UC-NRLF

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Dr. A. A. D'Ancona.

OUTLINES /_'

LIBRARY

OF

^f/ 0-:PV

HUMAN PHYSIOLOGY ,^

BY

F. SCHENCK, M.D., AND A. GURBER, M.D., PH.D.

Assistants in the Physiological Institute at Wurzburg

AUTHORIZED TRANSLATION FROM THE SECOND
GERMAN EDITION

BY

WM. D. ZOETHOUT, PH.D.

WITH A PREFACE
BY

JACQUES LOEB, PH.D.

Professor of Physiology, University of Chicago

NEW YORK

HENRY HOLT AND COMPANY
1900

Copyright, 1900,

BY

HENRY HOLT & CO.

ROBERT DRUMMOND, PRINTER, NEW YORK.

- . :

PREFACE TO THE AMERICAN EDITION

As the publishers wish me to write a preface to the
translation of Schenck and Giirber's "Outlines of Human
Physiology, ' ' I will briefly state my reason for having
recommended the translation of this book. It seems to me
that the present text-books of human physiology no longer
adequately express our knowledge of the laws of life
phenomena. A number of facts which throw new light upon
the subject have been established by the extension of physio-
logical research to Invertebrates, by the recently developed
experimental or rather physiological morphology, and by
the application of physical chemistry to physiological prob-
lems. It is uncertain how soon these new results will be
embodied in the text-books of human physiology. The
student will have to acquire his knowledge of these new
subjects for the present from the study of monographs'. In
order to give him the time to do this the contents 'of the
traditional text-book of human physiology should be made
accessible to him in a more condensed form. To my knowl-
edge no book answers this purpose better than Schenck and
Gurber's manual.

I have had no connection with the translation. The credit
as well as the responsibility belongs entirely to Mr. Zoethout.

JACQUES LOEB.

UNIVERSITY OF CHICAGO, November 2, 1900.

AUTHORS' PREFACE

AMONG the students of medicine there exists a need for an
outline of human physiology which contains its most impor-
tant facts in a concise form and gives the beginner a clear
viexv of the entire field. It is true, such manuals exist —
those of Oestreich, Breitenstein, Schmidt, Peter, etc. — but
as these contain many errors, they can hardly be regarded
as aids to the student, although in general use. For this
reason it appeared advisable to publish this manual.

In regard to the arrangement of the material, we believe
that we have not deviated to any great extent from the old
and tried system. Our object has been to lay stress upon
the undisputed facts, while we have not entered into the dis-
cussion of various unsettled questions. Yet in some in-
stances we were compelled to mention the various hypotheses
at present advanced.

The physiological methods are dealt with very briefly and
often merely indicated by a few words, as it was not our in-
tention to give elaborate descriptions of methods and
apparatus. Moreover, by a shorter presentation of the
methods the erroneous notion might be called forth that but
little is necessary to understand it. Hence a mere allusion
seems preferable, so that the student shall realize that this
manual does not contain all that he needs to know, but that
it gives only a survey of the general field of physiology and
cannot take the place of lectures and larger text-books.

Most of the illustrations of this book are copies of figures
found in well-known text-books and original papers. Many
of the figures have been kindly loaned by the publishers of

211

vi AUTHORS' PREFACE

Bernstein's Lehrbuch der Physiologic (Figs. I, 14, 16, 17 \
32-34, 37, 39-44. 46~48> and 51-53). We are indebted
to F. C. W. Vogel (Leipzig) for the plates of Figs. 5-8
(from Hermann's Handbuch der Physiologic, Bd. V), to
Edward Besolt (Leipzig) for the plates of Figs. 19, 22, 24,
45, 49, and 50 (from Rauber's Anatomic, etc.), and to
Fischer (H. Kornfeld, Berlin) for Fig. 23 (from Lenhossek:
Der feinere Bau des Nervensystems).

We are especially indebted to Professor Fick for advice
received in the planning of this work.

Dr. F. SCHENCK.

Dr. A. GiJRBER.

WURZBURG, October, 1897.

TABLE OF CONTENTS

PAGE

AUTHORS' PREFACE v

INTRODUCTION. GENERAL PHYSIOLOGY.. i

SECTION I

METABOLISM

CHAPTER

I. The Chemical Composition of the Human Body 12

II. The Blood 52

III. The Gases of the Blood and the Chemistry of Respiration 58

IV. The Circulation of the Blood 63

V. Respiratory Movements 80

VI. Lymph, Lymph Glands, and Spleen 87

VII. Secretions 91

VIII. Nutrition 114

IX. The Digestion of the Foodstuffs 123

X. Absorption and Assimilation of the Foodstuffs 141

XL The Changes of Blood in the Organs and Internal Secre-
tions 149

XII. Metabolism 155

SECTION II

THE TRANSFORMATION AND SETTING FREE OF ENERGY

XIII. Animal Heat 178

XIV. General Muscle Physiology 184

XV. Special Physiology of the Muscles 201

XVI. General Nerve Physiology 215

XVII. The Spinal Corel 226

XVIII. The Brain 235

XIX. The Peripheral Nerves and the Sympathetic System. . . . 250

XX. Sense Organs in General 255

vii

Viii CONTENTS

CHAPTER PAGE

XXI. Optics 257

XXII. The Ear 285

XXIII. Smell 296

XXIV. Taste 298

XXV. Cutaneous Sensations 300

XXVI. Organ Sensations 305

SECTION III
REPRODUCTION AND DEVELOPMENT

XXVII. Reproduction 307

XXVIII. Physiology of the Embryo . 313

XXIX. Pregnancy, Parturition, and Childbed 324

XXX. Development of the Body after Birth 327

INDEX 333

.3
Sa/

211

HUMAN PHYSIOLOGY

INTRODUCTION J///- "//

PHYSIOLOGY is the science of normar life. -jJjV may be
divided into: "Jij^ ' -,

1. General Physiology, i.e. the sciende, c©f £h0fc general
properties of life or of the character of the livjng substance.

2. Special Physiology, i.e. the science^, of^tfte vital
phenomena of individual living beings (e.g^mar^ animals,
plants), and of the single organs of the living £>eijigs,

This manual treats of the essentials of human physiology.
As an introduction, a brief survey of general physiology is
prefixed. \*\>*

GENERAL PHYSIOLOGY

1. METABOLISM. IRRITABILITY

The living body contains no other elements and forces
than those found in the inanimate world. There is no
special 4k Vital Force. " The properties of life are dependent
upon the chemical and physical properties of the living sub-
stance. The composition of this substance is not known ;
in fact, it is a question whether it is chemically an indi-
vidual substance or a mixture of different bodies.

The vital processes comprise chemical and physical
processes — the changes of matter and energy [metabolism].

Metabolism consists of two processes: On the one hand,
the living being continually splits up and, by the addition of

2 HUMAN PHYSIOLOGY

oxygen, oxidizes the organic compounds which compose its
body, thereby forming simple compounds (carbonic acid,
water, ammonia and simple ammonia derivatives, e.g. urea);
on the other hand, it again builds up its body substance
from materials of the outer world. The former process is
called dissimilation ; the latter, assimilation.

The power of assimilation varies in different living beings.
Plants containing chlorophyll are able, in the presence of
sunlight, *o ^assimilate very simple compounds (e.g. carbonic
acid, watty^/nito&tibs), oxygen being set free. Certain Bac-
teria cafiT'aSsitfiilate free nitrogen. Animals, however, do
not fornY:the»t.*0*Dody substance from inorganic but from
organic /compolmds which they obtain as foods from the
plants. »»Tfte animal body is able by reduction and synthesis
to form 'higher. organic compounds from the organic food-
stuffs. ««Ch£ building of fats from carbohydrates is an ex-
ample of *i«weIF-proven synthetical reduction taking place in
the anirfiahbejiy!

The •produote «of dissimilation of the animal world can be

1 * C C c »

reassiniilateci3?yt the plants, the water and the carbonic acid
directljv ^ut; 'the ammonia derivatives only after they have
been changed to nitrates by certain Bacteria found in the
soil. Thus the circulation of the carbon, hydrogen, and
nitrogen in the organic world is completed.

For the physiological combustion a continual supply of free
oxygen is not necessary. Frogs can live for a long time in an
atmosphere free of oxygen. In this case the organism obtains the
necessary oxygen from the oxygen which has been stored up in its
body in chemical combination. Many organisms, e.g. anaerobic
Bacteria, can generally live in an „ atmosphere free of oxygen and
still produce carbon dioxide, obtaining the oxygen from surround-
ing compounds which contain this element. Unlike the intensity
of the fire in a furnace, the intensity of the physiological combus-
tion cannot be increased by an increased supply of oxygen.

The theory of the transformation of energy is based upon
the law of conservation of energy discovered byj. R. Mayer
and H. Helmholtz. This law states that the total amount
of energy in the universe always remains constant, that no

METABOLISM. IRRITABILITY 3

energy is created or destroyed, and that energy can only
change from one form to another. By means of dissimila-
tion the stored-up chemical potential energy of the organic
substance is changed to kinetic energy, mainly to heat and
mechanical work, and, in smaller amounts, to electric force
(e.g. in the electric fishes) and light (e.g. in fire-flies). The
kinetic energy set free by dissimilation enables the living
body to perform its functions.

By assimilation kinetic energy is transformed into •chem-
ical potential energy and is stored up in the organic sub-
stances. This energy is derived ultimately from the
sunlight. Only in the presence of sunlight are plants
containing chlorophyll able to assimilate. For assimilation
not all the light-rays are suitable, only the red and yellow,
not the green, blue, and violet. All energy which enables
the living being to perform its functions is, therefore, sun-
light changed to chemical potential energy.

The changes of matter and energy in the living being can
be influenced by outside chemical and physical actions. Of
special importance are the influences by which the dissimila-
tion is increased. Such influences are called stimulating
agents or stimuli. The increased dissimilation brought
about by the stimulus is called stimulation, and the
resulting activity is the external expression of the stimula-
tion. The power of the living substance to respond to a
stimulus is called irritability.

For example: A muscle stimulated by an electric current
passes from the condition of rest into the condition of activity; by
it the processes of combustion are greatly increased, the muscles
shortened, and work performed.

The stimulus does not convey to the stimulated object
the energy set free upon stimulation, but only calls forth the
transformation of the already present chemical potential
energy into kinetic energy, just as the fuse of the gun calls
forth the explosion of the powder. Hence the effect of the
stimulation is not proportional to the stimulus.

A stimulation produced at a given part of an irritable

4 HUMAN PHYSIOLOGY

structure, e.g. a muscle-fibre, can spread itself throughout
the entire structure by conduction.
The stimuli are classified as :

(1) Chemical, — those which, by means of chemical action
upon the irritable substance, cause dissimilation. Electrical
stimuli act as chemical stimuli because the current produces,
by polarization at the places of entrance and exit, chemical
changes which are able to stimulate.

(2) Physical; this includes mechanical (hitting, pulling) ;
thermal (heating) and photical (light which, for example,
stimulates the retina). The action of these physical stimuli
can be reduced to a common principle, that of concussion,
by which chemical changes producing stimulation are called
forth.

Substances which can be decomposed by concussion are the
explosive bodies; they are compounds in which the union of the
atoms is unstable and which, by decomposition, form more stable
compounds. The irritable substance of the living being is, per-
haps, such an unstable compound.

Influences which decrease the amount of metabolism are
called inhibitory agents and their effect is called inhibition.
The condition of inhibition in which the vital phenomena
entirely cease without the power of life being destroyed is
called latent life or biostition. In biostition there are many
living beings at the lowest temperatures which do not
destroy life, also desiccated seeds of plants, spores of
Bacteria, etc.

Strong stimulation can also cause inhibition, which is then
called fatigue or exhaustion. This fatigue is due to the excessive
consumption of irritable material and partly to the harmful effect
of the dissimilation products (fatigue-substance) retained in the
irritable structure. A fatigued structure at rest recovers by means
of the reconstruction of the irritable substance and the removal of
the fatigue-substance.

MORPHOLOGICAL ELEMENTS OF THE LINING BEING

2. THE PHYSIOLOGICAL SIGNIFICANCE OF THE
MORPHOLOGICAL ELEMENTS OF THE LIVING
BEING

The characteristic chemical configuration of the living
substance is connected with the structure or organization of
the living being.

The structural elements, from which all living beings are
built up, are called cells. The characteristic constituents
of each cell are :

1. The protoplasm, a jelly-like mass, composed of a
liquid ground-substance and solid constituents (protoplasmic
framework, granules, chromatophores, and other inclosed
objects) ;

2. One or more nuclei found in the protoplasm, generally
spherical bodies composed of nuclear framework, nuclear
sap, nuclear membrane, and nuclear corpuscles.

Protoplasm and nucleus are the bearers of life.

The cells which compose the living being are physiologi-
cally of very different value. From a physiological stand-
point we can divide them into two groups:

1. Cells, each of which is an independent living being
(physiological individuals), e.g. all unicellular organisms
(protists) ; these are cells which possess all physiological
activities necessary for the maintenance of life.

Simpler physiological individuals than cells are not known.
Parts of cells (separate protoplasmic masses, single nuclei) are not
capable of independent existence.

2. Cells not capable of existence by themselves, but only
in physiological connection with other cells, for in them, as
in the members of an organism, some physiological processes
?re strongly developed, while others are more or less
undeveloped and taken up by cells of another kind. In this
case many cells together build the physiological individual,
and the processes necessary for the maintenance of life are
distributed among the different cells of the individual. As
in such cells the specially developed physiological processes

6 HUMAN PHYSIOLOGY

appear in an-almost pure form, they are physiologically more
simple, but for this reason also less independent, than unicel-
lular individuals.

All organisms composed of many physiologically different
cells develop from undifferentiated cells. The physiological
differentiation is accompanied by a morphological differen-
tiation, which is expressed in the various forms of the cells.

Although, in consequence of the division of labor, the
various kinds of cells have different functions, yet those
physiological processes which are connected with the char-
acteristic constituents of all cells must be common to all
kinds of cells. These physiological processes include in
general the processes which belong to the nourishment and
reproduction of the cells. These processes are governed by
the nucleus. The nucleus of the reproductive cells is the
bearer of the inheritable qualities of the organism.

The separation of the living substance into nucleus and
protoplasm is the morphological expression of the physio-
logical division of labor, the nucleus being predominantly
concerned with the nourishment and reproduction, while the
protoplasm chiefly reacts upon external influences.

3. GROWTH AND DEATH. ORIGIN AND DKYKLOP-
MKNT OF THE LIVING BEING

If in a living being assimilation and the addition of assimi-
lated products predominate over dissimilation, growth of the
organism results; if dissimilation predominates, the body
decreases. In each organism the assimilation predominates
at first, the body grows ; later on the activity of assimilation
decreases, the body begins to decrease, and this results in
physiological death or in death brought on by senile decay.

A new living being originates only by the growing and
the developing of a part separated from an already existing
living body. This^art grows and develops into a new living
being either alone or after the union with a part of a second
organism of the same kind. Life propagates itself from the
mother- to the daughter-organism.

ORIGIN AND DEVELOPMENT OF THE LIVING BEING 7

Nothing is known concerning the origin of the first living
being on earth, from which all others are descendants.

The morphological phenomena of growth and develop-
ment of a living being are the increase in cells and the
development of form.

Cells multiply by fission.

In this process, the nucleus is divided into two nuclei ; after
this the protoplasm divides into two parts, each part surrounding
one of the daughter-nuclei. The nuclear division is either direct
by die fission of the nucleus or indirect. The indirect division
takes place as follows: First the nuclear framework changes to a
thick skein-like fibre; this fibre divides, by transverse section, into
a number of segments, and each segment splits longitudinally into
two halves, each of which goes to build up one of the daughter-
nuclei. In this indirect nuclear division, the centrosomes have a
definite influence. These structures lying in the protoplasm near
the nucleus, in the form of two or more granules, divide, previous
to the nuclear division, into two parts and these, by means of
fibrilles which proceed from them, direct the course of the separat-
ing nuclear segments. (For details see text-book of Histology.)

The formation of a new organism results in one of two
ways. Either some cells separated from the mother organ-
ism by cell division continue to exist by themselves inde-
pendently and grow (asexual reproduction, reproduction
by fission or budding); or two cells, derived from one or
two sexually different living beings of the same species, unite
to form one living being (sexual reproduction, union of egg-
and sperm-cell).

The union of egg-cell and sperm-cell is the fertilization.
In this the nuclei of the cells unite into one nucleus. By
means of cell division, accompanied by cell differentiation,
the new organism grows from the fertilized egg.

In many species of living beings (e.g. vascular cryptogams,
hydromedusa) there is an alternation of generation in which one
generation propagates itself asexual ly, and the other sexually.

The morphological development of the individual organism
(ontogeny) results in the development of the daughter-
organism, derived from a single cell, or from the union of
egg-cell and sperm-cell, into a form similar or nearly similar

8 HUMAN PHYSIOLOGY

to that of the mother-organism. The mother-organism
transmits by heredity its characteristics to the daughter-
organism.

The species of organisms existing at present have not
always existed since the beginning of life, but have, in the
course of time, been developed from simpler forms of life
(development of species, phylogeny).

The forms which the growing organism assumes during
ontogeny are similar to the forms which the adults possessed
successively during the phylogeny. The ontogeny is a
short recapitulation of the phylogeny (biogenetic law of
Haeckel).

The cause of morphological development lies in the vari-
ability of the structure and functions of the living being, i.e.
in the quantitative and qualitative variability in the trans-
formation of energy and matter. The cause of this variability
is not known.

The principle according to which Darwin's theory of selection
explains the origin of species on the ground of variability is the
" natural selection in the struggle for existence. " The individuals
of a generation of a certain species differ slightly because of their
variability in structure and functions. Now, the struggle for
existence which the individual carries on with hostile beings of
the same or other species is endured best by those individuals
which have the most advantageous characteristics. These indi-
viduals are therefore sooner selected for further existence and for
reproducing offspring which inherit their characteristics. Such a
selection, carried on through many generations, at last produces
organisms which possess that characteristic developed to such an
extent that they really differ from their ancestral organisms.

The continuous selection of advantageous variations leads to
the "development of beings highly fitted for their environment.
In this manner originates the adaptation which we see in so many
organs and organisms.

While the Darwinian theory explains the origin of species on
the basis of the law of variability, it sheds no light on the cause of
this variability; in other words, it does not explain the very con-
dition necessary for the origin of species and therefore cannot be
regarded as a complete explanation of phylogeny.

The principle of the Darwinian theory is, no doubt, applicable
to the origin of many species. Whether it is by itself a sufficient

CORPOREAL LIFE AND SOUL LIFE 9

explanation of phytogeny, or whether, besides it, external or in-
ternal causes are active, remains a question.

According to another theory (Lamarckian), any influence acting-
continually upon the descendants of an organism so as to produce
the same changes will result in a change in the structure and
functions of the organism, and this change is inherited. In this
manner a new species originates.

Some authors assume that there is present in the living substance
a fixed tendency to develop and perfect itself.

4. CORPOREAL LIFE AND SOUL LIFE

The problem of Physiology is the investigation of the
objectively demonstrable processes of life. Besides these
there are processes which can be perceived subjectively only.
These are the phenomena of soul life, the conditions and
processes of consciousness. The investigation of soul life is-
the province of Psychology.

Psychical processes are always accompanied by and
dependent upon physiological processes in the central
nervous system. The study of the character of the physio-
logical processes which are associated with the psychical
is, of course, a problem of Physiology. Hence, in the
study of the central nervous system and sense-organs, the
physiologist cannot ignore the facts of psychology, even
though it is not his aim to explain the psychical phenomena.

Corresponding to the chief phenomena of life we may
divide human physiology into the following parts:

1. Metabolism.

2. The transformation and setting free of energy.

3. Reproduction and development.

PART I

METABOLISM

THE combustible constituents of our body continually
undergo chemical changes, in that they are burned by the
inhaled oxygen.

The products of combustion are removed from the tissues,
in which the combustion takes place, by the circulating
blood and lymph; one of these products, the carbonic acid
gas, is excreted from the body by the lungs ; the other
products, by glands.

That the body may continue to exist, new material for
combustion must be supplied to it from without. This is
effected by the partaking of nourishment which is made
absorbable by digestion, and, after absorption, supplied to
the tissues by the blood and then assimilated.

Metabolism, therefore, includes the following parts of
physiology:

1 . The chemical constituents of the body and their physio-
logical importance.

2. Blood, the gases of the blood and respiration, circuL-u
tion of the blood, respiratory movements, lymph.

3. Secretions.

4. Nutrition, alimentary principles, food, digestion, ab-
sorption and assimilation of the digested food.

5. Survey of metabolism as a whole.

ii

CHAPTER I
CHEMICAL COMPOSITION OF THE HUMAN BODY

THE fifteen elements of which the body is composed are
present in about the following proportions:

Carbon, 18.5$ Oxygen, 65.0$

Hydrogen, n.o$ Nitrogen, 2.5$

Sulphur, Phosphorus, Chlorine, Iodine, Fluorine, Silicon,

Potassium, Sodium, Calcium, Magnesium, Iron, — together

3*.

The adult human body contains about 3 g iron. Other ele-
ments, traces of which are sometimes found, must be regarded as
accidental constituents.

The body is, therefore, mainly composed of non-metals
(metalloids).

Oxygen, nitrogen, and, in small quantities, hydrogen are the
only free elements; only the free oxygen is of physiological im-
portance.

The greater part of these and all other elements are found in
both inorganic and organic compounds, in which they take the
following parts, in detail:

1. Carbon forms the basis of all the organic compounds of our
body. It unites with hydrogen and oxygen to form fats and
carbohydrates; with hydrogen, oxygen, nitrogen, and sulphur, to
form proteid bodies. It is, therefore, a constituent of the meta-
bolic products of these substances and this chiefly in the form of
carbonic acid, which is found throughout the body, partly in the
free state, partly in the carbonates or bicarbonates of the alkalies
and calcium.

2. Hydrogen is mostly (f) united with oxygen, forming water.
With chlorine, it forms hydrochloric acid ; with sulphur, sulphu-
retted hydrogen, found in the intestinal gases; with nitrogen,
ammonia and its salts. Above all, it is one of the chief constitu-
ents of the organic compounds.

3. Nitrogen appears in the inorganic compounds only as
ammonia, being united with hydrogen. It is found, however, in
many organic compounds, of which the proteids with their deriva-
tives and metabolic products are the most important.

T2

CHEMICAL COMPOSITION OF THE HUMAN BODY 13

4. Nine-tenths of the oxygen appears in the form of water; in
small proportions it is present in carbonic, sulphuric, and phos-
phoric acids and their salts. Besides this, it is present in all organic
compounds of the body (except in a few hydrocarbons in the
intestine).

5. A small part of the sulphur is present in the sulphates;
another, still smaller portion, in the sulphuretted hydrogen and
iron sulphide (intestine); by far the largest part is found in the
proteids, where it appears in two forms, as reduced (easily split off
by boiling with alkali) and as oxidized (strongly united with the
proteid molecule). It seems to be present in bcth forms in the
metabolic products of the proteids.

6. Phosphorus seems to be present in inorganic and organic
compounds only in the form of phosphoric acid which forms salts
with alkalies and calcium, the calcium salt forming a chief con-
stituent of the skeleton. Organic compounds containing phos-
phorus are lecithin, jecorin, protagon, nuclein.

7. Iron, deposited as inorganic, i.e. in a form demonstrable by
the ordinary reactions, in the liver and spleen (probably as oxide),
is found also in the contents of the intestine (as iron sulphide).
Of special physiological interest are the organic iron compounds,
the most important of which is haemoglobin, the red coloring
matter of blood. Many nucleo-albumins also contain a little iron.
The organic compounds of iron which do not give the general iron
reactions are called metal -organic compounds.

The elements thus far described are the most important as they
are the organogenic elements, so termed because they form the
organic substances of the body.

The other four elements which are united with organic sub-
stances, especially proteid substances, do not appear in metal-
organic compounds, hence it is concluded that these elements are
present in the organism only in the form of salts or inorganic com-
pounds.

8 and 9. Potassium and sodium, in about equal proportions,
uniting chiefly with carbonic, hydrochloric, and phosphoric acids,
form acid and neutral salts. Potassium salts predominate in the
tissue-cells, sodium salts in the tissue-fluids. The alkali-metals
also form salt-like bodies with the proteids.

10 and ii. Calcium and magnesium, as the salts of carbonic
and phosphoric acids, form the chief constituents of the bones.
Calcium, either alone or with phosphoric acid, is also united with
proteids.

12. Chlorine is present as free hydrochloric acid (in gastric
juice); or united with an alkali, especially sodium, predominates
in the tissue fluids. In gastric digestion, hydrochloric acid forms
acid hvdrochlorates with the products of proteid digestion.

14 HUMAN PHYSIOLOGY

13. Iodine is found in thyroiodine, a substance present in the
thyroid gland of adult man.

14. Fluorine, united with calcium, is present in the enamel of
the teeth.

15. Silicon is found in the hair; in which form it is present is
not known.

The chemical compounds found in the body may, from a
physiological standpoint, be divided into the following
groups :

1. Inorganic compounds (water and salts), i.e. saturated
compounds which cannot be transformed into more saturated
compounds by chemical processes in the body and, hence,
cannot furnish the body with energy for its functions. Their
importance for life is due to their physical properties ; they
also take part in chemical actions, but no utilizablc energy is
thereby gained.

2. Organic compounds which serve as sources of energy
for the organism (proteids, fats, carbohydrates) ; the stored -up
chemical energy is set free by their physiological combus-
tion.

3. Organic compounds which, as end-products of meta-
bolism, are formed by the physiological combustion (nitrog-
enous end-products of metabolism, such as urea and others)
and are destined to be excreted from the body.

1. THE INORGANIC COMPOUNDS OF THK BODY

I. Water is the most abundant constituent of our body,
amounting to about 65$ of the body weight of the adult.
In new-born children the proportion of water is above 70^.
The following table indicates the amount of water in the
different tissues and organs :

Adipose tissue 15$ Pancreas 78^

Bones 50$ Blood 79^

Liver 70$ Lungs 79^

Skin 70$ Heart

Spleen 77$ Kidneys

Muscles 77$ Vitreous humor

Brain and spinal cord. 78$ Cerebro-spinal fluid.. .

Intestine 78$

CHEMICAL COMPOSITION OF THE HUMAN BODY 15

The physiological importance of water is as follows :

(a) It serves as a solvent and as such it renders possible
physical and chemical processes such as diffusion, mechanical
movement, and the chemical action of dissolved substances.

(b) As a means of imbibition, which determines the semi-
solid consistency of the tissues.

(r) By evaporation from the lungs and body surface, it
takes heat from the body and, hence serves as a tempera-
ture regulator.

(d) It takes part in chemical processes, e.g. in the
hydrolytic splitting up.

2. Bases are not found in a free state but, united with
acids, are present in the form of salts. As more than suffi-
cient acids are present for the union with bases, acid salts
are formed. Under certain conditions the existence of a free
acid must be granted, namely, carbonic acid. Hydro-
chloric acid is found in a free state in the gastric juice ; it is
set free from sodium chloride by the gland-cell of the
mucosa.

3. Salts, formed by the union of acids and bases, in which
the hydrogen of the acid is replaced by the metal of the
base, are present in the body to a large extent. When the
tissue is burned the salts remain behind as ash. The ash,
however, is not identical with the original salts of the body,
as, by the incineration of the body, substances appear in the
ash which were not present in that form in the organism.
Originally they were present in organic compounds, e.g.
iron as a constituent of haemoglobin ; part of the sulphuric
and phosphoric acids were derived from the proteid, lecithin,
and nucleins. On the other hand, certain salts originally
present, as acid carbonates or phosphates, are converted
into neutral salts by combustion. Very often the salts can
be investigated only after the incineration of the tissue,
therefore the ash and its constituents must be taken into
consideration in studying the composition of the body.

The amount of the ash of the body is about 5$ of the body
weight, of which the skeleton furnishes over 80$ and the

1 6 HUMAN PHYSIOLOGY

muscles lofo The amount of ash in each tissue varies much
with age and nourishment. The ash percentage of tissues is
as follows :

Skeleton 22.0$ Heart 1.1$

Muscle 1.5$ Pancreas i.o^

Liver 1.3$ Brain and spinal cord, i.ojg

Spleen 1.2^ Blood °-9$

Lungs 1.1$ Kidneys 0.8$

Intestine 1. 1$ Skin °-7$

The ash contains (with the exception of iron oxide) only
neutral salts, derived from the bases potassium, sodium,
calcium, magesium, and from carbonic, sulphuric, phosphoric,
and hydrochloric acids. More than 80$ are phosphates
(chiefly calcium phosphate) ; the next largest in quantity are
the chlorides (sodium chloride); then follow the carbonates
and, last of all, the sulphates.

The salts of potassium and sodium, found in ash, are
soluble in water, while the carbonate and phosphate of
calcium and magnesium, iron oxide and iron phosphate are
insoluble in water. In the body fluid the carbonate and
phosphate of calcium and magnesium are acid and therefore
soluble in water. The carbonates of the alkalies are also
present in the body as acid salts (sodium bicarbonate).

When two or more salts of different bases or acids are dissolved
in water, they exchange their components reciprocally, in such a
manner that each base is united with each acid. In the body
fluid there are four bases and four acids; according to this theory,
sixteen salts ought to be formed. Moreover, the dibasic sulphuric
acid and carbonic acid form two salts with each base, while the
tribasic phosphoric acid forms three salts (the primary, secondary,
and tertiary salts). According to the theory, therefore, many
more salts must be formed. The quantity of each salt formed
depends, however, upon the chemical affinity and upon the abso-
lute quantity of the components entering into the reaction (law
of mass action). Hence, many of the salts formed according to
the theory may be present only in traces, and the number of salts
to be considered is much reduced. In reviewing the salts of our
body, an uncertainty always remains, so that the existence of
many salts is not absolutely proved.

CHEMICAL COMPOSITION OF THE HUMAN BODY 17

The most important salts of the body are :

1 . Sodium chloride (common table-salt). This is chiefly
found in the fluids of the tissues (o.6#); to a lesser extent,
in the cells. It serves as a solvent for certain proteids
(globulin) and supplies the osmotic pressure of the body fluid
which keeps in equilibrium the osmotic pressure of the cells.
This prevents the entering of water into the cells. In pure
water, all tissue cells die, swelling rapidly. For this reason,
in the investigations of living tissue, the so-called physio-
logical salt solution (0.6$ NaCl) is used. From the sodium
chloride, the gastric mucosa forms the hydrochloric acid of
the gastric juice.

2. Potassium chloride is the most important chlorine
compound in the cells and serves to maintain the osmotic
equilibrium. In the body fluids it is found in but small
quantities and is not of any special physiological significance.

3. Sodium carbonate is chiefly found in the tissue fluids
(0.2-0.3$). It imparts to these fluids their alkaline reaction
and basic nature.

4. Bicarbonate of sodium is also found in the tissue fluids ;
it is the carrier of the carbonic acid formed by combustion in
the body. (See Chapter III.)

5 . Potassium phosphate (probably the secondary) is an
important constituent of all cells. It is the most abundant
salt in the cells. It is doubtful whether the salt is merely
dissolved in the fluids of the cells or is united with their
organic constituents.

6. Neutral calcium carbonate forms a part of the salts of
bones, builds the otoliths of the ear, and perhaps also the
crystals of the spermatic fluid.

7. Acid calcium carbonate is dissolved in the tissue fluids.
It readily yields carbonic acid and is therefore, like bicarbon-
ate of sodium, of importance as a carrier of carbon dioxide
in the exchange of gases in respiration.

8. Neutral calcium phosphate is the chief mineral con-
stituent of the skeleton, of which it forms one-fifth by weight.

9. Acid calcium phosphate is dissolved in the tissue

1 8 HUMAN PHYSIOLOGY

fluids. In the coagulation of blood it is supposed to aid in
the formation of fibrin-ferment.

10. Magnesium carbonate and magnesium phosphate
are present in the bones and often accompany the calcium
salts, but in smaller quantities. Only in the muscles and in
the thymus does the magnesium phosphate exceed the
corresponding calcium salt.

11. In smaller quantities and without any known physiological
importance are the following: Potassium carbonate, the secondary
sodium phosphate, sodium sulphate, potassium sulphate, magnesium
sulphate, calcium fluoride (in bones and enamel of teeth).

2. THE ORGANIC ENERGY-YIELDING COMPOUNDS OF

THE BODY

A physiological principle according to which the following
substances maybe grouped is not yet known, as our knowl-
edge of the role of each one in metabolism is still too
limited. We may classify them from a chemical standpoint
as follows :

i. Carbohydrates; 2. Fats; 3. Proteids.

i. The carbohydrates derive their name from the fact
that, besides carbon, they contain hydrogen and oxygen in
the same proportion as water. This characteristic has no
reference to the chemical constitution of the substances.

The carbohydrates are aldehydes or ketones of hexatomic
alcohols or anhydrid unions of two or more molecules of
such aldehydes and ketones. Their number of carbon
atoms is six or a multiple of six.

Heating changes all carbohydrates to caramel having a
characteristic odor ; they are all stained red by thymol and
concentrated sulphuric acid.

They are classified as :

Monosaccharides. . . C,H10O •

o \.2t o '

Disaccharides C12H29On ;

Polysaccharides C,.H10O5.

The monosaccharides and disaccharides are also called
sugars; they have a more or less sweet taste, the disac-

CHEMICAL COMPOSITION OF THE HUMAN BODY 19

charides being sweeter than the monosaccharides. Sugars
are soluble in water and alcohol, but insoluble in ether;
they crystallize and dialyze. The polysaccharides are in-
soluble in water or form only colloidal solutions ; they
neither crystallize nor dialyze.

The monosaccharides (hexoses, glucoses) have the fol-
lowing constitution:

Aldehyde sugar (aldoses):

CH2OH.CHOH.CHOH.CHOH.CHOH.COH.

Ketone sugar (ketoses) :

CH2OH.CHOH.CHOH.CHOH.CO.CH2OH.

Characteristics of monosaccharides :

1. They are optically active, i.e. their solutions rotate
the plane of the polarized light ; most of them turn it to the
right; only fructose turns it to the left (hence called levu-
lose). The optical activity of the sugar is due to the pres-
ence of asymmetrical carbon atoms, i.e. carbon atoms whose
four valences are united to four different radicles or atoms.

2. The aldehyde sugars, like all aldehydes, are easily
oxidized, forming first monobasic and then dibasic acids.
The ketoses are also oxidized, whereby they are, at the
same time, split up into bodies containing less carbon.
Upon this fact, that the sugars are oxidizable, depends the
detection of sugar by the so-called reduction tests. Of these
the following are the most important :

(a) Trout mer 'JT test: Sugar solution mixed with potassium
hydrate and cupric sulphate, on boiling, gives a red precipi-
tate, the cupric oxide having been reduced to the insoluble
cuprous oxide.

(//) fiottgcr' s test: Basic bismuth nitrate, by heating with
sugar in an alkaline solution, is reduced to metallic bismuth
(black precipitate).

(c) Mulder 's test: Weak alkaline indigo solution, heated
with sugar, loses its color through reduction.

20 HUMAN PHYSIOLOGY

3. Moore' s test: Boiled with alkali, the sugar is oxidized
and assumes a brown color.

4. In an acetic acid solution, monosaccharides, like alde-
hydes and ketones, unite with phenylhydrazine, forming
hydrazones, water being set free. This, by the further
taking up of a molecule of phenylhydrazine and the separa-
tion of the water and t'he setting free of hydrogen, forms
phenylosazone. These compounds have characteristic crys-
tals and melting-points which may aid in the detection of
sugar.

5. Compounds of monosaccharides :

(a) Compounds of monosaccharides with bases are
called saccharates. Lead saccharates are insoluble in
ammonia and are therefore used for the precipitation
of sugar.

(/;) Compounds of monosaccharides with alcohols,
phenols, aldehydes, and organic acids are called gluco-
sides. By boiling with acids or by the action of main-
ferments, they are easily decomposed, under the
assumption of water, into their components.

6. The yeast-cell splits up nearly all the monosaccharides
into alcohol and carbonic acid (alcoholic fermentation) ; the
bacterium lactis splits up most of them into lactic acid (lactic-
acid fermentation).

Among the monosaccharides are grape-sugar, fructose,
galactosc, mannose. Grape-sugar is found in the animal
body; the others are of importance as foods.

Grape-sugar (glucose in a more restricted sense, or dex-
Jrose) is the aldehyde of sorbit, a hexatomic alcohol found
in the service-berry.

Grape-sugar is dextrorotatory (hence called dextrose),
reduces and forms, with phenylhydrazone, phenylglucosa-
zone, which crystallizes in branches having the melting-
point at 204° C. It is capable of alcoholic fermentation,
Its oxidation forms first gluconic acid 'monobasic) and then
saccharic acid (dibasic).

Grape-sugar is found in sweet fruits, in honey and, in

CHEMICAL COMPOSITION OF THE HUMAN BODY 21

small quantities, in the blood and lymph. It is the form in
which most of the carbohydrates in the body are carried by
the blood from one place to another (from intestine to the
liver, thence to the tissues, where the physiological combus-
tion takes place). Pathologically it appears, often very
abundantly, in the urine (diabetes mellitus).

Glucosamin, C6HUO.NH2 , is a nitrogenous derivative of grape-
sugar which is transformed into grape-sugar by the action of nitric
acid. It is obtained by the decomposition of chondroitin (a con-
stituent of cartilage) or of chitin (a constituent of integuments of
arthropods). This transformation is of importance in showing
how carbohydrates can be derived from proteids.

Inosit, C6H12O6 , a sweet-tasting substance, does not belong to the
sugars, as its carbons form a closed circular chain, six -CHOH—
groups forming a ring, and is therefore hexahydroxy-benzene.
Inosit is soluble in water, insoluble in alcohol and ether, optically
inactive, does not reduce nor ferment with yeast, but undergoes
lactic-acid fermentation. It crystallizes in prisms, grouped in
rosettes. Successively treated with nitric acid, ammonia, and
calcium chloride, it leaves, on drying, a rose-red spot. Inosit is
found in muscles; its physiological importance is unknown.

Disaccharides are anhydrid compounds of two monosac-
charide molecules of the same or different kinds:

2(C6H120(i)2-H20 = C,2H2201I.

In this group belong:

Cane-sugar = grape-sugar -j- fructose.

Milk-sugar (lactose) = grape-sugar + galactose.
Maltose = grape-sugar + grape-sugar.

By boiling with acids and by inverting ferments, these-
sugars, under the assumption of water, are split up into their
components. They are dextrorotatory, reduce (except
cane-sugar) and form phenylosazones. Lactosazone melts
at 200° ; maltosazone at 208°. The disaccharides do not
undergo alcoholic fermentation directly.

Cane-sugar and maltose are important foods. Lactose is
also an important food and is of special physiological interest
because it is a specific product of the animal body, being

22 HUMAN PHYSIOLOGY

formed by the activity of the milk-glands. It is found only
in milk, has but a slight sweet taste, and is somewhat less
soluble in water than the other sugars. Milk-sugar is
dextrorotatory (rotatory power 52.5°). It reduces, but
does not ferment with yeast, even after previous action of
the invertin, which otherwise splits up the disaccharides and
renders the yeast fermentation possible. On the other
hand, it is split up by bacterium lactis (lactic-acid fermenta-
tion), also by the Kephir fungus, which also produces alco-
holic fermentation. Through the oxidation of milk-sugar
there is formed, among others, mucic acid, an oxidation
product of galactose.

The polysaccharides are anhydrid compounds of several
molecules of the simple sugars. Their general formula is
(C(.H10Os);r, in which x is the still unknown factor by which
the formula must be multiplied to obtain the real size of the
molecule. In this group belong: vegetable starch (amy-
loses), animal starch (glycogen), dextrin, gums, and cellu-
lose. Some of the polysaccharides are insoluble in water
(cellulose) ; some swell up in water, forming a s'ticky fluid
(starch, gums) ; some are soluble, but are not clialyzable,
and are precipitated by alcohol (glycogen, dextrin). They
are dextrorotatory, do not reduce (except a few dextrins),
and do not ferment with yeast. Many ferments (diastase,
ptyalin) and boiling with strong mineral acids change the
monosaccharides, chiefly to grape-sugar. When gum is
oxidized, mucic acid is formed; the oxidation of starch,
glycogen, dextrin, yields saccharic acid. Most of the poly-
saccharides give color reaction with iodine: Starch gives
blue; glycogen, brownish red ; dextrin, blue or red;, cellu-
lose, after being treated with concentrated sulphuric acid,
gives blue.

Of the polysaccharides, only glycogen is found in the
animal body.

Cellulose is the chief constituent of wood fibre. Starch and
dextrin are important foods. Gum has only a technical value.
A carbohydrate, closely related to cellulose, is found in the

CHEMICAL COMPOSITION OF THE HUMAN BODY 23

envelopes of the Tunicates. A gum-like carbohydrate can be split
off from certain mucins (animal gum).

Glycogen is chiefly found in the liver and muscles. It is
formed, first of all, by the anhydrid union of several mole-
cules of the simple sugar, chiefly of dextrose, but also of
levulose and galactose. Glycogen can also be formed from
proteid.

Glycogen is dextrorotatory; boiling with acids splits it up
into dextrose only, hence in the formation of glycogen from
levulose and galactose, these must first be changed to dex-
trose.

Glycogen forms an opalescent solution in water and is
precipitated by the addition of half its volume of alcohol.
It /does not reduce nor ferment and, with iodine potassium
iodide, gives a brownish-red color which disappears on heat-
ing. Ferments (diastase," ptyalin) split it up, under the
assumption of water, into maltose and dextrose, dextrins
being intermediate products.

The object of glycogen formation in the animal body is
the storing up of carbohydrates in a form which, under the
given conditions, is insoluble (like the sugar in plants is
stored up as starch).

2. Fats are fatty acid esters of glycerin. The most im-
portant fatty acids' which take part in ester formation are:

Palmitic acid, C15H31COOH;
Stearic acid, C^H35COOH ;
Oleic acid, C^H^COOH,

Glycerin as a triatomic alcohol can unite with three mole-
cules of fatty acid :

/OH /0(C,.HS10)

C,HS-OH + 3CUHS1COOH = C3H5-O(C1(iH31O) + 3H2O.
\OH \0(C,6H310)

The glycerin-esters of palmitic, oleic, and stearic acids are
called palmitin, olein, and stearin, and a mixture of these
three is what is commonly known as fat.

The melting-point of stearin is 71.5°, of palmatin 62°, of

24 HUMAN PHYSIOLOGY

olein o°. According to the proportion of stearin and palma-
tin on the one hand and olein on the other, the natural fats
are solid at ordinary temperature, as tallow and butter, or
liquid, in which condition they are called oils.

In small quantities there are present in animal fats the glycerides
of butyric acid, C4H8O2 , caproic acid, C6H12O2 , caprylic acid,
CgH16O2 , capric acid, C]0H20Oi! , and myristic acid, CUHWO2.

Fats are insoluble in water and cold alcohol, but readily
soluble in hot alcohol and in ether. Stearin and palmitin
solidify in needle-shaped crystals. On heating, especially
with the anhydrid of phosphoric acid, the fats, in contra-
distinction from free fatty acids, yield the offensive-smelling
acrolein, a decomposition product of glycerin. The fats are
stained black by osmic acid. By boiling with alkalies,
especially in alcoholic solutions, also by the action of many
ferments (steapsin of the pancreatic juice) they are split up,
under the assumption of water into glycerin and free fatty
acids. The fatty acids unite with the alkali present, forming
salts of fatty acids, the soaps (sodium soap or hard soap,
potassium soap or soft soap).

If the fats contain free fatty acid (rancid fats), they can,
on melting, form an emulsion with water and a little soda;
in this process of emulsion the fats are finely divided, forming
a milky fluid. As emulsification is dependent upon the
presence of soap, formed by the union of fatty acid and
alkali, a purely neutral fat cannot be emulsified. The
emulsification of fat is of importance in the absorption of fat
in the food.

Fats are found in all parts of the body, generally stored
up in cells. The percentage of fat in the tissues varies very
much, as it is dependent upon the state of nutrition. In
lean meat there is but little above \% fat, while the quantity
of fat in a fattened animal may be above 30$. The tissues
containing the most fat are the subcutaneous tissue, the
mesentery, the bone marrow (adipose tissue), which may con-
tain about 80$ fat.

CHEMICAL COMPOSITION OF THE HUMAN BODY 25

The physiological functions of fat are :

(a) By their physiological combustion they are a source
of heat and force.

(b) Being poor conductors of heat, they shield the body
from rapid cooling.

(V) They serve as protective coverings for delicate organs
(eyes, kidneys).

Cholesterins are isomeric monatomic alcohols of unknown
constitution, having the empirical formula C2GH4.(OH).
They crystallize in rhomboid tables, are insoluble in water,
but readily soluble in hot alcohol and ether. Moistened
with concentrated sulphuric acid and a little iodine solution,
the cholesterin crystals become blue, green, and red. A
solution of it in chloroform is colored blood-red by concen-
trated sulphuric acid. Cholesterins are found in all parts of
the organism, chiefly in the brain and nerves, also in the
bile. With fatty acids they form esters, capable of saponifi-
cation with alkali and found in small quantities throughout
the whole body. The physiological function of cholesterin
is not known; its ester (lanolin) protects the skin and hairs,
for which, as it does not become rancid, it is well adapted.

Lecithins are ester-like compounds of glycero-phosphoric
acid with two fatty acid radicles on the one hand and of an
ammonia base, cholin, on the other. Cholin is trimethyl-
oxyethyl-ammonium-hydroxide. From cholin we obtain,
by reduction, neurin, and by oxidation, muscarin. Neurin
and muscarin are poisons, cholin is not.

The most common lecithin, stearic acid lecithin, is di-
stearyl-glycero - phosphoric acid trimethyl - oxyethyl - am-
monium-hydroxide :

CSH4-0-€UHM0

\0 /OH
\P=0

\Q r H

U.L,H.

OH.

Lecithin is insoluble but swells up in water, forming the

26 HUMAN PHYSIOLOGY

so-called myelin figures. It is soluble in ether and alcohol ?
has the consistency of wax and yields imperfect crystals only
at a very low temperature. Boiled with acids and alkalies,
it splits up into fatty acid, phosphoric acid and cholin.

Lecithin, no doubt partly united with proteid, is a con-
stituent of all animal cells. It is present in large quantities
in the brain, spinal cord, and yolk of birds' eggs.

Protagon, a substance containing phosphorus and nitrogen
(constitution unknown), is a constituent of nerves and yields
.similar decomposition products as lecithin. It can be extracted
from the brain by 85$ cold or 45$ warm alcohol and is thrown
down as crystals when cooled to o°. It swells up in water, form-
ing an opalescent solution and is soluble only in warm alcohol and
in ether. At 50° C. it is decomposed, giving rise to the following
glucoside-like cerebrins free from phosphorus: cerebrin, homoci-re-
brin, encaphalin. The cerebrins, boiled with dilute sulphuric
acid, yield galactose and a fat called cetylitl.

Jecorin, a glucoside-like body containing phosphorus, appears
to be related to protagon. It is found in the liver and other
organs.

The physiological significance of these substances is not known.

To the fatty bodies also belong a few coloring compounds,
stored up in the body as pigments, called chromophane and lipo-
chrome.

3. Proteids. — The term proteid is here used in its widest
sense ; it also includes the proteid-like bodies (albuminoids)
which are not regarded as real proteids by many authors.

(a) Composition of Proteids.

Proteids all contain: carbon 50-55$, hydrogen 6.5-7.3$,
nitrogen 15-17$, oxygen 19-24$, sulphur 0.3-2.4$.

Besides these, there are present phosphorus, iron, calcium, mag-
nesium, potassium and sodium; but these are not necessary con-
stituents of proteids, for they are united, either alone or with other
elements, to the already independent proteid molecule.

Nearly all proteid bodies contain a small amount of mineral
constituents which, on incineration, remain behind as the ash.
These are not present as impurities, but are chemically united with
the proteid.

Nothing is known for certain about the constitution, molecular
weight, and empirical formula of proteid. It is certain that the
proteid molecule is very large.

CHEMICAL COMPOSITION OF THE HUMAN BODY 27

The most reliable statements on this subject are concerning
the crystallized serum albumin of the horse, which is supposed to
have a molecular weight of 17,070 and the empirical formula
('...II^j-X^S^O^.. This number is calculated from the amount
Ol sulphur The sulphur of most proteids exists in two forms:

1. Easily split off by hot alkali ; with lead acetate it forms lead sul-
phide : reduced sulphur.

2. Firnilv bound to the proteid molecule, only demonstrable as sul-
pJiuric acid after the decomposition o/ 'the proteid: oxidized sulphur.

Such proteids must contain at least two atoms of sulphur.

In serum albumin the proportion between the firmly and the
loosely combined sulphur is as 2:3; the molecule, therefore,
contains at least five atoms of sulphur. This number must be
doubled as the serum albumin splits up into at least seven diges-
tion-products which contain sulphur; of these, three contain
sulphur in both forms. With ten atoms of sulphur in the mole-
cule the calculations from the elementary composition [C =
53.08$; H = 7.120; N = 15-93$; S = 1.875$; O = 21.995$]
furnish us with the above formula. According to the method of
determining the freezing-point, the molecular weight of 15,000
has been assigned to egg albumin.

(//) The Decomposition Products of Proteids.

By boiling with alkalies or acids and by putrefaction, proteids
are decomposed. The decomposition products are :

1. If the decomposition is long continued: ammonia, carbon
dioxide, acetic acid, oxalic acid, phenol, indol, skatol.

2. If the decomposition is not continued for a long time: amido
acids and hexo-bases.

The following are the most important amido acids :

Glycocoll, amidoacetic acid, NH2.CH2.COOH, is found chiefly
among the decomposition products of gelatin.

Leucin, amidocaproic acid, C4H9.CH(NH2).COOH, crystallizes
in radially striated spheres.

Tyrosin, oxyphenol-amidopropionic acid,

OH.C6H4.CHS.CH(NH1).COOHJ

crystallizes in rosette-like clusters and is colored red by Millon's
fluid.

Aspartic acid, amidosuccinic acid,

COOH.CH2.CH(NH2).COOH,

is extensively found as the amid (asparagin), in plants.

The Hexo-bases, lysine, arginine, and histidine, are nitrogenous
substances having strong basic properties, and containing six

28 HUMAN PHYSIOLOGY

atoms of carbon in each molecule. Some substances, containing
no sulphur, are composed of hexo-bases and give real proteid
reactions. These substances are therefore regarded as the simplest
proteids and are called protamine. From arginine urea may be
obtained by boiling with baryta water, proving that urea may be
formed from proteids by a simple process of splitting up.

By means of putrefaction, ether products may also be formed
which are not simple decomposition products of the proteid, but
which must be regarded as metabolic products of the bacteria
causing the putrefaction. These products are called ptomaws,
some of which are very poisonous.

Potassium-permanganate oxidizes proteids to oxyprotosulphonic
acid, which has still the character of a proteid but contains more
oxygen and the sulphur in a completely oxidized form.

Because of their decomposition products and their relation
to acids and bases with which they form salt-like combina-
tions, the proteids may be considered as condensation
products of^various, in part aromatic, amido acids. Otherwise
nothing is known as to their chemical constitution.

(c) PJiysical Properties of Proteids.

Most proteids are soluble in water or dilute salt solutions,
but insoluble in alcohol and ether.

They are levorotatory.

They dialyze (except peptone) with difficulty or not at all
through animal and vegetable membranes.

They do not readily crystallize. Crystals have, however,
been obtained from haemoglobin, vitellin, egg and serum
albumin, and from many vegetable proteids.

The fact that crystallizable proteids do not dialyze contradicts
the old classification of crystalloid and colloid bodies (although
this had already been proven untenable). Proteids do not dialyze
because their molecules are too large for the pores of the mem-
branes.

(d) Reactions of Proteids.

A. Precipitants of proteids.

i. Many proteids are rendered insoluble by heat: they
coagulate.

The coagulation temperature lies between 50° and 80°. The
exact temperature does not only depend on the nature of the
proteid but also on the concentration, the amount of salts present,

CHEMICAL COMPOSITION OF THE HUMAN BODY 29

and the reaction of the solution. In strongly acid or alkaline
solutions, coagulation does not occur.

The coagulation does not produce any real change in the nature
of the proteid ; probably only an anhydrid condensation or poly-
merization takes place. Coagulated proteid contains less ash than
non-coagulated proteid; hence by coagulation a part of the
mineral constituents of the proteid is split off.

2. Many proteids are precipitated by alcoliol. If the
action of the alcohol is allowed to continue, the precipitated
proteid is coagulated.

3. Nearly all proteids are precipitated by saturating their
solutions with neutral salts (sodium chloride, magnesium,
sodium, and especially ammonium sulphate). An acid
reaction favors this precipitation.

The precipitation by salts is first of all due to the fact that the
salts deprive the proteid of the solvent. Still, chemical action
is not excluded. In using ammonium sulphate, for example,
ammonia is set free, for the sulphuric acid unites with the precipi-
tated proteid and at last causes a splitting up of the proteid.

By precipitation by salts, proteids can be obtained in crystalline
form. Proteids cannot, like other substances, be crystallized by
mere evaporation of the water which holds them in- solution, for,
in proportion as the water is evaporated, the proteids are precipi-
tated and form a solid pellicle at the surface of the water. Hence
the solution does not reach the condition pf supersaturation
necessary for crystallization. This can, however, be -obtained by
using salt as a precipitant, whereby the concentration of the salt
is gradually increased either by the careful addition of the salt to
the solution or by evaporation. For this purpose, sodium or
ammonium sulphate is best.

4. Proteids are precipitated by concentrated mineral acids,
especially by nitric acid (Heller's test). Metaphosphoric
acid readily precipitates proteids, while the orthophosphoric
acid does so with difficulty.

5. Proteids are precipitated by the salts of the heavy
metals, copper sulphate, ferric chloride, neutral and basic
lead acetate, platinum chloride, corrosive sublimate in hydro-
chloric acid solution. In these, the heavy metals unite with
the proteids as a weak acid, forming a compound insoluble
in water.

30 HUMAN PHYSIOLOGY

6. Proteids are precipitated by some weak organic acids
or their salts in a solution of acetic acid : hydroferrocyanic
acid, potassium ferrocyanide and acetic acid, tannic acid,
picric acid, trichloracetic acid. In this case also compounds
insoluble in water are formed, in which the proteids seem to
take the part of a base.

7. Proteids are also precipitated by phosphotungstic and
phosphomolybdic acids and potassio-mercuric iodide in the
presence of free hydrochloric acid.

B. Color reactions of proteids.

1 . Xanthoproteic reaction. Proteids boiled with strong
nitric acid turn yellow, which is colored orange by ammonia.

2. Millon s reaction. Proteids boiled with mercuric
nitrate solution containing excess of nitric acid are colored
brick-red. This coloration depends upon the oxyphenyl
nucleus of the proteids (as in case of tyrosin).

3. Binrct reaction. If to a solution of proteid, sodium
hydrate and dilute copper sulphate be added, a violet or
rose-red color results. Biuret, a derivative of urea, also
gives this reaction.

4. Adamkicwicz reaction. To a solution of proteids in
acetic acid, add excess of concentrated sulphuric acid. A
reddish-violet color appears.

(V) Physiological Importance of Proteids.

The albuminous bodies are the most important constitu-
ents of our body, for all tissues and organs are composed
of them. Hence they are also called .the proteids (from
TtpGOTevGd). They form the chemical and physical basis of
the living substance and are present in the body partly in a
solution, e.g. the tissue fluids and cell saps; partly in a solid
form (more or less swollen), forming the cells and tissues.

The proteids (including the albuminoids) form about one
sixth of the body weight. About one half of all the proteids
of the body are contained in the muscles, which are composed
of about 2Ofc proteids. The liver, spleen, and blood also*
contain the same percentage of proteid. The nerves, brain.

CHEMICAL COMPOSITION OF THE HUMAN BODY 3T

and spinal cord have comparatively less proteids, only 8$.
The bones contain 14^ (mostly collagen); the skin contains
24$ (mostly collagen) ; the adipose tissue contains only a
small amount (hardly 3$) of proteids.

(/) Classification of Proteids.

Proteids are classified into: I. Albuminous bodies or
simple proteids; 2. Combined proteids; 3. Proteoses; 4.
Albuminoids.

I. Albuminous bodies or simple proteids are the proteids
in a more restricted sense of the word (native proteids) as
they are found in the albumin (white) of the egg. They are
soluble in water or in dilute salt solutions, are levorotatory
and give all the precipitations and color reactions.

In this class belong the albumins and globulins. The
Albumins contain more sulphur and give a weaker xantho-
proteic reaction than the globulins.

The albumins are soluble in water; most of the globulins,
are soluble only in a dilute salt solution. The globulins are
therefore precipitated by half saturation with ammonium sul-
phate or by complete saturation with magnesium sulphate.
The albumins are not so precipitated. The globulins, in
distinction from the albumins, are precipitated from their
solution by very dilute acids, even by carbonic acid.

Among the albumins there are serum albumin, egg albumin, lacf
albumin, muscle albumin. These albumins differ in their solubility,
coagulation temperature, and in their specific rotatory power.

Among the globulins we have serum globulin, egg globulin, fibrin-
ogen, myosinogen. From fibrinogen, a constituent of the plasma,
the insoluble^r/;;, is formed by the action of the fibrin ferment.
Myosinogen, a constituent of muscles, coagulates during rigor
mortis, yielding the myosin. The yolk of egg also contains a
globulin-like body, vitellin.

With acids and alkalies, the simple proteids form syntonin
(acid albumin) and alkali albumin. These are not coagulated
by heat and are precipitated by neutralizing their solutions.

32 HUMAN PHYSIOLOGY

Syntonin, alkali albumin, and coagulated egg albumin are also
called derived albumins, in distinction from the native albumins.

The simple proteids of our body are chiefly dissolved
in the blood, lymph, and serous fluids, and form the
material for replacing the proteid wastes in the tissues.
For this purpose, these proteids are continually circulated
through the body by means of the blood and lymph and are
therefore called circulating proteids, in distinction from the
deposited organ proteids. The circulating proteids are also
called dead proteids in distinction from the living proteids
of the tissues.

The term " living proteids" originated from the idea that the
proteids of the living substance, because of its peculiar reactions,
have different chemical properties and constitution from the
unorganized proteids. That such a difference exists cannot be
doubted, but what the difference is, is not known.

Recently peculiar phenomena have been observed in the plasma
which have been ascribed to the action of the proteids of the
plasma. These phenomena, the immuning and bactericidal action
of serum proteids upon pathogenetic micro-organisms, cannot be
explained by the physical and chemical properties of dead proteids
and are therefore regarded as vital phenomena.

II. Combined proteids are compounds of simple proteids
with other complex substances. They give the general
proteid reactions. They are precipitated by alcohol and, if
the action is continued for a long time, are coagulated by
it. They are precipitated by making the solutions weakly
acid, but are readily soluble in weak alkalies.

Although the substances included in this group differ greatly
from each other, still they have this in common, that they are
present in the tissue cells as organized proteids, or at least origi-
nate from decomposing protoplasm.

In this class belong:

(i) Compounds of simple proteids and pigments.

Haemoglobin, the important constituent of the red-blood
corpuscle, is composed of globin, a proteid, and haematin,
an organic pigment containing iron. No successful analysis
of human haemoglobin has been made. Haemoglobin of the
dog has the following composition: C 54.57^; H 7.22$;

CHEMICAL COMPOSITION OF THE HUMAN BODY 33

N 16.38$; O 20.93$; S 0.568$; Fe 0.336$. If haemo-
globin contained one atom of iron, the empirical formula
would be C636H1025N164O181S,Fe.

Haemoglobin is soluble in water and crystallizes directly
from its aqueous solutions in red, double-refractive prisms
and needles. Haemoglobin solutions absorb the yellowish-
green light of the solar spectrum. This is characteristic of
haemoglobin and may serve for the detection of blood pig-
ment.

Haemoglobin is decomposed and coagulated by heating.
It gives most of the proteid reactions. By boiling with
alkalies and lead acetate, however, it does not yield lead
sulphide.

Haemoglobin forms more or less unstable compounds with
oxygen, carbonic oxide, and nitric oxide. The compound
with oxygen is called oxyhaemoglobin and is of great physio-
logical importance.

Oxyh&mogfobin contains one molecule of haemoglobin and
one of oxygen or two atoms of oxygen to each atom of iron.
The oxygen is held but feebly, for even at body temperature
the oxyhaemoglobin decomposes into haemoglobin (also
called reduced haemoglobin) and free oxygen. Oxyhaemo-
globin is also reduced by putrefying substances and by
ammonium sulphide.

Oxyhaemoglobin has two absorption bands in the yellow-
green of the spectrum between the D and E lines. Reduced
haemoglobin has but one broad band in the yellow-green.

Methamoglobin is a stronger union of haemoglobin with oxygen.
It is formed by the addition of potassium ferricyanide to oxy haemo-
globin; it is reduced by ammonium sulphide. It has four
absorption bands, one of which, situated in the red, is very
characteristic.

The compounds of haemoglobin with carbon monoxide and
nitric oxide are of interest only as they are frequently the cause
of death. This is especially true of CO-hcemoglobin. Carbonic
oxide forms a stronger union with haemoglobin than oxygen does;
it therefore drives out from the oxyhaemoglobin the oxygen \\hich
is absolutely necessary for life. A solution of CO-haemoglubin
has a cherry-red color and a spectrum similar to ihut uf oxyhaemo-

34 HUMAN PHYSIOLOGY

globin, but ammonium sulphide does not change its two absorp-
tion bands to the single absorption band of reduced haemoglobin.
CO-haemoglobin gives a bright-red precipitate with sodium hydrate
or with potassium ferrocyanide and acetic acid.

By acids and alkalies, haemoglobin is broken up into its
components, globin (96$) and hsematin (4$).

Globin is a globulin-like proteid, showing all the charac-
teristics of a proteid, but containing no sulphur which is
easily split off.

Hczrnatin, C32H32N4O4Fe, is insoluble in water, but soluble
in dilute acids and alkalies and in alcohol containing am-
monia or sulphuric acid. The brownish-red acid haematin
solution has four absorption bands (like the methsemo-
globins) ; the carmin-red alkaline solution has but one absorp-
tion band, located in the orange. By ammonium sulphide,
haematin is reduced to hsemochromogen, which has two
absorption bands in the green. Haematin therefore corre-
sponds to oxyhaemoglobin ; haemochromogen, to reduced
haemoglobin.

If haematin is boiled with a little NaCl and acetic acid and the
mixture is allowed to cool and evaporate, brown crystals, the
so-called Teichmanri 's hcemin crystals, are produced. Hcumin is
haematin hydrochloride. This reaction can be used in the detec-
tion of blood. The reaction succeeds still better if potassium
iodide is used instead of NaCl; in this case the crystals are
haematin hydroiodide.

By the action of strong sulphuric acid, haematin loses its iron
and haematoporphyrin is formed. This is a red pigment and has
a narrow absorption band in the orange and a broad band in the
yellow-green. For the physiological importance of haemoglobin,
see Chapters II and III.

Hcematoidin is an orange-colored pigment crystallizing in rhombic
tables. It is formed from the blood pigment of old extravascular
blood-clots. It is supposed to be identical with the bile pigment,
bilirubin.

Melanine, a black pigment found in the body, is also supposed
to be derived from the haemoglobin.

(2) Compounds of simple protcids and carbohydrates.
Glyco-proteids. In this class are the mucins and mucous
substances, found in the secretions of the mucous glands and

CHEMICAL COMPOSITION OF THE HUMAN BODY 35

epithelial cells of mucous membranes, and in tendons and
the umbilical cord. They are insoluble in water, but, because
of their acid properties, give a neutral, stringy solution with
weak alkalies. They are not coagulated by boiling and are
completely precipitated from salt-free solutions by acids as
well as by alcohol and most of the proteid precipitants (not
by nitric acid, nor by acetic acid and potassium ferro-
cyanide). They give all the color reactions of proteids.
By boiling with acids, they split up into proteid and a poly-
saccharide, the animal gum. They serve to. lubricate the
mucous membranes, and to shield them from mechanical and
chemical injuries.

(3) Compounds of proteid with substances containing
phosphorus are nucleins and nucleo-albumins.

(a) Nucleins, so called because they were first obtained
from the nuclei offish-blood corpuscles, are divided into:

(a) Paranucleins, i.e. compounds of proteids and
phosphoric acid.

(/#) The true nuclcins, i.e. compounds of proteids
and nucleic acids which are composed of phosphoric
acid and xanthin or nuclein bases.

(b) Nucleo-albumins or nucleo-proteids are compounds of
nuclein and proteids. They are found in cells as the con-
stituents of the nucleus and of the protoplasm. The chro-
matin of the nucleus and probably the structure of the
protoplasm capable of staining, are composed of nucleo-
proteids. They are insoluble in water but soluble in dilute
alkalies, with which they form neutral compounds because
of their strong acidity. They are precipitated by acids and,
in their precipitated condition, they are coagulated by heat.
They also give most of the proteid reactions. Because of
their readiness to break up, it is difficult to isolate them.

By boiling with dilute acids or alkalies the nuclein is split
from the nucleo-albumin and, by continued action of these
reagents, this breaks up into proteid, phosphoric acid, and,
eventually, the xanthin bases (xanthin, guanin, adenin,
hypoxanthin, etc.), which are closely related to uric acid.

36 HUMAN PHYSIOLOGY

Some nucleo-proteids also contain iron, e.g. the hcemalogen of
the egg-yolk, so called because haemoglobin is supposed to origi-
nate from it.

The best-known nucleo-proteid is caseinogen of milk.
It is formed during secretion by the milk-gland. It is in-
soluble in water, forms soluble compounds with alkalies and
alkaline earths, and is split up by acids, yielding paranuclein.
Caseinogen is not coagulated by boiling, but it is precipi-
tated by weak acids. By the action of the ferment rennin
it yields casein, a proteid which forms an insoluble compound
with calcium.

III. Proteoses. — The proteoses are the products of the
splitting up of the simple and combined proteids. They are
formed during digestion of proteids or by the action of dilute
acids upon proteids, and they differ but little in elementary
composition from each other and from the proteids out of
which they are formed. Their formation does not depend
upon deep-seated chemical changes of the proteids, but only
upon the splitting up of a large molecule into many similar
smaller molecules, under the assumption of water. It is
only in the amount of sulphur they contain that they differ
from each other and from the mother-substances.

In the splitting up of simple proteids many intermediate
products are formed which are called the albumoses, while
the end-products are called peptones. According to their
origin, the albumoses are called fibrinoses, globuloses, vitel-
loses, caseoses, and myosinoses.

The proteoses (albumoses and peptones) are all readily
soluble in water, except heteroalbumose, and many of them
(peptones and some albumoses) are dialyzable. They are
not coagulated by heat; alcohol precipitates them with
difficulty but does not coagulate them. They are all levo-
rotatory. The rotatory power of all the proteoses formed
by gastric digestion from a simple proteid body is greater
than that of the undigested proteid, but the rotatory power
of the products formed by pancreatic digestion is smaller
than that of the original proteid.

CHEMICAL COMPOSITION OF THE HUMAN BODY 37

The proteoses give all the proteid color reactions, but not all
the precipitation reactions.

The proteoses behave towards the mineral acids and bases
like amido acids ; the acids are simply added to the ammonia
group, and the metals of the bases replace the hydrogen of
the carboxyl groups.

Proteoses, like native proteids, are neutral because the acid
carboxyl and the basic ammonium nucleus are both neutralized by
their intimate union. Mineral acids destroy this union, the strong
acid replacing the carboxyl, hence the compound formed is acid
because of the free carboxyl groups. If proteoses combine with
alkali, the ammonium group is set free and the compound formed
has an alkaline reaction. The power of proteoses to combine
with acids and alkalies is the greater the further the splitting up
of the proteid has been carried; it is greatest in peptone in which
the combining power is many times that of the native proteid.

The albumoses differ from the peptones not only in the
size of the molecule and the percentage of suphur, but also
in the precipitation by salts. Afbnmoses arc precipitated by
saturating their solution until ammonium sulphate; peptones
are not tlins precipitated.

Albumoses are divided into primary and secondary albu-
moses which differ from each other in their solubility. The
primary albumoses (protalbumose and heteroalbumose) are
precipitated from a neutral solution by saturating with NaCl.
The secondary albumoses (deuteroalbumose) are thus pre-
cipitated only from acid solutions; sometimes they are not
precipitated by NaCl at all.

The secondary albumoses are with greater difficulty precipitated
by other reagents also; they are not precipitated by nitric acid or
2% copper sulphate solutions, and their precipitation by potassium
ferrocyanide and acetic acid is slow and incomplete. The primary
albumoses obtained from the crystallized serum albumin contain
more firmly combined sulphur, the secondary has more loosely
combined sulphur.

Judging from the freezing-point, it is supposed that deutero-
albumose has a larger molecular weight than protalbumose.
Hence the deuteroalbumoses cannot be regarded as the splitting-
u p products of protalbumoses.

Peptones are not precipitated by any proteid precipitant

38 HUMAN PHYSIOLOGY

except tannic and phosphotungstic acid. They are more
dialyzable than the albumoses, yet their power of dialyzing
is only one-fourth of that of grape-sugar. They are solu-
ble in all proportions in water. Their solutions have a dis-
agreeable bitter taste.

The red color which peptones give in the biuret reaction
is highly characteristic of peptones, the other proteids giving
a reddish-violet color.

The various peptones differ from each other in the amount
of sulphur; some have loosely combined sulphur, others have
only firmly combined sulphur. They also differ in their
behavior towards the pancreatic ferment trypsin ; the ' ' hcmi-
pcptoncs" are split by trypsin into leucine, tyrosine, and
aspartic acid, etc. ; the "anti-peptones " not.

Nothing is definitely known as to the number of peptone mole-
cules formed from one molecule of simple proteid. From a
molecule of crystallized serum albumin, if the calculated molecular
weight, 17,070, is correct, at most ten molecules of peptones can
be formed, for one molecule of serum albumin contains ten atoms
of sulphur and each molecule of peptone must contain at least one
atom of sulphur, since peptone must still be regarded as a proteid.

Albumoses and peptones are found only in the alimentary
canal, having been produced by the digestion of the proteids
of the food. By their formation, the insoluble and coagu-
lable or at least undialyzable proteid of the food is rendered
into a soluble and dialyzable form suitable for absorption.

Proteoses-like bodies are also formed from native proteids by
the action of superheated steam. The products thus formed are
called atmidalbumoses and atmidpeptones. They have no loosely
combined sulphur and differ from the ordinary proteoses in their
precipitation. Atmidproteoses are not readily absorbed from the
intestine. Evidently by superheated steam the proteids are not
only split up but undergo other changes which make them more
or less unsuitable for nutrition.

IV. Albuminoids are derivatives of proteids, which still
have the characteristic percentage composition of proteids,
but differ from them chemically, physically, and especially
physiologically. Some of the albuminoids contain more
sulphur, others less, than the proteids. They do not give

CHEMICAL COMPOSITION OF THE HUMAN BODY 39

all the characteristic color reactions, because some do not
have the aromatic groups, hence all of them do not yield
tyrosin when boiled with alkalies. They do not dissolve
but swell up in water. They are not coagulated by heat.

Physiologically they differ from the proteids in that they
are either indigestible, or, if they can be digested and
absorbed, they cannot replace the used-up body proteids as
the other proteids can.

Also in regard to their functions in building up the body,
there is a great difference between the albuminoids and the
simple and combined proteids. The latter form the bases
of the living substance, and as such are the chief constituents
of the cells. The albuminoids, on the contrary, are present
only as intracellular substances ; they are indeed cell-
products and perhaps take a part in cellular metabolism, but
their chief physiological importance lies in their furnishing
the material for covering and framework. They form the
organic ground-substance of bones, cartilage, tendons, fascise,
connective tissue and of the covering of the body — epidermis,
hair and nails. They are the most important organic con-
stituents which furnish form and stability to the body.

The albuminoids are specific animal products. They are
formed by the cells themselves, being the intracellular sub-
stance. In the epidermal cells all the protoplasm is changed
to a certain kind of albuminoid substance. They are formed
from the proteids of the cells by chemical changes the
nature of which is still unknown.

Albuminoids unite with acids and alkalies ; in some of
them the amido-acid character is even more apparent than
in the other proteids. By digestion, albuminoids, if at all
digestible, yield proteoses-like products.

Among the albuminoids are :

i. Keratin, the chief constituent of the horny epithelial cells,
hair, nails, and of the membrane of nerves (here called neuro-
keratin). It is rich in sulphur (2—5^), most of which is loosely
combined so that it is easily split off by alkali. It gives all the
proteid reactions and in decomposing yields tyrosin. It is not

40 HUMAN PHYSIOLOGY

soluble in water; in general, it is not soluble without previous
decomposition. It cannot be digested.

2. Elastin, from the elastic fibres, has only firmly combined
sulphur. It gives the color reactions of proteids and yields the
corresponding decomposition products. It is insoluble in water
and can be digested by pancreatic juice, not by gastric juice.

3. Collagen forms the greater part of the albuminoids
found in our body. It forms the fibres of the connective
tissue and the organic basis of bones and cartilages. It
contains no loosely combined sulphur, does not give Adam-
kiewicz's and Miilon's reactions, neither does it yield tyrosin
when decomposing, hence it contains no aromatic group.
It contains a little more oxygen than the proteids, hence it
is perhaps formed from proteids by oxidation.

If collagen is boiled for a long time in water, it takes up
water and, on cooling, a solid jelly called gelatin is formed.
If gelatin is heated to 130° it again changes to collagen.
Gelatin is the hydrate of collagen. It is soluble in hot but
not in cold water (the reverse of native proteids) ; in cold
water it only swells up.

Gelatin is not precipitated by mineral acids, by potassium
ferrocyanide and acetic acid, nor by salts of heavy metals
(except mercuric chloride in hydrochloric acid). It is,
however, precipitated by salts. It gives the biuret and
xanthoproteic test".

Gelatin is digested with difficulty by pepsin but readily by
trypsin, gelatoses and gelatin peptones being formed.
Concerning the importance of gelatin as a food see Chapter
VIII.

4. Chondrin is a mixture of gelatin and chondroitin-sulphuric
acid which is an ethereal sulphate of chondroitin, a nitrogenous
derivative of carbohydrates; it can be isolated from cartilage by
dilute alkalies. If bones are boiled with dilute mineral acids, the
chondroitin yields acetic acid and the nitrogenous chondrosin.
Chondrosin reduces cupric oxide in alkali solutions, and by boil-
ing with barium hydrate yields glycuronic acid and glucosamine.

Ferments. — Among the proteid-like bodies are also
counted the unformed ferments. The composition of the

CHEMICAL COMPOSITION OF THE HUMAN BODY 41

ferments is unknown, but they have some properties in
common with proteids. They are soluble in water and
glycerin, are precipitated and partly coagulated by alcohol,
can be precipitated by salts, are not dialyzable, and give the
proteid color reactions. They are products of cellular
activity.

The unformed ferments here referred to are to be distinguished
from the formed ferments which are organisms (bacteria, fungi,)
which, by contact t split up, certain substances (e.g. yeast, bac-
terium lactis. See page 20).

Their most important property is that, in very small quan-
tities, they can chemically change unlimited quantities of
certain substances, without suffering any chemical change
themselves. Their action, in general, consists in a hydro-
lytic splitting up of the large molecule into smaller mole-
cules and in transforming the chemical potential energy into
kinetic energy. Their action depends upon the reaction and
concentration of the solution of the substances upon which
they act. The more concentrated the solutions, the less
active are the ferments. They are rendered inactive by
heating.

Ferments are classified as:

1. Coagulative ferments, which split up certain soluble proteids
into an insoluble and soluble part (e.g. the coagulative ferment
of blood, rennin of the stomach, myosin ferment).

2. Digestive ferments, which, by hydrolytic splitting up, change
the insoluble or soluble proteid of food not capable of absorption
into a soluble form capable of absorption. These include:

(a) Diastatic ferment (in saliva and pancreatic juice), which
changes starch to sugar.

(b) Proteolytic ferment (in gastric and pancreatic juices), which
changes simple proteids to proteoses.

(c) Stereolytic ferment (in pancreatic juice) which split neutral
fats into fatty acids and glycerin.

Concerning the action of these ferments in detail, consult the
proper section in special physiology.

42 HUMAN PHYSIOLOGY

3. END-PRODUCTS OF METABOLISM

To this class belong the substances which are formed by
the combustion of the energy-yielding substances of the
body (proteids, fats, carbohydrates). These products are
•excreted from the body.

It is possible and even probable that the end-products of meta-
bolism are not formed directly by combustion from the body-
substance, but that a series of intermediate substances are formed.
But nothing is known concerning these intermediate product.^ ;
everything that has hitherto been said about them is based on
mere assumption. We must therefore be satisfied with enumerat-
ing the end-products.

Among the end-products we may, in the first place, name
the already mentioned water and carbon dioxide, the chief
combustion products of all organic substances.

In abnormal conditions, organic substances of carbon, hydrogen
and oxygen which can still undergo oxidation are excreted from
the body. These are, evidently, products of incomplete combus-
tion. Such substances are:

1. Lactic acid, CsHfiOr There are three lactic acids.

(a) Ethyline lactic acid, CH2OH.CH2.COOH, is present
in the body in but very small quantities.

(b) Ethyliden lactic acid, CHyCHOH.COOH. Of these
there are two:

(1) The optically inactive fermentation lactic acid;
formed by the lactic-acid fermentation of carbo-
hydrates.

(2) Dextrorotatory sarcolactic acid, found in the
muscles and in urine.

Sarcolactic acid is a syrupy fluid, soluble in water, alcohol and
•ether. It forms a characteristic crystallizable salt with zinc; this
is of use in isolating the sarcolatic acid.

Lactic acid is present in the urine if the supply of oxygen is
deficient (dyspnoea).

2. /?-oxybutyric acid, CH3.CHOH.CH2.COOH, diacetic acid,
CH3.CO.CH2.COOH, and acetone, CH3.CO.CH3, appear in the
urine in certain diseases, especially diabetes. Acetone is present
in normal urine in very small quantities.

3. It may here be mentioned that oxalic acid, COOH.COOH,

CHEMICAL COMPOSITION OF THE HUMAN BODY 43

is present in small quantities in the urine (in the form of calcium
oxalate, yielding the "envelope crystals ").

While the combustion of fats and carbohydrates yields
only CO., and H.,O, combustion of proteids furnishes these
and a series of other products which contain the nitrogen,
sulphur, and phosphorus of the proteid. These products are
of importance in estimating the extent of proteid metabolism.

By the combustion of the proteid, its sulphur and phos-
phorus form sulpJniric and pJiosphoric acids, which are
excreted in the form of salts.

The nitrogenous cud-products of metabolism can unite
with still more oxygen ; hence, in the physiological combus-
tion of proteids, the proteids are not fully oxidized, but an
oxidizable residue is left which cannot be used in the body.
The nitrogeneous end-products are :

1. Ammonia, excreted in small quantities as ammonia
salts.

2. Urea, CO(NH.,)., , the diamicl of carbonic acid or
carbamid.

Urea crystallizes in colorless needles or long, rhombic
prisms ; it is neutral and has a cool saltpetre taste. It melts
at 130—132° C., but in solutions undergoes decomposition
at 60-70° C. It is soluble in water and in alcohol, but not
in ether.

Decomposition of urea. — On heating, dry urea forms am-
monia and biuret. Two molecules of urea form one mole-
cule of biuret and one of ammonia.

2CO(NH2), = NH2.CO.NH.CO.NH2 + NH3.

Biuret gives a reddish-violet color with copper sulphate
and potassium hydrate (origin of the term biuret reaction).

By heating with baryta-water, alkalies, and by the action
of certain micro-organisms (during alkaline urine fermenta-
tion) urea takes up water and forms ammonium carbonate.

An alkaline solution of sodium hypobromite decomposes
urea into carbon dioxide, wrater and nitrogen :

CO(NH2)2 + 3NaOBr = sNaBr + CO2 + 2H2O + Na.

44 HUMAN PHYSIOLOGY

Compounds of nrca. — With many acids and bases, urea
forms characteristic compounds. The acids unite with the
ammonia group, in which the nitrogen becomes quinquiva-
lent. The most important compounds are :

(a) Urea nitrate, CO(NH2)2.HNO.r It crystallizes in
smooth, hexagonal, colorless platelets, soluble in pure water
but soluble with difficulty in water containing nitric acid.
The crystals are obtained by adding an excess of strong
nitric acid to a concentrated solution of urea. The com-
pound serves for the detection and isolation of urea.

(b) Urea oxalate, [CO(NH2)J2.C2H2O4.

(c) A' white precipitate is formed when a urea solution is-
mixed with a solution of mercuric nitrate. The proportion
in which urea and mercuric nitrate unite varies with the con-
centration of the urea and the mercuric nitrate used. Upon
the precipitation of urea by mercuric nitrate depends Liebig's
titration method for estimating urea.

Synthesis of urea. — Urea is formed:

1 . By heating ammonium cyanate :

NH4.O.CN = CO(NH2)2. (Wohler, 1828.)

2. By heating ammonium carbonate with metallic sodium,
water being split off.

3. By passing an alternating electrical current through a
solution of ammonium carbamate, NH2.COONH4, water
being split off from the ammonium carbamate.

4. From carbonylchloride and ammonia:

COC12 + 2NH, = CO(NH2)2 + 2HC1.

5. From ethyl carbonate and ammonia:
CO,(C2H.)2 + 2NH, = 2(C2H..OH) + CO(NH2)2.

Presence and formation of nrca in the animal body — Urea
forms most of the solids of the urine of mammals. It is
present in small quantities in the blood, in all tissue fluids,
and in many organs of the body.

Urea is the most important nitrogenous end-product of

CHEMICAL COMPOSITION OF THE HUMAN BODY 45

proteid combustion. Other nitrogenous end-products are
present in but small quantities. The amount of urea ex-
creted depends, therefore, upon the extent of proteid meta-
bolism.

A large portion of the urea is formed in the animal body
synthetically from the combustion products of proteids,
namely, carbon dioxide and ammonia. That this formation
is possible is proven by the following facts:

Certain ammonia salts, especially ammonium carbonate,
introduced into the body do not appear in the urine as
ammonia salts, but the amount of urea is increased in pro-
portion to the ammonia salts taken. This is also true for
some substituted ammonia compounds, such as amido acids
(leucine, glycocoll, tyrosine and others).

That the ingested ammonia salt is really changed to urea and
does not merely increase proteid decomposition and thus the
excretion of urea, is proven by the fact that if a substituted
ammonia salt is ingested, the corresponding substituted urea is
formed. If meta-amido-benzoic acid, NH,.C6H+.COOH, is in-
gested, we find uramidobenzoic acid,

The place where the synthetical formation of urea from
ammonia takes place is the liver. If defibrinated blood con-
taining ammonium carbonate is passed through an excised
liver, into the portal vein and out of the hepatic vein, the
ammonium carbonate decreases, while the urea increases, in
the blood. If the liver is artificially cut off from the circula-
tion, the amount of urea is decreased, while the amount of
ammonia and also of amido acids (leucine, tyrosine) in the
urine is increased. This is also true for many diseases of
the liver.

The nature of the substituted urea shows the part played by the
•carbamic acid in urea formation. Perhaps carbamic acid and
ammonia are formed by the proteid metabolism and that these
.substances are changed to urea in the liver. Hence urea must be
regarded as the amid of carbamic acid.

The object of the formation of urea from ammonia salts

46 HUMAN PHYSIOLOGY

seems to be to change the injurious ammonia formed by
proteid metabolism into a harmless compound.

It is a question, however, whether all the urea formed in
the body is derived from ammonia or ammonia derivatives.
It is probable that some of the urea can also be directly split
off from the proteid.

3. Uric acid, C.H4N4O3, has the structural formula:

/NH-CO
CO/

. [Diureid of trioxyacrylic acid.]
NH-C-NHX

Pure uric acid crystallizes in colorless, rhombic prisms, but
directly from the urine it yields bundles of colored dumb-
bell and whetstone crystals. Uric acid is but slightly solu-
ble in cold water (0.05 g in one liter); it is a little more
soluble in hot water (0.5 g in one liter) or in the presence
of urea ; it is insoluble in alcohol and ether. As a dibasic
acid it forms neutral and acid salts. The neutral alkali
salts are quite soluble in water; the acid salts are also more
soluble than the free acid. But these are precipitated even
by the cooling of the urine and, as they take with them the
pigments of the urine, they form reddish precipitates (sedi-
mentum lateritium).

The salts of uric acid with the alkali-earths, most of the
metals, and also ammonia are not very soluble in water.

Because of the comparative insolubility of uric acid, it is
easily deposited in the kidneys, ureters and the tissues of the
body (gravel, gout).

If uric acid to which nitric acid has been added is evap-
orated to dryness and to the residue ammonia is added, a
reddish-violet color results which gives place to a bluish
violet on addition of sodium hydrate (inurcxidc test for uric
acid).

By careful oxidation of uric acid, allantoin and carbon
dioxide are formed : C5H4N4O3 + O + H2O = C4H6N4OS
(allantoin) + CO2.

CHEMICAL COMPOSITION OF THE HUMAN BODY 47

Allantoin is found in the allantoic fluid and in the urine of
newly born mammals. On oxidation it yields urea and oxalic
acid: C4H6N/)3 + O + 2H.,O = 2CO(NH,)a + C2O4H2.

Uric acid can be formed synthetically:

(a) By melting urea and glycocoll together:

3CO(NH2)2 + NH2.CH2COOH = CHtN4

($) From urea and trichlorlactamide :
2CO(NH2)2+C3C13O2H2NH2=C5H4N4O:5+C1XII4+H2O4-2HC1.

Presence and formation of uric acid in tJic animal body. —
Uric acid is found in small quantities in the urine, also in
the blood and the organs of the mammals. It is the chief
constituent of the urine of birds and reptiles. It is formed,
like urea, from the decomposed proteids. In the liver of
birds, uric acid appears to be formed synthetically from
lactic acid and ammonia salts. If the liver of a bird be
extirpated, the urine contains lactic acid and ammonia salts
instead of uric acid. Urea and amido acids given to birds
is excreted in the form of uric acid. Whether in mammals
uric acid is also formed synthetically is not known.

Uric acid is closely related to the nuclein bases; by reduc-
tion it can be changed to xanthin and hypoxanthin (see
below). Hence it is formed in the animal body probably
by the splitting up and oxidation of the nucleins.

It is supposed that the uric acid is especially formed from the
nucleins of the nuclei of the decomposed leucocytes. This is
based upon the facts that large increase and greater destruction
of leucocytes in the blood (leukaemia) is accompanied by greater
excretion of uric acid, and that by heating the pulp of spleen or a
boiled aqueous extract of spleen with blood, uric acid is formed.
In this, however, the oxidizing power of the blood is necessary.

The excretion of uric acid is increased by food rich in
nucleins. Uric acid introduced into the body of a mammal
is, for the greater part, excreted as urea.

4. Nuclein or xanthin bases. These are:

(a) Guanin, C5H3N5O.

(b) Xanthin, C5H4N4Or

48 HUMAN PHYSIOLOGY

(0 Adenin, C5H5N5.

(</) Hypoxanthin, C.H4N4O.

These substances are closely related to each other.
Hypoxanthin is an oxidation product of adenin, xanthin is
an oxidation product of guanin and of hypoxanthin. They
are regarded as the precursors of uric acid or urea, for by the
reduction of uric acid xanthin and hypoxanthin can be pro-
duced. They are formed by the splitting up of nucleins
(see page 35).

They are found in small quantities in urine, blood and the
organs, especially the liver and spleen. Their excretion is
increased during leukaemia.

5. Hippuric acid (Benzoylglycocoll),

CGH..CO.NH.CH2.COOH,

is found in the urine of plant-eaters. It is formed in the
kidneys by the synthesis of benzoic acid, C6H5.COOH, and
glycocoll, NH2CH2.COOH.

6. Kreatin and kreatinin.

Kreatin, C4H9N3O2, is methylguanidin-acetic acid:

NH - r/NH2

~\N(CH3)-CH2-COOH.

Guanidin is imido-urea: NH = C(NH.,).,.
Kreatinin, C4H7N3O, is the anhydrid of kreatin:

/NH-CO
NH ~ C/ \

\N(CH3)-CH,.

Kreatin can be synthetically formed from cyanamid and methyl-
glycocoll (sarcosin) :

0 +NH(CH3).CH2.COOH = NHzC

NH XN(CH3).CH2.COOH.

Kreatin and kreatinin crystallize in monoclinic prisms. Both
are soluble in water. The reaction of kreatin is neutral, that of
kreatinin, alkaline. By the action of alkalies both form decom-
position products, among others, urea.

CHEMICAL COMPOSITION OF THE HUMAN BODY 49

If to an alkaline solution of kreatinin a few drops of
sodium nitroprusside are added, a red color is produced
which soon disappears (Weyl's kreatinin test). This color
is not brought back by the addition of acetic acid, like that
of aceton. Kreatinin unites with zinc chloride, forming
kreatinin zinc chloride, a slightly soluble, double salt which
readily crystallizes.

Kreatin is found in the blood and in many organs,
especially in the muscles. It is regarded as a precursor of
urea. Kreatinin is a constituent of urine.

It is a question whether the kreatinin of urine is formed
from the kreatin of the muscles. The amount of kreatin in
the muscles is said to be increased by muscle activity, not
so the kreatinin of the urine. On the other hand, it has
been observed that kreatin fed to animals increases the
amount of kreatinin in the urine correspondingly.

Carnine, C,H8N4O3 , is also a constituent of muscles. By oxida-
tion with nitric acid it is changed to hypoxanthin.

Cystin, a nitrogenous body found in urine during pathological
conditions (increased putrefaction in the intestine, diseases of
intestine), is the disulphide of amido-ethylidene lactic acid:

CHS\ /CH3

COOH/\~ / \COOH.

NH2 NH^

Cystin is of interest because in it sulphur is excreted from the
body in unoxidized form.

7. Bile acids are the union of a nitrogenous with a non-
nitrogenous acid. The nitrogenous part is an amido-acid
(glycocoll or taurin) ; the non-nitrogenous part is a cholalic
acid (or fellic acid).

The bile acids are soluble in water and alcohol but in-
soluble in ether. They are precipitated in crystalline form
from the alcoholic solution by ether. They give a cherry-
red color with furfurol, or cane-sugar, and concentrated
sulphuric acid (Pettenkofer's test). They are monobasic
acids which form salts with alkalies. These salts are dextro-
rotatory.

5° HUMAN PHYSIOLOGY

In human bile there are:

(a) Glycocholic acid, C26H43NOG, a compound of glycocoll
and cholalic acid.

(b) Taurocholic acid, C2GH45NSO7 , a compound of taurin
and cholalic acid.

Cholalic acid, C24H40O5, is a monobasic acid with three
-OH-groups (trioxy-acids). It is an unsaturated compound
since it unites directly with bromine. Its constitution is
unknown, as is also its origin in the body. Its high per-
centage of carbon makes it probable that it is first formed by
synthesis.

Beside cholalic acid, there is present in the human bile another
non-nitrogenous constituent of the bile acids — f elite acid, C.,3H40O4.
In animals there are still other non-nitrogenous constituents of
bile acids, closely related to cholalic acid.

Glycocoll (amido-acetic acid), NH,CH2.COOH, is a
decomposition product of proteids. It is especially present
among the products of the splitting up of gelatin.

Taurin (amido-ethylsulphonic acid), NH2.C2H4.SO2OH
(the sulphur is directly united with the carbon, hence a
sulphonic acid), may also be regarded as a metabolic product
of proteid.

The bile acids are formed in the liver and secreted in the
form of sodium salts. They are, in part, absorbed from the
intestine, in part they are transformed into their anhydrids
(dyslysins) by putrefaction in the intestine. The bile acids
aid the absorption of fats in the intestine (see Chapter X).

8. Bile pigments. — The most important are:

(a) Bilirubin, a reddish-yellow pigment, C.V,H.J(.N4O6.
(&) Biliverdin, a green pigment, C32H3(,N4OS.

Biliverdin is an oxidation product of bilirubin. .The bile
pigments are weak acids, forming soluble salts with the
alkalies and insoluble salts with calcium (this last is found
in the gall-stones).

Bilirubin is slightly soluble in alcohol, readily in chloro-
stallizes in rhombic tables. Biliverdin is readily

R A R V

CHEMICAL COMPOSITION OF THE HUMAN BODY 51

soluble in alcohol, slightly in chloroform. Bilirubin, by the
reduction of nascent hydrogen, takes up water and forms
liydrobilirubiii, C;i2H4()N4O_ , which is identical with urobilin
(a pigment of urine). Urobilin cannot be changed back to
bilirubin by oxidation.

(i)iicliii s test.— \n a test-tube place some nitric acid con-
taining nitrous acid. Carefully cover it with an aqueous
solution of bile pigment. At the junction of the two liquids,
colored layers will be seen, which from the top downward
are green, blue, violet, red, reddish yellow. The pigments
to which the colors are due are formed by the oxidation
of bilirubin or biliverdin ; they represent various oxidation
stages of the bile pigment.

The bile pigments are made in the liver from the haematin
formed by the decomposition of the red blood corpuscles.
This haematin loses its iron :
C,2H,2N4O4Fe (haematin) + 2 H2O - Fe = C32H36N4OG (bilirubin).

9. Besides the end-products of metabolism above named, there
are present in the urine aromatic substances. It is not certain
\vhether these originate by metabolism or whether they are merely
products absorbed from the alimentary canal. By the proteid
putrefaction in the intestine, aromatic compounds are formed
(phenol, aromatic oxyacids, indol, skatol) which, in so far as they
are not cast out with the faeces, are absorbed by the body and are
in part oxidized (forming indoxyl, skatoxyl) and in part united
with sulphuric acid and excreted by the kidneys as such. For
further information, see Chapter VII and Chapter IX.

CHAPTER II
THE BLOOD

BLOOD is a red, opaque, salty fluid, having a character-
istic smell and a specific gravity of 1.053-1.066. It has an
alkaline reaction, the alkalinity being equal to that of a
0.2-0.4^ sodium carbonate solution.

The blood circulates through the entire animal body in a
closed system of vessels which is exceedingly ramified.
The most important physiological import of blood is to carry
foodstuffs to the organs and to remove the metabolic
products.

Blood is composed of a clear yellowish fluid, the plasma*
in which are suspended the solid constituents, the red and
white blood corpuscles. Histologically considered, blood is
a tissue with a liquid intercellular substance.

Blood coagulates within a few minutes after leaving the
vessels, i.e. it clots to a jelly-like mass. The coagulation
depends upon the separation of a proteid from the plasma,
the fibrin, which forms a fibrous mass inclosing the blood
corpuscles in its meshes. Gradually the clot shrinks, thereby
pressing out a clear, faintly yellowish fluid, the blood serum.
The coagulum with the inclosed corpuscles is called the
clot. Plasma is composed of serum and the fibrin-forming
proteid. Serum is plasma without its fibrin-forming proteid.
Blood from which the fibrin has been removed by whipping
(e.g. with a rod) is called defibrinated blood, and is com-
posed of serum and corpuscles. In whipping blood, the
fibrin clings to the rod.

The quantity of blood in man is about 7.5^ of the body

52

THE BLOOD 53

weight, hence adult man has about five liters of blood, of
which about 35$ vol. is blood corpuscles and 65$ vol.
plasma.

1. THE BLOOD CORPUSCLES

i. The red blood corpuscles of man are soft, elastic,
biconcave disks with circular outlines. They are 7— 8ju in
diameter, i.6yu thick, have a volume of 72 a3 and a surface
of I28/A In thin layers they are yellowish green, in thicker
layers red ; they are heavier than the plasma and therefore
sink to the bottom when blood is allowed to stand.

Man and most mammals have round, non-nucleated red blood
corpuscles; birds, reptiles, amphibians and fishes have oval,
nucleated red blood corpuscles.

One cb.mm. of human blood contains, in the male about five,
in the female about 4.5 million red blood corpuscles; their sur-
faces are 640 and 576 sq.mm. respectively. This immense surface
favors the taking up and the giving off of oxygen in external and
internal respiration. The number of blood corpuscles is found by
counting the number found in an accurately measured quantity of
blood diluted to a given extent. The counting is done with the
aid of a microscope and a specially constructed slide.

The number of red blood corpuscles is greater the higher the
altitude.

The red blood corpuscles contain 65$ water and 35$
solids. Of the solids the most important is

The red coloring matter of blood, haemoglobin, which
forms about 87-95$ of the solid constituents of the blood
corpuscle (11-15$ °f total blood); it is deposited in the
framework, the stroma, of the blood corpuscles.

The haemoglobin of the blood corpuscle becomes dissolved in
the fluid of the blood by the addition of water, ether, chloroform
or bile to the blood; also by decomposition, by freezing, and by
thawing of the blood and by the passing through of strong electric
shocks. Blood, in which the coloring is dissolved in the fluid, is
transparent (laky-blood).

The cause of this dissolving of haemoglobin in the blood fluid
after the addition of water, is the disturbance of the osmotic equi-
librium between the corpuscles and the surrounding fluid. The
corpuscles swell by the imbibing of water and are thereby

54 HUMAN PHYSIOLOGY

destroyed. Haemoglobin also leaves the blood corpuscles when
they are placed in the serum of another kind of animal. As such
serum has all the physical properties which make the existence of
the blood corpuscle possible, the cause of the passing out of the
haemoglobin must lie in the chemical difference of the various kinds
of serum. These differences are due to the proteids. The proteid
of one kind of serurn acts upon the corpuscle of another animal as
a poison (globulicidal action of the serum).

The quantity of haemoglobin is estimated by colorimetry. A
measured quantity of blood is diluted with water till it has the
same color as a haemoglobin solution of known strength; from the
extent of the diluting, the quantity of haemoglobin can be found.

For the chemical properties of haemoglobin, see page 32.

Haemoglobin is of physiological importance because of its
power to unite with oxygen, forming a weak compound
called oxyhaemoglobin ; it therefore serves as the oxygen
carrier (see pages 33 and 58).

The stroma of the red blood corpuscles, which remains
behind after the withdrawal of the coloring matter, is com-
posed of proteids, fat, lecithin, and cholesterin. Besides these
substances, the red blood corpuscles contain salts, especially
potassium chloride and potassium phosphate.

The red blood corpuscles are continually destroyed in the
body in large numbers. The places of destruction are the
liver and the spleen. A restitution of this loss by the forma-
tion of new corpuscles takes place in the red bone marrow
(in the embryo also in the liver and spleen), the corpuscles
being formed from colored nucleated blood cells, the
haematoblasts. They are formed from these haematoblasts
by indirect division. At first, they still contain a nucleus,
but later on the nucleus disappears.

2. The white blood corpuscles, also called leucocytes or
lymph corpuscles, are generally a little larger than the red
corpuscles; they are colorless cells with one or more nuclei.
They have no constant shape as they can change their form,
like the amoeba, and can also move about by the pushing
out and withdrawing of protoplasmic processes. At rest
they are spherical.

THE BLOOD 55

There are many kinds of leucocytes, which differ in their size
and in the proportion of their protoplasm and nucleus:

1. Small cells of 4-7A« diameter with little protoplasm and one
nucleus; few in number.

2. Larger cells of y-iOyU diameter with much protoplasm and
one or more nuclei (large uni-nuclear and poly-nuclear cells);
these make up the bulk of the leucocytes.

3. Granular cells of 8-14/1* diameter, with many granules in
their protoplasm; these granules stain differently in different cells.
Accordingly, we speak of oxyphile (eosinophile), basophile and
neutrophile cells, as the granules stain with acid, basic or neutral
stains.

The number of leucocytes is about 10,000 in one cu. mm.
(about 500 red to one white), but it varies greatly. The
leucocytes contain besides water chiefly proteids (especially
nucleins and nucleo-albumin) and in smaller quantities
lecithin, cholesterin, and salts.

The white blood corpuscles are able to pass through the
stomata of the walls of the capillaries and thus wander into
the tissues, hence they are also called wandering cells.
They are of physiological importance because they serve as
transports for many undissolved substances (fat, pigment)
and because they are able to destroy and remove foreign
bodies (e.g. Bacteria). They migrate in large numbers
from the vessels to those places where foreign substances
causing inflammation are present, and there they form the
pus. They are stimulated to activity by chemical action.
They originate in the lymph glands and spleen (see Chapter
VI).

Besides the red and white blood corpuscles, there are still other
constituents in the blood having a definite form, viz. :

Blood platelets, colorless, strongly refractive disks having a
diameter of £ or j- that of the red blood corpuscles. They are
apparently the nuclear remains of destroyed leucocytes.

Elementary granules, i.e. fat granules, which are brought to the
blood by the chyle.

2. THE BLOOD PLASMA

Pure plasma can he obtained by letting uncoagulated blood
stand at low temperature (about o° C. ). By this, coagulation is

56 HUMAN PHYSIOLOGY

prevented and the corpuscles sink and the clear supernatant fluid
is the plasma.

Plasma is a yellowish, alkaline fluid, having a specific
gravity of 1.03; it contains 9^ solids which are:
i. Proteids-(j-%f}\

(a) Scrum albumin (3-5^).

The albumins differ from each other in their specific rotatory
power, their coagulation temperature, and, as far as they are
crystallizable (as in serum of horse blood), in the forms of their
crystals.

(&) Serum globulin (3-4$).

The quantity of albumin and globulin varies much. In general
the albumin predominates in the blood of well-fed animals, while
globulin predominates in that of fasting animals.

(c) Fibrinogcn (o . I -0 . 3 $J .

Fibrinogcn is a globulin-like proteid from which fibrin is
formed when blood coagulates. The amount of fibrin is but
small (0.1-0.3$). Its volume, however, appears large as
it is swollen. The fibrin formation is most likely brought
about by the splitting of fibrinogen into two parts, one part
being the insoluble fibrin, the other a soluble proteid of
which little is known.

The coagulation is brought about by an unformed ferment
— thrombin. This ferment is not present in blood in healthy
blood vessels. It is formed, when blood is shed, by the
breaking down of the white blood corpuscles, especially the
poly-nuclear. Defibrinated blood is called blood scrum.

As long as blood is inclosed in blood vessels having sound
walls, coagulation does not occur. The coagulation of blood is
prevented by cooling, by the addition of saturated salt solutions,
e.g. magnesium sulphate, and by the addition of salts of oxalic,
hydrofluoric, and fatty acids. Soluble calcium salts seem to aid
in the formation of the coagulative ferment. The power of
coagulation can also be destroyed by the injection of proteoses
and of leech extract.

Coagulation is of importance in that the bleeding from
vessels is stopped by the clotting of the shed blood, as the

THE BLOOD 57

clot formed closes the opening of the vessel. In bleeders
the blood does not coagulate, hence fatal bleeding is apt to
occur.

2. Ether extracts: Fats, cholesterin, the ester of choles-
terin and fatty acid, lecithin (about 5^).

3. Carbohydrates in the form of grape-sugar (o. 1-0.2%).
In the body the carbohydrates are carried in the form of
grape-sugar by the blood from one place to another.

4. End-products of metabolism (urea, uric acid, kreatin,
xanthin, lactic acid and others) in small quantities.

5. Salts (0.8$), chiefly NaCl (0.6$) and neutral and acid
sodium carbonate ; also acid calcium carbonate and mag-
nesium sulphate in small quantities.

Alexines and antitoxins are proteid-like substances found in the
plasma or serum and protect the body against infectious diseases.
The alexines have a bactericidal action, i.e. they destroy the
pathogenic micro-organisms or inhibit their action. The antitoxins
render the poisonous metabolic products (toxins) of the micro-
organisms harmless. The alexines are also responsible for the
globulicidal action of the blood serum (see page 54).

CHAPTER III

THE GASES OF THE BLOOD AND THE CHEMISTRY OF
RESPIRATION

1. THE GASES OF THE BLOOD

For the analysis of the gases of the blood, it is placed, at body
temperature, in a vessel from which the air has been removed by
a mercurial air-pump. The gases leave the blood, entering into
the vessel; they can then be collected and analyzed.

The gases of the blood are oxygen, carbon dioxide, and
nitrogen. The oxygen is dissolved physically to only a very
small extent, the greater part being chemically united to the
haemoglobin, forming oxyh&moglobin. The oxygen must
be held chemically, as the quantity of the oxygen in the
blood is not proportional to the partial pressure * of the
oxygen upon the blood, as would be the case in a physical
solution.

Oxyhaemoglobin is a compound easily undergoing dis-
sociation ; by its dissociation the oxygen is set free.

The degree of dissociation of a compound, by which a gas is
set free, is dependent upon the temperature and the pressure of
the gas. In a vacuum and at the body temperature, oxyhaemo-
globin undergoes complete dissociation (not at o°) ; in other
respects, the amount of haemoglobin chemically united with oxygen
increases with the partial pressure of the oxygen, but not propor-
tionally as in the mere physical solution.

The carbon dioxide of the blood is also physically dis-
solved to but a small extent; most of it being chemically

* In a mixture of gases the partial pressure of one of the gases is that part
of the whole pressure which the gas exerts by itself.

58

THE GASES OF THE BLOOD 59

bound to the alkalies of the serum (chiefly to the sodium
bicarbonate and, in smaller quantities, to the acid calcium
•carbonate). As the whole blood contains more carbon
dioxide than the corresponding- amount of plasma, the blood
corpuscles also contain this gas in an easily dissociated form,
perhaps united with the haemoglobin or the alkali phosphate.

In a Vacuum, the blood loses all the carbon dioxide not
only from the acid but also from the neutral carbonates,
because it contains substances of a weak acid character,
which drive the carbon dioxide out of its union with alkalies.
These substances are the proteids and the haemoglobin.

The nitrogen of the blood is only physically dissolved.
The per cent of gases in the blood is :

Arterial Blood. Venous Blood.

Oxygen 19.2 vol. % 11.9 vol. %

Carbon dioxide 39-5 " 45-3 "

Nitrogen 2.7 " 2.7 "

These volumes of the gases are measured at o° C. and 760 mm
mercury pressure. The amount of oxygen in the arterial blood is
below that of saturation. By means of violent artificial respiration,
the amount of oxygen can be brought to 23^. The venous blood
is not half saturated with carbon dioxide.

Arterial blood is bright red; venous blood, dark red.

The difference in color of arterial and venous blood is due to
the difference in oxygen present. Artificially we can change
arterial blood to dark red by taking away its oxygen (shaking with
gases free of oxygen), and venous to a bright red by shaking with
oxygen.

When arterial blood becomes venous, the concentration and
alkalinity of the plasma are increased, for the following reasons:
The red blood corpuscles swell by the inhibition of water from the
plasma, leaving the plasma more concentrated. By the mass
action of the carbonic acid, hydrochloric acid is set free from the
sodium chloride; this hydrochloric acid enters the blood cor-
puscles, while the alkali carbonate remains behind. When blood
is rendered arterial, the opposite takes place.

Venous blood is found in the veins (except pulmonary
veins), in the right heart and in the pulmonary artery;

60 HUMAN PHYSIOLOGY

arterial blood is found in the arteries (except pulmonary
artery), the left heart, and the pulmonary veins. The
change from venous to arterial blood is brought about by the
taking up of oxygen and the giving off of carbon dioxide in
the lungs — pulmonary respiration. The change from arterial
to venous blood is brought about by the giving off of oxygen
and the taking up of carbon dioxide in the tissue — tissue
respiration.

2. PULMONARY RESPIRATION

The exchange of gases between the blood and the air of
the lungs depends upon the diffusion of gases through the
walls of the alveoli and capillaries. This diffusion takes
place from places of higher to places of lower gas pressure.

The inhaled or exhaled air contains the following gases:

Inspired Air. Expired Air.

Nitrogen 79.00 vol. # 80.0 vol. %

Oxygen 20.96 ^ 16.0 "

Carbon dioxide 0.04 " 4.0 "

The partial pressure at 760 mm Hg is:

Inspired Air. Expired Air.

Oxygen 152 mm Hg 122 mm Hg

Carbon dioxide 0.3 30 "

The pressure or tension of the gases of the blood is stated
in terms of the partial pressure of these gases in a vessel
.containing the blood, necessary to keep the quantity of the
gases in the blood constant. The tension is:

Arterial Blood. Venous Blood.

Oxygen 29.6 mm Hg 21.0 mm Hg

Carbon dioxide 22. o " 41.0 "

The partial pressure of oxygen in inspired air is larger
than its tension in the venous blood ; that of carbon dioxide
is less. Therefore an exchange of gases between the blood
and the air in the lungs takes place by diffusion through the
walls of the alveoli and of the capillaries.

THE GASES OF THE BLOOD 61

According to some authors, the parenchyma of the lungs plays
an active part in the giving off of carbon dioxide (in the same
manner as gland cells in the secretion).

The lowest barometric pressure at which respiration of the quiet
body can continue undisturbed is about 350 mm Hg.

The oxygen taken up by the blood favors the giving off
of carbon dioxide because by it the carbon dioxide tension
is increased, owing to the fact that oxyhaemoglobin is more
acid than reduced haemoglobin.

An adult man inhales in 24 hours about 700 g or 500
litres of oxygen and exhales 900 g or 450 litres of carbon
dioxide.

The ratio of the volume of the exhaled carbon dioxide to the
volume of the inhaled oxygen is called the respiratory quotient.
Concerning its value under various circumstances see Chapter XII.

Besides the lungs, the skin also throws off carbon dioxide in
small amounts (8.4 g per day).

3. TISSUE RESPIRATION

This consists of the giving off of oxygen by the blood to
the tissues and the taking up of carbon dioxide. This takes
place in the systemic capillaries. The giving off of oxygen
takes place because the oxygen tension in the blood is
greater than that in the tissues. Because of the continual
oxygen consumption, the oxygen tension in the tissues is o.
The carbon dioxide formed by the combustion of the tissues
accumulates to such an extent that its pressure is higher than
that of the carbon dioxide in the arterial blood, hence it
must pass into the blood.

The physiological combustion, by which oxygen of the blood is
consumed and carbon dioxide produced, does not take place in
the blood, but in the tissue. This is based on the following facts:

i. The extent of the physiological combustion is, up to a certain
limit, independent of the amount of blood in the body. After a
considerable loss of blood, warm-blooded animals show no change
in the amount of oxygen consumed and the carbon dioxide formed,
and in cold-blooded animals (frog) the physiological combustions
can take place when all their blood has been taken away and
replaced by an injected physiological salt solution.

62 HUMAN PHYSIOLOGY

2. If the processes of combustion, upon which the contraction
and work of muscles depend, took place in the capillary blood of
the muscle, the muscle fibre would be forced to do its work by
transforming the heat, supplied to it from the blood, into-
mechanical work. By heating the muscle fibre, however, we are
not able to obtain as powerful contractions as by physiological
stimulation, if we do not use temperatures which destroy the life
of the muscle (see heat-rigor, Chapter XIV). Besides this,
muscles from which the blood has been removed by injecting,
physiological salt solutions, and even isolated muscles, can, by
stimulation, be made to contract.

CHAPTER IV
CIRCULATION OF BLOOD

1. INTRODUCTION

1. IF the blood is to fulfill its function of carrying-
materials between the organs of the body, it must circulate
in the vascular system.

2. The blood flows from the left ventricle through the
aorta and systemic arteries to the capillaries, and from these
through the veins and right auricle to the right ventricle ;
thence through the pulmonary artery, capillaries, and veins
and through the left auricle back to the left ventricle
(Harvey, 1628).

The portal vein, formed from the capillaries of the intestine,
branches again into capillaries in the liver, which in turn give rise
to the hepatic veins.

3. The difference in blood pressure in the different parts
of the vascular system is the cause of the circulation of the
blood. The blood is driven from places of higher to those
of lower pressure.

4. The differences in pressure are caused by the rhythmic-
ally contracting ventricles which, during their contraction
(systole) empty their contents into the. aorta and pulmonary
artery and, during their relaxation (diastole), take the blood
from the auricles and veins.

5. The valves of the heart prevent the regurgitation of the
blood from the ventricles into the veins and from the arteries
into the ventricles and thereby determine the flow of blood
in one direction.

63

64 HUMAN PHYSIOLOGY

2. THE HEART

1. The structure of the heart. — The heart is a hollow
muscle, divided by a partition into two cavities, the left and
the right heart. Its cavity consists of a thin-walled auricle
and a thick-walled ventricle. The muscle fibres inclose the
cavities in different directions, some more or less obliquely,
some in the form of the figure 8, some circularly. The walls
of the left ventricle are thicker than those of the right
ventricle.

At the boundary between the auricle and the ventricle are
found the auriculo-ventricular valves, on the right side three
(tricuspid) and on the left two (bicuspid) membranes hang-
ing down into the ventricle. On the free edges of these
membranes are the cordae tendinea,-, which are connected
with the wall of the ventricle by the papillary muscles.

Between the left ventricle and the aorta and between the
right ventricle and the pulmonary artery are the three
pocket-like semi-lunar valves; the openings of the pockets
are toward the arteries.

2. Properties of cardiac muscle.

For the investigation of the physiological properties of the
cardiac muscle, the excised apex of the frog's heart is especially
adapted, as this contains no ganglionic cells.

The heart muscle-fibre is cross-striated, but differs from the
striated skeletal muscle in :

(a) Its structure. The cardiac muscle-fibres branch and anas-
tomose with each other.

(b) Its functions:

a. A stimulation, if at all active, always calls forth a
maximum contraction of the cardiac muscle, while a
skeletal muscle does not give a maximum contraction with a
weak stimulation.

ft. The cardiac muscle can be thrown into tetanus only
under certain abnormal conditions. If the cardiac muscle
is continuously stimulated, e.g. by a constant current or by
tetanizing induction shocks, generally no lasting contrac-
tion takes place (as in the skeletal) ; but the heart makes
rhythmical single contractions which at best fuse into an
incomplete tetanus (an irregular agitation and heaving of the
muscle).

CIRCULATION OF BLOOD 65

y. During its contraction the cardiac muscle is not
irritable (refractive) from the beginning to the maximum of
the contraction. During this time a stimulation is inactive.
In its relaxed condition, the cardiac muscle is again irritable;
if a stimulus is introduced during this stage, a new contrac-
tion occurs which is the greater in proportion as the stimu-
lation occurs later. When, in an independent rhythmically
beating heart, such an " extra contraction " is called forth
by an artificial stimulus during the diastole, the pause fol-
lowing upon this contraction and lasting to the next inde-
pendent beat is longer than the ordinary pause between two
independent beats. This lengthened pause is called the
compensatory pause.

The physiological contractions of the cardiac muscle con-
sist of single contractions which follow each other in a
definite rhythm. The contraction is called systole, and the
relaxation following upon it is called diastole.

The contraction of the heart begins at the mouth of the
veins, from these it travels through the walls of the auricle
and then through the walls of the ventricle. The whole
cardiac cycle lasts about 0.86 second, which may be divided
as follows:

1. Auricular systole (ventricles at rest), 0. 1 6 second.

2. Ventricular systole (auricles at rest), 0.3 second.

3. Pause, during which both auricles and ventricles are
at rest, 0.4 second.

The number of heart-beats in one minute in an adult
human being is on the average 70; in children it is higher
(first year 134); the number is increased by increase of tem-
perature (fever), muscular exertion, after the taking up of
food ; it depends also upon mental conditions.

The contraction of the ventricular or auricular wall does not
occur at all points simultaneously, but spreads itself along the
cardiac muscle, like the contraction waves in the fibres of skeletal
muscles. This is proven by the fact that the electrical phenomena
of the stimulated cardiac muscle dc not appear simultaneously at
all points, so that it is possible to demonstrate, as in the striated
skeletal muscle, a current of action. (See Chapter XIV.) From
the results of the electrical phenomena it can also be concluded
that the cardiac contraction corresponds to a twitch and not to a
short tetanus.

66 HUMAN PHYSIOLOGY

The heart contains within itself the processes which
stimulate it to its rhythmic activity, for it beats for some
time after it has been cut out of the animal immediately after
death. Concerning the nature of this stimulation nothing
is known.

Perhaps the cardiac muscle is stimulated directly by the
normal stimulus and not through the intervention of the
ganglionic cells and nerve-fibres found in the walls of the
heart.

In the mammalian heart the ganglionic cells lie in the auriculo-
ventricular groove, in the partition between the auricles, and in the
auricle near the mouth of the superior vena cava. Their function
is not known.

The embryonic heart has no ganglia and yet beats rhythmically;
in thai* case the cause of the rhythmic activity must certainly lie
in the muscle itself.

Concerning the influence of the central nervous system
upon the heart, see page 74.

3. The circulation of the blood in the heart.

(a) In the ventricle. — During the ventricular systole, the
cavities of the ventricles are reduced in size; the blood
which it contains is pressed out into the aorta and pulmonary
artery. The ventricles do not completely empty themselves
since, even in the strongest contraction, the cavities of the
heart are not entirely obliterated.

The auriculo-ventricular valves which float upon the blood
during the ventricular diastole are closed during the ventric-
ular systole so that the blood cannot regurgitate into the
auricle. When the pressure in the ventricle is increased by
the systole, the blood flows behind the valves and presses
their surfaces together so that they are completely closed.
The valves do not bulge into the auricles because they are
fastened to the papillary muscles which contract simultane-
ously with the walls of the ventricle.

The closure of the valves seems to follow the beginning
of the systole so quickly that no blood whatever re-enters
the auricle.

During the ventricular diastole the blood does not flow

CIRCULATION OF BLOOD 67

back from the arteries, as it accumulates in the pockets of
the semi-lunar valves, pressing their surfaces together and
thus closing them. The pressure in the ventricle after
diastole becomes less than that in the auricle, so that now
the blood flows from the auricle into the ventricle, after
having opened the auriculo-ventricular valves.

(lj) In tJic auricles. — The contraction of the auricle serves
chiefly to regulate the flow in the large veins. During the
ventricular systole when no blood is allowed to pass from
the auricle into the ventricle, it flows from the veins into the
dilating auricle. When, during ventricular pause, it is
streaming into the ventricle, the auricle decreases in size
proportionately to its decrease in contents.

4. The pressure in the heart.

For finding the pressure in animals, a long canula is pushed
either through one of the large cervical vessels into the right
auricle or ventricle, or through the carotid into the left ventricle.
The canula is connected with an instrument for measuring the
pressure (mercury or spring manometer). The extent of the
pressure is indicated by the number of millimeters of mercury
which it stands above the atmospheric pressure.

During the systole the pressure in the ventricles increases
rapidly at first and then more slowly. In the left ventricle
it reaches a height of 2OO, in the right ventricle, 60 mm Hg.
During diastole the pressure sinks rapidly and may become
negative, but before the next systole occurs it rises a little
because of the incoming blood.

The period of preparation lasts from the beginning of the
ventricular systole (or the closing of the auriculo-ventricular
valves) to the opening of the semi-lunar valves; it amounts to
0.05-0.1 second. It can be estimated in animals by registering
simultaneously the pressure in the left ventricle and in the aorta;
the semi-lunar valves open the moment the ventricular pressure
becomes greater than the aortic. In man, the length of this
period has been found by comparing the cardiac impulse and the
pulse curve.

The period of discharge is the period from the opening to the
closing of the semi-lunar valves; during this time the ventricular
pressure is higher than that of the aorta; length of period
0.18-0.20 second.

68 HUMAN PHYSIOLOGY

In the auricle the variations in pressure are much less than
in the ventricles. During the auricular systole the highest
pressure is 20 mm Hg.

5. The cardiac sounds, produced by the contraction of
the heart, are heard when the ear is applied to the chest-
wall.

The first sound, produced during the ventricular systole,
is dull, lasts as long as the systole, and can be best heard
over the ventricle. It depends upon the muscle tone (see
Chapter XIV) and upon the vibration of the auriculo-ven-
tricular valves produced by the sudden systolic contraction.
It is still audible in the bloodless heart.

The second sound is short, clear, and most distinct over the
aorta ; it is caused by the vibration of the semi-lunar valves
produced by their sudden closure.

6. The cardiac impulse, or apex beat, is synchronous with
the contraction of the heart and is felt at the fourth or fifth
intercostal space, about one and one-half inches to the left of
the sternum. It is produced mainly as follows: the tensely
contracted cardiac muscle at this point pushes forward the
soft part of the intercostal space; during the relaxation of
the heart, this part is pushed inward by the atmospheric
pressure.

Other factors, supposed to play a part in the formation of the
cardiac impulse, are the following:

During the systole, the apex of the heart is raised upward;
during the discharging of the blood, upward and backward, the
heart is pushed forward and downward; the arterial trunks, from
which the heart is suspended, when filling are slightly twisted and
when emptying untwisted from their spiral-like turning.

If a button [pelotte] is fixed upon the place of cardiac impulse,
so that it is moved by the beat of the heart, and if this movement
is transferred to a writing-lever, this lever will describe a curve
called the cardiogram. This cardiogram is similar to the pressure
curve of the heart, as it is, in reality, produced by the contraction
of the cardiac muscle; the two curves are, however, not identical,
since the cardiogram represents a pressure and volume curve.

7. The work of the heart. — The work which the heart
does during one contraction is equal to the product of the

CIRCULATION OF BLOOD 69

weight by the height to which the weight is carried. The
weight lifted is that of the amount of blood sent by a single
systole of the heart (pulse volume). The amount of blood
thus lifted is about 66 cc., and its weight 0.07 kg. The
height to which this is raised is equal to the blood pressure
in the aorta or in the pulmonary artery. In the aorta the
pressure is about I 50 mm of mercury or about two metres
of blood ; in the pulmonary artery, the pressure is about one-
third of that in the aorta. During one contraction, the left
ventricle, therefore, does the work of 0.07 X 2 or o. 14 kilo-
grammetre, the right ventricle 0.047. ^n all> the heart in
twenty-four hours does about 1 8,000 kilogrammetres of work.

The pulse volume is estimated by many authors as much greater
(up to 1 80 cc) and then the work done is correspondingly greater.

In this calculation, no account is taken of the work which the
heart does in imparting velocity, i.e. kinetic energy, to the blood
(about 0.3 m per second). But this work is very little compared
with that done to overcome the blood pressure, the former not
being more than ifc of the latter.

3. CIRCULATION OF THE BLOOD IN THE VESSELS

i. The blood pressure in the vessels. — The blood pres-
sure is the pressure of the blood upon the walls of the
vessels, this determining the tension of the walls.

The blood pressure in the larger vessels is measured by inserting
a c.anula into the vessel and connecting this c.anula with a register-
ing manometer. The pressure can also be determined without
any operation in many blood vessels of man, it being equal to the
pressure necessary to close these vessels. An artery is closed when
no pulse is felt peripheral to the compression. The capillary
prcssuie is found by pressing upon a glass plate, placed on the red
part of the skin, till the skin becomes pale.

The blood pressure in different parts of the vascular system
varies greatly. The difference in pressure is produced by
the activity of the heart and is the cause of the movement of
the blood. Each particle of blood is forced from a place of
higher to a place of lower pressure.

The blood pressure constantly decreases as we proceed

70 HUMAN PHYSIOLOGY

from the aorta or pulmonary artery, through the arteries,
capillaries, and veins, to the heart. The blood must conse-
quently flow in this direction. By this movement of the
blood, the difference in pressure is normally not entirely
equalized, because by each succeeding ventricular systole
the difference in pressure is increased.

In the aorta, the blood pressure undergoes variations of
about 150 mm Hg; in the larger arteries, about 1 10— 120 mm ;
in the capillaries, 24-54 mm; in the veins, only a few mm,
indeed in the large veins in and near the thorax it may be a
negative pressure of a few mm, i.e. it is less than the atmos-
pheric pressure. On cutting such a large vein, no blood
flows from the vessel, but air enters it. The cause of this
negative pressure in the veins is the negative pressure exist-
ing in the thoracic cavity which is increased during inspira-
tion (see Chapter V). The blood pressure in the pulmonary
artery is about 50 mm Hg.

The blood pressure in the arteries undergoes periodic
variations caused by the action of the heart ; these variations
are called the pulse. Each time that the ventricular systole
sends blood into the aorta and pulmonary artery, the
pressure in these vessels is suddenly increased ; after this,
the streaming of the blood to the capillaries causes a diminu-
tion in pressure. This periodic variation in pressure spreads
itself as a wave throughout the whole arterial system.

The pulsatory variations in pressure are the largest in the
aorta, where they amount to half of the average pressure ;
they become smaller in the peripheral arteries. In the
capillaries and the veins there is normally no pulse.

The rate of the pulse wave (not to be confounded with the rate
of the blood flow) can be found by determining the time elapsing
between the beginning of the cardiac impulse and the appearance
of the pulse in a peripheral artery. The rate is about six metres
in one second; it depends upon the tension and the elasticity of
the arterial walls. The length of the pulse wave is about i. 5 m.

If a lever is placed upon an artery so that it is moved by the
pulsating artery, and if this movement is transferred to and mag-
nified by a writing lever, a curve, the pulse curve, or sphygmogram,

CIRCULATION OF BLOOD

is produced. This curve describes more accurately the progress
of the pulse. The apparatus for the production of a pulse curve
is called a sphygmograph.

The pulse curve (Fig. i) ascends rapidly and then sinks
more slowly to the level of the abscissa. In the descent of

FlG. I.— PlTLSK CURVE (SPHYGMOGRAM) OF THE RADIAL ARTERY.

the curve there is regularly found a small elevation, called
the dicrotic wave. The cause of this wave is not fully
known. Often the descending part of the curve shows still
other smaller elevations which are supposed to be due to the
reflection of the pulse wave in the various parts of the arterial
system.

The blood pressure shows other periodic variations which are
synchronous with the respiratory movements; the pressure sinks
during inspiration and rises during expiration. This is chiefly
due to the fact that during inspiration the introthoracic pressure
and therefore the pressure upon the blood vessels in the thorax is
diminished, while during expiration it is increased. Hence the
blood vessels in the thorax are better filled with blood during
inspiration than during expiration.

In general the amount of blood pressure and its pulsatory
variations depend upon the state of fulness of the vessels,
the tonus of the muscles of the blood vessels, and upon the
number and strength of the cardiac contractions.

2. Rate of blood flow. — In the arteries the blood flows
with a periodically accelerating rate (corresponding to the
intermittent entrance of blood into the aorta) ; in the capil-
laries and veins the flow is uniform. The change from the
intermittent movement of the blood in the arteries to the
uniform movement in the capillaries is due to the extensi-
bility and elasticity of the arterial walls. In vessels with
rigid walls, each systole must force forward the column of
blood previously pressed out of the heart. In vessels with
elastic walls, the force of the systole is not directly trans-
formed into the movement of the blood, but is first changed
to the increased tension of the elastic walls, and this stored-

72 HUMAN PHYSIOLOGY

up energy is then gradually transformed into the energy of
the moving blood. This causes the flow to be continuous.

The change of the intermittent into the continuous movement
occurs, according to the same principle, in the fire-engine. The
water which enters the engine periodically, leaves it in a contin-
uous stream, being pressed out continuously by the compressed
air in the air-chamber.

The average velocity decreases as we proceed from the
arteries to the capillaries, and increases again from the capil-
laries to the veins. In the large arteries the rate is 200-400
mm per second; in capillaries 0.6-0.8 mm; in the large
veins it is but little less than in the arteries. The cause of
this difference is the difference in the total cross-section of
the various parts of the vessels. Through each total cross-
section of the vascular system there must pass in the same
unit of time the same quantity of fluid, in order that the flow
shall not become stationary and the blood collect in one
place. Now the cross-section of the aorta and the large
veins is much less than the total cross-section of all the
capillaries. As the rate is equal to the volume flowing
through in one second divided by the cross-section, it is
evident that the rate in the arteries and veins must be
greater than that in the capillaries.

The rate in the larger vessels of animals is found in the follow-
ing manner. A blood vessel is cut and between the cut ends a
sufficiently wide tube, the contents of which have been accurately
determined, is inserted. The blood must now pass through the
tube. The time taken by the blood to pass from one end of the
tube to the other is then determined. For this experiment, the
tube is previously filled with some indifferent fluid, which is forced
from it into the vascular system by the incoming blood. Accord-
ing to this principle, the haemodromometer of Volkmann is built,
as is also, though more complicated, the Stromuhr of Ludwig.

In the capillaries the distance traversed by a blood corpuscle is
measured directly with the aid of a microscope (e.g. in the web of
frog's foot).

The pulsatory changes in the rate of the arterial blood can be
investigated by the plethysmograph, an apparatus registering the
changes in the pulse- volume of a limb. The changes in volume
are due to the periodic increase and decrease in the supply of

CIRCULATION OF BLOOD 73

blood to the arteries of the limb, as the outflow of blood into the
veins is uniform.

3. The resistance to moving blood due to friction. —

The energy of the moving blood must overcome the resist-
ance due to the friction of the particles of blood upon each
other and upon the walls of the vessels. The friction is
greater the smaller the cross-section of the vessel.

In a given cross-section of a blood vessel, all the parts of
the blood do not move with the same velocity, but those in
the middle of the vessel move faster, while those touching
the walls move slowest; this is due to the resistance caused
by friction. In the swifter axial current float the specifically
heavier particles of the blood, the red blood corpuscles; in
the slower peripheral stream are found the lighter leucocytes.

4. Relation between fall in pressure, rate of flow and
resistance. — The energy is used for producing movement
and for overcoming resistance ; its consumption is the
greater, the greater the movement produced and the greater
the resistance overcome. The amount of energy consumed
in a given length of vessel is measured by the decrease in
pressure. The decrease in pressure in a unit of distance is
called the fall.

In a tube of uniform diameter, in which the resistance offered
by every cross-section is the same, and in which the rate of flow
is the same at all cross-sections, the decrease in pressure is pro-
portional to the distance traversed, i.e. theyfr// is uniform through-
out. But if the fluid flows through a tube of non-uniform bore,
the fall in the wider portions will be less than in the narrower
parts, because in the wider parts the resistance is less.

The question where the fall is greatest cannot be definitely
answered. In the vascular system the total cross-section
increases as we proceed from the arteries to the capillaries,
but the cross-section of the individual vessel decreases ; going
from the capillaries to the veins, it is the reverse. Now the
resistance is, on the one hand, the smaller the greater the
total cross-section; but, on the other hand, the greater the
smaller the individual cross-section. Of these two opposing

74 HUMAN PHYSIOLOGY

variations in resistance, the decrease predominates in the
larger arteries, while the increase predominates in the veins,
so that in the larger arteries the fall is but little; in
the veins, large. In regard to the extent of the fall in
the smaller arteries and capillaries, the evidences are con-
flicting.

5. Valves in the veins. — The circulation of blood in the
veins is aided by externally compressing them, as occurs by
the contraction of surrounding muscles ; the regurgitation of
the blood is prevented by valves, somewhat like the semi-
lunar valves, which allow the blood to flow in the direction
toward the heart only.
6. Circulation time.

To determine the time of a complete circulation ferrocyanide
of potassium is injected into the central end of a severed vein, the
time of injection being noticed. After some time the blood from
the peripheral end of the cut vein is tested for the salt by being-
colored blue with ferric chloride. The blood has completed the
entire circulation when the salt reappears at the peripheral end of
the vein.

In dogs the circulation time has been found to be fifteen
seconds, in man it is supposed to be twenty-two seconds.

4. IXXFRYATIOX OF THE OROAXS OF CIRCT LATK )X

The influence of the central nervous system on the organs
•of circulation (heart and muscles of vessels) serves to regu-
late the general velocity and distribution of the blood to the
different parts of the body. This is brought about by
changes in the number and strength of heart-beats and by
changes in the tonus of the muscles of the vessels, especially
of the arteries.

i. Innervation of the heart (see also page 66).

(a) The cardiac inhibitory nerves are the two vagi from
which fibres for the cardiac plexus are derived. Section of
the vagi results in increasing the pulse frequency. The
cardiac vagi are therefore continually stimulated (tonic).
Stimulation of the peripheral end of a cut vagus causes a
diminution in rate and strength of heart-beat or entire

CIRCULATION OF BLOOD 75

stoppage of the heart in diastole, depending upon the
strength of the stimulation. How the action of the vagus
on the cardiac muscle is brought about is not known.

Pathological-anatomical changes have been observed in the
cardiac muscle (atrophy and degeneration) after section. of vagus.

The centre for the cardiac inhibitory nerves lies in the
medulla oblongata. Its activity is increased by lack of
oxygen and increase of carbon dioxide in the blood, and by
increased blood pressure. It can also be stimulated in-
directly by stimulation carried to it by centripetal nerves
from the cerebral hemispheres.

The extent of its activity depends also upon psychical influences
(palpitation of the heart). Reflex cardiac inhibition takes place
if, e.g. in a frog, the sensory nerves of the abdomen are stimulated
by tapping the abdomen (Goltz's tapping experiment).

Atropin and curare in large doses destroy the action of the
vagus upon the heart; muscarin and nicotin stimulate the vagus
endings in the heart. The action of muscarin is neutralized by
atropin, that of curare by nicotin. Digitalin stimulates both the
vagus endings in the heart and the centre- in the medulla.

(lj) TJic cardiac accelerating nerves are the nervi accel >-
rantes which pass from the first thoracic and the cervical
ganglia of the sympathetic to the cardiac plexus. Stimula-
tion causes increase in the frequency and force of the heart-
beat.

It is supposed that their centre lies in the medulla
oblongata, and that this is also tonic. If the vagi are cut,
electric stimulation of the medulla causes acceleration of the
pulse.

2. Innervation of the blood vessels. — The muscles of the
vessels (smooth muscles) are most developed in the walls of
the arteries, less in the veins. The walls of the capillaries
are also supposed to be contractile, but this is independent
of the nervous system. The nervous elements for the muscles
of the vessels lie partly in the walls of the vessels themselves
(ganglionic cells, nerve plexus) and partly enter the walls
as vaso-motor nerves. There are nerves which constrict
and nerves which dilate the blood vessels.

7 6 HUMAN PHYSIOLOGY

(a) The vaso-constrictor nerves have their centre in the
medulla oblongata, extending from the upper part of the
fourth ventricle to the lower part of the calamus scriptorius,
on both sides. From this centre the nerve-fibres proceed
down the spinal cord and connect with the nerve-cells of the
gray matter ; from there the fibres pass through the anterior
roots and the rami communicantes into the sympathetic. The
sympathetic fibres proceed separately (e.g. splanchnic) or
with other peripheral nerves (e.g. trigeminus, sciatic) to the
blood vessels. Some vaso-motor fibres go directly to the
vessels without passing through the sympathetic (e.g. from
the roots of the lower lumbar and of the sacral nerves).
The vaso-motor nerves are perhaps not in direct contact with
muscle fibres, but pass first into the ganglionic cells of the
walls, from which the motor fibres proceed to the muscles.

The vaso-motor centre is tonic. Section of a vaso-motor
nerve causes a dilation of the vessels innervated by that
nerve.

If the cord is cut, dilation of the vessels supplied by the
sectioned vaso-motor nerves results; but eventually the tonus
is regained, evidently because the cells in the spinal cord,
through which the vaso-motor nerves pass, have assumed
the function of the centre. Even after section of a peripheral
vaso-motor nerve, the tonus is eventually regained ; in this
case, the ganglionic cells in the walls of the blood vessels
assume the role of the centre.

The activity of the vaso-motor centre is influenced :

1. Directly by lack of oxygen and the accumulation of
carbon dioxide in the blood ; this increases its action.
Hence asphyxia stimulates this as it does the cardiac inhibi-
tory centre.

2. By stimuli conducted to it through the nerves.

(a) Psychical processes can increase or diminish its.
activity (pallor by fear; blushing).

(b} The activity can be influenced reflexively.
We classify the centripetal nerves used in this reflex
action into:

CIRCULATION OF BLOOD 77

(<*) Pressor nerves, which produce a strong stimulation
of the centre and a constriction of the vessels, hence an
increase in blood pressure.

(/?) Depressor nerves, i.e. centripetal nerves which re-
flexively inhibit the action of the centre and thereby cause
decreased blood pressure.

Pressor nerves are found, e.g. in the trigeminus, superior
.and inferior laryngeal. An example of a depressor nerve is
the depressor nerve going from the heart to the vagus and
thence to the medulla; stimulation of this nerve causes a
lowering of the blood pressure, and decreases the rate of
heart-beat.

(li] The vaso-dilator nerves produce a widening of the
vessels by decreasing the tonus of their muscles.

Examples of vaso-dilator nerves :

1. Through the chorda tympani there pass fibres to the
submaxillary salivary glands ; the stimulation of this nerve
•causes dilation of the blood vessels of the gland.

2. Stimulation of the nervi erigentes (fibres passing from
the sacral plexus to the hypogastric plexus) causes accumula-
tion of blood in the penis and thus produces erection.

In general the vaso-dilators accompany the constrictor
nerves. In these cases the existence of the two kinds of
nerves can be demonstrated, as they possess different
irritability. The dilators are stimulated by a weak, slowly
interrupted electrical current, the constrictors need a stronger
and faster interrupted current.

After section, the dilators retain their irritability for a much
longer time than the constrictors, before degeneration sets in.

How the dilators diminish the tonus of the muscles is not
l^nown.

It is supposed that the centre for the vaso-dilators is situated in
the medulla.

The innervation of the blood vessels serves to regulate the
distribution of the blood to the different parts of the body.
This distribution, in so far as it is not dependent upon pure
mechanical conditions, is regulated by the tonus of the

78 HUMAN PHYSIOLOGY

muscles of the vessels in such a manner that, normally, each
part of the body contains the amount of blood that it needs.
The more active a certain part of the body is, the more
dilated are its blood vessels and the greater the quantity of
blood they contain. Simultaneously with the dilation in an
active part, there is a constriction in the resting parts of the
body.

When the body is at rest, the vessels in the abdomen and
the thorax contain more than one-half of all the blood.
During digestion, the quantity of blood in the intestine is
larger than during fasting. During work, the blood vessels
of the muscles are better filled with blood than during rest,
simultaneously the rrbdominal vessels innervated by the
splanchnic are constricted.

In the suprarenal glands a substance is formed which increases
the tonus of the muscles of the vessels. It acts directly upon the
muscle fibres (see Chapter XI).

Small losses of blood are compensated by general con-
striction of the vessels. But for great loss of blood, amount-
ing to over one-half of all the blood, this compensation is
not sufficient; the blood pressure sinks much, the valves do
not close completely and the circulation ceases. Death by
loss of blood in such cases does not take place because of
lack of any constituent of the blood, e.g. the haemoglobin,
but because the vessels are not sufficiently filled and this-
entails disturbances in the circulation. If the lost blood is
replaced by an indifferent fluid (0.9$ NaCl), the circulation
is resumed [transfusion]. If the loss of blood amounts to
more than two-thirds of all the blood, the haemoglobin
present is not sufficient for respiration, and, notwithstanding
that the circulation may be repaired, death takes place
because of lack of oxygen. In such a case, life can be saved
only by the transfusion of human blood. Blood from other
animals cannot be used because of globucidal action.

CHAPTER V
RESPIRATORY MOVEMENTS

THE object of the respiratory movements is, by alternately
increasing and decreasing the thoracic cavity, to suck the air
into the alveoli of the lungs, and after gas-exchange with
the pulmonary blood, to force it out again.

1. THE CHANGE IN THE FORM OF THE THORACIC
CAVITY AND OF THE LUNGS

The respiratory movements consist of the alternate increase
(inspiration) and decrease (expiration) of the thoracic cavity
in all directions.

1 . TJie dilation of the thoracic cavity in the perpendicular
diameter is produced by the contraction of the diaphragm.
which descends by the flattening of its convexity. In this
process the muscular portions play the most important part;
the central tendon is of secondary importance. The per-
ipheral parts of the diaphragm, which, in expiration, lie
against the thoracic walls, are during inspiration drawn
away from the walls. In expiration the intestine forces the
diaphragm upward into the thoracic cavity.

2. The dilation of the thoracic cavity in the horizontal
diameter is brougJit about by the elevation of tJie ribs.

Each rib is movably joined to the spinal column at two places:

1. By its head to two vertebrce.

2. By its tubercle to the transverse process of one vertebra.
The axis about which the rib turns passes through its neck, hence
passes in almost a horizontal anterior-posterior direction.

The ribs incline forward and downward. By their elevating the
degree of this inclination is lessened. By this means the cross-

79

HUMAN PHYSIOLOGY

section of the thoracic cavity is increased both in its anterior-
posterior and lateral diameter, as the horizontal distance between
the anterior ends of the ribs and the spinal column increases and
the lateral parts of the ribs move apart. Simultaneously with the
ribs, the sternum is raised and moved forward. The elevating of
the ribs and sternum is dependent upon the twisting of the
cartilage of the ribs. This increases the obtuse angle (facing
upward) formed by the cartilages of the ribs.

The elevating of the ribs in quiet breathing is brought
about by the external intercostal and the intercartilaginous
portion of the internal intercostals.

The fibres of the external intercostals, placed between the ribs,
slant forward and downward. As the ribs are raised, the insertion
points of any fibre approach each other, hence the contraction of
the muscle fibres elevates the ribs.

The intercartilaginous portion of the internal intercostals slants
downward and backward between two costal cartilages which
slant in the same direction as the muscles. Here also the points

I.

*,,

II. B

W

FIG. 2.

of insertion approach each other when the cartilages are raised.
But these intercartilaginous muscles are of importance only in the
lower costal cartilages.

In the above scheme (Fig. 2) W represents the spinal column;
B, the sternum ; Rl and J?n represent two ribs with their external
intercostal muscle, mr; Kv and A'u are two cartilages with their

RESPIRATORY MOVEMENTS 81

intercartilaginous muscles, mk. In I the position in expiration is
represented; in II, that in inspiration. It is evident that in
II mr and mk are shorter than in I.

In forced inspiration the following muscles aid in elevating the
ribs: scaleni, levatores costarum, serratus posticus superior,
sterno-cleido-mastoid ; also, after fixation of the arm, as by
gripping the table, the pectoralis major and minor and serratus
anticus major. During forced inspiration, the levatores alae nasi
contract, causing dilation of the nostrils, and also the crico-ary-
tenoideus postici which cause the dilation of the vocal bands.

The lowering of the ribs during expiration is brought
about by the sternum sinking by gravity and by the contrac-
tion of the internal intercostal muscles. These muscles
cross the externals and therefore act in the opposite direc-
tion.

In forced expiration the ribs are lowered by the serratus posticus
inferior and latissimus dorsi; further the upward movement of the
diaphragm is aided by the muscles of the abdominal walls and the
quadratus lumborum, which also aids in the lowering of the ribs.

In the male, the respiration is chiefly effected by the lower
parts of the thorax, in the female by the upper.

Normally, the intra-abdominal pressure sinks slightly
during inspiration and rises during expiration. Only when
the intestines are abnormally filled with food, faeces and
gases, does the intra-abdominal pressure rise during inspira-
tion and sink during expiration.

The lungs are two sacs with extensible and elastic walls,
placed hermetically in the thoracic cavity, so that their
external surface (pleura pulmonalis) is everywhere in close
contact with the inner surface of the thoracic wall (pleura
costalis), but the two pleura are not grown together. The
inner surface of the lungs is much increased by thin mem-
branous projections which form the walls of the alveoli.
The internal space of the lungs communicates with the at-
mosphere by means of air-passages (bronchi, trachea, phar-
ynx, nose). The atmospheric pressure, therefore, presses
upon the inner surface of the lung and keeps the external
surface of the extensible lung-wall against the thoracic wall.

82 HUMAN PHYSIOLOGY

After expansion of the thorax the atmospheric pressure
stretches the lung-sac and enlarges it.

Even in the expiratory position of the thorax, the walls
of the lungs are stretched. If, in a dead body, the thoracic
wall is opened so that the air can enter the pleural cavity,
the lungs withdraw from the thoracic walls. If, previous to-
opening the thorax, a manometer is connected with the
trachea, this will, on opening the thorax, indicate the
pressure which the tension of the pulmonary wall exerts.
In .the pleural cavity, in the expiratory position, there is a
corresponding negative pressure of about 3-5 mm Hg.
During ordinary inspiration this is increased by about 9 mm ;
during forced inspiration, by 30—40 mm.

2. THE VARIATION IN PRESSURE OF PULMONARY
AIR DURING RESPIRATION ; RESPIRATORY CA-
PACITY

During the inspiratory dilation, the pressure of the air in
the lungs sinks, while during expiration it rises. This
decrease in pressure causes the external air to rush in ; the
increase in pressure during expiration forces the air out of
the lungs. These respiratory changes in pressure amount,
in quiet breathing, to 1-3 mm Hg; in forced respiration
they are greater.

The respiratory volume is determined by exhaling into an instru-
ment used for measuring the volume of gases (gasometer, spirom-
eter) or by letting the inhaled or exhaled air pass through a,
gas-meter.

A part of the inspired air does no service in the gas-exchange,
as it does not reach the alveoli but remains in the air-passage
(trachea, bronchi, nose). The size of this "dead space" is
100-150 cc.

Tidal air is the air inhaled and exhaled during quiet-
respiration ; in the adult male it is about 500 cc.

Complcmcntal air is the air which can be inhaled, in
excess of the tidal air, by forced inspiration ; it is about
2500 cc.

Supplemental air is the air which can be expelled, besides,

RESPIRATORY MOVEMENTS 83

the tidal air, by the most forcible expiration ; it is about
1500 cc.

These volumes combined form the vital capacity (4500 cc),
i.e. the greatest possible inhaled and exhaled volume of air.

Residual air is the air which, after the deepest expiration,
remains in the lungs and may amount to about 1200 cc.

Because of the radiation of heat and the evaporation of
water from the mucous membranes, the inspired air in its
passage to the lungs is warmed to the body temperature and
saturated with water vapor.

Dust which has been brought to the air-passages by inspiration
is forced out by the movement of the cilia of the epithelial cells
pf mucous membrane.

Respiratory sounds. During breathing the movement of the
air produces sounds which may be heard by placing the ear upon
the chest-wall. Above the trachea and the bronchi there is heard
a blowing noise, like the sound of the German " ch " (bronchial
breathing), both during inspiration and expiration. Above the
tissue of the lungs we hear a sighing sound (vesicular murmur)
which is strong during inspiration, feeble during expiration.

3. FREQUENCY AND RHYTHM OF RESPIRATORY
MOVEMENTS. INNERVATION OF THE MUSCLES
OF RESPIRATION

Adults breathe about 18 times in one minute, children
oftener (during the first year, on the average, 44 times).

Expiration follows immediately upon inspiration. The
proportion of the length of the inspiration to that of expira-
tion is about as 10 : 12. Between the* end of expiration and
the beginning of the next inspiration there is, as a rule no
pause.

The motor nerves for the muscles of respiration proceed
from the spinal cord at the anterior roots of the cervical and
dorsal region. They are the phrenic nerves for the dia-
phragm and the intercostal nerves for the intercostal muscles.

The respiratory centre lies in the medulla oblongata, on
both sides of the posterior point of the fovea rhomboid.

84 HUMAN PHYSIOLOGY

Destruction of this spot causes immediate death because
breathing stops (hence the spot is called the nceud vital).

Some authors suppose that this spot is a nerve trunk which
unites the nuclei of the 5, 9, 10 and n cranial nerves with the
nuclei of the motor respiratory nerves. It has also been advanced
that the real respiratory centre lies not in the medulla but in the
spinal cord.

The centre is composed of an inspiratory and an expiratory
centre which act alternately; it is bilaterally double, but the
two parts are connected by commissural fibres so that they
are always stimulated simultaneously.

The nerves from the respiratory centre to the motor nuclei
of the nerves of respiration run in the two lateral columns of
the spinal cord (respiratory bundle].

The stimulation of the respiratory centre can be brought
about directly and indirectly.

i. Direct stimulation. — Normally the respiratory move-
ments take place involuntarily because the respiratory centre
is continually and directly stimulated. The normal stimula-
tion is automatic, not reflex for the centre retains its activity
after all the centripetal nerves which can stimulate it have
been severed.

The normal stimulation is the lack of oxygen and the
accumulation of carbon dioxide in the blood. As the arterial
blood contains so little oxygen and so much carbon dioxide,
the centre is stimulated even by the arterial blood. This
brings about the normal quiet breathing which is called
eupnoea.

If the blood is well aerated by deep respiration, so that it
contains much oxygen and little carbon dioxide, the respira-
tory centre is not stimulated. Hence, breathing is suspended
— apnoea.

Apncea is, indeed, partly due to a stimulation, by the expansion
of the lungs, of centripetal inhibiting vagus fibres (see below) ;
for, after section of the vagi, it is more difficult to produce apnoea.

The embryo in uterus is in apnoea, the blood of the mother
causing a sufficient gas-exchange in the placenta. If the circula-
tion of the umbilical cord (by compression, for example, of the

RESPIRATORY MOYEMEHTS 85

cord) or if gas-exchange in the placenta (by premature rupture
of the placenta) is prevented, lack of oxygen and accumulation of
carbon dioxide in the blood of the embryo takes place. This can
bring about respiratory movements before birth.

If, by lack of aeration, the arterial blood becomes poorer
in oxygen and richer in carbon dioxide than the normal
blood, respiration is increased, the inspirations becoming
deeper and more frequent — dyspnoea. Strong continued
dyspnoea finally produces death through paralysis of the
respiratory centre — suffocation, asphyxia.

The normal stimulation of the respiratory centre by lack
of oxygen and accumulation of carbon dioxide serves to
regulate the intensity of the respiratory movements accord-
ing to the need of the organism.

In the active muscle there are supposed to be formed other
products besides the carbon dioxide which stimulate the respiratory
centre.

Many authors suppose that the carbon dioxide does not only
stimulate the centre directly but also indirectly, in that it stimu-
lates the endings of the centripetal nerves in the tissue where it
is formed, and these in turn reflexly increase the respiration.

Increase of temperature augments the action of the
respiratory centre — Jicat dyspnoea (e.g. in fever).

2. Indirect stimulation of the respiratory centre is pro-
duced by stimulations carried to the centre by nerves.

(a) From the cerebral hemispheres, psychical influences
can modify the number, depth, and rhythm of inspirations.
On the one hand, we can, to a certain extent, voluntarily
influence respiration; while, on the other hand, respiration
is involuntarily influenced by the emotions (fear, anger,
etc.).

(fr) Reflex modifications of respiration are, e.g., the expul-
sive expirations which are called sneezing and coughing and
are produced by the stimulation of the sensory nerves of the
mucous membrane of the nose (trigeminus) and of the larynx
(superior laryngeal). Besides these respiration is reflexly
influenced by a large number of other sensory stimuli.

86 HUMAN PHYSIOLOGY

The most important reflex influence upon breathing is
brought about by the vagus. Section of both vagi causes
deeper but slower inspiration, so that the total quantity of
air expired during a long period of time is not altered.
Stimulation of a central end of a cut vagus produces no
typical alteration in respiration. Sometimes the effect is
predominantly inspiratory, sometimes expiratory. If the
lungs of an animal are artificially inflated, an expiratory
movement is produced ; by artificial expiration (sucking the
air out of the lung) an inspiratory movement is called forth.
It is therefore supposed that the vagus supplies the lungs
with two kinds of sensory fibres, of which the one stimulates
expiration, the other inspiration (inspiratory inhibiting and
expiratory inhibiting). Of these the first is stimulated by
inflation of the lung during inspiration, the second by the
collapse of the lung during expiration. By means of this
mechanism the inspirations are decreased or increased.

This action of the vagus seems to have for its object to
prevent the overfatigue of the muscles of respiration, for by
shallow breathing the muscles are less exerted.

CHAPTER VI
LYMPH, LYMPH GLANDS, SPLEEN

1. THE . LYMPH

FROM the blood capillaries there continually transudes to
the tissues a fluid, which, as tissue fluid, surrounds the cells
and carries to them their nourishment. After the giving off
of these substances and the taking up of the end-products of
metabolism, the tissue fluid goes as lymph from the minute
tissue spaces to the lymph vessels, then, proceeding through
the great lymph trunk (thoracic duct, right lymphatic duct)
empties into the blood vessels. A part of the tissue fluid
also passes directly through the capillary walls again into
the blood.

The lymph is a clear, salty fluid, having a specific gravity
of i .007— 1.043 which coagulates spontaneously after being
shed. It contains, as the cellular element, lymph corpuscles
identical with the leucocytes of the blood, and the plasma of
the lymph contains the same substances as the plasma of the
blood. These substances are about in the same proportions
as in the blood plasma except the proteid substances, the
percentage of which is somewhat smaller in the lymph than
jn the blood. The lymph found in the lymph vessels of the
intestine during digestion contains the absorbed fat in the
form of a fine emulsion and therefore has a milky appear-
ance ; it is called chyle.

In man, the quantity of lymph flowing from the thoracic duct
is estimated at i to 2 litre per day.

Lymph formation. — In the transudation of the lymph from
the blood capillaries, physical processes— filtration and

87

88 HUMAN PHYSIOLOGY

diffusion through the walls of the vessels — play a part. It
is still a question whether the physical processes alone cause
the lymph formation, or whether, besides them, a special
activity of the capillary endothelium aids in this formation,
whereby the lymph is secreted into the tissues (just as the
gland epithelium secretes the gland secretion).

TJic movement of lympJi. — The movement of the lymph is
maintained by the force which the ever following lymph
forming in the tissues exerts upon that previously formed.
The movement is aided by the compression of lymph vessels
by the skeletal muscles. The backward movement of the
lymph is prevented by the valves. Aspiration, by means
of the negative pressure in the thorax, also aids the move-
ment of the lymph.

Many animals are provided with lymph hearts which aid in the
circulation of the lymph.

The serous cavities (pleural, pericardial and peritoneal cavities)
may be regarded as very large lymph spaces; they generally con-
tain small quantities of serous fluid, corresponding to the lymph
in composition. Soluble substances injected into these serous
cavities are absorbed from the cavities partly by the blood capil-
laries, partly by the lymph vessels. Concerning the force \vhich
causes this absorption, the opinions of authors differ. But it is
certain that this absorption is aided by respiration. By means of
the alternate dilation and constriction of the lymph spaces of the
diaphragm and pleura, the lymph is now sucked from the serous
cavities into the lymph spaces and now forced from the lymph
spaces into the lymph vessels. Also finely divided solid substances
(e.g. fat, pigments) can be absorbed from the serous cavities by
the lymph vessels.

2. THE LYMPH GLANDS

These are composed of reticular connective tissue in
whose meshes are found groups of cells. Here the leucocytes
originate and are passed into the lymph which enters the
meshes by the afferent vessel and leaves by the efferent
vessel.

The lymph glands also filter the lymph and retain worn-
out lymph cells, aljo injurious substances, e.g. Bacteria,

LYMPH, LYMPH GL4NDS, SPLEEN 89

which enter the gland with the lymph. This prevents these
substances from entering the general circulation.

The retiform tissue through which lymph passes and which
serves for the formation of leucocytes is also found in certain
other bodies, e.g. in many parts of the mucous membrane (solitary
glands, Peyer^s patches of the intestine).

The thymus gland has the same structure and function as the
lymph glands. It is well developed in the embryo and child, but
begins to degenerate at the tenth year and finally disappears
entirely.

3. THE SPLKEX

The spleen consists of a framework which is made of a
trabecular tissue and supports the spleen-pulp, a reticular
tissue with many cellular elements. In many places the
cells are clustered, forming the spleen follicles. Some of
the cells of the pulp are leucocytes, some are large multi-
nuclear cells, some are red blood corpuscles and some are
cells which have ingested red blood corpuscles. According
to most authorities, the blood is supposed to flow from the
capillaries into the meshes of the pulp and from there through
the splenic vein.

In. the capsule of the spleen there are smooth muscle fibres
which by their contraction regulate the size of the spleen.

Leucocytes are formed in the spleen and thrown into the
blood, for the blood in the splenic vein contains more
leucocytes than the arterial blood. This function corre-
sponds to the anatomical structure of the spleen, which is
very much similar to that of lymph glands. But white blood
corpuscles are not only formed in the spleen as in the lymph
glands, but they are also destroyed there. This is supported
by the fact that we find in the spleen considerable quantities
of substances which have been derived irom the nuclei of the
destroyed white blood corpuscles. They are the xanthin
bases, decomposition products of nuclein, which must be
regarded as the precursors of uric acid. If the spleen-pulp
is heated with blood, uric acid is formed. As it is supposed
that, in mammals, uric acid is formed from the nucleins of

9° HUMAN PHYSIOLOGY

the nuclei, the spleen must be the chief place of uric acid
formation.

The fact that we find, in the spleen-pulp, cells which con-
tain red blood corpuscles, in all stages of decay, favors the
view that the red blood corpuscles are also destroyed in the
spleen. Red blood corpuscles are supposed to be formed
in the embryonic spleen.

The spleen can be extirpated without injury to the body ;
its functions can be entirely taken up by other organs (lymph
glands, red bone marrow, liver).

In many cases of infectious diseases, the spleen is much
enlarged. Some claim that the spleen produces cells
[phagocytes ?] which neutralize the cause of the disease.

CHAPTER VII
SECRETIONS

1. SECRETIONS IN GENERAL

SECRETIONS are of various significance for the animal
economy. Some serve to remove from the body the waste
products of metabolism (e.g. secretion of urine) ; some furnish
the fluids necessary for the digestion and absorption of foods ;
again, there are the secretions of milk-glands, the food for
the infant; the secretion of the sebaceous glands, a protec-
tive covering for the skin ; and the sweat secretions which
regulate the temperature of the organism.

Secretions are produced by the gland-cells, i.e. by modi-
fied epithelial cells. They are found:

(a) As isolated cells between other epithelial cells.

In this group belong the secreting epithelial cells of the mucous
membrane (globlet cells), cylindrical cells which, when empty of
secretion, contain granular protoplasm and oval nuclei; this
granular protoplasm during the formation of secretions changes to
a clear mass, the unchanged protoplasm and the nuclei withdraw-
ing to the bottom of the cell. The clear mass then leaves the
cell, is deposited on the free surface and constitutes the secretion.
In the globlet cells the formation and the pouring out of the
secretion take place simultaneously; finally the whole cell empties
itself and dies.

(/;) As congregated in the glands.

The glands are imaginations of the skin or mucous mem-
brane of various forms, some in the form of tubes (tubular),
some in the form of sacs (acinous), branched or unbranched.

The wall of the gland duct forms a layer of cells which is
supported by a membrana propria and surrounded by capil-

91

92 HUMAN PHYSIOLOGY

laries. The glands also contain lymph vessels, muscles and
nerves.

The secreting cells are generally only found at the closed
end of the gland duct, while the other part serves as an
excretory duct for the secretion.

The process of secretion is not merely a filtration of the
fluids of the blood through the walls of the gland, but is-
brought about by a special activity of the secreting gland -
cell, as the following shows:

1 . Most of the secretions contain substances not found as.
such in the blood, which must therefore have been made by
chemical processes in the gland-cells (e.g. the ferments of
digestive fluids, the caseinogen and the lactose of milk, etc.).

2. Secretion, in many cases, does not occur continually
but only at stated times, while blood pressure should cause
a continual filtration.

3. The pressure of the secretion in the duct of the gland
maybe higher than that of the blood. Furthermore, secre-
tion can take place in glands free from blood and even in
excised glands.

4. In many cases the secretion is accompanied by morpho-
logical changes in the cells of the gland.

5. Many secretions are under the influence of specific
secretory nerves. The nerve-fibres in the salivary glands
end in the gland-cells.

2. SALIVARY SECRETION

I. Composition of saliva. — The saliva of the mouth is a
secretion of all the glands of the mouth-cavity. It is a
colorless, cloudy, stringy fluid, having a weak alkaline
reaction. The amount secreted in twenty-four hours is
estimated at from one to two litres.

The cloudiness of the saliva is due to the mucin, salivary
corpuscles and discarded epithelial cells of the mouth-cavity.
The salivary corpuscles are recently loosened gland-cells
or migrated leucocytes.

The saliva contains 99-99.5$ water, 0.1-0.2^ salts (in-

SECRETIONS

93

eluding potassium sulphocyanate), o. 1-0.4$ organic material
including proteids, mucin and a diastatic ferment, ptyalin,
and last of all, gases, especially carbon dioxide.

2. Morphological phenomena accompanying salivary secre-
tion.— The buccal cavity contains two kinds of glands:

(a) Albuminous or serous glands furnish a secretion free
of mucin. To this class belong the parotid and, in many
animals (rabbits), the submaxillary also, and a part of the
glands of the mucous layer of the mouth-cavity.

The cells of the albuminous glands have, during rest, a
small amount of clear, finely granular protoplasm and a
small irregular nucleus. In the active condition the cells are
smaller, the amount of the granular substance is increased,
and the nuclei become more nearly spherical.

(/;) The mucous glands furnish a secretion containing

«i a, . a, «2

*>3 III. "3 2 03 IV.

FK;. 3. — REPRESENTING THE ORIGIN OF DEMILUNES. (After St&hr.)

mucin; this group contains all the glands except the albumi-
nous glands.

Many glands, e.g. the sub-maxillary glands of man, con-
tain both albuminous and mucous gland-cells.

In the mucous glands we find two kinds of cells :

i. The demilune of Giannuzi (also called border cells)

94 HUMAN PHYSIOLOGY

lying at the periphery of the gland wall. They are flattened
cells with protoplasm rich in granules.

2. Muciparous cells, reaching to the lumen of the gland
duct; their protoplasm is but slightly granular, more hyaline.

These two forms of cells are of the same kind, but are in
different conditions of secretion. The well-filled muciparous
cells, al , a.2 , #3 (Fig. 3, I) crowd the empty border cells
^i » ^2 > ^3 » away from the lumen. After discharging their
secretion, the hitherto muciparous cells are crowded away
by the now filled border cells and are themselves changed
to border cells (compare the change in the form of the cells
in the successive stages II, III, IV of Fig. 3).

3. Influence of tlie nervous system upon secretion. — The
salivary secretion is stimulated reflexly when food, especially
dry food, stimulates the nerves of the mucous membrane of
the mouth. Salivary secretion is, therefore, dependent upon,
the nervous system.

The submaxillary and sublingual glands are supplied
with the following secretory nerves :

(a) Fibres from the facial nerve which, passing through
the chorda tympani, approach the glands along with the
lingual. Stimulation of these fibres produces a rich flow of
thin secretion.

(&) Fibres from the cervical sympathetic; the stimulation
of these yields a scanty flow of thick saliva.

The chorda fibres also contain the vaso-dilators ; the
sympathetic contain the vaso-constrictors for the blood
vessels of the glands.

The parotid glands are supplied with the following secre-
tory fibres:

(a) Fibres from the glossopJiaryngeal passing through the
nervus Jacobsonii, Petrosus superficialis minor to the oticum
ganglion, from there through the auricula tcmporalis to the
gland. Stimulation of these produces a great flow of thin
saliva.

(b) Fibres of the cervical sympathetic^ stimulation of which
yields a scanty flow of thick secretion.

SECRETIONS 95

The centre of the secretory nerves is situated in the
medulla oblongata.

For some time after the section of the secretory nerves the
gland secretes continuously (paralytic secretion) till it finally dies
and degenerates. The cause of this paralytic secretion is still in
the dark.

The pressure of the secretion is measured by placing a canula
in the duct of the gland and connecting this with a manometer.
In the submaxillary of the dog the pressure during chorda stimula-
tion may be above 200 mm Hg, this being 100 mm more than the
blood pressure in the blood vessels of the gland.

The secretion of the salivary glands is said to be warmer than
that of the blood carried to the gland. Hence heat is produced
during salivary secretion.

The active gland shows certain electrical phenomena, the mean-
ing of which is not yet understood.

Upon nervous stimulation, secretion can go on in a bled
animal, in which case the gland is no longer supplied with
blood.

3. GASTRIC SECRETION

I. Composition of gastric juice. — Gastric juice, the secre-
tion of the gastric glands, is a clear, transparent or slightly
yellowish fluid, having an acid reaction and a specific gravity
of i .003—1 .006. It contains 0.29—0.60$ solids which include
o. 10-0. 17$ ash.

Its characteristic constituents are :

(a) Free hydrochloric acid, in man 0.2$; in dogs a little
more.

The gastric juice gives the following tests for free hydrochloric
acid: To gastric juice add Giinzburg's reagent (2 g phloroglucin,
i g. vanillin in 30 g absolute alcohol) and evaporate. This gives
a red color. Gastric juice imparts a blue color to methyl-violet
and congo-red.

(^) Pepsin, a ferment which in an acid solution digests
proteids and gelatin. According to its composition, it is a
proteid-like body. The antecedent of pepsin in the gastric
glands is the pepsinogen, a substance which can be extracted

96

HUMAN PHYSIOLOGY

from the gastric glands by a soda solution, and can be
changed to pepsin by hydrochloric acid.

(V) Rennin, a coagulating ferment, of unknown composi-
tion. It causes the casein coagulation of milk. Its antecedent
is rennet-zymogen, which can be extracted from the gastric
mucosa by water and can be changed to rennin by the
addition of acid.

The fasting stomach contains no gastric juice ; its mucous
membrane is covered with mucus.

2 . Morphological phenomena accom-
panying the secretion. — The tubular
glands of the mucosa may be classi-
fied as :

(a) Glands composed of only one
kind of gland-cell. They are found
in the pyloric end only and are there-
fore called pyloric glands.

(b) Glands composed of two kinds
of cells ; these are found in the fundus
— fundic glands.

The pyloric glands contain cylin-
drical cells which, in a single layer,
form the duct. The fundic glands
contain, besides the cylindrical cells
(the so-called chief or central cells),
also a second kind called the ovoid or
oxyntic cells. These ovoid cells lie
isolated between the chief cells and

the membrana propria and do not

f ,. „,, FIG. 4.— FUNDIC GLANDS.

form a continuous layer. The ovoid (After Heidenhain.)

cells are surrounded by secretory capil- The protoplasm of the

chief cells is clear, that of the

lary loops in a basket-like form, which ovoid cells is darker and
are connected with the lumen of the granular; Arrangement of

the ovoid (a) and chief cells
gland. (I)) of the fundic glands.

Both the fundic and pyloric glands form pepsin and rennin,
hence the cylindrical cells (chief cells of the fundic glands) must
be regarded as secreting pepsin and rennin.

SECRETIONS 97

The isolated pyloric end of the stomach secretes a gastric juice
"which is not acid. As the ovoid cells are lacking in this part, it
is supposed that the hydrochloric acid is secreted by these cells.

The morphological changes during the activity of the
cells are as follows: The chief cells, which are large and
granular during fasting, at first become still larger, but from
the sixth to the ninth hour of digestion they become smaller
and clearer. The ovoid cells, small during fasting, are much
enlarged during digestion.

Concerning the origin of the characteristic constituents of
gastric juice, nothing is kno\vn for certain. Both ferments must,
however, be regarded as a product of the gland-cells.

As to the formation of the hydrochloric acid it is difficult to
understand how a free strong acid can originate while the blood
and the secretory cells have an alkaline reaction. An explanation
has been sought in the mass action of weak acids (e.g. carbonic
acid) upon the chlorides of the blood. In the same way as
hydrochloric acid is set free by the mass action of the carbonic
acid of the blood upon sodium chloride and is then taken up by
the blood corpuscles (see page 59), the mass action of carbonic
acid in the ovoid cells might set free the hydrochloric acid.

Recently it has been supposed that the acid is not formed in the
gland-cells, but is formed from the chlorides of the food in the
following manner:

By dissolving in water a part of the sodium chloride of food is
split up into sodium and chlorine ions. The free sodium ions in
the stomach are supposed to pass through the walls of the stomach
by diffusion in exchange for the free hydrogen ions of the blood.
The walls of the stomach are impermeable to the chlorine ions,
hence they remain in the stomach and form, with the hydrogen
ions coming from the blood, the hydrochloric acid. This view is
based upon the following facts: (i) The cells remain alkaline
notwithstanding the acid formation; (2) If chlorides are not
present in the stomach, no free acid is supposed to be formed;
(3) The alkalinity of the blood and of the urine is increased after
the eating of sodium chloride.

3. Influence of tJic nervous system on see ret ion.

Observations on the secretion of gastric juice can be easily made
on men and animals by means of a gastric fistula.

Gastric secretion begins when food has been swallowed,
even when food passes out by an esophageal fistula so that

98 HUMAN PHYSIOLOGY

it does not reach the stomach. This secretion stops after
the cutting of the vagi.

The secretion is dependent upon psychical conditions, as
it can be brought about by the mere sight of food. After
section of the vagi, secretion still occurs when food is placed
in the stomach itself. Whether this secretion is a reflex
process in which the vagus does not participate, or whethtr
it is due to direct stimulation of the glands, is not known.

The secretion of the gastric juice is, therefore, called forth
by the sight and deglutition of food and is then continued
by the presence of the food in the stomach.

4. PANCREATIC SECRETION

I. Composition of pancreatic juice. — The pancreatic juice
from a newly placed fistula in the pancreatic duct is a clear,
thick fluid having a specific gravity of 1.03. Because of its
sodium carbonate (o.2#) it has a strong alkaline reaction*
Sometimes it coagulates spontaneously. From a permanent
fistula the secretion is not so thick (sp. gr. i.oi).

The pancreatic juice obtained by a temporary fistula con-
tains about 90$ water, that by a permanent fistula 98$.
The solids contain from 0.6-0.9$ asn» also organic sub-
stances, especially proteids (from a temporary fistula about
io#). The secretion from a temporary fistula is frequently
so rich in proteids that, on heating, it coagulates to a solid
mass. Pancreatic juice also contains leucin, fat, soaps in
small quantities, and the following three characteristic
ferments :

(a) A diastatic ferment, which acts upon starch like the
ptyalin of saliva.

(&) Trypsin, a ferment splitting proteids up into proteoses.
Trypsinogen, the antecedent of trypsin, is changed to trypsin
during secretion and also by the action of oxygen or organic
acids.

(c) Steapsin, a fat-splitting ferment, which splits the
neutral fats into glycerin and fatty acids.

SECRETIONS 99

2. Morphological phenomena accompanying tJic secretion.
• — The cells of the pancreatic glands have a striated outer
and granular inner zone. During activity the striated outer
zone is widened, the granular inner zone decreases, while
during rest the opposite take place (see Fig. 5). In the

FK;. 5. — GLAND-CELLS OF PANCREAS IN DIFEERENT STAGES OF SECRETION.

(After Heidenhain.)

. /. first stage of digestion (6-10 hours); the striated outer zone is much broader
than the granular inner zone. B, second stage of digestion (10-20 hours); the
striated outer zone is narrower and the inner granular zone is wider.

active condition the cells are separated by sharper (frequently
double) boundary lines than during rest.

3. Influence of tJic nervous system upon secretion. — Secre-
tory nerves for the pancreas are supposed to be present in
the vagus and in the sympathetic.

It has been stated that the pancreas of herbivorous
animals secretes continuously, while that of carnivorous
animals secretes periodically, i.e. only after the introduction
of food in the stomach.

Among the substances in the stomach which can reflexly cause
pancreatic secretion are chiefly acids, fats, and spices.

Concerning the effects of extirpation of the pancreas see
Chapter XI.

5. BILE SECRETION

I. Composition of bile. — Bile, the secretion of the liver,
is a reddish-yellow or green ropy substance, having an
intensely bitter taste. When it is poured from the liver it
contains about 1.5-3^ solids. During fasting the bile does
not flow directly into the intestine, but first into the gall-
bladder, where it is concentrated by the absorption of water
and the addition of.muU'S, so, that>it,coptaifl$ about, 16-17^

ioo HUMAN PHYSIOLOGY

solids. The amount secreted per diem in the adult is about
I litre.

Characteristic constituents of bile :

(a) Sodium glycocholate and sodium taurocholate (about
one-third of all the solids of bile). In man the sodium
glycocholate predominates, in the dog, sodium taurocholate.

To isolate the salts of the bile acids, proceed as follows:
Mix bile with animal charcoal, evaporate, extract the
residue with alcohol, add excess of ether; this precipitates
the salts of bile acids in delicate needle crystals (crystallized
bile). Concerning the characteristics of the bile acids see
page 49.

(/>) Bile pigments, bilirubin, biliverdin, and sometimes
also hydro-bilirubin ; see page 50.

Besides these, bile contains mucin, cholesterin, lecithin,
fat and fatty acids, salts (chiefly sodium carbonate and phos-
phate), and a little iron.

In the gall-bladder the solid constituents of the bile may be
precipitated as gallstones. These may be composed of a com-
pound of calcium with bilirubin or of cholesterin.

2. Chemistry of tJie liver. — The liver is the largest gland
in our body. It weighs about 1.5 kg and contains about
30$ solids, chiefly proteids (20$), some fats, extractives, and
a varying amount of carbohydrate in the form of glycogen
and grape-sugar. Its ash forms about \% of its weight and
is characterized by its high per cent of iron.

The iron in the liver is partly in inorganic, partly in organic
combination. The iron held in organic union is found in two
nucleo-proteids, hepatin and ferratin. In the hepatin the iron is
held very closely, but ferratin has more the character of an iron
albuminate since its iron can be split off by hydrochloric acid.

The iron of the liver, like the bile pigments, is derived from the
haemoglobin of the red blood corpuscles which are destroyed in
the liver. The iron is excreted chiefly by the walls of the intes-
tine, and in smaller quantities by the bile and urine.

Structure of the liver. — The gland-cells of the liver are

TvV\W tifH^/^5M^&ona! Cr^s o ha,v*nj> ,gTa,nular protoplasm and
one or/;fnfe^>^uclfci.r5 Tfee \prqtp^lism contains pigment

LIBRA

SECRETIONS 101

granules and fat droplets and, in well-fed animals, masses
of glycogen. In the fasting condition the cells are small,
cloudy, and have not well-defined contours ; during digestion
they are larger, the centre being clear and the periphery
containing large granules.

When a liver is cut through, the liver lobules (Fig. 6) can be
seen. These are composed of cells arranged in rows, radiating

from a vein (the vena centralis) in the
centre of the lobules to the circum-
ference. But these rows of cells are
not isolated, for each cell is connected
with those above and below it.

Between the cells are found both
the small bile ducts (the so-called bile
capillaries) and the blood capillaries.
The bile capillaries stand in the same
relation to the liver cells as the lumen
of other cells to the gland-cells. Two
FIG. 6.— CROSS-SECTION OF A cells form the wall of the bile capil-
LIVER LOBULE OF A PIG. lary, the latter being formed by two
RADIAL ARRANGEMENT OF groove-like depressions in the surfaces

of two neighboring cells which are
fitted together. Each liver cell comes

in contact with bile capillaries on more than one side. The bile
capillaries empty into the bile ducts coursing between the lobules.
The blood capillaries originate from the intralobular branch of
the portal vein, they traverse the lobules radially and finally join
the central vein of the lobule which connects with the intralobular
branch of the hepatic vein. The blood capillaries also run
between the liver cells, but in such a manner that the blood and
bile capillaries never touch each other but are surrounded on all
sides by liver cells. Hence, a liver cell or a part of a liver cell is
always placed between a blood and a bile capillary.

The branches of the hepatic artery run only in the intralobular
tissue; their capillaries empty in veins which end in the portal
vein. The lymph vessels accompany the portal vein.

4. The formation of bile.

The secretion of bile can be investigated by means of the biliary
fistula.

The secretion of bile is continuous, but is increased 3-5
hours after the taking of food. This increase of secretion
during digestion seems to be brought about by absorbed
substances which stimulate the liver directly. As such, the

102 HUMAN PHYSIOLOGY

bile elements (bile acids) absorbed from the intestine are
especially active.

The pressure in the bile ducts may be higher than that in
the portal vein, yet the secretion of bile is dependent upon
blood pressure. If the blood pressure decrease, less bile is
secreted and the bile contains more solids. Ligaturing the
portal vein, stimulation of the spinal cord and of the
splanchnic nerve (because of diminished amount of blood
carried to the liver, due to the constriction of the arteries),
cause inhibition of bile secretion.

Secretory nerves for the liver have not yet been demon-
strated.

5 . The discharge of bile.

The bile is driven out of the liver by the pressure of the newly
made bile. The ductus choledochus has at its opening into the
intestine a sphincter which regulates the flow of the bile. The
muscles of the gall-bladder and ductus choledochus also aid in
discharging the bile. The nerves for these muscles are supposed
to be the vagus and splanchnic.

If the flow of bile is prevented, the bile enters the lymph vessels
and thence passes into the blood (jaundice). The bile is then
excreted by the kidneys.

6. SECRETION OF INTESTINAL JUICK

To investigate the secretion of the intestinal glands, an intes-
tinal fistula must be made. A piece of the intestine is isolated
but. its connection with the mesentery is not severed. Either both
ends of this piece of intestine are sewn into the incision of the
abdominal wall, or only one end is thus fixed while the other is
closed by a ligature. The two ends of the main intestine are sewn
together.

1. Composition of intestinal juice. — The juice of the small
intestine is a colorless, alkaline fluid having a specific gravity
of 1.007. It contains besides salts, some proteids, a diastatic
and an inverting ferment, and, according to some authors, a
proteolytic ferment.

The large intestine furnishes a mucous secretion without
ferments.

2. The secretion. — The intestinal juice is the secretion of

SECRETIONS 103

the glands of Brunner in the duodenum and of the crypts of
Lieberkiihn in the whole intestine. Concerning the secre-
tion of Brunner's glands and the conditions of their secre-
tion nothing is known.

The crypts of Lieberkiihn of the small intestine are
simple tubular glands, placed in thick clusters between the
villi of the mucous membrane. They secrete the intestinal
juice containing the diastatic ferment. The secretion takes
place when the mucous membrane of the intestine is directly
or reflexly stimulated by the taking up of food. As the
secretion also takes place in those parts of the intestine not
directly stimulated, it is dependent upon the nervous system.
The secretory nerves are, however, not known.

The muciparous glands of the large intestine contain many
globlet cells forming mucus; these globlet cells are only
found occasionally in the glands of the small intestine.

The intestinal glands also seem to regenerate the epithelial
glands of the villi. In the intestinal glands new cells are con-
tinually formed by mitotic division; these new cells pass upward
to take the place of the broken-down epithelial cells of the free
surface of the mucous membrane.

7. RENAL SECRETION

i. Composition of urine. — Urine, the secretion of the
kidneys, is, in man, a yellow or reddish-brown fluid having
a specific gravity of 1.017-1.040. Its reaction is generally
acid (due to acid sodium phosphate), but after a meal of
vegetables containing the salts of vegetable acids, which in
the body form carbonates, it may be neutral or alkaline.
Its reaction is alkaline also during the period of greatest
gastric digestion because the alkalinity of the blood is
increased on account of the acid formation in the stomach,
and this excess of alkali is excreted in the urine.

When urine stands for a certain length of time, putrefaction sets
in by which the urea is changed to ammonium carbonate (alkaline
urea fermentation) ; this causes the urine to become alkaline.
Such alkaline urine is cloudy because of a precipitate of ammonio-

104 HUMAN PHYSIOLOGY

magnesium phosphate, ammonium urate, and the phosphates and
carbonates of the alkali earths.

The amount of urine excreted per day is generally about
1.5 litres.

Urine contains about 4$ solids, among which are :

(a) Nitrogenous wastes of metabolism: urea 2.3$ (35 g.
per day), uric acid (0.05$ in the form of acid salts of the
alkalies), hippuric acid, kreatinin (0.05$), xanthin, hypo-
xanthin, ammonia salts (0.04$). The urea contains 83-86^
of all the nitrogen of the urine.

To obtain the urea from urine, evaporate the urine to small
bulk and add nitric acid ; this throws down crystals of nitrate of
urea.

The uric acid crystallizes from the urine when that is mixed
with one-tenth its volume of concentrated hydrochloric acid and
left standing in the cold. This separation of the uric acid takes
place in concentrated and strongly acid urine without the addition
of hydrochloric acid (sedimentum lateritium, see page 46).

The urea contains 83-86$ of all the nitrogen of the urine ;
ammonia contains 3-4$; the remaining nitrogen is distributed
among uric acid, kreatinin, etc.

(b) Salts about 1.5^, chiefly sodium chloride (a little more
than if) and, in smaller quantities, phosphates, sulphates,
and traces of oxalates; among the bases are sodium, potas-
sium, magnesium, calcium, and traces of iron.

Besides the sulphates, the urine contains sulphuric acid combined
with the ethereal sulphates of the benzene derivatives, e.g. :

Phenyl-sulphuric acid CflH..O.SO2.OH

Kresyl-sulphuric acid C7H7.O.SO,.OH

Indoxyl-sulphuric acid or indican C8H6X.O SO2.OH

Skatoxyl-sulphuric acid C9H8N.O.SO,.OH

To demonstrate the presence of indican, add a like quantity of
concentrated hydrochloric acid and a little calcium chloride solu-
tion to the urine. Indigo is produced which may be collected by
shaking it with chloroform.

The benzene derivatives, with which the sulphuric acid unites,
are derived from the intestine, where they are formed by proteid
putrefaction: phenol, indol, skatol; the last two, after being

SECRETIONS 105

absorbed, arc oxidized to indoxyl and skatoxyl. From this
decomposition of the proteid in the intestine arise aromatic
oxyacids (oxyphenyl-acetic acid and oxyphenyl-propionic acid),
which are absorbed from the intestine and excreted by the kidneys.

(c) In small quantities there are present in the urine
urinary pigments, among which is sometimes found urobilin,
which is supposed to be identical with hydro-bilirubin.

Finally there are present in urine, gases, chiefly carbon
dioxide, traces of nitrogen and oxygen.

In certain diseases, e.g. diabetes, the urine contains
grape-sugar, aceton, oxybutyric acid and diacetic acid; in
inflammation of kidneys it contains proteids ; in icterus, bile
pigments and acids; and in haematuria, blood pigments.

2. The stmct lire of tJic kidneys.

The kidneys are composed of a uniformly darkly stained cortex
and a radially striated medulla consisting of a large number of
Malpighian pyramids.

In the cortex the uriniferous tubules of the gland are coiled
(convoluted tubules); in the medulla they are straight (tubuli
recti). Each uriniferous tubule begins in the cortex \R, Fig. 7)
as a spherical dilation, the Malpighian body (g), from which pro-
ceeds the convoluted tubule (f). This proceeds downward into
the medulla, M, as a straight tubule (e), then turns and forms the
loop of Henle. The ascending limb of Henle's loop joins the
intercalated part (c), which, turning downward towards the pelvis,
forms a straight collecting tubule (b). The collecting tubules join
to form a duct (a), which at the apex of the pyramids empties into-
the pelvis of the kidneys.

The Malpighian bodies are composed of a knot of blood vessels,
the glomerulus (£•), which is placed in the blind, sac-like ending
of the uniferous tubule (the Bowman capsule) so that it is almost
entirely surrounded by the capsule. The fold of the capsule
bordering on the glomerutus is composed, in young individuals,
of cuboidal cells, while in older persons the cells are flattened.
The outer fold of the capsule is made up of flat polygonal cells.
It is continued downward, forming the walls of the convoluted
tubule whose cells are radially striated and have granular proto-
plasm. The cells in the walls of Henle's loop, of the intercalated
portion, and of the collective tubules are cylindrical epithelial cells.

The uriniferous tubules are surrounded by connective tissue, in
which are found the blood vessels.

The branches of the renal artery proceed from the hilus to the
boundary between the cortex and medulla (</, Fig. 8). Here they

io6

HUMAN PHYSIOLOGY

give off branches which radiate outward (6) and send branches
to each of the glomeruli (c). After giving off these branches,
the arterial trunk ends in capillaries in the outer part of the
cortex (</).

Each glomerulus is formed by the afferent vessel (vas afferens)

FIG. 7. — DIAGRAM OF A URINARY TUBULE.

dividing into a great number of loops. These loops then join
each other again, forming the vas efferens (/') which passes out of
the glomerulus and then splits up into capillaries. The capillary
net in the cortex surrounds the convoluted tubules (g).

The arteriolae rectae (£) in the medullary portion are derived
partly from the vasa afferentia of the deepest glomeruli, partly
from the renal artery directly. These form straight capillaries in
the medulla, and at the papillae (m) form a ring-like capillary net-
work. The capillaries in the cortex empty into the veins radiating

SECRETIONS

107

F'

b

from the pelvis to the circumference (//) ; into these the smallest
veins of the medulla also empty (/). ^e

3. Conditions of renal secretion.

(a} The quantity of urine secreted
depends upon the blood pressure in
the renal artery; it decreases when,
e.g. by bleeding, the blood pressure
decreases; it increases when, e.g. by
ligaturing of other blood vessels, the
pressure in the renal arteries is in-
creased.

Partial closure of the renal vein (venous
statis) decreases renal secretion, which
appears to be due to the compression of
the urinary tubules by the strongly dilated
capillaries and smaller veins.

(/>) The renal secretion ceases for
a long time when the supply of blood
to the kidneys has been cut off by
compression of the renal artery for
but a few minutes.

(Y) There are certain substances
which, taken into the body, increase
renal secretion, e.g. water, urea, so-
dium chloride, sodium nitrate, caffein,
grape-sugar. The action of these
diuretics still takes place when the
renal secretion has been entirely
stopped by a too low blood pressure.
On the other hand, there are sub-
stances, e.g. atropin, which inhibit
renal secretion.

(d] Concerning the effect of the
nervous system upon renal secretion
— leaving out of consideration the in- NKYS.
direct influence of the vaso-motor nerves — nothing is yet
known.

Notwithstanding the fact that renal secretion depends

io8 HUMAN PHYSIOLOGY

upon blood pressure, we cannot regard it as a mere process
of filtration of the blood fluid through the walls of the urinary
tubules. This assertion is based upon the following; facts :

1 . The composition of the urine differs quantitatively from
that of proteid-free blood plasma. Many substances (e.g.
urea) are much more abundant in the urine than in blood.

2. The harmful effect of ligaturing the renal artery cannot
be explained on the theory of mere filtration.

Renal secretion is, therefore, dependent upon the special
activity of the gland-cells. These cells are temporarily
paralyzed by the stoppage of circulation (compression of
renal artery), so that they are not able to secrete. Diuretics,
in so far as they do not affect blood pressure, stimulate the
cells toward greater activity.

According to the theory accepted at present, renal secre-
tion takes place as follows: The cells of the Bowman capsule
secrete chiefly water, while the cells of the convoluted tubules
secrete the solid constituents of urine, and this secretion is
concentrated as it passes through the urinary tubule by the
absorption of water from it.

This view is based on the fact that sodium-sulphincligotate,
injected into the blood, is excreted by the kidneys, and is
found, during its excretion, only in the inner part of the cells
of the convoluted tubules and lower down in the lumen of
the urinary tubules, while it is never found in the cells of the
capsule.

Most of the substances excreted in the urine are not formed
in the kidneys but in other organs, and are carried by the
blood to the kidneys to be picked out by them. Some sub-
stances can also be made in the parenchyma of the kidneys,
e.g. the hippuric acid. That energetic oxidations take place
in the kidneys is proven by the facts that the blood in the
renal veins is venous, and that the secreted urine is often
warmer than the blood flowing to the kidneys.

Beside the end-products of metabolism, there are also-
excreted substances which are indeed normal constituents of
the body but which, for some reason, have accumulated in

SECRETIONS 109

the blood in too large quantities (e.g. many salts, grape-
sugar in case of glycosuria), also substances normally not
found in the body (e.g. drugs, such as potassium iodide,
salicylic acid, santonin, etc.).

4. Micturition. — The urine is driven from the urinary
tubules into the pelvis by the pressure of the secretion.
From the pelvis the urine is forced by the peristaltic contrac-
tions of the two ureters into the bladder. The bladder is
closed by the tonic contraction of the sphincter vesicae.
During micturition, the tonus of the sphincter is inhibited
and the contraction of the detrusor urinae diminishes the
compass of the bladder. The muscles of the bladder are
supplied with nerves from the sacral and lumbar nerves and
from the sympathetic. Their centre lies in the lumbar cord.

8. THE SECRETION OF SWEAT

1. Composition of sweat. — Sweat is a clear, colorless fluid
having a specific gravity of 1.003-1.006. Its reaction may
be acid, neutral or alkaline; it has a salty taste and charac-
teristic odor. It contains 0.85-0.91$ solids which include
•0.65$ salts (chiefly NaCl) and 0.24^ organic substances
(0.12$ urea). The amount daily secreted is very variable.
The secretion of sweat is closely related to the regulation of
temperature (see Chapter XIII).

2. Secretion of sweat. — The sudoriferous glands are long
unbranching tubules which form at the lower end a globular
mass (0.3—0.7 mm in diameter) composed of a coiled tube.
The walls of these coiled tubules have a single layer of
cuboidal cells.

The sweat secretion is dependent upon the nervous system.
Stimulation of the sciatic or brachial nerve of a cat produces
sweating of the -paw. It is not mere filtration of the blood
fluid, but depends upon the specific activity of the gland, as
the following facts show. Secretion of sweat does not take
place continuously, and twenty minutes after the amputation
of a limb, stimulation of the nerve still produces perspiration.

no HUMAN PHYSIOLOGY

The nerves of sweat secretion after leaving the cord run
through the sympathetic and later on join the nerves going
to the extremities. The center for the secretion of sweat is
supposed to be situated in the cord, for after the cord of a
cat has been cut in the cervical region, heat or dyspmea still
produces sweating of the hind legs. A primary sweat
centre is supposed to be situated in the medulla oblongata.
The secretion of sweat is inaugurated by increase in tem-
perature, asphyxia, poisons (pilocarpin), and also by psy-
chical influences (the sweat of fear). Atropin inhibits the
secretion.

9. SEBACEOUS SECRETION

The sebaceous secretion is an oily substance, consisting
mainly of cholesterin esters of fatty acids. Concerning its
composition but little is as yet known. The sebaceous
secretion oils the skin and hair.

The sebaceous glands are composed of a gland body
which is formed by a number of saccules. The outer cells
of these saccules are small cuboidal cells, while the inner
cells are large and spherical and fill the whole saccule and,
by their breaking up, form the secretion. The duct leading
from the gland to the exterior is formed by the continuation
of the outer hair-follicle; it is, therefore, formed from layers
of pavement epithelial cells.

Concerning the influence of the nervous system upon
sebaceous secretion nothing is known.

10. LACHRYMAL SECRETION

Tears are composed of a clear, alkaline salty fluid. They
contain about \% solids, chiefly salts (NaCl). Proteids are
present in small quantities.

The lachrymal glands are built like the albuminous sali-
vary glands. The tears are secreted continuously. Their
secretion is, however, under the influence of the nervous
system; it is increased by psychical influences (weeping),

SECRETIONS in

also reflexly when foreign substances irritate the conjunctiva
and by strong light falling upon the eye.

The secretory nerves pass through the lachrymal nerve,
the subcutaneous mallar nerve, and the cervical sym-
pathetic.

The tears flow through the ducts of the lachrymal gland
in the outer canthus of the eye into the conjunctival sac in
the inner canthus and thereby moisten the cornea and the
conjunctiva and remove foreign bodies out of the conjunc-
tival sac.

In the inner canthus of the eye the tears are taken up by
the puncta lachrymale of the caruncula lachrymalis and then
flow through the nasal duct into the inferior meatus of the
nose.

11. MILK SECRETION

I. Composition of milk. — Milk is a wrhite opaque fluid
having an amphoteric reaction, a sweet taste, and a specific
gravity of 1.028-1.034. It is an emulsion of fat in which
the fat droplets, of 1.5—5^ diameter, are surrounded by
pellicles of caseinogen.

The white color and the opaqueness of milk are due to
the fact that the light is totally reflected by the fat droplets.

Milk contains 13$ solids. The milk of young women
contains more solids than that of older women. The solids
are:

(a) Protcids (2.5$), chiefly the nucleo-proteid caseinogen.
This proteid is split up by rennin into paracasein a pro-
teid which forms with calcium salts an insoluble double salt
(casein) and a soluble proteid (whey proteid).

Besides the caseinogen, the milk contains, in smaller
quantities, two proteids which are coagulated by heat:
lactalbumin and lactoglobulin.

(/>) Carbohydrates (6#), namely, milk-sugar or lactose
(see page 21). When milk stands for a long time the lac-
tose undergoes lactic-acid fermentation (due to bacterium

H2 HUMAN PHYSIOLOGY

lactis). The lactic acid thus formed precipitates the case-
inogen (souring of milk).

(c) Fats (4$), in fine emulsions, not dissolved. Besides
the glycerides of palmitic, stearic, and oleic acid, milk
contains the glycerides of the lower fatty acids (butyric,
caproic, caprylic acid). On standing, the specifically lighter
fat globules rise upward, forming the cream.

(d} Cholesterin, lecithin, and a yellow pigment in small
quantities. Besides these the milk- is said to contain citric
acid, a product of the activity of the gland.

(e) Salts (0.5^), especially calcium phosphate, also potas-
sium chloride, a little sodium chloride, and a very little
magnesium sulphate and traces of iron. The calcium phos-
phate is present partly in solution as the acid salt and partly
in suspension as the neutral salt.

Furthermore the milk contains gases, chiefly carbon
dioxide, and less nitrogen and oxygen.

2. Conditions of the secretion of milk. — The secretion of
milk takes place only during the lactation period which lasts
about ten months.

The milk gland consists of 15-20 single tubular glands,
each one of which opens by a duct in the nipple. Just before
opening at the exterior, the tubules have a sac-like dilation.

The lactiferous ducts have a wall of cylindrical epithelium.
The cells of the gland proper form a single layer of epithelial
cells, whose height varies greatly. When the ducts are
filled with secretion these cells are low, but when the ducts
are empty they are cylindrical and filled with numerous fat
droplets. The cells of the gland do not perish during secre-
tion, hence only form the secretion and excrete it.

During the first days after delivery there are present in
the milk the so-called colostrum corpuscles which are
nucleated rudiments of cells containing many fat droplets.

The nervous system has an influence upon milk secretion,
for the emotions can alter the quantity and character of the
milk. As to the secretory nerves authors differ.

Nourishment has an effect upon the quantity and com-

SECRETIONS 113

position of the milk. A meal rich in proteids increases the
proteids and fat of milk ; carbohydrate food increases the
lactose, but fatty food does not increase the fat of the milk.
Caseinogen and lactose are formed in the milk glands, for
they do not occur in the blood.

Frequent discharge of the milk from the glands by nursing
the child or by milking increases the milk secretion.

CHAPTER VIII
NUTRITION

1. FOODSTUFFS (ALIMENTARY PRINCIPLES)

FOODSTUFFS are substances which the body must take up
in order to maintain its material existence, i.e. substances
by which the body can rebuild, restore, and replace the
parts which have been changed and used up by the vital
processes.

We may divide foodstuffs into the following classes :

1. Those not furnishing energy, i.e. foodstuffs which can-
not impart energy to the body (water and salts).

2. Tko$e furnishing energy i i.e. substances rich in poten-
tial energy, which by their physiological combustion furnish
the body with the energy it needs for its functions. This
class includes:

(a) Nitrogenous substances — protcids.

(b} Non-nitrogenous substances — carbohydrates and fats.

The energy-yielding substances are sometimes called
" foodstuffs " in a narrower sense.

Strictly speaking the inhaled oxygen also belongs to the
class of energy-yielding foodstuffs, for it is only by its union
with the above-named energy-yielding foodstuffs that their
chemical potential energy can be set free and can be used
by the body.

The water serves to replace the water lost in the secre-
tions, faeces, and expired air. The water formed in the body
by the combustion of organic substances containing hydrogen
can replace only a small amount of the loss, for the amount
so formed is only about 350 cc in 24 hours, while an adult

114

NUTRITION 1 1 5

person needs 2-2.5 litres. The amount of water needed is
determined by the amount lost in the urine, sweat, and
expired air.

The salts of the food in part replace the salts taken from
the tissue fluid by the excretory organs, and in part furnish
material for the formation of organic substances (nuclein,
haemoglobin). The following are the salts necessary as
foods :

The pJiospJiatcs of the alkalies are used in the building of
the tissues. Only in the presence of potassium phosphate
can the cell substance regenerate itself.

^Calcium and magnesium phosphate serve chiefly in build-
ing up the skeleton.

Salts of iron are used in the formation of the red blood
pigment.

The need of iron seems, as a rule, to be completely satisfied by
the organic iron (nucleo-proteids containing iron) which is taken
up with the other foodstuffs so that no other iron salts need to be
taken.

The salts enumerated thus far are found in sufficient
quantity in the foods generally taken, so that they do not
need to be specially added. The case is, however, different
with

Sodium chloride, which not only serves to replace the loss
from the body fluids, but serves, at the same time, as a con-
diment (see page I 1 8) and is therefore eaten in much larger
quantities than is really necessary. The average amount of
NaCl taken by the adult is about 17 grams, while the real
need is only about 2 grams.

The need of sodium chloride is greater among people living
upon vegetable food (Negro) than among those eating flesh
(Samoids, Tunguses). The reason for this has been sought in the
greater amount of potassium salts of the vegetables. The potas-
sium carbonate acts upon the sodium chloride in the body so that
sodium carbonate and potassium chloride are formed. These
substances are excreted by the kidneys. Hence by the partaking
of potassium salts the excretion of sodium and chlorine is increased
and therefore more sodium and chlorine must be taken up in the
food.

n6 HUMAN PHYSIOLOGY

The salts of the foodstuffs not only serve to replace the
same salts in the body, but also to form other salts present
in the organism which are not taken up with the food (e.g.
the alkali carbonates). Continued lack of salt in the food
(salt-hunger) results in death, even though food be given
in sufficient quantity.

Of the combustible foodstuffs, protcids serve to replace the
body-proteids destroyed by the physiological combustion.
There is no nitrogenous substance, besides proteid, which can
supply the body with material for building up its proteids.
Hence proteids are absolutely necessary for building up the
tissues. But all proteids are not capable of doing this, for
the albuminoids (gelatin) cannot entirely replace the proteids
of the body. Otherwise it appears that the various true
proteids (simple and combined proteids, proteoses) are of
equal value as food for replacing the body proteids. At all
events, it is not necessary that the same kinds of proteids
found in the body should be found in the food. For exam-
ple, the haemoglobin and nucleo-albumins in the body,
originate, no doubt, from the union of other proteids with
iron or phosphoric acid. The albuminoids of the body are
also formed from the true proteids, not from the albuminoids
of the food.

Proteids contain all the elements needed for replacing
organic substances in the body; fats and carbohydrates con-
tain only a part, viz. carbon, oxygen, and hydrogen.
Hence proteids alone must be sufficient to satisfy the demand
for combustible food for the body. We can, indeed, feed
the carnivorous animals on an exclusive proteid diet. This
cannot be done with man and vegetable-eating animals, for
the quantity of proteid necessary to support life cannot be
digested by them.

The fats and carbohydrates serve as material for combus-
tion which furnishes the body with energy for heat production
and for work. In metabolism, gelatin plays the same part.
It is often stated that fat serves mainly for heat production,

NUTRITION 117

while carbohydrates furnish energy for work, but there is, in
this respect, no such fundamental difference between them.

As nutrition on an exclusively proteid diet is at least
theoretically possible, we can express the amount of energy-
yielding foodstuffs necessary for nutrition in terms of the
amount of proteids needed. For a man of 70 kg body
weight, the amount of proteids must be about 700 grams a
day.

A part of this food must be proteid, it being absolutely
necessary. This amounts to about 70 g per day. It has
been observed that the body can get along with a much
smaller quantity of proteids (40 g per day), but such experi-
ments only lasted for a very short time, hence it is a ques-
tion whether the body can be nourished for a great length
of time with such a small amount of proteid.

After we have supplied the absolutely necessary proteid,
the remainder of the food needed can be taken in the form
of proteid, gelatin, fat, or carbohydrate or as a mixture of
these substances. The proportion in which the foods can,
in this case, replace each other is based upon the law of
isodynamics, which states that such quantities of combustible
foodstuffs as furnish the same amount of energy during their
physiological combustion are equivalent (see Chapter XIII).
In round numbers the following quantities furnish the
same amount of energy: 2.3 g proteid = I g fat = 2.3 g
carbohydrates.

For an exact application of the law of isodynamics in the prac-
tical study of nutrition it must be borne in mind that, in meta-
bolism, the proteids behave differently from the fats and
carbohydrates (see Chapter XII).

As a diet, the following is necessary:

Proteid. F;it. Carbohydrates.

Resting man 100 g 60 g 400 g

woman 90 g 40 g 350 g

Working man 130 g 100 g 500 g

The absolute amount needed by old people and children
is less. But if the food necessary for each kilogram of body

n8 HUMAN PHYSIOLOGY

weight is considered, it will be found that children need a
larger amount than adults. This is due to two causes:
first, a growing body needs relatively more food than an
adult, and secondly, the metabolism of children is relatively
greater than that of adults because of the greater proportion
of surface (thereby greater loss of heat) compared to the
heat producing mass (see Chapter XIII).

For one kilogram of body weight the following amounts
are necessary:

X

Age. Proteid. Fat. Carbohydrates.

2-6 years , . . 3.7 g 3.0 g 10.0 g

7-15 years 2.8 g 1.5 g 9.0 g

Adult 1.6 g 0.8 g 8.0 g

Besides the foodstuffs we still take up many substances
which are not necessary for the maintenance of the body,
but which are, nevertheless, of physiological importance.
They are the condiments. They include substances having
a specific taste and odor which stimulate the nervous system,
increase digestion, aid circulation, etc. Under this class
we may mention spices and certain alkaloids (caffein in tea
and coffee, theobromin in cocoa, nicotin in tobacco).

There are still other organic substances (e.g. vegetable
acid, many alcohols) which are also burned in the body and
can therefore be regarded as energy-yielding foodstuffs even
though they are not necessary for the body. As far as ethyl
alcohol is concerned, its worth as a food is doubtful since it
acts as a violent poison and its frequent use produces morbid
changes in almost all the organs of the body.

2. FOODS

The foods furnished us by nature are mixtures of the food-
stuffs. They may be classified as :

1. Food from the animal world.

2. Food from the vegetable world.

The composition of the chief foods is as follows :

NUTRITION 119

PERCENTAGE COMPOSITION OF CERTAIN FOODS.

Proteids

Fat.

Carbo-
hydrates

Water.

Salt.

Cellu-
lose.

I. A

NIMAL
2O. O

14-5
17.0

21-5

2-5
3-5

12.5

2ETABL

24-5
6.5
10. 0

" 5
7.0
6.0

2.O

2-5
2.O
O C

FOODS.

1.5

37-5
o-5
12.5
4.0
4.0

12.0
E FOOE

2.O
I.O
I.O
2.0

"•5
o-5

O.2
0-5

0.3

O.Q
0.6

6.0
4-0

s.

52.0

78.5

72.0

69.5
52.5

49-0
20.7
10.5

2-5
10. 0

76.6
43-6

80.5

64.5

87.5

87.0

73-5

12.5
12.5
13-5
14.0

35-5
40.5
75-o
88.0
89.0
85.0

I.O
I.O

i-5

i-5
0-5
0.7

I.O

3-5
i .0

0-5
•5
.0
o
.0
.0
o-5
o-5

Shellfishes

:•:;•:

Salmon

Human milk . .

Cow milk . . ...

Efiffifs

II. VE

6.0
4-0

0.3
i.5
°-3
0.6

I.O

i-5

i .0
4.0

Rice

White bread

Rye bread. . ...

Potatoes

Cabbage ....

Asparagus .

Fruit

Generally the animal foods predominate in proteids and
fat. Lean beef consists almost entirely of proteid, and can
therefore practically be regarded as a pure proteid food.
Butter is nearly altogether fat. Of the animal foods we find
carbohydrates only in the milk and, in very small quan-
tities, in the liver (lactose and glycogen respectively).

The vegetables chiefly contain the carbohydrates and but
little or no fat. Proteids are found in all vegetables,
especially in the legumes.

The following details deserve mention:

The muscles are called beef. They consist of the muscle fibre
proper and connective tissue; the first contains true proteids, the
other a substance yielding gelatin. The real proteid value of
meat is determined by the proportion of fibres and connective
tissue present.

The amount of fat found in beef varies much and depends upon
the feeding.

The manner of preparation (boiling, roasting, etc.) does not
alter the value of beef as a food. Boiled beef (meat from
which soup is made) has still the same food value as the red or
roasted meat, but is slightly less palatable because the extrac-
tives which give it taste have been removed. In beef tea (or

120 HUMAN PHYSIOLOGY

beef soup) there are, excepting the floating fat droplets and a
little gelatin, no combustible foodstuffs and it can therefore not
be regarded as a strengthening food. It contains besides the salts
(potassium phosphate) the extractives (kreatin, xanthin) which
impart to it a delicious flavor and a stimulative activity. It is
only a condiment.

Besides the beef of muscle, other animal organs are used as food;
some of these also contain large quantities of proteids and gelatin.

Human milk contains more sugar but less proteids and salts
than cow milk. To render cow milk like human milk (which is
necessary for the nursing child), it must be diluted with water and
lactose must be added.

The chief proteid of milk is caseinogen. The caseinogen of
cow milk is coagulated by rennin in larger flakes than that of
human milk and is therefore less accessible to the action of the
digestive fluids. Hence children frequently cannot use cow milk.
This difference in coagulation is not due to any chemical differ-
ence in the caseinogen, but to the different amounts of calcium
salts present in the milk.

The calcium salts of milk are used to build up the skeleton of
the growing organism.

The cream which rises to the top when milk stands, or which
can be centrifugal ized from milk, furnishes butter. The butter is
obtained by beating the cream which breaks the caseinogen
pellicles of the fat globules so that the fat globules flow together.

Unsalted butter consists chiefly of fat, 90$, mainly glycerides
of oleic, palmitic, and stearic acids and, in smaller quantities, of
butyric, caproic, and caprylic acids; it further contains 8$ water
and casein (2$), lactose and salts. The buttermilk which is left
can still be regarded as good food, as it contains much proteid
(3-4$) and sugar (4$).

When milk is coagulated by rennin, cheese (casein coagulate)
is formed; the residue is called whey. The casein incloses the
fat globules, and after the whey has been removed it undergoes a
putrefactive process, the ripening of cheese. By this process part
of the proteids. are peptonized, part are decomposed into amido
acids; besides this, fatty acids are set free. Cheese is a valuable
food because it contains much proteid and fat. Fat cheese con-
tains 25$ proteid and 30.5$ fat; poor cheese contains 34$ proteid
and 1 1.5$ fat.

The white of egg contains only egg albumin; the yolk of egg
contains, besides the proteids (vitellin), chiefly fat, lecithin, and
cholesterin.

All vegetables contain a substance not found in the animal
food — cellulose or wood fibre. This is but slightly or not

NUTRITION 121

at all digested in the intestine of man, but stimulates the
peristaltic movements, probably by mechanical stimulation
of the intestinal muscles. This causes vegetables to pass
through the intestine more rapidly than animal food. The
food of the vegetables is inclosed in cellulose coats and
hence is not directly accessible to the digestive fluids. By
preparing the vegetable foods (grinding, cooking, baking)
the cellulose envelopes are burst and the food proper can
then be readily acted upon by the digestive fluids.

As a food the vegetable proteid is of equal value to the
animal proteid. The carbohydrates of vegetables are gen-
erally present in the form of starch, and, to a smaller
extent, as sugar (dextrose, fructose, cane-sugar, maltose).
Starch is rendered more digestible by boiling, which causes
it to swell.

Grinding changes the grain foods to fine particles — flour. From
this the cellulose envelopes (bran) are removed by sifting. The
more bran the flour contains, the richer it becomes .in proteid, for
the richest proteid layer of the grain lies just below the cellulose
envelope. The flour is used in baking bread, etc. Th~ baking
is made possible by a proteid, called gluten. The leaven (yeast)
added to the dough, produces carbon dioxide by its sugar fermen-
tation which loosens the bread. In many kinds of bread (black
bread, graham bread), flour rich in 'bran is used, and the cellulose
of the bran aids the peristalsis of the intestine and prevents con-
stipation.

The leguminoses are peculiar because of their large amount of
proteid. They contain no gluten and can therefore not be used
in baking. They contain, however, a proteid called legumin
which forms, when boiled with lime water, an insoluble compound
with calcium. Hence they must always be boiled in soft water
(containing no lime), otherwise they remain hard.

To obtain nourishment from such foods as greens, cabbage,
lettuce, fruits, which are rich in water, a large quantity must be
ta^en. They are therefore not used as a principal food but only
as supplemental to others, and serve as condiments because of
their flavors. They also furnish the cellulose necessary for the
peristalsis.

As to the question whether animal food or plant food is
more suitable for man, it may be stated that a mixed diet
consisting of one-third animal and two-thirds vegetable food

122 HUMAN PHYSIOLOGY

is most suitable. Animal food is not suitable as an exclusive
diet because it contains no carbohydrates; on the other
hand, the vegetables contain too little proteid and no fat.
Also the structure of the digestive organs of man indicates
that he is intermediate between the exclusive carnivorous
and herbivorous animals. In flesh-eating animals the length
of the intestine is about five times that of the body (reckoned
from mouth to anus), in the plant-eaters it is more than
twenty times this length. The great length of the intestine
of herbivorous animals serves to offset the more rapid move-
ment of the food, in order that the food may be sufficiently
acted upon and absorbed. As the length of the intestine of
man is about ten times that of his body, he is intermediate
between the carnivorous and herbivorous animals.

As can be observed in vegetarians, man can indeed be nourished
by vegetable foods only, but there are no sufficient reasons for
excluding meat altogether from our diet. An exclusive meat diet
cannot be endured by man for any great length of time because
of the resulting disturbance in digestion.

As many of the foods supplied us by nature are odorless and
tasteless, we spice them. The physiological significance of spices
lies in the fact that they increase the secretion of the digestive
juices, thereby aiding digestion and stimulating the appetite.

Of the various drinks, which are chiefly spices (coffee, tea,
cocoa, alcoholic drinks), cocoa may also be considered as a food,
because it contains much proteid (12$), carbohydrates (13$), and
fat (in cocoa not freed of its fat, 49$). Beer also contains food-
stuffs (proteid up to o. 8j£, carbohydrates 5-6$). but it can never-
theless not be classified as a food, for. taken in large quantities,
the harmful effects of alcohol are manifested. Besides this, the
cost of beer is much too high in proportion to its food value.

Certain sensations — hunger and thirst — may be regarded
as the stimulations for taking up food and drink. (See
Chapter XXVI.)

CHAPTER IX
THE DIGESTION OF THE FOODSTUFFS

BY digestion most of the foodstuffs undergo physical and
chemical changes by which they are prepared for absorption
into the blood. Only a few foodstuffs, e.g. water, salts,
grape-sugar, can become part of our body without any
change. The most 'important alimentary principles, pro-
teids, fats, and many carbohydrates cannot be absorbed in
the form in whch they are furnished by nature.

The digestion proper is preceded by a mechanical tritura-
tion of the solid foods by biting and chewing.

Digestion itself consists of rendering the insoluble or
.slightly soluble and non-dialyzable foodstuffs soluble and
dialyzable. This is brought about by the digestive ferments
which, by hydrolytic splitting up, form smaller molecules
from the large molecules of the native foods. In this
manner proteids are split up into proteoses ; starch into
sugar; fats into glycerin and fatty acid.

The organ in which the digestion is carried on is the
alimentary canal (tractus intestinalis) ; it consists of mouth
and esophagus, stomach, small and large intestine.

1. DIGESTION IN THE MOUTH

i. Mechanical changes of food in the mouth. — The

mechanical processes in the mouth consist of cutting (biting),
chewing, and sucking.

Biting serves to cut off proper portions of the food. The
morsel is ground up more or less by chewing and, being

123

124 HUMAN PHYSIOLOGY

soaked by the saliva, forms a pulp so that the food is soft,
lubricated, and suitable for deglutition.

Biting and chewing are caused by the movement of the
upper and lower teeth against each other.

The lower jaw is raised (turning around a horizontal axis pass-
ing through both limbs of the jaw) by the masseter, temporal and
internal pterygoid muscles of both sides of the head. It is lowered
by the digastric, mylohyoid and geniohyoid. During the lower-
ing of the jaw, the hyoid bone must be fixed; this is performed
by the omo-, sterno-, and thyro-hyoid and the sternothyroid.
The lower jaw is moved forward in a horizontal direction by the
two external pterygoids; to the left, by the right external ptery-
goid; and to the right, by the left external pterygoid. The morsel
is held between the teeth, during chewing, by the buccinator from
the outside and by the tongue from the inside.

The tongue is pulled forward and downward by the genio-
glossus, while it is pulled downward and backward by the hyo-
glossus, and upward and backward by the palato- and stylo-
glossus.

The tongue is composed of vertical, longitudinal, and diagonal
fibres. By the combination of their contractions, it can assume
many varying positions.

Sucking serves to take up liquid food. By the sucking,
a negative pressure is produced in the mouth, and the fluid
to be taken up is thus sucked in.

Sucking is produced in one of two ways :

(a) By inspiration after separating the nasal passage from
the pharyngeal cavity by elevating the soft palate.

(b] After the mouth cavity is separated from the pharyn-
geal cavity by pressing the posterior part of the tongue
against the palate, the lower jaw is depressed and the
tongue is pulled backward and downward (pure mouth-suc-
tion).

The negative pressure in the mouth during pure mouth-suction
may, by repeated sucking, be made as low as 700 mm Hg below
atmospheric pressure.

2. Chemistry of digestion in the mouth. — Digestion in
the mouth only affects starch. This is split up by the ptyalin
of the saliva, the animal diastase, into sugar.

The animal diastase differs from that of the plants (the sugar-

THE DIGESTION OF THE FOODSTUFFS 125

forming ferment of sprouting barley) in that the former is most
active at 40°, while the latter acts most energetically at 60°.

Ptyalin is a proteid-like body. It can be obtained for experi-
ments in digestion from fresh or dried salivary glands by extracting
the gland with water or glycerin.

Ptyalin acts best in neutral solutions. It is rendered in-
active and is destroyed by alkalies and especially by mere
traces of free mineral acids. Organic acids only inhibit its
activity. Ptyalin is destroyed by temperatures above 60°.
Maltose is the chief product in the digestion of starch by
ptyalin, only little dextrose being formed. According to
later researches, the small amount of grape-sugar is not
formed by the direct action of ptyalin upon starch, but is
formed from maltose by the activity of a second ferment,
glucase. Ptyalin itself forms maltose only.

In this formation of maltose from starch, a number of in-
termediate products, called dextrins, are formed. These
dextrins differ from each other in their behavior towards
iodine and are called amylo-, erythro-, and achroo-dextrins,
according as they color blue or red or do not color with
iodine.

The saliva of carnivorous animals contains no ptyalin; in this
case, the saliva only seems to moisten and lubricate the dry food.
Mammals living in the water and not eating dry food have no
salivary glands.

Saliva also serves to moisten and clean the mouth.

3. Deglutition. — By deglutition or swallowing, the chewed
food is moved into the stomach.

The bolus is moved from the anterior end of the tongue
along the hard palate to the anterior pillars of the fauces.
By the stimulation of the sensory nerves ending in the
mucous membrane at this part, a reflex action is produced
which results in a forcible contraction of the mylohyoid and
hyoglossal muscles. By this the bolus is pushed backward
into the esophagus.

In order that food shall only escape backward, the pharyngeal
cavity must be separated from the mouth, nose, and larynx. This
is accomplished as follows:

126 HUM/IN PHYSIOLOGY

The opening into the mouth is closed by the posterior part of
the tongue being pressed against the hard palate and against the
neighboring anterior pillars of the fauces. The nasal cavity is
separated from the pharynx by the elevating of the soft palate (by
means of the levator palati mollis), by the arching of the posterior
walls of the pharynx (by means of the superior constrictors of the
pharynx), and by the meeting of the two posterior pillars of the
fauces at the median line. The opening into the larynx is closed
by the elevation of the larynx by means of the mylohyoid and the
geniohyoid and the digastric, to such an extent that it can be
covered by the root of the tongue and the epiglottis.

The first act of deglutition here described may occur with
so much force that by means of it the food reaches the
stomach. This is especially true for liquids and soft foods.
Only solid and dry foods remain in the pharynx or upper
part of the esophagus till the second step in deglutition
carries them downward.

The second part of deglutition consists of a peristaltic
movement, that is, a constriction of the esophagus beginning
at the top and travelling downward. The pharynx first
constricts by means of its constrictors, then the esophagus
by means of the constriction of the circular muscles. Thus
the parts of the pharynx and esophagus, successively con-
stricted, push the bolus toward the stomach.

The propagation of the contraction from one part of the
esophagus to another does not take place by the direct conduction,
in the muscles, but is dependent upon the central nervous system.
After the esophagus has been cut across, the wave of contraction
is set up in the lower part when it has ceased in the upper
segment.

The innervation of the. muscles of the buccal and pharyngeai
cavities is brought about by :

1. The third branch of the trigeminus: masseter, temporal,,
internal and external pterygoid, tensor palati rnollis, mylohyoid,
anterior belly of the digastric.

2. The facial: muscles of the face, buccinator, posterior belly
of the digastric, levator palati mollis, azygos uvulae.

3. The glossopharyngeal and vagus: stylopharyngeal, con-
strictors of pharynx and muscles of esophagus.

4. Hypoglossus : the tongue-muscles collectively and the genio-
hyoid and thyrohyoid.

The nerve centres which govern the processes of chewing, suck-

THE DIGESTION OF THE FOODSTUFFS 127

ing and swallowing lie in the medulla oblongata. (See Chapter
XVIII.)

2. GASTRIC DIGESTION

i. The movements of the stomach. — Both the cardiac
and pyloric openings of the stomach are generally closed
by the tonic contraction of the sphincters. During the act
of deglutition, the cardiac aperture opens by the relaxation
in the tonus of its muscles when the peristaltic contraction
has reached the lower end of the esophagus. The pylorus
opens and closes to admit part of the contents of the stomach
into the duodenum.

The stomach consists of two parts :

(1) The fundus with feeble muscles.

(2) The antrum with strongly developed muscles. The
two parts can be separated from each other by a sphincter-
like muscle.

Corresponding to the distribution of the muscles, the
movements of the pyloric part of the stomach are much
stronger than those of the fundus. In the antrum, the
pressure caused by the contraction of the muscles may be as
high as 130 mm Hg; the pressure in the fundus only 35 mm.

The movements of the fundus serve to mix the food with
the gastric juice, the movements of the antrum serve to
empty the contents of the stomach into the duodenum.

The length of time during which the different foods remain
in the stomach varies greatly. Fluid and soft foods are
forced into the intestine soon after being swallowed, but
solid food remains for a longer time in the stomach. The
last particles of food have left the stomach 7-8 hours after
a meal.

Even the excised stomach can execute movements. The
normal stimulation for the muscles of the stomach appears
therefore to be due to the nerve plexuses in its walls ; but
the central nervous system influences these movements.
There are motor and inhibitory nerve-fibres for the stomach.
These fibres run in the vagus and sympathetic and their

128 HUMAN PHYSIOLOGY

centres lie in the medulla, the corpora quadrigemina, and
the spinal cord.

Vomiting is the emptying of the contents of the stomach after
the cardiac sphincter has opened. It is brought about mainly by
the contraction of the diaphragm and the muscles in the abdominal
walls, by which the intra-abdominal pressure is increased to such
an extent that vomiting results. To a limited extent the antrum
also takes part in vomiting.

Vomiting is brought about reflexly (stimulation of the sensory
nerve in the stomach by abnormal substances) or by drugs which
directly affect the vomiting centre in the medulla or by psychical
influences (nauseating sights).

2. Chemistry of gastric digestion. — When the food has
reached the stomach it is still further subjected to the action
of salivary ferments (amylolytic period of gastric digestion)
for about half an hour. After this, the secretion of the acid
gastric juice stops the action of the ptyalin. Then the
action of the gastric juice begins.

The active constituents of gastric juice arc pepsin, hydro-
chloric acid, and rcnnin. The gastric jnicc digests protcids,
inverts cane-sugar, and curdles uiilk, but does not act upon
\fats.

(a) Proteid digestion. — Proteid digestion is brought about
by the action of free hydrochloric acid and of the pepsin ; by
means of these the proteids of the food are split up into
albumoses and peptones.

The role of the hydrochloric acid in proteid digestion is
twofold :

First, it causes the proteid body to swell more or less and
thereby facilitates the subsequent action of pepsin.

Secondly, in connection with pepsin it causes a peculiar
splitting of the proteids.

The hydrochloric acid can by itself split proteids into
albumoses and peptones, but to do so the acid must be
concentrated, or it must act at boiling temperature or for a
long time. Pepsin cannot split up proteids without the aid
of hydrochloric acid.

Perhaps the hydrochloric acid is the real splitting agent of the

THE DIGESTION OF THE FOODSTUFFS 129

gastric juice, while the function of the pepsin is to render the
proteid capable of being split up and it therefore only aids the
action of the acid.

The action of the hydrochloric acid is, however, not a fermenta-
tive action, as is the case in the formation of sugar from starch
where a small quantity of acid can split an unlimited amount of
starch. In the proteid digestion, the acid is used up, for it forms
with the digestion products the acid proteoses-chlor-hyd rates and
thus becomes inactive. Pepsin, as ferment, is unlimited in its
action.

Pepsin, a ferment of proteid-like composition, is destroyed
by heating, by strong alcohol, and by small quantities of
free alkali. The last, however, does not act thus in the
presence of undigested proteid, perhaps because the pepsin
unites with the proteid.

To obtain pepsin, extract the mucous membrane of the stomach,
especially that of the antrum, with glycerin or with a 0.2$ to 0.4$
hydrochloric acid solution.

The intermediate products thereby formed successively by
peptic digestion of proteids are:

1. A precipitate formed by neutralizing the solution.
Among the first products of peptic digestion, especially in
that of coagulated proteids, there is present a proteid coagu-
lated by heat, which, however, soon undergoes a still further
change.

2. Primary albumoses, protalbumose, and heteroalbu-
mose, precipitated from neutral solutions by saturation with
NaCl.

3. A deuteroalbumose, which is precipitated from acid
solutions by saturation with NaCl.

4. A deuteroalbumose, precipitated by saturation with
ammonium sulphate.

5. Peptones, not precipitated by ammonium sulphate (see
page 37).

During peptic digestion, not all the proteid is completely
changed to peptone ; the amount of the resulting peptone is,
e.g. in case of the crystallized serum albumin of horse blood,
only about one-half that of the original proteids; the residue
remains in the form of deuteroalbumose.

13° HUMAN PHYSIOLOGY

The individual proteids, including those of vegetable
origin, yield proteoses differing but slightly from each other.

The combined proteids are first split up by gastric juice
into their components ; after this, the proteids thus split off
are digested like simple proteids. Nucleins are not dissolved
by gastric juice; hence, in the digestion of caseinogen, the
insoluble paranuclein remains.

Of the albuminoids, only collagen is digested by pepsin.
It is first changed into its hydrate, gelatin, and from this, by
hydrolytic splitting up, gelatoses, corresponding to proteoses,
are formed.

The process of proteid digestion by gastric juice depends
upon :

1. The amount of free hydrochloric acid, the amount
most favorable for digestion being 0.2-0.4$.

The acidity of the stomach does not indicate the amount of free
hydrochloric acid present because, first, the gastric juice may
contain free organic acids, especially lactic acid, and, secondly,
the proteoses-chlor-hydrate has also an acid reaction (see page 1 29).
Free hydrochloric acid is present in the gastric juice only when it
gives the Giinzburg reaction (see page 95).

As artificial experiments in digestion show, the hydrochloric
acid can be replaced by other acids, but they are all inferior to it.
The lactic acid frequently formed in the stomach by the fermenta-
tion of carbohydrates also has digestive action; it is, however,
not a normal constituent of gastric juice and therefore its part in
digestion is -only incidental.

2. Upon the amount of pepsin. The intensity of the
digestion increases with the amount of pepsin present till it
reaches a certain limit. The increase is proportional to the
square root of the concentration of the pepsin.

3. Upon the kind of proteid present and its power of in-
bibition. Fibrin, which is strongly swollen, is sooner
digested than coagulated white of egg, which swells but little.
Native proteids are more easily digested than the coagulated,
and animal proteid more easily than plant proteid.

4. Upon the temperature. The gastric juice acts best at
37-40° C. At o° digestion stops, and at 80° the pepsin is
destroyed.

THE DIGESTION Oh' THE FOODSTUFFS 131

5. Upon the presence of the products of digestion. All
fermentation processes are hindered and finally arrested by
the accumulation of the resulting products. In peptic diges-
tion, the amount of accumulated proteoses must be very
large before it completely stops digestion. This .influence
of the products of digestion is not felt in the stomach because
the products formed are rapidly removed.

The products of digestion can also hinder the digestion
by uniting with the hydrochloric acid and thereby rendering
it inactive. In this case, free hydrochloric acid is lacking
and the addition of acid starts the digestion again.

6. Salts can inhibit peptic digestion either by preventing
the inhibition or by precipitating the pepsin. This last is
also accomplished by alcohol in strong concentration.

Auto-digestion of the stomach. — A piece of the mucosa of the

stomach heated in 0.2$ hydrochloric acid at 40° C. digests itself.
Why normally the mucous lining of the stomach does not digest
itself has received no satisfactory answer; it probably depends
upon the specific vital character of the epithelial cell of the
mucosa.

(b) The inversion of cane-sugar. — Cane-sugar is inverted
in the stomach, i.e. it is split up by the free hydrochloric
acid into dextrose and levulose.

(c] The coagulation of caseinogen. — The caseinogen of the
milk coagulates in the stomach, previous to its digestion.
This coagulation is brought about by the rennin, which splits
the caseinogen up into casein and a soluble proteid called
whey proteid. Casein unites with calcium, forming an in-
soluble compound, cheese. Hence calcium is necessary for
the coagulation of caseinogen, and coagulation can be pre-
vented by precipitation of the calcium salts, e.g. by oxalates.

Rennin, a ferment of unknown chemical composition, can
act in an acid, alkaline, or neutral medium.

Rennet, used in the manufacture of cheese, can be extracted
from the stomachs of calves.

As to the purpose of milk coagulation, see page 143.

Besides the above-named digestive actions, the gastric
juice has the special function of disinfectant. Pathogenic and

I32 HUMAN PHYSIOLOGY

putrefactive micro-organisms, introduced into the stomach
with the food, are killed and rendered harmless by the
gastric juice. This action is especially due to the free
hydrochloric acid, but also to its acid compounds with
proteoses.

Nutrition can go on normally after extirpation of the
stomach if small quantities of sterilized food are given at
frequent intervals. This has been proven in dogs and man.

Hence it has been concluded that the chief functions of
the stomach are, first, to disinfect the food and, second, to
serve as a reservoir for large quantities of food, which is
given out by the stomach to the intestine in such quantities
as can be quickly digested. The digestive function of the
stomach is, therefore, a secondary affair, seeing that the
pancreatic juice alone is sufficient for the digestion of pro-
teids.

I',. INTESTINAL DIGESTION

i. The movements of the intestine. — During digestion
the walls of the intestine make movements, called the peri-
staltic movements. These consist of periodic constrictions
of the intestine brought about by the contraction of the cir-
cular muscles. This constriction begins at the pylorus and
is propagated to the rectum in the form of a wave. By these
movements the chyme is forced from the pylorus towards
the rectum and at the same time mixed with the digestive
juices of the intestine.

Besides the peristaltic movements, the individual loops of
the intestine make movements to and fro, causing the food
to be mixed with the digestive fluids.

The cause of the peristaltic movements lies in the intestine
itself, for an excised loop of the intestine moves spon-
taneously. If the intestine is stimulated at a certain point,
the contraction begins at this point and spreads itself upward
and downward. The contractions are perhaps called forth
by the nervous plexures found in the walls of the intestine.

THE DIGESTION OF THE FOODSTUFFS 133

Moreover, the peristalsis is influenced by the central
nervous system. The vagus is the motor nerve, and the
splanchnic nerve the inhibitory nerve for the circular muscles.
Stimulation of this nerve brings about inhibition of the
peristaltic movements.

The contraction of the longitudinal muscles of the intestine
produces dilation. The splanchnic is supposed to be the motor
nerve for the longitudinal muscles, while the vagus is the inhibitory
nerve.

2. Chemistry of intestinal digestion. — The food, grad-
ually driven from the stomach into the intestine, continues
to be acted upon by the pepsin as long as free hydrochloric
acid is present. But the free hydrochloric acid is speedily
neutralized by the alkali of the secretions which are poured
upon the food. There are three secretions: pancreatic juice,
bile, and intestinal juice. Of these, the pancreatic juice is
the most important for digestion.

A. Pancreatic digestion. — The pancreatic juice changes
starch to sugar, proteids to peptone, and spl'its neutral fat
into glycerin and fatty acids. These actions are broiigJit
about by three ferments — aniylopsin, trypsin, and steapsin.

1. Action of aniylopsin. — Amylopsin splits up starch in
the same manner as ptyalin of the saliva. The starch forms
successively amylo-, erythro-, and achroo-dextrin, maltose,
and finally grape-sugar. The quantity of grape-sugar
formed is somewhat larger than that formed by ptyalin, per-
haps because the pancreatic juice contains more glucase than
the saliva.

2. Tryptic digestion. — Trypsin splits up proteid. It can
act in an acid medium, but acts best in an alkali medium.
This proteid digestion differs from peptic digestion in the
following particulars :

(a] The proteid digestion by trypsin is carried further than
that by pepsin. Peptic action stops at the formation of
peptones, but trypsin splits some proteids up into leucine,
tyrosine, and aspartic acid (see page 27). The peptones
which can be split up by trypsin are called hemipeptoncs ;

134 HUMAN PHYSIOLOGY

those not capable of such splitting up arc called antipep-
tones.

(b) While pepsin digests collagen but not nuclein, trypsin
digests nuclein but not collagen. Gelatin, however, is
readily digested by trypsin. The gelatin peptones are not
split up by trypsin into amido-acids. Elastin is not digested
by pepsin, but readily by trypsin.

(c) The products of proteid digestion by pepsin, injected into
the blood stream, stop the coagulation of the blood; not so the
products formed by tryptic digestion.

(d) The rotatory power of the collective products formed by
peptic digestion is greater than that of the undigested proteid,
while the rotatory power of the products of tryptic digestion is
smaller.

(e) In the presence of free hydrochloric acid, pepsin digests
trypsin, but in an alkali solution trypsin does not digest pepsin.

Trypsin is not digested by pepsin in the intestine, because the
free hydrochloric acid, in so far as it is not united with the
proteoses, is neutralized by the alkali of the intestinal juices.

During proteid digestion by trypsin the same intermediate
products arise as by peptic digestion. From coagulated
proteids there is formed in considerable quantities a soluble
proteid, coagulable by heat. Protalbumose and heterc-
albumose are not formed, but deuteroalbumose is directly
formed.

To obtain trypsin for experimental work, heat the pan-
creas with highly dilute acetic acid and extract the ferment
with glycerin. Trypsin is not found in the pancreas in the
form of active ferment, but as zymogen. This zymogen is
transformed into the active ferment by dilute organic acids.
The secretion obtained by a pancreatic fistula often contains
only zymogen, which is converted into active trypsin by
coming into contact with the acid chyme.

3. Action of stcapsin. — Steapsin of pancreatic juice is a
ferment which, by hydrolytic splitting up, changes neutral
fats into glycerin and free fatty acids. When alkali carbon-
ate is present in the intestine, soluble soaps are formed from
the fatty acids.

It has not yet been determined to what extent fats arc

THE DIGESTION OF THE FOODSTUFFS 135

split up. Till recently it was maintained that only a small
part of the fat is split up and that the large residue was
emulsified by the soap formed (see page 24) and absorbed
in the form of emulsion. Recently it has been supposed
that all the fat is split up before it is absorbed. After the
extirpation of the pancreas the absorption of fat is decreased.
In this case, however, fats are still split up by putrefaction
in the intestine.

B. The function of bile in the digestion. — -Bile contains no
ferment, hence it does not digest, but aids in the processes
of digestion.

1 . By aiding in neutralizing the free hydrochloric acid.
This stops the action of the pepsin upon the trypsin.

2. By aiding the action of pancreatic ferments.

3. By dissolving the free fatty acids.

Besides this, bile plays an important part in the absorption of
fats (see Chapter X).

Some authors ascribe an antiseptic action to bile, but others
deny this.

C. Digestion by the intestinal juice. — Intestinal juice con-
tains, besides a diastatic ferment, an inverting ferment which
changes cane-sugar into dextrose and levulose. Intestinal
juice also splits up lactose, this not being absorbed as such.
This action of the intestinal juice is supposed to be due to
a ferment called lactase.

The accounts of other ferments in the intestinal juice are
contradictory.

The intestinal juice, by its alkalinity, favors the action of
the pancreatic ferments and, by its mucin, favors the move-
ments of the chyme and the formation of fasces.

4. PUTREFACTION IN THE INTESTINE

In the intestinal canal, especially in the lower part of the
small intestine, processes of putrefaction, due to micro-
organisms, take place. These processes change the con-
tents of the intestine chemically.

136 HUMAN PHYSIOLOGY

The changes brought about by the putrefaction are, in
many respects, similar to those produced by digestion ; in
other respects, they are very different.

From proteids there arise by putrefaction :

1. Albumoses and peptones.

2. Fatty acids, amido-acids, and ammonia; by the putre-
faction of gelatin, glycocoll is also formed.

3. Phenol, paracresol, indol, skatol, phenylpropionic
acid, phenylacetic acid, paraoxyphenyl-acetic acid, paraoxy-
phenyl-propionic acid.

Indol, CgH7N, has the following constitution:

«

\NH/
Skatol, C9H9N:

C.H/C

\ NH

Part of the aromatic products of proteid putrefaction are
absorbed; they are then in part oxidized (indol forming indoxyl,
skatol forming skatoxyl). The aromatic oxy-acids are not
changed, but phenol, indoxyl and skatoxyl are excreted by the
urine as conjugated sulphates.

4. Gases: carbonic acid, hydrogen, marsh gas, and sul-
phuretted hydrogen.

Putrefaction, therefore, like tryptic digestion, forms pro-
teoses and amido-acids from proteids. But by putrefaction
there are also formed aromatic decomposition products
(phenol, oxy-acid, indol, and skatol), which are not formed
by the action of trypsin.

Fats are split into fatty acids and glycerin by putrefaction.
The fatty acids are in part still further decomposed into the
lower fatty acids.

From the carbohydrate, alcohol, lactic, acetic, and suc-
cinic acids are formed by putrefaction. Part of the starch is
first changed to sugar. The indigestible cellulose is also
acted upon by putrefaction ; this, however, does not form
sugar but organic acids (acetic, valerianic acid, etc.), car-
bonic acid, and methane. By this decomposition of the

THE DIGESTION OF THE FOODSTUFFS 137

cellulose, the food inclosed by it can be acted upon by the
digestive fluid.

Concerning the putrefactive decomposition of the constituents
of the digestive fluids, the following may be said: dyslysin is
formed from cholalic acid; stercobilin, the coloring matter of
faeces, from bile pigments.

5. THE FORMATION OF FAECES AND THE UTILIZA-
TION OF FOODSTUFFS

i. Composition of faeces. — The undigested, unabsorbed
residue of the food and the useless constituents of the ali-
mentary secretion are called faeces and are discharged
through the anus.

The fseces contain :

1 . Undigested and unabsorbed constituents of the food,
such as remains of plants, keratin, nuclein, muscle-fibres,
connective tissue, lumps of casein, starch granules, fat,
haematin.

2. Residue of digestive juices, e.g. cholalic acid, dyslysin
formed from bile acids, bile pigments, cholesterin, mucin.

3. Cast-off epithelial cells and their decomposition prod-
ucts.

4. Products of putrefaction: skatol, indol, iron sulphide,
fatty acids. Along with the faeces, the gases formed by
putrefaction (marsh gas, sulphuretted hydrogen) are dis-
charged.

5 . Mineral matter of the food and of the intestinal secre-
tions.

Finally, there are present in the fseces parasites of various
kinds.

The reaction of the faeces may be neutral, acid, or akaline.
Its odor is due to the skatol, indol, and other volatile sub-
stances. The color is generally light or dark brown ; the
pigment is the stercobilin produced by putrefaction from
bilirubin.

In the large intestine the faxes become solid by the
absorption of water, and here it is formed into balls.

I38 HUMAN PHYSIOLOGY

The amount of fseces daily discharged is about 120—150
grams, containing 30-37 grams solids.

2. Utilization of foodstuffs. — As the faeces contain un-
digested food, not all the food taken into the alimentary
canal is utilized by the body. The amount utilized by the
body can be found by subtracting the undigested food present
in the faeces from all the food taken by the mouth. As the
amount of undigested food in the faeces has never been
definitely determined, no accurate figure of the amount of
food absorbed can be given.

The amount absorbed must be taken into consideration in
formulating a diet. The animal foods are better absorbed
than the vegetable foods. There are absorbed :

Proteid Fat. Carbohydrate.

of meat and eggs 97$ 95$

" milk 89-99$ 95-97$ 100$

" white bread ....... 78$ 99$

" black bread c . 68-78$ 89$

" potatoes. . . 68$ 92$

" turnips 61$ 82$

The reasons why vegetable foods are so poorly absorbed
are :

(1) The food in vegetables is often inclosed in cellulose
membranes which prevent the action of digestive juices
upon the food. Hence vegetable foods are the better
absorbed in proportion as they are free from the cellulose
membrane in their preparation.

(2) The cellulose stimulates, perhaps mechanically, the
peristalsis. Vegetable foods are therefore more quickly
carried through the intestine than the animal foods ; in fact,
so rapidly that they are discharged as faeces before they have
been fully acted upon and absorbed.

(3) Defalcation. — The anus is kept closed by the tonic
contraction of the sphincters ani, internus and externus.
The action of the external sphincter is increased by the
voluntary contraction of the levator ani, which is placed like

THE DIGESTION OF THE FOODSTUFFS 139

a sling around the rectum. During defalcation the tonus of
the sphincters is inhibited, thus allowing the faeces to pass
out. The defalcation is produced by the peristalsis of the
rectum, aided by abdominal pressure. The muscles produc-
ing this pressure are the diaphragm and the muscles of the
abdominal walls.

The centre of defalcation is situated in the lumbar cord.
It is stimulated reflexly from the rectum. The inauguration
of the reflex depends, to a certain extent, upon the will.
The nerves going from the centre to the muscles of the
rectum run through the hypogastric plexus and the sympa-
thetic (ganglion mesentericum posticus) and the nervi
erigentes. The first-named nerves are supposed to be motor
nerves for the circular muscles and inhibitory nerves for the
longitudinal muscles; the last-named are supposed to be
motor nerves for the longitudinal muscles and inhibitory
nerves for the circular muscles.

Defalcation takes place in man at least once a day.

CHAPTER X
ABSORPTION AND ASSIMILATION OF FOODSTUFFS

1. GENERAL REMARKS ABOUT ABSORPTION AND
ASSIMILATION

UNDER absorption we include the processes whereby the
dissolved foodstuffs and the emulsified fats are taken up from
the mucous lining of the stomach and intestine and are
brought directly or by means of the lymphatics into the
blood, by which they are carried to the organs and tissues,
of the body.

By assimilation we understand the processes which the
absorbed foodstuffs undergo till as constituents of the cells
and tissues they are consumed in the activity of the tissues.

As the insoluble and undialyzable food is rendered soluble
and dialyzable by digestion, it is probable that osmosis-
of the soluble substance plays an important part in absorp-
tion. Still there are certain facts about absorption which
cannot be explained by the laws of osmosis as known to us
at present. Absorption often takes place contrary to the
laws of osmosis. On the one hand, water is absorbed from
a sodium chloride solution placed in the intestine even though
of higher osmotic pressure than the blood, whereas, accord-
ing to the laws of osmosis, water ought to pass from the
blood or lymph into the intestine. On the other hand,
undialyzable substances, like proteid and emulsified fat, are
taken from the intestine by the blood.

The force which causes this absorption contrary to the

140

ABSORPTION AND ASSIMILATION OF FOODSTUFFS 141

laws of osmosis is due to the activity of the epithelial cells.
This view is supported by the fact that when the intestinal
epithelial cells are rendered functionless by sodium fluoride
(which does not destroy the cells anatomically), absorption
follows the lawr of osmosis.

The seat of absorption is chiefly the intestine ; in a less
degree, the stomach. Pure water is not absorbed from the
stomach; on the contrary, wrater is passed by the mucous
lining into the stomach. Aqueous solutions of salts, sugar,
and peptones are absorbed when they are very concentrated.
Absorption from the stomach is favored by table-salt and
spices, such as mustard, peppermint, pepper. Alcohol and
other narcotics also favor absorption because they paralyze
the resistance which the epithelium of the stomach offers to
the absorption of foodstuffs.

Most of the absorption takes place in the small intestine,
where the surface for absorption is very large. The villi of
the mucous membrane of the intestine increase the absorp-
tion surface to twenty-three times what it wrould be if no
villi were present. One sq. cm. of the intestinal mucosa
contains about 2500 villi.

The epithelial cells of the intestinal mucosa are cylindri-
cal. The free surface of these cells is striated. Each villus
contains a central lacteal, and between this lacteal and the
outside border of the villus are the blood vessels, a mass of
capillaries, and the afferent and efferent vessels. The lac-
teal is surrounded by smooth muscle-fibres, by the contrac-
tion of which the villi are shortened, the lacteal is pressed
together, and the contents emptied into the lymph vessels.

In the large intestine also considerable absorption takes
place. Among other things water is here absorbed whereby
the contents of the intestine become more solid. Food is
also absorbed in the large intestine when, in soluble form,
it is forced through the anus into the intestine as nutritive
clyster.

The path of the absorbed food from the intestine is two-
fold: (i) The portal vein; (2) the lymph vessels.

142 HUM '/IN PHYSIOLOGY

Water, salts, sugar, and protcids arc absorbed by tJie
portal vein; fats are absorbed by the lyinpltatics. After the
water, salts, and sugar have traversed the epithelial layer,
they pass into the closely adjoining blood capillaries.
Thence they are carried with the blood through the portal
vein. When great quantities of fluids have been taken, a
part may reach the lymph vessels. It has been observed in
animals that the lymph in the thoracic duct is increased
only when a large quantity of water is imbibed, and that the
carbohydrates in the lymph are increased only during the
absorption of a large quantity of concentrated sugar solution.
The blood of the portal vein, however, always contains,
during absorption of carbohydrates, more sugar than arterial
blood. Observations upon human beings with thoracic duct
fistula, from which all the lymph from the intestine flows,
show that the lymph contains at best only traces of the
absorbed sugar.

That the absorbed proteids are carried through the portal
vein is proven by the facts that ligaturing the thoracic duct
does not interfere with the proteid nutrition and metabolism,
and that the lymph flowing from a thoracic duct fistula, as-
mentioned above, shows no increase of proteids during their
absorption.

Fats, on the other hand, are mostly absorbed by the
lacteals. During the absorption of fats the lacteals and the
thoracic duct appear white, because of the milky turbulence
due to the absorbed emulsified fat. But as all the fat eaten
cannot be demonstrated in the lymph flowing from the
thoracic duct or from a chylus fistula during the absorption
of fat, it has been assumed that part of the fat is absorbed
by the blood vessels.

2. ABSORPTION AND ASSIMILATION OF PROTEIDS

Before proteoses are absorbed into the blood, they undergo
a change in the wall of the intestine. The blood of the
portal vein and the lymph contain no proteoses. If proteoses

ABSORPTION AND ASSIMILATION OF FOODSTUFFS 143

are injected into the blood, they are rapidly excreted by the
kidneys.

The change from proteoses to simple proteids takes place
in the epithelial cells of the intestine, for the native proteids
of the body are increased when no other proteids than pro-
teoses are given in the food. Hence the real body proteid
must have been formed from the proteoses of the food.

If a solution of proteoses is heated at body temperature with
the fresh mucous lining of the intestine, the proteoses gradually
disappear without the further formation of decomposition products.
This supports the view that the proteoses are changed back to
native proteids.

Solutions of native proteids, acid and alkali albumin can
also be absorbed as such without previous digestion. It has
been observed that such proteids, placed in an isolated loop
of intestine free from ferment, are rapidly and completely
absorbed without albumoses and peptones having been
formed. These proteids, injected into the blood are
assimilated and used by the body ; this, however, is not true
of caseinogen, egg albumin, and haemoglobin, for they are
rapidly excreted by the kidneys if injected into the blood.

Large quantities of egg albumin solution taken into the
stomach can also be absorbed without previous digestion,
but are then excreted by the kidneys. Caseinogen and
haemoglobin are precipitated in the stomach and are there-
fore not absorbed without digestion and the transformation
into new proteid in the intestinal wall. This perhaps ex-
plains the meaning of the caseinogen coagulation by rennin,
for, if the caseinogen was not precipitated, it might be
absorbed as such and then be excreted by the kidneys.

Many soluble proteids can, therefore, be absorbed and
assimilated and used in the body without being digested or
changed ; others, on the contrary, must first be digested.
The object of digestion is therefore, first, to render insoluble
proteids soluble and, secondly, to change the proteids which
are soluble but cannot be assimilated to proteids which can
be assimilated.

144 HUMAN PHYSIOLOGY

Proteids which are soluble and can be assimilated are,
without doubt, also digested, but the extent of this digestion
cannot be stated. The digestion of proteids capable of
assimilation is, however, of real significance, since their rate
of absorption is thus increased.

Absorbed proteids reach the blood, most likely, chiefly in
the form of albumin, as the quantity of serum albumin of the
blood is increased by the eating of proteids.

Concerning the further history of proteids and assirrilation
nothing is known.

3. ABSORPTION AND ASSIMILATION OF FATS

From the fatty acids or soaps and glycerin formed by the
splitting up of fats during digestion, neutral fats are again
formed in the mucosa of the intestines. Even if fatty acids
or soaps are eaten, neutral fat is present in the lymph ; in
this case the glycerin necessary for the formation of neutral
fats must have been formed in the intestinal wall itself. If
a mixture of soap and glycerin is heated with the intestinal
mucous membrane, neutral fats are also formed. This forma-
tion of neutral fats takes place in the epithelial cells. During
the digestion of fats the epithelial cells of the intestine arc
filled with fat droplets of various sizes.

But the fat found in the epithelial cells is not necessarily
derived from the union of the fatty acid and glycerin taking
place in these cells ; for neutral fats in the emulsified state
may be taken up by them directly.

The opinion is current that most of the fat is absorbed in
the emulsified condition, and that only such a quantity of fat
is split up as is necessary to furnish the fatty acids or soap
needed for this emulsification. But the correctness of this
view is doubtful because the other necessary condition for
emulsification — the alkaline reaction of the contents of the
intestine — is frequently wanting. The contents of most of
the upper part of the small intestine have an acid reaction
due to free fatty acids ; yet here fats are also absorbed, as is

ABSORPTION AND ASSIMILATION Oh' FOODSTUFFS 145

shown by the milky contents of the lacteals. Hence it is
difficult to decide in how far the splitting up and emulsifica-
tion of fats take place.

The absorption of emulsified fat is supposed to be brought
about by the active movements of the striated border of the
epithelial cells.

The absorption of fats is aided by the bile. Animals with
a biliary fistula absorb but little of the fat eaten. This favor-
able action of bile is supposed to be due to the fact that it
dissolves free fatty acids and the insoluble calcium and mag-
nesium soaps, and that the striated border of the epithelial
cells is, by the bile, rendered permeable for the emulsified
fat. Both these actions are attributed to the bile salts.
The soda of the bile also aids in the emulsification of fats.

If, by pancreatic extirpation, the steaptic digestion is pre-
vented, the amount of fat absorbed is greatly reduced.
This, however, is not true for the fat of milk, for this is
already in a finely emulsified condition.

From the epithelial cells the emulsified fat is transferred
to the lymph and with this is carried through the thoracic
duct into the blood. The fat, in so far as it is not directly
oxidized, is stored up in the cells of the adipose tissues of
the body.

The amount of fat in the blood is somewhat greater during
fat absorption than during fasting. During starvation the
amount of fat in the blood is also increased, for then the fat
stored up in the tissues is transported by the blood to the
place of combustion.

Immediately after a meal rich in fat, large quantities of
fat appear in the liver cells (physiological filtration of fat),
which disappear after a short time.

4. ABSORPTION AND ASSIMILATION OF CARBO-
HYDRATES

The monosaccharides are carried by the portal vein to the
liver without having undergone any change in the walls of
the intestine.

146 HUMAN PHYSIOLOGY

Cane-sugar and lactose are generally not absorbed as such, but
are split up into their simple sugars. Only when they are taken
in very large quantities are they absorbed as such into the blood,
but are then excreted by the kidneys.

In the liver, the monosaccharides are changed to glycogen
and stored up in this form (see page 23). The object of
this glycogen formation is to prevent the sugar from too
great accumulation in the blood ; for if the percentage of
sugar in the blood rises above a certain limit (0.2$), the
excess is excreted by the kidneys.

The per cent of sugar in the portal vein during absorption
of carbohydrates is greater than that in arterial blood or in
blood from the hepatic vein.

Glycogen can be formed from dextrose, levulose, and
galactose. The glycogen formed from levulose and galactose
is identical with that formed from dextrose. When glycogen
is formed from levulose and galactose, they are first changed
to dextrose, for in the splitting up of glycogen only dextrose
results.

The amount of glycogen in the liver depends upon the
nutrition and upon the amount of material used up by the
body. After a long fast and also after severe muscular work
and strong cooling of the body, the liver is free from gly-
cogen. After a meal rich in carbohydrates the liver of a
rabbit contains as much as \j% glycogen. In the liver of a
criminal executed shortly after a meal, 6fc glycogen was
found. A liver free from glycogen is small and has a dark
brown color, while the liver rich in glycogen is large and.
has an ochre color. A liver rich in glycogen may weigh
three times as heavy as one poor in glycogen ; this is not
only due to the larger amount of glycogen, but also to the
large amount of other solids and of water present.

The glycogen is stored up in the cells in the form of flakes. It
can be obtained from the liver by cutting the liver into small pieces
and boiling in water to which a little acetic acid has been added.
By this the proteids are coagulated and the glycogen is dissolved,
forming an opalescent solution from which it may be precipitated
by alcohol.

ABSORPTION AND ASSIMILATION OF FOODSTUFFS 147

When needed, the glycogen in the liver is again trans-
formed into dextrose which is carried out by the venous
blood to the tissues. At this time the per cent of sugar in
the blood of the hepatic vein is greater than that in the
arterial blood or blood from the portal vein. Both the for-
mation of glycogen and its reconversion into sugar are
brought about by the liver cells.

Carbohydrates in the form of glycogen are also stored up
in the muscles, and are used up when needed, e.g. during
muscular activity. The muscle-glycogen is supposed not to
be identical with that formed in the liver. At all events the
glycogen of the muscles is not derived as such from the
liver.

When the carbohydrates in the food are present in excess,
the body, by reduction and synthesis, forms fat from them
and thus stores them up.

In diabetes mellitus the glycogenic function of the liver
is disturbed. This causes sugar to accumulate in the blood
to such an extent that it is excreted by the kidneys. We
can discriminate between two forms of diabetes, a mild form,
in which sugar appears in the urine only when carbohydrates
are eaten, and a severe form, in which sugar is excreted even
if no carbohydrates are eaten. In the latter case the sugar
is derived from the proteids. Nothing is positively known
concerning the immediate cause of diabetes. Artificial
diabetes may be produced :

1 . By the so-called diabetic puncture (Piqure) whereby a
part of the medulla at the lower end of the calamus scrip-
torius is destroyed. This seems to prove that the glycogenic
function of the liver is dependent upon the central nervous
system.

2. By extirpation of the pancreas (see Chapter XI).

3. By various poisons: phloridzin, curare, phosphorus,
corrosive sublimate.

The amido-acids (leucine, tyrosin, etc.) formed from the hemi-
peptones by pancreatic digestion are also absorbed, and in the liver
they are changed to urea.

I48 HUMAN PHYSIOLOGY

The products of putrefaction, phenol, aromatic oxy-acids, indol
and skatol are also absorbed in part, but are excreted by the.
kidneys (see pages 51, 104 and 136).

Besides the products of digestion of foods, some of the con-
stituents of the digestive fluids are absorbed, e.g. the bile
salts, which, arriving at the liver, stimulate the bile secre-
tion. The digestive ferments, pepsin and ptyalin, when
absorbed, are excreted by the kidneys, while trypsin and
steapsin are destroyed in the blood.

According to another view, the ferments excreted by the
kidneys are not derived from the intestine, but are absorbed,
in the form of zymogens, by the blood from the glands
between the periods of digestive activity.

Other mucous membranes, besides those of the stomach
and intestine, are able to absorb dissolved substances, but
such absorption is of no physiological importance.

The skin can absorb small quantities of certain substances.

Subcutaneous injection of foodstuffs. — Many foods can
be used by the animal economy when, in proper form, they
are directly introduced into the tissue fluids. This is true in
case of subcutaneous injection of native albumin, fat, or
dextrose.

CHAPTER XI

THE CHANGES OF BLOOD IN THE ORGANS. INTERNAL

SECRETION

FROM what has been said in the foregoing chapters, it
follows that the blood streaming through an organ is changed
not only in respect to its gases but that it must undergo
other changes as well. In the organs in which the physio-
logical combustion takes place, e.g. in the muscles, the
blood supplies the material for this combustion and acquires,
besides the carbon dioxide, other products of combustion,
especially those containing nitrogen. In the glands the
blood loses substances from which the secretions are formed ;
in the walls of the intestine it takes up the absorbed foods ;
in the liver and in the adipose tissue it either deposits the
carbohydrates and fats or, if necessary, takes them up.
Moreover, the 'blood as a tissue (see page 52) has its own
metabolism, by which it is chemically changed. The above-
mentioned changes in the blood have, in some cases, been
demonstrated. But in most cases a difference cannot be
detected, because the amount of the substance given up or
acquired by the blood in flowing through an organ is so
small in proportion to the amount of blood flowing to and
from that organ that it lies within the limits of error of
observation.

Besides the changes in the blood which we can under-
stand from the known physiological properties of the organ,
it undergoes still other changes, concerning the nature and
significance of which very little is known. Many organs
appear either to alter deleterious substances found in the

149

150 HUMAN PHYSIOLOGY

blood, by changing them into harmless products, or by
forming and giving up to the body substances which influence
either the metabolism or act upon the nervous or muscular
system. This process is called "internal secretion," since
these organs throw their products into the blood.

Among the organs which have an internal secretion are
all the blood glands, the thyroid and suprarenal glands, the
liver, the pancreas, and perhaps the testes.

Among the blood glands are also classed the spleen and thymus
gland, whose function is not so much a secretion as the formation
and destruction of blood corpuscles (see pages 88 and 89).

I. The thyroid gland. — The thyroid gland contains in its
connective tissue many completely closed vesicles. The
walls of these vesicles are formed by a single layer of
cuboidal cells and the vesicles are filled with a " colloid "
substance. The thyroid gland must be regarded as a true
ductless gland, the cuboidal cells being the secreting gland-
cells; the colloidal contents of the vesicles, the secretion.
The contents of the vesicles are emptied into the lymph
spaces between the vesicles and are thus carried to the
blood.

After the thyroid gland has been excised for goitre, a
series of severe disturbances has been observed which sooner
or later end in death (cachexia strumipriva). Diseases of
the nervous system (diminution of psychical functions,
idiocy, and motor and sensory paralysis or spasms), degen-
eration of the fiver and kidneys, disturbances in metabolism
and in the regulation of body heat set in. These phenomena
are also present during disease of the thyroid gland, when
oedamentous swelling of the skin and idiocy are especially
marked (myxcedema). In dogs, extirpation of the thyroid
gland produces death in a few days, preceded by strong
spasms and severe disturbance in nutrition. In rabbits,
extirpation of the thyroid is generally not fatal, but leads to
changes in metabolism, myxcedemous swelling of the skin,
scaly eruptions, and shedding of the hair.

The injurious effects of extirpation or disease do not appear

INTERNAL SECRETIONS 151

when a small part of the gland is retained or when the
thyroid gland is transplanted to the peritoneal cavity or when
fresh or dried thyroid glands are given by mouth. The
abnormal enlargement of the thyroid (goitre) can also be
relieved by feeding on thyroid glands.

One of the most striking effects of the therapeutical use of
thyroid preparation is the rapid fall in body weight and the
disappearance of body fat. This loss of weight is due, as
has been shown by experiments in metabolism, partly to
the withdrawal of water from the tissues, the water in the
urine being increased, and partly by the not inconsiderable
increase in combustion. By feeding a rabbit sufficiently with
thyroid glands, the combustion processes can be doubled.
The combustion of proteid, is, however, little affected as
long as non-nitrogenous material, especially fat, is present.

The thyroid gland is therefore indispensable for life.
Most likely its importance lies in the fact that it produces
one or more substances which are absolutely essential for the
normal course of life's processes. An excess of these sub-
stances produces severe disturbances in the nervous system
and metabolism, and can also produce death. From the
thyroid gland there has been isolated a substance containing
iodine, thyroiodin, which is believed to be the active principle
of the gland, for iodine has a certain therapeutical action
upon hypertrophic thyroid glands. But, as all thyroid glands
do not contain this substance, and as thyroiodin does not
show all the actions of the thyroid gland, we can hardly
regard it as the active substance.

The thymus is supposed to have the same function as the
thyroid gland, for feeding on thymus is said to have the same
result as feeding on thyroid glands.

II. Suprarenal capsules. — The suprarenal capsules con-
sist of cellular parenchyma surrounded by connective tissue
capsules. The parenchyma forms a clear cortical and a dark
red medullary portion. In both the cortical and the medul-
lary portion numerous nerve elements (non-medullated nerve
fibres, sympathetic ganglionic cells) are present. Because

152 HUMAN PHYSIOLOGY

of this abundance of nerve elements, the suprarenal capsules
have been regarded as nervous organs for the inhibition of
peristaltic movements of the intestine.

As extirpation of the suprarenal capsules results in a gen-
eral paralysis and finally death, they must be regarded as
vital organs. The injection of an aqueous extract of supra-
renal capsule is said to remove the effects of extirpation.
This aqueous extract contains two substances, whose chemi-
cal nature is not yet known. Of these the one causes a
considerable increase in blood pressure, while the other can
decrease the pressure but works more feebly than the first.
This increase in blood pressure caused by the first-mentioned
substance is due to a general contraction of the small
arteries. The anatomical part upon which this substance
acts lies in the walls of the blood vessel itself. It paralyzes
the central nervous system. It stimulates not only the
muscles of the blood vessels but also the skeletal muscles ;
hence its function seems to be to increase the tonus of the
muscles, both of the skeletal and of the blood vessels.

Concerning the manner in which the second substance
acts nothing certain has yet been determined.

Pathological changes in the suprarenal capsules are followed
by an abnormal coloring, bronzing, of the skin (which is also said
to follow the extirpation of the suprarenal capsule). This is called
Addison's disease.

The active substances of the suprarenal capsule extract are
rendered inert by passing them through the liver.

III. The liver. — Besides functioning in the

(1) Secretion of bile (see page 99),

(2) formation of glycogen (see page 146), and

(3) breaking up and formation of red blood corpuscles

(pages 54 and 100),

the liver also has the important function of

(4) changing the ammonia salts, produced by proteid

metabolism, into urea (in mammals) or into uric
acid (in birds and reptiles). (See pages 45 and

47.)

INTERNAL SECRETIONS 153

If the liver is isolated from the circulation -by joining the
portal vein directly with the inferior vena cava, the urine
excreted contains less urea and more ammonium salts than
normally and the animal shows symptoms of poisoning
characteristic of the ammonium compounds. Extirpation
of the liver in birds is followed by the appearance of
ammonia and lactic acid in the urine instead of uric acid.

The object of this change which the ammonia salts
undergo in the liver seems to be to change the poisonous
ammonia into harmless substance.

The liver, inserted as a filter between the capillary network of
the portal vein, acts upon the substances absorbed from the intes-
tine. In the first place, it changes the injurious products of
proteid putrefaction, phenol, skatol, indol, into the harmless
ethereal sulphates which are excreted in the form of alkali salts.
In the second place, the liver retains the vegetable and animal
poisons (alkaloids) incidentally introduced into the alimentary
canal ; these poisons are destroyed and excreted with the bile. In
the third place, metallic poisons (arsenic, antimony, lead) are
deposited in the liver and the body is thus shielded from their
injurious effect. These poisons are also finally excreted.

The anatomical relation between the spleen and the liver (the
splenic vein is a branch of the portal vein) points to a physiological
relation between these two organs. Perhaps the hoemoglobin set
free in the spleen by the breaking down of the red blood corpus-
cles is decomposed in the liver.

In the rabbit many lobes of the liver can be removed without
any disturbance being noticed. The extirpated lobes are soon
replaced.

IV. The pancreas. — Besides the secreting of pancreatic
juice, the pancreas plays an important part in the metabolism
of carbohydrates. After extirpation of the pancreas the
carbohydrates are no longer properly oxidized in the body
and hence are largely excreted with the urine (pancreatic
diabetes). If a small part of the pancreas is left, no diabetes
results. On the other hand, injection of pancreatic juice or
feeding with pancreas does not stop the diabetes, but in-
creases it. Extirpation of the pancreas causes the liver to
lose its power of forming glycogen, and the tissues their
power of oxidizing sugar.

154 HUMAN PHYSIOLOGY

V. The testes. — In addition to their function as repro-
ductive organs, the testes stand in close connection with the
whole body. This connection is, no doubt, brought about
by substances furnished by the glands to the blood, which
modify the vital processes. Extirpation of the testes (castra-
tion) in a boy is followed by disturbances in development.
The voice does not change at puberty, the muscles remain
soft, and there is no development of manly strength and
character. Also in adult man, castration, or premature
atrophy of the testes, is followed by disturbances in the
nervous system and psychical life. It is said that subcu-
taneous injection of testes-extract increases manly strength
and thereby increases the bodily and psychical well-being.
Nothing is known concerning the nature of the active sub-
stance.

Functions of a similar nature to those of the above-described
organs have been attributed to the ovaries, prostate, hypophyses,
and kidneys, but nothing certain is known about them.

CHAPTER XII
METABOLISM

WHILE we have thus far considered the individual sub-
stances taken up and cast out by our body and have
explained their importance, we shall now treat of the
balance, or the comparative composition of the quantities of
the substances taken up and cast out by the body collec-
tively. This balance not only gives us the extent of meta-
bolism, but also shows us the relation and the use of each
foodstuff to the animal economy. At the same time we can
thereby learn how a person can best support himself with
the most appropriate food at the least expense and how to
bring his body to a desired state of nutrition. Upon the
results of this balance of metabolism is based the practical
science of dietetics.

1. METHODS OF INVESTIGATION IX METABOLISM

To strike a balance of nutrition, we must know the quan-
tity taken up and given off.

The substances taken up are food and the inhaled oxygen.

The substances cast out of the body are found in the
urine, faeces, sweat, expired air; smaller amounts in the
sebum of the skin, in the cast-off horny epithelium, hairs,
nails, at times in the menstrual blood, milk, and semen.'
Of these, as a rule, only those present in the urine, faeces,
and expired air are taken into account in the balance of
nutrition. The others are present in such small quantities

i55

156 HUM4N PHYSIOLOGY

that they do not need to be considered or are excluded by
the condition of the experiment.

The ideal experiment in metabolism would be to estimate
quantitatively each individual constituent of the incomings
and outgoings and to use the results in striking the balance
of nutrition. But this is impossible because of unavoidable
difficulties in the methods of investigation. But to form a
correct conception of the extent and nature of the metabol-
ism, it is sufficient to know the amount of some of the con-
stituents or even some of the elements of the income and
outgo. Of these elements the most important are the
carbon, nitrogen, the oxygen of inhaled air, and frequently
the sulphur and phosphorus.

The nitrogen both of the income and outgo can be
directly determined by Kjeldahl's method, by which the
nitrogen of the substance to be analyzed is changed, by
boiling with concentrated sulphuric acid and mercury, into
ammonia, and as such it may be measured.

The carbon of the income and of the urine and feces is
determined by analysis. The expired carbon is calculated
from the amount of carbon dioxide exhaled.

The inhaled oxygen is either determined directly from the
amount of oxygen taken from the respired air or calculated
from the other data of the balance of nutrition.

The taking up of oxygen and the giving off of carbon
dioxide is called '"respiratory metabolism."

For investigating the respiratory metabolism, we may use
the apparatus of: (i) Pettenkofer-Voit, (2) Regnault-Reiset,
or (3) Geppert-Zuntz.

By the Pettenkofer-Voit apparatus the gaseous outgo of
carbon dioxide and water vapor is determined directly. This is
done as follows: A person breathes in a hermetically sealed
chamber. The percentage of carbon dioxide and water vapor of
the air inhaled is known, and the amount of respiration is measured
by a gasometer. The increase in carbon dioxide and \vater vapor
in the expired air is determined by taking an accurately measured
quantity of air from the chamber and passing it through a weighed
quantity of sulphuric acid and through potassium hydrate, the one

METABOLISM 157

retaining the water, the other the carbon dioxide. From the
increase in weight of the sulphuric acid and potassium hydrate,
the amount of water and carbon dioxide given off by the person
can be calculated.

The inhaled oxygen can be found indirectly as follows: The
sum total of the income (food -f oxygen) and the body weight at
the beginning of the experiment must be equal to the sum of the
outgoings and the body weight at the end of the experiment.
Hence

Oxygen = (final weight -f- outgoings) — (initial weight -(- food).

For this calculation the weight of the urine, faeces, and food,
and also that of the body at the beginning and at the end of the
experiment, must be determined.

In the respiratory apparatus of Regnault and Reiset, the inhaled
oxygen is measured directly. It consists of an air-tight chamber,
which is supplied from the outside with pure oxygen only, while
the carbon dioxide formed is absorbed by the potassium hydrate.
This causes a decrease in the volume of gas in the chamber, and
hence new quantities of oxygen are forced into the chamber.
The volume of oxygen used is thus determined, while the potas-
sium hydrate holds all the carbon dioxide.

While the calculation of the respiratory metabolism in the above-
described methods includes the gas-exchange of the skin, by the
method of Geppert and Zuntz the gas-exchange of the lungs only
is determined. In this, the experimenter does not breathe in a
closed chamber, but, the nose being closed, he breathes through
a closed mouthpiece which is connected with the so-called
M tiller's valves which separate the inspired from the expired air.

By this method also, the oxygen taken up and the carbon
dioxide given off is determined directly, for, in measured quanti-
ties of inspired and expired air, the oxygen and carbon dioxide are
determined by gas analysis. As the amount of air inhaled and
exhaled is measured by a gasometer, the total amount of oxygen
taken up and of carbon dioxide given off can be calculated.

Occasionally it may be of interest to know the changes in
the sulphur, phosphorus, and the salts. The sulphur and
phosphorus of the income are changed to sulphuric acid
and phosphoric acid by oxidation, and, as such, they are
estimated. In the same way the sulphur and phosphorus
of the faeces may be determined. In the urine the sulphur
and phosphorus are already oxidized to sulphuric acid and
phosphoric acid.

158 HUMAN PHYSIOLOGY

The salts of the income and outgo are determined in the
ash.

The water is generally accounted for as such in the
balance of nutrition.

To be of any value in judging the metabolism of the body,
the experiments on metabolism must be carried on for an
extended period. Unless otherwise indicated, the results of
such experiments are calculated upon a basis of twenty-four
hours.

2. THE VALUE OF THE RESULTS OF EXPERIMENTS
IN METABOLISM

Determination of the carbon furnishes the basis for study-
ing the history of all the organic foodstuffs in the body. If
carbon equilibrium is obtained, i.e. if as much carbon is
taken up as is given off, as great a quantity of organic sub-
stances is consumed in the body as is taken up. If more
carbon is taken up than is given off, the body stores up
organic substances ; but if more is given off than is taken up,
the body loses some of its organic constituents.

Determination of the nitrogen affords us information as to
the proteids in the body, for all the nitrogen of the income
is contained in the proteid. As the proteids contain on the
average \6% nitrogen, the amount of nitrogen found, multi-
plied by 6.25, gives the corresponding amount of proteid.
If the amount of proteid decomposed in the body is equiva-
lent to that taken up, the body is in nitrogenous equilib-
rium. If more nitrogen is taken up than is given off, flesh
is formed. But if the body gives off more nitrogen than it
takes up, it loses some of its proteids.

The proportion of the nitrogen to the carbon in the pro-
teids is as I : 3.3. From the estimated nitrogen of the in-
come and outgo, it can be calculated, by means of these
figures, how much of the carbon of the income and outgo
is derived from proteids. If the amount of carbon derived
from the proteid is subtracted from the whole quantity of

METABOLISM 159

carbon in the income and outgo, the remainder will indi-
cate the amount of carbon derived from the non-nitrogenous
fat and carbohydrates. We can thus determine how much
non-nitrogenous foodstuff is consumed in the body and
whether the body has increased or decreased in non-nitro-
genous substances.

Determination of tJic inhaled oxygen is of importance in
understanding the metabolic processes, for in warm-blooded
animals the amount of inhaled oxygen is a measure of the
extent of combustion taking place in the body. From the
amount of oxygen consumed, it can also be calculated how
much hydrogen, besides the carbon, is oxidized in the body.

In cold-blooded animals the estimation of oxygen is of little
value, as the oxygen inhaled is not directly used up, but is stored
up for a longer or shorter time, because these animals can live for
some time in an atmosphere free of oxygen. Warm-blooded
animals, on the contrary, do not store up oxygen to any great
extent and can therefore endure the lack of oxygen for but a few
minutes. An exception to this are the warm-blooded hibernating
animals, which appear to be able to store up, during the period of
activity, a considerable amount of oxygen.

The respiratory quotient, or the proportion between the
volumes of the carbon dioxide exhaled and oxygen inhaled,
tells us how much of the inhaled oxygen is used to oxidize
carbon, forming the carbon dioxide exhaled by the lungs,
and how much of it is used in oxidizing other elements,,
especially hydrogen.

When pure carbon is oxidized to carbon dioxide, the resulting
carbon dioxide has the same volume as the oxygen consumed.
In such a case the respiratory quotient is one. But if, in addition,
to carbon, hydrogen is also oxidized, then the resulting volume
of carbon dioxide is less than the oxygen used up, and the more
hydrogen is oxidized, the less is the volume of carbon dioxide.
In such a case the respiratory quotient is less than one.

The value of the respiratory quotient with carbohydrate
combustion is i; with proteid combustion, 0.8; with fat
combustion, 0.7.

Carbohydrates contain sufficient oxygen to oxidize all the

160 HUMAN PHYSIOLOGY

hydrogen, hence all the inhaled oxygen is used in the oxidation
of the carbon. One litre of oxygen used furnishes i litre of
carbon dioxide. Proteids and fats do not contain sufficient oxygen
to oxidize all their hydrogen. If i litre of oxygen is used to
oxidize proteids, 800 cc of carbon dioxide are formed ; if used to
oxidize fats, only 700 cc are formed.

The respiratory quotient can also be greater than one
when the amount of carbon dioxide is greater than that of
the oxygen taken up. This is the case when, in the body,
substances rich in oxygen, e.g. carbohydrates, are reduced
to products containing less oxygen, e.g. fats.

The respiratory quotient can also be less than it is during
oxidation of pure fat. This occurs when the oxygen intro-
duced is stored up in the form of compounds rich in oxygen.

The respiratory quotient is therefore subject to consider-
able variations. It is greatest during a carbohydrate diet,
smallest during a fat diet. But independently of the diet,
the respiratory quotient has been observed to undergo
periodic variations, for sometimes relatively more carbon
dioxide is given off; at another time relatively more oxygen
is taken up. This shows that the oxygen taken up is not
immediately used for the formation of carbon dioxide, but
first forms compounds rich in oxygen which are, at a later
time, completely oxidized to carbon dioxide and water.

Determining the amount of the sulphur and phosphorus
in the income and outgo is also of value in studying the
proteid metabolism.

The balance of water shows not only how much water has
been taken up and given off by the body, but also how much
water has been formed by combustion processes in the body.

In regard to the substances excreted in the faeces, it must
still be mentioned that the faeces contain not only end-
products of metabolism, but also undigested and unabsorbed
parts of the food. The quantity of the latter substances
must be subtracted from the food taken up, for the foodstuffs
not absorbed cannot be included in the metabolism. But we
have not yet been able to separate the end-products of meta-
bolism present in the faeces from the merely unabsorbed

METABOLISM 161

food. The amount of the nitrogen in the end-products of
metabolism present in the faeces of an adult man is estimated
at one gram per day. This figure is based on observations
made upon the faeces during inanition.

3. EXAMPLE OF A BALANCE OF NUTRITION

To illustrate the balance of nutrition we will assume the
following case : A man whose body weight at beginning of
experiment is 70 kg remains for twenty-four hours in the
chamber of Voit's respiratory apparatus. He is fed with
meat, bread, butter, potatoes, table-salt, and water. During
this time his body weight increases to 70. 1 38 kg.

i . The amount of food taken up is (in grams) :

Proteids 130 containing 69 C, 21 N

Fat 100 " 76 "

Carbohydrates 400 •• 176"

Salts 30

Water.. . 2100

Total income 2760 containing 321 C, 21 N

2. The amount of the outgo in urine, faeces, and respira-
tion is (in grams) :

Urine 1355 containing 1280 H2O, 24 salts, 12 C, 18 N

PYcces 120 " 85 " 6 " 18 " 3"

Respiration 1867 " 950 '' 250 "

Total outgo 3342 containing 2315 H3O, 30 salts, 280 C, 21 N

The person has therefore given off 3342 g, while the income is
2760 g. The body weight increased during this time 138 g.
Hence some other substance must have been taken in beside the
food, and this is the inhaled oxygen.

3. The amount of this oxygen can be calculated from the
above data according to the following formula :

( )xygen = (final body weight -|- outgoings) — (initial lx>dy weight -|- food)
= (70138 + 3342) - (70000 + 276o)g

= 720 g.

<+. From the foregoing we can strike the following balance
of nutrition (in grams):

1 62 HUMAN PHYSIOLOGY

Income (food -\- oxygen) ..... 34&o containing 321 C, 21 N, 30 salts
Outgo ...................... 3342 " 280" 21" 30 ••

Difference ................ +138 +41 C

This table teaches us the following facts :

1. The person was in nitrogenous equilibrium, for the
nitrogen of the outgo equals the nitrogen taken in with
the proteids of the food.

2. The person was not in carbon equilibrium, for the out-
go contains 41 g carbon less than the income. These 41 g
carbon have been stored up in the body.

From the figures of the nitrogen it can be calculated that
69 g carbon originated from the ingested and decomposed
proteid. Of the 321 g carbon ingested and of the 280 g
carbon going out, 69 g originated from the proteid, hence
252 g carbon in the form of non-nitrogenous food has been
ingested. Of this, 211 g [280 — 69] was given off, hence
41 g of carbon in tJie form of a non-nitrogenous substance is
stored np in the body.

3. Whether this 41 g carbon is stored up in the form of
fat or carbohydrate can be determined from the value of the
respiratory quotient. The volume of the exhaled carbon
dioxide amounts to 464 litres ; the volume of the consumed
oxygen is 503 litres. This would give us the value of the
respiratory quotient:

..,..

vol. O2 503

This respiratory quotient is less than one, i.e. some of the
oxygen inhaled has been used to oxidize hydrogen. It is,
however, much larger than that of proteid, which is to say,
that, beside the proteid, but little fat and much carbohydrate
has been consumed.

The following may still he said concerning the respiratory
quotient. By calculation it will be found that 53 g of the inhaled
oxygen have been used up, not in the oxidation of carbon, but in
the formation of water. The hydrogen necessary for this has been
derived from proteids and fats — not from carbohydrates, for they
contain sufficient oxygen to unite with all the hydrogen.

METABOLISM 163

Of the proteids of the food about 116 g have been consumed.
From the hydrogen and oxygen found in this quantity must be
subtracted, iirst, the amount found in the urea and, secondly, the
amount of hydrogen which can be oxidized by the oxygen present
in the proteid. This leaves 3. 5 g hydrogen, which need for their
oxidation 28 g of the inhaled oxygen.

Of the fat of the food about 90 g have been absorbed. For the
oxidation of the hydrogen found in it, 75. 5 g of the inhaled oxygen
are needed. 13ut of the inhaled oxygen there are remaining only
(53 — 28) = 25 g. Hence only 30 g of fat can have been oxi-
dized ; the remaining 60 g have been deposited in the body. 60 g
fat contain 45 g carbon, which corresponds quite closely with that
found in the experiment (41 g).

Hence carbon in the form of fat must Jiave been retained
in the body, while the carbon of carbohydrates has been
entirely oxidized.

4. There have, then, been deposited in the body 41 g of
carbon or about 55 g of fat. But the total increase in body
weight was 138 g, hence 83 g more. These 83 g can be
present in the body only as water. The balance-sheet of
the water shows that 2 1 oo g were taken up and 2315 g
given off, hence more water has been given off than taken
up. But it must be remembered that in the oxidations
taking place in the body, water has been formed. From
the oxidized carbohydrates 222 g and from the proteid 48 g
and from the fat 30 g of water have been formed, making a
total of 300 g. Of this, 215 g [2315 — 2100] have been
excreted, while the remaining 85 g remain in the body.
This agrees quite well with the observed figure.

5. The balance-sheet of the salts shows that as much salt
has been given off as taken up. Hence the body has neither
increased nor decreased in salt.

4. METABOLISM UNDER VARIOUS CONDITIONS

The extent of metabolism is influenced by:

(1) The amount and composition of the food;

(2) The work done and heat lost by the organism;

(3) The size of the body, age, and sex.
I. Influence of food upon metabolism.

1 64 HUMAN PHYSIOLOGY

A. Metabolism of the resting body during inanition.—

For a full understanding of the metabolic processes in the
body it is of great importance to know the extent of meta-
bolism going on during hunger when the body receives no
food or only part of the necessary food. In such a case, the
animal maintains the processes of combustion more or less
at the expense of its own body substance.

The inanition may either be complete, no food being taken
in at all, or partial when only one kind of foodstuff is taken,
or when all the necessary kinds are taken but in insufficient
quantities.

(a) Absolute inanition. — Even though no food is taken
at all, still the processes of combustion go on, although
somewhat reduced. But not all the factors of the total
metabolism are equally influenced. The giving off of in-
organic constituents, water and salts, steadily decreases
during the hunger period. The excretion of sodium chloride
soon ceases altogether, while of the other salts, especially
potassium and calcium phosphates, small quantities are
excreted even up to the time of death, for these salts are
rendered unnecessary by the continual breaking down of the
tissues. Shortly before death, the amounts of water and
salts excreted are increased; this corresponds to the in-
creased breaking down of the tissue immediately prior to
death.

The carbon dioxide decreases most during the first stages
of starvation; during the latter part it is but slightly
decreased. It is difficult to obtain accurate figures as to
this, for the extent of the decrease in the carbon dioxide
excretion is dependent upon the quantity and nature of food
eaten shortly before the beginning of starvation.

The oxygen taken up is also decreased during starvation,
but not to such an extent as the carbon dioxide excretion.
Hence the decrease in the extent of the combustion during
starvation compared with that of a well-fed animal is not
as great as the decrease in the formation of the carbon
dioxide. During starvation less carbon but more hydrogen

METABOLISM 165

is oxidized, so that the oxygen consumption is decreased at
most by 20—25$. Hence the respiratory quotient during the
first days of fasting is rapidly decreased, but after this
remains quite constant till a few days before death. The
more body fat there is present, the smaller the value of this
constant respiratory quotient. In animals well provided
with fat, the respiratory quotient has a value which it ought
to have when pure fats are oxidized. A few days before
death by starvation the respiratory quotient is increased
because of the increased proteid consumption.

The amount of proteid consumed (the nitrogen excretion)
decreases very rapidly to less than one-half and then remains
constant for a few days till a little while before death, when
it becomes larger than it was before starvation. The course
of proteid consumption during starvation depends upon the
amount of non-nitrogenous material for combustion stored
up in the body. Of this material the fats only are of impor-
tance, since the carbohydrates (glycogen) are already used
up in the first days of starvation. The longer the supply of
fat lasts, the longer it takes before the excretion of nitrogen
is increased.

That the excretion of nitrogen reaches its minimum during
the first days of starvation, that it then remains constant for
some time, and at last again increases, is evidently due to
the fact that, at first, less proteids are used in the process of
combustion than fats, and during the latter part more.

The amount of material lost is not the same for all organs.

o

The organs and tissues suffering most are the adipose tissue,
the muscles, and the abdominal glands; the heart, brain,
and muscles of respiration suffer less. During inanition the
body loses continually in weight, this loss being greatest
during the first days. Of this loss, two thirds is due to loss
in water, one third to loss in body proteid and fat. The
amount of fat lost is from two to four times that of the pro-
teids lost.

The time when death occurs is therefore dependent upon
the condition of the body nutrition at the beginning of star-

1 66 HUMAN PHYSIOLOGY

vation. Death occurs when a little more than one-half of
the body weight has been lost.

Besides the loss of material, starvation causes the following
results: The activity of the heart decreases, the number of beats
is lessened. General weakness sets in (psychical depression).
The body temperature remains the same except just before death,
when it falls considerably. • The indol and aromatic oxyacids of
the urine formed by putrefaction in the intestine disappear, but
phenylsulphuric acid is excreted with the urine till death sets in.

(/?) Partial inanition. — If only some constituents of food
necessary for life are given, or if all the constituents are
given but in insufficient quantities, death by starvation is but
delayed.

1. Lack of water in the food causes death more speedily
than lack of all food. This is evidently due to the fact that,
for the normal course of metabolism, a definite proportion
must exist between the water and the solid constituents of
the body. Besides this, dry food is very soon refused, so
that lack of water is finally followed by absolute starvation.

2. Salt-hunger. — If no salts are present in the food, the
excretion of salts steadily decreases and the excretion of
sodium chloride soon ceases altogether even at a time when
the body still contains considerable quantities of it. Potas-
sium and calcium phosphates are, however, continually
excreted. By eating organic foods the excretion of calcium
phosphate is somewhat decreased, because the salt, derived
from the breaking clown of the tissue, can be utilized in the
regeneration of the tissues. Still a part of the salts is con-
tinually lost, and since, for the maintenance of life, a certain
proportion must exist between the salts and the organic
constituents of the body, death finally sets in. Death is
preceded by weakness and paralysis.

3. Lack of all organic constituents in tJic food. — If no
organic foodstuffs arc given, the animal being supplied only
with water and salts, death by starvation occurs. The
phenomena of metabolism are practically the same as in
absolute inanition, the organism consumes its own body

METABOLISM 167

substance. Death, however, occurs a little later than in
complete starvation.

4. Lack of protcids. — If proteids are excluded from the
food, while sufficient water, salts, carbohydrates, and fats
are given, the body loses its proteids, and since the fats and
carbohydrates cannot shield it against the loss, death by
starvation results. The daily loss of proteid is, however,
slightly less than in absolute hunger, and hence death occurs
somewhat later and without the previous increase in nitrogen
excretion.

Notwithstanding the loss of body proteids, the body can
lay up fat if the food contains sufficient quantities of fats and
carbohydrates.

Even the taking up of gelatin cannot prevent the loss of
body proteids. But the loss of body proteid is less if
gelatin is eaten than if nothing but fats and carbohydrates
are taken. Proteoses, however, are able to replace all the
proteids used in the body.

5. Lack of fats and car boliydr cites in tJic food ivJiilc suffi-
cient protcids are fed. — Fats and carbohydrates can be com-
pletely replaced by proteids, at least in the carnivorous
animals. For example, by feeding upon lean meat, which
is nearly a pure proteid diet, a dog can maintain life. But
it is not possible to feed man for a long time exclusively
with proteid, as he cannot digest the necessary amount of
meat.

6. If all the necessary foods are given but in insufficient
amounts, t\vo cases are possible, (i) The quantity is abso-
lutely insufficient. The body now continually uses some of
its own constituents, hence death by starvation must finally
set in, but at a much later time than in absolute starvation.
(2) The quantity of food given is only relatively insufficient
to maintain the body at the beginning of starvation. In this
case, the body loses some of its substance until the amount
used and the amount taken are equal. Then the body
maintains itself. Hence the body emaciates, but death does
not result.

1 68 HUMAN PHYSIOLOGY

B. Metabolism during sufficient nutrition. — The partak-
ing of food increases the metabolism as compared with that
during inanition. In this respect the animal body is not
like a furnace in which increase of consumption follows in-
crease of supply, for the body can store up a considerable
amount of material for combustion. Besides this, the increase
in metabolism is less dependent upon the absolute quantity
of material furnished than upon the composition of the
material.

I. The effect of proteid upon metabolism. — The effect of
proteid upon metabolism can best be investigated in the
carnivorous animals, which can maintain life if merely pro-
teids are given in the food in addition to salts and water.
Suppose a dog is fed with as much proteid as it consumes.
Its body will be in nitrogenous equilibrium, for the nitro-
genous income and outgo are balanced. If to such a dog
more proteids are fed, the larger part is used, while only a
small part is stored up in the body as flesh.

By this laying up of flesh the demand for proteid is in-
creased, for the demand is proportional to the weight of the
body flesh. Nitrogenous equilibrium is again obtained,
when the proteids demanded by this newly laid up flesh
equal the increase in the quantity of the food proteids. But
the possibility of such storing up of flesh is limited, for the
digestive organs cannot cope with very large quantities of
proteids.

If a dog, maintained in nitrogenous equilibrium by proteids
only, receive less proteids, the body loses some of its flesh
till the amount of body proteid has reached the point where
the demand upon proteid is equal to the proteids supplied in
the food ; nitrogenous equilibrium is then once more estab-
lished. At a certain low limit of proteid supply, nitrogenous
equilibrium is not regained, for then the body continually
uses more proteid than is supplied, and hence death by
starvation must result.

The smallest amount of proteid with which an animal
living upon a pure proteid diet can maintain nitrogenous

METABOLISM 169

equilibrium is considerably more than the amount of proteid
decomposed during- starvation. If an animal takes up just
as much proteid as it decomposes during starvation, nitroge-
nous equilibrium is not obtained, but the animal decomposes,
in addition to the food proteid, some of its body proteid.
The more proteid is given in its food, the less body proteid
will be used, and when about two and one half times as
much proteid is fed as is decomposed during starvation,
nitrogenous equilibrium is obtained.

The facts derived from the study of metabolism during"
pure proteid feeding establish the following laws:

1. Within certain limits the body can maintain nitroge-
nous equilibrium with any amount of food proteid.

2. Increase in food proteid also increases the consumption
of proteids.

This increase in proteid consumption has been regarded as
" Luxus-consumption, " but it is not without beneficial effect, for
by it the power of the body is increased.

2. Effect of fats and carboJiydratcs on metabolism. — If a
person fed on a mixed diet (proteid, fats, carbohydrates,
water, and salts) and brought to a condition of nutritive
equilibrium is supplied with an increased amount of non-
nitrogenous foods (fats and carbohydrates), the amount of
non-nitrogenous material consumed in the body is increased,
but the consumption of proteids is decreased to an extent
expressed by the law of isodynamics (see page n/).
Hence, in reality, no general increase of combustion in the
body will take place. Fats and carbohydrates therefore
shield the proteids, and the proteid is stored up in the body
as flesh. If there is still more fat or carbohydrate present
in the food, these are stored up in the body, chiefly in the
form of fat.

As far as their influence upon the extent of metabolism is
concerned, there is no real difference between fats and carbo-
hydrates, but the carbohydrates are more easily oxidized and
shield the proteids better than fats. In general, they can
replace each other according to the law of isodynamics.

1 7° HUMAN PHYSIOLOGY

Gelatin also shields proteids, and even more so than
carbohydrates.

If, in the above assumed case where nutritive equilibrium
is maintained with a mixed diet, the amount of fat, carbo-
hydrate, or gelatin is increased while the amount of proteid
remains constant, the proteid saving is slight. In such
cases, the gelatin may shield 30^ of the proteids, the carbo-
hydrates i 5$, and the fats still less. But the shielding of
proteids is much more effective when, simultaneously with
an increase in the other foodstuffs, the amount of proteids is
decreased. When the proteid of the food is replaced by fat,
carbohydrates, or gelatin, a much smaller quantity of proteid
is able to keep the body proteid constant than if the diet
consists chiefly of proteids. The minimum amount of pro-
teid in a mixed diet, i.e. the absolutely necessary proteid
(see page 117), is for a man about 70 g daily; but it has
been observed that for a short time he can maintain his
body proteid with 40 g of food proteids. But with such
small quantities of proteids more fat and carbohydrates must
be supplied than would strictly follow from the law of
isodynamics. The foodstuffs which can shield the proteids
differ from each other in this capacity; the gelatin shields
proteids best, then the carbohydrates, and, least of all, the
fats. In regard to fats it must be added that the eating of
very great quantities may increase the consumption of pro-
teids.

If, in a sufficient, mixed diet, the proteids are increased,
the following results :

1. The extra proteid is, as in pure proteid diet, in part
deposited in the body, and part used up. Hence in a
mixed diet also, an increase in the supply of proteid causes
an increase in proteid consumption.

2. But by this increase in proteid consumption the oxida-
tion of fats and carbohydrates is somewhat lessened, so that
fat may be deposited.

3. In this case also, fats and carbohydrates spare the
proteids to such an extent that a greater part of the proteid

METABOLISM 171

is deposited and a smaller part oxidized than occurs in an
exclusive proteid diet.

From what has thus far been said, it follows that the
various foodstuffs are not of the same value for the organism.
In general, the body has the tendency to be less sparing
with the proteids than with the fats and carbohydrates.

It also appears that the body can maintain its equilibrium
by foodstuffs mixed in various proportions. The question
is, which is the most suitable mixture ? The most suitable,
or the rational diet for an adult man, is 100 g proteid, 60 g
fat, 400 g carbohydrates. These figures have been obtained
by various experiments in metabolism in men. From the
experiments it has been observed that the figures do not
differ to any large extent with the occupation and place of
dwelling of the subject experimented upon.

If the 60 g of fat are changed, according to the law of
isodynamics, into carbohydrates, the proportion of proteids
and carbohydrates in the daily meal is as I : 5.5.

If, in feeding, the object is not only to keep the body
weight constant but to increase either the flesh or the fat in
the body, more foodstuffs must be taken in. But to increase
either the body flesh or fat, it is not a matter of indifference
which foodstuff is increased.

The laying up of flesh can only be produced by proteid
food ; for from fat and carbohydrates no flesh can be
formed. But, by increasing the proteids of a diet predomi-
nating in proteids, little flesh is laid up. For the laying up
of flesh the most suitable diet is a moderate amount of
proteids besides large quantities of fats and carbohydrates.
But if considerable flesh is to be laid up, other conditions
than the nature of the food play an important part. For
example, the laying up of flesh (muscles) is especially favored
by proper muscular exercise (training).

Fattening of the body. — The fat laid up by the body
originates from :

(a] The fat in the food ; for if a fat containing specific
•constituents (rape-seed containing erucic acid) normally not

'72 HUMAN PHYSIOLOGY

found in the body is added to the food, we find this fat
deposited in the body.

(fr) The carbohydrates of the food from which by reduc-
tion and synthesis fat is formed. By a diet rich in carbo-
hydrates glycogen and fat are deposited in the body.
Consequently the respiratory quotient may be greater than
one; i.e. carbohydrates must have been reduced and changed
to fats in the body. By this process oxygen would be set
free, which could then be utilized, in connection with the
inhaled' oxygen, in the formation of carbon dioxide.

(c) It has been supposed that fats can be formed from
proteids, but no sufficient proofs have been furnished.

For the purpose of laying up fat the best diet consists of
a moderate amount of proteicl and an abundant supply of fat
and carbohydrate.

3. TJic effect of water and salts. — Increase of water taken
up does not change the amount of metabolism, but during
the first day the excretion of nitrogen is increased, due to
a better washing away of the nitrogenous end-products of
metabolism.

Neither does increase in sodium chloride produce any
changes in the extent of metabolism.

4. Effects of spices. — Alcohol does not change the meta-
bolism. Alcohol, like the other non-nitrogenous foodstuffs,
is completely oxidized soon after being taken into the body
and can therefore replace fats and carbohydrates. But, as
alcohol is a strong nerve poison, it cannot be regarded as a
valuable material for metabolism.

Concerning the effects of spices upon metabolism, authors
differ widely.

5. Effects of oxygen. — Voluntary increase or decrease in
the amount of respiration has no effect upon metabolism, for
the taking up of oxygen and the giving off of carbon dioxide
is not altered by increased or decreased ventilation during
a few minutes. The increased activity of the muscles of
respiration may, of course, influence metabolism. Diminu-
tion in the amount of haemoglobin in the blood, by loss of

METABOLISM i?3

lialf the blood, produces no change in the extent of meta-
bolism, for the lack of oxygen is completely covered by
increased respiration and heart activity, so that oxyhaemo-
globin is used to better advantage than normally. But if
real lack of oxygen occurs, e.g. in dyspnoea or excessive
muscle work, the metabolism does not decrease, but, on the
contrary, there is an increase in the decomposition of pro-
teids. But the combustion is, in this case, incomplete;
hence considerable quantities of lactic acid are excreted
with the urine (see page 42).

Increase or decrease in atmospheric pressure has, within
certain wide limits, no effect on the amount of combustion
in the body.

II. The effect of work and loss of animal heat upon
metabolism.

(a) Effect of muscular activity. — By muscular work the
respiratory metabolism and all the processes of combustion
are increased. The combustion process may be increased
four or five times the normal amount. During moderate
work the respiratory quotient is the same as during rest.
But during excessive work the increase in the excretion of
carbon dioxide may be greater than that of the oxygen
taken up, so that the respiratory quotient is increased.

The consumption of proteids is generally not increased by
work, hence the increase in combustion must be at the ex-
pense of non -nitrogenous substances, fat, or carbohydrates.
Often, however, the excretion of nitrogen is also increased
by muscular activity; this is always the case in exclusive
or predominating proteid diet. But if sufficient fats or
carbohydrates are present in the mixed diet, there is no in-
crease in nitrogenous excretions. During muscular activity,
the body generally consumes non-nitrogenous material.
But if the work is very excessive, an increase in the excretion
of nitrogen may result even with a mixed diet containing
much fat and carbohydrate. This is perhaps due to the fact
that excessive work injures the muscle tissue. To maintain
the body at its weight during work it must be supplied with

J74 HUMAN PHYSIOLOGY

more food than during rest. For work the rational diet is,
proteids 130 g, fat 100 g, carbohydrate 500 g. In this diet
the proteids are also increased because a man doing hard
work has a better developed muscular system and therefore
a greater demand for proteids than a resting or slightly
active persor. Hence the proper diet of a working man
serves not only to replace material consumed but, as the
power of work is proportional to the amount of muscle, to
increase the amount of flesh.

(b) Effect of the work of digestion. — In considering the
activity of the body, the material and energy used in the
processes of digestion and absorption must not be omitted.
Under digestive work we include the activity of the glands,
the movements of the alimentary canal, and the activity
which the epithelial cells of the intestine exhibit in taking
up material from the intestine and transferring it to the blood
or lymph. But it is impossible at present to say how much
of the increased metabolism observed after the taking up of
food is due to this increased activity and how much is due
to the increased supply of material for combustion. It is
nevertheless beyond doubt that the digestive work causes a
considerable increase in metabolism, and it has even been
asserted that the difference between the metabolism of a
fasting and that of a fed organism is entirely due to this
increase in the activity of the alimentary canal. But it is
supposed that the energy for this activity is not supplied by
fats or carbohydrates but by proteids, for during digestion
the nitrogenous excretion in the urine is greatest; hence
more proteids are consumed at this time.

(c) Effect of loss of body heat. — The human body main-
tains its own temperature independently of the external tem-
perature. This body temperature is maintained at its proper
height by continual combustion (see Chapter XIII). The
body continuously loses heat which must be replaced by the
combustion of new food material. The amount of heat
given off depends upon the external temperature ; the lower
this is, the more heat is lost by the body and the more oxi-

METABOLISM 175

dation must take place in order to maintain the body tem-
perature. Hence the extent of metabolism increases with
lowering- of the external temperature and decreases when
the external temperature increases. This change in meta-
bolism affects chiefly the combusion of fats and carbo-
hydrates. The increase in metabolism during loss of heat
is caused by a reflex increase in combustion in the muscles
which produces muscle contraction (shivering).

The power of the human body to adjust itself to great
variations in external temperature is limited. If the external
temperature is very low, the loss of heat may become greater
than the heat production and the body temperature falls.
The lower the body temperature falls, the more slowly the
vital processes take place and the less heat is produced
until, at last, the processes of combustion cease altogether
and the organism freezes to death. If the external tempera-
ture is so high that the body produces more heat than it can
give off, the body temperature rises. This causes an in-
crease in the vital processes and more heat is produced until,
at last, the body is overheated and death results. In the
increased metabolism the consumption of proteids is also
increased.

Within the limits in which the body can accommodate
itself, a fall in external temperature increases metabolism,
and a rise decreases it. But, outside of these limits, the
effects are exactly the reverse, for a decrease in external
temperature causes a fall, and an increase, a rise in the body
temperature. Hence, in the last-mentioned case, man is
like the cold-blooded animals, in which the metabolism rises
and falls with the external temperature.

But it will he shown that, for the regulation of the body tem-
perature, besides the mechanism for regulating the metabolism,
another and far better mechanism regulating the loss of heat is
present (see page 181).

(d) Effect of sensory stimulation and psychical activity.

— Stimulation of the skin and strong stimulation of the
retina by light increase the consumption of oxygen and
production of carbon dioxide. Hence during sleep the

I76 HUMAN PHYSIOLOGY

respiratory exchange of gases is considerably decreased.
Besides, during sleep the muscular movements, except those
of the heart and respiratory muscles, are reduced to a mini-
mum, and the muscle tonus also, which maintains the position
of the body, is inhibited. The proteid metabolism is not
affected by sleep.

It has not yet been definitely proven that psychical activity
has any effect upon metabolism.

III. Effect of the size of the body, age, and sex upon
metabolism. — Small persons have a relatively greater meta-
bolism than large persons, for, since in them the surface by
which heat is lost is larger in proportion to the heat-produc-
ing mass than in large individuals, the smaller person must
produce relatively more heat in order to keep a constant
body temperature than the larger person. Hence the
metabolism of a child is relatively greater, although abso-
lutely smaller than that of the adult (see page 1 1 8). In old
age the metabolism is smaller than in the prime of life.
Because of differences in the size of body, the metabolism in
a woman is less than in a man, therefore the diet for woman
is also less. An adult, resting woman needs 90 g proteids,
40 g fat, and 350 g carbohydrate daily. During pregnancy
the metabolism is increased. Sex itself has no influence
upon metabolism.

PART II

THE TRANSFORMATION AND SETTING
FREE OF ENERGY

The potential chemical energy of the body substance is
changed to kinetic energy (heat and muscular activity) by
the physiological combustion.

The cause of the transformation of energy lies partly in
the living substance itself, partly in the stimulations which
act upon the living substance. The stimulations either have
their origin in the body itself and serve to regulate the rela-
tion existing between the individual organs, or they originate
in the external world and serve by their stimulating effect
to connect the body with its environment. To receive these
external stimulations, the body is provided with special
organs, the sense organs. The stimulation is carried from
the sense organs by means of a special apparatus, the
nervous system, to the muscles in which the transformation
of energy chiefly takes place.

The study of the transformation and setting free of energy
may be divided into the following chapters :

1. Animal heat.

2. Muscular contraction.

3. Functions of the nervous system.

4. Functions of the sense organs.

177

CHAPTER XIII
ANIMAL HEAT

I. Heat production. — In the animal body the heat formed
originates from the potential chemical energy of the food.
In a resting body, in which no energy is used up for ex-
ternal work, as much heat is formed as corresponds to the
potential chemical energy set free during combustion.
Hence the law of conservation of energy holds good also for
the transformation of energy in the living body.

Heat can also be imparted to the body by the taking up of food
and drink warmer than the body, but this is of little importance
and does not occur regularly.

In the working body the energy transformed is equal to
the heat produced and the external work done.

The work of the heart, of the muscles of the alimentary canal,
and of the respiratory apparatus is not reckoned with the external
work, for their work is transformed into heat in the body.

The unit of heat is the calorie. A calorie is the amount of heat
needed to raise i kg of water from o° to i° C.

The unit of work is the kilogrammeter^ which is the work
done by raising I kg the distance of I meter. One calorie
equals 425 kilogrammeters.

The chemical energy of an oxidizable substance is indi-
cated by its heat of combustion, i.e. the heat set free by the
complete oxidation of the substance. The following table
gives the heat of combustion of a few substances :

Hydrogen 34-O calories.

Carbon 8.0 "

Fat. 9.3 "

Sugar 3.7

Starch 4.5 "

Proteid 5.5 "

178

ANIMAL HEAT 179

Proteids are not completely oxidized in the body, for the
urea formed from it can still undergo oxidation. If the heat
value of urea is subtracted from that of proteid, there remain
for one gram of proteid 4. 1 calories.

The physiological heat values are :

For i g proteid 4.1 cal. ; I g fat 9.3 cal. ; I g carbo-
hydrate 4. I cal.

As far as their heat production for the organism is con-
cerned, the following substances are isodynamic : 2.3 g
proteid (or gelatin) = I g fat = 2.3 carbohydrate.

If the extent of metabolism is known, we can calculate
from the heat value of the substances oxidized the amount
of heat formed. Conversely, by finding the amount of heat
produced we can calculate the extent of metabolism ; but
this calculation is not conclusive as to the individual kinds
of foodstuffs used.

The production of heat is measured by the water- or air-calo-
rimeter. In the water- calorimeter the body is placed in a tin
case which is surrounded by a layer of water. The heat given off
by the animal heats this water. The respiratory air is supplied
through tubes of which the one carrying the exhaled air passes
through the layer of water which surrounds the case, so that the
heat of the exhaled air is imparted to the water also. From the
increase in temperature of the water, the amount of heat lost by
the body can be calculated. This amount equals the heat formed,
for the body temperature is the same at the end as at the beginning
of the experiment. In the air-calorimeter the tin case is sur-
rounded by a layer of air whose expansion by the heat measures
the amount of heat set free.

The adult resting human being produces in twenty-four
hours about 2400 calories, or in one hour 100 calories.
This is 34 calories per kilogram of body weight in twenty-
four hours, and 1.4 cal. in one hour.

The amount of heat produced is dependent upon the same
circumstances as metabolism. Muscle activity increases
.heat production, for, of the extra energy set free thereby,
only a part can be used in the performance of work, the rest
being changed to heat. Of all the energy set free by ;i
working body, at most only one-fourth can be utilized for

l8o HUMAN PHYSIOLOGY

mechanical work ; the remaining, three-fourths is set free as
heat. During hard work an adult man produces in twenty-
four hours, for every kilogram of body weight, an amount
of heat, including the external work, equal to 55 calories.

2. The loss of heat. — The body continuously loses heat:

(1) By radiation and conduction from the surface of the
body to the surrounding air, which, as a rule, is colder than
the body.

(2) By the evaporation of water from the skin, especially
by the secretion of sweat. By this means the body can lose
heat when the surrounding medium has a higher temperature
than the body itself.

(3) By exhaling air which has been heated to the body
temperature and is saturated with water vapor. The water
vapor is imparted to the expired air by the evaporation of
water from the mucous membranes of the air passages.

(4) By heating up the ingested food and drink ; in other
words, by voiding excretions heated to the body tempera-
ture (urine, faeces).

Of all the heat lost by the body, about 8o# is lost by
radiation, conduction, and evaporation from the skin; about
15$ by evaporation from the mucous lining of the air
passages ; one half of the rest by expired air, and the other
half by the excretions.

The amount of heat which is lost in each of these ways is
variable. The lower the external temperature, the more
heat is lost by conduction from the skin and by heating the
inhaled air ; the loss of heat by evaporation is greater, the
drier the air and the greater the amount of sweat secreted.
The heat lost by expired air depends upon the frequency
and depth of respiration.

3. Body temperature. — Man belongs to the warm-
blooded or homoiothermic animals whose body temperature
is, apart from very slight variations, constant. The body
temperature of man is 36.5—37.5° C.

The body temperature is measured by placing a thermometer in
the rectum, vagina, mouth, or axilla, the arm being placed in the
proper position around the thermometer.

ANIMAL HEAT 181

The blood streams from the tissues where most of the
heat is produced (muscles and large glands) to the skin,
where it becomes cooled. The temperature of the muscles
is therefore somewhat higher, and that of the skin lower,
than that of the blood.

The body temperature shows some regular minor varia-
tions; shortly after midnight it is lowest (36.5°), while in the
afternoon it is highest (37.5°). It is somewhat increased by
the partaking of food and by muscle activity.

Mammals have about the same body temperature as man; in
birds it is higher (40-45°). The body temperature of cold-blooded
or poikilothermic animals is a few degrees (i-4°) higher than that
of the surrounding medium (provided they have not been placed
in a warmer or colder medium just previous to the measurement).

Hibernating mammals are, during their winter sleep, like cold-
blooded animals.

4. Regulation of body temperature. — The body tempera-
ture remains constant when the production of heat equals the
loss of heat. If changes occur in the production of heat
(e.g. by muscular activity) or in the loss of heat (e.g. in hot
or cold weather), the production and loss of heat must again
be regulated in order to keep the body temperature con-
stant. Concerning the nature of the regulation of tempera-
ture by the nervous system little is known.

Some authors think that there are in the central nervous system
certain centres (heat centres) by which the mechanism for regula-
tion of body temperature is governed. But the account given of
these centres and their mode of action is not satisfactory.

By the regulation of temperature both the production and
the loss of heat can be varied.

C 'hangcs in the production of Jicat occur when the loss of
body heat is altered by variations in the temperature of the
surrounding medium. In cold weather the production of
heat is increased to such an extent that involuntary muscular
contraction takes place (chattering of teeth, shivering).

In small animals the proportion of the surface by which
heat can be lost to the heat-producing body mass is greater
than in larger animals. Therefore, in order to maintain a

1 82 HUMAN PHYSIOLOQY

constant body temperature smaller animals must produce
more heat per kilogram of body weight than larger animals.
The adult human being produces, at rest, per kilo-hour 1.4
calories, while a child four years old produces about 2.5
calories, a rabbit 5.6 calories.

If the loss of heat is stated in terms of the unit of body surface,
it is found that it is about the same in animals of various sizes.
The amount of heat lost by man per square meter is about 1200
calories in 24 hours.

Variations in the loss of Jicat take place because of:

(1) Increased or decreased supply of blood to the skin,
whereby the heat carried to the cooling body surface is in-
creased or decreased. The supply of blood to the skin is
increased by the dilation of the cutaneous vessels and the
increase of pulse rate ; it is decreased by the contraction of
the vessels and the decrease of the pulse rate.

(2) Secretion of sweat, which, by evaporation, cools the
body.

(3) Increase or decrease in the frequency or depth of the
respirations, whereby more or less heat is given off by the
expired air.

Muscular activity, by which more heat is produced, or
raising of the external temperature (warm weather) are fol-
lowed by perspiration, increased pulse and respiration, and
dilation of the cutaneous vessels; lowering of the external
temperature (cold weather) causes constriction of the cuta-
neous vessels.

We can voluntarily regulate the loss of heat by warming
ourselves, by clothing, by the position of the body, and by
partaking of cold or warm drinks. We can regulate the
production of heat by voluntary muscular activity. In
animals hairs and feathers serve to regulate the loss of heat.

Our ability to keep the body temperature constant by
means of the heat-regulating mechanism is, however, limited.
This regulation of temperature fails when the temperature of
the surrounding medium is too high or too low, so that
changes in the production or loss of heat are no longer able

ANIMAL HEAT 183

to prevent the body temperature from rising or falling.
Very strong cooling also disturbs the regulation of tempera-
ture by paralyzing the muscles of the blood vessels so that
the cutaneous vessels become dilated to an abnormal extent.
When the temperature regulation fails, the body temperature
speedily sinks below 19° or rises about 42° and death results.
In fever, the regulation of temperature is disturbed; the
production of heat is increased, hence the body temperature
is abnormally high.

Within certain limits, the heat production in cold-blooded
animals is the larger, the higher the temperature of the external
medium, for, in these animals, the intensity of the combustion
taking place in the body increases with the raising of the external
temperature.

CHAPTER XIV
GENERAL MUSCLE PHYSIOLOGY

THE active movements of the body are produced by the
contraction of the muscles whose fibres shorten in their
longitudinal direction (contraction). They perform work
by the movement of the parts connected with them (bones).

The physiology of the movement may be divided into:

(1) General muscle physiology, the study of general properties
of muscles.

(2) Special muscle physiology, which treats of the actions of
individual muscles.

Anatomical considerations. — The striated muscle is composed
of muscle fibres, varying in length up to 12 cm and having a
diameter of 0.01-0.06 mm. These fibres are surrounded and held
together by connective tissue (perimysium internum and ex-
ternum). In this connective tissue are found nerves and blood
vessels. The muscle fibre is composed of a bundle of parallel
fibrils, between which there is a protoplasmic substance, the
sarcoplasm. The fibre is surrounded by a structureless covering,
the sarcolemma. Directly beneath the sarcolemma lie the muscle
corpuscles, spindle-shaped and nucleated protoplasmic bodies.

The smooth muscle is composed of fibre-like cells without any
sheath. The cells vary in length and diameter up to 0.5 mm and
0.02 mm respectively and contain rod-like nuclei. Sometimes
fibrils and sarcoplasma are found in smooth muscles.

The fibrils which seem to contain the contractile part are, in
the smooth muscle, composed throughout their entire length of
doubly refracting parts (anisotropic), while the striated muscle
fibril is composed of alternate doubly and singly refracting
(isotropic) parts. The striated appearance of muscles is caused
by the alternate arrangement of parts which vary in transparency.

In the middle of each isotropic (light) disk there is, in the
striated muscle, a narrow dark band called the intermediate disk,
or membrane of Krause, on both sides of which there is another
dark band called the secondary disk. In the centre of the aniso-

184

GENERAL MUSCLE PHYSIOLOGY 185

tropic (dark) disk there is a narrow light band, called the median
disk of Hensen. The physiological importance of these structures
is still unknown.

By double refraction exhibited by many crystals a single ray of
light is broken up into two rays. The double refractive muscle
substance has an optical axis in the longitudinal direction of the
fibres, in which the light is broken but once. The importance of
this doubly refracting substance of the muscle fibrils for the
property of contractility is not known.

The motor-nerve fibres are connected with the muscle fibres,
the axis cylinder of the nerve fibre forming a flat arborization
(end-plate) which lies in contact with the muscle fibres.

Nearly all the striated muscles can be voluntarily stimulated,
except the heart muscle. The stimulation of most of the smooth
muscles is not subject to our will, except the muscle of accommo-
dation of the eye.

The contraction of the muscle takes place when it is
stimulated. In a stimulated muscle the physiological com-
bustion is increased, whereby energy is set free which pro-
duces the contraction and performs the work. The manner
in which the potential chemical energy is transformed into
mechanical work is still unknown.

1. THE RESTING MUSCLE

i . Chemical properties of a resting muscle.

(a) Composition of muscles. — The reaction of a resting
muscle is neutral or feebly alkaline. A muscle contains
25$ solids, which include:

I. Proteids 20$.

If a fresh frozen muscle is cut up and the extract filtered at
about 3°, a cloudy neutral or feebly alkaline fluid is obtained.
This is the fluid contents of the fibres or the muscle plasma. At
higher temperatures it coagulates spontaneously and, the higher
the temperature, the more speedily it clots. The coagulation is
due to the formation of an insoluble proteid, myosin, from a
soluble proteid of the muscle plasma, myosinogen, by the action
of the ferment. Coagulation also occurs during rigor mortis.
The myosin forms about 20$ of the muscle proteids.

The solution which is left after myosin has been formed is called
the muscle serum. It has an acid reaction and contains about

1 86 HUMAN PHYSIOLOGY

muscle albumin. The remainder is chiefly composed of a
proteid, called myogen.

The muscle also contains an undissolved proteid of unknown
nature, collagen, and the nuclein-like phosphocarnic acid which,
by splitting up, yields phosphoric acid, a sugar-like product, lactic
acid, and carnic acid, a substance belonging to the peptones.

In addition to the above-named proteids, the muscles contain
a pigment, myohaematin, which is identical with the haemoglobin
of the blood; but it is not derived from haemoglobin, for animals
without blood also have this pigment in their muscles.

2. Carbohydrates, chiefly glycogen, stored up between
the muscle fibrils ; grape-sugar in small and varying amounts ;
inosit.

3. Fats, chiefly deposited in the intramuscular connective
tissue. The amount varies with nutrition.

4. End-products of metaboHsm, chiefly keratin and
xanthin bases; also sarcolactic acid.

5. Salts, especially potassium phosphate.

Muscles contain carbon dioxide, but no free oxygen can
be obtained from them.

(b) Chemical processes in tJie resting muscle. — The
physiological combustion in the resting muscle manifests
itself by the consumption of oxygen and the production of
carbon dioxide. This is evident from the fact that arterial
blood is changed to venous blood in the muscles.

2. Mechanical properties of a resting muscle. — The
muscle is elastic and, in the longitudinal direction of its
fibres, extensible. During this extension, the length of the
muscle increases, its thickness decreases ; its volume under-
goes no change.

The elongation during extension is not proportional to the
weight which causes the extension, for the extension pro-
duced by one and the same weight is the less, the more the
muscle is already stretched. Hence the curve of extension,
i.e. the curve whose abscissa represents the weight and
whose ordinate represents the length of the muscle, is not a
straight line, but a hyperbola (see page 192).

GENERAL MUSCLE PHYSIOLOGY 187

2. THE STIMULATED OR ACTIVE MUSCLE

i. Chemical processes in the active muscle. — In the

active muscle the processes of combustion are enormously
increased. During muscular activity the consumption of
oxygen and the formation of carbon dioxide maybe increased
to four or five times that during rest. During this activity
more carbohydrates or fats are used, while the consumption
of proteid remains the same, if sufficient fat and carbohy-
drate are present. But if these are not present in sufficient
quantities, the muscular activity takes place at the expense
of proteid. This is evident from the metabolism of the body
during rest and work. The taking up of oxygen and the
giving off of carbon dioxide are always enormously increased
by muscular activity, but the nitrogenous excretions are only
increased when the food does not contain sufficient non-
nitrogenous substances to supply the energy for the work,
€.g. during purely proteid diet.

The respiratory quotient is not changed by muscular
activity, if the work is not extreme; but if the work is
fatiguing, it is increased.

The amount of glycogen in the muscles and in the liver
is decreased by work. Body fat may also be lost by work.

The active muscle has an acid reaction. Sarcolactic acid
of the muscle is increased by activity.

Although no trace of free oxygen is present in the muscles of a
irog, still an excised frog-muscle placed in an atmosphere free of
oxygen can do work. They therefore contain oxygen stored up
in the form of chemical compounds which can be used when
necessary.

Muscles of warm-blooded animals contain, at best, only a small
supply of stored-up oxygen, for they lose their irritability soon
after the supply of arterial blood is cut oft.

The amount of substances capable of extraction with water is
decreased by activity, while those extracted by alcohol are
increased. It is said that the amount of phosphocarnic acid
[phosphorfieischsaure] in the muscles is decreased by activity.

1 88 HUMAN PHYSIOLOGY

2. The external phenomena during the transformation
of energy in an active muscle. — The transformation of
energy reveals kself in definite mechanical, thermal, and
electrical changes in the muscles.
A. Mechanical changes in the stimulated muscle.

(a) Contraction. — The stimulated muscle shortens in its
longitudinal direction, the diameter increases, while the
volume remains the same.

Both the anisotropic and the isotropic bands of the striated
muscle change in the same sense as the whole muscle.
That the volume of the anisotropic part is increased, while
that of the isotropic part is slightly decreased, is explained by
the passing of water from the isotropic to the anistropic part.
Besides this, the optical difference between the two parts
becomes less.

Twitching. — If a muscle is acted upon by a stimulus last-
ing for but a short time (by an induced electric current), it
draws itself together rapidly and then again immediately
lengthens. This is called a twitch.

The length of time consumed by a twitch is investigated by the
graphic method. The muscle is connected with a writing-lever
which is moved by its contraction and writes its movement on a
travelling surface. Such an apparatus for the graphical registra-
tion of a muscle contraction is called a myograph.

An isotonic contraction is a contraction during which the tension
(tonus) of the muscle remains constant. The isotonic contraction
curve shows the duration of the contraction during constant ten-
sion. To obtain such a curve a writing-lever must be used which
is thrown upward as little as possible by the contracting muscle.
A light lever is used and a weight is hung as near the axis as
possible, while the muscle is attached to the lever at considerable
distance from the axis. During normal physiological conditions,
a muscle does not contract isotonically. but always with change in
tension.

An isometric contraction is a contraction in which the shortening
of the muscle is completely prevented, so that tension is produced
without the shortening of the muscle. The changes in tension in
an isometric contraction can be registered by the so-called tension
recorder.

A noticeable length of time elapses between the moment
of stimulation and the beginning of contraction ; this time is

GENERAL MUSCLE PHYSIOLOGY

189

called the latent period. The contraction occurs at first
with increasing and then with decreasing rapidity till the
maximum is reached ; after this the muscle relaxes, at first
rapidly, but soon more slowly until it has acquired its former
length. Frequently the relaxation is not complete, especially
when the load of the muscle is small (see Fig. 9).

The length of the latent period for the skeletal frog-
muscle is, at room temperature, about o.oi second, for
human muscle 0.004 to o.oi second, for smooth muscle 0.4
to O.8 second.

Fi<;. 9 — ISOTONIC CONTRACTION OK A FROG-MUSCLE.

y, curve of contraction; r, moment of stimulation; from r to a, latent period;
from or to />. period of increasing energy; from b to c, period of decreasing
energy; Z, time-curve produced by a vibrating tuning fork (each vibration
equals o.oi second).

The duration of contraction for a skeletal muscle of a frog
at room temperature is about o. I to o. I 5 second, for a human
muscle a little less, for a smooth muscle i to 3 minutes.
Various striated muscles of the same animal contract with
different rapidity, e.g. the gastrocnemius of a frog contracts
more rapidly than the hyoglossus. Many animals (rabbits,
birds) have slowly contracting striated muscles which have
a red color and are poor in sarcoplasm, while they also have
rapidly contracting muscles which are white and contain
much sarcoplasm.

The extent of the contraction (height of contraction) in a
maximal contraction of a frog-muscle is about one-fifth of
the length of the fibre.

Conditions influencing the contraction.

I. Temperature. — Between the temperature of — 40° and
+ 40° C. the duration of the contraction and the latent

1 90 HUMAN PHYSIOLOGY

period are the shorter the higher the temperature. The
height of the contraction also changes with the temperature,
but it is not increased merely with the raising of temperature,
for a cold muscle may give greater contraction than a warm
muscle.

2. The load. — In general, the height of the contraction is
less the greater the load of the muscle. But it must be
.observed that the height of contraction of a muscle without
any load is slightly less than that of a moderately loaded
muscle.

3. Fatigue. — If a muscle has made many successive con-
tractions, the duration of the contraction and latent time
increases; the height of the contractions at first slightly
increases, but later on gradually decreases.

Concerning the influence of the strength of the stimulus,
upon contraction see page 197.

Wave of contraction. — Though but a limited portion of
a muscle is stimulated, the whole muscle contracts. The
contraction is propagated in the form of a wave in both
directions from the spot stimulated throughout the muscle
fibres. If the motor nerve of a muscle is stimulated, the
wave of contraction spreads from the place of entrance of the
nerve through the fibres.

The rapidity of the contraction wave is measured by
stimulating a certain part of the muscle and placing two
recording levers at unequal distances from the stimulated
spot. The increase in diameter of the muscle due to con-
traction will not meet the two levers at the same time, and
this difference in time will represent the length of time taken
by the contraction wave to travel through the distance which
separates the two levers.

The rate of the contraction wave in the skeletal muscle of
a frog at room temperature is three metres per second, for
the muscles of a rabbit four to five metres, and for a human
muscle ten to fifteen metres. In smooth muscles it is ten
to fifteen mm per second. The rate is decreased by cooling
the muscle and by fatigue. The duration of the contraction

GENERAL MUSCLE PHYSIOLOGY 191

wave in the cross-section of a fibre is of course less than the
duration of contraction of the whole muscle; it is about 0.05
to 0.09 second in the frog-muscle. The length of the con-
traction wave in the frog-muscle is 200—380 mm.

In striated muscles, except in the cardiac muscle, the
contraction does not pass from one fibre to another as it does
in the smooth muscles.

Superposition of twitches. Tetanus. — If a muscle is
stimulated by many single stimuli which follow each other
so fast that the interval between two successive stimulations,
is less than the duration of the contraction, the individual
twitches called forth by the individual stimulations combine.
But the increase in contraction which each successive
stimulation produces is smaller than that of the preceding.
Finally a maximum contraction is reached which cannot be
surpassed by the succeeding stimulations. If the interval
between the stimulations is small enough, a lasting contrac-
tion is produced by the combination of the twitches, which
is called tetanus. In a frog-muscle tetanus is produced at
room temperature when about 20 stimulations per second are
sent into the muscle.

In a muscle without any load, the height of a tetanic con-
traction may be 80$ of the length of the fibre. In a loaded
muscle it is less in proportion as the load is greater.

It is difficult to tetanize the cardiac muscle (see page 64).

The voluntary muscle contraction is also tetanic. This
is apparent from the variations frequently seen in the con-
traction of a voluntarily contracted muscle which can be
graphically registered by recording the thickening of the
muscle. There are about 8 to 12 oscillations in one second.

Muscle-sound. — If an artificially stimulated muscle is connected
with the ear by means of a sound-conductor, a sound is heard
which corresponds to the number of oscillations. From volun-
tarily contracted muscles a sound is also heard (19 vibrations per
second), but it is doubtful whether this sound is produced by the
oscillatory stimulation of the muscle daring voluntary contraction,
for a sound is also heard during a single twitch (see first cardiac
sound, page 68).

192

HUMAN PHYSIOLOGY

Extensibility of the tetanized muscle. - - The tetanized
muscle is more extensible than the resting muscle. The
curve of its extensibility resembles a hyperbola, but its
course is steeper than that of a resting muscle (Fig. 10).

10

30

40

D

B

FK;. 10. — CURVES OF EXTENSIBILITY OF A RESTING AND AN ACTIVE MTSCI.K

(DIAGRAMMATIC).

a, b. c, d, t: are the length of a resting muscle loaded with o, 10, 20. 30, 40
grams; the curve AB which joins the ends of these perpendiculars represents the
carve of extensibility. Correspondingly, CD represents the curve of extensibility
of the tetanized muscle.

Continuous contraction not tetanic. — By the action of con-
tinuous stimuli upon muscles (e.g. stimulation by ammonia,
a constant current) a continuous contraction is produced, of
which it has not been proven that it is produced by the
combination of twitches.

(/>) Work done by a stimulated muscle. — The work done
is the product of the weight raised by the height to which it
is raised. Other things being equal, the height of the con-
traction is proportional to the length of the fibres.

The force with which the weight is raised is, other things
being equal, proportional to the cross-section of the muscle.
In muscles in which the fibres run obliquely, the so-called
physiological cross-section, that is, the cross-section of all
the fibres, must be taken into consideration.

The absolute force of the muscle is equivalent to the
weight which just prevents the contraction of a maximal
tetanized muscle. The absolute force of the striated frog-

GENERAL MUSCLE PHYSIOLOGY 193

muscle is 3 kg for i sq. cm. of cross-section, of the human
muscle it is 10 kg.

The work done by an active muscle is zero if the load is
zero or if the load is so great that the muscle can no longer
raise it. Between these two extremes the amount of work
done increases with the increasing load up to a certain
maximum, beyond which it decreases.

The raising of the load to a height equal to the extent of
the contraction of the muscle is not the greatest 'amount of
work capable of being performed by the muscle. The
muscle does more work when

(1) The load is not raised, but is thrown upward; it can
then rise higher than the corresponding contraction of the
muscle.

(2) When the contracting muscle after it has raised the
load is gradually unloaded. Then the muscle shortens more
and performs new work by raising the lessened load. Many
muscles in the human body, because of the relation of their
joints, work according to this advantageous principle of
unloading.

In addition to the performing of real work, the muscles
also perform the function of keeping raised weights sus-
pended and of holding the individual parts of the body
together. This also takes place with expenditure of energy
by the tension of the muscles.

An adult man can perform, in eight hours, a work of
about 300,000 kilogrammetres.

B. The formation of heat hy active muscles. — Of the
energy set free by an active muscle at most only one-fourth
is used for the performance of work, the remainder being
transformed into heat.

The muscles work much more economically than the steam-
engine, for, in the best-constructed steam-engine, only one-tenth
of the energy set free by the burning of the coal is used in doing
work.

When no external work is done, all the transformed force
appears as heat; in this case we can calculate the extent of

194 HUMAN PHYSIOLOGY

metabolism by measuring the heat produced in the stimulated
muscle. When a tetanized muscle, carrying a load, holds
the load suspended, it no longer does any work, hence all
the transformed energy appears as heat.

To conduct the experiment in such a manner that the muscle
in acting shall do no external work, the raised weight is left on
the muscle, and when the muscle relaxes it is allowed to sink.
The heat produced by an excised frog-muscle is measured by the
thermo-electric method, a delicate thermopile being used. In
many cases the heat produced by a contracting muscle can be
directly measured by a delicate thermometer placed upon the skin
over the muscle.

By a single contraction the frog-muscle increases in tem-
perature by 0.001° to 0.005° C., during tetanus more.
The amount of heat produced by the twitching of a frog-
muscle of one gram is about three micro-calories. This
amount of heat is produced by the oxidation of 0.0008 mg
sugar.

C. Electrical phenomena in the active muscle. —The
part of the muscle in contraction is negative to the resting
part. The development of electricity during contraction
occurs mostly during the latent period, so that the negative
phase is nearly past before the contraction begins. The
wave of contraction is preceded by a " negative wave. ' '

Suppose AB in Fig. 1 1 to be a muscle fibre, the points
a and b of which are connected with a galvanometer L. If

C i>

FIG. ii.

we stimulate the muscle at C, immediately after the stimula-
tion has reached a an electric current passes through L
from b to a, a having become negative. Soon after this,
when the stimulation has reached b, the current passes
through L from a to b. These currents are called the
action-currents and follow each other with great rapidity.

GENERAL MUSCLE PHYSIOLOGY 195

They arc investigated with the same apparatus as the action-
currents of nerves (see page 217).

Secondary contraction, secondary tetanus. — If the nerve of
a muscle-nerve preparation is placed upon the surface of
another muscle, and if the latter or its nerve be stimulated,
both muscles are thrown into simple contraction or tetanus.
The action-current of the stimulated muscle passes over into
the nerve of the other muscle-nerve preparation and stimu-
lates it. Lasting contractions, not of a tetanic nature, do
not produce secondary tetanus.

If a muscle is cut across and one of the electrodes of a
galvanometer is connected with the transverse section, while
the other electrode is connected with the longitudinal sur-
face, a current passes through the galvanometer from the
longitudinal to the cut surface. This is called the current
of rest. At the cut surface the muscle dies and this is con-
nected with processes which render the dying part negative
to the part intact. If now the longitudinal surface is stimu-
lated, the intensity of the current of rest is decreased; this
is called the negative variation.

The electromotor force of the current of rest of a muscle
is about 0.07 volt.

The cause and the significance of these electrical phe-
nomena in stimulated and dying muscles is not well under-
stood.

3. THE STIMULATION AND THE IRRITABILITY OF
THE MUSCLE

The stimulations which call forth the activity of the
muscle may be divided into:

A. Indirect, i.e. stimulations which act upon the motor
nerves and thus upon the muscle. In this class belong the
normal physiological stimulations which are carried from the
central nervous system through the motor nerves to the
muscles.

B. Direct, i.e. stimulations which affect the muscles

196 HUMAN PHYSIOLOGY

directly. The muscle is directly irritable without the inter-
vention of the nerves, as is proven by the following facts:

(a) In the sartorius muscle of a frog the nerve fibres dis-
tribute themselves only in the middle of the muscle, for the
two ends, as proven by microscopic examination, are free
of nerve fibres for about one-eighth of the total length of the
muscle. Yet stimulation of the ends, free of nerve fibres,
produces contraction of the muscle.

(b) Ammonia stimulates the muscles directly, but does not
stimulate the nerve fibres.

(r) Curare paralyzes the nerve endings in the muscle.
In an animal poisoned with curare, stimulation of the nerve
has no effect upon the muscle, yet the curarized muscle is
directly irritable.

(W) 4< Idiomuscular" contraction is the local contraction
of the muscle fibres produced by the mechanical stimulation
of an abnormal muscle (fatigue, disease). This contraction
is produced only at the place of stimulation, the contraction
not being spread along the nerve fibres.

The direct stimuli of the muscles are :

1 . Mechanical. Cutting and pinching of the muscle stimu-
late it.

The external mechanical conditions also have an influence
on the irritability. With stimuli of the same strength, the
greater the resistance which the contraction of the muscle
encounters, the more energy is set free. This is useful, for
the muscle offers more force against greater resistance.

2. Thermal. Heating above 40° produces a continuous
contraction which finally goes over into heat rigor identical
with rigor mortis (see page 198). Below the temperature
of 40°, the irritability increases with the temperature.

3. CJicmical. Certain chemical agents stimulate the
muscle, e.g. ammonia, alkaline sodium, salt solutions; but
these speedily injure it so that it becomes non-irritable.
Other substances, such as acids, merely injure the muscle
without previously stimulating it. Physiological salt solu-
tion (o.6fc NaCl) is indifferent.

GENERAL MUSCLE PHYSIOLOGY 197

4. Electrical. A constant current of sufficient strength
passing through a muscle in its longitudinal direction causes
contraction when the current is made, and sometimes also
when the current is broken. During the passage of the
current through the muscle, the muscle undergoes a lasting
contraction, which is, however, less marked than the initial
or make contraction.

If the current is passed transversely through the muscle,
it does not stimulate it.

• By studying the nature of the wave of contraction, it has
been found that in the make contraction the stimulation
begins at the negative pole (kathode) and from there spreads
throughout the muscle, while in the break contraction it
begins at the anode.

Induction currents stimulate only at the kathode.

In order to stimulate, the current must be active for a
certain length of time ; currents lasting for a very short time
are not effective. The different kinds of muscles behave
differently in this respect. While striated muscles are more
affected by sudden changes in the intensity than by long
duration of the current, in case of smooth muscles it is the
reverse.

At the places of entrance and exit the current changes
the irritability of the muscle in the same manner as in the
nerve (see page 220).

The electromotor resistance of the muscle in the longitudinal
direction is two and one-half million, that in the transverse direc-
tion is twelve and one-half million, times greater than that of
mercury.

Relation between the stimulation and the contraction. — The
extent of the contraction (measured by the heat produced)
increases with the strength of stimulation up to the higher
limit, beyond which increase in the stimulation does not
produce an increase in contraction.

The irritability of the muscle is dependent upon the
normal vital processes, as well as upon the previously
mentioned influences (mechanical conditions, temperature,
chemical agents, electrical currents).

I98 HUMAN PHYSIOLOGY

Excised muscles of warm-blooded animals lose their
irritability in a few hours ; those of cold-blooded animals, at
a moderate temperature, in two to three days, while in a
lower temperature they retain their irritability for a long
time (as long as twelve days). Stoppage of circulation or
lack of oxygen soon destroys the irritability of muscles of
warm-blooded animals.

Irritability is maintained only by the proper alternate
succession of rest and activity. On the one hand, the
irritability is lost by complete rest (e.g. in limbs which
remain at rest for a long time in fixed bandages); on the
other hand, the irritability is decreased by too great stimu-
lation. Section of the motor nerve after some time also
destroys the irritability of the muscles and causes it to
degenerate.

Fatigue manifests itself by decrease in irritability and
ability to do work ; subjectively it manifests itself by painful
sensations in the muscle. The fatigue is due to :

(1) Decomposition products (e.g. sarcolactic acicl) pro-
duced by the prolonged activity of the muscle which
decrease the irritability.

(2) The disappearance of material for furnishing energy.
If the fatigued muscle is allowed to rest, it recovers and

the irritability increases by the removal of the fatigue-sub-
stance and by a fresh supply of oxidizable material.

Rigor mortis. — During the death of a muscle phenomena
similar to those of a contracting muscle appear, namely,
contraction (produced by the tension of the muscle in rigor
mortis), production of heat, consumption of oxygen, forma-
tion of carbon dioxide and lactic acid, disappearance of
glycogen, electrical phenomena. Rigor mortis has there-
fore been regarded as the last contraction of the dying
muscle.

Besides the above-named processes, the coagulation of
myosinogen also takes place ; this causes the dead muscle
to have a whitish, cloudy appearance.

The nervous system influences rigor mortis. Rigor mortis

GENERAL MUSCLE PHYSIOLOGY 199

sets in later in a muscle whose motor nerve has been cut
than in a muscle whose nerve has not been cut.

Heat rigor, which takes place when a muscle is killed by
heating it above 40° C., is identical with rigor mortis.

Physiological differences between smooth and striated
muscles. — The smooth muscles differ physiologically from
the striated in the following points :

1. The striated, except the cardiac muscles, are voluntary
muscles; the smooth, except the ciliary muscles of the eye
which function during accommodation, are involuntary.

2. The smooth muscles contract more slowly and the
contraction wave is much longer than in the striated muscles
(see page 190). Of the striated muscles, the cardiac muscle
contracts more slowly than the skeletal muscles. But in
the cardiac muscle the striation is less perfect than in skeletal
muscles. The more nearly perfect the cross-striation the
greater the velocity of contraction.

3. Smooth muscles are more readily stimulated by long
duration than by sudden changes in the intensity of the
electric current, while the striated muscles are more readily
stimulated by sudden changes in the intensity of the current.

4. In the smooth muscle the stimulation passes from one
fibre-cell to another, not so in the striated muscle (except
cardiac).

Protoplasmic and ciliary movement.

i. Protoplasmic movement. — White blood corpuscles, like
armcba, change their shape by the thrusting out and draw-
ing in of pseudopods. By attaching a pseudopod to the
underlying surface and drawing the body along by the con-
traction of the protoplasm, they are also able to move from
place to place. During rest the pseudopods are withdrawn
and the cell is spherical.

Within the limits of temperatures by which the cell is not
injured, the higher the temperature the greater the proto-
plasmic movements. At a temperature of a little above
40° C. the pseudopods are withdrawn ; in heat rigor the
cell is spherical. Lack of oxygen paralyzes.

200 HUMAN PHYSIOLOGY

If the cells are stimulated by an induction current, the
pseudopods are withdrawn. Stimulations which work upon
the cell from one side, e.g. chemical influences, may have
an orientating effect upon the movements of the cell. The
wandering of the leucocytes through the walls of the blcod
vessels into the tissues seems to be caused by chemical
stimulation falling upon the cell from one side only.

The constant electric current also orientates the movements of
naked protoplasmic bodies, by polarization at the places of
entrance and exit. In many amoebae the movements are always
towards the kathode. The orientating effects of chemical and
electric stimulations are called chematropism and galvanotropism.

2. Ciliary movements. — The epithelial cells of many
mucous membranes have, on their free surfaces, cilia which
move forward and backward in a definite direction. The
movement in one direction takes place with greater velocity
than in the opposite direction, hence light particles resting
on the surface of the mucous membrane are carried forward
in that direction in which the movement is stronger.

The ciliated epithelial cells of a mucous membrane stand
in close physiological relation to each other, so that the
movements of all the cilia occur in a definite, orderly
manner. The nature of this physiological relationship is
not known.

The activity of the cilia is favored by oxygen and by the
feeble alkalinity of the surrounding fluid.

In man, cilia are found in the mucous membrane of the
air passages, uterus, oviducts, and on the ependyma of the
cerebral ventricles. The movements of the cilia in the air
passages force the mucous and the inhaled dust outward ; the
movements of the cilia in the oviducts and uterus serve to
move the egg forward.

The spermatozoa are composed of a head and a long
thread-like tail. This tail, by making whiplike or pendu-
latory movements (analogous to the cilia of the ciliated cells),
propels the spermatozoa forward. These movements are
increased by the feeble alkalinity of the medium in which
the spermatozoa move ; they are decreased by acid fluids.

CHAPTER XV
SPECIAL PHYSIOLOGY OF THE MUSCLES

THE subjects of the special physiology of the muscles are :

1. The functions of the skeletal muscles in general.

2. Standing, walking, and running.

3. The voice.

1. FUNCTIONS OF THE SKELETAL MUSCLES IN
GENERAL

A. The bones and their articulations. — The bones are
rigid bodies which support the various soft parts of the
animal body. They are formed
so as to furnish the greatest
strength with the least bulk. To
accomplish this the long bones
are hollow, and in the short bones
the lamellae are especially closely
packed in the direction in which
the greatest pressure or pull is
exerted (see Fig. 12).

The articulations may be di-
vided into:

i. Synchondrosis, the articu-
lation of two bones by means of
cartilage. In synchondrosis, the ,.. (. I2._v,^ rART OF THE
bones retain, when no external FEMUR, SHOWING THE ARKANGE-

forces are active, a definite posi- **** OF THK^ LAMEIJ-*.

' (After II. Meyer.)

tion towards each Other; when The lamella are especially closely
external forces are applied, the packed in the direction in which

the weight of the body acts and
bones Can move upon each Other in which the muscles inserted upon

in all directions, the cartilage the ^chanter major act.
being twisted. Such movement is,

";^°

B R A R V

202 HUMAN PHYSIOLOGY

2. Joints, i.e. articulation without definite position of
equilibrium of the articulated bones.

The two surfaces by which the two bones are jointed touch
each other ; they are smooth and can move over each other,
and this movement is aided by the synovia, a fluid found in
the joints which acts as a lubricant.

Synovia is an alkaline stringy fluid which is rendered cloudy by
the remains of cells. It contains proteids, salts, and a nucleo-
albumin which is similar to but not identical with mucin. Its
composition varies with rest and activity.

Frequently there is found between the two bones of the
joint a cartilage which serves to give greater surface to the
joint and aids in the movement of the bones in cases where
the two heads of the bones do not fit into each other.

The joints are covered by the capsular membrane. This
is a connective tissue membrane fastened to the bones which,
by its flaccidity, allows the movements of the bones against
each other.

Many joints, amphiartrosis, have a membrane so tense that no
movement of the bones is possible. These joints are, from a
mechanical standpoint, equivalent to the synchondroses.

The surfaces of the joint are planes of rotation. A plane
of rotation is a plane described by a curve when it is rotated
around a straight line lying in the plane of the curve.

The joints are classified according to the form of the
curve describing the plane of rotation and the position of the
axis of rotation.

I. The curve is the arc of a circle.

(a] The straight line passes through the centre of the
circle. The plane of rotation is a part of a spherical surface.
A joint with such planes is called a ball-and-socket joint,
or arthrodia. In such a joint the jointed bones turn around
any number of axes of rotation which all pass through the
centre of the sphere. We may, however^ conceive of all
the possible movements as movements around three lines
perpendicular to each other and passing through the centre
of the sphere. Examples: hip-joint, shoulder-joint.

SPECIAL PHYSIOLOGY OF THE MUSCLES. 203

(b) The straight line docs not pass through the centre
of the circle.

(a) It lies on the concave side of the arc : oval plane,
oval joint .

The oval joint has two axes, of which one coincides with
the rotation axis of the plane of rotation ; the other, passing
through the centre of the arc, is perpendicular to the first
axis. Example: radio-carpal joint.

(#) The straight line lies on the convex side of the arc:
saddle-joint.

The saddle-joint has two axes which are analogous to
those of the oval joint. Example : joint between the trape-
zium and the metacarpus pollicis.

2. The curve has any form except that of a circle, and
the straight line may have any position.

Such joints are called hinge-joints; they have one axis of
rotation which coincides with the axis of the plane of rota-
tion. If one of the two bones forming a hinge-joint is
imagined to be fixed, a given point of the second bone,
on moving, describes a circle. Example: joints of the
phalanges.

As special cases we must also mention :

1 . The screwed- surface joint, a joint with one axis and in
which a given point of the supposed movable bone describes
a spiral line instead of a circle. In the screwed -surface joint
the bones, during turning, slide over each other in opposite
directions but move in the direction of the axis. Example:
the elbow.

2. The spiral joint. The plane of rotation of the spiral
joint may be conceived of as follows: The curve which by
its rotation describes the plane of rotation approaches during
this movement nearer to the straight line. A given point
in the curve, therefore, does not describe a circle but a
spiral. Hence a given point of the imaginary movable bone
describes not a circle but a spiral. Example: the knee.

Mechanisms by which the joints arc Jicld together. — Besides
the ligaments (ligamenta accessorial of the hinge-joint) and

204 HUMAN PHYSIOLOGY

the tension of the surrounding muscles, the bones of the
joints are held together by atmospheric pressure.

If, in a dead body, all the connections between the femur
and the pelvis are cut, and also the capsular membrane of
the hip-joint, the femur still remains in its socket because
atmospheric pressure presses the surfaces of the joint against
each other. The force with which the bones are held
together by atmospheric pressure is, in the hip-joint, about
22 kg, which is more than the weight of the limb.

Limitations in tJie movements of bones connected by joints.
— The movements of the bones are naturally limited, often
especially so by processes of the bone (e.g. the olecranon
process, which prevents the complete rotation of the elbow
forward) and by ligaments (e.g. the posterior crucial liga-
ment of the knee, which prevents the complete backward
bend of the knee).

B. Action of the muscles upon the bones. — By the con-
traction of a muscle its points of insertion are brought nearer
together. Hence a muscle can only act when its points of
insertion can approach each other.

But the line in i^Jiieh tJie in serf ion points approach each
other does not always coincide with the longitudinal direc-
tion of the muscle fibres, because the insertion points are
not free to approach each other in a straight line, but the
nature of their movement is determined by the nature of the
articulation.

If, for example, the two insertion points are attached to two
bones articulated by ball-and-socket joint, and if we imagine one
bone as immovable, then the insertion point on the other bone
can only assume points all of which lie in a spherical plane. If
the bones are articulated by a hinge-joint, the insertion joint on
the imaginary movable bone can move only in a circle.

By the contraction the insertion points approach each
other because the muscle fibres are stretched straight
between the insertion points.

If the muscle fibres are not stretched straight between the inser-
tion points but move over a pulley-like arrangement, the points

SPECIAL PHYSIOLOGY OF THE MUSCLES

205

of insertion can, by the contraction of the muscle, go farther
apart. This is the case, e.g., in the superior oblique muscle,
whose insertion on the eyeball is removed by the contraction of
the muscle from its insertion in the optic foramen, because the
trochlea serves as a pulley.

All the force of a ' contracting muscle is effective for
mechanical work only when the insertion points move in the
longitudinal direction of the fibres. In all other cases only
a part of the muscle force is effective. This part is found
by resolving the force into its components according to the
law of the parallelogram of forces.

EXAMPLE, — In Fig. 13, let AB and AC be two bones which by
the hinge-joint A move around a line passing
through A perpendicular to the plane of the
paper, /and^ are the insertion points of a
muscle fibre m, by the contraction of which
the point J^ is moved forward in the direction
perpendicular to AC (J is supposed to be
immovable). If the force of the muscle is
represented by the length of the lineJ^D, that
part of the force which causes /, to move
forward is found by resolving J^D into its
components. According to the law of the
parallelogram of forces, draw JJE and its per-
pendicular JJF. J^E indicates the amount of
force which causes Jl to move forward.

If, in a hinge-joint, the direction of pull of
a muscle acting upon a given point of the
movable bone does not fall in the plane of
the circle described by the moving point, the
muscle force must be resolved into three com-
ponents. One of these, the active component,
falls in the direction of the moving point, the other two, inactive,
are perpendicular to this and also to each other, and one of these
lies in the plane of the circle.

In a ball-and-socket joint the muscle force is resolved into two
components whose directions fall in the plane of traction of the
muscles and the centre of the ball. One of these components,
the active, lies in the direction in which the supposed movable
insertion point moves in this plane; the other is perpendicular to
this.

If two or more muscles work upon a movable bone, we
first determine the active component of each force, and of

206 HUMAN PHYSIOLOGY

these individual active components we find the single result-
ant according to the law of the parallelogram of forces.

Muscles acting in the same direction are said to be syner-
getic, while antagonistic muscles are those which act upon a
joint in opposite directions.

We may analyze the movements of the bones according
to the laws of the lever, for all movable bones may be con-
sidered as one- or two-armed levers. The length of the
lever-arms from force to fulcrum and that from fulcrum to
weight is the distance from the axis of the joint to the point
at which the force and the weight work.

In the body, the lever-arm of the force is generally smaller
than that of the weight. This is not unfavorable, however,
for by it we gain velocity, even though it be at the expense
of force.

During the motion of the supposed movable bone, the
amount of the effective force frequently changes because of
changes in the lever-arm either of the force or of the weight.

Of interest is the decrease of the weight-arm during the move-
ment, for thereby the muscle works more advantageously (see page
193). An example of a movement of the body during the unload-
ing [Kntlastung] of a muscle is the elevating of the body by the
knee-joint. In the position with flexed knee, the lever-arm of the
weight is the horizontal distance of the axis of the knee-joint from
the perpendicular line through the centre of gravity of the body,
which lies at the promontorium. This distance becomes smaller
as the body is elevated and, in the upright position, is zero. The
direction of pull of the quadriceps, which straightens the knee,
retains, during the movement, approximately the same distance
from the axis of the knee-joint.

2. STANDING, WALKING, RUNNING

The general erect position (standing) and the general
modes of locomotion (walking, running) have a typical form
in all people, for they are based upon a common principle,
that of the least muscular exertion. We are accustomed so
to stand and move that the muscles are as little exerted as
possible.

SPECIAL PHYSIOLOGY OF THE MUSCLES 207

In standing erect the position of the body is such that the
centre of gravity is vertically over the base formed by the
feet, and when the limbs are placed against each other, the
longitudinal axis of the body is nearly vertical.

The base of support is a hexagon whose angles are formed
by the heads of the first and fifth metatarsus and by the
calcaneum on both sides. The centre of gravity of the body
lies somewhat in front of the promontorium of the spinal
column.

The muscles which during quiet standing fix the limb are,
in reality, only:

1 . Calf-muscles. The contraction of these prevents the
body from falling forward which might be caused by the
bending of the lower part of the leg at the ankle-joint.

2. The muscles of the neck, by the contraction of which
the forward sinking of the head is prevented (lowering of the
chin upon the chest as in sleep).

3. To a smaller degree the neck and hip muscles, which
prevent the bending of the cervical and lumbar vertebrae.

Besides this the limbs are held firm by the following
ligaments :

(1) The superior ileo-femoral ligaments (ligamenta Ber-
tini) which prevent the body from falling backward by turn-
ing at the hip-joints.

(2) The posterior crucial ligaments of the knee-joints,
which prevent the body and the upper part of the legs from
falling forward by turning at the knee-joints.

As the arms hang loosely suspended by the sides of the
body, they need no mechanism for fixation.

Many authors suppose that the body is not thrown forward but
backward by the bending of the knees. If this is true, the fixation
of the knees is not caused by the posterior crucial ligaments, but
by the quadriceps femoris.

Turning the feet out aids in holding the lower limb against the
foot in the ankle, for in placing the feet outward the two axes of
the joints do not fall in the same direction but converge forward.
This makes a simultaneous rotation around both axes, without a
change in the position of the legs, impossible.

208 HUMAN PHYSIOLOGY

Locomotion. — In locomotion, the head, the trunk, and the
suspended arms must be regarded as a body balanced upon
the legs at the hip-joints. The legs support the body and,
by stretching, push it forward. The leg can swing forward
and backward without any muscular exertion. In order
that the one leg may swing forward, it is somewhat elevated
by a slight bending at the hip-, knee-, and ankle-joints; the
body is meanwhile supported by the other leg.

The top part of the body is slightly bent forward during
locomotion; this is the greater the faster the motion. The
forivard movement of the body is produced by the alternate
action of one leg supporting the body and pushing it forward
iv/iile tJie other, slightly dent, swings forward.

In walking, a period during which both feet are on the
ground is followed by a period in which only one is placed
on the ground while the other swings. In running, a period
during which neither foot rests on the ground is followed by
a period during which one stands while the other swings.

The process from the beginning of the swinging of one
leg until the beginning of the swinging of the other is called
a step. The velocity of locomotion is the greater the
longer the step and the greater the number taken in a given
time (or the smaller the duration of the step). The velocity
of locomotion during walking is limited — maximum 2.5 m
'per second — because, on account of the simultaneous resting
of both feet on the ground, the length and number of the
steps cannot exceed a certain amount. In running, the
velocity of motion can be greater than in walking because
the length and number of steps can be increased, on account
of the simultaneous swinging of both feet.

In walking, the velocity is the greater the lower the
position of the head of the femur. Synchronously with the
movements of the legs, a rhythmical pendulation of the arms
takes place, in opposite direction to that of the legs.

The alternate rising and sinking of the body during walk-
ing is small (about 32 mm).

The work done by the body during walking on a hori-

SPECIAL PHYSIOLOGY OF THE MUSCLES

209

zontal plane is about 3 kilogrammetres for each step; during
running it is more. This work is, however, not lasting,
since, during each step, the elevation of the body is lost.

3. VOICE AND SPEECH

1. Production of voice. — The larynx with the vocal
cords forms a reed organ with membranous reeds. During
the production of voice the inner borders of the vocal cords
approach each other and are stretched. When, now, the
expired air passes through the larynx, the vocal cords
vibrate. By this vibration of the cords, the glottis alter-
nately opens and closes so that the expired air is emitted
intermittently. In this manner, vibrations of the air are
produced which are strengthened by the resonance of the
pharynx and mouth and can be perceived as sounds by the
ear.

(a) The mechanism of 'the vocal chords. — The cartilages
concerned in the study of the vocal
cords are :

The cricoid, a cartilaginous ring
at the upper part of the tracheal
wall; it has the form of a signet
ring with the broad part on the
posterior side (cr, Fig. 14).

2. The thyroid (t/i) consists of
two perpendicular plates which
meet at a right angle in front ; the
posterior border is continued up-
ward as the large horn, and down-
ward as the small horn (a). The
points of the small horns form joints
with the sides of the cricoid. The

M.cric.thyr.

FIG.

14. — PROFILE OF THE

LARYNX.

///.thyroid cartilage; a, smaller
horn of the thyroid cartilage;
a>\ arytenoid ; ///, processus
muscular is ; r, processus voca-
lis ; <•//, vocal chords; cr, cri-
coid; />-/>, direction of move-
cartilage

c ,. . . . A ment of the thyroid

axis ol this joint around which the during contraction of the crico-
thyroid turns is horizontal from thyroid (J/. eric. Mrr.).
right to left.

3. The arytenoids (ar) arc two three-sided pyramids

2io HUMAN PHYSIOLOGY

whose bases are movably articulated with the posterior parts
of the upper surface of the cricoid.

The vocal cords are foldlike processes of the inner wall
of the larynx, which in front are attached to the posterior
wall of the thyroid ; at the rear they are attached to the vocal
processes, which are anterior processes of the triangular
bases of the arytenoids. During quiet breathing the space
between the vocal cords and the two arytenoids, called the
glottis, is open. The glottis has the form of an isosceles
triangle (Fig. 16, I). When the glottis, for production of
voice, must be narrowed, the arytenoids approach each
other until they come into contact and the vocal cords are
tense.

A. In the closing of the glottis, the following parts func-
tion:

1. The transverse and oblique aryteuoid muscles, which are
inserted on the posterior side of the two arytenoids and by
their contraction draw the posterior parts of the arytenoids
toward the median line (Figs. 15 and 16, II and III). -

2. The lateral crico-arytcnoid on both sides, which pro-
ceeds from the lateral surface of the cricoid upward and

'==jj^\.. M.aryt.tr.et obi. backward to the muscular pro-
cesses (lateral angle of the base
of the arytenoids). By the con-
traction of the muscles the
. arytenoids are turned about a

[-M.enc.ary.post J

vertical axis and the vocal pro-
cesses are drawn toward the
FIG. iq. — POSTERIOR VIEW OF ,. .. . . ..

LARYNX. median line. Its antagonist is

M. arvt. tr. et obi., transverse and the posterior crico-arytenoid,

S^iSftErt^w* which alone turns the ™cal

muscle. processes outward and, in con-

junction with the lateral, turns the whole arytenoid outward.
In this manner the glottis is opened.

B. To render the vocal cords tense, the following parts
function :

I. The erico-tJiyroid muscle, which pulls the thyroid

SPECIAL PHYSIOLOGY OF THE MUSCLES 211

forward and a little downward and hence increases the ten-
sion of the vocal cords attached to the thyroid.

2. The thyro-arytcnoid muscle, imbedded in the vocal
cords, function as the antagonist of the last-named muscle.
If it contracts simultaneously with the crico-thyroid muscle,
both it and the vocal cords which are formed by it are
rendered tense. Its contraction also aids in the -closing" of
the glottis, for the slightly outward-bent borders of the
vocal cords are stretched by its contraction.

Innervation : The crico-thyroid is innervated by the
superior laryngeal nerve ; all the others by the inferior
laryngeal.

I. II. III. IV.

FIG. 16. — RKPRKSKNTATION OF THE POSITION OF TIIK VOCAL CORDS

(DIAGRAMMATIC).

a, anterior end of the vocal cord; b and c, base of the arytenoid cartilages;
I, position of rest; II, the arytenoid have approached each other and the vocal
cords are in position for voice formation; III, form of the glottis during con-
traction of the transverse and oblique arytenoid muscles and the posterior
crico-arytenoid; IV, form of the glottis during contraction of the lateral crico-
arytenoid muscles.

(/?) The pitch, range, ami quality (timbre) of the human
voice. — The pitch of a reed pipe depends on the number of
vibrations of the reed. In a membranous reed, it depends
upon the length, thickness, and tension of the reed, hence
the pitch of the human voice is the higher the less the
length and thickness and the greater the tension of the
vibrating parts of the vocal cords.

Individual variations in the pitch of the voice are deter-
mined by the length and thickness of the vocal cords. The
vocal cords of a man, for example, are thicker and longer
(i 8 mm long) than those of a woman (12 mm long), hence
the man has a deeper voice than the woman.

212 HUMAN PHYSIOLOGY

Children do not show this difference in voice. The change of
the voice in man takes place at puberty. Castration prevents this
change.

One and the same individual produces tones of various
pitch by:

(1) Changes in the tension of the vocal cords, produced
by:

(a) Changes in the contraction of the muscles which
cause the tension of the cords to vary.

(<£) By changes in the force with which expired air is
emitted.

If the air is exhaled forcibly, the vocal cords are brought
into a new and slightly raised position which produces a
greater tension than when they are stretched straight
between their points of insertion.

The force of the exhaled air is generally 13-17 mm Hg.

(2) Variations in the length and breadth of the vibrating
parts of the vocal cords.

(a) Variation in the length of the vibrating part is pro-
duced by the greater or less pressing together of the aryte-
noids. If these are loosely pressed together, the edges of
the arytenoids also vibrate, but if they are firmly held, the
vocal cords only vibrate. In the first case the vibrating
reed is longer than in the second case.

(/>) By peculiarities in the contraction of the thyro-aryte-
noid muscle or by the so-called false vocal cords being
placed upon the true vocal cords so that only the small
inner margins of the true cords are allowed to vibrate. Be-
cause of the small extent of the vibrating part, the pitch is
high. ' It is used in the so-called falsetto.

(3) Variations in the thickness of the vocal cords.

Fibres of the thyro-arytenoid muscle, having a perpendic-
ular direction, by their contraction cause the upper and
lower surfaces of the vocal cords to approach each other and
thus change their thickness.

The range of the voice includes all the tones which an
individual can produce; generally it embraces two octaves.

SPECIAL PHYSIOLOGY OF THE MUSCLES 213

The range of the voice varies in different individuals. We
may classify them as:

Base, ranges from R to f .
Tenor, ranges from c to c"
Alto, ranges from/" to f".
Soprano, ranges from c' t

c to c'" .

The timbre of the voice depends upon the number and
strength of the overtones which accompany the fundamental
tone produced in the larynx. It is also dependent upon
accompanying noises. In one and the same individual we
can distinguish, by means of the timbre, the chest-tone from
the falsetto. The resonance of the chest-tone is chiefly
produced in the thorax and is deeper ; the resonance of the
falsetto is chiefly produced in the mouth, pharynx, and nose,
and is higher. The resonance only affects the timbre and
strength, not the pitch, of the voice.

The difference between the voice during singing and
speaking is not fully understood.

2. Speech. — The sounds of speech are produced by ex-
piration, which causes noises to be produced in the mouth
or nose and in the pharynx. These sounds may or may
not be accompanied by the voice.

Vowels are sounds of speech accompanied by the voice.
The tones which, produced in the buccal and pharyngeal
cavities, accompany the voice to give to it the vowel char-
acter, are called the determinants [Formanten] of the vowels.

Each vowel has one or two characteristic determinants
which are independent of the pitch of the voice. These are,
according to Helmholtz : for oo as in food,f\ for o as in no, b' ;
for a as in father, b" \ for a as in ate, f or //"; for c as in
scheme, f and d"" . Other authors give other determinants.

In the several vowels the determinants are different
because of the difference in the position of the buccal and
pharyngfeal cavities. For the production ofaasinfat/ter,
the cavity of mouth and pharynx has the shape of a funnel
with the apex toward the pharynx; for the production of o

214 HUMAN PHYSIOLOGY

as in no, and oo as in food, it has the form of a flask with a
short neck ; while for the production of a as in ate, and c
as in scJicme, it has the form of a flask with a long neck.

Perhaps there are, in the formation of vowels, besides these
definite determinants, others which are produced by the
resonance of the buccal and pharyngeal cavities, the pitch
of which depends upon the pitch of the voice, just as the
pitch of an overtone depends upon the fundamental tone.

Consonants are sounds not accompanied by the voice.
They are classified as :

1. Resonants; ;//, ;/, ng\ produced by closing the mouth
and driving the air through the nose.

2. Explosives; b, /, d, t, g, k\ produced by the forma-
tion of an obstruction to the expired air, or the removal of
such an obstruction (the nasal passage being closed).

3. Aspirates; iv, /, s, /, s/i, s, zh, tJi, j, ch\ produced
by driving the expired air through a constricted portion of
the mouth.

4. Vibratories; ;•; produced by the exhaled air throwing
the walls of a constricted portion of the buccal cavity into
vibration.

According to the position of the obstruction or constric-
tion in the buccal cavity we can distinguish between labials,
dentals, and gutturals.

The sound of Ji is formed when the exhaled air is un-
obstructedly driven through the mouth while the nasal
passage is closed.

CHAPTER XVI
GENERAL NERVE PHYSIOLOGY

1. THE CONSTRUCTION AND FUNCTION OF THE
NERVE ELEMENTS

THE nervous system is composed of nerve units called
neurons. The neuron is made up of:

(i) A nerve cell, and (2) its processes, which may be
divided into:

(a) Protoplasmic processes or dendrites, which are short,
much-branching processes, rapidly decreasing in size.

(/;) An axis-cytindcr process or neurite, which differs from
the dendrites in its hyaline, smooth appearance. Its thick-
ness is uniform throughout its course. At the end it splits
up into a group of brushes, the so-called end-tufts. Many
axis-cylinders give off lateral branches (collaterals) which
also end in tufts. The axis-cylinder, the most important
part of each nerve fibre, is sometimes longitudinally striated
owing to the fibrils of which it is composed. Between the
fibrils is found the neuroplasma, a finely granular substance.

The physiological processes in this nerve unit are such
that when the cell is stimulated either automatically (without
any outside stimulation) or by some outside stimulation,
which is taken up by the protoplasmic processes and
carried to the cell. The stimulation is also taken up by
the axis-cylinder which conducts it to the end-tufts. Thence
it is communicated to the organ with which the end-tufts are
connected (cells of other nerve elements, muscle fibres, or
gland cells.

The protoplasmic processes carry the stimulation celluli-

215

216 HUM/IN PHYSIOLOGY

petally, i.e. to their cells; the axis-cylinders carry it cellu-
lifugally, or from their cells. Accordingly, the peripheral
sensory nerves which carry the stimuli cellulipetally must
be regarded not as axis-cylinder processes but as elongated
protoplasmic processes.

The process of irritability and conductivity of the indi-
vidual neuron is tJie elementary physiological process wJiidi
lies at tJie basis of the functions of the nervous system.

The transmission of the stimulation from one neuron to another
is perhaps accomplished by delicate nerve fibril lae which connect
the end-tufts of one neuron with the protoplasmic processes of
another neuron. But it is difficult to demonstrate such fibrillae
anatomically.

Neuroglia and medullary sheaths appear to be supporting and
protecting organs for the real nerve-substance.

General nerve physiology is divided into two parts, corre-
sponding to the two parts of the neuron. .

1. General physiology of the nerve fibres, — including the
sensory nerves which must really be regarded as dendrites.

2. General physiology of the nerve cells.

2. GENERAL PHYSIOLOGY OF THE NERVE FIHRES

i. The irritability and conductivity of nerves. — The

nerve fibres serve to carry impulses from one end-organ, the
receiving organ (sense organ or nerve cell), to the other
end-organ (muscle, gland cell, or other nerve cell). The
stimulation of a nerve takes place normally in the receiving
organ, but can also be applied to any part of the nerve by
artificial stimulation.

The nature of the impulse and of the conduction of the
stimulation is not known. The only token of the impulse
which has been observed is an electrical phenomenon. An
active part of a nerve is negative to the resting part. The
significance of this phenomenon is not known.

In Fig. 17 let AB be a nerve; at a and b place the electrodes
of a galvanometer (Z), and stimulate the nerve at C by means of
an induction current. Shortly after stimulation the impulse

GENERAL NERl/E PHYSIOLOGY 217

reaches a, and an electric current passes from b to a through L.
When the impulse has passed a and is carried to b, a current passes
from a to If through L. These currents are called action currents.
Their rapidity is so great and they follow each other so closely that
they cannot be demonstrated by an ordinary galvanometer. They
can be demonstrated by a very sensitive electrometer (capillary
electrometer) or by a special apparatus in which the action upon
a magnetic needle is intensified by a series of action currents
moving in the same direction and rapidly following each other

FK;. 17.

through the galvanometer (Bernstein's repeating different ial
rheotome).

Cut a nerve across, place one electrode of the galvanometer on
the transverse section and the other on the longitudinal surface.
A current will pass through the galvanometer from the longitudinal
to the transverse section (current of rest). At the cut surface the
nerve immediately begins to die, and this is accompanied by
processes which make that part of the nerve negatively electrical
to the sound part. If in such a case a certain point in the longi-
tudinal surface be stimulated, the intensity of the current of rest
is decreased, that is, it undergoes a negative variation.

Aside from these electrical changes, the nerve impulse
can only be detected by the effects which it has upon the
end-organ (muscular contraction in the motor nerves, sensa-
tion in the sensory nerves).

2. Laws of conductivity of nerves.

(a) Isolated conduction. — In a nerve trunk composed of
many fibres the impulse does not pass from one fibre to
another.

(b) Double conduction. — A nerve artificially stimulated at
a certain point conducts the impulse not only in the direc-
tion in which it is conducted under physiological conditions,
but also in the opposite direction.

The nerve supplying the gracilis muscle of the frog divides into
two branches, of which the one supplies the upper and the other
the lower half of the muscle. At the forking of the nerve, the

2i8 HUMAN PHYSIOLOGY

axis-cylinders divide, so that each axis-cylinder gives a branch to
the lower and to the upper half of the muscle. If the muscle is
cut transversely without injury to the fork of the nerve and one of
the branches of the fork be stimulated, both halves of the muscle
contract. Hence the impulse of the stimulated nerve passes not
only in the centrifugal but also in the centripetal direction, and
then, in the other branch, passes in the centrifugal direction.

The electrical phenomenon also spreads in both directions from
the place artificially stimulated.

(e) Velocity of the impulse. — The velocity of the nerve
impulse in an excised frog nerve, at room temperature, is
27 metres per second. In man it has been variously stated
(between 30 and 60 m per second).

The velocity of the impulse is measured as follows : Take a frog
muscle-nerve preparation and stimulate the nerve in two places,
one at a place as near to, the other as far removed from, the mus-
cle as possible. Determine the difference in latent period (the
lapse of time between the stimulation and the beginning of con-
traction). This can be done best by graphically recording the
contraction. The latent period following the stimulation of the
point far removed from the muscle is greater than that following
the stimulation of the point near the muscle. The difference
between the latent periods is the time it takes for the impulse to
travel the distance between the two points stimulated. From this
it can be calculated how great a distance the impulse travels in one
second.

Experiments based on the same principle have been made upon
human beings, but the results are not constant.

3. Stimulation and changes in irritability. — The stimu-
lating influences in many cases also produce changes in
irritability and conductivity. Hence we may properly con-
sider these actions collectively.

(a) Mechanical influences. — Hitting, pulling, squeezing,
cutting, and drying stimulate the nerve, but also destroy its
irritability and conductivity.

(b) Thermal influences. — Temperatures above 45° C. and
below freezing-point destroy irritability and conductivity.
Within the limits of temperatures which are not injurious,
irritability and conductivity increase with the temperature.
Sudden great changes in temperature stimulate, e.g. touch-
ing a nerve with a red-hot needle.

GENERAL NERVE PHYSIOLOGY 219

(V) Chemical influences* — These maybe classified as:

1 . Those which destroy irritability and conductivity with-
out previously stimulating, e.g. acids, ammonia.

2. Those which first stimulate and then paralyze, e.g.
concentrated salt solution, glycerin.

If. a part of a motor nerve is acted upon by carbon
dioxide, that part of the nerve loses its irritability for elec-
trical stimulations, but does not lose its conductivity; for if
the stimulation is applied above the place acted upon by the
carbon dioxide, the impulse is still carried to the muscle.
Hence irritability and conductivity are to a certain extent
independent of each other.

(d) Electrical influences. — A constant current passed
longitudinally through a stretch of nerve of sufficient length
causes :

1. When made, stimulation and increased irritability at
the kathode (place of exit of current) ; decreased irritability
and conduction at the anode (place of entrance).

2. When broken, decreased irritability and conduction,
for a short time, at the kathode ; stimulation and also in-
creased irritability at the anode, lasting for a short time.
Stimulation by the electrical current which, in a motor
nerve, is manifested by the contraction of the muscle, as a
rule takes place only at the moment of the making and the
breaking of the current (make and break contraction) ; more
rarely it stimulates for some time during its passage through
the nerve (make-tetanus) and for some time after the break-
ing (break-tetanus). Hence the extent of stimulation of a
nerve depends chiefly on the changes in the strength of the
current, not upon its absolute intensity. Changes in the
strength of the current are the more effective the more
rapidly they take place. For this reason, when the current
is not suddenly made or broken but is made and broken
gradually, no contraction results. The make contraction is
stronger than the break contraction, so that a feeble but still
active current produces a contraction only at the make.

220 HUM/IN PHYSIOLOGY

The electric current does not stimulate if it passes trans-
versely through the nerve.

In Fig. 1 8 let Arbe the nerve of a muscle-nerve preparation, and
let the current enter at -|- and leave at — . Determine the latent
period for the make and break contraction
(in a similar manner as in determining the
velocity of the impulse, page 219). It will
be found that the latent period of the make is
greater than that of the break contraction.
If now the current is passed through the nerve
FlG- l8- in the opposite direction, it will be found that

the latent period of the make is smaller than that of the break
contraction. The difference in these latent periods corresponds
to the time taken by the impulse to travel through the piece of
nerve between the two electrodes. This proves that the stimula-
tion of the making of the current takes place at the kathode, while
that of the breaking occurs at the anode.

The changes in the irritability which the current produces at
the electrode are investigated as follows:

The nerve is stimulated near either electrode of the constant
current by a stimulus of constant strength, first before the con-
stant current is passed through the nerve, and then while the
constant current is passing through the nerve. Observe whether
the contraction in the second case is larger or smaller than that in
the first.

The irritability is changed during the entire passage of the
current. This condition of changed irritability produced by
the current is called clcctrotonns; the condition of increased
irritability at the kathode is called katelectrotonus, the con-
dition of decreased irritability at the anode is called anclcc-
trotonus. We may express these observations in the law:
The appearance of katelectrotonus and the disappearance of
an electrotonus stimulate.

The decreased conductivity occurring at the anode during
the making and, for a short period, at the kathode during
breaking, is so great, when strong currents are used, that- the
nerve at these places loses its conductivity altogether. If a
part of a nerve which has lost its conductivity is situated
between the place stimulated and the end-organ (muscle),
the stimulation has no result. This occurs in the following
cases:

GENERAL NERISE PHYSIOLOGY

221

(1) During making, when the anode lies between the
end-organ and the kathode. -

(2) During breaking, when the kathode lies between the
end-organ and the anode.

Law of contraction. — From the above-mentioned facts the
following relations between the stimulation of a muscle and
the strength of a current and its direction through the motor
nerve can be formulated :

Strength of Current.

Ascending Current.

Descending Current.

Make
Break

Contraction
Rest

Contraction
Rest

Moderate

Make
Break

Contraction

Contraction

Strong

Make
Break

Rest
Contraction

Contraction
Rest

The current is ascending when it passes through the nerve from
the muscle to the centre; it is descending when it passes from the
centre to the muscle.

The law of contraction may be explained thus : In a weak cur-
rent only a stronger stimulus is active, i.e. the appearance of
katelectrotonus stimulates; not so the disappearance of anelectro-
tonus, hence a contraction occurs only by the making. In a
moderate current both the appearance of katelectrotonus and the
disappearance of anelectrotonus stimulate, hence both a make and
a break contraction result.

In a strong ascending current the make contraction fails,
because the stimulation at the kathode cannot pass through that
part of the nerve where the conductivity has been decreased at the
anode. In a strong descending current the break contraction
fails, because the stimulation at the anode cannot pass through
the non-conducting part of the nerve at the kathode.

A current passing through a stretch of medullated nerve spreads
throughout the whole nerve; also to that part of the nerve beyond
the electrodes. If the two electrodes of a galvanometer are placed
upon the nerve exterior to the part stimulated, a current passes
through the galvanometer because of this spreading. This
phenomenon is of physiological interest, for this spreading is due
to a peculiar polarization of living nerve fibres. This spreading
of the current cannot be' demonstrated in a dead nerve. The

222 HUMAN PHYSIOLOGY

whole phenomenon has been called physical electrotonus in
distinction from physiological electrotonus (change of irritability).
The electrical resistance of the nerve in the direction of the
fibre is 2^- million, in the transverse direction 12^- million, times
as great as that of mercury.

Induced currents stimulate at the kathode only, hence act
as weak currents in respect to the law of contraction.

The uninjured motor nerves in the human body seem to
follow other laws of contraction than the excised nerves of
a nerve-muscle preparation. When one electrode is placed
on the skin above a nerve to be investigated and the other
on some indifferent part of the body (back, neck) remote
from the first electrode, a make contraction follows the
feeblest but yet effective current when the electrode placed
on the nerve is the kathode (kathode-make contraction).
A little stronger current produces anode-make and anode-
break contraction (when the electrode on the nerve is the
anode), and, in a very strong current, also the kathode-
break contraction. This apparent deviation from the law
of contraction is due to the nature of the spreading of the
current in the human body. The nerve, in this case, is
traversed by the branching currents in diagonal and trans-
verse directions, not merely longitudinally as in the excised
nerve.

(e) Irritability and conductivity depend also upon normal
vital conditions. Not only do excised nerves gradually
lose their irritability and conductivity, but also nerves which
have lost (by cutting, disease) their normal connection with
the nerve cells. A nerve thus severed dies, the axis-cylinder
and the medullary sheath disappearing and connective tissue
being deposited. Sometimes regeneration of the nerve trunk
still connected with the cell takes place.

A change in the irritability of the nerve by fatigue has;
not yet been definitely proven.

Nothing is known concerning the chemical composition of the
real nerve-substance. No processes of metabolism have ever been
demonstrated in the stimulated or unstimulated nerve. The
metabolism is, at any rate, even in stimulated nerves, very slight,,

GENERAL NERl/E PHYSIOLOGY 223

for nerves do not appear susceptible to fatigue, and the supply of
blood to them is small.

Neurokeratin is found in the neuroglia; fat, cholesterin, lecithin,
and protagon, in the medullary sheath.

4. The effect of the conduction of the impulse. — The

nature of the result of the conduction of the impulse to the
end-organ does not depend upon the nature of'the stimula-
tion, but upon the nature of the end-organ. For example,
each effective stimulation of a motor nerve is followed only
by a muscular contraction, of a secretory nerve by secretion,
of a sensory nerve only by sensation. In the last case only
that kind of sensation is produced which is specific for the
sense cell of the organ acted upon.

The nerve fibres may be classified as to the direction in
which they normally carry the impulse as:

1. Centrifugal (motor, secretory), conducting the impulse
from the nerve cell to the peripheral organ.

2. Centripetal (sensory, nerves acting reflexly), conduct-
ing from a sense organ to a nerve cell.

3. Intercentral conduction from one nerve cell to another.

Besides conducting the impulses the nerve fibres have an influ-
ence on the nutrition of the organs which they innervate. After the
nerves have been cut, the organs which they supply undergo dis-
turbances of nutrition, e.g. the dying of a muscle after section of
its nerves.

3. GENERAL PHYSIOLOGY OF THE NERVE CELLS

All the functions of the nervous system which we cannot
explain from the known functions of the nerve fibres we
ascribe to the nerve cell, for no other nerve elements are
known to which they can be ascribed. These functions do
not belong to the whole nerve cell, but to parts of the pro-
toplasm. The nucleus has probably only a trophic function.

The trophic action of nerve cells is illustrated by the fact that
nerve fibres separated from the nerve cells degenerate. In many
cases this is also true for end-organs (muscles) supplied by these
nerve fibres.

224 HUMAN PHYSIOLOGY

The nerve cells are irritable. Their physiological stimu-
lation is of two kinds :

1 . The stimulation originates by processes in the cells
themselves — automatic activity. The automaticity is either
tonic, when the impulse travels continuously through the
nerve fibre connected with the cell, or rhythmic, when the
impulse proceeds periodically down the nerve fibre. For
example, lack of oxygen and accumulation of carbon
dioxide stimulate the cells of the respiratory centre ; they
are conditions which the cell itself produces by its meta-
bolism. The automaticity of the respiratory centre is
rhythmic. The vaso-motor centre is also stimulated by
lack of oxygen and accumulation of carbon dioxide; its
automaticity is tonic.

2. The stimulation is carried to the cell by a nerve fibre.
As the stimulation can be conducted from this cell to its
axis-cylinder, there results the conduction of impulses from
one nerve fibre to another through the nerve cell. The
conduction of the impulse through the cell differs from that
through the fibres in the following points:

(a) The cell is able, independently, to modify the impulse
either

(cr) In intensity: it can increase or decrease the strength
of the impulse ;

(ft) In frequency of the impulse.

For example, the impulses which in the radiated reflexes
(see page 231) affect the muscles are not proportional to
the strength and frequency of the sensory stimulation which
calls forth the reflex.

(/;) The conduction is not double, but passes in one
direction only. In the spinal cord, for example, the impulse
passes, in reflex action, from the sensory nerve through the
cell to the motor fibres, but never in the reverse direction.
The electrical phenomena characteristic of the impulse can-
not be called forth in the sensory nerve by the stimulation
of the motor roots.

GENERAL NERYE PHYSIOLOGY 225

(V) The velocity of the conduction of the impulse through
the cells is much less than that through the fibres.

From a physiological standpoint, the individual processes
of conduction through the cells differ from each other only
in the number of the impulses passing through the neurons,
and in the modification of the impulse in the cells. From a
psychical standpoint we may classify the processes of con-
duction through nerve cells into:

1 . Conduction of impulses through the cells not accom-
panied by consciousness. This includes the reflexes, i.e.
the transferring of an impulse from a centripetal fibre through
a centre to a centrifugal fibre without resulting in conscious-
ness, which may indeed occur against the will.

2. Psycho-physical processes, which are accompanied by
consciousness. The transferring of the impulse from the
sensory nerve fibre through the central nervous system to
the motor nerve, wrhich occurs voluntarily, is called "volun-
tary reaction," in distinction from reflex action.

The chemical processes which take place in the resting and the
active nerve cells are not known. That they are intense is apparent
from the fact that even temporary cessation of the blood supply soon
causes injury. Death of the nervous system through asphyxia
occurs in warm-blooded animals in a few minutes.

CHAPTER XVII
THE SPINAL CORD

Anatomy. — The cylindrical spinal cord is composed of a column
of gray matter surrounded by a layer of white matter. In the cross-
section the gray substance has the form of an H.

Each half of the white substance is divided by the gray substance
into three columns, the anterior, lateral, and posterior. From
between the anterior and the lateral columns the anterior roots of
the peripheral nerves proceed, and from between the lateral and
the posterior columns, the posterior roots. In each of the three
columns the following separate bundles may be discriminated (com-
pare Fig. 19) :

1. In the anterior column :

(a) Direct pyramidal tract.
(£) Anterior ground bundle.

2. In the lateral column :

(c-) Crossed pyramidal tract.

(d) Direct cerebellar tract whose anterior part is called

Gower's column.
(?) Lateral bundles.

3. In the posterior column :

(/") Coil's column.
(£•) Burdach's column.

The white matter contains medullated nerve fibres ; the gray
matter is chiefly composed of nerve cells.

The functions of tJie spinal cord consist in conducting im-
pulses through fibres and cells. They may be divided into
three main groups :

(1) The conduction of the impulses in the motor tracts
from the brain through the cord to the peripheral nerves.

(2) The conduction of impulses from the peripheral
sensory nerves through the cord to the brain.

226

THE SPINAL CORD

227

(3) Conduction of impulses from the peripheral centripetal
nerves through the cells of the
gray matter of the cord to the
peripheral motor nerves — reflexes.

1. THE MOTOR TRACTS

These arc formed from fibres of
both pyramidal columns, the cells of
the anterior horns and the anterior
roots.

The pyramidal column descend-
ing from the brain gives off, at vari-
ous heights, fibres into the gray
substance, hence the cross-section
of this column decreases as it pro-
ceeds downward. The end-tufts of
the pyramid fibres come into con-
tact with the cells of the anterior
horns, those of the crossed pyram-
idal tract are in contact with cells
on the same side, while those of the
direct pyramidal tract are in contact
with cells on the opposite side.
The fibres of the direct pyramidal
tract cross in the anterior white

commissure just before their ending r

& FIG. 19.— CROSS-SECTION
at tne cells. THE SPINAL CORD AT VA-

The axis-cylinders proceed into

the anterior roots from trre cells of THE WHITE MATTER.
the anterior horn. (After Flechsis-)

T> .« i • * » , I» at sixth cervical nerve; II,

Pathological evidence shows that at third dorsal nerve; III, at

the paths just described are motor. twelUdT>r!al ' ne'rv'e- JY' at
There are diseases in which the fourth lumbar nerve. /?-, direct
motor nerves only are naralvzed I>>'ram!fla! tract: /f. crossed

> cuyzeu, pyramidal tract; AT, direct cere-

and in these cases the pyramidal kellar tract; g, Coil's column,
columns and the cells of the anterior horns undergo

OF

228 HUMAN PHYSIOLOGY

anatomical changes (disappearance of the nerve tissue and
the replacement of it by connective tissue). The results
of anatomic investigations of the course of these fibres
agree with the pathological evidences.

After transverse severing of the cord (by injury or disease)
a secondary degeneration of the pyramidal column below
the injury takes place. Since a nerve fibre, severed from
its nerve cell, degenerates (see page 223), this leads to the
conclusion that the cells of the pyramid fibres lie in the brain.

Of the nerves derived from the centrifugal tracts of the cord must
be mentioned the nerves for respiration and perspiration and the
vaso-motor nerves (see pages 75, 83 and 109). A few fibres
(vasodilators and motor fibres for the intestine) are supposed to
leave the cord by posterior roots.

2. THE SENSORY TRACTS

These are paths which, emanating from the fibres of the
posterior roots, pass, either directly or by the interposition of
cells throughout Coil's column through the direct cerebcllar
tract and, as scattered fibres, through the lateral bundle.

The peripheral sensory fibres end directly in the cells of
the spinal ganglia. They are really elongated dendrites of
these cells (see page 215). From these cells the axis-
cylinders proceed through the posterior roots into the spinal
cord and there separate into two large groups :

1. Fibres which cross the Burdach column diagonally,
reach Coil's column and through this proceed upward to the
brain.

2. Fibres the end-tufts of which come into contact with

the cells of the gray substance. The neurites of these cells

i
pass

(a) To the direct cerebellar tract on the same side, and in
this tract proceed upward to the brain. The cells of these
neurites lie in the columns of Clark, which are masses of
cells on the median side of the basis of the posterior horns.

(/;) Through the gray or white commissure to the other
side, and pass upward as scattered fibres in the lateral
bundles, or perhaps also in Gower's column.

THE SPINAL CORD 229

Tabes dorsalis is a disease of the spinal cord in which the
sensory nerves only are paralyzed, and the posterior roots
and Coil's columns are degenerated. Hence Coil's columns
are sensory tracts.

After transverse section of the spinal cord, secondary
degeneration of* the fibres of Coil's columns and the direct
cerebellar tract above the section takes place; hence the
cells of these fibres lie below the section.

Half-section of the cord. — If, by injury, one lateral half
of the cord has been cut through, motor paralysis below
and on t'he same side of the injury occurs, while on the
opposite side there is chiefly loss of sensation. The injured
motor columns lie, therefore, mainly on the same side as
the corresponding peripheral motor nerves. The injured
sensory columns lie, however, chiefly on the side opposite
to the corresponding peripheral sensory nerves ; this depends
upon the above-mentioned crossing (2/;) of the sensory fibres
in the gray matter.

This brief review of the sensory tracts relates, in general, the
facts as they are known at present ; but the conditions, in detail,
are much more complicated, for the long fibres in the spinal cord
give off branches downward and laterally, ending in the gray matter.
For example, each of the fibres of the posterior roots which enters
the posterior columns divides into two long branches, the heavier
one proceeding upward and finally, with Coil's column, reaches the
medulla oblongata ; the other going downward and, after a short
course, ending in the gray matter. Both these branches give off
collaterals which also end in the gray matter. The cells in the gray
substance to which the ends of the descending and collateral
branches go also give off neurites which, under the giving off of
collaterals, form long tracts or, after a short course, end in the gray
substance. Hence there is no such sharp distinction between the
long sensory tracts and the reflex tracts to be described presently,
as would appear from the above description.

3. REFLEXES OF THE SPINAL CORD

Nature of the reflex. — The reflex is the transferring of a
stimulation from a centripetal to a centrifugal nerve through
the centre. This occurs involuntarily. According to the

230

HUMAN PHYSIOLOGY

effect of the reflex in the end-organ of the centrifugal nerve,
we distinguish between reflex movement, reflex secretion,
and reflex inhibition. The reflexes of the spinal cord are
chiefly reflex movements.

The reflex tracts. — The connections of centripetal nerves
with motor nerves which are necessary for the production of
reflex movements may be :

(1) Direct. The end-tufts of the centripetal fibres and
the collaterals are in direct contact with the motor cells.

(2) Indirect. Between the centripetal and the motor
neurons other neurons intervene.

The direct and indirect tracts are illustrated in Fig. 20. In this
figure a represents the motor cells and roots ; b is a spinal ganglion
with its root. The sensory collateral r joins the motor cells directly,
forming a direct reflex tract. The sensory collateral c first joins the

cell d whose axis-cylinders make
connections with the motor cells
through the collaterals c, e, e.
This constitutes an indirect re-
flex tract.

The direct reflex tract dif-
fers, therefore, from the in-
direct in that but two kinds
of cells are intercalated in its
course, namely, the cells of
the spinal ganglion and the
motor cells of the anterior
horn. In the indirect tract
one or more cells are placed
between these two kinds of
cells.

It is apparent that the
union of centripetal with
motor nerves may take place

in a great many ways, as is also required by the manifold
spreading of the reflex. The fibres of these reflex tracts, by
which various heights of the gray matter are connected with

THE SPINAL CORD 231

each other, run chiefly in the anterior ground and lateral
bundles and the columns of Burdach.

Classification of the reflexes. — The reflex movements executed
by the aid of the spinal cord can most readily be studied in cold-
and warm-blooded animals in which the action of the brain is ex-
cluded by a section between the brain and spinal cord.

According to the degree of spreading of the reflex move-
ment we may discriminate :

1. Simple or partial reflexes. The stimulation of a
sensory spot is followed by the movement of only one
muscle or of a limited group of muscles. Example: knee-
jerk. If the sensory nerve of the ligamentum patellae is
stimulated by hitting the ligament, the quadriceps femoris
muscle contracts by reflex action and the lower part of the
leg is thrown forward.

2. Radiated reflexes. Stimulation of a sensory area
results in the contraction of large groups of muscles or of all
the muscles of the body. We may classify them as:

(a) Orderly radiated reflexes. The stimulation is fol-
lowed by a movement with the purpose of removing the
stimulus or fleeing from it. If, for example, the leg of a
decapitated frog is moistened with a drop of acid, the frog
wipes off the acid ; if the foot is pinched or pricked, it tries
to flee. These reflectory defensive movements can also be
observed in man during sleep.

The movements appear to us as voluntary movements,
but whether they are accompanied by consciousness in the
cells of the spinal cord cannot be determined, for we have
no knowledge of any subjective perception in the cells. It
is of interest to note that the cells of the spinal cord are able
independently to change the afferent impulses into a pur-
poselike muscular activity and are, therefore, from a physio-
logical standpoint, not different from the cells of the cerebral
hemispheres in which the psycho-physical processes take
place.

(&) Disorderly radiated reflexes or convulsive reflexes.

232 HUMAN PHYSIOLOGY

By stimulation of a sensory spot, uncoordinated contrac-
tions of larger groups of muscles, even of all the muscles,
may take place. Examples: convulsions during teething;
convulsions in strychnine poisoning. In adults convulsive
reflexes seldom occur, and only after very strong stimulation
(in intense neuralgia).

As a stimulation of any sensory fibre may call forth con-
vulsive reflexes, connections between all the sensory fibres
and all the motor fibres must exist. These connections are
normally irritable, but not all to the same extent, so that
the impulse radiates over certain tracts and thus causes
orderly reflexes.

Reflex time is the time elapsing between the entrance of
the impulse into the spinal cord and the passing out through
the motor paths. It is determined by measuring the time
elapsing between the beginning of the stimulation and the
beginning of the contraction, and subtracting from it the
latent period of the muscle and the time taken by the stimu-
lation to travel through the sensory and motor nerves. The
reflex time is 0.008-0.015 second.

Influences affecting the reflexes. — Reflex action depends
upon

(tf) TJic strength of the stimulus. — To call forth a reflex
the stimulus must be of a certain strength. Very strong
stimulations, however, can inhibit the reflexes. The reflex
time is, within certain limits, the shorter the stronger the
sensory stimulation.

(ft) The number and sequence of the stimuli. — A greater
number of successive and weaker currents can more readily
call forth reflexes than a single strong induction current.

(y) The plaec of stimulation. — The reflexes are more
easily called forth by stimulation of the sensory apparatus
in the skin than by direct stimulation of the nerve trunk.

Reflex irritability is increased by certain poisons (strych-
nine) and during tetanus. It is greater in children than in
adults.

It is decreased by certain poisons (chloroform, morphine,

THE SPINAL CORD 233

alcohol). In cold-blooded animals it increases with the
temperature.

Inhibition of reflexes.

1. Many reflexes can be inhibited by volition. But we
cannot voluntarily inhibit reflexes which are produced by
muscles which cannot be contracted voluntarily (e.g. the
contraction of the muscles of the uterus, contraction of the
pupil).

2. There are special reflex inhibition mechanisms which
are not dependent upon volition.

It is supposed that in man the centres of such mechanisms
lie in the ganglia of the brain, and that from it fibres pass
down the gray matter of the cord and act, in a manner still
unknown, upon the cells so" that the reflex is inhibited. If
the function of these fibres is abolished by transverse section
of the spinal cord, the reflexes below the level of the section / '
are increased.

In the frog reflex inhibition centres have been demon-
strated in the optic lobes, the stimulation of which prevents
the reflexes.

3. A reflex brought about by the stimulation of a sensory
nerve can sometimes be inhibited by the simultaneous stimu-
lation of another sensory nerve.

4. SPECIAL REFLEX CENTRES IN THE SPINAL CORD

There are in the spinal cord centres for certain move-
ments which can be brought into activity reflexly.

(1) In the cervical region are centres for the pupil reflex:
(a) A centre for the dilation of the pupil, in the upper

part of the cervical cord ;

(£) A centre for the constriction of the pupil, in the lower
part of the cervical cord.

This pupil reflex serves to regulate the amount of light
entering the eye. For details see page 267.

(2) In the lumbar region:
(a) Micturition centre.

234 HUMAN PHYSIOLOGY

The action of the centre for the sphincter vesicaj is tonic.
During micturition the tonus of the sphincter is decreased
and the centre for the detrusor is stimulated. This process
is called forth reflexly by the distension of the bladder, which
stimulates the nerves of the bladder and thereby reflexly
stimulates the detrusor and inhibits the sphincter.

(/;) Defalcation centre.

The tonus of the centre of the sphincters ani is inhibited
reflexly (by stimulation of centripetal nerves in the rectum
by the accumulated fasces) ; peristaltic movements of the
intestine are set up which, together with the pressure of the
-abdominal walls, remove the faeces.

(r) Centre for the erection of the penis, ejaculation, par-
turition (see third section).

CHAPTER XVIII
THE BRAIN

1. CONDUCTING TRACTS

The physiological significance of all the details of the course of
the fibres in the brain which anatomy has demonstrated is not
known. It is therefore sufficient for us to describe the chief con-
ducting tracts.

I. Course of til e tracts from the spinal cord info the brain.

A. The motor tract. — The crossed pyramidal tract forms
in the medulla oblongata the so-called decussation of tJie
pyramids, breaking through the anterior horn on its side
into the anterior ground bundle of the other side and joining
the direct pyramidal tract. From this point upward, the
two pyramidal tracts accompany each other, passing through
the pons, where they are crossed by cross fibres from the
cerebellum, then through the centre of the crusta cerebri,
the posterior limb of the inner capsule, and the corona
radiata, to the cortex of the cerebral hemispheres.

On its course from the cerebrum to the decussation, the
common pyramidal tract gives off fibres to the cells of the
motor fibres of the cranial nerves. The fibres of the pyramids
which come from both sides cross shortly before entering in
the nerve nuclei to which they go.

B. Tlie sensorv tracts.

(ioir s column, in the medulla called the funiculus gracilis,
ends mainly in cells of the nucleus of the funiculus gracilis.
From there, fibres penetrate forward through the gray sub-
stance and cross the fibres from the other side above and
behind the decussation of the pyramids. This crossing is

235

236 HUMAN PHYSIOLOGY

called the decussation of the fillet. After crossing, the fibres
lie dorsal to the pyramidal tracts ; they then join the sensory
fibres which, having perhaps already crossed in the cord,
run upward in the lateral bundles. The common sensory
tract thus formed, called fillet, passes upward through the
pons and the crura cerebri. Thence a part of the fibres go
to the ganglia of the corpora quadrigemina ; another part,
crossing the ventro-lateral nucleus of the thalamus opticus,
pass, always posterior to the pyramidal tract, through the
posterior limb of the internal capsule into the corona radiata
to the cortex of the cerebral hemispheres.

In their course the fillets receive fibres originating from
masses of cells in which the sensory cranial nerves, after
entering the brain, end; these fibres cross before joining the
fillet.

The nuclei of the motor and sensory cranial nerves lie in the
upward prolongation of the gray matter which forms the floor of
the fourth ventricle and, above it, the aqueduct of Silvius. The
cranial nerves, except the optic and olfactory, are analogous to the
spinal nerves. The optic nerve originates from the group of ganglia
in the anterior lobe of the corpora quadrigemina and the lateral
geniculate body. The olfactory nerve proceeds directly from the
cerebral hemispheres.

2. The direct ccrcbcllar tracts pass through the rcstiform
body [inferior cerebellar peduncle] to the cerebellum, where
they end in the gray matter of the worm. Besides this con-
nection of the cerebellum with the spinal cord there are
other fibres which unite the cerebellum with the cerebral
hemispheres. They are :

(a) Fibres which pass from the anterior and posterior
cortex of the cerebral hemispheres through the anterior and
posterior limbs of the internal capsule and the crura cerebri
to the nuclei of the pons. Thence they proceed backward
to the cerebellum through the middle peduncle of the cere-
bellum— frontal, temporal, and occipital regions being thus
joined to the cerebellum.

(/;) Fibres which proceed from the cerebral hemispheres
and, writh the fillet, pass through the thalamus opticus into

THE BRAIN 237

the red nucleus of the crura cerebri ; thence to the other side
through the pedunculi cerebelli into the cerebellum.

C. The short tracts of the spinal cord, which must be
regarded as reflex tracts and which run in the anterior
ground bundle and the Burdach column, cannot be traced
as separate tracts in the brain. There are also, no doubt,
many such pathways in the brain which connect the nerve
cells and serve as reflex tracts, for in the brain many reflex
processes take place.

II. In the cerebral hemispheres there are still a great
many fibres which connect various parts of the cerebral
hemispheres with each other. These are :

(1) Fibres in the corona radiata to the large ganglia of
the base (thalamus opticus, nucleus lenticularis, nucleus
candatus).

(2) The association fibres, by which various parts of the
right and left half of the cerebral cortex lying on the same
side are connected with each other.

(3) The commissural fibres which unite the right and left
half of the cerebral cortex. They pass through the corpus
callosum and the anterior commissure.

The association and commissural fibres are the conducting
paths in psycho-physical processes which are the bases of
the psychical phenomena (the utilizing of the sensation in
formation of concepts, etc.).

2. CENTRES IN THE MEDULLA OBLONGATA

The medulla oblongata is a part of the central nervous
system which is of special importance for the maintenance
of life. It contains the centres for the regulation of certain
processes which provide for the maintenance of normal
metabolism (centres for respiration, circulation, and the
movements and secretions of the alimentary canal). The
great importance of these centres for the life of the animal is
apparent from the fact that destruction of the medulla oblon-
gata is immediately followed by death, while the destruction

238 HUMAN PHYSIOLOGY

of other centres of the central nervous system is not directly
fatal. The centres of the medulla oblongata have already
been mentioned in the chapter on metabolism and their
properties have there been described in detail, so that a
simple enumeration will suffice here.

1. The respiratory centre (see page 83). By this
centre the muscles which cause alternate inspiration and
expiration (the diaphragm and the external intercostal for
inspiration, the internal intercostal for expiration) are stimu-
lated in an orderly manner. Its activity is dependent upon
the need of oxygen by the body, for lack of oxygen and
accumulation of carbon dioxide in the blood act as normal
stimuli for respiration. Reflexly the respiratory centre is
regulated by centripetal nerves, namely, the fibres of the
vagus leading from the lungs to the centre. The inspiratory
fibres of the vagus are stimulated during expiration, while the
expiratory fibres are stimulated during inspiration.

2. The centres for the organs of circulation (see page
74). These are :

(a) The cardio-inhibitory centre (of the inhibitory vagus
fibres).

(&) The centre for the sympathetic nerve from the cervical
and the first thoracic ganglia, which carry the accelerating
fibres to the heart.

(c) The centre for the constriction of blood vessels.

(d) The centre for the dilation of the blood vessels.
These centres serve to regulate the pressure of the blood

stream and its distribution in the various parts of the body
according to existing needs, by means of changes in the
number and strength of the heart-beats and in the tonus of
the muscles of the blood vessels.

The cardio-inhibitory centre and the vaso-constrictor
centre are tonic. They are stimulated by lack of oxygen
and accumulation of carbon dioxide in the blood. It appears
that this stimulation serves to protect the heart from too
speedy exhaustion during asphyxia, by decreasing its
activity, and to compensate the resulting reduction in blood

THE BRAIN 239

pressure by increasing the tonus of the muscles of the
vessels.

The cardie-accelerating centre is also supposed to be
tonic.

In general, the centres for the organs of circulation bring
about many reflex actions. This is clearly apparent from
the many and various actions by which these centres regu-
late the distribution of blood according to the needs of the
body.

3. Centres for certain movements and secretions of the
alimentary canal (see Chapters VII and IX). These are:

(a) Centres for biting, sucking, mastication, deglutition.,
vomiting i and perhaps also for the movements of tJie stomach
and intestines.

The centres of biting, sucking, and mastication are volun-
tarily stimulated by the cerebral hemispheres ; the other
centres are not subject to the will. Deglutition takes place
reflexly when the food has been pushed from the tongue
behind the anterior pillars of the soft palate. ' ' Empty
swallowing M is made possible by the swallowing of saliva;
without saliva it is impossible. The vomiting centre is not
only stimulated reflexly, but can also be stimulated by
psychical influence (sight of nauseous objects).

(b) Centre of salivary secretion, perhaps also for gastric,
intestinal, and pancreatic secretions.

The stimulation of these centres takes place involuntarily,
chiefly reflexly by the introduction of food in the alimentary
canal ; sometimes also, by psychical influences, sight of
tempting food stimulates salivary and gastric secretion.

4. Centres for the secretion of sweat and tears (see pages
109 and 1 10). — These centres also are not stimulated volun-
tarily. The perspiration centre is directly stimulated by the
raising of the temperature (heat) and also by lack of oxygen
and the accumulation of carbon dioxide in the blood
(asphyxia). Its activity is influenced by psychical condi-
tions (sweat of fear).

The stimulation of the centre for lachrymal secretion takes

240 HUMAN PHYSIOLOGY

place reflexly by stimulation of the conjunctival nerves,
by strong light, and by psychical influences (weeping).

5. In the medulla oblongata is situated a spot which is
connected with the glycogen and sugar formation in the liver
(see page 146). Destruction of this centre (Piqure) causes
diabetes mellitus.

6. It is supposed that there exists in the medulla oblon-
gata a centre which governs the reflex centres in the spinal
cord and binds these centres together. It is supposed to
be stimulated by lack of oxygen and accumulation of carbon
dioxide in the blood, wrhereby convulsion of all the muscles
in the body (asphyxia convulsion) is produced. Hence this
centre is also called the centre of convulsion.

3. CENTRES IN THE CEREBELLUM, PONS, CORPORA
QUADRIGEMINA, AND THE BASAL GANGLIA* OF
THE CEREBRAL HEMISPHERES

The centres here located serve, as far as we are acquainted
with their functions, to coordinate the movements of the
skeletal and eye muscles. They may be divided into two
groups.

i . Centres for the coordinated compensatory movements
maintaining the equilibrium of the body. — These centres
bring about a series of complicated orderly movements of
the muscles so that the body keeps its equilibrium. When,
for example, during standing or walking the equilibrium of
the body is destroyed so that the body threatens to fall, the
centres call forth such compensatory movements of the body
muscles that the equilibrium and the normal position are
regained. When the disturbance of the equilibrium is great,
these actions can be readily observed, but these compensa-
tory movements also take place when the position of the
body deviates but little from the normal position. In this
case the movements are less apparent and made so uncon-
sciously that our attention is called to them only in certain

* The basal ganglia are the thalamus opticus, nucleus caudatus, and the
nucleus lenticularis.

THE BRAIN 241

diseases. The centripetal nerves which acquaint these
centres with the position of the body are :

(a) The sensory nerves of the entire body which end in
the muscles, tendons, and joints and which notify the centre
of the relative position of individual members to each other
and of the extent of the tension of the muscles.

(b} The optic nerve, which, by means of visual perception,
acquaints the centre with the position of the body with refer-
ence to the objects of the external world.

(c) Certain fibres of the auditory nerve which end in the
semicircular canals of the internal ear. These semicircular
canals are sense organs for ascertaining the position and
movements of the head.

In the execution of compensatory movements all the
skeletal muscles take part.

As to the position of the centres, it is supposed that the
coordinated movements of the lower extremities which chiefly
function in locomotion and standing are governed by the
cerebellum. The centres in the corpora qnadrigemina are
supposed to regulate chiefly the movements of the arms and
hands.

Nothing is definitely known in detail concerning the posi-
tion and limits of the centres. This is not surprising when
it is borne in mind that in these centres the greater part of
all the sensory and motor nerves are connected.

If, because of pathological changes and disturbances, interrup-
tions in the connections between the afferent and efferent nerves
for these centres or in the centres themselves take place, a disturb-
ance in the coordinated movements of the body results. Hence
in locomotor ataxia, in which the sensory nerves of the lower limbs
are paralyzed, uncoordinated movements are made during walking.
A person suffering with locomotor ataxia cannot stand erect when,
by closing his eyes, he deprives himself of the only remaining
means of orientating himself.

It is also possible that each centre or its tract on one side only may
be paralyzed or abnormally stimulated by disease. The result is
that the strength of the stimulation which is unconsciously imparted
to the muscles is not equal on both sides. This results in abnormal
positions and movements of the body, called forced position and
forced movements because they are called forth involuntarily, indeed

242 HUMAN PHYSIOLOGY

against the will. Forced movements in animals are, for example,
the circus movements, clock-hand movements, rolling movements.
In normal individuals forced movements may be observed during
dizziness caused by rotation.

2. Centres for the movements of the eyes. — All the
centres for the movements of the eyes lie in the gray matter
forming the floor of the aqueduct of Silvius and the fourth
ventricle (except the centre for closing the eyelid and the
pupil reflex, see below and page 233).

(a) The centres for tJie coordinated movements of both
eyes. — Concerning the functions of the individual centres,
see page 280. Reflexes brought about by means of these
centres are:

1. Involuntary movements of the eye (afferent impulse
travelling through the optic nerve) by which the eye follows
a moving object or by which the glance is thrown upon a
luminous object.

2. Reflexes which are called forth by the sense organs
for perceiving the position and movements of the head
(semicircular canals of the ear, the centripetal nerve being
the auditory). In this group belong the compensatory
movements of the eyes which are involuntarily made when
the head is moved, in order that the line of vision may
remain on fixed objects.

Forced movements of the eye which occur in diseases of these
centres and their paths are called nystigmus.

(b) Centre for the common inner-nation of accommodation,
convergence, and contraction of the pupil. This is voluntarily
stimulated during near vision.

(c) Centre for the closing of tJie eyelids. This is volun-
tarily or reflexly stimulated. Reflex stimulation occurs
when the cornea or conjunctiva is touched (centripetal
nerve is the first branch of the trigeminus), or by stimulation
of the optic (blinking). The centrifugal nerve is the facial
which innervates the palpebrarurn orbicularis. The centre
is situated in the medulla oblongata.

Centres for the regulation of body temperature. It is supposed
by some authors that at the boundary between the medulla and the

THE BRAIN 243

pons and in the basal ganglia there are centres which regulate the
body temperature (see page 181), but the existence of these cen-
tres has never been definitely demonstrated.

Concerning the functions of the pineal gland nothing is
known. It is regarded as a rudimentary eye.

4. FUNCTIONS OF THE CEREBRAL CORTEX

Psycho-physical processes take place in the cells of the
cerebral cortex. The cerebral cortex is the seat of intelli-
gence. Human beings in which the cortex of the cerebral
hemispheres has been destroyed by disease, or animals in
which it has been extirpated, are stupid; they take no notice
of the external world, flee from no danger, do not independ-
ently seek their food, but they still manifest all the reflex
movements the centres for which are located in the lower
parts of the brain and spinal cord. In the animal world, the
cerebral hemispheres and the number of the convolutions
vary with the degree of intelligence.

The question whether the various psychical processes
(sensations, thought, will) are localized in various definite
parts of the cerebral cortex or whether all the parts of the
cortex have the same value in psychical processes is at
present variously answered by different authors. In higher
animals (monkeys and dogs) it has been attempted to
localize the functions of the cerebral hemispheres in two
ways : either by observing the results of the stimulation of a
definite part of the cerebral cortex, or by studying the dis-
appearance of functions after removal of such a definite part.

By the first method it has been found that in the cortex
there are a number of definite areas the stimulation of
which is always followed by the contraction of a definite
group of muscles. These areas, called motor areas, are, in
general, situated in the central convolutions.

It is noteworthy that, under certain circumstances, stimulation
of the cortex is followed simultaneously by the contraction of a
certain group of muscles and the relaxation of the corresponding
antagonistic muscles.

244 HUMAN PHYSIOLOGY

Partial extirpation often results in the temporary dis-
appearance of functions, but after some time these functions
reappear.

The results of experiments in stimulation and extirpation
have been variously interpreted. The adherents to the
localization theory hold that the effect of stimulation is pro-
duced by the stimulation of the motor centres which arc
employed in executing voluntary movements ; the opponents
of this theory hold that by this stimulation we do not really
stimulate the centres, but the motor fibres which pass through
the stimulated spot. The disappearance of a function by
extirpation and the subsequent reappearance of that function
depend, according to the adherents of the localization
theory, upon the fact that the centre in which the function
is located has been removed, but that subsequently other
centres have gradually taken up this function. In the re-
appearance of the function after partial extirpation the
opponents of the localization theory find support for their
position that the psychical functions are not definitely
localized. The first disappearance of the function they re-
gard as due to the inhibitory influences caused by the injury
[Hemmungserscheinungen] .

Although at present the views concerning the localization
of functions in the cerebral cortex of animals are at variance,
yet there are many observations which render it almost
certain that in man there is, to a certain extent, a localiza-
tion of the psychical functions in the cerebral hemispheres.

The theory of the psychological topography of the human
cerebral cortex is based upon:

(1) Anatomical and embryological investigations on the
course of fibres, by which parts of the cerebral cortex are
connected with each other as well as with other parts of the
central nervous system.

(2) Upon clinical observations in connection with the
results of pathological anatomical investigations.

Topography of the cerebral cortex of man. — The cere-
bral cortex of man may be divided into :

THE BRAIN

245

I. Sensory areas, i.e. centres in which the conscious sen-
sations are formed. There are four such areas.

(i) Centres for ordinary and tactile sensations. — These
lie in the anterior and posterior central gyri, the posterior
parts of the frontal lobe, the paracentral lobe, and the gyrus
fornicatus (compare Figs. 21-24).

FIG. 21.

FlCr. 22.

OF THE CEREBRAL HEMISPHERES.

CONVOLUTIONS

The centripetal fibres of the corona radiata of the tactile
centres are the indirect processes of the posterior roots
(fibres of the fillet and anterior peduncle which pass through
the ventro-lateral nucleus of the thalamus opticus and thence
into the corona radiata). In this area the sensations of the
skin and organs are perceived.

246

HUMAN PHYSIOLOGY

We do not exclude the possibility that some of the indefinite
organ sensations are perceived in centres situated lower down in
the brain.

(2) The auditory centre lies in the median and the pos-
terior part of the upper temporal convolution, and in the

Tactile area.

Parietal lobe
association-centre.

Association centre of
the occipito-temporal lobe.

Island of ReiL
ludiiury area.

FIG. 23.

Parietal lobe
association-centre

actory area.

Attociation centre of
the occipito-temporal lobe.

FIG. 24.
SENSORY AREAS OF THE CEREKRAL CORTEX.

The sensory areas are dotted. In Fig. 23 the temporal lobe is slightly drawn
downward in order to show the auditory centre. The island of Reil is seen at
the shaded portion.

transverse convolutions of the temporal lobes. The cen-
tripetal corona radiata fibres of the auditory centre are the

THE BRAIN 247

indirect continuations of the cochlear nerve (through the
lateral fillet and the internal geniculate body to the corona
radiata). The nervus vestibularis is supposed to be con-
nected with the centres for ordinary and tactile sensations,
not with the auditory centre.

(3) The visual centre lies in the cuneus, angular gyrus,
and occipital. Their centripetal corona radiata fibres lie in
the optic radiation of Gratiolet (continuation of the optic
tract through the external geniculate body and anterior
corpora quadrigemina into the corona radiata).

(4) The olfactory centre lies in the basis of the cortex of
the frontal lobe, in the basal portion of the gyrus fornicatus,
the island of Reil, the uncus, and the inner part of tLe tem-
poral lobes.

The position of the centre of taste is not yet known.

II. Motor areas are centres by which the voluntary
movements are inaugurated. They lie in the same portion
of the cortex as the centres for tactile sensations. Their
centrifugal corona radiata fibres are the pyramidal tracts the
origin of which lies in the central convolution. In the
upper part of this convolution originate the motor fibres for
the lower extremities; in the median, those for the upper
extremities; and in the lower portion, those for the face. In
the posterior part of the lower frontal convolution, generally
in the left cerebral hemisphere, are situated the motor
centres for the muscles which function in the production of
voice and speech (motor speech centre).

It is supposed that motor cells are also found in other sensory
areas, but this is not agreed upon by all authors.

III. Those parts of the cerebral cortex which do not
belong to the sensory or motor areas form, according to a
new theory, the association centres. These centres func-
tion in the formation of concepts from the sense percepts.
This view is, however, rejected by many authors.

It is supposed that the association centres differ anatomically
from the other centres in the following respects. The association

248 HUMAN PHYSIOLOGY

centres are supposed to be connected with each other and with the
sensory areas chiefly by association and commissural fibres, and to
contain relatively few corona fibres connecting it with the lower
parts of the brain. The larger part of the fibres from the corona
radiata are supposed to proceed to the sensory and motor areas.
Moreover, the individual sensory areas are supposed not to be con-
nected with each other by the association fibres, but only with the
association centres.

Nothing is known concerning the nature of the psycho-
physical processes which underlie psychical phenomena.
Up to the present time the investigations of these processes
have been limited to their duration.

Reaction time is the time elapsing between the beginning"
of the action of a sense stimulation and a most rapidly
executed muscular movement, e.g. of a finger. Both these
times are registered.

The measurements of the reaction time arc :

For optical stimulation 0.15-0.22 second.

" auditory " 0.12-0.1 8 <(

" tactile " 0.09-0.19 "

" taste " o. 16-0.22 "

The reaction time is smaller for areas which are more frequently
stimulated, e.g. the yellow spot, the tip of the finger, than for
areas less frequently stimulated, as the periphery of the retina, skin
of the arm. It is also dependent upon the degree of attention and
practice, and upon the psychical attitude. Individual peculiarities
also influence the reaction time.

When a very accurate registration of time must be made, for in-
stance by a person noting the passage of a star across the thread
of a telescope, the reaction time must be taken into consideration.
The individual variations of the reaction time are brought into
account by astronomers as "personal equation."

The more complex the psychical processes which intervene
between the sense stimulation and the reaction, and the
longer the time necessary for reflection, the greater will be
the length of time between the beginning of stimulation and
the reaction.

The elucidation of the psychical phenomena themselves (sensa-
tion, thought, volition, attention, memory, etc.) is the object of
Psychology.

THE BRAIN 249

The interruption of psychical functions by sleep can be
accounted for by the rest of the nerve cells of the cerebral
cortex. How this rest is brought about is not known. The
supposition that cessation in the activity of the cells is due
to fatigue or lack of blood in the cells of the brain does not
explain all the phenomena of sleep. Sleep also depends
upon the stimulation of the sense, organs. A person can
be made to sleep by withdrawing the stimulation of the
senses as far as possible. Customary sensations do not dis-
turb sleep, strange sensations do. Sometimes the cessation
of customary sensations awakes the sleeper. (The awaking
of the miller when the mill stops.)

During sleep only the functions of the cerebral hemispheres
cease ; the other centres of the central nervous system (reflex and
coordinated centres) may remain active. The eyelids are closed
during sleep, the eyes are turned inward and upward, the pupils
are contracted, respiration is slower. Metabolism is less during
sleep than during waking hours.

Dreams are due to less profound sleep. Somnambulism and hyp-
notism are abnormal conditions of partial sleep.

Chemical composition and metabolism of the central nervous
organs. — The white substance of the central nervous system con-
tains 31$ solids, including proteid and collagen 8$, lecithin 3$,
cholesterin and fat 15$, protagon 3^; besides these, some substances
containing nitrogen and phosphorus insoluble in ether (nuclein,
neuro-keratin, jecorin) 1.5$; salts 0.2$.

The gray substance contains 18$ solids, including proteid and
collagen io#, lecithin 3^, cholesterin and fat 3.5$, cerebrin and
substances insoluble in ether i$, salts 0.5$.

Nothing is known concerning the metabolism in the spinal cord
and brain. Metabolism is not increased to an appreciable extent
by mental work. The abundance of blood in the brain and the
fact that stoppage of blood supply paralyzes the nerve cells in a few
minutes, indicates that the metabolism is very energetic.

The cerebro -spinal fluid which surrounds the central nervous sys-
tem and fills its cavities has a specific gravity of 1.005. It con-
tains 1-1.5$ solids, in which proteids are either absent or only
present in traces. In it has been found a substance which reduces
cupric oxide and appears to be pyrocatechin.

CHAPTER XIX

THE PERIPHERAL NERVES AND THE SYMPATHETIC

SYSTEM

1. THE SPINAL NERVES

THE spinal nerves leave the spinal cord by the anterior
and posterior roots.

The anterior roots are motor, the posterior chiefly sensory
(Bell's law), but also contain a few motor nerves for the
muscles of the intestines.

The nerve fibres innervating a muscle do not all lie in the
same motor root, but a muscle is supplied with motor fibres
from several anterior roots. These fibres join each other
(plexus) and then proceed in a common trunk to the muscle.

The anterior roots contain fibres whose simultaneous stimula-
tion calls forth movements of entire muscle groups which re-
semble certain coordinated movements frequently executed in life.
For example, stimulation of the first dorsal root in a monkey re-
sults in the movements of the arm similar to those made in pluck-
ing fruit ; stimulation of the seventh cervical calls forth movements
of the arms similar to those made in climbing ; by stimulation of
the sixth cervical the hand is carried to the mouth. Perhaps the
cells from which these nerves originate lie together in special cell-
groups in the spinal cord, which may be regarded as coordinated
centres. From these centres the nerve fibres accompany each
other to the plexus.

The functions of the individual spinal nerves can be
learned from their anatomical connections.

2. CRANIAL NERVES

I. The olfactory nerve is the nerve of smell. The olfac-
tory bulb is the sub-cortical centre of this nerve ; in it cells
are interposed in the tract.

250

PERIPHERAL NERVES AND THE SYMPATHETIC SYSTEM 251

II. The Optic nerve is the nerve of sight. The fibres of
this nerve leave the brain by the optic tract. Their nearest
nuclei lie in the anterior corpus quadrigeminum and in the
lateral geniculate body. These parts are connected, on the
one hand, with the cerebral cortex by means of fibres of the
corona radiata and. on the other hand, with the more pos-
terior nuclei of the brain, especially the nuclei of the nerves
of the eye muscles. The optic tract passes over into the
cliiasnia, where a part of the fibres cross. Thence they pro-
ceed to the eye as the optic nerve. Because of this partial
crossing in the chiasma, the inner half of each retina is
innervated by fibres from the opposite side of the brain, while
the outer half receives fibres from the same side of the brain.

III. The oculo-motor, IV. the pathetic (trochlear), and
VI. the abducent are the motor nerves for the external and
internal eye muscles (except the dilator of the pupil) and
the levator palpebrae superioris. The trochlear innervates
the superior oblique, the abducent the rectus externus, the
oculo-motor all the other eye muscles.

V. The trigeminus contains:

1. Sensory fibres for the whole head except the jaws and
-ears, which are supplied by the glossopharyngeal and the
ramus auricularis vagi.

2. Motor fibres for the muscles of mastication (temporal,
internal and external pterygoid, and masseter) ; also for the
tensor palati mollis, mylohyoid, the anterior belly of the
digastric, and the tensor tympani.

3. Secretory fibres for the tear glands.

The lingualis trigemini nerve contains secretory fibres (for the
submaxillary and sublingual glands) ; also vaso-dilators and fibres
for taste, which, however, originally leave the brain in company
with the facial and glossopharyngeal and through the corda tympani
reach the lingual. Besides these, the trigeminus contains vaso-
motor and secretory nerves for the sweat glands of the face, which,
however, are derived from the sympathetic.

VII. The facial contains motor fibres for all the face
muscles, for the stylohyoid and the posterior belly of the
digastric, and for the stapedius muscles. It also contains

252 HUM4N PHYSIOLOGY

fibres which reach the sphenopalatinum ganglion through
the petrosus superficialis major ; thence they proceed to the
levator palati mollis and azygos uvulae. Besides these the
facial contains secretory and vaso-dilator fibres which, in the
chorda tympani, join the lingualis and with this proceed to
the salivary glands.

VIII. The auditory contains, in the nervus cochlearis,
the nerves of hearing. It also contains, in the nervus ves-
tibularis, fibres which proceed from the semicircular canal
of the internal ear, the organ of the sense of equilibrium, to
the brain. These fibres reflexly influence the coordinated
movements of the body for maintaining its position and
equilibrium.

IX. The glossopharyngeal contains:

1 . Sensory fibres for the posterior parts of the tongue,
pillars of the fauces, tonsils, jaw, and epiglottis.

2. Motor fibres for the stylopharyngeal muscles and the
median pharyngeal constrictor.

3. Nerves of taste. The nerves supplying the posterior
part of the tongue proceed thither directly. Those supply-
ing the anterior part pass from the petrosus ganglion of the
glossopharyngeal through the tympanic plexus to the genic-
ulate ganglion of the facial, thence they proceed through
the -chorda tympani to the lingual. It is supposed that some
of the taste nerves of the glossopharyngeal pass through the
tympanic plexus and the Jacobson's anastomoses to the
nervus petrosus superficialis minor, otic ganglion, lingual,
etc.

4. Secretory fibres which pass through the Jacobson's
nerve and the nervus petrosus superficialis minor, etc., to
the parotid glands.

X. Vagus and XI. spinal accessory form together a
mixed nerve whose centrifugal fibres originate from the
accessory, and the centripetal from the vagus. The external
branch of the accessory contains motor fibres for the sterno-
cleido-mastoid and the cucullaris muscle. The common
vago-accessory send fibres

PERIPHERAL NERVES AND THE SYMPATHETIC SYSTEM 253

(1) To the circulation apparatus:

(a) The inhibitory fibres.

(/;) Sensory and reflex-acting (depressor) to the
heart.

(2) To the respiratory apparatus:

(a) Motor fibres for the muscles of the larynx (in
the superior laryngeal for the crycothyroid, in the
recurrent laryngeal for the other muscles) and for the
bronchial muscles.

(/>) Sensory fibres for the larynx (laryngeal superior),
trachea, and lungs.

(3) To the muscles of the alimentary canal:

(#) Motor fibres for the movement and peristalsis of
the esophagus, stomach, and intestine.

(/;) Sensory fibres for the esophagus and stomach.
(c) Secretory fibres for the stomach and probably
also for the pancreas and glands of intestine.
In addition to these the vagus is supposed to contain fibres
which regulate the sugar formation in the liver.

XII. The hypoglossus is the motor nerve for the muscles
of the tongue.

3. SYMPATHETIC SYSTEM

The sympathetic nerves are connected with the central
nervous system by the rami communic antes, which pass from
the trunks of the spinal nerves to the sympathetic ganglia.
The sympathetic contains the vaso-motor fibres for the1 entire
body. These pass either directly to the vessels or first join
the peripheral nerves and, in common with them, continue
their course. The sympathetic also sends secretory nerves
to the sweat glands.

Besides these the sympathetic contains :
(i) In the cervical region

(rt) Fibres for the dilation of the pupil.
(/;) Secretory fibres for the salivary and lachrymal
glands.

(<•) Cardio-augmentor fibres.

254 HUMAN PHYSIOLOGY

\2) In the thoracic region

(a) Cardio-augmentor fibres (from the first thoracic
ganglion).

(b) The splanchnic nerve, which contains sensory
nerves for the intestine, and inhibitory nerves for the
peristaltic movements.

All the motor fibres contained in the splanchnic are in-
voluntary. The sympathetic fibres are non-medullated.

CHAPTER XX
SENSE ORGANS IN GENERAL

TPIE sense organs are the apparatus in which the periph-
eral sensory nerves end and which are stimulated by external
or internal influences. The sensory nerves take up the im-
pulse and carry it to the central nerve organ,.

The sense organs are built for the reception of " ade-
quate " stimuli and are generally acted upon by these.

The adequate stimuli for the eye are the ether vibrations of
certain length ; those for the ear are certain vibrations of air.

The stimulation of the sensory nerves produces sensations
in the cells of the cerebral cortex to which they lead.

The sensations may differ from each other in quality and
intensity.

As differing in quality we regard, e.g., the different sensations
of colors, or sounds, or smell, etc. ; while the light and dark
sensations, or the loud and low sound sensations, are regarded as
differing in intensity.

Law of tJie specific energy of the sensory nerves. — The
quality of the sensation is constant for each sensory nerve
and is independent of the nature of the stimulus.

For example, the stimulation of the optic nerve always causes
a sensation of light, whether the nerve be stimulated by the
adequate or by some other stimulus (mechanical, electrical).

In what manner the specific energy of the sensory nerve
is determined is not fully known. We know no differences
in the structure or physiological stimulation processes in the
nerve elements (fibres and cells) which could determine this.
difference in the specific enefgy of the sensory nerves.

255

256 HUMAN PHYSIOLOGY

It is to be noticed that the adequate stimulus does not objec-
tively contain the quality of the sensation which it produces. For
example, the vibrations of ether which act upon the eye have
nothing to do with the notion of light. The conception of light
consists only in subjective perception.

The intensity of the sensation is, other things being equal,
dependent upon the intensity of the stimulus.

The liminal intensity of a stimulus is the feeblest stimu-
lus still perceptible; the " difference-threshold " of the
stimulus is the smallest perceptible difference in the intensity
of two stimuli or the smallest perceptible change in a stimu-
lus. The size of the ' ' difference-threshold ' ' varies with the
absolute strength of the intensity of the stimulus. The
smallest perceptible change in the intensity of the stinuilns is
proportional to the absolute strength of the stimulus — \Veber* s
Law.

According to Fechner's psycho-physical law, the strength of
the sensations is related to the strength of the stimuli as a
logarithm to its number. The validity of Fechner's law is dis-
puted by many authors.

1 Objections have also been made against the general validity of
Weber's la\v.

Besides differences in intensity and quality we can discrimi-
nate between the duration of sensations, and in some (sight
and tactile) between the space conditions (place and extent
of sensation).

CHAPTER XXI
OPTICS

THE adequate stimuli for the eye are certain vibrations of
ether, called light because they call forth the sensations of
light. In order that an object shall be clearly seen, rays
of light must pass out from the object, which by refraction
in the eye form an inverted real image of the object on the
retina. The cones and rods are the elements of sight; they
form a mosaic of nerve elements of which every point upon
which light falls can be stimulated. Hence different object
points can, by their stimulation of various retinal points, call
forth separate sensations of light and can therefore be seen
as distinct points.

1. DIOPTRIC MECHANISM

Physical observations.

1. If a ray of light ($,, Fig. 25) passes from the medium J/j into
another medium Yl/0, it is refracted at the surface bounding the two
media (_/), i e. it takes another direction (*S"a). The angle a which
St forms with the perpendicular / upon the plane f is called the
angle of incidence. The angle ft which «S"a forms with / is called
the angle of refraction. The sine of the angle of incidence
divided by the sine of the angle of refraction is, for any given
pair of media, constant, and is called the index of refraction.
When the index of refraction of one medium is given, the light
passes from the air into that medium.

2. Homocentric rays, or rays coming from one luminous point,
falling upon the spherical surface between two media, are refracted
so that after the refraction they either cross each other at a point
(the real image point) or, prolonged backward, unite in a virtual
image point. This is strictly true only for a part of a bundle of

257

258 HUMAN PHYSIOLOGY

light, namely, for those rays which are approximately perpendicular
to the surface.

3. In refraction at a spherical surface the following equation
expresses the distance of the luminous and image point from the
surface :

^-f -? = .vV7_;/'),
CL (i r

1 2

in which », is the index of refraction of the first and ;/a that of
the second medium ; r is the radius of the spherical surface ; al

FIG. 25.

the distance of the luminous point ; a^ that of the image point.
In this formula r is positive when the convexity of the surface is
towards the side of the luminous point, negative when it is con-
cave with respect to the luminons point. al is positive when the
rays entering are divergent, that is, come from a real objector lumi-
nous point ; negative when the rays are convergent, that is, pass
to a virtual object point, a^ is positive for a real, negative for a
virtual, image point. In Fig. 26, in which O is the luminous point
and C the centre of curvature, all the values are positive. By
means of the formula the position of the image for a given posi-
tion of the luminous point can be found. The formula also teaches
that an object or luminous point placed in the image point B has
its image in the position of the previous luminous point O. Two
points, of which the one as image point has the other for its object
point, are called conjugated points.

The direction of the image point from a given luminous point is
found by drawing a straight line from the luminous point through
the centre of curvature C. This straight line is called the chief or
directing ray, and the centre of curvature is called the crossing

OPTICS

259

point of the directing rays, or the nodal point. The chief ray
drawn through the vertex of the refracting surface is called the
optical axis.

FIG. 26.

4. Rays parallel with the optical axis may be regarded as coming
from an infinitely distant object point lying in the axis. After
refraction they unite at a point on the optical axis, called the
second focal point; its distance from the surface is called the
second focal distance. Rays which, after refraction, run parallel to
the optical axis, pass, before refraction, through the first focal
point, whose distance from the surface is called the first focal dis-
tance. As in the formula for this case #, or a^ is oo , the focal dis-
tances designated by/~2 and/", are

X r

« X r

The vertical planes erected upon the optical axis at the focal
points are called ihe focal planes.

5. Construction of the image of a given object.

Let mm (Fig. 27) be a spherical surface separating the two media
J7j and M.,. Let A'' be the centre of curvature. AB is the optical

FIG. 27.

axis of the system, F^ the second, and F ^ the first, focal point. To
find the image of the luminous point Ol , draw the directing ray
O^K. Also draw a ray from Ol parallel to the optic axis ; this
cuts the surface at h^ and from h^ passes through F^ and its prolon-
gation cuts 6>jA'at Jj, which is the image point. In a similar way
the image point b.t of the luminous point O.2 is found. The image
formed in this case is real and inverted.

260 HUMAN PHYSIOLOGY.

6. It can also be seen from Fig. 27 that the size of the object is
to the size of the image as the distance of the object from the nodal
point K is to the distance of the image from K.

7. An optical system may contain several spherical surfaces separat-
ing several refracting media. If all the centres of a spherical surface
lie in a straight line, the system is called a centred system, and the
straight line in which all the centres are located is called the optical
axis. The refraction of such a system can be determined by find-
ing the refraction of each surface successively according to the above
formulae.

8. A system in which the entering rays are converged is called a
converging or collecting system [Sammelsystem] . (Parallel rays
are converged ; convergent rays are rendered more convergent ;
divergent rays are either rendered less divergent, parallel, or con-
vergent, according to the original degree of divergence. )

I. The dioptric system of the normal resting eye. — The
dioptric system of the eyes is a convergent system of three
approximately concentric spherical surfaces placed between
four media. The media are: air, aqueous humor,- lens,
vitreous humor. The surfaces of separation are the anterior
surface of the cornea and the anterior and posterior surfaces
of the lens. The optical axis is called the visual axis (see
Fig. 28, /, f.J.

The posterior surface of the cornea is disregarded because it is
parallel with the anterior surface and because the index of refrac-
tion of the cornea may be regarded as the same as that of the
aqueous humor.

The indices of refraction of the aqueous humor and of the
vitreous humor are 1.338, that of the lens is 1.455. The
radius of the curvature of the corneal surface is 8 mm, of the
anterior surface of the lens 10 mm, of the posterior surface
of the lens 6 mm. The distance of the anterior surface of
the cornea from the anterior surface of the lens is 3.6 mm,
the thickness of the lens is also 3.6 mm. The retina lies 15
mm behind the posterior surface of the lens. From these
data the dioptric action of the system can be found.

The indices of refraction can be determined only in the
dead eye, but the radii and the distances of the surfaces can
also be determined in the living eye.

The lens is composed of many layers, like an onion, and the

OPTICS 261

individual layers have various indices of refraction, the index
increasing as we proceed to the centre. Because of the order of
the layers, the actual total index of refraction is somewhat larger
than the index of the central layer.

The radii of curvature are determined from the size of the
reflected image of a known object which is formed, by reflection, at
the surface. To measure the size of these images accurately the
ophthalmometer invented by Helmholtz is used.

It has been found by calculation that the dioptric effect of
the eye can also be produced by a simple system, in which
the lens is not present and is replaced by vitreous humor,
and in which the reduction of refraction, due to omission of
the lens, is corrected by giving the only remaining refractive
surface (the surface of the cornea) a stronger curvature and
a different position. The system is therefore reduced to a
single spherical surface placed between two media (for the
aqueous and vitreous humor have the same index of refrac-
tion). The radius of this surface is 5.017 mm; the distance
of the centre of curvature (nodal point) from the anterior
surface of the cornea in the real (not reduced) eye is 7. 16
mm. The simplified system is called the reduced or sche-
matic eye, and by its aid we can construct the refracted ray
of light as indicated in Fig. 27. In Fig. 28 //is the position
of the surface of separation of the reduced eye.

Strictly speaking the system of the eye has two nodal points
(A'j and A',, Fig. 28, which lie 6.96 and 7.37 mm behind the vertex
of the cornea), but these lie so closely together that they may be
regarded as one. The two nodal points have the following char-
acteristic. A ray which, previous to refraction, passes in the direc-
tion of the first nodal point, passes, after refraction, through the
second nodal point and parallel to its original course. Correspond-
ing to the two nodal points there are also two spherical surfaces.
The points where the optical axis cuts these two surfaces are called
the chief points (h^ and //2, Fig. 28). The first chief point lies
1.94 mm and the second 2.36 mm behind the anterior surface of
the cornea. Planes erected perpendicular to the optic axis at the
chief points are called chief planes. The chief planes must be
regarded as conjugated planes of such a nature that an object which,
previous to refraction, is supposed to be located in the first chit f
plane, must have, after refraction, an image oT the same size in the
second plane.

262 HUM4N PHYSIOLOGY

The nodal, chief, and focal points of the eye are collectively
called the cardinal points ^(<c.t. infra}.

The second focal point of the eye lies 22.23 mm beind the
vertex of the cornea, the first focal point 12.92 mm (f2 and
/:, Fig. 28). The second focal plane nearly coincides with

FIG. 28. — CARDINAL POINTS OF THE EYE (see text).
GG' is the visual axis.

the retina. Images of infinitely removed objects having
parallel rays fall on the retina. Hence tJic normal retina can
clearly see objects at an infinite distance.

II. Accommodation. — The image of a near luminous point
falls behind the retina of the resting eye and no image is
formed on the retina. In its place a luminous circle
appears, the circle of diffusion, because the rays have not
yet united. As the circles of diffusion of a near luminous
point overlap each other the image of a near object on the
retina is not sharply defined, hence the resting eye cannot
clearly see near objects.

In order to form upon the retina a sharply defined image
of a near object, the refractive power of the eye is increased
by increasing the curvature of the surfaces of the lens. This
process is called accommodation.

OPTICS 263

In the condition of strong accommodation the radius of the
anterior surface of the lens is 6 mm, of the posterior surface
5.5 mm ; the anterior surface is also slightly pressed forward,
the posterior surface remains in its position. For this condi-
tion also a reduced eye may be constructed, the radius of the
spherical surface of separation being 4.53 mm, its centre of
curvature lying 6.79 mm behind the vertex of the cornea.
In this condition sharp images of objects 120 mm distant
from the vertex of the cornea are formed upon the retina.

Purkinje-Sanson images. — The change in the curvature
of the lens shows itself by changes in the size and position
of the image reflected from the surfaces. If a candle is held
on one side of the eye, three reflected images may be seen
if the eye is looked at from the other side (Fig. 29, /r").
The first image, formed by the cornea, is upright and clear;
the second, formed by the anterior surface of the lens, lies
near and a little behind the first; the third, formed by the
posterior surface of the lens, is small and inverted. If the

F N

FIG. 29.

eye is accommodated for near vision, b and c become smaller
and /; approaches a (Fig. 29, N) ; this is accomplished by
the stronger curvature of the surfaces of the lens.

Schemer's experiment. — In a cardboard make two pin-holes
near each other. Place the holes near one eye and, the other eye
being closed, look in the direction of a near point. If now the
experimenter look past the ppint into the distance, the first point
is seen double ; if the near point is looked at, only one point is
si'L'n. Of the rays emanating from the near point two thin bundles
pass through the pin-holes into the eye, which, when the eye is
accommodated, unite to form one image point on the retina ; but

264

HUMAN PHYSIOLOGY

if the eye is not accommodated, they illuminate two different points
of the retina because its two rays of light unite back of the retina.

Mechanism of accommodation (see Fig. 30). — The lens
L lies inclosed in the two leaves of the capsule of the lens.
The capsule of the lens at its border passes over into the

FIG. 30. — CHANV.KS IN THE LENS DVRINC, ACCOMMODATION.
(After Helmholtz.)

/"', far vision; N, near vision; w, musculus ciliaris; :,r, CjC, , xonule of /inn;
r, ciliary process; L, lens.

zonule of Zinn, zz and z^z^ a folded membrane whose
periphery is united with the choroid where this passes over
into the corpus ciliare (Y).

The intra-ocular pressure produced by the transudation
of tissue fluid from the blood vessels into the inner part of
the eye causes the. coats of the eye to be taut, and thereby
stretches the part at which the zonule is inserted into the
choroid. Hence the zonule and the capsule of the lens are
stretched and the lens is pressed together and flattened in
its anterior-posterior direction. This is the condition of the
lens in the resting eye (Fig. 30, F).

The fibres of the muscle of accommodation ;// (tensor of
the choroid or ciliary muscles) in the ciliary body pass from
the insertion point of the zonule to the place where the
choroid has grown together with the boundary between the
cornea and the sclerotic. By the contraction of these
muscles the part at which the zonule is inserted is pulled
slightly forward and inward (toward the axis of the eye) and

OPTICS 265

thus shortened. This slackens the zonule and the capsule
of the lens, and the lens, in consequence of its elasticity,
bulges forward so that its curvature becomes greater (Fig
30, N).

The muscles of accommodation have smooth fibres.

The oculo-motor nerve supplies them with motor fibres
which enter into the ciliary ganglion and thence proceed, as
the short ciliary nerves, to the eye.

The accommodation muscles of both eyes are innervated
simultaneously and to the same extent. Simultaneously with
these the internal rectus and the sphincter iridis of both eyes
are innervated, so that accommodation is always accom-
panied by convergence of the eyes and contraction of the
pupils.

Measure of accommodation. — The point which the resting,
eye sees clearly is called the far point ; the point which the
most strongly accommodated eye sees clearly is called the
near point. The range of accommodation is the distance of
the far point from the near point. The power of accommo-
dation is measured by the reciprocal of the near point minus
that of the far point, hence for the normal eye, in which the
near point is o. 12 m,

, or 8.3 diopters.

0.12 so 0.12

This number expresses the refractive power which a convex
lens must have in order to have the same dioptric effect as
the eye normally has during strongest accommodation.
The power of refraction (diopter) is expressed by the recip-
rocal of the focal length of the lens. A lens having the
focal length of I m has the value of I diopter. The power
of accommodation is therefore equal to that of a lens of o. 12
mm focal length. The power of accommodation decreases
with age, because the lens becomes hard (presbyopia).

Anomalies of refraction (near-sightedness or myopia, far-sighted-
ness or hypermetropia) are due to abnormal positions of the retina.
In myopia the retina lies too far back, ami parallel rays meet in

266 HUMAN PHYSIOLOGY

front of the retina; hence to unite them on the retina, the refrac-
tion of the eye must be decreased by placing before it a diverging
[concave] lens. In hypermetropia the retina lies too far forward,
and parallel rays meet back of the retina ; in order that in the rest-
ing eye they may unite in the retina, the power of refraction must
be increased, which is accomplished by the converging [convex]
lens. The normal eye is called emmetropic ; in it the second
focal point lies on the retina.

Periscopia is the power of the eye to see clearly points lying far
aside from the axis of the eye. The laws thus far enunciated apply
only to rays of light which are approximately parallel with the axis and
which meet the refracting surfaces nearly at right angles. Rays
from luminous points lying far to one side are not accurately united
into an image point, but are quite well concentrated at two points
on two small lines, of which the posterior one may be regarded as
the analogue of an image point. The real image points of lateral
and infinitely removed luminous points lie on a curved surface which
approximately coincides with the curved surface of the retina.
This is true, however, only for the unreduced eye. In the reduced
eye the curved surface does not coincide with the retina.

Imperfection in the dioptric apparatus.

1. Spherical aberration. — If a bundle of light falls obliquely
upon a spherical plane separating two media, the peripheral rays
are more refracted than the central rays, hence the rays are not
accurately united at one point. This is prevented in the eye by
the facts that the surface of the cornea is not perfectly spherical,
but is more strongly curved in the centre than at the periphery, and
that the iris cuts off the peripheral rays.

2. Chromatic aberration. — The various colors of the spectrum
are differently refracted, the violet being more strongly refracted
than the red ; hence the violet rays are brought to a focus sooner
than the red rays. This ordinarily causes no disturbance in vision,
but can be observed by covering half of the pupil of one eye with
a piece of cardboard and gazing with this eye upon a light object.
The borders of the object appear colored because of the chromatic
aberration.

3. Astigmatism. — The curvature of the surfaces of separation
may be unequally great in various meridians of the surface. Hence
the rays of light from a light-bundle falling upon a given meridian
will be refracted differently from those falling on another meridian
and will unite at another place. Suppose that the meridian having
the greatest curvature is at right angles to the meridian having the
least curvature. It will be found that the cross-section of the
bundle of light of parallel rays after refraction forms a straight line
at two places, the first of which has the direction of the meridian

OPTICS 267

having the least curvature, and the second the direction of the
meridian of greatest curvature. The normal eye is slightly astig-
matic, the vertical meridian having the greatest curvature. Be-
cause of astigmatism, of a number of black lines all crossing at a
common point only one is clearly seen; the others, especially the
one at right angles to that clearly seen, are less sharply defined.
Severe astigmatism causes disturbances in vision which may be
corrected by the use of cylindrical glasses.

Entoptical phenomena. — Opacities in the refracting media,
found in the normal as well as in the diseased eye (cells and fibres
cf the vitreous humor, accumulation of dust or flock of mucus in
the cornea, etc.), hinder the passage of light and cast shadows on
the retina which are seen as opaque objects in the luminous visual
field. They can be seen especially well when a source of light is
placed in the first focal point from which parallel rays pass through
the vitreous humor. If the eye is moved, the apparent position of
the opaque object also moves — muscse volitantes. Among these
also belong the shadows cast by the blood vessels (see page 270).
The capillary stream of the retina can, under certain conditions,
also be seen entoptically in the form of moving points.

III. Function of the iris. — The iris has two muscles

(with smooth fibres) :

1. The sphincter of the pupil, a circular muscle, by the
contraction of which the pupil is contracted, is innervated
by the fibres of the oculo-motor which pass through the
ciliary ganglia and the short ciliary nerves.

2. The dilator of the pupil, radial fibres by the contrac-
tion of which the pupil is dilated. It is innervated by the
sympathetic fibres which also pass through the ciliary
ganglia.

The inncrvation of both muscles is tonic. Section of the
oculo-motor causes dilation ; section of the sympathetic, con-
traction of the pupil.

The iris is opaque because of its pigment. It serves :

1 . As a diaphragm to cut off the peripheral rays and
thereby prevent spherical aberration (see page 266).

2. To regulate the amount of light entering the eye.
The more light the eye receives the more contracted the
pupil. This change in the width of the pupil follows reflex ly
upon changes in the amount of light entering the eye. The

268 HUMAN PHYSIOLOGY

centripetal nerve of this reflex is the optic nerve. By this
reflex contraction of the pupil the retina is saved from too
strong illumination, since the smaller the pupil the less the
light that enters the eye.

Normally both pupils are of the same size ; the change in
the pupil takes place in both eyes even when the light
entering one eye is changed (consensual pupil reflex). The
centres for this reflex lie in the cervical cord (see page 233).

The contraction of the pupil also takes place during
accommodation and convergence of both eyes. The centre
for this process is situated in the corpora quadrigemina (see
page 242).

The pupil is (i) contracted by sleep and by poisons
(physostigmin) ; (2) dilated by stimulation of many sensory
nerves, muscular exercise, dyspnoea, poisons (atropin).

IV. Ophthalmoscope. — Only light falling upon the most
anterior part of the eyeball enters the eye. Light falling
upon the side does not enter the eye because of the opacity

FIG. 31.

of the choroid and iris. The light which has entered the
eye is reflected by the retina back to its source. Hence we
cannot see the background of another person's eye because
no light emanates from our own eye by which the observed
eye is illuminated. But if a mirror, S, having an aperture
in its centre (Fig. 31) is placed between two eyes, A and
By in such a position that it throw's rays of light coming from

OPTICS 269

a light /% which is placed at the side of the head, into the
eye B, a part of the rays reflected by the background of
the eye leave B and pass through the aperture in the mirror
into the eye A. The eye A then sees the background of
the illuminated eye B. If both eyes are emmetropic ?nd at
rest, the light reflected by B passes out in parallel rays and
A sees the back of B erect and enlarged. If the light leaves
B in convergent rays (in case B is accommodated or myopic
— as represented in Fig. 31), the image of the retina can be
seen erect by placing a concave lens, making the rays
parallel or divergent, between A and B. If a convex lens
of sufficient strength is placed between B and 5, the reflected
rays form, at some point between .5 and the lens, a real and
inverted image of the background of B which can be
observed by the eye of the observer A (observation of in-
verted image).

In the albino, diffused light enters the eye through the trans-
parent iris which contains no pigment ; this light can illuminate the
background of the eye. If this diffused light is prevented from
•entering the eye, as by placing a diaphragm in front of the eye, the
background of such an eye also appears dark.

2. THE STIMULATION OF THE RETINA BY LIGHT.
SENSATION OF LIGHT

The elements of the retina sensitive to light are the cones
and rods. From them the stimulation passes through the
nervous portion of the retina and through the optic nerve to
the brain.

The nerve structure of the retina is found in the connective-tissue-
supporting elements and is composed of three neurons placed one
behind the other (see Fig. 32). They are :

(1) Neuro-epithelial cells, i.e. the cones (z*) and rods (j) with
their nucleated portion (cone and rod granules, st and -r,), which
are joined by processes to the outer processes of the

(2) Bi -polar cells (£). The inner processes of the bi-polar
cells join the protoplasmic processes of the

(3) Ganglionic cells (^), whose axis-cylinders form the optic
fibres.

In addition to these, still other cells and centrifugal nerve fibres
have been found in the retina, but their function is not known.

270

HUMAN PHYSIOLOGY

The mosaic arrangement of rods and cones lies in the external
layer of the retina (viewed from the centre of the
eyeball). To arrive at them, light coming from
the vitreous humor must first pass through all the
other layers of the retina.

The outer layer of the retina in the macula hitca
contains only cones ; in the otner portions it con-
tains cones and rods. In the central part of the
macula lutea, that is, in ihefovea centralis, the cones
have a diameter of 2-2. 5 ju ; at the periphery 6-7
// ; the rods have a diameter of about 2^.

External to the layer of rods and cones there is a
layer of epithelial cells with delicate protoplasmic
processes which reach down between the rods and
cones.

That the cones and rods are the retinal elements
MATIC REPRE- ^or ^e perception of light is proven by the shadows
SENTATION OF whichthe blood vessels of the retina cast. In a dark
THE RETINAL room a light is held to the side of the eye (at n, Fig.
33), while the other eye is closed. The light illu-
minates the retina at the point b, which is found by drawing a line
from a through the nodal point A" to the retina. From b light is
reflected by which other parts of the retina are illuminated ; the

FIG. 33.

cause of this sensation of light thus produced we refer to the exter-
nal world, hence we see the visual field dimly illuminated. One of
the rays reflected from b falls upon the retinal vessel g, and hence

OPTICS 271

the point c of the retina will remain dark and we see a dark spot
in the visual field in the direction cd (prolongation of a straight
line drawn from c through the nodal point). The shadows cast by
the retinal vessels upon the retina are perceived as black ramifying
lines in the visual field. If now the light is moved from a to a,
the apparent position moves from d to d, as illustrated in the figure.
From the extent of both movements the distance between g and c
may be calculated, and it has been found that this corresponds to
the distance between the vascular nerve-fibre layer and the layer cf
rods and cones.

The place where the optic nerve enters the eye [blind spot] is
not sensitive to light, because at that place no rods and cones are
present. This is demonstrated as follows :

FIG. 34.

Close the left eye, and with the right eye look at the cross a
(Fig. 34) while the page is held about 25 cm from the eye. The
black circle is then invisible because its image falls upon the blind
spot.

It has been supposed that in the sensitive apparatus n substance,
the so-called visual substance, is decomposed, and that this decom-
position calls forth the stimulation.

I. Objectively demonstrable changes in the retina pro-
duced by light. — Changes in the retina produced by light
have been demonstrated, but their relation to the sensation
of light is not known.

i. Visual purple (rhodopsin) is a red pigment found in
the external elongation of the rods. This is bleached by
light, the color being restored in the dark and also in the
excised eye (in rabbits in one half-hour, in frogs in one to
two hours). The restoration proceeds from the pigment
epithelium. Visual purple cannot be the only visual sub-
stance, for it is not present in the macula lutea of man, the
place of direct vision (see page 277).

The visual purple can be extracted from a fresh retina by an
aqueous solution of bile salts. This must be done in the dark or

272 HUMAN PHYSIOLOGY

by a sodium light, because the extracted visual purple is bleached
by daylight, not by red or yellow light. The composition of visual
purple is not known.

2. In the dark the pigment of the epithelial layer in a frog
collects in a cell body, while, in the light, it moves along
the processes between the cones and rods.

The pigment is not directly necessary for the perception of light,
for individuals in whom pigments are lacking (albino) are able to
see.

3. In frogs and fishes the inner processes of the cones
become shorter and thicker in the light.

4. In the illuminated retina certain electrical phenomena,
connected with the irritation, have been observed, but their
cause and significance are not known.

II. Visual sensation.

A. The intensity of visual sensation. — The intensity of
visual sensation is dependent upon :

1. The intensity of the stimulus. The stronger the light
the greater the intensity of the sensation. The sensibility
for perceiving the difference in the intensity of different lights
follows Weber's law (page 256).

2. The size of the illuminated portion of the retina. A
small light object may appear darker than a larger but less
luminous object.

3. The duration of the action of the light.

(a) The rise of visual sensation. — A considerable length
of time, about o. 16 second, elapses between the beginning
of the action of the light and the time that the sensation of
light has reached its greatest intensity. Hence a bright
light acting for a very short time may appear darker than a
less bright light acting for a longer time.

(/>) Disappearance of the visual sensation; positive after-
image.— If the light disappears suddenly, the visual sensa-
tion remains for a short time. This is called the positive
after-image. Upon this depends the well-known phenome-
non that if, in the dark, a glowing coal is moved forward and
backward, the coal does not appear as a luminous point at

OPTICS 273

each place where it actually is, but as a fiery stripe corre-
sponding to the path it describes. In this case, new points
of the retina are stimulated before the sensation of the
previously stimulated points has entirely disappeared.

The individual visual sensations produced by a series of
light stimulations rapidly following each other blend into
one visual sensation. Each individual stimulation increases
and each interval between the stimulations decreases, to a
certain extent, the retinal stimulation ; but if the light
stimuli follow each other sufficiently rapidly, the variations
in the sensations are so small that they are no longer per-
ceived. The intensity of the visual sensation in this case is
as great as that produced by a correspondingly feebler light
acting continually (Talbof s lazv).

(<r) Fatigue of the retina. Negative after-image or suc-
cessive contrast. — By long duration of the light, the intensity
of the sensation is decreased because of the fatigue of the
retina. A fatigued retina is less irritable than one not
fatigued. If one looks for some time at a light field placed
on a dark background and then at a uniformly light field,
this does not appear uniformly light, but upon it is seen a
dark area corresponding to the light field first looked at.
This phenomenon is called negative after-image or successive
contrast.

Adaptation or the adjustment of the retina to various in-
tensities of light depends upon fatigue and restoration. If
one enters from a light into a dark room, nothing is clearly
seen at first because the retina is fatigued ; gradually the
retina becomes more irritable, being rested, and one sees
much better in the dark. If one enters from a dark into a
lighted room, the light at first blinds because of the great
irritability of the retina, which is gradually decreased by
fatigue.

4. TIic illumination of the surroundings of the observed
object. — A light upon a dark background appears lighter
than upon a bright background (simultaneous contrast).
This contrast is greatest at the limit between the light and

274 HUMAN PHYSIOLOGY

the dark, e.g. a white object on a dark background appears
to be surrounded by a very dark border.

Irradiation. — Light objects upon a dark background appear
larger than they really are. This is due either to the fact that the
stimulation of a portion of the retina radiates to the neighboring
parts or that, because of imperfect accommodation, the image of
the light object is enlarged by circles of diffusion.

B. Quality of the visual sensation. — The retina is stim-
ulated only by rays whose wave lengths lie between 0.69/4
and 0.39^. These visible rays are found in daylight.

Strictly speaking, not all the visible rays are present in daylight,,
for those corresponding to the Fraunhofer lines are not present.

The sensation produced by daylight is white. A white
color of lower intensity is called gray. Objects which send
out no rays capable of stimulating the retina appear black.

The visible rays are the more refractive the shorter their
wave length. When the various rays are separated by pass-
ing the light through a prism, it is observed that they pro-
duce various visual sensations, called color sensations.

The sensation of

Red is produced by rays of 0.69 u wave-length.

Orange " " " " 0.64"

Yellow " " " " 0.59 " "

Green " " " " 0.53 " "

Blue " " " " 0.46"

Violet " " " " 0.39 " "

The sensations of color are produced by the simple or
homogeneous rays only in medium intensity. All rays which
in medium intensity appear colored are colorless in very
strong or weak intensity. If the intensity of homogeneous
rays is decreased, the relative brightness is changed. The
spectral red is brighter in medium intensity and darker in
lesser intensity than the blue. This, however, can be
observed only by the eye adapted to dim vision.

Mixed colors are produced by the simultaneous action of
rays of various wave lengths upon the retina. Of the mixed
colors one, i.e. purple, is not found in the spectrum. It
is produced by mixing red and violet. The mixed colors

OPTICS 275

appear whiter, less saturated, than the corresponding spec-
tral colors. For example, spectral red and yellow mixed
form an orange color which appears \vhiter than the orange
of the spectrum.

Complementary colors are two colors which by mixing
give the sensation of white. The following are pairs of
complementary colors: red and greenish blue, orange and
blue, green and indigo blue, greenish yellow and violet.

The theories of color reduce the many color sensations to the
simultaneous but unequal stimulation of a few primary colors. The
Young-Heljiholtz theory assumes three primary color sensations —
red, green, and blue, which by the action of a light are always
stimulated simultaneously but unequally by the individual homo-
geneous rays. By the mixing of the various primary colors, the
different color sensations are produced. If the three color sensa-
tions are equally stimulated, the sensation of white is produced.

Recently the idea has been advanced that only the cones of the
retina are the apparatus for the color sensations, and that with
these are connected three classes of nerves corresponding to the
three primary color sensations. The rods are supposed to be sen-
sitive only to white light of low intensity, and this sensation is
brought about by the decomposition of the visual purple. Accord-
ing to this view, only the rods are stimulated by light of very low
intensity, which therefore appears colorless, while such light is not
able to stimulate the cones. In dim light we therefore see chiefly
with the rods, in bright light with the cones.

Bering's theory of opposite colors assumes six primary color-
sensations, which are classified into three groups of two sensations
each :

i. White and black ; 2. Red and green; 3. Blue and yellow.
For each group a visual substance is assumed by whose changes
sensations are produced. The changes of the substance may be of
t\vo kinds ; the one kind produces one sensation, the other, oppo-
site in character to the first, produces the other sensation. Of the
two opposite processes, one is supposed to be the dissimilation, the
other the assimilation, of the visual substance.

The retina is sensitive to colors only in its central portion.
As we proceed to the periphery the power of discerning
colors decreases. The outermost parts of the retina are
color-blind.

Besides the color-blindness in the peripheral region of the retina,
pathological color-blindness ol the whole retina occurs.
This color-blindness may be :

276 HUMAN PHYSIOLOGY

1. Total, in which all color sensations are absent, all objects
appearing colorless.

2. Partial.

Partially color-blind persons have but two kinds of color sensa-
tions :

(a) The more general form, the red-green blindness, in which
only blue and yellow give rise to sensations, while red and green
appear colorless.

(b) The blue-yellow blindness, in which only the red and green
give rise to sensations, while blue and yellow appear colorless.

The red-green blind can be divided into two groups which are
separated from each other by typical differences in the lack of
color sensations. For the one red or bluish green are colorless,
for the other purple-red and green.

Color-blindness has been explained either by the lack of certain
primary sensations or by changes in the irritability of the elements
of color sensations.

The negative after-irrage of a color sensation has the
color complementary to the original color. A colored light
upon a colorless background calls forth a colored simul-
taneous contrast, in which the background has the color
complementary to that of the colored light.

3. VISUAL PKRCKI'TION

I. Monocular vision.

Space sensation of the retina. — We arc able to see
objects of the outer world clearly in their position because
we can distinguish different luminous object points. The
distinguishing of several object points is rendered possible
by the mosaic construction of the retina from elements each
of which produces a separate sensation when it is stimulated
by light from a luminous point. In the fovea centralis each
cone may be regarded as such an element, but at the
periphery of the retina several of the rods and cones collect-
ively form one element.

From experience we seek the source of the light which
has stimulated a sensational element, in the line drawn from
this element through the nodal point outward (see pages
258 and 261). Hence by vision with one eye u'c are able to
tell the direction in which the object lies.

OPTICS 277

Two separate object points are seen distinctly when their
image points fall upon two sensational elements separated
by at least one other element.

Acuteness of vision is the power by which two luminous
points can be distinctly seen. The acuteness of vision is the
greater the smaller the diameter of the sensational element
or the smaller " the smallest visual angle," when the lumi-
nous points can still be seen as distinct points. The visual
angle is the angle which the direction rays from the luminous
points form with each other.

\Ye can discriminate between direct and indirect vision.
A point seen by direct vision is called the fixed object point.
We see less distinctly by indirect than by direct vision.

The fovea centralis functions in direct vision. It has the
greatest acuteness of vision, and by means of it we can, under
favorable circumstances, distinguish two luminous points
which form a visual angle of 40 seconds. This corresponds
to a diameter of 3yu of the sensational element (a little more
than the diameter of a cone in the fovea). The peripheral
portions of the retina function in indirect vision and have less
acuteness of vision.

Oculists regard five minutes as normally the smallest visual
angle for the fovea, which is true for the method generally in vogue
for determining acuteness of vision (reading of letter).

The direction ray drawn through the fovea is called the
visual axis or line of fixation (see Fig. 28, G G'}\ in it lies
the luminous point which we fix upon in seeing. This line
does not coincide with the optical axis, but its anterior end
is a little inward from the optical axis. The angle formed
by these two lines is called the " angle a " and is about 7°.

The visual field is the field in which all the luminous
points seen by the stationary eye seem to lie. The visual
field therefore includes all the directions in which the station-
ary eye can see objects. Its extent is indicated by the
angles which the lines drawn from the limits of the visual
field through the nodal point form with the visual axis.
The extent of the visual field is outward 70-90°, inward

278

HUMAN PHYSIOLOGY

50-60°, upward 45-55°, downward 65-70°. The perimeter
is used in determining the field.

II. Movements of the eyes.

I. Movement of One eye. — (a) General observations.—
The external eye muscles turn the eyeball about a point
lying on the optical axis, 13.557 mm behind the cornea.
The eye and its socket form a ball-and-socket joint (see
page 202).

The monocular field of vision [Blickfeld] is the field which
includes all the luminous points that can be seen by the
moving eye, the head being held quiet.

Primary position is the position of the eye when a person
looks straight forward into the distance, the head being held

FIG. 35. — MUSCLE AND AXES OF ROTATION OF THE EYK. (After Helmholtz.)

#, rectus externus; s, rectus superior; i. rectus internus; /, obliquus superior;
«, trochlea; A, optical axis; D/), axis of rotation of the rectus superior and
inferior; J3, axis of rotation of the obliquus superior and inferior; vf insertion of
obliquus inferior.

erect. In the primary position the visual axis is horizontal
and parallel to the median plane of the body. For any
given position of the visual line it is mechanically possible
that the eye can still assume many positions because of its

OPTICS

279

ability to turn around the visual line as an axis. In reality
such a turning does not take place, but for each position of
the visual line the whole eye has a definite position. This
.is due to the peculiar coordination of the innervation of the
eye muscles. The position of the eye for any given position
of the visual axis is such as if it moved from the primary to
the new position by rotating around an axis perpendicular
to the visual axis in the primary and the new position.

r.sup.

r.inf
Fir.. 36. — ACTION OF THE KVK MUSCLES.

Lines described by the line of vision in the visual field when the eyeball is
turned from its primary position by some muscle of the eye. The movements of
the point of vision [Blickpunkt] corresponding to the angle of rotation are indi-
cated on the lines in degrees. The distance of the plane of the paper from the
point of rotation of the eye equals the line dd. The position which the horizontal
meridian in a primary position assumes is indicated at the end of each line.

(/>) Action of t lie individual muscles (see Figs. 35 and 36).
— The change in position of the eye may be stated as fol-
lows :

I. Change in the position of the anterior surface of the

280 HUMAN PHYSIOLOGY

cornea, i.e. raising, lowering, adduction (to nasal side) and
abduction (to malar side).

2. Deviation of the perpendicular meridian of the cornea
in the primary position from the perpendicular (wheel move-,
ment inward when the upper part of the meridian is bent
toward the median plane ; wheel movement outward when
this part is bent away from the median plane).

The eye is turned from the primary position :

1. By the rectus externus; abduction.

2. By the rectus internus; adduction.

3. By the rectus superior; upward, adduction and wheel
movement inward.

4. By the rectus inferior; downward, adduction and
wheel movement outward.

5. By the obliquus inferior; upward, abduction and wheel
movement outward.

6. By the obliquus superior; clown ward, abduction and
wheel movement inward.

The action of these muscles is illustrated in Fig. 36.

(c} Combined action of the muscles of otic eye. — The rectus
superior and obliquus inferior are always simultaneously
innervated (from a coordination centre) ; also the rectus
inferior and obliquus superior.

The secondary position, i.e. abduction, adduction, raising,
lowering, are not accompanied by wheel movements. By
simple raising and lowering, the adduction and wheel move-
ment produced by one of the active muscles is destroyed by
the opposite action of the other muscle. All other move-
ments (tertiary .position} are associated with wheel move-
ments. This wheel movement takes place:

1. Outward (p. inf.} by raising (r. sup.} and abduction
(r. cxt.}\

2. Inward (r. sup.} by raising (o. inf.} and adduction
(r. int.};

3. Inward (o. snp.} by lowering (r. inf.} and abduction
(r. «*.);

OPTICS 281

4. Outward (r. inf.} by lowering" (o. sup.) and adduction
(/-. ////.).

2. Combined action of the muscles of both eyes. — The
two eyes are moved simultaneously. They are innervated
from a common centre. The movements are as follows:

1. Rcct. sup. and obi. inf. on both sides — raising of both
eyes ;

2. Rcct. inf. and obi. sitp.-v\\ both sides — lowering of
both eyes ;

3. The left rcct. int. and right reef. cxt. — movement of
both eyes to the right ;

4. The left rcct. cxt. and right rcct. int. = movement of
both eyes to the left.

5. Rcct. int. on both sides — convergence;

6. Rcct. cxt. on both sides = divergence.

With the convergence is associated accommodation and con-
striction of pupil.

Binocular point of vision is the point in space on which
both eyes are fixed and in which, therefore, the two visual
axes meet.

Binocular field of vision is the field which includes all the
object points which can be perceived by the two eyes when
the head is held stationary.

The monocular fields of the two eyes nearly but not altogether
cover each other. But the binocular field of vision is much smaller
than that part of the monocular fields common to both eyes, for
the two visual axes cannot be directed simultaneously upon a point
upon which each visual axis can independently be directed.

III. Binocular vision.

i. Single vision with both eyes [diplopia]. — Those
objects in the outer world whose images fall on identical
points of both retinae are seen as single objects. Identical
points of the two retina; are therefore such points whose
simultaneous stimulation by a luminous object gives rise to
a single sensation.

A pair of identical points are, for example, the two fove;c
centralis, and also two points on both retina; equidistant and

282 HUMAN PHYSIOLOGY

located in the same direction from the foveae centralis (see
ig. 37)-

I r

FK;. 37.— IDENTICAL POINTS ON THE RETIN.K.

The right (r) and the left (/) retina are divided into the quadrants I, 2, 3, and
4 by the perpendicular and horizontal lines drawn through the fovea.' c. If the
points c and the corresponding dividing lines are placed over each other, every
point of one retina will be covered by its identical point of the other retina.

A luminous point whose image does not fall on identical
points of the retinae is seen double.

If identical points of the retinae are stimulated by different
objects, the two objects are not seen simultaneously, but first
one and then the other is seen, according to whether the
attention is first fixed upon the one or upon the other. This
is called the struggle of the two fields of vision [Wettstreit
cler Sehfelder].

For a given position of the eyes the field in which all
points are seen as single points is called the horopter.

To find the horopter, draw lines from a pair of identical points
through the nodal points ; the point where these two lines cross is
seen as a single point. All the points thus found form the horopter
for this given position of the eyes.

2. Perception of solidity. — By binocular vision we can
see an object from two different directions. Hence the posi-
tion of the object is where the two visual lines cut each
other. If a solid object is viewed with both eyes, two dis-
tinct images of the object are formed upon the retinae because
the two eyes view the object from two different points of
view. Hence the images falling upon identical points of the
retinae are not the same. Consequently only a part of the
points of the observed object appear as single points; the
others are seen double. This gives us the impression of a
solid body.

OPTICS 283

If we present to each eye, from its own standpoint, a pic- *
ture of the same body, the eyes see the pictured object
as a solid body. The instrument by which this is done is
called the stereoscope.

The judgment concerning the distance and the direction
of an object is based chiefly upon the degree of contraction
which the external eye muscles and the muscle of accom-
modation undergo in fixing the gaze upon the object. The
judgment of the size of the object is formed by comparison
with an object of known size, correction being made for the
distance of the object. Errors made in judging the distance
and direction of objects are called optical illusions.

1 . The protective organs of the eye. — By the closing of the
eyelid the eyeball is protected from injurious external influ-
ences. This is accomplished by the orbicularis palpebrarum,
which is innervated by the facial. The closing may be a
voluntary or a reflex act. The reflex closing is brought
about by too strong stimulation of the retina (blinking) or
by the stimulation of the cornea and conjunctiva.

The surface of the eye is kept moist and clean by the
tears. The tears flow from the efferent duct of the lachry-
mal gland into the conjunctival sac and are distributed by
the closing of the lid and by the movements of the eye. In
this manner the closing of the lid keeps the cornea moist
and clean. From the conjunctival sac the tears flow through
the nasal duct into the nose.

The Meibomian glands in the eyelids are sebaceous glands
whose secretion oils the borders of the lids. This prevents
the flowing of the tears over the lids.

2. Blood and lymph circulation in tJie eye. — The blood
enters the eye:

(1) By the central artery of the retina, which supplies the
retina with blood.

(2) By the ciliary arteries which pass to the choroid.
Communications exist between the branches of the vessels

of the retina and of the choroid, especially near the entrance
of the optic nerve.

284 HUMAN PHYSIOLOGY

The blood leaves the eye :

(1) By the central vein of the retina (from the retina).

(2) By the vorticose veins (from the choroid).

The aqueous humor may be regarded as lymph which, in
the posterior chamber of the eye, is secreted by the ciliary
processes and the posterior surface of the iris. The dis-
charge of the aqueous humor takes place in the anterior
chamber in the angle between the sclerotic and the iris.
The lymph is here absorbed into a venous vessel, the canal
of Schlemm (s, Fig. 30), There are no special lymph ves-
sels in the eye.

The vitreous Jiumor is a jelly-like tissue, consisting of an
alkaline fluid inclosed in a delicate membrane. This mem-
brane is composed of collagen ; the fluid contains 1 . 3$ solids,
including traces of albumin and globulin, also a proteid sub-
stance called mucoid, and finally 9$ salts. The lens is com-
posed of fibres which may be regarded as cells ; these contain
about 36$ solids, chiefly a globulin-like proteid (35$).

CHAPTER XXII

THE EAR

Tin; ear contains the sense organ of hearing and the
organ for perceiving the positions and movements of the
head.

1. THE AUDITORY ORGAN

The adequate stimuli for the auditory organ are the vibra-
tions of solid, liquid, or gaseous bodies, called sound waves,
because by their action upon the auditory organ they give
rise to the sensation of sound. These vibrations are usually

FIG. 38.— DIAGRAMMATIC VIFAV OF THE ORGANS OF THE KAR.

(After Helmholtz.)

/), external auditory canal; cc, membrana tympani; />/>', cavity of the tym-
panum with the auditory ossicles; 0, fenestra ovalis; r, fenestra rotunda; ./,
cochlea; A', Kustachian tube.

carried to the ear by air. But the vibrations can also be
carried to the ear through the bones of the head, as when

285

286

HUMAN PHYSIOLOGY

the source of the vibrations, e.g. a tuning-fork, is brought
into contact with them.

i . Conduction of sound in the ear to the sensory appa-
ratus (see Fig. 38).

(a) The propagation of sound in the external ear. — The
external auditory canal (I), Fig. 38) serves as a funnel which
by reflection from its wall gathers the sound vibrations and
conducts them undiminished to the ear-drum (cc) which
closes the bottom of the canal. The auricle or pinna of the
ear is the rudiment of the elongation of this funnel-like
passage. The membrana tympani is set in vibration by the
vibrations which have been conducted to it.

(b) The propagation of sound in the middle ear. — The
middle ear or tympanum (/>'/>, Fig. 38) is a cavity in the
petrous bone and contains air. Its outer wall is formed by
the drum, its inner wall by a bone in which are two aper-
tures closed by membranes, the round and oval fenestraj.

The membrana tympani is connected with the fenestra
ovalis by the auditory ossicles, which convey the vibrations

of the car-drum to the mem-
brane of the fenestra ovalis.
The auditory ossicles are the
hammer, anvil, and stirrup
(stapes), see Fig. 39.

The manubrium of the
hammer, Mm, is united with
the ear-drum, lying in its upper
vertical radius. From the neck
of the hammer proceed two

ligaments to the walls of the
FIG. 70.— AUDITORY OSSICLES. . . .

Mm, manubrium of malleus; Mcp, tympanum which allow the
head, and J//, long process, of the ham- hammer to move around Oil
mer- Tc. incus, or anvil-bone; fl>. short, . , . n . . «

and//, long, process of the anvil; s\ an approximately horizontal
stapes. sagittal axis. The head of the

hammer, Mcp, is united to the anvil by a joint which allows of
but little movement, and this movement is largely prevented
when the manubrium is moved inward by a coglike process*

Mcp

THE EAR 287

The anvil, Jc, has two processes, one behind, Jb,
which is movably connected with the posterior wall of the
tympanic cavity, and a lower process, Jl, whose point is
connected by means of a sesamoid bone with the stapes
(stirrup) S. The base (foot) of the stirrup is united with the
membrane of the fenestra ovalis (<?, Fig. 38).

The auditory ossicles form a lever turning- about the axis
of the hammer, one of whose arms is the manubrium of the
hammer, while the other arm extends from the axis to the
point of the lower process of the anvil and, through the
stirrup, is connected with the membrane of the fenestra
ovalis. If the drum vibrates transversely to and fro, its
movements are carried by the lever to the membrane of the
fenestra ovalis.

The sound-conducting apparatus of the middle ear is so
constructed that it is evenly set in sympathetic vibration by
sound vibrations of various lengths. A free and uniformly
stretched membrane gives out, when it is struck, a certain
note whose pitch depends upon the size and tension of the
membrane. Such a membrane is set in especially strong
vibration when in its neighborhood a note having the same
pitch as that produced by the membrane is sounded. The
drum of the ear has no definite note of its own because of its
complicated structure (funnel-shaped, being pulled inward
by the manubrium of the hammer). By this its tension in
different directions is not the same and therefore it. can have
no definite note of its own. It can therefore be set into
sympathetic vibration to the same extent by many different
notes.

The sound-conduction apparatus of the ear is provided
with a very effective damper, so that no perceptible after-
vibrations occur when the notes producing the vibrations
have ceased.

The following muscles are inserted on the auditor}' ossi-
cles:

(i) Tensor tympani, which lies in a bony canal extending
parallel with the Kustachian tube. It is united to the

288 HUMAN PHYSIOLOGY

manubrium of the hammer by a tendon bending around a
bony process. By its contraction the manubrium is bent
inward and thus stretches the drum. It is innervated by
the trigeminus.

(2) Stapcdius, whose tendon is attached posteriorly to the
head of the stapes. It is innervated by the facial.

The functions of these muscles are not fully understood. They
probably exist for the purpose of rendering the conducting appa-
ratus more fixed when a strong sound meets the ear in order that
the vibrations may be made weaker and thus prevent the auditory
nerve from being too strongly stimulated. By means of the tensor
tympani the tension of the membrana tympani can be accommo-
dated to very high notes.

The Eustachian tube, a narrow canal (/:, Fig. 38), passes
from the floor of the tympanic cavity forward and downward
and connects the middle ear with the pharynx. The tym-
panic cavity and the Eustachian tube are covered with
mucous membrane. The opening of the Eustachian tube
into the pharynx is generally closed by a fold in the mucous
membranes. During deglutition it is opened for a brief
period by the contraction of the tensor muscle and the
levator palati moll is. By the opening of the tube the pres-
sure of the external air and the air in the inner ear are
equalized, which is absolutely necessary for the normal con-
duction of sound into the middle ear. If the tube is closed
by catarrhal swelling of its mucous membrane, disturbances
in hearing result. The mucous membrane of the tube is
lined with cilia which move the mucus toward the pharynx.

(c) The conduction of sound in the internal ear. — The
internal ear, or labyrinth, is a cavity in the petrous bone and
is filled with a fluid. In the outer wall of the cavity are the
fenestraj rotundis and ovalis.

The anterior part of the internal car is the cochlea
(VI, Fig. 38), a spirally wound canal of two and one-half
turns, divided into two parts by a bony plate. As the bony
plate is interrupted in the cupola, the passages of the canal
communicate at this place (helicotrema). One of the
passages, the scala vestibuli, opens at the base of the cochlea

THE EAR 289

into the median part of the labyrinth, the vestibule, which
is separated from the middle ear by the fenestra ovalis.
The other passage of the cochlea, the scala tympani, ends,
at the base, in the fenestra rotundis (compare Figs. 40 and
40-

In the labyrinth, therefore, the passage from the fenestra
ovalis to the fenestra rotundis goes through the canals of the
cochlea. By the vibrations of the membranes of the fenestra
ovalis the water in the labyrinth is caused to vibrate and
presumably that in the cochlea, because the passage from the
fenestra ovalis to the other yielding place of the labyrinth

FIG. 40. — CROSS-SKCTION OF TIIK COCHLEA.

wall (the membrane of the fenestra rotundis) passes through
the cochlea. The movement of the water in the labyrinth
is rendered possible by the existence of this second flexible
part [membrane of the fenestra rotundis]. The partition in
the canal of the cochlea is partly membranous, and the
vibrations of the water of the labyrinth are conveyed to this
membrane. This membrane contains the sensory apparatus
which is stimulated by the vibrations.

2. The sound-sensations.

(a) The apparatus for the auditory sensations (Fig.
41). — The septum of the cochlea canals consists of:

i . The lamina spiralis ossea (Av>), which extends from the
axis of the cochlea (modiolus) into the lumen of the cochlea
canal.

290 HUMAN PHYSIOLOGY

2. The lamina spiralis membranacea forms the continua-
tion of the lamina ossea and extends to the outer wall of the
cochlea. It is formed by the basal membrane (/;), composed
of parallel transverse fibres, and contains the apparatus for

FIG. 41.— CROSS-SECTION OF ONE OF THE COILS OF THE COCHLEA.
(After Rauber.)

SV, scala vestibuli; S T, scala tympani; CC, canalis cochlea; Iso, lamina
spiralis ossea; l>, membrana basilans; from Us to /j/>, lamina spiralis mem-
branacea; Co, organ of Corti; tic, nerve bundle; A', membrane of Reissner.

auditory sensations, i.e. organs of Corti (Co), placed upon
the basal membrane. Each organ of Corti consists of:

1. The pillars of Corti (CC, Fig. 42), i.e. two pillars bent
in the form of the letter S, resting on the membrana basi-
laris. One is called the inner, the other the outer, pillar,
and the two unite at the top.

2. The cells of Corti or hair cells (//), cylindrical cells
of which one is placed internal and three or four external to
the pillars. At their free surface they are provided with
small hairs which project through perforations of a support-
ing membrane, the membrana reticularis. Above this is
placed another membrane, the membrana tectoria (Aft).

The membrane of Reissner (R, Fig. 41), which proceeds
obliquely upward from the lamina spiralis ossea and unites
with the upper wall of the cochlear canal, separates the
canalis cochleae (C C, Fig. 41), in which the organs of Corti
are placed, from the scala vestibuli. The canalis cochleae

THE EAR

291

ends in a blind sac in the cupola ; at the base it passes into
the inner chamber of the membranous labyrinth.

L.o:

M.b.

FIG. 42. — CROSS-SECTION OF THE LAMINA SPIRALIS MEMHRANACEA.

Z0, lamina spiralis ossea; N, cochlear nerve; n n, nerve fibres; C C, pillars of
Corti; J//, membrana tectoria; Mb, membrana basilaris; h, hair cells; Jlfy, mem-
brana reticularis; d, Deiter's cells; lid, habenula denticulata; Hp, habenula
perforata.

The membranous labyrinth (see Fig. 43) is a membranous
covering of the vestibule and the posterior part of the laby-

K

FIG. 43. — Tin-: MEMBRANOUS LADVRINTH (DIAGRAMMATIC).

U, utriculus with the semicircular canals; S, sacculus; C, cochlea; A', cupola;
v, cul-de-sac of the vestibule; C>, canalis reuniens; A', ductus endolymphaticus.

rinth, the semicircular canals (see page 294). In the vesti-
bule the membranous labyrinth is divided by constriction
into two parts, the anterior sacculus and the posterior
utriclus.

The membranous labyrinth is filled by the endolymph,

292 HUMAN PHYSIOLOGY

while the space between the membranous and the bony laby-
rinth is filled with the perilymph.

The auditory nerve divides into two branches :

1. The cochlcar nerve, the real nerve of hearing, enters
at the axis of the cochlea and in the lamina spiralis ossea
spreads out its fibres like a fan. Its fibres finally unite with
the hair cells of the organ of Corti (see Fig. 42, Ar, ;/ ;/).

2. The vestibular nerve (see page 295).

(b) The auditory sensation. — The membrana basilaris is
set in vibration by the perilymph. By this the cells of Corti
are probably mechanically stimulated and thus the auditory
sensation is produced.

Auditory sensations may be classified as tones and noises.
The tones (musical) are produced by regular vibrations and
may be distinguished by pitch and timbre. The pitch of a
musical tone depends upon its number of vibrations. The
greater the number of vibrations per second the higher the
pitch. The audible tones lie between those having 19 and
40,000 vibrations per second (i i^ octaves). The tones used
in music lie between those having 33 (contra C) and 4000
(a""] vibrations.

The time which the tone must act in order to be heard
depends upon the pitch of the tone. Those of higher pitch
need less time than the lower tones. In order to judge of
the pitch of a tone, at least 16 single vibrations must strike
the ear. If less than 16 vibrations strike the ear. we cannot
accurately judge of the pitch. Auditory sensations, how-
ever, are still produced if but two single vibrations reach the
ear.

The accuracy of determining the pitch of a tone varies
much in different individuals. It depends upon ability and
practice. Trained musicians can still discriminate between
the pitch of two tones having 1000 and 1001 vibrations
(musicians call this T^ of a whole note).

The perception of tones of different pitch has been explained by
Helmholtz by the resonance theory as follows :

The membrana basilaris decreases in width as we proceed from

THE EAR 293

the cupola to the base of the cochlea (see Fig. 44).
membrane is composed of transverse fibres,
its tension in this direction is greater than
that in the longitudinal direction, and there-
fore as a resonator it acts like the strings of
a piano. If one sings a certain note near
an open piano, the string which has the
same number of vibrations as the note sung
is set into sympathetic vibration, the other
strings remaining quiet. In the same man-
ner if a note strikes the membrana basilaris,
that segment of the membrane whose num-
ber of vibrations correspond to that of the
note will be made to vibrate. Each segment
which can vibrate by itself stimulates the
cells of Corti found on it, and therefore
only certain fibres of the auditory nerve FlG> 44._DiA(;KAM OF
are stimulated. The corresponding cerebral THE MEMBRANA BASI-
cells, because of their specific energy, per- LARIS, UNROLLED.
reive tones of certain pitch. a'd\ width of membrane

at the cupola; ad, width

The quality or timbre of tones. at the base of the coch-
Most tones are not simple tones but are *3th«* £&?$
accompanied by overtones which, as a Corti.
rule, are higher than the fundamental tone. Each tone, in
a mixture of tones, gives rise to a sensation, hence several
sensations are produced which we call the quality, or timbre.
The timbre of one and the same fundamental tone varies
with the number and strength of the accompanying over-
tones.

If two tones whose number of vibrations have a simple
ratio (1:2, 2:3,3:4, 4:5) are sounded simultaneously,
the resulting sound is agreeable- — consonance. The simul-
taneous sounding of two tones whose number of vibrations
are not in a simple ratio produces a disagreeable sound — dis-
sonance.

Frequently we are able to analyze a mixed sound into its
components; we are able, for example, to distinguish the
parts played by the different instruments of an jnrchestra.

If two tones differing but little in their number of vibra-
tions are sounded simultaneously in such a way that at one
time the crests of both waves correspond and at another the

294 HUMAN PHYSIOLOGY

crest of one corresponds to the trough of the other, beats
are heard, i.e. periodic increase and decrease in the auditory
sensation. Beats occurring more frequently than 32 per
second cause an auditory sensation called beat-tone.

These heat-tones are a purely subjective -phenomenon ; they can-
not, like other tones of a mixed sound, be demonstrated by the reso-
nator, for they do not affect the resonator. Hence the production
of auditory sensations by such tones cannot be explained by Helm-
holtz's theory of resonants.

The sensations of noises are produced by irregular vibra-
tions in which now one, now another portion of the basilar
membrane is set in vibration.

In the sense of hearing, as in sight, there are certain
phenomena produced by the rise and fall of the auditory
sensation, as also the phenomenon of fatigue.

Two sounds following each other are still heard as separate
sounds if the interval between them is not less than o. I
second.

The judgment of the direction and distance from which a
sound comes is very imperfect. Both ears serve in judging
of the direction of the sound, it coming from the direction
towards which the ear most stimulated is turned.

2. THE SENSE ORGANS FOR PERCEIVING THE
POSITION AND MOVEMENTS OF THE HEAD

The posterior part of the bony labyrinth is composed of
the three semicircular canals, which are bony canals bent in
the form of a C. They originate and end at the vestibule.
Each canal has at both ends a dilation (ampulla). The
planes of the superior-anterior canal lie in the vertical longi-
tudinal plane ; that of the inferior posterior in the vertical
transverse ; that of the lateral in the horizontal ' plane.
Hence the three planes of the semicircular canals are per-
pendicular to each other. The bony canals surround the
membranous labyrinth (see page 291).

The thin walls of the membranous labyrinth are thickened
in the utriculus and in the sacculus (maculae acusticaj utriculi
et sacculi) and in the ampulla; (crista; acusticae).

THE EAR 295

The epithelial cells covering the inner walls of the mem-
branous labyrinth form hair cells in the maculae and cristaj
whose hairs extend into the cavity of the membranous laby-
rinth. These hair cells are neuro-epithelial cells in which
the fibres of the auditory nerve end. A branch of the
cochlear nerve goes to the macula sacculi, while the vesti-
bular nerve goes to the macula utriculi and the cristae.

Upon both maculae lies a thin jelly-like membrane, the
membrane of the otoliths ; upon the surface of this membrane
lie the otoliths (consisting of calcium carbonate).

The fibres of the auditory nerve to this part of the laby-
rinth are, according to the prevalent theory, not nerves of
hearing, but serve to perceive the position and movements of
the head. Their neuro-epithelial cells are supposed to be
mechanically stimulated either by the pull which the otoliths
exert because of their weight or by the hydrostatic pressure
of the endolymph, which varies with the different positions
of the head. They may also be stimulated by the move-
ments of the endolymph brought about by movements of the
head.

Reflexly coordinated movements for the maintenance of
the normal position of the head and the equilibrium of the
body are in part called forth by impulses from the semicir-
cular canals and the otolith organs. The compensatory
movements of the eye (page 242) are also called forth by
the stimulations from the semicircular canals. Destruction
of the semicircular canals in animals is followed by disturb-
ances in the normal position and movements of the head and
of the whole body (forced positions and movements). It is
also followed by diminution of the energy and tonus of
skeletal muscles and disturbances in muscular sense.

CHAPTER XXIII
SMELL

THE organ of smell lies in the regio olfactoria of the nasal
mucous membrane (upper part of the septum nasi, upper

FIG. 45.

(After M. Schultze.)
A, epithelium of the mucous membranes
of the olfactory region; a a, olfactory cells;
b b, supporting cells; B, ciliated epithelial
cell from the regio olfactoria.

-5

FIG. 46. — OLFACTORY CELL OF
MAN. (After v. Brunn.)

I, cell-body with its nucleus; 2,
peripheral rod, with 3, its ex
tremity, furnished with hairs, 4; 5,
central filament (beginning of an
olfactory fibre).

meatus, upper part of the middle meatus). It is composed
of rods which lie between the epithelial cells. These rods
end externally in delicate hairs (Figs. 45 and 46) ; internally

296

SMELL 297

they are connected with the olfactory cells whose axis
cylinders pass through the cribriform plate to the bulbus
olfactorius (see page 250).

Adequate stimuli for the organ of smell are gases carried
through the nose by inspiration and diffused in the regio
olfactoria.

The liminal intensity of many substances is very small ;
I millionth of I milligram of musk or butyric acid in I litre
of air can be detected by the sense of smell, while of mer-
captan still less is necessary.

The organ of smell is very soon fatigued.

The sensations of smell have many different qualities
which have not yet been classified. Mixed odors are pro-
duced by the action of two or more odorous substances.
Some odors are able to neutralize each other.

Corrosive gases cause tactile sensations in the nasal mucous
membrane which may be accompanied by sensations of smell.

CHAPTER XXIV
TASTE

E organ of taste is composed of taste goblets which are
goblet-shaped structures with an aperture towards the buccal
cavity and contains spindle-shaped cells (see Figs. 47 and 48).
The branches of the nerves supplying these structures end

FIG. 47.— CROSS-SECTION OF THE TASTE PAPILLA OK THE TONGUE, IN WHICH
I.IK THE TASTE-BUDS.

between these cells. Taste-goblets are found in the epithe-
lium of the circumvallate, foliate, and fungiformes papillae of
the tongue, as also in the soft palate and the posterior pillars
of the fauces. The nerve of taste is the glossopJiaryngcal,
whose fibres reach the taste organs in part directly and in part
through the Jacobson's anastomose and lingual nerve (see
page 252).

Adequate stimuli for the organs of taste are liquid and dis-
solved substances, or at least such as are soluble in saliva.

The intensity of the taste sensation depends upon the
concentration of the solution. The liminal intensity is
different for the various tastable substances. The concen-
tration necessary for some substances is seen in the following
table :

298

TASTE 299

Aloe I : 900,000

Sulphuric acid I : 100,000

Sodium chloride I : 426

Cane-sugar I : 100

The intensity of taste sensation is greater the greater the
surface of mucous membrane affected. The taste sensation
is favored by pressing the tongue against the palate.

FIG. 48. — TASTE-BUDS HIGHLY MAGNIFIED.

The best temperatures for taste lie between 10° and
35° C.

Hot or cold water temporarily inhibits taste.
There are four qualities of taste sensations :

1. Sweet, caused by sugar, saccharin, and certain alco-
hols.

2. Bitter, caused by alkaloids.

3. Salt, caused by neutral salts.

4. Sour, caused by acids.

A solution tastes the more sour the greater the number of hy-
drogen atoms replaceable by metals contained in the unit of volume.

Many authors consider the alkaline and metallic taste as the fifth
and sixth qualities of taste sensation.

There are also mixed taste sensations of two or more
taste qualities.

The sensations of taste are often accompanied by tactile
sensations (astringent taste) and by sensations of smell
(bouquet of wines).

CHAPTER XXV
CUTANEOUS SENSATIONS

The sense organs here dealt with are chiefly located in the outer
skin, but are also found in some parts of the mucous membranes
bordering on the skin, for example that of the jaws, mouth, nose,
conjunctiva, anus, vagina, and urethra. One kind of these sense
organs is present not only in the skin and mucous membrane, but
in all organs of the body — the sense organs of pain.

i. The organs of the tactile sensation. — The cutaneous
sense organs are composed of the endings of sensory nerves
in the skin. These endings may be classified as follows:

1. Free nerve endings between the epithelial cells.

2. The ncrvc-wrcath of hairs which surround the hair-
bulb just beneath the opening of the sebaceous glands.

3. Tactile cells are found in the deepest layers of the
epidermis and the neighboring layers of the cutis vera in
which are found non-medullated nerve fibres.

4. End-bulbs. These are spherical or oval bodies com-
posed of a connective-tissue capsule and a granular jelly-like
medulla — in which the nerve fibres end. In this class
belong:

(a) The tactile corpuscles of Mcissner, elliptical, trans-
versely striated structures. The nerve endings in these
corpuscles form a complicated network.

(b) The end-bulbs of Krauze, cylindrical structures in
which the axis cylinders are straight and end free.

(c) The genital corpuscles, oval, unstriated bodies much
similar to the tactile corpuscles.

300

CUTANEOUS SENSATIONS. 301

(<r/) The Vater-Pacini corpuscles, whose capsule is com-
posed of many concentric lamellae.

2. Qualities of cutaneous sensations. — There are four
qualities of cutaneous sensations, viz., touch, heat, cold, and
pain.

These various qualities are located in various parts in the
skin. There are portions whose stimulation calls forth
tactile sensations only, so-called tactile or touch points; we
•can also discriminate warmth, cold, and pain points.

These four kinds of points are not evenly distributed over the
whole body. Some of them are lacking in certain regions of the
body, e.g. the central part of the cornea has only pain points, while
its peripheral portion is provided with pain and cold points. The
glans penis contains no tactile points ; a part of the mucous mem-
brane of the cheek lacks pain points.

In those regions of the body where the four kinds cf points are all
found, the pain points are generally most numerous, then follow the
tactile and cold points, while the warm points are least numerous.

(a) Tactile sensation. — The adequate stimulus for the
tactile sense organs is the pressure exerted upon the skin.
Concerning the nature of the stimulation of nerve endings
"by pressure nothing is known. Stimulation by pressure
occurs only at the boundary of the portion of the skin
pressed, where, therefore, a fall in pressure exists.

For example, if a finger is dipped in mercury, sensations of
pressure are not felt in the portion of the finger below the mercury,
but at the circle formed by the level of the mercury.

Tactile sensations can also be produced by pulling the skin. If
the pull is exerted upon a very small area of the skin, for example
upon an individual tactile point, the sensation produced is nearly
like that produced by pressure. Only when a larger portion is
stimulated can we differentiate between pull and pressure.

The organs for the tactile sensation are probably the nerve
wreaths of the hair [Haarnervenkranze] and the corpuscles
of Meissner, for the following reasons:

i. In the regions of the body covered with hair, a tactile
point is found very near the exit of each hair. The hair
serves as a tactile apparatus, forming a lever whose shorter
arm is in contact with the sensory mechani^rtiT the^kjinT
while the longer arm receives the stimulj^^^

•\ A R Y,

...

302 HUMAN PHYSIOLOGY

2. In those regions of the body not provided with hairs,
the division of the skin into tactile points corresponds with
the distribution of the Meissner corpuscles.

The number of tactile points varies in different parts of the
skin. In the palm of the hand there are from 40 to 50 in
I sq. cm.

The liminal intensity of the stimulus for the tactile sensa-
tion depends upon :

i. The place of stimulation. The lips, finger-tips, and
forehead are the most sensitive. For the finger-tips the
liminal intensity is 0.03 g acting upon I sq. mm. surface.
The least sensitive portions are those covered with thick
epidermis, for example the soles of the feet. 2. The extent
of surface stimulated.

With increase of surface, the liminal intensity first decreases
rapidly, then increases slowly.

3. The rapidity of the stimulus.

The liminal intensity is, to a certain extent, the smaller the
more rapidly the pressure is exerted.

The ability to distinguish two unequal pressure stimuli of
moderate intensity corresponds with the law of Weber (see
page 256). The difference-threshold is about -:{l-0- of the
already acting weight, i.e. we can recognize the difference
between two weights if they have the ratio of 29 : 30.

The law of Weber docs not hold good for very small or very
large weights.

The tactile sensations appear and disappear very rapidly.
Even 460 shocks per second are still perceived as individual
shocks.

(£) and (c) The sensations of heat and cold. — These
sensations are produced either by increasing or decreasing
the heat conveyed to the skin while the loss of heat remains
constant, or by increasing or decreasing the loss of heat by
the skin while the heat conveyed to it remains the same.
The last is the case, e.g., in applying warm or cold objects
to the skin. Sensations of temperature are produced chiefly

CUTANEOUS SENSATIONS 303

by changes in the temperature of the skin, to a less extent
by constant high or low temperature.

Under certain circumstances a paradoxical ^sensation of cold can
be produced by the application of a warm body to a cold point.

The detection of differences in temperature is most delicate
when the objects coming in contact with the skin have a
temperature between 27° and 33°. Between these tempera-
tures we are able to perceive a difference in temperature of
^L-0 C. For the higher and lower temperatures the detec-
tion of differences is less accurate.

The end-bulbs of Krause are probably the organs for the sensation
of cold ; the so-called genital corpuscles, for sensation of heat.

(d) Sensation of pain. — The pain points can be stimu-
lated by a great number of stimuli. The intensity of pressure
and temperature stimuli in order to produce a sensation of
pain must be greater than that necessary to produce sensa-
tions of touch and temperature.

The sense organs for pain are probably the free nerve
endings in the epidermis. In the central part of the cornea,
where only pain points are present, only free nerve endings
are found.

The sensation of pain appears and disappears more
slowly than tactile and temperature sensations. When the
stimulus is of short duration, it can be noticed that the sen-
sation of pain is preceded by a sensation of touch or tempera-
ture. When more than 20 stimuli per second are received,
we can no longer distinguish individual stimuli.

3. The localization of sensation in the skin. Sense of
locality. — The sensations produced by stimulation of the
skin are associated with conceptions of definite areas of the
skin. By this we are able to locate the place stimulated.

The measure of this power of localization is the distance
that two parts of the skin must be separated in order that by
their stimulation two distinct sensations shall result. The
power of localization has thus far been determined chiefly for
the tactile sensation.

The distance which these two points must be separated

3°4 HUMAN PHYSIOLOGY

depends on the manner of stimulation, that is, whether the
points are stimulated simultaneously or successively. If
stimulated simultaneously, the distances for various parts of
the body are as follows:

Tip of tongue i mm

Tip of finger 2 "

Lips. 4.5 "

Forehead 22 "

Back of hand 31 ' '

Upper arm and thigh 68 "

When the points are stimulated successively the distances
are much smaller, being equal to the distances which sep-
arate the individual tactile points. For successive stimula-
tion, therefore, each tactile point has a special space value.

An area of the skin in which two stimuli cannot be distinctly felt
is called a tactile area. The tactile areas for successive stimulation
are smaller than those for simultaneous stimulation.

CHAPTER XXVI
ORGAN SENSATIONS

THE organ sensations are produced by the stimulations of
sensory nerves of an organ by the internal processes taking
place in that organ.

They may be classified as follows :

1 . Sensations of pain may proceed from all organs of the
body. The quality of these sensations is the same as that
of the pain sensations from the skin. But the power of
localizing the pain in the organ is very imperfect.

2. The sensation of muscle tension. This enables us to
estimate the weight of a raised body. The muscular sense
is measured by determining the accuracy with which the
weight of a raised body is estimated.

These sensations are produced by the stimulation of the
sensory nerves not only in the muscles, but also in the
tendons. In fact the nerves of the tendons seem to be of
greater importance for the sensations of tension than those
of the muscles. But the nerves of the muscles sooner call
forth sensations of the degree of muscular activity (fatigue
sensation).

3. The position of the limbs of the body is probably per-
ceived by the sensibility of the joints, which may be regarded
as closely related to the tactile sensation of the skin.

The sensibility of muscles, tendons, and joints serves in
judging the position and movements of the body.

Centripetal fibres from the muscles, tendons, and joints
aNo call forth reflexly coordinated movements for the main-
tenance of the equilibrium of the body. If the centripetal

305

306 HUMAN PHYSIOLOGY

parts are diseased, as in locomotor ataxia (see page 229),
disturbances in the movements occur.

It is supposed by many authors that muscular sensations
are due to the fact that we are conscious of the degree of
innervation of the motor nerve in the central organs.

There are still a number of organ sensations which are of
such an indefinite character that at present little can, with
certainty, be said about them. The knowledge concerning
them is diminished by the fact that they are often accom-
panied by strong feelings (bonheur and ennui) by which their
quality is masked. They are generally called common sen-
sations and include hunger, thirst, itching, tickling, shudder-
ing, fatigue, pleasure, ennui, giddiness, etc.

Of special physiological interest are the organ sensations,
hunger and thirst, as they call for the partaking of solid and
liquid food. The sensation of hunger is the sensation of an
empty alimentary canal, which disappears even when the
stomach is filled with an undigestible substance. In the
sensation of hunger the sensory nerves of the stomach and
intestine seem to play a part. If the period of hunger is
long continued, an undefinable sensation of general need of
food is present.

Thirst is the sensation produced by dryness of the pharynx,
which disappears when the mucous membrane of the palate
and the pharynx is moistened. Hence the sensation of
thirst is produced by the stimulation of the sensory nerve of
the mucous membrane by drying.

PART III

REPRODUCTION AND DEVELOPMENT

CHAPTER XXVII
REPRODUCTION

The first living beings must have originated by spontaneous
generation (generatio tequivoca), i.e. the origination of living
beings from lifeless material. At present, spontaneous generation,
so far as we know, does not occur, and new living beings originate
by biogenesis, i.e. the formation of living beings from separated
parts of previously existing living beings.

Reproduction may be :

(</) Non-sexual (reproduction by fission, budding, spore forma-
tion). In this, one separated portion of a living being develops into
a new individual.

(b) Sexual reproduction, in which two sexually different cells
(egg and sperm cell) unite and develop into a new living being.
These two sexual cells may either originate from one individual or
from two sexually different individuals (male and female).

Human beings arc propagated by sexual reproduction in
which the egg-cell provided by the female unites with the
sperm-cell furnished by the male and from this a new indi-
vidual develops.

1. THE MALK SEX-PRODUCTS AND THEIR FORMA

TION

i . Composition of the seminal fluid. — The seminal fluid
is a viscid, whitish, turbid fluid having a peculiar odor and
a neutral or alkaline reaction in which are suspended the

307

308 HUMAN PHYSIOLOGY '

solid elements, the spermatozoa. The seminal fluid contains
iSfo solids which include chiefly proteids, as also lecithin,
cholesterin, fats, salts, and spermin (Diethylen diamine).

Spermin, having a constitution of C2H4<f ]sju//C.,H4 , is a

base and is present in the fluid as the salt of phosphoric acid
and by evaporation of the fluid is precipitated as crystals.
The spermatozoa contain the ordinary constituents of
nucleated cells, i.e. proteid, nucleo-albumin, nuclein, nuclein
bases, potassium phosphate.

The spermatic filaments or spermatozoa are cells with
pear- or oval-shaped heads and the attached rod-shaped
middle piece which passes over into the threadlike tail.
The length of the whole spermatozoon is 0.05 mm. The
cells are poor in proteids, the head being the nucleus, and
the middle piece and the tail the protoplasm.

The spermatozoon moves abbut by the whiplikc move-
ments of the tail and, during its movements, rotates about
its long axis. The movements of the spermatozoon are
most lively immediately after the ejection of the seminal
fluid. It is favored by weak alkali reaction. Strong alkalies
and also acid reactions inhibit the movements. In the
genital canals of the female the spermatozoa retain their
movements for a very long time.

2. Formation of the spermatozoa. — The formation of the
spermatozoa takes place in the convoluted tubules of the
testis. Certain cells of the walls of these canals change to
the spermatoblasts which grow out into the canal. By cell
division and the separation of the newly built cells the
spermatoblast forms the spermatozoon. In this the nucleus
forms the head, while the protoplasm forms the middle piece
and tail. Concerning details of the morphological changes
in this process the results of investigators are contradictory.
In the testis there is formed simultaneously, in some unknown
way, the fluid in which the spermatozoa are suspended.
The formation of spermatozoa in the testis takes place, no
doubt, continuously. The seminal fluid is passed into the

REPRODUCTION 309

vasa deferentia, where it is stored up. During the ejacula-
tion, it is mixed with the secretion of the vesicular seminales,
the prostate, and Cowper's glands. Very little is known
concerning the secretions of these glands or the nature and
importance of their secretions. The prostate is supposed to
secrete the spermin and odoriferous substance found in the
mixed seminal fluid.

3. Discharge of the seminal fluid. Ejaculation. — The
discharge of the seminal fluid takes place during erection by
the activity of certain muscles by which the fluid is forced
out of the vasa deferentia and the urethra.

(a) Erection. — During erection the blood vessels of the
penis are well filled. This filling of the penis is brought
about by

(1) Increase .of blood carried to it by the dilation of the
arteries. The dilation is produced by the vaso-dilator
nerves, the nervi erigentes (see page 77).

(2) The removal of the blood is prevented by the com-
pression of the venae profundae penis. The compression of
these veins is produced by the contraction of the musculus
trans versus perinei.

The centre by which the erection is brought about is sit-
uated in the lumbar cord. It can be stimulated either
reflexly by the stimulation of the sensory nerves of the penis
or by impulses from the cerebral hemispheres (psychical).

(b) Ejaculation. — The ejaculation is accomplished by the
peristaltic contractions of the muscles of the vasa deferentia
and vesicular seminales which drive the fluid into the urethra
and thence it is propelled forward by the contraction of the
bulbo- and ischio-cavernosus muscles. The passage of the
urinary bladder is cut off by the erection of the caput
gallinaginis. The act of ejaculation can be called forth
reflexly by stimulating the sensory nerves of the penis.
The centre of ejaculation lies in the lumbar cord.

The amount of seminal fluid discharged during one
ejaculation is I— 6 cc.

310 HUMAN PHYSIOLOGY

2. THE FEMALE SEXUAL PRODUCTS AND THEIR
FORMATION

1. The ovum. — The female sexual cell or egg is a
spherical cell having a diameter of o. 15-0.2 mm. Its proto-
plasm is called egg-yolk; its nucleus, germinal vesicle. It
is surrounded by the zona pellucida. In the yolk we can
distinguish :

(1) The real living substance, the protoplasm.

(2) The dcutoplasin, or yolk granules, which serves as
food.

In the human ovum there is but little deutoplasm in the
form of spheres, yolk granules, lying in the protoplasm. In
many animals, e.g. birds, much deutoplasm is present.
The nucleus of the egg is generally spherical, clear, and with
a double contour; it surrounds the germinal spot (macula
germinativa). The zona pellucida is 0.02-0.025 mm thick
and radially striated. These striations are caused by the
numerous perforations of the zona pellucida.

2. Formation of the ovum. — The eggs in the ovary are
placed in the Graafian follicle, a spherical vesicle, which in
mature condition has a diameter of 10-15 mm. The follicles
are imbedded in the connective-tissue stroma of the ovary
and are surrounded by a vascular capsule. The inner wall
of this capsule is surrounded by the membrana granulosa or
germinativa, composed of many layers of epithelial cells.
The epithelium forms at one place a great mass of cells,
called the discus proligerus, in which lies the ovum. The
cavity of the follicle between the discus proligerus and the
rest of the wall of the follicle is filled with a yellowish fluid
containing proteid.

The Graafian follicle originates as follows : The surface of
the ovary is covered with a cylindrical epithelium (the
so-called germinal epithelium) which covers also the tubular
invagination of the surface of the ovary. These invagina-
tions grow downward and are cut off by the stroma of the
ovary. The separated tubes develop into the Graafian
follicles. In the germinal epithelium the round egg-cells

REPRODUCTION 3 1 1

are already present and grow downward with the epithelium
of the tube. The first appearance of the follicle, that is, the
formation of the primordial egg, occurs in the embryo. At
first the follicles are only 0.03 mm in diameter. When fully
developed they pass through the deep layers of the stroma
to the surface of the ovary.

3. Ovulation or discharge of the ovum. — The discharge
of the egg takes place by the bursting of the ripe Graafian
follicle. This bursting is accomplished by the increase of
liquid in the follicle whereby it is enlarged and its walls are
rendered tense until they burst.

In the place formerly occupied by the follicle a cicatrix is formed
which is colored yellow by pigments : corpus luteum.

The contents of the follicle, including the egg, lying
among the cells of the discus proligerus, reaches the end of
the oviduct, whose fimbriated end lies close to the surface of
the ovary. By the ciliated epithelium the egg is carried
through the oviduct to the uterus.

In human females the discharge of the egg occurs regularly
every four weeks. It is accompanied by a capillary bleeding
from the mucous membrane of the uterus — menstruation, last-
ing from two to three days. The hemorrhage is preceded
by a separation of the mucous membrane and the formation
of a membrane, the decidua menstrualis, which is afterward
cast out. During menstruation 100-200 g blood are lost.

4. The maturation of the egg. — Previous to fertilization
certain changes take place in the egg which are collectively
called the maturation of the egg. The nucleus of the egg
moves towards the periphery and divides by indirect division
into two nuclei. One of these, called the polar body, is cast
out of the egg. The other nucleus again divides into two,
one of which, the second polar body, is also cast out. The
remaining nucleus, called the female pronucleus, travels to
the centre of the egg.

312 HUMAN PHYSIOLOGY

3. FERTILIZATION

The spermatozoa discharged during the act of coition into
the vagina of the female pass through the uterus and
oviduct into the upper part of the oviduct, called the am-
pullae. This is an active movement and takes place in the
direction opposite to that of the movement of the cilia of the
epithelium.

After discharge of the egg fertilization takes place, gen-
erally in the ampulla, by the entrance of one of the sperma-
tozoa into the egg. The spermatozoon forces its way
through the membrane of the egg and proceeds in a radial
direction towards its centre. The tail of the spermatozoon
becomes dissolved in the egg, while the head becomes the
male pronucleus. The male and female pronuclei increase
in size and approach each other. They are now similar in
appearance, so that they can no longer be distinguished.

After losing the nuclear membrane the nuclear fibres of
each nucleus break up into a number of loop-shaped pieces,
and these fragments are mixed. From the thus united egg
and spermatozoon the new individual develops by nucleus-
and cell-division and cell differentiation.

While the unfertilized eggs are soon destroyed, the fertil-
ized egg, passing in about three days through the duct into
the uterus, is held in the uterus. It sinks between the folds
of the mucous membrane of the uterus, which is greatly
thickened. The w^alls of the fold unite with the membrane
of the egg and cover the egg. This part of the mucous
membrane subsequently forms the placenta.

CHAPTER XXVIII
PHYSIOLOGY OF THE EMBRYO

1. SYNOPSIS OF SOME OF THE IMPORTANT FACTS
OF EMBRYONIC DEVELOPMENT

BY the process of fertilization the fertilized egg-cell
divides into many cells which form a one-cell layer below
the egg membrane, which takes no part in this cell division.
By this a cavity filled with fluid, the segmentation xravity, is
formed in the centre of the egg. The structure thus formed
is called a blastula, and the one-celled layer is called the
ectoderm. The blastula expands by the continual increase
of fluid in the segmentation cavity. Below the ectoderm a
second layer of cells, the endoderm, is formed. The manner
in which the endoderm is formed varies iii different animals.
Finally, at a thickened portion of the blastula, a third layer,
the mesoderm, is formed between the ectoderm and the
endoderm. From the ectoderm originate the epithelial cells
of the skin and its glands, the nervous system, the epithelium
of the sense organs, and the lens. From the endoderm are
formed the epithelial cells of the alimentary canal and its
glands and those of the urinary tubes. From the mesoderm
originate the blood and blood vessels, the muscles, connec-
tive tissue, and the reproductive cells.

The thickening of the walls of the blastula at which the
mesoderm originates is called the germinal disk ; in this the
first traces of the embryo are seen. The germinal disk
assumes a biscuit form, its borders curving inward and
thereby separating that part of the cavity of the blastula

313

HUMAN PHYSIOLOGY

chz

sK.

p1G 49> — DEVELOPMENT OF THE FCETAL MEMBRANES OK A MAMMAL.

(After Kolliker.)

I, ovum with zona pellucida, blastula, and embryonic area; 2, formation of
yolk-sac and amnion; 3, union of the folds of the amnion, forming the amniotic
cavity; formation of the allantois; 4, decrease of the yolk-sac, increase of the
allantois, formation of mouth and anus; 5, reduction of the yolk-sac; allantois
joined to the chorion, enlargement of the amniotic cavity; </, zona pellucida; </',
processes (villi) of zona; sh, serous membrane; sz, villi; ch, chorion, c/iz, chori-
onic villi; am, amnion; As, head-fold of amnion ; a/i, amniotic cavity; as, navel-
cord with the amnion; aa', ectoderm; ?', endoderm; mm' , mesoderm; dd, embry-
onic part of the endoderm; df, area vasculosa; sf, sinus terminalis; kk, cavity of
the blastula; ds, umbilical vesicle (yolk-sac); dg, passage of the umbilical vesicle;
at, allantois; e, embryo; r, space between chorion and amnion; vl, ventral body
wall; ////, pericardial cavity.

PHYSIOLOGY OF THE EMBRYO 315

lying below the germinal disk, i.e. the embryonic intestine,
from the part above, i.e. the yolk-sac. The connection
between these two cavities, as long as it is open, is called the
vitelline duct (see Fig. 49).

The ectoderm forms a fold over the curved germinal disk.
The inner leaf of this fold grows over the embryo and forms,
by separating from the blastula, the amnion, which at the
navel passes over into the skin of the embryo. The outer
leaf of the fold joins the zona pellucida and forms with it the
serous membrane, which later on is called the chorion. On
the surface of the chorion villus-like processes are formed
which unite with the mucous membrane of the uterus. From
the posterior part of the embryonic intestinal cavity a
tubular projection, the allantois or the urinary sac, grows
out into the space between the yolk-sac and the chorion.
Its inner part (lying in the embryo) becomes the urinary
bladder. The allantois grows outward until, in the third
week, it joins the chorion and forms with it the placenta.
The lumen of the allantois soon disappears and forms a cord
composed of mucous tissue and is called the umbilical cord.

Chronology of the development of the embryo.

First month.

First week. Passage of the egg through the tube ; fertilization ;
formation of the blastula.

Second week. Blastula attains a diameter of 5 mm ; villus-like
processes formed on the egg membrane ; first rudiments of embryo ;
formation of the spinal folds and of the medullary groove.

Third week. Embryo about 4 mm long. Formation of the
amnion, yolk-sac, and allantois. The yolk-sac circulation is
established.

Fourth week. Embryo from 8 to 1 1 mm long. The position of
the extremities is clearly visible. The three cerebral vesicles are
present.

Second month. Length of embryo 30 mm. The yolk-sac circu-
lation degenerates, while the placental circulation develops. Forma-
tion of the face ; disappearance of the gill-clefts and posterior gill
arches ; the extremities become jointed ; first points of ossification in
the hip-bone and lower jaw ; abdominal cavity closed ; kidneys
formed.

Third month. Length of embryo 70 mm. Commencement of
sexual differentiation.

316 HUMAN PHYSIOLOGY

Fourth month. Length of foetus 17 cm, weight 100 g. It is
possible to distinguish male and female organs from each other.
Placenta weighs 80 g. First movements of the extremities. Mcco-
nium in intestine.

Fifth month. Length of foetus 30 cm, weight 280 g. Hair on
the head and body [lanigo] appear. Beginning of sebaceous secre-
tions. Placenta weighs 178 g.

Sixth month. Length of foetus 34 cm, weight 700 g. The fat
layers of the skin develop. Movement of the embryo. Born dur-
ing this month the child makes feeble respiratory movements but is
not viable.

Seventh month. Length of foetus 38 cm, weight 1300 g. Born
during this month the child whines and is sometimes viable.

Eighth month. Length of foetus 42 cm, weight i57og. Tes-
ticles descend. Child is viable.

Ninth month. Length of foetus 65 cm, weight 1970 g.

The mature embryo is 50 cm long, weighs 3 kg.

2. METABOLISM OF THE EMBRYO

(a) Circulation. — In explaining the embryonic circulation
two periods must be kept distinct: (i) the period of vitel-
line [yolk-sac] circulation ; (2) period of the placental cir-
culation.

(i) Vitelline circulation. — The first formation of vessels
occurs near the germinal disk. From the cells of the
mesoderm originate the peripheral veins (sinus terminal is)
from which spring the blood vessels of the embryo. From
the wall of the vein solid cords of cells extend into the
embryo which anastomose and become hollow by the forma-
tion of intercellular spaces filled with an intercellular fluid.
The heart is formed from two symmetrical vessels in the
alimentary canal in the head which represent the primitive
aortae. These coalesce in the median line, forming a tube.
From this tube the heart is developed by the formation of
an S-like curve, whereby the tube is divided into an auricle,
ventricle, and truncus arteriosus. By a partition appearing
in the tube, the right and left heart are formed. From the
heart there spring originally two aortic arches which give
off the omphalo-mesenteric arteries. The branches of these
arteries pass through the germinal disk to the sinus ter-

PHYSIOLOGY OF THE EMBRYO 317

minalis, while veins proceed from the sinus to the heart.
The system of vessels thus formed is called the vascular
area. Shortly after the heart is formed it begins to beat
rhythmically, thereby setting in circulation the fluid formed
in the vascular system. It is worthy of note that the cardiac
muscle contracts rhythmically at a time when it contains no
ganglionic cells.

By means of the vitelline circulation the embryo is sup-
plied with nourishment which has been taken up by the
blood from the yolk-sac.

The red blood corpuscles originate from the so-called
blood islands, i.e. groups of cells in the cords from which
the blood vessels are developed. The cells of the blood
islands form blood pigment, separate, and then appear as
nucleated blood corpuscles suspended in the fluid.

(2) Placental circulation. — From the abdominal aorta
formed by the union of the primitive aortic arches proceed
the two umbilical arteries through the umbilical cord (the
Avail of the allantois) to the place where the allantois joins
the chorion and where the placenta originates. Here the
arteries split up into capillaries. From these capillaries
the blood is collected by the umbilical vein, which passes
through the umbilical cord to the navel; thence, as the
ductus venosus Arantii, under the liver to the inferior vena
cava.

At this time the right and the left heart are not yet com-
pletely separated. In the septum between the auricles exists
an aperture, the rafaula Eustachii. The pulmonary arteries
and the aorta are still united by one of the primitive aortic
arches,"" the so-called ductus Botalli. Part of the blood from
the right auricle passes, therefore, through the valvula Kus-
tachii directly into the left auricle and thence into the left
ventricle and aorta, while part of it passes from the right

* Corresponding to the live pairs of gill-arches, tive pairs of aortic arches are
formed which undergo the following changes : The first two pairs disappear; tin-
third pair forms the external carotids; the fourth arch on the left side tonn> the
aorta, on the right side, the right subclavian; the fifth on the 4eft side, the ductus
Uotalli and the left pulmonary artery ; on the right side the right pulmonary
artery.

3l8 HUMAN PHYSIOLOGY

auricle into the right ventricle and pulmonary artery and
thence directly through the ductus Botalli into the aorta.
Only a small part of the blood pases through the lungs of
the embryo. This peculiar arrangement of the blood vessels
becomes clear when we recollect that the exchange of <jases

O t">

in the embryo does not take place in the lungs and that
consequently only so much blood needs to flow through the
lungs as is sufficient to provide for their nourishment and
growth. After birth, when pulmonary respiration begins,
the division between the auricles of the heart is completed
and the ductus Botalli is obliterated.

The placenta is a very vascular structure, composed of
two united parts, one part the maternal, the other the fcetal,
portion. The vascular villi of the fcetal portion extend into
spacious blood cavities formed by the dilated capillaries of
the maternal portion. This great abundance of vessels in
the placenta, part of which belong to the foetus and part to
the mother, makes a rapid exchange of gases between the
maternal and the fcetal blood possible.

The formation of red blood corpuscles during the placental
circulation takes place chiefly in the liver and spleen of the
embryo.

During the middle of pregnancy the cardiac sounds of the
embryo can be heard at different parts of the uterus accord-
ing to the position of the embryo. The double sound is
often accompanied by noises caused by the circulation of
blood in the umbilical cord. The rate of the cardiac sounds
of the embryo is 120-160 in a minute. It is increased by
movements of the embryo.

(1)) Respiration. — In regard to the respiration of the em-
bryo, two periods can be distinguished. During the first
period corresponding to the vitelline circulation the supply-
ing of oxygen and removal of carbon dioxide is not brought
about by any special organs. Real respiration begins with
placental circulation. The taking up of oxygen and giving
off of carbon dioxide does not take place in the lungs but in
the placenta. The oxygen is supplied by the arterial blood

PHYSIOLOGY OF THE EMBRYO 319

of the mother, and the carbon dioxide of the embryo is taken,
up by it.

Metabolism and the corresponding need of oxygen in the
embryo is small. The exchange of gases in the placenta is
sufficient to maintain the embryo in apnoea. But this con-
dition ceases immediately when, by compression of the
umbilical cord or by premature rupture of the placenta, the
normal exchange of gases in the blood of the embryo is
stopped. The blood of the embryo then lacks oxygen,
while the carbon dioxide accumulates by which the respira-
tory centre is stimulated and premature respiratory move-
ments are made.

The lungs of the embryo are developed from two divertic-
uli of the ventral wall of the esophagus and contain no air
(atelectatic) ; the alveoli are formed, but are collapsed, i.e.
filled by cuboidal epithelial cells. No negative pressure
exists in the pleural cavity. When by the first inspira-
tory movement after birth air is forced in, the epithelial cells
of the alveoli are flattened, the alveoli contain air, and, after
some time, negative pressure is developed in the pleural
cavity. As to the origin of this negative pressure authors do
not agree.

(c) Nutrition of the embryo. — All the nourishment which
the embryo needs for its metabolism and growth is derived
from the mother organism. In regard to nutrition we can
distinguish two periods, one of which corresponds to the
vitelline circulation, the other to placental circulation.
During the first period the embryo is supplied with food by
the blood of the yolk-sac. The food transudes from the
vessels of the mucous membrane of the uterus through the
mucosa and egg membranes to the yolk-sac. During the
placental circulation, however, the embryo takes its food
from the blood of the mother present in the placenta. The
food transudes from the maternal vessels of the placenta into
the foetal placental vessels. As the yolk-sac is of no further
importance after the completion of the placental 'Circulation,
it gradually7 diminishes in sixe and finally dwindles away

320 HUMAN PHYSIOLOGY

almost entirely, what is left being called the umbilical
vesicle.

(d) Secretions of the embryo.

1. Meconium. — Meconium is a dark brownish-green mass
having the consistency of pitch. It is found in the intestine
of the embryo, from which it is discharged soon after birth.
It contains 20—28$ solids, which include mucin, bile acids,
bile pigments (bilirubin and biliverdin, but no hydrobili-
rubin), cholesterin, fats, soaps. Substances in the fajces of
the adult which indicate intestinal putrefaction are lacking
in meconium. Meconium may be regarded as a solidified
secretion of the glands of the intestines, and its composition
indicates that the liver is the chief seat of its formation.

The liver is formed early by diverticuli of the intestinal
wall in the form of the primitive liver ducts, which, In-
branching, form the smaller bile passages. The liver secre-
tions take place as early as the third month.

2. Formation of amniotic fluid. — The amniotic fluid is
found in the amniotic cavity and surrounds the embryo. It
has a weak alkaline reaction ; its specific gravity varies con-
siderably, 1.002—1.028. It contains some proteids, salts,
urea, allantoin, and kreatinin. The amniotic fluid is formed
not only by the- embryo, but also by the mother organism.
That part of this fluid is derived from the mother organism
is proved by the fact that sodium sulphindigotate injected
into the mother organism is found in the amniotic fluid, but
not in the embryo. Still the amniotic fluid is partly an
excretion product of the embryo, the urine of the embryo
being discharged into the amniotic cavity.

In the development of the urinary organs, the pro-
nephros, or Wolffian bodies, are first formed. These are
glandular organs lying on either side of the vertebral column.
They are composed of coiled urinifcrous tubules which
carry, at their closed end, a glomerulus and at the other
end, open into a common duct, the Wolffian duct. This
duct opens into the cloaca, whose anterior end forms the
urethra by the formation of the perineum. Later on the

PHYSIOLOGY OF THE EMBRYO 321

permanent kidneys are formed by the diverticuli of the
posterior end of the Wolffian duct. These diverticuli branch
and the branches become the uriniferous tubules of the kid-
neys; at their closed ends a glomerulus forms. In the
female the Wolffian duct is obliterated, while in the male it
forms the vas deferens.

3. The sebaceous secretion begins in the fifth month.
The substance thus secreted forms a fatty layer upon the
skin and is called the vernix caseosa.

The removal of metabolic waste products from the embryo
is accomplished not only by the glands (liver and kidneys),
but also by the exchange of gases between the fcetal and
the maternal blood in the placenta.

(e) Metabolism. — The metabolism of the embryo is small ;
little heat needs to be produced, for the loss of heat is ex-
ceedingly small. The muscular movements which could
increase metabolism are very limited. Hence the food sup-
plied to the embryo is chiefly used for its growth.

3. THE TRANSFORMATION AND SETTING FREE OF
ENERGY IN THE EMBRYO

(<?) Muscular movements. — The first appearance of the
skeletal muscle is during the second month of pregnancy.

Muscular movements, excepting the beat of the heart,
begin at the fifth or sixth month. They consist of jerky
movements of the limbs against the walls of the uterus.
The movements of the foetus appear to be reflex movements ;
they are increased when the foetus is pushed by pressing upon
the abdominal walls of the mother. At the close of preg-
nancy, weak rhythmic respiratory movements are sometimes
made, also movements of sucking and deglutition; swallowed
amniotic fluid may be found in the embryo.

(b) The development of the functions of the nervous
system. — The researches concerning the medullation of the
nerves furnish the basis for judging the development of these
functions. The nerve fibres at first have no medullary

322 HUMAN PHYSIOLOGY

sheath, but acquire this structure later on, and nerve fibres
of different functions acquire it at different periods. The
development of the medullary sheath can be readily investi-
gated, for the medullated nerve fibres are white, while the
fibres not containing this sheath appear gray. It may be
assumed that the function of the nerve fibre is only com-
pletely present when the nerve sheath has been formed.

In the .spinal cord the medullary sheaths of the anterior
and posterior roots are first formed, i.e. the tracts serving
for reflex actions. After this, the sheaths of the antero-
ground, the lateral ground bundle, and of Burdach's column,
i.e. bundles which contain fibres chiefly for the indirect
reflex tracts. Then the sheaths of the long sensory tracts
leading to the brain are formed, and finally the sheath of the
long motor tracts leading from the brain. From the succes-
sive developments of the medullary sheaths it is evident
that, in the spinal cord, the simpler reflexes appear first; next
the more complicated and radiated; and finally the paths
for the stimuli causing sensations and voluntary movements.

In the corona radiata, the centripetal fibres for the sensory
areas of the cerebral cortex are developed before the corre-
sponding centrifugal fibres; hence the conditions for the
formation of sensations are perfected before those for the
formation of voluntary movements. Some of the fibres for
the sensory areas develop after birth (see page 329).

In the medulla oblongata, however, there appear at an
early date groups of cells whose axis-cylinder processes
course down the anterior and lateral columns of the cord
(hence centrifugal fibres) ; these fibres are already medul-
lated when the sensory roots of the medulla have no medul-
lary sheaths. These cells and fibres are, therefore, well
developed and function at the time when the posterior roots
still appear embryonic. This indicates that the action of
centres is automatic and not reflex. The sensory nerves,
when fully developed, stimulate and eventually regulate the
centres which, prior to this, were already active. It must
be remembered that the medulla contains the important

PHYSIOLOGY OF THE EMBRYO 323

nerve centres which maintain the vegetative functions of the
body.

Little need to be said concerning the physiological devel-
opment of the sense organs. The only sensations which
can come into account in the fcetal life are the tactile, pain,
and, perhaps, some organ sensations. These evidently call
forth the movements of the foetus.

4. DIFFERENTIATION OF SEXES

The reproductive organs are developed as follows: On
the ventral side of the pronephros, the genital ridge and a
special duct, Miiller's duct, running parallel with the
Wolffian duct and also opening into the cloaca, are formed.
In the male the genital ridge forms the testis, the pronephros
forms the hydatid of the epididymus, the Wolffian ducts the
vas deferens ; the duct of Muller is obliterated except a small
rudiment, called the uterus masculinus. In the female the
genital ridge becomes the ovary, Muller 's duct the oviduct;
and the mouth of the Mailer's duct at the cloaca dilates and
forms the uterus-. The Wolffian duct disappears. Nothing
is known concerning the causes of sexual differentiation.

CHAPTER XXIX
PREGNANCY. PARTURITION. CHILDBED

DURING the development of the foetus in the uterus, the
following changes occur in the maternal organism: The
muscle fibres of the uterus increase in size and number and
the whole uterus increases enormously. In the virgin state
the uterus is 7 cm long, 3.2 cm broad, and weighs 30 g; at
the end of pregnancy it is 37 cm long, 26 cm wide, and
weighs about I kg. The intramuscular connective tissue
loosens and increases and the blood vessels, nerves, and
lymph vessels also increase. The mucous membrane of the
uterus thickens and grows over and covers the egg, forming
the decidua. That part of the wall of the uterus which
grows over the egg is called the decidua reflexa, while the
part bordering upon this is called the decidua vera. The
placental part of the decidua vera is called the decidua sero-
tina. As the uterus increases it fills the pelvic cavity and
forces the intestines aside and the diaphragm upward.
During pregnancy ovulation and menstruation cease.

The breasts begin to increase in size during the first
months of gestation, the nipple and the areola assume a dark
color, the milk glands yield spontaneously or upon pressing
a light-colored watery fluid.

Metabolism is increased during pregnancy.

The period of gestation reckoned from the day of the last
menstruation is about 270—280 days.

Parturition is effected by the contraction of the muscles
of the uterus by which pressure is exerted upon the contents
of the uterus. The pressure thus produced may be as much

32+

PREGNANCY. PARTURITION. CHILDBED. 325

as 100 mm Hg. By these contractions the foetus is pressed
against the cervical canal, which dilates and stretches so that
the uterus and the vagina form a common tube. The mem-
brane of the egg (the decidua reflexa of the utrinal mucous
membrane, the chorion and the amnion) are ruptured so
that the amniotic fluid is discharged. By further contraction
of the uterus the child is forced through the vagina and
pelvis, generally head-foremost. Parturition is aided by
compression of the abdomen. Soon after the birth of the
child the placenta is loosened by the further contraction of
the walls of the uterus and, under loss of some blood, is
discharged with the egg membranes (after birth).

The innervation of the uterus takes place by means of the
nerves from the lowest thoracic and from the lumbar cord.
A part of the fibres pass through the sympathetic, while
another part pass directly with the sacral nerves to the
uterus. The centre for the contraction of the uterus lies in
the lumbar cord. This centre can be stimulated reflexly by
stimulations from the centripetal nerves of the uterus. These
centripetal nerves are stimulated by the tension in the walls
of the uterus caused by the growing foetus. In dogs in
which the lumbar cord is separated from the rest of the
nervous system, normal parturition can still take place.

The duration of parturition varies. In case of the first-
born it may last 20 hours, but in subsequent cases it is
shorter. During parturition the contractions of the uterus
gradually become more intense, frequent, and longer until
the child is expelled. These contractions are accompanied
by pain. During each "pain" the temperature, rate of
pulse, and perspiration are increased.

After parturition the uterus assumes its normal form,
many of the muscle cells undergoing fatty degeneration.
The inner surface of the uterus acquires a new epithelial
lining, and after about four weeks the regeneration of the
mucous membrane is complete. As long as a mucous mem-
brane is not regenerated, it behaves like a wound and
secretes a corresponding wound secretion. This secretion

326 HUMAN PHYSIOLOGY

which is cast out is called lockia. The lochia is bloody
during the first days, during the fifth day it is serous, later
on it becomes grayish.

The breasts swell much during the second and third days
after parturition. The first secretion — colostrum — is a thick,
yellowish fluid, containing colostrum corpuscles (see page
112); at the third day real milk is secreted. The period of
lactation lasts about ten months, and during this time
menstruation does not take place.

CHAPTER XXX
DEVELOPMENT OF THE BODY AFTER BIRTH

1. INFANCY

DURING infancy the body is nourished by fluids only,
chiefly by milk. As the formation of the first teeth is con-
nected with the ability to take up solid food, the period of
infancy extends from birth till the first dentition.

(d) Circulation and respiration of the infant. — Imme-
diately after birth the circulation in the umbilical vessels
ceases, and the umbilical cord constricts. If it is then cut,
no bleeding, as a rule, results, yet to prevent possible bleed-
ing it is ligatured and cut. Animals cut the umbilical cord
with their teeth. The part of the umbilical cord left attached
to the child dries up and falls off after a few days. The
navel discharges matter for some time and heals after 12-14
clays.

Immediately after birth the first inspiration is made. The
alveoli of the lungs fill with air and their epithelial cells
become flattened. Simultaneously the blood streams more
abundantly through the vessels of the lungs. Gradually the
ductus arteriosus Botalli is obliterated and the septum
between the auricles is completed. The remains of the
umbilical arteries and veins degenerate to connective tissue.

The rate of the pulse during the first week is 120-140 per
minute; during the second year 1 10. The number of res-
pirations in the new-born is 44 per minute ; during the third
year 35~4O.

(/7) Nutrition and growth of the infant. —The normal
nourishment for the infant is the milk of the mother. The
replacement of this by other food (e.g. cow-milk or artificial

327

328 HUMAN PHYSIOLOGY

preparation) must be regarded as makeshifts and are often
not suited for the child. The average amount of milk which
the infant takes is as follows: During first day 30 grams,
second day 150, third day 400, fourth day 550 grams; after
one month 650, three months 750, four months 850, six to
nine months 950 grams.

The length of the body of the child at birth is about
50 cm.

The infant grows during the first month 4 cm, during the
second month 3 cm, during the third month 2 cm, and
during the following months 1 — 1.5 cm- The total increase
in length during the first year is about 2O cm, during the
second year 9 cm, and during the third year 7 cm. The
weight after birth is 3 kg. Immediately after birth the infant
loses from 100—300 grams of its body \veight. After this its
weight increases and after the tenth day it has regained its
previous weight. During the first five months the weight
of the normally nourished child increases on the average 20
to 30 grams daily; during the next seven months 10-15
grams daily. After one year the child weighs about 9 kg.

During the first days after birth the child discharges the
mcconium through the anus. Later on the stools of the
normally fed child are yellowish and of medium consistency.

(c) The nervous system and the senses of the infant.—
Concerning the physiological development of the central
nervous system during infancy the following maybe said:
At birth certain reflex and coordinated movements, those
necessary for the maintenance of life (respiration movements,
sucking, deglutition) are present. Sucking takes place
reflexly when a foreign body touches the lips. The coordi
nated movements which play a part in standing and walking
are not present in the human infant immediately after birth,
but are learned during the first or second year. This is also
true for the coordinated movements for speech. The reflex-
irritability is greater in the infant than in the adult. Reflex
cramps can be produced by relatively feeble stimulation of
sensory nerves (e.g. convulsions during dentition, tetanus).

DEVELOPMENT OF THE BODY AFTER BIRTH 329

At birth the conducting fibres for the sensory areas of the
cerebral cortex are not all medullated. The tracts for the
visual centre develop their sheaths at the time of birth, while
those of the auditory area are developed after birth. The
fibres of association develop about three months after birth.

As to the development of the senses the following facts
may be stated in regard to sight. During the fifth week,
fixation, associated movements of the eyes, closure of the
•eyelids when the macula lutea is illuminated, and accommo-
dation take place, Only during the fifth month is there a
development of orientation of the visual field and closure of
the eyelids when the periphery of the retina is illuminated.
Until the fifth month the eccentric visual sensations are not
utilized. The child, therefore, appears as if it had an ex-
tremely limited visual field. An object upon which the gaze
is fastened is, during the fifth month, followed by the eyes,
but moving objects upon which the gaze is not fixed do not
call forth, during the first period, fixation of the eye. At
first the infant does not see the objects as solid objects and it
lacks all judgment of size and distance. (The child reaches,
e.g., for the moon.) It is also asserted that at birth the
sense of color is absent, and that this begins to develop during
the sixteenth month and is completely developed in the fifth
or sixth year. The color sensations are first developed at
the centre and later on at the periphery of the retina.

The other senses function immediately after birth, but it
is said that the sense of hearing is then incompletely devel-
oped ; this corresponds to the imperfect development of the
tracts of the auditory centre in the new-born.

The change from infancy to childhood is marked by the
first dentition. The first teeth, the so-called milk-teeth,
develop in the following order:

Between seventh and eighth month the lower central in-
cisors.

Between eighth and tenth month the four upper incisors.

Between twelfth and fourteenth month the four small
inner molars and the two lower outer incisors.

33°

HUMAN PHYSIOLOGY

Between eighteenth and twentieth month the four
canines.

Between twenty-fourth and thirty-fourth month the four
smaller outer molars.

Between the age of 4^ and 5 years, the first four large
permanent molars appear.

2. CHILDHOOD

Childhood extends from the first dentition to puberty.
During this period the physiological functions are about the
same as in the adult human being, except that metabolism
is relatively greater than in the adult, as already explained
(see page I 18), and that the sexual functions are not present.
The second dentition takes place during childhood. It
begins during the seventh year and extends to the fifteenth
year. The temporary teeth are replaced by the permanent
set and four new large molars are added. Between the
ages of eighteen and twenty-five, and sometimes still later,
the last molars, the wisdom teeth, are finally developed.

The following table shows the changes in the length and
weight of the body at different ages :

M

in.

Wor

nan.

Age.

Length,
m.

Weight,
kg.

Length
in.

Weight.
kg.

Birth

O. c.

1.

o 5

T.

c. years. .

.O

1C

O qC

14

10 ....

.3

2C

.2

24

1C

.6

44

. C

4O

20

7

60

6

C2

•5Q

. 7

6c

6

cc

4.O

7

65

6

cc

60

6c

62

C2

c,4

80

.6

c8

. C

49

3. PUBERTY

Puberty is the period of sexual maturity, which begins at
the age between fourteen and seventeen. It is characterized

DEVELOPMENT OF THE BODY AFTER BIRTH 331

by many changes in the body. In the male the formation
of spermatozoa and beard take place, the larynx develops
more powerfully, and the voice changes. Sexual desires
awaken. The manly character appears. In castrated
children these phenomena are not observed. Female
puberty, which occurs a little earlier than in the male, is
accompanied by ovulation and menstruation, and the external
sexual organs are covered with hair and the mammary
glands develop.

4. OLD AGE, DEGENERATION, AND PHYSIOLOGICAL

DEATH

The prime of life in man extends from the twenty-fifth to
the forty-fifth year. After this degeneration sets in, the
body weight and length decrease. Metabolism and the
functions of the organs are reduced. In high old age a great
debility of the organs, especially of the brain and heart, sets
in, which finally results in physiological death or death by
senile decay. In the female this degeneration begins with
the climacteric, the cessation of ovulation and menstruation.
The greatest old age in man may be over one hundred
years. According to the mortuary statistics, the average
length of human life in civilized countries is thirty years.

INDEX

Absorption, 140
Accommodation, 262

centre of, 242
Acetone, 42, 105
Action-currents, 194, 217
Adamkiewicz' test, 30
Adaptation, 8
Aden in, 48
Adipose tissue, 14
After-images, 272. 273, 276
Albuminoids, 38
Albumins, 31
Albumoses. 36, 37, 129
Alcohol, 1 1 8, 122
Alexines. 57

Alimentary principles. 114
Alkali albumin, 31
Allantois, 315

Alternation of generation, 7
Amido acids, 27, 136
Ammonia, 43, 104, 196, 219
Amnion, 315
Amniotic fluid, 320
Amylopsin, 133
Anelectrotonus, 220
Animal heat, 174

Anterior ground bundle, 226-229, 237
Antipeptones, 38
Antitoxins. 57
Apex beat, 68
Apnoea, 84

Aqueous humor, 260, 284
Arginine, 27

Aromatic compounds. 51, 136
Articulations of bones. 2OI
Arytenoid cartilage, 209
Ash in tissues. 15
Aspartic acid. 27
Asphyxia, 85, 240
Assimilation. 2, 6, 140
Association centres. 247

fibres, 237
Astigmatism, 266
Atropin. 75. 107, no

Auditory centre, 246

nerve. 252, 292, 295

ossicles. 286

sensation, 292
Auricles of heart, 67
Auto-digestion of stomach, 131
Automaticity, 224
Axis-cylinder, 215

•Bacteria, metabolism of, 2
Balance of nutrition, 155, 161
Ball-and-socket joint, 202
Basal ganglia, 240
Bell's law, 250
Bile, 99, 101, 135. 145
acids, 49, TOO
pigments. 50, 100
Bilirubin, 50, 100
Biliverdin, 50, 100
Binocular vision, 281
Biostition, 4
Biuret reaction, 30. 38
Blind spot. 271
Blood, 14. 16, 52

color of, 59

corpuscles. 52, 53

flow, 71, 73

0.1 ses. 58

loss of, 78

platelets. 55

pressure, 73, 78, 152

and respiration. 71
in heart. 67
in vessels. 69

reaction of, 52, 59
Body temperature. 180, 242
Hone marrow. 54
Hones 14, l6, 2OI
Border cells. 93
Bottger's test, 19
Brain. 14. 16. 235
Burdach's column. 226, 237

Calcium 13, IJ, 115

333

334

INDEX

Calorie, 178

Canalis cochleae, 289, 290

Cane-sugar, 21, 131, 146

Carbohydrates, 136, 159, 186

absorption of, 145
classification of, 18
composition of, 18
digestion of, 124, 133

135

functions of, 116, 169
in blood, 57
Carbon, 12

dioxide, 42, 58, 85, 159, 187
equilibrium, 158
Cardiac accelerating centre, 238

" nerve, 75

cycle, 65
impulse, 68
inhibitory centre, 238

" nerve, 74
muscle, 64, 66, 191
sounds, 68, 318
Cardinal points, 262
Cardiogram, 68
Carnic acid, 186, 187
Carnin, 49

Caseinogen, 36, 131, 143
Cells, 5, 6

division of. 7
Cellulose, 22, 120, 136
Cerebellar tracts, 226-229, 236
Cerebellum, 240
Cerebro-spinal fluid, 14, 249
Cerebrum, 243
Cheese, 120
Chematropism. 200
Chief points, 261
Chlorine, 13
Chlorophyll, 2, 3
Cholesterin, 25
Chondrin, 40
Chorion, 315

Chromatic aberration, 266
Chyle, 87
Ciliary movements, 200

muscles, 264
Circles of diffusion, 262
Circulating proteids, 32
Circulation of blood, 63, 316

time, 74
Coagulation of blood, 52. 57

proteids of, 28
Cochlea, 288
Cochlear nerve, 292
CO-haemoglobin, 33
Cold, sensation of, 302
Collagen, 40
Color blindness, 275

Color sensations, 274
Colostrum, 112, 326
Combined proteids, 32, 130
Combustion, physiological, 61, 172
Commissural fibres, 237
Compensatory movements, 240

pause, 65

Complemental air, 82
Complementary colors, 275
Conductivity of nerves, 216-221

Conjugated points, 258

Consensual pupil reflex, 268

Consonance, 293

Consonants, 214

Contraction of muscles, 188-199

Convulsion centre, 240

Corona radiata, 235-237. 245-247.

Corpora quadrigemina, 236, 241

Corpus callosum. 237

Corti, organs of, 290

Cranial nerves, 236, 250

Cricoid cartilage, 209

Crypts of Lieberkuhn, 103

Curare, 75, 147, 196

Cystin, 49

Darwinian theory, 8
Death, 6

Defaecatio

234

Deglutition, 125, 239
Dendrites, 215
Dentition. 329
Depressor nerve, 77
Deuteroalbumose, 129
Development, 6-9, 313
Dextrin, 22

Dextrose (see Grape Sugar).
Diabetes, 42, 105, 147, "153, 240
Diapedesis, 200
Diaphragm, 79
Diastole, 63, 65
Dicrotic wave, 71
Diet, 117, 121, 171
Difference-threshold, 256
differentiation of cells, 6
Digestion, 123, 138

effect on metabolism, 174
Digitalis, 75
Diopters, 265
)ioptric mechanism, 257
)iplopia, 281
)isaccharides, 21

Assimilation, 2, 6 (see Metabolism).
Diuretics, 107
)uctus Botalli, 317
pmea, 42, 85

Car, 285
Ectoderm, 313

INDEX

335

Elastin, 40

Electrotonus, 219, 220

Elements found in body, 12

Embryo, 313

circulation in, 316
development of, 315
metabolism of, 319
respiration of, 84, 318

Emmetropia, 266

Endoderm, 313

Energy, 2, 3/."4, 177

Entoptical vision, 267

Eupneea, 84

Eustachian tube, 288

Extensibility of muscle, 186, 192

Eye, 257

circulation in, 283
movements of, 242, 278
muscles of, 279

Eyelids, 242, 283

Facial nerve, 251

Fasces, 137

Fat formation. 171

Fatigue, 4, 190. 198. 222

Fats, 23, 116, 134, 136, 144, 159, 169,

186

Feclmer's law, 256
Fellic acid, 50
Fermentation, 20, 22, 41
Ferments, 40
Ferratin, 100
Fertilization, 7, 312
Fibrin, 56
P'ibrinogen, 56
Field of vision, 278
Fillet, 236
Fluorine, 14
Focal distance, 259

points, 259
Foods, 1 1 8, 138

heat value of, 178
Forced movements, 241, 295
Fovea centralis, 270, 277

Galvanotropism, 200

'Gastric digestion, 127

juice, 95

secretion, 96
Gelatin, 40, Il6, 130
( irnninal disk, 313
( legation. 324
(Hands, 91
( ilobin, 34
(llobulin, 31

Glossopharyngeal, 252, 298

Glottis. 2IO, 211
Glycerine, 23

Glycocholic acid, 50, 100

Glycocoll, 27, 50

Glycogen, 22, 23, 146. 186, 240

Glycoproteids, 34

Glucosamin, 21

Gmelin's test, 51

Goitre, 151

Goll's column, 226-229, 235

Graafian follicles, 310

Grape-sugar, 20, 105, 146, 186

( Irowth, 6

Guanin, 47

Hsematoblasts, 54
Haematoidin, 34

Hsematin, 34, 51
Haemin. 34

Haemoglobin, 32, 52, 58, 78, 100, 143
Heart, 14, 16, 64
beat, 65. 66
work done by, 68
Heat,

centres of, 181

Joss of, 1 80

production of, 178, 193

regulation of, 181

value of foods, 178

sensations of, 301
Heller's test, 29
Helicotrema, 288
Hemipeptones, 38
Hepatin, 100
Heredity, 8
Hinge-joint, 203
Hippuric acid, 48. 108
Homocentric rays, 257
Homoiothermic animals, 180
Horopter, 282
Hunger, sensation of, 306
Hydrochloric acid, 15, 95, 97, 128
Hydrogen, 12, 178
Hypermetropia, 266
Hypoglossus, 253
Hypoxanthin, 48, 104

Identical points, 282

Inanition, 164

Index of refraction, 257, 260

Indican, 104

Indol, 51. 104, 136

Infancy, 327

Inhibition, 4

of heart, 74

of reflexes, 233
Inosit, 21
Intelligence, 243
Internal secretion, 149
Intestinal juice, 102. 135

336

INDEX

Intestinal digestion. 132

Intestine, 14, 16

Inversion of sugars, 21, 131

Iodine, 14, 151

Iris, 267

Iron, 12, 13, 100, 115

Irradiation, 274

Irritability, 3

of nerves, 216. 218. 222
of muscles, 196. 197

Isometric contraction, 188

Isotonic contraction. 188

Jaundice, 102, 105
Jecorin, 26. 249

Joints, 202

Katelectrotonus, 220
Keratin, 39
Kidneys, 14, 16, 105
Krause, end-bulbs of, 300
Kreatin, 48
Kreatinin, 48
Kresol, 104, 136

Labyrinth, 288. 294

Lachrymal secretion (see Tears).

Lactic acid, 42, 130. 187

Lactiferous glands, 112

Lactose (see Milk Sugar).

Larynx, 209

Latent period, 189

Lateral bundles, 226-229

Law of contraction. 221

Lecithin, 25

Legumes, 12 1

Leucin,,27

Leucocytes (see White Blood Cor-

puscles).

Light, wave lengths of, 274
Liminal intensity, 256, 297
Liver, 14, 16, 54, 100, 146, 152, 240
Localization theory, 243
Lochia, 326

Locomotion of body, 208
Locomotor ataxia, 241
Lungs, 14. 16, 58
Luxus consumption, 169
Lymph, 87

glands, 55, 88

Macula lutea, 270
Magnesium, 13, 18, 115
Maltose, 21, 125
Mastication, 121
Meconium, 320
Medulla oblongata, 237, 322

Meibomian glands, 283

Melamine. 34

Menstruation, 311

Mesoderm, 313

Mi-talx>lism, I. 155, 187, 249, 319

end products of, 42. 186
Methcemoglobin. 33
Micturition, 109, 233
Milk, in, 120

sugar, 21. 146
Millon's reaction, 30
Monosaccharides, 19
Moore's test, 20
Motor areas of brain, 247
Mucin, 34
Mulder's test, 19
Murexide test, 46
Muscarin, 75
Muscle, 14. 16

activity of. 187-204

composition of. 185. 186

irritability of, 196

physical properties of, 186

plasma. 185

reaction. 187

serum. 185

sounds. K»I

structure- of. 184

tonus. 152

Muscular activity. Hk-rt on metabo-
lism. 173
Myogt-n. 186
Myohaematin, 186
Myopia. 265
Myosin, 185

Negative- after-image. 273. 276

variation. 195. 217
XVrve impulse, 216

physiology, 215
Neurites. 215
Neurons, 215
Neuroplasm. 215
Xicotin, 75
Nitrogen. 12

in blood, 59
Nitrogenous equilibrium, 158, 168

metabolism, 187
Nodal point, 259, 261
Nceud vital. 84
Nuclein bases. 47
Nucleins, 35. 89
Nucleo-albumins, 35. 116
Niicleus. 5, 6

decomposition of. 35

of nerve cells, 223
Nutrition, 114
Xystigmus. 242

INDEX

337

Oculo-motor nerve, 251. 265

Old age, 331

( Ufactory evil. 296

centre, 247
nerve, 250, 296

Ontogeny, 8

Ophthalmometer, 261

Ophthalmoscope, 268

Optical axis. 259

Optic nerve. 251

Optics. 257

Organogenic elements. 13

Organ sensations, 305

Otoliths, 295

Oval joint, 203

Ovaries, 154. 310

Ovoid cells, 96

Ovum. 310

Oxalic acid. 42

( Kybutyric acid. 42, 105

Oxygen, 157, 172

in combustion. 2, 187
in human body, 13
in blood. 58
consumed daily, 61
in. muscles. 187

Ox/haemoglobin, 33, 54, 58

( Kyntic cells, 96

( ) cyprotosulphonic acid, 28

Pain, sensation of, 303
Pancreas. 14, 16. 153
Pancreatic digestion. 133

juice. 98

secretion. 9<)
Paralytic secretion, 95
Paranucleins, 35
Parturition, 324
Pathetic nerve, 251
Pepsin. 95, 128
Peptones, 36, 37, 129, 133
Periscopia, 266
Peristalsis, 121, 126, 132
Perspiration. 109. 180-183, 239
Pettenkofer's test, 49
Peyer's patches. 89
Phenol. 51. 104. 136
Phenylhydrazine, 20
Phlorid/in. 147
PhospluK-arnic acid. 187
Phosphorus. 13. 43, 147
Phylogeny. 8
Pilocarpin. no
Pineal gland. 243
Placenta. 312, 315. 318
Placental circulation. 317
Plants, assimilation in, 2
Plasma, 52. 55

Plethysmograph. 72

Poisons arrested by liver. 153

Polysaccharides, 22

Portal vein, 141

Positive after-image, 272

Potassium. 13, 115

Presbyopia, 265

Pressor nerves. 77

Pronephros. 320

Pronucleus, 312

Protagon, 26. 223, 249

Protamine, 28

Proteids, 26. 31. 173

absorption of. 142
decomposition of, 27. 136
digestion of. 128, 133
functions of. 30. 116, 167,187
reaction of, 28

Proteoses, 36, 142

Protoplasm, 5

Psycho-physical processes, 231, 237,
243. 247. 248

Ptomains. 28

Ptyalin, 93, 134

Puberty, 330

Pulse, 70

curve, 71
volume, 69

Pupil reflex, 233, 267

Purkinje-Sanson images, 263

Putrefaction in intestine. 135

Pyramidal tracts. 226-229. 235

Reaction time, 248

Red blood corpuscles. 53, 90

Reflex action, 224, 229

time, 232
Rennin, 96
Residual air, 83
Respiration, 58, 60, 61. 318. 327

innervation of. 83

movements of. 79

of muscles, 8 1

rate of, 83
Respiratory capacity, 82

centre, 83, 238

metabolism, 156

quotient. 6l, 159. 162, 187

sounds. 83

Reproduction, 6. 7. 307
Retina. 269
Rhodopsin. 271
Ribs, elevation ot. 70
Rigor mortis, 198

Saddle-joint. 203

Saliva, nl

Salivarv digestion, 124

338

INDEX

Salivary secretion, 93
Salt-hunger, 166
Salts, excretion of, 164
functions of. 115
in tissues, 15, 18, 172
Sarcolactic acid (see Lactic Acid).
Sarcoplasm. 189
Scala tympari, 289
vestibuli, 288
Schemer's experiment, 263
Sebaceous secretion, 1 10
Secondary contraction, 195
Secretions, 91

Semicircular canals, 241, 294
Seminal fluid, 307
Sensations, 255
Sense organs, 255
Sensory areas of brain, 245
Serous cavities, 88
Serum, 52

albumin, 56

globulin, 56

Sex, differentiation of, 323

influence on metabolism, 176
Silicon, 14
Skatol, 51, 104, 136
Skeleton, 16
Skin, 14, 16
Sleep, 249
Smell, sense of, 298
Sodium, 13

carlxmate, 17
chloride. 17. 97, 115, 164
Sound, 292

Space sensation of retina, 276
Specific energy of nerves, 255
Speech, 213
Spermatozoa, 200, 308
Spermin. 308
Spherical aberration, 266
Sphygmogram. 71
Spices, 172

Spinal accessory nerve. 252
cord, 226, 322
nerves, 250
Spiral joint, 203
Splanchnic. 102
Spleen, 14, 16, 54. 55, 89
Spontaneous generation. 307
Starch, 22
vStarvation, 164
Steapsin. 98, 134
Stereoscope, 283
Stimuli, 3, 197. 218

classification of. 4, 195
Stomach, 127, 132
Strychnin, 232
Successive contrast, 273

Sudoriferous glands, 109
Sulphur, 13. 43

of proteids, 27
Supplemental air. 82
Suprarenal glands, 78, 151
Sweat (see Perspiration).
Sympathetic nerves, 75, 94, 253
Synchondrosis, 201
Synergetic muscles, 206
Synovia, 202
Syntonin, 32
Systole, 63, 65

Tabes dorsalis. 229
Tactile areas. 304

corpuscles, 300

sensations, 245, 30x3
Talbot's law, 273
Taste buds. 298

sense of, 298
Taurin, 50

Taurocholic acid, 50, 100
Tears, no, 239, 283
Teeth. 329

Teichmann's crystals, 34
Temperature of body, 174, 180

effect of, on muscles, 189

" •' " nerves, 218
Testes, 154
Tetanus, 191
Thrombin, 56

Thymus gland, 89. 150, 151
Thyroid cartilage, 209

gland, 150
Thyroiodinc. 151
Tidal air, 82
Timbre of sound, 293
Tissue fluids, 87
Transfusion of blood, 78
Trigeminus. 251
Trochlear nerve. 251
Trommer's test, 19
Trypsin. 98
Tryptic digestion, 133
Tympanum, 286
Ty rosin, 27

Umbilical cord, 327
Urea, 43, 57, 104, 109

compounds of, 44

formation of. 45

heat value of. 179
Uric acid, 35. 46, 57, 89, 104
Jnne, 103. 107
Urobilin. 105

Vagus, 74, 84, 86, 98, 99, 102, 133, 252

INDEX

339

Valves of heart, 66, 67

of veins, 74
Vaso-motor centres, 76, 238

nerves, 75~77

Vater-Pacini corpuscles, 301
Ventricles of heart, 66
Vernix caseosa, 321
Villi, 103, 141
Visual angle, 277

axis, 260, 277

centre, 247

field, 277

perception, 276

purple, 271

sensations, 272
Vital capacity, 83

force, I

Vocal cords, 210
Voice, 209
Voluntary reactions, 225

Vomiting, 128
Vowels, 213

Water, 14. 42, 160, 172

functions of, 15, 114
lack of, 166

Wave of contraction, 190
Weber's law, 256, 272, 302
White blood corpuscles, 54, 89, 199
Wolffian bodies. 320
Work of muscles, 179, 180, 192
unit of, 178

Xanthin, 104

bases, 35, 47, 89
Xanthoproteic reaction, 30

Yellow spot, 270
Yolk sac, 315, 319

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-" Not too technical to be exceedingly useful and enjoyable to every
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anecdotes " (R*ooklyn Eagle). — "He writes brilliantly: even the laziest
or most indifferent will find that he chains the attention and makes a
perusal of the history of music a delightful recreation " (N. Y. Home
Journal).

" Capitally indexed. . . . Mr. Marchant has done his hard task of trans-
lating exceedingly well" (Transcript). — ". . . The pictures of the instru-
ments are clear and helpful " (<y. Y. Times). — "An unusually handsome
book" (Musical Record). — " This superb volume" ('I he Watchman). —
"This handsome volume, . . . elegantly printed on the best of p^per,
and the illustrations are numerous" (Christian Register).— "An excellent
translator " (Providence Journal). — " Well translated " (School and Home
Education) — "The translation is excellent; . . . handsomely bound"
(ffotne Journal),

HFlSJRY HOI T & TO 29 West 23d St., New York
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XII '99

AMERICAN SCIENCE SERIES

The two princip? 1 objects of the series are to supply the lack — in
gome subjects very great — of authoritative books \vhose principles
are, so far as practicable, illustrated by familiar American facts,
and also to supply the other lack that the advance of science per-
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latest generalizations.

1. Astronomy. By SIMON NEWCOMB, Professor in the Johns Hopkins University,

and BDWAHD S. HOLUEN, Director of the Lick Observatory, California,

Advanced Course. 512 pp. 8vo. $2.00 net.
The s.tine. Briefer Course. 3^2 p;>ges. 121110. $i 12 net.
The same Elementary Course. By E. S. HOLDEN. 446 pages. 12010.

$1.20 net.

2. Zoology. By A. S. PACKARD, Jr., Professor in Brown University. Advanced

Course. 722 pp. 8vo. $2 40 net.

The same. Briefer Course. (Revised ana snlarged. 1897.) 338 pp. $1.12 net.
The same. Elementary Course. 290 pp. 12010. 80 cents net.

3. Botany. By C. E. BESSEY, Professor in the University of Nebraska.

Advanced Course. 6n pp. 8vo. $2.20 net.

The same. Briefer Course. {Entirely new edition, 1896.) 356 pp. i2ino.
$1.12 net.

4. The Human Body. By H. NEWELL MARTIN, sometime Professor in the Johns

Hopkins University.

Advanced Course. (Entirely new edition, 1896.) 685 pp. 8vo. $2.50 net.

Copies without chapter on Reproduction sent when specially ordered.
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Fiiz, i8gS.) 408 pp. 12010. $1.20 net.

The same. Elementary Course. 261 pp. i2mo. 75 cents net.
The Human Body and the Effect of Narcotics. 261 pp. 121110. $1.20 net.

5. Chemistry. By IRA REMSKN, Professor in Johns Hopkins University.

Advanced Course (Inorganic entirely new edition, 1898.) 850 pp. 8vo.

$2.80 net.

The same. Briefer Course. (Entirely veiv edition, 1893.) 435 PP- $1.12 net.
The same. Elementary Course. 272 pp. i2mo. 80 cents net.
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Chemical Experiments. By Prof. REMSEN and Dr. W. W. RANDALL. (For

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6. Political Economy. By FRANCIS A. WALKER, President Massachusetts Insti-

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The same. Elementary Course. 423 pp. 12010. $1.00 net.

7. General Biology. By Prof. W. T. SHDGWICK, of Massachusetts Institute of

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8. Psychology. By WILLIAM JAMES. Professor in Harvard College. Advanced

C"urse. 689 -(-704 pp. 8vo. 2 vols. $4.80 net.
The same. Briefer Course. 478 pp. 12010. $1.60 net.

9. Physics. By GEORGE F. BARKER, Professor in the University of Pennsylva-

nia. Advancid Course. 902 pp. 8vo. $3.50 net.

10. Geology. By THOMAS C. CHAMBRRLIN and ROLLIN D. SALISBURY, Professors

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11. Finance. By HENRY CARTER ADAMS, Professor in the University of Michi-

gan. Advanced Course, xiii + 573 pp. 8vo. $3.50 net.

HENRY HOLT & CO.

29 West 23d Street, New York 378 Wabash Avenue, Chicago

(i, 1900)

Two MASTERPIECES ON EDUCATION

5th Impression of a fascinating book

JAMES'S TALKS ON PSYCHOLOGY

TALKS TO TEACHERS ON PSYCHOLOGY AND TO
STUDENTS ON SOME OF LIFE'S IDEALS. By WIL-
LIAM JAMES, Professor in Harvard University, Author of
"The Principles of Psychology," etc. xi -f- 301 pp., i2mo,
gilt top. $1.50, net.

In writing these " Talks " out, the author has gradually weeded out as much
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Contents : Psychology and the Teaching Art ; The Stream of Consciousness ;
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sity of Reactions ; Native and Acquired Reactions ; What the Native Reac-
tions Are ; The Laws of Habit ; The Association of Ideas ; Interest ; Atten-
tion ; Memory; The Acquisition of Ideas ; Apperception; The Will; The
Gospel of Relaxation ; On a Certain Blindness in Human Beings ; What
Makes Life Significant.

WALKER'S DISCUSSIONS IN
EDUCATION

By the late FRANCIS A. WALKER, President of the Massachu-
setts Institute of Technology. Edited by JAMES PHINNEY
MUNROE. 342 pp., 8vo. $3.00, net.
The author had hoped himself to collect these papers in a volume.

The Dial: "A fitting memorial to its author. . . . The breadth of his
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on every page."

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for what are commonly supposed to be dry and difficult subjects, and the ca-
pacity he had for contioversy, sharp and incisive, but so candid and generous
that it left no festering wound."

HFMRY HOI T & TO 29 West 23d St., New York
ME, INK. I nULl CX LA'. 378 wabash. Ave., Chicago

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