth- 
er, thus leaving between them a narrow fissure, which 
is the opening of the glottis. All the space outside the 
vocal chords is filled up by the lining membrane and 
muscles of the larynx. If you were to stretch two 
cords over the mouth of an empty barrel, and then lay 
a folded cloth on each side between the cord and its 
edge, you would have a tolerably correct idea of the 
anatomical arrangement of the larynx. The barrel 
would represent the larynx itself, the space between 
the two cords would be the glottis, and the folded 270 
PHYSIOLOGY AND HYGIENE. 
cloth would occupy the situation of the lining mem- 
brane and the muscles on each side. 
Now the opening of the glottis is too narrow to ad- 
mit the air in sufficient quantity to the lungs, since its 
capacity is only about one third as great as that of the 
trachea. How is it, therefore, that the lungs are filled 
through this constricted passage ? 
It is because the larynx is movable and takes part in 
the acts of respiration. Every time the chest expands 
to inhale the air, the glottis opens to admit it; and a 
series of alternate movements of expansion and collapse 
are thus performed by the glottis simultaneously with 
those of the chest and abdomen. They are accomplish- 
ed in this way. 
At their posterior extremity the vocal chords are at- 
tached to two small triangular cartilages, which are 
connected with the rest of the larynx by an articula- 
tion or joint at their inner angle. These are called the 
Arytenoid cartilages. Their muscles are so arranged 
that they may be turned or rotated upon their articula- 
tions, so as to move the vocal chords outward and thus 
separate them from each other. Very much in the 
same way a bell-cord is sometimes attached to the wire 
by a triangular brass plate, which turns upon a hinge 
at one corner; and when the cord is ptilled downward 
the brass plate rotates upon its hinge, and draws the 
wire -with it in the same direction. Accordingly, when 
both the arytenoid cartilages move at the same time, 
the vocal chords are stretched and separated from each 
other, and the opening of the glottis between them is 
widened to admit the passage of the air. 
The movements thus performed are called the Res- 
piratory Movements of the glottis. They are depend- 271 
THE CRANIAL NERVES. 
Fig. 51. 
Fig. 52. 
Fig. 51. Larynx viewed from above, 
with glottis narrowed. 
Fig. 52. Same, with glottis opened: 1. 
Orifice of glottis; 2,2. Vocal chords; 
3, 3. Arytenoid cartilages. 
ent upon the inferior laryngeal branch of the pneumo- 
gastric »nerve, which animates the muscles of this part. 
But, beside its power of motion, the glottis is en- 
dowed with an exquisite and peculiar sensibility, which 
is essential to the safety of life. 
So long as it is only air which enters the larynx, the 
natural movements of the part are performed with ease 
and regularity. But if any foreign substance, such as 
a crumb of bread or a drop of water, happen to get be- 
tween the vocal chords and seek to gain entrance into 
the trachea, the lining membrane of the larynx at once 
feels an irritation which excites all the muscles in its 
neighborhood to an active and determined resistance. 
They close the orifice of the glottis with a convulsive 
movement, and the foreign substance is at last expelled 
by the spasmodic efforts of coughing. This peculiar 
sensibility of the larynx is dependent upon the superior 
laryngeal branch of the pneumogastric nerve, distrib- 
uted to its lining membrane. 
This nerve, accordingly, is the safeguard of the glot- 
tis. It stands like a sentinel at the entrance of the air 272 
PHYSIOLOGY AXD HYGIENE. 
passages, to give notice of the intrusion of any foreign 
substance into the lungs, and thus protect them against 
injury from without. 
Another very important point in the history of the 
larynx is its connection with the act of swallowing. 
151. Protection of the Glottis during Deglutition.—As 
we have seen, the glottis communicates with the phar- 
ynx. But it is through this passage that all the food 
passes downward to the stomach. How is it, therefore, 
that it does not fall into the larynx, and thus produce 
strangulation every time the act of swallowing is per- 
formed ? 
First of all, it is because, at the instant the food is 
about to be swallowed, respiration stops. There are 
various nervous actions in the body which are said to 
be “ incompatible” with each other; that is, they can 
not be performed at the same time. Thus we can move 
the two hands over and over in a circle from behind 
forward, in front of the body, either alternately or to- 
gether; but we can not move one of them from be- 
hind forward and the other from before backward at 
the same time. Some inexplicable interference of the 
nervous system prevents it; so that, though the two 
movements may easily be performed separately, it is 
impossible to perform them together. In the same way 
we can turn the two eyes to the right or the left to- 
gether, but we can not turn one of them to the right 
and the other to the left at the same time. 
Now there is a similar nervous incompatibility be- 
tween the acts of swallowing and inspiration. It is a 
necessary preliminary to the deglutition of the food 
that respiration be suspended. The consequence is, that 
the glottis is not opened as usual, but remains a narrow THE CRANIAL NERVES. 
273 
chink, offering but little opportunity for the entrance 
of the food. 
Nevertheless, this accident sometimes happens, and 
every one knows the distress which is occasioned by 
even the smallest particle of food getting entangled in 
this way in the larynx. Whenever it occurs, we shall 
always find that the difficulty is caused in the same 
way, namely, by a sudden inspiration taken at the mo- 
ment when the food is being swallowed. We can not 
take such an inspiration voluntarily; but it is some- 
times produced by a sudden impression upon the senses, 
as of an unexpected sight or exclamation, or excitement 
of any kind. The nervous system is then, as it were, 
taken by surprise; its natural operation is disturbed, 
and a quick inspiration opens the glottis and sucks the 
food, with the air together, into the cavity of the larynx. 
It is evident, therefore, how carefully all sources of 
hurry or disturbance should be avoided during the mas- 
tication and swallowing of the food. The meals should 
be taken quietly, and no sudden interruptions of an ex- 
citing nature be allowed while they are going on. With 
children especially, where the nervous system is highly 
impressible, these precautions should be constantly ob- 
served ; for such an accident is always alarming, and 
may easily be fatal in its results. 
But the protection of the glottis in deglutition is also 
provided for by Nature in other ways. 
If we place the finger upon the larynx in front of the 
throat, and then go through with the movements of 
swallowing, we shall find that at the instant of deglu- 
tition the larynx is drawn rapidly upward beneath the 
base of the tongue. As the base of the tongue is at the 
same moment thrust backward, it tends to cover the PHYSIOLOGY AND HYGIENE. 
opening of the glottis, and still farther to obstruct its 
entrance. Furthermore, the lower constrictor muscles 
of the pharynx are themselves attached on each side to 
the lateral portions of the larynx, and from this situa- 
tion they encircle the pharynx behind. Now it is these 
muscles which act in deglutition; and at the same mo- 
ment that they compress the pharynx they necessarily 
draw also by their attachments upon the larynx, press 
its two sides more closely together, and thus shut up 
completely the orifice of the glottis. By the combined 
operation, accordingly, of these various movements, the 
glottis, which is opened in inspiration to admit the air, 
is securely closed in deglutition during the passage of 
the food. 
152. Production of Vocal Sounds in the Larynx.—The 
last function of the larynx is the formation oftheVoice. 
For the larynx is a musical instrument. It is here 
that all the vocal sounds are produced, and modulated 
from the higher notes to the lower, with all the altera- 
tions of tone that give variety and expression to the 
voice. These sounds are divided into vowels, conso- 
nants, and words by the motions of the lips and tongue; 
but the voice itself is formed in the larynx by the ac- 
tion of the vocal chords. 
Sound is caused by a vibration; and any body which 
is capable of vibrating will produce a sonorous effect. 
Thus a violin-string, when snapped by the fingers or set 
in motion by the bow, gives out a note which is higher 
or lower according to the rapidity of its vibration. To 
do this, however, it must be tense and elastic. If it be 
loose and flexible it is incapable of vibrating, and con- 
sequently can not produce a sound. The same string 
also will give out a deep sound when it is moderately 275 
tight, and a more acute one when it is stretched to a 
high degree of tension. In a flute or a trumpet, the air 
itself, which is always elastic, is thrown into vibration; 
and the sound which is produced varies with the width 
of the opening and the length of the column of air con- 
tained in the instrument. In an organ-pipe the reeds 
are first made to vibrate, and they then set in motion 
the column of air above them. The long and wide 
tubes thus give a deep sound, the short and narrow 
tubes an acute one. 
The formation of the voice in the larynx is somewhat 
similar. The first peculiarity to be noticed is that the 
voice is formed during expiration and not during inspi- 
ration. We always speak while the air is passing out 
through the larynx, and never while it is passing in- 
ward to the lungs. We drive the air forcibly through 
the larynx to produce a sound, just as we blow it 
through a horn or an organ-pipe for the same purpose. 
Secondly, when the voice is to be sounded, the vocal 
chords are drawn together and tightly stretched. In or- 
der to produce the necessary vibration, the orifice of 
the glottis must be narrowed, and the vocal chords 
thrown into a state of tension which will enable them 
to move rapidly like the strings or reeds of a musical 
instrument. Then the column of air passing between 
them is itself thrown into vibration, and thus produces 
the vocal sound. The note sounded by the voice will 
therefore be high or low, acute or grave, as the vocal 
chords are more or less tightly stretched, and as the ori- 
fice of the glottis is narrower or wider. In sounding a 
low note, the glottis is left comparatively open, and the 
vocal chords are loose ; in a high note, the vocal chords 
are tightened and brought • nearer together, so as to 
THE CRANIAL NERVES. 276 
PHYSIOLOGY AND HYGIENE. 
diminish the orifice of the glottis to its narrowest dh 
mensions. 
Finally, the larynx is raised and lowered during the 
formation of different sounds. If we place the finger 
upon this part, we shall find that when the lower notes 
are sounded it is drawn down toward the chest, while 
during the formation of acute sounds it is carried forci- 
bly upward. Thus the two columns of air above and 
below the glottis, in the trachea and in the pharynx, 
are lengthened or shortened, and widened or narrowed, 
as the sounds emitted by the larynx vary in character 
and tone. 
All the movements of the glottis in the formation of 
the voice, as well as those connected with respiration, 
depend upon the inferior laryngeal branch of the pneu- 
mogastric nerve. 
153. Distribution of the Pneumogastric to the Lungs. 
—The lower portion of the pneumogastric nerve also 
sends branches to the lungs. These branches form a 
plexus or network at the back part of the lungs by di- 
viding and again inosculating with each other, and 
from this plexus their filaments penetrate into the tis- 
sue of the organs, following the successive divisions of 
the bronchi and bronchial tubes (Fig. 50). They are 
distributed to the lining membrane of the bronchial 
tubes and the pulmonary lobules, and communicate to 
these parts a peculiar sensibility by which they are en- 
abled to perceive the condition of the air contained in 
the air vesicles and of the blood contained in the capil- 
lary blood-vessels. Accordingly, when the air becomes 
contaminated, these filaments receive the impression of 
its impurity. The pneumogastric nerve thus presides 
over the condition of the air passages throughout their THE CRANIAL NERVES. 
course, from the opening of the glottis to the termina- 
tion of the pulmonary vesicles. 
154. Distribution of the Pneumogastric to the Stomach. 
—Finally, the last branches of the pneumogastric nerve 
are distributed to the stomach. Here, as elsewhere, the 
nerve contains both sensitive and motor fibres. The 
sensitive fibres are distributed to the lining membrane 
of the stomach, the motor fibres to its muscular coat. 
Here there is also a peculiar sensibility, followed by a 
reflex action. For the lining membrane of the stomach 
is not endowed with ordinary sensibility. It does not 
feel the contact of the food as we could feel it with the 
fingers or the lips. But we know that when the food 
passes into the stomach, its presence excites the “ peri- 
staltic action” of the muscular coat, by which it is moved 
constantly from side to side, mingled thoroughly with 
the gastric juice, and finally carried onward through 
the pylorus into the intestine. This important move- 
ment is entirely involuntary, and is performed usually 
even without our knowledge. It is a reflex action, ex- 
cited by the peculiar sensibility of the lining membrane 
of the stomach, through the sensitive fibres of the pneu- 
mogastric nerve, and conveyed by its motor fibres to 
the muscular coat of that organ. 
The pneumogastric nerve, accordingly, controls the 
condition and actions of the upper part of the aliment- 
ary canal, from its commencement in the pharynx to 
the pyloric extremity of the stomach. 
Thus the cranial nerves, by their motor and sensitive 
filaments, preside over the sensibility and movements 
of the face, the functions of mastication and degluti- 
tion, the peristaltic movements of the stomach, the res- 
piratory and vocal movements of the glottis, and the 278 
PHYSIOLOGY AND HYGIENE. 
whole extent of the air passages throughout the 
lungs. 
1. What are the cranial nerves ? 
2. How many pairs are there of cranial nerves ? 
3. What nervous function is highly developed in the skin of the 
face ? 
4. At what part is sensibility more acute than elsewhere ? 
5. By what nerve is the face supplied with sensibility ? 
6. Why is it called the “fifthpair?” 
7. Why is it called the trigeminal nerve ? 
8. What is the Gasserian ganglion, and where situated ? 
9. How are the three great branches of the fifth pair distributed ? 
10. What effect is produced by any irritation of the fifth pair ? 
11. What is the cause of toothache? and in what nerve is the pain 
situated ? 
12. What becomes of the nerve when the tooth is extracted ? 
13. What is neuralgia ? 
14. What name is given to neuralgia of the face ? Why ? 
15. Which branch of the fifth pair is accompanied by motor fila 
ments ? 
16. What name is given to the nerve containing these filaments ? 
17. Why is it called the masticator nerve? 
18. What are the muscles of mastication? 
19. What is the situation of the temporal muscle ? 
20. What is the direction of its fibres ? 
21. What is the action of this muscle upon the lower jaw? 
22. Where is the masseter muscle situated ? 
23. What is its action on the lower jaw ? 
24. What other muscles take part in the movements of mastica 
tion ? 
25. Where are the pterygoid muscles situated ? 
26. What movements of the jaw are produced by them ? 
27. What other movements are performed by the face ? 
28. By what nerve are the muscles of expression animated ? 
29. Where does the facial nerve originate ? 
30. Where does it pass through the floor of the skull ? 
81. What is its subsequent course and distribution? 
QUESTIONS FOR CHAPTER XIV. QUESTIONS. 
279 
32. Is the facial nerve a sensitive or a motor nerve ? 
33. What effect is produced on the face by injury or disease of the 
facial nerve ? 
34. What nerves provide for the movements of the eyeball ? 
35. What nerve supplies the muscles of the tongue ? 
36. What is the pneumogastric nerve, and what is its final distri- 
bution ? 
37. What other name is given to this nerve, and why ? 
38. Where does the pneumogastric nerve originate ? 
39. Does it contain sensitive or motor fibres, or both ? 
40. Whence does it derive its motor fibres ? 
41. In what direction does it pass after emerging from the cavity 
of the skull ? 
42. What is the first branch of the pneumogastric nerve ? 
43. To what organ is the pharyngeal branch distributed ? 
44. What properties does it communicate to the pharynx ? 
45. What two branches are distributed to the larynx ? 
46. What is the peculiarity in the course of the inferior laryngeal 
branch ? 
47. What name was given to this nerve by Galen ? 
48. What property is communicated to the larynx by the superior 
laryngeal nerve ? by the inferior laryngeal nerve ? 
49. To what other organs are the branches of the pneumogastric 
distributed ? 
50. With what two important functions are the upper branches of 
the pneumogastric nerve connected ? 
51. Does the pharynx possess ordinary sensibility? 
52. What reflex action is produced by the sensibility of the phar- 
ynx? 
53. What name is given to the muscles of the pharynx ? and why ? 
54. By what nerve are they excited to act when food enters the 
pharynx ? 
55. Is the action of the pharynx in swallowing voluntary or invol- 
untary ? 
56. What effect is produced by irritation of the pharynx with for- 
eign substances ? 
57. What is the hanging palate? What is the uvula? 
58. What open passage is there behind the hanging palate ? 
59. How is the food, in swallowing, prevented from escaping into 
the back part of the nostrils ? 280 
PHYSIOLOGY AND HYGIENE. 
60. Where does the larynx communicate with the pharynx ? 
61. What are the vocal chords? and where are they attached? 
62. What is the opening left between them ? 
63. What is the size of the opening of the glottis compared with 
that of the trachea ? 
64. What movement takes place in the glottis at the time of inspi- 
ration ? 
65. To what are the posterior ends of the vocal chords attached ? 
66. In what direction can the arytenoid cartilages move ? 
67. What effect has this motion .n the vocal chords and the open- 
ing of the glottis ? 
68. What is the object of the opening of the glottis in inspiration ? 
69. What name is given to these movements of the glottis ? 
70. What is the peculiarity in the sensibility of the glottis ? 
71. What effect is produced by its irritation with a foreign sub- 
stance ? 
T" 72. What protective action does the superior laryngeal nerve exert 
over the air passages and lungs ? 
73. How is the food prevented from passing into the larynx in swal- 
lowing ? 
74. Why can we not swallow at the moment of inspiration ? 
75. Mention other examples of “ incompatible” movements. 
76. 'How is it that particles of food sometimes fall into the larynx 
in swallowing ? 
77. What precautions should be taken to prevent this accident? 
78. How does the action of the constrictors of the pharynx serve to 
prevent the food passing into the larynx ? 
79. What other function is performed by the larynx ? 
80. How is sound produced ? what gives the vibration in stringed 
instruments ? 
81. What must be the condition of a cord in order that it may vi- 
brate so as to produce a sound ? 
82. When does the same cord give an acute sound, and when a 
deep sound ? 
83. What gives the vibration in wind instruments ? 
84. What tubes give an acute sound, and what a deep sound ? 
85. Is the voice produced in inspiration or in expiration ? 
86. What is the condition of the vocal chords when the voice is 
sounded ? 
87. What is their condition in sounding a high note ? QUESTIONS. 
281 
88. What in sounding a low note ? 
89. Upon what nerve do the vocal movements of the glottis de- 
pend ? 
90. What is the distribution of the pneumogastric nerve in the 
lungs ? 
91. What kind of sensibility does it communicate to the lungs ? 
92. To what organ are the last branches of the pneumogastric nerve 
distributed ? 
93. To what part of the stomach are its sensitive fibres distributed ? 
94. To what part are its motor fibres distributed ? 
95. What reflex action of the stomach takes place through the 
pneumogastric nerve ? 
96. Name the various functions presided over by all the cranial 
nerves. 282 
PHYSIOLOGY AND HYGIENE. 
CHAPTER XV. 
Form of the Brain—its Anatomical Divisions.—Medulla Oblongata. 
—Cerebellum.—Pons Varolii.—Tuber Annulare.—Cerebrum.— 
Functions of the Cerebrum.—Memory.—Judgment.—Reason.— 
Effects of Injury to the Cerebrum.—Functions of the Tuber An- 
nulare.—Sensation and Volition.—Instinctive Movements.—Func- 
tions of the Medulla Oblongata.—Movements of Respiration—how 
performed.—Reflex Action of Medulla Oblongata.—Effects of In- 
jury to Medulla Oblongata.—Different kinds of Reflex Action in 
the Brain. 
THE BRAIN. 
155. The Brain is the great mass of nervous sub- 
stance which occupies the cavity of the skull. It is 
composed of various collections of gray matter, or 
ganglia, which are united with each other and with 
the spinal cord by numerous bundles of white nervous 
fibres. 
The brain, like the spinal cord, is double. It is formed 
of two great lateral masses which lie side by side in the 
skull, separated in front and above by a deep furrow or 
fissure, but connected beneath by the continuation of 
the nervous substance. It is also separated by trans- 
verse furrows, and by certain differences in structure, 
into three principal divisions, varying in size, appear- 
ance, and situation. These are the Cerebrum, the Cere- 
bellum, and the Medulla oblongata. 
156. Medulla Oblongata.—When the spinal cord en- 
ters the cavity of the cranium by the great foramen 
situated at the base of the skull, it expands, as we have THE BEALS'. 
283 
mentioned in a previous chapter, into a widened oblong 
mass, which still preserves the general external appear- 
ance of the spinal cord. This is the Medulla oblongata. 
Its increased width is partly owing to its fibres begin- 
ning at this point to turn and wind obliquely in vari- 
ous directions, but also to the fact that an important 
mass of gray matter is here buried in its substance, 
known as the “ganglion of the medulla oblongata.” 
Nearly all the cranial nerves also take their origin 
from this part, or its immediate neighborhood, and 
their fibres accordingly are added to those derived 
from the spinal cord. Like the spinal cord, therefore, 
the medulla oblongata consists of a collection of gray 
matter, covered and concealed by the white fibres upon 
its outer surface. 
157. Cerebellum.—Above and behind the medulla 
oblongata is the Cerebellum. This is a much larger 
nervous mass, and is instantly distinguished from those 
which have preceded by its peculiar appearance and 
structure. Its outside is composed, not of white, but 
of gray nervous matter, and this nervous matter is ar- 
ranged in abundant narrow laminae or convolutions, for 
the most part running transversely, and closely packed, 
like a gray cloth or shawl folded in many layers. In 
its interior, on the contrary, the cerebellum is composed 
of white substance. The columns of the spinal cord, 
while passing through the medulla oblongata, give off 
some of their fibres; and these fibres, turning obliquely 
upward and backward, spread themselves out in the 
thickness of the cerebellum, and finally come into con- 
nection with the gray matter upon its surface. 
Beside this, the two lateral halves of the cerebellum 
are connected with each other in a remarkable way. 284 
PHYSIOLOGY AMD HYGIENE. 
From the whole inner surface of it's gray matter there 
start on each side a multitude of white nervous fila- 
ments, which pass downward and forward toward its 
centre, gradually approaching each other, and uniting 
into a flattened bundle of parallel fibres. This ribbon- 
shaped bundle then emerges from the lower and front 
part of the cerebellum, curves round the base of the 
brain just in front of the medulla oblongata, and then 
returns upon the opposite side to spread out again in 
the substance of the other half of the cerebellum. 
Thus this mass of nervous fibres, spread out at their 
two extremities, but united into a parallel band at their 
middle, form a transverse communication between the 
right and left sides of the cerebellum. 
In its middle portion, where it encircles the base of 
the brain in an arched form,it is called the “Pons Va- 
rolii,” or the “ Bridge of Varolius,” because the fibres 
of the medulla oblongata, in continuing their course, 
pass underneath it, like a river under a bridge. 
158. Tuber Annulare.—Now where the fibres of the 
medulla oblongata pass under the pons Varolii, another 
deposit of gray matter is found in the interior of the 
mass. This collection of gray matter within, together 
with the prominence of the pons Varolii on the outside, 
gives to this part of the brain the appearance of a cir- 
cular or ring-like protuberance. It is therefore known 
by the name of the Tuber annulare; and the gray mat- 
ter in its centre is called the “ ganglion of the tuber an- 
nulare.” 
Beyond and in front of the tuber annulare the fibres 
coming from the spinal cord and medulla oblongata 
pass upward and onward in two great rounded bun- 
dles, which are called the “peduncles of the brain.” THE BRAI2T. 
285 
They have received this name because the two halves 
of the brain are supported upon these peduncles, like a 
flower upon its stem. Their fibres, running continual- 
ly upward, immediately after they have passed the 
level of the cerebellum spread out in a fan-like form, in 
front and behind, to the right and the left, and thus 
finally terminate in the gray substance of the cere- 
brum. 
159. Cerebrum.—The cerebrum is by far the largest 
of all the nervous masses contained within the skull. 
It overlaps all the remaining parts, in front, above, and 
behind, so that they are covered by it as if with a kind 
of vaulted roof or dome. The outer and upper part of 
this dome is formed of gray matter, folded and convo- 
luted in innumerable directions; its interior is formed 
mostly of white substance, viz., the fibres which, as we 
have already seen, pass upward from below, and thus 
connect this principal part of the brain with the medul- 
la and spinal cord. The two halves of the cerebrum 
are also connected, like those of the cerebellum, by a 
great bundle of transverse fibres, converging from the 
gray matter and passing from side to side; only this 
transverse band does not emerge from the brain, like 
the pons Varolii, but remains concealed and imbedded 
in its substance. 
At the base of the cerebrum, on each side, there are 
also two other deposits of gray matter, one in front and 
one behind, called respectively the “ striated bodies” 
and the “ optic thalami.” These ganglia form a part of the 
substance of the cerebrum, and stand, as it were, at its 
entrance or gateway, through which the fibres from be- 
low pass upward to its surface (Fig. 53). In the sub- 
stance of the cerebrum also, beneath the folded cover- 286 
PHYSIOLOGY AND HYGIENE. 
Fi-r. 53. 
Diagram of Human Brain, in vertical section, showing the situation of the dif- 
ferent ganglia and the course of the fibres.—1. Ganglion of the sense of 
smell; 2. Cerebrum ; 3. Corpus striatum ; 4. Optic thalamus; 5. Ganglion of 
the sense of sight; 6. Cerebellum; 7. Ganglion of the tuber annulare; 8. 
Ganglion of the medulla oblongata. 
ing of its gray matter, there are pillars, and vaults, and 
curtains, and galleries, and passage-ways, and many va- 
ried details of anatomical structure, too complicated for 
minute description. Many of these anatomical parts 
have uses which are still unknown to us; but we are 
acquainted with the structure and functions of the prin- 
cipal mass and its connection with the other portions 
of the brain. 
160. Functions of the Cerebrum.—The cerebrum is the 
organ of the mind. By that we mean that it is this di- 
vision of the nervous system through which the inteb 
lectual powers communicate with the body. Reason, 
judgment, memory are the mental faculties whose op- 
eration is connected with the function of the cerebrum. 
We know this because, when this part of the brain is 
injured, it is these faculties which are impaired, and 
when it is deficient they are absent to a corresponding 
degree. What is the nature of these faculties, and THE BRAIN. 
287 
how do they manifest themselves through the action 
of the brain ? 
The simplest and most fundamental of these powers 
is that of Memory. This faculty lies at the basis of all 
mental improvement, and even the simplest intellectual 
operation would be impossible without it. By it'alone 
we are enabled to retain the names of things and the 
meaning of words, so that we can write and speak. 
Nearly all our actions are guided by what has taken 
place before, and therefore, if we had no memory, most 
of our acts would be capricious and unreasonable. A 
deficiency of memory is the earliest indication of idiocy 
in children, and it is on account of the want of this fac- 
ulty that such children can not learn to read, and in 
many cases can not even talk. A deficiency of memory 
is also the most unfailing consequence of injury to this 
part of the brain. When an attack of apoplexy is com- 
ing on, an unusual forgetfulness is among the first symp- 
toms which are manifested; and in more permanent af- 
fections of the brain it gradually increases, until the 
power of recollecting even the days of the week or the 
events of the day is permanently lost. 
The next important intellectual faculty is Judgment. 
By this is meant the power of appreciating the true 
importance of things, and the relations of cause and ef- 
fect. A person who is deficient in this respect is liable 
to pay too much attention to things which are of little 
consequence, and to neglect those which are really im- 
portant. He is also unable to perceive that what hap- 
pens at one time is caused by something else which has 
preceded. He knows only that the two events have 
happened, but he does not see what is the connection 
between them. Accordingly, it is of no use to punish 288 
PHYSIOLOGY AND HYGIENE. 
an idiot, because he does not understand that the pun- 
ishment is a consequence of what he has done before. 
Finally, Reason is the faculty by which we compare 
the causes and consequences of things in such a way as 
to guide our actions. We can thus use the information 
acquired by memory and judgment to avoid difficulties 
and obtain success. An unreasonable person, therefore, 
is one who does not use the proper means to accomplish 
his purposes. This is characteristic of idiocy and of 
some kinds of insanity. 
All these mental faculties are liable to be developed, 
to a greater or less degree, in different persons, or even 
in the same person, at different ages. Like the sensi- 
bility of the skin, they are sometimes acute and some- 
times feeble. They are always diminished when the 
cerebrum is injured, even though the other functions 
of the nervous system may remain entire. 
Now all acts which are of an intelligent nature re- 
quire this operation of the mind; the simplest, as well 
as the most profound and complicated. For instance, 
we feel that the air of a room is cold, and we accord- 
ingly shut the window. This is a reflex action of the 
nervous system. The beginning of it is the sensation 
of cold; the end is the voluntary act of closing the 
window. But between the two there is an intellectual 
operation, by which we understand the cause of our 
sensation, and how we may remove it by the voluntary 
act. This mental process is especially connected with 
the function of the cerebrum. 
160. Functions of the Tuber Annulare. — The next 
function of the nervous centres which we shall study 
is the double function of Sensation and Volition. We 
have already spoken of these faculties in connection THE BRAIN. 
289 
with the sensibility and power of motion in the spinal 
nerves. But we have found that these organs only 
serve as conductors, and that the real functions have 
their seat in the interior of the brain. 
These faculties, however, are not situated in the cere- 
brum. The substance of the cerebrum is not even sen- 
sitive ; and, provided no other parts of the brain be in- 
jured, it may be cut or lacerated in any way without 
producing pain, as has often happened in accidents and 
surgical operations. Physiologists have seen reason to 
believe that the powers of sensation and volition are 
located farther down, in the gray matter of the Tuber 
annulare. What is the nature of these functions, and 
how are they connected with each other ? 
A complete sensation is always accompanied by con- 
sciousness. This is very different from the mere nerv- 
ous impression received by a sensitive nerve. For the 
nerve itself does not feel, it only conducts the impres- 
sion ; and the sensation is not perceived until it arrives 
at the brain, where consciousness resides. It is the gan- 
glion of the tuber annulare which thus receives the im- 
pression conveyed by the nerve, and instantly converts 
it into a conscious sensation. 
This ganglion is also the seat of volition. By this 
term we understand that nervous action by which we 
command the muscles through the influence of the will. 
This command is transmitted by the nerves, but its 
origin is in the brain. 
Now volition is entirely distinct from reason. The 
intention or desire to perform an act is a different thing 
from its positive execution. Even when we have al- 
ready determined to raise the arm or to advance a step, 
there still remains a nervous process by which the mus- 290 
PHYSIOLOGY AND HYGIENE. 
cles are actually set in motion. This process is the act 
of volition, and any movement so performed is called a 
“ voluntary” movement. 
But there are some voluntary acts which are per- 
formed independently of the mind. They have nothing 
to do with memory or judgment, and are executed in- 
stantly whenever we receive a particular sensation. 
This is the nature of all those acts which are per- 
formed by instinct. Thus the sight of a threatening 
object inspires terror, and we immediately endeavor to 
escape or defend ourselves from it. The sense of hun- 
ger leads us to take food; but this is simply because 
we desire it, and not because we reflect that it will nour- 
ish the body by the process of digestion, still less be- 
cause we remember how this process is accomplished. 
All the actions of this kind are voluntary, but they do 
not result from any reasoning power which precedes 
them. They are guided by a blind impulse, in which 
we recognize only the sensations which we receive and 
the desires which they excite. These instinctive and 
voluntary movements are performed by the reflex ac- 
tion of the tuber annulare. 
. \ 161. Function of the Medulla Oblongata.—There is 
another reflex action taking place within the brain 
which is more important than the rest, because it is 
more immediately essential to the continuance of life. 
It is that which presides over the movements of respi- 
ration. 
We have not yet learned why these movements take 
place. We have only seen that they go on with a con- 
tinued and harmonious action, the chest rising and fall- 
ing with unfailing regularity, and the diaphragm keep- 
ing pace with it in alternate contraction and relaxation. THE BRAIN. 
291 
But these movements are neither intentional nor vol- 
untary. They are not the result of any effort of the 
reason, for they are performed in the same way by 
idiots and by animals as by persons of mature years 
and the highest intelligence. Neither are they direct- 
ed by the will, for they go on when we pay no atten- 
tion to them and during sleep, as well as at other times. 
And in cases where the brain is extensively injured by 
violence or disease, when all the mental powers are 
abolished, and even volition and consciousness are sus- 
pended, the movements of respiration will often con- 
tinue with the same undeviating regularity as before. 
The whole mass of the cerebrum and the cerebellum, 
and both the white and gray substance of the tuber 
annulare, may be compressed or destroyed without ar- 
resting this necessary function of life. 
There is, however, another portion of the brain con- 
cealed in the posterior and lowermost region of the 
skull, which is smaller than the rest, but, at the same 
time, the most important of all, for it presides directly 
over the process of respiration. This is the ganglion 
of the Medulla oblongata. 
When the other parts of the brain are injured, vari- 
ous nervous and mental functions are impaired or 
abolished, but life itself continues. When the medulla 
oblongata is destroyed, respiration instantly ceases, and 
life at the same moment comes to an end. 
Accordingly, Nature has provided for the safety of 
this most important ganglion by burying it deeply un- 
der the remaining mass of the brain, and thus secure 
ing it from external violence. A blow upon the head 
which fractures the upper part of the skull may tear 
the substance of the brain and produce loss of memory 292 
and unconsciousness, but it seldom or never penetrates 
to the medulla oblongata. Neither can this part be 
easily reached from below, for it rests upon the base of 
the skull, exactly above the summit of the spinal col- 
umn. Even an internal apoplexy usually affects only 
the upper or middle portions of the brain. When it 
attacks the medulla oblongata, death is certain and im- 
mediate. 
Sometimes, when the spine is fractured very high up, 
just at the level of its junction with the skull, the bro- 
ken pieces are di’iven into the medulla oblongata and 
lacerate its substance. We then say that “the neck is 
brokenand such an accident is instantly fatal, for it 
stops at once the movements of respiration. 
In what way does this ganglion maintain the func- 
tion of respiration ? 
162. Reflex Nature of the Act of Respiration.—As we 
have already intimated, it is by means of a reflex ac- 
tion. All the nerves which are distributed among the 
blood-vessels receive an impression from the circulating 
blood. As this blood loses its oxygen and becomes 
charged with carbonic acid, the impression is conveyed 
inward by the nerves, and is thus transmitted to the 
medulla oblongata. Among those more especially sen- 
sitive to this impression is the Pneumogastric nerve, 
■which, as we have already seen, is distributed among 
the air vesicles of the lungs, and there perceives the 
earliest signs of the contamination of the blood. Ar- 
rived at the medulla oblongata, the impression thus 
conveyed is received by the gray matter of the gan« 
glion; it is then converted into a motor impulse, which 
is sent out by the intercostal and phrenic nerves, and 
the muscles of respiration are at once set in motion. 
PHYSIOLOGY AND HYGIENE. THE BRAIN. 
293 
The new air introduced into the lungs then relieves 
the nervous system by the supply of oxygen, and the 
muscles accordingly relax, to be again called into op- 
eration a few instants afterward by a repetition of the 
same process. This is the reflex action of the medulla 
oblongata. 
Now this nervous impression is not usually felt, be- 
cause it does not naturally give rise to any conscious 
sensation; but you can feel it very easily. 
Hold the breath for a few seconds, and you are im- 
mediately conscious of an unusual sensation in the 
chest. This is not like ordinary pain, or the sensation 
of cold or heat. It is a peculiar feeling of distress, 
which grows more intolerable every moment. It soon 
fills the chest with a sense of suflocation, and then 
spreads over the whole body, calling loudly for air and 
respiration, until its demands become too imperative 
for resistance. When you cease from voluntary oppo- 
sition, the movements of respiration begin again of 
themselves, and the feeling of suffocation passes off as 
the fresh air finds its way into the lungs. 
The nervous impression, accordingly, which excites 
the respiratory muscles is alternately produced and re- 
lieved as the air enters and is expelled from the pas- 
sages of the lungs; and the movements of respiration 
are repeated at regular intervals as often as they are 
required for the renovation of the blood. 
Thus various reflex actions are performed by the 
nervous ganglia in different parts of the brain. Some 
of them are accompanied by the exercise of reason and* 
other intellectual faculties; some of them call into op- 
eration only the powers of sensation and the will; while 
others, which are those most indispensable to life, go 294 
PHYSIOLOGY AND HYGIENE. 
on without our consciousness, by the simple operation 
of the nervous force. 
We have now gone through with the study of the 
great nervous masses of the spinal cord and the brain, 
and of the nerves connected therewith. Taken alto- 
gether, they form a division of the nervous system 
which is called the Cerebrospinal system, from the two 
principal nervous centres which it contains. This sys- 
tem presides over all those functions which connect the 
animal body with external objects, such as sensation, 
the will, the instincts, the voice, and the introduction 
of food and air info the body from without. 
But there is another class of functions which the ex- 
clusively internal in their operation, such as digestion, 
absorption, secretion, nutrition, and the circulation of 
the blood. These functions are also regulated and con- 
trolled by a set of nerves and ganglia, with which their 
organs are more especially connected; and this part 
of the nervous system is called the System of the Great 
Sympathetic. We shall proceed to the study of this 
system in the following chapter. 
1. Of what structures is the brain composed ? 
2. How are the two sides of the brain separated from each other ? 
3. How are they connected ? 
4. Name the three principal parts or divisions of the brain. 
5. What is the form and situation of the medulla oblongata ? 
6. What important mass of gray matter does it contain ? 
' 7. Of what is it composed on its outer surface ? 
8. What is the situation of the cerebellum ? 
9. Of what is it composed on its outer surface ? 
10. What is the arrangement of the gray matter on its exterior? 
11. Of what is it composed internally? 
QUESTIONS FOR CHAPTER XY. 295 
12. How are the two lateral halves of the cerebellum connected 
with each other ? 
13. What name is given to the transverse connecting band of the 
cerebellum ? and why ? 
14. What is the tuber annulare? and why is it so called? 
15. What collectioi of gray matter does it contain internally? 
16. What are the peduncles of the brain? and why so called? 
17. Where do the fibres of the peduncles terminate? 
18. Which is the largest division of the brain? 
19. What is the structure of its outer surface ? 
20. How are the two lateral halves of the cerebrum connected with 
each other ? 
21. Where are the striated bodies and optic ihalami situated ? 
22. What is the function of the cerebrum ? 
23. How do we know that the cerebrum is the organ of the mind ? 
24. Which is the simplest and most important of the mental facul- 
ties ? 
25. What is the definition of memory ? 
26. How is the memory affected in cases of injury or deficiency of 
the brain ? 
27. What is the faculty of judgment ? 
28. What is the faculty of reason ? 
29. How are acts of an intelligent nature performed ? 
30. Do sensation and volition depend upon the cerebrum ? 
31. In what part of the brain do these faculties reside ? 
32. What is the difference between a nervous impression and con- 
scious sensation ? 
33. What is the difference between intelligence and volition ? 
34. May an act be voluntary without being the result of intelli- 
gence ? 
35. What is an instinctive act ? 
36. Where is the seat of simple sensation and volition in the brain ? 
37. What is the most important reflex action taking place in the 
brain ? 
38. Are the movements of respiration voluntary or involuntary ? 
89. Do they require the co-operation of consciousness or sensation ? 
40. What parts of the brain may be destroyed without arresting 
respiration ? 
41. What part of the brain presides over the act of respiration ? 
42. How is the medulla oblongata protected by its situation ? 
QUESTIONS. 296 
PHYSIOLOGY AND HYGIENE. 
43. What do we mean by saying that “ the neck is broken?” 
44. Why is this accident immediately fatal ? 
45. How is the reflex act of breathing performed by the medulla 
oblongata ? 
46. What nerve is the principal agent in conveying the impression 
to the medulla oblongata ? 
47. Is this impression usually perceived ? 
48. How can it become perceptible ? 
49. What muscular action is excited by it ? 
50. By what nerves is the stimulus carried outward to the muscles ? 
51. Why are the movements of respiration repeated at regular in- 
tervals ? 
52. What is the cerebrospinal nervous system ? 
53. What is the general function of the cerebro-spinal nervous sys- 
tem? * SYSTEM OF THE GREAT SYMPATHETIC. 
297 
CHAPTER XVI. 
SYSTEM OF THE GEEAT SYMPATHETIC. 
General Structure of the great Sympathetic—its Ganglia—its Nerves. 
—Arterial Plexus—their Distribution—connection with the Cere- 
bro-spinal System.—Slow operation of Sympathetic Nerves.—Effect 
of Cold and Wet.—Inflammation of the Internal Organs.—How to 
avoid the effects of Exposure.—Different kinds of Reflex Action 
through Sympathetic and Cerebro-spinal Systems. 
163. General Arrangement of the Sympathetic System. 
—The system of the great sympathetic nerve consists 
of a double chain of very small ganglia, which extend 
from one end of the body to the other, in front of the 
spinal column, running through the deeper parts of the 
neck, and inclosed in the cavities of the chest and ab- 
domen. The successive ganglia are connected with 
each other by fine nervous fibres, which run upward 
and downward in the direction of the chain. From the 
ganglia there are also given off numerous interlacing 
nerves, which are distributed to the great internal or- 
gans of the body—to the heart, the lungs, the stomach, 
the pancreas, the liver, the intestine, and the kidneys. 
These nerves are smaller than those of the cerebro- 
spinal system, and are less distinctly visible, owing to 
their grayish color and greater delicacy of texture. 
A striking peculiarity in the course of the nerves be- 
longing to the sympathetic system is that they follow 
closely the distribution of the blood-vessels. Starting 
from the heart, they envelop the great vessels with a 
sort of network, or plexus, of fine interlacing nerves, 298 
PHYSIOLOGY AND HYGIENE. 
which is called the Arterial plexus of the sympathetic 
nerves. Each plexus is re-enforced by fibres from the 
adjacent ganglia, and sends off corresponding divisions 
with the arterial branches, which follow their successive 
ramifications, and thus accompany them all over the 
body, and penetrate with them into the substance of all 
the organs. 
In the neck and in the chest the sympathetic ganglia 
are regularly arranged in pairs, one on each side of the 
body, in front of the spinal column. This regularity is 
especially marked in the chest, where the ganglia are 
twelve in number, each one resting upon the head of 
the corresponding rib. But in the upper part of the 
abdomen their arrangement is different. Immediately 
behind the stomach, and about the great vessels given 
off from the aorta at this part, there is a collection of 
sympathetic ganglia varying in form and size. Of these 
ganglia there is one on each side, which is larger than 
the rest, and which, from its semicircular or half-moon 
shape, is called the Semilunar ganglion. All the gan- 
glia are united wdth each other and with those of the 
opposite side by a network of filaments, forming a close 
and intricate central plexus. 
From this plexus other bundles of interlacing fila- 
ments are given off, which follow the course of the 
blood-vessels to all the abdominal organs. It has there- 
fore received the name of the Solar plexus, because the 
other abdominal plexuses radiate from it in every di- 
rection like the rays diverging from the sun. Thus 
the solar plexus holds, as it were, the central place in 
the nervous system of the abdomen, and by its radi- 
ating filaments controls the action of the various or- 
gans contained in the abdominal cavity (Fig. 54). SYSTEM OP THE GREAT SYMPATHETIC. 
299 
Here, also, as in other parts of the body, the sympa- 
thetic plexuses and their branches follow the course of 
Fig. 54. 
Course and Distribution of the Great Sympathetic. 
the blood-vessels, embracing them every where with a 
network of intersecting fibres. 300 
PHYSIOLOGY AND HYGIENE. 
164. Action of the Sympathetic Nerves on the Internal 
Organs.—Accordingly, these nerves are every where 
in intimate connection with the vascular system. It is 
in this way that the different parts of the circulation 
are brought under control; so that the course of the 
blood may be hastened or retarded, and its quantity in- 
creased or diminished in various organs. Thus the 
functions of secretion, nutrition, and the like, which de- 
pend so much on the state of the circulation, are made 
to sympathize with each other in distant regions; and 
on this account the system of nerves now described has 
received the name of the “ sympathetic” system. 
The action of this system, however, and that of all 
the organs under its influence, is involuntary in charac- 
ter and entirely independent of our control. 
Nevertheless, the sympathetic system of nerves is 
connected with the cerebro-spinal system. For each 
principal ganglion sends out a branch of communica- 
tion which unites with another branch coming from a 
spinal or cerebral nerve near by; and thus the internal 
organs may be influenced, in a circuitous way, by im- 
pressions produced on the sensitive nerves. But this 
influence is always secondary and indirect in its opera- 
tion. 
165. Sluggish and continued Action of the Sympathet- 
ic Nerves.—The peculiarity of the nervous action of the 
sympathetic system is that it is sluggish and gradual 
in its operation. The cerebro-spinal nerves, on the con- 
trary, respond instantly to the stimulus which is applied 
to them. The sensibility of the skin feels at once any 
foreign body in contact with it, and the contraction of 
the voluntary muscles is immediate and momentary. 
But in the internal organs a certain time is requisite SYSTEM OF THE GREAT SYMPATHETIC. 
301 
for the operation of the nervous stimulus; and its ac- 
tion, when once excited, is slow and uniform. The peri- 
staltic movement of the intestines, for example, is not a 
prompt and instantaneous contraction, like that of the 
voluntary muscles, but a slow, continuous, and vermicu- 
lar motion, by which the food is steadily and gradually 
carried onward. 
The effect produced by the nervous action of the 
sympathetic system upon the internal organs often re- 
quires a still longer interval. Thus, when we are ex- 
posed to cold or dampness, we feel the impression upon 
the sensitive surface of the skin * immediately; but the 
inflammation which follows in the internal organs, such 
as pleurisy or sore throat, only comes twenty-four hours 
later. And the disturbance of the circulation so pro- 
duced, when once it is established, continues long after 
its cause has disappeared. Thus a cold or a pleurisy, 
which lasts a week, may be produced by an imprudent 
exposure which only continued for half an hour. 
166. Protection from Injury by Cold and Wet.—Accord- 
ingly, the greatest care should be taken to avoid such 
unnatural exposures. The immediate discomfort and 
annoyance produced by cold and wet is a notice given 
to the nervous system that, if the exposure be contin- 
ued, more serious consequences will follow, and that the 
internal organs will suffer in their turn. As soon as 
possible, therefore, after being wet or chilled, the body 
should be thoroughly warmed and dried. The princi- 
pal danger in such cases is in delay. For cold and wet 
do not usually do any harm to healthy and vigorous 
persons so long as the body is kept in active exercise, 
and the circulation maintained in a corresponding de- 
gree of rapidity. But after the work is done, or while 302 
the system is in repose, the same exposure that before 
produced only a healthy glow and reaction, if continued 
longer, will depress the vital powers and cause danger- 
ous injury to the internal organs. 
Thus, even at freezing temperatures, a man may walk 
about briskly in the open air with impunity; but sit- 
ting still in a cold room is always dangerous, and liable 
to produce the most serious results. 
The best protection, therefore, against the conse- 
quences of an unavoidable exposure is the active em- 
ployment of the muscles and limbs so long as the occa- 
sion for exposure continues; afterward the warmth of 
the body should be restored by artificial means with 
the least possible delay. 
167. Various kinds of Reflex Action.—The sympathetic 
system is thus a medium of communication between 
the different internal organs; and, owing to its connec- 
tion with the cerebro-spinal system, the internal organs 
are also brought into relation with the sensitive sur- 
faces and the voluntary muscles. There are, accord- 
ingly, in the living body, reflex actions of three differ- 
ent kinds, which take place, in whole or in part, through 
the sympathetic system. 
1. Reflex actions taking place from the internal organs 
to the voluntary muscles and sensitive surfaces.—The 
convulsions of young children are often caused by the 
irritation of undigested food in the alimentary canal. 
Attacks of indigestion will also sometimes produce tem- 
porary blindness, double vision, squinting, and even 
hemiplegia. 
2. Reflex actions taking place from the sensitive sur- 
faces to the involuntary muscles and the internal or- 
gans.—Imprudent exposure of the skin to cold and wet 
PHYSIOLOGY AND HYGIENE. SYSTEM OP THE GEEAT SYMPATHETIC. 
303 
will often bring on an affection of the bowels. Mental 
and moral impressions, conveyed through the senses, 
will affect the motions of the heart and disturb diges- 
tion and secretion. Terror or surprise will produce a 
dilatation of the pupil, and thus communicate an unu- 
sual and striking expression to the eye. Disagreeable 
sights or odors, or even unpleasant occurrences, in sen- 
sitive persons, will disarrange many of the internal func- 
tions of the body. 
3. Reflex actions taking place, through the sympathetic 
system, from one part of the internal organs to another. 
—The contact of food with the lining membrane of the 
intestine excites the peristaltic movement in its muscu- 
lar coat. The united action of the stomach, the liver, 
and other parts of the digestive apparatus takes place 
through the medium of the sympathetic ganglia and 
their nerves; and the vascular congestion of the differ- 
ent abdominal organs, at the period of their functional 
activity, depends upon the same influence. These ac- 
tions are not accompanied by consciousness, nor by any 
immediate action of the cerebro-spinal system. 
QUESTIONS EOR CHAPTER XVI. 
1. What is the general arrangement of the great sympathetic nerv- 
ous system ? 
2. What is the general course and distribution of the sympathetic 
nerves ? 
3. What is the arterial plexus of sympathetic nerves? 
4. What is the arrangement of the sympathetic ganglia and nerves 
in the neck and in the chest ? in the abdomen ? 
5. What is the situation of the semilunar ganglion ? 
6. What is the solar plexus of the sympathetic ? 
7. Over what functions does the sympathetic system preside ? 
8. Why is it called the “sympathetic” system? 
9. Is the action of the sympathetic system voluntary or involuntary ? PHYSIOLOGY AND HYGIENE. 
10. How is the sympathetic system connected with the cerebro-spi‘ 
nal system ? 
11. How does the action of the sympathetic system differ from that 
of the cerebro-spinal system ? 
12. What injurious effects are liable to be produced on the internal 
organs by exposure of the body to cold and wet ? 
13. What precaution should be taken to avoid these effects ? 
14. What reflex actions take place wholly or in part through the 
sympathetic system ? 305 
THE SPECIAL SENSES. 
CHAPTER XVII. 
THE SPECIAL SENSES. 
Definition of the Special Senses.—Nerves of Special Sense.—Organs 
of Special Sense.—The Sense op Sight.—Optic Nerve.—The Eye- 
ball—its different Parts.—Eield of Vision.—Line of distinct Vision. 
—Estimation of Distance.—Solidity and Projection.—Stereoscope. 
—Thaumatrope.—Internal Impressions.—Muscles of the Eyeball. 
—Eyelids.—The Tears.—Winking.—Meibomean Glands.—Lach- 
rymal Canal.—Practices injurious to the Sight.—Sense of Hear- 
ing.— Auditory Nerve. — Labyrinth. — Tympanum or Drum.— 
Chain of Bones.—Eustachian Tube.—External Ear.—Direction, 
Contrast, and Pitch of Sounds. — Sense of Smell. — Olfactory 
Nerves.—Nasal Passages.—Turbinated Bones.—Two kinds of Sen- 
sibility in Nose.—Uses of the Sense of Smell.—Sense of Taste. 
—Papillae of Tongue.—Two kinds of Sensibility in Tongue.—Glos- 
so-pharyngeal Nerve.—Uses of the Sense of Taste. 
The last department of the nervous system which we 
shall study is that of the Special Senses. By this term 
we mean the senses which give us the feeling of certain 
sensations different from those of ordinary touch, such 
as the sensation of light, of sound, of odors, or of taste. 
168. Nerves of Special Sense.—Each special sense has 
a nerve which is devoted to it, and which is called the 
Nerve of special sense. Each one of these nerves is so 
constituted that it can feel the particular sensation with 
which it is connected, hut can not perceive any of the 
others. Thus the nerve of the eye is sensitive to light, 
but not to sound; and the nerve of the ear is sensitive 
to sound, but not to taste or odors. Each nerve, there- PHYSIOLOGY AND HYGIENE. 
fore, is endowed with a special sensibility, which fits it 
to perform a special function. 
169. Organs of Special Sense.—For every special sense 
there is also a peculiar organ, of more or less compli- 
cated structure, to which the nerve is distributed. 
This is called the Organ of special sense. Thus, for 
the sense of smell, we have the nose; for that of taste, 
the tongue ; for that of sight, the eye; and for that of 
hearing, the ear. Each organ of special sense, beside 
its nerve, is provided with blood-vessels, lining mem- 
branes, muscles, and other parts, wThich assist in the per- 
formance of the entire function. 
We shall examine in succession, 1st, the sense of 
Sight; 2d, that of Hearing; 3d, that of Smell; and, 
4th, that of Taste. 
170. The Sense of Sight—Optic Nerve.—We are en- 
abled to perceive the impression of light by means of 
a peculiar nerve, situated at the base of the brain, 
which is called the Optic nerve. This nerve originates 
on each side from a pair of rounded ganglia, situated 
between the cerebrum and the cerebellum, which are 
the ganglia of the sense of sight (Fig. 53 [5]). From 
their giving origin to the optic nerves, and from their 
having the form of small rounded prominences, they are 
called the “optic tubercles.” From these ganglia the 
optic nerves curve outward and forward, embracing 
the peduncles of the cerebrum, and, continuing their 
course along the base of the brain, leave the cavity of 
the skull, each by a rounded opening called the “ optic 
foramen,” and terminate in the back part of the two 
eyeballs. 
But about the middle of their course these nerves 
present a remarkable connection or union with each 307 
other upon the median line. They approach each oth- 
er on each side, until they at last meet and become con- 
solidated into a single mass. At this point there is an 
interchange of fibres between the two nerves, so that 
some of the fibres belonging to the right optic nerve 
pass over to the left side, and some of those belonging 
to the left optic nerve pass over to the right side. This 
is called the Decussation of the Optic Nerves (Fig. 55). 
THE SPECIAL SENSES. 
Fig. 55. 
Course of the Optic Nerves in Man.—1, 2. Right and left eyeballs; 
3. Decussation of the optic nerves; 4,4. Optic tubercles. 
At this point there is also a connection between the 
two optic tubercles, some of the fibres passing directly 
across, behind the decussation, and returning to the op- 308 
PHYSIOLOGY AND HYGIENE. 
tic tubercle of the opposite side; and also a connec- 
tion between the two eyeballs, as some fibres pass di- 
rectly across, in front of the decussation from side to 
side. Thus the eyes are not so much two distinct or- 
gans as one double organ, both parts of which are as- 
sociated in the performance of a single function. 
From the place of decussation the optic nerves again 
diverge, and, passing through the optic foramina, reach 
the eyeball. Here each nerve spreads out into a thin, 
delicate, grayish expansion of nervous matter, which 
lines most of the interior of the eyeball. This expan- 
sion is called the Retina. It forms the termination of 
the optic nerve. 
171. Function of the Optic Nerves.—The optic nerves 
are the conductors of the sense of sight. When a ray 
of light falls upon the retina, the impression is conveyed 
inward along the fibres of the nerve until it reaches the 
gray matter of the optic tubercle. There it becomes a 
sensation, and we consequently perceive the impression 
of light coming from without. We also perceive its 
variations of intensity and color, whether it be strong 
or feeble, and whether it be blue, yellow, or red. 
Accordingly, if the optic nerves be divided or de- 
stroyed by disease, complete blindness is the result. 
For the impressions of light can no longer reach the 
optic tubercles, and therefore produce no sensation. 
An important reflex action also takes place in the 
optic tubercles. Whenever a strong light falls upon 
the retina the pupil of the eye is immediately contract- 
ed; if the light be diminished in intensity, the pupil 
again enlarges. The stimulus of the light, conveyed 
inward by the optic nerve, is converted into a reflex 
action by the optic tubercles, and is thence directed TUE SPECIAL SENSES. 
309 
outward by certain motor nerves to the muscular fibres 
which serve to contract the pupil. This shows what 
is called the “ sensibility of the pupil.” It is an invol- 
untary action, and will take place even in a state of un- 
consciousness, provided the optic tubercles, as well as 
the nerves, be uninjured. 
172. Structure of the Eyeball.—Thus far the appara- 
tus of vision consists only of a sensitive nerve and a 
ganglion, destined to convey and to receive the simple 
impression of the light. But, in order to understand 
the means by which the sense of sight is exercised in 
all its perfection, we must examine the special organ to 
which the optic nerve is attached. This organ is the 
Eyeball. 
The eyeball is a firm globular mass, situated in the 
bony cavity beneath the forehead which is called the 
“orbit.” Only a small part of the front of the eyeball 
is visible between the lids; but by placing the fingers 
over the eyelids, and between it and the bones of the 
orbit, we can easily feel its globular form. It consists 
externally of a strong and opaque white fibrous mem- 
brane, which envelops the internal parts like a sac or 
bag. This is called, from its hard and resisting tex- 
ture, the Sclerotic coat of the eyeball. 
The sclerotic coat extends all over the surface of the 
eyeball, excepting just at its front part. Here there is 
a circular spot, about one fifth of the whole surface of 
the eyeball, at which the white and opaque sclerotic is 
replaced by a firm but perfectly transparent and color- 
less membrane, through which the light gains admis- 
sion into the interior of the eye. In texture and ap- 
pearance this part of the eye is like a colorless and 
transparent piece of horn or tortoise - shell, and it is 310 
PHYSIOLOGY AND HYGIENE. 
therefore named the Cornea. In looking directly at the 
eye from the front, we do not observe the cornea, since, 
on account of its transparency, we see only the colored 
parts of the eye behind it. But if we look closely at 
the eye of another person in profile, we shall see the 
glassy surface of the cornea projecting in a rounded 
form in front of the other parts. 
The eyeball, accordingly, is covered every where by 
a dense and resisting envelope, of which the front por- 
tion, or the cornea, is colorless and transparent, while 
that on the sides and back, or the sclerotic, is white 
and opaque. 
It is therefore like a room with one window. The 
light will penetrate through this window and strike 
upon the back wall of the room, but it can not enter 
through any openings or crevices at the side. 
Immediately underneath the sclerotic is a second 
coat or membrane of the eyeball, called the Choroid 
coat, of a brownish black color. It is quite opaque, 
like the sclerotic, but is much softer in consistency, and 
is abundantly supplied with blood-vessels. The choroid 
is exceedingly important in the eye, to absorb the light 
which reaches it and prevent reflections; for such re- 
flections would interfere with the distinctness of illu- 
mination at the bottom of the eye. If you look at a 
glazed picture at a little distance, with the light com- 
ing from a window directly behind, you can not see the 
picture distinctly, owing to the reflection of light from 
the surface of the glass. For the same reason, spy-glass 
and microscope makers have learned to cover the in- 
side of their tubes with a layer of soft black paint, so 
that all the light may come in a direct line through the 
glass lenses, and none be reflected from the sides of the 311 
instrument. The choroid membrane serves a similar 
purpose in the eye. 
Beneath the choroid membrane comes the Retina. 
This, as we have already said, is the termination of the 
optic nerve, and consequently the most important part 
of the whole eyeball. As the nerve penetrates the back 
part of the eyeball, it passes through both the sclerotic 
and choroid coats, and then spreads out in a thin, soft, 
delicate, and semi-transparent layer, which lines the 
whole internal surface of the eyeball except in front, 
just at the opening of the cornea. The retina is the 
Sensitive part of the eye. It is this membrane which 
receives the rays of light entering at the front, and 
communicates their impression, through the fibres of 
the optic nerve, to the brain behind. But, though the 
retina is so sensitive to light and color, it can not con- 
vey the ordinary sensations of touch. Even when the 
membrane itself is cut or pricked, as in surgical opera- 
tions about the eye, it does not convey the feeling of a 
touch or a wound, but only the sensation of a flash of 
light. It is for this reason that a sudden blow upon 
the eyeball produces the appearance of an explosion of 
brilliant sparks. When the deeper parts of the eye are 
inflamed or otherwise disordered, the patient sometimes 
sees irregular flashes and points of light, owing to the 
unnatural irritation of the retina; and when this mem- 
brane is deeply injured by disease, it becomes insensi- 
ble, and the eye is consequently blind. 
Owing to the special sensibility of the retina, there- 
fore, its function is exclusively devoted to the percep- 
tion of light which reaches its surface from without. 
The globular cavity inclosed by the retina is occu- 
pied by a transparent, jelly-like substance, which is 
THE SPECIAL SENSES. 312 
PHYSIOLOGY AND HYGIENE. 
termed the Vitreous body, from its colorless and glassy 
appearance. It fills the interior of the eye, and keeps 
the other parts in their places by preserving the ten- 
sion of the external coats. 
173. Crystalline Lens.—Just in front of the middle of 
the vitreous body is another transparent and extremely 
important part of the eye, which is called the Crystal- 
line lens. It has the form of a circular, flattened glass 
bead, thicker in the middle and thinner at its edges. 
The lens is suspended in its position by a very thin and 
delicate membrane, which envelops its surface both in 
front and behind. It then stretches outward from the 
edges of the lens in a double layer, which soon after 
consolidates into a single membrane, called the “ hya- 
loid membrane,” and in this form it extends over the 
whole surface of the vitreous body. The crystalline 
lens is thus held in its place in front of the central part 
of the vitreous body (Fig. 56). 
Fig. 56. 
Vertical Section of the Eyeball.—1. Sclerotic; 2. Choroid ; 3. Retina; 4. Lens; 
5. Hyaloid membrane; 6. Cornea; 7. Iris; 8. Vitreous body. THE SPECIAL SENSES. 
313 
174. Function of the Crystalline Lens.—Now it is only 
by means of the crystalline lens that we are enabled to 
perceive the form and outline of things. For the retina 
itself is only sensitive to the impressions of light and 
color; that is, it can perceive the difference between 
light and darkness, and between the different colors, as 
red, blue, yellow, and green. But it has no power, by 
itself, of distinguishing the form of objects. The eye 
receives the light indifferently from every part of an 
object which may be situated in front of the cornea; 
and therefore, if it 
were provided with 
the retina alone, the 
rays of light from all 
parts of the object, 
diverging equally 
in every direction, 
would enter the eye 
and reach together every part of the retina, as in Fig. 
57, where the arrow,«, 5, represents the object, and the 
dotted line at the 
right represents the 
retina. Here all 
parts of the retina, 
1, 2, 3, 4, would re- 
ceive rays coming 
both from the point 
of the arrow, a, and 
from its butt, b. Thus the top, bottom, and sides of the 
object would all be indiscriminately mixed at the sur- 
face of the retina; and we should not be able to dis- 
tinguish its different parts, but should only receive the 
impression of a confused luminosity. 
Fig. 57. 
Vision without a Lens. 
Fig. 58. 
Vision with a Lens. 314 
PHYSIOLOGY AND HYGIENE. 
A “ lens” is any transparent body, having the figure 
described above, that is, rounded on its two opposite 
surfaces and thinner at its edges, which has such an ac- 
tion on the rays of light passing through it that it brings 
them together or concentrates them at a certain dis- 
tance beyond. Consequently, any brilliant point situ- 
ated in front of such a lens will produce another bril- 
liant point behind it; because its rays, which diverge in 
order to reach the lens, are again brought together by 
passing through it. We can see this effect with any 
convex lens of glass, such as the large magnifying 
glasses which are used for looking at pictures. 
If you hold a white screen or a sheet of paper at a 
distance of six or eight feet from a gas-light, the whole 
surface of the paper is equally and moderately illumin- 
ated, because the light, coming from all parts of the 
flame, is spread uniformly over its surface. But if you 
hold a lens between the light and the paper, you will 
see that it makes a spot which is brighter than the 
rest; and as you bring the lens slowly nearer and near- 
er to the paper, the middle of this spot grows brighter 
and brighter, until at last you have a distinct and bril- 
liant image of the flame in its centre, while the sur- 
rounding parts are dark. Not only all the light pass- 
ing through the lens is thus brought together in a 
small space, but all the light coming from the top of 
the flame is concentrated at one point, and all that com- 
ing from its bottom is concentrated at another; so that 
we can now distinctly perceive its form and outline. 
The crystalline lens performs the same service in the 
interior of the eye. With the lens interposed, all the 
rays emanating from the point of the arrow, a (Fig. 58), 
are concentrated at x, and all those emanating from its THE SPECIAL SENSES. 
315 
butt, £>, are concentrated at y. Thus the retina receives 
the impression of the point of the arrow separately from 
that of its butt, and all parts of the object in like man- 
ner are distinctly and accurately perceived. 
The retina, accordingly, is the sensitive screen upon 
which the light is thus concentrated. 
The spot at which a lens will thus concentrate the 
light passing through it is called its focus, and it is 
only at a certain distance that this concentration will 
be perfect. If we move either the screen or the lens 
backward or forward, so as to increase or diminish the 
distance between them, the brilliant spot fades away, 
to reappear when the two are again placed in their prop- 
er position. Now the crystalline lens is naturally 
placed at such a distance from the deeper parts of the 
eye that it concentrates the light to a focus exactly at 
the surface of the retina. 
175. Iris and Pupil.—In front of the crystalline lens 
there is suspended a muscular curtain with a circular 
opening or perforation at its centre. This curtain or 
partition is the Iris. It is so called on account of its 
variations of color, its surface presenting a mixture of 
different tints, which produce, all together, the effect of 
black, brown, blue, or gray. This is the colored circle 
which we see behind the transparent cornea, and the 
circular opening in its centre is the Pupil. 
The iris is composed of fine muscular fibres, which 
are arranged in two sets. Those of the first set radiate 
from the edges of the pupil outward, and serve to en- 
large the opening. The second run circularly round 
the pupil, and serve to draw it together like the mouth 
of a purse. The posterior surface of the iris is covered 
with a layer of black coloring matter like that of the 316 
PHYSIOLOGY AND HYGIENE. 
choroid coat. The iris itself is therefore opaque, and 
it admits the light to the interior of the eye only 
through the opening of the pupil. 
176. Movements of the Pupil.—The pupil, however, is 
movable. By the alternate action of the circular and 
radiating fibres of the iris, its opening may be enlarged 
or diminished, and a greater or smaller quantity of 
light admitted to the eye. We have already described 
the reflex action by which this is accomplished. When 
the light which strikes the retina is intense and daz- 
zling, the pupil contracts and shuts out a portion of it; 
when the light is dim and insufficient, the pupil enlarges 
and admits it in greater abundance. 
Accordingly, when we suddenly enter a brilliantly 
lighted apartment, the eye is at first dazzled by the in- 
tensity of the light; but it soon accommodates itself to 
the change by the contraction of the pupil, and the 
light no longer produces discomfort. On the other 
hand, on first passing from the light into a dark room, 
every thing is in obscurity, and none of the objects in 
the apartment are visible to us. But as the pupil en- 
larges and more light gains entrance to the eye, the va- 
rious objects become perceptible, until the room, which 
before appeared in total darkness, at last seems to be 
tolerably well lighted. 
This reflex action of the pupil takes place through a 
part of the sympathetic system. In the back part of 
the orbit of the eye there is a minute nervous ganglion, 
called the Ophthalmic ganglion. It communicates by 
slender filaments with the arterial plexus of the sym- 
pathetic nerve in the interior of the skull, and also with 
motor and sensitive branches of the cranial nerves. 
From its front part there pass off* from ten to fifteen THE SPECIAL SENSES. 
317 
delicate nerves which soon penetrate the sclerotic coat 
of the eyeball, and run forward beneath it until they 
reach the situation of the iris. These are called the 
Ciliary nerves. They are finally distributed to the 
muscular fibres of the iris, and alternately excite them 
to contract or enlarge the pupil. 
The movement of the pupil is therefore one of those 
reflex actions which take place partly through the cere- 
bro-spinal and partly through the sympathetic system 
of nerves. The impression upon the retina is first car- 
ried to the optic tubercle in the brain, while the im- 
pulse reflected thence is conveyed to the ophthalmic 
ganglion, and finally reaches the muscular fibres of the 
iris through the ciliary nerves. 
Between the front of the iris and the inner surface 
of the cornea is a space which is filled with a thin 
transparent fluid. From its watery consistency this 
fluid has received the name of the Aqueous humor. It 
completes the structures entering into the composition 
of the eyeball. 
There are several peculiarities in the function of the 
eye which require attention. 
177. Field of Vision.—First, there is only a small space 
in front of the eye in which objects can be seen distinct- 
ly. As the pupil will admit rays of light coming ob- 
liquely from various directions, there is, of course, a 
field or circle, of a certain size, within which objects 
can be perceived. This space is called the Field of 
vision ; and beyond its limits nothing whatever can be 
seen, because rays of light coming directly from the 
side or from behind can not enter the pupil. 
178. Line of distinct Vision.—But even within this 
field there is only a single spot in its centre at which 318 
PHYSIOLOGY AND HYGIENE. 
objects can be seen distinctly. Thus, if we stand in 
front of a row of upright stakes or poles, we can see 
those directly before the eye with perfect distinctness, 
but those placed at a little distance on each side are 
only perceived in a confused and uncertain manner. 
We can see that they are there, but we can not accu- 
rately distinguish their outlines. 
When we look at the middle of a printed page, di- 
rectly in front, we see the distinct forms of the letters; 
but at successive distances from this point, if the eye be 
kept fixed, we can distinguish first only the separate 
letters with confused outlines, then only the words, and, 
lastly, only the lines and spaces. 
This is because the rays of light which enter the 
crystalline lens directly from the front (as from a, Fig. 
Fig. 59. 
Lines of Distinct and Indistinct Vision. 
59), are concentrated by it to a focus at the retina (x)y 
and produce distinct vision; but those which enter it TIIE SPECIAL SENSES. 
319 
very obliquely (as from b), cross each other in the cav- 
ity of the eyeball, and so reach the retina separately 
(at y, z), thus producing indistinct and imperfect vision. 
There is, therefore, only a single line extending di- 
rectly in front of each eye within which objects are dis- 
tinctly seen. This is called the Line of distinct vision. 
We make up for this, however, by the great mobility 
of the eyes, which turn rapidly toward every part of a 
landscape, and in this way enable us to see the whole 
with distinctness. In reading a printed page, also, the 
eyes follow the lines from left to right, thus seeing each 
letter and word distinctly in succession. At the end 
of each line they return suddenly to the commence- 
ment of the next, and repeat this movement from the 
top to the bottom of the page. 
179. Single and distinct Vision with both Eyes.—Be- 
side this, even directly in front of us, there is only a cer- 
tain distance at which objects can be seen distinctly by 
both eyes. As the eyes are situated two or three inches 
apart from each other in their orbits, when they are 
both directed toward the same object, the lines of vis- 
ion for the two eyes converge and meet each other at 
the situation of the object. It is for this reason that 
we see only one object, though we look at it with two 
eyes; for, as the two lines of vision meet at a single 
point, the two distinct images exactly cover each oth- 
er, and so form but one (Fig. 60 [1]). 
But either within or beyond this point, vision be- 
comes imperfect and at the same time double. If we 
hold up one of the fingers before the face at the dis- 
tance of one or two feet, and in the same range with 
any small object, such as a door-knob, on the other side 
of the room, when both eyes are directed at the finger, 320 
PHYSIOLOGY AND HYGIENE. 
we see it single and distinctly, but the door-knob ap- 
pears double, one image on each 
side the finger. If we now change 
the direction of the two eyes and 
look at the door-knob, that, in its 
turn, will become distinct and sin- 
gle, while the finger will appear 
double, one on each side the door- 
knob. 
This is because, when both eyes 
are directed at the nearer object 
(Fig. 60 [1]), the farther one [2], 
will also be seen; but it will be 
seen indistinctly, because it is 
outside the line of distinct vision. 
But for the right eye it will be to 
the right of the line of vision, and 
for the left eye to the left of this 
line. The two images, therefore, 
do not correspond in situation, 
and the object consequently ap- 
pears double. 
In looking at a landscape, accordingly, when both 
eyes are directed at the foreground, the middle ground 
and the distance both appear dim and indistinct; and 
when the eyes are directed toward the distance, the 
foreground, in its turn, is imperfectly perceived. 
Thus we judge instinctively of the distance of differ- 
ent objects by the direction of the two eyes and their 
lines of distinct vision. 
180. Appreciation of Solidity and Projection.—But the 
combined action of the two eyes is also useful in anoth- 
er respect: it enables us to appreciate the qualities of 
solidity and projection. 
Pig. 60. 
Vision at different Distances. 
—a. Right eye; fc. Left eye; 
1. Near object; 2. Remote 
object. THE SPECIAL SENSES. 
321 
When we look at any solid ob- 
ject, such as a square box (Fig. 
61), at a short distance in front of 
us, the two eyes, being separated 
from each other by the distance be- 
tween their orbits, will see the ob- 
ject from two different directions. 
Both of them will see the front of 
the box (a), but, in addition, the 
right eye will see a little of its 
right side (b), and the left eye will 
see a little of its left side (c.) We 
can easily convince ourselves of 
this, in looking at such an object, 
by alternately closing first the 
right and then the left eye (as in 
Fig. 62), when we shall find that to the left eye the box 
appears as at a, and to the right eye it appears as at b. 
Fisr. 61. 
Vision of Solid Objects.—1, 
2. Right and left eyes; a, 
b, c. Solid object 
Fig. 62. 
Solid Object.—a. As seen by the left eye; b. As seen by the right eye. 
Consequently, the images of such a solid object, as 
perceived by the two eyes, are different. But as they 
are both in the line of distinct vision, and occupy the 
same spot, they are united with each other, and appear 
as one. It is from this union and fusion of t wo differ- 
ent images that we acquire the perception of solidity 
and projection. 322 
PHYSIOLOGY AND HYGIENE. 
Accordingly, a flat picture, however well it may be 
painted, can never deceive us in this respect; for we 
feel that precisely the same image is presented to both 
eyes, and consequently that it can have no real projec- 
tion. 
But when two pictures of the same object, taken in 
two different positions, are presented in such a way 
that only one of them is seen by the right eye and only 
the other by the left, the same effect may be produced 
as by the object itself, and the appearance of solidity 
and projection may he perfectly imitated. 
This is actually accomplished in the contrivance 
known as the Stereoscope. This is simply a box hold- 
ing two pictures, usually photographs, of the same ob- 
ject. One of the photographs, taken as the object 
would actually appear to the right eye, is seen by the 
right eye; and the other, taken as it would appear to 
the left eye, is seen by the left eye. Thus the two pict- 
ures combined seem to be but one, and a singularly de- 
ceptive resemblance to the real object is produced. 
Thus, within moderate distances, we perceive the pro- 
jection of solid bodies by the combined action of the 
two eyes. We also perceive variations in distance by 
the diflerent direction of the two lines of vision and the 
angle at which they meet. But at long distances both 
these distinctions cease; because the direction of the two 
eyes is then so nearly parallel that we can not perceive 
the difference between them. The colors of objects 
also become less brilliant as they are removed from us, 
and are also changed somewhat by the intervening at- 
mosphere. We can perceive, accordingly, the solidity 
and variation in color of a rock, a tree, or a house near 
by; but at a distance of some miles, even a large object, THE SPECIAL SENSES. 
323 
such as a mountain, loses its projection, and appears flat 
and gray against the horizon. 
181. Effect of Contrast in Light and Color.—Secondly, 
the strength of the impressions which we obtain by the 
sight depends upon their contrast. The lighted parts 
of a solid object appear not only more brilliant, but 
also of a different color from those which are in shad- 
ow; and the greater the contrast between these tints, 
the more readily we distinguish its different parts. 
The strongest of all contrasts is that between black 
and white, and therefore we very easily read a print- 
ed page, which is composed of black letters on a white 
ground. It is still easier to distinguish white letters 
on a black ground, because the eye is more attracted 
by the white surface which is lighted than by the black 
surface which is dark. Different colors are also modi- 
fied in their appearance by other colors with which 
they are associated. Thus a white surface will look 
blue by contrast with yellow or orange, and will as- 
sume a rosy tinge by contrast with green. If we look 
through blue spectacles, every thing will at first sight 
appear to be tinged with the blue color of the glass; 
but this impression will after a time pass away, and 
when the spectacles are again removed, surrounding 
objects will look yellowish by contrast. 
When different colors are closely mingled together 
they produce an intermediate tint. Thus blue and yel- 
low, when intimately mixed, produce green; yellow 
and red produce orange; red and blue produce pur- 
ple; and white and black grains, uniformly mingled, 
have the appearance of a continuous shade of gray. 
182. Persistence of Visual Impressions.—Thirdly, vivid 
impressions produced upon the eye remain for a short 324 
PHYSIOLOGY AND HYGIENE. 
time afterward. If a lighted stick be swung round rap- 
idly in a dark room, it appears like an unbroken circle 
of light. This is because the impression of the light, at 
any one point in the circle, remains until the revolving 
stick has again returned to the same spot; and a suc- 
cession of sparks, sent off rapidly from a knife-grinder’s 
wheel, produce the appearance of a continuous stream 
of fire. This is also illustrated by a familiar toy called 
the Thaumatrope. In this instrument a series of pict- 
ures of the same object in different positions, as of a 
horse leaping over a wall, are made to pass successively 
before the eye upon a revolving card. The different 
figures follow each other so rapidly that the eye can 
not perceive the interval between them, and they look 
like the same figure in active motion. 
183. Visual Impressions of Internal Origin.—Finally, 
the impressions of sight may be imitated by the internal 
action of the nervous system, so that we appear to see 
objects which are not presented to the eyes. This is 
also true of all the other senses, but the internal im- 
pressions belonging to the sense of sight are much more 
vivid than the rest. Thus, in a dream, or even in a rev- 
erie, we often see external objects, with all their peculi- 
arities of light, color, and form, nearly or quite as dis- 
tinctly as when awake, and much more distinctly than 
we perceive imaginary sounds or sensations of touch. 
It is this sense also which becomes most easily excited 
in certain nervous disorders, as in delirium, when the 
patient sees passing before his eyes faces, and figures, 
and landscapes, and towns, and cities, which are depict- 
ed upon his imagination with a remarkable force and 
distinctness. 
As the sense of sight, therefore, does not depend so THE SPECIAL SENSES. 
325 
directly as tlie other senses upon the actual contact of 
external objects, it is more readily called into activity 
when withdrawn from their influence. 
The organ of sight is provided with certain accessory 
parts, which enable it more perfectly to perform its 
functions. 
184. Movements of the Eyeball.—In the first place, the 
eyeball is movable within the orbit. It rests in this 
bony cavity, imbedded in a layer of fat, which acts like 
a soft and elastic cushion; and upon this cushion the 
eyeball is capable of turning in various directions. 
From the bony walls at the bottom of the orbit four 
slender muscles pass forward in a straight direction to 
be inserted into the sclerotic coat—one above, one be- 
low, one on the inside, and one on the outside of the 
eyeball. These are the “straight muscles of the eye- 
ball.” As they contract, they turn the eye upward or 
downward, inward or outward. Another muscle, very 
curiously constructed, is called the “ upper oblique 
muscle of the eyeball.” It arises, like the rest, from the 
back part of the orbit, and runs forward until it reaches 
its upper and inner portion near the bridge of the nose. 
Here the tendon passes through a fibrous loop attached 
to the bone, and then turns backward and outward, to 
be inserted into the upper part of the sclerotic coat 
near its middle. The tendon and the fibrous loop thus 
form a pulley, through which the muscle acts upon the 
eyeball. It is therefore sometimes known by the name 
of the “ trochlearis,” or pulley-like muscle. Finally, a 
sixth, or the “ lower oblique muscle,” starts from the in- 
ner and lower part of the orbit, and winds outward be- 
neath the eyeball, to be attached to the sclerotic at its 
outer part, nearly opposite the insertion of the trochle- 
aris. 326 
The two oblique muscles rotate the eyeball upon its 
axis. If you stand in front of a mirror and incline the 
head gently from side to side, you will see that the eyes 
turn at the same time in the opposite direction, revolv- 
ing easily in their orbits, so that each eye keeps its own 
level with the horizon. This is accomplished by the 
action of the oblique muscles'. All the muscles of the 
eyeball, by this combined or alternate contraction, thus 
enable the eye to move in various directions, and both 
enlarge the area of sight and assist in the expression 
of the face. 
185. Protection of the Eyeball from Injury.—The eye- 
ball is protected from external injury by the bony 
edges of the orbit. These are so arranged that, with 
the cheek-bones and those of the nose, they form a 
nearly continuous ridge or rampart about the front of 
the eye. A blow with a stick or other weapon, there- 
fore, hardly ever injures the eyeball, because it is 
caught by the projecting edges of this ridge. In order 
to reach the eye itself, the missile or weapon must be 
directed in a nearly straight line from before backward; 
and as this seldom happens, the eye usually escapes in- 
jury. 
186. The Eyelids and their Movements.—In front of 
the eyeball are the Eyelids. These are two horizontal 
curtains or folding-doors, which open and shut to ad- 
mit or exclude the light. Each is strengthened by a 
thin but firm cartilaginous plate, situated beneath the 
skin. The upper eyelid is much the larger and more 
movable of the two, and when the eyes are opened it 
is raised by a muscle attached to its upper edge, and 
drawn in beneath the roof of the orbit. When allowed 
to fall, it covers the -whole of the pupil and the greater 
PHYSIOLOGY AND HYGIENE. THE SPECIAL SENSES. 
327 
part of the cornea. It is therefore like a screen or Ve- 
netian window-blind, which may be raised or lowered 
at will in front of the transparent parts of the eye 
(Fig. 63). 
Fig. 63. 
External parts of the Eye.—1. Iris; and, 2. Pupil, showing through the trans- 
parent cornea; S. Front part of sclerotic coat, seen between the lids, and 
called, from its white color, the “white of the eye;” 4. Upper eyelid; 5. 
Lower eyelid. 
The inside of the eyelids are lined by a thin and 
transparent membrane, called the Conjunctiva, which 
also extends over the whole exposed portion of the eye- 
ball. The conjunctiva is supplied with a very import- 
ant watery secretion, by which its surface is constantly 
bathed, and its brilliancy and transparency kept unim- 
paired. This secretion consists of the tears. They are 
produced in a little gland, termed the “Lachrymal 
gland,” situated in the upper and outer part of the orb- 
it, and are conducted thence by a number of fine ducts, 
which open upon the conjunctiva near the outer corner 
of the eye. The watery fluid then runs along the edge 
of the lower eyelid toward the inner corner of the eye. 
187. The act of Winking.—But about five or six times 
a minute the tears are spread over the surface of the 
conjunctiva by the act of winking. This motion is per- 
formed by means of an oval shaped muscle, situated 328 
PHYSIOLOGY AND HYGIENE. 
immediately beneath the skin of the eyelids, which sur- 
rounds their opening with a thin and broad layer of cir- 
cular fibres. This is the Orbicularis muscle, so named 
from its orbicular or ring-like form. By its contraction 
it suddenly draws the eyelids together, and, as they in- 
stantly separate, they distribute the tears in a thin lay- 
er over the surface of the conjunctiva. 
This motion is extremely important. For, as the 
front surface of the eyeball is constantly exposed to 
the air, it loses its moisture by evaporation, and would 
soon become dry, wrinkled, and opaque. It is for this 
reason that immediately after death the eye becomes 
dull and tarnished, and loses its natural appearance of 
brilliancy. But during life the orbicularis muscle is 
constantly watching for the safety of the eyeball; and 
every few seconds, as soon as a little collection of the 
tears has accumulated below, it brings the eyelids to- 
gether with a quick, sharp motion, catches the watery 
fluid upon their edges, and so spreads it equally over 
the surface of the cornea. 
The motion of winking is a reflex action. It takes 
place, as a general rule, without our knowledge, and it 
is even difficult to resist it, for a long time, by any vol- 
untary effort. It is so rapidly performed that it does 
not usually attract our notice. For we have already 
seen that visual impressions made upon the eye remain 
for a very short time afterward; and though the lids 
are closed by each act of winking, the motion is so in- 
stantaneous that it does not interrupt the sensations of 
the eye, and it therefore passes unobserved. 
188. The Meibomean Glands and their Secretion.—In 
order to prevent the tears from being lost by running 
over the eyelids, the edges of the lids are smeared with THE SPECIAL SENSES. 
329 
a thick oleaginous secretion, like the “ sebaceous mat- 
ter” of the skin. Oily matters and water have such a 
repulsion for each other, that a little grease, rubbed on 
the edges of a cup, will retain the water and prevent 
its running over, though the cup may be filled even 
above the level of its brim. The same office is perform- 
ed by the oily secretion of the eyelids. It is supplied 
by a number of long slender glands, called the Meibo- 
mean glands, surrounded with clustered follicles, which 
are situated on the inside of each eyelid directly be- 
neath its lining membrane. They open by fine orifices 
along the margin of the lid, and keep this part covered 
with a thin layer of their secretion. 
Usually the sebaceous matter is sufficient to keep the 
tears within the eyelids; but the lachrymal glands are 
very sensitive to peculiar mental emotions. These emo- 
tions, by the sympathetic action of the nervous system, 
sometimes excite the glands to unusual activity, so that 
they pour out their secretion in increased abundance; 
and the tears, thus discharged in excessive quantity, 
run over the edge of the eyelids, and trickle down upon 
the cheeks and face. This is the act of weeping. 
189. Passage of the Tears into the Cavity of the Nos- 
trils.—From the front of the eye, the tears are collected 
by a minute orifice at the inner corner of each eyelid. 
These two orifices lead into two narrow tubes or canals, 
called the Lachrymal canals, which convey the tears 
into an enlarged cavity or sac at the upper and outer 
part of the nose. This sac is continued downward into 
a duct, called the “ nasal duct,” which opens into the 
interior of the nose, about its middle portion. Thus 
the tears, after performing their part in the protection 
of the eyeball, are conducted through the lachrymal 330 
PHYSIOLOGY AND HYGIENE. 
passages, to be finally discharged into the cavity of the 
nostrils. 
190. Sensibility of the Conjunctiva.—The surface of 
the conjunctiva possesses an extreme sensibility. This 
is not like the sensibility of the touch, but rather an 
irritability like that of the glottis, by which the con- 
junctiva resents the intrusion of foreign substances be- 
tween the eyelids. It is protected from this intrusion 
by the activity of the orbicularis muscle, which con- 
tracts spasmodically, and shuts the lids on the least ap- 
proach of external objects to the eye. It is still farther 
protected by the Eyelashes. These are the stiff curved 
hairs which grow from the outer margins of the lids, 
and project forward in front of their openings. Those 
of the upper lid are curved upward, those of the low- 
er lid are curved downward; and when the lids are 
brought near together, these two ranges of hairs stand 
like so many crossed sabres, or a kind of chevaux-de- 
frise, guarding the entrance to the eye. 
But if any foreign body should accidentally gain ad- 
mission, then the sensibility of the conjunctiva is ex- 
cited. Every one has felt the extreme irritation pro- 
duced by the entrance of a grain of dust, or a cinder, 
or the filing of a metal, beneath the eyelids. The front 
of the eyeball becomes blood-shot, the tears are poured 
out in abundance, the movements of winking follow 
each other with rapidity, and the attention is distract- 
ed from every other object by the discomfort of the 
suffering organ. 
This irritability of the conjunctiva is the safeguard 
of the eye. For if the foreign substance were allowed 
to remain, it would produce, after a time, a serious in- 
jury to the deeper parts, and thus permanently impair THE SPECIAL SENSES. 
331 
the sight. These deeper parts, although so important, 
are themselves insensible. But the conjunctiva stands 
in front of them, to give us notice of the approach of 
danger; and when the foreign body is not immediately 
discharged, this membrane is thrown into an excessive 
irritation, and gives us no rest until we have rid our- 
selves of the offending substance, and relieved the eye 
from the danger of its presence. 
191. Precautions proper to be observed in using the 
Eyes.—The eye, like other bodily organs, is susceptible 
of fatigue. After being exposed for a considerable 
time to a bright light, this fatigue is very perceptible, 
and the optic nerve is refreshed by the repose of twi- 
light or of a shaded apartment. There is no doubt 
that the regular refreshment of sleep during night is 
also necessary to the sense of sight as it is to the mus- 
cular system; and this, the most delicate and valuable 
of all the senses, is the most readily impaired by an un- 
natural want of sleep. 
The sight may also be injured by excessive or im- 
proper use during the day. 
This effect may be produced, first, by exposure of the 
eye to too brilliant a light. If we look for an instant 
at the sun, or even at an excessively strong artificial 
light, we feel for some seconds afterward that the eye 
is partially blinded. It can no longer distinctly per- 
ceive surrounding objects; and if we have been so im- 
prudent as to continue the unnatural exposure, its blind- 
ing effect lasts for a long time afterward. The eye 
may even be permanently injured by too violent or 
long-continued a stimulus of this kind. 
Secondly, the eye should not be employed for too 
long a time in the close examination of small objects. 332 
PHYSIOLOGY AND HYGIENE. 
Very small objects, seen at a short distance, require a 
greater exertion of the eye than larger ones which are 
more easily perceived. Thus it is exceedingly weari- 
some and injurious to read a book which is too finely 
printed, or in which the letters are too close together, 
or not sufficiently distinct. It is the worst possible 
economy, therefore, to read habitually books which are 
badly printed; for it is at the expense of the eyesight, 
which can not be replaced when once seriously im- 
paired. 
But the examination of minute objects, or the em- 
ployment of the eye in reading or writing, is much 
more injurious when continued with insufficient light. 
The light, of course, should never be dazzling, but it 
should always be sufficient to illuminate fully the print- 
ed page or other object which is under examination. 
Otherwise the eye becomes strained and wearied be- 
yond its natural power of endurance, and a repetition 
of such treatment will inevitably impair the sight. It 
is for this reason that reading by twilight is particularly 
dangerous; because the light fades at that time slowly 
and imperceptibly, and thus becomes exceedingly insuf- 
ficient before we notice its diminution. 
The light which is used should also be perfectly uni- 
form and steady. The diffused light of day is there- 
fore the best for reading or writing. A flickering and 
uncertain artificial light, on the other hand, is the worst; 
for its rapid and irregular changes from brightness to 
obscurity fatigue the optic nerve, and rapidly exhaust 
the sensibility of the eye. 
The use of the eye in studying minute objects should 
therefore be employed with moderation, and in such a 
way as to save the organ from unnatural irritation or 
fatigue. THE SPECIAL SENSES. 
192. The Sense of Hearing.—Sound is produced by the 
vibration of the atmosphere. Many solid bodies also 
are capable of vibi-ating, such as a metallic bell or the 
strings of a violin; but their vibration must be commu- 
nicated to the atmosphere in order to reach our ears 
and thus produce the sensation of sound. Accordingly, 
if a bell be rung under the receiver of an air-pump from 
which the air has been exhausted, it produces no sound. 
The metal itself may vibrate as usual, but its move- 
ments can not be communicated to the atmosphere, and 
consequently can not reach our organs of perception. 
Hearing is therefore the sense by which wTe perceive 
the sounds which are conducted by the atmosphere. 
193. Auditory Nerve.—The sense of hearing depends 
upon a special nerve, called the Auditory nerve. This 
nerve originates from the upper and back part of the 
medulla oblongata, whence it passes outward, curves 
round this portion of the brain, and, after a short pas- 
sage, penetrates by a rounded opening into a thick and 
triangular portion of the floor of the skull. This part 
of the bony walls of the cranium is much denser and 
harder than the remainder, and has therefore received 
the name of the “ stony” or “ petrous” bone. 
Within the petrous bone the auditory nerve presents 
a singular and complicated form. 
1 194. The Labyrinth.—It lies in a cavity which is ex- 
cavated in the substance of the bone, and in which it is 
protected from external injury by the thickness and 
density of the bony walls. This cavity, from its re- 
markable and varied configuration, is called the Laby- 
rinth. It consists, first, of a small rounded chamber, 
which serves as a kind of entrance or ante-room to the 
remainder, and is therefore termed the “ vestibule.” The 334 
PHYSIOLOGY AND HYGIENE. 
vestibule communicates with three narrow curved pas- 
sages, called the “ semicircular canals.” These canals 
are so placed that one is directed nearly upward and 
forward, the second nearly upward and sideways, while 
the third is horizontal. Both the vestibule and the 
semicircular canals are filled with a clear transparent 
fluid like lymph; and in this lymph there is suspended 
a membranous sheath or bag, which presents in its form 
an exact repetition of the bony cavities which inclose 
it, being enlarged at the situation of the vestibule, and 
sending out tubular prolongations into the semicircu- 
lar canals. Its interior is also filled with lymph, and it 
thus floats in the fluid of the labyrinth, but without 
touching the walls of the cavity. 
The auditory nerve is distributed to this sheath, its 
fibres spreading out in the substance of its membranous 
walls. 
The remaining part of the labyrinth is no less pecul- 
iar in its form. Just alongside the vestibule there is a 
double tubular canal, which winds round a hollow cen- 
tral axis, making nearly three complete turns, thus form- 
ing a kind of spiral cone, like a snail-shell, with its point 
directed forward and outward. From its resemblance 
to a snail-shell, this part of the labyrinth is termed the 
“ cochlea.” The spiral canals of the cochlea, which com- 
municate at one end with the vestibule, are themselves 
filled with lymph; and the remaining fibres of the audi- 
tory nerve pass upward along its hollow axis, spreading 
out successively in a membranous partition between the 
two parts of the double canal. Thus, when they arrive 
at the apex of the cone, the nervous fibres have all been 
exhausted, and the distribution of the nerve is com- 
plete. THE SPECIAL SENSES. 
335 
The whole of this part of the auditory apparatus, 
consisting of the labyrinth, the membranous bag which 
it contains, with the auditory nerve and its distribu- 
tion, being all contained within the bony floor of the 
skull, is called the Internal ear. 
195. Function of the Auditory Nerve.—The auditory 
nerve, like the optic, is a nerve of special sense. It can 
communicate the impression of sonorous vibrations, 
but it is not endowed, so far as we know, with any 
other kind of sensibility. 
196. The Tympanum of the Ear.—The internal ear 
communicates with the external atmosphere by a com- 
plicated apparatus of movable bones and membranes. 
In the outer part of the bony wall of the vestibule is 
a little oval-shaped perforation, not more than one 
eighth of an inch long and one sixteenth of an inch 
wide. This perforation in the bone, which is called the 
oval “ fenestra” or window, is closed by a thin fibrous 
membrane, which prevents the fluid of the vestibule 
from escaping. The name given to this opening is a 
very appropriate one; for the perforation in the bone 
is really a kind of window, and the fibrous membrane 
is the sash which closes it. As the light comes into a 
room through the glass pane of a window, so sounds 
enter the vestibule through the membrane of the oval 
fenestra. 
Immediately outside the wall of the vestibule, but 
still within the substance of the petrous bone, is an ir- 
regularly shaped cavity, much more spacious than the 
vestibule itself. At rather less than a quarter of an 
inch distance from the membrane of the oval fenestra, 
the mouth of this cavity is closed by another mem- 
brane stretched tightly across its diameter, and at- 336 
PHYSIOLOGY AND HYGIENE. 
tached, all around, to the edges of its bony walls. This 
outer membrane is called the “ Membrane of the Tym- 
panum,” and the cavity which it incloses is called the 
“ Tympanum,” or Drum of the ear. 
This name is also well chosen; for the exterior of 
the membrane of the tympanum is in contact with the 
atmosphere, and the sonorous vibrations of the air beat 
upon it, like the sticks upon the head of a drum. 
197. Chain of Bones.—But the sounds are transmit- 
ted from the membrane of the tympanum to the mem- 
brane of the oval fenestra by a curious chain of bones 
stretched from one to the other. These bones are three 
in number, and are named, from striking resemblances 
in their form, respectively the “ mallet,” the “ anvil,” 
and the “ stirrup.” The mallet is attached to the mem- 
brane of the tympanum, the anvil is articulated with it 
by a movable joint, and the stirrup is also articulated 
with the anvil by its point or narrow end, while by its 
oval base or foot-piece it is attached to the membrane 
of the oval fenestra (Fig. 64). 
It is easy to see, therefore, how the vibrations of the 
atmosphere, striking upon the membrane of the tym- 
panum, will be transmitted by the chain of bones to 
the membrane of the oval fenestra, and thus reach the 
fluid of the labyrinth, to be finally received by the ex- 
pansions of the auditory nerve. 
198. Eustachian Tube, and its Function.—Like other 
drums, the cavity of the tympanum is itself filled with 
air, and, like them, it also communicates with the exte- 
rior by a side opening. This is very essential; for, in 
order that a membrane may vibrate freely, the pressure 
of the air must be equal on both sides. Now the press- 
ure of the external atmosphere, as we know from the THE SPECIAL SENSES. 
337 
Fig. 64. 
Human Auditory Apparatus; showing the external ear, the auditory meatus, 
the tympanum, Eustachian tube, chain of bones, and labyrinth. 
changes of the barometer, varies from time to time ; and 
accordingly it would be sometimes greater and some- 
times less than that of the same air confined in a closed 
cavity. The vibrating power of the membrane would 
therefore be diminished, and it would be less capable 
of producing and conducting sound. For this reason a 
small opening is always made in the side of a drum, 
and through this opening the air inside and that out- 
side are constantly mingled, and maintained at the 
same degree of pressure. 
There is such an opening in the drum of the ear. 
From the fore part of the tympanum a narrow canal 
passes downward and forward, and, after continuing its 
course in this direction for about an inch and a half, it 
opens by a rounded orifice at the side and upper part 
of the pharynx. This canal is called the Eustachian 
tube, from the name of the anatomist who first described it. By holding the mouth and nose, and forcibly press- 
ing the air out of the lungs, we can feel it passing 
through the Eustachian tube, and finally penetrating 
into the cavity of the tympanum, which becomes dis- 
tended under the increased pressure. The tympanum, 
however, soon relieves itself after the pressure is taken 
off, the air escaping again through the same passage by 
which it entered. 
If the Eustachian tube be obstructed by inflamma- 
tion or swelling of its lining membrane, the hearing 
soon becomes impaired, from the imperfect vibration of 
the membrane of the tympanum. It is on this account 
that a common cold in the head is often accompanied 
by partial deafness. 
199. Variations in Tension of the Membrane of the Tym- 
panum.—Like the head of a drum, the membrane of the 
tympanum may be relaxed or tightened. This is done 
by the action of three small muscles which arise from 
the bony parts in the neighborhood, and are inserted 
into the little bones called the “ mallet” and the “ stir- 
rup.” By their alternate contraction and relaxation 
they draw these bones backward and forward, and so 
increase or diminish the tension of the membrane. 
200. External Ear and Auditory Meatus.—The mem- 
brane of the tympanum, as we have already seen, is in 
contact with the external atmosphere; but it is situated 
at the bottom of a deep passage or canal, about one inch 
in length, which penetrates the side of the head from 
without inward. This canal is the External auditory 
meatus. It is lined with a continuation of the skin, 
which is, however, very thin and delicate near its bot- 
tom. It is defended from the intrusion of insects and 
other foreign bodies by numerous fine hairs growing 
PHYSIOLOGY AND HYGIENE. THE SPECIAL SENSES. 
339 
from its surface, and by an adhesive and resinous-like 
secretion, termed the “ ear-wax.” 
At the outer orifice of the auditory meatus is the 
External ear (Fig. 65). This is an irregular trumpet- 
Fig. G5. 
External Ear.—1. Helix; 2. Anti-helix; 3. Tragus; 4. Anti-tragus; 5. Concha. 
The mouth of the auditory meatus is partially visible just behind the tra- 
gus. 
shaped expansion of cartilage, covered with skin, and 
folded in various ways so as to make a receptacle for 
the sounds approaching the ear, which it conducts to- 
ward the opening of the auditory meatus. Its outer 
edge is folded inward round nearly the whole of its 
circumference, thus forming a curved border, which is 
called the “helix.” Inside and in front of this is. an- 
other curved ridge, double at its upper end, but termi- 
nating in a single extremity below, called the “anti- 
helix.” About the middle of the front of the ear is a 
short ridge-like elevation, called the “ tragus,” and be- 
hind and below it another, somewhat similar, the “ anti- 340 
tragus.” In front of the curved edge of the anti-helix, 
and occupying the middle portion of the ear, is a deep, 
cup-shaped cavity, termed the “ concha.” At its bot- 
tom is the mouth of the auditory meatus, nearly con- 
cealed behind the eminence of the tragus. 
The external ear, which is loosely connected with the 
bones, has several muscles attached to it, so arranged 
as to move it upward, forward, and backward. In the 
human species these muscles are nearly inactive, and it 
is only very seldom that we meet with persons who are 
capable of moving the ears. But in many of the lower 
animals, such as the dog, horse, deer, rabbit, etc., the 
muscles of the ear are very active, and its movements 
consequently are rapid and various. The external or- 
gan is also larger and more spreading in these animals, 
forming a kind of natural ear-trumpet, which they turn 
in various directions, to catch the faintest indications 
of sound from a distance. 
201. Appreciation of the Direction of Sounds.—It is not 
so easy to distinguish the direction of sound as that of 
light. Indeed, whenever we see the light at all, we 
necessarily see the direction from which it comes. But 
it is not so with sounds. We may hear a sound per- 
fectly well, and yet be quite unable to tell from what 
point it reaches us; as when we hear the chirping of a 
cricket in a closed room, or the sound of a bell in a 
thick fog. Usually, however, we can judge of the di- 
rection of sounds, by noticing in which ear it is most 
acutely perceived, and in what way it is reflected by 
surrounding objects. 
202. Effect of Contrast in Sounds.—The hearing, like 
the sight, is more excited by the Contrast of impres- 
sions than by the impressions themselves. A continu- 
PHYSIOLOGY AND HYGIENE. THE SPECIAL SENSES. 
341 
ous and uniform sound, like the steady rumbling of car- 
riages, or the monotonous hissing of boiling water, 
after a time passes unobserved; but when the sound 
ceases, our attention is excited, and we then notice the 
silence which follows. 
203. Persistence of Sonorous Impressions — Musical 
Notes.—As in the case of the sight, also, an impression 
upon the ear remains for a very short time after it is 
produced. This interval has even been measured for 
the sense of hearing; for it is known that if the same 
vibration be repeated more rapidly than sixteen times 
in a second, it ceases to be a succession of distinct im- 
pulses, and becomes a continuous humming sound, or a 
musical note. If it be still more rapidly repeated, the 
note is higher in pitch, and so on. Thus a low note is 
one in which the vibrations are comparatively slow; a 
high note is one in which the vibrations are rapid. 
Accordingly, there are limits in each direction to the 
pitch of the high or low notes which are audible to us. 
If the vibrations be excessively rapid, the tympanum 
can not transmit them, and the sound becomes too fine 
to be perceived; if they be slower than sixteen times 
in a second, we then hear the distinct impulses, but no 
continuous musical note. 
By the sense of hearing, therefore, we ajspreciate the 
tone, the force, the pitch, and the direction of sonorous 
vibrations. By means of the articulate words and ex- 
pressions of human language, we also acquire ideas and 
information which are but little inferior in value to 
those obtained through the sense of sight. 
204. The Sense of Smell—Olfactory Nerves.—By the 
sense of smell we receive impressions from substances 
in a condition of gas or vapor. These vapors rise 342 
PHYSIOLOGY AND HYGIENE. 
from the bodies which produce them, and are diffused 
through the atmosphere. They then penetrate into 
the passages of the nostrils, and come in contact with 
their lining membrane, thus giving us the sensation of 
smells or Odors. 
The special nerves of the sense of smell are the Olfac* 
tory nerves. They originate on each side from the front 
part of the base of the brain, and then, running straight 
forward, enlarge into two oval masses, containing gray 
matter, and situated nearly side by side, just behind 
the middle of the base of the forehead, and immediately 
above the cavities of the nose. That part of the floor 
of the skull upon which these oval masses rest is in the 
form of a thin plate, and is so perforated with a multi- 
tude of little openings that it has received the name of 
the “ cribriform” or “ sieve-like” plate. Through these 
openings an abundance of fine nervous branches pass 
downward, and, after dividing and reuniting with each 
other in various directions, are distributed to the lining 
membrane of the upper part of the nasal passages (Fig. 
66). 
205. The Nasal Passages.—The nasal passages are two 
high and narrow canals, which extend from the open- 
ings of the nostrils in front to the top of the pharynx 
behind. Through them the air passes to the lungs in 
respiration when the mouth is closed. They are sepa- 
rated from each other by a thin upright partition, which 
is situated exactly in the middle line. This partition 
is composed partly of bone and partly of cartilage. Its 
front part, which is of cartilage, may be felt between 
the two nostrils at their entrance. 
The inner wall of each nasal passage, which is formed 
by the partition just described, is smooth and upright. THE SPECIAL SENSES. 
343 
Fig. 66. 
Distribution of Nerves in the Nasal Passages.—1. Olfactory nerve; 2.Nasal 
branch of fifth pair; 3. Ganglion of Meckel and its nerves. 
But its outer wall is made very uneven by three curi- 
ously rolled or twisted plates of bone, called, from their 
form, the Turbinated Bones, which project from it into 
the passage. These bones are placed one above an- 
other like so many shelves, and are therefore called 
the “ lower,” “ middle,” and “ upper” turbinated bones. 
They are all covered with the lining membrane of the 
nose, which follows every where their windings and in- 
equalities, so that its surface is considerably increased 
in extent. 
f 206. Different kinds of Sensibility in the Nasal Pas- 
sages.—Now the ramifications of the olfactory nerve 
are distributed to the lining membrane of the upper 
and middle turbinated bones. It is here, accordingly, 
that the sense of smell is located. Whenever an odor- 
iferous vapor passes through the nose with the atmos- 
phere, a portion of it rises to the upper part of the 
nasal passages, and, coming in contact with this por- 344 
PHYSIOLOGY AND HYGIENE. 
tion of the lining membrane, gives us the sensation of 
its peculiar odor. 
The lower part of the nasal passages, on the contra- 
ry, have no sense of smell, but are supplied with other 
nervous fibres. A small branch of the fifth pair of 
nerves (Fig. 66 [2]) penetrates the side of the nostril 
high up, and then, running in a curved direction for- 
ward, downward, and backward, is distributed to the 
lining membrane of the lower turbinated bone and the 
adjacent parts. By this nerve the lower portions of 
the lining membrane are provided with ordinary sen- 
sibility. They can feel the contact of solid bodies, or 
of sharp and irritating vapors. 
Thus the passages of the nose are endowed, in their 
different parts, wdth two different kinds of sensibility. 
In their upper portions, by means of the olfactory 
nerves, they are provided with the special sensibility 
of smell, by which we perceive sweet and sour odors, 
and all the different varieties of perfume, which are so 
easily recognized, but which have received no definite 
name. In their lower portions, by means of the nasal 
branch of the fifth pair, they possess the power of ordi- 
nary sensibility, by which we perceive the contact of 
sharp and pungent vapors, such as that of hartshorn or 
mustard. These pungent vapors are quite different in 
their nature from those which have an odoriferous 
quality. For the tx*ue odors, such as those of different 
flowers and the like, can only be perceived by the nose. 
But the pungent vapors are also irritating to other lin- 
ing membranes, such as those of the eyes and mouth, 
and even to the skin, if kept in contact with it long 
enough; only the lining membrane of the nose is more 
sensitive to them than the rest. THE SPECIAL SENSES. 
345 
Very often a real odor and a pungent vapor are ex- 
haled together from the same substance; as, for exam- 
ple, from mustard, from vinegar, or from Cologne water. 
But, in these cases, the odoriferous quality is always 
perceived by the upper part of the nasal passages, and 
the pungent or irritating quality by their lower part. 
207. Sympathetic Nerves in the Nasal Passages.—The 
organ of smell is also supplied with nerves belonging 
to the sympathetic system. Immediately behind the 
posterior boundary of the nasal passages, and beneath 
the floor of the skull, is a small swelling of gray nerv- 
ous matter, called, from the name of its discoverer, the 
Ganglion of Mechel (Fig. 66 [3]). This ganglion is 
connected by slender filaments with the sympathetic 
plexus of the great blood-vessels of the head, and also 
with branches of the sensitive and motor cranial nerves. 
Its fibres are sent to the lining membrane of the nose, 
and also to the small muscles which lift the hanging 
palate, and thus guard the posterior opening of the na- 
sal passages. 
208. Usefulness of the Sense of Smell.—The sense of 
smell is one of those which are possessed in much great- 
er perfection by some of the lower animals than by 
man. In the dog, the horse, the sheep, the deer, and 
many others, the nasal passages are much higher and 
deeper, the turbinated bones more extensively convo- 
luted, and the olfactory nerves themselves much larger 
and more sensitive. These animals can therefore dis- 
tinguish odors which are entirely imperceptible to us. 
They can perceive the odors of other animals while at 
a distance and out of sight. The dog can even distin- 
guish between the odors of different persons, and will 
follow the track of his master through a crowd of other 346 
PHYSIOLOGY AND HYGIENE. 
passers-by. Some animals, when irritated, give out 
strong and offensive odors, which excite the fear or dis- 
gust of their enemies, and accordingly serve them as 
means of defense. Many vapors which are dangerous 
to the health of the human species, and most kinds of 
putrescent and unwholesome food, are also accompanied 
by a disagreeable odor, which leads us to avoid them, 
and thus to escape their injurious effects. 
209. The Sense of Taste—Gustatory Nerve.—The sen- 
sibility to taste is located in the tongue. As we have 
already said, this is a muscular organ, covered, upon its 
upper surface, its edges, and part of its under surface, 
with a lining membrane. Over the whole middle and 
front part of the tongue this membrane is supplied with 
sensibility by a branch of the fifth pair of nerves; and, 
as this branch is that by which the corresponding por- 
tions of the tongue exercise the sense of taste, it has re- 
ceived the name of the Gustatory nerve. 
210. Distribution of the Gustatory Nerve upon the 
Tongue.—On the under surface of the tongue its lining 
membrane is thin and smooth, and allows the blood- 
vessels to be easily seen through its transparent sub- 
stance. But upon the upper surface of the organ this 
membrane is thickly set with a multitude of fine, thread- 
like prominences, something like the villi of the aliment- 
ary canal, which give it an opaque and velvety appear- 
ance. These prominences are termed the Papillce of 
the tongue. As the gustatory nerve branches and sub- 
divides in the substance of the lining membrane, it 
sends minute ramifications into the papillae, which pen- 
etrate them from below upward, and terminate near 
their free extremities (Fig. 67). Thus the upper sur- 
face of the tongue is covered with a minute distribu- THE SPECIAL SENSES. 
347 
Fig. 67. 
Diagram of Tongue, with its sensitive nerves and papillse.—1. Lingual branch 
of fifth pair, or gustatory nerve; 2. Glosso-pharyngeal nerve. 
tion of nervous filaments, through which it receives the 
impressions of taste. 
211. Requisite Conditions for the Sense of Taste—The 
sense of taste differs from the other special senses, in 
the first place, because it requires the actual contact of 
the substance to be tasted with the lining membrane 
of the organ. We can not perceive tastes as we can 
odors and sounds from a distance. The substance must 
be introduced into the mouth, and placed upon the sur- 
face of the tongue, before we can distinguish its flavor. 
Beside this, it must also be in the fluid form, or be al- 
ready in solution in some other liquid. A substance 
which is hard and insoluble has no taste. If we place 
upon the tongue a piece of dry salt or sugar, we do not 
perceive its flavor until a part of it has been dissolved 
in the fluids of the mouth. Then these fluids are ab- 
sorbed by the papillse of the tongue, and thus, coming 
in contact with their nervous filaments, communicate 
to us the sensation of taste. 
It is on this account that the sense of taste is so much 
facilitated by the movements of the tongue in mastica- 
tion and swallowing. For these movements, by hasten- 348 
PHYSIOLOGY AND HYGIENE. 
ing the solution of solid substances, and by constantly 
bringing fresh portions of the fluid into contact with 
the tongue, favor the absorption of the liquids, and en- 
able them to penetrate the papillae in greater quantity. 
Food, therefore, which has been hastily masticated, is 
imperfectly tasted; and in this way injurious sub- 
stances may pass into the stomach unnoticed, which 
should have been detected and stopped in mastication, 
212. Uses of the Sense of Taste.—The sense of taste, 
accordingly, as well as that of smell, is a means of dis- 
tinguishing between proper and unwholesome articles 
of food. Some substances, when taken into the mouth, 
are found to be repulsive, and are therefore rejected. 
In many of the lower animals, however, this office is 
performed exclusively by the sense of smell. The dog, 
for example, very seldom tastes any thing before eating 
it. He touches it with the point of his nose, and then 
either swallows it with avidity or refuses it altogether. 
It is because in him the sense of smell is more delicate 
than that of taste, while in man the sense of taste is 
more delicate than that of smell. 
The sense of taste is also useful in exciting the flow 
of the saliva and other secretions, by which the food is 
prepared for the digestive process. Substances which 
are destitute of flavor offer no stimulus to the salivary 
glands or to the muscles of mastication, and this process 
is therefore either neglected or slowly and laboriously 
performed. But substances which have a healthy and 
agreeable taste excite the natural actions of secretion 
and mastication, so that the movements go on almost 
involuntarily, and the food receives its due preparation 
in the mouth. 
213. The Sense of Taste associated with the Sense of THE SPECIAL SENSES. 
349 
Touch.—Another peculiarity of this sense is that the 
special nerve of taste is also a nerve of ordinary sensi- 
bility. We have already seen that the same parts of 
the tongue which possess the sense of taste have also 
the sense of touch developed to a remarkable degree; 
and these two properties are both supplied by the 
branch of the fifth pair which is distributed to this 
organ. In the nasal passages, the special sense of smell 
and the power of ordinary sensibility reside in different 
portions of the lining membrane; but in the tongue, 
the special sense of taste and ordinary sensibility are 
exercised by the same parts, and reside in the filaments 
of the same nerve. 
Accordingly, two kinds of qualities are distinguished 
by this organ in different substances. The first are the 
qualities of taste proper, which we call “ sweet,” “ sour,” 
“ salt,” “ bitter,” and the like; these are perceived by 
the special sensibility of the gustatory nerve, and belong 
only to the tongue. The second are the qualities which 
depend upon the consistency, mildness, ox pungency of 
the substance, such as a “watery,” “viscid,” “oily,” 
“ sharp,” or “ burning” taste. These are perceived by 
the ordinary sensibility of the tongue, and may also be 
distinguished, though in a less degree, by the surface 
of the skin or by the other lining membranes. 
There are certain substances which have at the same 
time a well-marked and usually agreeable taste and a 
penetrating, fragrant odor; such as coffee, peppermint, 
ginger, and the spices generally. These are called Aro- 
matic substances. Many of them have also more or less 
pungency mingled with their other qualities. They are 
employed either alone or for the purpose of flavoring 
other articles of food. 350 
PHYSIOLOGY AND HYGIENE. 
214. Posterior Portion of the Tongue.—That part of 
the tongue which is situated far hack in the mouth is 
smoother than the rest, and is provided with mucous 
follicles instead of papillae. This portion of the organ 
is also supplied with a different nerve, which, from its 
being distributed partly to the tongue and partly to the 
pharynx, is called the Glosso-pharyngeal nerve (Fig. 67 
[2]). This nerve also possesses the sensibility of taste, 
which is developed to a perceptible degree, especially 
for aromatic substances, in the back part of the tongue 
and the surrounding portions of the throat. The sen- 
sations of taste, however, are not especially excited in 
these situations until just at the moment of swallowing. 
At that time the food, carried back by the tongue, comes 
in contact with the lining membrane of these parts, and, 
being also compressed by the action of the muscles, 
calls into activity the sensibility of the glosso-pharyn- 
geal nerve. Once past this situation, however, it is be- 
yond the region of the special sense, and in the (Esopha- 
gus and the stomach its taste is no longer perceived. 
QUESTIONS FOR CHAPTER XVII. 
1. What are meant by the special senses ? 
2. What is the peculiarity of a nerve of special sense ? 
3. What is the structure of an organ of special sense ? 
4. What is the special nerve of the sense of sight? 
5. From what ganglia do the optic nerves originate ? 
6. What is the course and termination of the optic nerves ? 
7. What is the decussation of the optic nerves? 
8. How are the two optic tubercles connected with each other ? 
9. How are the two eyeballs connected with each other ? 
10. Are the eyes to be regarded as two distinct organs or as one 
double organ ? 
11. How do the optic nerves terminate in the interior of the eye- 
balls ? QUESTIONS. 
351 
12. What is the property or function of the optic nerves ? 
13. What is the effect of injury or division of the optic nerves ? 
14. What reflex action takes place through the optic tubercles? 
15. What do you mean by the sensibility of the pupil? 
16. Is this sensibility necessarily accompanied by consciousness ? 
17. What is the special organ of sight ? 
18. In what cavity is the eyeball situated ? 
19. What is the form of the eyeball ? 
20. What is the sclerotic coat of the eyeball ? What is its struct- 
ure and consistency ? 
21. What is the cornea, and where is it situated ? 
22. How does the cornea differ from the sclerotic ? 
23. Through what part does the light enter the cavity of the eye- 
ball? 
24. What is the choroid coat of the eye ? What is its color and con- 
sistency ? 
25. What is the use of the choroid coat ? 
26. What is the situation and structure of the retina ? 
27. What is the function of the retina ? 
28. Does the retina possess ordinary sensibility ? 
29. To what kind of impressions is it sensitive ? 
30. What is the effect of injury or disease of the retina ? 
31. What is the vitreous body of the eye, and why so called ? 
32. What is its use ? * 
33. What is the situation and form of the crystalline lens ? 
34. How is the lens held in its place ? 
35. What is the use of the crystalline lens ? 
36. What is the focus of a lens ? 
37. Where is the focus of the crystalline lens in the eye ? 
38. What is the iris ? and why so called ? 
39. What is the pupil? 
40. Of what tissue is the iris composed ? 
41. What two sets of muscular fibres does it contain ? 
42. What is the action of the diverging fibres ? 
43. What is the action of the circular fibres ? 
44. What ai-e the movements of the pupil on passing from the dark 
into the light ? from the light into the dark ? 
45. What ganglion and nerves of the sympathetic system take part 
in the reflex movements of the pupil ? 
46. What is the situation of the ophthalmic ganglion ? 352 
PHYSIOLOGY AND HYGIENE. 
47. What is the course and termination of the ciliary nerves ? 
48. Wbat is the aqueous humor of the eye ? 
49. What is the field, of vision ? 
50. In what part of the field of vision can objects be seen distinctly ? 
51. What is the line of distinct vision ? 
52. Why are objects outside this line seen indistinctly ? 
53. How do we compensate for this in using the eyes ? 
54. Why can an object be seen distinctly with both eyes only at a 
certain distance ? 
55. Why do objects appear single, though seen with two eyes ? 
56. How can we see an object indistinctly, and, at the same time, 
double ? 
57. Can we see all parts of a landscape distinctly at the same time, 
and why ? 
58. How do we judge of the distance of various objects ? 
59. How is the appearance of solidity or projection produced in vis- 
ion with two eyes ? 
60. Can a single flat picture ever represent a solid object so as to 
deceive the eye, and why ? 
61. What is a stereoscope, and how does it produce the appearance 
of solidity ? 
62. What is the effect of contrast on visual impressions ? 
63. What colors make the strongest contrast ? 
64. How can one color appear different by contrast with another ? 
65. What is the effect of mixing two different colors ? blue and yel- 
low ? yellow and red ? red and blue ? black and white ? 
66. Do the impressions of sight disappear immediately, or remain 
for a short time ? Give an instance. 
67. What is the thaumatrope, and how is its effect produced? 
68. How may the impressions of sight be produced without visible 
objects ? 
69. How are the movements of the eyeball provided for ? 
70. What are the direction and attachments of the straight muscles 
of the eyeball ? What is their action ? 
71. What are the direction and attachments of the upper oblique 
muscle of the eyeball? 
72. Why is it called the trochlearis muscle ? 
73. What are the direction and attachments of the lower obliqu*. 
muscle of the eyeball? 
74. What is the action of the two oblique muscles of the eyeball ? QUESTIONS. 
353 
75. What are the two uses of the movements of the eyeball ? 
76. How is the eyeball protected from external injury? 
77. What is the structure of the eyelids ? 
78. Which is the larger and more movable of the two ? 
79. How is it raised and lowered in front of the eye ? 
80. What is the conjunctiva ? 
81. How is the conjunctiva kept moist and transparent ? 
82. In what gland are the tears produced, and where is it situ- 
ated ? 
83. Where do the ducts of the lachrymal gland open upon the con- 
junctiva ? 
84. How are the tears spread over the surface of the conjunctiva ? 
85. By what muscle is the act of winking performed? 
86. What is the use of the act of winking, and how would the eye 
suffer if it were not performed ? 
87. Is the act of winking voluntary or involuntary ? 
88. Why does it usually pass unnoticed ? 
89. How are the tears prevented from running over the edges of 
the eyelids ? 
90. By what glands is the sebaceous secretion of the eyelids pro- 
duced ? 
91. How is the act of weeping produced ? 
92. How are the tears conveyed away from the surface of the eye- 
ball, and where are they finally discharged ? 
93. What are the eyelashes, and what is their use ? 
94. Is the conjunctiva sensitive or insensible ? 
95. How does its sensibility serve to protect the eye from injury ? 
96. How may the sight be injured by excessive use? by too bril- 
liant light ? by continued examination of small objects ? 
97. By reading with insufficient light ? 
98. What is the best kind of light for reading or studying ? 
99. What is the worst ? 
100. How is sound produced ? 
101. How is the vibration of the atmosphere necessary to our hear- 
ing sounds ? 
102. What is the definition of the sense of hearing ? 
103. What is the special nerve of the sense of hearing? 
104. What is the origin and course of the auditory nerve ? 
105. What is the situation of the petrous bone, and why so called ? 
106. What is the labyrinth, and why so called ? 354 
PHYSIOLOGY AND HYGIENE. 
107. What is the shape and name of the first portion of the laby- 
rinth ? 
108. What are the semicircular canals, and how do they differ from 
each other in their position ? 
109. What is contained in the cavities of the vestibule and the semi- 
circular canals ? 
110. Upon what are the fibres of the auditory nerve distributed in 
the vestibule and semicircular canals ? 
111. What is the name of the remaining portion of the labyrinth, 
and why so called ? 
112. Upon what are the fibres of the auditory nerve distributed in 
the cochlea ? 
113. What parts are included in the internal ear? 
114. What kind of sensibility resides in the auditory nerve ? 
115. What is the opening called the ovalfenestra, and where is it 
situated ? 
116. By what is the oval fenestra closed? 
117. What is the use of the oval fenestra? 
118. Where is the cavity of the tympanum or drum of the ear? 
119. What is the membrane of the tympanum? 
120. How are sounds transmitted from the tympanum to the oval 
fenestra ? 
121. What are the three bones of the chain, and why so called? 
122. Which of them is attached to the membrane of the tympanum, 
and which to the membrane of the oval fenestra ? 
123. What is contained in the cavity of the tympanum beside the 
chain of bones ? 
124. Why must a drum always communicate with the external at- 
mosphere ? 
125. By what opening does the tympanum of the ear communicate 
with the exterior, and where is it situated ? 
126. What effect is produced by obstruction of the Eustachian tube? 
127. How is the membrane of the tympanum relaxed and tight- 
ened? 
128. What is the external auditory meatus? 
129. How is it defended from the entrance of foreign bodies? 
130. What is the general form and structure of the external ear? 
131. What is its function ? 
132. What is the helix? the anti-helix? the tragus? the anti-tra- 
gus? the concha? QUESTIONS. 
355 
133. In which of the lower animals are the external ears movable ? 
134. What is the use of these movements ? 
135. How do we judge of the direction of sounds ? 
136. How is the sense of hearing affectgd by contrast of sounds ? 
137. What is the effect of the same sound long continued ? 
138. Are the impressions of sound immediately evanescent, or do 
they remain for a certain period ? 
139. How is a musical note produced ? 
140. What must be the frequency of the vibrations in order to pro- 
duce a continuous note ? 
141. What is the difference in the rapidity of the vibrations be- 
tween a high and a low note ? 
142. What do we learn by the sense of hearing ? 
143. What kind of impressions are perceived by the sense of smell? 
144. What are the special nerves of the sense of smell ? 
145. What is the origin, course, and distribution of the olfactory 
nerves ? 
146. What is the form and direction of the nasal passages ? 
147. With what do they communicate behind ? 
148. How are they separated from each other ? 
149. What are the turbinated bones, and why so called ? 
150. How many turbinated bones are there in each nasal passage, 
and how are they distinguished from each other ? 
151. With what are the turbinated bones covered ? 
152. Upon what part are the olfactory nerves distributed ? 
153. In what part of the nasal passages does the sense of smell re- 
side, and in what part the sense of touch ? 
154. What sensitive nerve is distributed to the lower part of the 
nasal passages ? 
155. What is the difference between odors and pungent vapors ? 
156. Name examples of each. 
157. What ganglion of the sympathetic system is connected with 
the organ cf smell ? 
158. Where is the ganglion of Meckel situated ? With what other 
nerves is it connected, and where are its nerves distributed ? 
159. In what animals is the sense of smell more acute than in man, 
and why ? 
160. How does the sense of smell serve as a protection—in ani- 
mals ? in man ? 
161. What is the organ of taste? 356 
PHYSIOLOGY AND HYGIENE. 
162. What is the principal nerve of the sense of taste? 
163. To what part of the tongue is the gustatory nerve distributed? 
164. What are the papillae of the tongue, and where situated ? 
165. What are contained in the papillae of the tongue ? 
166. What two conditions are essential to the sense of taste ? 
167. How do the movements of the tongue assist in the sense of 
taste? 
168. What is the use of the sense of taste ? 
169. What is the comparative delicacy of taste and smell—in the 
lower animals ? in man ? 
170. How does the sense of taste assist mastication and digestion? 
171. What other sensibility resides in the tongue beside that of 
taste ? 
172. What is the difference between the qualities of taste, and those 
of pungency and the like ? Give examples of both. 
173. What is an aromatic substance ? Give examples. 
174. How does the back part of the tongue differ from the front 
part? 
175. By what nerve is it supplied ? 
176. What kind of sensibility is especially developed in the back 
part of the tongue ? 
177. At what point does the sense of taste terminate? Section IV. 
DEVELOPMENT. CHAPTER XVIH. 
DEVELOPMENT. 
Definition of Development.—Newly-born Infant—its Weight—con- 
dition of its Skeleton.—Ossification of the Skeleton.—Spinal Col- 
umn.— Skull.—Fontanelles.—Pelvis.—Long Bones.—Respiration 
of the Infant — its Digestion and Nutrition — its Nervous Sys- 
tem. — Reflex Actions. — Formation of the Teeth. — First Set. — 
Childhood.—Muscular System of the Child.—Nervous and Mental 
Functions.—Preponderance of the Instincts.—Formation of new 
Set of Teeth.—Youth.—Continued Ossification of the Skeleton.— 
Union of the Bones.—Completion of Development. 
215. The Process of Development.—The newly-born 
infant is in a very different condition from that of a 
child or a grown-up person. It is feeble, and entirely 
dependent on the care of others for its existence almost 
from day to day. Many of its organs are very imper- 
fect, and the form and proportions of its whole body are 
different from those which it will afterward acquire. 
The growth of the infant into the child, and of the child 
into the adult, is not therefore simply an increase in 
size. It is a series of changes in the condition and struc- 
ture of its various parts, by which it passes through as 
many different stages or epochs of existence. This se- 
ries changes, by which the bodily frame is brought 
at last to the adult condition, is called its Development. 
216. General Condition of the Infant at Birth.—The 
weight of the newly-born infant is between six and 
seven pounds. The head and arms are larger, and the 
pelvis and lower extremities smaller, in proportion to 360 
PHYSIOLOGY AND HYGIENE. 
each other, than in the adult. The legs are curved in- 
ward at their lower part, so that the soles of the feet 
are not horizontal, but look obliquely inward toward 
each other. Even if the infant were strong enough, 
therefore, it could not walk, since the feet would not 
rest upon the ground by their soles, but by their outer 
edges. Both arms and legs, also, are habitually curled 
upward and forward over the chest and abdomen, and 
are not easily straightened. 
217. Condition of the Skeleton.—The skeleton at birth 
is soft and yielding, being composed, to a great extent, 
of cartilage. Some of the bones have already begun to 
show themselves in the interior of these cartilages ; but 
they are nearly all small and delicate, and many of them 
are still cartilaginous throughout. The bony parts, 
however, continue to enlarge at the expense of the car- 
tilage, until, at the end of some years after birth, the 
whole has been converted into the tissue of bone. This 
gradual change of the parts from the cartilaginous to 
the bony condition is called the Ossification of the skel- 
eton. 
218. The Spinal Column. — At birth each bone of the 
spinal column consists of three separate pieces, viz., one 
in front of the spinal cord, and one on each side behind 
it. These pieces are, of course, connected with each 
other by cartilage, and thus envelop the spinal cord 
with a series of soft and elastic rings. 
219. The Skull.—The bones of the skull are 
and flexible, and their edges are not yet united with 
each other. The skull of the infant, therefore, is not a 
firm and solid case, like that of the adult, but rather an 
elastic bag, formed of separate plates, held together by 
the skin and fibrous membranes. A remarkable pecul- DEVELOPMENT. 
361 
iarity of the skull at this time is that there are two open- 
ings in its bony parts, one at the back and one on the 
top of the head, where the brain is only covered by the 
skin and other soft tissues. These openings are called 
the Fontanelles, because we can feel the pulsations of 
the brain through them, like the bubbling of water in a 
fountain. 
220. Formation of the Fontanelles. — The fontanelles 
are formed in this manner. The ossification of the bones 
on the sides and upper part of the skull begins by a 
rounded spot in the middle of each one. From this 
spot the ossification extends outward in every direc- 
tion, thus gradually approaching the edges of the bone. 
When two adjacent bones meet, therefore, there will be 
a line where their edges are in contact with each other, 
but have not yet united; but when more than two 
bones meet in this way, there will be an empty space 
between them at their point of junction. Thus, ifiyou 
lay down three coins upon the table with their edges 
touching each other, there will be a three-sided space 
in the middle between them ; if you lay down four coins 
in the same manner, the space between them will be 
four-sided. Now at the back part of the head there is 
a spot where three bones come together in this way, 
leaving a small three-sided opening between them: this 
is called the “ posterior fontanelle.” On the top of the 
head four bones come together, leaving between them 
a large four-sided opening: this is called the “ superior 
fontanelle.” The fontanelles gradually diminish in size, 
owing to the growth of the bony parts around them, 
and are completely closed at the age of four years after 
birth. 
221. The Pelvis and Limbs.—The pelvis is also, at first, 362 
PHYSIOLOGY AND HYGIENE. 
in great measure cartilaginous, being composed, on 
each side, of three separate pieces of bone, with layers 
of cartilage between them. These three bones of the 
pelvis meet, in a kind of triangular union, in the cavity 
of the hip-joint. 
The bones of the arms and legs, at the time of birth, 
are only ossified in their middle portion, their two ends 
being still cartilaginous. The wrist is altogether car- 
tilaginous, and the ankle nearly so. Owing to this pre- 
ponderance of cartilage, the bones are soft and flexible. 
It is evident, accordingly, that the skeleton of the in- 
fant is not yet fit to sustain the weight of the body, nor 
to resist a strong muscular action. 
222. Organs of Respiration.—The function of respira- 
tion is very imperfectly performed for some time after 
birth. The lungs do not fully expand at once, and the 
air only penetrates into all the vesicles of their deeper 
parts after an interval of several days. To compensate 
for this, however, the skin is very delicate, transparent, 
ruddy, and vascular; and respiration, no doubt, takes 
place through it as well as through the lungs. Accord- 
ingly, the infant is more sensitive to cold than an older 
person, and the warmth of the body needs to be more 
carefully preserved by soft clothing and artificial heat. 
223. Organs of Nutrition. — On the other hand, the 
functions of digestion and nutrition are exceedingly ac- 
tive. But the infant takes only one kind of food, viz., 
the milk of the mother; and this fluid, as we have seen 
in a former chapter, contains all the materials necessary 
for the nourishment of its body. This food must be 
given in abundance,but at short intervals; for the stom- 
ach can not digest a large quantity at a time, and there- 
fore requires it to be more frequently supplied. DEVELOPMENT. 
363 
224. Nervous System. — The nervous system of the 
young infant is in a peculiar condition. The special 
senses, the sight, hearing, smell, and taste, are all imper- 
fect, and comparatively inactive. The consciousness 
and the will are also feeble, and the intelligence is still 
dormant. The involuntary and reflex actions, however, 
are highly developed. The movements of the arms and 
legs, and the various intonations of the voice, are near- 
ly all of a reflex nature, mostly performed by the ac- 
tion of the spinal cord and medulla oblongata. A large 
portion of the time is spent in sleep. For it is espe- 
cially during sleep that the functions of nutrition go on 
with the greatest activity and the tissues are consol- 
idated by the assimilation of the food. The business 
of the young infant is to feed and grow, and the ac- 
tion of his nervous system is almost entirely subservient 
to these two functions. He does not understand ar- 
ticulate language, nor notice its sounds sufficiently to 
remember or repeat them; and he is therefore called an 
infant, from the Latin word wfans, which signifies “ not 
speaking.” 
225. Appearance of the Teeth.'—Within the fii’st year 
after birth the Teeth begin to show themselves. For 
the infant, after a time, has acquired so much strength, 
and the different parts of his body are so fully devel- 
oped, that he will soon need food of a more solid form 
and greater variety. He will then require the organs 
of mastication, and these organs, accordingly, begin to 
be developed in advance. The incisor teeth are the 
first to emerge from the gums in the seventh and eighth 
months. At the end of a year there is one molar tooth 
on each side of each jaw, making four in all. At a year 
and a half the four canine teeth appear; and at two 364 
PHYSIOLOGY AND HYGIENE. 
years of age four other molar teeth are added to the 
preceding. There are then twenty teeth in all, or ten 
in each jaw, viz., four incisors, two canines, and four 
molars. They are all small, however, and are adapted 
to the size and form of the jaws at this age. They are 
called the Milk teeth, because they appear while the in- 
fant is still fed principally upon milk. 
226. Transition from Infancy to Childhood.—At the 
age of two years the infant has so far increased in 
muscular strength, and his skeleton has become so firm, 
that he can walk without assistance, and no longer re- 
quires the constant care and attendance of others. His 
teeth and digestive organs enable him to consume a 
variety of solid and nutritious food. His nervous sys- 
tem has also emerged from its condition of lethargy, 
and his senses are actively engrossed with surrounding 
objects. Finally, he has learned to understand and to 
speak articulate language. He is then no longer an in- 
fant, but a child. 
22 V. Growth of the Muscles during Childhood. — The 
term of childhood extends from the age of two years to 
that of thirteen. During this period the muscular sys- 
tem becomes actively developed; and the skeleton, 
though still imperfectly consolidated, is sufficiently 
strong to perform its function with the light weight of 
the body at this age. The child accordingly takes the 
greatest enjoyment in the active sports, in which he 
feels the increasing vigor of his muscles, and the free- 
dom and agility of his limbs. Nothing is more appro- 
priate or more useful at this age; for the frame is now 
being developed, not by passive feeding and care, as was 
the case in the infant, but in great measure by the nat- 
ural and active exercise of its own powers. DEVELOPMENT. 
365 
228. Development of the Senses.—The nervous system 
acquires an equal development, and the mental quali- 
ties at the same time become more active. The child 
learns rapidly, and is interested in every thing around 
him. But it is principally in the cultivation of the 
/Senses that he gains information. He learns the names 
and the forms of things, the meaning of words, and the 
employment of all the objects in common use. This 
knowledge is not acquired by steady mental applica- 
tion, which would be injurious to him at this age, but 
by the exercise of the senses, which are now, for the 
first time, endowed with their full vigor and sensibility. 
229. Activity of the Instincts.—The nervous system 
of the child is also distinguished by the active prepon- 
derance of the Instincts and the Impulses. It is by 
these that his actions are guided; and therefore, though 
his movements and acts are all voluntary in their na- 
ture, they do not, for the most part, depend upon the 
reasoning faculties, which are still imperfectly devel- 
oped. Accordingly, the child is to be governed princi- 
pally through his instincts and feelings, which should 
be guided in a healthy and natural direction. The do- 
minion of reason comes at a later period, when the en- 
tire development of the nervous system is complete. 
230. Change of Dentition.—During the period of child- 
hood a remarkable change takes place in the organs of 
mastication. It consists in the entire removal of the 
first set of teeth, and the appearance of a second or per- 
manent set, which take their places. This change is ef- 
fected in the following manner. 
At the time of birth, although no teeth are to be seen, 
there is still a complete set already existing in the jaw. 
These teeth, however, are not yet ossified, but consist 366 
PHYSIOLOGY AND HYGIENE. 
each of a soft vascular prominence, or papilla, called 
the pulp of the tooth, which is inclosed in a little sac or 
follicle, and buried deeply in the substance of the jaw. 
The upper surface of the pulp is covered with a very 
thin layer or crust of calcareous tissue, which is the com- 
mencement of the hard substance of the future tooth. 
As the pulp of each tooth increases in size, more and 
more of it becomes ossified, until at last it is ready to 
emerge from the gum. The teeth then make their ap- 
pearance in the order which we have described above, 
thus completing the first set at the end of two years. 
But, at the same time, there is another set of similar 
follicles and tooth-pulps, formed deep in the substance 
of the jaw, behind those of the first set. These tooth- 
pulps, however, are very small, and remain dormant, or 
grow very slowly during the first years of childhood. 
But about the sixth year they begin to grow more rap- 
idly. Their ossification also goes on with a correspond- 
ing activity, and they then begin to push their way to- 
ward the surface of the gum. They thus press upon 
the others, which yield before them, grow loose, and 
are finally detached. The first set are thus thrown 
off from their attachments to the jaw, and disappear. 
This process is called the Shedding of the milk teeth. 
As the milk teeth are thus removed, they are replaced 
by the new teeth of the second set, which soon after- 
ward emerge behind them. The teeth of the second 
set, however, are different from those of the first. They 
are harder in texture, and some of them are of larger 
size. They are also more numerous; for, instead of 
the twenty teeth which composed the first set, there 
are now thirty-two. This is because there are at this 
time three new permanent molars added on each side DEVELOPMENT. 
367 
of each jaw. The jaw itself also increases in size, to 
accommodate the larger number of teeth which it con- 
tains. 
The shedding of the milk teeth begins about the age 
of seven years. During the seventh and eighth years 
the incisor teeth are changed, and replaced by those of 
the permanent set. In the ninth and tenth years the 
two molar milk teeth are thrown off, and replaced in a 
similar way by the twro anterior permanent molars; and 
in the twelfth year the canine teeth are changed. The 
first of the three posterior molar teeth has already made 
its appearance; and in the thirteenth year the second 
emerges from the jaw. There remains only one, viz., 
the third posterior molar, or the last tooth in the back 
part of the jaw on each side. These teeth only appear 
from the seventeenth to the twenty-first year, and are 
therefore known by the name of the “ wisdom teeth.” 
They complete the development of the masticatory ap- 
paratus. 
With the exception, therefore, of the third posterior 
molar or “ wisdom” tooth, the entire change from the 
first to the permanent set is accomplished during the 
period of childhood. 
231. Transition from Childhood to Youth.—To the pe- 
riod of childhood succeeds that of Youth. During this 
epoch the consolidation of the skeleton goes on, and is 
particularly distinguished by the union of the different 
parts of the bones with each other. Thus the three 
bones of the pelvis on each side become united into one 
from the thirteenth to the fifteenth year; and the con- 
solidation of the ends of the long bones of the arms and 
legs with their middle portions is effected generally 
from the fifteenth to the twentieth year. At the same 368 
PHYSIOLOGY AND HYGIENE. 
time, these bones assume the form and dimensions which 
are characteristic of the adult, and the posture and 
movements acquire more firmness and solidity. The 
general development of the skeleton and limbs may be 
said to be terminated at the age of twenty years. 
232. Completion of the Process of Development.—Dur- 
ing the period of youth the nervous system becomes 
fully developed, and the mental powers are exercised 
with greater freedom than before. The youth begins 
to prepare for the active occupations of life by regular 
and continuous study; and the commencing supremacy 
of the reasoning faculties enables him to understand, 
not only the sensible qualities of surrounding objects, 
but their relations to each other, and the manner in 
which he may employ them for useful purposes. The 
body also acquires at this time a different appearance, 
and the proportions of its various parts are altered. 
The limbs are stronger, and the joints comparatively 
smaller than in the child; and many of the internal or- 
gans become altered in their size and weight, as com- 
pared with that of the whole body. Thus both the 
anatomical structure and the physiological actions of 
the bodily frame, having passed successively through 
their different stages of preparation and growth, arrive 
at last at the fully developed and adult condition. 
QUESTIONS FOR CHAPTER XVIII. 
1. What is meant by the development of the body ? 
2. What is the weight of the newly-born infant ? 
3. How do the proportions of its body differ from those of the 
adult? 
4. What is the position and form of the arms and legs ? 
5. What is the condition of the skeleton at birth ? 
6. What is meant by the ossification of the skeleton ? QUESTIONS. 
369 
7. What is the condition of the spinal column at birth ? of the 
skull ? 
8. What are the fontanelles ? and how are they formed ? 
9. What is the shape and situation of the posterior fontanelle ? 
10. What is the shape and situation of the superior fontanelle ? 
11. At what age are the fontanelles completely closed ? 
12. Of how many separate pieces is the pelvis composed at the time 
of birth ? 
13. What is the condition of the hones of the arms and legs ? of 
the wrist ? of the ankle ? 
14. Why is the skeleton of the infant unfit to sustain the weight of 
the body ? 
15. What is the state of respiration at birth ? 
16. How long does it require for the lungs to be completely filled 
with ah- ? 
17. How is this deficiency compensated for in the young infant? 
18. Why is the infant more sensitive to cold than the adult ? 
19. What is the state of digestion and nutrition in the infant ? 
20. What is the proper food of the infant ? 
21. Why should it be given at short intervals ? 
22. What is the state of the special senses in the infant ? of con- 
sciousness ? of the intelligence ? 
23. What kind of movements are those mostly performed by the in- 
fant? 
24. Why does the infant require a large amount of sleep ? 
25. Why is the newly-born child termed an infant ? 
26. At what time do the teeth begin to appear ? 
27. When do the incisors show themselves? the first molars? the 
canines ? the remaining molars ? 
28. How many teeth, in all, form the first set ? 
29. Why are they called milk teeth ? 
30. What is the difference between an infant and a child ? 
31. What is the extent of the period of childhood? 
32. What changes take place during childhood in the skeleton and 
the muscles ? 
33. Why should the child pass much of his time in active sports ? 
34. What part of the nervous system is most fully developed during 
childhood ? 
35. How does the child learn most easily and profitably ? 
36. What nervous actions are most fully developed in the child ? 370 
PHYSIOLOGY AND HYGIENE. 
37. What change takes place during childhood in the organs of 
mastication ? 
38. What is the condition of the first set of teeth at the time of 
birth ? 
39. What is the pulp of the tooth ? 
40. In what is it contained ? 
41. How is the pulp converted into the hard tooth ? 
42. At what time is the first set of teeth completely formed ? 
43. When and where are the second set of teeth formed ? 
44. How long do they remain dormant ? 
45. When do they begin to grow and become ossified ? 
46. What effect does this have on the teeth of the first set ? 
47. What becomes of the teeth of the first set ? 
48. How do the teeth of the second set differ from those of the first ? 
49. How many teeth are there in the second set ? 
50. What change takes place in the yaw at this time ? and why ? 
51. When does the shedding of the milk teeth begin? 
52. Which are the first teeth to be changed ? 
53. When are the molar teeth changed ? the canine teeth ? 
54. When does the Jirst posterior molar show itself? the second ? 
the third ? 
55. Why is the third posterior molar called the wisdom tooth f 
56. What is the next period to that of childhood ? 
57. What especial changes take place in the skeleton during the 
period of youth ? 
58. When are the three bones of the joelvis united? 
59. When does the consolidation of the long hones of the arms and 
legs take place ? 
60. At what age is the general development of the body complete ? GLOSSARY. 
Abdomen (Latin abdo, to hide). The lower part of the body situ- 
ated beneath the level of the diaphragm; the belly; so called because 
the abdominal organs are concealed or hidden in it. 
Absorption (L. ab, from, and sorbeo, to suck up). The imbibi- 
tion of a fluid by an animal membrane or tissue. 
Adipose Tissue. The fat. 
Air Vesicle. A minute vesicle containing air, which goes to make 
up the tissue of the lungs. 
Albumen (L. albus, white). An animal substance which coagu- 
lates when heated; so called because it turns white in coagulating. 
Hence, “ white of egg.” 
Albuminose. An animal substance, not coagulable by heat, pro- 
duced in digestion by the action of the gastric juice on albuminous 
substances. 
Albuminous Matter. Any animal substance resembling albumen. 
Alimentary Canal. A long tube, of varying form and size in its 
different parts, in which the preparation and digestion of the food, or 
“aliment,” is performed. It comprises the mouth, the pharynx, the 
oesophagus, the stomach, and the small and large intestine. 
Alkali (Arabic Al Kali, the soda-plant). A name given to cer- 
tain chemical substances which have the power of combining with acids 
in such a way as to neutralize their acidity; such as soda, potash, 
and the like. 
Alkaline Fluid. A fluid containing a perceptible quantity of an 
alkali. 
Anatomy (Greek ava, ana, through, and to jit), tomee, a cutting). 
Literally, “ dissection. ” The study of the different parts and struc- 
ture of the body. 
Anti-helix. The curved ridge in the external ear, situated inside 
and in front of the helix. 
Anti-tragus. A ridge-like elevation in the external ear, situated 
behind and below the tragus. ' „ 
Anvil. The middle one of the three small bones in the tympanum 
of the ear, resembling an anvil in shape. 
Aqueous Humor (L. aqua, water, and humor, a liquid). A thin 
watery fluid situated in the eye, between the front of the iris and the 
inner surface of the cornea. 
Apparatus. A collection of different organs, which are associated 
in the performance of the same function. 
Aorta. The great artery which passes off from the left ventricle 
of the heart, and which is the main trunk of the whole arterial system. 372 
GLOSSARY. 
Arch op the Aorta. The semicircular bend of the aorta, in the 
upper part of the chest, from which the main arteries to the arms and 
head are given off. 
Arterial Blood. The bright red blood contained in the left side 
of the heart and the arteries of the general circulation. 
Artery (Gr. ar)p, aer, air, and rr/psio, tereo, to keep). A vessel con- 
veying the blood from the heart outward to the organs ; so called be- 
cause the ancients thought these vessels contained air. 
Arytenoid Cartilages (Gr. apvraiva, arutaina, a kind of water-jug 
or pitcher). Two movable cartilages situated in the larynx, to which 
the vocal chords are attached posteriorly; so called from a supposed 
resemblance in their form to that of a water-pitcher. 
Assimilation. The process by which the ingredients of the food 
are converted into those of the tissues. 
Auditory Nerve (L. audio, to hear). The special nerve of the 
sense of hearing. 
Auricle (L. auricula, the outer ear). The smaller and thinner 
chamber of the heart on each side, which receives the blood directly 
from the veins; so called from a fancied resemblance in shape to a 
dog’s ear. 
Biceps Flexor (L.). A muscle situated upon the front part of the 
arm above the elbow, which serves to bend the elbow-joint. 
Bile. The secretion produced by the liver. 
Biliary Duct. A duct which conveys the bile from the liver to 
the intestine. 
Biliary Salts. Two peculiar substances, formed by the combina- 
tion of certain animal matters with soda, which are the most import- 
ant ingredients of the bile. 
Blood Globules. Minute rounded and flattened semi-fluid bodies 
of a red color, which are found in great abundance in the blood. 
Braciiialis Anticus (L.). A muscle situated upon the front 
part of the arm, which assists the biceps flexor in bending the elbow- 
joint. 
Brain. The mass of nervous substance contained in the cavity of 
the cranium. 
Bronchi. The two passages into which the trachea divides at the 
top of the chest, and which supply the lungs on each side with air. 
Bronchial Tubes. The small tubes into which the bronchi di- 
vide as they enter the substance of the lungs. 
Butyrine. An oleaginous substance which gives the peculiar fla- 
vor to the butter of cow’s milk. 
Calcaneum (L. calco, to kick or trample). The heel-bone. 
Canine Teeth (L. canis, a dog). The pointed teeth situated just 
outside the incisors, one on each side in each jaw; so called because 
they are very prominent in the dog, as well as in other carnivorous 
animals. 
Capillary Blood-vessels (L. capillus, hair). The smallest blood- 
vessels, intervening between the arteries and the veins; so called from 
their minute or hair-like dimensions. GLOSSARY. 
Carbonic Acid (L. carlo, a coal). A gas formed in respiration 
and exhaled with the breath; so called because it is also produced 
from burning coals. 
Cardia (Gr. Kapha, kardia, the heart). The upper orifice of the 
stomach, through which the food enters from the oesophagus , so call- 
ed because it is situated near the heart. 
Carnivorous Animals (L. caro, carnis, flesh; and voro, to devour). 
Animals that feed upon flesh. 
Caries (L. caries, rottenness). The partial decay of a bone or 
tooth. 
Carotid Arteries. The two main arteries which run upward, on 
each side of the neck, to supply the head and brain. 
Cartilage. A firm elastic substance, like India-rubber, attached 
to the bones in various parts of the body. 
Caseine (L. caseus, cheese). The albuminous ingredient of milk; 
so called because, when coagulated, it forms the substance of cheese. 
Catalysis (Gr. KaraXvu), kataluo, to dissolve or demolish). A pe- 
culiar chemical change, in which the ingredients of a substance are 
altered or decomposed by the mere contact of another substance. 
Cell. A minute form, occurring in animal and vegetable tissues, 
sometimes hollow and sometimes solid, and varying in shape, being 
globular, flattened, cylindrical, or irregular. 
Cellular Tissue. A tissue consisting of loosely interwoven fibrous 
bundles, which is placed between the muscles and other contiguous 
parts. 
Cerebellum (literally, the “ Little brain”). A convoluted gangli- 
on, smaller than the cerebrum, and situated at the back and lower 
part of the brain. 
Cerebrum. The largest portion of the brain, filling all the front 
and upper parts of the cranium. 
Cerebrospinal Nervous System. That portion of the nervous 
system consisting of the brain, the spinal cord, and the nerves belong- 
ing to them, through which the body is brought into nervous com- 
munication with the external world. 
Chest. The upper part of the trunk of the body, inclosed by the 
spinal column behind, the ribs on the sides, and the breast-bone in 
front. 
Chondrine (Gr. x°v$P°Q, chondros, cartilage). The albuminous 
ingredient of the cartilages. 
Choroid Coat (Gr. %taptop, chorion, the vascular part of the skin, 
and tidoc, eidos, form). A brownish-black membrane forming one of 
the envelopes of the eyeball; so called because it resembles the skin 
in vascularity. 
Chyle (Gr. xuAoe, chulos, juice). The white, milky-looking fluid 
produced in the small intestine by the digestion of fatty substances. 
Ciliary Nerves. A set of slender nerves, ten or fifteen in number, 
which are given off from the ophthalmic ganglion, and are finally dis- 
tributed to the muscular fibres of the iris. 
Cineritious Nervous Matter (L. cinis, cineris, ashes). The gray 
or ash-colored substance of a nervous ganglion. 
Circulation. The movement of the blood in a continuous round 374 
GLOSSARY. 
or circuit, from the arteries to the veins and from the veins back again 
to the arteries. 
Clavicle (L. clavis, a key). A slender bone, shaped somewhat 
like a key, placed horizontally at the bottom of the neck, between the 
top of the breast-bone and the point of the shoulder. The collar- 
bone. 
Clot. The firm, red, opaque, jelly-like mass, formed by the coag- 
ulation of the blood, and consisting of the fibrine and blood globules 
mixed. 
Coagulation. A process of solidification peculiar to the albumin- 
ous substances. 
Cochlea (L. cochlea, a snail-shell). A portion of the labyrinth of 
the ear, consisting of a double tubular canal, winding spirally round a 
central axis, like a snail-shell, and containing the terminal ramifica- 
tions of the auditory nerve. 
Collar-bone. See Clavicle. 
Colon (Gr. kihXvw, koluo, to restrain). The name given to the 
large intestine; because its contents move slowly. 
Concha (L. concha, a shell). The cup-shaped depression in the 
middle of the external ear, leading to the mouth of the auditory me- 
atus. 
Congestion (L. congero, congestum, to heap up). An unusual fill- 
ing of the vessels of a part with blood. 
Conjunctiva (L. conjungo, to join). The thin membrane which 
covers the front of the eyeball and lines the inner surface of the eye- 
lids ; so called because it joins the eyelids to the eyeball. 
Constrictors of the Pharynx (L. constringo, to tie up, as in a 
bundle). Three muscles which are wrapped round the pharynx so as 
to compress this canal and force the food through it from above down- 
ward. 
Contraction. The active shortening of a muscle or muscular 
fibre. 
Convulsion (L. convello, to tear). A violent and ipvoluntary con- 
traction of some or all of the muscles of the body and limbs. 
Cornea (L. cornu, a horn). A firm, transparent, and colorless 
layer, forming the front part of the eyeball, through which the light 
penetrates into the interior; so called from its resemblance to horn in 
texture and consistency. 
Cranial Nerves. The nerves connected with the brain; so called 
because they emerge through openings in the cranium. 
Cranium. The bony case containing the brain. 
Creatine and Creatinine (Gr. Kpsap, kreas, flesh). Two substan- 
ces produced in the process of excretion, formed in the tissue of the 
muscles and discharged from the body by the kidneys. 
Cribriform (L. cribrum, a sieve). Perforated with many little 
holes, like a sieve. 
Crown of a tooth. That portion of the tooth which projects above 
the jaw. 
Crystalline. The albuminous ingredient of the crystalline lens. 
Crystalline Lens. A transparent circular body, rounded on its 
front and back surfaces, situated in the eyeball, just behind the pupil. GLOSSARY. 
375 
It serves to concentrate the light passing through it at the surface of 
the retina. 
Decussation (L. decusso, to cut crosswise). A reciprocal crossing 
from side to side. 
Deglutition. The act of swallowing. 
Development. The process by which the body passes through 
successive changes or stages of growth, from infancy to adult age. 
Diaphragm (Gr. Siatppaypa, diaphragrna, a partition). The vault- 
ed muscular sheet which separates the cavity of the chest from that 
of the abdomen. 
Digestion. The liquefaction and preparation of the food in the 
alimentary canal. 
Duct. A narrow tube, usually destined to convey away a secre- 
tion from the gland in which it is produced. 
Emulsion (L. emulgeo, to milk). A permanent mixture of oil, mi- 
nutely divided, with a watery liquid; so called because it is white 
and milky in appearance. 
Enamel. The dense calcareous covering of the crown of a tooth. 
Endosmosis (Gr. ivCov, endon, within, and othismos, an 
impulsion). The force by which a fluid is made to penetrate an ani- 
mal substance or tissue. 
Epithelium (Gr. twi, epi, upon, and thele, a nipple). A lay- 
er of soft cells, covering the surface of the lining membranes and cer- 
tain parts of the skin. 
Eustachian Tube. A membranous canal, extending from the 
fore part of the tympanum of ear to the side of the pharynx, and 
serving to establish a communication between the cavity of the tym- 
panum and the external atmosphere; from Barthelemi Eustachi, an 
Italian anatomist of the sixteenth century. 
Excretion (L. excerno, excretum, to purge out). The process by 
which the waste materials of the body are changed and eliminated. 
A substance or fluid so produced is also called an excretion. 
Expiration. The act by which air is carried out of the lungs in 
breathing. 
Extensor Muscle. A muscle which serves to straighten or ex- 
tend a joint. 
External Ear. The trumpet-shaped expansion on the side of 
the head which serves to conduct sounds toward the mouth of the 
auditory meatus. It is that part commonly called the “ ear.” 
Facial Nerve. The seventh cranial nerve, distributed to the mus- 
cles of expression in the face. 
Femur. The thigh-bone. 
Fenestra (JL. fenestra, a window). The name sometimes given to 
a perforation in the walls of a cavity, as, for instance, the ‘ ‘ oval fenes- 
tra” in the outer wall of the vestibule of the ear. 
Ferment. A substance which causes fermentation. 
Fermentation (L. fermentesco, to rise, to puff up). A process of 
catalysis, by which bubbles of gas are formed in the fermenting sub- 
stance. 376 
GLOSSARY. 
Fibrine. An animal matter found in the blood, which has the 
property of coagulating spontaneously; so called because, when coag- 
ulated, it has a fibrous texture. 
Field of Vision. The circular space in front of the eyes within 
which objects can be perceived. 
Flexor Muscle (L.Jlecto,Jlexum, to bend). A muscle which serves 
to bend a limb or joint. 
Focus (L. focus, a fireplace). The spot at which the rays passing 
through a lens are brought together. 
Follicle. A little bag or sac, formed of an animal membrane, 
and usually opening by a minute orifice at one extremity. 
Follicles of Lieberkuhn. The simple tubular follicles of the 
lining membrane of the small intestine; so called from John Nathan- 
iel Lieberkiihn, a Prussian anatomist of the eighteenth century, by 
whom they were first described. 
Fontanelle (Italian fontanella, a little fountain). A name given 
to two spots in the cranium of infants, where the ossification of the 
skull is not yet complete, and where the pulsations of the brain can be 
felt through the soft parts, like the bubbling of water in a fountain. 
Foramen (L. foramen, a hole). A perforation ; usually in a hone. 
Function (L. fungor, functus, to perform). The office performed 
by any organ of the body. 
Fungus. A very simple kind of vegetable growth, formed entirely 
of cells. 
Gall-bladder. A sac or reservoir, communicating with the main 
biliary duct, in which a portion of the bile is stored up during the in- 
tervals of digestion. , 
Ganglion (Gr. yayy\iov, ganglion, a tumor). A collection of gray 
nervous matter containing nerve-cells, and acting as a nervous centre. 
Ganglion of Meckel. A small ganglion belonging to the sympa- 
thetic nervous system, situated beneath the floor of the skull, and giv- 
ing off nerves wrhich are distributed to the inner part of the nasal pas- 
sages and to the muscles of the hanging palate; from Meckel, a Ger- 
man anatomist of the eighteenth century. 
Gasserian Ganglion. A considerable ganglion, situated upon the 
fifth or “ trigeminal” nerve, within the cranium, at the level of its di- 
vision into three main branches; so called from Achilles Pirminius 
Gasser, a German anatomist of the sixteenth century, by whom it is 
said to have been discovered. 
Gastric Tubules. The elongated tubular follicles of the lining 
membrane of the stomach, by which the gastric juice is secreted. 
Gastrocnemius Muscle (Gr.). A strong muscle situated upon the 
back part of the leg, which serves to draw the heel upward. 
Gelatinous (L. gelatus, congealed). Like .jelly in consistency. 
General Circulation. The movement of the blood through the 
various tissues and organs, from the arteries to the veins, as distin- 
guished from the circulation through the lungs or any other particular 
organ. 
General Sensibility. The sensibility residing in the skin and 
some of the lining membranes, by which we acquire the perception of GLOSSARY. 
377 
the simpler physical qualities of external objects; such as their con- 
sistency, texture, temperature, etc. 
Germination (L. germino, to bud). The first growth or sprouting 
of a seed. 
Gland. An organ composed of follicles, lobules, and ducts, with 
blood-vessels interwoven, which produces a secretion from the mate- 
rials of the blood. 
Glandule. A little gland. 
Glosso-pharyngeal Nerve (Gr. yXuooa, glossa, the tongue, and 
$apvy%, pharunx, the throat). The ninth cranial nerve, which is dis- 
tributed to the back part of the tongue and to the pharynx. 
Glottis. The narrow opening or crevice in the upper part of the 
larynx, by which it communicates with the throat. 
Gluten. The albuminous matter of wheat flour; so called from 
its adhesive and glutinous consistency. 
Granule. A little grain. 
Gustatory Nerve (L. gusto, to taste). The special nerve of the 
sense of taste, being a branch of the third division of the fifth cranial 
nerve. 
Hanging Palate. A muscular curtain, hanging downward from 
the hack part of the roof of the mouth, which partially separates the 
cavity of the mouth from that of the pharynx. 
Helix (Gr. «\i£, helix, any thing twisted or convoluted). The out- 
er border of the external ear, which is rolled or convoluted inward. 
Hemiplegia (Gr. gpiovg, hemisus, half, and TrXgoooj, plesso, to 
strike). A paralysis of one lateral half of the body, and the limbs on 
the corresponding side. 
Hepatic Vein (Gr. rjirap, hepar, the liver). The vein which col- 
lects the blood from the liver and carries it onward to the heart. 
Herbivorous Animals (L. herba, grass, and voro, to devour). An- 
imals that feed upon, vegetable matters. 
Hyaloid Membrane (Gr. va\og, hualos, glass, and tidog, eidos, 
form). A very thin, transparent, and colorless membrane, which lines 
the inner surface of the cavity of the eyeball. 
Hydrophobia (Gr. uchup, hudor, water, and <po€og, phobos, fear). 
A disease induced by the bite of a mad dog, and characterized by ex- 
treme irritability of the spinal cord, so that the least external impres- 
sion causes violent reflex convulsions, especially of the muscles of deg- 
lutition ; so called because the animals and men affected by it were 
supposed to have an especial dread of water. 
Hygiene (Gr. vyiua, hugieia, health). The study of the laws of 
health and the means of its preservation. 
Hypoglossal Nerve (Gr. virb, kupo, under, and yXibooa, glossa, 
the tongue). The motor nerve distributed to the muscles of the 
tongue; so called because the trunk of the nerve runs for some dis- 
tance beneath the bottom of the tongue. 
Incisors (L. inciclo, incisum, to cut). The four front teeth in each 
jaw; so called because they are provided with a sharp edge and are 
adapted for cutting. 378 
GLOSSARY. 
« 
Infant (L. infans, not speaking). The child under two years of 
age; so called because he can not yet use articulate language. 
Insensible Transpiration. The name given to the perspiration 
when produced in its usual moderate quantity, so that it instantly 
evaporates; consequently being imperceptible or ‘ ‘ insensible. ’’ 
Inspiration. The act by which air is drawn into the lungs in 
breathing. 
Intercostal Muscles (L. inter, between, and costa, a rib). The 
muscles which are situated between the ribs, and which move the ribs 
in respiration. 
Intercostal Nerves. The spinal nerves which supply the inter- 
costal muscles. 
Internal Ear. That part of the auditory apparatus consisting of 
the labyrinth, its membranous bag and lymph-like fluid, with the 
ramifications of the auditory nerve; all contained within the sub- 
stance of the petrous bone. 
Intestinal Juice. A viscid secretion produced by the lining mem- 
brane of the small intestine. 
Iris (L. iris, the rainbow). The perforated muscular curtain situ- 
ated within the eye, in front of the crystalline lens; so called from its 
variegated color. 
Irritability. The property by which the nerves or other organs 
are thrown into excitement by any stimulus applied to their sub- 
stance. 
Ivory. A very dense' bony substance, forming the greater part of 
the teeth. 
Keratine (Gr. Kepac, her as, hom). The albuminous ingredient 
of the hair and nails; so called because the same substance is the in- 
gredient of horn. 
Labyrinth. A cavity, of singular and complicated form, situated 
in the substance of the petrous bone, and containing the terminal ram- 
ifications of the auditory nerve. 
Lachrymal Canals (L. lachryma, a tear). Two narrow canals or 
ducts, an upper and a lower, leading from the inner corner of the eye- 
lids toward the nose, and serving to convey away the tears from the 
surface of the eye. 
Lachrymal Gland. A lobulated gland, situated in the upper and 
outer part of the orbit of the eye, in which the tears are secreted. 
Lacteals (L. lac, milk). The lymphatic vessels of the small intes- 
tine, which become filled with white, milky-looking chyle during di- 
gestion. 
Lactic Acid. The acid produced by the souring of milk. It also 
exists in the gastric juice. 
Large Intestine. The last five feet of the intestine; so called 
on account of its capacity, being considerably wider than the small in- 
testine. 
Larynx (Gr. XapvyK, larunx). The cartilaginous box situated at 
the top of the windpipe, through which the air passes from the throat 
into the trachea. GLOSSARY. 
Ligament (L. ligo, ligare, to bind). A fibrous band or cord, serv- 
ing to attach two bones to each other. 
Line op Distinct Vision. The straight line extending in front 
of each eye, within which alone the eye can perceive objects distinctly. 
Lobule. A collection of little follicles or vesicles, or any division 
of a glandular organ communicating with a single duct. 
Lymph. A transparent colorless fluid, absorbed by the lymphatic 
vessels from various the body. 
Lymphatic Vessels. A set of very thin, delicate vessels, which ab- 
sorb the lymph from the tissues of the body and convey it inward to- 
ward the centre of the venous system. 
Mallet. The outermost of the three small bones in the tympa- 
num of the ear, having the form of a mallet, and attached to the mem- 
brane of the tympanum. 
Margarine (Gr. gapyapov, rnargaron, a pearl). A fatty or oleag- 
inous substance, which is intermediate in consistency between stearine 
and oleine. 
Marrow. A soft vascular substance contained in the cavities of 
the bones. 
Masseter Muscle (Gr. ficKjodogcu, massaomai, to chew). A strong 
muscle situated upon the side of the face, which moves the lower jaw 
from below upward in mastication. 
Mastication. The grinding up or comminution of the food by the 
action of the teeth. 
Masticator Nerve. The motor branch of the third division of the 
fifth cranial nerve, distributed to the muscles of mastication. 
Meatus (L.). A passage or canal. 
Medulla Oblongata. A nervous mass of an oblong shape, situ- 
ated at the lower part of the brain, and giving otf many of the cranial 
nerves. It contains the ganglion of respiration. 
Meibomean Glands. The glands situated on the inner surface of 
the cartilages of the eyelids, by which the oleaginous secretion of the 
lids is produced; from Henry Meibom, a German anatomist of the 
seventeenth century, who described the structure of the eyelids. 
Membrane. A thin and flexible expansion of tissue. 
Membrane of the Tympanum. A fibrous membrane stretched 
across the bottom of the external auditory meatus, and forming the 
outer wall of the tympanum. 
Mesentery (Gr. gkaoQ, mesos, in the midst, and tvripa, entera, the 
entrails). A broad membrane by which the intestines are attached 
to the spinal column. 
Milk Teeth. The first set of teeth, twenty in number, which make 
their appearance during infancy; so called because the food at that 
time consists principally of milk. 
Molar Teeth (L. mola, a mill). The side and back teeth, which 
are adapted for grinding the food, like mill-stones. 
Motor Nervous Fibres. Those nervous fibres which convey the 
stimulus to motion from the nervous centres outward to the muscles. 
Mucus. A ropy lubricating secretion, produced by the follicles 
and glandules in various parts of the body. 380 
GLOSSARY. 
Musculine. The peculiar albuminous ingredient of the muscular 
fibres. 
Nasal Duct. A duct which receives the tears brought from the 
eye by the lachrymal canals, and discharges them into the cavity of 
the nose about its middle portion. 
Nerve. A white cord composed of nervous fibres or filaments. 
Nerve-cells. Bounded cells, often .with slender prolongations 
running out from them, found in the gray substance of the nervous 
ganglia. 
Nervous Centre. A collection of gray nervous matter, which re- 
ceives impressions and originates the nervous impulses. 
Nervous Fibre or Filament. A white thread of minute size, 
forming the substance of the nerves, and having the power of conduct- 
ing the nervous stimulus. 
Nervous System. The entire collection of all the organs com- 
posed of nervous tissue, namely, the ganglia and the nerves, with all 
their connections, throughout the body. 
Neuralgia (Gr. vevpov, neuron, a nerve, and aXyog, algos, pain). 
A painful affection produced by irritation of the sensitive nerves, with- 
out manifest disease of the other tissues. 
Neurilemma. The fibrous sheath by which the filaments of a 
nerve are enveloped, and which protects them from injury. 
Nitrogen. A gas having but little chemical activity, which forms 
about four fifths of the bulk of the atmosphere. 
Nucleus (L. nucleus, a kernel). A round or oval spot, which is 
found upon certain cells, as, for instance, epithelium-cells and nerve- 
cells. 
Nutrition. The internal process of nourishment of the body or 
any of its parts. 
(Esophagus (Gr. oim, olffio, oio, oiso, to cany, and <j>ayio, phago, to 
eat). The muscular tube which conveys the food from the mouth to 
the stomach. The gullet. 
Oleine (Gr. tXaiov, elaion, oil). An oleaginous substance which is 
fluid at ordinary temperatures. 
Olfactory Nerves (L. ol/acio, to smell). The special nerves of the 
sense of smell. 
Ophthalmic Ganglion (Gr. o09aXpog, ophthalmos, the eye). A 
small ganglion belonging to the sympathetic nervous system, and sit- 
uated in the back part of the orbit of the eye, from which the ciliary 
nerves are given off to the iris. 
Optic Nerves (Gr. on-ropm, optomai, to see). The special nerves 
of the sense of sight, distributed to the interior of the eyeball. 
Optic Thalami. Two nervous ganglia, situated beneath the cere- 
brum and behind the striated bodies ; so called because they were for- 
merly supposed to be the origins of the optic nerves. 
Optic Tubercles. A pair of small rounded ganglia, situated near 
the middle part of the brain, from which the optic nerves take their 
origin. 
Orbicularis Muscle of the Eye. The muscle surrounding the GLOSSARY. 
381 
opening of the eyelids, by which the eye is suddenly and forcibly 
closed, as in the act of winking. 
Orbit. The bony cavity beneath the forehead in which the eye- 
ball is situated. 
Organ (Oik opyavov, organon, an instrument)'. Any part of the 
body which is adapted to perform a particular service, such as the 
heart, the stomach, the brain. 
Ossification (L. os, ossis, a bone, and facio, to make). The con- 
version of cartilage or other soft tissue into bone. 
Osteine (Gr. oortov, osteon, a bone). The albuminous ingredient 
of the bones. 
Oxygen. A gas forming one fifth part, by bulk, of the atmosphere, 
which is essential to respiration. 
Pancreas. A gland situated in the upper part of the abdomen, 
near the lower border of the stomach. 
Pancreatic Juice. The secretion produced by the pancreas. 
Pancreatine. The albuminous ingredient of the pancreatic juice. 
Papilla (L. papilla, a nipple). A minute conical prominence or 
elevation upon the surface of an animal membrane; thus the “ papil- 
be” of the tongue. 
Paralysis (Gr. TrapaXveo,paraluo, to loosen). A suspension or ab- 
olition of the power of sensation or motion ; more frequently of both. 
Paraplegia (Gr. TrapairXgaao), paraplesso, to strike with derange- 
ment). A paralysis of the lower limbs and lower half of the body. 
Parotid Gland (Gr. 7rapa, para, near, and ovq, mtoq, ous, otos, the 
ear). The salivary gland situated just in front of the ear. 
Par Vagum (L.). Literally, the “ wandering pair.” A name given 
to the pneumogastric nerves, on account of their long course and va- 
ried distribution. 
Peduncles of the Brain. Two rounded bundles of nervous fibres 
running upward and forward from the base of the brain, and termi- 
nating, on each side, in the substance of the cerebrum; so called from 
the botanical term “peduncle,” which signifies the stalk of a flower. 
Pelvis (L. pelvis, a basin). The hip-bone; so called because it is 
like a basin in shape. 
Pepsine (Gr. ttOrrw, pepto, to cook, to disintegrate by cooking). 
The most important ingredient of the gastric juice, which acts as a 
ferment in the digestion of the food. 
Peristaltic Action (Gr. 7r«piarsXXw, peristello, to wrap round). 
The peculiar movement produced by the successive contraction of cir- 
cular muscular fibres wrapped round a cylindrical tube, as in the 
oesophagus or the intestine. 
Perspiration (L. per, through, and spiro, to breathe or exhale). 
The watery secretion exuded upon the surface of the skin. 
Perspiratory Glands. Small glandular bodies, in the form of a 
coiled tube, situated immediately beneath the skin, by which the per- 
spiration is secreted. 
Petrous Bone (Gr. Trerpa, petra, a rock). One of the bones form- 
ing the base of the skull, and containing the internal ear and the tym- 
panum ; so called from its stony hardness. 382 
GLOSSARY. 
Pharynx (Gr. (papvyZ, pharunx, the throat). The muscular pas- 
sage leading from the back part of the mouth to the oesophagus. 
Phrenic A erve. The nerve of the diaphragm. 
Physiology (Gr. P/msis, Nature ■ and Xt'tyoc, logos, a dis- 
course). The study of the natural actions of the living body. 
Plexus (Gr. nXkKw, irXiS,m, pleko, plexo, to weave or plait together). 
A network of any thing interwoven, as of blood-vessels or nerves. 
Pneumogastric Nerve (Gr. 7rveuptvv, pneumon, the lungs, and 
yacm)p, gasteer, the stomach). The tenth cranial nerve, distributed 
principally to the lungs and the stomach. 
Pons Varolii (L.). Literally, the “ bridge of Varolius.” A trans- 
verse band of nervous fibres passing in a curved form from one side 
of the cerebellum to the other, and spanning the longitudinal fibres of 
the medulla oblongata, like an arched bridge spanning a stream; so 
called from Varolius, an Italian anatomist of the sixteenth century, 
who first described it. 
Portal Vein (L. porta, a gateway). The venous trunk formed by 
the union of all the veins coming from the intestine, and which con- 
veys the blood to the liver. 
Pterygoid Muscles (Gr. irTspv%, Trripvyog, pterux, pterugos, a 
wing). Two muscles situated between the “ pterygoid” or wing-like 
projections of the base of the skull and the lower jaw. They give to 
the jaw a lateral or grinding movement in mastication. 
Ptyaline (Gr. nrvtXov, ptuelon, saliva). The albuminous matter 
of the saliva. 
Pulmonary (L. pulmo, the lungs). Relating or belonging to the 
lungs. 
Pulmonary Artery. The great artery which receives the blood 
from the right ventricle of the heart and carries it toward the lungs. 
Pulmonary Circulation. The movement of the blood through 
the lungs, from the pulmonary artery to the pulmonary veins. 
Pulmonary Veins. The veins which bring the blood from the 
lungs to the left auricle of the heart. 
Pulp of a Tooth. The soft Arascular papilla or prominence around 
which the harder portions of the tooth are deposited. 
Pulsation of the Heart. The entire act, or movement, of the suc- 
cessive contraction and relaxation of the auricles and ventricles. 
Pulse (L. pulso, to beat). The rhythmical distension of an artery 
by the impulse of the blood from the heart. 
Pupil. The circular perforation in the centre of the iris, through 
which the light reaches the deeper parts of the eye. 
Pylorus (Gr. irvXiopog, puloros, a gate-keeper). The lower orifice 
of the stomach, through which the food passes into the intestine; so 
called on account of a circular band of muscular fibres by which the 
passage is guarded. 
Radial Artery. An artery which passes along the front of the 
wrist, at its outer part, to supply the palm of the hand. 
Receftaculum Chyli. Literally, the receptacle of the chyle. A 
small sac or dilatation situated at the commencement of the thoracic 
duct. GLOSSARY. 
383 
Rectum (L. rectus, straight). The last portion of the large intes- 
tine ; so called because it is nearly straight, in comparison with the 
remainder of the intestine. 
Recurrent Nerve (L. recurro, to run back). The inferior laryn- 
geal branch of the pneumogastric nerve; so called because it is given 
off from the main trunk of the pneumogastric at or near the top of 
the chest, and then returns in a direction from below upward, to reach 
the larynx in the upper part of the neck. 
Reflex Action of the Nervous System. An action by which the 
impression received by a nervous centre through the sensitive nerves 
is again reflected outward through the motor nerves, under the form 
of a stimulus to movement. 
Regimen. The systematic regulation of the food and drink. 
Relaxation. The inactive condition of a muscle or a muscular 
fibre. 
Rennet. The prepared tissues and fluids of the calf’s stomach, 
used for coagulating milk in the manufacture of cheese. 
Respiration (L. re, denoting repetition, and spiro, to breathe). 
The process by which the atmospheric air is introduced into the lungs 
for the renovation or arterialization of the blood. 
Retina (L. retis, a net). The membranous expansion of the optic 
nerve in the interior of the eyeball. 
Root of a Tooth. The elongated portion of the tooth which is im- 
bedded in the jaw. 
Saccharine. Containing or consisting of sugar. 
Saliva. The fluid secretion produced by various glands and poured 
into the cavity of the mouth. 
Salivary Gland. A gland which produces saliva. 
Sclerotic Coat (Gr. <ncA?jpoe, skleros, hard). A firm and resisting 
fibrous envelope, forming the outer coat of the eyeball. 
Sebaceous Matter (L. sebum, tallow). A substance of oleaginous 
composition, but nearly solid in consistency, like tallow. 
Secretion (L. secerno, secretum, to separate). The separation or 
production from the blood of a fluid destined for a special purpose. 
The fluid so produced is also called a secretion. 
Semicircular Canals. Three narrow curved passages, excavated 
in the substance of the petrous bone, and communicating with the cav- 
ity of the vestibule. They contain a clear colorless lymph, and a mem- 
branous sac corresponding to them in form, upon which a portion of 
the filaments of the auditory nerve are distributed. 
Semilunar Ganglion (L. semi, half, and lima, the moon). An im- 
portant ganglion of the sympathetic nervous system of a semilunar or 
half-moon shape, situated behind the stomach. 
Semilunar Valves. The three festooned or bag-like valves, of a 
half-moon shape, situated on each side of the heart, at the entrance 
of the great arteries. 
Sensation. The conscious perception of an impression made upon 
the nervous system. 
Sensitive Nervous Fibres. Those nervous fibres which convey 
impressions from without inward to the nervous centres. 384 
GLOSSARY. 
Serum (L. serum, whey, buttermilk). The clear, water}', amber- 
colored fluid which separates from the clot after the coagulation of the 
blood. It contains, beside water, albumen and mineral substances. 
Small Intestine. The first twenty-five feet of the intestine im- 
mediately following the stomach; so called on account of its small 
calibre, being only an inch and a half in width. 
Solar Plexus (L. sol, the sun). A radiating plexus or network of 
sympathetic nerves, spreading from the neighborhood of the semilunar 
ganglion outward, like the rays of the sun, to be distributed to the va- 
rious organs in the abdomen. 
Soleus Muscle (L.). A muscle situated on the back part of the 
leg, which assists the gastrocnemius in drawing the heel upward. 
Special Sense. A sense by which we receive particular sensa- 
tions, differing from those of general sensibility; such as those of sight, 
hearing, taste, and smell. 
Spinal Canal. A long cavity containing the spinal cord, inclosed 
in the bones of the spinal column. 
Spinal Column. The back-bone. 
Spinal Cord. A cylindrical mass of nervous matter situated in 
the cavity of the spinal canal, connected with the brain above, and 
giving off the spinal nerves from its two opposite sides. 
Spinal Nerves. The nerves connected with the spinal cord. 
Spine. A projecting point or ridge of bone. 
Spleen. A very vascular organ situated within the abdomen, near 
the left extremity of the stomach. 
Stearine (Gr. or tap, stear, suet, fat). A fatty or oleaginous sub- 
stance, Avhich when pure is solid at ordinary temperatures. 
Stereoscope (Gr. ortpibg, stereos, solid, and okottiuj, skopeo, to ex- 
amine). A box containing two different pictures of the same object, 
so arranged that, seen together, they produce a deceptive appearance 
of solidity. 
Stirrup. The innermost of the three small bones in the tympa- 
num of the ear, having the form of a stirrup, and attached to the 
membrane of the oval fenestra. 
Striated Bodies. Two oval ganglia situated, one on each side, 
at the under part of the cerebrum; so called because when cut open 
they present a striated appearance, owing to the white nervous fibres 
passing through the gray substance of the ganglion. 
Subclavian Vein (L. sub, under, and clavis, a key). The great 
vein bringing back the blood from the arm and side of the head; so 
called because it is situated underneath the clavicle or collar-bone. 
Sublingual Gland (L. sub, under, and lingua, the tongue). A sal- 
ivary gland situated beneath the tongue. 
Submaxillary Gland (L. sub, under, and maxilla, the jaw). A 
salivary gland, situated beneath the angle of the jaw. 
Sympathetic Nervous System. That portion of the nervous sys- 
tem consisting of a double chain of small ganglia, situated in front of 
the spinal column, and the nerves belonging thereto, by which a nerv- 
ous communication is established between the internal organs of nu- 
trition. GLOSSARY. 
385 
Temporal Artery. A small artery which passes upward just be- 
neath the skin in front of the ear, on each side, to supply the temples. 
Temporal Muscle. A fan-shaped muscle, situated upon the side 
of the head (on the temples), and attached to the lower jaw, which it 
moves from below upward. 
Tendon. A fibrous cord by which a muscle is attached to its 
bone. 
Tetanus (Gr. rtravog, tetanos, a stretching or extension). A dis- 
ease characterized by severe convulsions of the voluntary muscles, in 
which the body and limbs are forcibly extended or straightened. 
Thaumatrope (Gr. Savpa, thauma, a wonder, and rpoTrrj, tropee, a 
turning). A toy consisting of a revolving card with a number of pic- 
tures of the same object in different positions, the effect of which is to 
make it appear as if the object were in rapid motion. 
Thoracic Duct (Gr. 3wpa|, thorax, the chest). A narrow tube 
running from below upward within the back part of the chest, which 
is the main trunk of the lymphatic vessels. 
Tibia. The principal bone of the leg, below the knee. 
Tic Douloureux (French). Literally, the “ painful spasm. ” Neu- 
ralgia of the fifth cranial nerve or of some of its branches. 
Tissue. Any substance or texture in the body formed of various 
elements, such as cells, fibres, blood-vessels, etc., interwoven with each 
other. 
Trachea (Gr. rpa%aa, trac.heia). The cartilaginous and mem- 
branous tube leading downward from the larynx to the top of the 
chest. The windpipe. 
Tragus. A short ridge-like elevation in the front border of the 
external ear. 
Transfusion of the Blood (L. trans, over, across, and fundo, to 
pour). The operation of introducing fresh blood from the vessels of 
one living animal or man into those of another. 
Trigeminal Nerve (L. tres, three, and geminus, alike). The fifth 
cranial nerve; the great sensitive nerve of the face; called * ‘ trigemi- 
nal” because it divides, just before leaving the cavity of the cranium, 
into three nearly equal branches. 
Trochlearis Muscle (Gr. rpoyAta, trochilea, a pulley). The up- 
per oblique muscle of the eyeball; so called because its tendon passes 
through a pulley-like ring. 
Tuber Annulare (L.). Literally, the “annular” or “ring-like 
swelling.” A rounded protuberance of nervous matter, situated at the 
base of the brain, just in front of the medulla oblongata. 
Tubule. A little tube. 
Turbinated Bones (L. turbo, a whirling or convolution). Three 
rolled or convoluted plates of bone attached to the outer wall of each 
nostril. 
Tympanum of the Ear (L. tympanum, a drum). The cavity of the 
ear situated between the labyrinth and the bottom of the external au- 
ditory meatus, closed internally by the membrane of the oval fenestra 
and externally by the membrane of the tympanum. 
Urate of Soda. A substance formed of the combination of an 386 
GLOSSARY. 
animal acid with soda, produced, like urea, in the process of excretion, 
and discharged from the body by the kidneys. 
Urea. A substance produced in the process of excretion, and dis- 
charged from the body by the kidneys. 
Uvula (L. uva, a grape). Literally, a “little grape.” A conical 
fleshy appendage attached to the lower border of the hinging palate. 
Valvule Conniventes. The valve-like folds or projections of 
the lining membrane of the small intestine. 
Vascular. Containing or belonging to blood-vessels. 
Vein. A vessel serving to convey the blood from the various or- 
gans inward to the heart. » 
Venous Blood. The dark - colored blood contained in the right 
side of the heart and the veins of the general circulation. 
Ventilation. The method by which the air is renewed in apart- 
ments and dwellings. 
Ventricle (L. ventriculus, a little stomach). The larger and 
thicker chamber of the heart, on each side, which receives the blood 
from the corresponding auricle and discharges it into the artery. 
Ventricular Valves. The valves situated in the heart at the en- 
trance from the auricles to the ventricles. 
Vermicular Action (L. vermis, a worm). The muscular contrac- 
tion of certain parts of the alimentary canal; so called because it re- 
sembles a crawling or worm-like motion. 
Vesicle (L. vesicula, a little bladder). A small rounded sac or 
bag composed of a thin animal membrane. 
Vestibule. A rounded chamber in the petrous bone, forming a 
portion of the labyrinth. 
Villi (L. villus, hair, or the nap of shaggy cloth). The minute fil- 
amentous projections from the inner surface of the lining membrane 
of the small intestine. 
Vitreous Body (L. vitrum, glass). A colorless glassy-looking sub- 
stance, of gelatinous consistency, which fills the cavity of the eyeball 
behind the crystalline lens. 
Vocal Chords (L. vox, vocis, the voice). Two elastic bands of 
fibrous tissue, forming the lateral edges of the glottis. Their vibra- 
tions, communicated to the air, produce the sound of the voice. 
Volition (L. volo, to will). The nervous act by which we inteif- 
tionally excite the muscular contractions. 
Wisdom Teeth. The four posterior molar teeth; so called be- 
cause they do not make their appearance until the age of from seven-' 
teen to twenty years. INDEX. 
Absorbent vessels, page 127. 
of the abdomen, 129. 
Absorption, 119. 
of the food, 119. 
nature and method of, 121. 
by the blood-vessels, 122. 
by the lacteals, 127. 
of bile from the intestine, 140. 
of sugar from the liver, 142. 
of oxygen in respiration, 170. 
of nutritious material by the 
tissues, 212. 
Achilles, tendon of, 32. 
Adipose tissue, 61. 
Air, atmospheric, 158. 
composition of, 159. 
quantity of, used in respira- 
tion, 169. 
change of, in respiration, 170. 
contamination of, by respira- 
tion, 176. 
renovation of, by ventilation, 
176. 
Air passages, 161. 
Air vesicles of the lungs, 161, 163. 
Albumen, 64. 
of the blood, 146. 
Albuminose, 103. 
Albuminous matters, 63. 
different varieties of, 64. 
distinguishing properties of, 
64-66. 
proportion of, in different kinds 
of food, 67. 
decomposition of, in the body, 
68. 
digestion of, 102. 
of the saliva, 93. 
of the gastric juice, 101. 
of the intestinal juice, 109. 
Albuminous matters of the pancre- 
atic juice, 112. 
of the blood, 146. 
of the breath, 175. 
Alcohol, produced by fermentation, 
77, 79, 80. 
Alimentary canal, 85. 
different parts of, 86, 87. 
Animal heat, 200. 
necessary to life, 202. 
source of, 202. 
how produced, 203. 
variations and equalization of, 
203. 
regulation of, by perspiration, 
203-207. 
Anti-helix, 339. 
Anti-tragus, 339. 
Anvil, 336. 
Aorta, 185. 
arch of, 186,190. 
Apparatus, digestive, 85. 
Aqueous humor, 317. 
Aromatic substances, 349. 
Arterial blood, 172. 
change of, in the general cir- 
culation, 173. 
Arteries, 190. 
arrangement and distribution 
of, 190. 
elasticity of, 191. 
pulsation of, 191. 
carotid, 192. 
temporal, 192. 
radial, 192. 
movement of blood through, 
192. 
pressure of blood in, 193. 
Artery, pulmonary, 184. 
Arytenoid cartilages, 270. 388 
INDEX. 
Assimilation, 210. 
Auditory meatus, external, 338. 
Auditory nerve, 333. 
distribution of, 334. 
function of, 335. 
Auricles, of the heart, 183,184. 
Back-bone, 21. 
Beer, 80. 
Biceps flexor, 30. 
Bile, 135. 
formation of, in the liver, 136. 
accumulation of, in the gall- 
bladder, 137. 
composition of, 138. 
function of, in the intestine, 
139. 
decomposition and reabsorp- 
tion of, 140. 
Biliary duct, 88,135. 
Biliary salts, 138. 
crystallization of, 139. 
Bleeding, effects of, 156. 
how stopped, 152. 
Blood, 145. 
physical appearance of, 145. 
mineral ingredients of, 146. 
albuminous matters of, 146, 
147. 
globules of, 148. 
composition of, 150. 
coagulation of, 150. 
entire quantity of, 155. 
effects produced by loss of, 156. 
transfusion of, 156. 
two different kinds of, 156. 
absorption of oxygen by, 170. 
change of, in respiration, 171. 
venous, 171. 
arterial, 172. 
circulation of, 182. 
course of, through the heart 
and lungs, 186. 
movement of, through the ar- 
teries, 192. 
through the capillaries, 194. 
through the veins, 195. 
temperature of, 201. 
Blood-vessels, 182. 
different kinds of, 191-194. 
absorption by, 122. 
Bones, composition of, 19. 
structure of, 20. 
elasticity of, 35. 
of the infant, 360. 
ossification of, 360. 
consolidation of, in youth, 367. 
Brachialis anticus, 30. 
Brain, 231. 
termination of nervous fibres 
in, 242. 
paralysis from injury of, 245. 
anatomical structure of, 282. 
peduncles of, 284. 
Bread, 76. 
fermentation of, 77. 
baking of, 78. 
Bronchi, 161. 
Bronchial tubes, 162. 
Butter, 62. 
how obtained, 75. 
composition of, 75. 
Butyrine, 75. 
Calcaneum, 33. 
Calf, of the leg, muscles of, 32. 
Canals, lachrymal, 329. 
semicircular, 334. 
Capillary blood-vessels, 193. 
circulation in, 194. 
Carbonic acid, produced in fer- 
mentation, 77, 79. 
in respiration, 174. 
exhaled with the breath, 175. 
Cardia, 86. 
Carotid arteries, 192. 
Cartilage, 35. 
Cartilages, arytenoid, 270. 
Caseine, 64. 
coagulation of, in cheese-mak- 
ing, 76. 
Catalysis, 131, 214. 
Cells, glandular, of the liver, 62. 
vegetable, of yeast, 71. 
epithelium, of saliva, 93. 
Cellular tissue, 26. 
Cerebellum, 232. 
structure of, 283. 
Cerebro-spinal nervous system, 294. 
Cerebrum, 231. 
situation, form, and structure 
of, 285. INDEX. 
389 
Cerebrum, functions of, 286. 
Chain of bones in the tympanum 
of the ear, 336. 
Cheese, 76. 
Chest, framework of, 167. 
movements of, in respiration, 
168. 
Childhood, transition from infancy, 
to, 364. 
growth of muscles during, 364. 
development of senses in, 365. 
change of dentition during, 
365—367. 
Chondrine, 213. 
Chords, vocal, 269. 
action of, in the formation of 
the voice, 275. 
Choroid coat of the eyeball, 310. 
Chyle, 111. 
absorption of, 123,129. 
Ciliary nerves, 317. 
Circulation of the blood, 182. 
organs of, 182. 
through the heart and lungs, 
186. 
through the arteries, 192. 
through the capillaries, 194. 
through the veins, 195. 
rapidity of, 196. 
variations of, 197. 
influence of the sympathetic 
nerves on, 300. 
Clot, 151. 
Coagulation, 64. 
of milk, 65. 
of the blood, 150. 
importance of, 152. 
Coat of the eyeball, sclerotic, 309. 
choroid, 310. 
Cochlea, 334. 
Collar-bone, 160. 
Colon, 88. 
Column, spinal, 22. 
Columns, anterior and posterior, 
of the spinal cord, 242. 
Concha, 340. 
Congestion, periodical, of the inter- 
nal organs, 100,197. 
Conjunctiva, 327. 
sensibility of, 330. 
Constrictors of the pharynx, 266. 
Contraction of the muscles, 26. 
of the heart, 185. 
Contrast, effect of, in light and col- 
or, 323. 
in sounds, 340. 
Convulsions from affections of the 
spinal cord, 252. 
Cornea, 310. 
Cranial nerves, 232. 
functions of, 256. 
fifth pair of, 257. 
Cranium, 22. 
ossification of, 361. 
Cream, 75. 
Creatine, 220. 
Creatinine, 220. 
Cribriform plate of the floor of 
the skull, 342. 
Crystalline, 213. 
Crystalline lens, 312. 
functions of, 313. 
Crystals, of fat, 58, 59. 
of the biliary salts, 139. 
Curvatures of the skeleton, 36. 
Decussation of motor and sensi- 
tive fibres of the spinal cord, 244. 
of the optic nerve§, 307. 
Deglutition, 97. 
action of the pneumogastric 
nerve in, 266. 
protection of the nostrils and 
glottis during, 267, 272. 
Dentition of infancy, 363. 
change of, during childhood, 
365. 
Development, 359. 
of the skeleton, 360, 367. 
of the teeth, 363, 366, 367. 
of the muscles, 364. 
of the senses, 365. 
of the mental powers, 368. 
Diaphragm, 164. 
movement of, in respiration, 
165. 
Digestibility of different kinds of 
food, 105. 
Digestion, 83. 
nature of, 84. 
apparatus and organs of, 85, 
86. 390 
INDEX. 
Digestion of albuminous matters, 
102. 
of milk, 102,103. 
of starch, 109. 
of fat, 111. 
products of, 115. 
Digestive apparatus, 85. 
periodical excitement of, 131. 
Digestive secretions, 85. 
properties and action of, 91, 
99,109, 110. 
reabsorption of, 126. 
Drum of the ear, 335. 
Duct, biliary, 88. 
pancreatic, 88. 
thoracic, 127. 
of a gland, 215. 
nasal, 329. 
Ear, internal, 335. 
tympanum or drum of, 335, 
336. 
external, 338. 
Ear-wax, 339. 
Eggs, 73. 
composition of, 74. 
effect of cooking on, 74. 
Elastic ligaments, 24. 
Elasticity of the skeleton, 35. 
of the arteries, 191. 
of the vocal chords, 274. 
Emulsion of fatty substances, 60. 
in digestion, 112. 
Enamel of the teeth, 89. 
Endosmosis, 121. 
Epithelium cells from the saliva, 
93. 
Eustachian tube, 336. 
Excretion, 217. 
products of, 218-220. 
Exercise necessary to health, 37. 
most useful kinds of, 38. 
Expiration, movement of, 164,167. 
Expression, movements of, 261. 
Extensor muscles, 28. 
Eye, 306. 
structure of, 306. 
orbit of, 309. 
necessary precautions in using, 
331. 
Eyeball, 309-312. 
'Eyeball, movements of, 325. 
protection of, from mechanical 
injury, 326. 
Eyelashes, 330. 
Eyelids, 326. 
movements of, 327. 
in winking, 328. 
Face, sensibility of, 257. 
neuralgia of, 259. 
motor nerve of, 261. 
paralysis of, 262. 
Facial nerve, 261. 
Eats, 57. 
different varieties of, 57. 
crystallization of, 58. 
emulsion of, 60. 
condition of, in the body, 61. 
proportion of, in different 
kinds of food, 62. 
decomposition of, in the body, 
63. 
Fat vesicles of adipose tissue, 61. 
digestion of, 114. 
Femur, 23. 
Fenestra, oval, 335. 
Ferment, 65. 
of yeast, 77. 
of the gastric juice, 103. 
Fermentation, nature and defini- 
tion of, 65. 
of sugar, 56. 
of bread, 77. 
of wine, 79. 
of beer, 80. 
Fibres, muscular, 25. 
Fibres, nervous, 228. 
two different kinds of, 233. 
sensitive, 233. 
motor, 234. 
Fibrine, 64. 
in the blood, 147. 
coagulation of, 151. 
daily decomposition and reno- 
vation of, 154. 
Fifth pair of cranial nerves, 257. 
sensibility of, 258. 
neuralgia of, 259. 
motor portion of, 259. 
Flexor muscles, 28. 
of the arm, 31. INDEX. 
391 
Follicles of Lieberkiihn, 109. 
of a gland, 215. 
Fontanelles, 361. 
Food, nature and necessity of, 45. 
ingredients of, 46-69. 
different kinds of, 72. 
essential qualities of, 81. 
daily quantity of, 82. 
digestion of, 85. 
Foramen, optic, 306. 
Function, definition of, xiv. 
of the bones, 19. 
of the elastic ligaments, 24. 
of the muscles, 26. 
of the tendons, 30. 
of the teeth, 90, 91. 
of the saliva, 94. 
of the tongue, 95. 
of the gastric juice, 101. 
of the intestinal juice, 109. 
of the pancreatic juice, 111. 
of the villi of the intestine, 121. 
of the lymphatic vessels, 128. 
of the liver, 135. 
of the gall-bladder, 137. 
of the bile, 139. 
of the blood globules, 149,173. 
of the lungs, 160. 
of the diaphragm, 165. 
of the intercostal muscles, 167. 
of the heart, 183. 
of the auricles, 183. 
of the ventricles, 183. 
of the valves in the heart, 187. 
of the perspiration, 204. 
of the nervous system, 227. 
of the nervous filaments, 232. 
of the nervous centres, or gan- 
glia, 235. 
of the spinal nerves, 238. 
of the spinal cord, 249. 
of the cranial nerves, 256. 
of the fifth pair of cranial 
nerves, 257. 
of the masticator nerve, 260. 
of the temporal muscle, 260. 
of the masseter muscle, 260. 
of the pterygoid muscles, 260. 
of the facial nerve, 261. 
of the third, fourth, and sixth 
pairs of cranial nerves, 262. 
Function of the hypoglossal nerve, 
263. 
of the pneumogastric nerve, 
266, 269, 276, 277. 
of the cerebrum, 286. 
of the tuber annulare, 288. 
of the medulla oblongata, 290. 
of the cerebro-spinal nervous 
system, 294. 
of the sympathetic nervous 
system, 294, 300. 
of the optic nerves, 308. 
of the choroid coat of the eye, 
310. 
of the retina, 311. 
of the crystalline lens, 313. 
of the muscles of the eyeball, 
325, 326. 
of the tears, 327. 
of the orbicularis muscle of 
the eye, 328. 
of the Meibomean glands and 
their secretion, 328, 329. 
of the eyelashes, 330. 
of the auditory nerve, 335. 
of the tympanum and chain 
of bones, 336. 
of the Eustachian tube, 336. 
of the olfactory nerves, 342. 
of the gustatory nerve, 346. 
of the glosso-pharyngeal nerve, 
350. 
Functions, classification of, xv. 
Galen, functions of recurrent nerve 
discovered by, 265. 
Gall-bladder, 137. 
Ganglion, 234. 
of the spinal cord, 249. 
Gasserian, 257. 
of the pneumogastric nerve, 
264. 
of the tuber annulare, 284,289. 
of the medulla oblongata, 283, 
286,291. 
semilunar, 298. 
of the sense of sight, 286, 306. 
ophthalmic, 316. 
of Meckel, 345. 
Gas, oxygen, 158. 
carbonic acid, 77, 79, 174. 392 
INDEX. 
Gases, putrefactive, 67. 
Gasserian ganglion, 257. 
Gastric juice, 99. 
secretion of, 100. 
composition of, 101. 
action of, in digestion, 101, 
103. 
abundance of, 104. 
Gastric tubules, 99. 
Gastrocnemius muscle, 32. 
General sensibility, 247. 
acuteness of, in different parts, 
248. 
Germination of seeds, production 
of sugar in, 55. 
Gland, parotid, 91. 
submaxillary, 91. 
sublingual, 91. 
structure of, 215. 
lachrymal, 327. 
Glands, salivary, 91. 
perspiratory, 204. 
Meibomean, 328. 
Glandules, mucous, of the mouth, 
92. 
Globules of oil, 59. 
of milk, 62. 
of the blood, 148. 
Glottis, structure of, 269. 
movements of, in respiration, 
270. 
protection of, in deglutition, 
272. 
action of, in the formation of 
the voice, 275. 
Gluten, 64. 
of wheat flour, 77. 
Gullet, 86. 
Gustatory nerve, 346. 
distribution of, to the tongue, 
347. 
Hanging palate, 268. 
Hearing, sense of, 333. 
Helix of the ear, 339. 
Heart, the, 183. 
different cavities of, 184. 
movements of, 185. 
circulation of blood through, 
186. 
valves of, 187,188. 
Heart, involuntary action of. 189. 
nerves of, 297, 299. 
Heat, animal, 200. 
necessary to life, 202. 
source of, 202. 
how produced, 203. 
variations and equalization of, 
203. 
regulation of, by perspiration, 
203-207. 
Hemiplegia, 245. 
Hepatic vein, 125. 
Hip-bone, 22. 
Humor, aqueous, 317. 
Hyaloid membrane of the eye, 312. 
Hydrophobia, 252. 
Hygiene, definition of, 13. 
Hypoglossal nerve, 263. 
Infancy, condition of the organs in, 
359-364. 
Inferior laryngeal nerve, 265. 
Inorganic substances in the tissues 
and in the food, 46. 
Insensible transpiration, 205. 
Inspiration, movement of, 164. 
how excited, 292. 
Instinct, nature of, 290. 
Intercostal muscles, 167. 
Intestine, large, 88. 
Intestine, small, 86. 
secretion of, 109. 
peristaltic movement of, 112. 
complete digestion of food in, 
113. , 
villi of, 120. 
veins of, 123. 
lymphatics of, 128. 
Intestinal juice, 109. 
action of, on starch, 110. 
Iris, 315. 
Iron, combinations of, in the food, 
51. 
Irritability of nervous fibres, 232. 
of the glottis, 271. 
of the conjunctiva, 330. 
Judgment, faculty of, 287. 
Juice, gastric, 99. 
intestinal, 109. 
pancreatic, 110. INDEX. 
393 
Jumping, movements of, 34. 
Keratine, 213. 
Labyrinth, 333. 
Lachrymal canals, 329. 
Lachrymal gland, 327. 
Lacteals, 127. 
and lymphatics, 130. 
Lactic acid in souring milk, 65. 
in gastric juice, 101. 
Large intestine, 88. 
Larynx, 161. 
nerves of, 264, 265. 
structure of, 269. 
movements of, in respiration, 
270. 
production of the voice in, 
274. 
Leaping, movements of, 34. 
Lens, crystalline, 312. 
function of, 313. 
Lieberkuhn, follicles of, 109. 
Ligaments, 21. 
elastic, 24. 
Lime in the bones, 19. 
proportion of, in different tis- 
sues and fluids, 50. 
in the food, 51. 
in the blood, 146. 
Lining membrane of the mouth, 92. 
of the stomach, 98. 
of the small intestine, 109,119. 
of the pharynx, 267. 
of the larynx, 271. 
of the eyelids, 327. 
of the nasal passages, 343. 
Liver, 134. 
situation and vascularity of, 
134. 
structure and secretion of, 135. 
distribution of portal vein in, 
124. 
formation of sugar in, 141. 
Lobules of the liver, 135. 
of the lungs, 162. 
of a gland, 215. 
Lungs, 160. 
structure of, 161-163. 
penetration of air into, 164. 
elasticity of, 167. 
Lungs, distribution of blood-vessels 
in, 170. 
circulation through, 172,186. 
distribution of pneumogastric 
nerve in, 276. 
Lymph, 128. 
Lymphatic vessels, 127-130. 
Magnesia, combinations of, in the 
food, 51. 
Mallet, 336. 
Margarine, 57. 
Marrow of the bones, 20. 
Masseter muscle, 260. 
Mastication, 88. 
organs of, 89. 
importance of the saliva in, 94. 
action of the tongue in, 95. 
effect of, on the food, 96. 
muscles of, 260. 
Masticator nerve, 260. 
Meat, 72. 
composition of, 72. 
effect of cooking on, 73. 
Meckel, ganglion of, 345. 
Medulla oblongata, 232. 
structure of, 283. 
function of, 290. 
Meibomean glands, 328. 
secretion of, 329. 
Membrane, hyaloid, of the eye, 
312. 
Membrane, lining, of the mouth, 
92. 
of the stomach, 98. 
of the small intestine, 109,119. 
of the pharynx, 267. 
of the larynx, 271. 
of the eyelids, 327. 
of the nasal passages, 343. 
Membrane of the tympanum, 336. 
variations in tension of, 338. 
Memory, 287. 
Mesentery, 129. 
Milk, composition of, 74. 
fermentation and souring of, 
65. 
digestion of, 104. 
Milk globules, 62. 
Milk teeth, 364. 
shedding of, 366. 394 
INDEX. 
Molasses, how obtained, 56. 
Motion, function of, 238. 
Motor nerves of the eyeball, 262. 
of the tongue, 263. 
of the larynx, 265. 
Motor nervous fibres, 234. 
Motor portion of the fifth pair of 
cranial nerves, 259. 
Mouth, 86. 
preparation of the food in, 72. 
Movements of walking, 32. 
of running, 34. 
of leaping, 34, 35. 
of mastication, 91. 
of deglutition, 98. 
peristaltic, of the stomach, 100. 
of the intestine, 112. 
of respiration, 164. 
of the heart, 185. 
of expression, 261. 
of the glottis in respiration, 
- 269. 
of the pupil, 316. 
of the eyeball, 325. 
of the eyelids, 326. 
Mucous glandules of the mouth, 92. 
Mucus, 214. 
of the gall-bladder, 137. 
Muscles, structure and action of, 
25. 
contraction of, 26. 
relaxation of, 27. 
flexor and extensor, 28. 
attachment and mechanism 
of, 30. 
protective action of, 36. 
of respiration, 164. 
intercostal, 167. 
of mastication, 260. 
of expression, 261. 
of deglutition, 266. 
of the hanging palate, 268. 
of the eyeball, 325. 
orbicularis, 328. 
of the bones of the tympanum, 
338. 
of the external ear, 340. 
growth of, during childhood, 
364. 
Muscular fibres, 25 
Musculine. 213. 
Musical notes, how produced, 341. 
Nasal duct, 329. 
Nasal passages, 342. 
sensibility of, 343. 
sympathetic nerves in, 345. 
Nerve, definition of, 229. 
trigeminal, 257. 
masticator, 260. 
facial, 261. 
hypoglossal, 263. 
pneumogastric, 263. 
superior laryngeal, 264. 
inferior laryngeal, 265. 
optic, 306. 
auditory, 333. 
olfactory, 342. 
gustatory, 346. 
glosso-pharyngeal, 350. 
Nerve cells, 234. 
Nerves, spinal, 238. 
intercostal and phrenic, 246. 
cranial, 256. 
of the eyeball, 262. 
of the larynx, 264, 265. 
sympathetic, 297. 
of special sense, 305. 
ciliary, 317. 
Nervous centre, 234. 
Nervous fibres, 228. 
structure of, 229. 
irritability of, 232. 
sensitive, 233. 
motor, 234. 
Nervous system, general structure 
and functions of, 227. 
reflex action of, 235. 
cerebro-spinal, 238-294. 
sympathetic, 297. 
of the infant, 363. 
Network, capillary, 193. 
Neuralgia, 259. 
Neurilemma, 230. 
Nitrogen, 159. 
Nucleus of nerve cells, 234. 
Nutrition, functions of, xv. 
definition of, 210. 
Oblique muscles of the eyeball, 325. 
action of, 326. 
CEsophagus, 86. INDEX. 
395 
CEsophagus, peristaltic action of, 
97. 
Oil globules, 59. 
of the liver cells, 62. 
of milk, 62. 
Oleaginous substances, 57. See 
“ Fats.” 
Oleine, 57. 
Olfactory nerves, 341. 
distribution of, 343. 
Ophthalmic ganglion, 316. 
action of, 317. 
Optic foramen, 306. 
Optic nerves, 306. 
decussation of, 307. 
termination of, in the retina, 
308. 
Optic thalami, 285. 
Optic tubercles, 306. 
reflex action in, 308. 
Orbicularis muscle of the eye, 
328. 
Orbit of the eye, 309. 
Organ, definition of, xiv. 
of the voice, 274. 
of the mind, 286. 
of the sight, 309. 
of hearing, 337. 
of smell, 343. 
of taste, 346. 
Organs of digestion, 86. 
of respiration, 160. 
of circulation, 182. 
of secretion, 215. 
united action of, 227. 
Ossification of the skeleton, 360. 
Osteine, 213. 
Oxygen, 158. 
importance of, 159. 
absorption of, in respiration, 
170. 
quantity of, consumed in res- 
piration, 173. 
Palate, hanging, 268. 
Pancreas, 110. 
secretion of, 110. 
Pancreatic duct, 88. 
Pancreatic juice, 110. 
composition of, 111. 
action of, in digestion, 111. 
!Pancreatine, 111. 
properties and action of, 112. 
Par vagum, 264. See “Pneumo- 
gastric nerve.” 
Paralysis, 239. 
from injury of the spinal cord, 
243. 
from injury of the brain, 245. 
of the intercostal muscles, 247. 
of the diaphragm, 247. 
of the face, 262. 
Paraplegia, 244. 
Parotid gland, 91. 
Passages, air, 161. 
nasal, 342. 
Pelvis, 22. 
of the infant, 361. 
ossification of, 367. 
Pepsine, 101. 
action of, in digestion, 103. 
Peristaltic action of the oesophagus, 
97. 
of the stomach, 100. 
of the small intestine, 112. 
Perspiration, 204. 
composition of, 205. 
function of, 205, 206. 
daily quantity of, 207. 
Perspiratory glands, 204. 
Petrous bone, 333. 
Pharynx, 86. 
nerves of, 264. 
constrictors of, 266. 
Pharyngeal branch of the pneumo- 
gastric nerve, 264. 
Phrenic nerves, 247. 
Physiology, definition of, 13. 
usefulness of, 13. 
Plexus, arterial, of the sympathetic 
nerves, 298. 
solar, 298. 
Pneumogastric nerve, 263. 
pharyngeal and laryngeal 
branches of, 264, 265. 
action of, in swallowing, 266. 
distribution of, to the lungs, 
276. 
to the stomach, 277. 
Pons Varolii, 284. 
Portal vein, 123. 
distribution of, in the liver, 124. 396 
INDEX. 
Potash, combinations of, in the 
food, 51. 
Pressure on the blood in the ar- 
teries, 192, 193. 
Protection of the nostrils during 
deglutition, 267. 
of the glottis during degluti- 
tion, 272. 
from injury by cold and wet, 
301. 
of the eyeball from mechanical 
injury, 326. 
of the eye by the sensibility 
of the conjunctiva, 330. 
Pterygoid muscles, 260. 
Ptyaline, 93. 
Pulmonary artery, 184. 
Pulmonary veins, 184. 
Pulse, 191. 
rapidity and characters of, 192. 
Pulsation of the heart, 185. 
of the arteries, 191. 
Pupil of the eye, 315. 
sensibility of, 309. 
movements of, 316. 
dilatation of, from mental emo- 
tion, 303. 
Putrefaction, 66. 
warmth and moisture neces- 
sary for, 67. 
Pylorus, 86. 
Quantity of blood in the body, 
155. 
Quantity, daily, of food, 81. 
of saliva, 93. 
of gastric juice, 104. 
of bile, 139. 
of air used in respiration, 169. 
of oxygen consumed, 173. 
of carbonic acid exhaled, 174. 
of perspiration, 207. 
of urea produced by excretion, 
219. 
Radial arteiy, 192. 
Reabsorption of the digestive fluids, 
126. 
Reason, 288. 
Receptaculum chyli, 129. 
Rectum, 88. 
Recurrent laryngeal nerve, 265. 
Red globules of the blood, 148. 
Reflex action of the nervous sys- 
tem, 235. 
of the spinal cord, 250. 
of deglutition, 266. 
of the tuber annulare, 290. 
of respiration, 292. 
of the sympathetic system, 302. 
of the optic tubercles, 308,316. 
of winking, 328. 
Relaxation of the muscles, 27. 
of the heart, 186. 
Rennet, 76. 
Repose, necessity for, 39. 
Respiration, 158. 
organs of, 160. 
movements of, 164. 
frequency of, 169. 
quantity of air used in, 169. 
changes of the air in, 170. 
change of the blood in, 171. 
action of the blood globules in, 
173. 
evolution of carbonic acid in, 
174. 
exhalation of water and ani- 
mal vapors in, 175. 
contamination of the air by, 
176. 
movements of the glottis in, 
269. 
nervous centre of, 290. 
reflex nature of, 292. 
Respiratory movements of the 
chest, 164. 
of the glottis, 270. 
Retina, 811. 
termination of optic nerve in, 
308. 
Reunion of divided nerves, 240. 
Ribs, 166. 
movement of, in respiration, 
167. 
Roots of the spinal nerves, sensi- 
tive and motor, 240. 
Running, movements of, 341. 
Saliva, 91. 
secretion of, 92. 
composition of, 93. INDEX. 
397 
Saliva, daily quantity of, 94. 
function of, 94. 
Salivary glands, 91. 
Salt, common, an ingredient of the 
food, 48. 
proportion of, in the tissues 
and fluids, 48. 
importance of, 49. 
in the blood, 146. 
Salts, biliary, 138. 
crystallization of, 139. 
decomposition of, in the intes- 
tine, 140. 
Sclerotic coat of the eyeball, 309. 
Sebaceous matter of the skin, 207. 
of the eyelids, 329. 
Secretion, 214. 
of the saliva, 92. 
of the gastric juice, 99,100. 
of the intestinal juice, 109. 
of the pancreatic juice, 110. 
of the bile, 135. 
of the perspiration, 205. 
of the tears, 327. 
of the Meibomean glands, 329. 
Semicircular canals, 334. 
Semilunar ganglion of the sympa- 
thetic nerve, 298. 
Sensation, 238. 
ganglion of, 288. 
Sense of touch, 247, 248. 
of sight, 306. 
of hearing, 333. 
of smell, 341. 
of taste, 346. 
Senses, development of, 365. 
Sensibility, acuteness of, in differ- 
ent parts, 247. 
to pain, 248. 
to heat and cold, 249. 
of the face, 257, 258. 
of the glottis, 271. 
of the pupil, 309. 
of the conjunctiva, 330. 
Sensitive nerves of the face, 258. 
of the larynx, 264. 
Sensitive nervous fibres, 233. 
Serum, 151. 
Seventh pair of cranial nerves, 261. 
Sheath of the nerves, 230. 
Sight, sense of, 306. 1 
Sight, organ of, 309. 
Sinews, 30. 
Skeleton, 21. 
balancing of, 23. 
elasticity of, 35. 
ossification of, 360. 
Skull, 22. 
of the infant, 360. 
ossification of, 361. 
Small intestine, 86. 
entrance of food into, 108. 
secretion of, 109. 
peristaltic movement of, 112. 
digestion in, 110-116. 
lining membrane of, 109,119. 
villi of, 120. 
lymphatics of, 128. 
Smell, sense of, 341. 
nerves of, 342. 
usefulness of, 345. 
Soda, combinations of, in the food, 
51. 
in the biliary salts, 138. 
urate of, 220. 
Solar plexus of the sympathetic 
nerves, 298. 
Soleus muscle, 32. 
Solidity and projection, apprecia- 
tion of, by the eyes, 320. 
Sound, how produced, 274. 
Special sense, nerves of, 305. 
organs of, 306. 
Special senses, definition of, 305. 
Spinal canal, 231. 
Spinal column, 21. 
of the infant, 360. 
ossification of, 361. 
Spinal cord, 230. 
form and structure of,241,242. 
effects of injury to, 243. 
decussation of, 244. 
action of, as a nervous centre, 
249. 
reflex action of, 250. 
Spinal nerves, 231. 
distribution and functions of, 
238. 
effects of injury to, 239. 
reunion of, after division, 240. 
sensitive and motor roots of, 
240. 398 
INDEX. 
Spinal nerves, termination of, in 1 
the brain, 242. 
Starch, 51. 
of the potato, 52. 
of wheat flour, 52. 
of Indian corn, 53. 
proportion of, in different kinds 
of food, 53. 
effect of boiling on, 54. 
conversion of, into sugar, 54. 
change of, in bread-making, 78. 
digestion of, 109. 
Stearine, 57. 
crystallization of, 58. 
Stereoscope, 322. 
Stirrup, 336. 
Stomach, 86. 
lining membrane of, 98. 
secretion of, 99. 
peristaltic action of, 100. 
distribution of pneumogastric 
nerve to, 276. 
influence of pneumogastric 
nerve on, 277. 
Straight muscles of the eyeball, 325. 
Striated bodies, 285. 
Sublingual gland, 91. 
Submaxillary gland, 91. 
Sugar, 55. 
different varieties of, 56. 
quantity of, in various kinds 
of food, 56. 
fermentation of, 56. 
disappearance of, in the body, 
57. 
formation of, in the liver, 141. 
absorption and decomposition 
of, 142. 
Superior laryngeal nerve, 264. 
Swallowing, 97. See “ Degluti- 
tion.” 
Sympathetic nervous system, defi- 
nition and functions of, 294. 
general arrangement of, 297. 
influence of, on the internal 
organs, 300. 
sluggish and continued action 
of, 300. 
reflex action of, 302. 
Taste, sense of, 346. 
requisite conditions for, 347. 
Taste, uses of, 348. 
associated with the sense of 
touch, 95, 96, 349. 
Tears, secretion of, 327. 
passage of, into the nostrils, 
329. 
Teeth, 89. 
incisor, 90. 
canine, 90. 
molar, 90. 
first appearance of, 363. 
first set of, 364. 
second set of, 367. 
Temperature of the interior of the 
body, 201. 
Temporal artery, 192. 
Temporal muscle, 260. 
Tendon of Achilles, 32. 
Tendons, 30. 
Tetanus, 252. 
Thaumatrope, 324. 
Thigh-bone, 23. 
Thoracic duct, 127. 
Tibia, 23. 
Tic douloureux, 259. 
Tissue, cellular, 26. 
adipose, 61. 
Tongue, action of, in mastication, 
95. 
sensibility of, 95, 96, 257, 346, 
349. 
distribution of nerves to, 346, 
347, 350. 
Touch, sense of, 247, 248. 
in the tongue, 96, 349. 
! Trachea, 161. 
Tragus, 339. 
Transpiration, insensible, 205. 
Trigeminal nerve, 257. 
Trochlearis muscle of the eyeball, 
325. 
Tube, Eustachian, 336. 
Tuber annulare, 284. 
functions of, 288. 
Tympanum of the ear, 335. 
membrane of, 336. 
Urate of soda, 220. 
Urea, 219. 
how produced and discharged, 
219, 220. INDEX. 
399 
Uvula, 268. 
Valves of the heart, 187-189. 
of the veins, 196. 
Valvulse conniventes, 120. 
Vapor, animal, discharged with the 
breath, 175. 
Varolius, bridge of, 284. 
Vegetables, preparation of, by cook- 
ing, 81. 
Vein, portal, 123. 
hepatic, 125. 
subclavian, 128. 
Veins, pulmonary, 184. 
movement of the blood in, 195. 
valves of, 196. 
Venous blood, 171. 
change of, in respiration, 172. 
Ventilation, necessity for, 175. 
means of, 176. 
Ventricles of the heart, 183,184. 
Vermicular action, 97. 
Vestibule of the internal ear, 333. 
Villi of the intestine, 53. 
absorption by, 121. 
Vision, organ of, 309. 
with and without a crystalline 
lens, 313. 
field of, 317. 
line of distinct, 317. 
single and double, 319, 320. 
with both eyes, 319, 321. 
Visual impressions, persistence of, 
323. 
of internal origin, 324. 
Vitreous body of the eye, 312. 
Vocal chords, 269. 
action of, in formation of the 
voice, 275. 
Vocal sounds, how produced, 274. 
Voice, formation of, 274. 
Volition, 288, 289. 
Walking, movements of, 32. 
Washing, necessity for, 207. 
Water, 46. 
proportion of, in the animal 
tissues and fluids, 47. 
daily quantity of, required, 47, 
48. 
discharge of, from the body, 
48. 
in the blood, 146. 
exhalation of, with the breath, 
175. 
with the perspiration, 207. 
White globules of the blood, 150. 
Wine, 78. 
fermentation of, 79. 
sparkling or effervescent, 80. 
Winking, 327. 
how performed, 328. 
Wisdom teeth, 367. 
Yeast, vegetable growth of, 71. 
Youth, transition from childhood 
to, 367. 
development of the organs in, 
367, 368. 
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