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A 
COMPEND 
OF 
HUMAN PHYSIOLOGY. 
ESPECIALLY ADAPTED FOR THE USE OF 
MEDICAL STUDENTS. 
ALBERT P. BRUBAKER, A.M., M.D., 
BY 
ADJUNCT PROFESSOR OF PHYSIOLOGY AND HYGIENE IN THE JEFFERSON MEDICAL COL 
LEGE; PROFESSOR OF PHYSIOLOGY IN THE PENNSYLVANIA COLLEGE OF DENTAL 
surgery; lecturer on anatomy and physiology in the drexel 
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In the Office of the Librarian of Congress, at Washington, D. C. 
Press of Wm. F. Fell & Co., 
1220-24 Sansom St., 
PHILADELPHIA. PREFACE TO EIGHTH EDITION. 
The preparation of an eighth edition of the Compend of Physiology has 
furnished the opportunity for a revision of a portion of the text and for the 
insertion of some fifteen pages of additional matter, both of which it is 
believed will materially enhance its value for medical and dental students 
during their attendance on the lectures and in reviewing the subject prior 
to examinations. 
It is also believed that the chapters on the Physiologic Anatomy of the 
Skeleton and the Joints, the Physiology of Muscular Tissue and of Special 
Muscular Groups, will adapt it to the necessities of those Normal and High 
Schools in which it has already been in use. 
Notwithstanding the many additions which have been made in this and 
previous editions, care has been taken to keep the Compend what it was 
originally intended to be, viz.: a compact and convenient arrangement of 
the fundamental facts of human physiology. 
Again, my thanks are due to all those teachers who have kindly noticed 
and recommended the Compend to their students. That it may continue 
to merit the approval of both teachers and students is my earnest wish. 
ALBERT P. BRUBAKER. 
V TABLE OF CONTENTS. 
Introduction, 9 
General Structure of the Animal Body, 10 
The Skeleton, 32 
Structure and Mechanism of Joints, 37 
Physiology of the Tissues 26 
Chemic Composition of the Body, 14 
Foods and Dietetics, .... 73 
Digestion, 82 
Absorption, 98 
Blood, 106 
Circulation of Blood, 112 
Respiration, 120 
Animal Heat, 128 
Secretion, 131 
Mammary Glands, 133 
Vascular Glands, 136 
Excretion, 137 
Kidneys, . 137 
Liver, 145 
Skin, 149 
Nervous Tissue, Physiology of, 62 
Properties and Functions of Nerves, 67 
Cranial Nerves, 165 
Spinal Cord, 154 
Spinal Nerves, 156 
PAGE 
VII VIII 
TABLE OF CONTENTS. 
Medulla Oblongata, 178 
Pons Varolii, 183 
Crura Cerebri, 183 
Corpora Quadrigemina, 184 
Corpora Striata and Optic Thalami, 185 
Cerebellum, 1S6 
Cerebrum, 188 
Sympathetic Nervous System, 199 
Sense of Touch, 203 
Sense of Taste, 204 
Sense of Smell, 206 
Sense of Sight 207 
Sense of Hearing 218 
Voice and Speech, 226 
Reproduction, 228 
Generative Organs of the Female, 228 
Generative Organs of the Male, 231 
Development of Accessory Structures, 232 
.Development of the Embryo, 237 
Table of Physiological Constants, 243 
Table Showing Relation of Weights and Measures, . . . 246 
Index 248 
PAGE COMPEND 
OF 
HUMAN PHYSIOLOGY. 
INTRODUCTION. 
Definitions.—If the body of any animal be dissected it will be found 
to be composed of a number of well-defined structures, such as heart, lungs, 
stomach, brain, eye, etc., to which the term organ was originally applied, 
for the reason that they were supposed to be instruments capable of per- 
forming some important act or function in the general activities of the body. 
Though the term organ is usually employed to designate the larger and 
more familiar structures just mentioned, it is equally applicable to a large 
number of other structures which, though possibly less obvious, are equally 
important in maintaining the life of the individual, e. g., bones, muscles, 
nerves, skin, teeth, glands, blood-vessels, etc. Indeed, any complexly or- 
ganized structure capable of performing some function may be described as 
an organ. A description of the various organs which make up the body 
of an animal, their external form, their internal arrangement, their relations 
to each other, constitutes the science of Animal Anatomy. 
This may naturally be divided into :— 
1. Special Anatomy, the object of which is the investigation of the con- 
struction, form, and arrangement of the organs of any individual animal. 
2. Comparative Anatomy, the object of which is a comparison of the organs 
of two or more animals, with a view of determining their points of re- 
semblance or dissimilarity. 
Human Anatomy is that department of anatomical science which has 
for its object the investigation of the construction of the human body. 
An investigation of the vital phenomena exhibited by an animal, or of the 
9 10 
HUMAN PHYSIOLOGY. 
functions performed by its various organs, constitutes the science of 
Animal Physiology. 
This may naturally be divided into :— 
1. Special Physiology, the object of which is a study of the vital phenomena 
or functions characteristic of any individual animal. 
2. Contparalive Physiology, the object of which is a comparison of the 
vital phenomena or functions exhibited by the organs of two or more 
animals, with a view of unfolding their points of resemblance or dis- 
similarity. 
Human Physiology is that department of physiologic science which 
has for its object the study of the functions of the organs of the human 
body in a state of health. 
GENERAL STRUCTURE OF THE ANIMAL BODY. 
The body of every animal, from fish to man, may be divided into— 
1. An axial, and 
2. An appendicular portion. The axial portion consists of the head, neck, 
and trunk ; the appendicular portion consists of the anterior and posterior 
limbs or extremities. 
The Axial Portion of all mammals, to which class man zoologically be- 
longs, as well as of all birds, reptiles, amphibians, and fish, is characterized 
by the presence of a bony, segmented axis, which extends in a longitudinal 
direction from before backward, and which is known as the vertebral column 
or backbone. In virtue of the existence of this column all the classes of 
animals just mentioned form one great division of the animal kingdom, the 
Vertebrata. 
Each segment, or vertebra, of this axis consists of— 
1. A solid portion known as the body or centrum, and 
2. A bony arch arising from the dorsal aspect and surmounted by a spine- 
like process. At the anterior extremity of the body of the animal the 
vertebrae are variously modified and expanded, and with the addition of 
new elements form the skull. At the posterior extremity it rapidly dimin- 
ishes in size and terminates in man in a short, tail-like process. In many 
animals, however, the column extends for a considerable distance beyond 
the trunk into the tail. The vertebral column may be regarded as the 
foundation element in the plan of organization of all the higher animals 
and the center around which the rest of the body is developed and ar- 
ranged wTith a certain degree of conformity. In all vertebrate animals 
the bodies of the segment of the vertebral column form a partition which GENERAL STRUCTURE OF THE ANIMAL BODY. 
11 
serves to divide the trunk of the body into two cavities, viz., the dorsal 
and the ventral. 
The dorsal cavity is found not only in the trunk, but also in the head. 
Its walls are formed partly by the arches which arise from the posterior or 
dorsal surface of the vertebra and partly by the bones of the skull. If 
a longitudinal section be made through the center of the vertebral 
column, and including the head, the dorsal cavity will be observed running 
through its entire extent. Though for the most part it is quite narrow, at 
the anterior extremity it is enlarged and forms the cavity of the skull. 
Throughout this cavity is lined by a membranous canal, the neural canal, 
in which is contained the brain and the neural or spinal cord. Through 
openings in the sides of the dorsal cavity nerves pass out which connect the 
brain and spinal cord with all of the structures of the body. 
The ventral cavity is confined mainly to the trunk of the body. Its 
walls are formed by muscles and skin, strengthened in most animals by 
bony arches, the ribs. Within the ventral cavity is contained a musculo- 
membranous tube or canal known as the alimentary or food canal, which 
begins at the mouth on the ventral side of the head, and after passing 
through the neck and trunk terminates at the posterior extremity of the 
trunk at the anus. It may be divided into mouth, pharynx, esophagus, 
stomach, small and large intestine. 
In all mammals the ventral cavity is divided by a musculo-membranous 
partition into two smaller cavities, the thorax and abdomen. The former 
contains the lungs, heart, and its great blood-vessels, and the anterior part 
of the alimentary canal, the gullet or esophagus; the latter contains the 
continuation of the alimentary canal, that is, the stomach and intestines, 
and the glands in connection with it, the liver and pancreas. In the pos- 
terior portion of the abdominal cavity are found the kidneys and bladder, 
and in the female the organs of reproduction. The thoracic and abdominal 
cavities are each lined by a thin, serous membrane known, respectively, as 
the pleural and peritoneal membranes, which in addition are reflected over 
the surfaces of the organs contained within them. The alimentary canal 
and the various cavities connected with it are lined throughout by a mucous 
membrane. The surface of the body is covered by the skin. This is com- 
posed of an inner portion, the derma, and an outer portion, the epidermis. 
The former consists of fibers, blood-vessels, nerves, etc., the latter of layers 
of scales or cells. Imbedded within the skin are numbers of glands which 
exude, in the different classes of animals, sweat, oily matter, etc. Projecting 
from the surface of the skin are hairs, bristles, feathers, claws. Beneath 
the skin are found muscles, bones, blood-vessels, nerves, etc. 12 
HUMAN PHYSIOLOGY. 
The Appendicular Portion of the body consists of two pairs of sym- 
metric limbs which project from the sides of the trunk and which bear a 
determinate relation to the vertebral column. They consist fundamentally 
of bones surrounded by muscles, blood-vessels, nerves, and lymphatics. 
The limbs, though having a common plan of organization, are modified in 
form and adapted for prehension and locomotion, in accordance with the 
needs of the animal. 
Anatomic Systems.—All the organs of the body which have certain 
peculiarities of structure in common are classified by anatomists into sys- 
tems, e.g., the bones, collectively, constitute the bony or osseous system ; 
the muscles, the nerves, the skin, constitute, respectively, the muscular, the 
nervous, and tegumentary systems. 
Physiologic Apparatuses.—More important from a physiologic point 
of view than a classification of organs based on similarities of structure, 
is the natural association of two or more organs acting together for the 
accomplishment of some definite object, and to which the term physiologic 
apparatus has been given. While in the community of organs, which to- 
gether constitute the animal body, each one performs some definite func- 
tion, and the harmonious cooperation of all necessary to the life of the 
individual, everywhere it is found that two or more organs, though per- 
forming totally distinct functions, are cooperating for the accomplishment 
of some larger or compound function in which their individual functions 
are blended, e. g., the mouth, stomach, and intestines with the glands 
connected with them constitute the digestive apparatus, the object or func- 
tion of which is the complete digestion of the food. The capillary blood- 
vessels and lymphatic vessels of the body, and especially those in relation 
to the villi of the small intestine, constitute the absorptive apparatus, the 
function of which is the introduction of new material into the blood. The 
heart and blood-vessels constitute the circulatory apparatus, the function 
of which is the distribution of blood to all portions of the body. The 
lungs and trachea, together with the diaphragm and the walls of the chest, 
constitute the respiratory apparatus, the function of which is the introduc- 
tion of oxygen into the blood and the elimination from it of carbon dioxid 
and other injurious products. The kidneys, the ureter, and bladder consti- 
tute the urinary apparatus. The skin with its sweat-glands constitutes 
the perspiratory apparatus, the functions of both being the excretion of 
waste products from the body. The liver, the pancreas, the mammary 
glands, as well as other glands, each form a secretory apparatus, which 
elaborates some specific material necessary to the nutrition of the indi- GENERAL STRUCTURE OF THE ANIMAL BODY. 
13 
vidual. The functions of these different physiologic apparatuses, e. g., 
digestion, the absorption of food, and the elaboration of blood, the circula- 
tion of blood, respiration, and the production of heat secretion and excre- 
tion, are classified as nutritive functions, and have for their final object 
the preservation of the individual. 
The nerves and muscles constitute the nervo-muscular apparatus, the 
function of which is the production of motion. The eye, the ear, the nose, 
the tongue, and the skin with their related structures constitute, respectively, 
the visual, auditory, olfactory, gustatory, and tactile apparatuses, the func- 
tion of which as a whole is the reception of impressions and the transmission 
of nerve impulses to the brain, where they give rise to visual, auditory, 
olfactory, gustatory, and tactile sensations. 
The brain, in association with the sense organs, forms an apparatus 
related to mental processes. The larynx and its accessory organs, the 
lungs, trachea, respiratory muscles, the mouth and resonant cavities of the 
face form the vocal and articulating apparatus, by means of which voice 
and articulate speech are produced. The functions exhibited by the 
apparatuses just mentioned, viz., motion, sensation, language, mental and 
moral manifestations, are classified as functions of relation, as they serve 
to bring the individual into conscious relationship with the external world. 
The ovaries and the testes are the essential reproductive organs, the for- 
mer producing the germ-cell, the latter the spermatic element; together, 
with their related structures, the Fallopian tubes, uterus, and vagina in the 
female, and the urogenital canal in the male, they constitute the repro- 
ductive apparatus characteristic of the two sexes. Their cooperation 
results in the union of the germ-cell and spermatic element and the con- 
sequent development of a new being. The function of reproduction 
serves to perpetuate the species to which the individual belongs. 
The animal body is therefore not a homogeneous organism, but one com- 
posed of a large number of widely dissimilar but related organs. But as 
all vertebrate animals have the same general plan of organization, there is 
a marked similarity both in form and structure among corresponding parts 
of different animals. Hence it is that in the study of human anatomy a 
knowledge of the form, construction, and arrangement of the organs in 
different types of animal life is essential to its correct interpretation; 
hence it is that in the investigation and comprehension of the complex 
problems of human physiology a knowledge of the functions of the 
organs as they manifest themselves in the different types of animal life is 
indispensable. As many of the functions of the human body are not only 
complex, but the organs exhibiting them are practically inaccessible to in- 14 
HUMAN PHYSIOLOGY. 
vestigation, we must supplement our knowledge and judge of their func- 
tions by analogy, by attributing to them, within certain limits, the functions 
revealed by experimentation upon the corresponding but simpler organs of 
lower animals. This experimental knowledge, corrected by a study of 
the clinical phenomena of disease and the results of postmortem investi- 
gation, forms the basis of modern human physiology. 
CHEMIC COMPOSITION OF THE HUMAN 
BODY. 
Since it has been demonstrated that every exhibition of functional activ- 
ity is associated with changes of structure, it has been apparent that not 
only is a knowledge of the chemic composition of the body when in a 
state of rest, but to a far greater degree when in a state of activity, neces- 
sary to a correct understanding of the intimate nature of physiologic pro- 
cesses. Though the analysis of the dead body is comparatively easy, the 
determination of the successive changes in composition of the living body 
is attended with many difficulties. The living material, the protoplasm, is 
not only complex and unstable in composition, but extremely sensitive to 
all physical and chemic influences. The methods, therefore, which are em- 
ployed for analysis destroy its composition and vitality, and the products 
which are obtained are peculiar to dead rather than to living matter. 
Chemic analysis, therefore, may be directed— 
1. To the determination of the composition of the dead body. 
2. To the determination of the successive changes which the living proto- 
plasm undergoes during functional activity. 
A chemic analysis of the dead body, with a view of disclosing the sub- 
stances of which it is composed, their properties, their intimate structure, 
their relationship to each, constitutes what might be termed Chemic Anat- 
omy. An investigation of the living material and of the successive changes 
it undergoes in the performance of its functions constitute what has been 
termed Chemic Physiology or Physiologic Chemistry. 
By chemic analysis the animal body can be reduced to a number of 
liquid and solid compounds which belong to both the inorganic and or- 
ganic worlds. The compounds resulting from a proximate analysis have 
been termed proximate principles. That they may merit this term, how- 
ever, they must be obtained in the same form under which they exist in the 
living condition. The inorganic compounds consist of water and various CHEMIC COMPOSITION OF THE HUMAN BODY. 
15 
inorganic salts; the organic compounds consist of representatives of the 
carbohydrate, fatty, and proteid groups of organic bodies. 
The proximate principles thus obtained can be further resolved by an 
ultimate analysis into a small number of chemic elements which are iden- 
tical with elements found in many other inorganic as well as organic com- 
pounds. The different chemic elements which are thus obtained, and the 
percentage in which they exist in the body, are shown in the following 
table:— 
ELEMENTARY COMPOSITION OF THE BODY. 
Oxygen, . . . 72.00 
Hydrogen, . . 9.10 
Nitrogen, . . 2.50 
Carbon, . . . 13.50 
O. H. and C. are found in all the tissues and 
fluids of the body, without exception. 
O. H. C. and N. found in most of the fluids 
and all tissues except fat. 
Sulphur, . . .147 . . In fibrin, casein, albumin, gelatin; as potas- 
sium sulphocyanid in saliva; as alkaline 
sulphate in urine and sweat. 
Phosphorus, . 1.15 . . In fibrin and albumin; in brain; as trisodium 
phosphate in blood and saliva, etc. 
Calcium, . . 1.30 . . As calcium phosphate in lymph, chyle, blood, 
saliva, bones, and teeth. 
Sodium, ... .10 . . As sodium chlorid in all fluids and solids of 
the body, except enamel; as sodium sul- 
phate and phosphate in blood and muscles. 
Potassium, . . .026 . . As potassium chlorid in muscles; generally 
found with sodium as sulphates and phos- 
phates. 
Magnesium, . .001 . . Generally in association with calcium, as phos- 
phate, in bones. 
Chlorin, . . . .085 . . In combination with sodium, potassium, and 
other bases, in all the fluids and solids. 
Fluorin, . . . .08 . . As calcium fluorid in bones, teeth, and urine. 
Iron, 01 . . In blood-globules; as peroxid in muscles. 
Silicon, ... a trace . . In blood, bones, and hair. 
Manganesium, a trace . . Probably in hair, bones, and nails. 
Of the four chief elements which together make up 97 per cent. 
of the body, O. H. N. are eminently mobile, elastic, and possess great 
atomic heat. C. H. N. are distinguished for the narrow range and feeble- 
ness of their affinities and chemical inertia. C. has the greatest atomic 
cohesion. O. is noted for the number and intensity of its combinations 
and its remarkable display of chemic activity. 
Chemic Elements, with the exception of the gases, O. H. and N., 
do not exist alone in the body, but are combined in characteristic propor- 16 
HUMAN PHYSIOLOGY. 
tions to form compounds, the proximate principles, the ultimate compounds 
to which the fluids and solids can be reduced. 
Proximate Principles may be divided into four classes, viz. : Inor- 
ganic, organic non-nitrogenized, organic nitrogenized, and principles of 
waste. 
Substance. Where found. 
Oxygen, Lungs and blood. 
Hydrogen, Stomach and intestines. 
Nitrogen Blood and intestines. 
Carbonic anhydrid, .... Expired air of lungs. 
I. INORGANIC proximate principles. 
Carburetted hydrogen, 
Sulphuretted hydrogen, 
Water, Found in all solids and fluids. 
Sodium chlorid, In all fluids and solids except enamel. 
Potassium chlorid, .... In muscles, liver, saliva, gastric juice, etc. 
Ammonium chlorid, . . . Gastric juice, saliva, tears, urine. 
Calcium chlorid, Bones, teeth, urine. 
Calcium carbonate, .... Bones, teeth, cartilage, internal ear, blood. 
Lungs and intestines. 
Calcium phosphate, 
Magnesium phosphate, 
Sodium phosphate, 
Potassium phosphate, 
In all fluids and solids of the body. 
Sodium sulphate, 
Potassium sulphate, 
Universal except milk, bile, and gastric juice. 
Sodium carbonate, 
Potassium carbonate, 
Bones, blood, lymph, urine, etc. 
Magnesium carbonate, . . Blood and sebaceous matter. 
Oxygen is one of the constituent elements of all the fluids and solids of 
the body. It is found in a free state in the respiratory passages and intesti- 
nal tract; it is held in solution in the lymph and plasma and forms a loose 
combination with the hemoglobin of the blood-corpuscles. The function 
of the oxygen in the body appears to be the oxidation of albuminous, 
oleaginous, and saccharine compounds to their ultimate forms, urea, car- 
bonic acid, water, etc. As to whether this is brought about by direct oxi- 
dation or by a fermentative process is yet unknown. As oxygen only enters 
into combination under a high temperature, it is assumed that it exists in 
the body under the form of ozone, 03, which possesses remarkably active 
oxidizing powers. The seat of oxidation is at present located in the tissues, 
as the presence of ozone in the blood has not been positively demonstrated. 
Hydrogen is also a constituent element of almost all the compounds of 
the body; it exists in a free state in the intestinal tract, where it is produced 
by a decomposition of organic substances; it is also produced within the CHEMIC COMPOSITION OF THE HUMAN BODY. 
17 
tissues as a result of chemic changes. Its function is unknown, though 
it is asserted by Hoppe-Seyler that hydrogen unites with neutral oxygen, 
02, in the tissues, forming water and liberating oxygen in the nascent state, 
which becomes the oxidizing agent. The process is represented in the fol- 
lowing equation:— 
HH -f- 02 -f- n = H20 -f- On, 
in which n represents the oxidizable substance. 
Water is an essential constituent of all the tissues of the body, consti- 
tuting about 70 per cent, of the entire body weight. It is introduced 
into the body in the form of drink and as a constituent of all kinds of food. 
The average quantity consumed daily is about four pints. While in the 
body, water acts as a general solvent, gives pliability to various tissues, and 
promotes the passage of inorganic and organic matters through animal 
membranes. It also promotes chemic changes which are essential to 
absorption and assimilation of food and the elimination of products of 
waste. It is probable that water is also formed within the body by the 
union of oxygen with the surplus hydrogen of the food. It is eliminated 
by the skin, lungs, and kidneys. 
Sodium chlorid is present in all the solids and fluids of the body, with 
the exception of enamel. It regulates osmotic action, holds the albuminous 
principles of the blood in solution, and preserves the form and consistence 
of blood corpuscles and the cellular elements of the tissues by regulating 
the amount of water entering into their composition. 
Calcium phosphate is the most abundant of all the inorganic principles 
with the exception of water, and is present to a great extent in bone, teeth, 
muscles, and milk. It gives the requisite consistency and solidity to the 
different tissues and organs. In the blood, it is held in solution by the 
albuminous constituents. 
The Sodium and Potassium phosphates are present in most of the solids 
and fluids, and give to them their alkaline reaction. They are chiefly de- 
rived from the food. 
II. ORGANIC NONNITROGENIZED PRINCIPLES. 
The organic nonnitrogenized principles are derived mainly from the 
vegetable world, but are also produced within the animal body. They are 
divided into :—• 
i. The carbohydrates, comprising starch and sugar, bodies in which the 
oxygen and hydrogen exist in the proportion to form water, the amount 
of carbon being variable. 18 
HUMAN PHYSIOLOGY. 
2. The fats, bodies having the same elements entering into their composition, 
but with the carbon and hydrogen increased and the oxygen diminished 
in amount. 
3. Fatty acids. 
4. Alcohols. 
Dextrose Group. Cane-Sugar Group. 
Dextrose (Glucose, grape sugar). Saccharose (cane sugar). 
Levulose. Maltose. 
Galactose. Lactose. 
sugars, c. H. o. 
The members of the dextrose group have a composition as follows: 
CfiHi206, and are frequently spoken of as monosaccharids. The members 
of the cane-sugar group have a composition as follows: C12H22On, and are 
frequently spoken of as disaccharids. 
Dextrose has been found in many of the tissues and fluids of the body 
as a normal constituent. As it is readily assimilable, it is probable that 
under this form the carbohydrates are absorbed into the blood. As its name 
implies, it rotates the plane of polarized light to the right. 
Levulose is found in the stomach and intestine, and occasionally in the 
urine. It is formed by a decomposition of saccharose. While resembling 
dextrose in many respects, it differs from it in rotating the plane of polarized 
light to the left. 
Galactose can be obtained from brain substance by the action of boiling 
sulphuric acid and by the decomposition of lactose. It is also dextro- 
rotatory. 
Saccharose is the form of sugar largely consumed as food. It is largely 
distributed throughout the vegetable kingdom in the juices of fruits and 
plants. It is not found, however, as a constituent of any of the fluids or 
solids of the body. During its passage through the stomach and intestine 
it is converted by the action of ferments into equal parts of dextrose and 
levulose by the assumption of a molecule of water. Cane sugar is, there- 
fore, not absorbed under its own form, as it is nonassimilable, appearing in 
the urine after its injection into the blood. 
Maltose is the final product formed by the action of saliva and a pancreatic 
juice on starch paste. It is also nonassimilable, and is, probably, con- 
verted into dextrose after or during absorption. 
Lactose is the form of sugar naturally present in milk. It resembles the 
two preceding forms in being nonassimilable and nonfermentable. 
Glycogen is the only form of starch found as a constituent of the animal 
tissues. It is closely related to the sugars. CHEMIC COMPOSITION OF THE HUMAN BODY. 
19 
The sugar of the body is derived from the food. After being converted 
into dextrose in the alimentary canal, it is absorbed into the blood by the 
veins of the portal system, and for the most part stored up in the liver 
under the form of glycogen. When the tissues require sugar for the per- 
formance of their normal activities, it is returned to the circulation and 
carried to all portions of the body. Whatever the intermediate stages may 
be, sugar is ultimately oxidized, contributing to the production of heat. It 
is eliminated under the forms of C02 and H20. 
NEUTRAL FATS. C. O. H 
Palmitin 
Stearin. 
Olein. 
The Neutral fats, when combined in proper proportions, constitute a 
large part of the fatty tissue of the body; they are soluble in ether, chloro- 
form, and hot alcohol; insoluble in cold alcohol and water, and liquefy at 
a high temperature. When a neutral fat is subjected to a high temperature 
in the presence of water and an alkali, it is decomposed, with the assimila- 
tion of the elements of water, into a fatty acid and glycerin. The fatty 
acid combines with the alkali and forms an oleate, palmitate, or stearate, 
according to the fat used. A similar decomposition of the neutral fats is 
said to take place in the small intestine during digestion. When thoroughly 
mixed with pancreatic juice, the fats are reduced to a condition of emulsion, 
a state in which the fat is minutely subdivided and the small globules held 
in suspension. 
Palmitic acid. 
Stearic acid. 
Oleic acid. 
FATTY ACIDS. C. O. H. 
Propionic acid. 
Butyric acid. 
Caproic acid. 
The Fatty acids, combined with sodium, potassium, and calcium, are 
found as salts in various fluids of the body, such as blood, chyle, feces, etc. 
Phosphorized fats in nervous tissue, butyric acid in milk, propionic acid in 
sweat, are also constituents of the body. 
The Fats are derived from the food, both animal and vegetable. They 
are deposited in the form of small globules in the cells of the different tis- 
sues, are suspended in various fluids, are deposited in masses in and around 
various anatomic structures, and beneath the skin. Independent of the 
fat consumed as food, there is good experimental evidence that fat is also 
produced within the animal body from a partial decomposition of the albumin- 
ous compounds. Fat serves as a nonconductor of heat, gives roundness and 20 
HUMAN PHYSIOLOGY. 
form to the body, and protects various structures from injury. The fats 
are ultimately oxidized, thus giving rise to heat and force, and are finally 
eliminated as carbonic acid and water. 
Glycerin. Cholesterin. Alcohol. 
ALCOHOLS. 
Glycerin is chemically a triatomic alcohol in combination with the neu- 
tral fats of the body. During pancreatic digestion it is set free. It is sup- 
posed by many physiologists to be directly concerned in the production of 
glycogen. Cholesterin is a crystallizable substance largely present in the 
bile, though it is found in other fluids and solids. It is supposed to be a 
waste product of nervous matter. Alcohol has been found in the urine. 
It is supposed to be the result of an alcoholic fermentation in the intestine. 
The nitrogenized or proteid compounds are organic in their origin, being 
derived from the animal and vegetable world ; they are taken into the body 
as food, appropriated by the tissues, and constitute their organic basis ; they 
differ from the nonnitrogenized substances in not being crystalline, but 
amorphous, in having a more complex but just as definite composition, and 
containing, in addition to C. O. H., nitrogen, with, at times, sulphur and 
phosphorus. The proteids possess characteristics which distinguish them 
from all other substances: viz., a molecular mobility, which permits isom- 
eric modifications to take place with great facility; a catalytic influence, in 
virtue of which they promote, under favorable conditions, chemical changes 
in other substances; e.g., during digestion, salivin and pepsin cause starch 
and albumin to be transformed into sugar and albuminose respectively. 
Different proteids possess varying proportions of water, which they lose 
when subjected to desiccation, becoming solid; but upon exposure to 
moisture they again absorb water, regarding their original condition,—they 
are hygroscopic. Another property is that of coagulation, which takes place 
under certain conditions; e.g., the presence of mineral acids, heat, alcohol, 
etc. 
After death the nitrogenized compounds undergo putrefactive changes, 
give rise to carburetted and sulphuretted hydrogen and other gases. In 
order that these changes may take place it is essential that certain condi- 
tions be present, viz.: atmospheric air or some fluid containing oxygen, 
moisture, and a temperature varying between 6o° and 90° F. The cause 
of the putrefactive change is the presence of a minute unicellular organism, 
the bacterium termo. 
III. ORGANIC NITROGENIZED PRINCIPLES. CHEMIC COMPOSITION OF THE HUMAN BODY. 
21 
The nitrogenized bodies found in the organism are quite numerous, and 
although they resemble each other in many particulars, there are yet im- 
portant differences; they can be arranged into the following groups :— 
1. Native Albumins.—Proteid bodies soluble in water, many acids, and 
usually in alkalies ; coagulable at a temperature of from 140° to 163° F. 
a. Serum Albumin, the principal form of albumin found in the animal 
fluids and solids. 
b. Egg Albumin, not found in ordinary tissues, but present in white 
of egg. 
2. Globulins.—Proteid bodies insoluble in water, but soluble in solutions 
of sodium chlorid. 
a. Globulin, found in many tissues, but largely present in crystalline 
lens. 
b. Myosin, found in the muscles in life in a fluid condition; after 
death it undergoes coagulation, giving rise to the rigidity of the 
muscles. 
c. Paraglobulin, present in blood and obtained from it by passing a 
stream of carbon dioxid through it; it is also precipitated by adding 
sodium chlorid. 
d. Fibrinogen, present in serous fluid and blood, and can be precipi- 
tated by the prolonged use of carbon dioxid; it is also precipitated 
by the addition of 12 to 16 per cent, of sodium chlorid. 
3. Derived Albumins.—Proteid bodies which are not coagulable by heat; 
insoluble in pure water and in salt solutions; soluble in both acid and 
alkaline solutions. 
a. Acid Albumin, found principally in the stomach during first stage 
of digestion, the result of the action of the hydrochloric acid upon 
the albumin of the food. 
b. Alkali Albumin, found in the intestine during pancreatic digestion, 
the result of the action of alkalies upon the albumin of the food. 
c. Casein, the chief proteid of milk; it is precipitated by acetic acid 
and coagulated by rennet. 
4. Peptones.—These bodies are formed in the stomach and intestinal 
tract by the action of the gastric and pancreatic juices upon the albumins 
of the food. They are very soluble in water, alkaline and acid solutions; 
noncoagulable by heat; very diffusible. They are precipitated by tannic 
acid and alcohol. 
5. Albuminoids.—The albuminoids are the results of various modifications 
of albumins occurring during the nutritive process, as well as by the action 
of various external influences. 22 
HUMAN PHYSIOLOGY. 
a. Mucin, the characteristic ingredient of mucus secreted by the 
mucous membranes, giving to it its viscidity. 
b. Chondrin, found in cartilage. 
c. Gelatin, found in connective tissue, tendons, ligaments, bones, etc. 
d. Elastin, found in elastic tissue. 
e. Keratin, found in skin and epidermic appendages, nails, hair, horn, 
etc. 
6. Fibrin.—A filamentous albumin obtained by washing blood-clots. It 
is insoluble in water and mineral acids. 
As the properties of the compounds formed by the union of elements are 
the resultants of the properties of the elements themselves, it follows that 
the ternary substances, sugars, starches, and fats, possess a great inertia and 
a notable instability; while in the more complex albuminous compounds, 
in which sulphur and phosphorus are united to the four chief elements, 
molecular mobility, resulting in isomerism, exists in a high degree. As 
these compounds are unstable, of a greater molecular mobility, they are 
well fitted to take part in the composition of organic bodies, in which there 
is a continual movement of composition and decomposition. 
Urea, Xanthin, Sodium, 
Creatin, Tyrosin, Potassium, 
Creatinin, Hippuric Acid, Ammonium, 
Cholesterin, Calcium Oxalate, Calcium, 
IV. PRINCIPLES OF WASTE. 
Urates. 
These principles, which represent waste, are of organic origin, arising 
within the body as products of disassimilation or retrograde metamorphosis 
of the tissues; they are absorbed by the blood, carried to the various 
excretory organs, and by them eliminated from the body. 
The excrementitious substances will be fully considered under excretion. 
Proximate Quantity of the Chemical Elements and Proximate 
Principles of the Body, Weighing 154 lbs. 
lbs. 
OZ. 
Oxygen 
Hydrogen, . . . 
. . . 14 
Nitrogen, . . , 
• • • 3 
8 
Carbon, .... 
Calcium, . . . 
Phosphorus, . . 
. . . 1 
12 
Sodium, etc., . . 
154 
12 
lbs. 
OZ. 
Water, 
.in 
Albuminoids, .... 
• 23 
7 
Fats, 
Calcium phosphate, . 
• 5 
13 
Calcium carbonate, . 
. i 
Calcium fluorid, . . 
3 
Sodium sulphate, etc., 
154 
9 PHYSIOLOGY of the cell. 
23 
PHYSIOLOGY OF THE CELL. 
The Study of the Structure of the body reveals that it is composed 
of a number of dissimilar parts, such as the brain, heart, lungs, muscles, 
etc., to which the name organ has been given. The organs upon a closer 
examination can be resolved into elementary structures, to which the name 
tissue has been given. The study of the physical and physiologic proper- 
ties of the tissues has given rise to that department of anatomy known as 
histology, or, as it is largely prosecuted with the microscope, microsco- 
pic anatomy. Notwithstanding the complexity of the body, the number 
of constituent tissues is not great. They can be classified as follows:— 
1. Epithelial. 
2. Connective, comprising the areolar, adipose, fibrous, elastic, cartilage, 
and bone. 
3. Muscular. 
4. Nervous. 
The majority of the tissues, however, are not simple structures, but com- 
plexly organized masses, whose physiological properties are dependent upon 
and the resultant of the properties of the structural elements composing 
them. 
Cells.—When the tissues are subjected to microscopic analysis, it is 
found that instead of being homogeneous they are complex structures com- 
posed of simpler elements to which the name cell has been given. The 
cell constitutes the primary, elementary, structural, or form element of all 
tissues, and may be said to consist of a minute mass of living matter. 
Every organized body takes its origin in a single cell, the ovum. However 
complex its structures may become, it can be shown by an ultimate analysis 
that they are composed of similar cells or of fibers, which are the products 
or modifications of cells. The cell may be defined, therefore, as the pri- 
mary morphologic and physiologic unit of the organic world, to which every 
exhibition of life, whether normal or abnormal, is to be referred. 
Structure of Cells.—Cells vary in their anatomic constitution in the 
different structures of the body and may be classed in three groups, viz.:— 
1. Cells consisting of a cell substance, a nucleus, and one or more nucleoli, 
enclosed within a cell membrane, all these parts being found in the 
primitive ovum. 
2. Cells consisting of a cell substance and a nucleus only ; most of the cells 
of animal tissues have this structure. To this type of cell the name 
cytode has been given. 24 
HUMAN PHYSIOLOGY. 
3. Cells consisting of the cell substance only. 
Cells vary in size within considerable limits, from the size of a white 
blood cell, ysVjfth of an inch, to that of the multipolar cells in the anterior 
horns of the gray matter of the spinal cord, of an inch, or to that of 
the ovum, the T of an inch. They also differ considerably in shape, 
according to the locality in which they are found. When young and free 
to move in a fluid medium, they assume the spheric form ; when subjected 
to pressure, they may assume cylindric, polygonal, fusiform, and stellate 
forms. 
The Cell Substance consists of a soft, transparent, gelatinous, semi- 
fluid material, known as protoplasm or bioplasm. Though frequently 
homogeneous, it often exhibits a finely granular appearance. The charac- 
teristics of protoplasm, however, vary in different tissues and in different 
animals. While young cells consist almost entirely of protoplasm, mature 
cells contain, in addition, materials of an entirely different kind; e. g., 
globules of fat, granules of glycogen, mucigen, pigment, digestive ferments, 
as pepsin, trypsin, etc., substances which are produced by the physiologic 
action of the protoplasm. 
The chemic composition of living protoplasm is difficult of determina- 
tion. When dead, it is found to be composed of water, proteid material, 
a small quantity of glycogen, fat, and inorganic salts. 
When examined with the microscope, the cell substance or protoplasm 
exhibits a network, the spongioplasm, in the meshes of which is contained a 
transparent material, the hyaloplasm. The protoplasm of all cells pos- 
sesses, in a varying degree, the property of irritability; that is, of reacting in 
a definite manner to some form of excitation. The response will vary 
according to the character of the element stimulated. If it be a muscular 
fiber, there will result a contraction ; if it be a gland cell, a secretion. In 
some animal cells, as well as in many vegetable cells, currents are visible in 
the protoplasmic mass, which, in the absence of apparent external influences, 
are said to be spontaneous. Ameboid movements are observed in many 
animal cells, particularly when young. The irritability and other physio- 
logic properties of protoplasm are dependent upon a due supply of nour- 
ishment and the maintenance of a normal temperature. 
The Nucleus is an ovoid or spheric body embedded in the cell sub- 
stance. It consists of a distinct membrane, enclosing a clear nuclear sub- 
stance, which, however, is pervaded by an irregular network of fibers, 
which exhibit here and there enlargements, to which the term nucleoli is 
given. The meshes of this network contain a soft, interstitial substance. PHYSIOLOGY OF THE CELL. 
25 
The nuclear membrane and the fibers composing the network, staining 
readily with various dyes, are spoken of as chromatin ; the interstitial sub- 
stance, not staining, as achromatin. 
The Cell Membrane is a very thin, transparent, homogeneous, and 
elastic structure, completely enclosing the cell substance. It varies in 
thickness and consistency in different tissues. It is permeable to water and 
aqueous solutions of various organic and inorganic substances. The cell 
membrane has no special physiologic activity, merely serving as a protec- 
tive agent. It is a product of the cell substance. 
MANIFESTATIONS OF CELL LIFE. 
Growth and Assimilation.—All cells exhibit the three fundamental 
properties of life: growth, motion, and reproduction. Every living cell 
is, therefore, the seat of a series of chemic changes underlying the two 
phases of nutrition, assimilation and dissimilation. By the first process, 
the cell absorbs from its surroundings those materials necessary for its 
growth and physiologic activities. When newly reproduced, all cells are 
exceedingly small, but by the absorption of nutritive material and its sub- 
sequent assimilation and vitalization they gradually attain their mature size. 
Some of the absorbed material, instead of becoming an integral part of the 
protoplasm, is oxidized, giving rise to heat and force. As a result of cellu- 
lar activity, there is also formed within the cell special substances, which, 
being finally eliminated, play some important part in nutrition. Coincident 
with the assimilative process, there are changes taking place of a disassimi- 
lative character; absorbed material, as well as tissue itself, is constantly 
being reduced to simpler forms, as carbon dioxid, urea, water, etc. The 
nutrition of the cell is, therefore, an epitome of the nutrition of the body as 
a whole. 
Reproduction.— Like all organic structures, cells have a limited period 
of life ; their continual decay and death necessitates a capability of repro- 
duction. Cells reproduce themselves in the higher animals mainly by 
fission. This is seen in the white blood-corpuscles of the young embryos 
of animals; the corpuscle here consists of a cell substance and nucleus. 
When division of the cell is about to take place, the nucleus elongates, the 
cell substance assumes the oval form, a constriction occurs, which gradu- 
ally deepens, until the original cell is completely divided and two new 
cells are formed, each of which soon grows to the size of the parent cell. 
In cells provided with a cell membrane the process is somewhat differ- 26 
HUMAN PHYSIOLOGY. 
ent. In the ova of the inferior animal, after fertilization has taken place, 
a furrow appears on the opposite sides of the cell substance, which deepens 
until the cell is divided into two equal halves, each containing a nucleus; 
this process is again repeated until there are four cells, then eight, and so 
on until the entire cell substance is divided into a mulberry mass of cells, 
completely occupying the interior of the cell membrane. The whole pro- 
cess of segmentation takes place with great rapidity, occupying not more 
than a few minutes, in all probability. 
Motion.—In addition to the currents frequently observed in cell proto- 
plasm, various other forms of movement have been observed; ameboid 
movements, the projection of pseudopodia, the waving of cilia, the activity 
of spermatozooids, the migration of blood-corpuscles, are among the different 
types of movement exhibited by many of the cells of the body. 
By a combination of these primary structural elements, and of fibers and 
ground substances derived from or specially produced by them, all the 
tissues are formed which enter into the construction of the different organs 
of the body. 
PHYSIOLOGY OF THE EPITHELIAL AND 
CONNECTIVE TISSUES. 
Epithelial Tissue.—The epithelial tissue consists of one Or more 
layers of cells resting upon a homogeneous membrane, the other side of 
which is abundantly supplied with blood-vessels. The form of the epithe- 
lial cell, varying in different situations, may be flattened, spheroid, or col- 
umnar, and is related to some special function. When arranged in layers, 
the cells are united by an intercellular substance. The epithelial tissue 
forms a continuous covering for the surfaces of the body. The external 
investment, the skin, as well as the mucous membrane which lines the 
entire alimentary canal and its associated body cavities, is formed in all 
situations by the basement membrane, covered with one or more layers of 
cells. All materials, therefore, whether nutritive or excretory, must pass 
through epithelial cells before they can enter into the formation of tissues 
or be eliminated from them. Chemically, epithelial cells are composed 
largely of keratin, a small proportion of water, and inorganic salts. 
The consistency of epithelium varies in accordance with external influ- 
ences, such as want of moisture, pressure, friction, etc. This is well seen 
in the skin and palms of the hands and soles of the feet, where it acquires PHYSIOLOGY OF THE EPITHELIAL AND CONNECTIVE TISSUES. 
27 
its greatest density. In the intestines, lungs, and other cavities, where the 
reverse conditions prevail, the epithelium is extremely soft. The epithe- 
lial tissues possess varying degrees of cohesion and elasticity, which enable 
them to resist considerable pressure and distention without having their 
integrity destroyed. Being bad conductors of heat, they assist in prevent- 
ing rapid radiation from the body, and so maintain the normal temperature. 
The physiologic activity of all epithelial tissue depends upon a due supply 
of nutritive material furnished by the blood, which not only maintains its 
own nutrition, but affords material from which are formed the secretions of 
glands, whether of the skin or mucous membranes. 
The functions of the epithelial tissues are: — 
1. To serve as a protective covering to the underlying structures. 
Wherever there is repeated pressure, the epithelial cells become thick 
and indurated. Owing to their consistence they resist to some extent the 
injurious influences of acids and alkalies and various poisons. 
2. As an absorbing agent. Inasmuch as the skin and mucous membrane 
cover the surfaces of the body, it is obvious that all nutritive substances 
entering the body must first traverse the epithelium. The epithelial 
cells covering the skin, owing to their density, play but a feeble role 
in man. The mucous membrane of the alimentary canal is the principal 
absorbing surface. The character of its epithelium permits of the 
absorption of water, peptones, sugars, salts. The epithelium lining the 
pulmonary air-vesicles is actively engaged in taking up oxygen and 
giving out carbon-dioxid. 
3. As an eliminating agent. Waste products, however produced within 
the organism, must be taken up by the epithelium of the various excretory 
organs before being finally disposed of. The secretions of all glands are 
products of epithelial activity. 
Connective Tissue.—The bony skeleton of the body is supplemented 
by a finer skeleton, composed of connective tissue, which pervades the 
entire body, and which, under various forms, serves as a bond of connec- 
tion between its different parts, as a covering and protection for various 
organs, and as a basis of support for the elements of muscular, nervous, 
and glandular tissues. 
The connective tissues include several varieties, among which may be 
mentioned areolar, adipose, fibrous, elastic, cartilaginous, and osseous. 
Notwithstanding their apparent diversity, they have many points of simi- 
larity. They have a common origin, developing from the same embryonic 
material; they have much the same structure, passing imperceptibly into 28 
HUMAN PHYSIOLOGY. 
each other, and functionally perform the same office, viz., supporting and 
connecting the specific elements of the tissues or organs. 
Areolar Tissue.—This variety is found widely distributed throughout 
the body in all situations. It serves to unite the skin and mucous mem- 
branes to the structures on which they rest, to unite and support blood- 
vessels, muscles, nerves, etc. When examined with the naked eye it 
presents the appearance of fine, transparent, colorless fibers, of delicate 
membranous lamina, which cross each other in every direction, leaving 
spaces or areolae between them. Examined microscopically, these fibers 
are found to be composed of still finer white fibers cemented together by a 
transparent substance containing mucin. Other fibers are distinguishable 
by their straight course, their dark outline, their tendency to branch and to 
unite with adjoining fibers. When torn across they curl up at their extremi- 
ties, owing to their property of elasticity. Distributed throughout the 
meshes of the areolar tissue are found flattened, irregularly branched or 
stellate corpuscles, the connective tissue corpuscles, plasma cells, and 
granule cells. 
Adipose Tissue.—This exists very generally throughout the body, but is 
found most abundantly beneath the skin, around the kidneys, and in the 
bones. It is composed almost entirely of small vesicles more or less com- 
pletely filled with fat-globules. The wall of the vesicle is protoplasmic, 
and contains at some points an oval, flattened nucleus. Adipose tissue can 
arise wherever connective tissue is found. It would appear that the gran- 
ules of fat are produced by a transformation of the albuminous contents of 
the connective-tissue corpuscles. The vesicles are grouped together to 
form lobules, which in turn form irregular masses supported by connective 
tissue and blood-vessels. 
Retiform Tissue.—This is also a variety of connective tissue made up 
very largely of white fibers interlacing in all directions. The spaces or 
areolae are wanting in the usual ground substance, but are filled with fluid. 
Connective tissue corpuscles are abundant, but elastic fibers are absent. 
Adenoid tissue is but ordinary retiform tissue, the spaces of which, how- 
ever, are filled with lymph corpuscles. It is found in lymphatic glands, in 
the central nervous system, and other situations. 
Fibrous Tissue.—White fibrous tissue is exceedingly abundant and 
important. It forms the ligaments which hold the bones together, the 
tendons of the muscles, the membranes covering bones, cartilages, the septa 
of muscles, etc. Fibrous tissue is tough and strong but wholly inextensible, 
and, in consequence, is admirably adapted to fulfil various mechanical 
functions in the body. It is quite pliant, bending readily in any direction, PHYSIOLOGY OF THE EPITHELIAL AND CONNECTIVE TISSUES. 
29 
but difficult to break. When examined microscopically it is found to be 
composed of white fibers, resembling in all respects those of the areolar 
tissue. Treated with acetic acid they swell up and "become indistinct. 
When boiled they yield gelatin, a derivative of collagen. 
Elastic Tissue.—The elastic tissue is also an important member of the 
connective-tissue group. It is almost invariably associated with white 
fibers in some proportion, but in some tissues, as the ligamentum nuchse, 
the ligamenta subflava, the coats of the large blood-vessels, it exists almost 
alone. In its pure state it presents a distinctly yellow appearance. The 
fibers of which it is composed are transparent, but present a distinct out- 
line; they run almost parallel, but give off branches which unite to form a 
reticulated structure. As the name implies, these fibers are very extensible 
and elastic. 
Cartilage is a modified form of connective tissue. It is opaque, bluish- 
white in color, though in thin sections translucent. In some situations it 
is firm in consistence, in others soft and elastic. All cartilage consists 
primarily of a ground or fundamental substance throughout which are 
scattered cells. There are two principal varieties in the human body, viz., 
hyalin and fibrocartilage. 
Hyaline cartilage is the most typical form, the matrix of which being trans- 
lucent and homogeneous. It is found on the ends of bones entering into the 
formation of joints, where it forms articular cartilage, between the ribs and 
sternum, forming the costal cartilages. It is also found in other situations. 
Microscopically examined, the ground substance reveals the presence of 
oval or spherical corpuscles containing one or more nuclei. The cell sub- 
stance is frequently marked off from the ground substance by concentric 
lines, or fibers, which form a capsule for the cell. Repeated division of 
the cell substance frequently takes place, until the whole capsule is fully 
occupied with cells. The cell protoplasm is granular, and frequently con- 
tains drops of fat. According to some investigators the cell spaces are not 
isolated, but connected by fine channels, which in turn communicate with 
lymphatics. By these means nutritive fluid permeates the entire structure. 
Fibrocartilage consists of two varieties, white and yellow. 
While fibrocartilage consists of the usual ground substance pervaded 
by white fibers. It is firm and resistant, and found wherever strength and 
fixedness are required. Hence it is present between the vertebrae, forming 
the intervertebral discs, between the condyle of the lower jaw and glenoid 
fossa, in the knee-joint, around the margins of cup-shaped cavities, etc. In 
these situations it assists in maintaining the apposition of the bones, in giv- 
ing a certain degree of motility to joints, and in diminishing the effect of 30 
HUMAN PHYSIOLOGY. 
shock and pressure. The fibers of white cartilage are arranged in bundles 
and layers, the ground substances being relatively less abundant. Between 
the layers are the Usual cartilage corpuscles. 
Yellow Jibrocarlilage is found in the epiglottis, the external ear, Eus- 
tachian tube, and larynx. Primarily hyaline in character, the ground sub- 
stance becomes pervaded with yellow fibers which branch and interlace in 
all directions, forming a dense network, but are so arranged as to form 
small spaces in which are found cartilage corpuscles surrounded by a soft 
matrix. These fibers are very elastic, and give to this form of cartilage a 
considerable degree of elasticity. 
Osseous Tissue.—Osseous tissue, as distinguished from bone in the 
anatomic sense, belongs to the connective-tissue group, in which the funda- 
mental substance is permeated with insoluble lime salts, the phosphate 
and carbonate being the most abundant. With dilute solutions of hydro- 
chloric acid, these can be converted into soluble salts and dissolved out. 
The osseous matrix left behind is soft and pliable, and yields gelatin on 
boiling. The surfaces of all bones in the recent state, except where they 
are covered with cartilage, are invested with a fibrous membrane, the peri- 
osteum. The inner surface of this membrane is loose in texture, and sup- 
ports a fine capillary plexus of blood-vessels and numerous protoplasmic 
cells, the “ osteoblasts.” As this layer is directly concerned in the forma- 
tion of bone, it is spoken of as the osteogenetic layer. 
A section of any bone shows that it is composed of two kinds of tissue, 
compact and cancellated. The compact resembles ivory, and is found on 
the outer surface; the cancellated is spongy, and to the naked eye appears 
to be made up of thin, bony plates, which intersect each other in all direc- 
tions. It is found in great abundance in the interior of bones. The shaft 
of a long bone is hollow, the cavity extending almost from one extremity to 
the other. This central cavity, as well as the interstices of the cancellated 
tissue, is filled in the recent state with marrow. The marrow or medulla 
is a vascular tissue, the capillaries of which are supported by a delicate 
connective-tissue framework. In its meshes are to be found characteristic 
marrow cells, or osteoblasts, engaged in the formation of bone. The mar- 
row in long bones is yellow, from the presence of fat resulting from a trans- 
formation of the protoplasm of connective-tissue cells. In the cancellated 
tissue, especially near the extremities, the fatty transformation does not take 
place, and the marrow remains red. The cells are supposed to give birth 
to red corpuscles. 
Examined microscopically, a thin, transverse section of a bone reveals 
numerous small oval or round openings, which are the transverse sections PHYSIOLOGY OF THE EPITHELIAL AND CONNECTIVE TISSUES. 
31 
of canals which run, for the most part, in a longitudinal direction. These 
are the Haversian canals. In the living state, they are partly filled with 
blood-vessels and lymphatics. The canals are connected with each other 
and with the surfaces of the bones by numerous anastomosing branches. 
Around each Haversian canal is a series of concentric lamina, composed 
of fibers. Between every two laminae are found small cavities (lacunae) 
from which radiate in all directions small canals (canaliculi), which com- 
municate freely with each other. The Haversian canals, with their asso- 
ciated lacunae and canaliculi, form a series of intercommunicating passages, 
through which lymph passes for the nourishment of bone. In the cancel- 
lated tissue the blood-vessels pass through its interstices, and are supported 
by connective tissue. Bone cells, protoplasmic and nucleated, are found 
in each lacuna. When young, they are branched, sending their prolonga- 
tions into the canaliculi. 
Physical and Physiologic Properties of Connective Tissue.— 
Among the physical properties may be mentioned consistency, which varies 
from the semiliquid to the solid state. This variation depends upon the 
quantity of water in the individual tissues. Their cohesion, with the ex- 
ception of the softer varieties, is considerable, and offers great resistance to 
traction, pressure, torsion, etc. In the various movements of the body, in 
the contraction of muscles, in supporting weights, in diminishing the effects 
of shocks, the properties of consistence and cohesion play important parts. 
Wherever the various forms of connective tissue are found, their chemic 
composition and structure are found to be in relation to their mechanical 
function. If traction be the preponderating force, the structures become 
fibrous, as in ligaments and tendons, and the cohesion greatest in the longi- 
tudinal direction. If pressure be exerted in all directions, as upon mem- 
branes, the fibers become interlaced and so offer an uniform resistance. 
When pressure is exerted in a definite direction, as upon the ends of long 
bones, the tissue assumes the cartilaginous form. Elasticity is also a prop- 
erty of all connective tissues, but is most marked in those containing an 
abundance of yellow elastic fibers. Elasticity plays an important role in 
many physiologic acts. It not only opposes and limits forces of traction, 
pressure, torsion, etc., but upon their cessation returns the tissues or struc- 
tures to their original condition. It thus maintains the natural form and 
position of the organs by counterbalancing and opposing temporarily acting 
forces. 32 
HUMAN PHYSIOLOGY. 
THE SKELETON. 
Within the body of man and all vertebrated animals there is a highly 
developed framework, consisting of bones and cartilages, technically 
known as the skeleton (Fig. i), the function of which is to afford support 
to all the softer tissues, to afford attachment for muscles, and to protect 
many delicate organs from injury. In addition to the bony skeleton there 
is a secondary framework, composed for the most part of fibrous or con- 
nective tissue, which ramifies everywhere throughout the body, uniting its 
various parts and affording support and protection to the ultimate elements 
of the tissues. 
The skeleton naturally divides itself in accordance with the funda 
mental division of the body into— 
1. An axial, and 
2. An appendicular portion. The axial portion consists of the bones of the 
spine, the head, the ribs, and sternum; the appendicular portion consists 
of the bones of the extremities and the bony arches by which they are 
united to the trunk. 
The Axial Skeleton.—The axial skeleton consists primarily of the 
spinal column, placed in the middle of the back of the neck and trunk, 
where it forms the foundation of the entire skeleton. It is composed of a 
series of superimposed bones termed vertebra ; above, it supports the skull; 
laterally it affords attachment for the ribs, which in turn support the weight 
of the upper extremities; below, it rests upon the pelvic bones, which 
transmit the weight of the body to the inferior extremities. 
The Vertebral or Spinal Column consists in the child of 33 distinct 
bones, which are arranged in groups, named and numbered from their 
position, as follows: Cervical, 7; thoracic, 12; lumbar, 5; sacral, 5; 
coccygeal, 4, the latter being quite rudimentary. In the adult the sacral 
and coccygeal bones unite to form two separate composite bones, the sac- 
rum and coccyx. Owing to their mobility the former are termed true, the 
latter false vertebrae. While the vertebrae of each group have certain char- 
acteristics in common, the type is best shown by the thoracic vertebrae. 
The Thoracic Vertebrae present the following parts: — 
1. A body ox centrum, a short cylinder of bone slightly concave on its 
upper and lower surfaces, which is united to adjoining vertebrae by elastic 
discs of fibro-cartilage. 
2. A neural arch consisting of two symmetrical halves each arising from 
the back of the body and uniting in the median line. Each arch con- THE SKELETON. 
33 
sists anteriorly of the pedicle, posteriorly of the lamina. At the point 
of union of the arches there is presented a prominent spine of bone 
which collectively give to the column its spiny character. From each 
side of the arch arises the transverse process, which projects outward 
and slightly backward. From the superior and inferior border of each 
lamina project the superior and inferior articulating processes. 
The Cervical Vertebrae differ in some respects from the thoracic. The 
body is smaller, the neural arch larger, the spinous process shorter and 
often bifid. The transverse processes are broader and perforated by a fora- 
men. The first and second vertebrae deviate markedly from the usual 
type. The first vertebra, or atlas, possesses neither a body nor a spinous 
process. It is practically a large neural ring provided with two lateral 
masses of bone which support the weight of the head. The second verte- 
bra, or axis, has projecting from its body a vertical process, the odontoid 
process, around which the atlas bone rotates. 
The Lumbar Vertebrae are the largest in the spinal column. The 
centrum gradually increases in width and strength from above downward, 
in accordance with the increasing weight of the body. The arches and 
processes are correspondingly enlarged. 
The Sacrum is a triangular-shaped bone placed below the vertebrae. 
Its anterior surface is concave and presents four transverse ridges which 
mark the points of union of the primitive vertebrae and four openings on 
either side which communicate with the neural canal. The posterior sur- 
face is convex and marked by numerous partially developed processes 
which are homologous with the processes of the upper vertebrae. 
The Coccyx is a rudimentary bone formed by the fusion of the bodies 
of four undeveloped vertebrae and terminates the spinal column. 
The Spinal Column as a whole has an average length of about twenty- 
eight inches. Viewed laterally, it presents from above downward four 
curves. In the cervical and lumbar regions the curves are convex ante- 
riorly, in the thoracic and sacral regions concave. These curves, taken in 
connection with the elastic intervertebral discs, impart to the spinal column 
considerable elasticity. 
The Sternum is a thin, flat bone, situated in the median line in the 
anterior wall of the thorax. It consists of three segments, a superior, a 
middle, and an inferior, known respectively as the manubrium, the gladio- 
lus, and the xiphoid appendix. The lateral borders of the sternum present .Cervical 
vertebrae. 
Clavicle. 
Glenoid fossa. 
-Humerus. 
-Ilium. 
-Ulna. 
-Radius. 
-Acetabulum. 
-Carpus. 
-Metacarpus. 
—Phalanges. 
■Metatarsus. 
■Phalanges. 
Fig. i.—Bony Skeleton. 
34 THE SKELETON. 
35 
a series of depressions for the reception of the collar bone and the sternal 
ends of the cartilages of the first seven ribs. 
The Ribs form a series of narrow, curved, flattened bones, attached 
posteriorly to the dorsal vertebrae, and continued anteriorly to the median 
line by the intermediation of cartilage. There are 24 ribs in num- 
ber, 12 on each side. The first 7 are termed true ribs, from their at- 
tachment to the sternum; the remaining 5 are termed false ribs, of which 
the cartilages of the eighth, ninth, and tenth are attached to each other, 
while the eleventh and twelfth are free or floating. The ribs in- 
crease in length from the first to the seventh, and then decrease to the 
twelfth. Each rib consists of a beveled head for articulation with the 
dorsal vertebrse, a contricted portion, the neck, a tubercle for articulation 
with the transverse process, a curved shaft, compressed from side to side. 
Collectively the ribs form the lateral walls of the chest. The costal car- 
tilages are the continuations of the ribs, and serve to connect them to the 
sternum. 
The Thorax, as a whole, is a conical-shaped structure formed by the 
union of the thoracic vertebrae, the ribs, and sternum. It is compressed 
from before backward, so that the anteroposterior diameter is less than the 
transverse. The superior opening is oval in outline, measuring five inches 
from side to side, and two and one-half from before backward. The in- 
ferior opening is irregular, owing to the inclination of the ribs and the pro- 
jection of the lower end of the sternum. 
The Skull consists of 22 bones, of which 8 form the cranium, which 
encloses and protects the brain; the remaining 14 support the face and 
form the orbital, nasal, and mouth cavities. The cranial bones are:— 
1. The frontal bone, which forms the forehead and roof of the orbits. 
2. A pair of parietal bones, which form the sides and roof of the cranium. 
3. The occipital bone, which forms the back of the head and part of the 
base. It is perforated by a large opening, the foramen magnum, through 
which the spinal cord passes. On either side of the foramen there is a 
large condyle, which articulates with the lateral masses of the atlas. 
4. A pair of temporal bones, which aid in forming the sides and base of the 
skull and lodge the auditory organ. 
5. The sphenoid bone, an irregular-shaped bone, situated at the base of the 
skull, where it forms a keystone for the cranial arch. 
6. The ethmoid bone, situated between the skull and nasal chambers, and 
giving support to the olfactory organs. 36 
HUMAN PHYSIOLOGY. 
The facial bones are paired, two only being single. The paired bones 
are:— 
1. The superior maxi lire, or upper jawbones, situated one on either side of 
the middle line, assisting in the formation of the orbit, nose, and roof of 
the mouth. They also carry the upper teeth. 
2. The palatal bones complete the hard palate and assist in forming the 
posterior nares. 
3. The nasal bones, forming the bridge of the nose. 
4. The lacrimal bones, lying between the orbit and nose. 
5. The malar bones, lying beneath and to the outside of the orbit. 
6. The inferior turbinated bones, one in each nasal chamber. 
7. The inferior maxilla, or lower jawbone, is connected with the temporal 
bone on each side of the head. It carries the lower teeth and assists in 
mastication. 
8. The vomer forms a portion of the partition of the nose. 
THE APPENDICULAR SKELETON. 
The appendicular skeleton consists of:— 
1. The bones of the shoulder girdle and the bones of the arm, forearm, 
and hand. 
2. The bones of the pelvic girdle and the bones of the thigh, leg, and foot. 
The Shoulder Girdle is an imperfect bony arch connecting the limb 
directly with the axial skeleton. It consists of two bones, the clavicle and 
scapula. 
The clavicle is a cylindrical bone extending from the upper end of the 
sternum upward and outward to be attached to the acromion process of 
the scapula. 
The scapula is a flat triangular bone situated on the upper and back 
part of the thorax. It is not directly connected with the axial skeleton, 
being separated from it by a layer of muscle in which it is partly embedded. 
The posterior surface is divided by a spine of bone into two unequal 
portions. This spine gradually becomes more prominent as it passes from 
within outward; toward its termination it curves forward and forms the 
acromion process with which the clavicle articulates. The upper part of 
the outer edge of the scapula presents a slightly concave surface, pyriform 
in shape, which receives the upper extremity of the arm bone, known as 
the glenoid fossa. Overhanging this fossa is a strong bony process—the 
coracoid. 
The skeleton of the arm and hand consists of 30 bones, the largest of STRUCTURE AND MECHANISM OF JOINTS. 
37 
which, the humerus, lies in the arm. The ulna and radius are placed side 
by side in the forearm, and are so arranged that the radius can move to 
some extent around the ulna. The wrist or carpus contains 8 small bones, 
the metacarpus contains 5 long, cylindrical bones, the fingers 3, and the 
thumb 2. 
The Pelvic Girdle, which forms the bond of union between the leg and 
the axial skeleton, consists of a single bone, the os innominatum, on each 
side, which articulates with the sacrum posteriorly; arching forward, it 
meets with its fellow of the opposite side in the median line, thus forming 
the lateral and anterior walls of the pelvic cavity. In the young child, this 
bone consists of three distinct bones, the ilium, ischium, and pubis, which, 
in adult life, fuse together to form the single bone. At the point of union 
on the external surface there is formed a large cavity, the acetabulum, 
which lodges the head of the thigh bone. 
The skeleton of the leg and foot consists of 30 bones. The thigh bone, 
or femur, is the largest bone in the body, extending from the pelvic girdle 
to the knee. It is provided above with a rounded head, which fits into the 
acetabulum. This is connected with the shaft by a short neck, which forms 
with the latter an angle of 125 degrees. The lower extremity of the femur 
is enlarged to rest upon the bones of the leg. The leg bones are 2 in 
number, the tibia and fibula, the latter being placed external. In front of 
the knee is th& patella. The tarsus consists of 7 bones, one of which, the 
astragalus, is united to the tibia and fibula to form the ankle. The cal- 
caneum forms the heel. The metatarsus consists of 5 bones, each carrying 
a toe. There are 14 bones in the toes, 3 in each, except the large toe, 
which has but 2. 
STRUCTURE AND MECHANISM OF JOINTS. 
The various bones comprising the skeleton do not form a rigid frame- 
work, but are united by a variety of structures and in such a manner as to 
admit of varying degrees of movement. The points of union are termed 
articulations, or joints. 
The structures entering into the formation of joints are :— 
1. Bones, the articulating surfaces of which are often expanded and 
variously modified, as in the case of long bones. 
2. Hyaline cartilage, which covers the articulating surfaces. Owing to its 
smoothness it facilitates the gliding movements of opposed surfaces, and 
by its elasticity diminishes the force of jars and shocks imparted to the 38 
HUMAN PHYSIOLOGY. 
bones. White fibrocartilage in the form of interarticular discs is found 
in many joints. Placed between the ends of bones it subdivides the 
articulation and adjusts dissimilar surfaces. 
3. A synovial membrane, consisting of connective tissue mixed with elastic 
tissue. Its inner surface is lined with endothelium, which secretes the 
synovial fluid, a colorless, viscid, alkaline fluid containing much mucin, 
albumin, and fat. Its function is to lubricate the articular surfaces and 
diminish friction. 
4. Ligaments, tough bands of white fibrous tissue which pass from bone to 
bone in various directions. White fibrous tissue, being inextensible but 
pliant, maintains the bones in apposition and prevents displacement, but 
permits of easy movement within certain limits. 
Modes of Articulation.—All articulations are divided, according to 
the extent of movement, into— 
1. Synarthrodial, comprising those joints endowed with little or no motion ; 
e. g., joints or sutures uniting the bones of the skull. 
2. Afnphiarthrodial, comprising those joints endowed with a slight degree 
of mobility in consequence of an intervening plate of fibrocartilage and 
tough, unyielding ligaments; e.g., vertebral and pelvic joints. 
3. Diarthrodial, comprising those joints which are freely movable, the 
extent of movement, however, being variable. In all such joints the 
articulating surfaces are generally adapted to each other, are covered 
with smooth cartilage, lubricated with synovial fluid, and surrounded by 
ligaments which, while not preventing, yet limit the extent of movement. 
The diarthrodial joints may be divided according to the character of the 
movement into— 
a. Arthrodial, or gliding joints. 
b. Ginglymus, or hinge joints. 
c. Enarthrodial, or ball and socket joints. 
d. Trachoidal, or rotary joints. 
The articulations may also be grouped in accordance with the funda- 
mental divisions of the skeleton into— 
1. Axial. 
2. Appendicular. 
The axial articulations are quite numerous and may be grouped into those 
uniting:— 
i. The bodies of the vertebrae, the intervertebral joints. 
THE AXIAL ARTICULATIONS STRUCTURE AND MECHANISM OF JOINTS. 
39 
2. The vertebrae with the ribs, the costovertebral joints. 
3. The ribs with the sternum, the costosternal joints. 
4. The vertebral column with the head, the occipito-atlantal joints. 
The Intervertebral Joints are amphiarthrodial in character. The 
bodies of the vertebrae are united by tough, elastic discs of fibrocartilage 
which collectively constitute about one-quarter of the length of the vertebral 
column. The vertebrae are bound together by ligamentous bands situated 
on the anterior and posterior surfaces of their bodies and by short, elastic 
bands between the neural arches and processes. These structures combine 
to render the vertebral column elastic and flexible, and to enable it to resist 
and diminish the force of shocks communicated to it. 
The function of the intervertebral joints and associated structures is not 
only to impart to the vertebral column the physical properties just men- 
tioned, but to endow it with certain forms of movement necessary to the 
performance of various bodily activities. While the extent of movement 
between any two vertebrae is slight, the sum total of movement of all the 
vertebrae is considerable. Again, the extent of movement varies in different 
regions of the column, being limited and dependent upon the character of 
the vertebrae and the inclination of their articular processes. In the cer- 
vical and lumbar regions the movements of extension and flexion are freely 
allowed, extension being greater in the former, flexion being greater in the 
latter, particularly between the fourth and fifth vertebrae. Lateral flexion 
takes place in all portions of the column, but is particularly marked in the 
cervical region. A rotatory movement of the column as a whole takes place 
through an angle of 28 degrees. This is most marked in the lower cer- 
vical and dorsal regions. In the dorsal region the surfaces of the articular 
processes lie in the arc of a circle, the center of which is in front of the 
vertebra;, and in consequence permit of considerable rotation. In the lum- 
bar region the reverse condition obtains and rotation is almost impossible. 
The Costovertebral and Costosternal joints are diarthrodial in 
character. The former are formed by the apposition of the heads of the 
ribs with the dorsal vertebrae and the rib tubercles with the transverse pro- 
cesses, the latter by the anterior extremities of the ribs and sternum through 
the intermediation of the costal cartilages. Both sets of joints are provided 
with ligaments and closed synovial sacs. 
The function of the costovertebral joints is to permit of an elevation 
and depression of the ribs coincident with a forward and backward gliding 
movement, which is essential to changes in the diameters of the thoracic 
cavity during respiration. At the costosternal joints the movements are 40 
HUMAN PHYSIOLOGY. 
complex, the resultant, however, being an elevation of the anterior ex- 
tremities of the ribs and an advance of the sternum during inspiration. 
During expiration the reverse takes place. The resultant of a combination 
of all the movements permitted at these joints is an elevation of the thorax, 
an advance of the sternum, and in consequence an increase in the trans- 
verse and anteroposterior diameters during an inspiratory movement. 
The reverse of these movements takes place during an expiratory move- 
ment. 
The Occipito-atlantal joints are formed by the apposition of the 
superior concave surfaces of the lateral masses of the atlas and the convex 
surfaces of the occipital condyles. 
The Atlanto-axoidean joints are formed laterally by the articular pro- 
cesses, centrally by the odontoid process, the anterior arch of the atlas, 
and the transverse ligament. 
The function of these joints is to give to the head great variety and 
range in its movements. In flexion and extension, the movement takes 
place around a transverse axis, the occipital condyles gliding alternately 
backward and forward upon the lateral masses of the atlas. The rotation 
of the head is accomplished by a movement of the collar formed by the 
atlas and the transverse ligament around the odontoid process of the axis, 
which is so extensive as to permit of a range of vision through 180 degrees. 
THE APPENDICULAR ARTICULATIONS. 
The appendicular articulations comprise all those entering into the for- 
mation of— 
1. The shoulder girdle, arm, and hand. 
2. The pelvic girdle, leg, and foot. 
The Shoulder Girdle presents two articulations. The sternoclavic- 
ular, which unites the clavicle to the sternum, and the acromioclavicular. 
The function of these joints is to endow the shoulder girdle with con- 
siderable mobility—enabling it to execute a series of movements upon the 
thorax. 
The Shoulder Joint, formed by the union of the hemispheric head 
of the humerus and the glenoid fossa of the scapula, belongs to the en- 
arthrodiai, or ball and socket, variety. Though surrounded by ligaments 
and a synovial membrane, the bones are retained in position largely by at- 
mospheric pressure and muscular action. STRUCTURE AND MECHANISM OF JOINTS. 
41 
The function of this joint is to endow the arm with great freedom of 
movement. Being a typical enarthrodial joint, the movements can take 
place in all directions; and consist of flexion; extension; abduction, 
which, at an angle of 90 degrees, is checked by the locking of the great 
tuberosity of the humerus with the acromion process of the scapula ; ad- 
duction ; circumduction, in which the arm describes a cone the apex of 
which is in the joint, the base at the distal extremity; rotation, in which 
the humerus revolves outward or inward around a vertical axis drawn 
through its head. 
The Elbow Joint is formed by the union of the lower end of the 
humerus with the sigmoid cavity of the ulna and the cup-shaped de- 
pression on the head of the radius. Owing to the configuration of these 
bones, great security is afforded this joint, independent of its ligamentous 
attachment. 
The function of this joint is to permit movements of flexion and exten- 
sion only, the former being limited at an angle of 30 to 40 degrees by 
the contact of the coronoid process with the humerus, the latter by the 
contact of the olecranous process with the humerus, when the ulna is in a 
straight line. This joint is not, strictly speaking, a true ginglymus joint, 
inasmuch as flexion and extension are attended by a screw like move- 
ment as the ulna glides over the obliquely disposed articular surface of 
the humerus. 
The Superior Radio-ulnar Joint is formed by the lesser sigmoid cavity 
of the ulna and the vertical border of the head of the radius, the latter 
being held firmly in position by the orbicular ligament. 
The Inferior Radio-ulnar Joint is formed by the concavity on the 
inner aspect of the radius and the inferior extremity of the ulna. 
The function of these joints is to permit movements of pronation 
and supination of the hand. The disposition of the ligaments at both ar- 
ticulations allows the head of the radius to revolve around a vertical axis 
and the inferior extremity to revolve around the ulna. In both supination 
and pronation the radius carries the hand with it. 
The Radio-carpal, or Wrist Joint, is formed by the union of the infe- 
rior quadrilateral surface of the radius, the triangular fibrocartilage and 
convex surfaces of the carpal bones, the scaphoid, semilunar, and cunei- 
form. 
The Carpal, Metacarpal, and Phalangeal Joints are formed by the 
union of the bones entering into the formation of the skeleton of the hand. 42 
HUMAN PHYSIOLOGY. 
The function of these joints is to endow the hand with all varieties 
and combinations of movements, enabling it to perform a large number of 
delicate and complicated actions. 
The Pelvic Girdle presents anteriorly the interpubic joint and poste- 
riorly the sacro iliac joints. 
The function of these joints, which are amphiarthrodial in character, 
is not so much to permit of movement, which is slight, as to prevent the 
forward and downward displacement of the sacrum and to enable it to 
transmit the weight of the body through the pelvic girdle to the lower ex- 
tremities. 
The Hip Joint is formed by the acetabulum on the outer surface of the 
os innominatum and the globular head of the femur, both structures being 
accurately adapted to each other. To retain the femur in position the ace- 
tabulum is deepened by a rim of cartilage; to render the joint more stable 
and to limit the extent of motion it is provided with strong ligaments and 
strengthened by overlying muscles. 
The function of the hip joint is to permit all those movements of the 
trunk on the femur, or the reverse, which are involved in walking, running, 
rowing, and allied muscular acts. Being a typical enarthrodial joint, 
movements can take place in all directions within certain limits, and may 
be grouped as follows :— 
1. A pendulum-like movement in any plane. 
2. Rotation around the long axis of the limb. 
3. Circumduction, in which the limb describes a cone, the apex of which is 
in the joint, the sides being formed by the limb itself. 
The Knee Joint is formed by the apposition of the articular surfaces of 
the femur, tibia, and patella. It is partially subdivided by the interposition 
of two fibrocartilages. From the mechanical construction of this articula- 
tion displacement of the bones would readily take place were it not pro- 
vided, as it is, with a large number of ligaments, tendons, and synovial 
membranes, which are so arranged as to make it the most complicated 
joint in the body. 
The function of the knee joint, being ginglymus in structure, is to per- 
mit movements of flexion and extension, which cover an angle of about 
145 degrees. These simple movements, however, are complicated by a 
gliding of the condyles upon the tibial facets so that the points of contact 
are constantly shifting. Owing to the shape of the condyles, extension is 
accompanied by outward rotation and flexion by inward rotation. GENERAL PHYSIOLOGY OF MUSCULAR TISSUE. 
43 
The Ankle Joint unites the skeleton of the foot to the lower extremity 
of the leg, and is formed by the apposition of the convex surface of the 
astragalus and the concavity of the tibia, and embraced on either side by 
the external and internal malleoli. 
The function of the ankle joint is to permit of flexion and extension 
around an axis passing through the body of the astragalus, but at such an 
angle that the movements do not take place in a direct anteroposterior 
plane, but in a plane directed outward and forward. It serves to transmit 
the weight of the body to the foot. 
The Tarsal, Metatarsal, and Phalangeal Joints unite the bones of 
the foot. They are very numerous and abundantly supplied with liga- 
ments and synovial membranes. 
The function of these joints is to endow the arches of the foot with 
considerable elasticity, to diminish the effects of jars or shocks that are 
transmitted to the vertebral column, and to adapt the foot to changes of 
form necessitated by the acts of walking, jumping, etc. 
GENERAL PHYSIOLOGY OF MUSCULAR 
TISSUE. 
The Muscular Tissue, which closely invests the bones of the body, 
and which is familiar to all as the flesh of animals, is the immediate cause 
of the active movements of the body. This tissue is grouped in masses of 
varying size and shape, which are technically known as muscles. Muscles 
are so arranged and connected, for the most part with the bones, in such a 
manner, that by an alteration in their form they can change not only the 
position of the bones with reference to one another, but can also change 
the individual’s relation to surrounding objects. They are, therefore, the 
active organs of both motion and locomotion, in contradistinction to the 
bones and joints, which are but passive agents in the performance of the 
corresponding movements. In addition to the muscular masses which are 
attached to the skeleton, there are also other collections of muscular tissue 
surrounding cavities such as the stomach, intestine, blood-vessels, etc., 
which impart to their walls motility, and so influence the passage of mate- 
rial through them. 
Muscles produce movement of the structures to which ey are attached 
by the property with which they are endowed of changing their shape, 44 
HUMAN PHYSIOLOGY 
shortening or contracting under the influence of a stimulus transmitted to 
them from the nervous system. Muscles are, therefore, divided into:— 
1. Voluntary muscles, comprising those whose activity is called forth by 
stimuli of the nerves as the result of an act or effort of volition. 
2. Involuntary muscles, comprising those whose activity is entirely inde- 
pendent of the volition. 
The voluntary muscles are also known from their attachment to the 
skeleton as skeletal, and from their microscopic appearance as striped mus- 
cles. The involuntary muscles, from their relation to the viscera of the 
body, are known also as visceral, and from their microscopic appearance as 
plain or smooth muscles. 
General Structure, of Muscles.—All skeletal muscles consist of a 
central fleshy portion, the body or belly, which is provided at either ex- 
tremity with a tendon in the form of a cord or membrane by which it is 
attached to the bones. The belly is the contractile region, the source of 
the motor activity ; the tendon is an inactive region and merely transmits 
the movement to the bones. 
A skeletal muscle is a complex organ consisting of muscular fibers, con- 
nective tissue, blood-vessels, and lymphatics. The general body of the 
muscle is surrounded by a dense layer of connective tissue, the epimysium, 
which blends with and partly forms the tendon; from its inner surface 
septse of connective tissue pass inward and group the muscular fibers into 
larger and smaller bundles, termed fasciculi. The fasciculi invested by 
this special sheath, the perimysium, are irregular in shape, and vary con- 
siderably in size. The fibers of the fasciculi are separated from each other 
and supported by a delicate connective tissue, the endomysiutti. The con- 
nective tissue thus surrounding and penetrating the muscle binds its fibers 
into a distinct organ, and affords support to blood-vessels, nerves, and lym- 
phatics. The muscular fibers are arranged parallel to each other, and their 
direction is that of the long axis of the muscle. In length they vary from 
30 to 40 millimeters, and in diameter from 20 to 30 micromillimeters. 
The Vascular Supply to the muscles is very great and the disposition 
of the capillary vessels with reference to the muscular fiber is very charac- 
teristic. The arterial vessels, after entering the muscle, are supported by the 
perimysium ; in this situation they give off short, transverse branches, which 
immediately break up into a capillary network of rectangular shape within 
which the muscular fibers are contained. The muscular fiber in intimate 
relation with the capillary is bathed with lymph derived from it. Its con- 
tractile substance, however, is separated from the lymph by its own invest- GENERAL PHYSIOLOGY OF MUSCULAR TISSUE. 
45 
mg membrane, through which all interchange of nutritive and waste mate 
rials must take place. Lymphatics are present in muscle, but confined to 
the connective tissue, in the spaces of which they take their origin. 
The Nerves which carry the stimuli to a muscle enter near its geomet- 
ric center. Many of the fibers pass directly to the muscular fibers with 
which they are connected ; others are distributed to blood-vessels. Every 
muscular fiber is supplied with a special nerve-fiber except in those instances 
where the nerve trunks entering a muscle do not contain as many fibers as 
the muscle. In such cases the nerve fibers divide until the number of 
branches equals the number of muscular fibers. The individual muscle 
fiber is penetrated near its center by the nerve, the ends being practically 
free from nerve influence. The stimulus that comes to the muscle fiber acts 
primarily upon its center and then travels in both directions to the ends. 
Histology of the Muscular Fiber.—A muscular fiber consists of a 
transparent elastic membrane, the sarcolemma, enclosing the true muscular 
contents. Examined microscopically, the fiber presents a series of alternate 
dim and bright bands, giving to it a striated appearance. 
When the bright band is examined with high magnifying powers a fine, 
dark line is seen crossing it transversely. It was supposed by Krause to 
be the optical expression of a membrane which divides the cavity of the 
sarcolemma into a series of compartments, each of which contains a dim 
band of sarcous or muscle substance bounded at either extremity with the 
half of a bright band. This membrane has since been resolved into a row 
of granules. 
The muscular fiber also exhibits a longitudinal striation indicating that it 
is composed of fibrillse, placed side by side and embedded in some inter- 
fibrillar substance, to which the name sarcoplasm has been given. The 
fibrillse which are arranged longitudinally to the long axis of the fiber are 
grouped by the intervening material into bundles of varying size, the 
muscle columns. The fibrillse which extend throughout the length of the 
fiber are not of uniform thickness, but present at regular intervals well- 
marked constrictions. 
In the region of the dim band, the fibrilla presents itself in the form of 
a homogeneous prismatic rod, termed sarcostyle, separated from neighboring 
rods by a slight amount of sarcoplasm. Between two successive rods is 
found a dark granule united by a thin band of similar material to the ends 
of the rods. The transverse row of granules corresponds to Krause’s 
membrane. 
In the region of the granules there is a diminution of the sarcous sub- 46 
HUMAN PHYSIOLOGY. 
stance, but an increase in the amount of sarcoplasm, and as the latter is 
more transparent than the former, the fiber presents at this point a conspic- 
uous bright band. Rollet considers the sarcostyles to be pre-existent, not 
the result of postmortem or chemic changes, and the seat of the contrac- 
tile elements. The sarcoplasm is a passive material similar in its properties 
to protoplasm. 
Briicke has shown that when the muscular fiber is examined under 
crossed Nichol prisms the dim band appears bright and the bright band 
appears dim against a dark background, indicating that the former is 
doubly refractile, or anisotropic, the latter singly refractile, or isotropic. 
The fiber, therefore, appears to be composed of alternate discs of anisotropic 
and isotropic substance. 
Structure of Nonstriated Muscular Fiber.—As the name implies, 
the involuntary fiber is nonstriated, being apparently uniform and homo- 
geneous in appearance. When isolated the fiber presents itself in the form 
of an elongated fusiform cell varying from the one-tenth to the one-six 
hundredth of an inch in length. In some animals the fiber exhibits a 
longitudinal striation, as if it were composed of fibers. The cell is sur- 
rounded by a thin, elastic membrane, and contains a distinct oval nucleus. 
The fibers are usually arranged in bundles and lamellae, and held together 
by a cement substance and connective tissue. This nonstriated muscular 
tissue is found in the muscularis mucosae of the alimentary canal as well as 
in the muscular walls of the stomach and intestines, in the posterior part of 
the trachea, in the bronchial tubes, in the walls of the blood-vessels, and in 
many other situations. 
Chemic Composition of Muscle.—The chemic composition of 
muscle is imperfectly understood, owing to the fact that some of its constit- 
uents undergo a spontaneous coagulation after death, and that the chemic 
methods employed also tend to alter its normal composition. When fresh 
muscle is freed from fat and connective tissue, frozen, rubbed up in a mor- 
tar, and expressed through linen, a slightly yellow, syrupy, alkaline, or 
neutral fluid is obtained, known as muscle plasma. This fluid at normal 
temperature coagulates spontaneously and resembles in many respects the 
coagulation of blood plasma. The coagulum subsequently contracts and 
squeezes out an acid muscle serum. The coagulated mass is termed myosin. 
This proteid belongs to the class of globulins. Inasmuch as it is not 
present in living muscle, and only makes its appearance in the as yet living 
muscle plasma, it is probable that it is derived from some pre existing 
substance, which is supposed to be myosinogen. Myosin is digested by GENERAL PHYSIOLOGY OF MUSCULAR TISSUE. 
47 
pepsin and trypsin. According to Halliburton, muscle plasma contains the 
following proteid bodies: Myosinogen, paramyosinogen, albumin, myoal- 
bumose, all of which differ in chemic composition and respond to various 
chemic and physical reagents. 
Ferment bodies, such as pepsin and diastase; nonnitrogenized bodies, 
such as glycogen, lactic, and sarcolactic acid, fatty bodies, and inosite; 
nitrogenized extractives, e. g., urea, uric acid, kreatinin, as well as inor- 
ganic salts, have been obtained from the muscle serum. 
Metabolism in Muscles.—The chemic changes which underlie the 
transformation of energy in living muscles are very active and complex. 
As shown by an analysis of the blood flowing to and from the resting 
muscle, it has, while passing through the capillaries, lost oxygen and 
gained carbon dioxid. The amount of oxygen absorbed by the muscle, 
nine per cent., is greater than the amount of C02 given off, 6.7 per cent. 
There is no parallelism between these two processes, as C02 will be given 
off in the absence of oxygen, or in an atmosphere of nitrogen. 
In the active or contracting muscle both the absorption of oxygen and 
the production of C02 are largely increased, but the ratio existing between 
them differs considerably from that of the resting muscle, for the quantity 
of oxygen absorbed amounts to 11.26 per cent , the quantity of C02 10.8 
per cent. (Ludwig). Moreover, in a tetanized muscle the quantity of C02 
given off may be largely in excess of the oxygen absorbed. From these 
facts it is evident that the energy of the contraction does not depend upon 
the direct oxidation of certain substances, but upon the decomposition of 
some unstable compound of high potential energy, rich in carbon and 
oxygen. When the muscle is active, its tissue changes from a neutral to an 
acid reaction from the development of sarcolactic and possibly phosphoric 
acids. The amount of glycogen present in muscle, 0.43 per cent., 
diminishes, but muscles wanting in glycogen, nevertheless, retain their 
power of contraction. Water is absorbed. The amount of urea is not 
materially increased by muscular activity, unless it is excessive and pro- 
longed, and then only in the absence of a sufficient quantity of nonnitro- 
genized material. Coincident with muscular contraction, the blood-vessels 
become widely dilated, leading to a large increase in the blood supply and 
a rapid removal of products of decomposition. 
Rigor Mortis.—A short time after death the muscles pass into a con- 
dition of extreme rigidity or contraction, which lasts from one to five days. 
In this state they offer great resistance to extension, their tonicity disap- 
pears, their cohesion diminishes, their irritability ceases. The time of the 48 
HUMAN PHYSIOLOGY. 
appearance of this postmortem or cadaveric rigidity varies from a quarter 
of an hour to seven hours. Its onset and duration are influenced by the 
condition of the muscular irritability at the time of death. When the irri- 
tability is impaired from any cause, such as disease or defective blood sup- 
ply, the rigidity appears promptly, but is of short duration. After death 
from acute diseases it is apt to be delayed, but to continue for a longer 
period. 
The rigidity appears first in the muscles of the lower jaw and neck; 
next in the muscles of the abdomen and upper extremities; finally in the 
trunk and lower extremities. It disappears in practically the same order. 
Chemic changes of a marked character accompany this rigidity. The 
muscle becomes acid in reaction from the development of sarcolactic acid, 
it gives off a large quantity of carbonic acid, and is shortened and dimin- 
ished in volume. 
The immediate cause of the rigidity appears to be a coagulation of the 
myosinogen within the sarcolemma, with the subsequent formation of 
myosin and muscle serum. In the early stages of coagulation restitution 
is possible by the circulation of arterial blood through the vessels. The 
final disappearance of this contraction is due to the action of acids dissolv- 
ing the myosin, and possibly to putrefactive changes. 
Source of Muscular Energy.—According to most experimenters, it 
is certain that normal muscular activity is not dependent on the metabolism 
of nitrogenous materials, inasmuch as its chief end product, urea, is not 
increased. The marked production of C02 points to the combustion of 
some nonnitrogenous matter; e. g., glycogen, especially as this substance 
disappears during muscular activity. Muscles wanting in glycogen are, 
nevertheless, capable of contracting for some time. Moreover, there is no 
proof of the direct combustion of glycogen or any other carbohydrate. It 
has been suggested by Hermann that the energy of a muscular contraction 
may be due to the splitting and subsequent re-formation of a complex body 
belonging neither to the carbohydrates or fats, but to the albumins. To 
this body the term inogen has been given. This complex molecule, the 
product of the metabolic activity of the muscle cell, in undergoing decom- 
position would yield C02, sarcolactic acid, and a proteid residue resembling 
myosin. With the cessation of the contraction, the muscle protoplasm 
recombines the proteid residue with oxygen, carbohydrates, and fats, and 
again forms inogen. 
The phenomena of rigor mortis support such a view. At the moment of 
this contraction the muscle gives off C02 in large amounts, the muscle 
becomes acid, and myosin is formed. There is thus a close analogy GENERAL PHYSIOLOGY OF MUSCULAR TISSUE. 
49 
between the two processes; in other words, a contraction is a partial death 
of the muscle. As to what becomes of the myosin formed during a contrac 
tion, nothing is known. It may be used in the formation of new inogen. 
The Physical Properties of Muscular Tissue.—The consistency of 
muscular tissue varies considerably, according to the different states of the 
muscle. In a state of tension, it is hard and resistant; when free from 
tension, it is soft and fluctuating, whether the muscle is contracting or rest- 
ing. Tension alone produces hardness. The cohesion of muscular tissue 
is less than that of connective tissue, and is broken more readily. Cohesion 
resists traction and pressure, and lasts as long as irritability remains. 
The elasticity of a muscle, though not great, is almost perfect. After 
being extended by a weight, it returns to its natural form. The limit of 
elasticity, however, is soon passed. A weight of 50 or 100 grams will 
overcome the elasticity so that it will not return to its original length. In 
inorganic bodies the extension is directly proportional to the extending 
weight, and the line of extension is straight. With muscles the extension 
is not proportional to the weight. While at first it is marked, the elonga- 
tion diminishes as the weight increases by equal increments, so that the 
line of extension becomes a curve. In other words, the elasticity of a 
passive muscle increases with increased extension. On the contrary, the 
elasticity of an active is less than a passive muscle, for it is elongated more 
by the same weight, as shown by experiment. 
Tonicity is a property of all muscles in the body, in consequence of 
being normally stretched to a slight extent beyond their natural length. 
This may be due to the action of antagonistic muscles, or to the elasticity 
of the parts of the skeleton to which they are attached. This is shown by 
the shortening of the muscle which takes place when it is divided. Muscu- 
lar tonus plays an important role in muscular contraction. Being always 
on the stretch, the muscle loses no time in acquiring that degree of tension 
necessary to its immediate action on the bones. Again, the working power 
of a muscle is increased by the presence of some resistance to the act of 
contraction. According to Marey, the amount of work is considerably 
increased when the muscular energy is transmitted by an elastic body to the 
mass to be moved, while, at the same time, the shock of the contraction is 
lessened. The position of a passive limb is the resultant also of the elastic 
tension of antagonistic groups of muscles. 
Muscular Excitability or Contractility are terms employed to denote 
that property of muscular tissue in virtue of which it contracts or shortens 
in response to various excitants or stimuli. Though usually associated with 50 
HUMAN PHYSIOLOGY. 
the activity of the nervous system, it is, nevertheless, an independent en- 
dowment and persists after all nervous connections are destroyed. If the 
nerve terminals be destroyed, as they can be by the introduction of curara 
into the system, the muscles become completely relaxed and quiescent. 
The strongest stimuli applied to the nerves fail to produce a contraction. 
Various external stimuli applied directly to the muscle substance produces 
at once the characteristic contraction. The excitability of muscle is there 
fore an inherent property, dependent on its nutrition and persisting as long 
as it is supplied with proper nutritive materials and surrounded by those 
external conditions which maintain its chemic or physical integrity. 
Muscular Contractions.—All muscular contractions occurring in the 
body under normal physiologic conditions are either voluntary, caused 
by a volitional effort and the transmission of a nerve impulse from the 
brain through the spinal cord and nerves to the muscles; or reflex, caused 
by a peripheral stimulation and the transmission of a nerve impulse to the 
spinal cord, to be reflected outward through the same nerves to the muscles. 
In either case the resulting contraction is essentially the same. The normal 
or physiologic stimulus which provokes the muscular contraction is a 
nerve impulse the nature of which is unknown, but is perhaps allied to a 
molecular disturbance. After removal from the body muscles remain in a 
state of rest, inasmuch as they possess no spontaneity of action. Though 
consisting of a highly irritable tissue, they cannot pass from the passive to 
the active state except upon the application of some form of stimulation. 
The stimuli which are capable of calling forth a contraction may be 
divided into:— 
1. Mechanical. 
2. Chemic. 
3. Physical. 
4. Electric. 
Every mechanical stimulus of a muscle, e. g., pick, cut, or tap, providing 
it has sufficient intensity, and is repeated with sufficient rapidity, will cause 
not only a single but a series of contractions. 
All chemic agents which impair the chemic composition of the muscle 
with sufficient rapidity, e.g., hydrochloric acid, acetic and oxalic acids, dis- 
tilled water injected in the vessels, etc., act as a stimuli, and produce single 
and multiple contractions. Physical agents, as heat and electricity, also 
act as stimuli. A muscle heated rapidly to 30° C. contracts vigorously, 
and reaches its maximum at 450 C. Of all forms of stimuli the electric 
is the most generally used. Two forms are used—the induced current and 
the make-and-break of a constant current. GENERAL PHYSIOLOGY OF MUSCULAR TISSUE. 
51 
Changes in a Muscle During Contraction.—When a muscle is 
stimulated, either indirectly through the nerve or directly by any external 
agent, it undergoes a series of changes which relate to its form, volume, 
optical, physical, chemic, and electric properties. These changes in 
their totality constitute the muscular contraction. 
1. Form.—The most obvious change is that of form. The fibers become 
shorter in their longitudinal and wider in their transverse diameters, and 
the muscle as a whole becomes shorter and thicker. The degree of 
shortening may amount to 30 per cent, of the original length. 
2. Volume.—The increase in transverse diameter does not fully compen- 
sate for the diminution in length, for there is at the moment of contrac- 
tion a slight shrinkage in volume, which has been attributed to a 
compression of air in its interstices. 
3. Optical Changes.—If a muscular fiber be examined microscopically 
during its contraction, it will be observed that when the contraction 
wave begins both bright and dim bands diminish in height and become 
broader, though this change is more noticeable in the region of the bright 
band. This Englemann attributes to a passage of fluid material from 
the bright into the dim band. At the time of relaxation there is a re- 
turn of this material and the fiber assumes its original shape and volume. 
As the contraction wave reaches its maximum, the optical properties of 
both the isotropic and anisotropic bands change. The for7ner, which 
was originally clear, now becomes darker and less transparent, until at 
the crest of the wave it assumes the appearance of a distinct dark band. 
The latter, the anisotropic, which was originally dim, now becomes, in 
comparison, clear and light. This change in optical appearance is due 
to an increase in refrangibility of the isotropic and a decrease in the 
anisotropic bands coincident with the passage of fluid from the former 
into the latter. There is at the height of the contraction a complete 
reversal in the positions of the striations. At a certain stage between the 
beginning and the crest of the wave there is an intermediate point at 
which the striae almost entirely disappear, giving to the fiber an appear- 
ance of homogeneity. There is, however, no change in refractive power 
as shown by the polarizing apparatus. After the contraction wave has 
reached the stage of greatest intensity, there is a reversal of the above 
phenomena, and the fiber returns to its original condition, which is one 
of relaxation. 
Physical Changes.—The extensibility of muscle is increased during the 
contraction, the same weight elongating the fibers to a greater extent than 52 
HUMAN PHYSIOLOGY. 
during rest. The elasticity, or its power of returning to its original form, 
is correspondingly diminished. 
' Chemic Changes.—The metabolism of muscle during the contraction is 
very active. There is an increase in the production of carbon dioxid and 
the absorption of oxygen. The muscle changes from an alkaline or neu- 
tral to an acid reaction, from the development of sarcolactic acid. The 
muscle also becomes warmer. The electric changes will be treated of in 
connection with nerves. 
Transmission of the Contraction Wave.—Normally, when a mus- 
cle is stimulated by the nerve impulse the shortening and thickening of the 
fibers begin at the end organ and travel in opposite directions to the ends 
of the muscle. This change propagates itself in a wave-like manner and 
has been termed the contraction wave. If a stimulus be applied directly 
to the end of a long muscle, the contraction wave passes along its entire 
length to the opposite extremity in virtue of the conductivity of muscular 
tissue. The rapidity of the propagation varies in different animals—in 
the frog from three to four meters per second, in man from io to 13 meters. 
The length of the wave varies from 200 to 400 millimeters. 
Graphic Record of a Muscular Contraction.—The changes in the 
form of a muscle during contraction and relaxation have been carefully 
studied by recording the muscular movement by means of an attached 
lever, the end of which is applied against a traveling surface. The time 
relations of all phases of the muscular movement are obtained by placing 
beneath the lever a pen attached to an electro-magnet thrown into action 
by a tuning fork vibrating in hundredths of a second. A marking lever 
records simultaneously the moment of stimulation. 
Single Contraction.—When a single electric induction shock is ap- 
plied to a nerve close to the muscle, the latter undergoes a quick pulsa- 
tion, speedily returning to its former condition. As shown by the muscle 
curve (see Fig. 2), there is between the moment of stimulation and the 
beginning of the contraction a short but measurable period, known as the 
latent period, during which certain chemic changes are taking place pre- 
paratory to the exhibition of the muscular movement. Even when the 
electric stimulus is applied directly to the muscle a latent period, though 
shorter, is observable. The duration of this period in the skeletal muscles 
of the frog has been estimated at 0.01 of a second, but it has been shown 
by the employment of more accurate methods and the elimination of vari- 
ous external influences to be much less, not more than 0.0033 to 0.0025 °f 
a second. GENERAL PHYSIOLOGY OF MUSCULAR TISSUE. 
53 
The contraction follows the latent period. This begins slowly, rapidly 
reaches its maximum, and ceases. This has been termed the stage of rising 
or increasing energy. The time occupied in the stage of shortening is 
about 0.04 of a second, though this will depend on the strength of the 
stimulus, the load with which the muscle is weighted, and the condition of 
the muscular irritability. 
The relaxation immediately follows the contraction. This takes place 
at first slowly, after which it rapidly returns to its original length. This is 
the period of falling or decreasing energy and occupies about 0.05 of a 
second. The whole duration of a muscular contraction occupies, there- 
fore, about 0.1 of a second. 
Residual, or after-vibrations, are frequently seen which are due to changes 
Fig. 2.—Muscle Curve Produced by a Single Induction Shock Applied to a 
Muscle. 
a-f. Abscissa, a-c. Ordinate, a-b. Period of latent stimulation, b-d. Period of 
increasing energy, d-e. Period of decreasing energy, e-f. Elastic after-vibrations. 
(Landois.) 
in the elasticity of the muscle. The amplitude of the contraction depends 
upon the condition of the muscle, the load, the strength of stimulus, etc. 
Contraction of Nonstriated Muscle.—The curve obtained by regis- 
tration of the contraction of nonstriated muscle shows that it is similar in 
many respects to that of the striated muscle, except that the duration of 
the former is considerably longer than the latter. 
Action of Successive Stimuli.—If a series of successive stimuli be 
applied to a muscle, the effect will be different according to the rapidity 
with which they follow each other. If the second stimulus be applied at 
the termination of the contraction due to the first stimulus, a second con- 
traction follows similar in all respects to the first. A third stimulus pro- 
duces a third contraction, and so on until the muscle becomes exhausted. 
If the second stimulus be applied during either of the two periods of the 
first contraction, the effects of the two stimuli will be added together and 
the second contraction will add itself to the first. The maximum contrac- 54 
HUMAN PHYSIOLOGY. 
tion is obtained when the second stimulus is applied fa of a second after 
the first. 
Tetanus.—When a series of stimuli are applied to a muscle following 
each other with medium rapidity, the muscle does not get time to relax in 
the intervals of stimulation, but remains in a state of vibratory contraction, 
which may be regarded as incipient tetanus, or clonus. As the stimulation 
increases in frequency the vibrations become invisible, being completely 
fused together. There is, nevertheless, during the tetanic condition a series 
of continuous contractions and relaxations taking place. After a varying 
length of time the muscle becomes fatigued, and, notwithstanding the stim- 
ulation, begins slowly to elongate. The number of stimuli necessary per 
second for the production of tetanus varies in different animals; e. g., 2 to 
3 for muscles of the tortoise, io for muscles of the rabbit, 15 to 20 for the 
frog, 70 to 80 for the birds, 330 to 340 for insects. 
A Voluntary Contraction in man may be regarded as a state of 
tetanus, for if the curve of a voluntary movement be examined it will be 
found to consist of intermittent vibrations. The simplest voluntary move- 
ment of a muscle, however rapidly it may take place, lasts longer than a 
single muscular contraction due to an induction shock. The most rapid 
voluntary contraction is the result of from 2.5 to 4 stimulations per second 
and has a duration of from 0.041 to 0.064 of a second. A continuous 
voluntary contraction is an incomplete tetanus. The number of stimuli 
sent to the muscles is, on the average, 16 to 18 for rapid contractions, 8 to 
12 for slow contractions. 
The Production of Heat and its Relation to Mechanical Work. 
—The transformation of energy which takes place during a muscular con- 
traction, and which is dependent upon chemic changes occurring at that 
time, manifests itself as heat and mechanical work. While heat is being 
evolved continuously during the passive condition of muscles, the amount 
of heat is largely increased during general muscular contraction. A skele- 
tal muscle of a frog, e. g., the gastrocnemius, when removed from the body 
shows, after tetanization, an increase in its temperature of from o. 140 to 
0.180 C., and after a single contraction of from o.ooi° to 0.005° C. While 
every muscular contraction is attended by an increase in heat production, 
the amount so produced will vary in accordance with certain conditions, 
e.g., tension, work done, fatigue, circulation of blood, etc. 
Tension.—The greater the tension of a muscle, the greater, other con 
ditions being equal, is the amount of heat evolved. When the ends of a 
muscle are fastened so that no shortening is possible during stimulation the GENERAL PHYSIOLOGY OF MUSCULAR TISSUE. 
55 
maximum of heat production is reached. In the tetanic state the large in- 
crease in temperature is due to the tension of antagonistic and strongly con- 
tracted muscles. The evolution of heat, therefore, bears a relation to the 
resistance against which the muscle is acting. 
Mechanical Work.—If a muscle contracts loaded by a weight just suffi- 
cient to elongate it to its original length, heat is evolved, but no mechanical 
work is done, all the energy liberated manifesting itself as heat. When 
the weight which has been lifted is removed from the muscle at the height 
of contraction, external work is done. In this case the amount of heat 
liberated is less, owing to the work done, for some of the heat generated is 
transformed into mechanical motion. According to the law of the con- 
servation of energy, the amount of heat disappearing should correspond in 
heat units to the number of foot pounds produced by muscular contraction. 
Muscle Sound.—Providing a muscle be kept in a state of tension 
during its contraction, the intermittent variations of its tension cause the 
muscle to emit an audible sound. If the muscle be tetanized by induction 
shocks, the pitch of the sound corresponds with the number of stimuli per 
second. A voluntary contraction is attended by a tone having a vibration 
frequency of about 36 per second, which is, however, the first overtone of 
the true muscle tone, which is caused by a contraction frequency of about 
18 per second. This low tone is inaudible, from the low rate of vibrations 
per second. 
Muscular Fatigue.—Prolonged or excessive muscular activity is fol- 
lowed by a diminution in the power of producing work and in increase in 
the duration of the muscular contractions. Fatigue is accompanied by a 
feeling of stiffness, soreness, and lassitude, referable to the muscles them- 
selves. In the early stages of muscular fatigue, the contractions increase in 
height and duration, to be followed by a progressive decrease in height, 
but an increase in duration, until the muscle becomes exhausted. The 
cause of the fatigue is the production and accumulation of decomposition 
products, such as phosphoric acid and phosphate of potassium, C02, etc. 
A fatigued muscle is rapidly restored by the injection of arterial blood. 
Work Done.—Muscles are machines capable of doing a certain amount 
of work, by which is meant the raising of a weight against gravity or the 
overcoming of some resistance. The work done is calculated by multiply- 
ing the weight by the distance through which it is raised. Thus, if a 
muscle shortens four millimeters and raises 250 grams, it does work equal 
to 1000 milligram-meters, or one gram-meter. If a muscle contracts with- 
out being weighted, no work is done. Equally, when the muscle is over- 56 
HUMAN PHYSIOLOGY. 
weighted so that it is unable to contract, no work is done. The amount of 
work a muscle can do will depend upon the area of its transverse section, 
the length of its fibers, and the amount of the weight. The amount of work 
a laborer of 70 kilograms weight performs in eight hours averages 105,605 
kilogram-meters, or 340.2 foot tons. 
The individual muscles of the axial and appendicular portions of the 
body are named with reference to their shape, action, structure, etc.; e. g., 
deltoid, flexor, penniform, etc. In different localities, a group of muscles 
having a common function is named in accordance with the kind of motion 
it produces or gives rise to; e. g., groups of muscles which alternately 
bend or straighten a joint, or alternately diminish or increase the angular 
distance between two bones, are known respectively as flexors and extensors ; 
such muscular groups are in association with ginglymus joints. Muscles 
which turn the bone to which they are attached around its own axis without 
producing any great change of position are known as rotators, and are in 
association with the enarthrodial, or ball-and-socket joints. Muscles which 
impart an angular movement of the extremities to and from the median line 
of the body are termed abductors and adductors. 
In addition to the actions of individual groups of muscles in causing 
special movements in some regions, several groups of muscles are coordi- 
nated for the accomplishment of certain definite functions; e. g., muscles of 
respiration, mastication, expression. The coordination of axial and appen- 
dicular muscles enables the individual to assume certain postures, such as 
standing and sitting ; to engage in various acts of locomotion, as walking, 
running, swimming, etc. 
Levers.—The function or special mode of action of individual muscles 
can only be understood when the bones with which they are connected are 
regarded as levers whose fulcra or fixed points lie in the joints where the 
movement takes place, and the muscles as sources of power for imparting 
movement to the levers with the object of overcoming resistance or raising 
weights. 
In mechanics, levers of three kinds or orders are recognized, according 
to the relative position of the fulcrum or axis of motion, the applied power, 
and the weight to be moved. See Fig. 3. 
In levers of the first order the fulcrum, F, lies between the weight or 
SPECIAL PHYSIOLOGY OF MUSCLES. SPECIAL PHYSIOLOGY OF MUSCLES. 
57 
resistance, W, and the power of moving force, P. The distance PF is 
known as the power arm, the distance WF as the weight arm. As an 
example of this form of lever in the human body may be mentioned— 
1. The elevation of the trunk from the flexed position. The axis of move- 
ment, the fulcrum, lies in the hip joint; the weight, that of the trunk, 
acting as if concentrated at its center of gravity, placed between the 
shoulders; the power, the contracting muscles attached to the tuberosity 
of the ischium. The opposite movement is equally one of the first order, 
but the relative positions of P and W are reversed. 
2. The skull in its movements backward and forward upon the atlas. 
In levers of the second order the weight lies between the power and the 
fulcrum. As an illustration of this form of lever may be mentioned— 
1. The depression of the lower jaw, in which movement the fulcrum is the 
temporomaxillary articulation ; the resistance, the tension of the elevator 
muscles; the power, the contraction of 
the depressor muscles. 
2. The raising of the body on the toes—F 
being the toes, W the weight of the body 
acting through the ankle, P, the gastroc- 
nemius muscle acting upon the heel 
bone. 
In levers of the third order the power is 
applied at a point lying between the fulcrum 
and the weight. As examples of this form 
of lever may be mentioned— 
1. The flexion of the forearm—F being the elbow joint, P the contracting 
biceps and brachialis anticus muscles applied at their insertion, W the 
weight of the forearm and hand. 
2. The extension of the leg on the thigh. 
When levers are employed in mechanics, the object aimed at is the over- 
coming of a great resistance by the application of a small force acting 
through a great space so as to obtain a mechanical advantage. In the 
mechanism of the human body the reverse generally obtains, viz., the over- 
coming of a small resistance by the application of a great force acting 
through a small space. As a result there is a gain in the extent and rapid- 
ity of movement of the lever. The power, however, owing to its point of 
application, acts at a great mechanical disadvantage in many instances, 
especially in levers of the third order. 
Postures.—Owing to its system of joints, levers, and muscles, the human 
body can assume a series of positions of equilibrium, such as standing and 
Fig. 3.—TheThrek Orders of 
Levers. 58 
HUMAN PHYSIOLOGY. 
sitting, to which the name posture has been given. In order that the body 
may remain in a state of stable equilibrium in any posture, it is essential 
that the vertical line passing through the center of gravity shall fall within 
the base of support. 
Standing is that position of equilibrium in which a line drawn through' 
the center of gravity falls within the area of both feet placed on the ground. 
This position is maintained— 
1. By firmly fixing the head on the top of the vertebral column by the 
action of the muscles on the back of the neck. 
2. By making the vertebral column rigid, which is accomplished by the 
longissimus dorsi and the quadratus lumborum muscles. This having 
been accomplished, the center of gravity falls in front of the tenth dorsal 
vertebra; the vertical line passing through this point falls behind the 
line connecting both hip joints. In consequence, the trunk is not balanced 
on the hip joints, and would fall backward were it not prevented by the 
contraction of the rectus femoris muscle and ligaments. At the knees 
and ankles a similar balancing of the parts above is brought about by 
the action of various muscles. When the entire body is in the erect or 
military position, the arms by the sides, the center of gravity lies between 
the sacrum and the last lumbar vertebra and the vertical line touches 
the ground between the feet and within the base of support. 
Sitting erect is a condition of equilibrium in which the body is balanced 
on the tubera ischii, when the trunk and head together form a rigid column. 
The vertical line passes between the tubera. 
Locomotion is the act of transferring the body, as a whole, through 
space, and is accomplished by the combined action of its own muscles. 
The acts involved consist of walking, running, jumping, etc. 
Walking is a complicated act involving almost all the voluntary muscles 
of the body, either for purposes of progression or for balancing the head and 
trunk, and maybe defined as a progression in a forward horizontal direc- 
tion, due to the alternate action of both legs. In walking, one leg becomes, 
for the time being, the active or supporting leg, carrying the trunk and head, 
the other the passive but progressive leg, to become in turn the active leg 
when the foot touches the ground. Each leg, therefore, is alternately in an 
active and passive state. 
Running is distinguished from walking by the fact that, at a given mo- 
ment, both feet are off the ground and the body is raised in the air. 
While the limits of a compend do not permit of a description of the origin, 
insertion, and mode of action of the individual muscles of the body, it has 
been thought desirable to call attention to a few of the principal muscles SPECIAL PHYSIOLOGY OF MUSCLES. 
59 
whose function it is to produce special forms of movement, as well as loco- 
motion. (See Fig. 4.) The erect position is largely maintained by the 
fixation of the spinal column and the balancing of the head upon its upper 
extremity; the former is accompanied by the Erector spina muscle, named 
from its function and its fleshy continuations, situated on each side of the 
vertebral column. Arising from the pelvis and lumbar vertebrae, this muscle 
passes upward, and is attached by its continuations to all the vertebrae. Its 
action is to extend the vertebral column and to maintain the erect position. 
The head is balanced upon the top of the vertebral column by the com- 
bined action of the trapezius and suboccipital muscles forming the nape of 
the neck, and by the Sterno-cleido-mastoid muscle. This latter muscle 
arises from the inner third of the clavicle and upper border of the sternum. 
It is inserted into the temporal bone just behind the ear. Its action is to 
flex the head laterally and to rotate the face to the opposite side. When 
both muscles act simultaneously the head and neck are flexed upon the 
thorax. 
The Temporal and Masseter muscles, situated at the side of the head, 
arise respectively from the temporal fossa and the zygomatic arch and are 
inserted into the ramus of the lower jaw. Their action is to close the 
mouth and assist in mastication. The Occipitofrontalis, the Orbicularis 
palpebrarum, and Orbicularis oris muscles are largely concerned in wrink- 
ling the forehead, closing the eyes and mouth, and in giving various expres- 
sions to the face. 
The Deltoid is a thick, triangular muscle covering the shoulder joint. 
Arising from the outer third of the clavicle, the acromion process and the 
spine of the scapula, its fibers converge to be inserted into the humerus 
just above its middle. Its action is to elevate the arm through a right angle. 
Owing to its point of insertion it acts as a lever of the third order, but, 
notwithstanding the advantageous point of insertion, it acts at a consider- 
able disadvantage, owing to the obliquity of its direction. 
The Biceps muscle, situated on the anterior aspect of the arm, arises from 
the upper border of the glenoid fossa and the coracoid process, and is 
inserted into the radius just beyond the elbow joint. Its action is to flex 
and supinate the forearm and to place it in the most favorable position for 
striking a blow. When the forearm is fixed it assists in flexing the arm, as 
in climbing. 
The Triceps muscle, situated on the back of the arm, arises from the 
scapula and the posterior surface of the humerus, and is inserted in the 
olecranon process of the ulna. In its action it directly antagonizes the 
biceps, namely, extending the forearm. In so doing it acts as a lever of 60 
HUMAN PHYSIOLOGY. 
the first order. The short distance between the muscular insertion and the 
fulcrum causes it to act at a great mechanical disadvantage, but there is a 
corresponding gain in both speed and range of movement. The muscles 
of the forearm are very numerous. Their action is to impart to the fore- 
arm and hand a variety of movements, such as pronation, supination, 
flexion, extension, rotation, etc. 
The Pectoralis Major and Minor muscles form the fleshy masses of the 
breast. Arising from the inner half of the clavicle, the side of the sternum, 
and the outer surfaces of the third, fourth, and fifth ribs anteriorly, the mus- 
cular fibers converge to be inserted into the humerus and coracoid process. 
Their combined action is to adduct, flex, and rotate the arm inward, and 
to draw the scapula downward and forward, movements necessary to the 
folding of the arms across the chest. 
The Rectus abdominis and the Obliquus externus assist in forming the 
abdominal walls. 
The Glutei' muscles are three in number, arranged in layers, and form 
the fleshy masses known as the buttocks. They arise from the side of the 
pelvis and are attached to the femur in the neighborhood of the great tro- 
chanter. Their action is to extend the hips, to raise the body from the 
stooping position, to assist in walking by firmly holding the pelvis on the 
thigh while the opposite leg is advanced in the forward direction. 
The Rectus femoris wdth its associates, the rectus internus and externus 
and crureus, form the fleshy mass on the anterior surface of the thigh. The 
former arises from the anterior part of the ilium, the latter from the femur. 
Their common tendon, which is united to the patella, is continued as the 
ligamentum patellae, which is attached to the upper part of the tibia. The 
action of this muscular group is to extend the leg, to flex the thigh, and to 
raise the entire weight of the body, as in passing from the sitting to the 
erect position. 
The Biceps femoris muscle, situated on the outer and posterior aspect of 
the thigh, arises from the tuber ischii and is inserted into the head of the 
fibula. 
The Semimembranosus and the Semitendinosus muscles, situated on 
the inner and posterior aspect of the thigh, are inserted into the head of 
the tibia. Their combined action is to extend the hips and to flex the knee. 
Acting from below, they assist in raising the body from the stooping 
position. 
The Gastrocnemius muscle forms the enlargement known as the calf of 
the leg. It arises by two heads from the condyles of the femur. Its ten- 
don, the tendo-achillis, is inserted into the posterior surface of the heel Fig. 4.—Superficial Muscles of the Body. 
61 62 
HUMAN PHYSIOLOGY. 
bone. Its action is to extend the foot and to raise the weight of the body 
in walking and running. On the front of the leg are numerous muscles, 
e. g., Tibialis anticus, Peroneus longus, etc., the action of which is to flex 
the foot and to antagonize the gastrocnemius. 
PHYSIOLOGY OF NERVOUS TISSUE. 
The Nervous Tissue, which unites and coordinates the various organs 
and tissues of the body and brings the individual into relationship with 
the external world, is arranged in two systems termed the Cerebrospinal 
and the Sympathetic. 
The Cerebrospinal System consists in man and the higher animals 
of— 
1. The brain and spinal cord contained within the cavities of the cranium 
and spinal column respectively, and 
2. The cranial and spinal nerves. 
The Sympathetic System consists of— 
1. A double chain of ganglia connected together by nerves, situated on 
each side of the spinal column and extending from the base of the skull 
to the tip of the coccyx. 
2. Of various collections of ganglia situated in the head, face, thorax, 
abdomen, and pelvis; all the ganglia are united by an elaborate system 
of intercommunicating nerves, many of which are connected with the 
nerves of the cerebrospinal system. 
It is usually stated that the cerebrospinal system is the nervous system of 
animal life and presides over the functions of motion, sensation, etc., while 
the sympathetic is the nervous system of organic life and governs the 
functions of nutrition, growth, secretion, etc. There is reason to believe 
that this distinction of function between the two systems is not a natural 
but an artificial one; that the ganglia of the sympathetic system do not 
possess independent functions, but are rather modifiers of the action of 
nerves originating in the cerebrospinal system. 
Nervous Tissue is composed of two kinds of matter, the gray and 
white, which differ in their color, structure, and physiologic endowments; 
the former consists of vesicles or cells which receive and generate nerve 
force; the latter consists of fibers which simply conduct it, either from the 
periphery to the center or the reverse. PHYSIOLOGY OF NERVOUS TISSUE. 
63 
Structure of Gray Matter.—The gray matter, found on the surface of 
the brain, in the convolutions, in the interior of the spinal cord, and in the 
various ganglia of the cerebrospinal and sympathetic nervous systems, con- 
sists of a fine connective tissue stroma, the neuroglia, in the meshes of 
which are embedded the gray cells or vesicles. 
The cells are grayish in color, and consist of a delicate investing capsule 
containing a soft, granular, albuminous matter, a nucleus, and sometimes a 
nucleolus. Some of the cells are spherical or oval in shape, while others 
have an interrupted outline, on account of having one, two, or more pro- 
cesses issuing from them, constituting the unipolar, bipolar, or multipolar 
nerve cells. Cells vary in size : the smallest being found in the brain, the 
largest in the anterior horns of the gray matter of the cord. Some of the 
cell processes become continuous with the fibers of the white matter, while 
others anastomose with those of adjoining cells. 
Structure of White Matter.—The white matter, found for the most 
part in the interior of the brain, on the surface of the spinal cord, and in 
almost all the nerves of the cerebrospinal and sympathetic systems, consists 
of minute fibers cylindrical in form, arranged in bundles held together by 
connective tissue. The nerve fibers present considerable variation in size 
in different parts of the nervous system. The largest fibers are found in 
the peripheral nerves, where they have a diameter of °f an inch 5 
the smallest are found in the brain and spinal cord, where they have a diam- 
eter of only of an inch. 
A typical nerve fiber presents three well-marked structural elements, 
g. .— 
1. An external investing membrane, tubular in shape. 
2. An intermediate semifluid substance, the medulla or myelin. 
3. A dark central thread, the axis cylinder. 
Many fibers, however, are devoid of the medulla. This variation in 
structure has led to the division of the fibers into two groups, viz., the med- 
ullated and the nonmedullated. 
Medullated Nerve Fibers.—The external investing membrane of the 
nerve fiber, generally termed the neurilemma, is thin, transparent, homoge- 
neous, and closely applied to the medulla. Owing to its colorless appear- 
ance it can be seen only with difficulty in the recent condition; when 
treated with various reagents it becomes quite distinct. Physically it is 
quite resisting and elastic, resembling the sarcolemma of the muscle fiber. 
Its function is doubtless that of a protecting agent to the more delicate 
structure contained within it. 64 
HUMAN PHYSIOLOGY. 
The medulla or myelin, the white substance of Schwann, completely fills 
the tubular membrane and closely invests the axis cylinder. When the 
nerve is perfectly fresh, the medulla is clear, transparent, homogeneous 
highly refractive, and of an oleaginous consistence. When the nerve is 
subjected to reagents which alter its composition, the medulla becomes 
opaque and imparts to the nerve a white, glistening appearance. As to 
the function of the medulla nothing definite is known. By some it is re- 
garded as an insulating agent to the axis cylinder, .preventing the diffusion 
of nerve force to adjoining fibers. Inasmuch as it is wanting in a large 
proportion of fibers which conduct nerve force without diffusion, it is ques- 
tionable if this function can be assigned to it with any degree of certainty. 
The axis cylinder is in all probability the most essential element of the 
nerve fiber, as it is the only part uniformly continuous throughout its 
course. In the natural condition it is transparent and invisible, but when 
treated with proper reagents, it presents itself as a pale, granular, flattened 
band, albuminous in composition, more or less solid, and somewhat elastic. 
The axis is longitudinally striated, showing that it is composed of a num- 
ber of fibrillse. This is in all probability the most essential element of the 
nerve fiber and is the medium of the transmission of nerve force from the 
center to the periphery and in the reverse direction. 
Nodes or Constrictions of Ranvier.—At intervals of about 75 times its 
diameter the medullated nerve fiber undergoes a remarkable diminution in 
size, caused by an interruption of the medullary layer, so that the external 
investment lies directly upon the axis cylinder. These constrictions, taking 
their name from their discoverer, Ranvier, occur at regular intervals along 
the course of the nerve, separating it into a series of segments. The por- 
tion between the constrictions is known as the internodal Segment. It has 
been supposed that in consequence of the absence of the myelin at the 
constrictions, a free exchange of nutritive material and decomposition pro- 
ducts can take place between the axis cylinder and the plasma. 
Nonmedullated Nerve Fibers.—The nonmedullated nerve fibers con- 
sist only of an axis cylinder with the external tubular membrane. Though 
much less abundant than the former variety, they are distributed largely 
throughout the nervous system, but are particularly abundant in the sym- 
pathetic system. Owing to the absence of a medulla they present a rather 
pale or grayish appearance. Recent investigations would seem to show 
that all the nerve fibers which come from the spinal cord are at first medul- 
lated, but on passing through the sympathetic ganglia they are deprived of 
the medulla, this being more particularly the case with those branches 
which are distributed to the blood-vessels and abdominal viscera. PHYSIOLOGY OF NERVOUS TISSUE. 
65 
Structure of Nerve Trunks.—After their emergence from the brain 
and spinal cord, the nerve fibers are bound together by connective tissue 
into the form of continuous bundles, separate and distinct, which connect 
the brain and cord with all the remaining structures of the body. These 
bundles are technically known as nerves or nerve trunks. Each nerve is 
invested by a thick layer of lamellated connective tissue known as the 
epineurium,. A transverse section of a nerve shows that it is made up of 
a number of small bundles of fibers each of which possesses a separate in- 
vestment of connective tissue, the perineuriutn. Within this latter mem- 
Fig. 5.—Transverse Section of a Nerve (Median). 
ep. Epineurium. pe. Perineurium, ed. Endoneurium. 
brane are contained the ultimate nerve fibers, supported and separated by 
a fine stroma, the endoneurium. (See Fig. 5.) After pursuing a longer or 
shorter course, the nerve trunk gives off branches which interlace very 
freely with neighboring branches, forming a plexus, the fibers of which are 
distributed to associated organs and regions of the body. From their 
origin to their termination, however, nerve fibers retain their individuality 
and never become blended with adjoining fibers. 
As nerves pass from their origin toward their peripheral terminations 66 
HUMAN PHYSIOLOGY. 
they give off a number of branches, each of which becomes invested with 
a lamellated sheath which is an off-shoot from that investing the parent 
trunk. This division of nerve bundles and sheath continues throughout 
all the branchings down to the ultimate nerve fibers, each of which is sur- 
rounded by a sheath of its own, consisting of a single layer of endothelial 
cells. This transparent membrane, the sheath of Henle, is separated from 
the nerve fiber by a considerable space, in which is probably contained a 
quantity of lymph. 
Near their ultimate terminations the nerve fibers themselves undergo 
division, so that a single fiber may give origin to a number of branches, 
each of which contains a portion of the parent axis cylinder and the 
myelin. 
Nerves are channels of communication between the brain and spinal 
cord and the muscles, glands, blood-vessels, skin, mucous membrane, etc., 
in which they ultimately terminate. Any stimulation of a nerve, either in 
its course or at its termination, develops an excitation which travels through- 
out the length of the fiber. If the excitation develops a muscular move- 
ment, an act of secretion, or a change in the caliber of a blood-vessel, it is 
termed an efferent nerve. If the excitation develops in the brain a con- 
scious sensation, it is termed an afferent nerve. As far as can be deter- 
mined by microscopic and chemic investigations there is no difference 
between these two classes of fibers. 
Nerve Terminations.— 
1. Central. Both efferent and afferent nerve fibers, as they enter the spinal 
cord and brain, lose their external investments, and, retaining only the 
axis cylinder, ultimately become connected with the processes of the 
gray cells. 
2. Peripheral. As the nerves approach the tissues to which they are to 
be distributed, they inosculate freely, forming a plexus, from which the 
ultimate fibers proceed to individual tissues. 
Efferent Nerves.—In the voluntary or striped muscles the efferent 
nerves are connected with the contractile substance by means of the 
“ motorial end-plates; ” when the nerve enters the muscular fiber the 
tubular membrane blends with the sarcolemma, the medullary layer dis- 
appears, and the axis cylinder spreads out into the form of a little plate, 
granular in character, and containing oval nuclei. 
In the unstriped or involuntary muscles, the terminal nerve fibers form 
a plexus on the muscular fiber cells, and become connected with the granu- 
lar contents of the nuclei. PHYSIOLOGY OF NERVOUS TISSUE. 
67 
In the glands, nerve fibers have been traced to the glandular cells, where 
they form a branching plexus from which fibers pass into their interior and 
become connected with their substance, and thus influence secretion. 
Afferent Nerves terminate in the skin and mucous membranes, in 
three distinct modes, e.g., as tactile corpuscles, Pacinian corpuscles, and as 
end bulbs. 
The tactile corpuscles are found in the papillae of the true skin, especially 
on the palmar surface of the hands and fingers, feet and toes; they are 
oblong bodies, measuring about jJ5ths of an inch in length, consisting of a 
central bulb of homogeneous connective tissue surrounded by elastic fibers 
and elongated nuclei. The nerve fiber approaches the base of the corpus- 
cle, makes two or three spiral turns around it, and terminates in loops. 
They are connected with the sense of touch. 
The Pacinian corpuscles are found chiefly in the subcutaneous cellular 
tissue, on the nerves of the hands and feet, the intercostal nerves, the 
cutaneous nerves, and in many other situations. They are oval in shape, 
measure about the of an inch in length on the average, and consist of 
concentric layers of connective tissue ; the nerve fiber penetrates the cor- 
puscle and terminates in a rounded knob in the central bulb. Their func- 
tion is unknown. 
The end bulbs of Krause are formed of a capsule of connective tissue in 
which the nerve fiber terminates in a coiled mass or bulbous extremity; 
they exist in the conjunctiva, tongue, glans penis, clitoris, etc. 
Many afferent nerves terminate in the papillse at the base of the hair 
follicle ; but in the skin, mucous membrane, and organs of special sense 
their mode of termination is not well understood. 
All the nerves which emerge from the brain and spinal cord may be 
divided, according to the direction in which they carry nerve impulses, into 
two groups, viz.: Efferent and Afferent. 
The Efferent or Centrifugal nerves convey nerve impulses from the 
brain and spinal cord to various peripheral organs, and may be classified as 
follows:— 
1. Muscular or Motor nerves, as when they conduct nerve impulses to the 
muscles and give rise to muscular contraction. 
2. Glandular or Secretory nerves, as when they conduct nerve impulses to 
glands and excite secretion. 
PROPERTIES AND FUNCTIONS OF NERVES. 68 
HUMAN PHYSIOLOGY. 
3. Vascular or Vasomotor, as when they convey nerve impulses to the 
walls of the blood-vessels, and by stimulating or inhibiting the muscular 
fibers vary the caliber of the vessel. 
4. Inhibitory, as when they conduct impulses which inhibit the activity of 
an organ. 
The Afferent or Centripetal nerves convey impulses from the peri- 
pheral organs and tissues to the brain and spinal cord and may be classi- 
fied as follows:— 
1. Sensory-facient nerves, as when they conduct nerve impulses which 
give rise in the brain to conscious sensations. They may be subdivided 
into — 
a. Nerves of special sense, e. g., optic, olfactory, auditory, gustatory; 
as when they conduct impulses to the brain which give rise to visual, 
olfactory, auditory, and gustatory sensations. 
b. Nerves of general sensibility, e.g., tactile, thermal, sensory ; as when 
they conduct impulses to the brain which give rise to sensations of 
touch, changes of temperature, and pain. 
2. Reflex nerves, as when they conduct nerve impulses to the nerve centers 
to be reflected out, through efferent nerves, to muscles, glands, blood- 
vessels. 
Nervous Irritability, Excitability.—These terms are employed to ex- 
press that condition of a nerve which enables it to conduct nerve impulses 
from the centers to the periphery, from the periphery to the centers, and to 
respond to the action of artificial stimuli. A nerve is said to be excitable 
or irritable as long as it possesses these capabilities or properties. For the 
manifestation of these properties the nerve must retain a state of physical 
and chemic integrity ; it must undergo no change in structure or chemic 
composition. The irritability of an efferent nerve is demonstrated by the 
contraction of a muscle, the secretion by a gland, a change in the caliber of 
a blood-vessel, whenever a corresponding nerve is stimulated. The irrita- 
bility of an afferent nerve is demonstrated by the production of a sensation, or 
a reflex action whenever it is stimulated. The irritability of nerves continues 
for a certain period of time after the death of the animal, varying in different 
classes of animals. In the warm-blooded animals, in which the nutritive 
changes take place with great rapidity, the irritability soon disappears, a 
result due to disintegrative changes in the nerve, caused by the withdrawal 
of the blood supply. In cold-blooded animals, on the contrary, in which 
the nutritive changes take place relatively slowly, the irritability lasts, under 
favorable conditions, for a considerable time. Other tissues besides nerves PHYSIOLOGY OF NERVOUS TISSUE. 
69 
possess irritability, that is, of responding to the action of stimuli; e.g., glands 
and muscles, which respond by the production of a secretion or a contraction. 
Independence of Tissue Irritability.—The irritability of nerves is 
distinct and independent of the irritability of muscles and glands, as can 
be shown by the introduction of various chemic agencies into the circu- 
lation. Curara, for example, induces a state of complete paralysis, which 
is due not to an abolition of the irritability of either the nerve trunks or 
muscles, but to a modification of the end organs of the nerves just where 
they come into contact with the muscles. Atropine induces complete sus- 
pension of glandular activity by impairing the terminal organs of the 
secretory nerves just where they are in relation to the gland cells, without 
destroying the irritability of either gland or nerve. 
Stimuli of Nerves.—Nerves do not possess the power of spontaneously 
generating and propagating nerve impulses; they can only be aroused to 
activity by the action of an extraneural stimulus. In the living condition, 
the stimuli capable of throwing the nerve into an active condition act for 
the most part on either the central or peripheral end of the nerve. In the 
case of motor nerves the stimulus to the excitation, originating in some 
molecular disturbance in the nerve cells, acts upon the nerve fibers in con- 
nection with them. In the case of sensory or afferent nerves the stimuli act 
upon the peculiar end organs with which the sensory nerves are in connec- 
tion, which in turn excite the nerve fibers. Experimentally, it can be 
demonstrated that nerves can be excited by a sufficiently powerful stimulus 
applied in any part of their extent. 
Nerves respond to stimulation according to their habitual function; thus, 
stimulation of a sensory nerve, if sufficiently strong, results in the sensation 
of pain; of the optic nerve, in the sensation of light; of a motor nerve, in 
contraction of the muscle to which it is distributed; of a secretory nerve, 
in the activity of the related gland, etc. It is, therefore, evident that pecu- 
liarity of nervous function depends neither upon any special construction or 
activity of the nerve itself, nor upon the nature of the stimulus, but entirely 
upon the peculiarities of its central and peripheral end organs. 
Nerve stimuli may be divided into :— 
1. General stimuli, comprising those agents which are capable of exciting 
a nerve in any part of its course. 
2. Special stimuli, comprising those agents which act upon nerves only 
through the intermediation of the end organs. 
General stimuli :— 
i. Mechanical: as from a blow, pressure, tension, puncture, etc. 70 
HUMAN PHYSIOLOGY. 
2. Thermal: heating a nerve at first increases and then decreases its 
excitability. 
3. Chemic: sensory nerves respond somewhat less promptly than motor 
nerves to this form of irritation. 
4. Electric: either the constant or interrupted current. 
5. The normal physiologic stimulus :— 
a. Centrifugal or efferent, if proceeding from the center toward the 
periphery. 
b. Centripetal or afferent, if in the reverse direction. 
Special Stimuli :— 
1. Light or ethereal vibrations acting upon the end organs of the optic 
nerve in the retina. 
2. Sound or atmospheric undulations acting upon the end organs of the 
auditory nerve. 
3. Heat or vibrations of the air acting upon the end organs in the skin. 
4. Chemic agencies acting upon the end organs of the olfactory and 
gustatory nerves. 
As to the nature of the nerve impulse generated by the above stimuli but 
little is known. It is supposed to be a mode of motion, molecular or 
vibratory in character, which passes through the axis cylinder with a definite 
velocity. 
Rapidity of Transmission of Nerve Force.—The passage of a ner- 
vous impulse, either from the brain to the periphery or in the reverse direc- 
tion, requires an appreciable period of time. The velocity with which the 
impulse travels in human sensory nerves has been estimated at about 190 
feet per second, and for motor nerves at from 100 to 200 feet per second. 
The rate of movement is, however, somewhat modified by temperature, 
cold lessening and heat increasing the rapidity; it is also modified by elec- 
tric conditions, by the action of drugs, the strength of the stimulus, etc. 
The rate of transmission through the spinal cord is considerably slower 
than in nerves, the average velocity for voluntary motor impulses being 
only 33 feet per second, for sensitive impressions 40 feet, and for tactile 
impressions 140 feet per second. 
Electric Currents in Muscles and Nerves.—If a muscle or nerve 
be divided and nonpolarizable electrodes be placed upon the natural longi- 
tudinal surface at the equator, and upon the transverse section, electric 
currents are observed with the aid of a delicate galvanometer. The direc- 
tion of the current is always from the positive equatorial surface to the 
negative transverse surface. The strength of the current increases or PHYSIOLOGY OF NERVOUS TISSUE. 
71 
diminishes according as the positive electrode is moved toward or from the 
equator. When the electrodes are placed on the two transverse ends of a 
nerve, an axial current will be observed whose direction is opposite to that 
of the normal impulse of the nerve. 
The electromotive force of the strongest nerve current has been estimated 
to be equal to the 0.026 of a Daniell battery; the force of the current of 
the frog muscle about 0.05 to 0.08 of a Daniell. 
Negative Variation of Currents in Muscles and Nerves.—If a 
muscle or nerve be thrown into a condition of tetanus, it will be observed 
that the currents undergo a diminution or negative variation, a change 
which passes along the nerve in the form of a wave and with a velocity 
equal to the rate of transmission of the nerve impulse. The wave length 
of a single negative variation has been estimated to be 18 millimeters; the 
period of its duration being from 0.0005 t0 0.0008 of a second. 
It is asserted by Hermann that perfectly fresh, uninjured muscles and 
nerves are devoid of currents, and that the currents observed are the result 
of a molecular death at the point of section, this point becoming negative 
to the equatorial point. He applies the term “action currents” to the 
currents obtained when a muscle is thrown into a state of activity. 
Electric Properties of Nerves.—When a galvanic current is made 
to flow along a motor nerve from the center to the periphery, from the 
positive to the negative poles, it is known as the direct, descending, or 
centrifugal current. When it is made to flow in the reverse direction, it is 
known as the inverse, ascending, or centripetal current. 
The passage of a direct current enfeebles the excitability of a nerve ; the 
passage of the inverse current increases it. The excitability of a nerve may 
be exhausted by the repeated applications of electricity; when thus ex- 
hausted it may be restored by repose, or by the passage of the inverse cur- 
rent if the nerve has been exhausted by the direct current, or vice versa. 
During the actual passage of a feeble constant current in either direction 
neither pain nor muscular contraction is ordinarily manifested; if the 
current be very intense, the nerve may be disorganized and its excitability 
destroyed. 
Eleclrotonus.—The passage of a direct galvanic current through a por- 
tion of a nerve excites in the parts beyond the electrodes a condition of 
electric tension or electrotonus, during which the excitability of the nerve 
is decreased near the anode or positive pole, and increased near the cathode 
or negative pole; the increase of excitability in the catelectrotonic area, 
that nearest the muscle, being manifested by a more marked contraction of 72 
HUMAN PHYSIOLOGY. 
the muscle than the normal, when the nerve is irritated in this region. The 
passage of an inverse galvanic current excites the same condition of elec- 
trotonus ; and the diminution of excitability near the anode, the anelec- 
trotonic area, that is now nearest the muscle, being manifested by a less 
marked contraction than the normal when the nerve is stimulated in this 
region. Between the electrodes is a neutral point where the catelectrotonic 
area emerges into the anelectrotonic area. If the current be a strong one, 
the neutral point approaches the cathode; if weak, it approaches the 
anode. 
When a nervous impulse passes along a nerve, the only appreciable effect 
is a change in its electric condition, there being no change in its tempera- 
ture, chemic composition, or physical condition. The natural nerve cur- 
rents, which are always present in a living nerve as a result of its nutritive 
activity, in great part disappear during the passage of an impulse, under- 
going a negative variation. 
Law of Contraction.—If a feeble galvanic current be applied to a 
recent and excitable nerve, contraction is produced in the muscles only 
upon the making of the circuit with both the direct and inverse currents. 
If the current be moderate in intensity, the contraction is produced in 
the muscle both upon the making and breaking of the circuit, with both 
the direct and inverse currents. 
If the current be intense, contraction is produced only when the circuit 
is made with the direct current, and only when it is broken with the inverse 
current. 
The Reaction of Degeneration.—Two different applications of elec- 
tricity are used in electrophysiology and electrotherapeutics—the constant 
or galvanic, and the interrupted or faradic currents. Injured and paralyzed 
muscles and nerves react differently to these two kinds of stimuli, and the 
facts are of the greatest importance in the diagnosis and therapeutics of the 
precedent lesions. The principal difference of behavior relates to the 
reaction of degeneration—a condition produced by paralysis of any kind. 
It is characterized by a diminished or abolished excitability of the muscles 
to the faradic current, while there is at the same time an increased excita- 
bility to the galvanic current. The synchronous diminished excitability of 
the nerves is the same for either current. The term partial reaction of 
degeneration is used when there is a normal reaction of the nerves, but the 
muscles show the degenerative reaction. This condition is a characteristic 
of progressive muscular atrophy. 
Reflex Action.—Many of the muscular, glandular, and vascular reac- FOODS AND DIETETICS. 
73 
tions which are exhibited by different portions of the body are comprised 
under the term reflex action, for the reason that they are the immediate 
results of stimulations of afferent nerves at their peripheral terminations 
and, in a general way, may be said to take place independently of the brain. 
The conversion of an afferent impulse into an efferent impulse takes 
place in a nerve center, termed a reflex center. The parts involved in any 
reflex act are as follows:— 
1. A sentient surface : skin, mucous membrane, sense organ, etc. 
2. An afferent nerve fiber. 
3. A receptive center in connection with the afferent nerve. 
4. A commissural tract. 
5. An emissive center in connection with the efferent nerve. 
6. An efferent nerve. 
7. A responsive organ, muscle, gland, blood-vessel, etc. 
A stimulus of sufficient intensity applied to a sentient surface develops in 
the afferent nerve a series of nerve impulses which, traveling inward to the 
centers, are converted into efferent impulses and reflected outward to either 
muscle, gland, or blood-vessel, or all three simultaneously with the produc- 
tion of muscular contraction, glandular secretion, vascular contraction or 
dilatation. 
The reflex actions take place for the most part through the spinal cord 
and medulla oblongata, which, in virtue of their contained centers, coordinate 
the various organs and tissues concerned in the performance of the organic 
functions. The movements of mastication, the secretion of saliva, the 
muscular,glandular, and vascular phenomena of gastric and intestinal diges- 
tion, the respiratory movements, the mechanism of micturition, etc., are 
illustrations of reflex activity. (See function of spinal cord.) 
FOODS AND DIETETICS. 
During the functional activity of every organ and tissue of the body the 
living material of which it is composed, the protoplasm, undergoes more or 
less disintegration. Through a series of descending chemic stages it is 
reduced to a number of simpler compounds which are of no further value 
to the body and which are in consequence eliminated by the various elim- 
inating or excretory organs : the lungs, kidneys, skin, liver. Among these 
compounds the more important are carbon dioxid, urea, and uric acid. 
Many other compounds, inorganic as well as organic, are also eliminated 
by the water discharged from the body in which they are held in solution, 74 
HUMAN PHYSIOLOGY. 
Coincident with this disintegration of the tissues there is an evolution or 
disengagement of energy particularly in the form of heat. 
In order that the tissues may regain their normal composition and thus 
be enabled to continue in the performance of their functions, they must be 
supplied with the same nutritive materials of which their protoplasm orig- 
inally consisted, viz. : water, inorganic salts, proteids, sugar, fat. These 
materials are furnished by the blood during its passage through the capil- 
lary blood-vessels. The blood is a reservoir of nutritive material in a con- 
dition to be absorbed, organized, and transformed into new living tissue. 
Inasmuch as the loss of material from the body daily, which is very 
great, is supplied under other forms by the blood, it is evident that this 
fluid would rapidly diminish in volume wrere it not restored by the introduc- 
tion of new and corresponding materials. As soon as the blood volume 
falls to a certain extent, the sensations of hunger and thirst arise, which in 
a short time lead to the necessity of taking food. 
In addition to the direct appropriation of food by the tissues it is highly 
probable that an indefinite amount undergoes oxidation and disintegration 
without ever becoming an integral part of the tissues, and thus directly con- 
tributes to the production of heat. 
Inanition or Starvation.—If these nutritive principles be not supplied 
in sufficient quantity, or if they are withheld entirely, a condition of physio- 
logic decay is established, to which the term inanition or starvation is ap- 
plied. The phenomena which characterize this pathologic process are as 
follows, viz.: hunger, intense thirst, gastric and intestinal uneasiness and 
pain, muscular weakness and emaciation, a diminution in the quantity of 
carbon dioxid exhaled, a lessening in the amount of urine and its constitu- 
ents excreted, a diminution in the volume of the blood, an exhalation of a 
fetid odor from the body, vertigo, stupor, delirium, and at times convulsions, 
a fall of bodily temperature, and finally death from exhaustion. 
During starvation the loss of different tissues, before death occurs, aver- 
ages or 40 per cent., of their weight. 
Those tissues which lose more than 40 per cent, are fat, 93.3; blood, 75; 
spleen, 71.4; pancreas, 64.1; liver, 52; heat, 44.8; intestines, 42.4; 
muscle, 42.3. Those which lose less than 40 per cent, are the muscular 
coat of the stomach, 39.7; pharynx and esophagus, 34.2; skin, 33.3; 
kidneys, 31.9; respiratory apparatus, 22.2 ; bones, 16.7; eyes, 10; nervous 
system, 1.9. 
The fat entirely disappears, with the exception of a small quantity which 
remains in the posterior portion of the orbits and around the kidneys. 
The blood diminishes in volume and loses its nutritive properties. The FOODS AND DIETETICS. 
75 
muscles undergo a marked diminution in volume and becomes soft and 
flabby. The nervous system is last to suffer, not more than two per cent, 
disappearing before death occurs. 
The appearances presented by the body after death from starvation are 
those of anemia and great emaciation; almost total absence of fat; blood- 
lessness ; a diminution in the volume of the organs; an empty condition 
of the stomach and bowels, the coats of which are thin and transparent. 
There is a marked disposition of the body to undergo decomposition, 
giving rise to a very fetid odor. 
The duration of life after a complete deprivation of food varies from 
eight to thirteen days, though life can be maintained much longer if a 
quantity of water be obtained. The water is more essential under these 
circumstances than the solid matters, which can be supplied by the organ- 
ism itself. 
The different alimentary or nutritive principles which are appropriated by 
the tissues and which are contained within the various articles of food, 
belong to both the organic and inorganic groups and chemic compounds, 
and may be classified according to their composition as follows :— 
CLASSIFICATION OF ALIMENTARY PRINCIPLES 
1. Proteid Group.—Nitrogenized, C. O. H. N. S. P 
Principle. Where Found. 
Myosin, Flesh of animals. 
Vitellin albumin, Yolk of egg, white of egg. 
Fibrin, globulin, Blood contained in meat. 
Casein, Milk, cheese. 
Gluten, Grain of wheat and other cereals. 
Vegetable albumin, Soft growing vegetables. 
Legumin, Peas, beans, lentils, etc. 
Gelatin, Bones. 
2. Oleaginous Group.—C. O. H. 
Animalfats and oils, 
Stearin, olein, 
Palmitin, fatty acids, 
Found in the adipose tissue of ani- 
mals, seeds, grains, nuts, fruits, 
and other vegetable tissues. 
3. Carbohydrate Group.—C. O. H. 
Saccharose, or cane sugar, . . . Sugar cane. 
Dextrose, ox glucose, 
Levulose, or fruit sugar, . . . 
Fruits. 
Lactose, or milk sugar, Milk. 
Maltose, Malt, malt foods. 
Starch, Cereals, tuberous roots, and legu- 
minous plants. 
Glycogen, Liver, muscles. 76 
HUMAN PHYSIOLOGY. 
4. Inorganic Group.—Water, sodium and potassium chlorids, sodium, 
calcium, magnesium and potassium phosphates, calcium carbonate, and 
iron. 
5. Vegetable Acid Group.—Malic, citric, tartaric, and other acids, found 
principally in fruits. 
6. Accessory Foods.—Tea, coffee, alcohol, cocoa, etc. 
The proteid principles of the food after undergoing digestion and con- 
version into peptones are absorbed and transformed into the form of pro- 
teids characteristic of the blood plasma and the lymph. Of the proteids 
thus brought into relation with the living protoplasm, a small percentage 
only is utilized in the repair of its substance. This is known as tissue 
proteid. A large percentage circulating among and permeating the tissues 
is acted upon by them directly, and reduced to simpler compounds without 
ever becoming a part of the tissue itself. This is known as circulating 
proteid. In the process of tissue metabolism all the proteids suffer disin- 
tegration and give rise to the production of some carbon-holding com- 
pound, probably fat, and some nitrogen-holding compounds which eventu- 
ally produce urea. The intermediate stages are possibly represented by 
glycin, creatin, uric acid, etc. An excess of proteids in the food is fol- 
lowed by their decomposition, by the pancreatic juice, into leucin and 
tyrosin, which by the agency of the liver are converted into urea. The 
disintegration of the proteids is attended by the disengagement of heat: 
they thus contribute to the energy of the body. 
The oleaginous principles after digestion are absorbed into the blood, 
from which they rapidly disappear. It is probable that a portion of the 
fat enters directly into the composition of living protoplasm, out of which 
it again emerges at some subsequent stage in the form of small drops 
which make their appearance in the protoplasmic cells of the connective 
areolar tissue, thus giving rise to the adipose tissue. Another portion proba- 
bly undergoes direct oxidation. 
The carbohydrate principles after digestion are absorbed as dextrose 
and temporarily stored up in the liver as glycogen. The intermediate 
stages which sugar passes through and the combinations into which it enters 
between its absorption and its elimination are but imperfectly understood. 
That it contributes to the accumulation of fat is probable, though it is 
doubtful if it is ever converted into fat. A large percentage of the sugar 
absorbed is at once oxidized. The reduction of fat and sugar to carbon 
dioxid and water, under which forms they are eliminated from the body, 
is accompanied by the disengagement of a large quantity of heat. 
Water is present in all the fluids and solids of the body. It promotes FOODS AND DIETETICS. 
77 
the absorption of new material from the alimentary canal; it holds the 
various ingredients of the blood, lymph, and other fluids in solution; it 
hastens the absorption of waste products from the tissues, and promotes 
their speedy elimination from the body. 
Sodium chlorid is present in all parts of the body to the extent of no 
gm. The average amount eliminated daily is 15 gm. Its necessity as 
an article of diet is at once apparent. Taken as a condiment, it imparts 
sapidity to the food, excites the flow of the digestive fluids, promotes the 
absorption and assimilation of the albumins, influences the passage of nu- 
tritive material through animal membranes, and furnishes the chlorin for the 
free hydrochloric acid of the gastric juice. In some unknown way it 
favorably promotes the activity of the general nutritive process. 
The potassium salts are also essential to the normal activity of the 
nutritive process. When deprived of these salts animals become weak and 
emaciated. When given in small doses they increase the force of the heart 
beat, raise the arterial pressure, and thus increase the action of the circula- 
tion of the blood. 
The calcium phosphate and carbonate are utilized in imparting solidity 
to the tissues, more especially the bones and teeth. Many articles of food 
contain these salts in quantities sufficient to restore the amount lost daily. 
The vegetable acids increase the secretions of the alimentary canal and 
are apt, in large amounts, to produce flatulence and diarrhea. After enter- 
ing in combination with bases to form salts, they stimulate the action of the 
kidneys and promote a larger elimination of all the urinary constituents. 
In some unknown way they influence nutrition ; when deprived of these 
acids the individual becomes scorbutic. 
The accessory foods, coffee and tea, when taken in moderation, overcome 
the sense of fatigue and mental unrest consequent on excessive physical 
and mental exertion. Coffee increases the action of the intestinal glands 
and acts as a laxative. After absorption, its active principle, caffein, 
stimulates the action of the heart, raises the arterial pressure, and excites 
the action of the brain. Tea acts as an astringent, owing to the tannic acid 
it contains. One effect of the tannic acid is to coagulate the digestive fer- 
ments and to interfere with the activity of the digestive process. 
Alcohol, when introduced into the system in small quantities, undergoes 
oxidation and contributes to the production of force, and is thus far a food. 
It excites the gastric glands to increased secretion, improves the digestion, 
accelerates the action of the heart, and stimulates the activities of the 
nervous centers. In zymotic diseases, and all cases of depression of the 
vital powers, it is most useful as a restorative agent. When taken in 78 
HUMAN PHYSIOLOGY. 
excessive quantities it is eliminated by the lungs and kidneys. The meta- 
morphosis of the tissue is retarded, the elimination of urea and carbonic 
acid is lessened, the temperature lowered, the muscular powers impaired, 
and the resistance to depressing external influences diminished. When 
taken through a long period of time, alcohol impairs digestion, produces 
gastric catarrh, disorders the secreting power of the hepatic cells. It also 
diminishes the muscular power and destroys the structure and composition 
of the cells of the brain and spinal cord. The connective tissue of the body 
increases in amount, and subsequently contracting, gives rise to sclerosis. 
A Proper Combination of different alimentary principles is essential 
for healthy nutrition, no one class being capable of maintaining life for any 
definite length of time. 
The albuminous food in excess promotes the arthritic diathesis, manifest- 
ing itself as gout, gravel, etc. 
The oleaginous food in excess gives rise to the bilious diathesis, while a 
deficiency of it promotes the scrofulous. 
The farinaceous food, when long continued in excess, favors the rheu- 
matic diathesis by the development of lactic acid. 
The Quantities of the different nutritive materials which are required 
daily for the growth and repair of the tissues and for the evolution of heat 
have been variously estimated by different observers. The following table 
shows the average diet scale of Vierordt, and the amount of waste pro- 
ducts to which it would give rise :— 
Ingest a. 
Proteids, .... 120 grams. 
Fat, 90 “ 
Starch 330 “ 
Inorganic salts, . 32 “ 
Water, 2800 “ 
Oxygen, .... 700 “ 
Total, . . . 4072 “ 
COMPARISON OF THE INGESTA AND EGESTA. 
Egesta. 
Urea, 40 grains. 
Inorganic salts, . 32 “ 
Feces, 104 “ 
Carbon dioxid, . 800 “ 
Water, 3096 “ 
Total, . . . 4072 “ 
Other estimates as to the amounts of the organic substances required 
daily are as follows :— 
Ranke. 
Voit. 
Moleschott. 
Proteid, . 
. . IOO 
Il8 
130 grams. 
Fat, . . 
. . IOO 
50 
84 “ 
Starch, . 
. . 240 
500 
404 “ FOODS AND DIETETICS. 
79 
The Energy of the Animal Body.—The food consumed daily not 
only repairs the loss of material from the body, but also furnishes the 
energy to replace that which is expended daily in the shape of heat and 
motion. All the energy of the body can be traced to the chemic changes 
going on in the tissues and more particularly to those changes involved in 
the oxidation of the foods. 
The amount of heat yielded by any given food principle can be deter- 
mined by burning it to carbon dioxid and water, and ascertaining the 
extent to which it will, when so liberated, raise the temperature of a given 
volume of water. This amount of heat may be expressed in gram degrees 
of heat, i. <?., calories or kilogrammeters of work. A calory is the amount 
of heat required to raise the temperature of one gram of water one degree 
Centigrade. A kilogrammeter of work is the amount of heat required to 
raise one kilogram one meter in height. 
The following estimates give, approximately, the number of calories pro- 
duced when the food is reduced within the body to urea, carbon dioxid, 
and water:— 
1 gram of proteid yields 4500 calories, 
1 “ fat “ 9000 “ 
1 “ starch “ 4000 “ 
The total number of calories or gram degrees of heat yielded by any 
given diet scale can be readily determined by multiplying the above factors 
by the quantities of material consumed. The diet scale of Ranke, for ex- 
ample, yields the following amount:— 
ioo grams of proteid yield 450,000 calories, 
xoo “ fat “ 900,000 “ 
240 “ starch “ 960,000 “ 
Total, 2,310,000 “ 
It has also been determined experimentally that one gram of proteid, 
one gram of fat, and one gram of starch, when completely oxidized, will 
yield energy sufficient to do 1850, 3841, and 1657 kilogrammeters of work, 
respectively. 
The total energy of the Ranke diet scale can be easily calculated, e.g.:— 
xoo grams of proteid yield 185,000 kilogrammeters. 
100 “ fat “ 384,100 “ 
240 “ starch “ 397,680 “ 
Total, 966,780 “ 80 
HUMAN PHYSIOLOGY. 
It will be thus seen that the food consumed daily yields 2,310,000 gram 
degree units of heat, or 2310 kilogram degree units, which can be translated 
into its mechanical equivalent, 966,780 kilogrammeters of work. 
The Amount of Food required in twenty-four hours is estimated from 
the total quantity of carbon and nitrogen excreted from the body in 
twenty-four hours, these two elements representing the waste or destruction 
of the carbonaceous and nitrogenized compounds. It has been determined 
by experimentation that about 4600 grains of carbon and about 300 grains 
of nitrogen are eliminated from the body daily, the ratio being about 15 to 
1. That the body may be kept in its normal condition, a proper propor- 
tion of carbonaceous (bread) to nitrogenized (meat) food should be ob- 
served in the diet. 
The method of determining the proper amounts of both kinds of food is 
as follows:— 
1000 grs. of bread (2 oz.) contain 300 grs. C. and 10 grs. N. 
To obtain the requisite amount of nitrogen from bread, 30,000 grains, 
or about four pounds, containing 900 grains of carbon and 300 of nitrogen, 
would have to be consumed. Under such a diet there would be a large 
excess of carbon, which would be undesirable. On a meat diet the reverse 
obtains :— 
1000 grs. of meat (2 oz.) contain 100 grs. C. and 30 grs. N. 
To obtain the requisite amount of carbon from meat, 45,000 grains, or 
about 6]/2 pounds, containing 4500 grains of carbon and 1350 grains of 
nitrogen, would have to be consumed. Under such circumstances there 
would arise an excess of nitrogen in the system, which would be equally 
undesirable and injurious. By combining these two articles, however, in 
proper proportion, the requisite amounts of carbon and nitrogen can be 
obtained without any excess of either, e. g. :— 
2 lbs. of bread contain 4630 grs. C. and 154 grs. N. 
“ meat “ 463 “ “ “ 154 “ “ 
5093 C. 308 N. 
The amount of carbon and nitrogen necessary to compensate for the loss 
to the system daily would be contained in the above amount of food. As 
about ounces of oil or butter are consumed daily, the quantity of 
bread can be reduced to 19 oz. In the quantities of bread and meat 
above mentioned, there are 4.2 oz. albumin, 9.3 sugar and starch. FOODS AND DIETETICS. 
81 
The Alimentary Principles are not introduced into the body as such, 
but are combined in proper proportions to form compound substances, 
termed foods, e. g., bread, milk, eggs, meat, etc., the nutritive value of each 
depending upon the extent to which these principles exist. 
The following tables show the average composition of various articles of 
food:— 
COMPOSITION OF ANIMAL FOODS. 
In ioo Parts. 
Beef. 
Veal. 
Mutton. 
Pork. 
Fowl. 
Fish. 
Water, .... 
76.25 
77.82 
75-59 
72.57 
70.80 
79-3° 
Proteid, . . . 
20.24 
19.86 
17.XI 
I9-3I 
22.70 
18.30 
Fat, 
x.68 
0.82 
5-47 
5.82 
4.IO 
O.70 
Carbohydrates, 
0.50 
O.80 
0.60 
O.60 
1.20 
0.90 
Salts, .... 
1.38 
O.70 
1.23 
I.70 
1.20 
0.80 
COMPOSITION OF VEGETABLE FOODS. 
In ioo Parts. 
Brans. 
Peas. 
Potatoes 
Turnips. 
Cabbage. 
Asparagus. 
Water, .... 
13-74 
14.99 
75-47 
89.42 
89.97 
93-75 
Proteid, . . . 
23.21 
22.85 
i-95 
1-35 
I.89 
1.79 
Fat, 
2.14 
I.79 
oi5 
O.18 
0.20 
0.25 
Carbohydrates, 
53-67 
52.36 
20.69 
7-36 
4.87 
2.63 
Cellulose, . . 
3-69 
5-43 
0.76 
O.94 
I.84 
1.04 
Salts, .... 
3-55 
00 
XTi 
W 
1 
0.98 
O.75 
I.23 
0.54 82 
HUMAN PHYSIOLOGY. 
In ioo Parts. 
Wheat. 
Rye. 
Barley. 
Oats. 
Corn. 
Rice. 
Water,.... 
I3-56 
12.65 
13-77 
12.37 
13.IO 
13.12 
Proteid, . . . 
12-35 
12.55 
II.14 
IO.41 
vp 
bo 
Ln 
7.88 
Fat, 
i-75 
I.97 
2.16 
5-23 
4-57 
vr> 
00 
d 
Carbohydrates, 
67.90 
67-95 
64-93 
57-7« 
68.42 
76.55 
Cellulose, . . 
2.63 
3-°° 
5-31 
11.19 
2.50 
o-55 
Salts 
1.81 
1.88 
2.69 
3.02 
1.56 
1.05 
COMPOSITION OF CEREAL FOODS. 
Digestion is a physical and chemic process, by which the food introduced 
into the alimentary canal is liquefied and its nutritive principles transformed 
by the digestive fluids into new substances capable of being absorbed into 
the blood. 
The Digestive Apparatus consists of the alimentary canal and its 
appendages, viz.: teeth, salivary, gastric, and intestinal glands, liver, and 
pancreas. 
Digestion may be divided into seven stages: prehension, mastication, 
insalivation, deglutition, gastric and intestinal digestion, and defecation. 
Prehension, the act of conveying food into the mouth, is accomplished 
by the hands, lips, and teeth. 
DIGESTION. 
MASTICATION. 
Mastication is the trituration of the food, and is accomplished by the 
teeth and lower jaw under the influence of muscular contraction. When 
thoroughly divided, the food presents a greater surface for the solvent 
action of the digestive fluids, thus aiding the general process of digestion. 
The Teeth are 32 in number, 16 in each jaw, and divided into 4 in- DIGESTION. 
83 
cisors or cutting teeth, 2 canines, 4 bicuspids, and 6 molars or grinding 
teeth; each tooth consists of a crown covered by enamel, a neck, and a 
root surrounded by the crusta petrosa and imbedded in the alveolar pro- 
cess ; a section through a tooth shows that its substance is made of dentine, 
in the center of which is the pulp cavity, containing blood-vessels and nerves. 
The lower jaw is capable of making a downward and an upward, a 
lateral and an anteroposterior movement, dependent upon the construction 
of the temporomaxillary articulation. 
The jaw is depressed by the contraction of the digastric, geniohyoid, mylo 
hyoid, and platysma myoides muscles ; elevated by the temporal, masseter, 
and internal pterygoid muscles; moved laterally by the alternate contrac- 
tion of the external pterygoid muscles; moved anteriorly by the pterygoid, 
and posteriorly by the united actions of the geniohyoid, mylohyoid, and 
posterior fibers of the temporal muscle. 
The food is kept between the teeth by the intrinsic and extrinsic mus- 
cles of the tongue from within, and the orbicularis oris and buccinator 
muscles from without. 
The Movements of Mastication, though originating in an effort of 
the will and under its control, are, for the most part, of an automatic or 
reflex character, taking place through the medulla oblongata and induced 
by the presence of food within the mouth. The nerves and nerve centers 
involved in this mechanism are shown in the following table:— 
Afferent or Excitor Nerves. 
1. Lingual branch of 5th pair. 
2. Glossopharyngeal. 
NERVOUS CIRCLE OF MASTICATION. 
Efferent or Motor Nerves. 
1. 3d branch of 5th pair. 
2. Hypoglossal. 
3. Facial. 
The impressions made upon the terminal filaments of the sensory nerves 
are transmitted to the medulla; motor impulses are here generated which 
are transmitted through motor nerves to the muscles involved in the move- 
ments of the lower law. The medulla not only generates motor impulses, 
but coordinates them in such a manner that the movements of mastication 
may be directed toward the accomplishment of a definite purpose. 
Insalivation is the incorporation of the food with the saliva secreted 
by the parotid, submaxillary, and sublingual glands ; the parotid saliva, 
thin and watery, is poured into the mouth through Steno’s duct; the sub- 
INSALIVATION. 84 
HUMAN PHYSIOLOGY. 
maxillary and sublingual salivas, thick and viscid, are poured into the 
mouth through Wharton’s and Bartholini’s ducts. 
In their minute structure the salivary glands resemble each other. They 
belong to the racemose variety, and consist of small sacs or vesicles, which 
are the terminal expansions of the smallest salivary ducts. Each vesicle or 
acinus consists of a basement membrane surrounded by blood-vessels and 
lined with epithelial cells. In the parotid gland the lining cells are gran- 
ular and nucleated; in the submaxillary and sublingual glands the cells are 
large, clear, and contain a quantity of mucigen. During and after secre- 
tion very remarkable changes take place in the cells lining the acini, which 
are in some way connected with the essential constituents of the salivary 
fluids. 
In a living serous gland, e. g., parotid, during rest, the secretory cells 
lining the acini of the gland are seen to be filled with fine granules, which 
are often so abundant as to obscure the nucleus and enlarge the cells until 
Fig. 6.—Cells of the Alveoli of a Serous or Watery Salivary Gland. 
A. After rest. B. After a short period of activity. C. After a prolonged period of 
activity.—(Veo's Text-Book 0/Physiology.) 
the lumen of the acinus is almost obliterated. (See Fig. 6.) When the gland 
begins to secrete the saliva, the granules disappear from the outer boundary 
of the cells, which then become clear and distinct. At the end of the 
secretory activity the cells have become free of granules, have become 
smaller and more distinct in outline. It would seem that the granular 
matter is formed in the cells during the rest, and discharged into the ducts 
during the activity of the gland. 
In the mucous glands, e. g., submaxillary and sublingual, the changes 
that occur in the cells are somewhat different. (See Fig. 7.) During the in- 
tervals of digestion the cells lining the gland are large, clear, and highly 
refractive, and contain a large quantity of mucigen. After secretion has 
taken place the cells exhibit a marked change. The mucigen cells have 
disappeared, and in their place are cells which are small, dark, and com- DIGESTION. 
85 
posed of protoplasm. It would appear that the cells, during rest, elaborate 
the mucigen which is discharged into the tubules during secretory activity, 
to become part of the secretion. 
Saliva is an opalescent, slightly viscid, alkaline fluid, having a specific 
gravity of 1.005. Microscopic examination reveals the presence of 
salivary corpuscles and epithelial cells. Chemically it is composed of 
water, proteid matter, a ferment (ptyalin), and inorganic salts. The 
amount secreted in twenty-four hours is about 2 lbs. Its function is 
twofold:— 
1. Physical.—Softens and moistens the food, glues it together, and facili- 
tates swallowing. 
2. Cheniic.—Converts starch into sugar. This action is due to the 
Fig. 7.—Section of a "Mucous" Gland 
A. In a state of rest. B. After it has been for some time actively secreting.— 
(Lavdowsky.) 
presence of the organic ferment, ptyalin. Ptyalin is an amorphous nitrog- 
enized substance, which can be precipitated from the saliva by calcium 
phosphate. Its power of converting starch into sugar is manifested most 
decidedly at the temperature of the living body and in a slightly alkaline 
medium. The conversion of starch into sugar takes place through 
several stages, the nature of which depends upon the structure of the 
starch granule. This consists of two portions, a stroma of cellulose and 
a contained material, granulose, which is the more abundant and im- 
portant of the two. When subjected to the action of boiling water the 
starch granule swells up and bursts, forming a viscid, opalescent mass 
of starch paste. If saliva be now added to this paste and kept at a 86 
HUMAN PHYSIOLOGY. 
temperature of 104° F. for a few minutes, the paste becomes clear and 
limpid. The first stage in the digestion is now complete with the forma- 
tion of soluble starch. If the action of saliva be continued, a number of 
substances intermediate between starch and sugar are formed, to which 
the name dextrin has been given. Among these may be mentioned:— 
a. Erythrodextrin, which gives the reddish brown color with iodin. As 
the digestion continues and sugar is formed the erythrodextrin disap- 
pears, giving way to— 
b. Achroodextrin, which yields no coloration with iodin but which may 
be precipitated with alcohol. 
The sugar formed by the action of saliva is maltose, the formula for which 
is C12H22On. A small quantity of dextrose is also formed. 
NERVOUS CIRCLE OF INSALIVATION. 
Afferent or Excitor Nerves. 
1. Lingual branch of 5th pair. 
2. Glossopharyngeal. 
Efferent or Secretory Nerves. 
1. Auriculotemporal branch of 5th 
pair, for parotid gland. 
2. Chorda tympani, for submaxil- 
lary and sublingual glands. 
The centers regulating the secretion are two, viz.: The medulla oblon- 
gata and the submaxillary ganglion of the sympathetic, the latter acting 
antagonistically to the former. Impressions excited by the food in the 
mouth reach the medulla oblongata through the afferent nerves ; motor 
impulses are there generated which pass outward through the efferent 
nerves. 
Stimulation of the auriculotemporal branch increases the flow of saliva 
from the parotid gland; division arrests it. 
Stimulation of the chorda tympani is followed by a dilatation of the blood- 
vessels of the submaxillary gland, increased flow of blood (thus acting as 
a vasodilator nerve), and an abundant discharge of a thin saliva ; division 
of the nerve arrests the secretion. 
Stimulation of the cervical sympathetic is followed by a contraction of 
the blood-vessels, diminishing the flow of blood (thus acting as a vasocon- 
strictor nerve), and a diminution of the secretion, which now becomes thick 
and viscid; division of the sympathetic does not, however, completely 
dilate the vessels. There is evidence of the existence of a local vaso- 
motor mechanism, which is inhibited by the chorda tympani, exalted by 
the sympathetic. DIGESTION. 
87 
DEGLUTITION. 
Deglutition is the act of transferring food from the mouth into the 
stomach, and may be divided into three stages:— 
1. The passage of the bolus from the mouth into the pharynx. 
2. From the pharynx into the esophagus. 
3. From the esophagus into the stomach. 
In the first stage, which is entirely voluntary, the mouth is closed and 
respiration momentarily suspended; the tongue, placed against the roof 
of the mouth, arches upward and backward, and forces the bolus into the 
fauces. 
In the second stage, which is entirely reflex, the palate is made tense and 
directed upward and backward by the levatores-palati and tensores-palati 
muscles; the bolus is grasped by the superior constrictor muscle of the 
pharynx and rapidly forced into the esophagus. 
The food is prevented from entering the posterior nares by the uvula and 
the closure of the posterior half-arches (the palatopharyngeal muscles); 
from entering the larynx by its ascent under the base of the tongue and 
the action of the epiglottis. 
In the third stage, the longitudinal and circular muscular fibers, con- 
tracting from above downward, strip the bolus into the stomach. (For 
Nervous Mechanism of Deglutition, see Medulla Oblongata.) 
The Stomach.—Immediately beyond the termination of the esophagus 
the alimentary canal expands and forms a receptacle for the temporary re- 
tention of the food. To this dilatation the term stomach has been applied. 
This organ is somewhat pyriform in outline, and occupies the upper part of 
the abdominal cavity. It measures about 13 inches long, 5 deep, and 
2,% wide, and has a capacity of about five pints. It presents two orifices, 
the cardiac or esophageal and the pyloric; two curvatures, the lesser and 
the greater. 
The left or cardiac end of the stomach is enlarged and forms the fundus; 
the right end is much narrower and forms the pylorus. The stomach 
possesses three coats:— 
1. The serous or reflection of the peritoneum. 
2. The muscular, the fibers of which are arranged in a longitudinal, a cir- 
cular, and an oblique direction. At the pyloric end the circular fibers 
increase in number and form a thick ring or band, which is known as 
the sphincter of the pylorus. 
GASTRIC DIGESTION. 88 
HUMAN PHYSIOLbGY. 
3. The mucous, which is somewhat larger than the muscular coat, and in 
consequence is thrown into folds or rugae. The surface of the mucous 
coat is covered by tall, narrow columnar epithelium. 
Gastric Juice.—During the period of time the food remains in the 
stomach it is subjected to the disintegrating action of an acid fluid, the gas- 
tric juice. This fluid, secreted from glands in the mucous membrane, is 
thoroughly incorporated with the food in consequence of the contractions 
of the muscular coat. The food is gradually liquefied and reduced to a 
form which partly fits it for passage into the small intestine, and for absorp- 
tion into the blood. Gastric juice, when obtained in a pure state, is a clear, 
colorless fluid, decidedly acid in reaction, with a specific gravity of 1005. 
It is composed of the following ingredients :— 
COMPOSITION OF GASTRIC JUICE. 
Water, 994.404 
Hydrochloric acid, 0.200 
Organic matter (pepsin), 3 *95 
Inorganic salts, 2.201 
1000.000 
The water forms by far the largest part of this fluid, and serves the 
purpose of holding the other ingredients in solution, and by its saturating 
power brings them into relation with the constituents of the food. Of the 
inorganic salts the sodium and potassium chlorids are the most abundant 
and important. 
The hydrochloric acid, which exists in a free state, is present in variable 
amounts. In the above table the amount of parts per thousand is much 
less than usually stated. According to most observers it is present to the 
extent of from 0.2 to 0.3 parts per hundred. Though secreted as soon as 
the food enters the stomach, the acid cannot be detected in the free state 
until after the lapse of thirty or forty minutes. It acidulates the food and 
prevents fermentative changes. 
The pepsin which is present in gastric juice associated with the organic 
matter is a hydrolytic ferment or enzyme. When freed from its associa- 
tions and obtained in a pure state, pepsin presents the characteristics of a 
colloidal body, and resembles in its reactions the albuminoids. It is capa- 
ble, when brought into relation with acidulated proteids, of transforming 
them into new forms capable of absorption into the blood. 
Rennin.—In addition to pepsin a second ferment exists in the gastric 
juice to which the term rennin has been given. It possesses the power of 
coagulating the caseinogen of milk. It exists in the mucous membrane, DIGESTION. 
89 
from which it can be extracted by appropriate means. When rennin acts 
on caseinogen the latter is split into insoluble casein and a soluble albumin. 
Calcium phosphate is essential to the action of this enzyme. 
Gastric Glands.—Imbedded within the mucous membrane are to be 
found enormous numbers of tubular glands which, though resembling each 
other in general form, differ in their histologic details in different portions 
of the stomach. 
In the cardiac end or fundus the glands consist of several long tubules 
Fig. 8. 
Diagram showing the relation of'the ultimate twigs of the blood-vessels, V and A, and 
of the absorbent radicles to the glands of the stomach and the different kinds of epi- 
thelium, viz., above cylindrical cells; small, pale cells in the lumen, outside which 
are the dark ovoid cells.—( Yeo’s Text-Book of Physiology.) 
which open into a short, common duct, which opens by a wide mouth on 
the surface of the mucous membrane. Each gland consists primarily of a 
basement membrane lined by epithelial cells. In the duct the epithelium 
is of the columnar variety, resembling that covering the surface of the 
mucous membrane. The secretory portion of the tubule is lined by a layer 
of short, polyhedral, granular and nucleated cells, which, as they border the 90 
HUMAN PHYSIOLOGY. 
lumen of the tubule and thus occupy the central portion of the gland, are 
termed central cells. At irregular intervals, between the central cells and 
the wall of the tubule, are found large oval reticulated cells, which, on ac- 
count of their position, are termed parietal cells. (See Fig. 8.) 
Each parietal cell is in relation with a system of fine canals, which open 
directly into the lumen of the gland. It is estimated that the fundus con- 
tains about five million glands. In the pyloric end of the stomach, the 
glands are generally branched at their lower extremities, and the common 
duct is long and wide. The duct is lined by columnar epithelium, while 
the secreting part is lined by short, slightly columnar, granular cells. The 
parietal cells are entirely wanting. The epithelium covering the surface 
of the mucous membrane is tall, narrow, and cylindrical in shape, and 
consists of mucus-secreting goblet cells. The outer half of the cell con- 
tains a substance, mucinogen, which produces mucin. The gastric glands 
in both situations are surrounded by a fine connective tissue, which sup- 
ports blood-vessels, nerves, and lymphatics. 
Changes in the Cells During Secretion.—During the periods of rest 
and secretory activity the cells of the glands undergo changes in structure 
which are supposed to be connected with the production of the pepsin and 
hydrochloric acid. During rest, the protoplasm of the central cells becomes 
filled with granular matter, which during the time of secretion disappears, 
presumably passing into the lumen of the tubule, and as a result the 
protoplasm becomes clear and hyaline in appearance. The granular 
material is probably the mother substance,pepsinogen, which, inactive in 
itself, yields the active ferment, pepsin. The parietal cells during digestion 
increase in size, but do not become granular. It is at this period that they 
secrete the hydrochloric acid. After digestion they rapidly diminish in 
size and return to their former condition. The pyloric glands secrete 
pepsin only. 
Mechanism of Secretion.—In the intervals of digestion the mucous 
membrane of the stomach is covered with a layer of mucus. As soon as 
the food passes from the esophagus into the stomach, the blood-vessels 
dilate, the circulation becomes more active, and the membrane assumes a 
bright red appearance. Coincidently, small drops of gastric juice begin to 
exude from the glands, which, as they increase in quantity, run together 
and trickle down the sides of the stomach. This pouring out of fluid con- 
tinues during the presence of food in the stomach. 
The secretion of gastric juice is a reflex act, taking place through the 
central nervous system and called forth in response to the stimulus of food DIGESTION. 
91 
in the stomach. That the central nervous system also directly influences 
the production of the secretion is shown by the fact that mental emotion, 
such as fear and anger, will arrest or vitiate the normal secretion. The 
reflex nature of the process can be shown by experimentation upon the 
pneumogastric nerve. If during digestion, when the peristaltic movements 
are active and the gastric mucous membrane flushed and covered with gas- 
tric juice, the pneumogastric nerves are divided on both sides, the mucous 
membrane becomes pale, the secretion is arrested, and the peristaltic move- 
ments become less marked. Stimulation of the peripheral end produces 
no constant effects; stimulation of the central end, however, is at once 
followed by dilatation of the vessels, flushing of the mucous membrane, 
and a re-establishment of the secretion. It is evident, therefore, that dur- 
ing digestion afferent impulses are passing up the pneumogastrics to the 
medulla; efferent impulses, in all probability, pass through the fibers of the 
sympathetic nervous system to the blood-vessels and glands concerned in 
the elaboration of the gastric juice. After all the nervous connections of 
the stomach are divided, a small quantity of juice continues to be secreted 
for several days. This has been attributed to the action of a local nervous 
mechanism and to the direct action of the food upon the protoplasm of the 
secreting cells. 
Chemic Action of the Gastric Juice.—By the combined influence of 
the contraction of the muscular walls, the action of the gastric juice, and 
the temperature, the food is reduced to a semiliquid condition and acquires 
a distinct acid odor. This semifluid mass will vary in composition and 
appearance according to the nature of the food. To this matter the term 
chyme has been given. 
Meat is rapidly disintegrated by the solution of the connective tissue. 
The fibers thus separated are readily broken up into particles by solution 
of the sarcolemma. Well-cooked meat is more easily digested owing to 
the conversion of the connective tissue into gelatin. 
Connective tissues in the raw or imperfectly gelatinized condition are very 
slowly dissolved. Cartilage, tendons, and even bones, will in time be cor- 
roded and liquefied. 
Vegetables are not easily digested unless thoroughly prepared by suffi- 
cient cooking. The nutritive principles are enclosed by cellulose walls 
which are not affected by gastric juice. The influence of heat and moisture 
softens and ruptures the cellulose walls so as to permit the introduction of 
gastric juice and the solution of its nutritive principles. 
The principal action of the gastric juice, however, is to transform the 92 
HUMAN PHYSIOLOGY. 
different proteid principles of the food into peptones, the intermediate stages 
of which are due to the influence of the acid and pepsin respectively. As 
soon as any one of the albumins is penetrated by the acid it is converted 
into acid-albumin or parapeptone. In a short time this product, under the 
influence of the pepsin, changes into a somewhat different compound 
termed albumose, of which there are probably several varieties. The final 
stage is that of peptone, the form under which the proteids finally are ab- 
sorbed. 
The albumin molecule, moreover, is composed of two distinct portions, 
which may be termed, respectively, hemi- and anti-. In the process of 
digestion the molecule divides into these portions, each of which passes 
through practically the same changes, as shown by the following table:— 
Albumin. 
Anti-albumin 
Hemi-albumin 
Ilemi-albumose 
Anti-albumose 
Hemipeptone 
Antipeptone 
The hemipeptone differs from the antipeptone in the fact that it is 
capable of decomposition into leucin and tyrosin by the action of the 
pancreatic juice. 
Peptones.—Peptones are the final products of the digestion of proteid 
bodies, and differ from the bodies from which they are derived by the fol- 
lowing particulars: — 
1. They are diffusible ; i. e., capable of passing readily through animal mem- 
branes, a condition essential for their absorption. 
2. They are soluble in water and saline solution. 
3. They are noncoagulable by heat, nitric or acetic acids. They can be 
readily precipitated, however, by tannic acid, bile acids, and by mercuric 
chlorid. 
4. They are absorbable and assimilable by the blood, and by it transformed 
into serum-albumin. 
The duration of gastric digestion will depend largely upon the quantity 
and quality of the food. The average meal occupies from three to five 
hours. 
Movements of the Stomach.—As soon as digestion commences the 
cardiac and pyloric orifices are closed; the walls of the stomach contract DIGESTION. 
93 
upon the food, and a peristaltic action begins, which carries the food along 
the greater and lesser curvatures, and thoroughly incorporates it with the 
gastric juice. As soon as any portion of the food is digested it passes 
through the pylorus into the intestine. 
TABLE SHOWING DIGESTIBILITY OF VARIOUS ARTICLES OF FOOD. 
Eggs, whipped, 
Hours. 
Minutes. 
20 
“ soft boiled, 
3 
“ hard boiled, 
3 
3° 
Oysters, raw, . 
55 
“ stewed, 
3 
3° 
Lamb, broiled, 
30 
Veal, broiled, 
4 
Pork, roasted, 
5 
i5 
Beefsteak, broiled, 
-3 
Turkey, roasted, 
25 
Chicken, boiled, 
4 
“ fricasseed, 
45 
Duck, roasted, 
4 
Soup, barley, boiled, 
3° 
“ bean, 
3 
. . 
“ chicken, “ 
“ mutton, “ 
3 
30 
Liver, beef, broiled, 
Sausage, “ 
3 
20 
Green corn, boiled, 
3 
45 
Beans, “ 
3° 
Potatoes, roasted, 
30 
“ boiled, 
3 
3° 
Cabbage, “ 
4 
3° 
Turnips, “ 
3 
30 
Beets, “ 
3 
45 
Parsnips, “ 
30 
INTESTINAL DIGESTION. 
The process of digestion as it takes place in the small intestine is ex- 
ceedingly important and complex, and is brought about by the action of 
the pancreatic juice, the bile, and the intestinal juice. 
The contents of the stomach at the close of gastric digestion consist of 
water, inorganic salts, peptones, undigested albumins and starches, maltose, 
cane-sugar, liquefied fats, cellulose, and the indigestible portions of meats, 
cereals, fruits, etc. This so-called chyme is quite acid in reaction, and upon 
its passage through the now open pylorus into the intestine it excites a reflex 
stimulation and secretion of the intestinal fluids, which are decidedly 94 
HUMAN PHYSIOLOGY. 
alkaline in reaction, and which have neutralizing action on the chyme. 
As soon as the latter becomes alkaline and gastric digestion arrested, the 
various phases of intestinal dfgestion begin which eventuate in the trans- 
formation of all the remaining undigested nutritive materials into absorbable 
and assimilable compounds. 
The Small Intestine is about 22 feet in length and about \l/2 inches 
in diameter. Like the stomach, it possesses three coats, as follows:— 
1. The serous, or peritoneal. 
2. The muscular, the fibers of which are arranged for the most part cir- 
cularly. Some of the fibers are so arranged as to form longitudinal 
bands. 
3. Mucous, which presents a series of transverse folds known as the val- 
vules conniventes. 
Intestinal Glands.—In that portion of the small intestine known as 
the duodenum, are to be found a number of small branched tubular glands 
(Brunner’s), the acini of which are lined by short cylindrical cells, similar 
to those lining the pyloric glands. From the duodenum to the termina- 
tion of the intestine the mucous membrane contains an enormous number of 
tubular glands (Lieberkiihn’s) formed by an inversion of the basement 
membrane and lined by epithelial cells. The common secretion of these 
intestinal glands forms the intestinal juice. This is a thin, opalescent, 
slightly yellow fluid, alkaline in reaction, and contains water, salts, and 
proteid matter. 
The function of the intestinal juice is but incompletely known. It ap- 
pears to have the power of converting starch into dextrose ; it is doubtful 
if it is capable of digesting either albumins or fats. Its most distinctive 
action is the inversion of cane-sugar, maltose, and lactose into dextrose, and 
thus preparing them for absorption. This change is dependent on the 
presence of a ferment body known as invertin. 
The Pancreatic Juice is secreted by the pancreas, a flattened gland 
about six inches long, running transversely across the posterior wall of the 
abdomen behind the stomach; its duct opens into the duodenum. 
The pancreas is similar in structure to the salivary glands, consisting of 
a system of ducts terminating in acini. The acini are tubular or flask- 
shaped, and consist of a basement membrane lined by a layer of cylindrical, 
conical cells, which encroach upon the lumen of the acini. The cells 
exhibit a difference in their structure (Fig. 9), and may be said to consist 
of two zones, viz., an outer parietal zone, which is transparent and appar- 
ently homogeneous, staining rapidly with carmin ; an inner zone, which DIGESTION. 
95 
borders the lumen, and is distinctly granular and stains but slightly with 
carmin. These cells undergo changes similar to those exhibited by the 
cells of the salivary glands during and after active secretion. As soon as 
the secretory activity of the pancreas is established, the granules disappear, 
and the inner granular layer becomes reduced to a very narrow border, 
while the outer zone increases in size and occupies nearly the entire cell. 
During the intervals of secretion, however, the granular layer reappears 
and increases in size until the outer zone is reduced to a minimum. It 
would seem that the granular matter is formed by the nutritive processes 
occurring in the gland during rest, and is discharged during secretory 
activity into the ducts, and takes part in the formation of the pancreatic 
secretion. 
The pancreatic juice is transparent, colorless, strongly alkaline, and viscid, 
Fig. 9.—One Saccule of the Pancreas of the Rabbit in Different States 
of Activity. 
A. After a period of rest, in which case the outlines of the cells are indistinct, and the 
inner zone, i e., the part of the cells (a) next the lumen (c), is broad and filled with 
fine granules. B. After the gland has poured out its secretion, when the cell out- 
lines (d) are clearer, the granular zone (a) is smaller, and the clear outer zone is 
wider.—(Fee’s Text-Book 0/Physiology, after Kiihne and Lea.) 
and bas a specific gravity of 1.040. It is one of the most important of the 
digestive fluids, as it exerts a transforming influence upon all classes of ali- 
mentary principles, and has been shown to contain at least three distinct 
ferments. It has the following composition :— 
Water, 900.76 
Albuminoid substances, 90.44 
Inorganic salts 8.80 
1000.00 
COMPOSITION OF PANCREATIC JUICE. 96 
HUMAN PHYSIOLOGY. 
The pancreatic juice is characterized by its action:— 
1. Upon starch. When starch is subjected to the action of the juice it is 
at once transformed into maltose; the change takes place more rapidly 
than when saliva is added. This action is caused by the presence of a 
special ferment, amylopsin. 
2. Upon albumin. The albuminous bodies are changed by the juice into, 
first, an alkali albumin, then into albumose, and ultimately into true 
peptone. As in the case of gastric digestion, the albumin molecule 
is divided into a hemi and an anti half. The albumin does not swell 
up, as is the case in gastric digestion, but is gradually corroded and 
dissolved. This change is due to the presence of the ferment, trypsin. 
Long-continued action of trypsin converts the hemi peptones into two 
crystalline bodies, leucin and tyrosin. 
3. Upon fats. The most striking action of the pancreatic juice is the emul- 
sification of the fats or their subdivision into minute particles of micro- 
scopic size. This change takes place rapidly and depends upon the 
alkalinity of the fluid and the quantity of albumin present, combined 
with the intestinal movements. The neutral fats are also decomposed 
into their corresponding fatty acids and glycerin ; the acids thus set free 
unite with the alkaline bases present in the intestine and form soaps. 
This decomposition of the neutral fats is caused by the ferment, sleapsin. 
The Bile has an important influence in the elaboration of the food and 
its preparation for absorption. It is a golden-brown, viscid fluid, having a 
neutral or alkaline reaction and a specific gravity of 1.020. 
COMPOSITION OF BILE. 
Sodium glycocholate, 
Sodium taurocholate, 
Water, 859.2 
9M 
Fat, 9.2 
Cholesterin, 2.6 
Mucus and coloring matter 29.8 
Salts, 7.8 
1000.00 
The biliary salts, sodium glycocholate and taurocholate, are characteristic 
ingredients, and are formed in the liver by the process of secretion from 
materials furnished by the blood. It is probable that they are derived from 
the nitrogenized compounds, though the stages in the process are unknown. 
They are reabsorbed from the small intestine to play some ulterior part in 
nutrition. DIGESTION. 
97 
Cholesterin is a product of waste taken up by the blood from the nervous 
tissues and excreted by the liver. It crystallizes in the form of rhombic 
plates, which are quite transparent. When retained within the blood, it 
gives rise to the condition of cholesteremia, attended with severe nervous 
symptoms. It is given oil in the feces under the form of stercorin. 
The coloring matters which give the tints to the bile are biliverdin and 
bilirubin, and are probably derived from the coloring matter of the blood. 
Their presence in any fluid can be recognized by adding to it nitric acid 
containing nitrous acid, when a play of colors is observed, beginning with 
green, blue, violet, red, and yellow. 
The Bile is both a secretion and an excretion; it is constantly being 
formed and discharged by the hepatic ducts into the gall bladder, in which 
it is stored up during the intervals of digestion. As soon as food enters the 
intestines it is poured out abundantly by the contraction of the walls of the 
gall bladder. 
The amount secreted in twenty-four hours is about pounds. 
Functions of the Bile.— 
1. It assists in the emulsification of the fats and promotes their absorption. 
2. It tends to prevent putrefactive changes in the food. 
3. It stimulates the secretion of the intestinal glands, and excites the normal 
peristaltic movement of the bowels. 
The digested food, the chyme, is a grayish, pultaceous mass, but as it 
passes through the intestines it becomes yellow from admixture with the 
bile. It is propelled onward by vermicular motion—by the contraction of 
the circular and longitudinal muscular fibers. 
During the passage of the digesting food through the intestinal canal the 
nutritive products, the peptones, the dextrose and levulose, the fatty emul- 
sions, the fatty acids and their soaps, are absorbed into the blood, while the 
undigested residue is carried onward by the peristaltic movements through 
the iliocecal valve into the large intestine. 
Intestinal Fermentation.—Owing to the favorable conditions for 
fermentative and putrefactive processes—e.g., heat, moisture, oxygen, micro- 
organisms—the food when consumed in excessive quantity, or when acted 
on by defective secretions, undergoes a series of decomposition changes 
which are attended by the production of gases and various chemic com- 
pounds. Grape sugar and maltose are partially split into lactic acid, this 
into butyric acid, carbon dioxid, and hydrogen. Fats are reduced to 
glycerol and fatty acids; the glycerol, according to the organisms present, 
yields succinic and other fatty acids, carbon dioxid, and hydrogen. 98 
HUMAN PHYSIOLOGY. 
The proteids, under the prolonged action of the pancreatic juice, are de- 
composed, and yield leucin and tyrosin; the former is split into valerianic 
acid, ammonia, and carbon dioxid; the latter is split into indol, which is 
the antecedent of indican in the urine. Skatol is another proteid deriva- 
tive constantly present in the fecal substance. 
The Large Intestine extends from the iliocecal valve to the anus, 
and measures about five feet in length. It also consists of the three coats : 
the serous, the muscular, and mucous. The mucous membrane contains a 
number of mucous glands, the secretion from which lubricates the surface 
of the canal. The ascending portion of the large intestine possesses the 
power of absorption, and hence its contents become less liquid and more 
consistent. As the residue passes toward the sigmoid flexure it acquires 
the characteristic of the fecal matter. This consists of the undigested por- 
tions of the food, decomposition products, mucus, and inorganic salts. 
Defecation is the voluntary act of extruding the feces from the rectum, 
and is accomplished by a relaxation of the sphincter ani muscle, the contrac- 
tion of the muscular walls of the rectum, aided by the contraction of the 
abdominal muscles. 
ABSORPTION. 
The terra absorption is applied to the passage or transference of material 
into the blood from the tissues, from the serous cavities, and from the 
mucous surfaces of the body. The most important of these surfaces, espe- 
cially in its relation to the formation of the blood, is the mucous surface of 
the alimentary canal; for it is from this organ that new materials are de- 
rived which maintain the quality and quantity of the blood. The absorp 
tion of materials from the interstices of the tissues is to be regarded rather 
as a return to the blood of liquid nutritive material which has escaped 
from the blood-vessels for nutritive purposes, and which, if not returned, 
would lead to an accumulation of such fluid and the development of drop- 
sical conditions. 
The anatomic mechanisms involved in the absorptive process are, pri- 
marily, the lymph spaces, the lymph capillaries and blood capillaries ; sec- 
ondarily, the lymphatic vessels and larger blood-vessels. 
Lymph Spaces, Lymph Capillaries, Blood Capillaries.—Every- 
where throughout the body, in the intervals of connective tissue bundles, 
and in the interstices of the several structures of which an organ is com- 
posed, are found spaces of irregular shape and size, determined largely by ABSORPTION. 
99 
the nature of the organ in which they are found, which have been termed 
lymph spaces or lacunce, from the fact that during the living condition they 
are continually receiving the lymph which has escaped from the blood- 
vessels throughout the body. In addition to the connective tissue lymph 
spaces, various observers have described special lymph spaces in the testicle, 
kidney, liver, thymus gland, and spleen; in all secreting glands between 
the basement membrane and blood-vessels; around blood-vessels (perivas- 
cular spaces), and around nerves. The serous cavities of the body, peri- 
toneal, pleural, pericardial, etc., may also be regarded as lymph spaces, 
which are in direct communication by open mouths or stomata with the 
lymphatic capillaries. This method of communication is not only true of 
serous membranes, but to some extent also of mucous membranes. The 
cylindrical sheaths and endothelial cells surrounding the brain, spinal cord, 
and nerves can also be looked upon as lymph spaces in connection with 
lymph capillaries. 
The lymphatic capillaries, in which the lymphatic vessels proper take 
their origin, are arranged in the form of plexuses of quite irregular shape. 
In most situations they are intimately interwoven with the blood-vessels, 
from which, however, they can be readily distinguished by their larger 
caliber and irregular expansions. The wall of the lymph capillary is 
formed by a single layer of epithelioid cells, with sinuous outlines, and 
which accurately dovetail with each other. In no instance are valves 
found. In the villus of the small, intestine the beginning of the lacteal is 
to be regarded as a lymph capillary, generally club-shaped, which at the 
base of the villus enters a true lymphatic ; at this point a valve is present, 
which prevents regurgitation. The lymphatic capillaries anastomose freely 
with each other, and communicate on the one hand with the lymph spaces, 
and on the other with the lymphatic vessels proper. 
As the shape, size, etc., of both lymph spaces and capillaries are deter- 
mined largely by the nature of the tissues in which they are contained, it 
is not always possible to separate the one from the other. Their function, 
however, may be regarded as similar, viz.: the collection of the lymph 
which has escaped from the blood-vessels, and its transmission onward into 
the regular lymphatic vessels. 
The blood capillaries not only permit the escape of the liquid nutritive 
portions of the blood through their delicate walls, but are also engaged in 
the reabsorption of this transudate as well as in the absorption of new 
materials from the alimentary canal. The extensive capillary network 
which is formed by the ultimate subdivision of the arterioles in the sub- 
mucous tissue and villi of the small intestine forms an anatomic arrange- 100 
HUMAN PHYSIOLOGY. 
ment well adapted for absorption. It is now well known that in the 
absorption of the products of digestion the blood capillaries are more active 
than the lymphatic capillaries. 
Lymphatic Vessels.—The lymphatic vessels constitute a system of 
minute, delicate, transparent vessels, found in nearly all the organs and 
tissues of the body. Having their origin at the periphery in the lymphatic 
capillaries and spaces, they gradually converge toward the trunk of the 
body and empty into the thoracic duct. In their course they pass through 
numerous small ovoid bodies, the lymphatic glands. 
The lymphatic vessels of the small intestine {the lacteals) arise within 
the villous processes which project from the inner surface of the intestine 
throughout its entire extent. The wall of the villus is formed by an eleva- 
tion of the basement membrane, and is covered by a layer of columnar epi- 
thelial cells. The basis of the villus consists of adenoid tissue, fine plexus 
of blood-vessels, unstriped muscular fibers, and the lacteal vessel. The 
adenoid tissue consists of a number of intercommunicating spaces, containing 
leukocytes. The lacteal vessel possesses a thin but distinct wall composed 
of endothelial plates, with here and there openings which bring the interior 
of the villus into communication with the spaces of the adenoid tissue. 
The structure of the larger vessels resembles that of the veins, consisting 
of three coats:— 
1. External, composed of fibrous tissue and muscular fibers, arranged 
longitudinally. 
2. Middle, consisting of white fibers and yellow elastic tissue, nonstriated 
muscular fibers, arranged transversely. 
3. Internal, composed of an elastic membrane, lined by endothelial cells. 
Throughout their course are found numerous semilunar valves, looking 
toward the larger vessels, formed by a folding of the inner coat and 
strengthened by connective tissue. 
Lymphatic Glands.—The lymphatic glands consist of an external 
capsule composed of fibrous tissue which contains non-striped muscular 
fibers; from its inner surface septa of fibrous tissue pass inward and sub- 
divide the gland substance into a series of compartments which communi- 
cate with each other. The blood-vessels which penetrate the gland are 
surrounded by fine threads, forming a follicular arrangement, the meshes of 
which contain numerous lymph corpuscles. Between the follicular threads 
and the wall of the gland lies a lymph channel traversed by a reticulum of 
adenoid tissue. The lymphatic vessels after penetrating this capsule pour 
their lymph into this channel, through which it passes; it is then collected ABSORPTION. 
101 
by the efferent vessels and transmitted onward. The lymph corpuscles 
which are washed out of the gland into the lymph stream are formed, most 
probably, by division of pre-existing cells. 
The Thoracic Duct is the general trunk of the lymphatic system into 
which the vessels of the lower extremities, of the abdominal organs, of the 
left side of the head, and left arm empty their contents. It is about 20 
inches in length, arises in the abdomen, opposite the third lumbar vertebra, 
by a dilatation, the receptaculum chyli; ascends along the vertebral column 
to the seventh cervical vertebra, and terminates in the venous system at 
the junction of the internal jugular and subclavian veins on the left side. 
The lymphatics of the right side of the head, of the right arm, and the right 
side of the thorax terminate in the right thoracic duct, about one inch in 
length, which joins the venous system at the junction of the internal jugular 
and subclavian on the right side. 
The general arrangement of the lymphatic vessels in shown in P'ig. 10. 
The Blood-vessels which are concerned in the conduction of fresh 
nutritive material from the alimentary canal have their origin in the elabo- 
rate capillary network in the mucous membrane. The small veins which 
emerge from the network gradually unite, forming larger and larger trunks, 
which are known as the gastric, superior, and inferior mesenteric veins. 
These finally unite to form the portal vein, a short trunk about three inches 
in length. The portal vein enters the liver at the transverse fissure, after 
which it forms a fine capillary plexus ramifying throughout the substance 
of the liver; from this plexus the hepatic veins take their origin, which 
finally empty the blood into the vena cava inferior. (See P'ig. 11.) 
Absorption of Food.—Physiologic experiments have demonstrated 
that the agents concerned in the absorption of new materials from the ali- 
mentary canal are :— 
1. The blood-vessels of the entire canal, but more particularly those uniting 
to form the portal vein. 
2. The lymphatics coming from the small intestine, which converge to 
empty into the thoracic duct. 
As a result of the action of the digestive fluids upon the different classes 
of food stuffs, albumins, sugars, starches, and fats, there are formed pep- 
tones, glucose, and fatty emulsion, which differ from the former in being 
highly diffusible, a condition essential to their absorption. In order that 
these substances may get into the blood, they must pass through the layer 
of cylindrical epithelial cells and the underlying basement membrane, and 
into the lymph spaces of the villi and submucous tissue. The mechanism 102 
HUMAN PHYSIOLOGY. 
Fig. 10.—Diagram Showing the Course of the Main Trunks of the Absorb- 
ent System. 
The lymphatics of lower extremities (D) meet the lacteals of intestines (LAC) at the 
receptaculum chyli (RC), where the thoracic duct begins. The superficial vessels 
are shown in the diagram on the right arm and leg (S), and the deeper ones on the 
arm to the left (D). The glands are here and there shown in groups. The small 
right duct opens into the veins on the right side. The thoracic duct opens into the 
union of the great veins of the left side of the neck (T).—(Veo’s Text-book of 
Physiology.) ABSORPTION. 
103 
by which the cells effect this passage of the food is but imperfectly under- 
stood. Osmosis and filtration are conditions, however, made use of by the 
cells in the absorptive process. 
The products of digestion find their way into the general circulation by 
two routes : — 
I. The water, peptones, glucose, and soluble salts, taker passing into the 
lymph spaces of the villi, pass through the wall of the capillary blood- 
Diagram of the portal vein (pv) arising in the alimentary tract and spleen 1$), and 
carrying the blood from these organs to the liver.—(Yeo's Text-Book of Physi- 
ology.) 
Fig. ii. 
vessel; entering the blood, they are carried to the liver by the vessels 
uniting to form the portal vein; emerging from the liver, they are 
emptied into the inferior vena cava by the hepatic vein. 
2. The emulsified fat enters the lymph capillary in the interior of the 
villus; by the contraction of the layer of muscular fibers surrounding it 
its contents are forced onward into the lymphatic vessel or lacteal, 104 
HUMAN PHYSIOLOGY. 
thence into the thoracic duct, and finally into the circulation at the junc- 
tion of the internal jugular and subclavian veins on the left side. 
Absorption of Lymph.—Similar to the absorption of food from the 
alimentary canal is the absorption of lymph from the lymph spaces of the 
organs and tissues. During the passage of the blood through the capillary 
blood-vessels, a portion of the liquor sanguinis or plasma or lymph passes 
through the capillary wall out into the lymph spaces. The tissue cells are 
thus bathed with this new material; from it those substances are selected 
which are necessary for their growth, repair, and all purposes of nutrition. 
An excess of nutritive material, far beyond the needs of the tissues, transudes 
from the blood-vessels, and it is this excess w'hich is absorbed by the lym- 
phatics and returned to the blood by the thoracic duct. It is quite probable 
also that a portion of this transudate is reabsorbed by the blood-vessels. 
Properties and Composition of Lymph and Chyle.—Lymph, as 
found in the lymphatic vessels of animals, is a clear, colorless, or opalescent 
fluid, having an alkaline reaction, a saline taste, and a specific gravity of 
about 1.040. It holds in suspension a number of corpuscles resembling in 
their general appearance the white corpuscles of the blood. Their number 
has been estimated at 8200 per cubic millimeter, though the number varies 
in different portions of the lymphatic system. As the lymph flows through 
the lymphatic gland it receives a large addition of corpuscles. Lymph 
corpuscles are granular in structure, and measure j/w of an inch in 
diameter. When withdrawn from the vessels, lymph undergoes a spon- 
taneous coagulation, similar to that of the blood, after which it separates in 
serum and clot. 
Water, 96.536 
Proteids (serum-albumin, fibrin-globulin), .... 1.320 
Extractives (urea, sugar, cholesterin), 1-559 
Fatty matters, a trace. 
Salts, 0.585 
100.000 
COMPOSITION OF LYMPH. 
Chyle.—Chyle is the fluid found in the lymphatic vessels, coming from 
the small intestine after the digestion of a meal containing fat. In the 
intervals of digestion, the fluid of these lymphatics is identical in all respects 
with the lymph found in all other regions of the body. As soon as the 
emulsified fat passes into the lymphatic vessels and mingles with the 
lymph it becomes milky in color, and the vessels which previously were 
invisible become visible, and resemble white threads running between the 
layers of the mesentery. Chyle has a composition similar to that of lymph, ABSORPTION. 
105 
but it contains, in addition, numerous fatty granules, each surrounded by an 
albuminous envelope. When examined microscopically the chyle presents 
a fine molecular basis, made up of the finely divided granules of fat. 
Water, 902.37 
Albumin, 35.16 
Fibrin, 3.70 
Extractives, 15.65 
Fatty matters, 36.01 
Salts, 7.11 
COMPOSITION OF CHYLE. 
1000.00 
Forces Aiding the Movement of Lymph and Chyle.—The lymph 
and chyle are continually moving in a progressive manner from the peri- 
phery or beginning of the lymphatic system to the final termination of the 
thoracic duct. The force which primarily determines the movement of the 
lymph has its origin in the beginnings of the lymphatic vessels, and depends 
upon the difference in pressure here and the pressure in the thoracic duct. 
The greater the quantity of fluid poured into the lymph spaces the greater 
will be the pressure and consequently the movement. The first movement 
of chyle is the result of a contraction of the muscular fibers within the walls 
of the villus. At the time of contraction, the lymphatic capillary is com- 
pressed and shortened, and its contents forced onward into the true lym- 
phatic. When the muscular fibers relax, regurgitation is prevented by the 
closure of the valve in the lymphatic at the base of the villus. 
As the walls of the lymphatic vessels contain muscular fibers, when they 
become distended these fibers contract and assist materially in the onward 
movement of the fluid. 
The contraction of the general muscular masses in all parts of the body, 
by exerting an intermittent pressure upon the lymphatics, also hastens the 
current onward; regurgitation is prevented by the closure of valves which 
everywhere line the interior of the vessels. 
The respiratory movements aid the general flow of both lymph and chyle 
from the thoracic duct into the venous blood. During the time of an in- 
spiratory movement the pressure within the thorax, but outside the lungs, 
undergoes a diminution in proportion to the extent of the movement; as a 
result, the fluid in the thoracic duct outside of the thorax, being under a 
higher pressure, flows more rapidly into the venous system. At the time 
of an expiration, the pressure rises and the flow is temporarily impeded, 
only to begin again at the next inspiration. 106 
HUMAN PHYSIOLOGY. 
BLOOD. 
The Blood is a nutritive fluid containing all the elements necessary for 
the repair of the tissues; it also contains principles of waste absorbed from 
the tissues, which are conveyed to the various excretory organs and by them 
eliminated from the body. 
The total amount of blood in the body is estimated to be about one-eighth 
of the body weight; from 16 to 18 pounds in an individual of average 
physical development. The quantity varies during the twenty-four hours, 
the maximum being reached in the afternoon, the minimum in the early 
morning hours. 
Blood is a heterogeneous, opaque, red fluid, having an alkaline reaction, 
a saline taste, and a specific gravity of 1.055. 
The opacity is due to the refraction of the rays of light by the elements 
of which the blood is composed. The color varies in hue, from a bright 
scarlet in the arteries to a deep purple in the veins, due to the presence of 
a coloring matter, hemoglobin, in different degrees of oxidation. 
The alkalinity is constant, and depends upon the presence of the alka- 
line sodium phosphate, Na2HP04. 
The saline taste is due to the amount of sodium chlorid present. 
The specific gravity ranges within the limits of health from 1.045 to 1 °75- 
The odor of the blood is characteristic, and varies with the animal from 
which it is drawn, due to the presence of caproic acid. 
The temperature of the blood ranges from 98° F. at the surface to 107° 
F. in the hepatic vein; it loses heat by radiation and evaporation as it 
approaches the extremities and as it passes through the lungs. 
Blood Consists of Two Portions:— 
1. The liquor sanguinis or plasma, a transparent, colorless fluid, in which 
are floating— 
2. Red and white corpuscles ; these constituting by weight less than one- 
half, 40 per cent., of the entire amount of blood. 
Water, 902.00 
Albumin, 53°° 
Paraglobulin, 22.00 
Fibrinogen, 3.00 
Fatty matters, 2.50 
Crystallizable nitrogenous matters, 4.00 
Other organic matter, 5.00 
Mineral salts, 8.50 
1000.00 
COMPOSITION OF PLASMA. 
Dalton. BLOOD 
107 
Water acts as a solvent for the inorganic matters and holds in suspension 
the corpuscular elements. 
Albumin is the nutritious principle of the blood; it is absorbed by the 
tissues to repair their waste and is transformed into the organic basis char- 
acteristic of each structure. 
Paraglobin or Jibrinoplastin is a soft, amorphous substance precipitated 
by sodium chlorid in excess, or by passing a stream of carbonic acid 
through dilute serum. 
Fibrinogen can also be obtained by strongly diluting the serum and 
passing carbonic acid through it for a long time, when it is precipitated as 
a viscous deposit. 
Fatty matter exists in small proportion, except in pathologic conditions 
and after the ingestion of food rich in oleaginous matters; it soon disap- 
pears, undergoing oxidation, generating heat and force, or is deposited as 
adipose tissue. 
Sugar is represented by glucose, a product of the digestion of saccharin 
matter and starches in the alimentary canal; glycogenic matter is derived 
from the liver. 
The saline constituents aid the process of osmosis, give alkalinity to the 
blood, promote the absorption of carbonic acid from the tissues into the 
blood, and hold other substances in solution; the most important are 
the sodium and potassium chlorids, the calcium and magnesium phos- 
phates. 
Excrementitious matters are represented by carbonic acid, urea, creatin, 
creatinin, urates, oxalates, etc. ; they are absorbed from the tissues by the 
blood and conveyed to the excretory organs, lungs, kidneys, etc. 
Gases.—Oxygen, nitrogen, and carbonic acid exist in varying proportions. 
BLOOD CORPUSCLES. 
The corpuscular elements of the blood occur under two distinct forms, 
which, from their color, are known as the red and white corpuscles. 
The red corpuscles as they float in a thin layer of the liquid sanguinis 
are of a pale straw color; it is only when aggregated in masses that they 
assume the bright red color. In form they are circular and biconcave; 
they have an average diameter of the of an inch. 
In mammals, birds, reptiles, amphibia, and fish the corpuscles vary in 
size and number, gradually becoming larger and less numerous as the scale 
of animal life is descended, e. g. :— 108 
HUMAN PHYSIOLOGY. 
TABLE SHOWING COMPARATIVE DIAMETER OF RED CORPUSCLES. 
Mammals. 
Man, 35hss 
Chimpanzee, jAi 
Ourang, 33s3 
Dog, 3A1 
Cat, Has 
Hog, 
Horse, ibW 
Ox, jjW 
Birds. 
Eagle, tbti 
Owl, X7‘B3 
Sparrow, 2Atr 
Swallow, 
Pigeon, XBV3 
I urkey, 35*5 
Goose, XB3B 
Swan, ibVb 
Reptiles. 
Turtle, fjVr 
Tortoise, xJr,5 
Lizard, xAs 
Viper, ,jV« 
Amphibia. 
Prog. nh 
1 °a<b rAs 
Proteus, jJ;, 
Siren, 
Amphiuma, 3^3 
Fish. 
1 Perch, 5ogs 
1 Carp, 2141 
f Pike, insB 
> Eel, y li s 
1 
In man and the mammals the red corpuscles present neither a nucleus 
nor a cell wall, and are universally of a small size. They can be readily 
distinguished from the corpuscles of birds, reptiles, and fish, in which they 
are larger, oval in shape, and possess a well-defined nucleus. 
The red corpuscles are exceedingly numerous, amounting to about 
5,000,000 in a cubic millimeter of blood. In structure they consist of a 
firm, elastic, colorless framework, the stroma, in the meshes of which is 
entangled the coloring matter, the hemoglobin. 
CHEMIC COMPOSITION OF RED CORPUSCLES. 
Water, 688.00 
Globulin 282.22 
Hemoglobin, 16.75 
Fatty matter, 2.31 
Extractives, 2.60 
Mineral salts, 8.12 
1000.00 
Hemoglobin, the coloring matter of the corpuscles, is an albuminous com- 
pound, composed of C. O. H. N. S. and iron. It may exist either in an 
amorphous or crystalline form. When deprived of all its oxygen, except 
the quantity entering into its intimate composition, the hemoglobin becomes 
dark in color, somewhat purple in hue, and is known as reduced hemoglo- 
bin. When exposed to the action of oxygen it again absorbs a definite 
amount and becomes scarlet in color, and is known as oxy-hemoglobin. 
The amount of oxygen absorbed is 1.76 C.C. (y’jy cubic inch) for one milli- 
gram (g’y grain) of hemoglobin. 
It is this substance which gives the color to the venous and arterial 
blood. As the venous blood passes through the capillaries of the lungs, 
the reduced hemoglobin absorbs the oxygen from the pulmonary air and 
becomes oxy-hemoglobin, scarlet in color, and the blood becomes arterial. 
When the arterial blood passes into the systemic capillaries, the oxygen is BLOOD 
109 
absorbed by the tissues, the hemoglobin becomes reduced, purple in color, 
and the blood becomes venous. A dilute solution of oxy-hemoglobin gives 
two absorption bands between the lines D and E of the solar spectrum. 
Reduced hemoglobin gives but one absorption band, occupying the space 
existing between the two bands of the oxy-hemoglobin spectrum. 
The function of the red corpuscle is, therefore, to absorb oxygen and 
carry it to the tissues; the smaller the corpuscles and the greater the num- 
ber, the greater is the quantity of oxygen absorbed ; and, consequently, all 
the vital functions of the body become more active. 
The white corpuscles are far less numerous than the red, the proportion 
being, on an average, about one white to 350 or 400 red ; they are globular 
in shape, and measure the of an inch in diameter, and consist of 
a soft, granular, colorless substance, containing several nuclei. 
The white corpuscles possess the power of spontaneous movement, alter- 
nately contracting and expanding, throwing out processes of their substance 
and quickly withdrawing them, thus changing their shape from moment to 
moment. These movements resemble those of the ameba, and for this 
reason are termed ameboid. They also possess the capability of moving 
from place to place. In the interior of the vessels they adhere to the inner 
surface, while th,e red corpuscles move through the center of the stream. 
The white corpuscles are identical with the leukocytes, and are found in 
milk, lymph, chyle, and other fluids. 
Origin of Corpuscles.—The red corpuscles take their origin from the 
mesoblastic cells in the vascular area of the developing embryo. 
In the adult they are produced from colorless nucleated corpuscles re- 
sembling the white corpuscles. The spleen is the organ in which they 
are finally destroyed. 
The white corpuscles originate from the leukocytes of the adenoid tissue, 
and subsequently give rise to the red corpuscles and partly to new tissues 
that result from inflammatory action. 
When blood is withdrawn from the body and allowed to remain at rest, 
it becomes somewhat thick and viscid in from three to five minutes; this 
viscidity gradually increases until the entire volume of blood assumes a 
jelly-like consistence, which occupies from five to fifteen minutes. 
As soon as coagulation is completed, a second process begins, which 
consists in the contraction of the coagulum and the oozing of a clear, 
straw-colored liquid, the serum, which gradually increases in quantity as 
COAGULATION OF THE BLOOD. 110 
HUMAN PHYSIOLOGY. 
the clot diminishes in size, by contraction, until the separation is completed, 
which occupies from twelve to twenty-four hours. 
The changes in the blood are as follows:— 
Before coagulation. 
jLiq. Sanguinus 
or 
Plasma. 
Water. 
Albumin. 
Fibrinogen. 
Salts. 
Living blood. 
• Consisting of 
Corpuscles. Red and white. 
After coagulation. 
Crassamentum. 
Clot or coagulum. 
Containing 
Fibrin. 
Corpuscles. 
Dead blood. 
Water. 
Albumin. 
Salts. 
Serum. 
Containing 
The serum, therefore, differs from the liquor sanguinis in not containing 
fibrin. 
In from twelve to twenty-four hours the upper surface of the clot presents 
a grayish appearance, the buffy coat, which is due to the rapid sinking of 
the red corpuscles beneath the surface, permitting the fibrin to coagulate 
without them, which then assumes a grayish-yellow tint. Inasmuch as the 
white corpuscles possess a lighter specific gravity than the red, they do not 
sink so rapidly, and becoming entangled in the fibrin, assist in forming the 
huffy coat. Continued contraction gives a cupped appearance to the surface 
of the clot. 
Inflammatory states of the blood produce a marked increase in the 
buffed and cupped condition, on account of the aggregation of the corpus- 
cles and their tendency to rapid sinking. 
Nature of Coagulation.— Coagulated fibrin does not preexist in the 
blood, but is formed at the moment blood is withdrawn from the vessels. 
According to Denis, a liquid substance, plasmin, exists in the blood, 
which, when withdrawn from the circulation, decomposes into fibrin and 
metalbumin. 
According to Schmidt, fibrin results from the union of fibrinoplastin 
(paraglobulin) and fibrinogen, brought about by the presence of a third 
substance, the fibrin ferment. 
According to Hammersten and others, the fibrin obtained from the blood 
after coagulation comes from the fibrinogen alone, the conversion being 
brought about by the presence of a ferment substance, paraglobulin in this 
case having nothing to do with the change. This view is supported by the BLOOD, 
111 
fact that the quantity of fibrin obtained from the blood is never greater than 
the quantity of fibrinogen previously present. The origin of the ferment is 
obscure, but there is reason to believe that it comes from the injured vascu- 
lar coats or from the breaking of the white corpuscles. 
Conditions Influencing Coagulation.—The process is retarded by 
cold, retention within living vessels, neutral salts in excess, inflammatory 
conditions of the system, imperfect aeration, exclusion from air, etc. 
It is hastened by a temperature of ioo° F., contact with air, rough sur- 
faces, and rest. 
Blood Coagulates in the body after the arrest of the circulation in the 
course of twelve to twenty-four hours; local arrest of the circulation, from 
compression or a ligature, will cause coagulation, thus preventing hemor- 
rhages from wounded vessels. 
The Composition of the Blood varies in different portions of the 
body. The arterial differs from the venous, in being more coagulable, in 
containing more oxygen and less carbonic acid, in having a bright scarlet 
color, from the union of oxygen with hemoglobin; the purple hue of 
venous blood results from the deoxidation of the coloring matter. 
The blood of the portal vein differs in constitution, according to differ- 
ent stages of the digestive process; during digestion it is richer in water, 
albuminous matter, and sugar; occasionally it contains fat; corpuscles are 
diminished, and there is an absence of biliary substances. 
The blood of the hepatic vein contains a larger proportion of red and 
white corpuscles; the sugar is augmented, while albumin, fat, and fibrin 
are diminished. 
Pathologic Conditions of the Blood.— 
1. Plethora—increase in the volume or quantity of blood. 
2. Anemia—deficiency of red globules with increase of water. 
3. Leukocythemia—increase of white and diminution of red corpuscles. 
4. Glycohemia—excess of sugar in the blood. 
5. Uremia—increase in the amount of urea. 
6. Cholesteremia—an excess of cholesterin in the blood. 
7. Thrombosis and embolism—clotting of blood in the vessels and dissemi- 
nation of coagula. 
8. Lipemia—an excess of fat. 
9. Melanemia—pigment in the blood. 112 
HUMAN PHYSIOLOGY. 
CIRCULATION OF THE BLOOD. 
The Circulatory Apparatus by which the blood is distributed to all 
portions of the body consists of a central organ, the heart, with which is 
connected a system of closed vessels known as arteries, capillaries, and 
veins. Within this system the blood is kept, by the action of the heart, in 
continual movement, distributing nutritious matter to all portions of the 
body and carrying waste matters from the tissues to the various eliminating 
organs. 
The heart is a hollow, muscular organ, pyramidal in shape, measuring 
about 5 *4 inches in length, about in breadth, weighing from 10 to 12 ozs. 
in the male and from 8 to 10 ozs. in the female. Situated in the thoracic 
cavity, between the lungs, its base is directed upward, backward, and to 
the right; its apex is directed downward and to the left. 
Pericardium.—The heart is surrounded by a closed fibrous membrane 
called the pericardium. The inner surface of this membrane is lined by a 
serous membrane, which is also reflected over the surface of the heart; 
between the two surfaces of the serous membrane is found a small quantity 
of fluid, the pericardial fluid, which lubricates the surfaces and prevents 
friction during the movements of the heart. The interior of the heart is 
also lined by a serous membrane called the endocardium. 
Cavities of the Heart.—The general cavity of the heart is subdivided 
by a longitudinal septum into a right and left half; each of these cavities is 
in turn subdivided by a transverse constriction into two smaller cavities 
which communicate with each other and are known as the auricles and 
ventricles, the orifice between the auricle and ventricle being known as 
the auriculoventricular orifice. The heart, therefore, consists of four 
cavities, a right auricle and ventricle and a left auricle and ventricle. 
Into the right auricle the two terminal trunks of the venous system, the 
superior and inferior vence cavce, empty the venous blood which has been 
collected from all parts of the system; from the right ventricle arises the 
pulmonary artery, which, passing into the lungs, distributes the blood to the 
walls of the air cells of the lungs; into the left auricle empty four pulmo- 
nary veins, which have collected the blood from the lung capillaries; from 
the left ventricle springs the aorta, the general trunk of the arterial sys- 
tem, whose branches distribute the blood to the entire system. 
The Valves of the Heart.—The valves of the heart are formed by a 
reduplication of the endocardium strengthened by connective tissue. At 
the auriculoventricular openings on the right and left sides of the heart re- BLOOD 
113 
spectively are found the tricuspid and mitral valves. The tricuspid valve 
consists of three, the mitral of two, cusps or segments, which project into 
the interior of the ventricle when it does not contain blood. At their bases 
the segments are united so as to form an 
annular membrane attached to the margin 
of the orifice. To the free edges of the 
valves are attached numerous fine threads, 
the chordce tendinece, which are the ten- 
dons of the small papillary muscles spring-, 
ing from the walls of the ventricles. 
The Semilunar Valves.—At the open- 
ings of the pulmonary artery and the aorta 
are found three cup-shaped or semilunar 
valves, the free edges of which are di- 
rected away from the interior of the heart. 
The anatomic arrangement of the valves 
is such that upon their closure regurgita- 
tion of the blood is prevented. 
Movement of the Blood.—The blood 
within the vascular apparatus is in con- 
tinual movement from the left side of the 
heart, through the arterial system, capil- 
laries, and veins, to the right side, and 
from the right side, through the pulmon- 
ary artery, capillaries, and veins, to the 
original point of departure. The cause 
of this movement is the difference of 
pressure which exists between the blood 
within the aorta and the terminations of 
the venae cavae, and between the blood of 
the pulmonary artery and the pulmonary 
veins. 
The function of the heart is to propel 
the blood through the blood-vessels, which 
it does by raising or maintaining this 
higher pressure in the aorta and pul- 
monary artery. This is accomplished by 
alternate contractions and relaxations of 
its muscular walls. These two movements are known respectively as the 
systole and the diastole. 
Fig. 12.—Scheme of the Circu- 
lation. 
a. Right, b. left, auricle. A. Right, 
B. left, ventricle, i. Pulmonary 
artery. 2. Aorta. 1. Area of pul- 
monary, K. area of systemic, 
circulation, o. The superior vena 
cava. G. Area supplying the in- 
ferior vena cava, u. d, d. Intes- 
tine. m. Mesenteric artery, q. 
Portal vein. L. Liver, h. He- 
patic vein.—(Landois.) 114 
HUMAN PHYSIOLOGY. 
Course of the Blood through the Heart.—The venous blood returned 
to the heart by the superior and inferior venae cavas is emptied during the 
diastole into the right auricle, in the contraction of which it is forced 
through the right auriculoventricular opening into the right ventricle and 
distends it. Upon the contraction of the ventricle the blood is propelled 
through the pulmonary artery into the lungs, where it undergoes aeration 
and is changed in color. 
The arterial blood is now collected by the pulmonary veins and poured 
into the left auricle; thence it passes into the left ventricle, which becomes 
fully distended. Upon the contraction of the ventricle, the blood is pro- 
pelled into the aorta, and by it distributed to the system at large, to be 
again returned to the heart by the veins. 
Regurgitation from the ventricles into the auricles during the systole is 
prevented by the closure of the tricuspid and mitral valves; regurgitation 
from the pulmonary artery and aorta into the ventricles during the diastole 
is prevented by the closure of the semilunar valves. 
While there is but one circulation, physiologists frequently divide the 
circulatory apparatus into :— 
1. The systemic circulation, which includes the movement of the blood 
from the left side of the heart through the aorta and its branches, through 
the capillaries and veins, to the right side. 
2. The pulmonary circulation, which includes the course of the blood from 
the right side through the pulmonary artery, through the capillaries of 
the lungs and pulmonary veins, to the left side of the heart. 
3. The portal circulation, which includes the portal vein. This is formed 
by the union of the radicles of the gastric, mesenteric, and splenic veins, 
and carries the blood directly into the liver, where the vein again divides 
into a fine capillary plexus from which the hepatic veins arise which 
empty into the ascending vena cava. 
Movements of the Heart. — At each revolution, during the systole, 
the heart hardens and becomes shortened in its long diameter; its apex is 
raised up, rotated on its axis from left to right, and thrown forward against 
the walls of the chest. The impulse of the heart, observed about two 
inches below the nipple, and one inch to the sternal side, between the fifth 
and sixth ribs, is caused mainly by the apex of the heart striking against the 
chest walls, assisted by the distention of the great vessels about the base of 
the heart. 
Sounds of the Heart.—If the ear be placed over the cardiac region, BLOOD, 
115 
two distinct sounds are heard during each revolution of the heart, closely 
following each other and which differ in character. 
The sound coinciding with the systole in point of time, the first sound, 
is long and dull, and caused by the closure and vibration of the auriculo- 
ventricular valves, the contraction of the walls of the ventricles, and the 
apex beat; the second sound, occurring during the diastole, is short and 
sharp, and caused by the closure of the semilunar valves. 
The capacity of the left ventricle when fully distended is estimated at 
from four to seven ounces. 
The Frequency of the Heart’s Action varies at different periods of 
life, but in the adult male it beats about 72 times per minute. It is influ- 
enced by age, exercise, posture, digestion, etc. 
Age.—Before birth, the number of pulsations per minute averages . . 140 
During the first year it diminishes to 128 
During the third year diminishes to 95 
From the eighth to the fourteenth year averages 84 
In adult life the average is 72 
Exercise and digestion increase the frequency of the heart’s action. 
Posture influences the number of pulsations per minute; in the male, 
standing, the average is 81; sitting, 71; lying, 66;—independent, for the 
most part, of muscular effort. 
The Rhythmic Movements of the heart are dependent upon— 
1. An inherent irritability of the muscular fiber, which manifests itself as 
long as the nutrition is maintained. 
2. The continuous flow of blood through its cavities, distending them and 
stimulating the endocardium. 
The Force Exerted by the Left Ventricle at each contraction has 
been estimated at 52 pounds. If a tube be inserted into the aorta the pres- 
sure there will be sufficient to support a column of blood nine feet, or a 
column of mercury six inches, in height, the weight in either case being 
about four pounds. The estimation of the force which the heart is required 
to exert to support this column of blood is arrived at by multiplying the 
pressure in the aorta (four pounds) by the area of the internal surface of the 
left ventricle (about 13 inches), each inch of the ventricle being capable of 
supporting a downward pressure of four pounds. 
Work Done by the Heart.—The work done by the heart is estimated 
by multiplying the amount of blood sent out from the right and left ven- 
tricles at each contraction by the pressure in the pulmonary artery and 116 
HUMAN PHYSIOLOGY. 
aorta respectively; e.g., when the right ventricle contracts it forces out one- 
quarter pound of blood, and in so doing must overcome a pressure in the 
pulmonary artery sufficient to support a column of blood three feet in 
height; that is, must exert energy sufficient to raise % pound 3 feet, or 
% X 3 or Pound 1 foot. When the left ventricle contracts it sends out 
X pound of blood, and in so doing the left ventricle must overcome a 
pressure in the aorta sufficient to support a column of blood 9 feet in 
height; that is, must exert energy sufficient to raise X pound 9 feet, or 
)(X9or 2X P0U11(ls 1 foot. Work done is estimated by the amount of 
energy required to raise a definite weight a definite height; the unit, the 
foot-pound, being that required to raise one pound one foot. 
The heart, therefore, at each systole exerts energy sufficient to raise 3 foot 
pounds, and as it contracts 72 times per minute, it would raise in that time 
3 X 72 °r 216 foot-pounds; and in one hour 216 X 6° or 12,960 foot- 
pounds; and in twenty-four hours 12,960 X 24 or 311,04° foot-pounds, 
or 138.5 foot-tons. 
Influence of the Nervous System upon the Heart.—When the 
heart of a frog is removed from the body it continues to beat for a variable 
length of time, depending upon the nature of the conditions surrounding 
it. The heart of warm-blooded animals continues to beat but for a very 
short time. The cause of the continued pulsations of the frog heart is the 
presence of nervous ganglia in its substance. These ganglia have not been 
shown to exist in the mammalian heart, but there is reason to believe that 
the nervous mechanism is fundamentally the same. 
The ganglia of the heart are three in number, one situated at the opening 
of the inferior vena cava (the ganglion of Remak), a second situated in 
the auriculoventricular septum (the ganglion of Biddle), and a third situ- 
ated in the interauricular septum (the ganglion of Ludwig). The first two 
are motor in function and excite the pulsations of the heart; the third is 
inhibitory in function and retards the action of the heart. The actions of 
these ganglia, though for the most part automatic, are modified by impres- 
sions coming through nerves from the medulla oblongata. When the in- 
hibitory center is stimulated by muscarin the heart is arrested in diastole; 
when atropia is applied the heart recommences to beat, because atropia 
paralyzes the inhibitory center. 
The nerves modifying the action of the heart are the pneumogastric 
(vagus) and the accelerator nerves. 
The pneumogastric nerve, after emerging from the medulla, receives 
motor fibers from the spinal accessory nerve. It then passes downward, 
giving off branches, some of which terminate in the inhibitory ganglion. BLOOD 
117 
Stimulation of the vagus, by increasing the activity of the inhibitory center, 
arrests the heart in diastole with its cavities full of blood ; but as the stimu- 
lation is only temporary, after a few seconds the heart recommences to 
beat; at first the pulsations are weak and feeble, but soon regain their 
original vigor. After the administration of atropia in sufficient doses to de- 
stroy the termination of the pneumogastric, stimulation of its trunk has no 
effect upon the heart. The inhibitory fibers in the vagus are constantly 
in action, for division of the nerve on both sides is always followed by an 
increase in the frequency of the heart’s pulsations. 
The accelerator fibers arise in the medulla, pass down the cord, emerge 
in the cervical region, pass to the last cervical and first dorsal ganglia of 
the sympathetic, and thence to the heart. Stimulation of these fibers 
causes an increased frequency of the heart’s pulsations, but they are dimin- 
ished in force. 
ARTERIES. 
The Arteries are a series of branching tubes conveying blood to all 
portions of the body. They are composed of three coats :— 
1. External, formed of areolar and elastic tissue. 
2. Middle, contains both elastic and muscular fibers, arranged transversely 
to the long axis of the artery. The elastic tissue is more abundant in the 
larger vessels, the muscular in the smaller. 
3. Internal, composed of a thin homogeneous membrane, covered with a 
layer of elongated endothelial cells. 
The arteries possess both elasticity and contractility. 
The property of elasticity allows the arteries already full to accommo- 
date themselves to the incoming amount of blood, and to convert the 
intermittent acceleration of blood in the large vessels into a steady and 
continuous stream in the capillaries. 
The contractility of the smaller vessels equalizes the current of blood, 
regulates the amount going to each part, and promotes the onward flow 
of blood. 
Blood Pressure.—Under the influence of the ventricular systole, the 
recoil of the elastic walls of the arteries, and the resistance offered by the 
capillaries, the blood is constantly being subjected to a certain amount of 
pressure. If a large artery of an animal be divided, and a glass tube of 
the same caliber be inserted into fis orifice, the blood will rise to a height 
of about nine feet; or if it be connected with a mercurial manometer, the 
mercury will rise to a height of six inches. This height will be a measure 
of the pressure in the vessel. The absolute quantity of mercury sustained 118 
HUMAN PHYSIOLOGY. 
by an artery can be arrived at by multiplying the height of the column by 
the area of a transverse section of that artery. 
The pressure of the blood is greatest in the large arteries, but gradually 
decreases toward the capillaries. 
The blood pressure is increased or diminished by influences acting upon 
the heart or upon the peripheral resistance of the capillaries, viz.:— 
If, while the force of the heart remains the same, the number of pulsa- 
tions per minute increases, thus increasing the volume of blood in the 
arteries, the pressure rises. If the rate remains the same, but the force 
increases, the pressure again rises. Causes that increase the peripheral 
resistance by contracting the arterioles, e.g., vasomotor nerves, cold, etc., 
produce an increase of the pressure. 
On the other hand, influences which ditninish either the volume of the 
blood, or the number of pulsations, or the force of the heart, or the peri- 
pheral resistance, lower the pressure. 
The Pulse is the sudden distention of the artery in a transverse and 
longitudinal direction, due to the injection of a volume of blood into the 
arteries at the time of the ventricular systole. As the vessels are already 
full of blood, they must expand in order to accommodate themselves to the 
incoming volume of blood. The blood pressure is thus increased, and the 
pressure originating at the ventricle excites a pulse wa7ie, which passes 
from the heart toward the capillaries at the rate of about twenty-nine feet 
per second. It is this wave that is appreciated by the finger. 
The Velocity with which the blood flows in the arteries diminishes 
from the heart to the capillaries, owing to an increase in the united sectional 
area of the vessels, and increases in rapidity from the capillaries toward the 
heart. It moves most rapidly in the large vessels, and especially under 
the influence of the ventricular systole. From experiments on animals, 
it has been estimated to move in the carotid of man at the rate of sixteen 
inches per second, and in the large veins at the rate of four inches per 
second. 
The Caliber of the Blood-vessels is regulated by the vasomotor 
nerves, which have their origin in the gray matter of the medulla oblongata. 
They issue from the spinal cord through the anterior roots of spinal nerves, 
pass through the sympathetic ganglia, and ultimately are distributed to the 
coats of the blood-vessels. They exert at different times a constricting and 
dilating action upon the vessels, thus keeping up the arterial tonus. 
Capillaries.—The capillaries constitute a network of vessels of micro- 
scopic size, which distribute the blood to the inmost recesses of the tissues, BLOOD. 
119 
inosculating with the arteries on the one hand and the veins on the other; 
they branch and communicate in every possible direction. 
The diameter of a capillary vessel varies from the to the s'oVgths 
of an inch; their walls consist of a delicate homogeneous membrane, the 
TtnnR>ths of an inch in thickness, lined by flattened, elongated, endothelial 
cells, between which, here and there, are observed stomata. 
It is through the agency of the capillary vessels that the phenomena of 
nutrition and secretion take place, for here the blood flows in an equable 
and continuous current, and is brought into intimate relationship with the 
tissues—two of the essential conditions for proper nutrition. 
The rate of movement in the capillary vessels is estimated at one inch in 
thirty seconds. 
In the capillary current the red corpuscles may be seen hurrying down 
the center of the stream, while the white corpuscles in the still layer adhere 
to the walls of the vessel, and at times can be seen to pass through the 
walls of the vessel by ameboid movements. 
The Passage of the Blood through the capillaries is mainly due to 
the force of the ventricular systole and the elasticity of the arteries; but it 
is probably also aided by a power resident in the capillaries themselves, the 
result of a vital relation between the blood and the tissues. 
The Veins are the vessels which return the blood to the heart; they 
have their origin in the venous radicles, and as they approach the heart 
converge to form larger trunks, and terminate finally in the venae cavae. 
They possess three coats— 
1. External, made up of areolar tissue. 
2. Middle, composed of nonstriated muscular fibers, yellow, elastic, and 
fibrous tissue. 
3. Internal, an endothelial membrane, similar to that of the arteries. 
Veins are distinguished by the possession of valves throughout their 
course, which are arranged in pairs, and formed by a reflection of the in- 
ternal coat, strengthened by fibrous tissues; they always look toward the 
heart, and when closed prevent a return of blood in the veins. Valves are 
most numerous in the veins of the extremities, but are entirely absent in 
many others. 
The Onward Flow of Blood in the veins is mainly due to the action 
of the heart, but is assisted by the contraction of the voluntary muscles and 
the force of respiration. 
Muscular contraction, which is intermittent, aids the flow of blood in the 120 
HUMAN PHYSIOLOGY. 
veins by compressing them. As regurgitation is prevented by the closure 
of the valves, the blood is forced onward toward the heart. 
Rhythmic movements of veins have been observed in some of the lower 
animals, aiding the onward current of blood. 
During the movement of inspiration the thorax is enlarged in all its 
diameters, and the pressure on its contents at once diminishes. Under 
these circumstances a suction force is exerted upon the great venous trunks, 
which causes the blood to flow with increased rapidity and volume toward 
the heart. 
Venous Pressure.—As the force of the heart is nearly expended in 
driving the blood through the capillaries, the pressure in the venous system 
is not very marked, not amounting in the jugular vein of a dog to more 
than J2_th that of the carotid artery. 
The time required for a complete circulation of the blood throughout the 
vascular system has been estimated to be from twenty to thirty seconds, 
while for the entire mass of blood to pass through the heart 58 pulsations 
would be required, occupying forty-eight seconds. 
The Forces keeping the blood in circulation are— 
1. Action of the heart. 
2. Elasticity of the arteries. 
3. Capillary force. 
4. Contraction of the voluntary muscles upon the veins. 
5. Respiratory movements. 
RESPIRATION. 
Respiration is the function by which oxygen is absorbed into the 
blood and carbonic acid exhaled. The appropriation of the oxygen and 
the evolution of carbonic acid takes place in the tissues as a part of the 
general nutritive process, the blood and respiratory apparatus constituting 
the media by means of which the interchange of gases is accomplished. 
The Respiratory Apparatus consists of the larynx, trachea, and lungs. 
The Larynx is composed of firm cartilages, united together by liga- 
ments and muscles; running anteroposteriorly across the upper opening 
are four ligamentous bands, the two superior, or false vocal cords, and the 
two inferior, or true vocal cords, formed by folds of the mucous membrane. 
They are attached anteriorly to the thyroid cartilages and posteriorly to the RESPIRATION. 
121 
arytenoid cartilages, and are capable of being separated by the contraction 
of the posterior crico-arytenoid muscles, so as to admit the passage of air 
into and from the lungs. 
The Trachea is a tube from four to five inches in length, three-quarters 
of an inch in diameter, extending from the cricoid cartilage of the larynx 
to the third dorsal vertebra, where it divides into the right and left bronchi. 
It is composed of a series of cartilaginous rings, which extend about two- 
thirds around its circumference, the posterior third being occupied by fibrous 
tissue and nonstriated muscular fibers, which are capable of diminishing its 
caliber. 
The trachea is covered externally by a tough, fibro-elastic membrane, 
and internally by mucous membrane, lined by columnar ciliated epithelial 
cells. The cilia are always waving from within outward. When the two 
bronchi enter the lungs they divide and subdivide into numerous and 
smaller branches, which penetrate the lung in every direction until they 
finally terminate in th& pulmonary lobules. 
As the bronchial tubes become smaller their walls become thinner; the 
cartilaginous rings disappear, but are replaced by irregular angular plates 
of cartilage ; when the tube becomes less than the of an inch in diame- 
ter they wholly disappear, and the fibrous and mucous coats blend together, 
forming a delicate elastic membrane, with circular muscular fibers. 
The Lungs occupy the cavity of the thorax, are conical in shape, of a 
pink color and a spongy texture. They are composed of a great number of 
distinct lobules, the pulmonary lobules, connected together by interlobular 
connective tissue. These lobules vary in size, are of an oblong shape, and 
are composed of the ultimate ramifications of the bronchial tubes, within 
which are contained the air vesicles or cells. The walls of the air vesicles, 
exceedingly thin and delicate, are lined internally by a layer of tessellated 
epithelium, externally covered by elastic fibers, which give the lungs their 
elasticity and distensibility. 
The Venous Blood is distributed to the lungs for aeration by the pul- 
monary artery, the terminal branches of which form a rich plexus of capil- 
lary vessels surrounding the air cells; the air and blood are thus brought 
into intimate relationship, being separated only by the delicate walls of the 
air cells and capillaries. 
The thoracic cavity in which the respiratory organs are lodged is of a 
conical shape, having its apex directed upward, its base downward. Its 
frame-work is formed posteriorly by the spinal column, anteriorly by the 
sternum, and laterally by the ribs and costal cartilages. Between and over 122 
HUMAN PHYSIOLOGY. 
the ribs lie muscles, fascia, and skin; above, the thorax is completely 
closed by the structures passing into it and by the cervical fascia and skin; 
below, it is closed by the diaphragm. It is therefore an air-tight cavity. 
The Pleura.—Each lung is surrounded by a closed serous membrane, 
the pleura, one layer of which, the visceral, is reflected over the lung, the 
other, the parietal, reflected over the wall of the thorax; between the two 
layers is a small amount of fluid which prevents friction during the play of 
the lungs in respiration. 
Owing to the elastic tissue which is present in the lungs, they are very 
readily distensible, so much so, indeed, 
that the pressure of the air inside the 
trachea and lungs is sufficient to distend 
them until they completely fill all parts 
of the thoracic cavity not occupied by 
the heart and great vessels. The elas- 
tic tissue endows them not only with 
distensibility, but also with the power of 
elastic recoil, by which they are enabled 
to accommodate themselves to all varia- 
tions in the size of the thoracic cavity. 
When the chest walls recede the air 
within the lungs expands and presses 
them against the ribs ; when the chest 
walls contract, the air being driven out, 
the elastic tissue recoils and the lungs 
return to their original condition. The 
movements of the lungs are therefore 
entirely passive. 
As the capacity of the chest in a 
state of rest is greater than the volume 
of the lungs after they are collapsed, 
it is quite evident that in the living 
condition the lungs are distended and in a state of elastic tension, which 
is greater or less in proportion as the thoracic cavity is increased or dimin- 
ished in size. The elastic tissue, always on the stretch, is endeavoring to 
pull the visceral layer of the pleura away from the parietal layer, but is 
antagonized by the pressure of the air within the air passages. This con- 
dition of things persists as long as the thoracic cavity remains air tight; but 
if an opening be made in the thoracic wall, the pressure of the external air 
which was previously supported by the practically rigid walls of the thorax 
Fig. 13.—Diagram of the Respira- 
tory Organs. 
The windpipe leading down from the 
larynx is seen to branch into two 
large bronchi, which subdivide after 
they enter their respective lungs. RESPIRATION. 
123 
now presses upon the lung with as much force as the air within the lung. 
The two pressures being neutralized, there is nothing to prevent the elastic 
tissue from recoiling, driving the air out, and collapsing. The elastic ten- 
sion of the lungs can be readily measured in man after death by inserting 
a manometer into the trachea. Upon opening the thorax and allowing the 
tissue to recoil, the air presses upon the mercury and elevates it, the extent 
to which it is raised being the index of the pressure. Hutchinson calcu- 
lated the pressure to be one-half pound to the square inch of the lung 
surface. 
Respiratory Movements.—The movements of respiration are two, and 
consist of an alternate dilatation and contraction of the chest, known as 
inspiration and expiration. 
1. Inspiration is an active process, the result of the expansion of the 
thorax, whereby air is introduced into the lungs. 
2. Expiration is a partially passive process, the result of the recoil of the 
elastic walls of the thorax, and the recoil of the elastic tissue of the lungs, 
whereby the carbonic acid is expelled. 
In Inspiration the chest is enlarged by an increase in all its diameters, 
viz. :— 
1. The vertical is increased by the contraction and descent of the dia- 
phragm when it approximates a straight line. 
2. The anteroposterior and transverse diameters are increased by the 
elevation and rotation of the ribs upon their axes. 
In ordinary tranquil inspiration the muscles which elevate the ribs and 
thrust the sternum forward, and so increase the diameters of the chest, are 
the external intercostals, running from above downward and forward, the 
sternal portion of the internal intercostals, and the leva tores costarum. 
In the extraordinary efforts of inspiration certain auxiliary muscles are 
brought into play, viz.: the sternomastoid, pedorales, serratus tnagnus, 
which increase the capacity of the thorax to its utmost limit. 
In Expiration the diameters of the chest are all diminished, viz.:— 
1. The vertical, by the ascent of the diaphragm. 
2. The anteroposterior, by a depression of the ribs and sternum. 
In ordinary tranquil expiration the diameters of the thorax are dimin- 
ished by the recoil of the elastic tissue of the lungs and the ribs ; but in 
forcible expiration the muscles which depress the ribs and sternum, and 
thus further diminish the diameter of the chest, are the internal intercostals, 
the infracostals, and the triangularis sterni. 
In the extraordinary efforts of expiration certain auxiliary muscles are 124 
HUMAN PHYSIOLOGY. 
brought into play, viz.: the abdominal and sacrolumbalis muscles, which 
diminish the capacity of the thorax to its utmost limit. 
Expiration is aided by the recoil of the elastic tissue of the lungs and ribs 
and the pressure of the air. 
Movements of the Glottis.—At each inspiration the rimaglottidis is 
dilated by a separation of the vocal cords, produced by the contraction of 
the crico-arytenoid muscles, so as to freely admit the passage of air into the 
lungs : in expiration they fall passively together, but do not interfere with 
the exit of air from the chest. 
Nervous Mechanism of Respiration.—The movements of respira- 
tory muscles, though capable of being modified to a certain extent by 
efforts of the will, are of an automatic character, and called forth by nerv- 
ous impulses emanating from the medulla oblongata. The respiratory 
center, the so called vital point, generates the nerve impulses, which, travel- 
ing outward through the phrenic and intercostal nerves, excite contractions 
of the diaphragm and intercostal muscles respectively. This center is for 
the most part automatic in its action, though it is capable of being modified 
by impulses reflected to it through various sensory nerves. 
This center may be stimulated :— 
1. Directly, by the condition of the blood. An increase of carbonic acid 
or a diminution of oxygen in the blood causes an acceleration of the 
respiratory movements; the reverse of these conditions causes a diminu- 
tion of the respiratory movements. 
2. Indirectly, by reflex action. The medulla may be excited to action 
through the pneumogastric nerve, by the presence of carbonic acid in the 
lungs irritating its terminal filaments; through the fifth nerve, by irrita- 
tion of the terminal branches; and through the nerves of general sensi- 
bility. In either case this center reflects motor impulses to the respira- 
tory muscles through the phrenic, intercostals, inferior laryngeal, and 
other nerves. 
Types of Respiration.—The abdominal type is most marked in young 
children, irrespective of sex, the respiratory movements being effected by 
the diaphragm and abdominal muscles. 
In the superior costal type, exhibited by the adult female, the respiratory 
movements are more marked in the upper part of the chest, from the 1st to 
the 7th ribs, permitting the uterus to ascend in the abdomen during preg- 
nancy without interfering with respiration. 
In the inferior costal type, manifested by the male, the movements are RESPIRATION. 
125 
largely produced by the muscles of the lower portions of the chest, from the 
7th rib downward, assisted by the diaphragm. 
The respiratory movements vary according to age, sleep, and exercise, 
being most frequent in early life, but averaging 20 per minute in adult life. 
They are diminished by sleep and increased by exercise There are about 
four pulsations of the heart to each respiratory act. 
During inspiration two sounds are produced; the one, heard in the 
thorax, in the trachea and larger bronchial tubes, is tubular in character; 
the other, heard in the substance of the lungs, is vesictclar in character. 
AMOUNT OF AIR EXCHANGED IN RESPIRATION, AND CAPACITY 
OF LUNGS. 
The tidal or breathing volume of air, that which passes in and out of the 
lungs at each inspiration and expiration, is estimated at from 20 to 30 cubic 
inches. 
The complemental air is that amount which can be taken into the lungs 
by a forced inspiration, in addition to the ordinary tidal volume, and 
amounts to about 110 cubic inches. 
The reserve air is that which usually remains in the chest after the ordi- 
nary efforts of expiration, but which can be expelled by forcible expiration. 
The volume of reserve air is about 100 cubic inches. 
The residual air is that portion which remains in the chest and cannot 
be expelled after the most forcible expiratory efforts, and which amounts, 
according to Dr. Hutchinson, to about 100 cubic inches. 
The Vital Capacity of the chest indicates the amount of air that can 
be forcibly expelled from the lungs after the deepest possible inspiration, 
and is an index of an individual’s power of breathing in disease and pro- 
longed severe exercise. The combined amounts of the tidal, the comple- 
mental, and reserve air, 230 cubic inches, represents the vital capacity of an 
individual five feet seven inches in height. The vital capacity varies chiefly 
with stature. It is increased eight cubic inches for every inch in height 
above this standard, and diminishes eight cubic inches for each inch below it. 
The Tidal Volume of air is carried only into the trachea and large 
bronchial tubes by the inspiratory movements. It reaches the deeper 
portions of the lungs in obedience to the law of diffusion of gases, which is 
inversely proportionate to the square root of their densities. 
The ciliary action of the columnar cells lining the bronchial tubes also 
assists in the interchange of air and carbonic acid. 126 
HUMAN PHYSIOLOGY. 
The entire volume of air passing in and out of the thorax in twenty-four 
hours is subject to great variation, but can be readily estimated from the 
tidal volume and the number of respirations per minute. Assuming that 
an individual takes into the chest 20 cubic inches at each inspiration, and 
breathes 18 times per minute, in twenty-four hours there would pass in and 
out of the lungs 518,400 cubic inches, or 300 cubic feet. 
Chemistry of Respiration.—As the inspired air undergoes a change 
in composition during its stay in the lungs which renders it unfit for further 
respiration, it becomes requisite, for the correct understanding of respiration, 
to ascertain the composition of both inspired and expired air. 
Composition of Air. — Chemic analysis has shown that every 100 
volumes of air contains 20.81 volumes of oxygen, and 70.19 volumes of 
nitrogen, and 0.03 volume of carbonic acid. Aqueous vapor is also present, 
though the quantity is variable. The higher the temperature the greater 
the amount. 
The Changes in the Air effected by respiration are— 
Loss of oxygen, to the extent of five cubic inches per 100 of air, or one in 
20. 
Gain of carbonic acid, to the extent of 4.66 cubic inches per 100 of air, or 
.93 inch in 20. 
Increase of water vapor and organic matter. 
Elevation of temperature. 
Increase, and at times decrease, of nitrogen. 
Gain of ammonia. 
The total quantity of oxygen withdrawn from the air and consumed by 
the body in twenty-four hours amounts to 15 cubic feet, and can be readily 
estimated from the amount consumed at each respiration. Assuming that 
one cubic inch of oxygen remains in the lungs at each respiration, in one 
hour there are consumed 1080 cubic inches, and in twenty-four hours 
25,920 cubic inches, or 15 cubic feet, weighing 18 ounces. To obtain this 
quantity, 300 cubic feet of air are necessary. 
The quantity of oxygen consumed daily is subject to considerable varia- 
tions. It is increased by exercise, digestion, and lowered temperature, and 
decreased by the opposite conditions. 
The quantity of carbonic acid exhaled in twenty-four hours varies greatly. 
It can be estimated in the same way. Assuming that an individual exhales 
.93-)- cubic inch at each respiration, in one hour there are eliminated 1008 
cubic inches, and in twenty-four hours 24,192 cubic inches, or 14 cubic 
feet, containing seven ounces of pure carbon. RESPIRATION. 
127 
The exhalation of carbonic acid is increased by muscular exercise, nitrog- 
enous food, tea, coffee, and rice, age, and by muscular development; 
decreased by a lowering of temperature, repose, gin and brandy, and a dry 
condition of the air. 
As there is always more oxygen consumed than carbonic acid exhaled, 
and as oxygen unites with carbon to form an equal volume of carbonic acid, 
it is evident that a certain quantity of oxygen disappears within the body. 
In all probability it unites with the sulphur hydrogen of the food to form 
water. 
The amount of watery vapor which passes out of the body with the ex- 
pired air is estimated at from one to two pounds. 
The organic matter, though slight in amount, gives the odor to the breath. 
In a room with defective ventilation the organic matter accumulates and 
gives rise to headache, nausea, drowsiness, etc. Long-continued breathing 
of such air produces general ill health. It is not so much the presence of 
C02 in increased amount as the presence of organic matter which necessi- 
tates thorough ventilation. 
Condition of the Gases in the Blood. 
Oxygen is absorbed from the lungs into the arterial blood by the coloring 
matter, hemoglobin, with which it exists in a state of loose combination, 
and is disengaged during the process of nutrition. 
Carbonic acid, arising in the tissues, is absorbed into the blood in con- 
sequence of its alkalinity, where it exists in a state of simple solution and 
also in a state of feeble combination with the carbonates, soda and potassa, 
forming the bicarbonates. 
Nitrogen is simply held in solution in the plasma. 
Exchange of Gases in the Air Cells.—From the difference in ten- 
sion of the oxygen in the air cells (27.44 mm. of Hg) and of the oxygen 
in the venous blood (22 mm. Hg), and from the difference of the carbonic 
acid tension in the venous blood (41 mm. Hg) and in the air cells (27 mm. 
Hg), it might be concluded that the passage of the gases may be due 
solely to pressure. The absorption of oxygen, however, does not follow 
absolutely the law of pressure; that chemic processes are involved is 
shown by the union of oxygen with the hemoglobin of the blood corpuscles. 
The exhalation of C02 is also partly a chemic process, as it has been 
shown that the quantity excreted is greatly increased when oxygen is simul- 
taneously absorbed. Oxygen not only favors the exhalation of loosely 
combined C02, but favors the expulsion of that which can only be excreted 
by the addition of acids to the blood. 128 
HUMAN PHYSIOLOGY. 
Changes in the Blood during Respiration. 
As the blood passes through the lungs it is changed in color, from the 
dark purple hue of venous blood to the bright red scarlet of arterial blood. 
The heterogeneous composition of venous blood is exchanged for the 
uniform composition of the arterial. 
It gains oxygen and loses carbonic acid. 
Its coagulability is increased. Temperature is diminished. 
Asphyxia.—If the supply of oxygen to the lungs be diminished and 
the carbonic acid retained in the blood, the normal respiratory movements 
cease, the condition of asphyxia ensues, which soon terminates in death. 
The phenomena of asphyxia are violent spasmodic action of the respi- 
ratory muscles attended by convulsions of the muscles of the extremities, 
engorgement of the venous system, lividity of the skin, abolition of sensi- 
bility and reflex action, and death. 
The cause of death is a paralysis of the heart from over distention by 
blood. The passage of the blood through the capillaries is prevented by 
contraction of the smaller arteries, from irritation of the vasomotor center. 
The heart is enfeebled by a want of oxygen and inhibited in its action by the 
inhibitory centers. 
The Functional Activity of all the organs and tissues of the body is 
attended by the evolution of heat, which is independent, for the most part, 
of external conditions. Heat is a necessary condition for the due perform- 
ance of all vital actions; although the body constantly loses heat by radia- 
tion and evaporation, it possesses the capability of renewing it and main- 
taining it at a fixed standard. The normal ternperature of the body in the 
adult, as shown by means of a delicate thermometer placed in the axilla, 
ranges from 97.250 F. to 99.50 F., though the mean normal tempera- 
ture is estimated by Wunderlich at 98.6° F. 
The temperature varies in different portions of the body according to 
the degree in which oxidation takes place, being the highest in the muscles 
during exercise, in the brain, blood, liver, etc. 
The Conditions which Produce Variations in the normal tempera- 
ture of the body are age, period of the day, exercise, food and drink, 
climate, season, and disease. 
Age.—At birth the temperature of the infant is about 1° F. above that of 
the adult, but in a few hours falls to 95.50 F., to be followed in the course 
ANIMAL HEAT. ANIMAL HEAT. 
129 
of twenty-four hours by a rise to the normal or a degree beyond. During 
childhood the temperature approaches that of the adult; in aged persons 
the temperature remains about the same, though they are not as capable of 
resisting the depressing effects of external cold as adults. A diurnal 
variation of the temperature occurs from i.8° F. to 3.7° F. (Jurgensen); 
the maximum occurring late in the afternoon, from 4 to 9 p.m., the mini- 
mum, early in the morning, from 1 to 7 A. M. 
Exercise.—The temperature is raised from x° to 20 F. during active 
contractions of the muscular masses, and is probably due to the increased 
activity of chemic changes ; a rise beyond this point being prevented by its 
diffusion to the surface, consequent on a more rapid circulation, radiation, 
more rapid breathing, etc. 
Food and Drink.—The ingestion of a hearty meal increases the tempera- 
ture but slightly; an absence of food, as in starvation, produces a marked 
decrease. Alcoholic drinks, in large amounts, in persons unaccustomed to 
their use, cause a depression of the temperature amounting to from i° to 
2° F. Tea causes a slight elevation. 
External Temperature.—Long-continued exposure to cold, especially if 
the body is at rest, diminishes the temperature from i° to 2° F., while 
exposure to a great heat slightly increases it. 
Disease frequently causes a marked variation in the normal temperature 
of the body, rising as high as 107° F. in typhoid fever, and 105° F. in 
pneumonia; in cholera it falls as low as 8o° F. Death usually occurs 
when the heat remains high and persistent, from 106° to no° F.; the 
increase of heat in disease is due to excessive production rather than to 
diminished elimination. 
The Source of Heat is to be sought for in the chemic decompositions 
and hydrations taking place during the general process of nutrition, and the 
combustion of the carbonaceous compounds by the oxygen of the inspired 
air ; the amount of its production is in proportion to the activity of the in- 
ternal changes. 
Every contraction of a muscle, every act of secretion, each exhibition of 
nerve force, is accompanied by a change in the chemic composition of the 
tissues and an evolution of heat. The reduction of the disintegrated tissues 
to their simplest form by oxidation, the combination of the oxygen of the 
inspired air with the carbon and hydrogen of the blood and tissues, results 
in the formation of carbonic acid and water and the generation of a large 
amount of heat. 
Certain elements of the food, particularly the nonnitrogenized sub- 
stances, undergo oxidation without taking part in the formation of the tis- 130 
HUMAN PHYSIOLOGY. 
sues, being transformed into carbonic acid and water, and thus increase the 
sum of heat in the body. 
Heat-producing Tissues.—All the tissues of the body add to the 
general amount of heat, according to the degree of their activity. But 
special structures, on account of their mass and the large amount of 
blood they receive, are particularly to be regarded as heat producers; 
e. g. 
1. During mental activity the brain receives nearly one-fifth of the entire 
volume of blood, and the venous blood returning from it is charged with 
waste matters, and its temperature is increased. 
2. The muscular tissue, on account of the many chemic changes occur- 
ring during active contractions, must be regarded as the chief heat-pro- 
ducing tissue. 
3. The secreting glands, during their functional activity, add largely to the 
amount of heat. 
The entire'quantity of heat generated within the body has been demon- 
strated experimentally to be about 2300 calories, a calory or heat unit 
being that amount of heat required to raise the temperature of one kilo, 
of water (2.2 pounds) i° C. This quantity of heat, if not utilized and re- 
tained within the body, would elevate its temperature in twenty-four hours 
about 6o° F. That this volume of heat depends very largely upon the 
oxidation of the food stuffs can be shown experimentally. 
The normal temperature of the body is maintained by a constant expen- 
diture of the heat in several directions:— 
1. In warming the food, drink, and air that are consumed in twenty-four 
hours. For this purpose about 157 heat units are required. 
2. In evaporating water from the skin and lungs; 619 heat units being 
utilized for this purpose. 
3. In radiation and conduction. By these processes the body loses at least 
50 per cent, of its heat, or 1156 heat units. 
4. In the production of work; the work of the circulatory, respiratory, 
muscular, and nervous apparatus being performed by the transformation 
of 369 heat units into units of work. 
The nervous system influences the production of heat in a part by in- 
creasing the amount of blood going through it by its action upon the vaso- 
motor nerves. Whether there exists a special heat center has not been 
satisfactorily determined, though this is probable. SECRETION. 
131 
The Process of Secretion consists in the separation of materials from 
the blood which are either to be again utilized to fulfil some special pur- 
pose in the economy, or are to be removed from the body as excrementi- 
tious matter; in the former case they constitute the secretions, in the latter, 
the excretions. 
The materials which enter into the composition of the secretions are de- 
rived from the nutritive principles of the blood, and require special organs, 
e.g., gastric glands, mammary glands, etc., for their proper elaboration. 
The tnaterials which compose the excretions preexist in the blood, and 
are the results of the activities of the nutritive process; if retained within 
the body they exert a deleterious influence upon the composition of the 
blood. 
Destruction of a secreting gland abolishes the secretion peculiar to it, 
and it cannot be formed by any other gland; but among the excreting 
organs there exists a complementary relation, so that if the function of one 
organ be interfered with, another performs it to a certain extent. 
SECRETION. 
CLASSIFICATION OF THE SECRETIONS. 
PERMANENT FLUIDS. 
Serous fluids. 
Synovial fluid. 
Aqueous humor of the eye. 
Vitreous humor of the eye. 
Fluid of the labyrinth of the internal 
ear. 
Cerebrospinal fluid. 
TRANSITORY FLUIDS. 
Mucus. 
Sebaceous matter. 
Cerumen (external meatus). 
Meibomian fluid 
Milk and colostrum. 
Tears. 
Saliva. 
Gastric juice. 
Pancreatic juice. 
Secretion from Brunner’s glands. 
Secretion from Lieberkiihn’s glands. 
Secretions from follicles of the large 
intestine. 
Bile (also an excretion). 
EXCRETIONS. 
Perspiration and the secretion of the 
axillary glands. 
Urine. 
Bile (also a secretion). 
Seminal fluid, containing spermato- 
zoids. 
FLUIDS CONTAINING FORMED ANATOMIC ELEMENTS. 
Fluid of the Graafian follicles, 132 
HUMAN PHYSIOLOGY. 
The Essential Apparatus for secretion is a delicate, homogeneous, 
structureless membrane, on one side of which, in close contact, is a capil- 
lary plexus of blood-vessels, and on the other side a layer of cells whose 
physiologic function varies in different situations. 
Secreting organs may be divided into membranes and glands. 
Serous membranes usually exist as closed sacs, the inner surface of which 
is covered by pale, nucleated epithelium, containing a small amount of 
secretion. 
The serous membranes are the pleura, peritoneum,pericardium, synovial 
sacs, etc. 
The serous fluids are of a pale amber color, somewhat viscid, alkaline, 
coagulable by heat, and resemble the serum of the blood; their amount 
is but small; the pleural varies from four to seven drams; the peritoneal 
from one to four ounces; the pericardial from one to three drams. 
The synovial fluid is colorless, alkaline, and extremely viscid, from the 
presence of synovin. 
The function of serous fluids is to moisten the opposing surfaces, so as 
to prevent friction during the play of the viscera. 
The mucous membranes are soft and velvety in character, and line the 
cavities and passages leading to the exterior of the body; e.g., the gastro- 
intestinal, pulmonary, and genito-urinary. They consist of a primary 
basement membrane covered with epithelial cells, which in some situations 
are tessellated, in others, columnar. 
Mucus is a pale, semitransparent, alkaline fluid, containing epithelial 
cells and leukocytes. It is composed, chemically, of water, an albuminous 
principle, mucosin, and mineral salts; the principal varieties are nasal, 
bronchial, vaginal, and urinary. 
Secreting Glands are formed of the same elements as the secreting 
membranes, but instead of presenting flat surfaces, are involuted, forming 
tubules, which may be simple follicles, e. g., mucous, uterine, or intestinal; 
or compound follicles, e. g., gastric glands, mammary glands ; or racemose 
glands, e. g., salivary glands and pancreas. They are composed of a base- 
ment membrane, enveloped by a plexus of blood-vessels, and are lined by 
epithelial and true secreting cells, which in different glands possess the 
capability of elaborating elements characteristic of their secretions. 
In the Production of the Secretion two essentially different processes 
are concerned :— 
i. Chemic.—The formation and elaboration of the characteristic organic 
ingredients of the secreted fluids, e.g., pepsin, pancreatin, takes place MAMMARY GLANDS. 
133 
during the intervals of glandular activity, as a part of the general func- 
tion of nutrition. They are formed by the cells lining the glands, and 
can often be seen in their interior with the aid of the microscope; e. g., 
bile in the liver cells, fat in the cells of the mammary gland. 
2. Physical.—Consisting of a transudation of water and mineral salts from 
the blood into the interior of the gland. 
During the intervals of glandular activity only that amount of blood 
passes through the gland sufficient for proper nutrition; when the gland 
begins to secrete, under the influence of an appropriate stimulus, the blood- 
vessels dilate and the quantity of blood becomes greatly increased beyond 
that flowing through the gland during its repose. 
Under these Conditions a transudation of water and salt takes place, 
washing out the characteristic ingredients, which are discharged by the 
gland ducts. The discharge of the secretions is intermittent; they are re- 
tained in the glands until they receive the appropriate stimulus, when they 
pass into the larger ducts by the vis a tergo, and are then discharged by the 
contraction of the muscular walls of the ducts. 
The activity of glandular secretion is hastened by an increase in the 
blood pressure and retarded by a diminution. 
The nervous centers in the medulla oblongata influence secretion— 
1. By increasing or diminishing the amount of blood entering a gland. 
2. By exerting a direct influence upon the secreting cells themselves, the 
centers being excited by reflex irritation, mental emotion, etc. 
MAMMARY GLANDS. 
The Mammary Glands, which secrete the milk, are two more or less 
hemispherical organs, situated in the human female on the anterior surface 
of the chest. Though rudimentary in childhood, they gradually increase 
in size as the young, female approaches puberty. 
The gland presents at its convexity a small prominence of skin, the nip- 
ple, which is surrounded by a circular area of pigmented skin, the areola. 
The gland proper is covered by a layer of adipose tissue anteriorly and 
attached posteriorly to the pectoral muscles by a meshwork of fibrous tissue. 
During uterogestation the mammary glands become larger, firmer, and 
more lobuiated; the areola darkens and the veins become more prominent. 
At the period of lactation the gland is the seat of active histologic and 
physiologic changes, correlated with the production of milk. At the close 
of lactation the glands diminish in size, undergo involution, and gradually 
return to their original nonsecreting condition. 134 
HUMAN PHYSIOLOGY. 
Structure of the Mammary Glands.—Each mammary gland consists 
of an aggregation of some 15 or 20 lobes, each one of which is surrounded 
by a framework of fibrous tissue. The lobe is provided with an excretory 
duct, which, as it approaches the base of the nipple, expands to form a 
sinus or reservoir, beyond which it opens by a narrowed orifice on the sur- 
face of the nipple. On tracing the duct into a lobe it is found to divide 
and subdivide, and finally terminate in lobules or acini. Each acinus con- 
sists of a basement membrane, lined by low po.lyhedral cells. Externally 
it is surrounded by connective tissue, supporting blood-vessels, lymphatics, 
and nerves. 
MILK. 
Milk is an opaque, bluisli-white fluid, almost inodorous, of a sweet taste, 
an alkaline reaction, and a specific gravity of 1.025 to When exam- 
ined microscopically it is seen to consist of a clear fluid, the milk plasma, 
holding in suspension an enormous number of small, highly refractive oil 
globules, which measure, on the average, the an ' 'n diam- 
eter. Each globule is supposed by some observers to be surrounded by a 
thin, albuminous envelope, which enables it to maintain the discrete form. 
The quantity of milk secreted daily by the human female averages about 
two and a half pints. The milk of all the mammalia consists of all the dif- 
ferent classes of nutritive principles, though in varying proportions. The 
relative proportions in which these constituents exist are shown in the fol- 
lowing table of analyses :— 
COMPOSITION OF MILK. 
In ioo Parts. 
Human. 
Cow. 
Goat. 
Ass. 
Sheep. 
Mare. 
Water, .... 
88.00 
86.87 
87-54 
91-57 
82.27 
88.80 
Caseinogen, . . 
2.40 
3-98 
3.°° 
1.09 
6.10 
2.I9 
Lactalbumin, . . 
0.57 
O.77 
0.62 
0.70 
I. OO 
O.42 
Fat, 
2.90 
3-5° 
4.20 
1.02 
5-30 
2.50 
Lactose, .... 
5-87 
4.00 
4.00 
5-50 
4.20 
5-5° 
Salts, 
0.16 
0.17 
0.56 
0.42 
I.OO 
0.50 MAMMARY GLANDS. 
135 
Caseinogen is the chief proteid constituent of milk, and is held in solu- 
tion by the presence of calcic phosphate. On the addition of acetic acid 
or of sodic chlorid up to the point of saturation, the caseinogen is precipi- 
tated as such, and may be collected by appropriate chemic methods. When 
taken into the stomach caseinogen is coagulated, that is, it is separated into 
casein or tyrein and a small quantity of a new soluble proteid. The fer 
ment which induces this change is known as rennin. The presence of cal- 
cic phosphate is necessary for this coagulation. 
The Fat of milk is more or less solid at ordinary temperatures. It is a 
composition of olein, palmitin, and stearin, with a small quantity of butyrin 
and caproin. When milk is allowed to stand for some time the fat glob 
ules rise to the surface and form a thick layer known as cream. When 
subjected to the churning process, the fat globules run together and form a 
coherent mass—the butter. 
Lactose is the particular form of sugar characteristic of milk. It be- 
longs to the saccharose group and has the following composition: C12 II22- 
On. In the presence of the Bacillus acidi lactici the lactose is decomposed 
into lactic acid and carbon dioxid, the former of which will cause a coag- 
ulation of the caseinogen. 
Mechanism of Secretion.—During the time of lactation the mam- 
mary gland exhibits periods of secretory activity which alternate with peri- 
ods of rest. Coincidently with these periods, certain histologic changes 
take place in the secreting structures of the gland. At the close of a period 
of active secretion each acinus presents the following features : The epi- 
thelial cells are short, cubical, nucleated, and border a relatively wide 
lumen in which is to be found a variable quantity of nondischarged milk. 
After the gland has rested for some time active metabolism again begins. 
The epithelial cells grow ahd elongate; the nucleus divides into two or 
three new nuclei, and at the same time the cell becomes constricted; the 
inner portion is detached and is discharged into the lumen. Coincidently 
with these changes oil globules make their appearance in the cell proto- 
plasm, some of which are discharged separately into the lumen, while others 
remain for a time associated with the detached cell. From these histo- 
logic changes it would appear that the caseinogen and the fat globules are 
metabolic products of the cell protoplasm and not derived directly from the 
blood. That lactose has a similar origin appears certain from the fact that 
it is not found either in the blood or any other tissue of the body, and that 
it is formed independently of carbohydrate food. The water and inorganic 
salts are doubtless secreted by a mechanism similar to that of all other se- 
creting glands. 136 
HUMAN PHYSIOLOGY. 
VASCULAR OR DUCTLESS GLANDS. 
The Vascular Glands are regarded as possessing the power of acting 
upon certain elements of the food and aiding the process of sanguinifica- 
tion; of modifying the composition of the blood as it flows through their 
substance, by some act of secretion. 
The vascular glands are the spleen, suprarenal capsules, thyroid and 
thymus glands. 
The Spleen is about five inches in length, six ounces in weight, of a 
dark-bluish color, and situated in the left hypochondriac region. It is cov 
ered externally by a reflection of the peritoneum, beneath which is the proper 
fibrous coat, composed of areolar and elastic tissue and nonstriated muscu- 
lar fibers. From the inner surface of the fibrous envelope processes or 
trabeculae are given off, which penetrate the substance of the gland, form 
ing a network, in the meshes of which is contained the spleen pulp. The 
splenic artery divides into a number of branches, some of which, when 
they become very minute, pass directly into veins, while others terminate 
in true capillaries. 
As the capillary vessels ramify through the substance of the gland, their 
walls frequently disappear and the blood passes from the arteries into the 
veins through lacunce. 
The splenic or Malpighian corpuscles are small bodies, spherical or 
ovoid in shape, the of an inch in diameter, situated upon the sheaths 
of the small arteries. They consist of a delicate membrane containing a 
semifluid substance composed of numerous small cells resembling lymph 
corpuscles. The spleen pulp is a dark-red, semifluid substance, of a soft 
consistence, contained in the meshes of the trabeculte. In it are found 
numerous corpuscles, like those observed in the Malpighian bodies, blood- 
corpuscles in a natural and altered condition, nuclei, and pigment-granules. 
Function of the Spleen.—Probably influences the preparation of the 
albuminous food for nutrition; during digestion the spleen becomes larger, 
its contents are increased in amount, and after digestion it gradually dimin- 
ishes in size, returning to the normal condition. 
The red corpuscles are here disintegrated, after having fulfilled their 
function in the blood, the splenic venous blood containing relatively a 
small quantity. 
The white corpuscles appear to be increased in number, the blood of the 
splenic vein containing an unusually large proportion. 
The spleen serves also as a reservoir for blood when the portal circula- 
tion becomes obstructed. KIDNEYS. 
137 
The nervous system controls the enlargement of the spleen; division of 
the nerve produces dilatation of the vessels, stimulation contracts them. 
The Suprarenal Capsules are triangular, flattened bodies, situated 
above the kidney. They are invested by a fibrous capsule sending in 
trabeculae, forming the framework. The glandular tissue is composed of 
two portions, a cortical and medullary. The cortical is made up of 
small cylinders lined by cells and containing an opaque mass, nuclei, and 
granular matter. The medullary consists of a fibrous network containing 
in the alveoli nucleated protoplasm. 
The Thyroid Gland consists of a fibrous stroma, containing ovoid 
closed sacs, measuring on the average of an inch, formed of a delicate 
membrane lined by cells; the contents of the sacs consist of yellowish 
albuminous fluid. 
The Thymus Gland is most developed in early life and almost disap- 
pears in the adult. It is divided by processes of fibrous tissue into lobules, 
and these again into follicles which contain lymphoid corpuscles. 
The functions of the vascular organs appear to be the more complete 
elaboration of the blood necessary for proper nutrition; they are most highly 
developed during infancy and embryonic life, when growth and develop- 
ment are most active. 
EXCRETION. 
The Principal Excrementitious Fluids discharged from the body 
are the urine, perspiration, and bile; they hold in solution principles of 
waste which are generated during the activity of the nutritive process, and 
are the ultimate forms to which the organic constituents are reduced in the 
body. They also contain inorganic salts. 
The Urinary Apparatus consists of the kidneys, ureters, and bladder. 
KIDNEYS. 
The Kidneys are the organs for the secretion of urine; they resemble 
a bean in shape, are from four to five inches in length, two in breadth, 
and weigh from four to six ounces. 
They are situated in the lumbar region, one on each side of the vertebral 
column behind the peritoneum, and extend from the nth rib to the crest 
of the ilium ; the anterior surface is convex, the posterior surface concave, 
the latter presenting a deep notch, the hilus. 138 
HUMAN PHYSIOLOGY. 
The kidney is surrounded by a thin, smooth membrane composed of 
white fibrous and yellow elastic tissue ; though it is attached to the surface 
Fig. 14.—Longitudinal Section through the Kidney, the Pelvis of the 
Kidney, and a Number of Renal Calyces. 
A. Branch of the renal artery. U. Ureter. C. Renal calyx, i. Cortex, i'. Medullary 
rays. 1". Labyrinth, or cortex proper. 2. Medulla. 2'. Papillary portion of me- 
dulla, or medulla proper. 2". Border layer of the medulla. 3, 3. Transverse sec- 
tion through the axes of.the tubules of the border layer. 4. Fat of the renal sinus. 
5,5. Arterial branches. *. Transversely coursing medulla rays.— (Tyson, after 
Henle.) 
of the kidney by minute processes of connective tissue, it can be readily 
torn away. The substance of the kidney is dense but friable. 
Upon making a longitudinal section of the kidney it will be observed KIDNEYS. 
139 
that the hikes extends into the interior of the organ and expands to form 
a cavity known as the sinus. This cavity is occupied by the upper dilated 
portion of the ureter, the interior of which forms the pelvis. The ureter 
subdivides into several portions, which ultimately give origin to a number 
of smaller tubes termed calyces, which receive the apices of the pyramids. 
The Parenchyma of the Kidney consists of two portions, viz.:— 
1. An internal or medullary portion, consisting of a series of pyramids or 
cones, some twelve or fifteen in number. They 
present a distinctly striated appearance, a con- 
dition due to the straight direction of the tubules 
and blood-vessels. 
2. An external or cortical portion, consisting of 
a delicate matrix containing an immense num- 
ber of tubules having a markedly convoluted 
appearance. Throughout its structure are found 
numerous small ovoid bodies termed Malpighian 
corpuscles. 
The Uriniferous Tubules.—The kidney is a 
compound tubular gland composed of microscopic 
tubules, whose function it is to secrete from the 
blood those waste products which collectively con- 
stitute the urine. If the apex of each pyramid be 
examined with a lens, it will present a number of 
small orifices which are the beginnings of the urin- 
iferous tubules. From this point the tubules pass 
outward in a straight but somewhat diverging 
manner toward the cortex, giving off at acute 
angles a number of branches (Fig. 15). From 
the apex to the base of the pyramids they are 
known as the tubules of Bellini. In the cortical 
portion of the kidney each tubule becomes enlarged 
and twisted, and after pursuing an extremely 
convoluted course, turns backward into the medullary portion for some 
distance, forming the descending limb of Henle’s loop; it then turns 
upon itself, forming the ascending limb of the loop, reenters the cortex, 
again expands, and finally terminates in a spherical enlargement known as 
Muller's or Bowman's capsule. Within this capsule is contained a small 
tuft of blood-vessels constituting the glomerulus, or Malpighian corpuscle. 
Structure of the Tubules.—Each tubule consists of a basement mem- 
Fig. 15.—Diagrammatic 
Exposition of the 
Method in which the 
Uriniferous Tubes 
Unite to Form Primi- 
tive Cones. — (Tyson, 
after Ludwig.) 140 
HUMAN PHYSIOLOGY. 
brane lined by epithelial cells throughout its entire extent. The tubule 
and its contained epithelium vary in shape and size in different parts of 
its course. The termination of the convoluted tube consists of a little sac 
or capsule, which is ovoidal in shape and measures about of an inch 
in size. This capsule is lined by a layer of flattened epithelial cells, which 
is also reflected over the surface of the glomerulus. During the periods 
of secretory activity, the blood-vessels of the glomerulus become filled with 
blood, so that the cavity of the sac is almost obliterated; after secretory 
activity the blood-vessels contract and the sac cavity becomes enlarged. 
In that portion of the tubule lying between the capsule and Henle’s loop 
the epithelial cells are cuboidal in shape; in Henle’s loop they are flat- 
tened, while in the remainder of the tubule they are cuboidal and 
columnar. 
Blood-Vessels of the Kidney.— The renal artery is of large size and 
enters the organ at the hilum ; it divides into several large branches, which 
penetrate the substance of the kidney between the pyramids, at the base 
of which they form an anastomosing plexus, which completely surrounds 
them. From this plexus vessels follow the straight tubes toward the apex, 
while others, entering the cortical portion, divide into small twigs, which 
enter the Malpighian body and form a mass of convoluted vessels, the 
glomerulus. After circulating through the Malpighian tuft, the blood is 
gathered together by two or three small veins, which again subdivide and 
form a fine capillary plexus, which envelops the convoluted tubules; from 
this plexus the veins converge to form the emulgent vein, which empties 
into the vena cava. 
The Nerves of the Kidney follow the course of the blood-vessels and 
are derived from the renal plexus. 
The Ureter is a membranous tube, situated behind the peritoneum, 
about the diameter of a goose-quill, 18 inches in length, and extends from 
the pelvis of the kidney to the base of the bladder, which it perforates in 
an oblique direction. It is composed of three coats, fibrous, muscular, and 
mucous. 
The Bladder is a reservoir for the temporary reception of the urine 
prior to its expulsion from the body; when fully distended it is ovoid in 
shape, and holds about one pint. It is composed of four coats, serous, 
muscular, the fibers of which are arranged longitudinally and circularly, 
areolar, and mucous. The orifice of the bladder is controlled by the 
sphincter vesicce, a muscular band about half an inch in width. 
As soon as the Urine is formed it passes through the tubuli uriniferi KIDNEYS. 
141 
into the pelvis, and from thence through the ureters into the bladder, which 
it enters at an irregular rate. Shortly after a meal, after the ingestion of 
large quantities of fluid, and after exercise, the urine flows into the bladder 
quite rapidly, while it is reduced to a few drops during the intervals of di- 
gestion. It is prevented from regurgitating into the ureters on account of 
the oblique direction they take between the mucous and muscular coats. 
Nervous Mechanism of Urination.—When the urine has passed into 
the bladder, it is there retained by the sphincter vesicse muscle, kept in a 
state of tonic contraction by the action of a nerve center in the lumbar 
region of the spinal cord. This center can be inhibited and the sphincter 
relaxed, either rejlexly, by impressions coming through sensory nerves from 
the mucous membrane of the bladder, or directly, by a voluntary impulse 
descending the spinal cord. When the desire to urinate is experienced, 
impressions made upon the vesical sensory nerves are carried to the centers 
governing the sphincter and detrusor urines muscles and to the brain. If 
now the act of urination is to take place, a voluntary impulse originating 
in the brain passes down the spinal cord, and still further inhibits the 
sphincter vesicae center, with the effect of relaxing the muscle, and of 
stimulating the center governing the detrusor muscle, with the effect of 
contracting the muscle and expelling the urine. If the act is to be sup- 
pressed, voluntary impulses inhibit the detrusor center and possibly stimulate 
the sphincter center. 
The genitospinal center controlling these movements is situated in that 
portion of the spinal cord corresponding to the origin of the 3d, 4th, and 
5th sacral nerves. 
URINE. 
Normal Urine is of a pale yellow or amber color, perfectly transparent, 
with an aromatic odor, an acid reaction, a specific gravity of 1.020, and a 
temperature when first discharged of ioo° Fahr. 
The color varies considerably in health, from a pale yellow to a brown 
hue due to the presence of the coloring matter, urobilin or urochrome. 
The transparency is diminished by the presence of mucus, the calcium 
and magnesium phosphates, and the mixed urates. 
The reaction of the urine is acid, owing to the presence of acid phosphate 
of sodium. The degree of acidity, however, varies at different periods of 
the day. Urine passed in the morning is strongly acid, while that passed 
during and after digestion, especially if the food is largely vegetable in 
character, is either neutral or alkaline. 
The specific gravity varies from 1.015 to 1.025. 142 
HUMAN PHYSIOLOGY. 
The quantity of urine excreted in twenty-four hours is between 40 and 
50 fluidounces, but ranges above and below this standard. 
The odor is characteristic, and caused by the presence of taurylic and 
phenylic acids, but is influenced by vegetable foods and other substances 
eliminated by the kidneys. 
COMPOSITION OF URINF.. 
Other nitrogenized crystalline bodies, uric acid, prin- 
cipally in the form of alkaline urates, 
Creatin, creatinin, xanthin, hypoxanthin, 
Hippuric acid, leucin, tyrosin, taurin, cystin, all in 
small amounts, and not constant, 
Mucus and pigment, 
Salts:— 
Water, 967. 
Urea, i4-23° 
10.635 
Inorganic: principally sodium and potassium sul- 
phates, phosphates, and chlorids, with magnesium 
and calcium phosphates, traces of silicates and 
chlorids, 
Organic: lactates, hippurates, acetates, formates, 
which appear only occasionally, 
8.135 
Sugar, a trace. 
Gases (nitrogen and carbonic acid principally). 
1000.00 
The Average Quantity of the principal constituents excreted in 
twenty-four hours is as follows :— 
Water 52 fluidozs. 
Urea, 512.4 grains. 
Uric acid, 8.5 “ 
Phosphoric acid 45.0 “ 
Sulphuric acid, 31.11 “ 
Inorganic salts, 323.25 “ 
Lime and magnesia, 6.5 “ 
To Determine the Amount of solid matters in any given amount ot 
urine, multiply the last two figures of the specific gravity by the co-efficient 
of Haeser, 2.33 ; e. g., in 1000 grains of urine having a specific gravity 
1.022, there are contained 22 X 2-33 = S1- grains of solid matter. 
Organic Constituents of Urine.—Urea is one of the most important 
of the organic constituents of the urine, and is present to the extent of 
from 2.5 to 3.2 per cent. Urea is a colorless, neutral substance, crystalliz- 
ing to four-sided prisms terminated by oblique surfaces. When crystalliza- KIDNEYS. 
143 
tion is caused to take place rapidly, the crystals take the form of long, 
silky needles. Urea is soluble in water and alcohol; when subjected to 
prolonged boiling it is decomposed, giving rise to carbonate of ammonia. 
In the alkaline fermentation of urine, uiea takes up two molecules of water 
with the production of carbonate of ammonia. 
The average amount of urea excreted daily has been estimated at about 
500 grains. As urea is one of the principal products of the breaking up of 
the albuminous compounds within the body, it is quite evident that the 
quantity produced and eliminated in twenty-four hours will be increased by 
any increase in the amount of albuminous food consumed, by a rapid de- 
struction of albuminous tissues, as is witnessed in various pathologic 
states, inanition, febrile conditions, fevers, etc. A farinaceous or vegetable 
diet will diminish the urea production nearly one-half. 
Muscular exercise when the nutrition of the body is in a state of equi- 
librium does not seem to increase the quantity of urea. 
Seat of Urea Formation.—As to the seat of urea formation, little 
is positively known. It is quite certain that it preexists in the blood and is 
merely excreted by the kidneys. It is not produced in muscles, as even 
after prolonged exercise hardly a trace of urea is to be found in them. 
Experimental and pathologic facts point to the liver as the probable organ 
engaged in urea formation. Acute yellow atrophy of the liver, suppurative 
diseases of the liver, diminish almost entirely the production of urea. 
Uric Acid is also a constant ingredient of the urine and is closely allied 
to urea. It is a nitrogenized substance, carrying out of the body a large 
quantity of nitrogen. The amount eliminated daily varies from five to ten 
grains. Uric acid is a colorless crystal belonging to the rhombic system. 
It is insoluble in water, and if eliminated in excessive amounts it is de- 
posited as a “ brick red ” sediment in the urine. It is doubtful if uric acid 
exists in a free state, being combined for the most part with sodium and 
potassium bases forming urates. It is to be regarded as one of the termi- 
nal products of the disassimilation of albuminous compounds, and is prob- 
ably produced in the liver. 
Hippuric Acid is found very generally in urine, though it is present only 
in small amounts. It is increased by a diet of asparagus, cranberries, plums, 
and by the administration of benzoic and cinnamic acids. It is probably 
formed in the kidney. 
Kreatinin resembles the kreatin derived from muscles. It is a colorless 
crystal, belonging to the rhombic system. Its origin is unknown, though it 
is largely increased in amount by albuminous food. About 15 grains are 
excreted daily. 144 
HUMAN PHYSIOLOGY. 
Xanthin, Sarkin, Oxaluric Acid, and Allantoin are also constituents 
of urine. They are nitrogenized compounds and are also terminal products 
of albuminous compounds. 
Urobilin, the coloring matter of the urine, is a derivative of the bile pig- 
ments. It is particularly abundant in febrile conditions, giving to the urine 
its reddish-yellow color. 
Inorganic Constituents of Urine.—Earthy Phosphate. Phos- 
phoric acid in combination with magnesium and calcium is excreted daily 
to the extent of from 15 to 30 grains. The phosphates are insoluble in 
water, but are held in solution in the urine by its acid ingredients, alkalinity 
of the urine being attended with a copious precipitation of the phosphates. 
Mental work increases the amount of phosphoric acid excreted, a condition 
caused by increased metabolism of the nervous tissue. 
Sulphuric acid in combination with sodium and potassium constitute the 
sulphates, of which about 30 grains are excreted daily. Sulphuric acid 
results largely from the decomposition of albuminous food and from increased 
destruction of animal tissues. 
The Gases of urine are carbonic acid and nitrogen. 
Mechanism of Urinary Secretion.—As the kidney anatomically pre- 
sents an apparatus for filtration (the Malpighian bodies) and an apparatus 
for secretion (the epithelial cells of the urinary tubules), it might be inferred 
that the elimination of the constituents of the urine is accomplished by the 
twofold process of filtration and secretion ; that the water and highly 
diffusible inorganic salts simply pass by diffusion through the walls of the 
blood-vessels of the glomerulus into the capsule of Muller, while the urea 
and remaining organic constituents are removed by true secretory action of 
the renal epithelium. Modern experimentation supports this view of renal 
action. 
The secretion of urine is therefore partly physical and partly vital. 
The filtration of urinary constituents from the glomerulus into Muller’s 
capsule depends largely upon the blood pressure and the rapidity of blood 
flow in the renal artery and glomerulus. Among the influences which 
increase the pressure and velocity may be mentioned increased frequency 
and force of the heart’s action, contraction of the capillary vessels of the 
body generally, dilatation of the renal artery, increase in the volume of the 
blood. 
The reverse conditions lower the blood pressure and diminish the secre- 
tion of urine. 
The elimination of the organic matters by secretory activity of the renal LIVER. 
145 
epithelium seems to be well established by modern experiments. These 
substances, removed from the blood in the secondary capillary plexus of 
blood-vessels, by a true selective action of the epithelium, are dissolved and 
washed toward the pelves by the liquid coming from the capsules. 
The blood supply to the kidney is regulated by the nervous system. If 
the renal nerves be divided, the renal artery dilates and a copious flow of 
urine takes place. If the peripheral ends of the same nerves be stimulated, 
the artery contracts and the urinary flow ceases. The same is true of the 
splanchnic nerves, through which the vasomotor nerves coming from the 
medulla oblongata and spinal cord pass to the renal plexus. 
The Liver is a highly vascular, conglomerate gland, appended to the 
alimentary canal. It is the largest gland in the body, weighing about four 
and one-half pounds; it is situated in the right hypochondriac region, and 
retained in position by five ligaments, four of which are formed by duplica- 
tures of the peritoneal investment. 
The proper coat of the liver is a thin but firm fibrous membrane, closely 
adherent to the surface of the organ, which it penetrates at the transverse 
fissure, and follows the vessels in their ramifications through its substance, 
constituting Glisson's capsule. 
Structure of the Liver.—The liver is made up of a large number of 
small bodies, the lobules, rounded or ovoid in shape, measuring the of 
an inch in diameter, separated by a space in which are situated blood- 
vessels, nerves, hepatic ducts, and lymphatics. 
The Lobules are composed of cells,'which, when examined microscopi- 
cally, exhibit a rounded or polygonal shape, and measure, on the average, 
the xtfVffth of an inch in diameter ; they possess one, and at times two, nuclei; 
they also contain globules of fat, pigment matter, and animal starch. The 
cells constitute the secreting structure of the liver, and are the true hepatic 
cells. 
The Blood-vessels which enter the liver are— 
1. The portal vein, made up of the gastric, splenic, superior, and inferior 
?nesenteric veins. 
2. The hepatic artery, a branch of the celiac axis, both of which are in- 
vested by a sheath of areolar tissue; the vessels which leave the liver are 
the hepatic veins, originating in its interior, collecting the blood distrib- 
LIVER. 146 
HUMAN PHYSIOLOGY. 
uted by the portal vein and hepatic artery, and conducting it to the 
ascending vena cava. 
Distribution of Vessels.—The portal vein and hepatic artery, upon 
entering the liver, penetrate its substance, divide into smaller and smaller 
branches, occupy the spaces between the lobules, completely surrounding 
and limiting them, and constitute the interlobular vessels. The hepatic 
artery, in its course, gives off branches to the walls of the portal vein and 
Glisson’s capsule, and finally empties into the small branches of the portal 
vein in the interlobular spaces. 
The interlobular vessels form a rich plexus around the lobules, from 
which branches pass to neighboring lobules and enter their substance, 
where they form a very fine network of capillary vessels, ramifying over 
the hepatic cells, in which the various functions of the liver are performed. 
The blood is then collected by small veins, converging toward the center 
of the lobule, to form the intralobular vein, which runs through its long 
axis and empties into the sublobular vein. The hepatic veins are formed 
by the union of the sublobular veins, and carry the blood to the ascending 
vena cava; their walls are thin and adherent to the substance of the hepatic 
tissue. 
The Hepatic Ducts or Bile Capillaries originate within the lobules, 
in a very fine plexus lying between the hepatic cells; whether the smallest 
vessels have distinct membranous walls, or whether they originate in the 
spaces between the cells by open orifices, has not been satisfactorily deter- 
mined. 
The Bile Channels empty into the interlobular ducts, which measure 
about of an inch in diameter, and are composed of a thin, homo- 
geneous membrane lined by flattened epithelial cells. 
As the interlobular bile ducts unite to form larger trunks, they receive an 
external coat of fibrous tissue, which strengthens their walls; they finally 
unite to form one large duct, the hepatic duct, which joins the cystic duct; 
the union of the two forms the ductus communis choledochus, which is 
about three inches in length, the size of a gbose quill, and opens into the 
duodenum. 
The Gall Bladder is a pear-shaped sac, about four inches in length, 
situated in a fossa on the under surface of the liver. It is a reservoir for 
the bile, and is capable of holding about one ounce and a half of fluid. It 
is composed of three coats,— 
1. Serous, a reflection of the peritoneum. 
2. Fibrous and muscular. 
3. Mucous. LIVER 
147 
Functions of the Liver.—The liver is a complex organ having a 
variety of relations to the general processes of the body. While its physi- 
ologic actions are not yet wholly understood, it may be said that it— 
1. Secretes bile. 
2. Forms glycogen. 
3. Assists in the formation of urea and allied products. 
4. Modifies the composition of the blood as it passes through it. 
The Secretion of Bile.—The characteristic constituents of the bile do 
not preexist in the blood, but are formed within the interior of the liver 
cells out of materials derived from the venous and arterial blood. The 
hepatic cells absorbing these materials elaborate them into bile elements, 
and in so doing undergo histologic changes similar to those exhibited by 
other secretory glands. The bile once formed, it passes into the mouths 
of the bile capillaries, near the periphery of the lobules. Under the influ- 
ence of the vis a-tergo of the new-formed bile it flows from the smaller into 
the larger bile ducts, and finally empties into the intestine, or is regurgi- 
tated into the gall bladder, where it is stored up until it is required for the 
digestive process in the small intestine. The study of the secretion of bile 
by means of biliary fistulse reveals the fact that the secretion is continuous 
and not intermittent; that the hepatic cells are constantly pouring bile into 
the ducts, which convey it into the gall bladder. As this fluid is required 
only during intestinal digestion, it is only then that the walls of the gall 
bladder contract and discharge it into the intestine. 
The flow of bile from the liver cells into the gall bladder is accomplished 
by the inspiratory movements of the diaphragm, the contraction of the 
muscular fibers of the biliary ducts, as well as the vis-a tergo of new-formed 
bile. Any obstacle to the outflow of bile into the intestine leads to an 
accumulation within the bile ducts. The pressure within the ducts in- 
creasing beyond that of the blood within the capillaries, a re absorption of 
biliary matters by the lymphatics takes place, giving rise to the phenomena 
of jaundice. 
The Bile is both a secretion and an excretion ; it contains new constitu- 
ents which are formed only in the substance of the liver, and are destined 
to play an important part ultimately in nutrition; it contains also waste 
ingredients which are discharged into the intestinal canal and eliminated 
from the body. 
Glycogenic Function.—In addition to the preceding function, Bernard, 
in 1848, demonstrated the fact that the liver, during life, normally produces 
a sugar-forming substance, analogous in its chemical composition to starch, 148 
HUMAN PHYSIOLOGY. 
which he terms glycogen ; also that when the liver is removed from the 
body, and its blood-vessels thoroughly washed out, after a few hours sugar 
again makes its appearance in abundance. 
It can be shown to exist in the blood of the hepatic vein as well as in a 
decoction of the liver substance by means of either Trommer'sor Fehling’s 
tests, even when the blood of the portal vein does not contain a trace of sugar. 
Origin and Destination of Glycogen.—Glycogen appears to be 
formed de novo in the liver cells, from materials derived from the food, 
whether the diet be animal or vegetable, though a larger percent, is formed 
when the animal is fed on starchy and saccharin, than when fed on animal 
food. The glucose, which is one of the products of digestion, is absorbed 
by the blood-vessels, and carried directly into the liver ; as it does not ap- 
pear in the urine, as it would if injected at once into the general circulation, 
it is probable that it is detained in the liver, dehydrated, and stored up as 
glycogen. The change is shown by the following formula:— 
Glucose. 
Water. 
Glycogen. 
CfiH1206 H20 — C6H10O5. 
The glycogen thus formed is stored up in the hepatic cells for the future 
requirements of the system. When it is carried from the liver it is again 
transformed into glucose by the agency of a ferment. Glycogen does not 
undergo oxidation in the blood; this takes place in the tissues, particularly 
in the muscles, where it generates heat and contributes to the development 
of muscular force. 
Glycogen, when obtained from the liver, is an amorphous, starch-like 
substance, of a white color, tasteless and colorless, and soluble in water; by 
boiling with dilute acids, or subjected to the action of an animal ferment, 
it is easily converted into glucose. When an excess of sugar is generated 
by the liver, it can be found, not only in the blood of the hepatic vein, 
but also in other portions of the body; under these circumstances it is 
eliminated by the kidneys, appearing in the urine, constituting the condi- 
tion of glycosuria. 
Formation of Urea.—The liver is now regarded by many physiologists 
to be the principal organ concerned in urea formation. The liver normally 
contains a certain amount of urea, and if blood be passed through the 
excised liver of an animal which has been in full digestion, a large amount 
of urea is obtained. The clinical evidence proves that in destructive dis- 
eases of the liver substance there is at once a falling off in urea elimination. 
Various drugs which increase liver action increase the urea in the urine. SKIN. 
149 
Elaboration of Blood.—Besides the capability of secreting bile, the 
liver posesses the property of so acting upon and modifying the chemic 
composition of the products of digestion as they traverse its substance, 
that they readily assimilate with the blood, and are transformed into mate- 
rials capable of being converted into the elements of the blood and solid 
tissues. 
The albuminous particularly requires the modifying influence of the liver; 
for if it be removed from the portal vein and introduced into the jugular 
vein, it is at once removed from the blood by the action of the kidneys. 
The blood of the hepatic vein differs from the blood of the portal vein 
in being richer in blood corpuscles, both red and white; its plasma is more 
dense, containing a less percentage of water and a greater amount of solid 
constituents, but no fibrin; its serum contains less albumin, fats, and salts, 
but its sugar is increased. 
Influence of the Nervous System.—The nervous system directly 
controls the functional activity of the liver, and more especially its glyco- 
genic function. It was discovered by Bernard that puncture of the medulla 
oblongata is followed by such an enormous production of sugar that it is at 
once excreted by the kidneys, giving rise to diabetic or saccharin urine. 
This part of the medulla is, however, the vasomotor center for the blood- 
vessels of the liver. Destruction of this center, or injury to the vasomotor 
nerves emanating from it in any part of their course, is followed at once by 
dilatation of the hepatic blood-vessels, slowing of the blood current, a pro- 
found disturbance of the normal relation existing between the blood and 
liver cells, and a production of sugar. Many of the hepatic vasomotor 
nerves may be traced down the cord as far as the lumbar region, while 
others leave the cord high up in the neck and enter the cervical ganglia of 
the sympathetic and so reach the liver. Injury to the sympathetic ganglia 
is often followed by diabetes. Peripheral stimulation of various nerves, 
e. g., sciatic, pneumogastric, depressor nerve, as well as the direct action of 
many drugs, impair or depress the hepatic vasomotor center and so give 
rise to diabetes. 
SKIN. 
The Skin, the external investment of the body, is a most complex and 
important structure, serving— 
x. As a protective covering. 
2. An organ for tactile sensibility. 
3. An organ for the elimination of excrementitious matters. 150 
HUMAN PHYSIOLOGY. 
The Amount of Skin investing the body of a man of average size is 
about twenty feet, and varies in thickness, in different situations, from the 
£th to the x<T(Tlh °f an inch. 
The skin consists of two principal layers, viz., a deeper portion, the 
Corium, and a superficial portion, the Epidermis. 
The Corium, or Cutis vera, may be subdivided into a reticulated and 
a papillary layer. The former is composed of white fibrous tissue, non- 
striated muscular fibers, and elastic tissue, interwoven in every direction, 
forming an areolar network, in the meshes of which are deposited masses 
of fat, and a structureless amorphous matter; the latter is formed mainly of 
club-shaped elevations or projections of the amorphous matter, constituting 
the papillce ; they are most abundant, and well developed, upon the palms 
of the hands and the soles of the feet; they average the an inch 
in length, and may be simple or compound; they are well supplied with 
nerves, blood-vessels, and lymphatics. 
The Epidermis, or Scarf Skin, is an extravascular structure, a product 
of the true skin, and composed of several layers of cells. It may be divided 
into two layers, the rete mucosum, or the Malpighian layer, and the horny 
or corneous. 
The former closely applies itself to the papillary layer of the true skin, 
and is composed of large, nucleated cells, the lowest layer of which, the 
“ prickle cells,” contain pigment granules, which give to the skin its varying 
tints in different individuals and in different races of men ; the more super- 
ficial cells are large, colorless, and semitransparent. The latter, the cor- 
neous layer, is composed of flattened cells, which, from their exposure to 
the atmosphere, are hard and horny in texture; it varies in thickness from 
|th of an inch on the palms of the hands and feet, to the 5th of an inch 
in the external auditory canal. 
APPENDAGES OF THE SKIN 
Hairs are found in almost all portions of the body, and can be divided 
into— 
1. Long, soft hairs, on the head. 
2. Short, stiff hairs, along the edges of the eyelids and nostrils. 
3. Soft, downy hairs, on the general cutaneous surface. They consist of a 
root and a shaft, which is oval in shape, and about the of an inch 
in diameter; it consists of fibrous tissue, covered externally by a layer of 
imbricated cells, and internally by cells containing granular and pigment 
material. SKIN. 
151 
The Root of the hair is embedded in the hair follicle, formed by a tubular 
depression of the skin, extending nearly through to the subcutaneous tissue; 
its walls are formed by the layers of the corium, covered by epidermic cells. 
At the bottom of the follicle is a papillary projection of amorphous matter, 
corresponding to a papilla of the true skin, containing blood-vessels and 
nerves, upon which the hair root rests. The investments of the hair roots 
are formed of epithelial cells, constituting the internal and external root 
sheaths. 
The hair protects the head from the heat of the sun and cold, retains the 
heat of the body, prevents the entrance of foreign matter into the lungs, 
nose, ears, etc. The color is due to the pigment matter, which, in old age, 
becomes more or less whitened. 
The Sebaceous Glands, imbedded in the true skin, are simple and 
compound racemose glands, opening, by a common excretory duct, upon 
the surface of the epidermis or into the hair follicle. They are found in 
all portions of the body, most abundantly in the face, and are formed by a 
delicate, structureless membrane, lined by flattened polyhedral cells. The 
sebaceous glands secrete a peculiar oily matter, the sebum, by which the 
skin is lubricated and the hairs softened; it is quite abundant in the region 
of the nose and forehead, which often present a greasy, glistening appear- 
ance; it consists of water, mineral salts, fatty globules, and epithelial cells. 
The vernix caseosa, which frequently covers the surface of the fetus at 
birth, consists of the residue of the sebaceous matters, containing epithelial 
cells and fatty matters; it seems to keep the skin soft and supple, and 
guards it from the effects of the long-continued action of water. 
The Sudoriparous Glands excrete the sweat. They consist of a mass 
or coil of a tubular gland duct, situated in the derma and in the subcutane- 
ous tissue, average the of an inch in diameter, and are surrounded by 
a rich plexus of capillary blood-vessels. From this coil the duct passes in a 
straight direction up through the skin to the epidermis, where it makes a 
few spiral turns and opens obliquely upon the surface. The sweat glands 
consist of a delicate homogeneous membrane lined by epithelial cells, whose 
function is to extract from the blood the elements existing in the perspira- 
tion. 
The glands are very abundant all over the cutaneous surface, as many as 
3528 to the square inch, according to Erasmus Wilson. 
The Perspiration is an excrementitious fluid, clear, colorless, almost 
odorless, slightly acid in reaction, with a specific gravity of 1.003 to 1.004. 
The Total Quantity of perspiration excreted daily has been estimated 152 
HUMAN PHYSIOLOGY. 
at about two pounds, though the amount varies with the nature of the food 
and drink, exercise, external temperature, season, etc. 
The elimination of the sweat is not intermittent, but continuous; but it 
takes place so gradually that as fast as it is formed it passes off by evapora- 
tion as insensible perspiration. Under exposure to great heat and exercise 
the evaporation is not sufficiently rapid, and it appears as sensible perspira- 
tion. 
Water, 995 573 
Urea, *. 0.043 
Fatty matters, 0.014 
Alkaline lactates . 0.317 
Alkaline sudorates, . . 1.562 
Inorganic salts, 2.491 
1000.00 
COMPOSITION OF SWEAT. 
Urea is a constant ingredient. 
Carbonic acid is also exhaled from the skin, the amount being about 2|5th 
of that from the lungs. 
Perspiration regulates the temperature and removes waste matters from 
the blood ; it is so important, that if elimination be prevented death occurs 
in a short time. 
Influence of the Nervous System.—The secretion of sweat is regu- 
lated by the nervous system. Here, as in the secreting glands, the fluid is 
formed from material in the lymph spaces surrounding the gland. Two 
sets of nerves are concerned, viz., vasomotor, regulating the blood supply; 
and secretory, stimulating the activities of the gland cells. Generally the 
two conditions, increased blood flow and increased glandular action, co-exist. 
At times profuse clammy perspiration occurs, with diminished blood flow. 
The dominating sweat center is located in the medulla, though subordi- 
nate centers are present in the cord. The secretory fibers reach the perspi- 
ratory glands of the head and face through the cervical sympathetic; of the 
arms, through the thoracic sympathetic, ulnar, and radial nerves; of the 
leg, through the abdominal sympathetic and sciatic nerves.. 
The sweat center is excited to action by mental emotions, increased tem- 
perature of blood circulating in the medulla and cord, increased venosity of 
blood, and many drugs, rise of external temperature, exercise, etc. CEREBROSPINAL AXIS. 
153 
CEREBROSPINAL AXIS. 
The Cerebrospinal Axis consists of the spinal cord, medulla oblon- 
gata, pons Varolii, cerebellum and cerebrum, exclusive of the spinal and 
cranial nerves. It is contained within the cavities of the cranium and 
spinal column, and surrounded by three membranes, the dura mater, 
arachnoid, and pia mater, which protect it from injury and supply it with 
blood-vessels. 
MEMBRANES. 
The Dura Mater, the most external of the three, is a tough membrane, 
composed of white fibrous tissue, arranged in bundles, which interlace in 
every direction. In the cranial cavity it lines the inner surface of the 
bones, and is attached to the edge of the foramen magnum; sends processes 
inward, forming the falx cerebri, falx cerebelli, and tentorium cerebelli, 
supporting and protecting parts of the brain. In the spinal canal it loosely 
invests the cord, and is separated from the walls of the canal by areolar 
tissue. 
The Arachnoid, the middle membrane, is a delicate serous structure 
which envelopes the brain and cord, forming the visceral layer, and is then 
reflected to the inner surface of the dura mater, forming th& parietal layer. 
Between the two layers there is a small quantity of fluid which prevents 
friction by lubricating the two surfaces. 
The Pia Mater, the most internal of the three, composed of areolar 
tissue and blood-vessels, covers the entire surface of the brain and cord, to 
which it is closely adherent, dipping down between the convolutions and 
fissures. It is exceedingly vascular, sending small blood-vessels some dis- 
tance into the brain and cord. 
The Cerebrospinal Fluid occupies the subarachnoid space and the 
general ventricular cavities of the brain, which communicate by an opening, 
the foramen of Magendie, in the pia mater, at the lower portion of the 
4th ventricle. This fluid is clear, transparent, alkaline, possesses a salt 
taste and a low specific gravity; it is composed largely of water, traces of 
albumin, glucose, and mineral salts. It is secreted by the pia mater ; the 
quantity is estimated from two to four fluidounces. 
The function of the cerebrospinal fluid is to protect the brain and cord 
by preventing concussion from without; by being easily displaced into the 
spinal canal, prevents undue pressure and insufficiency of blood to the 
brain. 154 
HUMAN PHYSIOLOGY. 
SPINAL CORD. 
The Spinal Cord varies from 16 to 18 inches in length ; is half an inch 
in thickness, weighs I y2 ozs., and extends from the atlas to the 2d lumbar 
vertebra, terminating in the filum terminale. It is cylindrical in shape, 
and presents an enlargement in the lower cervical and lower dorsal regions, 
corresponding to the origin of the nerves which are distributed to the 
upper and lower extremities. The cord is divided into two lateral halves 
by the anterior and posterior fissures. It is composed of both white or 
fibrous and gray or vesicular matter, the former occupying the exterior of 
the cord, the latter the interior, where it is arranged in the form of two 
crescents, one in each lateral half, united together by the central mass, the 
gray commissure; the white matter being united in front by the white 
commissure. 
Structure of the Gray Matter.—The gray matter is arranged in the 
form of two crescents, united by a commissural band, forming a figure re- 
sembling the letter H. Each crescent presents an anterior and a posterior 
horn. The center of the commissure presents a canal which extends from 
the fourth ventricle downward to the filum terminale. The anterior horn 
is short and broad and does not extend to the surface. The posterior horn 
is narrow and elongated and extends quite to the surface. It is covered 
and capped by the substantiagelatinosa. The gray matter consists primarily 
of a framework of fine connective tissue, supporting blood-vessels, lymphatics, 
medullated and non-medullated nerve fibers, and groups of nerve cells. 
The Nerve Cells are arranged in groups, which extend for some dis- 
tance throughout the cord, forming columns more or less continuous. The 
first group is situated in the anterior horn, the cells of which are large multi- 
polar and connected with the anterior roots of the spinal nerves. The 
second group is situated in the posterior horn, the cells of which are spin- 
dle-shaped, and from their relation to the posterior roots are supposed to 
be sensory in function. The third group is situated in the lateral aspect 
of the gray matter, and is quite separate and distinct, except in the lumbar 
and cervical enlargements, where it blends with those of the anterior 
horn. A fourth group is situated at the inner base of the posterior horn ; 
it begins about the 7th or 8th cervical nerve and extends downward 
to the 2d or 3d lumbar, being most prominent in the dorsal region. This 
column is known as Clark’s vesicular column. 
Structure of the White Matter.—The white matter surrounding each 
lateral half of the cord is made up of nerve fibers, some of which are con- SPINAL CORD. 
155 
tinuations of the nerves which enter the cord, while others are derived from 
different sources. It is subdivided into— 
1. An anterior column, comprising that portion between the anterior roots 
and the anterior fissure, which is again subdivided into two parts:— 
a. An inner portion, bordering the anterior median fissure, the direct 
pyramidal tract, or column of Tiirck, containing motor fibers which 
do not decussate, and which extends as far down as the middle of 
the dorsal region. 
b. An outer portion, surrounding the anterior cornua, known as the 
anterior root zone, composed of short, longitudinal fibers which serve 
to connect together differ- 
ent segments of the spinal 
cord. 
2. A lateral column, the portion 
between the anterior and pos- 
terior roots, which is divisible 
into— 
a. The crossed pyramidal 
tract, occupying the pos- 
terior portion of the lateral 
column, and containing 
all those fibers of the 
motor tract which have 
decussated at the medul- 
la oblongata; it is com- 
posed of longitudinally 
running fibers which are 
connected with the mul- 
tipolar nerve cells of the 
anterior cornua. 
b. The direct cerebellar 
tract, situated upon the surface of the lateral column, consisting of 
longitudinal fibers which terminate in the cerebellum; it first appears 
in the lumbar region, and increases as it passes upward. 
c. The anterior tract, lying just posterior to the anterior cornua. 
3. A posterior column, the portion included between the posterior roots 
and the posterior fissure, also divisible into two portions:— 
a. An inner portion, the postero-internal column, or the column of 
Goll, bordering the posterior median fissure, and 
Fig. 16.—Scheme of the Conducting Paths 
in the Spinal Cord at the 3D Dorsal 
Nerve. 
The black part is the gray matter, v. Ante- 
rior, hw, posterior, root. a. Direct, and, g, 
crossed, pyramidal tracts, b. Anterior col- 
umn, ground bundle, c. Goll’s column, d. 
Postero-external column, e and f. Mixed 
lateral paths, h. Direct cerebellar tracts.— 
(Landois.) 156 
HUMAN PHYSIOLOGY. 
b. An external portion, the postero-external column, the column of 
Burdach, lying just behind the posterior roots. They are composed 
of long and short commissural fibers which connect together different 
segments of the spinal cord. 
SPINAL NERVES. 
Origin.—The spinal nerves are thirty-one in number on each side of the 
spinal cord, and arise by two roots, an anterior and posterior, from the 
anterior and posterior aspects of the cord respectively; the posterior roots 
present near their emergence from the cord a small ganglionic enlarge- 
ment ; outside of the spinal canal the two roots unite to form a main trunk, 
which is ultimately distributed to the skin, muscles, and viscera. 
The Function of the Anterior Roots is to transmit efferent impulses 
from the centers to the periphery. Irritation of these roots causes— 
1. Convulsive movements in the muscles. 
2. Secretion of glands, and 
3. Changes in vascular caliber. 
Division of these roots is followed by— 
1. Loss of muscular movement. 
2. Cessation of secretion, and 
3. Loss of vascular changes. 
The Function of the Posterior Roots is to transmit afferent impulses 
from the periphery to the spinal cord and brain. Irritation of these roots 
produces— 
1. Reflex activities. 
2. Conscious sensations. 
Division of these roots is followed by— 
1. A loss of reflex activity and 
2. By a loss of sensation in all the parts to which they are distributed. 
The ganglion on the posterior root influences the nutrition of the sensory 
nerve; for if the nerve be separated from the ganglion, it undergoes 
degeneration in the course of a few days in the direction in which it 
carries impressions, i. <?., from the periphery to the centers; if the nerve be 
divided between the ganglion and the cord, the central end only undergoes 
degeneration. The nutrition of the anterior root is governed by nerve cells 
in the gray matter of the cord ; for if these cells undergo atrophy, or if the 
nerve be divided, it undergoes degeneration outward. SPINAL CORD. 
157 
COURSE OF THE ANTERIOR AND POSTERIOR ROOTS. 
The Anterior Roots pass through the anterior columns, horizontally, 
in straight and distinct bundles, and enter the anterior cornuae, where they 
diverge in four directions :— 
1. Many become connected with the prolongations of the multipolar nerve 
cells. 
2. Others leave the gray matter, pass through the anterior white commis- 
sure, and enter the anterior columns of the opposite side. 
3. A considerable number enter the lateral columns of the same side, through 
which they pass to the medulla oblongata, where they decussate and fin- 
ally terminate in the corpus striatum of the opposite side. 
4. Others traverse the gray matter horizontally, and come into relation 
with the cells of the intermediary lateral column. 
The Posterior Roots enter the posterior horns of the gray matter— 
1. Through the substantia gelatinosa. 
2. Through the posterior columns ; of the former, some bend upward 
and downward, and become connected with the anterior cornuse; others 
pass through the posterior commissure to the opposite side; of the latter, 
fibers pass into the gray matter to the posterior vesicular columns, passing 
obliquely through the posterior white columns upward and downward 
for some distance, and enter the gray matter at different heights. 
Decussation of Motor and Sensory Fibers.—The Motor fibers, 
which conduct volitional impulses from the brain outward to the anterior 
cornuse, arise in the motor centers of the cerebrum ; they then pass down- 
ward through the corona radiata, the internal capsule, the inferior portions 
of the crura cerebri, the pons Varolii, to the medulla oblongata, where the 
motor tract of each side divides into two portions, viz.: — 
1. The larger, containing 91 to 97 per cent, of the fibers, which decussates 
at the lower border of the medulla and passes down in the lateral column 
of the opposite side, and constitutes the crossed pyramidal tract. 
2. The smaller, containing three to nine per cent, of the fibers, does not decus- 
sate, but passes down the anterior column of the same side, and constitutes 
the direct pyramidal tract, or the column of Tiirck. Some of the motor 
fibers of these two tracts, after entering the anterior cornuse of the gray 
matter, become connected with the large multipolar nerve cells, while 
others pass directly into the anterior roots. Through this decussation 
each half of the brain governs the muscular movements of the opposite 
side of the body. 
The Sensory fibers, which convey the impression made upon the peri- 158 
HUMAN PHYSIOLOGY. 
phery to the cord and brain, pass into the cord through the posterior roots 
of spinal nerves; they then diverge and enter the gray matter at different 
levels, and at once decussate, passing to the opposite side of the gray 
matter. The sensory tract passes upward, through the cord, the medulla, 
pons Varolii, the superior portion of the crura cerebri, the posterior third 
of the internal capsule, to the sensory perceptive center, located in the 
hippocampus major and unciate convolution (Ferrier). Through this decus- 
sation each half of the brain governs the sensibility of the opposite half of 
the body. 
Properties of the Spinal Cord.—Irritation applied directly to the 
anterolateral white columns produces muscular movements but no pain; 
they are, therefore, excitable but insensible. 
The surface of the posterior columns is not sensitive to direct irritation, 
except near the origin of the posterior roots. The sensibility is due, how- 
ever, not to its own proper fibers, but to the fibers of the posterior root 
which traverse it. 
Division of the anterolateral columns abolishes all power of voluntary 
movement in the lower extremities. 
Division of the posterior columns impairs the power of muscular coordi- 
nation, such as is witnessed in locomotor ataxia. 
The gray matter is probably both insensible and inexcitable under the 
influence of direct stimulation. 
A transverse section of one lateral half of the cord produces :— 
1. On the same side, paralysis of voluntary motion and a relative or absolute 
elevation of temperature and an increased flow of blood in the paralyzed 
parts ; hyperesthesia for the sense of contact, tickling, pain, and tempera- 
ture. 
2. On the opposite side, complete anesthesia as regards contact, and tick- 
ling and temperature, in the parts corresponding to those which are 
paralyzed in the opposite side, with a complete preservation of voluntary 
power and of the muscular sense. 
A vertical section through the middle of the gray matter results in the 
loss of sensation on both sides of the body below the section, but no loss of 
voluntary power. 
I. As an Independent Nerve Center. 
The spinal cord, in virtue of its contained nerve-cells, is capable of 
transforming afferent nerve impulses arriving through the afferent nerves 
FUNCTIONS OF THE SPINAL CORD, SPINAL CORD. 
159 
Fig. 17.—Diagram Showing the Course, through the Spinal Cord, of the 
Motor and Sensory Nerve Fibers. 
H and B' represent the right and left hemispheres of the brain, from which the motor 
fibers take their origin, and in which the sensory fibers terminate. The motor tract 
from the right side,i, passes down through the eras, through the pons to the medulla 
oblongata, where it divides into two portions : ist, the larger portion, 97 per cent., 
crosses over to the opposite side of the cord and passes down through the lateral 
column. It gives off fibers at different levels, which pass into the gray matter and 
become connected with the muscles, M, through the multipolar cells; the smaller 
portion, three per cent., does not cross over, but descends on the same side of the 
cord in the anterior column and supplies the muscles, m. The same is true for the 
motor tract for the left hemisphere. 
The sensory fibers from the left side of the body enter the gray matter through the 
posterior roots. They then cross over at once to the opposite side of the cord and 
ascend to the hemisphere partly in the gray matter, partly in the posterior column. 
The same is true for the sensory nerves of the right side of the body. 160 
HUMAN PHYSIOLOGY. 
into efferent impulses, which are reflected outward through efferent nerves 
to muscles producing motion, to glands exciting secretion, to blood-vessels 
changing their caliber. All such actions taking place independent of 
either sensation or volition are termed reflex actions. The mechanism 
involved in every reflex action consists of a sentient surface, an afferent 
nerve, a receptive center in connection with the nerve, a commissural fiber, 
an emissive center, an efferent nerve, and a responsive organ, muscle, 
gland, or blood-vessel. 
The reflex excitability of the cord may be— 
1. Increased by disease of the lateral columns, the administration of 
strychnia, and, in frogs, by a separation of the cord from the brain, the 
latter apparently exerting an inhibitory influence over the former and 
depressing its reflex activity. 
2. Inhibited by destructive lesions of the cord, e.g., locomotor ataxia, 
atrophy of the anterior cornuse, the administration of various drugs, and, 
in the frog, by irritation of certain regions of the brain. When the cere- 
brum alone is removed and the optic lobes stimulated, the time elapsing 
between the application of an irritant to a sensory surface and the 
resulting movement will be considerably prolonged, the optic lobes 
(Setschenow’s center) apparently generating impulses which, descending 
the cord, retard its reflex movement. 
All movements taking place through the nervous system are of this reflex 
character, and may be divided into excito-motor, sensori-motor, and ideo- 
motor. 
Classification of Reflex Movements. (Kiiss.) They may be divided 
into four groups, according to the route through which the centripetal and 
centrifugal impulses pass :— 
1. Those normal reflex acts, e.g., deglutition, coughing, sneezing, walk- 
ing, etc.; pathologic reflex acts, e.g., tetanus, vomiting, epilepsy, which 
take place both centripetally and centrifugally through spinal nerves. 
2. Reflex acts which take place in a centripetal direction through a cere- 
bro-spinal sensory nerve, and in a centrifugal direction through a sym- 
pathetic motor nerve, usually a vasomotor nerve, e.g., the normal reflex 
acts, which give rise to most of the secretions, pallor, and blushing of 
the skin, certain movements of the iris, certain modifications in the beat 
of the heart; the pathologic, which, on account of the difficulty in ex- 
plaining their production, are termed tnetastalic, e. g., ophthalmia, coryza, 
orchitis, which depend on a reflex hyperemia; amaurosis, paralysis, 
paraplegia, etc., due to a reflex anemia. 
3. Reflex movements, in which the centripetal impulse passes through a SPINAL CORD. 
161 
sympathetic nerve, and the centrifugal through a cerebro-spinal nerve; 
most of these phenomena are pathological, e.g., convulsions from intesti- 
nal irritation produced by the presence of worms, eclampsia, hysteria, etc. 
4. Reflex actions, in which both the centripetal and centrifugal impulses 
pass through filaments of the sympathetic nervous system, e.g., those 
obscure reflex actions which preside over the secretions of the intestinal 
fluids, which unite the phenomena of the generative organs, the dilatation 
of the pupils from intestinal irritation (worms), and many pathological 
phenomena. 
Laws of Reflex Action. (Pfluger.) 
1. Law of Unilaterality.—If a feeble irritation be applied to one or 
more sensory nerves, movement takes place usually on one side only, and 
that upon the same side as the irritation. 
2. Law of Symmetry.—If the irritation becomes sufficiently intense, 
motor reaction is manifested, in addition, in corresponding muscles of the 
opposite side of the body. 
3. Law of Intensity.—Reflex movements are usually more intense on the 
side of the irritation ; at times the movements of the opposite side equal 
them in intensity, but they are usually less pronounced. 
4. Law of Radiation.—If the excitation still continues to increase, it is 
propagated upward, and motor reaction takes place through centrifugal 
nerves coming from segments of the cord higher up. 
5. Law of Generalization.—When the irritation becomes very intense, it 
is propagated in the medulla oblongata; motor reaction then becomes 
general, and it is propagated up and down the cord, so that all the 
muscles of the body are thrown into action, the medulla oblongata acting 
as a focus whence radiate all reflex movements. 
Special Reflex Movements. 
There are a number of reflex movements taking place through the spinal 
cord, a study of which enables the physician to determine the condition of 
its different segments. They may be divided into :— 
1. Skin or superficial, and 
2. Tendon or deep reflexes. 
The skin reflexes are induced by irritation of the skin and mucous mem- 
branes, e.g., pricking, pinching, scratching, etc. The following are the 
principal skin reflexes :— 
I. Plantar reflex, consisting of contraction of the muscles of the foot, in- 
duced by stimulation of the sole of the foot; it involves the integrity of 
the reflex arc through the lower end of the cord. 162 
HUMAN PHYSIOLOGY. 
2. Gluteal reflex, consisting of contraction of the glutei muscles when the 
skin over the buttock is stimulated; it takes place through the segments 
giving origin to the 4th and 5th lumbar nerves. 
3. Cremasteric reflex, consisting of a contraction of the cremaster muscle, 
and a retraction of the testicle toward the abdominal ring, when the skin 
on the inner side of the thigh is stimulated ; it depends upon the integrity 
of the segments giving origin to the 1st and 2d lumbar nerves. 
4. Abdominal reflex, consisting of a contraction of the abdominal muscles 
when the skin upon the side of the abdomen is gently scratched ; its pro- 
duction requires the integrity of the spinal segments from the 8th to 
the 12th. 
5. Epigastric reflex, consisting of a slight muscular contraction in the 
neighborhood of the epigastrium when the skin between the 4th and 
6th ribs is stimulated ; it requires the integrity of the cord between the 
4th and 7th dorsal nerves. 
6. Scapular reflex consists of a contraction of the scapular muscles when 
the skin between the scapula is stimulated ; it depends upon the integrity 
of the cord between the 5 th cervical and 3d dorsal nerves. 
The superficial reflexes, though variable, are generally present in health. 
They are increased or exaggerated when the gray matter of the cord is 
abnormally excited, as in tetanus, strychnia poisoning, and in disease of the 
lateral columns, leading to arrest of their normal functions. The tendon or 
deep reflexes are also of great value in diagnosing the condition of the 
spinal segments. They are induced by a sharp blow upon a tendon. The 
following are the principal forms:— 
X. Patella reflex or knee jerk, consisting of a contraction of the extensor 
muscles of the thigh when the ligamentum patella is struck between the 
patella and tibia. This reflex is best observed when the legs are freely 
hanging over the edge of a table. The patella reflex is generally pre- 
sent in health, being absent in only two per cent. ; it is greatly exag- 
gerated in lateral sclerosis, in descending degeneration of the cord; it is 
absent in locomotor ataxia and in atrophic lesions of the anterior gray 
cornute. 
2. Ankle Jerk or Reflex.—If the extensor muscles of the leg be placed 
upon the stretch and the tendo Achillis be sharply struck, a quick exten- 
sion of the foot will take place. 
3. Ankle Clonus.—This consists of a series of rhythmical reflex contrac- 
tions of the gastrocnemius muscle, varying in frequency from six to ten 
per second. To elicit this reflex, pressure is made upon the sole so as to 
suddenly and energetically flex the foot at the ankle, thus putting the SPINAL CORD. 
163 
tendo Achillis upon the stretch. The rhythmical movements thus pro- 
duced continue so long as the tension is maintained. Ankle clonus is 
never present in health, but is very marked in lateral sclerosis of the 
cord. 
The toe reflex, peroneal reflex, and wrist reflex are also present in scle- 
rosis of the lateral columns and in the late rigidity of the hemiplegia. 
Special Nerve Centers in Spinal Cord.—Throughout the spinal cord 
there are a number of special nerve centers, capable of being excited re- 
flexly and producing complex coordinated movements. Though for the 
most part independent in action, they are subject to the controlling influences 
of the medulla and brain. 
1. Ciliospinal center, situated in the cord between the lower cervical 
and 3d dorsal vertebra. It is connected with the dilatation of the 
pupil through fibers which emerge in this region and enter the cervical 
sympathetic. Stimulation of the cord in this locality causes dilatation 
of the pupil on the same side; destruction of the cord is followed by 
contraction of the pupil. 
2. Genitospinal center, situated in the lower part of the cord. This is a 
complex center and comprises a series of subordinate centers for the 
control of the muscular movements involved in the acts of defecation, 
micturition, ejaculation of semen, the movements of the uterus during 
parturition, etc. 
3. Vasomotor centers, giving origin to both vasoconstrictor and vasodilator 
fibers, which are distributed throughout the cord. Though acting 
reflexly they are under the dominating influence of the center in the 
medulla. 
4. Sweat centers are also present in various parts of the cord. 
2. As a Conductor. 
The lateral columns, particularly the posterior portions, the “ pyramidal 
tracts,” and the columns of Ttirck, are the channels through which pass 
the voluntary motor impulses from the brain to the large multipolar nerve 
cells in the anterior cornuse of gray matter, and through them become 
connected with the anterior roots which transmit the motor stimuli to 
the muscles. 
The anterior columns, especially the portion surrounding the anterior 
cornuae, the “ anterior radicular zones,” are composed of short longitudinal 
commissural fibers, which serve to connect together different segments of 
the spinal cord, a condition required for the coordination of muscular 
movements. 164 
HUMAN PHYSIOLOGY. 
The posterior columns are composed of short and long commissural 
fibers which connect together different segments of the cord. They are 
insensible to direct irritation, but aid in the coordination of muscular move- 
ments in walking, standing, running, etc. Degeneration of the posterior 
columns gives rise to the lack of muscular coordination observed in loco- 
motor ataxia. 
The gray matter, and especially that portion immediately surrounding 
the central canal, transmits the sensory nerve fibers from the posterior roots 
up to the brain. Decussation of the sensory fibers takes place throughout 
the whole length of the gray matter. 
The multipolar cells of the anterior cornuce are connected with the 
generation and transmission of motor impulses outward; are centers for 
reflex movements; are the trophic centers for the motor nerves and muscu- 
lar fibers to which they are distributed. The anterior roots give passage 
to the vasoconstrictor and vasodilator fibers which exert an influence 
upon the caliber of the blood-vessels. Complete destruction of the anterior 
horns is followed by a paralysis of motion, degeneration of the anterior 
roots, atrophy of muscles and bones, and an abolition of reflex movements. 
Paralysis from Injuries of the Spinal Cord. 
Seat of Lesion.—If it be in the lower part of the sacral canal, there is 
paralysis of the compressor urethrae, accelerator urinae, and sphincter ani 
muscles ; no paralysis of the muscles of the leg. 
At the Upper Limit of the Sacral Region.—Paralysis of the muscles of 
the bladder, rectum, and anus; loss of sensation and motion in the muscles 
of the legs, except those supplied by the anterior crural and obturator, viz.: 
psoas iliacus, Sartorius, pectineus, adductor longus, magnus, and brevis, 
obturator, vastus externus and internus, etc. 
At the Upper Limit of the Lumbar Region.—Sensation and motion para- 
lyzed in both legs ; loss of power over the rectum and bladder; paralysis 
of the muscular walls of the abdomen interfering with expiratory move- 
ments. 
At the Lower Portion of the Cervical Region.—Paralysis of the legs, 
etc., as above ; in addition, paralysis of all the intercostal muscles and con- 
sequent interference with respiratory movements; paralysis of muscles of 
the upper extremities, except those of the shoulders. 
Above the Middle of the Cervical Region.—In addition to the preceding, 
difficulty of deglutition and vocalization, contraction of the pupils, paraly- 
sis of the diaphragm, scalene muscles, intercostals, and many of the acces- 
sory respiratory muscles; death resulting immediately from arrest of re- 
spiratory movements. CRANIAL NERVES. 
165 
CRANIAL NERVES. 
The Cranial Nerves come off from the base of the brain, pass through 
the foramina in the walls of the cranium, and are distributed to the skin, 
muscles, and organs of sense in the face and head. 
According to the classification of Soemmering, there are 12 pairs of 
nerves, enumerating them from before backward, as follows, viz.:— 
1st Pair, or Olfactory. 7th Pair, or Facial, Portio dura. 
2d Pair, or Optic. 8th Pair, or Auditory, Portio mollis. 
3d Pair, or Motor oculi communis. 9th Pair, or Glosso-pharyngeal. 
4th Pair, or Patheticus, Trochlearis. 10th Pair, or Pneumogastric. 
5th Pair, or Trifacial, Trigeminus, nth Pair, or Spinal accessory. 
6th Pair, or Abducens. 12th Pair, or Hypoglossal. 
The Cranial Nerves may also be classified physiologically, according 
to their function, into three groups:— 
1. Nerves of special sense. 
2. Nerves of motion. 
3. Nerves of general sensibility. 
1st Pair. Olfactory. 
Apparent Origin.—From the inferior and internal portion of the ante- 
rior lobes of the cerebrum by three roots, viz. : an external white root, 
which passes across the fissure of Sylvius to the middle lobe of the cere- 
brum ; an internal white root, from the most posterior part of the anterior 
lobe; a gray root, from the gray matter in the posterior and inner portion 
of the inferior surface of the anterior lobe. 
Deep Origin.—Not satisfactorily determined. 
Distribution.—The olfactory nerve, formed by the union of the three 
roots, passes forward along the under surface of the anterior lobe to the 
ethmoid bone, where it expands into the olfactory bulb. This bulb con- 
tains ganglionic cells, is grayish in color, and soft in consistence; it 
gives off from its under surface from 15 to 20 nerve filaments, the true 
olfactory nerves, which pass through the cribriform plate of the ethmoid 
bone, and are distributed to the Schneiderian mucous membrane. This 
membrane extends from the cribriform plate of the ethmoid bone downward, 
about one inch. 
Properties.—The olfactory nerves give rise to neither motor nor sensory 
phenomena when stimulated. They carry simply the special impressions 166 
HUMAN PHYSIOLOGY. 
of odorous substances. Destruction or injury of the olfactory bulbs is 
attended by a loss of the sense of smell. 
Function.—Governs the sense of smell. Conducts the impressions 
which give rise to odorous sensations. 
Apparent Origin.—From the anterior portion of the optic commissure. 
Deep Origin,—The origins and connections of the optic tract are very 
complex. The immediate origins are bands of fibers from the thalamus 
opticus and anterior corpora quadrigemina. The corpora geniculata are 
interposed ganglia. The ultimate roots are traced— 
1. By a broad band of fibers—“the optic radiation of Gratiolet ”—to the 
psycho-optic centers in the occipital lobes. 
2. To the gyrus hippocampi and sphenoidal lobes. 
3. Through the corpus callosum to the motor areas of the opposite cerebral 
hemispheres. 
4. To the frontal region by “ Meynert’s Commissure.” 
5. To the spinal cord. 
6. To the corpora geniculata, pulvinar, and anterior corpora geniculata by 
ganglionic roots. 
Distribution.—The two roots unite to form a flattened band, the optic 
tract, which winds around the crus cerebri to decussate with the nerve of 
the opposite side, forming the optic chiasm. The decussation of fibers is 
not complete; some of the fibers of the left optic tract going to the outer 
half of the eye of the same side, and to the inner half of the eye of the 
opposite side; the same holds true for the right optic tract. 
The optic nerves proper arise from the commissure, pass forward through 
the optic foramina, and are finally distributed in the retince. 
Properties.—They are insensible to ordinary impressions, and convey 
only the special impressions of light. Division of one of the nerves is 
attended by complete blindness in the eye of the corresponding side. 
Hemiopia and Hemianopsia.—Owing to the decussation of the fibers 
in the optic chiasm division of the optic tract produces loss of sight in the 
outer half of the eye of the same side, and in the inner half of the eye 
of the opposite side, the blind part being separated from the normal part 
by a vertical line. The term hemiopia is applied to the loss of function or 
paralysis of the one-half of the retina; hemianopsia is applied to the 
blindness in the field of vision. If, for example, the right optic tract be 
divided, there will be hemiopia in the outer half of the right eye and inner 
2d Pair. Optic. CRANIAL NERVES. 
167 
half of left eye, thus causing left lateral hemianopsia, and as the two 
halves are affected which correspond in normal vision, it is spoken of as 
homonymous hetnianopsia. Lesion of the anterior part of the optic chiasm 
causes blindness in the inner half of the two eyes. 
Functions.—Governs the sense of sight. Receives and conveys to the 
brain the luminous impressions which give rise to the sensation of sight. 
The reflex movements of the iris are called forth by the optic nerve. 
When an excess of light falls upon the retina the impression is carried 
back to the tubercula quadrigemina, where it is transformed into a motor 
impulse, which then passes outward through the motor oculi nerve to the 
contractile fibers of the iris and diminishes the size of the pupil. The 
absence of light is followed by a dilatation of the pupil. 
3d Pair. Motor Oculi Communis. 
Apparent Origin.—From the inner surface of the crura cerebri. 
Deep Origin.—By three sets of filaments coming from the oculo- 
motorius nucleus, which lies under the aqueduct of Sylvius; these three 
groups of filaments are destined for the innervation of the muscles of the 
eyeball, the sphincter pupillae, and the ciliary muscle. By filaments coming 
from the lenticular nucleus, corpora quadrigemina, optic thalamus ; these 
filaments converge to form a main trunk, which winds around the crus 
cerebri, in front of the pons Varolii. 
Distribution.—The nerve then passes forward, and enters the orbit 
through the sphenoidal fissure, where it divides into a superior branch dis- 
tributed to the superior rectus and levator palpebrce muscles; an inferior 
branch sending branches to the internal and inferior recti, and the in- 
ferior oblique muscles; filaments also pass into the ciliary or ophthalmic 
ganglion; from this ganglion the ciliary nerves arise which enter the eye- 
ball, and are distributed to the circular fibers of the iris and the ciliary 
muscle. The 3d nerve also receives filaments from the cavernous plexus 
of the sympathetic and from the 5th nerve. 
Properties.—Irritation of the root of the nerve produces contraction 
of the pupil, internal strabismus, muscular movements of eye, but no pain. 
Division of the nerve is followed by ptosis (falling of the upper eyelid), 
external strabismus, due to the unopposed action of the external rectus 
muscle; paralysis of the accommodation of the eye; dilatation of the 
pupil from paralysis of the circular fibers of the iris and ciliary muscle; 
and inability to rotate the eye, slight protrusion, and double vision. The 168 
HUMAN PHYSIOLOGY. 
images are crossed ; that of the paralyzed eye is a little above that of the 
sound, and its upper end inclined toward it. 
Function.—Governs movements of the eyeball by animating all the 
muscles except the external rectus and superior oblique, the movements of 
the iris, elevates the upper lid, influences the accommodation of the eye 
for distances. Can be called into action by (1) voluntary stimuli, (2) by 
reflex action through irritation of the optic nerve. 
' 4th Pair. Patheticus. 
Apparent Origin.—From the superior peduncles of the cerebellum. 
Deep Origin.—By fibers terminating in the corpora quadrigemina, 
lenticular nucleus, valve of Vieussens, and in the substance of the cerebellar 
peduncles; some filaments pass over the median line and decussate with 
fibers of the opposite side. 
Distribution.—The nerve enters the orbital cavity through the sphe- 
noidal fissure, and is distributed to the superior oblique muscle; in its 
course receives filaments from the ophthalmic branch of the 5 th pair and 
the sympathetic. 
Properties.—When the nerve is irritated muscular movements are pro- 
duced in the superior oblique muscle, and the pupil of the eye is turned 
dozunward and outward. Division or paralysis lessens the movements 
and rotation of the globe downward and outward. The diplopia conse- 
quent upon this paralysis is homonymous, one image appearing above the 
other. The image of the paralyzed eye is below, its upper end inclined 
toward that of the sound eye. 
Function.—Governs the movements of the eyeball produced by the 
action of the superior oblique muscles. 
6th Pair.* Abducens. Motor Oculi Externus. 
Apparent Origin.—From the groove between the anterior pyramidal 
body and the pons Varolii, where it arises by two roots. 
Deep Origin.—From the gray matter of the medulla oblongata. 
Distribution.—The nerve then passes into the orbit through the sphe- 
noidal fissure, and is distributed to the external rectus muscle. Receives 
* The 6th nerve is considered in connection with the 3d and 4th nerves, since they 
together constitute the motor apparatus by which the ocular muscles are excited to 
action. CRANIAL NERVES. 
169 
filaments from the cervical portion of the sympathetic, through the carotid 
plexus, and sphenopalatine ganglion. 
Properties.—When irritated, the external rectus muscle is thrown into 
convulsive movements and the eyeball is turned outward. When divided 
or paralyzed, this muscle is paralyzed, motion of the eyeball outward past 
the median line is impossible, and the homonymous diplopia increases as 
the object is moved outward past this line. The images are upon the same 
plane and parallel. Internal strabismus results because of the unopposed 
action of the internal rectus. 
Function.—To turn the eyeball outward. 
5th Pair. Trifacial. Trigeminal. 
Apparent Origin.—By two roots from the side of the pons Varolii. 
Deep Origin.—The deep origin of the two roots is the upper part of 
the floor and anterior wall of the fourth ventricle, by three bundles of fila- 
ments, one of which anastomoses with the auditory nerve; another passes 
to the lateral tract of the medulla; while a third, grayish in color, goes to 
the restiform bodies, and may be traced to the point of the calamus scrip- 
torius. 
Filaments of origin have been traced to the “trigeminal sensory nucleus,” 
located on a level with the point of exit of the nerve, and to the posterior 
gray horns of the cord, as low down as the middle of the neck. 
Distribution.—The large root of the nerve passes obliquely upward 
and forward to the ganglion of Gasser, which receives filaments of com- 
munication from the carotid plexus of the sympathetic. It then divides 
into three branches:— 
1. Ophthalmic branch, which receives communicating filaments from the 
sympathetic, and sends sensitive fibers to all the motor nerves of the 
eyeball. It is distributed to the ciliary ganglion, lacrimal gland, sac 
and caruncle, conjunctiva, integument of the upper eyelid, forehead, side 
of head and nose, anterior portion of the scalp, ciliary muscle, and iris. 
2. Superior maxillary branch, sends branches to the spheno-palatine 
ganglion, integument of the temple and lower eyelid, side of forehead, 
nose, cheek, and upper lip, teeth of the upper jaw, and alveolar processes. 
3. Inferior maxillary branch, which, after receiving in its course filaments 
from the small root and from the facial, is distributed to the submaxil- 
lary ganglion, the parotid and sublingual glands, external auditory 
meatus, mucous membrane of the mouth, anterior two-thirds of the tongue 
(lingual branch), gums, arches of the palate, teeth of the lower jaw 170 
HUMAN PHYSIOLOGY. 
and integument of the lower part of the face, and to the mtiscles of 
tnastication. 
The small root passes forward beneath the ganglion of Gasser, through 
the foramen ovale, and joins the inferior maxillary division of the large 
root, which then divides into an anterior and posterior branch, the former 
of which is distributed to the muscles of mastication, viz.: temporal, mas- 
seter, internal and external pterygoid muscles. 
Properties.—It is the most acutely sensitive nerve in the body, and 
endows all the parts to which it is distributed with general sensibility. 
Irritation of the large root, or any of its branches, will give rise to 
marked evidence of pain; the various forms of neuralgia of the head and 
face being occasioned by compression, disease, or exposure of some of its 
terminal branches. 
Division of the large root within the cranium is followed at once by a 
complete abolition of all sensibility in the head and face, but is not attended 
by any loss of motion. The integument, mucous membranes, and the eye 
may be lacerated, cut, or bruised without the animal exhibiting any evidence 
of pain. At the same time the lacrimal secretion is diminished, the pupil 
becomes contracted, the eyeball is protruded, and the sensibility of the 
tongue is abolished. 
The reflex movements of deglutition are also somewhat impaired; the 
impression of the food being unable to reach and excite the nerve center in 
the medulla oblongata. 
Galvanization of the small root produces movements of the muscles of 
mastication ; section of the root causes paralysis of these muscles, and the 
jaw is drawn to the opposite side by the action of the opposing muscles. 
Influence of the Special Senses.—After division of the large root 
within the cranium, a disturbance in the nutrition of the special senses 
sooner or later manifests itself. 
Sight.—In the course of twenty-four hours the eye becomes very vascular 
and inflamed, the cornea becomes opaque and ulcerates, the humors are 
discharged, and the eye is totally destroyed. 
Smell.—The nasal mucous membrane swells up, becomes fungous, and 
is liable to bleed on the slightest irritation. The mucus is increased in 
amount, so as to obstruct the nasal passages; the sense of smell is finally 
abolished. 
Hearing.—At times the hearing is impaired from disorders of nutrition 
in the middle ear and external auditory meatus. 
Alteration in the nutrition of the special senses is not marked if the sec- CRANIAL NERVES. 
171 
tion is made posterior to the ganglion of Gasser, and to the anastomosing 
filaments of the sympathetic which join the nerve at this point; but if the 
ganglion be divided, these effects are very noticeable, due to the section of 
the sympathetic filaments. 
Function.—Gives sensibility to all parts of the head and face to which 
it is distributed ; through the small root endows the masticatory muscles 
with motion; through fibers from the sympathetic governs the nutrition of 
the special senses. 
7th Pair. Portio Dura. Facial Nerve. 
Apparent Origin.—From the groove between the olivary and restiform 
bodies at the lateral portion of the medulla oblongata and below the margin 
of the pons Varolii. 
Deep Origin.—From a nucleus of large cells in the floor of the 4th 
ventricle, below the nucleus of origin of the 6th pair, with which it is 
connected. Some filaments are traceable to the lenticular nucleus of the 
opposite side. Some of the fibers cross the median line and decussate. It 
is intimately associated with the nerve of Wrisberg at its origin. 
Distribution.—From its origin the facial nerve passes into the internal 
auditory meatus, and then, in company with the nerve of Wrisberg, enters 
the aqueduct of Fallopius. The filaments of the nerve of Wrisberg are 
supplied with a ganglion, of a reddish color, having nerve cells. These 
filaments unite with those of the root of the facial to form a common 
trunk, which emerges at the stylomastoid foramen. 
In the aqueduct the facial gives off the following branches, viz.:— 
1. Large petrosal nerve, which passes forward to the sphenopalatine, or 
Meckel’s ganglion, and through this to the levator palati and azygos 
uvulae muscles, which receive motor influence from this source. 
2. Small petrosal nerve, passing to the otic ganglion and thence to the 
tensortympani muscle, endowing it with motion. 
3. Tympanic branch, giving motion to the stapedius muscle. 
4. Chorda tympani nerve, which, after entering the posterior part of the 
tympanic cavity, passes forward between the malleus and incus bones, 
through the Glaserian fissure, and joins the lingual branch of the 5th 
nerve. It is then distributed to the mucous membrane of the anterior 
two-thirds of the tongue and the submaxillary glands. 
After emerging from the stylomastoid foramen, the facial nerve sends 
branches to the muscles of the ear, the occipitofrontalis, the digastric, the 
palatoglossi, and palatopharyngei; after which it passes through the parotid 172 
HUMAN PHYSIOLOGY. 
gland and divides into the temporofacial and cervicofacial branches, which 
are distributed to the superficial muscles of the face, viz.: occipitofrontalis, 
corrugator supercilii, orbicularis palpebrarum, levator labii superioris et 
alaeque nasi, buccinator, levator anguli oris, orbicularis oris, zygomatici, 
depressor anguli oris, platysma myoides, etc. 
Properties.—Undoubtedly a motor nerve at its origin, but in its course 
receives sensitive filaments from the 5th pair and the pneumogastric. 
Irritation of the nerve, after its emergence from the stylomastoid fora- 
men, produces convulsive movements in all the superficial muscles of the 
face. Division of the nerve at this point causes paralysis of these muscles 
on the side of the section, constituting facial paralysis, the phenomena of 
which are a relaxed and immobile condition of the same side of the face ; 
the eyelids remain open, from paralysis of the orbicularis palpebrarum; 
the act of winking is abolished ; the angle of the mouth droops, and saliva 
constantly drains away ; the face is drawn over to the second side; the face 
becomes distorted upon talking or laughing; mastication is interfered with, 
the food accumulating between the gums and cheek, from paralysis of the 
buccinator muscle ; fluids escape from the mouth in drinking; articulation 
is impaired, the labial sounds being imperfectly pronounced. 
Properties of the Branches given off in the Aqueduct of Fallopius.—The 
large petrosal, when irritated, throws the levator palati and azygos uvulae 
muscles into contraction. Paralysis of this nerve, from deep-seated lesions, 
produces a deviation of the uvula to the sound side, a drooping of the palate, 
and an inability to elevate it. 
The small petrosal influences hearing by animating the tensor tympani 
muscle; when paralyzed, there occurs partial deafness and an increased 
sensibility to sonorous impressions. 
The tympanitic branch animates the stapedius muscle and influences 
audition. 
The chorda tympani influences the circulation and the secretion of 
saliva in the submaxillary glands, and governs the sense of taste in the 
anterior two-thirds of the tongue. Galvanization of the chorda tympani 
dilates the blood-vessels, increases the quantity and rapidity of the stream 
of blood, and increases the secretion of saliva. Division of the nerve is 
followed by contraction of the vessels, an arrestation of the secretion, and 
a diminution of the sense of taste, on the same side. 
Function.—The facial is the nerve of expression, and coordinates the 
muscles employed to delineate the various emotions, influences the sense 
of taste, deglutition, movements of the uvula and soft palate, the tension of CRANIAL NERVES. 
173 
the membrana tympani, and the secretions of the submaxillary and parotid 
glands. Indirectly influences smell, hearing, and vision. 
8th Pair. Portio Mollis. Auditory Nerve 
Apparent Origin.—From the upper and lateral portion of the medulla 
oblongata, just below the margin of the pons Varolii. 
Deep Origin.—By two roots from the floor of the 4th ventricle, each 
root consisting of a number of gray filaments, some of which decussate in 
the median line ; the external root has a gangliform enlargement contain- 
ing fusiform nerve cells. 
Distribution.—The two roots wind around the restiform bodies and 
enter the internal auditory meatus, and divide into an anterior branch dis- 
tributed to the cochlea, and a posterior branch distributed to the vestibule 
and semicircular canals. 
Properties.—They are soft in consistence, grayish in color, consisting 
of axis cylinders with a medullary sheath only; they are not sensible to 
ordinary impressions, but convey the impression of soimd. 
Function.—Governs the sense of hearing. Receives and conducts to 
the brain the impression of sound, which gives rise to the sensations of 
hearing. 
gth Pair. Glossopharyngeal. 
Apparent Origin.—Partly from the medulla oblongata and the inferior 
peduncles of the cerebellum. 
Deep Origin.—From the lower portion of the gray substance in the 
floor of the 4th ventricle. 
This nerve has two ganglia; the jugular ganglion includes only a portion 
of the root filaments; the ganglion of Andersch includes all the fibers of 
the trunk. 
Distribution.—The trunk of the nerve passes downward and forward, 
receiving near the ganglion of Andersch fibers from the facial and pneu- 
mogastric nerves. It divides into two large branches, one of which is 
distributed to the base of the tongue, the other to the pharynx. In its 
course it sends filaments to the otic ganglion; a tympanic branch which 
gives sensibility to the mucous membrane of the fenestra rotunda, fenestra 
ovalis, and Eustachian tube; lingual branches to the base of the tongue ; 
palatal branches to the soft palate, uvula, and tonsils ; pharyngeal branches 
to the mucous membrane of the pharynx. 
Properties.—Irritation of the roots at their origin calls forth evidences 
of pain; it is, therefore, a sensory nerve, but its sensibility is not so acute 174 
HUMAN PHYSIOLOGY. 
as that of the trifacial. Irritation of the trunk after its exit from the 
cranium produces contraction of the muscles of the palate and pharynx, 
due to the presence of anastomosing motor fibers. 
Division of the nerve abolishes sensibility in the structures to which it is 
distributed and impairs the sense of taste in the posterior third of the 
tongue (see Sense of Taste). 
Function.—Governs sensibility of pharynx, presides partly over the 
sense of taste, and controls reflex movements of deglutition and vomiting. 
10th Pair. Pneumogastric. Par Vagum. 
Apparent Origin.—From the lateral side of the medulla oblongata, just 
behind the olivary body. 
Deep Origin.—In the gray nuclei in the lower half of the floor of the 
4th ventricle and in the substance of the restiform body. Some filaments 
are traced along the restiform tract, toward the cerebellum, and others to the 
median line of the floor of the 4th ventricle, where many of them decussate. 
This nerve has two ganglia, one in the jugular foramen, called the gan- 
glion of the root, and another outside of the cranial cavity on the trunk, the 
ganglion of the trunk. 
Distribution.— The filaments from the root unite to form a single trunk, 
which leaves the cavity of the cranium, through the jugular foramen, in 
company with the spinal accessory and glossopharyngeal. It soon receives 
an anastomotic branch from the spinal accessory, and afterward branches 
from the facial, the hypoglossal, and the anterior branches of the two upper 
cervical nerves. 
As the nerve passes down the neck it sends off the following main 
branches:— 
1. Pharyngeal nerves, which assist in forming the pharyngeal plexus, 
which is distributed to the mucous membrane and muscles of the pharynx. 
2. Superior laryngeal nerve, which enters the larynx through the thyro- 
hyoid membrane, and is distributed to the mucous membrane lining the 
interior of the larynx, and to the cricothyroid muscle and the inferior 
constrictor of the pharynx. The “ depressor nerve," found in the rabbit, 
is formed by the union of two branches, one from the superior laryngeal, 
the other from the main trunk ; it passes downward to be distributed to 
the heart. 
3. Inferior laryngeal, which sends its ultimate branches to all the intrinsic 
muscles of the larynx except the cricothyroid, and to the inferior con- 
strictor of the pharynx. CRANIAL NERVES. 
175 
4. Cardiac branches given off from the nerve throughout its course, which 
unite with the sympathetic fibers to form the cardiac plexus, to be dis- 
tributed to the heart. 
5. Pulmonary branches, which form a plexus of nerves and are distributed 
to the bronchi and their ultimate terminations, the lobules and air cells. 
From the right pneumogastric nerve branches are distributed to the 
mucous membrane and muscular coats of the stomach and intestines, to the 
liver, spleen, kidneys, and suprarenal capsules. 
Properties.—At its origin the pneumogastric nerve is sensory, as shown 
by direct irritation or galvanization, though its sensibility is not very 
marked. In its course it exhibits motor properties, from anastomosis with 
motor nerves. 
The pharyngeal branches assist in giving sensibility to the mucous 
membrane of the pharynx, and influence reflex phenomena of deglutition 
through motor fibers which they contain, derived from the spinal accessory. 
The superior laryngeal nerve endows the upper portion of the larynx 
with sensibility; protects it from the entrance of foreign bodies; by con- 
ducting impressions to the medulla, excites the reflex movements of deglu- 
tition and respiration ; through the motor filaments it contains produces 
contraction of the cricothyroid muscle. 
Division of the “ depressor nerve ” and galvanization of the central 
end retard and even arrest the pulsations of the heart, and by depressing 
the vasomotor center diminish the pressure of blood in the large vessels, by 
causing dilatation of the intestinal vessels through the splanchnic nerves. 
The inferior laryngeal contains, for the most part, motor fibers from 
the spinal accessory. When irritated, produces movement in the laryn- 
geal muscles. When divided, is followed by paralysis of these muscles, 
except the cricothyroid, impairment of phonation, and an embarrassment 
of the respiratory movements of the larynx, and, finally, death from suffo- 
cation. 
The cardiac branches, through filaments derived from the spinal acces- 
sory, exert a direct inhibitory action upon the heart. Division of the 
pneumogastrics in the neck increases the frequency of the heart’s action. 
Galvanization of the peripheral ends diminishes the heart’s pulsation, and, 
if sufficiently powerful, paralyzes it in diastole. 
The pulmonary branches give sensibility to the bronchial mucous 
membrane and govern the movements of respiration. Division of both 
pneumogastrics in the neck diminishes the frequency of the respiratory 
movements, falling as low as four to six per minute; death usually occurs 
in from five to eight days. Feeble galvanization of the central ends of the 176 
HUMAN PHYSIOLOGY. 
divided nerves accelerates respiration ; powerful galvanization retards, 
and may even arrest, the respiratory movements. 
The gastric branches give sensibility to the mucous coat, and through 
sympathetic filaments, which join the pneumogastrics high up in the neck, 
give motion to the muscular coat of the stomach. They influence the 
secretion of gastric juice, aid the process of digestion and absorption from 
the stomach. 
The hepatic branches, probably through anastomosing sympathetic fila- 
ments, influence the secretion of bile and the glycogenic function of the 
liver; division of the pneumogastrics in the neck produces congestion of 
the liver, diminishes the density of the bile, and arrests the glycogenic 
function ; galvanization of the central ends exaggerates the glycogenic 
function and makes the animal diabetic. 
The intestinal branches give sensibility and motion to the small intes- 
tines, and when divided, purgatives generally fail to produce purgation. 
Function.—A great sensitive nerve, which, through anastomotic fila- 
ments from motor sources, influences deglutition, the action of the heart, 
the circulatory and respiratory systems, voice, the secretions of the stomach, 
intestines, and various glandular organs. 
nth Pair. Spinal Accessory 
Apparent Origin.—By two sets of filaments :— 
1. A bulbar or medullary set, four or five in number, from the lateral or 
motor tract of the lower half of the medulla oblongata, below the origin 
of the pneumogastric. 
2. A spinal set, from six to eight in number, from the lateral portion of the 
spinal cord, between the anterior and posterior roots of the upper four or 
five cervical nerves. 
Deep Origin.—The medullary portion arises in a nucleus in the lower 
half of the floor of the 4th ventricle, common to the pneumogastric and 
glossopharyngeal nerves. The spinal portion has its origin in an elongated 
nucleus lying along the external surface of the anterior cornua of the spinal 
cord, extending down to the 5th cervical vertebra. 
Distribution.—From this origin the fibers unite to form a main trunk, 
which enters the cranial cavity through the foramen magnum, where it is 
at times joined by fibers from the posterior roots of the two upper cervical 
nerves, and sends filaments to the ganglion of the root of the pneumo- 
gastric. After emerging from the cranial cavity through the jugular fora- 
men, it sends a branch to the pneumogastric and receives others in return, CRANIAL NERVES. 
177 
and also from the 2d, 3d, and 4th cervical nerves. It divides into two 
branches :— 
1. An internal or anastomotic branch, made up of filaments coming prin- 
cipally from the medulla oblongata, and is distributed to the muscles of 
the pharynx through the pharyngeal nerves coming from the pneumo- 
gastric ; to all the muscles of the larynx, except the cricothyroid, through 
the inferior laryngeal nerve; to the heart, by filaments which reach it 
through the pneumogastric nerve. 
2. An external branch, which is distributed to the sternocleidomastoid and 
trapezius muscles ; these muscles also receiving filaments from the cer- 
vical nerves. 
Properties.—At its origin it is a purely motor nerve, but in its course 
exhibits some sensibility from anastomosing fibers. 
Destruction of the medullary root, by tearing it from its attachment by 
means of forceps, impairs the action of the muscles of deglutition and 
destroys the power of producing vocal sounds by paralysis of the laryngeal 
muscles, without, however, interfering with the respiratory movements of 
the larynx, these being controlled by other motor nerves. The normal 
rate of movement of the heart is also impaired by destruction of the medul- 
lary root. 
Irritation of the external branch throws the trapezius and sternomastoid 
muscles into convulsive movements, though section of the nerve does not 
produce complete paralysis, as they are also supplied with motor influence 
from the cervical nerves. The sternomastoid and trapezius muscles per- 
form movements antagonistic to those of respiration, fixing the head, neck, 
and upper part of the thorax, and delaying the expiratory movement during 
the acts of pushing, pulling, straining, etc., and in the production of a pro- 
longed vocal sound, as in singing. When the external branch alone is 
divided, in animals, they experience shortness of breath during exercise, 
from a want of coordination of the muscles of the limbs and respiration ; 
and while they can make a vocal sound, it cannot be prolonged. 
Function.—Governs phonation by its influence upon the vocal move- 
ments of the glottis; influences the movements of deglutition, inhibits the 
action of the heart, and controls certain respiratory movements associated 
with sustained or prolonged muscular efforts and phonation. 
12th Pair. Hypoglossal or Sublingual. 
Apparent Origin.—By two groups of filaments from the medulla ob- 
longata, in the grooves between the olivary body and the anterior pyramid. 178 
HUMAN PHYSIOLOGY. 
Deep Origin.—From the hypoglossal nucleus situated deeply in the 
substance of the medulla, on a level with the lowest portion of the floor of 
the 4th ventricle; some decussating filaments have been traced to a higher 
encephalic center. 
Distribution.—The trunk formed by a union of the root filament passes 
out of the cranial cavity through the anterior condyloid foramen, occa- 
sionally receiving a filament from the lateral and posterior portion of the 
medulla oblongata. After emerging from the cranium, it sends filaments 
to the sympathetic and pneumogastric; it anastomoses with the lingual 
branch of the 5th pair, and receives and sends filaments to the upper cer- 
vical nerves. The nerve is finally distributed to the sternohyoid, sterno- 
thyroid, omohyoid, thyrohyoid, styloglossi, hyoglossi, geniohyoid, geniohyo- 
glossi, and the intrinsic muscles of the tongue. 
Properties.—A purely motor nerve at its origin, but derives sensibility 
outside the cranial cavity from anastomosis with the cervical, pneumogas- 
tric, and 5th nerves. 
Irritation of the nerve gives rise to convulsive movements of the tongue 
and slight evidences of sensibility. 
Division of the nerve abolishes all movements of the tongue and inter- 
feres considerably with the act of deglutition. 
When the hypoglossal nerve is involved in hemiplegia, the tip of the 
tongue is directed to the paralyzed side when the tongue is protruded, due 
to the unopposed action of the geniohyoglossus on the sound side. 
Articulation is considerably impaired in paralysis of this nerve, great 
difficulty being experienced in the pronunciation of the consonantal sounds. 
Mastication is performed with difficulty, from inability to retain the food 
between the teeth until it is completely triturated. 
Function.—Governs all the movements of the tongue and influences 
the functions of mastication, deglutition, and articulate language. 
MEDULLA OBLONGATA. 
The Medulla Oblongata is the expanded portion of the upper part ot 
the spinal cord. It is pyramidal in form and measures one and a half 
inches in length, three-quarters of an inch in breadth, half an inch in 
thickness, and is divided into two lateral halves by the anterior and pos- 
terior median fissures, which are continuous with those of the cord. Each 
half is again subdivided by minor grooves into four columns, viz.: ante7-ior MEDULLA OBLONGATA. 
179 
Pyramid, lateral tract and olivary body, restiform body, and posterior 
pyramid. 
i. The anterior pyramid is composed partly of fibers continuous with those 
of the anterior column of the spinal cord, but mainly of fibers derived 
from the lateral tract of the opposite side by decussation. The united 
fibers then pass upward through the pons Varolii and crura cerebri, and 
for the most part terminate in the corpus striatum and cerebrum. 
Fig. 18.—View of Cerebellum in Section, and of 4TH Ventricle, with the 
Neighboring Parts.—(From Sappey.) 
i. Median groove 4th ventricle, ending below in the calamus scriptorius, with the 
longitudinal eminences formed by the fasciculi teretes, one on each side. 2. The 
same groove, at the place where the white streaks of the auditory nerve emerge 
from it to cross the floor of the ventricle. 3. Inferior peduncle of the cerebellum, 
formed by the restiform body. 4. Posterior pyramid; above this is the calamus 
scriptorius. 5. Superior peduncle of cerebellum, or processus e cerebello ad testes. 
6, 6. Fillet to the side of the crura cerebri. 7, 7. Lateral grooves of the crura cere- 
bri. 8. Corpora quadrigemina.— {After Hirschfeld and Leveille.) 
2. The lateral tract is continuous with the lateral columns of the cord ; 
its fibers in passing upward take three directions, viz.: an external bun- 
dle joins the restiform body, and passes into the cerebellum ; an internal 
bundle decussates at the median line and joins the opposite anterior pyra- 
mid ; a middle bundle ascends beneath the olivary body, behind the 
pons, to the cerebrum, as the fasciculus teres. The olivaty body of each 180 
HUMAN PHYSIOLOGY. 
side is an oval mass, situated between the anterior pyramid and restiform 
body; it is composed of white matter externally and gray matter inter- 
nally, forming the corpus dentatum. 
3. The restiform body, continuous with the posterior column of the cord, 
also receives fibers from the lateral column. As the restiform bodies 
pass upward they diverge and form a space, the 4th ventricle, the floor 
of which is formed by gray matter, and then turn backward and enter 
the cerebellum. 
4. The posterior pyramid is a narrow, white cord bordering the posterior 
median fissure ; it is continued upward, in connection with the fasciculus 
teres, to the cerebrum. 
The Gray Matter of the medulla is continuous with that of the cord. 
It is arranged with much less regularity, becoming blended with the white 
matter of the different columns, with the exception of the anterior. By the 
separation of the posterior columns, the transverse commissure is exposed, 
forming part of the floor of the 4th ventricle; special collections of gray 
matter are found in the posterior portions of the medulla, connected with 
the rootg of origin of different cranial nerves. 
Properties and Functions.—The medulla is excitable anteriorly and 
sensitive posteriorly to direct irritation. It serves— 
1. As a conductor of sensitive impressions upward from the cord, through 
the gray matter to the cerebrum. 
2. As a conductor of voluntary impulses from the brain to the spinal cord 
and nerves, through its anterior pyramids. 
3. As a conductor of coordinating impulses from the cerebellum, through 
the restiform bodies to the spinal cord. 
As an Independent Reflex Center.—The medulla oblongata con- 
tains special collections of gray matter, which constitute independent nerve 
centers which preside over different functions, some of which are as fol- 
lows, viz.: — 
1. A center which controls the movements of mastication, through afferent 
and efferent nerves. (See page 82.) 
2. A center reflecting impressions which influence the secretion of saliva. 
(See page 86.) 
3. A center for sucking, mastication, and deglutition, whence are derived 
motor simuli exciting to action and coordinating the muscles of the palate, 
pharynx, and esophagus, necessary for the swallowing of the food. The 
secretion of'saliva is also controlled by a center in the medulla. MEDULLA OBLONGATA. 
181 
NERVOUS CIRCLE OF DEGLUTITION. 
2d and 3d Stages. 
Excitor 
or 
Centripetal 
Nerves. 
Palatal branch of the 5th pair. 
Pharyngeal branches of the glosso-pharyngeal. 
Superior laryngeal branches of the pneumogastric 
Esophageal branches of the pneumogastric. 
Motor 
or 
Centrifugal 
Nerves. 
Pharyngeal branches of the pneumogastric, derived 
from the spinal accessory. 
Hypoglossal and branches of the cervical plexus. 
Inferior or recurrent laryngeal. 
Motor filaments of the 3d division of the 5th pair. 
Portio dura. 
4. A center which coordinates the muscles concerned in the act of vomiting. 
5. A speech center, coordinating the various muscles necessary for the ac- 
complishment of articulation through the hypoglossal, facial nerves, and 
the 2d division of the 5th pair. 
6. A center for the harmonization of muscles concerned in expression, 
reflecting its impulses through the facial nerve. 
7. A cardiac center, which exerts (1) an accelerating influence over the 
heart’s pulsations through accelerating nerve fibers emerging from the 
cervical portion of the cord, entering the inferior cervical ganglion, and 
thence passing to the heart; (2) an inhibitory or retarding influence upon 
the action of the heart, through fibers of the spinal accessory nerve run- 
ning in the trunk of the pneumogastric. The cardio-inhibitory center is 
in a state of tonic excitement and continuously sending impulses to the 
heart which exert an inhibitory influence upon its action. It may be 
stimulated directly by anemia as well as venous hyperemia of the blood- 
vessels of the medulla and increased venosity of the blood. It is excited 
reflexly by the stimulation of the central end of the vagus, sciatic, and 
splanchnic nerves. 
8. A vasomotor center, which, by alternately contracting and dilating the 
blood-vessels through nerves distributed in their walls, regulates the 
quantity of blood distributed to an organ or tissue, and thus influences 
nutrition, secretion, and calorification. The vasomotor center is situated 
in the medulla oblongata and pons Varolii, between the corpora quadri- 
gemina and the calamus scriptorius. The vasomotor fibers having their 
origin in this center descend through the interior of the cord, emerge 
through the anterior roots of spinal nerves, enter the ganglia of the sym- 
pathetic, and thence pass to the walls of the blood-vessels, and maintain 
the arterial tonus; they may be divided into two classes, viz.: vaso- 
dilators, e. g., chorda tympani, and vasoconstrictors, e. g., sympathetic 
fibers. 182 
HUMAN PHYSIOLOGY. 
Division of the cord at the lower border of the medulla is followed by a 
dilatation of the entire vascular system and a marked fall of the blood pres- 
sure. Galvanic stimulation of the divided surface of the cord is followed 
by a contraction of the blood vessels and a rise in the blood pressure. 
The vasomotor center is stimulated directly by the condition of the 
blood in the medulla oblongata. When it is highly venous it becomes very 
active and the blood-vessels throughout the body are contracted and the 
blood current becomes swifter; sudden anemia of the medulla has a similar 
effect. This center may be increased in action, with attendant rise of blood 
pressure, by irritation of certain afferent nerve fibers. These are known 
as pressor fibers. On the other hand, its action may be depressed by 
other afferent fibers with attendant fall of blood pressure. These are 
known as depressor fibers. 
9. A diabetic center, irritation of which causes an increase in the amount 
of urine secreted and the appearance of a considerable quantity of sugar. 
10. Respiratory center, situated near the origin of the pneumogastric 
nerves, presides over the movements of respiration and its modifications, 
laughing, singing, sobbing, sneezing, etc. It may be excited rejlexly by 
the presence of carbonic acid in the lungs irritating the terminal pneumo- 
gastric filaments; or automatically, according to the character of the 
blood circulating through it; an excess of carbonic acid or a diminution 
of oxygen increasing the number of respiratory movements; a reverse 
condition diminishing the respiratory movements. 
it. A spasm center, stimulation of which gives rise to convulsive phe- 
nomena, such as coughing, sneezing, etc. 
12. A center for certain ocular functions, governing the closure of the 
eyelids and dilatation of the pupil. 
13. A sweat center is also localized in the medulla. 
NERVOUS CIRCLE OF RESPIRATION 
tj. . 
Centripetal 
Nerves 
Pulmonary branches of the pneumogastric. 
Superior laryngeal. 
Trifacial, or 5th pair. 
Nerves of general sensibility. 
Sympathetic nerve. 
(Entirely Reflex'). 
Motor 
, 
Nerves 
Phrenic, distributed to the diaphragm. 
Intercostals, distributed to the intercostal muscles. 
Facial nerve, or portio dura, to the facial muscles. 
External branch of spinal accessory, to the trapezius 
and sternocleidomastoid muscles. CRURA CEREBRI. 
183 
PONS VAROLII. 
The Pons Varolii unites together the cerebrum above, the cerebellum 
behind, and the medulla oblongata below. It consists of transverse and 
longitudinal fibers, amidst which are irregularly scattered collections of gray 
or vesicular nervous matter. 
The transverse fibers unite the two lateral halves of the cerebellum. 
The longitudinal fibers are continuous— 
1. With the anterior pyramids of the medulla oblongata, which, interlacing 
with the deep layers of the transverse fibers, ascend to the crura cerebri, 
forming their superficial or fasciculated portions. 
2. With fibers derived from the olivary fasciculus, some of which pass to 
the tubercula quadrigemina, while others, uniting with fibers from the 
lateral and posterior columns of the medulla, ascend in the deep or 
posterior portions of the crura cerebri. 
Properties and Functions.—The superficial portion is insensible and 
inexcitable to direct irritation ; the deeper portion appears to be excitable, 
consisting of descending motor fibers; the posterior portions are sensible 
but inexcitable to irritation. 
Transmits motor impulses and sensory impressions from and to the 
cerebrum. 
The gray ganglionic matter consists of centers which convert impressions 
into conscious sensations and originate motor impulses, these taking place 
independent of any intellectual process; they are the seat of instinctive 
reflex acts, the centers which assist in the coordination of the automatic 
movements of station and progression. 
CRURA CEREBRI. 
The Crura Cerebri are largely composed of the longitudinal fibers of 
the pons (anterior pyramids, fasciculi teretes); after emerging from the pons 
they increase in size, and become separated into two portions by a layer of 
dark gray matter, the locus niger. 
The superficial portion, the crusla, composed of the anterior pyramids, 
constitutes the motor tract, which terminates, for the most part, in the cor- 
pus striatum, but to some extent, also, in the cerebrum ; the deep portion, 
made up of the fasciculi teretes and posterior pyramids and accessory fibers 184 
HUMAN PHYSIOLOGY. 
from the cerebellum, constitute the sensory tract (the tegmentum), which 
terminates in the optic thalamus and cerebrum. 
Function.—The crura are conductors of motor impulses and sensory 
impressions ; the gray matter, the locus niger, assists in the coordination of 
the complicated movements of the eyeball and iris, through the motor oculi 
communis nerve. They also assist in the harmonization of general muscular 
movements, section of one crus giving rise to peculiar movements of rota- 
tion and somersaults forward and backward. 
The Corpora Quadrigemina are four small, rounded eminences, two 
on each side of the median line, situated immediately behind the 3d 
ventricle, and beneath the posterior border of the corpus callosum. 
The anterior tubercles are oblong from before backward, and larger than 
the posterior, which are hemispherical in shape; they are grayish in color, 
but consist of white matter externally and gray matter internally. 
Both the anterior and posterior tubercles are connected with the optic 
thalami by commissural bands named the anterior and posterior brachia, 
respectively. They receive fibers from the olivary fasciculus and fibers 
from the cerebellum, which pass upward to enter the optic thalami. 
The corpora geniculata are situated, one on the inner side and one on 
the outer side of each optic tract, behind and beneath the optic thalamus, 
and from their position are named the corpora geniculata interna and 
externa ; they give origin to fibers of the optic nerve. 
Functions.—The Tubercula quadrigemina are the physical centers of 
sight, translating the luminous impressions into visual sensations. Destruc- 
tion of these tubercles is immediately followed by a loss of the sense of 
sight; moreover, their action in vision is crossed, owing to the decussation 
of the optic tracts, so that if the tubercle of the right side be destroyed by 
disease or extirpated, in a pigeon, the sight is lost in the eye of the oppo- 
site side, and the iris loses its mobility. 
The tubercula quadrigemina as nerve centers preside over the reflex 
movements which cause a dilatation or contraction of the iris, irritation of 
the tubercles causing contraction, destruction causing dilatation. Removal 
of the tubercles on one side produces a temporary loss of power of the 
opposite side of the body, and a tendency to move around an axis is mani- 
fested, as after a section of one crus cerebri, which, however, may be due 
to giddiness and loss of sight. 
CORPORA QUADRIGEMINA. CORPORA STRIATA AND OPTIC THALAMI. 
185 
They also assist in the coordination of the complex movements of the 
eye, and regulate the movements of the iris during the movements of 
accommodation for distance. 
CORPORA STRIATA AND OPTIC THALAMI. 
The Corpora Striata are two large ovoid collections of gray matter, 
situated at the base of the cerebrum, the larger portions of which are 
imbedded in the white matter, the smaller portions projecting into the 
auterior part of the lateral ventricle. Each striated body is divided, by a 
narrow band of white matter, into two portions, viz. :— 
1. The caudate nucleus, the intraventricular portion, which is conical 
in shape, having its apex directed backward, as a narrow, tail-like process. 
2. The lenticular nucleus, imbedded in the white matter, and for the 
most part external to the ventricle; on the outer side of the lenticular 
nucleus is found a narrow band of white matter, the external capsule ; and 
between it and the convolutions of the island of Reil a thin band of gray 
matter, the claustrum ; the corpora striata are grayish in color, and when 
divided present transverse striations, from the intermingling of white 
fibers and gray cells. 
The Optic Thalami are two oblong masses situated in the ventricles 
posterior to the corpora striata, and resting upon the posterior portion of the 
crura cerebri. The internal surface projecting into the lateral ventricles is 
white, but the interior is grayish, from a commingling of both white fibers 
and gray cells. Separating the lenticular nucleus from the caudate nucleus 
and the optic thalamus is a band of white tissue, the internal capsule. 
The internal capsule is a narrow, bent tract of white matter, and is, for 
the most part, an expansion of the motor tract of the crura cerebri. It 
consists of two segments, an anterior, situated between the caudate nucleus 
and the anterior surface of the lenticular nucleus, and a posterior, situated 
between the optic thalamus and the posterior surface of the lenticular 
nucleus. These two segments unite at an obtuse angle, which is directed 
toward the median line. Pathologic observation has shown that the nerve 
fibers of the direct and crossed pyramidal tracts can be traced upward 
through the anterior two-thirds of the posterior segment into the centrum 
ovale, where, for the most part, they are lost; a portion, however, remain- 
ing united, ascend higher and terminate in the paracentral lobule, the 
superior extremity of the ascending frontal and parietal convolutions. 
The sensory tract can be traced upward, through the posterior third, into 186 
HUMAN PHYSIOLOGY. 
the cerebrum, where they probably terminate in the hippocampus major 
and unciate convolution. 
Functions.—The corpora striata are the centers in which terminate 
some of the fibers of the superficial or motor tract of the crura cerebri; 
others pass upward through the internal capsule, to be distributed to the 
cerebrum. It might be inferred, from their anatomical relations, that they 
are motor centers. Irritation by a weak galvanic current produces mus- 
cular movements of the opposite side of the body; destruction of their 
substance by a hemorrhage, as in apoplexy, is followed by a paralysis of 
motion of the opposite side of the body, but there is no loss of sensation. 
When the hemorrhagic destruction involves the fibers of the anterior two- 
thirds of the posterior segment of the internal capsule, and thus separates 
them from their trophic centers in the cortical motor region, a descending 
degeneration is established, which involves the direct pyramidal tract of the 
same side and the crossed pyramidal tract of the opposite side. 
Destruction of the posterior one-third of the posterior segment of the 
internal capsule is followed by a loss of sensation on the opposite side of 
the body and a loss of the senses of smell and vision on the same side 
(Charcot). The precise function of the corpora striata is unknown, but 
they are in some way connected with motion. 
The optic thalami receives the fibers of the tegmentum, the posterior por- 
tion of the crura cerebri. They are insensible and inexcitable to direct 
irritation. Removal of one optic thalamus, or destruction of its substance by 
disease or hemorrhage, is followed by a loss of sensibility of the opposite 
side of the body, but there is no loss of motion; their precise function is 
also unknown, but in some way connected with sensation. In both cases 
their action is crossed. 
CEREBELLUM. 
The Cerebellum is situated in the inferior fossae of the occipital bone, 
beneath the posterior lobes of the cerebrum. It attains its maximum 
weight, which is about five ozs., between the twenty-fifth and fortieth 
years, the proportion between the cerebellum and cerebrum being I to 84. 
It is composed of two lateral hemispheres and a central elongated lobe, 
the vermiform process ; the two hemispheres are connected with each other 
by the fibers of the middle peduncle forming the superficial portion of the 
pons Varolii. It is brought into connection with the medulla oblongata 
and spinal cord through the prolongation of the restiform bodies; with 
the cerebrum, by fibers passing upward beneath the corpora quadrigemina CEREBELLUM. 
187 
and the optic thalami, and then forming part of the diverging cerebral 
fibers. 
Structure.—It is composed of both white and gray matter, the former 
being internal, the latter external, and convoluted, for economy of space. 
The White matter consists of a central stem, the interior of which is a 
dentated capsule of gray matter, the corpus dentatum. From the external 
surface of the stem of white matter processes are given off, forming the 
lamina, which are covered with gray matter. 
The Gray matter is convoluted and covers externally the laminated pro- 
cesses; a vertical section through the gray matter reveals the following 
structures:— 
1. A delicate connective tissue layer, just beneath the pia mater, containing 
rounded corpuscles, and branching fibers passing toward the external 
surface. 
2. The cells of Purkinje, forming a layer of large, nucleated, branched 
nerve cells sending off processes to the external layer. 
3. A granular layer of small but numerous corpuscles. 
4. Nerve fiber layer, formed by a portion of the white matter. 
Properties and Functions.—Irritation of the cerebellum is not fol- 
lowed by any evidences either of pain or convulsive movements; it is, 
therefore, insensible and inexcilable. 
Coordination of Movements.—Removal of the superficial portions 
of the cerebellum in pigeons produces feebleness and want of harmony in 
the muscular movements; as successive slices are removed, the movements 
become more irregular, and the pigeon becomes restless; when the last 
portions are removed, all power of flying, walking, standing, etc., is en- 
tirely gone, and the equilibrium cannot be maintained, the power of coor- 
dinating muscular movements being entirely gone. The same results have 
been obtained by operating on all classes of animals. 
The following symptoms were noticed by Wagner, after removing the 
whole or a large part of the cerebellum :— 
1. A tendency on the part of the animal to throw itself on one side, and to 
extend the legs as far as possible. 
2. Torsion of the head on the neck. 
3. Trembling of the muscles of the body, which was general. 
4. Vomiting and occasionally liquid evacuations. 
Forced Movements.—Division of one crus cerebelli causes the animal 
to fall on one side and roll rapidly on its longitudinal axis. According to 
Schiff, if the peduncle be divided from behind, the animal falls on the same 188 
HUMAN PHYSIOLOGY. 
side as the injury; if the section be made in front, the animal turns to the 
opposite side. 
Disease of the cerebellum partially corroborates the result of experi- 
ments ; in many cases symptoms of unsteadiness of gait, from a want of 
coordination, have been noticed. 
Comparative anatomy reveals a remarkable correspondence between the 
development of the cerebellum and the complexity of muscular actions. 
It attains a much greater development, relatively to the rest of the brain, in 
those animals whose movements are very complex and varied in character, 
such as the kangaroo, shark, and swallow. 
The cerebellum may possibly exert some influence over the sexual func- 
tion, but physiologic and pathologic facts are opposed to the idea of its 
being the seat of the sexual instinct. It appears to be simply a center for 
the coordination and equilibration of muscular movements. 
CEREBRUM. 
The Cerebrum is the largest portion of the encephalic mass, constitut- 
ing about four-fifths of its weight; the average weight in the adult male is 
from 48 to 50 ounces, or about three pounds, while in the adult female it is 
about five ounces less. After the age of forty the weight of the cerebrum 
gradually diminishes at the rate of one ounce every ten years. In idiots 
the brain weight is often below the normal, at times not amounting to more 
than 20 ounces. 
The Blood Supply to the cerebrum is unusually large, considering its 
comparative bulk, nearly one-fifth of the entire volume of blood being dis- 
tributed to it by the carotid and vertebral arteries. These vessels anasto- 
mose so freely, and are so arranged within the cavity of the cranium, that 
an obstruction in one vessel will not interfere with the regular supply of 
blood to the parts to which its branches are distributed. A diminished 
amount, or complete cessation, of the supply of blood is at once followed 
by a suspension of its functional activity. 
The cerebrum is connected with the pons Varolii and medulla oblongata 
through the crura cerebri, and with the cerebellum through the superior 
peduncles. It is divided into two lateral halves, or hemispheres, by the 
longitudinal fissure running from before backward in the median line; each 
hemisphere is composed of both ivhite and gray matter, the former being 
internal, the latter external; it covers the surfaces of the hemisphere which 
are infolded, forming convolutions, for economy of space. CEREBRUM. 
189 
Fissures. 
1. The fissure of Sylvius is one of the most important; it is the first to 
appear in the development of the fetal brain, being visible at about the 
third month ; in the adult it is quite deep and well marked, running from 
the under surface of the brain upward, outward, and backward, and forms 
a boundary between the frontal and temporosphenoidal lobes. 
2. The fissure of Rolando is second in importance, and runs from a point 
on the convexity near the median line transversely outward and down- 
ward toward the fissure of Sylvius, but does not enter it. It separates 
the frontal from the parietal lobe. 
3. The parietal fissure, arising a short distance behind the fissure of Ro- 
lando, upon the convexity of the hemisphere, runs downward and back- 
ward to its posterior extremity. 
4. The parieto-occipital fissure, separating the occipital from the parietal 
lobes. Beginning upon the outer surface of the cerebrum, it is continued 
on the mesial aspect downward and forward until it terminates in the 
calcarine fissure. 
5. The callosomarginalfissure lying upon the mesial surface, where it runs 
parallel with the corpus callosum. 
Secondary fissures of importance are found in different lobes of the 
cerebrum, separating the various convolutions. In the anterior lobe are 
found the precentral, superior frontal, and inferior frontal fissures ; in 
the temporosphenoidal lobes are found the first and second temporo- 
sphenoidal fissures; in the occipital lobe, the calcarine and hippocampal 
fissures. 
Convolutions. Frontal lobe. 
The ascending frontal convolution situated in front of the fissure of 
Rolando, runs downward and forward; it is continuous above with the 
anterior frontal, and below with the inferior frontal convolution. 
The superior frontal convolution is bounded internally by the longitu- 
dinal fissure, and externally by the superior frontal fissure ; it is connected 
with the superior end of the frontal convolution, and runs downward and 
forward to the anterior extremity of the frontal lobe, where it turns back- 
ward, and rests upon the orbital plate of the frontal bone. 
The middle frontal convolution, the largest of the three, runs from be- 
hind forward, along the sides of the lobe, to its anterior part; it is 
bounded above by the superior and below by the inferior frontal fissures. 
The inferior frontal convolution winds around the ascending branch of 
the fissure of Sylvius, in the anterior and inferior portion of the cerebrum. 
Parietal Lobe.—The ascending pai-ietal convolution is situated just 190 
HUMAN PHYSIOLOGY. 
behind the fissure of Rolando, running downward and forward; above, it 
becomes continuous with the upper parietal convolution, and below, winds 
around to be united with the ascending frontal. 
Fig. 19.—Diagram Showing Fissures and Convolutions of the Left Side of 
the Human Brain. 
F. Frontal. P. Parietal. O. Occipital. T. Temporo-sphenoidal lobe. S. Fissure 
of Sylvius. S'. Horizontal. S". Ascending ramus of S. c. Sulcus centralis, or 
fissure of Rolando. A. Ascending frontal, and B. Ascending parietal, convolution. 
Fj. Superior, F2. Middle, and F3. Inferior frontal convolutions, fj. Superior, 
f2. Inferior, frontal fissures. f3. Sulcus prsecentralis. P. Superior parietal lobule. 
P2. Inferior parietal lobule, consisting of Po Supramarginal gyrus, and P'2. Angular 
gyrus, tp. Sulcus interparietalis. c m. Termination of callosomarginal fissure. 
Oj. First, Oo. Second, 03. Third, occipital convolutions, p o. Parieto-occipital 
fissure, o. Transverse occipital fissure. o2. Inferior longitudinal occipital fissure. 
Tj. First, T2. Second, T3. Temperosphenoidal, convolutions. t\. First, /2. Second, 
temporosphenoidal fissures.—(Landois’ Physiology.} 
The upper parietal convolution is situated between the parietal and 
longitudinal fissures. CEREBRUM. 
191 
The supramarginal convolution winds around the superior extremity of 
the fissure of Sylvius. 
The angular convohction, a continuation of the preceding, follows the 
parietal fissure to its posterior extremity, and then makes a sharp angle 
downward and forward. 
Temporosphenoidal Lobe.—Contains three well-marked convolu- 
tions, the superior, middle, and inferior, separated by well-defined fissures, 
and continuous posteriorly with the convolutions of the parietal lobe. 
The Occipital Lobe lies behind the parieto-occipital fissure, and con- 
tains the superior, middle, and inferior convolutions, not well marked. 
The central lobe, or island of Reil, situated at the bifurcation of the 
fissure of Sylvius, is a triangular-shaped cluster of six convolutions, the 
gyri operli, which are connected with those of the frontal, parietal, and 
temporosphenoidal lobes. 
Upon the inner or mesial aspect of the hemisphere are found (Fig. 16)— 
1. The paracentral lobule, lying in the region of the upper extremity of 
the fissure of Rolando; it contains the large giant cells of Betz. Injury 
to this convolution is followed by degeneration of the motor tract. 
2. The gyrus fornicatus, lying below the callosomarginal fissure. Run- 
ning parallel with the corpus callosum, it terminates at its posterior 
border in the hippocampal gyrus. 
3. The gyrus hippocampus (H) is formed by the union of the preceding 
convolution with the occipitotemporal. It runs forward and terminates 
in a hooked extremity—uncus. 
4. The quadrate lobule or precuneus lies between the upper extremity of 
the callosomarginal fissure and the parieto-occipital. 
5. The cuneus lies posteriorly to the quadrate lobule. It is a wedge- 
shaped mass enclosed by the calcarine and parieto-occipital fissures. 
Structure.—The gray matter of the cerebrum, about one-eighth of an 
inch thick, is composed of five layers of nerve cells:— 
1. A superficial layer, containing a few small multipolar ganglion cells. 
2. Small ganglion cells, pyramidal in shape. 
3. A layer of large pyramidal ganglion cells with processes running oft 
superiorly and laterally. 
4. The granular formation containing nerve cells. 
5. Spindle-shaped and branching nerve cells of a moderate size. 
The white matter consists of three distinct sets of fibers :— 
X. The diverging or peduncular fibers are mainly derived from the columns 
of the cord and medulla oblongata; passing upward through the crura 192 
HUMAN PHYSIOLOGY. 
cerebri, they receive accessory fibers from the olivary fasciculus, corpora 
quadrigemina, and cerebellum. Some of the fibers terminate in the 
optic thalami and corpora striata, while others radiate into the anterior, 
middle, and posterior lobes of the cerebrum. 
2. The transverse commissural fibers connect together the two hemispheres, 
through the corpus callosum and anterior and posterior commissures. 
3. The longitudinal commissural fibers connect together different parts of 
the same hemisphere. 
Fig. 20.—Diagram Showing Fissures and Convolutions on Mesial Aspect of 
the Right Hemisphere. 
Median aspect of the right hemisphere. CC. Corpus callosum divided longitudinally. 
Gf. Gyrus fornicatus. H. Gyrus hippocampi, h Sulcus hippocampi. U. Unci- 
nate gyrus, cm. Calloso marginal fissure. F. P'irst frontal convolution, c. Ter- 
minal portion of fissure of Rolando. A. Ascending frontal, B. Ascending parietal, 
convolution and paracentral lobule. Precuneus or quadrate lobule. Oz Cu- 
neus. Po. Parieto-occipital fissure.’ o\. Transverse occipital fissure, oc. Calcarine 
fissure, oc1. Superior, oc". Inferior, ramus of the same. D. Gyrus descendens. 
T4. Gyrus occipitotemporalis lateralis (lobutus fusiformis). Tg. Gyrus occipitotem- 
poralis medialis (lobulus lingualis). 
Functions.—The cerebral hemispheres are the centers of the nervous 
system through which are manifested all the phenomena of the mind ; they 
are the centers in which impressions are registered, and reproduced subse- 
quently as ideas ; they are the seat of intelligence, reason, and will. 
However important a center the cerebrum may be for the exhibition of 
this highest form of nervous action, it is not directly essential for the con- CEREBRUM. 
193 
tinuance of life, for it does not exert any control over those automatic reflex 
acts, such as respiration, circulation, etc., which regulate the functions of 
organic life. 
Fig. 21.—Side View of the Brain of Man, with the Areas of the Cerebral 
Convolutions according to Ferrier. 
The figures are constructed by marking on the brain of man, in their respective 
situations, the areas of the brain of the monkey as determined by experiment, and 
the description of the effects of stimulating the various areas refers to the brain of 
the monkey. 
i. Advance of the opposite hind limb, as in walking. 2, 3, Complex movements of 
the opposite leg and arm, and of the trunk, as in swimming, a, b, c, d. Individual 
and combined movements of the fingers and wrist of the opposite hand. Prehensile 
movements. 5. Extension forward of the opposite arm and hand. 6 Supination 
and flexion of the opposite forearm. 7. Retraction and elevation of the opposite 
angle of the mouth, by means of the zygomatic muscles. 8. Elevation of the ala 
nasi and upper lip, with depression of the lower lip on the opposite side. 9, 10. 
Opening of the mouth, with (9) protrusion and (10) retraction of the tongue ; region 
of aphasia, bilateral action. 11. Retraction of the opposite angle of the mouth, the 
head turned slightly to one side. 12. The eyes open widely, the pupils dilate, and 
the head and eyes turn toward the opposite side. 13, 13'. The eyes move toward 
the opposite side with an upward (13) or downward (13') deviation. The pupils are 
generally contracted. 14. Pricking of the opposite ear, the head and eyes turn to 
the opposite side, and the pupils dilate largely. 194 
HUMAN PHYSIOLOGY. 
From the study of comparative anatomy, pathology, vivisection, etc., 
evidence has been obtained which throws some light upon the physiology 
of the cerebral hemispheres. 
1. Comparative anatomy shows that there is a general connection between 
the size of the brain, its texture, the depth and number of convolutions, 
and the exhibition of mental power. Throughout the entire animal 
series, the increase in intelligence goes hand in hand with an increase in 
the development of the brain. In man there is an enormous increase in 
size over that of the highest animals, the anthropoids. The most culti- 
vated races of men have the greatest cranial capacity; that of the edu- 
cated European being about 116 cubic inches, that of the Australian 
being about 60 cubic inches, a difference of 56 cubic inches. Men dis- 
tinguished for great mental power usually have large and well-developed 
brains; that of Cuvier weighed 64 ozs.; that of Abercrombie 63 ozs.; 
the average being about 48 to 50 ozs.; not only the size, but, above all, 
the texture, of the brain must be taken into consideration. 
2. Pathology.—Any severe injury or disease disorganizing the hemispheres 
is at once attended by a disturbance, or entire suspension, of mental 
activity. A blow on the head, producing concussion, or undue pressure 
from cerebral hemorrhage, destroys consciousness; physical and chemical 
alterations in the gray matter have been shown to coexist with insanity, 
loss of memory, speech, etc. Congenital defects of organization from 
imperfect development are usually accompanied by a corresponding de- 
ficiency of intellectual power and the higher instincts. Under these 
circumstances no great advance in mental development can be possible, 
and the intelligence remains at a low grade. In congenital idiocy not 
only is the brain of small size, but it is wanting in proper chemical com- 
position, phosphorus, a characteristic ingredient of the nervous tissue, 
being largely diminished in amount. 
3. Experimentation upon the lower animals by removing the cerebral 
hemispheres is attended by results similar to those observed in disease 
and injury. Removal of the cerebrum in pigeons produces complete 
abolition of intelligence, and destroys the capability of performing spon- 
taneous movements. The pigeon remains in a condition of profound 
stupor, which is not accompanied, however, by a loss of sensation, or of 
the power of producing reflex or instinctive movements. The pigeon 
can be temporarily aroused by pinching the feet, loud noises, light placed 
before the eyes, etc., but soon relapses into a state of quietude, being 
unable to remember impressions and connect them with any train of 
ideas, the faculties of memory, reason, and judgment being completely 
abolished. CEREBRAL LOCALIZATION OF FUNCTION. 
195 
CEREBRAL LOCALIZATION OF FUNCTION. 
From experiments made upon animals, and the results of clinical and 
post-mortem observations upon men, it has been shown that the phenomena 
of organic and psychical life are presided over by anatomically localized 
centers in the brain. A knowledge of the position of these centers becomes 
of the highest importance in localizing the seat of lesions, thrombi, hemor- 
rhages, new growths, etc., which show themselves in paralysis, epilepsies, 
etc. It has not been possible to thus localize all functions, and to many 
parts of the brain no special use can be assigned. The following are the 
centers most definitely mapped out and that are of paramount importance :— 
Motor Centers.—These are in the cortical gray matter, and are ar- 
ranged along either side of the fissure of Rolando. This area is known 
as the motor area or motor zone, stimulation of which is followed by con- 
vulsive movements of the muscles of the opposite side of the body, while 
destruction of the gray matter of this area is followed by permanent paral- 
ysis of the muscles of the opposite side. From experiments made upon 
monkeys Ferrier has mapped out a number of motor centers which he has 
transferred to corresponding localities on the human brain (see Fig. 17). 
The descriptive test of the figure renders his results intelligible. Patho- 
logical studies have largely confirmed his deductions. In a general way 
it may be said that the upper third of the ascending frontal and parietal 
convolutions about this fissure preside over the movements of the leg of 
the opposite side of the body; the middle third controls the movements of 
the arm; the upper part of the inferior third is the facial area. The lowest 
part of the inferior third governs the motility of the lips and tongue, and 
this space, with the posterior extremity of the third frontal convolution, 
constitutes the speech center. 
The experiments of Horsley and Schafer have enabled them to furnish 
a new diagrammatic representation of the motor area and to more accurately 
define the special areas upon the lateral and mesial aspects of the brain of 
the monkey. The boundaries of the general and special areas as deter- 
mined by these observers will be readily understood by an examination of 
Figs. 22 and 23. 
For diagnostic purposes the motor areas for the face and limbs have been 
subdivided as follows :— 
I. The face area may be divided into an upper part comprising about one- 
third, and a lower part comprising the remaining two-thirds. In the 
upper part are centers governing the movements of the muscles of the 196 
HUMAN PHYSIOT.OGY. 
opposite angle of the mouth and of the lower face. The anterior portion 
of the lower two-thirds controls the movements of the vocal cords and 
may be regarded as a laryngeal center; the posterior portion governs the 
opening and shutting of the mouth and the protrusion and retraction of 
the tongue. 
2. The upper limb area may be subdivided as follows: The upper part 
controls the movements of the shoulder; posterior and below this point 
are centers for the elbow; below and anteriorly, centers for the wrist 
and finger movements, while lowest and posteriorly centers governing the 
thumb. 
3. The leg area may be subdivided as follows: The anterior part, both on 
the mesial and lateral surfaces, contains centers governing the hip and 
Fig. 22.—Diagram of the Motor Areas on the Outer Surface of a Monkey’s 
Brain.—(Horsley and Schafer.) 
thigh movements; in the posterior part are centers for the movements of 
the leg and toes. The center for the big toe has been located in the 
paracentral lobule. 
4. The trunk area, situated largely on the mesial surface, contains anter- 
iorly centers governing the rotation and arching of the spine, while 
posteriorly are found centers governing movements of the tail and pelvis. 
5. The head area, or area for visual direction, contains centers excitation 
of which causes “ opening of the eyes, dilatation of the pupils, and turn- 
ing of the head to the opposite side, with conjugate deviation of the eyes 
to that side.” 
The centers of origin of the nerves for the ocular muscles lie in the gray 
matter of the aqueduct of Sylvius. Destruction of the gray matter at these CEREBRAL LOCALIZATION OF FUNCTION. 
197 
points is followed by paralysis of the muscles of the opposite side of the 
body, and morbid growths, hemorrhages, or thrombi of the vessels of the 
part result in abnormal stimulation or interference of the functions corre- 
sponding to the nature and extent of the lesion. Cerebral or Jacksonian 
epilepsy is a result of local cortical disease. 
Center for Speech.—Pathological investigations have demonstrated 
that the left 3d frontal convolution is of essential importance for speech. 
Adjoining this convolution are the centers controlling the motility of the 
lips, tongue, etc. In the majority of the cases the speech centers are on the 
left side of the brain, though in exceptional cases they are on the right 
side, especially in left-handed people. In deaf-mutes this convolution is 
very imperfectly developed, while in monkeys it is quite rudimentary. 
Fig. 23.—Diagram of the Motor Areas on the Marginal Convolution of a 
Monkey’s Brain.—(Horsley and Schafer.') 
Lesions of the 3d frontal convolution on the left side, if the patient be 
right-handed, produce the various forms of aphasia or the partial or com- 
plete loss of the power of articulate speech. 
Aphasia is of many degrees and kinds. In ataxic aphasia the patient is 
unable to communicate his thoughts by words, there being an inability to 
execute the movements of the mouth, etc., necessary for speech. In 
agraphic aphasia there is an inability to execute the movements necessary 
for writing, though the mental processes are retained. In the ataxic form 
the lesion is in the 3d frontal convolution, and in the agraphic form it is 
in the arm center. 
In amnesic aphasia there is a loss of the memory of words, the purest 198 
HUMAN PHYSIOLOGY. 
examples of which consist of the affections known as word deafness and 
word blindness. In word deafness the patient cannot understand vocal 
speech, though he is capable of hearing other sounds. This condition is 
associated with lesion of the first temporal convolution. In word blindness 
the patient cannot name a 
letter or a word when 
printed or written, though 
he can see all other objects. 
This condition is associated 
with impairment of the visual 
centers. 
Fig. 24 will illustrate the 
conditions in the various 
forms of aphasia. Impres- 
sions are constantly passing 
from eye and ear to the 
visual and auditory centers 
and there registered. Com- 
missural fibers connect these 
centers with the arm and 
speech centers, which in turn 
are connected by efferent 
fibers with the muscles of 
the hand and vocal appara- 
tus. Muscular movements 
of the eyes, hand, and mouth 
are also registered by means 
of the afferent fibers, s, s', . 
Sensory Centers.— 
These are the centers in 
which the sensory impres- 
sions are coordinated, and 
in which they probably become parts of our consciousness. The most im- 
portant are: — 
The visual center, located in the occipital lobe and especially in the 
cuneus. Unilateral destruction of this area results in hemianopsia, or 
blindness of the corresponding halves of the two retinae. Destruction of 
both occipital lobes in man results in total blindness. Stimulation or irri- 
tation of the visual center causes photopsia, or hallucinations of sight, in 
corresponding halves of the retinae. There have been instances of injury of 
Fig. 24. SYMPATHETIC NERVOUS SYSTEM. 
199 
these parts when sensations of color were abolished with preservation of 
those of space and light, thus showing a special localization of the color 
center. Late experiments show that the centers of the two hemispheres are 
united, as ocular fatigue of a nonused eye was proportional to the fatigue 
of the exercised one. 
The auditory centers are located in the temporosphenoidal lobes. Word 
deafness is associated with softening of these parts, and their complete 
removal results in deafness. 
The gustatory and olfactory centers are located in the uncinate gyrus, 
on the inner side of the temporosphenoidal lobes. There does not seem to 
be any differentiation, up to this time, of these two centers. 
The center for tactile impressions was located by Ferrier in the hippo- 
campal region. Horsley and Schafer found that destructive lesions of the 
gyrus fornicatus was followed by hemianesthesia of the opposite side of the 
body, which was more or less marked and persistent. These observers 
conclude that the limbic lobe “ is largely, if not exclusively, concerned in 
the appreciation of sensations painful and tactile.” 
The superior and middle frontal convolutions appear to be the seat of 
the reason, intelligence, and will. Destruction of these parts is followed 
by proportional hebetude, without any impairment of sensation or motion. 
SYMPATHETIC NERVOUS SYSTEM. 
The Sympathetic Nervous System consists of a chain of ganglia 
connected together by longitudinal nerve filaments, situated on each side of 
the spinal column, running from above downward. The two ganglionic 
cords are connected together in the interior of the cranium by the ganglion 
of Ribes, on the anterior communicating artery, and terminate in the gan- 
glion impar, situated at the top of the coccyx. 
The chain of ganglia is divided into groups, and named according to the 
location in which they are found, viz.: cranial, four in number; cervical, 
three; thoracic, twelve; lumbar, five; sacral, five; coccygeal, one. Each 
ganglion consists of a collection of vesicular nervous matter, bundles of 
nonmedullated nerve fibers, imbedded in a capsule of connective tissue. 
The ganglia are reinforced by motor and sensory fibers from the cerebro- 
spinal nervous system. 
The Ganglia have distinct nerve fibers from which branches are dis- 
tributed to the glands, arteries, muscles, and to the cerebral and spinal 200 
HUMAN PHYSIOLOGY 
nerves; many pass, also, to the visceral ganglia, e. g., cardiac, semilunar, 
pelvic, etc. 
Cephalic Ganglia. 
1. The ophthalmic or ciliary ganglion is situated in the orbital cavity pos- 
terior to the eyeball; it is of small size and of a reddish-gray color; 
receives filaments of communication from the motor oculi, ophthalmic 
branch of the 5th pair, and the carotid plexus. Its filaments of distri- 
bution are the ciliary nerves, which consist of— 
a. Motor fibers for the circular fibers of the iris and ciliary muscle. 
b. Sensory fibers for the cornea, iris, and associated parts. 
c. Vasomotor fibers for the blood-vessels of the choroid, iris, and 
retina. 
d. Motor fibers for the dilator fibers of the iris. 
2. The sphenopalatine, or Meckel’s ganglion, triangular in shape, is 
situated in the spheno-maxillary fossa; receives filaments from the facial 
(Vidian nerve), and the superior maxillary branch of the fifth nerve. Its 
filaments of distribution pass to the gums, the soft palate, levator palati, 
and azygos uvulae muscle. 
3. The otic, or Arnold’s ganglion, is of small size, oval in shape, and situ- 
ated beneath the foramen ovale; receives a motor filament from the 
facial, and sensory filaments from the glossopharyngeal and 5th nerve; 
sends filaments to the mucous membrane of the tympanic cavity and to 
the tensor tympani muscle. 
4. The submaxillary ganglion, situated in the submaxillary gland, receives 
filaments from the chorda tympani, sensory filaments from the lingual 
branch of the 5th nerve, and filaments from the sympathetic. The 
chorda tympani nerve supplies vasodilator and secretory fibers to the 
submaxillary and sublingual glands. The 5th nerve endows the glands 
with sensibility, while the sympathetic supplies secretory or tropic fibers. 
Cervical Ganglia. 
The superior cervical ganglion is fusiform in shape, of a grayish-red 
color, and situate opposite the second and third cervical vertebra; it sends 
branches to form the carotid and cavernous plexuses which follow the 
course of the carotid arteries to their distribution ; also sends branches to 
join the glossopharyngeal and pneumogastric, to form the pharygeal 
plexus. 
The tniddle cervical ganglion, the smallest of the three, is occasionally 
wanting; it is situated opposite the 5th cervical vertebra; sends branches 
to the superior and inferior cervical ganglion and to the thyroid artery. SYMPATHETIC NERVOUS SYSTEM. 
201 
The inferior cervical ganglion, irregular in form, is situated opposite the 
last cervical vertebra; it is frequently fused with the first thoracic ganglion. 
The superior, middle, and inferior cardiac nerves, arising from these 
cervical ganglia, pass downward and forward to form the deep and super- 
ficial cardiac plexuses located at the bifurcation of the trachea, from which 
branches are distributed to the heart, coronary arteries, etc. 
The Thoracic Ganglia are usually twelve in number, placed against 
the heads of the ribs behind the pleura; they are small in size and gray in 
color ; they communicate with the cerebrospinal nerves by two filaments, 
one of which is white, the other gray. 
Thz great splanchnic nerve is formed by the union of branches from the 
6th, 7th, 8th, and 9th ganglia; it passes through the diaphragm to the 
semilunar ganglion. 
The lesser splanchnic nerve is formed by the union of filaments from the 
10th and nth ganglia, and is distributed to the celiac plexus. 
The renal splanchnic nerve arises from the last thoracic ganglion and 
terminates in the renal plexus. 
The semilunar ganglia, the largest of the sympathetic, are situated by 
the side of the celiac axis; they send radiating branches to form the solar 
plexus; from the various plexuses, nerves follow the gastric, splenic, he- 
patic, renal, etc., arteries, into the different abdominal viscera. 
The Lumbar Ganglia, four in number, are placed upon the bodies of 
the vertebra; they give off branches which unite to form the aortic lumbar 
plexus and the hypogastric plexus, and follow the blood-vessels to their 
terminations. 
The Sacral and Coccygeal Ganglia send filaments of distribution to 
all the blood-vessels of the pelvic viscera. 
Properties and Functions.—The sympathetic nerve possesses both 
sensibility and the power of exciting motion, but these properties are much 
less decided than in the cerebrospinal system. Irritation of the ganglia 
does not produce any evidence of pain until some time has elapsed. If 
caustic soda be applied to the semilunar ganglia, or a galvanic current be 
passed through the splanchnic nerve, no instantaneous effect is noticed, as 
in the case of the cerebrospinal nerves; but in the course of a few seconds 
a slow, progressive contraction of the muscular coat of the intestines is 
established, which continues for some time after the irritation is removed. 
Division of the sympathetic nerve in the neck is followed by a vascular 
congestion of the parts above the section on the corresponding side, attended 
by an increase in the temperature ; not only is there an increase in the 202 
HUMAN PHYSIOLOGY. 
amount of blood, but the rapidity of the blood current is very much has- 
tened and the blood in the veins becomes of a brighter color. Galvaniza- 
tion of the upper end of the divided nerve causes all of the preceding 
phenomena to disappear; the congestion decreases, the temperature falls, 
and the venous blood becomes dark again. 
The sympathetic exerts a similar influence upon the circulation of the 
limbs and the glandular organs; destruction of the 1st thoracic ganglion 
and division of the nerves forming the lumbar and sacral plexuses is fol- 
lowed by a dilatation of the vessels, an increased rapidity of the circulation, 
and an elevation of temperature in the anterior and posterior limbs; gal- 
vanization of the peripheral ends of these nerves causes all of these phe- 
nomena to disappear. Division of the splanchnic nerve causes a dilatation 
of the blood-vessels of the intestine. 
These phenomena of the sympathetic nerve system are dependent upon 
the presence of vasomotor nerves, which, under normal circumstances, 
exert a tonic influence upon the blood-vessels. These nerves, derived 
from the cerebrospinal system, the medulla oblongata, leave the spinal cord 
by the rami communicanles, enter the sympathetic ganglia, and finally 
terminate in the muscular wall of the blood-vessels. 
Sleep is a periodical condition of the nervous system, in which there is 
a partial or complete cessation of the activities of the higher nerve centers. 
The cause of sleep is a diminution in the quantity of blood, occasioned by a 
contraction of the smaller arteries under the influence of the vasomotor 
nerves. 
During the waking state the brain undergoes a physiological waste, as 
a result of the exercise of its functions; after a certain length of time its 
activities become enfeebled, and a period of repose ensues, during which a 
regeneration of its substance takes place. 
When the brain becomes enfeebled there is a diminished molecular 
activity and an accumulation of waste products; under these circumstances 
it ceases to dominate the medulla oblongata and the spinal cord. These 
centers then act more vigorously and diminish the caliber of the cerebral 
blood-vessels through the action of the vasomotor nerves, producing a con- 
dition of physiologic anemia and sleep; during this state waste products 
are removed, force is stored up, nutrition is restored, and waking finally 
occurs. THE SENSE OF TOUCH. 
203 
THE SENSE OF TOUCH. 
The Sense of Touch is a modification of general sensibility, and 
located in the skin, which is especially adapted for this purpose, on account 
of the number of nerves and papillary elevations it possesses. The structures 
of the skin and the modes of termination of the sensory nerves have already 
been considered. 
The Tactile Sensibility varies in acuteness in different portions of the 
body, being most marked in those regions in which the tactile corpuscles 
are most abundant, e. g., the palmar surface of the 3d phalanges of the 
fingers and thumb. 
The relative sensibility of different portions of the body has been ascer- 
tained by means of a pair of compasses, the points of which are guarded by 
cork, and then determining how closely they could be brought together, and 
yet be felt at two different points. The following are some of the measure- 
ments : — 
Point of tongue, of a line. 
Palmar surface of third phalanx, I line. 
Red surface of lips, 2 lines. 
Palmar surface of metacarpus, 3 “ 
Tip of the nose, 3 “ 
Part of lips covered by skin, 4 “ 
Palm of hand, 5 “ 
Lower part of forehead, 10 “ 
Back of hand, 14 “ 
Dorsum of foot, 18 “ 
Middle of the thigh, 30 “ 
The sense of touch communicates to the mind the idea of resistance only, 
and the varying degrees of resistance offered to the sensory nerves enable 
us to estimate, with the aid of the muscular sense, the qualities of hardness 
and softness of external objects. The idea of space or extension is obtained 
when the sensory surface or the external object changes its place in regard 
to the other; the character of the surface, its roughness or smoothness, is 
estimated by the impressions made upon the tactile papillae. 
Appreciation of Temperature.—The general surface of the body is more 
or less sensitive to differences of temperature, though this sensation is 
separate from that of touch ; whether there are nerves especially adapted 
for the conduction of this sensation has not been fully determined. Under 
pathologic conditions, however, the sense of touch may be abolished, 
while the appreciation of changes in temperature may remain normal. 204 
HUMAN PHYSIOLOGY. 
The cutaneous surface varies in its sensibility to temperature in different 
parts of the body, and depends, to some extent, upon the thickness of the 
skin, exposure, habit, etc.; the inner surface of the elbow is more sensitive 
to changes in temperature than the outer portion of the arm ; the left hand 
is more sensitive than the right; the mucous membrane less so than the 
skin. 
Excessive heat or cold has the same effect upon the sensibility; the tem- 
peratures most readily appreciated are those between 50° F. and 1150 F. 
The sensations of pain and tickling appear to be conducted to the brain, 
also, by nerves different from those of touch; in abnormal conditions the 
appreciation of pain may be entirely lost, while touch remains unimpaired. 
THE SENSE OF TASTE. 
The Sense of Taste is localized mainly in the mucous membrane 
covering the superior surface of the tongue. 
The Tongue is situated in the floor of the mouth ; its base is directed 
backward and connected with the hyoid bone, by numerous muscles with 
the epiglottis and soft palate; its apex is directed forward against the pos- 
terior surface of the teeth. 
The substance of the tongue is made up of intrinsic muscular fibers, the 
linguales ; it is attached to surrounding parts, and its various movements 
performed by the extrinsic muscles, e. g., styloglossus, geniohyoglossus, etc. 
The mucous tnembrane covering the tongue is continuous with that lining 
the commencement of the alimentary canal, and is furnished with vascular 
and nervous papillae. 
The papilla: are analogous in their structure to those of the skin, and are 
distributed over the dorsum of the tongue, giving it its characteristic rough- 
ness. 
There are three principal varieties:— 
1. The filiform papillce are most numerous, and cover the anterior two- 
thirds of the tongue; they are conical or filiform in shape, often pro- 
longed into filamentous tufts, of a whitish color, and covered by horny 
epithelium. 
2. The fungiform papillce are found chiefly at the tip and sides of the 
tongue; they are larger than the preceding, and may be recognized by 
their deep red color. 
3. The circumvallate papillce are rounded eminences, from eight to ten in THE SENSE OF TASTE. 
205 
number, situated at the base of the tongue, where they form a V-shaped 
figure. They are quite large, and consist of a central projection of 
mucous membrane, surrounded by a wall, or circumvallation, from which 
they derive their name. 
The Taste Beakers, supposed to be the true organs of taste, are-flask- 
like bodies, ovoid in form, about 7th of an inch in length, situated in the 
epithelial covering of the mucous membrane, on the circumvallate papillae. 
They consist of a number of fusiform, narrow cells, and curved so as to 
form the walls of this flask-like body; in the interior are elongated cells, 
with large, clear nuclei, the taste cells. 
Nerves of Taste.—The chorda tympani nerve, a branch of the facial, 
after leaving the cavity of the tympanum, joins the 3d division of the 5th 
nerve between the two pterygoid muscles, and then passes forward in the 
lingual branches, to be distributed to the mucous membrane of the anterior 
two-thirds of the tongue. Division or disease of this nerve is followed by 
a loss of taste in the part to which it is distributed. 
The glossopharyngeal enters the tongue at the posterior border of the 
hyoglossus muscle, and is distributed to the mucous membrane of the base 
and sides of the tongue, fauces, etc. 
The lingual branch of the trifacial nerve endows the tongue with gen- 
eral sensibility ; the hypoglossal endows it with motion. 
The nerves of taste in the superficial layer of the mucous membrane 
form a fine plexus, from which branches pass to the epithelium and pene- 
trate it; others enter the taste beakers, and are directly connected with the 
taste cells. 
The seat of the sense of taste has been shown by experiment to be the 
whole of the mucous membrane over the dorsum of the tongue, soft palate, 
fauces, and upper part of the pharynx. 
The Sense of Taste enables us to distinguish the savor of substances 
introduced into the mouth, which is different from tactile sensibility. The 
sapid quality of substances appreciated by the tongue are designated as 
bitter, sweet, alkaline, sour, salt, etc. 
The Essential Conditions for the production of the impressions of 
taste are— 
1. A state of solubility of the food. 
2. A free secretion of the saliva, and 
3. Active movements on the part of the tongue, exciting pressure against 
the roof of the mouth, gums, etc., thus aiding the solution of various 
articles and their osmosis into the lingual papillae. Sapid substances, 206 
HUMAN PHYSIOLOGY. 
when in a state of solution, pass into the interior of the taste beakers, and 
come into contact, through the medium of the taste cells, with the ter- 
minal filaments of the gustatory nerves. 
THE SENSE OF SMELL. 
The Sense of Smell is located in the mucous membrane lining the 
upper part of the nasal cavity, in which the olfactory nerves are distributed. 
The Nasal Fossae are two cavities, irregular in shape, separated by 
the vomer, the perpendicular plate of the ethmoid bone, and the triangular 
cartilage. They open anteriorly and posteriorly by the anterior and pos 
terior nares, the latter communicating with the pharynx. They are lined 
by mucous membrane, of which the only portion capable of receiving odor- 
ous impressions is the part lining the upper one-third of the fossae. 
The Olfactory Nerves, arising by three roots from the posterior and 
inferior surface of the anterior lobes, pass forward to the cribriform plate 
of the ethmoid bone, where they each expand into an oblong body, the 
olfactory bulb. From its under surface from 15 to 20 filaments pass 
downward through the foramina, to be distributed to the olfactory mucous 
membrane, where they terminate in long, delicate, spindle-shaped cells, the 
olfactory cells, situated between the ordinary epithelial cells. 
The olfactory bulbs are the centers in which odorous impressions are 
perceived as sensations, destruction of these bulbs being attended by an 
abolition of the sense of smell. 
In animals which possess an acute sense of smell there is a corresponding 
increase in the development of the olfactory bulbs. 
The Essential Conditions for the sense of smell are— 
X. A special nerve center capable of receiving impressions and transforming 
them into odorous sensations. 
2. Emanations from bodies which are in a gaseous or vaporous condition. 
3. The odorous emanations must be drawn freely through the nasal fossae; 
if the odor be very faint, a peculiar inspiratory movement is made, by 
which the air is forcibly brought into contact with the olfactory filaments. 
The secretions of the nasal fossae probably dissolve the odorous particles. 
Various substances, as ammonia, horseradish, etc., excite the sensibility 
of the mucous membrane, which must be distinguished from the perception 
of true odors. THE SENSE OF SIGHT. 
207 
THE SENSE OF SIGHT. 
The Eyeball.—The eyeball, or organ of vision, is situated at the fore 
part of the orbital cavity and supported by a cushion of fat; it is protected 
from injury by the bony walls of the cavity, the lids and lashes, and is so 
situated as to permit of an extensive range of vision. The eyeball is loosely 
held in position by a fibrous membrane, the capsule of Tenon, which is 
attached on the one hand to the eyeball itself and on the other to the walls 
of the cavity. Thus suspended, the eyeball is capable of being moved in 
any direction by the contraction of the muscles attached to it. 
Structure.—The eyeball is spheroidal in shape and measures about T%ths 
of an inch in its anteroposterior diameter, and a little less in its transverse 
diameter. When viewed in profile it is seen to consist of the segments of 
two spheres, of which the posterior is the larger, occupying |ths, and the 
anterior the smaller, occupying of the ball. 
The eye is made up of several membranes concentrically arranged, within 
which are enclosed the refracting media essential to vision. These mem- 
branes, enumerated from without inward, are— 
1. The sclerotic and cornea. 
2. The choroid and iris. 
3. The retina; the refracting media are the aqueous humor, the crystalr 
line lens, and vitreous humor. 
The Sclerotic and Cornea.—The sclerotic is the opaque fibrous mem- 
brane covering the posterior |ths of the ball. It is composed of connective 
tissue arranged in layers, which run both transversely and longitudinally ; 
it is pierced posteriorly by the optic nerve about of an inch internal to 
the optic axis. The sclerotic by its density gives form to the eye and pro- 
tects the delicate structures within it, and serves for the attachment of the 
muscles by which the ball is moved. 
The cornea is a transparent nonvascular membrane covering the anterior 
£th of the eyeball. It is nearly circular in shape and is continuous at the 
circumference with the sclerotic, from which it cannot be separated. The 
substance of the cornea is made up of thin layers of delicate, transparent 
fibrils of connective tissue more or less united together; between these 
layers are found a number of intercommunicating lymph spaces lined by 
endothelium, which are in connection with lymphatics. Leucocytes or 
lymph corpuscles are often found in these spaces. The anterior surface of 
the cornea is covered by several layers of nucleated epithelium, which rest 
upon a structureless membrane known as the anterior elastic lamina. The 208 
HUMAN PHYSIOLOGY. 
posterior surface is covered by a similar membrane, the membrane of 
Descemet, which becomes continuous at its periphery with the iris; it is 
also covered by a layer of epithelial cells. At the junction of the cornea 
and sclerotic is found a circular groove, the canal of Schlemm. 
The Choroid, the Iris, the Ciliary Muscle, and Ciliary Processes 
together constitute the second or middle coat of the eyeball. 
The choroid is a dark-brown membrane which extends forward nearly 
to the cornea, where it terminates in a series of folds, the ciliary processes. 
In its structure the choroid is highly vascular, consisting of both arteries and 
veins. Externally it is connected with the sclerotic by connective tissue ; 
internally it is lined by a layer of hexagonal pigment cells which, though 
usually classed as belonging to the choroid, is now known to belong, em- 
bryologically and physiologically, to the retina. From without inward may 
be distinguished the following layers 
1. The lamina supra choroidea. 
2. The elastic layer ofSattler, consisting of two endothelial layers. 
3. The chorio-capillaris, choroid proper, or membrane of Ruysch, a thick, 
elastic network of arterioles and capillaries lying within the outer layer of 
veins and arteries called the vena vorticosae. 
4. The lamina vitrea, or internal limiting membrane. 
The choroid with its contained blood-vessels bears an important relation 
to the nutrition of the eye ; it provides for the blood supply, for drainage 
from the body of the eye, and presents an uniform and high temperature to 
the retina. 
The iris is the circular variously-colored membrane placed in the an- 
terior portion of the eye just behind the cornea. It is perforated a little to 
the nasal side of the center by a circular opening, the pupil. The outer or 
circumferential border is connected with the cornea, ciliary muscle, and 
ciliary processes; the free inner edge forms the boundary of the pupil, the 
size of which is constantly changing. The framework of the iris is com- 
posed of connective-tissue blood-vessels, muscular fibers, and pigmented 
connective-tissue corpuscles. The anterior surface is covered with a layer 
of epithelial cells continuous with those covering the posterior surface of 
the cornea; the posterior surface is lined by a limiting membrane bearing 
pigment epithelial cells continuous with those of the choroid. The various 
colors which the iris assumes in different individuals depend upon the 
quantity and disposition of the pigmentary granules. 
The muscular fibers of the iris, which are of the nonstriated variety, are 
arranged in two sets,—the sphincter and dilator. 
The sphincter pupillce is a circular flat band of muscular fibers surround- THE SENSE OF SIGHT. 
209 
ing the pupil close to its posterior surface; by its contraction and relaxa- 
tion, the pupil is diminished or increased in size. The dilator pupilla 
consists of a thin layer of fibers arranged in a radiate manner; at the mar- 
gin of the pupil they blend with those of the sphincter muscle, while at the 
outer border they arch to form a circular muscular layer. 
The ciliary muscle is a gray circular band consisting of unstriped mus- 
cular fibers about Tjth of an inch long running from before backward. 
It is attached anteriorly to the inner surface of the sclerotic and cornea, and 
posteriorly to the choroid coat opposite the ciliary processes. At the an- 
terior border of the radiating fibers and internally are found bundles of 
Fig. 25.—Sclerotic Coat removed to show Choroid, Ciliary Muscles, and 
Nerves. 
a. Sclerotic coat. b. Veins of the choroid, c. Ciliary nerves, d. Veins of the choroid, 
e. Ciliary muscle, f. Iris.—(From Holden’s Anatomy.) 
circular muscular fibers, constituting the annular muscle of Muller. The 
ciliary muscle thus consists of two sets of fibers, a radiating and circular, 
both of which are concerned in effecting a change in the convexity of the 
lens in the accommodation of the eye to near vision. 
The Retina forms the internal coat of the eye. In the fresh state it is a 
delicate, transparent membrane of a pink color, but after death soon becomes 
opaque; it extends forward almost to the ciliary processes, where it termi- 
nates in an indented border, the ora serrala. In the posterior part of the 
retina at a point corresponding to the axis of vision is a yellow spot, the 
macula lutea, which is somewhat oval in shape and tinged with yellow 210 
HUMAN PHYSIOLOGY. 
pigment. It presents in its center a depression, the fovea centralis, cor- 
responding to a decrease in thickness of the retina; about of an 
inch to the inner side of the macula is the point of entrance of the optic 
nerve. The arteria centralis retina pierces the optic nerve near the 
sclerotic, runs forward in its substance, and is distributed in the retina as 
far forward as the ciliary processes. 
The retina is remarkably complex, consisting of ten distinct layers, from 
within outward, supported by connective tissue. These are as follows, 
viz. :— 
1. Membrana limitans interna. 
2. Fibers of optic nerve. 
3. Layers of ganglionic corpuscles. 
4. Molecular layer. 
5. Internal granular layer. 
6. Molecular layer. 
7. External granular layer. 
8. Membrana limitans externa. 
9. Jacobson’s membrane, or layer of rods and cones. 
10. The layer of pigment cells. 
The most important of these, however, is the layer of rods and cones in 
the external portion of the retina. The rods are straight, elongated cylinders 
extending through the entire thickness of Jacobson’s membrane. They 
consist of an external portion, which is clear, homogeneous, and highly re- 
fracting, and of an internal portion, which is slightly granular and less 
refractive; the outer end of each rod is in direct contact with the pig- 
mentary epithelium lining the choroid, while the inner end, tapering to a fine 
thread, pierces the external limiting membrane and passes into the external 
granular layer. The cones consist also of two portions, the inner of which 
is somewhat thicker than the rod and rests upon the limiting membrane; 
the outer portion tapers to a fine point, which is known as the cone-style. 
The cones, as a rule, are somewhat shorter than the rods. The propor- 
tion of rods to cones varies in different parts of the retina, though there are 
on the average about fourteen rods to one cone. In the macula lutea, where 
vision is most acute, the rods are almost entirely absent, cones alone being 
present. All the retinal elements at this point are changed. The nerve 
fiber layer is absent, the axis cylinders radiating in such a manner as to 
leave the spot free from their covering. The remaining layers are all 
thinned and the stroma reduced to a minimum. The optic nerve after 
passing forward from the brain penetrates in succession the sclerotic, 
choroid, and retina; the nerve fibers then spread out over the anterior THE SENSE OF SIGHT. 
211 
surface of the retina and become connected with the large ganglionic cells, 
the 3d layer of the retina. 
The number of optic nerve fibers in the retina is estimated to be about 
800,000, and for each fiber there are about seven cones, one hundred rods, 
and seven pigment cells. The points of the rods and cones are directed 
toward the choroid, or away from the entering light, and dip into the pig- 
mentary layer. They, with the pigment layer, are the elements interme- 
diating the change of the ethereal vibrations into nerve force; out of these 
nerve vibrations the brain fashions the sensations of light, form, and color. 
The vitreous humor, which supports the retina, is the largest of the re- 
fracting media; it is globular in form and constitutes about £ths of the 
ball; it is hollowed out anteriorly for the reception of the crystalline lens. 
The outer surface of the vitreous is covered by a delicate, transparent mem- 
brane, termed the hyaloid me?nbrane, which serves to maintain its globular 
form. 
The aqueous humor found in the anterior chamber of the eye is a clear 
alkaline fluid, having a specific gravity of 1.003-1.009. It is secreted most 
probably by the blood-vessels of the iris and ciliary processes. It passes 
from the interior of the eye, through the canal of Schlemm and the meshes 
at the base of the iris, into the anterior circular vein. 
The crystalline lens, enclosed within its capsule, is a transparent bicon- 
vex body, situated just behind the iris and resting in the depression in the 
anterior part of the vitreous. The two convexities are not quite alike, the 
curvature of the posterior surface being slightly greater than that of the an- 
terior. The lens measures about |d of an inch in the transverse diameter 
and of an inch in the anteroposterior diameter. 
The suspensory ligament, by which the lens is held in position, is a firm, 
transparent membrane, united to the ciliary processes. A short distance 
beyond its origin it splits into two layers, the anterior of which is inserted 
into the capsule of the lens and blends with it; the posterior, passing inward 
behind the lens, becomes united to its capsule. The anterior layer pre- 
sents a series of foldings, Zone of Zinn, which are inserted into the inter- 
vals of the folds of the ciliary processes. The triangular space between 
the two layers is the canal of Petit. 
Blood-vessels and Nerves.—The structures composing the eyeball are 
supplied with blood by the long and short ciliary arteries, branches of the 
ophthalmic; they pierce the sclerotic at various points and are ultimately 
distributed to all tissues within the ball. 
The nerve supply comes largely from the ophthalmic or ciliary ganglion. 
This is a small body, situated in the posterior part of the orbit; it receives 212 
HUMAN PHYSIOLOGY. 
motor fibers from a branch of the motoroculi, or 3d nerve; a sensory 
branch from the ophthalmic division of 5th nerve, and fibers from the 
cavernous plexus of the sympathetic. From the anterior border of the 
ganglion proceed the ciliary nerves, which, entering the eyeball, endow its 
structures with motion and sensation. 
The Eyeball a Living Camera Obscura.—The eyeball may be com- 
pared in a general way to a camera obscura. The anatomical arrangement 
of its structures reveals many points of similarity. The sclerotic and choroid 
may be compared with the walls of the chamber; the combined refractive 
media, cornea, aqueous humor, lens, and vitreous humor, to the lens for 
1. Anterior chamber filled with aqueous humor. 2. Posterior chamber. 3. Canal of Petit. 
a. Hyaloid membrane, b. Retina (dotted line), c. Choroid coat (black line), d. 
Sclerotic coat. e. Cornea, f. Iris. g. Ciliary processes, h. Canal of Schlemm 
or Fontana, i. Ciliary muscle.—{From Holden’s Anatomy.) 
r 
Fig. 26.—Diagram of a Vertical Section of the Eye. 
focusing the rays of light; the retina, to the sensitive plate receiving the 
image formed at the focal point; the iris, to the diaphragm, which by cutting 
off the marginal rays prevents spherical aberration and at the same time 
regulates the amount of light entering the eye; the ciliary muscle, to the 
adjusting screw, by which distinct images are thrown upon the retina in 
spite of varying distances of the object from which the light rays emanate. 
The structures just enumerated are those essential for normal vision. 
The relationship of the various structures composing the eyeball is shown 
in Fig. 26. THE SENSE OF SIGHT. 
213 
The Dioptric, or Refracting apparatus, by which the rays of light enter- 
ing the eye are so manipulated as to produce an image on the retina, 
consists of the cornea, aqueous humor, crystalline lens, and vitreous humor. 
A ray of light in passing through each of these media will undergo refrac- 
tion at their surfaces and ultimately be brought to a focus at the retina. 
Inasmuch as the two surfaces of the cornea are parallel and its refractive 
power practically the same as the aqueous humor, the media may be re- 
duced to three, viz.:— 
1. Cornea and aqueous humor. 
2. The lens. 
3. The vitreous humor. 
Fig. 27.—Diagram Showing the Course of Parallel Rays of Light from A, in 
their Passage through a Biconvex Lens, L, in which they are so Re- 
fracted as to Bend Toward and Come in a Focus at a Point, F.—(From 
Yeo’s Text-Book 0/ Physiology.) 
Fig. 28.—Diagram Showing the Course of Diverging Rays which are Bent to 
a Point Further from the Lens than the Parallel Rays in Preceding 
Figure.— (From Yeo’s Text-Book 0/ Physiology.) 
The refracting surfaces may also be reduced to three, viz.:— 
1. Anterior surface of the cornea. 
2. Anterior surface of lens. 
3. Posterior surface of lens. 
The refraction effected by the cornea is very great, owing to the passage 
of the light from the air into a comparatively dense medium, and is sufficient 
of itself to bring parallel rays of light to a focus about ten millimeters behind 
the retina. This would be the condition in an eye in which the lens was 
congenitally absent. Perfect vision requires, however, that the convergence 214 
HUMAN PHYSIOLOGY. 
of the light shall be great enough that the image may fall upon the retina. 
This is accomplished by the crystalline lens, a body denser than the cornea 
and possessing a higher refractive power. The manner in which a biconvex 
lens focuses both parallel and divergent rays is shown in Figs. 27 and 28. 
The function of the crystalline lens, therefore, is to focus the rays of light 
with the formation of an image on the retina. 
The Retinal Image corresponds in all respects to the object from which 
the light proceeds. The existence of this image can be demonstrated by 
removing from the eye of a recently killed animal a circular portion of the 
sclerotic and choroid posteriorly and then placing at the proper distance in 
front of the cornea a lighted candle ; an inverted image of the candle will 
be seen upon the retina. The size of the retinal image depends upon the 
visual angle, which in turn depends upon the size of the object and its 
distance from the eye. At a distance of 15.2596 meters the image of an 
object one meter high would be one millimeter, or a thousand times smaller 
than the object. 
Accommodation.—By accommodation is understood the power which 
the eye possesses of adjusting itself to vision at different distances. In a 
normal or emmetropic eye parallel rays of light are brought to a focus on 
the retina; but divergent rays, that is, rays coming from a near luminous 
point, will be brought to a focus behind the retina, provided the refractive 
media remain the same ; as a result, vision would be indistinct, from the 
formation of diffusion circles. It is impossible to see distinctly, therefore, 
a near and distant object at the same time. We must alternately direct 
the vision from one to the other. A normal eye does not require adjust- 
ing for parallel rays; but for divergent rays a change in the eye is necessi- 
tated ; this is termed accommodation. In the accommodation for near 
vision the lens becomes more convex, particularly on its anterior surface; 
the increase in convexity increases its refractive power; the greater the 
degree of divergence of the rays previous to entering the eye, the greater 
the increase of convexity of the lens and convergence of the rays after 
passing through it. By this alteration in the shape of the lens we are 
enabled to focus light rays coming from, and to see distinctly, near as well 
as distant objects. 
Function of the Ciliary Muscle.—Though it is admitted that the 
change in the convexity of the lens is caused by the contraction of the 
ciliary muscle and the relaxation of the suspensory ligament, the exact 
manner in which it does so is not understood. When the eye is in repose, 
as in distant vision, the suspensory ligament is tense and the lens possesses THE SENSE OF SIGHT. 
215 
that degree of curvature necessary for focusing parallel rays. In the volun- 
tary efforts to accommodate the eye for near vision, the ciliary muscle con- 
tracts, the suspensory ligament relaxes, and the lens, inherently elastic, 
bulges forward and once again focuses the rays upon the retina. It is, 
therefore, termed the muscle of accommodation, and by its alternate con- 
traction and relaxation the lens is rendered more or less convex, accord- 
ing to the requirements for near and distant vision. 
Range of Accommodation.—Parallel rays coming from a luminous 
point, distant not less than 200 feet, do not require adjustment; from this 
point up to infinity no accommodation is required for perfect vision. This is 
termed tht punctum remotum, and indicates the distance to which an object 
may be removed and yet distinctly seen. If the object be brought nearer 
to the eye than 200 feet, the accommodative power must come into play; 
the nearer the object the more energetic must be the contraction of the 
ciliary muscle and the consequent increase in the convexity of the lens. At 
a distance of five inches, however, the power of accommodation reaches 
its maximum ; this is termed the punctum proximum, and indicates the 
nearest point at which an object may be seen distinctly. The distance 
between these two points is the range of accommodation. 
Optical Defects.—Astigmatism is a condition of the eye which pre- 
vents vertical and horizontal lines from being focused at the same time, 
and is due to a greater curvature of the cornea in one meridian than 
another. 
Spherical aberration is a condition in which there is an indistinctness of 
an image from the unequal refraction of the rays of light passing through 
the circumference and the center of the lens; it is corrected mainly by the 
iris, which cuts off the marginal rays, and only transmits those passing 
through the center. 
Chromatic aberration is a condition in which the image is surrounded by 
a colored margin, from the decomposition of the rays of light into their 
elementary parts. 
Myopia, or shortsightedness, is caused by an abnormal increase in the 
anteroposterior diameter of the eyeball, or by a hypernormal refracting 
power of the lens; it is generally due to the first cause; the lens, being too 
far removed from the retina, forms the image in front of it, and the percep- 
tion becomes dim and blurred. Concave glasses correct this defect by pre- 
venting the rays from converging too soon. 
Hypermetropia, or longsightedness, is caused by a shortening of the 
anteroposterior diameter or by a subnormal refractive power of the lens; 216 
HUMAN PHYSIOLOGY. 
the focus of the rays of light would, therefore, be behind the retina. Con- 
vex glasses correct this defect by converging the rays of light more 
anteriorly. 
Presbyopia is a loss of the power of accommodation of the eye to near 
objects, and usually occurs between the ages of forty and sixty; it is reme- 
died by the use of convex glasses. 
The Iris.—The iris plays the part of a diaphragm, and by means of its 
central aperture the pupil regulates the quantity of light entering the 
interior of the eye; by preventing rays from passing through the margin of 
the lens it diminishes spherical aberration. The size of the pupil depends 
upon the relative degree of contraction of the circular and radiating fibers; 
the variations in size of the pupil from variations in the degree of contrac- 
tion depend upon different intensities of light. If the light be intense, the 
circular fibers contract and diminish the size of the pupil; if the light 
diminishes in intensity, the circular fibers relax and the pupil enlarges. 
Point of Most Distinct Vision.—While all portions of the retina are 
sensitive to light, their sensibility varies within wide limits. At the macula 
lutea, and more especially in its most central depression, the fovea, where 
the retinal elements are reduced practically to the layer of rods and cones, 
the sensibility reaches its maximum. It is at this point that the image is 
found when vision is most distinct. The macula and fovea are always in 
the line of direct vision. From the macula toward the periphery of the 
retina there is a gradual diminution in sensibility and a corresponding decline 
in the distinctness of vision. In those portions of the retina lying outside 
the macula the indistinctness of vision depends not only on diminished 
sensibility, but also upon inaccurate focusing of the rays. 
Blind Spot.—Although the optic nerve transmits the impulses excited 
in the retina by the ethereal vibration, the nerve fibers themselves are insen- 
sitive to light. At the point of entrance of the optic nerve, owing to the 
absence of the rods and cones, the rays of light make no impression. This 
is the blind spot. As this spot is not in the line of vision no dark point is 
ordinarily observed in the field of vision—that circular space before a fixed 
eye within which objects are perceptible. 
The rods and cones are the most sensitive portions of the retina. A ray 
of light entering the eye passes entirely through the various layers of the 
retina and is arrested only upon reaching the pigmentary epithelium in 
which the rods and cones are imbedded. As to the manner in which the 
objective stimuli, light and color, so-called, are transformed into nerve im- 
pulses but little is known. It is probable that the ethereal vibrations are THE SENSE OF SIGHT. 
217 
transformed into heat, which excites the rods and cones. These, acting as 
highly specialized end organs of the optic nerve, start the impulses on their 
way to the brain, where the seeing process takes place. As to the relative 
function of the rods and cones, it has been suggested, from the study of 
the facts of comparative anatomy, that the rods are impressed only by differ- 
ences in the intensity of light, while the cones in addition are impressed by 
qualitative differences or color. 
Accessory Structures.—The muscles which move the eyeball are six 
in number : the superior and inferior recti, the external and internal recti, 
the superior and inferior oblique muscles. The four recti muscles, arising 
from the apex of the orbit, pass forward and are inserted into the sides of 
the sclerotic coat; the superior and inferior muscles rotate the eye around 
a horizontal axis; the external and internal rotate it around a vertical 
axis. 
The superior oblique muscle, having the same origin, passes forward to 
the inner and upper angle of the orbital cavity, where its tendon passes 
through a cartilaginous pulley; it is then reflected backward and inserted 
into the sclerotic just behind the transverse diameter. Its function is to 
rotate the eyeball in such a manner as to direct the pupil downward and 
outward. 
The inferior oblique muscle arises at the inner angle of the orbit and 
then passes outward and backward, to be inserted into the sclerotic. Its 
function is to rotate the eyeball and direct the pupil upward and outward. 
By the associated action of all these muscles, the eyeball is capable of 
performing all the varied and complex movements necessary for distinct 
vision. 
The eyelids, bordered with short, stiff hairs, shade the eye and protect it 
from injury. On the posterior surface, just beneath the conjunctiva, are 
the Meibomian glands, which secrete an oily fluid; it covers the edge of 
the lids, and prevents the tears from flowing over the cheek. 
The lacrimal glands are ovoid in shape, and situated at the upper and 
outer part of the orbital cavity; they open by from six to eight ducts at the 
outer portion of the upper lids. 
The tears, secreted by the lacrimal glands, are distributed over the cor- 
nea by the lids during the act of winking, and keep it moist and free from 
dust. The excess of tears passes into the lacrimal ducts, which begin by 
two minute orifices, one on each lid, at the inner canthus. They conduct 
the tears into the nasal duct, and so into the nose. 218 
HUMAN PHYSIOLOGY. 
THE SENSE OF HEARING. 
The Ear, or Organ of Hearing, is lodged within the petrous portion 
of the temporal bone. It may be, for convenience of description, divided 
into three portions, viz.:— 
1. The external ear. 
2. The middle ear. 
3. The internal ear, or labyrinth. 
The External Ear consists of the pinna or auricle and the external 
auditory canal. The pinna consists of a thin layer of cartilage, presenting 
a series of elevations and depressions ; it is attached by fibrous tissue to the 
outer bony edge of the auditory canal; it is covered by a layer of integu- 
ment continuous with that covering the side of the head. The general 
shape of the pinna is concave and presents a little below the center a deep 
depression, the concha. The external auditory canal extends from the 
concha inward for a distance of about 1J inches. It is directed somewhat 
forward and upward, passing over a convexity of bone, and then dips 
downward to its termination; it is composed of both bone and cartilage, 
and lined by a reflection of the skin covering the pinna. At the external 
portion of the canal the skin contains a number of tubular glands, the 
ceruminous glands, which in their conformation resemble the perspiratory 
glands. They secrete the cerumen, or earwax. 
The Middle Ear, or Tympanum, is an irregularly-shaped cavity hol- 
lowed out of the temporal bone and situated between the external ear and 
the labyrinth. It is narrow from side to side but relatively long in its 
vertical and anteroposterior diameters; it is separated from the external 
auditory canal by a membrane, the membrana tympani; from the internal 
ear it is separated by an osseomembranous partition which forms a common 
wall for both cavities. The middle ear communicates posteriorly with the 
mastoid cells, anteriorly with the nasopharynx by means of the Eustachian 
tube. The interior of this cavity is lined by mucous membrane continuous 
with that lining the pharynx. 
The membrana tympani is a thin, translucent, nearly circular membrane, 
measuring about | of an inch in diameter, placed at the inner termina- 
tion of the external auditory canal. The membrane is inclosed within 
a ring of bone which in the fetal condition can be easily removed, but in 
the adult condition becomes consolidated with the surrounding bone. The 
membrana tympani consists primarily of a layer of fibrous tissue, arranged 
both circularly and radially, and forms the membrana propria ; externally THE SENSE OF HEARING. 
219 
it is covered by a thin layer of skin continuous with that lining the auditory 
canal; internally it is covered by a thin mucous membrane. The tympanic 
membrane is placed obliquely at the bottom of the auditory canal, inclining 
at an angle of 45 degrees, being directed from behind and above downward 
and inward. On its external surface this membrane presents a funnel- 
shaped depression, the sides of which are somewhat convex. 
The Ear Bones.—Running across the tympanic cavity and forming an 
irregular line of jointed levers is a chain of bones which articulate with 
A.G. External meatus. M. Membrana tympani, which is attached to the handle of the 
malleus, n, and near it the short process. p,h. Head of the malleus, a. Incus; 
k, its short process with its ligament; /, long process, j. Sylvian ossicle. S. 
Stapes. Ax, Ax, is the axis of rotation of the ossicles ; it is shown in perspective, 
and must be imagined to penetrate the plane of the paper, t. Line of traction of the 
tensor tympani. The other arrows indicate the movement of the ossicles when the 
tensor contracts. 
Fig. 29.—Tympanum and Auditory Ossicles (Left) Magnified, 
each other at their extremities. They are known as the malleus, incus, and 
stapes. 
The form and position of these bones are shown in Fig. 29. 
The malleus consists of a head, neck, and handle, of which the latter is 
attached to the inner surface of the membrana tympani; tbz incus, or anvil 220 
HUMAN PHYSIOLOGY. 
bone, presents a concave, articular surface, which receives the head of the 
malleus; the stapes, or stirrup bone, articulates externally with the long 
process of the incus, and internally, by its oval base, with the edges of the 
foramen ovale. 
The Tensor Tympani Muscle consists of a fleshy, tapering portion, 
half an inch in length, which terminates in a slender tendon ; it arises from 
the cartilaginous portion of the Eustachian tube and adjacent surface of the 
sphenoid bone. From this origin the muscle passes nearly horizontally 
backward to the tympanic cavity; just opposite to the fenestra ovalis its 
tendon bends at a right angle over the processus cochleariformis and then 
passes outward across the cavity to be inserted into the handle of the mal- 
leus near the neck. 
The Stapedius Muscle emerges from the cavity of a pyramid of bone 
projecting from the posterior wall of the tympanum; the tendon passes 
forward and is inserted into the neck of the stapes bone posteriorly near its 
point of articulation with the incus. 
The laxator tympani muscle, so-called, is now generally regarded as liga- 
mentous in nature, and not muscular. 
The Eustachian Tube, by means of which a free communication is 
established between the middle ear and pharynx, is partly bony and partly 
cartilaginous in structure. It measures about ij inches in length; com- 
mencing at its opening into the naso-pharynx, it passes upward and out- 
ward to the spine of the sphenoid bone, at which point it becomes some- 
what contracted; the tube then dilates as it passes backward into the middle 
ear cavity; it is lined by mucous membrane, which is continued into the 
middle ear and mastoid cells. 
The Function of the Ear, as a whole, is the reception and transmis- 
sion of aerial vibrations to the terminal organs concealed within the in- 
ternal ear and which are connected with the auditory nerve fibers. The 
excitation of these end organs caused by the impact of the vibrations 
arouses in the auditory nerve impulses which are then transmitted to the 
brain, where the hearing process takes place. In order to appreciate the 
functions of the individual parts of the ear a few of the characteristics of 
sound waves must be kept in mind. 
Sound Waves.—All sounds are caused by vibrations in the atmosphere 
which have been communicated to it by vibrating elastic bodies, such as 
membranes, strings, rods, etc. These vibrating bodies produce in the air 
a to-and-fro movement of its particles, resulting in a series of alternate 
condensations and rarefactions, which are propagated in all directions. A THE SENSE OF HEARING. 
221 
complete oscillation of a particle of air forward and backward constitutes a 
sound-wave. Musical sounds are caused by a succession of regular waves, 
which follow each other with a certain rapidity. Noises are caused by the 
impact of a series of irregular waves. 
All sound waves possess intensity, pitch, and quality. The intensity, or 
loudness, of a sound depends upon the amplitude of the vibrations or the 
extent of its excursion. Th& pitch depends upon the number of vibrations 
which affect the auditory nerve in a second of time; the pitch of the note 
C, the first below the leger line of the musical scale, is caused by 256 
vibrations per second; the pitch of the same note an octave higher is 
caused by 5x2 vibrations per second. If the vibrations are too few per 
second they fail to be perceived as a continuous sound; the mininum 
number of vibrations capable of producing a sound has been fixed at 16 per 
second; the highest pitched musical note capable of being heard has been 
shown to be due to 38,000 vibrations per second. In the ascent of the 
musical scales there is, therefore, a gradual increase in the number of vibra- 
tions and a gradual increase in the pitch of the sounds. Between the two 
extreme limits lies the range of audibility, which embraces eleven octaves, 
of which seven are employed in the musical scale. 
The quality of sound depends upon a combination of the fundamental 
vibration with certain secondary vibrations of subdivisions of the vibrating 
body. These so-called over-tones vary in intensity and pitch, and by 
modifying the form of the primary wave produce that which is termed the 
quality of sound. 
Function of the Pinna and External Auditory Canal.—In those 
animals possessing movable ears, the pinna plays an important part in the 
collection of sound-waves. In man, in whom the capability of moving the 
pinna has been lost, it is doubtful if it is at all necessary for hearing. 
Nevertheless, an individual with dull hearing may have the perception of 
sound increased by placing the pinna at an angle of 45 degrees to the side 
of the head. The external auditory canal transmits the sonorous vibra- 
tions to the tympanic membrane. Owing to the obliquity of this canal it 
has been supposed that the waves, concentrated at the concha, undergo a 
series of reflections on their way to the tympanic membrane, and, owing to 
the position of this membrane, strike it almost perpendicularly. 
Function of the Tympanic Membrane.—The function of the tym- 
panic membrane appears to be the reception of sound vibrations by being 
thrown by them into reciprocal vibrations which correspond in intensity and 
amplitude. That this membrane actually reproduces all vibrations within 222 
HUMAN PHYSIOLOGY. 
the range of audibility has been experimentally demonstrated. The mem- 
brane not being fixed, as far as its tension is concerned, does not possess a 
fixed fundamental note, like a stationary fixed membrane, and is therefore 
just as well adapted for the reception of one set of vibrations as another. 
This is made possible by variations in its tension in accordance with the 
pitch of the sounds. In the absence of all sound the membrane is in a 
condition of relaxation; with the advent of sound-waves possessing a 
gradual increase of pitch, as in the ascent of the musical scale, the tension 
of the tympanic membrane is gradually increased until its maximum ten- 
sion is reached at the upper limit of the range of audibility. By this 
change in tension certain tones become perceptible and distinct, while 
others become indistinct and inaudible. 
Function of the Tensor Tympani Muscle.—The function of this 
muscle is, as its name indicates, to increase the tension of the membrane in 
accordance with the pitch of the sound wave. The tendon of this muscle 
playing over the processus cochleariformis and attached at almost a right 
angle to the handle of the malleus will, when the muscle contracts, pull the 
handle inward, increase the convexity of the membrane, and at the same 
time increase its tension ; with the relaxation of this muscle, the handle of 
the malleus passes outward and the tension is diminished. The contrac- 
tions of the tensor muscle are reflex in character and excited by nerve 
impulses reaching it through the small petrosal nerve and otic ganglion. 
The number of nerve stimuli passing to the muscle and determining the 
degree of contraction will depend upon the pitch of the sound wave and the 
subsequent excitation of the auditory nerve. The tensor tympani muscle 
may be regarded as an accommodative apparatus by which the tympanic 
membrane is adjusted to enable it to receive vibrations of varying degrees 
of pitch. 
Function of the Ossicles.—The function of the chain of bones is to 
transmit the sound wave across the tympanic cavity to the internal ear. 
The first of these bones, the malleus, being attached to the tympanic mem- 
brane, will take up the vibrations much more readily than if no membrane 
intervened. Owing to the character of the articulations, when the handle 
of the malleus is drawn inward, the position of the bones is so changed 
that they form practically a solid rod, and are therefore much better adapted 
for the transmission of molecular vibrations than if the articulations remained 
loose. As the stapes bone is somewhat shorter than the malleus, its vibra- 
tions are smaller than those of the tympanic membrane, and by this 
arrangement the amplitude of the vibrations is diminished, but their force 
increased. THE SENSE OF HEARING. 
223 
The Function of the Stapedius Muscle is, according to Henle, to fix 
the stapes bone so as to prevent too great a movement from being communi- 
cated to it from the incus and transmitted to the perilymph. It may be 
looked upon, therefore, as a protective muscle. 
The Function of the Eustachian Tube is to maintain a free com- 
munication between the cavity of the middle ear and naso-pharynx. The 
pressure of air within and without the ear is thus equalized, and the vibra- 
tions of the tympanic membrane permitted to attain their maximum, one of 
the conditions essential for the reception of sound waves. The impairment 
in the acuteness of hearing which is caused by an unequal pressure of the 
air in the middle ear can be shown :— 
1. By closing the mouth and nose and forcing air from the lungs through 
the Eustachian tube into the ear, producing an increase in pressure. 
2. By closing the nose and mouth, and making efforts at deglutition, which 
withdraws the air from the ear and diminishes its pressure. In both in- 
stances the free vibrations of the tympanic membrane are interfered with. 
The pharyngeal orifice of the Eustachian tube is opened by the action of 
certain of the muscles of deglutition, viz.: the levator palati, tensor 
palati, and the palato-pbaryngei muscles. 
The Internal Ear, or Labyrinth, is located in the petrous portion of 
the temporal bone, and consists of an osseous and membranous portion. 
The Osseous Labyrinth is divisible into three parts, viz.: the vesti- 
bule, the semicircular canals, and the cochlea. 
The vestibule is a small, triangular cavity, which communicates with the 
middle ear by the foramen ovale; in the natural condition it is closed by 
the base of the stapes bone. The filaments of the auditory nerve enter the 
vestibule through small foramina in the inner wall, at the fovea hemi- 
spherica. 
The semicircular canals are three in number, the superior vertical, the 
inferior vertical, and the horizontal, each of which opens into the cavity of 
the vestibule by two openings, with the exception of the two vertical, which 
at one extremity open by a common orifice. 
The cochlea forms the anterior part of the internal ear. It is a gradually 
tapering canal, about l| inches in length, which winds spirally around a 
central axis, the modiolus, 2J times. The interior of the cochlea is partly 
divided into two passages by a thin plate of bone, the lamina osseous spir- 
alis, which projects from the central axis f across the canal. These 
passages are termed the scala vestibuli and the scala tympani, from their 
communication with the vestibule and tympanum. The scala tympani 224 
HUMAN PHYSIOLOGY. 
communicates with the middle ear through the foramen rotundum, which, 
in the natural condition, is closed by the 2d membrana tympani; superiorly 
they are united by an opening, the helicotrema. 
The whole anterior of the labyrinth, the vestibule, the semicircular canals, 
and the scala of the cochlea, contains a clear, limpid fluid, the perilymph, 
secreted by the periosteum lining the osseous walls. 
The Membranous Labyrinth corresponds to the osseous labyrinth 
with respect to form, though somewhat smaller in size. 
The vestibular portion consists of two small sacs, the utricle and 
saccule. 
The semicircular canals communicate with the utricle in the same man- 
ner as the bony canals communicate with the vestibule. The saccule com- 
municates with the membranous cochlea by the canalis reuniens. In the 
interior of the utricle and saccule, at the entrance of the auditory nerve, are 
small masses of carbonate of lime crystals, constituting the otoliths. Their 
function is unknown. 
The membranous cochlea is a closed tube, commencing by a blind 
extremity at the first turn of the cochlea, and terminating at its apex by a 
blind extremity also. It is situated between the edge of the osseous lamina 
spiralis and the outer wall of the bony cochlea, and follows it in its turns 
around the modiolus. 
A transverse section of the cochlea shows that it is divided into two 
portions by the osseous lamina and the basilar membrane:— 
1. The scala vestibuli, bounded by the periosteum and membrane of 
Reissner. 
2. The scala tympani, occupying the inferior portion, and bounded above 
by the septum, composed of the osseous lamina and the membrana 
basilaris. 
The true membranous canal is situated between the membrane of Reiss- 
ner and the basilar membrane. It is triangular in shape, but is partly 
divided into a triangular portion and a quadrilateral portion by the tectorial 
membrane. 
The organ of Corti is situated in the quadrilateral portion of the canal, 
and consists of pillars of rods of the consistence of cartilage. They are 
arranged in two rows—the one internal, the other external; these rods rest 
upon the basilar membrane; their bases are separated from each other, but 
their upper extremities are united, forming an arcade. In the internal row 
it is estimated there are about 3500, and in the external row about 5200 of 
these rods. 
On the inner side of the internal row is a single layer of elongated hair THE SENSE OF HEARING. 
225 
cells; on the outer surface of the external row are three such layers of hair 
cells. Nothing definite is known as to their function. 
The endolymph occupies the interior of th,e utricle, saccule, and mem- 
branous canals, and bathes the structures in the interior of the membranous 
cochlea throughout its entire extent. 
The Auditory Nerve at the bottom of the internal auditory meatus 
divides into— 
1. A vestibular branch, which is distributed to the utricle and semicircular 
canals. 
2. A cochlear branch, which passes into the central axis at its base and 
ascends to its apex ; as it ascends, fibers are given off, which pass between 
the plates of the osseous lamina, to be ultimately connected with the 
organ of Corti. 
The function of the semicircular canals appears to be to assist in main- 
taining the equilibrium of the body; destruction of the vertical canal is 
followed by an oscillation of the head upward and downward; destruction 
of the horizontal canal is followed by oscillations from left to right. When 
the canals are injured on both sides, the animal loses the power of main- 
taining equilibrium upon making muscular movements. 
Function of the cochlea. It is regarded as possessing the power of 
appreciating the quality of pitch and the shades of different musical tones. 
The elements of the organ of Corti are analogous, in some respects, to a 
musical instrument, and are supposed, by Helmholtz, to be tuned so as to 
vibrate in unison with the different tones conveyed to the internal ear. 
Summary.—The waves of sound are gathered together by the pinna 
and external auditory meatus, and conveyed to the membrana tympani. 
This membrane, made tense or lax by the action of the tensor tympani 
and laxator tympani muscles, is enabled to receive sound waves of either 
a high or low pitch. The vibrations are conducted across the middle ear 
by a chain of bones to the foramen ovale, and by the column of air of 
the tympanum to the foramen rotundum, which is closed by the 2d 
membrana tympani, the pressure of the air in the tympanum being regu- 
lated by the Eustachian tube. 
The internal ear finally receives the vibrations, which excite vibrations 
successively in the perilymph, the walls of the membranous labyrinth, the 
endolymph, and, lastly, the terminal filaments of the auditory nerve, by 
which they are conveyed to the brain. 226 
HUMAN PHYSIOLOGY. 
The Larynx is the organ of voice. Speech is a modification of voice, 
and is produced by the teeth and the muscles of the lips and tongue, 
coordinated in their action by stimuli derived from the cerebrum. 
The Structures entering into the formation of the larynx are mainly 
the thyroid, cricoid, and arytenoid cartilages; they are so situated and 
united by means of ligaments and muscles as to form a firm cartilaginous 
box. The larynx is covered externally by fibrous tissue, and lined inter- 
nally with mucous membrane. 
The Vocal Cords are four ligamentous bands, running antero posteri- 
orly across the upper portion of the larynx, and are divided into the two 
superior or false vocal cords, and the two inferior or true vocal cords; 
they are attached anteriorly to the receding angle of the thyroid cartilages 
and posteriorly to the anterior part of the base of the arytenoid cartilages. 
The space between the true vocal cords is the rima glotlidis. 
The Muscles which have a direct action upon the movements of the 
vocal cords are nine in number, and take their names from their points of 
origin and insertion, viz.: the two crico thyroid, two thyro-arytenoid, two 
posterior crico-arytenoid, two lateral crico-arylenoid, and one arytenoid 
muscles. 
The crico-thyroid muscles, by their contraction, render the vocal cords 
more tense by drawing down the anterior portion of the thyroid cartilage 
and approximating it to the cricoid, and at the same time tilting the poste- 
rior portion of the cricoid and arytenoid cartilages backward. 
The thyro-arytenoid, by their contraction, relax the vocal cords by draw- 
ing the arytenoid cartilage forward and the thyroid backward. 
The posterior crico-arytenoid muscles, by their contraction, rotate the 
arytenoid cartilages outward and thus separate the vocal cords and enlarge 
the aperture of the glottis. They principally aid the respiratory movements 
during inspiration. 
The lateral crico- arytenoid muscles are antagonistic to the former, and 
by their contraction rotate the arytenoid cartilages so as to approximate the 
vocal cords and constrict the glottis. 
The arytenoid muscle assists in the closure of the aperture of the glottis. 
The inferior laryngeal nerve animates all the muscles of the larynx, with 
the exception of the crico thyroid. 
Movements of the Vocal Cords.—During respiration the movements 
of the vocal cords differ from those occurring during the production of voice. 
VOICE AND SPEECH. VOICE AND SPEECH. 
227 
At each inspiration the true vocal cords are widely separated, and the 
aperture of the glottis is enlarged by the action of the crico-arytenoid mus- 
cles, which rotate outward the anterior angle of the base of the arytenoid 
cartilages; at each expiration the larynx becomes passive; the elasticity of 
the vocal cords returns them to their original position, and the air is forced 
out by the elasticity of the lungs and the walls of the thorax. 
Phonation.—As soon as phonation is about to be accomplished a marked 
change in the glottis is noticed with the aid of the laryngoscope. The true 
vocal cords suddenly become approximated and are made parallel, giving 
to the glottis the appearance of a narrow slit, the edges of which are capa- 
ble of vibrating accurately and rapidly ; at the same time their tension is 
much increased. 
With the vocal cords thus prepared, the expiratory muscles force the 
column of air into the lungs and trachea through the glottis, throwing the 
edges of the cords into vibration. 
Th& pitch of sounds depends upon the extent to which the vocal cords 
are made tense and the length of the aperture through which the air passes. 
In the production of sounds of a high pitch, the tension of the vocal cords 
becomes very marked and the glottis diminished in length. When grave 
sounds having a low pitch are emitted from the larynx, the vocal cords are 
less tense and their vibrations are large and loose. 
The quality of voice depends upon the length, size, and thickness of the 
cords, and the size, form, and construction of the trachea, larynx, and the 
resonant cavities of the pharynx, nose, and mouth. 
The compass of the voice comprehends from two to three octaves. The 
range is different in the two sexes, the lowest note of the male being about 
one octave lower than the lowest note of the female; while the highest note 
of the male is an octave less than the highest note of the female. 
The varieties of voices, e.g., bass, baritone, tenor, contralto, mezzo- 
soprano, and soprano, are due to the length of the vocal cords, being 
longer when the voice has a low pitch, and shorter when it has a high pitch. 
Speech is the faculty of expressing ideas by means of combinations of 
sounds, in obedience to the dictates of the cerebrum. 
Articulate sounds may be divided into vowels and consonants. The vowel 
sounds, a, e, i, o, u, are produced in the larynx by the vocal cords. The 
consonant sounds are produced in the air passages above the larynx by an 
interruption of the current of air by the lips, tongue, and teeth; the conso- 
nants may be divided into :— 
1. Mutes, b, d, k,p,t, c,g. 
2. Dentals, d,j, s, t, z. 228 
HUMAN PHYSIOLOGY. 
3. Nasals, m, n, ng. 
4. Labials, b,p,f, v, m. 
5. Gutturals, k, g, c, and g hard. 
6. Liquids, /, m, n, r. 
REPRODUCTION. 
Reproduction is the function by which the species is preserved, and 
accomplished by the organs of generation in the two sexes. 
GENERATIVE ORGANS OF THE FEMALE 
The Generative Organs of the Female consist of the ovaries, Fallo- 
pian tubes, uterus, and vagina. 
The Ovaries are two small, ovoid, flattened bodies, measuring i yz 
inches in length and of an inch in width ; they are situated in the cavity 
of the pelvis, and imbedded in the posterior layer of the broad ligament; 
attached to the uterus by a round ligament, and to the extremities of the 
Fallopian tubes by the fimbriae. The ovary consists of an external mem- 
brane of fibrous tissue, the cortical portion, in which are imbedded the 
Graafian vesicles, and an internal portion, the stroma, containing blood- 
vessels. 
The Graafian Vesicles are exceedingly numerous, but situated only in 
the cortical portion. Although the ovary contains the vesicles from the 
period of birth, it is only at the period of puberty that they attain their full 
development. From this time onward to the catamenial period there is a 
constant growth and maturation of the Graafian vesicles. They consist of 
an external investment, composed of fibrous tissue and blood-vessels, in the 
interior of which is a layer of cells forming the membrana granulosa; at 
its lower portion there is an accumulation of cells, the proligerous disc, in 
which the ovum is contained. The cavity of the vesicle contains a slightly 
yellowish, alkaline, albuminous fluid. 
The Ovum is a globular body, measuring about the of an inch in 
diameter; it consists of an external investing membrane, the vitelline mem- 
brane; a central granular substance, the vitellus, or yelk ; a nucleus, the 
germinal vesicle, in the interior of which is imbedded the nucleolus, or 
germinal spot. REPRODUCTION. 
229 
The Fallopian Tubes are about four inches in length, and extend out- 
ward from the upper angles of the uterus, between the folds of the broad 
ligaments, and terminate in a fringed extremity which is attached by one 
of the fiinges to the ovary. They consist of three coats:— 
1. The external, or peritoneal. 
2. Middle, or muscular, the fibers of which are arranged in a circular or 
longitudinal direction. 
3. Internal, or mucous, covered with ciliated epithelial cells, which are 
always waving from the ovary toward the uterus. 
The Uterus is pyriform in shape, and may be divided into a body and 
neck; it measures about three inches in length and two inches in breadth 
in the unimpregnated state. At the lower extremity of the neck is the os 
externum; at the junction of the neck with the body is a constriction, the 
os internum. The cavity of the uterus is triangular in shape, the walls of 
which are almost in contact. 
The walls of the uterus are made up of several layers of non-striated 
muscular fibers, covered externally by peritoneum, and lined internally by 
mucous membrane, containing numerous tubular glands, and covered by 
ciliated epithelial cells. 
The Vagina is a membranous canal, from five to six inches in length, 
situated between the rectum and bladder. It extends obliquely upward 
from the surface, almost to the brim of the pelvis, and embraces at its 
upper extremity the neck of the uterus. 
Discharge of the Ovum.—As the Graafian vesicle matures, it increases 
in size, from an augmentation of its liquid contents, and approaches the 
surface of the ovary, where it forms a projection, measuring from % to 
l/i an inch in size. The maturation of the vesicle occurs periodically, 
about every twenty-eight days, and is attended by the phenomena of men- 
struation. During this period of active congestion of the reproductive 
organs, the Graafian vesicle ruptures, the ovum and liquid contents escape, 
and are caught by the fimbriated extremity of the Fallopian tube, which has 
adapted itself to the posterior surface of the ovary. The passage of the 
ovum through the Fallopian tube into the uterus occupies from ten to four- 
teen days, and is accomplished by muscular contraction and the action of 
the ciliated epithelium. 
Menstruation is a periodic discharge of blood from the mucous mem- 
brane of the uterus, due to a fatty degeneration of the small blood-vessels. 
Under the pressure of an increased amount of blood in the reproductive 
organs, attending the process of ovulation, the blood-vessels rupture, and a 230 
HUMAN PHYSIOLOGY. 
hemorrhage takes place into the uterine cavity; thence it passes into the 
vagina. Menstruation lasts from five to six days, and the amount of blood 
discharged averages about five ounces. 
Corpus Luteum.—For some time anterior to the rupture of a Graafian 
vesicle, it increases in size and becomes vascular; its walls become thick- 
ened from the deposition of a reddish-yellow, glutinous substance, a pro- 
duct of cell growth from the proper coat of the follicle and the membrana 
granulosa. After the ovum escapes, there is usually a small effusion of 
blood into the cavity of the follicle, which soon coagulates, loses its color- 
ing matter, and acquires the characteristics of fibrin, but it takes no part in 
the formation of the corpus luteum. The walls of the follicle become con- 
voluted, vascular, and undergo hypertrophy, until they occupy the whole 
of the follicular cavity. At its period of fullest development, the corpus 
luteum measures of an inch in length and ]/z an inch in depth. In a 
few weeks the mass loses its red color and becomes yellow, constituting 
the corpus luteum, or yellow body. It then begins to retract and becomes 
pale ; and at the end of two months nothing remains but a small cicatrix 
upon the surface of the ovary. Such are the changes in the follicle if the 
ovum has not been impregnated. 
The corpus luteum, after impregnation has taken place, undergoes a much 
slower development, becomes larger, and continues during the entire period 
of gestation. The difference between the corpus luteum of the unimpreg- 
nated and pregnant condition is expressed in the following table by Dalton:— 
At the end of 
three weeks. 
One month. 
Corpus Luteum of Menstruation 
Three-quarters of an inch in diameter; central clot red- 
dish ; convoluted wall pale. 
Corpus Luteum of Pregnancy. 
Smaller; convoluted 
wall bright yellow; clot 
still reddish. 
Larger; convoluted wall 
bright yellow; clot still reddish. 
Two months. 
Reduced to the condi 
tion of an insignificant 
cicatrix. 
Seven-eighths of an inch in 
diameter; convoluted wall bright 
yellow; clot perfectly decolor- 
ized. 
Four months. 
Absent or unnotice- 
able. 
Seven-eighths of an inch in 
diameter; clot pale and fibrinous; 
convoluted wall dull yellow. 
Six months. 
Absent. 
Still as large as at the end of 
second month; clot fibrinous; 
convoluted wall paler. 
Nine months. 
Absent. 
Half an inch in diameter; cen- 
tral clot converted into a radiat- 
ing cicatrix ; external wall toler- 
ably thick and convoluted, but 
without any bright yellow color. REPRODUCTION. 
231 
GENERATIVE ORGANS OF THE MALE. 
The Generative Organs of the Male consist of the testicles, vasa 
deferentia, vesiculse seminales, and penis. 
The Testicles, the essential organs of reproduction in the male, are two 
oblong glands, about I y2 inches in length, compressed from side to side, 
and situated in the cavity of the scrotum. 
The proper coat of the testicle, the tunica albuginea, is a white, fibrous 
structure, about the of an inch in thickness; after enveloping the testicle, 
it is reflected into its interior at the posterior border, and forms a vertical 
process, the mediastinum testes, from which septa are given ofif, dividing 
the testicle in lobules. 
The substance of the testicle is made up of the seminiferous tubules, which 
exist to the number of 840; they are exceedingly convoluted, and when un- 
raveled are about 30 inches in length. As they pass toward the apices of 
the lobules, they become less convoluted, and terminate in from 20 to 30 
straight ducts, the vasa recta, which pass upward through the mediastinum 
and constitute the rete testis. At the upper part of the mediastinum the 
tubules unite to form from 9 to 30 small ducts, the vasa efferentia, which 
become convoluted and form the globus major of the epididymis ; the con- 
tinuation of the tubes downward behind the testicle and a second convolu- 
tion constitutes the body and globus minor. 
The seminal tubule consists of a basement membrane lined by granular 
nucleated epithelium. 
The Vas Deferens, the excretory duct of the testicle, is about two feet 
in length, and may be traced upward from the epididymis to the under sur- 
face of the base of the bladder, where it unites with the duct of the vesicula 
seminalis to form the ejaculatory duct. 
The Vesiculae Seminales are two lobulated, pyriform bodies, about 
two inches in length, situated on the inner surface of the bladder. 
They have an external fibrous coat, a middle muscular coat, and an 
internal mucous coat, covered by epithelium, which secretes a mucous fluid. 
The vesiculse seminales serve as reservoirs, in which the seminal fluid is 
temporarily stored up. 
The Ejaculatory Duct, about y of an inch in length, opens into the 
urethra, and is formed by the union of the vasa deferentia and the ducts of 
the vesiculse seminales. 
The Prostrate Gland surrounds the posterior extremity of the urethra, 
and opens into it by from 20 to 30 openings, the orifices of the prostatic 232 
HUMAN PHYSIOLOGY. 
tubules. The gland secretes a fluid which forms part of the semen and 
assists in maintaining the vitality of the spermatozoa. 
Semen is a complex fluid, made up of the secretions from the testicles, 
the vesicula seminales, the prostatic and urethral glands. It is grayish- 
white in color, mucilaginous in consistence, of a characteristic odor, and 
somewhat heavier than water. From half a dram to a dram is ejaculated 
at each orgasm. 
The Spermatozoa are peculiar anatomical elements, developed within 
the seminal tubules, and possess the power of spontaneous movement. 
The spermatozoa consist of a conoidal head and a long, filamentous tail, 
which is in continuous and active motion; as long as they remain in the 
vas deferens they are quiescent, but when free to move in the fluid of the 
vesiculae seminales become very active. 
Origin.—The spermatozoa appear at the age of puberty, and are then 
constantly formed until an advanced age. They are developed from the 
nuclei of large, round cells contained in the anterior of the seminal tubules, 
as many as 15 to 20 developing in a single cell. 
When the spermatozoa are introduced into the vagina, they pass readily 
into the uterus and through the Fallopian tubes toward the ovaries, where 
they remain and retain their vitality for a period of from eight to ten days. 
Fecundation is the union of the spermatozoa with the ovum during its 
passage toward the uterus, and usually takes place in the Fallopian tube, 
just outside of the womb. After floating around the ovum in an active man- 
ner, they penetrate the vitelline membrane, pass into the interior of the 
vitellus, where they lose their vitality, and along with the germinal vesicle 
entirely disappear. 
Segmentation of the Vitellus.—After the disappearance of the sperma- 
tozoa and the germinal vesicle there remains a transparent, granular, albu- 
minous substance, in the center of which a new nucleus soon appears; this 
constitutes the parent cells, and is the first stage in the development of the 
new being. 
Following this, the vitellus undergoes segmentation ; a constriction ap- 
pears on the opposite side of the vitellus, which gradually deepens, until the 
yelk is divided into two segments, each of which has a distinct nucleus and 
nucleolus; these two segments undergo a further division into four, the 
four into eight, the eight into others, and so on, until the entire vitellus is 
DEVELOPMENT OF ACCESSORY STRUCTURES. REPRODUCTION. 
233 
divided into a great number of cells, each of which contains a nucleus and 
nucleolus. 
The peripheral cells of this “ mulberry mass ” then arrange themselves 
so as to form a membrane, and as they are subjected to mutual pressure, 
assume a polyhedral shape, which gives to the membrane a mosaic appear- 
ance. The central part of the vitellus becomes filled with a clear fluid. A 
secondary membrane shortly appears within the first, and the two together 
constitute the external and internal blastodermic membranes. 
Germinal Area.—At about this period there is an accumulation of cells 
at a certain spot upon the surface of the blastodermic membranes which 
marks the position of the future embryo. This spot, at first circular, soon 
becomes elongated, and forms the primitive trace, around which is a clear 
space, the area pellucida, which is itself surrounded by a darker region, 
the area opaca. 
The primitive trace soon disappears, and the area pellucida becomes 
guitar-shaped; a new groove, the medullary groove, is now formed, which 
develops from before backward, and becomes the neural canal. 
Blastodermic Membranes.—The embryo, at this period, consists of 
three layers, viz.: the external and internal blastodermic membranes, and a 
middle membrane formed by a genesis of cells from their internal surfaces. 
These layers are known as the epiblast, mesoblast, and hypoblast. 
The epiblast gives rise to the central nervous system, the epidermis of the 
skin and its appendages, and the primitive kidneys. 
The mesoblast gives rise to the dermis, muscles, bones, nerves, blood- 
vessels, sympathetic nervous system, connective tissue, the urinary and re- 
productive apparatus, and the walls of the alimentary canal. 
The hypoblast gives rise to the epithelial lining of the alimentary canal 
and its glandular appendages, the liver and pancreas, and the epithelium of 
the respiratory tract. 
Dorsal Laminae.—As development advances, the true medullary 
groove deepens, and there arise two longitudinal elevations of the epiblast, 
the dorsal lamince, one on either side of the groove, which grow up, arch 
over, and unite so as to form a closed tube, the primitive central nervous 
system. 
The Chorda Dorsalis is a cylindrical rod running almost throughout 
the entire length of the embryo. It is formed by an aggregation of meso- 
blastic cells, and situated immediately beneath the medullary groove. 
Primitive Vertebrae.—On either side of the neural canal the cells of 
the mesoblast undergo a longitudinal thickening, which develops and ex- 234 
HUMAN PHYSIOLOGY. 
tends around the neural canal and the chorda dorsalis, and forms the arches 
and bodies of the vertebrae. They become divided transversely into four- 
sided segments. 
The mesoblast now separates into two layers; the external, joining with 
the epiblast, forms the somatopleure; the internal, joining with the hypo- 
blast, forms the splanchnopleure ; the space between them constituting the 
pleuro-peritoneal cavity. 
Visceral Laminae.—The walls of the pleuro-peritoneal cavity are 
formed by a downward prolongation of the somatopleure (the visceral 
lamince), which, as they extend around in front, pinch off a portion of the 
yelk sac (formed by the splanchnopleure), which becomes the primitive 
alimentary canal; the lower portion, remaining outside of the body cavity, 
forms the umbilical vesicle, which after a time disappears. 
Formation of Fetal Membranes.—The amnion appears shortly 
after the embryo begins to develop, and is formed by folds of the epiblast 
and external layer of the mesoblast, rising up in front and behind and on 
each side; these amniotic folds gradually extend over the back of the 
embryo to a certain point, where they coalesce and enclose a cavity, the 
amniotic cavity. The membranous partition between the folds disappears, 
and the outer layer recedes and becomes blended with the vitelline mem- 
brane, constituting the chorion, the external covering of the embryo. 
The Allantois.—As the amnion develops, there grows out from the 
posterior portion of the alimentary canal a pouch, or diverticulum, the 
allantois, which carries blood-vessels derived from the intestinal circulation. 
As it gradually enlarges, it becomes more vascular, and inserts itself be- 
tween the two layers of the amnion, coming into intimate contact with the 
external layer. Finally, from increased growth, it completely surrounds 
the embryo, and its edges become fused together. 
In the bird, the allantois is a respiratory organ, absorbing oxygen and 
exhaling carbonic acid; it also absorbs nutritious matter from the interior 
of the egg. 
Amniotic Fluid.—The amnion, when first formed, is in close contact 
with the surface of the ovum; but it soon enlarges, and becomes filled 
with a clear, transparent fluid, containing albumin, glucose, fatty matters, 
urea, and inorganic salts. It increases in amount up to the latter period of 
gestation, when it amounts to about two pints. In the space between the 
amnion and allantois is a gelatinous material, which is encroached upon 
and finally disappears as the amnion and allantois come in contact, at about 
the fifth month. REPRODUCTION. 
235 
The Chorion, the external investment of the embryo, is formed by a 
fusion of the original vitelline membrane, the external layer of the amnion, 
and the allantois. The external surface now becomes covered with villous 
processes, which increase in number and size by the continual budding 
and growth of club-shaped processes from the main stem, and give to the 
chorion a shaggy appearance. They consist of a homogeneous granular 
matter, and are penetrated by branches of the blood-vessels derived from 
the aorta. 
The presence of villous processes in the uterine cavity is proof positive 
of the previous existence of a fetus. They are characteristic of the 
chorion, and are found under no other circumstances. 
At about the end of the second month the villosities begin to atrophy 
and disappear from the surface of the chorion, with the exception of those 
situated at the points of entrance of the Yetal blood-vessels, which occupy 
about of its surface, where they continue to grow longer, become more 
vascular, and ultimately assist in the formation of the placenta; the remain- 
ing of the surface loses its villi and blood-vessels and becomes a simple 
membrane. 
The Umbilical Cord connects the fetus with that portion of the 
chorion which forms the fetal side of the placenta. It is a process of the 
allantois, and contains two arteries and a vein, which have a more or less 
spiral direction. It appears at the end of the first month, and gradually 
increases in length, until, at the end of gestation, it measures about 20 
inches. The cord is also surrounded by a process of the amnion. 
Development of the Decidual Membrane.—The interior of the 
uterus is lined by a thin, delicate mucous membrane, in which are im- 
bedded immense numbers of tubules, terminating in blind extremities, the 
uterine tubules. At each period of menstruation the mucous membrane 
becomes thickened and vascular, which condition, however, disappears 
after the usual menstrual discharge. When the ovum becomes fecundated, 
the mucous membrane takes on an increased growth, becomes more hyper- 
trophied and vascular, sends up little processes or elevations from its sur- 
face, and constitutes the decidua vera. 
As the ovum passes from the Fallopian tube into the interior of the 
uterus, the primitive vitelline membrane, covered with villosities, becomes 
entangled with the processes of the mucous membrane. A portion of the 
decidua vera then grows up on all sides and encloses the ovum, forming 
the decidua reflexa, while the villous processes of the chorion insert them- 
selves into the uterine tubules and in the mucous membrane between 
them. 236 
HUMAN PHYSIOLOGY. 
As development advances the decidua reflexa increases in size, and at 
about the end of the fourth month comes in contact with the decidua vera, 
with which it is ultimately fused. 
The Placenta.—Of all the embryonic structures, the placenta is the 
most important. It is formed in the third month, and then increases in size 
until the seventh month, when a retrogressive metamorphosis takes place 
until its separation during labor, at which time it is of an oval or rounded 
shape, and measures from seven to nine inches in length, six to eight inches 
in breadth, and weighs from 15 to 20 ounces. It is most frequently situated 
at the upper and posterior part of the inner surface of the uterus. 
The placenta consists of two portions, a fetal and a maternal. 
The fetal portion is formed by the villi of the chorion, which, by devel- 
oping, rapidly increase in size and number. They become branched and 
penetrate the uterine tubules, which enlarge and receive their many ramifi- 
cations. The capillary blood-vessels in the anterior of the villi also enlarge 
and freely anastomose with each other. 
The maternal portion is formed from that part of the hypertrophied and 
vascular decidual membrane between the ovum and the uterus, the decidua 
serotina. As the placenta increases in size, the maternal blood-vessels 
around the tubules become more and more numerous, and gradually fuse 
together, forming great lakes, which constitute sinuses in the walls of the 
uterus. 
As the latter period of gestation approaches, the villi extend deeper into 
the decidua, while the sinuses in the maternal portion become larger and 
extend further into the chorion. Finally, from excessive development of 
the blood-vessels, the structures between them disappear, and as their walls 
come in contact, they fuse together, so that, ultimately, the maternal and 
fetal blood are only separated by a thin layer of a homogeneous substance. 
When fully formed, the placenta consists principally of blood-vessels inter- 
lacing in every direction. The blood of the mother passes from the uterine 
vessels into the lake surrounding the villi; the blood from the child flows 
from the umbilical arteries into the interior of the villi; but there is not at 
any time an intermingling of blood, the two being separated by a delicate 
membrane formed by a fusion of the walls of the blood-vessels and the 
walls of the villi and uterine sinuses. 
The function of the placenta, besides nutrition, is that of a respiratory 
organ, permitting the oxygen of the maternal blood to pass by osmosis 
through the delicate placental membrane into the blood of the fetus; at 
the same time permitting the carbonic acid and other waste products, the 
result of nutritive changes in the fetus, to pass into the maternal blood, and 
so to be carried to the various eliminating organs. REPRODUCTION. 
237 
Through the placenta also passes all the nutritious materials of the 
maternal blood which are essential for the development of the embryo. 
At about the middle of gestation there develops beneath the decidual 
membrane a new mucous membrane, destined to perform the functions of 
the old when it is extruded from the womb, along with the other embryonic 
structures, during parturition. 
DEVELOPMENT OF THE EMBRYO. 
Nervous System.—The cerebro-spinal axis is formed within the me- 
dullary canal by the development of cells from its inner surfaces, which as 
they increase fill up the canal, and there remains only the central canal of 
the cord. The external surface gives rise to the dura mater and pia mater. 
The neural canal thus formed is a tubular membrane; it terminates pos- 
teriorly in an oval dilatation, and anteriorly in a bulbous extremity, which 
soon becomes partially contracted, and forms the anterior, middle, and pos- 
terior cerebral vesicles, from which are ultimately developed the cerebrum, 
the corpora quadrigemina, and medulla oblongata, respectively. 
The anterior vesicle soon subdivides into two secondary vesicles, the 
larger of which becomes the hemispheres, the smaller the optic thalami; 
the posterior vesicle also divides into two, the anterior becoming the cere- 
bellum, the posterior the pons Varolii and medulla oblongata. 
About the seventh week the straight chain of cerebral vesicles becomes 
curved from behind forward and forms three prominent angles. As devel- 
opment advances, the relative size of the encephalic masses changes. The 
cerebrum, developing more rapidly than the posterior portion of the brain, 
soon grows backward and arches over the optic thalami and the tubercula 
quadrigemina; the cerebellum overlaps the medulla oblongata. 
The surface of the cerebral hemispheres is at first smooth, but at about 
the fourth month begins to be marked by the future fissures and convolu- 
tions. 
The Eye is formed by a little bud projecting from the side of the anterior 
vesicle. It is at first hollow, but becomes lined with nervous matter, form- 
ing the optic nerve and retina ; the remainder of the cavity is occupied by 
the vitreous body. The anterior portion of the pouch becomes invaginated 
and receives the crystalline lens, which is a product of the epiblast, as is 
also the cornea. The iris appears as a circular membrane without a cen- 
tral aperture, about the seventh week; the eyelids are formed between the 
second and third months. 
The Internal Ear is developed from the auditory vesicle, budding from 238 
HUMAN PHYSIOLOGY. 
the 3d cerebral vesicle; the membranous vestibule appears first, and from 
it diverticula are given off, which become the semicircular canals and 
cochlea. 
The cavity of the tympanum, the Eustachian tube, and the external 
auditory canal are the remains of the first branchial cleft, the cavity of this 
cleft being subdivided into the tympanum and external auditory meatus by 
the membrana tympani. 
The Skeleton.—The chorda dorsalis, the primitive part of the vertebral 
column, is a cartilaginous rod situated beneath the medullary groove. It 
is a temporary structure, and disappears as the true bony vertebrae develop. 
On either side are the quadrate masses of the mesoblast, the primitive ver- 
tebrae, which send processes upward and around the medullary groove, and 
downward and around the chorda dorsalis, forming in these situations the 
arches and bodies of the future vertebrae. 
More externally the outer layers of the mesoblast and epiblast arch 
downward and forward, forming the ventral laminae, in which develop the 
muscles and bones of the abdominal walls. 
The true cranium is an anterior development of the vertebral column, 
and consists of the occipital, parietal, and frontal segments, which corre- 
spond to the three cerebral vesicles. The base of the cranium consists, at 
this period, of a cartilaginous rod on either side of the anterior extremity 
of the chorda dorsalis, in which three centers of ossification appear, the 
basi-occipital, the basisphenoidal, and the presphenoidal. They ultimately 
develop into the basilar process of the occipital bone and the body of the 
sphenoid. 
The entire skeleton is at first either membranous or cartilaginous. At 
the beginning of the second month centers of ossification appear in the jaws 
and clavicle; as development advances, the ossific points in all the future 
bones extend, until ossification is completed. 
The litnbs develop from four little buds projecting from the sides of the 
embryo, which, as they increase in length, separate into the thigh, leg, and 
foot, and the arm, forearm, and hand; the extremities of the limbs undergo 
subdivision, to form the fingers and toes. 
Face and Visceral Arches.—In the facial and cervical regions the 
visceral laminae send up three processes, the visceral arches, separated by 
clefts, the visceral clefts. 
The first, or the mandibular arches, unite in the median line to form 
the lower jaw, and superiorly form the malleus. A process jutting from 
its base grows forward, unites with the frontonasal process growing from REPRODUCTION. 
239 
above, and forms the upper jaw. When the superior maxillary processes 
fail to unite, there results the cleft-palate deformity; if the integument also 
fails to unite, there results the hare-lip deformity. The space above the 
mandibular arch becomes the mouth. 
The second arch develops the incus and stapes bones, the styloid process 
and ligament, and the lesser cornua of the hyoid bone. The cleft between 
the first and second arches partially closes up, but there remains an open- 
ing at the side which becomes the Eustachian tube, tympanic cavity, and 
external auditory meatus. 
The third arch develops the body and greater cornu of the hyoid bone. 
Alimentary Canal and its Appendages.—The alimentary canal is 
formed by a pinching off of the yelk-sac by the visceral plates as they grow 
downward and forward. It consists of three distinct portions, the fore gut, 
the hind gut, and the central part, which communicates for some time with 
the yelk sac. It is at first a straight tube, closed at both extremities, lying 
just beneath the vertebral column. The canal gradually increases in 
length, and becomes more or less convoluted; at its anterior portion two 
pouches appear, which become the cardiac and pyloric extremities of the 
stomach. At about the seventh week the inferior extremity of the intestine 
is brought into communication with the exterior, by an opening, the anus. 
Anteriorly the mouth and pharynx are formed by an involution of epiblast, 
which deepens until it communicates with the fore gut. 
The liver appears as a slight protrusion from the sides of the alimentary 
canal, about the end of the first month; it grows very rapidly, attains a 
large size, and almost fills up the abdominal cavity. The hepatic cells are 
derived from the intestinal epithelium, the vessels and connective tissue 
from the mesoblast. 
The pancreas is formed by the hvpoblastic membrane. It originates in 
two small ducts budding from the duodenum, which divide and subdivide, 
and develop the glandular structure. 
The lungs are developed from the anterior part of the esophagus. At 
first a small bud appears, which, as it lengthens, divides into two branches; 
secondary and tertiary processes are given off these, which form the bron- 
chial tubes and air cells. The lungs originally extended into the abdomi- 
nal cavity, but became confined to the thorax by the development of the 
diaphragm. 
The bladder is formed by a dilatation of that portion of the allantois 
remaining within the abdominal cavity. It is at first pear shaped, and 
communicates with the intestine, but later becomes separated, and opens 240 
HUMAN PHYSIOLOGY. 
exteriorly by the urethra. It is attached to the abdominal walls by a 
rounded cord, the urachus, the remains of a portion of the allantois. 
Genito-urinary Apparatus.—The Wolffian bodies appear about the 
thirteenth day, as long, hollow tubes running along each side of the primi- 
tive vertebral column. They are temporary structures, and are sometimes 
called the primordial kidneys. The Wolffian bodies consist of tubules 
which run transversely and are lined with epithelium; internally they be- 
come invaginated to receive tufts of blood-vessels; externally they open 
into a common excretory duct, the duct of the Wolffian body, which unites 
with the duct of the opposite body, and empties into the intestinal canal 
at a point opposite the allantois. On the outer side of the Wolffian body 
there appears another duct, the duct of Muller, which also opens into the 
intestine. 
Behind the Wolffian bodies are developed the structures which become 
either the ovaries or testicles. In the development of the female the 
Wolffian bodies and their ducts disappear; the extremities of the Mullerian 
ducts dilate and form the fimbriated extremity of the Fallopian tubes, while 
the lower portions coalesce to form the body of the uterus and vagina, 
which now separate themselves from the intestine. 
In the development of the male the Mullerian ducts atrophy, and the 
ducts of the Wolffian body ultimately form the epididymis and vas defer- 
ens. About the seventh month the testicles begin to descend, and by the 
ninth month have passed through the abdominal ring into the scrotum. 
The kidneys are developed out of the Wolffian bodies. They consist of 
little pyramidal lobules, composed of tubules which open at the apex into 
the pelvis. As they pass outward they become convoluted and cup-shaped 
at their extremities, receive a tuft of blood-vessels, and form the Malpig- 
hian bodies. 
The ureters are developed from the kidneys and pass downward to be 
connected with the bladder. 
The Circulatory Apparatus assumes three different forms at different 
periods of life, all having reference to the manner in which the embryo 
receives nutritious matter and is freed of waste products. 
The vitelline circulation appears first and absorbs nutritious material 
from th’e vitellus. It is formed by blood-vessels which emerge from the 
body and ramify over a portion of the vitelline membrane, constituting the 
area vasculosa. The heart, lying in the median line, gives off two arches 
which unite to form the abdominal aorta, from which two large arteries 
are given off, passing into the vascular area; the venous blood is returned REPRODUCTION. 
241 
by veins which enter the heart. These vessels are known as the omphalo- 
mesenteric arteries and veins. The vitelline circulation is of short dura- 
tion in the mammals, as the supply of nutritious matter in the vitellus soon 
becomes exhausted. 
The placental circulation becomes established when the blood-vessels in 
the allantois enter the villous processes of the chorion and come into close 
relationship with the maternal blood-vessels. This circulation lasts during 
the whole of intra-uterine life, but gives way at birth to the adult circula- 
tion, the change being made possible by the development of the circulatory 
apparatus. 
The heart appears as a mass of cells coming off from the anterior por- 
tion of the intestine; its central part liquefies, and pulsations soon begin. 
The heart is at first tubular, receiving posteriorly the venous trunks and 
giving off anteriorly the arterial trunks. It soon becomes twisted upon 
itself, so that the two extremities lie upon the same plane. 
The heart now consists of a single auricle and a single ventricle. A 
septum, growing from the apex of the ventricle, divides it into two cavities, 
a right and a left. The auricles also become partly separated by a septum 
which is perforated by the foramen ovale. The arterial trunk becomes 
separated, by a partition, into two canals, which become, ultimately, the 
aorta and pulmonary artery. The auricles are separated from the ven- 
tricles by incomplete septa, through which the blood passes into the ven- 
tricles. 
Arteries.—The aorta arises from the cephalic extremity of the heart and 
divides into two branches, which ascend, one on each side of the intestine, 
and unite posteriorly to form the main aorta; posteriorly to these first aortic 
arches four others are developed, so that there are five altogether running 
along the visceral arches. The two anterior soon disappear. The third 
arch becomes the internal carotid and the external carotid; a part of the 
fourth arch, on the right side, becomes the subclavian artery, and the 
remainder atrophies and disappears, but on the left side it enlarges and be- 
comes the permanent aorta; the fifth arch becomes the pulmonary artery 
on the left side. The communication between the pulmonary artery and 
the aorta, the ductiis arteriosus, disappears at an early period. 
Veins.—The venous system appears first as two short, transverse veins, 
the canals of Cuvier, formed by the union of the vertebral veins and the 
cardinal veins, which empty into the auricle. The inferior vena cava is 
formed, as the kidneys develop, by the union of the renal veins, which, in 
a short time, receive branches from the lower extremities. The subclavian 
veins join the jugular as the upper extremities develop. The heart descends 242 
HUMAN PHYSIOLOGY. 
in the thorax, and the canals of Cuvier become oblique; they shortly com- 
municate by a transverse duct, which ultimately becomes the left innomi- 
nate vein. The left canal of Cuvier atrophies and becomes a fibrous cord. 
A transverse branch now appears, which carries the blood from the left car- 
diac vein into the right, and becomes the vena azygos minor; the right car- 
diac vein becomes the vena azygos major. 
Circulation of Blood in the Fetus.—The blood returning from the 
placenta, after having received oxygen and being freed from carbonic acid, 
is carried by the umbilical vein to the under surface of the liver; here a 
portion of it passes through the ductus venosus into the ascending vena cava, 
while the remainder flows through the liver and passes into the vena cava 
by the hepatic veins. When the blood is emptied into the right auricle it 
is directed by the Eustachian valve through the foramen ovale, into the left 
auricle, thence into the left ventricle, and so into the aorta to all parts of 
the system. The venous blood returning from the head and upper extremi- 
ties is emptied, by the superior vena cava, into the right auricle, from which 
it passes into the right ventricle, and thence into the pulmonary artery. 
Owing to the condition of the lung only a small portion flows through the 
pulmonary capillaries, the greater part passing through the ductus arteriosus, 
which opens into the aorta at a point below the origin of the carotid and 
subclavian arteries. The mixed blood now passes down the aorta, to sup- 
ply the lower extremities, but a portion of it is directed, by the hypogastric 
arteries, to the placenta, to be again oxygenated. 
At birth, the placental circulation gives way to the circulation of the 
adult. As soon as the child begins to breathe, the lungs expand, blood 
flows freely through the pulmonary capillaries, and the ductus arteriosus 
begins to contract. The foramen ovale closes about the tenth day. The 
umbilical vein, the ductus venosus, and the hypogastric arteries become 
impervious in several days, and ultimately form rounded cords. TABLE OF PHYSIOLOGICAL CONSTANTS. 
243 
TABLE OF PHYSIOLOGICAL CONSTANTS. 
Mean height of male, 5 feet 6)4 inches; of female, 5 feet 2 inches. 
Mean weight of male, 145 pounds; of female, 121 pounds. 
Number of chemic elements in the human body : from 16 to 18. 
Number of proximate principles in the human body ; about loo. 
Amount of water in the body weighing 145 pounds: 108 pounds. 
Amount of solids in the body weighing 145 pounds: 36 pounds. 
Amount of saliva secreted in 24 hours: about 3)4 pounds. 
Function of saliva: converts starch into maltose. 
Active principle of saliva: ptyalin. 
Amount of gastric juice secreted in 24 hours: from 8 to 14 pounds. 
Functions of gastric juice : converts albumin into peptone. 
Active principles of gastric juice : pepsin and hydrochloric acid. 
Duration of digestion: from 3 to 5 hours. 
Amount of intestinal juice secreted in 24 hours: about 1 pound. 
Function of intestinal juice : converts starch into maltose. 
Amount of pancreatic juice secreted in 24 hours: about 1)4 pounds. 
Active principles of pancreatic juice: trypsin, amylopsin, and 
steapsin. 
Functions: 
1. Emulsifies fats. 
2. Converts albumin into peptone. 
3. Converts starch into maltose. 
Amount of bile poured into the intestines daily: about pounds, 
1. Assists in the emulsification of fats. 
2. Stimulates the peristaltic movements. 
3. Prevents putrefactive changes in the food. 
4. Promotes the absorption of the fat. 
Functions : 
Amount of blood in the body: from 16 to 18 pounds. 
Size of red corpuscles: of an inch. 
Size of white corpuscles: 2 oW °f an inch- 
Shape of red corpuscles : circular biconcave discs. 
Shape of white corpuscles : globular. 
Number of red corpuscles in a cubic millimeter of blood (the cubic of 
an inch): 5,000,000. 244 
HUMAN PHYSIOLOGY. 
Function of red corpuscles : to carry oxygen from the lungs to the tissues. 
Frequency of the heart’s pulsation per minute: 72 on the average. 
Velocity of the blood movement in the arteries: about 12 inches per 
second. 
Length of time required for the blood to make an entire circuit of the vas- 
cular system : about 20 seconds. 
Amount of air passing in and out of the lungs at each respiratory act: 
from 20 to 30 cubic inches. 
Amount of air that can be taken into the lungs on a forced inspiration: 
110 cubic inches. 
Amount of reserve air in the lungs after an ordinary expiration : 100 cubic 
inches. 
Amount of residual air always remaining in the lungs: about 100 cubic 
inches. 
Vital capacity of the lungs: 230 cubic inches. 
Entire volume of air passing in and out of the lungs in 24 hours: about 
400 cubic feet. 
Composition of the air: nitrogen, 79.19; oxygen, 20.81, per 100 parts. 
Amount of oxygen absorbed in 24 hours: 18 cubic feet. 
Amount of carbonic acid exhaled in 24 hours: 14 cubic feet. 
Temperature of the human body at the surface: F. 
Amount of urine excreted daily: from 40 to 50 ounces. 
Amount of urea excreted daily: 512 grains. 
Specific gravity of urine: from 1.015 to 1.025. 
Number of spinal nerves : 31 pairs. 
Number of roots of origin: two; 1st, anterior, efferent; 2d, posterior, 
afferent. 
Rate of transmission of nerve force: about 100 feet per second. 
Number of cranial nerves : 12 pairs. 
1. Olfactory, or 1st pair. 
2. Optic, or 2d pair. 
3. Auditory, or 8th pair. 
4. Chorda tympani for anterior % of tongue. 
5. Branches of glosso-pharyngeal, or 8th pair, 
for posterior of tongue. 
Nerves of special sense: 
Motor nerves to eyeball and accessory structures : motor oculi, or 3d 
pair; pathetic, or 4th pair; abducens, or 6th pair. 
Motor nerves to facial muscles: portio dura, facial, or 7th pair. 
Motor nerve to tongue: hypoglossal, or 12th pair. 
Motor nerve to laryngeal muscles: spinal accessory, or nth pair. TABLE OF PHYSIOLOGICAL CONSTANTS. 
245 
Sensory nerve of the face: trifacial, or 5th pair. 
Sensory nerve of the pharynx : glosso-pharyngeal, or 9th pair. 
Sensory nerves of the lungs, stomach, etc.: pneumogastric, or loth pair. 
Length of spinal cord: 16 to 18 inches; weight \]/z ounces. 
Point of decussation of motor fibers: at the medulla oblongata. 
Point of decussation of sensory fibers : throughout the spinal cord. 
Function of antero-lateral columns of spinal cord: transmit motor 
impulses from the brain to the muscles. 
Functions of the posterior columns: assist in the coordination of mus- 
cular movements. 
Functions of the medulla oblongata: controls the functions of insaliva- 
tion, mastication, deglutition, respiration, circulation, etc. 
Functions of the corpora quadrigemina: physical centers for sight. 
Functions of the corpora striata: centers for motion. 
Functions of the optic thalami: centers for sensation. 
Function of the cerebellum: center for the coordination of muscular 
movement. 
Function of the cerebrum : center for intelligence, reason, and will. 
Center for articulate language : 3d frontal convolution on the left side 
of cerebrum. 
Number of coats to the eye : three; 1st, cornea and sclerotic; 2d, choroid ; 
3d, retina. 
Function of iris: regulates the amount of light entering the eye. 
Function of crystalline lens: refracts the rays of light so as to form an 
image on the retina. 
Function of retina : receives the impressions of light. 
Function of membrana tympani: receives and transmits waves of sound 
to internal ear. 
Function of Eustachian tube : regulates the passage of air into and from 
the middle ear. 
Function of semicircular canals : assist in maintaining the equipoise of 
the body. 
Function of the cochlea: appreciates the shades and combinations of 
musical tones. 
Size of human ovum: of an inch in diameter. 
Size of spermatozoa : of an inch in length. 
Function of the placenta: acts as a respiratory and digestive organ for the 
fetus. 
Duration of pregnancy : 280 days. TABLE SHOWING RELATION OF WEIGHTS AND 
MEASURES OF THE METRIC SYSTEM TO APPROX- 
IMATE WEIGHTS AND MEASURES OF THE U. S. 
MEASURES OF LENGTH. 
One Myriameter = 10,000 meters = 32800. feet. 
One Kilometer = 1,000 “ = 3280. “ 
One Hectometer = 100 “ = 328.0 “ 
One Decameter = xo “ = 32.80 “ 
One Meter 
the ten millionth part of a 
quarter of the Meridian of 
the Earth 
- = 39.368 inches. 
One Centimeter 
One Decimeter —the tenth part of one meter = 3.936 “ 
[ the one hundredth part of 
[_ one meter. 
One Millimeter 
f the one thousandth part 
L of one meter 
►= -393 (S) 
► = -°39UV) “ 
WEIGHTS. 
One Myriagram = 10,000 grams = pounds Troy. 
One Kilogram at 1,000 “ = 2% “ “ 
One Hectogram = 100 “ = “ 
One Decagram =10“ = “ 
One Gram 
One Decigram = the tenth part of a gram = 1.543 (i/4) “ 
the weight of a cubic cen- 
timeter of water at 40 C. 
= 15-434 grains. 
One Centigram 
the hundredth part of one 
gram 
= -154 04) “ 
One Milligram 
the thousandth part of one 
gram 
-= -OI5(A) “ 
MEASURES OF CAPACITY. 
10 cubic Meters or the! 
measure of 10 Milliers of 
water 
One Myrialiter = 
= 2600. gallons. 
One Kiloliter = 
I cubic Meter or themeas-1 
ure of 1 Millier of water, j 
100 cubic Decimeters or'i 
the measure of 1 Quintal 
of water 
= 260. “ 
One Hectoliter = 
= 26. “ 
One Decaliter = 
10 cubic Decimeters or'] 
the measure of 1 Myria- 
gram of water 
= 2.6 “ 
1 cubic Decimeter or the 1 
measure of 1 Kilogram 
of water J 
One Liter = 
100 cubic Centimeters or 1 
the measure of I Hecto- 
gram of water J 
= 2.1 pints. 
One Deciliter = 
= 3.3 ounces. 
One Centiliter = 
10 cubic Centimeters or ] 
the measure of 1 Deca- 
gram of water 
= 2.7 drams. 
1 cubic Centimeter or the 1 
measure of 1 Gram of 
water. J 
One Milliliter = 
= 16.2 minims. INDEX. 
PAGE 
ABDUCENS NERVE, .... 168 
Aberration, chromatic, .... 215 
, spherical, 215 
Absorption, 98 
by lacteals, ‘ ' 100 
by blood-vessels, ...... 101 
of oxygen in respiration, . . 126 
Accommodation of the eye, .... 214 
Adipose tissue, uses of in the body, . 19 
Adult circulation, establishment of at 
birth, 242 
Air, atmospheric, composition of, . . 126 
, amount exchanged in respira- 
tion, 126 
, changes in during respiration, 126 
Albumin, uses of, in the body, ... 21 
Albuminoid substances, 21 
Alcohol, action of, 77 
Alimentary principles, classification 
of, 75 
, albuminous principles, ... 76 
, saccharin principles 76 
, oleaginous principles, .... 76 
, inorganic principles, .... 76 
Alimentary canal, development of, . 238 
Allantois, development and function 
of, . 234 
Amnion, formation of, 234 
Animal heat, 128 
Anterior columns of spinal cord, . . 155 
Area, germinal, 237 
Arteries, properties of, 117 
Articulations, 35 
, axial, 35 
Asphyxia, 128 
Astigmatism, 215 
Axis, cerebro-spinal 153 
cylinder of nerves, 64 
Bladder, urinary, 140 
Blastodermic membranes, 233 
Blood, 106 
, composition of plasma . . . 106 
, coagulation of, 109 
, coloring matter of, 108 
, changes in, during respira- 
tion, 128 
PAGE 
Blood, circulation of, 112 
, rapidity of flow in arteries, . 118 
, rapidity of flow in capillaries, 119 
, pathological conditions of, . in 
, corpuscles, 107 
, origin of, 109 
pressure, 117 
Bone, structure of, 30 
Burdach, column of, 156 
QANALS OF CUVIER, .... 241 
Capillary blood-vessels, .... 118 
Capsule, internal, 185 
, external, 185 
Cartilage, 29 
Caudate nucleus, 185 
Cells, structure of, 23 
, manifestation of life by, . . 25 
of anterior horns of gray 
matter, 155 
Center for articulate language, . . . 197 
Cerebrum, 188 
, fissures and convolutions, . . 189 
, functions of, 192 
, localization of functions, . . 195 
, motor area of, 195 
, special centers of, 196 
Cerebellum, 186 
, forced movements of, ... . 187 
Cerebral vesicles of embryo, .... 237 
Chemical composition of human body 14 
elements, proximate quantity 
of in body, 13 
Chorda dorsalis, 233 
tympani nerve, course and 
function of, 171 
Chorion, 235 
Chyle 104 
Ciliary muscle, 209 
Circulation of blood, 112 
Claustrum, 185 
Cochlea, . 223 
Columns of spinal cord, 155 
Corium, 150 
Corpora Wolffiana, 240 
qttadrigemina 184 
Corpus luteum, 230 
striatum, 185 
247 248 
INDEX 
PAGE 
Corti, organ of, 224 
Cranial nerves, 165 
Crura cerebri, 183 
Crystalline lens, 211 
■TXECIDUAL MEMBRANE, . 235 
Decussation of motor and sen- 
sory fibers, . 157 
Deglutition, 87 
, nervous circle of, 181 
Development of accessory structures 
of embryo, 232 
Digestion, 82 
Ductus arteriosus, 241 
venosus, 242 
"p'AR, 218 
Electrotonus, 71 
Embryo, development of, 237 
Endolymph, 225 
Epidermis, 150 
Epididymis, 231 
Eustachian tube, 220 
Excretion, 137 
Eye, 207 
, refracting apparatus of, . . . 213 
, blind spot of, 216 
"C'ACIAL NERVE, 171 
paralysis, symptoms of, . 172 
Fallopian tubes, 229 
Feces, 98 
Fat, uses of in the body, 19 
Female organs of generation, .... 228 
Fissures and convolutions of brain, . 189 
Foods and Dietetics. 
, animal, 81 
, vegetable, 81 
, cereal, 82 
, percentage composition of, 78 
, daily amount required, ... 80 
, albuminous principles of, . . 73 
, saccharin principles of, . . . 75 
, oleaginous principles of, . . 75 
, inorganic principles of, . . . 76 
Fovea centralis, 216 
ALVANIC CURRENTS, EF- 
feet on nerves, 71 
Ganglia, 199 
, ophthalmic, 200 
, Gasserian, 169 
, spheno-palatine, 200 
, otic, 200 
. sub-maxillary, 200 
, semilunar, 201 
Gases of the intestine, 97 
, condition of, in blood, . . , 127 
Gastric juice, . 88 
.action of, 91 
Generation, male organs of, .... 231 
PAGE 
Generation, female organs of, . . . 228 
Globules of the blood, 106 
of the lymph 104 
Glomeruli of the kidneys, 140 
Glosso-pharyngeal nerve, 173 
Glottis, respiratory movements of, . 124 
Glycogen, 148 
Glycogenic function of the liver, 125, 147 
Goll, column of, 155 
Graafian follicles, 228 
Gray matter of nervous system, . . 63 
HAIR> *50 
A Hemoglobin, 108 
Hearing, sense of, 218 
Heart, 112 
, valves of, 112 
, sounds of, . 1 114 
, influence of pneumogastric 
nerve upon, 116 
Heart, ganglia of, 116 
, force exerted by left ventricle, 115 
, work done by, 115 
, course of blood through, . . 114 
, influence of nervous system 
upon, 116 
Hyaloid membrane, ....... 211 
Hypermetropia, 215 
Hypoglossal nerve, 177 
TNCUS BONE, 220 
Insalivation, 83 
, nervous circle of, 86 
Inspiration, movements of thorax in, 123 
Internal capsule, 185 
, results of injury to 186 
Intestinal juice 04 
Iris, 208 
, action of, 216 
Island of Reil, 191 
. 137 
, excretion of urine by, . 141 
T ABYRINTH OF INTERNAL 
ear, 223 
, function of cochlea, .... 225 
, function of semicircular canals 225 
Language, articulate, center for, . . 197 
Larynx, 120 
Lateral columns of spinal cord, . . 155 
Laws of muscular contraction, ... 46 
Lens, crystalline, 211 
Lime phosphate, 17 
Liver, 145 
. secretion of bile by 147 
, glycogenic function of, . . . 147 
, elaboration of blood, .... 149 
cells, 145 
Localization of functions in cerebrum, 195 
Lungs, 121 INDEX. 
249 
PAGE 
Lungs, changes in blood while passing 
through, .... 128 
Lymph, 104 
Lymphatic glands, 100 
vessels, origin and course of, . 100 
1WTAMMARY GLANDS, ... 133 
Malleus bone, 219 
Mastication, 82 
, nervous circle of, 83 
, muscles of, 83 
Medulla oblongata, 178 
, properties and functions of, . 178 
Membrana basilaris 224 
tympani, 218 
Menstruation, 229 
Middle ear, 218 
Milk, 134 
Motor centers of cerebrum, .... 195 
Muscles, properties of, , . 43 
Myopia 215 
TSJERVE, OLFACTORY, ... 165 
, motor oculi, 167 
, pathetic, 168 
, trigeminal, 169 
, abducens, 168 
, facial, 171 
, auditory, 173 
, glosso-pharyngeal, 173 
, pneumogastric, 174 
, spinal accessory, 176 
, hypoglossal, 177 
, cells, structure of, 63 
, fibers, terminations of, ... 66 
, force, rate of transmission of, 70 
, roots, function of anterior and 
posterior, 157 
Nerves, centrifugal and centripetal, 
67, 68 
, cranial, . . 165 
, decussation of motor and sen- 
sory 157 
, vaso-motor, 181 
, properties and functions of, . 67 
, spinal, 156 
Nervous tissue, physiology of, . . . 62 
, white and gray matter of, . . 63 
, cerebro-spinal, 62 
, sympathetic, 199 
Nucleus caudatus, 185 
lenticularis, 185 
QLFACTORY NERVES, ... 165 
Ophthalmic ganglion, 200 
Optic nerves, 166 
, thalamus, 185 
, functions of, 186 
Organs of Corti, 224 
Otic ganglion, 200 
Ovaries, 228 
PAGE 
Ovum, 228 
, discharge of from the ovary, 229 
Oxygen, absorption of by hemoglobin, 108 
pACINIAN CORPUSCLES, . 67 
Pancreatic juice, 94 
Patheticus nerve, j68 
Peptones 21 
Perilymph, 224 
Perspiration, 151 
Petrosal nerves, large and small, . . 171 
Phonation, . . 227 
Physiology, definition of, 9 
Placenta, formation and function of, . 236 
Pleura, 122 
Pneumogastric nerve, 174 
Pons varolii, 183 
Portal vein, 101 
Posterior columns of spinal cord, . . 164 
, functions of, ....... . 164 
Prehension, 82 
Presbyopia, 216 
Pressure of blood in arteries, . . . . 117 
Proximate principles, 16 
, inorganic 16 
, organic, non-nitrogenized, . 17 
, organic, nitrogenized, .... 20 
, of waste, 22 
quantity of chemical elements 
in body, ...» 22 
Ptyalin, 85 
Pulse, 118 
Pyramidal tracts, 157 
DED CORPUSCLES OF 
blood, 107 
Reflex movements of spinal cord, . . 160 
, action, laws of, 161 
Reproduction 228 
Respiration, 120 
, movements of, 123 
, nervous mechanism of, ... 124 
, types of, 124 
, nervous circle of, 182 
Retina, 209 
OALIVA, 85 
v"* Sebaceous glands, 151 
Secretion, 131 
Semicircular canals, 224 
Semen, 232 
Sight, sense of, 207 
Skeleton, 32 
, appendicular, 36 
Skin, 149 
, relative sensibility of, ... . 20X 
Smell, sense of, 206 
Sounds of heart, 114 
Spermatozoa, 232 
Spheno-palatine ganglion, 200 
Spinal accessory nerve, 176 
Spinal cord, 154 250 
INDEX. 
PAGE 
Spinal cord, membranes of, ... . 153 
, structure of white matter, . . 154 
, structure of gray matter, . . 154 
, properties of, 158 
, function of as a conductor, . 163 
, as an independent center, . . 158 
, decussation of motor and sen- 
sory fibers, 157 
, reflex action of, 161 
, special centers of, . . . . 163 
, paralysis, from injuries of, . . 164 
, nerves origin of, 156 
, course of anterior and posterior 
roots of, 157 
Spleen, 136 
Starvation, phenomena of, 74 
Stomach, 87 
Submaxillary ganglion, 200 
Sugar, uses of, in the body, 76 
Supra-renal capsules, 137 
Sudoriparous glands, 151 
Sympathetic nervous system, .... 199 
, properties and functions of, . 201 
'T'ASTE, SENSE OF 204 
, nerve of, 205 
Teeth, 82 
Tensor tympani muscle, 220 
Testicles, 231 
Thoracic duct, 101 
Thorax, enlargement of, in inspiration, 122 
Tissues, physiology of, 26 
Tongue, 204 
PAGE 
Tongue, motor nerve of 205 
, sensory nerve of, 205 
Touch, sense of, 203 
Tiirck, column of, 157 
UMBILICAL CORD 235 
Urea, . 142 
Uric acid, 143 
Urine, 14! 
, composition of, 142 
, average quantity of constitu- 
ents secreted daily, 143 
Urination, nervous mechanism of, . 141 
Uterus, 229 
UAPOR, WATERY, OF 
* breath, 127 
Vascular glands, 136 
system, development of, . . . 240 
Vaso-motor nerves, origin of, ... . 181 
Veins, 119 
Vesiculae seminales, 231 
Vision, physical center for 184 
— , psychical center for, .... 198 
Vital capacity of lungs, 125 
Vocal cords, 226 
Voice 226 
\X7ATER, AMOUNT OF IN 
body, 17 
Wolffian bodies, 240 Catalogue No. 8. 
June, 1896. 
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? QUIZ-COMPENDS ?—Continued. Moullin’s 
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