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TEXTBOOK

OF

PHYSIOLOGY

BY

WINFIELD S. HALL, Ph.D. (Leipzig), M.D. (Leipzig).

I'K'ifessor of Physiology, Northwestern University Medical School, Chicago.

Member of the American Physiological Society, Fellow of

the American Academy' of Medicine.

ILLUSTRATED WITH 343 ENGRAVINGS AND SIX COLORED PLATES

L KA BROT II E RS & CO.

PHILADELPHIA \M> NEW YORK

1 8 9 9 .

•^UB&A*k

Entered according to Act of Congres?, in the year 1°.*'.'. by

LEA BROTHERS & CO.,

in the Office of the Librarian of Congress at Washington. All rights reserved.

?3^r
MI4-

%n

TO HIS TEACHER

C A E L L U D W I G

THIS BRIEF WORK
IS

DEDICATED

IX

REVEBENOE AND GRATITUDE

BY

THE AUTHOR.

Digitized by the Internet Archive

in 2010 with funding from
Columbia University Libraries

http://www.archive.org/details/textbookofphysioOOhall

PREFACE.

Physiology is an experimental and superstructure science oc-
cupying a field quite as definite as Anatomy, Chemistry and Phy-
sics, the three foundations on which it is built. Though all
physiologists impress these facts in their teaching, no volume
has hitherto been based on the advantages of presenting the sub-
ject concretely within its own proper boundaries, and in its in-
structive connections with the sciences whence it is derived.

In approaching Physiology from this standpoint the author has
summarized in the Introduction those principles of Physics and
Chemistry which have a general application, and has prefixed to
each chapter an abstract of the facts drawn from all three of the
basic sciences which are to be applied in the succeeding text.
This method possesses the obvious teaching value of confining the
subject-matter of each chapter strictly to Physiology and present-
ing it in logical relations.

The plan of the work adapts it to the needs of several classes of
readers. Medical students will, it is hoped, find a clearly defined
exposition of Physiology proper, its relevant facts from Chemistry,
Physics and Morphology, and accompanying outlines enabling
them to arrange their knowledge in an orderly and logical man-
ner. Students in literary or scientific institutions who are pre-
paring for the study of medicine or of physiology as a specialty,
will find the method of the book equally adapted to their needs,
inasmuch as the general and special introductions review matter
which has been the subject of detailed study in the laboratories
of Physics, Chemistry and Biology, and which forms the basis of
Physiology.

The aame reasons render the method of the book convenient for
the practitioner. The style is as brief and concise as compatible
with the needs of students, and space has thereby been gained for
the inclusion of clinical applications of physiological facts and
principles.

6

6 PREFACE.

Readers interested in physiological chemistry will find the
structural formulas and reaction- of the complex bodies involved
in physiology worked out in as much detail as the present status
of chemistry will allow. The newer literature of this subjecl i-

noted in references.

Though the volume embodies original work on the part of the
author, free use ha- been made of the great heritage of physio-
logical knowledge without which no adequate presentation of the
subject would he possible.

The author wishes to express here his obligations to Professor
Piersol for the use of many of his excellent histological illustra-
tions ; to Professor E. B. Wilson for the use of several fine figures
from his work on " The Cell in Development and Inheritance" ;
and to Professor Waller for several valuable engravings from his
Text-book of Physiology. Several authors have contributed one
or two figures each. Many have been taken from my Laboratory
Guide in Physiology.

In the preparation of the text the author wishes to acknowledge
his indebtedness to his associate, Professor W. K. Jaques, for much
valuable material on the subject of The Blood, especially for Plates
I. and II. showing varieties of red and white corpuscles ; to Dr.
Achard, a former pupil of Professor Bowditch, for the excellent
contribution on Internal Secretions. The chapter on the physi-
ology of the (\nt ml Nervous System was prepared by my associate,
recently deceased, Dr. P. L. Holland, Instructor in Clinical
Neurology. For the proof-reading and for many valuable addi-
tions to this chapter I am indebted to my associate, Dr. C. L.
Mix, Instructor in Anatomy and Physiology of the Nervous
System.

Winfield S. Hall.

Chicago, July, 1899.

CONTENTS.

INTRODUCTION r 17

PART I.
GENERAL PHYSIOLOGY.

CHAPTER I.

THE PHYSIOLOGY OF THE CELL : CYTOLOGY 31

A. Living Substance: Protoplasm 32

1. Tin- Physical Properties of Protoplasm.

2. The Chemical Properties of Protoplasm.

3. The Morphology <>f Living Substance.
". The Structure of Protoplasm.

b. The Structure of the Cell.

(1) Cytoplasm; (2) The Nucleus; Nucleoplasm ; (3) The Centro-
Bome.
r. Form and Size of the Cell.

4. Th'- Individualization of Living Substance.

B. The Phenomena of Life 42

1. Nutrition.

". Absorption and Excretion.
/;. Metabolism.

(1) Chemical Phases ; (2) Physical Phase-: (3) Morphological Phases.

2. Moto-Sensory Activities of Life.
". Motion : < lontractility.

b. Bensibility : Irritability.
'■',. Reproduction.

CHAPTER II.

THE PHYSIOLOGY OF CONTRACTILE AND IRRITABLE TISSUES.

INTRODUCTION 57

A. Physical [ntrodi ction

1. Elements and Batteries.

2. Key- and Electrodes.

.;. Methods of Modifying the Current.

i. The [nductorium,

.". The Measurement of Electricity.

<;. Methods of Recording Results.

//. ANATOMII \i. INTRODUCTION 67

1. The Structure (if Muscles,

2. The Structure of Nerves.

i be Muscle-Nerve Preparation.

7

s CONTENTS.

THE PHYSIOLOGY OF CONTRACTILE AND CBEITABLE TISS1 Eg

.!. The Muscle-Nerve Preparation "4

1. Srimiili.

2. Changes Which Take Place in a Muscle in Response to Stimuli.

a. ( !hange in Form.

(1) Change in Length ; (2) Change in tin- Transverse Dimensions;
The Work Done by a Contracting Muscle.

b. Chemical I bangee Which Take Place in a Contracting Muscle.

c. Thermal Changes Which Take Place in a Contracting Muscle.
<l. Electrical Changes Which Take Place in a Contracting Muscle.

.'{. The Relation of the Nerve to Various Stimuli.
". Properties of Nerve Trunks.
b. Conductivity.
c Irritability.

'/. Pfluger's Law of Contraction.
e. The Application of the Laws of Electrotonus.

/.'. Tin: General Structure ant) Function of the Nervous System . . '.'4

(1) The Neuron; (2) Features of the Spinal Cord; (3) Reflex Action;
(4) Nerve Centers.

PART II.
SPECIAL PHYSIOLOGY.

Division A. NUTRITION.

The Physiology of the Intebnax Relations 101

Division B. MOTO-SENSORY ACTIVITIES.

The Physiology of the External Relations 42:<

Division C. REPRODUCTION (317

CHAPTER III.

CIRCULATION : INTRODUCTION.
A. The Comparative Physiology of the Circulation . . . 104

1 . The Circulating Fluids.

2. The Organs which Cause the Circulation.

B. Anatomical Introduction 107

1. The Blood- Vascular System.

2. The Lymphatic System.

3. The Spleen.

4. Histogenesis of the Circulatory Organs and Tissues.

C. Physical Introduction 116

1. The Flow of Liquids Through Tul.es.

2. Manometers.

]>. Historical Introduction 123

THE PHYSIOLOGY OF CIRCULATION.
.1. Classification of the Fluids, Tissues and Obgans . . 130
B. The Circulating Fluids 130

CONTENTS. •'

1. The 151 1.

I. The Physical Properties.

II. The Morphology of the Blood.
a. The Red Blood < lorpuscles.

h. The White Blood Corpuscles.
c. Other Morphotic Elements.

III. The Chemical Properties of the Blood.

IV. The Functions of Various Portions of the Blond.
V. The Total Quantity of Bl 1 in an Animal.

VI. The Protection of the Blood Supply.
a. The Location of the Vessels.
/;. The Coagulation of the Blood.
VII. The Effect of Hemorrhage.
VIII. The Transfusion of Blood.
IX. The Physiological Variations of the Blood.

2. The Lymph.

I. The Physical Properties.
II. Tin- Morphology of the Lymph.
III. The Chemical Properties of the Lymph.

C. The Formation and Destruction of the Corpuscles. . . io2

1. The Formation of Bed Blood Corpuscles.

2. The Decay and Destruction of the Bed Blood Corpuscles.

3. The Formation and Destruction of Leucocytes.

4. Summary of the Functions of the Spleen.

D. The Circulation of the Fluids 154

1. The Action of the Heart.

2. The Circulation of the Blood.

". The Circulation in the Arteries.
//. The Circulation in the Capillaries,
c. The Circulation in the Veins.

3. The Circulation of the Lymph.
". In the Lymph Radicles.

b. In the Lymphatics.

E. The Control of- the Organs of Circulation 181

1. The Innervation of the Circulatory System.

«. The Innervation of the Heart.
//. The Innervation of the Arteries.

2. Adaptative < loordination of the Activities <>f the < lirculatory < Organs.

( H.VPTER IV.
RESPIRATION: INTRODUCTION.

RESPIRATION DEFINED AND CLASSIFIED 180

.(. Comparative Phybiolooy oi Respiration 190

l. Respiration in Individuals of a Lower1 Order.
J. Respiration in Individuals of a Higher Order,
i < or. He mi- Respiration.
Respiration by < ■ill-.
ration by Lungs.

/;. Anatomical Introduction 191

lie Histology of the Respiratory Organs.

c. Physic \i. i ntrodi < tion. I1M

'I le Solution of ( l:i-i - in Liqu el .

10 CONTENTS.

THE PHYSIOLOGY OF RESPIRATION.
A. The Mechanical and Physical Features of Respiration . vm

1. Structural Features.

o. ( lhange in Thoracic I diameters.
//. Muscles of Respiration.

2. Observation of Changes in the Diameters of the Thorax.

3. Physical Effects of the < lhanges of the Thoracic I diameters.
a. [ntra-thoracic Pressure.

//. Respiratory Pressure.

c Intra-abdominal Pressure.

il. Lung < lapacity.

c. Types of Respiration.

/. Modifications of the Respiratory Act.

B. THK Chemistry OF RESPIRATION 212

1. External Respiration.

a. Respiratory Changes in the Air Breathed.

(1) Composition of the Normal Ainiosphere; (2) Qualitative Changes Produced
by Respiration : (3 ) Quantitative ( Jhanges of the Air in Respiration.

b. Respiratory Changes in the Blood.

(1) The Gases of the Blood; (2) The Relation of Oxygen in the Bl 1 ; (3) The

Relation of Carbon Dioxide in the Blood; (4) The Influence of Blood-Gases
upon the Spectrum.

2. Internal or Tissue Respiration.

♦ CHAPTER V.

DIGESTION.

INTRODUCTION 233

A. Comparative Physiology of Digestion 233

1. Intra-Cellular Digestion.

2. Digestion by Secreted Ferments.

3. The Evolution of Salivary Glands.

4. The Evolution of Oral Teeth.

B. Anatomical INTRODUCTION 237

1. A Summary of the Anatomy of the Digestive System.

2. The Innervation of the Digestive System.

C. Secretion 244

1. Genera] ( lonsiderations.

2. Secretion Defined.
:;. Secreting Glands.

4. Internal Secretion. Functions of the Vascular Glands.

i>. Chemical Introduction 257

1. Fundamental Carbon Compounds.

2. The Carbohydrates.

3. The Fats.

4. The Proteids.

5. Ferments and Enzymes.

/;. Foodstuffs and Foods 279

1. Definitions.

2. ( 'hemical ( lomposition of Milk and of the Animal Body.

3. Classificati f Foodstuffs.

4. Foods.

5. Preparation ofFoods.

CONTENTS. 11

DIGESTION 292

A. Salivary Digestion 293

1. The Saliva.

a. The Secretion of Saliva.

b. The Composition of Saliva.

2. The Chemistry of Salivary Digestion.

3. Factors which Influence Salivary Digestion.

4. Mastication.

5. Deglutition.

B. Gastric Digestion 309

1. The Gastric Juice.

a. The Secretion of Gastric . I nice.

b. The Composition of Gastric Juice.

2. The Chemistry of Gastric Digestion.

3. Fact' us which Influence Gastric Digestion.

4. The Movements of the Stomach.

5. Vomiting.

C. Intestinal Digestion :*-i4

1. The Digestive Fluids of the Intestine.

a. The Secretion of Pancreatic Juice.

b. The Composition of Pancreatic Juice.

c. The Composition of the Bile.

2. The Chemistry of Intestinal Digestion.

a. The Action of the Pancreatic Juice.

b. The Action ofthe Bile.

c. The Action ofthe Succua Entericus.
'/. The Digestion of Milk : A. Summary.

3. The Factors which Influence Intestinal Digestion.
". The Influence of Bacteria.

//. The Influence of < lellulose.

4. The Remnants of Intestinal Digestion: Faeces.

.">. The Movements of the Intestines.

<;. Defecation.

CHAPTER VI.

ABSORPTION'.
INTRODUCTION Z-U

1. Absorption Defined.

2. Structures Involved in Absorption.

.';. Physical Forces Influencing Absorption.
l. Former Theories of Absorption, Reviewed.

THE PHYSIOLOGY OF ABSORPTION 852

1. Absorption from Different Portions of the Alimentarj (anal.
". Absorption from the Month.

//. Absorption from the Stomach,

c Absorption from the Small Intestines.

d. Absorption from the Largs Intestine.

2. Absorption of Different Foodstuffs.
</. The Absorption of Water.

//. The Absorption of Salts.

I be A bsorpti f < Carbohydrates.

'/. The A bsorpl ion of Proteids.

I he Absorption of Fata.

12 CONTENTS.

CHAPTEB VII.

METABOLISM.

INTRODUCTION 359

1. Metabolism Defined and Classified.

2. Metabolic Tissues and ( >rgans.

:;. The Income and Outgo of Matter.

4. Equilibrium.

.">. The Circulation of the Elements.

<;. The circulation of Typical Compounds.

7. The Character of the Metabolic Changes.

ANIMAL METABOLISM.
A. Metabolic Changes of Different Classes of Foodstuffs. . 367

1. Carbohydrates.

a. Absorption Form.

b. Circulation Form.

c. Metabolism.

</. Excretion of Carbohydrate Katabolites.

2. Proteids.

a. Absorption Form.

b. Circulation Form.
r. Metabolism.

d. Nutritive Value of Proteids.

e. Laws of Nitrogen Equilibrium.

3. Fats.

a. Absorption Form.

b. Circulation Form.

c. Metabolism.

d. Fat Deposits.

4. The Inter-relations of the Foodstuffs in Nutrition.

B. Summary of Anabolism and Katabolism 382

1. Anabolism.

2. Katabolism.

C. The Income of Energy 387

1. The Potential Energy Represented by the Foodstuffs.

2. The Potential Energy Represented by Common Foods.

3. The Energy Represented by a Typical Menu.

I). The Liberation of Energy 392

1. The Liberation of the Potential Energy of the Organism.

2. The Transformation of Energy.
.">. The Conservation of Energy.

4. The Expenditure of the Kinetic Energy of the Organism.

E. Animal Beat 394

1. General I Considerations.

2. Method of Determining the Mean Temperature.

3. Factors which Cause Variations of the Temperature.

di climate; (2) Sex; (3) A.ge; (4) Seasons; (5) Extreme Temperature Ar-
tificially Produced; (6) Day and Night; (7) Muscular Work ; (8) Mental

Work; (9) F 1 ; (lO)Sleep; (11) Path-, (12) Drugs; (13) Individual

Difference; (14) Limits of Temperature Compatible with Life.

4. Temperature Topography in Man.

5. Heat Regulation or Thermotaxis.

CONTENTS. 13

CHAPTER VIII.

EXCRETION.
INTRODUCTION 40:3

1. Definitions.

2. General Considerations.

3. Anatomy of the Kidney.

a. Blood Supply of the Kidney.

b. The Driniferous Tubules.

c The Innervation of the Kidney.

THE PHYSIOLOGY OF EXCRETION.

A. Renal Excretiox 409

1. The Urine.

a. General Characters.

(1) Quantity; (2) Specific Gravity; (3) Reaction; (4) Color.

b. Chemical Composition. Tabulated.

c. The Urinary Constituents Separately Considered.

(1) Organic Constituents; (2) Inorganic Constituents.

2. The Process of Urinary Excretion.

a. Glomerular Excretion.

(1) Experiments and Conclusions from same; (2) Factors Influencing Glom-
erular Excretion.

b. Glandular Excretion.

c. The Egestion of Urine. Micturition.

B. Pulmonary Excretion 425

C. Cutaneous Excretion- 425

1. Tile Sweat.

(i. General < Iharacters.

Quantity; {b) Specific Gravity ; (c) Reaction.
b. < 'hemieal ( (imposition.

(1) Organic Constituents; (2) Inorganic Constituents.

2. The Process of Cutaneous Excretion : Perspiration.

(1) The Influence of the Nervous System upon Cutaneous Excretion.

(2) Factor- which < lause a Variation in the Quantity of Perspiration.

D. Intestinal Excretion 12s

DIVISION B.

THE PHYSIOLOGY OF THE EXTERNAL RELATION'S: THE MOTO-

SENSORY ACTIVITIES B9

CHAPTER IX.

THE SKJX: THE DERMAL SYSTEM.

INTI:m|iii TION 12:'

1. Summary of the Morphological Features of the Dermal System, The His-

togenesis and Histology of the System.

2. Tin- Glands of the Dermal System.

THE PHYSIOLOGY OF THE DERMAL SYSTEM. . . . 1 ;:,

1. Protection.

2. Thermol;
Excretion.

t. Respiration.

ii coy TESTS.

(ii \ri t.i; x

SKXSATJOX.
I \ I IH (DUCTIOX 138

A. General Sensations hi

I. Subjective.

i i\ e-objecl i\ e.
( 'nnmioii Si nsation.

II - I mi : : Suffocation ; (d) Fatigue; (< | Pain ;

Shivering; (g) Tickling; (A) Sexual Sensation.
Objective.

I. The Tactile or Pressure Sense.
1 1. The Posture Sense.

Sense of Equilibrium; {!>) Muscular Sense.

III. The Temperature Sense.

B. Special Sensation (Objective): The Special Senses 157

IV. Smell.
V. Taste.

VI. Hearing.
VII. Vision.

CHAPTEE XI.

THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

A. The Nei ron: Structural and Functional Unit of the Nervous

System 528

1 . The Structure of the Neuron.
n. General Description.

I,. Types of Neurons.

c. Interrelations of the Neurons.

d. The Neuronal Cell-body.

e. The Dendrites.
/. The A sons.

g. Axonic < Jollaterals.

2. The Physiology of the Neuron.

a. Cellulipetal and Cellulifugal Messages.

//. The Dynamic Polarity of the Neuron.

c. Changes within the Neuron during It- Activity.

il . Function of khe Nerve-fiber.

/ . Function of End-organs.

/. Effect of Structural Modification upon the Function of the Neuron.

;/. Effecl of Mutilation upon the Neuron.

A. Post-natal Neuronic 1 >evelopment.

/;. Conduction and Reflex Action: The Physiology of the Spinal

Cord .VI4

1. The S | >in;i I Cord as a Conductor of Nervous Impulses.

</. The < lourse of Sensorj Impulses.

h. The < lourse of Motor I mpulses.
•_'. The Spinal Cord as a Reflex Center.

a. Reflex Action.

i General Considerations; (2) The Purposeful Character of Reflex Action;

The Time Required for Reflex Action; (4) The Inhibit! f Reflex

Action.

b. The Reflexes.

CONTEXTS. 15

(1) Superficial Reflexes; (2) Deep Reflexes; (3) Organic Reflexes ; (4) Rela-
tion of Reflex Action to Higher Psychic Phenomena.
c. The Location of Reflex Centers.

3. The Trophic Functions of the Spinal Cord.

4. Tlu- Physiology of the Medulla Oblongata or Myelencephalon.

a. The Medulla as a Medium of Conduction.

b. The Medulla as an Independent Center.

'. COORDINATION AND EQUILIBRIUM: TlIE PHYSIOLOGY OF THE CERE-
BELLUM OR MeTENCEPHALON 567

1. Coordination: Adjustment of Muscular Action.

2. Equilibration: The Maintenance of the Equilibrium.

D. Vision, Coordination of Equilibration-Movements: The Physi-
ology of the Mid-Brain or Mesencephalon 580

E. The Physiology of the Inter-brain or Thalamencephalon . 584

/'. Conscious Sensation, Voluntary Motion, Intellect: The Physi-
ology of the Cerebrum or Prosencephalon 585

1. Introductory.

". The Vascular Supply of the Brain.
b. The Movements of the Brain.
-. Tie- Physiology of the Cerebrum.
>/. ( teneral < lonsiderations.

b. Localization of Functions in the Cerebrum.

l | Experiments upon Monkeys; (2) Results of Observations upon Man.

c. The Higher Cerebral Functions.

CHAPTER XII.

TIIK PHYSIOLOGY OF THE MFSCULAR SYSTEM.

.1. General Activities of Muscular Tissue 598

i:. Enumeration and Classification of those Muscular Activities

Arising from a chanok in Form 600

1. The Involuntary Museles.

2. Tin- Voluntary Muscles.

". Muscular Organs : The Tongue;

b. Muscle-bone Organs : The Skeletal Muscles.

(1) Genera] Functions of Muscle-bone Organs; (2) Special Functions
of Muscle-bone Organs ; <■'•) Animal Mechanics.

C. Special Muscular Organs: The Larynx 610

i. Bummary of the Ajiatomy of the Larynx.

". The Skeleton of the Larynx.
//. The Musclet of the Larynx.

•■. Tin- Innervation of the Larynx
_'. 'I'll'- Mechanics of the Larynx.

(1) The Abduction of the Glottis; (2) The Adduction of the Glottis;
The Tension of the Vocal < !ordi ; (4) Tie- Levere of the Larynx.
'.'>. The Acoustics of the Larynx.
i. The Voice : Phonation.
". Speech,
b.

16 CONTENTS.

division a

CHAPTER XIII.

REPRODUCTION.
Tin'. Physiology and Morphology of Reproduction. 61i

1. The Ovum.

l.'. Maturation.

3. Fertilization.

■\. Segmentation.

5. TheEmbryo: Histogenesis.

a. The Development of tin- Germ-layer.

//. The Development of the Primitive Segments.

c. The I>( j-ciiiiiin^ of the Nervous System.

d. Tin- Mesenchyme.

e. The Origin of the Urinary System.

/. Summary of Early Development : Histogenesis
(i. The Foetus: Organogenesis.

a. The Circulatory System.

b. The Respiratory System.

c. The Digestive System.

d. The Uro-genital System.

i\ The Central Nervous System.

7. The Foetal Envelopes.

<(. The Fietal Membranes.

//. Maternal Portion of Envelopes: Deciduse and Placenta.

8. The Physiology of the Embryo and Fcetus.
a. Nutrition.

/;. Moto-sensory Activity.

9. The Physiology of Maternity.

a. Pregnancy ami Parturition.

b. Lactation.

PHYSIOLOGY.

INTRODUCTION

.4. THE SCOPE OF PHYSIOLOGY AND THE PROB-
LEMS WITH WHICH IT DEALS.

1. DEFINITIONS.

Physiology treats of the functions of different tissues and
organs of living organisms. Living organisms are divided into
plant and animal kingdoms, so there is Plant Physiology and
Ani null Physiology. It has been customary to subdivide the latter
into ( bmparative Physiology, treating of the ways in which the
different functions — digestion, circulation, etc. — are performed in
tli^ different classes of animals, and Human Physiology, treating
of the special physiology of man. Another subdivision of the
subject is into General Physiology, treating of the general functions
of cells and tissues, and Special Physiology, treating of the special
functions of organs and systems of organs.

Defined in more general terms, — Physiology is the science of the
phenomena of living naiure. Reduced to its final elements, a
natural phenomenon always involves matter and energy. A
general knowledge of the properties of matter and of energy is of
great importance to him who would study the phenomena of life.

2. MATTER.

All of the substance <>r materia] in the universe, which appeals
t<« our senses, has weighl and resistance, and i.~ called 'ponderable
matter, — it may \><- weighed in n balance. It is with this form of
matter alone that physiology deals. Physicists, chemists, and
astronomers find it a necessity to assume the existence of another
form of matter.

This other form of matter fills all space not actually occupied
by atoms of ponderable matter ; it transmits the -mi's beat and

2 17

18 INTRODUCTION.

light to us through space. This form of matter cannot be weighed
in a balance, and is called imponderable matter.

Solid
A- to aggregate condition j Liquid.

Gaseous.

Mattei-

Ponclerable

MolSe '

j, .. , Indefinite

Particle J

> Definite.
Atom J

[mponderable.

Physiological problems involve ponderable matter in some of
the forms indicated and under the influence of energy.

3. ENERGY.

Energy is the capacity or power to do world This capacity for
power to do work may be manifested or not. We speak of the
pent-up energy of a charge of gunpowder, also of the tremendous
energy of the explosion ; we speak of a man of energy, but we do
not expect the man to manifest his energy constantly. This dual
idea of energv is expressed in its classification as potential energy
and kinetic energy ; i. c, latent and active energy. Energy is fur-
ther classified as to its nature. That form of energy most uni-
versal in its influence is gravitation : according to the law of
gravitation, " Every particle of ponderable matter in the uni-
verse attracts every other particle with a certain force."

a. The Transformation of Energy.

The changes above mentioned, by which potential energy may
be changed into kinetic energy, is not a transformation in the
sense here intended, — it is simply a liberation of latent energv,
whereas the reverse operation would be a making latent of active
or kinetic energy.

By the Transformation of Energy quite a different process is
indicated. If one hold an object in an elevated position, and re-
lease it, it falls to a position of equilibrium. The motion of the
mass is lost but the shock of impact has transmitted the motion
of the mass to the physical and chemical units of the mass — the
atoms — and thi> atomic vibration appeals to our senses not as
motion, but as heat. The energy of mass or molar motion is
thus transformed into the energy of atomic motion or heat. The
intensity of atomic motion may be so great, i. e.} the heat may
be so great, that the vibrations appeal not only to our temperature
sense as heat, but also to our eyes as light. Still another form,
into which energy may be transformed, is electricity. Thus gravi-

LAW OF THE CONSERVATION OF ENERGY. 19

tation is a general and ultimate form of energy which may un-
dergo various transformations.

Another ultimate form of energy, especially manifested in the
form of heat, light, or electricity, is chemical affinity. By virtue
of molecular attraction every molecule of matter is attracted by
every other molecule in proportion to their respective masses, and
with a force varying inversely as the square of the distance be-
tween them, irrespective of the kind of matter ; but, by virtue of
a peculiar affinity between atoms of certain different kinds of
matter, these atoms are drawn into new and most intimate con-
tact, manifested by heat or light or electricity, and resulting in a
new combination of matter, having physical properties different
from those of either constituent. This kind of energy, and its
transformation forms, are of the most fundamental importance to
phvsiology ; and constant reference must be made to them.

Matter is transformable, but is not destructible. Energy is
transformable ; is it destructible? Matter may be so transformed
a- x<> make it useless to man, i. c, lost to use, but not destroyed ;
in the same way energy may be dissipated into space but not de-
stroyed. This great met was discovered, and demonstrated by
Julius Mayer, and by Helmholtz, and may be looked upon as the
most important advance of physical science during this century.
It is called the law of the conservation of energy.

b. Law of the Conservation of Energy.

Ganot expresses this law as follows: ■ "The total amount of
energy possessed by any system of bodies (e. y., the solar system)
i- unaltered by any transformations arising from the action of one
part of 1 1 1 « - system upon another, and can only be increased or di-
minished by effects produced upon the system by external agents."

The experimental proof of the truth of this law involves the
reduction of all forms of energy to units. The unit of heat energy,
called the calorie or gramme-calorie, is that amount of heat required

to raise one gramme of water one degree of temperature. II' it is
required to reduce unite of motion to units of heat one has only to

remember thai experiment has proven that 125.5 gramme-, falling

through a distance of one meter, would, by impact with an abso-
lutely resistant surface, generate enough heat to raise the tem-
perature of l gramme of water 1° Centigrade. Tin- i- known as
the Mechanical Equivalent <>/' Heat. The principles involved in
the traii-formation of energy, and the conservation of energy, are
fundamental, and we shall presently see their inestimable impor-
tance in any clear conception of the phenomena of Living nature.
All natural phenomena involve matter and energy. The phe-
nomena of living nature can differ from those of lifeless nature

20 INTRODUCTION.

only in the matter or in the energy involved. We are al once
brought face to face with the most difficult problem <>f Physiology
— the abstract differentiation between the living and the lifeless.

Let ns approach this subject by an enumeration of the kinds of
matter of which living beings are composed, it was formerly
supposed that an analysis of the animal body would reveal chem-
ical elements peculiar to living bodies. Chemistry has, however,
established no fact more thoroughly than that the animal, or plant,
body contains no new kinds of matter. Analysis shows the pres-
ence of carbon, hydrogen, nitrogen, oxygen, sulphur, phosphorus,
chlorine, and of sodium, potassium, calcium, magnesium, iron —
occasionally traces of silicon, manganese, fluorine, lithium, bro-
mine, and iodine are found. These are the most common elements
in the surface of the earth. After rinding that living nature dif-
fers in no way from non-living nature as to the kinds of matter
involved, the physiologist turned to the investigation of the kinds
and forms of energy, expecting to find associated with life a new
energy. Until quite recently, most physiologists, since the time
of Johannes Midler, have believed that the energy manifested in
living nature is identical with that manifested in non-living nature,
and, further, that it obeys the same laws of transformation in liv-
ing as in lifeless bodies. This belief was based upon observation
in a large number of physiological phenomena. For example, it
has been demonstrated that the heat and mechanical energy which
an animal may expend is exactly equivalent to the potential energy
represented by the food which the animal absorbs. There remain,
however, many unsolved problems regarding the energy involved
in absorption, secretion and excretion. The more these problems
are studied, the clearer seems to be the indication that energy may
undergo, in the animal or plant organism, a transformation not
observed outside of living organisms. Along with this indication
comes repeated and indubitable proof that, whatever transforma-
tions energy may undergo within the living organism, the quantity
of energy that leaves the organism, dissipated into space as heat or
motion, is exactly equal to the quantity that enters the organism
as potential energy. Whatever may be said about vital energy,
it is certain that it does not mean that any new energy is created
by living organisms.

In discussing the matter involved in living organisms, the
elements which occur in living bodies were enumerated, but the
study of the combination of these atomic elements into molecules
was omitted. In lifeless nature we find as typical molecules,
H20, CG2, CaCO,, MgO03, NaCl, OaSO,, KX( >,* Fe2< >,, PbS, etc.

These typical compounds, which make up a large proportion of
the earth's crust, are composed each of three to six atoms of two
to three kinds of matter. There are, however, in the realm of
inorganic nature, some very large and complex molecules, e. g.: —

A LIVING ORGANISM. 21

Crystalline amnionic ferric alum Fe2(S04)3(NH4)2S04+24H20.
This complex molecule contains 104 atoms, and has 962 times the
weight of H. One of the simplest molecules met among the
products of life is the glucose molecule (C6Jl1206)> whose 24 atoms
weigh 180 times as much as an atom of hydrogen. Egg albumen
was given by Hofmeister the formula : C904H3.,2N.2O(.(jS2 ; its 646
atoms weigh 4,618 times as much as hydrogen. Zinoffsky deter-
mined the formula for the haemoglobin of the horse's blood cor-
puscle to be : C-10HmnX.,14FeS.,0J.,,. This prodiguous molecule
has 2,304 atoms and a molecular weight of 16,710. Here we have
struck the key-note of the difference between living and lifeless
nature. In its composition, living matter differs from lifeless matter
not in the kind of material elements but in the complexity of the com-
binations. A similar course of reasoning, applied to the energy,
would result in the conclusion that : The energy invoiced in the
phenomena of living nature differs from the energy involved in the
phenomena of lifeless nature only in the complexity of the transform-
ations.

4. LIFE.

Having now determined the essential difference between living
and lifeless nature as to the matter and energy, let us investigate
the nature of life in the abstract. Compare a dead with a living
organism ; take, for example, a frog just dead. We observe a
cessation of activity, i. e.} a cessation of manifest energy. The
breathing movements cease, the heart ceases to beat, the animal
ceases to take food; it becomes cold; if Ave stimulate it there is
no response ; in a few hours disintegration of the material begins.
Bow shall we interpret this change? The activities which have
ceased were the activities which adjusted the animal to its environ-
ment ; built up its tissues from its food ; and brought a continuous
supply of oxygen to enter into combination with the tissues, and
liberate the energies which were manifested in the phenomena <>{'
life. With the los< of life has been lost the energy necessary to
adjust the internal needs of the body to the action of the environ-
ment. Herbert Spencer defines life as" The <-onf in nous adjustment
of internal relations to external relations.'" Though this reasoning
and the explanation clear our conception of life somewhat, still
life remain-, and will long remain a mystery. A concrete idea of

the typical phenomena of life may besi be gained from the ob-
servation of a living organism.

.-,. A LIVING ORGANISM.

Such an organism begins it- lit'' as ;> minute globule (cell) "I
sensitive, spontaneously moving matter (protoplasm). The orig-
inal volume i- always increased (growth) by addition of mutter

22 INTRODUCTION.

from within (intussusception). Having attained a certain maxi-
mum of volume (maturity) the organism retains essentially the
same volume for a time (adult life), and finally divides into equal
or unequal parts (reproduction), the parts divided off beginning
again the cycle of life, reaching, at maturity,a form always resem-
bling the parent organism in form and activity. During the
whole period of life there are certain activities which are mani-
festations of energy, liberated within the organism through a proc-
ess analogous to a combustion of tissue (respiration, — destructive
metabolism), which tissue is regenerated by the building up in the
tissue (constructive metabolism) of elements or compounds taken
in as food, dissolved (digestion), and carried to the Masted tissues
(circulation). After growth is completed, and reproduction con-
summated, the wasting of the organism progresses faster than the
regeneration (period of senility), and finally, the internal rela-
tions (needs) fail to be adjusted to the external relations (condi-
tions of environment); and the organism ceases to live (death).

McKendrick ( "General Physiology," p. 31) gives the follow-
ing valuable recapitulation of the essential characters of a living
being : —

(a) Molecular complexity; heterogeneity of parts, and chemical insta-
bility of the organic compounds forming it.

(b) Waste, and incessant repair of organic materials.

(c) The conversion of kinetic into potential energy, as the framework
of the body is built up, or stores of reserve material are formed.

(d) Liberation of kinetic energy in various modes, and, in particular,
as mechanical movement, heat and electricity.

(e) Organization, or the adaptation of certain parts of the body to
particular functions.

(/) A regular evolution from origin of death.

(</), Origin from a parent, and the possibility of producing the ele-
ments of offspring.

(//) A power of variability and of adaptation to external conditions.

Physiology deals with the problem of Xttuitiox ; including
digestion, absorption, respiration, circulation, wn&tructive and de-
structive metabolism, secretion and excretion ; with the problems of
Moto-Sexsory ACTIVITY, including the functions of the motor
and nervous systems of the special senses ; and, finally with the
problems of REPRODUCTION.

PHYSIOLOGY, AND OTHER NATURAL SCIENCES.

23

B. THE RELATION OF PHYSIOLOGY TO THE
OTHER NATURAL SCIENCES.

fa

To <U

w

2

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HH

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09

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5

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Chemistry.

Physics.

Astronomy.

Geology.

1. Anatomy.

Science of living forms

2. Paleontology.
Science of fossil forms.

■ Gross.

V

Plant

Minute. J I Animal.

f Paleophytology.
I Paleozoology.

General.

fl. Physiology.

Science of functions of liv-
ing organisms. ( Special.

f Plant

or
*- Animal.

2. Psychology.

Science of psychic phenom-

f Comparative.
I Human.

I'harmacoloyy.

a . - .v . . , f Comparative.

Science ol the action of < TT r

, l Human.

drugs.

. Embryobgy. , Comparativ.

Science of Development of J
structures and functions. ( Special.

Pafkobgy. /-Comparative.

Science of diseased forms J General
and functions. ( Special

r Plant

or
*- Animal.

Plant

Animal.

k !
i

Anthropology.

The Biology of Man.

«. Physical Anthropology.

The Animal, Homo.
/>. Ethnology.

Races of 1 1 >> sapiens.

<■. Ethnography.

raphical distributioa
of the races.

24

INTRODUCTION.

C. THE DEVELOPMENT OF PHYSIOLOGY AS A
SCIENCE.

HISTORICAL REVIEW.

•"■ill 1

ll!> B.( .

3d b.< .

>>

i

1

1 [eraclee and Empedoclea ■"

1 [ippocratee I 160 B.( ,

\ 1 i-i. .1 !• :;- 1 1

Erasifltratua 280 b.< , 1.

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1st B.C.

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J. J, ParacelauB (1490).

XII.
XIII.

XIV.

XV.

XVI.

Servetus (1511).
Harvey.
1 Haller.

XVII.

XVIII.

XIX.

5

u

4)

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0

S

'Miiller.
WShler, Hoppe-Seyler, Briike,
Lieblg, Bonge, Ludwig,
Voit, Efammersten, DuBois-Beymond,
PflOger, Halliburton, Marey,
Zanat, Bernard,
KQhne, Weber, Bering, e(oZ.

,T1h' first traces of vague physiological conceptions arc lost in
the unpenetrable darkness of prehistoric times. These vague con-

DEVELOPMENT OF PHYSIOLOGY AS A SCIENCE. 25

ceptions find expression in mythology. In mythology there is no
classification of knowledge : all knowledge being made to do
homage to higher beings or deities, and this sum of human knowl-
edge, as it existed in prehistoric times, must be looked upon as an
indivisible whole from which, in the lapse of centuries, there grad-
ually crystallized out : theology, philosophy, medicine, and natural
science. In this mythological period life was characterized by
motion. Wind, water, fire, stars, sun, and moon were personified.
In historic times the first traces of a science based upon observa-
tion was, curiously enough, metaphysics or psychology.

This first attempt at biological science laid as the corner-
stone of its foundation the proposition, "The human being is
dual — the physical and the psychical — the body and the soul,"
and rounded its dome with the theory of metempsychosis, or wan-
dering of the soul. From India this system of philosophy grad-
ually made its way through Egypt to Greece, where it was
championed by Pythagoras. It is remarkable that many of the
philosophers of antiquity promulgated theories which are again,
after a lapse of twenty-five centuries, forming the foundations of
modern science. This is especially true of the theories regarding
the origin and development of living nature. Anaximander (620
b. C.) believed that man descended from animal-like progenitors,
who originally lived in water. Heracles (500 B. c.) had a concep-
tion of the "Struggle for Existence." Empedocles (504 b. C.) be-
lieved that, in the realm of living nature, plants originated first,
then lower animals, then higher animals, and finally man. He be-
lieved that the active factor in this development was the destruc-
tion, in their struggle for existence, of the animals unfavorably
constructed, while those capable of survival propagated the species,
and transmitted their favorable structures. In the fifth century
B. C. Hippocrates systematized medicine and founded the Regular
School. His additions to knowledge were unimportant in Mor-
phology and Physiology. His materia mcdica, Therapy, and
practice of medicine were incomparably superior to what had pre-
ceded, and stood iiniinpeached for six centuries. In the fourth cen-
tury ]'.. C. Aristotle, the great observer of the phenomena of living
nature, and the great collector of facts, laid the first enduring
foundation for the biological sciences. In the third century B. C.
Erasistratus, of the Alexandrian school, was the first to attempt a
philosophy of physical life — a theory of physiology. He gave
definite form to ;t theory, which had its origin among the pupils of
Plato, and which reached its highest development under Galen and
hie school. This theory is called the Pneuma Theory, and, accord-
ing to it, the Pneuma ZOtikon — life-giving spirit, or breath of

life — resided in the heart, while the Pneuma psychikon — the
soul — resided in the brain. Medical science having taken definite

26 INTRODUCTION.

and authoritative form under Hippocrates, and physiology having
been crystallized by the Pneuma theory of Erasistratus, there was
a lapse of 4(>o years before there appeared the spirit who was des-
tined t<» dominate the medical profession for more than thirteen
centuries.

GALEN.

In the second century a.d. Galenus, a surgeon in the Roman

army, made systematic dissections of the bodies of apes and other
animals. ( ialen realized that medicine and surgery could not suc-
ceed unless based upon an exact knowledge of the structure of the
body, and upon a knowledge of the vital functions ; and, to the
end last named, he performed vivisections upon apes and pigs,
establishing the functions of the vagus, or pneumogastric nerve,
and the intercostal nerves, and the effects of section of the spinal
cord. After collecting a great mass of morphological and physio-
logical knowledge he founded a system of medicine. His system of
physiology was based upon the Pneuma theory, which, briefly
expressed, was : Pneuma psychikon — the soul — resided in the
brain and nerves, and presented the psychic phenomena, thought,
sensation, and voluntary motion ; Pneuma zotihm — life-giving
spirit, or breath of life — entered the body through the lungs, re-
sided in the heart, .and expressed itself in heart-beat, pulse, and
bodily warmth ; while the Pneuma phydkon resided in the abdo-
men, and presented the functions of nutrition, growth, secretion,
and reproduction. No subsequent Roman even approached the
colossal work of Galen, so it is easy to understand that, after the
fall of Rome, his was the only authority recognized until the new
birth — the renaissance — of art, literature, philosophy, religion,
and science, in the fifteenth and sixteenth centuries. If, in all
those thirteen centuries, any man doubted the statements or theo-
ries of Galen, he did not publish it, for Galen's authority was un-
impeachable. The first recorded combatant of Galen was Para-
celsus (1493 A.D.). Though he founded an untenable theosophistic
philosophy, the simple fact of his impeachment of ( ialen's theories
set the scientific world thinking. The feature of his system was,
Unity in Nature ; Nature a macrocosmus, and Man a microcos-
mus. Early in the sixteenth century Vmdius, Eustactiio and
FaUoppia, through dissection, extended the knowledge of anatomy ;
while Servetus disproved Galen's statement that the blood goes
directly from the right heart to the left heart, and Argentieri con-
tended that the blood nourished the tissues of the body. These
advances prepared the way for the next great light in the renais-
sance of science.

HALLER. 27

HARVEY. (1578-1659.)

This great experimenter and observer was taught by his pred-
ecessors that the blood was in motion within the arteries and
veins, and that the heart movements were the cause of this motion,
but it remained for him to demonstrate that the arteries and veins
were connected by smaller vessels (though, through lack of a
microscope, he never saw them), and that the blood circulated
within a closed system of tubes from the left heart through the
arteries and capillaries, and back through veins to the right heart,
thence to the lungs, and completed the circuit by entering the left
heart. Xext to this great triumph stands that notable proposition,
first formulated by Harvey, " Onxne vivum ex ovo." The history
of this proposition is most interesting. Twice it has been refuted,
and twice the fallacies of the refutation have been demonstrated.
Established at first on an observation of higher plants and animals,
it was combatted by the early microscopists, who found, in their
nutrient infusions, a rapid development of infusorian life with no
discoverable eggs or germs. A century later Treviranus proved
the fallacy of this "Spontaneous Generation" theory through the
discovery of the real method of reproduction of these organisms ;
so the theory that " all life is front an, egg" had stood its first as-
sault. The improvement of the microscope, however, revealed
the microbe. Nutrient fluids were seen to be soon swarming with
life ; the Spontaneous Generation theory was again revived, Har-
vey's theory again combatted ; Pasteur has, however, in recent
times, with his more exact instruments and methods, established,
experimentally and conclusively, the verity of Harvey's propo-
sition, u All life 18 from an egg."

The microscope lias been mentioned. It was in the latter part
of the seventeenth century that Van Dyke and Leeuwenhoek
invented the compound microscope, and IJeeuwenhoek, with M<il-
pighi and Schwammerdamm, made rapid strides in histological re-
search. Up to the beginning of the eighteenth century, physiology
had aol been a separate and independent science.

HALLER.

It was Bailer who, by his power of systematizing and general-
izing, collected the facte peculiarly physiological, and constructed
them into his renowned work-, " Elements of the Physiology of the
Human Body." lint Bailer was, unfortunately, a philosopher
rather than a philosophical investigator. He promulgated two
theories which have had a retarding effect on Physiology; viz.,
The Preformation Theory and the Theory of Vital Energy. Ac-
cording to the first theoty the form of the organism, existed in the egg,
:in<l embryological development was simply increase in size; while.

28 INTRODUCTION.

according to the second theory the Energy of Idfe, is peculiar to
life, i.e., not transformable from physical and chemical energy,
and, for that reason, called Vital Energy. This theory of a
peculiar Vital Energy lias retained ;i most tenacious hold on
Physiology, and only through the combined efforts of a galaxy of
experimenters in the first three-fourths of this century has the
theory that the energy manifested in the phenomena of life is
peculiar to life been abandoned. For a time it was hoped that all
of the phenomena could be accounted for in the usual transforma-
tion forms of energy. More exact and extended recent experi-
mentation makes it evident that there is a transformation form of
energy peculiar to life. The living organism is not believed to he
able to make energy, hut simply to give it a new and unexpected
form under certain circumstances. It is important to note, in this
connection, that this newly discovered form of energy obeys, with
the other forms, the law of the conservation of energy.

At the end of the eighteenth century Priestly and Lavoisier dis-
covered oxygen. Girtanner demonstrated that it is this constituent
of the atmosphere which, in the lungs, effects the change between
venous and arterial blood.

JOHANNES MULLER.

The spirit which inspired and dominated physiological investi-
gation during the first half of this century was Johannes Midler.
Though he believed in a special Vital Energy, he believed that it
followed implicitly the laws of energy in physics and chemistry,
and set about, with physical and chemical methods, to investigate
the phenomena of living nature. Johannes Midler was an inde-
fatigable worker, an accurate and exact observer, a broad and
judicious generalizer, and a profound philosopher. He was master
of the whole field of Morphology and Physiology as it existed at
the beginning of this century. He founded the new sciences of
Comparative Physiology and Physiological Psychology, and laid for
modern experimental Physiology the broad and deep foundations
which have sustained the great superstructure erected by his pupils
and successors during; the last four decades. Soon after his death
physiologv was divided into chemical and physical physiology.
The physiological chemists of this century are Wohler and Liebig ;
Voit, Pfliiger, and Zunst, Kiibne, Hoppe-Seyler, Hammarsten,
Bunge, and Halliburton, Chittenden and At water.

The investigators in the field of physical physiology arc first of
of all, Ludwig, Weber, DuBois-Reymond, and Brucke ; then
Many, Claude Bernard, Helmholtz, Hering, Hitzig, (Joltz,
Preyer, et <il. Inasmuch as frequent reference must be made to
these men during the course of our study, a detailed account of
each man will not be entered upon here.

JOHANNES MVLLER. 29

The great discoveries of this century, which have been of the
greatest importance to physiology, are : (i) The Law of the Con-
servation of Energy j (u) The discovery of the cellular structure of
animal organisms; (in) The discovery of the genealogy of the
organic world ; i.e., The establishment of the Evolution Theory.

These three great principles have already been of inestimable
value to physiology, but their service has only just begun.

PART I.

GENERAL PHYSIOLOGY.

CHAPTER I,

THE PHYSIOLOGY OF THE CELL: CYTOLOGY.

A. LIVING SUBSTANCE: PROTOPLASM.

1. THE PHYSICAL PROPERTIES OF PROTOPLASM.

2. TIIK CHEMICAL PROPERTIES OF PROTOPLASM.

3. Tin: MORPHOLOGY OF LIVING SIT.STAXCE.

a. Tin: Stbuctttbe of Protoplasm.

b. Tin: Stki< tube of THE Cell.

(1) Cjlh, phi SHI.

(.') The Nucleus; Nucleoplasm.
(3) The Oentrosome.

C. FOBM AND BlZE OF Tin: ('ELL.

4. TIIK INDIVIDUALIZATION OF LIVING SUBSTANCE.

/;. TIIK PHENOMENA of LIFE.
l. NUTRITION.

". AB80BPTIOK and Excbetion.

//. Ml. I IBOLISM.

i < /<> mil ni Phases.

I 'I, </ i, ill I 'I,

; Morphological I'll" • .

.'. KOTO SENSORY ACTIVITIES OF I. IFF.
". M< > 1 1 < i s : ( on thai ri i.n v.
I>. SEKSIBILI TV : [BBITABILITY.

&EPROD1 I l [ON.

81

THE PHYSIOLOGY OF THE CELL.

THE PHYSIOLOGY OF THE CELL:
CYTOLOGY.

A. LIVING SUBSTANCE: PROTOPLASM.

1. THE PHYSICAL PROPERTIES OF PROTOPLASM.

One's knowledge of a substance is gained through the senses.
The most far-reaching sense — vision — is the one usually appealed
to first, and one naturally determines first of all whether the sub-
stance is solid or fluid, whether it is transparent or opaque.
Through other senses one determines whether the substance is
heavy or light, etc.

Protoplasm exists only in minute portions, so mixed with the
substances which it has formed that it is visible only through the
aid of a microscope. That instrument reveals protoplasm as a
viscous fluid. The consistency is more fluid in the active proto-
plasm of a growing plant or animal than in the dormant proto-
plasm of a seed. Whether protoplasm is thin viscous or thick
viscous in consistency depends upon the amount of water which
it imbibes. Seeds sometimes become very dry. When placed in
the ground they cannot germinate, — the protoplasm cannot pass
from its dormant condition to an active one, — until it first absorbs
water; a portion of which is absorbed by the protoplasm and a
portion by the stored nutriment of the seed.

In thin layers or threads protoplasm is gray and translucent.
In thick threads or globules immersed in water it seems to be
somewhat more strongly refractive than the water.

When a minute organism or cell, consisting of a drop of pro-
toplasm enclosed in a delicate membrane, is studied in distilled
water, it will be observed to swell up, almost bursting the enclos-
ing membrane, but there is no evidence that any of the proto-
plasm passed through the membrane. If one immerse- the or-
ganism in a five per cent, salt solution, it will shrivel, indicating
that something has passed out of the membrane, but there is no
evidence that any of the protoplasm has passed through the mem-
brane. Protoplasm imbibes water, but it is not diffusible.

Incidental to the observations just described, it would be noticed
that tlie protoplasmic organism sinks to the bottom of the dis-
tilled water, and rises to the top of the strong salt solution. — it i>
heavier than distilled water, and it is lighter than the salt solution.
Protoplasm has a specific gravity greater than 1. If one were to
increase the specific gravity of the surrounding liquid until the
protoplasmic body would just float, neither rising nor Billing, be
would have only to determine the specific gravity of the liquid to

THE CHEMICAL PROPERTIES OF PROTOPLASM. 33

know that of the protoplasm. In this way Jensen, in 1893,
found the specific gravity of a paramoecium to be 1.25. Living
organisms may change their specific gravity through the absorp-
tion and deposit of heavy mineral substances such as CaCO„ or
SiO., , or through the formation and retention of such substances
a> carbonic acid gas or fat.

2. THE CHEMICAL PROPERTIES OF PROTOPLASM.

As Nature's unaided vision reveals nothing of the physical
properties of protoplasm, so does her unaided taste and smell re-
veal nothing of the chemical properties of protoplasm. \Te bring
to the aid of these primitive chemical tests refined process of
analysis, through the aid of which one gains a knowledge of the
elements which combine to form protoplasm. Pure protoplasm
has not been analyzed, because it cannot be gotten in sufficient
quantity.

There are reasons for believing that pure protoplasm does not
differ much from albumin in composition. Egg albumin must
contain all of the elements found in protoplasm, because the pro-
toplasm of the chick is built up from the albumin of the egg.
Albumin consists of carbon, hydrogen, nitrogen, oxygen, and sul-
phur, with certain mineral salts, associated in loose chemical
combination — salts which represent phosphorus, chlorine, sodium,
potassium, calcium, iron, and magnesium. The analysis of the
bodies of animal and plant organisms reveals the universal pres-
ence in these bodies of the following elements : C, H, N, O, S, P,
( I. \a, K, Ca, Mg, and Fe. Rarely one or more of the follow-
ing elements is found : Si, Li, Fl, I, Br, Al, Mn.

•Iu>t why living matter should be constructed from the elements
named, rather than from such elements as lithium, berylium,
boron, titanium, chromium, zinc, lead, etc., has been the subject
ofsome controversy. Verworn (" Allgemeine Physiologie/'s. 106)
calls attention to the fact that the elements of which living matter
i- composed .ire element- of light atomic weight. The following
table may throw some light upon the question : —
3

:;i

//// PHYSIOLOG V OF THE CELL

Tl

— f

— _•

-

. =j

• - — r

r x / -

■

. -

' ' - '"

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—

THE MORPHOLOGY <>F LIVING SUBSTANCE. 35

The facts above tabulated justify one in making two generali-
sations : (i) The elements which enter into the composition of
living substance are, in general, those of lightest atomic weight,
(ii^ The elements which enter into the composition of living sub-
stance are. without exception, abundant elements of wide — prac-
tically universal — distribution.

The chemical compounds which are found in living matter may
be divided into organic and inorganic. The organic compounds
may be classified as proteids, fats, and carbohydrates. The pro-
teids are very similar to living protoplasm in composition. As an
example of proteids, one may take pure egg albumin, whose for-
mula, according to Hofmeister, is C>IUH:,.,.,X:,( >66S2. All proteids
contain C, H, X, ( ), and either S or P. The nucleo-proteids con-
contain phosphorus. Fats and carbohydrates are non-nitrog-
enous substances. The typical fat — tripalmitin — has the formula
( \H. ((.',, II ...,< >.,').,. The typical carbohydrate — glucose — has the
formula ( LH1206. Note that these compounds are both formed of
carbon, hydrogen, and oxygen, and that the proportion of oxygen
in the fat is very much smaller than that in the carbohydrate.
Some of the inorganic compounds associated with living matter
are: NaCl, Xa.CO.., Xa,HP()4, Ca3(P04).„ NaHC03, MgCl2,
KHSOr

3. THE MORPHOLOaY OF LIVING SUBSTANCE.
a. The Structure of Protoplasm.

If protoplasm be studied under very high powers of the micro-
scope it will present an appearance such as shown by Butschli in
the accompanying figures (Figs, la and 16). This appearance
has been differently interpreted by different observers. Butschli
and his followers contend that protoplasm is a " foam-like, alveolar
structure, like an emulsion, in which the firmer portion forms the
walls of separate chambers rilled with the more liquid substance"
(Wilson). Fleming, Van Beneden, Strasburger and others believe
'•that the more -olid portion consists of coherent threads which
extend through the ground substance," usually forming a fine
meshwork or reticulum (Wilson). Adopting the more generally ac-
cepted second interpretation, we have protoplasm represented by
two substances, (i) the more dense and refractive reticulum,
thread work, or spongioplasm, and, (ii) the less dense, ground
substance, cytolymph, or hyaloplasm. Lower powers of the micro-
Bcope reveal minute granule- which are shown by Butschli's fig-
ures to l.c located in the threads of the reticulum or spongioplasm.
Some of the granules may be only apparent, and represent the
confluence of several threads of spongioplasm ; but some are
undoubtedly actual granules of living substance.

36

THE PETSIOLOG V OF THE CELL.

These granules are culled microsomes, and have been beld by
some investigators to be the " elementary units of structure stand-
ing between the cell ami the ultimate molecules of living matter"
(Wilson).

It. Structure of the Cell.

Living substance or protoplasm exists only within structures
called cells. The early microscopists saw the little polyhedral,
cellulose chambers of plants, and chose the word cell as most ap-

FlG. 1".

Fig. Li.

[fMMfifrf

Epidermal cell of an earthworm (X 3000).

Expanded end of a rhizopod'a pseudopod
(X3( ).

propriate. The contents of this little chamber were collectively
called protoplasm by Mohl (1846), but its importance was over-
looked. Schultz, Kolliker, and others recognized finally that the
protoplasm is essential, and that the cell wall is unessential ; the
amoeba and the white blood-corpuscle, for example, having no
cell wall. Schultz (1863) defined the cell as "a simple globule
of protoplasm containing a nucleus." After the discovery of the
centrosome by Van Beneden (1870) it became necessary to define
the cell anew. In 1890 Bauer defined it as " a globule of proto-
plasm containing a nucleus and centrosome." But certain lower
forms of life, as most bacteria, have no nucleus or centrosome. In
1895, Yerworn of Jena defined the cell as " a body consisting es-
sentially of protoplasm in its general form, including the unmodi-

STRUCTURE 01 THE (ELL.

37

fied cytoplasm, and the specialized nucleus and centrosome ; while,
as unessential accompaniments, may be enumerated : (i) the cell
membrane (n) starch grains (in) pigment granules (iv) oil glob-
ules (v) chlorophyll granules." Wilson (1896) most effectually
defines the typical eell diagrammatically. (See Fig. 2.) ft A care-

Fi<;. 2.

Attraction Sphere inclosing the Centrosomes.

Nucleus

Plasmosome or

true nucleolus.

( lir. i matin-
net work.

Liuin-netwnrk.

Karyosome or

net-knot.

Plastida l> ing in
the oytoplasni.

Vacuole.

Lifeless"!' bodies
(lucta pi asm)
suspended in
the cytoplas-
mic reticulum.

Diagram of a cell. (After WlLS >v )

tul Btudy of this diagram in connection with Graf's drawing of a
nephridial cell from a leech (Fig. 3) will give the reader a clear
conception of the present knowledge of the structure of the cell.
The living -ill istanee of the cell is called protoplasm. That por-
tion of* the living substance which is outside of the nucleus is
called cytoplasm, while the living matter of the nucleus is called
nucleoplasm.

1. Cytoplasm. — In most unicellular organisms, and sometimes
in metazoa, the cytoplasm is differentiated into the inner endo-
plasm and a somewhat denser exoplasm. Thelatter produces the
cell membrane when that is present, or in its absence takes its
place. Cilia arc outgrowths from the exopksm. Wilson calls
attention to the fact, that " it appears to be a general rule thai the
onclens is surrounded by protoplasm of relatively slight differenti-
ation (endoplasm), while the more highly differentiated products
of cell activity arc laid down in the more peripheral region of the
eell. The fad thai the reticulum of the cytoplasm lias not been

38

THE PHYSIOLOGY OF THE CELL

found in :ill cells — especially certain planl cells — leads some
biologists to look upoD it as an incidental, or even accidental,
structure rather than a typical one. Besides the division of the
cytoplasm into exoplasm and endoplasm, it may be divided into
spongioplasm and cytolymph. The spongioplasm may be repre-

Fig

Section through a nephridial cell of tli>- leech, Clepsine. i Drawn by Arnold Graf from ■

of l * i — own preparations. |

The center oi tlie cell is occupied by a large \ acuole, filled n iib ;i watery liquid. The cyto-
plasm forms a very regular and distinct reticulum with scattered microsomes which become
very large in the peripheral zone. The larger pale bodies, lying in the ground-substance, are
excretory granules [i. e., metaplasm . The nucleus, al the right, is surrounded by ;i thick
chromatic membrane, is traversed by a very distinct linin-network, contains numerous scat-
tered chromatin-granules, and a Bingle large nucleolus within which is a vacuole. Above are
two isolated, nuclei showing nucleoli and chromatin-granules suspended on the linin-threads.
[Wilsoh : 'I'Ik Cell, in Development and Inheritance, 1896.]

sented by the peticulum made up of threads of dense protoplasm
in which the microsomes float, or, in the absence of a reticulum,
the spongioplasm is represented only by the microsomes which
float in the cytolymph. The plastids are differentiations <»f the
cytoplasm. They are capable of growth and division. They may
be looked upon as metabolic organs of the cell. Theyform Btarch
grains, chlorophyll grains, or pigmenl corpuscles, from constituents
of the cytolymph. Those that form starch grains are called

STRUCTURE OF THE CELL. 39

amyloplasts ; those that form chlorophyll are called chloroplasts,
and those that form pigment grains are called chromoplasts. In-
closed within the cytoplasm, and formed from it either by the
plastids, the nucleus, or otherwise, are many lifeless products of
cell metabolism — starch grains, chlorophyll grains, pigment grains,
oil globules, excretory grannies, etc. Some of these represent re-
serve nutriment, and some of them, waste matter. The vacuole is
a globule of food material, or of waste material in solution. It is
seen only in lower forms of plant and animal life.

2. The Nucleus : Nucleoplasm. — " A fragment of a cell de-
prived of its nucleus may live for a considerable time, and mani-
fest the power of coordinated movement without perceptible im-
pairment. Such a mass of protoplasm is, however, devoid of the
powers of assimilation, growth, and repair, and sooner or later
dies. In other words, those functions that involve destructive
metabolism may continue for a time in the absence of the nucleus ;
those that involve constructive metabolism cease with its removal.
The nucleus is generally regarded a controlling center of cell
activity, and hence a primary factor in growth, development, and
the transmission of specific qualities from cell to cell, and so from
one generation to another" (Wilson).

(a) The Structure of the Nucleus is shown, in a general
wav, in the diagram of the typical cell (Fig. 2). Note, in that
figure: (a) The nuclear membrane; (ft) The nuclear reticulum
divided into (i) the chromatin reticulum, and (n) the linin reticu-
lum ; if) tne Nucleoli represented by (i) the true nucleolus or
plasmosome, and (n) the net-knots or haryosomes ; (o) The nuclear
sap or karyolymph which tills the meshes of the network.

(6) The Chemistry of the Nucleoplasm may be briefly
summarized : (a) Chromatin is the substance which forms the
chromatin reticulum and the karyosomes. (ft) Limn is the sub-
stance which forms the linin or achromatic network. (;-) Para-
Hnin forms the karyolymph or nuclear sap. (d) Pyrenin forms
tin- plasmosomes. (•) Amphipyrenin forms the substance of the
nuclear membrane. It is probably identical with linin (Wilson).

■ \. The Centrosome. — This body is now generally regarded as
the especial organ of cell division and in this sense as the dyna-
mic center of the cell. The centrosome was discovered, and de-
scribed by Van Beneden (1876-1883), and named by Boveri
1888). The structure of the resting centrosome is sufficiently

shown in the diagram of the cell. It IS shown there lying in the

cytoplasm beside the nucleus, — its typical position, — though it may
lie within the auclear membrane. The function of the centro-
-onie U bo prominent n pari of the process of cell division thai it
will be described under reproduction of the cell.

40

THE PHYSIOLOGY OF THE CELL.

c Form and Size of the Cell.

The simplest form is spherical, but many ('actors work together
to modify this primitive form, so thai one may find cells that are
regularly or irregularly spherical, polyhedral, prismatic, cylin-
drical, discoidal, fusiform, or linear. Some cells, as the ganglion
cells, may be too irregular to admit of any of these rather definite
terms.

The ovarian egg of the bird or reptile is a cell, which differs
from the typical cell only in having a prodigious store of fat and
other food materials, thus stored for the nourishment of the de-
veloping animal. The ovarian egg of an ostrich is several centi-
meters in diameter. On the other hand some cells are exceedingflv

O */

minute. Eberth's Typhus bacillus is about <).!>/< in diameter, i.e.,
eleven thousand, lying side by side, would hardly reach one centi-
meter. The average animal cell is about 10// in diameter.

4. THE INDIVIDUALIZATION OF LIVING SUBSTANCE.

Definition. — An organic individual is a wnijied mass of living
substance in a form capable of maintaining itself. The smallest
mass of living substance capable of maintaining itself is a cell.
The cell is, therefore, an elementary organism ; it is, at the same
time, the lowest order of individual, or an individual of the first
order. Ex. : Amoeba Paramecium, Stentor, Vorticella, Desmid,
Yeast-cell, Protococcus, Ovum, Leucocyte. Note that, in the
examples cited, all but the last two are actual, independent indi-

Fig. 4.

Protospongia Haeckelii, an individual of the II order.

viduals leading a separate existence ; while the ovum is a single
cell capable of producing an individual capable of self-maintenance,
and the leucocyte is virtually and potentially an individual, but it

THE INDIVIDUALIZATION OF LIVING SUBSTANCE.

41

has merged its individuality in that of the great organism of which
it is a part. Thus we may find two series of examples, one rep-
resenting actual, and one virtual individuals. The latter, in turn,
may be subdivided into a series representing individual develop-
ment (ontogenic series), and one representing stages of tissue de-
velopment.

Colonies of cells, similar as to form and function, constitute
individuals of the second order. Ex. : Protospongia, Eudorina,
Morula or Blastula stage of development, any tissue. In the
animal kingdom Protospongia Haeckelii (Fig. 4), and in the plant,
Eudorina elegans (Fig. 5), we see examples of colonization and
combination for mutual help and protection. This marks a long
step in the advance of living organisms, but all of the cells are
practically alike in form and function.

.V unified mass of living substance, composed of two or more
colonies of similar cells, — two or more tissues, — forms an indi-
vidual of the third order. Ex.: Hydra (Fig. 6), the Thallophytes

Fig. 5.

Fig. 6.

Eudorina elegans, an Individual of the III order. Hydra, an Individual of the ill order.

among plants, Gastrula stage of development, an organ. This
marks another long Btep in organic evolution — specialization of
structure and function.

Individuals of the fourth order are composed of organs, tissues,
and cells arranged in systems, such as the digestive Bystem. Ex.:
Mini, Tree. Men and other animals organize colonies or states
which represenl individuals of the fifth order. The following
table gives ;i general view of the individualization of living sub-
stance :

r_-

THE PHYSIOLOGY OF THE CELL.

ii.

in.

v.

VI.

I'll W. [NDIVIDUALS.
T \ \u\nM |< >| RIES.

VlRTl \l. lM'l\ ll.l ILS.

Ontogi kii Serii s.

A ii i ' i I'a. I >eaniid, Paramo - < tyum, n itli
cium, Diatome, Vorticella, tation nucleus.
Protococcus.

Protos] gia, Eudorina.

Bydra, Thallophyta.

Man, Tree.

i- t Morula,
tation -

V Blastula.

< rastrula.

Adult : Man.
Colony or State.

BlSTOG) KH Si RIES.

( ell : Leucocj te.

Tissue: Cartilage.

( nrgan : Stomach.

Systems of Organs:

'Man.

B. THE PHENOMENA OF LIFE.

1. NUTRITION.

The general term nutrition includes all those activities of the
organism directed toward the procuring of food, digestion, ab-
sorption, the chemical changes within the ti>sucs (metabolism),
respiration, and excretion.

a. Absorption and Excretion.

1. Absorption and Excretion of Gaseous Material. — Every
living organism ceases t<> live when deprived of oxygen. Oxygen
exists in a gaseous form as a constituent of the atmosphere (21
per cent.); and it is dissolved in water, so that it is accessible to
terrestrial and aquatic plants and animals. For multicellular
organisms the law may he stated thus: Every active cell of every
living organism requires oxygen for the maintenance of activity.
In the whole organic kingdom the absorption of oxygen — Respi-
ration — is associated with the excretion of carbon dioxide and
water, and with the production of heat. How are we to interpret
these general facts? It was formerly believed that oxygen di-
rectly oxidized the living matter in the same way that it directly
oxidizes the carbon and hydrogen of a candle, this process result-
ing, in both cases, in the formation of carbon dioxide and water,
and the production of heat. Pfluger of Bonn found by experi-
ment, that frogs can live several hours in an atmosphere of nitro-
gen, and continue to produce carbon dioxide. From this and

THE PHENOMENA OF LIFE. 43

other experiments Pfluger concluded, that "The first Impulses to
the chemical processes of respiration are not given by the oxygen
which enters from without ; but that primarily a decomposition of
molecules takes place within the protoplasm, resulting in the lib-
eration of carbon dioxide, and that hence the incoming oxygen
effects a simple restitution of the integrity of the new molecules
which are formed." This gradual breaking up of the highly com-
plex protoplasm into simpler and simpler bodies which combine
with oxygen, liberating the energies for the life processes, is called
katabolism or destructive metabolism. The reverse process — an-
abolism, assimilation, or constructive metabolism — is one of the
most interesting and important processes in the realm of nature.
Inasmuch as katabolism, or destructive metabolism, ends with the
liberation of carbon dioxide and water, with the consumption of
oxygen, and the production of heat, may we not expect that the
building up of living matter — anabolism, assimilation, constructive
metabolism would begin with the consumption of carbon dioxide
and water, and the liberation of oxygen, and that the process would
require heat from some external source? This process, which one
would expect, is exactly that which is actually going on in nature.
Every green plant absorbs, as food, carbon dioxide and water ;
these arc taken into the protoplasm, and, under the influence of
the green plant coloring matter — chlorophyll — and of the light
and heat of the sun, the carbon dioxide and water are combined
to form dextrose (Ct.H1906). After dextrose is once formed, the
protoplasm of the cells i< able to appropriate it to build up proto-
plasm. In recapitulation we may say, then : (i) All living cells
absorb free oxygen in their respiratory process. (n) All living
alls excrete carbon dioxide, in their respiratory process, (in) All
[in, a pin, it nils absorb carbon dioxide as food, (iv) All green
plant rills excrete oxygen as a waste product in their nutritive process.
'1. The Absorption and Excretion of Liquid Substances.

— Most of the water used in the plant economy i< absorbed in the
fluid state. .Much water leaves the bodies of both plants and
animals in the form of gas or vapor, but a large part of this is
not the product of excretion, it is the product of evaporation.
All of the water used in the animal economy is absorbed in the
fluid state. Moreover all inorganic matter is absorbed into cells
in the form of solution in water. With few exception- it i- also
true thai the food of mosi animals, though received into the ali-
mentary canal in the solid state, is changed to the fluid state — by
solution in water — before it is absorbed by the cells which line
the alimentary canal. A mosi interesting problem presents itself
at this point — The selective powers of living <-<Hs. Qving side by
side in the -<■;, are one-celled animals, — some species bearing sili-

cious -hell-, while other ypecies hear calcareous shells. The fir.-t

4-t

THE PHYSIOLOGY OF THE CELL.

species has selected the silica from the sen water, while the second
has selected the calcium carbonate. Growing side by side in the
shallow sea water may be several species of the seaweed — Fucus,
— but each species will have -elected differenl Inn constanl pro-
portions of the mineral matter dissolved in the sea water. The
following table from Pfeffer, cited by O. Elertwig, illustrates the
point in question : —

A-li-l ..\-i I i i ENTS.

Potassium oxide . . . . Ka0

Sodium oxide N;i._.o

( !alcium oxide ( !aO

Silica SiO.

Focus
Vesiculosus.

24.54
9. 78 I
1.35?

NODOSl 3.

111.07 .

26.59?

12.80?

1.20

Fucus
Serb \ i i -.

I M

31.37
16.36?

ii. \»

Laminabia
Digit vt \.

j j. in

24.09

11.86

1.569

Iii the bodies of higher animals each cell is bathed in blood, or

lymph, containing many food materials in solution, but the bone
cells select the ( !a( !( )., and ( 'a.,(P04)2, while the muscle cells select
from the nutrient fluid proteids with various salts; and so on,
every cell selecting the needed food, and rejecting what is not
needed.

3. The Absorption of Solid Bodies. — Can living cells absorb
and appropriate as food solid bodies? This can only be accom-
plished by cells devoid of a cell membrane, or cells having holes
in the membrane. As most cells are enclosed in a membrane, it is
clear that the absorption of solid bodies is limited to naked animal
cells, i. c, to the Rhizopoda and Ciliata among lower animals, and
to leucocytes, and possibly ciliated epithelium, among higher ani-
mals. The ability to absorb particles is of very great importance
to the higher animals, and is utilized under the following circum-
stances : (i) During embryonic development in absorbing use-
less parts, (ii) During life in disposing of solid impurities,
broken-down, red-blood corpuscles, etc. (in) During infectious
disease the leucocytes constitute a bodyguard in opposing the
spread of microbes in the blood and tissues by simply absorbing
and digesting them. Metchnikoff says: "Between micro-organ-
i>ms and leucocytes an active war is raging. This is settled in
favor of one or the other party, resulting in the death or the re-
covery of the affected animal."

h. Metabolism.

'flic term metabolism is used to designate the chemical changes
to which matter is subjected under the influence of life. When
the chemical change combines simpler into more complex sub-

THE PHENOMENA OF LIFE. 45

stances, the term anabolism, or constrictive metabolism, is used ;
while for the reverse process katabolism, or destructive metabolism.

is used.

1. Chemical Phases. — It has already been stated that under
the influence of chlorophyll and sunlight the plant cell is able to
cause a combination of carbon dioxide and water to form dextrose,
and that the cell protoplasm has the power of replenishing its sub-
stance from the dextrose ; further, that through successive combi-
nations with oxygen the protoplasm is, step by step, reduced to
simpler compounds, until it is finally expelled from the organism
in the form of carbon dioxide and water. This is, in fact, about
all that is known with absolute certainty. It was formerly be-
lieved that the combination of carbon dioxide and water was di-
rect, and as follows : 6CO.,+()H,0=C,.H,,0,-+60. , ; but it is
now believed that the combination is indirect, and somewhat as
follows : C( )L, + H20=024-CH20 (Formic Aldehyde) and 6CH2< >
=CI.H1.,()). (Dextrose). It has been convenient to describe the
two extreme steps of the process of metabolism, first the combina-
tion of the inorganic elements of our environment — CO„ and H„0

2 2

— within a green plant cell, under the influence of the energy of
the sunlight, to form dextrose, and finally the katabolism, or de-
structive metabolism, of the animal cell into the same inorganic
elements. Between these two extremes are many intermediate
steps. In the plant kingdom the steps are ascending ones, for the
protoplasm of the plant cell is able to make a long list of carbo-
hydrates, then of fats and oils, then of proteids, and finally, to re-
plenish its own substance, or to make protoplasm. The slight
activities of the plant require katabolism of living substance for
the liberation of the needed energy, but, on the whole, anabolism,
or constructive metabolism, predominates, and the plant kingdom
bequeaths to the animal kingdom a rich legacy of starch, cellulose,
sugar and other carbohydrates, of oils and of proteids. Animals,
on the other hand, are unable to appropriate either the free inor-
ganic elements or the free sun-energy of their environment ; they
depend directly or indirectly upon plants or plant products. The

active life of animals involves the dissipation of much energy.

This energy ie Liberated by the katabolism of living substance j so,
in the animal kingdom, katabolism, or destructive metabolism,
predominates.

The following figure illustrates the relation of anabolism and
katabolism, — of constructive and destructive metabolism in the

plant and animal kingdom. (See Fig. 7.)

In the successive metabolic changes ferments play a very im-
portant part. A ferment i- n proteid body, capable of causing a
chemical change without itself being consumed or essentially
altered. It \- clem- from this definition thai ;i very small amounl

4G

THE PHYSIOLOGY OF THE CELL.

of ferment is able to accomplish a very large amount of work.
Examples : Diastase, Ptyalin, Pepsin, etc., etc.

Fig. 7.

Plants.

PrOt<>l>1nxin

Annuals.

**/

"^

Heat te made

&

Heat is

latent. .£,

/\^>

^

Prolei

<?s

libera tul.

/V^/

v-/\

/1y^ Carbohydrates
% Starch

co2 B20
NaCl. KNOsCa UPO{ Fe2(SOt)

HKSC-t CO2 II20 COX2Ht

Diagram illustrating the relation of plants and animals t<i anabolism and katul«>lisin.

2. Physical Phases. — Incidental reference has already been
made to the liberation of energy and to the making latent of
energy. As stated in the introduction, the law of the conser-
vation of energy applies to animal bodies as it does to a steam
engine.

(a) Forms of Energy. — (1) Atomic Attraction or Chemical
Energy, (11) Molecular Attraction or Cohesion, (in) Molar At-
traction or Gravitation, (iv) Heat, (v) Light, (vi) Electricity,
(vil) Magnetism, (vin) Mechanical Energy, Pressure, Tension.

(b) The Cell's Source of Energy (a) Chemical Energy. —
The combination of atoms into molecules leads to a liberation oj energy
while fh<j separation of a molecule into its atomic elements requires
energy. For example, the combination of hydrogen and oxygen
into water liberates heat ; while the decomposition of water into
its constituents requires the expenditure of energy. But in the
usual chemical reaction there is both a separation and a combina-
tion of the atoms.

This leads to the formulation of the following law : If, in a
chemical reaction, stronger affinities arc satisfied than broken, energy
irill be liberated ; if, on the other hand, stronger affinities are broken
than satisfied, energy will be required to bring about the reaction.
Examples :
(1.) C,H.(CrH,,.COO-),, + 163G = 55H20 + 57COa + Energy
(11.) 6'CO + 6H20 + Energy = C(.HI20,. + 602.

Potential chemical energy is the common source from which
spring all the other forms of energy involved in the phenomena
of life.

(/5) Energy of Heed and light. — The source of tins form of
energy for the realm of living nature is sunlight, and, as pre-

MOTO-SENSORY ACTIVITIES OF LIFE.

il

viously stated, it makes its entrance into this realm through the
chlorophyll-bearing plant-cell. Moreover, not all of the energy
of sunlight is thus utilized, the cell selects energy as it does mat-
ter. Pfeffer's observations have led to the following figure. (See
Fig. 8.) As to the action of the warmth of the sun's rays upon

Fig. 8.

Light energy i degree of illumination
/

Cht mical activity

Curve of AnaboUsm tin rate being most rapid when
the light comesfrom the yellow of the spectrum.

A ' B C1 D ' E F I G ' H

lied Orange Yellow Green Blue Indigo

Pfeffer's diagram showing the relation of ligbt to assimilation in chlorophyll-bearing plants.

animal metabolism, it is rather indirect than direct, as it simply
economizes animal heat and so decreases katabolism or destructive
metabolism. The same may he said of such artificial measures as
shelter, clothing and heating, — they all economize animal heat,
thus decreasing katabolism.

(c) The Cell's Manifested Energy. — This appears in the
form of cell-motion, of heat, and in certain organisms in the form of
light or of electricity.

2. MOTO-SENSORY ACTIVITIES OF LIFE.

Let us, for a moment, recall Spencer's definition of Life: "Life
i- the continuous adjustment of internal relations to external rela-
tion-." The same idea may be stated in slightly different terms :
Life in an organism is ;i correlation of energies, manifested by a
continuous adjustment of it- internal activities to its environment.
All the activities of an individual may be divided into two classes :
1-t. Egoistic Activities — which contribute to self-preservation j
Egoism : Individualism : 2d. Phyletio Activities — which contribute
to the preservation of the nice; Phyleticism ; Altruism. In the

lii-t case We find th<' organism in ;i Struggle lor life — life of self;

in the second case we see the organism sacrificing self for the pres-
ervation of the species. Applied more specifically to physiology,
the fir-t class of activities are those which contribute to the pro-
curing of nutriment, to self-defend against danger, and, in higher

Is THE PHYSIOLOGY OF THE CELL.

animals to the pursuit of pleasun ; while the second class is repre-
sented by reproduction, protection of offspring, etc., and in higher
animals philanthropy. Self-defence as well as the procuring of
food usually involves motion ; frequently also locomotion, od the
part of the organism. Motion is always in response to a stimu-
lus : but response to a stimulus involves irritability. It must be

evident, then, thai the activities of the to-.-cn.~ory organs and

tissues are inter-dependent and thai they must follow a particular
sequence. Let us turn our attention first to motion and contrac-
tility.

a. Motion and Contractility.

For the most part the motion of living organisms is due to their
possession of the property of contractility, but there are among the
plants various other methods of moving the parts of the individ-
ual, or even of moving the whole individual (locomotion), than
through contractility of living substance. It would seem as if
Nature had tried various experiments and had finally in the higher
animals specialized the property of contractility as the most efficient
method of producing motion.

1. Motion Without Contractility. — (a) Motion Through
Swelling of the ( !ell Wall. — The spores of the common horse-
tail rush, Equi8etum, are provided with four little cellulose ap-
pendages (elaters) which wrap tightly around the body of the spore
when moist and extend when dry. The alternation of these two
conditions, accompanied by an alternation of flexion and extension,
causes the little spore to move slowly over the surface of the soil,
to some distance from the parent plant.

(b) Motion Through Change of Cell Turgor. — The
closing of leaves at night and their opening in the sunlight is
a phenomenon known to every school child. How do the leaf-
lets of the clover, oxalis, or sensitive plant close together? In
the axil of every leaf is a motile organ composed of thick-walled
parenchyma cells between the fihro-vascular bundle and the epi-
dermis below, while the fibro-vascular bundle, though flexible, is
not extensible. The tissues above the fibro-vascular bundle are
very scantily represented. When the parenchyma cells above
mentioned become turgid with water'the leaf-stalk is erected ; if
the water is suddenly allowed to escape from the cells the leaf
falls to the nocturnal or sleeping position by its own weight.
When the proper stimulus comes, the protoplasm imbibe- water
again and the leaf is erected.

(c) Motion through Change of Specific Gravity. — Cer-
tain marine animals of low rank ( Radiolaria, Siphonophora) utilize
their own excretions to buoy them up. By retaining their carbon
dioxide it so decreases their specific gravity that they rise to the

MOTION AND CONTRACTILITY,

49

top of the water. On the other hand, by giving off the carbon
dioxide, or by deposit of calcium salts or of silica within their
tissues they will again sink.

(//) Motion through Secretion. — The movements of des-
mids and diatoms were, for a long time, a subject of study. It
finally became apparent that the minute organism was leaving be-
hind it a little trail of secreted mucus, which served the double
purpose of anchoring it to its place and of pushing it along.

(,) Motion through Growth-tension. — The seedpodofthe
touch-me-not grows in such a way that the opposite segments exert
a nicely-balanced tension against each other. If the ripe pod be
gently pressed the equilibrium is destroyed and the pod flies to
pieces, throwing the seeds out.

2. Motion Through Contractility. — (a) Amoeboid Motion. —
The amoeba when in a state of rest is spherical, and presents
to the medium in which it floats the minimum surface. Its
motion consists in the pushing out of a portion of its periphery.
(See Fig. 9.) This act increases the surface exposed to the me-

Fig. 9.

An amoeba in different phases of motion {A be). Ciliated epithelial cells (J? a). Sperma-
tozoa with motile Qagella (lib).

dium and thus increases the opportunity for the exchange of oxygeD
and carbon dioxide. It also increases the opportunity to get food.
The hungry amoeba is always active. The extensions of its proto-
plasm— it-' pseudopodia — may !><■ numerous, and they vary from
minute to minute. This form of motion is observed also in the
white blood-corpuscles or leucocytes.

(h) Ciuaky Motion. — Many cells are provided with fine pro-
toplasmic extensions, which are permanentand maycoverthe whole
aurface of the cell, or a limited surface, and may !»<• numerous or

few. In active '•••11- the ''ilia arc in ;i -late ofconstanl motion, which

consist* iii ;i quick whip-like motion in one direction, followed by
-.: alow return. All of the cilia on the end of a ciliated cell of the
human respiratory tract (Fig. !>, B <>) move in the same direction
4

50

/ '///■ /'// ) -i"i '". V "i i in: (in

hi the same time. Furthermore, fill of the cilia of all the cells
in anv region acl in unison, an undulatory motion running over
the whole surface. The result of such a movcmcnl of the cilia
is to carry over the surface any small particles or accumulations
of secretions. Cilia arc capable of a prodigious amount of work.
The ciliated epithelium of a frog's (esophagus will carry a 7o-
mgm. lead weighl up a fiO-degree incline when the lead presents
;i> much as 'J'1 square millimeters. One form of ciliary motion
is thai presented by the spermatozoa. (Fig- '•'• B b.\ Here the
din cilium, or Hagellum, possesses a -cull-like motion, which pro-
pels the spermatozoon through liquids or over moisl surfaces.

(c) Mrsii i.ai: Motion, or Motion by Fibrillary Con-
tractility.— A third form of motion is that through contraction
of fibrillse. Contractile fibers appear very low in the animal scale.
The Stentor, — Protozoa, Ciliata, — (See Fig. 10, a, b), possesses
numerous fine fibrillse in the exoplasm of the cell. Through the
contraction of these fibrillse the body may retract upon the little fool
until it assumes a nearly spherical form. The closely related Vror-
ticella has ;i long slim pedicel to its bell-shaped body. The stalk
has the property of retracting into a closely coiled spiral, a striking
view under the microscope. Figure L0, c, r/, e, shows the mechan-
ism which produces this remarkable effect. There is a single con-

Fig. 10.

[Uustrating fibrillary contractility: a. Stentor open 5 contracted.

contracted, with e) section of pedicel 01 same. / and g Neuro-muscle cells of a
coelenterate. Note that the nucleated body of these cells possesses a sensitive, tactile flagellum
(*), and a contractile fibrilla < /«)• The second one of these cells ciatly interest

cause the thread of protoplasm betwi lj of the c<-ll and the motor fibrilla is the

functional equivalent of a motor or efferent i

tractile lil>ril passing spirally down the inside of the sheath of the
pedied. Contraction of this fibril tend- to straighten it, throwing
the pedicel in to a spiral. Next in the progressive series the neuro-

SENSIBILITY: IRRITABILITY.

51

muscular cell of the medusa may be named. (See Fig. 10, f,g. )
Muscular tissue is fairly well developed in Vermes, and very
highly developed in the higher Arthropoda, especially the insecta.

Figure 11, a, 6, c, shows some forms of muscle fibers or cells from
vertebrate animals. Figure 11, d} shows a portion of a fibrilla
from a muscle fiber of an insect's wing. For a further description
of the miiM'le-tissue of the higher animals see the anatomical in-
troduction t<» the next chapter.

Fig. 11.

c J,

a. Kon-etriated muscle cell. ''. Striated muscle cell of frog's heart, c. Striated muscle
cell of mammal's heart. </. Striated muscle cell of insect's wing.

Muscle tissue is sensitive to various stimuli applied either di-
rectly to the muscle or indirectly to the nerve which supplies
tin/ muscle. When stimulated, the muscle responds by making a
contraction which consists in a decrease in length with increase of
the thickness, the volume remaining the same. Other important
changes take place in a muscle-cell incident to its contraction, viz.:
The chemical changes which liberate the mechanical energy of
motion, also a certain amount of heat energy. These changes

will be discussed at length in the chapter on (Ik; physiology of

contractile and irritable tissues.

//. Sensibility : Irritability.

The mosi noticeable foci observable in the Vorticella is its mo-
tion. After observing tin- motion for a time, one asks: Why
does it move? II' the microscope slide upon which it i> resting
be jarred, or if it lie touched l>\ some foreign body, the contrac-
tion will take place. Evidently the organism as a whole, or some
specialized portion of it, \- sensitive to these mechanical stimuli.

52 THE PHYSIOLOGY OF THE CELL.

When the amoeba, resting quietly on the slide, suddenly thrusts
out a pseudopodium the immediate cause is do1 so evident. The

cause is internal. The amoeba is hungry, and like all hungry
organisms, it starts upon a foraging tour. In every ease motion,
indeed all cell activity, is in response to stimuli. The ability to
respond t<> stimuli is e;dled irritability. This is the characteristic
of living matter, by which it is susceptible to changes in its en-
vironment; it is the primary distinguishing feature of living
matter. Without it the living organism, being unconscious of
changes in its environment, could originate no activity which
would bring it into harmony with its surroundings, and its de-
struction through hunger or accident would inevitably soon ibllow.
A complete, successful, adaptative action then requires : 1st, Irri-
tability; 2d, Motion and coordination in space and time.

Some stimuli are external to the organism and apparent to the
observer; others are internal and not apparent. The invisible
stimuli are just as real as the visible ones. The internal stimulus,
which starts the amueba in quest of food, is probably a chemical
one.

(1) Stimuli Classified. — The following forms of energy act as
stimuli for most cells : (i) Heat, (n) Light, (in) Electricity, (iv)
Mechanical Stimuli, (v) Chemical Stimuli.

(2) Action of Stimuli. — (a) The same stimulus may produce
qudte different effects in different organisms. (Ex. + Heliotropism,
+ Chemotropisni, + Galvanotropism.)

(6) Quite different stimuli will produce the same effect in the same
protoplasmic body, IF the sensitive body is highly specialized, e. g.}
a muscle-cell responds to all stimuli by contracting, a gland-cell
by secreting, while the stimulation of the optic nerve can only pro-
duce the sensation of light.

(c) However localized the application of the stimulus, the effect is
always transmitted to mare or less remote parts of the organism :
therefore, we must infer the conductivity of living matter.

(d) Stimuli are more rapidly transmitted in animal than in plant
bodies. [Human nerves, 34 ft. per second. Plant tendril 1 ft.
in several minutes.]

(r) The action of stimuli is more or less transient, i. r., the stimu-
lated organism returns after a short period, more or less completely,
to its former state of rest.

(/) Over-stimulation always leads to exhaustion, recognized at
the point where even a strong stimulus fails to elicit a response.

c. Reproduction.

Reproduction has already been mentioned as one of the phyletic
or altruistic functions for the reason that it invariably involves on
the part of the individual sacrifice of self for species.

In a general way the lower animals undergo a greater self-sac-

REPRODUCTION.

53

rifioe in the reproduction of offspring while the higher annuals
undergo a greater self-sacrifice in the support and protection ot
offspring. Let us proceed to the description of the phenomena ot

cell reproduction.

1 Cell-Reproduction.— It was demonstrated by V irenow that
every cell is from a cell—" Omms cellula e cdluki."

Fig. 12.

The lower figures Illustrate

l.in-.t ox Amitotic eeU-diviiion. I 5 Division of the Amaba.
thedlfrWonof theStenlor. n. nucleus; «•. Contractile vacuole,

•■ \., spontaneous generate f cells occurs either iu plants or

in animals The many millions of cells of which the body o
man \. composed bave been produced by the repeated division oi

,„„. „.|| fcne ovu/m} ;,, which the life of every animal con mces.

— Hertwig.

:.i

THE PHYSIOLOGY OF THE CELL.

The re are two methods of cell-reproduction — direct and indirect.

(,,) I n the I >i rect ob A mitotic M ethod t be division i >f the
cell protoplasm usually begins in the nucleus followed by the cyto-
plasm. The contractile vacuole usuallytakes pari in the division.
(Sec Fig. 12.) This form of cell-reproduction may lie observed
" in glandular epithelia, in the cells of transitory embryonic en-
velopes, and in tumors and oilier pathological formations." —
Wilson.

(/,) The [ndirect : Mitosis ob Karyokinesis. — In this
method the nucleus plays the principal role, the chromatin pre-
senting a series of striking appearances, called the karyokinetic
figures. This form of cell-reproduction is now held to l>c typical
for Dearly all healthy nucleated cells.

Karyokinesis, mitosis, or indirect cell division, presents a very
long series of changes sufficiently different one from another to
lead to the description of twelve to fifteen different stages. < >.
Hertwig and Wilson use four principal phases, one phase fre-
quently representing several stages.

Following these authors mitosis may be thus briefly summa-
ri/.ed : In its vesting condition, which immediately precedes mitosis,
one may observe a walled nucleus, with granular chromatin and a
more or less clearly defined centrosome, which may have pre-
viously divided, but which is dormant.

Fig. 13.

(M)

Prophases of Karyokinesis. /. Division and migration of centrosome; 77. Resolution of chro-
matin into well-defined thread; III. Segmentation of same into chromosomes; IV. develop-
ment of amphiastt rs; chromosomes equatorial. [ Wilson.)

(«) The Prophases or preparatory stages. (Fig. 13.) (i) Division
of the centrosome and migration of each young centrosome, along

REPRODUCTION.

55

Fig. 14.

the circumference of the nucleus to an opposite pole of the nucleus.
(n) Resolution of the chromatin substance of the nucleus into a
well-defined thread or spirem, which is
coiled within the nucleus, (in) Segmen-
tation of the spirem into a definite number
of chromosomes. " Every species of plant
or animal has a fixed and characteristic
number (8 to 36, 10 in man) of chromo-
somes which regularly recurs in the division
of all of its cells. In all forms arising by
sexual reproduction the number of chro-
mosomes is even." (Wilson.) (iv) De-
velopment of the Amphiaster which consists
of two polar asters, in the center of each
of which lies a centrosome, also the spindle.

Metaphase of Karyokiuesis.

(Wilson.)

The aster lies in the

cytoplasm, while the spindle, formed of numerous meridional

Fig. 15.

Anaphases of Karyokiuesis. (Wilson.)

Fig. 16.

fibrilhe, formed from the achromatic network, occupies the nucleus,
whose walls have in the meantime disintegrated and disappeared.
(v) The chromosomes assume a position in
the equatorial plane of the spindle forming
the equatorial plate.

(,'i) Metaphase. (Fig. 14.) Longitudinal
division of each chromosome. "The
daughter nuclei receive precisely equiva-
lent portions of chromatin from the mother
nucleus." (Wilson.)

(j) Anaphases. (Fig. 15.) (i) Diver-
gence of the two sets of daughter chromo-
..I Karyokii.. i somes toward tin' poles of the spindle.
Probably drawn by the meridional libers
of tin' spindle, which seem to he attached to them, (n) The
divergence of tin- daughter asters reveals an inner spindle, this
lir-t visible al the equator of the nucleus, and called the interzonal

Telophase
(Wilson.)

56 THE PHYSIOLOGY OF THE ('ELL.

filters, (in) Division of the centrosome preparatory to the next
mitosis.

{<)) Telophases. (Fig. 10.) "The entire cell divides in two in
a plane passing through the equator of the spindle, each of the
daughter-cells receiving a group of chromosomes, half of the
spindle and one of the asters with its centrosome." (Wilson.)
(n) The chromatin becomes distributed in granular form, as
found at the beginning, (in) The nucleus provides itself with
another nuclear membrane.

CHAPTER II.

THE PHYSIOLOGY OF CONTRACTILE AND IRRITABLE
TISSUES. INTRODUCTION.

A. PHYSICAL INTRODUCTION.

1. ELEMENTS AND BATTERIES.

2. KEYS AND ELECTRODES.

3. METHODS OF MODIFYING THE CURRENT.

4. THE INDUCTORIUM.

5. THE MEASUREMENT OF ELECTRICITY.

6. METHODS OF RECORDING RESULTS.

B. ANATOMICAL INTRODUCTION.

1. THE STRUCTURE OF MUSCLE.

2. THE STRUCTURE OF NERVES.

3. THE MUSCLE-NERVE PREPARATION.

THE PHYSIOLOGY OF CONTRACTILE AND IRRITABLE

TISSUES.

A. THE MUSCLE-NERVE PREPARATION.

1. STIMULI.

2. CHANCES WHICH TAKE PLACE IN A MUSCLE IN RESPONSE TO

STIMULI.
<i. Change in Form.

( 1 ) < '/m iiiji i a Length.

Change in the Transverse Dimensions,
Tin ]\'iirl; Done hi/ n Contracting Muscle.

b. Chemical Changes which take Place in a Conteacting Muscle.
'■. Thermal Changes which take Place in a Contracting Muscle.
</. Electrical Changes which tare Place in a Contracting Mi scle.

:;. THE RELATION OF THE NERVE TO VARIOUS STIMULI.
•i. Properties of Nerve Trunks.
i>. Conductivity.

c. [rritaeilitt.

'/. I'i n qbr's Law op Contraction.

e. Till. Aimm.k \TioN OP THE Laws OP ElECTROTONUS.

B THE GENERAL STRUCTURE AND FUNCTION OF THE NERVOUS

i I EM.

' I ) Tin \i in nil .

(2) Features of the Spinal Cord.

/.'< it' i Art in ii.

i WeriH i ' ,ii' i

57

:,s

CONTRACTILE AND IRRITABLE TISSUES.

II. THE PHYSIOLOGY OF CONTRACTILE
AM) IRRITABLE TISSUES.

I INTRODUCTION.

A. PHYSICAL INTRODUCTION.

Incident to the investigation of the properties of muscles and
of nerves, various stimuli are employed. The stimulus most used
is electricity. It is taken for granted that the student has made
himself acquainted with the general principles of electricity before
beginning the study of physiology. The electrical appliances
used in the physiological laboratory being somewhat specialized,
require a brief description.

1. ELEMENTS AND BATTERIES.

The Daniell element or cell is used most in the physiological
laboratory. Fig. 17 shows such a cell to be composed of four

parts : The outer glass receptacle
usually of one or two quarts capacity ;
s^ ^vx ^»c the copper plate, a thin sheet of copper ;

^*v, the porous cup, of unglazed earthen-
ware, and the zinc plate, which stands
in the porous cup. The Daniell cell
is a two-fluid cell : Outside of the
porous cup, and surrounding the cop-
per plate, there is a saturated solution
of copper sulphate ; inside of the cup,
surrounding the zinc plate, there is 10
per cent, sulphuric acid. The zinc
plate must have its surface amalga-
mated to prevent its too rapid con-
sumption and the evolution of hy-
drogen gas. The zinc plate is the positive plate, while the copper
plate is the negative one. Upon each plate there is a binding-
screw, through which the wires maybe fixed to the plates. The
distal ends of the wires are called the poles or electrodes. The
electrode, which is attached to the negative (copper) plate is the
positive electrode or anode, while the electrode, which is attached
to the positive plate, is the negative electrode or kathode. No
chemical action takes place in the cell until the electrodes are
brought into contact with each other when zinc is consumed with
the formation of zinc sulphate and the liberation of nascent hy-

The Daniel] ce

KEYS AXD ELECTRODES.

59

drogen ; the latter displaces from the copper sulphate copper,
which is deposited upon the copper plate.

The amount of electrical energy liberated by one cell is
frequently insufficient to meet the requirements of a physiological
experiment. In such a case recourse is had to the multiplication

Fig. 18.

The DuBois-Reyinond key.

of cells to form a battery. The high resistance of animal tissues
to the passage of an electrical current makes it necessary to adopt
a particular method of joining up the cells of the battery ; /'. e.}
the cells arc joined up in scries or tandem.

■2. KEYS AND ELECTRODES.

The key mosl used in physiological experimentation is the Du
Bois-Reymond key (see Fig. 1*). This key has the advantage
of permitting two distinct uses : ( i ) as a simple contact key, ( n) as
a short-circuiting key. It is evident in the second case dial when
(he key is closed the circuit i- "short-circuited," and the current
I i:i--< - from the |>o-itive to the negative side through the key.

Winn the key IS opened ;i~ shown in Fig. 1!», //, the current ia

thrown into the Longer circuit and musl traverse the nerve which
lies upon the electrodes. This ie the usual method of using the
DuBois-Keymond key, especially with induced currents.

CO

CONTRACTILE AND IRRITABLE TISSUES.

When a constant current passes from metallic electrodes into
animal tissue there is a decomposition of the tissue fluids and a

Fig. 19.

II

Showing uses df the DuBoia-Reymond key.

gradual polarization of the electrodes which disturbs the results of
the experiment. To avoid this various non-polarizable electrodes
have been devised (see Fig. 20). The non-polarizable electrode
shown in Fig. 20, A, consists of a glass tube (7) into which an

Fig. 20.

2 2S 7£-

S(J=^

Electrodes : A, kaolin electrode ; .t, zinc rod ; zs, saturated solution of ZnS04 ; /, glass tube ;
K, plug of plastic kaolin. Ii, v. FleischPs brush electrode, in which a camel's-hair brush is
substituted for the kaolin plug. C, Hand electrodes, made by pushing the common battery
wires through rubber tubing — for insulation— and binding together with thread.

amalgamated zinc rod (s) extends, immersed in a saturated solution
of zinc sulphate (aw). The zinc rod is held in position by a piece
of rubber tubing, and has a binding screw at the outer end. The
end of the glass tube opposite to the zinc rod is provided with a
pencil of kaolin paste (kaolin powder with NaCl 0.6 per cent,).
In FleischPs electrode (B) a brush is used instead of the kaolin
pencil. The hand electrodes (C) consist simply of platinum or
copper wires insulated with glass or rubber.

3. METHODS OF MODIFYING THE CURRENT.

It frequently becomes necessary to change either the direction,
the course or the strength of the current.

METHODS OF MODIFYING THE CURRENT.

01

Fig. 21.

1. To Change the Direction or the Course of the Current.
— For this a Pohl's commutator is generally used (see Fig. 21).
The two binding posts to which the bridge is hinged may be
called the " bridge-posts."
The battery-wires should
be joined to these posts.
The cylindrical handle
which is used in tipping
the bridge to the right or
the left is of non-conduct-
ing material. The current
passes into the upright arm
of the bridge, thence into
the semi - circular span,
whence it passes to the
mercury cup into which the span dips, completing the circuit
through the cross-bars when the bridge is tipped to the left (posi-
tion cd, Fig. 22), or completing it direct when the bridge is tipped
to the right (position ab). The change from one position to the
other thus changes the direction of the current beyond the com-
mutator.

Fig. 22.

I'ohl's commutator.

Showing use of I'ohl's commutator.

If the cross-bars are removed the current may be thrown at
will into a circuit joined at ab or one joined at cd, thus changing
the course of the circuit.

2. To Change the Strength of the Current. — (a) The cur-
rent may be increased BY THE COMBINATION OF CELLS in a
Batteky. If the external resistance is high, which is the case in
nil physiological or therapeutic uses of electricity, the cells com-
posing the battcrj should be joined in scries.

(b) THE CUBRENT MAY BE VARIED BY VARYING THE Ex-

ternal Resistance ((7= -5 1 ■ This may be accomplished by
joining a resistance bos or rheostat in the circuit. There are two

way- of doing this: (l) To join the rheostat in the long circuit,

by which method a removal of the plugs will decrease the cur-
rent by adding resistance to its passage; (11) to join the rheostat
in Bhort-circuit, by which method a removal of plugs will oppose
an increased resistance to the short circuit, throwing more current

<;•_>

CONTRACTILE AND IRRITABLE TISSUES.

into the long circuit. The first method causes a gradual decrease
of the current from a maximum to a minimum ; while the second
and more generally employed method causes a gradual increase
from zero to a maximum. The resistance box presents the disad-
vantage thai the resistance is added or subtracted step by step.
Many physiological experiments require the currenl to change by
infinitesimal increments. DuBois-Reymond contrived an instilment
which accomplishes this result, the rheocord (Fig. 23). The

Fig. S.\.

24.

DuBois-Reymond's rheocord.

DuBois-Reymond rheocord differs from the rheostat in substituting

for the low resistance spools two parallel platinum wires (»■//•')
which are connected by a bridge (/>). As the bridge is slowly
moved from position 0 to position 100, the resistance of the plati-
num wires (l!J) is as slowly added to the short circuit. Bringing

the bridge back to the zero
point and removing the plug
which represents 11), one may
-lowly slide the bridge up to
100 again adding another
ohm, and so on until 15 or
20 i2 have been thrown into
the short circuit.

(c) The Current maybe
VARIED by leading off or de-
riving any desired portion of
the principal current. For
this purpose one may use the
simple rheocord. (Fig. 24.)
When the principal circuit
is closed the current passes
from the cell to post .1 of the
rheocord, along the ( ierman
silver wire until it reaches
the sliding contact (s) when
two ways are open to it : ( I )
through the wire to B and back to the cell, or (n) through the
galvanometer circuit. The amount of current which will pass
along these two ways will be reciprocally proportional to the fe-

The simple rheocord.

THE IX D I TCTt > R IUM.

63

sistances offered by the two circuits. When the sliding contact

(■<) is in contact with B the derived or galvanometer current will
be /evil, when it is in contact with A the derived current will he
at its maximum. The principle involved in the Ludwig compen-
sator and in the round compensator is the same as that utilized in
the simple rheocord.

4. THE INDUCTORIUM.

The induced current is much used in this field of experimental
physiology. Several special forms of inductorium have been

Fig. 25.

The inductorium.

contrived. That of DuBois-Reyraond is shown in Fig. 25.
Two binding posts connect directly with the primary circuit. By

Fig. 26.

Plan of Neefa Interrupter.

connecting the battery t<> these an induced currenl i- made every
time the primary currenl is closed or opened. By connecting the

(14

CONTRACTILE AND IRRITABLE TISSUES.

battery wires at (J and A the primary current is closed and
opened automatically through the reciprocal action on the electro-
magnet 1) and the elasticity of

• i,' ti-

the hammer IT. For a clearer

plan of this mechanism sec
Fig. 26. But this arrange-
ment leads to " extra currents"
in the inductorium which mod-
ify the induced current as
shown by the full lines of the
next diagram. (Fig. 27.) Von
Helmholtz contrived an ar-

Scherne of the induced currents. P,, abscissa
of the primary, and S„, of the secondary current ;

A, beginning, and E, end of the inducing current ;
1, curve of the primary current weakened by an
extra-current; 3, where the primary current is
opened ; 2 aud 4, corresponding currents induced
in the secondary spiral; IV,, height, i. e., the
strength of the constant inducing current ; 5 and
7, the curve of the inducing current when it is
opened and closed through Ilelmholtz's modifica-
tion ; 6 aud 8, the corresponding currents induced
in the secondary circuit.

Capillary elect rometer.

rangement by which the influence of the
extra currents could be suspended and the
"make" current equalize with the " break"
current. The connection g with the screw/
(Fig. 26) makes the primary circuit, draws
the hammer down until it touches/', which
short-circuits a portion of the primary cur-
rent, weakens the magnet, releases the
hammer, and again throws all of the pri-
mary current into the long circuit. Thus
the primary circuit is never broken, but
rapidly varies between its maximum and
minimum as shown at 5 and 7. (Fig. 27.)
In the meantime the induced current gives
practically equal make and break shocks
as shown by the dotted lines 6 and 8.

5. MEASUREMENTS OF ELECTRICITY.

The delicate galvanometers of Wiedemann or of Thompson
are familiar to the student through his work in physics. These
instruments are used in physiology to measure muscle and nerve
currents.

METHODS OF RECORDING RESULTS.

65

Another instrument much used in physiology is the capillary elec-
trometer, whose construction is shown in Fig. 28. The electrometer
and the microscope are so mounted that all required adjustments
are made bv turning fine-adjustment screws. If the two platinum
wires (Pt, Pt') arc joined up with non-polarizable electrodes, and
if these are touched to portions of a body which represent different
electric potential, the mercury will instantly move along the
capillary, the direction of its motion indicates the direction of the
muscle or nerve current, and the extent of the motion indicates
the strength of the tissue current.

6. METHODS OF RECORDING RESULTS.
a. The Direct Method.

This method consists in the quick, inexpensive and direct ob-
servation of the results of various stimuli with tabulation of the
observations.

h. The Graphic Method.

This somewhat more elaborate method is so much more satis-
factory that it is now universally used in laboratory experiments.
The contraction of a muscle in response to a stimulus lifts a lever
whose extremity is provided with a writing point. This writing
point traces the movements of the lever upon a moving surface.
Various devices have been employed to furnish the moving sur-
face ; the pendulum myograph, the spring myograph (Fig. 29)

Fig. 29.

and the rotating cylinder. The Latter appliance has come into

general use for graphically recording various movements and lias

G6

CONTRACTILE AND IRRITABLE TISSUES.

received the name Kymograph or wave writer (see Fig. 30). The

instrument figured is only one of numerous forms. Some are
propelled by clock-work, some by steam or electric motor, some
by weight and pulley. The form of the recorded wave depends

in part upon the speed of rotation of the
Fig. 30. r\ Under. The height of the wave —

the ordinate — depends solely on the
rise of the lexer; hut the outline of the
wave, espeeially its extent along the
base line — its abscissa — depends upon
the relative speed of two movements :
(i) the rate of rotation of the drum ;
and (n) the rate of movement of the
lever.

c.

The Time Record.

Th
by an

This is frequently necessary. In
work upon the circulatory and respira-
tory systems it is sufficient to have a
time record in seconds; such a record
can be readily gotten from a contact
(•lock which beats seconds, joined in
circuit with a time-marker or chron-
ograph. In muscular-nerve physiol-
ogy it is necessary to record the time
iu shorter intervals.
e Tuning Fork (Fig. 31), whose vibrations are maintained
electric current, is usually used for this purpose. Yibra-

kymograi>h.

Fig. 31.

The tuning-fork as an interrupter,

tions numbering 50 to 200 per second may be recorded upon a
moving surface by the Deprez signal (Fig. 32), which is joined in
circuit with the tuning fork.

. 1 A \ 1 TOMIOA L INTR OD UCTION.
Fig. 32.

67

The Deprez signal.

B. ANATOMICAL INTRODUCTION.

1. THE STRUCTURE OF MUSCLE.

The unit of structure of muscular tissue is the muscle-cell or
muscle-fiber. The muscle-cell is a multinuclear cell of prodigious
size, some of them reaching a length of 12 cm. (Felix, quoted by
Biederman in Electro-Physiology) , while they have a diameter rang-
ing from 0.013 to 0.010 mm., making them easily visible to the
unaided eye as fine threads. If one examine a muscle he will
find it to be enclosed in a sheath of glistening connective tissue —
epimysium — and to be readily divisible
into prismatic bundles or muscular fas- ^ig. •i',i-

da ill, cadi of which is in turn surrounded :: ,
by a connective tissue sheath, the peri- \s^f:
mysium. The accompanying figure ( Fig.
33) show- a cross-section of a fasciculus
the perimysium not being depicted. The
fasciculus is in turn composed of muscle-
fibers or muscle-cells, the spaces between
which are occupied by delicate connective
tissue, tlie ervdomymim. Note the dark
spots in tlw periphery of the filters.
These are the nuclei. Each liber or
cell i- surrounded by :i delicate cell-wall (Kolliker) the sarco-
lemma, shown in the figure as n thin black line surrounding each
cell. A- in the typical cell we have the cytoplasm divided into
two fairly distincl substances -spongioplasm and cytolymph — so
here we find structures which musf represent their homologues,

viz.: /il, rill" and SCWCOplasm. In the figure the shaded areas

(areas of Cohnheim) into which the cro — ection of each fiber is

Cross-section of a fasciculus of
muscle.

68

CONTRACTILE AND IRRITABLE TISSUES.

divided represents bundles of fibrilla — muscle columns, which are
separated by the sarcoplasm.

The proportion of sarcoplasm to fibrillar substance may vary
enormously, alike in the muscles of different animals, and in the
differenl muscles of the same species. "Those muscle

fibers which serve the most persistent or most strenuous action are
richest in sarcoplasm." "The greal pectoral muscle of

the l>est fliers (among the birds) consist.- exclusively, or almost
exclusively, of plasmic (rich in sarcoplasm) fibers, while in the
weak-winged fowls it consists predominantly of aplasmic (poor in
sarcoplasm) fibers." * * "There can be no doubt that en-

ergetic chemical changes go on in the sarcoplasm, as is proved by
the frequent appearance within it of fat drops." * * " All

indication- favor the proposition that the sarcoplasm furnishes the
pabulum which nourishes the fibrillar substance during its ac-
tivity." * * * "If, then, it really is the rdle of the inter-
fibriilar plasma (sarcoplasm) to preside over the nutrition of the
contractile substance, the greater abundance of sarcoplasm in the
muscles which serves the most strenuous and persistent functions
i- readily intelligible. — (Quotations from Biederman's Electro-
Physiology.)

Fig. 35.
Fig. :;4.

B

m

'« l

-

Voluntary muscle, por-
tions of two fibers showing
the characteristic trans^ erse
markings ; the lighter band
is divided by the row of
minute beads constituting
the intermediate disk : a,
termination o f muscular
substance and attachment of
adjoining fibrous tissue ; ?<,
nuclei of muscle-fibers.

( I'll BSOL.)

Wing muscles of an insect.

The structure of the fibrilla has been a matter of investigation
for many years. Many of the points at issue are still unsettled.

Fig;. 34 shows a view of a human muscle-fiber under rather
high magnification. Xote the alternating light and dark bands;

THE STRUCTURE OF MUSCLES.

69

and that the light bands are subdivided by a tine dotted line.
This line is called Krcuusefs membrane because it has been thought
to be a membrane. The whole liber is composed of a great num-
ber of parallel fibrilke. Each fibrilla is segmented and presents
the same alternating dark and light segments shown by the fiber
as a whole. Furthermore each fibrilla possesses a portion of the
" Krause membrane/' It must be evident that the areas of
Cohnheim represent cross-sections of the fibrilhe.

Fig. 36.

Fig. 37.

s.e.

Diagram of a sarcomere. A, extended ; B, contracted.

Isolated sarcous elements.
A, side view ; B, end view.

The most favorable material for the study of the finer structure
of the fibrilhe is presented by the wing muscles of insects.
Schaefer's preparations shown in Fig. 35 give a very good idea of
this structure. The portion between two Krause membranes is
called a sarcomere. Note that in the extended condition (A) the
dark band has a light line dividing it transversely ; this light line
i- called the line or plane of Hensen (see Fig. 36, Alt). This

Pig. 38.

ml

Hi

i< i\ l '■' as it-

11* Nil

Two moacalar fibers from tin: psoas of ;i guinea-pig, showing the terminations <>\'
a. ii, tin.- primitive fibers with their transition Into the terminal plates, /', /'. Note d
with nuclei, continuous with the sarcolemma. Note nuclei in muscle. I After M< i<

the iirr\ es
eurilemma

I.N DEII K. )

plane of Hensen disappears when the fibrilla i> contracted (see
Fig. •';<;, Bh). Bach sarcomere then is occupied by dark and light
matter. The dark matter seems to l><- more solid than the lighl
matter. It i- called a sarcoma element. From the figures given

CONTRACTILE AND IRRITABLE TISSUES.

one cannoi see jusl how the matter of the sarcous element is dis-
posed but an end view (Fig. 37, B ) shows it to be porous and
that the white matter takes the form of cylindrical extensions
which till the pores. Halliburton looks upon the sarcous element
as representing spongioplasm and the clear Bubstance as represent-
ing the hyaloplasm (cytolymph).

The blood Bupplyofthe muscle is distributed as fine capillaries
which occupy spaces between the fibers but never pierce the sar

oolemma. Th<

Fig. 39.

Nen >' endings in tendon.

nerves

however, terminate in end-
plates which lie within the
sarcolemma (see Fig. 38).
There are nerve-endings in
the tendons also. These
nerves are sensory nerves
and are stimulated by sud-
den change of tension upon
the tendon. Fig. '-'>U shows
this as well as the way in
which the muscle fibers pass
into tendon fibers.

2. THE STRUCTURE OF NERVES.

A nerve-trunk, such as one rinds in his dissections is constructed
as shown in Fig. 40, with a loose connective tissue sheath

FlG. 40.

Section of portion of a nerve-trunk including three
bundles, or funiculi, surrounded by the perineurium
i p) ; the funiculi, together with the blood vessels and
adipose tissue, are united by the more general epineu-
i-i inn (e) ; the sections of the individual nerve-fibers are
held in place by the endoneurium ; /, fat-cells, near
which are the sections of blood vessels. (After Pn b>
sol.)

Medullated nerve fibers. .1
and 7> surface views of sheath
and w h i t e s n b S t a n ce 0 E
Schwann, C optical section
showing fibrillated structure of
the axis-cylinder.

THE MUSCLE-NEB 1 'E PREPAID ITIO X.

71

(epmeurium) surrounding and separating the nerve-bv/ndles. Each
bundle is ensheathed in p< rim urium which sends extensions of en-
doneurium into each bundle. The bundles consist essentially of
a great number of nerve fibers. A medullated nerve fiber (see
Fig. 41) is composed essentially of an axis-cylinder surrounded
by the medullary sheath or white substance of Schwann, which is

Fig. 42.

A lis- cylinder, highly magnified.
Bhowing the fibrils composing it,
I St haefeb, after M. Schultze.)

Fig. 43.

Section across five nerve-fibers. (Magnified
1000 diameters.)

The nerve was hardened in picric acid and
stained with picro-carmine. The radial stria-
tion of the medullary sheath is very apparent.
In one tilier the rays are broken by shrinkage
Of the axis-cylinder. The fibrils Of the axis-
cylinder appear tubular. (SCHAKPEK.)

in turn enclosed in the primitive sheath. The axis-cylinder is
composed in turn of fibrillse (see Fig. 42). The fibrils seem to
be separated by a ground substance as shown by Schaefer (Fig. 48).

3. THE MUSCLE-NERVE PREPARATION.

The general principles of the physiology of contractile and irri-
table tissues are universally demonstrated with the tissues of a
frog. Various muscles and nerves are used for these experiments
but the one mosl used is the gastrocnemius muscle with the sciatic
nerve which supplies it.

The accompanying figure -hows sufficiently the anatomy of the
- leg.

T<« make a muscle-nerve preparation one destroys the brain of
the frog (pith- it) pin- it dorsum upwards upon a cork board and
removes the -kin from the Leg, thigh and pelvic region. II' the
-mall. glistening tendon of the biceps be severed, where it is in-
serted upon the tibia, and the muscle dissected out and removed

71'

CONTRACTILE AND IRRITABLE TISSUES.

one will find below where it lay the large trunk of the Bciatic
nerve with the accompanying blood vessels — sciatic artery and
sciatic and femoral veins. It' the urostvle he removed the seiatic

Fig. 11.

Showing anatomy of the frog's leg. A, ventral ; B, dorsal view,

plexus will be revealed so that by gently lifting the nerve with a
fine glass rod it may be easily dissected out from its spinal origin

Fig. 45.

.1, glass nerve-honk foi lifting a nerve while dissecting it out ; B, muscle-nerve prepara-
tion as it appears when minpleted.

to the gastrocnemius. The rest of the dissection required to pro-
duce the preparation as shown in Fig. 45 is readily made, the
femur may be clamped to a support and the tendon attached to the

THE MUSCLE-XERVE PREPARATION.

73

lever of a myograph through a hook or thread. (See Fig. 4(3.)
Contraction of the muscle will raise the lever, and the latter may

Fig. 46.

The simple myograph.

be made to trace its movements graphically upon a rotating cylin-
der or kymograph.

74 CONTRACTILE- AND IRRITABLE TISSUES

THE PHYSIOLOGY OF CONTRACTILE AND
IRRITABLE TISSUES.

A. THE PHYSIOLOGY OF MUSCLE AND NERVE.

In the following brief summary of electro-physiology facts and
principles of fundamental importance only will be presented —
facts which may be utilized in subsequent work in physiology,
pharmacology, electro-diagnosis, and electro-therapeutics.

1. STIMULI.

While one is dissecting out a muscle-nerve preparation he is cer-
tain to notice several muscular contractions, caused usually by the
severing of the nerve or of some of its branches, or by various
conditions present during the preparation. If one mount the pre-
paration in the myograph, letting the nerve rest upon the glass-
slide, he may further test the effect of mechanical stimuli. The
muscle responds when the nerve is severed with knife or scissors ;
it responds if it is pinched with forceps or pricked with a needle.
If the muscle is exposed to the atmosphere it will begin after a
time to contract rather spasmodically when there is no apparent
stimulus ; the contractions increase in extent and frequency until
the muscle is practically tetanized. What has been takiug place ?
The dry atmosphere has taken up the water from the tissue plasma,
leaving the salts in concentrated solution ; these salts may have
caused the contractions of the muscles. Apply a strong solution
of common salt to the nerve of a fresh preparation, and it will
begin, almost at once, a series of contractions quite like those de-
scribed above, producing a " salt-tetanus." By applying glycerine
to a fresh nerve a similar result is obtained. Such stimuli are
called chemical stimuli.

If a fresh nerve be touched with a hot wire a response i> elicited
from the muscle. Temperatures between 0° C. and 100° C. do
not produce contractions of the muscle unless there is a sudden
change from one of the extremes to the other. Extreme tempera-
tures only are efficient stimuli.

If while dissecting out a muscle-nerve preparation with a silver
probe and steel scissors, one touch the two instrument- together
when both are in contact with the tissues of the frog, a vigorous
contraction will be observed. The conditions were such as to
cause the passage of an electric current from one metal to the
other through the tissues of the frog. The tissues responded to
the stimulus with a contraction. Mount the preparation and lay
the nerve across the electrodes of a Daniell cell. Every time the

STIMULI. 75

circuit is " made " with the contact key the muscle contracts ;
every time the circuit is " broken " the muscle contracts, but it
does not usually contract during- the passage of a current. These
stimuli have all been applied to the nerve (indirect stimulation) ;
one may apply the same stimuli to the muscle itself1 (direct stim-
ulation ), and will elicit a response in most cases, though it soon
becomes evident that the muscle is not as sensitive to the various
stimuli as the nerve is. In the case of the glycerine the muscle
does not respond at all. An important law of electro-physiology
may be readily demonstrated at this point. If a curarized sar-
torius muscle be ligatured in the middle tightly enough to sever
the muscle substance but leave the connective tissue intact ; and
if this muscle be fixed in the middle, leaving the two ends free
to fasten to levers, one can stimulate the two segments of the
muscle and note the effect of the two poles, anode and kathode.
Nonpolarizable electrodes should be used for this purpose, and one
should touch each segment of the muscle. If one segment con-
tracts on make it is the kathode segment; if only one segment
contracts on break it is the anode segment. Reverse the current
with a Pohl's commutator and the same is true — the make con-
traction is kathodic and the break contraction anodic. If both
contract on making the current, the kathode segment begins first ;
if both contract on break the anodic segment begins first. The
following laws of electrical response may be formulated : Law I.
The make stimulus is kathodic; the break stimulus is anodic. Law
II. Tin- " make" or kathodic stimulus of a current is more irritating
to nerve or muscle than the "break" or anodic stimulus.

A question which naturally arises very early in the study of
various stimuli is : Does the way in which a given stimulus is
applied to a nerve affect the response which the muscle gives? If
one gently tap a nerve which is lying upon a glass plate a slight
contraction of the muscle will follow. A somewhat harder tap
will cause ;i somewhat more vigorous response, but the maximum
response is soon elicited. After that any increase in the strength
of the stimulus will not cause an increase in the response. In a
similar way a very weak electrical stimulus will cause a weak" re-
sponse, a stronger stimulus, a stronger response, etc.; but the
maximum response is elicited with what is really a very mild
stimulus, beyond this maximum response any increase of stimulus
will not elicit a greater response.

Another way of varying the stimuli is to vary the lime of ap-
plication or the rate of change of conditions. One may sever or
crush a nerve bo -lowly that the muscle will nol respond. One
may raise the temperature so slowlj thai the nerve may lie cooked
without having culled forth :i response, one may, through flic
I b ■ paralyze the nerve-endingB "I the muscle by curarizing the frog.

76 CONTRACTILE AMi llllllTAULK TISSUES.

Fleischl rheonom, send an electric current into a nerve so slowly
that the muscle will not respond. The lt< i i<-i-:i 1 principles here

illustrated may be thus summarized :

('/) There are four kinds of stimuli : (i) Mechanical; (n)
Chemical; (in) Thermal; (rv) Electrical.

(ti) Whatever stimulus he applied to a specialized sensitive
tissue the response is the same in general character, /. <:, muscle
always responds by contraction.

(■/-) The strength of the response may vary with the strength
of the stimulus, but it is not at all proportional to the strength of
the stimulus.

(8) A stimulus may be applied to a nerve so slowly that there
is no response on the part of the muscle.

2. CHANGES WHICH TAKE PLACE IN A MUSCLE IN RE-
SPONSE TO STIMULI.

After having- watched the response of muscle tissue to the
stimuli discussed in the preceding section the following facts
must have become evident: (i) Muscle-tissue is irritable; (n)
Nerve-tissue is irritable; (in) Muscle-tissue transmits a stimulus
from one part of a muscle to another ; it, therefore, possesses the
power of conductivity ; (iv) Nerve-tissue possesses the power of
conductivity; (v) In response to stimulus a muscle changes its
form.

In the light of the experiments and discussions which have
preceded, one may form a general conception of what takes place
in contractile and irritable tissues in response to a stimulus. (i)
Some internal change (chemical) occurs in the nerve at the point
where the stimulus is applied ; this internal change is the in-
visible manifestation of the irritability of the nervous tissue, (n)
The internal change begun at the point of stimulation is propa-
gated along the nerve trunk ; indeed, along the axis-cylinders,
because the nerve loses its insulating sheath before it reaches its
final distribution, (in) It is transmitted to the individual muscle-
fibers through the end-plates of the nerves which lie just within
the sarcolemma of each fiber, (rv) It is propagated through the
contractile substance of the fiber, so that all the fibers of the
muscle contract at practically the same time, (v) There are in-
ternal changes in the muscle and nerve, which accompany the
more evident change of form which takes place in the muscle.

These internal changes arc : Chemical, thermal and electrical,
as subsequent observation will demonstrate.

a. Change in Form.
1. Change in Length. — In studying the change in form
which a muscle undergoes incident to its response to a stimulus it

CHANGE IN FORM.

11

is customary to mount a muscle-nerve preparation in a myograph
whose lever may trace upon a kymograph any changes in length
which the muscle may undergo. Almost any efficient stimulus
may be used ; the only requirement being that in its application to
the nerve it must be sudden in its beginning, instantaneous in its
duration, and sudden in its cessation. It is impossible to fill
these requirements with chemical or thermal stimuli ; but possible
to do so with various mechanical and electrical stimuli. It is cus-
tomary to use electrical stimuli. The " break " induction shock is
especially adapted to this purpose.

Fig. 47.

lU yAAAAAAAAAATWWVWli Chronogram &

Tracing of single muscular contraction,
period of relaxation ;

1-2, latent period ; 2-3, period of contraction ; 3-4,
-5, period of elastic after-effect.

(a) As the Result of Oxe Shock the muscle in contraction
will trace upon a rapidly moving surface such a curve as is shown
in Fig. 47. Such a tracing of a single muscular contraction re-
veals certain important facts regarding the response of a muscle
to a stimulus, (i) On abscissa 11(8) indicates the time of stimu-
lation. Xote that muscle, whose lever was tracing abscissa 7, did
not begin to shorten until about yi-g- of a second had elapsed.
This is called the latent period. (11) The period of contraction
shows a slight acceleration at first, followed by a period of maxi-
mum rate of shortening (between a and b) after which there is a
retardation of the rate of shortening until at 3 the apex of the
curve is reached and for an instant retains this position of maxi-
mum contraction, (nr) The period of relaxation follows imme-
diately, but the rate of relaxation is less rapid at the beginning of
this period than toward the end. Note that the period of relaxa-
tion (3-4) is Longer than the period of contraction, (iv) If the
muscle fa moderately loaded and the lever without a rest or stop

the muscle will relax beyond its original position of rest ; that is,
the curve will pass below the abscissa, but will instantly recover
itself coming above the abscissa. This is simply an after-effeel

due to the elasticity of the muscle and to tin; general conditions to

which it i- subjected.

78

( n.XTl:. 1 1 TILE AXI) UllllT. 1 11LE TISS I rES.

(b) Suppose a muscle be given a second stimulus before it has
had time to complete its response to the first, what will the result

Myogram

Tracing of a doable muscle curve ( Foster. )

be? Fig. 48 shows the typical result as traced by Foster, (i)
Note that the crest of the second wave is higher than that of the
first, (il) The contraction of the second is more rapid and its
relaxation more rapid than observed in the first contraction.

(c) The Summation of the Effects of Stimuli is well illu-
strated in Waller's figure (Fig. 49). With a comparatively slow

Fig. 49.

Myogram

Chronogram

Summation of contractions : composition of tetanus. (After Waller. )

moving cylinder and stimuli given at the rate of ten per second
the lever will drop back nearly to the abscissa, to rise again with
another stimulus. With twenty shocks per second the lever re-
mains nearly stationary. With thirty shocks per minute the
lever traces a perfectly straight line. This is a tetanus of the
muscle. Tetanus is a sustained contraction of a muscle caused by
a series of rapidly repeated stimuli. One may voluntarily bring
a muscle into a state of sustained contraction. Though one is
not conscious of the process which is going on in the nerve and
muscle he may infer from the foregoing that during sustained con-
traction there is a series of rapidly repeated stimuli passing from
the central nervous system to the muscle. The greatest number
of voluntary movements which one can make in a second is limited
tn eight or ten. The observations of Schaefer and of von Kries
show "that the graphic record of even the steadiest voluntary

CHANGE IX FORM.

79

movement exhibits a tremor " of 8 to 12 vibrations per second
(Waller).

Fig. 50.

The effect of temperature upon muscular contraction. 1, normal; 2, cooling; 3, very cold.

(Waller.)

It is generally accepted that in a sustained voluntary contrac-
tion the impulse-frequency is about 10 per second. Involuntary
contractions are slower in rhythm ; the heart-beat represents not a
tetanic condition of the ventricles but a " long twitch." Con-
clusive evidence of this is shown in the fact that only one change
of electric condition occurs in the heart muscle at each contraction.

('/) The Form of the Muscle Curve is Modified by
the Temperature of the Muscle. When the temperature
is only a little below normal the latent period is longer, the rise
36 sadden. When the temperature is very low the contraction
and relaxation are both much prolonged and the shortening much
less than normal. (See Fig. 50.)

(e) If a muscle be subjected to a series of equal stimuli at short
intervals (6 to 10 per sec.) each one of the first 10 or 12 contrac-
tions will be higher than the previous one, giving rise to the so-
called "staircase" myogram. This seems to indicate that one re-
sponse better fits the muscle for successive ones.

(/) THE Mix i,i;-Ci i;\i; [8 MODIFIED BY DRUGS. Fig. ol
-how- the effect of veratrin. Notice that though the contraction

Fig. 51.

Effect of reratrln upon the myogram, (W.w.i i a.)

i- about ;i- sudden ;i- usual the relaxation is much retarded — forty
seconds not sufficing t<> bring the lever back i<> the abscissa.

( f/ ) The Mi -< le-Ci rve i- Modified by the Load which
the muscle must lift. A moderate load is Likely t<> net as ;i supple-1

80 CONTRACTILE AND IRRITABLE TISSUES.

mentary stimulus to a muscle causing it to contrad more with the
load than without it. as the load is increased, however, two modi-
fications may be ooted iii the myogram ; (i) The latent period is
longer because more time is required to generate sufficienl energy
to overcome the inertia of the load, (n) As the load increases
the curve becomes progressively lower though the actual work
done may be greater,

2. Change in the Transverse Dimensions of the Muscle. —
The volume of the muscle remaining practically the same there
must bean increase in the transverse dimensions sufficienl to com-
pensate for the decrease in the length of the muscle. This thick-
ening of the muscle may be recorded in two ways : (i) by resting
the muscle on a horizontal plate or within a shallow horizontal
trough and resting a tracing lever upon its upper surface; (n)
by clasping the muscle gently in a forceps-lever and transmitting
the movement through a pair of Marey tambours.

If one places a lever at each end of a long muscle like the
sartorius it becomes at once evident not only that there is a thick-
ening of the muscle during contraction, but that the thickening
progresses as an undulation from one end of the muscle to the
other when the muscle is stimulated at one end. The rate of
propagation of this wave has been measured and is equal to from
1 to 3 meters per second according to the various conditions of the
experiment.

3. The Work Done by a Contracting Muscle. — The condi-
tions under which most muscular contractions are studied as out-
lined in the foregoing paragraphs make it easy to estimate the
work which the contracting muscle actually performs. Work
done equals the product of the weight raised and the height
through which it is raised. {W = g x h.) If a muscle lift 100
gms., 5 mm. the work equals 50 gm.-cm. If a strong muscular
contraction fail to lift a weight no wrork is done though energy
has been liberated in the muscle. If a loaded muscle be thrown
into tetanus work is done only when the lever is raised, and not
during the time when the weight is sustained. Energy is liber-
ated, however, and the muscle is fatigued, but the energy does not
take the form of mechanical work in the technical sense of that term.

The amount of work which a muscle can perform varies ac-
cording to several factors.

(a) Work is Modified by the Strength of the Sti.m-
ilis. The weakest efficient stimulus will cause a series of con-
tractions lifting a given weight through a very short distance.
This minimum efficient stimulus is also termed the " stimulus of
UmincU intensity." Let the stimulus be gradually increased, the
height of contraction will be rapidly increased to a maximum.
The stimulus whose intensity is just great enough to cause the

CHEMICAL CHANGES. 81

maximum contraction is called the "stimulus of optimum intensity."
Let the stimulus be increased ; the contraction will not be greater,
on the other hand it is likely to be less because of fatigue from
over-stimulation.

(b) Work is Modified by the Interval of time which
elapses between the stimuli. The minimum interval, just short
of a tetanic contraction, is unfavorable to the muscle because
there is a rapid accumulation within the muscle, of carbon diox-
ide, sarcolactic acid, etc., which cause the rapid fatigue of the
muscle. The optimum interval is such that the products of
katabolism incident to the liberation of energy may be carried
away from the muscle by the circulation. There can hardly be an
optimum interval, then, for a muscle which has been removed from
the organism. There is, however, an interval most favorable
under the conditions, and that interval is from 1 to 3 or 4 seconds.

(6) Work is Modified by the Load, («) The disposition
of the load : (i) If a weight is simply hung upon the lever it
stretches the muscle even when the latter is at rest ; this tends to
exhaust the muscle somewhat and it cannot accomplish so much
as if " after-loaded." (n) If the lever comes to a rest at the end
of the relaxation of the muscle there is no stretching of the mus-
cle between contractions. This is called " after-loading " a mus-
cle. The short period of absolute repose between contractions is
advantageous to the muscle.

(fi) The amount of the load also modifies the amount of the
work which a muscle is able to accomplish. A muscle will lift
a hundred grammes as high as it will lift one gramme, thus doing-
one hundred times as much work in one contraction. The total
work done in a series of contractions leading to fatigue will be
greater for medium (50 gms. to 100 gms.) weights than for heavy
weights (200 gms. to 250 gms.) though the work of one contraction
may be two or three times as great in the case of the heavier load.

(c) Work is Modified also by the Dimensions of the
Resting Muscle. The extent of a contraction varies with the
length of the contracting fibers; while the strength of the con-
traction varies with the number of the contracting fibers, /. <:,
with the sectional area of the muscle. Both of the work factors
(a x h) are modified by the twit factors of the muscle volume :

Sectional area (a) and length (/) ; that is, g varies as a, ami h

varies as I, therefore, g x h varies as a x / or IT varies as a x I.

b. Chemical Changes which take place in a Contracting

Muscle.

The chemical composition of < I < : i * I mammalian muscle (issue is
approximately as given in the following table:
8

82 CONTRACTU.]-: AXI> IMUTMIU-: TISSUES.

Water ".', 77.5$

Solids 25 —22.5

N it rogen ous - 1 ■ — 22

Proteid Is — ^"

Nil rogenous metabolites about 1

K reatin, Xanthin, etc.

Non-nitrogenous aboul 0.5 — 1

( larbonydrates 0.5 — 1

hm-it.. .....(nice

[norganic (carbonate and phosphate of Kand Na )... about 1

The difficulty of determiDing just what chemical changes take
place in a living muscle incident to its activity must be evident.
The only index of these changes which present methods make
possible is analysis of dead muscle that lias been at rest and of
dead nuisele that has been fatigued just before being killed.
Analvsis of the gas consumed and given off by a resting or con-
tracting muscle also affords data. From these various methods
it has been conclusively determined that contracting muscle pro-
duces : (i) more carbon dioxide, and (n ) more sarcolactic acid j
and that it consumes : (i) more oxygen, and (u) more glycogen.

In this connection it is important to note that the muscle is
chemically active when it is apparently at rest. Muscular tissue
is the most important heat producing tissue of the body. Heat
production continues while the muscle is quiescent. This constant
heat production is in part at the expense of the proteids of the
muscle plasma (sarcoplasm) as well as of the proteids of the
sarcous elements. The katabolism of these nitrogenous substances
yields a series of nitrogenous katabolites, among which may be
enumerated : Kreatin, xanthin, glycocoll, ammonium lactate.

The reaction of muscle changes with vigorous activity. Resting
muscle is faintly alkaline or amphicroic because of the potassium
and sodium carbonates and phosphates present. Accumulation of
carbonic and sarcolactic acid in the muscle soon changes the reac-
tion to a distinctly acid one.

The chemical changes which take place in muscle will be
further discussed under Physiology of the Muscular System.

Sv

c. Thermal Changes Which Take Place in Contracting

Muscle.

The chemical changes above enumerated are, in largest part,
oxidations, leading to the production of considerable quantities of
( '.'< ).,. ]>ut such changes are always accompanied by the evolution
of heat not less surely in muscle than in a furnace. Vigorous
and continued contractions produce considerable heat. One's im-
pulse to be more active in cold than in warm weather is in re-
sponse to the need of the organism for more heat. Heat is
constantly liberated in muscle tissue, but more is liberated when

CHEMICAL CHANGES. 83

the muscle is actively contracting than when at rest. This may
be demonstrated by the use of thermo-electric couples, one set of
which may be introduced into the gastrocnemius of one side, the
other set into the other gastrocnemius, while the long connecting
circuit pa>ses to a galvanometer. (See Fig. 52.) Any increase
in the temperature of the

contracting muscle is indi- Fig. .">•_>.

cated by a deflection of the
galvanometer needle. This
arrangement enables one to
demonstrate the liberation
of heat in contracting mus-
cle. The second needle
may be placed in a liquid
whose temperature may be
raised or lowered to bring;

flip o-il vinonieter needle to Diagram of thermo-electric couples. When both

lue ^cUwuiomeiLi iiiAUie 10 couples have the same temperature the galvanometer
rest at the zero position ; the ueedle remains at rest.

temperature of the liquid

may be determined by a delicate thermometer. Multiplication of
the number of couples of needles makes the apparatus more deli-
cate. Heidenhain gives the rise of temperature for one contraction
of a frog'.- gastrocnemius as 0.001 to 0.005 of a degree Centi-
grade ; and Helmholtz found a rise of temperature amounting to
0.14°— 0.18° C. after two or three minutes of tetanization.

'/. Electrical Changes which Take Place in Muscle.

In the process of dissecting out a muscle-nerve preparation one
i- likely to drop the cut-off central end of the sciatic nerve upon
the gastrocnemius muscle. Should this occur a contraction of the
muscle is almost sure to take place. Galvani performed this ex-
periment and cited it as a proof that electricity exists in animal
tissues. Follow the line of experimentation. Make two prepara-
tion-, lay them upon a glass plate, place the nerve of preparation
" upon the muscle of preparation />, so that it shall touch two
well separated regions, but not the intermediate portion of the
muscle. The muscle of preparation a will contract when the
contact i- made, and it will probably repeal the contraction sev-
eral time-; on subsequenl contacts. Stimulate preparation h while
the nerve of a lie- upon it in contact at two points; the muscle
of " contracts with every contraction of h. This is called a sec-
ondary contraction, and preparation a which contracts second-
arily i- called a rheoscopic />r< zparation or a "physiological rheo-
seope." What is it iii the cut-off nerve that causes a contraction
of it- muscle ; Wh;it i- it iii n dissected-oul muscle (/>) tint causes

84 CONTRACTILE AND IRRITABLE TISSUES.

a contraction of :i second preparation (a) ; or in the contracting
muscle (A) that causes a contraction of the muscle whose nerve
lies upon it ? The stimulus which elicits a response from the
rheoscopic preparation (a) can nol be mechanical. Jt must be
chemical, or thermal, or electrical, [f electrical, it should be
detected through the use of the galvanometer or electrometer.
Place upon the center and end of a muscle contracting from me-
chanical stimulus, non-polarizable electrode- which are connected
with a galvanometer or electrometer and a deflection of the gal-
vanometer needle or a change in position of the mercury maniscus
of the electrometer demonstrates the presence of an electrical cur-
rent or better a difference of electrical potential of the two regions
of the muscle. This difference of electrical potential was the
stimulus which caused the secondary contraction of the rheoscopic
preparation. But the latter contracted also when touched to the
resting muscle. It was once supposed (DuBois-Reymond) that
the difference of electrical potential exists in all muscles at rest,
and the terms, " current of rest," and "current of action," were
n^vd, Hermann demonstrated, however, that a resting muscle
when uninjured lias no current and that injury induces a current
in a general way proportional to the extent of the injury. The
term " current of rest," then became misleading and was displaced
by the term, "demarcation current" or "current of injury."

It lias been found that: (i) Normal Mn.sc/c at rent is iso-electric,
i. e., gives no evidence of a difference of electric potential in differ-
ent regions, (n) Local injur// induces a difference of potential,
instantly indicated by the galvanometer or electrometer. (in)
Local action induces a difference of potential, indicated by the
galvanometer or electrometer. The current of a galvanic cell
pa<>cs from the zinc plate to the copper plate, — from the plate
where there is chemical action to the plate where there is no chem-
ical action. The current of an injured muscle passes from the in-
jured portion to the normal portion, i. e., from the portion where
there is much chemical action toward the portion where there is
little chemical action.

The current of action is, in the same way, from the portion
most active to that least active.

Both of these factors may be at work at the same time ; i. e., an
injured muscle may be made to contract. The current of injury
passes through the galvanometer from the normal to the injured
portion. The point of injury is the point of least activity, that is,
the change from rest to action will be greater at the normal part.
Therefore the current of action will pass through the galvanometer
from the injured to the normal. Thus stimulation of an injured
muscle Mill cause the needle to swing back toward the opposite
direction. This phenomenon is called the negative variation.

CHEMICAL CHANGES.

85

Fig. 53.

These relations are represented diagrammatically in the accompany-
ing figure. (Fig. 53.)

If the electrodes be placed one upon the
base of the ventricle and one upon the apex
of the ventricle of the heart there will fol-
low a double variation with each heart cycle.
In the first phase of the cycle the base is
negative to the apex, in the second phase of
the cycle the apex is negative to the base,
thus leading to the term, " diphasic varia-
tion " of the heart.

In this connection it may be stated that
all active tissues manifest the presence of
difference of potential in different regions.
For example, the outer surface of the hand
is negative to the inner surface ; the fundus
of a gland is negative to the hilus ; the optic
nerve is negative to the cornea, etc.

Normal

Injured

Fatigue.

Diagram showing direc-
tion of the " current of in-
jury" ( S > ) and of the
"current of action" (£Ci > ).
Also the "negative varia-
tion "of needle during action
of injured muscle.

In response to various stimuli muscle tis-
sue undergoes changes in form, in tempera-
ture, in elect rieed condition, all of these forms
of energy being liberated through the chem-

ieal changes which accompany them. Mention has been made
above of the accumulation in the muscle of the products of the
chemical changes ; also of the gradual decrease in the height of
successive contractions after the muscle has been contracting many
times. These two phenomena are the distinctive phenomena of
fatigue and the first is the cause of the second. The accumulation
of the products of chemical action is the cause of the progressively
decreasing power of the muscle.

The decreasing power of the muscle manifests itself by a de-
creasing height of the contraction waves. Just at first the waves
may increase in height, the stair-case contractions, then there will
lie a greater <>r smaller number of waves of nearly the same length ;
finally, alter a variable time, the waves begin to shorten up until
there i- do response to the recurring stimuli. Then the muscle is

-aid to be fatigued. The conformation of the series of fatigue
waves will vary considerably with the way in which the load is
disposed. Fig. 54, /, -how- a typical fatigue tracing from an
"after-loaded" muscle, while // -hows that from a "loaded"
muscle. In the latter the stretching during the period of rest ir-
ritates the muscle and brings it finally into a state of typical
tetanus. The fatigue is postponed by taking an optimum or at

86

CONTRACTILE AND IRRITABLE TISSUES.

least advantageous rate of stimulation. It' the stimuli come in
too rapid succession fatigue is hastened. If a fatigued muscle is
given a few moments respite or rest, it recovers in pari and will
respond vigorously to subsequent stimulation, bul tires very

Fig. 54.

Scries of contractions of an "after loaded" muscle

Series of contractions of a "loaded" imiscle

Showing the effect <>f disposition of load on the contraction "t muscle modifying the amoun.

i if work done.

quickly again. A muscle which is in its normal situation, receiv-
ing the benefit of exchange of material through the circulation,
will accomplish much more work before fatiguing than will be
the case with an excised muscle. Furthermore, the intact muscle
will recover in a short time, while the excised muscle makes only
a modentte recovery through the removal of ('()., by diffusion.
Fatigue is accompanied by a decrease of extensibility and elastic-
ity, in common words a stiffness.

/'. Rigor.

After the death of a muscle it undergoes certain changes which
are similar to those which take place during fatigue ; namely, the
accumulation of ( '()., and of sarcolactic acid. Accompanying these
chemical changes there is the "stillness of death/' — rigor mortis,
— due to the coagulation of the myosin. If fresh muscle substance
be coagulated by heat, — o0° C. to 60° C, — there will also be a
formation of CO., and sarcolactic acid, accompanied by the " stiffen-

RELATION OF NERVE TO VARIOUS STIMULI 87

ing of heat " or rigor ccdoris. The three processes ; viz., fatigue
with the decrease of elasticity, rigor mortis and rigor ealoris, are
closely related both physically and chemically.

3. THE RELATION OF THE NERVE TO VARIOUS STIMULI.
The living nerve in its normal position in the animal body
functions as a conductor of impulses. These impulses may arise
in the central nervous system and be conducted to various pe-
ripheral organs; or they may arise in various peripheral (sense)
organs and be conducted to the central nervous system. In either
case the nerve neither adds to nor subtracts from the original im-
pulse which it receives but transmits it along the course of the
nerve from one end to the other. Just how these impulses are
transmitted is unknown. One can follow the steps of the chem-
ical changes that are propagated along a fuse or of the physical
changes that are propagated along a wire conductor of electricity,
but the physical and chemical changes which are propagated
along the axis-cylinder of a nerve are still unknown quantities as
to their exact nature. It is generally accepted that they are ulti-
mately chemical and that the initiatory chemical (metabolic)
changes are accompanied by electrical changes, probably also by
thermal changes.

a. The Properties of Nerve Trunks.

The fundamental and essential property of a nerve trunk is
conductivity. The experiments which are described above make
it evident that a nerve trunk is not only a conductor of an impulse,
but that a stimulus in any part of its course may start from that
point a change which will be propagated apparently in a perfectly
normal way, to the normal terminus of the nerve and there trans-
mitted to the structures normally receiving impulses from the
nerve. For example, an injury or an electric shock to the
Bciatic nerve sets into operation at the point of the stimulus a
change which is propagated to the muscles supplied by the nerve,
:md these structures give the normal response to the impulse.
The second property of ;i nerve is irritability or excitability.

Ik Conductivity.

The rate of propagation of an impulse along a nerve may be
determined by stimulating ;i nerve near to its muscle, or five or
-i.\ centimeters farther away from the muscle. The response to
tin- stimulus must lie recorded upon a rapidly moving surface,
such ;i- the spring myograph | Fig. 29), and the time in hundredths
of ;i second musl be recorded upon the -.one surface by a tuning
fork (Fig. '.I I, the difference in time elapsing between stimulus and

,xs

ioSTRACTILE AND IRRITABLE TISSUES.

response in the two cases is the time required to traverse the five
or six centimeters of extra nerve In tins way the rate of propa-
gation or conduction may be determined. This method of experi-
mentation lias given the following result- : Helmholtz found the
rate of transmission in the motor nerves of a frog to be '11 m. per
second. The rate of conduction in sensory nerves is about 35 m.
per second.

The conductivity of a nerve is decreased by low temperature
and increased by high temperature.

The conductivity may be destroyed by the direct application of
alcohol or ether to the nerve trunk while its irritability will not
be much affected. "Carbon dioxide may destroy the irritability,
though leaving the conductivity unimpaired." (Lombard.)

.1 strong constant current decreases the conductivity of a nerve in
the region of the anode during the passage of the current and in the
region of the kathode after removal of the current. This modifica-
tion of conductivity may be called Law III. of electrotonus ;
Laws I. and II. were given above.

c. Irritability.

If a constant current traverse a nerve entering and leaving by
non-polarizable electrodes the nerve will be thrown into a state
called electrotonus. The condition of electrotonus is characterized
by a moderate change in conductivity, mentioned above, and a
profound change in irritability. The irritability of the nerve is
increased in the region of the kathode and decreased in the region
of the anode. In Fig. 55 the line A B may serve for both nerve
and abscissa. The curve I—I' indicates the degree of irritability ;
note that the irritability is increased in the region of the kathode
and decreased in the region of the anode. It indicates also that

Digram illustrating electrotonus. X.-P.K., non-polarizable electrodes ; .1"., anode; A"'..
kathode; /./'. curve illustrating degree of irntabilityj-decreased in tin- region of the anode

and increased in the region el' the kathode.

the influence <»f the two electrodes decreases as the distance from
the pole increases ; and that in the intra-polar region there is a
neutral area where the irritability is neither increased nor de-

RELATION OF NERVE TO VARIOUS STIMULI.

89

creased. The region of decreased irritability in the neighborhood
of the anode is said to be in a condition of anelectrotonus ; the
region of increased irritability in the neighborhood of the kathode
is -aid to be in a condition of katelectrotonus. The change in
irritability manifests itself when a stimulus is applied to the nerve
in the region of anelectrotonus or of katelectrotonus. Arrange
the apparatus as indicated in the diagram (Fig. 56). Through

Fig. 56."

Arrangement of apparatus for demonstrating electrotonus.

the agency of commutator Cone can make either electrode the
kathode by reversing the current. Through commutator C one
can throw the stimulus at m, the muscular end of the nerve, or at
e, the central end of the nerve. Arrange the apparatus so that the
kathode is near the muscle as indicated in the figure. Before
"making" the constant or "polarizing" current stimulate with
the induced current at m or c, using a "break-shock" that will
cause a moderate contraction, i. e., bring the secondary coil just
inside tin.' minimum limit of stimulation. Turn on the polarizing
current after a lew moments, stimulate at ///, in the katelectrotonic
region ; the response will be noticeably greater than the normal.
Stimulate at c in the anclect rotonic region ; the response will be
Doticeably Less than the normal. Reverse the direction of the
polarizing cm-rent bringing the anode nearer to tlie muscle. The
region which before was in a condition of katelectrotonus is now-
iii a condition of anelectrotonus mid conversely. Stimulate iii the

region m and the response will now lie Less than normal because
th< irritability of the nerve ha- been decreased in the region of
the anode, in the region of anelectrotonus. On the other hand

the response :it <■ will !»<• greater than normal because of the inllii-

ence of the kathode, inducing n state of katelectrotonus. These
facte are summed up in :i law of electrotonus :

!. iv. The passage of a constant current through a nerve

90

CONTRACTILE AM> lllllll'.UM.E TISSlls.

modifies its irritability, increasing it in the region of the kathode
(state of katelectrotonus) and decreasing it in the region of the
dimdi' (state of anelectrotonus).

d. Pfluger's Law of Contraction.

If one stimulate the nerve of a muscle-nerve preparation,
and note visually or graphically the response which the muscle
gives he will find that with uniform and favorable conditions the
preparation will respond in a uniform way to a varying stimulus.
The stimulus should be varied in two ways : (i) as to direction ;
(n) as to strength. If the current pass along the nerve toward
the muscle, i. e., the kathode being placed nearer to the muscle
the current is called a " descending" one; if the anode is nearer
to the muscle the current is called an "ascending" one.

To vary the strength of the current one should use either a
simple rheocord or a DuBois-Reymond rheocord, so that the
strength may be varied by infinitesimal increments. Non-polar-
izable electrodes are preferable, though platinum electrodes may
be used with good results. Choose healthy, vigorous frogs ; pith
them two or three hours before they are to be used. Protect the
preparation against rapid drying by mounting it in a moist
chamber. With all conditions favorable the results will be as
follows : A very weak ascending current will affect the muscle
first, causiug a slight contraction on make. With a somewhat
stronger current there will be a contraction on make of both
ascending and descending currents. A further increase in the
strength of current will call forth a response on both make and
break of both ascending and descending current. As the current is
gradually increased from this point it will be noted that the con-
tractions are not equal in extent ; some are stronger and some are
weaker ; the weaker ones finally drop out and the stronger ones
increase in strength. These strong contractions occur on the make
of the descending current and on the break of the ascending current.
The results may be thus tabulated :

Descending.

Am ENDING.

Current.

M A K I'..

Break.

Make.

Break.

Weak

Contract.

c
c

Rest.

c

R

Contract.
C
B

Rest.
C

C

It now becomes necessary to account for these results using the

RELATION OF NERVE TO VARIOUS STIMULI.

91

laws which have been formulated. To that end let us here pre-
sent the laws again.

Law i. The make stimulus is kathodic j the break stimulus is
anodic.

Law ii. The miih, or kathodic stimulus of a current is more irri-
tating to nerve or muscle thou the heath or anodic stimulus.

Law in. A strong constant current decreases the conductivity of
a nerve in the region of the anode during the 'passage of the current
ami in the region of the kathode after removal of the current.

Law iv. The passage of a constant current through a nerve modi-
fies its irritability, increasing it in the region of the kathode (state of
katelectrotonus) and decreasing it in the nylon of the anode
(state of anelectrotonus).

The results tabulated above may be graphically represented as
shown in the accompanying figure (Fig. 57).

Fig. 57.

Current Deccnding
Weak - 1^ -—&

Ascending

— -I-

\z. ite

^T

3*

Strong-

^z ^

-tr

+■

_Ja.bc

Diagram showing schematically the results of Pfliiger's law of contraction. KMC, kathodic
make contraction ; ALC, anodic break contraction.

Note that with a weak descending current there is a " kathodic
make contraction " (KMC) ; that with a medium descending cur-
rent there is both an "anodic break contraction" (ABC) and a
''kathodic make contraction" (KMC). The other indicated re-
sults will be found to correspond to the table. Why is there a
kathodic make contraction only, with a weak descending current?
Because (i) the make contraction starts at the kathode (Law I.) ;
(ii) there will be a kathodic contraction before there is an anodic
contraction in accordance with law n. These laws account also for
the results obtained with an ascending current. With a medium
current, kathodic make contraction is in response to law I. The
fact that there is an anodic break contraction indicates that in re-
sponse to law ii. the break stimulus has become sufficiently strong
n, cause ;i response. The same thing is true for both ascending
and descending currents. In the case of :i strong descending cur-
rent we gel :i kathodic m;ike cont ract ion in response to law I. In

response to an anodic break stimulus there is no cont met ion be-
cause according to law in. the conductivity is decreased in the re-

92

CONTRAGTl L E AM> III HIT. HI I. E 7 'ISS I ' ES.

gion of the kathode at the moraenl of 1 he break of a strong current.
At the make of a strong ascending current there is no response
though there has been a strong kathodic stimulus because the

conductivity of the nerve is much decreased in the region of the
anode during the passage of the strong current (Law m.). In
this case the anodic break stimulus causes a contraction because
the region of reduced kathodic conductivity is not between the
stimulated point and the muscle.

e. The Application of the Laws of Electrotonus.

In the application of the laws of electrotonus to the problems
of electro-diagnosis or electro-therapeutics there are some compli-
cating factors to consider. If the electrodes (usually metallic-
plates covered with chamois or sponge which is moistened when
in use) are placed over the course of a nerve the current will dif-
fuse widely through the tissues from the anode and converge
again upon the kathode on leaving the tissues (see Fig. 58). Let

Fig. 58.

Application of the laws of electrotonus.

NN' represent a nerve trunk, the current enters it at a a a a tra-
versing it and leaving by k k k. As the current converges to-
ward the kathode it traverses the nerve trunk again entering at
a' a' a' and leaving at k' h' k' .

But the point where a current enters a nerve is called the
anode and the point where it leaves the kathode. This leads to
the differentiation of four physiological poles while there are only
two physical poles.

(i) The physiological anode under the physical anode ; (a, a,
etc.).

RELATION OF NERVE TO VARIOUS STIMULI. 93

(11) The physiological kathode under the physical anode ;
(k, lct etc.).

(in) The physiological anode under the physical kathode;
(a' , a' , etc.).

(iv) The physiological kathode under the physical kathode ;
{¥, kf, etc.).

A contraction caused by the influence of the current at the
physiological kathode under the physical anode is called an anodic
make contraction {AMC). A contraction caused by the influ-
ence of the current at the physiological anode under the physical
anode is called anodic break contraction (ABC). In a similar
way there may be a kathodic make contraction {KMC), and a
kathodic break contraction (KBC).

It is important to determine which of these various stimuli
will be most effective. In addition to the above laws of electro-
tonus one will need to apply a fifth law.

Law V. The denser the current, all other thine/* being equal, the
stronger tiic stimulus. In the figure note that the current is denser
at the physiological anode under the physical anode than at the
physiological kathode under the physical anode.

The kathodic make contraction is stronger than the anodic break
contraction.

(1) KMC> ABC.

This is in accordance with laws I. and n., law v. not apply-
ing here because the density is the same, providing the nerve is
equally near the surface under the two poles. For similar
reasons, the anodic make contraction is stronger than the kathodic
break contraction.

(2) AMC> KBC.

If KMC is greater than ABC and if AMC is greater than
KBC avc may conclude that :

(3) KMC + AMC > ABC + KBC or the sum of

the make stimuli must be greater than the sum of the break stimuli,
in consequence of this, the contraction which occurs at make (in re-
sponse to the double stimulus), is greater than the contraction which
occurs at brail; (in response to the double stimulus).

The anodic make contraction (AMC) ma ji or may not be stronger

than the anodic break contraction (A ll< ' }, i. e.,

(I) AMC> ABC or AMC < ABC.

In tlii- case we have the stronger effect at the physiological

kathode (Law [.) to offset the greater density of the current at

the physiological anode (Law v.) one may be stronger than the

other, but the difference is at mosl slight.

\\< are now in a position to understand what will take place

when the current i- progressively increased from weak to strong.

The results may be thus tabulated i

94 CONTRACTILE AXE IRRITABLE TISSUES.

Weak Current KMC

Medium Current KMC AMC ABC

Strong Current KMC AMC ABC KBC

The above table gives the normal reaction. //" degeneration
has iikkIc some progress the weak current elicits the anodic make con-
traction (AM( ' ) before if does the kathodic make contraction ( KMC ),
an important fact in electro-diagnosis.

B. THE GENERAL STRUCTURE AND FUNCTION OF
THE NERVOUS SYSTEM.1

We have studied the way in which contractile and irritable
tissues respond to certain external and artificial stimuli. Before
we enter upon the special physiology of the various organs and
systems of organs it will be profitable for us to briefly consider :
(i) what relation nervous tissue bears to the organism as a
whole ; (n) whence come the various stimuli which influence the
operation of the different organs and tissues of the body; (in)
what tissues (besides contractile tissues) are influenced in their
activity by the central nervous system.

1. GENERAL CONSTRUCTION OF THE NERVOUS SYSTEM
AND ITS RELATION TO THE ORGANISM AS A WHOLE.

Though the tissue of the nervous system is disposed in prom-
inent structures which may be called organs, e. g., brain, spinal
cord, etc., these structures are not organs in the same sense that
the lungs are organs belonging to the respiratory system. The
whole nervous system is really one organ. This organ is composed
of (i) a parenchymal tissue, which is the specialized tissue of the
organ, endowed with a specialized function ; and (n)a supporting
tissue. As in other organs, so here the supporting tissue belongs
to the connective tissue series, the more delicate connective tissue
of the deep-lying portions of the central nervous system being
somewhat specialized and called neuroglia, while the remainder
represents the more common forms of areolar, fibrous and elastic
connective tissues.

a. The Neuron.

The parenchymous or active tissue of the nervous system is

composed of nerve cells. The nerve cell is so highly specialized

1 The student is not in a position to comprehend the way in which tin- various
systems of organs and tissues (circulatory system, respiratory Bystem, digestive

system, etc. ) are governed ; how they are influenced by outside condition-, and
how one system exerts an influence upon another, unless lie has at least a general
idea of the construction of the nervous system and the functions of its various
structures. It is the objeel of this section to give a brief outline of the most essen-
tial features of the nervous system.

CONSTRUCTION OF THE NERVOUS SYSTEM.

95

Fig. 59.

NERVE CELL.

NAKED
AXIS-CYLINDER

DENDRITES.

AXIS-CYLINDER PROCESS.

COLLATERAL BRANCH.

AXIS-CYLINDER

CLOTHED WITH

MEDULLARY

SHEATH.

AXIS-CYLINDER

CLOTHED WITH

MEDULLARY •

SHEATH AND

NEURILEMMA

MEDULLARY SHEATH.

"AXIS-CYLINDER.

NEURILEMMA.

AXIS-CYLINOER
CLOTHED WITH-— '
NEURILEMMA

NAKED
AXIS-CYLINDER."

TERMINAL BRANCHES.

Schema "i a n< luron. i \n,r Verwobn.)

96 CONTRACTILE AM) IRRITABLE TISSUES.

a structure that it has received the special name Neuron. The
neuron is the unit of structure of the nervous system. .1 neuron
(see Fin1. 59) consists of a neural cell-body with all of its processes.

The protoplasm of the <-cll body presents a delicate fibrillated
structure. The fibrillae seem to be continuous with those which
(•institute the one or two axis-cylinders which arc among the cell
processes. Besides the fibrils, the cell protoplasm is more or less
charged with fine dark granules, which arc important in the metab-
olism of the cell, increasing during periods of rest and decreasing
during periods of activity. Occupying a fairly central position in
the cell-body is a relatively large nucleus, with a distinct nucleolus
( plasmosome).

The cell-processes arc numerous and complex. As to struc-
ture they may be arranged in two classes : (i) The protoplasmic
process, — short and much branched, their tree-like appearance
giving them the name Dendrites, (n) The axis-cylinder process,
Avhich is usually much elongated, little branched near the cell-
body and usually insulated in a medullary sheath. As to function,
cell-processes either bring impulses to the cell-body or they carry
impulses away from it. Those which bring impulses to the cell-
body are called afferent cell-processes and those which carry im-
pulses away are called ejj'ercnt processes. The protoplasmic proc-
esses are without exception afferent.

If a cell has only one axis-cylinder it is without exception
efferent. If it has two, one of them is afferent and one efferent.
These facts readily lead to confusion in the use of terms. To
avoid this confusion the best authorities are now adopting a new
term to represent the efferent process — the term Neuraxon or
Neurite, or Axon. As now understood the term <l< mdrite always
refers to an afferent process. All neuraxons are axis-cylinders
structurally. Most dentrites arc protoplasmic processes, but some
(the sensory nerves) have become modified into axis-cylinder-.

/>. Features of the Spinal Cord.

The nerve trunks with which one deals in the experiments in
muscle-nerve physiology are really bundles of insulated neurax-
ons. They normally carry motor impulses to the muscles from
the cell-body which they represent. But where is this cell-body
located ? If one follow the nerve trunk he will find that just before
peaching the central system it divides into two roots, an anterior
(or ventral) mot and a posterior (or dorsal) root. If the anterior
root be stimulated one will observe the same response as if the
trunk had been stimulated in the same way nearer to the muscle.
If the posterior root be stimulated no such response will be ob-

CONSTRUCTION OF THE NERVOUS SYSTEM.

97

served.1 ( hie is justified in inferring that the neuraxons which
he is tracing left the spinal cord by the anterior roots. A trans-
verse section of the spinal cord should show the large cell-bodies
in the anterior gray horn (see Fig. 60). Xote their numerous

Fig. 60.

Pgh

rCca

Agh

Mi.

Half of a section through the lumbar cord. Ra, anterior root ; Rp, posterior root ; Rip, inner
portion of the posterior rool ; Op, posterior commissure ; ''mi, anterior commissure ; Cr, central
canal. The fine net-work of medullary fibers in the gray matter and the net-work of medullary
fasciculi in the otherwise gray posterior commissure are not shown. Agh, anterior gray horn ;
Pgh, posterior gray horn, i Bdibgkb after Deitebs.)

branches. In a few cases the neuraxons may be traced into the

nerve bundles which make up the anterior root. From the ac-

companying diagram note that the motor neuron in question is in

communication — through its dendrites : (i) with motor neurons

from the brain and Ml) with sensory neurons. (See Fig. Gl.)

The motor neuron normally sends a motor impulse to the

muscle which it supplies, only when it receive- an impulse through

it- dendrites. From the connection which it has it is evident that

it may receive Buch an impulse from one or the other of two

sources: (ij from the brain; (ii) from the sensory system of

nerves. If the motor impulse originates in the brain it is sent

through the centra] motor neuron to the peripheral motor neuron,

thence through it to the muscle. Two neurons, two cells, are re-

1 There may be ■< general response, tin- nature of which will !><■ explained later ;
l>ut there will be no definite response of the particular muscles supplied by the
motor nerve in question.

7

'..V

CONTRACTILE AND IRRITABLE TISSUES,
Fig. 61.

1 X ti )k

Schematic representation of the coarse of the fibers in the spinal cord. (Whitaker.)
I. rii: Motor Tract. ». Central neuron: Lateral pyramidal tract (Py I) and anterior pyram-
idal tract ( I';/ <i): terminal arborization in the anterior born, '>. Peripheral neuron: an-
terior horn cells — anterior root (r. a) — motor nerve muscle. II. Fhi Sensory Tract, n. Periph-
eral neuron: sensory nerve | ». p), spinal ganglion [Sp) — posterior root (r. y/i of the spinal
cord. In tin- posterior r""i zone ot' the posterior columns each fiber divides into an
ascending and a descending branch (short and long fibers). The short tracts curve into the
posterior horn as : 1. Keflex collaterals to the anterior horn, shorter reflex arc, longer reflex
tracts (intercalation of another neuron). •-'. Fibers to tic cells of the middle /one ,.i the
gray substance. ■ '•. Fibers to the cells of Clarke's columns (c). i. Fibers to the central ami
especially the medial anterior icon cells (commissural cells). 5. Fibers to the posterior horn
cells. The long tracts (6) pass first into Burdach's column, higher also into (toll's column, ami

GEXEEAL FUNCTIONS OF NERVOUS system. 99

thus to the nuclei of the posterior columns in the medulla, i Here they join the fillet.) 6.
Central neuron. It begins with the cells of the terminal places of the peripheral, enumer-
ated under - to 6. 1. if" in those which have been enumerated under 2 as "column cells"
arise the fibers of the anterior ground bundle of the same side (fal) ( fl) and the columns
,.f Gowers (GV. 2, From those mentioned under 3: the lateral cerebellar tract of the same

From those under 4 : fibers which cross in the anterior commissure to the anterior
lateral column (htl) I fl ' to ascend in the other side 1. From those under .3 : fibers to the lat-
eral limiting layer (fl i and to the ventral tield of the posterior columns. In addition to this is
represented the manner in which the collaterals are given off and the termination Of the cen-
tral short tracts i which quickly bend again into the gray substance) of the anterior lateral col-
umns, the ••inland cells" (Cjolgi) in the posterior horn; the decussation in the posterior
commissure is not clear. There are contained in the posterior roots apparently other individual
fibers which have their neuron cells in the anterior horn, but in man this is not yet satisfac-
torily established.

quired to transmit an impulse from the brain to the peripheral
organs. This holds good for secreting and excreting organs as
well as for motor organs. But the peripheral motor neuron may
he influenced by sensory neurons, by neurons which bring impulses
to the central nervous system from the skin and various sensitive
organs of the periphery. Note in the diagram that these peripheral
sensory neurons (sensory neurons of the first order) enter the spinal
cord by the posterior root, and that they communicate (i) either
directly or indirectly with a motor neuron ; (11) either directly or
indirectly with the brain. Xote that a spinal ganglion (Sp) is
located upon the posterior root. This ganglion of the posterior
root is the location of the cell-bodies of the peripheral sensory
neurons. From the peripheral sense organ to the cell-body in ques-
tion the impulse is conducted along an afferent axis-cylinder
which is a modified dendrite. From the cell-body the impulse is
conducted into the spinal cord along an efferent axis-cylinder or
neuraxon. This neuraxon sends off collateral branches which
communicate directly with peripheral motor neurons, of the same
segment, or indirectly with motor neurons of neighboring segments
of the cord, or finally directly or indirectly with the brain through
a central sensory neuron (or neuron of the second order).

2. GENERAL FUNCTIONS OF THE NERVOUS SYSTEM.

a. Reflex Action.
A careful study of these relations between the sensory and
motor neurone makes it evident that the activity of any peripheral
motor (or glandular) organ may be influenced in one or the other
of two ways: (i) through the direct influence of impulses enter-
ing the central system by the sensory neurons of the s:une (or
neighboring) segment which furnishes the motor nerve supply;
or (ii) through the influence of the brain. The first method of
influencing the activity of an organ is culled reflex. Note thai
refles action involves typically two neurons : the peripheral sensory
neuron and the peripheral motor neuron. Reflex response to a
stimulus, ;i~ when one jerk- his hand from a hot object, is accom-
plished in the following manner : (i) The sensory nerve endings
in the -kin are stimulated by the hot object ; (n) The stimulus
starts a message or impulse along the afferent nerve to the cell-

LOO CONTRACTILE AND IRRITABLE TISSUES.

body in the posterior root ganglion; (in) The cell receives the
impulse and transmits it along the efferent neuraxon to neighbor-
ing motor neurons (and to the brain) ; (iv) The motor neurons
respond to this stimulus by causing in certain muscles of the arm
the contractions necessary to remove the band from the painful
object.

b. Voluntary Action.

In the meantime the sensory impulse lias been transmitted to

the brain and the individual becomes conscious not only that his
hand lias suffered an injury but that a reflex act has occurred
through which the hand has been removed from the immediate
danger. The consciousness of injury aroused in the brain may be
the stimulus to further acts on the part of the organism toward
further protection or toward repair of injury already done. These
secondary and conscious acts of adaptation cannot be classified as
reflex ; they are voluntary acts, suggested by the brain, which in
turn is actuated by the stimulus described above, possibly also by
visual and other supplementary stimuli.

c Nerve Centers.

1. Centers in the Spinal Cord. — In describing reflex action
each segment of the cord has been described as a center toward
which afferent impulses come, and from which efferent responsive
impulses are sent out. Each segment of the spinal cord is thus a
motor center for a limited number of muscles. But there arc other
centers in the spinal cord. There are centers which preside over :
(i) the nutrition of tissues: i. e., trophic centers to muscles,
nerves, bones, joints ; (n) walls of blood vessels; i. e., vaso-dila-
tors ; (in) secretion of skin — sweat centers ; (iv) centers connected
with micturition, enHion of the penis, parturition, and defecation.

The motor, trophic, and vaso-dilator centers are distributed along
the whole extent of the spinal cord; but the centers enumerated un-
der (iv) are probably located in the lumbar enlargement of the cord.

2. Centers in the Medulla Oblongata. — In the spinal bulb,
or medulla oblongata, there are numerous reflex centers, whose
action will be discussed later :

(i) Respiratory; (il) Vasomotor ; (in) ('<ir<li<ic centers; (iv) also
centers for coughing, sneezing, mastication, deglutition, vomiting,
coordinating, convulsor, closure of eyes, dilation of pupil, salivary,
sudorific, diabetic, etc. Most of these centers are located in the
floor of the fourth ventricle.

?>. Nerve Centers in the Brain. — (a) The Cerebellum con-
tains the following centers : (i) Centers for the coordination of
movements; (n) Emotional Centers ; (m) Centers for Muscle Tonus.

(b) The CEREBRUM contains the following centers: (i) Smell;
< ii ) Taste ; (in) Hearing ; (iv) Vision ; (v) Speech ; (vi) Various
motor centers ; (vn) Thermogenic centers.

PART II.

SPECIAL PHYSIOLOGY.

Division A. NUTRITION.

THE PHYSIOLOGY OF THE INTERNAL RELATIONS.

Division B. MOTO-SENSORY ACTIVITIES.

THE PHYSIOLOGY OF THE EXTERNAL RELATIONS.

Division C. REPRODUCTION.

DIVISION A.

NUTRITION.

Chapter III. CIRCULATION.

Chapter IV. RESPIRATION.

Chapter V. DIGESTION.

Chapter VI. ABSORPTION.

Chapter VII. METABOLISM.

Chapter VIII. EXCRETION.

NUTRITION.

INTRODUCTION.

The general term Nutrition is applied in Physiology to all of
those activities, collectively taken, which are involved in supplying
the cells of the body witli food, in building this food up into eel)
Btibstance, in liberating the energy from it by katabolic processes
and in ridding the body of the waste material, which results from
i li'>-<- pr<

101

1 ( 12

SPECIAL PHYSIOLOGY.

A genera] idea of the activities and organs involved in nutri-
tion may be gained from the following table :

A( TIVITIE8.

i ii .. \n- ob Tissues.

1.
2.

Perception.
Prehension,

Organs of the Special Senses.
Bands, Teeth, etc.

:;.
4.
5.
G.

Preparation.
Mastication.
Deglutition.
DIGESTION.

Elands, etc.
Tooth.

[nvol. Muscles of Pharynx and QEsophagus.
Secretory Apparatus: Gastric Glands, Liver,
Pancreas, Intestinal < Hands.

8.

ABSORPTION.
CIRCULATION
Selection.

Epithelium of Alimentary ('anal.
Blood ami Lymph Circulatory Systems.
Individual < Jells "t tin- body.

10.

METABOLISM.

{

1

i. ANABOLISM.
ii. EATABOLLSM.

Individual < lells of the body.
Individual Cells of the body.

11.

RESPIRATION.

f

I

i. Extei mil i:.

[ Circulation (b)]
ii. Internal R.

1. ungs, Air Passages, Muscles of Respiration.
Individual Cells of the Body.

12.

Rejecti i' waste

products from the

( ells of the- body.

13.

[Circulation (<•)]
EXCRETION.

j

(
(
(

ii. Pulmonary

Kidney-.

Lungs.

Sweat-glands.

1. Micturition

Liver.
Bladder, etc.

14.

EGESTION.

2. Expiration

:;. Perspiration ....

Air passages.

skin.

[tectum.

To illustrate the table we may followthe steps of a cat's nutrition :
(i) Through the organs of scent and sight she perceives her
prey, (n) With claws and teeth the prehension or catching is
accomplished, (in) The preparation is in this case a simple kill-
ing, but man prepares his food usually by cooking, (iv) She
masticate* it; (V) swallows it; (vi) digests it. (vn) The di-
gested portion is absorbed; passes through the circulation, (vm)
to the cells of the body, where each cell selects (ix) an appropri-
ate part, which it builds up ( x') into cell substance. After a time
the cell protoplasm is broken down (x") incidental to the func-
tional activity of the cell ; the balance of chemical affinity is im-
mediately restored by the introduction into the cell of the oxygen
(xi") which has been brought from the lungs (xT) by the
circulatory system. The products of katabolism are promptly re-
jected (xii) from the cell, carried to the periphery by the circula-
tion where they are excreted (xni) by the proper organs and
finally <j<cfr,l (xix) from the body.

After a moment's reflection it will be seen that — either directly
or indirectly — every organ and every function of the organism is
brought into action in nutrition, except those of reproduction.

INTRODUCTION. 103

Inasmuch as the circulatory system is variously and repeatedly
involved in nutrition it will be more advantageous to treat that
first than to interrupt the course of the discussion after the subject
of digestion is opened. Respiration being a collateral branch of
nutrition, a similar course may profitably be pursued regarding it.
With an understanding of the circulation and respiration at com-
mand we may enter upon the uninterrupted discussion of digestion;
absorption ; metabolism ; and excretion.

OH A.PTEB I II.

CIRCULATION : [NTRODUCTION.

.1. Till: COMPARATIVE PHYSIOLOGY OF THE CIRCULATION.

1. THE CIRCULATING FLUIDS.

2. THE ORGANS WHICH CAUSE THE CIRCULATION.

/;. ANATOMICAL [NTRODUCTION.

1. TIIK BLOOD-VASCULAB SYSTEM.

2. THE LYMPHATIC SYSTEM.

3. THK SPLEEN.

4. BISTOGENESIS OF TIIK CIRCULATORY ORGANS AND TISSUES.

C. PHYSICAL [NTRODUCTION.

1. THE FLoW OF LIQUIDS THROUGH TUBES.

2. MANOMETERS.

I). HISTORICAL INTRODUCTION.

INTRODUCTION.

As soon iis an animal attains to the dignity of an individual of
the third order (See Individualization of Living Matter, Gen.
Physiol., Part I.) ; i. e.} a- soon as it has more than an eetoderm
and entoderm the necessity arises of conveying to the middle layer
or mesoblast the nourishment obtained from the environment by
the layers which lie in immediate contact with the environment.
And thus the circulatory system is horn of necessity. It is a
system of tubes taking up fluid or gaseous food from the hypo-
blast and conveying it to all parts of the body. This system of
tubes, filled with a fluid kept in circulation through the agency of
the heart, has fine ramifications in all parts of the body, and
Berves not alone to carry nourishment, but also to remove the
waste material from the active cells. Further, the blood serve- as
a distributor of warmth and moisture in the body.

A. THE COMPARATIVE PHYSIOLOGY OF THE
CIRCULATION.

The primary object of the circulation i- the distribution of nu-
triment to tissues which do not lie in or adjacent to absorbing
surfaces. Secondarily the fluids in circulation carry oxygen from
the absorbing surfaces to the other active tissues, and finally these
fluids carry to the periphery of the organism for excretion certain

104

THE CIRCULATING FLUIDS. 105

waste products which are of no further use to the system. As a
u common carrier" the circulatory system is the servant of the
fundamental process of nutrition. In each one of its various
capacities it seems to be essential to the organism.

In the description of this system it is convenient to treat (i)
the circulating- fluids, and (n) the organs which cause the circula-
tion of the fluids.

1. THE CIRCULATING FLUIDS.

(a) The Most Primitive Coxdition is represented by the
coderderates whose gasbrovascular system of canals is filled with a
fluid which is composed of the digested or partly digested ingesta
and of imbibed water. This fluid may be called a drouhiting
chyme. It is devoid of corpuscular elements. The oxygen which
it holds in solution may be absorbed by the cells which are ad-
jacent to the canals, but it lacks any special agent to serve as an
oxygen carrier.

(6) Xext ix Order as a circulating fluid may be considered
the circukUing chyle or hydrolymph of echinoderms, lamelti-
branchiate niolhisi-*, tunioates and the amphioxus. This fluid dif-
fers from the circulating chyme in having passed into the organism
through an absorbent surface of epithelium. It is a selected fluid
and, therefore, much more uniform in its composition than is the
crude circulating chyme. This circulating chyle is corpusculated.
The corpuscles are not particularly abundant and are similar to
the lymph corpuscles and leucocytes of higher vertebrates, — being
capable of amoeboid movements and varying much in size.

('•) Tin: Term hosmolym/ph is applied to the circulating fluid
possessed by worms, most molluscs, and aiihropods. Hsemolymph
is distinguished from hydrolymph in having haemoglobin or other
oxygen-carrier in solution.

(d) Tin: Most Complete System of circulating fluids is
possessed by the vertebrates (amphioxus excepted). The circu-
lating chyle is received into the lymphatic system o<* vessels and
mixed with true lymph. This soon mixes with the blood, — the
most complex of ;ill circulating fluids. The blood of vertebrates
consists of (a) m fluid-plasma, quite like the fluid portion or plasma
of the lymph, (ft) corpuscular elements which in turn are : ( i ) the
leucocyte- which an- practically the same as the lymph corpuscles,
inj the red corpuscles which are characteristic of the vertebrates,

though they have been also observed ID a lew isolated invertebrate

genera. The essential feature of the red blood-corpuscle is
//" moglobin.

The h;eino|\ iiipli contains various oxygen-carriers, or respira-
tory pigments (haemoglobin, beemerythrin, beemocyanin), in so-

106 CIRCULATION: INTRODUCTION.

In t ion , while the blood contains haemoglobin in corpuscular form.
These haemoglobin corpuscles arc retained within a definite system
of canals, the blood-vascular system ; while the lymph circulates
in a vaso-lacunar system similar to that po>H—ed by most of the
invertebrates. Note (i) that in the circulating chyme the sole
function of the fluid is to carry nutriment; (it) that the hydro-
lymph carries nutriment to the tissue- and excrement from them;
(in) that the hsemolymph carries nutriment and oxygen to the
tissues and excrement from them ; (iv) that in the Mood-lymph
systems the same functions arc performed, but then.' is a differen-
tiation of structure and composition between Mood and lymph
and the functions arc performed more perfectly because of this
specialization.

2. THE ORGANS WHICH CAUSE THE CIRCULATION.

(a) The Ccelenterates have a system of canals which are
really diverticula from the gastric cavity. The fluid within this
gastro-vascular system of canals is set in motion by the general
movements of the animal.

(6) The Lowest Order of circulatory system is that in which
the hydrolymph and hsemolymph of the invertebrates flow. As
a general rule the lymph is kept in motion by the rhythmical con-
tractions of some portion or portions of the canal system. These
pumping organs are called hearts. The animal kingdom presents
hearts of various forms and degrees of complexity, but they all
have this in common that they represent dilatations of the blood
vessels. In Mollusca and Arthropoda the heart is located dorsally,
in Vertebrates it is ventral. There are two general methods of
propulsion : (i) Peristalsis. The earthworm possesses a series of
segmental arterial arches connecting the ventral and dorsal trunks.
The rhythmic peristalsis of these arches keeps the blood (hsemo-
lymph) in circulation. The amphioxus has a similar system
physiologically ; the contractile portions are upon the ventral vein
forcing the lymph to the branchial system (respiratory heart) and
upon the dorsal artery, forcing the lymph through the systemic
capillaries (systemic heart), (ii) Pumping. The second method
of propulsion is by a force-pumping mechanism, the essential fea-
tures of which are the strong muscular walls, the valves, and the
filling chambers. The first of these insures a comparatively quick
and strong contraction of the walls of the heart upon the fluid
contents, but the pressure (intra-vcntricular) is equally distributed
over the walls of the organ and the fluid is as likely to go back
through the way by which it entered as to go forward unless it be
blocked. The valves at the entrance of the heart stop this re-
gurgitation and insure the forward movement of the circulating

THE HEART. 107

fluid. To be mechanically effective the heart must till quickly.
This necessity is satisfied in arthropoda by a rilling chamber
around the heart — the pericardium — into which the blood flows
daring cardiac contraction. When the heart relaxes the collected
lymph quickly enters its cavity through the open valves. A sim-
ilar function is performed by the auricles of the mollusks.

In most invertebrates the blood escapes into tissue spaces at the
end of its arterial flow.

After traversing the tissue spaces and lacux.-e the lymph
makes its way into the vessels which return it to the organ of pro-
pulsion. The lacunae and tissue spaces of invertebrates corre-
spond to the lymph or serous cavities and lymph radicles of the
higher animals.

(c) The vertebrates, — above Amphioxus, — possess the high-
est type of circulatory system — the blood is propelled by a heart
fully equipped with valves and filling chambers. The Amphi-
oxus has two hearts, — respiratory and systemic. Fishes have a
respirator v heart whose strength is sufficient to carry the blood
through the systemic vessels after it has been aerated.

In the Amphibia and lower Reptiles there are two auricles but
only one ventricle which must serve both as respiratory and sys-
temic heart. In these animals there is, to a certain extent, a mix-
ture of the aerated and unaerated blood. The devices for insuring
the purer blood current for the cephalic end of the animal are to
say the least ingenious. In crocodiles, birds and mammals the
heart is double, each half being composed of an auricle and a ven-
tricle. The right half of the heart is the respiratory heart and
tin' left side the systemic heart.

The morphological details by which these various points are ac-
complished are matter for anatomy rather than for physiology.

/;. ANATOMICAL INTRODUCTION.

1. THE BLOOD-VASCULAR SYSTEM.

Structural feature- of the heart and vessels which are of especial
physiological importance.

a. The Heart.

]. The Musculature. — (a) Several muscle layers ; longitudi-
nal, oblique and circular, bo intricately arranged that ■ system

of liber- may often be traced iii .-ill of the directions in turn.

(j) Many liber- or bundles arise from the auriculo-ventricular
ring, and after making their circuit, return again to an opposite
Begmenl of the ring.

ION

CIRCULATION: INTRODUCTION.

(;-) Some bundles arise from the ring, make their winding cir-
cuit and terminate in a papillary muscle.

(d) The bases of the aorta
Fig. 62. :,11<l pulmonary arteries arc

surrounded by circular heart
fibers, and further, many of
the longitudinal fibers arise
from the region of the great
vessels.

(s) The musculature of the
left ventricle is very much
heavier than that of the right.
(Fig. 62.)

2. The Valves. — (a) From
the auriculo-ventricular ring
valves, convex on the auric-

Cross-section through a completely contracted lllar surface, project toward
human heart, a1 the iiinctiou of the middle and ,i o ,i * •

lower thirds. (KrehL.j the center ot the ring.

(fi) Each cusp, or flap, is
much thicker near its origin on the ring than near the free margin.

(j) Each cusp is stayed or guyed, from the ventral side, by
several tendonous cords which pass from the apex of a papillary
muscle to different parts of the
cusp, (see Fig. 63.)

(ft) The cusps meet at a, not
in a common tangent line, but
in a common tangent plane.

3. The Cavity of the Heart.
— (a) The dilated cavity of the
left ventricle is an inverted ob-
lique, quadrilateral pyramid,
presenting irregularities of sur-
face, due to columnese carnese
and papillary muscles. Its
volume in the adult male is
about 180 c.c. (fi) The con-
tracted cavity of the left ven-
tricle presents in the upper seg-
ment a quadrilateral outline, in

the lower segment, a triangular ggSf^'SL'' *"" °f ^^
outline. From the central cav-
ity, which at the end of systole may be almost obliterated, nu-
merous crevasses pass out into the wall of the ventricle. These
crevasses represent spaces between the fleshy columns or papillary
muscles. ( Fig. 62, )

(/-) The dilated cavity of the right ventricle presents, on cross

\t'u-r Krehl. Diagram showing the general
trrangement of the auricle-vent valves, a.v.r.,

THE BLOOD VESSELS.

109

section, a crescentic outline. It is much shorter than the cavity
of the left ventricle, though its volume is the same.

(d) The closed cavity of the right
ventricle presents a series of irregn- pIG ^4,

lar crevasses which together describe
a crescentric held. (Fig. 62.)

b. The Blood Vessels.

1. The Arteries and Veins are

composed of practically the same ele-
ments in the same arrangement ; the
principal difference being the propor-
tion of the different tissues entering
into the composition of the several
layers. The walls of the arteries are
thicker, very much thicker. (Fig. 04.)

Fig. 65.

r fegTSiggtec^feJJ-j b^i-y

Transverse section through a micro-
scopic artery and vein in the epiglottis
of a child." A, the artery, showiog
the nucleated endothelium, the circular
muscular media, and at */ the fibrous-
tissue adventitia ; V, the vein, showing

the same layers ; the media is very much
thinner than in the artery. (KLEIN'S

Atlas, j

This is important for the
following considerations :
First, The greater thickness
enables them to sustain the

xJfi&^ikifi^r1 J>^^* greater blood-pressure; Sec-
>^^^5^~Cc3?^^{ ond, Their greater resistance

m of thoracic aorta as seen under alow power, enables tliein to withstand
«, the inner e,,at consisting of three layers, viz.: i. ,..:,,,., nvtorn'il nvoaairra p

Epithelium seen as a fine \. 2. 8ub-epithelial. ::. ,mm" t.\uiii.ii pieeauie, e.

Elastic layer- in the part of the inner coat, al Its ,, from mUSClllar eontrac-
jiirii.'ticin with the middle, a layer of longitudinal mus- «7, '

cular fibers is represented as cut across. &, middle coal tioli or pressure 01 clothing,
•ritb its elastic membrane ; c, outer coat with two vasa . . .. ,

-■iimmc after Toldt.j thus the parts supplied are

subjected to a minimum ac-
cidental variation of blood-supply ; Third, Their greater thick-
ness makes them less vulnerable in accidents. The large arte-
ries have relatively more elastic tissue, while the small arteries

and arteriole- have relatively more muscle-tissue. The reason is

evident : The large vessels receive the direct impulse from the

1 1(1

CIRCULATION: INTRODUCTION.

heart-beat. The heart can rest n part of the time. The walla
of* the arteries are under continuous, though varying -train.
Muscle tissue alone could not long endure the strain of unremit-

Fig. 66.

Fig. 68.

Epithelial layer
lining theposterior

till :l ul IV (2-iO

diameters, l (After

B( ll.u.ri.l;.)

FlG. 6

A small artery, J. and vein, r. from the Buhcutaneoas connective

rtic network of ar- ti^ f the rat, treated with citrate of silver. 1 17". diameters.) ". <>,

hi). Si ii mi i B after endothelial cells « i 1 1 • />. /<, their nuclei ; »<, </<, transverse markings due

i "i.i' i. to staining of substance between the muscular fiber-cells : <■. <■. nuclei <>f

conned ive tissue corpuscles attached to exterior of vessel. [S> iiakfkr. )

ting work ; only the unsensitive, unresponsive, elastic tissue can
be safely put to so prodigious a strain. In the small arteries and
arterioles the lateral pressure is very much less. The muscle
tilier- of these vessels, supplemented by a small amount of elastic
tissue, are quite sufficient to sustain it. Further, the supply of
blood to speeial organs is controlled by these muscle-fibers acting
under the influence of the vaso-motor nerves. (See Figs. *;.">, 66.)

THE LYMPHATIC SYSTEM.

Ill

2. The Capillaries. — The capillary wall, consisting as it does
of simple endothelial plates, can not withstand much pressure.
Most of the energy exerted by the heart has been expended in
overcoming the resistance between the heart and the capillaries so

Fig. 69.

Fig. 70.

Capillary vessels from the bladder of the
cat. magnified. The outlines of the cells Rre
stained by nitrate of silver. Schaefer.)

Capillary blood vessels in the web
of a frog's foot, as seen with the
microscope. (A. Thomson. The
arrows indicate the course of the
blood.

that the millions of capillaries are easily able to withstand the dis-
tributed remnant of pressure. Any increase of capillary pressure
tends t<> increase the spaces between the endothelial plates and
thus in turn to facilitate not only diapedesis of white blood cor-
puscles, but transudation of plasma. (See Figs. 09 and 70.)

■2. THE LYMPHATIC SYSTEM.

a. Lymphatic Follicles and Glands.

Lymphatic tissue is composed of two elements: 1st. A connec-
tive 1 1 — ii*- reticulum associated with stellate connective tissue
<-clb. This is called the A(l<n<>i<l Reticulum. 2d. Small round
cells which are enclosed within the meshes of the reticulum (Fig.
71). The lymphatic tissue, or adenoid tissue, is frequently found
in small quantities along the arteries associated with the perivas-
cular lymph channels; but it is usually collected in well-defined
-t ructuree called Lymph follicle-.

1. Lymph Follicles are simple lymphatic nodules which occur
in greaf numbers in the mucous membrane of the respiratory and
alimentary tracts. Each follicle is surrounded by a delicate but
close-meshed wall or capsule of fibrous connective tissue. Within
this capsule the whole space is tilled with typical Lymphatic and
adenoid tissue.

112

CIRCULATION: INTRODUCTION.

A lymph follicle receives its blood-supply from a vascular en-
velope composed of ;i louse meshwork of arterioles, from which
capillary Loops penetrate to the center of the follicles and return
the venous blood to the corresponding meshwork of venules.
Bach follicle has an afferent lymphatic, which brings a stream of
lymph which oozes through the adenoid tissue, and, emerging with
fewer old leucocytes and more young ones, is carried off by the
efferent lymphatic. Within the follicle old leucocytes which come
laden with different materials, gathered in their wanderings, be-
come helplessly entangled in the adenoid meshes and disintegrate.

Within the follicle is a closely-packed group of leucocytes which
are undergoing rapid reproduction by karyokinesis. Such a

Fig. 71.

Diagrammatic section of the lymphatic glands. ". /.. afferent, e. /. , efferent lymphatics ; C,
cortical substance; M, reticulating cords of medullary substance ; I. h., lymphoid tissue,/.*.,
lymph-sinus; c, fibrous coal sending trabecular, tr, into the substance of the gland. iS< haefeb. j

group of leucocytes is called a Lymph Knot; and this is the
source of the young leucocytes which join the efferent stream. So
the efferent stream from a lymph follicle or lymph gland may not
contain more leucocytes than the afferent stream, hut there will
be more young active ones and fewer old sluggish ones. (Fig. 72.)
■2. A Lymph Gland is simply a collection of lymph follicles.
The structural variations are shown in Fig; 71. The func-
tions are the same. The favorite locations of the lymphatic
glands seem to be the mesentery, the groin, the axilla and the
neck; though they are very generally hut sparsely distributed in
subcutaneous tissues.

LYMPHATICS OR LYMPH-VESSELS.

113

b. Lymphatics or Lymph-vessels.

(a) Lymph Radicles and Lymph Capillaries. — A lymph
radicle or rootlet is simply a connective tissue space which is lined
with endotheloid plates. These spaces are very irregular, sometimes
narrow chinks and crevasses, sometimes comparatively wide spaces.

Lymph capillaries conduct the lymph from these irregular col-

Fig.

Fig. 73.

Simple lymph-follicle from
conjunctiva of dog: «, lym-
phoid tissue, limited by the
ftbrona capsule (6) c, surround-
ing connective tissue. (After
PlEESOL.)

Elements of adenoid tis-
sue from partially brushed
section of lymphatic gland
of child : a, fibers of reticu-
lum ; b, lymphoid cells ; c,
expanded connective-tissue
plate. (After Piersol.)

leetmg-spacea to the lymph-vessels. Even the capillaries and the

smaller lymphatics are irregular in lumen. (See Fig. 74.)

(6) Lymph Trunks. — All of the larger lymph-vessels are pro-

Fig. 74.

Lymphatic plexus of central tendon of diaphragm of rabbit, pleural tide. Ki.kin.) a,
larger resseli with lanceolate cells and anmei b, e, lymphatic capillaries with wavy-

boi dered cells.

vided with valve-. The larger trunks have a regular Lumen and
walls quite like those of a blood vessel. (Sec Figs. 7 1 and 75.)

8

114

CIRCULATION: INTRODUCTION.
Fig. 7-"). Pio. 76.

Perivascular lymphatic
f6) enclosing a small artery
[a), from the silvered mes-
e ry of frog ; c, brandl-
ing lymphatic capillary.
(After Piersol.)

isj't w&y

mi

*-.--

Transverse section <>t' human tho-
racic duct : '. </', and ", respectively
the Inner, middle and outer tunics ;
x, endothelial lining, beneath which
lies the fibrous stratum containing
network of longitudinal elastic
fibers [y) ; :. longitudinally dis-
posed bundles of muscular tissue
within adventitia; v, capillary
blood vessels. (After Piersol.)

THE SPLEEN.

(a) Development. — In the human embryo its development
begins about the end of the second month. Its beginning may be

Fig. 77.

■in « itii a low power.
, in one of which

arterial twig-, . ,

Vertical section of a small superficial portion of. the human spleen, as -■•■■n mu
A, peritoneal and fibrous covering j b, trabei ala, c, c} Malpighian corpuscles, in
an artery is seen cut transversely, in the other longitudinally; d, injected art
spleen-pulp. (St blaefer after Koixikek.)

found in the mesentery posterior to the stomach and immediately
dorsal to the duodenum. At this point a very small terminal

THE SPLEEN.

115

branch of the cceliac artery, the future splenic artery, shows in the
perivascular lymph channels an accumulation of large lymphoid
cells with large granular nuclei. The steps of the development
are : The progressive development of lymphatic tissue, the pene-
tration of the mass by terminal branches of the advancing splenic
artery, the development of non-striated muscle tissue around the

Fig. 78.

Thin section of spleen-pulp, highly magnified, shoving the mode of origin of a small vein
io the interstices of the pulp, v, the vein, filled with blood-corpuscles, which arc in continuity
with others, 6/, filling up the interstices of the retiform tissue of the pulp ; w, wall of the vein.
The shaded bodies amongst the red blood-corpuscles are white corpuscles.

arterial branches and in a coarse mesh-work throughout the mass,
the pushing out of the mesentery which forms a splanehnopleuric
cover for the spleen, and the definite encapsulement of the organ
with connective tissue and non-striated muscular tissue.

(b) STRUCTURE. — Inasmuch as the spleen begins in a develop-
ment of Lymphatic tissue, it is to be expected that its structure is
analogous to thai of a lymph gland. Such is the case. The
spleen sustains to the blood vascular system somewhat the same
relation that the lymph glands sustain to the lymph vascular sys-
tem : and the blood oozes through the spleen reticulum in much
the same way that lymph oozes through a lymph gland (Figs. 77
and 78).

1. HISTOGENESIS OF THE CIRCULATORY ORGANS AND

TISSUES.

The circulatory system is that system which more than any
other is -hut off from the outside world. One would expeel that
tlii- system of organs, which is, jmr excellence, a system devoted
to internal relations, should he derived from the entoderm ; ami
it i-. Yon remember that the entoderm is curly differentiated
into hypoblast, mesoblasl and notocord. In this differentiation

the mesoblasl ha- withdrawn farther from the outside world than

the entoderm, The mesoblasl early divides into primitive

110 CIRCULATION: INTRODUCTION.

segments, somatopleure, splanchnopleure and mesenchyme. The
last named arises latest and is derived from the lirst three [Hert-
wigl. From the mesenchyme are derived all the organs and tis-
sues of the circulatory system: (i) The Mood itself is purely a
derivative of the mesenchyme, (n) The blood vessels and lym-
phatics are also derived solely from the mesenchyme ; viz., the
endothelial layer of the intima, the involuntary muscle fibers of
the media and the elastic libers of the vessel walls, (in) The
spleen, lymphatic glands and the red-marrow of bones are also
wholly mesenchymal tissues, — excepting the splanchnopleuric
peritoneum of the spleen. The nerves which supply the muscles
of the heart and blood vessels arc derived from the ectoderm and
are distributed to the circulatory system through the vago-sym-
pathctic nervous system.

C. PHYSICAL INTRODUCTION.

1. THE FLOW OF LIQUIDS THROUGH THE TUBES.

The analogy between the nervous system and a telegraphic sys-
tem is a striking one and frequently cited ; even more striking
is the analogy between the circulatory system and the water-sup-
ply system of a city. The water-supply starts from a central
pumping station, — or elevated reservoir, — passes through large
mains at first, and is distributed through branches that are smaller
and smaller as they subdivide on their way to different houses.
The blood-supply starts from the centrally located, pumping
heart, passes through large trunks at first, and is distributed
through branches that get smaller and smaller as they subdivide
on their way to different tissues.

The physical laws of the circulation are the physical laws of
the flow of liquids through tubes. No adequate knowledge of the
circulation can be gotten without first a knowledge of the physical
laws.

«. The Flow of Liquids under Continuous Pressure.

" The flow of liquid is caused by a difference of pressure between
the different parts of a mass of liquid." (Daniell.)

The attraction of the earth — gravitation — furnishes the continu-
ous pressure which causes a flow of liquids along channels or
through tubes. The conditions necessary are an elevated source
and a low outlet. Let us take, for example, a reservoir as a
source of flow. Let an aperture be made in the reservoir any
distance (//) below the surface of the water. The pressure upon
the water just inside the aperture is greater than pressure at the

PH1SICAL IXTROD UCTION.

11

surface — atmospheric pressure — because it supports the weight of
the superposed water. It will therefore flow away from the
higher pressure within the aperture toward the lower pressure
without the aperture.

1. Velocity. — Torricelli's Law: The rate at which a liquid is
discharged through on orifice in the waU of <t reservoir is equal to
the velocity which would be required by a body jailing freely through
a height equal to the distance between the orifice and the surface of
the liijiiiii.

From the law of falling bodies we know that the velocity (r) is
equal to the square root of twice the product of the height by the ac-
celeration due. to gravitation (g), i. e., v =V2gh =s/2 x 981 x h
= 44.3 >/h. Velocity thus obtained is expressed in centimeters
per second.

2. Discharge. — Within reasonable limits velocity is not modi-
fied by the size of the aperture. Discharge (Z>) on the other
hand, is equal to the

product of the area (a) Fig. 7'.).

of the jet by the velocity.
One would think that the
area of the jet would equal
the area of the aper-
ture, but such is not the
case. The fluid streams
toward the aperture
from various directions
and the jet is, in a way,
;i resultant of the various
streams just referred to
and emerges convergent to
reach a minimum diam-
eter in the " vena cont-
racta " very near the ap-
erture. The real diam-
eter of the jet is the di-
ameter of the vena con-
tracta. A practical veri-
fication of the principle
i- much simplified by

inserting into the aperture a shorl smooth nozzle. The diam-
eter of the j«'t will equal the diameter of die nozzle. The dis-
charge (D) equals the product of the urea of the jet (a) by Ihe
velocity (»), i. e., I) = <t x v, but a = xr2 and v = I l.3\/// ; there,
fore, D- l \:.\-rVh.

Note that 44.3/t represents a constant factor thai is the same in

I IN

CIRCULATION: INTRODUCTION.

all experiments; so thai the discharge will vary as the square of
the radius of the jei and the square root of the height, i. e., I>

varies as r2>/h.

.'!. Pressure. — The pressure may be looked upon as the stress

upon

the liquid at I be point <>'

Fig.

>bservation. Take, for example,
the pressure of the water on the bot-
tom of a reservoir (Fig. 7!)). Every
square centimeter of the bottom sup-
ports the weight of the column of
water whose vertical dimension is
the depth of the water and whose
area (a) is 1 sq. cm. The area of
the bottom of the reservoir is not a
factor in the pressure. The height
of the reservoir, or rather the depth
of the water, is the only matter of
importance. In reservoir />' the
pressure upon area (1 sq. cm.) h is
the same as that upon area a of res-
ervoir A, because the height of the
column is the same. In reservoir ( '
the pressure upon area (1 sq. cm.) c
is the same as that upon area a or b,
because the area is the same and the
height of the column of water is the
same. If in reservoir B the pres-
sure on area h is equal to that on area a, so must the pressure on
area b' equal that on area a or area h, because the fluid will trans-
mit pressures equally in all directions. Then the lateral pressure
around the bottom of the reservoir must be as great as the down-
ward pressure. Such is the case. In the reservoir shown in Fig.
80 the pressure at the nozzle would be found by finding the weight
of a volume of liquid whose area equals the area of the lumen of
the nozzle and whose height is the depth of the liquid above the
middle of the lumen of the nozzle.

(a) The Measurement of Pressure, (a) The Unit. — The

pressure of the liquid or the stress of the liquid at the point of
observation is a form of energy. To express this energy in dynes :
P (in dynes per sq. cm.) = hgs. h = depth of liquid, g = accel-
eration of gravitation (i'<Sl ), g = specific gravity. It is customary,
however, to express the pressure in height above orifice or "head,"
and to ignore the factors g and g. This is especially convenient
because the pressure is usually measured with a mercury manom-
eter and expressed in "centimeters of mercury," meaning that the
pressure is sufficient to support a column of mercury so many
centimeters high.

Reservoir with lateral nozzle.

77/ YSIl 1 1 /. INTROD UCTIOX.

119

Fig. 81.

(ti) The Mercury Manometer. — (See Fig. 81). This instrument
consists of a U-shaped tube, one of whose limbs is usually bent at
right angles to facilitate its juncture with other
apparatus. Both ends of the tube (it and /;')
are left open. That limb through which the
pressure is transmitted (n) is called the proxi-
mal /iiii/>, the other the distal limb. When £.
the pressure is positive the mercury will
rise in the distal limb ; when negative it
will fall in the distal limb. The rise in
the distal limb (///) will be accompanied by
a corresponding fall in the proximal limb
(to'); the total pressure will be represented
by a column of mercury equal to 2m or x.
But a part of that pressure is due to an in-
troduced error when the fluid in the proximal
tube above the mercury is water or blood,
or a salt solution. We have introduced more
of this (in centimeters) than was in the prox-
imal tube before.

If the fluid which has been introduced with
the fall of the mercury in the proximal col-
umn is, say, ^ the weight of mercury, then
if //( =13 cm., the real rise of mercury due to
initial pressure is represented by 20 em. of

>x

mercury minus 1 cm. of mercury correction, Mercury manometer.
or 25 cm. mercury. Let us express the re-
lation- in more definite terms. Suppose the proximal limb to be
filled with water (Sp. (Jr. Hg=13.596). The corrected height (It)
of the column of mercury, when m is the rise in the distal
column :

// = 2m -

L3.596

27.192*/! - m
L3.596

26.192m
13.59G '

Tfu pressure in grammes per unit area f />) is equal to the height
of the column multiplied by the 8p.gr. of mercury.

V

hs =

26.192m

1 :;..-.« m;

x 13.596= 26.192m.

One may readily gel the pressure per sq. centimeter by measur-
ing in cm. the rise of mercury in the distal column and multiplying
that by 26.192 (26.2).

I'lu />,< isur< in dynes per unit area | P) is Pound by simply multi-
plying ji by //, for /' = hgs and /> = hs.

I' -= hgs = 981 x 26.192m = 2569 1/// dyne- per sq. cm.

I 21 1

CIRCULATION: INTRODUCTION.

To express 1 1 1 < - pressure in dynes per sq. cm. <>nc has only to ob-
serve in and multiply thai by 25694.

i; i Tin Piezometer is a simple instrument consisting of an up-
righi tube connected directly with the point at which the pressure
is to be measured. (Sec Fig. 82, I, II, etc.) Thepressure at the
bottom causes the liquid t<> rise in the piezometer until the weight
of the column balances the pressure at the base. To compute the
/' in dynes or the /> in gms. one applies the principles given above
lor the mercury manometer : A equals the rise in the tube as there
is no correction in this case. * for water would equal I ; so thai
p = h and /' = 981A.

(il) Pick's Spring Manometer, the Sphygmoscope, Tambours, Roy's
Piston, and other instruments of the same class are lor the obser-
vation of varying pressures and are constructed rather for qualita-
tive than for quantitative observations.

Fig. 82.

:y'

I i m it v

Reservoir with Piezometers.

(6) The Pressure of Liquid Flowing through Tubes. —
Fig. 82 illustrates an experiment with a reservoir, a horizontal
delivery tube and a series of piezometers. The piezometers indi-
cate faithfully the pressure of the liquid at the point where they
are severally in communication with the delivery tube. The pres-
sure in piezometer I is higher than that in II, that in II is higher
than that in III and so on. Note that the pressures are progres-
sively and regularly less as we proceed from the reservoir to the
end of the delivery tube. If there were only one piezometer and
that located at position VI the water would maintain the same
level which it shows in the first experiment. If there were sixty
'piezometers instead of six, along the same delivery tube the water
in every piezometer would rise to the line PD. This line is called
the pressure-slope.

LIQUIDS UNDER INTERMITTENT PRESSURE. 121

Why is the pressure loss in VI than in V? When the stream
of water has reached the point VI it has still to overcome the
resistance between that point and the delivery (D). The pressure
upward at VI is just the same as the pressure to the right ; i. e.,
the weight of the column of liquid in piezometer VI just balances
the "back-pressure" or resistance to the flow to D. Piezometer
A' measures the resistance beyond V, and therefore must stand
higher. The reservoir may be looked upon as a gigantic piezom-
eter. Continue the line DP to the reservoir ; the point PH is
the pressure-slope. All of that head of liquid between the line
PH.r and the exit (//) of the delivery tube is called the pres-
sure head or resistance head. The head or stand of liquid below
the line PH.r represents the quantity of potential energy which is
made kinetic and consumed in overcoming the resistance offered
by the delivery tube.

What becomes of the potential energy represented by that por-
tion of the water between PH,r and Y"Hy ? That energy is the
source of the velocity with which the liquid jets from the end of
the delivery tube. If one wishes to find the velocity he has only
to use the distance i/.v or the distance y'T> for h in the formula
r = >/'2r/h. The stand or head of liquid between PH.v and \\\//
is called the velocity head.

The velocity head (VH) plus the pressure head (PH) is called
the driving head (PH + VH = DH).

In studying the laws of the flow of liquid through tubes under
constant pressure we have to consider the following factors: (//.)
Driving head, (ti) resistance head, (j) velocity head, (o) lateral
pressure a- indicated by the piezometers, (s) resistance.

The solution of the following problems will thrown much light
upon the practical problems of the circulation : (i) What is the
total effect of increasing or of decreasing the driving head (a) ?
(ii) What is the effect of increasing or of decreasing the resist-
ance U), the driving head remaining the same? (in) What is the
effect "1" a simultaneous increase of («) and increase of (s)? (iv)
The effect of a simultaneous increase <>f (a) and decrease of (s) ?
(v) Decrease of (a) and increase of (e)? (vi) Decrease of (a) and
decrease of (e)? (vn) How may (y) be increased without increas-
ing {a.)'! (vni) How may (S) lie increased without increasing (a) ?
(i.\) What factor- cause a variation of velocity? (x) Of lateral
pressure ?

I). The Flow of Liquids Under Intermittent Pressure.
It i- understood by intermittent pressure that the pressure

-hall be exerted in ;i rlivt limieal -erics of ini|>iil>es such as is ol>-

ed in tin- working of a />"ih/>.

122 CIRCULATION: INTRODUCTION.

1. Intermittent Pressure Through Inelastic Tubes. — If a
pump replace the reservoir <>f Fig. 82, it will be found that the
liquid will flow from the distal end of the delivery tube in << series
of jets corresponding to tin- action of the pump, and that the
lateral pressure, as indicated by the piezometers, will also vary
with the actios of the pump, being highest ;it the tnomenl that the
liquid ia being driven from the delivery tube with greatest force.

(a) With Low Terminal Resistance in the delivery tube
the rise and fall of pressure is moderately accentuated.

(/>) With High Terminal Resistance, such as is afforded by
a capillary tube at 1), the rise and fall of the pressure within the
delivery tube is greatly accentuated.

2. Intermittent Pressure Through Elastic Tubes. — Instead
<>f an inelastic delivery tube use a thin rubber tube.

((() With Low Terminal Resistance one notes no essential
difference from previous observations with the inelastic tube.

(A) With High Terminal Resistance, however, there is a
marked transformation in the character of the stream. It issues
from the fine terminal capillary not in jets, but as a continuous
a ml, tinder favorable circumstances, constant stream.

How is this accomplished? The sudden influx of liquid
thrown into the tube by the pump expands the tube, bringing into
play its elasticity. When the pump reverses and the valve closes
the walls of the tube contract upon the contents and force liquid
out of the nozzle while the pump is tilling. If the pump acts
quickly enough, the jet from the nozzle of the delivery tube may
be not only continuous, but quite constant.

The quantity of liquid delivered from a capillary nozzle under
such conditions is naturally much greater than the quantity de-
livered from the same capillary nozzle with an inelastic delivery
tube. Other advantages will be discussed later.

c. The Flow of Liquids Influenced by Other Factors.

(a) The Size of the Tube. — If there were no friction the size
of the tube Mould be of no consequence. The liquid which lies next
to the wall of the tube, i. e., the liquid which wets the wall, does
not flow at all; the layer next to the wetting layer flows more
slowly than any other layer and the layer that is farthest from the
wall of the tube flows most rapidly.

The middle, rapidly flowing current has friction against the
next external less-rapidly flowing current ; and thus a large por-
tion of the kinetic energy may be expended in overcoming friction
'or resistance. Naturally the larger the tube the smaller the pro-
portion of friction. We may formulate the following law : The
resistance is in inverse proportion to the diameter of. the tube.

PRAXAGORAS. 123

Further : The resistance in a given tube increases with the velocity
of flow.

(6) The Change of Course, through bending of the tube causes
a change in the distribution of the resistance ; (greater in front of
the bend and less beyond it) but does not affect the final discharge
or velocity.

(c) The Effect of Varying Lumen is to cause a variation
of thi' velocity with the varying lumen. " Leonardo da Vinci," who
was a great hydraulic engineer as well as a great painter, formu-
lated this law: The velocity of the current at any point is inversely
proportional to its cross-sectional una.

The cross-sectional area of the capillaries taken together equals
500 to 700 times the cross-sectional area of the aorta.

(d) The Effect of BRANCHING is to introduce eddies and
whirls into the stream. This causes increased resistance. If the
ramification of the tubes leads to greater sectional area the velocity
will decrease proportionally ; if to smaller sectional area the
velocity will increase proportionally.

D. HISTORICAL INTRODUCTION.1

1. ARISTOTLE.

Dalton thus summarized the ideas entertained by Aristotle, re-
garding the heart and blood vessels :

"I. The heart is an organ for giving to the blood its final
elaboration, and for communicating to it the necessary clement of
vital heat.

" II. The perfected blood is received from the heart into the
blood vessels arteries and veins alike, and brought by their
branches and ramifications into proximity with the solid tissues
which it nourished by exudation.

"III. The pulsation of the heart is a momentary dilatation
from expansion of the blood in its cavities; this expansion being
produced by the animal heat combining with the ingredients of the
blood. The pulsation of" the blood vessels is due to the same
cause, and is simultaneous with that of the heart; the impulse
originating in the cardiac cavities being at once communicated to
the blood in every part/5

It may be added that Aristotle followed Hippocrates in the use

of the word artery (dprypia) for the trachia and not for a blood
-< I.

2. PRAXAGORAS.

The predecessors of Praxagoraa believed that all of the blood
- pulsate. Praxagoraa Bhowed that the vessels could be di-

the facta briefly summarized here the author i- Lndebtsd to Dalton' s ad-
mirable Little rolume on the Doctrines of the Circulation,

124 CIRCULATION: INTRODUCTION.

vided into two classes, the blood vessels (veins) and the air vessels

(arteries), to which he applet! (lie old term df/TV^ftia, distinguish-
ing these air vessels from the trachia by calling the latter the
" rough air-tube/' Anzfinia ror/.x-ca.

O 7 . ft J

3. THE ALEXANDRIAN SCHOOL.

This school was founded by Ptolemy. It was a real university.
Here Euclid taught geometry ; Archimedes taughl physics; Strabo
and Eratosthenes taughl geography, and Hipparchus and Ptole-
miuus taught astronomy.

Among the great teachers of medicine were Herophilus and
Erasistratus. " It was in their time and at the Alexandrian
school that the dissection of the human body was first legalized/'
* * * by the Ptolemies, the bodies of condemned criminals being
devoted to this purpose. Notwithstanding these facilities, it was
anatomy and not physiology which was the gainer. It was at
this school that the pneuma theory (see General Introduction) was
first elaborated. The teachings of Praxagoras and Aristotle, as
outlined above, were accepted and taught for four or five centuries.

Erasistratus accurately described the valves of the heart, but
he did not know their function. "The diastole of the heart, in
the physiology of the period, is an active expansion, drawing into
the right ventricle, as if by suction, a little blood to be used for
the nourishment of the lung, and into the left ventricle a little
pneuma (air) to supply the arteries."

"The terminal ramifications (of the blood vessels) are so small
that the blood is retained within them by the ' coaptation ' of their
walls. Consequently, although the mouths of the vein and the
artery lie side by side, the blood, nevertheless, remains in its own
vessels, and nowhere penetrates into those of the pneuma, when the
system is in its normal condition, lint when, from any disturbing
cause, the blood is forced over from the reins into the arteries a morbid
action results"

4. GALEN.

By dissections ( ialen determined the structural features of the
foetal circulation and the changes which take place in the circula-
tory system after birth. As Galen resorted to vivisection, he was
able to refute some of the ancient dogmas which were based upon
the observation of the dead body, and some of the hypotheses re-
garding the living body.

The first notable advance made by Galen was his demonstration
that the arteries norma//;/ contain blood. His part of the contro-
versy regarding this subject appears in a special treatise entitled :
" Whether the arteries naturally contain /dood." (Galenius, Opera
Omnia, Vol. IV., p. 703.)

GALFX. 125

" The general features of Galen's physiology are to be found
in his books on : The Functions of the Parts ; The Causes of the
Pulse; The Use of Respiration ; The Physiological Forces.

"In this system the liver was the central organ of nutrition
and sanguinification. From it all the veins took their origin, and
in its glandular tissue the blood was prepared from the elements
of the digested food, brought to it by the portal vein." * * *
"The blood in the venous system provided for the general nour-
ishment of the tissues. On the other hand, the arteries were also
full of blood, but of a different kind. The venous blood was
dark, thick and rich in the grosser elements of nutritive material.
The arterial blood was thinner, warmer, bright-colored, and,
above all, spirituous ; i. e., it contained an abundant supply of the
vital spirits, which it distributed throughout the body. Its
warmth it obtained from the heart, and especially from the left
ventricle in which the animal heat was generated; its vital spirits
being * * derived from the inspired air of the lungs.

Tlm.< the arteries contained vital spirits, not in the form of a distinct
gaseous body, but amalgamated with the other ingredients of the
blood/' " As the liver was the origin of the veins, so the heart
was the origin of the arteries."

The phenomenon of the pulse was thus explained : " This is a
force of off ire expansion dilating the artery and attracting the
fluids into its cavity from either direction ; while its subsequent
contraction causes an expulsion of its contents toward every 'point."
" The heart dilates to attract the necessary materials ;
remains fixed while using what it lias drawn into it ; and contracts
when discharging its superfluities." * * * (( The various acts
of reception and delivery are thus accomplished by the cardiac
movements aided by the valves."

"The functions of the heart and blood vessels are inseparably
connected with the act of respiration." * * * " The prime
object of respiration is the introduction of the pneuma, or spirits,
the characteristic ingredient of arterial blood."

Recall thai Erasistratue and the Alexandrian school had taught
1 1 1 : 1 1 the blood mighl pass from veins to arteries, under abnormal
conditions, wound or inflammation. Galen says, "The arteries
anastomose with the veins over the whole body, and they mutually re-
'■'/'■< from each other blood and xj/irits (nveuua) through certain in-
visible and extremely minute passages." (Passages, in (he tissue,
and in the intraventricular septum.) (Galenius, Opera Omnia,
Vol. III., p. 155.)

Note thai tin' communication of the veins and arteries was not
an observed fad in Galen's time, hut on hypothesis to account for

For the influence of Galen's doctrine upon medical teaching
< }( neral I nt reduction.

L26 CIRCULATION: INTRODUCTION.

5. VESALIUS.

Galen's knowledge of anatomy and physiology was gained
largely from hi-^ surgical operations and from dissection and vivi-
sections of lower animals. Vesalius founded his anatomy upon
the human body. This led to many points of controversy between
Vesalius and Galen and naturally hindered the acceptance of the
views of Vesalius by his contemporaries who were disciples of*
Galen. Vesalius was professor of anatomy ai three universities
in Italy (Padua, Bologna, Pisa), visiting each in turn. At that
time anatomy and physiology had not been recognized as separate
departments of biological science. Vesalius, though radical in
his anatomy, was conservative in his physiology, accepting the
former doctrines with slight modifications. He did not accept
without question Galen's theory that the venous and arterial Mood
communicated through the intra-ventricular septum.

Reirardino; the communication between different sets of vessels
in the tissues Vesalius says: "The branches of this vein (the
vena cava) distributed through the body of the liver, come in con-
tact with those of the portal vein ; and the extreme ramifications
of these veins inosculate with each other, and in many places appear
to unite and be continuous. (Vesalius, De Humani corporis
fabrica. Lib. VI., Cap. XV.)

6. SERVETUS.

This unique character was a theologian, lawyer, and physician
by education though he never successfully practised any of these
professions. In both theology and medicine he was a heretic and
because of the enthusiasm of his heresy he scarcely escaped being
classed as a criminal in the eyes of the law. The great work of
his life was a book entitled : " Christianismi Restitutio" In this
book, which was a plea for the restoration of Christianity to its
original form, he had occasion to discuss at length the " f Divine
Philosophy' of the life and spirits in the corporeal frame. After
giving the usual account of the vital spirits as produced in the
heart, and the animal spirits in the brain, he proceeds to explain
how it is that the life, or soul, is not seated in the substance of the
-olid organs, but in the blood, and that the life itself is the blood
as taught by Holy Writ." * * "It [the vital spirit] is gen-

erated from the mixture made in the lungs between the inspired
air and the finely elaborated blood which the right ventricle of the
heart communicates to the left. This communication, however, does
hi/I take place through the median wall of the heart, as commonly be-
lieved : but, by a grand device, the refined l>loo<l is driven fr&m the
right ventricle of the /war/, in a long course through the lungs. I>;/
the lungs it is prepared, assuming a bright color, and from the ram.

HARVEY. 127

arteriosa [pulmonary artery] is transferred into the arteria venosa
[pulmonary veins]." * * *

" By means of the same device, which in the liver makes a
transfusion from the portal vein to the vena cava for the blood,
there is in the lung- a transfusion from the vena arteriosa to the
arteria venosa for the spirit." (Servetus — Translated by Dalton.)

" His account of the mode of communication, in the lungs, be-
tween the two sets of vessels is very striking ; he says that it is by,
' another kind of vessel, formed from the vein and the artery/ as
if he had devined the existence of the pulmonary capillaries "
(Dalton).

7. COLOMBO.

Colombo, a pupil of Vesalius, demonstrated, "that that portion
of the blood which was to replenish the arterial system passed
from the right side [of the heart] to the left through the lungs,
and, furthermore that its arteriaUzaMon fool; place in these orggns,
a ikI not in tin ventricle.''

He demonstrated by vivisection that the pulmonary veins do
not pul-ate. He did not know of the branchial arteries and -up-
posed that a portion of the blood which passed to the lungs from
the right side of the heart went for the nourishment of the lung
-ul>-tance.

8. FABRICUS.

Hieronymus Fabrieus demonstrated the existence of the valves
as "a general feature of the venous system, and described them
in such a way that there was no longer any uncertainty as to their
reality or importance."

All the dissections, and vivisections and speculations of the
anatomists and physiologists had not, up to the end of the seven-
teenth century, revealed the fact that there musl be return to the
circulatory center — liver and heart as then understood — from the
periphery, but the veins as well as the arteries were supposed to
carry efferent streams into peripheral parts — legs, arm-, head.
The prodigious inconsistencies attending tins theory neither
seemed to arouse question, oor to incite to investigation.

!). HARVEY.

In 1628 William Harvey published ;i work on the circulation
(Harvey, De Motu Cordis et Sanguinis. Frankfort, L628).

In tin- remarkably concise and conclusive treatise Harvey sum-
marizes the work of nine years of investigation on the circulation.
I [, successfully demonsl rates :

Thai the heart passively dilates and actively contracts \ (n)
thai the auricles contract before the ventricles do ; fin) thai the

L28 CIRCULATION: INTRODUCTION.

contraction of the auricles forces the blood into the ventricles ;
(iv) that arteries '"have no 'pulsific' power/' /'. e., they dilate
passively, "since the pulsation of the arteries is nothing else than

the impulse of the Mood within them ;" (V) that the heart is the
organ of propulsion for the blood ; (vi) that in passing from the
right ventricle to the left auricle, " the blood transudes, through the
pulmonary parenchyma, from the right ventricle of the heart into
the arteria venosa (pulmonary veins) and the left ventricle; (vn)
that the quantity and rate of passage of blood peripherally from the
heart makes it a physical necessity that most of the blood return
to the heart ; (vm) that the blood does return to the heart by way
of the veins; Harvey could not find evidence of anastomosis be-
tween arteries and veins and did not believe that such existed.
He believed that the blood Jittered through the tissues.

He demonstrated to the full satisfaction of most of his colleagues
that the blood made a complete circuit of the arteries and veins
propelled by the heart, i. c, he demonstrated the circulation of the
blood.

10. MALPIGHII.

Marcello Malpighii, made professor of medicine in Bologna
University in 1661, had the aid of a microscope and was therefore
in a position to clear up the problem as to how the blood passes
from the arteries to the veins. Malpighii demonstrated the capil-
lary circulation in the lung of a frog.

THE PHYSIOLOGY OF CIRCULATION. 129

THE PHYSIOLOGY OF CIRCULATION.

A. CLASSIFICATION OF THE FLUIDS, ^ISSUES AND ORGANS.

B. THE CIRCULATING FLUIDS.

1. THE BLOOD.

I. THE PHYSICAL PROPERTIES.
II. THE MORPHOLOGY OF THE BLOOD.

a. The Red Blood Pressure.

b. The White Blood Corpuscles.
e. other Morphotic Elements.

III. THE CHEMICAL PROPERTIES OF THE BLOOD.

IV. THE FUNCTIONS OF VARIOUS PORTIONS OF THE BLOOD.
V. THE TOTAL QUANTITY OF BLOOD IN AN ANIMAL.

VI. THE PROTECTION OF THE BLOOD SUPPLY.
». The Location of the Vessels.
b. The Coagulation of the Blood.
VII. THE EFFECT OF HEMORRHAGE.
VIII. THE TRANSFUSION OF BLOOD.
IX. THE PHYSIOLOGICAL VARIATIONS OF THE BLOOD.

2. THE LYMPH.

I. THE PHYSICAL PROPERTIES.
EL THE MORPHOLOGY OF THE LYMPH.
III. THE CHEMICAL PROPERTIES op THE LYMPH.

C. THE FORMATION AND DESTRUCTION OF THE CORPUSCLES.
1. THE FORMATION OF RED BLOOD CORPUSCLES.
l'. THE DECAY AND DESTRUCTION OF THE BED BLOOD < 0RPU8CLES.
:;. THE FORMATION AND DESTRUCTION op LEUCOCYTES.
I. SUMMARY op pin; FUNCTIONS OF THE SPLEEN.

J). TH!". CIRCULATION OF THE FLUIDS.

1. THE ACTION <>P TUP EEART.

2. TUP I ll:< ULATION OF THE BLOOD.

n. Tin; < n:< ii.ation IN Tin; ARTERIES.

b. Till. Cl» l I.ATIoN IN THE CAPILLARIES.

e. Tin; Circulation in the Veins.
.;. THE « Il:< ULATION <»| THE LYMPH.

n. In iiii; LYMPH Rai»m i.i.-.

/-. In iiii. I.vmi'ii a 'i i< >.
/•;. THE CONTROL OF THE ORGANS 01 I LR( I LATION.
i. Till. [NNERVATION OF Till. I ll:< I LATORY SYSTEM.

«. Tin; INNERVATION <>i iiii. HEART.

b. Tin. |sm.i:\ Alios oi i in. Aim BBIE8.

■i. AHAPTATIVP COORDINATIVE OF TUP ACTIVITIES OF THE I [R-
CULATORY ORGANS.

9

130

CIRCULATION.

THE PHYSIOLOGY OF CIRCULATION.

L CLASSIFICATION OF THE FLUIDS, TISSUES AND

ORGANS.

Fluids of the Circulatory Sj stem.

I'.l 1. /

Lymp

/'■'

y Plasma.

„Red.
White.

\
Leucocj tea.

\ /

NCorpuscli — . Lymphocytes.

/

,..,,. r Red Mai row of Bones,

rissues and Organs for the l-m-matum I , , , ,

, ■ .■ ,• i I.vni]ili Glands,

or I >es1 niri i. in .it i orpuscles. i ,

I Spleen.

Organs of Transmission of Fluii

(If [{ln.nl.

Of Lymph.

r Heart.

1 Lrteries.

, Capillaries,

v. Veins.

i i.\ oiph-radicles.

i Lymphatics.

< trgans of Control.

j — " << - <£S£

. Parts of V ago-Sympathetic System.
' Vaso-Motor Nerves.

II. THE CIRCULATING FLUIDS.

1. THE BLOOD.

I. THE PHYSICAL PROPERTIES.

1. Physical Constitution of the Blood. — The blood is a
liquid. The fact that the blood is not transparent loads at once
to the conclusion that it i- not a homogeneous Liquid, but that there
are particles held in suspension. Johannes Miiller succeeded in
separating the liquid from the suspended particles by filtration.
Before that time, however, the microscope had revealed the fact
that the particles were corpuscles <>r cells, — highly specialized
cells, however. The Liquid in which the corpuscles are suspended
is called Liquor sanguinis or plasma. There are three methods of
procedure in separating blood into it> physical components :

(a) By Filtration. — rohannes Miiller succeeded in filtering
frog's blood after adding to it a small quantity of MgSO^ or

THE PHYSICAL PROPERTIES.

131

NaJSO, or i per cent, sugar. He tailed to filter mammalian
blood after the same method ; but Alex. Schmidt has done so re-
peatedly with horse's blood if proper precautions are taken, in-
stantly subjecting the drawn blood to 0°(\, mixing with 20 per
cent, of its volume of Xa.SO, ; and filtering after an hour or two.

Pig. 83.

ii,. hematocrit. The attachment at tbi upper end of the vertical ghaft Is made to rotate

at a ipeed of 7000 to Ht i per minute by meant* of the gear-work ol the body ol the instr int.

Kach arm of ti latin a attacl ml l« provided with a capillar] tube which is graduati

ixions. If the nil"- i»' filled with M I and rotated for 2 or 3 minutes at the speed above

mentioned thi corpu t le* will be thrown to the r end and the volume percent maj be read

,,H on the ml"-. An enlarged view of tube with centrifugalized blood.

b) I'.-. 81 B8IDBNCE. — II" the blood of a mammal, — especially
,,f;i horse, — be mixed as above described, with 20 percent, of its
volume of saturated solution of MgS04 or N:i,SOl ami subjected
instantly to freezing temperature ii is fo I that the corpuscles

L32 CIRCULATION.

will sink t<> the bottom leaving the clear plasma above. This is
facilitated l>v oiling the inner Burface of the receptacle. If the
conditions are very favorable the blood from the jugular vein of a
horse may separate without the addition of the salt solution.

(e) By CenTRIPUGATION. — If the blood of any animal be
drawn into a capillary tube and instantly subjected to eentrifuga-
tion the heavier corpuscles are thrown to the outer end of the
tube and the separated plasma and corpuscles may be quantitatively
determined. Fig. 83 shows a centrifuge or hematocrit ; a speed
of 7, 0(H) to 10,000 rotations per minute is sufficient to throw all the
corpuscles to the outer end of the tubes in 2 or 3 minutes. The
volume per cent, may be read off on the graduated capillary tube.

2. Color. — The color of the blood in the body varies from
light scarlet in the arteries to a dark bluish-red in the veins.
Owing to the physical properties mentioned above the blood is
opaque — even thin layers of it obstructing the light. The bright
red color of the albino's eyes is due to the blood of the central
artery of the retina — unobstructed from view by the translucent
iris. The pink color of the lips, nails, conjunctiva and oral
mucous membrane in health is due to the blood. If the blood is
lessened in quantity as in anaemia the pink gives place to a pale
or even waxy white color ; while in asphyxia and certain serious
heart lesions these parts take on a ghastly bluish color.

3. Odor. — Any one who has been present at a slaughtering has
noticed the peculiar odor emitted by the freshly shed blood. This
odor is somewhat different in the blood of different animals and
is due to the presence in somewhat varying relative amounts of
volatile fatty acids. In blood which has been shed for some time
the odor may be revived by liberating these volatile fatty acids
with concentrated H2S04.

4. Taste. — Blood has a saline taste clue to the salts dissolved
in the plasma.

5. Specific Gravity. — The specific gravity of the blood as a
whole is 1056 to 1051) in man, and 1051 to 1055 in woman ; in
children it is less and is subject to greater variations. This is a
composite specific gravity made up of plasma 1007 and blood cor-
puscles 1 105. It is due to this difference in the specific gravity
of the plasma and corpuscles that separation by sedimentation or
by centrirugation is possible. As the specific gravity of the blood
has some clinical importance it may be determined as follows
(Landois) : Take 10 small beakers each containing a few c.c. of
XaSO,, the first beaker containing a solution having Sp. Gr. of
1050, the next 1052, and so on. Eject a small drop of blood
into each in turn, from the horizontally placed tip of a pipette
and watch the results : if it sinks in 1050, remains stationary in
L052 and rises in 1054, the Sp. Gr. is 1052.

,£>'

o

<D

THE MORPHOLOGY OF THE BLOOD. 133

2. THE MORPHOLOGY OF THE BLOOD.

a. The Red Blood Corpuscles.

1. Form. — The red blood corpuscles of man are circular, bi-
ooncave discs.

The accompanying figure (Fig. 84) shows the typical corpuscles

Fig. 84.

Fig. 85.

En man blood corpuscles. ", red corpuscles, Red globules of the blood, adhering together, like

seen flatwise; '<, rea corpuscles, seen edgewise; rolls of coin. (Dalton.j
e, white corpuscles. | Dalton.)

when seen under the most favorable circumstances, floating in
fresh plasma.

Fig. 80.

Fig. 87.

tie blood, shrunken, with their Red corpusclei of blood, after the Imbibition ol

Dotchi 'i (Dalt water, i Dalton, i

l-".» CIRCULATION.

[fthe film of blood is Bomewhaf deep and the glass on which it
is spread is jarred or shaken the discs readily form into roulettes like
rolls of coins (see Fig. 85). [f after being drawn the blood is ex-
posed to the air too long, or if the plasma be diluted with a hyper-
istonic fluid, or fluid of greater density than the plasma the ivl cor-
puscles become crenated as shown in Fig. 86. [f on the other hand
the plasma be diluted with a hypisotonic fluid, i. e., of less density
than the plasma, the corpuscles at once swell and assume a form
shown in Fig. ST. finally becoming quite spherical. If pure water
be used the haemoglobin will be gradually dissolved and the cor-
puscles appear bleached out. Let a very thin film of blood be
"spread" npon a cover glass, "fixed" by heating at 100° C,
and stained with a fluid of the following formula :

( Ehrlich-Bondi powder (Griibler) 1 gm.

< One-half per cent, acid Fuchsin 5 c.c.

I Aqua dist 2o c.c.

Most of the red corpuscles of the field will have the form
shown in Plate I. (1). An occasional one may have one of the
other forms : Normoblasts, (2), microblasts, (•'}), or megaloblasts,

2. Size. — There are two methods of determining the size of a
microscopic object, (i) Its image may be projected upon a scale
by a camera lucida and the dimensions determined, (n) A much
more convenient method is to measure directly, objects in the field
of the microscope, with the aid of an eyepiece micrometer. By
one or the other — usually the latter — of these methods the aver-
age diameter of the red blood corpuscles has been determined,
and is 7.7 //, or 7.7 micro-millimeters [a micro-millimeter is one-
thousandth of a millimeter]. It has been found that there is
considerable variation in these dimensions, measurements of nor-
mal corpuscles varying from 6.7// to 9.3//. The maximum
thickness of a red blood corpuscle is about 1.9//. The size is
somewhat diminished by septic fever, asphyxia, or the adminis-
tration of considerable morphia ; and is increased by alcoholi-m,
quinine, or watery condition of the blood. The size of the red
blood corpuscles has had considerable medico-legal importance ;
but the fact that the corpuscles of animals frequently associated
with man fall within the limits of variation of human corpuscles,
has led to a general distrust of this evidence. The average diam-
eter of the red blood corpuscles of a dog is 7.3 fi (varying from
6.6 fi to !i //), of a eat 6.5 fi and of a rabbit (5.9 //..

3. Number. — (a) Tin-; Instruments Itsi:i> to Count the
Corpuscles. — The total number of corpuscles can only be esti-
mated. The number pro unit volume can be exactly determined
by -mil instruments as the Gower's Hemacytometer or the Zeiss

THE MORPHOLOGY OF THE BLOOD.

135

blood-corpuscle counter. The use of either of these instruments
involves the dilution of the blood with a known quantity of some
other liquid. Fig-. 88 shows a Zeiss counter in its case. The in-

Fig

The Thoma-Zeiss blood-count r. The mixing pipette iu which each volume of blood is
dilated to 100 to 200 volumes. .1, li and C, plan and elevation of the counting slide.

strument consists of a diluting pipette and a ruled slide for the
microscope stage. In diluting the blood the observer draws from
a fresh drop of blood a quantity sufficient to fill the pipette to the
line marked 1, then a quantity of the diluting fluid sufficient to
fill the pipette to the line marked 101. The mixing chamber of
the pipette contains 100 volumes of fluid, one of which is blood.
The inner circle of the slide is ruled into squares whose sides are
i mm. The ring surrounding the inner circle is a groove whose
Office is to receive the excess of blood placed upon the inner sur-
face.

The quadrangular plate outside of the groove stands JL mm.
higher than the ruled circle. When a cover-glass rests upon the
quadrangular plate it incloses over each square of the ruled circle
a volume of fluid whose dimensions are fo uiiu.x u\ mm. x y-g-
Him. = 4 (J'0 (| cubic mm.

(h) Tin: Use of the Zeiss Cobpuscle Counter. — One

dilute- the blood a- directed above, mixes it thoroughly by
-baking, and force- oul a drop of the mixture upon the ruled

circle. The cover-glass i- put in place, the slide brought under
the focus of ;i microscope and the average number of corpuscles
determined in each square. This average is multiplied by 400,-

000 to 'jet the number of red blood corpuscles in one cubic milli-
meter of blood. If one u-e- pure water the corpuscles will swell ;

if one u-e- 2 per cent, -alt solution they will shrivel. If the
Dumber alone is to be determined tin- change in size is of little

136

CIRCULATIOS.

importance, and one may dilute with :i 2 per cent, solution of
sodium chloride. If, however, one wishes to determine number
and size at the same time it is necessary to dilute the blood with

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Appearance of slide under about 500 diameters magnification. One counts all corpuscles
which lie upon the right and lower boundaries of each square.

a fluid which will not extract water from the corpuscles, i. e.
with an isotonic fluid. Such a fluid is the aqueous humor of the
eye, which may be collected in sufficient quantity in sterilized
pipettes from fresh ox-eyes, using one pipette for each eye. More
usual is blood serum, collected from a clot. The difficulty of
having these fluids always at hand makes the use of an "artificial
serum " most advisable.
Artificial serum :

Solution of p;nm arabic (sp. gr. 1020) 20 c.c.

NaCl ( " " " ) 30 c.c.

Na2S04 ( " " " ) 30 c.c.

80 c.c.

Using this fluid one may with an eye-piece micrometer and a Gower
or Zeiss counter determine at once the size and the number per
unit volume. The normal average number of red blood corpuscles
per cubic millimeter of blood is, in man 5,000,000, in woman
4,500,000. In any particular specimen of blood the number of
red blood corpuscles per cubic millimeter will vary with varying

THE WHITE BLOOD CORPUSCLES OR LEUCOCYTES. 137

proportions of plasma and corpuscles. It follows then that any-
thing which tends to increase the volume of the blood plasma will
decrease the number of corpuscles per cubic millimeter of blood ;
while anything which tends to decrease the volume of the plasma
will increase the number of corpuscles per cubic millimeter of
blood; i. c, the relative number of red blood corpuscles varies
inversely as the amount of plasma. The relative number of red
blood corpuscles will be increased by the passage of the blood
through cutaneous arterioles and capillaries, after use of solid
food, and after free perspiration, diuresis or diarrhoea. The rela-
tive number of red blood corpuscles will be decreased by the
passage of the blood through intestinal capillaries after a fluid
meal ; also by any causes leading to sudden decrease in perspira-
tion or excretion of water from the kidneys.

If the corpuscles do not vary in size it is clear that in succes-
sive examinations of the blood of the same individual the propor-
tions of red corpuscles found by centrifugation will be approxi-
mately proportional to the number per cubic millimeter. If the
corpuscles vary in size the number will not be proportional, an
increase in number being accompanied by a corresponding decrease
in size.

(6) The White Blood Corpuscles or Leucocytes.

These cells are composed of unmodified protoplasm. They are
wholly unspecialized and are the potential equivalents of a primi-
tive unicellular animal ; c. (/., the amceba. They are identical
with the lymph corpuscles and with the wandering connective
(issue cells. In summing up their physical and morphological
characters Landois says : " These cells consist of more or less
spherical masses of protoplasm which is sticky, highly refractile,
-oft. mono- or multi-nucleated, capable of amoeboid movement
and devoid of an envelope [cell membrane]." They vary much
in Bize — Aft to 13 ju — as well as in numerical proportion to the
red blood corpuscles, the average proportion being 1 to 350. This
proportion is increased during pregnancy, after parturition, and is
very lunch decreased by fasting. This proportion may be de-
termined while making ;i count of the red corpuscles. It is neces-
Bary to stain the white corpuscles in order to be able to readily

distinguish them from the red. To this end Toisson's solution

i- used as a diluting fluid.1

1 Toiuon'a solution :

Methyl riolet 6 b 025

Sal I 1

N:i.-I ), S

Glycerine 30

\'iu:i <li-t. q. t. ad 200

138 CIRCULATION.

This is i" be used 1—200 ; i. e.f till the diluting pipette to the line
0.5, instead of 1, with blood before diluting.

Thr abnormal increase in the relative number of leucocytes is
characteristic of the disease leukaemia ; and may lie associated
with other affections of the Mood or blood-forming organs.

The minute structure of the leucocyte is not revealed to the eye
without the use of some system of differential staining. To
Ehrlich we are indebted for the first systematic work in this field.
He found that grannies in the cytoplasm reacted differently to
aeid, neutral and basic stains. The granules which take the acid
stain, cosin, he called eosinophiles, those which take the neutral
dyes he called neutrophiles, and so on, differentiating different
classes of granules. As the subject was studied it was found that
classification of the leucocytes, according to their reaction to the
stains, is convenient and valuable clinically. The term eosino-
phil and neutrophile has come to be applied to the leucocyte and
not to the granules alone. The most common leucocyte is the
polymorpho-nuclear neutrophile, or simply neutrophile; also found
sparingly in normal blood is the eosinophile. The accompanying
plate (Plate II.) gives the varieties of leucocytes.

There may be an abnormal proportion of the normal leucocytes
or there may be an appearance, in considerable numbers, of the
rarer forms of leucocyte. This subject is discussed in extenso in
the clinical treatises on the blood.

c. Other Morphotic Elements of the Blood.

1. Blood Platelets of Bizzozero are "pale, colorless; oval,
round or lenticular discs of variable size " — av. ■"] a — whose
origin, function and destiny are vet under discussion, and the
confusion of theories makes it unsafe to venture an opinion. This
much, however, seems certain : The plates disintegrate directly
after the shedding of blood, and inasmuch as the microscope re-
veals little clumps of the granular debris of the plates where the
fibrin fibrils cross, the theory that these problematic bodies are
active agents in coagulation seems to have a justifiable basis. The
part they play is probably to furnish one s< nine < >f the fibrin ferment.

2. Elementary Granules are minute particles of proteid matter
probably arising from the disintegration of white corpuscles or of
the blood-platelets.

III. THE CHEMICAL PROPERTIES OF THE BLOOD.

a. Chemical Composition.

Analysis of the blood proves it to be composed of 77o to S00
parts of water and 200 to 225 parts of solids. The solids are

-

:

-

'J io

THE CHEMICAL PROPERTIES OE THE BLOOD.

139

\\>'l to 2l7Jparts of organic and 7 to 8 parts <»f inorganic matter.
The organic matter is composed of haemoglobin, of proteids, fats,
and traces of sugar, while the inorganic matter is composed of
NaCl, KC1, NaHC03, Na2HP04, CaHP04, CaS()4, MgCl2, etc.

The best idea of the chemical composition of the blood as a
whole may be obtained by first separating the blood into plasma
and corpuscles by centrifugation, and then analyzing each sepa-
rately. Human blood so treated would give approximately the
results recorded in the following table, which is the result of an
analysis reported by Halliburton :

Chemical
composition

of Blood.

Plasma Av.

Max. 567.
Miu. 456.

Take 100
parts.

f Water 90.29^

( \ Serum Albumin 1 - „ ^

Proteids -< Serum Globulin i" '• ■'

0lya°lc ■{ ( l-il.rin .... 0.4*

Solids
9.71 ,

I

Inorganic

(I.S.V,

L Extractions : Fats.ete .0.56

f \ NaC1 >.

Soluble J KC1 |

) Salts. I NaHCO, .... 0.85*

\ I Na„HP04 >

Insoluble ( CaHPO«

V. Salts. \ CaS04 J 100.00

[Water 68.80*

f

( lorpuscle8.

Av. !> .

Max. 54. 1 .

] Solids .
Min. 43.3*. i S1.2J

Take 100
parts.

Organic

:i0.4

Proteids globin I tin I ' e-
29.79*. - 27

I Globulin
I Globulin .'. 2.43*

^27.36*

Fats. jJrV'1!"- !

( Cholosteriu J

NaCl
Inorganic J M^g,

L.Mg,(P04)a
Fe. [Sec Bae matin. ]

0.61*

(I. so,
100.00

Reaction. — The reaction of the blood arises not from any pecu-
liarity of the corpuscles but from the plasma. This fluid is a
complex one and among other constituents contains Xa.,IIP()| and
NaHCOg which give it an alkaline reaction in freshly shed blood ;
but -lied blood rapidly loses its alkalinity.

The average alkalinity of the blood is equal to that of a 0.2 per
cent, solution of . sodium hydrate. The reaction of the blood may
be qualitatively determined by placing :i drop upon the surface of
;i plaster of Paris disc which has been impregnated with neutral
litmii-. II' after a moment's contact the blood be wiped off the
fiini blue will be seen. The alkalinity of the blood may be de-
creased during health by (i) great muscular exertion, and (n) by
exposure of the blood to the conditions of coagulation. Patho-

L40 CIRCULATION.

logically the alkalinity of the blood may be increased by persistent
vomiting, and decreased by (i) anaemia, (n) uraemia, (nij rheuma-
tism, (iv) high fever, (v) diabetes, (vi) cholera.

The quantitative determination of the degree of alkalinity of the
blood becomes a matter of some clinical importance. The chem-
ical composition of the blood is remarkably constant considering
the complexity of its composition and the complexity of the proc-
esses involved in its rejuvenation and the complexity of the proc-
esses which free it of waste products. Through excess of inor-
ganic salts in the food a temporary excess of those salts may exist
in the blood ; but the increased endosmosis of fluids and the in-
creased excretion of urine and perspiration very soou carry off the
excess of salts and water and restore equilibrium. Excess of fats
and carbohydrates is deposited in the form of fat, thus restoring
very readily the equilibrium in the blood, but leading eventually
to an excess of fat deposit in the system.

Excess of proteids may be broken up, fats formed from the car-
bonaceous portion and deposited in that form. On the other
hand a deficient supply of any of these may be for a short time over-
come by the use of reserve materials ; but sooner or later the de-
ficiency will manifest itself in various disturbances of the general
nutrition. Experience has proven that that constituent of the
blood most important, from a clinical standpoint, is the haemoglo-
bin. The only function of haemoglobin is to transfer oxygen
from the lungs — the seat of external respiration, — to the cells, — the
seat of internal respiration ; and though the plasma assists in this
function it is quite insufficient alone and in fact a small decrease
in the haemoglobin is soon attended by a disturbance in general
nutrition through lack of a proper supply of oxygen to the active
cells, i. e., cells of secretion and excretion as well as muscle and nerve
cells. Moreover, the important part that iron plays in the func-
tions of haemoglobin, the great difficulty with which iron is as-
similated, together with the important proteid constituents of haemo-
globin make that compound a most sensitive and reliable index of
the general nutrition both as to organic and inorganic compounds.
It is, then, a matter of the greatest clinical importance to be able to
determine with reasonable accuracy the amount of haemoglobin
present in the blood.

b. Quantitative Determination of Haemoglobin.

1 . Dry Haemoglobin contains about 0.42 per cent, of Fe. All
the iron of the blood is in the haemoglobin. It therefore follows
that the quantity of the iron in the ash of a weighed quantity of
blood is an exact index of the quantity of haemoglobin present.
This method is very valuable for certain physiological investiga-

o a
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QUANTITATIVE DETERMINATION OF BMMOGLOBIN 141

tions, but the time required to make a quantitative estimation of
the iron is too great to justify this method for clinical use.

2. (a) It Has Been Found that Sunlight or lamplight in
passing through diluted blood before entering the slit of a spectro-
scope suffers an absorption of a part of the yellow and a part of
the green of the spectrum ; and the latter appears with two black
bands through those colors — one just at the right of the D lines
and a broader one just at the left'of the E line (Plate III.). It
has been further discovered that a quantitative variation of the
haemoglobin causes a broadening of these bands. Preyer has used
this as a basis for a quantitative determination for clinical pur-
poses. The accompanying Plate shows, in spectra 2, 3 and
4, the influence of a varying quantity of haemoglobin upon the
transmission of light by the prisms. An 0.8 per cent, solution of
haemoglobin absorbs most of the light, while a solution one-tenth

Fig. 90.

Gpwer*i (MemogloWnometer- ^.PJP«tte bottle for distilled water; li, ca ary Dinette- C

gradaatetabe; D, tube with atandard dilution ; F, lancet for pricking the finger. (Chapman.)

thai Btrength would absorb little light ; namely, the two extremes
of red and \ iolel and two characteristic band- in the yellow and
green. Study carefully the location and width of these absorption

band-.

(6) A Variation of this Method which gives much more
exad results is described in Long's Chemical Physiology (pp. L50
to 156). In tlii- method the spectroscope is converted into a
spectrophotometer and the quantity of light transmitted is measured.
The basis of the determination being the fad thai equal dilutions
of haemoglobin transmit equal amounts of light.

1 42

CIRCULA TION.

:'». Colorimetric Methods of Determining- the Haemoglobin.
(a) The I1.i:matim»mi:ti:i: consists of two glass cells with parallel
i-idrs 1 cm. apart. One cell contains a known dilution of haemo-
globin [or of picrocarminate of ammonium] as a standard. In
the other cell a measured quantity of blood i- diluted with a mea-
sured quantity of 1 1 .,( ) until its color is the same as the standard
solution, the per cent, quantity in the second cell would be the
same then as in the firsl or standard <»1 1 and the degree of dilu-
tion being known the quantity of haemoglobin in the Mood tested
may be easily computed.

(6) Gower's II.i:.mi»(;i.()i:in<»mi:i'i:i; (see Fig. 90). The prin-
ciple here is exactly the same as in the above ; but the apparatus
is very compact and the quantity of blood necessary for a tesl is
only 20 cubic millimeters. The instrument is, therefore, much
better adapted to clinical purposes than is the ha?matinometer.
(r) Fleischl's H.k.momktki: (see Fig. 91). This instrument

is similar in principle
though the standard
solution is here repre-
sented by a plate of
colored glass. The ad-
vantages of the instru-
ment are that it is coin-
pact and portable and
requires only a few 1 5—
10) cubic millimeters of
blood ; it has, however,
the disadvantages that
the examinations must
be made by lamp- or
gaslight, and the range
of error in reading is
very wide, the reading
by two individuals fre-
quently differing by as
much as 10 per cent.

b'leisi btl'a hsemometer.

IV. FUNCTIONS OF THE VARIOUS PARTS OF THE BLOOD.

a.

Plasma.

This part of the blood carries in liquid form the nutriment of
the body. The nutriment enters the alimentary canal in the form
of various liquid or solid proteids, carbohydrates, and fats, with
salts, -olid or in solution in water. During digestion the proteids
arc changed to peptones, the carbohydrates to soluble sugars, the
fats to fatty acid- and soaps ; and the salts are dissolved so that

THE TOTAL QUANTITY OF THE BLOOD. 143

the nutriment absorbed is much more uniform in both physical
and chemical properties than "was the food.

During absorption the peptones are changed to scrum globulin
and serum albumin, the fatty acids and soaps are changed t<>
emulsions. Soon after absorption the sugars arc deposited as
sdveoo-en in the liver or consumed in the muscles, the fats are
likewise disposed so that the plasma is kept fairly uniform in the
quality of its nutriment. Its functions are : (i) to carry absorbed
nutriment to the metabolic tissues ; (it) to carry excrement to the
organs of excretion ; (in) to assist in carrying oxygen to the
tissues and in carrying C02 from tissues to lungs.

b. Corpuscles.

1. The Red Blood Corpuscles. — These modified cells are
oxygen carriers. The oxygen is held chemically by the haemo-
globin and carried from the lung capillaries to the metabolic tis-
Bues where it is just as essential as the nutrients.

2. The White Blood Corpuscles. — (i) These cells carry solid
particles from one part of the organism to another (see Decay and
Destruction of Red Blood Corpuscles), (n) They fill breaks in
the continuity of tissues and, with fibrin, build new tissue into
the wound, (in) They surround foreign bodies (e. g.} slivers)
protecting the tissues from extensive laceration and assisting the
organism in throwing out the offending object by forming a mi-
nute abscess or "fester," which if not opened will usually break
spontaneously, the sliver will be extruded and the opening close
and heal spontaneously. In this complete process the leucocytes
perform a most important part, (iv) The leucocytes "police"
the organisms protecting it as far as possible from the invasion of
pathogenic microbes. These are usually engulfed, digested by
the leucocytes and expelled from the system. When conditions
an- unfavorable the leucocytes may not be able to successfully
perform this service.

V. THE TOTAL QUANTITY OF THE BLOOD.

In cases of severe hemorrhage, where the quantity of blood lost
e;m In- more or Less accurately determined, it may he important to

know the total amount of blood in the body in Order to estimate

the proportion thai has been lost. There are two methods for de-
termining the total quantity of blood.

1. The Determination in a Dead Animal. — Welcker's (Zeitsch.
f. rationale medicin, L858) method is a- follows: (i) Bleed the
animal, taking the weight of the blood bo obtained. (II) Of the
blood firs! drawn, deiibrinate a few grammes to dilute and use as a
color standard, (in) Wash oul the circulatory system with warm

144 CIRCULATION.

normal saline solution, determining the blood by diluting the
standard -\vith a measured quantity of water to the same color.
(iv) Remove and hash all tissues, making an aqueous extract,
whose blood content may he determined as in (ill). The sum of
amounts (i), (m) and (iv) is the total. This varies somewhat for
different animals ; usually from JL to yL of the body weight,
averaging -jL in man and the dog, ^ in the cat, ^ in the rabbit
and in the newborn child.

2. The Determination in a Live Animal. — This was accom-
plished by Grehant and Quinquand (Jour, de l'anat. et physiol.,
etc., Paris, 1882, No. 6, p. 564), by allowing the animal to re-
spire a known quantity of CO with oxygen, afterward determining
the amount of CO in a small amount of drawn blood. Then,
Total blood : Drawn blood :: total ( '0 : drawn CO.

V. THE PROTECTION OF THE BLOOD SUPPLY.

If the blood plays such an important part in the economy of
the body, may wre not expect that some provision is made for the
protection of animals, in a measure at least, from accidental breaks
in the integrity of the system of tubes in which the blood circu-
lates? If any slight accident may sever an artery from which the
blood can flow unhindered, then surely would animal life be pre-
carious. But there have arisen in the animal kingdom two
methods of protection against the accident indicated above.

a. Location of the Vessels.

All important vessels are loaded very deeply. The somewhat
superficial position of the human femoral artery in the upper part
of the thigh, and of the axillary artery hold only for man since he
assumed the erect posture ; in the other mammals these arteries
lie well protected behind the thigh and arm.

b. The Influence of the Intima.

Many small vessels both veins and arteries lie near the surface
of the body. What special provision is made for these ? The
inner coat of a severed small vessel either mechanically or by
some ferment influence is a most important factor in the ready
formation of a clot.

c. The Coagulation of the Blood.

The most important protection against excessive bleeding is the
tendency of the blood to undergo a change as soon as it passes
through a wound in a vessel. This remarkable change which the
blood undergoes involves a chemical reaction between certain con-

THE COAGULATION OF THE BLOOD.

145

stituents of the blood ; the wonderful feature about this reaction
is the fact that normally it is adjusted in time and place to the
severing of the continuity of a blood vessel.

The principal gross phenomena of coagulation, as observed in a
beaker of drawn blood, arc : (i) the formation within two minutes
of a jelly-like layer over the surface of the blood ; (n) the forma-
tion of a similar layer, within two to seven minutes, around the

Fig. 92.

Fig. 93.

Bow] of recently coagulated blood, showing the
whole mass uniformly solidified. iDalton.)

Bowl of coagulated blood, after twelve
hours ; showing the clot contracted and
floating in the fluid serum. (Dalton.)

Bides of the vessel ; (in) the formation of a complete homogeneous
clot in from seven to sixteen minutes (see Fig. 92) ; (iv) the con-
traction of the clot, which results in the exudation of serum from
it- surface. Eventually the contraction is so extensive that the
clot occupies about one-half of the entire volume, and usually
reste upon the bottom of the dish (see Fig. 93). The time re-
quired to completely coagulate the blood to a condition shown in
Fig. 9:3 is in man 2— 1G min., in the horse 5—13 min., in the dog
|— 3 min., in the rabbit J-H niin. In the pigeon the coagulation
i- almost instantaneous.

CoagvlaJtUm is hastened hi/: (i) temperature above normal body
temperature; (n) contact with foreign matter; (m) agitation;
( IV ) addition of calcium salts.

( 'oagvilation is retarded or prevented by: (i) low temperature;

fnj addition of an equal volume of saturated solution of MgS04
or \a,SO( ; ( I n ) addition of oxalates, which precipitate the calcium
as an oxalate ; (rv) addition of leech extract ; (v) injection of solu-
tion of commercial peptones into the vascular system of an animal
before an ezperimenl will retard coagulation. These are some of
the questions which have presented themselves for solution, in
this connection :

I ) \\'h;it eon- tit i lent- of the blood take pari in the reaction '.'

ci) Whence are these constituents derived?
(■',) What are the factors which determine the time ami place
of coagulation ?

10

146 CIRCULATION.

All of these questions have been variously answered by various
investigators. A review of the history of this investigation would
consume too much time. Of the long list of students of these
questions the name of Alexander Schmidt, who for over thirty
years, has been experimenting in this Held at the, Physiological
Laboratory of Dorpat University, Russia, stands in the front
rank. The Swedish investigator Hammarsten stands next in rank
to Schmidt in this field. Alexander Schmidt's original theory
published in 186] was: Fibrinogen,, Fibrinopladin and Fibrin
Ferment are the three fibrin factors and their combination is de-
termined in time and place by the liberation of the ferment at the
point of rupture of the endothelial lining of the blood vessels from
leucocytes and endothelial plates. Hammarsten and Schmidt have
more recently found that fibrinoplastin is not a necessary factor.
Hammersten and the Dorpat School have further found that, " un-
less a certain amount of salts be present coagulation takes place
slowly or only partially." Freund has shown that, " the process
of coagulation is always accompanied by an excretion [separation]
of phosphates of the alkaline earths. ' Fibrin contains a constant
amount of these phosphates. Coagulable fluids coagulate after
the addition of these salts. This is true too of sulphates of these
metals, e. g., 0aSO4." The theory of Wooldridge deserves men-
tion here only to afford an opportunity to quote Halliburton's
statement regarding it : " 1. The whole theory is based upon ex-
periments with peptone-plasma ; but such plasma performs differ-
ently from normal plasma. 2. It is difficult from Wboldridge's
publications to find a logical basis for his conclusions." This
statement was made ten years subsequent to the publication of the
theory. Hammarsten' s theory published in 1891 is, briefly stated,
as follows : Coagulation is caused by Fibrinogen and Fibrin Fer-
ment in the presence of neutral salts of the alkaline earths, es-
pecially CaSC)4 and CaHPOr

To Alexander Schmidt and the Dorpat School we must give
the credit of making the most profound investigation of this sub-
ject. Most writers do Schmidt the injustice of only associating
his name with the first theory which he published in the first
years of his work, wholly ignoring all his subsequent investiga-
tions and the subsequent recasting of his theory. His publication
in 1892 on Blut lehrc is the most comprehensive treatise ever pub-
lished on coagulation. Every step of the theory is based upon
repeated experiment upon perfectly normal blood. Schmidt em-
phasizes the fact that coagulation is brought about by the action
of a ferment upon the fibrinogen ; both of which exist in the blood.
He further emphasizes the necessity of the presence of the calcium
salts. His investigation, however, does not stop at this point; he

1 The alkaline earths are ( a, Sr and Ba. The blood contains calcium phosphate.

THE COAGULATION OF THE BLOOD. 147

and his pupils have sought the source of the fibrin-factors and
fiud that not in the blood-corpuscles, not in the blood platelets
and not in the endothelial cells alone is found the source of fibrin
ferment but that it arises wherever protoplasm undergoes de-
structive metabolism ; and concludes finally : '* Fibrin-ferment is
present in the free state not only in circulating blood in small
quantities but also in small quantities is widely distributed through-
out the entire organism." He finds by experiment that it is less
active in circulating blood than in freshly shed blood and deter-
mines the cause to be a rapid chemical change which takes place
in the ferment immediately after the blood is shed. He calls the
more active form Thrombin and the less active form in circulation
Pro-4hrombin. Further he and others find that it is a nueleo-
aJbumin derived from the katabolism of the nucleus. As to
Fibrinogen : he has also found that widely disseminated and has
traced it back as a derivative from Paraglobulin, this in turn is
derived from Preglobulin, and this from cyto</lobnlin which is a
derivative of cell protoplasm or cytoplasm. The relation of these
products to cell protoplasm on the one hand and to coagulation on
the other is shown in the following diagram.

r Nucleic Acid.

\ Nucleiu. ,

Nucleoplasm. - /

I Nucleic-albumin — (

^Prothrombin 'Thrombin \

Cell
Proto-
plasm.

Fluid.

Fibrin.

Fibrin.

/< 'ytin. / Fibrinogen

,. . i •Paraglobulin-v

plasm, icv, ,,.,],,. /Preglobulin-C x \

bin-< \ ? j

Plasma contains Calcium salts,

Pekelharing's theory must be mentioned here. Briefly stated it
is as follows : Thrombin differs from nucleio-albumin in itsrichness in
cult-iii in sn/ts. Fit, rili contains much calcium. Fibrin is probably a
calcium compound of fibrinogen. In coagulation the calcium salt is
probably dissociated from fibrin ferment end associated with fibrin-
ogen precipitating the latter in fine threads. The difficulty with this
theory ia thai it seems either to necessitate a quantitative rela-
tion between the amount of fibrin-ferment and the amount of
fibrin precipitated, or to make the thrombin ;i carrier of the
calcium, in which case we would have to answer some puz-
zling questions as to where and how the changes occur. lint
the investigators in this field uniformly give the quantity of
ferment ae minute, and ascribe to it a real ferment action so
tli.it the small amounl suffices to produce a considerable effect
if the time be sufficient ; furthermore the calcium salts pres-

148 CIRCULATION.

cut in the plasma would seem to satisfy the conditions. All things
considered the later theory of Schmidt and Hammersten is as sat-
isfactory as any.

VI. THE EFFECT OF HEMORRHAGE.

Repeated experiment has shown that one-fourth or one-third of
the blood may be drawn without causing serious symptoms, and
about one-half without causing death. One-half the circulating
blood is supposed to be practically the limit. Whether the with-
drawal of blood shall be more or less dangerous to life depends
upon several complicating factors:

(a) The time consumed in the withdrawal of the blood is an
important factor. The experiments of Prevost and Dumas in
1823, and more recently those of Nasse, Vierordt and others,
have shown that during a slow withdrawal the blood will be re-
plenished from the lymph and plasma of the tissues and if the
hemorrhage cover sufficient time much more than 5 per cent, of
the body-weight may be withdrawn ; e. g., Tolmatscheff in 71
days drew from a dog blood equal in weight to 15 percent, of the
body-weight. It is clear that in this case the withdrawal was
sufficiently slow to enable the corpuscle-making organs to actually
replenish the corpuscular elements. In this way may be demon-
strated the rate at which the blood may be replenished. AVhen
the hemorrhage takes place within a shorter period — as one hour —
the plasma alone will be in part replenished so that the blood last
drawn would be much poorer in corpuscles than the blood first
drawn.

(/>) The eircumstcmces under which the hemorrhage takes place
enters as a factor into the effect. For example, loss of a given
quantity of blood from an animal under ana?sthesia causes less
disturbance of the system than the loss of the same quantity as a
result of an accident. In the latter case shock enters in as a
strong factor ; in fact, it is much the stronger factor of the two.

VII. TRANSFUSION.
a. The Transfusion of Blood.

The first recorded transfusion of blood was attempted by Lower
in 1665. He successfully made a direct tranfusion of blood from
one dog to another directly after the latter had been bled to the
death-limit. The measure of the success of the transfusion is the
fact that the second dog lived and showed no serious sequelae of
the operation.

In l(i<)7 Denis successfully transfused the blood of a lamb to
the circulatory system of a man. Subsequent attempts gave such

THE TRANSFUSION OF AN ARTIFICIAL SERUM. 149

a largo percentage of failure that it fell quite into disrepute in the
medical profession until after a long series of experiments upon
lower animals. These experiments — for the most part performed
during- this century and many of them recently — have demon-
strated the following facts : — (i) The blood of the same species, or
even of the same genus, may be directly transfused, but the danger
of coagulation is very great, (it) The defibrinated blood of the
same species or genus may be transfused (Indirect Transfusion),
but the danger here rests in the introduction of a fluid which
contains a very much larger percentage of thrombin than exists
in normal blood ; this excess of thrombin induces coagulation on
the slightest provocation. The process of defibrination subjects
the blood to the danger of introduction of particles of foreign
matter — even bacteria.

All of these make the dangers of the transfusion of defibrinated
blood too hazardous to be recognized by the medical profession
as a solution of the question.

b. The Transfusion of an Artificial Serum.

It has been found that the most serious symptoms of rapid
hemorrhage arise from sudden decrease of the amount of circu-
lating fluid, together with a moderate fall of blood-pressure; thus
the principal indication to fulfill is to replenish the qvbcmUty of
fluid without reference to the corpuscles or to the nutritive elements
of the plasma. The fluid introduced must be of such a character
as to cause no disturbance of the system. Warm, sterilized normal
salt solution (XaCl 0.6 per cent.), injected either subcutaneously
or into an exposed vein, has been successfully used in surgical and
obstetrical cases.

A transfusion fluid most successfully used in Europe is accord-
ing to the following formula :

EL Bugar 35

NaCl (i

NaOH 0.05

BjOdiat ad 1000.00

The solution is filtered and sterilized and injected at blood-tem-
peral ure.

[ndications fob Tkansi-'i sm>\ : (i) Dangerous hemorrhage

injection of one of the above fluids. (Il) ( '() poisoning indicates

the immediate indireel transfusion of blood of the same species.

If the collapse ifl not too far advanced revival is possible.

150 CIRCULATION.

VI I r. QUANTITATIVE AND QUALITATIVE VARIATIONS
OF THE BLOOD.

a. Methods of Observation.

((/) Determination of the proportion of plasma and corpuscles
by the use of the hcematokrit.

(i) Determination <>t" the number of red ami of white corpuscles
per en. mm. blood, by the use of the ( rower or Zeiss A" macytometi r.

(/-) Determination of the size of the red blood corpuscles by the
use of a microscope provided with an eyepiece micrometer.

CM Determination of the number or presence of the various
varieties of leucocytes by the aid of reagents, etc., for Ehrlich's
method of staining.

(■) Determination of the quantity of haemoglobin, by the use ot
the hsematinometer, the hiemoglobinometer, or the spectro-pho-
tometer.

h. Variations.

1. Conditions of the Blood which depend upon Quantita-
tive Variation of some or all of its Constituents, (a) The
Quantity of Blood as a Whole cannot readily be determined
in the living animal, but marked increase or decrease may be de-
termined clinically by symptoms or by the history.

(a) Increase of the blood as a whole (Polycemia or Plethora),
indicated by swollen veins, hard, full pulse, etc.

(fi) Decrease of the blood as a whole {Oligcemia vera or Ancemia),
indicated by paleness or even marked pallor of skin and especially
of mucous surfaces, e. g., lips, or conjunctiva.

The history is also a very important aid to diagnosis and prog-
nosis.

(/>) Changes in the Quantity of different constituents of the
blood.

(a) Increase in plasma (Hydrozmia), after sudden decrease of
excretion of water, which may occur within physiological limits
after a sudden change from hot to cold weather or wet
weather.

{fi) Decrease in plasma (Oligemia Sicca), observed within physi-
ological limits after eopious perspiration, diuresis, or diarrhoea.

(y) Increase in the relative number of red blood corpuscles
( Plethora polycythemia), likely to occur when such periodic hem-
orrhages as menstruation or nosebleed arc suddenly stopped.

(d) Decrease in the relative number of red blood corpuscles
(A)Hiiiiia vera) or oligocythsemia.

(s) Increase in the relative number of leucocytes, especially of
the neutrophil variety of leucocytes. This may be moderate in
extent and transitory (leucocytosis), or it may be excessive in ex-

THE CHEMICAL PROPERTIES; OF THE LYMPH

151

tent and persistent, indicating a serious departure from the normal
(leucocythemia or leukaemias).

2. Conditions which Depend upon the Qualitative Varia-
tion of Constituents of the Blood. — (a) Change in the quality
of the plasma ; containing too little nutriment or too much waste
matter.

(,i) Decrease in the haemoglobin of the red blood corpuscles.

(;-) Increase in the size of the red blood corpuscles, or increase
in the relative number of megaloblasts, associated with pernicious
anaemia.

(o) Decrease in the size of the red blood corpuscles or increase
in the relative number of microblasts, associated with anremia.

(£) Presence of many red blood corpuscles of irregular size and
shape, associated with pernicious anaemia.

2. THE LYMPH.

I. PHYSICAL PROPERTIES.

Like blood this liquid is composed of a plasma in which cor-
puscles float. The lymph plasma is quite like blood plasma in its
composition and in its power to coagulate.

1. Color. — The lymph of the smaller lymphatics has a light
yellowish color : That of the thoracic duct is yellowish opalescent
or even milky. It assumes the latter color after a meal when it
i- laden with fat. In that condition it is usually called chyle.

2. The Specific Gravity of the lymph is 1012-l<r2L>.

II. THE MORPHOLOGY OF THE LYMPH.
The morphotic elements of the lymph are the leucocytes. (Quid

III. THE CHEMICAL PROPERTIES OF THE LYMPH.

< i.N-'l II I I \ I -.

W \ I I B.
EfOLIDS.

Organic.

Proteidi (Serum albumin, lerum globulin, fibrin)

I ;it-. Lecithin and Cboleeterln

Sugar

'attic.

Sodium chloride . . . .

Hodium carbonate

Other -;iit- containing K, Ca, and tracea of M( and Ft ■■<
cbloridea, lulphatet or phosphate*

1 IM II.
OF 1)1 Hi.

90.67

'.p.:::;

:- .,1
2.21

6.10

ii.2:i
0.79

L52 CIRCULATION.

G. THE FORMATION AND DESTRUCTION OF THE
CORPUSCLES.

1. THE ORIGIN OF THE RED BLOOD CORPUSCLES.

1. During1 Intrauterine Life. — The prenatal origin of the
corpuscles may be subdivided into two periods : the embryonic
period, and the foetal period.

(a) Tin: Embryonic Period is characterized by the formation
of blood and Mood vessels in the vascular area of the egg and of
blood vessels within the embryo. In both cases the fundaments
of the circulatory system are formed from mesenchyme cells.
Kcgarding the primitive red blood corpuscles we should remem-
ber that they "exhibit amoeboid movements, have less than the
usual quantity of haemoglobin, are nucleated, globular, larger and
more irregular and variable than the permanent corpuscles."
Next they become normally colored, but they retain the nucleus
during intrauterine life. They are capable of multiplication by
karyokinesis. The relative number of non-nucleated corpuscles
rapidly increases during the foetal period, in mammals, until at
birth no nucleated corpuscles remain.

(/>) The Foetal Period. After the establishment of the
different systems of organs the formation of blood corpuscles goes
on within the embryo. Xeumann and Lowit observed the forma-
tion of nucleated blood corpuscles in the feetal liver and in the
spleen ; while Foa and Sa viola observed it in the lymphatic glands.

•2. During Extrauterine Life. — "The balance of evidence
points to the formation of red-blood corpuscles in extrauterine
life — in all higher vertebrates — by the same process as in foetal
life, i. e., by karyokinesis of a typical cellular clement — the ery-
throblast — which, during extrauterine life, is chiefly found in the
red marrow of bones." (Bizzozero, Neumann.) The transition
from the foetal method to the extrauterine method is not a sudden
one, and the foetal method may be later employed after severe
hemorrhages.

2. DECAY OF THE RED BLOOD CORPUSCLES.

Investigation has revealed the following facts: (i) There are
fewer red corpuscles in the hepatic vein than in the portal vein.
(ii) The bile pigments are formed from haemoglobin, (in) Dis-
integrated red corpuscles are to be seen in the cells of the spleen
pulp. The conclusions to be drawn from these fact- arc : (i) The
corpuscles in question meet their end in the liver and spleen, (ir)
At least a part of the haemoglobin is lost in the excretion of the bile
pigments. Further investigation shows that a part of the disin-
tegrated corpuscles is taken up by the leucocytes and carried to

SUMMARY OF THE FUNCTIONS OF THE SPLEEN. 153

the red marrow of bones — possibly to the spleen, and, in the
former location at least, utilized by the erythroblasts in building
up new corpuscles. It is estimated that the life of a red blood
corpuscle is about three or four weeks.

3. THE FORMATION AND DESTRUCTION OF LEUCOCYTES.

The leucocytes are formed chiefly as lymph corpuscles in the
lymphatic glands. The fine meshed adenoid tissue of these glands
seems to catch and hold all of the senile leucocytes and to allow
only the more active corpuscles to pass through. Although
many leucocytes are stopped by the lymphatic glands, there are
very many more in the efferent than in the afferent stream. The
necessary inference is that the lymph gland firms these new leuco-
cytes and they enter the lymph stream and so pass into the circu-
lation.

What has been observed in the relation of the lymphatic glands
holds for the spleen, one of whose functions seems to be to detain
the leucocytes which have engulfed senile red blood corpuscles.
In some way the broken down red corpuscle is transferred to
the liver, probably through the agency of the leucocytes. The
-picnic vein contains far more leucocytes than the splenic artery.
The spleen must be a nidus for their formation.

4. SUMMARY OF THE FUNCTIONS OF tTHE SPLEEN.

The spleen is as completely and exclusively connected with the
circulatory system as is the heart. The general function of the
spleen seems to be to keep the corpuscular elements of the blood
constant, or at least to assist in that important office.

Fig.

94.

' C.

-v_ /Z-"'''' 3'

AbscUto ; Procure = 0

/.'/.' r»ry waves ; CCC, waves of rhythmical contraction of muscle tissue of cap-
rale and tralx'cuki- ; mm .-.-.r curring i ~. bours after a meal. Waves R R evidently de-
pend upon general blood-pressure Bearl waves 'I" uol -i><>u in the oncometer curve. The
> c probably show an Independent action "i the spleen directed to the partial emptying
out of it- blood. The (rave '/ it probablj caused by :i heaping up of absorbed food-stuns.

The specific functions of the spleen are obscure. Some idea of
n- functions may be gained l>v the following methods :

(a) By Extirpation. — The removal of a dog's spleen seems
t-i make do essential difference in In- general physical condition.
After a few weeks an enlargement of the Lymph glands and an
increase of tin- red marrow of the long bones occur.

154

CIRCULATION.

(b) By Chemical Examination it is found, 1st, thai the

spleen yields a preponderance of those inorganic salts found in

F 95 the red blood corpuscles ; 2d, that the

extractives arc such as are produced

by the breaking up of proteids.

(c) By Microscopic Examina-
tion after Hemorrhage. — The
spleen normally contains large leu-
cocytes which have taken in one or
more red blood corpuscles, but after
hemorrhage also numerous red nucle-
ated hematol dasts (homologues to the
erythroblasts of red marrow of bones).

(d) By Oncometer Curves. (See
Fig. 94.) — An oncometer is a metallic
case made for the purpose of enclos-
ing an active organ. The space be-
tween the organ and the case is
filled with warm saline solution.
Any change in the volume of the
organ affects the recording apparatus
by transmission through a column
of liquid which is continuous with
that which surrounds the organ.

I). THE CIRCULATION OF THE
FLUIDS.

The best general idea of the course
which the blood takes in its circuit
through the body may be gotten from
such a schema as that shown in the
accompanying figure 59.

1. THE ACTION OF THE HEART.

In order to observe directly the
movements of the heart one may in-
stitute artificial respiration, open the
chest, tying all bleeding vessels, open
the pericardium, and note at leisure

Diagram of the circulation. 1, heart; -1 ' _ . ...

2, lungs. 3, head and upper extrenri- the movements OI the Organ "Willie

ties ; 4, spleen ; 5, intestine ; 6, kid- ., , •■ .-, i • i. i i i

ney; 7, lower extremities; 8, liver, it WOl'lvS Under the Sllglltlv Changed

(DALTUN) conditions.

In such an experiment one may observe : (i) A series of con-
tractions (systole) alternating with a series of dilatations (diastole).

CHANGES OF POSITION OF THE HEART. 155

(n) Auricular contraction precedes ventricular contraction, (in)
Auricular contraction begins with the contraction of the muscle
fibers which encircle the large veins, immediately thereupon in-
volving the whole auricular wall, (iv) The auricles contract
simultaneously, but are not completely emptied by the beginning
of ventricular contraction, (v) Auricular systole ends at the
moment that ventricular systole begins, (vi) The ventricles be-
gin their contraction simultaneously and cease simultaneously.

o. Changes of Form which the Heart Undergoes.

(a) Observed in the open Thorax of a mammal, which is
lying upon its back.

(«) During diastole the transverse diameter becomes markedly
greater and the dorso-ventral diameter less than in systole giving
an elliptical outline.

Q9) During systole the transverse diameter becomes shorter and
the dorso-ventral longer, approaching a circle in outline. The
three factors which work together to produce this change are :
(i) The intra-ventricular change of pressure ; (n) the force of
gravitation ; (in) the atmospheric pressure.

(//) Observed in tup: closed Thorax of a mammal by the
use of needles passed through the thoracic wall into the heart wall
at different angles and locations. For the following facts we are
indebted to Haycraft :

(«) During diastole the heart hangs passive in its pericar-
dium, suspended by its connection with the great vessels which
enter or leave its base. While filling all of its dimensions in-
crease, though the lateral diameter may increase somewhat more
than the dorso-ventral, owing to the bulging out on the right side
of the flaccid right ventricular wall.

(,'i) During systole all of the dimensions of the heart decrease
but any increase of lateral over dorso-ventral dimension is com-
pensated during systole so that the cross section of the heart at
the end of systole presents nearly a circular outline. The antero-
posterior dimensions, or the distance between base and apex, also
decreases, but tin-apex is not in consequence drawn away from
the chest wall. The reason for this will be discussed under the
n<wt topic.

/>. Changes of Position of the Heart Incident to its Activity.

1 . Mechanical Factors which Tend to Produce a Change
in the Position of the Heart. — (a) Th<- Asymmetrical Position
which the apex takes during diastole; either (i) because of the
action of gravity in the <l<»r~;il position, or (n) because of the con-
tact with the chest wall in the normal position. (/?) The first

156

('WCI'LATIOX.

Fig

factor together with the fact that whenever the pressure increases
within a liquid-filled sack, the latter tends to erect and stand in
such a position that the tension on each part of the wall shall be
equal. A condition of pressure- and tension-equUiJbrivm, of closed
cavities, (y) Whenever a closed receptacle ejects its contents
through action of a force mechanically within itself, the structure
undergoes a recoil in obedience to Newton's law of motion that
{i action and reaction are equal in opposite directions." (V)) The
base of the heart is relatively firmly fixed ; the vertebral column

forming the basis of fixation,
the large vessels being held
well in place by strong con-
nective tissue attachments.
Besides this the arch of the
aorta passes over the root of
the left lung, while the pul-
monary artery passes directly
into the root of both lungs.
2. The Influence of the
Enumerated Factors upon
the Action of the Heart. —
(a) The Suddex Rise of
Ixtra-vexteicular Pres-
sure During Auricular
Systoee would have two
tendencies : (i) To cause the
apex to assume a more sym-
metrical position with respect
to the base, i. e., to give the
apex an impulse against the
chest wall ; (11) the light au-
ricles would tend to recoil
strongly, but this would be
largely counteracted by tis-
sues above the auricles, as
well as by the weight of the
columns of blood in the vena
cava anterior and the pulmonary veins.

(b) The Great Rise ix Ixtra-vextricular Pressure
During Ventricular Systole gives the apex a sudden and
strong impulse toward the point of symmetry, i. e., toward the
thoracic wall just at the beginning of ventricular systole (see Fig.
96). After the position of symmetry has been assumed there will
be a tendency for either a sustained crest or for a gradual fall,
the latter owing to a decrease in the dimensions of the ventricle
and not to a falling from the position of symmetry.

A diagram showing Ludwig's theory of the erec-
tion of the ventricle during systole. The base of
the heart AB is rather firmly fixed. In diastole the
apex takes the position ABC as outlined in the fig-
ure. In systole it tends to erect by intra-ventricu-
lar pressure and stand in the position ABC'.

CHAXGES OF POSITIOX OF THE HEART.

157

(c) There will be a Recoil of the Heaet when the con-
tents of the ventricular cavity are ejected into the arteries ; but
the direction of recoil is at nearly right angles with the direc-
tion of the movement of the apex when coming into the position
of symmetry, i. c, the direction of recoil is in the line determined
approximately by the axis of the left ventricle.

Observation of the heart in the closed thorax may be made with
a cardiograph. This instrument, shown in Fig. 97, consists of

The cardiograph. (Chapman.)

a pair of Marey tambours. The receiving tambour is provided
with a button .1, which is placed over the site of the apex beat of
the heart. Movements of the button affect directly the mem-
brane of the receiving tambour. Through the connecting tube,
/, movements of the receiving tambour are transmitted to the re-
cording tambour, />, whose membrane supports the recording lever,
d. The tracing point of this lever may be brought into contact
with a kymograph drum and a permanent and exact record made
of the movements of the thoracic wall produced by the apex beat
of the heart.

Prom what has been said regarding the relative influence of the
erection and the recoil of the ventricle it is evident that the recoil
will variously affeel the cardiogram according to the position of
the subject under observation, Furthermore the force of the re-
coil will l>c broken by just that factor which emphasizes the action
of heart in assuming a symmetrical position, namely the fixing of

the base of the heart. The recoil affects the cardiogram in differ-
ent way-, if it appears ;it nil. If there is only one superimposed

wave beyond the Systolic rise that one wave may be taken to rep-
resent the effect of the closure of the semilunar valves, unless it
thin 0,1 of a second from the beginning of the systolic wave.

L58

( ll;< ULATION.

Any wave between the systolic wave crest and the semilunar wave
may be taken as the recoil wave. Especially strong is the evi-
dence favoring that interpretation, provided the wave in question
falls between 0.05 second and 0.1 second after the beginning of

Fig. 98.

Cardiogram taken by Chauveatj and Mahey. a = Auricle wave: » = Systolic rise;

/■ = Recoil wave ; v = Valvular wave.

Fig. 99.

Cardiogram taken by Edgben,
Fig. 100.

Cardiogram taken by Sanderson, with fast drum.

Fig. 101.

Cardiogram taken at the Physiological Laboratory of the
Northwestern University Medical School.

the systolic wave. Should the cardiogram present other small
superimposed crests they may be interpreted as instrumental, i. e.,
formed by secondary vibrations of the membranes or of the elastic
media of transmission. (See Figs. 98, 99, 100, 101.)

WTRA-VENTRICULAR PRESSURE. 159

c. Changes of Pressure Within the Heart Incident to Its

Activities.

Intra- Ventricular Pressure.

The strong contractions of the muscle tissue of the walls of the
heart cause the cavity of the ventricle to be decreased in volume
during- systole ; while the relaxation permits the increase of the
volume of the ventricular cavity during diastole. This cavity is
constantly filled with blood. At the beginning of systole there is
about 180 c.c. of blood in each ventricle ; at the end of systole the
ventricles are practically empty. The contraction of the ven-
tricles subjects the liquid contents to sufficient pressure to eject
it into the aorta and pulmonary artery. Liquids flow from a
point of higher pressure to a point of lower pressure. The pres-
sure in the arteries named must be sufficient to overcome all re-
sistance beyond, otherwise the blood could not flow out of them
through the capillaries and into the veins. The pressure in the
ventricles, in turn, must be higher than the pressure in the large
arteries, otherwise the blood could not flow from the ventricles
into the arteries. The pressure necessary to force the blood out
rtf the ventricles is produced by the contraction of the ventricular
walls upon the ventricular contents. The ventricle is then a
foree-pwmp.

The ancients, from Aristotle to and including Galen, believed
the heart to be a suction-pipe. They thought that the ventricles
actively dilated, drawing the blood in ; then actively contracted,
forcing it out. (See Historical Introduction to the Circulation.)
Harvey showed that the dilatation of the ventricles is passive, and
that only the contraction is active.

The question of intra-ventricular pressure has been a much de-
bated one for a long period.

Physiologists have endeavored to determine not only the range
of variation of pressure within the ventricles, but also the varia-
tion- of pressure which occur between the maximum and the
minimum; in other words, to determine the qualitative as well as
the quantitative changes of pressure.

Three different devices have been contrived for this purpose.
Chauveau and Marey w^'A a modification of the Marey tambours.
The recording tambour having the usual contraction but the re-

Ceiving tambour was a small inflated rubber bulb. A double-

Lumened tube, bearing one bulb at its end, connected with one

lumen and another bulb a few centimeters above the end, connected
with the other lumen, was joined to two recording tambours, one

communicating with each bulb. The tube was introduced, through
the jugular vein, into the rfghi side of the heart. The bulbs were
-o located thai the end bulb passed into the cavity of the right,

1G0

crnrrLATiox.

In Ira-auricular Tracing

Intro-ventricular Tracing

Cardiogram

ventricle while the other one reached to the auricular cavity. A
third pair of tambours was arranged to record the movements of
the apex of the heart. In this way three synchronous tracings

were recorded : varia-
Fio. 102. tionsof the intra-aurie-

idar pressure, variations
of the iiitra-rentriciilor
'pressure and cardiogram
(see Fig. 102).

These tracings make
it evident: (i) that au-
ricular pressure reaches
a maximum before ven-
tricular pressure begins ;
(n) that during high
ventricular pressure the

Intracardiac pressure tracings obtained by ChAuveatj auricular pressure IS at
anil MAREY. The vertical lines show the "synchronous minimum Tln'c mnfVi

parts of the tracings. A, A' A", effectof auricular systole : a minimum, im.smeui-

B, B', B", effect of ventricular systole; (', C", C", effectof nrl lmwpvpv rrivAS rmlv

closure of ventricular systole. uu> V w.e vel> glvtJS UUV

qualitative changes, and
is subject to errors in its elastic transmission.

In 1878 Goltz and Gaule (" Ueber die Saugkraft des Herzens,"
Archiv f. d. ges. Physiol., Bd. XVII., S. 100) used a new
technique. They devised a mercury manometer provided with a
reversible valve. Turned in one direction the manometer records
only maximum pressures, reversed it records only minimum
pressures. This manometer was put into communication with
the ventricular cavities through an inelastic connecting tube in-
troduced along a blood vessel into the cavity to be tested. This
method showed a maximum (left) irUra-veMrioular pressure of
176 to 234 mm. of mercury ; a minimum pressure of — 30 mm.
to — 38 mm. of mercury. In the right ventricle the maximum
was 26 to 72 mm.; the minimum was — 8 to — 25 mm. In
every experiment the maximum pressure in the left ventricle
was 18 to 22 mm. greater than the maximum aortic pressure.
Note that the minimum pressure is less than atmospheric pres-
sure. That seems to justify the conclusion that the ventricle
exerts a suction equal to 30 to 38 mm. of mercury. In this
connection we must not forget that the heart is inclosed in a
sealed cavity whose pressure is usually negative, though this
negative pressure is greater during inspiration than during expi-
ration. If a minimum manometer be introduced into the thorax
the mercury will fall from 9 to 40 mm. according to the character
of the respiration, 9 in quiet inspiration and 30 to 40 in forced
inspiration. In any particular observation the manometer registers
the lowest pressure reached in any inspiration made by the animal

ISTRA-VEXTRICULAR PRESSURE. 161

during the observation. If the manometer tube be passed on into
the ventricle it will register the lowest pressure reached in any di-
astole during the experiment.

If the intra-veiitrioilar is no lower than the intra-thoracic pres-
sure there could be no suction of the blood from the thoracic ves-
sels or auricles into the heart. The figures given above for
intra-ventricular pressure and intra-thoracic pressure indicate that
there may or may not be a slight suction upon the thoracic blood.
In quiet breathing one would expect the negative pressure of the
ventricle to exceed that of the thorax by about 20 mm. stand of
mercury.

In 1894 Professor Gaule, lecturing before his students in the
University of Zurich, said in this connection, "At the beginning
of diastole any occurrence of negative intra-ventricular pressure
is to be attributed to the sudden widening of the base of the aorta
on the closure of the semilunar valves, thus suddenly opening the
upper end of the ventricular cavity."

A third method of recording the variations of intra-ventricular
pressure has been elaborated by Rolleston. His instrument con-
sists of a delicate brass cylinder with hard-rubber piston. The
piston receives the pressure of the atmosphere upon one side and
that of the blood upon the other, — the blood-pressure being trans-
mitted to the cylinder through a long trochar introduced into the
ventricular cavity. The piston in turn moves a writing lever
whose rise and fall is controlled by the resistance to torsion of a
steel ribbon. This apparatus has the great advantage of showing
not only qualitative but quantitative changes of pressure, for the
value of the steel spring may be determined in advance. " Rol-
leston's conclusions are as follows : (i) There is no distinct and
separate auricular contraction marked in the curves obtained from
either right or left ventricles, the auricular and ventricular rises

Fig. 103.

Carre from li-ft ventricle. (Rollestoh.) -//, Zero line, or at spheric pressure; .1,

part of curve due to Lntra-auriculai pressure; ». auriculo-ventricular valves close; ", semi-
lunar valves open ; C, semi-lunar valves close ; CA, period of ventricular diastole.

of pressure being merged into one continuous rise, (n) The
auriculo-ventricular valves are closed before any great rise of
pressure within the ventricle above thai which results from the

11

162 CIRCULATION.

auricular systole, (in) The semilunar valves open al the point
situated about the junction of the middle and upper thirds of the
ascending limb of the curve (o) and the closure about the begin-
ning <>t' the descending limb (<■). (rv) The minimum pressure in
the ventricle may (all below that of the atmosphere but the
amount varies considerably. (Rolleston, quoted by Halliburton,
Handbook, p. 420.) (See* Fig. 103.)

The facts regarding the changes of intra-cardiac pressure may
be summed up as follows :

(a) The active work of the auricle is accomplished in its sys-
tole, which drives into the ventricle the blood which it has re-
ceived from the veins. The thin-walled auricle, in common with
the thin-walled veins, expands, under the negative intra-thoracic
pressure, to receive the venous blood which rushes into the thorax
during inspiration. The structure of the auricles is such that the
pressure within them can never fall below that of the thorax in
general.

(6) The active work of the ventricle is accomplished in its
systole, which drives into the arteries the blood which it has re-
ceived from the auricle.

(c) Passively the walls of the ventricle will be dilated by the
negative intra-thoracic pressure, but the pressure within the ven-
tricle could, by this cause, never exceed (negatively) the negative
pressure of the thorax. But the negative pressure of the ventricle
frequently does exceed the negative pressure of the cavity which
contains it. There are two ways to account for this :

(a) The natural position of absolute relaxation does not com-
pletely close the ventricular cavity. The active contraction of
systole carries the walls beyond this position of absolute relaxation
in order to completely empty the ventricle. At the end of systole
the walls spring back by their natural elasticity to the position of
absolute relaxation, thus exerting a momentary negative pressure
beyond that of the surrounding thorax.

(/?) The sudden expansion of the upper part of the ventricle
by the widening aorta, as suggested by Gaule, has been mentioned
above. But in these changes the walls of the ventricle are abso-
lutely passive.

<h The Cardiac Cycle.

The term e<ir<H<i<- <■_!/<■!<■ has been applied to the ever-recurring
series of events which are repeated about once every second in
the human heart. Briefly rehearsed, these events are : (i) The
auricular systole, which empties the auricle and fills the ventricle,
and which ends with the closure of the auriculo-ventricular valves,
(n) The ventricular systole, which empties the ventricle into the
artery through the forced semilunar valves. During the ventric-

THE CARDIAC CYCLE.

163

2

Ventricular

Systole.

iirsi or
Diastole.

1

Auricular
Systole.

M

s ' .— 1

B

■5"

S >• H

o

o

0
H
O

51

O
1=0

oi w "-5

3

bd

M >.
£ d

B > W

p

( Contraction

of

Ventricular

Walls.

Aspiral ion
of
Thorax, Elas-
ticity of

Lungs, .Muscular

( 'mil ractions,

etc., etc.

Contraction

of

Auricular Walls.

o o
f w
<j o
S M
B

To
Arteries.

To

Auricle.

a

2. H
2. °
o'

0

>
00

o
r.
f.

3

M

To

Auricle.

To
Will riole.

03* ,J

P

r c z - O
2 2 ~ z 2
5 § 2. ? *

""^ >■ -^2. zr< g
- -. 3* - "

Opkn to Ventricle

by
Relaxation of Walls

and
Opening Of Valves.

•~

on

o

IS

3

w

w
a
a

H

0

^ i — 5. fl
9 Q - X'

Li in ked to v< ins

by

Counter Pressure

and

Contraction of Veins.

a

>

p §

5

as

6

3

O
5

Filling

*j

-
— X
67 > -.

i

<!
cd

o

*+>
c+
CD

Q

"-S

!-••

o
Q

■-3

CD

n;i

CIRCULATION

ular systole the auricle is filling, (in) Rest, which includes all of
the ventricular diastole and a Little more than half of the auricular
diastole. During the rest period blood is flowing freely into the
auricle and through the auriculo-ventricular valve into the ven-
tricle.

Fig. 104.

t t

Systole J

Diastole

Time relations of heart cycle. t= 0.1 Becond of time; o.«. = auricular systole, 0.1 sec.
v.s. •= ventricular systole, 0.3 sec: V.D. = ventricular diastole, 0.7 sec.; 4.2). = auricular
diastole, 0.5 sec. Total cardiac cycle, 0.8 sec.

The time of the average heart cycle in the human male adult
is 0.8 second, which is distributed as follows :

The ventricular systole consumes <>.:} second; diastole, 0.5
second. The auricular systole consumes 0.1 second and the di-
astole 0.7 second. Heart systole, 0.4 second; heart diastole, 0.4
second. (See Fig. 104.)

1. Data
tween 140-20(1 mm

< . The Work Done by the Heart.

(i) Maximum pressure in left ventricle varies be-
Hg. (il) The maximum pressure in right
ventricle about GO mm. Hg. (in) The amount of blood ejected
against the above pressure varies, for the left [or right] ventricle
from 120 to ISO ,•.<•.

2. To Derive a Special Formula for Work of Heart.
Formula: Let 11= work done.

" i^= height in cm.

" g = weight in grammes.

" //; = centimeters of Hg pressure.

" b = number c.c. of blood ejected at one systole.
Now a general formula for work done when the work is to be ex-
pressed in Gm.-cm. is: W=g x H. To determine IT, we have
to first find the value of g and H. A pressure of m cm. of mer-
cury would be equal to a pressure of lo.fi m cm. of water and

n cm. of blood. The work done in ejecting from the heart

g grammes of blood against m cm. of mercury pressure would be
the same as the work done in raising g gms. of blood to the height

THE SOUNDS OF THE HEART. 165

of , ^__ cm. Now what is the weight of b c.c. of blood ? Nat-
1.055 °

orally the volume times the specific gravity or g = b x 1.055.

The formula would therefore be :

Ax 1.055 13.6 x m
II = — ; — - x _, ^>r — or If = 1.5.6 bm.
1 l.Ooo

•">. Problems. — (a) How much does the left ventricle perform in
each systole if 120 c.c. of blood is ejected against 14 cm. of pres-
sure ? W= 13.6 x 120 x 14 = 22848 gramme-centimeters. (6)
How much work does the heart perform at each systole if the
right ventricle expels the same quantity of blood against two-
fifths as great pressure '.'

\V= [13.6 x 120 x 14] + [l3.6 x 120 x — ^— 1 or — of

work done by left ventricle alone = 31987 gramme-centimeters.
('•) How much work will the heart do in 24 hours if it ejects
150 c.c. of blood into the arteries against 150 mm. of Hg pressure
at the rate of 60 beats per minute. W== 13.6 x 15 x 150 x 60
X 24 = 2,1 15,07 2,000 gramme-centimeters, (rf) If that repre-
Bents the number of gramme-centimeters of work done by the heart
of a man of 60 Ko. weight ; how many meters would that amount
of work lift his body vertically?

„. 136 x 15 x 150 x 60 x 60 x 24 ,. ^ r

lodo x ioo x~6o- " = 352'5 meters-

It would take about two hours of hard climbing for a man to lift
lii- body through ."550 meters ; so that the heart can do about one-
fourth as much work as all of those skeletal muscles involved in
locomotion or, in fact, in manual labor.

/. The Sounds of the Heart.

1. Character. — There is a succession of two sounds separated
by a pause — hib-dup — lub-dup, etc. The first sound (bib) is

longer in duration and lower in pitch than the second.

■l. Cause of the Heart-sounds, (a) The First Sound. —
It is synchronous with ventricular systole; it is therefore univer-
sally associated with the events which are taking place in the
heart :it the time: (i) Vigorous muscular contractions ; (n) fric-
tion of blood rushing through the semilunar valves; (in) friction
of surface of hear! incident to its change of shape within the peri-
cardium; (iv) friction of hearl against neighboring structures in
the thorax incident to its change of position In the thorax. As

166 rincUL \Tlo.x.

any one of these four factors may be variously modified by various

diseases, il is evident that a close study of the normal heart sounds
is of great importance.

(6) The Second Sound of the hear! is synchronous with the
closure of the semilunar valves of the aorta and pulmonary artery,
and as the quality of the sound is such as might readily be at-
tributed to the closure of those valves, it is now (|in'tc generally
interpreted in that way. The fact that a lesion of these valves
makes a marked change in the quality of the second sound would
seem to demonstrate conclusively that the closure of the semilunar
valves is at least the most important factor in the second sound.
The most advantageous position for hearing the first sound is at
the apex, while the second sound is most easily heard over the
base of the heart.

2. THE CIRCULATION OF THE BLOOD.

The problems of this field of physiology are physical problems,
of the flow of liquids through tubes. As far as arterial circula-
tion is concerned the phenomena are those of the flow of liquids
through elastic tubes wider the influence of an intermittent initial force.
For the physical presentation of these problems see the physical
introduction to this chapter.

a. The Circulation in the Arteries.

1. Cause. — There is one, and only one, cause for the flow of
blood in the arteries ; namely, ventricular systole. The high intra-
ventricular pressure induced by the systolic contraction is trans-
mitted to the large arterial trunks. The blood flows from the left
ventricle to the aorta because the pressure is higher in the ventricle
than in the aorta ; it flows from the aorta into its branches because
the pressure is higher in the aorta than in its branches, and so on,
the energy of ventricular systole being gradually expended in
overcoming resistance, so that the lateral pressure gradually de-
creases from the ventricle to the capillaries.

The initial energy is, however, not all expended in forcing the
blood to and through the capillaries, so that there is still a small
residuum of heart energy left when the blood enters the veins to
assist other factors in returning the blood to the heart.

2. Blood Pressure. («) Methods of Determining. — The
blood-pressure is usually determined by the use either of a mer-
curial manometer or of a spring manometer. The mercurial
manometer was first used and modified for this purpose by Lud-
wig. His complete apparatus for measuring and recording the
quantity and variations of blood-pressure consists of the mercurial
manometer whose proximal limb is connected to the artery through

THE CIRCULATION IN THE ARTERIES.

167

a lead or rubber tube and canula filled with a solution which will
retard the coagulation of the blood. The distal limb is fitted with
au ivory float which bears a tracing point. The complete manom-
eter as described is fixed to a recording apparatus which consists
of a rotating cylinder propelled by clock-work. Originally the
whole apparatus was called a hymographwn (wave- writer) ; later
the term kymographion, shortened to kymograph, has been applied
to the recording drum which is now extensively used in experi-
mental physiology.

The spring manometer of Fick utilizes the principle that pres-
sure of liquid within a tube tends to straighten the tube. A thin
C-shaped steel tube is brought into connection with an artery.
The pressure of the blood transmitted through the connections to
the liquid with the C-tube will straighten it slightly. The proxi-
mal end of the tube being fixed, the distal end moves back and
forth with each variation of pressure.

The mercury manometer gives a very exact measure of the
amount of the pressure within the artery but the inertia of the

Curve of intra-vcntricular pressure

Curve of Intro-aortic pressure

Zero Pressure

-Zero-Presiure

ill I

Showing the relation of arterial pressure to intra-ventricular pressure. 'i'i
«. beginning of auricular systole; >>, opening of Bemi-lunar valve ; <■, maximi
re; •/. closure of semi-lunar valves.

Time relations:
maximum of systolic

mercury is too great to follow faithfully the minor variations of
pressure : It -hows the Traube-Hering curve, the respiratory wave
and the systolic wave but it does not show the dicrotic wave.
The spring manometer on the other hand shows the dicrotic wave
B8 well 8S the other-.

(h) Relation <>i Arterial Pressi be to [ntra-ventrio
[jlab Pressure. — As stated above, the arterial pressure is the
transmitted, intra-ventricular pressure. The accompanying figure

li;s

CIRCULA 7VO.Y.

(Fig. 10.")) shows that pressure within the aorta does not rise until
the opening of the semilunar valves ; that the crest of the systolic
wave of aortic pressure coincides, near the heart, with the erest of
the intra-ventrieular (systolic) wave ; that there is no " plateau "
of pressure in the artery ; that the closure of the semilunar valves
marks the beginning of the fall in the ventricular wave and a super-
imposed (dicrotic) arterial wave ; and that arterial pressure con-
tinues to fall until the semilunar valves open again.

(c) Variations of Arterial Pressure. — (a) Cydical vwri-
ations may be considered as : (i) Cycle of variation due to heart
contraction. (See Fig. 106, Waves III and IV.) The rounded
systolic wave, as shown by a mercurial manometer, or the systolic
with its superimposed dicrotic wave, belongs to this class, (n)
Cycle of variations due to the rhythmical action of the respiratory
musculature. (See Fig. 106, Wave II.) Respiratory wave n is
the result of the influence of the respiratory musculature. How
is this result brought about? Note : 1st, that the pressure rises
during inspiration ; 2d, that it falls during expiration ; 3d, that
the maximum pressure occurs after the end of the inspiratory
movement ; and 4th, that the minimum pressure occurs after the

Exp.

Fig. 106.

Systolic wave HI

Insp.

I Tonus-ivave"o?'ft:-C—~-

Exp.

Insp.

Exp.

"o dSvT-

Insp.

Dicrotic wave IV
/

Exp.

Insp.

Exp.

Zero-

pressure

A typical tracing of arterial blood-pressure. /, Traube-Hering curve or tonus-wave is a
wave of /order ; //, respiratory wave, is a wave of // order, i. e., Buperimposed upon /. Iff.
systolic waves, are waves of /// order, i. c, superimposed Upon //. IV, Dicrotic wave, is re-
eorded by Kick's spring kymograph, is a wave of IV order.

end of expiration. The pressure rises during inspiration because
there is greater negative pressure in the thorax, drawing more
venous blood to the right auricle and leading either to a greater
quantity of blood being ejected from the heart at each systole, or
to an increase of the rate of the heart beats. (Sterling and others
have observed the latter.) The pressure falls during expiration
for reasons the converse of those just stated. The maximum
pressure occurs after the end of inspiration and the minimum
pressure after the end of expiration, because there is a lapse of
about one second before the change wrought by respiratory move-
ments can have its effect <>n the quantity of blood ejected from the
left ventricle.

THE CIRCULATION IN THE ARTERIES.

169

(/?) Periodic variation, due to changes in arterial tonus or to the
degree of constriction under the influence of the vaso-motor nerves.
(See Fig. 10(3, wave /.) These long waves are called Traube-
Hering curves because first discovered and described by those
whose names they bear.

3. The Velocity of the Flow. — (a) Methods of Determin-
ing.— (a) Vblkmann's hewrwdrornometer, shown in Figs. 107 and 108.
As the cut indicates, this instrument consists of a U-shaped tube,

Fig. 107.

Volkmann'a tuemodromometer foi measuring the rapidity of the arterial circulation.

about 25 <iii. in Length. The Lumen of the tube is made continu-
ous with the Lumen of the artery by severing the latter and placing
the proximal end over an entrance cannula and the distal end
over an exit cannula. Two o-way stopcocks control the entrance
and exit. In the adjustment shown in the left-hand figure the
blood passes directly through the instrument. When the cocks

are turned ;i- indicated in the right-hand figure the Mood passes

along the l'-tnbe. In making an observation the tube was filled

with water, which \v;i- driven into the artery when the tube filled.
The time required fa- the stream to advance 25 cm. was taken to

equal the velocity of flow in the artery of the same Lumen. The
results wen- I'm- -ix.it «»f the actual velocity because of the resist-
ance of the apparatus, mid the contraction of the distal end artery

due to the action of the water upon it.

170

CIRCULATION.

Fig. 109.

(j) Chauveau's dromograph consisted of a brass tube to be in-
serted into the lumen of a severed artery. The blood flowing
through the tube pressed against the lower end of a needle pivoted
in the wall of the tube; deflecting it from its
zero position by overcoming a resistance. The
distal end of the needle indicated upon a dial
the relative velocity* of the stream within the
tube.

(;-) Linliriifs stromuhr is a modification of
the principle used by Volkmann. The U-tube
is replaced by a double chamber ( Fig. 109)
whose volume is known. Instead of stop-
cocks, the chambers opening through plate J)
communicate with the cannula? which open
through plate I. After one of the chambers
is tilled the plate J> is quickly rotated through
180°, with the aid of the milled head above
H. This reverses the direction of the stream
through the chambers. The proximal cham-
ber (C) is tilled with oil, the distal chamber
(B) with normal saline solution, through the
tube (H), which is thereupon clamped. The
proximal cannula (F) is inserted into the prox-
imal end of the cut artery. The plate I) is
turned just enough to shut off the continuity
of the lumen. To make an observation, turn
the plate D to 0°, taking the time to fifths of
a second ; the blood rushes through the proximal cannula up into
chamber ( ' ; the oil floats upon the blood without mixing with it,
and flows into chamber B, pushing the warmed saline solution
into the distal portion of the artery. When the blood has reached
the point at which the oil stood in the first adjustment the instru-
ment is reversed, time noted, and the chamber B (now the oil-
filled, proximal chamber) receives the blood from the proximal
cannula (A), while the blood in chamber ( ' is passed on into the
artery.

With this instrument one determines in advance the radius (/•)
of the cannula, which is chosen for an artery of approximately
equal radius ; the quantity (//) which the chamber contains. Dur-
ing the experiment one observes the time (t) in seconds required to
fill the chamber; it number of times. The following formula may
be used : Velocity (r) equals a constant factor (A') multiplied by
the number of times the chamber filled (/() and divided by the time

/ , _., . . A // i

(r) required to fill it // times, or v =—r- •

1 The general formula <,dven is derived thus :

(i) Discharge equals velocity times area of lumen : D = va.

Ludwig's stromuhr.

THE CIRCULATION IN THE ARTERIES.

171

(h) Variation of Velocity. — From the formula » = - , it

a

is evident that the velocity will vary directly with the discharge
and inversely as the area \ \v varies as D; ©varies as — I in other

words the velocity will be increased by anything which increases
the discharge and by anything which decreases the sectional area
of the vessels through which the blood flows.

(«) The/'"/'-' and rateofthe cardiac systole cause a marked vari-
ation in the velocity of the flow. Experiments demonstrate that
the discharge of a nozzle will be increased by increasing the height
of water in reservoir above the nozzle (I) varies as s/h , see Physical
Introduction) and further that the discharge will be increased
under intermittent pressure when either the rate or force of the
muscular contractions is increased, and much more if both rate
and force be increased together. "We may say then that the velocity
increases with rate of heart beat when all other variables remain con-
stant and with force of heart beat other variables remaining constant.

Fig. 110.

Relation "f velocity to area.

I.< i arterial velocity ;•

Venous velocity = or '.., v

r
( apillury velocity

When both rate and force are increased the velocity will be very
much increased. When one of these factors increases while the
other decreases the velocity mayor may not be increased (v varies
as rate x force).

D

a) .'. r = -^

ni Hut I) ''" and a = nr2.

i

fivi .•. v <l" or (/ - - ; , ia a conatanl quantity and tnaj be repre
rtrH ~i' i irr*
■ented by A', whose value may be calculated once for all for each instrument

.-. v=K- a genera] formula for the rtromuhr.

172 CIRCULATION.

Q9) The sectioned area is also an important factor. Anything
which causes an increase in the sectional area will cause a decrease
in the velocity; and conversely. "The velocity of the current
in various sections of the vessels must be inversely as their sec-
tional area." Volkmann determined the average velocity of the
capillaries to be approximately -^-J-^- as great as the velocity in the
aorta. We may reason backwards and conclude that the combined
sectional area of all the capillaries equals approximately 500 times
the sectional area of the aorta at the base (see diagram, Fig. 110).
The vaso-motor muscle-nerve system may induce variation of
terminal sectional area and therefore influence velocity in periphery.

4. The Pulse. — Though this topic should logically come under
consideration with (2) Variations of Blood-pressure, its importance
clinically and the fact that a number of extra factors are involved
in it justify a separate discussion.

The determination of blood-pressure with the Ludwig or Fick
instrument is immediate or direct while the determination of the
pressure by an examination of a superficially located artery is
mediate or indirect. In the first case the character of the arterial
walls or of the tissues overlying the artery cuts no figure while in
the examination of the pulse these are important factors. Until
comparatively recently no other means for the examination of the
pulse has been used than palpation with the finger tips ; even now
this method is most important and the t<i<-fii* erudiius reveals to
the physician all important variations of the pulse.

(a) Instruments foe Recording the Pulsations of an
artery are called Sphygmographs. There are several forms. The
one in most common use by clinicians is the Dudgeon sphygmo-
graph. An essential feature of this instrument is a system of
compound levers which transmits the movement of the arterial
wall from the foot or pad which rests upon the skin over the
artery to a tracing point connected with the last lever. This
system of levers multiplies the motion of the foot about fifty
times. A second feature of the instrument is a recording appa-
atus consisting of a clock-work which turns a pair of small cylin-
ders between which runs a slip of blackened paper. The tracing
point rests upon this paper and records there the magnified move-
ments of the foot or pad.

The Sphygmograph has the great advantage that it makes a
record of the variation of pressure, and when properly used may
reveal many facts about the general condition of the circulatory
system. The disadvantages of this instrument are that slight
variations in the location of the artery in different individuals
lead to variations in the tracing; that accumulation of fat on the
wrist may also " obscure " the artery and make the use of the
sphygmograph difficult or make the results of no value ; and,

THE CIRCULATION IN THE ARTERIES. 173

finally, faulty adjustments of the instrument lead to widely vary-
ing results with the same pulse. When the sphygmograph is
used with all its disadvantages known and carefully weighed, or
avoided, it may be a most valuable adjunct in physical diagnosis,
especially for making a permanent record of a pulse for subse-
quent reference or comparison.

(b) The Pulse-tracing or Sphygmogram. — It will be seen
at once by reference to Fig. Ill that upstroke A and downstroke
B represent the rise and fall in pressure due to ventricular systole
and diastole. Obeying the general laws of liquids under inter-
mittent pressure, the impulse, or pulse, is transmitted along the
arteries as a wave or undulation of the arterial walls. The sud-
den upstroke A indicates the sudden influx of blood into the aorta
during svstole, while the gradual fall of the part B indicates the
gradual fall of arterial pressure during diastole. The small waves,
1, 2 and 3, superimposed upon B, are called in order : 1. Tidal
wave, or predicrotic ; 2. Dicrotic; 3. Postdierotic. The apex (.1)
is called the Percussion wave or Systolic wave. The dicrotic
wave is due to the closure of the semilunar valves. The predi-
crotic and postdierotic waves are due to the elastic tension of the
arteries. Once set in motion the wall tends to continue to vibrate
under the influence of a series of secondary waves.

These secondary waves fall into two classes. Fig. Ill gives a
series of sphygmograms from normal individuals in widely vary-
ing states of blood-pressure, the highest pressure being shown in
sphygmogram No. (1). From No. (1) to No. (11) the arterial
blood-pressure is progressively lower, even merging into the pa-
thological in Nos. (10) and (il), which were taken in the fever
stage of acute " cold."

Fig. ill.

Sphygmograms from normal individuals.

The two classes of super! m posed curves come out into promi-
nence in tlii- series : The Predicrotic and Postdierotic waves as
shown in No-. (3), (4) and (5), which are typical, and average
normal tracings, belong clearly to the class shown on the down-
stroke B of Nil-. ( 1 ) and (2), where no dicrotic wave may be dif-
ferentiated. There may be four, live or even six or seven of these
wavelets on a high-pressure sphygmogram. They are called
"elasticity waves." With gradually decreasing pressure the less
tense mid very extensible arterial wall shows a decreasing tendency
to transmil these waves until finally they are nol discernible.

174 CIRCULATION.

The dicrotic wave, however, is more and more pronounced with
gradually decreasing pressure. Note wavelet 2 in tracings Nos.
(•">) to (1 1). Tn Xos. (3), (4) and (5) where we have both elastic-
ity waves and the dicrotic on the tracing, the dicrotic is probably
a resultant of two causes: (1st) the cause of the second elastic
wave and (2d) the closure of the semilunar valves, because there
would naturally be an elastic wave at 2 any way and beginning
with tracing No. (3), some extra cause seems to be operating to
emphasize or increase wavelet 2. Finally in tracing Xo. (6).
The conditions necessary for the transmission of the elasticity
waves have disappeared while the dicrotic continues to increase.

(c) Variations <>f the Pulse-rate are found to depend
upon age, height, muscular activity, stateofthe emotions. Then be-
sides a certain range of individual variation there is a wide range
of pathological variation.

(a) Variation with aye : At birth the rate is 130 to 140. By
about the 18th year it gradually decreases to the average for adult
life which is from 60 to 75 or not far from 70 per minute. This
rate is maintained until the beginning of the senile period between
the 50th and 60th year when there is a gradual increase to 80 or
more per minute.

Q9) Variation with height : Short individuals have a faster rate
than tall ones ; a height of 140 to 150 cm. (4 ft. 8 to 5 ft.) cor-
responding to a rate of 74 per minute while 180 cm. (6 ft.) cor-
responds to 60 per minute.

(}') There is a variation of the pulse rate with varying muscu-
lar activity, the rate being increased to a greater or less extent by
exercise.

(o) With emotional excitement the pulse may be greatly in-
creased in rate.

b. The Circulation in the Capillaries.

1. Cause and Variations. — The ultimate cause of the blood-
pressure in the capillaries is, of course, the force of ventricular
systole. Though the capillary pressure, and therefore capillary
flow, is ultimately caused by systole, it is immediately varied by
change in the lumen of the arterioles. If, for example, the local
blood supply is increased, by a widening of the arterioles under
the influence of the vaso-motor nerve-muscle apparatus, then the
capillary pressure will be much increased. On the other hand, if
the local blood supply be decreased through narrowing of the
arterioles the capillary tension will be much decreased. In the
first case the resistance offered by the arterioles is decreased, while
in the second case it is increased. But the resistance offered by
the arterioles is the variable factor of the peripheral resistance.
The greater the arteriole resistance the less the capillary pressure

CIRCULATION IN THE CAPILLARIES.

175

and conversely. Or it may be thus stated : The greater the sec-
tional area of the arterioles the greater the capillary pressure, and
conversely.

To sum up then : The capillary pressure varies, (i) directly as
the energy of the heart's systole ; and (n) directly as the sectional
area of the arterioles. It may be further stated that the local
capillary pressure, and consequently local plasma supply to the
tissues varies directly as the local sectional arteriole area.

Fig. 112.

Capillary plexus in the portion of a web of a frog's foot, magnified il<> diameters. 1, trunk

of vein; 2,2,2, its branches; :'., :',, pigment cells. (Carpenter.)

2. Results. — This relation between the condition of the arte-
rioles and capillary pressure is a most important physiological fact.
For a concrete case let us suppose that the blood, rich in food-
stuffs from a recent meal, is on its way from the digestive organs
t<» the general system ; the individual resumes his work, which, let
ii- suppose, is manual labor involving especially the muscles of
the arms ; the arteriole- of the arms dilate ; the local blood-sup-
ply i- much increased, probably doubled ; the veins and lym-
phatics are rapidly emptied by the working of the muscles; with
the foil of tension in the arterioles has come an increase of capil-
lary pressure, the increase is so great thai the rich plasma is forced
through the permeable capillary walls ami bathes the muscle-
cells. I nder -iich conditions a certain amount of the waste prod-
uct- will enter the capillaries near their junction with the veins,
where the pressure is low, bu1 much will also have the working

176

CUU'ULATIOX.

muscle by way of the lymph radicles and lymphatics, some will

be retained and after a few hours the muscle will be fatigued, or

will "feel tired " — a rest is in order. During rest the arterioles

contract, capillary pressure falls and the accumulated product- of

destructive metabolism readily find their way into the capillaries,

are carried to the organs of excretion and thrown out of the

system.

3. Method of Determining Capillary Pressure. — Von Kries

used a glass plate of known dimensions, to which was hung a

scale-pan, the weight of the scale-pan and plate plus the weight

necessary to exclude the blood from the capillaries equals the

pressure for the area of the plate. If the area of the plate be 100

square millimeters ; if the weight of the apparatus be 5 gms. ; if

the weight added to suppress capillary circulation be 22.2 gms.,

and if Pc be the capillary pressure per sq. mm., then 100 Pc =

27200 milligrams ; Pc = 272 mgs., Expressed in height of column

272
of mercury : Pc = ^-^ = 20 millimeters of mercury. Several

13.6
have

been used which involve the same

Fig. 113.

different methods

principle.

A slight modification of v. Kries's method (see Fig. 113) may

be used. The plate which rests upon
the finger has no raised plate of known
area ; it therefore becomes necessary to
determine the area of the part from
which capillary circulation is excluded.
Suppose its diameter to be 8 mm. ;
weight of apparatus, 3.35 gms. ; weight
added to stop capillary circulation in
area exposed, 20 gms. ; total weight =
23.35 gms.

From the experiment above cited
one may make the following general

formula : Pc = when ir = weight

"U
in milligrams ; when a = area in square

mm. ; when </ = sp. gr. of mercury.
But a = ~r, therefore the formula be-
comes :

w 1 w _ 1

Pc = - -,- =

Apparatus for determining the cap-
illary pressure.

«rV

But

"7

is a

xg /-.
constant quantity, >r and /• only
being variable, so that we may give as a general formula for

r, ""

thi> apparatus : Pc = K ., or the capillary pressure equals a

DIAPEDESIS.

Ill

constant (0.0234) multiplied by the weight required to exclude the
capillary circulation from an area and divided by the radius of the
area squared. The result thus obtained is in millimeters, ami rep-
resents the height of a column of mercury which would balance
the capillary pressure.

The various results of von Kries, Ray and others vary from
15 mm. Hg to 50 mm. Hg, according to the relation of the
various factors involved in the capillary pressure at the time of
determination. The position of the part has been found to be an
important element. If the hand be held above the level of the
shoulder, for example, the capillary pressure will be much decreased.

4. Diapedesis. (See Fig. 114.) — The term diapedesis is used
to express the passage of corpuscles through the capillary wall. The

Fig. 114.

Diapedesis. l, adhesion (■> wall: 2, finding opening by pseudopod: •■, traversing the
wall: 4. resumption of active form ; .1, normal field; Bhowing large capillary with corpuscles
in center "f blood stream ; /-', field of irritation, leucocytes leaving current and sticking to
wall, causing a partial blocking of tl<>w of red corpuscles.

passage of white corpuscles through the capillary wall is a normal
process and La the result of an amoeboid movemenl of the leuco-
cyte ; but the passage of red corpuscles is looked upon as an ab-
normal process by xaoei physiologists. The process may be an-
alyzed Into several acts: (i) Adhesion to wall; (n) finding of
opening by pseudopod ; (in) the ameboid movements and flow-
ing of protoplasm incident to traversing the wall ; (iv) resumption
of typical form and migration through tissues. The immense
importance of tin- process was firsl emphasized by Conheim. In

inflammation both red anil white corpuscles (but the white are far

more numerous) migrate in myriads into the tissues. \l<vr the
white corpuscles may In Bacrificed for the good of the organism.
I lead leucocytes are called pus corpuscles.
12

ITS CIRCULATION.

c. The Circulation in the Veins.

1. Forces Involved in Venous Circulation. — (a) Residuum
of heart-pressure exerted through the capillaries. (/?) Action of
diaphragm and intercostals in causing negative intra-thoracic pres-
sure during inspiration, actually lifting the column of blood in the
ascending vena cava. (-/) Ventricular systole causing negative
intra-thoracic pressure at end of systole and beginning of diastole,
through the sudden decrease in volume of heart, (o) Action of
muscles pressing upon the veins, (e) The force of gravitation,
which materially assists in tilling the ventricles and the left auricle,
as well as in assisting the How in the jugulars and descending or
anterior vena cava, while it retards the flow in the veins below the
heart. (£) Contraction of the mouths of the veins. (/,) Under
certain circumstances, positive intra-abdominal pressure, during
inspiration and expiration (forced). (#) Negative intra-thoracic
pressure through pushing out of the anterior thoracic wall by the
apex-beat of the heart.

Of these forces the first three are the efficient forces of venous
circulation, the remaining forces are either so small in relation to
the first three that they may be ignored or they act only under
special conditions. The force of gravitation, though it assists the
downward flow in all veins and retards the upward flow, may
rather be recorded among the factors which modify venous circu-
lation. Any action of the walls of the abdominal cavity (descent
of diaphragm in inspiration or contraction of the lateral walls in
expiration) will force toward the thoracic cavity any blood in the
abdominal veins, but it will, to the same degree, keep out of the
abdominal veins any blood in the legs.

2. Causes and Variations of Venous Pressure. — The forces
involved in venous circulation, as enumerated above, are the causes
of blood-pressure in the veins. These factors vary greatly in dif-
ferent parts of the venous system ; e. ;/., in the venules the prin-
cipal factor is the residuum of heart-force. In the veins of the
limbs one important factor is muscle-movement causing a flow to-
ward the heart through a pressure exerted upon the walls of the
veins ; this increases the pressure within the veins and forces the
blood to move in the direction of least resistance.

The distal flow is blocked by the valves of the veins and the
flow toward the heart is thus increased. In the large venous
trunks near the thorax the negative intra-thoracic pressure —
caused by inspiration, by cardiac systole and by the apex beat —
is the principal factor of venous circulation, operating not by
causing higher pressure at the periphery, but by causing lower
pressure at the center. The quickening of venous circulation
through musele-movements, whether these movements be passive

THE CIRCULATION IN THE VEINS.

179

or active, is the basis of the theory of massage. All the varied
phases of massage treatment have developed from this point, and
all have the effect of quickening venous and lymphatic circulation
primarily and of recuperating and rejuvenating the tissues'! sec-
ondarily. Active muscular exercise not only quickens venous
and lymphatic circulation directly in the manner described, but
also indirectly through causing an increase in the frequency and

Fig. 115.

Plethysmograph of Mosso. (Marey. )

strength of ventricular systole and furnishing a larger residuum
of cardiac force for venous circulation.

3. The Plethysmograph. — This instrument comprises a me-
tallic or glass case which is made to enclose an arm or leg, the

Fir;. 116.

Pletbysmogrom. Respiration iras suspended. The small waves // are due to 'the Influence of

the heart ;> i < > 1 1< -.

..p<n end of the case being closed with guttapercha (see Fig. I 1 5).
A small tube from the plethysmograph connects with a pressure
apparatus, and another with a recording tambour. Any changes

ISO

CIRCULATION.

in the volume are accurately recorded by the tracing lever upon a
kymograph drum. The accompanying plethysmograms taken by
the author during a elas> demonstration show the general influence
of the circulation upon the volume of the arm.

Fig. 117.

<%,

E

\

I

AT"

E

X

I

E \ 1 EI E I EI

R

R

n

R

R

R

Plethysmogram. The influence of respiration is added t<> thai of the heart. /.', indicates res-
piratory wave ; E, exspiratory portion ; I, inspiratory portion.

These tracings justify the following conclusions :
Fig. 116. The volume of the arm (or other portion of the body)
is affected by the cardiac contractions.

Fig. 118.

Plethysmogram. The influence of muscular contraction is added t<> that of respiration
and heart contractions. The arm is emptied and the curve drops during contraction. The
respiratory waves are well marked in portions of the tracings.

Fig. 117. The volume of the arm is influenced by the respira-
tory movements, being increased during expiration and decreased
during inspiration. The reason for the decrease during inspira-
tion is that the increased negative intra-thoracic pressure empties
the veins of the arm.

CIRCULATION OF THE LYMPH. 181

Fio-. 118. The volume of the arm is influenced by muscular
movements, being- increased during relaxation and decreased dur-
ing contraction. The reason for the decrease during muscular con-
traction is that the pressure of the contracted muscles upon the
veins and lymphatics empties them toward the heart. This is a
demonstration of the validity of the point given above [C, (1), (o)] ,
where muscular contraction was given as one of the forces which
cause venous blood flow.

3. THE CIRCULATION OF THE LYMPH.
a. In the Lymph Radicals.

1. Causes and Variation. — After the plasma has oozed
through the capillary wall and become lymph, it receives pressure
from three sources : (i) The capillary pressure which caused it to
filter through the capillary wall is not all expended in that proc-
ess ; or, expressed differently, as long as more plasma is passing
into the tissues, the plasma or lymph already there is forced on
through the minute lymph radicals, (n) Endosmosis is the prin-
cipal physical factor of lymph circulation in the lymph radicals of
the intestinal mucous membrane, (in) The physiological factor
selection plays a still more important role, but it cannot be meas-
ured. Variation of any of these factors — the first through varia-
tion of capillary pressure, or the second and third through the
conditions in the alimentary canal — will cause a variation of pres-
sure, and, as a consequence, a variation of the flow in the lymph
radicals.

b. In the Lymphatics.

1. Causes and Variation. — (i) Residuum of the pressure in the
Lymph radicals is a strong factor, (n) The most important factor
• if lymph circulation in the limbs is muscular activity. As is the
cage with the venous circulation, so here the efficiency of muscular
activity depends upon the presence of valves within the vessels.
The numerous lymphatic glands in the course of the lymphatics—
especially in the axilla and groin — act somewhat like valves in
Staying the reflux of the column of lymph after it has once passed.
(ill) In all those lymphatics near the thorax the negative pressure

of that cavity during inspiration acts as a strong motive factor.
Variation of" muscular activity is the most important variable
factor in 'he lymphatic circulation.

/;. THE CONTROL OF THE ORGANS OF CIRCULATION.

I. THE INNERVATION OF THE CIRCULATORY SYSTEM.

When we remember thai the general How ..I' U I, in response

to arterial pressure, U affected directly by the activity of the

182

CIRCULATION.

heart and reciprocally by the sectional area of the arterioles and
capillaries it is clear thai the problem of determining the exact
status of the circulation can only be solved by knowing the value

of both variable factors,

which solution is not facili-
tated by the fact that both
the heart-activity and the
sectional area of the arte-
rioles are variously affected
by different local ami gen-
eral stimuli. These different
stimuli affect the circulatory
organs usually through the
medium of the nervous sys-
tem though certain stimuli
may act directly upon the
muscle tissue of the heart or
arteries.

'/. The Innervation of the
Heart.

1. The Heart as Influ-
enced from Within. — The
heart of an amphibian or
reptile has a ganglion in the
venous sinus — Remak's — one
in the interauricular wall —
the ganglion of Ludwig or v.
Bezold — and a pair of ganglia
in auriculo-ventricular sep-
tum— Bidder's. The heart
of the mammal differs from
this only in having a group
of several ganglia -where the
frog or turtle has one ; but
the three groups of ganglia
in the mammalian heart are
looked upon as anatomically
homologous to the corre-
spondingly located single
ganglia of the amphibian
heart, and as physiologically
equivalent to them. General
laws based upon experiments
with cold-blooded animals

Diagram of the nerve supply of the heart. Con-
tinuous lines show vagus origin of cardiac plexus ;
dotted lines show sympathetic origin of that plexus.
VC, vagus center in floor of 4th vent.: SCS, Car-
diac branch of the snp. cerv. symp.; BtCS, cardiac
branch of the mid. cer. symp.; l-VII. rami com-
municantes from spinal cord to ggl. of symp. syst. ;
ICS, inf. cerv. symp. cd. Dr.: UP, Cardiac plexus.
Shown only in part, in the Fig. Ct, '</. PI, Beside
arch of aorta. (2), ant. cd. pi. under arch of aorta.

: . coronary plexuses arc really div. of the gen.
cardiac plexus : TCV, thoracic card. Dr. of vagus ;
GR, ganglion of vagus root; GT, ganglion of vagus
trunk; SCV, sup. cardiac hr. vagu- ; TCV. inf.
cardiac l>r. vagu-: /.'/.. recurrent lary., giving
branch to cardiac plexus ; GCP, great card.pl. of
ind sympathetic fibers ; ScG, superior cer-
vical ggl. symp., MCG, uied. cervical ggl. symp.:
TCG, inf. cervical ggl. Bymp.; StC, stellate gang,
sympathetic; AV$, Annulus of Vieussens around
siibclavial arterv.

THE INNERVATION < >F THE HEART. 183

hold good for mammals. The heart of a frog continues to beat
some time after removal and is especially adapted for certain
experiments. Stannius's experiment consists in first cutting
off from the auricles and ventricles, through ligature or in-
cision, the influence of Remak's ganglion, the auricles and
ventricles become quiet : Second, dividing by ligature or in-
cision, auricles and ventricle at their junction — the ventricle be-
gins to beat, the auricles remain quiet. The experiment was
formerly interpreted thus : The heart muscle acts under the in-
fluence of three ganglia — or groups of ganglia — Remak's and
Bidder's ganglia afford positive stimulation, while the Ludwig
ganglion or group of ganglia retard or inhibit the heart action.
The influence through Remak's and Bidder's ganglia exceed the
influence of the Ludwig ganglion ; therefore when all are intact,
the heart beats. When the influence of Remak's ganglion is re-
moved the influence of the Bidder's ganglia is not sufficient to
overcome the inhibition of the Ludwig ganglion; therefore, the
auricles and ventricles stand still. When the inhibitory influence
of the Ludwig ganglion is removed the ventricle starts into activ-
ity. This ingenious and plausible theory has been shaken bv the
investigations of Gaskell and others. They have found that when
properly sti undated and nourished, small pieces of the ventricle,
which are wholly free from ganglia, will continue to beat rhythmic-
ally for a considerable period ; further, that special stimuli are
transmitted through muscle tissue. It appears from this that the

BHYTHMICAI, BEATING OF THE HEART HAS ITS IMMEDIATE CAUSE

in tin; protoplasm of the muscee cells. The beat may be
varied in rate and fora by stimuli affecting the cells from without.
Whether any part of this extracellular stimulus originates in the
cardiac ganglia is still an open question. These ganglia may act
merely like storage centers or distributing centers for the central
nervous system.

Prom the Stanniu- experiment it seems that the cardiac ganglia
may affect the rate and force of the heart-beat; but we must not
forget that in this experiment a profound departure from any pos-
sible normal condition is made and we must not impose too much
confidence in the inductions derived from the effects. From the
connections of the cardiac ganglia with the cardiac plexus of
nerves we Bhould expect their function to be lor the most part

III! lll'lll .

■i. The Regulation of the Heart by the Central Nervous
System. — [f the cardiac plexus of a dog be followed upward from

tli< month of the anterior vena cava it will be found to represent

two symmetrically Located sources, one to the right and one to the
left. If we follow the left we will find the three or more nerve
trunk- converging toward the inferior cervical sympathetic gang-

184 i n:< ULATION.

lion. Here there are connections anteriorly along tin- vago-sym-
pathetic trunk toward the brain and laterally via the Annulua of
Vieussens, to the first thoracic ganglion of the sympathetic.
Whether these connections represent afferent or efferent nerves is
impossible to determine by other means than by physiological
experimentation. Suppose the vago-sympathetic trunk to be
divided high up in the neck and the distal end stimulated with an
induction current, the result will be a slowing or stopping of the
heart-beat : if the stimulation be made lower down and at dif-
ferent points the result will be the same until the inferior cervical
ganglion i- reached, when the results will be variable and am-
biguous. If the Annulus of Vieussens be divided and the distal
end- stimulated there will be either acceleration of the /•"/< of beat
or augmentation of the stn ngth i >f 1 teat i »f the heart. If the Kami
C'ommunicantes II or III be divided and stimulated distally there
Anil be acceleration or augmentation of heart activity. From
experiments we may conclude that the vago-sympathetic
trunk i in man the vagus) contains fibers whose stimulation causes
slowing or enuimtkoj of the heart-beat, while the sympathetic
contains fibers whose stimulation has the reverse effect, i. e., that
of acceleration or AUGMENTATION. Through further experi-
mentation the inhibitory fiber- may lie traced along the vagus
through the jugular foramen, along the trunk of the spinal acces-
sory to its origin in the floor of the fourth ventricle in the poste-
rior part of the medulla oblongata. In a similar way the accelera-
tor filters may be traced through the Rami Communicantes, along
interior nerve roots into the spinal cord, and up to the
medulla oblongata where its exact origin has not been determined.
In man the main cardiac branch of the sympathetic is called N.
Accelerans cordis, and is not ensheathed with the vagus in any
part of its course.

^ e have now found that the inherent property of the heart
muscle to produce an uninterrupted series of alternating contrac-
tions and relaxations is governed by the central nervous system
in a way analogous to the way in which a horse is governed by
the driver: the inhibitory vagus-fibers checking the speed of the
heart-beat and the acceleratory fibers of the sympathetic stimulat-

_ "lie heart to greater speed, or greater force, as the case re-
quires. But what causes the central nervous system to -end these
- _ - of inhibition or augmentation t<» the heart'.' Here we
must recall the general principle that, all messages sent out from
ttral nervous system — all efferent nerve impulses — art in re-
sponse, (l to afferent nervt impulses, brought to the central nervous
system through nerves which carry impulses only from the periph-
era to the cuter — the sensory nerves; ci) to direct stimulation
of the center. As an example of I the sudden withdrawal of

THE INNERVATION OF THE HEART. 185

the hand from a needle point is accomplished through contraction
of muscles in the arm in response to an efferent motor me-- g
from the center which in turn is stimulated by the afferent mes-
sage of pain from the skin, reaching the center through a sensory

nerve. If we look for the afferent nerve osory nerve- —

which carry messages to the center from the heart or some part of
the periphery we shall find them represented by only the general
sensory nerves, either spinal or sympathetic, and these affect the
heart-beat only indirectly, after a too complex inter-central inter-
change to be accepted as a simple refk-x. ~\\ e must look for another
way in which the center may be affected. (Hi The center may.
however, be directly stimulated. Physiological examples of the
direct stimulation of a center are not numerous and are confined
for the most part to the circulatory and respiratory centers. This
direct stimulation of respiratory and circulatory centers is made

ssible by the fact that the activity of these organs is din
toward the supply of the system with blood sufficient in quantity
and proper in quality. The nerve centers in the medulla being
a part of the system so supplied, are at once affected by variations
in blood-pressure or in the quantity of OOa and of O brought by
the blood-supply.

(a) Stimulation <»f the Caedk (-inhibitory Center, /o/-
lowed by slowing of iJu heart-beat, (a Direct. — ( i ) Sudden anemia
of the medulla oblongata, as would be produced experimentally by
ligation of the carotids and vertebral arteries. ri Sudden venous
hyperemia in the medulla oblongata, as would be produced ex-
perimentally by ligation of the jugular vein-, (ill) By increase
of the 00 . as would occur in suspended respiration, thus any inter-
ference with a proper oxygenation of placental blood during preg-
nancy or parturition will cause a slowing of the foetal heart-beats.
Increased blood-pressure in the cerebral arteries.
- Indirect. — Strong stimulation of any sensory nerve, •.;/..
tapping the exposed intestines of a frog with a scalpel handle will
cause inhibition of the heart.

(h) Stimulation of Cardio-Aocelerator, or cardio-aug-
mentor centers, followed either by acceleration of rate, or augmen-
tation of force, or both.

Stimulation maybe direct or indirect, but uncertainty about the
location of the center confines our knowledge t-- that gained by a
stimulation of accelerator fibers which always, of course, causes
acceleration or augmentation of heart activity with associated rise
in blood-pressure. Indirect stimulation of tin- cardio-accelerator
i- illustrated in the -ip|»iir_r of cold water, which has a
-trorr_r accelerating effect upon the heart, probably through stimu-
lation of the cardio-accelerator ••enter, through afferent fibers of
the sympathetic nervous system.

186 CIRCULATION.

3. The Mechanical Stimulation of the Heart. — (a) Through
increased flow of blood to the heart due to negative intra-thoracic

pressure. This increase of bl 1 in the heart cavities seems to

stimulate it directly without the intervention of the nerve-appa-
ratus.

(ji) Through increased resistance in the aorta ; due in turn to
increased peripheral resistance.

b. The Innervation of the Arteries.

Though the arterioles and small arteries may change their caliber
through such local influences as changes in temperature, their
variations in caliber are, for the most part, due to the influence of
nerves upon the circular muscle-fibers. The nerves which control
the arterial supply of the muscles are called VASO-MOTOB NERVES.
Experiment has proven that there are two kinds of nerves sup-
plying the arteries, as there are two kinds of nerves supplying the
heart: (i) there are fibers which augment the tonicity of the ves-
sels by causing contraction. These nerves are called VASO-CON-
STRICTOE NERVES ; (n) there are fibers which inhibit the stimulus
given to the muscles by the vaso-constrictor nerves, these are called
vasodilator nerves. To get a clear idea of the action of vaso-
constrictor and vaso-dilator nerves it is necessary to take a con-
crete case. The subrnwdllary salivary (//end is supplied by two
nerves: (i) a branch of the sympathetic which accompanies the
artery ; (n) the chorda tympani nerve. Both of these nerves sup-
ply fibers to the arterioles of the gland. Under the influence of
the sympathetic the arterioles are kept usually in a state of mod-
erate contraction called " tonus." This condition of tonus, which
is the usual condition of all the small arteries and arterioles of the
body, is maintained by rapidly repeated moderate stimuli passing
from the vaso-constrictor center in the medulla oblongata out to
the arteries in all parts of the body. If these stimuli are increased
or decreased the tonus becomes higher or lower accordingly, /'. e.,
the vessels are constricted by the contracting circular muscles, or
they are dilated by the blood-pressure after relaxation of the cir-
cular muscles. To return to our example — the arterioles of the
submaxillary salivary gland are governed by the general condi-
tion of the vaso-constrictor apparatus ; and, according as the gen-
eral tonus is high or low, the local blood supply will be under
higher or lower pressure, but not necessarily modified in quantity.
If an especially free local blood supply be necessary — as is the
case when the gland is actively secreting — some local inhibitory
influence must be brought to bear upon the vaso-constrictor nerves
to suspend their action and to allow the arterioles to dilate widely
under the influence of the blood-pressure. This local inhibitory

THE INNERVATION OF THE ARTERIES. 187

influence is furnished by the chorda tympani nerve, which is called
a vaso-dilator and has upon the muscular tissue of the arteries an
influence analogous to that which the vagus has upon the muscle
tissue of the heart. From this it would seem that the primary
function of the vaso-constrictor nerves is to govern general blood-
pressure through general changes in the tonus of the small arteries
and arterioles, thus increasing or decreasing terminal resistance.

The above example further indicates that the primary function
of the vaso-dilator nerves is to control local blood supply through
suspending the action of vaso-constrictors, thus allowing the blood
vessels to dilate. This is in general the relation of the two sys-
tem- of vaso-motor nerves.

1. The Vaso-constrictor System : Tonus of Blood Vessels. —

The vaso-constrictor center was located by Ludwig and his
pupils in the floor of the fourth ventricle — in the medulla oblon-
gata. That this is a general center is proven by this experiment.
Stimulation causes general contraction of all the arteries ; while
paralysis of the center, as by over-stimulation, causes general dil-
atation. From this center nerve fibers pass down the lateral
tract- of the spinal cord, from which they emerge through the an-
terior nerve roots and pass into the sympathetic system through
the rami communicantes. From the sympathetic system they
supply all arteries of the body cavity and some of the arteries of
neck anil mouth as branches of that system ; while the arteries of
tli*- skeletal muscles and skin are supplied by branches which have
left the sympathetic Bystem and are distributed along with
branches of the spinal or cranial nerves. Besides this general
center in the medulla there are local centers in the gray matter of
the spinal cord ; further, some of the ganglia of the sympathetic
Bystem may act ;i- local centers. The action of the local centers
mav cause a local change in arterial tonus.

(a) Direct Stimulation of the Vaso-constrictor Cen-
ter.— (i) An excess of CO., in the blood supplying the center
acts as a stimulus and causes a constriction of the arteries in gen-
eral, (n) Sudden anaemia of the medulla as the effect of a severe
hemorrhage or of ligation of the arteries bringing the local supply.
uii, Venous hyperemia as the effect of the ligation of the jugu-
lars. It i- probably the exec-- of <'(), which is active in this

case, (rv) Poisons, e. g., Btrycbnia, nicotine, etc.

(h) Reflex Stimi latton. — (i) Through "pressor" afferent
• fibers whose stimulation may cause a reflex constriction of
the arteries generally, (ii) Through " depressor " afferenl nerve
lil.er-. These are uo1 widely disseminated ; mo-t of them are lo-
cated in the depressor aerve (superior cardiac in man), which
- upward from the ventricular walls, through the vagus to
the vaso-motor center. The ventricular termini of this nerve are

188 CIRCULATION.

stimulated by an excessively high arterial pressure. The return
passage is not Benl to the heart, but to the vaso-constrictora of the
abdominal cavity, and take- the form of an inhibition, in conse-
quence of which the arteries of the abdomen relax, the blood-pres-
sure falls and the heart is relieved of its excessive work.

2. The Vaso-Dilator System. — That there is a system of
nerves emanating from a special center, whose function is to sus-
pend or inhibit Locally the general action of the vaso-constrictor
system is abundantly proven by such physiological experiments as
that upon the submaxillary gland. It has been further proven
that the center is in the medulla — or at least above the spinal
cord — hut its exact location has not been determined. The dis-
tribution of the vaso-dilator fibers is in a general way parallel to
that of the vaso-constrictor fibers ; they may supply a particular
locality in the same trunk with vaso-constrictor, motor and sen-
sory fibers, or they may form a separate nerve, as is the case in
the chorda tympani. All vaso-motor fibers are efferent; the
afferent members of the reflex circuit is represented in part by the
blood supply of the center in the case of the vaso-constrictor
center. This condition is possible in that case because the influ-
ence of the vaso-constrictor system is for the most part general;
but the local action of the vaso-dilator system makes direct stim-
ulation of the vaso-dilator center practically impossible. As n<>
afferent vaso-dilator fibers have been found, it is probable that the
afferent member of the circuit is represented by the sensory nerve
coming from any given locality.

2. ADAPTATIVE COORDINATION OF THE ACTIVITIES
OF THE CIRCULATORY ORGANS.

In our study of motion in general physiology we found that a
successful adaptative motion must be coordinated in time or in
space and time and controlled in force. In the same way the activ-
ities of the circulatory organs, depending as they do, upon muscle
contractions, must be perfectly coordinated in time and controlled
in force. This is accomplished, as we have seen, through the
central nervous system ; its coordinating messages are sent to the
heart and arteries through augmentor and inhibitory cardiac and
vaso-motor fibers. Through the agency of this most complicated
nerve apparatus the following general adaptative adjustments are
accomplished :

[. Regulation of temperature,
n. Regulation of secretion and excretion.

in. Regulation of supply of food and oxygen to working organs.

iv. Regulation of general blood-pressure,
v. Regulation of local blood How : To secreting glands ; to
working organs; in blushing; in pallor, etc. Most of these will
be discussed under different headings.

CHAPTER IV.
RESPIRATION. INTRODUCTION.

RESPIBATION DEFINED AND CLASSIFIED.

A. COMPARATIVE PHYSIOLOGY OF RESPIRATION.

1. RESPIRATION IN INDIVIDUALS OF A LOWER ORDER.

2. RESPIRATION IN INDIVIDUALS OF A HIGHER ORDER.

(1) CiTAXKors Respiration.

(2) Respiration by Gills.

(3) Respiration by Lungs.

B. ANATOMICAL INTRODUCTION.
THE HISTOLOGY OF THE RESPIRATORY ORGANS.
C. PHYSICAL INTRODUCTION.
THE SOLUTION OF GASES IN LIQUIDS.

RESPIRATION.
INTRODUCTION.

RESPIRATION DEFINED AND CLASSIFIED.

From our studies in general physiology we know that that
peculiar form of energy which we call life exists only in associa-
tion with living cells or with living organisms, that it is liberated
only through a katabolism or destructive metabolism of living
cell protoplasm and that this katabolism is possible in the pres-
ence of oxygen. The frequent use of such expressions as " The
spark of life" " The flame of life," etc., indicates the analogy
between the liberation of life energy and the liberation of the
heal and light-energy of fuel. It was once thought that these
two processes were quite alike — each being a combustion or direci
oxidation. The oxygen of the atmosphere unites directly with
the carbon and hydrogen of the candle, of wood, of coal, or of
illuminating lni- to form CO, and 1 1 .,( ) — the process being attended

with the liberation of energy ; now the oxygen of the atmosphere
forme combinations in the tissues :ui<l the combinations finally re-
nd in the formation of COj, II.,<) and COXJI, — the process be-
ing attended with the liberation of life energy. These two proc-
.'. bich seem so much alike are essentially different in a very
important point. In the combustion of the hydrocarbons of the
candle the affinity of oxygen for the carbon and hydrogen is so
greal that, if once started the combustion proceeds by the invasion

L89

190 RESPIRATION: INTRODUCTION.

of the molecules l>v the oxygen, which breaks tli*- Itoiid between
carbon ami hydrogen and joins with each.

In the katabolism of the living protoplasm of the cell, the ex-
ceedingly complex protoplasmic molecule separates into two, per-
haps more, simpler molecules; these simple molecules, which
probably represent proteids, may again separate into -till simpler
ones. Bach change from a complex to a more simple compound
leads (i) to a liberation of energy, which may manifest itself in
any of the activities of life, and (n) to a combination of simpler
molecules with oxygen furnished by the cell sap or cell plasma.
In the latter case, then, the oxygen steps in to complete a mole-
cule already nascent, while in the former case it is the cause of
dissolution. To sum up the comparison : Oxygen is the cause
of combustion but the complement of kataJbolism. This general proc-
ess of supplying the cells of a living organism with the requisite
oxygen is called Respiration.

1. Definition. — Respiration is a general term which includes
all of those activities involved in the furnishing of oxygen to the
tissues of a living organism.

2. Classification. — The essential act of respiration is the taking
up of oxygen by the living cell from the tissue plasma. In the
large animals a more or less complex series of preliminary acts
are necessary in order to furnish the tissue plasma with oxygen,
and of this series of acts the interchange of gases between the
blood and the medium surrounding the animal is the most
prominent. This has led to the following classification : (r) In-
ternal respiration or cell respiration, (n) External respiration or
somatic respiration.

A. COMPARATIVE PHYSIOLOGY OF RESPIRATION.

1. RESPIRATION BY INDIVIDUALS OF THE I, II, AND III

ORDER.

It has just been stated that the oxygen required in the cell at
the moment of katabolism is furnished by the cell sap or cell
plasma in which it is held in simple solution. If the cell is an
independent organism, e. g., an amoeba, the oxygen of the cell
plasma is immediately replenished from the water which surrounds
the amoeba. This is respiration in its simplest form. If the or-
ganism be an individual of the n or in order the process is es-
sentially the same.

2. RESPIRATION IN INDIVIDUALS OF THE IV ORDER.

1. Cutaneous Respiration. — The common earthworm or angle-
worm has well developed digestive, circulatory, nervous, repro-

ANATOMICAL INTRODUCTION. 191

ductive and motor systems, but has no definite respiratory system.
It has been found that the rich cutaneous capillary plexuses fur-
nish to the blood an ample supply of oxygen which finds its way
easilv through the delicate cuticle, attracted by the low oxygen-
pressure in the cutaneous capillaries. In the amphibia the moist
skin facilitates the diffusion of oxygen and in this class of verte-
brates cutaneous respiration is important though always secondary
to respiration by gills or lungs. A frog can live some time after
the lungs have been removed.

2. Respiration by Gills. — Many invertebrates, e. g., mollusca
and aquatic arthropoda and all lower vertebrates, including tuni-
cates, Enteropneusta, Amphioxus and all fishes breathe by means
of gills. A gill is an organ presenting numerous filamentous
branches whose delicate covering membrane affords slight resist-
ance to the diffusion of oxygen into the blood from the water
with which the gill is bathed.

3. Respiration by Lungs. — Most amphibians and all reptiles,
birds and mammals breathe atmospheric air into sac-like organs
called lungs. The environment and habits of these animals
necessitate the protection of the lungs within the body cavity.
Here the blood in the capillaries is distributed over the surface of
the minute air-cells and the air, which has been warmed and
freed from dust in its passage through the air channels, exchanges
its oxygen easily through the thin, moist membrane of the air sac
for the excess of CO., in the blood.

/;. ANATOMICAL INTRODUCTION.

The skeletal features particularly important in considering the
physiology of respiration arc summarized below under physiology
of respiration because it contains matter not introduced into the
anatomies, and intimately and indissolubly associated with the
physiology of the mechanics of respiration.

for the same reasons the muscles <>f respiration are enumerated
and classified under mechanics of respiration.

The following additional facts of gross anatomy should be noted :

("I The Nasal Respiratory Passages are tortuous, irregular
in Lumen, lined with a mucous membrane always well moistened
with mucus, and provided, near the external opening, with nu-
merous rather -till' hair-. The ed'eel of this structure is to warm

and i'yce of dust the inspired air.

(h) Tin; Respiratory Tract Crosses the alimentary trad
in the pharynx, a cavity common to both tracts. The respiratory
passage is protected during the act of swallowing: (i) posteriorly

by the epiglottis and the adduction of the vocal cords (for details

Bee deglutition) ; mi ) anteriorly by the elevation of the sofl palate,
and the elevation of the uvula. (See deglutition.)

192

RESPIRATION : INTRODUCTION.

(c) Tm: Trachea and Bronchi aim-: Strengthened and

held open by heavy rings of cartilage. Thus protected the air
passages remain open even when subjected to considerable

pressure.

(«/) Tin: Trachea and Bronchi are Lined with a ciliated
columnar epithelium, which is kept moistened with mucus secreted
by the mucous glands of the submucosa as well as by goblet cells.
The ciliary motion carries all secretions as well as particles of

Fig. 120.

Longitudinal section of the human trachea, including portions of two cartilaginous rings.
(Klein.) (Moderately maguitied.) a, ciliated epithelium; 6, basement-membrane ; ''.su-
perficial part of the mucous membrane, containing the sections of numerous capillary blood
vessels and much lymphoid tissue ; </, deeper part of the mucous membrane, consisting mainly
of elastic fibers ; c, submucous areolar tissue, containing the larger blood vessels, small mucous
glands (their ducts and alveoli are seen iu section), fat, etc.; /, fibrous tissue investing and
uniting the cartilages; g, a small mass of adipose tissue in the fibrous layer; //, cartilage.
(SCHAEFEE.)

dust which pass the barriers in the nasal passages, upward toward
the larynx from the deeper passages of the lungs. (See Figs.
120 and 121.)

(e) The Trachea Branches into two large bronchi, of which
the left subdivides into two and the right into three subdivisions.
The five branches subdivide dichotomously, until every lobule of
the lung is supplied with a fine terminal bronchus which ends in
delicate saccate air spaces or alveoli. " The part of the pulmonary
parenchyma in communication with a single terminal bronchiole

A NA TO MICA L IS TR OD I TITOS.

193

forms a pyramidal mass, whose apex corresponds to the terminal
bronchus and whose base, when reaching the free surface of the

Fig. 121.

Section of a small bronchial tube from a pig's lung. (Schaefer.)
Fig. 122.

on of injected lung, Including several contiguou ilveoll. (F. E. Schultze.1 (Highl]

magnified.) ". ". t alveoli; c,c, partitions betwee Ighborlng alveoli, seen In

mall arterial branch giving off capill: to the alveoli. The looping of the ves-

.,i the parti Between the capillaries is seen the

homogeneoui! alveolar w;iii with Quclel ol connective-tl tie corpuscles and elastic dbers.

' -i II \ II I l: )

I ung, appears ae one of the polygonal areas marking the exterior
of the lung." | Piereol.)
L3

194 RESPIRATION: INTRODUCTION.

This pyramidal mass is called a lobule. Within the lobule the
terminal bronchus subdivides i 1 it < > two or three alveolar ducts, besel
with air-sacs, and the alveolar ducts, without subdivision, open
info or widen on) into, "blind" irregular, or pyramidal spaces the
infundibula. The infundibulum is beset on all sides with air-sacs
which open into the infundibulum but do not communicate with
each other.

(/) Tin-: Impure Blood, brought from the righl heart by ///<•
pulmonary artery, is distributed to the lung tissue through branches

which follow the subdivisions of the bronchi finally reaching the
lobule as an arteriole which subdivides into a network of tine
capillaries lying in the walls of the alveoli or air-sacs. The ve-
nous blood is thus brought into intimate relation with the atmos-
pheric air which enters the alveoli. Fig. 122 shows the capillary
network which surrounds the alveoli.

D. PHYSICAL INTRODUCTION.

THE SOLUTION OF GASES IN LIQUIDS.

If one were to place a liter of hydrant water under the receiver
of an air pump, he would find that the water subjected to a
vacuum would give oif gas vigorously ; the quantity depending
upon the conditions which had existed before the experiment. An
analysis of this gas would show it to be nitrogen, oxygen, and
carbon dioxide, or the same gases to which the water had been
exposed in its contact with the air. If we expose H20 to an
atmosphere of HC1 gas it will rapidly absorb large quantities,
forming the common hydrochloric acid. So it becomes evident
that water may hold considerable quantities of gases in solution.
Just how much gas any liquid will absorb depends upon the nature
of the gas and the nature of the liquid ; but the amount of any
particular gas which a particular liquid will absorb varies with
the pressure of the gas in the atmosphere to which the liquid is
subjected. For example, if the amount of oxygen in the air
were doubled, water would absorb twice as much; but if it were
reduced to one-half or one-third of its present proportion, water
would absorb proportionately less. Any change in the proportion
in the air is quickly responded to by a readjustment of the pro-
portion in the water through simple diffusion, to again reach an
equilibrium.

The following laws have been formulated by McGregor Robert-
son (Physiological Physics, p. 291) :

(a) Tin: (Jasks Most Readily Liquefied are Those
Which are Absorbed in the Greatest Amount. ('<>.,,
XH3, and HO are at once most easily liquefied and absorbed.

PHYSR • [ L INTR OB UCTION. 1 (J 5

Oxygen, nitrogen, and hydrogen are liquefied with difficulty and
are feebly absorbed.

(b) Different Liquids Absorb Different Quantities of
the Same Gas. The coefficient of absorption («) or the solubility
of a gas is the volume of gas absorbed by a unit volume of the
liquid at 0°C. and 760 mm. Xote that (a) is determined for con-
stant temperature and pressure.

_ O 0.0489 0.05 rt/xe . CO., 1.7967

a for j^ = T()^M — or 0.05 ; a for ^ = ^^

1.8 . N 0.02348

To - 18 ' a for h;o = Looooo a0235-

(c) The Amount of Gas Absorbed by the Same Liquid
Varies with the Temperature. — The higher the temperature
the smaller the amount of gas which may be held in solution, and
conversely. Heating a liquid drives off much of the dissolved
gas. One volume of H20, at 15° C. and 760 mm. pressure, ab-
sorbs of oxygen, 0.03415 ; of carbon dioxide, 1.002 ; of nitrogen,
0.01682 volumes.

(d) The Amount of Gas Absorbed by the Same Liquid
Varies with the Pressure. — The higher the pressure of the
gas above the liquid the greater the amount which will be dis-
solved by the liquid. If the pressure be relieved, as in the open-
ing of a bottle of " soda-water," the gas (C02) escapes rapidly with

effervescence. One volume of H.fO at 0°C. and pres-

.,, , . , 0.0489

sure will absorb or oxygen = 0.024o.

(e) The Absorptive Power of a Liquid fob a Particu-
lar Gas is [ndependent of Other Gases Which it May
Already Hold i.\ Solution. — Thus a liquid in contact with a
mixture of gases absorbs a quantity of each gas, just as if it were
the only one present, the amount being determined by the coeffi-
cient of absorption, and the pressure of the gas in the mixture, or
the Partial Pressure.

(/) Kami GAS FORMING A PART OF A MECHANICAL MIX-
TURE Exerts a Partial Pressure Proportional to its
Part of the Mixture. — Taking the proportions of the gases
in the atmosphere, one concludes thai as oxygen represents 20.96y&
(say 21^)) of the mechanical mixture, its partial pressure would be
-1/ of the whole pressure, i. e.} 21^ of 760 i mercury or at-
mospheric pressure. Partial pressure lor oxygen in pure ;iir is
.21 / 7<;o = 158 mm. mercury. Partial pressure forCO-iu pure

air i- .0004 X 760 » 0.3 mm. mercury. It IS estimated that in

196 RESPIRATION: INTRODUCTION.

the alveoli of the lungs the partial pressure for oxygen is 122
mm.; and for ( !< ).„ 38 mm.

We may now make the following application of the foregoing
principles: The absorption of oxygen by water (or blood plasma)
at 0°C. and TOO mm. barometer pressure, with a partial pressure

equal to 20.96^ of an atmosphere equals: a' = 0.0489 x

= 0.01, i. c, 100 volumes of water or plasma would absorb under
the conditions named about one volume of oxygen.

The absorption of oxygen at 37.5°C. and partial pressure — 20.96

20.96

per cent, of 760 mm. a" = 0.026 x = 0.0054 +, i. e., 100

volumes of water or plasma would absorb under the conditions
named about one-half volume per cent, of oxygen.

The absorption of oxygen at 37.5°C. and partial pressure of the

16

alveoli or 16 percent, of 760 mm. a'" = 0.026 x = O.O04 +,

i. c, blood plasma at body temperature would absorb from the
alveoli of the lungs 4 c. c. oxygen for every liter of plasma. If
absorption of oxygen were to depend solely upon its physical rela-
tion to plasma this would be practically the limit of absorption.
The absorption of CO, at 37.5°C.1 the partial pressure of CO.,

5 "
in the alveoli being 5 per cent, of TOO mm. a'" = 0.569 x

= 0.028 -f , i. e., if in the alveoli of the lungs the atmosphere con-
tains 5 per cent, of CO.,, 100 volumes of plasma would absorb 2.8
volumes of CO., ; or, in other words, CO., can, according to this
course of reasoning, be diffused from the blood into the air pas-
sages only when the amount in the plasma exceeds 2.8 c. c. per 100
c. c. plasma. Furthermore, that this proportion would represent
approximately the proportion of CO., in arterial blood, as far as
it could exist under physical laws.

1 a for " at 37.5°C. and 760 mm. = 0.569 volumes per cent.
11., ( .)

THE STRUCTURAL FEATURES. 107

THE PHYSIOLOGY OF RESPIRATION.

A. THE MECHANICAL AND PHYSICAL FEATURES OF RESPIRATION.

1. STRUCTURAL FEATURES.

a. Changes of Thoracic Diameters.

b. Muscles of Respiration.

2. OBSERVATION OF CHANGES IN THE DIAMETERS OF THE
THORAX.

3. PHYSICAL EFFECTS OF THE CHANGES OF THE THORACIC
DIAMETERS.

a. Intra-Thoracic Pressure.

b. Respiratory Pressure.

c. Intra-Abdominal Pressure.

d. Lung Capacity.

e. Types of Respiration.

/. Modifications of the Respiratory Act.

B. THE CHEMISTRY OF RESPIRATION.

1. EXTERNAL RESPIRATION.

a. Respiratory Changes in the Air Breathed.

(1) Composition of the Normal Atmosphere.
■_■ i Qualitative Changes Produced by Respiration.

Ci) Quantitative Changes of the Air in Respiration.
h. Respiratory Changes in the Blood.

(1) The Gases of the Blood.

(2) Tin Relation of Oxygen in the Blood.

(3) The Relation of curium Dioxide in the Blood.

(4) Tin Iiijlin /in of Blood-Gases upon the Spectrum.

2. INTERNAL OR TISSUE RESPIRATION.

A. THE MECHANICAL AND PHYSICAL FEATURES OF
RESPIRATION.

1. THE STRUCTURAL FEATURES.

If the constituents of the atmosphere were compelled to make
their way through the respiratory passages by simple diffusion the
amount of oxygen received into the blood would at besl permit a
iMo-t sluggish katabolism. It may have been observed that the
frog uses the floor of the mouth as a sort of bellows to pump air
into the lungs, while an occasional spasmodic contraction of the
body wall forces the air out. In birds the clastic bony thorax is
compressed by muscles of the body walls; this action forces the
air out of the Lungs. Relaxation of the abdominal muscles allows
the thorax to regain it- original volume and air rushes in to fill
the Lungs. In mammals the condition is quite opposite. The
inspiration representing the muscle-contraction and the expiration
representing relaxation.

198 RESPIRATION.

The anatomical characters of the mammalian thoracic skeleton,
which are of especial importance physiologically, are : (i) The
greater mobility of the posterior than the anterior part of the thor-
acic skeleton, (ii) The posterior slant of the ribs, (in) The
double vertebra] attachment of the ribs, making an axis 01 rota-
tion which does nol coincide with the axis determined by the
simple raising and lowering of the ends of the ribs, (iv) The no-
ticeable angle which the fourth, fifth and sixth ribs make with
their cartilages, (v) More important than any skeletal character
is the fact that the thoracic cavity is separated from the abdom-
inal cavity by a muscular partition which is very convex upward
or anteriorly. When the radial muscle fibers of this diaphragm
contract the arch is flattened, the contents of the abdomen pressed
farther downward, the capacity <>f the thorax suddenly increased ;
hut any increase in the capacity of the thorax must lead to a rare-
faction of the air, or to negative pressure. This tendency to the
production of negative pressure is speedily satisfied by the influx
of air through the respiratory passages filling the lungs, which in
turn fill the increased space of the thorax. Through the action of
the diaphragm, then, the antero-posterior dimension of the thorax
is increased.

a. The Changes of the Thoracic Diameters.

(a) The Antero-posterior Dimension is actively in-
creased by the contraction of the diaphragm and passively de-
creased by the relaxation of the diaphragm. It may be actively
decreased by a contraction of the abdominal muscles, which forces
the contents of the abdomen np against the diaphragm, distending
its arch, thus further encroaching upon the thoracic cavity and
forcing air out of the kings.

(6) The Dorso-ventral Dimension is increased by the con-
traction of the external intercostal muscles. The mechanism <>f
the movement is as follows : (i) Ribs more and more mobile from
before backwards; (ii) Ribs slant posteriorly ; (in) External in-
tercostals having their origin on the posterior margin of a rib,
pass ventrally and posteriorly to be inserted upon the anterior
margin of the next succeeding rib. With all of these peculiarities
of structure a contraction of the external intercostal- must result in
an elevation of the ends of the ribs and a carrying of the sternum
further away from the vertebral column. Still another factor in
this is the opening of the angle between 4th, 5th ami 6th costal
cartilages and their ribs. The dorso-ventral dimension is de-
creased by the elasticity of the thorax which causes it to return to
it- former size on relaxation of the external iutercostals.

{(■} The Lateral Dimension. — By virtue of the double ver-

CHANGES IN THE DIAMETER OF THE THORAX. 199

tebral attachment of the ribs, mentioned above, the action of the
external intercostals is not only to carry the end of a rib farther
from the vertebral column as its general line approaches a posi-
tion perpendicular to the spine but also to carry the middle of the
rib farther from the median line of the thorax as the plane, which
it- curve determines, approaches the perpendicular to that line.
It might at first be supposed that a contraction of the diaphragm
would pull in the walls of the thorax, thus decreasing the lateral
dimensions ; but Briicke showed conclusively that though it un-
doubtedly exerts a strong tension on the thoracic wall the high-
domed mass of abdominal viscera, upon which the force of the
diaphragm is directly exerted, is pressed downward and outward
against the upper abdominal walls and so neutralizes the tendency
in the opposite direction.

b. The Muscles of Respiration.

1. Muscles of Quiet Respiration. — (a) Inspiration. — (i)
The diaphragm ; (n) the M. levatores costarum longus et brevis ;
(in) Mm. intercostales externi et intercartilaginei.

(6) Expiration. — Ordinary quiet expiration is non-muscular,
depending upon the weight and elasticity of the tissues. Inspira-
tion throws the tissues out of the position of rest and they fall or
sink back to that position during expiration.

2. Muscles of Forced Respiration. — (a) Inspiration. — («)
Upper ribs raised by : (i) The three M. scaleni ; (n) M. serratus
post, superioris ; (in) M. cervicalis asccndens. (fi) Sternum is
raised by : (rv) Museums sterno-cleido-mastoideus ; (v) M. sterno-
hyoideus; (vi) M. sterno-thyroideus ; (vn) M. thvro-hyoideus.
(;-) The hyoid bone is raised by: (vm) M. mylo-hyoideus ; (ix)
14. stylo-hyoideus ; (x) M. genio-hyoideus ; (xi) M. digastricus.
{$) The shoulder girdle is raised and drawn backward by : (xn)
M. trapezius; (xm) Mm. rhotnboidei, major et minor ; (xrv) M.
levatores anguli scapuli. (s) Lower ribs drawn toward the raised
and lived upper ribs by: (xv) I Vetoralis major et minor ; (xvi)
subclavius ; (xvn) serratus magnus.

6) Expiration. — ('/) Abdominal contents compressed and
forced against diaphragm by: (i) M. obliquus externus ; (ii) M.
obliquus interims; (in) M. transversus abdominis ; (rv) M. rectus
abdominis; (v) M. levator ani. (ji) Ribs are depressed by: (vi)
M. rectus abdominis; (vn) M. quadratus lumborum; (vrn) M.
serratus posticus inferior; (ix) M. triangularis sterni.

_'. OBSERVATION OF CHANGES IN THE DIAMETER OF THE

THORAX.

I In observations of the dorso-ventral and the lateral diameter are
ii Bually taken in the plane of the nipples or in the plane of the

•_»( II )

IlKSPWATIOS.

junction of the ninth rib with its costal cartilage. These thoracic
planes must be taken perpendicular to the axis of the thorax.

Fig. 123.

The stethograph.

1. The Calipers. — This instrument is
ratus for determining; the diameter. As

Fig

a most reliable appa-
usually constructed, a
graduated arc near the hinge of the instrument

Stethograph tambour.

enables one to read off at once the number of
centimeters between the points of the two limbs
of the instrument. One may measure the dorso-
ventral or the lateral diameter of the thorax
when the thorax is in repose, or at the end of
forced inspiration or of forced expiration.
Such observations give not only the actual di-
ameters, but the amount of expansion of the
chest during the respiratory movements.

2. The Stethograph. — The accompanying
figures (Figs. 123 and 124) show a convenient

form of this instrument. As

the name suggests, the pur- •

pose of this instrument is to

record the movements of the

chest. Recourse is had to the

tambours. Fig. 124 shows

the receiving tambour, whose

membrane is held in a conical

position by the spiral spring

(A). The button of the re-
ceiving tambour follows the

movements of the chest wall ;

the changes of pressure in the receiving tambour arc communicated

through a rubber tube, and the record is received upon carboned

paper. Fig. 125 gives a normal stethogram. Note ( i ) that the rise

Normal stethogram of dorao-ventral diameter
nipple plane.

CHANGES IN THE DIAMETER OF THE THORAX. 201

(inspiration) is more rapid than the fall (expiration) ; that (it) both
inspiration and expiration are more rapid at first and gradually slow
< >ffat the end of the act; (in) that there is a moment between the acts
when there seems to be no movement at all ; (iv) that this moment of
perfect inactivity is longer at the end of expiration than at the end
of inspiration.

5. The Thoracometer. — This instrument not only traces a
stethooram but the height of the waves bear an accurate and un-
varying ratio to the movements of the chest wall. The instrument
is used for quantitative work upon the thorax. The instrument
consists of a thoracic frame similar to that of the stethograph
shown above, but the rod which holds the receiving tambour is
replaced by the rod shown in Fig. 126. The essential features of

Fig. 126.

Thoracometer attachment to the stethograph. The thoracometer differs from the stethograph
in the substitution of this rod and spring for the rod ami tambour of the stethograph. The
cord which runs over the thoracometer pulley (15, C) passes to the writing Lever.

the thoracometer are : (i) a spiral spring fitted with a button which
follows the movements of the chest wall; (n) an inelastic cord
to transmit the movements of the button to a recording lever
which, by weight or spring, is brought back to normal after being

Fir;. 127.

Tracings taken with the thoracometer. The ratio of the short r » . 1 1 » » - long arm of the trac-
ing lever being 0.25 the actual height of these waves multiplied bj that constant will give the
• ni of iIm- thoracic wall. Snowing variation of lateral diameter :ii 9th rib, during quiet
breathing. The height of the measured wave i- - nun., the constant 0.25, the lateral diameter
changed 2 mm,

displaced by a movement of the button ; (ni) pulleys for chang-
ing the direction of the cord; (iv) n recording lever fitted with
;i tracing point ; (v) a carboned drum lor recording the movements
of the lever. The arms of the lever being known the relation of
the height of the wave to the actual movements of the chest1 may

21 12

RESPIRATION.

be determined. Figs. L 27 and L28 show two thoracometer tracings j
both in the plane of the junction of the ninth rib with the costal
cartilage. From the recorded observations one may draw the
following conclusions : (i) the dorso-ventral diameter varies more
than the lateral diameter, expanding normally aboul two or three

Fig. 128.

Showing variation of dorso-ventral diameter at plane of 9th rib, during quiet breathing.
The height of the measured wave is 20.5 mm., the constant 0.25; the dorso-ventral diameter
changed 5.12 miu. during the act whose record La measured.

times as much as the latter; (n) successive respiratory acts differ,
some being beyond the average in depth of inspiration and some
beyond the average in extent of expiration.

4. The Belt Spirograph. — Various forms of the belt spiro-
graph or pneumograph have been devised to give variations in

Fig. 129.

The bt'li spirograph.

the circumference of the thorax. Most of these devices are
modeled after Marey's pneumograph, which consists of a cylin-
drical tambour with membranous end. From the two ends of

CHANGES IN THE DIAMETER OF THE THORAX.

203

the cylinder an inelastic cord girths in the chest. Increase of the
girth extends the membranous end of the cylinder, lowers the
pressure in the cylinder, while a decrease in girth increases the
pressure in it. Thus the changes in circumference incident to res-
piration may be recorded. Like the spirograph the pneumograph
of Marey is reliable only for showing qualitative changes of the
circumference. If one wishes to measure these changes it will
be necessary to use some such instrument as the one here figured
(Fig. 129). In the figure a is an elastic belt having pulleys

Fig. 130.

Thechesl pantograph. For measuring and recording chest contours. The instrument is
constructed of brass or of wood with brass or steel semi-circle. Tlve joints a, b, x, and y move
easily in the plane of the instrument. The semi-circle, 40 in. in diameter, rotates at x around
the diameter t r. The point f is tixed to a table. With / a fixed point all movements of t, the
tracing point, are accompanied by corresponding movements of r, the recording point. The
triangle fr 6 and fta are similar triangles in all positions of the instrument fb : fa : :fr : ft;

but

: therefore, the distance fr is always J the distance ft.

which arc adjustable along the belt. The pulley is shown in C.
Fig. 129, 1), shows a plan of the thorax with the belt adjusted.
An inelastic cord, tied into an eye in pulley No. 1, passes around
the chest oxer pulley No. 1 and one or two other pulleys to change
the direction, finally passing to a recording lever adjusted like the
one used with the thoracometer. Changes in girth arc very accu-
rately recorded by this device.

Study of tracings justifies the following conclusions: (i) The
respiratory act- — a- indicated in the change in girth — are not
uniform, an occasional one — every eighth to twelfth — being much
more extensive in inspiration, Bometimee followed by one or two
Bomewhal deeper in expiration, (n) Variation in rate of inspira-
tion accompanies the variation in extent of the inspiratory or ex-
piratory act-.

'>. The Chest Pantograph. — This instrumenl in tracing upon

" millimeter" or " ordinate " | taper an outline of the thorax at any

21 1 1

RESPIRA TION.

level enables one to determine quantitatively nol only any diameter
luit the area also, as well as any peculiarities of sectional contour.

Fig. 131.

1 ' 1 — 1 1 1 1 ' 1

— __ _- -1— ~~

^ *^^

T , T-[

'\ ! ' /^

^-^^-^~X~r^

, .{- j : ^ /;■■ - l-4-i

i ontours of chest, taken with ches) pantograph.

Just this feature of the instrument enables it to do what the
other appliance- above decribed fail to do. For description of this

INTRj 1- THOBA QIC 1 '11 ESS I '1! E. 205

instrument see explanation of Fig. 130. If the subject to be ex-
amined sit beside a table on which the instrument is fixed ; if the
seat be adjusted in height to bring the plane of the thorax to be ex-
amined into the plane of the instrument, i. c, on a level with the
top of the table ; if a sheet of millimeter paper be fixed to the table
under the recording pencil /■ ; and if the tracing point t be swept
around the thoracic wall a record of the chest contour will be traced
upon the paper. The accompanying Fig. 181 shows two such
contours from healthy well-developed young men. Two milli-
meters in the figure equal one centimeter of actual measurement.
The inner contour is that of forced expiration while the outer one
is that of forced inspiration. In contour .1 the increase of lateral
diameter by forced inspiration is 2 cm. while the increase of dorso-
ventral is 3 cm. In the same contour the cross sectional area of
the thorax in the plane of the ninth rib is represented by 25.52 of
the larger squares containing 25 square cm.; total area = 637.5
square cm. while the cross sectional area of the chest in forced
expiration is 517.5 square cm. Forced inspiration shows an in-
crease of 120 square cm. or about 23 per cent, over cross section
area of forced expiration. Furthermore, both contours show a
prominence on the right side (left in the figure) possibly due to
stronger musculature on that side.

3. THE PHYSICAL EFFECTS OF THE CHANGES OF THE
THORACIC DIMENSIONS.

<i. Intra-thoracic Pressure.

[ntra-thoracic pressure is the pressure in the thoracic cavity
outside of the air passages ; that is in the pleural and mediastinal
cavities especially, though it affects the blood and lymph vessels
of the thorax which arc not in cither of the two cavities men-
tioned. If one introduce into the pleural or the mediastinal cavity
;i cannula whose external end communicates through a tube with
;i recording tambour or with a manometer it will be found that
there is ;i fill of the recording lever or of the mercury, indicating
a fall of pressure below the atmospheric pressure. It fact, the
recording lever or the mercury will not again rise to the level of

atmospheric pressure; but will oscillate up and down below the
/•to line, being lower during inspiration than during expiration.
Fig. L32 'jive- ;i tracing of intra-thoracic pressure ( /. 7'.), atmos-
pheric (A. P.), intra-abdominal pressure ( I. A.) and a stethogram

(8.). The tracings were taken from a rabbit ler ether, and are

simultaneous. The thing which mus1 be first established is the
relation between the intra-thoracic pressure and the respiratory
movements. When thecbesl wall rises in inspiration — tracing #,
phase /—note tint the thoracic pressure falls to the minimum ;

206

RESPIRATION.

when the chesi wall falls in expiration (>'-/*,') the intra-thoracic
pressure reaches a maximum. This maximum does uol reach the

Fig. 132.

Int. Ab lorn

Infra-thoracic

J

U

vj

! I i

I I i I

J

L

k

A.P.= 0

Simultaneous tracings of intra-thoracic pressure. (/. 7*. j, intra-abdominal pressure (LA.

and a stethogram.

zero-line under ordinary circumstances. That is, intrathoracic
pressure is always negative, hut it is more negative during inspiration
than during expiration. If the lungs were inelastic sacs the pres-
sure between the lungs and the thoracic wall — intra-thoracic —
pressure would become zero almost instantly on the cessation of
the inspiratory act. But while the thoracic wall is by its elasticity
regaining its original position of repose at the end of expiration
the elastic sacs within the thorax are contracting by virtue of their
elasticity. Now, inasmuch as the elasticity of the lungs had to
be overcome by the negative pressure outside of them it is easy
to see that when there is no obstruction to the exit of air from
the lungs they will tend to assume their position of repose more
quickly than will the thoracic wall, that is, they will tend to pull
away from the thoracic wall, leaving a negative pressure in the
pleural cavity.

fi ES PIRATOBY I'll ESS I ' R E.

207

Fig. 133.

Intra-thoracic pressure may lie positive if there is a forced ex-
piration with occluded exit of air ; or in a quick expiration with a
partial obstruction to the free exit of air the pressure in the pleural
cavity will be positive. In Fig.
133 the nostrils of the rabbit
under observation Mere held
shut at x. The vigorous respi-
ratory acts which the animal
made in its effort to get air
made the inspiratory pressure
much lower than usual and the
expiratory pressure much higher
than usual, reaching almost as
far on the positive side of the
zero line as on the negative side.

Physiologically the intra-tho-
racic pressure is positive during
the forced expiration of cough-
ing, sneezing, and straining at
stool, or lifting. The face be-
comes red in the two last be-
cause the positive pressure is sustained, blocking venous flow to
the heart.

b. Respiratory Pressure.

Respiratory pressure is the pressure in the air passages. It is
always negative during inspiration and always positive during ex-
piration. If it were not negative during inspiration the air would
not flow into the lungs and if it were not positive it would not
flow out of the lungs during expiration. In quiet breathing the

Fir;. 134.

Tracing of intra-thoraeie pressure show-
ing influence of an obstruction in the air
passages introduced at A'.

Cradio-pneumatogrami ihowing Influence of the pulsation of the thoracic arteries upon

respiratory pr« ssure.

respiratory pressure is only slightly positive and slightly negative.
Should the air-passages become partially obstructed as in sneezing,
or coughing, the positive pressure of expiration may be very high.
Daring lifting or straining :it -tool the positive pressure in the air

208

RESPIRATION.

passages exc< eds the positive pressure in the pleura by the amounl of
the elasticity of the Lungs. If (»nc hold in the month or nose a tube
whose distal end is connected with a recording tambour one will

notice that the recording lever rises and falls synchronously with
ventricular systole, or with the pulsations of the thoracic arteries.
To successfully trace this " cardio-pneumatogram " one must
either breathe very quietly or suspend respiration altogether for
short periods during which the tracing may he taken. Note in
the accompanying tracings indubitable evidence of systolic and
dicrotic pulse waves which have been transmitted through the air
of the respiratory passages and thence to the recording lever via
the tambour and tube.

c. Intra-abdominal Pressure.

Intra-abdominal pressure is zero or very near zero ± at the end
of expiration in quiet breathing ; that is, when thoracic and

abdominal walls are in a state
of perfect repose. When the
diaphragm descends in inspi-
ration the pressure becomes
decidedly positive, forcing ab-
dominal viscera and wall out-
ward against atmospheric
pressure. (Sec Fig. 132, 7.
A.) If the viscera and wall
regain their position of repose
in response to the elasticity of
the abdominal wall there will
be but one wave of positive
pressure and that is caused by
the descent of the diaphragm,
and occurs when intra-thoracic
pressure is lowest. If there
is an active contraction of ab-
dominal muscles — as in the
case in Fig. 132 — there will
be a second rise of pressure
due to that contraction, and it
will occur during expiration.
These relations are well shown
in the tracing. The influence
of intra-abdominal pressure
upon venous and lymphatic circulation has been discussed above.
Coughing and sneezing cause a sudden positive pressure of moderate
degree, but straining at stool, lifting, and straining in parturition

Hutchinson's spirometer.

LUNO CAPACITY. 209

cause a sustained positive pressure of high degree, and a consequent
forcing of blood and lymph already in large abdominal vessels into
the thorax, but a blocking of any further entrance of venous blood
or of lymph into the abdomen, thus backing it up in the veins of
the lower extremities.

d. Lung Capacity.

This expression is used to indicate the quantity of air flowing
into or out of the lungs during respiration. The instrument used
to measure the air is called a Spirometer. If the air is collected
over water it is a Wet Spirometer (see Fig. 136), if in an elastic
bag, a Dry Spirometer. The results obtained from observations
will vary within wide limits and according to the combination
of several factors, e. c/., stature, girth of chest, muscular de-
velopment, habits, age, sex, accumulation of fat, etc., etc. If an
average-sized man, of average muscular development, breathe
quietly into a spirometer it will be observed that only 300 to 500
c.c. flow into and out of the instrument with each respiration. This
quantity of air involved in normal quiet respiration is called
Tidal Air. The quantity will vary from 300 c.c. in perfect rest
to 500 c.c. or more, during or just after moderate exercise, as
walking.

But if the exercise be more than the most moderate, the respi-
rations will deepen until the tidal air may reach 1,000 c.c, or even

Fig. 137.

/A /\ f\

A

/ \ Comple- r \ mental &f4

Air 0^=_

1600 C.C

j£s^^ "l^f "\^J}L^]^

ipi Bspr

000 C.C.
1600 C.C.

\ / Re- \?-W serve

\ / Air

"~ZZ^=r^l==- = — ~

^L_j=^r--—--

1600 C.C.

^midmm*E=

~ ,T "■ 1^_ ■ -

—

-

i liagraiu of in ag capacity.

more, [f500cc.be arbitrarily assumed as tidal air, then the ex-
cess which maybe inspired in forced inspiration is called Com-
i'i.kmkvi ai. An;, and for men of average stature and develop-
ment tlii- will approximate L, 600 C.C. If at the cud of such a

forced inspiration an expiration is begun which empties out the
1,600 <-.(•. and the 600 c.c, it will be found that the muscles of

1 i

210

RESPIRATION.

forced expiration can force out still more air to the extent of an-
other 1,600 c.c. This last air of forced expiration is called Re-
serve AlR. The total quantity expired alter forced inspiration
is called Vital Capacity and is the sum of the tidal, comple-
n.ental and reserve (500 + 1,600 + 1,600 = 3,700 c.c). Bui at
the end of forced expiration the lungs are not empty. There -till
remains a so-called Residual Quantity, which i- estimated at
l,600c.c. It is an accidental forcing out of a part of this residual
air that causes such inconvenience when one gets a forcible and
unexpected thump on the thorax.

A diagram representing these terms and definitions will be
found in Fig. 137.

e. Types of Respiration.

1. Diaphragmatic, Inferior Costal and Superior Costal Types.
— An infant breathes almost exclusively by means of contractions
of the diaphragm. The flattening of the arch of the diaphragm
presses upon the abdominal viscera and pushes out the abdominal
walls ; this type of respiration is called abdominal or diaphragmatic.
At about the age of puberty there is, in all European races at Least,

Fig. 138.

Fig. 139.

The changes of the thoracic and abdominal
walls of the male during respiration.

The same in tin' female. I m xchhtsoit.)

a distinct difference in the male and female respiratory movements.
(See Figs. 138 and 139.) The narrower, continuous, ventral line
shows the position of repose, the heavier, continuous line shows
the position at the end of medium inspiration. Xote that in the

MODIFICATIONS OF THE RESPIRATORY ACT

211

male the line is somewhat further advanced in the lower costal
and abdominal regions than is the case in the female, while in the
female the upper costal region is advanced relatively further.
These two types are called respectively the inferior costal and
superior costal type. Note that in deep inspiration, shown in the
interrupted line, the inferior costal type of the male is more pro-
nounced, i. <:, in deep inspiration the 9th rib girth expands most
in the male, while it is the girth in the nipple plane which expands
most in the female. There has been some controversy as to the
reason for this difference. Is it fundamental or incidental ? Is it
due to sexual life ; viz., child-bearing in the female ? If so, all
women <>f all races should show it. Some authorities (Mays and
Kellogg) say that the American Indian women and Chinese women
do not show the superior costal type of breathing, and, therefore,
the difference must be incidental and probably depends upon dress.

Fig'. 140.

i heyne-Stokes respiration.

2. The Cheyne-Stokes Type of Respiration. — The accompany-
ing figure represents a stethogram with a slowly rotating drum.
Note the series of rather rapid, deep respiratory movements alter-
nating with perfect rest in the recorded case above. Sometimes,
however, there is an alternation of a series of deep with a series of
-hallow respirations. In the latter form it i- frequently to be no-
ticed in children during sleep. It is seen in chloral poisoning,
morphine poisoning and in nervous diseases which interfere with
the action of the center. The Cheyne-Stokes respiration in its
physiologic forme seems to bear to respiration a relation analogous
to that which the Traube-Hering pressure curves bear to circula-
tion, both rhythms originate in the medullary centers ; the first
governing respiratory rhythm and the -croud governing vaso-con-
rtrictor tonus. The cycle of the Cheyne-Stokes movement i- re-
peated once to three time- pei- minute.

./'. Modifications of the Respiratory Act.
I. Coughing. — Winn the respiratory mucous membrane, in or

below the larynx, is irritated by inhaled du.-t, or gasee or by ex-

212 RESPIRATION.

iided secretions — mucus or muco-pus — the system makes an effort
to expel the offending substance by a forcible expiration accom-
panied by a closure of the larynx followed by its sudden opening
and an explosive expulsion of the air in the upper air passages
this blast of air usually carries with it the irritating matter.

'1. Sneezing. — When the nasal mucous membrane is irritated
in any way a similar expulsion of the air through the nose serves
to remove the irritating matter. Both coughing and sneezing are
preceded by an inspiration of more than usual depth.

3. Yawning. — If for any reason the respiration has fallen be-
hind the requirements of the system for oxygen there is an invol-
untary effort on the part of the respiratory system to make the
deficiency good. This is accomplished through a prolonged and
very deep inspiration, followed by a very complete expiration and
this in turn followed by a rather dee]) inspiration after which the
respiration proceeds in the usual quiet rhythm.

4. Hiccoughing. — Hiccough consists in a sudden contrac-
tion of the diaphragm which causes a spasmodic inspiration ; this
is blocked by the sudden closure of the glottis, causing the char-
acteristic sound. Certain kinds of gastric irritation, especially
the taking of dry food or the mechanical irritation which the
stomach undergoes incident to inordinate laughing where it is sub-
jected to a series of quick pressures by the abdominal muscles.
In the first case a drink of water usually stops the hiccough, in
any case it is likely to stop if the attention is either closely fixed
upon it or completely diverted from it.

5. Sighing. — Sighing is very similar to yawning in its mechan-
ism except that its cause is due primarily to the emotions. Grief,
sorrow and even extreme fatigue may be accompanied by sighing.

6. Crying and Laughing. — These are purely emotional in
their origin and consist of a deep inspiration (in crying) usually fol-
lowed by a series of spasmodic vocalized expirations (in laughing
usually). But crying and laughing are subject to so many in-
dividual peculiarities in sound and in facial expression that it is
impossible to draw a distinct picture of either or a definite line
between them.

7. Sobbing. — After prolonged crying the respiration is likely
to take the form of sobbing which is a series of convulsive in-
spirations accompanied by partial closure of the glottis.

B. THE CHEMISTRY OF RESPIRATION.

1. EXTERNAL RESPIRATION.

a. Respiratory Changes in the Air Breathed.

1 . Composition of the Normal Atmosphere. — The open at-
mosphere is a mixture of gases in the following approximate pro-
portions :

THE CHEMISTRY OF RESPIRATION. 213

r Nitrogen, including Argon,, etc., 79.00 ~) . 1nn

. . Oxygen, 20.96'-,

Atmosphere gjj^ ^.^ 0J)4 j parts.

^XH.{, H.,0 ; organic matter, in small variable
quantities. Though the quantity of H.,0 in the air is consider-
able— over 1 per cent. — it is not customary to reckon it in the
gaseous constituents. How is the air changed during its stay in
the lungs? An apparatus may be constructed which will show
both qualitatively and quantitatively the principal changes effected.
If a small animal be confined in a sealed chamber and provided
with dried air which has been deprived of all CO., it will be found
that the air on leaving the chamber has received considerable CO.,
and H20 and a small amount of organic matter and that it has a
higher temperature. Systematically enumerated the changes in
respiration are :

2. Qualitative Changes Produced by Respiration. — (a)
Change of Temperature. — Air below 8(3° C. would always
be increased in temperature, though not quite to blood tempera-
ture, 38° C. In ordinary quiet respiration of air at ordinary
room temperature (20° C.) the expired air has a temperature be-
tween 36° C. and 87° C. Very cold air would not be raised to
that temperature, and very warm air (40° C.) would not be lowered
to that temperature.

(6) Change ix Proportion of C02. — The CO., is always in-
creased. If the inspired air be pure the expired air will contain
4 per cent, to 5 per cent. (4.34 per cent.) CO.,.

(<•) Change in Proportion of Oxygen. — The oxygen is
always decreased. If the inspired air be pure, i. c, has 20.96 per
cent, oxygen, one-fourth of the oxygen is consumed at one breath-
ing of the air. With successive re-breathing less and less oxygen
i- consumed, but eventually it can all be taken out of the air,
leaving the hitter quite free of oxygen and composed of 79 per
cent, of nitrogen ; ('(), IT.,0, etc., 21 per cent.

(d) ( 'hanoi: in Volume. — [fthe volume of inspired air be com-
pared with that of the expired air it will be found that it is greater ;
but we musl not forge! thai the expired air has a higher tempera-
tare, and thai increase in temperature makes a marked difference
in the volume of gases. I f we reduce it to the same temperature
it will be found to have actually decreased slightly in volume.

Now, one liter of oxygen, combined with carl , makes one liter

of carbon dioxide al the same temperature and pressure. If the
'ii of the inspired air has :ill combined with carbon, why
should then- be any decrease in volume? Bui the oxygen of the
inspired air doe- n.,t all combine with the carbon ; some of it com-
bines with hydrogen to form 1 1 ,0, and thai causes the difference

in volume.

21 t

RESPIRATION.

Fig. 141.

(e) Change in the Proportion of Water. — The water is
generally increased, though it may be decreased. Though the cool
inspired air may be saturated with water at thai temperature, the

raising of the temperature in the
air passages increases the capac-
ity of the air for water and nunc
is taken up from the moist mu-
cous membrane. If warm air
is saturated with moisture before
entering the Lungs it will take
up very little more. If warm
air lie dry — the usual condition
in furnace-heated bouses — it will
take up moisture very rapidly
from the nasal passages and
trachea and upper bronchi. This
is irritating to the delicate mem-
branes and is one of the many
causes for catarrh.

(/) Organic Matter in mi-
nute quantities is added to the
air in the lungs.

3. Quantitative Changes of
the Air in Respiration. — (a)
The Estim ath >x of the ( )x v-
gex and CO., ix Expired A 1 1:.
— The accompanying Fig. 141
shows a very efficient and sim-
ple appliance for the determina-
„ tion in question. The expired

expired air. (kfter Waller. ) R, a 100 c.c. „|r ;1nalv/ed should reoresent

receptacle graduated to one-tenth e.c. between au «maiV^(l snouiu npiescm

75and 100; F-f, Filling flask and tube for filling the well-mixed product of manv
and emptying receptacle; ''. Connecting tube . . * . J

with screw clips ai 1, 2 and 3 ; KOH, absorp- expirations. lhlS mav l)C ac-
tion flask for C02 containing a strong solution -,. , -. . . . .* ~

of potassium hydrate ; P, absorption flask for Complished by inspiring irom

o, containing sticks of phosphorus in water. ,i l i •

in using the apparatus the filling fiask is in the open atmosphere and expir-

filled with acidulated water and raised till the • • t cnirmrmrm* nr similar

liquid stands at 0 ; (n) in clip 1 ; lower F to ing mro a Spirometer 01 SlUlliai

draw in too c.« • ..fcspiivji air; (.it) dose l receptacle. After sufficient time

opeu 2, raise i till liquid rises to 0, close •_», i

under the pressure the KOH absorbs the COg h;ls elapsed for complete (litfll-
in one or two minutes; iiy) Drop /•' till the ' IT

liquid iD F (£) has the same height as I ; read siOll 01 tllC gases and cooling

loss in volume of gas ; this loss is the CO» ab- , 1 . ., .

sorted by KOH; (v) open 3; raise F till I to room temperature KM) C. C
stands a1 0: close 3; the phosphorus absorbs the i i w ^ ^ ^

oxygen in a few-minuted; fvi) lower /'till /. milV he drawn ott and analyzed.

and^are in line and read ofl- loss of volume in pinarjy a correCtion must be

made for temperature and pres-
sure and all corrected readings given for 0°C. and 7<i<) mm.
pressure. The quantity of oxygen and of C02 in the open atmos-
phere may be determined as a preliminary step in the experiment.

THE CHEMISTRY OF RESPIRATION.

215

The above described observation gives the oxygen and CO, which
exist after a single respiration of the air. From the data the
amount of CO., added in a given time to the air in respiration
may be fairly accurately determined.

(6) Estimation of C02 axd H.,0 Exhaled. — A simple
apparatus for accomplishing this is shown in Fig. 142. The
general construction is as follows : (d) An animal-cage for which,
for small animals, like rats or guinea-pigs, a large, wide-mouthed

Fig. 142.

KOH BaiOH)2 CaCk Animal CaCk CaCk
cage

Apparatus for the cxtirnation of Co., and II„o iu exhaled air.

bottle may be used , (a) KOH ; (b) Ba(OH), ; (c) CaCl2, free the
afferent current of air of all C02 and H.,0, so that the animal
inspires an atmosphere of nitrogen and oxygen in proportions that
may be accurately determined ; (<■) and (/) are calcium tubes for
absorption of the water, the increase in weight is equal to the water
which leaves the animal cage during the experiment; (//) is a
Geissler potash bull) for absorption of CO.,, its weight is taken
before and after the observation ; the Ba(OH)2 flask (A) indicates
whether all of the COa has been absorbed by the potash bulbs;
(i-l.-) is a siphon apparatus for drawing the air through the appa-
ratus. The 10-liter bottle- are graduated so thai the quantity of
expired air may !><■ determined. The amount of oxygen in this
expired air may be determined as above shown, and by taking the
weight of the animal cage svith and without the animal before and
after the experiment we have data for determining: (1) The
amount of oxygen consumed per kilogramme animal per hour ;
' 11 } th- amount of ( ( ), and of 1 1 ( ) excreted per kilogramme per

216

i:i:spiratiox.

hour. Unless the experiment is continued over considerable time
the water excretion is only approximately determined. If there
is no micturation or defecation by the animal the difference of

fe

weight in the calcium tubes will give the water excreted by lungs
and skin. If there is micturation, a part of the water caught by
the tubes will have been evaporated from the urine. If the animal

THE CHEMISTRY OF RESPIRATION.

217

be introduced into the cage just after voiding the urine, and if the
amount of urine in the bladder at the end of the observation be
determined it will be possible to make a fairly accurate estimate
of the amount of water excreted during the period of observation.

W lnii it i- desired to observe the respiration of a man or larger
animal one usee such an apparatus as thai shown in Fig. II-'!, as
elaborated l>\ Voil and his pupils in Munich. The second figure
1 1 ig. Ill] gives the plan of the apparatus. A small portion of the

218 RESPIRATION.

air which passes through the respiratory chamber is diverted through
the small tube ./. The pump and valve apparatus at m and w'
Deed nol be described. At ee'the ET20 is absorbed by the II..SO,
and at t,t' the C02 is absorbed by Ba(OH)2. The small gas meter
beyond measures the quantity thus analyzed. Several portions
are usually diverted through duplicate apparatus. (See Fig. 11:;.)
All air not analyzed is measured by the large gas meter | G). This
apparatus enables one to determine for a large animal or for a man
the respiratory relations under various circumstances: (i) Rest;
(ii) work; (in) fasting; (iv) various diets; (v) drugs, etc.

(c) The Respiratory Quotient. — This is the ratio between
the volume of CO., exhaled and the volume of oxygen absorbed
in the lungs. In the human subject, on an average diet, the air
loses by absorption in the lungs 4.7s volumes per cent, of oxygen
and receives from the blood 4..*j4 volumes per cent, of CO., ; hence

the respiratory quotient: R. Q. = -^— = -r^=0.901.

The respiratory quotient varies considerably in different species,
and in the same animal under different conditions. Just how
these variations arise will be made clear if we study the relation
of these two gases in a combustion. If one liter of oxygen at
0° C. and TOO mm. pressure unite with carbon to form C(X that
gas at 0° C. and 760 mm. will measure exactly one liter, so that

the combustion quotient oi pure carbon is : — — y-=l. suppose

now that we burn starch or cellulose, or any carbohydrate. Six
molecules of oxygen (09) will unite with each molecule of carbo-
hydrate to form six molecules of C02 and release the five mole-
cules of H.,0. But the H90 is not taken into account in combus-
tion quotients or respiratory quotients ; so that the combustion

quotient of a carbohydrate would be .- ?=1. It must be evi-
dent that in the oxidation of carbohydrates in the animal organ-
ism the ratio would be the same, i. c, R. Q. for carbohydrates
_6COa

~ <>(h=1'

In the combustion or in the metabolism of fats the ratio is
modified by the presence of a quantity of hydrogen whose oxygen
is not provided for by the oxygen present in the fat molecule.
Let us take tripalmitin as an example : Its formula is C3H5[CH3-
(CH2)14COOH] 3 or C,H-,( ( !16H ,,< >2 ), or C51H9806. To oxidize the
tripalmitin molecule it will require 51 02 to form 51 C02 ; but to
oxidize the hydrogen of the molecule it will require 49 atoms of
oxygen, six of which already exist in the molecule, leaving 43
atoms or 21.5 molecules to be supplied ; (51 x 21.5 = 72.5); it

RESPIRATORY CHANGES IN THE BLOOD. 219

will require then a total of 72.5 molecules of oxygen to yield 51
of CO.,, the combustion quotient or the R. Q. for tripalmitin

510~CO, nMnnA n, .

= 7qk r\ = 0. /034. lhe respiratory quotient tor proteids can

not be so accurately determined but it ranges for different proteids
between 0.75 and 0.81.

From what has been said it is evident that the variations of
respiratory quotient must vary with the proportion of carbohy-
drates, fats, and proteids in the diet: (i) in herbivora, R. Q.
= 0.9 to 1.0 ; (n) in carnivora, 0.75 to 0.80; (in) in omnivora,
0.80 to 0.90. During fasting the animal consumes its own tis-
sues;— i. e.} the reserve fats and proteids — and the respiratory quo-
tient ranges from 0.70 to 0.75. In the child the respiratory
quotient is lower than in the adult, due undoubtedly to the more
active proteid metabolism in the growing individual. The ratio
is higher in the daytime than at night, because the muscular ac-
tivity is greater during the day and muscular activity is accom-
panied by a free katabolism of dextrose (carbohydrate) in the
muscle while the muscle tissue itself (proteid) is katabolized no
more during work than during rest.

The following table illustrates some of the points mentioned
above :

Ammai..

1 lONDITIONS.

» o - VoL

R- Q- - voi:

C02

02

Ox.

On carbohydrate diet. (Herbivorous.)

1.00

Horse.

(in carbohydrate diet (Herbivorous.)

1.00

Sheep.

On carbohydrate diet (Herbivorous.)

0.88

Babbit

On carbohydrate diet (Herbivorous.)

0.90-1.00

Uog.

On mixed diet (Omnivorous.)

.0

Caff.

On milk diet.

0.86

Man.

On carbohydrate diet. (Omnivorous.)

0.8-0.90

Dog.

On Sesh diet (Carnivorous.)

0.7

1 at

' in flesh and milk diet

0.8

Rabbit

l 'asting.

0.7

Dog.

I j-i in-.

0.7

Marmot.

Awake.

0.8

Marmot.

Asleep. (Hibernating.)

0.5

b. Respiratory Changes in the Blood.

1. The Gases of the Blood. — One of the functions of the
blood is to carry oxygen from the Lungs to the tissue, and carbon

dioxide from the tissue to t he lungs. The next step in our in-

quiry la to subject arterial and venoue blood to ;i vacuum to de-
termine how much oxygen and C02 arterial and xenons blood will
yield under those condition-.

(a) The Method of Extracting th e Gases <>i the Blood
i- shown in Fig. I 15. Winn subjected to a vacuum the gases
leave the blood, and after being freed from moisture 1 1 1 < - n may be

220

RESPIRATION.

drawn first into the 6 sed

Fig. L45.

mercury bulb (M), and then, through
adjustmenl of the three-way tap
(ST), sent into the eudiometer
( E), where they are collected
above mercury and may be sub-
sequently analyzed.

(6) The Results. — One hun-
dred c.c. of blood, whether arte-
rial or venous, yields about 60
e.e. of mixed gases. Pfliiger
found in the arterial blood of
the dog 58.3 volumes per cent.
of gases composed of oxygen,
22.2 per cent., CO., 34.3 per
cent., and nitrogen, 1.8 per cent.
Zuntz found that venous blood
contains 7.1 o volumes per cent,
less oxygen, and 8.2 per cent,
more CO., than does arterial
blood ; nitrogen being the same
in both.

2. The Relations of Oxygen
in the Blood. — If the oxygen
is in a state of simple solution
in the blood as it is in the water
— as described in the physical
introduction — we shall expect it
to give up its oxygen to a form-
ing vacuum in proportion to the

Plan Of apparatus for extracting the gases of falling OXygCU-prCSSUre. Slip-
the blood. To extract gases from the blood; msilro thf> Pvnnvimenr

i :.c. of blood is drawn in the blood-bulb B P<>Se we make tlie expel inn ill.

from the artery or vein.. By closing tap land 7g -p- ^ \ Let t}ie Jine

opening tap 2, the blood is exposed to the con- \^v"-' & /

ditions which exist in the rest of the apparatus. It() ()f \\\^ figure represent the

Suppose that the movable mercury bulb Mm & *■

had been previously held at the level of the oTadlKll tall Ol OXVgCll prCSSUre.

fixed mercury bulb M\ if it be lowered to the ■ . .. J ° .

position shown in the figure there will he a It the line xu represents the

rarefaction of the air in /•', /'. and M, and the ... n -i; ,1__J •

gases will begin to escape from the bl 1. [fa quantity 01 OXygen dissolved 111

vacuum be previously established in the appa- ,1 1.1,,, „1 fl),.n •lceordino- to the

ratus above tap2,the turning of that tap will nu DIOOa, men ac<oiuing 10 uit,

8ubJeci th.ebl l*° a vacuum, the gases will physical l;lvVS given above the

escape With such force as tO till the frotli- I . O

chamber F with froth or bubbles from the J [(Mll'V-DaltOll UlW of absorption

blood; but the drying-tube l> removes all , • - • <i

moisture from the gases, which may be drawn ot eases the decrease 111 the

through the three-way tap 3 T into mby lower- ' . r v 1 i

me Mm. It now, 37 be turned to the left 90° quantity 01 dissolved oxygen

and Mm be raised the extracted gases will pass 1 -1 \ _____* A „l^ u,, «

Eudiometer E where it is received above mer- would be represented also by a

cury and may be measured. A repetition of i- ->. 1 ^ t| (,lirvi, .,../) renrn-

the process with a warming of the blood-bulb lmc »"> l,m Tn( CUrv< H^C/repre-

wiii e,,:, i,ie the e g , ,er i men t er 10 extract aii of Sl,nts xvi,.lt aetuallv takes place: i.

the gases. . # I

c, the oxygen is given 011 very
slowly until the pressure is reduced to one-third or one-fourth and
then it escapes very rapidly and not proportionally to the pressure.

RESPIRATORY CHANGES IN THE RLOOD.

221

On the other hand, if the oxygen-pressure is gradually increased,
as in the line On' , the quantity of that gas does not increase pro-
portionately, but is represented by the curve Op'n', i. e., the oxy-

Fig. 146.

Diagram showing relation of oxygen in the blood.

gen is absorbed very rapidly at first and very slowly later. But
we have ignored the fact that the blood is composite. Let us make
the experiment with plasma, or better, with serum. We will re-
lease only a small quantity of oxygen by reducing the pressure to
zero — a quantity represented by the line xP, and the line nP
represents the gradual decrease with decreasing pressure. It ap-
pears then that the small quantity of oxygen which is associated
with the plasma obeys the Henry-Dalton law, and must, there-
fore, be simply dissolved. If the red blood corpuscles, or better,
if a strong solution of haemoglobin, be subjected to the same ex-
periment, we will find that at first no oxygen is given up, then
suddenly all of it is given up rapidly with the falling pressure,
but not proportionately to the pressure. (See curve HIiO.) If
the pressure be gradually iucreased the oxygen will be taken up
very rapidly at first until the haemoglobin is satisfied after
which no more will be taken up. (See curve Oh' H' .) The
quantity of oxygen absorbed by the haemoglobin of a given
(jiiantity of blood may be represented by the line PO. From
this we find : (i) the haemoglobin takes up vastly more oxygen
than does plasma; (n) the small amount of oxygen held by the
plasma is in simple solution and obeys the Henry-Dalton law ;
(m) the oxygen which is held by the haemoglobin is not dis-
solved ; it i- held by chemical affinity, the combination being
called oxyhemoglobin and written Hb-O; (iv) the oxygen can be
separated from haemoglobin only at low oxygen-pressure, and
unite- with haemoglobin readily at much below atmospheric oxy-
gen pressure.

:;. Relation of CO, in the Blood.— We have found thai less
than three volumes percent. ofCOa represents the equilibrium of
absorption of thai gas in the Lungs. From the physical law-
above given we Bhould expeel the quantity of* CO., in the blood to

be small and the amount left iii the blood after having passed (he

Lungs, i. >., the amount of COa in arterial blood, to approximate
the equilibrium, 3 volume- per cent.

222 RESPIRATION.

The report of a series of experiments will aid us at this point
of the discussion :

Experimenl (a) If arterial blood be subjected to a zero C02
pressure it will give off l<> volumes percent. ofCOr

Experiment (/>) If plasma be subjected to similar conditions it
will give off 13 to 26 (average 20) volumes per cent, of CO.,.

(<■) If venous Mood be observed in the same way 45 to 40' vol-
umes per cent, of ( '< >., will be collected.

(d) The red-blood corpuscles alone yield under similar condi-
tions about 15 volumes percent, of ( '( )., (5 per cent, to 7| percent.
of whole blood).

(e) Plasma plus weak acid will yield in vacuo about 30 volumes
per cent. ( !( ).,.

(/) Plasma plus Hb will yield in vacuo about 30 volumes per
cent. ( '< ).,.

These experiments and observations justify the following con-
clusions :

(a/) More CO., is contained in the blood than can be accounted
for on the basis of physical laws.

(// ) The plasma contains about two-thirds of the CO., and it is,
for the most part, in chemical combination.

(cf) The CO., of the plasma must in part be held in weak
chemical combination and in part in strong chemical combination ;
because a part of the chemically combined C02 is released at zero
C02 pressure. At this point it is necessary to inquire : (i) In
what chemical combinations docs CO., exist in the plasma? (n)
Is one of these affected by CO, pressure "? Carbon dioxide exists
in the plasma in combination with sodium as XaHCO, and
Na2C03. Of these two compounds the former is a weak one and
at zero CO, pressure will part with that gas according to the fol-
lowing equation :

2XaHCOa = Na2COa + H,0 + CO,.

Now, the addition of a weak acid, or of HbO, further decom-
poses the Na20O3, thus liberating the last of the C02. The
Xa,( ) probably joining to 2XaH,P(.>, to make 2Xa,HP04 + H,0.

('/') About one-third of the CO, of the blood is held by the
red-blood corpuscles. It is supposed that this is for the most part
held in a loose chemical combination with the haemoglobin of the
corpuscles, in fact with the globulin component of the haemo-
globin.

(<■') Haemoglobin, especially oxy-luemoglobin, acts as an acid,
and the more stable carbonates of the blood are broken up in the
presence of HbO and a zero C02 pressure.

Our next task is to weave these facts and conclusions into a
consistent theory. Preliminary to this let us define the word

RESPIRATORY CHANGES IN THE BLOOD. 223

tension as used by the physiologist in this connection. If the
partial pressure of a gas be increased or decreased the quantity
absorbed will rise or fall accordingly. It is evident that the gas
must be under a certain degree of pressure to prevent its passing
out of solution. The gas in solution is said to be under tension.
" If the partial pressure of this gas (in the air) diminishes, the gas
in solution is given off until the partial pressure of the gas in the
air and the tension of the gas in solution are equal." Tension is
expressed in the same terms as pressure, i. c, in mm. of mercury.
The tension of CO, in the tissues = 7.(j<> per cent, of 7(30 mm. =
58.25 mm. In the venous blood =41.4; in arterial blood =
21.28 ; while the partial pressure of this gas in the alveoli equals 5
per cent, of 7(50 mm. of mercury equal to 38 mm. of mercury. In-
asmuch as the NaHG03 of the plasma will tend to change to a more
stable compound, giving up one-half of the CO., in the lower CO
tension of the lungs, we shall expect to find the C02 passing regu-
larly from a place of high tension to one of low tension. It will
naturally then diffuse rapidly from the tissues with their tension
of 58 -f to the blood, which enters the capillaries of the tissues
with a tension of 21 +, and leaves the capillaries en route for the
lungs with a C02-tension of 41 +, nearly double what it entered
the tissues with, but still considerably below tissue tension (58).
It must be stated at this point that the diffusion is made possible
by two tilings working together, both tending to take up simply
dissolved ( '< ), from the plasma, store it away, so to speak, in "a
chemical combination, (i) The haemoglobin, which just parted
with its oxygen, may now satisfy its affinities with CO.,, which it
does, thus making place for more C02 to diffuse into the plasma.
(ii) C02 has a strong affinity for sodium. This element does not
exist free or in loose combination, except with Na2HPO,. So
that the phosphoric acid is forced to part with its second atom of
sodium, as shown in the following equation :

XaJII'O, + COa + lip = NaH2P04 + NaHCOs

The venous blood passes to the lungs, having received an increase
iii C02 which has been largely taken into such chemical combina-
tion- as NTaHCOy Leaving the amount dissolved in the plasma
varying little probably from that which is found in the arterial
blood. Reaching the Lung capillaries tli<' conditions are reversed.
'I'll.- high oxygen tension (122) of the alveoli favors the reversal

of the reaction between the Ikiiik ig l« >bi n mid the o.wgen and carbon

dioxide gas. The stronger affinity of haemoglobin for oxygen causes
ii t<. drop the ( o and take up oxygen forming Hb-< >, the C02 is
first taken up by the plasms thus further increasing the ex-
tension in thai Liquid mid further hastening diffusion toward the
alveoli. Besides this interchange we must not forgel thai the low

224

RESPIRATION.

C02-tension in the lungs favors the reversal of the reaction between
NaH2P< ), and the XalK !( >3so that we have the following reaction :

XallJ'O + XalK !< ).( = Na2HPO + H20 + ( < >.

.Inst how far this reaction between phosphoric acid and carbonic
acid plays a part in actual respiration is still undetermined.
Equally undetermined is the importance of the relation between
III) and CO.,. That the reactions take place when plasma or a
solution of these compounds is under experimental test is demon-
strated. But we must remember that we have only to account for
an addition of six volumes per cent, of C02 in the tissues and a re-
lease of the same amount in the lungs and it is not certain that the
reaction in question plays any important part in it. It may be that
the transfer of C02 is accomplished solely through the laws of
diffusion without the intervention of chemical reactions.

Fig. 147.

Red Or. Yel. Green. Blue

Indigo Violet

I, spectrum of oxyhemoglobin ; II, spectrum of reduced hemoglobin. (After D ALTON.)

4. The Influence of Blood-gases upon the Spectrum. — In

any spectroscopic examination of the blood account must be taken
of the fact that haemoglobin reacts very differently under differ-
ent conditions : (i) When combined with oxygen as oxyhemo-
globin (Hb-O) it shows two absorption bands as shown in Fig.
147, I; (n) when it is deprived of its oxygen, i. c, reduced to
hemoglobin the light absorption takes place in one broad band
which nearly corresponds to the two above with the space between
them. (See Fig. 147, II.)

2. INTERNAL OR TISSUE RESPIRATION.

The terms external and internal respiration are used to designate
different phases of the same general process. The essential proc-

INTERNAL OR TISSUE RESPIRATION.

225

ess is the providing of oxygen to the active cells, where it is com-
bined with the cell plasma either in some of the steps of anabol-
i.-m or in some of the earlier katabolic steps. This ultimate step of
respiration is called "tissue respiration," or "internal respiration."
A still better term would be cell respiration. Cell respiration then
consists in taking up of oxygen from the intercellular plasma and
utilizing it in metabolic, — usually katabolic, — processes. The ul-
timate products of katabolism are CO.,, H..O, etc. These end pro-
ducts are useless to the cell and are ejected into intercellular
plasma. It is evident from this that cell-respiration is simply one
phase of cell nutrition which deals with the gaseous elements of
assimilation (oxygen) or of excretion (CO.,). The term external
respiration is applied to all those processes by which air is intro-
duced into the lungs, the oxygen taken up by the blood, the CO.,,

Fig. 148.

*fJBTT»

Diagram showing relation between external ami internal respiration.

given nil' by the blood and the transfer made with the tissue
plasma. The relations between external respiration and inter-
nal or cell respiration may best be illustrated by a diagram-
matic scheme of the respiration. The oxygen of the atmos-
phere enters the /one of tidal air where the oxygen pressure
may lie represented by 0, from this zone it rapidly diffuses
with the zone of reserve air where the oxygen pressure is
lower and may be represented by 0' . Thence it diffuses into
smaller bronchioles and alveoli where the pressure is still lower
and may In- represented by 0". The lower pressure (O"') of the
capillaries invites it to pass through the two delicate membranes
which separate it from the lumen of the capillary. Once in the

blood current it is swept along a- lll>-<) to the active cells where

the oxygen pressure is practically zero (0///;). Here the haemoglo-
bin gives up it- oxygen, or the oxygen i.~ dissociated, is dissolved
in the cell plasma in part or passes directly into the living cells
where it is at once chemically combined in the cell metabolism.

lint the blood, now robbed of oxygen, is in the presence of very
I.-,

226 RESPIRATION.

high GO, pressure, the haemoglobin is instrumental in holding
chemically a certain amount, — lei us say provisionally, as Bb-COj,
— the resl is taken up in simple solution in the plasma. Thus
la<lcn the blood is broughl back to the air cells of the lung where
the haemoglobin at once releases the C02 and takes up oxygen,
forming again Hb-O. The C02 after its release from the cor-
puscles is in the plasma from which it rapidly difftises into the
alveoli, because of the low 0O2-pressure there. The relations
may also he expressed thus: ()-pressure in tidal air (158 mm.)
> O-pressure in reserve air > O-pressure in residual air (122
mm.) > O-pressure in capillary I •"'><> mm.) > O-pressure in tissues.
C02-pressure in tidal air 0.3 mm. < C02-pressure in reserve air
< ("'(). -pressure in residual air (38 mm.) < 002-pressure in capil-
lary (41 mm.) <( 'O-pressure in tissues (58.25 mm.).

Richert (American Text-book of Physiology, p. 526) uses the
following very effective method to show why the O passes from
the alveoli of the lungs into the blood and C02 in the reverse
direction :

o co2

Tension in alveolar air 122 38

Pulmonary membrane 1 —

Tension in venous blood 22 + 41 +

In a similar way he shows graphically why the diffusion cur-
rents are reversed in the tissues :

O oo_,

Tensions in arterial blood 29. <J4 21.28

Blood vessel walls— - I

Tensions in tissues 0.0 58.25

Having defined the external and the internal respiration and
having shown the forces which operate in the movements of the
gases of respiration it remains to treat briefly the relation of cell
respiration to general cell metabolism. This has been done in
some detail under General Physiology so that a brief summary is
all that is here required.

Summary of the Principles of Cell Respiration.

(1) The increase of the supply of oxygen does not increase the
activity of the cell or tissue.

(2) The increase of cell activity is accompanied by an increase
of need for oxygen followed by an increase of the supply of oxygen.

(3) The amount of C02 given off by the cell is proportional to
its activity; and is, therefore, <i measure of cell activity.

(4) Cell activity takes the form of lil>< ration of energy. This

THE CONTROL OF THE RESPIRATION. 227

energy is the potential energy of cell protoplasm (or energy-pro-
ducing material held by the protoplasm — see metabolism) and is
liberated not by direct oxidation, as in combustion; but by in-
direct oxidation.

(a) " Bv integration of O a force-yielding storage-substance is
formed " (Waller).

(//) By disintegration of this substance carbon dioxide is liber-
ated in company with other material katabolitcs and energy in the
form of heat, work, and electricity.

C. THE CONTROL OF THE RESPIRATION.

1. INNERVATION OF THE RESPIRATORY ORGANS.

a. General Experiments and Conclusions.

A dissection of the respiratory system would reveal the presence
of the intercostal nerves, one just posterior to each rib, giving off
fine branches to the intercostal muscles ; followed toward the cen-
tral nervous system, these nerve trunks are found to emerge from
the spinal cord by two roots, an anterior nerve-root and a poste-
rior nerve-root. ( )ne would find the diaphragm supplied by a pair
of large nerves which may be traced up through the mediastinum
out of the thorax, into the deep muscles of the neck where they
are found to be a part of the cervical plexus and to arise from the
111, IV and Y cervical nerve-roots ; these are the phrenic nerves.
Further, we remember that the vagus gave off, besides the cardiac
branches, the superior laryngeal and inferior laryngeal and the re-
maining trunk is largely distributed to the tissue of the lungs,
though a part of the trunk extends as far as the stomach. If we
follow the distribution of the vagus in the lungs we will find that
its branches enter the root of each lobe and are distributed
along the air passages supplying the mucous membrane and the
involuntary muscles of the bronchioles. Physiological experi-
ment alone can determine the action of these different nerves.

1. Experiments. — (i) Cut one or more of those lower inter-
costal nerves which supply the abdominal muscles ; the muscles
will cease to net in expiration.

(ll) Cut one or more of those upper intercostal nerves which
supply the external and internal intercostal muscles; the muscles
in question cease to act, i, c, the external intercostals cease to ele-
vate the ribs in inspiration and the internal intercostals cease to

depress the ribs in expiration.

(in) Cut the posterior nerve-roots of any of the intercostal
nerves; the results above observed in cutting (he whole nerve

trunk are noted in thi- ease.

(IV) ('ut the anterior nerve roots of any of the nerves in qucs-

228 RESPIRATION.

t i « » 1 1 ; the result is the -nine as it' the whole trunk were severed.

ivi Cut the phrenic aervesj the diaphragm ceases its move-
ments.

(vi) ( 'ut the vagi: inspiration is deeper and the respiratory
movements slower.

(vii) ('ut the superior laryngeal ; ;i tickling of the larynx will
not cause coughing — expiration.

(viii) ('nt the inferior laryngeal or recurrent laryngeal ; all eon-
traction- of glottis and tracheal muscles cease.

i ix ) ( 'nt the spinal cord just above the first intercostal ; all res-
piratory movements of the ribs and of the abdominal muscles cease.

i x i ( "ut the spinal cord just posterior to the medulla oblongata ;
all respiratory movements of the ribs, diaphragm and abdominal
muscles cease, but the glottis, larynx and aostrils will make spas-
modic efforts at inspiration.

( xi i ( nt or -ever brain from medulla — everything else being in-
tact, the rhythm and depth of the respiratory movements are not
disturbed. Excite the animal; no change in depth or rhythm.

2. Conclusions from these experiments in order :

(i) The lower intercostal nerve- carry motor fibers of both in-
spiration and expiration.

(ii) The upper intercostal nerves carry motor fibers of both in-
spiration and expiration.

(in, iv) The motor fibers pass out of the spinal cord via the an-
terior nerve roots.

(v) The phrenic nerve is the motor nerve of the diaphragm,
and. therefore, a motor nerve of inspiration.

Any of these conclusions may be verified by stimulating the
distal end of any of the cut nerves; in every case the muscles
supplied will contract, showing the nerves to be, in part at least,
afferent motor nerves.

(vi) From experiment (vi) it is difficult to say exactly what
the function of the vagus is. Inasmuch as the nerve is supplied
largely to mucous membranes, we cannot expect it to be motor in
its action. Suppose the distal end be stimulated ; no very no-
ticeable change takes place. Now stimulate the central end ; res-
piratory movements are at once affected. A carefully adjusted
stimulus of the central ends may lead to normal respiratory move-
ments. A strong stimulation to the central end of the vagus
will lead to a more rapid rate of respiratory movements and a
final standstill of the diaphragm cither at the end of expiration
or inspiration, i. e., diaphragm either in tetanus or in paralysis.
These results prove the vagus to carry afferent or sensory fibers,
and the ambiguous results may be accounted for as the result of
two lands of sensory fibers, one kind stimulating the inspiratory
center and another kind stimulating the expiratory (enter.

THE ACTION OF THE RESPIRA10RY CENTER,

229

( vii) The superior laryngeal is a sensory nerve stimulating ex-
plosive expiratory acts.

(viii) The recurrent laryngeal is the motor nerve of the
glottis, laryngeal and trachea. Stimulation of the distal end con-
firms the conclusion-.

for the muscles of this Fig. 149.

region contract vigor-
ously.

(ix) The respiratory
center for intercostals
and abdominal muscles
is above the dorsal
cord.

(x) The general re-
spiratory center i- not
posterior to the medulla.

(xi) The general re-
spiratory center is
not anterior to the
medulla. The center is
located in tin medulla,
in the floor of the fourth
ventricle, just posterior
to the cardio-inhibitory
center. Jt is found to
be symmetrically lo-
cated in the two lateral
halves, though these
communicate and act in
harmony they may be
separated ami still act
synchronously, but may
lie made to act inhar-

. . . . Schema of innervation of respiratory organs ; /.v.-i.v--

moniOUSly ov Special piratory center in the spinal cord, I, vagus with superior
,• i •" ,'. i i/i laryngeal, Inferior laryngeal ami pulnionarj branches.

Stimulation ol one-liali. Phrenic supplying the diaphragm ; intercostals supplying
I-"..,.l, I...U' ; t'.n.flw i. I , ""' Inspiratory and expiratory muscles of the thorax and
i.aui nan l- inirnei in- the expiratory muscles of the abdomen. All cutaneous
Ij.,.. I . .. ' . )• . sensory nerves affect the respiratory center. Nasal sensory

11 ' l " au may precipitate sneezing or otherwise affect respiration,
inspiratory and of an ex-
piratory nucleus. From experiments (x) and (xi) it is dear that
th<- center is automatic. From experiments (vi) and (vn) it i-
-how n that the center is also reflex.

b. The Action of the Respiratory Center.
1. Through its Automatic Action the center would -<\u\ in-
termittent spasmodic inspiratory or expiratory impulses along the
efferent nerve- to the re- pi i-.i i ory muscles. The automatic action

230 RESPIRATION.

of the respiratory system is analogous to that of the circulatory
system.

'_'. Reflex influence from the Periphery is an importanl factor in
the control of the rhythm and <!<'|>tli of the respiratory movements.
There are two ways in which this is accomplished viz., directly and
indirectly.

(a) Direct Reflex Stimulation may in turn be accom-
plished : (i) through ttu- influence of tin blood supply; (n) through
the influence of sensory impulses. (a) The influence of the blood
supply. In this connection we remember thai the cardiac center
in the medulla is affected by the quantity and quality of the
blood which it receives from the heart through the carotid and
vertebral arteries. In the same way the respiratory center is
affected by Mood from the same source. In this case the quality
of the blood is of more importance than the quantity, i. e., it is
the quantity of oxygen and of carbon dioxide which stimulates
the center. Each inspiratory act is precipitated by the stimulat-
ing presence of an excess of CO., in the respiratory center, while
the expiratory acts are less affected by the CO., of the blood until
this accumulates to an abnormal degree ; even then it may be rather
lack of oxygen than excess of CO,, which causes the change in
respiratory movements. Fredrick performed a most interesting
experiment with two dogs. The vertebral arteries were ligatcd ;
the carotids of dog A were joined through cannulse to the distal
ends of those of dog 15 and those of dog B connected with those
of dog A, so that the blood of dog A circulated in the head of
dog B and vice versa. The experiment consisted in suddenly
closing the trachea of dog A ; after a few moments dog B began
to gasp for breath. The reason is clear : the excess of CO., from
the circulation of dog A stimulated the respiratory center of dog
B, leading to his much increased respiratory movements.

(;9) ruder the influence of the sensory impulse we may tirst
enumerate those which come from the vagus. When the lungs
become distended to a certain degree the sensory fibers of the
vagus send an impulse to the center which precipitates an expira-
tion. Again, an impulse from the superior laryngeal may cause a
spasmodic contraction of the abdominal muscles, causing a cough.
Certain irritating gases — CI, S( )„ etc., affect the sensory nerves of
the nose and larynx, and cause the center to block all respiration.
Such gases are called irrespirable.

(/>) Indirect Reflex Stimulation of the respiratory mechan-
ism may be correctly so distinguished because the respiratory acts
are induced or influenced by impulses from nerves only indirectly
connected with the respiratory mechanism. A sudden dash of
cold water will cause an inspiration. When a child is being de-
livered feet tirst at birth care must be taken that the delivery be

UNUSUAL RESPIRATORY CONDITIONS. 231

made rapidly, or that the body be protected from drafts of air, for
the stimulation by the air may cause inspiration and the child
may draw the respiratory passages full of mucus, which will
greatly complicate the induction of normal respiration.

3. Cerebral or Voluntary Influence on the Respiration.

Besides the automatic action and the reflex influence of the center,
there is a marked influence from the cerebrum. In fact, if one gives
his attention to it he may govern his respiratory movements as to
rhythm ami depth up to a certain point. Certain states of mind
may modify respiration — coughing, crying, sighing, etc. One
cannot, however, stop respiration voluntarily long enough to take
his life. The accumulated impulses finally become too strong to
control by the mind and the diaphragm descends.

c. Unusual Respiratory Conditions.

In contradistinction to the usual and normal respiration, which
is called Eupncea, there are several conditions which deserve
mention.

1. Apncea. — Complete cessation of respiration. One can " hold
his breath " much longer if he precedes his efforts by a series of
rapid, deep breaths. If the air be vigorously and rapidly forced
into the lungs of an animal by artificial respiration for a minute,
some time will elapse before the animal evinces any tendency to
breathe. The most natural inference — that he has O enough to last
a minute or two — is not the correct inference, for experiment has
shown that the blood may accumulate a marked excess of CO be-
fore the center is able to overcome inhibition, which it is re-
ceiving from some source. And what source? From the over-
stimulated sensory ends of the vagus.

2. Hyperpncea. — Usually deep breathing, such as one is led
to from too strenuous muscular exertion.

3. Dyspnoea. — Painful breathing. All conditions which di-
minish the O or increase the CO., in the blood circulating through
the medulla, if carried beyond a certain point, produce a labored
respiration which can no longer be recognized as hyperpncea. All
the phenomena of* extreme forced respiration, together with signs
of the greatest discomfort, or even pain, make up the svmptom-
oomplex of dyspnoea. It i< not an infrequent symptom of dis-
ease, mimI may occur under the following conditions :

(a) Direct limitation of the activity of the respiratory <>r</<tns:
(i) Diminution of respiratory surface, as in pneumonia, or acute
oedema of lungs, (it) Entrance of air or fluid into pleural cavities
— pneumothorax and bydrothorax. (ni) Obstruction of trachea
or larynx; croup, etc., strangulation, (iv) Contraction of bron-
chioles— asthma.

232 RESPIRATION.

(8) Enfeeblement of circulation, (i) In degeneration "1' heart
muscle, (ii) Valvular disease of heart.

4. Asphyxia. — This term is \\>>'<\ to express the condition <»f
collapse after a failure of the system to gel < > or to eliminate ( K)2.
Such a condition is always preceded by (i) Hyperpncea; (ii)
Dyspnoea, and (in) Convulsions. Death by asphyxia occursiD four
stages, the three ju>t noted, followed by collapse and death. The
term is used to indicate death by drowning, by suffocation, by
strangulation, etc.

CHAPTER V.
DIGESTION.

INTRODUCTION.

A. COMPARATIVE PHYSIOLOGY OF DIGESTION.
1. INTRA-CELLULAR DIGESTION.
•2. DIGESTION BY SECRETED FERMENTS.

3. THE EVOLUTION <>F SALIVARY GLANDS.

4. THE EVOLUTION OF ORAL TEETH.

B. ANATOMICAL INTRODUCTION.
1. A SUMMARY OF THE ANATOMY OF THE DIGE3TIVE SYSTEM.
•2. THE INNERVATION OF THE DIGESTIVE SYSTEM.

C. SECRETION.

1. (JEN KRAI. CONSIDERATIONS.

2. SECRETION DEFINED.
.;. SECRETING GLANDS.

i. INTERNAL SECRETION. FUNCTIONS OF THE VASCULAR GLANDS.

1). CHEMICAL INTRODUCTION.

1. FUNDAMENTAL CARBON COMPOUNDS.

2. THE CARBOHYDRATES.
.".. THE FATS.

l. THE PROTEIDS.

-. FERMENTS AND ENZYMES.

/.'. FOODSTUFF3 AND FOODS.

1. DEFINITIONS.

2. CHEMICAL COMPOSITION OF MILK AND OF THE ANIMAL- BODY.
:;. CLASSIFICATION OF FOODSTUFFS.

4. FOODS.

.-. PREPARATION OF FOODS.

DIGESTION. [NTRODUCTION.

A. THE COMPARATIVE PHYSIOLOGY OF DIGESTION.

I. INTRACELLULAR DIGESTION.

In the nature of the case an organism which consists of only
one cell imi-t take in nutriment through the ectosarc or exoplasm

into the endosarc or endoplas f the cell. II' the nutriment be

fluid the absorption is a simple process, influenced largely by the
physical laws of osmosis, and may be followed by a rapid assimi-
lation of theabsorbed nutriment. II' the nutrimenl be solid the
process of taking it through the ectosarc i- a mechanical one ;in<l
is accomplished by movements of the protoplasm. Oncethesolid

233

234 DIGESTION: INTRODUCTION.

particle of food is engulfed in the endosarc a true process of diges-
tion or solution is accessary before the nutriment may be assimi-
lated or built up into cell protoplasm. For a concrete description
of the whole process of nutrition, including digestion, in the uni-
cellular animals, particularly the amoeba, the reader is referred to
General Physiology (p. 12). The digestion in unicellular ani-
mal- is necessarily of the intracellular type. The Ccelenterates
afford an example of a type of animal in which a definite tissue is
sel apart for the function of digestion. This specialized tissue,
the entoderm, lines a cavity or a more or less complex series of
cavities formed by an invagination or dipping in of the surface of
the developing organism. Solid nutriment taken into these
cavities is taken up by the endodermal cells which line the cavity,
and digested within them. The product of digestion is in part
passed on to the non-digesting tissues by diffusion or by circulation
through the gastrovaseular ca/nals. Among the ccelenterates at
least one form has been discovered — " the fresh water medusa —
in which, the cells which line the mouth of the gastric tube have
the function of secreting a digestive fluid " (T^ankester). But this
coelenterate retains the primitive intracellular method of digestion
throughout the greater part of the gastric tube.

2. DIGESTION BY SECRETED FERMENTS.

The transition from the primitive to the higher mode of diges-
tion is a gradual one. The lowest worms — Turbellaria — have the
intracellular mode, and the mesoblastie cells of echinoderm larvae
manifest the same property. Tn this connection one recalls also
the intracellular digestion of bacteria, etc., by the leucocytes of
the higher animals.

All higher invertebrates and vertebrates possess an alimentary
canal through which the food passes while being acted upon by
various ferments which produce a progressive series of digestive
changes. This canal is usually differentiated into several distinct
divisions in which particular steps of the process are performed.
In the early part of the process the food is triturated. Either
before, during or after trituration it is softened and lubricated by
secretion of the alimentary canal. The food is passed along the
canal by a peristaltic motion of involuntary muscles within the
wall of the canal. Dissolved (digested) portions of the food are
removed by absorption through the wall of the alimentary canal.
The absorption surface is much increased (i) by the coiling of
the digestive tube, (II) by the folds of the lining of the tube, and
(ill) by finger-like projections on the surface of the folds, the last
method for the increase of surface being especially pronounced in
the higher vertebrates.

THE EVOLUTION OF ORAL TEETH. 235

3. THE EVOLUTION OF SALIVARY GLANDS.

The walls of the oral cavity are provided with mucous glands
which are all developed by invagination of the epiblastic epithe-
lium of that cavity and have the form of simple or compound
tubular glands. In the lower vertebrates there is no very marked
difference in the structure or function of the glands in the differ-
ent regions of the oral cavity, except that those of the tongue are,
perhaps, somewhat more highly developed and more active than
those of the palate, cheeks or sublingual region. Among the
higher amphibia, where the tongue is so often used as an organ of
prehension, the lingual glands are highly developed and their se-
cretion is driven out upon the surface of the tongue with every
contraction of that organ. The aquatic reptiles have illy devel-
oped oral glands, while the terrestrial reptiles, like the terrestrial
amphibians, have well developed lingual glands, as well as sub-
maxillary glands, the latter secreting in some lizards a poisonous
mucus. In birds the lingual, and in many cases the sublingual,
glands are well developed, while the labial, buccal and submax-
illary are naturally absent. In the mammals three pairs of large,
ordinarily acinous, glands predominate over the smaller and more
scattered buccal glands. These, from their positions, are distin-
guished as the PAROTID, SUBMAXILLARY and SUBLINGUAL glands.
" From our knowledge of the influence which the secretion of these
glands has on the starchy foods in ourselves, it is often thought
that therein lies their primary function. Certain considerations
seem to show that this is not a correct view. In the Cetacea and
other aquatic mammals, and in the blood-sucking Desmodus, the
glands ai( -mall, while the kangaroo, which dwells in the arid
plains of Australia, has the glands in question of great size. It
would seem that the prime function of these structures is to afford
a Bupply of water for the -olid food. A physiological advantage
i- gained by the fact that this water has the temperature of the
body." (Jeffrey Bell.)

"The well-known fact in human physiology that the secretion
of the parotids Is more watery and that of the submaxillary and
sublinguals more viscid, is paralleled in comparative anatomy by
the huge size "I' the parotid- in animals which masticate dry foods,

a- do the I [erbivora, and by the greal size of the submaxillary in
BUch animals as the ant-eater, which requires a viscid fluid for the
purpose of catching its prey." (W. A. Forbes.)

I THE EVOLUTION OF ORAL TEETH.

Among the lower vertebrates one find- teeth located in the oral
cavity and the inner rarface of the branchial arches in immense
uumbers,— -as palatal, lingual, and pharyngeal teeth, — but they

■j:u\

DIGESTION: TNTBODUCTION.

Fig. 150.

are also distributed in close-sei rows over the whole surface of the
.skin, and produce, aa in the sharks, a strong but flexible coat-of-

mail. (Hertwig.)

The reader remembers thai
the oral mucous membrane is
derived from the invaginated
epiblast ; that, in common with
the skin, it presents mesen-
chymal papillae ; and that these
papillae obey the general biolog-
ical law of the physiological di-
vision of labor accompanied by
differentiation of structure.

With these facts and consid-
erations in view let us study the

Fig. 151.

rii -i stage of development of a Bhark's derma]

tooth. '/'///, em i membrane from epiblast;

m/, odontoblast layer from mesenchyme: mi,
cemeutuni fundament; sg, squamous epiblast.

development of a

shark's dermal tooth.
(See Figs. 150 and
151.)

Compare it with
that of the shark's
oral tooth (see Fig.
152) ; also with that
of a higher verte-
brate.

From these figures
it is evident: (i) That
the dermal and oral
teeth of the shark are
practically identical

Fig. L52.

Second stage of a shark's dermal tooth.

dent iin

enamel : l>,

in development and struc-
ture ; and (n) that both
are modified mesenchymal
papillae. The epithelial
tract of the oral mucous
membrane which share- in
the formation of the teeth
has sunk deep down in the
form of a ridge on the in-
ner surface of the mandib-
ular arch, and into the
loose connective tissue. It

Dental ridge and enamel organ of a shark's oral_to6th- n,)W represents a special

organ, — the enamel organ
or dental organ. In sharks
and in lower vertebrates generally the replacement of old teeth by

/-/ r, successh e generation

U I'.. I

of teeth (Alter Heet-

ANATOMICAL INTRODUCTION. 237

new ones is an unlimited process (see Fig. 152, I— IV) ; but as
the rank becomes higher the process is more limited, and in
mammals the replacement occurs only once ; — i. e., the " milk
teeth " arc replaced by the permanent tcct/i. One finds, therefore,
in mammals that the dental organ or enamel organ has only two
papilla^, one of them giving rise to a temporary tooth and one to
a permanent tooth.

In all of those lower vertebrates provided with oral teeth those
organs are used as instruments of prehension or of defense or of-
fense. Even in the highest vertebrates the teeth retain the prim-
itive function to a limited extent. In the higher mammalia an-
other function becomes prominent, viz., that of grinding the food.
This function is most highly developed in the herbivora and om-
nivora, in which divisions of mammals the teeth arc strongly
mollified structurally to adapt them to this end. Among the
carnivora the primitive functions predominate and the teeth are
correspondingly modified to adapt them for the most efficient
prehension, and offense and defense.

In primitive man the teeth are typical of the omnivora. In
highly civilized man the teeth are, with each succeeding century,
becoming weaker. They develop more variably, erupt more ir-
regularly in time and place, and they decay earlier. All of these
facts are indications of degeneration, and point toward an ulti-
mately toothless human race.

II. ANATOMICAL INTRODUCTION.

1. A SUMMARY OF THE ANATOMY OF THE DIGESTIVE

SYSTEM.

a. The System in General.

(a) The Digestive System consists of the alimentary canal
together with certain (/funds whose ducts open into the canal.
(6) The Alimentaby Canal begins with the mouth and ends

with the anus. It consists of: (a) The oral cavity ; (A) the
pharyngeal cavity; (c) oesophagus; (d) stomach; (e) small intes-
tine, composed of duodenum, jejunum, and ileum; (/') large in-
testine, composed of caecum, colon, and rectum.

(<■) The Tube is lined throughout with mucous membrane, out-
ride of which is a submucous coat. Both of these coats vary
much in different portions of the tube. The mucous epithelium
of the mouth and oesophagus is stratified while thai of the stom-
ach and intestines is columnar. The glands of the mucosa are

variously modified in different parts of the anal. The subinucosa

is tliin in the mouth and pharynx, but abundant in all other parts
of the tracts.

238

DIGESTION: INTRODUCTION.

('/) The Wall of the Free Tube — from the beginning of
the oesophagus to the anus — contains muscular coats, covered ex-
ternally with a fibrous coat. All of thai portion of the canal
within the abdominal cavity receives an outer peritoneal investment.

Fig. 153.

PHARYNX

(ESOPHAGUS
VENA CAVA

THORACIC DUCT

DUODENUM

STOMACH

PANCREAS

LACTEALS

OECUM

(OPEN)

VERM I FORM
APPENDIX

Diagram of the digestive tract. (Alter L&NDOIS.)

(e) A Typical Portion of the wall of the alimentary canal
consists of: (\) Mucous membrane, whose epithelium is the seen -tin;/
and absorbing portion of the wall; (n) Submucous coat, whose
loose fibrous structure permits free folding and free movement of
the mucosa, and furnishes a favorable course for blood vessels,
lymphatics and nerves; (in) Muscular coat, whose two or three
layers of involuntary muscle tissue perform the slow peristaltic
contractions which are so important a factor in digestion ; (iv)
Fibrous coat, which lends additional strength to the walls of the
tube. Usually included with this coat is the pavement epi-
thelium of the peritoneum.

PARTICULAR SEGMENTS OF THE TRACT. -39

(/) The Epithelium of the Mucous Membrane is hypo-
blastic in origin except in the mouth, upper pharynx and lower rec-
tum. The serous epithelium of the peritoneal covering of the
tube is from the splanchnoplewic mesoblast. All of the structures
between these two epithelial boundaries (nerve-tissue excepted)
represent mesenchymic mesoblast. The nerves invade these tissues
from the •• neuroblastic ' '' epiblast.

(;/) Upon the Inneb Subpace of the mucous lining, innumer-
able glands open. These glands are developed in the embryo by
evagination from the mucous surface ; the gland epithelium has,
therefore, the same histogenesis as the mucous epithelium from
which it evaginated ; the epithelium of all glands opening into the
mouth being epiblastic, and that of all glands opening in the
stomach, for example, being hvpoblastic.

(A) A Large Pbopobtion <>f these Glands are mucous
secreting glands. In certain locations the glands present both
structural and functional modifications ; in the stomach the pep-
tic glands present structurally the striking parietal or acid cells
while, functionally, these glands secrete both pepsin and hydro-
chloric acid.

( /) Besides these Glands within the Wall of the canal
there are several large glands, — salivary glands and pancreas, —
which lie quite outside that wall of the canal and pour their secre-
tion into the canal through a duct whose epithelial lining is con-
tinuous with the epithelium of the canal. The active cells of
these glands are modified epithelial cells, and, with the lining of
the duct are derived, in the embryo, by evagination from the lin-
ing of the alimentary canal.

b. Particular Segments of the Tract.

1. The Oral Cavity. — This portion of the alimentary canal is
especially adapted, by its firm stratified epithelium, to receive solid
food. The skeletal and muscular structures which surround this
cavity perform important parts in its functions. The skeletal
portion of the roof of the cavity is formed by the superior max-
illary bone presenting the palatal plate and the alveolar ridge,
while the skeletal portion of the floor of the cavity is formed by
the inferior maxillary bone presenting an alveolar ridge. These
alveolar ridges are armed with teeth which are set in bony sockets
lined with periosteum.

(a) Tin; TEETH.- — For a description of the minute structure of
the teeth the reader is referred to any work on histology. There

are two sets of teeth, ;i temporary set and :t 'permanent set. The

time of eruption i- important to the physiologist, because it is in-
dicative of the kind of food which the organism requires. The

time of Eruption of the Teeth is shown in Figs. I-Tl mid loo.

240

DIGESTION: INTRODUCTION.

Mul ms

Conine

Temporary teeth. (Time given in months.)

(6) The Muscles of Masticatios arc those which produce

the movements of the inferior maxillary hone, especially the tem-

porales, the masseter, the pterygoid, also those which produce

yu, j-j movements of the cheeks and

tongue.

('•) The Glands of the
Mouth arc the numerous
mucous glands whose func-
tion is to keep the mouth
moist, also the highly devel-
oped salivary glands. There
are three pairs of salivary
glands, the submaxillary, the
sublingual " and the parotid.
(For Figures see Secretion.)
(d) The Tongue lies in
the floor of the mouth, and is
composed mainly of longi-
tudinal and transverse muscle
fibers, through whose com-
bined action the tongue may
be retracted, protruded, raised, lowered, or circumducted.

This organ is most useful in mastication. In some animals it is
used as an organ of prehension. In most animals it is used as a
tactile organ. In the
mucous membrane of
the tongue are located
the principal end-or-
gans of the sense of
taste. Especially adap-
ting the surface of the
tongue for these vari-
ous functions are the
papillae which are of
three varieties : (i) the
circumvallate, (u) the
fungi-form, and (in)
the conical. The first
two forms named con-
tain taste buds. (See
Fig. lot).) (For other
figures see Taste.)

2. The Pharynx. — The uvula marks the boundary between the
oral cavity and the pharynx. This cavity is common to the di-
gestive and respiratory systems. The portion of it which is con-
cerned in swallowing is lined with stratified epithelium and is

Fig.

Molars

Bicuspids

Canine

Permanent teeth. (Time given in years. )

PARTICULAR SEGMENTS OF THE TRACT.

241

supplied with mucous glands. Its walls contain three sets of
muscles (Pharyngeal constrictors) whose contraction aids in deglu-
tition.

Fig. 156.

Section of circum vallate papilla, human. The figure includes
one Bide of the papilla ami the adjoining part of the vallum.
(Magnified 150 diameters.) (Heitzmann.) /:', epithelium;
i, . taste-bud ; C, corium with injected blond vessels ; M, gland

With duet. (ScHAKFKK.)

3. The (Esophagus. — This is the tube which leads from the
pharynx, through the thorax to the stomach. It possesses the
four typical coats described above. The mucous membrane pre-

Fio. 157.

m of the stomach.

sente longitudinal folds, and its epithelium is stratified. The
numerous mucous glands dip down into the submucosa. The two
heavy muscular coats serve the function of deglutition.

1. The Stomach. — This very important viscua is :i dilation of
the alimentary canal. It bas the four typical coats; mucosa,
n;

2 1 2

DIGESTION: INTRODUCTION.

submucosa, muscular and fibrous. It is the firsl portion of the
canal within the abdominal cavity and i>, therefore, the first t<»
have a peritoneal investment. The mucosa is provided with two
varieties of glands (peptic and pyloric) which will be described
under gastric digestion. This coat lies in prominent folds or rugae
upon the subjacent tissues. The muscular coat consist- of two
principal layers of involuntary muscle, an inner circular and an
outer longitudinal layer while an imperfect oblique layer may be
found at the cardiac end. The orifice between the oesophagus
and the stomach is called the < 'ardia ( Fig. 157, C). It is guarded
by a sphincter. The orifice between the stomach and duodenum is

called the Pylorus (157,
j>). It is also guarded
by a sphincter. At a
point about two-thirds
of the distance from the
cardia to the pylorus is a
band of especially strong
circular muscles. This
has been called by Hof-
meister and Schutz the
"Sphincter antri pylo-
rici " (Fig. 157, S. A.
I\). The portion of the
stomach between this
sphincter and the pylo-
rus is called the An-
trum (A). The middle
third of the stomach is
called the preantral segment (P. A.). The antral and preantral
segments together make the Pyloric portion, while the segment
nearest the cardia is called the < 'ardiac portion. The use of these
terms will be necessary in the description of the movements of the
stomach.

5. The Small Intestine. — This is a tube of fairly equal caliber
lying in coils in the abdominal cavity. It is lb' to 20 feet in
length and passes into the caecum through the ileo-ca?cal valve.
It is sub-divided into three portions, the duodenum, jejunum and
ileum. The four coats of the small intestine differ from those of
the stomach principally in the variations of the mucous membrane.
The folds of the latter are transverse and are called valvules
conniventes. (See Fig. 158.)

Upon these ridges the mucous membrane presents two important
features, (i) the villi which are finger-like projections into the
lumen of the intestine, (it) the crypts of Lieberkuhn which dip
down from the general surface of the mucosa to the muscularis

Longitudinal section of human -mall intestine, shoving
general relation of the folds constituting the vahukc eon-
niventes in the mucosa and submucous coat ; the latter

contributes the lilirous n,iv over which the mucosa with it-
villi and glands extends. (After PlKKSOL.

IXXERVATloX OF DIGESTIVE SYSTEM.

243

Fig. 159.

mucosa. The crypts will be described under digestion and the
villi under absorption.

Tributary to the duodenum are two most important glandular
bodies, the pancreas and
the liver. As the latter
has little to do with diges-
tion and much to do with
metabolism it will be de-
scribed in the chapter on
metabolism. The pan-
creas is a tubulo-racemose
gland resembling the sali-
vary glands except that the
alveoli are tubular. The
secreting epithelium of the
pancreas is hypoblastic in
origin, being derived from
the primitive mid-gut by
imagination.

6. The Large Intes-
tine.— This portion of the
intestine consists of the cre-
eiim with its vermiform ap-
pendix, the capacious, and
t ransversely c< rostricted co-
lon, and the rectum. The
structure of the walls is
quite similar to that of the
small intestine except that
there art.' no villi, and the
tubular gland- differ from
the crypts of Lieberkiihn
in having a greater pro-
portion of the miieiis se-
creting goblel cells.

2. THE INNERVATION
OF THE DIGESTIVE
SYSTEM.

Diagram of principal
nerves involved in degluti-
tion, secretion and diges-
tion : show in^ the Lingual
branch of the I ' pair, the
chorda tympanic branch of the 17/, the glosso-phi
the vagus (X), the hypoglossal {XII), the Buperio

I tie Innen atli

i' in.

n of the digestive

iryngeal ( IX ),
r cervical can-

■-•I I i>k:i:stio.\: ixiL-nnrcTiox.

glion (S.S.G. ) which scuds a branch to the parotid gland (/') and
one to the base of the tongue which divides and supplies both
sublingual (Slg) and submaxillary (Sm) glands.

The vagus gives oil' the superior laryngeal (8.L.) and the inte-
rior laryngeal branohes; gives off branches to the cardiac plexus,
(Cd.PL) and, passing down the oesophagus, gives oil' branches for
the (esophageal j)lexus (Oc.PI.). The left vagus (/,. I'. ) supplies
the lesser curvature of the stomach while the right (/>. V.) passes
behind the stomach and joins with the large and small splanchnic
(Maj.Spl. and Min.Spl.) to form the solar plexus (8). This great
plexus supplies the small intestine and sends a large communi-
cating branch (C) to the mesenteric ganglion and ple\n>(J/).
This plexus also receives branches from the AT and XII I), and
the / and II I. It supplies the large intestine. The hypo-
gastric nerve (Jff.N.), with branches from the // and /// sacral
nerves make up the hemorrhoidal plexus about the rectum
(IIP/.).

('. SECRETION.
1. GENERAL CONSIDERATIONS.

The tissue-activity of the organism may be conveniently divided
into three groups :

(a) Muscular activity, the general function of muscular tissue,
manifesting itself in motion and heat; (l>) nervous activity, the
general function of the nervous tissue, including all nervous acts
from sensation to reason ; (c) glandular activity, the general
function of epithelial and lymphoid tissue including all of those
metabolic changes which result in the elaboration of a special
mixture either (i) by separating (selecting) out of the liquids of the
body, compounds which already exist, forming of these a new
combination for a special purpose ; or, (n) by actually forming
new substances which maybe combined with selected or separated
substances to make a special mixture. Of these forms of glandu-
lar activity one may cite numerous examples : (i) the elaboration
of lymph, urine, perspiration j (n) gastric juice, pancreatic juice,
saliva, bile, synovial fluid, lachrymal fluid, sebaceous matter,
milk, etc. If one classifies as glandular all those tissues which
possess the power of elaboration by selection or formation, he will
find that he has included practically the whole of the derivatives
of the hypoblast, special portions of the epiblast, the whole of the
derivatives of the splanchnopleure and somatopleure together with
the mesoblastic epithelium of the genito-urinary system, and the
mesoblastic lymphoid tissue. There seems to be no doubt that
all of the tissues enumerated possess this power to a greater or less
extent. The glandular activity of the hypoblastic epithelium is

THE INNERVATION OF THE DIGESTIVE SYSTEM. 245

specialized in such organs as the pancreas and liver, and such
specialized portions of the mucous membrane as the gastric and
enteric glands. But the whole epithelium contains a large pro-
portion of the mucus-secreting goblet cells ; some writers stating
that any cell of the mucous membrane may become a goblet cell,
secrete its mucus and resume its original form as a columnar
epithelial cell. Even absorption of the products of digestion from
the alimentary canal is not a simple diffusion and filtration but is
attended with a marked activity of the epithelium first in certain
degree of selection and second in a partial elaboration, changing
the peptone to a higher proteid form before it is passed into the
capillaries of the portal system, also changing fatty acids and
glycerine to fat. That portion of the epiblast which lines the
mucous openings of the body, e. g., mouth, nose, anus, and
urethra ; and such mucous surfaces as the vulva, prepuce and
conjunctiva are richly supplied with mucous glands ; but the
goblet cells are absent from all of these locations except the res-
piratory region of the nasal mucous membrane. In that portion
of the epiblast which covers the general surface of the body the
glandular activity is subordinated to the function of protection.
There are innumerable sebaceous glands and sweat glands but the
general surface cannot be called a glandular one.

The endothelial lining of all serous cavities is now conceded to
have a general glandular activity. The serous fluid which oc-
cupies these cavities is not identical with blood plasma, and though
an increased venous pressure leads to an increase of the volume of
lymph and serum, these fluids differ quantitatively from plasma.
Such a difference cannot be accounted for by purely physical
law- of Hltration and diffusion, there must be a selective activity
on tiie part of the endothelial tissues. This selective activity
manifested by endothelial tissue in general justifies its classifica-
tion among glandular tissues. In the same category belongs
the endothelium of the circulatory system ; though glandular ac-
tivity has been demonstrated only in the endothelium of capil-
laries and lymph radicals. The genito-urinary system furnishes
numerous example- of glandular activity ; the ovary and testes,

and the genital duct- and canals including the oviduct, uterus,

vagina, vas deferens, seminal vesicles and prostate ; the kidney
and urinary passages. The epithelial tissues of all of the organs
enumerated are glandular tissues. It is to be noted here that the
secretion of the genital gland- is largely composed of cellular ele-
ments ; the same may be said of the lymphoid ti-sues of the cir-
culatory system and of the preliminary secretion (colostrum) of

the mammary glands.

L»4i; DIGESTION: INTRODUCTION.

2. SECRETION DEFINED.

The term secretion may be defined as the special activity of
the glandular tissues, or better the elaboration of fluid or semi-
fluid mixtures by selection from the fluids which surround the
active cells or by formation from the substance of the active cells.
In the secretion of the gastric juice the water and the inorganic
salts arc selected from the tissue plasma which bathes the glandular
epithelium ; the hydrochloric acid is formed probably by a reaction
between salts of the plasma. It is necessary, however, that these
salts be taken into the secreting epithelium and brought under
the influence of special forces in order that the reaction may take
place. The pepsin of the gastric juice is formed from the proto-
plasm as a product of cell metabolism.

The term secretion in its most general application may be ap-
plied to the part which the epithelial cells take in modifying the
fluids which filter and diffuse through them. That the absorbing
epithelium of the alimentary canal modifies the absorbed liquid is
now practically beyond question. Jn the first place there is a cer-
tain selection of the absorbed liquid from the general mixture of
digested foodstuffs and in the second place these absorbed sub-
stances are modified on their passages through the cells. We have
to deal here with a clear case of secretion.

These examples of secretion in its broadest sense fall naturally
into two groups : In the case of the gastric juice the elaborated
fluid is selected or formed, to be poured out upon the surface of
the mucous membrane for a particular use there. In the case of
the lymph plasma there is a selection of the substances which are
to filter or diffuse through the endothelium from one cavity or
vessel into another cavity or vessel, to be retained in the system.
In the case of absorption the selected and modified products of di-
gestion are passed into the circulation to be retained and further
utilized. We thus have in the gastric juice an example of what
has been called an external, secretion, while in the formation of
lymph and the modification of the products of absorption ex-
amples of an internal secretion.

The hypoblastic epithelium of the liver forms products which
not only afford examples of the two kinds of secretion already
named, but of a third kind as well. The bile, composed of sub-
stances which assist in digestion and in absorption, is an external
secretion ; the glycogen formed from the absorbed dextrose and
later thrown into the blood as dextrose, is an internal secretion ;
while the urea and related bodies formed in the liver are thrown
into the blood, not to be utilized by the system, but to be secreted
by the kidneys.

In the above presentation of the subject the terms glandular
epithelium and secretion have been used in the most general

GLANDS.

247

sense. The part which the epithelium plays in the elaboration
of the products of digestion are still subjects of controversy. It
will be best here to present more in detail the subject of external
secretion and the specialized glandular epithelium ((/lands), which
elaborate these secretions. Howell demies a gland as " a structure
composed of one or more gland-cells epithelial in character, which
forms a product — secretion — which is discharged either upon a
free epithelial surface (external secretion), such as the skin or mu-
cous membrane, or upon the closed endothelial surface (internal
secretion) of the blood and lymph cavities."

The one example of a unicellular gland is the mucus-secreting
goblet cell. It is more in harmony with the above presentation
of the general physiology of glandular tissues to consider the
goblet cells as representing unspecialized glandular tissue cells.

One phase of the process of differentiation which marks the
progress of evolution is the development of glandular organs. A
glandular organ or gland may be defined as a structure composed
of a specialized portion of glandular tissue which elaborates by se-
lection or formation a special secretion, which is discharged either
upon an epithelial surface (external secretion), or upon an endo-
thelial surface (infernal secretion).

3. GLANDS.
The following figure illustrates gland types :

Diagram illustrating the forme of glands: .1, simple tabular; /■', compound tubular;
C, modified (coiled) tubular; />, simple saccular; /-.', compound saccular, or racemose.
I PiEBSOL.)

As examples of the simple tubular gland one may cite the
glands of the Large intestine (Fig. Mil), the crypts of Lieber-
kiilin, the peptic glands, etc.

The compound tubular gland is represented in human anatomy

by the pyloric glands (Fig. L 6 2) and the glands of Brunner as

complex examples; while the pancreas (Fig. L63), kidney

and liver represent compound tubular glands of successively in-

248

DIGES1 ION: TNTROD I '< 'TION.
Pig. 161.
b

<M

Simple tubular gland of large intestine.

creasing complexity. The
sweat glands are coiled tubu-
lar glands. The simple sac-
cular glands, though promi-
nent in the amphibia as the
mucus-secreting glands of the
skin, do not occur in the higher
animals. The compound sac-
cular or racemose glands are
represented in the human
anatomy by the salivary glands
(Fig. 104). Some authors
classify these as compound tu-
bular glands.

A discussion of the blood
and nerve-supply of the vari-
ous digestive glands, of the
histological changes of the

Pyloric mucous membrane showing compound

tubular glands. ". mouth ; /'. duel ; c, >■ pound

fundus showing branches cut at various angles ;
•/. muse, mucosa;. (After Bend a.)

IXTEHXA L SECBETWXS.

249

glandular epithelium during activity and of the chemical compo-
sition of the secretion, will be found in connection with the phys-

iology of the gland.

4. INTERNAL SECRE-
TIONS.

Under this head it is pro-
posed to deal briefly with
the Function* of the Vascu-
lar Glands, also called the
ductless glands.1

The functions of the vas-
cular glands have been,
until quite recently, a mat-
ter of somewhat vague spec-
ulation. Even now these
functions are not by any
means clearly established
and fully understood ; but so much work has been done, experi-
mental and clinical, especially on the thyroid glands, the adrenal

P

Section of the pancreas of the dog. (Klein.1
(/, termination of a duct in the tubular alveoli, alv.

Fig. 164.

Section of human lubmaxillary gland.

capsules and the pituitary body, thai the theories advanced as
to their functions have the advantage of strong probability.

1 For this lection [ am indebted to Dr. B. J. Achard, of Roselle, III. The
limitations of a brief student manual has made it impossible to use more than half
of the valuable materia] received from Dr. Achard. The Author.

DIGESTION: INTRODUCTION.

a. The Thyroid Gland.

The thyroid gland is situated at the upper part of the trachea
and consists of two lateral lobes, placid one on each side of that
tube, and connected by a narrow transverse portion, the isthmus.
Thethyroid is of a brownish-red color. Its weight varies from
one to two ounce.-. It is larger in females than in males, and
becomes slightly increased in size during menstruation and after
maternity. It occasionally becomes enormously hypertrophied,
constituting the disease called bronchocele or goitre.

The accessory thyroids, or parathyroids, seem to occur in all
mammals. ( )ne of these bodies is attached to the external or pos-
terior surface of the lateral lobes of the thyroid ; in some animals
(dog, cat, rabbit, etc.), there is an additional lobe on each side,
imbedded in the substance of the thyroid proper. Histologically
the parathyroids do not resemble the thyroid gland (vide infra).
They present a general appearance of embryological tissue, and,
for this reason, have been regarded as an immature form of thy-
roid tissue, which, under the stimulus of increased functional ac-
tivity, is capable of developing into normal thyroid tissue.

Fig. 165.

Section of the thyroid gland of a child. Two complete vesi-
cles and portions of others are represented. The vesicles are
filled with colloid, which also occupies the interstitial spaces.
In the middle of one of the spaces a blood vessel is seen cut

obliquely, and close to it is a plasma-cell. Between the cubical
epithelium-cells smaller cells like lymph-corpuscles are here
and there seen. (Schaefek.)

There is, however, no satisfactory evidence that such a trans-
formation may take place. The histological and embryological

evidence seems to indicate that the two tissues are not only funda-
mentally different in structure, but probably also different in
origin.

The thyroid body is invested by a thin capsule of connective
tissue, which projects into its substance and imperfectly divides it

THE THYROID GLAXD. 251

into masses of irregular form and size. When the organ is cut
into it is seen to be made up of a number of closed vesicles con-
taining a yellow glairy fluid and separated from each other by in-
termediate connective tissue. Each vesicle is lined by a single
layer of epithelium, the cells of which, though differing somewhat
in shape in different animals, have always a tendency to assume
the columnar form. Between the epithelial cells exists a delicate
reticulum. The vesicles are of various sizes and shapes, and con-
tain as a normal product a viscid, homogeneous, semi-fluid, slightly
yellowish material, which frequently contains blood, the red blood
corpuscles of which are found in it in various stages of disinte-
gration and decolorization, the yellow tinge being probably due
to the haemoglobin, which is thus set free from the colored cor-
puscles.

The thyroid gland is for the animal economy a most important,
indeed, necessary, organ. Its removal or destruction is followed
by serious disturbances of nutrition, and is immediately or ulti-
mately fatal, because products of the normal metal )olism attack
and harm the central nervous system, so that nervous disturbances
and depression occur as wTell as disturbances of nutrition (tetanus
and cachexia). The reintroduction of thyroid material (by graft-
ing, subcutaneous or intervascular injection, or absorption from
the alimentary canal), causes an amelioration, or even an entire
removal of all toxic symptoms.

It follows from the foregoing that the thyroid tissue produces
normally some material which is in some way essential to the
nutrition of the body, and which acts as an antitoxic to those
products of normal metabolism which produce tetanus and cachexia
in thyroidectomized animals. Such a material lias been isolated
by Baumann, and is called thyroiodin, or iodothyrin. It is an or-
ganic compound of iodin, is produced by the thyroid gland from
truce- of iodin contained in the food and carried into the blood.
According to the experiments of Roos, it preserves the beneficial
effects of thyroid tissue, and acts like the latter in thyroidecto-
mized animal-.

Tin- fact that extract- of thyroid tissue, or iodothyrin, when
absorbed into the blood, ameliorate or remove the evil effects re-
sulting from ,i loss of function of the thyroid gland seems to prove
that the normal function of the thyroid is not merely to excrete
poisonous material after the manner of the kidneys. It indicates
on the contrary that these tissues act normally by giving off a
material to the blood which in some wayaffects favorably the nu-
trition of all or a pari of th<- tissues of the body. Histological
research -how- that, a- far a- the thyroid bodies proper are con-
cerned, this Becretion is contained in the BO-called colloidal mate-
rial which accumulates in the interior of the vesicles, and that the

252 DIGESTION: INTRODUCTION.

mechanism of secretion consists in a rupture of the walls of the
vesicles at some point, whereby the contents are discharged into
the surrounding lymph spaces.

The most important fact to l>c discovered is the manner of ac-
tion of this secretion upon the tissues of the body. There are two
hypotheses proposed :

( i ) The function of the thyroid secretion is antitoxic, i. c, it
antagonizes an unknown toxic substance supposed to be formed in
the body in the course of normal metabolism. When the thyroid
tissues are removed, this poisonous material, imperfectly excreted,
accumulates in the blood and produces the l'atal symptoms of thy-
roidectomy by auto-intoxication.

(n) The secretion of the thyroid acts normally by promoting or
regulating the metabolism of other parts of the body, particularly
perhaps the nervous tissues.

As yet no decisive or even probable proof for either view has
been given, and in working out the problem there are two great
facts to be explained : (i) that complete removal of the thyroid
tissue causes malnutrition, affecting, it seems, especially the central
nervous system ; and (n) that the injection or ingestion of thyroid
extracts in this condition restores metabolism more or less com-
pletely to a normal state.

An interesting phase in the physiology of the thyroid is the
functional relation between the thyroid and the parathyroid bodies.

Gley was the first to prove the physiological importance of the
parathyroids. He showed that in rabbits complete extirpation of
the thyroid lobes alone is not followed by fatal results, as long as
the parathyroids remain. Removal of both thyroid and parathy-
roid tissue is in most cases followed by typical symptoms of com-
plete thyroidectomy, resulting in the death of the animal. The
latter result has been contested by some observers, but renewed
investigations have demonstrated its accuracy. Gley's explana-
tion is that after removal of the thyroid its function is vicariously
assumed by the parathyroids, and his conclusion : that the func-
tional value of the two tissues is identical. But recent work tends
to throw doubt on this conclusion. Vassale and Generali state
that in dogs and cats the removal of all four parathyroids causes
acute symptoms of complete thyroidectomy and finally death, al-
though the thyroid proper be practically uninjured ; but the com-
plete removal of the thyroid lobes is not immediately injurious, if
the parathyroids (even only one) are left. They contend that the
result usually attributed to the extirpation of the thyroid is really
due to the simultaneous removal of the parathyroids.

This result has been partly confirmed by Rouxeau and Gley.
Moussu, from a study of over 150 thyroidectomies and parathy-
^ iridectomies, arrives at these conclusions :

THE THYROID GLAND. 253

(i) " The organs of the thyroid system have two distinct func-
tions, one thyroidal and one parathyroidal. The thyroids do not
act vicariously for the parathyroids, and cic< versa.

(ii) " The thyroid function is the same for all domestic animals
and for birds. Its suppression has always the same result, viz. :
development of cretinism, if it is caused under identical conditions.

(in) " Cretinism occurs only in the young. It is the more
acute the earlier the subjects are operated on.

(iv) "In adults thyroidectomy does not cause acute symptoms,
not even in carnivora. The operation is generally survived for a
long period, but may be followed by progressive cachexia or by
myxoedema.

( v ) " The parathyroid Junction is for flic most vital conditions of
/if, indispensable. It seems to influence immediately the nutrition
of tissues.

(vi) " Its suppression causes rapid death if total, alarming dis-
turbances if partial.

(vn) " The symptoms of parathyroid insufficiency seem to show
certain analogies with those of the Basedow's disease.

(viii) " The acute symptoms, such as tetanus, tachycardia,
dyspnoea or polypnoea, etc., following operations on the goitre in
man are parathyroid symptoms.

(ix) "The chronic symptoms, such as lowering of temperature,
weakening of the intellectual faculties, myxoedema, etc., are ex-
clusively thyroid symptoms.

(X) " Strumiprive cachexia must develop fatally if thyroid-
ectomy is performed during infancy and adolescence.

" In all operations on the thyroid organs the first duty of the
surgeon is to look for and to respect the parathyroids in oil coses."

Von Cyon lias made a full and exhaustive study of the relation
of the thyroid gland and the heart. He states that a suppression
of the thyroid function (through illness or extirpation) and like-
wise an increase of the functional activity (injection of iodothyrin)
have an "immense" influence on the entire nervous system of
heart and blood vessels. He proves that the vagus participates
in the innervation of the thyroid gland, or is, at least, closely con-
nected with it, and offers, in his discussion of the hypotheses on
the functions of the thyroid ( vide supra) the following conclusions :

(XI) "The function of the thyroid gland is to make harmless
th'' -.ilt- of iodin, which have a toxic effect on the vagi and
sympathetic nerves, by converting them into an organic com-
pound : the iodothyrinf which has a stimulating effect on the
same nerves, and increases their power.

(xii) "The thyroid gland function- mechanically as a safe-
guard for ii" brain against engorgement. In a sudden increase
of blood-pressure, whether from increased activity of the heart or

254 DIGESTION: INTRODUCTION.

from increased resistance of the peripheral blood-currents, the thy-
roid gland is capable of passing a large amount of blood in a shorl
time through its vessels, taking it thus directly from the arterial
back into the venous circulation and preventing its entrance into
the cerebral circulation."

Other investigators confirm these theories of ( rley and von ( "von.

b. The Suprarenal Capsules.

The suprarenal capsules, or bodies, are found constantly in all
classes of vertebrates, and seem, therefore, to be organs of funda-
mental importance. They are two small flattened glandular bodies,
of a yellowish color, situated at the hack part of the abdomen, be-
hind the peritoneum, and immediately in front of the upper part
of either kidney.

On making a perpendicular section the glands are seen to con-
sist of two substances — external or cortical, and internal or med-
ullary. The former, which con-
F,,;- 1,1,;' stitutes the chief part of the

"Ip/'j ■?.--, - > " v r-l organ, is of a deep-yellow color
)'i' V-j 00\ and consists chiefly of narrow col-

■] umnar masses placed perpendicu-
| • ;j larly to the surface. The medul-

\ - ;!|| lary substance is soft, pulpy, and

J of a dark-brown or black color.

. 5j Brown-Sequard stated in 1856

W;<^ <£-'''' -: : - ■ ' ^hat extirpation of both supra-

Fie~ from the outermost layer of the renals is USUally fatal to the aili-
cortical suhstence of a suprarenal body. ma] anc] more rapidly fatal than

(-M haefer after Ebeeth.) 1

the removal of both kidneys.
Recent experiments seem to corroborate this statement. The fact
that in some species of animals accessory suprarenals occur may
explain why extirpation is not always fatal.

On removal of only one of the bodies no noticeable disturb-
ances have been observed. After complete removal, with ulti-
mately fatal results, the prominent symptoms were : Extreme
muscular weakness, asthenia, and, in the ease of dogs examined
during this period, a great fall in the blood-pressure, together
with a feeble heart-beat, have been ascertained. It is worthy of
notice that in Addison's disease these symptoms occur, together
with the familiar pigmentation; the explanation of these symp-
toms is, however, still sub judice.

The effects of injections of suprarenal extracts in living animals,
on the vascular and respiratory organs, have recently been studied
by Oliver and Schaefer, and by Cybulski and Szymonowicz.

Extracts of the medullary portion of the suprarenals, injected

HYPOPHYSIS CEREBRI. 255

into the veins of an animal, caused pronounced slowing of the
heart beat and a large rise of blood-pressure. If the animal was
first given atropin to paralyze the inhibitory nerves to the heart,
or, if the vagi were previously cut, the injection was followed
usually by a marked quickening instead of slowing of the heart
beat, and by a greater rise of blood-pressure. The organs of res-
piration were not atfected so seriously. A temporary slowing and
shallowing of the respirations could usually be noticed. According
to Oliver and Schaefer the heart is influenced by the direct action
of the extract upon the cardio-inhibitory center. The enormous
rise of blood-pressure is due to constriction of the arterioles.

Blood drawn from the suprarenal vein and injected into the
circulation of normal animals causes the same symptoms, though
less intense, as injection of extract, while blood drawn from other
veins has no effect.

From the above it seems certain that a material formed by the
secretory activity of the gland cells occurs normally in the venous
blood flowing from the gland. Probably it is a normal product
of metabolism of the medullary cells of the gland, and is secreted
and discharged directly into the blood. It must, therefore, exert
continually a stimulating effect upon the heart and blood vessels.
This assumption is confirmed by the fact that after complete extirpa-
tion of both glands the blood-pressure is greatly depressed.

The normal function of the suprarenal bodies consists in furnish-
ing this stimulating substance to the blood. It is believed that
it- ••fleets are exerted mainly on the muscular tissue, at any rate
it has a general tonic or augmenting action on all varieties of mus-
cles found in the body, or perhaps the effect may be on the nerve
centers controlling the muscular action rather than on the tissues
directly. It i- impossible at present to decide the exact mode of
action.

c. Hypophysis Cerebri.

The hypophysis cerebri (or pituitary body) is a small reddish-
gray mass, weighing from five to ten grains. It is very vascular
and consists of two loin-, separated from one another by a fibrous
lamina. Of these, the anterior is the larger, of an oblong form
and somewhat concave behind, where it receives the posterior
lobe, which i- pound. The two lobes differ both in origin and
structure. The anterior lobe, of a dark, yellowish-gray color, is
developed from the ectoderm of the buccal cavity, and resembles
to a considerable extent, in microscopic structure, the thyroid
body. It i- thus a glandular structure. According to Sailer it
cannot be called strictly a ductless gland, since it possesses an
imperfectly developed system of duct- opening between the dura
and pia maier. ii ]- evidently a secretory structure, and the fact

256 DIGESTION: INTRODTJi 'TION.

that the secretion is discharged between 1 1 * < • meningeal membranes

suggests sonic special connect inn with the physiology of the brain.
The posterior lobe is developed by an outgrowth from the em-
bryonic brain, and during fetal life contains a cavity which com-
municates through the infundibulum with the cavity of the third
ventricle. It is always -mall and has the appearance of a rudi-
mentary organ.

The clinical observations as to the function of the pituitary
body have been limited to the glandular lobe. In many cases of
acromegalia this presents pathological changes. Extracts of the
gland have been used in some cases and some of the disagreeable
features have shown amelioration, lint the evidence at hand is
not satisfactory and the nature of the connection between acro-
megalia and the functional disturbance of the hypophysis, if any
exists, needs more complete investigation.

Howell has made experiments with extracts of both lobes of the
hypophyses (of sheep) separately. Injections of extracts of the
glandular lobe gave little or no effect, while injections of extracts <>/
the infundibular lobe h<nl a distinct and remarkable effect on theheart
rate and blood-pressure, which, resembles in some respects, 'tin! differs
in others from that of suprarenal extracts.

Extracts injected in normal animals with vagi intact caused a
pronounced slowing of the1 heart beat, similar to that from supra-
renal extracts, but lasting a much longer time. The heart beats
were not only slowed, but considerably augmented in force.
The blood-pressure rises to a considerable extent, owing ap-
parently to the peripheral constriction of blood vessels. If the
dose was a maximal one, and followed too quickly by a second in-
jection, there was little or no effect, but if the dose was not too
strong, and sufficient time was allowed for the effects to wear off,
they could be repeated. With each repetition the effects decrease
progressively in intensity.

Authorities consulted in preparation of the section on internal
secretions :

Dr. L. Hermann. Lehrbuch der Physiol., 8te Ann.]

Gray's Anatomy. (Phila., 1887.)

< rEG en bower. Lclirt). (1 . Anat. il. Menschen, 2te Ann.

Pepper. System of Med., vol. iii.

W. H. Howell. Internal secretions, considered in their physiological,

pathological and clinical aspects ,• physiology of internal secretions. Tr.

Cong. Am. Phys. and Sura.. N. Haven, 1897, iv.
IvATZENSTElN. Velier die j'erdndern n</en i n iter Schildd riise nacli E.vtir-

jtation iter Znfiiliranlen Nerven. Arch. i'. Anat. u. Physiol.. Leipz.,

1897.
Munck. Zur Lehre von der Schilddrdse. Arch. f. Path. Anat. (etc.).

Berlin, 1897, cl.
Gbaseb. Ueber den gegenwartigen Stand der Schilddr&sen frage. Munches

med. Wohnschr., 1897, xliv.

The function of Hie thyroid gland. X. Y. Polyclin., 1897, ix.

CHEMICAL IXTBOD UCTION.

257

MoussTJ. Recherches sur leg functions thyroidienne et parathyroidienne,

Eec. de Med. V6t, Paris. 1897 ; 8-s.; iv.
VON Lyon. Berlrage zur Physiol, der Schilddruse und dcs Herzens,

Arch. f. et ges. Physiol. Bonn, 1898, lxx., etc.

D. CHEMICAL INTRODUCTION.

1. FUNDAMENTAL CARBON COMPOUNDS.

One cannot gain a definite idea of the metabolic processes oi
nutrition without knowing the chemical composition of the body
and of foodstuffs, and following, as closely as may be, the chem-
ical reactions which take place during the processes of digestion,
and the processes of constructive and of destructive metabolism.

The author proposes to summarize here a few of the facts of
chemistry that may be convenient for reference during the study
of the succeeding chapters on nutrition.

The chemistry of the carbon compounds is the basis for physio-
logical chemistry.

The compounds of carbon with hydrogen form the basis for the
consideration of all of the higher carbon compounds.

The simplest compound of carbon and hydrogen is marsh gas or
methane, CH4.

A clear notion of the relations of various compounds involved
in nutrition can only be gained through a study of the structural
formulae of those compounds. Let us, therefore, use the structural
formula? as far as possible.

H

The structural formula of methane is : H — C — H. As these

H
five atoms must be conceived as occupying
positions iu tri-dimensional space, we may
assume that they arc symmetrically ar-
ranged with the carbon atom in the center.
That gives us a tetrahedron with each
hydrogen atom equidistant from each
other hydrogen atom. The space relations
of the atom- being as yet Largely con-
jectural we will !»<• content with repre-
senting tli<- molecule on a plane surface.
All of the hydrogen atom- arc displaca-

ble. Tiny may he displaced singly by

monad- or monivalcnt radicle-, or by two diads, etc., etc.

One fundamental method of combination of carbon atom- is
through dropping two hydrogen atom-:

17

Space relationi "i the atome in
methane.

258 DIGESTION: INTRODUCTION.

II H H H

H— C—

j HI — C— II or H— C— C— H ,

H H H H

This compound is called Ethane, and may be written C2H( or
( II— CH3.

The third carbon compound in the series is Propane, written
C3H8 ; CH3— CH2— CH3 or :

H H H

H • C— C— C • H .

H H H

The fourth member of the series is Butane: C4Hlu ; CH3 —
CH — CH2— CH3 or :

H H H H
H ■ C— C— C— C ■ H

H H HH

The series may be continued through Pentane, Hexane, Hep-
tane, Octane, Dodecane and Hecdeeane, which are called the normal
paraffins.

If one study the structural formula of butane, he finds that
the same number of atoms may be differently arranged and -till
satisfy all of the bonds :

H

HOH

1 H

H-C— CH

1 H

HCH

H

The two forms of butane which exist can only be accounted tor
in this way. This property of the molecule is called Isomerism.
The first butane is normal butane, the second isobutane. As the
series advances the possibility of isomerism rapidly increases.
Besides the normal pentane above given there are : Isopentane, —

CHEMICAL ISTRODUCTIOS . 259

and Me8opentane

H

HC-H

|

H

H

HC-

-C-

-CH

1

H

H

H-CH

H

H

H-C-H

H

1

H

HC-

-C-

-C-H,

H

1

H

H-CH

H

note that all of these forms of pentane have the formula C-H12. It
is hardly necessary to say that this property gives rise in the
higher carbon compounds to an almost interminable series of
combinations.

Let us now turn our attention to some of the derivatives of the
series of hydrocarbons. If one of the atoms of hydrogen be re-
moved from CH4 a monad radicle methyl will result: Methyl =

H

( II — ; H*C — . In a similar way arise the monad radicles:
H

H H

E%/=C2H6— \ CH3— CH2— ; II C— C—

II II

II H H
Propyl — C-H.— ; CI I,— CI I — (II — ; BC— C— C— ,

II II H

BiUyl=: (',11,— ; I'rn/,//=(':\\n— ; Hexyl= C(.II|:t— ; etc.

When one of the monad radicles takes the place of one of the
hydrogen atoms of a molecule <>l* water an alcohol results :

I . ■< ) methyl alcohol.

260

DIOESTIOX: INTRODUCTION.

Ajiother way of representing the matter is to conceive one of
the atoms of hydrogen of the hydrocarbon (methane, ethane, etc.)
to be exchanged for Oil or hydroxyl which may be written :

H
CH3-OH or H-COH.
H

In the same way arises the series of primary monatomic alcohol:

II H
Ethyl alcohol,— C2H3OH ; CH3— CH2OH ; H-C— C— OH

H H

Propyl alcohol— C3Hr-OH ; CH3— CH2— CHpH ; or :

H H H
HC— C— C-OH, etc.
H H H

In the propyl alcohol it is evident that the hydroxyl may dis-
place a hydrogen from the central carbon atom instead of one of
the end atoms giving the

H H H

formula H-C — C — OH or secondary propyl alcohol.
H 6 H
H

This is the first one of a series of secondary monatomic alcohols.
Table showing the normal paraffin series with the correspond-
ing radicles and primary monatomic alcohols :

The 1'araffixs.

General ) CnH-iu+t or
Forinuhe: J(C'H3)2(— CH2)n-2

Radicles.

Methane, CHa— H
Ethane, CH3— CH.
Propane, CH3— CH2— CH3
Butane, CH3(CH2)„CH3
Pentane, CH3— (CH2)3— CHa
Hexane, CH ,— (CH2)4— CH.
Heptane. CH3— (CHa)8— CHa
Octane, CH3— (CH2)a— CHa

Ci.II-.'u— 1 or

CH3 — (Clio ),,_!■< 'II „-

Methvl, CH3—
Ethyl, ill, -CH.,—
Propyl. CH3— CH,— CH„—
Butyl.CHj,— (CHa)2— CH,-
Pentyl, CH3— (CH2)3— CHa—
II. wi, CH3— (CH2)4— CH2—
Heptyl. CH ,— (CH2)5— CHS—
Octyl, CII3— (CII..)"0— (II,—

Ai.( ■mini..

c,,ir-'"-i OH or

CHa (( II,),, ,( H,olI

Methyl alcohol : HCH.-OE
Ethyl alcohol : CH.-CH.— OH
Propyl alcohol : < II :— cii.,-CH„oir
Butylalcohol: CH3— (CH2)a— CHaOH
Pentyl alcohol : CH„— (CH.)3— CH20H
Hexyl alcohol: CH3— (CH2)3— CH2OH
Heptyl alcohol: CH3— (CH2)a— CH "II
Octyl alcohol: CH3— (CHa>8— CH,OH

CITE MICA L IXTR OB UCTIOX.

261

Any primary alcohol when oxidized step by step undergoes the
following- change as the first step :

Ethyl alcohol + oxygen = water -I- ethyl aldehyde :

H H H H

HC— C • O H+O; = H20+HC— C : 0
H H H

The second step consists in the addition of an oxygen atom to
the molecule thus : ethyl aldehyde + oxygen = acetic acid
(number 2 in the fatty acid series).

H H

H OH

H-C— C:0 + O = HC— GO or CH — COOH
H H

The group COOH is called the oarboxyl group.
Table showing the primary monatomic alcohols and the corre-
sponding oxidation products — aldehydes and fatty acids.

Au oHOLS.

Aldehydes.

Fatty Acids.

'11 1 11., — CH2-OH

CH3-(CH2)H^CH0

CH,-(CH2)^C00H

Methyl alcohol: H-CH.-OH
Ethyl alcohol : CH,— CH,-OH
Propyl alcohol :

CH,— (CH.),— CH20H
Kutvl alcohol :

CH,— (CH,)2— CHjj-OH
Pentyl alcohol :

CH, 1 B,) -ill, oil

Methyl aldehyde : H-CHO
Ethyl" aldehyde : CH3— CHO
I'ropvl aldehyde :

CH,— (CH,h— CHO
Butyl aldehyde :

CH,— (CH,)a— CHO
Pentyl aldehyde :

CHa— (CH,),— CHO

Formic acid: HCOOH
Acetic acid: CH3— COOH
Propionic acid : CH,- (CHj),- COOH
Butyric acid ;l CH3— (CH.,)„— COOH
Pentvlic acid :' CH3— (OH'^j— COOH
Hexylic acid: CH3— (CH2)4— ( '( h ill
Heptylic acid: CH,— (CH,),— COOH
Octvlic acid : CH,— (CH.)a— COOH
Nonylic acid: CH3— (CH2)7— COOH

1 1 igher normal fatty acids whose formula3 may be written from
the above generalized formula are : 10th Capric acid, 12th
Laurie acid, 14th Myristic acid, 16th Palmitic, 17th Margaric,
L8th Stearic, 20th Arachnic, 30th Melissic acid.

The oxidation of tin; primary monatomic alcohols gives rise to
;i -eric- of n/( Ir/iyt Irs of the monatomic alcohols.

The oxidation of* the secondary monatomic alcohols gives rise to
a aeries of ketones. The first step in the oxidation may be repre-
sented thus :

Secondary propyl alcohol -f ()= II., O + ketone of secondary
propyl alcohol.

'Corresponding to butyric acid i- iaobutyric add, written: h'II.),, CH
'•>• »U ; and corresponding to pentvlic acid ie ite Leomere valerianic acid (CEL)>

i ii < ii. cook

262 I)I<;l-:STIOX: IXTHODCCTION.

H H H H H

H-C— C— CH + 0 = 11/) + H-C-C-C-H

H 6 H H O H

H

Note that the ketone contains two methyl radicals joined by
CO. Its chemical name is Dimethyl ketone. The ketone derived
from secondary butyl alcohol has the formula : CH.5 — CH., — CO —
CH3, and may be called Methylethyl ketone A further oxidation
breaks up the ketone into its elements yielding; acids which con-
tain fewer atoms of carbon than the secondary alcohol from which
they were derived.

The Diatomic Alcohols or Glycols. — The combination ol two
carbon atoms in the paraffin-ethane (CH} — CH3) may, under cer-
tain conditions, be brought about with fewer than six hydrogens,
yet all of the bonds of carbon will be satisfied. The following
formula shows the structure of this molecule :

H H

H-C = CH •

It is called Ethylene, has the general formula CnH.,u. It is also
called olefiant gas, and is the first of a series of Olefines.

The second member of the series is Prophylene with the formula

H H H

CH3 — CH=CH2; H-C — C=C-H. The third member

H

of the series is Butylene : CH3 — CH2 — CH = CH, The
olefines have two bonds satisfied in such a way that they may
readily be loosed from their connection in the olefine and take up
other monad atoms or radicals. For example in ethylene (CH.,=
CH.,) the double bond which joins the carbons may be conceived to

H H

stand thus : H-C — CH, and require union with monads. If

these two bonds be satisfied with hydroxy! we have :

H H

H-C — C H

O O

H H

ethylene alcohol or glycol.

THE OXALIC ACID SERIES. 263

In the same way we may derive propylene alcohol or pro-
pylene glycol :

H H H
H-C — C — C-H, or CH3 — CHOH — CH2OH.
H 6 6
H H

Remember that the oxidation of the primary monatomic alcohols
leads to the formation of a series of normal fatty acids. The oxi-
dation of the primary diatomic alcohols or primary glycols leads
to the formation of two series of acids :

1. The Lactic Acid Series. — Ethylene glycol + O, = H20 +
glycollic acid.

H,0 -f H • CHOH — COOH

In a similar way lactic acid is derived from propylene.

2. The Oxalic Acid Series:

Ethylene glycol -j-20.,=2H.,0-f- oxalic acid.
( H2OH— CH2OH + 20;= 2H20 + COOH— COOH.
On the next page is a table showing the Olefines, the Primary
Diatomic Alcohols, the Lactic Acid Series and Oxalic Acid Series
with the general (a) quantitative and (/>) structural formulae :

H

('-

H
- C H

6 1

o

O

+

H

H

O

204

i >i<; /:\ri<>x .■ rsrnonnTioy.

W

c

_^

-

-

•_

/

pg

O^

i

<

1

w

w

•

m

0

u

1

"

-

<

o
c
o

5 8 8 8
R I Li

| '- 1 - 'S •" go ^olo jj.§ §

H a 2 > — r~s-
C £ X d< < 2h M-aJtSg

W

o

o

_i

_

o

1

■/.

M

o

O

fc

u

o

K

a

o

i

a

W

o

L

a ° c

"— '§ — j

I I

1 a a ~ ^ -° - ► -"o

I— ' .'a c— oW »bd
■eSW-|o^t>^o-3o

23 fl & & J

w

o

=

lj

u

o

II

>H

»

w

►J

r,

_

O

o

«

o

W

|

o

H

u

o
o
►J

=
r.

<!

L

a"
o

- Q. Q

-Si

^c

- —
CO

I I

i-- .- a

nRffia

a —

- _r
— —

K — - _ — _

| .— ,-., ! I— I .

i*.— ™~' >.~ >.*

V V.

i

~

u

'/.

1

w

a

=

fc

5

n

W

u

u

o

L

w

'-

r.

«=

~

- =

II II

W W

B o

. W OIK .r\ffl I a* I sT I

* i

o

V M .

o— 2 -= 3Q T M

>.— =-~ >.r -'•

re

a p. =: c H - c

TBI ATOMIC ALCOHOLS AND DERIVATIVES.

265

The Triatomic Alcohols and Derivatives.

The series of triatomic alcohols begins with the tri-carbon radi-
cle propenyl which is derived from propane :

H H H
HC— C— CH .

When the three open bonds are satisfied with hydroxyl we have
propenyl alcohol, glycerol or glycerine :

H H H
HC— C— CH .
6 6 6
H H H

Tt is evident that in the propenyl radical two of the open bonds
may be reciprocally satisfied giving rise to a monad radical allyl
and its corresponding alcohol :

H H H
BC=C— C— H

Allvl radical.

H H H
HC=C— CH
OH

Allyl alcohol.

The acid series corresponding to this alcohol is called Oleic
Acid Scries, oleic acid being the xvin member of the series which
begins with in, acrylic acid.

Table showing the Triatomic Alcohol series and some of the
monad derivatives of the series, with the generalized quantitative
and (structural) formulae.

Vo.

Thiai-
Mvmc'j' ABBOV.

' i,II,u— ,

' II CH,)n-4

I II. I II

Al.i num..

CnH«o-i(OH)a

< II f< ll.,):,-«

I Hull ,< II nil

III Propenyl.

Glycerol.

IV
XVIII

H « II mi I II ii I ii'.n I HOB
< 11,011

MuN ID

II VllliOl AKIIllN.

( 11 I' .1, 1

CH,-(CH)-n_«

-(('llj I 11

Allvl.
II ill Ml 1 II

111. 1 11 Aril) SBBIE8.

' dHju— »Oj

CH,— (CH d 1

-mi 1 OOH

\i iv lie acid.

II < 11 - 11 ("OOH
i rotonic ii.'iil.
CH,— (CH)jCOOH

Olel !'•'-/.

III nil,,,, «llu

' OOH or « ,. 11 ,11

266 DIGESTION: INTRODUCTION.

The tetmtomic alcohol* begin with the derivative of butane hav-
ing the formula :

II II II II

HC— c— c— CH-

When each of these open bonds is satisfied we have the tetrad
alcohol Erythrol ( !H2OH— (( !HOH ) — ( !H2OH. The hexatomic
alcohols begin with mannitol or mannite whose formula is CH OH —
(CHOH) — CH2OH.

Benzole and its Derivatives.

The carbon compounds thus far considered are arranged with
the carbon atoms forming a chain. There is some departure from
this rule in the isomeres of the fundamental compounds, but the
"chain-type" is dominant. In benzole and its derivatives we
have a radical departure from this type in the "ring-type."

H

C

Benzole

H-C OH

HC C-H

C

H

Note that the four bonds of the carbon atoms are reciprocally
satisfied as indicated, the particular location of the double bond
being, of course, conventional. Note also that this hydrocarbon
has a much larger proportion of carbon than is the case in the
chain-type of hydrocarbons. The hydrogen atoms are displaca-
ble by monads or monad radicals, thus giving rise to a long
series of Benzole derivatives or "Aromatic compounds." Phenol,
Carbolic acid, Phenyl-hydroxide or hydroxy benzole has the fol-
lowing formula :

OH

C

H-C CH
HC CH

C

H

BENZOLE AND ITS DERIVATIVES. 267

If two of the H's be displaced by hydro xyl the relative posi-
tion of these two hydroxyls is not a matter of indifference ; if
they are adjacent to each other, thus :

OOH
H-C° 2C-OH
H.C5 3CH

CH

it is called orMo-dihydroxy benzole (catechol).

If the two hydroxyls are not adjacent, but occupy the positions
1*3 or 1*5 the compound is called me&z-dihydroxybenzole (resor-
cinol). If the radicles are symmetrically opposite, as at position
1*4, the compound is a para-compound, in this case, paro-dihy-
droxvbenzole (quinol or hydroquinone).

A few examples will show the general structure of the bodies.

(1) Orthohydroxy benzoic or salicylic acid

OOH

Q
H-C C— C-OH

H-C CH
CH
or CLH/OH— COOH.

(2) Para-ethyl-phenol or p-hydroxyphenyl ethyl :

COH
/
H.C CH

H-C CH

C

I ?
II >C— < 'II

XT JT

orC II -on— c. II

Para-hydroxyphenyl-a-amido-propionic acid or Tyrosin :

268 DIGESTION: INTRODUCTION.

H MI.
H-0- C— COH
H O
C

HC C— H

H.C OH

//

C

OH

or O.H/OH— CH — CHXH?— COOH.

6 4 Z I

2. THE CARBOHYDRATES.
a. Glycoses or Monsaccharids.

This most important class of organic compounds includes vari-
ous aldehydes, ketones of the higher alcohols beginning with the
triatomic propenyl alcohol or glycerol :

Glycerol + oxygen = water + glycerose,

2 [CH..OH — CHOH — CH..OH] +0, =

9TT 0_l f CH2OH — CHOH — CHO, aldehyde of glycerol.
^±i2u+ >y CH-0H — CO — CH2OH, ketone of glycerol.

The aldehydes in the carbohydrate series are called Aldoses,
while the ketones are called Ketones. Having three carbon atoms
they are called Trioses. The glycoses include triosis, tetroses,
pentroses, hexoses, heptoses, octoses and nonoses.

(a) Trioses, — Ex. Glycerose a mixed aldose and ketose (C.{Hf03).

(/9) Tetrose, — Ex. Erythrose which is the aldose of erythrol,
and has the formula :

CH2OH— CHOH— CHOH— CHO ; or C4Hs04.

(j) Pentose — Ex. Xylose and Arabinose both having the for-
mula (C5H10O6).

(J) Hexoses or Glucoses represent aldoses and ketoses of the
hexatomic alcohols mannitol, dulcitol and sorbitol.

(i) Dextrose ; d-glucose, grape-sugar, is the aldose of sorbitol:
CH2OH— (CHOH)4— CHO, or C6H1206. Destrose is a sweet,
crystalline substance, whose solutions rotate polarized light to the
right, i. e.} dextro-rotary.

(il) Levulose, d-Fructose, Fruit-sugar, is the ketose of man-
nitol : CH2OH(CHOH)3— CO— CH2OH. This sugar occurs in
honey and in many fruits.

SUCROSES OR DisAcciIARIDS.

269

(iij) Galactose, or d-galactose is the aldose of dulcitol.

i iv i Mannose is the aldose of mannitol.

The hexoses or glucoses are incomparably more important than

any of the other glycose:-

h. Sucroses or Disaccharids.

These are double-grouped sugars which represent a combination of
two hexose groups minus a molecule of water. The following for-
mula represents what takes place in the molecule in the formation
of saccharose.

(«) Saccharose or Cane Sugar.

H H H OH X)
H-C— C— C— C— C— C-H

■N

dextrose

O () () H O

!

H H H h
H

H

plus

f

, — H,0 = Saccharose

H H H O O O

H-C— C— C— C— C— C-H levulose

OH OH OH H

H

(6) LACTOSE is likewise composed of a galactose group with
a dextrose group dehydrated.

H H

< ialactose : II-( ' — C

OH OH H

i

H20 = Lactose.

oil OHH O

•/'

C— C— C— C— H

o

II

plus ;H!

O OH OH OH OH o
Dextrose: H;< — ( — ( — ( 5— ( .'— ( H
II II II H II

(c) M A LTOSE 18 ;m end product of the action of amvlolytie fer-
iii' in- upon starch, the hydrolysis of the starch molecule being
effected before it- cleavage into maltose and a dextrine. Thedex-
trinc is in turn subjected to hydrolytic cleavage resulting in mal-
tose and another dextrine. The structure of the maltose mole-
cule has nol been sufficiently fully studied to presenl here. Ms
quantitative formula is ( \JIJ >ir in common with dextrine,
lactose and fructose it reduces [Tenling'e solution.

270

DIGESTION: ISTHODrCTlOX.

c. The Polysaccharids or Amyloses.

To this class of carbohydrates belong the starches, gums, dex-
trines and cellulose. The molecular constitution is unknown.
The members of the class have in common the general formula
(C6H10O5)n. T<> the quantity n various values have been assigned.

Carbohydrates. -

f Trioses :
| Tel roses :
Monosaccharides, Pentoses :
or Glycoses.

< rlycerose.
Erythrose.
Xylose, Arabinose.

Hexoses, or
t rlucoses.

c Saccharose.
Disaccharids, or J Lactose.

SuCTOSeS. *] Maltose.

( Isomaltose.

Dexl rose, or < Irape-sugar.
Levulose, Fructose, or Fruit-sugar.
< Galactose.
Mannose.

Polysacchnids, or

Amy loses.

The Dextrines.

Amylo-Dextrine.
Erythro-Dextrine.
Achroodextrine a.

A ch rood ex trine /3.

The Gums : Gum arabic, etc.

The Starches : Vegetable starch ; glycogen.

( Cellulose.

3. THE FATS.

In our review of the fundamental carbon compounds we have
found a series of normal fatty acids which are derived from the
monatomic alcohols. These fatty acids have the general struc-
tural formula :

CH— (CH.,)u_,— COOH. The 16th member of this series is
Palmitic acid," "which has the formula CH3 — (CH.,)U — COOH.
Propenyl alcohol or glycerol is the first member of the series of
triatomic alcohols and has the formula : CH..OH — CH( )H —
CH2OH or C3H5(OH)3.

When these two bodies are brought together under proper con-
ditions there is a combination of one molecule of glycerol with
three molecules of the fatty acid to form one molecule of PalmiHn
or Tripahrtitin, one of the common fats :

CH3(CH2)U— COO H HO "— CH2

< CH3— (CH2),— COO H HO— CH

CH,— (CH ,), — COO H HO — CH2

=3H2< )+ [CH -( CH2 ), -COO] 3-C3H5.

3 Palmitic acid -f glycerol = water -f Palmitin or Tripalmitin.

THE PROTEIDS. 271

In a similar way Stearin or Tristearin is formed from three
molecules of stearic acid and glycerol, and has the formula:

[CB _(cha,-cool-cjC

Olein is a similar combination of three molecules of oleic acid
(which is the 18th member of the oleic acid series, derived from
the triatomic alcohols), and has the formula: [CHS — (0H.,)U —
(CH )., — C< )( ..)] 3 — C3H. or (C18H3302)3 — C3HS. Palmitin, stearin
and olein are the fats which are deposited in the adipose tissue of
the animal body. Palmitin has a melting; point of 45°C, stearin,
53°— 66°C; olein, 0°C. The animal fats are mixtures of these
three constituents in various proportions peculiar to each species
of animal.

The melting point of a mixture is the proportional average for
the fats which compose the mixture. Both palmitin and stearin
have a melting point above animal temperature. The fat of the
animal body is always in a fluid state during life. The mixture
of the three constituents must include sufficient olein to insure the
fluidity of the fat at body temperature. But the melting point of
the fat of different animals varies through a wider range than
does the temperature of the animals. Certain of the chemical re-
actions of fats will be discussed in connection with their digestion
and metabolism.

4. THE PROTEIDS.

The term proteids is a general one which includes a class of
compounds of which egg-albumin, serum-albumin, haemoglobin
and fibrin may serve as examples. Though any of these may
serve a- animal food in common with the carbohydrates and the
fats, they stand much nearer to living protoplasm than do carbo-
hydrates and fats.

In fact the living matter which we call protoplasm and which
possesses the marvelous power of liberating the energy which we
call life, if deprived of life and subjected to chemical analysis, is
shown to be only a mixture of proteids, together with various
substances which may represent foodstuffs, in various stages of
anabolism or cleavage products of protoplasm in various stages of
katabolism. .lust what changes take place between the departure
of life and the resolution of the protoplasm into the various com-
pounds just referred to, it is impossible to say. Of the various
foodstuffs and katabolites found in protoplasm it is likely that
all or oearly all are purely incidental to the life processes and

that the matter which actually possesses life, I. '., the true pro-
toplasm, U a substance quite like the simple proteids chemically.
The chemistry of the proteids is still a collection of facts
which fail to reveal the quantitative formula, much less the struc-
ture of the molecule. The aural trustworthy analysis of egg-

272 DIGESTION: INTRODUCTION.

albumin is that of Franz Hofmeister (Zeitsch. fur physiol.
Chemie, Bd. Hi, L 89 2) which resulted in the following formula:

Egg-albumin = COT4H3ffiN62066S2.

Though the molecular formula for egg-albumin may be modi-
fied by subsequent investigations it serves to indicate : (1) That
typical proteids contain ( ), II, O, N, and S, (2) that typical pro-
teids are made up of exceedingly large and complex molecules.

Besides the elements above enumerated some of the proteids
(nucleo-proteids) contain phosphorus and some (chromo-proteids)
contain iron.

The indiffusibility of most of the proteids may be due to the
great size of the molecule.

The proteids are necessary constituents of animal foods. There
is a certain minimum proteid requirement for every animal. If
the food contain less than that the animal must die of malnutri-
tion. On the other hand carbohydrates or fats or both of these
may be withheld from an animal and no serious result will follow.

The reasons for these facts will be given later. The facts are
mentioned here to impress the student with the great importance
of the proteids in nutrition.

Certain chemical characteristics of the proteids will be mentioned
in connection with their classification.

CLASSIFICATION OF PROTEIDS.
a. Simple Proteids.

1. Albumins. — Soluble in water ; and in a saturated solution of
MgS04 or XaCl; insoluble in a saturated solution of (NH4)2S04.
The albumins are coagulated by moderate heat, 03° to 75° C., and
respond typically to the xanthoproteic test, Millon's reagent and
other general proteid tests. The following native albumins may
be given, (i) Egg-albumin, precipitated by ether (Halliburton),
(n) Serum-albumin, not precipitated by ether (Halliburton). It
is the principal proteid constituent of blood plasma, (in) Laeto-
albumin is one of the proteid constituents of milk. When milk is
boiled the lacto-albumin coagulates and collects upon the surface
in a thin membrane, (iv) Myo-albumin is one of the proteids of
muscle-tissue, (v) Vegetable albumin, of which there may be
several kinds.

2. Globulins. — Insoluble in water, in saturated solutions of
MgSO,, XaCl, and (XHJ,S04 ; but soluble in dilute XaCl solu-
tion : (i) Serum-globulin, one of the proteids of blood-plasma and
of lymph, (n) Fibrinogen is the plasma or lymph-proteid which
is coagulated or precipitated under the influence of fibrin ferment
and the calcium salts. The coagulated form probably somewhat
modified chemically is called fibrin, (in) Myosinogen, the prin-

CLASSIFICATION OF PROTEIDS. 273

cipal proteid of living muscles. It coagulates after death and is
in its modified form called myosin, (rv) Myo-globulin, associated
with myosinogen in the composition of muscle-tissue, (v) Globin,
one of the constituents of haemoglobin, (vi) Vegetable globulin,
there are probably several forms.

b. Combined Proteids.

1. Nucleo- Proteids. — These bodies are native compounds of
nuclei n with proteid. The nuclein contains phosphorus, hence all
nucleo-proteids contain phosphorus, most of them contain iron, (i)
( '<is< in, the principal proteid of milk. In the non-coagulated con-
dition it is usually called cuseinogen. (n) YiteUin, the principal
proteid of egg-yolk, (in) Nuekin, or cell-nudein, the chief pro-
teid of the nuclei of animal and vegetable cells.

2. Chromo-Proteids are native compounds of a proteid with
an animal pigment : (i) Hcemoglobin, globin with hsematin in a
true chemical combination. The pigment is hsematin which con-
tains iron. (n) Histo-ha matin, tissue hsematin especially the
hsematin of muscle tissue, also called myo-hsematin.

e. Derived Proteids.

To this class belong all of those modified proteids which are de-
rived from native or combined proteids by physiological processes.

1. Albuminates. — These bodies are derived from the native
proteids through the action of an acid or alkali, (i) Acid-
albumin, formed in the stomach by the action of HC1 or other
aci<! upon albumin. Syntonin is a corresponding variation of
myosin, (n) Alkali-albumin, formed in the small intestine by
the action of the alkaline pancreatic juice upon the native proteids
of the foods.

2. Proteoses and Peptones. — These substances are derived
from oative proteids, or from albuminates by hydrolysis, prob-
ably by a hydrolytic cleavage of proteid- especially of the al-
buminate derivatives of native proteids.

'/. Albuminoids.

These substances are closely related chemically to the other
proteid- and are derived from the native proteids by metabolic
process* s.

1. Native Albuminoids. — These include those albuminoids
which exisl normally in the animal body, (i) Collagen. The
substance of which white fibrous connective tissue is composed.
It is also ;i constituent of bone and of cartilage, (n) Elaetin.
Ili'- substance of which yellow, elastic fibers of connective tissue

i- formed. (m) Mucin. The chief constituent of the secretion

]-

274 DIGESTION: INTRODUCTION.

of mucous glands and an important constituent of the secretion of
all of the digestive glands. It is a combination of a proteid with

a carbohydrate and has been classified among the combined pro-
teid- as a glyco-proteid. (iv) Keratin. The horny material which
is characteristic of the corneous layer of the epidermis, of nails,
hair, horns, hoofs and feathers. Keratin has a much larger pro-
portion of sulphur than other proteids have. Neuro-keratin is
found in the medullary sheath of nerves.

2. Derived Albuminoids. — This class contains one example
namely: (i) Gelatin, which is derived from <-(>ll<t<i<n by hydration.
It is an artificial product and is prepared by long boiling of any
of the connective tissues of the animal body. The collagen at first
insoluble, becomes hydrated and soluble gelatin, which on cooling
sets into a jelly. When the excess of water evaporates the mass
is amorphous and vitreous. It is soluble in hot water, indiffusi-
ble, gives most of the general proteid reaction and what is of great
importance is digestible. It follows the general course of proteid
digestion and is absorbed as gelatin-peptone. This gelatin-pep-
tone can be katabolized in the tissues but it can not be built up
into tissue protoplasm. Its importance in nutrition will be dis-
cussed under metabolism.

Protenoid Substances.

Enzymes. — The origin and the behavior of unorganized fer-
ments leave little doubt that they are of the nature of proteids,
perhaps typical proteids. Among the unorganized ferments
may be mentioned : (i) Thrombin ; (n) rennin ; (in) ptyalin ;
(iv) pepsin ; (v) trypsin; (vi) amylopsin ; (vn) steapsin ; (vni)
iuvertin.

5. FERMENTS AND ENZYMES.
a. Ferments in General.

Every living cell has the power to cause chemical reactions.
Food materials are absorbed by the cell and are either first built
up into protoplasm by a series of anabolic reactions, to be later
subjected to a series of katabolic reactions, or directly subjected
to katabolism. A tissue cell of a complex organism selects from
the tissue plasma which surrounds the cell, the materials which
are to enter the series of metabolic changes. A unicellular organ-
ism -elects the materials from the liquid or other medium which
immediately surrounds it. The materials so selected may be
called the cell-foods. The foods selected by different one-celled
organisms are as different as the heredity and environment of the
organisms.

Whether or not the food must be built up into living protoplasm

FERMENTS AND ENZYMES. 27.")

before it can be broken up into simpler bodies is still a matter of
controversy. There is no doubt, however, that sooner or later all
of the material absorbed by the living cell must be katabolized or
broken up into simpler compounds.

After a certain number of katabolic changes the organism seems
to have exhausted the energy of the material as far as it is capable
of doing so. The final products of the katabolism (katabolites)
are useless to the organism and are rejected (excreted). Among
the katabolites are : CO., H20, NH3,CH4, H„ H.,S.

These all represent compounds or elements whose energy is
practically exhausted. There are many cell katabolites which
are more or less complex and represent much energy : Sugar,
Alcohol, Acetic Acid, Butyric, etc., etc.

Among the above mentioned katabolites are several which are
gaseous. If these gaseous materials are given off in sufficient
quantities they escape in bubbles. If the unicellular organism,
• '. ;/., the yeast cell, is living in nutrient fluid containing sugar
— dextrose — it will take up the sugar, and will excrete alcohol and
( < >_.. Tin' ( '< >2 escapes in gaseous form. The observation of this
phenomenon gave rise to the term fermextatiox. The organism
which causes the fermentation is called a FERMENT. In the light
of the chapters on general or cellular physiology and of the intro-
ductory statements above it must be evident that fermentation is a
phase of cellular nutrition. The term has been extended to include
all of those phases of the nutrition of u ni<-</t 'n(tt /■ organisms which irt-

,-oln the consumption of complex substances and the excretion of sim-
pler ones. The term ferment is applied to all the unicellular organ-
isms which cause fermentive or putrefactive changes. As examples
of these organisms one may enumerate: (r) The yeast plant,
8accharomyces cerevisice, which consumes sugar and excretes alcohol
and ('()_,. (n) The Bacterium lactis which consumes milk-sugar
and water and excretes lactic acid (CyBL^Ojj-f H20= 4 C3H 03.
'Hi) The Mycodermi aceti, which consumes alcohol and oxygen and
excretes acetic acid (C2H60+0=H20+C3H402). (rv) Pasteur's
Fermentum butricum, one of the vibriones, which consumes lactic
acid, malic acid, tartaric acid, or mucic acid and excretes butyric
acid, with a combination of various accompaniments (CO,, ELO,
II . or acetic acid) according to the food consumed, (v) The
Vibrios which consume proteid matter and produce in a liquid
containing it what is known as putrid fermentation or putrefaction.
Among the excreta may be enumerated : Leucin, tyrosin, for-
mic, acetic, proprionic, butyric, valerianic, caproic and oaprylic
acids; ammonia, ethvlainine, propylamine, trimethylamine, CO

II S, II and N.

All of the ferments enumerated above are micro-organisms*
the Baccharomyces being a unicellular fungus and the remaining

L'TU DIGESTION: INTRODUCTION.

examples being bacteria. These organisms, though perhaps Less
sensitive to variations m the supply of oxygen than most living
things, nevertheless arc much influenced in their activities by
the presence <>{' five oxygen. The subject was most exhaustively
studied by Pasteur. Summing up his studies Pasteur said (Comp^
Rend, de 1' Acad. des Sci., Vol. 7.",, p. 784): "The weight of
yeast which is produced under these conditions (i. e., in the pres-
ence of free oxygen gas) during the decomposition of sugar in-
creases progressively, and approaches the weight of the decom-
posed sugar, in exact proportion as its life goes on in the presence
of increasing quantities of free oxygen gas.1 Guided by these
facts L have been gradually led to look upon fermentation as a
necessary consequence of the manifestation of life when that life
goes on without the direct combustion due to free oxygen. We
may see as a consequence of this theory that every organism, every
cell which lives or continues its life without making useof atmospheric
air, or which uses it in quantities insufficient for the whole of the
phenomena of its own nutrition must j)o.w.ss the characteristics of a
ferment with regard to the substance which is the source of its total or
complemental heat."

Thus saccharomyces supplements the energy liberated through
oxidation of its own tissues with free atmospheric oxygen, by
energy liberated through katabolism of sugar. Some organisms,
notably the vibriones, dispense with atmospheric oxygen alto-
gether, carrying on all their life activities with the energy
liberated through the katabolism of proteids.

b. Enzymes.

In our discussion of ferments we have mentioned only elemen-
tary unicellular organisms. In every case the organisms recog-
nized as ferments live in a fluid or semifluid medium. Their
pabulum is readily absorbable by the organism. We come now,
however, to the consideration of Nature's method of adaptation to
new conditions. In a grain of corn or barley the embryo plant is
imbedded in a quantity of starch stored up by the parent plant
for the nourishment of the germinating plantlet. Though the
food supply surrounds the embryo it is an insoluble and unab-
sorbable solid.

How is it to be made soluble and absorbable? The cells of the
embryo secrete diastase which brings about the hydrolysis or hydro-
lytic cleavage of the starch molecules changing them to dextrose which
is soluble ami absorbable. The plant kingdom abounds in similar
examples. Diastase and similar substances are called ferments or

1 " In fermentation without oxygen, the rutin between the sngar decomposed,
and the yeast formed, is from 60 or 80 to 1, while in fermentation in the presence
of oxygen it is onlv 4 or 10 to 1."

FERMENTS AND ENZYMES. -"

Enzyme*. It is not alive ; it is not organized, and has, therefore,
been called an unorganized ferment. The distinction between an
organized and an unorganized ferment, or between a ferment or-
ganism and an enzyme, may be more apparent than real. It is
most probable that the distinction is simply one of location of the
reaction, i. e., (i) intra-ceUular fermentation caused by an enzyme
upon absorbed substances ; (n) extra-cellular fermentation caused
by an enzyme upon nnabsorbed, nnabsorbable substances.

But animal cells produce enzymes also. When solid food is
taken into the alimentary tract it may be insoluble and unab-
BOrbable, as is the ease, for example, with starch and lean meat.
Unless these foods be rendered soluble they will be useless to
the organism. Specialized cells along the alimentary canal secrete
enzymes which bring about the hydrolytic cleavage of the food-mole-
cules changing them to forms which are soluble and absorbable. The
specialized cells in question do not absorb the products of fer-
mentation (digestion). Other cells and specialized tissues absorb
the nutriment which is distributed throughout the organism by
still other organs and tissues. The cells which secreted the
enzyme finally receive their sustenance from the common treasury
— the blood.

Enzymes may be classified as follows :

1. Amylolytic Enzymes. — Diastase, Ptyalin, Amylopsin, which
change starch to maltose or dextrose, dextrine being an inter-
mediate substance. The ultimate change wrought in the starch
may be summed up in the following equations : (C6H10O5)n-|-
iill ( ) = nC6H12Og, dextrose or in the following equation:

(c6h10o6)»+|h2o=|c12h22ouj

Starch + water = maltose.

Tin- steps of this process have been studied by numerous inves-
tigators. Neumeister'a results will be given later under salivary
digestion. The steps of the process for ptyalin or amylopsin are
probably, in a general way, typical of all enzyme action.

•_'. Inverting Enzymes. — The Tnvertin which the yeast plant
secretes for splitting cane-sugar into dextrose and levulose may
be cited as an example. A similar enzyme, secreted iii the small
intestine, changes cane-sugar and maltose to dextrose.

Proteolytic Enzymes. — The Pepsin, secreted in the stomach,
and the Trypsin, secreted by the pancreas, represent this class.
They acl upon proteids, converting them into peptones through
several intermediate steps.

1. Fat-splitting Enzymes. — An example of this is the Steapsin
of the pancreatic juice. It acts uponfal causing each molecule to

278 DIGESTION: INTRODUCTION.

take up three molecules of water and split into three molecules of
fatty acid and one molecule of glycerine.

"). Coagulating Enzymes. — Such as Rennin and Thrombin,
the first precipitating caseinogen as casein and the second precipi-
tating fibrinogen as fibrin. Note (he radical difference between
the firsl four classes and the hist class. The first four classes
change insoluble substances to soluble ones ; the fifth class
changes soluble1 substances to insoluble one-.

c. Conditions of the Activity of Ferments and Enzymes.

(a) The Optimum Temperature is 35 c C. to 1<> C, while

the maximum is below the boiling point, the enzymes being de-
stroyed by boiling. The action of enzyme-, is progressively Less
as the temperature falls from the optimum, being completely sus-
pended by a zero temperature.

(6) The Enzyme is not Quantitatively Involved in
the Reaction which it causes. The quantitative relations be-
tween AgCl precipitated from a solution of chlorides by a certain
amount of AgN< )., is definite and unvarying. Time is not a factor
in the amount of AgCl thrown down. An enzyme, however, can
work a greater change in two hours than in one. The smaller the
amount of enzyme the longer the time it will require to work a
particular change. Just what part the enzyme plays in the reac-
tion is unknown. If it enters into the reaction by being molec-
ularly incorporated in certain stages of the process it is later dis-
engaged in its original form and may repeat its hydrolytic change
upon fresh molecules of the pabulum. This repetition is not with-
out limit, however ; the enzyme becomes exhausted after a while
and is no longer able to excite the reaction.

(c) Another Condition of the Action of an enzyme which
is of the greatest importance to the higher organism is the inhibi-
tory influence of the accumulation of the products of enzyme <irti<n>.
When peptones have reached a certain degree of concentration
they stop the further action of the enzymes until the product
already formed is removed (by absorption), when the enzyme re-
sumes activitv. The pathogenic germs which often threaten hu-
man life are inhibited by the accumulation of their own excreta.
If a modified form of this excretion be introduced into the organ-
ism in the early stages of the development of the micro-organism,
its activitv (virulence) can be much weakened or completely
aborted. The whole system of serum therapy, for example, with
antitoxin, etc., depends upon this fundamental principle.

FOODSTUFFS AXD FOODS. 279

E. FOODSTUFFS AND FOODS.

1. DEFINITIONS.

Gould defines foodstuffs : "The materials that may be employed
for the purpose of nourishment and tissue-formation." The same
lexicographer defines foods : " The substances ordinarily employed
as aliments." This distinction is not as clear-cut in the defini-
tions as it is in use. The term foodstuff is employed as a generic
term including all of those chemical compounds, " proximate
principles of the older physiologists," which maybe employed for
the nourishment, growth and repair, of the organism.

Examples : Starch, sugar, fat, albumin.

A food is an article of diet which may be composed of one or
more foodstuffs : Bread, composed of starch, glutin, fat, inorganic
salts, water, etc., etc. Beefsteak, composed of various proteids,
fats, inorganic salts, water, etc. ; Potatoes, composed of starch,
proteid, salts, cellulose, and water.

2. CHEMICAL COMPOSITION OF MILK AND OF THE
ANIMAL BODY.

How shall we obtain a comprehensive idea of foods and food-
stuffs '? Nature furnishes every young mammal with a food —
milk — which most perfectly satisfies the requirements enumerated
above, growth and repair, and whose analysis may give us a clue
to the chemical characters that foodstuffs should possess :

Water 87. %

( betnioai m ih i v
of milk.

Solids. -

r PrntPids f Caseinogen.

1101,1,1 s- ( Lact-albumin. 4. $

Organic. fOlein, .43 "i

| Palmitin, .33 ,,„,

Fats. | Stearin, .16 \ > ' , f,

I Bui j 'in, < aprioin, | '

I. Caprilin, .07 J

Carbohydrates Lactose. 4.4$

L Inorganic:— CaHP04, CaC03, Na< I, MgCl2, etc. O.G^

When we compare the chemical constituents of the mammalian
body with the chemical composition of that food — milk — which
nature furnishes to young mammals, we find an exact correspond-
ence in the general constituents, i. e., each contains water in large
proportion, proteids, fats, carbohydrates and salts, composed largely
of phosphates, chlorides and carbonates. The mosl noticeable
difference between the two lists is the great variety <>f proteids in
the mammalian body, while there arc only two or three varieties
in milk. If, of a family <>f young mammals, a part be sacrificed
to chemical analysis at birth and the resl after their period of
growth on a milk diet, the results of the analysis will be prac-
tically identical qualitatively, but all of the constituents will be

280

i>i<;i:sti<>\: INTRODUCTION.

found much greater in quantity in those which have had the milk
diet. Such an experiment demonstrates conclusively that out of a
few kinds of proteids many kinds may be built up.

The following table giving the chemical constituents of the
animal body will show what the carnivorous animal eats.

Chemical

Composition

of the

Animal

Body.

Water ;,i , 67

Solids. J

Organic.

Albumins

< rlobulins.

Serum Albumin.

Myo-alburnin.

Serum Globulin.
Fibrinogen.

Myosin.
Myo-globulin.
< rlobin.
Crystallin.

N:icli'o-| r iti 1 Is \ucli in

Proteids.

( Ihromo
Proteids

Haemoglobin.
His tc-Hae matin.

f Collagen.

Albuminoids. J Elastin.

i Mucin.

I. Keratin.

Thrombin.

Rennin.

Ptyalin.

Pepsin.

Trypsin.

Amylopsin,
| Steapsin.
L Invertin.

Fats

Enzymes.

C Palmitin.

Sharin.
I l Hem, etc.

Carbo f Glycoses: — Dextrose,

hvdrates 1 Saccharoses :— Lactose, during lactation.

( Ainyloses : — Glycogen.

Inorganic.

XaCl, CaHT04, CaC03
K< 1. < a3(P01),, Na„COa
MgCl2, Nas IIPo,, NaHCOa
CaCl2, XalloPo,.

Fe in organic com-
bination in hitma-
tin and tissues in
general.

As the next step in our discussion let us make a list of those
ingested by a carnivorous animal. The wolf or fox catches and
eats rabbits or birds. This food of the carnivorous animal has
already been analyzed and we see that it corresponds in every re-
spect to the body which it must nourish. Our first and most nat-
ural thought is that the proteids of the rabbit become the proteids
of the wolf, kind for kind, i. <\, the myosin or muscle-proteid of
the rabbit becomes the muscle-proteid of the wolf. But this nat-
ural inference is fallacious. All proteids are, during digestion,
reduced to peptones from which, after absorption into the circula-
tory system, the various proteids of the carnivorous animals are
built up. If there be an excess of proteid in the blood this excess
may be deposited in the changed form of fat. Further, the quality
and quantity of fat in the wolf does not correspond to the quality
and quantity of this constituent in the rabbit. The only infer-

IXORGAXJC FOODS.

2S1

ence possible is that the rabbit fat, after being taken up into the
blood of the wolf, is partially consumed in Borne metabolic process
and partially deposited, but the several constituents — olein, pal-
matin and stearin — are deposited in a new proportion peculiar to
the wolf. Similar observations and conclusions might be made
regarding the carbohydrates. But where does the rabbit obtain
this ample list of constituents '? He does not get his food so nearly
prepared as does the fox. He eats only herbaceous material — he
is herbivorous. His diet of barks, vegetables and tender herba-
ceous shoots, if subjected to chemical analysis, will be found to
contain, besides water, very large quantities of carbohydrates and
very small quantities of fats and proteids. Among the carbohy-
drates the principal constituent is cellulose, though there is also a
small quantity of glucose and starch. The wolf is quite unable
to accomplish the first step in the digestion of cellulose.

3. CLASSIFICATION OF FOODSTUFFS.

Foodstuffs.

Inorganic.

Organic.

Carbohy-
drates.

Fate.

Proteids.

NaCl, Kd.

Xa„i 0,Ko(0„ MgCO,.

Na-SO*, K„s<i,. HgScL

NaJll'o./K'Jil'o,, MgHPO«, CaHPO*.

Xa, K, fa, etc., combined with fruit acids: I Tartaric,

citric, malic, etc ).
Fe combined with animal proteids (Haemoglobin)

and with vegetable compounds (Chlorophyll).

Amylosea

Saccharoses.

Glyooses.

(Starch.

Glycogen.
(.Cellulose.

I ( lane Sugar.
- Lactose.
I Maltose.

( Dextrose.

l.<\ ulose.
I Galactose.

( I'alniil in.

Stearin.
I Olein.

f Albumins. I

Globulins. Animal and vegetable varieties.

Nucleo-Frotetds. I

Chromo-Prol

Albuminoids, ( lollagen. etc.
Derived Albuminoid-) relatin.

I. FOODS'
[. INORGANIC FOODS.

a.

Water.

Water comprises between r> t per cent, and rO per cent, of the
mammalian body. It Le a general solvenl and diluent. All of

'In the preparation of this section I have drawn freely upon Dr. W. Oilman
Thompson' i admirable work on Practical Dietetics. ( I >. A. <v Co., L893. |

282 DIGESTION: INTRODUCTION.

the secretions of the body arc composed very largely of water. It
is an absolutely indispensable food. An adult requires from
2000 c.C. to 2500 C.C. every 24 hours. Of this about .1 is taken
in the form of liquid food (soup and beverages), leaving about
600 C.C. to 800 c.c. (3 to 4 glasses) per day to be taken as " drink-
ing-water." Many people take much less water than this. "One
of the most universal dietetic failings is neglect to take enough
water into the system." (Thompson.)

One of the most important uses of water is as a thermolytic
agent, regulating the body temperature through distributing the
body heat, and through liberating heat from the surface of the
body by evaporation of perspiration.

Beverages are drinks which represent aqueous solutions or dilu-
tions of various organic, usually vegetable products : tea, coffee,
cocoa, chocolate, lemonade, and allied drinks, cider, beer, ale,
wine, brandy, etc. They serve to relieve thirst, as nutrients, as
diuretics, as diaphoretics, as diluents, as demulcents, as tonics, as
stimulants, as intoxicants.

Some of these offices are necessary, some are permissible, while
some are not, from a physiological standpoint, permissible.

b. Salts.

Salts in general serve the following uses in the system :

1. "To regulate the specific gravity of the blood and other
fluids of the body."

2. " To regulate the chemical reaction of the blood and the
various secretions and excretions."

3. " To preserve the tissues from disorganization and putrefac-
tion."

4. " To control the rate of absorption by osmosis."

5. " To enter into the permanent composition of certain struc-
tures, especially the bones and teeth."

6. "To enable the blood to hold certain materials in solution."

7. " To serve special purposes, such, for example, as the influ-
ence of sodium chloride on the formation of hydrochloric acid,
and that of lime salts in favoring coagulation of the blood." — (W.
G. T.)

As a rule, little care need be given to the salts, because the
vegetable and animal foods of a mixed diet all contain salts, mak-
ing, when taken together, a list sufficient in quantity and quality,
with the single exception of the sodium salts. Plants are espe-
cially rich in potassium salts and comparatively poor in sodium ;
thus herbivorous animals need more of the sodium salts, especially
sodium chloride, than appears in the vegetable diet, and to this
end eat earths rich in these salts — thus have been established the
"deer-licks," visited by the herbivora of a whole region.

ORGANIC FOODS.

283

( arnivora seem to get a sufficient supply of the salt? from the
flesh of the herbivora which they consume. Omnivora need sup-
plementary sodium salts in proportion to the part which vegetables
play in their diet. Vegetarians need extra sodium chloride. Cer-
tain disturbances of nutrition (anaemia, rachitis, etc.) arise from
or result in a deficiency of certain minerals or mineral salts. A
serious problem confronting- the clinicians has been to determine
the form of mineral nutriment best adapted to the animal organism
suffering from malnutrition. Whether the needed salts should
be given directly as such, or whether vegetable and animal foods
rich in the needed salts should be made predominant in the diet,
are the alternatives between which the clinicians wavered for
many years. The general consensus of opinion, as expressed in
practice, is in favor of the second alternative. Patients who need
more iron are given eggs, lean meats, cereals, peas, beans and
"greens" rich in chlorophyll. Patients who need bone-making
salts are given, among other foods, an abundance of milk, which
contains calcium salts in a form and proportion which seem best
adapted to the system.

II. ORGANIC FOODS.
IA. VEGETABLE FOODS.

In these bodies the carbohydrates predominate. The following
table of analysis by Dr. C. E. Woodruff, Asst. Surgeon U. S.
Army, gives vegetable foods with the constituent foodstuffs and
energy represented :

I OOD.

Sn.'ar
Bj nip

Tapio
Cornstarch j

Macaroni

I Imir

< ornmeal
Oatmeal
Beam '.i pea*

Onion*

W i 0:1:. PRO! BIDS. I a re.

13.7

2.0

12.4
18.1
12.6
15.0

7.U

)•_'.<;
78.8

7.1

9.0

11.0
9.2
1 5. 1
23. 1
2.1
I.)
2.1

0.4
0.3
1.0
8.8
7.1
2.0
0.1
0.3
0.6

Carbo-
hydrates.

97.8ji

;,.-,.n

97.8

79.4
76.8
749
70.6
68.2
59.2
17.'.)
10.1
5.5

s ii/rs.

0.2%

•j.:;

0.4
0.8
0.5
l.l
2.0
3.1
L.O
0.6
1.1

Energy in k ilo-
Calories per lb.

1820 Calorics

1023

L820

L630 "
1 106
1644

1645 "
1850 "
1615

375

225

155

a. Sugars.

Tlii- general sub-class of the carbohydrate foodstuffs has the
great advantage thai it requires little or n<> digestion, may be
directly absorbed and scry readily assimilated. The most com-
mon food-sugars ares Cane-sugar, glucose, and milk-sugar.
Cane-sugar or saccharose is derived from the sap of sugar-cane,
beet-roots, and maple trees. Glucose or dextrose is manufactured

284 DIGESTION: INTRODUCTION.

from Btarch, make- a prominent constituent of powdered sugar and
i- used in the table syrups. It is the most common fruit and vege-
table sugar; in grapes, cherries, figs, dates, bananas, onions, tur-
nip-, cabbage, etc.

Milk-sugar or lactose constitutes about 4 per cent, of cows' milk
and is usually used only in milk. Honey is a natural Byrup
formed by flowers and collected by bees. Konig's analysis gives :
Water, 16.13 per cent. ; fructose, 78.74 per cent. ; saccharose,
2.69 per cent. ; nitrogenous matter, 1.29 per cent.; salts. 0.12
per cent.

6. Foods in which Starch Predominates.

1. Cereals. — These comprise grains including wheat, corn, rice,
rye, oats, barley. The cereals with potatoes form the most com-
mon source of starch. The cereals are usually used in the form
of meal or flour. Xot only do the cereal- contain considerable
proteids with some fats, but in the preparation of these meals and
flours for eating it is customary to make important addition- in
the form of milk, eggs and fat so that the resulting preparation is
a complex food which generally represents all of the foodstuffs in
a proportion approaching that of a typical diet.

The following table illustrates this as far as it concerns bread
and crackers.

Composition of Beeads and Crackers (Clark quoted by

Thompson).

Food.

Water.

XlTRIENTS.

Proteids.

Fats.

Carbo-
hydrates.

Salts.

Wheat bread.

B.S

1.9

■

1.0*

Graham bread.

:;4.'J

65. -

9.5

1.4

.-,::.:;

1.6

I: v.- bread.

30.0

7m.ii

8.4

0.5

59.7

1.4

Soda < Trackers.

8.0

92.0

10.3

9.4

70.5

1.8

(irahaui

5.0

95.0

9.8

13.5

69.7

2.0

oatmeal "

4.9

'.'."".. 1

10.4

13.7

69.6

1.4

Oyster "

3.8

96.2

11.::

4.-

. . .5

2.6

Oraham bread

100*

14.-

oo 2

83.7

To compare
nutrients

the
of

Tv| icil lit
nutriment.

100;t

17.5

-.4

I
73.8 (

graham bread
wiib a typical
diet.

2. Other Starchy Foods. — Tapioca and arrow-root are pre-
pared from the root-stalk> of certain tropical and subtropical
plants. Sago is extracted from the pith of certain tropical palms.
Tapioca and sago are practically pure starch, while arrow-root
contains II <> 15.4 per cent., proteids 0.8 per cent., and starch
s:;.:; per cent.

3. Legumes. — Beans and peas contain, besides a large amount
of starch, so large a proportion of proteids that they may be used

GREEN VEGETABLES.

285

as one of the recognized sources of proteids, though the animal
foods form the most important source of proteids.

4. Roots and Tubers. — White potatoes, sweet potatoes, beets,
carrots, parsnips, turnips, radishes, etc., represent this class of
vegetable foods. All of this class are rich in salts, especially the
salts of potassium. The nutrient portion of potatoes consists
largely of starch ; while in the other vegetables enumerated it
consists chiefly of sugar.

The following table, combined from analyses by Letheby and
by Konig, gives the nutrient values of the

Roots and Tubers.

l""ODS.

Water.

Proteids.

Fats.

Sugar.

Starch.

Cellu-
lose.

Salts.

Anal-
yst.

white).

75.04

2.10

0.2

3.2

18.8

0.7

Letheby

sweet i.

67.5

1.S

0.3

10.2

16.0

6.45

2.6

Pa ven

Parsnips.

82.0

1.1

0.5

5.8

9.6

1.0

Letheby

<arr..t>.

83.0

1.3

0.2

8.4

No -tarch

1.0

"

< >ui"ii>.

86.0

1.86

0.1

2.8

"extractives"

-

0.7

0.7

Konig

Beet-rcM,t.

S7.1

1.4

0.6

1.0

0.9

«

" Extrac-

Turnips.

91.2

1.0

0.2

4.1

tives" 1.9

0.9

0.75

All of the foods in the above table are preserved for use in win-
ter, during which season the absence of green vegetables makes
them especially desirable and palatable.

5. Green Vegetables. — These are used mostly " in season."
Tiny represent very little nutriment but serve rather to sharpen
the appetite for heavier foods. Spinach is rich in iron and is an
especially fine food for use when more iron should be introduced
into th<- system.

Lettuce and celery both act as sedatives on the nervous system.
Rhubarb has a laxative action, while asparagus acts as a diuretic.
The following table gives analysis of a few of the more important
green vegetables.

Composition of Gbeek Vegetables (Konig, <| noted
by W. G. T.).

U aiii:

1 ' 1 : - ■ X 1 II.-.

Fair

Ml.

1 CTBAO-
i [ON.

i i i i i -
i ..-i

Salts

■

-11

i. a

0.4

11.0

l.i

1

BO.O

1.9

0.2

1.8

90.4

2.8

0.4

1 ..:

2 1 :

0.9

0.0

0.1

1.94

2.0

0.4

l.i

i i

21.9

0.7

i 0

286

DIGESTION: INTRODUCTION.

To this same class belong cucumbers, egg-plant, pumpkin,
squash, and vegetable marrow.

6. Fruits. — The following table gives the composition of the
principal fruits \\>a\ in this country:

Fruits.

:-

.;

C -'

y. 5

■j:

3 M

z -

--

■/'.

I'kiit.

i

- —

-
Z

1 i:i i Ai n.s.

y- -/.

- _

'il

pa

-

-
<
■I.

-

-

3

fc

_

o

i.pple.

83.6 £

0.4

7.7

0.8

5.2

2.0

0.3

Bauer.

Pear.

83.0

0.36

8.26

0.2

:;.:,!

1.::

0.3

"

Peach.

83.0

0.65

4.5

0.9

7.2

6.06

ii.T

"

( ir;i|ic.

78.2

0.6

14.36

0.8

1.96

::j;

0.5

••

Strawberry.

87.66

1.1

6.3

0.9

0.5

•-'.:;

0.8

"

Currant.

34.8

0.5

6.4

2.15

0.9

4.6

0.7

"

Orange pulp.

89.0
19.9

0.7

2.1

4.6

32.2

2.44

0.9

11.:;

1.8
0.6

0.5

l.f,

Fat.

Cherry.

0.3

Yeo.

Raisin.

32.0

31.2

2.4

4.0

57.26

49.8

0.5

4.5

i.;

5.0

1.2
2.86

"

Fat.

.V in.

Fig.

1.44 | 1.2

"

Thompson gives the following list of uses for fruits :

(a) " To Furnish Xutrimp:nt." — The nutriment is chiefly

found in the sugar. The most nutritious fruits are : fig, prune,

grape, date, banana, cherry.

(6) "To Convey Water to the System and Relieve

Thirst." — Besides melons, the orange, lemon, grape, and pear

seem best adapted to this purpose.

(c) "To Introduce Various Salts and Organic A« ros
Which Improve the Quality of the Blood and React
Favorably Upon the Secretion." — The salts of especial im-
portance are citrate, tartrate and malate of sodium and potassium.
Citric acid and the citrates predominate in lemons and oranges ;
tartaric acid and the tartrates in grapes, and malic acid and the
malates in apples, pears, peaches, apricots, gooseberries, currants
(and rhubarb). The alkalinity of the blood and secretions is
increased with a fruit diet, owing to the release of the K and Xa
from the organic acids and their combination as carbonates, phos-
phates, etc.

(The tomato is really a fruit, though in the diet it is associated
with the green vegetables. It contains oxalic acid, which i- in-
jurious in uric acid diathesis.)

(d) T<> Serve as Therapeutic Agents. — (i) "As anU-

ANIMAL FOODS. 287

scorbutics; (n) as diuretic*; (in) as laxatives and cathartics" The
antiscorbutic action of such fruits as apples, lemons and oranges is
due to their abundance of the salts of potassium, magnesium and
calcium. The diuretic action of fruits is due in part to the water
which they contain. The citrates which oranges and lemons con-
tain are especially stimulating to the action of the kidneys. The
laxative action of fruits is best marked in apples, figs, prunes,
dates, grapes, peaches and berries.

(e) Fruits "Stimulate the Appetite, Improve Digestion,
axd Give Variety to the Diet." (Quotations from G. W.
Thompson.)

IB. FATS AND OILS.

These important foods are found both in the vegetable and in
the animal kingdom and may be considered here. Twenty per
cent, of the normal body weight consists of fat. This is in small
part derived directly from the fat of the food, but rather from the
sugars and starches, with a small portion from the proteids.
Most of the ingested fat is oxidized at once and supplies a con-
aiderable part of the animal heat. One may thus summarize the
uses of the fats. The ingested fats serve :

(a) " To Furnish Energy for the Development of
Heat."

(b) "To Spare the Tissues from Disintegration, for al-
though their combustion in the body results largely in the pro-
duction of heat, they also take part to some extent in tissue for-
mation."

The deposited tat- serve :

(<■) "To Store Energy ix Potential Form."

('/ ) " Through the Subcutaneous ( !oat of Adipose tissue,
to conserve the heat of the body."

(') "To LUBRICATE and make more plastic various structures
of the body and give rotundity to the form." (Quotations from
W. <i. T.)

The must important vegetable oils are : Olive oil, cotton-seed
oil, used in dressings and cooking, and the oil of nuts.

Animal tin- and oils are: Butter, cream, suet, lard, and the
tiit- of beef, mutton, pork and fish. The yolk of eggs is also rich
in oil.

\C. ANIMAL FOODS, IN WHICH THE PROTEIDS
PREDOMINATE.

The animal food- presenl ;i much Less extensive variety than do
the vegetable food-. The most important animal food is that one
which nature preparee tor nil young mammals, viz., milk.

288

DIGESTION: IXTRODrCTlOX.

a. Milk.

One analysis of cow's milk ( 'liungc's) was given at the head of
this section.

The following table gives the analysis of cow's milk and human
milk by A. H. Leeds. (Quoted from \Y. G. Thompson.)

"Soi m> Daisy Milk."

Human Milk.

Reaction.

Faintly acid.

Alkaline.

Specific gravity.

1029.7

L031.3

Bacteria.

Alwavs present.

Absent.

Fats.

::.7.".

4.1:5

Lactose.

1.42

7.0

Proteids.

3.76

2.0

Salts.

0.68

0.2

Total Solids.

12.61 £

1.; 33

Water.

87.39 $

si;.);;.

Thompson enumerates the following as " the more important
uses of milk ":

1. Purely as Food : (d) " As Infant Food."
(6) " As a Food for Adults."

(c) " As A Source of special food products and derivatives
such as cream, butter, cheese, buttermilk, koumiss."

(./ ) " As a Most Important Constituent in various com-
posite foods, as bread, omelet, etc."

(e) As a Vehicle for the administration of other foods for in-
valids, e. g., egg-albumin, beef meal, cocoa, meat juice, peptonoids,
etc., etc.

2. Therapeutic Uses of Milk : (/) " As a Diuretic."

(//) " For its Soothing Effect on diseased mucous mem-
branes of the alimentary canal."

(A) "To Loosen a Cough (when given hot)."

(j) " For Rectal Injection," really a food in this case.

fk\ " As a Vehicle for the administration of medicines. The
following table gives the constituents of the more important de-
rivatives of milk."

Food. Water.

Proteid. Fat.

Sugar.

Salts. Analyst.

Milk. M..s
Skimmed milk. 88.
(ream. 66.
Cheese. 36.8
Butter. 6.0

1.

4.

2.7

33.5

0.;;

;:.;

1.8

26.;

24.3

lil.o

4.8
5.4
2.8

0.; Parkes.

0.8

1.8

5.4

2.;

b. Eggs.

Milk is nature's food for young mammals, and eggs are nature's
food for young birds. Both of these natural foods contain all of

MEATS. 289

the foodstuffs necessary for a developing animal. Bauer gives
the average weight of the hen's egg as 50 grammes, of which the
shell represents 7 gms. or 14 per cent., the white 27 gms. or 54
per cent., and the yolk 10 gms. or 32 per cent. Parkes allows
only 10 per cent, of the weight for the shell, the yolk and white
together being composed of: Water, 73.5 per cent. ; proteids,
13.5 ; fats, 11.6 ; and salts, 1 per cent.

Eggs represent a concentrated diet, and though they contain
considerable fat they are classed as a proteid food. Egg-albumin
digests more easily in the natural uncooked state than when
coagulated by cooking. Raw eggs are, however, quite un-
palatable to most people and it is customary to cook them. Egg-
albumin begins coagulation at 56.5° C. (about 134° F.) and the
process progresses to about 70° C. (or 160° F.). If the tem-
perature is raised to the boiling point the albumin becomes very
densely coagulated and difficult of digestion. The most prevalent
method of eating eggs is in various milk compounds : omelet,
.-(•rambled, custards, etc., etc.

This mixing of the egg with milk seems to correct the difficulty
of indigestible coagula, besides making a most palatable food.

c. Meats.

We generally rely upon the lean meat of various animals for our
supply of proteids, though it must not be forgotten that many of
the cereal.- and the legumes contain a very large proportion of pro-
teids ; a proportion quite sufficient to insure the proper nutrition
• >f the body without resort to the addition of lean meats. The
variety which i> giveu by the addition of meats to the diet would
justify it. however, even if there were no other reasons favorable
to it. Liebig said, " It is certain that three men, one of whom
has had a full meal of meat and bread, the second cheese or salt
fish (and bread), and the third potatoes, regard a difficulty which
presents itself from entirely different points of view." The ag-
gressive peoples of northern Europe and the western continent
are the meat-eating people of the world. Besides overcoming the
very great difficulties of a northern climate they have outstripped

their vegetarian competitors in almosl every field of human en-
deavor, -lu-t what gives to ;i meal diet this subtle influence is a
problem. Thai the influence exists is not a matter of controversy.
In it- extremes we see the difference in meat and vegetable diet

wrought upon the lion and the ox ; the vegetarian, tl l:Ii strong,

i- -low, clumsy and lazy ; the meat-cater quick, graceful and

alert.

The author doe- not wi-h to he understood to approve of an
exclusively meal diet. Man i- omnivorous. If meat makes too

1!)

290 DIGKSTlnS: ISTimltUCTION.

great a proportion of his diet disturbances of nutrition are almost
sure to manifest themselves.

The fact is, Americans and Englishmen eat rather too much
meat already.

We neeil meat, l>iit we do uot need it in immoderate quantities.

The following table gives the composition of some of the more
common meats (including fish and "shell-fish").

1 W \ 1 1 k. I'K'.i i n>~. Fat. ( A1:l;'-

III OB ITES.

-mi-. Ami.v-i.

Beefsteak.

:i.i

20.5

3.5

Fat beet

51.

1 1.8

29.8

I. .an beet

72

19.3

3.6

Fat mutton.

53.

12. 4

31.1

Lean mutton.

72

1-.::

4.9

Veal.

63

16.5

15.8

Fat pork.

39

9.8

4.-.'.!

Bacon.

15

B.8

7::.::

Smoked liam.

27.0

34.0

36.0

i lalves' liver.

72.3

20.1

5.6

Poultry.

74.

21.

3.8

\\ hite fish.

7-.

18.

■-'.'.i

Canned salmon.

63.6

21.6

13.4

Crabs.

-4.

15.

1.0

I >.. sters.

-7.

6.

1.2

1.6

4.4

Parkes.

l'avv.

L8

4.7

„

10.0 Parkes.

1.5 Payen.

1.2 Parkes.

1. Parkes.

1.4 Woodford.

5. PREPARATION OF FOODS.

Thompson says that, " it is owing to the practice of cookery
that the dietary of civilized man has been so much enlarged, and
that it covers a wider range of materials than that which serves
for the nourishment of lower animals."

The cooking of food serves the following purposes : (i) To ren-
der the organized structure of such foods as meats and vegetables
more tender, therefore, more easy to masticate and to digest, (ii)
To render the foods more palatable through the flavors developed
in cooking. Important as this is to those who have been used to
cooked foods it is easy to see that it might be quite unimportant
to the savage ; the Eskimo, for example, seem- to prefer his meat
raw. (in) To kill any parasites and germs which may be in the
food as received from the market.

The cooking is accomplished in the following general ways :
(i) boiling, (ii) -tewing, (in) steaming, (iv) frying, (v) baking,
(vi) roasting and broiling.

In boiling and stewing the cooking is conducted by a tempera-
ture which does not exceed 100° C. (212° F.). The two proc-
esses differ in this way: the food to be boiled is plunged into
boiling water, this coagulates or hardens the surface, thus retain-
ing within the mass the juices ; the food to be stewed is put into
cold water and the whole brought gradually to a boiling tempera-
ture, this process tends to extract the juices and to macerate the
tissues somewhat. During the period of cooking which follows

PREPARATION OF FOODS. 291

the above-described preliminary the two processes consist alike in
keeping- the temperature at 100° C. In steaming the food is sub-
jected to the steam which escapes from water boiling in an un-
sealed receptacle. The steam does nor exceed 100° C. The
effect is quite like that of boiling.

In frying the heat is transmitted to the food through the
medium of heated fat or oil. Fats used in cooking may be heated
to 400c F. before they begin to smoke. The food cooks there-
fore much more rapidly with this process than with those above
described. The fit may sear the outside of the food or may per-
meate it to a greater or less extent. In any case the digestibility
i- somewhat decreased, in some cases it may be very much so.

In baking, roasting, and broiling the heat, as it radiates from
coals or from stone or metal surfaces, is applied direct to the food.

The temperature may thus be much higher than that of boiling
water.

In a general way it may be said : (i) That all foods that are
cooked at all should be kept at 100° C. long enough to destroy
parasites and bacteria. ( u ) That e^, unless incorporated as con-
stituents in composite foods, should be cooked as little as possible,
the less the better. (in) That starchy foods should be very
thoroughly cooked, (rv) That meats in general should be cooked
just long enough to develop the flavors most agreeable to the re-
cipient.

DIGESTION.

A. SALIVARY DIGESTION.

1. THE SALIVA.

a. The Secretion of Saliva.

b. The < Iomposition of Saliva.

2. THE CHEMISTRY OF SALIVARY DIGESTION.

3. FACTORS WHICH [NFLUENCE SALIVARY DIGESTION.

4. MASTICATION.

5. DEGLUTITION.

B. GASTRIC DIGESTION.

1. Till". GASTRIC JUICE.

a. Tin. Secretion of Gastric Juice.

b. Thk Composition of Gastric Juice.

2. THE CHEMISTRY OF GASTRIC DIGESTION.

3. FACTORS WHICH INFLUENCE GASTRIC DIGESTION.

4. THE MOVEMENTS OF THE STOMACH.

5. VOMITING.

C. INTESTINAL DIGESTION.

1. THE DIGESTIVE FL11HS OF THE INTESTINE.

a. Tjik Secretion of Pancreatic Ji r< e.
l. Tin-: Composition ok Pancreatic Juice.
<-. 'I'm; Composition of the Bile.

2. THE CHEMISTRY or INTESTINAL DIGESTION.

a. The Action of thk Pancreatic Juice.

b. Tin: A.CTION OF Tin: III i.e.

c Tin; Action of the Succus Enterk i s.
d. Tin: Digestion of Mile: A Summary.

::. THE FACTORS WHICH [NFLUENCE INTESTINAL DIGESTION.
«. Tin: Influence of Bacteria.
/.. Tin: Influence ok Cellulose.

4. THE REMNANTS OF INTESTINAL DIGESTION: E.Ecl.s.

5. Till: MOVEMENTS OF THE INTESTINES.

6. DEFECATION.

292

SALIVAS Y DIG EST [OX.

293

DIGESTION.
A. SALIVARY DIGESTION.

1. THE SALIVA.

a.

The Secretion of Saliva.

The term saliva is applied to the fluid secreted into the oral
cavity. There are three principal pairs of glands whose secretion

Fig. 168.

Alveoli of a Berous glaud-parutid. .1, at rest ; />'. after a short period of activity : <'. after
a prolonged period of activity. In .1 and B the nuclei are obscured by the granules of zymo-
gen. (SCHAEFEB.J

tonus a part of the saliva : the parotids, the submaxillary, and the
sublingual. Besides these six glands there are innumerable smaller
mucous glands whose secretion serves only to moisten the surfaces
of the membrane while the secretion of the salivary glands proper

Fig. 169.

Fig. 170.

Mni. ,u- .ill- from frosb submaxillary

gland* "i the dog. ", from a resting or

loaded gland; '/. from a gland irbicfa baa

ome lime ; "', ft,' similar

cell* which have been treated with dilute

acid. ISCHAEFKB.)

Mm - acini of human lin rual

cells km, being loaded « itli
ilie slightly-staining secretion, appear
clear and transparent; e,c, crescentic
masses of granular cells tbe deml-lunes
of lleideiiiiain : ft, Interacinous c -

live tissue, ( \ Iter I'l EBBOL.J

serves especially to moisten the f"'"l during masticatioE and to add

to it ;i digestive ferment. These glands may \»- <livi<lci| into two

294 DIGESTION.

classes od the basis of the morphological changes which the cells
of the glands undergo during the period of rest and activity. Fig.
L68 Bhows the cells of serous glands, the parotid, while Fig. 160
shows the cells of a mucous gland, the submaxillary. Note that
the cells of the serous parotid gland arc subspherical and nearly
fill the alveolus, leaving a narrow inter-cellular cleft which
widens into a definite lumen when the cells are depleted by se-
cretion. The nucleus is located in the center of the cell but i>
obscured at times by the numerous granules. As is shown in the fig-
ures of the parotid the granules vary in number during the different
stages of the cell's rest and activity. They accumulate during
rest and disappear during activity. The same general observa-
tion may be made upon the secreting cells of all of the digestive
glands. The serous cells take the protoplasm-stain, carmine, very
deeply. The secretion from a serous gland is thin and watery.
The cells of the mucous, submaxillary gland, on the other hand,
are pyramidal in shape. A distinct lumen always exists in the
alveolus. The nucleus is located near the outer end of the cell.
The general appearance of the resting, mucous cell is much less
opaque than that of the resting, serous cell. There are, however,
numerous granules, hut these are less abundant near the lumen of
the alveolus and more abundant in the neighborhood of the nuclei.
This is well shown in Piersol's figure (Fig. 170). Just what is
the significance of the demi-lunesof Heidenhain is still a matter of
controversy. They may represent exhausted cells pushed to one
side by the active cells, or they may represent nascent cells which
are destined to take the place of cells which lie nearer to the lumen.

The fact of greatest significance to the physiologist is the ac-
cumulation of granules in the gland-cells during rest and their
disappearance during activity. That these granules bear some
relation to the organic constituents of the secretion of the cells can
be accepted as beyond question. Just what that relation is ha s not
vet been definitely determined. The principal organic constitu-
ents of the saliva are mucin, ptvalin and albumin. The work of
Langley (Journal Physiology, Vol. X., p. 433) upon the fresh
gland shows that the granules of the mucus-secreting cell may
be converted into mucin by simple addition of water. There can
be no doubt that such a change takes place during secretion.
The granules of the mucous cells may then be looked upon as
the mother of mucin — mucinogen. The granules of the ptyalin-
secreting cells probably represent the mother substance of ptvalin.
But the changes which take place in the cell during secretion arc-
not confined to the solution of the granules and the expulsion of
the product into the lumen of the alveolus. Extensive anabolic
processes take place.

The cytoplasm is replenished and the increase in size of the nu-

SALIVARY DIGESTION. 295

cleus indicates that the nucleoplasm is replenished also. During
the resting stage the protoplasm undergoes a change, probably
katabolic, by which the granules are again formed and the cell be-
comes " leaded," ready for another period of secretion.

This cycle of cell activity is controlled by influences outside of
the cell. It is important for the organism that all of the secreting
cells of a gland act in harmony, and that the secretory phase ot
the activity occurs at the time when food is in process of masti-
cation. The coordination of the activity of the gland with the
associated functions can only be brought about by the agency of
the nervous system.

The nerve supply of the salivary glands represents two general
sources : (i) cerebral ; (n) sympathetic.

The cerebral innervation of the salivary glands is represented
on the parotid gland by branches received directly from the auric-
ulo-temporal branch of the inferior maxillary division of the V.
cranial nerve. But these fibers come ultimately from the glosso-
pharyngeal or IX. cranial nerve and pass from that nerve to the
auriculotemporal through the tympanic nerve, the small super-
ficial petrosal and the otic ganglion. The cerebral innervation of
the submaxillary and sublingual glands is represented by branches
received directly from the lingual branch of the inferior maxillary
division of the V. cranial nerve. These fibers come ultimately
from the facial or VII. cranial nerve and pass from that nerve to
the lingual through the Chorda tympani, so called because it tra-
verses the tympanic cavity. (See Tympanum under Hearing.)

The sympathetic innervation of the salivary glands is repre-
sented by branches from the superior cervical ganglion of the
sympathetic system. These branches reach the glands by follow-
ing the blood vessels.

In a general way one may say that the nerve supply of all the
digestive glands is derived, like that of the salivary glands, from
cranial and sympathetic sources. A study of Fig. L59, giving
the innervation of the digestive system, shows that this is true of
the innervation of the stomach, of the small intestine, of the liver
and of the pancreas. .lust how much influence upon these struc-
tures the vague may exert through its connections in the solar
plexue Is at presenl quite unknown. The points which the inner-
vation of the salivary glands possess in common with that of the
other digestive glands, together with the fact that the nerves
which Bupply the salivary glands are readily accessible to experi-
mentation, has led physiologists to experiment extensively upon
the influence of stimulation upon these glands, with a view to thus
getting a clue to the influence of the nervous system upon secre-
tion in general. The results are definite and conclusive with re-
speet to the salivary gland- them-el yes, and suggestive, if nothing

more, with reaped to digestive glande in general.

296 DIGESTION.

If the Chorda tympanihe severed and its distal * ■ 1 1< 1 electrically
stimulated one may observe:

(i) A dilatation of the Mood vessels, and (11) a profuse How <>t
thin watery saliva from the glands which it supplies. It' the
sympathetic branches to these glands be severed and electrically
stimulated one may observe : (i) a contraction of the blood
vessels, and (il) a scanty secretion of thick viscid saliva. In the
case of the parotid gland stimulation of the peripheral end of
the divided parotid portion of the glosso-pharyngeal in any part
of its course causes : (i) vaso-dilatation ; and ( ii) profuse watery
secretion, while stimulation of the peripheral end of the divided
sympathetic branches to that gland causes : (i) vaso-constriction ;
but, iu most animals, no secretion of saliva.

Various theories have been advanced to account for the phe-
nomena observed and to harmonize the results of physiological
experiments with the observations of the histological changes in
the gland-cells during the cycle of cell activity.

That the increased pressure of the tissue-plasma resulting from
the vaso-dilatation bears an important relation to the pouring out
of a watery secretion by the cells has been generally accepted
since the time of Lud wig's early experiments in this field in 1851.

The theory which presents itself at once is that the water and
salts of the secretion are products of filtration from the tissue-
plasma. If this be a tenable proposition, two things must be
observed; first that the proportion of water and salts in the sa-
liva must be the same as in the tissue-plasma ; second, that the
pressure of the secretion in the ducts of the gland will be less
than the pressure of the blood in the vessels of the gland. But
the water and the salts of the secretion are far different in pro-
portion,— the water and salts of the plasma being about 90.3 per
cent, and 0.85 per cent, respectively, while they occur in the se-
cretion in the proportions of 99.4-f and 0.36.

As to the pressure, Ludwig (Zeitsch. f. rat. Mai., 7.V-77 — $.
271) found in the same experiment a blood-pressure in the caro-
tid artery of 112 mm. of mercury and a secretory pressure in the
duct of the submaxillary rising to 190 mm. of mercury pressure
when the gland is influenced by stimulation of the chorda tym-
pani. Heidenhain (Stud. 'I. physiol. Inst. :n Breslau) found
even greater differences between blood-pressure and secretory
pressure. In the light of these observations it is evident that the
secretion of water and salts is not << process of filtration. The next
question which presents itself is : Do not the laws of diffusion
and osmosis supplement and reinforce those of filtration?

The two most important factors in osmosis are: (I) The quan-
titative composition of the solutions separated by the membrane,
and consequently the partial osmotic pressure exerted by the
several constituent- ( Reid, in Schaefer's Textr-book of Physiology,

SALIVARY DIGESTIOX. 297

Vol. I., p. 278). (n) The coefficients of diffusion of the various
constituents (Reid). The first one of these two factors operates
in the following manner : If pure water be separated by a mem-
brane from a solution of sodium chloride the water will diffuse
much more rapidly toward the salt solution than will the salt solu-
tion toward the water, so that the liquid will rise on the side of
the denser liquid. The process of interchange continues until the
liquid on both sides of the membrane has the same quantitative
composition. But during the progress of salivary secretion water
passes constantly from the plasma where it forms only 90.3 per
cent, of the liquid into the alveoli of the salivary glands where it
forms 99.4 per cent, of the liquid.

It might be urged that the hydrostatic pressure overcomes any
osmotic pressure that may exist on the opposite sides of the secret-
ing cells. But we are seeking a factor to reinforce the hydrostatic
pressure which was already too low to account for the secretory
pressure. It is evident that the laws of osmosis will not assist us
in accounting for the phenomena. To test the second factor of
osmosis, the coefficients of diffusion of the various constituents,
one may take for example a comparison of the two salts Nad and
KC1, both of which are constituents of both plasma and saliva.
NaCl forms 0.55 per cent, and KC1 0.03 per cent, of plasma.
The coefficient of diffusion of KC1 is nearly |- that of NaCl.
Maeignae [Ann. de Ohim., Paris, 1874-, T. II., p. o4-6), demon-
strated that the rapidity of diffusion of the more diffusible of a pair
of salt* diffusing simultaneously is found to be increased, that of the
less diffusible diminished (Reid). For example, NaCl has about
;f times the diffusibility of Na.,S04 when diffusing separately ;
when diffusing simultaneously the NaCl is increased and the
\;i,SO( diminished, the ratio being nearly 3:1.

If a similar relation holds for NaCl and KC1 in salivary secre-
tion we shall be prepared to find in the saliva that the KC1 in-
stead of being Jg- of the NaCl is increased to say yV or even -jL.
lint in the saliva the KC1 : NaCl :: 3 : 5 (!).

When the two principal factors of osmosis are considered they
are found to be completely inadequate to account for the phe-
nomena of salivary secretion. The other factors of osmosis, char-
acter of membrane, pressure, temperature, are oaturally the same
for both ~;ilt- and drop out of this calculation. We are forced to
a further conclusion thai : the secretion of the water and the salts of
th< saliva is not a process <>j osmosis. Finally : //"■ secretion of the
water a, id the salts of the saliva cannot be accounted for through
the combined influence of the law- of filtration and the laws of
P.ut these are the only known physical laws that may
apply t.. this case. The cells which separate the plasma from
the -:ili\:i are living cells. Every living cell undergoes metabolic
changes} building up a portion of the material, taken from the

298 DIGKSTins.

medium id which the cell exists, into protoplasm and retaining a
portion as cell-plasma or cell-sap. Every living cell has the power
to select, from the medium in which the cell exists, the materials
which are to be used by the eell in its metabolism. In a complex
organism the cells <•< >mprising the different tissues arc differentiated
in function. A differentiation of function involves a differentia-
tion of cell metabolism with all that that entails. In term- of
these fundamental principles of biology one may say that the cells
of the salivary glands receive from the organism nutriment and
protection while they give to the organism the results of special-
ized activity. The selection of particular constituents in particu-
lar proportion and the throwing out of a particular mixture of
katabolites (excretions) is nothing new; it is an attribute of every
living cell. This is no attempt to tell just how the cell accom-
plishes this feat. The phenomenon is as inexplicable as life itself.
This is an attempt to show that in the formation of a special
secretion we have to deal with no new manifestation of cell life
but with a slight specialization of inherent cell-attributes.

Of the various theories advanced to account for the phenomena
of salivary secretion, that of Heidenhain as modified by Langley
seems to be most reasonable. The essential features of this theory
may be thus summarized :

(a) The Cerebral Nerves supply the glands with vaso-dilator
fibers and with secretory fibers. In harmony with this hypothesis
is the fact that if atropine be injected into the gland stimulation
of the chorda tympani will cause no secretion, though the vaso-
dilatation leads to increased vascularity of the gland.

The secretory fibers have been paralyzed by the atropine.

(b) The Sympathetic Nerves supply the glands with vaso-con-
stricUyr fibers and with secretory (trophic) fibers.

(c) The Secretory Fibers, or at least secretory impulses,
may be classified as : («) Those which control the secretion of water
and salts; (/?) those trophic fibers which control the metabolism of the
cells: (i) anabolic secretory, (n) katabolic secretory.

In the dog the cerebral nerve contains many fibers of class (a)
and few of class (,3), while the sympathetic contains many of class
(ti) and few or none of class (a).

To get a connected idea of the cycle of activity of the salivary
gland let us begin with the period of rest or recuperation, (i)
The reflex influence of the cerebral nerves is suspended because
the sensory nerves of the mouth are no longer stimulated by the
presence of food and the process of mastication. (11) With sus-
pension of the activity of the vaso-dilator fibers the general and
practically constant vaso-constrictor impulses through the sym-
pathetic nerves reduces the blood supply to the gland, (in) The
katabolic impulses cause the cells to change some of the proto-

COMPOSITION OF SALIVA.

299

plasm, both cytoplasm and nucleoplasm, to those granular forms
which, during the secreting period, may be so readily changed to
constituents of the secretion, (iv) Anabolic impulses are un-
questionably received by the cell during the resting stage, but the
very great production of granules and the noticeable depletion of
both cytoplasm and nucleoplasm makes it likely that the kata-
bolic processes preponderate.

Consider now the changes which are wrought during the se-
creting period : (i) The reflex influence of the cerebral nerves is
brought into action through the stimulation of the sensory nerves
of the mouth, and vaso-dilatation results, (u) Along with the
increased blood supply come impulses through those secretory
nerves (a) which control the secretion of water and of salts. The
increased pressure of the tissue-plasma as well as the increased
quantity of the tissue-plasma facilitates this phase of the secret* >ry
activity of the cells, and they "select" certain proportions of
water and salts and pass them into the lumen of the alveolus,
(ill) Through the sympathetic system especially come katabolic
impulses which lead to the final step of katabolism necessary to
change the granular material to the stage represented in the secre-
tion. For example, mucinogen granules are changed to mucin,
and the ptyalin granules (ptyalinogen) to ptyalin. (iv) Through
the sympathetic system especially come anabolic impulses which
cause the cell to select nutrient materials from the abundant plasma
and replenish cytoplasm and nucleoplasm, the former collecting
in the form of clear, non-granular protoplasm at the base of the
cell, while the latter fills out the somewhat shrunken nucleus.

This presentation, based upon the Heidenhain theory, must be
understood as a purely tentative one. It seems to harmonize all
of the phenomena as now understood.

The secretion of saliva has been discussed at some length, because
it i- better understood than is the secretion of the other digestive
juices and may be accepted as probably typical in a general way
of :ill "I' them.

b. The Composition of Saliva.

Herter (Hoppe-Seyler, " Physiol. Chem.," /:<!. //..>. 191),
the following analysis of human submaxillary saliva :

Water.

e'lves

Human

Submaxillary

Saliva,

Solids.

1 Dorganic,

Soluble.

[oHOluble.

99. 1 1

Ptyalin, )

M 111 u^. 1

IP. IT.",

| \:.< 1 0.186 "J

< KCI 0.094 [
| Na,COa .

1 i. -o, 1 1

0.86

fCaCOj 0.018 1
lCa»i P04) . i

1.026

::im.

I > Id EST I OS.

Hammerbacher (Zeitsch. f. physiol. chem., Bd. V.) gives the
following analysis of human mixed saliva :

I I inn:lh

Mixed
Saliva.

f Water.

Solids.

( i] gan ic

I 'ganic.

i Mucin and epithelium,
i Ptj alin and globulin.

( Potassium Sulpho-cyanide .00 I ,)

I NaCl, KC1 |

N;i.. CO,,* \< ".

I Mg3(P00j„Ca3(P04)3 j

1I9.42 i

0.22
0.14

0.22
100.00

2. THE CHEMISTRY OF SALIVARY DIGESTION.

The only chemically active agent in saliva is ptyalin. Ptyalin
is an amylolytic enzyme, and its action is therefore confined to
the change of starch to sugar and to the products intermediate

between starch and sugar. Brown and Morris, quoted by Halli-
burton, sum up this change in the following reaction :

10(C6H10O6)n+4nH2O = 4nC12H22O11+(C6H10O5)n+(C6H,0O6)n
Starch -4- water = maltose + achroodextri n -f erythrodextrin.

Most investigators agree that the first change is to soluble
starch, " amidulin" or amylodextrine, which gives a blue color
with iodin ; and that no erythrodextrin remains at the end of the
reaction, but that there may be several forms of achroodextrin
present.

Neumeister (Lehrbuch <h physiol. ('hemic, 1893, S. 232) gave
the following diagram as representing approximately what takes
place in the action of ptyalin or amylopsin upon starch :*

1 In order that the reader may get a more concrete idea of the series of changes
which this diagram eontemplates it may he well to insert the quantitative molec-
ular formuhe worked out by Lintner and Dull (Ber. d. deuisch. chem. Gesell., Bd.
26, S. 2533).

Starch (C6H10O5)u(=llls') (-(-ptyalin) =

Amidulin \ ( C12H,0O10)5t ; ( + ptyalin ) -j-3H2< > =
Anivlodextrin I

".Maltose + 3 Erythrodextrin (fptvalin) + 611,0=

6 Maltose f '•» Achroodextrin « i -|-ptyalin)+45HsO =

C,,II-<>n 9 (CV.H-oOio);,

45 Iso-maltose

45 C12H20O10 H-< X +ptyiilin ) =

4"> Maltose

45 C12H23O11
This series of reactions does not include the variations of achroodextrin for the
very g 1 reason that these dextrines are largely hypothetical.

THE CHEMISTRY OF SALIVARY DIGESTION. 301

Starch + ptyalin -f water
Amylodextrin

Erythrodextrin + maltose

Achroodextrin a -f maltose

Achroodextrin ,3

Achroodextrin y

or
Maltoidextrine

-f maltose

-f maltose

Maltose

-f Maltose

The changes which glycogen (C6H10Og)n, undergoes during diges-
tion are the same as those which starch undergoes. (Kiilz and
Vogel, in Zefoch.f. Biologie, 1895, Bd. 31, S. 108.)

It was originally supposed that starch was changed to dextrose,
but it has been demonstrated that maltose is first formed and that
only a very small proportion of dextrose is formed either through
ptyalin or amylopsin. (Musculus and Gruber, Zeitsch. f. physiol.
( 'In in., Bd. II., S. 177.) It must be remembered that though ptyalin
is capable of working all of the changes ascribed to it when the
time is sufficient, the amylolytic changes are interrupted very early
in their course by the acid reaction of the stomach and arc not
resumed until the products are again subjected to the influence of
an amylolytic enzyme in the small intestine. ruder the usual
Conditions the products of ptyalin digestion would include maltose,

achroodextrin a,/? and y, erythrodextrin, and probably amylodex-
trin, there would also remain much unchanged starch. All of
these excepting the starch are soluble, and maltose is crystalline
and diffusible. It is either hydrated in the alimentary canal by
invertin, or an allied enzyme, and changed to dextrose, in which
form it is absorbed; or M is taken up by the absorptive epithelium

a- maltose and changes within the epithelium to dextrose, in which

form it i- passed into the capillaries of the portal system. It is
certain thai it due- nut enter the circulation as maltose.

302 DIGESTION.

:>. FACTORS WHICH INFLUENCE SALIVARY DIGESTION.

a. The Preparation of the Food.

The importance of a most thorough cooking of starch and starchy
fond- can scarcely be too strongly emphasized.

The starch is deposited in Btratified grains which have alternat-
ing layers of pure starch or granulose and of starch-cellulose,
which also forms the outer layer of the starch grain. Starch-cel-
lulose is quite indigestible by the ptyalin or amylopsin, and it is
only with difficulty permeated by these enzymes, so that digestion
of uncooked starch grains is very much retarded. Moist heat has
the effect of swelling the granulose and bursting the starch-cellu-
lose envelopes, thus liberating the pun- starch which makes an
opalescent paste if the water is sufficient in quantity. In any case
it is made readily miscible with the saliva, and thus the action of
the ptyalin is much facilitated.

b. The Mastication of the Food.

If the starchy food be bolted in unbroken pieces it is evident
that, however thoroughly the food may be cooked, and however
active and abundant the enzyme may be, the amylolytic action of
the ptyalin must be slight, because not brought into proper phys-
ical relation to the starch.

A thorough mastication of the food breaks it up into minute
pieces and mixes the saliva with it, so that the enzyme is brought
into contact with a much larger proportion of starch than could
be possible otherwise.

The time required for thorough mastication is another important
element because the change in the starch may be well advanced
before the food leaves the mouth.

c. The Temperature of the Mixture.

After the well cooked food is thoroughly masticated there are
other important conditions which must be fulfilled if the digestive
changes are to be rapid and extensive. The temperature affects
the operation of any enzyme. The optimum temperature is approxi-
mately that of the bl< >< >d ( 37° C. -40° C). Outside of these limits
the action is progressively slower the farther removed from the
optimum. The action is wholly suspended at 0° C. but the en-
zyme is not destroyed. The action is wholly suspended at 65°-
70° C. and the enzyme is destroyed. Much has been said about
thi' effect of cold drinks upon digestion. A large portion of what
has been said cannot be verified by experiment. Experiment
has demonstrated that if the contents of a beaker be diluted with
lo volumes of water at 0° C. the action of the ptyalin will be
much retarded, partly because of the dilution and partly because

THE TIME OF SALIVARY DIGESTION. 303

of the marked change of temperature. When cold water is taken
with meal- it is usually taken in moderate quantities so that the
dilution is not sufficient to retard the action of the enzyme. It is
usually taken sufficiently slowly to be warmed to almost blood
temperature before it reaches the stomach so that a glass of cold
water taken a little at a time during the progress of a meal can-
not be said to effect any demonstrable retardation upon salivary
digestion in the stomach.

d. The Reaction of the Mixture.

The saliva is faintly alkaline because of the Xa.,00., which it
contains. It is not necessary, however, that the reaction of the
mixture of food and saliva be alkaline. The ptyalin acts quite as
well in a neutral as in a faintly alkaline medium. Even a weak
acid reaction does not stop — though it retards — the action of the
enzyme, provided the acid be an organic acid like lactic acid.
When HC1 is combined with a proteid, as acid-albumin or syn-
tonin, it will cause an acid reaction, but when the reaction is only
faintly acid the action of the ptyalin may proceed, though at a
slower rate. Free HVl will, however, stop the action of the
ptyalin and destroy it when it is present in even so small a propor-
tion as 0.003 per cent. (Chittenden, in Studies from the Lab. of
Physiol. Chem. Yale, Vol. I., 1884). The free use of sour pickles
and acid drinks must retard the action of the ptyalin. In the
light of what will follow (e) it is evident that these acid foods may
be taken late in a meal with less effect upon salivary digestion
than when taken early in a meal.

e. The Time of Salivary Digestion.

The food is retained in the mouth not more than one minute at
the longest. In this time the change has only begun, even when
all the conditions are most favorable. The hydrochloric acid of
the gastric juice is not present in the stomach until the stimulating
presence of food induce- it- secretion. After it begins to be se-
creted -nine minutes elapse before the quantity of combined acid
i- sufficient to essentially retard the salivary digestion. It is esti-
mated thai from 30 minutes to 45 minutes, or even more may
elapse before salivary digestion is wholly suspended by the ac-
cumulation of free IK 1.

The following conditions favor a prolongation of the time of
salivary digestion : (i) The retardation of the secretion of hydro-
chloric acid. Nothing so quickly brings aboul a secretion of this
acid as a glass of cold water. It is evident then thai the drink-
ing of water ;it the beginning of a meal will \cw\ to shorten the
period of salivary digestion, (ii) The retardation of the per-

304 DIGESTION.

mention of the food by the acid. If the food is semi-solid the
acid permeates it slowly; if it is fluid the acid becomes readily
mixed by diffusion as well as by movement- of the stomach.

Soups and drinks bring the contents of the stomach into a
soupy mass which is readily acidified as soon as the 11(1 begins
to be secreted. In this case again fluids at the beginning of the
meal are unfavorable to the prolongation of the time of salivary
digestion.

It is doubtful if in the average case there is any advantage in
thus prolonging salivary digestion. The amylopsin of the pan-
creatic juice is a more active amylolytic enzyme than is ptyalin,
and it has all the time necessary for its action without encroach-
ing upon the time of other digestive processes.

4. MASTICATION.^

This process is a purely mechanical and physical one which is
wholly a voluntary one. With this process are associated those
gustatory sensations and perceptions which are so enjoyable to
most of mankind. The movements of the jaws, cheeks and tongue
stimulate the flow of saliva and insure the thorough mixing of that
secretion with the food (insalivation). The insalivation of the
food produces three effects: (i) To digest with ptyalin the starch
of the food; (n) to lubricate with mucus the mass of food, thus
preparing it for deglutition; (in) to dissolve with the water of the
saliva the soluble portions of the food, — salt, sugar, etc.

In the discussion of the factors which influence salivary diges-
tion the importance of the division of the food into fine particles
was mentioned. It is quite as important in digestion by the
other digestive fluids that the food be triturated. The enzyme
gets access only to the surface of the particles of food if the same
volume of food present twice the surface one would expect it to
digest in one-half the time, and such is approximately the case.
Eight 1 mm. cubes of coagulated egg- albumin would contain the
same amount of albumin as one 2 mm. cube. They would aggre-
gate twice the surface, and the time of digestion would be ap-
proximately half as long in the case of the 1 mm. cubes as in the
case of the 2 mm. cubes.

The structures involved hi mastication may be classified as skeletal,
muscular and nervous.

1 It is proposed to discuss t lie movements of the different segments of the
alimentary canal in connection with the digestive changes effected in the several
portions, progressing step by Btep from the oral to t lie anal end of the tract The
movements of the mouth are an important factor in salivary digestion. The
movements of t lie stomach influence gastric digestion profoundly, and the move-
ments of the intestine influence not only digestion, but also absorption in that
s '<i'inent of the canal.

THE MUSCLES AND NERVES OF .MASTICATION. 305

a. The Skeletal Structures of Mastication.

These include the maxillary bones as representatives of the
endoskeleton, and the teeth as representatives of the exoskeleton.
The development of the teeth, in the race and the individual, has
been treated above. The function of mastication is variouslv
specialized in different orders of mammals. It reaches its highest
development in herbivora — whose food is difficult to masticate
and yet requires the finest trituration in order to be digestible.
The teeth of herbivora are the most perfect dental organs in the
animal kingdom. The incisors are cupped and the molars have
alternating ridges of dentine and enamel, and are self sharpen-
ing. The carnivorous animals bolt their food with little chewing.
The teeth which are well developed are the great, prehensile
canines and the trenchant molars which are especially adapted for
breaking the bones of the prey. The omnivorous animals, to
which kind man belongs, possess edged incisors; meager can-
ines, scarcely prehensile in man, though distinctly so in the go-
rilla ; and molars with rounded cusps well adapted to crush,
but not at all capable of cutting the food. The movements of
the jaws differ distinctly in the different orders of animals above.
The chopping movement is peculiar to the carnivora ; the herbiv-
ora give the mandible a wide lateral, and antero-posterior excur-
sion, while the omnivora possess all of these movements in a
moderate decree.

b. The Muscles and Nerves of Mastication

include :

("j The flexors or levators of the mandible : (i) The masseter ;
Hi) the temporal, and (in) the internal pterygoids. All of these
are innervated through the inferior maxillary division of the fifth
cranial nerve.

(/>) The extensors or depressors of the mandible : (i) The di-
gastric; (ii) the mylo-hyoid, and (in) the genio-hyoid. (i) and
(II) innervated by the inf. max. division of the V, and (ill) inner-
vated by the hypoglossal.

(c) The lateral movements of the jaws are produced by the otter-
natt action of the external pterygoids. — Inf. max. div. of Y.

('/) Protrvders of th> mandible: The external pterygoids acting
togetfu r.

Retractor of the mandible: The posterior portion of the
temporal.

( /' j The dull; a, u\ liji muscles • Buccinator and orbicularis

oris, innervated by the buccal branch of the facialis.
(y) The lingual muscles innervated by the lingual branch of the
20

306 DIGESTION.

inferior maxillary division of the trigeminus and by the hypo-
glossus.

c. The Process of Mastication.

The food is cut by the incisors and crushed between the
molars. The cheeks and tongue assist in bringing the food be-
tween the molars. The movements of the masticatory apparatus
in itself tends t<> stimulate the flow of saliva ; the presence of
food, especially acid, sweet or dry food, tends also to stimulate
the secretion of saliva.

The movements of mastication mix the saliva thoroughly with
the food. The gustatory apparatus is stimulated by all substances
which are soluble in water, and the olfactory apparatus by all
volatile substances. The sensations derived from these two
sense organs make up the so-called "tastes" and "flavors" of
the foods. The pleasure derived from eating consists : (i) in the
satisfying of the hunger, (n) in the enjoyment of the tastes and
flavors. Hunger seems to be nature's warning of need for nutri-
ment; while the pleasures of the taste and smell, besides assisting
the animal in the choice of food, repay the animal for a thorough
mastication of it.

5. DEGLUTITION.

After the food is made ready for the stomach, by mastication,
it is gathered, by the tongue, into a bolus or rounded mas- be-
tween the tongue and the hard palate, and passed back to the
pharynx, whose walls by a convulsive reflex act pass it to the
oesophagus, along which it is pressed, by a peristaltic wave, into
the stomach. The whole process of swallowing as here briefly
outlined is called deglutition. The length of time required to per-
form the act is not commensurate with its complexity. The proc-
ess may be analyzed as consisting of a voluntary and an involun-
tary part.

a. The Voluntary part of Deglutition.

This consists in (\) tin- formation of tin' bolus by the cheek-,
palate and tongue; and (n) in the pressing <>j tin bolus backward
through the isthmus of the fauces, i. <■., between the anterior pil-
lars of the fauces which are the ridges marking the location of
the palato-glossal muscles. Once the bolus of solid food (or the
"swallow" of liquid) passes this Rubicon there is no turning
back, the muscles of the pharynx grasp it reflexly and hurry it
forward by wholly involuntary processes. The muscles and
nerves of this voluntary initiatory step of deglutition have been
enumerated under mastication in which function they are impor-
tant factor-.

THE INVOLUNTARY PART OF DEGLUTITION. 307

h. The Involuntary Part of Deglutition.

This consists in the transit of the bolus through the pharynx ;
and in its passage along the oesophageal canal.

1. Pharyngeal Deglutition. — The transit of the food through
the pharynx is attended with two dangers, namely, the danger of
a falling of a portion into the larynx, and the danger of regurgi-
tation of a portion into the posterior nares. Pharyngeal degluti-
tion consists, then, of three acts: transportation of the food;
guarding against a false passage into the larynx ; guarding against
a false passage into the posterior nares.

(a) Transportation of the food through the pharynx and into
the cesophagus is, according to Kronecker and Metzger (Arch.f.
Physiologie, 1883, S. 328), accomplished in two phases, a projec-
tion phase and a clearing-up phase. AVhen the bolus reaches the
isthmus of the fauces the tongue is closely approximated to the
palate, blocking the way to the front. A convulsive contraction
of the mylo-hyoid muscles puts the bolus under pressure and pro-
jects it across the pharyngeal cavity; the way is cleared by the
simultaneous contraction of the hyoglossi muscles which move the
root of the tongue backward and downward. This movement de-
presses the epiglottis over the opening of the larynx, thus guard-
ing that passage. In the case of liquid or semi-solid food the
entire transit of both pharynx and cesophagus is made in 0.1
second. The force of gravitation assists in this preliminary act —
0u projection of fh<- bolus. The clearing-up phase of pharyngeal
deglutition consists in a general peristaltic constriction passing
from above downwards and beginning 0.3 second after the con-
Btriction of the mylo-hyoids.

Th<- first step in this phase consists of a contraction of the longi-
tudinal muscles of the pharynx which serves to pull the walls of
the pharynx toward the bolus of food. The second step follows
the guarding of the respiratory openings.

(b) The Guarding op the Posterior Nares is insured by

th^ elevation of the -oft palate through the contraction of the
levator palati and tensor palat i muscles ; by the contraction of the
palato-pharyngei muscles, and by the elevation of the uvula
through the azygos uvulse muscle.

((■) The Guarding of the Laryngeal Opening is insured
in pari by the depression of the root of the tongue through the
hyoglossi muscles as described above. Supplementing this and
following it in time U the closure of the laryngeal opening by the
adduction of the vocal cords. ( For muscles and nerves see larynx.)

The second step in the cleanng-up phase of food transportation
through the pharynx consists of a peristaltic action of the con-
strictors of the pharynx. By this last act of pharyngeal degluti-

308 DIGESTION.

tion any particles of food and any accumulated mucus are cleared
from the pharynx and started along the oesophagus.

The two phases of deglutition above described (projective and
clearing-up), seem to play parts of differenl relative importance
according to the physical condition of differenl foods. In the
case of liquid or very soft food the projection phase is the more
important.

In drinking the cycle of swallowing acts follow in such rapid
succession that there is not time for one to l>e completed before
another is induced. Through the influence of the central nervous
system all that portion of one deglutition, incompleted when a
second deglutition supervenes, is suspended or inhibited.

Kronecker and Meltzer found that about 1.2 seconds elapse
between the beginning of the contraction of the mylo-hyoid and
the beginning of the contraction of the upper segment of the
oesophagus. There would be five complete pharyngeal acts in six
seconds ; this is just about the usual rate of deglutition when
drinking. The (esophageal peristaltic waves must then be sus-
pended during the progress of drinking. The observers cited
found, furthermore, that the constrictors of the pharynx, though
they would have time to contract, actually remain at rest ; the deg-
lutition being in this case a scries of projections followed at the
end by a clearing-up contraction of pharynx and (esophagus.

In the case of solid food in a well-formed bolus of considerable
consistency the clearing-up phase always follows the projection of
the bolus across the pharyngeal cavity.

2. (Esophageal Deglutition. — The bolus is passed along
the oesophagus by a peristalsis which differs from peristalsis of
the lower segments of the alimentary canal in being more under
the immediate control of the central nervous system, as evi-
denced by the fact that removal of a segment of the (esophagus
does not block the progress of the peristalsis, while the severing
of a nerve suspends the peristalsis in the segment supplied by the
severed nerve.

c. The Influence of the Nervous System upon Deglutition.

(a) The Ci inter for involuntary pharyngeal and (esophageal
deglutition lies in the upper end of the medulla, anterior to the
respiratory center. The boundaries of the center have not been
clearly defined.

(//) The Afferent or Sensory Impulses which precipitate
the act of involuntary deglutition reach the center through the
pharyngeal and the superior laryngeal branches of the vagus, and
the palatal branches of the superior maxillary divisions of the
trigeminus. The contact of the bolus of food with the mucous
membrane supplied by the above-named nerves is a sufficient
stimulus normally.

GASTRIC DIGESTION. 309

( <• i The Efferent on Motor Impulses which put the muscles
of deglutition into activity arc the hypoglossal to the tongue and
to the muscles which raise the larynx, the ghsso-pharyngeal, vagus,
facial and trigeminus to the palate, fauces and pharynx, and the
vagus to the larynx and oesophagus.

II. GASTRIC DIGESTION.

1. THE GASTRIC JUICE.

a. The Secretion of Gastric Juice.

1. The Structure of the Gastric Glands. — The general fea-
tured of the secretion of gastric juice are the same as those of the
secretion of saliva. The differences are specific rather than gen-
eric and are incident to the location and the specialized function.

The gastric glands are usually classified as cardiac and pyloric,
because the glands of these two regions differ both functionally
and structurally. The cardiac glands (see Fig. 171) possess two
kinds of active cells, the "chief" or central cells and the pari-

,t<ll fills.

The columnar central cells are filled with a fine reticulum, and
possess an amount of granular matter varying with the phase of
activity. The discoidal or crescentic parietal cells do not lie be-
side the main lumen of the gland, but each cell possesses a di-
verticulum from the main lumen. (See Fig. 172.)

Besides the diverticula shown in Fig. 172 there are minute
capillary branches of each diverticulum, which surround the
parietal cells. (See Fig. 173.)

There has been some controversy about the function of
these '•ells. The following facts deserve consideration in this
connection: (i) The cells vary in size during different phases
of glandular activity, being larger at the beginning than at the
end of Becretion. (\\) Each cell is provided with a special sys-
tem of little duets or liuneiia. (in) The parietal cells are the
only cells peculiar to the cardiac end of the stomach, (iv) The
Becretion from the cardiac end of the stomach contains hydro-
chloric acid, while the secretion from the pyloric end of the
Stomach contain- no hydrochloric acid. This was demonstrated

by Hcideiihain, who separated the two portions of the stomach,
giving each in turn an external fistulous opening. From the
cardiac end of the stomach only was the secretion acid in reac-
tion. These tact- seem to justify the following inferences:
M) The parietal cells are directly associated in the function of se-
cretion of gastric juice, (n) They secrete a liquid that must find

it- way into the main lumen of the gland. (ill) They secrete a
liquid peculiar to the secretion of the cardiac end of the stomach.

310

DIGESTION.

Fig. 171.

Portion of cardial- gland "i
dog, highly magnified: a, a, the

central or chief Cells next the
lumen (c); b, b, the parietal <>r
acid cells connected with the lu-
men of the i niic by short lateral
branches « hieh extend to the
cells. (Piersol.)

Fig. 17:

A cardiac gland from the dog's stomach. (Highly
magnified, i (Klein.] '/, duel or mouth of the gland; o,
base or fundus of one "t it- tubules, On the right the
base of a tubule more highly magnified ; c central cell : p,
parietal cell.

A cardial- gland prepared l>y

Golgi'a method, Bhowing mode
of communication of I he parietal
cells with the gland-lumen.

(S( OAEFEB Utter E. MVLI.ER. )

GA S TBIC DIi mSTION.

311

Fig. 174.

(IV) Hydrochloric acid being the only liquid peculiar to the
cardiac end of the stomach, the parietal cells must, therefore, secrete
hydrochloric acid. This course of reasoning is sufficiently con-
vincing to satisfy most physiologists of the probability that in the
parietal cells we sec the site of the formation of hydrochloric, but
it is reasoning by exclusion and cannot be accepted as an absolute
demonstration.

The central cells are common to the cardiac and the pyloric
glands. The secretion of pepsin is a function common to the
cardiac and pyloric ends of the stomach.
The central cells of these glands are larger
at the beginning than at the end of secre-
tion. They contain many granules at the
beginning of secretion and few at the end of
that process. There can be little doubt that
the pepsin of the gastric juice is formed in
the central or chief cells of the cardiac and
pyloric gland-.

The pyloric glands differ from the cardiac-
glands, first in general form — the duct- of
pyloric glands being long and relatively
wide Into this duct empty several more
or less tortuous tubules (See Fig. 174).

2. The Secretion of Pepsin. — This is
one of tlic essential constituents of the gas-
tric juice and its formation within the cells
corresponds closely to the formation of the
ptyalin in the cells of the salivary glands.
The granules formed in the cells during the
period of rest represent a mother-substance
of pepsin or a zymogen which has been called
pepsinogen. During the secretion of gas-
tric juice the zymogen is subjected to a fur-
ther metabolism which changes ii to pepsin ;
;ii any rate pepsin is one product of this final
metabolism. The pepsin-secreting power of
the pyloric glands is much below thai of the
cardiac glands. It is contended by some1
that any pepsin found in the pyloric seg-
ment of the stomach, or extracted from the
mucous membrane of thai aegmenl \\;i- se-
creted by the cardiac glands and -imply absorbed by the pyloric
mucous membrane, or taken up by '• infiltration." Heidenhain's
investigations have, however, demonstrated conclusively thai
pepsin '■■ secreted by il" pyloric glands.

1 \V:i--!ii;inii. •' !>• iii'/i turn* nummda" Berolini, 1839; Von Wittich, ifUber
■■ j-in u irk ii n- der Pylonu driisen," Areh.f. a. gt . Phy iologie, Bonn, 1*7:;.

A pyloric gland, from a sec-
tion "i' Hi'- dog's stomach.
(Ebsteiw.) »•. mouth : ».
iurk ; h , ;i deep portion of :>
tubule iiii transveraelj ,

(.-i II Ml I B, I

312 DIGESTION.

3. The Secretion of Rennin. — Much that has been said
regarding the secretion of pepsin is equally true for the milk-
curdling enzyme, rennin. Rennin is Becreted by the central or

chief cells of the cardiac and pyloric glands. It is secreted more
abundantly by the cardiac than by the pyloric glands. It exists
in the gland cells in a granular zymogen (renninogen) which may
be extracted as such and then changed to the active form, rennin.
In fact, the first zymogen found Mas that of rennin.1 The
granules of pepsinogen and renninogen exist together in the gland
cells and it is impossible to differentiate them morphologically.
They may, however, be separated chemically.

4. The Secretion of Hydrochloric Acid. — Hydrochloric
acid is almost without doubt secreted by the parietal cells of the
cardiac glands. From what materials and by what process the
acid is formed is an undecided question.

" There is little doubt that the material for the formation of the
HC1 is the sodium chloride, which forms a large part of the ash
or blood and lymph. The plasma and lymph is alkaline through
presence of sodium carbonate. How can chlorine be liberated
from the sodium chloride of the alkaline plasma? Only two
methods are possible : 1st, either the CI must be separated from
Na through some active energy as electricity, — in electrolysis, —
or, 2d, the CI must be displaced by another acid. There is no
ground for believing that the separation is effected by electricity "
(Bunge : Physiological Chemistry). But it is generally believed
that only a stronger acid can displace a weaker one. In 1871
Julius Thomsen demonstrated that "every acid can displace, from
its combination with any base, a part of any other acid." (J.
Thomsen, " Thermo-chemische Untersuchungen," Poggmdorff
Ami., 143, 1871.) This ability is not through affinity alone but
through another characteristic which Thomsen called "avidity"
When equal parts of HC1 and acetic acid act together upon Xa .,( '< ) ..
in aqueous solution only JU of the Xa will combine with the acetic
acid ; so the latter acid has only ^ the aridity of HO. But if
the proportion of acetic acid be increased, more than -^ of the Xa
will combine as sodium acetate ; and the more, the greater the pre-
ponderance of acetic acid.2

1 Hammersten, Jahresber. iib. d. Fortschr. d. Thier.-Chem., Wiesbaden, 1872.

2 As an example of the above let us take equal parts of these acids and Xa.,( '< >;;
in excess. The following equation would represent the relations in question :

70 !<Ua } + 35 Na*°°3 = { fs^CJU >, ! + 2 HC1 + 68 H-QHA
4- 35 H,0 + :;•". ( .'(),.

Now if the avidity of CjHgOg'H is only J? that of HC1 then let us take 34
times as many molecules of the former as of the latter : The following equation
would represent the relations in question :

3 i , ,|p< VII \ JNaMJ,, _ ( Xa.C2HA j- + 33 C2H802-H J + **»" + LU*

GASTRIC DIGESTION. 313

This displacement of a stronger acid by a weaker one when the
latter is increased in proportion is called the " mass-effect " of weak
aeids. " Even CO., (or H..CO.,) one of the weakest acids, must be
able through mass effect to displace a small part of any other acid "
(Bunge). The reaction might be written thus :

2 NaCl + 1000 H2C03 = 999H,C03 + 2HC1 + Na2C03.

Maly, — followed by Halliburton', — has suggested that the
Ca( 1., and Xa.,HP04 of the blood are bro tight together in the se-
creting cells and form the following reaction :

2 Xa.HPO, + 3 CaCl, = Ca3( T04)2 + 4 NaCl + 2 HC1.

Maly also suggested the following reaction as an alternative :

NaH2P04 + NaCl = Na2HPO, + HC1.

That any one of these reactions occurs has not been demon-
strated. Most physiologists believe that the chlorine is liberated
chemically in some way from one of the chlorides of the blood.
But, as Bnnge says, " There is less obscurity in the liberation of
free H('l than in the ability of the parietal cells to secrete the HC1
toward the lumen of the gland and discharge the other products
toward the blood." In other words, even after we have ac-
counted chemically for the formation of the hydrochloric acid we
will still have to fall back upon the vital activity of the cell to
account for its ability to select from the blood the compounds
needed in the reaction, and to return to the blood a part of the
products of the reaction while another part is secreted into the
lumen of the gland.

5. The Influence of the Nervous System Upon the Se-
cretion of the Gastric Juice. — Recall the innervation of the
stomach : (i) The left vagus distributed to the smaller curvature
Buperficially ; the right vagus passing behind the viscus and in-
corporated in the solar plexus, in part to return, accompanied by
sympathetic fibers from the splanchnics, and distributed to the
greater curvature superficially, (n) The gangliated i>l<:vus of
Auerbach lying between the muscular coats of the stomach, (in)
The gangliated plexus of Meissner Lying in the submucosa. (iv)
The special plexuses of Openchowski,1 which innervate the <-<n-<lin
ami pylorus.

Note thai the innervation is cerebral and sympathetic; thus far
it i- like the innervation of the salivary glands. Note, further,
thai there are presenl in the stomach at leasl two distinct difluse,

1 "lil.ir die nervosen Vorrichtungen di Magens," Centralbl. /. Physiol.,
1889, B. III.

314 DIGESTION.

gangliated plexuses. Ganglia represent either relay stations
reflex centers, or both. Organs which are richly supplied with
ganglia are usually somewhat independent pf the central nervous
system, and respond readily to Local influei

To Pawlow2 we are indebted for a solution of the problem con-
cerning tlic function of the various nerves which supply the
stomach. Pawlow divided the oesophagus in the <1- *l^ ~ on which
he operated, making a double fistulous opening on the neck.
This enabled him to feed the dogs by mouth, but diverted the swal-
lowed food so that ir did not reach the stomach. This he called
"pseudo-feeding." Through the distal end of the oesophagus he
was able to introduce into the stomach food which had not been in
the month — " true feeding " A third variation consisted in pre-
senting to the longing eyes and nose of the animal food which he
was allowed to receive into neither mouth nor stomach — "psychic
j> eding."

The following results were obtained : (i) After feeling, whether
psychic, pseudo, or true feeding, gastric juice is freely -

But in the case of psychic feeding, after the dog learned by
perience that the food presented was not actually to be given him
the secretion did not take place, (n) A latent period clap-.- be-
tween the beginning of stimulation and the beginning <:<f secretion.
(in) The latent periods for the three different methods do not
differ essentially (about 7 min. in the d _

These facts point directly to the central nervous system as the
strongest factor in inducing and controlling the secretion of gastric
juice.

Pawlow varied his experiment- by severing in turn the sym-
pathetic and the vagus innervation: (rv) Cutting off the influ-
ence of the sympathetic system through the splanchnic did not
stop the secretion of gastric juice when the proper stimulus was
applied in one oi' the form- of feeding. | v i Cutting off the direct
influence of the brain through the vagi stopped all reflex secretion
of gastric juice, though the severing of one vagus did not suffice
to produce this effect. (Vii) Stimulation of the distal ends of the
divided vagi caused secretion of gastric juice.

The inferences to be drawn from these observations are obvious.

That the mechanical stimulation of the mucous membrane by
the contact of the -olid food cause- little secretion i- demonstrated
by Pawlow's experiment, in which pebble- were introduced into
the stomach followed by no measureable secretion. Altera series
of experiments Heidenhain [Arch. f. <L ges. PhysioL, 1S79, Bd.
XIX.) concluded that " certain products of digestion when abi
stimulate the flow of gastric juict :'" Chischin (Inaug. Dissertation,

- •• I >ie Innervation der Masrendrusen beim Hunde."' Arckiv f&r Pk

Leipzig. 1 B

CHEMICAL COMPOSITION OF THE GASTRIC JUICE. 315

St. Petersburg, 1894. Quoted from Edkins, in Schaefer's Text-
book of Physiology) after experimenting with various foods and
products of digestion sums up the question thus : "At thi time
of taking food th< first flow of gastric juice is determined by the reflex
psychic influences involved in taking food. TJu digested proteids
— (peptones —an abh later to evoke a secretion at a time presumably
when the psychic influence begins to wane." (Edkins.) Thi- sug-
gested the introduction of peptone per os. The experiment re-
Bulted in an immediate secretion of large quantities of gastric
juice with high acidity and well marked digestive powers. The
therapeutic significance of this observation is apparent.

Different foods influence in a different manner the secretion of
the gastric juice. "When bread alone i- taken the gastric juice
- sses a "low acidity but a high degree of peptic power \
whereas with milk a high degree of acidity i- shown but a much
lower degree of digestive (peptonizing) power." (Edkins.) At-
tempt- to systematize effects of a mixed menu have been unsuc-
cessful.

h. Chemical Composition of the Gastric Juice.

The most reliable complete analyses of gastric juice are those
made by Carl Schmidt.1 The human gastric juice was collected
from a healthy woman who had a permanent gastric fistula made
accessary by a traumatic stricture of the oesophagus. The anal-
ysis of gastric juice from the carnivorous animal is the mean of ten
determination- from a dog whose salivary ducts had Ween ligated.

COSBTITUEJITS '■! nil. OaSTBH J PICE.

If (MAN.

I>'.'..

Water.

99.440

1

-

0.560

2.694

j inie.

0.319

1.713

■ >,in. Mucin, etc.

Inorganic.

0.241

0.981

m

2

0.334

Na< 1

0.146

KCI

0.055

0.112

NU.el

0.006

0.026

0.047

1
1

0.171

1 ePO

0.013

0.008

Note rliat the principal organic substances are the enzyme-.
.Mucin i- alwaye a constituent of the secretion of a mucous mem-
brane. Among the salts one note- the presence of chlorides and
phosphates but the absence of carbonates which formed an impor-

1 Quoted from Maly in Hermann's rlandbncb, Bd. V., \ 2, "»7o.

lomc unaccountable reason the analysis of Schmidt gives If I as 0.02 pet
'■<iit. wlii'li i- abont one-fifteentfa the quantity which Bunge PhysioL chemie)
r<.-|»i,n- ;i- the result of repeated testa o? the H< 1 content of gastric juice We
may, therefore, accept the quantity of HC1 as being about 0.3 per cent.

316 DIGESTION.

tant constituent of the saliva causing it- alkalinity. The acidity
of the gastric juice is not always due to BEC1, but frequently to

lactic acid, which is the product of a lactic arid fermentatioD
which takes place in the contents of the stomach. Note that the
gastric juice of the dog is much richer in both organic and inor-
ganic constituents than is human gastric juice. The HC1 in the
gastric juice of the dog ranges from 0.3 per cent, to (».~> per
cent. That it should be stronger is to be expected first because
the diet of the carnivorous animal is largely a proteid diet which
must follow either an acid pepsin digestion or a trypsin digestion.
The bones which carnivorous animals eat can only be digested by
a strongly acid gastric juice.

2. THE CHEMISTRY OF GASTRIC DIGESTION.

Experiment shows that the active agents of the gastric juice are
the enzymes and the acid.

If a typical proteid, such as coagulated egg-albumin, be put
into a neutral solution of pepsin it will not be dissolved.

If a proteid be put into a 0.1—0.3 per cent. HO solution it
will be modified both physically and chemically — it will swell up
and become clearer, some proteids actually passing into a clear
solution. The chemical change, though not understood in detail,
is recognized as a chemical association, or possibly a typical chem-
ical combination of the HO molecule with the proteid molecule.
Such a compound is called an albuminate and is classified as one of
the derived proteids. This particular albuminate is called aeid-
albumin, or syntonin. Acid-albumin, or syntonin, is precipitated
by neutralizing the solution. It can be re-dissolved by weak acid
or be converted into alkali-albumin by weak alkali.

It must be evident from the above that of the active agents the
acid must act first upon the albumin and globulin classes of pro-
teids. If one bring gastric juice — either secreted or artificial —
into contact with a native proteid under favorable conditions the
proteids will be rapidly changed to syntonin. Upon thi> syntonin
the pepsin acts, inducing a series of hydrolytic cleavages.

As in the hydrolytic cleavages which starch undergoes under
the influence of ptyalin, so here the process represents several
steps. Just how many steps there are between the acid-albumin
or syntonin and the final product, peptone, is still an open ques-
tion. The mid-products between the albuminates and the pep-
tones are called proteoses in general.1

1 The mid-products of the native albumins are called the albumoses; of the
globulin-, globvloses; of casein, caseinoses, etc., etc, bat these distinctions, if justi-
fied by our present chemical knowledge, are certainly not necessary at present.
Let us, therefore, group all of the mid-products between the syntonins and the
peptone- as proteoses.

THE CHEMISTRY OF GASTRIC DIGESTION. 317

Of the proteoses two steps have been demonstrated, viz., pri-
mary proteoses and secondary proteoses. The secondary proteoses
are appropriately so-called because they not only follow the
primary proteoses in time, but are derived from them. The
primarv proteoses exist in two chemically separable forms named
by Neumeister (Lehrbuch d. physiol. chemie) proto-albumoses
(proto-proteoses) and hetero-albumoses (hetero-proteoses).

The deutero-albnmoses exist in forms which are not chemically
separable, but which give rise to a series of peptones also insepa-
rable chemically. A part of the peptone formed by peptic prote-
olysis undergoes under the influence of trypsin, further change
which results in the formation of tyrosin, leucin and allied ni-
trogenous bodies. The other part of the peptone is not acted
upon by trypsin. The discovery led to Kiihne's (Verhandb. die
Naturh. Med. Ver. zn Heidelberg, 1877, Bd. I., S. 233) hy-
pothesis, published oyer twenty years ago, that there is during
peptic proteolysis a cleayage of the molecule into two coordinate
ones which he designated hemi- and ^// //-peptone, etc. Certain
chemical considerations led Kiihne and his school to believe that
this coordinate cleavage takes place very early in the proteolysis
and that once the cleavage occurs there are two practically
parallel series of changes, one resulting in anti-albumoses and
anti-peptone, the other resulting in hemi-albumoses, hemi-pep-
tone. Two decades of investigation by Kiihne and his pupils
have resulted in most notable contributions to the subject of
peptic and tryptic proteolysis, and the chemistry of the products
<>f" proteolysis.

The hypothesis of Kiihne, though it has formed the working
basis <>f this school during the period mentioned, falls far short
of an adequate demonstration. In summing up the experimental
evidence on this subject Moore says in his chapter on "The
Chemistry of the Digestive Processes" (Schiifcr's text-book of
Physiol., Vol. C, p. 120): "This [the series of proteolytic
changes] i- all easily accounted for on the supposition thai a
variable fraction of the proteid molecule is easily attacked and
brok.n off into amido-acids [leucin, etc.] by trypsin, bul it is very
difficult to explain on the supposition thai the proteid molecule,
early in the process of decomposition breaks up into two halves,
of which one changes through the stages of hemialbumose and
hemipeptone into amido-acids, while the other, passing through
antialbumose, halts al antipeptone."

We have two hypotheses: (i) Kiihne'- hypothesis of cleavage
into two coordinate hemi- and anti- molecules ; :in<l fn) Moore's
hypothesis of cleavage, from ih<- proteid molecule of subordinate,
amido-acid molecules. The render remembers thai in salivary di-
gestion the starch molecule is subjected to a series of hydrolytic

31S

DIGESTION.

cleavages, l>ut that these cleavages arc not coordinate. In each
cleavage a subordinate molecule maltose is splif off from the car-
bohydrate molecule until the whole carbohydrate molecule is
finally broken up into maltose molecules. According to .Moore's
hypothesis: "The different proteids, especially the proteoses,
differ so little in chemical composition that the difference in their
nature is probably due to a difference in atomic grouping. *
Sonic of these groups are much more susceptible of decomposition

than others. *

Those albumoses which yield much amido-

acid contain in their molecules more groups which are decompos-
able by trypsin. * * Those which yield much antipeptone con-
tain less of these decomposable groups. * * In all cases that
substance which we call antipeptone is the remainder after all of
those groups which are attackable by trypsin have been removed
in the form of amido-acids." The process which Moore outlines
is in harmony with the facts and is analogous to ptyalin digestion.
Moore's hypothesis presents no hypothetical substances ; it utilizes
only substances separable by chemical methods from all other sub-
stances.

The facts of peptic proteolysis may be summarized in the fol-
lowing table :

Series I.

Native Proteid.
Syntonin.

Primary Proteoses.

Series II.

Native Proteid,

Characteristics.

Responds to xanthoproteic test, to Millon's test.
Is indiffusible.

Soluble in dilute acids, insoluble in water, in-
diffusible.

Proto-proteose fSoluble in ]]..<>; precipitated by Mg304, NaCl

\ or(NH4)aS04 in Sat. Sol. Diffusible.

Hetero-proteose | Soluble in dilute NaCl solution, precipitated by

Diffusible.

Secondary Proteoses. Deutero-proteoses.

Peptones.

1V||| 'S.

lllll-lV 111 VI. 11.1, ..l.V . .-... .1 V .- ... , |..- i|. ...... .

j Sat. Sol. Nal'l .ir MgS04 and (NH.j.SO,.

Soluble in water. Precipitated by (NU.^So,.
Diffusible.

Soluble in water, not precipitated by (Nil ,).,so,.
Diffusible.

3. FACTORS WHICH INFLUENCE GASTRIC DIGESTION.

1. The Preparation of Food. — Inasmuch as gastric digestion
is confined to proteids it is now in order to determine the influence
of cooking upon proteolysis. Proteids may be divided into two
classes for the consideration of this subject.

(a) Proteids which are Coagulated by Heat. — This class
includes the native albumins and globulins. As already men-
tioned under cooking, the application of high temperatures to any

FACTORS WHICH INFLUENCE GASTRIC DIGESTION. 319

of this class of proteids decreases the ease with which it may be
digested. In the preparation of egg* (uncom pounded) ; of clear
lean meat, of beef juice or blood (serum albumin and serum-
globulin) just as little heat should be applied as is possible to do
and make a palatable dish.

(6) Proteids which are Not Coagulated by Heat — Albu-
minoids. Collagen is the sole representative of this class which is
important here. Collagen enters into the formation of all of the
connective tissues of the animal body. In preparing most cuts of
meat one has to deal with a large proportion of connective tissue.
If properly prepared it is digestible and nourishing, if not so pre-
pared it is almost indigestible itself and its presence keeps the
digestive juices from gaining proper access to the simple proteids
and thus prolongs very greatly the period of their digestion.
When connective tissue is subjected to heat in the presence of
moisture the collagen becomes hydrated into gelatin. The meat
is then easily masticated, the digestive juices readily penetrate it
and the gelatin itself is readily digested.

2. The Mastication of Food. — Under mastication the impor-
tance of this process was urged.

.;. The Reaction of the Contents of the Stomach. — From
what appeared above it is evident that gastric digestion cannot
proceed in an alkaline medium. The first step in the process
being the formation of acid-albumin, it is important to determine
what acids may serve the purpose.

(") The Kind of Acid Xecessaiiy. — The hydrochloric
arid of the gastric juice is nature's acid. Under certain condi-
tion- lactic acid appears in moderate quantities. Any conditions
which lead to a decrease in the hydrochloric acid favor the ap-
pearance of lactic acid, a fermentation product. In peptic prote-
olysis lactic <i<-i<! may take the p/<t<r of hydrochloric acid. Several
organic acids are taken with the food : (iodic a<-i<l, in vinegar ;
malic acid, in rhubarb, strawberries, apples, etc.; citric acid, in
lemons and oranges, and tartaric acid, in grapes. Any of these
acids may supplement, or even replace, the hydrochloric acid in
gastric digestion.

{>>) The Amount or A< n> Necessary. — Experiment shows
that though <».:; per cent, is the strength of the hydrochloric acid
in pure gastric juice, thai is not the strength necessary for the for-
mation of acid-albumin. The (bods taken into the stomach dilute
the acid very much, so that it is hardly likely that the acid of the
stomach during digestion represents more than o.l per cent, of

the whole contents of the Stomach. Digestion proceeds rapidly in

HClofthal strength. Jusi how strong the other acids should be
is not determined. It i- not likely that they could be effective in
Lets than ".I per cent. strength. Experiment has shown that o.l

320 DIGESTION.

percent, to 0.4 per cent, represent average favorable limits with
sonic variation in the Lower limit for different organic acids. The
presence of moderate quantities of organic acids probably exerts
relatively little effect upon digestion. The tendency of many to use
these acids very freely, together with the influence which the
presence of other acids lias upon the secretion of hydrochloric acid
makes this question of importance to the clinician. If one were
to drink a large quantity of lemonade at the beginning of a meal
it is evident that the strong acid reaction of the stomach would
greatly retard salivary digestion. Jt is also certain that it would
decrease the secretion of hydrochloric acid. On the other hand,
a moderate amount of any acid drink or food toward the end of
the meal may serve an important purpose in supplementing the
acid of the gastric juice.

4. The Influence of Temperature. — What was said of the in-
fluence of temperature upon salivary digestion applies equally to
gastric digestion.

5. The Influence of Dilution. — Much has been said and writ-
ten against the drinking of cold water with meals, and especially
at the beginning of meals. There is more misconception regard-
ing water than any other food. Without entering into a discus-
sion of the details of the question, and without citing the numerous
and reliable authorities, the author will briefly state a few of the
fundamental facts regarding the relation of water to nutrition ;
(i) Water is a prime necessity to the animal body. Lack of suf-
ticient water is just as certain to lead to a derangement of the nu-
trition of the body as is lack of sufficient solid food. Most people
use too little water ; few people use too much water, (n) The
free use of water does not tend directly to the accumulation of fat.
The statement that it does so is a fallacy which arises from these
facts : The free use of water facilitates the processes of nutrition
and economizes food by utilizing a greater proportion of it.
Under such conditions any excess of food tends to be deposited as
reserve material in the form of fat. The reasonable thing to do,
if one wishes to decrease the tendency to accumulate fat, is not to
induce a pathological condition by the decrease of the water; but
to simply decrease the fat-forming material, >. e., decrease tin carbo-
hydrates and fats, (ill) Cold water stimulates the free secretion
of gastric juice. Cold water in moderate quantity at the begin-
ning of a meal thus hastens the gastric digestion and makes more
efficient the antiseptic action of the gastric juice. Recalling what
wras said regarding the relation of water and other diluents to sali-
vary digestion it is evident that several of the factors which hasten
and facilitate gastric digestion at the same time retard or stop
salivary digestion. We have to choose between these two alter-
natives. Which process is the more important to the system?

THE MOVEMENTS OF THE STOMACH. 321

The amylolytic enzyme of the pancreatic juice is much more active
than is ptvalin. The conditions for digestion of starches are more
favorable in the intestine than in the stomach.

By far the most important processes which take place in the
stomach are : (i) The disinfection of the stomach contents by the
hydrochloric acid ; (n) the digestion of proteids. The prolong-
ing of salivary digestion is of much less importance than either
of these. The reasonable thing to do is to stimulate the secretion
of gastric juice. Water is, next to peptone, the most efficient agent
in the stimulation of the secretion of gastric juice.

6. The Influence of the Movements of the Stomach. — The
movements of the stomach facilitate gastric digestion (i) by mix-
ing the gastric juice with the food, and (n) by removing those
portions already digested.

We shall find that movements of the stomach (to be discussed
later) are wholly involuntary. If they are to be controlled or modi-
fied in character it must be through the influence of reflexes {in-
herent reflexes, which see). One may indirectly influence the rate
of the heart by influencing the factors which control the heart. In
the same way, to a smaller extent, perhaps, one may influence the
movements of the stomach by influencing the factors which con-
trol the stomach musculature. Cannon (''The Movements of the
Stomach/5 American Journal of Physiology, Vol. I., p. 359), after
a series of observations on the influence of the emotions upon the
movement of the stomach, thus summarizes his results : " The
stomach movements are inhibited (actually stopped) whenever the
cat -hows signs of anxiety, rage or distress." That strong emotions
inhibit the movements of the human stomach and thus retard gas-
tric digestion is beyond doubt.

4. THE MOVEMENTS OF THE STOMACH.

The most recent and most valuable contribution to our knowl-
edge of the movements of the stomach has been made by Cannon,
cited above, who has worked under the inspiration of Prof. Bow-
ditch, of Harvard. The l!i'>ii/</<n Rays were utilized in producing

a Beriee of -ketches of the stomach in action. To make the con-
tent- of the stomach opaque to the rays subnitrate of bismuth was

mixed with the food. A clear conception of the gastric move-
ment- ;iik| of the ell'ect of tllC-c tnovel I Mil t S may I )(■ gotten by rc-

producing bere some of Cannon's figures and quoting his sum-
mary :

i", "The Stomach Consists of two physiologically distinct
parts: the pyloric pari and the fundus. Over the pyloric part,

while food i- present, constriction waves continually course toward

the pylorus. The fundus is the active reservoir for the food and

822

DIGESTION.

Fig. 175.

Fig. 179.

//.a.m.

3:p.m.

Fig. 176

Fig. 180.

/2:m.

f:p.m.

Fjg. 177.

Fig. 181.

/.p.m.

sp.m.

Fig. 178.

2 p.m.

Fig. 182.

^

s.jop.m.

6. p.m.

The movements of the stomach.

These figures present the " outlines of the shadow of the contents
of the stomach cast on a fluorescent screen by the Rontgen raw
* * * They show the change in the appearance of the stom-
ach at intervals of one hour from the time of eating until the
stomach is nearly empty." (Cannon.)

VOMITING. 323

squeezes out its contents gradually into the pyloric part." (Fig.
155.)

(A) •• Fin-: Stomach is Emptied by the formation between the
fundus and the antrum of a tube (preantral portion) along- which
constrictions pass. (See Fig. 157.) The contents of the fundus
arc pressed into the tube and the tube and antrum slowly cleared
of food by the waves of constriction."

(<■) " The Food in the Pyloric Portion is first pushed for-
ward by the running wave, and then by pressure of the stomach
wall is returned through the ring of constriction ; thus the food is
thoroughly mixed with gastric juice and is forced by an oscillating
progress to the pylorus." (See Fig. 175 et seg.)

{'I) "The Food in the Fundus is not moved by peristalsis,
and consequently it is not mixed with the gastric juice ; salivary
digestion can, therefore, be carried on in this region for a con-
siderable period without being stopped by the acid gastric juice."

(c) "The Pylorus Does not Open at the approach of every
wave but only at irregular intervals. The arrival of a hard
morsel causes the sphincter to open less frequently than normally,
thus materially interfering with the passage of the already lique-
fied food."

(/) " Solid Food Remains in the antrum to be rubbed by the
constrictions until triturated, or to be softened by the gastric juice,
or later it may be forced into the intestine in the solid state."

(//) "The CONSTRICTION Waves have, therefore, three func-
tion-; the mixing, trituration and expulsion of food."

5. VOMITING.

a. The Mechanism of Vomiting.

In discussing this subject one must differentiate between, (i)
ii j i 1 « 1 vomiting without nausea ; and, (ii) violent vomiting with
nausea. Dogs and infants are likely to overload the stomach.
The Latter responds by a firm contraction of the pylorus or
sphincter antri pyloric! followed by a general contraction of the
wall- of the stomach, the result being a regurgitation of a part
of the ju-t swallowed food. That there is no nausea associated
with this act i- evidenced by the fact that the "dog returneth to
hi- vomit," eating the food a second time; if" the dog were
nauseated he would not do that. l>ut in adult man, "■ the act of
vomiting i- generally preceded by a feeling of nausea, and usually
there is a rush of saliva into the mouth, caused by a refles stimu-
lation through the afferent fibers of the gastric vagus and the ef-
ferenl chorda tympani" (Stirling). After this a deep inspiration
i- taken and the glottis closed bo that the diaphragm is firmly
pressed down upon the abdominal contents; and it is kept con-

32-4 DIGESTION.

tracted while a violent contraction of the abdominal muscles
forcibly compresses the stomach, whose contents are ejected. This
movement is so sudden that the sluggishly contracting involuntary
muscles of the stomach walls do not have time to assist.

b. The Influence of the Nervous System upon Vomiting.

(a) The Efferent Impulses pass to the pyloric sphincter.-,
the diaphragm, the abdominal muscles and the muscles of the
larynx and pharynx through the vagus, phrenic, lower intercostals
and the superior maxillary division of the V .

(6) The Vomiting Center, though not definitely located, exists
somewhere in the medulla. The muscles which are most active
in vomiting are the respiratory muscles. The vomiting center
must be associated with the respiratory center ; it may he identical
with the respiratory center in whole or in part, or it may, under
particular conditions, simply dominate the respiratory center. The
vomiting center, indefinite though it is anatomically, is definitely
influenced by certain different impulses.

(c) The Afferent Impulses reach the medullar center through :
(i) the vagus, which is stimulated by any gastric irritant ; (n) the
trigeminus and the glosso-pharyngeal, which is stimulated when
the uvula and fauces are tickled ; (in) the afferent nerves supply-
ing the urogenital tract, stimulated by irritation of that tract, e. //.,
uterine nerves stimulated during pregnancy ; (iv) finally, impulses
may reach the vomiting center from the cerebrum or cerebellum
which may induce vomiting. These impulses may be caused by
certain pathological conditions, or may be induced through the
cerebrum by certain sights, odors or taste, or may be induced
purely psychically through the memory of certain experiences
which were associated with nausea. Disturbances of equilibrium
may through this same central influence induce vomiting.

Drugs which induce vomiting are called emetics.

C. INTESTINAL DIGESTION.

1. THE DIGESTIVE FLUIDS.

a. The Secretion of Pancreatic Juice.

The pancreas represents the compound tubular type of glands
The general arrangement of its ducts and tubular alveoli is shown
in Fig. 161 under Secretion. The structural changes which take
place in the cells of the pancreas during secretion are quite like
those which are observed in the salivary glands during their
activity, and these changes have the same significance. The ac-
companying figure (Fig. 183) shows the principal characteristic
of these changes. During the resting stage the cells become

THE COMPOSITION OF THE PANCREATIC JUICE. 325

loaded with zymogen granules, and their outlines are less clearly
seen. After a period of secretion the granules become much less
numerous, striae appear in the cytoplasm, the unmodified cyto-

Fig. 183.

Part of an alveolus of the rabbit's pancreas. A, at rest ; B, after active secretion, a, the
inner granular zone, which in _I is larger and more closely studded with fine granules than in
/.'. in which the granules are fewer and coarser; b, the outer transparent zone, small in A,
in B. and in the latter marked with faint striae ; c, the lumen, very obvious in B, but
indistinct in A ; </. an indentation at the junction of two cells, only seen in B. (From
& HAEFEB after FOSTEB and KCiine.)

plasm is relatively much more abundant. The appearances
justify the conclusion that parts of the secretion — the ferments —
are formed from the granules ; that these granules become ex-
hausted during secretion and are formed during rest at the expense
of the cytoplasm. The cy t< tplasm, in its turn, is replenished during
the secretory activity of the gland, the cells apparently seizing the
opportunity when the blood supply is abundant to secure the
needed nutriment. During the resting period the granules are
finned at the expense of the cytoplasm. The secretion of pan-
creatic juice varies with the phase of digestion, beginning soon
after a meal and reaching a maximum (in the dog), from one to
three hours after the meal and gradually decreasing as digestion
progresses. This relation of pancreatic secretion to conditions in
the alimentary canal makes it certain that the secretion is a
reflex act.

The experiments ofDolinsky (Archives des Sei. biologique, St.
Petersburg, 1895, Vol. III., p. 399) show that this reflex act is
stimulated especially by the presence of acid in the alimentary
tract ; i. e., anything which will stimulate the How of gastric juice
will in turn stimulate the flow of pancreatic juice. Alkalies in
the stomach diminish the secretion of pancreatic juice. Pawlow
has shown that the vagus contain- the secretory nerves of the
pancreas. Extirpation of the pancreas is followed by diabetes.

b. The Composition of the Pancreatic Juice.

The sensitiveness of the pancreas to any operative procedures
make- it difficult to gel a normal secretion from a fistula. The

326

DIGESTION.

establishment of the fistula is followed by inflammatory changes.
Before these changes occur a secretion may be caughi which is
called temporary. After the inflammatory changes have subsided
the secretiou approaches the normal qualitatively though it con-
tains a much smaller proportion of solids.

The following table gives two analyses by Carl Schmidl (Quoted
by Maly in Hermann's Handbuch d. Physiol., Bd. Y. (2), S.
189) from temporary and permanent fistulas ; also an analysis by
Zawadsky (Cmtralbl. f. Physiol., L891, Bd. V., S. 179) of nor-
mal human pancreatic juice :

Chemical Composition of Pancreatic Juice.

Constituents.

From \ Temporary
Fistula (Dog).

From \ Permanent
|[-i U la (Dog .

III M \\ Panc.

Juice.

W VI 1 v..

Solids :

90.08
9.92

9.0-4
0.88

97.68
2.32

1.64

0.68

0.33

0.25
0.09
0.01

86. 105
13.595

Organic: Enzymes, etc.
Inorganic.

13.251
0.344

Na.cn
NaCl
KC1
Ca, Mgand Na phosphates.

0.06
11.74
trace.
0.08

The pancreatic juice contains several important constituents:

1. Enzymes. — (i) An amylolytic enzyme. — Amylopsin.

(n) A proteolytic enzyme. — Trypsin.
(ill) A fat-splitting enzyme. — ^teapsin.
(iv) A milk-curdling enzyme.

2. Alkaline Salts: Na2COs, and Na3P04.

The influence of the salts is to make the alkalinity of the pan-
creatic juice equal to 0.2-0.4 per cent, of XaOH.

c. The Composition of the Succus Entericus.

This fluid is secreted by the crypts of Lieberkiihn. The secre-
tion is caught by making a fistula. The Vella-Thiry fistula is>
formed "by cutting across the intestine at two places, 10—30 cm.
apart, without interfering with the blood supply, restoring the
continuity of the intestine, * * * stitching both ends of the
isolated piece to the abdominal wall, leaving a double fistulous
opening" (Moore). Fluid caught from such a fistula is limpid,
opalescent, has a specific gravity ranging from 1.010 to 1.014, an
alkalinity of nearly 0.5 per cent. Xa< > I E - it contains proteids, and
coagulates on standing. It contains 2 to 3 per cent, of solids, of
which 0.7 per cent, to 0.9 per cent, is ash. Human succus en-
tericus from the ileum near the ileo-caecal valve1 contained a much
smaller proportion of solids, and had a Sp. Gr. 1.0069.

» Tabby and Manning, Guy's Hosp. Rep., London, 1891, Vol. XL VIII., p.
277. Quoted by Moore.

THE CHEMISTRY OF INTESTINAL DIGESTION.

327

The most important constituents of the suceus entericusare : («)
An enzyme : Tnvertine. (b) Alkaline salts : Na2003, etc.

<J. Composition of the Bile.

The consideration of the bile in its relation to metabolism will
be taken up later. It will be sufficient to summarize its compo-
sition here, and to discuss under digestion only those features
which especially influence digestion.

Table Showing the Composition of Human Bile.

( ONSTITUENTS.

From Gall-bladder.*

From Fistula.**

Watkr.

89.81

98.72

Solids.

10.19

1.28

Organic:

( rlycocholate of sodium.

| 5.65

0.16

Taurocholate of sodium.

0.06

Choleeterin, lecithin, fats and soaps.

3.09

0.04

Mucin, pigment, epithelium, etc.

1.45

0.15

Inorganic salts :

0.63

0.84

Na i 03, NaJll'o,

Note that the bile contains no ferment. Its most important
constituents arc the Na.,COv the Na2HP04 and the glycocholate
and taurocholate of sodium.

2. THE CHEMISTRY OF INTESTINAL DIGESTION.
a. The Action of the Pancreatic Juice.

The pancreatic juice is active chemically through its alkaline
Baits and its enzymes. The alkaline salts of the intestinal fluids
neutralize the acids which enter the duodenum from the stomach
and, in the typical case, make the intestinal contents distinctly
alkaline. In an alkaline medium all of the enzymes act more
vigorously than in a neutral or faintly acid medium.

1. The Amylolytic Enzyme — Amylopsin. — This enzyme is
practically identical with ptyalin in all its properties except that its
action i- very much more rapid. Like ptyalin it acts best in an
alkaline medium, and like thai enzyme it changes starch to mal-
tose. In the discussion of salivary digestion it cannol have es-
caped the attention of the reader thai the ptyalin, under the most
favorable circumstances, digests only a small proportion of the
starch. Due to the imperfect cooking to which starchy foods are
so frequently subjected, to the imperfect mastication and insaliva-
tion which are so prevalent, and to the almost universal dilution
of the contents of the stomach with liquid foods or drinks, the

action of the ptyalin i- reduced t() :i most unimportant role. It

i- lo tin- amylolytic enzyme of the pancreatic juice that we must

look for the digestion of the amyloses.

328 DIGESTION.

The conditions under which this enzyme acts arc most favor-
able, the temperature, the reaction, the degree of dilution, the
trituration of the foods by the stomach arc all favorable to rapid
action of the amylopsin. Even raw starch is readily digested in
vitro by the amylopsin. The conditions to which incompletely
cooked starch is subjected in the stomach probably make it
more easily digestible than is the raw starch used in laboratory
experiments.

One may thus sum up the action of amylopsin : (I) It acts
upon raw or cooked starch causing a series of hydrolytic cleavages
identical with those caused by ptyalin (which Bee). The hy-
drolysis is probably complete, resulting finally in producing mal-
tose, from starch, (n) It acts upon the dextrines which have
been previously formed by ptyalin ; viz.: amylodextrin, ervthro-
dextrin, the achroodextrins '/, jS, and r, completing the hy-
drolytic changes already begun; thus producing maltose from dex-
trines. (in) It acts upon glycogen changing if In maltose through
a series of cleavages parallel to or identical with those observed
in the amylolytic digestion of starch.1

2. The Proteolytic Enzyme — Trypsin. — The proteid-digest-
ing enzyme of the pancreatic juice differs from that of the gastric
juice in requiring an alkaline medium instead of an acid medium
for its activity.

The first step of tryptic proteolysis is the formation of alkali-
albumin. This at once initiates a series of hydrolytic changes
which though parallel to the changes of peptic proteolysis are not
identical with them. The proteoses formed cannot be chemically
separated into primary and secondary proteoses. There is, there-
fore, no profa (proteose and no heteroproteose. D 'uteroproteoses are
formed passing in several slightly varied forms but all of them
fulfilling the requirements of deuteroproteose or deuteroalbumose.
The deuteroproteose formed in tryptic proteolysis is apparently
identical in its response to chemical reactions with the deuteropro-
teose formed in peptic proteolysis. Xeumeister finds that there are
several deuteroproteoses formed in tryptic digestion, and that all
of them yield on further cleavage both peptone and amido-acids.
The deuteroproteose of peptic proteolysis apparently gives rise to
two coordinate peptones (whose mixture is called amphopeptone),
one of which (the hypothetical hemi peptone) may be decomposed
under the influence of trypsin into a scries of amido-acids while
the other (antipeptone) can not be so decomposed. The deutero-

1 The fact that the amylolytic ferment is absent from the pancreatic juice of in-
fants makes it evident that they are not prepared by nature lor starchy foods.
Milk is nature's fond for mammalian young, as witness all'indicatinns both in the
mother and offspring. In the young mammal there are: (i) abundant and ac-
tive milk-curdling' enzymes; (in Proteolytic enzymes; (in) a fat-splitting
enzyme, and (iv) an inverting enzyme.

THE CHEMISTRY OF INTESTINAL DIGESTION.

329

proteose of trvptic proteolysis gives rise to peptone and to the
series of amido-acids, i. <-., there is experimental evidence of a
subordinate hydrolytic cleavage of deuteroproteose but no experi-
mental evidence of a coordinate cleavage into two peptones. In
the terms of those who contend for a coordinate cleavage one may
Bay that the deuteroproteose of trvptic digestion is anii-deuteropro-
teose, and the peptone is anUpeptone, while the fteww-group wher-
ever formed in the proteolysis is instantly decomposed into amido-
acids.

The action of trypsin upon native proteids and upon peptic
proteolytes may be thus summarized :

Table of Tryptic Proteolysis.

Of Xative Proteid

Of Peptic Proteolytes

Pro

teid

Proto-proteosc

Hetero-proteose

Deutero-proteose

Peptone

Alkali-

Albumin

Proto-proteosc

Hetero-proteose

Z>ck'. ■- y-pnteam

1

1

/\

Deutero-proteose

A

A

Deuterupriteoae ~] Amido-
Anti-dnuter"prtUnsc\ acids

Peptone

X \

yK

dmidv-acide

AmiUo-acide

/ \

X-i.

Leucin

/ \

ptptune

Tyrunn

s

'

f Uptime 1 Amida-
' Anti-peptone] acide

j/\

T Peptone "]

j Peptone I Amido-
[A n ti-peptone\ <U&U

The peptone (antipeptone) of trvptic digestion is the form in
which most of the proteid foodstuffs are absorbed. From this
substance and from some sulphur-containing compound, protoplasm
and other higher proteids seem to be built up by a process of
anaboli8m. It is important to determine the constitution of the
substance. There is strong evidence that it is identical with Sieg-
fried's Fkischsdure {Archiv f. And. u. Physiol, Leipzig, 1894,8.
401 ; Zeilch. /'. Physiol Chem., Strassburg, 1896. Bd. XXL, S.
360).

Both compounds read the same in the biuret test; both fail to
respond to Millon'e reagent; both are very hygroscopic; both
yield, on decomposition with hydrochloric acid, lysin and lysa-
tinin. Pleischsaure has been obtained directly from the products
of advanced tryptic digestion. Both of the bodies under consid-
eration are easily soluble in water. From a hoi alcoholic solution
Fleischsaure crystallizes in minute crystals. Siegfried has deter-

330 DIGESTION.

mined the formula of Fleischsaure to be C,0H15N3O8 (mol. wt.
257), Sjoquist (quoted by Moore from Skand. Arch. f. PhysioLj
Leipzig, l<s!(<i, Bd. V., S. 277) determined the molecular weight
of antipeptone (cryoscopic method) to be 250. In the lighi of
these facts it seems eertain that antipeptone and Fleischsaure are
either identical or closely allied and that the quantitative formula
for the two is probably represented in the determined formula for
Fleischsaure.

Frequent reference has been made to the amido-aeids formed
in trvptic proteolysis and to organic bases (lysin, lysatin, etc.)
formed in the hydrolvtic decomposition of proteids. The compo-
sition of these bodies may be briefly summarized.

(a) Lucein or Esobutyl-a-amido-acetic acid.

(( H )_CH— CH — CH-XH- COOH.

The proteids yield, on decomposition the following per cents, of
leucin : Egg albumin, 22.6 per cent.; casein, lil.l per cent.;
muscle, 18 per cent.; vegetable albumin, 17.3 per cent.; fibrin,
7.9 per cent, in digestion, 14 per cent, in decomposition with
H.,S04 ; gelatin, 1.5 per cent, to 2 per cent. (Maly).

(b) Tvrosix or p-oxyphenyl-a-amido-propionic acid.

Q.H/OH— CH — CHXH — COOH.

In decomposition of various proteids the largest proportion of
tyrosin was obtained from casein (4.1 per cent.), followed in turn
by fibrin (3.3 per cent.) egg albumin or vegetable albumin, and
muscle (1 per cent.), while gelatin yielded none.1

It must be remembered that these results represent the greatest
quantity of tyrosin or leucin which it is possible to split off from
the proteids mentioned. The amount actually formed in diges-
tion is probably much smaller.

(c) Butalaxix or Amido-valerianic acid.

(CH3)2— CH— CHXH — ( XX )H.

{<!) ASPAKTIC Acid or Amido-succinic acid.

< << )< )H_( H — CHXH — COOH.

(c) Glutamic Acid or Amido-pyrotartaric acid.

COOH— CH — CM ,— ( 1 1 XII — COOH.

Besides these amido-acids certain bases which are formed in
tryptic digestion as well as in decomposition of proteids.
(/) Lvsix or a-s-diamido-caproic acid.

'Quoted from Maly in Hermann's Handboch, Bd. V. (2), S. 209.

THE FAT-SPLITTING ENZYME— STEAPSIN. 331

CH2XH — (CH.,)3— CH XH- COOH.

(</) Lysatin (or methyl guanidin butyric acid).

H\ - C<rNH?

n.> _ i. <x-CH3— CH — CH — CH 2— COOH.

(/<) Lysatixix.

m> _ l <^.CH3— CH2— CH2— CH2— CO

Lysatin belongs to the same series with kreatin, and lysatin in
is homologous with kreatinin, i. c, it is lysatin minus H.,0.

Ammonia (NHj is formed in both tryptic digestion and decom-
position.

3. The Fat-Splitting Enzyme — Steapsin. — Fats are not
changed chemically in any of the digestive processes which
take place before they reach the small intestine. Adipose tis-
sue, consisting of collagen and fat, is broken up in the stomach
by the peptic digestion of the collagen (or gelatin), which re-
leases the fat. Animal fat is fluid at the temperature of the
animal body.

The released and fluid fat is mixed with the acid chyme in the
form of small globules and passes into the duodenum. The alka-
line salts of the pancreatic juice and bile neutralize all free hydro-
chloric acid and change the reaction to neutral or alkaline in the
duodenum.

A simple fat, as tripalmitin, is a combination of three fatty acid
molecules with propenyl, the glycerol radical. The general struc-
tural formula of the fatty acids of the primary monatomic alcohol
scries is: CH, — (CH2)n_, — COOH. The formula of palmitic
acid, the 10th member of the series, is : CH.{ — (CH.,),, — COOH ;
of stearic add the 18th member; CH— (CH.,)1(.— COOH. Tri-
palmitin has the following structural and quantitative formula? :

( 'H —(Cir,), —COO— C : n2
CH _(CHji _('()()_('• ||

( || -fCNj, _C()()_C: HJ j

or [rH-fui^-rooj-rji,. or (CwH8l02)3 ' C8H6.

Oleic acid belongs to the triatomic alcohol series whose acids
possess the following general formula: CH8 — (CH2)n , — (CH). —
cooil. Oleic acid i- the L8th member of die series and has

332 DIGESTION,

the formulae: CH3— (CH2)U— (CH)2— COOH or C18H3402. Tri-
olein has the constitution indicated in the formula :

CH3— (CH2)U— (CH)2— COO— C:H,

CII — (( JHJj — (( !H)2— ( !( )0— ( • 1 1

CH3— (CH2)U— (CH)2— COO— < !:H.

[( !H3-(CH2)u-(CH)2-COO]3-C3Hs

Animal fat is a mixture of tri-palmitin, tristearin, and triolein
in various proportions. Certain fats and oils, especially vegetable
oils, have various other members of the fatty acid or oleic acid
series.

The task which presents itself now is to find the eifect of
steapsin upon these compounds. Let tri-palmitin be taken as a
type. Steapsin brings about a hydrolytic cleavage of the mole-
cule into its constituents :

[CH — (CH.,), — COO]3C3Hs + 3H..O =
C3H5-(OH)3 + 3CH3— (CH2)14— COOH

Tri-palmitin -f- 3 water = glycerol + 3 palmitic acid.

This hydrolytic cleavage of the fats leads to an accumulation
of glycerin and of various fatty acids in the intestine. The pres-
ence of the fatty acids induces, or facilitates three important
changes in the contents of the small intestine.

(a) Emulsificatiox. Oil is emulsified when it is separated into
minute globules which are suspended in the medium and remain
separate. If the globules remain separate indefinitely showing no
tendency to coalesce the emulsion is said to be permanent ; while
in a temporary emulsion the oil globules gradually coalesce and
rise to the top of the medium. Emulsions may be classified also
on the basis of their formation whether meehanical or chemical.
If an oil be vigorously shaken with a viscous menstruum, such as
egg-albumin, or a gum or sugar syrup, the division of the oil may
be as fine and the persistence of the emulsion as permanent as in
the case of a chemical emulsion. The success of this mechanical
emulsion will depend largely upon the vigor and the time of the
mechanical agitation. A chemical, also called spontaneous, emul-
sion is produced when the conditions are favorable for the forma-
tion of soaps in the fat. Under these conditions a fat or oil will
v< ry soon be transformed into a permanent emulsion without the
help of shaking, without mechanical aid, though the process is
hurried if the materials are shaken or stirred. Both fatty acids
and alkalies are present ; soap is formed and the contents of the

THE ACTION OF THE BILE. 333

small intestine are mixed by the peristaltic action of the intestinal
walls. The conditions are thus favorable for both chemical and
mechanical action.

(b) Saponification. As has already been stated the conditions
favorable to the formation of soap exist in the small intestine.
The pancreatic secretion, the bile, and the snccus entericus all
contain Na2C03. When a fatty acid and Na2C03 come together
a sodium soap is instantly formed :

2CH3— (CH2)U— COOH+Na2C03=
H20-f C02+ 2 CH3— (CH2)14— COONa

2 Palmitic acid + sodium carbonate = H20+C02-f-2 soap.

(c) Reaction. The influence of steapsin upon the reaction in
the small intestine has only recently come to the attention of
physiologists. As stated above, the first effect of the alkaline
secretions of the small intestine is to neutralize all the free acid of
the chyme, and to make the contents of the small intestine neutral
or alkaline. The second effect is to liberate from the fats a series
of fatty acids, and from Na„C03> carbonic acid gas. These acids
though weak suffice to give the contents of the small intestine an
acid reaction. But what is of very great importance to the or-
ganism these particular acids do not interfere with the digestive
processes going on in the small intestine.

4. The Milk- Curdling Enzymes. — Pancreatic juice or an
aqueous extract of fresh pancreas has the power to curdle milk.
That the pancreatic juice has the opportunity to curdle milk, even
when a full meal is made of that food, is hardly likely.

h. The Action of the Bile.

This secretion contains no enzyme. Its action is, however, veiy
important when taken in connection with the action of the fat-split-
ting enzyme of the pancreatic juice. The glycerine liberated by
the hydrolytic cleavage of the fats is soluble in water and is prob-
ably absorbed readily as glycerine; the fatty acids liberated in
tlie process are insoluble in water and have a melting point con-
siderably above the temperature of the blood (palmitiu at 62° C,
-tea rin 69 ( '. ). It' they are not dissolved they would pass through
the alimentary canal unabsorbed. A part of the fatty acids is com-
bined as soap w bich is soluble. < tf the Na.,( !( )., required lor this pro-
cess the bile furnishes much the greater part. Any fatty acid not
combined in soap ie dissolved in the glycocholates of sodium and of
potassium. When the bile secretion is diverted from the alimentary

canal through a li-liila a large part of the ingested Cat .', to \ appears

in the faces a- fatty acid-. Munk (Virchaw'a Archiv, 1890, Bd.

334 DIGESTION.

< IXXII., S. 302, quoted from Moore) found that the absorption
of fats of high melting point suffered more than that of fats of low
melting point. Now, the fats of high melting point contain a pre-
ponderance of stearin whose acid (stearic acid) has a high melting
point (69 C.) and thus resists other intestinal solvents of fatty
acids.

Another most important property of the bile salts is their ability
t<> dissolve the soaps of the alkaline earths. Most drinking water
contains calcium and magnesium salts in solution. These salts
combine at once with fatty acids to make calcium or magnesium
soaps, or they displace Xa from the soluble soaps already formed.
These soaps of Ca and Mg are insoluble in water and but for the
presence of the glycocholate of Xa and K would pass out of the
alimentary canal unabsorbed (Xeiuneister, Lehrbuch der physiol.
Chemie, Jena, 1893).

One may summarize as follows the action of the bile in the
digestive process :

(«) It assists in the emulsification of fats.

(1) It assists in the saponification of fats.

(;-) Its glycocholates and taurocholates assist in the solution of
fatty acids.

(d) Its salts in solution dissolve the soaps of the alkaline earths
(insoluble in water).

(i) Bile stimulates the contraction of the muscularis mucosa of
the villi, thus accelerating the absorption.

(C) It acts as a " natural laxative" through (i) lubrication of
the faeces; (n) stimulation of the muscular action in peristalsis.

| jj ) It diminishes putrefaction in the large intestine.

c. The Action of Succus Entericus.

Reference has already been made to the fact that the Xa.CO^
which makes 0.25 per cent, to .5 per cent, of the intestinal juice,
assists the pancreatic juice and bile in the emulsification and saponi-
fication of fats.

The most important constituent of the intestinal juice is the
inverting enzyme, Invertin. This enzyme acts upon disaccharids,
and through hydrolvtic cleavage resolves them into two coordi-
nate monosaccharid molecules. The amylolytic enzymes of the
saliva and pancreatic juice change starch to maltose, a disaccharid.
The sugar of milk is lactose, a disaccharid. An important article
of diet is cane sugar, another disaccharid. All of these disac-
charids possess the quantitative formula VVJ1.J)U.

Experiment has determined that none of these disaccharids ap-
pear in the blood. Only monosaccharide appear in the blood.
The change from disaccharids to monosaccharids must take place
before the sugar is discharged into the portal blood. The intesti-

THE DIGESTION OF MILK. 335

nal canal possesses in the invertin an enzyme capable of inducing
the required changes :

(a) Maltose + H..O -f- invertin = invertin + 2 dextrose.

GuH^Oi, + H2G = 2C6H120.

(b) Lactose + water = dextrose -f- galactose.
GJBLO,. + H,C) = C.H.,0,. +Q.H o .

12 22 11 ' 2 o 12 b ■ (> 12 o

(c) Saccharose + water = dextrose + levulose.

C12H22Ou + H20 = C6H1206 + C6H1206.

For the structural formula? the reader is referred to the intro-
duction to this chapter.

d. The Digestion of Milk : A Summary.

Milk is a perfect food (for composition see foods). Its carbo-
hydrate lactone is already in solution. Its proteids are lact-albn-
min and caseiuogen. Its fat is a composite of many simple fats,
such as tri-olein, tri-palmitin and tri-stearin, with lower members
of the palmitin series : the triglycerides of butyric (4th in the
series) ; caproic (<>th) ; caprilic (8th) ; capric (10th), and myristic
(14th), acids. All of these lower members are present in very
small and variable quantities. To their variation is due the
various flavors of butter. Small quantities of lecithin and eholes-
terin are also present.

-Milk is not acted upon by any constituent of the saliva. In
the stomach it is first curdled by the action of the enzyme ram in.
The curdling of milk consists in the coagulation of the casein-
ogen ; after coagulation the caseinogen is called casein. The ca-
sein and the lact-albnmin undergo the typical proteid digestion.
The proteid pellicles which surround the oil globules are digested
off and the oil escapes. After passing into the small intestine the
digestion of the milk proteids is completed by the trypsin ; the
fats are acted upon by the steapsin forming an emulsion, and a
long series of soaps, and free fatty acids. The lecithin is broken
up into its constituents : For each lecithin molecule : (r) two
fatty acid molecules, (n) glycero-phosphoric acid (nr) cholin.1

1 Dipalmitic lecithin lias the following structural formula :

1! ' « II

l4— C-0-C:H

" | OH

II' OPO Ml

o 1 °

II - -II

i 0 C:H,

C ;H,
I 0 :• H,
-CH,-N< +3H20

on

•J Palmitic acid

plus

( rlvcero-phos-

phoric arid

plus

I liuliu or i ii

methyloxyethyl-

ainiuiiuiiiiii-

bydroxide.

The dotted liu<- indicate where the cleavage of 1 1 • « - molecule takes place.

336 DIGESTION.

The lactose of the milk undergoes bydrolytic cleavage into
dextr< ise ;in<l galactose.

3. FACTORS WHICH INFLUENCE INTESTINAL DIGESTION.

Such factors as cooking, mastication, and temperature have
Little direct influence upon intestinal digestion. Even the in-
direct influence is slight because the pancreatic juice can digest

raw starch ; the stomach retains the food until the imperfections of
mastication arc largely corrected ; and its sojourn in the stomach
certainly gives it the temperature of the body. There are three
important factors yet to consider:

a. The Influence of Bacteria upon Intestinal Digestion.

"The food in the alimentary canal is acted upon, not only by
the digestive secretions and their enzymes, but to a greater or less
extent by certain bacteria, which are never entirely absent, al-
though the amount of their action varies greatly under healthy
conditions, with the nature of the food and the class of the animal.
Under abnormal conditions the growth of these organisms maybe
greatly increased, and nutrition be seriously impaired by the turn-
ing t<> their own uses the products of normal digestion, and leaving,
for the service of the animal, only degradation products inadequate
or wholly unsuited for the purposes of its metabolism." (Moore.)

The effect of cooking and of the HC1 of the gastric digestion is
to practically free the chyme which enters the duodenum of all or
nearly all bacterial life. We may look upon the bacteria of the
intestinal tract as parasites introduced with the food and thriving
only moderately when all of the conditions are normal. When
the digestion is deranged the conditions may be favorable to the
excessive development of various bacteria (organized ferments)
whose food is robbed from the host and whose excreta may be ex-
tremely deleterious to the host. It has been contended that these
parasites are "beneficial?'; a similar contention might be made in
behalf of certain vermin (!) Parasitism is not beneficial.

Nuttall and Thierfelder (Zeibsch.f. physiol. Chemie, 1895, Bd.
XXI., S. 10!)) have demonstrated that young animals with sterile
alimentary tract, sterile air and sterile food grow just as well as
the control animals under the usual conditions. This applies as
well for vegetable foods as for animal foods. Animals live and
thrive in spite of their bacterial parasites and not because of them.

The action of bacteria may be discussed in its relation to differ-
ent parts of the alimentary tract, and in its relation to different
foodstuffs.

1. The Action of Bacteria in Different Parts of the Ali-
mentary Canal. — (a) Bacteria of the Mouth have no influ-

INTESTINAL DIGESTION. 337

ence upon intestinal digestion, though they may menace the teeth
of the animal.

(6) Bacteria of the Stomach are introduced with the food
and, as mentioned above, are usually destroyed by the HC1 when
that acid is sufficiently strong (0.2 per cent, to 0.3 per cent.).
When the HOI is very weak, much delayed in secretion or
wholly absent the development of Bacterium lactis and various
t'ermentive and putrefactive forms is favored. In the case of
11. lactis one might make an exception to the statement made
above that bacteria and their excreta are not beneficial. Peptic
digestion can only proceed in the presence of an acid. Lactic
aeid can take the place of HC1 in forming acid albumin or syn-
tonin. In the absence of HC1 lactic acid, the excreta of B. lactis
may be advantageous to the system.

(c) Bacteria of the Small Intestine. — The acid reaction
of the chyme representing free HO and acid albumin is neutral-
ized and replaced with an acid reaction due to the accumulation of
organic acids. At first these organic acids are fatty acids released
by steapsin from neutral fats ; these are, however, absorbed as ab-
sorption progresses : the acid reaction arising from this source will
tend to decrease. But it has been observed (Macfadyen, Nencki,
Sieber — Arch.f. Exp. Path. u. PharmacolX that the acid reaction
usually found at the lower end of the ileum in man is due princi-
pally to acetic acid, with only traces of fatty and other acids. It
seems likely that, in the small intestine, the acidity due to fatty
acids is replaced from above downwards by acidity due to fermen-
tation of carbohydrates. Moore and Rockwood (Jour. Physiol.,
L897, Vol. XXI., p. 373)3 in a very extended and recent series
of observations upon the dog, cat, white rat, guinea-pig and rabbit,
conclude: (r) "The reaction is not normally aeid throughout
the entire length of the small intestine, and the alkalinity in-
creases in passing down the intestine." (n) "The presence of
fat in the food causes in carnivora an acid reaction which persists
until the lower third of the intestine is reached." (in) " The al-
kalinity is much greater in herbivora than in carnivora ; * *
also, in carnivora tin- alkalinity is markedly increased by carbo-
hydrate food." (IV) " It is probable that in the animals observed

any extensive bacterial decomposition of carbohydrates that may

occur take- place in the large intestine." (Quoted from Moore.)
('/) Bacteria of the Large [ntestine. — In this segment

of the alimentary canal the reaction is conceded by all to be alka-
line, due to tin- neutralization of any aeid entering the csecum by
the distinctly alkaline secretions of the mucous membrane. In the
large intestine profound changes take place under the influence of
putrefactive bacteria. The proteide are especially attacked in this
segment of the canal, the acid reaction of the small intestine pro-

22

338 DIGESTION.

tec ting them normally from putrefactive changes in that portion
of the canal.

2. The Action of Bacteria in Relation to Different Foodstuffs.
— (a) Bacterial Action <»n ( Iarbohydrates consists < i ) in the
fermentation of the sugars with the formation of ethyl alcohol,
acetic, lactic, butyric, and succinic acids, with the liberation of
('()., and H; (n) in the decomposition of cellulose with the for-
mation of marsh gas (CH4) and C02; ( in ) in the decomposition of
starch with products similar to (i). The fermentation and de-
composition of carbohydrates hen-ins in the small intestine and
progresses with increasing activity through the caecum, then with
decreasing activity to the rectum.

(6) Bacterial Action on Proteids seems to he inhibited by
the acid reaction of the small intestine. As soon as the contents
of the alimentary tract become alkaline the decomposition of
proteids is facilitated. There are two series of products formed
during the putrefaction of proteids and the proteolytes. The
members of the first series are derived from tyrosin in the fol-
lowing manner :

(Baumann, Bench, d. deutsch. chem. GeselL, 1879, Bd. 12,
S. 1450.)

H

C H N:H„

H c C— C— C— COH+H2 =

I H HO
HOC OB

('

H

NH3+C6H4-OH— (CH2)2— COOH.

Tryosin or jp-oxyphenyl-amido-propionic acid -fH2 =

„ f p-hydroeumaric acid or
3~*~ \^-oxyphenyl-propionie acid.

^-Hydroeumaric acid parts with C( >., and becomes p-ethylphenol
(C Il-OH — C.,II.) which has not, however, been found in the
intestine, though it occurs in experiments in vitro, p-ethylphenol

next becomes oxidized ( + 30) to ^-oxyphenyl-acetic acid. This
in turn gives up C02 and becomes yy-cresol (p-methyl phenol)
which is again oxidized to ^-oxybenzoic acid — not yet found in
the intestine.

INTESTINAL DIGESTION. 339

Oxybenzoic acid gives up 0O2 and forms phenol :

CJH/OH— COOH = CO,+C.H.OH

^-oxybenzoic acid = CO., -(-phenol. .

The second series of products is less understood.
Indol has the following structure :

H

C

HC C

— CH

HC C
C

«'.H

N

H

H

Skatol

or

Methyl-

■indol has the
H
C

following

XT

structure

H-C C-C-C-H

II H

HC C CH

/
C N

H

Both of these bodies are soluble in water, from which solution
they crystallize in small scales. Both are in part absorbed and
in part passed out with the faeces.

b. The Influence of Cellulose upon Intestinal Digestion.

In the case of herbivora it has been demonstrated by Bunge
[Physiologische Chemie, 18!t4, 8. 75] that cellulose is important
not as :t nutrient but "in giving bulk and looseness to the food
and in mechanically inducing peristalsis by irritation of the mu-
cous membrane." To the herbivora it is indispensable, to omniv-
ora lik<' man it is advantageous in moderate quantities, to car-
nivora it lias do advantages. Herbivora digest 60— 70 per cent.
of it, man, 4-60 per cent, according to the condition of the cel-
lulose. Under the influence of bacteria it is subjected to a hydro-
lytic cleavage represented in the following equations :

[C8H10O6+H8O=3CO3+3CHJII

The reaction is varied by the production also of acetic, propionic,
butyric, and valerianic acids.

340 DIGESTION.

4. THE REMNANTS OF INTESTINAL DIGESTION.
The Faeces.

The faces represent thai part of the content- of the alimentary
tract which is nut absorbed into the circulation. The contents
represent not only the ingested food hnt portion- of various secre-
tions and of excretion.-, besides bacteria and their excreta, and
epithelial elements from the mucous membrane. The hulk of the
faeces is modified by the proportion of indigestible material in the
ingesta. The fasces of the herbivora are very copious, while those
of carnivora are comparatively -canty. In man the weight will
vary from 170 gms. to 400—500 gms. according to diet. The
amount of water varies with the character of the food and with
the habit of the animal ; free and frequent passages having more
water than those associated with constipation. The longer the
frecal matter is retained the larger the proportion of water ab-
sorbed from it.

The composition of the fasces may be classified thus :

Gases: N, H, CO,,. Il,s. < II,.

Liquids: H20 (68 to 82£ normally).

Solids : Undigested Food. —Fata, fragments of meat, starch.

Indigestible Mutter. Col hi lose, ligaments from meat, keratin, mucin, gunis.

Composition
of the
Fseci

Bactt ria and the resin*. J'roilur/s of their Deeoni]>o-ition of Foods. Lower
fatty arid-, lactic acid, tyrosin and it* decomposition products, phenol;
hitmatin, insoluble BOaps of I 'a and Mg.

Bile Residues: Mucus, cholesterin, bilary acids, stercobilin.

Excrelin. — C7BH166S( >_..

Inorganic Salts. — Soluble salts of Na, K, Mg, etc.

Insoluble salt* of Ca, Mg, Fe, etc.

5. THE MOVEMENTS OF THE INTESTINES.

The movements of the intestines are together called peristalsis.
Peristalsis consists of a progressive wave of contraction which
usually passes from above downwards. This wave of* contraction
involves especially the circular fibers whose progressive contrac-
tion has the mechanical effect of sliding a small ring along the gut
contracting the lumen upon the contents. Accompanying the
contraction of the circular fibers and just preceding it is a con-
traction of the longitudinal fibers. This combined vermicular
peristalsis is very effective in pushing on the contents of the canal.

The peristalsis of the intestinal tract is stimulated by the pres-
ence of food in general; but it is especially stimulated by the
presence of such sharp pieces of cellulose as occur in coarse
meals of the cereals. The vagus seems to be the efferent nerve.
Section of the vagus causes cessation of all reflex peristalsis. Sec-

DEFECATION. 341

tion of the splanchnics causes vaso-dilatation with profuse secretion
of the succus entericus.

6. DEFECATION.

Ingestion begins with a voluntary act and is consummated with
an involuntary act. Egestion or defecation begins with an in-
voluntary act and is consummated with a voluntary act.

As the food approaches the rectum it gradually loses water and
greater force is required to move it along the canal ; accordingly
the circular muscular coat is thicker in the lower end of the canal,
reaching a maximum in the external sphincter of the anus.

The slow contractions of these muscles gradually advance the
fseces to the rectum where their accumulation periodically stimu-
lates a strong expulsatory contraction of the circular muscle fibers
of that viscus. This, though purely involuntary, is not outside
the consciousness of the individual. The final conscious act con-
sists in voluntarily inhibiting or suspending the tonic contraction
of the external sphincter. In the absolutely typical and normal
condition the contraction of the walls of the rectum suffices to rid
it of the accumulated fieces. Frequently the force of these muscles
must be supplemented. This is accomplished by a voluntary
contraction of the abdominal muscles, which causes a high pressure
within the abdominal cavity, the intravenous pressure in the
hemorrhoidal veins is positive, and there is a tendency for these
veins to become permanently distended, causing haemorrhoids.

CHAPTER VI.
ABSORPTION.

INTRODUCTION.

1. ABSORPTION DEFINED.

2. STRUCTURES INVOLVED IN ABSORPTION.

.".. PHYSICAL FORCES [NFLUENCING ABSORPTION.
4. FORMES THEORIES OF ABSORPTION, REVIEWED.

THE PHYSIOLOGY OF ABSORPTION.

1. ABSORPTION FROM DIFFERENT PORTIONS OF THE ALIMEN-

TARY (ANAL.

a. Absorption From the Mouth.

l>. Absorption From the Stomach.

<■. Absorption From the Small Intestines.

(I. Absorption From the Large Intestine.

2. ABSORPTION OF DIFFERENT FOODSTUFFS.

a. The Absorption op Water.

b. The Absorption op Salts.

c The Absorption of Carbohydrates.

d. The Absorption of Proteids.

e. The Absorption of Fats.

ABSORPTION. INTRODUCTION.

1. ABSORPTION DEFINED.

The term absorption in its general sense means imbibition and
applies with special fitness to the "drinking in " of a liquid by
any porous body such as a sponge. In this sense it is a purely
physical process depending upon the capillary attraction exerted
by the capillary pores of the body upon the liquid. This term
has been extended to include such processes as the taking-in of
water by germinating seeds, a purely physical process depending
upon the laws of diffusion or osmosis. It was the most natural
thing to extend the term to the process by which an organism
takes up food from the medium in which it exists or from canals
in which foods have been dissolved or otherwise prepared. Ab-
sorption, then, is that function of the organism, through the exercise of
which the system takes in nutriment through </ boundary epithelium.
It has been thought that the absorption by the system, of the
products of digestion is a purely physical process depending upon
the interaction of two or three factors : osmosis, nitration.

342

STRUCTURES INVOLVED IN ABSORPTION.

343

Whether or not physical forces alone are sufficient to account
for the phenomena of absorption will be discussed later. In the
definition (if absorption reference was made to the " boundary epi-
thelium." The boundary epithelia of the mammalian body are : (i)
the epithelium of the alimentary canal ; (n) epithelium of the lung
passages ; (he) the epithelium of the urinary tract ; (rv) the cuticle.

Of these boundaries the first is preeminently an absorptive sur-
face while the second is equally absorptive and excretory ; the
third is wholly excretory, and the fourth is practically non-ab-
sorptive ; and its excretory and secretory functions are secondary
to it- especial function — protection.

It will be understood from this expression boundary epithelium,
that the physiologist looks upon the contents of the alimentary
canal, lung passages, and

renal passages as being really Fig. 18-4.

outside of the organism though
, i, dosed by the body. What
is in the alimentary canal is
really not yet within the
organism. When it passes
within the outer boundary of
the outer layer of cells, then
it is within the organism, and
the passage from the alimen-
tary canal into the epithelial
cells which surround this
canal constitutes absorption.

■2. STRUCTURES INVOLVED
IN ABSORPTION.

Whatever forces may be
involved in the process of ab-
sorption,— whether physical,
mechanical, or vital, — the
area of absorbing surface
mii-t l>e an important factor
in the total amount absorbed.

Under Digestion, Introduc-
tion, mention was made of the
prominent transverse folds
of the mucosa of the -until in-
testine. These valvules <■<,,!-
niventes make the mucous sur-
face ahont three times ae greal
:i- :i straight cylindrical Lining of the same ennui would he. Upon
tlii— fohhd mucous surface the microscope reveals innumer-

Section of injected Btnall intestine of cat : ", '»,
mucosa: a, villi; /, their absorbent vessels ; A,
simple follicles : c. muscularis mucosae ; </, submu-
cosa; '. <'. circular and longitudinal layers of
muscle; i. fibrous coat, All the dark lines repre-
sent i>l [vessels filled with tin- Injection mass.

"i.. j

344

ABSORPTION: INTRODUCTION.

able minute finger-like projections — the villi. These projections

are subevlin lrie.il in form and the axis of the cylinder may he

Fig. 185.

»;, •}-.■ ''v.vr; WZr -— r'
i.V i *.• iv/^^

&

*S

?*-.

If

S&

^

Showing the frequent inequality of the villi. (Benda.

Cross-section of an intestinal villus, e, columnar epithelium ; .</, goblet-cell, its mucus is Been
partly extruded ; 1, lymph corpuscles hot ween the *pit luliu ni-ei-lls ; h, basement-membrane;
<■, blood-capillaries; m, Bection of plain muscular fibers; ../.. central lacteal. (Schaefbr.)

taken as averaging about eight times the radius of the base. The
area of the villus would then be about l(j times as great as the

STRUCTURES INVOLVED IN ABSORPTION.

345

area of the base, or the area of the whole surface occupied by villi
is multiplied approximately 16 times through the means of the villi.
Thus the area of the epithelial surface is many times as great as
the area of the intestine when considered as a smooth cylinder.

The accompanying figures show the structure and grouping of
the villi. Xote in Fig. 184 the coats of the intestine : the in-

Fig. 187.

Fig. 188.

■a.

Luteals, thoracic duct, etc. a, intestine;
h, rena cava inferior ; c, e, right and left sub-
clavian veins ; d, poinl of opening of thoracic
< I iif-t into left subclai Ian. | Da i i

view of the principal branches of the vena
portae. ',..■ 1, lower surface of the right lobe
of the liver; •_', stomach ; 8, spleen; i, pan-
creas ; 5, duodenum ; 6, ascending colon ; 7,
small Intestine: 8, descending colon ; a, vena
portee dividing in the transverse assure of the
liver: 6, splenic vein; c, right gastroepiploic ;
d, inferior mesenteric ; e, superior mesenteric
vein ; /, superior mesenteric artery. (Quain. )

jected arteries and capillaries; the lymph radical in the second
and fifth villi from the left. The ends of the cells shown in the
third villus from the left. Fig. 185 shows the marked inequality
frequently to be noted in the length of the villi. In Fig. 186
the minute structure of the villus is shown. Note, especially, the
numerous capillaries which lie jusl beneath the basement mem-
brane; the muscle-fibers, and the large "central lacteal" or
lymph radicle.

346

IBSOBPTION: INTRODUCTION,

In the intestine of such animals as the cat, rat, and rabbit the
longer villi reach well toward the middle of the intestine.

The two courses which absorbed material takes are: (i)
through the lacteals, and thoracic duct to the venous system
(See Fig. is?); through the vena portae to the liver (see Fig. 187).

Fig. 189.

I . . lat i m.s ci villi luting peristalsis

3. PHYSICAL FORCES INFLUENCING ABSORPTION.

Just how far physical forces enter into the act of absorption has
been a subject of controversy for a long time. Recent investiga-
tions tend to minimize the importance of the physical forces and
to magnify that of the more distinctly physiological factor " selec-
tion." The student is, however, unable to understand the litera-
ture of the subject without at least a general knowledge of Os-
mosis and Filtration.

a. Osmosis.

The term osmosis is applied to diffusion taking place through
a membrane. But diffusion involves a mutual or reciprocal in-
terchange of space or a mutual interpenetration independent of
any mechanical mixture or chemical reaction.

Let the open end of a large glass tube have an animal mem-

OSMOSIS.

347

brane stretched across it and fixed in place ; let the tube be partly
filled with a solution of any crystalline substance easily soluble in
water ; and let this dialyzer or endosmometer be lowered into a jar
or beaker of distilled water until the liquid within the dialyzer
stands on the same level as that outside. These conditions ful-
filled, one will observe, after a few hours, that the liquid within is
higher than that in the beaker outside, making it evident that
water has passed through membrane into the dialyzer or osmom-
eter. A chemical test of the liquid outside readily reveals the
fact that some of dissolved salt has passed through the membrane
into the distilled water. The raising of the liquid in the dialyzer
above the level of that outside involves a certain amount of energy.
This energy is measurable and may be determined with a mercury
manometer or by simply calculating- the weight of the column of
water supported by the pressure. This is called endosmotic pres-
suri or osmotic pressure.

1. Laws of Osmotic Pressure. — The work done by Pfeffer
("Osmotische Qntersuchungen," Leipzig, 1877) establishes the
following laws of osmotic pressure :

Law I. " The osmotic pressure of a dilute solution at constant
temperature is proportional to its concentration." (Reid, in
Schaefer's Text Book, Vol. I., p. 265.)

Law II. " At constant concentration of a dilute solution the 08-
moMe pressure is proportional to the absolute temperature. (Reid.)'
These two laws are well illustrated in the following data from
Pfeffer's •■ Untersuchungen." Cane sugar was used.

i. Varying Concentration;
( Ionstant Temperature (14°

1

ii. Varying Temperature,
Constant Concentration (1
Per Cent.).

. I i: n ION ni
SOU I KM*.

1 *

2*

1

8 .

08MO1 [I Pkessi i:i

IS MM. ,,l HO.

536
1016

■-'OS1.'

3075

I I Mi'i B \l i RE.

II.

14.15°

36 '

Peessi be.

Observed.

( lalculated.

;,n

510

512

567

520

529

Note thai law i for osmotic pressure ia the equivalent of Boyle's
law for the pressure volume of a gas ; and that law n is the equiva-
lent of Charles' law for the temperature-volume of a gas.2

1 '/'/« absolute temperalun (in degrees centigrade) ia calculated from — 273 <'•
Thua a temperature of 15° C. equals (273 L5) 288° A.bs.

*Charlei L<<" : "The volume of a gas, if the pressure remain the same, is <li-
n-i-tlv proportional \>> it- absolute temperature. It' the pressure and volume both
vary, then their product ia proportional to the absolute temperature." I I taniell'a
Physics, p. 77. |

:'»4s ABSORPTION: INTRODUCTION.

Law iii : u The osmotic pressure of a dissolved substance is exactly
the same as the gas 'pressure, measured by the manometer, which one
would observe if he could remove ili<: solvent and leave the dissolved
substance, as a gas filling the some volume." (Nernst's "Theoret-
ical Chemistry." Cited by Reid.)

Yan't Hoff calls attention to the fact that "the hypothesis of
Avogadro1 then is not merely capable of extension by the law of
Henry to solutions of gases, but to solutions of matter which is
not gaseous under ordinary circumstances. From the foregoing
Reid formulates the following :

Law iv : "Equal volumes of gases or dilute solutions at the same
gas or osmotic pressure, and at the same temperature, contain equal
numbers of molecules" (Schaefer's Text-book of Physiology, Vol.
II., p. 266.)

Within certain limitations Dalton's law for gas mixtures2 holds
for the osmotic pressure of a mixture of substances :

Law v. <l The total osmotic pressure of a mixture of substances
(in solution) is equal to the sum of the partial osmotic pressures of
the several components." (Reid.)

Adie (Jour. Chem. s<><\ Loudon, 1891, Vol. LIX., p. .'544,
cited by Reid) calls attention to the fact that " when the two or
more constituents of the solution have a common ion each salt
diminishes the dissociation of the other, so that the pressure of the
mixture is less than the sum of the pressures of the two com-
ponents.

For example the osmotic pressure of 1:40 solution of A1.,(S04)3
is 1.27, of a 1:40 solution K,S04 is 1.29. The sum of the
pressures is thus 2. 56. But the pressure of 1:40 solution
K2A12(S04)4 is not 2.56 but 2.:)!).

The osmotic pressure of a solution is a measure of the osmotic
activity. The above laws take into consideration only temperature,
degree of concentration, and the influence of mixtures ; but most im-
portant factors are the character of the membrane and of the solvent.

Summing up this brief discussion of osmosis one may give the
following factors as concerned in the rate of osmosis :

(r) The quantitative composition of the solutions separated by
the membrane, and consequently the partial osmotic pressure
exerted by the several constituents.

(n) The coefficients of diffusion of the various constituents.

(in) The character of the membrane.

( iv) The character of the solvent.
(V) The temperature.

1 Avogadro's hypothesis : Equal volumes of all gases contain the same number of
molecules.

1 Tin- pressure exerted by each component of a mixture of gases is independent
of the pressures exerted by the rest of the components.

THE PHYSICAL THEORY. 349

(vi) The hydrostatic pressure upon the two sides of the mem-
brane (filtration).

b. Filtration.

Filtration is the passage of a liquid through a membrane under
the influence of pressure. It is a purely mechanical process. In
the animal body any filtration which may occur is complicated
with an osmosis which is going on at the same time, for in every
ease the relation of liquid, membrane and filtrate are such as have
just been described under osmosis.

In fact factor (vi) above gives hydrostatic pressure as one of the
variables, so that in the living organism cases of filtration maybe
classified as cases of osmosis where the principal determining factor
is hydrostatic pressure.

The following factors are active in filtration :
(i) The porosity of the membrane,
(n) The degree of pressure.

(in) The character of the liquid to be filtered.

(iv) The temperature of the liquid.
(v) The action of the liquid upon the membrane.

(vi) The osmotic relations of liquid to filtrate.

4. FORMER THEORIES OF ABSORPTION REVIEWED.

a. The Vital Energy Theory.

The earlier theories of the physiologists regarding the forces in-
volved in absorption are very well represented by Tiedemann and
Gmelin (quoted by Heidenhain, Arch. f. d. ges. Physiol., 1888,
Bd. XLIII., S, 09) who likened it to secretion, and conceived
that it was practically the same process reversed in direction ; he
ascribed to the cell the force necessary to accomplish this work
and looked upon it as one of the manifestations of the vital energy
of the cell.

h. The Physical Theory.

The next generation of physiologists experienced a reaction
against the vital-energy theory. The physical phenomena of dif-
fusion, osmosis, and imbibition were better understood. Ludwig,
Briicke and their associates were devoting their energies toward
th<- solution of physiological problems through the laws of chem-
istry, physics and mechanics. These efforts had a most salutary
effect upon physiology. That field of human knowledge assumed
under these men the dignity of an experimental science. The
methods of investigation were the exact methods of the chemical
or physical laboratory.

It wa- the hope of thi- school of physiologists to account for

all of the phenomena of life as the manifestation of the action,

350 ABSORPTION: INTRODUCTION.

and more or less complex interaction of the forces already known
in chemistry and physics. They considered that the processes of
digestion arc chemical processes, pure and simple; that the proc-
esses oj absorption arc 'physical and mechanical processes pure and
simple.

The epithelium of the alimentary canal represents a dialyzer
membrane : on one side is the blood containing oon-diffusible
proteids, on the other the products of digestion containing divisi-
ble proteids. If the salts in the contents of the alimentary canal
make too strong a solution (<■. </., MgSOJ water diffuses rapidly
into the canal and a serous catharsis follows. In the usual rela-
tion between the blood plasma and the contents of the canal the
water readily diffuses into the blood. Filtration was invoked to
assist osmosis where that failed to satisfy the requirements.
Briicke called attention to the fact that peristalsis causes an in-
creased pressure in certain portions of the canal. The contrac-
tion of the villi empties them, driving the contents of* the lymph
radical on into the lacteals, and the contents of the capillaries on
into the venules of the portal system. The valves in the lacteals
and the veins prevent regurgitation of the lymph and blood when
the muscles of the villi relax. The natural elasticity of the villi
tends to cause them to regain their original si/x> thus making a
negative pressure within the villi. Attention was also called to
the fact that at the point where a peristaltic wave contracts the
canal to one half or one third its usual lumen the apices of the villi
come together while there is still liquid around their bases (Fig.
188). A further contraction puts the liquid thus enclosed under
pressure. The direction of this pressure will assist its filtration
into the villi.

Absorption of fat globules was looked upon as a purely me-
chanical process in which the epithelial cells through their mar-
ginal rods or the lymph corpuscles engulfed the globules and
transported them bodily to the lacteals. It was expected that
this array of physical and mechanical forces would account for all
the phenomena of absorption. More searching investigations on
the part of the champions of the physical theory revealed the in-
adequacy of physical laws, as understood by physicists to account
for the observed physiological phenomena.

c. The Selection Theory.

The pendulum of thought has swung back toward the vital
theory again. We do not use " vital energy " in our terminology
because the literature of the past prejudices us against that ex-
pression. We say knowingly that the cell "selects" the ma-
terials which are to be absorbed, but the mystery is as great in
selection as when the thing was accomplished by virtue of a

THE SELECTION THEORY. 351

■• vital energy." Moore sums up well our present views on ab-
sorption. " The cells of a secreting gland take up certain ma-
terials from the lymph in which they are bathed, and from these,
in some manner, elaborate certain products which are passed into
the gland lumen as a secretion. Similarly, the absorbing cells of
the intestine take up certain products of digestion from the in-
testinal contents by which they are bathed, and build up from
these, certain materials which pass into the lymph (and plasma).
fib thai absorption may be regarded as a sort of reversed secretion.
In both raxes the process is a selective one.

The character and rate of the secretion are much influenced by
the amount and the pressure of the blood in the gland ; similarly
the character and rate of absorption are influenced by the condi-
tions which exist in the alimentary tract. Instead of looking
upon the physical forces of diffusion and pressure as the sole fac-
tor- of absorption we now recognize them as modifying factors.

The following are some of the facts which prove that the proc-
ess of absorption is not one of simple diffusion: (a) Alkali-
albumin and acid-albumin are practically indiffusible, yet they are
readily absorbed from the large intestine, also from a loop of
small intestine in the absence of all proteolytic enzymes, (b)
" The rate of absorption, from the intestine, of various dissolved
substances is not proportional to their diffusion coefficients."
Rohmann (Arch.f. d. ges. Physiologic, Bd. XLL, S. 411), found
that from a mixture of equal parts of Na2S04 and dextrose the
more slowly diffusible dextrose is much more rapidly absorbed
than the sodium salt. These facts and many others lead physiolo-
gists to attribute to the selective power of the tiring epithelial cells the
typical phenomena of absorption, recognizing meantime that osmosis
and filtration an modifying factors.

352 Mison I'T/oy.

THE PHYSIOLOGY OF ABSORPTION.

I. ABSORPTION FROM DIFFERENT PORTIONS OF THE
ALIMENTARY CANAL.

a. Absorption from the Mouth.

That a certain amount of the soluble portions of the food Is
absorbed by the mucous membrane cannot be doubted. But oral
absorption is solely incident to the sense of taste and is too slight
to be taken into account as a factor in nutrition.

1). Absorption from the Stomach.

The investigations of recent years tend to minimize the impor-
tance of the stomach, not only in digestion, but also in absorption.
Before the subject was investigated with sufficient care it was
taught that water and salts are absorbed freely by the stomach.
It may be demonstrated, however, that only a very small propor-
tion (about 1 per cent.) of the water is absorbed even when a con-
siderable quantity of water alone is taken into the stomach.

Salts and sugars in solution are absorbed most readily when the
degree of concentration is considerable ; the minimum degree at
which absorption may take place being ."> per cent, for salts and
5 per cent, for sugars ; the most favorable degree of concentration
being 20 per cent, for grape sugar while in the small intestine it
is 0.5 per cent.

The proteoses and peptones are probably absorbed to a certain
extent by the gastric mucous membrane, at any rate the presence
of these products of gastric digestion greatly stimulates the activ-
ity of the gastric glands.

Alcohol is freely and rapidly absorbed by the stomach.

c. Absorption from the Small Intestines.

Absorption from mouth and stomach seems to be purely inci-
dental. If there is a specialized organ of absorption, that organ
must be the villus of the small intestine. The villus seems to be
especially fitted structurally for absorption; it is the organ which
absorbs nearly all of the liquid nutriment for the organism ; no
other function may be ascribed to it.

These considerations justify us in calling the villus the organ of
absorption.

From the lumen of the small intestine the villi absorb the pro-
ducts of gastric and of intestinal digestion ; sugars, proteoses,
peptones, fatty acids, soaps, water, salts, etc.

THE ABSOEPTIOX OF WATER AXD SALTS. 353

d. Absorption from the Large Intestine.

Water and salts are readily absorbed by the large intestine.
This visens seems to be an important site for the absorption of
water, as the intestinal contents pass the ileocecal valve in a
liquid state — simulating chyme — and enter the rectum in a pasty
condition, the water having- been largely absorbed.

About 14 per cent, of the proteids and small amount of sugars
and fats are also absorbed from the large intestine.

Most interesting of all is the fact that enemata of undigested
proteid, syntonin or alkali-albumin, even dilute egg-albumin, is
absorbed in sufficient quantity to nourish an animal.

2. THE ABSORPTION OF DIFFERENT FOODSTUFFS.

a. The Absorption of Water.

As has been stated above water is absorbed principally from
the small and large intestines. The portion absorbed from the
former is absorbed mostly from the lower segment, namely the
ileum, while it is the tirst portion of the large intestine that takes
np most of the water which remains in the intestinal contents
when they pass the ileocecal valve.

The significance of these facts regarding the absorption of water
i- not difficult to see. If the water were largely absorbed in the
stomach and the upper part of the small intestine the absorption
of the other products of digestion from the small intestine would
be much hindered, because experiment has shown that the ab-
BOrption of the dissolved foodstuffs is much facilitated by dilute
solution*. Furthermore the movements of a viscous mass, de-
prived of most of its water, would be much hindered.

Altogether it seems most natural and advantageous for the
water to be absorbed late in the general process of absorption.

I>. The Absorption of Salts.

If the law- of diffusion dominate the process of absorption,
and if osmotic pressure is the principal force involved in this proc-
ess, we shall expect to see these physical laws and forces espe-
cially evident in the absorption of salts and their solvent water.
'I he -.ion- catharsis referred to above seems to be an example of

a diffusion of water from the blood into the lumen of the intes-
tine, induced by the high concentration of the salt solution in the
intestine. When such condition- e\i-t iii a dialy/cr, water passes

through the membrane from the Less concentrated into the more
concentrated solution, while -alt passes from the more concen-
trated into the Less concentrated solution. The watery -tools fol-
lowing ingestion of strong solutions of MgSO. and related salts

35 1 IBSORPTION.

seem t<> confirm this theory. Recent experiments by Wallace
and Cashny (" Intestinal AJbsorption and Saline Cathartics," Am.
Jour. Physiol., Vol. I., No. [V., July, 1898) show that "Dilute
solutions (isotonic) of the saline cathartics retard the absorption

of fluid from the stomach and small intestine, and thus act by
rendering (keeping) the contents more watery and more easily
moved through the lower pails of the alimentary canal."
"They (dilute solutions of the cathartics) do not necessarily in-
crease the fluid of the bowel, but merely fail to be absorbed and
thus render the faeces more fluid and more easily moved through
the large intestine."

The same observers found that if a hyperistonic solution of
M<>SO, be introduced into the intestine it is reduced to the iso-
tonic condition by interchange with the blood ; while if a hypis-
tonic solution of MgSO, be introduced into the intestine it is
raised to the isotonic condition by interchange with the blood,
probably by giving uj» water to the blood.

If instead of using one of the salts, which clinical observations
have led us to classify as cathartic salts, NaCl be used it will be
found (Heidenhain, Pfliiger's Archiv., 1894, Vol. 56, S. 579) that
dilute solutions (0.3-0.5^)) are completely absorbed, both the
water and the salt passing into the blood. Wallace and Cushny
observed a similar phenomenon.

Evidently, then, the absorption of salts (and water) obeys the
laws of diffusion more or less faithfully aoeording to the salt in
Sol H t ion.

Why NaCl should pass the epithelial boundary so readily while
the passage of MgS04 is practically barred out, can only be ac-
counted for on the basis of a selective act on the part of the
epithelial cells. From the accounts of experiments with the two
classes of salts represented by NaCl and MgSO, one can scarcely
avoid the conviction that the presence of such salts as MgS04 in
the intestine affects the epithelium by suspending its selective power
(turf reducing them to a mere passive membrane subject to the laws <f
simple diffusion. That such an effect, especially when produced
by strongly hyperistonic solutions may be deleterious to the sys-
tem is not unlikely. The question deserves investigation.

Summarizing, one may say : The soluble salts, common in the
foods, nee readily absorbed by the epithelium of the small intestine.
The absorption, though influenced by the laws of diffusion, responds
primarily to the selective power of the epithelial oils.

c The Absorption of Carbohydrates.

The whole process of carbohydrate digestion points toward the
monosaccharids as the form in which carbohydrates are to be ab-
sorbed.

THE ABSORPTION OF PROTEIDS. 355

The fact that only the monosaecharids, especially dextrose, may
be found in the blood of the portal vein seems to confirm this
indication. Rohmann (Pfluger>s Arch., 1887, Bd. XLL, S. 411)
found that starch solution disappears rapidly from an intestinal
loop. The succus entericus has almost no action upon starch. It
must then be absorbed as starch by the epithelial cells. It leaves
those cells as dextrose. The cells must, then, have the power to
digest starch. Experiments of other investigators also point to
similar conclusions.

Under the usual conditions, however, it is certain that by far
the greater part of the carbohydrates is absorbed in the form of
monosaecharids, dextrose, levuhse, c/alactoxc, from the small intes-
tine, an unimportant fraction may be absorbed in the form of
disaecharids, or even polysaccharide ; a small proportion is
absorbed by the stomach and large intestine.

d. The Absorption of Proteids.

A- in the case of carbohydrates so in the case of proteids the
processes of digestion are processes of solution and change from
indiffusible to diffusible forms. That the solution of proteids is
necessary would seem certain ; yet, diluted, not dissolved, egg-
albumin is absorbed from the large intestine when given as an
enema ; and diluted egg-albumin is absorbed (16—33 per cent.)
from a loop of intestine in the absence of all proteolytic enzymes.
Actual chemical solution is then not a necessary preliminary to
absorption ; it is only necessary that the proteid be in a dilute liquid
form. When the ideas of physiologists on this problem were
made to harmonize with the osmosis theory the reduction to a
diffusible peptone was looked upon as a necessary preliminary to
absorption. Though peptone is diffusible its diffusibility is much
too low, its rate much too slow, to account for what actually takes
place in the alimentary canal. Acid-albumin or alkali-albumin is
absorbed from a loop of intestine almost as completely as are pep-
tones and proteoses, though much more slowly than they (/. e.,
about 60-70 percent, in 24 hours. — Huber, 1891). The amount
of leucinf tyrosin} and allied bodies formed in normal digestion is
probably very small because of the rapid absorption of the
proteoses and peptones ; naturally then the amount of these amido-
acicU normally absorbed will be small. A small amount of pro-
teids IS absorbed from the stomach, about 14 per cent, from the
large intestine, and all the remainder — 80-85 per cent. — from the
small intestine.

Summary : A large proportion of the proteids are absorbed by the
small intestine in the form of proteoses and peptones. A small part
of the proteids may be absorbed from the alimentary canal in the
form "f alkali-albv/min or acid-albumin <>r even as native proteid.

356 ABSORPTION.

e. The Absorption of Fats.

The digestive processes of the small intestine change fal to a
mixture of: fatty acids, glycerine, soaps, and emulsified fats.

The fatty acids arc soluble in the bile acids. Glycerine and the
sodium and the potassium soaps are soluble in water, calcium and
magnesium soaps are soluble in the bile salts, — probably changed
to sodium soaps. The large amount of emulsion as compared to
the amounts of the other forms found in the intestine together
with the discovery of innumerable oil globules in the epithelial
cells during absorption ; and the appearance of oil globules, —
emulsion, in the chyle of the lacteals during absorption led phys-
iologists to conclude that the fat is absorbed, for the most part, in
the form of an emulsion. Earnest efforts have been made to
reconcile this theory with the recognized limitations of fixed
epithelial cells.

Before we accept the emulsion theory of absorption the follow-
ing facts should be considered :

(«) Ingested soluble soaps are absorbed (Radziejcwski, Virch.
Arc/,., Bd. LVL, S. 211— cited by Moore).

(ti) Soap and glycerine are absorbed and synthesized, after
absorption and before the lacteals are reached, into neutral fat
which circulates through the lacteals as a typical chyle emulsion.
The epithelial cells when treated with osmic acid show abundant oil
globules. (Perewoznikoff, cited by Moore, r3chaefe^a Physiology,
Vol. I., p. 451.)

(}-) Ingestion of free fatty acid and glycerine is followed by a
synthesis within the epithelium and the appearance of fat globules
there. (Will., Arch.f. d. ye*. Physiol., Bd. XX., S. 255, quoted
by Moore.)

(3) Ingestion of free fatty acid alone was followed by the ap-
pearance of fat globules in the epithelial cells. In this case the
cells must have furnished, from some source, the glycerine con-
stituent of the fat formed.

(s) Steapsin acts rapidly upon the fat and in the usual time
consumed in intestinal digestion would be able to change the usual
amount of fatty food into fatty acid and glycerine. (Kachford, in
Jour. Physiol., Vol. XII., p. 92, quoted by Moore.)

(£) It has been objected to the soap theory that the amount of
Xa,( !03 necessary to saponify the fat of one meal would be three or
four times as much as the whole body contains. Moore calls atten-
tion to the fact that once the soap passes into the epithelium the
Xa is of no further use in the cell and can be used over and over
again as a carrier. One can conceive of a sodium atom (i) being
carried into the intestine as a part of the secretion combined with
C( )., ; (n) dropping the CO., to join with a molecule of palmitic or

THE ABSORPTION OF FATS. 357

other fatty acid and passing into the cell ; (ill) dropping the
palmitic acid for — OH; (iv) passing to the intestinal surface of
the cell ; (v) saponifying another molecule of palmitic acid
carrying it into the cell ; and again joining with — OH, etc.,
etc., repeating the cycle indefinitely. The formation of soap on
the outer side of the epithelium is a spontaneous chemical reaction.
The breaking up of that molecule to liberate palmitic acid for
synthesis with glycerine and Na for synthesis with — OH is prob-
ably due to a torment action of the cell. Note that a mystic vital
force is called in at the critical point. The same force must be
invoked to put the XaOH out on the proper side of the cell.

(;j) Fatty acids are soluble in bile acids. A series of observa-
tions by Altmann and by his pupil, Krehl (Arch. f. Anat. u.
Phy8., Leipzig, 1889, Supl. Bd., 8. 86, cited by Moore) show that
the fatty acids dissolved in the bile acids are absorbed, and syn-
thesized into neutral fats with formation of fat globules in the
epithelium.

From the observations above cited it is evident : (i) That the
appearance of fat globules in the epithelial cells and the lacteals
does not necessarily demonstrate that the fat is absorbed as an
emulsion ; (n) that the appearance of fat globules in the epithe-
lial cells and the lacteals after ingestion of soaps or of fatty acid
and glycerine does demonstrate that the elements of fats may be-
absorbed in this form and neutral fat synthesized by the cells
from the elements ; (in) that special cell activity is necessary in
either rase.

When two alternatives are presented the physiologist is wise to
accept with suspended final judgment the one which is most rea-
sonable and most in harmony with other similar processes. Ab-
Borption of fat in globules is wholly inexplicable; absorption of
i'at in solution, as soaps and fatty acids, is only partly inex-
plicable.

Summary: The Emulsion Theory of fat $bsorption is that by
fur tin greater 'pari of the fat 'passes into the cells in the form of small
globules, neutral fat in emulsion, or of fatty acid in emulsion, while
a minute portion may be absorbed as soap.

The Solution Theory of fat absorption is that at themomentof
entering the epithelial cell the fat or fat elements are in solution either
ns soaps in aqueous solution or as fatty acids in solution in bilary
acids ; tlmi the absorbed elements ore synthesized in the epithelial cell
forming neutral fat which appears in globules, and that these
globules pass from the cells into the lacteals, forming the milky chyle.

CHAPTER VII.
METABOLISM.

I N TRODUCTIOX.

1. METABOLISM DEFINED AND CLASSIFIED.

2. METABOLIC TISSUES AND ORGANS.

3. THE [NCOME AND OUTGO <>K MATTER.

4. EQUILIBRIUM.

5. THE CIRCULATION OF TDK ELEMENTS.

6. THE CIRCULATION OF TYPICAL COMPOUNDS.

7. THE CHARACTER OF THE METABOLIC CHANGES.

ANIMAL METABOLISM.

A. METABOLIC CHANGES OF DIFFERENT (LASSES OF
FOODSTUFFS.

1. CARBOHYDRATES.

a. Absorption Form.

b. CIRCULATION FORM.

c. Metabolism.

-/. Excretion of Carbohydrate Katabolites.

2. PROTEIDS.

a. Absorption Form.

b. Circulation Form.

c. Metabolism.

d. Nutritive Value of Proteihs.

e. Laws of Nitrogen Equilibrium.

3. FATS.

a. Absorption Form.

b. Circulation Form.

c. Metabolism.

d. Fat Deposit.

4. THE INTER-RELATIONS OF THE FOODSTUFFS IN NUTRITION.

B. SUMMARY OF ANABOLISM AND KATABOLISM.

1. ANABOLISM.

2. KATABOLISM.

C. THE INCOME OF ENERGY.

1. THE POTENTIAL ENERGY REPRESENTED BY THE FOODSTUFFS.

2. THE POTENTIAL ENERGY REPRESENTED BY COMMON FOODS.

3. THE ENERGY REPRESENTED BY A TYPICAL MENU.

I). THE LIBERATION OF ENERGY.

1. THE LIBERATION OF THE POTENTIAL ENERGY OF THE OR-
GANISM.

358

METABOLIC TISSUES AXD OMGANS. 359

2. THE TRANSFORMATION OF ENERGY.

3. THE CONSERVATION OF ENERGY.

4. THE EXPENDITURE OF THE KINETIC ENERGY OF THE OR-
GANISM.

E. ANIMAL HEAT.

1. GENERAL CONSIDERATIONS.

2. METHOD OF DETERMINING THE MEAN TEMPERATURE.

:;. FACTORS WHICH CAUSE VARIATIONS OF THE TEMPERATURE.
(i) Climate. (2) skx. (3) Age. (4) Seasons. (5) Extreme Tem-
perature Artificially Produced. (6) Day and Night. (7) Muscu-
lar Work. (8) Mental Work. (9) Food. (10) Sleep. (11) Baths.
(12) Drugs. (13) Individual Difference. (14) Limits of Temper-
ature Compatible with Like.

4. TEMPERATURE TOPOGRAPHY IN MAN.

5. HEAT REGULATION OR THERMOTAXIS.

METABOLISM.
INTRODUCTION.

1. METABOLISM DEFINED AND CLASSIFIED.

The German physiologists were first to separate out from the
general territory of nutrition a separate field in which to include
all those chemical processes by which matter is transformed from
non-living nutrients to living protoplasm, and from living proto-
plasm to dead excreta. This clia.iv/c of matter was called Sloff-
wechsel : our technical term METABOLISM is used to cover the same
field. Reference was made to the building up of nutrients into
living protoplasm and a reversed process. These two phases of
in (tabolism are called respectively Anaboli&m and Katabolism.
These term3 are aot so circumscribed, however, as might seem
from the foregoing: Anaboli&m includes all those chemical
changes by which molecular structure becomes more complex
and energy is in<i<h latent ; while katabolism includes all the
chemical changes by which molecular structure becomes more
simple and energy is liberated.

2. METABOLIC TISSUES AND ORGANS.

All specialized function- of the living organism are performed
by specialized tissues or organs or systems of organs. .Metabolism
i- nol a specialized function; it include- the chemical phases of
all tissue activity, and is usually incidental to a primary function.
For example : the primary function of the glandular tissues is se-
cretion ; but incidental to the secretion is a -eric- of chemical
changes which may be considered under the head of metabolism.
In ;i similar manner muscular and nervous tissue possess primary

360

METABOLISM : 1STROD UC1 ION.

functions peculiar t<> them and undergo metabolic changes in the
performance of those functions. All active tissues, then, are meta-

Fio. 190.

Diagrammatic representation of two hepatic lobules. The left-hand lobule i> represented with
the intralobular vein cut across : in the right-hand one the Bection takes the course of the intra-
lobular vein, ji, intralobular branches of the porta] vein ; A. intralobular branches of the
hepatic veins ; g, sublobular vein ; e, capillaries of the lobules. The arrows indicate the direc-
tion of the course of the blood. The liver-cells are only represented in one part of each lobule.
(SCHAEFER.)

Fig. 192.

Diagram of the structure of the liver.
P. V., the portal or interlobular vein,
which breaks op into the capillary net-
work of the lobule ; H. V., central intra-
lobular vein, a branch of the hepatic;
JI. A., hepatic artery, supplying nutri-
tion to the interlobular structures and
terminating in the lobular capillary net-
work ; />'. I)., the interlobular bile-duct
which takes up the bile-capillaries at the
periphery of the lobule. (1'ikrsol.)

Section of rabbit's liver with the intercellular
net-work of bile-canalieuli injected. (Highly
magnified, i Two or three layers of cells are rep-
resented ; ''.blood-capillaries. (From Schaefek
after HEBENG.)

bolic tissues. The metabolic tissues may be classified as : muscular,
nervous, and glandular. If there is an organ that may properly

METABOLIC TISSUES ASD ORGAXS.

361

be classified as an organ of metabolism, that organ is the liver.
The external secretion of the liver is made up largely of sub-
stances which are practically useless to the system. The internal

Fig. 193.

Hepatic-cells still containing glycogen, n, ami with their glycogen dissolved out, '/, c. In c
{here was less glycogen present than in b, and the section is differently prepared. (From
SOHAEFKB after HkideniiaIX.)

secretion is composed either of substances on their way to excre-
tion or to further katabolism in the muscles. To be concrete,

Fig. 194.

Lobule of rabbit'i liver, w ■--. i- and Mle-ducU Injected. ", central vein ; '•, />, peripheral or
Interlobular reini : e, Interlobular bile-duct. (Cadiat.)

the bile pigments, salt.-, and acids, the area and uric acid, and the
glycogen and dextrose are products of liver metabolism. Metab-
olism i- it- principal function. The liver is the greal central

362 MET IBOLISM: INTRODUCTION.

whirlpool of the circulating nutrients ; it is the center of body
metabolism ; it may be called the organ of metabolism. The
anatomical features of the liver which arc of special importance to
the physiologist may be thus summarized :

1. The liver is supplied with Mood from two sources: (a)
Portal venous system from the capillaries of the intestines to the
interlobular branches of the portal veins. (6) Hepatic artery
bringing arterial blood which mixes with the portal blood within
the lobule. (See Figs. 11)0 and 191.)

2. The hepatic veins collect the blood and carry it to the vena
cava. (See Fig. 15)1.)

•"'>. The Hilary secretion is collected by minute bile capillaries,
the mesh-work of which is so tine that every secreting cell is in
contact with a bile capillary on at least two sides. (See Figs-
L92-193.)

4. The bile secretion is collected at the periphery of the lobule
by the interlobular bile ducts. (See Fig. 194.)

3. THE INCOME AND OUTGO OF MATTER.

The manifestations of life are the manifestations of kinetic
energy. In the animal organism the energy is received as po-
tential chemical energy and expended almost wholly as kinetic
energy. As far as it is known, energy exists in nature only in
association with matter: gravitation, molor motion, chemism,
heat and light are all intimately associated with matter, and if
transmitted, that transmission can take place only through the
agency of matter. If, then, the animal organism is to receive>
transform and expend energy, it must receive, transform and ex-
crete matter. The whole process is called nutrition. We have
followed the process through the reception of food materials into
the alimentary canal, their partial transformation (their digestion)
in the stomach and intestine and their absorption into the organ-
ism. The amount of the income is the amount of absorbed
matter, and the amount of the outgo is the sum of the excretions
from kidneys, skin, lungs, etc.

4. EQUILIBRIUM.

If the absorbed matter equals in weight the excreted matter, the
body will neither increase nor decrease in weight ; it Mill be in
equilibrium. Perfect equilibrium seldom exists ; during youth
there is a gradual increase in weight ; during adult life there is
approximate equilibrium, while during the senile period there is
usually a gradual decrease in the body weight. But this onlv in-
dicates the general course of the curve of income and outgo.
Many factors enter into the problem of body growth and equilib-

EQUILIBRIUM.

363

rium to cause numerous minor curves to l>e superimposed upon
the general curve. The occurrence of one or two large waves on
that part of the curve which represents the period of growth gives
rise to the " wave-theory of growth." Besides these large waves
there arc small waves occurring each year, and possibly even
smaller diurnal waves, so that the composite curve would be
something like the following:

Fig. 195.

j/\

^^

*j h

,- K /

y :

bO y)S.

10 yrs. So yrs. JO yrs. 40 yrs.
Childhood \ Toutli | ^idult Life

Curve showing the variation of weight with advancing age.

60 yrs. 70 yrs. 80 yrs.
The Senile Period

The Physiological test of equilibrium is made by taking the
weight at short intervals. The method is like getting an idea of
business by noting the daily balances, it shows the equilibrium
but gives only a vague idea of the magnitude of the exchange
between debit- and credits. In the chemical test of equilibrium,
on the other hand, the debits and credits of an organism are de-
termined by finding the quantity of absorbed material and by de-
termining the quantity of urea, water and carbon dioxide excreted.
If the nitrogen of the egesta equals the nitrogen of the ingesta,
the organism is said to be in a state of "nitrogen-equilibrium."
If the total egesta equals the total ingesta the organism as a whole
is in a ,-tatf of equilibrium.

5. THE CIRCULATION OF THE ELEMENTS.
(") CARBON. — This element enters the system as an important
constituent of all the foodstuffs. It is built up into all of the tis-
sues and eventually it i- combined with oxygen to form CO^ which
i- excreted by the lungs in the gaseous form, or it may be com-
bined withO, X, and II in urea or uric acid, <•(<•., and excreted

by the kidney-.

(h) Hydrogen enter- the system as ;i constituent of all food-
Btuffe including water. Like carbon it is ;i constituent of all
tissues. It i- excreted in the form of II,<) by kidneys, -bin, mid

bin-- : though a part i- excreted 8J :i constituent of urea, uric acid

and allied bodies. Most of that hydrogen win eh enters the system
combined with oxygen in water leave- the body as water, never
having been separated from the oxygen.

364 METABOLISM: INTRODUCTION.

(c) Nitrogen is brought to the system only through the proteid
funds. 1 1 is a necessary constituent of all active tissues, muscle-
tissue, glandular-tissue, and nerve-tissue. In the metabolism of

the tissues it is, step by step, fvct'il from its complex combinations
until finally it is excreted by the kidneys with C, II, and O in
urea, uric acid, etc.

(d) Oxygen enters the system uncombined and variously com-
bined. As a gas it enters the lungs, is taken up by the haemo-
globin, transported to the tissues where it plays a prominent part
in katabolism. It finally leaves the cell combined with II in
H.,(), with C in C02, or with C, II and N in urea or uric acid.
In these forms it is excreted by the lungs, skin or kidneys. A
large quantity of oxygen enters the system in combination in the
various foodstuffs. This part of the oxygen is excreted in the
same combinations as the oxygen of respiration.

(c) Phosphorus enters the system with the proteids. Though
phosphorus is a constituent of few proteid foods (nuclein, nerve-
tissue, blood-plasma, lymph, and milk), one or more of these is
usually associated with each kind of nitrogenous food, so that the
system receives a considerable amount. In the body it is a consti-
tuent of the tissues and fluids enumerated above ; and, combined as
Ca.5(PG4)2, it is a most important constituent of bone. It is ex-
creted by the kidneys as calcium, magnesium or ammonio-magne-
sium phosphate.

(/) Sulphur is received in combination in proteids, is built
up into the body-proteids and is excreted by the kidneys as free
sulphuric acid, or as HKS04 or HXaS04, or it may be joined to
phenol as phenolsulphuric acid, phenolsulphate of potassium, etc.

(g) CHLORINE enters the body in combination with sodium. As
far as is known, it is separated from this combination, if at all,
only in the parietal cells of the peptic glands. That part of the
HC1 which is absorbed from the alimentary canal comes into con-
tact with Na2C03, or XalICO, of the blood and forms H20, C02
and NaCl, which are excreted.

(//) Iron is the most important of the metals and at the same
time is the most difficult one of them to absorb and assimilate.
Recent investigations of Bunge and others demonstrate that iron
may be assimilated and built up into haemoglobin only when it is
absorbed in the form of an organic compound. Whether it is nec-
essary that it should be received into the alimentary tract in the
organic form, or whether it may be raised, by the process of di-
gestion, from the inorganic to the organic combination and be ab-
sorbed and assimilated, was for a long time a debated question ;
but investigation has demonstrated that even in the form of a
chloride the iron is raised to a peptonate or albuminate in the ali-
mentary tract and absorbed.

EQUILIBRIUM. 365

Iron is an essential constituent of haemoglobin. After it has
served its purpose it may be excreted by the kidneys, by the epi-
thelium of the intestines ; even a small part is lost with the
cuticle, hair, nails, etc.

( /) Othee Metals arc usually assimilated in chemical asso-
ciation with organic foodstuffs, and are excreted by the kidneys.
A small amount of sodium, calcium, etc., is secreted by the pan-
creas and the liver, and is poured into the alimentary canal.
A part of these metals is reabsorbed in combination as soap ;
all that is not reabsorbed is lost, in this way, to the organism.

<;. THE CIRCULATION OF TYPICAL COMPOUNDS.

(a) Watee. — Our remote ancestry had undoubtedly an aquatic
habitat. It has been said that, "man is, in a sense, an aquatic
animal." It is true that about 60 per cent, of the body is water,
that every active cell of the body is bathed in liquid and that even
the surface of the body is, during health, usually covered with a
film of moisture in the form of " sensible " or " insensible " perspi-
ration. The organism can live many days without solid food, but
deprivation of water for a very few days suffices to cause death.

The water is in part taken with the food and in part taken as
drink. Water which is taken as such undergoes no change while
in the system, except that an occasional molecule is joined by Hy-
dration to some organic molecule. It is absorbed by the intestinal
epithelium, even when it is taken between meals; when it is
taken with a meal it is likewise passed on into the intestine with
the chyme, to be absorbed by the intestinal epithelium. Water is
the general solvent and diluent of the system. It makes possible
tli'' absorption of the digested foods and the excretion of waste
products. Of all the water excreted by the kidneys, skin and
Lungs, a large part is water which enters the system as such ; an-
other pint is the product of the oxidation of the hydrogen of the
tissues in katabolism, while another portion lias been released
from complex molecules by dehydration, also a katabolic process.

ih) SODIUM CHLOBIDE is taken as such with food. It is in
solution in all the fluids of the body. It probably assists in en-
dosmosis. It i- probably the source of the chlorine element of the

HC] of the gastric juice. (See "Secretion of IK'l.") Sodium
chloride may be formed in the system. It may be formed iii the
organism by a combination of absorbed hydrochloric acid with
the carbonate or bicarbonate of -odium, as suggested under " chlor-
ine" It i- excreted by the kidneys and skin and is secreted by
lachrymal glands and -a I i vary glands. It is in fact a constituent

of every secretion and excretion.

Otheb Compounds in this class arc of not very great

physiological importance.

366 METABOLISM.

7. THE CHARACTER OF THE METABOLIC CHANGES.

1 . Association and Dissociation.

Haemoglobin is associated with oxygen in the Lungs and disso-
ciated from oxygen in the tissue capillaries. Recent investiga-
tions indicate that the calcium phosphate of the milk is "asso-
ciated " with one of the organic constituents, probably the casein,
and that it retains this association through the steps of digestion
and absorption possibly also to be assimilated in association with
the foodstuffs. In bone and dentine, however, it is eventually
dissociated and deposited as insoluble calcium phosphate. One
or more molecules of water may be associated with another mole-
cule in crystallization and dissociated when thecrystal is dissolved
or dehydrated.

2. Synthesis and Decomposition.

These terms are applied to a class of chemical changes which
involves a more profound alteration in the structure of the mole-
cule than that body undergoes in the preceding process i Association
and Dissociation). The combination of a fatty acid with glycer-
ine is a synthesis, while the breaking up of a fat into these two
constituents is an example of a decomposition.

3. Hydration and Dehydration.

These terms signify the addition or subtraction of a molecule of
water; it is only a specialized sort of synthesis or decomposition.
Hydrolytic changes are especially common in the digestive proc-
ess. Recall the addition of a molecule of water followed by a
cleavage (hydrolytic cleavage) of the hydrated molecule into dex-
trine, and of a secoud molecule of water to maltose to make dex-
trose, while the dehydration of the same molecule of dextrose take-
place in the liver, after absorption, reducing the dextrose to the
amylose radicle (< '6H10< ).), which taken // times is synthesized into
a glycogen molecule (CGH10O.)u.

4. Reduction and Oxidation.

These terms need no explanation. In plants the reduction
processes predominate and the liberated oxygen escapes into the

general atmosphere. During reduction processes energy is used
to consummate the change and energy is made latent. In the
animal kingdom oxidation processes predominate ; oxygen is
taken from the atmosphere to consummate the change and carbon
dioxide is returned to the atmosphere. Oxidation liberates latent
energy.

( ARBOHYDRA TES. 367

Summary : " The chemical processes of ffie animal organism may
h< represented as a series of syntheses and decompositions, or of an-
abolic and hatabolic changes, by virtue of which the highly complex
and slightly oxidized constituents of the body and of foodstuffs arc
decomposed into simple and highly oxidized compounds, which arc re-
mooed from the body by the various organs of excretion^ The dif-
ferent between the potentiality of the ingesta andtheegesta represents
flic potential energy liberated in the organism as the kinetic energy of
Ufe.

ANIMAL METABOLISM.

A. THE METABOLIC CHANGES OF DIFFERENT
CLASSES OF FOODSTUFFS.

1. CARBOHYDRATES.

1. Absorption Form. — It will be remembered that during
the process of digestion the carbohydrates are for the most part
changed to dextrose. There i* no evidence that other diffusible
<>r even indiffusible carbohydrates may not be absorbed, i. e., pass
into the epithelium of the alimentary tract ; all the carbohydrate
matter found in circulation in the portal system is, however, dex-
trose. It is evident then that if cane sugar is absorbed by the
epithelium, it undergoes hydrolytic cleavage in the epithelium and
enters the circulation as dextrose ; so that, in whatever form the
carbohydrate is absorbed it is changed to dextrose by the epithe-
lium and passed into the capillaries of the i><>rfal system.

2. Circulation Form. — In the blood all sugars normally ap-
pear as dextrose. The blood of the portal vein may have as
much as 0.3 per cent., while that of the general circulation has
usually about 0.1 per cent. Furthermore, the above mentioned
high percentage for the portal circulation may lie observed only
after a meal rich in carbohydrates, while the amount quoted for
the genera] circulation is more or less constant. The blood which
enters the liver may have 0.3 per cent, dextrose, the blood which

leaves uniformly has 0.1 per cent, dextrose. With these facts in
view, it is evident that the liver musl effect a profound change iii
the carbohydrate material brought to it by the portal system.

:;. Metabolism of Carbohydrates. — The blood entering the
liver after a meal brings a much larger amount of carbohydrate
materia] than i- carried away by the hepatic vein. That this
- of carbohydrate- must be stored in the liver is the neces-
sary conclusion ; yet if :, freshly excised liver he tested for dex-
trose that substance will not he found in greater quantity than

368 . 1 \ 7.1/. I L METABOLISM.

may be accounted for by the portal blood present. A special
treatment reveals another form of carbohydrate — glycogen.

(a) Glycogen (< !6H]0Os)n was discovered and described by
Claude Bernard in 1857. Bernard's theory as to its relation to
general nutrition is substantially the one which is accepted to-
day. Briefly outlined the preparation of glycogen is as follows :
(«) Kill an animal after a heavy carbohydrate meal, (h) Excise
liver, hash same and plunge it into boiling water, which has the
double function of extracting glycogen and of stopping post-
mortem change of glycogen to dextrose, (c) Filter. The
opalescent nitrate contains glycogen or "animal starch." If one
subject this animal starch to the iodine test a wine-color will result.
The microscope reveals the presence of glycogen in liver cells,
deposited in the substance of the cytoplasm. (See Fig. 1 !»•!.)
But the carbohydrates do not represent the sole source of glycogen ;
for an animal deprived of both carbohydrates and fats will still
form glycogen in the liver on a pure proteid diet. Such is not
the case, however, on a pure fat diet. Whether, with a mixed
diet of carbohydrates and proteids, a part of the proteids are used
in the formation of glycogen remains yet undetermined.

(b) Transformation of Glycogen in the Metabolic Tis-
sfes. — In plants the starch formed in the chlorophyll gi'ains of
the leaves must b2 changed to a soluble form — dextrose, for ex-
ample— before it can be carried by the circulatory system of the
plant (fibro-vascular system) to distant parts of the plants for de-
posit, or for further metabolism. In animals the glycogen is only
temporarily stored in the liver. It is to be used in the general
metabolic tissues of the body — for the most part the muscles. It
cannot be carried to the muscles in the insoluble form in which it
is deposited in the liver. The liver possesses an amylolytic fer-
ment which changes the animal starch to dextrose. In this sol-
uble and diffusible form it enters the circulation, is carried to the
metabolic tissues, absorbed or "selected" by the active cells of
these tissues, and is by them metabolized. Just at this point we
enter a controversial field. All are agreed that within the muscle
cells the dextrose is subjected to a series of metabolic changes
whose ultimate result is the liberation of energy. Some believe
that before the foodstuff can yield to the animal organism its po-
tential energy it must he built up by flic cell into living ceU-proto-
pla8m. Others believe that the energy of the foodstuffs may be
directly liberated without the necessity of a long series of anabolic
changes preceding those katabolic changes which must finally lib-
erate the energy. Here are certain facts which deserve consider-
ation in this connection : (i) Glycogen is found in abundance in
the muscle. Its source must be dextrose taken up from the blood
by the muscle cells. But glycogen can be formed from dextrose

CARBOHYDRATES.

369

onlv bv the steps which represent anabolic changes. (Dehydra-
tion followed by recombination of n times the C6H10Os radicle into
a glycogen molecule ) The energy made latent in this anabolism
is represented by 242 calories per gramme glycogen. To anabo-
lize glycogen and nitrogenous foodstuffs into muscle protoplasm
would require not less than 1476 calories of energy; a total of
about 1716 calories. The katabolism of muscle protoplasm yields
4000 calories per gramme muscle. The remaining 840 calories
of energy is contained in the urea. The net gain in energy is rep-
resented by 2290 calories.

But the direct katabolism of dextrose would yield 3940 calories
of energy. There would be a loss of 1650 calories, or about 41
per ceut. of the energy of the foodstuff. Animals able to directly
katabolize dextrose in the muscle cells would have an advantage
over those not having that ability. (See Fig. 196.)

Fig. 196.

Muscle protoplasm- 5636 calories

Proteids = 5650 calories

Glycogen =/<i<'

Urea plane = 1650 calories
of energy

DtastratingdiagrammaticaUy the advantage of direel over Indl

tli-- urn

•( kataboUain ni dextrose In

(\\) [f dextrose is firsl buill up into muscle protoplasm, all
katabolism of the nitrogenous cell-protoplasm should result in the
liberation of nitrogenous compounds (e. g.) kreatin. The katabo-
lism incident to muscle contraction should yield such nitrogenous

24

370 ANIMAL METABOLISM.

katabolites in proportion to the muscular energy expended. J>ut
these nitrogenous katabolites :ire further changed and appear in
the excreta as area, C02 and H20. The urea then should be ;i
measure of muscular work ; bui urea does not essentially vary
with varying muscular activity. The hypothesis that the dextrose
i> anabolized to the plane of cell protoplasm is not in harmony
with the facts of excretion and the evidence is strong against the
hypothesis, (in) [f dextrose may lie directly katabolized from
the dextrose or from the glycogen plane the katabolites C02 and
II.,() should vary with muscular activity. The excretion of
('<)., and II..O varies directly with muscular activity. This is in
harmony with the facts of excretion and is strong evidence in its
favor.

4. The more Permanent Deposit of Carbohydrates. — That
this occurs not in the form of carbohydrates but in the metabo-
lized form of fat has been demonstrated. A part of the carbo-
hydrate foodstuff in circulation as dextrose is absorbed by living
connective tissue cells and transformed into fat which is de-
posited in the cells and held as a reserve of potential energy to
be called out when the more easily metabolized glycogen and dex-
trose are insufficient for the needs of the system. What is the
character of the change the dextrose molecules must undergo to
make palmitin ".' We know that palmitic acid is readily synthe-
sized with glycerine to form tri-palmitin. The storage of fat
must involve the following general changes :

(i) 3 x Palmitic acid = 3[CH3(CH2)14-COOH]= 3[C^202]

= C48H9G06"

(ir) 8 x Dextrose = 8 [C6H1206] = C^H^.

(in) 8 Dextrose + Glycerol = Tri-palmitin + 3H20 + 42< ).

The formation of fat from dextrose must be attended by the libera-
tion of oxygen. This is an anabolic process to consummate which
requires energy amounting to about 5500 calories per gramme fat.
That it takes place in one reaction as written above is not prob-
able. That it is eventually a combination of dextrose and glycerol
is an undemonstrated hypothesis. That the process whatever it
may be is an anabolic one attended with the liberation of oxygen and
th< making latent of energy is beyond question,

5. Excretion of Carbohydrate Katabolites. — The katabolism
of carbohydrates yields ( '(_)., and II .,( ). These waste materials are
excreted by the lungs, skin and kidneys unchanged or recombined
but for the most part unchanged.

2. PROTEIDS.

1 . Absorption Form. — Most proteids enter the epithelium from
the alimentary canal as peptones and proteoses. A small por-
tion may enter as acid-albumin or alkali-albumin or even native

PROTEIDS. 371

proteid. Within the epithelium these proteids undergo a change.
Evidence of this is cited in the facts that neither peptone nor
proteose is found in either blood or lymph ; and that when in-
jected into the circulatory system is promptly excreted as such.
The living cells of the intestinal epithelium must be able there-
fore to transform the proteids absorbed into the normal proteids
of the circulation. This combination consists in a recombination
of simple nitrogenous molecules into more complex ones with
liberation of water.

2. Circulation Form. — The blood contains plasma-proteids, —
serum albumin and serum globulin, — and corpuscle proteids.
There can be no doubt that the absorbed proteid foodstuff enters
the plasma, increasing its quantity of one or both proteids. There
is no storehouse for reserve proteids except so far as the circula-
tion itself serves such a purpose. The absorbed proteid, trans-
formed through the metabolic activity of the cells of the intestinal
epithelium into serum albumin and serum globulin is received by
tin porta! system and thence distributed to the system as constitu-
ents of blood-plasma, lymph-plasma, and tissue-plasma. Every
living cell of the system may select from the plasma which bathes
it Buch variety and quantity of the plasma proteids as are neces-
Bary in carrying on the cell activities.

3. Metabolism of Proteids. — As in the case of carbohydrates,
so here, the question as to whether or not all katabolism of pro-
teids proceeds from living cell- protoplasm is a controversial one.
Mam' of the cytologists would answer the question affirmatively.
There are strong indications amounting almost to a demonstration,
that only a part of the proteid is anabolized to the plane of living
cell-protoplasm while a part is directly katabolized. Among the
considerations favoring the second position one may mention : (i)
The correspondence of proteid katabolism rather to the variation
of proteid consumption than to special cell activity. This is
especially marked in the case of the muscle-metabolism and will
be treated Inter, (n) Albuminoids — e. g., gelatin — can not be
built up into tissue though they may be used as energy-producing
nitrogenous foods.

The preponderance of evidence in favor of the view that not all
proteids are firsi raised to the plane of living protoplasm before
being katabolized leads to the division of the proteid supply into
two parts: (i) Tissue-producing proteids; (n) energy-producing
proteids. This division corresponds roughly to Volt's classificav
tion into "organ proteid mid eireulating-proteid." It is now be-
lieved thai all metabolic changes are intracelhdar, so thai Voit's
terms seem less appropriate than the terms suggested above. The
tissue proteid Lb thai portion of the nitrogenous foodstuff whieh
i- built up !>v the cells into living protoplasm. The energyrpro-

372 ANIMAL METABOLISM.

ducing proteid is that portion which is directly k&tabolized within
the cell under the influence of the living protoplasm, — and serves the
sole purpose of producing energy. It must not be forgotten that
the tissue proteid in its final katabolism incident to the special
activity of the cell yields energy also. Whether one follows the
changes of tissue proteids or of energy-producing proteids he
eventually considers the decomposition — direct or indirect — of a
nitrogenous foodstuff from the proteid level to the urea level. In
general proteids represent 5650 calories per gramme; proteid while
the unavailable energy of a gramme of proteid represents 1650
calories (Rubner) ; the net energy represented by one gramme
of proteid material being about 4000 calories. Much remains yet
to be determined regarding the specific changes which the proteid
undergoes in this decomposition. This much is known : (i) Some
of the proteid is reduced to CO.,, H20, XH3, etc., and these in part
recombine, forming urea in which NH3 is combined with C, Or
and H ; (n) some of the proteid is changed more directly to urea ;
glycocoll, leucin, kreatin, and sarcolactic acid being mid-products
of the katabolism. Hofmeister's1 formula for albumin will give
us some idea of the complexity of a typical proteid : C204H322X,.2O66S2.
Hill's diagram (Fig. 197) represents graphically the relation be-
tween proteid and urea.

Fig. 197.

5650 Calories per gramme. The Proteid Level. (Egg-Albumin)

(a) Letting the egg albumin represent the proteids we see that

431 atoms of oxygen will oxidize one molecule of the albumin

to 204CO2 -(- 83H20 + 52NH3 -f 2S03. But these elementary

compounds are in part recombined before excretion. Nascent

XH3 radicles combine instantly with C02 and H.,0 to make arn-

i * n r, - OH + NH, n n - OXH4
monmm carbonate : O = (J _ qtt , tntxx = U = C _ rwxr

•^ 3 4 )

the ammonium carbonate is dehydrated to form ammonium car-
bamate, and again dehydrated to form urea :

1 Zeitsch. f. phys. chem., Bd. 16, S. 187. Quoted bv Bunge, Physiol. Chem.,
1894, p. 55.

PROTEIDS. 373

avtt ATW 1VTT

0:C_^-5;-H;0=0:C_^{j-H20=0:C_^;;

(b) Glycoeott (or Glycin, or Auiido-acetic acid)

H
H>N— C— COH
H HO

i Direct :

H
H HO

r-N,

H > X— C— C-OH 1 = H-C— C— C-OH + 0:C_JJ
L H O J H H 6

2 Glycocoll=Sarcolactic acid + urea.

II Indirect :

H
5>N— C— COH+30=2C02+H20+NH3

H HO

which may recombine, as in the case of albumin, to form urea.
(c) Lrucia or Iso-butyl-amido-acetic acid :

HH
H V

H H-C-H H N

H-C — C — C— C— C-OH

H H H H 6

1 1 ) Direct :

HH
H v

HHCHH X

2[H-C— 6— C— C— C-O-H] + 3oo=OC~*[[-

it j'r i'i i'i 6 ' -

+11C02+11H20

2 Leucin plus oxygen»urea, carbon dioxide and water.

(n) [ndireci : Leucine + L50 = 6COa -f 5H20 + Nil, Leu-
cin plus oxygen carbon dioxide, water, and ammonia.

i<i) Krealvn or methyl-guanidin-acetic acid,

374 ANIMAL METABOLISM.

HN=C~^5?H _CH2— COOH

II

H (-"H

h) Direct: IH>-C— ('— x H N—H+30

O H

C

XH,

H
= CO>-fO:C~^^ + II-()-C— (;— N<^
~ 2 (') H

Kreatin plus oxygen = CO.,, urea and glycocoll.
(n) Indirect: Kreatin +60=3NH3+4C02.

(in) It is possible that in kreatin we have the most important
preliminary katabolite of muscle protoplasm. It is found in con-
siderable amount in muscle; it is therefore ingested with lean
meat. But experiment shows that ingested kreatin follows a
course of katabolism different from that formed in the muscles,,
namely that it is dehydrated in the liver and excreted by the kid-
neys as kreatinin.

H H

§ HO N-C:0

H-N:C [C:0-H20=H-N( '

N— C:H2 X— C:H2

CH3 (II,

Kreatin minus water = Kreatinin.

But the kreatin which is formed in the muscle is also trans-
formed there ; that is, kreatin represents a preliminary katabolite
which is further katabolized in the muscle. Small amounts of
glycocoll and considerable amounts of sarcolactic acid are found
in the muscles. When glycocoll or sarcolactic acid or ammonium
lactate is introduced into the system it is promptly changed in the
liver to urea, CO., and H..O. Glycocoll may, however, be com-
bined with members of the benzole series (see Hippuric acid un-
der anabolism).

The observations of Gaglio, V. Frey, Marfori, Minkowski and
others (quoted by Schaefer, Text -book of Physiology, Vol. I., p.
905) make it certain : (1) that sarcolactic acid is formed in various
metabolic tissues ; (2) that it circulates in the form of an acid or

PROTEIDS. 375

ammonium salt in the blood ; and (3) that it is changed in the
liver to urea and certain by-products.

There is no positive proof that kreatin is a forerunner of sarco-
lactie acid. The probabilities are favorable to such a relation.
The course of katabolism may, in the light of recent work in this
field, be assumed to be something as follows :

(i) Kreatin + 30 = CO.,+ urea + glycoeott.

(ii) G\ycocoR=TJRVA+sarcolatic add (CH3— CHOH— C'OOH).

(in) Sarcolactic acid -j- XH, = Ammonium lactate

NH4

H

()

[H-C-

_C_COOH]

H

H

(iv) 2 Ammonium lactate + 120 = 5CO, -j- 5H20 + Ammo-
nium carbonate.

(v) Ammonium carbonate — H20 =Ammonium carbamate.

(vi) Ammonium carbamate — H..O = urea.

Note : (1) That the series of changes suggested here represent
a step by step process by which a complex body is reduced to a
series of simple bodies ; (2) that the processes are, with one ex-
ception (in), oxidations, dehydrations and decompositions.

Where do these problematic changes take place? As is al-
ready indicated above, the kreatin of the body has two sources.

A part comes from the ingested lean meat and is dehydrated
in the liver, forming kreatinin ; a part is formed in the muscles
and is probably changed at once to urea, CO., and glycocoll, or pos-
sibly directly to sarcolactic acid, urea and (.'().,. In either case
the products of katabolism which enter the circulation are sarco-
lactic ;nid and the elements of urea, or, more likely, ammonium
lactate and ammonium carbonate.1

Ammonium lactate and ammonium carbonate brought to the
liver arc promptly subjected to the changes indicated in equations
(rv), (v) and (vi).

AS with kreatin so with leucin, there arc two sources in the
system of an omnivorous or a carnivorous animal: (i) From the
alimentary tract where leucin is a product of trypsin decomposition
of peptone. A pari of the leucin so formed is absorbed and car-
ried to the liver in the portal circulation, (ii) But aside from
tIiI— source leucin is one of the mid-products of normal proteid
katabolism and is found in small amounts in all liquids of the

1 We can imagine thai the products of reactions | in j and < i v |; or possibly the
products of ;i hydrolytic cleavage of kreatin | >;• -s into the circulation. Thus :
Kreatin -(- 1II.O— Ammonium lactate -f- Ammonium Carbonate.

376 ANIMAL METABOLISM.

body. In due time it makes its journey to the liver with the
general circulation, and in that organ is further katabolized to

its simpler elements, and is excreted as urea, CO and H ,( ).

That the liver is seat of this change is practically demonstrated
by the observation that when the liver becomes extensively dis-
eased leucin accumulates in the blood to a more than normal de-
vice and is finally excreted unchanged by the kidneys.

Glycocoll or glycin may be considered a normal mid-product
ofproteid katabolism, and if a dog be fed benzoic acid he will
excrete, via the kidneys, hippuric acid which is a combination of
benzoic acid and glycocoll. This indicates that the glycocoll must
have been furnished by the system. That it was furnished for
this particular purpose is not probable. Without much chance
of error we may assume that the glycocoll used by the dog's
liver in the above mentioned case was present as a normal
constituent of the blood and that had not the benzoic acid
from the portal circulation been brought into relation with the
glycocoll it would have been katabolized in the liver to the urea
plane either directly or indirectly. This is confirmed by the ob-
servation that when glycocoll is fed to a dog it appears in the
urine as urea — having been changed in the liver. We may thus
sum up the answer to the questions which introduced this para-
graph : (i) The early steps in proteid katabolism take place in the
various metabolic tissues, principally the muscles, — though the ali-
mentary tract is the scene of certain preliminary changes and
some changes may be wrought in the blood itself, (n) The final
steps of proteid katabolism take place in the liver.

4. The Nutritive Value of Proteids. — Preliminary to a dis-
cussion of this topic it will be necessary to define two expressions
which have much significance in physiology.

(a) Nitrogen Equilibrium is an expression signifying the bal-
ance of nitrogen income and outgo. It means that the nitrogen
which the body loses in the excreta — principally in the urea in man
— is just covered by the nitrogen received in the proteid foods. If
the excreted nitrogen is in excess of the ingested nitrogen it must
be evident that the excess must have come from the nitrogen sup-
ply of the system. For a very short time this excess might be
furnished by katabolism of energy-producing proteids. But at
longest a few days would suffice to expend all the available reserve
of proteid in blood, lymph plasma and tissue plasma ; and the
excess would then be drawn from the living active cells of muscles,
glands and nervous system. The organism gives up this life bal-
ance very reluctantly and under such circumstances the proteid
excretion is reduced to a minimum. On the other hand, when
the ingested nitrogen is in excess of the excreted nitrogen the bal-
ance is in favor of the organism. It might at first be expected

PROTETDS. 377

that the system would guard this credit very carefully and store
it away in increased volume of living tissue, e. g., increased muscle
tissue, increased gland tissue and increased nerve tissue. Under
two conditions and under definite limitations this may be true.
First, the growing animal utilizes a part of the nitrogenous bal-
ance to build up new tissues. Second, after a period of starvation
— negative nitrogen balance — the emaciated living tissues will
utilize a large part of the positive nitrogen balance, when the tide
turns, to build up and reconstruct the wasted tissues. In both of
these cases, however, when the normal growth or condition is
reached an excess is not utilized to build up more muscle or more
brain, but the system uses it day by day in increased proteid met-
abolism, thus balancing increased income by increased excretion.
The normal animal with a sufficient diet maintains a nitrogen
equilibrium.

(b) Carbon Equilibrium signifies a balance of income and
outgo of carbon in food and excretions. Excess of carbon against
the organism is an index of a draft on carbonaceous tissue. All
tissues are carbonaceous, but not all tissues are necessarily drawn
upon to furnish the carbon for increased katabolism. The carbon
reserve in the deposited fats usually furnishes the balance. On
the other hand a carbon-balance in favor of the system is usually
deposited as fat. A negative nitrogen balance may exist at the
same time that there is a positive carbon balance. Under such
circumstances the animal might increase in weight at the same
time that its muscle tissues are wasting through lack of sufficient
proteid. A positive nitrogen balance and a negative carbon bal-
ance may exist together and yet the animal may increase in weight.
We may now discuss the nutritive value of proteids. The usual
method of solving such questions is to institute two experiments :
1st, deprive the animal of the foodstuff in question ; 2d, furnish
the animal with no other than the one under consideration, mean-
time watching the progress of metabolism. This method, though
open to the objection that so radical a change may not leave the
animal in a really normal condition, has yielded some very im-
portant results. Pettenkoffer and Yoit kept a 30-kilogram dog
in nitrogen and carbon equilibrium on 1500 grammes of lean meat
per day. By increasing the amount to 2500 grammes per day
the animal maintained nitrogen equilibrium and laid on lat.
Pfluger kepi a dog in weight-equilibrium for a period of eight
month- on a Lean meat diet. That the weight remained the same

lor bo long a period is sufficient proof that the nitrogen equilib-
rium and the carbon equilibrium were both maintained. These
experiments demonstrate that the carnivorous animal may get all
of it- required tissue material and energy-producing material

from ;i pure proteid diet. Jusl how far this could be shown to

378 . l X/M. I L MET. VBO L ISM.

hold for omnivorous or herbivorous animals has not been deter-
mined. There is do reason to doubt that if the proteid could be
presented in a palatable form the results would be practically the
-.line in these animals as in the carnivora. One may safely as-
sume then that ingested proteid may be used by the system, (i)
immediately iu a series of ka'abolic processes which liberate the
energyfor the life processes ; (n) as the nitrogenous factor in the
building up of protoplasm ; (ni) as the carbon and hydrogen fac-
tors in the formation of fat. The term proteid as here used is
intended to include all nitrogenous foods.

One class of proteids — the albuminoids, does not conform com-
pletely to the statement just made for proteids in general. The
albuminoids, of which gelatin is an example, can not be built uj>
into living cell protoplasm. Experiment shows that an animal
will die about as quickly when kept on a carbohydrate, fat, and
gelatin diet as when kept on a carbohydrate and fat diet. The
gelatin can be immediately oxidized and may be substituted for a
part of carbohydrate or fat, but it can not be built up into living
protoplasm. In other words the albuminoids seem to be able to
play the role of energy-producing proteids, but not of tissue-form-
ing proteids. The relation of the albuminoids to nutrition seems
to be in harmony with the hypothesis that only a part of the
nitrogenous food is actually built up into living protoplasm, while
the rest is katabolized from the proteid level, direct. This is, in
fact, one of the strongest confirmatory considerations and amounts
almost to a demonstration of the tenability of the hypothesis. In
summing up one may say that the proteids furnish the material
necessary (i) for the rebuilding of cell protoplasm; (n) for direct
nitrogenous katabolism ; (m) for deposit ax reserve fat ,- and finally,
(iv) this foodstuff may take the place of a part of the carbohydrate,
a pure proteid diet actually furnishing material for glycogen and
dextrose in the normal relations if somewhat less in quantity.

5. The Laws of Nitrogen Equilibrium. — When an animal
receives a scanty supply of proteid in a mixed diet the organ-
ism economizes its tissue proteid as well as its energy-forming
proteid by using carbohydrates and fats for energy production,
even if need be drawing upon the reserve fat of the system for
this purpose. There is a certain minimum beyond which the
proteid can not be reduced without disturbing nitrogen equilib-
rium, for there is always some katabolism of living protoplasm
and if the organism is not receiving proteid sufficient in quantity
and proper in quality to replace this waste there will be more
nitrogen egested than ingested.

When an animal receives an abundant supply of proteid in a
mixed diet the organism seems to kataboli/e the usual amount of
tissue-proteid and to draw freely upon the energy-producing pro-

PROTEIDS. 379

teid for the production of energy. If the quantity of carbohy-
drates and fat is sufficient to admit of it a portion of the food
supply is stored as fat. Whether this stored fat comes from in-
gested fat. from carbohydrates or from proteids is a matter still
in controversy. In either case the proteid is so far katabolized as
to release the nitrogen which immediately finds its way to the egesta
as urea or related nitrogenous excreta. From this it appears that
with small nitrogenous ingestion there is small nitrogenous eges-
tion, while with abundaut nitrogenous ingestion there is corre-
spondingly increased nitrogenous egestion. In general, then :
(") Law i, the lcatabolism of proteids varies with fix- supply oj
proteids, nitrogenous equilibrium being maintained within com-
paratively wide limits of supply.

(b) Law ii. The lcatabolism of proteid is nearly independent
of muscular work.

(«) Liebig's Theory. Liebig believed : (i) that all assimilated
proteid is built up into living protoplasmic tissues ; (n) that
everv manifestation of life, — muscular contractions, secretion,
thought — is the result of a breaking down of living tissues; (in)
that this katabolism of protoplasm releases nitrogen or nitrogen
compounds which found their way more or less directly to the ex-
creta ; and (iv) that the quantity of nitrogen in the excreta is a
measure of the katabolic activity. This theory is so reasonable
that it stood unassailable for a considerable period. If it is in
harmony with the facts of nutrition one would expect a marked
variation of the quantity of nitrogen elimination following mus-
cular work.

(0) Experiment of Fick and WisUeenus. These two young men,
who later attained world-wide renown and recognition as physiolo-
gist and chemist, respectively, put Liebig's theory to a practical
test. After using a non-nitrogenous diet for a period of seventeen
hour-, they began the ascent of the Faulhorn, whose summit they
reached after eight hours of the most fatiguing muscular exertion,
having lifted their bodies through a vertical distance of 1956
meter-. Fick weighed 66 kilogrammes, he had performed 129,-
096 kilogram-meters of work in climbing, meantime the heart and
respiratory muscles bad performed work which was estimated to
amount to aboul 30,000 kilogram-meters, making a total of 160,-
000 kilogram-meters of energy of muscular contraction. During
the climb mid -ix hour- subsequent to it the non-nitrogenous diet
was continued. Daring the whole observation period of thirty-
one hours the renal excretion was periodically taken and kept for
analysis. \i' Liebig's theory were tenable then the nitrogen ex-
cretion 'luring and subsequent to the climb should have been
in i I'L increased because muscle katabolism was much increased.
J>ut analysis showed no essential increase of the nitrogen elimxna-

380 ANIMAL METABOLISM.

tion ! The result of this experiment was generally accepted as
conclusive that the Liebig theory is untenable. Voil and Petten-
lioffer subjected a dog to alternating days of rest and hard work
in a treadmill. The chemical analysis of the excreta showed that
the uitrogen metabolism is practically the same on work days as
on test days. The experimenters then made a similar test upon a
man, who alternated rest with work in a respiratory chamber. It
\\;i- found that nitrogen excretion, and therefore proteid kata-
holism, is practically independent of muscular contraction, ('are
has been taken not to leave the impression that proteid metabo-
lism is independent of katabolism in muscle tissue; katabolism in
muscle tissue progresses while the muscles are at perfect rest ;
i. c, while no contractions are occurring. This rest-katabolism of
muscle tissue liberates heat energy. This process involves the
activity of living muscle protoplasm, and there is no reason to
doubt that incident to this heat production and incident to con-
traction a certain amount of living protoplasm is katabolized, and
this certain amount seems to be practically the same whether the
muscle protoplasm expresses its energy in the form of mechanical
work or in the form of heat. In either case the muscle cells seem
to be able to utilize absorbed dextrose and the energy-producing
proteids in this energy liberation. Whether the energy to be
liberated is heat energy or mechanical the carbohydrates can be
used as well as the circulating proteid, so that with sufficient and
uniform food there will be a nearly uniform nitrogen excretion,
any variations being independent of the variations of mechanical
energy liberated.

Relation of non-nitrogenous metabolism to muscular work. The
experiments of Voit and PettenhofFer with men and animals in
respiratory chambers demonstrate that the energy of muscular
work, under norma/ conditions, comes mainly, if not exclusively, from
the oxidation of non-nitrogenous material.

3. FATS.

1. Absorption Form. — Fats are absorbed in the form in
which the digestive processes have them, — named in the order of
their relative quantities: (i) Fatty Acids and glycerol, (il) Soaps,
(in) Emulsions.

2. Circulation Form. — One would seek in vain for either
fatty acid, glycerol or soap in the portal system as well as in the
lacteals. If fatty acid be fed to a dog it will appear in the lac-
teals as fat in emulsion. To absorbed fatty acid glycerol is joined
to make a fat which enters the lacteals in minute subdivision — an
emulsion — which is emptied by the thoracic duct into the general
circulation.

FATS. 381

3. Metabolism of Fats. — The fat of each species possesses a
particular proportion of the three components : Palmitin, Stearin,
and Olein. If a dog- be fed on lean meat plus palmitin plus olein
in sufficient quantities he will lay on fat ; analysis of this fat will
show that it is a typical dog-fat having the usual proportion of
stearin. From such an experiment one must conclude that the
dog has the power to change either palmitin or olein into stearin,
or that he has the power to form stearin from proteid. As
above cited the dog may lay on typical fat on a pure proteid
diet. It is then certain that the stearin may have been formed
from the proteid and not from other fats and if the stearin why
not the others, also ? Is there anything to prove that all of
the fat was not directly katabolized to furnish the immediate
source of energy and that proteid was the source of all the
fat ? No, and such may have been the case. Another exper-
iment, however, proves that a foreign fat, rape oil, may be de-
posited unchanged. If such is the case with a foreign fat may
it not also be true of those varieties of fat found normally in the
body of the animal under consideration ? This is believed to be
the case. It is believed that excess of fat may be deposited as re-
serve. Regarding that which is katabolized immediately little is
known as to the location of the katabolism. It may be oxidized
in the blood ; it is more likely that it is oxidized in the metabolic
tissues. In any case the end products are C02 and H.,0 and these
katabolites are excreted by lungs, skin and kidneys. In the an-
abolism of fatty acid and glycerine little energy is made latent.
In the katabolism of fat to its end products CO., and H.70 a rela-
tively large amount of energy is liberated. The calorimeter
shows that one gramme of pure fat will liberate about 9400
calorics of energy on oxidation. This is much more than is lib-
crated by the same amount of proteid. There are 155 atoms in
a molecule of tri-palmitin, whose oxidation requires 145 atoms of
oxygen. There are 644 atoms in a molecule of albumin whose
oxidation requires 131 atoms of oxygen. If the relative amount
of oxygen required to be taken as an index of the energy liberated
t Inn the fat would have about 1.5 times the amount of energy
represented by the albumin. It lias nearly 1.7 times the energy
of albumin, which fact i- probably due to difference in molecular
constitution, i. '•., in the- relative amounts of CO.,, H.,(), and NH3
formed on oxidation.

1. Fat Deposit. — ('/) From //><■ carbohydrates <>/ the food
(see carbohydrates), (fi) Fromthe proteids of the food. — Proteid
contains 15 per cent, of nitrogen and 50 per cent, of carbon.
I res contains 16 per cent, of nitrogen ami 20 per cent, of carbon.

Prom tlii- it follow- that less than I of the carbon of proteid
will be eliminated with tin; urea which carries off all the nitrogen.

::s-j

ANIMAL METABOLISM.

V\ 1 this carbonaceous residue the organism seems able to l>uil<l

up t';it. In an experiment upon a dog which Mas in nitrogen
equilibrium a pure proteid food containing 68 grammes nitrogen
and 250 grammes carbon was given. When <>7.!» grammes of
uitrogen had been eliminated only 207 grammes of carbon had
been eliminated. There was a balance of 4.*> grammes of carbon
retained and laid on as fat; 58 grammes representing 17 per cent.
of the total carbon, (y) From the Fats of the Food. — It was for-
merly supposed that much of the deposited fat came from the in-
gested fat. It is clear in the light of recent investigation that at
most only a small portion of it has this source.

4. THE INTERRELATIONS OF THE FOODSTUFFS.

The following figure (Fig. 198) affords a graphic illustration of
the interrelations which have already been discussed.

Fig. 198.

Diagram illustrating the interrelation of the foodstuffs.

B. SUMMARY OF ANABOLISM AND KATABOLISM.

1. ANABOLISM.

Frecpuent reference has been made to anabolism and many ana-
bolic changes have been given. It is proposed here to enumer-
ate these, explaining such as have not already been discussed.

(a) The synthesis of fatty acids and glycerol in the epithelium
of the alimentary tract.

(6) The synthesis of a molecules of dextrose with dehydration
of same to form glycogen in the liver and in the muscles.

(c) The recombination of peptone molecules into scrum albu-
min and serum globulin in the epithelium of the villi.

(d) The synthesis of carbohydrates to form fat for deposit in
adipose tissue. This process is accompanied by liberation of
oxygen.

FATS. 383

(e) The anabolism of proteid foodstuff, or blood proteids into
living- protoplasm.

i f) Synthesis of Phenol with Sulphuric Acid.

Phenol differs from benzole in the replacement of one of the
hydrogen atoms by the OH radical.

H H

( C

/ / ^

H-C C-H *^ j H.c C.H

Benzole : ; Phenol :

H-C OH H-C C-O-H

c c

H H

Benzole, phenol, and benzoic acid are frequent constituents of
the products of digestion and of urine. Benzoic acid given with
the food appears in the urine in some derived form brought about
by a synthesis. The reaction may be represented by the follow-
ing equation :

H

C

H-C C-0-HH()S

u— 0=H.,0+C,.H.OSO,K.

H-C OH

C

H

Phenol -f Acid Sulphate of Potassium = Water + Phenol-Sul-
phate of Potassium.

(</) Synthesis of Benzoic acid with glycocoll.

Benzoic acid differs from phenol in the substitution of the
COOII radical in the place of the OH. Glycocoll or amidoacetic
acid is formed from acetic acid by the substitution of XH2 for H

thug :

H O
Glycocoll: orglycin: rr>^ — * — C — (* — H

II

The synthesis takes place with the Liberation of a molecule <»t
water .-Hid the formation of one molecule <>t" bippuric acid, a con-
stanl hut not an important constituenl of urine:

384 ANIMAL METABOLISM.

H

•

C
HC C-H II

II ()

lie C-

()

-C— on + 11

\

— C— COH=

II

H

H

c

H20+

HC C.H

()
H-C C— C—

X

H O

C— COH

H
H

C

Benzoic acid +Glycin= Water -j-Hippuric acid or Benzamido
acetic acid.

2. KATABOLISM.

The cases already discussed will simply be enumerated here.

(«) The hydrolytic cleavage of dextrine molecules by the cells of
the intestinal epithelium with the formation of dextrose.

(6) The hydrolytic cleavage of glycogen into n molecules of
dextrose for each molecule of glycogen. This takes place in the
liver and in the muscles.

(c) The formation in metabolic tissues of such mid-products of
katabolism as kreatin, leucin, tyrosin, glycocoll, etc.

(d) The formation in the metal x>lic tissues of such secondary
products of katabolism as sarcolatic acid, ammonium lactate,
ammonium carbonate, etc.

(e) The formation, in the liver, of such end-products of katabo-
lism as urea, CG2, H.,0.

(/) The katabolism of tyrosin.

(i) Tyrosin or p-oxy-phenyl-amido propionic acid-(-H.,=NH3
-f p-oxy-phenyl-propionic-acid or p-hydro-cumaric acid. Thus :

H

C

H-C C-

H
-C-

HH

V
N

-C-

-C:OH

+

H2=

H
•O-c C-H

H

6

KATABOLISM- 385

H

C' H H

HC C-C— C— C •<> H

NHs+ ^ H H (')

HOC <

C

H

(n) Para-oxv-phenvl-propionic acid — CO.,=para-ethvl-phenol.

m H

H H

H-C 0— C— C-H+30=

H H
HOC CH

C

H

C H
H-C C— C— C-OH

H90+ H j0

H-OC C-H

//
C

H

Para-ethyl phenol + 30 = H,() + para-oxy-phenyl-aceticacid.

(IV) Para-oxy-phenyl-acetic acid — C02 = pani-methyl-phenol
or para-cresol.

(Sec formula under (in) for indication of the change.)

(v) Para-methyl-phenol +30 — H2()+ para-oxy-benzoic acid.

(\i) Para-oxy-benzoic acid — C02 = phenol.

These last Bteps in the procese take place in the manner indi-
cated in the earlier step-.

Phenol ia absorbed and as we have seen above may be synthesis
with acid sulphate of potassium.

(a) The kataboli&m of the red blood corpuscle. The very great
importance of the red blood corpuscle, in its relations to the gen-
eral organism, justifies the discussion of its katabolism at some;
length, though our knowledge of this process is somewhat, frag-
mentary. The red blood corpuscle has m limited period of ac-
tivity. At the end of thai period the physical anion between
th<- hemoglobin and the stroma of the corpuscle is dissolved.
25

386

ANIMAL MET A HOLISM.

There is not sufficient evidence, either from histological or from
chemical investigations, to warrant us in sayiDg thai the "break-
ing down" of the corpuscle occurs in the liver; it may occur
in the liver or in the red marrow of bones — it does oi-m,- in
the spleen. The debris of red blood corpuscles may always be
found in the spleen, either in spleen cells or in leucocytes.
Whether the senile red blood corpuscle is caught in the spleen
pulp and incidentally engulfed by leucocytes or whether it is
caught in the general circulation by the leucocytes and brought to
the spleen is not known — probably both methods occur.

The following diagram indicates in a general way the steps in
the katabolism of the red blood corpuscles.

The Red Blood Corpuscle.

Haemoglobin

C6IX|H,)(irtX ,.,<), T,,S2Fe

+

Stroma
Leucin, etc.

Hreniatin
CS,HS NAFe

G-lobin

Leucin, etc.
Hsematoporphyrin
G,2IL,,NA
+ 2HO

Bilirubin Bilirubin
C16H18N203 C,fiHlsN,0:i

+ 0

T
Biliverdin
ClnHlsNA

Bilirubin

Biliverdin
CANA

We may sum up the katabolism of the red blood corpuscle by
saying that it is broken up into biliverdin, bilirubin, iron and a
series of such bodies as leucin which are probably excreted in the
form of urea, uric acid or allied bodies. Notice that some of the
decompositions are effected through oxidation and some through
hydrolysis. But bilirubin and biliverdin are normally excreted
by the liver. How do the products of the first steps in the de-
composition make their way from the spleen to the liver? It has
been demonstrated by Socin and many others that blood plasma
which is free from corpuscles is also free from iron. Then the
haemoglobin does not pass from the spleen to the liver dissolved in
the plasma. Lymph which is free from corpuscles is free from
iron. We are forced to the conclusion that haemoglobin is carried
from the spleen to the liver by white blood corpuscles. Many ob-

THE IXC03IE OF ENERGY.

387

servers have seen liver leucocytes filled with minute particles of
matter which, when properly treated, give a micro-chemical reaction
of iron. This is confirmatory of the above conclusion.

The liver will continue to secrete bile, and as a part of the bile
bilirubin and biliverdin, after the spleen is extirpated. It is evi-
dent, then, that the spleen is not the only place where the first
steps of red blood corpuscle katabolism may occur. Possibly it
occurs normally in the spleen and is taken up vicariously by liver
or red bone marrow after the extirpation of the spleen. Most im-
portant to note is the fact that iron, which is the most difficult of
metals to assimilate, is, early in the katabolic process, split off and
retained in the system.

C. THE INCOME OF ENERGY.

The income of energy is represented by the potential chemical
energy of the food absorbed. To determine the amount of energy-
income it is first necessary to determine the potential energy of
foodstuffs and second to determine the amount of foodstuff ab-
sorbed. The first step to take in dealing with either matter or
energy is to establish units by which these entities may be meas-
ured. The calorie is that amount of heat required to raise 1
gramme of water 1° C. The large calorie or kilogramme-calorie
is that amount of heat required to raise 1 kilogramme of water
1° C. One kilogramme-calorie would raise 500 grammes of
water 2° C, or 100 grammes 10° C.

Specific heat is the amount of heat required to raise the tempera-
ture of a given body 1 ° C. Water being the standard, the speci-
fic heat of the animal body is 0.8.

Quantity of heat in a body = Wt. x Sp. H. x t., e. //., of a 10-
kilo., dog at 38° C. =10 x 0.8 x 38 = 30.4 kilogramme-
calories.

( ulorimetry is a term applied to the determination of heat units
or calories dissipated by any body. The determination is made
through the agency of the calorimeter.

The calorimeter 1 1 : i s undergone many variations since .first de-
vised by Lavoisier and La Place in 1780. The firsi calorimeter,
— trie ice calorimeter, — was arranged with a double jacket of ice.
The- body whose heat radiation was to be determined was placed
in a cage within the inner [ce jacket. The amounl of ice melted
by the radiated heat gave an index of the amount of heat given off.

The water calorimeter of Crawford (1788) was similarly
arranged except thai the heat was received by a water jacket and

the rise in temperature of the water indicated the amount of heat

given off.

The air calorimeter, fir-t used by ScharHng (1849) has been

388

AMMAL METABOLISM.

found more reliable than either of the earlier tonus. In ite 1 >< ~t
form as used by Haldane, White and Washburn {British Med.
Journ., Loud., 1897, Vol. II., p. LI, cited bySchaefer) it consists
of an animal chamber or combustion chamber (1 ) and a control
chamber (Fig. li»!i). The body whose heal is to !><■ determined

Fig. 199.

Diagram of air calorimeter. B, base ; F, layer of felt ; ''.cage: A, ventilation tubes ; 8, aii
apace; M, mercury manometer; If, hydrogen flame. (After H.u.iiank, White and Wash

BURN.)

is put into cage 1. In the control cage (2) hydrogen is burned in
quantity sufficient to keep the mercury manometer balanced. The
number of c.c. of hydrogen burned in an experiment is observed.
The calories (gramme-calories) produced by one c.c. of hydrogen
is known. Thus the gramme-calories given off by the body to
be tested becomes known. Through the aid of the calorimeter
one may determine not only the heat given off by the combustion
of any oxidizable material — (carbon, hydrogen, alcohol, fat,
starch, albumin, etc.), but also the amount radiated or conducted
away from any body, < . ;/., a living animal. With the means at
hand to determine the potential energy of foodstuffs and the lib-
erated and expended energy resulting from the katabolism of the
food it is possible to test the law of the conservation of <ncrgy as
applied to the animal organism and to ascertain whether or not
it may be verified, in living organisms as in the realm of physical
science. The first step to be taken is the determination of the
potential energy of the different classes of foodstuffs.

1. THE POTENTIAL ENERGY REPRESENTED BY
FOODSTUFFS.

It is customary to use one heat equivalent for carbohydrates,
one for proteids, and one for fats. The value used is an assumed
one. The following table gives the calories represented in dif-
ferent foods and other substances involved in nutrition :

THE POTENTIAL EXEEGT OF COMMON FOODS.

389

Substance (1 gm. dry).

Heat of Combustion

Substance (1 gm. dry).

Heat of Combustion

Starch or Glycogen
Cane sugar

4. 182 calories
1176

Egg white 4896
■■ yoke 6460

| 5678 Calories

Dextrose

3940 "

Lean beef

5656 "

Lactose

4162 "

Casein

5849 "

Carbohydrates

4181 "

Vegetable proteids

5500 "

Proteids

5650 "

Ilea

2523

Fat

9686 "

Proteid unavailable energy

1650

Fat

9423

Proteid available energy

4000

Batter

7264

Carbon per gramme

8080

Fats

9400

Hydrogen per gramme

34662

Note that the value assumed for carbohydrates is not an arith-
metical average, though it approximates an average. In com-
puting' the energy represented by a particular menu, one deals
with several carbohydrates in various proportions. Instead of
computing the different carbohydrates separately, it is customary
to assume a convenient factor which is an approximate average,
and to multiply the amount of all carbohydrates by that factor.
The other foodstuffs are treated similarly.

2. THE POTENTIAL ENERGY OF COMMON FOODS.

To determine the energy which any food represents it is only
necessary to find by analysis the amount of proteid, of fat and of
carbohydrate which the food contains, and to multiply these
amounts by the factors given in the table of energy of foodstuffs.
For example: Oatmeal contains 7.0 per cent, of H.,0 ; 15.1 per
cent, proteid ; 7.1 percent, fat; 68.2 per cent, carbohydrate, and
2 per <cnt. salts. One hundred grammes of oatmeal represent in
energy :

From proteid 15.1 x 4000 cal. = (50400

From fat 7.1x9400 " = 66740 »

From carbohydrate, 68. 2 x 4180 « = 285076

Total 412216 calories

The energy of one pound of oatmeal is gotten by multiplying
tIiI— by l.o. The following table gives the energy value of a few
common food-.

i (market condition}.

Calories per hki gms.

Calories per pound.

Wheat Bread

leal
« ornmeal
Beam "r Peas
Potal

Milk

286,304
112,216
867,428

84,162

,<■ 044

146,781
ii 1,900
184,400

l.:;oi,Jll

1,878,709

1,670,866

1,680,091

382,516

J 268,810

t ||.i. 291,000]

< 666 91 i

I [doz. 880,416]

522,220

1,974,841

390

ANIMAL METABOLISM.

3. THE ENERGY REPRESENTED BY A TYPICAL MENU.

a. An Ideal Ration for an Average Man at Light Work.

The ration given in the following table was arranged by Mrs. E.
H. Richards, and is given by Thompson in his practical dietetics.

Amount.

Prot.il.

Fat.

< arbohydrate.

Materials.

( rms.

Oz.

< .iu~.

Oz.

( .in-.

Oz.

' .in-.

Oz.

< :i lories.

Bread

Meal

453.6
226.8
226.8
28.3
113.2
156.6
28.3
14.17

16
8

8
1
4
16

1

y*

31.75
34.02
12.52
6.60
3.63
IS. 14

1.12
1.20

O. II

0.23
0.18
0.64

2.20

11.34
2.04

7.. ".(I
4.42
18.14

0.08
0.40
o.o:
0.26
0.16
0.64

257.28

9.04

[,223,674.40
242,672.
69 256

( i\ stera

.Milk

Broth

Sugar

9.60

4.88

'.to. 72

27.36

0.34

n.17
3.20
0.96

137,028.
76,466. 1 1
622,285.60

1 1 I 364 8 i

Butter

0.14

kh;.s

12.27

57.'.i7

0.50

1 1 5 398

:;-:i.> 1

Totals

2,601,649.20

h. Rations for Average Men Under Different Conditions.

The diet should vary with the requirements of the system. The
ration which is adequate for a dry goods clerk would be totally
inadequate for a lumberman in the northern forests. One does
light work in a warm room; the other does heavy work out of
doors in the coldest weather. The ration suggested under a would
be proper for an indoor and sedentary occupation. The following ta-
ble compiled by Atwater (Quoted here from Thompson's Practical
Dietetics) gives an idea of requirements under various conditions.

Conditions.

Man at light indoor work
Man at light out-of-door work
Man at moderate " "

Man at hard " "

Man at very bard out-of-door work in winter
United States Army ration
United States Navy ration
College foot hall team
Team-til'-, marble cutters, Boston
Laborers of Lombardy, Italy

Proteids.

Fat.

Carbo-
hydrates.

Energy in
Calories.

110

ilu

3: in

2,634. 200

no

100

400

3,052,000

125

125

450

3,556,000

150

1.50

5011

4,105,000

180

200

GOO

.-.Oil-.ODO

120

lfil

454

3,851,000

143

184

52(1

4,998,000

181

292

...)/

5,742.1100

254

363

826

7,804,000(0

82

40

362

2,192,000C)

e. Rations varied for Sex and Age.
(Compiled from Thompson's Practical Dietetics.)

Variations of Sex and Age.

Children to 1% yrs. old

Children V/z to 6 yrs. old

Children <i to 15 yrs. old

Women with light exercise (Atwater)

Women of moderate work (Voit)

Aged women

Aged men

Sewing girl, London, 93c. per week

Factory girl, Leipzig, 11.21 per week.

Proteids.

Fats.

Carbo-
hydrates.

28

37

75

20-36

30-45

60-1)0

5.-,

411

200

36-70

35-48

90-250

75

43

325

70-80

37-50

250- ton

80

80

300

92

44

400

80

50

260

loo

68

350

53

33

316

52

53

301

Calories
Energy.

767,000

1,418,000

2,041,

2,300,000
2,426,000
1,859,000

2,477.

1,820,000
1,940,

THE TS0DYNAM1G EQUIVALENTS OF FOODSTUFFS. 391

d. To Arrange a Menu for Particular Conditions.

If, for example, one wishes to arrange a winter diet for a stu-
dent whose age is twenty-tour years, weight 70 kilogrammes, who
is warmly clad and who takes a moderate amount of light exercise
in the open air, he would choose a diet which represents about
3,000,000 calories of energy. If the subject does not crave fat
the carbohydrates must predominate as energy producers. Take,
say, proteids 125 grammes, fat 90 grammes, and carbohydrates
sufficient to bring the calories to 3,000,000, i. e., carbohydrates
395.7. With the help of such tables of food analyses as are given
above under foodstuffs (p. 283 et seq.) one can choose a variety
and still keep the several foodstuffs approximately as suggested.

c. The Isodynamic Equivalents of Foodstuffs.

In making up dietaries one must frequently take into account
the fact that fat may replace carbohydrates or vice versa, and that
proteid may replace either. This interrelation of the foods in
nutrition necessitates the use of certain coefficients called isody-
"namic equivalents.

The isodynamic eopuivalent may be expressed thus :

(n\ 4000

(I) Of proteid to fat : d [1.) = ^ = 0.4255.

(il) Of proteid to carbohydrate: o I \ =

4000

4180 = 0-957-

(in) Of carbohydrate to fat : d l-j\ = ^ -- =0.44;").

With the aid of these coefficients one may readily compute the
amount of one food to be substituted for another when a change
of proportion is indicated. Suppose one wishes to modify the
"light work menu" given above by substituting fats for the
carbohydrates in execs.- of 350 grammes, 389.84 — 350 =s 39.84
grammes. How much fat is equivalent to 39.84 grammes carbo-
hydrates? <U'.\ =0.445. 39.84 x 0.445= 17.73 grammes of

•6)

fit : 57.97+ 17.73= 75.7 grammes fat. The modified "light
work menu" now consists of: proteids L06.8, fat 75.7, carbohy-
drates 350, bvi U represents the same energy as before; it is iso-
dynamic with the menu as tabulated. It may be said here that
the proteid should never fill below LOO grammes per day for an
adull man or 80 grammes per day for an adull woman.

392 ANIMAL METABOLISM.

IK THE LIBERATION OF ENERGY.

a. The Primary Literation of the Potential Energy of the

Organism.

The potential chemical energy of the tissues and fluids of the
body represents the capital of the organism. But this energy
must be liberated — must he made kinetic — in order to figure in
the lite processes of the organism. In the calorimeter the energy
of the foodstuffs; is liberated by a process of rapid oxidation or
combustion. In the animal organism the energy is liberated by
a process of slow oxidation usually associated with step-bv-step
katabolism. It has been demonstrated that the heat is produced in
the same aggregate quantity, whether the katabolism or oxidation
be slow or rapid. The heat energy determined by the calorim-
eter, then, will be actually liberated in the organism ; and if a
man has a daily energy-income of 3,000,000 calories and is in a
condition of material equilibrium, 3,000,000 calories of energy
must be daily liberated and expended.

If the question arises : By what process or processes is the .
energy liberated ? the answer is briefly : The processes of katabo-
lism are the processes of energy liberation. The two processes are
inseparable because in a sense identical.

In what form and hi what location is flic energy liberated?

It has been intimated that all of the energy is liberated in two
general forms and in three locations : (i) In the form of heat and
mechanical motion in the muscles ; (n) as heat in the active
glands; (ill) as heat and something analogous to electricity, —
nervous energy, — in the central nervous system and that the pro-
portions of the total energy liberated in the several locations re-
spectively are approximately as 1(3:3:1 or 80J6 : lo'/ : 5f .

b. The Transformation of Energy.

Much of the energy liberated as energy of motion is converted
into heat before leaving the body. This transformation occurs by
virtue of friction of the tissue and fluids. As an extreme ex-
ample let us take the energy of the systole of the beaut which will
sum up to a prodigious amount during 24 hours. The immense
sum of energy is all liberated as energy of motion, but all except
an infinitesimal amount is transformed by friction of blood on
walls of vessels to heat and leaves the body in that form. If the
work done by the heart of the adult at each contraction is 320
grammeters, and if the heart beat about 72 times per minute
then the work- of the heart would amount to 77,970 calories in 24
hours (42o..") grammeters = 1 gramme-calorie) or about g1^ of

EXPENDITURE OF KINETIC ENERGY. 393

the total energy usually expended, or about -f^ of a heavy
day's work. Nervous energy is also transformed to heat
energy.

c. The Conservation of Energy.

The law of the conservation of energy holds as absolute sway in
the animal onmnism as in the non-living world about us. Every
calorie of energy taken in either remains as stored up potential
energy or it eseapes from the body in the form of heat, of me-
chanical motion, or as in case of urea, as unliberated potential en-
ergy. The unliberated energy is, however, correeted for in the
above and subsequent calculations. Rubner (Zett&ch. f. Biol.
Munchen, 1894, XXX., S. 73) has been successful in practically
demonstrating that in the animal body the law of the conservation
of energy holds good. The subject of his experiment was a 1 ^-kilo-
gramme dog which was confined in a calorimeter cage, thus confin-
ing the energy liberated to heat energy. The dog received during the
peri< id 228.06 grammes of proteid and 340.4 grammes of fat. This
food represented a total of 4,1 1 1,970 calories. The amount of heat
actually given off during this period, as shown by the calorimeter
was 3,958,000 calories. Thus 96 per cent, of the energy received
as potential energy of food appeared as kinetic heat energy. The
remaining 4 per cent, may represent the mechanical energy of the
movements made in eating the food or other movements made
even in a confined space. In another experiment the net energy
received in the ingesta 278,500 calories ; the heat energy given
off 276,800; in this case over 99.3 per cent, of the energy was
given off as heat leaving less than 0.7 per cent, for mechanical
energy.

d. The Expenditure of the Kinetic Energy of the Or-
ganism.

All of the kinetic energy of the body is finally expended in

■ or the other of two forms : as heat ; or as motion. A certain

amount of energy which enters the system as potential energy
leaves as potential energy. The matter holding this energy is
urea, uric acid, faeces, milk, the reproductive products and the oil
secreted by the .-kin, or other epidermal products which are shed,
moulted or abraded.

We are now in :i position to take an exact account of the in-
come and expenditure of the energy of the organism and may ex-
press the fact that the two amount- are equal through the use of
a Balanc* Sheet.

394

ANIMAL METABOLISM.

Balance Sheet of Energy fob Man at Light Work.

Income [a Calories.

Expenditure in
i laloi U -.

I \ , ome : —

Proteids : 110 grammes (5 4000 calories

140,000

Fats : 100 grammes <" 9400 calories

940,000

Carbohydrates : W0 grammes (§ 4180 calories

1,672, t

Expenditure : —

Mechanical work, 212, 750 kilogrammeters

500,000

[425.5 grammetera equivalent to calorie]
Heal losl is 1900 grammes of excreta

17. :.ou

[Cooling from 37°C. to 12°C. : L900 25 calories]

Heal required to warm 13000 grammes air from

12°C. to37°C.

84,500

[Specific heal of air = 0.26, .\ 13000X 25 x .26]

Evaporating 330 grammes of water from lungs

192,600

[i gramme requires 582 calories]

Evaporating 660 grammes of water from skin

384,120

Radiation and conduction from skin about

1,843,820

3,052,000

3,052,000

With varying muscular activity and varying external tem-
perature there will be a fluctuation of the credit side of the ac-
count. If the balance is against the system the reserved nutrients
are called out for an immediate adjustment of the account. Later
the reserve is made good by a more liberal diet.

E. ANIMAL HEAT.

a. General Considerations.

The subject of animal heat belongs logically under Lih< ration
of Energy. Many of the things usually discussed under animal
heat have already been treated above. The very great im-
portance of certain phases of this subject justifies especial em-
phasis under a separate heading.

From what has preceded it goes without saying that the heat
of the animal body is the liberated heat of metabolism. This
heat is subject to constant additions through metabolic activity of
the tissues and to constant subtractions through radiation or con-
duction from the surface. ^-r;^— |

One of the most remarkable mechanisms in the animal body is
the heat-regulating apparatus. Through its operation certain
animals are able to maintain a fairly constant temperature what-
ever the temperature of their surrounding medium may be.
Animals thus able to maintain an even temperature in an uneven
medium are called Homoiothcnnx ; {pfJDtOQ — like) while animals
which are not able to maintain an even temperature, but whose
temperature varies with that of the surroundings are called
Poikilotherms (jzor/doz — varied). Poikilothermal or " cold-
blooded" animals, by virtue of their sluggish metabolism, have
a temperature somewhat higher than the medium when the latter
has a relatively low temperature ; but above a certain point the

METHOD OF DETERMINING TEMPERATURE. 395

temperature of the animal falls somewhat below that of the me-
dium. This is well illustrated by the frog. The frog's tem-
perature in water at 2.8° C. is 5.3° C, in water at 20.(5° C. is
20.7° C. and in water at 41° C. is 38° C. The poikilothermal
animals are the reptiles, amphibia, fishes, and invertebrates.

The homoiothermal or " warm-blooded " animals include the
birds and mammals. The following mean temperatures per rec-
tum have been determined : Horse, 37.9°C; cow, 38.6°C;
sheep, 40.2°C; dog, 38.6°C.; cat, 38.7°C; pig, 38.7°C.; rab-
bit, 39.2°C; guinea-pig, 38.7°C; white rat, 38°C; monkey,
38.4°C.; common fowl, 41.<5°C.; duck, 42.1°C.; pigeon, 40.9°C.;
whale, 38.8°C; seal, 38.9°C.j great titmouse (a bird), 44°C,
(111°F.) ; yellow hammer, 43.2°C.

b. Method of Determining the Mean Temperature.

The usual method of determining the temperature of an animal
is to insert a mercury thermometer into some inclosed space, hold-
ing it in position until the thermometer registers. Various loca-
tions are chosen : the mouth, the axilla, the groin, the rectum,
and the vagina. The location most usually chosen — the mouth —
is the one which is subject to the greatest accidental variations.
Observation has shown that the most reliable and unvarying tem-
perature may be gotten by inserting the thermometer several cen-
timeters (3— G cm.) into the rectum or vagina.

The thermometer should register tenths of a degree. The tem-
peratures recorded above are in the Centigrade scale, in which the
difference in the stand of the mercury column at freezing and at
boiling is divided into 100 parts or degrees Centigrade. The
Fahrenheit scale, most used in America, differs from the Centi-
grade in arbitrarily assuming for the freezing point -(-32° and
for the boiling point +212°, dividing the space between these
two points into 180° F., 1° F. is equal to £°C, or 0..". C;
while 1°C. = 1.8° F. To reduce a centigrade reading to Fahren-
heit it ig only necessary to multiply by 1.8 and add 32°; i. <■.,
38 C.=[38x 1.8+32] 100.4° F. '

To reduces Fahrenheit reading to Centigrade one subtracts 32°
and multiplies by 0.5, thus loo.4°F. (100.4 - 32° = 68.4 x .5)
= :;s C.

Prom what will follow it will be evident that iii the collection

of data for comparison uniformity of method must be observed
throughout :i Series of observations. If one wishes to determine

the mean rectal temperature in the human subject he should make
tic observations at a particular time in the day, otherwise his re-
sults will be varied by two factors. 1 1' he wishes t«. compare oral
with rectal temperature he should observe as indicated above,

396 ANIMAL METABOLISM.

every precaution to eliminate every other variable except tl ae

whose value he wishes to determine. If he attempt- to compare
the early morning temperature of a man with the evening oral

temperature of a child his results will be valueless.

c. Factors Which Cause Variations of Temperature.

1. Climate. — There is very little difference in the body-tem-
perature of the race- inhabiting frigid, temperate and torrid zone- ;

but it' a native (if the frigid zone travels into the torrid zone his
temperature will rise several tenths of a degree higher than the
normal for the reason that his organs of heat regulation can not
easily adjust themselves to so profound a change in the environ-
ment, and the heat accumulates in the body. When, on theother
hand, a native of the torrid zone is subjected to a frigid tempera-
ture, his heat production cannot keep pace with the heat expendi-
ture and his temperature falls slightly below the normal.

2. Sex. — Sex exerts little influence. Extended observations
have determined that the temperature of a bitch is 0. 2°C lower
than that of a dog ; that the temperature of a female duck is 0.3°
C. higher than that of the male duck ; that the temperature of
the mare is 0.4°C. higher than that of the stallion. This differ-
ence is small and inconsistent. The results for the human sub-
ject are contradictory, but the temperature of the woman seems
to be slightly higher than that of the man.

<*>. Age. — Infants and children have a mean temperature higher
than the mean temperature of the adult by about 0.4° C. After
puberty the temperature reaches the level of the adult tempera-
ture, which level it maintains throughout life with possibly a
slight rise in rectal temperature with old age.

4. The Changing Season. — The oral temperature follows the
seasons, being slightly higher in summer and slightly lower in
winter. The rectal temperature is higher in the winter and early
spring than at any other time during the year. (Bosanquet, Lan-
cet, London, 1895, Vol. I., p. 072.)

Animals have a remarkable resistance to the extremes of climatic
changes, the body temperature not rising perceptibly when the
external rises several degrees Centigrade above the temperature of
the blood. On the other hand animals and men subjected to
sudden fall of temperature in winter will maintain an equable
temperature.

5. Extreme Temperatures Artificially Produced. — AVhen
an animal is subjected to extreme heat much in excess of that
which it may experience with the changing seasons it is able to
maintain a fairly even temperature for some time if flic heaied
air be dry, while in moist heat the temperature quickly rises and

VARIATIONS OF TEMPERATURE.

397

death ensues. The reason for this is simple : in dry air the
evaporation from the surface keeps the temperature down ; while
in moist air the evaporation is reduced or quite suspended and
the animal has no defense against the extreme high temperature.

When a homoiothermal animal is subjected to extreme cold the
protective process consists in retaining enough of the liberated
heat to keep the temperature up to normal. The coat of hair or
feathers or subcutaneous fat usually suffices in all animals which
are accustomed by nature to low temperature. Animals not so
protected succumb soon.

Cold-blooded animals, especially fish, may be cooled to so low
a temperature, — 1° C. to — 3° C, that there is a torpor simu-
lating death ; but with gradual rise of temperature the life proc-
esses start up again.

6. The Influence of Day and Night. — The following chart
gives the result of observations by Jiirgensen and Liebmeister
( Handbuch der Paihologie imd Therapie des Meters, Leipzig,
1875). Xote that the lowest temperature is at 5:00 A. M., and
the highest from 5:00 p. M. to 7:00 P. M. The range is just 1°
C. or 1.8° F.

Fig

. 200.

:;:..-,

37:25 °c

...

87.1

\y^

2 P.M.

30.25

1A.M. 12 M. 3 P.M. GP.M. 'J P.M. 12 3 A.M. 5 A M. 8 A.M.

Daily variation of temperature. (After J0EGEN8EN, )

The cause for these variations seems to be the bodily activity
of the day and the rest of the night because in men who work
nights and sleep during the day the curve is practically reversed.

7. Muscular Work. — The muscles are the heat-producing
organs par excellence, 80 per cent, of the heat energy of the body
being liberated in the muscles. The heat-producing function
of the muscles is not by any mean- independent of their con-
tractility. Just how far these two functions are interdependent
is undetermined. It is certain that when an urgent call for more
heal i- made upon the system the muscles respond with involun-
tary jerky contractions (sAtverin^). The natural impulse is for
the animal to begin active voluntary exercise to " warm up."
On the other hand, heal is produced in the muscles when they
are apparently at perfed rest so far as any visible or sensible
contractions are concerned ; yet if the muscles are paralyzed l>\
curare they lose their heat-producing power and the animal ie .it

398 ANIMAL METABOLISM.

the mercy of external temperature, /'. e., potentially a "cold-
blooded " animal. There is an increased production of heat dur-
ing exercise; if the increased amount of heat is not given off from
the body as fast as it is Liberated within the body there will be
a rise of temperature. Repeated observations by numerous ob-
servers show thai vigorous muscular exercise may be attended by
a rise of as much as 1.2° C.

8. Mental Work. — For reasons similar to those cited above
under muscular work, there is a rise of temperature accompanying
vigorous mental work. This rise is local and may or may not be
communicated in perceptible degree to the system in general,
though it is usually conceded that the general temperature may
rise as much as 0.7° C. with mental work.

9. Food. — The increased activity of the digestive glands, and of
the involuntary muscles of the digestive system causes a some-
what increased production of heat. At the same time a large
proportion of blood is collected in the central organ — less upon
the surface — and the heat expenditure is decreased. These two
things, working together, tend to raise the temperature. When
other factors tend to lower the temperature a meal would have
the effect of keeping up the temperature when it would otherwise
fall. This is the effect of a dinner at night.

10. Sleep. — Sleep in itself has no influence directly upon tem-
perature. Perfect rest which accompanies sleep causes a slower
production of heat and consequently a fall of temperature.

11. Baths. — When a warm-blooded animal is immersed in a
bath it is at the mercy of two factors : heat-production and heat-
conduction. The first factor is not likely to differ much from the
normal, so that the principal factor is the temperature of the bath.
If it is above blood temperature the body-temperature will rise.
If the temperature of the bath is below that of the blood, — the
usual condition, — the temperature will tend to fall, though it must
be remembered that the heat-producing factor may in this case
be an important one. If the temperature of the bath is much
below that of the blood the fall of body temperature may be con-
siderable. A 12-minute bath in sea water at <!.7° C caused a
fall of oral temperature from 36.7° C. to 84° C.

12. Drugs. — Alcohol, by increasing cutaneous circulation,
causes a fall of temperature.

Chloroform, ether, morphine, chloral, and nicotine cause a fall of
temperature through decreased heat production.

Ourari causes fall through paralysis of the muscles followed by
decreased heat production.

Oocain, atropin, caffein, and veratrin raise the temperature
through decreased heat radiation or increased heat production.

13. Individual Differences of Temperature. — The mean

HEAT REGULATION OR THERMOTAXIS. 399

temperature of individuals of the same species living under ex-
actly the same circumstances will not always be the same. The
mean temperature of one man may differ by as much as 0.7°C.
from that of another, all conditions being apparently the same.

14. The Limits of the Variations. — Pembrey gives the max-
imum range of normal human temperature as 2° C. (3.6° F.).
•• By exposure to cold, especially when subjects are drunk, the
temperature may fall as low as 24° C. without a fatal issue."
(Pembrey-Schaefer's Text-book of Physiology, Vol. I., p. 821.)

The maximum temperature compatible with life as reported by
Wunderlich is 44.75°C. (112.6°F.). Death followed.

(1. Temperature Topography.

(>i) Temperature in Superficial Cavities:
(i) Bend of knee=35°C.
(n) Inguinal fold = 3o.8°C.
(in) Closed axilla = 36. 5°C.
(IV) Mouth (under tongue) = 37.2°C.
(v) Rectum = 38 °C.
(VI) Vagina = 38.3 °C.
(6) Temperature of Fluids and Tissues :
(i) Blood in left heart = 38.8 °C.
(ii) Blood in right heart = 38.8°C.
(in) Blood in hepatic vein = 39.7 °C.
(iv) Blood in crural vein = 37.2°C.

e. Heat Regulation or Thermotaxis.

1. Relation of Heat-Generation to Heat-Expenditure. —
In order to maintain an even temperature of body in a medium
of widely varying temperature it is necessary that the organism
be provided with some means of adjusting either the rate of heat
production or the rate of heat radiation. The factors which work
together to maintain the thermotaotic condition are called thermo-
genetic and thermolytic factors. These two factors have the fol-
lowing relation to Thermotaxis; the greater the thermogenesis
tin- higher the temperature; the greater the thermolysis the
lower the temperature. If* we represent the temperature which
i- produced in the body by the interaction of these factors by/,
tlie thermogenetic factor by g, and the thermolytic factor l>v / then :

H

(a) Variation of ( )\i; Faotob. — From the above expression
n jj evidenl thai the temperature will be increased (raised ) by an in-

4(10 ANIMAL METABOLISM.

crease of </, 1 t = j J or by a decrease of I j t= -j— ^ I. Id ver-
bal expression : — ,'//<• temperature will be raised by an increase of
heat-formation or by a decrease of heafaradiation.

Furthermore, the temperature may be lowered by a decrease of

heat-formation l^= '"' 1, or by an increase of heat^radiaMon,

(-5)-

{/)) Variation of Both Factors Together. — Both of

these factors may increase at the same time. The situation may

be expressed mathematically as follows :..../ = ■ , .

id

If in — n ; i, e., if both arc increased proportionally there will be

no change in the temperature for the expression reduces at once to

the normal, t = . If m > n ; i. e., if heat-formation increases

■more than heat-liberation the temperature will rise. If hi <«/ i.e.,
if the heat-liberation increases more than the heed-formation there will
be a fall of temperature.

But the thermotactic factors may both decrease at the same

-9
time ; expressed mathematically as follows :. . . J = j— .

n

If 1 = - ; i. e.} if heat-generation is decreased proportionally
with heat-radiation the temperature would remain unchanged. If
m > n ; i. e., if heat-generation is decreased more than is heat-radi-
ation there would be a decrease (fall) in temperature. If m < n ;
*. e., if heat-generation is decreased less rapidly than is heat-libera-
tion there would be an increase (rise) in temperature.

2. Thermotactic Centers. — (a) Thermogenetic Centers :
(i) On median side of corpus striatum ; (ii) between corpus stri-
atum and optic thalmus ; (in) in anterior end of optic thalmus.

Thermogenetic centers may be : Thermoaug mentor or Thermoin-
hibitory and the thermogenetic impulses pass from the centers to the
metabolic tissues along the trophic nerves supplying those tissues.

(b) Thermolytic Centers. — The factors of thermolysis are :
(i) radiation ; (n) evaporation.

Both radiation and evaporation must take place from the sur-
face of the skin or respiratory mucous membranes, principally the
former.

Dilatation of the cutaneous arterioles favors both radiation and
increased secretion of perspiration. Contraction of the arteri-
oles has the reverse influence upon radiation and evaporation. It
then becomes evident that both factors of thermolysis may be in-

HEAT REGULATIOX OB THERMOTAXIS. 401

creased by vase-cutaneous dilatation. The vaso-motor centers
may be classified as (a) vase-constrictor and (ff) vaso-dilator.

(a) The vaso-constrictor center is bilateral and is located in the
anterior end of the floor of the fourth ventricle. This center is
always in action and constant impulses from it to the various ves-
sels causes their tun us. This center seems to be general in its
jurisdiction and various stimuli may, through its action, cause
general increase or decrease of vaso-constriction accompanied by
general rise or fall of blood-pressure.

(i) The vaso-dilator centers are not centralized in some circum-
scribed part of the brain or cord, but "diffuse," i. c, small local
centers are located intra- and extra-cranially along the central
nervous axis. The purpose of this becomes evident when we
remember that these centers act locally, their apparent function be-
ing to increase l<>c<il blood supply.

" There is in some degree an inverse relation between the ves-
sels of the skin and those of deeper parts on reflex stimulation of
vaso-motor centers. The cutaneous vessels are often dilated while
those of the deeper parts are constricted." (Am. Text-book,
quoting from Franck, p. 502, 1896.) This fact makes it evident
that the whole surface of the skin may flush through vasodilata-
tion, but the blood-pressure still kept up by vaso-constriction in
the deep-lying tissues.

Evaporation is increased or decreased through the influence of
. — (.;) //" sweat-center, which is bilateral and located in the medulla.

All of these centers are stimulated reflexly by the temperature of
the medium which comes in contact with the skin. If cold, then
the thermogenetic center is stimulated and the metabolic tissues be-
gin a more active katabolism. Meanwhile the heat supply is con-
served by a withdrawal of the blood from the periphery, i. e.,
vaso-oontrictor center stimulated. Presently the heat accumulates
through conservation and production, and a reaction sets in cx-
pressed by ;i cutaneous vaso-dilatation. The blood comes to the
surface, warms the -kin, and by exposure falls in temperature to
the normal.

<)n the other hand, when the medium is too hot, the sensory
DerveS in the -kin carry impulses to the centers: (I) the thernio-

genetic activity i- inhibited ; (n) the sweat-center is stimulated, the
perspiration pours out upon the skin ami its evaporation cools the
body. The interaction of the controlling factors keeps the tempera-
ture within about one-half degree of the average, i. *.. within ;i range
of aboul one degree, though under Less usual circumstances 2°C.
Various causes may operate to bring about an abnormally bigh

or low temperature, especially the Conner. This condition which
i- :i pathological one i- a symptom incident to many diseases and

will he treated in lull under Pathology.

CHAPTER VIII.
EXCRETION.

INTRODUCTION.

1. DEFINITION'S.

2. GENERAL CONSIDERATIONS.

3. ANATOMY OF THE KIDNEY.

a. Blood Supply of the Kidney.

b. The Urinieeeous Tubules.

c. The Innervation of the Kidney.

THE PHYSIOLOGY OF EXCRETION.

A. RENAL EXCRETION.

1. THE URINE.

a. General Characters.

(1) Quantity.

(2) Specific Gravity.

(3) Reaction.

(4) Color.

b. Chemical Composition. Tabulated.

c. The Urinary Constituents Separately Considered.

(1) Organic Constituents.

(2) Inorganic Constituents.

2. THE PROCESS OF URINARY EXCRETION.

a. Glomerular Excretion.

(1) Experiments and Conclusions from same.

(2) Factors Influencing Glomerular Excretion.

b. Glandular Excretion.

c. The Eoestion of Urine. Micturition.

B. PULMONARY EXCRETION.

C. CUTANEOUS EXCRETION.

1. THE SWEAT.

a. General Characters.

(a) Quantity; (b) Specific Gravity; (c) Reaction.

b. Chemical Composition.

(1) Organic Constituents.

(2) Inorganic Constituents.

2. THE PROCESS OF CUTANEOUS EXCRETION: PERSPIRATION.

(1) The Influence of the Nervois System Upon Cutaneous Excre-
tion.
CI) Factors Which Cause a Variation in the quantity of Perspi-
ration.

I). INTESTINAL KXCRETION.
402

DEFIXITIOXs. 403

EXCRETION. INTRODUCTION.

1. DEFINITIONS.

Excretion. — " The separation of waste products of an organ
or of the body of a whole, out of the blood. The material so
excreted " (Gould). Comparison of this definition with that of
secretion (p. 246) shows that excretion is looked upon as a
special form of secretion ; the distinction being that secretion
is elaboration of any product from constituents of blood or lymph
while excretion is the separation of waste products from the blood
or lymph.

Egestion. — " The expulsion of excrements or of excretion."
(Gould.)

Egesta. — " (pi. of egestum, fecal matter.) The discharges of
the bowels or other emunctory organs." (Gould.) Let us make
a specific application of these definitions. The parietal cells of the
gastric glands take up NaCl and II..CO,, or CaCl., and Xa,HP04
from the blood, where they form normal constituents ; and these
active cells elaborate new products.

An excretion differs from a typical secretion in that the former
represents waste products which escape, from the place where the
katabolism occurred, into the lymph or blood and so circulate
through the system until brought to some organ whose active
cells have the power to select and separate these waste products out
of the blood. For example, urea is secreted (internal secretion)
by the liver, but excreted by the cells of the convoluted tubules
of the kidney.

The term egestion is a general one and includes all of those
acts which have as their end the throwing out of excretions espe-
cially, though the term may, not improperly, be used to include
not only the throwing out of the excreta, but also of matter
which ha- never formed a part of the body, e. </., the undigested
portion of food ; and also the unabsorbed part of the inspired
air — the nitrogen.

Egestion, then, is represented by the following special acts;
(1) Defecation, (2) Micturition, (3) Perspiration, (4) Expiration.
The matter thrown out of the organisms by these acts maybe

called, collectively, BGEST-A ; while the term EXCRETA may be

used only for that part of the egesta which was at one time a con-
stituent of the body and has been reduced t<> a condition useless
to the organism and has been excreted by the Lungs, the skin, the
kidneys or the liver.

4 0 1 EXCRETION: WTRODl '< TIOX.

2. GENERAL CONSIDERATIONS.

We have now followed the process of nutrition to its last stage,
— ridding the body of the waste product.-. We have studied the
process and products of digestion and have enumerated the factors
involved in the absorption of digested foods ; we have studied

examples of the anabolic changes which occur during the assim-
ilation of the absorbed matter, and of the katabolic changes
which occur incident to the activity of the tissues. We have
noted from time to time the formation of some body useless to
the animal organism. Frequently, indeed, these bodies are worse
than useless, — they may be poisonous. In either ease it is acc-
essary that the organism be provided with some means of throw-
ing off the useless or poisonous matter. But what is the charac-
ter of this waste matter as we have, up to this point, noted it?
1st. There was a gas — CO., — the product of the oxidation of the
tissues. 2d. There was water, in part the unchanged water of
imbibition, in part the product of oxidation of the hydrogen of
the tissues. 3d. There was solid material composed of: (i) cer-
tain organic bodies — urea, hippuric acid ; (n) inorganic salts —
NaCI, HKS04, etc. If one were to compare this list of material
" outgo " with the list of material " income " — the foods — one
would note a remarkable parallelism in the general character of
the matter, i. e.} both lists contain a gas, water, and solids com-
posed of organic and inorganic matter, the organic matter con-
taining nitrogenous and non-nitrogenous bodies and the inorganic
matter containing a long list of chlorides, phosphates, and sul-
phates. But the parallelism vanishes as soon as one glances at
the specific character of the "income" and "outgo" matter: the
" income " represents matter of high potentiality, while the
" outgo " represents matter completely, or almost completely, de-
pleted of its energy. The method of liberation and expenditure
of this energy has been discussed.

The only situations where the waste products could be thrown
out of the system are the boundary surfaces. These boundary
surfaces include the skin and all of the mucous surfaces, including
the genito-urinary epithelium. Of all these possible situations
certain locations are specialized for typical secretion only (e. </.,
genital, conjunctival epithelium), certain locations are specialized
for absorption only (villi of small intestines) ; certain locations
are devoted in part to secretion and in part to absorption (epithe-
lium of stomach and large intestine). The only portion of the
boundary epithelium which is specialized exclusively for excretion
is the renal epithelium. The pulmonary epithelium is nearly as
much devoted to absorption as to excretion. The general cutane-
ous surface is, first of all, an organ of protection, secondarily, an

ANATOMY OF THE KIDXEY

405

Fig. 201.

organ of thermolysis where the water secreted by the sweat glands
serves a specific purpose. Quite subordinate to the two functions
mentioned above, the skin is an organ of excretion supplementing
the work of the kidneys in
the excretion of water.

Of the epithelium lining
the alimentary canal it can
not be said that it is excre-
tory in any sense. A por-
tion of the secretion (mucus,
etc.), passes out of the ca-
nal with the fa?ces, but it is
secreted for a particular lo-
cal function and is not sepa-
rated out of the blood to rid
the system of it. The he-
patic epithelium, however,
forms seyeral excreta, among
which are urea, which is ex-
creted by the kidney, and
bile pigments which are ex-
creted by the liver itself.

To summarize : excretion
takes place at four more or
less specialized parts of the
boundary epithelium : (i)
the ratal epithelium, (n) the
pulmonary epithelium, (in)
fin general cutaneous surface,
(iv) the hepatic epithelium.

The physiologically im-
portant features of the struc-
ture of thr Lungs and of lln'
liver have been summarized
under respiration and meta-
bolism. The structure of
tin- -kin will be given under
tin' subject, External Rela-
tions. The only organ
solely excretory in it- func-
tion i- the kidney whose
anatomy may !><■ here summarized

Vascular supply of kidney. (Cadiat.) Diagram-
matic. ". pari of arterial arch ; /», Interlobular ar-
tery; <•, glomerulus; </, efferent vessel passing to
medulla a* false arteria recta ; <■. capillaries <>t cor-
tex : /. capillaries of medulla; g, venous arch: h,
itraigm reins "i medulla : j, vena Btellula ; i, inter-
lobular vein. (Sr II VI I I I.

ANATOMY OF THE KIDNEY.

The following summary presents the facts of greatest impor-
tance t'» t 1 1 * - physiologist.

401 ;

EXCRETIOS : IXTHOnrcTIO X.

a. The Blood-Supply of the Kidney.

(1) The large short renal artery direct from the abdominal
artery carries to the kidney its supply of arterial blood. Its
size is wholly out of proportion to the kidney, making it evident
at once that another purpose than simple nourishment of the kid-
ney tissue is to be accomplished.

(2) The large, short renal rein emptying direct into the vena
cava offers slight resistance to the return of the blood.

Fig. 202.

Diagram of the course of two uriniferoua tubules. (Klein.)

(3) The formation of a network of arterial and venous arches
between the cortex (A, Fig. 202) and the medulla (B C, Fig. 202)
in and just below the plane a' (see a and g, Fig. 201).

THE URIXIFEROUS TUBULES.

407

(4) The interlobular cortical arteries passing upward from this
plane, (6, Fig. 201.)

(5) The glomeruli or tufts of capillaries on either side of the in-
terlobular arteries, (c, Fig. 201.) Each glomerulus is supplied
by an afferent arteriole and is emptied by an efferent venule.

(6) The capillaries of the cortex (e, Fig. 201) surrounding in a
network the tubules of the cortex and fed by the efferent venules.

(7) The capillaries of the medulla fed by the true and false ar-
teria rectee. (df and <l, Fig. 201.)

(8) The interlobular vein* collecting the blood from the cortex
and through the venous arches passing it into the larger branches
of the renal vein.

b. The Uriniferous Tubules.

(1) ( 'apsule of Bowman inclosing a glomerulus. The glomer-
ulus, though inclosed by the capsule, is outside of the uriniferous

Fig. 203.

Tnbules from a section of dog's kidney, a, capsule, Inclosing the glomerulus ; », oeck of the
capsule : e, e, convoluted tubules ; ''. Irregular tubules ; d, collecting tube ; e, e, spiral tubes ; ./',
part of the ascending limb of Benle's loop, here (in the medullary ray) narrow. (Schaefeb
after K i i

canal, because the capsule is reduplicated, one layer of it lying
upon the glomerulus. (", Fig. 203, and 1, Fig. 202.)

(2) I'll'' //"•/.• of the capsule, beyond which the real tubule
begins.

(3) The proximal convoluted tubule (3, Fig. 202, c, Fig. 203),
clotbed with striated cuboidal epithelium.

408 EXCRETION: ISTRODUCTIOS.

(4) The spiral portion ( 1 and e, Figs. 202 and 203), with
low granulo-striated epithelium and wavy course.

(•"») The descending limb of Hull's hop (5, Fig. -<>*J), pos-
sessing the narrowest Lumen of the entire tubule surrounded by
flattened plates whose nuclei project into the Lumen of the tubule.

(6) The loop of J loilc and the ascending Ihiih of limit's
lnnr (6, 7, s, 9, Fig. 202; and/, Fig. 203) with polyhedral
• ill- and flattened nuclei.

(7) The irregular portion and the distal convoluted portion
(lo, 11, Fig. 202) ; (I, and c, Fig. 203) whose epithelium is sim-
ilar to that of the proximal convoluted portion.

(8) The collecting tubules of the medullary ray (12, 1.3, Fig.
202; and d} Fig. 2< >3), with cuboidal transparent epithelium.

(9) The excretory ducts of the medullary portion (14, 15, Fig.
202), whose epithelium consists of large, well-defined, columnar
cells with ellipsoidal nuclei near the base.

c. Innervation of the Kidney.

The kidney is supplied by branches from the renal plexus which
surrounds the renal artery. The renal plexus is, in turn, "formed
by filaments from the solar plexus, the outer part of the semilu-
nar plexus, and the aortic plexus. It is also joined by filaments
from the splanchnic nerves. The nerves from these sources — fif-
teen or twenty in number — have numerous ganglia developed
upon them. They accompany branches of the renal arterv into
the kidney." (Gray.)

The ultimate origin of this plexus is a center in the floor of the
fourth ventricle, anterior to the vagus center. Section of the
nerve-tract anywhere between the center and kidney causes in-
crease in size of kidney and polyuria or hyduria. Stimulation of
the peripheral end causes shrinking of the kidney and decrease of
excretion. These experiments lead to the conclusion that the renal
plexus carries principally vaso-constrictor fibers. Other experi-
ments show that there are vaso-dilator fibers. The existence of
a specific secretory center has not been demonstrated. That some
local center must exist is indicated by the response of the excised
kidney, in size and activity of excretion to certain perfused drugs.

THE URINE. 409

THE PHYSIOLOGY OF EXCRETION.
A. RENAL EXCRETION.

1. THE URINE.

a. General Characteristics.

1. The Quantity. — An average sized man passes about 1500
c.c. in 24 hours. This amount varies from 1200 c.c. to 1700 c.c.
according to various conditions, the chief factors which increase
the quantity being increased imbibition and decreased perspiration.
Either of these two things or both together usually accounts for
increased urinary excretion.

2. The Specific Gravity. — The urine consists of a number of
soluble solids in solution. The amount of the solids is less vari-
able than the amount of the water but the proportion may vary
considerably. The specific gravity varies between the usual normal
limits 1015 and 1025. The factors enumerated above which in-
crease the quantity, at the same time decrease the specific gravity
because it is the water rather than the solids which is increased.
If the limits given above are exceeded in either direction the
cause Bhould be determined. To pass beyond these limits does
not by any means necessarily indicate a pathological condition.
Halliburton gives as extreme physiological limits 1002, after ex-
cessive imbibition and 1035, after copious sweating. But these
are unusual limits, and habits which could lead to such extreme
dilution or condensation of urine might readily lead to nutritional
disturbances.

'.',. The Reaction. — Normal human urine is usually acid when
passed. The urine of carnivora is strongly acid; that of herbiv-
ora and vegetarians is either faintly acid or alkaline. The acidity
of urine is due to the presence of acid sodium phosphate (NaH2PQ4).
In average mine about 60 percent, of the phosphoric acid present
[g in the form of Xm 1 1 ,!'( )(. When other acids pass into the
blood from the metabolic tissues or the absorptive surface they
take bases from the monohydrogen phosphate and thus increase
the dihydrogen phosphate, bo increasing the acidity indirectly, the
add body in the urine being in every case dihydrogen phosphate,
particularly NaH^PO.

Bunge called attention to the fact that the secretion of HC1 into
the 1 1 mien (, ft he Btomach i- accompanied by a quantitative (internal)

Secretion of bases into the circulation. This will tend to decrease

tin- acidity of the urine, because the alkali thus Liberated combines

with the acid- produced in other metabolic processes forming

410

EXCRETION.

neutral salts and protecting monohydrogen phosphate from the
acid- in question. This accounts in part for tin- decreased acidity
of the urine during digestion.

The reason for the alkalinity of the urine of herbivora is that
their food contains a considerable quantity of alkaline basee (Na
and K) in combination with organic acids (tartaric, citric, malic).
These acids become oxidized in the body and the metals combine
with CO, to make carbonates whose excretion in the urine neu-
tralizes the acids and leaves the liquid alkaline in reaction.

To summarize : The reaction <>/ the urine is, in man, normally
acid. The acidity is due to acid phosphates. The acidity is in-
creased by increased protcid metabolism. The acidity is decreased
by ingestion of the bases in combination irif/i organic acids. The
acidity is decreased by the secretion of IK'/. The alkalinity of the
blood is decreased (acidity of urine increased) by tin- secretion of
Uile and pancreatic juice.

4. The Color. — The normal light yellow varies with the specific
gravity shading into brown with increasing specific gravity and be-
coming almost as clear as water with decreasing specific gravity.

b. The Chemical Composition of the Urine.

Parkes.

BUNGE.

The Chief Urinary Constituents.

Urine
Water
Solids

(1) Organic

(o) Nitrogenous
(a) Urea
(01 Kreatiuin
(y) Uric Acid

(5) Hippuric Acid
(e) Xanthin Bodies
(£) Aruido-Acids

(6) Aromatic Substances

(c) Carbohydrates

(d) Other organic bodies including j
Pigments

(2) Inorganic

(a) Acids

(a) Chlorine

(|3) Phosphoric [P206]

(y) Sulphuric [S03]

(b) Bases

(a) Sodium
(01 Potassium
(yj Ammonia

(6) Calcium
(«) Magnesium

Percent- Quantities ^Bie- ^diem Pe^cliem

1,ebody°- meat-d
weight.

Composi-
tion.

Grammes
100.00
95.164
4.836
3.003
2.336
2.212

ll.Olill

0.037
0.027

0.666

24 hours.

water
diet.

bread,

butter

and water

Grammes Grammes Grammes Grammes

1500

1427.46

72.r.4

45.04

35.04 +

33.18

0.91

0.55

0.40

10.00

1.833

27.50

0.846

12.117

0.500

7.50

.211

3.16

.134

2.01

II. IKS

14.83

ii.7::n

11.09

.167

2.50

.051

0.77

.017

0.26

.014

0.21

23.9657
22.8600
1.1057
0.6794
0.5284
0.5000
0.0140
0.0084

II.OIMill

0.1510

0.4263
0.2045
0.1260
0.0480
0.0305
0.2218
0.1661
0.0420
0.0130

o. 4

0.0003

1672c.c 1920c.c

90.607
•>

70.761

67.200
2.163

1.398

19.846
11.928

3. si 7
3.437

4.674
7.918
3.991
3.308

0.328
0.291

45.44.S
1

21.814

20.600
0.961
0.253

13.634
7.919
4.996
1.658
1.265
5.715
3.923
1.314

0.339
0.139

c. The Urinary Constituents Separately Considered.

The quantity of water eliminated from the system by way of
the kidneys is far more constant than the quantity ingested, the

THE URINARY CONSTITUENTS. 411

range of the former being about 500 c.c. (1200-1700) while the
range of the latter is as much as 1000 c.c. One of the excretory
organs must present a range sufficiently wide to cover that shown
by the water imbibed. The skin fulfills this requirement. The
relation between the quantity of water ingested and that excreted
by skin and kidneys together, with the reciprocal relations be-
tween skin and kidneys will be discussed at length with the func-
tions of the skin.

The quantity of solids excreted by the kidneys is subject to a
considerable range. Xote in the above table that with a meat
diet the solids are about twice as great in quantity as with a bread
diet : and that with a mixed diet (second column) the quantity is
midway between that of the pure proteid and the vegetarian diet.
By far the greater part of the solids leaves the body by the kidneys.

1. Organic Compounds. — The relation between organic and
inorganic varies within rather wide limits ; for a mixed diet the
organic : inorganic :: 5:3 ; for a meat diet the organic matter is
probably at least four times as great in quantity as the inorganic,
while with the vegetarian diet the relations approach those of a
mixed diet.

i<i) Nitrogenous Compounds. About 94 per cent. ( 15
grammes daily) of the nitrogen leaves the body through the kid-
neys, the remaining 6 per cent. (1 gramme daily) leaves the body
in the intestinal secretions, cutaneous and pulmonary- The nitro-
genous excreta are much affected by the diet. Xote that with a
im ;it diet they aggregate twice as much as with a mixed diet. Of
tin- nitrogen of the urine about 86 per cent, is in the urea, 3 per
cent, in kreatinin, 2 per cent, in uric acid and xanthine bodies, 6
per cent, iu other nitrogenous compounds including hippuric acid,
amido-acids, indol, skatol, pigments, and neucleo-albumin ; and
•') per (int. in ammonia.

Ammonia -hould probably be classified with the nitrogenous
compounds, but inasmuch as it appears as a base among the in-
organic constituents of the urine the author has classified it as an
inorganic base, under which head it will be discussed.

(o.) Urea <>r carbamide, 0:C io-pr2 > '■" the most important of

-'
the nitrogenous compounds. The average amount is aboul 33

grammes per day, though with a meat diet it may be twice as

great. No portion of the urea is formed in the kidney. That

organ i- the excretory organ alone. A- already stated above,
under metabolism, nearly all of the urea i- formed in the liver;
and, for the mo-t part, probably from ammonium carbonate by
double dehydration. The source of the ammonium carbonate
from the products of katabolism has been discussed above. (Sec
metabolism.

412 EXCRETION.

(,i) Kreatinin or Glycolyl methyl guanidin or

I IX

C

ii

I

X— ( ':< >

7— X— C:II,

CH3

As has been stated above the kreatinin of the urine probably
conies from the kreatin ingested with lean meat. This ingested
kreatin is dehydrated in the liver and excreted directly by tin-
kidneys. The fate of the kreatin which is found in the muscles
is still a matter of conjecture. The fact that when food is free
from kreatin the urine is free from kreatinin would seem to indi-
cate that the sole source of kreatinin is the kreatin of the food.
On the other hand the excretion of kreatinin during starvation
-ecu is to decrease the force of the preceding observation. The fact
that kreatin is present to the extent of 0.3 per cent, in muscle
tissue does not necessarily indicate that it is one of the usual mid-
products. It may accumulate to the extent indicated above and
remain a fairly constant constituent, little being normally added to
the supply and little taken away. If it is being constantly formed
it is probably completely katabolized to H..O, CO.,, and NIL, and
the end katabolites built up to the urea level again ; or it may be
subjected to such a series of changes as that outlined on page 375.

(;-) Uric acid: Uric acid is the principal constituent of avian
excrement. In the mammalian urine it is an important and con-
stant constituent, though the quantity is small compared with that
of urea. The fact that when uric acid is given to a mammal,
mixed with food, it is hydra ted and oxidized to urea and ( '( ).,
(Emil Fischer, Ber. d. deutcher Chem. Gaz., Bd. 17, 1884)
makes it probable that uric acid may be one of the antecedents
of urea. That such is the case has not been demonstrated, how-
ever. Medicus's formula for uric aeid is as follows :

H o
N— C H
0:C< C_N

N— C— N>( :()
H H

Note that the addition of 2H,0 -+- 30 would reduce this mole-
cule to 2 urea + •'>('().,. Normal urine contains no free uric acid,
but contains several combinations of uric acid with bases : Am-
monium urate, sodium urate, potassium urate, calcium urate,

THE URINARY CONSTITUENTS. 413

lithium urate, etc. Their composition is shown by simply dis-
placing: one or more of the hydrogen atoms with the metal. The
displaceable hydrogen atoms are indicated by heavier type in the
formula. Little is known of the relation which these combina-
tion- sustain to the metabolism.

Carnin or Di-methyl uric acid has been found in traces in
urine : the two CH3 radicals displace the two hydrogen atoms in-
dicated above.

Considerable difficulty has been experienced by those who have
worked in this field in determining the relations of the metals to
the uric acid. To facilitate the explanation of this subject as now
understood, Ave may represent the uric acid formula thus : H2U ;
H, being the two displaceable hydrogen atoms and U representing
the remainder of the uric acid formula : M2U would represent a
neutral urate (e. g., Xa.,U neutral sodium urate) ; MHU would
represent an acid urate or a biurate; H.JJ-MHU would represent
a hyper-acid salt or quadriurate. Neutral urates are decomposed
by H2CO, or by carbonates. They cannot then exist in the blood
or in the urine. The acid urates (MHU) are very stable salts ;
they are less soluble than the neutral salts, but much more soluble
than uric acid.

Though urine when excreted contains no free uric acid, this ap-
pears usually after as a crystalline deposit after the urine has
Btood, which represents a part of the uric acid freed from the
metals. It has been supposed that it was set free by the acid
phosphates present in the urine:

MHU + MH;P04 = H2U + M2HP04.

Sir William Roberts (quoted by Hopkins, in Sehaefer's Text-
book, Vol. I., p. 589) believes that the above reaction does not
represent completely the situation; "thai uric acid is excreted as <i
quadriurate ; thai, bt ing in aqueous solution, the quadriurates ore
in a siai< of unstable equilibrium and tend at once to decompose ac-
cording to the equation : "

(i) Mill III =MHU + II, I".

Thus Liberating the uric acid which is precipitated. After this
preliminary decomposition the following reaction takes place, in
which two molecules of biurate are combined to form one of quad-
riurate :

(m 2MHU+MH,P04= Mill II_,!'-f MJII'O,

This quadriurate may now be decomposed (i) and the resulting

414 EXCRETION.

biurate combined (n), and so on until all of the urates are decom-
posed and the uric acid liberated.

Hopkins calls attention to the fact that it is not demonstrated
that equation (i) occurs first. The uric acid may be excreted as
a biurate and formed by acid phosphate into quadriurate as shown
in equation (n). The two equations could alternate just the same
according to this proposition and the uric acid be eventually all
liberated.

The amount of uric, acid is only about J gramme daily on a
usual mixed diet. The ratio of uric acid to urea is thus about
1:60. Some have emphasized this ratio as having considerable
physiological significance, being a physiological en nstant, A glance
at the table giving the composition of urine shows that diet alone
may disturb this ratio — with a meat diet the ratio is 1:48 — while
with a bread diet it is 1:82.

As shown by Camerer {Zeitsch. f. Biol., Mimchen, 1896) the
amount of uric acid excreted is a measure of the nucleopivteids in-
gested.

The absolute amount of uric acid excreted is "■ increased by exces-
sive exercise and diminished by rest." (Hopkins.)

Even on the same diet and with the same habits some indi-
viduals will excrete a much larger amount of uric acid than others.
This individual element must be taken into consideration in
clinical cases.

(o) Hippuric acid or benzamido-acetic acid, or benzovlglycin :
QEL-CO • NH-CH.,-COOH.

DO L

Under metabolism it was stated that in the system hippuric
acid is formed by a synthesis of benzoic acid with glycocoll or
amido-acetic acid. We may go a step further and say that when
any of the benzole derivatives which contain only one side chain
is ingested it is usually oxidized to benzoic acid and this in turn
synthesized with glycocoll to form hippuric acid. Such benzole
derivatives are toluene, C6H_— CH3 ; cinnamic acid, C(.H.— CH*
OH-COOH ; phenyl-propionic acid, CBH5-CH2-CH2-COOH.
Aromatic bodies of this class are present in epidermal tissues of
fruits and vegetables. If one eats apple skins he will increase the
excretion of hippuric acid. Hippuric acid then has a double
origin : (i) Aromatic bodies in the ingesta; (n) proteid katabolism.
The fact that hippuric acid does not entirely disappear from the
urine during starvation indicates that the aromatic bodies may re-
sult from katabolism of proteids.

Hippuric acid may combine with metals to form hippurates, in
which form it appears in the urine.

(s) The Xanthin Bodies. — These bodies, together with uric acid,
belong to a group of compounds known as alloxuric bodies. They
represent the combination of two radicals, alloxan

THE URINARY CONSTITUENTS.

415

H

N— C:°

0:C

/ 1

C:0

\ I
N— C:0

H

and urea.

Lee 2-ives these bodies the following skeletal structure

N— C

C

C— N

>C

N— C !— N

(i) Xanthin has the following formula :

H'

N— C H"

0:C< C— N>C.0

N— C=N
H„,

The hydrogen atoms printed in heavy type are displaceable atoms-

Xanthin arises from the decomposition of nuclein and is found
in all tissues and liquids of the body.

(n) Heteroxanthin or Monomethi// Xanthin, (C,.H6N402) is found
in small amounts in the urine. The methyl radical displaces hy-
drogen atom number one (H7).

(in) Paraxaidhin, IXmethyl-xardhin or Theobromin is the alka-
loid of cocoa. The methyl radicals occupy the positions H7 and
H". This theobromin loses one methyl radical and is excreted
BS monomethyl xanthin.

(iv) Trirnethyl-Xanihin, or Caffein, or Them is the alkaloid of
coffee and tea. The methyl radicals occupy the positions IF, H"
and IT" and the body is dcmcthylated to mono-methyl-xanthin^for
excretion. This is the body which imparts to coffee and tea their
stimulating effects.

(v) Ouanm, or Imido-xanthin formed by substituting Nil for
one '-I' the 0 atoms. This is one of the katabolites of nuclein.

IIN:C

II II

N— C II

X— C=N
II

C:0

41<;

EXCRETION.

(vi) Hypoxanthin or Sarein is next to xanthin the most im-
portant xanthin body of the urine. It has one less O than
xanthin, hence its name:

FTC

II H

N-C H

c— s

N— C— N

(':()

(vn) Adertin or Imidosarrin is formed by substituting XHfor
the O. It sustains to the metabolism a relation similar to the other
Ix xlies of the group.

The xanthin bodies arise from the katabolism of nucleo-pro-
teids. When nucleo-proteids are freely ingested uric acid and the
xanthine are freely egested. As the metabolic tissues contain
nucleo-proteids there is naturally a moderate excretion of the
bodies at all times. Normally excreted to the amount of 0.1 per
cent, of the total nitrogen (/. e., xanthin nitrogen = 0.1 per cent,
total N). The free ingestion of green vegetables raises the nitro-
gen of the xanthin to O.b' per cent, of the total nitrogen. In
certain forms of leukaemia their amount is greatly increased.

(C) Amido Acids when ingested are usually katabolized and ap-
pear as urea in the urine. But in acute yellow atrophy of the
liver and in phosphorus poisoning these bodies pass into the urine
unchanged. Leucin and Ti/rosiii are the chief amido-acids so ex-
creted. Cystin, or DUhio-diamido-ethicU me-lactic-acid =

H NH2
HC— C— COH

H S 6

H S O
HC— C— COH
H XH2

This is on its face a double molecule. It is an oxidation syn-
thesis of two cystein molecules : Cystein or Amido-thiopropionic
acid

H

H-C-
H

NH2

s
H

-COH

6

is a katabolite of proteid, probably the sulphur-containing kata-
bolite, but it is normally decomposed to simpler products. If not

THE URINARY CONSTITUENTS. 417

so decomposed it may enter into the following reaction : 2 ( lystein
-+- O = Cystein -+- H.O. Cystein is quite insoluble in water and
appears in urinary sediment in he\ag<>nal-plate-crystals or it may
form calculi. Certain families present the peculiarity of excret-
ing considerable quantities of cystein (0.5 to 1.0 gramme daily).

(6) Aromatic and Nitrogenous-Aromatic Compounds. —
This class of urinary constituents is derived almost wholly from
absorbed aromatic bodies. Some of these may exist as such in
vegetal »le tissues, some of them are liberated from or split off
from proteid during the digestive and decomposition processes
which go on in the alimentary canal. Some of these serve an im-
portant office in furnishing a vehicle for the removal of the sul-
phuric acid ; the bodies go formed are called Conjugated Sulphates.

There are three subdivisions of this class, viz : (i) Hydroxyl
aromatic bodies, (ii) Carboxy acids, (in) Conjugated Sulphates.

(a) Hydroxyl Aromatic Bodies.

(i) Phenol, oxybenzole, phenyl-bydroxide, carbolic acid:

( Il.-OH. (For structural formula see Digestion-Introduction.)

( 'PT
(in Kresol, para-kresol, C6H4 <^tt'- This body is much more

abundant than Phenol.

(nil Pyrocatechin or ortho-dihydroxybenzole (C„H4 = (OH).,),
and it- isomere Hydrochinin or para-dihydroxybenzole C6H4=
(OH)2 are both found inhuman urine; the first only in small
quantities ; the second only rarely and in traces.

(IV) Tnosit or bexahydroxybenzole, CaH1206. The quantitative
formula of this body is very misleading. One would take it for
dextrose or at least a carbohydrate. It was so considered until
recently. After excessive imbibition of water this body, which
seem- to be normally present in all the metabolic tissues, will ap-
pear in the urine. It- structural formula is as follows :

H OH

7
C

II o.II

llo^r H

II N)M

C

/.
no ii

( 'arboxy acids,
(\) Para-hydroxypheDyl-acetic acid,

( II 0H

' (ii coon.

27

U8 EXCRETION.

(uj Para-hydroxyphenyl-propionic acid,

nTr OH
6U4<CH2— CH2— COOH.

(in) Di-hydroxyphenyl-acetic acid,

CH '(()11^
6rL3<CH2— COOH.

(iv) Tri-hydroxyphenyl-propionic acid,

CH J()U)
6±12<CH2— CH3— COOH.

(;-) The Conjugated Sulphates. Incident to the fermentative
processes which go on in the alimentary tract phenol, kresol,
indol and skatol are formed. These bodies are in part absorbed
and pass into the circulation ; their accumulation in the blood
would be verv deleterious to the system. In the liver they meet
the acid sulphate of potassium or sodium, or sulphuric acid and
enter into a series of harmless combinations which are in due time
excreted by the kidneys.

(i) Phenol sulphate of Potassium has been discussed above.
Phenol may also be conjugated with H2S04 or with NaHS04.

(n) Para-kresol-sulphate of Potassium.

Kecall that para-kresol = para-methylphenol and the composi-
tion of this body will be at once understood :

H
C

KO-n-o

Ho C— C U — O

ir

HOC CH

C
H

Para-kresol may also be conjugated with H.,S( )( or with NaHS04.
(in) Indoxylsulphate of Potassium or Indican.

Indol is one of the katabolites of intestinal fermentation: —

H H

KO-n — o

HC C — CH. H-C ('-('•() 1)—0

II U

H-C C CH H-C C CH

C N C N

H H H H

THE CARBOHYDRATES OF THE URINE. 419

If H, be displaced by — OH indoxyl results. The conjuga-
tion of KHS04 with indoxyl results in the formation of indican
with the release of H..O. Indoxyl may also conjugate with
H>o or NaHS04.

(iv) Skatoxyl Sulphate of Potassium.

Skatol = Methyl-Indol, the Ht of indol giving place to QH3.
One of the hydrogen atoms of the methyl may be displaced with
KSO, — to form the body in question.

H

H K-OH— ()
H-C C— C— CO U — ()

HC C C-HH

C N
H H

c. The Carbohydrates of the Urine.

{o.) Dextrose. — The urine of the average individual, living an
ordinary life, upon an ordinary diet, generally contains sugar,
— dextrose (Hopkins). This normal sugar is small in amount.
Excessive ingestion of sugar is likely to be followed by a much
increased excretion of sugar — alimentary glycosuria. In certain
diseased conditions — especially in diabetes mellitus — the excretion
of dextrose ia excessive sometimes exceeding 500 grammes a day.
— pathological glycosuria.

{i\ Lactose is a normal constituent of the urine of women dur-
ing lactation. It may be found in minute quantities, and during
a portion only of the lactation period. When lactation is sud-
denly cheeked the excretion of Lactose may be considerable.

(;-) Pentoses (e. ;/.. xylose, arabyiose) C.IIhO. appear in the
urine after the ingestion of cherries, plum-, etc., where pentoses
exist as •■ fruit-gums."

(<1) Tsomaltose \e said to be present in normal urine (Baisch,
Zeitsch. /'. Physiol. Chem., Bd. XX., 8. 249, quoted by Hopkins).

(e) Glycuronic Acid, COOH— -(CHOH)4— CHO is derived
from glucose by oxidation of the primary alcohol group CH2OH
to the carboxy] group COOH. It is excreted only in traces in
the urine, hm i- generally conjugated with some of the aromatic
bodies to form: 1-t, Pbenol-glycuronic acid; 2d, [ndoxyl-gly-
curonic acid ; or, 3d, Skatoxyl-glycuronic acid.

420 EXCRETION.

(I. Other Organic Compounds.

(a) Oxalic Acids (COOH2), or HOC— COH, is a normal

() ()

(•(Hist it unit of urine. It is supposed to *•< u i m ■ from ingested veg-
etable oxalates, though it docs not wholly disappear from the
urine during flesh diet or during starvation (Marfori — quoted by
Hopkins, Schaefer's Text-book, Vol. L, p. 614). It readily
forms calcium oxalate, which is found in crystalline form in
urinary deposits.

(,5) The Fulfil Acid Series. — Traces of such volatile fatty acids
as acetic, formic, propionic, and butyric acids. They are sup-
posed to be the result of bacterial decomposition in the large in-
testine. These acids once absorbed are less readily oxidized in
the system than the higher members of the same series.

(r) Urinary Pigments. — As stated above under (4) color the
normal color (light yellow) varies in a general way with the rela-
tive amount of water present, getting darker with increasing
specific gravity. If the color of the urine were due to the pres-
ence of one pigment only, it would be possible to contrive a scale
of colorimetrie tests which might be of considerable clinical value.
But there are at least four pigments present and the color of each
is different, so that the change of the color of the urine depends
upon the relative amounts of these four pigments and is a qualita-
tive change as well as a quantitative one. Thus far attempts at
a colorimetrie determination have proved of no value. The four
urinary pigments now known are: (i) Urochrome, (n) Urobilinr
(in) Uroerythrin, (iv) Hoematoporphyrin.

(i) Urochrome. This pigment of the urine maybe separated by
extraction with alcohol, urine which has already been saturated
with ammonium sulphate. After the urochrome is removed the
urine is almost colorless. The pigment is easily soluble in water.
Aqueous solutions of pure pigment have the typical urine color.
It seems certain that urochrome is the pigment which more than
any other gives the usual color to the urine.

(n) Urobilin, as its name implies, is closely related to the bile
pigments. It is unquestionably identical with stercobilin, a pig-
ment of the f;eces also derived from the bile. It is found in the
bile which has undergone partial decomposition without access of
air. It seems to be identical with hydrobilirubin, though this
ha- not been demonstrated. Hydrobilirubin is derived from
bilirubin by hydration and reduction.

( yaj^o, + h2o + H2= ca\(\

Bilirubin + H.,() + H2 = Hydrobilirubin or Urobilin.

OTHER ORGA NIC ' ( '( )M POl S'DS. 42 1

(m) Urosrythrin is the pigment which colors urinary deposits
pink. It exists in normal urine in traces only. Neither phys-
iological nor pathological importance has been ascribed to this
pigment.

(iv) Hcematoporphyrin (C.,.,H.jVX40.) is present only in traces
in normal urine, but may become an important constituent in cer-
tain pathological urines.

(v) ( hromogens are present in the urine and the use of reagents
tin' general analytical purposes may cause the appearance of some
pigment which may be confusing if not understood. Indoxyl is a
chromogen which easily oxidizes to indigo blue or its isomere in-
digo red. The following equation represents the reaction l :

H H

0

HC C C-OH-HOC C OH

HC C C- C C CH

C N \ H H X H
H H j 0 H

H H

C C

H-C C — CO O-C-C C-H
HC c C c C C-H

C N N C

H H H H

■1 indoxyl + 20 = 2H20 + indigo blue ( CH, < jjj° > C =\

Oxidizing agents added to the urine may give rise to either or
l)»th of these pigments (indigo blue, indigo red). But the addi-
tion of nitric acid readily decolorizes these pigments by further

oxidation.

Pathological urines may contain normal pigments in abnormal
quantities or such abnormal urinary pigments as: Haemoglobin,
methcemoglobin, bilirubin, biliverdin, carboluria, <•(<■.

•_!. Inorganic Constituents of the Urine.— (a) A< ids. — (a)
Sulphuric '"■ill a in! its compounds are excreted to tli<' extenl of 2
to 2.5 grammes per diem on ;i mixed diel and as low as 1 | grammes
oo ;i bread diet. (See table of urinary constituents.) The sul-

1 The added oxj gen at imi are repres mted in heavier tj pe,

422 EXCRETION.

phiir is ingested as a constituent of the proteids. The excreted
sulphur i- in pari ( \ | combined in such forms as cystin, i .. . — i I »] n
also sulpho-cyanides, and bilary taurin (pathologically), but mosl

of it ( I ) is in tin- form of sulphates. < )f these the conjugated sul-
phates, discussed above under aromatic comp ds, comprise 1"

per cent., while the inorganic sulphates comprise !,(» per cent.
The inorganic sulphates arc Na,S( >4J X ; 1 1 1 S< )r K S( )r and K I \&i > ..

(ff) Phosphoric acid and its compounds arc excreted to tin ex-
tent of about •'! grammes daily ou an average diet. This quantity
is somewhat increased by ;i meat diet and reduced to about half
as much on a bread diet. There are phosphates present in abun-
dance in vegetable foods, but they are mostly in insoluble forms
(unabsorbed) forms. There are phosphates of Ca and Mg; but
most of the phosphoric acid is combined with \a and K.

To the acid sodium phosphate (NaH2P04) the urine owes its
acid reaction. Calcium phosphate may form a characteristic por-
tion of the deposit from feebly acid urine ; while the triple phos-
phates of magnesium and ammonium frequently separate out in
crystals which take the forms of " feathery-stars " or "coffin-
lids." Phosphates are decreased in nephritis and are increased in
certain neuroses.

if) Hydrochloric acid is chiefly combined with sodium. In
this form the major portion of chlorine is absorbed and excreted;
the integrity of the sodium chloride molecule being usually un-
impaired during the metabolic processes. The amount of NaCl
in the circulating fluid remains fairly constant. An increased in-
gestion of this salt is followed by an increased excretion of it.
Na( 1 seems to be retained in the system during febrile conditions
and to be excreted more freely after the condition becomes normal.

(d) Other acids (i) Carbonic acid is present in acid urine and
carbonates in alkaline urine; (n) Nitric acid combined as nitrates
which are not products of metabolism but are ingested with the
food.

(h) Bases.

(«) Sodium in common salt is used so freely by many as a con-
diment that its excretion may vary within wide limits ; 5 grammes
per diem is the amount given by Hopkins as average. Parkes
in the above table gives more than twice that much. This differ-
ence is undoubtedly due to individual differences in the use of
salt with the food. This metal is excreted mostly as a chloride,
but also as a sulphate and a phosphate.

(■i) Potassium varies very much with the diet, being much more
abundant with a meat diet than with a vegetable diet.

(j) Calcium and (n) Magnesium are both present in considerable
quantities in the food, but as they are in insoluble forms (phos-
phates) a small amount only is absorbed. These salts are impor-

PROCESS OF URINARY EXCRETION. ±23

taut in bone-making and tooth-development, and arc there-
fore found in abundance in both milk and eggs. Hoppe-Seyler
(Z itsch. f. physiol < h m., 1 891, Bd. XV., S. 161 , Quoted by Hop-
kins) found that the excretion of calcium salts is much more
abundant during rest than during exercise.

2. THE PROCESS OF URINARY EXCRETION.
a. Glomerular Excretion.

1. Experiment. — It has been discovered that the newt has, in
common with several other amphibia, a double renal circulation.
The glomeruli arc supplied by the renal venae porta?, branches
from the femoral vein.

Experiment (i). Inject sugar (or any crystalline and easily dif-
fusible substance) into the blood. It will reappear in the urine.
Tie the renal arteries, the sugar Mill cease to be excreted. Con-
clusion : Sugar is thrown out of the blood by the glomeruli.

Experiment (n). Inject urea into the blood. It will be ex-
creted. Tie the renal arteries. The urea will continue to appear
in abnormal amounts.

EXPERIMENT (in). — Inject a mixture of sugar and urea.
Both will be excreted. Tie the renal artery : Sugar will cease to
be excreted, but the urea will continue to appear in abnormal
amounts ; thus the results of experiments (i) and (n) are con-
firmed.

This series of experiments was first performed by Nussbaum.
From these experiments and many others we may accept it as con-
clusively demonstrated that ///<• glomeruli accrete the water anil
easily diffusible salts.

2. Factors Influencing Glomerular Excretion. — (a) It
Varies with Blood-pressure. — But blood-pressure varies as
the heart-force — terminal resistance remaining the same — or, as
terminal resistance, the heart-force remaining ilie same.

\l>) It varies with the fullness of the vascular system, (i) in-
creased after copious drinking of water j (ii) decreased after co-
pious perspiration. Now t hi- increase or decrease of water occurs
without any essential change in blood-pressure ; therefore the

glomeruli must have an independent acti< ther than filtration.

Diuretics net by modifying - e one of these factors: (i)

Digitalis, by increasing heart-force, (n) The nitrites, by causing
local dilatation of vasffi efferentia, and, therefore, increased local
pressure, (in) Caffein and many other drugs, however, stimulate

the 'j hind i ilar activity of the epithelium of t he convoluted tubules,

and, therefore, increase the urea, uric acid, etc., of the urine with-
out appreciably varying the volume. Lauder Brunton, of Ox-
ford, urges the greal importance of distinguishing two classes of

IJ I EXCRETION.

diuretics : Isti Thos2 which stimulate glomsrular excretion of
water and salts, and, 2d, Those which stimulate glandular excre-
tion of the poisonous urea, etc.

('/) But, as convenient as it is to believe that the process of
glomerular excretion is one of simple filtration, i.e., varies exactly
as the pressure, we are forced by numerous observations and ex-
periments to believe that some other factor or factors are ai work
in the process. A.ny condition which increases the pressure, but at
the same time decreases the velocity, will decrease the rate of ex-
cretion of water. A partial occlusion of the renal vein has the
effect of increasing pressure and decreasing velocity. A complete
occlusion of that vein stops water excretion and injures the organ
so that a removal of the occluding ligature is followed by a co-
pious excretion of albuminous urine. It is supposed that the high
pressure in the glomerulus mechanically stops filtration by pr» —
ing the glomerular epithelium against the walls of the Bowman's
capsule ; further, that this pressure and tension on the glomerular
epithelium injures it so that it is no longer able to perform a se-
lective activity, and lets serum albumin filter through. On the
whole, it is concluded (Hermann's Handbueh der Physiologie,
B. V., S. 338) that it is rather increase in velocity than simple in-
crease in pressure, which is the essential factor.

/>. Glandular Excretion or Excretion by the Epithelium
of the Convoluted Tubule.

Experiments of Nussbaum produce practically conclusive evi-
dence that the epithelium of the convoluted tubule is the seat
of the excretion of urea and allied bodies. Von Wittich ob-
served that in birds, whose urine contains little water, urates may
be detected microehemically in the epithelium of the tubules, but
not in Bowman's capsule. If the kidneys be extirpated the urea
and allied bodies accumulate in the blood ; therefore, these bodies
are not formed by the glandular cells of the convoluted tubules ;
these cells only " separate them out of the blood" and excrete
them. We cannot properly speak of the secretion of urine by
the kidneys, but rather the excretion.

The influence of the nervous system upon the activity of the
kidney in excretion seems to be not perfectly made out. All of
the facts can be explained by assuming that the fibers of the renal
plexus (see Introduction to Excretion) are vaso-motor and not-
secretory. The kidney is influenced on the one hand by local
blood-pressure and on the other by the constituents of the blood.
In the case of the active cells of the kidney as in the case of the
intestinal cell we must ascribe a selective function. Dextrose
and urea circulate side by side. The cells of the kidney let urea

CUT. [ NE( > J !S EXt 'B ETION. 425

pass. They do not normally let any appreciable amount of dex-
trose pa--.

c. The Egestion of Urine — Micturition.

The urine passes from the pelvis of the kidney through the
ureters to the bladder, where it is retained until that viscus is
sufficiently full to stimulate its sensory nerves and so appeal to
the consciousness of the individual. The act of micturition con-
sists in voiding- the urine in response to this " appeal of nature."
The act is partly voluntary and partly involuntary. The initi-
atory act is voluntary and consists in relaxation of the sphincter
whose tonic contraction retains the urine between the egestive
ait-. Once the sphincter is relaxed the contraction of the in-
voluntary muscular coats of the bladder is sufficient to empty the
viscus, though this force may be supplemented by contraction of
the abdominal walls. The final act is the voluntary contraction of
the accelerator urines muscle.

The innervation of the bladder is from two sources : (i) From
the lower dorsal and upper lumbar via the mesenteric ganglion
and the hypogastric nerves. Stimulation of these causes con-
traction of the circular fibors of the bladder and the sphincter.
(id From the second and third sacral via the nervi erigentes.
Stimulation of these causes relaxation of the sphincter and con-
traction of the detursor urinse.

B. PULMONARY EXCRETION.

< >f the products of excretion practically all of the CO,, aboul
one-sixth of the water and minute quantities of certain organic
materials are excreted by the lungs, and leave the body in expira-
tion. For the details of tin- subjectsee Respiration.

a CUTANEOUS EXCRETION.

Excretioo is only an incidental function of the skin and is
secondary to protection, to general sensation and to thermolysis.
Tint this is true is evident from the faci that the sebaceous glands
secrete fatty products whose function is to keep the skin pliable
and non-absorbent, while the other glands — the sweat-glands —
produce a fluid which i- almost wholly water and whose primary
function ie the regulation of heat by facilitating heat radiation
(thermolysis). The reciprocal relation between the amount of
water which leaves the body by the kidneys and that which leaves
the body by the sweat glands i- an evidence that the skin must
not be ignored as an organ of excretion.

iL'li

EXCRETION.

1. THE SWEAT.
a. General Characters.

1. Quantity. — The amounl of sweai formed in a day varies
between very wide limits ; the minimum being aboul 500 grammes
and the maximum being aboul 2000 grammes for 2 1 hours,
though it may reach a rate of louo grammes per diem for an
hour or more in ari experiment. To collect the excretion for • \-
perimental purposes the subject's arm or leg may be enclosed in
a rubber bag ; or the subjed may be placed miked in a ventilated
chamber, as in the experiment- of Voil and Pettenkoffer. In
such an experiment Schierbeck (Archiv /'. Physiol., Leipzig,
1893, S. 1 li; ; Quoted by Reid in Schaefer's Textbook, Vol. L,
p. (ill) found with progressively increasing temperature a pro-
gressively increasing excretion of water and of CO,.

Excretion of H,() and CO., by Skin at Various
Temperatures of Surrounding Air.

Temperature of
( hamber.

H,,() Excretion.
Grammes per hour)

11, o Excretion.

(( rrammes per 24

hours.

( !l >._, Excrel ion. < !( l3 1 ixcrel ion.
(Grammes per (' rrammes per
hour.) 24 hours.)

29.8( C
30.4°"
31.5°"
32.8°"
33.8°"
35.4°"
18. 4°"

22.2

27. s
71.9
73. 1
82.6
106.8
158.8

532.8
667.2
L725.6
1761.6
1982. 1
2563.2
3811.2

0.37
ii W
0.37
0.35
0.87
1.04
1.23

S.il

9.6

3.9

8.4

20.9

25.0

29.5

2. The Specific Gravity of human sweat is from loo:) to
1006 ; the greater the quantity the lower the specific gravity.

3. The Reaction of sweat is acid, though when the excretion
is copious it may become neutral or even alkaline in reaction.
The acidity is due to NaHP< ),. ( )n standing- the reaction changes
from acid to alkaline due iu part to the change of urea to am-
monium carbonate.

/>. Chemical Composition of Sweat.1

Sweai

100.00

Water

98.88

Solids

1.12

(1) Organii

0.66

(a) Fats and Fatty acids

0.41

Hi) Epithelium

0.17

u) i rea and other Nitrogenous compounds

0.08

(2) 1 'ganic

o.n;

Sodium 1 Shloride

0.28

(6) Other Salts

0.18

'From Charles' Physiol. Chemistry, p. 349; Quoted by Halliburton: Text-
1 k <>f' < hem. Physiology, p. 820.

PERSPIRATION. 427

1. The Organic Constituents of Sweat. — These arc in excess
of the inorganic, but not so much in excess as in the ease with
urine.

(a) Tiik Fats and Fatty Acids arc largely derived from
secretion of the sebaceous -lands, but when the sweat is col-
lected from the palm of the hand it still contains a small amount
o'i fats and volatile fatty acids. The reaction of the sweat is in
part due to the presence of fatty acids. The volatile fatty acids
present are : formic, acetic, propionic, butyric, caproic.

(6) The Epithelium is carried away mechanically. The
epithelial scales are composed chiefly of keratin, of which sulphur
is an important constituent. This is one of the ways in which
the sulphur leaves the body.

(c) Urea and Othee Nitrogenous Compounds have been
demonstrated by Argutinsky ( Archiv f. d. ges. Physiol., 1890,
Bd. XVI., quoted by Reid, S. 594) to be present in the sweat ; in
one case finding 0.363 grammes of urea in 220 c. c. sweat collected
in half an hour. According to Reid the nitrogen excreted by
the -kin may equal 4.7 per cent, of that by the urine. This
amount is greatly increased in uremic conditions. Uric acid, krea-
tinin. etc., have also been found.

2. The Inorganic Constituents of Sweat. — These are made
up chiefly of sodium chloride; Among of her salts are : potassium
chloride, acid -odium phosphate, sodium and potassium sulphates,
calcium and magnesium phosphates. The salts are thus qualita-
tively equivalent to those of the urine.

2. THE PROCESS OF CUTANEOUS EXCRETION— PERSPI-
RATION.

1. The Influence of the Nervous System upon Cutaneous
Excretion. — The sweat-glands arc provided with (a) secretory,
and (6) vaso-motor nerve.-; the latter are represented by both con-
strictor and dilator fibers. The secretory fibers radiate from a
center (or probably several center-), in the central nervous sys-
tem— ,.,,nl and medulla. The centers arc stimulated directly ;
id by a highly venous condition of the blood; (in by a high
temperature of the blood ; (in) from the cerebr ; (rv) by poi-
sons; pilocarpin, strychnia, nicotine, etc. The centers are stim-
ulated reflexly by subjecting the skin to a high temperature.

_'. Factors which cause a Variation in the Quantity of
Perspiration.— 'I'he total perspiration — 500 grammes to 2 kilo-
grammes daily — either evaporates a- it i- formed — insensible perspi-
ration, or it collects upon the -iii-race of the skin — sensible perspi-
ration.

The total amount of perspiration varies 1 1 1 with the temperature

t28 EXCRETION.

of the air, iii) with the proportion of water in the blood, (m) with
blood-pressure, (iv) with the velocity of the blood-flow, arising
usually from muscular activity, (v) with the activity of kidneys
ami bowels, (vi) with the state of the emotions, (vn) with general
systemic conditions — certain diseases arc accompanied by profuse
diaphoresis, (vin) individual peculiarity, (ix) drugs (pilocarpin).
In variables (i) to (v) an increase <>f the variable causes an in-
crease of the perspiration. In (vi) anything which causes the
skin t<> Hush is likely to he accompanied by perspiration, though
there is a "cold sweat " also which may accompany fear.

The amount of sensible 'perspiration will depend primarily upon
all of the factors which cause a variation in the total amount of
perspiration, and secondarily upon the condition of the atmosphere,
being increased by higher temperature and decreased by increasing
the capacity of air for moisture.

J). INTESTINAL EXCRETION.

Of the various fluids and solids poured into the alimentary
canal by the surrounding or tributary glandular epithelium, by
far the greater part is to be considered to be typically secretion,
for it is introduced into the lumen of the canal to serve a par-
ticular purpose ; after serving that purpose it may be reabsorbed
or passed out with the egesta. There are, however, certain sub-
stances which must be recognized as excretions : (a) The Bile Pig-
ments: (i) Bilirubin ; ( n ) Biliverdin ; (ni) Hydrobilirubin (Ster-
cobilin); (ft) The Fat-like Oonstitutents of the Bile : (i) Cholesterin
((',.] I ,:jOII), (ii) Lecithin,

(CnH2n_A)2

//

C3H3

\
OPOOH-OC2H4N(CH3)3OH

Lecithin and cholesterin are constituents of nerve tissue. They
must be looked upon as nerve katabolitcs and the liver the organ
for the excretion of those katabolites which are peculiar to nerve
tissue. (7) Salts. Certain salts, calcium salts especially, of the
bile and of other intestinal liquids must be looked upon as on the
way out of the system.

DIVISION B.

THE PHYSIOLOGY OF THE EXTERNAL RELATIONS:
THE MOTO-SENSORY ACTIVITIES.

Chapter IX. THE DERMAL SYSTEM : PROTECTION.

Chapter X. SENSATION.

Chapter XI. PHYSIOLOGY OF THE CENTRAL NERVOUS

SYSTEM.
Chapter XII. PHYSIOLOGY OF THE MUSCULAR SYSTEM.

CHAPTER IX.
THE SKIN: THE DERMAL SYSTEM.

INTRODUCTION.

1. SUMMARY OF THE MORPHOLOGICAL FEATURES OF THE DERMAL
SYSTEM. TIIK BISTOGENE8IS AND HISTOLOGY OF THE SYSTEM.

2. Till: GLANDS OF THE DERMAL SYSTEM.

THE PHYSIOLOGY OF THE DERMAL SYSTEM.

E PROTECTION.

•1. THERMOLYSIS.

3. EXCRETION.

4. RESPIRATION.

THE SKIN: THE DERMAL SYSTEM.
INTRODUCTION.

Tin: -kin may be looked upon as an organ. Those structures
indissoluble associated with the skin both histogenetically and
functionally may. with the skin proper, be failed the Dermal
SyffU in.

Tin- system of organs represents histogenetically epiblast proper
and dermal mesenchyme; the former giving origin to those tis-
sues and organs which are distinctively dermal, and the latter fur-
uishing the substratum upon which these distinctive structures are
built or supported. Functionally the dermal system is par ex-
cellence, the system <>\' external relations, which fad has a definite
relation to the histogenesis, theepiblasl coming from the ectoderm
of the gastrula.

129

130

THE DERMAL SYSTEM.

1. SUMMARY OF THE MORPHOLOGICAL FEATURES OF
THE DERMAL SYSTEM.

From a physiological standpoint the following points regarding
the structure of the skin and its associated organs are of impor-
tance :

The dermal system of organs involves, without exception, (a)
mesenchymal tissues as foundation, and (l>) an epiblastic surface
as superstructure.

<i. The Dermis or Corium.

The Mesenchyme may be represented by the close-felted corium
with its blood vessels and lymph vessels; by the dentine of a
tooth, or by the dense transparent substance of the cornea.
(See Fig. 204, c,f.)

Via. 20-4.

Section of human skin : (/.stratum corneum : i>, stratum lucidum ; e, stratum granulosum : </,
stratum Malpighii ; e,f, papillary and reticular layers of corium : .'/, stratum of adipose tissue;
A, i, spiral and straight portions of duct of sweat-gland ; k, coiled portion of sweat-gland ; /,
vascular loops occupying papilla; of corium. (Piebsol.)

The mesenchymic dermis, or true skin is everywhere beset
with minute papillae (Figs. 204, 205). The papillae are very
vascular (Fig. 208) and through more or less specialized nerve-
endings they are especially sensitive (Fig. 205). These papillae
are variously modified in structure in different parts of the dermal

THE DERMIS OR CORIUM.

431

system; they form the ll1'- 205.

basis of a hair follicle
(Fig. 209), they form the
basis of the nails (Fig.
207), and of teeth. With-
in them are located the
special tactile corpuscles.
In a further modification
they form the lingual pa-
pillae (7. v.). The marked
vascularity of the papillae
facilitates the support ot
the tissues which are as-
sociated with them in the
formation of hair, nails,
teeth, etc. The nerve

supply insures the extreme sensitiveness cf the dermal tissues
enumerated : teeth, hair, nails ; but it is the root or matrix which
is sensitive, not the hair, nail, or tooth itself.

a, nerve fiber ; b, tactile papillae, containing a Meiss-
ner tactile corpuscle; e, vascular papillae. (After
Bend a.}

Fig. 206.

m of epidermis. H, hornj layer, consisting ol uperflcial horny scales ; no, swollen-

oul bornj cells; i.l. stratum lucidum ; V, rete 1 or Malpighian layer, consisting of p,

prickle-cells, several rows deep; e, elongated cells forming a single stratum near the corlum ;

pr., stratum granulosum "i Langerhans, Jusl below tin- stratum lucidum; n, pari of a
plexus of nerve-flben In the luperflcial layei "f the cutis vera From this plexus Ane varicose

llbrili maj >■■ ti I passing up between the epithelium-cells of the Malpighiao layei

iHt'HAEFEB :ill. i RAMVIKB.J

132

THE DERMAL SYSTEM.
Fig. 207.

Section across the nail and nail-bed. (100 diameters.) P, ridges with blood vessels ; B,
rete mucosuni; .V, nail. (Schaefeb after Heitzmann.)

Fig. -Jos.

Duct of a sweat-gland passing through the epidermis. 'Magnified 200 diameters. > BjP.papilla?
with blood vessels injected ; l'. rete mucosum between the papilla ; E, stratum corneum ; /'/,
stratum granulosum ; D, sweat-duct, opening on the surface at p. (Schaefeb after Heitz-

MANN. )

THE EPIDERMIS.

433

b. The Epidermis.

[ The epiblast may be represented by the cuticle of the skin,
by the imbricated scales which compose a hair, by the active cells
of the cutaneous glands, by the enamel of the teeth, or by the
delicate cuticle which covers the cornea or the tympanic mem-
brane. (See Fig. 204, a, b, c, <L)

The epiblast presents a series of layers whose cells are gen-
erated^ by karyokinesis at the surface of the corium from the

Fig. 200.

Fig. 210.

Piece of human hair. (Magnified) A,
seen from the surface ; B, in <>j>tir;il s< c-
tion. '•, cuticle: /, fibrous substance ;
m, medulla, the air having been expelled
by Canada balsam. (Schaefer,)

Elair-folllcle in longitudinal section.
a, montb of follicle ; b, neck ; e, bulb ; -/,

■ . dermic coat ; A outer t-aheath; g,

Inner root-sbeatn; h, hair; k, Its mh-
ilnlla ; /, hair-knob; m, adipose tissue;
". hair mnsi le . o, papilla of Bkiu ; p,
papilla ^f liair; i, tele mucosum, con-
tinuous »iiii outer root-sheath; >■/',
horny layer ; '. sebaceous gland.

<-' H Ml i ': .i|t, i BlSSl LDESKL)

columnar or cuboidal cells of the stratum malpighii (Fig. 2()ii).
The constant formation of new cells ai this level pushes out the
older cells which through Loss of water and through other phys-
ical and metabolic changes die, and become insensible, horny
scales. The particular form and aggregation of these horns'
28

434

THE DERMAL SYSTEM.

scales differ much in different locations. On the general cutane-
ous surface they arc simple dry scales which arc constantly shed;
on the hair (Figs. 209 and 210), teeth, or uails (Fig. 207), there is
an accumulation which takes a distinctive form ami which serves
as an organ of protection, defence or offense, and is only period-
ically shed or is worn off to keep pace with growth (or conversely i.
In the case of man the hair and nails arc usually artificially eared
for, the occupation of man not usually wearing the growth away
fast enough.

Fig. 211.

2. THE GLANDS OF THE DERMAL SYSTEM.
a. Protective Glands.

a. The Sebaceous Glands arc present over the whole surface
of the body except the soles of the feet, the palms of the hands,
the dorsal surface of the third phalanges (sec Fig. 211). The

ducts of the glands open at the roots of
the hairs on all hairy surfaces, but on the
lips, the prepuce and the corona of the
glans penis the ducts open free upon the
surface. The secretion of the sebaceous
glands is called sebum.

Specialized forms of the sebaceous
glands are : (i) Preputial glands, whose
secretion — the smegma preputii — differs
from sebum in containing substances
which give it a characteristic odor. Musk
is from the preputial gland of the musk
deer, (n) Anal glands, which are only
slightly modified in the human subject
may be strongly modified in other mam-
malia. In the otter, hyena, and civet
the anal glands secrete a modified sebum
which serves for sexual attraction. In
the skunk the secretion serves for defense,
(in) The meibomian glands arc slightly
modified sebaceous-glands which open
upon the edge of the eyelid ; the oily sur-
face thus produced prevents the overflow
of tears, (iv) The Uropygial Glands of
many birds is a specialized sebaceous gland. The oil which it
secretes is spread upon the feathers by the bird and serves to pro-
tect the feather-coat against absorption of water, (v) The Lach-
rymal ('/and whose secretion keeps the delicate mucous membrane
of the conjunctiva moist and freed from dust, belongs to the
dermal system, and to the protective glands of that system, though

Section of portion of sebaceous
gland from human scalp, includ-
ing part of acinus : a, membrana
propria; b, peripheral layer of
cuboidal cells ; c, elements in
which fatty metamorphosis is
beginning; <!, cells tilled with
fatty particles and exhibiting
marked intra-cellular net-
works ; e, nuclei of cells.
(PlEBSOL.)

DERMAL PROTECTIVE STRUCTURES. 435

morphologically they are more closely related to the salivary
glands.

6. Secretory Glands.

The mammary glands, unquestionably dermal glands, may have
been derived phylogenetically from sweat glands. The secretion
tunned and the method of its formation makes the lactiferous
glands clearly analogous (if not homologous) to the sebaceous
glands. (See Lactation under Reproduction.') Pigeons possess
lactiferous glands which are clearly sebaceous glands and are
tributary to the crop. This "pigeon milk" contains fat, a
proteid clotting with rennet, globulin, salts, and water.

c. Excretory Glands.
The sweat glands (Fig. 211). See Cutaneous Excretion.

THE PHYSIOLOGY OF THE DERMAL SYSTEM.
1. PROTECTION.

The skin, being the organ of external relations, must necessarily
stand between the general organism and its environment.

a. The Nerves of the Skin.

The skin is provided with sensory nerve-ends : this lends to
protection in putting the animal on guard against various dangers.
Some of these sensory area- are highly specialized, e. ;/., the cornea
and lens, admitting light to the retina; the taste buds, — facilitat-
ing the access of solutions to the gustatory nerves; the moist
nasal epiblasl facilitating the influence of odors upon the olfactory

lier

b. Dermal Protective Structures.

The skin is provided with various structures for special protec-
tion against mechanical injury, e. g.} the nails protect the finger-
tips and toe-tips ; hair protects the organism against mechanical
injurs', — witness its cultivation for that purpose by football
players, — it serves a more important office, however, in protection
again cold. In this connection may be mentioned the further pro-
tection of the eve by the li«l> whose periodical winking during
working hour- and continued closing during sleeping hours serve
to protect the eye' against dust and drying. The eyelashes pro-
ted the eye against bite of solid matter thai might otherwise
strike the eye. The browe shed off the perspiration. All of these
protective structures are dermal. The teeth arc, however, more
distinctly prehensile and offensive than defensive ; though the der-
mal teeth of sharks are defensive and protective and the oral teeth

43(> "PHYSIOLOGY OF THE DERMAL system.

are the homologues of the dermal teeth. (See Digestion, — intro-
duction, comparative.)

c. The Sebaceous Glands.

The skin is provided with oil glands or sebaceous glands whose
function is to secrete oil for the hair and cuticle, keeping both soft
and pliable and especially non-absorbent. As indicated in the
introduction the oil glands may take various specialized forms as
lor offense, defense, or sexual attraction. The chemical composi-
tion of the sebum is not very well known, because the normal
cutaneous secretion is notformedin sufficienl quantity for analysis.
Tin' cheesy contents of a distended sebaceous cyst consist of water
31.7 per cent., epithelium anil nucleo-albumin (casein) 01.7 per
cent., fat 4.2 per cent., fatty acids 1.2 per cent., salts 1.2 per
cent. In the typical secretion the proportion of fat and fatty acids
is probably much greater and that of epithelium and nucleo-albu-
min1 much smaller. The fat consists of a mixture of glycerine
fats, with whose composition the reader is familiar, and of choleste-
rin fats. Cholesterin is a monatomic alcohol having the formula
C2.H4,OH. Cholesterin fat of palmitic acid is CH3— (CH2)14—
COO-C.,.H4.. The fatty acids consist, according to Schmidt, of
butyric, valeric, and caproic acids. It is to the fatty acids that
secretion owes its distinctive odor. Free cholesterin and isocho-
lesterin are present.

Two especially interesting facts regarding the sebum are : First ;
tin eholesterin fats resist putrefaction, i. e., they resist the use of the
skin (is <i culture field for bacteria. Second, the homology of the
mammary glands with the sebaceous glands receives an extra
element of probability in the fact that the nucleo-albumin of ike
sebum is casein.

2. THERMOLYSIS.

The common cutaneous surface, with its vascular cutis vera and
its sweat glands, forms the myan of Thermolysis. Just how the
skin governs the rate of heat elimination is discussed in full under
Animal Heat.

3. EXCRETION.

Third in importance among the functions of the skin is excre-
tion. Here is an instance where an excretion performs an im-
portant office incident to its final exit from the body. Every
gramme of water which eyaporatcs on the surface of the skin
eliminates 582 calories of heat, or takes that much away from the
body.

1 The identity of the nucleo-albumin with casein is questioned by Weymouth
Reid, but is not questioned by Halliburton and others.

CUTANEOUS RESPIRATION. 437

It is evident that Excretion and Thermolysis are intimately asso-
ciated. The greater the occasion for free evaporation of water in-
cident to thermolysis, the greater the excretion of water by the
skin. But if there is a given amount of water to be eliminated
from the system, it is evident that the other water-eliminating
organs must give off correspond i ugly less Mater. Such is the
ease ; after profuse perspiration the urine is less voluminous and
more highly colored. Conversely, a marked decrease of perspi-
ration will be occasion for a marked increase of the volume of
urine, which will be more watery. Not only is there a reci-
procity, there is also a vicarious relation between skin and kid-
neys. \\ 'hen one is disabled the other performs as much as pos-
sible of the function of the disabled organ.

4 RESPIRATION.

In many of the lower animals, particularly in amphibia, the
skin is an important organ of respiration. The moisture of its
surface facilitates the exchange of gases by diffusion in these
animals.

In the higher vertebrates respiration is an unimportant func-
tion of the skin.

CHAPTER X.

SENSATION. INTRODUCTION.

A. GENERAL SENSATION.

1. SUBJECTIVE.

2. SUBJECTIVE-OBJECTIVE.

Common SENSATION.
(«) Hunger.

(b) Thirst.

(c) Suffocation.

(d) Fatigue.

(e) Pain.

(/) Kit leering.

(g) Tickling.

(h) Sexual Sensation.

3. OBJECTIVE.

I. The Tactile or Pressure Sense.
II. The Posture Sense.

(a) Sense of Equilibrium,
{b) Muscular Sense.

III. The Temperature Sense.

B. SPECIAL SENSATION (OBJECTIVE): THE SPECIAL SENSES,

IV. Smell.
V. Taste.

VI. Hearing.
VII. Sight.

SENSATION.
INTRODUCTION.

Every animal organism is provided with organs which make
the cerebral sensory centers cognizant of certain conditions and
changes of the environment. In other words, certain conditions
of the environment act as stimuli to more or less specialized periph-
eral organs. The effect of a stimulus is transmitted along an
afferent nerve to the brain, where it so affects the cerebral centers
as to cause a consciousness of the stimulus, — a sensation. Through
intercentral action between the sensory centers and the higher
cerebral centers the animal sums up the sensations received from
an object making a complete conscious perception. An interpreta-
tion of perceptions producing not only a mental picture of an ob-
ject and its properties, but giving the animal an idea of the relation
of the object under consideration to other objects, is called a
conception,

438

AVT.fi OD UCTIOX. 439

Note that a conscious sensation involves attention ; that percep-
tion involves memory ; and that conception involves reason. The
clearness of the sensation, perception and conception is propor-
tional to the attention, memory and reasoning' involved in them.
Sensation furnishes pabulum for all higher forms of mental
activity.

The ectoderm is the embryonic layer which gives rise to the
peripheral organs of sensation as well as to the sensorium. The
specialized epithelium of the sense-organs is from the epiblastic
division of the ectoderm, while the sensorium is from the neuro-
blastic division of that layer.

It will be profitable at this point to express in tabulated form
the relations between the specific stimuli of the environment, the
more or less specialized peripheral sense-organs which receive the
stimuli and the special sensations aroused in the sensorium.
(Table : See next page.)

Xote that there is a departure from the time-honored classifica-
tion of the senses as : " Five : Feeling, taste, smell, hearing and
.seeing." The first one of these has, under careful investigation,
been resolved into several distinct senses, one classification of
which is given in the table.

Sensory nerve-endings may be classified, on the basis of struc-
ture, into specialized and non-specialized. The specialized nerve-
endings, those enumerated in the table, below the dash, — are those
which seem to be especially adapted structurally for response to
particular stimuli. For example, the structure of the retina, ex-
ceedingly complex and highly specialized, seems to be especially
adapted to receive the light, while the organ of Corti, just as com-
plex, seems to be especially adapted to receive sound. Moreover,
the retina i- sensitive to light only of all the stimuli of the en-
vironment, or if there is a response to any other kind of energy
it always affects the sensorium as light. In the same way sound
alone of all the stimuli of the environment affects the organ of
Corti. Another structural distinction is found in the fact that
the specialized nerve-endings are all located in particular organs
also especially adapted to receive the special stimulus ; lor ex-
ample, the refractive media of the eve focus the light upon the
retina, and the muscles of the eye direct the organ toward the
source of light. The non-specialized nerve-endings are more or
widely distributed over the surface of the skin and mucous
membranes. They are not located in specialized organs and are
nut evidently adapted to receive special stimuli. It may he that
the '• tactile cells and corpuscles " are the end-organs of touch and
muscular sense, and it may be that the filamentous endings or the
end-bulbs are the end-organe of the temperature sense ; hut, these
distinctions, if they exist, remain yei to he demonstrated.

410

SENSATION.

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GENERAL SENSATIONS. 441

Sensation- may be classified into three categories on the basis of
the source of the stimulus :

1. Sensations which are the immediate result of the reaction of
the organism to the conditions of the environment: Pressure
sense, posture sense, temperature sense, smell, taste, hearing, vis-
ion. Because these sensations are caused by objects wholly out-
side of the organism they are called Objective Sensations.

2. Sensations in which the immediate source of the stimulus
is within the organisms, though the ultimate source is in the en-
vironment. An example of this class of sensations is hunger.
Something within the organism produces a conscious call for nour-
ishment. This may be so urgent as to occasion considerable
discomfort, merging into actual pain if not satisfied. The ulti-
mate cause of hunger is in the environment, but the stimulus can-
not be classified with the general or special stimuli enumerated in
the accompanying table. Thirst and weariness also belong clearly
to this class of sensations. Pain and sexual sensation may belong
to this class or to the preceding. In these two sensations the
stimulus may be mechanical and may be traced more or less im-
mediately to the environment. This class of sensations may, for
want of a more concise term, be called Objective-Subjective sensa-
tions.

• I. Sensations which accompany dreams, hypnosis, hysteria, and
various states of the central nervous system and which merge
from the perfectly normal into the pathological. These sensa-
tions are just as real to the subject as are the objective sensations,
1 > 1 1 1 an observer traces no connection to an external stimulus.
This class of sensations are called Subjective Sensations. They
partake of the nature of a memory of previous sensations, but
they are more than that. A subjective sensation is an actual re-
experiencing of a former sensation.

THE PHYSIOLOGY OF SENSATION.
A. GENERAL SENSATIONS.

The term general sensations is used to include a class of sen-

satione excluded by the well-defined special senses, i. e., the gen-
eral senses are those with no specialized peripheral organs.

1. SUBJECTIVE GENERAL SENSATIONS.

This class of sensations has been sufficiently discussed above.

2. OBJECTIVE SUBJECTIVE SENSATIONS.
For the definition of this class see the Introduction.

442 SENSATION.

a. Hunger, b. Thirst, c. Suffocation.

These three sensations are Nature's admonitions to — 1 1 j > j > I \ the
organism with solid, liquid or gaseous nourishment. The greater
the urgency for satisfaction of the need the greater the discomfort
when it is not satisfied. The animal organism can live only a
short time without oxygen. When the supply of oxygen is cui
off the sensation of suffocation begins within a few seconds and
increases rapidly in intensity, passing very soon into a paroxysm
of the most agonizing pain ending in convulsions and death if the
need is not supplied.

Next to oxygen in urgency is the need for water. If there is
little perspiration the thirst may be mild for 24 hours. As soon
as the sensation of thirst becomes thoroughly fixed upon the con-
sciousness of the animal nothing can dislodge it. The discomfort
becomes more and more intense until death supervenes.

The animal organism can do without food for many weeks if all
activity can cease. Bears hibernate for several months. Indians
accustom themselves to 48- and 72-hour fasts in order to be able
to endure without much discomfort the exigencies of war and the
chase. To those who are accustomed to three regular meals each
day the missing of one meal is likely to cause considerable discom-
fort, but the feeling is one of emptiness rather than of real hunger.
If one fill the stomach with water the discomfort soon disap-
pears and real hunger begins to appear in a variable time after-
wards. Hunger and thirst are in the healthy individual infal-
lible signs of the needs of the organism. These senses may,
however, become perverted, or, at least, the actual sensation may be
misinterpreted. For example, a child with an overfilled stomach
may call for more — having misinterpreted the vague feeling of
discomfort in the gastric region for hunger.

(I. Fatigue, e. Pain.

These two sensations apprise the organism of over-stimulation.
Moderate over-stimulation is followed by a feeling of fatigue.
Nature is requesting a rest. Excessive over-stimulation lead- to
a feeling of actual pain. Nature is (l<i>i<tii<Hii</ a rest. The most
usual occurrence of weariness is after muscular or nervous activity;
the most usual occurrence of pain is after stimulation of some of
the peripheral end-organs by some of the external stimuli: pres-
sure, tension, heat, cold, chemical energy, sound or light. But
pain may be purely subjective sensation, having no apparent con-
nection with objects outside of the organism but arising from cer-
tain conditions in the central nervous system. Some painful
sensations maybe accurately localized, while others are localized in
a most general way only. The more acute the tactile sense of a

OBJECTIVE GENERAL SENSATION. 443

part, the more accurate the localization of pain in the part. Pain
is the most general of all sensations. Some contend that there is
a special set of nerves to convey the sensation of pain together
with certain other sensations. But the fact that every sensation
of which the brain may be conscious and every activity of which
the organism is capable may be accompanied by pain, and the fact
that abnormal conditions of the system may be accompanied by
pain makes it highly improbable that any particular set of nerves
is to be looked upon as pain nerves. Pain is distinctly a common
sensation.

/. Shivering, g. Tickling. A. Sexual Sensation.

These sensations have certain features in common. They all
begin in definite objective sensations and partake of the nature of
aftersi msation. If the cold points of a considerable area are
stimulated so that the superficial tissues become chilled the
shivering sensation is induced. Once started it is likely to con-
tinue some time after the local reaction has occurred. Moreover
the sensation frequently occurs when there is no objective cause ;
/. e., it may have its origin in the central nervous system. Tick-
ling sensation is usually caused by alight stimulation of the tactile
nerve-endings, but in many individuals the sensation may be
aroused by "make-believe" movements on the part of another,
or even an active imagination may induce the sensation. Tick-
ling may have its origin in the central nervous system. Sexual
sensation may be stimulated peripherally by mechanical stimuli
or centrally. In fact, the most effective stimulus is the central
one. If the stimulation be carried to the point of the final, cul-
minative Bensation (orgasm) this is to be looked upon as the in-
direct after-sensation and not the direct objective sensation, and it is
the indirect after-sensation which belongs to the category of the
heading.

:;. OBJECTIVE GENERAL SENSATION.

Preliminary to a discussion of the general sensations of the
periphery one may profitably review the structure of the sensory
nerve endings. These endings may be classified as non-specialized
and specialized. The non-specialized are called filamentous and are
distributed to the skin, cornea and mucous membranes (see Fig.
■J I 2). '/'/" specialized sensory nerve endings represent three genera :
tactile cells, tactile corpuscles, and end-bulbs. Figures 213 and
~l\ 1 represent simple and compound tactile cells. The simple tactile
cells differ from the filamentous endings in having a discoidal
termination associated with a slightly modified epithelial cell.
The compound tactile cell lies within the epidermis of the main-

444

SENSA TION.

malian or avian skin. Note the discs and the two or three cells
enclosed in a sheath.

The /a,-/!/, corpuscles are located in the corium of skin and
mucous membrane. The spherical end-bulbs, shown in Fig. 215

Fio. 212.

[ntra-epithelia] nerve-termination in the anterior epithelium of the cornea, as -ecu in an
oblique section, a, an axis cylinder; 6, sub-epithelial nerve-fibrillae ; c, intra-epithelial net-
work ; d, epithelial cells. (Klein.)

are found in the conjunctiva and other mucous membranes of man.
The genital corpuscles (Fig. 216) are found upon the glans penis,
the glans clitoris and other associated surfaces in mammals in

Fig. 213.

Fig. 214.

Special nerve-endings within the epider-
mis ; gold preparation : X, nerve-fiber en-

ii i in<; the epithelium and dividing into the
fibrils which arc connected with the lac-
tile disks (m): upon these latter rest tin-
tactile cells, c. (PlEBSOIi after Uanvikk.)

i on i pound tactile cells from the duck's tongue.
i [zqcierdo. ) A. composed of three cells, with
two interposed disks, into which the axis-cylin-
der of the nerve. //. is observed to pass ; in 1!

there is l.ut ■ tactile disk inclosed between

two tactile Cells. (SCHAKFEB.)

general. The tactile corpuscles of Meissner are located as shown in
Fig. 217, in papillse of the corium upon the palms of the hands,
the soles of the feet and upon the volar surfaces of lingers and
toe- in num. The complex internal structure of these bodies is

OBJECTIVE GEXEEAL SENSATION.

44--,

shown in Fig. 218. There can be little doubt that these special-
ized sensory nerve endings are the organs of touch, if it is a&-

Fig. 216.

Simple spherics] end-bulb from the human
conjunctival mucous membrane : », the
medullaii.l nerve-fiber which disappears
within the capsule. (After Kbacsk.)

< .enital corpuscle from the human clitoris ;
this ending represents a group of partly
fused simple spnerical end-bulbs : n, nerve-
fibers entering the capsule. (ScHAEFER
after Krause.)

missible to call them organs. Of the several species of end-bulbs
only one will be given, — The Pacinian body (Fig. 219). These

Fig. 217,

m

a or -kin showing two papilla and di li rmia. a, rasi ulai papilla n Lth

capillary loop passing from subjacent ressel.c; b, nerve-papilla with tactile corpuscle,!. The

. iiii.it- tranireme fibroua markings j d, nerve passing op to it; /,/, icctlona of spirally

winding -• ii m i i i: after Bmusii klj

structures are widely distributed in mammals. They occur in
sub-cutaneous tissue along the nerve- supplying the skin, especially

1 16

SENSATION.

of the hands and feet, the externa] genitalia, the joints of the
extremities, periosteum of certain bones, the peritoneum.

The various structures jusl described receive at the periphery
various sensations. The faci thai the tactile corpuscles of Meissner
are most numerous in those locution- where the tactile sense is
most acute justifies the conclusion that these structures represenf
peripheral receptive tissues for mechanical stimuli ; but does not

Fig. 218.

Vv;. 210.

Meissner' s corpuscle from the
human corium. n, upper portion,

in which the epithelial cells alone A Pacinian corpuscle from the mesen-

are represented. The nuclei of tery of the cat a, the medullated nerve-

those cells are in the broader peri- fiber; h. the concentric capsules. (Klein.)

]>heral portion of the cytoplasm;
A. nerve-dendrite coiled about the
epithelial cells ; c, nerve-tilier.

ISOHM and JlAVIDOFF.)

justify the conclusion that none of the other sensory nerve endings
respond also to various mechanical stimuli. It is probable that
some of the endings described respond to mechanical stimuli and
some to thermal. The mechanical stimuli may be further sub-
divided, some of them in the form of pressure affect the cutaneous
and articular surfaces, while others in the form of varying tension
affect the tendons and muscles. The varying tension of the tissue
may affect the nerve-endings as varying pressures, however.
Further, the thermal stimuli are to be subdivided: bodies lower
in temperature than the skin stimulate certain nerve endings,
while bodies of higher temperature stimulate other nerve endings.
Whether these nerve-endings differ from each other structurally

THE SEXSE OF TOUCH. 447

as well as functionally or differ only functionally is unknown.
In short the sensations classified in the above table are the result
of the stimulation of some one or more of the sensory nerve-
endings enumerated in the opposite brace ; this is all that ran be
said with certainty at present.

I. THE TACTILE SENSE : THE SENSE OF TOUCH.

In man this sense is most acute in the finger tips, the lips, and
the tongue. In quadrupeds the sense is most acute in the lips,
tongue or proboscis. This sense alone brings to one only an idea
of the state of the substance — whether it is solid, liquid or gaseous ;
of the surface of a solid — whether it is smooth or rough, and if
the latter the particular character of the roughness ; whether it is
oily or sticky, or whether it is bounded by curved surfaces or by
planes, edges, or angles, or a combination of these features. The
character of a liquid may be determined, whether it is light,
limpid like water, or heavy like mercury, or whether it is gel-
atinous, viscous, slimy or oily. The only character of a gas that
appeals to the tactile mechanism is the negative one that it affords
no resistance to the movements of hands or ringers. The sum of
the knowledge which may be derived through touch alone is
greater than that which may be derived through any other one
sense. Experience derived from both touch and sight will enable
one to infer from lights and shades and lusters what touch would
definitely reveal. One instinctively verifies these inferences by
touching the object with the fingers. The tactile sense is used in
two different ways: first, to announce to the central nervous sys-
tem when some resistant object touches the surface of the body ;
second, to investigate the properties of certain objects of the
environment. In the first the organism is passive, in the second
ii is active. Thefirst is a means of protection, the second a means
of adding to one'- knowledge. A similar classification of function
may be made for all of the objective sensations. In serving the
first one of these purposes the tactile mechanism must be able to
differentiate stimulation of different portions of the periphery. It

i- not enough to know that some sharp point is touching the sur-
face of the body, but to avoid injury it is important to know just
where the point i-. This is accomplished by what is called the
power of localization. Through this power the central nervous
system is conscious, e. </., thai in a particular location a sharp
point i- touching the periphery. This knowledge enables the
organism to protect it-elf from unnecessary injury. The tactile
mechanism is also endowed with the power to estimate pressure.

Those portions Of tin- -kin most acute in their tactile sensibility

are, at tin- same time, most acute in their power of localization,

148 SENSATION.

but not in their power to estimate pressure. This has led to two
methods of testing the tactile sense : one to measure the power to
estimate pressure, and the other, the power of localization.

To te-t the pressure sensibility one places upon a certain <-n-
ticular area a series of. weights of exactly the same surface of con-
tacl and approximately the same temperature. Such experiments

have revealed the facts that the parts most sensitive to pressure
are the forehead, the temples, the hack of the hand and the flexor
surface of the forearm. In these localities 2 mgm. can be felt,
while the finger tips can not feel a weight of less than 5 to 15 mgm.

Regarding the power to differentiate increments in the weights
used as stimuli it may he said that : the greater the inital stimulus
the greater the increment must he in order to he discernible. This is
the basis for Weber's law : " The amount of stimulus necessary to
provoke a perceptible increase of 8ensCttion ahrai/s /tears the same
ratio to the amount of stimulus already applied" (cited by Sewall
ill the American Text-book of Physiology, p. <H:5(>). Fechner
studied this same problem and reached similar results which he
formulated in his " psycho-physical law " : "The intensity of sensa-
tion varies with the logarithm of the stimulus." That is, if a series
of stimuli represent the intensities : 10:100:1000:10000, the sen-
sations would represent the intensities 1:2:3:4. These laws hold
in the main for medium stimulation ; for very light or very strong
stimulation they do not hold, the sensation being more acute for
moderate stimuli. Another law of Weber (Hermann's Handbuch
der Physiohgie, Bd. III., 2, S. 336) may be thus formulated : Ij
two e<]ual weights have different areas of contact the one that touches
the larger surface feels the header.

The Power of Localization is tested by use of the ajsthesiometer
which is similar to a pair of dividers or draftsman's compass. In
using the instrument the points are lightly' touched to the surface
of the skin. The greater the acuteness of tactile sense, or the
more acute the power of localization the nearer the points may be
brought together and yet be felt as two points. Beyond a certain
minimum distance the points can no longer be distinguished as
two, but feel like one point.

The following table shows results of tests which were made to
determine whether all points are equally sensitive and especially
whether symmetrically located points on the same individual are
equally sensitive.

Showing variations of symmetrically located points on the same
individual. From this table one is justified in three inferences :

1. Symmetrically located points in the human body may not
possess the same acuteness of tactile perception.

2. There is a very great variation in the acuteness of sensation
in different parts of the cutaneous surface of the same individual.

THE SENSE OF TOUCH.

449

3. The more acute the tactile perception of a part the more
likelv it is to vary in acuteness from its laterally homologous point.

Table I. of Tactile Sensibility.

Individual A.

Individual B.

Right.

Left.

Right.

Left.

Ti]> of Tongue.
Palm of 3d Phalanx.

1.2 mm.

1.2 mm.

1.2 mm.

1.2 mm.

2.0

2.5

2.00

1.5

•• '< 2d

3.75

3.25

3.5

3.5

Tip of Nose.

5.5

5.5

8.0

8.0

Back of 2d Phalanx.

9.0

11.0

9.9

8.0

Back "i" Hand.

15.0

20.0

17.0

22.0

Forearm.

24.0

24.0

42.0

42.0

Sternum.

32.0

32.0

42.0

42.0

Back.

66.0

66.0

77.0

77.0

Tests upon a number of individuals yielded the results recorded
in Table II., showing not only the variations of tactile sensibility
in different parts of the same individual, but also the variations of
different individuals.

Table II.

Showing Degrees of Tactile Sensibility of Cutaneous
Surface of Body.

Portion of the Body Tested.

Man.
mm.

Boy aet 13.
mm.

Woman,
mm.

Man.

mm.

L Tip of tongue.

.7

1.

.6

.8

2. Buddie of dorsum of tongue.

1.1

1.1

1.

1.6

::. < tenter of hard palate.

1.6

4.

2.3

1.1

i i nder lip | red surface).

.7

2.1

1.7

2.1

5, i pper lip ( " " )

1.3

1.2

1.5

3.

'',. Tip of nose,

4.

2.

1.2

2.5

; Tip of chin.

5.

6.

6.

2.8

- 1 iici-k over malar bones.

5.

4.

4.

6.5

9. Lobe of ear (ventral surface).

4.5

6.7

8.2

5.6

10. Neck ventral Burface).

3.

4.1

3.1

5.8

1 1. Neck < dorsal surface 1.

2.2

3.7

1.8

5.4

12. Neck (lateral sui 1

2.2

3.2

2.0

5.4

18. I orehead.

5.1

4.9

4.8

5.2

1 1. Tip- 'it In. I

1.

1.1

1.4

1.

IS. Palmar surface of second phalanges "i Angers.

1.1

2.

3.8

1.6

16 Dorsal " " " " " " (transverse).

5.

3.2

8.6

1.1

" " " (longitudinal).

7.:.

3.

6.1

5.

l- Palmar surface of hand.

2.1

8.2

1.2

2.3

19. Thenar bypothenar eminences,

,8

2.1

4.2

2.2

20 Dorsum of hand (longitudinal).

5.6

4.8

6.5

8.6

21, Doi -;ii surface of forearm,

5.7

IB

5.3

5.

22. " " " upper-arm.

l.s

1.7

5.8

5.2

1 in of hand (trans

4.7

2.S

1.2

6.

'21. I lexor surface forearm.

:;.:'.

:t.2

1.5

2.8

ipper-arm,

1.7

1.5

1.7

Jo 1 ioi -urn o| foot,

12.

1...

19.

21.

27. I- lexor surface of thigb <i ran

86.

.Ill

84.

33.

of leg.

1.-..

23.

21.

30.

■ ral dona! region,

88.

::7.

III.

acral

80.

28.

31.

82,

31 . " oervical n

82.

.".'.1.

37.

ii region (over spine),
:c<. " 'i " "

13.

16.

13.

IS.

111.

13.

17.

11.

al " " "

12.

1 1

15.

10

i -in ijh •,■ thigh (longitudinal),

64.

57.

61.

69

I'll

450 SENSATION.

Table II. justifies the following conclusions :

1. There is very great variation in the acuteness of percep-
tion in different parts of the same individual.

2. There is considerable variation in the acuteness of tactile
perception in different individuals.

3. When the points determine a line which is transverse to
the axis of a limb they may be distinguished as two at a much
smaller distance than is the case when the line is parallel to the
axis of the limb.

4. The tactile sense is best developed in persons whose senses
in general are well developed, for example, Mr. Z, a laboring man
was compared with Miss X in twelve points of observation and
she uniformly excelled him. But not in tactile sense alone did
Miss X excell Mr. Z. Her sense perceptions in general were
more acute.

5. The further one goes from the tips of fingers, toes or tongue,
the less acute is the tactile perception.

6. The least sensitive parts of the body are those subject to
more or less constant pressure, the epidermis is, in such locations,
very thick.

7. The tactile sensibility is much more acute on all flexor sur-
faces than upon the corresponding extensor surfaces. For "evi-
dence see Table III.

Table

III.

Flexor Surfaces.

Extensor Surfaces.

Over Pectoralis Major.

20 mm.

Over Scapula.

32 mm.

Umbilical Region.

18 "

Dorsal Region.

53 "

Neck (ventral).

11 "

Neck (dorsal).

15 "

Arm.

15 "

Arm.

17 "

Forearm.

7 "

Forearm.

11 "

Wrist.

7 "

Wrist.

9 "

Thigh.

45 "

Thigh.

53 "

Leg.

9 "

Leg.

15 "

Average. 16.5 25.6

II. THE POSTURE SENSE.

The organism is provided with a mechanism through which it
is made continually conscious not only of the general position of
the body in space, but of the relative position of different parts
of the body. The consciousness of general position in space is
called the sense of equilibrium, the consciousness of the position
of different parts of the body is inseparable from muscular sensa-
tion ; and is probably incidental to it, These two sensations
together give the organism a clear consciousness of its position or
posture ; i. e., gives the Posture Sensation.

THE SENSE OF EQUILIBRIUM.

451

a. The Sense of Equilibrium.

The maintenance of equilibrium is of prime importance both
in animal locomotion and in all positions of rest except that of
absolute relaxation in a decumbent position. The -whole mech-
anism of equilibrium includes the nicely adjusted muscular action
required to hold head and body poised upon the base of support,
and it includes the sensation necessary to make the central nervous
system cognizant of any disturbance of the poise. This sensory
part of the mechanism is the one now under consideration. The
principal end-organ of equilibrium seems to be the system of
semicircular canals connected with the inner ear. If this were
the only end-organ the sense of equilibrium might probably be
classed as a special sense. But the complete sensation of equi-
librium is a combination of sensations from various sources ;
it might, in fact, be called, rather, a 'perception of equilibrium,
rather than* a simple sensation. (See Introduction.) The sen-
sory nerves from the soles of the feet, from the ischial skin when
sitting, from the muscles and tendons, from the articular surfaces,
and from the eves all bring sensations which contribute to the
general sensation or perception of equilibrium. If any part of the
mechanism is disabled the equilibrium is in part impaired. The
parts intact may by especial activity cover the deficiency in the
mechanism, but though the equilibrium may be apparently perfect
the sense of equilibrium is not perfect.

In this place we may discuss those features of the semi-circular
canals which especially fit them for end-organs for the perception
of the position of the axis of the body in space. Fig. 220 shows

Fig. 220.

Fig. 221.

X n

o

Membranous labyrinth. < '-. semi-circular ca- Diagra atic horizontal section through

oal; I'. Qtriculus; S, sacculns; A, aqueduct <>f the bead to illustrate the planes occupied bj
restibnle; Cr, ductna reunieni ; Co, cochlea. the semi-circular canals, i Waller.)

tin- membranous labyrinth with its three canals, two saccate struc-
tures and the cochlea. Note: (i) Thai each canal has an en-
largement oear one end — the ampulla; (it) Thai the three canals
lie in different plane-.

Fig. 221 gives Waller's diagram showing certain important

I.VJ

SENS l/7"\

space relations of the canals. Note (m) Thai the superior canal
of the right side lies in a plane parallel to that of the posterior
canal of the left side, while the lefl superior plane is parallel to
the righl posterior plane, and the two horizontal plane- are
parallel; (iv) That thesis plain- represent the three dimensions
of space; (v) Thai the ampulla? of any pair of parallel canals are
at opposite extremities of the canal. — e. g., the ampulla of the
left superior canal is opposite to ampulla of the right poste-
rior canal.

Fig. 222 shows the minute structure of the crista acustica of an

Fig. 222

Longitudinal section of an ampulla through the crista acustica. am/)., cavity of the ampulla ;
- mi-circular canal opening out of it ; c, connective tissue attached t.> the « all "i the meni-
- ampulla and traversing the perilymph : i . • . flattened epithelium of ampulla : A, amli-
tory hairs projecting from the columnar cells of the auditory epithelium into tin- cupula, <«/<.
term.; p, blood vessels ; n, nerve-fibers entering the base of the crista and passing into the co-
lumnar cells. (S< iiai.i i ec

ampulla. The Long, delicate bristles are epiblastic in their origin.

Note \ in that each specialized epithelial eell is intimately con-
nected with a branch of the vestibular nerve (see Fig. 223), and
that the bristles are really agglutinated structure-, each formed of
several fibrillae (see Fig. 223, A'): (vni) that the saccule and the
utricule are each provided with a small specialized surface similar
to that of the crista.

THE MUSCULAR SENSE.

453

Pig. 223.

If the head or the whole body be rotated upon its antero-pos-
terior axis in the direction from left to right, the endo-lvmph of
the right horizontal canal will flow toward the ampulla of the
canal where the pressure would increase,
while the eudolymph of the left hori-
zontal canal will flow away from the
ampulla of that canal, tending to de-
crease the pressure. According- to the
hypothesis of (/rum-Brown, fairly con-
firmed by experiment this difference of
pressure is the efficient stimulus. Other
movements of the head, or of the body
as a whole, affect other pairs of semi-
circular canals in a way similar to that
indicated above.

Through this mechanism and its cen-
ter in the cerebellum the individual is
made conscious of every position and
every change of position of the head in
-pace. If in an animal one of the semi-
circular canals be opened, the animal
has the sensation which accompanies
fall of pressure in that canal, and makes
efforts to compensate it by "forced
movements" which really carry the ani-
mal*- body in the direction opposite to
that in which it feels it is turning. Such observations have

seemed to ( linn the hypothesis of Crum-Brown, which is now

generally accepted. Lee (Jour, of Physiol., XVII., p. 192) looks
upon the saccule and utricle as the organs of static eqiiUibrium, in
which, when the animal is at rest, the weight of the otoliths under
gravitation stimulates the macula? acusticse. The fact that in fishes
these structures are highly developed seems to confirm Lee's hy-
pothesis, for in tln-<' animal- there is no supplementary cutaneous
stimulation like the solar or ischeal stimulation in man, and the
fish must depend entirely upon these structures for its sense of
position.

I,. The Muscular Sense.

Supplementary to the sense of position in space is the sense of
muscular tension, [fone stand ereci and a- -till as possible with

the heel- together he will not be eon-eioii- of a ny e-.-ent ia I change

of equilibrium vet he will be conscious of a slight variation of the
distribution of weighl upon the soles of the feet and especially
conscious of variations in tin-ion of differenl sete of muscles ami
tendon- involved in the maintenance of the ereci position. If one

Auditory epithelium from the
macula acusticaof the saccule of
an alligator. ( Highly magnified. )
<-, c columnar hair-cells ;/,/, fiber-
cells ; ». nerve-fiber, losing its
medullary sheath and apparently
terminating in the columnar au-
ditory cells: actually, however,
the nerve-fibrils arborize around
these cells ; li , bristle or hair; b! ,
base of h crs ■ • i « I it u\ into fifcrilo
[S» ii mi i b after Retzius.)

454 SENSATION.

fix a tracing point to the head and stand under a horizontal trac-
ing surface so adjusted as to record any change of position it will
lie noticed that the position of the point changes from moment to
moment — never returning exactly to the starting point exoepl
sometimes by accident. As a general rule the taller the subject
the greater the amplitude of his oscillations. A study of these
tracings and of the sensations which one experiences while stand-
ing erect indicate that such a position i- maintained particularly
through the muscle sense. One is conscious at one time of a
greater ten-ion upon, say, the muscles of one side of the body than
upon those of the other, and is conscious at the same time of a
slight change of the direction of the body axis. A moment later
he is conscious of a greater tension upon the sets of muscles which
before were less tense and conversely. The muscles are in a state
of mild tonic contraction constantly, but the tension of any one
group <>f muscles varies continually, the action being so coordi-
nated as to maintain the body erect within very narrow limits.
One has not the sensation of losing and regaining the balance, but
he has the sensation of shifting of pressures upon the soles of the
feet, also of changing of tension in muscles and tendons so that one
may say that the coarse adjustment of equilibrium is effected
through the semi-circular canals, Avhile the fine adjustment is
effected through a combination of muscle sense and plantar reflex.

Besides the important part which the muscle-sense plays in the
maintenance of equilibrium it serves the organism in adjusting all
motor activities to the required conditions. The consciousness of a
certain amount of tension upon muscles or tendons seems to be
the thing which governs the amount of energy liberated in the
muscle to accomplish a subsequent similar act. Every one has
experienced the surprise and awkwardness in coordination which
is likely to occur when in a flight of stairs one step is much lower
than the others. The usual energy and space adjustment has been
ordered in the central nervous system in response to previous
muscular sense. The new conditions take the nerve-muscle system
by surprise. This is not the case when the vision supplements
the other equilibration apparatus. If one sees an unusual step
he voluntarily modifies the course of the reflexes.

The following tests were made upon a number of medical stu-
dents to determine the acuteness of their muscular sense : (i)
Two clamp-holders differing from each other in weight by eight
per cent, were handed in turn to each student and were alternately
lilted by both right and left hand-. The determination made by
each student was recorded without communication with other- in
order that the judgment of one should not influence that of an-
other. Kesults : There were sixteen answer- : twelve were cor-
rect a- to which was heavier. The average per cent, of excess of

THE TEMPERATURE SENSE.

A"j

weight estimated for the heavier object was 7.0 per cent., maxi-
mum fifteen per cent., minimum three per cent, (n) Two bottles
differing from each other by eight per cent, in weight were similarly
tested by a number of students with the following results : There
were nineteen answers, of which eighteen were correct as to which
object was the heavier. The average per cent, of excess of weight
estimated for the heavier object by the eighteen correct answers was
11.7 per cent., the maximum being twenty-five per cent, and the
minimum two per cent. The results of these two tests make it evi-
dent that the muscular sense is less acute than the tactile sense. In
common with other senses it may be much improved by practice.
Produce dealers can by experience estimate with astonishing ac~
coracy a particular weight of any commodity.

III. THE TEMPERATURE SENSE.

The sense of temperature is a very unreliable index of the ac-
tual temperature of any .-ubstance because the cutaneous surfaces
yield us only relative ideas. We can say whether or not a sub-
stance is warmer or cooler than the skin, but we cannot say how

Fig. 224.

Two nun thou tag areas of temperature Bense. The maps each represent an area of one sq.
in. mi tin; back of tbe left band of .Mr. A anil of Mr. B. The axis or the limb i- from righl t"
left, "r horizontal, as tin- figure stands. The " 1 1 < »t " spots an- shaded horizontally : tin- " cold "
spots vi rticaj - especially endowed with tactile Bense are dotted. The tactile »i»'t

'/ meat In.; the " hot " >|M>t // measures ,;; , sq. in.

many degrees of temperature it has. Knowing the probable tem-
perature of the -Kin one can, by practice, usually guess approxi-
mately what the temperature i- ; bul al besl the determination i-
based upon a series of judgments all of them Bubjed to consid-
erable error.

Not all portions of the surface of the Bkin are able to yield
temperature sensations and nol all portions so endowed yield sen-

156 SENSA TION.

sations of both heat and cold; hut one small area responds to
cold, one to heat, and another to neither. The areas which do
not respond to heat or cold arc not insensible, they are endowed
with the tactile sense. All portions of the skin are sensitive to
pressure stimuli ; but most persons seem to be more sensitive to
very light pressure stimuli upon the tactile areas than upon the
temperature areas (hot and cold spots) : this may be an illusion due
to the partial distraction of the attention by the sensation of cold
or heat and pressure when an object touches a temperature area
while there is no such distraction when the object touches a tactile
area.

The accompanying maps show the distribution of these areas
on particular surfaces and give a general idea of the relative sizes,
shapes and areas of cold, hot and pressure spots. From these
maps and many others the following conclusions have been drawn :

(«) Certain areas of the skin are functionally differentiated to
receive stimuli from objects warmer than the skin, certain areas to
receive stimuli from objects colder than the skin.

(6) Homologous areas on different individuals are different
from each other as to distribution of the cold and heat areas.

(r) The total area sensitive to cold is much greater than the
total area sensitive to heat. If a piece of cold metal one inch
square were laid upon the surface mapped from Mr. A's hand it
would stimulate 49.5 cold-areas and 27 pressure-areas, or a total
of 76.5 areas. If a piece of warm metal be applied to the same
area it would stimulate 23.5 heat-areas and 27 pressure-areas =
50.5. This may account for the illusion that when two pieces
having the same weight, one being cold and the other warm are
laid upon contiguous areas the cold one will seem to be heavier
than the warm one.

(d) As a rule the longitudinal axis of an area corresponds to
the longitudinal axis of the part (arm or leg) examined.

(e) Symmetrically located areas on the same individual vary
considerably in their distribution of heat, cold and pressure
sensibility.

(/) Special areas, — i. e., heat-areas or eold-areas, — are smaller
on individuals showing greater sensibility in the sesthesiometer
experiments.

\ff) Certain small areas seem to be sensitive to neither pressure,
heat, nor cold when the stimuli are moderate.

(/*■) A test-point, though varying only slightly in temperature,
may, at one location, feel cool, on another cold, and on a third
very cold.

(j) On the palm of the hand the points specialized in sensi-
bility to heat or cold were smaller and fewer than in the same
area on the back of the hand.

THE SPECIAL SENSES.

457

(k) A cold penny placed on the palm of the hand feels much
smaller than when placed on the back of the hand.

B. THE SPECIAL SENSES.

An organ of special sense involves : (i) a sensory end-organ
limited in location and specialized in structure ; (n) an afferent
conducting path which differs in no way histologically from other
axis-cylinders, though it corresponds to a dendrite of the neuron,
histogenetically ; (in) a brain-center which is a portion of the
general sensorium ; (iv) inter-central conducting paths between
the sensorium and higher cerebral centers.

An act of special sensation involves: (i) special stimulation of
the end-organ ; (n) transmission to the sensorium ; (in) sensation,
or consciousness of the stimulation ; these steps usually lead to
the following : (iv) perception of the stimulating object ; (v) con-
ception of the object in its relation to other objects.

The special sensations include seeing, hearing, smelling, tasting,
or vision, audition, olfaction, and the gustatory sense.

The researches of Kupffer ("Cephalic Nerves," Verh. Anat.
Ges., Miinchen, V., 22) and Froriep (" Sense Organs" Arch. f.
Anatomie, 1886) show the origin of the organs of special sense
from primitive structures in the lower vertebrates.

Fig. 225 is a reproduction of Kupffer' s figure of the branchial
sense organs of the larval cyclostome, — petromyzon. Note in the

Fig. 225.

N.C.

Larral petromyzon showing branchial sensory ganglia, (Edinger after Kupffer.)

figure the five cephalic ganglia: i, ciliary ganglion; n, tri-
geminus; in, acustico-facial ; iv, glosso-pharyngeal ; v, vagus,
which is continuous with the lateral nerve. Note the chain of
epibranchial ganglia from I to 12; the anterior four being much
crowded together, the last eight being evidently segmental, the
5th, 6th, : ■ 1 1 ' I 7th corresponding definitely with the en, rv, and
\ cephalic ganglia respectively. Note also the brain (Br.), spinal

t58

SENSATION.

cord (Sp. Cd.)} leDSofthe eye(£), the nasal pit (//), the hypophysis
or preoraJ pit (Hy), mouth (.1/), the gill clefts (CI), the otocyst
(Ot), and the notocord | X. C).

Kupffer says regarding the development of sense organs :
"There can be little doubt thai the lateral ganglia (cephalic gan-
glia) and their sense organs as one scries and the epibranchial
ganglia and their sense-organs as another series are common to all
vertebrates. It seems certain that the ear, probable that the olfactory
orpin and possible that the eye all belong to the lateral scries."

Froricp discovered a series of rudimentary sense-organs asso-
ciated with the epibranchial ganglia. They are now generally
known as branchial sense-organs. Minot (1892) believed
it probable that further investigation would "demonstrate the exist-
< in-, ofbothseries in the embryos of all vertebrates." Edinger, writ-
ing in 1 Sid!, cited recent literature showing that the probability
of 1 892 has become practically a certainty. We are, then, justified
in looking upon the mammalian ear as a highly specialized prod-
uct of evolution of one pair of a long series of lateral sense-
organs. In the higher vertebrates the other lateral sense-organs
are either specialized in other directions (eye, olfactory organ), are
rudimentary in the adult, are rudimentary and transitory in the
embryo, or, finally, wholly wanting even in the embryo.

Fig. 226.

~^ — ^~, — r"~ i .

p^jWm r Pi I

Section "f olfactory mucous membrane.

IV. THE SENSE OF SMELL.

1. STRUCTURE OF THE OLFACTORY ORGANS.

The end-organ of smell may be described as the regio olfaetoria,
or upper part of the nasal passage, embracing the whole surface

THE SENSE OF SMELL.

459

Fig. 22"3

of the upper, with the upper part of the middle turbinated bone,
also the upper one-third of the nasal septum. This region is out
of the direct line of respiration, and all of the lower region or
all of the nasal passage not included in the above enumeration is
called the regio respiratoria. The regici olfactoria is so constructed
as to present a very large surfaee to the air which passes through
it. The mucous membrane of the olfactory region has a very
thick, spongy corium in which are located the mucus-secreting
glands of Bowman ; and through which pass the fibers or fiber-
bundles of the olfactory nerves, on their way to the cribriform
plate of the ethmoid bone. (See Fig. 226.) The epithelium
(See Fig. 'I'll) consists of two kinds of
cells. The epithelium proper or the sup-
porting cells occupy most of the surface
and extend to the corium by branching
proximal ends. Between the supporting
cells lie the olfactory cells or the fla ol-
factoria. The bodies of these cells lie
deep in epithelial layer, and there is a
thin, rod-like extension passing out to the
surface of the epithelium distally, while
the proximal extension is really a naked
axis cylinder which, joining several of its
fellows, passes as a non-medullate nerve
into the olfactory bull) which lies above
the cribriform plate. The interesting
morphological feature shown here is in
the homology between the olfactory cells
and r 1 1 * • cell- of the spinal ganglia. The
distal, protoplasmic extension of the olfac-
torve.ll i- the afferent cell-branch or the
dendrite, while the proximal, protoplasmic
extension is the efferent cell-branch or the u

neurite or neuraxon, here modified into a gS"SS!^SSiiSaSf &
naked axis-cylinder. This cell is a *^.#S&^^$S£

neuron of the I Order. iphersd rods ;e, their extremi-

. . . . . ties, seen in 1 to be prolonged into

1 hi- neiiraxon Undergoes arborization fine bairs; d, their central ftla-

■ , ,. i i-l 1 in. -lit-. (Si ii \ i. i i i: :i It 6 r

in the olfactory glomeruli, where tneyare .,„,,,/. ;

in communication with the dendrites of

the mitral cells of* the olfactory bulb. (See accompanying Fig.

22 J

2. PHYSIOLOGY OF THE SENSE OF SMELL.

Olfactory sensation may be stimulated by gaseous or volatile
substances, the requisite conditions seem to be thai the matter
shall be finely divided and diffused through the air. The acl of

cells and terminal nerve-fibers
r the olfactory region. (Highly

4<;o

SENSATION.

inhalation curries a direct current of the odor-laden air along the
regio respiratoria, but it diffuses readily into the regio olfactoria.
To aid this diffusion must mammals intuitively "sniff" when

Diagram to show the relations of cells and fibers in the olfactory Imlli. olf.c, olfactory cells
of M. Scliultze iii the olfactory mucous membrane, sending their basal processes as non-medul-
lated nerve-flhers into tbe deepest layer of the olfactory bulb {olf.n.)\ gl., olfactory glomeruli
containing the terminal arborizations of the olfactory libers and of processes from the mitral
cells : in, mitral cells, sending processes down to the olfactory glomeruli, others Laterally to end
in free ramification in the nerve-cell layer, and their axis-cylinder processes, ". ". upwards, to
turn sharply backwards and become libers of the olfactory tract (lr.nl/.). Numerous collat-
erals Lire seen curving off from these fibers ; n', a nerve-fiber of the olfactory tract apparently
ending in a free ramification in the olfactory bulb. lSCHAEFKR.1

they wish to " scent " an object. The sniffing consists in a series
of quick inspirations. The rarefaction of the air in the olfactory
region incident to the sniffing facilitates rapid diffusion of the
odor-laden air into that region.

The stimulation of the olfactory cells by the odoriferous sub-
stance can take place only through <lir<<-t c<>nt<tct of the substance
with the cells. To this end the substance passes into solution in
the film of moisture which covers the epithelial surface. The
stimulating substance is in solution when the stimulation takes
place. The sense of smell is much impaired or even suspended
if the olfactory epithelium should become dry from any cause.
On the other hand, odoriferous substances in solution in water do
not stimulate the sense of smell when the water fills the nose.
The water impairs the sensibility of the olfactory cells. But if
an odoriferous substance in solution in normal saline solution be
brought into contact with the olfactory epithelium the olfactory
cells respond to the stimulus.

THE SENSE OF TASTE,

401

The intensity of the sensation varies with : (i) The area of the
olfactory surface ; (n) the concentration of the odoriferous sub-
stance; and (in) the frequency of conduction of the vapor to the
olfactory region (the frequency of the " sniffs "). (Landois.)

The acuteness of the sense of smell varies with : (i) The size
of the olfactory area ; and (n) practice.

All attempts at a satisfactory Glassiftaation of odor* have failed.
The French chemist, Septimus Piesse, arranged a scale of odors
which he called the " Odophone" ; but it was too arbitrary to be
accepted.

The use of the sense of sme/t to the system is primarily as a
means of protection, warning the animal against the introduction
of noxious foods, air or drinks into the system. Secondarily it
is cultivated by some of the human family as a means of sense-
gratification — of sensual gratification. Next to the seeking of
pleasurable tactile sensations, it is the lowest form of sensuality.

i if1'

V. THE SENSE OF TASTE.
1. STRUCTURE OF THE GUSTATORY ORGANS.

The tongue serves the function under consideration, but that or-
gan serves also other functions, e. //., mastication, deglutition, and
articulation of speech. The
tongue is not the special-
ized end-organ of taste.
The specialized organ is
the taste-bud. (Fig. 229.)
Numerous taste-buds may
In- found in the epithelium
of the oral mucous mem-
brane. The accompanying
figure ( Fig. 230) shows
that the taste-bud is an epi-
thelial structure ; i. e.f thai
it i- ;i group of modified
epil helial cells. The pave-
nient epithelium of the oral
mucous membrane is not
adapted to the ready ab-

-"'•I'""11 «'f' liquid- The aection through the middle of a tMte-bud. p.gusta,

bundle of gpindle-shaped '"' x~ istatory cell ; r, sustentaci • cell : m.

i i • l lynipn cell, containing lattj granules; e, superficial

Cells presenting their ends cells of the stratified epithelJ ; n, nerve-fibers. (Ban-

;it the surface "I the general

epithelium is well adapted to the ready absorption of Liquid, and
this absorption of liquid seems t<> be an important pari of the
special function of the taste-buds. The accompanying diagram

1

t62

SENSATION.

(Fig. 231) makes it evident that li<|tii<l absorbed from the suri
(x) of the epithelium will pass, by capillary attraction, betw

surface

(■in

Fig. 231.

Various cells from taste-bad of rabbit, (ni n » diameters.] ". four gustatory cells from central
part; b. two Bustentacular cells, and one gustatory cell, in connection ; <■. three sustentacula!

cells. ( Kn'.ki.manx. ,

the spindle-shaped gustatory cells and be brought into intimate
contact with the filamentous ends of the gustatory nerve.

If the liquid he an aque-
ous solution "of some sub-
stance capable of stimulat-
ing the sensation of taste,
the effect of the stimulation
will be propagated along
the afferent dendrite to the
cell-body of the neuron,
which lies in the ganglion
of the nerve trunk, thence
through the neuraxon to
the central nervous sys-
tem, within which a neu-
ron of the second order
transmits it to the sensor-
ium. There hasbeen much
controversy as to whether
the gustatory nerve-fibers
are all contained in the
glosSo-pharyngeal trunk,
or whether some of them
may not reach the oral mu-
cous membrane through
the lingual branch of the
trigeminus. Both nerves
undoubtedly contain gus-
tntory fibers. The gustatory fibers may readily pass from one
trunk to another in the tympanic plexus, a condition which is

eiuxn of/ordpr

Neumxo

Diagram of taste-bud with gustatory nerve. Note
thai the epithelial cells which compose the taste-bud
air broad encasing cells, (o) or slender gustatory cells.
(i>) Note the afferent dendrite arborizing among the
gustatory cells and the afferent neuraxon passing
into t he central nervous system [C.N.) where it comes
into relation with neurons of the II order. The cell
body is located in the trunk-ganglion of the nerve of
taste. (Quain after Retzius. )

THE SENSE OF TASTE. 463

known to exist in the ease of the secretory and vaso-clilator fibers
of the salivary glands {quid ride). There is probably one source
for the gustatory nerve-fibers, and that source is probably the
trunk (petrous) ganglion of the glosso-pharyngeal nerve.

The taste-buds are distributed (i) over the lateral surfaces of
the eireumvallate papillae; (n) upon the fungiform papillae; (ill)
upon the papillae of soft palate, uvula, anterior pillars of the fauces,
and surface of epiglottis.

2. PHYSIOLOGY OF THE SENSE OF TASTE.
a. A Summary of the Facts Concerning- Taste.

Many of the perceptions attributed to taste really depend quite
as much upon smell as upon taste. We usually apply the term
flavor to those sensations which depend upon both smell and taste ;
- . </., one speaks of the flavor of roast beef or of coffee. The fact
that closure of the nose impairs the flavor of the beef or coffee, in-
dicates that a part of the flavor is to be attributed to the sense of
smell. The sense of taste alone seems to be confined to sensation
arising from four distinct stimuli : (i) sweet; (n) bitter ; (in) acid ;
(iv) salt. All purely taste sensations are either modifications of or
combinations of these four fundamental sensations. The sense of
taste may be excited only by those substances which pass into
solution ; i. e., insoluble substances are tasteless.

The sensation will vary in strength with : (i) the size of the
area stimulated, being more intense the greater the area stimulated ;
(u) the concentration of the .solution, being more intense the stronger
tlir -olution ; (in) the temperature of the solution, being more in-
tense ill' oearer the temperature is to that of the blood ; (iv) the
mechanical friction of the tongue against the palate, being stronger
with moderate friction than without it.

The sense of taste varies in acuteness : (i) through certain heredi-
tary influences; and(ii) through cultivation. A good example oi
marked acuteness of taste acquired by cultivation, may be found
in the professional tea-tasters, and wine-tasters.

I). Practical Tests of the Sense of Taste.

1. To Determine the Acuteness of Taste. — Make four standard
solutions as follow-: (i) Sugar: 1 gm. of dry saccharose in KM)
e.o. distilled water, (n) Qmninei I centigramme in LOOOcc.oi
distilled water, (m) Acetic acid: I gm. of glacial acetic acid in
loon o.c. distilled water, (rr) Salt: I gm. of dry .-odium chlo-
ride ill 100 r.e. distilled Water.

In the use of these solutions prepare die gustatory surfaces by
thoroughly rinsing the mouth with distilled water, or with boiled
water. Taken uniform quantity of the -olution into the mouth

164

SENSATION.

at each observation. A convenient quantity is 1 c.c. or a common
teaspoonful. Rinse the mouth before each new observation.

The following table gives results obtained by a Dumber of ob-
servers. (The numbers indicate the number of parts of water ti>
one of the substance to be tasted. |

Mr.

-

Quinine.

Acetic Acid.

Salt.

A.

700

1,000

7.

125

B

600

i,l

8,

500

c.

—

250

4,400

—

I>.

300

■Jim i.OOO

3,

700

E

7(Mi

1,000

F.

100

400.

6,000

600

G.

333

400, i

6,000

—

II.

500

4i mi, 000

4,500

180

I.

500

450,000

6, )

325

J.

650

200,000

7,500

325

At.

1 to 520

1 to 444,

1 to 5640

1 I..469

Besides the results here recorded numerous data were furnished
by other observers.

(a) This table and the supplementary data justify the follow-
ing conclusions :

( '/ 1 The acuteness of taste for sugar varies from one part of
pure cane sugar in 300 part> of water, to 1 in 70S, with an aver-
age of 1 in 520.

Q9) The acuteness of taste for salt varies from 1 in 325 to 1 in
TOO, with an average of 1 in 4<>!».

(;') The acuteness of taste for acetic acid varies from 1 in 3,000
to 1 in 8,000, or an average of 1 in 5,640.

(o) The acuteness of taste for sulphate of quinine varies from
1 in 200,000 to 1 in 1,000,000, with an average of 1 in 444,000.

From these results it is evident : (i) that there is considerable
individual variation ; (n) that the taste is more acute for the less
common stimuli of bitter and acid than for the more common
stimuli of salt and sweet.

(6) Several students recorded a marked decrease in the acute-
ness after the use of tobacco.

(c) One student recorded a noticeable increase in the stimulation
when the solutions were warmed from 20°C. to 40°C.

(d) One observer found that the tip and edge of the tongue
were more acute than other parts of the tongue in detecting slight
differences in tin1 strength oftJie solutions.

(e) One observer, reporting a series of very careful experiments
upon four individuals, three of whom are members of the same
family and accustomed to the free use of salt and vinegar in their
regular diet, concluded : That the fourth individual, not accus-
tomed to the free use of salt and vinegar, has a greater sensitive-
ness for saline and sour -ubstances than do the three individuals
who are so accustomed.

THE SENSE OF TASTE.

465

Fig. 232.

( /' ) As to the interval of time between the application of the
stimuli and the taste perception the observations seem to justify
the following conclusions:

(a) The interval between stimulation and sensation (latent in-
terval) varies inversely as the number of papillae per unit area in
the portion of the gustatory apparatus stimulated.

Q9) The interval between stimulation and sensation varies di-
rectly as the blood-supply or blood-pressure of the part at the
time of stimulation.

2. To determine localization of the sense of taMe, i. e., to find
whether there are areas of gustatory region which are especially
sensitive to particular stimuli ; quinine, for example.

Solution: Through the aid of a probang or of a camel's-hair
brush apply to different limited areas of the tongue, palate, fauces
and buccal mucous surface either the standard solutions given
above or somewhat stronger solutions of the same substances.

Results : The following
figure (Fig. 232) gives the
results which coincided sub-
stantially with those of other
< >1 (servers: Outline of tongue
showing location of tonsils
( T), foramen ca?cuni (F.
('.), circumvallate papillae
( ( '. P.) and fungiform pa-
pilla; ( F. P. ) upon the left
side, while the right side
shows the outline of the area
particularly sensitive to qui-
nine ( ) acid (....),

salt ( — • — ) and sugar

( ) respectively.

" CEhrwall has examined
the different fungiform pa-
pillae over the tongue with
reference to their sensitive-
ness to taste-stimuli. One hundred and twenty-live separate |>;i-
pilke were tested with succinic acid, quinine and sugar. Twenty-
-even of the papilla? gave no response at all, indicating that they

were devoid of taste fibers.1

Of the remaining ninety-eight, twelve perceived acid alone,
three perceived Bugar alone while none were found which reacted
to quinine alone. The t-ict thai some papillae respond to only one
form of taste sensation ie evidence in favor of the view thai there

•The 27 papilla which gave no response to war, sweet, or bitter, may hare
been sensitive to nit
SO

Localization of ia-te. Bitter. -
salt, — — — ; -

.'H id.

466 SENSATION: HEARING.

are separate nerve-fibers and endings for each fundamental sensa-
tion ; 1 >i 1 1 a majority of the papilla? (83) arc provided with more
than one variety of taste-fibers." (Henry Sewall, in American
Text-book of Physiology.)

VI. HEARING.

INTRODUCTORY.

i. Physiological Acoustics.

2. Comparative Anatomy and Physiology of the Auditory Organ.

3. Embryology of the Auditory Organ in Vertebrates.
i. Summary of the Anatomy and Bistology of tup: Ear.

THE PHYSIOLOGY OF HEARING.

1. The Transmission ok Sound.

a. The Part Played by the External Ear.
1). The /''in Played by tin: Middle Ear.

2. The Reception of Sound.

:\. The Sfnsation and Perception of Sound.

VII. HEARING.
INTRODUCTORY.

1. PHYSIOLOGICAL ACOUSTICS.

a. Definitions.

(a) Acoustics is the Science of Sound, and comprises the
study of sounds and of the vibrations of elastic bodies. Acou-
stics is concerned particularly with questions of the production,
transmission and comparison of sounds.

(7>) " Sound is always the result of rapid oscillations imparted
to the molecules of elastic bodies, when the state of equilibrium
of these bodies has been disturbed either by a shock or by fric-
tion." (Ganot.) Such bodies, always representing ponderable
matter, tend to regain their position or condition of equilibrium
only after performing on each side of that position very rapid
vibratory movements the amplitude of which quickly decreases,
The term sound is also applied to the sensation which these vibra-
tions arouse in the brain.

(c) The term physiological acoustics may be applied to that por-
tion of the general field of acoustics, which deals with the pro-
duction, transmission and comparison of the sounds made by
animals, or of the sounds serving as stimuli for animal sense-

THE PROPAGATION OF SOUND. 467

organs. Physiological acoustics deals, then, with the physical
principles involved in the production of the voice; with speech,
music, and the transmission of these sounds by the organ- of
hearing to the auditory nerve ends.

b. The Production of Sound.

That sound is produced by the vibration of elastic bodies may
be readily confirmed by experiment. Ganot suggests the follow-
ing experiment : Hold a bell-jar so that its axis is horizontal and
its rim free. Tap it gently with a pencil ; it emits a continuous
musical sound. Lay any small body, like a piece of crayon or a
nail, in the jar on its lower wall ; hit the jar a smart rap ; it emits
a musical sound as before, and in the meantime is causing the free
object within to jump about at a lively rate. The object is being
struck at short intervals by the vibrating wall of the jar. In a
similar manner a tuning fork or a violin string will throw off light
objects which are placed upon it while it is emitting a sound.
Si, mid is produced by the vibration of elastic bodies. A musical
son nil or four \< a regular continuous sound. A noise is an irregu-
lar discontinuous sound.

c. The Propagation of Sound.

Sound can In propagated only through the medium of ponderable
mattery for if the air be withdrawn from the receiver of an air-
pump a music-box in operation within the receiver, surrounded by
the imponderable, luminiferous ether, can not be heard.

Si, a, ,il is propagated through elastic, ponderable matter. All
gases, liquids, and solids may transmit sounds. These bodies are
acted upon by the vibrating source of the sound and are thrown
into a series of waves which rapidly spread in all directions from
tin' center of disturbance, in water-waves, or the undulations
which sweep over the Burface of a body of water, the individual
molecules rise and fall, describing an ellipse whose long axis is
transverse to the direction of propagation. In sound-waves the
molecules move to and fro in a line parallel to the direction of
propagation. This lead- to <i series of alternating condensations
null rarefactions of ihr medium.

1 . Velocity of Propagation of Sound. — (a ) I \ Gases. — New-
ton determined that the velocity of the propagation of sound in
directly as the square root of tin elasticity of the gas, and

inversely as the square rout of if* density I r = j. This for-
mula with modifications for temperature, and barometric pressure
yields the following results: velocity of sound in carbon dioxide,
856 ft. per -<■<•.; oxygen, L040 ft.; air, L093 ft.; hydrogen, I'm;.;.

468 SENSATION: BEARING.

(b) In LIQUIDS. — The same general formula I r = I- I as

given for gases applied with modifications for liquids. The co-
efficient of elasticity (e) is very high for liquids, and though the
density ((/) is also great the high elasticity makes the velocity of
sound in liquids much higher than it is in gases. For water the
velocity is 4708 ft. at 80° C. to 5013 ft. per sec. at 30° C.; for
absolute alcohol, 3854 ft. per sec. at 23° C.j for a solution of
NaCl, 5132 ft. per sec. at 18° ('.

(c) In Solids. The velocity in feet per second in caoutchouc,
1!»7 ft.; in lead, 4030 ft.; in copper, 11,666 ft.; in steel wire,
15,470 ft.

2. Reflection and Refraction of Sound. — The echo, familiar to
every youth, is a simple reflection of sound. The reflection of
sound is subject to the following laws : (i) The angle of reflection
of sound is equal to the angle of refraction, (n) The incident son-
orous ray and the reflected ray are in the same plane perpendicular
to the reflecting surface.

A sound-lens made of two circular sheets of collodion cemented
together at their edges and inflated with CO., will bring sound
waves to a focus. The ticking of a watch held beyond the princi-
pal focus of such a lens may be clearly heard in the conjugate
focus of the lens though the conjugate focal distance may be
many feet.

d. The Properties of Sound.

One sound may vary from another in intensity or loudness, in
pitch and in quality.

1. Intensity. — (a) The intensity of sound varies inversely as-
the square of the distance of the sonorous body from the ear.

I I varies as y^ ) *

(6) The intensity of sound increases with the amplitude of
the vibrations of the sonorous body.

(c) The intensity of sound depends on the density of the air
through which the sound is propagated.

(d) The intensity of sound is modified by the motion of the
atmosphere, i. e., by the wind.

(e) The intensity of sound is increased by the proximity of a
sonorous body. (c. //., The sounding box of a violin intensifies
the sound produced by the vibration of the strings.)

2. Pitch. — The expression, " pitch of a sound," refers to the
number of vibrations of the sonorous body in a unit of time.
The greater the number of vibrations per second the higher the

THE PROPERTIES OF SO CXI). 469

pitch ; the fewer the vibrations the lower the pitch. The number
of vibrations which a sonorous body will make in a second de-
pends upon several variable factors. In physiological acoustics
we are interested particularly in the vibrations of strings and of
membranes because the human voice is the sound of the vibrating
strings — tht vocal cords — and the hearing of the human voice and
other sounds depends upon the vibration of a stretched membrane,
the nu mbrana tympani.

(a) The Pitch of a Vibrating String. — "The vibration
of a string stretched between two points depends upon the reflec-
tion, at either end, of the wave motion transmitted along the
string. If a succession of waves travel along the string each
wave will in turn be reflected at one end and travel back along the
string, to be reflected again at the other end. The motion of any
point of the string is, accordingly, the resultant of the motions due
to waves travelling in both directions. If a string is to remain in
a state of vibration it follows that the modes of vibration must be
such that the distance between the two ends (the fixed points or ter-
minal nodes) contains an integral multiple of half the length of a

wave" (Shaw) (7. e., <=, when <= the distance— length of string

— n the integral multiple and /. the fundamental wave-length.

For the fundamental pitch of a string a = 1 ; / = -x , and

In seeking a general formula for the pitch of a vibrating string
we must first find an expression for the velocity of the undulation
which sweeps along such a string. The fundamental equation for
the velocity of an undulation is v = /:», i. e., if n waves pass a fixed
point in a second, and if each wave has a length / from crest to
crest (node to node in the string); then the velocity would be n
times/. But we are seeking the value of n in terms applicable
t<> the conditions. Our fundamental equation for n is from the
above (v=An | :

M "= ■•

We know the value of / in terms of length of string when the
string i- giving it- fundamental tone:

(H) X = 2l

It remains to express v in term- of ten-ion, etc., applicable to tin-
string. " A waveofany length travels along ataul Btringwith a
velocity equal to tli<- Bquare root of the tin-ion (in dynes) divided
by tli<- mass of a unit of it- length expressed in grammes per
centimeter." (Lord Rayleigh, Sound, Vol. I., Chap. I.)

470 SENSATION: HEARING.

W -4

For the tension in dynes is equal to 981 x the weight in grammes :
x = 98 If/. fi or the mass of a unit of length expressed in grammes
per centimeter is really the density multiplied by the volume.
The volume of a unit length equals xr2, representing the density
or specific gravity by d, then ii = r:ro.

(-•) -JSMJ1F

Substituting in (i) the values of v and k we have
. 1 |981v

Equation (v) expresses the number of vibrations per second in
terms of length, radius, tension (weight) and density. Expressed
as a variable by dropping the constants :

t \ 1 I 9

(vi) ft varies as — - ---

rl \ o

The verbal expression of the formula (vi) is : The vibration fre-
quency (pitch) of a string varies: (i) inversely as the radius; (n)
inversely as the lenf/th ; (in) directly as the square root of the tension
in grammes; (iv) inversely as the square root of the density.

(b) The Pitch of a Vibrating Membrane may be deter-
mined by the above formula (vi) under certain conditions : (i)
The membrane must be circular (7), like a drum head; (n) the
tension must be equal in all directions in the plane of a circle ( //);
(in) the thickness must be equal in all parts (/•) ; (iv) the density
must be equal in all parts. Once these conditions are filled we
have in a vibrating membrane the equivalent of an infinite num-
ber of strings of equal length, tension, radius, and density, which
will of course vibrate in unison, i. e., the membrane will give the
same fundamental tone as that given by a string representing a
diameter of the membrane.

(c) The Musical Scale. — The standard pitch of an instru-
ment is A which represents 435 vibrations per second ; it is the
middle A of the piano-forte. Xote that the tone ( " has just twice
the number of vibrations of C. This relation holds good through-
out the whole musical scale : A' has (435x2=) 970 vibrations
per second ; while A — 1 (one octave below middle -A) has (A|i=)
'111 I vibrations per second. The lowest C (C — 3) of the piano
has 32 -f vibrations per second and the lowest (7(0 — 4) of the

AUDITORY ORGANS. 471

pipe organ has 1(3 -f vibrations per second. Cu has 1044 vibra-
tions per second; C'm, 2088; CIV, 4176; Cv, 8352; CVI,
16704; Cvu, 33408.

Fig. 233.
C D E F G A B C'

O

-o-

a

-Gh

a

-©-

L'01 2935$ 326 YK 348 391 % 435 489 *{ 522

i ■■ % ■ U ■■ H ■ M ■■ % ■■ >H •• 2

3. Quality. — The variation in quality depends upon the com-
bination of harmonics or overtones. The degree of complexity of
a sound — the number of overtones present — together with the rel-
ative prominence or loudness of each overtone, is interpreted
mentally as giving a distinctive quality, or timbre, or character to
the sound heard. When one hears the A of a violin he ndt only
recognizes the pitch and intensity, but he is able to say that it is
produced by the violin. One does not consciously hear the har-
monies or overtones as a rule; he hears only the fundamental
tone of a certain quality. The flute gives practically a pure fun-
damental tone without any overtones. With a series of flutes
which produce notes whose frequencies are in the ratios : 1:2:3:4:5,
so mounted in a wind apparatus that they may be made to sound
with a loudness which can be separately regulated, one can buUd
up any quality of sound. Thus the infinite variety of sounds one
hears in nature is very simply explained. Even the different
vowel Bounds depend for their differences upon the modification in
quality of a fwndamental laryngeal tone — given a particular quality
by resonance of the organs of articulation — pharyngeal, oral and
nasal cavities [Medical Physics, Daniell).

2. COMPARATIVE ANATOMY AND PHYSIOLOGY OF THE
AUDITORY ORGANS.

There is do reason to believe that any of the Protozoa are sen-
sitive to atmospheric vibrations. If they respond to the audible
vibrations of the liquid media in which they rest, it is probable
thai these vibration- are really mechanical stimuli for their light

unicellular bodies.

Some Coelenterata possess auditory vesicles lined with epithelial
clu. provided with bristle-like cilia, an otolith, and innervated
by a nerve. Fig. !■'> I -how- a section through such a simple
auditory organ :

472

SENSATION: HEARING.

Fig. 234.

Among the Echinodermata only deep-sea holothurians, Elasi-
poda, possess auditory vesicles (56 in Dumber). These are lo-
cated along the course of the nerve
cords and possess numerous otoliths.

The Vermes, as represented by the
common earthworm, Tju/mbricus, though
externally sensitive to the vibrations
of the solids upon which they rest, are
quite insensible to vibrations of the air.
The microscope reveals no auditory
vesicle in the earthworm.

The auditory vesicles of the moUvsca
are constructed upon the same general
plan as those of the medusa. Fig. 235
shows Claus's section of the auditory
vesicle of a heteropod mollusk. In
most Lamellibranchs and Gasteropoda
and in the nautilus the auditory ves-
icles are innervated from the pedal
ganglia.

The Arthropoda have more highly developed external ears than
can be found elsewhere among the invertebrates. The Crustacea

Fig. 2.°,.").

Auditory vesicle of a jelly-fish in-
closing fluid provided with one or
more otoliths. X [nerve ; Ot, oto-
lith : //:, auditory rolls with hairs,
///*.;;( Mills alter (lais.)

Auditory vesicle of a heteropod mollusk [Plerotrachea). N, auditory nerve:0<, otolith in
fluid of vesicle; We, ciliated cells on inner wall of vesicle; He, auditory _ceDs ; Ce, central

cells. (Mills after Curs.)

as represented by the crayfish has auditory organs at the base of
the antennules. " Here the auditory sac is permanently open,

AUDITORY ORG AXs.

473

though protected by bristle-like seta?. Within this sac a part of
the wall is raised up into a ridge and the cells that form it are
provided with delicate setae at their free end and with nerve fibers
at their base within. The sac is filled with a gelatinous fluid con-
taining minute otoliths. Vibrations of the external medium set
the otoliths in motion ; these beat upon the seta?, and these seta?
affect the cells on the acoustic ridges, which, in turn, stimulate the
nerve fibers which are in direct communication with the brain."
(Bell.) The grasshopper, representing the Inxeeta, has a tym-
panum. This is a modification of the chitinous integument and
consists of a cavity across which a delicate chitin membrane is
stretched ; held taut by a delicate rim which in turn is stretched
by a number of small radial muscles attached externally. Within
the tympanum is an auditory ridge homologous to that described
above in the crayfish.

The Vertebrata show the ear in its highest development ;
though the lowest of the vertebrates (Tunicata, Amphioxus, etc.)

Fig. 236.

Diagram! i" show the relations of the auditory labyrinth in the vertebrate series. .1, fish ; /.',

bird : C, mammal : », utriculus, with 1 1 1 * - three semi-circular canals ; », sacculus; •■, cochlea;

/ . aqueductua veetibull : '<, lagena : er, canalis reuniens. in C, r is seen to divide into separate

for the utriculus and sacculus ; the vestibule is seen i" have a caeca] sack at < ; /■. coil

of iii' cochlea. (After Waldei i b, >

give evidence of ;i continuity of the development from lower in-
vertebrate forms. In all animals, — invertebrate and vertebrate

alike — that possess an auditory vesicle tins is invaginated from

the epiblasi and the pore which originally communicated with the
exterior may remain open throughout adult life.

All higher vertebrates possess an internal ear (modified audi-
tory vesicle) of considerable complexity, showing a vestibule and a
series "f semicircular canals. The mammals possess in addition a
complei structure called the cochlea. Waldeyer's figure (Fig.

474

SENSATION: HEARING.

236) shows the variations in the structure of the auditory vesicle
in fishes, birds, and mammals. The embryology and the anatomy
of the mammalian ear may be taken to represent the higher
vertebrates.

3. EMBRYOLOGY OF THE AUDITORY ORGAN IN
VERTEBRATES.

a. Comparative Embryology.

The origin of the ear from one of the lateral ganglia of the
petromyzon, as maintained by Kupffer and now generally accepted
has been discussed above. (See p. 458.)

The lowest mammals show a clear relation to the birds in the
early steps of development ; a relation which is not by any means
effaced in the adult structure.

b. Special Embryology of the Human Ear.

1. Development of the External Ear. — The external meatus
corresponds to the invaginated part of the branchial cleft and is

Fig. 237.

/ mo

Development of the pinna. 1, tragus; 2, 3, <\ Helix; -}, anthelix ; 5, antitragus; 6, tsnii
lobaris. (Mihot.)

therefore lined with epiblast. The pinna is developed (Fig. 237)
from six eminences which surround the external end of the
meatus. By the fourteenth week the form has already approx-
imated that of the adult ear.

Sometimes the pinna is arrested in its development. The small,
round, thick ear, such as shown in I), is almost sure to be asso-
ciated with a greater or less degree of arrest of psychical develop-
ment.

•1. Development of the Middle Ear. — For the details of the
development of the middle ear, especially the bones of the middle

SPECIAL EMBRYOLOGY OF THE HUMAN EAR.

475

ear, see any work on the histogenesis of the pharynx. The fol-
lowing is a summary :

(i) The tympanic cavity and the Eustachian tube are developed
from the first branchial pouch, hence called the " tnbo-tympanal
pouch. " It is lined with hypoblast.

(n) The malleus is developed from a part, probably the cerato-
branchial segment, — of the 1st branchial areh.

(in) The incus is developed from a part, — probably epibranch-
ial segment of the 1st branchial arch.

(iv) The stapes is developed as an osseous deposit in the liga-
mentous connective tissue, connecting the fenestra ovalis with the
incus. The hole in the stapes, which gives it its distinctive form,
was occasioned originally by the presence of an artery, around
which the ossification took place.

3. The Development of the Labyrinth. — The Otocyst: In
the earliest stages of embryonic development when the anterior
end of the neural tube has been definitely divided into primary
fore-brain, mid-brain, and hind-brain vesicles, there appears on
either side of the hind-brain vesicle a minute pit, which is in-
vaginated from the epiblast and therefore lined with epiblast.
This pit, the beginning otocyst, continues its invagination until it
divides off from epiblast and begins a gradual migration through
the delicate mesenchymal embryonic tissue toward its. future posi-
tion (see Fig. 238, A and B).

Fig. 238.

Development of the membranous labyrinth. Beginning of otocysl En the human embryo.
1, 2.4 mm. in length; /.'. i mm. in length; C, otocyst or human embryo i weeks (Hi8>;2>,
ii man embryo 5 weeks ( ll i~): /•.', membranous labyrinth of 2 months embryo (His). (Minot.j

In the meantime the otocyst rapidly enlarges and by the
fourth week the aaccus endolymphaticus («. e.) is beginning its
development | Fig. 238, ( ' ).

The third stage makes the development of the semicircular

canals (Fig. 238, l> and E). Note the order in which these are

developed. Note also the development of the cochlea.

476

SENSATION: HEARING.

From this scries of figures it is evident that the epithelial lin-
ing of the membranous labyrinth is epiblastic. At first composed
of undifferentiated columnar cells there comes to be, in man, sis
area- within the membranous labyrinth where the epithelium is
highly differentiated. Of these the most highly specialized is the
organ of Corti, which undoubtedly represents the end-organ for
the perception of sound. Besides the organ of Corti there is one
specialized area in each semicircular canal. The Cinsba acu8tica}
and one in the Utriculus, the Macula acustica utriculi.

1. SUMMARY OF THE ANATOMY AND HISTOLOGY OF THE

EAR.

(a) The organ of hearing is divisible into (i) external, (n)
middle, and (in) internal ear ; or (i) pinna and meatus, (n)
tympanum, and (in) labyrinth. (See Fig. 239.)

Fig. 239.

.Mmmm

Diagram intended to illustrate the processes of hearing. AG, external auditory meatus ; T,
tympanic membrane; A', malleus; n, incus; P, middle ear; o, fenestra ovalis ; r, fenestra ro-
tunda; pi, scala tympani; vt, scala vestibuli; V, vestibule; S, saccule: U, utricle; //, semi-
circular canals ; Til, Eustachian tube. Long arrow indicates line of traction of tensor tym-
pani ; short curved one that of Stapedius. (After LANDOIS.)

(6) The tympanum lies in a hollow in the petrous portion of
the temporal bone. The tympanic membrane (T) cuts it off from
direct connection with the external atmosphere. The Eustachian
tube (TE) brings it into indirect connection with the air through
the pharynx and external respiratory passages. The tympanum
consists of a chain of bones : the malleus (h), the incus («) and
the stapes (.s). The malleus is fastened to the membrana tympani
and the stapes to the membrane which closes the foramen ovalis.

(c) The labyrinth lies within a cavity in the petrous portion of

ANATOMY AXD HISTOLOGY OF THE EAR.

477

the temporal. The cavity with it* various canals is called the
bony labyrinth.

(d) Within the cavity of the bony labyrinth, but very much
smaller than the cavity lies the membrcmous labyrinth. (See Figs.
236 and 238.) From the embryology it is evident that the
epithelium of this membraneons labyrinth is epiblastic. Between
tin- structure and the bony wall there is a considerable space
occupied by two large lymph channels. The one above the epi-
blastic membranous labyrinth is the scala vestibuli, so called be-
cause it is continuous with the vestibule. The one below is

Fig. 240.

Section of oue whorl of cochlea.

called the scala tympani, which passes into the foramen rotundum
separated from the tympanum by a thin but dense and strong
membrane. Fig. 240 shows a cross-section of one whorl of
the cochlea, witli the membranous labyrinth, marked C.c. (Canalis
eochlcaris) and the largo lymph spaces above and below.

(e) Note the little bony shelf (Lamina spiralis) which extends
out from the inner wall of the bony canal and reaches about three-
fifths of the way across to the outer wall, where there is a corre-
sponding ridge The space between the spiral lamina and the
outer ridge is spanned by a dense membrane (membrana basilaris)
which Lb composed in its 2£ spiral turns of about 24,000 parallel,
radial fibrillar. The length of the fibrillar which constitute the
basilar membrane varies; i. <■., the width of the membrane varies

in different part- of the cochlea !

(i) At the beginning of the basal coil of the cochlea, 0.041 mm.
(in Average for basal coil of cochlea, <>._1 mm.

ill i Average for middle eoil of cochlea, 0.3 I nun.

(rv) Average for apical eoil, 0.36 mm.
(\) Length af >i\<\ of apical turn, 0.495.

ITS

SENSATION: HEARING.

The longest fibrilla is 12 times the Length of the shortest one.

( f ) Between the basilar membrane and the membrane of Reiss-
ner is the epiblastic end-orgaD of bearing — the organ of Corti,
whose genera] structure is indicated in Fig. 2 tO.

(.7) Tlie Organ of Corti consists essentially of : (i) The rods or
pillars of Corti, which are secured by the epiblastic cells c and cf
(Fig. 241), and are chitinous in their general character, (n) The

Section of Corti's organ from guinea-pig's cochlea: ST, scala tympani ; TC, tunnel of Corti j

/;. bony tissue of spiral lamina ; u, til in jus tissue covering same continued a~ substantia propria
or basilar membrane; c,cft protoplasmic envelope of Corti' s pillars (<■, e'); d, endothelial
plates :/. heads of pillars containing oval area- ; g, head-plates of pillars : /'. //', inner ami outer
hair cells ; m, membrana reticularis ; k, I, cells of Eenson and of Claudius ; ,,, nerve-fibers : i.
cells of Deiters. (1'ieksol.)

inner <i ikI outer hair cdls so called from the short bristle-like hairs
which extend from the upper ends. There are five rows of hair
cells, one inner numbering about 3500 and four outer numbering
about 12000. (in) The supporting cells or cells of Deiters. ( i\)
The reticular membrane, continuous with the outer ends of the
rods of Corti and of the same sort of material as they, (v) The
filamentous endings of the auditory nerve about the proximal
ends of the hair cells.

(/i) There is an area of specialized innervated epithelium in the
saccule and one in the utricle.

(/) The three specialized epithelial areas in the semicircular
canals have been depicted and discussed under Maintenance of
Equilibrium (q. v.).

(£) Fig. 240, T, shows some typical otoliths.

TRANSMISSION OF SOUND. 479

THE PHYSIOLOGY OF HEARING.

1. THE TRANSMISSION OF SOUND.
a. Part Played by the External Ear.

1. The Pinna or Auricle. — The part which it plays in man is
so slight as to be practically disregarded. Abnormal projection
of tragus over mouth of meatus obstructs sound waves.

2. Meatus Externus. — («) The Calibre is usually smallest
at inner end near membrana tympani, though it is smaller in the
middle (inner end of cartilaginous portion) than between that and
the membrana tympani. If there is an abnormal narrowing of
the inner segment there is no impairment of the hearing. If there
is an abnormal narrowing of the outer end there is an unmistaka-
ble impairment of hearing.

(b) Course. — The meatus presents two segments meeting at an
obtuse angle, the cartilaginous portion passes upwards and inwards
and backwards, the bony portion passing downwards, forwards
and inwards. This makes a direct transmission impossible ; the
sound waves must be reflected at least twice before impinging
upon the membrana tympani.

(<•) Reflecting Surfaces. — The description already given
would lead us to suppose that these surfaces are conical ones, but
the cross-section of the meatus is always elliptical in general out-
line and there is a depression on the posterior wall of the carti-
laginous segment and one on the (Ulterior wall of the bony segment.
The more external depression presents an ellipsoidal surface, while
the more internal one presents a paraboloid surface. Professor
Dencfa in his text-book on the diseases of the ear cites this fact
:i- advantageous but avoids telling what the advantages of a para-
boloid surface are in this particular situation. Its advantages as
a light reflector when the light is placed in the focus are familiar
in every schoolboy. What are its advantages here?

('I) Tin; Bairs and SECRETIONS of the meatus are for pro-
tection.

?». The Membrana Tympani. — (a) General Structure: This
delicate membrane possesses a skin, a mesenchymal framework and

a hypoblastic m/UCOUB membrane The mesenchyme consists of

inelastic connective tissue fibers which arc either circular <>r radial.
The accompanying figure (Fig, 242) shows the general course of

the radial and circular fibers of the middle layer or framework

of the membrane.

(b) The angle at which the membrane tympani is set with re-
sped to the axis of the bony segment of the meatus is not with-
out importance. The lower half of the membrane inclines to-

ISO

SENSATION: II KM! ISC

wards the axis of the meatus leaving an angle of about 55° and
the upper half of the membrane inclines .-till more, leaving about
45° or less between membrane and axis. (Sec Fig. 243.)

Fig. 245

Photographic representation of right membrana tympani, viewed from within. 1, divided

head of malleus ; 2, neck ; 3, handle, with attachment of tendon of tensor tympani ; 4, divided
tendon ; 5, (i, long handle of malleus : 7, outer radiating and inner circular fibers of tympanic
membrane ; 8, fibrous ring encircling membrana tympani ; 9, 14, 15, dentated fibers of < i ruber ;
10, 11, posterior pocket connecting with malleus; 12, anterior pocket; 13, chorda tympani
nerve. (Alter Flint and Rudinger.)

(c) The Area of the Membrane: It presents an elliptical sur-
face whose axes are about 1 0 and 8 mm. The area would be ap-
proximately («.=7r>'2 ; «=3.1416 x(4.5)2=) 63.5 sq. mm.

(d) The Question of Fwndamenixd Tone : Every fixed taut
string and typical drum membrane possesses a fundamental tone.
If the membrana tympani possessed a fundamental tone it would
greatly impair its utility as a transmitting membrane for sounds
of different pitch. The membrana tympani does not possess a fun-
damental tone because : (i) It is elliptical in outline, (n) Its

TRANSMISSION OF SOUND.

481

vibrations are dampened by the attachment of the handle of the
malleus, (in) The connective tissue fibers which radiate outward
from the handle of the malleus as a part of the substantia propria
of the membrane are of various lengths and of slightly varying
tension. A fundamental tone for themem&ranatympani is therefore
ail acoustic impossibility.

(i) Tin external convexity of its radiating fibers: Helmholtz
has shown that an impulse against the convex surface of the
taut membrane will have a greater effect in driving the handle of
the malleus inward than would be the case if the taut membrane
were a plane surface. When we consider, however, that the di-
rection of this increased force would be as indicated by the arrow

Fig. 243.

Fig. 244.

Lever system of the ear.

Showing incline of membrana
tympani.

". Fig. '14'.), instead of the direction of arrow b the required di-
rection ; the advantage is not so great as might first appear, be-
ing approximately two-fold, or the intensity is about doubled.

//. Part Played by the Middle Ear or Tympanum.

{a) Tlir Eustachian tube permits equalization of pressure inside
and outside of the cavity.

(b) Tin /< n ■■/• system.

(o.) For the transmission of sound the malleo-incudal combi-
nation moves as one lever, while the stapes simply transmits the
movements of the end of the incus to the oval window.

(,*) For protection of the membrane which closes the oval win-
dow and to which the stapes is attached the malleo-incudal

articulation is subjed to motion in such a direction as to permit

the handle of the malleus to be displaced outward without carry-
ing the inCUS with it.
v,\

182

SENSATION: HEARING.

(y) The lever arms (Fig. 244) have the ratio »>..'> mm. to
9.5 mm. The maximum movement of the end of the handle of
the malleus is 0.097 mm., almost 1 mm. The distance traveled

by the weight would be = - — tti- — = .0643 or a little more

9.5

than A of a mm. ( Ilelmholtz). In the meantime the force has

9.5
been augmented l>v the ratio ,. ; or about 1.5 times. Summing
& J 6.3 b

it up: flic foot qfthestapes vibrates through two-thirds the amplitude

irith 1 \ times the force represented in the vibration of the malleus

handle.

Fig. 24o.

Diagram, showing the shape and dimensions of the foot of the stapes (a), and the effect of
infraction of the stapedius muscle (sip.), lifting the " toe" of the stapes up from the plane of

contract

the foramen (as). (After Tkstit. )

(o) The size of the foot of the stapes :

The area of the fenestra = 3.8 sq. mm.

The area of the foot is 2.65 sq. mm.

The area of the annular ligament is 1.15 sq. mm.

c. The Summed-up Force.

(a) As all of the energy received by 63.5 sq. mm. of tympanic
membrane is transmitted to 2.(35 sq. mm. of stapes we have a
proportionally greater intensity of vibration.

(i'i) The convexity of the membrane increased the intensity.
Assume a ratio of 2:1.

(}-) The lever system increases the intensity by a ratio of

9.5

^V. Summing up these ratios we have a final intensity (J) bear-
ing the following ratio to the initial intensity (/) :

/ 63.5 2 9.5

i= 2.<n x i x <;.:; =72-16<

RECEPTION OF SOUND. 483

The intensity per unit area is multiplied about 72 times in the
course of its transmission. On the other hand, the amplitude is
decreased to only § of the original amplitude.

d. The Movements of the Stapes.

The full-line figure indicates the position of the stapes when the
stapedius muscle {xtp, Fig. 245) is relaxed. The dotted outline in-
dicates the position of the stapes when the muscle is strongly con-
tracted. This shows the motion of the stapes to be a rocking
around the pivot, p. The wider area of the annular ligament an-
teriorly permits the motion. The maximum amplitude of the
upper end of the stapes is about 0.064 mm. or J* mm. That
would give the anterior end of the foot an amplitude considerably
more than -jL mm. and the posterior end or heel an amplitude of
about zero or even possibly a slight negative vibration. But these
are the conditions when the pitch is low, the amplitude of the
membrana tympani great and the stapedius strongly contracted.
These conditions would be likely to exist when the ear is re-
ceiving loud noises.

In the reception of the musical tones of the human voice or
of a musical instrument it is not probable that the rocking mo-
tion exists. The amplitude of the motion may be as little as

e. The Perilymph of the Scala Vestibuli.

This takes up the vibrations of the foot of the stapes and trans-
mits them to the organ of Corti, and through the scala tympani
back to the foramen rotundum, whose membrane serves to equalize
and temper the pressure within the labyrinth.

2. THE RECEPTION OF SOUND.

The end-organ of sensation is the organ of Corti. The modified
epiblastic cells are the hair cells of the organ of Corti. About
these modified epiblastic cells, or special receiving cells, the den-
drite- of the cochlear branch of the auditory nerve arborize. The
cell body of the auditory neuron of the /order (whose dendrites
arborize about the hair cells) lies in the spiral ganglion; the
neuraxon, oeurite or axon passes to the sensorium of the central
nervous system. The way in which the terminal nerve ends are
stimulated is a matter of speculation.

(in IIki.mhoi/iz's Theory briefly expressed is : 1st. Thevibra-

tion- of tin- medium received by the iueinbran;i tympani are trans-
mitted across the tympanic cavity and to the perilymph of the
vestibule, with somewhat decreased amplitude, but much increased
intensity, as given in detail above. 2a. The perilymph n> well as

484 SENSA 1 1 ON : UK. 1 R TN( I

the endolympb of various canals of the cochlea take up vibrations
which correspond in number per second (pitch) with their own.
3d. The hair-cells resting upon fibrillse which are set into vibra-
tion vibrate with the fibrillse and thus stimulate the nerve fila-
ments which arborize around thein.

(/>) 'I'm: Telephone Theoky of Wai.lkr. — Waller's theory
makes the basilar membrane analogous to the telephone membrane
which, as we know, may be thrown into vibrations of varying
pitch, even reproducing a piece of music with its complex chords.
The movements of the membrane here represent a resultant of
all the impulses which affect it, and bodies resting upon such a
membrane would likely be affected in a manner analogous to the
way in which tine sand on a vibrating plate is affected ; /. e.}
throw into an infinite variety of resultant patterns or combina-
tions. This theory makes perception of different tones a per-
ception of different combinations.

3. THE SENSATION AND PERCEPTION OF SOUND.
d. The Range of Auditory Sensation and Perception.

1. The Range of Pitch. — (a) The lower limit is generally ac-
cepted as 1G vibrations per second.

(6) The upper limit is far beyond the upper note of the piano-
forte, being usually somewdiere in the octave between CVI and
Cvn above middle C, i. e., representing between 10,704 and
33,408 vibrations per second. (International pitch.)

(c) The range would thus be for the human ear 10 to 11
octaves. The range for one particular human ear would prob-
ably not exceed 9 or 10 octaves, because an ear that can perceive
33,000 vibrations per second would not perceive 16 vibrations
per second as a continuous musical tone, but as a rapid succession
of noises. Nine octaves may be accepted as the average limit
for the individual human ear.

(d) Problems :

(i) If the human ear can distinguish musical tones over a range of 9
octaves, how many fibrillse of the basilar membrane would represent
one tone ?

(n) How many hair cells of the inner row would represent one tone?

(in) If the human perception is capable of distinguishing stimuli
affecting two adjacent hair-cells, what fraction of a tone should be dif-
ferentiated ? '

The range of perception of pitch varies with age. At the age
of ten years the upper limit of pitch is about 40,000 per second
(EVIr), while at the age of fifty years it has receded to about
30,000 per second (BVI).

1 Weber says : "Accomplished musicians can appreciate differences in pitch as
small as ^ of a tone."

VISION. 485

2. The Range of Intensity. — The lower limit of the range
of intensity represents the acuteness of the hearing for faint
sounds. Schafhautl says : " A person of acute hearing can de-
tect the sound made by a cork ball weighing one milligram
(0.001 gm.) falling one millimeter (1 mm.) upon a glass plate 91
millimeters distant from the tip of the tragus and directly opposite
to the meatus."

b. Judgments Based upon Auditory Sensations and Percep-
tions. Estimate of Distance and Direction
of Source of Sounds.

This topic belongs to psychology. It may be briefly stated
that the estimate of direction and distance is neither a sensa-
tion, a perception, nor a conception, but is the result of sub-
conscious reasoning based upon a series of sensations, percep-
tions and conceptions. The young child estimates direction and
distance only after many sensations have been received. With in-
creasing experience the estimation of direction and distance be-
comes gradually more perfect. At first the result of a conscious
effort it becomes eventually subconscious — really reflex.

VII. VISION.

INTRODUCTORY.

1. Physiological Optics.

2. Comparative Physiology of Vision.
Embryology of the Human Eye.

\. nm.maiiv of the anatomy anh histology of the eye.

THE PHYSIOLOGY OF VISION.

A. Visual Optics: Tin: Eye as an Optical Instument.
i. Visual Refraction : The Refractive Apparatus of the Eye.
". Application of the Lowe of Refraction to the Mammalian Eye.
h. Accommodation.

(1) Tin' Mechanism of Accommodation.
(■i) Tin- Range "f" Accommodation.
r. Imperfections of the Refractive Apparatus of the Eye.
2, Visual Mechanics: The Directive Apparatus of the Eye.
". Monocular Fixation.
//. Binocular Fixation "ml Convergence,
a. Visual Sensatiom : 'I'm: Eye as the Sensb-oboan of Vision.

1. III. I IN \\. Bh IMI LAI ION.

ii. Tin stimuli.

ii. Tin Irritability of tfu Retina.

i , Factor! [nvolved in Retinal Irritability.
I ►irecl and [ndirecl Vision.

ise, SENSATION: VISION.

2. Visiai. Sensations.

a. Fundamental Sensations.
I 1 ) Form.

(2) Intensity.

(3) Color.

//. Secondary Sensations.

(1 ) After-images.

(2 1 Contrast.
c. Color-Blindness.

(1) Complete Color-Blindness.

(2) Yellow-Blue Blindness.

(3) Red-Green Blindness.

(4) Acquired.

(5) Normal Color-Blindness.

3. Visual Perceptions and Judgments.

a. Acuteness of Vision.

b. Visual Estimates.

(1) Estimate of Distance.

(2) Estimate of size.

VII. VISION.

INTRODUCTORY.

1. PHYSIOLOGICAL OPTICS.
a. Definitions.

(a) Optics is the science of the phenomena of LiyJit. It com-
prises the study of the sources of light ; the production of light ;
the propagation of light, and its various properties.

(6) Light is a Mode of Motion. The luminosity of a
body is due to an infinitely rapid vibratory motion of its mole-
cules, which, when communicated to the ether is propagated in all
directions in the form of spherical waves, and this vibratory mo-
tion, transmitted to the retina, calls forth the sensation of vision.
(Ganot.) The vibrations of the ether are transverse to the direc-
tion of the undulation — i. e., they are transversal vibrations.

(c) A Luminous Ray is the direction of the line in which the
light is propagated. Every luminous body emits divergent, rec-
tilinear rays from all points of its surface, and in all directions.

(W) A Medium is any space or substance which light can tra-
verse. Media may be transparent, or translucent.

Transparent media may be of various densities, glass is more
dense than water, and water more dense than air, lower strata of
air more dense than higher strata.

(e) The Term Physiological Optics may be applied to that
portion of the general field of optics which deals with the transmis-
sion of light through the media of the organ of vision. Physiological

REFRACTION.

487

optics deals properly with refraction, though reflection is also fre-
quently treated under this head.

b. Refraction.

Prop. i. When a ray of light passes from one medium into
another medium in a line perpendicular to the plane separating
the two media, the ray will continue its course in an unbroken
straight line in the second medium.

Prop. ii. When a ray of light passes from one medium into
another medium in a line not perpendicular to the plane sepa-
rating the two media, the ray will be broken at the surface of the
second medium.

Fig. 246.

I diagram t" Illustrate refraction.
PROP. ill. The plane determined by the two segments of the

broken ray i- perpendicular to the plane which separates the two
media. Corollary. If the surface separating the two media be a
curved one the plane determined by the ray will be perpendicular

to a plane tangent to the curved surface at the point of intersec-
tion of the ray.

Prop. i\'. Efthe second medium be denser than the first me-
dium the angle between the ray and the normal will be less ill

the second medium than in the lir-t and conversely.

488

SENSATION: VISION.

Prop. v. The ratio between the sine of the angle of incidence
and the sine of the angle of refraction is constant for any two
media.1

sin / : sin !{'.; sin i ; sin /•.

As

-in

sin R

is a constant for any particular medium it is cus-

tomary to use ii. to express this constant for air and each other
medium respectively.

PjROP. vi. If a ray pass from any medium through a denser
medium which is bounded by twit parallel planes, it emerges from
the denser medium in a line parallel to its course before meeting
that medium. (See Fig. '247.)

Fig. 247.

Diagram showing path of ray through a denser medium bounded by two parallel sides.

Prop. vii. If a ray pass from any medium through a denser
medium which is not bounded by two parallel planes it emerges
in a line not parallel to its original course but invariably refracted
toward the base.2 (See Fig. 248.)

1 A Normal is a line perpendicular to the surface of a medium at the point of
incidence. The angle of incidence is the angle between the incident ray and the
normal ( as /_a ). The sine of the angle of incidence in Fig. 246 is the line «iS7 meas-
ured upon the radius aO. The angle of refraction is the angle between the
refracted ray and the normal /a/ONf. The index of refraction of any medium
is the ratio between the sine of the angle of refraction in that medium compared
with the sine of the angle of incidence when light passes from air into the medium

in question. For example, index of refraction for water = —. = -=1.33.

' sin r 6

2 "A prism in optics is any transparent medium comprised between two plane
faces inclined to each other." (Ganot. ) The apex of the prism is the line of in-
tersection of the two planes. The base of the prism is the boundary surface op-
posite the apex, unless otherwise defined it is understood to be perpendicular to a
plane bisecting the angle of the apex. The angle of the prism is the angle be-
tween the bounding planes. The angle of deviation is the angle between the inci-
dent ray and the emergent ray.

REFRACTION.

489

Prop. viii. The rays of light emitted from a luminous poiut
in the optical axis will, on passing through a convex lens, be con-
verged toward the optical axis, i. c, more convergent or less

divergent.1

Diagram showing path of ray through a prism. Note that the incident ray is bent to the
horizontal direction in the prism and is refracted again on emerging, still farther toward the
base. If the two ra\ > (incident and emergent) be extended in the dotted lines they will meet
at an angle indicated in the figure. This angle is called the angle of deviation. (Wrongly indi-
cated in the figure, unfortunately.)

1 A convex, km is the optical equivalent of an infinite number of prisms stand-
ing base to base.

A ro/icave lens is the optical equivalent of an infinite number of prisms standing
apex to apex.

The optical asm is the line perpendicular to the plane of a lens and passing
through its optical center.

The optical center is a point in the optical axis, any ray passing through which
suffers no deviation.

The principal foeta is that point at which parallel rays meet in passing through
;i convex Lens. A concave lens has no real focus, but a virtual focus in the nega-
tive direction.

The principal focal distance is the distance between the optical center of the con-
vex lens and the principal focus (/). ( Fig. 240. )

Fig. 249.

Tangent

Incident ran

J**

A,

\ \

J D

Focus

<: k

_Je_

^F

r

/

Diagram t" demonstrate the ralueof the principal focal distance (/ ).
What i- the value i,i' / in termi of the known factors: radius of curvature (r)
and index rt refraction — ' Fig. 249. Note that: Z D=s /.< — Z<; but

I'.IO

SENSATION: VISION.

Prop. ix. Kays of lighi emitted from a luminous point in the
optical axis will, on passing through a concave lens, be diverged
from the optical axis or will become more divergent or less
convergent.

Fig. 250.

The relation of the conjugate foci to the principal focal distance.

Prop. x. The sum of the reciprocals of the conjugate focal
distances is equal to the principal focal distance,1 or

- when o = distance of object, i = dis-

1 1 1

= /'°r/= o + i

O J

tance of image, and /== principal focal distance

/_% : /_r\'.\:fi ; let Z. *= 1> *• e-> hit the angle of incidence be taken as a meas-
ure: then /_r = fi; but /_D=/_r — /_i.'./_D = n — 1. Suppose the point
of incidence I to he indefinitely near to O, then /A 10F and IOC are right angled
at 0. /_ IFO= /_D; /_ 100= /_ i. Measure the angles i and D by their com-
mon tangent 10 which we will call t. then /_ i: /_ D\ '. : .; therefore /_ > ' '■ Z D

::/':/■; but /_I) = l>- — 1 and Z.i=l ; therefore, !:,» — !::/':/• or /=

>-l,

which was to be determined.

For a biconvex lens, f=— —

" 2 (a* — 1)

1 Conjugate Foci. If the source of light be near enough to the lens so that the
rays are not parallel, but divergent, the lens will not bring them to a focus BO SOOU
as in the first case, e. ,'/. , rays from the point 0 would be focused at the point /.
The distance /'is by definition invariable. The distance o and i may vary at will.
What is the relation between these distances? (See proposition X. )

To Solve : (1) When o = 2/; what is the value of /'.'

(2) When o •< 2/'; how does i compare with 2/?

(3) When o > 2/; how does i compare with 'If!

(4) When o = x ; what is the value of i '.'
(o) When o =/; what is the value of i?

(6) Does o vary as . ; does i vary as ?

i o

(7) < oven '/ = 20 cm. ; 1 = 20 cm. ; to find /'.

(8) Given 0 — 100 cm. ; / = 10 cm. ; to find i.

(9) Given i' = 5 cm. ; / = 5 m. ; to find o.

Before proceeding with the theoretical application of the laws of refraction to
tlie human eye the student will do well to review again such problems as the
following :

SIMPLE DIOPTRIC SYSTEM.

491

A Simple Dioptric System.

The simplest dioptric system is one in which the ray passes
from one medium into a second medium of different refractive in-
dex, the surface of separation of the two media being a spherical
surface. In the accompanying figure (Fig. 251) the spherical

Diagram to show the cardinal points of a single dioptric system.

surface, *', s, p, x"t separates the medium 31, whose refractive in-
dex is 1 from the medium 3F , whose refractive index is 1.5.

Note the following cardinal pointe of a simple dioptric system :

The center of curvature of the spherical surface (n) in the nodal
point.

That radius which is the center of symmetry of the dioptric
system (i. e.} n, p) is called the principal axis of the system. In
this axis lie the first and second principal foci, f and /' respec-
tively. The point where the optical axis cuts the spherical
surface ( p) is called the principal point. The plane tangent to
tin -pherical surface at this point is the principal plane. Planes
perpendicular to the optical axis at / and / are called the first
anil second principal focal planes respectively.

(liven the radius of curvature and the index of refraction to lo-
cate upon the principal axis the principal foci.

Problems: -(1) Given a biconvex lens, focal distance =/ to construct the
image of a point located at o = 2/

2 Given a biconvex lens, focal distance = / ; t<> construct the image of a
line whose middle point lie- in the optical axis of the lens and at a distance of 1/
from the optical center of the lens.

.; Given a biconvex lens whose radios of curvature for both surfaces is equal
to it- focal distance to determine the index of refraction of the lens substance.

I i liven ;i biconvex lens whose radius of curvature is •", cm., lor both surfaces
and whose index of refraction i> 1.5; to construct the image of a line 2 cm. in
length 1 to tin- optica] axis and one of whose extremities lies in the optical axis
at a distance of in cm. from the optical center.
Wliat are the dimensions of the image?

Suppose the object in the above problem !"■ removed to a distance of 20
cm., what w the length of the image ? What are the limits of size of image for
varying distances of the object

li the distance of the image remains the same ami if its length remains the
bow long most tie- object he in terms of length of image [I), when the> object
i_ located at a distance o 2/ from the optical center of thelens. At distance
o = 4/; o = 10/; o = 100/; o =- 1000/7

492 SENSATION: VISION

Neumann has given the following construction :
(i) Erecl at a and /> perpendiculars to the principal axis, (ii)
Lay off, uj)on each, the two indices of refraction of the two media
measured from the origin of each perpendicular, in the same linear

units used in measuring the radius. In the figure let /"• and pd
represent the index of refraction of the medium M, and na and
pb the index of refraction of medium J/'. The continuation of
line <«I cuts the principal axis in the point/ the first principal
focus, while the line 6c cuts it in the point f, the second princi-
pal focus. The geometrical figure shows the following important
properties of the dioptric system :

(i) The distance from the first principal focus to the principal
point equals the distance from the second principal focus to the
nodal point.

(1) Mathematically expressed : pf = nf.

(n) The ratio of the second focal distance {pf) to the first
(pf) is equal to the ratio of the index of refraction of the sec-
ond medium (IP) to that of the first (if).1

(2) Mathematically expressed : pf : pf = u : //.'.

But if pf= nf, substitute the value in the second equation ;

(3) nf :pf = ;i:!>.';

assume the medium M to have an index of refraction ju= 1.

(4) nf :pf=l ://.

(5) pf = nf Xfi';

or, more concisely,

C5') p=u'n.

(Seep and n in Fig. 251.)

This derived property of construction merits a separate formu-
lation.

(in) The distance from the second principal focus to the princi-
pal point equals the product of the distance from that focus to
nodal point multiplied by the index of refraction of the second
medium (p=;/.'n) ; or using values / and f and r for the first and
second principal foci and the radius, the law may be thus formu-
lated : the first principal focal distance plus the radius of curva-
ture equal the product of the second principal focal distance
multiplied bv the index of refraction of the second medium

(/+>■ =./V\ .

Note in addition the following facts regarding the effect of such

a dioptric system upon light.

'Refraction and Accommodation of the Eye. — Landolt, p. 85.

COMPARATIVE PHYSIOLOGY OF VISION.

-±93

1st. The ray rs meeting the spherical surface perpendicularly,
will not be refracted at s, but will pass on through the nodal point.

2d. The ray r's', parallel to the principal axis in the first
medium is refracted at the spherical surface and cuts the principal
axis at/', — it passes through the second principal focus.

3d. The ray r' V, cutting the principal axis at / in the first
medium (31), is refracted at g" and traverses the second medium
parallel to the principal axis.1

2. COMPARATIVE PHYSIOLOGY OF VISION.

The most primitive manifestation of sensitiveness to light is that
manifested by most unicellular organisms. Most protophyta gather
upon the best illuminated side of an aquarium.
Most multicellular alga? show sensitiveness to
light either by movements of the plant as a whole
or by movements of the chlorophyll grains with-
in the plant cell. One can recall various ex-
ample- of light stimulation — heliotropism — in
higher plants. But plants have no specialized
organs responsive to light ; simply primordial
protoplasm and the green pigment chlorophyll.

Many protozoa show a sensitiveness to light.
Pelamyxa and Pleuronema, amoeba-like ani-
mals, both contract all pseudopodia when light
falls upon them. If one side of an aquarium
is in deep shade these protozoa present in the
aquarium will always be found there.

Many nrfenterata possess eye-spots which
must be recognized as the most primitive organ
of vision. The eye spots are simply patches
of pigment which are more sensitive to light
than is protoplasm generally.

Echinoderma possess these primitive eyes in a
very simple form. The eye spots at the end of a
starfish's arms consist of a group of little in vagi-
Dated pit-, the cells of which are developed from
a red pigment, and arc in communication with
the nerve-ring through special sensory nerve-
fibers.

Turbellariana (vermes) have eyes in which the pigment-contain-
ing cells arc differentiated from the sensitive cells. Some of these

'Problems: i. Construct the image of a line whose central point is in the
principal axil at a distance (d) from the nodal point.

ii. Given the Length ol the object (A) at the distance (d) to determine the
length of the image I t) in terms <>i' \ <i, and/ (the focal distance).

in. 'liven >, d, r, /and u (the index of refraction) to determine the Length of
tin- image in terms of \ d, f* and /-.

Part of the compound
eye of Phryganea, an
anthropod. i'he retinal
cells are Been t" be
united Into a retinula,
/•, which is differentiated
into a rhabdom, m, pos-
teriorly ; ■■, <-, crystalline
cone ; ./, facet of com-
pound eye; /<</, pigment,
( From Bell after Gre-

NOCHEB.)

494

SENSATION: VISION.

Fig. 253.

low worms have several hundred eyes, but the higher worms are
represented by the pqlychaetae, which have a pair in each segment,
each eye having a lens, a gelatinous vitreous humor, a layer of
rods and a layer of pigment. The common earthworm is blind.
The molluscs which are not blind have more primitive eyes than
the higher worms. The cephalopod mollusc, however, has a
highly developed eye, comprising a cornea, a lens, a ciliary body,
a retina with internal and external layers, a pigment layer (cho-
roid), an optic nerve. The eye is subspherical in shape and is
protected by spherical fibrous layer- homologous with the sclera
of a vertebrate's eyes.

The arthropoda show a remarkably perfect development in an-
other direction ; in the compound eye. The highest Crustacea

and insecta possess a pair of these eyes,
each having many hundred facets each
with its minute lens (corneal facet), its
pigment sheath and its retinule homol-
ogous to retina of a simple eve. (Fig.
252.)

The vertebraJta all have eyes not very
unlike those of man which may be
taken as a type of vertebrate eye.

3. EMBRYOLOGY OF THE HUMAN
EYE. (Hertwig's Summary.)

1. The lateral walls of the primary
fore-brain vesicle are evag-inated to
form optic vesicles. (Figs. 253 and
254.)

2. The optic vesicles, remain united
by means of a stalk the future optic
nerve, with that part of the primary
fore-brain vesicle which becomes the
Thalamencephalon.

3. The optic vesicle is converted
into the optic cup through the invagi-
nation of its lateral and lower walls by the fundaments of the lens
and the vitreous body.

4. At the place where the lateral wall of the primary optic
vesicle encounters the outer germ-layer, the latter becomes thick-
ened, then depressed into a pit and finally constricted off as a lens.
(Figs. 255, 256 and 257.)

5. The cells of the posterior wall of the lens vesicle grow out
into the lens-fibers, those of the anterior wall become the lens
epithelium. (Figs. 257, 260 and 261.)

Chick. 48 hrs. (Kolliker.)

EMBRYOLOGY OF THE HUMAX EYE.

495

6. The fundament of the lens is enveloped at the time of
its principal growth by a vascular capsule (tunica vasculosa lentis)
which afterwards entirely disappears except as given in 7.

Fig. 254.

Cross-section head of fish embryo. (Bal-
four.)

Fig. 255.

From 48-hour chick. (Mar-
shall.)

7. Its anterior part becomes the transparent anterior part of
the lens capsule. (Fig. 260.)

Fig. 256.

Fig. 257.

Eorizontal-MCtion 54-hour chick. (KOi

I.IKKK.)

■ ■< i Ion 64-hour chick. | M la-
sh U.I,. )

8. The development of the vitreous body is associated with
the formation of the choroid fissure. (Figs. 258 and 259.)

49(3

SENSATION: VISION.

!). The optic capsule has double walls (inner and outer epi-
thelial) which are continuous with each other at the opening of
the cup around the lens and along the choroid fissure. (Figs.
256, 257 and 258.)

Fig. 258.

Fig. 259.

Diagram showing cho-
roid fissure.

Cross-section distal part of optic nerve
13-day rabbit. (Mixot. )

Fig. 260.

,fWW-

10. Mesenehymic cells migrate in between the lens and some-
what closely applied epidermis to form the cornea and.Descemet's
membrane, the latter being separated from tunica vasculosa lentis
by a fissure — anterior chamber (Figs. 260 and 261).

11. The optic cup is differen-
tiated into a posterior part within
which its inner layer becomes
thickened and constitutes the ret-
ina and an anterior part which be-
gins at the ora serrata, becomes
much more reduced in thickness
and extends over the front sur-
face of the lens, growing into the
anterior chamber of the eye until
the originally wide opening of the
cup is reduced relatively to the size
of the pupil.

12. The anterior attenuated por-
tion of the cup is, in turn, divided
into two zones of which the pos-
terior zone becomes folded at the
equator of the lens to form the
ciliary processes, whereas in front

it remains smooth, so that the whole cup three parts may be dis-
tinguished : Retina propria, Pars ciliaris retina?, Pars iridica re-
tina? (Fig. 261).

13. Corresponding to the three portions of the epithelial optic
cup, the adjoining mesenchymal envelope (choroid) takes on some-

Horizontal section 64-day rabbit. I Note
invasion of mesenchyme.) (Kolliker.)

DEVELOPMENT OF THE OPTIC NERVE.

497

what different conditions as : (a) Choroid proper ; (6) Connective
tissue stroma of ciliary body and ciliary muscles ; (c) Connective
tissue stroma of iris and muscles of iris.

Fig. 261.

From section of eye of 13-day chick.

14. The skin surrounding the cornea becomes infolded to form
the upper and lower eyelids and the nictitating membrane (rudi-
mentary in man as the plica semilunaris).

15. The epithelial layers of the edges of the two eyelids grow
together in the last three months of development but become
separated again before birth.

The Development of the Optic Nerve.

L6. That part of the central nervous system between the re-
tinal cup and the thalamencephalon is the fundament of the optic
nerve. Lieberkiihn believed that the nerve-fibers are developed in
loco from lie cells surrounding the hollow stalk. Such fibers would
be homologous to intra-central commissural fibers. He observed
outgrowths from these cells but he did oot trace their course or
history.

17." Bis, Kolliker, \V. M filler and others presented the theory
thai the cells which Lieberkiihn described simply formed support-
ing tissue and that the fibers made their way in from without.

18. His, Kolliker and others believed that the filters origi-
nated in the thalamencephalon and grew outward toward the retina
through optic nerve fundament.

19. W. Midler from observations on petromyzon contended
that the fibers grow inward from sense cells in the retina. Later
he has been joined by Bis, Kiebel, Froriep, Kollikerand Edinger.

32

498

SENSATION: VISION.

I. SUMMARY OF THE ANATOMY AND HISTOLOGY OF

THE EYE.

The following features of the anatomy of the eye arc of special
importance in the discussion of the function oj the organ.

(a) The eye is nearly spherical in form and possesses three
coats : (i) Avery dense strong outer coat, — the sclera, modified
anteriorly into a transparent cornea. (Fig- 262, 2, '■'>. ) ( 1 1 ) A very

Fig. 262.

Horizontal section of the righl eyeball. 1, optic nerve ; '-'. sclerotic coat : :'>, cornea ; 4. canal
ot'Sclilciuiii; .:>, choroid coat ; ii, ciliary muscle ; 7, iris ; 8, crystalline lens ; '.», retina ; 10, hyaloid
membrane; 11, canal of Petit ; 12, vitreous body ; 13, aqueous humor. iDai/ton.)

vascular middle layer — the choroid, pigmented to brownish-black
color internally. Anteriorly this coat has an aperture — the pupil
— and is modified in the region surrounding the pupil into an
opaque pigmented contracting and expanding diaphragm. The
contraction of the pupil is accomplished by circular muscles while
its expansion is brought about by radial muscles, (in) The retinal
cup with its outer layer of pigment cells and its inner cerebro-
neuro-epithelial layer. The retina is modified anteriorly, possess-
ing a ciliary and an irideal portion which line the ciliary body and
iris respectively.

(6) The eyeball is occupied by the principal refractive media of
the eye; (i) The lens just behind the iris ; (n) the aqueous humor
between the lens and the cornea ; (in) the vitreous humor back of
the lens.

AXATOMY OF THE EYE.

49i>

(c) The lens is held in position by the suspensory ligament
whose radiating fibers pass out and come into intimate contact
with the pars ciliaris retina1.

{<J) The ciliary body (Fig. 263) consist essentially of two sets
of muscle fibers : (i) The meridional libers which extend from the
annular tendon (Fig. 26-*), e) backwards gradually merging into the
stroma of the choroid as indicated in the figures ; (n) the annular
fibers which form a ring around the inner margin of the ciliary
body.

Fig. 263.

Section of the ciliary region of the eye iii man. ", meridional muscular fasciculi of the mus-
CUlua ciliaris ; li, deeper-seated radiating fasciculi ; c, C, e, annular plexus ; d, annular muscle
of Miiller ; f, muscular lamina on the posterior surface of the iris ; t/, muscular plexus at the
ciliary border of the iris; e, annular tendon of the musculus ciliaris; h, ligamentum pecti-
natuiii. (After Foster.)

(<) The retina presents an outer layer of black, pigment cells
and an inner layer which represents the end-organ of vision (Fig.
204). The inner layer is subdivided into a neuro-epithelial and
a cerebral layer, (i) The neuro-epithelial layer comprises, besides
a supporting epithelium (not shown in the figure) an epithelium
sensitive to light. These specialized cells remind one strongly of
the lil.i olfactoria. The rods especially present the elements of a
typical neuron : the afferent member (a), the body (b) and the
efferent member (<■). The cones are not very different (see Fig.
264). rii<' efferent member of these epithelial neurons arborize
in the outer reticular layer with the neurons of the cerebral layer.
Like the mitral cells of the olfactory lobe (7. v.) these neurons of*
the second order arborize with several of the epithelial neurons.
iii) The cerebral layer consists of two series of neurons whose cell
bodies form the inner nuclear layer and the ganglion cell layer.
These two -eric- of neuron-, differ slightly as to the disposition of
their parts. Those which conned with the cones arborize with
the ganglion cells in the inner reticular layer; those which con-
neet with the rods arborize :t r< »n n< I the bodie- of the ganglion cells
in the ganglionic layer. The oeuraxons of the ganglion cells
pass along the inner surface of the retina, i. <■., next to the vitreous

humor, to join with the filters making the optic nerve.

51 M t

SENSATION: VISION

( /' ) The eyeball rests in a bony sockel on a bed of iiit. It is
provided with lids, lashes and brows and a lachrymal apparatus
by way of protection ; and with four straight and two oblique

I Qternal limiting membrane ...

\m e-fiber

layer.

i ianglion-cell

layei

< lerebral
layer.

Neuro-
epithelial

laver.

I ir reticular

layer.

I t nuclear

layer.
( luter reticular

layer.

outer nuclear
laver.

Limiting meiu-
brane.

and cones

Pigment layer.

Fig. 264.
V ii n - bodj .

Inner laj er '>i
optic \ esicle.

< Inter layer of
optic vesicle.

I tiagram showing the essential structures of the retina. Note that the upper part of the figure
Ls thai which is next to the vitreous body, or the inner surface of the retina, while the lower
part is the other surface of the retina. (Cajal's figure, somewhat modified.)

muscles to direct it. The straight muscles arc superior, external.
inferior and internal recti. The oblique muscles are the superior
and inferior oblique.

THE PHYSIOLOGY OF VISION.

If the student has mastered the general principles of refraction,
and has familiarized himself with the structure of the eve he is
ready to consider the function of the organ.

Vision comprises two distinct phases of activity : (r) Optical
in which phase the eve as an optical instrument focuses upon the
retina images of objects ; (n) Sensory in which the sensorium is
made conscious of the form and color of the image through the
neuro-epithelial cells — rods and cones — and the two orders of
seii-ni'v neurons.

VISUAL REFRACTION. :><>1

A. VISUAL OPTICS: THE EYE AS AN OPTICAL
INSTRUMENT.

Possessing a lens, with an adjustable focal distance, a dia-
phragm with an adjustable aperture, a pigment lining for absorp-
tion of dispersed light, and a screen for the reception of the
image, the eye must at once be recognized as a typical optical in-
strument. Used as it is for viewing distant objects whose image
is infinitesimal compared with the object, the eye resembles a
telescope. But the adjustable diaphragm in front of the lens, and
the screen for the reception of the image are points which make
it more strongly resemble the photographic camera.

All of the optical instruments consist of two distinct mechan-
isms : (i) a refractive apparatus for focusing the rays of light,
(n) a directive apparatus for directing the axis of the instrument
at the object whose image is to be viewed.

1. VISUAL REFRACTION: THE REFRACTIVE APPARATUS

OF THE EYE.

Before entering upon the consideration of this topic it might be
interesting to note that the mechanical and thermal stimuli of
one's environment are quite unmodified preparatory to their stimu-
lation of the sensory end-organs, and the pressures and tensions
and temperature act directly upon the sense-organs transmitted
practically unmodified through the superficial layers of the cuticle.
The chemical agents, however, which serve to stimulate the sen-
sory nerves of smell and taste must enter into solution before
the end-organs are stimulated. Furthermore the vibrations of
ponderable matter must, be condensed and intensified by the
transmitting apparatus of the ear before they can sufficiently
Btimulate the end-organs of hearing.

Finally the vibrations of the imponderable, luminiferous ether
can only be recognized as lighl by the primitive eye spots of the
coelenterates and echinoderms. Nature has, through the lapse of
the ages, evolved a visual sense-organ which is able to recognize
not only the difference between light and darkness, but also to
perceive the form and color of distant objects. In order to ac-
complish tlii-, pays of light are focused into a clearly defined
image through the refractive apparatus of the eye.

a. Application of the Laws of Refraction to the Mammalian

Eye.

The dissection of an eye reveals several refractive media (cornea,
aqueous bumor, Lens, and vitreous bumor) and several curved
surfaces bounding these media. In determining the focal distance

51 »•_'

SENSATION: VISION.

of a lens one must know the radius of curvature and the refractive
index, [n determining the focal distance of a system of refractive
media and surfaces one must know ( 1 ) the radius of curvature of
each surface, (2) the refractive index of each medium, and (."5) the
location of their cardinal points upon the principal axis of the
system.

The mammalian eve receives it- light through media and sur-
face'-, as indicated in the following :

Media.

[odes of
Refraction.

Surface.

Radius.

1.000
1.3365

Tear Film.

• >\ er \ni. Surf ( lornea.

7.829 nun.

( lornea.

L.3367

\ ni. ( lonieal Surface.

7.829 mm.

Aq. Bumor.

1 ! (6 -

Post Cornea] Surface.

7.829 nun.

Lens.

1.4371

Ant. Surface.

10.0 mm.

Vii. Humor.

1.3365

Post. Surface.

6.0 mm.

This array of media and surfaces would seem to make a problem
too intricate to solve with the means at our disposal. Notice, first
that the tear film and the ant. and post, corneal surfaces have the
same radius of curvature ; i. e., though curved surfaces they are
parallel and form a case under the following theorem : " If a ray
pass from any medium through a denser medium which is hounded

Fig. 265.

I— plus S Cm '

Showing the mathematical features of the reduced eye For detailed explanation of the fig-
text (1), (2) and (3). The figure is multiplied by fiye in its linear dimensions.

by two parallel planes it emerges from the denser medium in a
line parallel to its course before entering that medium." It is
customary at this point to take the anterior surface of the cornea
as the first refractive surface and //. = 1 .3365.

Notice that the index of refraction of the aqueous humor and
vitreous humor are the same. It is now evident that we have to

APPLICATION OF THE LAWS OF REFRACTION. 503

deal with three media (air, aqueous or vitreous humor, and lens),
with three surfaces (ant. corneal surface, ant. and post, lens sur-
face), whose radii are 7.829, (3 and 10 respectively. But even
this great step toward simplifying the problem leaves us with a
Ions; road before us unless we can find a short cut. " It has been
shown mathematically that a complex optical system consisting of
several surfaces and media, centered on a common optical axis,
may be treated as if it consisted of two surfaces only." (Text-
book of Physiology— Foster, 1891— Vol. IV., p. 9.) The loca-
tion of these surfaces and the cardinal points is given as follows
by Landolt :

1. The Normal Eye. — The point /• (Fig. 265) where the prin-
cipal axis cuts the cornea is 22.8237 mm. from the second prin-
cipal focus f (the retina); c, the center of curvature of the cor-
nea ; .s, the point where the optical axis cuts the anterior surface
of the lens, is 3.6 mm. from r, the point where the optical axis
cuts the posterior surface of the lens 7.2 mm. from /• ; I, the cen-
ter of curvature of ant. surface of lens ; /', the center of curva-
ture of posterior surface of lens.

2. The Accurate Mathematical Reduction. — The reduction
referred to in the text above is represented by the two refractive
surfaces with nodal points n and n', radii of 5.215 mm. each and
cutting the optical axis at p and 7/, located 1.7532 mm. and 2.11
mm. respectively from r.

3. The Final Approximate Reduction. — Xote that p is less
than 0.36 mm. from p' . One may assume one nodal /joint N} and
on* refracting surface between the computed ones, cutting the
principal axis at P, and introduce an error too slight to be con-
sidered. But this brings us back to the "simplest possible dioptric
system" already described.

I Taxing reduced the eye to a simple dioptric system and having
familiarized himself* with the optical properties of the simple
dioptric system the student may now profitably consider some of
t 1 1 * - practical applications of the optical properties.

4. The Visual Angle. — The visual angle is the angle which the

object subtends at the nodal point — the angle /■ in Fig. 266.

This angle is measured by it- tangent; for very large angles, i.e.}

when a large object i- viewed at very near range — the tangent

/' x'
should !)<• measured upon the distance d : tangent /■' = — = — ;

the angle v=2 angle '■'. For medium and for small angles

it i- sufficiently exact to use the form : tangenl /•=' = ' . It

i- evident that the object o subtends the same angle as does the
object 0 and it- length measured upon it- distance gives the same
visual angle v \ to be concrete : a cent held Dear enough to the eye

51 » \

SENSATION: VISION.

could obscure :i greal edifice which is some distance away. Helm-
lioltz determined the minimum visual angle to be 50 seconds.
The maximum visual angle for direct and distinct vision is not
great, say 3°— 5°, but varying considerably with different indi-
viduals. The maximum visual angle for indirect vision is very
great — for a white or luminous body 1 xinii- 50°— 60° to the rae-
dian side of the line of vision, 60° above ihe line of vision, 70°
below the line of vision and more than 90c laterally from the
line of vision, or over 150° in the horizontal plane and about
130° in the vertical plane. (See perimeter chart, Fig. 27.*>.)

Fig. 266.

Illustrating the visual mirilr (r) and the relation of the distance (</) to the length of the object
(o ! and image (/). X, the nodal point ; n, the focal distance, the image heing on the retina.

5. The Line of Vision. — Referenee has been made to the line
of vision. This is the line determined by the nodal point of the
eye and the " point of fixation " or the point at which the eye is

Pig. 267.

Illustrating the optical axi- and visual line. Angle a = 5°. F, fovea centralis, or central
pit iif the macula lutea ; O.D., optic disc, or blind spot, marking the entrance of the optic nerve

directed. Within the eye the extended line of vision as just de-
fined meets the retina in the center of the macula lutea, in the
fovea centralis. This line of vision does not lie in the maihemai-

APPLICATION OF THE LAWS OF REFRACTION. 505

iced axis of the cornea, lens or vitreous humor, but crosses the
mathematical-optical axis in the nodal point. It meets the retina
between the fovea and optic disc, and passes through the center of
the cornea while the line of vision passes the cornea to the median
side of the optical axis. The angle between the optical axis and
the line of vision is one of about 5 degrees. (See Fig. 2(>7.)

(>. The Size of the Retinal Image. — Given the distance of
the object (tl) the size of the object (/') and the distance from the
nodal point to the retina (/;) it is very simple to compute the size
of the retinal image (.r) from the equation : x : n = A: d or x =

-t; ii is a constant and equals 1.5677 cm. then x= 1.5677 —. .

Express A and d in centimeters and x will be in centimeters.

To determine the minimum width of the retinal image which is
able to excite the sense of vision, i. c, which the subject is able to
see ; put a black dot 0.2 mm. in diameter upon a white card and
move it away from the eye until it can just be seen. Substituting

1.567 x 0.2

0.2 mm for / in the formula ; x = -4-^ — — r-, gives the diameter

d (in mm.) ' fe

of the smallest visible image.

7. The Optic Disc or Blind Spot. — (a) The Location of the
Blind Spot may be determined as follows (Marriotte's Experi-
ment) : On a white card make a black cross and a circle about
three inches apart. Closing the left eye hold the card vertically
about ten inches from the right eye so as to bring the cross to the
1 1 ft side of the circle. Look steadily at the cross with the right
eye, when both the cross and the circle will be seen. Gradually
bring the card toward the eye, keeping the axis of vision fixed
upon the cross. At a certain distance the circle will disappear,
/'. ' .. when its image falls upon the entrance of the optic nerve. On
bringing the card nearer, the circle reappears, the cross of course
being visible all the time.

(A) Tin: OUTLINE of the Blind Spot may be determined as
follows: Make a cross on the center of a sheet of white paper and
place it on the table about 30 centimeters from the cornea ; close
the left eye and look steadily at the cross with the right eye.
Wrap a penholder in white paper, leaving only the tip of the pen

point projecting; dip the latter in ink, of dip the point of a white
feather in ink, and keeping the head steady and the axis of vision
lived, place the pen point near the cross and gradually move it to

the righl until the black' becomes invisible. Mark this spot.
Carry 'In blackened point -till further outward until it becomes
visible again. Mark this outer limit. These two points give the

OUter and inner limit- of the blind spot. Begin again, moving the
pemil lir-t in an upward, then in a downward direction, in each

case marking where die pencil becomes invisible. If this be done

506 SENSATION: VISION.

in several diameters an outline of the blind spot is obtained, even
little prominences showing the retinal vessels being indicated.

(c) The Size of the Optic Disc may be readily determined by
using the formula given above. Let x equal the long axis of the
disc; d the distance from the nodal point to the sheet of white
paper upon which the map of the white disc was drawn.1

b. Accommodation.

When the normal eye at perfect rest is directed at a distant object
the image is formed upon the retina, i. e., the principal focal dis-
tance of the resting normal eye is 15.077 mm. As long as the
object is sufficiently distant to make the rays of light from any
point of the object practically parallel the image is focused upon
the retina of the normal eye without any change in the dioptric
system of the eye, i. e., with the elements of the dioptric system
in the state of rest. The minimum distance to which an object
may be brought without requiring a readjustment of the elements
of the dioptric system is found to be about 6 m. (20 ft.). In prac-
tical ophthalmology this distance is taken as infinity ( oo) in all
those problems which involve parallelism of the incident rays.

If an object be moved along the optical axis or visual line of a
dioptric system the focus will recede and the distance from the
nodal point to the image will exceed the focal distance, i. e.} the
image would be formed behind the retina. The image can be
seen only when it is focused upon the retina. The eye possesses
the means of adjusting itself to this requirement. The process of
adjustment is called accommodation. When the object is at
infinity — G meters or more — the distance of the image (/ or n)
equals the principal focal distance (/). In the process of ac-
commodation the distance of the image is made to equal /. But

/= r, therefore the distance of the image depends upon the

radius of curvature of the refracting surface and the index of
refraction. To make the distance of the image equal the original
value of/, i. e., to bring the image back to the retina i must be

decreased. The distance of the image li ==. — —I can only be de-
creased by decreasing the radius of curvature or by increasing the
index of refraction ; the last alternative is impossible. The image,
is foamed upon the retina by increasing the radius of curvature of
the crystalline tens. The process of accommodation is the process
of varying the curvature of the crystalline lens.

1 . The Mechanism of Accommodation. — Various ways have

1 This distance equals the distance of the cornea from the paper plus 7 mm.

ACCOMMODATION. 507

been suggested by which the radius of curvature of the lens might

be increased ; the theory now generally accepted is that of Helm-

holtz : '

Fig. 268.

showing the mechanism of accommodation. The horizontally shaded lens and the unshaded

iris show the position of the parts when at rest; the vertically shaded lens and iris show the
position during accommodation for a near point m, meridional muscle; e, circular muscle;
>./... suspensory ligament. (After Landolt.)

(") Tin: Change ix the Lexs is accomplished through the
interaction of two forces: (i) The elasticity of the lens-body;
and (n) the contraction of the ciliary muscles. The lens when
left to itself tends to become more spherical than it is when the
eye is at rest; it tends by its elasticity to take the position V ;
but the elasticity of the choroid coat through its relaxed ciliary
muscles (m) and through its inelastic tendons the "suspensory
Ligaments" (8.L.) exert a still stronger tension in the opposite
direction and the lens is flattened and drawn down to the position
/. All that is necessary to cause the lens to take the position V
or any position between / and V is for the ciliary muscle to con-
tract, thus relaxing the suspensory ligaments and allowing the
l*n- to become by its own elasticity more nearly spherical. There
are two ways of convincing one's self of the increase in convex-
it v of the lens during accommodation.

(d) The direct observation of the change in the lens may be
accomplished by looking from the side at the margin of the iris
when the eye of the subject is at rest, i. e., focused upon a distant
object. Lei the subject suddenly change focus to a very near ob-
ject. The iris at the margin of the pupil will be seen to advance
toward- the cornea— pushed out by the lens. (See Fig. 2(is.)

(ff\ The indirect observation of the change may be accom-
plished by looking diagonally at the subject's eye (Fig. 269, E),
while a light shines upon the eye from position L. The light

1 I'ii-i published in hit Hand-bitch der phyriologfochen Optik. Heidelberg, 1866.
Given in full in the last edition, edited 03 Arthur Komg, Berlin, 1896, pages
130 1 •".<;.

;>< IS

SENSATION: VISION.

will be reflected from the anterior surface of the cornea, from Hm-
anterior surface of the lens, and from the posterior surface of the
lens. When the lens is at rest the images will have to each other

Fig. 269.

Showing the change in the position of the image reflected from the anterior surface of the
crystalline lens. .1. position of images when the eye is at res( (r C) ; l'>, position of images
when the lens is more spherical through accommodation (a — ('); C, a geometrical figure show-
ing the reason for the change in position : K. observer's eye ; /,, candle.

the relation indicated in .1, Fig. 269. If the subject accommo-
dates, the middle image will move over toward the corneal image,
as shown in B-<i, Fig. 269. The geometrical figure shows how
this change is brought about. Utilizing this principle, Helmholtz
contrived an instrument which he called the Phakoscope.

{J>) The Pupil Changes its Position both passively and ac-
tively. Its passive change, as it is pushed out by the bulging lens,
has been referred to above. Its active change may be observed
readily if one looks into the eye of a subject from the front, while
the subject directs his vision to some distant object. Let the sub-
ject then look at a near object and the observer will see the pupil
contract. This contraction is accomplished through the action of
circular irideal muscles. The reason for the contraction of the
pupil is next to seek. One looks at near objects in order to study
their detail of structure ; detail of structure can be brought out in
an image of a dioptric system only when the spherical aberration,
caused by the margins of the lens, is corrected. Work with a mi-
croscope soon impresses the fact that for high magnification (near
vision) clear definition is possible only when the diaphragm ad-
mits rays to the center of the lens exclusively. In the same way
in near vision, the eye, by contracting its pupil (its iris dia-
phragm), brings about a clear definition of the image.

ACCOMMODATION. 509

(a) The most important function of the iris is that which it per-
forms in conjunction with the lens in the act of accommoda-
tion.

ii) The relation of the pupil to accommodation is not the sole
function of the iris. This changeable diaphragm serves also an
important purpose in cutting out an excess of light. Tf one shade
the eyes of a subject and then suddenly allow the light to strike
them, the pupil will be observed to contract through the action of
the circular muscles of the iris. This is a reflex act in response
to the over-stimulation of the retina, the optic nerve acting as a
sensory clement, while the oculo-motorius is the motor element of
the reflex arc.

(y) In this connection it may be added that the iris is an im-
portant clinical index of certain conditions. The sympathetic
nervous system, from the cilio-spinal center supplies the radiating
fibers ; so that anything which profoundly aifects the sympathetic
system will cause a dilatation of the pupil. A strong emotion,
especially fear, causes a dilatation of the pupil. In deep chloro-
form narcosis, or in the last stage of asphyxia, the pupils dilate.
The mydriatic drugs (belladonna, atropia, etc.) cause dilatation.
Paralysis of the oculo-motorius causes dilatation. The pupil con-
tracts normally during sleep, during accommodation and strong
light. When the cervical sympathetic is paralyzed, when a my-
otic drug — as physostigmin orcsarine — is applied locally or opium
taken internally the pupil also contracts.

2. The Range of Accommodation. — This is the amount of
refractive change induced by the eye in adjusting for its point of
nearest vision — punctum proximum — after it has been at rest, i. e.,
after it has beeD adjusted to its point of farthest vision — iie, punc-
tiiui remotum.

(a) To Determine the Punctum Proximum one has only to
record in meters the distance from the cornea to the printed page3
when the subjeel can sec the lines perfectly clearly; that is with-
out noticing any blurring of the letters. Suppose this distance
be 1" cm., then one writes punctum proximum = .01 meter.

b) To Determine the Punctum Remotum let the subject

look at an object six meters away. If lie can make out the de-
tails of the object and can read letters 1 cm. in height and
with Strokes - nun. in width one will credit him with a punctual

remotum of infinity ( x ). If the subject cannot see distant ob-
ject- bring the object nearer until he can see its details of struc-
ture. L.i ii- suppose thai it must be brought to a distance of 50
cm. before the subjeel can make out its details, then one writes
punctum remotum 0.5 m.

(c) To Determine the Range of accommodation. Lei
/.' th< distance of punctum remotum, then the static refraction,

:>1<> SENSATION: VISION.

or the; refraction when the eve is at rest may be represented by r
which is the reciprocal of the distance. (Bonders.)

(" '-ji

When R = oo , r = 0 ; when /' = .5 in., r = 2.
Let P be the distance of the punctum proximum and p the
maximum refraction of the eye.

(n) /> = p

When P = 10 cm.; or .1 m., p = 10.

Representing the range of accommodation by a or — , Donders

A

expressed the range in terms of 73 and 73 thus :

1 1 1

(IH) A = P-R

( ^ PR

(iv) A =

B— P

5 x .1

Substituting P = .5 m. and P = .1 m. we get .1 =

= .125 m. That is, the accommodation is equal to a lens

whose focal distance is .125 m. or m. But that is an X diop-

tre lens.1 Substituting R = x and P = ,1m. we get A = —

which is indeterminate. In order to avoid this complication and
to simplify the process ophthalmologists use the simple equation :

(V) a = p — r.

Substituting p = 101) and r = 2D one gets a = SI) instead of
.125 m. Using the formula one avoids the difficulty noted above
in the use of Donders' formula ; e. g.} take P = oo and P =

1 Lenses are now almost universally numbered according to the metric system.
A lens with a focal distance of 1 m. is called a 1 dioptre lens or 1 _D. A lens of
50 cm. or •' m. is called a 2 I> lens and so on. ^ m. corresponding to 3D, \ m. to
4J), jm. "to 5 1), I m. to 8 D, fa m. to 10 I), 2 m. to \ D or .5 D, 4 m. to .25 D,
8 m. to .125 I), etc.

AO'QMMODATIOy.

511

.1 m., then r = OD and p = 10D. a = _p — r = 107)— OD
= 10 dioptres of accommodation. Now in certain eases (see
Hvpermetropia) the pnnetnm remotum is beyond infinity (!).

If the punctum remotum is "beyond infinity " that is equivalent
to saying that the eye at rest does not focus parallel lines (from
infinity) upon the retina, but the lines must be more than parallel,
/. ... from beyond infinity ; or, better, convergent; but if they are
convergent they would meet behind the cornea. The punctum
remotum for hyperopes is then negative in direction and is equal
to the distance, beyond the cornea, at which the convergent lines

would meet if prolonged. It follows that p is in the case of

hyperopes negative. Our formula (3) would take the form :

(:»').

1

T

(-*)-*

P + K

Therefore formula (5) becomes (5') a = p + r. Now, in deter-
mining /• one may use a convex lens of such strength as to give

Fig. 270.

Age 10 13 20 23 30 33 iO 43 30 33 CO 03 TO 73 SO

p=14

?~ «
V

- •

•^ a

=: s

'•ZZ 7

S o

5

3 i

Q

h

^ 2

o" '

=: -/

-3
-i

-■;

N*

\

\fl

>v

'%

*SJ«S

^

<^/

^,

Lot-

it in n

Of functu

m n>

inutu

m.

"

- ihowingtbe Influence of age upon the location of the punctum proxlmum and tin
punctum remotum, and upon the range of accommodation. (After Landolt.)

the raya the requisite convergence. The value of the lena in
dioptres i-, of course, the \ ;i 1 1 1<- of r. [n the hyperope a is always
greater than p. A- Hie determination <>!' the punctum remotum

512 SENSATION: VISION.

of the byperotic eye is a matter for the clinician to deal with, we
will omit its determination here.

('/) 'I'm-: I Ni-'Lri-:Ncr. of Age upon the range of accommoda-
tion is well shown in the accompanying chart (Fig. 270). The
average 10-year-old boy or girl has a range of (a=p — r) 14
dioptres. At '25 years the range has decreased through a reces-
sion of the punctum proximum t< > (a = p — r=8 — 0) 8 D.
At 4-"> years it is :} J); at 50 years, 2 P: at <;<» year.-,
1 />. Note that the punctum remotnm begins to recede at
50 to 55 years and at 60 years, jp = + .5 and r=— .5, so that
a=.5_(_.5)=l D.

e. Imperfections of the Refractive Apparatus of the Eye.

It will be remembered that the sole function of the eye as a re-
fractive apparatus is to focus rays from any object, near or far,
upon the retina ; that when the accommodative (focusing) ap-
paratus is at rest the image of an object 6 m. or more distant is
formed upon the retina in the normal eye (/=■£). The distance
of the image depends, then, upon the value of /. But the
principal focal distance depends in turn upon the radius of curva-
ture, the index of refraction and the location on the optical axis
of the elements of the dioptric system. In the nature of the case
the index of refraction cannot change perceptibly. In the prin-
cipal imperfections of the refractive apparatus of the eye the posi-
tion of the elements of the dioptric system upon the optical ap-
paratus is faulty. If the screen (retina) is too far back the rays
will come to a focus before reaching the retina. The subject will
attempt to correct the difficulty by bringing the object near to the
eve, thus increasing the conjugate focal distance until the image
falls upon the retina. This bringing of the object near to the eye
is a sign of a condition of the eye, which has, in consequence,
been called "near-sightedness." The oculists call this condition
myopia, and correct it by placing before the eyes concave or
divergent lenses which enable the subject to see distant objects.

The retina may be too close to the nodal point; that is, the
eyeball may be flattened in the antero-posterior diameter. In that
case rays of light from a distant object would not be brought to
a focus by the time they reach the retina. The subject will at-
tempt to correct the difficulty by bringing into action the accom-
modative apparatus of the eye thus bringing the focus nearer to
the nodal point until it falls upon the retina and the object is
clearly seen. This condition is called far-sightedness or hyper-
rnetropia. The oculists correct it by placing before the eyes
convex or convergent lenses which enable the subject to see dis-
tant objects without the help of accommodation.

MONOCULAR FIXATION. 513

The radius of curvature of the cornea may be different in
different planes. If the radius is shorter in the horizontal than in
the vertical plane the rays which lie in that plane will be focused
nearer to the nodal point than will those which lie in the vertical
plane. It must be evident that the eye would, under such condi-
tions, be quite unable to focus both horizontal and vertical lines
at the same time. Bringing the object nearer does not relieve the
subject; using the accommodation does not help the condition.1
The most effective way of relieving the condition without arti-
ficial means is for the subject to bring the eyelids very close to-
gether leaving only a narrow horizontal slit. In this way all of
the rays are cut out except those in one plane and if these do not
fall upon the retina when the eye is at rest the subject may bring
the object nearer to the eye or may use the accommodation.' This
condition of the eye is called, by the oculists, astigmat'mn and it is
corrected by placing before the eyes plano-convex cylindrical
lenses which increase the curvature of the refracting surface in one
plane only. It is only necessary to adjust the axis of the cylinder
at such an angle as to increase the curvature in the plane where
it is smallest (or decrease it through the use of plano-concave
cylinders in the plane where it is greatest) to put the dioptric sys-
tem into approximately perfect condition.

2. VISUAL MECHANICS.

As the telescope or the camera must be provided with a directive
apparatus, by means of which the direction of its optical axis
may be changed so the eye is provided with an apparatus for
changing the direction of the line of vision. In directing the
vision from one point or object to another the axis of the eye is
turned upward, or downward, or outward, or inward, or is cir-
cumducted, in short, the axis of the eye has an absolutely uni-
versal motion within its limits.

a. Monocular Fixation.

The term monocular fixation i- used to designate the mechanical
adjustment of the eye to bring the image of the object upon the
macula lute;,, the most sensitive portion of the retina. If one
study the movements of one eye (the other being shaded) lie will
find th.it it readily follows the movements of an object held in
front of it, however, quickly or through whatever angles or direc-
tions it may be moved by the observer. The directive apparatus
of the eye consists of the sis muscles mimed in the anatomical in-
troduction moving the eye about three different axes of rotation :

'I' !■ held by some ophthalmologists, however, I hat a modified accommodative
bcI may contract the ciliary muscles in one plane more than in another and thus
correel or at Lead partially correct the condition.

.">14 SENSATION: VISION.

;i A horizontal axis about which the eye rotates upward and
downward ; (n) a vertical axis about which the eye rotates from
right to left; and (in) a Longitudinal axis which coincides practic-
ally with the physiological axis or line of vision :ni<l about which
the eye rotates (slightly) when the oblique muscles are in action.
These three axes are rather arbitrarily located. Inasmuch as the
eye is a spherical body resting in a hollow spherical socket, and
inasmuch as it rotates freely in any direction about the intersec-
tion of the three assumed axes it is somewhat simpler to take a cen-
tral point of rotation about which the eye may rotate in any direc-
tion whatsoever under the action of one or more of its six muscles.

Fig. 271.

M

Superior
j Rectus
■7\ i 3 )
Inferior I )

Oblique ^ /

Internal
- — > -<-
Rectus( s)

R <3J x-

Diagram to illustrate the directions toward which the optical axis is directed or inclined by
ili' contraction of the individual muscles. MM' \- the median line ; R, the right eye, and /.
the left one. The numbers in parenthesis (3, 4 and 6), indicate the innervation of the muscle.
(After Waller, j

Waller's excellent diagram (Fig. 271) given in the accompanying
figure, will enable the student to interpret the mechanism of the
directive power of the eye. Take, for example, the movement of
the optical axis of the right eye outward or away from the median
line in the horizontal plane. This movement is accomplished
by the external rectus innervated by the sixth nerve. Again take
the movement of the axis of the eye upward in the vertical plane.
It is evident that the superior rectus alone cannot accomplish
tli is ; but that that muscle must act in conjunction with the in-
ferior oblique. In a similar manner movement vertically down-
ward requires the combined action of the inferior rectus and the
superior oblique.

In general the contraction of a single muscle causes a rotation
of the eye in the direction indicated in the diagram for that mus-
cle ; while rotation in any other direction than the six which are
indicated by the arrows requires the interaction of the two mus-
cles, and frequently the coordinative influence of two nerves. To

BISOt. ri.Ai: FIX A TIOX.

515

circumduct the eye, sweeping its axis around a circle requires the
action of all of the muscles, acting two or three at a time;
an action the exactness of adjustment and the complexity of co-
ordination of which must compel the admiration of any student
of mechanics.

b. Binocular Fixation.

This expression is used to designate the coordinated binocu-
lar movement which results in directing the physiological axes
of both eyes upon the same object. If the object fixed by
both eyes be a small one its image falls upon the fovea centralis ;
if it be a large one it will be disposed about that point symmetric-
ally as shown in Fig. 272.

The lower part of the ob- Fig. 272.

ject being focused upon the
upper segment of the two
retin;e, and the right part
of the object being focused
upon the left part of the
two retiiur, that is upon
the median segment of the
right retina and the ex-
ternal segment of the left
retina.

It is evident that we
have to deal with a com-
plex mechanical action :
( i j With double monocular
fixation ; and (il) with con-
vergence of the visual axes

of the eyes. If one refers

to Waller'- diagram he can
readily tabulate the muscles
involved in directing the
two eye- in any particular
direction. If in Fig. 'l~'l
the object 0 move toward

the right eye along the
visual axis ONF the fixa-
tion of the right <■}<• will
not need t<» be readjusted.
I f however the visual axis
of the lefl eye ONF' fol-
low- the movement of the object it will have to deflect to the right,
dm- making a greater angle (AF'Om) with the median line(mm/)

in 1 1 . . w i m u the symmetrical correspondence
of the retina] field] V, nodal point; /•'. fovea cen-
tralis. The observer la supposed to be looking down

H i the optical apparatus from above. Note thai the

line CD. which Is on the lower side of the object, is the

(deol the im^''. Lnd that the line BD, which

i- the righl tide of the object, is the left side of the

Image, which iirin^- II al the Inner teg i of the

right retina and the outer Begmenl of the left retina,

516 'SENSATION: I'/x/o.v.

than existed before. This increase of the angle of convergence is
brought about by the internal rectus. If through weakness or
through paralysis this muscle is unable to rotate the eye far
enough to bring the points 0, X', and /•'' into a straighl line then
the retinal image would not fall upon the field [af b' c' df) and
there would be a double visual sensation. " double- vision " or di-
plopia. Failure for any other reason to produce perfect binocu-
lar fixation leads to the same derangement of vision. This is the
principal — though not especially frequent — imperfection of the
directive or mechanical apparatus of the organ of vision and is
often corrected by oculists through the use of prismatic lenses
which bend the optical axis bringing the image upon the proper
field of the retina.

B. VISUAL SENSATION.

THE EYE AS THE SENSE-ORGAN OF VISION.

The retina is the end-organ of vision ; its function is to receive
the impression of the image focused upon its surface by the
optical apparatus and to transmit the impression to the brain.
About all that can be said is that the lights, shades and colors of
the retinal image start in the neuro-epithelial cells metabolic
changes which arc influenced more or less by the action of the
light upon the pigments in the associated tissues. The neuro-
epithelial cells are composed of an afferent element represented by
the cones or rods of the external layer of the retina that is the
scene of the metabolic changes referred to above. The chemical
changes start, along the afferent element (dendrite) toward the
cell body, an impulse which is transmitted by the efferent element
(neurite) to the first neuron of the cerebral layer of the retina,
thence by the second neuron to the sensorium of the brain.

The phases of visual sensation which seem most profitable to
briefly discuss are retinal stimulation, retinal irritability, and
visual sensations.

1. RETINAL STIMULATION.

a. The Stimuli.

(a ) The Kinds of Stimuli which lead to visual sensation are
limited normally to : (i) diffuse light in its various colors and to
(ii) images of objects. In either case the stimulus is light, but it
seems expedient in view of what is to follow to differentiate be-
tween the light in general and images of objects. The retina, in
common with all highly specialized tissues responds to all stimuli

THE IRRITABILITY OF THE RETINA. 517

with the same general sensation. If one press upon the side of
the eyeball a ring of light will be seen upon the opposite segment
of the retina. The retina is stimulated under the finger but it is
referred to the opposite side. When a mechanical shock to the
head make- one " see stars " these luminaries are real sensations
due to the mechanical stimulus. Electricity may also produce the
sensation of light.

Light being a mode of undnlatory motion it may vary in two
ways : (i) In the number of vibrations per unit time, (n) in the
amplitude of the vibrations. The first variation is comparable
to the variation in the pitch of sound and leads to the color scale,
the second variation is comparable to loudness and is recognized
in the intensity of the sensation.

(b) The Duration of the Stimulus may be very short. An
electric spark whose duration is less than a millionth of a second
is long enough to produce a sensation (Waller). The sensation
which a stimulus calls forth is of much longer duration than the
stimulus itself. This is made evident when one looks at a rapidly
rotating wheel ; a spoke occupies a particular position for only an
infinitesimal fraction of time, yet it calls forth a sensation. In
the position which the spoke takes during the next infinitesimal
unit of time another sensation is induced ; but the sensation of the
previous stimulus persists and the two sensations blend. The re-
sult of this blending of the images of the rotating spokes is to
produce the effect of a solid wheel. In a similar way if a lumi-
nous body be attached to the rim of the rotating wheel the sensa-
tion which it produces will not he a point of light, but a more or
less elongated line of light. The faster the rotation of the wheel
the longer the arc of light until finally the speed of the rotation
may be great enough to extend the line of light around the whole
circumference of the circle in :I solid ring of light. Charpentier
says that an interval of 0.027 second must elapse between two
Bashes of light in order that both can be seen separately.

I). The Irritability of the Retina.

1. Factors Involved in Retinal Irritability. — (a) Tin-:
Structure of the Retina hears an important relation to its
irritability. The two kinds of ueuro-epithelial cells — the pods

and the con* are not equally distributed over the retina. There

are no rods in the macula lutea ; this portion of the retina pos-
-,.--,._ the cone- only. The macula 1 1 1 1 < •: i i> especially sensitive
to th<- fine line- of images focused upon it ; i. <■., it is the only
portion of the retina from which one may receive a clearly-defined
image. Thai portion of the retina outside of the macula Lutea is
only faintly sensitive to form, hut i- very sensitive to light and

518 SENSATION: VISION.

responds to very slight modifications in the intensity of the stim-
ulus.

(6) The Retinal Pigments bear some relation to the irrita-
bility of the retina. Melanin or fuscin is the brownish-black
pigment which makes up the pigment layer of the retina. This
pigment seems to form a stuck from which other pigments may be
replenished. Rhodopsin, or " visual purple," is found in the rods
and is, therefore, absent from the macula lutea. Chromophanes
are red, green and yellow oil globules found in the cones. The
chromophanes are not. found in the eyes of mammals.

(c) Varying Irritability of Different Areas of the ret-
ina is probably due to varying distribution of the rods, cones and
pigments. The following facts are important in this connection :
(i) The macula lutea is the area of clearest definition of form; it
is in fact the only area sensitive to the fine structural details of an
image. (II) The macula lutea possesses cones, but no rods, and in
its most sensitive area — the fovea centralis — the cones are brought
into special prominence by the thinning out of all the other ele-
ments, (in) The portion of the retina most sensitive to variations
of the intensity of diffused light is that portion outside of the
macula, (iv) The portion of the retina outside of the macula is
richly studded with rods, and each rod possesses its supply of rho-
dopsin. (v) A solution of rhodopsin bleaches in the light. The
retinal image may be actually "fixed" by treating with 4 per
cent, solution of potassium alum, the retina which has just been re-
moved immediately after thorough exposure following rest in the
darkness. The "fixed" image is called an optogram.

These facts seem to justify the conclusion that the cones are tJte
structure* which receive form-pictures and the pigmented rods are the
sfrite fit re* which receive light and color impressions.

2. Direct and Indirect Vision. — These terms designate
respectively the central field of clear definition and the sur-
rounding field of indistinct definition. One may get a very
good idea of the difference between direct and indirect vision
by holding before one eye (the other being shaded) at a dis-
tance of 30 cm. a printed page. Direct the line of vision at a
small word ; the surrounding words will be recognized for a
distance of perhaps 2 cm. in any direction, but by studying the
sensation very carefully, keeping one particular letter constantly
fixed in the line of vision, that one letter is the only letter upon
the page that is absolutely clearly defined. The image of that
letter lies upon the center of the fovea centralis, the two adjacent
letters lie upon the slanting sides of the fovea, their definition is
only slightly less distinct than that of the central letter. The
form of the next adjacent words can be made out with sufficient
clearness to enable the observer to say definitely what the words

THE IRRITABILITY OF THE RETINA.

519

are but he would be quite unable to detect any slight typographical
imperfections in the words. The field of direct vision may be
taken bo be that which is focused upon the macula lutea which is
1.25 mm. in diameter, subtending about 5° of angle at the nodal
point.

(k) Indirect Monoculae Vision. — The field of indirect
vision includes all of the visual field outside of that of direct
vision. The accompanying figure (Fig. 273) shows the field
of indirect vision for white light bounded by the shaded por-
tions of the figure. Xote in the center the 5° circle of direct
vision within which the form and structural features of ob-
jects are clearly defined. Xote the blind spot (i>) at the right
of the macula in the figure, and showing that the optic nerve
enters the eye to the median side of the fovea located from 12.5°
to 17.5° from the center and a little above the horizontal line

Fig. 273.

j. 1 1

Perimeter chart with tracings. (Ebapart.)

from the fovea. Note that the boundary of tin; field for the in-
direct vision of the white lighi crosses the upper vertical meridian
at 55 ( the median meridian at (id , the lower vertical meridian

at 7" and t he external meridian beyond 90°. The determination
of i be line bounding the Held of vision is called perimetry) t he record
and the instrument used in getting it, n 'perimeter. The field for

520 SENSATION: VISION.

yellow lighl is within thai for white, the field for blue light is
within that for yellow, the Held fur red light .-till further with-
drawn from the periphery, and the field for green very much
smaller than that for red. Perimetry has considerable clinical
importance because in certain pathological conditions the perim-
eters are considerably modified either by being generally con-
tracted orby being dotted with islands of total or partial blindness.
(6) Indirect Binoculab Vision. — To determine just what
the field of indirect binocular vision is one has only to find the
overlapping areas of indirect monocular vision when both eyes are
directed to the same point. The accompanying figure ( Fig. 'l~'-\) is
for the right eye. If one trace upon the same chart the field sen-
sitive to white light in the left eye the open external end of the
field will extend off to the left and the circular median end to the
right reaching the 00° circle. The right and left perimeters will
thus overlap in an almost circular area hounded right and left by
the GO0 circle, above by the 55° circle and below by the 70°
circle. The field thus hounded is that for binocular indirect
vision for white light.

2. VISUAL SENSATIONS.

a. Fundamental Sensations.

The sensations which light induces in the sensorium may not be
so easily differentiated as are those of sound, but they are closely
analogous to sound. In sound we differentiate pitch, loudness
and quality, dependent respectively upon number of vibrations
per unit of time, upon the amplitude of the vibrations, and upon
combinations of overtones ; in light we differentiate eolor, intensity,
and form dependent respectively upon number of vibrations per
unit time, upon the amplitude of the vibrations and upon combi-
nations of intensities (lights and shadows).

1. Form. — The sensation of detail in structure is clearest at
the fovea centralis and decreases progressively in every direction
from that point in the retina. That this specialization of form-
sensation is in some way connected with the fact that, of the rods
and cones, cones only arc present in the macula and these are
brought into special prominence in the fovea, has been suggested
above. But the color sensation is also induced by stimulation of
the fovea, though Kiihue and others show that differentiation of
color is less acute at the fovea than in area outside of it.

2. Intensity. — Intensity depends upon the amplitude of the
vibration of the medium which last transmits the light to the eye.
As in the case of intensity of sound this may depend upon the

1 IS UAL SENSA TIOXS.

521

amplitude of vibration of the sonorous or the luminiferous body,
or upon the summation of the effects of several vibrating bodies.
The sound produced by two sonorous bodies of the same pitch
and amplitude will be more intense because of the summation of
the undulations; in the same way the light produced by two can-
dles will be more intense than that produced by one.

The sensation induced bv lights of varying intensity is not com-
mensurate with the intensity, but obeys Weber's law of sensation :
"The smallest change in the magnitude of a stimulus, which one
can appreciate through a change in one's sensation always bears the
game proportion to the whole magnitude of the stimulus. (As
formulated by Foster.) Applied to vision, the proportion is 1 to
1»m i, that is, 0.1 candle-power added to or subtracted from a 10-
candle-power light, 1 candle added to or subtracted from a 100-
eandle-power light, and 10 candles in a 1000-candle -power light
can be detected, and so on.

3. Color. — Color depends upon the number of vibrations of
a luminous body ; as pitch depends upon the number of vibra-
tion-of a sonorous body. The white light that comes from the
sun may be readily decomposed into a number of principal colors
and an innumerable number of intermediate mixtures. The prin-
cipal colors have the following rate of vibration : Red, 392 tril-
lions of vibrations per second; orange, 532 trillions; yellow, 563
trillions; green, 607 trillions; blue, 653 trillions; indigo, 676
trillions ; violet, 757 trillions. These vibrations range in wave-
lengths from 766 millionths of a millimeter to about half of that

Fig. 274.

( ' Grecni*h-bhu: )
i pan 1 1

(On • nisk-yeUow)
Yellow

Indigo

Orange

i teometrical color table.

length. The colore named above are the principal or the clearly
pronounced colors of the spectrum ; from three of these all other
colors may be produced, these three are the fundamental or pri-
mary colors: red, green, violet. The accompanying figure (Fig.
27 1) -how- graphically the relation which these colors bear to

522 SENSATION: VISION.

each other. Not only does a combination of nil of the colors pro-
duce while, lint n combination of certain of the colors to pairs

produces white ; these pairs are called complementary colors : (i)
red and greenish blue ; (n) yellow and indigo; (in) orange and
evan blue; (iv) violet and greenish-yellow.

Plow the different colors can stimulate the retina has Keen the
subject of considerable controversy.

(a) The Young-Helmholtz Theory, assumes that there are
in the retina three different kinds of sensory elements which re-
spond to the three different primary colors, — red, green and violet,
— and that "every color of tlic spectrum excites all of the elements,
.some of them feebly, others strongly" (Landois). The perception of
color is then a resultant of the combined sensations brought to the
sensorium by the three sets of elements.

(6) The Hering Theory is based upon the prineiples of
metabolism and upon the color-law of Grassman : "If two simple
but non-complementary spectral colors be mixed with each other
they give rise to the color-sensation which may be represented by
a color lying in the spectrum between both and mixed with a cer-
tain quantity of white ;" i. e., every color sensation except those
of the primary colors may be produced by a color of the spectrum
plus white. Hering assumes : (i) That light produces metabolism
in the retina; (n) that the metabolic processes are in part anabolic
and in part katabolic ; (in) that white, red, and yellow sensations
are katabolic, i. e., accompanied by disintegration and fatigue ;
and that black, green, and blue sensations are anabolic, i. e., ac-
companied by integration and rest; (iv) these metabolic processes
are assumed to be paired ; i. e., white and black sensations affect
the same visual substance in opposite directions ; red and green
stimulate another visual substance ; and yellow and blue stimulate
a third. Now according to Grassman's law' of color sensation :
Any color sensation, except that of a primary color, may be pro-
duced by a color of the spectrum plus white. Hering assumes
that white visual substance is katabolizcd not only when one sees
white but incidentally in all color sensations except primary ones.

(c) The Franklin Theory is not antagonistic to either of
the foregoing, but rather supplementary. It is based upon the
facts of comparative physiology, and assumes that the rudimen-
tary eye distinguishes between light and dark only and possesses
neither form nor color senses ; so that the fundamental point of
departure is a sensation of simple light or dark (Hering's white
and black sensation) produced by stimulation of a fundamental
" visual gray" which causes an accentuation of either the white or
the black in it, — (presumably by modifications in the metabolism
set up). This theory assumes that the yellow-blue substance was
next developed and the red-green last.

COLOR-BLINDNESS. 523

The adherents of either the Young-Helmholtz or the Hering
theory, especially the latter, may well accept the Franklin theory
as supplementary, as it accounts easily for the fact that red-green
color-blindness is most common, and yellow-blue blindness rather
rare, while inability to see black and white is only found in cases
of congenital, total blindness. Furthermore, reference to the perim-
eter chart shows that white-black covers the largest area of the
retina, yellow-blue an area within that which red-green is smallest
and quite near the center.

b. Secondary Sensations.

1 . After -images. — If one fix the gaze upon a brightly illumi-
nated figure or pattern for 15 seconds and then direct it toward a
plain surface the image of the pattern gazed at will be seen upon
the plain background of the second field of vision. If the after-
image has the same colors as the first it is called a positive after-vm-
ar/c. Positive after-images are usually caused by strong stimuli
of short duration rather than by moderate stimuli of long dura-
tion. If the after-image is in the complementary color of the
original pattern it is called a negative after-image. If one gaze
intently at a green pattern then turn to a red field the pattern ap-
pear- deep red upon the red field. It will also appear red upon
a neutral field. Negative after-images ore <i sign of retinal fatigue.

2. Contrast. — Contrast is the accentuation of a color-sensation
through contiguity or succession of another color, especially a
complementary color. A piece of note-paper may look white
upon a black background, but if it is put upon a really white back-
ground it will be >(H'i\ to be fir from white. In a similar manner
blue or yellow accentuate each other as do red and green. Various
other combinations have this reciprocal effect. If the effect is pro-
duced by looking at the two contrasting colors at the same time
the sensation i^ called simultaneous contrast; if by looking at the
contrasting colors one after another it is called successive contrast.

c Color-Blindness.

Of the male population 4 per cent, or 5 per cent, and of the
female population about 1 per cent, are unable to differentiate cer-
tain colors. Such persons are called "color-blind."

1. Complete Color-blindness. — (Achr atopsy.) Individuals

thus afflicted can distinguish lights and shades but have do color
sense whatever. According to the tiering theory they lack- both
the red-green and the yellow-blue visual substance; according to
the Franklin theory they represent cases of arrested development
of color sense in a condition representing a very primitive con-
dition when only the mental color substance is present.

524 SENSATION: VISION.

2. Yellow-blue Blindness. — In this condition the blue end <>f
the spectrum is absolutely dark ;ui<l the yellow may be more or
less illuminated but void of color. This represents also an arrest
of development ; l>nt this arresl occurs after considerable progress
lias been made.

'.]. Red-green Blindness. — By far the mosl common form of
color blindness, this is assumed l>\ the Franklin theory to repre-
sent the last step in the development of the color sense and, there-
fore, the firsl to fail in case of an arrest of development.

4. Acquired Color-blindness may result from disease of the
retina.

5. Normal Color-blindness exist- in the periphery of the ret-
ina. Passing from without inwards the outermost sensation is
that of white (and black) ; the next that of yellow and blue, fol-
lowed by red and green. (See Perimetry.)

3. VISUAL PERCEPTIONS AND JUDGMENTS.

One may have a sensation of black lines upon a white surface
without perceiving in the lines a letter or word. The retino-cere-
bral apparatus brings to the sensorium of the untutored savage the
same sensations as it does to the sensorium of the scholar. The
savage " senses " a written word upon a page, hut does not perceive
it ; on the other hand, the scholar may " sense " the twigs upon the
forest path without perceiving in their position and condition the
track of an animal. Simple sensation involves nothing higher
than the sensorium. There is no reason to believe that the sen-
sorium brings to the consciousness of different individuals different
sensations. Perception involves cerebration in the interpretation
of sensations. Perception involves previous knowledge or mem-
ory of the same or related sensations. Effectual perception, like
effectual marksmanship, depends upon the man behind the instru-
ment.

Visual perception is the seeing with understanding. Visual
judgments are based upon visual perceptions and represent conclu-
sions reached after comparison of previous perceptions.

a. Acuteness of Vision.

It is frequently necessary to test the acuteness of vision through
a comparison of visual perceptions. An individual whose acute-
ness of vision is in question presents himself to the ophthalmologist
for examination. If the subject is schooled in interpreting dim
and distorted images he may mislead the observer for a few mo-
ments with his acute perception, hut the faulty sensation must
sooner or later reveal itself. The observer will present to the
subject a -eric- of letters in unusual combinations, so that there

VISUAL ESTIMATES. 525

will be no way in which he can get a clue for his judgment to
work upon.

To be more concrete : The acuteness of vision is tested by
reading letters of various heights at various distances. The nor-
mal eye (emmetropic eye) should see clearly at 6 m. — the ocu-
list's infinity — letters which subtend an angle of 5' ; i. c, letters
li cm. in height. At 12 meters the normal eye should distinguish
and name letters which are 2J cm. in height. These letters sub-
tend an angle of 5' — the minimum angle of clear vision. If the
individual can see at (5 m. only what he should see at 12 m., he is

6

credited with : \ ision = 9 ; if he can see at 6 m. what he

6

should see at 30 m., he is credited with : Vision = 0„. If bv

cultivation the visual power has been brought up above the aver-
age bo that he can see at b' m. what the average eve must bring to

•") m. to see, he will be credited with : Vision = «>•

a

The acuteness of vision varies much with the habits and employ-
ment of the individual. Persons employed at fine, close work ac-
quire a microscopic vision ; i. e., ability to see and interpret the
minutest detail of structure. Persons employed in vocations which
require long-distance vision acquire telescopic eyes; i. e., ability to
see and interpret structure of distant objects. Sailors and range-
men possess this ability to a marked degree.

h. Visual Estimates.

1. Estimate of Distance. — This judgment is based upon a
combination of* at least two sensations or perceptions : (r) sensation
of the accommodation required to focus the image of the object upon
tin' retina ; (ii) the sensation of the convergence required to direct
tin' two visual lines at 1 1 1 < - same object in the binocular vision.
These sensations are examples of muscular-sense. One estimates
these muscular efforts instinctively. Upon these instinctive esti-
matee one bases his judgment of the distance of an object. But
other considerations may enter in to assist in the estimate of dis-
tance. For example, a movement of the head or body causes a
displacement of nearer objects in the background formed by more
distinct objects; "in- Learns by experience howmuch this displace-
ment should l»e for given distances : 1 1 : « I bases his judgment ac-
cordingly. The known Bize of an object i- mi important factor in
the estimate of it- distance. In this estimate one instinctively
measures the image and compares it with the image of the same
object ;it ;i -hoit distance.

526 SENSATION: VISION.

c(

2. Estimate of Size. — This judgment is based upon two per-
ptions : (i) the size of the image ; and (n) the distance of the
object. Various other considerations may enter in to modify the
judgment.

The subject of visual illusions belongs more properly to psy-
chology than to physiology and will, therefore, not be discussed

here.

CHAPTER XI.

THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

A. THE NEURON: STRUCTURAL AND FUNCTIONAL UNIT OF THE
NERVOUS SYSTEM.

1. THE STRUCTURE OF THE NEURON.

a. General Description,

h. Types of Neurons.

e. Interrelations of the Neurons.

<J. The Neuronal Cell-body.

e. Tin Dendrites.

f. The Axons.

g. Axonic Collaterals.

2. THE PHYSIOLOGY OF THE NEURON.

a. < 'ellulipetal and < \ llulifugal Messages.
]>. Tin Dynamic Polarity of the Neuron.

c. Changes within the Neuron During Its Activity.

d. Function of the Nerve-fiber.

e. I'n action of End-organs.

f. Effect of Structural Modification upon the Function of the Neuron.

g. Effect of Mutilation upon theNeuron.
h. Post-natal Neuronic Development.

11. CONDUCTION AND REFLEX ACTION: THE PHYSIOLOGY OF
THE SPINAL CORD.

1. THE SPINAL CORD AS A CONDUCTOR OF NERVOUS IM-

PULSES.

a. The Course of Sensory Impulses.
h. The Course of Motob Empulses.

2. THE SPINAL CORD AS A REFLEX CENTER.

n. Keflex Action.

] ; i,i hi rul < Considerations.

(2) Tin Purposeful Character of Reflex Action.

(3) Tin Time Reguiredfor Reflex Action.
| I) Tin Inhibition of Reflex Action.

b. Tin: REFLEXES.

( ] j Sii/n rficial Reflexes,

hi 'ii Reflexes,
('.',) Organic Reflexes.
1 1 i:./.iti,,,i of Reflex Action /« Higher Psychic Phenomena..
r. Tin. Lot \ i ion "i Reflex Centers.
:;. Tin; TROPHIC FUNCTIONS OF Till: SPINAL CORD.
I. Till; PHYSIOLOGY op THE MEDULLA OBLONGATA <>K MYE-
LENCEPHALON.

a. The Medulla \- \ Medium of Conduction,
/,. Tin. Medulla as w Independent Center.

I COORDINATION AND EQ1 [LIBRI1 M; Tin. PHYSIOLOGY OF Tin:
I i i:i i-.i.i.i.i \l oi: METENCEPHALON.

•V_'7

528 THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

1. COORDINATION: ADJUSTMENT OF MUSCULAR A.CTION.

2. EQUILIBRATION: THE MAINTENANCE OF THE EQUILIB-

RIUM.

D, VISION. COORDINATION OF EQUILIBRATION-MOVEMENTS: THE
PHYSIOLOGY OF THE MID-BRAIN OB MESENCEPHALON.

/'. THE PHYSIOLOGY OF THE [NTERBRAIN OB THALAMENCEPHA
LON.

F. CONSCIOUS SENSATION, VOLUNTARY MOTION, INTELLECT: THE
PHYSIOLOGY OF THE CEREBRUM OR PROSENCEPHALON.

1. INTRODUCTORY.

a. The Vasi ilai: Supply OF THE Bbain.

b. The Movements of the Brain.

2. Till". PHYSIOLOGY OF THE CEREBRUM.

a. General Considerations.

b. Localization of Function in the Cerebrum.

(1) Experiments upon Monkeys.

(2) Results of Observations upon Man.
(c) The Higher Cerebral Functions.

THE PHYSIOLOGY OF THE NERVOUS
SYSTEM.1

A. THE NEURON: STRUCTURAL AND FUNCTIONAL
UNIT OF THE NERVOUS SYSTEM.

1. THE STRUCTURE OF THE NEURON.

In the study of the physiology of the nervous system, a definite
comprehension of the neuron is, perhaps, the first requisite. The
older manner of regarding the nervous system a> functioning ac-
cording to it- larger anatomical divisions and their inter-relation-
.-hips, gave place to that which recognized the nerve-cell and the
nerve-fiber as the basal elements of nerve-function ; this idea
has in turn given way to the more exact conception of the neuron
forming the functional unit of this mechanism, which in the
human organism readies its highest development. Only within
the last two decades has investigation enabled us to predicate with

!For the embrvological introduction to this chapter the student is referred to
tin- iliapter on Reproduction and Development of the Embryo, p. 617 et seq.

For general introduction the student is referred to the chapter on General
Physiology, p. 94 et seq.

Furthermore, it is assumed that a study of the anatomy of the nervous system
has been made ; and, therefore, to the largest extent possible it will besought to
avoid entering that field here.

THE STRUCTURE OF THE NEURON.

529

certainty, that all nervous phenomena depend upon the functional
activity of these units, and only within the last ten years have we
learned with definiteness the nearer nature of these units.

(a) General Description. — The term Neuron signifies a nerve-
unit, or a nerve-cell with its processes. Waldeyer first used it in
L891.

Recall from embryology the formation in the impregnated
ovum of three distinct cell-layers, of which the external one, the
epiblast, by a process of dipping in, forms the primitive streak

Fig. 275.

Golgi'l cell— type i. Cell from the optic tract of the cat laterally from the lateral geniculate
body. Radiating from the cell-body are to be Been very many protoplasmic processes which
■bow a broad Wedge of Origin and branch characteristically ; the single axi- cylinder process
n, baa a smooth surface and tolerably even caliber, which is maintained for a considerable difr
tanee from the cell. It gives off a few delicate lateral branches or collaterals, c. 'After Eft -
locks.) lig. 59, referred to above, is also an example of Type i.

or groove This groove sinks still deeper into the subjacent mes-
oblastic layer, it- edges finally rasing to form of it a canal, ex-
tending the length of the embryo, and, eventually separated from
the superficial epiblastic membrane, form- the primitive cerebro-
spinal axis; in this way we remember the epiblastic origin of the
nerve-cell, the neuron. Following a little further, one sees how
tlii- canal, the central canal, with it- epithelial lining develop-, at
the cephalic end, the complex brain, and how the re-t of the tube

develops into the intricate structure of the spinal cord, from which
cerebrospinal axi- there separate oil', in time, isolated foci of
epiblastic cell-, which we later come to recognize a- ganglia, -im-

530 THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

atcd either in close proximity to, or remote from the central axis :
;ind at last, in the fully developed foetus, a minute examination of
the entire nervous system reveals nothing but a complex prolifer-
ation of epiblastic cells, the neurons, with their supporting con-
nective tissue and their blood-supplying vessels. Further, in its
later, fuller development, we discover but a greater wealth of
neurons, to account for the vastly augmented phenomena of nerv-
ous activity in adult life.

The cell-body is of different sizes and shapes in different por-
tions of the nervous system. In the ganglia of the posterior
spinal roots, unipolar cells are found; in the cortex of the brain
there are bipolar cells, and in various parts of the nervous sys-
tem, multipolar cells, as in the motor centers in the cerebral cor-
tex, and in the anterior horns of the spinal cord. (For figure
of a typical neuron, see Fig. 59, p. 95). These cell bodies, of
various shapes and sizes, are made up of protoplasm, contained
within a limiting membrane. This protoplasm presents a delicate
fibrillated structure, the fibrillations seeming to be continuous with
the component fibrils of the axon (see below). Besides the fibrils,
the cell protoplasm is more or less charged with fine dark gran-
ules, the "dark bodies of Nissl." Occupying a fairly central po-
sition in the cell-body is one relatively large nucleus, with a dis-
tinct nucleolus. The cell-bodies are most numerous in the gray
matter of the nervous system, cerebral and cerebellar cortices, ba-
sal ganglia of brain, gray matter of pons, medulla oblongata and
spinal cord, and in the ganglia throughout the body.

The neuroblasts, or embryonic cells from which are developed
the neurons, are isolated oval or pear-shaped cells (His) without
processes. Later, at the end of the cell directed away from the
epiblastic surface, there arises a process, which becomes the axis-
cylinder process, axon, neurite or neuraxon. Subsequently from
''he opposite extremity of the cell-body appears one or several proc-
esses, the dendrites. These, as the name indicates, divide into
numerous branches, like the limbs of a tree, and they increase in
number and in extent, as their function, in its development, be-
comes more and more involved. Embrvologieally then, it will be
seen that both the axon and the dendrites grow out of the cell-
body.

(6) Types of Neurons. — Morphologically, Golgi was able to
distinguish two general types of neurons, which have been generally
adopted, and are spoken of as Grolgi's "cell-type I " and "type II."

"The cell-type i, as described by Golgi, agrees, in the main,
with the general description of a central nerve-cell given by Deit-
ers, being characterized by much-branched protoplasmic processes
(usually multiple) and the single axis-cylinder process. That the
latter was unbranched, however, as Deiters maintained, Golgi de-

THE STRUCTURE OF THE XEUROX.

531

Fig. 276.

nied, and the discovery of side branches (or collaterals) upon the
axis-cylinder processes, first of the pyramidal cells of the cerebral
cortex, and later upon those of the Pnrkinje cells of the cerebellum,
represents an advance of a degree
of importance utterly beyond
Golgi,s conception at that time.

" These side branches given off
bv the axis-cylinder process of
cell-type i, were usually delicate
and exercised a hardly perceptible
influence upon the caliber of the
main fiber, which retained its in-
dividuality at least for a long
distance from the cell. Golgi
noted that these side branches ex-
isted also upon the motor fibers
of the anterior horns (since dis-
pn »ved) and that similar ones were
given off by the fibers of the
white fasciculi of the spinal cord,
whence they ran into the gray
matter."

The distal extremity of the
axon usually breaks up into an
arborization, the single branches
of which are in a relation of con-
tiguity with the dendrites of an-
other neuron, or as in the case of a
peripheral motor neuron, are flat-
tened out on the muscle fibers,

forming the end-plates of the fayer of the cerebellum of a cai aged eight
1 days. (After Van Oehuchten.j

Golgi's cell — type n, Nerve-oell with short
branched axis cylinder from the granular

nerve.

Cell-type n differs from type i, characteristically only in the
branching of the axon. In type n this process begins to divide
very soon after its exit from the cell-body, into a large number
of minute branches, forming a dense arborization, whose main
branch Lb distinguishable only a shorl distance from the cell-body.

Golgi's inference thai cell-type i is motor while cell-type n is
sensory has since been disproved.

(<■) Interrelations of the Neurons. — A point <»t' great impor-
tance, with reference both to the physiology and the pathology of
the nervous system, is the independence of each individual neuron as
regards .ill other neuron-, histologically. Ili- and Fore! were
the first to enunciate this doctrine. It had previously been held
thai the branching processes of neighboring neurone formed a true
net-work, by ;i species of anastomosis, so to speak. Bui Ili-,

532 THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

from embryology, and Forel, from pathological anatomy and ex-
perimental pathology, were able to state the principle of con-
tiguity as explaining the interrelationships of neurons, — a prin-
ciple now generally accepted as true, although future more minute
microscopical investigation may disclose a joining together of* the
ultimate branches of correlated neurons. Within the hist ten
years our knowledge of the structure of neurons has been greatly
enriched by the researches of Ramon y Cajal. He has given us :
(«) Confirmatory evidence of the independence structurally of each
neuron with reference to the rest, the collateral branches from
the axons forming anastomoses no more than the dendrites ; d'i) A
fairly correct idea of the great numbers and significance of these
axonic collaterals ; and (j) A demonstration of the general simi-
larity of structure of the neurons everywhere, notwithstanding the
fact of many minor dissimilarities.

From his study of the axonic collaterals Ramon y Cajal was
able to state that they leave the axon by wedge-shaped buddings,
almost at right angles to it. Such branches in the spinal cord
penetrated deeply into the gray matter and formed free arboriza-
tions among cells there located, coming into relation with their
dendrites. They were met with fairly constantly in the white
tracts of the spinal cord, but are probably not to be found on the
axons constituting the ventral roots of the cord. A peculiar dis-
position of the axons making up the posterior roots was observed.
Here the axon arises from a cell in the ganglion located on the
root, and passes into the posterior part of the cord itself. Upon
entering the cord it divides distinctly into two branches, one as-
cending and one descending, both becoming longitudinal in the
posterior columns of the cord. From them both collaterals pass
horizontally to communicate with cells at various levels in the
gray matter. These collaterals entering the gray matter from the
dorsal tracts are conspicuous features of nearly all cross-sections of
the spinal cord. The same disposition of cranial nerve-fibers,
centripetally directed, was observed by Kolliker. In these suit-
divisions and collaterals of the sensory fibers given off at dif-
ferent levels in the cord and medulla oblongata, doubtless lies the
anatomical explanation of simple and complex reflex actions and
probably also of the simultaneous production of reflex action with
consciousness of the stimulus producing it.

Ramon y Cajal also showed that in all probability Golgi's cell-
type i differs from cell-type II only in the destination of their re-
spective axons, that of the former ending in an arborization at a
considerable distance from the cell-body, while that of the latter
divides up near the cell-body, each being peculiarly adapted to
the function required of it.

In this way is explained the more frequent occurrence of cells

THE STRUCTURE OF THE XEUROX.

533

of type i which are found almost exclusively in paths uniting
more or less distant portions of gray matter, and the finding
of cells of type n only in gray matter, in which are found
numerous cells, with their communications formed by the mi-
nutely branching axis-cylinder processes (dendraxons). Inter-
mediate forms of axonic branching have been described, occurring
in the spinal cord and in the cerebellum.

The more recently introduced methods, methods of staining
nerve-tissue with methylene blue, either intra vitam, as suggested
by Ehrlich, or post mortem, have confirmed largely the results ob-
tained previously by other methods. They have perhaps given
rise to greater uncertainty as to the ultimate anastomosis on the
one hand, or relationship of contact on the other, between associ-
ated neurons. Leaving that point for the future to decide, the
neuronal theory considers the nervous system, aside from its neu-
roglia, blood vessels and lymphatics, as made up of countless indi-
vidual nerve-elements, or neurons. Each of these is a complete
cell, and throughout life it is morphologically, and in a sense also
physiologically, independent of every other neuron, establishing
communication with other neurons only by contiguity, as the leaves
of two trees may touch, without substance actually passing
between them. The axon found in nerve-fiber, like the proto-
plasmic process (dendrite) found in gray matter, forms an integral
part of a nerve-unit, with organic connection somewhere with a
nerve cell, or cell-body. In higher animals, the conduction of
mrvous impulses usually proceeds along several neurons in
our direction, superim-
posed upon each Other, Fig. 277.
forming chains, each neu-
ron of the chain being
in a position to be affected
by, and in its turn to af-
fect, one or several other
neurons. Though vary-
ing in detail of construc-
tion, all neurons show
general similarity of form.

■• 'flic nerve life of the

individual, including all
hi- reflex, instinctive and
volitional activities, is
tin- sum-total of the life of

In- milliard of neurons."

'I. The Neuronal Cell-body. — Neuron*
do single body-cells, possess, like liver-cells or spleen-cells, certain
general cell-characteristics, such a- cytoplasm, nucleus and nu-

constituting as they

534

THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

cleolus, a fad which, however, docs not explain their superiority
in function over other cells. Chemical biology may some day

Fig. ^7s.

Fig.

*. Pigment

<Mm?

indicate the essential dif-
ferences. Within the last
four years, the existence of
a centrosome and centro-
sphere in nerve-cells taken
from lower and higher ani-
mals has proved a still
closer similarity between
them and other cells.
Whether the centrosome
and centrosphere exist for
any more important pur-
pose than to aid in cell-
division, is still doubtful.
It has been demonstrated
that they are found in cells
that have lost all tendency
to divide, which would sug-
gest some further function
presided over by them.

The cell-bodies of neu-
rons vary in size from four to one hundred and thirty-five or more
micro-millimeters in diameter. Many are of characteristic ap-
pearance, as for example, the unipolar cells of the spinal ganglia,

THE STRUCTURE OF THE X EUR OX.

535

the bottle-shaped cells of Purkinje in the cerebellum, and the
pyramidal cells of the cerebral cortex. Among the smaller cells
are the grannies of the bnlbns olfactorius and the small cells of
the cerebellum, while many of the larger ones, as the multipolar
cells of the ventral horns of the cord, and the cerebellar cells of
Purkinje are distinctly visible to the naked eye. Figures 277-
281 show the structure of a neuronal cell-body.

Fig. 2S1.

Figs. 277-281. Neuronal cell-body. J-'itjs. 277 and 278, cells from the anterior horn of a hu-
man spinal cord. Fixed with alcohol and stained with methyl-blue; 279, ganglion-cell fixed
with alcohol and stained with tuematoxylln; 2.S0, ganglion-eel I from anterior horn of foetal
dog. (After an original preparation by Kamox t Cajal.) Prepared with Uolgi's method. 281,
neuroglia. 'Alter an original preparation by Weigakt.) Ni-uroylia-libers blue ; axis-cylinders
Mack. (After an original preparation by NlSSL.) (Figure and description from the author's
translation of Edikgkb's Anatomy qf tJu Central Nervous System.)

(< ) The Dendrites. — The dendrites, or protoplasmic processes,
resemble more closely in appearance the cell-body itself than docs
the axon. Leaving the cell-body by broad thick bases, they di-
vide and subdivide into numerous (jne twigs, which end in free
extremities, and these free ends, as has been stated before, communi-
cate with the branches of other neurons only by entering into con-

tad with the latter. The dendrites of one cell, as well as those of

different cell-, vary in length, and it has also been claimed that,
under certain conditions, a given dendrite may lengthen or shorten,

a theory of vasl importance, if true, as explaining the "making"
and " breaking " of nerve-currents, so to Bpeak. In some cells

on.- dendrite may !"■ greatly developed, while the other- remain

536 THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

small and slender. Enlargements along the course of the den-
drites have been observed, although they may arise from arti-
ficial causes. The dendrites are seldom straight in their course,
usually irregular in direction, in somewhat marked contrast to
the axons. The branching of a dendrite may occur near to or at
some distance from its origin at the cell-body. With some cells
the dendritic tufts cover a surprisingly large area; in others they are
relatively insignificant in extent. Again, from some cell-bodies
the dendrites originate apparently from nearly every point in the
cell-surface, whereas in others, a more or less considerable portion
of this surface is smooth and unbroken. Some cells are called
adendritic, from the apparent absence of dendrites ; but with the
axons of such cells there issue various branches, united at first with
the axons, but soon leaving the latter and dividing in a manner
characteristic of dendrites. They have been variously termed
dendrites and axonic collaterals. The unipolar cells of the
posterior spinal ganglia might be classed under this category,
were it not that in the embryo, these cells are bipolar, and the
two processes are merged into one at or a little before birth.
The single dendrite of these cells is like an axon in so far
as it is a medullated fiber coming from the periphery, whereas
dendrites within the cerebro-spinal axis are devoid of myelin
sheaths, as are the cell-bodies themselves.

The dendrites of certain nerve-cells are further characterized by
numerous minute buds, short lateral branches with clubbed ex-
tremities, to which the name gemmules has been applied. They
appear uniformly on the dendrites of the pyramidal cells and on
those of Purkinje's cells, when treated with nitrate of silver.
They are, in all probability, not artificial products, but their func-
tion has not yet been determined.

(/) The Axons differ in many ways from dendrites : (a) They
leave their respective cell-bodies by narrow wedge-shaped begin-
nings, contrasting with the broad central ends of dendrites. (/3)
The dark bodies of Nissl found in the cell-body and its dendrites,
after treatment with alcohol, are not found in the axon, (y) The
caliber of the axon varies less with its length than does that of
the dendrites from the same cell, and it is usually maintained in-
tact for some distance. This is true, even in the dendraxons of
Golgi's cell-type II. (o) The surface of an axon is smooth, its
contour regular, and it pursues a fairly direct course, though not
always the shortest one to its destination.

The length of an axon varies from a few millimeters to half
the height of an individual. The longest ones are those of the
motor paths, and are usually mona.cons, i. e., they form each the
single axon from their respective cell-bodies. Most neurons are
monaxonic ; those of the posterior spinal ganglia may be called

THE STRUCTURE OF THE NEURON. 537

diaxonic from the division of their axons, soon after entering
the cord (also called schizaxons), while there are found other
nerve-cells giving off several axons, which are hence polyaxonic.
These latter neurons are rare. Ramon y Cajal finds them in the
sympathetic system, notably in Auerbach's and Meissner's plex-
uses. Neurons without axons (aitoxons) arc found in the bulbus
olfactorius, retina, and in the baskets of Purkinje's cerebellar
cells. The distal terminals of axons are usually branched and
free. The branches may form an arborization around a single
cell, or they may spread over a considerable area, thus establish-
ing relationship with dendrites of a large number of neurons.

It perhaps seldom happens that the terminals of a given axon
are in relationship with the dendrites of only one other neuron,
but usually with many others, which explains Cajal's term " ava-
lanche conduction." Among the curious forms of axonic terminals
observed may be mentioned the " climbing fibers " in the cere-
bellar cortex, the " discs " in Meissner's corpuscles and epithelial
surfaces. But it must not be forgotten that many axons terminate
in close contact with the cell-bodies of the secondary neurons,
without the usual intervention of dendrites from the latter.

Axons of Golgi's cell-type I, are usually single and are
generally, but not always, medullated. External to this myelin
sheath is the neurilemma, which is wanting, however, within the
cerebro-spinal axis. (See Fig. 59, p. 95.) The axons in the
sympathetic system are non-medullated, but have a neurilemma.
The medullary sheath, when present, is usually wanting near the
cell-body, and also on the axonic terminals, even when these are
within the central nervous system, or form motor end-plates.

(rj) Axonic Collaterals. — By the aid of its roll ate rah a given axon
<ntcr~ into relationship which many nerve-cells, lying between its
proximal and distal ends, a fact which explains complicated re-
flexes.

The number of collaterals which an axon possesses varies in dif-
ferent parts <>f the nervous system. Some, like those in the ven-
tral horns of the cord, are without collaterals. In general it may
be stated that those axons which course through the cerebro-spinal
axis are provided with collaterals, while those in the peripheral
nervous system are devoid of them, and when present, they are
more numerous along that part of the axon near the cell-body
(cytoproxima] end) than beyond, in the cytodistal part. This
Lead* as to suppose that in the spinal cord more collaterals are in
the column of Burdacb than in that of Goll, which is true ; the
latter fasciculus, made up of the cytodistal portions of axons
which lower down in the cord occupy Bnrdach's column, is prac-
tically free from collaterals. The collaterals ure usually medul-
lated, and terminate in free end.-, forming arborizations.

538 THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

2. THE PHYSIOLOGY OF THE NEURON.

(a) Cellulipetal and Cellulifugal Messages. — Spontaneous
activity is not a property of a nerve-eel] ; hence its function may,
in a sense, be regarded ;is always called forth by some irritation
external to the cell or its branches. This external irritation maybe
transmitted to it through some neighboring neuron or other struc-
ture, or it may arrive from some source more remote. In mon-
axons the impulse passes always away from the cell-body, hence
is cellulifugal. By the splitting of the axon into its terminal
fibers and fibrils is presented a good instance of the law of the
multiplication of effect, as, for example, in the distribution of the
terminal fibrils of a lower motor neuron among the muscle-fibers
of its correlated muscle. Again, the stimulation of a single gan-
glion-cell in the retina is transmitted by its axons to several central
cells in the anterior corpus quadrigeminum, or in the optic lobe.
An apparent exception to, though in reality a confirmation of, the
law of centrifugal function of axons is provided by the optic
nerves, in which certain fibers functionate in a peripheral direc-
tion, their cell-centers, however, from which arise their impulses,
being located in the corpus quadrigeminum. The explanation of
this fact is not clear. It has been demonstrated that there are
in the optic nerve, fibers, the stimulation of which causes contrac-
tion of the corresponding retinal cones. Others have associated
them with the nutrition of the retina. But whatever their
function is, it is exerted in conformity with the general law in a
cellulifugal direction.

How is it with diaxons? In the spinal ganglia both the spinal
and the peripheral processes have the characteristics of a true axis-
cylinder, myelin sheath, terminal arborizations. But one is cel-
lulipetal, the other cellulifugal, in action. Is the peripheral proc-
ess, whose function is cellulipetal, an axon, or is it a transformed
dendrite? Human ontogeny sheds no light on this question, but
a study of the lower vertebrates proves the dendritic nature of
these peripheral branches which, during the process of develop-
ment, have become extended to a great length, and have assumed
the histologic appearance of an axis-cylinder (see Fig. 282). In
some of the invertebrates we find two types of peripheral sensory
neurons, one with its cell-body in the central nervous apparatus,
corresponding to the human type ; the other represented by a cell-
body and its dendrites in the integument, while its axon is directed
centrally. The latter type corresponds to the peripheral nerve-
cells of the human sense-organs and has been called " sense-cell
(Sinneszelle)."

In all these forms of nerve-elements we find the law governing
the reception and transmission of nervous impulses to be the same.

THE PHYSIOLOGY OF THE XEUROX.

539

The cell-body receives the impulse either directly or through
its dendrites, aud transmits it through its neuraxon. We see,
further, that as the dendrites
provide for the reception of
stimuli from a larger field
than that represented by the
cell-body itself, so, in many
instances, is the discharge of
these stimuli also accomplish-
ed over a large tract, through
the medium of the axou.
This occurs not only through
its terminal filaments but by
means of its numerous col-
laterals. In this manner the
peripheral sensory neuron in
vertebrates is in relation with
all the levels of gray matter
lying between its place of
entrance into the spinal cord
and its terminal branching in
the nucleus of the posterior
column to which it passes.

An analogous disposition
of the olfactory neurons has
been demonstrated. In ad-
diti< m to the collateral branch-
es, so-called "lateral" fibrils, given off by the axonic stem be-
fore its sheath commences, are found. Their function is supposed
to be receptive and not emissive, playing an important role in reflex
phenomena. They have been called axodendrites.

(6) The Dynamic Polarity of the Neuron. — The idea of
dynamic polarization given in the foregoing formed the subject of
a heated controversy between different observers, and divided
tin m into two schools. Of these Golgi headed those which denied
the existence of such polarization, basing their opinion on the ex-
istence of globular cells (or adendritic cells) to be found in various
parts of the nervous system. These cells were apparently pro-
vided with a Bingle process, an axis-cylinder. From this they
concluded that the dendrites, when present in a nerve-cell, did
not participate ill it- nervous function, but were trophic organs.

The opposing school, including Van Gehuchten, II. y. Cajal,

von Lenhoss6k, and other.-, insisted on the dendrite- possessing a
Strictly nervous function. They demonstrated in these globular

cells the existence of dendrite- (axodendrites) joining the axis-cyl-
inderand passing with it to join the cell-body. They also pointed

A, sensor)- epithelium of earthworm ; B, of a
snail. Xote that the dendritic portion of the
neuro-epithelial cells (d) is a single branch ex-
tending to the surface of the epithelial layer, and
that the axon, neuraxon or neurite (n) extends
from the cell body to the central nervous system
or to some ganglion. (After Retzius.)

540 THE PHYSIOLOGY OF Till: NERVOUS SYSTEM.

to Golgi's cell-type n, in which the axis-cylinder process arises
from the dendrites instead of from the cell-body, as proof of the
anatomical and functional identity of the protoplasm in the den-
drites and the cell-body. From this, further, they formulated
the doctrine that an adendritie cell in fact could >\\\\ exemplify
the law of dynamic polarization, the cell-body itself receiving
the stimuli directly, and not by any means through the axis-cylin-
der, as contended by Golgi.

(c) Changes Within the Neuron During its Activity. — As to
the molecular movements and chemical changes occurring in the
protoplasm of a neuron (cell-body and dendrites), while they
doubtless present the physical basis of nervous manifestations, we
have learned as yet but little. They are supposed to occur simul-
taneously with the respective phenomena, and to be propagated in
the form of a wave (von Lenhossek).

The conditions necessary to nervous conduction and to auto-
matic activity, or the spontaneous discharge of nervous function, co-
exist in the protoplasm of a neuron ; the substance of the axon is
only an organ of transmission.

Von Lenhossek has maintained that not all dendritiform proc-
esses are dendrites, but that they may be demonstrated at times
to be modified forms of neuraxons. And while this does not com-
bat the law of dynamic polarity, to which he subscribes, he differs
somewhat from others of that school in his idea of what determines
the order and the disposition of the dendrites. They believed
these to be dependent on the functional associations of a neuron.
A"on Lenhossek believes this purpose could be served by fewer
points of contact, and considers some of the dendrites as forming
nutrient processes. A difference in the responsiveness must be
imputed to the different dendrites of a neuron, as necessary to ex-
plain isolated conduction. The neuronal protoplasm is probably
not always nor generally, equally excited by every irritant. One
may regard its qualities of sensitive reaction as so regulated, that
they respond only to certain forms of irritation, just as certain
waves of sound excite vibrations in a cord of corresponding length,
but not in other cords. This " corresponding susceptibility " may
be physically represented by certain states of equilibrium and ar-
rangements of the protoplasmic molecules. It would render un-
necessary the supposition that the production of new associations
in the psychic sphere provokes, as a material accompaniment, the
formation of new dendritic branches, but that existing dendrites,
hitherto idie, would supply the mechanism needed.

((}) Function of the Nerve-fiber. — The term nerve-fiber is
used to designate not an anatomical unit, but one of those cell-
branches which connect the neuronic cell-body with parts located
at considerable distance from that body. The nerve-fiber may be

THE PHYSIOLOGY OF THE NEURON. 541

dendritic, as in sensory nerves, or axonic. As stated above, when
it is dendritic the substance of the nerve-fiber is protoplasmic,
like that <>f the cell-body. But when it is an axon its structure
is more fibrillated — a typical axis-cylinder, and it is rather to this
structure that the term " nerve-fiber" applies. (Figs. 40, 41, 42
and 4:>, p. 70 </ 8eq., show the structure of typical nerve-fibers.)

Histologically, and in this restricted sense, we distinguish two
kinds of nerve-fibers, (a) those which are surrounded by a medul-
lary sheath, and (J3) those which are devoid of such covering.
The physiological importance of this sheath, or of its absence, is
not well understood. It has been regarded as an insulating sub-
stance, implying a similarity between a nerve-fiber with the cur-
rent passing through it and an electric wire with its current. The
existence of unsheathed nerve-fibers, however, tends to disprove
this hypothesis. We know that the medullary sheath is found
generally on nerve-fibers which conduct sensory and motor im-
pulses, extending from a point near their respective cell-bodies to
the terminal branches. Certain cranial nerves, as well as those
fibers belonging to the sympathetic system and conveying doubt-
less both afferent and efferent impulses, are either entirely devoid
of such a sheath or have only a rudimentary one. Of the cranial
nerves belonging to this category the olfactory and the pneumo-
gastric form striking examples. In general it may be accepted
that those efferent fibers which arise from centers in the cerebro-
spinal axis that are not under voluntary control are naked (Re-
mak's fibers). Ontogeny teaches that medullated nerve-fibers
acquire their medullary sheaths at different stages of development,
the time being in close relationship with the developing function
of the fibers. This function is a single one, the conduction of
nervous impulses. Each fiber performs its function in one direc-
tion only, and that is determined in the beginning, when the
neuron of which the fiber is a part puts forth its branches, to
establish communication with its surrounding structures.

(e) Function of End-organs. — At the peripheral extremities
of the teleneurons we often find specialized structures forming a
pail of the neuron itself, or in close relationship with it. These
Structures are known as end-organs. In motor neurons they take
the form of end-plates closely applied to the muscle-cells, and
offer the medium of communication of impulse, resulting in a
change of form of the muscle cells. (See Fig. .'J.s, p. (>!).) In
Sensory neuron- they vary according to the kind of sensation

served (see chapter on special senses).

In this connection the question naturally arises, what deter-
mines the quality of impulse traversing a given neuron".' Is it

dependent on the cell-body, the dendrite.-, the neuraxon, or the

end-organs, either separately or collectively? Different forms of

542 THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

stimuli applied t<> any part of a nerve-trunk or its center pro-
duce lint one result, and that result depends apparently on the
end-organ. 11' it be a motor nerve, motion in the respective
muscle results. It' it l>e a sensory nerve, the sensation usually
excited by the nerve is experienced. Apparently, therefore, the
nature of the impulse need not vary at all, wherever the neuron
may he located or whatever may he the resultant sensation or
manifestation, hut at the terminus of the conducting path the im-
pulse produces a result of a character dependent on the end-organ
or end-connections.

Experiments have proved that an isolated nerve conducts
equally well in one direction as in the other, and while the me-
chanical, chemical and electric stimuli, used in the experiments,
may be neither identical with nor even similar to the natural ex-
citants of nervous impulses, it is perhaps less important to know
the nature of the impulse received by a neuron than it is to define
its power of transmitting it further. For example, in a nerve-
muscle preparation stimuli of various kinds when applied to the
nerve produce contraction in the muscle. Manifestly here the
end-plates are of prime importance as constituting the connection
between nerve-fiber and muscle-fiber. And this suggests the idea
that, for the efferent neurons, at least, the end-plates alone deter-
mine the quality of the nervous impulse. This is comparable
with the various recording instruments that may be attached to an
electric wire. The agent is the same, but the effect varies with
the receiver used. In the peripheral sensory neurons, however,
there seem to be special adaptations for the reception of stimuli,
mechanical, chemical, etc. Thus in the skin mechanical and
thermal stimuli are most effective. In the nasal mucosa and the
taste-buds are found end-organs adapted to the reception of chem-
ical stimuli.

From these considerations it appears that, while nervous im-
pulses are excited differently according as the sensory end-organs
(including, of course, those placed dee]) in the tissues as well as
the superficial ones) are adapted to receive impressions, and while,
further, the externalization of nervous energy, manifested by mo-
tion, secretion, nutrition, etc., depends largely on the peripheral
end-organs, the character of nervous impulses never varies and
may be identical in all instances.

(/) Effect of Structural Modification on the Function of the
Neuron. — Comparative anatomy as well as human pathology
shows the adaptation of the conducting paths to the functional re-
quirements. In those vertebrates which have either rudimentary
or undeveloped anterior or posterior extremities, the correspond-
ing nerve-trunks and spinal roots are diminutive. After amputa-
tion of a limb its proper nerves with their extensions into the cord

THE PHYSIOLOGY OF THE NEURON. 543

undergo a degeneration from disuse in proportion to the part
lost.

(</) Effect of Mutilation upon the Neuron. — The cell-body of
the neuron sustains an important relation to the nutrition of the
neuron as a whole. The axon and dendrites are dependent upon
the cell-body for their trophic supply. When a peripheral nerve-
trunk is divided the distal portion dies because the sensory fibers
are cut off from the posterior spinal ganglia, where their cell-
bodies are situated ; and the motor fibers die because they are cut
off from their cell-bodies in the ventral horns of the spinal cord.
This form of degeneration is called Wallerian, after the law of
Waller, who first discovered it. But another form of degenera-
tion takes place in the part still attached to the cell-body — a slow
defeneration which ascends toward the cell-bodv. This is called
retrograde degeneration .

The amputated portion of an axon changes profoundly and rap-
idly. The myelin is broken up and absorbed, the process itself
disappears more or less completely, and finally not a vestige of
nerve-structure may remain. The stump of axon remaining be-
hind also degenerates slowly, though not so completely.

(h) Postnatal Neuronic Development. — Constituting what
may be designated as a third function, although it is merely a
property by which the first one, enumerated above, is more exten-
sively operative, is the ability on the part of certain neurons,
notably those of the cerebral cortex, to develop additional den-
drites, to form new relationships with cells that hitherto were
foreign. On this hypothesis rests the enormous development of
the cerebrum of an individual undergoing education. As such
development depends largely upon the extensive and diverse cor-
relation of existing cells and centers, it will readily be seen how
great is the demand for new dendrites. Possibly also new axons,
if not entire neurons, are required and furnished in a manner as
yet unknown.

It is further stated that newly proliferated dendrites may soon
again disappear, after the particular object served by them is no
Longer required. This may be a species of atrophy from disuse,
but it i- sometimes likened to amoeboid movement, the cell-proto-
plasm being protruded and withdrawn according to the need.

The functions of the single neuron indicate those of systems of

neurons, which may be considered as a reinforcement of the former.
In addition, however, by reason of the numerous associations ex-
isting between neuron- of one system, and those of other systems,

intricate and complex actions, expressions of nervous activity, are
possible. In studying these relationships more closely, an addi-
tional power of Some neuron- over others is found, viz.: the power
of restraining, or inhibiting their action. A familiar example of

•")44 THE PHYSIOLOGY OF THE NERVOUS system.

this is met with in the two sets of neurons making uj> the motor

chain from the cerebral center to the muscle. Of these two sets
of neurons, the upper (archineurons) restrain the lower (teleneu-
rons) in their function. This is shown by the phenomenon of
muscle-reflexes, which are present only when the teleneurons are
functionally intact. In health these reflexes are but moderately
active, owing to the inhibition of the archineurons. If through
disease of the latter, the inhibition is withdrawn, then the tele-
neurons are freer to act, and increased reflexes are noted.

B. THE PHYSIOLOGY OF THE SPINAL CORD.

Physiologically the spinal cord must be considered as extend-
ing beyond its upper anatomical limits. Indeed, a better term
were " cerebro-spinal cord," to indicate that the cerebral stem is
merely a continuation of the spinal. Usage, however, sanctions
the term spinal cord, and it will be employed here in its extended
sense.

1. THE SPINAL CORD AS A CONDUCTOR OF NERVOUS IM-
PULSES.

In its function of conducting nervous impulses the spinal cord
differs from a peripheral nerve only in its complexity. Essen-
tially its fibers, while forming large tracts, are similar to those of
the peripheral nerves in function. But we find here, in addition,
collections and chains of cell-bodies, toward and from which the
fibers conduct impulses. We have already seen that the cell-body
of a neuron is a trophic center for its branches, and serves to re-
ceive, and possibly modify, impulses coming to it, and to dis-
charge them through the axon. Each of the cell-bodies found in
the spinal cord in such numbers represents a neuron, just as each
one in the posterior spinal ganglia docs, and as, indeed, every cell-
body in the nervous system. And while they may be regarded as
centers, they are in one sense only mid-stations in the course of
an impulse through a neuron.

With these considerations always before us, let us endeavor to
learn more of the conductive functions of the cord. And first of
all comes the fact that all impressions received from the outside
world as well as those coming from the structures of the body it-
self, and all impulses resulting in motion, secretion or other mani-
festation of nervous energy, must pass through the cerebro-spinal
cord. These may be summed up as afferent impressions and effe-
rent impulses. And the center, toward which the one class goes
and from which the other departs, the mental organ, made up also
of neurons, is for the individual the center of the universe, where
are received his impressions of everything external to his body as

THE COURSE OF SENSORY IMPULSES.

•345

well as of the changing conditions of the body itself, and from
which emanate all his voluntary and involuntary acts.

a. The Course of Sensory Impulses.

Among the efferent impressions must he placed all such as ar-
rive through our senses, general and special ; in addition, subcon-
scious information of the changing conditions of insensible por-
tions of the body.

In tracing the paths taken by these impressions through the
cord, ontogeny and morbid anatomy have greatly furthered our
knowledge. Bv means of a series of examinations of the nervous
system corresponding in time to newly developing nervous phe-
nomena we learn that new tracts of nerve-fibers develop from time
to time. And evidences of degeneration of these various tracts,
furnished by morbid anatomy, together with the losses or distur-

Fig. 283.

bances of function previously noted clinically have aided us in
establishing clearly the courses followed by such impulses.

In this manner it has been demonstrated that, in general, affe-
rent impulses enter the cord through the posterior roots and as-
cend through it- posterior ami Lateral tracts, while efferent im-
pulses on the other hand descend through the anterior and lateral
tracts of the cord. (See Figs. ('»" and n' 1 , \>\>. !»7 ami '.is. ,

Under the head of sensations, — impressions received through
the senses, — we distinguish <-<nniii<>n and special sensations. The
former include tactile, pain, thermal and muscular sensations;
the latter, visual, olfactory, auditory and gustatory sensations.

Tactile, pain, thermal and muscular impressions arrive at the

546

THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

cord through the sensory teleneurons < •< ( 1 1 1 : i i 1 1 < •< I in the posterior
spinal roots and their analogues in the cranial nerves, the various
filters combined in the nerve-roots. LSTol until after their entrance

into the cord are they
separated from each oth-
er and follow different
tracts. These tracts arc
not all definitely known.
The fibers subserving
muscular sense enter the
j)o.-t( ro-lateral columns
directly and ascend in
them, being pushed in-
ward by newly arrived
fibers until they come to
occupy the postero-me-
dian column. A.scending
to the medulla oblongata
they enter into an ar-
borization with dendrites
from the cell-bodies of the nuclei graciles and cuneati, whose axons,
in turn, lead into the cerebellum.

Fig. 285

POSTERIOR
ROOT

i>>. '< >v / ) Bundles

C^

ANTERIOR
ROOT-BUNDLES

Sections of human spinal cord. Fig. 283, the lower cervical region.

Fig. 284, the mid-dorsal region.

Kiu. •-'>■"', tin" luid-lumliar regions, showing tlic principal groups of nerve-cells, and on i ^

side of each section the i Lucting tracts as thej occur in the several regions. (Ma

about seven diameters, i

". '». c, groups of cells of the anterior horn ; </, cells of the lateral horn ; < . middle group of
cells ; f, cells of Clarke's column ; g, cells of posterior horn ; c, c, central canal ; "... anterior
commissure. (Schaefer.)

THE COURSE OF MOTOR IMPULSES. 547

The fibers which conduct pain and thermal sensations are prob-
ably closely associated with each other. From the prominent
part played by the loss or perversion of these two forms of
sensation early in the history of cases of syringo-myelia, in
which the spinal gray matter is usually first affected, we are
justified in concluding that the fibers conducting these impres-
sions, soon after entering the cord, pass into the gray matter and
these arborize with secondary neurons. About the latter much
uncertainty prevails. By some their axons after crossing over
in the commissure are thought to extend upward in the an-
tero-lateral ascending (Gower's) tract. (See Figs. 283-285).
By others they are conceived as forming the first in a series of
short loops lying in the lateral marginal zone and dipping at
short intervals into the gray matter to arborize there with the
next higher neuron of the series, and so on up to the medulla.

The difficulties encountered in determining the course of pain
and thermal impressions after they quit the telenenrons are almost
if not quite insurmountable. Even in the peripheral nerves a
lesion causing more or less permanent motor loss often produces
only passing sensory disturbances. In the higher links of the
chain it is possible that lesions may be compensated for by more
numerous inter-communications, rendering it more difficult by a
single lesion entirely to interrupt the path. Experiments on
lower animals have not advanced our knowledge materially in
thi- matter, owing to uncertain interpretation of sensations expe-
rienced by them.

In tracing the path of tactile impressions through the cord sim-
ilar difficulties are encountered. They are believed to follow
the course of muscular sensation, at least in part, crossing over
in the posterior commissure to ascend in the ventral portion of
the posterior columns. Some tactile fibers, however, decussate
and ascend in the antero-lateral ground-bundle along with the
pain fibers.

All of these fibers conducting sensory impressions coming into
consciousness pass up through the lemniscus, or fillet, of the me-
dulla, pons, mid-brain, and cross to the internal capsule, where
they are situated posteriorly, and radiate to the Rolandic areas, oc-
cupying portion.- of these areas corresponding to the motor fields.

A. The Course of Motor Impulses.

Motor impulses arising in COntigUOUS cells in the same areas,

nd through the pyramidal trad by the neuraxons of these

Cells. They extend through I he i utenial capsule, t he erusta, pons,

and medulla, lying ventral to the fibers we have just been con-
sidering. In the lower purl of the inedulhi the larger part ol*

548

THE I'llYsiOLOGY OF THE NERVOUS SYSTEM.

these pyramidal fibers decussates and descends in the opposite
lateral column, while a smaller number descends in the anterior

column of the same side. The latter, just before entering into
communication with their secondary neurons, pass over through

Fia. 286.

Diagram showing the probable relations of some of the principal cells of the cerebro-spinal
system to one another. 1, a cell of the cortex cerebri ; 2, its axis-cylinder or nerve process pass-
ing down in tin- pj ramidal tract, ami giving off collaterals, sunn.' of which, :;. :;. end in arbori-
zations around cells of the anterior horn of the spinal cord, the main fiber having a similar end-
ing at4; call., a collateral passing t'> the corpus callosum ; sir, another passing to the corpus
striatum ; 5, axis-cy linder process of anterior cornu-cell passing to form a terminal arborization
in the end-plate of a muscle-fiber, m ; 6, a cell of one of tin- spinal ganglia, its axis-cylinder
process bifurcates, ami one branch, 7. passes to the periphery t<> end in an arborization in tin'
sensory surface, *. The oilier (central ) I nan eh bifurcates after entering the cord (at 8), and its
divisions pass upwards ami downwards (the latter tor a short distance only I; 9, ending of the
descending branch in a terminal arborization around a cell of the posterior horn, the axis-cyl-
inder process of which, again, ends in a similar arborization around a cell of the anterior horn

in, a collateral passing from the ascending division directly to envelop a cell of the anterior
horn ; 1 1. one passing to envelop a cell of ( larke's coin tun ; 12, a collateral having connections
like those of 9 ; 13, ending of the ascending division of the posterior root-fiber around one of
i he , ells of t he posterior columns of the bulb or medulla oblongata ; 14, 14, axis-cylinder proc-
esses Of Cells of the posterior horn passing to form an arborization around the motor cells;

15, a fiber of the ascending cerebellar tract passing up to form an arborization around a cell of
the cerebellum ; in, axis-cylinder process of this cell passing down the bulb and cord, and giv-
ing oil' collaterals to envelop the cells of the anterior horn : 17. axis-cylinder process of one of

the ceils of the posterior column of the hull, passing as a fiber of the fillet to the cerebrum, ami

forming a terminal arborization around one of the smaller cerebral cells : 18, axis-cylinder

process of this cell, forming an at borization around the pyramid-cell, 1. (Sch vi 1 1 b. )

REFLEX ACTIO X. 549

the anterior commissure of the spinal cord, and in the opposite

anterior horn arborize with dendritic fibers from cells in that
horn. To other cells in this location come the fibers of the
crossed pyramidal tract and form with them similar arborizations
(see Fig. 286). The lower neurons send out their axons as motor
fibers of the anterior roots and peripheral nerves to the muscles,
where they end in the familiar " plates " in contact with the mus-
cle-fibers. It is scarcely necessary here to call to mind the fact
that two neurons constitute the motor chain from the cerebral cor-
text to any muscle remote or near, while the sensory impressions
arrive at the sensorinm only after several additional interruptions.
The thalamus opticus, and nucleus candatns contain cell-stations
for some of these fibers, and the anterior corpora quadrigemina and
the external corpora geniculata, for fibers of the optic tracts.

It is important to remember that sensory impressions, entering
into consciousness (perception), must do so by way of this devious
and complex path, and motor impulses, resulting from their per-
ception, must descend by the two-link chain described. Thus a
circuit is formed, whereby conscious sensation results in voluntary
muscular contraction.

2. THE SPINAL CORD AS A REFLEX CENTER.

By virtue of its conductive function, which is only slightly
differentiated from that of peripheral nerves, the spinal cord pos-
sesses another function, distinctive in itself. A sensory impres-
sion entering the cord by the teleneurons, which we have been
studying, instead of ascending to the cerebral cortex and becom-
ing an element of consciousness, may be conducted by collaterals
of the sensory teleneuronic axons direct to the motor teleneurons
arising in the anterior horns of the cord. This is a short circuit
and forms the path taken by those subconscious sensations which
arouse involuntary muscular contraction, giving us the phenomenon
called reflex action. In some conditions of disease and in certain
form- of intoxication, every voluntary muscle of the body can be
made to contract reflexly, in health comparatively few respond,
while in other diseased conditions reflex action is diminished or

entirely lost.

a. Reflex Action.

1. General Considerations. — Before considering the more im-
portant reflexes of the body, let us endeavor to account for the
lad of increased reflex action in one disease and loss of reflex ac-
tion in another. Recall, first, thai true reflex action is involun-
tary motion resulting from unperceived sensation. Now let us
suppose the sensation to be perceived ; that is to say, it ascends to

550 THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

the cerebral cortex. Two things may result : either a voluntary
action superseding the reflex, <>r a voluntary inhibition. If the
latter take place, an impulse descending the motor archineurons
interferes with the reflex activity of the teleneurons, and no reflex
occurs. From this it is clear that the only restraint exercised over
reflex activity is exerted through the motor archineuron. Sup-
pose this to be interrupted by a lesion anywhere in its path. The
inhibition is withdrawn, the lower neuron is unhindered, and
heightened reflex action is observed.

The mere presence of reflex action is indicative of the fact that
the motor and sensory teleneurons with their collateral branches
of communication are intact. Loss of reflexes implies an interrup-
tion to this circuit, called the reflex are. And as the arc is com-
posed of a sensory neuron and a motor neuron, the lesion may be
located in either one or the other. If there be a lesion of the
motor arm of the reflex are, not only is reflex action lost hut also
voluntary action, and complete paralysis is present in the part.
If reflex action alone is lost, while voluntary action is possible,
the lesion must be in the sensory arm of the reflex arc. In the
latter case other sensory disturbances are to be looked for.

Reflex action constitutes in its varied forms a most important
part of the life of every animal. In the lowest organisms it is of
paramount value, the relations existing between stimuli received
from the environment and the reactions thereto on the part of the
animal making up the sum of its existence. Ascending the scale
of development, reflex actions multiply in number and diversity,
and there is gradually evolved an additional higher form of nerve-
center than that concerned in reflex action, one which provides for
the storing up of impressions, for comparisons between them, and
for all the phenomena of psychic activity.

But in the presence of this more recently developed, higher
nerve-center, the subsidiary centers of reflex action have not be-
come less important for the life of the individual, even if some-
what overshadowed. In human physiology, the subject here con-
sidered, we find reflex action forming the basis of the vegetative
functions, so-called, and so well developed, indeed, that in the ab-
sence or loss of the higher psychic centers, life still is continued
by reason of the activity of the reflex centers in the medulla
spinalis and oblongata. Under the chapters on respiration and
circulation ((j. v.) it will be found that these vital functions de-
pend on the condition of aeration of the blood. That provides the
stimulus to the respiratory and circulatory centers in the bulb,
and by reflex action resulting in the necessary contraction and re-
laxation of the muscles of the chest- walls and the heart, these
phenomena recur in a continuous succession of cycles, and so life
is prolonged.

REFLEX ACTION. 551

2. Purposeful Character of Reflex Action. — In observing
results of experiments on animals the purposeful character of the
reflexes is striking. In all reflex movements, whether of a simple
or complex nature, the response is in proportion to the strength
and nature of the stimulus, that is, the afferent impulse. Reflex
movements may be divided into the three following groups : (a)
Simple or partial reflexes, (b) Extensive incoordinate reflexes
<>r reflex spasms, (c) Extensive coordinated reflexes.

(a) The Simple ok Partial Reflexes are characterized by
the fact that stimulation of a sensory area discharges movements
in one muscle only, or at least in one limited group of muscles,
i . </., contact with the conjunctiva causes closure of the eyelids.

(6) The Extensive Incoordinate Reflexes or Reflex
Spasms : These movements occur in the form of clonic or tetanic
contraction in individual muscles, or all of the muscles of the body
may be implicated.

< 'auses. — A reflex spasm depends upon a double cause : («) The
gray matter of the spinal cord may be in a condition of exalted
excitability so that the nervous impulse after having reached the
center, is easily transferred to the neighboring centers. This ex-
cessive excitability is produced by certain poisons, more especially
by strychnin, brucin, caffein, atropin, nicotin, carbolic acid, tet-
anin. The slightest touch applied to an animal poisoned with
strychnin is sufficient to throw the animal at once into spasms.
Pathological conditions may cause similar results, as in hydrophobia
and tetanus. On the other hand, the central organ may be in
such a condition that extensive reflexes cannot take place ; thus
in the condition of apnoea the spasms that occur in poisoning with
strychnin do not take place.

(ft) Extensive reflex movements may also take place when the
discharging stimulus is very strong. For example, this condition
occurs in man when in great pain ; thus, intensive neuralgia may be
accompanied by extensive spasmodic movement — Tic douloureux.

Strychnin is the most powerful reflex-producing poison known.
When a large dose is given to an adult the lower jaw becomes
immovable, the neck rigid, the pupils dilate, the reflexes are
heightened so that the muscles contract spasmodically and pain-
fully, resulting in paroxysmal attacks of tonic contraction of the
extensor muscles of the body, in which the patient assumes the
position of opisthotonos. If the heart of a frog be ligatured and
the poison afterwards applied directly to the spinal cord, reflex
spasms are produced, proving thai Btrychnin acts upon the spinal

Cord. We Can ]>ro\f that strychnin does not produce spasm by

acting mi the brain, muscle or nerve. Destroy the nerve high up
and injcci a small dose of strychnin into the dorsal lymph-sac; in

a l'<\\ minutes all the muscles Of the body, except those supplied

552 THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

by the divided nerve will be in spasms, showing that although
the poisoned blood has circulated in the nerves and muscles of
the legs, it does not act on them. Destroy the spinal cord and
the spasms cease at once.

Summation <>J Stimuli: By this term is meant that a single
weak stimulus, which in itself is incapable of discharging a reflex
act, may if repeated sufficiently often produce this act. The sin-
gle impulses are conducted to the spinal cord in which the process
of summation takes place. It is believed by some to be extremely
probable that all reflex acts arc due to the repetition of impulses
in the nerve centers, — summation of stimuli.

(c) Extensive Coordinated Reflexes are due to stimula-
tion of a sensory nerve causing the discharge of complicated reflex
movements, in whole groups of different muscles, the movements
being powerful in character. Example : the protective move-
ments of pithed or decapitated frogs. If a drop of a dilute acid
be applied to the skin of such a frog, it strives to get rid of the
offending body and it generally succeeds. Thus when a drop
of acid is placed on the right flank of a brainless frog, the right
foot is almost invariably used to rub off the acid. If the right
foot be cut off or otherwise hindered from rubbing off the acid the
left foot is, under exceptional circumstances, used for this purpose.
This at first sight appears like an intelligent choice ; indeed so
purposeful are these acts and the actions of groups of muscles so
adjusted to perform a particular act that Pfl tiger regarded them as
directed by and due to consciousness of the spinal cord. If many
instances occurred where evidences of a variable automatism which
we call volition, were manifested by the cord, we should be led
to believe that the choice was determined by an intelligence.
But as has been abundantly observed, a frog in which the brain
has been removed having only the spinal cord, makes no sponta-
neous movement.

Vicarious reflex movements are observed in mammals, though
not to such an extent as in frogs. In dogs in which partial
removal of the cerebral hemispheres has apparently heightened the
reflex excitability of the spinal cord, the remarkable scratching
movements of the hind leg which are called forth by stimulating
a particular spot on the loins or the side of the body are exerted
by the leg of the opposite side if the leg of the same side be
gently held. In this case the vicarious movements are ineffectual,
the leg not being, as in the case of the frog, crossed over so as to
bear on the spot stimulated and this therefore cannot be considered
as an act of intelligence. The mechanical nature of reflex action
can be further illustrated. If aflame be applied to the side or part
of the body of an eel, the body is moved away from the flame. If
the bodyof a decapitated snake is brought into contact at several

REFLEX ACTION. 553

places with an arm or stick, complex reflex movements are excited,
the effect of which is to twine the body around the object. A de-
capitated snake will with fatal readiness twine itself around a red-
hot iron.

In the reflex acts which have been under consideration we have
observed that the resultant movements are coordinated, and not only
are many distinct muscles brought into play but certain definite
relations between the contraction of each muscle and the con-
traction of other muscles sharing in the movements are maintained.
In the absence of coordination the movements would become ir-
regular and ineffectual. There is reason to believe that this
coordination of voluntary muscular movement takes place in the
part of the spinal cord which carries out the movement and not in
the brain, though under normal conditions the latter may be con-
scious of the Avhole movement, including its coordination. As
may be inferred from what has already been said, the characters
of a reflex movement are dependent on the intrinsic condition of
the cord. The action of strychnin, already alluded to, is an in-
stance of an augmentation of reflex action. Conversely by various
influences of a depressing character, as by various anesthetics or
other poisons, reflex action may be lessened or prevented. So also
various diseases may so affect the spinal cord as to produce
either increased reflex excitability so that a mere touch mar
produce a violent movement, or diminished reflex excitability so
that it becomes difficult or impossible to call forth a reflex action.

Coordinated reflexes may occur in man during sleep and during
pathological conditions. Reflexes are more easily and more com-
pletely discharged when the specific end-organ of the afferent
nerve i- stimulated than when the trunk of the nerve is stimu-
lated in its course; by gently tickling the skin a reflex act is more
readily evoked than by a strong stimulus applied to sensory nerve.

:J. The Time Required for Reflex Actions. — In the frog, de-
ducting the time taken in the transmission of impulses along
nerves, the time consumed in the cord (reflex time) varies from
(i. (ids t<» 0.015 second ; if the reflex crosses to the other side it is
one-third longer. It is lessened by heat, and by the influence of
a strong stimulus.

A. Inhibition of the Reflexes. — Within the body there are
mechanisms which can suppress or inhibit the discharge of the
reflexes, and they may therefore be termed mechanisms inhibiting
the refle

t") Voluntas? [nhibition.- — The observations of every-day

lite teach thai reflex acts can lie inhibited to ;i certain extent by

action of the will. The eyelids may he kept open when the eye-
ball i- touched ; movement of a part may be arrested when the shin
i- tickled. If, however, the stimulus he strong and i~ repeated with

55 1 THE PHYSIOLOGY OF THE NEEVOUS SYSTEM.

sufficienl frequency, the reflex impulse ultimately overcomes the
voluntary effort, [nhibitory acts arc not all similar in character;
for example, when we voluntarily stop the muscular acts which re-
sult from tickling the sole of the foot, we achieve this by throw-
ing into action an opposing group of muscles, but it is doubtful
whether inhibition is to be wholly explained as a matter of mus-
cular antagonism. When the brain of a frog is removed and the
effects of a shock have passed off the reflex excitability of the
animal is found to be increased. This suggests the idea that in
the intact nervous system the brain is exerting some inhibitory
influence on reflex actions. Ef a frog from which the cerebral
hemispheres have been removed (the optic lobes, bulb, and spinal
cord being left intact) be tested by applying a drop of acid on its
skin, it will be found that the reflex excitability is increased. If,
however, the optic lobes be stimulated by applying a crystal of
salt the reflex acts are prolonged or suppressed. Similar results
may be obtained by stimulating in mammals the corpora quadri-
gemina, which bodies are analogous to the optic lobes of frogs.

(6) Beyond Voluntary Inhibition are those reflex move-
ments which cannot at any time be performed voluntarily. Thus
erection, ejaculation, parturition and the movements of the iris
are neither direct voluntary acts, nor can they, when they are ex-
cited reflexly, be suppressed by the will. It will be recalled that
the action of such nervous centers as the vaso-motor and res-
piratory may be either inhibited or augmented by afferent im-
pulses. The micturition center in the mammal may be inhibited
by impulses passing downward to the lumbar cord from the brain
or upward along the sciatic nerves. In the case of dogs whose
spinal cord has been divided in the thoracic region, micturition
set up as a reflex act by simple pressure on the abdomen, is at
once stopped by sharply pinching the skin of the leg, and it is a
matter of common experience that in man micturition may be
suddenly checked by an emotion or other cerebral event.

(c) Unconscious Cerebral Inhibition is a prominent fea-
ture of reflex action. Strong stimulation of a sensory nerve in-
hibits reflex movements. If the toes of one foot of a frog are
dipped into dilute sulphuric acid at a time when the sciatic of the
other leg is being powerfully stimulated with an interrupted cur-
rent the period of incubation of the reflex act will be found to be
much prolonged and in some cases the reflex withdrawal of the
foot will not take place at all ; and this holds good not only in the
complete absence of the optic lobes and bulb, but also when a
portion of the spinal cord, sufficient to carry out the reflex action
in the usual way, is left. The brain does, it is apparent, act as an
inhibitory organ, but we must not draw too closely upon the in-
hibitory cardiac mechanism as analogous. In the mechanism of

THE REFLEXES. 555

cardiac inhibition we have to do with libers whose exclusive duty
it is to act under control of the center in the medulla, as the
brake mechanism of the heart. In the present state of our
knowledge the fact must suffice that experiments on animals show
that the brain may inhibit particular spinal reflex movements, but
also habitually exercises a restraining- influence on the reflex ac-
tivitv of the whole cord, though Ave are unable to state exactly
how the inhibition is carried out.

b. The Reflexes.

From the inherent forms of reflex action down to the simplest
muscular contraction following unperceived stimulation the human
individual presents numerous gradations. By their functions,
normal or deranged, they reveal the actual conditions of the
nerve-elements composing their respective reflex-arcs. Among
them are differentiated the superficial or cutaneous reflexes, the
deep or tendon-reflexes, and the organic or visceral reflexes.

1. Superficial Reflexes. — (a) Plantar; elicited by stroking
or scratching the sole of the foot, which causes attempts to with-
draw the foot from the source of irritation.

(6) Gluteal ; a contraction of the gluteal muscles en masse
when the buttock is gently pricked or scratched.

(c) Cremasteric ; when the thigh is irritated on its inner sur-
face by grasping, stroking, scratching, etc., the homolateral testicle
is distinctly retracted.

(<1) ERECTILE REFLEX OF Penis; produced by gentle friction
of the glans penis, especially of the frsenum, resulting in turgidity
of the organ and erection. Its analogue in the female pertains to
the erection of the clitoris.

(i ) ABDOMINAL; consisting of a retraction of the anterior ab-
dominal walls when the skin is slightly irritated.

(/) MAMMARY ; in women, a retraction of the epigastrium
when the mammary region is tickled.

(a) Palmar; corresponding to the plantar, usually less devel-
oped than the latter.

(A) Laryngeal ; irritation of the lining of the larynx, as also
of the bronchi, produces coughing.

( /) Pharyngeal ; attempts to extrude contents of the pharynx,

even to 1 1 1 « - point of vomiting, when the fauces or lining of the
pharynx i- stimulated.

i/.) Nasal ; causing sneezing when the nasal mucous membrane
is irritated.

(I) ( 'ovnvTi v.\ i. ; closure of the eyelid when anything foreign
touches the conjunctiva or the eyelashes.

2. Deep Reflexes. — (a) Tendo-Aohillia Reflex. When the ex-

556 THE PHYSIOLOGY OF THE NERVOUS SYSTEM.)

tended leg is supported at the knee, the hand pressing firmly
againsl the ball of the foot, a tap on the tendo-Achillis causes con-
traction of the gastrocnemius and sulcus, and the heel is jerked
up. This reflex may be present or absent in health.

(6) Ankle Clonus. — If the half-extended leg be supported at
the knee, and the hall of the foot be suddenly pressed up, put-
ting the tendo-Achillis on a stretch, in certain instances there re-
sults a scries of clonic contractions of the calf-muscles Avith
consequent alternate extension and flexion of the foot, which
continues as long as the pressure is maintained on the ball of the
foot and ceases as soon as the foot is released from pressure. It
is probably never present in health.

(c) Patellar Reflex (knee-jerk). — When the thigh is sup-
ported by the hand or by being crossed over the other thigh, and
the leg is flexed at the knee, thus securing relaxation of the quadri-
ceps extensor, a tap on the tendon just below the patella causes
the leg to be suddenly extended. This reflex is normally present,
but its exaggeration and its loss arc both indicative of disease.

In conditions of exaggerated knee-jerk, if the hand be applied above
the patella, pressing it down with a sudden movement, sometimes a
clonic contraction of the quadriceps occurs and the patella is alter-
nately raised and lowered. This is the patellar clonus.

(d) Triceps Reflex (elbow-jerk). — This is analogous to the
knee-jerk and is elicited by supporting the arm in the hand, on the
examiner's knee, or by leaning on a table, the forearm being
somewhat flexed, and then tapping the triceps tendon just above
the olecranon. In health it may be absent or present. Its ex-
aggeration is indicative of disease.

(e) With the arm in the foregoing position tapping the supi-
nator and extensor muscles of the forearm often elicits contrac-
tion of them, with corresponding movements.

(/) Biceps Reflex. — If the flexed forearm be supported at
the elbow, the wrist slightly flexed and also supported, tapping
on the tendon of the biceps sometimes causes contraction of that
muscle.

(g) With the arm in the position last described, tapping the
pronator and extensor muscles of the forearm causes at times con-
traction of them and movements of the forearm, hand and lingers
accordingly.

(/<) Inferior Maxillary Reflex. — If the mouth be opened
and a flat instrument resting on the lower teeth be tapped, some-
times the jaws shut by reflex movement.

3. Organic Reflexes. — Under this head are included many of
the functions of different organs of the body on which the well-
being of the organi-ni as a whole depends, some of them indeed

THE REFLEXES. 557

being of vital importance. Like the superficial and deep reflexes
they are expressed by muscular activity, but unlike them usually
the synergic function of several groups of muscles is required for

their execution.

i. The Alimentary Tract.

(a) Sucking. — When the mother's nipple is placed in the
mouth of a newborn infant and a few drops of colostrum tasted
by it, there ensues a form of peristaltic, vacuum-producing move-
ment of the tongue and lips, which at first is probably reflex in its
nature.

(6) Deglutition. — The presence of food in the back part of
the mouth and in the pharynx brings on successive dilatations and
contractions in the segments of the oesophagus from above down-
ward, constituting the act of swallowing. Only the initial part of
this act is under voluntary control. The rest is purely reflex.

(e) Gastric Movements. — These are induced by the presence
of food in the stomach, and, as is well-known, serve as an impor-
tant factor in gastric digestion. Closely associated with it and yet
distinct from it is

\'h The Pyloric Reflex, by virtue of which the contents of
the stomach are retained in it until gastric digestion is complete.
It consists of a firm contraction of annular muscle-fibers, and of a
subsequent relaxation of these fibers permitting the stomach con-
tent- to pass into the duodenum.

(' ) Tin: Ixtk-tixal Movements. — These are perhaps not to
In- disassociated from those of the stomach, which they resemble
;it least to some extent. They are, too, similarly caused by the
presence of the ingested food in them.

Whether a separate reflex act, or accomplished by the aid of
duodenal peristalsis, the emptying of bile from the gall-bladder
into the bowel is probably reflex. The presence of muscle-fibers
in its walls would point to this.

if) Defecation. — While to a certain extent a voluntary act,
defecation i- reflex to a degree. Indeed, it is highly probable
thai the inhibition of the act of emptying the rectum is the volun-
tary act. while the withdrawal of the inhibition (relaxing the
sphincter ani) permit- the act of defecation to be accomplished
either entirely reflexly or by the aid of the voluntary action of
the diaphragm and abdominal muscles.

It will be -ecu t 1 1 : 1 1 t he-c ivl|e\r- connected with tile II I i I llellt alW

canal, may all be included under two forms of muscular activity :
peristalsis and constriction. Strictly speaking, annular contrac-
tion of the alimentary tube, constriction, is a part of peristalsis,
but ;i- exemplified by the cardiac and pyloric end- of the stomach

THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

and by the sphincter ani muscles, constriction mu-t be distin-
guished as a separate reflex act.

The subject of the reflexes connected with the alimentary canal
w<»uld not be complete without mention of the occasional reverse
movements.

iv) Emesis. — This is a reflex, very complicated in mechanism.
In it- simplest form it arises from irritant ingesta exciting spas-
modic contraction of the stomach and extrusion of it- contents
through the relaxed oesophagus. But many other stimuli are
capable of producing the motor phenomenon of vomiting. Tims
nauseating odors, certain visual impressions, such as the sight of

lil 1, or of objects which arc associated in the memory with a

former nausea are examples of the numerous sensory avenues
through which the emetic reflex may be excited.

(A) Duodenal Regurgitation. — This may accompany the
preceding or it may occur independently of it. Usually, however,
it result- in vomiting, as the presence of bile in the stomach is ir-
ritating, producing nausea.

ii. Tin Qenito-TJrinary Tract.

(a) Micturition. — This act is allied to that of defecation, be-
ing voluntarily inhibited, and taking place reflexly on the with-
drawal of the inhibition (relaxation of the vesical sphincter).

(6) Seminal Emission. — In the male, this may be a purely
reflex act or it may be led up to by voluntary movements. In
the latter case, illustrated by coitus, when the excitation of the
glans penis has reached a certain stage the reflex contraction- of
the ejaculatory muscles proceed without possibility of farther
voluntary inhibition. In sleep the act may occur as a purely
reflex one, the stimulus being supplied by too- great warmth of
the parts, irritation within the vesico-urethral canal or subcon-
sciously by dreams.

In tlie female, excitation of the walls of the vagina, principally
of the introitus and of its upper part, is the normal causal factor
of this reflex act.

(c) Parturition. — The gravid uterus is capable of voiding it-
contents independently of voluntary control, as demonstrated in
cases of transverse lesion of the cord above the parturition center.
Usually in the second stage of labor, voluntary muscular contrac-
tion in the diaphragm and abdominal walls reinforces the reflex
act.

in. The Pupillary Reflex.

When the light entering the eyeball i- suddenly increased in
intensity the iris contract- leaving a smaller pupil. Relaxation
follow- if the light is subdued.

THE REFLEXES. oo$

When an object seen at a distance of two feet or more is quickly
moved up near the eyes, and the gaze he fixed on it, the eyes
converge and the pupils become narrow. This is the pupillary
reflex of accommodation.

When the skin of the side of the neck is painfully irritated, the
pupil expands in some individuals. These are the forms of the
pupillary reflex, as it appears in health. In nervous disease
there may be a dissociation of these forms, or there may be total
immobility of the irides.

iv. The Circulatory System.

Throughout the system of blood vessels of the body we find an
accompanying intricate nerve-supply, through which medium the
muscular walls of the blood vessels are influenced to contract or
to relax, and so control the volume of blood in a given part. In
the heart, there are met everywhere in its muscular walls nerve-
fibers originating in the cardiac ganglia, in those of the sympa-
thetic system elsewhere, and in the medulla oblongata. None of
these is subject to voluntary control, and stimuli arriving through
them originate by irritation of the centers directly or by sensory
impressions received by these centers. In the latter case it will
be seen that a true reflex mechanism is called into play.

Dilatation and contraction of the smaller, peripheral blood
vessels, giving rise to the phenomena of blushing and pallor re-
spectively, are often due to sensory stimulation. This may result
as a simple reflex act or with the interposition of an emotional
i psychic) state. It may not be unjustifiable to consider the latter
ae a complex reflex action, as when the sight of an accident
happening to another produces pallor, for example. It is also a
well-recognized fact that an organ in active functional state is pro-
vided with more blood than when quiescent, i. e., relaxation of its
vessel-walla occurs in the presence of that which excites its func-
tion. A- an example of this may be cited the stomach ; its blood
vessels are comparatively turgid when fond is taken, and con-
tracted during ;i fast.

v. The Respiratory Tract.

Mention has already beeE made of the influence of the blood
on the centers of respiration, varying with its degree of oxy-
genation. It is well known thai respiration may not be vol-
untarily long suspended, the venous blood stimulating to renewed
respiratory movements overc ing voluntary inhibition.

Certain volatile gases, as well as odor- of certain kinds, stim-
ulate respiration, while others depress it, both acting in a more or

560

'/'///•: PHYSIOLOGY OF THE NERVOUS SYSTEM.

less complicated, reflex manner. Here too, an emotional state

may be, as it were, interposed.

4. Relation of Reflex Action to Higher Psychic Phe-
nomena.— From the foregoing will be seen in part the important
n>lr of reflex action. While the vegetative functions are nearly

entirely maintained by it, in some form or other, many of the
other body-functions are also purely reflex in their character.
Nor is it difficult to conceive the complicated processes of percep-
tion, conception, memory, and other psychic phenomena, as reflex
acts of greater complexity, i. c, involving more sets of neurons
than the simpler ones just considered.

c. The Location of Reflex Centers.

A diagram of the various reflex-centers corresponding to the
reflex actions above mentioned, must of necessity include not only
the axile motor cell-groups giving origin to the motor nerves that
produce the respective movements, but also the various sensory
centers in the same cerebro-spinal stem capable of stimulating
those motor cell-groups. In the cases of the organic reflexes, as
well as in those of many of the superficial reflexes, these sensory
centers are very numerous and their connections with the motor
centers multiplex. Furthermore, such a diagram could be of little
service in diagnosis in the absence of other symptoms, since the
loss of any given reflex is not evidence always of disease of either
center, but may be due to a lesion located anywhere in the reflex-
are. As an aid, however, to the location of lesions, recognized as
being in the cerebro-spinal stem, the following table may lie of
service :

Reflex.

Location of Center.

Plantar.

I and II. Sacral Segments.

Gluteal.

IV and V. Lumbar.

Cremasteric.

I-III. Lumbar.

Erectile of Penis.

I— II. Lumbar.

Abdominal.

YII-XI. Dorsal.

Epigastric.

IV-VII. Dorsal.

Mammary.

II-XII. Dorsal.

Scapular.

Y. ( 'ei-viral to I Dorsal.

Palmar.

VII. Cervical to 1 Dorsal.

Laryngeal.

X. Crania] Nerve. Bulb.

Pharyngeal.

IX. Cranial Nerve. Bulb.

Xasal.

A'. Cranial Nerve. Bulb.

< Conjunctival.

Y. ( 'ranial Nerve. Bulb.

Tendo-Achillis.

III-Y. Sacral.

Ankle Clonus.

Y. Lumbar.

Patellar.

II. Lumbar.

Extensors <>f Hand.

VI. Cervical.

Flexors of Hand.

VII VIII. Cervical.

THE TROPHIC FUNCTION OF THE SPINAL COED.

561

Reflex.

Location op Center.

Pronotor of Hand.

VIII. Cervical.

Triceps.

VI. Cervical.

Supinator of Hand.

V. Cervical.

Biceps.

IV— V. Cervical.

Inf. Maxillary.

V. Cranial Nerve. Bulb.

Defecation.

IV. Lumbar.

Micturition.

III. Lumbar.

Seminal Emission.

IV. Lumbar to III Sacral.

Parturition.

I— II. Lumbar.

Intestinal Movements.

X. Cranial Nerve in Bulb.

Duodena] Regurgitation.

I— V. Dorsal (Splanchnic).

Pylorus.

X. Cranial Nerve in Bulb.

< iastric Movements.

X. Cranial Nerve in Bulb.

Emesis.

X. Cranial Nerve in Bulb.

Deglutition.

IX and X. Cranial Nerve in Bulb.

Sucking.

V, VII, and XII. Cranial Nerves in Bulb.

Respiration :

Tip of Calamus scriptorius.

Expiration.

X. Cranial Nerve in Bulb.

Inspiration.

X. Cranial Nerve in Bulb.

Circulation :

Cardiac acceleration.

II— 1 1 1, w seq., Dorsal.

< lardiac inhibition.

X. Cranial Nerve in Bulb.

Vaso-motor dilatation, blitstk.

VII. Cranial to ID Sacral.

Vaso-motor constriction, pallor.

II. Dorsal to II Lumbar inclusive.

Pupillary.

IV. Cervical to III Dorsal.

Vaso-motor.

Floor of tbe fourth ventricle.

Salivary secretion.

VII. Cranial Nerve in Bulb. Chorda

Tympani.

3. THE TROPHIC FUNCTION OF THE SPINAL CORD.

In considering the functions of the spinal cord, sight must not
be lost of the inherent property of cell-bodies here, as indeed
everywhere throughout the nervous system, to maintain the nu-
trition of the more distant parts of the respective neurons. And
as we have Btudied at length the functions of conduction and re-
flex action in the cord, — functions that are not performed by it
exclusively, — so it will be propel- here briefly to consider its
trophic function.

Lesions <>f the cell-bodies themselves compromise the nutrition
of the entire neurons; Lesions of the branches alone affect the
part- distal to the lesion. The degenerations resulting from such
lesions have enabled us to trace with a fair degree of certainty
the courses of the various neurons of the cord. [Of. Editiger
on the Centred Nervous System.}

It i- of prime importance to remember that the trophic influence
of the motor neurons is extended beyond the motor end-plate- to
the muscles themselves ; so thai the nutrition of the muscles is
intimately related to that of the nerve-trunks supplying them,
both depending on the trophic influence of the cell-body. From
this (ad it follow- that a destructive lesion of the cell-bodies of

562 TEE PHYSIOLOGY OF THE NERVOUS SYSTEM.

the peripheral motor neuron-. as well as one interrupting their
eellulifugal nerve-currents, causes not only degeneration in the
respective nerve-fibers, l>ut also atrophy of the muscles innervated
by them. Non-destructive lesions may perverl the nutritional
influence and produce a condition of dystrophy.

4. THE PHYSIOLOGY OF THE MEDULLA OBLONGATA OR
MYELENCEPHALON. '

Like the spinal cord the medulla oblongata is both a path of
communication between the higher centers and the periphery, and
an independent center regulating function.- of the utmost impor-
tance in the system.

a. The Medulla as a Medium of Conduction.

The paths in the medulla which transmit volitional motor im-
pulses are the best understood ; little i> known regarding the
functional activity of the numerous afferent and efferent tracts
which connect the medulla with the cerebellum and cerebral
ganglia, or of the specific functions of the various gray centers of
the medulla itself. We are more indebted to the careful study
which has been made of secondary degeneration of the medullary
tracts and to the phenomena of disease than to any direct experimen-
tation. Direct experiments on the medulla itself are full of diffi-
culties and the results complicated.

That the pyramids are the paths of volitional motor impulse is
proved most satisfactorily by the secondary degeneration which
ensues in them in consequence of destruction of the cortical mo-
tor centers. The pyramid degenerates on the same side as the
cortical lesion and as far as the point of decussation of the pyra-
mids and thence the degeneration is continued downward in the
pyramidal tract of the lateral column of the spinal cord on the
opposite side and partly also, as will be remembered, in the an-
terior pyramidal tract of the same side, for a certain distance at
least. Experimental evidence as to the result of section of the
pyramids is somewhat uncertain, but in monkeys and man there
can be no question as to their being the motor path- between the
cortex and the anterior horns of the spinal cord.

As to the exact position and course of tracts serving cutaneous
and general sensibility the same uncertainty, if not a greater, ex-
ists, as in respect to those paths in the spinal cord. But the
best evidence, both physiological and pathological, goes to show
that in the medulla oblongata they run on side- opposite to the
parts where they are distributed. Above the decussation of the

'Though tlif cord and medulla have been considered as a unit, it seems profit-
able to consider here briefly the functions peculiar to the latter.

THE MEDULLA As AN INDEPENDENT CENTER. 563

pyramids both motor and sensory tracts of the left half of the
bodv lie in the right half of the medulla oblongata and vice versa.

h. The Medulla as an Independent Center.

A- such it presides over and regulates functions, on the due
performance of which life essentially depends, as well as many
others of considerable complexity but of less vital importance.
All of the cranial nerves with the exception of the first four (viz.,
the olfactory, optic, motor-oculi and pathetic) have their primary
origin in the medulla oblongata, and the third and fourth nerves,
though springing from nuclei in the floor of the aqueduct of
Sylvius, are also connected with the sixth pair through the pos-
terior longitudinal tracts. Should all the encephalic centers above
the medulla oblongata he removed, the mutilated organism, even
of a warm-blooded animal, can live and breathe. The functions
depending on the spinal centers will go on automatically and
under reflex actions will be called forth in regions innervated,
especially by the medulla itself. Thus the eyelids will close if
the conjunctiva he touched ; the lingual, oral and facial muscles
will contract and the ear twitch on irritation of the sensory nerves
in reflex relation with the movements in question. But the move-
ment- capable of being elicited through the medulla oblongata are
in many instances of a remarkable degree of complexity. Thus if
a morsel of food he placed on the hack of the tongue the combined
and coordinated movements of the lips, tongue, palate and pharynx
concerned in the mechanism of deglutition will he executed with
:i- great precision as in perfectly normal conditions. In a young
animal, bo mutilated, the introduction of the nipple between the lips
will he sufficient to set up the appropriate movements of sucking.

Occasionally human infants are horn entirely without cerebral
centers above the medulla oblongata, and yet an acephalous infant

sucks and swallows as well as the perfectly developed child when

put to the mother's breast. The medulla oblongata is the coor-
dinating center of all these associated movements. Destruction
of the medulla oblongata causes their instant and permanent anni-
hilation.

The various afferent and efferent nerves concerned in the mech-
anism, viz., tin- hypoglossal, glosso-pharyngeal, facial and t ri-facial,
.ill spring directly from gray nuclei in the medulla. Fig. 287

show- the locution of the principal center- of the medulla. The

plexiform arrangement -ecu in the nerves which are concerned in
the movements of the Limbs is not manifesl in the case of the
crania] nerves, except in those of the pharyngeal plexus ; but there
can he little doubt that there, as in the spinal center-, the nuclei of
the various nerves concerned in special physiological coordinations

564

THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

arc so connected together that :i coordinate synergy is occasi sd

by stimulation jusl as readily as a single muscular contraction, on
stimulation of an undivided muscle-nerve.

The movements concerned in the production of articulate speech
have also probably their primary coordinating centers in the me-
dulla oblongata. This is indicated more particularly by the phe-
nomena of disease in this
Fia 287. region in man. In " Bul-

bar Paralysis," the dis-
ease usually begins with
slight defect in the speech
and the patient has diffi-
culty in pronouncing the
dentals and Unguals : the
_T7 voice becomes nasal. The
paralysis starts in the
tongue and the superior
laryngeal muscle gradu-
}W ally becomes atrophied
and finally the mucous
membrane is thrown into
folds. When the lips
become involved the pa-
tient can neither whistle
£n nor pronounce the vowels
"o"and"a." The mus-
cles of the vocal cords
waste and the voice be-
come- enfeebled. Death
sometimes results from
an aspiration pneumonia,

Schematic transparent section of medulla oblongata, sometimes from chokinti',
showing the principal centers. The numerals V to XI f _ . *"'

refer to the nuclei of origin of the respective cranial more l'arelv 11*0111 ail 111-
nerves. Vis the motor nucleus; /.' r. tin- roots of the , * n ,

fifth nerve; V, sensory nucleus ; V", sensory nucleus Vol VCUient of tile respira-

and ascending root; AMY, root of sixth nerve; AM'//, tAl.,. nnnim' ■ Tl-mrli ton io

root of seventh nerve : /'//.. j>\ raniitl : Pt/fcr., decussation lOr\ CeillClS. J. He UIHJH

ofthe pyramids ; O.s., superior olive ; 0, olive- &/., genu • fnnT1J Tn /Ipnpnd on n

of the facial. (Stewart.) IS iounu to uepeuu una

process of defeneration
specially in the nuclei ofthe hypoglossal, accessorius, vagus, facial
and glosso-pharyngeal to a greater or less extent. The order of
progression of the symptoms indicates a functional association of
the nuclei which are implicated, but the exact anatomical details
are still obscure.

The medulla oblongata is a center of facial and of some other
forms of what is usually regarded as emotional expression. Vul-
pian has shown that if a young rat be deprived of all encephalic
centers above the medulla oblongata, pinching of the toes will

THE MEDULLA AS AN INDEPENDENT CENTER. 565

cause not merely movements of the limbs but also a cry of pain.
If the medulla be now destroyed pinching the toes will cause re-
flex movements of the limbs as before, but no cry will be elicited.
The cry as of pain is, however, no real sign of pain, but only a
reflex action of the laryngeal and expiratory muscles.

The coordination of the respiratory movements is one of the
most important functions of the medulla oblongata. So long as
the medulla is intact the function of respiration goes on in an
automatic or reflex manner with the most perfect regularity and
rhythm. When the medulla is destroyed respiration ceases and
death ensues in all animals which cannot live by cutaneous res-
piration alone, like the frog. The chief center of coordination of
the respiratory movements is situated near the beak of the calamus
scriptorius, coinciding, or being in the closest relation, with the
nuclei of the vagus nerves. From this point proceed the impulses
which excite the associated and coordinated movements of the dia-
phragm, thoracic walls and air passages.

If the spinal cord be cut above the origin of the phrenic nerve
the thoracic muscles and diaphragm speedily cease to act effectively
for purposes of respiration, but as it has been shown, may still
continue to act rhythmically and to respond to stimulation of cer-
tain sensory surfaces for a short period after section of the cord
below the calamus. In some animals respiratory movements con-
tinue for a longer or shorter period after complete removal of the
medulla oblongata. The respiratory center is in reality not a
single cell group, but a bilateral group, each in relation to the
vagus center of its own side. The two act normally in perfect
unison, but they may be divided by a longitudinal incision in the
median line, and then they lose their absolute synchronism and
each half of the respiratory apparatus may perform its function
independently of the other. The respiratory centers are in rela-
tion, however, not only with the afferent impressions conveyed by
the vagus, but also witli those of the sensory nerves in general
and very manifestly with those of the head and chest. Hence a
sudden stimulation of these surfaces, such as by a dash of water,
causes active inspiratory movements. Hut a sudden stimulation
of :i sensory surface or sensory tract causes spasmodic arrest for
a time, either in tin gtate of inspiration or under certain circum-
stances of expiration. 1 ne rhythmical alternation of inspiratory
movements i- not, however, entirely dependent on rellex excita-
tion, for respiratory movements may continue after all the afferent
nerves connected with the center have been divided. In this

case there i- ;i true automatic activity influenced by the state of
the blood it-elf. The diminution of oxygen and accumulation

of oxidation product- in the blood act a- a stimulus to the respi-

ratory centers. When the blood i- artificially byperoxygenated

566 THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

the movements of respirati some to complete stand-till, a con-
dition termed apnoea. Non-aeration of the blood, resulting from
obstruction of the respiratory functions, powerfully excites the
movements of both inspiration and expiration, and ultimately, if
the obstruction continues, causes general convulsions of the whole
body as in asphyxia. The respiratory mechanism, though essen-
tially automatic or reflex, is to a great extent under the control of
the will. It is by the volitional control we possess over the res-
piratory movements, that we are enabled to combine them with
those of articulation for the purposes of speech and vocalization
and in a similar manner by closure of the glottis and forcible con-
traction of the expiratory muscles we can aid the expulsion of the
contents of rectum and genito-urinary organs. Our volitional
control over the respiratory mechanism is limited.

Irritation of the branches of the vagus distributed to the ali-
mentary canal induces vomiting, in which there is a combination
of movements. The essentials are, dilatation of the cardiac ori-
fice of the stomach and forcible pressure on this viscus by the ex-
piratory muscles of the abdomen. It is customary to consider a
special vomiting center, which is supposed to coordinate all these
movements, but it is now held by physiologists that the facts do
not justify a center distinct from the respiratory center, with such
modifications as are conditioned by the starting point of the ex-
citing stimulus.

The medulla oblongata also excites a controlling influence on
the action of the heart and the state of the blood-pressure. The
rhythmical movements of the heart are independent of the medulla
oblongata and of the cerebro-spinal centers in general, and are
conditioned mainly by the intrinsic ganglia of the heart itself;
the heart muscle contracts rhythmically on stimulation apart from
all nerves or ganglia.

It will be recalled that the inhibitory nerves of the heart run
in the trunks of the vagi, also that cutting the vagi causes an in-
crease in the number of heart-beats ; stimulating the cut ends
causes a diminution in the number of heart beats. A greater or
less degree of inhibition is constantly maintained by the medulla,
as is shown by the acceleration of the heart's action which fol-
low- section of the vagi. The fibers which cause the inhibition
of the heart, spring from the spinal accessory nucleus and be-
long to the motor or centrifugal system. The accelerator nerves
of the heart travel through the last cervical and first dorsal gan-
glia of the sympathetic. Stimulation of these nerves, as has been
proved by Gaskell, increases the strength as well as the rate of
the cardiac contractions.

The arterial walls are maintained in a continual state of tone
which varies within certain limits, either automatically or in re-

ADJUSTMENT OF MUSCULAR ACTION. 567

flex relation with certain local and general afferent stimuli. The
tone of the 1 >1< >< ><1 vessels is in a large measure dependent upon
the gray matter of the spinal cord, the various segments of which
may be regarded as more or less independent vaso-motor centers.
But the predominating influence in the vascular system and the
presiding influence over the variations in the blood-pressure de-
pend upon the center in the medulla oblongata. As long as
the medulla is intact, all the centers situated above it maybe
removed without greatly influencing the tone of the blood vessels
or interfering with the variations of the blood-pressure. If,
however, the cord be severed below the calamus scriptorius a
general vaso-motor paralysis ensues with enormous fall of the
blood-pressure, owing to the greatly increased vascular area.
More precisely the center corresponds to the ganglionic cells of
the upper oliva or the antero-lateral nucleus. This region, or its
homologue in other animals, is termed the vaso-motor center and
this center is supposed to be connected with all the afferent nerves
capable of modifying its influence. Stimulation of the sensory
nerves causes an excitation of the vaso-motor center and constric-
tion of the arteries.

The medulla oblongata is a coordinating center of reflex actions
essential to the maintenance of life. If all the centers above the
medulla oblongata be removed life may nevertheless continue.
The respiratory movements may go on with their accustomed
regularity and rhythm ; the heart will continue to beat and the
circulation be regulated as under normal conditions ; the animal
may swallow food if it be placed in its mouth, may react in
apparently purposive manner to impressions made on the sensory
nerve-, withdrawing its limbs or endeavoring to remove itself from
the cause of irritation, or even utter a cry of pain, and yet will
be merely an unconscious, unintelligent reflex mechanism.

C COORDINATION AND EQUILIBRATION.

THE PHYSIOLOGY OF THE CEREBELLUM OR
METENCEPHALON.

1. COORDINATION: ADJUSTMENT OF MUSCULAR ACTION.

Regarded merely a- a most complicated mechanism of bony
frame-work and muscles, so adjusted as to permit almost an in-
finity of movements, changes of position, yet always in conformity

with the natural force of gravity, even to the most casual investi-
gator a correlating influence ie apparent, an arrangement by which
any change of position in a part of the body Is accomplished
through a nicely opposed action of two <>r more Beta of muscles.

Of these one relaxes a- the oilier contracts, or where several

568

THE PHYSIOLOGY OF THE NERVOUS SYSTEM

groups are concerned differenl degrees of change in tension occur
in the different groups, t < » ju-t the extenl necessary to produce the
desired movement. Such a movemenl may be initiated by a dis-
tinct, voluntary impulse, bul this voluntary impulse is apparently
very simple in comparison with the complexity of the resultant
muscular actions. Later, in considering the functions of the
cerebral cortex, we shall sec mure clearly li<>w Buch a result i- ob-
tained. I Jut it is evident that however such actions are produced,
there must be operative some controlling force, whereby the con-

Fig. 288.

Semi-diagrammatic transverse section of ;i cerebellar convolution of ;i mammal. .1. molec-
ular layer; /•'. granular layer; C, zone of tin- white substance; ./.cell of PurKinje; '>. small

star-shaped cell of the molecular layer ; </, terminal descending arborizations surr 'Hug the

cells of Purkinje; e, superficial star-shaped cells; ./'. large star-shaped cells of the granular
layer ; g, granules with their ascending axis-cj tinders bifurcated at i ; A. mossy tiher* : /, neu-
roglia cell with plume ; '«. neuroglia cell of the granular layer ; n, climbing fibers : ". ascend-
ing collaterals of the axis-cylinders of the Purkinje cells. (Cajal.)

traction and relaxation of opposed groups of muscles are properly
adjusted, giving steadiness of action, and avoiding trembling,
wavering, and other incoordinated movements. Such a force must
l>e efferent, i. e., exerted on the motor mechanism. And the cen-
ter from which it rises must he in intimate relationship with those

ADJUSTMENT OF MUSCULAR ACTION. 569

afferent nerve-currents through which, either as general or as
BpeciaJ sensation, we recognize our position relative to our sur-
roundings. Such afferent impulses in all probability arrive
through all the varied sense-apparatus, as may be learned when
one or more is wanting.

This center of unconscious control of muscular movement de-
termined by unperceived sensation, so to speak, is the cerebellum.
The controlling force which it exercises is equilibration. Through
its peduncles connecting its hemispheres with the cerebrum, with
the medulla and cord, and with each other, it receives afferent
impulse- and emits efferent ones. (See Fig. 288.)

Though there is a more general agreement among physiologists
a- to the results of lesions of the cerebellum than of any other
portion of the encephalon, there seems to be a correspondingly
greater difficulty in finding such a definition of the functions of
tin- organ as shall have a clinical and physiological value.

Experiments prove satisfactorily that destruction of the cerebel-
lum in the lower mammals is followed by long continued, if not
permanent, disorders of coordination and equilibration.

The cerebellum, like the cerebrum, does not respond to me-
chanical irritation. It has been found that if the induced current
be applied to the cortex of the cerebellum in rabbits a series of
ocular and other movements occur, depending upon the point
which is stimulated. Electric stimulation of the cerebellum pro-
duces simultaneous movements of both eyes in different directions,
according as the electrode is applied to different parts of its
surface.

Besides these ocular movements, certain movements of the head
and limbs were likewise produced. In some experiments in
which the head was maintained in a fixed position, only move-
ment- of the eye- and also sometimes of the limbs could be
observed, but when the head was released, the movements of
the eye- coincided with movements of the head. Along with
these effects the pupils were observed to become contracted on
irritating the cerebellum. The contraction of the pupil is specially
marked on the eye of the same side. The pupil may remain con-
tracted for some time alter the electric current has been removed.
Vomiting or signs of sexual excitemenl have been observed.

A-ide from these objective effects, there occur certain conditions
of consciousness or subjective sensations which have an important
bearing on the true significance of the cerebellar movements.
These modifications of consciousness must, however, be regarded

Incident only and not connected with cerebellar action as

such. The subjective phenomena depend not on the cerebellum,
but on the cerebral hemispheres.

The cerebellum seems to be a complex arrangement of Individ-

570 THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

ual, differentiated centers which in associated action regulate the
various muscular adjustments necessary to maintain equilibrium
and steadiness of the body. AVe should therefore expect to find
that a lesion which annihilates the functional activity of any of
the individual cerebellar centers should manifest itself in a ten-
dency to the overthrow of the balance in the direction naturally
opposed by this center. This is in accordance with the facts of
experiments. Stimulation of the anterior part of the middle lobe
excites muscular combinations which would counteract a tendency
to fall forward. Hence destruction of this part shows itself in a
tendency to fall forward. In this we see both the negative effect
caused by the removal of the one center, and the positive effects
excited by the unopposed and antagonistic centers. In a like
manner stimulation of the posterior part of the middle lobe calls
into play the muscular adjustments necessary to counteract a
backward displacement of the equilibrium ; and a destruction of
this region manifests itself in a tendency to fall backwards.

The lateral lobes of the cerebellum contain centers for complex
adjustments against lateral, combined with diagonal and rotary,
displacements to the opposite side, and hence, as has been found by
experiments, lesions of the lateral lobes exhibit themselves in dis-
turbances of the equilibrium either laterally to the side opposite
the lesion or, as the resultant of lateral and rotary displacement, in
rolling over to the side of the lesion. The effects of a lesion may
therefore vary, — a fact which may account for some of the dis-
crepancies among the results obtained by different experimenters.

Every form of active muscular exertion necessitates the simul-
taneous cooperation of an immense assemblage of muscular move-
ments throughout the body to secure steadiness and maintain the
general equilibrium ; and on the hypothesis that the cerebellum is
the center of these unconscious adjustments, we should expect the
cerebellum to be developed in proportion to the variety and com-
plexity of the motor activities of which the animal is capable.
The facts of comparative anatomy and development are entirely in
harmony with this hypothesis. In the reptiles and amphibia,
whose movements are groveling and sluggish or of the simplest
combination, the cerebellum is of the most rudimentary character,
while in mammals it is richly laminated and the lateral lobes
highly developed in proportion to the motor capabilities, repre-
sented in the motor zone of the cerebral hemispheres.

If we compare the relative development of the cerebellum in
the several orders of the same class of animals we find it highest
in those which have the most active and varied motor capacities,
irrespective of the grade or organization otherwise ; and the cere-
bellum of the adult is, relatively to the cerebrum, much more
highly developed than that of the newborn infant, a relation

ADJUSTMENT OF MUSCULAR ACTIOS. 571

which evidently coincides with the growth and development of the
muscular system.

The mechanism of cerebellar coordination is essentially inde-
pendent of consciousness and volition. The displacement of
equilibrium in any direction not only calls into play by reflex or
responsive action the compensatory motor adjustments, but also
induces conscious or voluntary efforts of a similar or antagonistic,
compensatory nature. Thus a tendency to fall forwards, while
renexlv calling into action the muscular combinations which pull
the body backward, may also excite consciousness and cause
voluntary effort in the same direction. The same muscular adjust-
ments which are capable of being effected by the cerebellum are
also under the control of the will and may be carried out by the
cerebral hemispheres independently of the cerebellum. Hence it
is that lesions of the cerebellum do not cause paralysis of voluntary
motion of the muscles which are concerned in these actions.

The statement has been made and adopted as a fact in certain
quarters that lesions of the cerebellum produce paralysis of mo-
tion on the opposite side of body. In these cases, as has been
pointed out by Vulpian, the hemiplegia is not the result of the
cerebellar lesions as such, but of compression or interference with
the subjacent tracts of the pons and medulla. As these decussate
in the medulla oblongata the effects of compression by a tumor of
the lateral lobe of the cerebellum is paralysis of the opposite side
of the body. Lesions of the cerebellum which do not exert such
an influence on the subjacent tracts do not cause hemiplegia on
the opposite side.

The disturbance of equilibrium is ahvays most marked imme-
diately after the infliction of injury to the cerebellum. This,
which has been by many looked upon as a sign of irritation, is to
be accounted for by the sudden derangement of the self-adjusting
mechanism on which the maintenance of equilibrium mainly de-
pends. A-, however, the animal may supplement the loss of this
mechanism by conscious efforts, in process of time it acquires the
power of voluntary adaptation and thus is enabled to maintain its
equilibrium, though perhaps with less degree of security than
before.

The more extensive the lesions the greater the disturbance of

the mechanism and the greater the difficulty of effecting through
conscious effort all the muscular adjustments necessary to main-
tain the balance. The disturbances of equilibrium are therefore
of a more enduring character and it is only by a long process of
training that volitional accommodation replaces a mechanism es-
sentially independent <>f consciousness. Even should this point
he reached, the constant attention necessary t<> preserve steadiness
ill' movement and prevent displacement of equilibrium would be

572 THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

a heavy strain on the animal's power; and it would be in accord-
ance with this condition that prolonged or varied muscular exer-
tion should cause great apparent exhaustion, actually verified by
experiments on animals.

The cerebellum was regarded by many of the older writers as
the seal of common sensibility. The opinion was founded chiefly
on the continuity of the posterior columns of the spinal cord with
the restiform bodies. That these arc mediately related with the
posterior columns through the olivary bodies, has been established
by the researches of Meynert and other anatomists, the relation
being- mainly crossed, i. e., the restiform body on one side being
related to the opposite posterior column. The posterior columns
being regarded as the path of common or tactile sensation, the
axiom that the cerebellum was a seat of common sensibility seemed
well founded. But more recent investigations into the sensory
paths of the spinal cord do not support this view of the func-
tions of the posterior columns. Brown-Sequard has shown by
direct experiment that section of the restiform bodies does not
cause loss of tactile sensation. These facts in conjunction with the
results of experimental lesions and diseases of the cerebellum af-
ford overwhelming evidence against the view that the cerebellum
is the seat of common sensation. Neither Flourens, Vulpian,
Lucieni, Ferrier nor other recent experimenters have ever ob-
served cutaneous anaesthesia in animals deprived of the cerebellum.

Through what system of fibers, or pathway, does the cere-
bellum act so as to call forth the muscular adjustments requisite
for equilibration '.' If the restiform bodies be examined for the
purpose of ascertaining this point one finds that if this tract be
injured the most turbulent disorders follow, similar to injury of
the semicircular canals. If the olivary bodies be injured distur-
bances of the equilibrium result, with rolling, forced movements
and deviation of the optic axes similar to those caused by lesions
of the middle cerebellar peduncles. These facts render it prob-
able that it is through the medium of the olivary bodies that the
impressions conveyed by the posterior columns of the cord ascend
to the cerebellum through the restiform tracts, and that it is the
interruption of these connections which leads to disorders of the
equilibrium. The restiform bodies are also related, as has already
been described, to the direct cerebellar tracts derived from the cells
of Clarke's column. It seems fairly well established that the resti-
form tracts convey tactile impressions which excite and regulate
cerebellar co;ird ination.

Relations to the Labyrinth.

The relation between the cerebellum and the auditory nerve is
suggested by anatomical considerations. The so-called auditory

RELATIONS TO THE LABYRINTH. 573

nerve ought to be subdivided into the vestibular nerve or nerve
of tonus, coordination, and equilibration, and the cochlear nerve or
nerve of hearing, just as in times past the seventh nerve of Willis
became generally known as the facial nerve and the auditory
nerve. The vestibular nerve passes from the ampullae of the
semicircular canals partly to the dorsal auditory nucleus, and
partly to the cerebellum, perhaps directly, by way of the direct
sensory cerebellar tract in the inner division of the corpus resti-
forme. This dorsal auditory nucleus is further connected on the
one hand with the superior olive having connections with the
posterior quadrigeminal bodies, and on the other hand with the
cerebellum. Further than this almost nothing is known of the
central path of the nerve. The cochlear division of the auditory
nerve seems to have nothing- to do with the cerebellum physiolog-
ically, because lesions of the cerebellum do not impair the sense
of hearing in animals, nor do diseases of the cerebellum in man
cause deafness, except in such cases as lead to direct implication
by means of pressure or otherwise of the cochlear division of the
auditory nerve or the ventral auditory nucleus.

There is thus an important influence exerted by the semicircular
canals upon the function of coordination, and we have just noted
the anatomical foundation for this influence in the connections
which exist between the labyrinth and the cerebellum. There is
further a remarkable and significant similarity between lesions of
the individual semicircular canals and injury of certain regions of
the cerebellum, and also between direct irritation of the canals
and electrical irritation of different portions of the cerebellar
cortex. Experiments involving the local irritation of the laby-
rinth in man have led to an hypothesis which assumes that stimu-
lation of the superior vertical canal causes phenomena similar to
those produced by irritation of the posterior cerebellar centers;
stimulation of the posterior vertical canal, phenomena similar to
those produced by irritation of the anterior cerebellar centers;
and stimulation of the horizontal canal, phenomena similar to
those produced by irritation of the lateral cerebellar centers.

Various forms of irritation applied to the semicircular canals
also bring out ocular movements and movements of the head and
body exactly like those produced by stimulation of various por-
tion- of the cerebellum. Similarly, if air or liquids lie injected
into the ear of man where the menihraiia tyinpani has been rup-
tured, the eyes turn to right or left, depending upon the side
which i- injected, and ;i feeling of vertigo occurs.

Animals deprived of their cerebral hemispheres are not only
able to maintain their equilibrium l»ut are also capable of coordi-
nated locomotion in their usual manner. The mechanism of this
lo. on iot ion, like the mechanism of equilibration, consists ( I ) of an

57*1 THE PHYSIOLOGY OF THE NERVOUS system.

afferenl system and (2) of a coordinating center, (3) an efferent or
motor system !>v which the center is brought into relation with
the muscles of the trunk and limb.

I, notion involves a vast complexity of motor adjustments of

the head, trunk and limbs, beyond the simple combinations of the
muscles of the limbs which are coordinated in the spinal ford.
The (inter of gravity is continually varying with each movement
of the limbs j this necessitates perpetual readjustment of the trunk
and limbs. By stimulation of the spinal cord below the calamus
scriptorius the limbs of rabbits, as shown by Ludwig, may be
tin-own into coordinated and alternating actions, such as running
and leaping, but the spinal centers alone are unable to provide for
the execution of these movements. These require the presence
and activity of the mesencephalic and cerebellar centers. When
one learns to execute movements, the sense of vision aids in a
large measure in directing the body and limbs to carry out the end
desired, and one is guided also by the sensations and impressions
arising in connection with muscular action. When these move-
ments have been learned neither vision nor the sense of muscular
action seems necessary and the most complex coordinations can be
executed with precision without attention or consciousness. What
has at one time required a conscious effort becomes an organized
reflex, provided for in the mechanism of the lower centers.

Instinctive or Emotional Expression.

Animals deprived of their cerebral hemispheres are still capable
of exhibiting, in response to various forms of sensory stimulation,
special and general reactions, more or less complex, which do not
at all differ in character from those which are associated with
emotion or feeling.

The outward expression of feeling does not necessarily imply
the existence of pain or feeling as a state of consciousness. As all
the physical manifestations of feeling are capable of being called
forth in animals deprived of their cerebral hemispheres, which
alone are the substrata of consciousness, we must regard them as
merely the reflex or instinctive response of centers in which sen-
sory impressions excite variously the motor, vasomotor, and secre-
tory apparatus. The phenomena observed in animals deprived
of their cerebral hemispheres are in all respects analogous to those
observed in human beings under the influence of chloroform which,
:i- proved by actual experiment, first annihilates the excitability
of the hemispheres, a condition coinciding with abolition of con-
sciousness,— but the mesencephalic and lower centers retain their
excitability long after tlii- point has been reached. Hence with
impressions which under normal conditions would excite not only

THE MAINTENANCE OF EQUILIBRIUM. 575

pain lmt also accompanying groans, erics, or other physical mani-
festations, when the cerebral hemispheres have been removed the
physical manifestation- alone occur, and conscious suffering is
absent.

The center- of emotional expressions are therefore situated be-
low the centers of conscious activity and ideation, and must neces-
sarily be in relation with every form of centripetal and centrifugal
impulse through which signs of feeling may be induced or mani-
fested. These conditions are not furnished below the mesen-
cephalic centers. With these, however, as the experiments of
Vulpian and others have shown, every form of reaction, excepting
perhaps the reactions special to the olfactory nerve, may be elicited
in response to appropriate peripheral stimulation, in all respects
like those shown by unmutilated animals.

But, although the facts above related prove that in the absence
of the cerebral hemispheres, acts of extraordinary complexity, —
equilibration, coordinated locomotion, adaptive reactions and signs
of feeling in response to sensory stimulation, — are capable of being-
carried out, it is a problem of surpassing difficulty to analyze the
mechanism of the various manifestations and specialize the centers
in which they are individually localized.

2. EQUILIBRATION : THE MAINTENANCE OF EQUILIBRIUM.
An animal deprived of its cerebral hemispheres is capable, not
only of maintaining its equilibrium, if undisturbed, but of regain-
ing it when overthrown. Considerable complexity and diversity
of muscular movement- all adapted for the purpose, are called into
play according to the conditions under which the animal may be

placed.

The maintenance of equilibrium involve- the conjoint operation
of three separate factors: (1) A 9ystem of afferent nerve- and
organs. (2) A coordinating center. (3) Efferent tracts in con-
nection with the muscular apparatus concerned in the action.
The faculty of equilibration is overthrown by lesion- of the affer-
ent apparatus alone or by le-ion- of encephalic center alone, or by
lesions of the efferent tract alone or by conjoint lesion- of all.
Various degrees and forms of disturbance of this function will re-
sult, according to the nature, extent and position of the lesion. In
many respects the maintenance of the equilibrium resembles the
tone of the muscles. Lesions of the afferent nerves, central gan-
glia or motor nerve* destroy the tone of muscles, and according
as tlii- occur- iii |„,t|| or only in one group of antagonistic mus-
cles we have complete muscular oaccidity, flexion, or lateral dis-
tortion. So in regard to equilibrium, similar lesions may cause
complete overthrow, or various form- of distortion exhibited as
reeling, staggering, rotation, etc.

576 nil PHYSIOLOGY OF Till-: NERVOUS SYSTEM.

The afferent apparatuses of a compound nature but mainly con-
sists of three greal systems, a\ which the maintenance of equil-
ibrium and coordination depends. These three systems are:
( 1 I ( Organs for the reception and transmission of common sensory
impressions. (2) Organs for the reception and transmission oi
visual impressions. (•">) The semi-circular canals of the internal
ear and their afferent nerves. Each of these systems will be con-
sidered separately.

1. The Influence of Tactile Impressions. — A frog deprived
of its cerebral hemispheres, l>nt in which the optic lobes and
cerebellum are intact .-till preserves the power of maintaining its
equilibrium. If now the skin be removed from the hinder ex-
tremities the animal at once loses this power and falls like a log,
when the basis of support is tilted. The removal of the skin
has destroyed the receptive organs of those sensory impressions
which are necessary to excite the coordinating center so that the
various combinations of muscles shall maintain the animal in
equilibrium. It is a law laid down by Volkmann and verified
by all subsequent observers, that reflex reactions are more capable
of being excited by impressions on the peripheral extremities of
afferent nerves than by stimuli applied to any other part of their
course. A similar result ensues in man, as has been shown by
Heydwhen the soles of the feet are rendered insensible by chloro-
form or refrigeration. The individual experiences great diffi-
culty in maintaining equilibrium when the eyes are shut, and he
oscillates and sways in a very pronounced manner. In loco-
motor ataxia, one of the characteristic symptoms in addition
to the locomotor incoordination, is the difficulty, or absolute im-
possibility, of maintaining the equilibrium when the eyes are
shut. When the individual tries to stand with his feet together and
hi- eyes shut, he oscillates greatly or actually falls if unsupported,
and it is difficult or altogether impossible for him to stand or walk
in the dark though the eyes are open. In this disease there i-
diminution or absence of sensibility to tactile impressions, so that
the patient feels as if something soft were interposed between his
feet and the ground, or he doe- not feel the ground at all. The
impairment or abolition of tactile sensibility is capable of being
compensated for, up to a certain point, at least, by visual and
other forces, but when the eyes are shut, or the light withdrawn,
equilibrium becomes difficult or impossible. Even in normal in-
dividuals the visual sense aids the tactile power. If a perfectly
normal person stands with his feet close together and the eyes closed
he perceive- more or less oscillation. ( lonsciousness i> not a neces-
sary condition for perfect equilibrium. If, however, equilibration
be deranged the condition is made known to the consciousness in
a painful manner in the form of vertigo or sense of insecurity.

THE MAINTENANCE OF EQUILIBRIUM. 577

2. The Influence of Visual Impressions. — Equilibration and
motor coordination may be acquired in the first instance and ex-
ercised without the aid of the eves, as exemplified in those born
blind. But in general, the motor adjustments used in regulating
equilibrium are guided by the sense of sight. The child who
learns to walk keeps his eyes continually on his limbs and the sur-
rounding objects, and sees that his movements are made in accord-
ance with the end desired.

When the movements become organized and automatic by fre-
quent repetition the guidance of the eyes ceases to be so necessary
and the impressions, conditioned by the movements themselves,
are sufficient to insure the requisite simultaneous and successive
motor adjustments. But, even then, visual impressions, though
not closely affecting consciousness, are not inoperative, as is
proved by the uncertain and wavering character of motor adjust-
ments, even of the most habitual or automatic character, when the
eyes are shut or the light withdrawn. When there is defect or
total default of tactile sensibility, equilibration is impossible, ex-
cept with the aid of vision. The sense of sight may compensate
for a total absence of tactile (including muscular) sensibility, and
an individual who has no sensibility in his lower extremities, and
who falls like a log when he shuts his eyes, may stand or walk if
he look- at his feet. This, however, always implies strained ef-
fort and speedily induces fatigue.

It would seem that the act of keeping the eyes open is of itself
an aid to equilibration, though the eyes are useless as organs of
vision. It has been observed that patients suffering from loco-
motor ataxia who were previously entirely blind, and able to stand
with their eyes open, oscillate much more when they are shut.
This is probably due to the interruption of the act of fixed atten-
tion, of which the steady gaze, even with sightless orbs, is the
physical expression.

The influence of vision on equilibration is further shown in the
disturbances created by unusual movements in the field of vision,
either by movements of the objects themselves, or induced by
faults in the oculo-motor apparatus. We associate position in
space, not only with certain tactile sensations, but with a certain
definite relation to surrounding objects. When the whole field of
vision is in motion, or the positions of familiar object- are dis-
torted by obliquity of the optic axis, there i^ a disturbance of the
customary relations between the visual and tactile Bensations and
a distressing sense of insecurity result — -the individual not being
able to discriminate clearly whether be himself or the objects
around him are iii motion or displaced. The difficulty of equilibra-
tion under such circumstances gives rise to the sense of vertigo,
which is merely the subjective side of the physiological disturb-
87

578 THE PHYSIOLOGY OF THE XEI!YOlrS SYSTEM.

ance. Oscillation <»f' the eyeballs <ir nystagmus, or the occurrence
of paralysis in one of the ocular muscles, such as the external
rectus, is a familiar cause of the vertigo which is caused by a lack
of harmony between the visual and tactile experiences and asso-
ciations of our relations to surrounding objects. It has been found
by Cyon that pigeons are similarly affected by distortion of the op-
tic axis. On placing prisms before their eyes be observed marked
disorder of equilibrium amounting, in some cases, to actual falling
down.

:). The Influence of Labyrinthine Impressions. — The im-
pressions which are generated in the semicircular canals of the
internal ear form the most important factor in the afferent ap-
paratus of the mechanism of equilibration and more clearly indi-
cate the essentially reflex nature of the mechanism.

When the membranous canals are injured very remarkable dis-
turbances of equilibrium ensue which vary as Flourens first
pointed out with the seat of lesion. According to the observa-
tions of Flourens and Cyon on pigeons, when the horizontal canal
is divided on the side, the head is thrown into a series of oscilla-
tions in a horizontal plane around the vertical axis. When the
posterior vertical canals are divided the disturbance of equilibra-
tion is of a similar character, but more violent. In this case the
movements of the head are in a vertical plane around a horizontal
axis. Section of the posterior vertical canals causes movements
of the head from behind forward and from right to left, or vice
versa. There is profound disturbance of equilibration and the
animal tends continually to turn somersaults heels over head.
The plane of the movements of the head in this case is diagonally
around a horizontal axis. Thus, analysis of the movements con-
sequent on section of the respective canals, shows that they take
place in the plane of the canals operated on.

It has been observed that the disturbances of equilibrium after
section of one or more of the canals on one or both sides are of
comparatively short duration. When the whole of the semi-
circular canals on one side are destroyed the disturbances of
equilibrium are also transitory. When all the canals are de-
stroyed on both sides the disturbances of equilibration are of the
most pronounced character. Goltz describes a pigeon so treated,
which always kept its head with the occiput touching the breast,
the vertex directed downwards with the right eye looking to the
left, and the left looking to the right, the head being almost in-
cessantly swung in this position in a pendulum-like manner.
Cyon says it is impossible to give an idea of the perpetual move-
ments to which the animal is subject. It can neither stand, nor
lie still, nor fly, nor maintain any fixed attitude. It executes
violent somersaults, now forward, now backward, rolls round

THE MAINTENANCE OF EQUILIBRIUM. 579

and round, or springs in the air and foils back to recommence
anew. It is necessary to envelop the animals in some soft cover-
ing to prevent their dashing themselves to pieces by the violence
of their movements, and even this is not always successful.
The extreme agitation is manifest only during the first few
days following the operation, and the animal may then be set free
without danger, but is still unable to stand or walk, and tumul-
tuous movements come on from the slightest disturbances.

In what maimer do injuries of the semicircular canals cause
disorders of the equilibration ? The first supposition which sug-
gests itself is that these disorders are related to the disturbance of
the sense of hearing. It has, however, been abundantly proven
that this is not the case.

The phenomena observed in connection with lesion of the semi-
circular canals clearly point to these organs as the source of impres-
sion which are necessary for the maintenance of the equilibrium
and without which optic and tactile impressions alone barely suf-
fice even after prolonged education.

■i. Symptoms of Cerebellar Disease. — The most characteristic symp-
tom of cerebellar disease in man, apart from indirect complications, is
an uncertain or reeling gait, like that of alcoholic intoxication. But
this symptom, though general and pathognomonic, has not always been
observed in eases in which it lias been proved by post-mortem examina-
tion that disease of considerable extent has existed in the cerebellum
during lifb. Unless the disease has been of a sudden character, none
of the violent and tumultuous disorders which characterize the abrupt
lesions of physiological experiments have been met with, and this is
a feet which the gradual subsidence of the symptoms in the lower ani-
mals would lead us to expect. It is also true that limited lesions can
run their course without manifest symptoms, particularly when the
Lesion involves a lobe or part of it. But when the whole cerebellum
has hern involved, or has been greatly or completely atrophied, careful
observation has never tidied to discover a greater or less degree of
awkwardness of movements and instability of equilibrium.

.Many of the cases of atrophy of the cerebellum on record have been
found in imbeciles, but it is clear from other evidences that the imbe-
cility or impaired intelligence is only a symptom of cerebral defect coin-
cident with that which has led to the cerebellar symptom. The most
remarkable case is that of Alexandrine Labrosse, reported by Corbette.
Tins lt i i " 1 lived to the age Of eleven years, and it was found after death

thai the cerebellum was entirely atrophied, its place being occupied
by a cyst containing serum. Physically she was \\ ell de\ eloped for her
age, bul -he was five years of age before she was able to stand, ami at
the age of seven she was very insecure on her legs ami often fell. Her
Intelligence was defective ami her articulation indistinct, but all her
sensory faculties wen- normal.

An almost e<piall\ remarkable brain was examined by I'errier. It

was thai of a girl who died of phthisis at the age of fifteen. Nothing
was ascertained respecting her early life. She was somewhal weak in
intellect, but not to any greal extent, and had the narrow palate of the
imbecile. Owing to this her articulation was somewhal indistinct. No

580 THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

deficiency existed as regards her sensory faculties, general or special,

and iIk ly peculiarity observable in her motor powers was a general

muscular weakness and a tremor of the hands when Bhe was using
them, 1 > 1 1 1 this was attributed to the debility associated with her
phthisical condition, and she could walk well and steadily, though she
was never known to run.

At'ier death no abnormality could be detected in the cerebrum, which
was well developed, hut the cerebellum was very illy developed; in
fact, it was arrested at a very early stage. The left lobe was a mere
pallida, the vermiform process a minute nodule, obscurely marked with
Laminae, while the right lobe, which contributed the main portion, was
only a half of a square inch in superficial area and only a quarter of an
inch in thickness at its base. The pons was indicated by only a few
transverse libers, which barely concealed the pyramidal tracts in their
course from the foot of the cerebral peduncles. The corpora quadri-
gemina had a normal size and appearance ; the olivary bodies of the
medulla oblongata were only obscurely indicated. With the exception
of the cerebellum and the peduncles, which were reduced to insig-
nificant dimensions, the rest of the brain and all the cranial nerves
were perfectly normal in appearance.

It is evident from examination of repeated cases that, though cere-
bellar disease in man is frequently associated with symptoms similar to
i hose which result from experimental lesions in the lower animals, yet
the organ may be almost entirely degenerated without any more obvi-
ous symptoms than a greater or less degree of unsteadiness of move-
ment or instability of equilibrium. If the cerebellum were absolutely
necessary for the coordination of movements it would be impossible to
harmonize the actual facts of clinical observations with a hypothesis so
formulated. For, in the case of Alexandrine Labrosse, it would have
been impossible for her to walk at all if the coordinated movements
were dependent on the cerebellum as the organ of equilibration. If.
however, we regard the cerebellum as an organ of equilibration, it will
be possible to bring all the symptoms, acute and chronic, into harmony
With this hypothesis.

I). VISION, COORDINATION OF EQUILIBRATION
MOVEMENTS.

THE PHYSIOLOGY OF THE CORPOEA QUADRIGEMINA' OR
MESENCEPHALON.

The fibrous connections of the two anterior quadrigemina are as
follows :

( i ) AVith the cortex of the occipital lobe of the same side through
anterior arms of the corpora quadrigemina. (n ) AVith the pos-
terior and lateral tracts of the spinal cord. ([II) AVith the optic
tract, through the anterior arms of the corpora quadrigemina.

'Of the mesencephalon the corpora quadrigemina represent only the roof.
The optic tracts form a prominent feature of the walls of the mid-hrain. The base
of the mid-brain includes prominent " masses of fibers which arise in the fore-
brain and inter-brain and traverse the mid-brain on their way to parts beyond"

I Edinger). It is from nuclei in the base of the mid-hrain that tin ulo-motoriufl

and trochlears arise.

CORPORA QUADRIGEMINA OR MESENCEPHALON. 581

The fibrous connections with the posterior quadrigemina are the
following- : (i) With the cortex of the temporal lobe of the same
side through the posterior arms of the corpora quadrigemina. (n)
With the tegmentum through the lemniscus lateralis, which de-
livers to the posterior corpora quadrigemina acoustic fibers, prob-
ably also Hlirrs from the posterior tract of the spinal cord, (in)
With the inferior commissure of the optic tract through the poste-
rior arms of the corpora quadrigemina.

The optic lobes or corpora bigemina of fishes, batrachians and
birds arc structurally homologous with the anterior corpora quad-
rigemina of mammals.

Fig. 289.

corjxM ye/ue /«/.

'ens oculomoforius

cortex cerebri

im of the probable relations of some of the nerve-cella and fibers belonging to the reti-
nal and "-Hi raJ ritual apparatus, (Schakfkr.)

The obvious anatomical em meet ion bel ween the optic tracts and
the anterior quadrigemina] tubercles of mammals is sufficient to
indicate thai these centers have some important relations to ret-
inal impressions. (Study Fig. 289.)

582

THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

The facts of anatomy as well a> those of physiological and
pathological experiments indicate thai the corpora quadrigemina,
though not the centers of vision proper, arc center- of coordination
between retinal impressions and motor reactions or adjustments of
considerable complexity. It is difficult, if at all possible, to dif-
ferentiate dearly between the effects of Lesions of the corpora
quadrigemina and of those tracts with which they arc related. In
this connection a study of Fig. 290 may be suggestive.

Fk

290.

Showing the minute structure of the mid-brain-roof. Two sections are placed side by side
for comparison of t lie layers. The right-hand section is from a frog : the left-hand cue from a
lizard. Various connecti6ns may be traced between the optic trac! and the stratum medullare
profundum. When one remembers thai tin- //-. tecto-spinates.et teclo-bulbares are traced into the
stratum medullare profundum we .see a basis foi ^dinger's suggestion that "through this
structure there arises an extraordinarily great opportunity for the transmission of light
impressions to the general sensory tract." | Edinger, y. edit., p. 116. >

When the hemispheres are removed the pupils will contract to
light and the eyes are moved in response to retinal impressions
and in accordance with variations in the position of head and
body.

The movements of the iris and eye-mnscles are presided over
by the nuclei of the third and fourth nerve- situated in the ven-
tral aspect of the aqueduct of Sylvius. After removal of the cere-
bral hemispheres in dogs, it has been found that the application
of electrical stimulation to the floor of the aqueduct of Sylvius
and posterior part of the third ventricle gives rise to different
ocular movements, according to the position of the electrodes.

Flourens found that destruction of the optic lobes in birds
caused blindness and dilatation of the pupils with cessation of their
reactions to light ; and he also found that the relations of the op-

CORPORA QUADRIGEMINA OR MESENCEPHALON. 583

tie lobes were entirely crossed, e. </., destruction of the left lobe
causing- total loss of vision in the right eye and destruction of the
right lobe causing total loss of vision in the left eye. The cross
relations bit ween the eyes and optic lobes have their foundation
in the decussation of the optic tracts in the optic chiasma, but
the extent of the decussation varies in different animals. De-
structive lesions of one optic tract in man causes homonomous
hemianopsia of both eyes. Experiments have shown that after
enucleation of one eye in cats and dogs, partial atrophy occurs
in both optic tracts, but to a much greater extent in the tract of
the opposite side.

It has been observed that lesions of the corpora quadrigemina
in various animals give rise to marked disturbances of equili-
brium and irregularity of movement. While able to make coor-
dinated movements of defense and the like, they had entirely
lost the power smoothly to coordinate equilibration movements.
That this coordination of equilibrium is not due merely to the
blindness resulting from the destruction of the optic lobes is
shown by the fact that a frog deprived of its cerebral hemispheres
and also of its eyes, is still able to maintain its equilibrium as
before. If the optic lobes alone are destroyed, exact equilibra-
tion is impossible, even though all the other encephalic centers are
retained.

Effects of Irritation. — The excitability and effects of irrita-
tion of the corpora quadrigemina or optic lobes, by various stim-
uli, have been differently stated by different observers. Ferrier
maintains that mechanical irritation of the surface of these bodies is
capable of inducing distinct indication of excitability. The act of
merely touching these ganglia with a sponge is sufficient to cause
general and more or less indefinite movements of the trunk and
limb-. The slightest superficial puncture of the corpora quadri-
gemina in rabbitB causes them to start suddenly and bound away as
if in great agitation and alarm. These symptoms speedily subside
and it is almost impossible to discover any signs of anatomical lesion
from the Blight puncture which is sufficient to give rise to these
manifestations. Much, however, depends on the vital condition
of these ganglia at the time of experiment. When they are ex-
hausted by -hock or hemorrhage or paralyzed by narcotics excita-
tion may have little or no perceptible effects. The optic lobes
have been found extremely sensitive to electrical currents.

The explanation of the effects of irritation of the corpora quad-
rigemina and of the relation between these and the effects of de-
structive lesions, is a matter of speculation only. Though elec-
trical stimulation i- not strictly localizable, and there is always a

ri-k of diffusion, il has been shown that mere mechanical irrita-
tion of tin- surface of the corpora quadrigemina is sufficient to

584 THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

produce motor manifestations, in which case obviously conduction
t<> subjacent or neighboring tracts can play no part. The strength
of current sufficient to produce active manifestations when ap-
plied to the surface of the corpora quadrigemina is very weak
and barely perceptible when applied to the tip of the tongue;
so that the risk of diffusion is very slight, and it is a fact which
cannot be explained away by mere diffusion to subjacent struc-
tures. Irritation of the posterior tubercles differs from that of the
anterior in at least one important particular, viz.: the excitation
of cries of various kinds. These are not observed on irritation
of the anterior tubercles. If it were merely a matter of diffusion
to subjacent tracts, the same results should occur in both cases.
Then again there is an anatomical difference between the anterior
and posterior quadrigemina which supports the view that the phe-
nomena are due to the direct excitation of these ganglia as such.
The surface of the anterior quadrigeminal bodies is composed of
zonal fibers, superficial gray matter and medullary fibers which
are directly related to the optic tracts, structures, however, are
not found in the posterior bodies.

Human pathological and clinical observation teaches that the
constant symptoms accompanying disease of the corpora quadri-
gemina are : stumbling gait, disorders of vision, and sometime-
disturbances of hearing.

E. THE PHYSIOLOGY OF THE INTER-BRAIN OR
THALAMENCEPHALON.

Almost nothing is known of the physiology of the inter-brain.
Certain features of its structure are suggestive, however, of func-
tions which it may some time be demonstrated to possess.

(a) As A Relay Station the inter-brain seems to serve its
principal function. " The nuclei of the inter-brain receive fibers
from the basal ganglia of the fore-brain and give off posteriorly
new tracts to centers which lie at a lower level. * * * We see
in the thalamencephalon a great center which is inserted between
an important part of the cerebrum and nearly all other parts of
the brain " (Edinger, V. Edit., p. 134). That the development
of this segment of the brain is largely dependent upon that of the
cerebrum is evident from the fact that "with the development of an
extended cerebral cortex more <nxl more bundles ojijicor which pass
front it into the ganglia of the thalamus" (Edinger, p. loo).

(6) As a Sensory Center the inter-brain must be given some
credit. Fig. 289 shows the lateral geniculate body, a part of the
thalamus, as a May station between the retina and the cerebral
cortex of the visual center in the occipital lobe. In a similar
way the internal geniculate body is a way station on the path of
auditory sensation.

THE VASCULAR SUPPLY OF THE BRAIN. 585

F. THE PHYSIOLOGY OF THE CEREBRUM OR
PROSENCEPHALON.

1. INTRODUCTORY.

a. The Vascular Supply of the Brain.

1. The Arteries of the Brain. — Our knowledge of the vascular sup-
ply of the brain has been rendered more accurate owing to the indepen-
dent labors of Huebner and Duret. The entire arterial supply of the
brain has been divided into two systems, viz : a basal and a cortical
arterial system. Here we shall have to deal more particularly with the
latter. For the full description of the source and arrangement of the
basal system the student is referred to his anatomical text-books.

(a) The Distribution of the Cerebral Arteries. — From the basal
arterial system as represented by the circle of Willis, numerous small
branches pass off nearly at right angles and enter the ganglia near the
base of the brain; these are called terminal or end-arteries because
they do not anastomose with one another nor do they anastomose with
the vessels of the cortical arterial system. The anterior cerebral and
the middle cerebral are the main arteries of the fore-brain. The former
supplies the superior frontal and anterior two-thirds of the middle
frontal convolution and the upper extremity of the ascending frontal.
Its branches are distributed to the upper half of the median surface
<»(' the cerebral hemisphere from the frontal apex to the sulcus occipi-
talis, and on the lateral surface to the superior half of the frontal and
parietal lobes.

The middle cerebral artery supplies the lower half of the frontal and
parietal lobes, and the upper two-thirds of the temporal and occipital
Lobes on the lateral surface of the hemisphere, while on the median sur-
face it -applies a small area, including the hippocampal region and the
apex of the temporal lobe. It supplies the corpus striatum and the
caudate and lenticular nuclei.

The posterior cerebral artery is distributed to the posterior two-thirds
of the basal aspect of the brain, extending up laterally to include the
lower third of the temporal and occipital lobes, and on the median sur-
face, t he inferior one-fourth.

Prom the distribution of the anterior, middle and posterior cerebral
arteries we see that they determine the blood supply to certain regions.
Each main artery gives off secondary and tertiary branches. These
tertiary branches in their turn give off numerous fine arterioles, which,
according to Duret, do not anastomose with one another, although
a Communication may take place to a certain extent between the
branches of contiguous areas. Opinions differ considerably upon the
question of anastomosis between the vessels of the cortical system. Bueb-
ner, basing his opinion upon the resull of his injections, believes that
there i- ;i free ;i n;i - 1 omosis between the main vessels, and also between

the secondary branches of t he \ essels of t he cortex, the anastomosis be-
ing effected through vessels not less than a millimeter in diameter.
He doe- nut believe thai collateral compensation is effected solely
through the circle of Willis. In consequence of this view, objection is
taken t<> the statement that an artery supplies any definite region or
convolution. In support of Huebner' s view, we have the facl admitted
by Chared that in certain cases of arterial obstruction by embolism or
thrombosis there is an exemption from softening which would point to

586 THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

the establishment of a collateral circulation. Duret contends that such
an anastomosis is absenl or extremely ran-, and he maintains that it is
only through the terminal filaments of the branchlets that communica-
tions occur. Such communications, however, he believes may vary in
numher in different individuals. Cohnheim also maintains that there
arc anastomoses between the larger branches of trunk arteries, but that
all the cerebral arteries more or less resemble true terminal or end
arteries, in that they communicate with other vessels through their ulti-
mate capillary loops only.

(b) Structure of the Cerebral Arteries. — The cerebral arteries
have less muscular element than those of the body generally. In the
larger arteries the tunica adventitia is directly continuous with pia
mater, whilst in smaller vessels the sheath becomes an extremely tine
membranous investment, either structureless or faintly striated, and
with nucleated connective tissue corpuscles upon it.

The vessels of the cortex lie in channels — the perivascular channels
of His. Numerous delicate fibrillar processes which arise from the
stellate cells of the cortex traverse this perivascular space and form
connection with the arterial sheath. The capillaries of the cortex are
of extremely fine caliber (not over 4 « in diameter) and of less diameter
than the red-blood corpuscles. Bevan L3wis says, however, that we
must allow for possible shrinking of the vessel by emptying its channel,
as well as for a constricting effect of reagent, and that we can scarcely
conclude that even these minute ramifications do not permit the passage
of the red-blood corpuscle.

2 Arterioles of the Cortex. — In his monograph on the structure of
the cerebral cortex, Meynert showed that in the cerebral cortex with a
large number of arterioles from the broad expansion of pia, all these
arterioles were about the same size and entered adjacent portions of
the brain tissue. Each one, moreover, represented to a certain degree,
an independent circulatory area. This observation led him to the be-
lief that in the mass of tissue supplied by a small number of larger ar-
terial branches it would be quite possible for differences of blood supply
to exist simultaneously in adjacent portions of that tissue. From this
he inferred that partial functional hyperaemia of separate cortical areas
is readily possible and that the so-called cortical areas could be func-
tionally hypenemic when the other cortical centers were functionally at
rest. The blood supply to the brain would in this way be determined
by the functional hyperemia of the areas which were in a state of
activity. In the pia mater we have then main arteries with their branch-
lets and filaments, and a great number of minute arteriole twigs pass-
ing at right angles into cortex. These are commonly known as nutri-
ent arteries. In cases of embolism or thrombosis, therefore, not only
does the gray matter of the cortex suffer, but also the subjacent white
matter, the amount of destruction, of course, depending upon the size
of the vessel obstructed and the amount of communication existing be-
tween it and its neighbors. Meynert states that the larger branches of
the arteries or the surface of the brain do not lie within the pia, but in
the sub-arachnoid spaces.

3. The Venous Circulation. — The venous circulation within the
cranium presents several peculiar features; the blood flows along the
longitudinal sinus toward the occiput, and hence its course is opposed
in direction to the blood issuing from the cortical veins which open
into the sinus in a forward direction. Hence the fact that the blood
which enters the brain by ascending arteries reaches the sinuses by as-
cending veins is made use of to explain the occurrence of thrombosis

THE VASCULAR SUPPLY OF THE BRAIN. 587

in these vessels, the explanation being that their gravitation is opposed
to flow of blood. In this way morbid processes affecting the scalp,
such as erysipelas, caries, carbuncle, may readily affect intracranial
structures by means of the communication with intracranial veins,
e. g., those of the nose, the facial through the ophthalmic, the mastoid
veins, aud the veins of the diploe. Cerebral anaemia is sometimes
produced owing to hydrostatic causes as when a person who has been
in bed for a long time and whose blood is small in amount is suddenly
raised into the erect position. Such a condition is not infrequently
attended by loss of consciousness. Liebermeister regards the thyroid
gland as a collateral blood reservoir, which empties its blood towards
the head during such changes of the position of the body.

4. Lymphatic System. — To the study of the lymphatic system of the
brain considerable importance is attached, and our knowledge upon
this difficult subject may be attributed chiefly to the labors of Ober-
steiner, Key, Retzius, Schwalbe, Meynert and Bevan Lewis. Ober-
steiner was the first to define the nature and connections of the lymph
channels. Bevan Lewis is, however, to be credited with having given
us the latest and most advanced details as to the relationship of the
cortical nerve-cells to these lymph channels, both in health and dis-
ease. It will perhaps simplify the subject if Ave diverge for a moment
to consider the endocranial fluids in general.

(a) Movements and Inter-relations of the Endocranial
Fluids are important factors in the nutrition of the brain. If the
brain were surrounded merely by rigid cranial walls, a partial change
in the distribution of arterial blood would be conceivable. A func-
tional increase, however, would be possible only upon one of two con-
ditions, viz.: A corresponding collateral arterial diminution, or a trans-
fer of venous blood in the direction of the sinuses. For the first
condition Lewis thought it would be difficult to explain an appropriate
mechanism. A venous transfer would be altogether too slow and there
could not be any continuous action because the propulsion of the ve-
nous current, dependent upon the respiratory movements, would give
rise to a frequently interrupted flow of venous blood in the brain. The
cranial cavity is not entirely filled by the brain, it includes in addition
a number of spaces filled with lymphatic fluid. The dura mater is
separated from the arachnoid by a comparatively small space which is
lined by the endothelium. This space communicates with the lym-
phatic glands of the neck, and with the sub-dural spaces which do not
immediately surround the nerve roots, but do so in common with the
arachnoid and are connected with the lymphatic spaces of peripheral
nerves. As an example we have the communication between the audi-
tory labyrinth and the sub-dural space through the space which sur-
rounds the auditory nerve. In the tissue of the dura itself there are
also lymph spaces which arc connected with the subdural space.

(b) The Explanation of the So-called Lymph Cisterns is to be
found in tin- relationship of the arachnoid membrane to the pia. They
an- connected by means of a net-work of threads and trabecules of con-
nective tissue and at the base of the brain by li ica lis of perforated meni-
branes. At tin- summit of the convolutions the threads of this net-
work are narrower than over the sulci : while at the base of the brain
Where the subarachnoidal -pace- arc dilated there may he no trabec-
ular .M < \ ii < it enumerates the following cisterns which belong to the

-nrface of the cortex: (i) the space of the fossa Sylvii: (II) farther

back the cysterna chiasmatis. In the brain cortes all the vessels are
inclosed within channel-, known as the perivascular channels of His.

588 THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

These channels are noticeable in hardened sections and most markedly
so in cases of atrophy of the cortex.

The study of the lymph connective tissue is of greal importance in
cerebral pathology, but it is yet to he shown how the individual ele-
ments ol'this system undergo morbid Changes and cause alterations ill
the movements of the lymph.

5. Cerebro-spinal Fluid. — The cerebro-spinal Quid in the brain is se-
creted by the epithelium of the choroid plexus in the lateral, the third
and the fourth ventricles, and possibly from the general epithelial lin-
ings of these cavities. The fluid is transparent and has a Sp. Gr. of
about 1010. The view that the lymph cisterns act as water cushions to
minimize the shock to the brain and to compensate for variations in the
blood-pressure is supported by the fact that in cases of spina bifida the
cerebro-spinal fluid can be readily driven from the spinal cord into the
cranial cavity by pressure of the tumor, so that it may be assumed a
passage may be as readily effected in the reverse direction.

<;. Quantitative Relation Between Blood and Cerebro-spinal
Fluids. — There is an intimate relation between the amount of cerebro-
spinal fluid and blood within the cranial cavity. Formerly it was
taught that as the skull is a rigid box, and as the brain substance and
its fluid are practically incompressible, no variation in the amount of
blood in the brain could be possible. This, however, is now proved to
be erroneous. The average quantity of cerebro-spinal fluid within the
cranium is about two ounces, and if it be suddenly withdrawn epilepsy
or convulsions may be produced, or if it be rapidly increased in amount
coma may result. This fluid has also important mechanical functions,
protecting delicate parts of the brain from injury, and distributing vi-
bratory impulses. The presence of the cerebro-spinal fluid is, as
pointed out by Donders, of great importance in regulating the pressure
uniformly when brain movements occur, so that every systolic and ex-
piratory dilatation of the blood vessels is concentrated upon those parts
of the cerebral membrane which do not offer any resistance.

b. The Movements of the Brain.

The movements of the brain are of three kinds : (i) Pulsatile move-
ments communicated from the pulsations of the large basal cerebral
vessels, (u) Respiratory movements ; brain rising during expiration,
and falling during inspiration, (in) Vascular elevation and depression,
which alternate and are due to periodic dilatation and contraction of
the blood vessels. This last is a periodic arterial dilatation regulated
by the vaso-motor center and occurring from one to six times per
minute. These movements have been investigated chiefly over the
fontanelles of children and where the membranes have been exposed by
trephining. The advance of the dilatation wave within the rigid
cranial walls aids in the establishment of currents of brain fluid
whereby metabolic waste products are carried off through the lym-
phatic fluid. The brain and the fluid surrounding it are subjected to a
certain mean pressure which depends upon the blood-pressure within
the vascular system. Naunyn and Schreiber showed that cerebral
pressure must be slightly less than pressure within the carotid before
the symptoms proper to pressure on the brain occur. The vascular
wave causes an expansion of the cerebral mass, followed by a contrac-
tion.

Meynert concluded that all stimuli acting on the sensorium create
vascular movements and disturb the periodic changes in the condition

THE PHYSIOLOGY OF THE CEREBRUM. 589

of the vessels and that of the psychic influences -which may cause eleva-
tion of blood-pressure, the emotions act more readily and bring about a
greater chance than purely intellectual processes. Great variations of
brain pressure arc almost constantly attended by symptoms of disturb-
ances of the nutrition of the brain. If the pressure is moderate the symp-
toms may remain latent or only show themselves as headache, vertigo,
weakness or disturbance of the sensory function. During sleep the cir-
culation of the lymphatic fluid in the brain effects the removal of the
waste products and this is to a great extent dependent upon the vascu-
lar movements of the brain. Burckhardt regards the influence of this
vascular wave as far more powerful than that of the respiratory wave.
The irregularities of vascular wave movements which occur when the
individual is awake indicate that in certain parts of the brain there is
an independence of action just as we know it to be the case in reflex
arterial constrictions on the surface of the body.

Pulsatory movements originate from the circle of Willis ; the arte-
ries ascend and their currents are directed upward, as is also the case
with the venous currents. The arteries at the base are first to enlarge
with the blood flow, then the wave passes into all the branches of the
vessels. The brain, however, is ouly able to enlarge concentrically to-
ward the ventricles on account of the resistance ottered by the roof of
the skull to the swellings of the convolutions. This concentric swell-
ing of the brain is almost constant and the pressure is neutralized in the
ventricles, partly owing to the tact that there is a displacement of cere-
bro-spinal fluid in the ventricles. When the engorgement of the
walls of the ventricles ceases, the blood supply which reaches the cor-
tex through the long arteries is carried downward.

The act of inspiration causes a fall, that of expiration causes an ele-
vation of pulse wave. This influence is most noticeable during forced
efforts of expiration and depends upon variations in the venous pres-
sure. As a result of venous pressure, concentric swelling of the hemi-
spheres occurs. The venous pressure acts from the vertex downward
instead of from the base upward as does the pulse wave.

2. CONSCIOUS SENSATION, VOLUNTARY MOVEMENTS,
MEMORY, REASON.

THE PHYSIOLOGY OF THE CEREBRUM.

a. General Consideration.

We have already briefly discussed the actions which an animal is
capable of, when all the centers above the medulla oblongata have
been removed, and we have endeavored t<> assign to the medulla
oblongata and cord the functions proper to each. In a similar
manner the functions of all the parts of the encephalon may be
determined by ;i study and analysis of tin' various forms of ac-
tivity which are manifested by animals from which all centers
situated in advance of the optic thalami and optic lube- have been

removed.

When we turn from the consideration of these fact-- themselves
t<. the theory of their explanation we enter on a vexed question in
physiology. One fundamental fad seems, however, indisputable

590

THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

and established, viz.: Thai in the absence of cerebral hemispheres^
the lower centers are of themselves incapable of originating active
manifestations of any kind. When the hemispheres are removed
all the actions of the animal become the immediate and necessary

response to the form and intensity of the stimulus communicated
to its afferent nerves. Without such excitation from without the
animal remains motionless and inert. It is true that some of the
phenomena would seem opposed to this view, hut this is only in
appearance, not in reality. Thus a frog may occasionally move
its limbs spontaneously and a bird may yawn, shake its feather-,
or change the foot, but these actions are the result of impressions
arising from cutaneous irritation caused by the wounded surface
resulting from the operation. The relation between the cerebrum
and the sensory and motor tracts is shown and described in some
detail in Plates I Y. and V. The reader will find it profitable at
this point to make a careful study of these plates, also of figures
291, 292 and 293.

Fig. 291.

Tran >\ lis. section of the cerebrum, showing the probable disposition of tin- commissural ami
projection-fibers. A, corpus callosum; B, anterior commissure ; C, pyramidal pathway formed
ni' the projection-fibers. (Cajai.)

If we inquire into the nature of the processes which immediately
precede this responsive activity, we are led to ask, are these actions
merely reflex or are they accompanied by sensation ? If we de-
fine sensation as the consciousness of impression, it will be seen
that the problem which confronts us for solution is whether there
is a consciousness accompanying the acts of these animals that are
minus their cerebral hemispheres, in other words are these ani-
mals, under the conditions of the experiments, capable of psychic
activity '.'

If we were to accept without question the metaphysical view,
the answer would not be difficult, viz.: that abolition of the hemi-

ving course <*i Sensory Fibre* from Periphery to Cord, Cerebrum
I Cerebellum. |Gray, after Flatau.]

ral station on sen lory tract Entering- as posterior root the axon <li\i<l<-s Into short

wending branch (i, 2, 3, (). Thelattei may soon terminate

id to medullai centri id ti

1 h<- farther one pro< eeds from the Bource ol a fibre (4) the nearer

le find it to the posterioi median plane ol the cord Prom the »». %rac. and nuc. cuneatm the

into the Ifmi toward the median line, decussate with corresponding fibres "i oppo

' '-/ the lemni u » 1 and form the medial lemnist us, with which most ol the fibres pro

through the medulla, the pons, and the ci cortex, Th< id lies in the tegmen

.■.Minn .,1 the i 11 1 < inrii . apsule, th< <> the

lutlined in figure showing mesial aspect oi lefl hall ol the brain ol
il branches tracts, but the on< outlined Is the moil

Important

PLATE V.

Diagram showing course of Motor Fibres from the Cerebrum and Cord to the
Periphery. [Gray, after Flatau.]

The motor impulses proceed from the pyramidal cells of the motor area of the cortex to the pyra-
midal fibres, via the corona radiata to the motor nuclei of the cranial and the spinal nerves, the former
lying in the brain stem and the latter in the anterior horns of the spinal cord. Note that the motor
fibres lie anterior to the sensory in the internal capsule (Compare Plate IV. j, and that they pass into the
crura cerebri lving in the most ventral portion in what is known as the Pes, thence through the pons and
medulla, where thev are visible as two compact bundles, the pyramids (Py). At the lower end of the
medulla, in the region of the first and second cervical nerves, there is a decussation of the pyramids, one
portion of each pyramid decussates and passes down the cord in the lateral pyramidal column, while
the other passes without decussating down the anterior pyramidal column or column of Tiirck. Note that
collaterals from the fibres of the column of Tiirck, pass to the opposite side of the cord through the anter-
ior commissure to motor cells of opposite side : so that eventually all of the motor tract crosses to the
opposite side, where they arborize around motor cells of the anterior horns. The axons from these cells
pass out the anterior roots and are distributed to muscles and glands.

THE PHYSIOLOGY OF THE CEREBRI')!.

591

spheres abolishes certain fundamental powers of mind, that the
functions of the lower centers lie outside of the sphere of the mind

Fig. 292.

Fig. 293.

Probable direction of the currents and the
nervous protoplasmic connections in the cell of
tin cerebral cortex. A, small pyramidal a II :
/;. large pyramidal cell: C, D, polymorphous
cells : /.'. terminal fiber coming from other
nerve-centers; /^collaterals of the whi
bet; G, axis-cylinder bifurcating in the white
matter. (Cajal.)

proper. But this way of look-
ing at the subject does not har-
monize with known physiolog-
ical facts. It is known that
areas may be cut away from the
hemispheres involving the terri-
tory of intellectual consciousness
without interfering with con-
sciousness ; the will may be
abolished while consciousness
remains. Hence we are Dot
entitled to Bay that mind as a unit has a local habitation in any
one pari of the encephalon but rather thai mental manifes-
tations depend on the conjoint action of several parts. If we

Human cortex stained with Wefgert'j hsma-
toxylin on the left, and by Uol&rs method on
the right.

592 THE PHYSIOLOGY OF THE XEJIVOI'S SYSTEM.

study the uervous results which arc brought about by external
StimulatlOD of animals it will he found impossible to determine
how far the element of consciousness inter- into the reaction.
Tims a seven1 pinch on the tail or foot of a brainless rabbit elicits,
nut merely convulsive reflex movements, but calls forth a repeated
and prolonged cry which is characteristic of pain. But may it
qo1 I'c that the mesencephalon is a center of reflex action of a
special form, differing from the spinal cord not in kind, but in de-
cree of complexity '.' Just as the medulla oblongata is a more
highly specialized and complex center than the spinal cord, so the
mesencephalon may be the center of still more highly specialized
reflex action. Hence the plaintive cry may be purely a reflex
phenomenon, not depending on any true sense of pain.

b. Localization of Functions in the Cerebrum.

The phenomena of disease throw light on this question ; for
example, if a disease can occur which will practically detach the
cerebrum from the mesencephalon and leave thought and speech
intact we may expect to collect symptoms and testimony which
will point to the location or localization of the consciousness of
impressions. If the crus cerebri or the posterior part of the
internal capsule be diseased, which are not uncommon occurrences
in clinical experiences, the individual has absolutely no conscious-
ness of tactile impressions made on the opposite side of his body.
In the mesencephalon alone therefore sensory impressions are not
correlated with modifications of consciousness ; hence we must
conclude that sensation is a function of the higher centers. We
may conclude from the homology of the mesencephalon of man
with that of the lower vertebrates that all are of the same type
and only differ in degree of independence.

The following words of Herbert Spencer (Principles of Psychol-
ogy, L870) contain the pith of our knowledge with reference to
special location of mental action : " Whoever calmly considers the
question cannot long resist the conviction that different parts of
the cerebrum must in some way or other subserve different kinds
of mental action. The different parts of the cerebrum do sub-
serve different kinds of mental action, but they only subserve,
and we cannot as yet determine where or how the different kinds
of mental action are ultimately served." Further, Herbert
Spencer says : "Localization of function is the law of all organ-
ization whatsoever, and it would be marvelous were there here
an exception. Either there is some arrangement, some organiza-
tion in the cerebrum or there is none. If there is no organization
the cerebrum is a chaotic mass of fibers incapable of performing
any orderly action. If there is some organization it must consist

LOCALIZATION OF FUNCTIONS IN THE CEREBRUM. 593

in the same physiological division of labor in which all organiza-
tion consists, and there is no division of labor physiological or
other, but what involves the concentration of special kinds of
activity in special places."

It has already been learned from the facts of human physiology
and pathology that consciousness is inseparable from the activity
of the cerebral hemispheres, and that therefore, however much
the responsive actions of the lower ganglia may resemble con-
scious actions, they do not come within the sphere of truly phys-
ical phenomena.

Up to a recent date, the results of experimental physiology and
human pathology had been considered as opposed to the localiza-
tion of special functions in distinct regions of cerebral hemi-
spheres. Many unquestionable facts of clinical medicine, how-
ever, such as limited paralysis in connection with limited cerebral
lesions, appeared wholly inexplicable except on the hypothesis of
a differentiation of function in the cerebral hemispheres. In more
recent time- established coincidence of aphasia or loss of speech,
with disease of a certain region in the left hemisphere, served still
further to cause thoughtful students of this >nbject to seek rational
explanations upon the basis of a differentiation of function in the
cerebrum.

Hughlings Jackson from a minute and careful study of the
phenomena of unilateral and limited epileptiform convulsions ar-
rived at the conclusion that they were due to irritation or discharge
of energy from certain convolutions of the opposite cerebral hemi-
sphere, functionally related to the corpus striatum and muscular
movements. Though he furnished many arguments in favor of
thi- hypothesis, since verified, his views were regarded, at the
time. ;i- merely ingenious speculations and devoid of any actual
proof that the gray matter of the convolution was really excite-
able. Experimental physiologists had all failed to obtain evi-
dence of the susceptibility of the cerebral cortex to any of the
ordinary stimuli of nerve-, mechanical, chemical, thermal or even
electrical. This apparent inexcitability of the cerebral cortex
greatly retarded the progress of cerebral physiology.

A new era in cerebral physiology was inaugurated by the dis-
covery by Fritsch and Hitzig in 1870 that the application of the
galvanic currenl to the surface of the cerebral hemisphere in dogs
rise to movements on the opposite side of the body — move-
ments which varied with the position of the electrodes.

The phenomena of localized and universal convulsive move-
ments, attributed by Hughlinge Jackson to vital irritation of cer-
tain regions of the cortex, are precisely of the -: • nature as

those induced by electrical irritation of the same regions. The
great and significant feature of the reactions produced by elec-

594

THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

trica] excitation of the cortex is thatthey arc definite, may be pre-
dicted and vary with the position of the electrodes. So, as will
be seen later, areas in close proximity to each other, separated
only by a few millimeters or less, react to the electrical current in
a totally different manner. If there were no functional differ-
entiation of the areas under stimulation the diverse effects would
be absolutely incomprehensible on any theory of mere physical
conduction. Movements of the limbs can only be excited from
certain points, all others being ineffective.

1. Experiments upon Monkeys. — The surface of the cerebral
hemispheres in monkeys is divided into certain lobes and convo-
lutions by primary and secondary fissures. The general arrange-

Fi.i. 294.

Outline of brain of monkey (Macacus) to show principal sulci (fissures) and gyri (convolu-
tions. Natural size. Over each sulcus, purposely printed very thick, the name is written in

italics, over each gyrus ill SMALL CAPITALS, J1 indicates the small depression, hardly to lie

called a sulcus, which is supposed to be homologous with the superior frontal sulcus of man :

:<imI a, ii, :, similarly indicate sulci whose homologies arc DOl certain. (FOSTER after llORSLEY
and SCHAEFEB.)

ment of these varies somewhat from that of the human brain ;
however the homologies may be traced with fair accuracy, and
the results obtained from experiments are indicative of the func-

PLATE VI

Chart of Localization of Cortical Centres Determined on
External Surface of Cerebrum. (Gray.)

FIG. 2.

Chart of Localization of Cortical Centres Determined on
Medial Surface of Cerebrum. (Gray.)

LOCALIZATION OF FUNCTIONS IX THE CEREBRUM. 595

tions of homologous areas of the human brain. Electrical stim-
ulation of certain areas gives rise to definite response. The foL-
lowing arc the principal phenomena usually observed :

(a) Stimulation of the upper portion of the ascending parietal
lobule causes the opposite hind limb to be advanced as in walk-
ing, the thigh being flexed on the pelvis, the leg extended, the
foot flexed and the toes spread and extended. (See Figs. 294
and 295.)

{/>) On the upper extremity of the ascending parietal and ad-
joining portion of the ascending frontal convolution : Flexion
with outward rotation of the thigh, rotation inwards of the leg
with flexion of the toes.

(c) On the ascending frontal convolution, at the base of the
superior frontal : Extension forwards of the opposite arm as if the
animal tried to reach and touch something in front.

(<f) On the ascending frontal convolution at the bend of the
knee of the praecentral sulcus : Flexion and supination of the fore-
arm.

(e) On the ascending frontal convolution below 4 : Retraction
and elevation of the angle of the mouth.

(/) On ascending frontal convolution below 5 : Elevation of
the ala of nose and upper lip.

(y) On the lower extremity of the ascending parietal convoke
tion : Opening of the mouth with protrusion and retraction of
tin- tongue.

(h) On the lower extremity of the ascending parietal convolu-
tion : Retraction of the angle of the mouth.

(j) ( )n the superior temporal convolution : Pricking up of the
opposite ear, turning of the head and eyes to the opposite side,
dilatation of the pupils.

(/.■) Stimulation of the central lobe, or Island of Reil causes
no motor reaction-.

(J) Stimulation of the occipital lobe causes no motor reaction.

(///) Horsley and Beevor have made important contributions to
the physiology of the mesial aspect of the brain. They found
that the marginal convolution — located above the ealloso-mar-

ginal fissure — is excitable throughout, except in the prse-frontal
region (F. 1.'., Fig. 296). The figure shows the results obtained
by the experimenters referred to.

2. The Results of Observations upon Man. — Clinical obser-
vation has enabled us to determine with considerable accuracy the

outline of motor and of -en-orv areas on the cortex of the hu-
man brain. A comparison of Plate III. with Fig. 252 will show-
that the motor area of the human cerebral cortex i> Located, like
that of the monkey, upon either side of the fissure of Rolando
on the lateral aspect of the cerebrum and upon the posterior por-

59G THE PHYSIOLOGY OF THE NERVOUS SYSTEM.

tii f the marginal convolution on the mesial aspect of the

cerebrum. For obvious reasons the determination within the
motor ana of minute fields which serve as centers for voluntary
control of limited groups of muscles has do! advanced as far in
the human subject as in the monkey. On the other hand, and for
reasons jusl as obvious, the determination of the location and out-
lines of sensory and speech areas lias progressed much farther in
man than in the monkey.

We have now traced sensory impressions to the cerebral cortex,
to the sensorium ; we have found how one cortical portion commu-
nicates with another, and we have traced motor impulses from the
cortical centers of voluntary motion, through the pons, medulla
and cord to the muscles. It will be seen that sensation followed
l>v a responsive voluntary motion is analogous to a reflex act, dif-
fering from it only in the presence of consciousness of lh< 'process.

c. The Higher Cerebral Functions.

It is not within the province of this brief manual to discuss the
higher cerebral functions or the intellect of man. For a treat-
ment of t\\\< subject the student is referred to the various work-
on psychology.

Innumerable clinical observations make it certain that the
physical basis of the mind of man is the cerebral cortex. That
certain attributes of the mind are lost with the functional destruc-
tion of certain portions of the cortex indicates that the localiza-
tion of function is not confined to sensation and to volition.

Through the interrelation and interaction of cerebral centers
one is not only conscious of sensation, but he interprets the sensa-
tion, referring it to some object outside of the brain itself. Such
an interpretation of sensation is called Perception.

Sensations and perceptions affect the brain structure in some
mysterious way leading to a retention of the impression, with
ability on the part of the subject to call up the impression again :
Memory and Recollection.

Through the aid of the memory a series of sensations and per-
ceptions may be combined, into a clear mental picture : Conception.

Conception merges into Imagination, for the latter is the
• power of the mind to create mental pictures out of the data de-
rived from experience." These mental pictures may either be
faithful reproductions of previous sensations and perceptions : Re-
presentative imagination (Conception); or it may construct entirely
new pictures combined from various elemental sensations and per-
ceptions : Constructive imagination, or Imagination proper.

Given the powers enumerated and defined above the mind is
able to make a series of judgments or conclusions, i. c, to Reason.

THE HIGHER CEREBRAL FUNCTIONS. 597

A- a result of reason the subject may deliberately enter upon a
certain line of action. The power of the mind to will to do is

called Volition or The Will.

Sensations though the medium of memory may call forth in the
mind a series of Emotions : fear, anger, love, hatred, etc.

CHAPTER XII.

THE PHYSIOLOGY OF THE MUSCULAR
SYSTEM.1

A. GENERAL ACTIVITIES OF M I'SCULAR TISSUE.

B. ENUMERATION AND CLASSIFICATION OF THOSE MUSCULAR
ACTIVITIES ARISING FROM A CHANGE IN FORM.

1. THE INVOLUNTARY MUSCLES.

2. THE VOLUNTARY MUSCLES.

a. Muscular Organs: The Tongue.

b. Muscle-bone Organs : The Skeletal Muscles.

(1) General Functions of Muscle-bone Organs,

(2) Special Functions of Muscle-bone Organs.

(3) Animal Mechanics.

G. SPECIAL MUSCULAR ORGANS: THE LARYNX.

1. SUMMARY OF THE ANATOMY OF THE LARYNX.

a. The Skeleton of the Larynx.

b. The Muscles of the Larynx.

c. The Innervation of the Larynx.

2. THE MECHANICS OF THE LARYNX.

(1) The Abduct inn of the Glottis.

(2) The Adduction of the Glottis.

(3) The Tension of the Vocal Cords.

(4) The Levers of the Larynx.

3. THE ACOUSTICS OF THE LARYNX.

4. THE VOICE : PHONATION.

a. Speech.

b. Song.

THE PHYSIOLOGY OF THE MUSCULAR

SYSTEM.

A. GENERAL ACTIVITIES OF MUSCULAR TISSUE.

Under the influence of the nervous system various chemical,
thermal, electric and morphotic changes occur in constant succes-
sion in muscle tissue. In our study of metabolism Ave found
that in this tissue the most active metabolic changes take place.
Even when a muscle is said to be resting, i. e., not undergoing
morphotic changes, the metabolism within the tissue may be
very active.

1 Introductory to this subject review, under General Physiology, the topics :
"Motion" and "Contractility."

598

ACTIVITIES OF THE MUSCULAR TISSUES. 599

(a) Chemical Changes. — Under general metabolism we
found that muscle tissue is the scene of important chemical
changes. Most important among these changes is the oxidation
of dextrose, with the attendant consumption of oxygen and
liberation of CO., and H2C The katabolism of energy-producing
(" circulating ") proteids must now be recalled. The result of
this katabolism is the formation of nitrogenous (kreatin, etc.) and
non-nitrogenous molecules of simple structure (0O2+H2O, etc.).
Next in importance is the destructive metabolism of muscle pro-
toplasm. Incident to this katabolism oxygen is consumed and
CO.,, H.,0 and a nitrogenous molecule, — kreatin, for example, — are
liberated. Recent investigations in this field make it certain that
a part at least of the carbon, hydrogen and oxygen liberated
in muscle katabolism takes the form of sarco-lactic acid, — CH3*-
CHOHCOOH, — which gives the acid reaction to fatigued muscle.

(6) Thermal Changes. — Incident to the katabolic changes
just enumerated energy must be liberated. This energy may take
different forms. In a resting muscle the energy is liberated in the
form of heat. Recall the fact that the muscle-tissue is the tissue
of thermogenesis. It is probable that in simple thermogenesis the
katabolism involves almost exclusively the dextrose and " circulat-
ing" or energv -producing proteids leaving the muscle protoplasm
unimpaired. The thermogenetic activity of muscle-tissue is
under the direct control of thermogenetic centers in the brain.

(c) Electric Changes. — Katabolism of muscle-tissue and of
circulating nutrients within muscle-tissue is always attended with
the liberation of heat-energy. It may or may not be attended with
the liberation of electric energy. It seems fairly well established
that electric changes manifest themselves only when the muscle
contracts (The current of injury — demarkation current — excepted).
That part of the muscle where the contraction wave begins is
electro-negative to that part of the muscle yet uninfluenced by the
contraction wave. In the beating heart the base is electro-nega-
tive to the apex when the systole begins, and at the end of systole
tin- apex is electro-negative to the base.

((J) Changes of Fobm. — One of the forms of* energy liberated
in muscle metabolism is mechanical energy. Mechanical energy
manifests itself by moving matter through space. In the loco-
motion of an animal mechanical energy is manifested. Animal
locomotion in higher animals i- performed by use of the skeletal
structures as levers. The levers arc eel in motion by the tension
of muscle-tendons. This tension is possible only as a result of a
change of form of the muscle. The muscle contracts by increas-
ing it- lateral dimensions at the expense of its longitudinal

dimensions. This brings the origin and insertion of the muscle
nearer together, [fthe origin of the muscle is a fixed point, tension

600 PHYSIOLOGY OF THE MUSCULAR SYSTEM.

will be exerted upon the insertion. Thus the change of form of mus-
cles makes it possible for them to perform mechanical work as one
of the manifestations of the energy liberated in muscle metabolism.

H. ENUMERATION AND CLASSIFICATION OF THOSE

MUSCULAR ACTIVITIES ARISING FROM

CHANGE IN FORM.

1. THE INVOLUNTARY MUSCLES.

a. Non- Striated Involuntary Muscles.

(a) Characteb of Contraction. — Slow, somewhat prolonged
and relatively weak. Examples: (i) Peristaltic contraction of
Avails of alimentary canal and of ducts of associated glands,
(n) Contraction of bladder in act of micturition, (in) Contrac-
tion of walls of blood vessels, (iv) Contraction of uterine walls
in act of parturition, (v) Contraction of ciliary muscles in act of
accommodation, (vr) Contraction of the erector pili muscles in
" Cutis anserina." (vn) Contraction of gland-ducts in general.

(6) Mechanics of Movements Produced by Unstriped
Muscle. — In examples (i), (n), (in), (iv) and (vn), the walls of
the cylindrical or subspherical organs in question, contract upon
the more or less fluid contents of the organs. There is no lever-
age and no antagonistic muscular action. The contraction pro-
duces pressure of the wall toward the center of the enclosed space.
The pressure is equal upon all equal areas of the wall and the
tendency is to drive the liquid contents toward the direction of
least resistance, toward the physiological outlet of the cavity. In
examples (v) and (vi) the muscles contract against the elasticity
of certain tissues which oppose their action. During relaxation
of the muscle the elasticity of the tissues restores the relations of
the tissues to their usual position.

6. Striated Involuntary Muscle.

(a) The Heart is a Striated Involuntary Muscle. — The
contractions of the heart arc peristaltic in character. Though peri-
stalsis is somewhat obscured in the heart-action in higher vertebrates
one has only to refer to the action of that organ in lower vertebrates
or in the embryonic life of higher vertebrates to be convinced of the
truth of the statement. The character of the contractions of heart-
muscle differs very much from that of other involuntary muscles :
first, in the rapidity of the contractions ; and second, in the force of
the contraction. It is probable that the striation is the effect of this
difference of action rather than its cause.

(b) The mechanics of the heart-action are of the same order as
in the examples cited above, being a contraction of the walls of a

THE VOLUNTARY MUSCLES. 601

hollow organ upon the contents expelling them in the- direction of
least resistance.

2. THE VOLUNTARY MUSCLES.

a. Muscular Organs : The Tongue.

A purely muscular organ like the tongue of one of the higher
animals, the proboscis of the elephant or the prehensile upper lip
of the horse and allied animals, notably the tapir, present the
most perfect types of universal motion in the animal economy.
The tongue may be lengthened or shortened, raised or lowered,
swept from side to side, or circumducted at will. The highly
mobile and prehensile tongue of the cow may even present various
combinations of these movements in different portions of the
tongue. The movements may be rapid and strong. From the
standpoint of mechanics the tongue represents a flexible lever of
the third class whose fulcrum is the base of the tongue and whose
weight may be represented by the tip. The power is applied be-
tween the fulcrum and the weight by the contraction of the mus-
cles on one side of the lever to turn the tip in that direction. The
central portion of the lever would be represented by the relaxed
muscles on the convex side of the tongue.

b. Muscle-bone Organs : The Skeletal Muscles.

Muscle alone or bone alone could not accomplish locomotion or
any of the general movements of the body. A locomotors organ
among the vertebrates has two essential components : viz., muscle
and bone. The so-called skeletal muscular system is a system
composed of mu8cle~bone organs.

1. The General Functions of Muscle -Bone Organs. —
(a) Flexion anj> Extension are terms applied to the bend-
ing and the unbending of segments of the body or of its appen-
dages. For example, the forearm may be flexed upon the upper
arm, and then straightened out or extended. The fingers are flexed
when one grasps an object and extended when one releases the ob-
ject. The thigh may be flexed upon the abdomen ; the leg may
Ik- fl<\cd upon the thigh ami the foot may be flexed upon the leg.

(6) Adduction and Abduction are term- applied to the car-
rying of arms or legs toward or away from the median ventral
plane of the body.

The confusion which exists in the application of some of these
term-, especially of abduction, adduction, flexion and extension
of arm, necessitates their further illustration. To that end lei us
recall the general disposition of the muscle-bone organs in a
typical mammal. (See Fig. 295.)

Adduction i- the bringing of the femur or humerus toward the
median ventral plane of the body or the bringing of ;i digit

602

I'lIYslnl.ni;)- OF THE MlsciLMi SYSTEM.

toward the axis of the pes or the manus. Abduction is motion
in the opposite direction. Man in his erect position with the
arms held in the horizontal plane laterally may bring them toward
the median ventral plane, keeping them in the horizontal plane —
Ventral Adduction of the Humerus — or he may bring them to the
same median plane above the head — Anterior Adduction of the

Hand-
Flexion —

Diagram of typical mammalian skeleton.

Humerus — or he may bring them down to the sides — Lateral Ad-
(I net Ion of the Humerus. In a similar manner there may be Pos-
terior and Ventral Adduction of the Thigh or Femur, but, except in
the case of contortionists, the hip joint will not admit of lateral
adduction. When the typical mammal stands upon all-fours the
anterior and posterior extremities of one side define a ventral plane.
In flexion the femur moves anteriorly in that plane until, in extreme
flexion, it rests upon the abdomen. The humerus in flexion moves
posteriorly in the vertical plane until, in extreme flexion, it rests
against the thorax or slides along the thoracic wall until its axis ap-
proaches or even passes a line parallel to the axis of the body. In
man, when in the erect position, with the arms extended horizontally
in front (ventrally) and parallel to each other, the arms would be
flexed upon the body by bringing them down to the thoracic walls,
keeping them in the vertical plane throughout the movement.

(c) Rotation. — Certain joints, notably the ball-and-socket
joints at the proximal extremities of humerus and femur, admit
of a rotation of the limb about its axis. If one rests the weight
upon the heel the toe may be swung to right or left through an
angle of about 90°. It is neither the ankle-joint nor the knee-
joint which moves in this ease, but the hip-joint, the head of the
femur rotating readily within the acetabulum of the innominate
bone. In a similar way the arm may be rotated upon its axis
through the rotation of the head of the humerus in the glenoid
cavity of the scapula. Another rotating articulation is found be-

MUSCLE-BOXE ORGANS.

603

tween the two bones of the forearm ; the radius, rotating upon
the external condyle of the humerus, is thrown obliquely across
the ulna in pronation and drawn back parallel to the ulna in
supination. Under the head of rotation one may enumerate : (i)
rotation proper ; (11) pronation and supination.

(d) Circumduction. — All joints which are subject to the four
motions, flexion, extension, adduction and abduction, are subject
also to the movement called circumduction. One may swing the
arm or the leg around in a circle ; this is circumduction, and it
is clearly a combination of the four motions just enumerated.
The muscles and nerves involved in such a motion are simply a
combination of those involved in the four primary movements
taken together.

What muscles are involved in the above enumerated functions ?
What is the innervation of the muscles ? Through which spinal
nerve does the innervation come ? Opposite which spinous process
is the deep origin of the enumerated nerves ? Whence comes the
blood-supply of the muscles ? All of these questions are of im-
portance to the clinician. They are briefly answered in the fol-
lowing table, the data for which have been taken from Quain,
Ediuger and Gowers :

2. Special Functions of Muscle-bone Organs. — (a) Motions
of the Cranium ITi'<>x the Spinal Column.

H N f -
HON.

MfSCLE.

INNERVATION.

NERVE
ROOT.

SEGMENT OF CORD.

Rectus i lap, Ant. Maj.
ri Rectos < ap. Ant. Min.
■„ Bterno-4 lledo. Mast.

-

Suboccipital

spinal Accessory
Deep br. of Cerv. PL

IC

i lie

XI (ran
11 c

Hot, Occ. A At,
Bet. An. .V: All.
Jug. Fnrani.

Body 2d i !er,

Re< in- | ap. Post Maj.

Rectus < lap. Post. Min.
= Sup. Oblique
f ( lomplexut Bivent

=

2

_ Splenius Cap. ("'"Hi
i ppei -■ g. I rapezim

Suboccipital

Gt. Occipital
Int. Br. Post I > i v . (it.
Ext. Br. Post l»iv. Cer.
Spinal Accessory.
Ant Div. :•• IC.

IC

II ('

6-7-8 C

_■ 3 l

\ 1 Iran

Bet. Occ. & At.

Bet Ax. A- Atl.
Opp, body -i c
Opp. 4-6-6 C Sp.
Bet. Ax. & At.
Jug. l'nrani.
Opp. 1-2 C Sp.

Rd

1' I

ti Lateralis
/in^
Splenius
< lompli

Bivent. !

Sterno-Mastoid

Suboccipital
Spinal Accessory
Ant. I'iv. ::-» Cerv.
Ext Br. Post. Div. Cer.
Suboccipital
Gt Occipital
Int. Br. Post Div, Cer.
Spinal Accessory
Deep Br, 1 ex Pli

DeepBi Cer? Plex,

Suboccipital

i.i Occipital

Int Br, Post l»iv i . ,

Suboccipital

l.xt Br, Post Div, ' ■ i

Suboi cipital

i.i Occipital

I C

II •
3 i '

I c

21

II c

.' <

Bet Or. .V At.

.1 iik. l'lirani.

Op. 1 2 C. Sp.

Op. linil. '.' |l ('. Sp.]

Bet At. a \\
opp. HimI. ■_' C.
Op. I, 5, 6C. Sp.
.( ii k- roram.

Opp. HimI. •_' C,

-

a
2

itoid f

- < Ompl. I'.IV. r,|

■ide acting with it.

Red 1 >p \u\
Splenitis

- i racbelo Mast.
Reel I ap Po ' Maj.
It.i Oblique

i c

1 I
1 (•

op. Bd. 2C.
Bet At a Ax.

Op I'M. -' C
i MIC. sp.

Hit \t A \\

Op Bd.2C.[1 C Sp. |
Bet \ i a Lj
op. Bd. 2C.

<i<>4 PHYSIOLOGY OF I'll/: MUSCULAR SYSTEM.

(h) Movements of CJppee Arm.

7l"N~ MUSCLES.

INM.I:\ LTION.

M ERV]
ROOT.

BEG. "i COED.

BLOOD -1 PPLY.

a
o

'B

E

Latissimus Dorsi
Teres Major
Post. Si g. of Delt,
Coraco-brach,

L. Subscapular 7 C Bel S 6 C. Sp. Axillan
Subscapular 7 C Bet. 5-6 C. Sp.
Circ. Br. Cerv. PI. 4-5 C Op. 2-3 C. Sp. Post. Circum.
Musculo Cutan. 5-7 C Op. 3 C. Sp. Brachial

Pectoralis Maj.
Ant. A Mid.Sg. Del.
Coraco-brach.
Supra-Spinatus

Ant. Thr. Br. C. PI. 7C Bet. 5-6 C. Sp.
Circumflex •»-.-> c Bet. 2-6 1 Sp
Musculo Cutan. 5-7 C <>p. 3 C. Sp.
Supra-scapular 5-6 C Bet. cr, C. Sp.

A x diary
Ant. < irciiui.

Brachial

Post. & Supra Sp.

_ a Pect. Maj. low ^
2^ Latissimus 1 >orsi
S3 Teres Maj.
^-o Long lid. Triceps
< ' Coraco-brach.

Ant. Thoracic 7 (' B< i i i : < Sp
L. Subscapular 7 c "
Muse. Br. Subsc. ti-7 "
L. Br. Circum. i;i 5-7
Musculo Cutan. 5-7 (' 4-5-6

Axillary
Brachial

Ant. & Mid. Sg. Del.

Supra-spinatus

Infra-spinatus

Upper Br. Circum.
Suprascapular

4-5 C
5-6 C
5-6 C

Bet. 2-6 C. Sp.

5-6

5-6

( 1 rcumflex
Post. Supra Sp.

■3 .F

Pect. Maj. Upper Pt.

until horizontal
then low ]>t. acts
Subscapularis
Coraco-brach ialis

Ant. Thoracic
External and

Internal
Subscapular

Musculo Cutan.

7C

4-8 C

5-7 C

Bet. 5-0 c. Sp.

Bet. 5-6 C. vp.

5-6

Axillary

Subscapular
Brachial

Post. Seg. Deltoid
Infraspinatus
Teres Minor

Sup. Br. ('ileum.
Supra-scapular
Br. of circum.

4-5 C

5-6 C
t-5 1 ■

Bet. 2-6 C. Sp. Post. Circum.
5-6 Subscapular
5-7 Axillary

(c) Movements of Forearm.

F l' NO-
TION.

Ml SCLES.

INNERVATION.

NERVE
ROOT.

■SEG. OF CORD. BLOOD SUPPLY.

0
M

Biceps
Brachialis Ant.

Supinator Long
Flex. < !arp. Rad.
Flex. Carp. Ulnar
Flex. Sub. Dig.

Musculo Cutaneous

Br. Musculo Spiral

Br. Musculo < utan.

Br. Musculo Spiral

Br. Muse. Sp. Med.

Ulnar.

Muse. Br. Median

5-8 C
4-8 ( '

8C 1 D
4-8 C

Op. :: C. Sp. Brachial
Bet. 3-6 " Brachial
Op. 3 " Brachial
Bet. 3-6 " Radial
3-6 " Radial
Op. 6-7 " Ulnar
Bet. 3-6 " Ulnar & Med.

5 =

Triceps

A aconeus

Ext. < arp. Had. Long

Kxt. Carp. Rad. Brev.

Ext, Carp, llnaris

Musculo Spiral

1'ost. Interosseous

4-5 C.

Bet. 3-6 Brachial
3-6 Brachial

3-6 Ttadial
3-6 Ba.lial

3-6 Ulnar

& .

a a
■a.2

00

Supinator Long.

Supinator Brev.

Biceps

Flex. Carp. Rad.

Musculo Spiral
Post, interosseous

Musculo Cutaneous
Median

4-7 C
"

Bet. 3-6 C. Sp. Radial

:;-i;

3-6 Brachial

3-6 ttadial

Prona-
tion.

Pronator Rad. Ter.
Pronator Quadrat us

Ant. Thoracic

Median

8 C I D

5-8 C

5-6 Rad. & Ulnar
5-6 Had. & Ulnar

(d) Movements of the Hand.

FUNC-
TION.

MUSCLES.

INNERVATION.

NERVE

ROOT.

SEG. OK CORD.

BLOOD SUPPLY.

o

J.

Flex. carp. Ulnar
Palmaris Brev.
I'almaris Long.
E'inger Flexors

Ulnar
Median
Median
Median & Ulnar

8C1D

1 8 C

8 C 1 D

Op. 6-7 C. Sp.
Bet. 5-6
5-6

Op. 0-7

Ulnar

Ulnar. Bad. Med,

Sri

"•7

Ext. Carp. Bad. Long
Kxt. Carp. Rad. Brei
Ext. Carp. Ulnaris
Finger Extensors

Musculo Spiral
Lost. Interos,

"

4-7 C

Bet. 3-6
3-6
3-6
3-6

Badial
Ulnar

Ulnar. Bad. Med.

MUSCLE-BONE ORGANS.
{() Movements of Thigh.

605

FUNC-
TION.

Abduc-
tion.

INNERVATION.

SERVE
BOOT.

Psoas Magnus
lliacus

Adduct. Long.
Adduct Brevis.
Bartorius
Pectineus
Gracilis
Rectus Femoris

1-2 Lumbar
Ant. (rural
i ibturator
( obturator
A hi. i rural
Ant. Crur. & Obt
Ant. Crur. & Obt.
Ant. (.'rural

:;-4 L
(! L
1-4 L

6 I.
Above

SEG. of CORD.

<>p. 11 I>- Sp.
But. 11-12
Op. 12

Bet n-12
Above

Tensor Vag. Peru. Supt. Gluteal

1-4 L Op. 1 L. Sp.

( rluteus Max.
Gluteus Med.
Gluteus Min.
Biceps Few.
Semimembram isus
Semiter Dinosus

Sup. Gluteal S. Sc. Above Above

Adduct Mag.
Adduct. Long.
Adduct. Brev.
Pectineus
i rracilis

Sup. Glut. Br.Gt.Sc.

Ant. ('rural
( Ibturator

Glut Medius
Glut Minimus
Tens. Vag. Fern.

See above

- —

Br. from Sacral

Pyriformie

~. V ( lemelli inf. et Sup.

l\ Obturator int et Ext Obst & Br. from Sc.

— z Quadratus Femoris 5th numb. 1st Sc.

Botat'n i.lut. Med. (ant bun.) See above
inw'd. ( Hut Min.

1-4 L

A I ii > \ .'

Above

Above Above

1-4 L Op. 1 L. Sp.

1-4 L

BLOOD SUPPLY.

llio Lumb.
Obt. Glut.
Ob. Gl. Int. C.

Br. Prof. Fern.
Ob. Gl. Int. C.

Br. Prof. Fein.
Ext. Circum.

Scitaic. Glut.

Prof. Fern.

(lb. Gl. Int. C.

Gluteal.
Ext Circum.

(/) Movements of Leg and Foot.

gȣ -u8ci.es. inneevation. Ȫ

SEG. of COED.

BLOOD SUPPLY.

^ Biceps Femoris Sup. Glut. S. Scia. 2-3 L Op. 1 L. Sp.

c n Semimembra i- ' " "

a r Semitendinosis " " " "

I- Popliteus Int. Popliteal :t-4 S

Gracilis Obt J'.r. Gt Sciat Abv.
g -. Bartorius Ant < rural 6 L

( iastrocnemius Int. Popliteal Abv.

Prof. Femoris

l'r. I'cm. Post.Tb.
Prof. I'cm.
Popliteal
Post. Tib.

■— ~ Rectos Femoris Ant. (rural Abv.

Vastus Externus
^ — - Vastus internus

_ u n ii

Bet n-12.

. i ,i

Anast Mn-
pop. Pro. I'cin.

'- Tibialis Anticus Ant. Tibial Abv.

- )•• roneua I eri ius " " "
e£ Ext. Long Dig.
^ Ext. Prop. Hailucius " "

Pet. 11-12.

int. Tibial

Per hi

A ni. Peron.
Ant. Tibial

- min- Popliteal Abv.

: _ '1 ibialii P Post. Tibial 1-2 L
Peroneua Longus Musculo Cutan, 1 G I.

P( 'i- 1:

^ Plantaria int Popliteal Abv.

- Flex. Lot i ibial

Bet liu

Post Till.
Peroneal
Post. Till.
Pe al

Post. Tib.

.• Tibialis Posticus 1 dual Abv.
■ Perom Musculo < alas

Bet ii 12

Post 1 lb.

Per al

-' Ext. Long Hallucius Ant 'I Ibial
-"Hi Ibiali* Antlcui

Bet, ii 12.

Ant, Tibial

606 PHYSIOLOGY OF THE MUSCULAR SYSTEM

In the compilation <>i' the above table it was found that the
statements of Gray, Quain and other anatomists do not agree as
to the function of particular muscles. In all such cases the
author has accepted the authority of Duchenne, whose classic
work, " Physiologie des Mouvemente" -till remains without an
equal.

:;. Animal Mechanics. — Animal mechanics is the applica-
tion of the laws of mechanics to animal motion. The bones are
used as levers; the articular surfaces of bones usually serve as ful-
crums, while the power is exerted by the muscles. In a vast ma-
jority of cases the bone- represent levers of the third class — in
which rapidity of motion is attained at the expense of power. In
other words, the arrangement of the bone-muscle organs is such
that a contraction of a muscle — moderate in extent and rate of mo-
tion— is manifested by a movement of the limb which is much in
excess, as to extent and rate, of the movement of the power.

In solving problems in animal mechanics the principal factors
to be considered are : (i) the relative length of the two lever-arms ;
(n) the relative size of the muscles involved in any movement;
(ill) The direction in which the power acts, and (IV) the weight
to be moved.

(a) Problems in Animal Mechanics. — Two typical problems
in animal mechanics are the following :*

1. Determine, in a particular case, the ten-ion exerted upon
the tcndo-Achillis in supporting the weight ('50 kilograms) of the
subject upon the ball of the foot.

2. How much tension would there be on the biceps tendon in
the subject upon your dissecting table when he holds a ten-kilo,
iron ball in the most advantageous position"? This is a typical
problem and its solution will make the difficulties to be encoun-
tered apparent. It will also show that nothing more than an ap-
proximate solution can be attained without an extended and de-
tailed study.

Solution. — The principal muscle involved in the required
action being the biceps, the most advantageous position is the one
in which that muscle exerts its power in a line perpendicular to
the lever. Placing the subject's arm as nearly as possible in that
position, one takes the following measurements: (i) The long
arm of the lever; this would he from the center of articulation be-
tween the humerus and the ulna, to the center of the 10-ko. ball,

1 Both of ili<-' problems stated above are problems in "muscle statics." Such
problems deal with ten-inn upon muscles when the limb Is in a certain fixed )">-i-
tion. There are much more complicated problems which deal witli the energy ex-
erted in a more or less complex movement when t he leverages and angles of ten-
sion are constantly varying. Such problems in "muscle dynamics" can only be
solved by the application of higher mathematics. Otto Fischer, of Leipzig, lias
done much to throw light upon this field of physiology. See his " Beitrage mr
MuskelrStatik" ; also " Beitrage zu 'inn- Muskel-dynamik.

J/7 ISC ■LE-BOXE ORGANS.

607

which would be, approximately, to the distal extremities of the
metacarpal bone (36 cm.), (n) The short arm of the biceps lever ;
thi> would be the distance from the center of the insertion of the bi-
ceps to the fulcrum — the center of articulation (6 cm.), (in) The
-hurt arm of the lever for the Brachialis anticus. If the Brachi-
als amicus were exactly parallel to the Biceps the short arm
would be the distance from the insertion to the fulcrum (5 cm.), as
in the biceps ; but it is not parallel.

Fig. 296.

Mechanics of flexion of tbe forearm. [The upper a La to be understood as a'.]

A line drawn from the fulcrum perpendicular to the axis of the
lirach. ant.,/"', i- shorter than the line fa. The angle between
the Brachialis anticus and the Biceps is approximately 10° ;
therefore the angleo/a' would be approximately 10°; then a'/is
die cosine 1" or 98 per cent, of the radius a f (5 cm.) or 4.!i cm.

(iv) The power-arm of the Supinator longus is the perpendic-
ular distance from the fulcrum to the line of force oi the Supinator
longus and is represented by the line /'x, which is 1.* cm. Xow
the carpal and digital flexors which take origin from the humerus
act ;i- forearm flexors alter having flexed the carpus and digits. In
the action under consideration they would not be brought into
forcible action as carpal and digital flexors. We may therefore
ignore them and confine our discussion to the three muscles men-
tioned above.

In the action of the Biceps the long arm i- • !<; cm. and the

short arm 6 cm.; iii the action of the Brach. Ant. the long arm

i- 36 'in. and the -hort arm l.!l cm.; in the action of the Sup,
Long, the long arm i- 36 cm. and the -liort arm I.S cm. Re-

608 PHYSIOLOGY OF I Hi: MUSCULAR SYSTEM

during these to percent, rutin- we have: For the Biceps, which
we will designate as b, 16.6 per cent, leverage; for the Brach.
ant., which we will designate as a, 13.6 per cent, leverage; and
for tlif Sup. long., which we will designate as 8, 13.3 per cent.
leverage.

But there is another important consideration : Fick has dem-
onstrated thai when the fibers are parallel the strength of two
muscles is proportional to the areas of their cross sections (Her-
mann's Handbuch der Physiologie, I., p. 295). The average ratio
of the diameter of the three muscles in question i- 1 : "_' : 1 respec-
tively; hut the areas of the cross sections would be proportional
to the squares of the diameters <>r as 1 <> : 4 : 1, respectively. This
mean- that with the same leverage the Biceps would lilt four times
as much as the Brachialis anticus and that the Brachialis anticus
would, with the same leverage, lift four times as much as the Supi-
nator longus.

We have now discussed the relation of these three factors as to
leverage and as to relative power exerted.

As to leverage one may say: The power of the three muscles
varies in proportion to biceps leverage (bt) : brachialis anticus
leverage {aty ; supinator longus leverage (sty respectively, or
mathematically expressed, P varies as bl : al : si or varies as
16.6 : L3.6 : 13.3. As to cross section one may say: The power
varies in proportion to the respective cross sections (s) or P varies
as 6s : as : ss = 16 : 4 : 1. Now when any function varies with
two or more variable factors, its variation when influenced by the
action of all of these factors at once would be represented by the
product of the several variables. Then the power varies as the
levei-age times the cross section of each of the muscles when all act
together, or expressed mathematically, P varies as 6(/xs) : a(Jxs)
: 8{lxs).

A(/xs)=: 16.6x16= 265.6 or 70.7 ft of the total power ex-
erted; a(lxs) = 13.6x4 = 54.4 or ld.3'/ of the total power
exerted; g(/x«) = 13.3x1 = 13.3 or 4.0^ of the total power
exerted ; total = 333.3 or 100.0^.

But the weight supported by the action of these muscles is
10 kilos. If the biceps does 70.7 '/ of the total work, it Mould
support 7.97 kilos. What would he tension upon the tendon of
the biceps when it is supporting 7.07 kilos, at the end of its lever?
One needs only to use the 16.6 '} leverage (7.97 -s- 16.6 '/ ) to find
that the ten-ion would be 47.8 kilos. A similar process shows
that the approximate tension upon the tendon of the Brachialis
anticus is 12 kilos, and upon the tendon of the Supinator longus
3 kilos.

b The Amount of Contraction of a Muscle bears a fairly
constant ratio to the restine-length of the muscle. This law of

MUSCLE-BONE ORGANS. 609

muscle physiology was discovered and demonstrated by Ed. Fr.
Weber ( * 'Mechanik d\ r rru nschlichen Gi hwerkzi uge" 1 85 1 | and was
cited by Strasser (' f Funlctionellen Anpassung der Quergestreiften
Muskeln, 1883) as an example of the adaptation of muscle-tissue to
the mechanical requirements of the body. Weber showed that the
maximum contraction of which a muscle fiber is capable is ap-
proximately 47 y of its resting-length. Both Weber and Strasser
looked upon this as the factor which determines the length of the
muscles, and the location of their points of origin and insertion.
In all of the skeletal muscles the tension of the contracting mus-
cle is greater than the weight lifted. The farther the insertion of
a muscle from a joint (fulcrum) the less the tension upon the mus-
cle and the greater the amount of contraction or shortening neces-
sary ; but the inherent structure of striated muscle-tissue seems to
set 47 / as the limit of the extent of its contraction. The fact
that all skeletal muscles actually do contract that much (varying,
however, in -pecial instances from 44 '/ to U2 '/ ) indicates that the
position of the origin and insertion or the length of muscle-tissue
(excluding tendon) between the origin and insertion; or, more
likely, that both ofthesi structural features have been determined by
tin fans of selection on, I mm- represent in oil highly organized ani-
mals the most perfect mechanical adjustment consistent irith tin inhe-
r< /'/ properties of muscle tissue.

(c) Problems in Human Locomotion. — (a) The muscles used
in locomotion. Let a person stand erect with heels together ; let
him take several steps forward and stop in a position similar to
the one which he had at the beginning. What is the mechanism
of starting f What muscles are involved in starting ? What is
the mechanism of locomotion / What muscles are involved in
Locomotion? What is the mechanism of equilibration while
walking? What muscles are involved in maintaining the equil-
ibrium while walking? What is the mechanism of stopping f
What muscles are involved in stopping? How is the equilibrium
maintained during the process of stopping ? What muscles are
involved in the maintenance of equilibrium while standing?
How does running differ from walking in respect to the starting,
the lofomotioii, the equilibration and the stopping t

ii) Ttu energy involved in locomotion. How far is the body
lifted at each step when one walks over a level surface? When
one walks up an incline of 30 degrees? When one walk- down
an incline of 30 degrees? Does one do work while walking
down hill? [f so, how may it be computed? If not. why does
oik- become fatigued in descending an incline? How much
energy will a 7<»-kilo. man expend in walking 1 kilo, on n level
road? (Suppose the man to be 17'_; cm. in height, and to have
n pubic heighl of 88 cm.) A pari of the energy will !><■ ex-

BIO PHYSIOLOGY OF THE MUSCULAR SYSTEM.

pended : i in Lifting t 1 j o bod] part, in maintaining equil-

ibrium ; [ni) a part in overcoming resistance. Express in kilo-
gram-meters the amount in (i). How could (n) be determined?

C. SPECIAL MUSCULAR ORGANS: THE LARYNX.
I. SUMMARY OF THE ANATOMY.

From tli'- standpoint of the physiologist, the following anatom-
ical fact- are important :

a. The Skeleton of the Larynx.

The skeletal foundation of the larynx consists of nine cartilag -.
of which five are physiologically important:

1. The Thyroid Cartilage. — This is the largest, and it gives
to the larynx it- specific shape. The prominent anterior aspect
of this cartilage may be felt in the throat. The flattened sides
make it evident that a cross section of the larynx would reveal for
the thyroid a triangular outline, with apex forward. The pos-
terior segment is absent.

2. The Cricoid Cartilage. — This is a complete ring fitted in-
side and below the thyroid, to whose inferior cornea it is artic-
ulated laterally. The anterior aspect of the cricoid is narrow
while the posterior aspect is wide, coming well up into the thyroid
spaa .

:;. The Arytenoid Cartilages. — These cartilages are attached
to the npper posterior margin of the cricoid cartilage. The gen-
eral outline of one of these cartilages i- approximately triangular,
and the articulation i- such as to allow the cartilage- to rotate
around an axi- parallel to the axis of the larynx, moving in a
plane at right angle- to the axis of the larynx. When the aryte-
noids are in a position of rest, one aide coincide- approximately
with the antero-posterior line of the larynx. The anterior angle
serves for the attachment of the vocal cord- and is called the
Processus vocaJUs.

The axi- of rotation of the two arytenoid cartilage- i- displace-
able.

4. The Epiglottis. — This i- a thin spatulate cartilage, above
the anterior superior margin of the thyroid ; its principal function
- to be the protection of the larynx during deglutition.

//. The Muscles of the Larynx.

There are five muscles, or pair- of muscles which are impor-
tant to the physiologist.

1. The Transverse Arytenoid Muscle. — This passes from
one arytenoid cartilage to the other. It- contraction tend- to
draw tic- - toward the median line. (><■>■ Fig. 'I'-1' . A.)

THE MECHANICS OF THE LARYNX. 611

2. The Posterior Crico-arytenoids. — Each of these two mus-
cles has its origin on the cricoid cartilage. After passing upward
and outward each is inserted into an arytenoid cartilage. Con-
traction of these muscles tends to rotate the arytenoid cartilages
upon their axis, so that tin processus vocalis is abducted.

Fig. 297, P.C.A.

3. The Lateral Crico-arytenoids. — The origin is on the inner
lateral aspect of the cricoid cartilage. Passing upward and back-
ward, each i- inserted into the outer aspect of the corresponding
arytenoid. Contraction of these muscle- tends to adduct tic pro-

- vocalis. (See Fig. 2(.»7. LJ'.A.)

4. The Thyro-arytenoid Muscles arise from the inner ante-
rior aspect of the thyroid and pass directly back in the plane of
the vocal cords to be inserted into the outer anterior side of the
arytenoids. Contraction of the thyro-arytenoids alone would ad-
duct. This pair of muscles is involved especially in the "fixing "
of the arytenoid cartilages.

5. The Crico-thyroid Muscles arise on the lower posterior
part of the thyroid cartilage, externally, and pass downward and
forward to be inserted into the cricoid cartilage. Contraction of
these muscles lifts the anterior segment of the cricoid cartilage,
or at least draw- the anterior segments of the thyroid and cricoid
cartilages nearer together. The result of this is to carry the up-
per posterior margin of the cricoid cartilage farther away from
the upper anterior part of the thyroid cartilage. In other words,
to increase fh< distana between the two points of attachment <>f tltc
vocal cords. In other words, they are t< ».-«>rs <>/ tfu cords.

c The Innervation of the Larynx.

i") The Sensory Nerve of the larynx i- the superior laryn-
geal branch of the vagus.

(6) The .Motor Innervation i- through the inferior laryngeal
for all the muscle- except the Crico-thyroid, i. <.. the tensors of
the cords. These muscles are innervated by the superior laryn-
geal. From thi- it i- clear that with loss of sensation of the
larynx there is loss of proper phonation.

i'. THE MECHANICS OF THE LARYNX.

In the diagrammatic representation of the larynx a- seen from
above, ;. ,., in line of it- axi-, note especially the following
features :

T.i '. Thyroid cartilage.

S.i .T.C. Superior cornu of the thyroid cartilage.

( .' . Cricoid cartilage, posterior-superior aspect.

A.C. Arytenoid cartila i

G12

PHYSIOLOGY OF THE MUSCULAR system.

Fig. 29'i

.r.= Axis of articulation of an arytenoid cartilage.

T.A.= Thyro-arytenoideus muscle.

a.= Arytenoideus muscle.

P.C.A.= Post. Crico-arytenoideus.

L.< \A.= Lateral ( !rico-arytenoideus muscle.

V.C The vocal cords are attached anteriorly to the inner sur-
face of the upper anterior segmenl of
the thyroid cartilage and posteriorly
to the processus vocalis of the two
arytenoid cartilages, respectively.

From the figure given it would
seem that the Arytenoideus and Pos-
terior Crico-arytenoidei would act
together in rotating the arytenoid
cartilage about the axis x in the direc-
tion of the arrow a. Also that the
thyro-arytenoidei and the lateral
crico-arytenoidei would act together
in the reversed rotation as indicated
by the arrow b ; furthermore, that
the first action would tend to sepa-
rate the vocal cords, while the second
would approximate them.

But this is only a part of the truth. The axis of rotation of

Diagram of muscles of larynx.

the arytenoid cartilages are not fixed ; they arc displaceable.

Fig. 298.

Diagram showing the action of the laryngeal muscles.

1. The Abduction of the Glottis. — In the three diagram-
matic figures (Fig. 298, A, B and C)the continuous lines represent
the larynx at rest ; i. c, in the position which the parts assume
during quiet breathing. Fig. 298, A, shows in the dotted lines

THE ACOUSTICS OF THE LARYNX. 613

the position produced by a contraction of the posterior crico-ary-
tenoid muscles. The arytenoid cartilages have been rotated out-
ward, the axes have been displaced outward, and the opening has
changed from triangular to pentagonal. This position is assumed
in deep inspiration. These muscles are sometimes called abduc-
tors of the glottis, because they separate the lateral boundaries of
the glottis from the median line.

2. The Adduction of the Glottis. — Adduction of the lateral
boundaries of the glottis may be accomplished in two ways :

(a) Adduction by Rotation of the arytenoid cartilages on
their axes and approximation of vocal cords alone. This is done
by the Thyro-arytenoidei muscles acting or in conjunction with the
lateral crico-arytenoidei.

(b) Adduction by Displacement of the arytenoid cartilages
toward the median line, by the contraction of the Arytenoid leus
muscle, supplemented by the Thyro-arytenoidei and the lateral
Crico-arytenoidei. The action of the last muscles being clearly to
overcome the tendency of the Arytenoideus to rotate the tips of
the cartilages outward. This second form of adduction com-
pletely closes the larynx, and the groups of muscles which per-
form the act are often called the Sphincters of the Larynx.

3. The Tension of the Vocal Cords necessary to the produc-
tion of sound is brought about by the combined action of the ad-
ductors (6), which simply approximate the cords, and the Crico-
thyroidei, whose contraction brings the ventral edges of the cricoid
and thyroid cartilages nearer together, separates their dorsal as-
pects and thus puts the vocal cords on the stretch.

4. The Levers of the Larynx are levers of the first class.

3. THE ACOUSTICS OF THE LARYNX.

The larynx is a musical instrument supplied with a device for
setting the air into vibration. The air thus set to vibrating is
ii"t -imply the air that is being emitted from the respiratory or-
gans, but the air which fills the air passages of the lungs. Even
the tissues of the chest and head participate, to a limited extent,
either a- resonating or as reflecting surfaces. The rate of vibra-
tion is determined wholly by the vocal cords acting as vibrating
strings. The pitch of voice depends, then, solely upon the vocal
cords, while the timbre or quality depends upon the size of the
chest and the size and space relations of those parts of the respi-
ratory passages, including the mouth, external to the vocal cords.

How does the pitch of the voice vary ? Wehaveonly to apply
the law- < if the transverse vibrations of strings to the solution of the

problem. If we let I equal the length of the string, /• its radius,

rf its density, £ the tension with which it is stretched, and AT the

C.14 PHYSIOLOGY OF THE MUSCULAR SYSTEM.

number of vibrations per second, we would have the following
formula (for derivation sec Physiological Acoustics) :

Now it and 2 may be discarded when we express it as a variable,
so we would have :

(2) N varies « -^Jj

We see, then, that the number of vibrations per second, i. e., the
pitch of the voice, depends upon four variables, and we may ex-
press them separately thus :

(i) N varies as ; (ri) N varies as -j ■

(in) N varies as V t ; (iv) N varies as^j , •

These laws apply to the human voice in the following manner :
(«) The pitch varies inversely as the ratlin* of the vocal cord,

I N varies as- I, but the radius of the vocal cord varies with (i)

age, becoming thicker with advancing age ; (n) with sex, being
thinner in females than in males ; (in) besides these general vari-
ations of pitch which depend upon age and sex there are iiidirirf-
ual differences which lead to difference of pitch in two persons
of the same age and sex.

(,3) Tfie pilch varies inversely as the length, I N varies as . I ;

The length of the vocal cords vary with (r) age, for they take a
part in the general body growth. They vary also (n) with sex,
reaching in the average man a length of 15 mm., while in women
they are but 1 1 mm. in average length.

(y) The pitch varies ax the square-root of the tension, (iWaries as
«/ 1). The tension varies solely with the muscular activity of
the muscles of phonation. (See above.)

It may be interesting to note here that in raising the pitch of
the voice voluntarily from any chosen key-note to its fifth, whose
number of vibrations would represent the ratio %- when compared
with the key-note, it would require a tension of |, the original
tension, or 2{ times the original tension to produce \\ times the
original number of vibrations per second, or to raise the pitch from
do to sot. From this it is evident that the production of high
notes must be a severe physical tax upon the muscles of phonation.

SPEECH. 615

(o) Pitch varies inversely as the square root of the density,

( X varies as. J I • But in the human vocal cords there is no

essential variation in the density of the vocal cords with age, sex
or other variable factors so that this law does not apply to the
larynx though it does to other musical instruments.

4. THE VOICE: PHONATION.

Man possesses the function of phonation in its highest form.
All animals which possess a voice are able to use it in expressing,
t<> their associates, the various emotions and passions which move
the animal mind. In most of the higher mammals phonation
takes on two forms : (i) articulate phonation, in which the voice
comes in short vowel tones with consonants marking the beginning
of the tone (the dog's "bow-wow," the cat's " meaow," the cow's
"moo"). These are all words; they are used to express the
passions, the emotions, or the desires of the animals. Man pos-
sesses a series of these monosyllabic race words which take the
form of exclamatory, grunts, cries, shrieks, cooings, guffaws, etc.,
through which every passion of the human soul is instantly made
known to every member of the genus Homo within range of the
voice. Most races have developed articulate phonation into a
complicated succession of articulated sounds called xj><<el> through
the agency of which various shades of meaning may be commu-
nicated to one's associates, and a sustained and continuous
succession of ideas be communicated to the hearers, (n) CJn-
articulated continuous phonation or song, used primarily in the
expression of the more pleasurable emotions, also of pathos.

a. Speech.

The highest form of articulate phonation Is called speech. The
simplest existence of ;i member of civilized society requires of an
individual a vocabulary of 300 to 500 words in the expression
<>f his thoughts, — emotions, desires, etc. Some Individuals use
in the course of a year many thousand different words in the ex-
pression of their thoughts. The lull vocabulary is no greater
tax upon the vocal apparatus than is the scanty one because no
on.- language possesses more than •">') to 50 different elementary
sounds ; anil words represent various combinations of these ele-
mentary sounds. Elementary sounds are made: (u either with
opeu organs of articulation, and modified in quality by various
positions of the resonating surfaces, vowels; (n) or with the
articulating organs : lip-, tongue, teeth and palate obstructing,
more or less, the passage of the sound or breath, consonants. In
one sense speech consists of a -eric- of vowel sounds separated

G16

PHYSIOLOGY OF THE MUSCULAR SYSTEM.

from each other (articulated) <>r joined In each other by :i scries of
consonants.

The Vowels of the English language are a, e, i, <>, u. Konig
gives the fundamental vowel positions of the modifying organs as
resulting in the five vowel sounds : 65, 6, ii, a, e. All other Eng-
lish vowel sounds are formed of combinations or modifications of
these fundamental tones. The English I (long i) is a combination
of a, e, the English n (long n) is a combination of e, 66. Impor-
tant modifications are made by changes in the quantity of the
vowel sound. The English language has at least seventeen rec-
ognized vowel sounds.

The Consonants of the language may be classified on the
basis of their acoustic qualities as H<jni<h or semi-vowels : m, n, 1,
r, s, w, y1 ; and mutes, including all the remaining consonants.
On the basis of the mechanism of formation consonants may be
classified as : (i) explosives, as b, p, d, t, k, g ; (ii) aspirates, as f,
v, w, s, th(in), 1, sh, ch, h ; (in) vibratives, as r ; (i\-) resonards,
as m, n, ng. Briicke gives the fundamental consonant positions as
follows : (i) articulated between the lips, labials; (u) articulated
between tongue and hard palate, palato-lingual ; (in) articulated
between tongue and back portion of hard palate or the soft palate ;
(iv) articulated between the two vocal cords.

The following table of consonants embodies the ideas of Briicke
in a form somewhat better adapted to the English consonant sounds.

OKAL.

NASAL.

PLACE OF ARTICULATION.

Momentary.

Continuous.

I '< • j 1 1 i 1 1 1 1 • >i i -~

Aspirates.

Vocals.

Aspirates.

Vocals.

\"(icals.

Labials.
Labiodentals.
Linguo-dentals.
Palato-linguals :

Anterior position.

Middle position.

Posterior position.

P

t

Cll

k

b

d

j
g

f
th(in)

s
sh

w
thie)

zh, r

y

m

n

ng

The relation of speech to the central nervous system is dis-
cussed at length under the physiology of the brain (q. v.).

I>. Song.

The musical scale is discussed under Physiological Acoustics
(<(. v.). Though the human ear is able to appreciate a range of
musical tones from a vibration rate of 16 per second up to Hi, TOO
or 33,408 per second ; i. e., a range often or eleven octaves; the
human voice is able to cover a range of (possesses a compass of)
///• * i c aves, in rather rare cases of three octaves. The two-octave
ranjje of the male voice is below that of the female voice. The
reason for this is discussed above.

ly sometimes replaces i as a pure vowel.

DIVISION a

CHAPTER XIII.

REPRODUCTION.

THE PHYSIOLOGY AND MORPHOLOGY OF REPRODUCTION.

1. THE OVUM.

2. MATURATION.

3. FERTILIZATION.

4. SEGMENTATION.

5. THE EMBRYO: HISTOGENESIS.

a. The Development of the Germ-layers.

b. The Development of the Primitive Segments.
c The Beginning of the Nervous System.

d. The Mesenchyme.

e. The Origin of the Urinary System.

/. Summary of Early Development: Histogenesis.

6. THE FOETUS: ORGANOGENESIS.

n. The Circulatory System.
b. The Respiratory system.
e. The Digestive system.
d. The Cro-GenitAX System.
r. The Central Nervous SYSTEM.

7. THE FGETAL ENVELOPES.

a. The Fcetax Membranes.

//. Maternal Portion of Envelopes: Deciduve and Placenta.

B. THE PHYSIOLOGY OF THE EMBRYO AND FCETUS.

a. Nutrition.

b. Moto-Sen80RY Activity.

I Hi; PHYSIOLOGY OF MATERNITY.
«. Pregnancy and Parturition.
b. Lactation.

REPRODUCTION.'

The parental phases of reproduction include nil of those activi-
ties involved in the production of offspring. Two general phases
in the production of offspring are (i) the transmission of heredi-
tary characters and (ii) the nourishment and protection of the
young during n Longer or shorter period of development.

'The introduction to the processes of reproduction may be found in Pari One —
( ellular Biology. It is proposed to 'jive here :i very brief summary of mammalian
1. 1 luction and development, especially emphasizing the physiological phases <>t

ili>- i

(117

618

nnvnmn'rrins.

Fig. 299.

In mammalian reproduction one may profitably consider the
following special processes: (i) The formation of the germ cells ;
the maturation of the germ cells ; the conjugation
or fusion of the germ cells (fertUizatiori) ; (ii) the
segmentation of the fertilized ovum ; the intra-
nt, rim development successively, of the blastoderm,
the gastrula, the three-layered embryo, and the
foetus ; parturition; lactation; extror-vierine de-
velopment.

Some of these processes represent activities of
the parents; some, those of the developing young.
The paternal portion of the general process con-
sists in the production of* tin- male germ cells and
assisting in the nourishment and protection of
the young during its extra-uterine development.
The male reproductive cell, — the spermatozoon,
(Fig. 299) — serves the double purpose: (i) Of*
transmitting to the offspring the hereditary char-
acters of the paternal ancestral line ; and (ii) of
inducing in the ovum the process of segmentation.
The maternal portion of the general process
consists in the production of the female germ cells
and the protection and nourishment of the young
during intra-uterine development and infancy,
and assisting in its nourishment and protection
during childhood and youth.
The offspring is passive as an in-
dividual during intra-uterine life,
but its cells and tissues are exceed-
ingly active. The activity takes
the form of the following proc-
esses : Segmentation, formation
of embryonic layers, development
of tissues and organs drawing sus-
tenance for these structures from
the maternal organism.

Without further following the
distinction between parental and
embryonic processes we may now
summarize the whole process of
reproduction and development.

i TTTT1 nVTTTWT Semi-diagrammatic representation of a.

i. inii v v urn. mammalian ovum [Highly magnified. 1 g>,

rpi • i • 1 zona pellncida; vi, vitellus; gv, germinal

lhe ovum IS a Simple, Single vesicle ;?«, germinai spot (SriiAi-.i.

cell. The parts of this gigantic

cell have received special names : the cell-wall is called the viteHim

e—\

Human sperma-
tozoa. }--'iJ'-. 1, in
profile ; 2, viewed on
the fiat : !>, head ; c,
middle- piece : d,
tail ; e, end-piece of
the tail, which is
described as a dis-
tinct part by Bet-
zius. (Si ii'akki.i:
after Retzius.

MATURATION.

G10

membram ; the protoplasm, with its reserve nutriment is called
the yolk, the nucleus becomes the germinal vesicle ; the nucleolus
the germinal dot. (Fig. 300.)

2. MATURATION.

Before the egg is ready to
be fertilized the process of ma-
turation takes place in the fol-
lowing manner, in the egg of
an eehinoderm : (Fig. 301, a
tog.)

(i) The germ iiiative vesicle
gradually moves from the cen-
ter of the egg towards its sur-
face, its nuclear membrane
disappears and the germinative
dot breaks up into small hardly
visible fragments.

(u) There arises out of a
part of the nuclear substance
of the germinative vesicle a
nuclear spindle which pursues r4
still further the direction taken K
by the germinative vesicle until
it touches with its apex the
Burface of the yolk, where it
assumes a position with its long
axis in the direction of a radius
of the sphere.

(in) A genuine process of
cell-division soon takes place
here, which is to be distin-
guished from the ordinary cell-
division only in this that the
two products of cell-division are
of <ry unequal -ize.

More exactly expressed tin-
process is ■■> cell-budding (gem-
mation). This process of gem-

ination OCCUrS tu ice. The two

.-mall cell- are culled polar
bodi< -.

(iv) After the conclusion of the gecond process of budding the
remaining pari of the spindle, one-fourth of the original spindle, is

left iii the Cortical layer of the yolk. From tin- arises a new, -mail

vesicular nucleus, which consists of a homogeneous fluid substance

fe

f>20

i;i:ri:<>i>r<rii>\\

without distinct nucleolus. From its peripheral position it usu-
ally migrates slowly back toward the middle of the egg. Thus
it completes in four phases the process of maturation. There is

QO reason to doubt that the process of
maturation in the mammalian egg is
in any important feature different from
that in the egg of the echinoderm.

I 3. FERTILIZATION.

fe

%

• II

Fertilization is the union of egg-
cell and spermatic cell ; without this
union no further development of the
egg is possible. The spermatic cell is
the male element of reproduction ; in
most animals, both vertebrate and in-
vertebrate, the sperm cell is a flagellate
cell whose head represents the nucleus
and whose flagellum represents the pro-
toplasm. The male element being the
active one in reproduction the fla-
gellum serves as a locomotors organ.
(Figs. 299 and 302.)

Fertilization may take place within
the body of the female or external to it,
internal or external fertilization. (Inter-
nal: most vertebrates — External: fishes,
amphibia and most invertebrates.)

(I) At fertilization only a single
spermatozoon penetrates a sound egg,
which occurs at the apex of the cone
of attraction.

(II) The head of the spermatozoon
is converted into the spermatic nu-
cleus, around which the neighboring
protoplasmic granules are radially
arranged. (Fig. 31 >•">. )

(in) The egg-nucleus and sper-
matic-nucleus migrate toward each
other and in most instances immedi-
ately fuse to form the segmentation nu-
r/m's. ( Figs. 304 and 305.)
Fertilization depends on the copulation of two cell-nuclei which
are derived from the male-cell and a female-cell. The male and
female nuclear substances contained in the spermatic-nucleus and
egg-nucleus are bearers of the peculiarities which are transmissi-
ble from parents to their offspring.

1 fcW'V

THE EMBRYO.

621

4. SEGMENTATION.

Fertilization is in most cases immediately followed by further
development which begins with the division of the egg-cell into
an ever increasing number of ever decreasing-sized cells — the
process of segmentation or cleavage. (Fig. 306, A to F.)

(a) Internal Phenomena of Segmentation ; 1st. Thecleav-
agt a n el' us, at first spheroidal, forms the center of a radiation which
affects the whole yolk-mass, but it soon begins to be slightly elon-
gated, to Income less and less distinct. The monocentric radia-
tion is divided ; the two newly formed radiations thereupon move
to the poles of the elongated nucleus ; they rapidly separate and
finally each occupies a half of the egg.

The nucleus while in the process of division consists of an
acromatic and a chromatic figure — the former a spindle composed

matioii of tin' yitellns in tin1 Impregnated egg of the rabbit. (Dalton alter Cosi I ..

of a definite number of fibers, the latter the same number of V-
shaped nuclear segments — chromosomes, which lie upon the sur-
face of the middle of the spindle. 2d. The chromosomes split
lengthwise and their halves move in opposite directions, apex
first, to the polar centrosomes, where they form the daughter stars,
late- the daughter nuclei.

b External Phenomena of Segmentation consist in the
division of the egg-contents into cell.-, the number of which cor-
respond to the Dumber of nuclei.

5. THE EMBRYO.
Beginning with :i single cell — the egg-cell — we have followed
the development of a mass of cleavage cell — the morula, blas-

tuhi, of which there are four forms.

622

lll-:i'lini>rrrinx.

a. The Development of the Germ-layers.

1. The Blastula, with one germ-layer.

(a) In Amphioxus the cleavage cavity is very large and its
Mall consists of a single layer of cylindrical cells of nearly uni-
form size. (Fig. 307, ".)

(I,) I \ A.MPHIBIA, the cleavage cavity is small ; the wall con-
sists of a thin pole composed of small cells and a thick pole com-
posed of several layers of large cell-. ( Fig. 308, />.)

Fig. 307. !'"■• 308.

The process of blastulation. </, blastula of Amphioxus ,
it, blastula of tritou (amphibian); c, blastula of bird
'.<■., cleavage cavity. ( After Hertwig.)

Fig. 309. (,•) In Fishes, Rep-

T'/-/-/'l\-!-jA.j^rr~~. - tiles AND l>li:i>s the

cleavage cavity is fissure-
like or wanting ; the roof
is the germ-disc and the
floor is the yolk mass
which is not divided into
cells. (Fig. 309, c.)

(il) In Mammals —
Man — the cleavage cavity
i> spacious and filled with
albuminous fluid ; the wall is a single layer of hexagonal cells,
with exception of one pole, whose larger cells in a mass extend
into the cavity.

2. The Gastrula. — With tiro germ-layers. The invagination
of the blastula forms the two layers of the gastrula ; the outer layer
is the ectoderm or epiblast, the inner layer is the entoderm or hypo-
blast ; the cleavage cavity is obliterated ; the invagination cavity
is the ccelenteron, its external mouth the primitive mouth, blasto-
pore, primitive groove, or prostoma.

(a) In Amphioxus the blastopore is large, the coelcnteron capa-
cious, each germ-laver composed of single sheet of cylindrical
cells. (Fig. 310.)

THE DEVELOPMENT OF THE GERM-LAYERS.

623

(6) In Amphibia, the blastopore is small, the mass of yolk
cells is ventral to the ccelenteron, which is arched upward and is
fissure-like. (Fig. 311.)

(«■) Ix Fishes, Reptiles and Birds the" blastopore is cres-
centic, the germinal disc becomes two-layered by means of in-

Fig. 310.

Fig. 311.

Fig. 312.

The p latrulatlon. Gaatrula of ampbloztu (a); of amphibian (ft); of bird

mammal rabbil | d\ eet., ectoderm . etti., entoderm : >>>.. blastopor primitive mouth ; coel.,

rou : '/.'..'./., ilnr-:il and rentral Lips : y.c, y.p., volk celu and jrolk plus : m.. meaoblast.
All. i Hkbtwio.)

growth of cells from the blastopore. The ccelenteron is ventral
to the lower layer of cells — i. e.f il La ventral t<» the hypoblast.
(Fig. 312.)

G24

REPRODUCTION.

(tJ) In Mammals the blastopore is minute and circular, and
Over a thickened pole the co'lenteron and cleavage cavity are one
and the same cavity.

In all vertebrates the gastrula presents bilateral symmetry and
anteroposterior differentiation ; the blastopore is always posterior
— and dorso-ventral differentiation — the yolk mass i> always ven-
tral.

:',. The Embryo with three germ layers.

in all vertebrates there are formed from the root" of the coelen-
teron two lateral evaginations of the inner germ-layer or hypo-

Fig. 313.

Fig. 314.

6 c d

blast, by means of which the ccelenteron
is divided into a median cavity — the in-
testine— and two lateral cavities, ccelo-
mic cavities, or body cavities. The "pri-
mary inner germ-layer thus becomes dif-
ferentiated into : (i) The second inner
germ-layer — hypoblast, (n) Splanch-
nopleure and somatopleure. (in) Xoto-
chord. These are gradually separated
from each other by constrictions.

The form lit' the blastopore and
its metamorphosis in the chick eui-
liryn. a, blastopore of triton ; '< to
e, blastopore of a chick gradually
transformed from a transverse
crescentie slit to a longitudinal
groove— the primitive groove (e.
p.ff.). (After IIektwig.)

The development, i. e., differen-
tiation of the mesoblastic plates
takes place from before backward
while the growth takes place at the
blastopore, thus pushing the em-
bryonal layers forward from that

THE BEGIXX1XG OF THE XERVOUS SYSTEM.

625

point. During; the growth of the mesoblast the blastopore has
been metamorphosed into the primitive groove (Figs. 313, 314).
The primitive groove undergoes degeneration and is not converted
into any organ in the adult.

6. The Development of the Primitive Segments.
In the mammals, birds, reptiles, amphibians and fishes^

nib.

the mesoblast first ap-
pears as lateral somatic
and splanchnic plates.
At the time when these
are constricted off from
the coelenteron the free
edges fuse and immedi-
ately thicken along the
dorsum either side of
the notochord. This
thickened plate is the
primitive segment-plate.
immediately after for-
mation this segment
plate begins segmenta-
tion, first in the trunk
(3(M>0) and later in
the head, eleven in num-
ber (Figs. 315-319).

Fig. 317.

The derivation of the mesoblast and notochord from the
primary Inner germ layer (hypoblast). < Iross suet ion of the
amphioxus (815);of an amphibian (816); of ;i bird (317),
and "i a in. iic (mammal) | </i ; </'■• epiblast ; <»'>.. mesoblast ;
Av.. hypoblast : coel., coelenteron ; .v, notocnord, Note that
in the amphibian (61 the mesoblast is pretty clearly divided
into somatopleure (m) and splanchnopleure («p.). (Hebt-
u ii. after Baleotjb, Bleape, et "/.)

<-. The Beginning of the Nervous System.

The central nervous system of vertebrates is one of die first to
be established after the separation <>f the germ into the three
primitive layers, epiblast, mesoblast and hypoblast. It is de-
veloped out of a broad hand of the epiblast, the medullary plate,

which lie- in the median lin<- jii-l over the notochord. A long this
40

626

i;i:i'i:ni>[-crio.x.

band the epiblastic cells become elongated cylindrical, while the
remaining epiblasi is composed of flattened plates joining by their

Fig. 318.

Transverse section of embryo chirk, through closed portion of medullary canal. Me, medul-
lary canal ; ep, epiblast ; ////, hypoblast ; .U<i, Md', outer and inner laminae of mesoderm i
somatopleure and splanchnopleure ; p, peritoneal space; ch, chorda dorsalis; ao, aorta; 2V,
neural tube; P.sP, primitive segment plate. (KOlliker.)

edges. An e vagi nation of the
margins of the band forms the
dorsal folds or medullary folds.
A continuation of the evaei-
nation and a coalescence of
the edges of the folds accom-
plishes a closure of the neural
tube. (Figs. 315-318.)

The part of the neural
tube which forms the brain
becomes segmented early in
the second day of incubation,
twenty-fourth to thirtieth
hour in the chick, into three
primary brain-vesicles : (i)
the primary fore-brain vesicle,
(n) the mid-brain reside, (in)
the primary hi n< /-/train reside.
Between the thirtieth and
thirty-sixth hour of incuba-
tion the primary fore-brain
vesicle gives off two lateral
evaginations, — the optic vesi-
cles,— and the primary hind-
brain vesicle becomes divided
into the cerebellar reside and
the medullar vesicle. The

,:»

Embryo of chick, about the fortieth hour of
incubation. Cfe, cephalic extremity; P»,primi-
tive segments or proto-vertebree; /'//, dorsal plates,

still widely separated in the caudal region: /'/-,
primitive groove, i Koi.likei;. )

THE MESENCHYME. 627

closure of the neural tube or canal begins at the mid-brain and
progresses anteriorly over the fore-brain and posteriorly over the
cerebellar and medullar vesicles and proceeds along the spinal
cord finally closing it in at the posterior end. (Fig- 318.)

Now it will be remembered that the blastopore, by virtue of the
metamorphosis of the crescentic fold is now located at the anterior
end of the primitive groove. The closing of the neural canal
posteriorly includes the anterior end of the primitive groove with
the blastopore. It thus transpires that the blastoporic canal forms
a direct communication between the neural canal and the coelente-
ron or alimentary canal. This connection persists some time and
is known as the neurenteric canal. It finally becomes obliterated
thr< nigh fusion of its walls. Thus the last vestige of the blasto-
pore of the higher vertebrates becomes extinct in the early stages
of embryonic development.

<I. The Mesenchyme.

Soon after the formation of the primitive segments, these, which
are at first solid, soon acquire a small cavity around which the
cells are arranged into a continuous epithelium. The part of the
wall lying at it- lower median angle begins to grow with extra-
ordinary rapidity and to furnish a mass of embryonic connective
tissue which spreads itself around the cord and neural tube (Hert-
wig). Out of the dorsal and lateral parts of the primitive segment
arises the trunk musculature. The mesenchyme arises from three
other places of the mesoblast besides the primitive segments, i. c,
from the splanchnopleure, from the somatopleure and from that
wall of the primitive segment turned toward the epiblast. These
four origins of the mesenchyme justify a classification of this im-
portant embryonic structure as (i) axial mesenchyme, (n) splanchnic
mesenchyme, (ni) somatic mesenchyme and (iv) dermal mesenchyme.

Thf method by which the mesenchyme arises is peculiar: (i)
there is a rapid growth of the cells at some point in the mesoblast,
accompanied by (n) a vigorous amoeboid movement. This com-
bination make- invagination or evagination of a body of cells a
mechanical impossibility, instead of that process, individual <■<■//■•<
the parent epithelium and, by virtue of their continued
amoeboid movements, wander between the Bomatopleure and epi-
blast or between the splanchnopleure and hypoblast, as the case
may be. The origin and destiny of the mesenchyme have been

foe more than a deeade a riddle whose solution lias engaged the

attention of Hi-, Kolliker, Heape, Waldeyer and other embryoJ-
ogists.

At the time of the (brmaiioii of the mesenchyme— end of first
day in 1 1 1 * - chick — two necessities begin to press themselves upon
the developing organisms: (i; necessity for mechanical support,

628 REPRODUCTION.

and (n) necessity for nutrition. The first of these necessities
urges itself upon the axial part of the embryo, for there the deli-
cate nervous system is passing rapidly through the steps of its
development. The need for nutriment will not be felt by the
epiblast or by the hypoblast, for these layers are next to the sup-
ply of nourishment ; but by the mesoblast, in contact with neither
white nor yolk. It is a law of biology that hungry organisms are
restless while satiated organisms are sluggish. Recall at this point
the fact that the mcsoblast cells which form the somatopleuric and
splanchnopleuric mesenchyme free themselves from the mesoblast
by dint of amoeboid movements. These restless hungry cells are
out foraging. The leucocytes of the adult body are the descend-
ants of these restless, hungry, foraging cells of the primitive
mesenchyme. How are the two necessities mentioned above sat-
isfied ?

(a) The Necessity for Support for the axial nervous system
is satisfied by the axial mesenchyme which closes about the
central nervous system and the notochord, and later develops
into the axial skeleton with at/ its associated connective f issue.

(6) The Necessity for Nutriment is solved by the somato-
pleuric and splanchnopleuric mesenchyme in the following man-
ner, as represented by Kolliker and subscribed to by Hertwig :
" At the end of the first day of incubation the masses of cells
which represent the mesenchyme arrange themselves iu cylin-
drical or irregularly limited cords which join themselves together
into a close-meshed network ; they are the first fundaments, both
of the blood vessels and of their contents — the blood. In the
spaces of the network are to be found groups of indifferent cells
which afterwards become embryonic connective tissues.'1'' In the
beginning of the second day of incubation the " cords " acquire
an internal cavity and become bounded superficially by a single
layer of flattened polygonal cells — the future endothelium of the
blood vessels. "The cavity of the vessel is probably formed by
the penetration of fluid into the originally solid cord, thus form-
ing the plasma of the blood by which the cells are pressed apart,"
some of these forming the vessel wall, some remaining floating in
the fluid and becoming the leucocytes and red blood corpuscles.
The red blood corpuscles originate, at the first, in the vascular
area of the yolk, from yolk nuclei. They are nucleated during
the early embryonic life of mammals and man and increase in
numbers rapidly by division.

e. The Origin of the Urinary System.

Before the activities of life begin to make themselves manifest
by the expenditure of energy, as in the transportation of matter
through space, e. g., the action of the heart walls in the circula-

SUMMARY OF EARLY DEVELOPMENT. 629

tion of the blood, — there is no need of an excretory system. If
we admit then that the need for an excretory system arises during
the third day in the chick, to what shall we attribute the actual
appearance, during- the second day, of a rudimentary urinary sys-
tem ? It must be attributed to heredity. It is generally ad-
mitted that the genealogy of vertebrates extends through trun-
cates back to worms. From your studies in zoology you recall
the segmental organs of the higher worms. A pair is located in
each segment and each segmental organ is composed of: (1) a
ciliated funnel, (2) a convoluted tubule, (3) a glandular segment,
and (4) a muscular bladder which opens externally. But this
segmental arrangement of the excretory organs is an expensive
and clumsy solution of the matter. In the lower vertebrates we
see the following improvements : The uriniferous tubules are seg-
mental, but instead of opening individually on the surface of the
animal, as in worms, there is a collecting tube which transfers the
accretion of all the tubules of one side of the body to a posterior
and ventral orifice opening near or into the cloaca. In all
the higher vertebrates, including man, the primitive kidney or
pronephros is << segmental organ, and is quite rudimentary,
never performing the function of excretion, even in the embryo.
" The pronephros of the chick is located between the 7th and
11th somites. The pronephric duct, at its first appearance, is a
short canal-like perforation of the wall of the body, which begins
in the body cavity with one or several ostia and opens out upon
the skin with but a single external orifice. Originally the outer
and inner openings lie near together; later they move so far apart
that the outer opening of the canal united with the hind-gut."
( Her twig.)

/. Summary of Early Development.

If the student has observed carefully the character of the de-
velopmental changes he has noted three phases of development
going on at tin- same time: (i) The tendency to iinc</it<i/ (jroirtli,
manifested at particular places and occurring at particular times
resulting in the general morphological unfolding; (n) the histo-
logical differentiation manifesting itself in the development of new
tissues (histogenesis); (in) the physiological division of labor,
manifested by the general division of the functions into those of
external relations and those of internal relations ; and by the begin-
ning development of various Systems of organs : Nervous system,

circulatory system, excretory system, etc.

("; Tin: I'imm epleof Unequal < rROWTH is manifested in the
chick during its first two days of development by: (i) Theinvagi-
nation of the blastopore; (n) The evagination of the medullary
fold-; (in) the evagination of the three primary brain vesicles

630

REPRODUCTION.

from the anterior end of the neural tube; (rv) the subsequent
evaginatioD of the optic vesicles from the fore-brain vesicle; (v)
The evagination of the lateral folds of mesoblast from the median
hypoblast; (vi) the separation of the muscle plates and their sub-
sequent segmentation ; (vn) the general emigration, from the meso-
blast, of the elements of the mesenchyme ; (vm) the invagination
of the pronephric canals.

(/>) The Principle op Histological Differentiation i-

manifested in histogenesis

Histogenesis.

Origin
of Tissues.

I.

ECTODERMIC

TissrKs.
Tissues of Ex-
ternal Rela-
tion.

II.
Entodermic
Tissues.
Tissues i if In-
ternal Rela-
tion.

EPIIJLAST

Proper.

Nervous Sys-
tem.

Neuroblast.

Mesoblast.

Hypoblast.

NOTOCHOBD.

[ Cuticlt and appendages, e.g., Hair, Nails,
Sebaceous and Sweat Glands, Enamel
of Teeth,
J Epithelium of Conjunctiva and Cornea.
' " " Nasal trad with glands.

" " Mouth with glands.

" Anus and lower rectum.
" " Auditory canal.

Central Nervous System, i.e., Brain and
Cranial Nerves, Spinal Cord and Spi-
nal Ncr\ es.

I Retina, Cryst. Lens,

Sensory Taste Buds, Auditory

Apparatus, j Nerves, Olfactory

I uerves.Tactile Bodies.

Primitive I Voluntary muscular

SrijiiKiils. \ system.

f Somatic Pleura and
c. , , I " Peritoneum.

Somatopleure. ) Epithelium of Qenito-

L urinary tract.

Splanchno- ! L^^exa&' perioar"
Jl ' '""'■ I Splanchnic peritoneum.

Connective Tissues :
Boue, cartilage, liga-
ment, dentine, areo-
lar tissue, tendon.
Involuntary Mus-
cular System,
Vascular ENDO-
THELIUM, Blood &
Spleen.

Mesenchyme.

Epithelium of digestive tract (exclusive
of mouth and anus). Inclusive of
Liver, Pancreas.
Epithelium of respiratory tract.

" " Urinary Bladder and

Urethra.
" " Eustachian Tube and

Tympanum.
" Tonsils.
" " Thymus Body,

" Thyroid Body.

6. THE FOETUS : ORGANOGENESIS.

The terms foetus and embryo are used synonymously by some
authors, while by others they are given different significations-
Gould defines foetus as, " the embryo in later stages of develop,
ment," but uses embryo and foetus synonymously. The author,

THE CIRCULATORY SYSTEM. 631

following in a general way the Am. Text-book of Obstetrics, will
use the terms in the following sense : the embryo is the young in
its early stages of development when tissues are being developed ;
the foetus is the young at a later stage of development when organs,
(specially systems of organs, are being given their finishing touches:
i. e., the term embryo covers the period of histogenesis, and the
term fcetus covers the period of organogenesis.

Under the caption foetus we shall briefly discuss the develop-
ment of the various systems of organs.

a. The Circulatory System.

1. General Considerations. — («) The simplest heart among
the vertebrates is a rhythmically contracting tube : the heart of
the highest vertebrate is at first a rhythmically contracting tube.

(,3) Intermediate classes of vertebrates have two- and three-
chambered hearts, and the highest classes have the four-cham-
bered heart : the heart of the highest vertebrate passes from the
original tubular condition through the two- and three-chambered
condition during foetal development and finally after birth as-
sumes the functionally four-chambered heart.

(y) The one- and tivo-chambered condition of the heart makes it
necessary for the heart contractions to propel the blood in one cir-
cuit through a double system of capillaries : (i) the capillaries of
the respiratory system, and (n) the capillaries of the general cir-
culation. The circulatory system of the highest vertebrates passes
through this condition and reaches, in extra-uterine life, a condi-
tion in which one-half of the heart propels the blood through the
respiratory system while the other half propels it through the
genera] system.

(o) In flu: lower vertebrates the blood passes from the heart
directly into a system of branchial arches or gill-arches ; the
highest vertebrate possesses this system of gall-arches during the
early part of its development. These arches are gradually re-
duced during the three- and four-chambered stages. Our aortic
ami pulmonary arches represent the last two pairs of arches.

(i) In the amphibia <ni<l reptiles, classes of vertebrates which
).<,"«" three-chambered hearts — the purer blood passes to the
anterior part of the body ; while the less pure blood passes to
the posterior part of the body. In the human foetus the func-
tionally three-chambered heart distributee the blood in a simi-
lar way. This probably accounts, in part, for the large head and

small legs of the foetus. (Fig. 320.)

2. Special Metamorphosis of the Heart. — During the second
day of the chick's development the heart ie practically a straight
tube formed by the fusion, along the median line, of a double,
tubular heart-fundament ; continuous posteriorly with the two

.;:;•_•

REPRODUCTION.

Omphalo-mesaraic veins and anteriorly with the bifurcated aorta.
The endothelial partition of the heart soon disappears, leaving a
single tube with somewhat thickened muscular walls. ThedorsaJ
aorta;, in the meantime, pass laterally around the alimentary canal

Fig. 320.

lt.Com.Carotid

Superior Vena Cat

Umbilical

Vein

Diagram of the foetal circulation. (Kirke. )

and fuse ventrally, forming the single aortic trunk which joins the
anterior end of the heart or Bulbus Arteriosus. As soon as the
posterior venous junctions and the anterior arterial junction has
been effected the already slowly and irregularly beating heart
begins to send the elements of the blood through the system of
tubes, the direction of the stream being at first determined not
by valves but by virtue of a postcro-anterior peristalsis.

THE BESPIRATORY SYSTEM.

633

During the subsequent few hours the pulsations become regular
and rapid, and the development of valves accompanies the grad-
ual metamorphosis of the heart. The metamorphosis of the heart
may be considered in four principal changes. (Figs. 321, 322,
323.)

CHANGE DURING PERIOD.

itrve of Heart-tube, through increase
II. in length of Heart and no increase in
length of pericardium.

Dilatation laterally of venous end
and general

Dilatation of central or ventracular

segment ami
Dilatation of Bulbus Arteriosus.

Division of whole Heart :
1st. Auricle into left ami right.
IV. 2d. Ventricle into left ami right.

3d. Bulbus Arteriosus into Aorti
and Pulmonary Artery.

CONDITION AT END OF PERIOD.

Straight muscular tube.

Heart in S-shaped curve, with venous
end in left dorsal region and arterial
end in right ventral region.

Heart of Two Chandlers, one double-
lobed, single-chamber auricle dor-
sally and a single-chambered ven-
tricle ventrally.

Heart of Four Chambers. Left Au-
ricle, Left Ventricle and Aorta con-
tinuous and Right Auricle, Right
Ventricle and Pulm. Art. continu-
ous.

IV.

Fig. 321.

Development of the heart. The four principal stages being shown at I-IV; <i and b are two
phases of the same stage. ( HEETWIG. )

b. The Respiratory System.

1. General Considerations. — («) The simplest vertebrate res-
piratory system is composed of a scries of gill-arches : The
highest vertebrate has giU-arehes in early embryonic life

(3) In /I"1 highest fishes there is a combination of gills and
swim-bladder which is a saccate evagination or outgrowth of the
alimentary trad : //' amphibia the gills are usually secondary in
importance to the saccate lungs which are homologous to the
swim-bladder : //* //"■ highest vertebrate the gills arc rudimen-
tary structures confined to embryonic life and never functional
while the function of respiration is performed during the whole
period of extra-uterine life by the Lungs.

2. Special. The Development of the Lungs. — At the be-
ginning of the third day in the chick, on the tenth day in t he
rabbit and in the human embryo when it reaches a length of about
1 mm. there arises on the ventral sideof the oesophagus a groove

634

REPRODUCTION.

which is slightly enlarged ;it its anterior end. Soon the groove-
like evagination becomes separated from the alimentary tube by

Fig. 322. Fig. 323.

Heart of the human foetus, at the end of the
sixth month, a, inferior vena cava ; //, superior
vena cava ; c, cavity of the right auricle, laid open
from the front ; </, appendix auricularis ; e, cavity
of the right ventricle ; /, Eustachian valve. The
bougie, placed in the inferior vena cava, can be
seen .passing behind the Eustachian valve, just
below the point/, then crossing, behind the right
auricle, through the foramen ovale, to the left side
of the heart. (Dalton.)

two small sacs towards the two sides of
of the right and left lung;.

Fig. 324.

Heart of infant, showing the dis-
appearance of the arterial duct after
birth. 1, aorta; 2, pulmonary ar-
tery ; '■'•. '■'<, pulmonary branches ; I.
ductus arteriosus becoming obliter-
ated. (Damon.)

two lateral ridges ; this
is the first indication of
a differentiation into
oesophagus and trachea.
There then grow out
from the enlarged pos-
terior ends of the groove
the body — the fundaments

Early development of the lung. /. trachea ; o< , .esophagus : h, m, I, upper, middle and lower
right lobes ; //'. /'. upper and lower left lobes ; .s'/y/., splanehnopleure ; Ms, mesenchyme. (From
BERTWIG after HIS. I

These lung sacs are enveloped in a thick layer of mesenchymic
connective tissue which is covered externally by the thin splanch-

THE DIGESTIVE SYSTEM.

635

nopleure — the future lung-pleura. Two stages are recognizable
in the metamorphosis of the primitive luug-sacs of man and of
mammals.

(i) The first bud-like outgrowths on the two sides of the body are
not symmetrical because the left lung-sac produces tiro and the right
hmg-sac produces three bud-like enlargements (Hertwig). These
buds are the fundaments of the lobes of the lungs. From this
point on the division is dichotomous. Continuous division and
evagination proceed during six months in the human embryo.
During this period the terminal branches are simply saccate or
vesicular and are called primitive lung resides. (Fig. 324, b.)

(n) During the last three months of intra-uterine life, " there
arise close together on the fine terminal of the bronchial tree — on
the alveolar passages and on their terminal vesicular enlargements
— very numerous small evaginations — the pulmonary alveoli "
(K(')lliker). These are only ^ to J as large in the foetus as in the
adult, and the extra-uterine growth of the lung is to be attributed
to their expansion rather than to their multiplication.

c. The Digestive System.

1. General. — («) In all vertebrates the stomach is produced
by a simple dilatation of the alimentary canal, just behind the
heart in the lower vertebrates and

ju-t posterior to the diaphragm in
mammalia. (Fig. 325.)

ii) In nil vertebrates two glands
are evaginated from the duode-
num ; — the liver is evaginated
into the ventral mesentery and
pancreas into the dorsal.

2. Special Development of
Digestive Glands. — (a) The

LIVES early becomes bilobed, —
later these two primitive! lobes

are variously subdivided in dif-
ferent classes of vertebrates, —
;ui«l the evaginations take the form
of thick-walled tube- or "hepatic
cylinders" which unite into a net-
work. The small lumina of the cylinders become the bile duets
which are surrounded by the secreting parenchyma of the liver.
This latter, as well as the epithelial lining of all gall duets, is
of hypoblastic origin, while the connective tissue framework and
the vascular system of the liver is from the mesenchyme, the
organ being encapsuled with splanchnopleure or splanchnic peri-
toneum.

Fig. 325.

Derelo] nl of the alimentary canal, oe,

oesophagus ; St. stomach: S, small intestine;
/.. large Intestine; y, yolk dud ; /'. duode-
num ; ./, jejunum ; /, ileum ; M>. '/'<', !>(',
ascending, transverse and descending colon;
R, rectum ; A , anus.

G30

REPRODUCTION.

(b) The Pancreas follows a general course of development

quite parallel to that of the liver.

d. The Uro-Genital System.

tl

le

For general considerations see above under "Origin oi
Urinary System."

1. The Indifferent Stage. — This stage is characterized by all
the organs being contained in two longitudinal uro-genital ridges,
one on each side of the body and projecting from the dorsal wall

into the peritoneal cavity.
At the caudal end of the
abdomen the two ridges
draw closer together and
finally come into contact
with the anal region of
the alimentary canal.
The substance of the
ridge comprises the
Wolffian body of mesone-
phros and the genital epi-
thelium. The ducts are
two in number and are
the result of longitudinal

division of the original
pronephric duct. The
inner one of the two re-
sulting ducts is the meso-
nephric or Wolffian duct
and during the period
when the mesoncphros
functions as a urine-ex-
creting organ conducts
the urine to the cloaca ;
this condition is per-
manent in fishes and
amphibians. The outer

Diagram of the indifferent fundament of the uro-genital
Bystem of a mammal at an early stage. /*, kidney : fed,
sexual gland; »«. primitive kidney; ».</, mesonephric
duct; i, ni, Mullerian duet : mg', its anterior end : ^A,guber-

oaculum Bunteri | sonephric inguinal ligament); /</.

ureter; hi', it- opening into tin- urinary bladder; »</".

mil", openings of tin- mesonephric and Mullerian duets one of the resultill<r ducts
into the sinus nrogenitalis {wg\; md, rectum; cl, cloaca: , o _

ijhii. sexual eminence: gw, sexual ridges; el', externa] jg the .Mullerian duct,
orifice of the cloaca; /<'</. urinary bladder; Mil', its elon- -., . . . .

gation into the nrachus (the future lig. vesico-umbilicale). Jsow 111 the male the

"lll:IW"" Wolffian duct becomes

the genital (hid, while in the female the Mullerian duet becomes
the gt nital duet.

2. The Differentiated Stage. — (a) Changes Common to
\)( fi ji Sex ES are : (i) The union of the caudal ends of the uro-gen-
ital ridges to form a single median CTRO-GENlTAii CORD, (n) The
ducts of the uro-genital cord open into a cloaca with the rectum.

THE URO-GENITAL SYSTEM.

63'

(in) The cloaca gradually divides into the uro-genital sinus and the
anus, (iv) The allantois also opens into the cloaca and in extra-
uterine life the dilated
remnant of the allan-
fois becomes the urinary
Madder, (v) From the
lower > nd of the mesone-
phric or Wolffian duct
tht /' ' vaginates the meta-
nephric duct or ureter.
This grows into that part
of the uro-genital ridge
which lies just posterior
to the Wolffian body or
mesonephros. The mass
of the uro-genital ridge
now lying about the di-
lated and divided ureter
is the fundament of the
metanephroe or perma-
nent kidney. While the
fundament with the
ureter gradually ad-
vances anteriorly, the
end <»f the ureter differ-
entiates into the pelvis,
calyces and the collect-
ing tubules of the pyra-
midal portion, and the
cortical fundament grad-
ually develops the mal-
pighian corpuscles and
the convoluted tubules.
(vi ) The genital epithe-
lium in the region of
tin- mesonephros de-
velops into the '/'nihil

gland, while the Wolffian
body — mesonephro — lapses into functional or rudimentary ap-
pendages of thai gland.

Diagram to illustrate the development of the male sexual
organs of a mammal from the indifferent fundament of
the uro-genital system. The persistent part- of the origi-
nal fundament are indicated by continuous lines, the
parts which undergo degeneration by dotted lines. 1 lotted
lines an- also employed to show the position which the
male sexual organs take- after the completion of the de-
gcenans testiculorum. n, kidney; h, testis; »A, epididy-
mis; /"', paradidymis; /"/. hydatid of tin- epididymis;
*/, ras deferens ; mg, degenerated MOllerian duct: »»/.
uterus masculinus, remnant of the Mullerian ducts ; gh,
gubernacnlum Hunteri : hi, ureter; hi', it- opening into
tin- bladder; sbl, resicnls seminales; /*'</, urinary blad-
der; KbV ', it- upper tip, which i- continuous with the
ligamentnm resfco-umbilicale medium (uracbue
urethra; pr, prostata: dej, external orifice of the ductus
ejacnlatorii. The- letters nhf. /<'. »V Indicate the position
of the sexual organ- after the descent has taken place.
| Bkbtwio.)

(538

Diagram to illustrate the development of the female sexual organs of a mammal from the
indifferent fundament of the uro-genital system. The persistent parts of the original funda-
ment are indicated by continuous lines, the parts which undergo degeneration by dotted lines.
Dotted lines are also employed to show the position which the female sexual organs take after
the completion of the descensus, n, kidney : ei, ovary ; ep, epoophoron : pa, paroophoron ; hy,
hydatid; t, Fallopian tube (oviduct); ug, mesonephric duct ; ul, uterus ; sch, vagina ; &?, ure-
ter ; hlil, urinary bladder ; hbl' ' , its upper tip. which is continuous with the ligaiiicntmn \ esiCO-
umiiilicale medium; hr, urethra; vv, vestibulum vagina'; rm, round ligament (inguinal liga-
meiit of the primitive kidney); lo', ligameutum ovarii. The letters /", ep', , /', /</ indicate the
positions of the organs after the descent. (Figure and description from HEBTWIG. j

(6) Sexual Differ extiatiox. (Hertwig.) (See Figs. 326-328.)

Male Sexual Parts.

Indifferent: Common form Fpn...lp <(.v,..,i Pftrt«,
from which both arise. female Hmi.iI 1 arts.

Testis.

Seminal Ampulla? and Tube.

Germical Epithelium. ovary.

(Ovarian follicles.)

(a) Epididtmus.
(/*) Paradidymus.

Mesonephros or (") EpoOphoron.

Wolffian Body. (6) Paroophoron (Parovarium
or organ of Rosemuller).

\'as Deferens and
Seminal Vesicles.

Mesonephric Duct.

Hydatid of Epididymus.
Sinus Frostaticus (Uter. masc. .

Mollerian Duct. Uterus and Vagina.

Oviduct and Fimbriae.

Kidney.

Metanephros. Kidney.

Ureter.

Metanephric Duct.

Ureter.

Gubernaeulum Hunteri,

Inguinal ligt. of Mesoneph,

'Round Ligament.

I retina. Membranous and
Prostatic Part.

sinus Urc-genitalis.

Vestibulum Vagina-.

c The Central Nervous System.

1. General Considerations. — (a) In all vertebrates the central
nervous system is developed out of the thickened region of the

THE CENTRAL NERVOUS SYSTEM.

639

outer germ-layer which is designated as the medullary plate. The
medullary plate is folded together to form the neural tube.

(,3) In the lowest vertebrates the neural tube is not differentiated
into brain and spinal cord. In the higher vertebrates there is at
first no differentiation between brain and spinal cord.

if) J" fishes the brain consists of five lobes not very unlike in
size. An early step in the development of the brain of higher
vertebrates is the formation of five lobes or vesicles.

(o) The ascending scale of vertebrates is marked by an increas-
ing preponderance of the cerebrum over the other segments of the brain.
The highest vertebrate in its embryonic development shows an ever
increasing preponderance of the cerebrum over other parts.

Fig. 329.

Fig. 330.
cbl. os.v.

or. p

A somewhat later >tage of the human brain. Cbm., cerebrum
(prosencephalon); /n/.; infundibuluin; Th., inter-brain (thala-
nieneephalon); Ms., mid-brain (mesencephalon); cbl., cerebellum
(metencephalon); or., area rhomboidalis ; M.O., medulla oblongata
(myelencephalon); rc., flex, nuchal flexure. (After 1 1 is.)

2. Special : Development and Metamor-
phosis of the Human Brain. — («) The part
of the neural tube which forms the brain be-
comes segmented into the three primary brain
vesicles mentioned above.

(jS) The lateral walls of the fore-brain vesi-
cle- are evaginated to form the Optic Vesicles
and the anterior wall to form the secondary
Fore-brain Vesicle, the Cerebrum or Prosen-
cephalon.

(,) The Hind-brain vesicle is divided by
constriction into the vesicle of the Cere-
bellum— Metencephalon — and the M edulla
— Myelencephalon.

(o) Thus from the three primary brain vesi-
cles there arise five secondary ones arranged in a single series,
one al't.r the other in a -i raight line ( Fig. '-V1U) ■.
(i) ( lerebrum — prosencephalon.

Inter-brain — thalamencephalon — with the laterally at-
tached optic vesicles.

Primitive brain and
■pinal 'ord Mt' man. 1,
-. ■'.. tin- three primary
ii r a i N resiclet i fore-,
)n i '1 - a n il b ind-
l.rain ;. /. prosenceph-
alon : Op.v., optic resi-
de ; //.. thalamenceph-
alon ; ///.. mesencepna-

1 • * ri ; '//.//. aural pits :

TV., metencephalon; r.,
mreleocepbalon. (After

ll.ll.KIJ.

C4II

REPRODUCTION.

(in) Mid-brain — mesencephalon.

( 'iv) ( lerebelluni — metencephalon.

(v) Medulla oblongata — myelencephalon.

(i) The originally straight axis uniting the brain-vesicles to one
another later becomes, at certain places, sharply bent : (i) The
Nuchal Flexure is a ventral bending of the medulla, forming the
nuchal protuberance dor sally, (ii) The Pontal Flexure is a dorsal
bending in the region of the pons varolii, (hi) The Cephalic
Flexure is a marked and persistent ventral bending of the mid-
brain, resulting in the cephalic protuberance. The nuchal and the
cephalic protuberances arc obscured by subsequent development.
(Fig. 331.)

Fig. 331.

MESENCEPHALON

CHOROID

PLEXUS

FORAMEN

OF MON RO

CAUDATE

NUCLEUS

INFUN Dl BULUM

EREBELLUM

OURTH
VENTRICLE

OBLONGATA

Lateral view of the braii) of a calf embryo of five em. The outer wall of the hemisphere i«
removed, so a< to give a view of the interior of the left lateral ventricle, hs, cut wall of hemis-
phere ; si, corpue striatum; am, hippo-campus major (cornu ammonis); d, choroid plexus of
lateral ventricle : fm, foramen of Monro: up, optic tract : in, infundibulum ; ml,, mid-brain ;
ri,, cerebellum; TV. V, roof of fourth ventricle; p«, pons Varolii, close to which is the fifth
nerve with Gasserian ganglion. (From Hektwig after Mihalkovic8. i

(£) In the metamorphosis of the vesicles the following processes
take place : (i) Certain regions of the walls become thickened,
other regions become thinner and do not develop nervous sub-
stance (roof-membranes of third and fourth ventricles) ; (n)
The walls of the vesicles may be evaginated or invaginated ; (in)
Some of the vesicles greatly exceed in their growth the remaining
ones (cerebrum, cerebellum). (Fig. 331.)

The four ventricles of the brain and the aqueduct of Sylvius
are derived from the cavities of the vesicles.

Of the five vesicles the mid-brain undergoes the least meta-
morphosis.

The cerebral vesicle is divided by the development of the
longitudinal fissure and the falx cerebri into lateral halves, the
cerebral hemispheres.

In man the cerebral hemispheres finally exceed in volume
all the remaining parts of the brain and grow out in every
direction forming a "cerebral mantle" over the other segments
of the brain.

THE FCETAL ENVELOPES.

641

The Development of the Braix (Hertwig). See Fig. 332.

The
Develop-
ment of the
Brain.

Primary Fore-
brain Vesicle.

Mid-brain
Vesicle.

Primary Hind-
brain Vesicle.

Fluor, (f); Roof, (r);
Walls, w).

j f Olfactory Lobes, (f)

Fore-hriin ' Cerebral Cortex. »r Aw)

' rk rim 1 Ant. Perf. Lamina, u'i

Pros™ halon I Corpus striatum, (f,
i rosencepnaion ^ Corpus Oallosum. (r&w)

II.

Inter-braix.

Optic Thalamus

Thalamenceph-

alon.

III.
Mid-brain.
Corpora Quad ri-

gemina.

Mesence]>halon.

IV.

Hind-brain.

Cerebellum.

Metencephalon.

V.

After-brain.
Medulla Obl.
Myelencepha-
lou.

f Optic Chiasm, if) "1

Roof-memb. of3d V. ir) I
< iptic Thalami. (w)
Tuber Cinereum with -

infundibulum. (f)
Corpora Albieantia. (f)
Pineal Gland, (r) J

( Post. Perf. Lamina, (f) 1
I Peduncles uf Cerebrum. I
J (f) I

Corpora Quadrigemina. j"

(r)

[ Laipieus. (w)

J

\ P.»ii> Varolii, (f)
Cerebellar Cortex, fr & I

1 w) I

Crura Cerebelli ad Pon- |

[ tern, (w) J

f Medulla Oblongata, (f) 1
Roof-memb. of 4th Ven- |
•{ tricle. (r) j-

I Peduncles of Cerebel-
L lum. (w) J

Cavity.

Lateral
Ventricles.
(l-2d Ven.)

Third
Ventricle.

The
Aqueduct of

Sylvius.

Fourth
Ventricle.

Fourth
Ventricle.

..tudinal and vertical diagrammatic section of a vertebrate brain. Lamina terminalis. is
represented by the strong black fine joining Pn and Py. 0(f, olfactory lobes or rhinencephalon;
amp, cerebral hemispheres, mantle or prosencephalon : :'• with II, Py and /'». thalamencepha-
lon or Inter-brain; .'/.'<, ///. mid-brain or mesencephalon; Cb, PV, metencephalon ; 4, fourth
ventricle; AfO, medulla. (Hdxlbt.)

7. THE FCETAL ENVELOPES.

a. The Foetal Membranes.

The term foetal membranes may be used for that portion of the
foetal envelopes developed from the ovum. A part of the foetal
envelopes is produced by the maternal organism. If one refers to
Fig. ;il t, "J, he will find a cresoentic dark field which repre-
sents a transverse ridge of epiblasl anterior to the embryo near
the anterior margin of the blastoderm. As Boon as tli<' mesoblast
is formed, ;m<l divided into somatopleure and splanchnopleure, the

41

642

REPRODUCTION.

former takes part in the formation of this fold while the Latter
with the hypoblast remains in close contact with the yolk. By
the time that the primitive segments begin to appeal- the amni-
otic fold has taken on a horseshoe shape enclosing the head end
of the embryo and sending two ridges toward the caudal end of
the embryo. A cross section of the embryo at this stage will ap-
pear something like Fig. 333. The two lateral folds approach

Fig. 333.

I>iagraniruatie figures of the development of the fatal membranes, af, amniotic fold : i . epi-
lilast : m, mesoblast ; h, hypoblast ; pp, pleuro-peritoneal cavity. Note that the amniotic sac is
Lned with epiblast, and that the chorion is lined with somatopleure, the epiblast being external,
land covering the chorionic villi. (The Allantois is by mistake Chantoifl in Fig. 334.)

each other over the median dorsal line of the embryo and meet
and fuse from before backwards, thus forming a double sac, an
inner true < nnn ion, composed of epiblast internally and somato-
pleure externally ; and an outer false amnion or cliorion, composed
of epiblast externally and somatopleure internally (see Fig. 334).
The chorion presents villi over a considerable portion of the sur-
face of the ovum. At first these villi are practically equal in de-
velopment but after the allantoic becomes developed, the villi in
the region of that organ are rapidly increased in size, while those
in other regions become obliterated. These facts are represented
in Figs. 335 and 339.

The allantois is an evagination from the ventral side of the
primitive hind gut and is composed of hypoblast internally and
splanchnopleure externally. "While the yolk-sack (dsj decreases
in size the allantois (al, Fig. 335) increases ; finally reaching the
chorion where it forms the foetal portion of the placenta. The
allantois is accompanied by two umbilical arteries and an um-
bilical vein. These send branches into the chorionic villi of the
placenta. The umbilical cord is composed of the arteries and
vein, the shriveled yolk-stalk, the allantoic stalk, a gelatinous

THE F(ETAL ENVELOPES.

613

embryonic connective tissue and the whole enclosed in amnion.
A careful study of Figs. 334 and 335 Avill reveal the relations of
these structures much more clearly than a description could do.

Fig. 335.

Diagrammatic figures, Illustrating the development of 1 1 < « - mammalian embryo and the foetal
membranes. I, the blastodermic resicle Invested In the zona pellucida, ;m<l showing al Its
upper pole the embryonic area; 2, shows the pinching off the embryo from the yolk-sac, and

the formation of the amnion ; ■'•, further development "i amnion, and oon incemeni of allan-

toii : i. completion of amnion and growth of allantois. The false amnion, or subgonal mem

off villous process. B, the allantois has grown all round the vesicle, and gives off

. the villi which are much larger than before. The yolk-sac i> greatlj reduced In

■Use. a. epiblasl of embryo ; "'. epiblasl of non-embryonic pari of blastodermic vesiole; til.

allantois; am, amnion; eh, chorion; eh 2, chorionic villi; d, zona pellucida; d', processes of

Ed, embryonic hypoblast; dt , ai •■ da, yolk-stalk; dt, yolk-sao; e, embryo;

hh, pericardial cavity; >. non-embryonic hypoblast; kh, ■ ; i \ i r \ of blastodei ■ ■ Icle; /■-,

beao-fold of amnion ; m, embryonic mesoblast ; n, non-embryonio mi obla I pace between

■ i false amnion . h i;ii e amnion, or subgonal membrane* . veil-fold of ai

-inn- terminalis; (, prooei es of zona pellucida; vl, renl i : • i body-wall of embryo. (KOlliki b.j

c,i I i:i:ri:oi)r<riox.

b. Maternal Portion of Envelopes : Deciduae and Placenta.

The maternal organism plays an important part in the forma-
tion of the foetal envelopes. Figs. 336, 337, 338 show the forma-
tion of the deciduae. Fig. 339 shows the three portions of the

Fig. 336.

Fig. 337.

Impregnated uterus, with
folds of decidua growing up
around the egg. The narrow
opening, where the folds ap-
proach each otber, is seen over
the most prominent portion
of the egg. (Dalton.)

Pregnant uterus ; showing the
formation of the placenta by tin'
local development of the decidua
aud the chorion. (Dalton.)

decidua? ; (i) Decidua vera lining the body of the uterus ; (n)
Decidua rejiexa, reflected over the egg, (in) Decidua serotina
where the chronic villi are developed. The relation of the ma-
ternal to the foetal mem-
Fxg. 338. branes is shown in Fig.

33*. Fig. 339 shows
similar structures some-
what less diagrammatic.
Ihe Placenta is com-
posed of the serotine
decidua with its large
venous sinuses through
which the maternal blood
circulates ; of the chor-
ion and amnion with the
foetal arteries and vein.
In the placenta the ma-
ternal and foetal blood
come into relation.
There are three tissue
layers between the fetal
and maternal blood. The

Pregnant human uterus ami its contents, about the qt»iK1qq+ onrl enmntn

end ofthe seventh month ; showing the relations of the tpilMUbt ami soinaiu-
cord. placenta and membranes. — 1, Decidua vera : 2, De- -l..... „f +U0 inline onrl

eidua rellexa::!. Chorion ; 4, Amnion. (I (ALTON., pitlUC Ol llie \ 111 lib ami

NUTRITION.

645

the endothelium of the capillaries. Through these fissures the
foetus receives nourishment from the maternal organism.

8. THE PHYSIOLOGY OF THE EMBRYO AND FOZTUS.
a. Nutrition.

1. Foods, Digestion and Absorption. — The origin of the
animal individual from an ovum is practically universal,
(protozoa excepted, perhaps). The fertilized ovum consists of
the minute segmentation-nucleus and the yolk-mass which repre-
sents the first installment of maternal nourishment. The yolk-
mass is relatively large in birds and reptiles and relatively small
in mammals.

Fig. 339.

Diagrammatic view of a vertical transverse Bectlon of the uterus al the seventh or eighth
w.-ek of pregnancy. •■, e, &, cavity of uterus, which becomes the cai ii\ of the decidua, opening
:it <•. c, the cornua, into the Fallopian tubes, and at t» into the cavity of the cen i\, which is
closed by a plus of mucus; dv, decidua vein; dr, decidua reflexa, with the sparser villi Im-
bedded in it- substance ; dt, decidua serotina, Involving the more developed chorionic villi of
the commencing placenta. Tin' Coins is seen lying in the amniotic sac; passing up from the
umbilicus i- seen the umbilical cord ami it- vessels passing to their distribution in the villi of

the chorion; also the pedicle of the yolk-saok, which lie-in the cavity between the i tionand

chorion, (Ai.i.i.n Thomson.)

{a) Birds may l»<- taken as an example of those animals whose
embryos are provided with a large yolk-mass. The hen's egg
weighs 50 'jut-., of which ■> gms. is shell and 45 gms. food. The
whim, weighs •''>*» gms. and consists of proteids (albumins and
globulins) '■'> gms., /ate 0.3 gms., sofa 0.1 gms., walker 26.6 gms.

646 REPRODUCTION.

The yoi.k weighs L5 gms. and consists of proteids, 1.7 gme., fat
.". gms., vitelline, nuclein, glycogen 0.2 gm., Lecithin 1 gm., softs

<>.] gm., water i) gms. rl"l i< - suits < tain bone-making material,

— phosphates and carbonates, — also blood and tissue constituents,
— chlorides, phosphates and carbonates.

The chicken from a 50-gm. egg weighs 35 gms., 1<> gms.
having been lost in katabolism, and passed through the pores of
the shell as ('<), and II..O. The small amount of nitrogenous
excreta remains within the shell, generally within the cloaca of
the chick- to be voided soon after it leaves the shell. The chicken
is 80 per cent, water (28 gms. water and 7 gms. solids), while the
egg is 7!>.l per cent, water.

{!)) Mammals present a more complex problem. The mamma-
lian ovum has a small proportion of yolk and is retained within
the uterus of the mother long after this meager supply is ex-
hausted. After the yolk-mass is exhausted the embryo " takes
root" in the maternal tissues and draws plasma and oxygen from
the mother. The mammalian mother furnishes her intra-uterine
offspring with two sources of food the yolk-mass and her own blood.
Besides this there is a special provision for the extra-uterine period
when the young mammal is more or less helpless ; viz., the mill:
which the mother secretes.

(a) The Yolk-mass probably has about the same chemical com-
position in the mammal as in the bird. This yolk-mass must
be digested. It is surrounded by the hypoblast which is to fur-
nish the epithelium of the alimentary tract. There are no glands
to secrete a digestive fluid at the period when the yolk is consumed,
yet the yolk can be absorbed only after solution. The hypoblastic
cells lining the yolk sac and coelenteron must digest and absorb
the yolk-mass. In this connection it must not be forgotten that
the white of the bird's q^ is outside of the epiblast of the chorion
and must be absorbed by the chorion. In the mammal the
epiblast of the chorion is the principal absorbing surface.

(/?) The maternal blond is the source from which the mammalian
fetus draws sustenance. The special organs involved in this proc-
ess have been mentioned above. Maternal red corpuscles do not
pass into the foetus. Maternal white corpuscles probably do pass
from maternal to foetal circulation, it is easy to see how all
soluble salts can readily pass from maternal to foetal plasma and
the effect of various drugs upon the fetus when given to the
mother demonstrate that they do pass from one to the other. Just
how plasma-proteids pass from the mother to the fetus is a puzzle
still unsolved. Some have suggested that the maternal plasma-
proteids are peptonized, diffuse through the dividing membranes,
and changed back to proteid ; others think the white corpuscles
carry proteid from mother to young.

NUTRITION. 647

Toward the end of intra-uteriue life the mammalian foetus swal-
lows a portion of the amniotic fluid. The amount of amniotic
fluid is very small at lirst, but increases progressively with the
period of gestation. This fluid diffuses or filters into the amniotic
sac from the maternal, and, perhaps, foetal lymph spaces. It con-
tains water (an important constituent of egabryonic tissue) and va-
rious -alts with small portions of other foodstuffs.

2. Circulation. — (a) The Cii:< tlatiox of the Embryo is
the vitdlint circulation or the system of vessels which spread over
the volk beginning with the area vasculosa. The principal arteries
are the paired vitelline arteries which pass out on either side
branching profusely as far as the vena terminalis. From the vena
terminalis or terminal sinus a system of venules and veins brings
the blood back to the venous sinus, from which it passes into the
heart.

(b) The CracuLATiON of the Foetus, " Foetal ( ^rculation" a
diagram of which appears above (Fig. 320), is a special adaptation
of the permanent circulation. The permanent circulation sends the
blood to the lungs for oxidation of the haemoglobin, but the foetal
lungs not being functional there is a means provided to direct the
blood stream from them. This necessitates two important struc-
ture- peculiar to the fetus : (i) The foramen ovale through inter-
auricular septum ; (n) the ductus arteriosus from the pulmonary
arterv to the arch of the aorta. Other peculiarities of the total
circulation are: (hi) the hypogastric arteries which carry impure
blood from the iliac arteries to the umbilical arteries through
which it passes to the placenta for oxidation of the haemoglobin;
(IV) The ductus venosus, from the umbilical vein to the vena cava,
which provides for the direct passage of a large portion of the
pure blood to the left side of the heart through the foramen ovale.
The four structural peculiarities of the fetal circulation, lead to
tin' following functional peculiarities: (i) the circulation of ve-
noii- blood in the hypogastric and umbilical arteries; (ii) of arte-
rial blood in the umbilical vein and ductus venosus ; (in) of arte-
rial blood in the ascending vena cava, mixed, however, with
venous blood from the lower extremities; (iv) of the mixed
blood (the purest which enter- the heart) in the arteries of the
head and anterior extremities ; (v) of the least pure blood, — fur-
ther mixed with the blood from tin; ductus arteriosus, — to the
posterior extremities and the placenta.

.;. Respiration. — In bird- and reptiles the respiration takes
place readily through the porous -lull, and shell-membrane, the
vitelline arteries bringing the impure blood from the body of the
embryo out upon the Burface of the yolk. If the shell be var-
nished the chick' will -mother.

In m.imin;il- the respiration i- carried on through the placenta.

648

j;i:i'i;ni,ccT/n.\.

The blood of the fetus is brought into relation with the maternal
blood. The oxygen pressure in the foetal blood is much lower
than that in the maternal blood, so that the oxygen passes readily
from maternal to the foetal blood through the dividing membranes.
4. Metabolism and Excretion. — In the parasitic life led by
the embryo and foetus the anabolic processes are greatly in excess
of the katabolic processes. The food is presented to the foetus so
nearlv ready for assimilation that almost no energy is consumed
in preparation of the food. This food must be transported, how-
ever, and this transportation by the circulatory system involves
the liberation of kinetic energy of mechanical motion. This en-
ergy can be liberated only through katabolism of embryonic
tissues and fluids. The katabolites are for the most part CO, and
H..O, but some nitrogenous compounds (urea, etc.) are formed, and
these must be thrown out of the body of the embryo. At an early
period of foetal life the mesonephros — later the metanephros or
permanent kidney — becomes functional and excretes urea, etc.,
which finds its way out of the cloaca or of the bladder, and enters
the amniotic fluid. The amniotic fluid — as stated above — may be
swallowed by the foetus during the later stages of intra-uterine life.
This accounts for the presence of urea in the alimentary tract of
the newborn.

6. Moto-Sensory Activity.

That the foetus is conscious of any sensation is not even re-
motely probable. That the foetus responds reflexly to various

Fig. 340.

The human mammary gland. (Kikkic.

stimuli is beyond question. The " quickening," which takes
place at the middle of the period of intra-uterine life is the be-
ginning of general body movements. From the first quickening
to within about a week of delivery the movements increase in
frequency, strength and evident reflex character.

LACTATIOX.

f}49

9. THE PHYSIOLOGY OF MATERNITY.

a. Pregnancy and Parturition.1

b. Lactation.

The milk-secreting glands are cutaneous, and the glandular
epithelium is epiblastic in origin. The accompanying figure gives

Fig. 341.

Fig. 343.

Alveoli of the mammary gland of the bitch under different conditions of activity. A, section
through the middle of two alveoli at the commencement of lactation, the epithelial cells being
Been in profile ; B, an alveolus in full secretory activity. (Schaefer after BLeidenhaik.)

the most important anatomical features of the mammary gland.
(Fig. 340.)

The secretion of the milk is
analogous to the secretion of the
oil of oil glands in that the cellular
elements of the gland-epithelium
are sacrificed in the process.
Figures -">11 and 342 show the
glandular alveoli under different
stages of activity.

Milk has, under the microscope
the appearance shown in Fig.
343. The corpuscular elements
are either colostrum corpuscles, or
casein-pellicled oil globules.

Milk i- :i physiological emul-
sion and has the chemical constitu-
tion shown in the following table :

'These topici though properly in the field of physiology are extensively dis-
cussed in wuk- <.n obstetrics. They need not In- taken op here.

Globulet and molecules ofcow'a milk.
X 40D. (Kikki i

650 in:rn<>i>r<Ti(jy.

( loMPOsmois "i 1 1 1 m \n Milk.

Watei . 902.717

Casein (desiccated) 29.000

Lilfln-protcill 1.000

Albumin

Butter 26.000

Sugar of milk 37.000

Sodium lactate 0.-120

Sodium chloride 0.240

Potassium chloride 1.1 In

Sodium carbonate 0.053

Calcium carbonate , 0.00!)

Calcium phosphate 2.310

Magnesium phosphate <t.420

Sodium phosphate 0.225

Ferric phosphate 0.032

Sodium sulphate 0.074

Potassium sulphate ....

1000.000

Gases in f (^*> -en .J'??} 30 parte per 1000

, .. { ^Nitrogen 12. 1/ > .r ,r

solution /, i • -i i,. - i in volume.

( ( arbonic acid 1<>..)4 )

Milk contains food for the teeth and food for the bones, food
for the muscles and food for the nervous system. It is a perfect
food, satisfying every need of the developing infant.

IXDEX OF COMPARATIVE PHYSIOLOGY.

Note : For convenience of ready reference, an alphabetical, rather than a sys-
tematic, outline has been followed in each of the great divisions of plants and
animals.

Plants

Animals

chromosomes, 55
heliotropism, 493
rate of transmission of stimuli, 52
Protophyta, sensitiveness to light, 493
bacteria, cause of fermentation, '27'),
276
effect on cellulose, 339
influence on intestinal digestion,
336, 337
desmids, organisms of first order, 42

motion by secretion, 49
diatoms, organisms of first order, 42

motion by secretion, 49
Protococcus, simple organization,

40, 42
Saccharomyces cerevishe, see yeast

plant
yeast plant

fermentation, 276

'His katabolites, 27o
invertin, 277
simple organization, 40
Algfe

sensitiveness to Light, 193
Eudorina elegans, organism of
second order, 41, 42
example of colonization, 41 ;
Fig. •".
Fucus, selective power of living

cells, 44
Laminaria digitata, selective power
of Living cells, 44
Thallophyta, organisms of third order,

41, 42
Acrogens
Equisetum, motion of spores by
swelling of cell-wall, 18
Phsenerogams
barley, function of enzyme in the

grain, 276
clover, motion by changes in cell-

turgor, I -
corn, function of enzyme in the
grain, 276

li-. motion by changes in cell-
turgor, I-
- nsitive-plant, physiology of mo-
tion. I-
touch-me-not, motion of leed pod
by growth tension, 19

or, I

chromosomes, number per cell, 55
glycogen, animal starch, 368
homoiotherms, 394

effects of extreme cold on body
temperature, 397
poikilotherms, 394, 395
stimuli, rate of transmission, 52
temperature, mean, method of de-
termination, 395
Invertebrates

alimentary canal, differentiation,

234
circulatory system, organs of cir-
culation, 100
venous sinuses, 107
fertilization, external, 620
lymphatics, lacuna1, 107
neurons, sensory, types, 538
poikilotherms, 395
respiration by gills, 191
Protozoa

absence of ovum, 645
sensitiveness, to Light, 493
to atmospheric vibrations,
471
Amoeba
cell-divisions, 53 ; Fig. 12
digestion and assimilation, 234
individual of I order, 40, 42
irritability, 52
motion by contractility, 49
resemblance to leucocytes, 137
respiration, L90
Ciliata, absorption of solids, 11
Paramecium

individual of first older, 10, 12

protoplasm, specific gravity of,

Pelamvxa, sensitiveness to Hunt,

193"
Pleuronema, sensitiveness to

Light, I'.':'.
Radiolaria, motion by change of

i» cific gravity . L8
Rhuopoda

absorption of solids, 1 1

structure of protoplasm, 36
8 ten tor

cell-division, 53 ; Fig, L2

individual of first order, Id

652

TNDEX OF COMPARATIVE PHYSIOLOGY

Animals, [nvertebratea

motion by fibrillary contractil-
ity, 50
Vorticella
individual of first order, W, 12
motion by fibrillary contractil-
ity, 50, 51
Metazoa, differentiation of proto-
plasm intoendo- and exoplasm,
37
Protospongia, individual of second
order. 12
colonization of cells, 41
( loelenterata

circulatory organs, 106
digestion, specialization of

entoderm, 23 I
gastro-vascular system, 105
sensitiveness, to light, 501

to Bound, 471
vision, organs of, 193
Hydra, individual of third order,

41, 42; Fig. 6
jelly-fish, see Medusa
Medusa

auditory vesicle, 472 ; Fig. 234
digestive fluid, 234
neuromuscular cell, 50, 51 ;
Fig. K)
Siphonophora

motion by change of specific
gravity, 48
Echinodermata

circulatory system, hydro-
lymph, 105
digestion, intracellular, in

larva-, 234
hearing, sensitiveness to sound,

472
reproduction, maturation of

ovum, 619, 620
vision, organs of, 493
perception of light, 501
Asterias gracilis, see also star-fish
reproduction, fertilization of
ovum, 620; Figs. 302-305
maturation of ovum, 619 ;
Fig. 301
Holothuroidea, sensitiveness to
sound, 472
Elasipoda, sensitiveness to
sound, 472
star-fish, organs of vision, 493
Vermes

circulatory system, h;erno-

lymph, 105
digestion, intracellular, 234
hearing, sensitiveness to sound,

472
motion, 51

urinary segmental organs, 629
vertebrates, relation in geneal-
ogy to, 629

Animals, [nvertebrates

vision, eyes, 193, I'.'l
angleworm, see earthworm
earthworm

circulatory system, heart, lot;
hearing, sensith eness to sound,

172
nervous system, sensory epithe-
lium, 539 : Fig. 2-2
protoplasm, structure of, 36;

Fig. la
respiration, L90, 191
vision, absence of eyes, 49 1
Leech, protoplasm, structure, 37,

38 ; Fig. 3
Lumbricus, see earthworm
PdychasUz, eyes, 494
TwrbeUai'ia, digestion, intracellu-
lar, 234
organsof vision, eye-, 19:;
Arthropods

circulatory system, hremo-
lymph, 105
heart, location, 106, 107
hearing, external ears, 472
muscular motion, development

of, 51
respiration by gills, 191
vision, compound eye, 494
Crustacea, hearing, auditory
organs, 472
vision, compound eyes, 494
c ray- fish, auditory organ, 472
Insecta

hearing, tympanum of ear, 473
muscular system

development of muscular

motion, 51
striated muscle-fiber, 51 ;

Fig. lid
structure of fibrillse of wing,
68, 69 ; Fig. 35
vision, compound eyes, 494
grasshopper, auditory apparatus,

473
Phrvganea, compound eve, 493 ;
Fig- 252
Mollus. >a

circulatory system
hydrolymph, 105
heart, location, 106, 107
hearing, auditory vesicles, 472
respiration by gills, 191
visual organs, 494
Cephalopods, visual organs, 494
Gasteropoda, auditory vesicle, 472
Heteropods, auditory vesicle, 472;

Fig. 2:55
Lamellibranehs

auditory vesicle, 472
circulatory system, hydro-
lymph, 105
Nautilus, auditory vesicle, 472

1XDEX OF COMPARATIVE PHYSIOLOGY.

653

Animals, Invertebrates

Pterotrachea, auditory vesicle,

472 ; Fig. 235
snail, sensory epithelium, 539 ;
Fig. 282
Tunicata

circulatory system, hydro-
lymph, 105
hearing, development of the

ear, 473
relation in genealogy to worms

and vertebrates, 629
respiration by gills, 191
Enteropneusta

respiration by gills, 191
Vertebrates

circulatory system
development, 107
fluid of circulation, 105
heart, 631
location, 106
digestive system

differentiation of alimentary

canal, 234
embryology, 635
gastrula, bilateral symmetry, 624
hearing, development of the ear,

473
nervous system

development, 63S, 639
relation between limbs and size
of spinal cord, 542
respiratory system, development,

633
suprarenal capsules, presence of,

254
vision, eyes, 494
higher, internal ear, 473
lower, circulatory system, peristaltic
cardiac contractions, 600
digestive system, oral glands, 235
nervous Bystem, dendritic nature

of sensory axon. 538
special sense organs, origin, 457
teeth, 235

function. 'I'M
replacement, 236, 237

Acraniata
Ampiiioxus
blastopore, 622
blastula, 622 ; Fig. 307
circulatory system
hydrolymph, 105
heart, 106

respiratory and systemic,
107
gastrula, 623 ; Fig. 310
Bearing, development of the

ear, 178
respiration by jril Is, I'.u

' r.uiiala

I ishet

i,la-i

onore. '>-■

Animals, Vertebrates

brain, homology of optic
lobes, 581
lobes, 639
circulation, respiratory heart,

107
cleavage cavity, 622
fertilization, external, 620
freezing temperature, effect

of, 397
hearing, auditory labyrinth,
17:; ; Fig. 2*36
significance of the maculae
acusticse, 453
poikilotherms, 395
primitive segments, develop-
ment of, 625
respiration, 633
by gills, 191
vision, development of optic
vesicles, 495 ; Fig. 254
Cyclostomes, origin of special

sense organs, 457
eel, mechanical nature of reflex

action, 552
Petromyzon

branchial sensory ganglia,

457 ; Fig. 225 "
hearing, origin of ear, 474
vision, development of optic
nerve, 497
shark

teeth, 236, 337
dermal, 236; Figs. 150, 151
function of dermal, 435
oral, 236 ; Fig. 152
replacement, 236, 237
Amphibians

circulatory system
heart, anatomy, 107
innervation, 182
three-chambered, 631
digestion, development of

lingua] and oral -lands, 235

embryology, blastopore, 623
cleavage cavity, 622
fertilization, external, 620
gastrula, 623; Fig. 311
primitive segments, devel-
opment of, 625

excretion, double renal cir-
culation, 423

nervous Bystem, development

of cerebellum, 570
poikilotherms, 395
respiration, development of,
633

gills, I'.tl

lungs, 191

skin, 437

Batrachia, homology of optic
Lobes, 581

lr..-

654

INDEX OF COMPARATIVE PHYSIOLOGY

Animals, Vertebral* -

cilia of oesophagus, amount of

work performed, 50
circulatory system
capillary plexus, web of
foot, 111, Fig. To : 175,
Fig. 112
cardio-inbibitory center,
indirect stimulation, 185
heart, beating after re-
moval. L83
ganglia, 182
striated muscle-cell, 51 ;
Fig. lib
equilibration
influence of tactile impres-
sions, 576
relation of optic lobes, 583
leg, anatomy of, 72 ; Fi.lc- 44
life and death, nature of, 21
lymphatics, perivascular, of

mesentery, 114 ; Fig. 75
muscle-nerve preparation, 71
Pfl tiger's law of contrac-
tion, 90
stimuli, 74-76
nervous system

brain, absence of sponta-
neity after removal of
cerebral cortex, 590
inhibitory power of, 554
unconscious cerebral in-
hibition, 554
cells and terminal nerve-
fibers of olfactory region,
459 : Fig. 227
cord, apparent psychic
function, 552
effect of strychnin, 551
rate of transmission of
stimuli along nerves, 88
reflex action, time re-
quired, '>'>'■>
structure of midbrain-roof,
582 : Fig. 290
poikilotherm, 395
respiratory system

effect of paralysis of respi-
ratory center, 565
movements of, 197
relation to skin, 191
newt, double renal circulation,

42:;
Triton, blastopore, '''24: Fig.
313a
blastula, 622 ; Fig. 308
Reptiles

circulatory system
heart, anatomy, 107
ganglia, 182
three-chambered, 631
digestive system, develop-
ment of oral glands, 235

Animal-. Vertebrates

egg, a cell, 40

Bize of yolk-mass, 645
embryology, blastopore, 623
cleavage cavity, 622
primitive segments, 625
nervous system, development

of cerebellum, 570
poikilotherms, 395
respiration, in the embryo,
I '.47
by lungs, 101
crocodile, double heart, 107
lizard, midbrain-roof, struc-
ture, 582 ; Fig. 290
submaxillary glands and se-
cretion, 235
snake, mechanical nature of re-
flex action. 552, 553
turtle, ganglia of heart, 182
Birds

circulation, double heart, 107
digestion, development of

oral gland-. 235
• gg, a cell, 40

Bize of yolk-mass, 045
source of food for embryo,
288
embryology
blastopore, 623
blastula, 622 ; Fig. 309
cleavage cavity. 622
primitive segments, 025
hearing, auditory labyrinth,
47:( ; Fig. 236
comparative embryology of
the ear, 474
muscles, pectoral, plasmic

fibers, 68
nervous system

cerebral cortex, effect of

removal, 590
optic lobes, effect of de-
struction, 582
homology of, 581
respiration, in enibryo, 647
by lungs, 191
movements of, 197
thyroid gland, function, 253
urates in epithelial cells of

renal tubules. 424
uric acid, amount in excre-
ment, 412
uropygial glands, 434
chick, blastopore, 024 ; Figs.
313 b, <: d, ::14
embryo. 626 : Figs. 318, 319
heart, development. 631, 632
mesenchyme, formation' of,

027, 628
nervous system, development

of, 02i'."
respiration, development of

IXDEX OF COMPARATIVE PHYSIOLOGY

655

Animals, Vertebrates

lungs, 633, 634
urinary system, origin, 628,
629
pronephros, 629
vision, development of eye,
497 ; Fig. 261
development of optic ves-
icle, 494, 495 ; Figs. 253,
255, 256, 257
duck, temperature

influence of sex, 396
rectal, 395
touch, compound tactile cells,
tongue, 444 ; Fig. 214
great titmouse, temperature,

rectal, 395
lien, temperature, rectal, 395
weight and analysis of egg,

289
yolk-mass of ovum, 645
ostrich, size of cell of egg, 40
pigeon, blood, time required
for coagulation, 145
equilibration, influence of
semicircular canals, 578
influence of tactile and vis-
ual impressions, 578
lactiferousglands and "milk, "

435
temperature, rectal, 395
yellow-hammer, temperature,
rectal, 395
Mammals

circulatory system
heart, double, 107
form-changes, during

pulsation, 155
ganglia, 182
striated-muscle cell, 51 ;
Fig. lie
digestive svstem, oral glands,

235
embryology
blastopore, 62 I
cleavage cavity, 622
embryo and membranesde-
velopment, 643; Fig. 335
nutrition of embryo, 6 16
primitive segments, 625
yolk-mass, size, 6 15
genital corpuscles, 1 1 1
Dealing, auditory labyrinth,
173 ; Fig. 236
cochlea, development, 1*3
embryology, comparative,

of ear, 17 I
phylogeny of i ar, 158
milk, analysis of, 279
nervouf j item, cerebellum,
development, 570
c e re b ra 1 convolutions,
transverse section,

Animals, Vertebrates

Fig. 288
connections between optic
tracts and anterior cor-
pora quadrigemina, 581
phonation, 615
Pacinian bodies, 445
respi rat ion , anatomy of
thoracic skeleton, 198
embryonic, 647
movements of, 197
pulmonary, 191
sniffing in scenting, 460
teeth, 237
thyroid glands, accessory,

250 _
uric acid in urine, 412
water in bodv, percentage,
281
ant-eater, submaxillary glands,

size, 235
ape, dissection by Galen, 26
bear, absence of food during

hibernation, 442
calf, embrvo, lateral view, 640 ;

Fig. 331
Garnivora
cellulose, uselessness of, in

food, 339
constituents, chemical, of

body, 280
dentition, 305
diet, proteid, results of, 377,

378
faeces, 340

ingesta, analyses, 280
intestine, small, acid reac-
tion, 337
leucin, origin, 375
mastication, 305
respiratory quotient, 219
salt, source of, 283

teeth, 237

thyroidectomy, effect of, 253
urine, reaction, 409
cat

blood-corpuscle, red, size, 134
capillary vessels, structure,

111 ; Fig. 69
cerebellum, cell, 531 ; Fig.

276
intestine, small

reaction, 337

structure, 343 ; Fig. 184
villi, length, 316
nutrition, 102

Optic tract, cell, 529 ; Fig.
275

effect "f enucleation of one
eve, 583

parathyroids, effeel oi re-
moval, 252

phonati 615

656

INDEX OF COMPARATIVE PHYSIOLOGY.

Animals, Vertebrates

respiratory quotient, 219
Btomacb, effect of emotions,

32]
temperature, rectal, 395
thyroids, accessory, 250
< 'etacea, oral glands, 13 I
civets, anal glands, 434

cow, milk, analysis, 288

la ciosc, percentage, 284
microscopic appearance,
649 ; Fig. .">4:s

phonation, 615

temperature, rectal, 395

tongue, mobility, 601
Desmodus, oral glands, 235
dog

absorption of fatty acids, 380

benzoic acid, eliminated by
kidneys, 376

beyond — voluntary inhibi-
tion, 554

blood
coagulation, time required,

145
corpuscle, red, size, 134
gas, determination of

amount, 220
transfusion by Lower, A.

D. 1665, 148
withdrawal, effect of, 148

cardiac plexus, 183

conservation of energy, 393

cortex cerebri, electrical ex-
citability, 593

equilibrium, nitrogen and
carbon, 377

fat-deposit, source of, 382

feeding, pseudo-, true, and
psychic, 314

gastric juice, constituents,
315, 316

glycocoll, fate of, when fed
to dog, 376

heat of body, determination
of quantity, 387

intestine, small, reaction, 337

lymph-follicle of conjunctiva,
113 ; Fig. 72

mammary yland, 649 ; Figs.
341, 342

metabolism, of fats, 381
of nitrogen in rest and
labor, 380

optic tract, effect upon, of
enucleation of one eye, 588

pancreatic juice, analysis, 326
secretion of, 325

parathyroids, effect of re-
moval, 252

phonation, 615

reflex movements, vicarious,
552

Animals, Vertebrates

respiratory center, intlm ace
of blood upon, 230
quotient, 219
Bahvary secretion, nerves of,

•J! IS '

spinal cord, cell from anterior
born, 5:; I ; Fig. 280

spleen, effect of removal, 15:;

stearin, formation of, inde-
pendent of diet. 381

suprarenale, effect of removal.
25 I

temperature, influence of Bex,
396

rectal, 395

thyroids, accessory, 250

ventricle, third : electrical

stimulation, 582
vomiting, mechanism, 323
elephant, range of motion of
purely muscular organs : pro-
boscis, 601
fox, analysis of ingesta, 280
gorilla, dentition and mastica-
tion, 305
guinea-pig

intestine, small, reaction, 337
motor end-plates, 69 ; Fig. 38
niusele-ribers of psoas, struc-
ture, 69 ; Fig. 38
organ of Corti, 478 ; Fig.

241
respiration, water and car-
bonic acid gas exhaled.
215
temperature, rectal, 395
Herbivora
cellulose, influence on intes-
tinal digestion, 339
deer-licks, necessity of, 282
diet, proteid, effect of, 378
dentition, 305
fseces, 340
intestines, small, reaction,

337
mastication, method, 305
parotid glands, large size, 235
respiratory quotient, 219
teeth, 237

urine, explanation of reac-
tion, 409, 410
horse

blood, filtration, 131
separation by subsidence,

131, 132
time required for complete
coagulation, 145
prehensile upper lip ; range

of motion, (501
respiratory quotient, 219
temperature, influence of sex,
396

IXDEX OF COMPARATIVE PHYSIOLOGY.

657

Animal*, Vertebrates

rectal, 395
hyena, anal glands, function,

' 4::4
kangaroo, oral glands, func-
tion, 235
lamb, transfusion of blood bv

Denis, A. D. 1667, 148
lion, effect of meat diet, 289
Macacos, see monkey
marmot, respiratory quotient,

219
monkey

cortex cerebri, determination

of motor areas, 595, 596

localization, 594

principal gvri and sulci,

594 ; Fig* 294

pyramidal tracts as motor

patlis, 562
temperature, rectal, 395
muskdeer, preputial glands, 434
otter, anal glands, function, 434
ox, effect of vegetable diet, 289
respiratory quotient, 219

pig

dissection by Galen, 26
temperature, rectal, 395
rabbit
blood, size of red corpuscle,
134
time required for coagula-
tion, 145
cerebellum, effect of electrical

stimulation, 569
corpora quadrigemina, effect

of puncture, 583
eye, development, 496 ; Fig.

260
gastrnla, 623 ; Fig. 312
ingesta, analysis of, and an-

abolism of, 286
intestine small, reaction, 337

villi, length, 346
liver, lobule, injected, 361 ;
Pig. 194
section of, :;<;<) ; Fig. 192
lymphatic plexus, central
tendon of diaphragm, 113;
Fig. 7 1
42

Animals, Vertebrates

optic nerve, cross-section,

496 ; Fig. 259
pancreas, alveoli before and
after active secretion, 325 ;
Fig. 183
paratbvroids, importance of,

252"
reflex cry of pain in absence

of brain, 592
respiration, influence of ob-
struction of air on intra-
thoracic pressure, 207 ;
Fig. 133
respiratory quotient, 219
time of development of

lungs, 633
tracings of atmospheric,
intra-abdominal and in-
tra-thoracic pressure,
205, 206 ; Fig. 132
spinal cord, coordinated
movement by electrical
stimulation of, 574
temperature, rectal, 395
thyroids, accessory, 250
rat

artery and vein, structure,

110 ; Fig. 68
emotional expression, center

in medulla, 56.4, 565
intestine, small, reaction,
337
villi, length, 346
respiration, estimation of
water and carbonic acid
gas exhaled, 215
temperature, rectal, 395
seal, temperature, rectal, 395
sheep

hypophysis cerebri, effects of

extracts of, 256
respiratory quotient, 219
temperature, rectal, 395
skunk, anal glands, function,

434
tapir, range of motion of pro-

lioscis, 601
whale, temperature, rectal, 395
wolf, analysis of ingesta, 280

GENERAL INDEX.

ABDOMINAL reflex, 555
Abduction, 60*

Absorption, 42, 342

defined, 342

of foodstuffs, 353

former theories of, reviewed, 349

of gaseous material, 42

of liquid substances, 43

physical forces of, 346

physiology of, 352

relation to nutrition, 102

of solid bodies, 44

structures involved in, 343*
Acceleration of heart, 184
Accommodation, 506

mechanism of, 506*

range of, 509
Acid, hydrochloric, secretion of, 312

sarcolactic, 373

uric, 412
Acoustics, 466

physiological, 466
Action, reflex, 99

voluntary, 100
Activities, egoistic, 47

moto-sensory, 47

phyletic, 47
Addison's disease, 254
Adduction, 601*
Afferent impressions, 544
After-images, 523
Air, complemental, 209*

reserve, 209

residual, 209*, 210

tidal, 209-"-

Albuminates, 27.'!

derived, 27 I

Albuminoid, '■'<~\
Albumins. 272

Alexandrian -eliool, 25

Alimentary canal, 237

bacteria in, :'>■''>•'>
Allantoic, 637, 641*
Altruism, 1<

Amalgamation of battery zinc, 68
Amnion, 6 1 1
Amoeba, 40, 12. 68*

phases of motion, 19
Ampnioxus, circulation in, 105
Ampbipyrenin, 88
Amyloplasl
Amylopsin, 327
Amyloses, 270

Anabolism, 359, 382

Anaemia, 150

Anatomy of the eye, 498

of frog's leg, 72*
Animal heat, 394

mechanics, 606*

metabolism, 367
Ankle clonus, 556
Anode, 58

Aorta, section of wall, 109*
Apnoea, 231
Aqueous humor, 498
Archineurons, 544
Arteries, hypogastric, 647

innervation of, 186
Artery, elastic tissue of, 110*

endothelial lining of, 110*

pulmonary, 194*

section of, 109*
Arthropoda, heart of, 106
Arthropods, ha?molymph, 105
Asphyxia, 232
Astigmatism, 513
Atmosphere, composition of, 212
Atomic weight, relation to living or-
ganisms, 33
Auditory nerve, 572

organs, comp. anatomy, 471*

invertebrates, embryology of, 474
Auerbach, plexus of, 313
Aves, heart of, 107
Avogadro's hypothesis, 348
Axis cylinder, 530

structure of, 71*
Axon, 530, 536, 540
Axodendrites, 539
Axonie collaterales, 537

BACTEBIUM lactis, 337
Balance sheet of energy, 393
Basedow's disease, 253
Batteries, 58*
Belt-spirograph, 202*
Beverages, 282
Biceps reflex, 656
Bile, 246

action of, 338

composition of, 827
Binocular fixation, 515
Bizzozero, blood-platelets of, 138
Blastula, 11, 42, 622*
Blindness, color, 523
Blind Bpot, location of, 505
659

600

GENERAL INDEX.

Blind, outline of, 505
Blood, 130

chemical composition of, 139

properties of, 138

circulation of, 154

coagulation <>t", 144

color of, 132

corpuscle counter of Zeiss, 135

flow, regulation of, 188

velocity of, 169, 171

functions of parts of, 142

gases of, 219, 224

morphology of, 133

odor of, 133

platelets of Bizzozero, 138

pressure, methods of determining,
Kit'.

quantity of, 143

reaction of, 139

relation of CO., in, 221
of oxygen in, 220

respiratory changes in, 219

specific gravity of, 132

supply, protection of, 144

taste of, 132

transfusion of, 148

variations of, physiological and
pathological, 150

vessels, location of, 144
tonus of, 187
Blushing, 559

Body, chemical composition, 279
Bowman's capsule, 424
Boyle' s law, 347
Brain, arteries of, 585

cortex, arterioles of, 586

development of, 639, 641

lymphatics of, 587

man's, observations on, 595

movements of, 588

vascular supply of, 585
Bronchus, section of, 193*
"Bulbar paralysis," 564
Bulbus arteriosus, 632
Burdach, column of, 537

CALCIUM salts, 146
Calipers, 200
Calorimeter, air, 387

water, 387
Calorimetry, 387
(anal, alimentary, 237
Capacity of lungs, 209

vital, 209, 210
Capillaries, anastomoses of, 111

circulation in, 174, 175

endothelium of, 111*
Capillary pressure, 176*
Carbamide, 411
Carbohydrates, absorption of, 354

form of, 367

circulation form of, 367

Carbohydrates, metabolism of, 367
Carbon dioxide, proportion of, in air,
213, 215*
equilibrium, 377

hydrates, 268, 419

Cardiograms, l-">s

( lardiograph, 157*

( iardiorpneuButtogram, 207*

< asein, 335

( 'ells, abreast in battery, 59
body, 530

form and size of, 40
metabolism of, 44

physiology of, 31

reproduction of, 53

selective powers of, 43, 44

sources of energy, 46

structure of, 35

tandem in battery, 59
Cellulifugal messages, 538
Cellulose upon intestinal digestion, 339*
Center, cardio-accelerator, 185

cardio-inhibitory, 185

in cerebellum, 100

in cerebrum, 100
Centers, in medulla, 100

vaso-dilator, 401

in spinal cord, 100

thermolytic, 400

thermotactic, 400

vaso-constrictor, 187, 401
Centigrade reduced to Fahrenheit, 395-
Central Nervous System, 638*
Centrosome, 38

in nerve cells, 534
Centrosphere, 534
Cephalic flexure, 640
Cereals, 284
Cerebellar disease, symptoms of, 579

vesicles, 626
Cerebellum, 567, 572, 639

development of, 570

physiology of, 567
Cerebral hemispheres, 640
Cerebrospinal fluid, 588
Cerebrum, 585, 590*, 639

introductory, 585

localization of functions in, 592:

physiology of, 589
Charles's law, 347
Chemistry of respiration, 212
Chest-pantogram, 204*

pantograph, 203*
Chlorophyll grains, 37, 38
Chorda tympani, 295, 296
Chorion, 641*
Chromatin reticulum, 38
Chromophanes, 518
Chromoplasts, 38
Chromo-proteids, 273
Chromosomes, 54*, 55*
Chronogram, 77*
Chronograph, 66

GENERAL INDEX.

661

< h\ie, circulating, 105

< ilia. 36

Ciliary body. 499*
Ciliata, motion in, 50
Circulation, H>4

in arteries, 166

of blood, 166

in capillaries, 174

classification of fluids and tissues,
130

comparative physiology of, 104

<>t' the elements, 363

historical introduction, 123

introduction, 104

of lymph, 181

organs of, innervation, 181*

outline, 129

physical introduction, 116

relation to nutrition, 102

in veins, 178

of typical compounds, 365
Circulatory organs, coordination of, 188

system, development of, 631*

reflexes of, 559
Circumduction, 603
Cleavage, 621*
Cloaca, 636
Coagulation of blood, 144

factors of, 147

hastened by, 145

influenced by calcium salts, 146

phenomena of, 145*

retarded by, 145
Cochlea. 473

section of, 477
Cochlear nerve, 573
Coelenterates, circulation in, 105

circulatory organs, 106

neuro-muscle cell of, 50*
Collaterals, 531, 537
4 lolonization, 41

< '■■lor blindness, 523

< ornmutator, Pobl's, 61*

< kmception, 438, 596

< ionductivity, 87
Conjugate foci. 190
Conjunctiva] reflex, 568

< on-ervation of energy, 19, .'588
' loosonanta, the, 616
Contractility, 17

Contraction, efled of temperature upon.

laws of, Pfluger, 90
•■ stair-case, 85
summation of, 78*

< iodrdination, 567

of activities of circulatory system,
188

by the medulla, B67
1 no, 130
corpora quadrigemina, 580

irritation of, ">83

' orpn icles, counting of, L36

Corpuscles, functions of, 143

red, decay of, 152

form of, 133

number of, 134

origin of, 152

size of, 134

white, 137
Corti, organ of, 476, 478*

pillars of, 478
I iougbing, 211
Cremasteric reflex, 555
Crista acustiea, 452*, 470
( rving and laughing, 212
Current, ascending, 90

change of course of, 61

direction of, 61

strength of, 61

"demarkation," 84

descending, 90

electric, in muscle, 85*

induced, 64*

of injury, 84

methods of modifying, 60

varied, 62
Curve, Traube-Hering, 167, 168*
Cutis anserina, 600
Cycle, cardiac, 163
Cytology, 31
Cytolymph, 37
Cytoplasm, 36

D ALTON'S law, see Charles's law
Daniell, the Daniell cell, 58
Decidua?, 644*
Decidua reflexa, 644*

serotina, 644*

vera, 644*
Defecation, 341, 557
Degeneration, retrograde, 543

Wallerian, 543
Deglutition, 30G, 557

influence of nervous system on, 308

involuntary part of, 307

oesophageal, 308

pharyngeal, 307

relation to nutrition, 102

voluntarv part of, 306
Dendrite, 530, 535, 536
Dcndraxons, 533, 536
Depressor nerve, 187
Deprez tignal, 07*

Dermal system, 429
excretion by, 436

glands of, 13 1
morphology of, 130
physiology of, 135
protection by, 435
respiration by, 137

D.smi.l, 40, 12
Dermis, tbc, 430

I tevelopmenl of labyrinth, 1 7 -"•

of optic nerve, 197
Disaccharids, 269

662

GENERAL INDEX.

Diameter, dorso-ventral, tracing of, 202*

thoracic, changes of, 198, 199

effects of changes, 205
Diapedesis, 177*
Dicrotic pulse wave, 173
Digestion, 293

anatomical introduction, 237*

chemical introduction, 257

coelenterates, 234

comparative physiology of, 233

ferments, 234

fluids of, 324

fundamental carbon compounds, 257

gastric, 309

gastric, chemistry of, 316

factors which influence, 318

influence of dilution on, 320

of movements of stomach on, 321

of temperature on, 320

intestinal, 324

chemistry of, 327

introduction, 233

relation to nutrition, 102

salivary, 293

chemistry of, 300
factors influencing, 302
time required for, 303
Digestive system, development of, 635*

innervation of, 243*
Dioptric system, principal axis of, 491

principal foci of, 491

principal plane of, 491

simple, 491*
Diplopia, 516

Discharge of liquids through tubes, 117
Disease, cerebellar, symptoms of, 579
Dromograph, Chauveau's, 170
Duct, thoracic, section of, 114*
Ductus arteriosus, 647

venosus, 647
Dynamic polarity of neuron, 539
Dyspnoea, 231

EAR, lever system of, 481*
middle, 481
Echinoderms, circulation in, 105
Efferent impulses, 544
Egesta, 403
Egestion, 403

relation to nutrition, 102
Eggs, 288
Elbow-jerk, 556

Electricity, measurements of, 64
Electrodes, 60*

brush, 60*

hand, 60

nonpolarizable, 60*
Electrometer, capillary, 64*
Electrotonus, 88

apparatus for demonstrating, 89

application of laws of, 92, 93

laws of, 89
Elements, 58*

Elements, sarcous, 119*
Embryo, the, 621, 624, 630

physiology of, 6 1")
Embryology, human ear, 474*

auditory organ in vertebrates, 474
human eye, 494*
Embryonic connective tissue, 628
Emcsis, ">">N
Emotions, 597
Emulsification, 332
Endocranial fluids, 587
End-organs, 541
Energy, balance sheet of, 393
cells, manifestation of, 47
sources of, 46
chemical, 46

conservation of, 19, 388. 393
defined, 18
forms of, 40
heat and light, 46
income of, 387
kinetic, of an organism, 393
liberation of, 392, 394
manifested by living organisms, 21
potential of an organism, 392
transformation of, 18, 392
vital theory of, 27
Enzymes, 274, 276
amylolytic, 277

condition favoring activity, 278
effect of temperature on, 302
fat-splitting, 277
inverting, 277
pancreatic juice, 326
proteolytic, 277
Epidermis, the, 433
Epiglottis, 610
Equilibration, 575
Equilibrium, 451, 567
carbon, 377
disturbance of, 571
maintenance of, 478, 575, et seq.
nitrogen, 376
physiological test of, 363
tactile impressions in, 576
visual impressions on, 577
Erector pili muscles, 600
Erectile reflex of the penis, 555
Eudorina, 41*, 42
Excreta, 403
Excretion, 42, 403-404^
cutaneous, 425, 427
definitions, 403
dermal system, 436
epithelium of convoluted tubule, 424
the foetus, 648
glandular, 424
glomerular, 423
intestinal, 428
introduction, 403
physiology of, 409
pulmonary, 425
relation to nutrition, 102

GENERAL INDEX.

663

Excretion, renal, 409

urinary, 425

urinary, in amphibians, 423
Expression, emotional, ">74
External ear, development of, 474
Extension, 601*
Eye, anatomy and histology of, 498*

human, embryology of, 494*

lens of, 498

normal, 503

optical instrument, 501

F.ECES, 340
Fahrenheit reduced to Centigrade,
395
Falx cerebri, 640
Fatigue, 85, 86*, 442
Fats, 270, 286, 380

absorption of, 356

form of, 380

circulation form of, 380

deposit, 381

metabolism of, 381
Ferments, 274, 275

conditions favoring activity, 278

fibrin, 146

digestion by secreted, 234
Fermentation, 275
Fertilization, 618, 620*

external, 620

internal, 620
Fibrin-ferment, 146
Fibrinogen, 146
Fibrinoplastin, 146
Fick, experiment of, 379
Filtration, 346, 449
Flexion, 601*

Flow of liquids through tubes, 116
Focus, principal, 489
Foetal circulation, 647

membranes, 641*
Foetus, 630

circulation of, 647

circulatory system of, 631*

development of lungs in, 633*

digestive system of, 635*

heart of, 631*

moto-sensory activity of, 648

nutrition of, 6 15

physiology of, 6 15

respiration in, 6 17

respiratory system of, 633
Follicles, lymphatic, 111, 113*
Foods, 279, 281

animal, in which proteids predomi-
nate, 287

common, potential energy of, 389

Inorganic, Jsl

mastication of, 302, 319

organic, 283

preparation of, 290, 302, 318

■tons, 279

absorption of, 358

Foods, action of bacteria upon, 338

classification of, 281

definition, 279

interrelations of, 382*

isodynamic equivalents of, 391

potential energy of, 388

vegetable, 283"
Foramen ovale, 647
Fore-brain vesicle, 626
Fovea centralis, 504, 518
Franklin's theory of visual sensations, 522
Fruits, 286

Frog's leg, anatomy of, 72*
Fucus nodosus, 44

serratus, 44

vesiculosus, 44
Functions of cerebrum, 596
Fundamental tone, 480

GASES, absorption of, 195, 196
blood, 219

solution of, in liquids, 194

tension of, 223
Gastric juice, chemical composition of,
315

nervous system on secretion of, 313

secretion of, 309

movements, 557
Gastrula, 41, 42, 622*
Generation, spontaneous, 27
Genital corpuscles, 444

duct, 636

gland, 637
Germ layers, development of, 621
Germinal dot, 619*

vesicle, 619
Glands, 247* 248*

cardiac of stomach, 320*

excretory, see cutaneous excretion,
435

lymphatic, 111, 112*

protective of dermal system, 434

pyloric of stomach, 311

salivary, 235, 293*

sebaceous, 434, 436

secretory, 435

thyroid, 250*

< llobulins, 272

< ilomeruli, 407*

Glottis, 612, 613

< iliitcal lellex, 555

< Hycocoll, 37.">
Glycogen, 368, 646
Glycoses, 268

' loll, column <>f, 587

Granules, elementary, of blood 138

( i in—man's law, 822

Gustatory organs, the structure of, 461*

H.KM LCYTOMETEE, Gower's, 131
1 [emadromometer, Vblkmann's,
169
Bsmaglobinometer, Gower's, 141*, 142

084

GENERAL INDEX.

I [sematinometer, 1 12
1 [sematocrit, 131*
I Ii.-iiuivt luiii, H>.">
Hsemocyanin, L05

Haemoglobin, colorimetric method of
determining, 142

in solution in ha-molymph, 10")

spectroscopic determination, 111
Hsemolymph, 105
Hsemometer, Fleischl's, 142*
Hearing, 466

introduction to, 166

physiology of, 479
Heart, acceleration of, 189

action of, 154

cardiac cycle, 162, 103

centers in medulla, 185

changes of form of, 155

of position of, 155, 156*

development of, G33*

inhibition of, 184

innervation of, 182*

mechanical stimulation of, 186

musculature, 107

recoil of, 157

regulation of, 183

section of, 118*

sounds of, 165

stimulation of, mechanical, 186

striated involuntary muscle, 600

time of cardiac cycle, 1(54

values of, 108*

work done by, 164
Heat, animal, 394

centers, 400

mechanical equivalent of, 19

regulation, 399
Heidenhain, theory of, 299
Helmholtz's theory of reception of

sound, 483
Hemorrhage, effect of, 148
Hepatic cylinders, 635
Heredity,' 629

Hering's theory of visual sensations, 522
Hiccoughing, 212
Hind-brain vesicle, 626
Hippuric acid, 414

Histogenesis of circulatory organs, 115
History of physiology, 24
Homoiotherms, 394

Human ear, special embryology of, 474*
Hunger, 442
Hydra, 41* 42
Hydrsemia, 150
Hydrolymph, 105
Hypermetropia, 512
Hyperpncea, 231

INCIDENCE, angle of, 488
1 Income of energy, 362, 387
Individuals classified, I-

defined, 40

real, 41, 42

Individuals virtual, 1 1 , 12

Individualism, 17

Individualization of living -ulistance. 40

Indol, 339, 118
Induction currents, 6 1
[nductorium, 63*
inferior maxillary reflex, 556
inhibition of heart, 18 1
[nterbrain, 584, 639
Interrupter, Xeefs, 63*
Intestinal digestion, factors which in-
fluence, 336
influence of bacteria upon, 330

of cellulose upon, 339
Intestine, Large, 243

absorption from, 353

bacteria of, 337
Intestine, small, '_' 1"J :

absorption from, 352

bacteria of, 337
Intestines, movements of, 340
Intima, influence of, in coagulation, 144
Intralobular veins, 407
Introduction, general, 17
Invertin, 334
Iris, function of, 509
Irritability, 51, 88
Island of Reil, 595
Isodynamic equivalents of foodstuffs, 391

KARYOKINESIS, 54::
anaphases of, 55*

metaphase of, 55*

phases of, 54*

telophases of, 56
Karyolymph, 38
Karvosomes, 38
Katabolism, 359, 384
Katabolites, carbohvdrate, excretion of,

370'
Kathode, 58

Key, the Du Bois-Reymond, 59*, 60*
Kidney, the anatomy of, 405

blood-supply of, 406*

innervation of, 408

primitive, 029
Knee-jerk, 556
Krause's membrane, 69
Kreatin, 369, 373
Kreatinin, 374, 412
Kymograph, 66*

T ABYRINTH, development of, 475*

I j Lactation, 649*

Lactose, 335

Laminaria digitata, 44

Laryngeal reflex, 555

Larynx, acoustics of, 013

anatomy of, 010

cartilages of, 010

innervation of, 011

levers of, 613

mechanics of, 611

GENERAL INDEX.

665

Larynx, muscles of, 610*
Laughing and crying, 212
Law, Grossman, 522

Tonicelli's, 117
Laws of stimulation, 52
Lecithin, 646
Lee's hypothesis, 453
Lens. 489, -".ii7

concave, 489

convex, 489

of the eye. 498
Leucocytes, 40, 42. 1S7

destruction of, 153

eosinophile I PI. II.), 138

in diapedesis, 177*

format ion of, 153
Leucoeytliremia, 151
Leucocytosis, 150
Leukaemia, 151
Leucin, 373

Liberation of energy, 392
Life, defined, 21

phenomena of, 42
Ligament, suspensory of the eye, 499
Light, 486

relation of, to plant assimilation,
47*
Linin reticulum, 38
Liquids, flow of, through tubes, 116
Liver, the, 238, 635

secretions, external and internal,
246
Living organisms, relation of atomic

weight to, 33

substance, individualization of, 40
Localization, the power of, 448
Locomotion, 609
Longitudinal fissure of brain, 640
Lungs in foetus, 633

section <>f, 193*

vesicles, 635*
Lymph, 151

chemical properties of, 151

circulation of, 181

cisterns of brain, 587

follicles and glands, 111

physical properties of, 1">1

radicles, 1 1'A*
Lymphatic, perivascular, 114*

system, 1 1 1

MA< I LA acustica utriculi, 176
lutea, 518
Malpigbi, 27

Mammal-, heart of, 1 n7
Mammary reflex, 555

Manometer, mercury, 119*
ition, 30 1
muscles of, 240, 805
nerves of, 305
process of, 306
relation to nutrition, 102

skeletal -t met u n- of. 305

Maternity, the physiology of, 649
Matter, imponderable, defined, IS

of living organisms, 2i I

ponderable, defined, 17
Maturation, 618, 619*
Mean temperature, the determination of,

395
Meats. 2s'.i

Meatus externus, 479
Mechanics, animal, 606*
Medulla, conduction by, 562

coordinating center, 567

independent center, 563

oblongata, 639*

physiology of, 562
Medullary folds, 626

vesicles, 626
Meissner's corpuscles, 537

plexus of, 313

tactile corpuscles of, 446
Membrani tympani, 479*
Memory, 589, 596
Menu, typical, energv represented by,

390
Mercury manometer, 119*
Mesenchyme, 627

axial, 628

time of formation, 627
Mesonephros, 637*
Metabolic changes, the character of, 366

tissues and organs, 359*
Metabolism, 358

animal, 367

carbohydrates, 367

cell, 44

chemical phases, 45

defined, 44

classified, 359

fats, 381

foetus, 648

introduction, 359

physical phases, 46

proteids, :>71

relation to nutrition, 102
Metencephalon, 567* 580* 639*
Methane, 25]

Method, graphic, of recording, 65
Microsomes, 37
Micturition, 425, 558
Mid-brain vesicle, < • — ' •

Middle ear, 481

development of, 17 I
Milk, 288* 649

chemical composition of human, 650

Curdling enzymes, '.','■'>'.',

digestion of, •*'>;,'">

gases in, ii">o

therapeutic uses of, 288
Monaxons, 536
Mollusca, heart of, 106
Molluscs, circulation in, 105

hamolvmph in, 105

Monkey, brain of, 69 1

666

GENERAL INDEX.

Monkey, experiments on, 594
Monocular fixation, 513
Monosaccharide, 268
Morphology of living substance, 34
Morula, 41, 42
Motion, amoeboid, 48

ciliary, 49*

and contractility, -17

flagellate of spermatozoa, 49*

muscular, 50

through cell turgor, 48

contractility. Is

growth, 48

Becretion, 48

specific gravity, 48

swelling cell walls, 48

without contractility, 48
Motor impulses, the course of, 5 17
Moto-sensory activities of life, 47
Mouth, absorption from, 352

bacteria of, 336

glands of, 240
Movements, cranium, 603

forearm, 604

hand, 604

leg and foot, 605

thigh, 605

upper arm, 604

voluntary, 589
Mullerian duct, 636*
Muscle-bone organs, 601

special features of, 603

change in form, 76

in length, 76

in response to stimuli, 76

in transverse dimensions, 80

chemical changes in, 81

contraction of, 608

current, diagram of, 85*

curve, effect of drugs upon, 79*
of load upon, 79
of temperature upon, 79*

electrical changes in, 83

insect' s wing, 68*

involuntary, 600

nerve preparation, 71, 72*

nerve physiology, 74

plates in, 69*.

of respiration, 199

section of, 67*

skeletal, 601

structure of, 67

thermal changes in, 82

tissue, 51*

voluntary, 68* 601
Muscular action, adjustment of, 567

special, 610

sense, 453

system, 598

physiology of, 598

tissue, 598

changes in during activity, 599
Musical scale, 470*

Myclencephalon, 5 6 2, t;:;<i

Myogram, 77

double stimulus, 78*
effect of vciatrin upon, 79*

Myograph, simple, 73*
spring, 65*

Myopia, 512

NASAL reflex, 555
•• Near-sightedness," 512
Nerve, auditory, 572

centers in brain, 100
in cerebellum, 100
in cerebrum, 100

cochlear, 573

depressor, 187

endings in tendon, 70*

fiber, function of, 540

glosso-pharyngeal, 462

inferior laryngeal, 611

optic, development of, 497

phrenic, 565

pressor, 187

superior laryngeal, 611

structure of, 70*

trigeminus, 462

trunks, properties of, 87

vagus, 566

vaso-constrictor, 186

vaso-dilator, 186

vaso-motor, 186

of Willis, 573
Nervous system, beginning of, 625*

general functions of, 94, 99

conduction, 540

definition of, 529

interrelations of, 531

mutilation of, 543

physiology of, 528, 538

scheme of, 95*

structure of, 528

tvpes of, 530
Neural tube, 626*, 638
Neurentic canal, 627
Neuroblasts, 530

Neuro-muscle cell of cadenterate, 50*
Neuron, 94, 528, 542, 543

changes during activity, 540
Neuronal cell-body, 533
Neuronic development, postnatal, 543
Nitrogen equilibrium, 376

laws of, 378
Noise, 467
Nuchal flexure, 640
Nudein, 646
Nucleolus, 38
Nucleoplasm, 36, 38
Nucleo-proteids, 273
Nucleus, 38
Nutrition, 101

activities of, 102

of the cell, 42

GENERAL INDEX.

667

ODOPHOXE, 461
< Esophagus, 241

Oils. 287

Olfactory organs, structure of, 458*

region, nerve fibers of, 459, 460
< tligsemia sicca, 150
Optic disc, 505

nerve, development of, 497

vesicles, 626, 639*
Optical axis, 489

center, 489
Optics, physiological, 486
Optogram. 518
Organ, of Corti. 439, 476, 478*

histogenesis of circulatory, 115
Organic reflexes, 556
Organism, a living, defined, 21
Osmosis, 346

Osmotic pressure, laws of, 347
Otocvst, 475
Ovum, 40, 42, 618*
Oxygen, discovery of, 28

proportion of, in air, 213

PACINIAN bodv, the, 445
Pain, 442
Palmar reflex, 555
Pancreas, 636
Pancreatic juice, action of, 327

alkaline salts of, 326

composition of, 325

enzymes of, 326

secretion of, 324
Paramecium, 40, 42
Pars ciliaris retina^, 496
Parturition, 558, 649
Patellar clonus, 556

reflex, 556
Pepsin, secretion of, 311
I '.[.tone, 273
Perception, 438, 596
Perimetry, 519

Perilymph of scala vestihuli, 483
Period, latent, in muscle response, 77
Perspiration, 427

factor- causing variation, 427

insensible, 427

■enable, 427
Peristalsis. 340

vermicular, 340
Pfl tiger's law of contraction, 90, 91*
Phakoscope, 508
Pharyngeal reflex, 565
Pharynx, 240

Plionution, ol">

Phrenic nerve, BOS

Physical theory of absorption, 849

Physiological acoustics, 166

optic-. 186

test of equilibrium, 363
Physiology, animal, denned, 17
' of the cell, 81

of cerebellum, 567

Physiology of the cerebrum, 585, 589

comparative, defined, 17

of contractile and irritable tissues,
57, 58

of corpora quadrigemina, 580

development of, 24

of embryo and fcetus, 645

general, 30

defined, 17

history of, 24

human, defined, 17

of maternity, 649

of medulla oblongata, 562

of muscle and nerve, 74

of muscular system, 598

plant, defined, 17

problems of, 22

relation to other natural sciences, 23

of respiration, 197
comparative, 190

special, 101

defined, 17

of spinal cord, 544

of thalamencephalon, 584

of vision, 500
Piezometer, 120*
Pigments, respiratory, 105
Pinna, 479
Pitch, range of, 484
Placenta, 644*
Plasma, function of, 142
Plasmosome, 38
Plethora, 150

Plethysmogram, 179*, 180*
Plethysmography 179*
Pneuma theory, 25, 124
Pohl's commutator, 61*
Poikilotherms, 394
Point of fixation, 504
Polyaxon, 537
Polysaccharids, 270
Pontal flexure, 640
Posture sense, 450
Preformation theory, 27
Pregnancy, 649
Pressor nerve, 1 87

Pressure, arterial, relation of, to intra-
ventricular, 167

blood, methods of determining, 166,
168

regulation of, 188

capillary, 176*

intermittent, 121

intra-abdominal, 206* 208

intra-aortic, 167*

uitra-auricular, 160*
intra-cardiac, 160*
Lntrarthoracic, 205, 206*, 207*
intraventricular, 166, 157

curve' of, 161

lateral, 120

of liquids, measurement ofi 1 18

in tubes, 1 18

668

GENERAL INDEX.

Pressure, respiratory, 20'

Blope, 120

venous, L78
Primitive segments, development of, 625 ::
Principal focus, 189
Prism, 488*
Processus vocalis, 610
Pronation, 603
Pronephros, 629
Prosencephalon, 585, 039
Proteids, 271, 370

absorption of, 355

absorption form of, 370

circulation form of, 371

classification of, 272

metabolism of, 371 ;

nutritive value of, 376
Proteoses, 273
Pro-thrombin, 147
Protococcus, 40, 42
Protoplasm, 31

chemical properties of, 32

properties of, 31

structure of, 34
Protozoa, motion in, 50
Psychic phenomena, 560
Pulse, 172, 173, 174
Punctum proximum, 509

remotum, 509, 511
Pupil, the, 508
Pupillary reflex, 558
Pyloric reflex, 557
Pyramidal cells, 535
Pyrenin, 38

AUOT1ENT, the respiratory,

REASON, 589, 596
Recollection, 596
Record of time, 66
Recording of results, 65
Reflex, abdominal, 555

action, 99, 549

character of, 551

time required for, 553

biceps, 556

centers, locations of, 560
spinal cord as a, 549

conjunctival, 555

cremasteric, 555

erectile, of penis, 555

gluteal, 555

inferior maxillary, 556

laryngeal, 555

nasal, 555

palmar, 555

patellar, 550

pharyngeal, 555
pupillary, 558
pyloric, 557
spasms, 551
tendo-achillis, 555

218

Reflex, triceps, 556

deep, 555

alimentary tract, 557

inhibition of, 553

superficial, 555
Reflexes, the, 555
Refraction, 487'*

angle of, 188

laws of, the mammalian eve, 501
Refractn e apparatus of the eye, 512
Rcgio olfactoria, 458

respiratoria, 459
Regurgitation, duodenal, 558
Remak's fibers, 5 1 1
Rennin, 335

secretion of, 312
Reproduction, 52, 617

amitotic, 54

direct, 5 1

mitotic, 54
Reptilia, heart, of, 107
Reservoir, 117*

with piezometers, 120*
Resistance to current, til
Respiration, anatomical introduction,
191

apparatus of Voit, 216*, 217*

in the cell, 226

changes in air breathed, 21 2,213,214

chemistry of, 212

Cheyne-Stokes, 211*

comparative physiology of, 190

control of, 227

cutaneous, 190

defined and classified, 189

direct reflex stimulation of, 230

external, 212

forced, muscles of, 199

by gills, 191

indirect reflex stimulation of, 230

internal or tissue, 224, 225*

introduction, 189

by lungs, 191

mechanical and physical features, 197

muscles of, 199

nasal passages, 191

physical introduction, 194

physiology of, 197

quiet, muscles of, 199

relation to nutrition, 102

structural features, 197

types of, 210*

voluntary influence on, 231
Respiratory center, action of, 229

organs, innervation of, 227

system, development of, 633

tract, reflexes of, 559
Retina, 499

irritability of, 517

layers of, '499

pigments of, 518

propria, 496

structure of, 517

GENERAL IXDEX.

669

Retinal image, size of, 505

stimulation, 51(5
Rheocord, Du Bois Reymond's, 62*

simple, 62*
Rhodopsin, 518
Rigor caloris, 87

mortis, 86
Rods and cones, 499, 500
Roots, 285
Rotation, 602
Rugae of stomach, 242

OALIVA, 293

0 composition of, 299

secretion of, 293
Salts in nutrition, 282

absorption of, 353
Saponification, 333
Sarcolemma, 67
Sarcomere, 69*
Barcoplasm, 68
Sarcous element, 69*
Scala vestibuli, 483
Secretion, 244

denned, 246

internal, 247, 249

salivary, cerebral nerves in, 298

sympathetic nerves in, 298

secretory fibers in, 298
Segmentation, 618, 621*
Selection, power of living cell, 43, 44

relation to nutrition, 102

theory of absorption, 350
Serum, artificial, recipe for, 149

transfusion of, 149
Semicircular canals, 473*, 573
Seminal emissions, 558
Sensation, a, 438

conscious, 589

general, 438, 441

introduction, 438

objective, 441, 443

physiology of, 441

of posture, 450

vi«ual, 516

Sense-cell, "sinneszelle," 538
of -mell, 458

of smell, physiology of, 459
of taste, 163
Sensibility, 51

iv Impulses, the course of, 545*
I differentiation, 638
ition, I (3
Shivering, .".97, 443
Sighing, 212

Skatol, 339, 419
Skin, the, 129

nerves of, 135
Smell, physiology of tin- tense of, 159

• of, I5S
zing, 212
Sobbing, 212
Solution of gases in liquids, 194

Song, 616
Sound, 466

intensity of, 468

of heart, 165

musical, 467

perception of, 484

pitch of, 468

production of, 467

properties of, 468

propagation of, 467
of in gases, 467
of in liquids, 467
of in solids, 467

quality of, 471

range of intensity of, 485

reception of, 483

reflection and refraction of, 468

sensation of, 484

theories of reception of, 484

transmission of, 479

velocity of propagation, 467
Special senses, the, 457
Specialization of function, 41
Specific heat, 387
Spectroscope, to determine haemoglobin.

141
Spectrophotometer, to determine Hb..

141
Spectrum, effect of blood gases upon.

224*
Speech, 615
Spermatozoa, 618*
Sphygmographs, 172
Sphygmograms, 173*
Spinal cord as a conductor of nervous

impulses, 544

course of fibers in, 98*

features of, 96

physiology of, 544

as a reflex center, 549

section of, 97*

trophic function of, 561
Spirometer, 208*
Spleen, functions of, 153

oncometer curve of, 153*, 154

minute structure of, 114*

section of, 114*
Stapes, movements of, 483*
Static equilibrium, 453
Steapsin, 331
Stentor, 40, 42, 50* 5:5
Stethogram, 200,* 206*
Btethograph, 200*
Stimulation, laws of, 52

retinal, 516

Stimuli, 71, 76

action of, 52

classified, 5-j

relation of nerve to, 87
Stimulus, break, anodic, 75

make, kathodic, 76

Stomach, 241*

absorption from, 352

670

CKXh'IlAL IM)KX.

Stomach, bacteria of, 337

coats of, 242

contents, reaction of, 319

movements of, 321*
Structure of cell, 35
Stromulir, Lad wig's, 170*
Submaxillary gland, vaso-motor nerves

of, 186
Succus entericus, 334

composition of, 326
Sucking, 557
Sucroses, 269
Suffocation, 442
Sugars, 283

Suprarenal capsules, 254*
Supination, 603

Suspensorv ligament of the eye, 499
Sweat, 426

center, 401

chemical composition of, 427

inorganic constituents of, 427

organic constituent's, 427

quantity of, 426

reaction of, 426

specific gravity of, 426
System, vascular, 107

vaso-constrictor, 187

vaso-dilator, 188

TACTILE corpuscles, 444
sense, the, 447

sensibility, 449, 450
Tambour, of stethograph, 200*
Taste, acuteness of, 463

bud, 461*

localization of the sense of, 465

physiology of sense of, 463

sense of, 461
Teeth, 237, 240*

evolution of, 235, 236*
Teleneurons, 544
Telephone theory of Waller, 484
Temperature, factors which vary, 396

mean, the determination of, 395

regulation of, 188, 399

sense, the, 455*

topography, 399
Tendo-achillis reflex, 555
Tendon, nerve-endings in, 70*
Tension of gases, 223
Thalamencephalon, 584, 639*

physiology of, 584
Thallophytes, 41, 42
Thermo-electric couples, 83*
Thermolysis, 42.'), 436
Thermolvtic centers, 400
Thermotactic centers, 400
Thermotaxis, 399
Thirst, 442
Thoracometer, 201*

tracing, 201*
Thrombin (fibrin ferment), 147
Tickling, 443

Tissue, adenoid, 11-'!*
Tongue, 240, 241*
Tonus of blood vessels, 187
Torricellfa law, 117

Touch, the sense of, 447
Trachea and bronchi, 192*
Tract, segments of digestive, 239
Transformation of energy, 18
Transfusion of blood, 148

indications for, 149
Triceps reflex, 556

Trophic function of the spinal cord, 561
Trypsin, 328
Tubers, 285
Tubes, elastic, 122

inelastic, 122
Tubo-tympanal pouch, 475
Tunicates, circulation in, 105
Tuning fork, 6(i*
Tympanum, 481
Types of respiration, 210*

UMBILICAL cord, 641*
Urea, 375, 411
Ureter, 637*
Uric acid, 412

amount of, 414
Urinary bladder, 637*

constituents, 410

excretion, 423

system, early development of, 629
histogenesis of, 630
origin of, 628
Urine, 409

carbohydrates of, 419

chemical composition of, 410

color of, 410

egestion of, 425

fatty acids of, 420

inorganic constituents of, 421

organic compounds of, 411, 420

pathological, 421

pigments of, 420

quantity of, 409

reaction of, 409

sp. gr. of, 409
Uriniferous tubules, 407*
Uro-genital cord, 636

ridge, 637

system, 636

stages of development of, 636*

YAGUS, inhibitory nerve of heart,
184, 566

Valves of heart, 108*

Valvules eoimiventes, 343
Vaso-constrictor center, 401
Vaso-dilator centers, 401

system, 188
Vaso-constrictor nerves, 186, 187

-dilator nerves, 186

-motor nerves, 186
Vegetable-, green, 285

GENERAL INDEX.

671

Vein, section of, 109*

circulation in, 178

intralobular, 407
Velocity, 117

of blood flow, 169
Vermes, hemolymph in, 105

muscular tissue in, 51
Vertebrate, amphibia, heart of, 107
Vestibule, 473*
Villi during peristalsis, 346*
Vision, 486

acuteness of, 524

comparative physiology of, 493

definitions, 486

direct, 518

indirect, 518

influence of age upon, 512

line of, 504

physiology of, 500
Visual alible, 503*

estimates, 525

mechanics, 513

optics, 501

perceptions and judgments, 524

refraction, 501

-insitiun. 516, 520
Vitelline, 646

membrane, 618
Vitreous humor. 498
Vocal cords, 612, 613
Voice, 615
Volition, 597
Vomiting, 323, 569

drugs which produce, 324

influence of nervous system on, 324

Vomiting, mechanism of, 323
Vorticella, 40, 42, 50*
Vowels, the, 616

WALLERIAN degeneration, 543
Water, 281
absorption of, 353
proportion of in respired air, 214,
215*
" Wave theory of growth," 363
"Weber's law, 448

law of sensation, 521
Will, the, 597
Willis, nerve of, 573
Wolffian body, 636*
duct, 636* 637
Work done by contracting muscle, 80
modified by dimensions of muscle,

81
modified by load, 81
modified by strength of stimulus, 80
modified by time between stimuli,
81

VANTHIN bodies in urine, 414

VAWNING, 212
I Yeast-cell, 40
Yoke, 619

Young-Helmholtz theory of visual sen-
sations, 522

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